CN218300556U - White light source based on high-luminous-flux laser - Google Patents

White light source based on high-luminous-flux laser Download PDF

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Publication number
CN218300556U
CN218300556U CN202222075382.7U CN202222075382U CN218300556U CN 218300556 U CN218300556 U CN 218300556U CN 202222075382 U CN202222075382 U CN 202222075382U CN 218300556 U CN218300556 U CN 218300556U
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laser
phosphor
white light
laser diode
light source
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Inventor
保罗·鲁迪
詹姆斯·W·拉林
埃里克·古坦
特洛伊·特罗蒂尔
迈尔文·麦克劳林
詹姆斯·哈里森
斯滕·海克曼
迈克尔·坎托雷
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Kyocera Sld Laser Co
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Kyocera Sld Laser Co
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Priority claimed from US16/449,126 external-priority patent/US11437774B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V5/00—Refractors for light sources
    • F21V5/007—Array of lenses or refractors for a cluster of light sources, e.g. for arrangement of multiple light sources in one plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0087—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for illuminating phosphorescent or fluorescent materials, e.g. using optical arrangements specifically adapted for guiding or shaping laser beams illuminating these materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
    • H01S5/0217—Removal of the substrate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
    • F21V29/50—Cooling arrangements
    • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V9/00—Elements for modifying spectral properties, polarisation or intensity of the light emitted, e.g. filters
    • F21V9/30—Elements containing photoluminescent material distinct from or spaced from the light source
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/30—Semiconductor lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
    • H01S5/0202—Cleaving
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/02208—Mountings; Housings characterised by the shape of the housings
    • H01S5/02212—Can-type, e.g. TO-CAN housings with emission along or parallel to symmetry axis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/02208—Mountings; Housings characterised by the shape of the housings
    • H01S5/02216—Butterfly-type, i.e. with electrode pins extending horizontally from the housings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0225—Out-coupling of light
    • H01S5/02253—Out-coupling of light using lenses
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0225—Out-coupling of light
    • H01S5/02255—Out-coupling of light using beam deflecting elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/023—Mount members, e.g. sub-mount members
    • H01S5/02325—Mechanically integrated components on mount members or optical micro-benches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0233—Mounting configuration of laser chips
    • H01S5/02345—Wire-bonding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/0235—Method for mounting laser chips
    • H01S5/02355—Fixing laser chips on mounts
    • H01S5/0237—Fixing laser chips on mounts by soldering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/024—Arrangements for thermal management
    • H01S5/02476—Heat spreaders, i.e. improving heat flow between laser chip and heat dissipating elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2004—Confining in the direction perpendicular to the layer structure
    • H01S5/2009—Confining in the direction perpendicular to the layer structure by using electron barrier layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4031—Edge-emitting structures

Abstract

Embodiments described herein provide a white light source based on high-luminous-flux laser. The white light source based on the high-luminous-flux laser comprises: a plurality of Surface Mount Device (SMD) packages and a plurality of electronic board components. A plurality of SMD packages are arranged in an array pattern and are each electrically coupled to one of the plurality of electronic board members. Each of the plurality of laser packages includes one or more laser diode devices, a phosphor member, and at least one common support member. The phosphor member converts a portion of the electromagnetic radiation from each laser diode device into emitted electromagnetic radiation and outputs white light. The utility model discloses can realize economic efficient white light source.

Description

White light source based on high-luminous-flux laser
The application is a divisional application of a Chinese national phase application with an international application date of 2020, 6 and 18 months, an international application number of PCT/US2020/038504 and a utility model name of a white light source based on high-luminous-flux laser, and the Chinese national phase application has an entry national phase date of 2022, 2 and 21 months, an application number of 202090000815.9 and a utility model name of a white light source based on high-luminous-flux laser.
Cross Reference to Related Applications
This application is a continuation-in-part application of U.S. application 16/449,126 filed on day 21, 6, 2019, of U.S. application 16/014,010 filed on day 21, 6, 2018, and of U.S. application 14/829,927 filed on day 19, 8, 2015, the entire contents of which are incorporated herein by reference for all purposes.
Technical Field
The present application relates to light sources, and more particularly to high luminous flux laser based white light sources.
Background
At the end of the 18 th century, thomas edison invented a bulb. Conventional light bulbs, commonly referred to as "edison bulbs," have been used for over a hundred years in a number of applications including lighting and displays. Conventional bulbs use a tungsten filament encapsulated in a glass bulb that is sealed in a base and screwed into a socket. The socket is coupled to an AC power source or a DC power source. Conventional light bulbs are commonly found in houses, buildings and outdoor lighting and other areas where lighting or displays are required. Unfortunately, conventional light bulbs suffer from the following drawbacks:
conventional light bulbs dissipate more than 90% of the energy as heat energy.
Conventional bulbs often fail due to thermal expansion and contraction of the filament elements.
The spectral range of light emitted by conventional light bulbs is wide, most of which is imperceptible to the human eye.
Conventional light bulbs emit light in all directions, which is disadvantageous for applications requiring strong directionality or focusing, such as projection displays, optical data storage, etc.
To overcome some of the drawbacks of conventional light bulbs, fluorescent lamps have been developed. Fluorescent lamps use an optically transparent tube structure filled with a halogen gas (usually also containing mercury). A pair of electrodes is coupled between the halogen gas and to an alternating current power supply through the ballast. Once the gas is excited, it discharges and emits light. Typically, the optically transparent tube is coated with a phosphor that is excited by light. Many building structures use fluorescent lamps, and more recently, fluorescent lamps have been assembled into base structures that are in turn coupled into standard sockets.
Light Emitting Diodes (LEDs) are rapidly becoming the lighting technology of choice due to the high efficiency, long lifetime, low cost and non-toxicity offered by solid state lighting technology. LEDs are two-lead semiconductor light sources, typically based on p-i-n junction diodes, that emit electromagnetic radiation when activated. The emission of an LED is self-emitting, typically in a lambertian mode. When an appropriate voltage is applied to the leads, the electrons and holes will recombine within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of light is determined by the band gap of the semiconductor.
The earliest LED appeared in 1962, and as a practical electronic component, it emitted infrared light of low intensity. Infrared LEDs are still often used as emitting elements in remote control circuits, such as in remote controls for various consumer electronics products. The intensity of the first visible LEDs is also low and limited to red. Modern LEDs can possess visible, ultraviolet, and infrared wavelengths with very high brightness.
The earliest blue and violet gallium nitride (GaN) based LEDs were fabricated using metal-insulator-semiconductor structures due to the lack of p-type GaN. The first p-n junction GaN LED was confirmed by Amano et al using LEEBI treatment in 1989 to obtain p-type GaN. They obtained the current-voltage (I-V) curve and electroluminescence of the LED, but did not record the output power or efficacy of the LED. Nakamura et al, in 1991, demonstrated a p-n junction GaN LED with 42uW output power at 20mA using a low temperature GaN buffer layer and LEEBI treatment. Nakamura et al demonstrated the first p-GaN/n-InGaN/n-GaN DH blue LED in 1993. The LED emits strong band-edge InGaN light in the blue wavelength range under forward bias with an emission wavelength of 440nm. At 20mA of forward current, the output power and EQE were 125uW and 0.22%, respectively. In 1994, nakamura et al demonstrated and commercially available a blue LED with an output power of 1.5mW, an EQE of 2.7% and an emission wavelength of 450 nm. On 7/10/2014, the nobel physics prize was awarded to Isamu Akasaki, hiroshi Amano and Shuji Nakamura due to "the invention of high efficiency blue light emitting diodes that made bright and energy efficient white light sources possible", or less formally called LED lamps.
By combining a GaN-based LED with a wavelength converting material, such as a phosphor, a solid state white light source is realized. This technology of generating white light using GaN-based LEDs and phosphor materials is now illuminating our surrounding world as it has more advantages over incandescent light sources, including lower power consumption, longer lifetime, higher physical strength, smaller size and faster conversion. Light emitting diodes are now used in a variety of applications such as aircraft lighting, automotive headlamps, advertising, general lighting, traffic lights, and camera flashes. LEDs support the development of new text, video displays and sensors, while their high slew rates are also useful in advanced communication technologies.
While effective, LEDs still have several limitations that are expected to be overcome in accordance with the utility model described in the following disclosure.
SUMMERY OF THE UTILITY MODEL
Some embodiments of the present invention provide an apparatus and method for an integrated white electromagnetic radiation source that uses a combination of a laser diode excitation source based on gallium and nitrogen containing materials and a light emitting source based on phosphor materials. In the present invention, a violet, blue or other wavelength gallium and nitrogen material based laser diode source is tightly integrated with a phosphor material, such as a yellow phosphor, with designated scattering centers disposed within the excitation plane or bulb to form a compact, high brightness and efficient white light source. In one example, the white light source may be provided for a specific use, may be provided in a general use, or the like.
Additional benefits over the prior art may be realized using some embodiments of the present invention. In particular, the utility model discloses can realize economic efficient white light source. In particular embodiments, the present optical device may be manufactured in a relatively simple and cost-effective manner. Depending on the particular implementation, one of ordinary skill in the art may use conventional materials and/or methods to make the present devices and methods. In some embodiments of the invention, the gallium and nitrogen containing laser diode source is based on c-plane gallium nitride material, while in other embodiments, the laser diode is based on non-polar or semi-polar gallium and nitride material. In one embodiment, the white light source is configured from a chip-on-substrate (CoS) with integrated phosphor on the substrate to form a chip-on-substrate and phosphor (CPoS) white light source. In some embodiments, the light source and the phosphor are arranged on a common support member, wherein the common support member may be an encapsulating member.
According to one embodiment, there is provided a white light source based on high-luminous-flux laser light, comprising: a plurality of Surface Mount Device (SMD) packages; and a plurality of electronic board members, the plurality of SMD packages being arranged in an array pattern and each electrically coupled to one of the plurality of electronic board members, each of the plurality of SMD packages including: one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source; a phosphor member configured as a wavelength converter and an emitter and coupled to one or more laser diode devices; at least one common support member configured to support one or more laser diode devices, the at least one common support member comprising one or more angled portions, and a planar portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the planar portion, and an upper surface of each angled portion is disposed between and at an inverted angle relative to an upper surface of the buffer feature, wherein the buffer feature is disposed on an upper surface side of each angled portion in a direction perpendicular to a length of a cavity member of the laser diode device supported by the angled portion; an output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm; a free space extending from the output face on each of the one or more laser diode devices to the phosphor member, having a non-guiding property capable of transmitting a laser beam from the output face to an excitation surface of the phosphor member; a range of incident angles between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off normal incidence to the excitation surface, and the beam spot is configured to a particular geometric size and shape; wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength; and characterizing a reflection pattern of the phosphor member such that a laser beam from each of the one or more laser diode devices is incident on a beam spot area on the excitation surface of the phosphor member, and a white light emission is output from the same beam spot area, the white light emission comprising a mixture of wavelengths characterized at least by the emitted electromagnetic radiation having the second wavelength.
In one embodiment, the electronic board member comprises a heat sink, and the plurality of SMD packages are configured to transfer thermal energy from the one or more laser diode devices and from the phosphor member to the heat sink.
In one embodiment, the plurality of SMD packages is arranged on the electronic board member in at least one of a one-dimensional (1D) array pattern or in a two-dimensional (2D) array pattern.
In one embodiment, further comprising a plurality of optical components, wherein one or more of the plurality of optical components is coupled to the white light emission output from the phosphor component of each of the plurality of SMD packages.
In one embodiment, the plurality of optical members includes collimating optics configured to collect white light emissions and focus the white light emissions in a collimated and/or directed emission pattern.
In one embodiment, further comprising one or more common optical components coupled to the white light emission output from the phosphor component of each of the plurality of SMD packages.
In one embodiment, the one or more common optical components include a lens array having a dedicated lens element associated with the white light emission output from the phosphor component of each of the plurality of SMD packages.
In one embodiment, further comprising an optical device coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the optical device is configured to shape the white light emission into a predetermined pattern.
In one embodiment, further comprising active optics coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the active optics are configured to dynamically shape the white light emission into different predetermined patterns.
In one embodiment, a laser beam from at least one of the one or more laser diode devices is modulated in a predetermined data pattern to generate a signal for wireless data transmission.
In one embodiment, a single electronic board member other than the plurality of electronic board members is further included, and each of the plurality of electronic board members is coupled to the single electronic board member.
In one embodiment, the phosphor member comprises a plurality of scattering centers to scatter electromagnetic radiation having a first wavelength in a laser beam incident on the phosphor member.
According to one embodiment, a high-luminous-flux laser-based white light source includes: a power source; and a plurality of laser packages arranged in an array pattern and electrically coupled to a power supply, each of the plurality of laser packages comprising: one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source; a phosphor member configured as a wavelength converter and an emitter and coupled to one or more laser diode devices; at least one common support member configured to support one or more laser diode devices, the at least one common support member comprising two or more angled portions and a flat portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the flat portion and an upper surface of each angled portion is disposed between and at an inverted angle relative to an upper surface of the buffer feature, wherein the buffer features are disposed on an upper surface side of each angled portion in a direction perpendicular to a length of a cavity member of the laser diode device supported by the angled portion; an output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm; a free space between the output face on each of the one or more laser diode devices and the phosphor member having non-guiding properties capable of transmitting the laser beam from the output face to the excitation surface of the phosphor member; a range of angles of incidence between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off-normal incident to the excitation surface, and the beam spot is configured to a particular geometric size and shape; wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength longer than the first wavelength; and characterizing a reflection pattern of the phosphor member such that a laser beam from each of the one or more laser diode devices is incident on a beam spot area on the excitation surface of the phosphor member, and a white light emission is output from the same beam spot area, the white light emission comprising a mixture of wavelengths characterized at least by the emitted electromagnetic radiation having the second wavelength.
In one embodiment, the plurality of laser packages includes at least one of a can type package, a surface mount type package, or a flat type package.
In one embodiment, the power supply includes a plurality of electronic board members, wherein each of the plurality of laser packages is electrically coupled to one of the plurality of electronic board members.
According to one embodiment, the method is characterized by comprising the following steps: a power source; and a plurality of Surface Mount Device (SMD) packages arranged in an array pattern and electrically coupled to a power supply, each of the plurality of SMD packages comprising: one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source; a phosphor member configured as a wavelength converter and an emitter and coupled to one or more laser diode devices; at least one common support member configured to support one or more laser diode devices, the at least one common support member comprising two or more angled portions and a flat portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the flat portion and an upper surface of each angled portion is disposed between and at an inverted angle relative to an upper surface of the buffer feature, wherein the buffer features are disposed on an upper surface side of each angled portion in a direction perpendicular to a length of a cavity member of the laser diode device supported by the angled portion; an output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm; a free space between the output face on each of the one or more laser diode devices and the phosphor member having non-guiding properties capable of transmitting the laser beam from the output face to the excitation surface of the phosphor member; a range of incident angles between a laser beam from each of the one or more laser diode devices and an excitation surface of the phosphor member such that the beam spot is configured to a particular geometric size and shape; wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength; a plurality of scattering centers associated with the phosphor member to scatter electromagnetic radiation having a first wavelength incident on the phosphor member; and wherein a white light emission is output from the phosphor member, the white light emission being characterized by at least emitted electromagnetic radiation having a second wavelength.
In one embodiment, the laser beam from each of the one or more laser diode devices is incident on a same beam spot area on the excitation surface of the phosphor member, and the white light emission is output from the same beam spot area.
In one embodiment, the laser beam from each of the one or more laser diode devices is incident on a different beam spot region on the excitation surface of the phosphor member, and white light emissions are output from the different beam spot regions, the white light emissions including the same wavelength characterized by the same emitted electromagnetic radiation.
In one embodiment, the laser beam from each of the one or more laser diode devices is incident on a different beam spot area on the excitation surface of the phosphor member, and a white light emission is output from the different beam spot areas, the white light emission comprising a mixture of wavelengths.
In one embodiment, the power supply includes a plurality of electronic board components, wherein each of the plurality of SMD packages is electrically coupled to one of the plurality of electronic board components.
According to one embodiment, a white light source based on high-luminous-flux laser light is characterized by comprising: the SMD package includes a common support member and a plurality of surface mount device SMD packages arranged in an array pattern on the common support member. Each of the plurality of SMD packages includes: one or more laser diode devices, each laser diode device comprising a gallium and nitrogen containing material and configured as an excitation source, and a phosphor member configured as a wavelength converter and an emitter and coupled to the one or more laser diode devices. The output face is configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet emission and/or blue emission having a first wavelength ranging from 400nm to 485 nm. The free space is between the output face on each of the one or more laser diode devices and the phosphor member, having non-guiding properties capable of transmitting the laser beam from the output face to the excitation surface of the phosphor member. The range of angles of incidence between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member is such that, on average, the laser beam is off normal incidence to the excitation surface, and the beam spot is configured to a particular geometric size and shape. The phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength. A reflection pattern of the phosphor member is characterized such that a laser beam from each of the one or more laser diode devices is incident on a beam spot area on an excitation surface of the phosphor member, and a white light emission is output from the same beam spot area. The white light emission includes a mixture of wavelengths characterized at least by the emitted electromagnetic radiation having the second wavelength.
In one embodiment, the common support member comprises a heat sink, and the plurality of SMD packages are configured to transfer thermal energy from the one or more laser diode devices and from the phosphor member to the heat sink.
In another embodiment, a plurality of SMD packages are arranged in a one-dimensional (1D) array pattern on a common support member.
In another embodiment, a plurality of SMD packages are arranged in a two-dimensional (2D) array pattern on a common support member.
In another embodiment, the high-luminous-flux laser-based white light source further comprises a plurality of optical members, wherein one or more of the plurality of optical members is coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages. The plurality of optical members may include collimating optics configured to collect white light emissions and focus the white light emissions in a collimated and/or directed emission pattern.
In another embodiment, the high-luminous-flux laser-based white light source further comprises one or more common optical members coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages. The one or more common optical components may include a lens array having a dedicated lens element associated with the white light emission output from the phosphor component of each of the plurality of SMD packages.
In another embodiment, the high-luminous-flux laser-based white light source further comprises an optical device coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the optical device is configured to shape the white light emission into a predetermined pattern.
In another embodiment, the high-luminous-flux laser-based white light source further comprises active optics coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the active optics are configured to dynamically shape the white light emission into different predetermined patterns.
In another embodiment, a laser beam from at least one of the one or more laser diode devices is modulated in a predetermined data pattern to generate a signal for wireless data transmission.
In another embodiment, the high-fluence laser based white light source further comprises a common electronic board member, wherein each of the plurality of SMD packages is coupled to the electronic board member and the electronic board member is coupled to the common support member.
In another embodiment, the high-fluence laser based white light source further comprises a plurality of electronic board members, wherein each of the plurality of SMD packages is coupled to one of the plurality of electronic board members, and each of the electronic board members is coupled to the common support member.
In another embodiment, the high-luminous-flux laser-based white light source further comprises a case member, wherein the common support member and the plurality of SMD packages are arranged within the case member.
In another embodiment, the phosphor member comprises a plurality of scattering centers to scatter electromagnetic radiation having the first wavelength in the laser beam incident on the phosphor member.
In yet another embodiment, the phosphor member comprises ceramic Yttrium Aluminum Garnet (YAG) doped with Ce or single crystal YAG doped with Ce or powdered YAG containing a binder material; wherein the phosphor member has an optical conversion efficiency of greater than 50 lumens per watt, greater than 100 lumens per watt, greater than 200 lumens per watt, or greater than 300 lumens per watt.
According to another embodiment, a white light source based on high-luminous-flux laser light is characterized by comprising: a common support member and a plurality of laser packages arranged in an array pattern on the common support member. Each of the plurality of laser packages includes: one or more laser diode devices, each comprising a gallium and nitrogen containing material and configured as an excitation source, and a phosphor member configured as a wavelength converter and an emitter, and coupled to the one or more laser diode devices. An output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emissions having a first wavelength ranging from 400nm to 485 nm. The free space is between the output face on each of the one or more laser diode devices and the phosphor member, having non-guiding properties capable of transmitting the laser beam from the output face to the excitation surface of the phosphor member. The range of incident angles is between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off-normal incident to the excitation surface and the beam spot is configured to a particular geometric size and shape. The phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength. A reflection pattern of the phosphor member is characterized such that a laser beam from each of the one or more laser diode devices is incident on a beam spot area on the excitation surface of the phosphor member and a white light emission is output from substantially the same beam spot area, the white light emission comprising a mixture of at least wavelengths of the emitted electromagnetic radiation having the second wavelength.
In one embodiment, the plurality of laser packages includes at least one of can type packages, surface mount type packages, or flat type packages.
According to yet another embodiment, a white light source based on high-luminous-flux laser light, comprising: a common support member and a plurality of Surface Mount Device (SMD) packages arranged in an array pattern on the common support member. Each of the plurality of SMD packages includes: one or more laser diode devices, each laser diode device comprising a gallium and nitrogen containing material and configured as an excitation source, and a phosphor member configured as a wavelength converter and an emitter and coupled to the one or more laser diode devices. The output face is configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet emission and/or blue emission having a first wavelength ranging from 400nm to 485 nm. The free space is between the output face on each of the one or more laser diode devices and the phosphor member, having non-guiding properties capable of transmitting the laser beam from the output face to the excitation surface of the phosphor member. The range of incident angles is between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off-normal incident to the excitation surface and the beam spot is configured in a particular geometric size and shape. The phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength. A plurality of scattering centers are associated with the phosphor member to scatter electromagnetic radiation having a first wavelength incident on the phosphor member. A white light emission is substantially output from the phosphor member, the white light emission including a mixture of wavelengths characterized at least by the emitted electromagnetic radiation having the second wavelength.
In one embodiment, the phosphor member is characterized by: a reflective mode such that the laser beam from each of the one or more laser diode devices is incident on a spot area on the excitation surface of the phosphor member and the white light emission is output from substantially the same spot area, or a transmissive mode such that the laser beam from each of the one or more laser diode devices is incident on the excitation surface of the phosphor member and the white light emission is output from the emission surface of the phosphor member.
In another embodiment, the phosphor member is characterized by a reflective mode such that the laser beam from each of the one or more laser diode devices is incident on a different beam spot area on the excitation surface of the phosphor member and a white light emission is output from substantially the different beam spot areas, the white light emission comprising the same wavelength characterized by the same emitted electromagnetic radiation.
In yet another embodiment, the phosphor member is characterized by a reflective mode such that the laser beam from each of the one or more laser diode devices is incident on a different beam spot area on the excitation surface of the phosphor member and a white light emission is substantially output from the different beam spot areas, the white light emission comprising a mixture of wavelengths.
In various embodiments, the laser device and the phosphor device are mounted on a common support member with or without an intermediate substrate, and the phosphor material is operated in a transmissive mode, a reflective mode, or a side-pumped mode to generate a laser-based white light emitting light source. Merely by way of example, the invention may be applied to applications such as white lighting, white point lighting, flashlights, automotive headlamps, all-terrain vehicle lighting, flash sources such as camera flashlights, light sources used in recreational sports such as cycling, surfing, running, racing, rowing, unmanned aircraft, robots, other mobile applications or robotic applications, light sources for precautionary measures in security, defense applications, multicolor lighting, lighting for flat panels, medical, metrology, return light and other displays, high intensity lights, spectroscopy, entertainment, theatre, music and concerts, analytical fraud detection and/or identification, tools, water treatment, laser flares, target locking, communications, liFi, visible Light Communications (VLC), sensing, detection, distance detection, light radar (LIDAR), pressure swing, transportation, leveling, curing and other chemical processing, heating, cutting and/or melting, pumping other optics, other optoelectronic devices and related applications, and light source lighting, and the like.
Laser diodes are ideal as phosphor excitation sources. For space brightness (light intensity per unit area) 10000 times higher than that of a conventional LED, extreme directivity of laser emission, and no sag phenomenon (droop phenomenon) causing trouble to the LED, the laser diode enables features that cannot be realized by the LED and other light sources. In particular, since laser diode output beams of more than 0.5W, more than 1W, more than 3W, more than 10W, and even more than 100W can be focused to less than 1 mm in diameter, less than 500 microns in diameter, less than 100 microns in diameter, and even less than 50 microns in diameter, more than 1W/mm can be achieved 2 、100W/mm 2 Even more than 2500W/mm 2 The power density of (a). When this very small and powerful laser excitation beam is incident on the phosphor material, an extremely bright white or point source of light is obtained. Assuming a white light emitting phosphor conversion of excitation light of 200 lumens per watt of excitation light, a 5W excitation power can produce 1000 lumens in a beam diameter of 100 microns or 50 microns or less. Heretofore, unprecedented light source brightness may allow for regular changes in applications such as spot lighting or distance measurement, where parabolic reflectors or lens optics may be combined with point sources to produce highly collimated white light spots that may travel much further distances than were ever possible using LED or bulb technology.
In one embodiment, the present invention provides a CPoS laser-based white light source that includes a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist. In one example, the height is characterized by a dimension that is less than 12.5mm and greater than 0.5mm, although variations may exist. In yet another alternative example, the length and width are characterized by dimensions of less than 30mm, less than 15mm, or less than 5mm, although variations may exist. The apparatus has a support member, and at least one gallium-nitrogen containing laser diode device and phosphor material overlying the support member. The laser device is capable of emitting a laser beam having a wavelength preferably in the blue region of 425nm to 475nm, or in the ultraviolet or violet region of 380nm to 425nm, but other wavelengths are also possible, for example in the cyan region of 475nm to 510nm or in the green region of 510nm to 560 nm. In some embodiments, two or more laser diodes or laser bars are included in an integrated white light source. According to the present invention, combining multiple laser light sources can provide many possible benefits. First, the excitation power can be increased by beam combination to provide stronger excitation pits and thus produce a brighter light source. Similarly, the reliability of the source can be improved by using multiple sources under lower driving conditions to achieve the same excitation power as a single light source driven under more severe conditions (e.g., higher current and voltage). A second advantage is that by rotating the first free-space diverging elliptical laser beam by 90 degrees relative to the second free-space diverging elliptical laser beam and superimposing the central ellipse on the phosphor, it is possible to obtain a more circular spot. Alternatively, a more circular spot can be achieved by rotating the first free-space diverging elliptical laser beam 180 degrees relative to the second free-space diverging elliptical laser beam and eccentrically overlapping the ellipses on the phosphor to increase the spot diameter in the direction of slow axis divergence. In another configuration, more than 2 lasers are included and some combination of the above beam shaping spot geometry shaping is achieved. A third important advantage is that lasers of multiple colors or wavelengths can be included to provide improved performance, such as improved color rendering or color quality. For example, two or more blue excitation lasers with slightly offset wavelengths (e.g., 5nm, 10nm, 15nm, etc.) may be included to create a larger blue spectrum. In one embodiment, a single laser chip is configured within the laser-phosphor light source. By placing multiple laser chips in a predetermined configuration, multiple excitation beams can be superimposed on the phosphor dots to create a more ideal dot geometry. In an alternative embodiment, a laser diode ("multi-stripe laser") having a plurality of adjacent laser stripes is included in the integrated white light source. Multiple stripes may provide greater excitation power, supporting brighter light sources and/or improved or modified spot patterns on the phosphor. In a preferred embodiment, the phosphor material may provide a yellowish light in the range of 550nm to 590nm, such that when mixed with the blue light of the laser diode, white light is generated. In other embodiments, phosphors with red, green, yellow, and even blue light may be used in combination with a laser diode excitation source to produce white light with color mixing.
In one embodiment, the device layer comprises a superluminescent light emitting diode or SLED. SLEDs are similar in many respects to edge-emitting laser diodes; however, the emitting surface of the device is designed to have a very low reflectivity. The SLED is similar to a laser diode in that it is based on an electrically driven junction that is optically active and generates Amplified Spontaneous Emission (ASE) when injected with current, and can gain over a wide range of wavelengths. When the light output starts to be dominated by ASE, an inflection point appears in the light output versus current (LI) characteristic, where the unit of light output per unit of injected current becomes very large. This inflection point in the LI curve is similar to the threshold of a laser diode, but much softer. SLEDs have a layered structure designed with one or more light emitting layers covered above and below with a material of lower optical index, so that laterally guided optical modes can be formed. SLEDs are also fabricated with features that provide lateral optical confinement. These lateral confinement features may consist of etched ridges with air, vacuum, metal or dielectric material surrounding the ridges and providing a low optical index cladding. Lateral confinement features may also be provided by shaping the electrical contacts so that the injected current is confined to a limited area in the device. In such a "gain-guided" structure, the optical index of the light-emitting layer with injected carrier density provides the optical index contrast required for lateral confinement of the optical mode by dispersion. The emission spectral width is typically much wider (> 5 nm) than that of laser diodes and has advantages in reducing image distortion in displays, improving eye safety, and enhancing measurement and spectral application capabilities.
SLEDs are designed to have high single pass gain or amplification for spontaneous emission generated along the waveguide. SLED devices will also be designed to have low internal losses, preferably below 1cm -1 However, SLEDs can operate with internal losses higher than this. Ideally, the emitting surface reflectivity would be zero, however in practical applications, zero reflectivity is difficult to achieve and is designed to be less than 1%, less than 0.1%, less than 0.001%, or less than 0.0001% reflectivity. Reducing the emitting surface reflectivity can reduce feedback into the device cavity, thereby increasing the injection current density at which the device will begin lasing. Very low reflectivity of the emissive facets can be achieved through the addition of anti-reflective coatings and through a combination of angling the emissive facets relative to the SLED cavity such that the facets normal to the facets and the propagation direction of the guided mode are substantially non-parallel. Typically, this would mean a deviation of greater than 1-2 degrees. In practice, the ideal angle depends in part on the antireflective coating used, and the tilt angle must be carefully designed to avoid nulls in the relationship between reflectance and angle for optimum performance. The facets may be tilted with respect to the propagation direction of the guided mode in any direction with respect to the propagation direction of the guided mode, although some directions may be easier to manufacture, depending on the method of facet formation. The etched facets provide high flexibility for facet angle determination. Alternatively, a very common method of achieving angular output to reduce structural interference in the cavity would bend and/or angle the waveguide relative to a cleave plane formed on a predetermined crystallographic plane in the semiconductor chip. In this configuration, the angle of light propagation is not orthogonal to the cleave plane at a specific angle designed for low reflectivity. The low reflectivity facets may also be formed by roughening the emitting surface to enhance light extraction and limit reflective light coupling back into the guided mode. The SLED is applicable to all embodiments according to the invention and the device can be used interchangeably with a laser diode device when appropriate.
The apparatus typically has free space with unguided laser beam features that transmit the emission of the laser beam from the laser device to the phosphor material. The laser beam spectral width, wavelength, size, shape, intensity, and polarization are configured to excite the phosphor material. The laser beam can be configured by positioning it at a precise distance from the phosphor to take advantage of the beam divergence characteristics of the laser diode and achieve the desired spot size. In one embodiment, the angle of incidence from the laser to the phosphor is optimized to achieve the desired beam shape on the phosphor. For example, due to the asymmetry of the laser aperture and the different divergence angles of the beam on the fast and slow axes, the shape of the spot on the phosphor generated from the laser, arranged orthogonal to the phosphor, will be elliptical, with the fast axis diameter typically being larger than the slow axis diameter. To compensate for this, the laser beam incident angle on the phosphor can be optimized to stretch the laser beam in the slow axis direction so that the laser beam is more circular at the phosphor. In an alternative embodiment, a laser diode with multiple parallel adjacent emitter stripes may be configured to produce a wider and/or more powerful excitation spot on the phosphor. By making the spot laterally wider, the spot can be more rounded with respect to the faster divergence angle of the laser emission in the vertical direction. For example, the spacing of two or more laser bands may be 10-30 μm, 30-60 μm, 60-100 μm, or 100-300 μm. In some embodiments, the parallel strips have slightly detuned wavelengths to improve color quality. In other embodiments, free-space optics, such as a collimating lens, may be used to shape the beam before it is incident on the phosphor. In one example, a re-imaging optic is used to reflect and shape the light beam onto the phosphor member. In an alternative example, reflected incident light from the phosphor that would otherwise be wasted is recycled by the re-imaging optics by being reflected back to the phosphor.
The excitation light beam has a polarization purity greater than 50% and less than 100%. As used herein, the term "polarization purity" means that greater than 50% of the emitted electromagnetic radiation is in a substantially similar polarization state, such as a Transverse Electric (TE) or Transverse Magnetic (TM) polarization state, but may have other meanings consistent with ordinary meaning. In one example, the laser beam incident on the phosphor has a power of less than 0.1W, greater than 0.5W, greater than 1W, greater than 5W, greater than 10W, or greater than 20W.
The phosphor material may be operated in a transmissive mode, a reflective mode, or a combination of transmissive and reflective modes, or in a side pumped mode or other modes. Phosphor materials are characterized by good conversion efficiency, resistance to thermal damage, resistance to optical damage, thermal quenching characteristics, porosity to scatter excitation light, and thermal conductivity. The phosphor may have a surface that is intentionally roughened to increase light extraction from the phosphor. In a preferred embodiment, the phosphor material consists of a yellow YAG material doped with Ce, has a conversion efficiency of more than 100 lumens per watt, more than 200 lumens per watt or more than 300 lumens per watt and can be a polycrystalline ceramic material or a single crystal material. The white light apparatus also has an electrical input interface configured to couple electrical input power to the laser diode device to generate a laser beam and excite the phosphor material. The white light source is configured to produce a white light output of greater than 1 lumen, 10 lumens, 100 lumens, 250 lumens, 500 lumens, 1000 lumens, 3000 lumens, or 10000 lumens. The support member is configured to transfer thermal energy from the at least one laser diode device and the phosphor material to the heat sink. The support member is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt, which represents a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, copper tungsten, aluminum, alumina, siC, sapphire, alN or other metal, ceramic or semiconductor.
In a preferred configuration of the integrated white light source, the common support member comprises the same substrate as the substrate to which the gallium and nitrogen containing laser diode chip is directly bonded. That is, the laser diode chip is mounted or attached downward to a substrate composed of a material such as SiC, alN, or diamond, and the phosphor material is also mounted to the substrate, so that the substrate becomes the common support member. The phosphor material may have an intermediate material located between the substrate and the phosphor. The intermediate material may be comprised of a thermally conductive material such as copper. The laser diode may be attached to the first surface of the substrate using conventional die attach techniques using a solder such as AuSn solder, a SAC solder such as SAC305, a lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. Similarly, the phosphor material may be bonded to the substrate using soldering techniques or sintered silver techniques, but other techniques are also possible, such as gluing techniques or epoxy techniques. Optimizing bonding for lowest thermal impedance is a key parameter for heat dissipation from the phosphor, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material.
In an alternative configuration of the white light source, the laser diode is bonded to an intermediate substrate disposed between the gallium and nitrogen containing laser chip and the common support member. In such a configuration, the intermediate substrate may be composed of SiC, alN, diamond or other material, and the laser may be attached to the first surface of the substrate using conventional die attach techniques, using solder such as AuSn solder, SAC solder such as SAC305, leaded solder or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material can be dispensed or deposited using standard processing equipment and cycling temperatures, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The second surface of the substrate may be attached to the common support member using similar techniques, but may be other techniques. Similarly, the phosphor material may have an intermediate material or substrate located between the common support member and the phosphor. The intermediate material may be comprised of a thermally conductive material such as copper or copper tungsten. The phosphor materials may be bonded using soldering techniques, sintered silver techniques, or other techniques. In this configuration, the common support member should be constructed of a thermally conductive material such as copper or copper tungsten. Optimizing the bonding for lowest thermal impedance is a key parameter for heat dissipation from the phosphor, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material.
In yet another preferred variation of this CPoS white light source, the gallium-nitrogen containing laser epitaxial material may be attached to the substrate member using a method for stripping and transferring the gallium-nitrogen containing epitaxial material to a common support member. In this embodiment, the gallium and nitrogen epitaxial material is released from the gallium and nitrogen containing substrate on which it is epitaxially grown. As one example, the epitaxial material may be released using a Photoelectrochemical (PEC) etching technique. And then transferred to a substrate material using a technique such as wafer bonding in which a bonding interface is formed. For example, the bond interface may consist of Au — Au bonds. The substrate material preferably has a high thermal conductivity, such as SiC, wherein the epitaxial material is subsequently processed to form a laser diode having a cavity member, a front side and a back side, and electrical contacts for injecting current. After laser fabrication is complete, phosphor materials are introduced onto the substrate to form an integrated white light source. The phosphor material may have an intermediate material located between the substrate and the phosphor. The intermediate material may be comprised of a thermally conductive material, such as copper. The phosphor may be attached to the substrate using conventional die attach techniques using solder such as AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. Optimizing the bonding to achieve the lowest thermal resistance is a key parameter for phosphor heat dissipation, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material. The benefits of using this embodiment with both stripped and transferred gallium and nitrogen containing materials are reduced cost, improved laser performance, and a higher degree of flexibility in using the technique for integration.
In some embodiments of the integrated white light source, the present invention may include safety features and design considerations. In any laser-based light source, safety is a critical aspect. It is critical that the light source not be damaged or altered in a way that produces a laser diode beam that is harmful to humans, animals or the environment. Thus, the overall design should include safety considerations and features, and in some cases even active components for monitoring. Examples of design considerations and features for safety include positioning the laser beam relative to the phosphor in such a way that if the phosphor is removed or damaged, the exposed laser beam will not cause it to reach the external environment in a deleterious form (e.g., a collimated coherent beam). More specifically, the white light source is designed such that the laser beam is directed away from the outside environment and towards a surface or feature that will prevent the laser beam from being reflected to the outside world. In one example of passive design features for safety, beam dumps are included and/or absorbing materials can be specifically positioned where the laser beam will impinge in the event of a removed or damaged phosphor. In some embodiments, a thermal fuse is added, wherein the fuse creates an open circuit and shuts down the laser diode in unsafe conditions.
In some embodiments of the present invention, the safety features and systems use active components. Examples of active components include photodiodes/photodetectors and thermistors. Strategically located detectors designed to detect direct blue light, scattered blue light, or phosphorescence (e.g., yellow phosphorescence) from a laser may be used to detect phosphor failure that may expose a blue beam. Upon detection of such an event, a closed circuit or feedback loop will be configured to stop supplying power to the laser diode and effectively turn it off. For example, a detector for detecting the phosphor emission may be used to determine if the phosphor emission is rapidly decreasing, which would indicate that the laser light is no longer effectively striking the phosphor for excitation, and may mean that the phosphor is removed or damaged. In another example of an active security function, a blue sensitive photodetector may be placed to detect reflected or scattered blue light from the laser diode, so that if the phosphor is removed or damaged, the amount of detected blue light will increase rapidly and the laser will turn off to be turned off by the security system. In yet another example of an active security feature, a thermistor may be positioned near or below the phosphor material to determine if there is a sudden increase in temperature, which may be the result of an increase in direct radiation from the blue laser diode, indicating that the phosphor is damaged or removed. Also in this case, the thermistor signal trips the feedback loop to stop the power supply to the laser diode and shut it down. Of course, these are merely exemplary embodiments, and there are several configurations for the photodiode and/or thermistor that are integrated with the laser-based white light source to form a safety feature (e.g., a feedback loop) to stop operation of the laser.
In many embodiments of the present invention, an electrostatic discharge (ESD) protection element is included. For example, an ESD protection element would be used to protect an integrated white light source from damage that may occur due to the sudden flow of current resulting from charge accumulation. In one example, a surge voltage suppression (TVS) element is employed.
In some embodiments of integrated white light sources, final packaging needs to be considered. There are many packaging aspects that should be considered, such as form factor, cost, functionality, thermal impedance, sealing characteristics, and basic compatibility with the application. The form factor will depend on the application, but it will generally be desirable to manufacture a packaged white light source of minimum size. Cost should be minimized in all applications, but in some applications cost will be the most important consideration. In such a case, it may be desirable to use off-the-shelf packaging in high volume production. Functional options include the existing guidance and characterization of the light emission for this application and the integration of features such as photo detectors, thermistors, or other electronic or optoelectronic components. For optimum performance and lifetime, the thermal impedance of the package should be minimized, particularly in high power applications. Examples of sealing configurations include open environments, environmental seals, or hermetic seals. Typically for GaN-based lasers, a hermetic package is required, but other packages are also contemplated and deployed for various applications. Examples of off-the-shelf packages for integrated white light sources include TO cans, such as TO38, TO56, TO9, TO5 or other TO can type packages. Flat packages with windows may also be used. Examples of flat packages include butterfly packages, such as TOSAs. Surface Mount Device (SMD) packages may also be used, which are attractive due to their low cost, good hermetic seal, and potentially low thermal resistance. In other embodiments, custom packages may also be used. In another embodiment, a "Flash" package may be used to integrate a white light source. For example, the package may be used to adapt a laser-based white light source to a camera flash application. One standard packaging format for LEDs today employs flat ceramic packages, sometimes referred to as "flash" packages, because the devices built on these platforms are used primarily for camera flash and cell phone applications. A typical flash package includes a flat ceramic substrate (alumina or AlN) with connection pads for the LED and ESD devices, and leads that provide locations for clamping or soldering external electrical connections to power the devices. The phosphor may be included near the LED die by molding or other silicone-containing dispensing applications. This layer is then overmolded, typically with a clear silicone lens, to improve light extraction. The main advantages of this format of package are the very small overall package size (-3 mm x-5 mm), reasonable light output performance (hundreds of lumens), small light source size and low overall cost of the LED device. This packaging style can also be achieved by using a laser plus phosphor design style, which may eliminate packaging and lens steps, providing an LED replacement with excellent spot size and brightness. If a protective cover is required to contain the laser and phosphor subassemblies, a hollow glass dome may be used to provide protection.
In some embodiments of the present invention, an integrated white light source is combined with an optical component to manipulate the white light produced. In one example, white light sources may be used in spotlight systems, such as flashlights or automotive headlamps or other lighting applications where light must be directed or projected to a designated location or area. In one embodiment, the reflector is coupled to a white light source. In particular, parabolic (paraolic) (otherwise known as parabolic (paraolic) or parabolic (paraolic)) reflectors are deployed to project white light. By positioning the white light source in the focal point of the parabolic reflector, the plane wave will be reflected and propagate as a collimated beam along the axis of the parabolic reflector. In another example, a lens is used to collimate the white light into a projection beam. In one example, a simple aspheric lens would be placed in front of the phosphor to collimate the white light. In another example, total internal reflector optics are used for collimation. In other embodiments, other types of collimating optics may be used, such as spherical lenses or aspherical lenses. In several embodiments, a combination of optical devices is also used.
In particular embodiments of the above general invention, the present invention is configured for side pumped phosphors operating in a transmissive mode. In this configuration, the phosphor is located in front of the laser plane of the output laser beam, wherein both the laser and the phosphor are arranged on the support member. The gallium-nitrogen containing laser diode is configured with a cavity having a length greater than 100 μm, greater than 500 μm, greater than 1000 μm, or greater than 1500 μm and a width greater than 1 μm, greater than 10 μm, greater than 20 μm, greater than 30 μm, or greater than 45 μm. The cavity is configured at the end and has a front side and a back side, wherein the front side includes an output side and emits a laser beam incident on the phosphor. The output face may include an optical coating to reduce reflectivity in the cavity. The back surface may be coated with a high reflectivity coating to reduce the amount of light emitted from the back surface of the laser diode. The phosphor is composed of Ce-doped YAG and emits yellow light. The phosphor is shaped as a block, plate, sphere, cylinder, or other geometric shape. In particular, the primary dimension of the phosphor geometry may be less than 50 μm, less than 100 μm, less than 200 μm, less than 500 μm, less than 1mm, or less than 10mm. Operating in a transmissive mode, the phosphor has a first major side for receiving an incident laser beam and at least a second major side, wherein a majority of the useful white light will exit the phosphor for coupling to an application. To improve efficiency by maximizing the amount of light leaving the second side of the phosphor, the phosphor may be coated with a layer configured to modify the reflectance of certain colors. In one example, a coating configured to increase the reflectivity of yellow light is applied to the first side of the phosphor such that the amount of yellow light emitted from the first side is reduced. In another example, the coating for increasing the reflectance of blue light is spatially patterned on the first side of the phosphor to allow excitation light to pass through, but prevent backward propagating scattered light from escaping. In another example, an optical coating configured to reduce reflectivity to yellow and blue light is applied to at least the second side of the phosphor to maximize light escaping from the major side where useful light exits. In an alternative embodiment, a powdered phosphor, such as a yellow phosphor, is dispensed into a transparent plate or solid structure using a binder material and is configured to emit white light when excited by and combined with a blue laser beam. The powdered phosphor may be composed of a YAG-based phosphor and other phosphors.
Thermal impedance is a critical consideration with respect to connecting the phosphors to the common support member. The best joining materials, interface geometry, and joining process practices should be used to minimize the thermal resistance of the joint to achieve the lowest thermal resistance with sufficient reflectivity. Examples include AuSn solder, SAC solder (e.g., SAC 305), lead-containing solder, or indium, but other solders are also possible. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material can be dispensed or deposited using standard processing equipment and cycling temperatures, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The joint may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), thermal adhesive, and other materials. Alternatively, the joint may be formed by a metal-metal bond (e.g., au-Au bond). The common support member with the laser and phosphor materials is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt, which represents a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, copper tungsten, aluminum, alumina, siC, sapphire, alN or other metal, ceramic or semiconductor. The side-pumped transmission device has a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist. In one example, the height is characterized by a dimension that is less than 12.5mm and greater than 0.5mm, although variations may exist. In yet another alternative example, the length and width are characterized by dimensions of less than 30mm, less than 15mm, or less than 5mm, although variations may exist.
In an alternative embodiment of the present invention, the plurality of phosphors is operated in a transmissive mode for emitting white light. In one example, a violet laser diode is configured to emit a wavelength of 395nm to 425nm and excite a first blue phosphor and a second yellow phosphor. In this configuration, the first blue phosphor plate may be fused or bonded to the second yellow phosphor plate. In a practical configuration, the laser beam will be directly incident on the first blue phosphor, where a portion of the blue light will excite the second yellow phosphor to emit yellow light to combine with the blue light and produce white light. Furthermore, the violet pump will be substantially fully absorbed, since the possibly non-absorbed substances in the blue phosphor will subsequently be absorbed by the yellow phosphor. In an alternative practical configuration, the laser beam will be directly incident on the second yellow phosphor, where a portion of the violet electromagnetic emission will be absorbed by the yellow phosphor to excite yellow light, while the remaining violet light will pass to the blue phosphor and produce blue light, to combine the yellow light with the blue light and produce white light. In an alternative embodiment, a powdered phosphor mixture would be dispensed into a transparent plate or solid structure using a binder material such that the different colored phosphors (e.g., blue and yellow phosphors) mix and are configured to emit white light when excited by a violet laser beam. The powdered phosphor may be composed of YAG-based phosphors, luAG phosphors, and other phosphors.
In an alternative embodiment of the multi-phosphor transmission example according to the present invention, a blue laser diode operating at a wavelength of 425nm to 480nm is configured to excite the first green phosphor and the second red phosphor. In this configuration, the first green phosphor plate may be fused or bonded to the second red phosphor plate. In a practical configuration, the laser beam will be directly incident on the first green phosphor, where a portion of the green light will excite the second red phosphor to emit red light to combine with the green phosphor emission and the blue laser diode emission to produce white light. In an alternative practical configuration, the laser beam would be directly incident on the second red phosphor, where a portion of the blue electromagnetic emission would be absorbed in the red phosphor to excite the red emission, while a portion of the remaining blue laser emission would pass to the green phosphor and generate green light, combining with the red phosphor emission and the blue laser diode emission to generate white light. In an alternative embodiment, a powdered phosphor mixture would be dispensed into a transparent plate or solid structure using a binder material such that the different colored phosphors (e.g., red and green phosphors) are mixed and configured to emit white light when excited by and combined with a blue laser beam. The powdered phosphor may consist of YAG-based phosphors, luAG phosphors and other phosphors. A benefit or feature of this embodiment is a higher color quality that can be achieved from white light consisting of red, green and blue light emissions. Of course, other variations of the present invention are possible, including the integration of more than two phosphors, and may include one or a combination of red, green, blue, and yellow phosphors.
In several embodiments according to the present invention, the laser-based integrated white light source is configured as a high CRI white light source with a CRI of more than 70, more than 80 or more than 90. In these embodiments, phosphors in the form of a plurality of mixed powder phosphor compositions or a plurality of phosphor plate configurations or the like are used. Examples of such phosphors include, but are not limited to, YAG, luAG, red nitrides, aluminates, oxynitrides, caMgSi 2 O 6 :Eu 2+ 、BAM:Eu 2+ 、AlN:Eu 2+ 、(Sr,Ca) 3 MgSi 2 O 8 :Eu 2+ And JEM.
In some configurations of high CRI implementations of integrated laser based white light sources, a blue laser diode excitation source operating in the wavelength range of 430nm to 470nm is used to excite:
1) Yellow phosphor + red phosphor, or
2) Green phosphor + red phosphor, or
3) Cyan phosphor + orange phosphor, or
4) Cyan phosphor + orange phosphor + red phosphor, or
5) Cyan phosphor + yellow phosphor + red phosphor, or
6) Cyan phosphor + green phosphor + red phosphor.
In some alternative configurations of high CRI implementations of integrated laser based white light sources, a violet laser diode excitation source operating in the wavelength range of 390nm to 430nm is used to excite:
1) Blue phosphor + yellow phosphor + red phosphor, or
2) Blue phosphor + green phosphor + red phosphor, or
3) Blue phosphor + cyan phosphor + orange phosphor, or
4) Blue phosphor + cyan phosphor + orange phosphor + red phosphor, or
5) Blue phosphor + cyan phosphor + yellow phosphor + red phosphor, or
6) Blue phosphor + cyan phosphor + green phosphor + red phosphor.
In an alternative embodiment of the multi-phosphor transmission example according to the present invention, a blue laser diode operating at a wavelength of 395nm to 425nm is configured to excite the first blue phosphor, the second green phosphor and the third red phosphor. In this embodiment of this configuration, the first blue phosphor plate may be fused or bonded to a second green phosphor plate, which is fused or bonded to a third red phosphor plate. In a practical configuration, the laser beam will be directly incident on the first blue phosphor, where a portion of the blue emission will excite the second green phosphor and the third red phosphor to emit green and red emissions, which combine with the first phosphor blue emission to produce white light. In an alternative practical configuration, the violet laser beam would be directly incident on the third red phosphor, where a portion of the violet electromagnetic emission would be absorbed by the red phosphor to excite the red emission, while the remaining portion of the violet laser emission would pass to the second green phosphor and produce green emission to combine with the red phosphor emission, and a portion of the violet laser diode would pass to the first blue phosphor to produce blue emission to combine with the red and green emission to produce white light. In an alternative embodiment, a powdered phosphor mixture would be dispensed into a transparent plate or solid structure using a binder material such that the different colored phosphors (e.g., red, green, and blue phosphors) are mixed and configured to emit white light when excited by a violet laser beam. The powdered phosphor may consist of YAG-based phosphors, luAG phosphors and other phosphors. A benefit or feature of this embodiment is that higher color quality and color rendering quality can be achieved from white light consisting of red, green and blue emissions. Of course, other variations of the present invention are possible, including the integration of more than two phosphors, and may include one or a combination of red, green, blue, and yellow phosphors.
In yet another variation of the side-pumped phosphor configuration, a "point source" or "point source-like" integrated white light emitting device is implemented. In this configuration, the phosphor most likely has a cubic geometry or a spherical geometry such that white light can be emitted from more than 1 primary emission surface. For example, in a cube geometry, all six faces of the cube may emit white light, or in a sphere configuration, the entire surface may emit to create a perfect point source. A first powerful advantage of this configuration is that the white light spot size is controlled by the phosphor size, which can achieve a smaller spot size than alternative transmissive or reflective mode configurations by avoiding the spot size growth that occurs in the phosphor due to scattering, reflection, and lack of efficient absorption by the phosphor. An ultra-small spot size is desirable for most effective collimation in directional applications. A second advantage of this configuration is that the ideal heat dissipation configuration can be thermally and mechanically attached to the heat sink, wherein for the phosphor member it is the same as the reflective mode configuration with the entire bottom surface of the phosphor. Furthermore, since the laser diode assembly does not require thick or angled intermediate support members to elevate the beam and control the angular incidence as in the reflective mode configuration, the laser can be mounted closer to the base assembly to achieve a shorter heat conduction path to the heat sink. A third advantage is the inherent safety design, since the primary emission may come from the top surface of the phosphor orthogonal to the laser beam direction, so that in case of phosphor cracking or damage, the laser beam will not be directed in the direction of white light capture. In this configuration, if the phosphor is to be removed or destroyed, the laser beam will be incident on the side of the package. Furthermore, such a configuration would avoid potential problems in a reflective configuration where an escaping beam could result from reflection of an incident beam at the top of the surface. In such a side-pumped configuration, the reflected beam will be substantially contained in the package. A fourth advantage is that since the laser diode or the SLED device can be mounted flat on the base member, the assembly process and components can be simplified. In this side-pumped configuration, it may be advantageous to promote primary emission from the top surface of the phosphor. This can be achieved by treatments that promote light escape from the top surface, such as applying an anti-reflection coating or roughening, and by treatments that reduce light escape from the side and bottom surfaces, such as applying a highly reflective layer, such as a metal or dielectric layer.
In some configurations of this embodiment, the phosphors are attached to a common support member, where the common support member may not be completely transparent. In this configuration, the surface or side to which the phosphor is attached may impede the emission of light, thus reducing the overall efficiency or quality of the point source white light emitter. However, such obstruction to the emission of light may be minimized or mitigated to provide very efficient illumination. In other configurations, the phosphor is supported by an optically transparent member such that light is freely emitted in all directions from the phosphor point light source. In one variation, the phosphor is completely surrounded or encapsulated by an optically transparent material, including a solid material such as SiC, diamond, gaN, or other solid material, or a liquid material like water or a more thermally conductive liquid.
In another variation, the support member may also serve as a waveguide for the laser light to reach the phosphor. In another variation, the support member may also serve as a protective safety measure to ensure that the directly emitted laser light is not exposed as it travels to reach the phosphor. Point sources capable of producing true omnidirectional emission are increasingly useful as point sources become smaller due to the fact that the production of emission aperture and emission angle is preserved or lost with the addition of subsequent optics and reflectors. In particular, for example, a small optic or reflector may be used to collimate the small point light source. However, if the same small optic and/or reflector assembly is applied to a large point source, optical control and collimation can be impaired.
In some embodiments according to the present invention, the periodic 2D photonic crystal structure may be applied to a single crystal or polycrystalline phosphor material structure. The photonic crystal structure will serve to suppress emission in a given direction and redirect light out of the photonic crystal in a direction suitable and selected for device design. Today's phosphor structures are primarily lambertian emitters, except where the waveguide and critical angle play a role. Today, many phosphors meet the basic material requirements needed to create photonic crystal structures (dielectric or metal dielectric materials with low light absorption). Adding a photonic crystal structure to the phosphor plate material will enable enhanced light extraction in one direction over the other in these materials. This can separate excitation and emission characteristics, allowing greater design flexibility.
In yet another variation of the side pumped phosphor embodiment, the phosphor is excited from the side and is configured to emit mostly white light from the top surface. In this configuration, the phosphor is likely to have a cubic geometry, a cylindrical geometry, a polyhedral geometry, a hexagonal geometry, a triangular geometry, a pyramidal geometry, or other polygonal geometry, wherein the white light is configured to emit primarily from the top surface of the phosphor. In this configuration, the laser beam will enter the phosphor from a first side of the phosphor where a portion of the laser excitation light with the first wavelength will be converted to a second wavelength. This first side of the phosphor may be configured for changing the reflectivity, e.g. coated or treated, to reduce the reflectivity in the blue or violet wavelength range and/or to increase the reflectivity in the phosphor emission wavelength range (e.g. yellow). In one example of a side pumped embodiment, the laser excitation beam is incident on the first side of the phosphor at a brewster angle. In further examples, additional sides of the phosphor may be coated, treated or shaped to increase the reflectivity to the laser excitation wavelength and the phosphor conversion wavelength, so that light within the phosphor can reflect inside the phosphor until it escapes from the phosphor from the top. Special phosphor shaping or coating techniques may be used to increase the proportion of light that escapes from the top surface. A first powerful advantage of this configuration is that the white light spot size is controlled by the phosphor size, which can achieve a smaller spot size than alternative transmissive or reflective mode configurations by avoiding the spot size growth that occurs in the phosphor due to scattering, reflection, and lack of efficient absorption by the phosphor. An ultra-small spot size is desirable for most effective collimation in directional applications. A second advantage of this configuration is that the ideal heat dissipation configuration can be thermally and mechanically attached to the heat sink, where it is the same for the phosphor member as a reflective mode configuration with the entire bottom surface of the phosphor. Furthermore, since the laser diode assembly does not require thick or angled intermediate support members to elevate the beam and control the angular incidence as in the reflective mode configuration, the laser can be mounted closer to the base assembly to achieve a shorter heat conduction path to the heat sink. A third advantage is the inherent safety design, since the primary emission may come from the top surface of the phosphor orthogonal to the laser beam direction, so that in case of phosphor cracking or damage, the laser beam will not be directed in the direction of white light capture. In this configuration, if the phosphor is to be removed or destroyed, the laser beam will be incident on the side of the package. Furthermore, such a configuration would avoid potential problems in a reflective configuration where an escaping beam could result from reflection of an incident beam at the top of the surface. In such a side-pumped configuration, the reflected beam will be substantially contained in the package. A fourth advantage is that since the laser diode or SLED device can be mounted flat on the base member, the assembly process and components can be simplified. In this side-pumped configuration, it may be advantageous to promote primary emission from the top surface of the phosphor.
In all side pumps and transmission embodiments of the present invention, additional features and designs may be included. Shaping of the excitation laser beam to optimize the beam spot characteristics on the phosphor can be achieved, for example, by careful design consideration of the angle at which the laser beam is incident on the phosphor, or by using integrating optics (e.g., free space optics such as a collimating lens). In some embodiments, a re-imaging optic, such as a re-imaging reflector, is used to shape the excitation light beam and/or recapture the excitation light reflected from the phosphor. Safety features such as passive features like physical design considerations and beam dump and/or active features like thermal fuses, photo detectors or thermistors may also be included, which may be used in a closed loop to turn off the laser when indicating a signal.
Point source omnidirectional light sources may be configured for a variety of types of illumination patterns, including 4-pi spherical illumination, to provide broad illumination of a three-dimensional space such as a room, lecture hall, or stadium. In addition, optical elements may be included to manipulate the white light produced, thereby producing highly directional illumination. In some embodiments, a reflector such as a parabolic reflector or a lens such as a collimating lens is used to collimate white light or to produce a spotlight that can be applied to an automobile headlight, flashlight, spotlight, or other lamp. In other embodiments, point source illumination may be modified with cylindrical optics and reflectors to linear omnidirectional illumination or linear directional illumination. In addition, point source illumination is coupled into the planar waveguide for planar 2-pi spherical emission, planar 4-pi spherical emission to produce a non-glare illumination pattern emitted from the planar surface.
In another particularly preferred embodiment of the integrated white light source, the invention is configured for reflective mode phosphor operation. In one example, the excitation laser beam enters the phosphor through the same major surface as the emission of useful white light. That is, when operating in a reflective mode, the phosphor may have a first major surface configured to receive an incident excitation laser beam and emit useful white light. In this configuration, the phosphor is located in front of the laser plane of the output laser beam, wherein both the laser and the phosphor are arranged on the support member. The gallium-nitrogen containing laser diode is configured with a cavity having a length greater than 100 μm, greater than 500 μm, greater than 1000 μm, or greater than 1500 μm and a width greater than 1 μm, greater than 10 μm, greater than 20 μm, greater than 30 μm, or greater than 45 μm. The cavity is configured at the end and has a front side and a back side, wherein the front side includes an output face and emits a laser beam incident on the phosphor. The output face may include an optical coating to reduce reflectivity in the cavity. The back surface may be coated with a high reflectivity coating to reduce the amount of light emitted from the back surface of the laser diode. In one example, the phosphor may be composed of Ce-doped YAG and emit yellow light. The phosphor may be a powdered ceramic phosphor, a ceramic phosphor plate, or may be a single crystal phosphor. The phosphor is preferably formed as a generally planar member such as a plate, sheet, or the like having a square, rectangular, polygonal, circular, oval, or the like shape and is characterized by a thickness. In a preferred embodiment, the length, width and/or diameter dimensions of the large surface area of the phosphor are greater than the thickness of the phosphor. For example, the diameter, length, and/or width dimensions may be 2 times greater than the thickness, 5 times greater than the thickness, 10 times greater than the thickness, or 50 times greater than the thickness. In particular, the phosphor plate may be configured as a circle having a diameter of more than 50 μm, more than 100 μm, more than 200 μm, more than 500 μm, more than 1mm or more than 10mm and a thickness of less than 500 μm, less than 200 μm, less than 100 μm or less than 50 μm.
In one example of an embodiment of the present invention reflective mode CPoS white light source, optical coatings, material selection, or special design considerations are required to improve efficiency by maximizing the amount of light leaving the major surface of the phosphor. In one example, the back surface of the phosphor may be coated with a reflective layer or have a reflective material located on the back surface of the phosphor adjacent to the primary emission surface. The reflective layer, coating or material helps to reflect light that strikes the rear surface of the phosphor so that it is reflected and exits through the major surface, thereby capturing useful light therein. In one example, the coating is configured to increase the reflectivity for yellow and blue light and is applied to the phosphor prior to attaching the phosphor to the common support member. In another example, the reflective material serves as a bonding medium to attach the phosphor to the support member or the intermediate substrate member. Examples of reflective materials include reflective solder and reflective glue, but other materials are possible. In some configurations, the major top surface of the phosphor into which the laser excitation beam is incident is configured to reduce the reflectivity to blue or violet excitation beam wavelengths and/or phosphor emission wavelengths such as yellow wavelengths. This can be accomplished by optical coating of the phosphor with a dielectric layer, shaping of the phosphor surface, and roughening of the phosphor surface, or other techniques This reduced reflectivity is now present. In some examples, the laser beam incident angle is configured at or near the brewster angle, where light with a particular polarization is preferably transmitted through the major surface of the phosphor. Very good transmission can be challenging due to the divergence of the laser light resulting in a change in the angle of incidence of the plane wave within the beam, but ideally, most of the light incident on the phosphor will be at or near brewster's angle. For example, a YAG or LuAG phosphor may have a refractive index of about 1.8 in the violet and blue wavelength ranges. With respect to Brewster's angle, as arctan (n) 2 /n 1 ) Given by θ B (wherein, n is 1 Is the refractive index of air, n 2 Is the refractive index of the phosphor) will be about 61 degrees (or about 55 to 65 degrees) off-axis from normal incidence. Or alternatively, about 29 degrees (or about 25 to 35 degrees) from an axis parallel to the phosphor surface.
Thermal impedance is a critical consideration with respect to connecting the phosphors to the common support member. The best joining materials, interface geometry, and joining process practices should be used to minimize the thermal resistance of the joint to achieve the lowest thermal resistance with sufficient reflectivity. Examples include AuSn solder (e.g., SAC 305), leaded solder, or indium, but other solders are also possible. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The joints may also be formed of thermally conductive glue, thermal epoxy, and other materials. The common support member with the laser and the phosphor material is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt, which represents a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, copper tungsten, aluminum, siC, sapphire, alN or other metal, ceramic or semiconductor. The reflective mode white light source device has a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist. In one example, the height is characterized by a dimension that is less than 12.5mm and greater than 0.5mm, although variations may exist. In yet another alternative example, the length and width are characterized by dimensions of less than 30mm, less than 15mm, or less than 5mm, although variations may exist.
Reflective mode integrated white light source embodiments of the present invention are configured with a phosphor member attached to a common support member with a larger major surface configured to receive laser excitation light and emit useful white light at an orthogonal angle (about 90 degrees) or a non-perpendicular angle (about 0 degrees to about 89 degrees) to the axis of the laser diode output beam used to excite the phosphor. That is, the output laser beam is directed at the emitting surface of the phosphor at an angle between 0 and 90 degrees. In this configuration, the property that the laser beam is not in the same direction as the emission of the primary phosphor emitting surface is a built-in security feature. That is, the laser beam is directed away from, or opposite to, the direction in which the useful white light exits the phosphor. Thus, if the phosphor cracks or breaks during normal operation or tampering, the laser beam will not be directed to the outside world and may cause damage thereto. Instead, the laser beam will be incident on the surface of the backing to which the phosphor is attached. As a result, the laser beam may be scattered or absorbed rather than leaving the white light source and entering the ambient environment. Additional safety measures may be taken, such as using a beam dump function or using an absorbing material, such as a thermal fuse that heats up and creates an open circuit within the laser diode driver circuit.
One example of this reflective mode integrated white light source embodiment is configured with a laser beam perpendicular to the primary phosphor emitting surface. In this configuration, the laser diode would be in front of the primary emission surface of the phosphor where it would block the useful white light emitted from the phosphor. In a preferred embodiment of this reflective mode integrated white light source, the laser beam will be configured with an angle of incidence away from the phosphor axis to strike the phosphor surface at an angle between 0 and 89 degrees or at a "glancing" angle. In some configurations, the angle of incidence is configured at or near the brewster angle to maximize the transmission of the laser excitation light into the phosphor. In the preferred embodiment, the laser diode device is located on the side of the phosphor rather than in front of the phosphor where it does not substantially block or obstruct the emitted white light. Furthermore, in this configuration, the built-in security feature is more optimized than the normal incidence configuration because the incident laser beam is not directly reflected from the back surface of the support member with the phosphor attached therein when incident at an angle with the phosphor damaged or removed. By striking the surface at a declination or glancing angle, any potentially reflected component of the light beam can be directed to remain within the device without leaving the external environment where it can pose a hazard to humans, animals and the environment.
In all reflective embodiments of the present invention, additional features and designs may be included. Shaping of the excitation laser beam to optimize the beam spot characteristics on the phosphor can be achieved, for example, by careful design consideration of the angle at which the laser beam is incident on the phosphor, or by using integrating optics (e.g., free space optics such as a collimating lens). Beam shaping may also be achieved by using two or more adjacent parallel emitter stripes spaced 10 μm to 30 μm apart, or 30 μm to 50 μm apart, or 100 μm to 250 μm apart so that the beam expands on the slow divergence axis from the laser emission aperture. Beam shaping may also be achieved by re-imaging optics. Safety features such as passive features like physical design considerations and beam dump and/or active features like photo detectors or thermistors of the closed loop or feedback loop type may also be included to turn off the laser when indicating a signal. In addition, optical elements may be included to manipulate the white light produced. In some embodiments, a reflector such as a parabolic reflector or a lens such as a collimating lens is used to collimate white light or to produce a spotlight that may be applied to an automobile headlight, flashlight, spotlight, or other lamp.
In some embodiments according to the invention, the plurality of laser diode sources are configured to excite the same phosphor or phosphor network. According to the present invention, combining multiple laser light sources can provide many possible benefits. First, the excitation power can be increased by beam combination to provide stronger excitation pits and thus produce a brighter light source. In some embodiments, a single laser chip is configured within the laser-phosphor light source. By including a plurality of lasers each emitting 1W, 2W, 3W, 4W, 5W or more power, the excitation power can be increased, which will increase the light source brightness. For example, by including two 3W lasers exciting the same phosphor area, the excitation power can be increased to 6W to double the white light brightness. In the example of generating approximately 200 lumens of white light per 1 watt of laser excitation power, the white light output would increase from 600 lumens to 1200 lumens. Similarly, source reliability can be improved by using multiple light sources under lower driving conditions to achieve the same excitation power as a single light source driven under more severe conditions (e.g., higher current and voltage). A second advantage is that by rotating the first free-space diverging elliptical laser beam by 90 degrees relative to the second free-space diverging elliptical laser beam and superimposing the central ellipse on the phosphor, it is possible to obtain a more circular spot. Alternatively, a more circular spot can be achieved by rotating the first free-space diverging elliptical laser beam 180 degrees relative to the second free-space diverging elliptical laser beam and eccentrically overlapping the ellipse on the phosphor to increase the spot diameter in the direction of slow axis divergence. In another configuration, more than 2 lasers are included and some combination of the above beam shaping spot geometry shaping is achieved. A third important advantage is that the multiple color lasers in the emitting device can significantly improve the color quality (CRI and CQS) by improving the spectral fill in the violet/blue and cyan regions of the visible spectrum. For example, two or more blue excitation lasers with slightly detuned wavelengths (e.g., 5nm, 10nm, 15nm, etc.) may be included to excite the yellow phosphor and create a larger blue spectrum.
In one embodiment, the present invention provides an integrated white light source. The integrated white light source includes a laser diode device comprising gallium and nitrogen containing materials and configured as an excitation source, and a phosphor member configured as a wavelength converter and an emitter and coupled to the laser diode device. The integrated white light source further comprises a common support member configured to support the laser diode device and the phosphor member, a heat sink thermally coupled to the common support member, the common support member configured to transport thermal energy from the laser diode device and the phosphor member to a thermal energy sink, and an output face configured on the laser diode device to output a laser beam consisting of electromagnetic radiation selected from violet emission and/or blue emission having a first wavelength ranging from 400nm to 485 nm. Furthermore, the integrated white light source further comprises a free space between the output face and the phosphor member having non-guiding properties capable of transmitting the laser beam from the laser diode device to the excitation surface of the phosphor member, a transmission angle range being incident between the laser beam and the excitation surface of the phosphor member such that on average the laser beam deviates from normal incidence with respect to the excitation surface, and a beam spot area configured with a certain geometrical size and shape. The phosphor member converts a portion of the electromagnetic radiation from the laser beam having the first wavelength into emitted electromagnetic radiation having a second wavelength longer than the first wavelength. The integrated white light source further comprises a plurality of scattering centers associated with the phosphor member to scatter electromagnetic radiation having the first wavelength from the laser beam incident on the phosphor member. Furthermore, the integrated white light source comprises a reflective mode with the phosphor member such that the laser beam is incident on a beam spot area on the excitation surface of the phosphor member and a white light emission is output from substantially the same beam spot area, the white light emission consisting of various mixed wavelengths including at least electromagnetic radiation emitted from the phosphor member having the second wavelength. Further, the integrated white light source includes a form factor having a package of integrated white light sources, the form factor having length, width, and height dimensions.
In another embodiment, the present invention provides an integrated white light source based on a laser beam. The integrated white light source includes a laser diode device comprising gallium and nitrogen containing materials and configured as an excitation source, and a phosphor member configured as a wavelength converter and an emitter and coupled to the laser diode device. Further, the integrated white light source comprises a shaped support member having at least one flat surface portion and one or more wedge-shaped portions having inclined planes. Each inclined plane forms a wedge angle with respect to the surface normal of the flat surface area. The planar surface region is configured to support the phosphor member with the excitation surface. Each tilted plane is configured to have one of the one or more laser diode devices attached thereto. Further, the integrated white light source comprises an output face arranged on the laser diode device to output a laser beam consisting of electromagnetic radiation selected from the group consisting of violet light and/or blue light of the first wavelength range of 400nm to 485 nm. The integrated white light source further comprises a free space between the output face and the phosphor member, the free space having non-guiding properties capable of transmitting the laser beam from the laser diode device to the excitation surface of the phosphor member. Furthermore, the integrated white light source further comprises a range of angles of incidence between the laser beam and the excitation surface of the phosphor member such that on average the laser beam is off normal incidence with respect to the excitation surface, and a beam spot area configured with a certain geometrical size and shape. The phosphor member converts a portion of the electromagnetic radiation from the laser beam having the first wavelength into emitted electromagnetic radiation having a second wavelength longer than the first wavelength. A plurality of scattering centers associated with the phosphor member scatter electromagnetic radiation having a first wavelength from the laser beam incident on the phosphor member. Furthermore, the integrated white light source comprises a reflective mode with the phosphor member such that the laser beam is incident on a beam spot area on the excitation surface of the phosphor member and outputs a white light emission from substantially the same beam spot area. The white light emission is comprised of various mixed wavelengths including electromagnetic radiation emitted from the phosphor member having at least a second wavelength. Further, the integrated white light source includes a form factor having a package of integrated white light sources, the form factor having length, width, and height dimensions.
In yet another embodiment, the present invention provides an integrated white light source package. The integrated white light source package includes one or more laser diode devices, each laser diode device containing a gallium and nitrogen containing material and configured as an excitation source, and a phosphor member configured as a wavelength converter and emitter and coupled to the laser diode device. The integrated white light source package further comprises a shaped support member having at least one flat surface portion and one or more wedge-shaped portions with inclined planes and configured to integrate the one or more wedge-shaped portions in one piece of material or a substrate structure in the flat portion, or as a base for separately attaching the one or more wedge-shaped portions to support one or more laser diode devices in a Surface Mount Device (SMD) package. In addition, the integrated white light source package further comprises an output face configured on the one or more laser diode devices to output a laser beam consisting of electromagnetic radiation selected from the group consisting of violet and/or blue light having a first wavelength in the range of 400nm to 485 nm. The integrated white light source package further comprises an optical path between the output face and the phosphor member, the free space having non-guiding properties capable of transmitting the laser beam to the excitation surface of the phosphor member. Furthermore, the integrated white light source package further comprises a range of angles of incidence of the laser beam on the excitation surface of the phosphor member, such that on average the excitation spot on the excitation surface is configured to have a geometrical size and shape, from a lower limit to an upper limit of the laser beam. Furthermore, the integrated white light source package further comprises a frame member having a base with a surrounding edge to form a cavity for holding a shaped support member therein to support at least the phosphor member, the one or more laser diode devices, and a surrounding edge attached to seal the cavity.
A further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and the drawings.
Drawings
Fig. 1 is a simplified diagram illustrating a laser diode device configured on a semipolar substrate according to the present invention.
Fig. 2 is a simplified diagram illustrating a laser diode device configured on a polar c-plane substrate according to the present invention.
Fig. 3 is a simplified schematic cross-section of a conventional ridge laser diode planar substrate according to the present invention.
Fig. 4 is a simplified diagram illustrating a conventional chip on laser diode substrate (CoS) according to the present invention.
Fig. 5 is a simplified diagram illustrating an epitaxial preparation process flow for epitaxial transfer to a carrier wafer in accordance with the present invention.
Fig. 6 is a simplified diagram illustrating a bonding-etching process flow for epitaxial layer transfer to a carrier wafer in accordance with the present invention.
Fig. 7 is a simplified diagram illustrating a side view of a die expansion with selective area bonding in accordance with the present invention.
Fig. 8 is a simplified diagram illustrating an example of an LD epitaxial structure according to an epitaxial transfer embodiment of the present invention.
Fig. 9 is a simplified diagram illustrating an example of an LD device structure formed on a carrier wafer by the epitaxial structure in fig. 8 according to the present invention.
Fig. 10 is a simplified diagram illustrating a chip on substrate (CoS) fabricated via wafer level laser processing after transfer of a gallium-containing nitrogen epitaxial layer according to an embodiment of the present invention.
Fig. 11 is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and phosphor member integrated on a substrate, wherein the phosphor is configured for transmissive operation, according to an embodiment of the invention.
Fig. 12 is a simplified diagram illustrating a laser-based integrated white light source according to an embodiment of the present invention, wherein a laser diode prepared in a gallium-containing nitrogen epitaxial layer is transferred to a substrate member, a phosphor member is integrated on the substrate member, wherein the phosphor is configured for transmissive operation.
Fig. 13 is a simplified diagram illustrating the device configuration of fig. 12, but configured with a variation of phosphor configured with a coating or variation that increases useful white light output, according to an embodiment of the present invention.
Fig. 14 is a simplified diagram illustrating an example of an elliptical projected laser beam from a conventional laser diode according to one embodiment of the present invention.
Fig. 15 is a simplified diagram illustrating a side view of a laser beam incident normal to the phosphor member according to an embodiment of the present invention.
Fig. 16 is a graph illustrating an example calculation of elliptical beam diameter and the ratio of beam diameter to emitter distance from the phosphor according to one embodiment of the invention.
Fig. 17 is a simplified diagram illustrating the device configuration of fig. 12, but with a distortion of the laser beam that is configured by collimating optics before being incident on the phosphor, according to an embodiment of the present invention.
Fig. 18 is a simplified diagram illustrating an example of an enhanced elliptical laser beam profile from a conventional laser diode having a projection surface that is tilted with respect to the fast axis of the laser diode, according to an embodiment of the present invention.
Fig. 19 is a simplified diagram illustrating an example of a more circular laser beam profile from a conventional laser diode having a projection surface that is tilted with respect to the slow axis of the laser diode, according to an embodiment of the present invention.
Fig. 20 is a simplified diagram illustrating a side view of a laser beam projected onto a phosphor member in an oblique direction according to an embodiment of the present invention.
Fig. 21 is a graph illustrating an example calculation of elliptical beam diameter and the ratio of beam diameter to emitter distance from the phosphor, which is tilted at an angle of 33 degrees with respect to the slow axis, according to an embodiment of the present invention.
Fig. 22 is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and phosphor member integrated on a substrate, wherein the phosphor is configured at an angle relative to the laser diode to shape the beam, according to an embodiment of the invention.
Fig. 23 is a simplified diagram illustrating a laser-based integrated white light source according to an embodiment of the present invention, wherein a laser diode prepared in a gallium-nitrogen containing epitaxial layer is transferred to a substrate member, a phosphor member is integrated on the substrate member, wherein the phosphor is configured at an angle with respect to the laser diode to shape the beam.
Fig. 24 is a simplified diagram illustrating a laser-based integrated white light source according to an embodiment of the present invention, wherein a laser diode prepared in a gallium-containing nitrogen epitaxial layer is transferred to a substrate member, and a phosphor member is integrated on the substrate member, wherein the phosphor is configured as a point light source.
Fig. 24A is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and phosphor member integrated on a substrate member, wherein the laser excites or pumps the phosphor member primarily from the side of the phosphor, according to an embodiment of the invention.
Fig. 24B is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and a phosphor member integrated onto a substrate, wherein the laser primarily excites or pumps the phosphor member from the phosphor-side surface according to an embodiment of the present invention.
Fig. 25 is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and a phosphor member integrated on a common support member, wherein the phosphor is configured for reflective operation and the laser beam is incident non-perpendicularly to the phosphor, according to an embodiment of the present invention.
Fig. 25A is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and a phosphor member configured to be integrated on a common support member, such as an encapsulation member, wherein the phosphor is configured for reflective operation and the laser beam is incident non-perpendicularly to the phosphor, according to an embodiment of the present invention.
Fig. 26 is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and phosphor member integrated on a common support member, wherein the phosphor is configured for off-axis reflective operation and the laser beam is configured with collimating or shaping optics, according to an embodiment of the present invention.
Fig. 27 is a graph showing an example calculation of elliptical beam diameter and the ratio of beam diameter to emitter distance from the phosphor tilted at an angle of 45 degrees with respect to the fast axis and 22 degrees with respect to the slow axis for reflective phosphor operation, according to one embodiment of the invention.
Fig. 28 is a simplified diagram illustrating a laser-based integrated white light source with a laser diode and a phosphor member integrated on a common support member, wherein the phosphor is configured for reflective operation, the laser beam having biaxial rotation relative to the phosphor to be non-perpendicularly incident to the phosphor relative to the slow and fast axes, according to an embodiment of the invention.
Fig. 28A is a simplified diagram illustrating a laser-based integrated white light source with two laser diode devices and a phosphor member configured to be integrated on a common support member, such as a packaging member, wherein the phosphor is configured for reflective operation, and two output beams of the laser diodes change the excitation spot geometry and/or increase the total power in the laser emission point.
Fig. 28B is a simplified diagram illustrating a laser-based integrated white light source with a laser diode device and a phosphor member configured for integration on a common support member such as an encapsulation member, wherein the phosphor is configured for reflective operation, and the laser diode device is configured as a multi-band laser diode with multiple adjacent output bands of emitted light beams to increase the spot diameter in the slow axis direction and/or to increase the total power in the laser emission spot.
Fig. 29 is a simplified diagram illustrating a white light source based on a transmission mode phosphor integrated laser mounted in a can package according to an embodiment of the present invention.
Fig. 30 is a simplified diagram illustrating a white light source based on a transmission mode phosphor integrated laser mounted in a can package and sealed with a cap, according to an embodiment of the present invention.
Fig. 31 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount device package according to an embodiment of the present invention.
Fig. 31A is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount device package according to an embodiment of the present invention.
Fig. 31B is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount device package according to an embodiment of the present invention.
Fig. 31C is a simplified diagram illustrating a white light source with multiple laser diode devices based on a reflective mode phosphor integrated laser mounted in a surface mount device package, according to an embodiment of the present invention.
Fig. 31D is a simplified diagram illustrating a white light source with multiple laser diode devices based on a reflective mode phosphor integrated laser mounted in a surface mount device package, according to an embodiment of the present invention.
Fig. 31E is a simplified diagram illustrating a pump-mode phosphor integrated laser based white light source mounted in a surface mount device package, according to an embodiment of the present invention.
Fig. 32 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package and sealed with a cover, according to an embodiment of the present invention.
Fig. 32A is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package and sealed with a cover, according to an embodiment of the present invention.
Fig. 33 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package with an integrated beam collection security feature according to an embodiment of the present invention.
Fig. 33A is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package with an integrated beam collection security feature according to an embodiment of the present invention.
Fig. 33B is a simplified diagram illustrating a white light source based on a reflective mode phosphor-integrated laser mounted in a surface mount package with integrated re-imaging optics to reflect and refocus an incident laser beam reflected from the phosphor, according to an embodiment of the invention.
Fig. 33C is a simplified diagram showing a white light source based on a reflective mode phosphor-integrated laser mounted in a surface mount package with integrated re-imaging optics to reflect and focus a direct laser beam onto the phosphor member.
Fig. 33D is a simplified diagram showing a white light source based on a reflective-mode phosphor-integrated laser mounted in a surface-mount package with a shield or aperture.
Fig. 34 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package, sealed with a cover, and mounted on a heat sink according to an embodiment of the present invention.
Fig. 34A is a simplified diagram illustrating a reflective mode phosphor integrated laser based white light source mounted in a surface mount package mounted on a star plate, according to an embodiment of the present invention.
Fig. 35 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a flat package with collimating optics according to an embodiment of the present invention.
Fig. 36 is a simplified diagram illustrating a white light source based on a transmissive mode phosphor integrated laser mounted in a flat package with collimating optics according to an embodiment of the present invention.
Fig. 37 is a simplified diagram illustrating an integrated laser based white light source mounted in a flat package and sealed with a cover, according to an embodiment of the present invention.
Fig. 38 is a simplified diagram illustrating an integrated laser based white light source operating in a transmissive mode with a collimating lens according to an embodiment of the present invention.
Fig. 39 is a simplified diagram illustrating an integrated laser based white light source operating in a reflective mode with a collimating reflector according to an embodiment of the present invention.
Fig. 40 is a simplified diagram illustrating an integrated laser based white light source operating in a reflective mode with a collimating lens, according to an embodiment of the present invention.
Fig. 41 is a simplified diagram illustrating an integrated laser based white light source mounted in a can package with a collimating reflector according to one embodiment of the present invention.
Fig. 42 is a simplified diagram illustrating an integrated laser based white light source mounted in a can package with a collimating lens according to an embodiment of the present invention.
Fig. 43 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package mounted on a heat sink with a collimating reflector according to an embodiment of the present invention.
Fig. 43A is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package mounted on a star plate with a collimating reflector, according to an embodiment of the present invention.
Fig. 44 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package mounted on a heat sink with a collimating reflector, according to an embodiment of the present invention.
Fig. 45 is a simplified diagram illustrating a white light source based on a reflective mode phosphor integrated laser mounted in a surface mount package, with a collimating lens and a reflector member mounted on a heat sink, according to an embodiment of the present invention.
Fig. 46 is a simplified diagram illustrating the geometry of a laser pumped phosphorescent white light emitter operating in a reflective mode according to an embodiment of the present invention.
Fig. 47 is a schematic diagram illustrating a phosphor plate including a defective region according to some embodiments of the present invention.
Fig. 48 is a cross-sectional view illustrating an alternative phosphor plate including replacement defect regions according to some embodiments of the present invention.
Fig. 49 is a plan view illustrating (a) laser spots irradiated on a phosphor plate, according to some embodiments of the present invention; (B) One or more defect regions on the phosphor plate in a horizontal direction to confine the laser spot; (C) One or more defective areas in the vertical direction on the phosphor plate to confine the laser spot.
Fig. 50 is a cross-sectional view of pump laser light incident on a phosphor plate containing defect regions that are non-periodically spaced in a direction parallel to the projection of the laser fast axis, according to an embodiment of the invention.
Fig. 51 is a cross-sectional view of pump laser light incident on a phosphor plate containing defect regions that are non-periodically spaced in a direction parallel to the projection of the laser fast axis, according to another embodiment of the present invention.
Fig. 52 is a cross-sectional view of a pump laser incident on a phosphor plate configured as a photonic crystal with a Chirped patterning on an excitation surface, according to an embodiment of the invention.
Fig. 53 is a cross-sectional view of pump laser light incident on a phosphor plate containing defect regions that are non-periodically spaced in a direction parallel to the projection of the laser fast axis, according to yet another embodiment of the present invention.
Fig. 54 is a perspective view of an integrated white light source with a common support member according to one embodiment of the present invention.
Fig. 55 is a perspective view of an integrated white light source with a common support member according to another embodiment of the present invention.
Fig. 56 is a perspective view of a common support member for an integrated white light source according to an embodiment of the present invention.
Fig. 57 is a perspective view of a partially encapsulated white light source in accordance with an embodiment of the present invention.
Fig. 58 is a perspective view of a partially encapsulated white light source according to another embodiment of the present invention.
Fig. 59A is a schematic diagram illustrating the steps of packaging an integrated white light source according to one embodiment of the invention.
Fig. 59B is a schematic diagram illustrating a step of packaging an integrated white light source according to an embodiment of the invention.
Fig. 60 is a schematic diagram illustrating a hermetically sealed package with a window attachment and a block attachment in accordance with an embodiment of the present invention.
Fig. 61 is a schematic diagram illustrating an integrated white light source with a laser and phosphor attached to a package support member according to one embodiment of the invention.
Fig. 62 is a schematic top view and cross-sectional view illustrating an exemplary solder composite preform for packaging an integrated white light source, in accordance with an embodiment of the present invention.
Fig. 63 illustrates three exemplary process flows for applying solder in a hermetic seal for a white light source package to attach a window member to a frame member, according to some embodiments of the present invention.
FIG. 64 is an example spectral diagram showing a blue laser phosphor converted cold white device with the addition of red laser 625nm or red laser 650nm, with the top reaching warm white 3000K.
Fig. 65 is a graph showing an example of radiant luminous efficiency (LER, luminous flux per radiant flux of emitted light) of laser-based warm white light emission at various CCT simulations incorporating 630nm or 650nm red laser diodes.
Fig. 66 is a schematic top view showing a high-luminous-flux laser-based white light source composed of a 1D array of SMD packages according to an embodiment of the present invention.
Fig. 67 is a schematic top view showing a high-luminous-flux laser-based white light source composed of an SMD packaged 2D array according to an embodiment of the present invention.
Fig. 68 is an example schematic diagram illustrating a high lumen 2D array of laser-based white light SMDs where each SMD has one or more designated optical elements coupled to its white light emission according to one embodiment of the present invention.
Fig. 69 is an example schematic diagram of a high lumen 2D array of laser-based white light SMDs where the array of nxm SMDs share a common optical element, according to an embodiment of the present invention.
Fig. 70-72 are schematic diagrams of high luminous flux high brightness light sources according to some embodiments of the present disclosure, wherein each high brightness light source includes a white light source based on an SMD laser.
Fig. 73 is a schematic diagram of an exemplary high luminous flux high brightness light source including a single high brightness SMD laser based white light source, according to an embodiment of the present invention.
Fig. 74 is a schematic diagram of an exemplary high luminous flux high brightness light source including individual high brightness SMD laser based white light sources configured in a rectangular pattern, according to an embodiment of the present invention.
Fig. 75 is a schematic diagram of an exemplary high luminous flux high brightness light source consisting of individual high brightness SMD laser based white light sources configured in a circular pattern, according to an embodiment of the present invention.
Detailed Description
The present invention provides a method and apparatus for emitting white electromagnetic radiation using a combination of a laser diode excitation source based on gallium and nitrogen containing materials and a light emitting source based on a phosphor material. In the present invention, a violet, blue or other wavelength laser diode light source based on gallium and nitrogen materials is tightly coupled (phosphor integrated) with a phosphor material to form a compact, high brightness and efficient white light source.
By way of background, while LED-based light sources provide great advantages over incandescent-based light sources, challenges and limitations related to the physical characteristics of LED devices still exist. The first limitation is the so-called "Droop" phenomenon that plagues GaN-based LEDs. The droop effect causes the power to flip when the current density increases, which forces the LED to be at 10-200A/cm 2 The peak in external quantum efficiency is reached at very low current densities in the range. Therefore, to maximize the efficiency of LED-based light sources, the current density must be limited to low values, where the light output is also limited. The result is LED chip output power per unit area [ flux ]]Low, which forces a large LED chip area to be used to meet the brightness requirements of most applications. For example, a typical LED-based light bulb requires 3mm 2 To 30mm 2 The epitaxial area of (a). A second limitation of LEDs is also related to their brightness, more specifically, their spatial brightness. Conventional high brightness LEDs emit about 1W of power per square millimeter of epitaxial area. With some advances and breakthroughs, the epitaxial area per square millimeter may increase by a factor of 5-10 to 5-10 watts. Finally, LEDs fabricated on conventional c-plane GaN are subject to strong internal polarization fields, which spatially separate the electron and hole wave functions, resulting in inefficient radiative recombination. Since this phenomenon becomes more pronounced in InGaN layers where the indium content increases with increasing wavelength emission, the performance of UV or blue GaN based LEDs is extended to the blue-green or green region It has been difficult.
An exciting class of new laser diode-based solid-state lighting is rapidly emerging. Like LEDs, laser diodes are dual-lead semiconductor light sources that emit electromagnetic radiation. However, unlike the output from LEDs that are primarily spontaneous emission, the output of laser diodes is primarily composed of stimulated emission. The laser diode comprises a gain medium, which functions to provide light emission by recombination of electron-hole pairs, and a cavity region, which functions as a resonator for the gain medium emission. When an appropriate voltage is applied to the leads to adequately pump the gain medium, the gain overcomes the cavity losses and the laser diode reaches a so-called threshold condition in which a sharp increase in the light output versus current input characteristics is observed. Under threshold conditions, carrier density clamps (clamps), stimulated emission dominates emission. Since the droop phenomenon that plagues LEDs depends on carrier density, the clamped carrier density within a laser diode provides a solution to the droop challenge. In addition, laser diodes emit highly directional and coherent light with spatial brightness orders of magnitude higher than LEDs. For example, commercially available edge-emitting GaN-based laser diodes can reliably generate about 2W of power in a 15 μm wide, 0.5 μm high aperture, which corresponds to over 250,000W/mm 2 . This spatial brightness is more than 5 orders of magnitude higher than the LED, or in other words, 10,000 times brighter than the LED.
Laser light was shown in 1960 by theomore h.maiman at mary hous research laboratory. The laser utilizes a solid state flash lamp to pump a synthetic ruby crystal to generate 694nm red laser. Early visible laser technologies included lamp-pumped infrared solid-state lasers that converted the output wavelength to visible light using special crystals with nonlinear optical properties. For example, a green-lamp pumped solid-state laser has 3 stages: the lamp is driven by electric power, the lamp excites the gain crystal, laser is generated at 1064nm, and 1064nm enters the frequency conversion crystal and is converted into visible light of 532 nm. The green and blue lasers thus produced are known as "tube pumped solid state lasers with second harmonic generation" (LPSS with SHG), with a wall plug efficiency of about 1% higher than that of Ar ion gas lasers, but still too low in efficiency, bulky, expensive, fragile, and suitable for widespread deployment beyond professional scientific and medical applications. To increase the efficiency of these visible lasers, high power diode (or semiconductor) lasers are used. These "diode pumped solid state lasers with SHG" (DPSS with SHG) have 3 stages: the 808nm diode laser is driven by electric power, the lamp excites the gain crystal, laser is generated at 1064nm, and 1064nm enters the frequency conversion crystal and is converted into visible light of 532 nm. With the development of high power laser diodes and the development of new special SHG crystals, it has become possible to directly convert the output of an infrared diode laser to produce blue and green laser outputs. These "direct frequency doubling diode lasers" or SHG diode lasers have 2 stages: the 1064nm semiconductor laser is driven by electric power, and 1064nm laser enters the frequency conversion crystal and is converted into visible 532nm green light. These laser designs are aimed at improving efficiency, reducing cost and size compared to DPSS-SHG lasers, but the required dedicated diodes and crystals become challenging today.
Based on almost all of the pioneering work of the above-mentioned GaN LEDs, visible laser diodes based on GaN technology have emerged rapidly over the last 20 years. The only currently feasible direct blue and green laser diode structures are fabricated from wurtzite AlGaInN material systems. The fabrication of light emitting diodes from GaN-related materials is controlled by heteroepitaxial growth of GaN on foreign substrates such as Si, siC and sapphire. Laser diode devices operate at such high current densities that crystalline defects associated with heteroepitaxial growth are unacceptable. For this reason, very low defect density, free-standing GaN substrates have become the substrate of choice for GaN laser diode fabrication. Unfortunately, such large GaN substrates are expensive and large diameters cannot be widely obtained. For example, 2 "diameter is currently the most commonly used bulk GaN c-plane substrate size for which laser quality is good, and recent advances have enabled 4" diameters, which are still relatively small compared to the 6 "and larger diameters commercially available for mature substrate technology. Further details of the invention may be found in the present specification, and more particularly below.
Use the utility model discloses realize additional benefit relative to the existing technique that already exists. In particular, the utility model discloses can realize economic efficient white light source. In particular embodiments, the present optical device may be manufactured in a relatively simple and cost-effective manner. Depending on the embodiment, one of ordinary skill in the art may use conventional materials and/or methods to make the present devices and methods. In some embodiments of the invention, the gallium and nitrogen containing laser diode source is based on c-plane gallium nitride materials, while in other embodiments, the laser diode is based on non-polar or semi-polar gallium and nitride materials. In one embodiment, the white light source is comprised of a chip-on-substrate (CoS) with integrated phosphor on the substrate to form a chip-on-substrate and phosphor (CPoS) white light source. In some embodiments, an intermediate substrate member may be included. In some embodiments, the laser diode and the phosphor member are supported by a common support member, such as a package substrate. In this embodiment, there may be a substrate member or an additional support member included between the laser diodes and the common support member. Similarly, there may be a substrate member or an additional support member included between the phosphor member and the common support member.
In various embodiments, the laser device and the phosphor device are mounted on a common support member with or without an intermediate substrate, and the phosphor material is operated in a transmissive mode, a reflective mode, or a side-pumped mode to produce a laser-based white light emitting light source. Merely by way of example, the invention may be applied to applications such as white lighting, white point lighting, flashlights, automotive headlamps, all-terrain vehicle lighting, flash sources such as camera flashlights, light sources used in recreational sports such as cycling, surfing, running, racing, rowing, unmanned aircraft, robots, other mobile applications or robotic applications, light sources for precautionary measures in security, defense applications, multicolor lighting, lighting for flat panels, medical, metrology, return light and other displays, high intensity lights, spectroscopy, entertainment, theatre, music and concerts, analytical fraud detection and/or identification, tools, water treatment, laser flares, target locking, communications, liFi, visible Light Communications (VLC), sensing, detection, distance detection, light radar (LIDAR), pressure swing, transportation, leveling, curing and other chemical processing, heating, cutting and/or melting, pumping other optics, other optoelectronic devices and related applications, and light source lighting, and the like.
Laser diodes are ideal as phosphor excitation sources. For a space brightness (light intensity per unit area) 10000 times higher than that of the conventional LED and an extreme directivity of laser emission, the laser diode enables features that cannot be realized by the LED and other light sources. In particular, since a beam of laser diode output carrying more than 0.5W, more than 1W, more than 3W, more than 10W, or even more than 100W can be focused to a very small spot size of less than 1mm diameter, less than 500 μm diameter, less than 100 μm diameter, or even less than 50 μm diameter, more than 1W/mm can be achieved 2 、100W/mm 2 Or even more than 2500W/mm 2 The power density of (a). When this very small and powerful beam of laser excitation light is incident on the phosphor material, a final white light point source can be achieved. Assuming a white light emitting phosphor conversion of excitation light per watt of phosphor is 200 lumens, a 5W excitation power can produce 1000 lumens in a beam diameter of 100 μm or 50 μm or less. Such point sources are a constantly changing endeavor in applications such as spot lighting or distance measurement where parabolic reflectors or lens optics can be combined with the point sources to produce highly collimated white light points that can travel much further distances than previously possible using LED or bulb technology.
In some embodiments of the present invention, the gallium and nitrogen containing light emitting device may not be a laser device, but may be configured as a superluminescent diode or Superluminescent Light Emitting Diode (SLED) device. For purposes of the present invention, SLED devices and laser diode devices are used interchangeably. The SLED is similar to a laser diode in that it is based on an electrically driven junction that is optically active and produces Amplified Spontaneous Emission (ASE) when injected with current and can gain over a wide range of wavelengths. When the light output starts to be dominated by ASE, an inflection point appears in the light output versus current (LI) characteristic, where the unit of light output per unit of injected current becomes very large. This inflection point in the LI curve is similar to the threshold of a laser diode, but much softer. An advantage of SLED devices is that they can combine the unique properties of high light emission power and very high spatial brightness of laser diodes, which makes them ideal for both high efficiency long throw illumination and high brightness phosphor excitation applications with a broad spectral width (> 5 nm) that in some cases provides improved eye safety and image quality. The wider spectral width results in a low coherence distance similar to that of LEDs. The low coherence distance provides improved safety, e.g. with improved eye safety. Moreover, the wider spectral width can substantially reduce optical distortion in display or lighting applications. As an example, a distorted pattern, known as a "speckle", is the result of an intensity pattern produced by the mutual interference of a set of wavefronts on a surface or in a viewing plane. The general equation commonly used to quantify the degree of speckle is inversely proportional to the spectral width.
In an example application of the present invention, a laser diode device or a superluminescent diode (SLED) device according to the present invention may be used as a preferred light source for a Visible Light Communication (VLC) system, such as a Li-Fi communication system. VLC systems are those that use modulation of visible, ultraviolet, infrared, or near infrared light sources for data transmission. VLC systems using visible light source modulation would be an advantageous application of the present invention for two reasons. First, due to the increased carrier recombination rate (which is due to the large amount of stimulated emission found in laser diodes and SLEDs), the bandwidth will be higher than would be expected when using light emitting diodes. In LEDs, diode lasers, and SLEDs, the recombination rate will increase with increasing carrier density, however, unlike SLEDs and diode lasers, where the efficiency peaks at a relatively high carrier density, the efficiency of LEDs peaks at a very low carrier density. Typically, the LED peak efficiency is at a carrier density 2-3 orders of magnitude lower than that found under typical SLED or laser diode operating conditions. The modulation and thus the data transmission rate should be significantly higher than those achievable with LEDs.
Also, in white light based VLC light sources, violet or blue "pump" light sources consisting of LEDs or laser diodes or SLEDs are used to optically excite or "pump" phosphor elements to produce a broad spectrum covering wavelengths corresponding to green and red and sometimes blue. The spectrum from the phosphor and the unabsorbed pump light are combined to produce a white light spectrum. The laser and SLED light sources have significantly narrower spectra than the blue LED; < 1.5nm and < 5nm, respectively, compared to about 20nm for a blue LED. The narrower FWHM makes it easier to isolate the pump light signal from the phosphor emission using a notch (i.e., bandpass) filter. This is important because, while the phosphor-derived component of the white light spectrum comprises a large portion of the total optical power emitted by the device, the long recombination lifetime in the phosphor results in a very low modulation rate for the phosphor-emitted component of the spectrum.
In one embodiment, a plurality of laser dies emitting at different wavelengths are transferred to the same carrier wafer in close proximity to each other; preferably within 1 millimeter of each other, more preferably within about 200 μm of each other, and most preferably within about 50 μm of each other. The laser die wavelengths are selected to be separated in wavelength by at least twice the full width at half maximum of their spectra. For example, three dies emitting at 440nm, 450nm and 460nm, respectively, are transferred to a single carrier chip, wherein the spacing between the dies is less than 50 μm and the width of the dies is less than 50 μm, such that the total lateral center-to-center spacing of the laser light emitted by the dies is less than 200 μm. The compactness of the laser die allows its emission to be simply coupled into the same optical train or fiber waveguide, or projected in the far field into overlapping spots. To some extent, the laser can be operated effectively as a single laser light source.
This configuration provides the advantages of: each individual laser light source is independently operable to communicate information using, for example, frequency and phase modulation of the RF signal superimposed on a DC offset. The time-averaged proportion of light from different light sources can be adjusted by adjusting the DC offset of each signal. At the receiver, the signals from the individual laser light sources will be demultiplexed by using notch filters on individual photodetectors that filter out the phosphor-derived component of the white light spectrum as well as the pump light from all but one of the laser light sources. Such a configuration would provide advantages over LED-based VLC light sources: the bandwidth will simply scale with the number of laser emitters. Of course, similar embodiments with similar advantages can be constructed with SLED emitters.
In one embodiment, the present invention provides a laser-based white light source that includes a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist. In an alternative example, the height is characterized by a dimension that is less than 12.5mm and greater than 0.5mm, although variations may exist. In yet another alternative example, the length and width are characterized by dimensions of less than 30mm, less than 15mm, or less than 5mm, although variations may exist. The apparatus has a support member, and a phosphor material and at least one gallium-nitrogen containing laser diode device overlying the support member. The laser device is capable of emitting a laser beam having a wavelength preferably in the blue region of 425nm to 475nm, or in the ultraviolet or violet region of 380nm to 425nm, but may also be of other wavelengths, for example in the cyan region of 475nm to 510nm or in the green region of 510nm to 560 nm.
In some embodiments according to the invention, the plurality of laser diode sources are configured to excite the same phosphor or phosphor network. According to the present invention, combining multiple laser light sources can provide many possible benefits. First, the excitation power can be increased by beam combination to provide stronger excitation pits and thus produce a brighter light source. In some embodiments, separate, independent laser chips are configured within the laser-phosphor light source. By including a plurality of lasers each emitting 1W, 2W, 3W, 4W, 5W or more power, the excitation power can be increased, which will increase the light source brightness. For example, by including two 3W lasers exciting the same phosphor area, the excitation power can be increased to 6W to double the white light brightness. In the example of generating approximately 200 lumens of white light per 1 watt of laser excitation power, the white light output would increase from 600 lumens to 1200 lumens. Similarly, the reliability of the light sources can be improved by using multiple light sources under lower driving conditions to achieve the same excitation power as a single light source driven under more severe conditions (e.g., higher current and voltage).
A second advantage is that by rotating the first free-space diverging elliptical laser beam by 90 degrees relative to the second free-space diverging elliptical laser beam and superimposing the central ellipse on the phosphor, it is possible to obtain a more circular spot. Alternatively, a more circular spot can be achieved by rotating the first free-space diverging elliptical laser beam 180 degrees relative to the second free-space diverging elliptical laser beam and eccentrically overlapping the ellipses on the phosphor to increase the spot diameter in the slow-axis divergence direction. In another configuration, more than 2 lasers are included and some combination of the above beam shaping spot geometry shaping is achieved. A third important advantage is that the multiple color lasers in the emitting device can significantly improve color quality (CRI and CQS) by improving spectral fill in the violet/blue and cyan regions of the visible spectrum. For example, two or more blue excitation lasers with slightly detuned wavelengths (e.g., 5nm, 10nm, 15nm, etc.) may be included to excite the yellow phosphor and create a larger blue spectrum.
As used herein, the term GaN substrate is used in connection with group III nitride based materials, including GaN, inGaN, alGaN, or other group III containing alloys or components used as starting materials. Such starting materials include polar GaN substrates (i.e., substrates whose largest area surface is nominally the (h k l) plane, where h = k =0,l is non-zero), non-polar GaN substrates (i.e., substrate materials having a largest area surface oriented from the aforementioned polar direction toward the (h k l) plane at an angle ranging from about 80-100 degrees, where at least one of l =0,h and k is non-zero), or semi-polar GaN substrates (i.e., substrate materials having a largest area surface oriented from the aforementioned polar direction toward the (h k l) plane at an angle ranging from about +0.1 to 80 degrees or 110-179.9 degrees, where at least one of l =0,h and k is non-zero). Of course, there can be other variations, modifications, and alternatives.
Laser diode devices can be fabricated on offcuts in a conventional orientation such as a polar c-plane gallium-containing nitride film or substrate (e.g., gaN), in a non-polar orientation such as the m-plane, or in a semi-polar orientation such as {30-31}, {20-21}, {30-32}, {11-22}, {10-11}, {30-3-1}, {20-2-1}, {30-3-2}, or in a direction within +/-10 degrees of the c-plane, and/or in +/-10 degrees of the a-plane, and/or in any of these polar, non-polar, and semi-polar planes within +/-10 degrees of the m-plane.
Fig. 1 is a simplified schematic diagram of one example of a polar c-plane laser diode formed on a gallium and nitrogen containing substrate with a cavity with a cleaved mirror (cleavedmirror) or etched mirror in line in the m-direction. The laser stripe region is characterized by a cavity orientation substantially in the m-direction, which is substantially orthogonal to the a-direction, but may be other, e.g., the cavity is substantially in-line in the a-direction. The laser stripe region has a first end 07 and a second end 09 and is formed in the m-direction on a {0001} gallium-containing nitrogen substrate having a pair of cleavage mirror or etch mirror structures facing each other. For example, the gallium nitride substrate member is a bulk GaN substrate characterized by having a non-polar or semi-polar crystal plane region, but may be otherwise. The bulk GaN substrate may have a thickness of less than 10 5 cm -2 Or at 10 5 To 10 7 cm -2 Surface dislocation density in between. The nitride crystal or wafer may include Al x In y Ga 1-x-y N, wherein x is more than or equal to 0, and y, x + y is less than or equal to 1. In a specific embodiment, the nitride crystal includes GaN. In one embodiment, the GaN substrate has about 10 in a direction substantially orthogonal or oblique to the surface 5 cm -2 And about 10 8 cm -2 A concentration of threading dislocations in between.
FIG. 2 is a simplification of one example of a semipolar planar laser diode formed on a gallium and nitrogen containing substrateSchematic view of a substrate with cavities aligned on the projection of the cleave or etch mirror in the c-direction. The laser stripe region is characterized by a cavity orientation in projection substantially in the c-direction, which is substantially orthogonal to the a-direction, but may be other, e.g. the cavity is substantially in line in the a-direction. The laser stripe region has a first end 07 and a second end 09 and is formed on a semipolar substrate such as 40-41, 30-31, 20-21, 40-4-1, 30-3-1, 20-2-1, 20-21, or on the off-cuts of these planes forming angles within +/-5 degrees from the c-plane and the a-plane gallium-nitride containing substrate. For example, the gallium-nitrogen containing substrate member is a bulk GaN substrate characterized by having a non-polar or semi-polar crystal plane region, but may be otherwise. The bulk GaN substrate may have less than 10 5 cm -2 Or at 10 5 To 10 7 cm -2 Surface dislocation density in between. The nitride crystal or wafer may include Al x In y Ga 1-x-y N, wherein x is more than or equal to 0, and y, x + y are less than or equal to 1. In a specific embodiment, the nitride crystal includes GaN. In one embodiment, the GaN substrate has about 10 in a direction substantially orthogonal or oblique to the surface 5 cm -2 And about 10 8 cm -2 A concentration of threading dislocations in between.
The example laser diode device in fig. 1 and 2 has a pair of cleaved or etched mirror structures facing each other. The first cleaved or etched face includes a reflective coating, while the second cleaved or etched face does not include a coating, an anti-reflective coating, or an exposure to gallium and nitrogen containing materials. The first cleaved or etched face is substantially parallel to the second cleaved or etched face. The first and second cleavage planes are provided by a scribe and break process according to an embodiment or by an etching technique using an etching technique such as Reactive Ion Etching (RIE), inductively coupled plasma etching (ICP) or Chemically Assisted Ion Beam Etching (CAIBE) or other methods. The first and second mirror surfaces each include a reflective coating. The coating is selected from the group consisting of silicon dioxide, hafnium dioxide, and titanium dioxide, tantalum pentoxide, zirconium oxide, including combinations thereof, and the like. Depending on the design, the mirror may also include an anti-reflective coating.
In a specific embodiment, a facet forming method includes subjecting a substrate to a laser to form a pattern. In a preferred embodiment, the pattern is configured to form a pair of facets of a ridge laser. In a preferred embodiment, the pair of facets face each other and are aligned parallel to each other. In a preferred embodiment, the method uses a UV (355 nm) laser to scribe the laser bars. In one embodiment, the laser is configured on a system that allows for precise scribing in different patterns and profile configurations. In one embodiment, laser scribing may be performed on the back side, the front side, or both, depending on the application. Of course, there can be other variations, modifications, and alternatives.
In one embodiment, the method uses backside laser scribing or the like. For backside laser scribing, the method preferably forms continuous line laser scribing perpendicular to the laser bars on the backside of the GaN substrate. In one embodiment, the laser scribe is typically about 15-20 μm deep or other suitable depth. Preferably, back-scoring may be advantageous. That is, the laser scribing process does not rely on the pitch of the laser bars or other similar patterns. Thus, according to a preferred embodiment, backside laser scribing may result in a higher density of laser stripes on each substrate. However, in one embodiment, the backside laser scribing may result in adhesive tape residue on the facets. In one embodiment, backside laser scribing typically requires that the substrate be placed face down on the tape. For front side laser scribing, the back side of the substrate is in contact with the tape. Of course, there can be other variations, modifications, and alternatives.
It is well known that etching techniques such as Chemically Assisted Ion Beam Etching (CAIBE), inductively Coupled Plasma (ICP) etching or Reactive Ion Etching (RIE) can produce smooth and vertically etched sidewall regions that can act as facets in etched facet laser diodes. In an etch-side process, a masking layer may be deposited and patterned on the wafer surface. The etch mask layer may be comprised of a dielectric, such as silicon dioxide (SiO) 2 ) Silicon nitride (SixNy), combinations thereof, or other dielectricsA material. Further, the mask layer may be composed of a metal layer such as Ni or Cr, but may be composed of a metal combination stack or a stack containing a metal and a dielectric. In another approach, a photoresist mask may be used alone or in combination with dielectrics and/or metals. The etch mask layer is patterned using conventional photolithography and etching steps. Alignment lithography may be performed using a contact aligner or a stepper aligner. Such lithographically-defined mirrors provide a high level of control to design engineers. After patterning of the photoresist mask on top of the etch mask is completed, the pattern is transferred to the etch mask using wet or dry etching techniques. Finally, the facet pattern is etched into the wafer using a dry etching technique selected from CAIBE, ICP, RIE and/or other techniques. The etched faceted surface must be perpendicular to the surface plane of the wafer to a height of between about 87 degrees to about 93 degrees or between about 89 degrees to about 91 degrees. The etched surface areas must be very smooth with root mean square roughness values less than about 50nm, 20nm, 5nm, or 1nm. Finally, the etch must be substantially free of damage, which can act as a non-radiative recombination center, thereby reducing the catastrophic optic damage (COMD) threshold. CAIBE may provide very smooth and low damage sidewalls due to the etch chemistry, while providing a highly vertical etch due to the ability to tilt the wafer table to compensate for any inherent angle in the etch.
The laser stripe is characterized by a length and a width. The length ranges from about 50 μm to about 3000 μm, but is preferably between about 10 μm and about 400 μm, between about 400 μm and about 800 μm, or between about 800 μm and about 1600 μm, but may be others. The stripes also have a width ranging from about 0.5 μm to about 50 μm, but preferably between about 0.8 μm and about 2.5 μm for single lateral mode operation, or between about 2.5 μm and about 50 μm for multi lateral mode operation, but may be other dimensions. In one embodiment, the device has a width ranging from about 0.5 μm to about 1.5 μm, a width ranging from about 1.5 μm to about 3.0 μm, a width ranging from about 3.0 μm to about 50 μm, and the like. In one embodiment, the width is substantially constant in size, although minor variations may exist. The width and length are typically formed using masking and etching processes commonly used in the art.
The laser stripe is provided by an etching process selected from dry etching or wet etching. The device also has an overlying dielectric region that exposes the p-type contact region. Overlying the contact region is a contact material, which may be a metal or a conductive oxide or a combination thereof. The p-type electrical contacts may be deposited by thermal evaporation, e-beam evaporation, electroplating, sputtering, or other suitable technique. Overlying the polished region of the substrate is a second contact material, which may be a metal or a conductive oxide or a combination thereof and includes an n-type electrical contact. The n-type electrical contacts may be deposited by thermal evaporation, e-beam evaporation, electroplating, sputtering or other suitable technique.
Given the higher cost of gallium-nitrogen containing substrates, the difficulty of scaling up gallium-nitrogen containing substrates, the inefficiencies inherent in small wafer processing, and the possible supply limitations, it becomes highly desirable to maximize the utilization of the available gallium-nitrogen containing substrates and overlying epitaxial material. In the fabrication of lateral cavity laser diodes, it is often the case that the minimum die size is determined by device components such as wire bond pads or mechanical processing considerations, rather than by the laser cavity width. Minimizing die size is critical to reducing manufacturing costs because smaller die sizes allow a greater number of devices to be fabricated on a single wafer in a single process. The present invention is a method of maximizing the number of devices that can be fabricated by setting gallium and nitrogen containing substrates and capping epitaxial material by expanding the epitaxial material on a carrier wafer via a die expansion process.
In some embodiments, the GaN surface is oriented substantially in the c-plane, m-plane, {40-41}, {30-31}, {20-21}, {40-4-1}, {30-3-1}, {20-2-1}, {20-21}, and the device has a laser stripe region formed overlying a portion of the cleaved crystal orientation surface region. For example, the laser stripe region is characterized by a cavity orientation in projection substantially in the c-direction, which is substantially perpendicular to the a-direction. In one embodiment, the laser stripe region has a first end 07 and a second end 09. In a preferred embodiment where the laser is formed in a semipolar orientation, the device is formed on a projection of the c-direction onto a nitrogen-gallium-containing substrate having a pair of cleavage mirror structures facing each other.
In a preferred embodiment, the device has a first cleavage face disposed on a first end of the laser stripe region and a second cleavage face disposed on a second end of the laser stripe region. In one embodiment, the first cleaved surface is substantially parallel to the second cleaved surface. A mirror surface is formed on each cleavage surface. The first cleavage face includes a first mirror face. In a preferred embodiment, the first mirror surface is provided by a top side skip scribe and break process. The scribing process may use any suitable technique, such as diamond scribing or laser scribing or a combination. In a specific embodiment, the first mirror comprises a reflective coating. The reflective coating is selected from the group consisting of silicon dioxide, hafnium dioxide, and titanium dioxide, tantalum pentoxide, zirconium oxide, including combinations thereof, and the like. The first mirror may also have an anti-reflection coating.
Also in a preferred embodiment, the second cleavage face comprises a second mirror face. According to one embodiment, the second mirror is provided by a top side skip scribe and break process. Preferably, the scribe is a diamond scribe or a laser scribe or the like. In one embodiment, the second mirror includes a reflective coating, such as silicon dioxide, hafnium dioxide, and titanium dioxide, tantalum pentoxide, zirconium oxide, combinations, and the like. In one embodiment, the second mirror comprises an anti-reflective coating.
Similar to edge-emitting laser diodes, SLEDs are typically configured as edge-emitting devices, where high-brightness, high-directivity optical emission exits the waveguide directed outward from the side of the semiconductor chip. SLEDs are designed to have high single pass gain or amplification for spontaneous emission generated along the waveguide. However, unlike laser diodes, they are designed to provide insufficient feedback into the cavity to obtain a lasing condition with a gain equal to the total loss in the waveguide cavity. In a typical example, at least one of the waveguide ends or facets is designed to provide very low reflectivity back into the waveguide. Several methods can be used to achieve reduced reflectivity at the waveguide ends or facets. In one approach, an optical coating is applied to at least one side, where the optical coating is designed for low reflectivity, e.g., less than 1%, less than 0.1%, less than 0.001%, or less than 0.0001% reflectivity. In another approach for reducing reflectivity, the waveguide end is designed to be tilted or angled with respect to the direction of light propagation so that light reflected back into the chip does not structurally interfere with light in the cavity to provide feedback. The tilt angle must be carefully designed to avoid nulls in the reflectivity and angle relationship for optimum performance. The tilted or angled facet approach can be implemented in a number of ways, including providing an etched facet designed with an optimal lateral angle with respect to the direction of light propagation. The tilt angle is predetermined by the lithographically defined pattern of etched facets. Alternatively, angular output may be achieved by bending and/or angling the waveguide relative to a cleave plane formed on a predetermined crystallographic plane in the semiconductor chip. Another way to reduce reflectivity is to provide a rough or patterned surface on the face to reduce feedback to the cavity. The roughness may be achieved using chemical etching and/or dry etching, or with alternative techniques. Of course, there may be other methods for reducing feedback to the cavity to form the SLED device. In many embodiments, a number of techniques can be used in combination to reduce facet reflectivity, including the use of low reflectivity coatings, in combination with output facets that are angled or tilted with respect to the direction of light propagation.
In a specific embodiment on a non-polar Ga-containing substrate, the device is characterized in that the spontaneously emitted light is polarized in a direction substantially perpendicular to the c-direction. In a preferred embodiment, the spontaneously emitted light is characterized by a polarization ratio perpendicular to the c-direction of greater than 0.1 to about 1. In a preferred embodiment, the spontaneously emitted light is characterized by a wavelength ranging from about 430nm to about 470nm to produce blue light, or about 500nm to about 540nm to produce green light, and the like. For example, the spontaneously emitted light may be purple (e.g., 395 to 420 nanometers), blue (e.g., 420 to 470 nanometers); green (e.g., 500 to 540 nm) or otherwise. In a preferred embodiment, the spontaneously emitted light is highly polarized and is characterized by a polarization ratio greater than 0.4. In another embodiment on a semipolar 20-21 Ga-containing substrate, the device is further characterized in that the spontaneously emitted light is polarized substantially parallel to the a-direction or perpendicular to the cavity direction, i.e. oriented in projection in the c-direction.
In one embodiment, the present invention provides an alternative device structure capable of emitting light at wavelengths of 501nm and greater in ridge laser embodiments. The device has the following epitaxially grown elements:
An n-GaN or n-AlGaN cladding layer having a thickness of 100nm to 3000nm and a Si doping level of 5X 10 17 cm -3 To 3X 10 18 cm -3 ；
The n-side SCH layer is composed of InGaN, the mole fraction of indium is between 2% and 10%, and the thickness is from 20nm to 250nm;
a plurality of quantum well active region layers consisting of at least two 2.0nm to 8.5nm InGaN quantum wells, gaN, or InGaN barriers, the quantum wells separated by 1.5nm or more, and optionally up to about 12nm;
a p-side SCH layer comprising InGaN with a mole fraction of indium between 1% and 10% and a thickness from 15nm to 250nm, or an upper GaN guiding layer;
an electron blocking layer composed of AlGaN, wherein the molar fraction of aluminum is between 0% and 22%, has a thickness between 5nm and 20nm and is doped with Mg;
a p-GaN or p-AlGaN cladding layer with a thickness of 400nm to 1500nm and a Mg doping level of 2 x 10 17 cm -3 To 2X 10 19 cm -3 (ii) a And
a p + + -GaN contact layer of 20nm to 40nm thickness, a Mg doping level of 1 × 10 19 cm -3 To 1X 10 21 cm -3 。
Fig. 3 is a cross-sectional view of the laser device 200. As shown, the laser device includes a gallium nitride substrate 203 having an underlying n-type metal back contact region 201. For example, the substrate 203 may be characterized by a semi-polar or non-polar orientation. The device also has an upper n-type gallium nitride layer 205, an active region 2 07 and an upper p-type gallium nitride layer configured as a laser stripe region 209. Each of these regions is formed using at least Metal Organic Chemical Vapor Deposition (MOCVD), an epitaxial deposition technique of Molecular Beam Epitaxy (MBE), or other epitaxial growth techniques suitable for GaN growth. The epitaxial layer is a high quality epitaxial layer overlying the n-type gallium nitride layer. In some embodiments, the high quality layer is doped with, for example, si or O to form an n-type material, of which about 10 16 cm -3 And 10 20 cm -3 Doping concentration in between.
Depositing n-type Al on a substrate u In v Ga 1-u-v N layers, wherein u is more than or equal to 0, and v, u + v are less than or equal to 1. The carrier concentration may be at about 10 16 cm -3 And 10 20 cm -3 Within the range of (a). The deposition may be performed using Metal Organic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy (MBE).
For example, a bulk GaN substrate is placed on a susceptor in an MOCVD reactor. After shutting down, evacuating, and backfilling the reactor (or using a load lock configuration) to atmospheric pressure, the susceptor is heated in the presence of a nitrogen-containing gas to a temperature between about 1000 to about 1200 degrees celsius. The susceptor is heated to approximately 900 to 1200 degrees celsius under flowing ammonia gas. The flow of a gallium-containing metal organic precursor, such as trimethyl gallium (TMG) or triethyl gallium (TEG), is initiated in a carrier gas at a total rate of about 1 to 50 standard cubic centimeters per minute (sccm). The carrier gas may include hydrogen, helium, nitrogen, or argon. The ratio of the flow rates of the group V precursor (ammonia) to the group III precursor (trimethylgallium, triethylgallium, trimethylindium, trimethylaluminum) during growth is between about 2000 and about 12000. The flow of disilane in the carrier gas is initiated, with a total flow rate of approximately 0.1sccm to 10 sccm.
In one embodiment, the laser stripe region is a p-type gallium nitride layer 209. The laser stripe is provided by a dry etch process, but a wet etch may also be used. The dry etch process is an inductive coupling process using chlorine-containing species or a reactive ion etch process using similar chemistry. The chlorine-containing substance is generally derived from chlorine gas or the like. The device also has an overlying dielectric region that exposes 213 the contact region. The dielectric region is an oxide, such as silicon dioxide or silicon nitride, and the contact region is coupled to the upper metal layer 215. The upper metal layer is preferably a multilayer structure comprising gold and platinum (Pt/Au), palladium and gold (Pd/Au), or nickel gold (Ni/Au), or a combination thereof.
The active region 207 preferably includes one to ten quantum well regions or double heterostructure regions for light emission. In n-type Al u In v Ga 1-u-v After deposition of the N layer to achieve the desired thickness, the active layer is deposited. The quantum well is preferably InGaN with GaN, alGaN, inAlGaN, or InGaN barrier layers separating them. In other embodiments, the well layer and the barrier layer each comprise Al w In x Ga 1-w-x N and Al y In z Ga 1-y-z N, wherein 0 is not less than w, x, y, z, w + x, y + z is not more than 1, wherein w is less than u, y and/or x is more than v, z, such that the bandgap of the well layer is less than the bandgaps of the barrier layer and the N-type layer. The well layer and the barrier layer each have a thickness between about 1nm and about 20 nm. The composition and structure of the active layer is selected to provide light emission at a preselected wavelength. The active layer may be undoped (or unintentionally doped) or may be n-type or p-type doped.
The active region may also include an electron blocking region, and the heterostructures are confined separately. The electron blocking layer may include Al s In t Ga 1-s-t N, where 0. Ltoreq. S, t, s + t. Ltoreq.1, has a higher bandgap than the active layer and can be p-doped. In a specific embodiment, the electron blocking layer comprises AlGaN. In another embodiment, the electron blocking layer comprises an AlGaN/GaN superlattice structure including alternating AlGaN layers and GaN layers, each with a thickness between about 0.2nm and about 5 nm.
As noted, a p-type gallium nitride or aluminum gallium nitride structure is deposited over the electron blocking layer and the active layer. The P-type layer may be doped with Mg to about 10 16 cm -3 And 10 22 cm -3 And a thickness of between about 5nm and about 1000 nm. The outermost 1-50nm of the p-type layer may be more heavily doped than the remainder of the layer to enable improved electrical contact. The device also has an upper dielectric regionA domain, for example, silicon dioxide, which exposes contact region 213.
The metal contacts are made of a suitable material such as silver, gold, aluminum, nickel, platinum, rhodium, palladium, chromium, and the like. The contacts may be deposited by thermal evaporation, e-beam evaporation, electroplating, sputtering, or other suitable techniques. In a preferred embodiment, the electrical contact serves as a p-type electrode for the optical device. In another embodiment, the electrical contact serves as an n-type electrode for the optical device. The laser devices illustrated in fig. 1 and 2 and described above are generally suitable for relatively low power applications.
In various embodiments, the present invention achieves high output power from a diode laser by broadening portions of the laser cavity member from 1.0-3.0 μm for a single lateral mode range to 5.0-20 μm for a multiple lateral mode range. In some cases, a laser diode having a cavity with a width of 50 μm or more is used.
The laser stripe length or cavity length ranges from 100 to 3000 μm and employs growth and fabrication techniques such as those described in U.S. patent application No. 12/759,273, filed 4/13/2010, which is incorporated herein by reference. For example, laser diodes are fabricated on nonpolar or semipolar gallium-containing substrate substrates, where the internal electric field is substantially eliminated or reduced relative to polar c-plane oriented devices. It will be appreciated that a reduction in internal field generally enables more efficient radiative recombination. In addition, the heavy holes on the non-polar and semi-polar substrates are lighter in weight, so that better laser gain characteristics can be obtained.
Fig. 3 illustrates an example cross-sectional view of a gallium and nitrogen based laser diode device. An epitaxial device structure is formed on top of the gallium and nitrogen containing substrate member 203. The substrate member may be an n-type dopant doped with O and/or Si. The epitaxial structure will include an n-side layer 205, such as an n-type buffer layer composed of GaN, alGaN, alINGaN, or InGaN, and an n-type cladding layer composed of GaN, alGaN, or AlINGaN. The n-type layer may have a thickness in the range of 0.3 μm to about 3 μm or to about 5 μm and may be doped with n-type carriers such as Si or O in concentrations up to 1 × 10 16 cm -3 To 1X 10 19 cm -3 In the meantime. Overlying the n-type layer is an active region and a waveguide layer 207. This region may contain an n-side waveguide layer or a Separate Confinement Heterostructure (SCH), such as InGaN, to help guide the modes optically. The InGaN layer is composed of 1 to 15% mole fraction InN, has a thickness ranging from about 30nm to about 250nm, and may be doped with an n-type species, such as Si. Overlying the SCH layer is a light emitting region, which may be composed of a double heterostructure or quantum well active region. The quantum well active region may consist of 1 to 10 quantum wells, with a thickness ranging from 1nm to 20nm, consisting of InGaN. The quantum well light emitting layers are separated by barrier layers composed of GaN, inGaN, or AlGaN. The thickness of the barrier ranges from 1nm to about 25nm. Overlying the light emitting layer is an optional AlGaN or InAlGaN electron blocking layer having 5% to about 35% AlN, and optionally doped with a p-type species, such as Mg. Also optional is a p-side waveguide layer or SCH, such as InGaN, to help guide the modes. The InGaN layer is composed of 1 to 15% mole fraction InN, has a thickness ranging from 30nm to about 250nm, and may be doped with a p-type species such as Mg. Covering the active region and the optional electron blocking layer and the p-side waveguide layer are the p-cladding region and the p + + contact layer. The p-cladding region is composed of GaN, alGaN, alINGaN, or a combination thereof. The thickness of the p-type cladding layer is in the range of 0.3um to about 2 microns, and the doping concentration is 1 × 10 16 cm -3 To 1X 10 19 cm -3 Mg in between. A ridge 211 is formed in the p-cladding region using an etching process selected from a dry or wet etching process for lateral confinement in the waveguide. A dielectric material 213, such as silicon dioxide or silicon nitride, is deposited on the surface regions of the device and an opening is created on top of the ridge to expose a portion of the p + + GaN layer. A p-contact 215 is deposited on top of the device to contact the exposed p + + contact region. The p-type contact may be composed of a metal stack containing one of Au, pd, pt, ni, ti, or Ag, and may be deposited using electron beam deposition, sputter deposition, or thermal evaporation. An n-contact 201 is formed at the bottom of the substrate member. The n-type contact may be composed of a metal stack comprising one of Au, al, pd, pt, ni, ti, or Ag, and may be deposited using electron beam deposition, sputter deposition, or thermal evaporation.
In a number of embodiments according to the present invention, the device layer includes a superluminescent light emitting diode or a SLED. In all applicable embodiments, the SLED device can be interchanged or combined with a laser diode device according to the methods and structures described in the present disclosure. SLEDs are similar in many respects to edge-emitting laser diodes; however, the emitting surface of the device is designed to have a very low reflectivity. The SLED is similar to a laser diode in that it is based on an electrically driven junction that is optically active and produces Amplified Spontaneous Emission (ASE) when injected with current and can gain over a wide range of wavelengths. When the light output starts to be dominated by ASE, an inflection point appears in the light output versus current (LI) characteristic, where the unit of light output per unit of injected current becomes very large. This inflection point in the LI curve is similar to the threshold of a laser diode, but much softer. SLEDs have a layered structure designed with one or more light emitting layers covered above and below with a material of lower optical index, so that laterally guided optical modes can be formed. SLEDs are also fabricated with features that provide lateral optical confinement. These lateral confinement features may consist of etched ridges with air, vacuum, metal or dielectric material surrounding the ridges and providing a low optical index cladding. Lateral confinement features may also be provided by shaping the electrical contacts so that the injected current is confined to a limited area in the device. In such a "gain-guided" structure, the optical index of the light-emitting layer with injected carrier density provides the optical index contrast required for lateral confinement of the optical mode by dispersion.
SLEDs are designed to have high single pass gain or amplification for spontaneous emission generated along the waveguide. SLED devices will also be designed to have low internal losses, preferably below 1cm -1 However, SLEDs can operate with internal losses higher than this. Ideally, the emitting surface reflectivity would be zero, however in practical applications, zero reflectivity is difficult to achieve, and the emitting surface reflectivity is designed to be less than 1%, less than 0.1%, less than 0.001%, or less than 0.0001% reflectivity. Reducing the reflectivity of the emitting surface can reduce feedback into the device cavityThereby increasing the injection current density at which the device will begin lasing. Very low reflectivity of the emissive facets can be achieved through the addition of anti-reflective coatings and through a combination of angling the emissive facets relative to the SLED cavity such that the surfaces normal to the facets and the propagation direction of the guided mode are substantially non-parallel. Typically, this would mean a deviation of greater than 1-2 degrees. In practice, the ideal angle depends in part on the antireflective coating used, and the tilt angle must be carefully designed to avoid nulls in the reflectivity versus angle relationship for optimum performance. The facets may be tilted with respect to the propagation direction of the guided mode in any direction with respect to the propagation direction of the guided mode, although some directions may be easier to manufacture depending on the method of facet formation. The etched facets provide superior flexibility for facet angle determination. Alternatively, a very common method of achieving angular output to reduce structural interference in the cavity would bend and/or angle the waveguide relative to a cleave plane formed on a predetermined crystallographic plane in the semiconductor chip. In this configuration, the angle of light propagation is not orthogonal to the cleave plane at a specific angle designed for low reflectivity.
The spectrum emitted by a SLED differs from a laser in many ways. While the SLED device produces optical gain in the laterally guided mode, the reduced optical feedback at the emission face results in a broader and more continuous emission spectrum. For example, in a fabry-perot (FP) laser, reflection of light at the end of a waveguide limits the wavelengths of light that may experience gain to those that cause structural interference depending on the length of the cavity. The FP laser is thus comb-shaped in spectrum with peaks and troughs corresponding to the longitudinal modes, with the envelope defined by the gain medium and the transverse modes supported by the cavity. Also, in lasers, feedback from the emitting facet ensures that the transverse mode will reach the threshold with a finite current density. When this occurs, a subset of the longitudinal modes will control the spectrum. In the SLED, optical feedback is suppressed, which reduces the comb-like peaks in the gain spectrum to valley heights, and also pushes the threshold out to higher current densities. The SLED will then be characterized by a relatively broad (> 5 nm) and incoherent spectrum with advantages for spectroscopy, eye safety and reduced speckle. As an example, a distorted pattern, known as a "speckle", is the result of an intensity pattern produced by the mutual interference of a set of wavefronts on a surface or in a viewing plane. The general equation commonly used to quantify the degree of speckle is inversely proportional to the spectral width.
In an example application of the present invention, a laser diode device or a Super Light Emitting Diode (SLED) device according to the present invention may be used as a preferred light source for a Visible Light Communication (VLC) system, such as a Li-Fi communication system. VLC systems are those that use modulation of visible, ultraviolet, infrared, or near infrared light sources for data transmission. VLC systems using visible light source modulation would be an advantageous application of the present invention for two reasons. First, due to the increased carrier recombination rate (which is due to the large amount of stimulated emission found in laser diodes and SLEDs), the bandwidth will be higher than would be expected when using light emitting diodes. In LEDs, diode lasers, and SLEDs, the recombination rate will increase with increasing carrier density, however, unlike SLEDs and diode lasers, where the efficiency peaks at a relatively high carrier density, the efficiency of LEDs peaks at a very low carrier density. Typically, the LED peak efficiency is at a carrier density 2-3 orders of magnitude lower than that found under typical SLED or laser diode operating conditions. The modulation and thus the data transmission rate should be significantly higher than those achievable with LEDs.
Also, in white light based VLC light sources, violet or blue "pump" light sources consisting of LEDs or laser diodes or SLEDs are used to optically excite or "pump" phosphor elements to produce a broad spectrum covering wavelengths corresponding to green and red and sometimes blue. The spectrum originating from the phosphor and the unabsorbed pump light are combined to produce a white light spectrum. The laser and SLED light sources have significantly narrower spectra than the blue LEDs; < 1.5nm and < 5nm, respectively, compared to about 20nm for a blue LED. The narrower FWHM makes it easier to isolate the pump light signal from the phosphor emission using a notch (i.e., bandpass) filter. This is important because, while the phosphor-derived component of the white light spectrum comprises a large portion of the total optical power emitted by the device, the long recombination lifetimes in the phosphors result in very low modulation rates for the phosphor-emitted components of the spectrum.
In one embodiment, a plurality of laser dies emitting at different wavelengths are transferred to the same carrier wafer in close proximity to each other; preferably within 1 millimeter of each other, more preferably within about 200 microns of each other, and most preferably within about 50 microns of each other. The laser die wavelengths are selected to be separated in wavelength by at least twice the full width at half maximum of their spectra. For example, three dies emitting at 440nm, 450nm and 460nm, respectively, are transferred to a single carrier chip, wherein the spacing between the dies is less than 50 microns and the width of the dies is less than 50 microns, such that the total lateral spacing, center-to-center, of the laser light emitted by the dies is less than 200 microns. The compactness of the laser die allows its emission to be simply coupled into the same optical train or fiber waveguide, or projected in the far field into overlapping spots. To some extent, the laser can be operated efficiently as a single laser light source.
This configuration provides the advantages of: each individual laser light source is independently operable to communicate information using, for example, frequency and phase modulation of an RF signal superimposed on a DC offset. The time-averaged proportion of light from different light sources can be adjusted by adjusting the DC offset of each signal. At the receiver, the signals from the individual laser light sources will be demultiplexed using notch filters on individual photodetectors that filter out the phosphor-derived component of the white light spectrum and the pump light from all but one of the laser light sources. Such a configuration would provide advantages over LED-based VLC light sources: the bandwidth will simply scale with the number of laser emitters. Of course, similar embodiments with similar advantages can be constructed with SLED emitters.
After the laser diode chip is manufactured as described above, the laser diode may be mounted to a substrate. In some examples, the substrate is composed of AlN, siC, beO, diamond, or other materials (e.g., metals, ceramics, or composites). The substrate may be a common support member into which the phosphor members of the CPoS will also be attached. Alternatively, the substrate may be an intermediate substrate intended to be mounted to a common support member, with the phosphor material attached therein. The substrate member may be characterized by a width, a length, and a thickness. In examples where the substrate is the common support member for the phosphor and laser diode chips, the substrate will have a width and length with dimensions ranging from about 0.5mm to about 5mm or to about 15mm, and a thickness ranging from about 150 μm to about 2 mm. In examples where the substrate is an intermediate substrate between the laser diode chip and the common support member, it may be characterized by a width and length dimension ranging from about 0.5mm to about 5mm and a thickness ranging from about 50 μm to about 500 μm. The laser diode is attached to the substrate using a bonding process, a soldering process, an adhesive process, or a combination thereof. In one embodiment, the substrate is electrically isolated and has a metal pad deposited on top. A laser chip is mounted to at least one of those metal pads. The laser chip may be mounted in a p-side down or p-side up configuration. After bonding the laser chip, wire bonds are formed from the chip to the substrate so that the final chip-on-substrate (CoS) is complete and ready for integration.
A schematic diagram illustrating a CoS based conventional laser diode formed on gallium and nitrogen containing substrate technology in accordance with the present invention is shown in fig. 4. The CoS is composed of a substrate material 401 configured to serve as an intermediate material between the laser diode chip 402 and the final mounting surface. The substrate is provided with electrodes 403 and 405, which may be formed with a deposited metal layer, such as Au. In one example, ti/Pt/Au is used for the electrodes. Wire bonds 404 are configured to couple electrical power from electrodes 403 and 405 on the substrate to the laser diode chip to generate a laser beam 406 output from the laser diode. The electrodes 403 and 405 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device and activate the laser.
In another embodiment, gallium and nitrogen containing laser diode fabrication includes an epitaxial release step to strip the epitaxially grown gallium and nitrogen layers and prepare them for transfer to a carrier wafer, which may include a substrate, after laser fabrication. The transfer step requires the epitaxial layer to be accurately placed on the carrier wafer to enable the subsequent process of placing the epitaxial layer in the laser diode device to be performed. The process of attaching to the carrier wafer may include a wafer bonding step in which the bonding interface comprises metal-metal, semiconductor-semiconductor, glass-glass, dielectric-dielectric, or a combination thereof.
In yet another preferred variation of this CPoS white light source, the gallium-nitrogen containing laser epitaxial material may be attached to the substrate member using a method for stripping and transferring the gallium-nitrogen containing epitaxial material to a common support member. In this embodiment, the gallium and nitrogen epitaxial material is released from the gallium and nitrogen containing substrate on which it is epitaxially grown. As one example, the epitaxial material may be released using a Photoelectrochemical (PEC) etching technique. And then transferred to a substrate material using a technique such as wafer bonding in which a bonding interface is formed. For example, the bond interface may consist of Au — Au bonds. The substrate material preferably has a high thermal conductivity, such as SiC, wherein the epitaxial material is subsequently processed to form a laser diode having a cavity member, a front side and a back side, and electrical contacts for injecting current. After laser fabrication is complete, phosphor materials are introduced onto the substrate to form an integrated white light source. The phosphor material may have an intermediate material between the substrate and the phosphor. The intermediate material may be comprised of a thermally conductive material such as copper. The phosphor material may be attached to the substrate using conventional die attach techniques, such as AuSn solder, but may be other techniques, such as SAC solder such as SAC305, leaded solder, or indium, but may be other. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. Sintered silver attachment material can be dispensed or deposited using standard processing equipment and cycling temperatures with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. Optimizing the bonding for lowest thermal impedance is a key parameter for heat dissipation from the phosphor, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material. The benefits of using this embodiment with lift-off and transferred gallium and nitrogen containing materials are reduced cost, improved laser performance, and a higher degree of flexibility for integration using this technique.
In this embodiment, a gallium-nitrogen containing epitaxial layer is grown on a bulk gallium-nitrogen containing substrate. The epitaxial layer stack includes at least one sacrificial release layer and a laser diode device layer overlying the release layer. After the epitaxial layer is grown on the bulk gallium and nitrogen containing substrate, the semiconductor device layer is separated from the substrate by a selective wet etching method, such as PEC etching, which is configured to selectively remove the sacrificial layer and enable release of the device layer to the carrier wafer. In one embodiment, a bonding material is deposited on a surface overlying a semiconductor device layer. The bonding material is also deposited as a blanket coating or patterned on the carrier wafer. The semiconductor device layers are selectively masked using standard photolithographic processing. The wafer is then subjected to an etching process, such as a dry etching or wet etching process, to define on the sidewalls of the mesa structures via the structures exposing the sacrificial layer. As used herein, the term mesa region or mesa is used to describe the patterned epitaxial material on a gallium-containing nitrogen substrate ready for transfer to a carrier wafer. The mesa region may be of any shape or form, including a rectangular shape, a square shape, a triangular shape, a circular shape, an oval shape, a polyhedral shape, or other shapes. The term table top should not limit the scope of the present invention.
After defining the mesas, a selective etch process is performed to completely or partially remove the sacrificial layer while leaving the semiconductor device layers intact. The resulting structure includes undercut mesas composed of epitaxial device layers. The undercut mesa corresponds to a cut-out on which the semiconductor device is to be formed. In some embodiments, a protective passivation layer may be used on the sidewalls of the mesa regions to prevent exposure of the device layer to the selective etch when the etch selectivity is not perfect. In other embodiments, protective passivation is not required, as the device layer is not sensitive to selective etching, or measures are taken to prevent etching of sensitive layers, such as shorting the anode and cathode. The undercut mesas corresponding to the device dice are then transferred to a carrier wafer using a bonding technique in which bonding material overlying the semiconductor device layer is joined with bonding material on the carrier wafer. The resulting structure is a carrier wafer including a gallium and nitrogen containing epitaxial device layer overlying the bonding region.
In a preferred embodiment, the PEC etch is configured as a selective etch to remove the sacrificial layer. PEC is a photo-assisted wet etching technique that can be used to etch GaN and its alloys. The process includes an upper bandgap excitation source and an electrochemical cell formed from a semiconductor and an electrolyte solution. In this case, the exposed (Al, in, ga) N material surface serves as an anode, while the metal pad deposited on the semiconductor serves as a cathode. The upper bandgap light source generates electron-hole pairs in the semiconductor. Electrons are extracted from the semiconductor via the cathode while holes diffuse to the surface of the material to form an oxide. PEC etching is typically used only for n-type materials, since the diffusion of holes to the surface requires energy bands that are curved at the surface to facilitate the collection of holes, although several methods have been developed to etch p-type materials. The electrolyte then dissolves the oxide, resulting in wet etching of the semiconductor. Different types of electrolytes (including HCl, KOH and HNO) 3 ) Have been shown to be effective in PEC etching of GaN and its alloys. Etch selectivity and etch rate can be optimized by choosing a favorable electrolyte. It is also possible to generate an external bias between the semiconductor and the cathode to aid the PEC etching process.
The preparation of the epitaxial wafer is shown in fig. 5. The substrate 500 is covered by a buffer layer 501, a selectively removable sacrificial layer 507, another buffer layer 501', a device layer 502, and a set of contact layers 503. The sacrificial regions are exposed by etching vias that extend under the sacrificial layer and divide the layers 501, 502, 503 and 507 into mesas. A layer consisting of bonding medium 508 is deposited overlying the mesa. In some embodiments, the bonding layer is deposited before the sacrificial layer is exposed. And finally, removing the sacrificial layer through a selective process. This process requires the inclusion of a buried sacrificial region that can be selectively etched by band gap PEC. For GaN-based semiconductor devices, inGaN layers (e.g., quantum wells) have proven to be an effective sacrificial region in the PEC etching process. The first step shown in fig. 5 is etching from top to bottom to expose the sacrificial layer, followed by bond metal deposition, as shown in fig. 5. After the sacrificial region is exposed, the mesa is undercut using band gap selective PEC etching. In one embodiment, the band gap of the sacrificial region and all other layers is selected such that only the sacrificial region will be able to absorb light and thus be etched during PEC etching. Another embodiment of the invention relates to a light emitting device that uses a sacrificial region with a higher bandgap than the active region so that both layers absorb during the bandgap PEC etching process.
In one embodiment involving a light emitting device, an insulating protective layer on the sidewalls can be used to prevent active area etching during band gap selective PEC etching. An etching process is used to expose the device layers, and an etch-resistant protective layer is deposited covering the edges of the device layers so that they are not exposed to the etching chemistry. The sacrificial layer is then exposed by etching the via. A bonding layer is deposited and the sacrificial layer is removed using a selective etch process. In some embodiments, the bonding layer is deposited after the selective etching. Such a workflow is advantageous when the device layer is susceptible to damage from the etching process used to remove the sacrificial layer. Band-gap selective PEC etching is used to undercut the mesa as the sacrificial region is exposed. At this point, the selective area bonding process is used to continue manufacturing the device. In another embodiment, the active region is exposed by dry etching, and both the active region and the sacrificial region absorb the pump light. A conductive path is made between the p-type and n-type cladding layers around the active region. As in solar cells, carriers are swept away from the active region due to the electric field present in the depletion region. By electrically connecting the n-type and p-type layers together, holes can be continuously cleared from the active region, slowing or stopping PEC etching. In other embodiments involving electronic devices or power electronic devices that do not include a light emitting layer, no special measures need to be taken to protect the semiconductor device layers during the selective etching.
The sacrificial layer used to strip the substrate by photochemical etching will contain at least a low bandgap or doped layer that will absorb the pump light and have a higher etch rate relative to the surrounding materials. The sacrificial layer may be deposited epitaxially and the alloy composition and its doping may be selected so that the hole carrier lifetime and diffusion length are higher. Defects that reduce hole carrier lifetime and diffusion length must be avoided by growing the sacrificial layer under growth conditions that promote high material crystalline quality. One example of a sacrificial layer is an InGaN layer that absorbs at the external light source wavelength. The etch stop layer is designed to have a very low etch rate to control the thickness of the adjacent material remaining after the substrate is removed to allow better control of the etch process. The etch characteristics of the etch stop layer may be controlled by the alloy composition and doping alone or in combination. Potential etch stop layers are AlGaN or GaN layers with a higher bandgap than the external light source. Another potential etch stop layer is a highly doped n-type AlGaN or GaN layer that reduces the minority carrier diffusion length and lifetime, thereby significantly reducing the etch rate of the etch stop material.
In some embodiments, PEC etching can be achieved without the use of an active region protection layer by electrically shorting the p-side to the n-side of the laser diode pn junction. Etching in the PEC process is achieved by dissolving AlInGaN material at the wafer surface while transferring holes to the etching solution. These holes are then recombined in solution with electrons extracted at the cathode metal and etching solution interface. In this way, charge neutralization is achieved. Selective etching may be achieved by electrically shorting the anode and cathode. Electron-hole pairs generated in the light emitting layer of the device are swept out of the light emitting layer by the electric field of the p-n junction. Little or no etching of the light emitting layer occurs because holes are swept out of the active region. The accumulation of carriers creates a potential difference that drives the carriers through the metal interconnect, shorting the anode and cathode where they recombine. The flat band condition in the sacrificial region results in the accumulation of holes, which results in rapid etching of the sacrificial layer. In one embodiment, a metal interconnect that shorts the anode and cathode may be used as an anchor region to mechanically hold the gallium and nitrogen containing mesa in place prior to the bonding step.
The relative etch rates of the sacrificial and active regions are determined by many factors but primarily by the hole density in the active region in steady state. If the metal interconnect or anchor resistance is large, or if the cathode or anode is in electrical contact with p-type and n-type, respectively, the cladding region resistance is too large or the schottky barrier is large, then carriers may accumulate on both sides of the pn junction. These carriers will create an electric field that opposes the electric field in the depletion region and will reduce the magnitude of the electric field in the depletion region until the rate at which the photogenerated carriers drift out of the active region is balanced by the rate at which the carriers recombine through the metal layer that shorts the cathode and anode. Some recombination will occur by photochemical etching and it is desirable to prevent the formation of a photobias on the active region since this is proportional to the hole density in the active region.
In one embodiment, the gallium and nitrogen epitaxial semiconductor layers are transferred to the carrier wafer using thermocompression bonding. In this embodiment, thermocompression bonding involves bonding the epitaxial semiconductor layer to the carrier wafer at an elevated temperature and pressure using a bonding medium disposed between the epitaxial layer and the handle wafer. The bonding medium may be composed of a plurality of different layers, but typically comprises at least one layer (bonding layer) composed of a relatively ductile material with a high surface diffusion rate. In many cases, this material consists of gold, aluminum or copper. The bonding stack may further include an adhesion promoting layer disposed between the bonding layer and the epitaxial material or the handle wafer. For example, a gold bonding layer on a silicon wafer may cause silicon to diffuse to the bonding interface, which may reduce the bonding strength. The inclusion of a diffusion barrier layer such as silicon oxide or nitride limits this effect. A relatively thin layer of a second material may be applied on a top surface of the bonding layer to promote adhesion between the bonding layer disposed on the epitaxial material and the handle. Certain bonding layer materials that are less ductile than gold (e.g., al, cu, etc.) or deposited in a manner that results in a rough film (e.g., electrodeposited) may require planarization or roughness reduction by chemical or mechanical polishing prior to bonding, and furthermore, the active metal may require special cleaning steps to remove oxides or organic materials that may interfere with bonding.
Thermocompression bonding can be achieved at relatively low temperatures, typically below 500 degrees celsius and above 200 degrees celsius. The temperature should be applied high enough to promote diffusion between the bonding layers at the bonding interface, but not so high as to promote unwanted alloying of the various layers in each metal stack. The application of pressure increases the rate of bonding and causes some elastic and plastic deformation of the metal laminates, thereby making them better and more uniformly contacted. The optimum bonding temperature, time and pressure will depend on the particular bonding material, the roughness of the surface forming the bonding interface, and the susceptibility of the handle wafer to fracture or damage to the device layer under load.
The bonding interface need not consist of the entire wafer surface. For example, instead of blanket deposition of bonding metal, a photolithographic process may be used to deposit metal in discrete areas separated by areas without bonding metal. This may be advantageous in the case of certain weak bonding areas or subsequent processing steps without bonding assistance, or in the case of the need for an air gap. One example of this is to remove the GaN substrate using wet etching of the epitaxially grown sacrificial layer. To access the sacrificial layer, vias must be etched in either surface of the epitaxial wafer, and if the vias are etched from the bonding face of the wafer, the wafer is most easily preserved for reuse. Once bonded, the etched through-hole forms a channel that can direct the etching solution from the edge to the center of the bonded wafer, so that the substrate region containing the through-hole does not come into intimate contact with the handle wafer, thereby forming a bond.
The bonding medium may also be an amorphous or glassy material that bonds during reflow or during anodization. In anodic bonding, the medium is a glass with a high ionic content, wherein mass transport of the material is facilitated by applying a large electric field. In reflow bonding, the melting point of the glass is low, and contact and good bonding can be formed under moderate pressure and temperature. All glass bonding is relatively fragile and requires that the coefficient of thermal expansion of the glass be close enough to the bonding target wafers (i.e., gaN wafer and handle). The glass in both cases can be deposited by vapor deposition or by a spin-on-glass process. In both cases, the extent and geometry of the bonding region may be limited by the photolithography or screen printing process.
In this work, "gold-gold" metal bonding is used as an example, and a wide variety of oxide bonds, polymer bonds, wax bonds, and the like may be suitable. Submicron alignment tolerances can be achieved using commercially available chip bonding equipment. In another embodiment of the present invention, the bonding layer may be a variety of bonding pairs, including metal-metal, oxide-oxide, solder alloy, photoresist, polymer, wax, and the like. Only epitaxial chips that make poor contact with the bond on the carrier wafer will bond. On commercially available chip or flip chip bonders, sub-micron alignment tolerances may exist.
In one example, an oxide is coated on the exposed planar n-type or p-type gallium and nitrogen containing material or on the exposed planar n-type or p-type gallium and nitrogen containing material, the gallium and nitrogen containing material is coated onto a surface of a carrier wafer consisting essentially of oxide using a direct wafer bonding surface, or the carrier wafer is provided with an oxide layer thereon. In both cases, the oxide surface and exposed gallium and nitrogen containing material on the carrier wafer are cleaned to reduce the amount of hydrocarbons, metal ions and other contaminants on the bonding surfaces. The bonding surfaces are then brought into contact and pressed at elevated temperature to effect bonding. In some cases, the surface is chemically treated with acid, base, or plasma treatment to create a surface that creates weak bonds when in contact with the oxide surface. For example, the exposed surface of a gallium-containing material may be treated to form a thin layer of gallium oxide, which is chemically similar to an oxide, and the bonding surface will bond more easily. Additionally, the oxide of gallium and nitrogen containing materials and the now gallium oxide terminated surfaces may be chemically treated to promote the formation of dangling hydroxyl groups (and other chemicals) when the surfaces are brought into contact, and subsequently rendered permanent when treated at elevated temperatures and elevated pressures.
In an alternative example, an oxide is deposited on the device layer mesa region to form the bonding region. The carrier wafer is also prepared with an oxide layer to form the bonding region. The oxide layer overlying the carrier may be patterned or may be an overlying layer. The oxide surface on the carrier wafer and the oxide surface overlying the mesa device layer mesa region are cleaned to reduce the amount of hydrocarbons, metal ions and other contaminants on the bonding surface. The bonding surfaces are then brought into contact and pressed at elevated temperature to effect bonding. In one embodiment, a Chemical Mechanical Polishing (CMP) process is used to planarize the oxide surface, making it smooth to improve the bonding achieved. In some cases, the surface is chemically treated using acid, base, or plasma treatment to create a surface that produces weak bonds when in contact with the oxide surface. The bonding is performed at high temperature and high pressure.
In another embodiment, the bonding medium may be a dielectric, such as silicon dioxide or silicon nitride. Such a dielectric may be desirable where low conductivity at the bonding interface is desired to achieve increased frequency operating characteristics, such as by reducing device capacitance. The bonding medium comprising the bonding interface may be comprised of many other materials such as an oxide-oxide pair, a semiconductor-semiconductor pair, spin-on glass, solder alloy, polymer, photoresist, wax, or combinations thereof.
The carrier wafer may be selected based on any number of criteria including, but not limited to, cost, thermal conductivity, coefficient of thermal expansion, size, electrical conductivity, optical properties, and process compatibility. The patterned epitaxial wafer is prepared in a manner that allows for subsequent selective release of the bonded epitaxial region. In addition, the patterned carrier wafer is prepared such that the bond pads are arranged to enable a selective area bonding process. These wafers may be prepared by a variety of process flows, some embodiments of which are described below. In a first selective area bonding step, the epitaxial wafer is aligned with pre-patterned bond pads on a carrier wafer and the mesas are bonded to the bond pads using a combination of pressure, heat and/or sonication.
In one embodiment of the present invention, the carrier wafer is another semiconductor material, a metal material, or a ceramic material. Some potential candidate materials include silicon, gallium arsenide, sapphire, silicon carbide, diamond, gallium nitride, alN, polycrystalline AlN, indium phosphide, germanium, quartz, copper tungsten, gold, silver, aluminum, stainless steel, or steel.
In another embodiment, the carrier wafer may be selected based on size and cost. For example, single crystal silicon wafers can be up to 300 mm or 12 inches in diameter and are most cost effective. By transferring gallium and nitrogen epitaxial material from a 2 inch bulk gallium and nitrogen containing substrate to a large silicon substrate with a diameter of 150 mm, 200 mm, or 300 mm, the effective area of a semiconductor device wafer can be increased by as much as 36 times or more. This feature of the invention allows high quality gallium and nitrogen containing semiconductor devices to be mass produced using the infrastructure already established in silicon foundries.
In another embodiment of the present invention, the carrier wafer material may be selected to have thermal expansion characteristics similar to group III nitrides, high thermal conductivity, and may be used as a large area wafer compatible with standard semiconductor device fabrication processes. The carrier wafer is then processed so that the structure can also serve as a substrate for a semiconductor device. The carrier wafer may be singulated into individual dies by sawing, cleaving or scribe and break processes. By combining the functions of the carrier wafer and the finished semiconductor device substrate, the number of components and operations required to build a packaged device is reduced, thereby significantly reducing the cost of the finished semiconductor device.
In one embodiment of the present invention, the process of bonding the semiconductor device epitaxial material to the carrier wafer may be performed prior to selectively etching the sacrificial region and subsequently releasing the gallium and nitrogen containing substrate. Fig. 6 is a schematic diagram illustrating a process including first forming a bond between gallium and nitrogen containing epitaxial materials formed on a gallium and nitrogen containing substrate, and then subjecting the release material to a PEC etching process to release the gallium and nitrogen containing substrate. In this embodiment, an epitaxial material is deposited on a gallium and nitrogen containing substrate such as a GaN substrate by an epitaxial deposition process such as Metal Organic Chemical Vapor Deposition (MOCVD), molecular Beam Epitaxy (MBE), or the like. The epitaxial material is comprised of at least a sacrificial release layer and a device layer. In some embodiments, a buffer layer is grown between the substrate surface region and the sacrificial release region. In fig. 6, a substrate wafer 600 is covered by a buffer layer 602, a selectively etchable sacrificial layer 604, and a collection 601 of device layers. A process for depositing a bonding layer 605 along with a cathode metal 606 that will be used to facilitate photoelectrochemical etching, thereby selectively removing the sacrificial layer 604.
In a preferred embodiment of the present invention, the bonding process is performed after the selective etching of the sacrificial region. This embodiment provides several advantages. One advantage is that the selective etchant is more accessible to uniformly etch the sacrificial region across a semiconductor wafer that includes a substrate 600 containing bulk gallium and nitrogen, such as GaN and epitaxial device layers containing bulk gallium and nitrogen. A second advantage is the ability to perform multiple bonding steps. In one example, an "etch then bond" process flow may be deployed in which mesas 603 are retained on substrate 600 by controlling the etch process so that not all of sacrificial layer 604 is removed. The substrate wafer 600 is covered by a buffer layer 602, a selectively etchable sacrificial layer 604 and a collection of device layers 601. Bonding layer 605 is deposited with cathode metal 606, and cathode metal 606 will be used to facilitate a photoelectrochemical etching process to selectively remove sacrificial layer 604. The selective etching process is carried out to the point where only a small portion of the sacrificial layer 604 remains, so that the mesas 603 remain on the substrate 600, but the unetched portions of the sacrificial layer 604 are easily broken during or after bonding the mesas to the carrier wafer 608.
A key challenge of this etch-then-bond embodiment is to mechanically support the undercut epitaxial device layer mesa region 603 from spatial offset prior to the bonding step. If mesas 603 are offset, the ability to accurately align and arrange them to carrier wafer 608 will be compromised, and thus the ability to manufacture with acceptable yields will be compromised. This challenge of mechanically securing the mesa region 603 in place prior to bonding can be accomplished in a variety of ways. In a preferred embodiment, anchor regions (not shown) are used to mechanically support mesas 603 to gallium and nitrogen containing substrate 600 prior to the bonding step, where they are released from gallium and nitrogen containing substrate 600 and transferred to carrier wafer 608.
The anchor regions are special features that may be designed into the photomask that may attach the undercut device layer to the gallium-nitrogen containing substrate 600, but are too large to undercut by themselves, or due to the design of the mask including regions where the sacrificial layer 604 is not removed, or these features may be comprised of metal or dielectric material that resists etching. These features act as anchors, preventing the undercut device layer 603 from detaching from the substrate 600 and preventing the device layer 603 from moving spatially. Attachment to the substrate 600 may also be achieved by incomplete removal of the sacrificial layer so that there is a weak connection between the undercut device layer 603 and the substrate 600 that can be broken during bonding. The surfaces of the bonding material on carrier wafer 608 and device wafer 600 are then brought into contact and form a stronger bond than undercuts the attachment of device layer 603 to the anchor or remaining material of sacrificial layer 604. After bonding, the isolation of carrier wafer 608 and device wafer 600 transfers device layer 603 to carrier wafer 608.
In one embodiment, the anchor regions are formed of wider features than the device layer mesas 603 so that the sacrificial regions in these anchor regions are not completely removed during the undercut of the device layer 603. In one example, the mesa 603 is held on the substrate 600 by deposition of an etch-resistant material that serves as an anchor by connecting the mesa 603 to the substrate 600. In this example, a buffer layer 602, a selectively etchable sacrificial layer 604, and a set of device layers 601 cover a substrate wafer 600. Bonding layer 605 is deposited with a cathode metal that will be used to facilitate a photoelectrochemical etching process to selectively remove sacrificial layer 604. A layer of etch resistant material, which may be comprised of metal, ceramic, polymer, or glass, is deposited so that it is connected to both the mesa 603 and the substrate 600. By performing the selective etching process in this way, the sacrificial layer 604 can be completely removed and only the etch-resistant layer connects the mesa 603 to the substrate 600.
In another example of an anchoring technique, the mesa 603 is held on the substrate 600 by using an anchor composed of epitaxial material. In this example, a buffer layer 602, a selectively etchable sacrificial layer 604, and a set of device layers 601 cover a substrate wafer 600. The bonding layer 605 is deposited with a cathode metal that will be used to facilitate a photoelectrochemical etching process to selectively remove the sacrificial layer 604. The anchors are shaped such that during the etching process, a small portion of the sacrificial layer 604 remains unetched and creates a connection between the undercut mesa 603 and the substrate wafer 600.
In one embodiment, anchors are located at the ends or sides of the undercut die so that they are connected by a narrow undercut region of material. In this example, the narrow connecting material is remote from the bond metal and is designed such that the undercut material is cleaved at the connecting material rather than across the die. This has the advantage of keeping the entire width of the grains undamaged, which would be advantageous. In another embodiment, geometric features are added to the connecting material to act as stress concentrators and the bonding metal may extend onto the narrow connecting material. The bonding metal reinforces the body of connecting material. Adding these functions may increase the control of the disconnected position. These features may be triangular, circular, rectangular or any deviation that narrows the connecting material or gives the connecting material edges a concave profile.
In another embodiment, the anchors have a lateral extent small enough that they can be undercut, but a protective coating can be used to prevent etching solution from entering the sacrificial layer of the anchor. This embodiment is advantageous in the case where the width of the crystal grains to be transferred is large. The unprotected anchor needs to be larger to prevent complete undercutting, which reduces the grain density and reduces the efficiency of utilization of the epitaxial material.
In another embodiment, anchors are located at the ends of the die and the anchors form a continuous band of material connected to all or a plurality of the die. This configuration is advantageous because the anchors can pattern in the material near the edge of the wafer or photolithographic mask, otherwise material utilization is poor. This allows the device material in the center of the pattern to remain highly available even as the grain size becomes larger.
In a preferred embodiment, the anchors are formed by depositing regions of etch resistant material that will bond well to the epitaxial material and the substrate material. These regions cover a portion of the semiconductor device layer mesas and portions of the structure, such as the substrate, that will not undercut during the etching process. These regions form a continuous connection such that after completely undercutting the semiconductor device layer mesa, it provides mechanical support that prevents the semiconductor device layer mesa from detaching from the substrate. A metal layer is then deposited on top of the semiconductor device layer mesa, on the sidewalls of the semiconductor device layer mesa, and on the bottom of the etched region around the mesa such that a continuous connection is formed. For example, the metal layer may comprise about 20nm titanium to provide good adhesion and covered with about 500nm gold, but of course the choice of metal and thickness may be other. In one example, the length of the metal coated semiconductor device die sidewalls is from about 1nm to about 40nm and the upper thickness is less than the width of the semiconductor device die, such that the sacrificial layer is completely etched in the region proximate the metal anchors where etchant access to the sacrificial layer would be limited.
The mesa region may be formed by dry or wet chemical etching and in one example will include at least a p + + GaN contact layer, a p-type cladding layer comprised of GaN, alGaN or InAlGaN, a light emitting layer such as quantum wells separated by a barrier, a waveguide layer (e.g., an InGaN layer) and an n-type cladding layer comprised of GaN, alGaN or InAlGaN, a sacrificial layer, and a portion of the n-type GaN epitaxial layer beneath the sacrificial layer. A p-contact metal is first deposited on the p + + GaN contact layer to make high quality electrical contact to the p-type cladding layer. A second metal stack is then patterned and deposited on the mesa, overlying the p-contact metal. The second metal stack comprises an n-contact metal which forms a good electrical contact with the n-type GaN layer under the sacrificial layer, and a relatively thick metal layer metal which acts as a mesa pad and cathode. The bonding/cathode metal also forms a thick layer covering the mesa edges and provides a continuous connection between the mesa top and the substrate. After the sacrificial layer is removed by selective photochemical etching, the thick metal provides mechanical support to hold the mesa in place on the GaN wafer until bonding with the carrier wafer is performed.
The use of a metal anchor has several advantages over the use of an anchor made of epitaxial device material. A first advantage is the density of transferable mesas on a Donor wafer (Donor wafer) comprising an epitaxial semiconductor device layer and a bulk substrate comprising gallium and nitrogen. The anchors made of epitaxial material must be large enough not to be undercut completely by the selective etching or they must be protected in some way by a passivation layer. The inclusion of large untransferred anchors will reduce the mesa density on the epitaxial device wafer. It is preferable to use the metal anchor because the metal anchor is made of a material resistant to etching, and thus can be made in a small size without affecting the mesa density. A second advantage is that it simplifies the mesa processing because a separate passivation layer is no longer required to isolate the active region from the etching solution. Removing the active region protection layer reduces the number of fabrication steps while also reducing the required mesa size.
In a specific embodiment, the cathode metal stack further comprises a metal layer intended to increase the strength of the metal anchor. For example, the cathode metal stack may be comprised of 100nm Ti to promote adhesion of the cathode metal stack and provide good electrical contact to the n-type cladding layer. The cathode metal stack may then comprise a layer of tungsten having an elastic modulus of about four times that of gold. The incorporation of tungsten will reduce the thickness of the gold to provide sufficient mechanical support to maintain the mesa after it is selectively etched undercut.
In another embodiment of the invention, the sacrificial region is completely removed by PEC etching and the mesa is held in place by any remaining defect posts. It is well known that PEC etching leaves intact material around defects that are recombination centers. Other mechanisms by which the mesa may remain in place after the complete sacrificial etch include static or van der waals forces. In one embodiment, the undercut process is controlled such that the sacrificial layer is not completely removed.
In a preferred embodiment, a semiconductor device epitaxial material with an underlying sacrificial region is fabricated with a dense array of mesas on a gallium-nitrogen-containing bulk substrate overlying a semiconductor device layer. The mesas are formed using a patterning and wet or dry etch process, where the patterning includes a photolithography step that defines the size and spacing of the mesa regions. Dry etching techniques are candidates, such as reactive ion etching, inductively coupled plasma etching, or chemically assisted ion beam etching. Alternatively, wet etching may be used. The etching is configured to terminate at or below a sacrificial region below the device layer. This is followed by a selective etching process, such as a PEC, to completely or partially etch the exposed sacrificial region, such that the mesa is undercut. This undercut mesa pattern pitch will be referred to as the "first pitch". The first pitch is typically a design width suitable for fabricating each epitaxial region on the substrate, while not being large enough for the intended complete semiconductor device design, which typically desires a larger inactive area or area for contacts, etc. For example, the mesas will have a first pitch ranging from about 5 μm to about 500 μm or to about 5000 μm. Each of these mesas is a "die".
In a preferred embodiment, the dies are transferred to the carrier wafer at a second pitch using a selective bonding process such that the second pitch on the carrier wafer is greater than the first pitch on the gallium-nitrogen containing substrate. In this embodiment, the crystal grains have an expansion pitch for so-called "grain expansion". In one example, the dice have a second pitch to allow each die to be a semiconductor device with a portion of the carrier wafer, including contacts and other components. For example, the second pitch will be about 50 μm to about 1000 μm or to about 5000 μm, but may be as large as about 3-10mm or more in the case where larger semiconductor device dies are required for this application. The larger second pitch may enable simpler mechanical processing without the expense of expensive gallium-nitrogen-containing substrates and epitaxial materials, allow space for additional features to be added to the semiconductor device chip, for example, without the need for expensive bond pads of gallium-nitrogen-containing substrates and epitaxial materials, and/or allow smaller epitaxial layers comprising gallium-nitrogen-containing epitaxial wafers to be assembled on a much larger carrier wafer for subsequent processing, thereby reducing processing costs. For example, a grain expansion ratio of 4 to 1 reduces the density of the gallium and nitrogen containing material by a factor of 4, and thus fills the carrier wafer with an area 4 times that of the gallium and nitrogen containing substrate. This corresponds to turning a 2 inch gallium nitride substrate into a 4 inch carrier wafer. In particular, the present invention increases the use of substrate wafers and epitaxial material through a selective area bonding process to transfer individual epitaxial material dies to a carrier wafer in such a way as to increase the die pitch on the carrier wafer relative to the original epitaxial wafer. The arrangement of the epitaxial material eliminates the need for device assembly using expensive gallium and nitrogen containing substrates, and the overlying epitaxial material, which is typically fabricated on gallium and nitrogen containing substrates, can be fabricated on lower cost carrier wafers, allowing for more efficient utilization of the gallium and nitrogen containing substrates and the overlying epitaxial material.
Fig. 7 is a schematic diagram of a die-spreading process with selective area bonding according to the present invention. According to one embodiment of the present invention, a device wafer is prepared for bonding. The wafer consists of a substrate 706, a buffer layer 703, a fully removed sacrificial layer 709, a device layer 702, a bonding medium 701, a cathode metal used in the PEC etch removal of the sacrificial layer, and an anchor material 704. A mesa region formed in a gallium and nitrogen containing epitaxial wafer forms a release layer and a block of epitaxial material defined by the process. The single grains of epitaxial material are formed at a first pitch. A carrier wafer 707 is prepared that is comprised of the carrier wafer 707 itself and the bond pads 708 at the second pitch. The substrate 706 is aligned with the carrier wafer 707 such that a subset of the mesas on the gallium-nitrogen containing substrate 706 having the first pitch are aligned with a subset of the bond pads 708 on the carrier wafer 707 at a second pitch. Since the first pitch is greater than the second pitch and the mesa will include a device die, a basis for die spreading is established. A bonding process is performed and after the substrate 706 is separated from the carrier wafer 707, a subset of the mesas are selectively transferred to the carrier wafer 707. The process 707 is then repeated with a second set of mesas and bond pads 708 on the carrier wafer until the carrier wafer 707 is completely filled with epitaxial mesas. The gallium and nitrogen containing epitaxial substrate may now optionally be prepared for reuse.
In the example shown in fig. 7, one-quarter of the epitaxial grains are transferred in this first selective bonding step, leaving three-quarters on the epitaxial wafer 706. The selective area bonding step is then repeated to transfer the second quarter, third quarter, and fourth quarter epitaxial grains to the patterned carrier wafer 707. This selective area bonding may be repeated any number of times and is not limited to the four steps shown in fig. 7. The result is an epitaxial die array 707 on the carrier wafer having a wider die spacing than the original die spacing on epitaxial wafer 706. The die pitch on epitaxial wafer 706 will be referred to as pitch 1 and the die pitch on carrier wafer 707 will be referred to as pitch 2, where pitch 2 is greater than pitch 1.
In one embodiment, the bonding between the carrier wafer 707 and the gallium-nitrogen-containing substrate 706 with epitaxial layers is performed between a bonding layer that has been applied to the carrier wafer 707 and the gallium-nitrogen-containing substrate 706 with epitaxial layers. The bonding layer may be a variety of bonding pairs including metal-metal, oxide-oxide, solder alloy, photoresist, polymer, wax, and the like. Only epitaxial grains that make poor contact with the bond on the carrier wafer 707 will bond. Sub-micron alignment tolerances may exist on commercial die bonders. The epitaxial wafer 706 is then pulled apart, breaking the epitaxial material at the weakened epitaxial release layer, so that the desired epitaxial layers remain on the carrier wafer 707. Herein, a "selective area bonding step" is defined as a single iteration of the process.
In one embodiment, the carrier wafer 707 is patterned in such a way that only selected mesas can be contacted with metal bond pads on the carrier wafer 707. When the epitaxial substrate 706 is pulled apart, the bonded mesas break off at the weakened sacrificial regions, while the unbonded mesas remain attached to the epitaxial substrate 706. The selective area bonding process may then be repeated to transfer the remaining mesas into the desired configuration. This process may be repeated through any number of iterations and is not limited to the two iterations shown in fig. 3. The carrier wafer 707 may have any size including, but not limited to, about 2 inches, 3 inches, 4 inches, 6 inches, 8 inches, and 12 inches. After all desired mesas are transferred, a second band gap selective PEC etch can be selectively used to remove any remaining sacrificial region material to create a smooth surface. Standard semiconductor device processing may now be performed on the carrier wafer. Another embodiment of the present invention includes fabricating a device component on a dense epitaxial wafer prior to the selective area bonding step.
In one example, the present invention provides a method for increasing the number of gallium and nitrogen containing semiconductor devices that can be fabricated from a given epitaxial surface area; wherein the epitaxial layer comprising gallium and nitrogen overlies the gallium and nitrogen containing substrate. Patterning epitaxial material containing gallium and nitrogen into grains having a first grain spacing; transferring die from the gallium and nitrogen containing epitaxial material having the first pitch to a carrier wafer to form a second die pitch on the carrier wafer; the second die pitch is greater than the first die pitch.
In one example, each epitaxial device die is an etched mesa having a pitch that is between about 1 μm and about 100 μm wide, or between about 100 μm or about 500 μm wide, or between about 500 μm and about 3000 μm wide, and a length of about 100 μm to about 3000 μm. In one example, the second die pitch on the carrier wafer is between about 100 μm and about 200 μm or between about 200 μm and about 1000 μm or between about 1000 μm and about 3000 μm. In one example, the second pitch of the dies on the carrier wafer is about 2 times to about 50 times the pitch of the dies on the epitaxial wafer. In one example, semiconductor LED devices, laser devices, or electronic devices are fabricated on a carrier wafer after epitaxial transfer. In one example, the semiconductor device includes GaN, alN, inN, inGaN, alGaN, inAlN, and/or InAlGaN. In one example, the gallium and nitrogen containing material is grown on a polar, non-polar or semi-polar plane. In one example, one or more semiconductor devices are fabricated on each grain of epitaxial material. In one example, device components that do not require epitaxial material are placed in the spaces between epitaxial dies.
In one embodiment, the device dies are transferred to a carrier wafer such that the distance between the dies is enlarged in both the lateral and transverse directions. This may be accomplished by spacing the bond pads on the carrier wafer at a pitch that is greater than the pitch of the device dies on the substrate.
In another embodiment of the present invention, device dies from multiple epitaxial wafers are transferred to a carrier wafer such that each design width on the carrier wafer contains dies from multiple epitaxial wafers. It is important that when transferring dice from multiple epitaxial wafers at closer spacing, the dice that are not transferred on the epitaxial wafers do not inadvertently contact and bond to dice that have been transferred to the carrier wafer. To accomplish this, the dies from the first epitaxial wafer are transferred to the carrier wafer using the method described above. A second set of bond pads is then deposited on the carrier wafer and formed to a thickness such that the bonding surface of the second pads is higher than the top surface of the first set of transferred dies. This is done to provide sufficient clearance for bonding of the die to the second epitaxial wafer. The second substrate transfers the second set of dies to the carrier. Finally, the semiconductor device is fabricated and a passivation layer is deposited, and then the deposition of the electrical contact layer allowing each die is driven individually. The dies transferred from the first and second substrates are spaced apart at a pitch that is less than the second pitch of the carrier wafer. The process can be extended to transfer dies from any number of substrates and to transfer any number of devices per die from each substrate.
An example of an epitaxial structure of a laser diode device according to the present invention is shown in fig. 8. In this embodiment, the n-GaN buffer layer is followed by a sacrificial layer and is grown with the n-contact layer, which will be exposed after transfer. Overlying the n-contact layer is an n-cladding layer, an n-side separation confinement heterostructure (n-SCH) layer, an active region, a p-side separation confinement heterostructure (p-SCH) layer, a p-cladding layer, and a p-contact region. In one example of this embodiment, an n-type GaN buffer layer is grown on a c-plane oriented bulk GaN wafer. In another example, the substrate comprises a semi-polar or non-polar orientation. Overlying the buffer layer is a sacrificial layer consisting of InGaN wells separated by GaN barriers, the composition and thickness of the wells being selected so that the wells absorb light having a wavelength shorter than 450nm, but in some casesIn embodiments, the absorption edge will be as short as 400nm, and in other embodiments as long as 520nm. Covering the sacrificial layer is an n-type contact layer doped with 5 × 10 18 cm -3 Of silicon (2), but may be 5X 10 17 And 1X 10 19 cm -3 Other doping levels in between. Overlying the contact layer is an n-type cladding layer composed of a GaN or AlGaN layer having a thickness of 1 micron with an average composition of 4% AlN, but in other embodiments may range in thickness from 0.25 to 2 μm with an average composition of 0-8% aluminum nitride. Overlying the n-cladding layer is an n-type waveguide or Separate Confinement Heterostructure (SCH) layer that helps provide a refractive index contrast with the cladding layer to mitigate confinement of the optical mode. The nSCH is InGaN with a composition of 4% InN and a thickness of 100nm, but in other embodiments, the InGaN nSCH can range in thickness from 20nm to 300nm and 0-8% InN, and can be composed of several layers with different compositions and thicknesses. Covering the n-SCH is a luminescent quantum well layer consisting of two 3.5nm thick In layers 0.15 Ga 0.85 N quantum wells consisting of 4nm thick GaN barriers, but in other embodiments there may be 1 to 7 luminescent quantum well layers consisting of 1nm to 6nm thick quantum wells separated by 1nm to 25nm thick GaN or InGaN barriers. Covering the light emitting quantum well layer is an optional InGaN pSCH with a composition of 4% InN and a thickness of 100nm, but in other embodiments the thickness of the nSCH may range from 20nm to 300nm, with InN of 0-8%, and may be composed of several layers of different compositions and thicknesses. Overlying the pSCH is an optional AlGaN Electron Blocking Layer (EBL) having a composition of 10% AlN, but in other embodiments the AlGaN EBL composition may range from 0% to 30% AlN. The p-type cladding layer covering the EBL is composed of a GaN or AlGaN layer with a thickness of 0.8 microns with an average composition of 4% AlN, but in other embodiments may range from 0.25 to 2 μm in thickness with an average composition of 0-8% aluminum nitride. The p-cladding layer terminates at the free surface of the crystal with a highly doped p + + or p contact layer to achieve high quality p-type electrical contact to the device.
Once the laser diode epitaxial structure is transferred onto a carrier wafer as described in the present invention, the die can be fabricated into a laser diode device using wafer level processes. The wafer processing steps may be similar to those described in this specification for the more conventional laser diode. For example, in many embodiments, the bonding medium and the dies will have a total thickness of less than about 7 microns so that the wafer can be patterned using standard photoresist, photoresist dispensing techniques, and contact and projection lithography tools and techniques. The aspect ratios of these features are compatible with thin film deposition using evaporators, sputtering and CVD deposition tools, such as metal and dielectric layers.
The laser diode device may have a laser stripe region formed in the transferred gallium-nitrogen containing epitaxial layer. If the laser is formed on a polar c-plane, the laser diode cavity can be aligned in the m-direction with the cleaving or etching mirror. Alternatively, if the laser is formed on a semipolar plane, the laser diode cavity may be aligned in projection in the c-direction. The laser stripe region has a first end and a second end and is formed on a gallium and nitrogen containing substrate having a pair of cleaved or etched mirror structures facing each other. The first cleaved surface includes a reflective coating and the second cleaved surface does not include a coating, an anti-reflective coating, or an exposure to gallium and nitrogen containing materials. The first cleavage plane is substantially parallel to the second cleavage plane. The first and second cleavage planes are provided by a scribe and break process according to an embodiment, or by an etching technique using an etching technique, such as Reactive Ion Etching (RIE), inductively coupled plasma etching (ICP) or Chemically Assisted Ion Beam Etching (CAIBE) or other methods. Typical gases used in the etching process may include Cl and/or BCl 3 . The first and second mirrors each include a reflective coating. The coating is selected from the group consisting of silicon dioxide, hafnium dioxide, and titanium dioxide, tantalum pentoxide, zirconium oxide, including combinations thereof, and the like. Depending on the design, the mirror may also include an anti-reflective coating.
In one embodiment, a method of facet formation includes subjecting a substrate to a laser to form a pattern. In a preferred embodiment, the pattern is configured to form a pair of facets of the ridge laser. In a preferred embodiment, the pair of faces face each other and are aligned parallel to each other. In a preferred embodiment, the method uses a UV (355 nm) laser to scribe the laser bars. In one embodiment, the lasers are configured on a system that allows for precise scribing in different patterns and profile configurations. In some embodiments, laser scribing may be performed on the back side, the front side, or both, depending on the application. Of course, there can be other variations, modifications, and alternatives.
In one embodiment, the method uses backside laser scribing or the like. For backside laser scribing, the method preferably forms continuous line laser scribes that are perpendicular to the laser bars on the backside of the GaN substrate. In one embodiment, the laser scribe is typically about 15-20 μm deep or other suitable depth. Preferably, back-scoring may be advantageous. That is, the laser scribing process does not rely on the pitch of the laser bars or other similar patterns. Thus, according to a preferred embodiment, backside laser scribing may result in a higher density of laser stripes per substrate. However, in one embodiment, the backside laser scribing may cause the tape to leave a residue on the facet. In one embodiment, backside laser scribing typically requires that the substrate be placed face down on the tape. For front side laser scribing, the back side of the substrate is in contact with the tape. Of course, there can be other variations, modifications, and alternatives.
It is well known that etching techniques such as Chemically Assisted Ion Beam Etching (CAIBE), inductively Coupled Plasma (ICP) etching or Reactive Ion Etching (RIE) can produce smooth and vertically etched sidewall regions that can act as facets in etched facet laser diodes. In an etch-side process, a masking layer may be deposited and patterned on the wafer surface. The etch mask layer may be comprised of a dielectric, such as silicon dioxide (SiO) 2 ) Silicon nitride (SixNy), combinations thereof, or other dielectric materials. Further, the mask layer may be composed of a metal layer such as Ni or Cr, but may be composed of a metal combination stack or a stack containing a metal and a dielectric. In another approach, a photoresist mask may be used alone or in combination with a dielectric and/or metal. The etch mask layer is patterned using conventional photolithography and etching steps. Contact aligners orA step aligner to perform alignment lithography. Such lithographically-defined mirrors provide a high level of control to design engineers. After patterning of the photoresist mask on top of the etch mask is completed, the pattern is transferred to the etch mask using wet or dry etching techniques. Finally, the facet pattern is etched into the wafer using a dry etching technique selected from CAIBE, ICP, RIE and/or other techniques. The etched faceted surface must be perpendicular to the surface plane of the wafer to a height of between about 87 degrees to about 93 degrees or between about 89 degrees to about 91 degrees. The etched faceted surface region must be very smooth with a root mean square roughness value of less than about 50nm, 20nm, 5nm, or 1nm. Finally, the etch must be substantially damage free, which can act as a non-radiative recombination center, thereby reducing the catastrophic optic damage (COMD) threshold. CAIBE may provide very smooth and low damage sidewalls due to the etch chemistry, while providing a highly vertical etch due to the ability to tilt the wafer table to compensate for any inherent angle in the etch.
In one embodiment, the device layer comprises a superluminescent light emitting diode or SLED. SLEDs are similar in many respects to edge-emitting laser diodes; however, the emitting face of the device is designed to have a very low reflectivity. The SLED is similar to a laser diode in that it is based on an electrically driven junction that is optically active and produces Amplified Spontaneous Emission (ASE) when injected with current and can gain over a wide range of wavelengths. When the light output starts to be dominated by ASE, the light output versus current (LI) characteristics show inflection points where the unit of light output per unit of injected current becomes very large. This inflection point in the LI curve is similar to the threshold of a laser diode, but much softer. SLEDs have a layer structure designed with one or more light emitting layers covered above and below with a material of lower optical index, so that laterally guided optical modes can be formed. SLEDs are also fabricated with features that provide lateral optical confinement. These lateral confinement features may consist of etched ridges with air, vacuum, metal or dielectric material surrounding the ridges and providing a low optical index cladding. Lateral confinement features may also be provided by shaping the electrical contacts such that the injected current is confined to a limited area of the device. In such a "gain-guided" structure, the optical index of the light-emitting layer with injected carrier density provides the optical index contrast required for lateral confinement of the optical mode by dispersion. The emission spectral width is typically much wider (> 5 nm) than that of laser diodes and has advantages in reducing image distortion in displays, improving eye safety, and enhancing measurement and spectral application capabilities.
SLEDs are designed to have high single pass gain or amplification for spontaneous emission generated along the waveguide. SLED devices will also be designed to have low internal losses, preferably below 1cm -1 However, SLEDs can operate with internal losses higher than this. Ideally, the emitting surface reflectivity would be zero, however in practical applications, zero reflectivity is difficult to achieve and is designed to be less than 1%, less than 0.1%, less than 0.001%, or less than 0.0001% reflectivity. Reducing the reflective surface reflectivity can reduce feedback in the device cavity, thereby increasing the injection current density at which the device will begin lasing. Very low reflectivity of the emissive facets can be achieved through the addition of anti-reflective coatings and through a combination of angling the emissive facets relative to the SLED cavity such that the surfaces normal to the facets and the propagation direction of the guided mode are substantially non-parallel. Typically, this would mean a deviation of greater than 1-2 degrees. In practice, the ideal angle depends in part on the antireflective coating used, and the tilt angle must be carefully designed to avoid nulls in the reflectivity versus angle relationship for optimum performance. The facets may be tilted with respect to the propagation direction of the guided mode in any direction with respect to the propagation direction of the guided mode, although some directions may be easier to manufacture depending on the method of facet formation. The etched facets provide high flexibility for facet angle determination. Alternatively, a very common method of achieving angular output to reduce structural interference in the cavity would bend and/or angle the waveguide relative to the cleave plane formed on a predetermined crystallographic plane in the semiconductor chip. In this configuration, the angle of light propagation is not orthogonal to the cleave plane at a specific angle designed for low reflectivity. Can also be achieved by The low reflectivity facets are formed in a manner that roughens the emitting facets to enhance light extraction and limit reflective light coupling back into the guided mode. The SLED is applicable to all embodiments according to the invention and the device can be used interchangeably with a laser diode device when appropriate.
The laser stripe is characterized by a length and a width. The length ranges from about 50 μm to about 3000 μm, but is preferably between about 10 μm and about 400 μm, between about 400 μm and about 800 μm, or between about 800 μm and about 1600 μm, but may be others. The stripes also have a width ranging from about 0.5 μm to about 50 μm, but preferably between about 0.8 μm and about 2.5 μm for single lateral mode operation, or between about 2.5 μm and about 35 μm for multi lateral mode operation, but may be other sizes. In one embodiment, the device has a width ranging from about 0.5 μm to about 1.5 μm, a width ranging from about 1.5 μm to about 3.0 μm, a width ranging from about 3.0 μm to about 35 μm, and the like. In one embodiment, the width is substantially constant in size, although minor variations may exist. The width and length are typically formed using masking and etching processes commonly used in the art.
The laser stripe is provided by an etching process selected from dry etching or wet etching. The device also has an overlying dielectric region that exposes the p-type bonding pad. Overlying the contact region is a contact material, which may be a metal or a conductive oxide or a combination thereof. The p-type electrical contacts may be deposited by thermal evaporation, e-beam evaporation, electroplating, sputtering, or other suitable technique. Overlying the polished region of the substrate is a second contact material, which may be a metal or a conductive oxide or a combination thereof and includes an n-type electrical contact. The n-type electrical contacts may be deposited by thermal evaporation, e-beam evaporation, electroplating, sputtering, or other suitable technique.
An example of machining a laser diode cross section according to one embodiment of the present invention is shown in fig. 9. In this example, an n-contact 901 is formed on top of an n-type gallium and nitrogen contact layer 902 and an n-type cladding layer 903, which n-type cladding layer 903 has been etched to form ridge waveguide 904. An n-type cladding layer 903 overlies an n-side waveguide layer or Separate Confinement Heterostructure (SCH) layer 905, and the n-side SCH overlies an active region 906, the active region 906 containing a light emitting layer, e.g., quantum wells. The active region overlies an optional p-side SCH layer 907 and an Electron Blocking Layer (EBL) 908. An optional p-side SCH layer covers the p-type cladding layer 909 and the p-contact layer 910. Below the p-contact layer 910 is a metal stack 911 comprising a p-type base and bonding metal for attaching the transferred gallium and nitrogen containing epitaxial layer to a carrier wafer 912.
Once the laser is fully processed within the gallium and nitrogen containing layers that have been transferred to the carrier wafer 912, the carrier wafer 912 must be diced. A variety of techniques may be used to dice the carrier wafer 912, and the optimal process will depend on the material selection of the carrier wafer 912. For example, for Si, inP or GaAs carrier wafers that are very easy to cut, scribe and break processes using conventional diamond scribing techniques may be the most suitable cutting process. For harder materials, such as GaN, alN, siC, sapphire or other materials where dicing may be more difficult, laser scribing and breaking techniques may be most appropriate. In other embodiments, a sawing process may be the best way to dice the carrier wafer into individual laser chips. During sawing, a rapidly rotating blade with a hard cutting surface (e.g., diamond) is used, usually in conjunction with a water spray to cool and lubricate the blade. Examples of tool saws commonly used to cut wafers include Disco saws and Accretech saws.
The diced laser chips on the carrier wafer are themselves chip-on-substrate (CoS) by selecting a carrier wafer material, such as AlN, beO, diamond, or SiC suitable as a substrate between the laser chips and the mounting surface. This wafer level packaging feature is a great benefit of the stripped and transferred gallium-containing nitrogen epitaxial layer embodiments of the present invention. The substrate may be a common support member into which the phosphor member of the CPoS will also be attached. Alternatively, the substrate may be an intermediate substrate intended to be mounted to a common support member, with the phosphor material attached therein. The substrate member is characterized by a width, a length, and a thickness. In examples where the substrate is the common support member for the phosphor and laser diode chips, the substrate will have a length ranging in size from about 0.5mm to about 3mm or to about 5mm, a width ranging from about 0.3mm to about 1mm or from about 1mm to about 3mm, and a thickness ranging from about 200 μm to about 1 mm. In examples where the substrate is an intermediate substrate between the laser diode chip and the common support member, it may be characterized by a length having a dimension in the range of from about 0.5mm to about 2mm, a width having a dimension in the range of from about 150 μm to about 1mm, and a thickness that may range from about 50 μm to about 500 μm.
A schematic of CoS based on an exfoliated and transferred epitaxial gallium-containing nitrogen layer according to the present invention is shown in fig. 10. The CoS consists of a substrate material 1001, the substrate material 1001 consisting of a carrier wafer with transferred epitaxial material and a laser diode disposed within the epitaxial layer 1002. Electrodes 1003 and 1004 are electrically coupled to the n-side and p-side of the laser diode device and are configured to transmit power from an external source to the laser diode to generate a laser beam 1005 output from the laser diode. The electrodes are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire may be formed on the electrode to electrically couple to the laser diode device and activate the laser. The integrated CoS device with transferred epitaxial material provides advantages over the conventional configuration illustrated in fig. 4, such as size, cost, and performance, due to low thermal impedance.
This embodiment describes a process and device description for a laser diode formed in a gallium and nitrogen containing epitaxial layer that has been transferred from a native gallium and nitrogen containing substrate, as described in U.S. patent application No. 14/312,427 and U.S. patent publication No. 2015/0140710, the contents of which are incorporated herein by reference. For example, such GaN transfer techniques may enable lower cost, higher performance, and more highly manufacturable process flows.
In this embodiment, the carrier wafer may be selected to provide a desirable substrate material for an integrated CPoS white light source. That is, the carrier wafer used as the laser diode substrate will also serve as a common support member for the laser diode and the phosphor to enable an ultra-compact CPoS integrated white light source. In one example, the carrier wafer is formed of silicon carbide (SiC). SiC is an ideal candidate due to its high thermal conductivity, low electrical conductivity, high hardness and robustness, and wide availability. In other examples, alN, diamond, gaN, inP, gaAs, or other materials may be used as the carrier wafer and resulting substrate for CPoS. In one example, the laser chip is diced such that there is an area intended for the phosphor in front of the front laser facet. According to this embodiment, the phosphor material will then be bonded to the carrier wafer and configured for laser excitation.
After the laser diode is fabricated on the substrate member, in some embodiments of the present invention, the configuration of the integrated white light source will enter into the integration of the phosphor with the laser diode and the common support member. Phosphor selection is a key consideration in laser-based integrated white light sources. The phosphor must be able to withstand the extreme light intensity and associated heating caused by the laser excitation spot without degradation. Important features considered for phosphor selection include:
High conversion efficiency of the optical excitation power into white lumens. In the example of a blue laser diode exciting a yellow phosphor, a conversion efficiency of over 150 lumens per optical watt, or over 200 lumens per optical watt, or over 300 lumens per optical watt is desirable.
High optical damage threshold capable of withstanding laser powers of 1-20W in a spot comprising a diameter of 1mm, 500 μm, 200 μm, 100 μm or even 50 μm.
A high thermal damage threshold capable of withstanding temperatures in excess of 150 ℃, in excess of 200 ℃ or in excess of 300 ℃ without decomposition.
Low thermal quenching characteristics so that the phosphor remains effective when it reaches temperatures in excess of 150 ℃, 200 ℃, or 250 ℃.
High thermal conductivity to dissipate heat and regulate temperature. Thermal conductivities of greater than 3W/mK, greater than 5W/mK, greater than 10W/mK and even greater than 15W/mK are desirable.
The appropriate phosphor emission color for this application.
Suitable porosity characteristics that result in the expected scattering of coherent excitation, without unacceptable reduction in thermal conductivity or optical efficiency.
The appropriate form factor for the application. Such form factors include, but are not limited to, blocks, plates, discs, balls, cartridges, rods, or similar geometric elements. The appropriate choice will depend on whether the phosphor is operated in a transmissive or reflective mode and on the absorption length of the excitation light in the phosphor.
Surface conditions optimized for the application. In one example, the phosphor surface may be intentionally roughened to improve light extraction.
In a preferred embodiment, a blue laser diode operating in the wavelength range of 420nm to 480nm will be combined with a phosphor material that provides a yellowish emission in the range of 560nm to 580nm, so that when mixed with the blue emission of the laser diode, white light is produced. For example, to meet the white point on the black body line, the energy of the combined spectrum may consist of approximately 30% from the blue laser emission and approximately 70% from the yellow phosphor emission. In other embodiments, phosphors with red, green, yellow, and even blue emission can be used in combination with laser diode excitation sources in the violet, ultraviolet, or blue wavelength ranges to produce white light through color mixing. While such white light systems may be more complex due to the use of more than one phosphor member, advantages such as improved color reproduction may be achieved.
In one example, light emitted from the laser diode is partially converted by the phosphor element. In one example, the partially converted emitted light produced in the phosphor element results in a color point that is white in appearance. In one example, the color point of the white light is located on the planckian black body point locus. In one example, the color point of the white light is within du 'v' of less than 0.010 of the planckian black body point locus. In one example, the color point of the white light is preferably located within du 'v' of less than 0.03 of the planckian black body point locus.
The phosphor material may be operated in a transmissive mode, a reflective mode, or a combination of transmissive and reflective modes, or other modes. The phosphor material is characterized by excellent conversion efficiency, thermal damage resistance, optical damage resistance, thermal quenching characteristics, porosity for scattering excitation light, and thermal conductivity. In a preferred embodiment, the phosphor material consists of a yellow YAG material doped with Ce, has a conversion efficiency of more than 100 lumens per watt, more than 200 lumens per watt or more than 300 lumens per watt and can be a polycrystalline ceramic material or a single crystal material.
In some embodiments of the present invention, the environment of the phosphor can be independently adjusted to result in high efficiency with little or no added cost. Phosphor optimization for laser diode excitation may include high transparency, scattering or non-scattering properties, and the use of ceramic phosphor plates. The reduced temperature sensitivity may be determined by the doping level. A reflector may be added to the back of the ceramic phosphor to reduce losses. The shape of the phosphor may be configured to increase in-coupling, increase out-coupling, and/or reduce back-reflection. Surface roughness is a well-known way to increase light extraction from solid materials. Coatings, mirrors or filters may be added to the phosphor to reduce the amount of light exiting the non-primary emission surface, promote more efficient exit of light through the primary emission surface, and promote more efficient incoupling of laser excitation light. Of course, there can be additional variations, modifications, and alternatives.
In some embodiments, certain types of phosphors will be optimally tuned with the laser excitation source in this desired application. As an example, doping with Ce 3+ Ionic ceramic Yttrium Aluminum Garnet (YAG), or YAG-based phosphors, may be desirable candidates. Doped with a substance such as Ce to achieve the appropriate emission color, and typically includes porosity features to scatter the excitation source light and properly break coherence in the laser excitation. As a result of its cubic crystal structure, YAG: ce can be produced as highly transparent single crystal and polycrystalline bulk materials. Transparency and brightness depend on the stoichiometric composition, dopant content, and the overall processing and sintering route. Transparency and scattering centrality can be optimized for a homogeneous mixture of blue and yellow light. Ce can be configured to emit green emission. In some embodiments, YAG mayDoped with Eu to emit red light emission.
In a preferred embodiment according to the present invention, the white light source is configured with a ceramic polycrystalline YAG: ce phosphor comprising an optical conversion efficiency of more than 100 lumens per optically excited watt, more than 200 lumens per optically excited watt or even more than 300 lumens per optically excited watt. In addition, the ceramic YAG Ce phosphor is characterized by a temperature quenching characteristic of greater than 150 ℃, greater than 200 ℃ or greater than 250 ℃, and a high thermal conductivity of 5-10W/mK to effectively dissipate heat to the heat sink member and maintain the phosphor at an operable temperature.
In another preferred embodiment according to the invention, the white light source is configured with a Single Crystal Phosphor (SCP), such as YAG: ce. In one example, ce: Y can be grown by Czochralski technique 3 Al 5 O 12 And (6) SCP. Ce based SCP in this embodiment according to the invention is characterized by an optical conversion efficiency of more than 100 lumens per optically excited watt, more than 200 lumens per optically excited watt, or even more than 300 lumens per optically excited watt or even higher. In addition, the single crystal YAG: ce phosphor is characterized by a temperature quenching characteristic of greater than 150 ℃, greater than 200 ℃ or greater than 300 ℃, and a high thermal conductivity of 8-20W/mK to effectively dissipate heat to the heat sink member and maintain the phosphor at an operable temperature. In addition to high thermal conductivity, high thermal quenching threshold, and high conversion efficiency, the ability to shape phosphors into minute shapes that can be used as ideal "point" light sources when excited with a laser is an attractive feature.
In some embodiments, the YAG: CE may be configured to emit a yellow emission. In an alternative or the same embodiment, the YAG: CE may be configured to emit green light emission. In yet another alternative or the same embodiment, YAG may be doped with Eu to emit red light emission. In some embodiments, the LuAG is configured for transmission. In alternative embodiments, silicon nitride or aluminum oxynitride may be used as the crystalline host material for red, green, yellow, or blue light emission.
In an alternative embodiment, a powdered single crystal or ceramic phosphor, such as a yellow phosphor or a green phosphor, is included. The powdered phosphor may be dispensed on a transparent piece for transmissive mode operation, or on a solid member (with a reflective layer on the back of the phosphor), or between the phosphor and the solid member for reflective mode operation. The phosphor powders may be held together in a solid structure using a binder material, which is preferably an inorganic material with a high optical damage threshold and favorable thermal conductivity. The phosphor powder may include a colored phosphor and be configured to emit white light when excited by and combined with a blue laser beam or excited by a violet laser beam. The powdered phosphor may include YAG, luAG, or other types of phosphors.
In one embodiment of the present invention, the phosphor material comprises a yttrium aluminum garnet matrix material and a rare earth doping element, or the like. In one example, the wavelength converting element is a phosphor comprising a rare earth doping element selected from Ce, nd, er, yb, ho, tm, dy, and Sm, combinations thereof, and the like. In one example, the phosphor material is a high density phosphor element. In one example, the high-density phosphor element has a density greater than 90% of a pure host crystal. YAG (YAG: ce) doped with cerium (III) can be used 3+ Or Y 3 Al 5 O 12 :Ce 3+ ) Where the phosphor absorbs light from the blue laser diode and emits light in a wide range from greenish to reddish, most of the output is yellow. This yellow emission combined with the remaining blue emission results in "white" light that can be tuned to a color temperature of warm white (yellowish) or cool white (bluish). Ce can be regulated by replacing cerium with other rare earths (e.g. terbium and gadolinium) 3+ YAG, and may even be further tuned by replacing some or all of the aluminum in the YAG with gallium.
In alternative examples, various phosphors may be applied to the present invention, including, but not limited to, organic dyes, conjugated polymers, semiconductors, such as AlInGaP or InGaN doped with Ce 3+ Ionic Yttrium Aluminum Garnet (YAG) (Y) 1-a Gd a ) 3 (Al 1-b Ga b )5O 12 :Ce 3+ ，SrGa 2 S 4 :Eu 2+ ， SrS:Eu 2+ Terbium aluminium based garnets (TAG) (Tb) 3 Al 5 O 5 ) And the colloidal quantum dot film contains CdTe, znS, znSe, znTe, cdSe or CdTe.
In other alternative examples, some rare earth doped sialon materials (sialon) may be used as the phosphor. beta-SiAlON doped with europium (III) absorbs the ultraviolet and visible light spectra and emits a strong broadband visible emission. Its brightness and color do not change significantly with temperature due to the temperature-stable crystal structure. In one alternative example, green and yellow SiAlON phosphors and red CaAlSiN may be used 3 A basal (CASN) phosphor.
In yet another example, a white light source can be fabricated by combining a near-UV emitting laser diode with a mixture of efficient europium based red and blue emitting phosphors plus green emitting zinc sulfide (ZnS: cu, al) doped with copper and aluminum.
In one example, the phosphor or phosphor blend may be selected from (Y, gd, tb, sc, lu, la) 3 (Al,Ga,In) 5 O 12 :Ce 3+ ，SrGa 2 S 4 :Eu 2+ ，SrS:Eu 2+ And a colloidal quantum dot film containing CdTe, znS, znSe, znTe, cdSe, or CdTe. In one example, the phosphor is capable of emitting substantially red light, wherein the phosphor is selected from the group consisting of: (Gd, Y, lu, la) 2 O 3 :Eu 3+ 、Bi 3 +；(Gd,Y,Lu,La) 2 O 2 S:Eu 3+ 、Bi 3 +、 (Gd,Y,Lu,La)VO 4 :Eu 3 + 、Bi 3+ ；Y 2 (O,S) 3 :Eu 3+ ；Ca 1-x Mo 1-y Si y O 4 Wherein x is more than or equal to 0.05 and less than or equal to 0.5, and y is more than or equal to 0 and less than or equal to 0.1; (Li, na, K) 5Eu (W, mo) O 4 ；(Ca,Sr)S:Eu 2+ ；SrY 2 S 4 :Eu 2+ ； CaLa 2 S 4 :Ce 3 +；(Ca,Sr)S:Eu 2 +；3.5MgO×0.5MgF 2 ×GeO 2 :Mn 4 +(MFG)； (Ba,Sr,Ca)Mg x P 2 O 7 :Eu 2+ 、Mn 2 +；(Y,Lu) 2 WO 6 :Eu 3+ 、Mo 6 +； (Ba,Sr,Ca) 3 Mg x Si 2 O 8 :Eu 2+ 、Mn 2 +, in which 1<x≤2；(RE 1-y Ce y )Mg 2-x Li x Si 3-x P x O 12 Wherein RE is at least one of Sc, lu, gd, Y and Tb, 0.0001<x<0.1 and 0.001<y<0.1；(Y,Gd,Lu,La) 2-x Eu x W 1-y Mo y O 6 Wherein x is more than or equal to 0.5 and less than or equal to 1.0, and y is more than or equal to 0.01 and less than or equal to 1.0; (SrCa) 1-x Eu x Si 5 N 8 Wherein x is more than or equal to 0 and less than or equal to 0.3; srZnO 2 :Sm 3+ ；M m O n X, wherein M is selected from the group of Sc, Y, lanthanides, alkaline earth metals and mixtures thereof; x is halogen; m is more than or equal to 1 and less than or equal to 3; and 1. Ltoreq. N.ltoreq.4, and wherein the lanthanide doping levels may range from 0.1 to 40% spectral weight; and Eu 3+ Activating phosphate or phosphate borate; and mixtures thereof. Further details of other phosphor materials and related art can be found in U.S. patent No.8,956,894 to raining et al entitled "white light device using non-polar or semi-polar gallium-containing materials and phosphors," 2-17-2015, which is commonly owned and hereby incorporated by reference.
In another preferred embodiment according to the invention, the white light source is provided with a Single Crystal Phosphor (SCP) or a ceramic plate phosphor selected from the group consisting of lanthanum silicon nitride compounds and lanthanum aluminium silicon oxynitride compounds, which comprises Ce 3+ The atomic concentration of the ions ranges from 0.01% to 10%. Optionally, containing Ce3 + Ionic lanthanum silicon nitride and lanthanum aluminum silicon oxynitride compounds include LaSi 3 N 5 :Ce 3+ Or LaAl (Si) 6-z Al z )(N 10-z O z ):Ce 3+ (wherein z = 1). In this embodiment according to the present invention, based on LaSi 3 N 5 :Ce 3+ Or LaAl (Si) 6-z Al z )(N 10-z O z ):Ce 3+ (wherein z = 1) the SCP or ceramic plate is characterized by more than 100 lumens/light excitation watt, or more than 200 lumens/light excitation watt, or even more than 300 lumens/light excitation watt or more. Further, single Crystal Phosphor (SCP) or ceramic plate phosphor LaSi 3 N 5 :Ce 3+ Or LaAl (Si) 6-z Al z )(N 10- z O z ):Ce 3+ (wherein z = 1) is characterized by a temperature quenching characteristic of greater than 150 ℃, greater than 200 ℃, or greater than 300 ℃, and has>A high thermal conductivity of 10W/m-K to efficiently dissipate heat to the heat sink components and maintain the phosphor at an operable temperature. In addition to high thermal conductivity, high thermal quenching threshold, and high conversion efficiency, the ability to shape the phosphor into minute shapes that can be used as an ideal "point" light source when excited with a laser is an attractive feature.
In some embodiments of the present invention, the ceramic phosphor material is embedded in a binder material, such as a silica gel. This configuration is generally less desirable because the adhesive material generally has poor thermal conductivity and therefore can be very hot, with rapid degradation and even burning. Such "embedded" phosphors are typically used in dynamic phosphor applications, such as color wheels that rotate a wheel to cool the phosphor and spread excitation spots in a radial pattern around the phosphor.
For integrated white light sources based on laser diode excitation, adequate heat dissipation from the phosphor is a critical design consideration. In particular, optically pumped phosphor systems have a source of phosphor loss that results in thermal energy and thus must be dissipated to a heat sink for optimal performance. These two major sources of loss are the stokes losses, which are the result of converting higher energy photons to lower energy photons, so that the energy difference is the energy lost by the system being produced and dissipated as heat. In addition, measuring the quantum efficiency or quantum yield of the portion of the absorbed photon that is successfully re-emitted is not a unity, such that there is heating from other internal absorption processes associated with the unconverted photon. Root of herbaceous plant Depending on the excitation wavelength and the conversion wavelength, stokes losses can result in more than 10% incident optical power loss, more than 20% incident optical power loss, and more than 30% and more incident optical power loss to result in thermal power that must be dissipated. Quantum losses can result in an additional 10% of the incident optical power, greater than 20% of the incident optical power, and greater than 30% and greater of the incident optical power to result in thermal power that must be dissipated. Laser beam powers in excess of 1W/mm can be produced for focusing to laser beam powers in the range of 0.5W to 100W for spot sizes less than 1mm diameter, less than 500 microns diameter, or even less than 100 microns diameter 2 、100W/mm 2 Or even more than 2500W/mm 2 The power density of (a). As an example, we can work with a 0.1W/mm, assuming that the spectrum consists of 30% of blue pump light and 70% of converted yellow light, and assuming the best case of Stokes and quantum losses 2 、10W/mm 2 Or even more than 250W/mm 2 The total loss of 10% in the phosphor of (a) calculates the dissipated power density in the form of heat. Thus, even for this best case example, there is an enormous amount of heat to dissipate. This heat generated in the phosphor under high intensity laser excitation can limit phosphor conversion performance, color quality, and lifetime.
For optimal phosphor performance and lifetime, not only should the phosphor material itself have a high thermal conductivity, but it will also be attached to a substrate or common support member with a high thermal conductivity joint to keep the heat away from the phosphor and transport it to the heat sink. In the present invention, the phosphor is either attached to a common support member as with the laser diode in CPoS, or to an intermediate substrate member which is subsequently attached to the common support member. Candidate materials for the common support member or the intermediate substrate member are SiC, alN, beO, diamond, copper tungsten, sapphire, aluminum, and the like. Care must be taken to interface the phosphor to the substrate member or the common support member. The joining material should be composed of a high thermal conductivity material, such as solder (or the like), and be substantially free of voids or other defects that would impede heat flow. In some embodiments, sizing may be used to secure the phosphor. Ideally, the phosphor bonding interface will have a relatively large area, with flat surfaces on both the phosphor side and the support member side of the interface.
In the present invention, the laser diode output beam must be configured to be incident on the phosphor material to excite the phosphor. In some embodiments, the laser beam may be directly incident on the phosphor, and in other embodiments, the laser beam may interact with optics, reflectors, or other objects to manipulate the laser beam prior to being incident on the phosphor. Examples of such optics include, but are not limited to, ball lenses, aspheric collimators, aspheric lenses, fast or slow axis collimators, dichroic mirrors, turning mirrors, optical isolators, but may be others.
The apparatus typically has free space with non-guided laser beam features that transmit the emission of the laser beam from the laser device to the phosphor material. The laser beam spectral width, wavelength, size, shape, intensity, and polarization are configured to excite the phosphor material. The laser beam can be configured by positioning it at a precise distance from the phosphor to take advantage of the beam divergence characteristics of the laser diode and achieve the desired spot size. In one embodiment, the angle of incidence from the laser to the phosphor is optimized to achieve the desired beam shape on the phosphor. For example, due to the asymmetry of the laser aperture and the different divergence angles of the beam on the fast and slow axes, the shape of the spot on the phosphor generated from the laser, arranged orthogonal to the phosphor, will be elliptical, with the fast axis diameter typically being larger than the slow axis diameter. To compensate for this, the laser beam incident angle on the phosphor can be optimized to stretch the laser beam in the slow axis direction so that the laser beam is more circular at the phosphor. In other embodiments, free-space optics, such as a collimating lens, may be used to shape the beam before it is incident on the phosphor. The light beam has a polarization purity of greater than 50% and less than 100%. As used herein, the term "polarization purity" means that greater than 50% of the emitted electromagnetic radiation is in a substantially similar polarization state, such as a Transverse Electric (TE) or Transverse Magnetic (TM) polarization state, but may have other meanings consistent with ordinary meaning.
The white light apparatus also has an electrical input interface configured to couple electrical input power to the laser diode device to generate a laser beam and excite the phosphor material. In one example, the laser beam incident on the phosphor has a power of less than 0.1W, greater than 0.5W, greater than 1W, greater than 5W, greater than 10W, or greater than 20W. The white light source is configured to produce a white light output of greater than 1 lumen, 10 lumens, 100 lumens, 250 lumens, 500 lumens, 1000 lumens, 3000 lumens, or 10,000 lumens or more.
The support member is configured to transfer thermal energy from the at least one laser diode device and the phosphor material to the heat sink. The support member is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt, less than 5 degrees celsius/watt, or less than 3 degrees celsius/watt to characterize a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material, such as copper with a thermal conductivity of about 400W/(mK), aluminum with a thermal conductivity of about 200W/(mK), 4H-SiC with a thermal conductivity of about 370W/(mK), 6H-SiC with a thermal conductivity of about 490W/(mK), alN with a thermal conductivity of about 230W/(mK), synthetic diamond, sapphire, or other metal, ceramic, or semiconductor with a thermal conductivity of about > 1000W/(mK). The support member may be formed from a growth process such as SiC, alN or synthetic diamond and then mechanically shaped by machining, cutting, trimming or molding. Alternatively, the support member may be formed of a metal such as copper, copper tungsten, aluminum, or the like by machining, cutting, trimming, or molding.
In a preferred configuration of the CPoS white light source, the common support member comprises the same substrate as the substrate to which the gallium and nitrogen containing laser diode chip is directly bonded. That is, the laser diode chip is mounted or attached downward to a substrate composed of a material such as SiC, alN, or diamond, and the phosphor material is also mounted to the substrate, so that the substrate becomes the common support member. The phosphor material may have an intermediate material located between the substrate and the phosphor. The intermediate material may be comprised of a thermally conductive material such as copper. The laser diode may be attached to the first surface of the substrate using conventional die attach techniques using solder such as AuSn solder, but may be other techniques, such as SAC solder such as SAC305, leaded solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. Similarly, the phosphor material may be bonded to the substrate using a soldering technique, such as AuSn solder, SAC solder, lead-containing phosphor, or with indium, but it may be other techniques, such as sintered silver interface material. The joint may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), thermal adhesive, and other materials. Alternatively, the joint may be formed by a metal-metal bond (e.g., au-Au bond). Optimizing the bonding for lowest thermal impedance is a key parameter for heat dissipation from the phosphor, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material.
In this alternative configuration of the CPoS white light source, the laser diode is bonded to an intermediate substrate disposed between the gallium and nitrogen containing laser chip and the common support member. In this configuration, the intermediate substrate may be composed of SiC, alN, diamond, etc., and the laser may be attached to the first surface of the substrate using conventional die attach techniques using solder such as AuSn solder, but may be other techniques. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution or deposition of sintered silver attachment material can be used with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The second surface of the substrate may be attached to the common support member using similar techniques, but other techniques are also possible. Similarly, the phosphor material may have an intermediate material or substrate located between the common support member and the phosphor. The intermediate material may be comprised of a thermally conductive material such as copper. The phosphor materials may be bonded using a soldering technique. In this configuration, the common support member should be constructed of a thermally conductive material such as copper or copper tungsten. Optimizing the bonding for lowest thermal impedance is a key parameter for heat dissipation from the phosphor, which is critical to prevent phosphor degradation and thermal quenching of the phosphor material.
In a specific embodiment of the present invention, the CPoS white light source is configured as a side pumped phosphor for operation in a transmissive mode. In this configuration, the phosphor is positioned in front of the laser face that outputs the laser beam, so that the laser beam generated upon activation is incident on the back face of the phosphor, with both the laser and the phosphor being disposed on the support member. The gallium-nitrogen containing laser diode is configured with a cavity having a length greater than 100 μm, greater than 500 μm, greater than 1000 μm, or greater than 1500 μm long, and a width greater than 1 μm, greater than 10 μm, greater than 20 μm, greater than 30 μm, or greater than 45 μm. The cavity is configured with a front or front mirror and a back or back mirror on the ends, wherein the front face comprises an output face and is configured to emit a laser beam incident on the phosphor. The front face may be provided with an anti-reflection coating to reduce reflectivity or be completely uncoated to allow radiation to pass through the mirror without excessive reflectivity. In some cases, the coating may be configured to slightly increase the reflectivity. Since no laser beam will be emitted from the rear end of the cavity member, the rear surface orThe back mirror is configured to reflect radiation back into the cavity. For example, the back side includes a highly reflective coating having a reflectivity of greater than 85% or 95%. In one example, the phosphor is doped with Ce 3+ An ionic ceramic Yttrium Aluminum Garnet (YAG) and emits a yellow light emission. The phosphor is shaped as a block, plate, sphere, cylinder, or other geometric shape. The shape of the phosphor is configured as a block, plate, sphere, cylinder, or other geometric shape. In particular, the geometric primary dimension of the phosphor may be less than 50 μm, less than 100 μm, less than 200 μm, less than 500 μm, less than 1mm, or less than 10mm. Operating in a transmissive mode, the phosphor has a first major side (back side) for receiving an incident laser beam, and at least one second major side (front side) where most useful white light will exit the phosphor to couple to the application. The phosphor is attached to a common support member or substrate located in front of the output face of the laser diode such that the first major side of the phosphor configured to receive excitation light will be located in the optical path of the laser output beam. The laser beam geometry, size, spectral width, wavelength, intensity, and polarization are configured to excite the phosphor material. One advantage of transmissive mode phosphor operation is that the mitigation of the excitation source prevents or impedes the emission of any useful white light emission from the primary emission surface. In addition, by excitation from the back side of the phosphor, there will be no impediments associated with the excitation source or light beam that may make integration of optics difficult to collimate or project white light. Ce can be configured to emit green light emission in alternative embodiments. In yet another alternative or identical embodiment, YAG may be doped with Eu to emit red light emission. In alternative embodiments, silicon nitride or aluminum oxynitride may be used as the crystalline host material for red, green, yellow, or blue light emission.
Fig. 11 shows a schematic diagram illustrating a transmissive embodiment of a CPoS integrated white light source based on a conventional laser diode formed in gallium-nitrogen containing substrate technology in accordance with the present invention. The laser-based CPoS white light source consists of a substrate material 1101 that serves as a common support member configured to serve as an intermediate material between the laser diode chip 1102 and the final mounting surface and as an intermediate material between the phosphor material 1106 and the final mounting surface. The substrate 1101 is provided with electrodes 1103 and 1104, which may be formed with a deposited metal layer, such as Au. In one example, ti/Pt/Au is used for the electrodes. The bonding wires 1105 are configured to couple electric power from the electrodes 1103 and 1104 on the substrate 1101 to the laser diode chip 1102 to generate a laser beam output from the laser diode. The laser beam output excites a phosphor plate 1106 located in front of the laser output face. Phosphor plate 1106 is attached to the substrate over mesa 1107 or recessed area. The electrodes 1103 and 1104 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Wire bonds 1105 may be formed on the electrodes to couple power to the laser diode device 1102. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different substrate or common support member geometry designs, different laser output beam orientations relative to the phosphors, different electrode and electrical designs, and so forth.
Fig. 12 shows a schematic diagram illustrating an alternative transmissive embodiment of a CPoS integrated white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. The laser-based CPoS white light device consists of a substrate material 1201 that serves as a common support member configured to serve as an intermediate material between the laser diode 1202 (which is formed in the transferred gallium-nitrogen containing epitaxial layer) and the final mounting surface, and as an intermediate material between the phosphor plate material 1206 and the final mounting surface 1207. The laser diode or CoS substrate 1201 is configured with electrodes 1203 and 1204, which may be formed by depositing a combination of metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, etc. The laser beam output excites a phosphor plate 1206 located in front of the laser output face. Phosphor plate 1206 is attached to the substrate on mesa 1207 or recessed area. The electrodes 1203 and 1204 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires (not shown) may be formed on the electrodes to couple electrical power to the laser diode device 1202 to generate a laser beam output from the laser diode. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different substrate or common support member geometric designs, different directions of the laser output beams relative to the phosphors, different electrode and electrical designs, and so forth.
In many embodiments of the present invention, the connection interface between the phosphor and the common support member must be carefully designed and handled. The thermal resistance of the connection joint should be minimized using suitable connection materials, interface geometry, and connection process practices to achieve a sufficiently low thermal resistance to allow heat dissipation. Also, the attachment interface may be designed to increase the reflectivity to maximize the useful white light exiting the emitting surface of the phosphor. Examples include AuSn solder, SAC solder (e.g., SAC 305), leaded solder, or indium, but other solders are also possible. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The joints may also be formed of thermally conductive glue, thermal epoxy, and other materials. The common support member with the laser and the phosphor material is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt, which represents a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, copper tungsten, aluminum, siC, sapphire, alN or other metal, ceramic or semiconductor. The side-pumped transmission device has a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist.
In order to improve the efficiency of the integrated white light source, measures may be taken to minimize the amount of light exiting the first surface, wherein the laser excitation light is incident on the phosphor and to maximize the light leaving the second primary white light emitting side of the phosphor, where the useful white light leaves. These measures may include the use of filters, spectrally selective reflectors, conventional mirrors, spatial mirrors, polarization-based filters, holographic elements, or coatings, but may be others.
In one example for a transmissive mode phosphor, a filter is positioned on the back side of the phosphor to reflect the backward propagating yellow emission toward the front of the phosphor where it has another chance of leaving the primary emission surface into useful white light. In this configuration, the reflector would have to be designed not to block the blue excitation light from the laser. The reflector may be constituted by a spectrally selective Distributed Bragg Reflector (DBR) mirror consisting of 2 or more alternating layers of different refractive index designed to reflect yellow light over a wide range of angles. The DBR may be deposited directly on the phosphor using techniques such as e-beam deposition, sputter deposition, or thermal evaporation. Alternatively, the DBR may be in the form of a plate-like element applied to the phosphor. Since in a typical white light source consisting of a mixture of yellow and blue light emissions, the yellow emission comprises about 70% of the energy, this method of reflecting yellow light may be a sufficient measure in many applications. Of course, there can be additional variations, modifications, and alternatives.
In another example for a transmissive mode phosphor, a filter system is positioned on the back side of the phosphor to reflect the backward propagating yellow emission and the backward scattered blue excitation light towards the front of the phosphor where it has another chance to leave the primary emission surface into useful white light. The challenge with this configuration is to allow forward propagating blue pump excitation light to pass through the filter and not to allow backward scattered propagating blue light to pass through. One way to overcome this challenge is to use a filter designed to be incident angle reflectivity dependent and configure the laser at an incident angle where the reflectivity is a minimum, e.g., normal incidence. Also, in this configuration, the reflector may be configured from DBR mirrors such that one DBR mirror pair will reflect yellow light and a second DBR pair will be used to reflect blue light with a determined angular relationship. The DBR may be deposited directly on the phosphor using techniques such as e-beam deposition, sputter deposition, or thermal evaporation. Alternatively, the DBR may be in the form of a plate-like element applied to the phosphor. Of course, there can be additional variations, modifications, and alternatives.
Fig. 13 shows a schematic diagram illustrating an alternative transmissive embodiment of a CPoS integrated white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, with the laser diode chip formed from a transfer epitaxial layer. Of course, conventional implementations of chips on substrates such as those shown in fig. 4 and 11 may be used for this implementation that includes optical elements for improved efficiency. The laser-based CPoS white light device is composed of a substrate material 1201 that serves as a common support member configured to serve as an intermediate material between the laser diode 1202 (which is formed in the transferred gallium-nitrogen containing epitaxial layer) and the final mounting surface, and as an intermediate material between the phosphor plate material 1206 and the final mounting surface 1207. The laser diode 1202 or the CoS substrate 1201 is configured with electrodes 1203 and 1204 that may be formed with a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, etc. The laser beam output excites a phosphor plate 1206 located in front of the laser output face. In this embodiment, phosphor plate 1206 is coated with a material 1208 configured to increase the efficiency of the white light source, such that more useful white light exits from the primary emission surface of phosphor plate 1206. In this embodiment, the coating 1208 is configured to increase the reflectivity of the yellow and possibly blue light emissions so that the light is reflected back to the front emitting surface. The phosphor plates are attached to the substrate on the mesa 1207 or recessed area. The electrodes 1203 and 1204 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire (not shown) may be formed on the electrode to couple electric power to the laser diode device to generate a laser beam output from the laser diode. Of course, this is only one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different substrate or common support member geometry designs, different laser output beam orientations relative to the phosphors, different electrode and electrical designs, and so forth.
A second approach to overcome the challenge of reflecting the backward propagating blue and yellow emissions while allowing the forward blue emission to pass through is to utilize a filter system that combines a yellow spectrally selective reflector, such as a DBR and a polarization-based reflector for the blue light. Since the blue light emission from the laser excitation source may be highly polarized at a polarization ratio of greater than 90% or greater than 95%, and the backward-propagating scattered blue light will have mixed polarizations, the polarization-based reflector may be configured as a filter that allows the polarization state of the laser diode output beam (e.g., TE) to freely pass through while acting as a reflector for other polarization states. Such a configuration would likely require two elements that could be combined into a single piece. The first element would be a yellow reflector, such as a DBR mirror pair or another single or multilayer film designed to reflect yellow light. The second element will be a polarization sensitive material such as plastic, ceramic, metal, or glass. The DBR or other yellow reflective material may be deposited directly on the phosphor or on the polarizing filter element using techniques such as e-beam deposition, sputter deposition, or thermal evaporation. Alternatively, the DBR may be in the form of a plate-like element applied to the phosphor. The polarization sensitive element may be deposited on the phosphor or positioned, glued or attached to the back of the phosphor. Of course, there can be additional variations, modifications, and alternatives.
A third approach to overcome the challenge of reflecting the backward propagating blue and yellow emissions while allowing the forward blue emission to pass through is to utilize a filter system that combines yellow spectrally selective reflectors, such as DBRs, with a spatially based reflector for the blue light. Such a configuration would likely require two elements that could be combined into a single piece. The first element would be a yellow reflector, such as a DBR mirror pair or another single or multilayer film designed to reflect yellow light. The second element will consist of an element that reflects blue light and will be applied to the back of the phosphor in a selective manner such that it is not present where the laser beam is incident on the phosphor, but is present on areas where the laser beam is not incident. The second element can be another DBR coating stack or a broadband reflector material such as Ag or Al. Both the first element, such as the DBR and other yellow reflective materials, and the second element, which spatially reflects blue light, can be deposited directly on the phosphor or on the polarizing filter element using techniques such as e-beam deposition, sputter deposition, or thermal evaporation. Alternatively, the DBR may be in the form of a plate-like element applied to the phosphor. The polarization sensitive element may be deposited on the phosphor or positioned, glued or attached to the back of the phosphor. Of course, there can be additional variations, modifications, and alternatives.
In other embodiments, a coating or other material may be used to reduce the reflectivity of the front emitting surface of the phosphor. In yet another embodiment, a coating or additional element may be applied to reduce the reflectivity of the incident beam on the phosphor surface. In configurations using off-axis laser beam incidence angles, such measures to reduce the reflectivity of the laser beam on the phosphor may be critical.
In the present invention, the laser diode output beam must be configured to be incident on the phosphor material to excite the phosphor. The apparatus typically has free space with unguided laser beam features that transmit the emission of the laser beam from the laser device to the phosphor material. The spectral width, wavelength, size, shape, intensity, and polarization of the laser beam are configured to excite the phosphor material. In particular, in many applications it is desirable to have a circular laser excitation beam, so that the illuminated spot on the phosphor is also circular, and the resulting white light emission radiates from a circular area. Such a circular area is advantageous for forming a collimated or point source of light using conventional optics and reflectors commonly used for circular emission. In addition, the circular beam creates some symmetry in the phosphor so that there are no hot spots that could cause a change in phosphor conversion efficiency or even initiate a faulty mechanism in the phosphor.
This same concept can also be used to create other shapes such as elliptical, conical, rectangular, or other shapes for applications requiring a non-circular beam. In automotive headlamps, for example, it is desirable to customize the spatial pattern to produce illumination in a desired area and to produce a deeper spot in the beam pattern to avoid glare to other oncoming drivers.
The inherent divergence characteristics of the output beam from a typical edge-emitting diode laser result in a beam that spreads in the x-direction (slow divergence axis) and the y-direction (fast divergence axis) as the beam propagates in free/unguided space. A complicating problem is the different divergence rates of the beams in the fast and slow axes that result from the waveguide confinement features in the laser diode. For example, a typical Full Width Half Maximum (FWHM) beam divergence angle ranges from about 5-20 degrees in the slow axis to 10 to 40 degrees in the fast axis, but may be others. Another measure of divergence of the laser beam is that the power has been reduced to 1/e 2 The divergence angle adopted by the spots in the horizontal output beam. For this 1/e 2 By way of example, typical beam divergence angles range from 10-30 degrees in the slow axis to 20 to 80 degrees in the fast axis, but may be other. Thus, the ratio of fast axis to slow axis divergence angle ranges from about 2. The resulting spot projected from the free-space/unguided laser beam is elliptical in shape, usually with a fast axis diameter larger than the slow axis diameter. FIG. 14 shows a schematic diagram illustrating one example of an elliptical output beam from a laser diode having θ 1 Fast axis divergence angle, D 1 Diameter of fast axis spot, theta 2 Slow axis divergence angle of, and D 2 Diameter of the slow axis spot.
Fig. 15 schematically illustrates a simplified example of a geometry that can be used to calculate the beam diameter in either the fast or slow axis, with the laser diode at a distance L from the plane. In order to calculate the numerical value of the spot diameters D1 and D2, the laser diode aperture size, and the distance of the flat projection surface from the laser aperture must be known. FIG. 16 shows the fast axis spot diameter D 1 Diameter of slow axis spot D 2 And a plot of the ratio of the fast axis to the slow axis diameter for varying distances L from the laser aperture. The example calculation of FIG. 16 assumes 1/e of 40 degrees 2 Fast axis divergence angle, 1/e of 20 degrees 2 Slow axis divergence angle, aperture width of 25 μm, and aperture height of 1 μm. As seen in the figure for this example, for a projection surface (i.e., phosphor) greater than 100 μm away from the laser aperture, the beam rapidly becomes elliptical with a fast axis diameter approximately 2 times larger than the slow axis diameter. At a distance of about 70 μm away from the aperture, the fast axis diameter and the slow axis diameter are nearly equal, about 50 μm. Therefore, to achieve the most circular spot with this laser diode configuration, the phosphor should be placed approximately 70 μm in front of the laser diode, where the spot diameter would be 50 μm. While it would be advantageous to have a circular beam without using additional optics to collimate and shape, such a design may not be the most practical implementation because the phosphor is located near the laser, which may create assembly and manufacturing challenges. Moreover, very small beam diameters with very high powers of more than 1W or more than 4W can cause problems in the phosphor if the phosphor quality and/or heat dissipation cannot withstand high power densities. However, as the phosphor is moved further from the aperture, the beam quickly becomes elliptical, which in many applications will not be as ideal as a circular spot.
In one embodiment of the present invention, collimating optics are positioned between the laser diode and the phosphor to collimate and shape the output laser beam. By placing free space optics in front of the output laser beam, the beam shape can be shaped to provide a circular beam profile and collimated so that the phosphor can be located some distance in front of the face with larger tolerances and maintain a relatively constant spot size. In one example, an aspheric lens is used to collimate and/or shape the laser beam. In an alternative embodiment, the laser beam is collimated using Fast Axis Collimation (FAC) and/or Slow Axis Collimation (SAC) lenses. In alternative embodiments, various combinations of other optics may be included to shape, collimate, direct, filter, or manipulate the beam. Examples of such optics include, but are not limited to, re-imaging reflectors, ball lenses, aspheric collimators, dichroic mirrors, turning mirrors, optical isolators, but may be others.
Fig. 17 shows a schematic diagram illustrating a transmissive phosphor embodiment of a CPoS integrated white light source including free-space optics to collimate and shape a laser beam for incidence on a phosphor in accordance with the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Of course, conventional implementations of chips on a substrate such as those shown in fig. 4 and 11 may be used for this integrated free-space optical implementation. The laser-based CPoS white light source is composed of a substrate material 1301 that serves as a common support member configured to serve as an intermediate material between the laser diode chips 1302 formed on the transmitting gallium-nitrogen containing epitaxial layer and the final mounting surface, and as an intermediate material between the phosphor plate material 1305 and the final mounting surface. The laser diode 1302 and/or the substrate 1301 are configured with electrodes 1303 and 1304, the electrodes 1303 and 1304 can be formed from a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, titanium, or others. The laser beam output is coupled to an aspheric lens 1305 for collimation and beam shaping to produce a more circular beam, which then excites a phosphor plate 1306 located in front of the aspheric lens 1305. Phosphor plate 1306 is attached to the substrate on mesa 1307 or recessed area. The electrodes 1303 and 1304 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire (not shown) may be formed on the electrode to couple electric power to the laser diode device to generate a laser beam output from the laser diode. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
In an alternative preferred embodimentBeam shaping can be achieved by tilting the phosphor excitation surface relative to the laser diode aperture and positioning the laser diode at a designed distance from the phosphor to take advantage of the beam divergence characteristics of the laser diode and achieve the desired spot size. This "optics-free" beam shaping embodiment is advantageous over embodiments that incorporate optical elements for beam shaping and collimation. These advantages of this embodiment for a white light source device include a simplified design, a lower cost bill of materials, a lower cost assembly process, and a white light source that may be more compact. In one embodiment, the angle of incidence from the laser to the phosphor is optimized to achieve the desired beam shape on the phosphor. As discussed for the example of fig. 16, by positioning the phosphor approximately 70 μm away from the laser aperture, a relatively uniform beam with a diameter of approximately 50 μm can be achieved. In addition to controlling the distance of the laser from the phosphor, the angle of incidence of the laser beam can also be used to control the shape of the beam incident on the phosphor. As an example, fig. 18 shows the effect on the spot size when the phosphor or projection surface is tilted with respect to the fast axis. By tilting along this axis, a larger fast axis diameter D is produced on the phosphor 1 So that the beam spot becomes more elliptical. According to the same principle, as illustrated in FIG. 19, when the phosphor or the projection surface is rotated around the slow axis, the slow axis diameter D can be increased 2 So that the spot diameter ratio becomes closer to 1 and the beam becomes more circular.
Fig. 20 schematically illustrates a simplified example of a geometry that may be used to calculate the beam diameter (r 1+ r 2) in the fast or slow axis, the laser diode being a distance L away from the tilted phosphor or projection surface, which is tilted from the fast or slow axis by an angle ω. By implementing this geometry, the optimal order and optimal phosphor tilt angle can be determined for relatively circular beam shapes. For example, FIG. 21 shows the fast axis spot diameter D 1 Slow axis spot diameter D 2 And a plot of the ratio of fast axis spot diameter to slow axis spot diameter for varying distance L from the laser aperture, assuming a phosphor tilt angle of 33 degrees with respect to the slow axis. The example calculation of FIG. 21 assumes 1/e of 40 degrees 2 Fast axis divergence angle, 1/e of 20 degrees 2 Slow axis divergence angle, aperture width of 25 μm, and aperture height of 1 μm. As seen in the figures for this example, for a projection surface such as a phosphor, a beam ratio of 1 occurs at a distance L of about 600 μm isolating the laser aperture and the phosphor, where the beam diameter D is 1 And D 2 Is about 500 μm. This configuration is optimized to maintain a beam ratio of 1 and corresponding spot size even over a large range of L.
Fig. 22 shows a schematic diagram illustrating a transmissive phosphor embodiment of a CPoS integrated white light source including a tilted phosphor design to achieve a more circular excitation spot on the laser in accordance with the present invention. In this embodiment, a conventional baseplate containing a complete laser diode chip is mounted on the substrate. The laser-based CPoS white light source is comprised of a substrate material 2201 that serves as a common support member configured to serve as an intermediate material between the laser diode chip 2202 and the final mounting surface and as an intermediate material between the phosphor material 2206 and the final mounting surface. The laser diode or CoS is configured with electrodes 2203 and 2204, which can be formed by a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, etc. Wire bond 2205 is configured to couple electrical power from electrodes 2203 and 2204. The phosphor plate 2206 is tilted around the slow axis of the laser diode output to result in a more circular excitation spot on the phosphor. For example, according to the calculations in FIG. 20, phosphor plate 2206 may be positioned at an angle of approximately 33 degrees. Phosphor plate 2206 is attached to a substrate on mesa 2207 or recessed area. The electrodes 2203 and 2204 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire (not shown) may be formed on the electrode to couple electric power to the laser diode device to generate a laser beam output from the laser diode. Of course, this is merely an example of a configuration, and many variations are possible on this embodiment, including but not limited to different shaped phosphors, different phosphor angles or orientations, different geometric designs of the submount or common support member, different directional output beams of the laser in relation to the phosphors, different electrodes and electrical designs, and the like.
Fig. 23 shows a schematic diagram illustrating a transmissive phosphor embodiment of a CPoS integrated white light source including a tilted phosphor design to achieve a more rounded excitation spot on the laser in accordance with the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Of course, conventional implementations of chips on a substrate such as shown in fig. 4 and 11 can be used for this tilted phosphor implementation. The laser-based CPoS white light source is composed of a substrate material 2301 that serves as a common support member configured to serve as an intermediate material between the laser diode chips 2302 formed on the transmitting gallium-nitrogen containing epitaxial layer and the final mounting surface, and as an intermediate material between the phosphor plate material 2305 and the final mounting surface. The laser diode or CoS is configured with electrodes 2303 and 2304, which may be formed by a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, etc. The phosphor plate 2305 is tilted around the slow axis of the laser diode output to produce a more circular excitation spot on the phosphor. For example, according to the calculation in fig. 20, phosphor plate 2305 may be positioned at an angle of about 33 degrees. Phosphor plate 2305 is attached to a substrate on mesa 2307 or recessed area. The electrodes 2303 and 2304 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire (not shown) may be formed on the electrode to couple electric power to the laser diode device to generate a laser beam output from the laser diode. Of course, this is merely an example of a configuration, and many variations are possible on this embodiment, including but not limited to different shaped phosphors, different phosphor angles or orientations, different geometric designs of the submount or common support member, different directional output beams of the laser in relation to the phosphors, different electrodes and electrical designs, and the like.
In an alternative embodiment of the present invention, the plurality of phosphors is operated in a transmissive mode for emitting white light. In one example, a violet laser diode is configured to emit a wavelength of 395nm to 425nm and excite a first blue phosphor and a second yellow phosphor. In this configuration, the first blue phosphor plate may be fused or bonded to the second yellow phosphor plate. In a practical configuration, the laser beam will be directly incident on the first blue phosphor, where a portion of the blue light will excite the second yellow phosphor to emit yellow light to combine with the blue light and produce white light. Furthermore, the violet pump will be substantially fully absorbed, since the possibly non-absorbed substances in the blue phosphor will subsequently be absorbed by the yellow phosphor. In an alternative practical configuration, the laser beam will be directly incident on the second yellow phosphor, where a portion of the violet electromagnetic emission will be absorbed by the yellow phosphor to excite yellow light, while the remaining violet light will pass to the blue phosphor and produce blue light, to combine the yellow light with the blue light and produce white light.
In an alternative embodiment of the multi-phosphor transmission example according to the present invention, a blue laser diode operating at a wavelength of 425nm to 480nm is configured to excite the first green phosphor and the second red phosphor. In this configuration, the first green phosphor plate may be fused or bonded to the second red phosphor plate. In a practical configuration, the laser beam will be directly incident on the first green phosphor, where a portion of the green light will excite the second red phosphor to emit red light to combine with the green phosphor emission and the blue laser diode emission to produce white light. In an alternative practical configuration, the laser beam would be directly incident on the second red phosphor, where a portion of the blue electromagnetic emission would be absorbed in the red phosphor to excite the red emission, while a portion of the remaining blue laser emission would pass to the green phosphor and generate green light, combining with the red phosphor emission and the blue laser diode emission to generate white light. A benefit or feature of this embodiment is a higher color quality that can be achieved from white light consisting of red, green, and blue light emissions. Of course, other variations of the present invention are possible, including the integration of more than two phosphors, and may include one or a combination of red, green, blue and yellow phosphors.
In yet another variation of the side-pumped phosphor configuration, a "point source" or "point source-like" CPoS white light emitting device is implemented. In this configuration, the phosphor will have a three-dimensional geometry, such as a cubic geometry or a spherical geometry, such that white light can be emitted from multiple primary emission surfaces, ideally from the entire surface area of the three-dimensional phosphor geometry. For example, in a cube geometry, all six faces of the cube may emit white light, or in a sphere configuration, the entire surface may emit to create a perfect point source. In some practical implementations of the present invention, some surfaces of the three-dimensional phosphor geometry may not freely emit light due to obstructions or obstructions. For example, in some configurations of this embodiment, the phosphors are attached to a common support member, where the common support member may not be completely transparent. In this configuration, the mounting surface or support member will block phosphor emission from the side or portion facing the mounting surface or support member. This obstruction can reduce the overall efficiency or quality of the point source white light emitter. However, such barriers to light emission can be minimized or mitigated using various techniques to provide a very efficient point source of light. In one configuration, the phosphor is supported by an optically transparent member such that light is freely emitted in all directions from the phosphor point light source. In one variation, the phosphor is completely surrounded or encapsulated by an optically transparent material, including a solid material such as SiC, sapphire, diamond, gaN, or other solid material, or a liquid material like water or a more thermally conductive liquid.
Fig. 24 shows a schematic diagram illustrating a point source laser pumped phosphor embodiment of a CPoS integrated white light source including a phosphor with a three-dimensional geometric design to provide a point source in accordance with the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Of course, conventional implementations of chips on a substrate such as shown in fig. 4 and 11 can be used for this point source phosphor implementation. The laser-based CPoS white light source is comprised of a substrate material 2401 that serves as a common support member configured to serve as an intermediate material between the laser diode chip 2402 formed on the transmitting gallium-nitrogen containing epitaxial layer and the final mounting surface and as an intermediate material between the phosphor plate material 2405 and the final mounting surface. The laser diode or CoS is configured with electrodes 2403 and 2404, which may be formed from a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, etc. The three-dimensional phosphor member 2405 is configured in front of the laser diode such that the output laser beam 2406 is incident on the excitation side of the phosphor, and a plurality of sides of the phosphor member 2405 are configured to emit white light. Almost all sides of the phosphor member 2405 may emit light, but in some embodiments, such as the embodiment shown in fig. 24, emission may be blocked from the mounting surface of the substrate on which the phosphor member 2405 is attached to the mesa 2407 or recessed region. Electrodes 2403 and 2404 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires (not shown) may be formed on the electrodes to couple electrical power to the laser diode device to generate a laser beam 306 output from the laser diode. Of course, this is merely an example of a configuration, and many variations are possible on this embodiment, including but not limited to different shaped phosphors (e.g., spherical or hemispherical), different phosphor angles or orientations, different geometric designs of the submount or common support member, different directional output beams of the laser in relation to the phosphor, different electrodes and electrical designs, and so forth.
In some embodiments according to the present invention, the periodic 2D photonic crystal structure may be applied to a single crystal or polycrystalline phosphor material structure. Such a structure would serve to suppress emission in a given direction and redirect light away from the crystal in a direction appropriate and selected for device design. Today's phosphor structures are primarily lambertian emitters, except where the waveguide and critical angle play a role. Today, many phosphors meet the basic material requirements needed to create photonic crystal structures (dielectric or metal dielectric materials with low light absorption). Adding a photonic crystal structure to the phosphor plate material will enable enhanced light extraction in one direction over the other in these materials. This can separate excitation and emission characteristics, allowing greater design flexibility.
In yet another variation of the side pumped phosphor embodiment, the phosphor is excited from the side and is configured to emit mostly white light from the top surface. In this configuration, the phosphor is likely to have a cubic geometry, a cylindrical geometry, a polyhedral geometry, a hexagonal geometry, a triangular geometry, a pyramidal geometry, or other polygonal geometry, wherein the white light is configured to emit primarily from the top surface of the phosphor. In this configuration, the laser beam will enter the phosphor from a first side of the phosphor where a portion of the laser excitation light with the first wavelength will be converted to a second wavelength. This first side of the phosphor may be configured for changing the reflectivity, e.g. coated or treated, to decrease the reflectivity in the blue or violet wavelength range and to increase the reflectivity in the phosphor emission wavelength range (e.g. yellow). In one example of a side pumped embodiment, the laser excitation beam is incident on the first side of the phosphor at a brewster angle. The additional sides of the phosphor may be coated, treated or shaped to increase the reflectivity to the laser excitation wavelength and the phosphor conversion wavelength so that light within the phosphor can reflect inside the phosphor until it escapes from the phosphor through the top. Special phosphor shaping or coating techniques may be used to increase the proportion of light that escapes from the top surface. A first powerful advantage of this configuration is that the white light spot size is controlled by the phosphor size, which can achieve a smaller spot size than alternative transmissive or reflective mode configurations by avoiding the spot size growth that occurs in the phosphor due to scattering, reflection, and lack of efficient absorption by the phosphor. Ultra-small spot sizes are desirable for most effective collimation in directional applications. A second advantage of this configuration is that the ideal heat dissipation configuration can be thermally and mechanically attached to the heat sink, wherein for the phosphor member it is the same as the reflective mode configuration with the entire bottom surface of the phosphor. Furthermore, since the laser diode assembly does not require thick or angled intermediate support members to elevate the beam and control the angular incidence as in the reflective mode configuration, the laser can be mounted closer to the base assembly to achieve a shorter heat conduction path to the heat sink. A third advantage is the inherent safety design, since the primary emission may come from the top surface of the phosphor orthogonal to the laser beam direction, so that in case of phosphor cracking or damage, the laser beam will not be directed in the direction of white light capture. In this configuration, if the phosphor is to be removed or destroyed, the laser beam will be incident on the side of the package. Furthermore, such a configuration would avoid potential problems in a reflective configuration where an escaping beam could result from reflection of an incident beam at the top of the surface. In such a side-pumped configuration, the reflected beam will be substantially contained in the package. A fourth advantage is that since the laser diode or the SLED device can be mounted flat on the base member, the assembly process and components can be simplified. In this side-pumped configuration, it may be advantageous to promote primary emission from the top surface of the phosphor. This can be achieved by treatments that promote light escape from the top surface, such as applying an anti-reflection coating or roughening, and by treatments that reduce light escape from the side and bottom surfaces, such as applying a highly reflective layer, such as a metal or dielectric layer.
Fig. 24A shows a schematic diagram illustrating a side pumped phosphor in an embodiment of an integrated laser-phosphor white light source according to the present invention comprising a phosphor with a three-dimensional geometric design to provide a point source of light. The laser-based white light source is composed of a substrate material 2501 that serves as a common support member configured to serve as an intermediate material between the laser diode chip 2502 and the final mounting surface and as an intermediate material between the phosphor material 2506 and the final mounting surface. The substrate 2501 is configured with electrodes 2503 and 2504, which may be formed with a deposited metal layer, such as Au. In one example, ti/Pt/Au is used for the electrodes. In this example, the laser diode chip is mounted p-side down, with wire bond 2505 configured from the n-side of the chip to the substrate. The electrical power supplied to the electrodes 2503 and 2504 on the substrate supplies current to the laser diode chip to generate a laser beam 2508 output from the laser diode. The laser beam output excites a phosphor 2506 located in front of the output face of the laser. The phosphor 2506 is attached to the substrate 2501 on the mesa 2507A or recessed region. The electrodes 2503 and 2504 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device to generate a laser beam output from the laser diode 308. The emission beam 2508 is configured to excite the phosphor 2506 on the side surfaces, wherein at least white light or wavelength converted light 2509 is emitted from the top surface of the phosphor 2506. In this embodiment, the top surface of phosphor 2506 is configured to reduce reflectivity to facilitate light emission, which may be configured by optical coating, roughening, or another process. The sides of the phosphor 2506 may also be configured to aid in light emission, but may preferably be coated or treated to reflect or contain light in the phosphor to promote top surface emission. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors (e.g., cubic, triangular, or other polygonal geometries), different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
Fig. 24B shows a schematic diagram illustrating a side pumped phosphor in an alternative embodiment of an integrated laser-phosphor white light source according to the present invention, comprising a phosphor with a three-dimensional geometric design to provide a point source of light. The laser-based white light source is comprised of a substrate material 2501 that serves as a common support member, e.g., surface of a package member, configured to serve as an intermediate material between the laser diode chip 2502 and the final mounting surface. The substrate 2501 is configured with electrodes 2503 and 2504, which may be formed with a deposited metal layer, such as Au. In one example, ti/Pt/Au is used for the electrodes. In this example, a laser diode chip 2502 is mounted in a p-side down manner, and a bonding wire 2505 is arranged from an n-side of the chip 2502 to a substrate 2501. Supply current to electrodes 2503 and 2504 on the substrate is routed to laser diode 2502, which generates laser beam 2508 output from laser diode 2502. The laser beam 2508 excites a phosphor 2506 located in front of the output laser face and mounted on the substrate 2501 or support member 2507B. The support member 2507B acts as an intermediate material between the laser diode 2502 and the final mounting surface, such as a package member surface. Electrodes 2503 and 2504 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire 2505 may be formed on the electrode to couple electric power to the laser diode device to generate a laser beam output from the laser diode 2502. The emission beam 2508 is configured to excite the phosphor 2506 on the side surfaces, wherein at least white light or wavelength converted light 2509 is emitted from the top surface of the phosphor 2506. In a preferred embodiment, the top surface is configured to reduce reflectivity to facilitate light emission, which may be configured by optical coating, roughening, or another process. In a preferred embodiment, the sides of phosphor 2506 can be configured to contain light and promote primary emission from the top surface. In alternative embodiments, the phosphor may also be configured to contribute to luminescence, but may preferably be coated or treated to reflect or contain light in the phosphor to promote top surface emission. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors (e.g., cubic, triangular, or other polygonal geometries), different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
In other variations, the support member may be used to manipulate light in an integrated white light source. In one example, the optically transparent support member may serve as a waveguide for the laser light to reach the phosphor. In another example, the optically transparent support member may be configured to transmit laser light to the phosphor member. In other examples where the support member of this variation manipulates light, the support member may be shaped or configured to form a reflector, mirror, diffuser, lens, absorber, or other member that manipulates light. In another variation, the support member may also serve as a protective safety measure to ensure that the directly emitted laser light is not exposed as it travels to reach the phosphor. Point sources capable of producing true omnidirectional emission are increasingly useful as point sources become smaller due to the fact that the production of emission aperture and emission angle is preserved or lost with the addition of subsequent optics and reflectors. In particular, for example, a small optic or reflector may be used to collimate the small point light source. However, if the same small optics and/or reflector assembly is applied to a large point source, optical control and collimation can be diminished.
In another particularly preferred embodiment of the CPoS white light source, the present invention is configured for reflective mode phosphor operation. In one example, the excitation laser beam enters the phosphor through the same major surface as the emission of useful white light. That is, when operating in a reflective mode, the phosphor may have a first major surface configured to receive an incident excitation laser beam and emit useful white light. In this configuration, the phosphor is located in front of the laser face that outputs the laser beam, wherein both the laser and the phosphor are disposed on the support member. The gallium-nitrogen containing laser diode is configured with a cavity having a length greater than 100 μm, greater than 500 μm, greater than 1000 μm, or greater than 1500 μm and a width greater than 1 μm, greater than 10 μm, greater than 20 μm, greater than 30 μm, or greater than 45 μm. The cavity is configured with a front side and a back side at the end, wherein the front side comprises an output side and emits a laser beam incident on the phosphor. The front face may be provided with an anti-reflection coating to reduce reflectivity or be completely uncoated to allow radiation to pass through the mirror without excessive reflectivity. In some cases, the coating may be configured to slightly increase the reflectivity. Since no laser beam will be emitted from the rear end of the cavity member, the back surface or mirror is configured to reflect radiation back into the cavity. For example, the back side includes a highly reflective coating having a reflectivity greater than 85% or 95%. In one example, the phosphor may be composed of Ce-doped YAG and emit yellow light. The phosphor may be a ceramic phosphor, and may be a single crystal phosphor. The phosphor is preferably formed as a generally planar member such as a plate, sheet, or the like having a square, rectangular, polygonal, circular, oval, or the like shape, and is characterized by a thickness. In a preferred embodiment, the length, width and/or diameter dimensions of the large surface area of the phosphor are greater than the thickness of the phosphor. For example, the diameter, length, and/or width dimensions may be 2 times greater than the thickness, 5 times greater than the thickness, 10 times greater than the thickness, or 50 times greater than the thickness. In particular, the phosphor plate may be configured as a circle having a diameter greater than 50 μm, greater than 100 μm, greater than 200 μm, greater than 500 μm, greater than 1mm, or greater than 10mm, and a thickness less than 500 μm, less than 200 μm, less than 100 μm, or less than 50 μm. A key benefit of the reflective mode phosphor is that it can be configured to have very good heat dissipation properties, since the back of the surface of the phosphor can be directly heat spreaded to the common support member or intermediate substrate member. Since the phosphor is preferably thin, the thermal path is short and can travel quickly to the support member. In an alternative or identical embodiment, the YAG: CE can be configured to emit green light emission. In yet another alternative or identical embodiment, YAG may be doped with Eu to emit red light emission. In alternative embodiments, silicon nitride or aluminum oxynitride may be used as the crystalline host material for red, green, yellow, or blue light emission.
In one example of an embodiment of the present invention reflective mode CPoS white light source, optical coatings, material selection, or special design considerations are required to improve efficiency by maximizing the amount of light leaving the major surface of the phosphor. In one example, the back surface of the phosphor may be coated with a reflective layer or have a reflective material located on the back surface of the phosphor adjacent to the primary emission surface. The reflective layer, coating or material helps to reflect light that strikes the rear surface of the phosphor so that it is reflected and exits through the major surface, thereby capturing useful light therein. In one example, the coating is configured to increase the reflectivity for yellow and blue light and is applied to the phosphor prior to attaching the phosphor to the common support member. Such a coating may consist of a metal layer, such as silver or aluminum, or others, such as gold, which will provide good thermal conductivity and good reflectivity, or may consist of a dielectric layer configured as a single layer, multiple layers, or DBR group, but may be others. In another example, the reflective material serves as a bonding medium for attaching the phosphor to the support member or the intermediate substrate member. Examples of reflective materials include reflective solders such as AuSn, snAgC (SAC), or lead-containing phosphors, or reflective glues, but may be others. Thermal impedance is a critical consideration with respect to connecting the phosphors to the common support member. The best joining materials, interface geometry, and joining process practices should be used to minimize the thermal resistance of the attachment joint to achieve the lowest thermal resistance with sufficient reflectivity. Examples include AuSn solder, SAC solder, leaded solder, indium, and other solders. In one alternative, a sintered silver paste or film may be used for the attachment treatment at the interface. Sintered silver attachment material can be dispensed or deposited using standard processing equipment and cycling temperatures with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The joint may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), thermal adhesive, and other materials. Alternatively, the joint may be formed by a metal-metal bond (e.g., au-Au bond). The common support member with the laser and phosphor materials is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt to characterize a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, aluminum, siC, sapphire, alN or other metal, ceramic or semiconductor. A reflective mode white light source device has a form factor characterized by a length, a width, and a height. In one example, the height is characterized by a dimension that is less than 25mm and greater than 0.5mm, although variations may exist. In one example, the height is characterized by a dimension that is less than 12.5mm and greater than 0.5mm, although variations may exist. In yet another alternative example, the length and width are characterized by dimensions of less than 30mm, less than 15mm, or less than 5mm, although variations may exist.
The reflective mode CPoS white light source embodiments of the present invention are configured with a phosphor member attached to a common support member, with a larger major surface configured to receive laser excitation light and emit useful white light at an orthogonal angle (about 90 degrees) or a non-perpendicular angle (about 0 degrees to about 89 degrees) to the axis of the laser diode output beam used to excite the phosphor. That is, the output laser beam is directed at the emitting surface of the phosphor at an angle between 0 degrees and 90 degrees, where 90 degrees (orthogonal) is considered normal incidence. The inherent geometry of this configuration (where the useful white light would leave the phosphor toward the outside world or direct the laser beam away in the opposite direction) is ideal for safety. As a result of this geometry, if the phosphor is damaged or removed during operation or upon intervention, the laser beam will not be directed to the outside world where it would be harmful. Instead, the laser beam will be incident on the surface of the backing to which the phosphor is attached. By properly designing this back surface, the laser beam can be dispersed, absorbed, or moved away from the outside world, rather than away from the white light source and into the surrounding environment.
In one embodiment of this reflective mode CPoS white light source, the laser beam is arranged orthogonal to the phosphor primary emission surface. In this configuration, the laser diode would be in front of the primary emission surface of the phosphor where it would block the useful white light emitted from the phosphor. This can result in loss or inefficiency of the white light device and can result in difficulty in efficiently capturing all of the white light emitted from the phosphor. Such optics and reflectors include, but are not limited to, aspheric lenses or parabolic reflectors. To overcome the challenges of normal incidence reflective mode phosphor excitation, in a preferred embodiment, the laser beam may be configured with an incident angle off-axis from the phosphor such that it strikes the phosphor surface at an angle between 0 and 89 degrees, or a "glancing" angle. In this preferred embodiment, the laser diode device is located near or laterally adjacent to the phosphor, rather than in front of the phosphor, where it will not substantially block or obstruct the emitted white light, and importantly, allow optics such as collimating lenses or reflectors to access the useful light and project it into the application. Furthermore, in this configuration, the built-in security features are more optimized than the normal incidence configuration because the incident laser beam is not directly reflected from the back surface of the support member in which the phosphor is affixed when incident at an angle with the phosphor damaged or removed. By striking the surface at a declination or glancing angle, any potentially reflected component of the light beam can be directed to remain within the device without leaving the external environment where it can pose a hazard to humans, animals and the environment.
In some configurations, the major top surface of the phosphor into which the laser excitation beam is incident is configured to reduce the reflectivity to blue or violet excitation beam wavelengths and/or phosphor emission wavelengths such as yellow wavelengths. This reduced reflectivity may be achieved by optical coating of the phosphor with a dielectric layer, shaping of the phosphor surface, and/or roughening of the phosphor surface, or other techniques. In some examples, the laser beam incident angle is configured at or near the brewster angle, where light with a particular polarization is preferably transmitted through the major surface of the phosphor. Very good transmission can be challenging due to the divergence of the laser light resulting in a change in the angle of incidence of the plane wave within the beam, but ideally, most of the light incident on the phosphor will be at or near brewster's angle. For example, a YAG or LuAG phosphor may have a refractive index of about 1.8 in the violet and blue wavelength ranges. With respect to Brewster's angle, as arctan (n) 2 /n 1 ) Given by theta B (wherein, n 1 Is the refractive index of air, n 2 Is the refractive index of the phosphor) will be about 61 degrees (or about 55 to 65 degrees) off-axis from normal incidence. Or alternatively, about 29 degrees (or about 25 to 35 degrees) from an axis parallel to the phosphor surface.
Fig. 25 shows a schematic diagram illustrating an off-axis reflection mode implementation of a CPoS integrated white light source according to the present invention. In this embodiment, gallium-containing nitrogen stripping and transfer techniques are utilized to fabricate very small and compact substratesA component in which the laser diode chip is formed from a transferred epitaxial layer. Further, in this example, the phosphor is made at an angle ω relative to the fast axis of the laser beam 1 And (4) inclining. The laser-based CPoS white light source is comprised of a common support member 2511, the common support member 2511 serving as a common support member configured to serve as an intermediate material between a laser diode chip or laser diode CoS 2512 formed on a transmitting gallium-nitrogen containing epitaxial layer 2513 and a final mounting surface and as an intermediate material between a phosphor plate material 2516 and the final mounting surface. The laser diode or CoS 2512 is configured with electrodes 2514 and 2515, which may be formed from a combination of a deposited metal layer and a metal layer including, but not limited to, au, pd, pt, ni, al, ti, and the like. Laser beam 2517 excites phosphor plate 2516 located in front of the laser output face. Phosphor plate 2516 is attached to a common support member on plane 2518. The electrodes 2514 and 2515 are configured for electrical connection to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device 2512 to generate a laser beam 2517 that is output from the laser diode and incident on the phosphor 2516. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
Fig. 25A shows a schematic diagram illustrating an off-axis reflection mode embodiment of an integrated laser-phosphor white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Further, in this example, the phosphor is tilted at an angle ω 1 relative to the fast axis of the laser beam. The laser-based white light device includes a support member 2511 that serves as a support member for a laser diode CoS 2512, the laser diode CoS 2512 being formed in a transferred gallium and nitrogen containing epitaxial layer 2513. The phosphor material 2516 is mounted on a separate support member 2518A, where the support members 2511 and 2518 are to be attached to a surface in a common support member (not shown), such as an encapsulating member (e.g., a surface mount package). The laser diode or CoS 2512 is configured with electrodes 2514 and 2515, which can be formed with deposited metal layers and combinations of metal layers including, but not limited to, au, pd, pt, ni, al, ag, ti, or other substances such as transparent conductive oxides, e.g., indium tin oxide. The laser beam 2517 excites a phosphor material 2516 located in front of the laser output face. The electrodes 2514 and 2515 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device 2512 to generate a laser beam 2517 that is output from the laser diode and incident on the phosphor 2516. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different geometric designs of the substrate or support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
The inherent divergence characteristics of the output beam from a typical edge-emitting diode laser result in a beam that spreads in the x-direction (slow divergence axis) and the y-direction (fast divergence axis) as the beam propagates in free/unguided space. A complicating problem is the different divergence rates of the beam in the fast and slow axes that result from the waveguide confinement features in the laser diode. For example, a typical Full Width Half Maximum (FWHM) beam divergence angle ranges from about 5-20 degrees in the slow axis to 10 to 40 degrees in the fast axis, but may be others. Another measure of divergence of the laser beam is that the power has been reduced to 1/e 2 The divergence angle adopted by the spots in the horizontal output beam. For this 1/e 2 By way of example, typical beam divergence angles range from 10-30 degrees in the slow axis to 20 to 80 degrees in the fast axis, but may be other. Thus, the ratio of the fast axis to slow axis divergence angle ranges from about 2 to about 4. The resulting spot projected from the free-space/unguided laser beam is elliptical in shape, usually with a fast axis diameter larger than the slow axis diameter. For a laser beam configured for off-axis incidence in the fast axis direction as shown in fig. 25, the elliptical nature of the beam will be exacerbated, Since the angle will increase the shaft diameter D 1 As shown in fig. 18.
In one embodiment of the present invention, the elliptical nature of the beam incident from beam divergence and off-axis laser beam excitation is mitigated using beam shaping optics (e.g., collimating optics). This optics will be located between the laser diode and the phosphor to shape and/or collimate the output laser beam before it is incident on the phosphor. By placing free space optics in front of the output laser beam, the beam shape can be shaped to provide a circular beam profile and collimated so that the phosphor can be located some distance in front of the face with larger tolerances and maintain a relatively constant spot size. In one example, an aspheric lens is used to collimate and/or shape the laser beam. In an alternative embodiment, the laser beam is collimated using Fast Axis Collimation (FAC) and/or Slow Axis Collimation (SAC) lenses. In an alternative embodiment, various combinations of other optics may be included to shape, collimate, direct, filter, or otherwise manipulate the beam. Examples of such optics include, but are not limited to, ball lenses, aspheric collimators, dichroic mirrors, turning mirrors, optical isolators, but may be others.
Fig. 26 shows a schematic diagram illustrating an off-axis reflection mode implementation of a CPoS integrated white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, with the laser diode chip formed from a transfer epitaxial layer. Further, in this example, the phosphor is made at an angle ω relative to the fast axis of the laser beam 1 And (4) inclining. The laser-based CPoS white light source is comprised of a common support member 2511, the common support member 2511 serving as a common support member configured to serve as an intermediate material between a laser diode chip or laser diode CoS 2512 formed on a transmitting gallium-nitrogen containing epitaxial layer 2513 and a final mounting surface and as an intermediate material between a phosphor plate material 2516 and the final mounting surface. The laser diode or CoS 2512 is configured with electrodes 2514 and 2515, which may be formed by depositing a metal layer and a metal layer including, but not limited to, au, pd, pt, ni, al, ti, etcAnd (4) combining and forming. Laser beam 2517A is passed through aspheric lens 2519 to shape and/or collimate the beam before it is incident on phosphor plate 2516. Phosphor plate 2516 is attached to a surface 2518 of a common support member. The electrodes 2514 and 2515 are configured for electrical connection to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device 2512 to generate a laser beam 2517A that is output from the laser diode and incident on the phosphor 2516. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
In an alternative preferred off-axis reflective mode embodiment, beam shaping may be achieved by rotating the laser beam relative to the tilted phosphor excitation surface. By rotating the laser about the beam emission axis, the phosphor tilt will move from increasing the fast axis beam diameter to increasing the slow axis beam diameter, thus compensating for the slow axis beam axis diameter diverging more slowly and resulting in a more circular beam. This two-axis tilt or swivel embodiment of "optics-free" beam shaping is advantageous over embodiments that incorporate optical elements for beam shaping and collimation. These advantages of this embodiment for a white light source device include a simplified design, a lower cost bill of materials, a lower cost assembly process, and a white light source that may be more compact. In one embodiment, the angle of incidence from the laser to the phosphor is optimized to achieve the desired beam shape on the phosphor.
In some configurations, the major top surface of the phosphor in which the laser excitation beam is incident is configured to reduce the reflectivity to blue or violet excitation beam wavelengths and/or phosphor emission wavelengths such as yellow wavelengths. This reduced reflectivity may be achieved by optical coating of the phosphor with a dielectric layer, shaping of the phosphor surface, and roughening of the phosphor surface, or other techniques. In some examples, the laser beam incident angle is configured as Brewster's angle or Close to the brewster angle, wherein light with a particular polarization is preferably transmitted through the main surface of the phosphor. Very good transmission can be challenging due to the divergence of the laser light resulting in a change in the angle of incidence of the plane wave within the beam, but ideally, most of the light incident on the phosphor will be at or near brewster's angle. For example, a YAG or LuAG phosphor may have a refractive index of about 1.8 in the violet and blue wavelength ranges. With respect to Brewster's angle, as arctan (n) 2 /n 1 ) Given by θ B (wherein, n 1 Is the refractive index of air, n 2 Is the refractive index of the phosphor) will be about 61 degrees (or about 55 to 65 degrees) off-axis from normal incidence. Or alternatively, about 29 degrees (or about 25 to 35 degrees) from an axis parallel to the phosphor surface.
As discussed for the example of fig. 16, by positioning the phosphor approximately 70um away from the laser aperture, a relatively uniform beam with a diameter of approximately 50um can be achieved. In addition to controlling the distance of the laser from the phosphor, the angle of incidence of the laser beam can also be used to control the shape of the beam incident on the phosphor. As an example, fig. 18 shows the effect on spot size when the phosphor or projection surface is tilted with respect to the fast axis. By tilting along this axis, a larger fast axis diameter D is produced on the phosphor 1 So that the beam spot becomes more elliptical. In accordance with the same principles, as illustrated in FIG. 19, the slow axis diameter D may be increased when the phosphor or projection surface is rotated about the slow axis 2 So that the spot diameter ratio becomes closer to 1 and the beam becomes more circular.
For a given phosphor tilt (ω) relative to the fast axis 1 ) The rotation (omega) of the laser beam spot can be optimized 2 ) To achieve a more circular beam shape on the phosphor. As an example, FIG. 27 shows the fast axis spot diameter D 1 Diameter of slow axis spot D 2 And a plot of the ratio of the fast axis spot diameter to the slow axis spot diameter for different distances L from the laser aperture, assuming a tilt angle of the phosphor relative to the fast axis (ω), the 1 ) Is 45 degrees and the laser rotates 22 degrees (ω) 2 ) To tilt the beam with respect to the slow axis. The example calculation of FIG. 27 assumes a 1/e of 40 degrees 2 Fast axis divergence angle, 1/e of 20 degrees 2 Slow axis divergence angle, aperture width of 25 μm, and aperture height of 1 μm. As seen in the graph for this example, for a projection surface such as a phosphor, the beam scale quickly approaches 1 at a distance L of about 200 μm and saturates at a distance L of about 800 μm. Thus, in this example, for distances L of 200 μm and greater (where a desired spot size with a diameter of 200 μm and greater may be achieved), a beam with a diameter ratio of about 1 may be achieved.
Fig. 28 shows a schematic diagram illustrating an off-axis reflection mode embodiment of a CPoS integrated white light source with laser rotation according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. In this example, the phosphor is tilted at an angle ω 1 with respect to the fast axis of the laser beam and the laser is rotated at an angle ω 1 with respect to the slow axis. The laser-based CPoS white light source is comprised of a common support member 2801, the common support member 2801 serving as a common support member configured to serve as an intermediate material between a laser diode chip or laser diode CoS 2802 formed on a transmitting gallium-nitrogen containing epitaxial layer 2803 and a final mounting surface, and as an intermediate material between a phosphor plate material 2806 and the final mounting surface. The laser diode or CoS is configured with electrodes 2804 and 2805, and the motor may be formed from a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, ti, and the like. The laser beam 2807 excites a phosphor plate 2806 located in front of the laser output face. Phosphor plates 2806 are attached to a common support member on surface 2808. Electrodes 2804 and 2805 are configured for electrical connection to an external power source, such as a laser driver, a current source, or a voltage source. A bonding wire may be formed on the electrode to couple electrical power to the laser diode device to generate a laser beam 2807 output from the laser diode 2802 and incident on the phosphor 2806. Of course, this is just one example of a configuration, and many variations of this embodiment are possible, including but not limited to different shaped phosphors, different geometric designs of the substrate or common support member, different orientations of the laser output beam relative to the phosphor, different electrode and electrical designs, and so forth.
In some embodiments according to the invention, the plurality of laser diode sources are configured to excite the same phosphor or phosphor network. According to the present invention, combining multiple laser light sources can provide many possible benefits. First, the excitation power can be increased by beam combination to provide stronger excitation pits and thus produce a brighter light source. In some embodiments, a single laser chip is configured within the laser-phosphor light source. By including a plurality of lasers each emitting 1W, 2W, 3W, 4W, 5W or more power, the excitation power can be increased, which will increase the light source brightness. For example, by including two 3W lasers exciting the same phosphor area, the excitation power can be increased to 6W to double the white light brightness. In the example of generating approximately 200 lumens of white light per 1 watt of laser excitation power, the white light output would increase from 600 lumens to 1200 lumens. For example, in some embodiments, a single laser diode operating at 3-4W output power may enable a white light source of at least 500 lumens. The light output can be increased to at least 1000 lumens of white light source by adding a second 3-4W laser diode, or to at least 2000 lumens by adding a second, third and fourth 3-4W laser diode. Similarly, the reliability of the source can be improved by using multiple sources under lower driving conditions to achieve the same excitation power as a single source driven under more severe conditions (e.g., higher current and voltage).
A second advantage of having two or more laser diode excitation beams incident on the phosphor to form a spot is that a more desirable spot geometry, e.g., a more circular spot, is obtained. In one example, separate individual laser chips or CoS devices are configured within the light source such that the beams are rotated relative to each other and the fast axis of the first beam is rotated to the fast axis of the second beam, e.g., by about 90 degrees. That is, by positioning multiple laser chips in a predetermined configuration, multiple excitation beams can be superimposed on the phosphor spot to produce a more ideal spot geometry.
A third important advantage is that the multiple color lasers in the emitting device can significantly improve the color quality (CRI and CQS) by improving the spectral fill in the violet/blue and cyan regions of the visible spectrum. For example, two or more blue excitation lasers with slightly detuned wavelengths (e.g., 5nm, 10nm, 15nm, etc.) may be included to excite the yellow phosphor and create a larger blue spectrum. The blue laser source may have only 1 or 2nm FWHM, as compared to a LED-based white light source with blue light emission of about 20-30nm FWHM. White light from lasers based on similar color targets lacks a CRI of about 5-10pts due to this narrower emission of a single laser. By adding a second, third, nth laser with a different emission wavelength than the first laser, these empty regions of the power spectrum can be filled and improved color quality can be obtained.
The choice of the wavelength of the emitter is determined by the desired final spectrum and the quality of the color to be achieved. Violet light, while not contributing to the visible color quality, has the ability to fluoresce materials in our surrounding world, making it slightly luminous relative to its environment under near ultraviolet stimulation. This additional color benefit can be simply incorporated into a laser plus phosphor device by adding a near ultraviolet (400-430 nm) laser to provide sufficient violet light in the final spectrum emitted by the device.
In addition to improving color quality, replacing spectral components with narrower spectral components can provide improved overall luminous efficiency of the power spectrum and higher power efficiency for the device. An example of this would be to replace the green or yellow phosphor with a larger FWHM (80-100 nm) with a suitable LED or laser device with a lower FWHM (LED-20 nm, laser-1 nm). A real world example of this improvement can be seen today in the use of AlInGaP red LEDs (20 nm FWHM) instead of red phosphor (90 nm FWHM). Due to the improved luminous efficiency, the overall device performance is much higher for the red LED based spectrum than the comparable red phosphor spectrum.
In several embodiments according to the present invention, the laser-based integrated white light source is configured as a high CRI white light source with a CRI of more than 70, more than 80 or more than 90. In these embodiments, phosphors in the form of a plurality of mixed powder phosphor compositions or a plurality of phosphor plate configurations or the like are used. Examples of such phosphors include, but are not limited to, YAG, luAG, red nitrides, aluminates, oxynitrides, caMgSi 2 O 6 :Eu 2+ 、BAM:Eu 2+ 、AlN:Eu 2+ 、(Sr,Ca) 3 MgSi 2 O 8 :Eu 2+ And JEM.
In some configurations of high CRI implementations of integrated laser based white light sources, a blue laser diode excitation source operating in the wavelength range of 430nm to 470nm is used to excite:
1) Yellow phosphor + red phosphor, or
2) Green phosphor + red phosphor, or
3) Cyan phosphor + orange phosphor, or
4) Cyan phosphor + orange phosphor + red phosphor, or
5) Cyan phosphor + yellow phosphor + red phosphor, or
6) Cyan phosphor + green phosphor + red phosphor.
In some alternative configurations of high CRI implementations of integrated laser based white light sources, a violet laser diode excitation source operating in the wavelength range of 390nm to 430nm is used to excite:
1) Blue phosphor + yellow phosphor + red phosphor, or
2) Blue phosphor + green phosphor + red phosphor, or
3) Blue phosphor + cyan phosphor + orange phosphor, or
4) Blue phosphor + cyan phosphor + orange phosphor + red phosphor, or
5) Blue phosphor + cyan phosphor + yellow phosphor + red phosphor, or
6) Blue phosphor + cyan phosphor + green phosphor + red phosphor.
Fig. 28A shows a schematic diagram illustrating an embodiment of an off-axis reflective mode phosphor and two laser diode devices of an integrated laser-phosphor white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Further, in this example, the phosphor is made at an angle ω relative to the fast axis of the laser beam 1 And (4) inclining. The laser-based white light source consists of two or more laser diodes comprising a support member 801, the support member 801 serving as a support member for two laser diodes 802 formed in the transferred gallium-nitrogen containing epitaxial layer 803. The phosphor material 806 is mounted on a support member 808, wherein the support members 801 and 808 are to be attached to a common support member, e.g. a surface in a package member, e.g. a surface mount package. The laser diode or CoS device 802 is configured with electrodes 804 and 805 that can be formed by depositing a metal layer and a combination of metal layers including, but not limited to, au, pd, pt, ni, al, ag, ti, or other substances such as transparent conductive oxides, e.g., indium tin oxide. The multiple laser beams 807 excite a phosphor material 806 located in front of the laser output face. In the preferred embodiment according to fig. 28A, the laser diode excitation beams 807 are rotated relative to each other such that the fast axis of the first beam is aligned with the slow axis of the second beam to form a more circular excitation spot. Electrodes 804 and 805 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on the electrodes to couple electrical power to the laser diode device to generate a plurality of laser beams 807 incident on the phosphor 806. Of course, this is only one example of a configuration, and many variations on this embodiment are possible, including but not limited to more than two laser diodes, e.g., three of four laser diodes, different shaped phosphors, different geometric designs of the substrate, support member, different orientations, strings of laser output beams relative to the phosphors, and the like Inline or parallel laser diode wiring, different electrodes and electrical designs, including individually addressable lasers, etc.
In another example of a multi-laser embodiment according to the present invention, two or more laser stripes are formed on a single laser chip or substrate to form a multi-stripe or multi-laser configuration. This example may provide all of the same benefits previously described for multiple individual lasers, but may improve spot geometry in a slightly different manner. By disposing the plurality of laser stripes adjacent to each other with a predetermined size spacing in the horizontal direction or the slow axis direction, the excitation spot generated on the phosphor from the laser beams emitted by the plurality of laser stripes may be substantially more circular than the elliptical excitation spot generated from a single emitter. That is, the laser beams from adjacent laser stripes will overlap in the horizontal direction according to the design, so that the excitation spot width in the slow axis direction will increase. Since in a typical configuration the laser excitation beam will be much larger in the vertical or fast axis divergence direction, by enlarging the spot in the horizontal direction, the beam will become more circular. In one embodiment of this configuration, the laser diode with a plurality of adjacent laser stripes, the multi-stripe laser is comprised in an integrated white light source. Multiple stripes may provide greater excitation power, supporting brighter light sources and/or improved or modified spot patterns on the phosphor.
Fig. 28B shows a schematic diagram illustrating an embodiment of an off-axis reflective mode phosphor and a dual stripe laser diode of an integrated laser-phosphor white light source according to the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, with the laser diode chip formed from a transfer epitaxial layer. Of course, other embodiments are possible, such as conventional laser diode devices or lasers on a substrate. Further, in this example, the phosphor is made at an angle ω relative to the fast axis of the laser beam 1 And (4) inclining. The laser-based white light source is composed of a support member 801, the support member 801 serving as a support member for the laser diode CoS 802 formed in the transferred gallium-nitrogen-containing epitaxial layer,the laser diode CoS 802 forms a multi-stripe or dual stripe 803 laser diode configuration. The phosphor material 806 is mounted on a support member 808, wherein the support members 801 and 808 are to be attached to a common support member, e.g. a surface in a package member, e.g. a surface mount package. The multi-stripe laser diode or CoS 802 is configured with electrodes 804 and 805 formed by depositing a metal layer and a combination of metal layers including, but not limited to, au, pd, pt, ni, al, ag, ti, or other transparent conductive oxides such as indium tin oxide. The dual stripe laser diode emits at least two laser beams spaced apart a predetermined distance in the lateral or slow axis direction, which serves to increase the width of the excitation spot and make it more circular. The dual beam output emission 807B excites the phosphor material 806 located in front of the laser output face. The electrodes 804 and 805 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires may be formed on a plurality of adjacent laser beams 807 output from the laser diodes and incident on the phosphor 806. Of course, this is only one example of a configuration, many variations of this embodiment may exist, including but not limited to more than two emitted light beams, e.g. 3 or more laser stripes for 3 or more emitted light beams, different shaped phosphors, different geometric designs of the substrate and common support member, different orientations of the laser output beams relative to the phosphors, individually addressable laser stripes to operate individually, different electrodes and electrical designs, etc.
Of course, the reflective mode embodiment configurations shown in fig. 25, 26 and 28 are merely examples, and a wide range of other arrangements, geometries and designs exist. In one specific example, in an alternative embodiment of this dual-rotation off-axis laser beam incidence configuration, the phosphor can be tilted with respect to the slow axis of the laser diode, rather than rotating the laser diode as shown in fig. 28. One benefit of this alternative embodiment would be the simplification of the common support member geometry, which can be easier to manufacture. However, a disadvantage of this alternative embodiment is that the phosphor will no longer be parallel to the horizontal base, which can create difficulties in collecting and collimating useful white light. In the examples of fig. 25, 26 and 28, the phosphor would be held in a horizontal orientation, with the laser rotated/tilted to achieve the desired laser incidence configuration. However, this is just one example, and the phosphor may be tilted with respect to the horizontal axis in other arrangements.
For the example in fig. 28 of the present invention where the laser diode is rotated about its emission axis, consider the polarization of the emitted laser beam. Because the phosphor and the laser are co-packaged together, the need for an environmental protection window over the phosphor is eliminated. This results in a high efficiency feature of the design because the reflective losses of the window are eliminated. In particular, by using a highly polarized laser diode with the polarization, most of the losses (i.e., > 30%) are eliminated, since this is the s-polarized incident light incident on the phosphor. By co-packaging, we avoid this window and avoid the > 30% loss. In designs where the laser and phosphor are not co-packaged, a window is required on the phosphor and the laser light that reaches the window will experience a large amount of reflection of about 30% or more. It is possible to apply an anti-reflection coating on this window, but this requires a reflective coating design that is expensive and complex, since the laser light is incident on the window at a variety of emission angles due to the possible non-collimation of the laser light.
In other variations, the support member may be used to manipulate light in an integrated white light source. In one example, an optically transparent support member may be used as a waveguide for the laser light to reach the phosphor. In another example, the optically transparent support member may be configured to transmit laser light to the phosphor member. In other examples where the support member of this variation manipulates light, the support member may be shaped or configured to form a reflector, mirror, diffuser, lens, absorber, or other member that manipulates light. In another variation, the support member may also serve as a protective safety measure to ensure that the directly emitted laser light is not exposed when it travels to reach the phosphor. Point sources capable of producing true omnidirectional emission are increasingly useful as point sources become smaller due to the fact that the product of emission aperture and emission angle (product) is preserved or lost with the addition of subsequent optics and reflectors. In particular, for example, a small optical device or reflector may be used to collimate a small point source of light. However, if the same small optic and/or reflector assembly is applied to a large point source, optical control and collimation can be impaired.
In all embodiments of the CPos white light source, the final package needs to be considered. There are many packaging aspects that should be considered, such as form factor, cost, functionality, thermal impedance, sealing characteristics, and basic compatibility with the application. The form factor will depend on the application, but it will generally be desirable to manufacture a packaged white light source of minimum size. Cost should be minimized in all applications, but in some applications cost will be the most important consideration. In such a case, it may be desirable to use off-the-shelf packaging in high volume production. Functional options include the guidance and characterization of the light emission that is currently used for this application, and the integration of features such as photodetectors, thermistors, or other electronic or optoelectronic components. For optimum performance and lifetime, the thermal impedance of the package should be minimized, particularly in high power applications.
The package is characterized by a sealing arrangement. One example of a sealed configuration includes an open environment that exposes the white light source to ambient conditions. This embodiment is advantageous in some embodiments with robust laser diode and phosphor designs intended for open environment operation. As one example, the laser diode chip may be encapsulated in a protective layer to prevent oxidation, chemical reactions, or contamination of the laser diode. In some embodiments, the laser is formed from a substantially aluminum-free non-polar or semi-polar design, wherein the laser diode facet regions are not susceptible to oxidation and degradation. Similarly, the phosphor may also be encapsulated in a protective layer to prevent oxidation, chemical reaction, or contamination of the phosphor.
In a preferred embodiment of the invention, the integrated white light source is characterized by an environmentally sealed package or a sealed package. For environmentally sealed configurations, the package housing may prevent dust and other particles from interacting with the laser or phosphor. For a sealed package, the package should be sealed and the leak rate is very small or non-existent. For sealed packages, it is often advantageous to backfill a combination of oxygen and nitrogen, such as Clean Dry Air (CDA), but other gases, such as nitrogen, are also possible. Typically for GaN-based lasers, hermetic packaging is required, but other packages are also contemplated and deployed for various applications. Examples of off-the-shelf packages for CPoS white light sources include TO cans, such as TO38, TO56, TO9, TO5, or TO46. Flat packages with windows may also be used. Examples of flat packages include butterfly packages, such as TOSAs. Surface Mount Device (SMD) packages may also be used, which are attractive due to their low cost, good hermetic seal, and potentially low thermal resistance. In other embodiments, custom packages may also be used.
In another embodiment, a "Flash" package may be used to integrate a white light source. For example, the package may be used to adapt a laser-based white light source to a camera flash application. One standard packaging format for LEDs today employs flat ceramic packages, sometimes referred to as "flash" packages, because the devices built on these platforms are used primarily for camera flashes and cell phone applications. A typical flash package includes a flat ceramic substrate (alumina or AlN) with connection pads for the LED and ESD devices, and leads that provide locations for clamping or soldering external electrical connections to power the device. The phosphor may be included near the LED die by molding or other silicone-containing dispensing applications. This layer is then overmolded, typically with a clear silicone lens, to improve light extraction. The main advantages of this format of package are the very small overall package size (-3 mm x-5 mm), reasonable light output performance (hundreds of lumens), small light source size and low overall cost of the LED device. This packaging style can also be achieved by using a laser plus phosphor design style, which may eliminate packaging and lens steps, providing an LED replacement with excellent spot size and brightness. If a protective cover is required to contain the laser and phosphor subassemblies, a hollow glass dome may be used to provide protection.
For example, the package is small and may include flat package ceramic multilayer or single layer. This layer may comprise copper, copper tungsten based, such as butterfly encapsulated or capped CT-MOUNT, Q-MOUNT or others. In one embodiment, the laser device is soldered on a CTE-matching material (e.g., alN, diamond compound) with low thermal resistance and forms a packaged chip on the ceramic. The package is then assembled on a second material with low thermal resistance, such as copper, including, for example, active cooling (i.e., simple water channels or micro-channels), or directly forming the base of the package equipped with all connections (such as pins). The flat package is equipped with an optical interface, such as a window, free-space optics, connectors or optical fibers to guide the light generated and an environmental cover.
Fig. 29 shows a schematic diagram of one example of encapsulating a CPoS white light source in accordance with the present invention. In this example, a transmissive mode white light source is configured in a TO can type package. The TO can has a base member 2901 with a standoff member 2902 protruding, where the standoff member is configured TO transfer heat from the standoff TO the substrate where it is then routed TO a heat sink. The base member may be composed of a metal, such as copper, copper tungsten, aluminum, or steel, among others. A transmissive white light source 2903 according to the invention is mounted on a support 2902. Mounting to the mount may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but could be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. Bonding wires 2904 and 2905 are used to form electrical connections from the p-electrode and n-electrode of the laser diode. Wire bonds connect the electrodes TO electrical feedthroughs 2906 and 2907, and electrical feedthroughs 2906 and 2907 are electrically connected TO external pins 2908 and 2909 on the back side of the TO can substrate. The pin is then electrically coupled to a power source to energize the white light source and produce a white light emission. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. Of course, the example in fig. 29 is only one example, and the purpose is to illustrate one possible simple configuration of a packaged CPoS white light source. In particular, since can type packages are popular with laser diodes and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
Fig. 30 is a schematic view of a CPoS white light source configured in a can-type package as shown in fig. 29, but with an additional cover member to form a seal around the white light source. As seen in fig. 30, a TO can type package 2901 has a lid 2912 mounted TO a substrate. The cap may be welded, brazed, electrowelded, or glued to the base. The cover member has a transparent window region 2913 configured to allow the emitted white light to pass therethrough to the external environment available in the application. The type of seal may be an environmental seal or a hermetic seal, and in one example, the sealed package is backfilled with nitrogen or a combination of nitrogen and oxygen. In some embodiments, a lens or other type of optical element is incorporated directly in the cover member to shape, direct, or collimate the white light. Of course, the example in fig. 30 is only one example, and is intended to illustrate one possible configuration of the sealed white light source. In particular, this embodiment may be suitable for applications requiring hermetic sealing, since the TO can type package is simply hermetically sealed. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included.
An alternative example of packaging a CPoS white light source in accordance with the present invention is provided in the schematic diagram of fig. 31. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3101 with a reflective mode white light source 3102 mounted on the base member, wherein the base member is configured to direct heat away from the white light source and to a heat sink. The base member is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material can be dispensed or deposited using standard processing equipment and cycling temperatures, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires 3103 and 3104 are used to form electrical connections from the p-and n-electrodes of the laser diode to the internal feedthroughs 3105 and 3106. The feedthrough is electrically coupled to an external lead, e.g., 3107. The external leads may be electrically coupled to a power source to energize the white light source and produce white light emissions. The top surface 3108 of the surface mount package may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31 is only one example, and is intended to illustrate one possible simple configuration of a surface mount package CPoS white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of packaging a white light source according to the invention is provided in the schematic diagram of fig. 31A. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3201 with a reflective mode phosphor member 3202 mounted on a support member or base member. The laser diode device 3203 may be mounted on the support member 3204 or the base member. The support member and the base member are configured to direct heat away from the phosphor member and the laser diode device. The backing member is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire or other metal, ceramic or semiconductor. Mounting to the base member may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but could be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires 3205 and 3206 are used to form electrical connections from the p-and n-electrodes of the laser diode to the inner feedthroughs 3207 and 3208. The feedthrough is electrically coupled to an external lead. The external leads may then be electrically coupled to a power source to energize the white light source and produce a white light emission. The top surface of the base member 3201 may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with the downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31A is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of packaging a white light source according to the invention is provided in the schematic diagram of fig. 31B. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a common supporting base member 3201. The reflective mode phosphor member 3202 is attached to a base member, which may also include an intermediate substrate member between the phosphor member 3202 and the base member 3201. Laser diode 3203 is mounted on angular support member 3214, with angular support member 3214 attached to base member 3201. The base member 3201 is configured to conduct heat from the white light source to the heat sink. The base member 3201 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member 3201 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires 3207 and 3216 are used to form electrical connections from the electrodes of the laser diode to member 3216. Bonding wires 3205 and 3206 are formed into the internal feedthroughs 3209 and 3210. The feedthrough is electrically coupled to an external lead. The external leads may then be electrically coupled to a power source to energize the white light source and produce a white light emission. The top surface of the base member 501 may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with downwardly directed or reflected light. Moreover, all surfaces within the package, including the laser diode device and the base member, may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to the open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31B is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of a packaged white light source comprising 2 laser diode chips according to the invention is provided in the schematic diagram of fig. 31C. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3201 with a reflective mode phosphor member 3202 mounted on a support member or base member. The first laser diode device 3223 may be mounted on the first support member 3224 or the base member. The second laser diode device 3225 may be mounted on the second support member 3226 or the base member. The first and second support members and the base member are configured to direct heat away from the phosphor member 3202 and the laser diode devices 3223 and 3225. The base member is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but could be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires are used to make electrical connections from the p-and n-electrodes of the laser diode to the internal feedthroughs. The feedthrough is electrically coupled to an external lead. The external lead may be electrically coupled to a power supply to energize the laser diode source to emit a first laser beam 3228 from the first laser diode device 3223 and a second laser beam 3229 from the second laser diode device 3225. The laser beam is incident on the phosphor member 3202 to produce an excitation spot and a white light emission. The laser beams preferably overlap on the phosphor 3202 to produce an excitation spot of optimized geometry and/or size. For example, in the example according to fig. 31C, the laser beams from the first laser diode and the second laser diode are rotated 90 degrees with respect to each other such that the slow axis of the first laser beam is aligned with the fast axis of the second laser beam. The top surface of the base member 3201 may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with the downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to the open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31C is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of a packaged white light source comprising 3 laser diode chips according to the present invention is provided in the schematic diagram of fig. 31D. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3201 with a reflective mode phosphor member 3202 mounted on a support member or base member. The first laser diode device 3223 may be mounted on the first support member 3222 or the base member. The second laser diode device 3225 may be mounted on the second support member 3224 or the base member. The third laser diode device 3227 may be mounted on the third support member 3226 or the base member. The support member and the base member are configured to direct heat away from the phosphor member and the laser diode device. The base member 3201 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to base member 3201 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but may be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires are used to make electrical connections from the p-and n-electrodes of the laser diode to the internal feedthroughs. The feedthrough is electrically coupled to an external lead. The external leads may be electrically coupled to a power supply to energize the laser diode source to emit a first laser beam from the first laser diode device 3223, a second laser beam from the second laser diode device 3225, and a third laser beam from the third laser diode device 3227. A laser beam is incident on the phosphor member 502 to generate an excitation spot and a white light emission. The laser beams are preferably superimposed on the phosphor to produce an excitation spot of optimized geometry and/or size. The top surface of the base member 3201 may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with the downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31D is only one example, and is intended to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of packaging a white light source according to the invention is provided in the schematic diagram of fig. 31E. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3201 that serves as a common support member for a side pumped phosphor member 3232 mounted on a substrate or support member 3239 and a laser diode device 3234 mounted on a substrate or support member 3235. In some embodiments of the present invention, the laser diode and/or phosphor member may be mounted directly onto the base member 3201 of the package. The support member and base member are configured to direct heat away from the phosphor member 3232 and the laser diode device 3234. The base member 3201 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting of the substrate or support building to the base member may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Electrical connections from the p-electrode and n-electrode can be electrically coupled to electrodes 3236 and 3237 on the substrate member, and then electrodes 3236 and 3237 will be coupled to internal feedthroughs in the package member. The feedthrough is electrically coupled to an external lead. The external leads may be electrically coupled to a power source to energize the laser diode source and generate a laser beam that is incident on the sides of the phosphor member 3232. The phosphor member 3232 may preferably be configured for dominant white emission 3238 from a top surface of the phosphor member 3232. The top surface of the base member 3201 may be composed of, coated with, or filled with a reflective layer to prevent or mitigate any losses associated with the downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device 3234 and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to the open environment. In some examples of this embodiment of the integrated white light source device, an electrostatic discharge (ESD) protection element, such as a surge voltage suppression (TVS) element, is included. Of course, the example in fig. 31e is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
Fig. 32 is a schematic view of a CPoS white light source configured in an SMD type package as shown in fig. 31, but with an additional cover member to form a seal around the white light source. As seen in fig. 32, the SMD type package has a base member 3241 with a white light source 3242 mounted on the base. Mounting to the substrate may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. Overlapping the white light source is a cover member 503 attached to the base member around the sides. In one example, the attachment may be a welded attachment, a brazed attachment, an electro-welded attachment, or an adhesively attached to the base member. The cover member has at least one transparent window area, which in a preferred embodiment will consist essentially of a transparent window area, such as a transparent flat top cap or lid as illustrated in fig. 32. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. The type of seal may be an environmental seal or a hermetic seal, and in one example, the sealed package is backfilled with nitrogen or a combination of nitrogen and oxygen. Bonding wires 3244 and 3245 are used to form electrical connections from the p-electrode and n-electrode of the laser diode. Wire bonds connect the electrodes to electrical feedthroughs 3246 and 3247, and electrical feedthroughs 3248 and 2907 are electrically connected to external leads, such as 3248, on the outside of the sealed SMD package. The lead is then electrically coupled to a power source to energize the white light source and produce a white light emission. In some embodiments, a lens or other type of optical element is incorporated directly in the cover member to shape, direct, or collimate the white light. Of course, the example in fig. 32 is only one example, intended to illustrate one possible configuration of the encapsulated white light source. In particular, since the SMD type package is simply hermetically sealed, this embodiment may be suitable for applications requiring a hermetic seal.
Fig. 32A is a schematic view of a white light source configured in an SMD type package as shown in fig. 31B, but with an additional cover member to form a seal around the white light source. As seen in fig. 32A, the SMD type package has a base member 3201 with a white light source mounted to the base member or base member, which is made up of a reflective mode phosphor member 3202 and a laser diode member 3203. Mounting to the substrate and/or base may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. Overlapping the white light source is a cover member 3254 that is attached around the sides to the base member. In one example, the attachment may be a welded attachment, a brazed attachment, an electro-welded attachment, or an adhesively attached to the base member. The cover member has at least one transparent window area, which in a preferred embodiment will consist essentially of a transparent window area, such as a transparent flat top cap or flat top cover 3254 illustrated in fig. 32A. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. The type of seal may be an environmental seal or a hermetic seal, and in one example, the sealed package is backfilled with nitrogen or a combination of nitrogen and oxygen. Bonding wires 3205 and 3206 are used to form electrical connections from the p-electrode and n-electrode of the laser diode. The bonding wires connect the electrodes to electrical feedthroughs that are electrically connected to external leads on the outside of the sealed SMD package. The leads are electrically coupled to a power source to energize the white light source and produce white light emissions. In some embodiments, a lens or other type of optical element is incorporated directly in the cover member to shape, direct, or collimate the white light. Of course, the example in fig. 32A is only one example, intended to illustrate one possible configuration of the encapsulated white light source. In particular, this embodiment may be suitable for applications requiring a hermetic seal, since SMD type packages are simply hermetically sealed.
Of course, a suitable assembly process is required to manufacture the integrated laser based white light source as shown in fig. 32A and in accordance with other embodiments of the present invention. In many embodiments, the assembly process for such devices will follow today's standard semiconductor and LED assembly processes. As an example, a general assembly process would follow the following steps:
i) The laser is attached to heat a conductive member, such as the first substrate member and optionally the second substrate member, or the second and third substrate members.
II) the composite laser and the thermally conductive member are connected to a common support member, such as a package member [ e.g. an SMD package ], or a substrate member.
III) the phosphor is attached to a common support member, such as a package member [ e.g., SMD ] or a substrate member.
IV) an ESD protection device [ e.g., TVS ] or other peripheral component is attached to the package member, the base member, or the substrate member.
V) the subassembly that is required to be electrically connected to the package is wire bonded to the feedthrough.
VI) performing operation verification test.
VII) the frame assembly is attached to the package or substrate or the frame + lid assembly is attached to the package or substrate.
VIII) attaching the completed SMD package to a next level board, such as MCPCB, FR4 or a suitable carrier substrate.
In step I, the laser device will be attached to the heat conducting member by selecting various materials to provide mechanical stability, alignment and thermal conductivity to suit the specific requirements of the product application. These material choices and processes may include, but are not limited to, gold-to-gold interconnects, standard lead-free solder attachment by dispensing or stencil application or using a preformed attachment, standard leaded solder attachment by dispensing or stencil application or using a preformed attachment, die attach epoxy using dispensing and screen application, or sintered silver solder using dispensing, stencil or preforming.
In step II, the combined member consisting of the laser and the thermally conductive member will then present a similar set of material choices for attaching it to the package or substrate. Material selection and process selection are as follows. Depending on the choice of materials, the process flow may be adjusted so that each subsequent step in the process shifts the temperature of the device lower than the previous step. Thus, the earlier joints or connections do not experience secondary backflow. Typical pick and place type operations, whether heated/pressurized in situ or reflowed, will be used for this attachment process. These material choices and processes may include, but are not limited to, gold-to-gold interconnects, standard lead-free solder attachment by dispensing or stencil application or using a preformed attachment, standard leaded solder attachment by dispensing or stencil application or using a preformed attachment, die attach epoxy using dispensing and screen application, or sintered silver solder using dispensing, stencil or preforming.
In step III, the attachment of the phosphor subassembly will depend on the structure and design of the subassembly. For a single piece of solid object, the phosphor can be handled by pick and place operations, just as today handles LED attachment. This requires the substrate of the phosphor subassembly to be prepared for standard metallization attachment, and the following materials may be used. These material choices and processes may include, but are not limited to, gold-to-gold interconnects, standard lead-free solder attachment by dispensing or stencil application or using a preformed attachment, standard leaded solder attachment by dispensing or stencil application or using a preformed attachment, die attach epoxy using dispensing and screen application, or sintered silver solder using dispensing, stencil or preforming.
For less rigid phosphor subassemblies, it uses a binder such as phosphor and silicone. The method of attachment is simple, namely adhering the phosphor and silicone slurry to the package surface during the silicone drying step. Methods of application of the phosphor paste will include, but are not limited to, dispensing and curing processes, spray and cure processes, processes using silicone dispensing and cure electrophoretic deposition, processes of mechanical imprinting/embedding of powders into package metallization surfaces, settling deposition processes, or spray dispensing and curing processes.
In step IV, the ESD or other peripheral component attachment process may follow an industry standard attachment protocol that will include one or more of a solder dispensing/stencil or pre-form attachment process, an ESD or peripheral attachment or reflow process through a pick and place operation.
In step V, wire bonding of the attached subassembly will use industry standard materials and processes. This would include wire selection of Al, cu, ag and Au. Alternatively, the application may also use tape bonding, if desired or applicable. Typical wire bonding techniques will include ball bonding, wedge bonding, and consistent bonding techniques known in the semiconductor industry.
In step VI, where the device is fully attached to the sub-assembly, an operation verification test may be performed during assembly to verify that the operation is correct before submitting the final assembly (frame and lid) to the SMD component. In the event that the device is not operational, an opportunity is provided to repair the component prior to sealing. This test would involve a simple electrical turn-on of the device to verify proper operation of the laser and possibly a soft ESD test to verify proper operation of the ESD/TVS assembly. Typical operating values for voltage, current, light output, color, spot size and shape will all be used to determine proper operation.
In step VII, the frame assembly and attachment steps will be used to prepare the device to be sealed from the environment. Depending on the degree of sealing required for the device, the frame will be attached to the SMD by the selected material. In one example of the sealing material and process, including the attachment of AuSn to the metallization frame and package surface to provide a true hermetic seal. The AuSn dispensing and templating process places the AuSn in place on the SMD. The frame was then picked and placed on the wet AuSn, followed by a reflow step. In a second example of a sealing material and process, an epoxy material is used if the sealability and gas leakage requirements are sufficient to meet the product service conditions. The epoxy material is typically stencil printed or dispensed, followed by pick and place of the frame and a subsequent epoxy curing step. In a third example of an encapsulation material and process, indium metal is used to compress and mechanically attach indium to SMDs and frame surfaces by placing thin indium wires on the attachment surfaces and applying heat and pressure to the indium using the frame as a pressing member.
Another method of the frame assembly process is to first attach a transparent cover (usually glass) to the frame and then attach the combined element to the SMD as described above, otherwise the separate cover attachment step would follow the same process and material selection, but the surfaces would be the top of the frame and the bottom of the cover.
In step VIII, the step of attaching the completed SMD to the next level board will employ industry standard attachment methods and materials. These material choices and processes may include, but are not limited to, gold-to-gold interconnects, standard lead-free solder attachment by dispensing or stencil application or using a preformed attachment, standard leaded solder attachment by dispensing or stencil application or using a preformed attachment, die attach epoxy using dispensing and screen application, or sintered silver solder using dispensing, stencil or preforming.
In all embodiments, a transmissive mode and a reflective mode of an integrated CPoS white light source according to the present invention safety features and design considerations may be included. In any laser-based light source, safety is a critical aspect. It is critical that the light source not be damaged or altered in a way that produces a laser diode beam that is harmful to humans, animals or the environment. Thus, the overall design should include safety considerations and features, and in some cases even active components for monitoring. Examples of design considerations and features for safety include positioning the laser beam relative to the phosphor in such a way that if the phosphor is removed or damaged, the exposed laser beam will not cause it to reach the external environment in a deleterious form (e.g., a collimated coherent beam). More specifically, the white light source is designed such that the laser beam is directed away from the outside environment and towards a surface or feature that will prevent the laser beam from being reflected to the outside world. In one example of passive design features for safety, beam dumps are included and/or absorbing materials can be specifically positioned where the laser beam will impinge in the event of a removed or damaged phosphor.
In one embodiment, an optical beam dump is used as an optical element that absorbs a laser beam that may otherwise be hazardous to the external environment. Design concerns in the beam dump will include management and reduction of laser beam back-reflection and scattering, and dissipation of heat generated by absorption. In a simple solution where the optical power is not too high, the absorbing material may simply be a piece of black velvet or matte paper that is attached to the backsheet material by glue, solder or other material. In high power applications, such as those that would be included in a high power laser system, the beam dump must typically contain more fine features to avoid back-reflection, overheating, or excessive noise. Even with the mitigation of direct reflections, collecting the laser beam by a simple plane can result in an unacceptably large amount of light escaping to the outside world, where it can pose a hazard to the environment. One way to minimize scattering is to use porous or dark-colored cavity material lined with absorbing material to collect the light beam.
One common type of beam dump suitable for most midrange power lasers is an aluminum cone (cone) with a larger diameter than the beam, anodized black and enclosed in a black, ribbed can. A beam with only the cone point exposed to the front face; typically, the incoming light is wiped across the cone at an angle, which alleviates performance requirements. Any reflections from this black surface are then absorbed by the can. The ribs help to keep light from easily escaping and improve heat transfer to the surrounding air. (https:// en. Wikipedia. Org/wiki/Beam _ dump).
An example of an encapsulated CPoS white light source including beam dump safety features in accordance with the present invention is provided in the schematic diagram of fig. 33. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package. The example SMD package has a base member 3301 with a reflective mode white light source 3302 mounted on the base member, where the base member 3301 is configured to direct heat away from the white light source and to a heat sink. The base member 3301 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, alumina, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member 3301 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The joint may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), thermal adhesive, and other materials. Alternatively, the joint may be formed by a metal-metal bond (e.g., au-Au bond). Bonding wires 3303 and 3304 are used to form electrical connections from the p-and n-electrodes of the laser diode to internal electrical feedthroughs 3305 and 3306. The feedthrough is electrically coupled to an external lead, such as 3307. The external leads may be electrically coupled to a power source to energize the white light source and produce white light emissions. In the event of phosphor damage or removal and the laser beam being reflected from the support member of the phosphor, the example beam 3308 is configured in the optical path of the laser diode. In this example, the shape of the beam dump is like a cube, but this is just one example, and the shape, size and position of the beam dump will be optimized based on providing a safety function while not unacceptably including the efficacy of the white light source. In this example, the face of the beam dump configured to be in the path of the reflected beam may be comprised of a porous material with a deep cavity through the cubic beam dump. In addition, the beam dump may include: an absorber that absorbs the laser beam and makes the beam well heat sink to the package member and a heat sink that dissipates thermal energy generated during absorption of the laser beam. The sides of the beam dump member 508 that are not in the path of the laser beam may be comprised of a reflective material to increase the useful output white light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. Of course, the example in fig. 33 is only one example, and the purpose is to illustrate one possible simple configuration of a packaged CPoS white light source with a built-in security feature. In other embodiments, more than one security feature may be included, a security system consisting of multiple security elements may be included, and such a security system may consist of active and passive security elements. Also, the security element or system may be included in a flat package, a custom package, or a can package, including other packages.
An alternative example of a packaged white light source according to the invention is provided in the schematic diagram of fig. 33A. In this example, the reflection mode white light source is configured in a Surface Mount Device (SMD) type package including a beam dump member as a safety feature. The example SMD package has a common supporting base member 3401. The reflective mode phosphor member 3402 is attached to a base member, which may further include an intermediate substrate member between the phosphor member 3402 and the base member 3401. The laser diode 3403 is mounted on the angle support member 504, with the angle support member 3401 attached to the base member 3401. The base member 3401 is configured to conduct heat from the white light source to the heat sink. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. The mounting to the base member 3401 may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment can avoid the thermal load limitations of downstream processing, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires 3405 are used to form electrical connections from the electrodes of the laser diode to the member 3406. Bonding wires 3407 and 3408 are formed in the internal electrical feedthroughs 3409 and 3410. The feedthrough is electrically coupled to an external lead. The external leads may be electrically coupled to a power source to energize the white light source and generate a laser beam 3411, the laser beam 3411 being incident on the phosphor member 3402 to produce white light emission. The beam dump 3412 is located on the opposite side of the phosphor member 3402 from the laser excitation source. The beam dump 3412 provides an important safety feature for absorbing stray violet or blue laser light reflected from the top of the phosphor member 3402. Further, in extreme cases where the phosphor member 3402 is removed or damaged to create a potentially dangerous situation (where a full or near full power laser beam is reflected off of a base member or other reflector), a beam dump will be used to absorb most of the light and prevent the dangerous laser beam from being exposed to the outside world. The beam dump means may also be comprised of functional elements, such as electrostatic discharge (ESD) protection elements, such as surge voltage suppression (TVS) elements. In some embodiments, the beam dump is a thermal fuse that is used to heat and create an open circuit to turn off the laser diode when directly exposed to the laser beam. The top surface of the base member 3401 may be composed of or coated with a reflective layer to prevent or mitigate any losses associated with the light being directed or reflected downward. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. Of course, the example in fig. 33A is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
Of course, the beam dump is just one example of a laser safety feature, but many others may exist. In general, the laser diode should not be configured to point to the outside environment so that direct laser light will not spill into the outside world if there is a damage or destruction event.
In some embodiments of the present invention, the thermal fuse is integrated into a package with the phosphor member. Thermal fuses are simple devices configured to conduct electricity under normal operation, typically consisting of low melting point alloys. In one example, the thermal fuse is composed of a metallic material with a low melting point and is configured to be rapidly heated when directly or indirectly irradiated with light of a violet or blue laser beam. The rapid heat generation in the thermal fuse material causes the material to melt, creating a break in the molten metal, which breaks the conductive path and prevents current from passing through the melter.
In this embodiment of the present invention, the thermal fuse is included in a circuit that supplies a current input from an external power supply to the gain element of the laser diode. In the case where the phosphor member is included, destroyed, or removed, the thermal fuse is physically positioned at a position where the output of the violet or blue laser beam will be incident. That is, the thermal fuse is placed in a location where the beam is not expected to be unless an upstream fault has occurred in the beam line in the package. In the case of such an event, the violet or blue laser will irradiate the fuse material, causing a temperature rise at or above the melting point, resulting in melting of the thermal fuse element. This melting will then break the circuit and destroy the circuit from the external power supply to the laser diode gain element, thereby shutting down the laser device. In this preferred embodiment, the thermal fuse can cut power to the laser without the need for an external control mechanism.
There are many variations to the fusible alloy thermal fuse structure according to the present invention. In another example, a tension spring welded in place within a fusible alloy ball may be utilized. The springs and alloy provide the electrical circuit. When the alloy becomes soft enough, the spring is free to stretch, breaking the circuit connection. In some embodiments, the melting point may be suitably selected to only break the connection in the handling device when a sufficient temperature has been met or exceeded.
In some embodiments of the present invention, the safety features and systems use active components. Examples of active components include photodetectors/photodiodes and thermistors. A photodiode is a semiconductor device that converts light into an electric current, wherein the electric current is generated when light in a specific wavelength range is incident on the photodiode. A small amount of current is also generated in the absence of light. Photodiodes may be combined with components such as filters to provide wavelength or polarization selection of light incident on the detector, built-in lenses to focus the light or manipulate the light incident on the detector, and may have larger or smaller surface areas to select a certain responsivity and/or noise level. The most popular type of photodiode is based on Si as the light absorbing material in which a depletion region is formed. When a photon is absorbed in this region, an electron-hole pair is formed, which results in a photocurrent. The main parameter defining the sensitivity of a photodiode is its Quantum Efficiency (QE), which is defined as the percentage of incident photons that generate electron-hole pairs that subsequently contribute to the output signal. For silicon detectors operating at wavelengths in the 800-900nm region, quantum efficiencies of about 80% are common. The sensitivity of a photodiode can also be expressed as the photodiode current (in amps) per watt of incident illumination. This relationship leads to a tendency of responsivity to decrease as the wavelength becomes shorter. For example, at 900nm,80% QE indicates a response of 0.58A/W, while at 430nm, the same QE gives only 0.28A/W. In alternative embodiments, photodiodes based on other materials such as Ge, inGaAs, gaAs, inGaAsP, inGaN, gaN, inP or other semiconductor-based materials may be used. The photodiode may be a p-n type, p-i-n type, avalanche photodiode, single-row carrier photodiode, partially depleted photodiode, or other type of diode.
The reduced responsivity with such shorter wavelengths makes it difficult to implement high performance silicon based photodiodes in the violet or blue wavelength range. To overcome this difficulty, blue enhancement and/or filter techniques may be used to improve the responsivity of this wavelength range. However, such techniques may result in increased costs, which may be incompatible with certain applications. This challenge can be overcome using a variety of techniques, including deploying new technologies for blue enhanced silicon photodiodes or using photodiodes based on different material systems, such as GaN/InGaN based photodiodes. In one embodiment, a photodiode comprising InGaN and/or GaN is combined with an integrated white light source. In one embodiment, the photodiode and the laser diode are integrated with the laser diode by monolithic technology or by integration onto a common substrate or support member as the laser diode to form an integrated GaN/InGaN based photodiode.
In another embodiment of the present invention, to overcome the difficulty of implementing low-cost silicon-based photodiodes that can operate with high responsivity in the blue wavelength region, ultraviolet, violet, or blue laser light can be down-converted to a wavelength more suitable for high responsivity light detection using a wavelength converting material (e.g., phosphor) according to the criteria required by embodiments of the present invention. For example, if a photodiode operating in the green, yellow or red wavelength range is relatively low cost and has a suitable responsivity to the power level associated with the converted wavelength, a phosphor may be coated on the photodiode to convert the laser light to red, green or yellow emission. In other embodiments where the detector is not coated, but a converter member such as a phosphor is placed in the optical path of the laser beam or the scattered laser beam and the photodiode.
Strategically positioned detectors designed to detect direct blue emission from a laser, scattered blue emission, or phosphor emission (e.g., yellow phosphor emission) may be used to detect failure of the phosphor to expose a blue beam, or other failure of the white light source. Upon detection of such an event, a closed circuit or feedback loop will be configured to stop supplying power to the laser diode and effectively turn it off.
For example, a photodiode that may be used to detect phosphor emission may be used to determine if the phosphor emission is rapidly decreasing, which would indicate that the laser light is no longer effectively striking the phosphor for excitation, and may mean that the phosphor is removed or damaged. In another example of an active security function, a blue sensitive photodetector may be placed to detect reflected or scattered blue light emission from the laser diode, so that if the phosphor is removed or damaged, the amount of detected blue light will increase rapidly and the laser will be turned off by the security system.
In a preferred embodiment, an InGaN/GaN-based photodiode is integrated with a white light source. InGaN/GaN based photodiodes may be integrated using discrete photodiodes mounted in packages, or may be integrated directly with a laser diode onto a common support member. In a preferred embodiment, an InGaN/GaN-based photodiode may be monolithically integrated with a laser diode.
In yet another example of an active security feature, a thermistor may be positioned near or below the phosphor material to determine if there is a sudden increase in temperature, which may be the result of an increase in direct radiation from the blue laser diode, indicating that the phosphor is damaged or removed. Also in this case, the thermistor signal trips the feedback loop to stop the power supply to the laser diode and shut it down.
In some embodiments, additional optical elements are used to recycle the reflected or stray excitation light. In one example, the reflected laser beam is re-imaged back onto the phosphor using re-imaging optics, thereby recycling the reflected light.
An alternative example of a packaged white light source including re-imaging optics in accordance with the present invention is provided in the schematic diagram of fig. 33B. In this example, the reflective mode white light source is configured in a Surface Mounted Device (SMD) type package that includes re-imaging optics as a security feature and as a photon recovery feature. The example SMD package has a common supporting base member 3401. The reflective mode phosphor member 3402 is attached to a base member, which may further include an intermediate substrate member between the phosphor member 3402 and the base member 3401. The laser diode 3403 is mounted on an angle support member 3404, wherein the angle support member is attached to the base member 3401. The base member 3401 is configured to conduct heat from the white light source to the heat sink. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. The mounting to the base member 3401 may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Bonding wires 3405 are used to form electrical connections from the electrodes of the laser diode to the member 3406. Bonding wires 3407 and 3408 are formed in the internal electrical feedthroughs 3409 and 3410. The feedthrough is electrically coupled to an external lead. The external leads may be electrically coupled to a power source to energize the white light source and generate a laser beam 3411, the laser beam 3411 being incident on the phosphor member 3402 to create a main excitation spot and produce a white light emission. The re-imaging optics 3414 are located on the opposite side of the phosphor member 3402 from the laser excitation source. The re-imaging optics 3414 are used to redirect or refocus a portion of the excitation light reflected from the top surface of the phosphor member 3402. To avoid a decrease in brightness or an increase in spot size, the re-imaging optics 3414 may produce a reflected excitation spot on the phosphor member 3402 that is similar in size and shape to the primary excitation spot. Alternatively, the re-imaged excitation spot may be smaller than the main excitation spot. This re-imaging optics 3414 serves as a safety feature to prevent stray reflected laser light from escaping the package, and can enhance the efficiency of the white light device by recycling wasted reflected excitation light back onto the phosphor member 3402. The top surface of the base member 3401 may be composed of, coated with, or filled with a reflective layer to prevent or mitigate any losses associated with downwardly directed or reflected light. Also, all surfaces within the package, including the laser diode 3403 and the substrate member, may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to the open environment. Of course, the example in fig. 33B is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
An alternative example of a packaged white light source including reflective optics in accordance with the present invention is provided in the schematic diagram of fig. 33C. In this example, the reflective mode white light source is configured in a Surface Mount Device (SMD) type package that includes re-imaging optics to provide beam shaping benefits, manufacturability benefits, and a possible reduction in thermal impedance. In this example, the SMD package has a common support base member 3401. The reflective mode phosphor member 3402 is attached to a base member, which may also include an intermediate substrate member between the phosphor member and the base member. The laser diodes on substrate 3413 are mounted directly to the base of the package without the need for angled support members as in fig. 33B and other embodiments. The base member is configured to direct heat away from the white light source and to the heat sink. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member 3401 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Electrical connections are made from the electrodes of the laser diode by electrical coupling to feedthroughs in the package that connect to external leads. The external leads may be electrically coupled to a power source to energize the white light source and generate a laser beam 3411, the laser beam 3411 being incident on the re-imaging optics 3414, the re-imaging optics 3414 being on an opposite side of the phosphor member relative to the laser excitation source. The re-imaging optics 3414 are used to redirect or refocus the direct laser beam 3411 from the laser diode into the incident beam 3416 on the top surface of the phosphor 3402. In an alternative configuration, the re-imaging optics 3414 may be placed in an alternative location relative to the laser and phosphor. This general example of using re-imaging optics provides the following advantages: it is possible to provide a more desirable spot size and geometry, as controlled by the re-imaging optics, and without the need to include intermediate members, such as angled support members, for easier manufacturing and lower thermal impedance. Moreover, this example provides a security benefit. The use of re-imaging optics 3414 may enable very round excitation spots and/or very small excitation spots, e.g., less than 1mm, less than 500 μm, less than 300 μm, less than 100 μm, or less than 50 μm. This re-imaging optics 3414 serves as a safety feature to prevent stray reflected laser light from leaving the package, and can enhance the efficiency of the white light device by recycling wasted reflected excitation light back onto the phosphor 3402. The top surface of the base member 3401 may be composed of, coated with, or filled with a reflective layer to prevent or mitigate any losses associated with downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. Of course, the example in fig. 33C is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
In some embodiments of the present invention, additional elements may be included within the encapsulation member to provide the function of shielding or blocking stray or reflected light from the laser diode device. By blocking optical artifacts (e.g., reflected excitation light, phosphor flash patterns, or light emitted from the laser diode that is not in the primary emission beam, such as self-luminescence, scattered light, or light exiting the back), light emission from a white light source may be more desirable when integrated into an illumination system. Moreover, by blocking such stray light, the integrated white light source will be intrinsically safer. Finally, the shield may act as an aperture such that the white light emitting aperture from the phosphor member passes through the aperture in the shield. This aperture feature may form an emission pattern from a white light source.
An alternative example of a packaged white light source including reflective optics in accordance with the present invention is provided in the schematic diagram of fig. 33D. In this example, the reflective mode white light source is configured in a Surface Mount Device (SMD) type package that includes shielding to provide additional benefits (e.g., improved white light emission spatial pattern, reduction of unwanted optical artifacts, such as reflected excitation light or unwanted laser emission, and/or improved security by preventing stray laser light from exiting the package). In this example, the SMD package has a common support base member 3401. The reflective mode phosphor member 3402 is attached to the base member 3401 and is at least partially enclosed by a shield or aperture member. The shield 3425 is provided with at least one protrusion 3426 extending over the emitter face of the laser diode. The on-substrate laser diode 3423 is mounted to the angled support member 3404 and attached to the base of the package. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. The substrate member 3401 is composed of a thermally conductive material, such as copper, copper tungsten, aluminum, siC, steel, diamond, composite diamond, alN, sapphire, or other metal, ceramic, or semiconductor. Mounting to the base member 3401 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The mounting tabs may also be formed from thermally conductive glue, thermal epoxy (e.g., silver epoxy), and other materials. Electrical connections are made from the electrodes of the laser diode by electrical coupling to feedthroughs in the package that connect to external leads. The external leads may be electrically coupled to a power source to energize the white light source and generate a laser beam that is incident on the phosphor 3402 within the shield 3425. The shield is configured with an aperture 3427 to allow emission of white light. In an alternative configuration, the shield 3425 may surround the entire laser diode and provide a further level of security. The use of aperture 3427 may enable very ideal or very round excitation spots and/or very small excitation spots, e.g. less than 1mm, less than 500 μm, less than 300 μm, less than 100 μm, or less than 50 μm. The top surface of the base member 3401 may be composed of, coated with, or filled with a reflective layer to prevent or mitigate any losses associated with downwardly directed or reflected light. Moreover, all surfaces within the package including the laser diode device and the substrate member may be enhanced to increase reflectivity, thereby helping to improve the output of useful white light. In this configuration, the white light source is not covered or sealed such that it is exposed to an open environment. Of course, the example in fig. 33D is only one example, and the purpose is to illustrate one possible simple configuration of a surface mount package white light source. In particular, since surface mount type packages are popular with LEDs and other devices and may be off-the-shelf, they may be one option for low cost and highly adaptable solutions.
In many applications according to the invention, the packaged integrated white light source will be attached to a heat sink member. The heat sink is configured to transfer thermal energy from the packaged white light source to the cooling medium. The cooling medium may be an active cooling medium, such as a thermoelectric cooler or microchannel cooler, or may be a passive cooling medium, such as an air-cooled design with features (e.g., fins, posts, rods, plates, tubes, or other shapes) that maximize surface and increase interaction with air. The heat sink will typically be formed of a metallic piece, but may be other, such as a thermally conductive ceramic, semiconductor, or composite material.
The heat sink member is configured to transfer thermal energy from the packaged laser diode based white light source to the cooling medium. The heat sink member may be comprised of metal, ceramic, composite, semiconductor, plastic, preferably a thermally conductive material. Examples of candidate materials include: copper, which may have a thermal conductivity of about 400W/(mK), aluminum, which may have a thermal conductivity of about 200W/(mK), 4H-SiC, which may have a thermal conductivity of about 370W/(mK), 6H-SiC, which may have a thermal conductivity of about 490W/(mK), alN, which may have a thermal conductivity of about 230W/(mK), synthetic diamond, composite diamond, sapphire, or other metals, ceramics, composites, or semiconductors, which may have a thermal conductivity of about > 1000W/(mK). The heat sink member may be formed of a metal such as copper, copper tungsten, aluminum, etc. by machining, cutting, trimming, or molding.
The attachment joints connecting the encapsulated white light source according to the invention to the heat sink member should be carefully designed and processed to minimize thermal impedance. Therefore, the appropriate attachment material, interface geometry, and attachment process practices must be selected for a suitable thermal impedance with sufficient attachment strength. Examples include AuSn solder, SAC solder (e.g., SAC 305), leaded solder, or indium, but other solders are also possible. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The joint may also be formed of thermally conductive glue, thermal epoxy (e.g., silver epoxy), thermal adhesive, and other materials. Alternatively, the joint may be formed by a metal-metal bond (e.g., au-Au bond). The common support member with the laser and phosphor materials is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt, which represents a thermal path from the laser device to the heat sink.
Fig. 34 is a schematic diagram of a CPoS white light source configured in a sealed SMD mounted on a heat sink member in accordance with the present invention. The encapsulated white light source 3602 in an SMD package is similar to the example shown in fig. 32. As seen in fig. 34, the SMD type package has a base member 3601 (i.e., base member 3241 in fig. 32), the base member 3601 carrying a white light source 3602 mounted to the base member 3601, the cover member 603 providing a seal for the light source. The mounting to the base member 3601 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attach material can be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The cover member has at least one transparent window area. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. The SMD packaged base member 3601 is attached to the heat sink member 3604. The heat sink member 3604 may be composed of a material such as metal, ceramic, composite, semiconductor, or plastic, preferably a thermally conductive material. The material mounted to the base member 3601 includes copper, copper tungsten, steel, siC, alN, diamond, composite diamond, sapphire, or other materials. Of course, the example in fig. 34 is only an example, and is intended to illustrate one possible configuration of the white light source according to the present invention mounted on a heat sink. In particular, the heat sink member may include features to aid in the transfer of heat, such as fins.
An integrated laser and phosphor based light source, mounted in a package such as an SMD, may be attached to an external board to allow electrical and mechanical mounting of the package. In addition to providing electrical and mechanical interfaces to the SMD package, these boards also provide a thermal interface to the outside world, such as a heat sink. Such a board may also provide improved handling of small packages such as SMDs (typically less than 2cm x 2 cm) during final assembly. In addition to custom board designs, there are many industry standard board designs, including Metal Core Printed Circuit Boards (MCPCBs) with substrates that are Cu, al, or Fe alloys, fiber filled epoxy boards, such as FR4, flex boards/hybrid flex boards (which are typically polyimide structures with Cu interlayers and dielectric insulation to be used in applications that require bending around non-planar surfaces), or standard heat sink material boards that can be mounted directly to existing metal frames in larger systems.
In many embodiments according to the invention, a board having a complete SMD attached to the next level will use industry standard attachment methods and materials. These material choices and processes may include, but are not limited to, gold-to-gold interconnects, standard lead-free solder attachment by dispensing or stencil application or using a preformed attachment, standard leaded solder attachment by dispensing or stencil application or using a preformed attachment, die attach epoxy using dispensing and screen application, or sintered silver solder using dispensing, stencil or preforming.
Fig. 34A is a schematic view of a white light source configured in a sealed SMD mounted on a board such as a star plate according to the present invention. The sealed white light source 3612 in the SMD package is similar to the example shown in fig. 32A. As seen in fig. 34A, the SMD type package has a base member 3611 (i.e., base member 3201 in fig. 32A) with a white light source 3612 mounted to the base, and a cover member 3613, the cover member 3613 providing a seal for the light source 3612. Mounting to the base member 3611 may be accomplished using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but could be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. The cover member 3613 has at least one transparent window area. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. Attached to the star plate member 3614 is a base member 3611 of the SMD package, which is configured to allow electrical and mechanical mounting of the integrated white light source, to provide electrical and mechanical interfaces to the SMD package, and to provide a thermal interface to the outside world, such as a heat sink. Heat sink member 3614 may be comprised of a metal, ceramic, composite, semiconductor, plastic, etc., material, preferably a thermally conductive material. Examples of candidate materials include aluminum, aluminum oxide, copper tungsten, steel, siC, alN, diamond, composite diamond, sapphire, or other materials. Of course, the example in fig. 34A is only an example, and is intended to illustrate one possible configuration of the white light source according to the present invention mounted on the heat sink. In particular, the heat sink may include features to aid in transferring heat, such as fins.
In some embodiments of the present invention, the CPoS integrates a white light source in combination with an optical component to manipulate the white light produced. In one example, white light sources may be used in spotlight systems, such as flashlights or automotive headlamps or other lighting applications where light must be directed or projected to a designated location or area. As an example, to direct light, it should be collimated so that photons comprising white light propagate parallel to each other along the intended propagation axis. The degree of collimation depends on the light source and the optics used to collimate the light source. For the highest degree of collimation, a perfect point source with 4-pi emission and a diameter of the order of submicron or micrometer is desired. In one example, a point light source is combined with a parabolic reflector, where the light source is placed at the focal point of the reflector, and the reflector converts a spherical wave produced by the point light source into a collimated beam of a plane wave propagating along an axis.
In one embodiment, the reflector is coupled to a white light source. In particular, parabolic (or called parabolic (paraolic) or parabolic (paraolic)) reflectors are deployed to project white light. By positioning the white light source in the focal point of the parabolic reflector, the plane wave will be reflected and propagate as a collimated beam along the axis of the parabolic reflector.
In another example, a simple single lens or lens system is used to collimate the white light into a projection beam. In one particular example, a single aspheric lens is placed in front of the white light emitting phosphor element, and the aspheric lens is configured to collimate the emitted white light. In another embodiment, a lens is configured in the lid of the package containing the integrated white light source. In some embodiments, a lens or other type of optical element is incorporated directly in the cover member to shape, direct, or collimate the white light. In one example, the lens is composed of a transparent material such as glass, siC, sapphire, quartz, ceramic, composite materials, or semiconductors.
Such white light collimating optics may be combined with white light sources at different levels of integration. For example, the collimating optics may be located within the same package as the integrated white light source in a common package configuration. In another level of integration, the collimating optics may be located on the same substrate or support member as the white light source. In another embodiment, the collimating optics may be located outside the package containing the integrated white light source.
In one embodiment according to the present invention, a reflective mode integrated white light source is configured in a flat type package with a lens member to produce a collimated white light beam as illustrated in fig. 35. As seen in fig. 35, the flat type package has a base member or housing member 3501 with a collimated white light source 3502 mounted to the base and configured to produce a collimated beam of white light that exits a window 3503 configured in a side of the base member or housing member 3501. Mounting to the substrate or housing may be achieved using soldering or gluing techniques, for example using AuSn solder, SAC solder such as SAC305, lead-containing solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. The sintered silver attachment material may be dispensed or deposited using standard processing equipment and cycling temperatures, and has higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm cm, whereas pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. Electrical connections to white light source 3502 may be made by wire bonding to feedthroughs 3504, the feedthroughs 3504 being electrically coupled to external pins 3505. In this example, the collimated reflective mode white light source 3502 includes a laser diode 3506, a phosphor wavelength converter 3507 configured to accept a laser beam emitted by the laser diode 3506, and a collimating lens, such as an aspheric lens 3508 configured in front of the phosphor 3507 to collect the emitted white light and form a collimated beam. The collimated light beam is directed to a window 3503, where the window 3503 is formed of a transparent material. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. The external pins 3505 are electrically coupled to a power source to energize the white light source 3502 and produce white light emissions. As seen in the figures, any number of pins may be included on the flat package. In this example there are 6 pins, and a typical laser diode driver requires only 2 pins, one for the anode and one for the cathode. Thus, the extra pins can be used for additional components, such as safety features like photodiodes or thermistors that monitor and help control temperature. Of course, the example in fig. 35 is only one example, intended to illustrate one possible configuration of the encapsulated white light source.
In one embodiment according to the present invention, a projection mode integrated white light source is configured in a flat type package with a lens member to produce a collimated white light beam as illustrated in fig. 36. As seen in fig. 36, the flat type package has a base member or housing member 3501 with a collimated white light source 3512 mounted to the base and configured to produce a collimated beam of white light that exits a window 3503 configured in a side of the base member or housing member 3501. The mounting to the base or housing member 3501 may be accomplished using soldering or gluing techniques, such as AuSn solder, SAC solder such as SAC305, leaded solder, or indium, but could be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface. Standard processing equipment and cyclic temperature distribution can be used or sintered silver attachment materials deposited, with the added benefit of higher thermal conductivity and improved electrical conductivity. For example, auSn has a thermal conductivity of about 50W/mK and an electrical conductivity of about 16 micromm x cm, while pressureless sintered silver may have a thermal conductivity of about 125W/mK and an electrical conductivity of about 4 micromm x cm, or pressure sintered silver may have a thermal conductivity of about 250W/mK and an electrical conductivity of about 2.5 micromm x cm. Due to the extreme variation in melting temperature from paste to sinter (260-900 ℃), the treatment avoids the thermal load limitations of downstream processes, allowing very good and consistent bonding throughout the entire device. Electrical connections to white light source 3512 may be made by wire bonding to feedthroughs 3504, the feedthroughs 3504 being electrically coupled to external pins 3505. In this example, the collimated projection mode white light source 3512 includes a laser diode 3516, a phosphor wavelength converter 3517 configured to accept a laser beam emitted by the laser diode 3516, and a collimating lens, such as an aspheric lens 3518 configured in front of the phosphor 3517 to collect the emitted white light and form a collimated beam. The collimated light beam is directed to a window 3503, where the window 3503 is formed of a transparent material. The transparent material may be glass, quartz, sapphire, silicon carbide, diamond, plastic, or any suitable transparent material. The external pins 3505 are electrically coupled to a power source to energize the white light source 3512 and produce white light emissions. As seen in the figures, any number of pins may be included on the flat package. In this example there are 6 pins, and a typical laser diode driver requires only 2 pins, one for the anode and one for the cathode. Thus, the extra pin can be used for additional components, such as safety features like a photodiode or thermistor that monitors and helps control the temperature. Of course, the example in fig. 36 is only one example, and is intended to illustrate one possible configuration of the sealed white light source.
The flat type package example shown in fig. 35 and 36 according to the present invention is illustrated in an unsealed configuration without a lid to show an example of an internal configuration. However, the flat package is simply sealed with a lid member or a cap member. FIG. 37 is an example of a sealed flat package with a collimated white light source inside. As seen in fig. 37, the flat-type package has a base member or housing member 3521 with external pins 3522 configured to electrically couple to internal components (e.g., a white light source, a security feature, and a thermistor). The sealed flat package is configured with a window 3523 for directing a collimated beam of white light away from the cover or cap 3524 to form a seal between the external environment and the internal components. The cap or lid may be welded, brazed, electrowelded, glued to the substrate, and the like. The type of seal may be an environmental seal or a hermetic seal, and in one example, the sealed package is backfilled with nitrogen or a combination of nitrogen and oxygen.
Fig. 38 shows a schematic diagram illustrating a transmissive phosphor embodiment of an integrated white light source including white light collimation optics in accordance with the present invention. In this embodiment, a very small and compact substrate member is fabricated using gallium-containing nitrogen lift-off and transfer techniques, wherein the laser diode chip is formed from a transfer epitaxial layer. Of course, conventional chip-on-substrate implementations such as those shown in fig. 4 and 11 may be used for this integrated collimated white light implementation. The laser-based CPoS white light source consists of a substrate material 3701 that serves as a common support member configured to serve as an intermediate material between the laser diode chip 3702 formed on the transmitting gallium-nitrogen containing epitaxial layer and the final mounting surface and as an intermediate material between the phosphor plate material 3705 and the final mounting surface. Laser diode 3702 and/or the substrate are configured with electrodes 3703 and 3704, which electrodes 3703 and 3704 can be formed from a combination of deposited metal layers and metal layers including, but not limited to, au, pd, pt, ni, al, titanium, or other metal layers. The bonding wires may be configured to couple electrical power to electrodes 3703 and 3704 on the laser diode. The laser beam 3706 is incident on the phosphor 3705 to form white light exiting the phosphor 3705. The white light leaving the phosphor 3705 is coupled into a lens, such as an aspheric lens 3707 for collimation and beam shaping. The electrodes 3703 and 3704 are configured to be electrically connected to an external power source, such as a laser driver, a current source, or a voltage source. Bonding wires (not shown) may be formed on the electrodes to couple electric power to the laser diode device to generate a laser beam output from the laser diode. Of course, this is only one example of a configuration with integrated collimating optics, and there are many variations on this embodiment that could include using a conventional chip-on-substrate configuration as shown in fig. 4 for integrating collimating optics with the laser diode and phosphor. In other alternatives, phosphors with different sizes and shapes may be used, substrates or common support members of different geometric designs may be used, different orientations of the laser output beam relative to the phosphor may be utilized, different electrodes and electrical designs may be performed, and so on.
Fig. 39 shows a schematic diagram illustrating a reflective mode phosphor embodiment of the integrated white light source according to fig. 25, but further comprising reflector optics, such as a parabolic reflector to collimate the white light. In this embodiment, the gallium-nitrogen-containing laser diode 2511 or the chip-on-board is mounted on the common support member 2512, and the common support member 2512 may be a substrate member for the laser diode 2511. The common support member also supports a phosphor member 2516 configured to be in the path of the laser diode output beam 2517, where the laser diode beam may exit the phosphor and emit white light. A reflector member 3715, such as a parabolic reflector, is positioned relative to the primary emission surface of the phosphor member 2516 such that the phosphor member 2516 is proximate the focal point of the reflector member 3715. Reflector member 3715 is configured to collect and collimate the white light emission from phosphor 2516 into a beam of white light projected along axis 3716. Reflector member 3715 is configured with an opening or other entrance for laser beam 2517 to enter the interior of the reflector to interact with phosphor 2516. In other alternatives, phosphors with different sizes and shapes may be used, different geometric designs of the substrate or common support member may be used, different orientations of the laser output beam relative to the phosphor may be utilized, different collimating or other optics may be used, and different electrode and electrical designs may be performed, etc.
Fig. 40 shows a schematic diagram illustrating a reflective mode phosphor embodiment of the integrated white light source according to fig. 28 according to the present invention, but further comprising a lens such as an aspheric lens to collimate the white light. In this embodiment, the gallium and nitrogen containing laser diode 2802 or a chip on board is mounted on a common support member 2801, and the common support member 2801 may be a substrate member for the laser diode 2802. The common support member 2801 also supports a phosphor member 2806 configured to be positioned in the path of the laser diode output beam 2807, wherein the laser diode output beam 2807 may exit the phosphor member 2806 and emit white light. A lens member 3725, such as an aspheric lens, is positioned in front of or above the primary emitting surface of the phosphor member 2806. The lens 3725 is configured to collect and collimate the white light emission from the phosphor member 2806 into a beam of white light projected along the axis 3716. The lens 3725 is supported by mechanical support members, which may be additional members 3726 or may be directly supported by a common support member. In other alternatives, phosphors with different sizes and shapes may be used, substrates or common support members of different geometric designs may be used, different orientations of the laser output beam relative to the phosphor may be utilized, different collimating or other optics may be used, and different electrode and electrical designs may be performed, etc.
Fig. 41 shows a schematic view of a CPoS white light source configured in a can package as shown in fig. 30, but with additional reflector members configured to collimate and project white light. An example configuration for collimated white light from a TO can package according TO fig. 42 includes a TO can substrate 2901, a cap 2912 configured with a transparent window region 2913 mounted TO the substrate. The cap 2912 may be welded, brazed, electrowelded, or glued to the substrate. Reflector member 3733 is disposed outside of window region 2913, wherein reflector member 3733 serves to capture the emitted white light passing through the window, collimate the light, and then project the light along axis 3734. Of course, this is only an example, intended to illustrate one possible configuration that combines an integrated CPoS white light source according to the present invention with collimating optics. In another example, the reflector may be integrated into the window member of the cap, or contained within the TO package member.
In an alternative embodiment, fig. 42 illustrates a schematic view of a CPoS white light source configured in a can package as shown in fig. 30, but with an additional lens member configured to collimate and project white light. An example configuration for collimated white light from a TO can package according TO fig. 42 includes a TO can base 2901, a cap 2912 configured with a transparent window region 2913 mounted TO the base. The cap 2912 may be welded, brazed, electrowelded, or glued to the substrate. An aspheric lens member 3743 is disposed outside of the window region 2913, with the lens 3743 serving to capture the emitted white light through the window, collimate the light, and then project the light along an axis 3744. Of course, this is only an example, intended to illustrate one possible configuration that combines an integrated CPoS white light source according to the present invention with collimating optics. In another example, the collimating lens may be integrated into a window member on the cap, or may be contained within an encapsulating member.
In an alternative embodiment, fig. 43 provides a schematic view of a white light source configured in an SMD type package as shown in fig. 32, but with additional parabolic components configured to collimate and project white light, in accordance with the present invention. An example configuration for collimated white light from an SMD type package according to fig. 43 includes an SMD type package 3751 including a substrate and a cap or window area, and an integrated white light source 3752. The SMD package is mounted to a heat sink member 3753 configured to transport and/or store heat generated in the SMD package from the laser and phosphor members. Reflector member 3754, such as a parabolic reflector, is configured as a white light emitting phosphor member having a white light source at or near the focal point of the parabolic reflector. The parabolic reflector is used to collimate and project the white light along the projection axis 3755. Of course, this is only an example, intended to illustrate one possible configuration of combining an integrated white light source according to the present invention with reflector collimation optics. In another example, the collimating reflector may be integrated into the window means of the cap or may be contained within the package means. In a preferred embodiment, the reflector is integrated with or attached to the substrate.
In an alternative embodiment, fig. 43A provides a schematic illustration of a white light source constructed in an SMD type package according to the present invention as shown in fig. 34A, but with an additional parabolic reflector member or alternative collimating optics, such as a lens configured to collimate and project white light or TIR optics. An example configuration for collimated white light from an SMD type package according to fig. 43A includes an SMD type package 3661 including a substrate 3611 and a cap or window area, and a laser-based integrated white light source 3662. The SMD package 3661 is mounted to a star plate member 3614 configured to allow electrical and mechanical mounting of the integrated white light source, provide electrical and mechanical interfaces to the SMD package 3661, and provide a thermal interface to the outside world, such as a heat sink. Reflector member 3764, such as a parabolic reflector, is configured as a white light emitting phosphor member having a white light source at or near the focal point of the parabolic reflector. The parabolic reflector 3764 is used to collimate and project white light along a projection axis 3765. Of course, this is only an example, intended to illustrate one possible configuration of combining an integrated white light source according to the present invention with reflector collimation optics. In another example, the collimating reflector may be integrated into the window member of the cap, or may be contained within the package member. The collimating optics may be lens members, TIR optics, parabolic reflector members, or alternative collimating techniques, or a combination. In an alternative embodiment, the reflector is integrated with or attached to the substrate.
In an alternative embodiment, fig. 44 provides a schematic illustration of a white light source configured in an SMD type package as shown in fig. 32, but with an additional lens member configured to collimate and project white light. An example configuration for collimated white light from an SMD type package according to figure 44 includes an SMD type package 3261 comprising a base and cap or window area, and an integrated white light source 3262. The SMD package 3261 is mounted to a heat sink member 3773 configured to transport and/or store heat generated in the SMD package 3261 from the laser and phosphor member. The lens component 3774, such as an aspheric lens, is configured with a white light emitting phosphor component of the white light source 3262 to collect and collimate a substantial portion of the emitted white light. The lens member 3774 is supported by the support member 3775 to mechanically support the lens member 3774 in a fixed position relative to the white light source 3262. Support member 3775 may be comprised of metal, plastic, ceramic, composite, semiconductor, etc. The lens member 3774 serves to collimate and project white light along a projection axis 3776. Of course, this is only an example, intended to illustrate one possible configuration of combining an integrated white light source according to the present invention with reflector collimation optics. In another example, the collimating reflector may be integrated into the window means of the cap or may be contained within the package means. In a preferred embodiment, the reflector is integrated with or attached to the substrate.
In one embodiment according to the present invention, fig. 45 provides a schematic view of a white light source configured in an SMD type package as shown in fig. 32, but with additional lens and reflector members configured to collimate and project white light. An example configuration for collimated white light from an SMD type package according to figure 45 includes an SMD type package 3261 comprising a base and cap or window area, and an integrated white light source 3262. The SMD package 3261 is mounted to a heat sink member 3783 configured to transport and/or store heat generated in the SMD package 3261 from the laser and phosphor member. A lens component 3784, such as an aspheric lens, is configured with a white light source 3262 to collect and collimate a substantial portion of the emitted white light. A reflector housing member 3785 or lens member 3784 is disposed between the white light source 3262 and the lens member 3784 to reflect any stray light or light that would otherwise not reach the lens member into the lens member to collimate and help form a collimated light beam. In one embodiment, the lens component 3784 is supported by the reflector housing component 3785 to mechanically support the lens component 3784 in a fixed position relative to the white light source 3262. Lens member 3784 is used to collimate and project white light along projection axis 3786. Of course, this is only an example, intended to illustrate one possible configuration of combining an integrated white light source according to the invention with reflector collimation optics. In another example, the collimating reflector may be integrated into the window means of the cap or may be contained within the package means. In a preferred embodiment, the reflector is integrated with or attached to the substrate.
A device integrating a laser plus a phosphor light source in a package, such as an SMD, may be attached to an external board to allow electrical and mechanical mounting of the package. In addition to providing electrical and mechanical interfaces to the SMD package, these boards also provide a thermal interface to the outside world, such as a heat sink. Such a board may also provide improved handling of small packages such as SMDs (typically less than 2cm x 2 cm) during final assembly. In addition to custom board designs, there are many industry standard board designs including Metal Core Printed Circuit Boards (MCPCBs) with substrates (which are Cu, al, or Fe alloys), fiber filled epoxy boards, such as FR4, flex boards/hybrid flex boards (which are typically polyimide structures with Cu interlayers and dielectric insulation to be used in applications requiring bending around non-planar surfaces), or standard heat sink material boards that can be mounted directly to existing metal frames in larger systems.
A further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and the drawings.
Additional features and designs may be included in all side pump and transmission and reflection embodiments of the present invention. Shaping of the excitation laser beam to optimize the beam spot characteristics on the phosphor can be achieved, for example, by careful design consideration of the angle at which the laser beam is incident on the phosphor, or by using integrating optics (e.g., free space optics such as a collimating lens). Safety features such as passive features like physical design considerations and beam dump and/or active features like photo detectors or thermistors may also be included, which may be used in a closed loop to turn off the laser when indicating a signal. In addition, optical elements may be included to manipulate the white light produced. In some embodiments, a reflector such as a parabolic reflector or a lens such as a collimating lens is used to collimate white light or to produce a spotlight that may be applied to an automobile headlight, flashlight, spotlight, or other lamp.
In one embodiment, the present invention provides a laser-based white light source that includes a form factor characterized by a length, a width, and a height. The apparatus has a support member, and at least one gallium-nitrogen containing laser diode device and phosphor material overlying the support member. The laser device is capable of providing a laser beam emitting in the blue region, preferably at a wavelength of 425nm to 475nm, or in the ultraviolet or violet region at a wavelength of 380nm to 425nm, but other wavelengths are possible, such as the cyan region at 475nm to 510nm or the green region at a wavelength of 510nm to 560 nm. In a preferred embodiment, the phosphor material may provide a yellowish light in the range of 560nm to 580nm, so that when mixed with the blue light of the laser diode, white light is generated. In other embodiments, phosphors with red, green, yellow, and even blue light may be used in combination with a laser diode excitation source to produce white light emission with color mixing. The apparatus typically has free space with unguided laser beam features that transmit the emission of the laser beam from the laser device to the phosphor material. The spectral width, wavelength, size, shape, intensity, and polarization of the laser beam are configured to excite the phosphor material. The beam can be constructed by positioning the beam at a precise distance from the phosphor to take advantage of the beam divergence characteristics of the laser diode and achieve the desired spot size. In other embodiments, free-space optics, such as a collimating lens, may be used to shape the beam before it is incident on the phosphor. The light beam may be characterized by a polarization purity of greater than 60% and less than 100%. As used herein, the term "polarization purity" means that greater than 50% of the emitted electromagnetic radiation is in a substantially similar polarization state, such as a Transverse Electric (TE) or Transverse Magnetic (TM) polarization state, but may have other meanings consistent with ordinary meaning. In one example, the laser beam incident on the phosphor has a power of less than 0.1W, greater than 0.5W, greater than 1W, greater than 5W, greater than 10W, or greater than 20W. The phosphor material is characterized by excellent conversion efficiency, thermal damage resistance, optical damage resistance, thermal quenching characteristics, porosity for scattering excitation light, and thermal conductivity. In a preferred embodiment, the phosphor material consists of a yellow YAG material doped with Ce, has a conversion efficiency of more than 100 lumens/watt, more than 200 lumens/watt or more than 300 lumens/watt and may be a polycrystalline ceramic material or a single crystal material. The white light apparatus also has an electrical input interface configured to couple electrical input power to the laser diode device to generate a laser beam and excite the phosphor material. The white light source is configured to produce a white light output of greater than 1 lumen, 10 lumens, 100 lumens, 250 lumens, 500 lumens, 1000 lumens, 3000 lumens, or 10000 lumens or more. The support member is configured to transfer thermal energy from the at least one laser diode device and the phosphor material to the heat sink. The support member is configured to provide a thermal impedance of dissipated power of less than 10 degrees celsius/watt or less than 5 degrees celsius/watt that characterizes a thermal path from the laser device to the heat sink. The support member is composed of a thermally conductive material such as copper, copper tungsten, aluminum, siC, sapphire, alN or other metal, ceramic or semiconductor.
According to one embodiment, the present invention provides a dynamic laser based light source or light projection device comprising a micro-display, such as a micro-electromechanical (MEMS) scanning mirror, or a "flying mirror" or Digital Light Processing (DLP) chip to dynamically modify the spatial pattern and/or color of the emitted light. In one embodiment, the light is pixelated to activate some pixels and not activate others to form a spatial pattern or image of white light. In another example, the dynamic light source is configured to control or direct the light beam. This control or pointing may be accomplished by user input consisting of a dial, switch or joystick mechanism, or may be guided by a feedback loop including sensors.
According to one embodiment, the present invention provides a dynamic laser based light source or light projection device comprising a housing having an aperture. The device may comprise an input interface for receiving a signal to activate a dynamic feature of the light source. The apparatus may include a video or signal processing module. In addition, the device comprises a light source based on a laser source. The laser source includes a violet laser diode or a blue laser diode. The dynamic light signature output consists of phosphor emission excited by the output beam of the laser diode (or a combination of the laser diode and the phosphor member). Violet laser diodes or blue laser diodes are fabricated on polar-oriented, non-polar-oriented, or semi-polar-oriented gallium-containing substrates. The device may include a micro-electromechanical system (MEMS) scanning mirror, or "flying mirror," configured to project laser or laser pumped phosphor white light to a specific location of the outside world. By rasterizing the laser beam using MEMS mirrors, pixels can be formed in two dimensions to create a pattern or image.
According to one embodiment, the present invention includes a housing having an aperture and an input interface for receiving one or more signals, such as an image frame. The dynamic light system further comprises a processing module. In one embodiment, the processing module is electrically coupled to the ASIC to drive the laser diode and the MEMS scanning mirror.
In one embodiment, a laser driver module is provided. The laser driver module is adapted to, among other things, adjust the amount of power to be supplied to the laser diode. For example, the laser driver module generates a drive current based on one or more pixels from one or more signals, such as an image frame, the drive current being suitable for driving a laser diode. In one embodiment, the laser driver module is configured to generate a pulse modulated signal at a frequency range of about 50 to 300 MHz.
According to one embodiment, the present invention provides a dynamic laser based light source or light projection device comprising a housing having an aperture. The device may comprise an input interface for receiving a signal to activate a dynamic feature of the light source. The apparatus may comprise a video or signal processing module. In addition, the device comprises a light source based on a laser source. The laser source includes a violet laser diode or a blue laser diode. The dynamic light signature output consists of phosphor emission excited by the output beam of the laser diode (or combination of laser diode and phosphor member). Violet laser diodes or blue laser diodes are fabricated on polar-oriented, non-polar-oriented, or semi-polar-oriented gallium-containing substrates. The apparatus may include a laser driver module coupled to a laser source. The apparatus may include a Digital Light Processing (DLP) chip including a digital mirror device. The digital mirror device includes a plurality of mirrors, each mirror corresponding to one or more pixels of one or more image frames. The device includes a power supply electrically coupled to the laser source and the digital light processing chip.
The apparatus may include a laser driver module coupled to a laser source. The apparatus includes optics disposed proximate the laser source, the optics adapted to direct the laser beam to the digital light processing chip. The device includes a power supply electrically coupled to the laser source and the digital light processing chip. In one embodiment, a user of the device may activate the dynamic nature of the light source. For example, a user may activate a switch, dial, feel, or trigger to change the light output from a static mode to a dynamic mode, from one dynamic mode to a different dynamic mode, or from one static mode to a different static mode.
In a particular embodiment of the invention comprising a dynamic light source, the dynamic feature is activated by a feedback loop comprising a sensor. Such sensors may be selected from, but are not limited to, microphones, geophones, hydrophones, chemical sensors, e.g. hydrogen sensors, CO 2 Sensors, or electronic noise sensors, flow sensors, water meters, gas meters, gathered meters, altimeters, airspeed sensors, speed sensors, rangefinders, piezoelectric sensors, gyroscopes, inertial sensingAccelerometers, MEMS sensors, hall effect sensors, metal detectors, voltage detectors, photoelectric sensors, light detectors, photo-resistors, pressure sensors, strain gauges, thermistors, thermocouples, pyrometers, thermometers, motion detectors, passive infrared sensors, doppler sensors, biosensors, capacitance sensors, video sensors, transducers, image sensors, infrared sensors, SONAR, LIDAR, and the like.
In one example of a dynamic light signature including a feedback loop with a sensor, a motion sensor is included. The dynamic light source is configured to illuminate a location where motion is detected, and the motion is detected by sensing a location space of the motion and controlling an output beam to the location. In another example of a dynamic light signature including a feedback loop with a sensor, an accelerometer is included. The accelerometer is configured to predict where the laser source device is moving and to control the output beam to that location, even before the user of the device can move the light source to point it at the desired location. Of course, these are only examples of implementations of dynamic light sources with a feedback loop comprising a sensor. There may be many other implementations of the inventive concept that include combining a dynamic light source with a sensor.
In some embodiments, the integrated white light source device includes an electrostatic discharge (ESD) protection element. For example, an ESD protection element would be used to protect an integrated white light source from damage that may occur due to the sudden flow of current resulting from charge accumulation. In one example, a Transient Voltage Suppression (TVS) element is employed.
In certain embodiments of the integrated white light source device, the light source may be operated in an environment comprising at least 150000 ppm oxygen.
In certain embodiments of the integrated white light source device, the support member comprises a material selected from the group consisting of copper, copper tungsten, aluminum, silicon, and combinations of any of the foregoing.
In certain embodiments, the integrated white light source device comprises a microchannel cooler thermally coupled to the support member.
In some embodiments, the integrated white light source device comprises a heat sink thermally coupled to the common support member. In one example, the heat sink has fins or measures for increasing the surface area.
In some embodiments, the integrated white light source device comprises a heat sink coupled between the common support member and the heat sink.
In certain embodiments of the integrated white light source device, the optical coupler comprises one or more optical filters.
In certain embodiments of the integrated white light source device, the output light beam is geometrically configured to optimize interaction with the phosphor material.
In some embodiments of the integrated white light source device, the white light source is configured in a package. In one example, the package is hermetically sealed.
In some embodiments of the integrated white light source device, the white light sources are configured in a package, such as a flat package (flat package), a surface Mount package, such as an SMD, a TO9 can, a TO56 can, a TO-5 can, a TO-46 can, a CS-Mount, a G-Mount, a C-Mount, a micro-channel cooled package, or the like.
In some embodiments of the integrated white light source device, a reflector or lens is used to collimate the emitted white light.
In another aspect, the present invention provides an apparatus configured as a laser pumped solid state white light source operating in a reflective mode. Fig. 46 shows a schematic of such a device. The phosphor plate 4605 is illuminated by blue or violet laser light from the laser diode 4603, with the emission centerline incident at some angle α relative to the top surface of the phosphor plate 4605. Alternatively, the angle of incidence is sometimes described as an angle relative to the surface normal, equal to 90- α. In embodiments where the laser is not collimated with a lens, the laser is divergent such that the Full Width Half Maximum (FWHM) angle 2 δ of the laser is relatively large. Numeral 4602 represents the centerline direction of laser emission, 4601 and 4604 correspond to the upper and lower limits of the FWHM angle, respectively. The center line 4602 is incident on the phosphor at an angle α, while the upper extremity of the far field is incident at α - δ and the lower extremity is incident at α + δ. In other words, the angle of incidence of the laser light on the top surface of the phosphor plate 4605 varies from α - δ to α + δ across the major axis of the spot 4606. Referring to FIG. 46, the diverging laser light causes an elongated spot 4606 to appear on the phosphor plate 4605. Cross-sectional lines 4607 of the spot 4606 are shown with dashed lines parallel to the fast axis of laser propagation.
In some embodiments, the angle of incidence at which the laser light strikes the phosphor may be provided in a range between 0 degrees and 89 degrees relative to the surface normal. In one embodiment, even laser light emitted parallel to the phosphor surface (close to 90 degrees relative to the surface normal) will have some interaction with the phosphor due to divergence. There may be sufficient reasons to choose a configuration where the exciting blue laser never interacts with the surface to maintain its coherence. The angle of incidence between the laser beam and the phosphor member includes an angle of incidence with respect to the fast axis and an angle of incidence with respect to the slow axis. At least one of the angle of incidence with respect to the fast axis or the angle of incidence with respect to the slow axis is an off-normal angle ranging between 0 degrees and 89 degrees. In another embodiment, a 0 degree laser beam incident normal to the phosphor surface will also have +/-20 degrees of light from the surface normal, since there will be divergence when the laser is provided without collimation. This may also be an interesting configuration where the phosphor is located at the base of a parabolic mirror, the laser diode is mounted in space, and the collection and propagation of the light emitted by the phosphor is only truly reflected light. In some embodiments, for most configurations of having a laser-based white light source in a reflective mode or a transmissive mode, the excitation laser may be configured to strike the phosphor surface with the laser beam at an angle of incidence with respect to the fast axis, the angle of incidence being between 25 degrees and 45 degrees. The angle of incidence between the laser beam and the phosphor member without any collimation includes an angle of incidence with respect to the fast axis, and is characterized by an angular range between 5 degrees and 65 degrees, due to an angular divergence of about +/-20 degrees without collimation.
In some embodiments, the laser is incident as a pump laser into the phosphor plate for exciting the phosphor material to produce emitted light having a longer wavelength than the pump laser. Typically, the spectrum of the emitted light is substantially white light emission. In some embodiments, variations in the angle of incidence of the pump laser light from the laser diode 4603 have several effects on the operation of the apparatus. First, the white light emission spectrum of the device comes from a portion of the pump laser light that is reflected or scattered from the top surface of the phosphor plate 4605, or from another portion of the scattering center deep in the volume of the phosphor plate 4605. Different angles of incidence may cause a change in the proportion of incident laser light scattered from the top surface, and hence cause the spectrum of the white light emission to be non-uniform over the same area of the spot 4606. Secondly, since the relationship between the laser power emitted from the laser diode 4603 and the angle is symmetrical with respect to the emission center line, a change in the laser incident angle requires that the laser power per unit area of the phosphor plate 4605 also change over the area of the spot 4606. This may result in the intensity of the white light emitted varying significantly over the area of the spot 4606. Third, the optical properties of phosphor plate 4605 can cause spatial non-uniformity of the emission spectrum and spectral variations measured at different angles in the far field, which would be true for both embodiments with non-collimated pumped lasers and collimated pumping.
If the phosphor plate 4605 contains many scattering centers in the top surface or body, the direction of travel of the pump laser light transmitted into the phosphor plate 4605, as well as the longer wavelength emitted light emitted by the phosphor member (after it absorbs the pump laser light), will be highly randomized due to the many scattering events it experiences. Examples of highly scattering phosphor members would include, but are not limited to, composite or polycrystalline phosphor materials. Alternatively, the phosphor member is composed of a sintered phosphor powder of uniform composition. The powdered phosphor material exhibits a strong optical anisotropy such that the random orientation of the phosphor particles results in strong scattering of light when switching between particles. The sintered phosphor material is a solid with a large void volume fraction in a vacuum or in an air-filled environment. The refractive index of phosphors differs significantly from air or vacuum. Furthermore, sintered phosphor materials based on phosphors with two or more compositions or phosphors combined with some matrix material that has sufficiently different refractive indices of the fluorescent components or of the matrix material, also differ greatly in refractive index. In these types of sintered phosphor materials, scattering is very significant at the interface between these phosphor materials of different compositions or at the interface defined by the foreign matrix material. Furthermore, the intensity or nature of the scattering may also vary strongly with the wavelength of the light, due to, for example, strong dispersion of the optical index with wavelength. In this case, the scattering of the pump laser light may be significantly different from the scattering of the phosphorescent emission light, and thus the spatial and angular emission spectra remain inhomogeneous.
On the other hand, if the phosphor plate 4605 is made of a single crystal phosphor, its composition and crystal orientation are highly uniform and contain no or hardly any scattering centers within the body of the phosphor member. In this case (and where the scattering properties of the phosphor material are weak), most of the pump laser light entering the phosphor member will be absorbed by the phosphor and down-converted to produce emitted light, since there is little chance of light being scattered back from the phosphor. The uniformity of the white light spectrum of the phosphor emission at different viewing angles is then limited by the difference between the intensity of the pump laser light scattered at the top (excitation) surface of the phosphor plate 4605 and the intensity of the angular distribution of the longer wavelength white light emission from the phosphor. Furthermore, light emitted by phosphors having longer wavelengths may propagate through the bulk of the phosphor member without significant scattering. This single crystal phosphor plate based laser pumped solid state white light source configuration is problematic because a significant portion of the phosphor emitted light can pass through the extent of phosphor plate 4605 and be emitted at any edge of the phosphor member without resulting in white light emission. Furthermore, if there is a small amount of scattering by the volume or upper and lower surfaces of the phosphor, the phosphor emission light propagating away from the area of the spot 4606 may scatter out of the phosphor plate 4605 and be collected by any focusing optics. This will result in a halo or halo of longer wavelength around the white spot 4606.
In one particular aspect, the present disclosure provides a method of introducing features into a phosphor member intended to improve spatial or angular uniformity of a white light spectrum of phosphor emission light converted from incident laser light. Optionally, these features are provided on the surface of the phosphor member or within the bulk to alter the scattering pattern of the laser light or to alter the angular distribution of the phosphor emitted light.
In one embodiment, the feature introduced into the single crystal phosphor member comprises a modification of the surface morphology or internal structure of the phosphor member. Alternatively, the modifications may be some defect areas formed by a focused laser beam. In particular, laser cutting techniques may be applied. In one example, a so-called stealth laser cutting technique is used, which is a laser-based material cutting technique that uses a laser having a wavelength that is not strongly absorbed or reflected by the material. The laser beam for stealth dicing is focused by a lens so that the point of maximum optical power density is within the thickness of the material being diced. When the peak power density of the focused laser beam exceeds the material dependent threshold, nonlinear effects will result in very high absorption only near the point of maximum optical power density. While elsewhere in the laser path, the laser beam is not focused sufficiently to cause nonlinear effects that drive strong absorption, and the absorption remains relatively weak. Optionally, the position or focal length of the focusing lens may be adjusted to control the depth of the point of maximum optical power density within the cut material. Optionally, a Translatable stage (Translatable stage) may be used to move the cut material laterally under the laser optical system, thereby allowing laser cutting of arbitrary patterns at one or more depths within the cut material.
In an alternative example, conventional ablative laser scribing is used, where the scribing laser wavelength is strongly absorbed by the scribing material, causing the scribing material to ablate through the entire thickness of the scribing material or until the scribing laser is sufficiently attenuated that such ablation no longer occurs. Stealth laser dicing has advantages over conventional ablative laser dicing in that defect regions can be formed within the thickness of the diced material and surrounded by undamaged material by a narrow border region. This allows the scattering features to be formed throughout the thickness of the material without cutting through the entire thickness of the material, resulting in the material separating into pieces. This technique also does not require cutting from both sides of the material.
Damage to a surface or internal structure by a focused laser beam includes the formation of one or more voids, cracks, and areas of melted and resolidified material. These defects in the material can act as optical scattering centers and can be used to alter the way light propagates in the material. In case of a phosphor plate for manufacturing a laser-based white light illumination system in reflective mode, the pump laser light is incident on the top excitation surface of the phosphor plate at a certain fixed angle. A portion of the pump laser beam is reflected from the top excitation surface of the phosphor plate, while the remainder is transmitted into the phosphor plate, scattered by multiple scattering centers on the excitation surface or inside the phosphor plate, and absorbed by the phosphor and converted to longer wavelength phosphor emitted light and output again through the top excitation face. In another case of a phosphor plate for manufacturing a white light source based on laser light in a transmissive mode, pump laser light incident through a top excitation surface of the phosphor plate is scattered by a plurality of scattering centers inside a body of the phosphor plate while being converted into phosphor emission light. A portion of the pump laser beam is transmitted through the phosphor plate to mix with the light emitted by the phosphor, thereby outputting a white light emission through the emission surface (alternating with the excitation surface, typically the bottom surface) of the phosphor plate. Designing different scattering centers inside or on the surface of the phosphor slab becomes important to control the white light emitted by the phosphor, so that the phosphor has an enhanced intensity in a controlled direction, spectral range and spot size in either the reflective or transmissive mode.
Fig. 47 is a schematic diagram illustrating a phosphor plate including a defective region according to some embodiments of the present invention. As shown, phosphor plate 4701 includes a defective area created by stealth laser dicing. A continuous defective region 4702 having a linear shape in one dimension through the phosphor plate is completely embedded in the phosphor plate 4701. The continuous defective region 4702 is characterized by having a width 4703, a vertical extent 4705, a distance 4706 below an upper surface 4708 of the phosphor plate 4701, and a distance 4704 above a lower surface 4709 of the phosphor plate 4701, for example. Alternatively, a discontinuous defective region 4707 may be included. The discontinuous defect region 4707 is characterized by a plurality of linear defect portions having different lengths along the same dimension on the phosphor plate 4701, and other characteristics are substantially similar to those used to characterize a continuous defect region. Although the linear nature of the defect region is shown in fig. 47, the scribe feature of the defect region may be of any shape, limited only by the Translation capability (Translation capability) of the stage used to prepare or program the stealth laser cut. For example, circular or curved features, randomly positioned features, dot and hexagon patterns, and the like may be created.
Fig. 48 is a cross-sectional view illustrating an alternative phosphor plate including replacement defect regions according to some embodiments of the present invention. In one embodiment, the phosphor plates contain defective areas resulting from stealth laser dicing. For phosphor plate a, multiple defective regions 4802 are created by one laser pass, where each defective region is completely enclosed within the bulk of the phosphor plate. Optionally, the defect region 4802 is located at a uniform distance below the upper (excitation) surface of the phosphor plate. For another phosphor plate B, multiple passes of laser light produce multiple defective regions 4803. Each defect region formed during each laser pass does not overlap other defect regions formed by previous laser passes. Optionally, the depth of the defect area below the upper surface of the phosphor plate is controlled by the position or focal length of the laser focusing lens. For yet another phosphor plate C, the plurality of defective regions 4804 is created by multiple passes of laser light, with successive passes of laser light configured to create overlapping damage regions and acting as scattering centers continuously through the thickness of the phosphor plate. For yet another phosphor plate D, the plurality of defective regions 4805 are generated by a plurality of laser passes, with successive laser passes configured to generate non-overlapping damage regions at different depths of the phosphor. Optionally, the lateral position of the damaged area varies at each depth. Such a configuration would be advantageous when it is desired to have variations in the amount of scattering from different depths in the phosphor plate. This configuration will also provide scattering centers at all depths of the device without the need for full-thickness cuts that would result in the phosphor plate separating into multiple discrete pieces.
In some embodiments, longer wavelength light is emitted by the phosphor material from the same area of size, shape and location on the excitation surface of the phosphor plate as the incident pump laser spot. In other words, the white spot has a uniform ratio of pump laser to phosphor emission over its entire area when imaged by the optical element. If the phosphor plate contains an insufficient density of scattering centers, as in the case of a single crystal phosphor, the longer wavelength light emitted by the phosphor will be trapped in the phosphor plate and propagate away from the pump laser spot area and then be scattered out of the phosphor plate. This results in a light spot consisting of a white central spot surrounded by a yellow halo.
In one aspect, the present invention provides a method of forming a defect region as a scattering center in a phosphor plate to improve its scattering properties. In some embodiments, the defect region is configured to surround the pump laser spot and scatter the light emitted by the phosphor that would otherwise propagate through the phosphor and may form a yellow halo or be wasted at the edge of the phosphor plate. Fig. 49 is a plan view illustrating (a) laser spots irradiated on a phosphor plate according to some embodiments of the present invention; (B) One or more defect regions on the phosphor plate in a horizontal direction to confine the laser spot; (C) One or more defective areas in the vertical direction on the phosphor plate to confine the laser spot. As shown in part a of the figure, the laser spot 4902 is the region illuminated by the incident pump laser light surrounded by a halo or halo 4903 of the long wavelength phosphor emitted light. In part B of the figure, the defect regions are formed by laser cutting and are configured as two sets of horizontal lines 4904 and 4905. Optionally, two sets of defect regions 4904 and 4905 are formed around the pump laser spot 4902. Optionally, the horizontal line defects are configured to prevent light emitted by the phosphor from propagating a significant distance from the pump laser spot 4902 before being scattered out of the phosphor. In section C of the figure, one or more vertical passes in the stealth laser dicing process are performed to create defect regions configured as two sets of vertical lines 4906 and 4907 that act as scattering centers that prevent light from propagating a significant distance within the phosphor. Alternatively, two sets of vertical defect regions 4906 and 4907 are formed around the pump laser spot 4902 in addition to the two sets of horizontal defect regions 4904 and 4905.
In some other embodiments, the laser-cut defect regions are configured as concentric circles or ellipses around the pump laser spot. In some additional embodiments, the defect regions are configured as squares, rectangles, hexagons, or other polygons, among other shapes. In some embodiments, scattering centers are formed in the region of the laser spot to improve scattering of one or both of the laser pump light and the phosphor emission. Depending on the embodiment, different shapes can be chosen to produce the best effect, i.e. a brighter white light spot substantially at the pump laser spot, with a substantially uniform spectrum over the spot area.
In some embodiments, the scattering centers generated due to damage caused by laser scribing are arranged in such a way that the density of defect regions is not uniform within the pump laser spot. Fig. 50 is a cross-sectional view of a pump laser incident on a phosphor plate containing defect regions that are non-periodically spaced in a direction parallel to the projection of the laser fast axis, according to an embodiment of the invention. In this example, the laser diode 5003 irradiates the phosphor member 5005. The emission directions 5001, 5002 and 5004 represent pump lasers with relatively divergent beams around the center line 5002. The emission direction 5001 corresponds to an upper limit, and the emission direction 5004 corresponds to a lower limit of the full width at half maximum of the pump laser light. On the top surface of the phosphor plate 5005, the upper and lower limits of the pump laser beam define the area of the pump laser spot. Referring to fig. 50, a plurality of defect regions 5006 are formed in the body of the phosphor plate 5005 by laser scribing. The pitch of defect regions 5006 varies parallel to the laser spot length in a direction parallel to the laser fast axis projection. Optionally, the effect of introducing such a pitch variation is to change the scattering and extraction efficiency of the pump laser and phosphor emissions over the pump laser spot area. Regions with widely spaced laser scribing features will have less scattering and will exhibit longer path lengths for the phosphor emitted light to travel from one side of the pump laser spot to the other. Such a configuration would be advantageous where the surface texture of the phosphor is such that the proportion of laser light scattered from the top surface of the phosphor increases as the angle of incidence decreases. By introducing a non-uniform density of scattering centers, the light emitted by the phosphor can preferentially diffuse from one region of the pump laser spot to another to compensate for the reduced pump efficiency.
In a separate embodiment, the scattering centers formed in the phosphor by laser scribing are arranged in a manner that they have different lateral distributions and densities at different depths in the phosphor. One advantage of this configuration is that it enables one set of scattering centers near the surface of the phosphor to be configured to efficiently scatter short wavelength pump laser light, while one or more sets of scattering centers near the middle or bottom of the phosphor plate are configured to efficiently scatter light emitted by the phosphor having longer wavelengths. Since the short wavelength blue light will be strongly absorbed in the phosphor, the two sets of scattering centers are spatially separated, providing selectivity in controlling the scattering distribution of the pump laser light relative to the light emitted by the phosphor.
In an alternative embodiment, the non-collimated pump laser has a diverging beam, such that the pump laser is incident on the phosphor surface at different angles of incidence at different locations. Variations in the angle of incidence can result in angular variations in the specularly reflected laser light, variations in the angular distribution of diffusely scattered light from the rough random phosphor surface, and variations in the proportion of laser pump light transmitted into the phosphor material. In some embodiments, the surface texture is modified to induce spatial variation in the transmission of the pump laser light into the phosphor, or spatial variation in the diffuse reflection of the pump laser light from the top surface of the phosphor, in order to modulate the white light intensity and color point within the laser spot region (of the phosphor emission).
As an example, fig. 51 shows a schematic cross-sectional view of a pump laser light incident on a phosphor plate provided with a non-uniform Chirped pattern (Chirped patterning) of the phosphor surface, according to an embodiment of the present disclosure. The laser diode 5103 illuminates the phosphor member 5105. The phosphor surface is patterned with regions where the surface texture is modified to induce a change in the transmission of the pump laser light to the phosphor member 5105. The patterned surface region 5106 corresponding to the shallowest incident angle 5101 has a patterned surface texture including steep sidewalls inclined toward the pump laser light incident at an angle closer to normal incidence. Each steep sidewall is characterized by a width that is visible from the incident laser light. Optionally, the plurality of steep sidewalls are substantially linear strips parallel to each other that surround in a plurality of rows a portion of the spot area on the patterned surface area 5106 that receives the laser beam having the shallowest incident angle. Optionally, the plurality of steep sidewalls are curved to substantially match the shape of the beam spot region. In addition, another patterned surface region 5107, corresponding to the center line emission angle 5102 of the pump laser, is patterned with linear stripes shallower than the linear stripe sidewalls in region 5106, so that the pump laser incident around the center line is still at an angle closer to normal incidence. Furthermore, the other patterned surface region 5108, which corresponds to the laser with the steepest angle of incidence 5104, is not textured because the pump laser light is already incident on the phosphor at some angle close to normal incidence.
In some embodiments, the phosphor plate is patterned using a wet or dry etch process, wherein features are defined using a nanoimprint lithography or optical lithography process. These features may also be formed by micromachining processes such as laser ablation. These features will form so-called photonic crystals, where a periodic variation of the refractive index of the optical medium will result in a combination of allowable and unallowable frequencies of light and propagation directions through the medium. Optionally, the optical medium (or photonic crystal) is part of a phosphor plate. Optionally, the optical medium is attached on top of the phosphor plate. Such an embodiment presents one of two advantages. First, the photonic crystal can be designed such that light from the pump laser, with well-known frequency and angle of incidence onto the phosphor plate, can be efficiently scattered into the phosphor. In some embodiments, the geometry of the photonic crystal is spatially varied such that at a point in the laser beam spot region projected directly onto the phosphor plate, the photonic crystal is optimized such that the laser is incident at a particular angle to the laser beam spot region to couple to the phosphor plate. For this purpose, the photonic crystal may be configured to be one-dimensional or two-dimensional. Such a configuration is very advantageous for manufacturing a laser-based solid-state white light source with a violet or ultraviolet pumped laser. In such devices, the pump laser hardly utilizes the luminous efficiency of the white light source, and there is no need to scatter a portion of the pump laser into the emitted white light spectrum to produce the white light spectrum.
In such a configuration, it is highly advantageous to efficiently couple the laser light into the phosphor. In one example, fig. 52 shows a schematic cross-sectional view of pump laser light incident on a phosphor plate configured as a photonic crystal, according to an embodiment of the present disclosure. Referring to fig. 52, defect regions 5206 in the photonic crystal 5205 are periodically spaced in a direction parallel to the projection of the laser fast axis. The laser diode 5203 irradiates the photonic crystal 5205. The laser beam emission from the laser diode 5203 diverges with a beam direction that changes from a first line 5201 to a second line 5204 around a center line 5202. The first line 5201 and the second line 5204 correspond to an upper-bound direction and a lower-bound direction of laser emission around the center line 5202, respectively. Alternatively, the upper or lower bound direction refers to the full width at half angle, respectively. Alternatively, the photonic crystal 5205 is part of a phosphor plate, patterned and etched using a mask to create a one-dimensional or two-dimensional pattern 5206. Optionally, the pattern 5206 includes air-filled voids in the phosphor plate. Optionally, the voids are filled with a dielectric material.
In another embodiment, it is a further advantage that in the thick slab of the phosphor member, the light emitted by the phosphor is output in all directions with relatively equal probability. As previously mentioned, this emission is undesirable because most of the phosphor-emitted light is output perpendicular to the thickness of the phosphor plate, and is therefore either guided by total internal reflection or traverses the width of the phosphor plate before encountering the scattering center. Such laterally guided modes are a particularly important problem in single crystal phosphors with few scattering centers. Adding a photonic crystal to the phosphor plate can improve performance by suppressing the transmission of the laterally guided mode, thereby shifting most of the phosphor emission of the phosphor to vertical emission. A second advantage is that the photonic crystal can be designed to expand or contract the emission angle of the phosphor plate to better match the emission angle of the scattered pump laser, which will reduce color non-uniformity over the viewing angle of the white light spot.
In one embodiment, a nanoscale surface roughness texture may be formed to provide the desired photonic crystal scattering centers, or to provide phosphor feature scattering centers directly. For example, a moth-eye structure comprising patterned or nano-scale random pits is provided to the surface of the photonic crystal. Such a coarse texture of small scale can act to reduce the average refractive index of the surface. Reducing the surface index of refraction is desirable because it reduces a) diffuse reflection, b) fresnel reflection, and c) total internal reflection of light within the photonic crystal. Thus, it is more advantageous to use moth-eye roughness texture on the photonic crystal surface to promote directional scattering of the pump laser light, thereby enhancing phosphor conversion to produce phosphor emission. Alternatively, these nanoscale structures are typically created by high-energy plasma etching of the surface of the material and appropriate reactive chemical selection of the material. Fig. 53 shows such a structure on the surface of a phosphor plate according to an embodiment of the invention.
Referring to fig. 53, the laser diode 5303 illuminates the phosphor member 5305. The surface of the phosphor member 5305 is patterned, with a plurality of regions 5306 in the surface modified into a moth-eye structure. The region 5306 corresponding to the shallowest incident angle 5301 is provided with a patterned inducing steep sidewall facing the pump laser such that the laser light is incident on the patterned surface of the phosphor member 5305 at an angle closer to normal incidence. The region 5307 corresponding to the centerline emission angle of the pump laser beam is patterned with shallower sidewalls than the sidewalls in the region 5306, so that centerline light from the pump laser is incident on the patterned surface of the phosphor member 5305 at an angle closer to normal incidence. These are just one example of many possible nanoscale rough textures that may be provided to form photonic crystals or directly to the excitation surface of the phosphor member to produce the desired scattering of the pump laser light and phosphor emission to improve the beam quality of the white light source. Alternatively, the photonic crystal having the moth-eye structure may be applied to a white light source based on a reflection mode and a transmission mode of a phosphor.
In one embodiment, the present invention provides an encapsulated white light source having a common support member. Fig. 54 is a perspective view of an encapsulated white light source with a common support member according to an embodiment of the present invention. Referring to fig. 54, a packaged white light source includes at least one laser diode 5402, a phosphor member 5403, a shaped support member 5401, electrical terminals 5408 and 5409, and a wire 5404 that forms an electrical connection with the laser diode. It will be appreciated that additional elements may be included in this encapsulated white light source.
In a particular embodiment, the shaped support member 5401 includes a substantially flat surface portion to which the phosphor member 5403 is attached using solder, brazing, a sintered material, or a thermally conductive adhesive. In another particular embodiment, the shaped support member 5401 includes one or more wedge-shaped portions having an inclined plane 5405 to which one or more laser diodes 5402 are attached. The laser diode 5402 is attached using solder, sintered material, or thermally conductive adhesive. The inclined plane 5405 arranges the laser diode 5402 in such a way that a laser beam emitted therefrom is guided to the top surface of the phosphor member 5403 with an incident angle in the range from 0 degrees to 90 degrees (measured from the normal to the top surface of the phosphor). Typically, the angle of incidence is in the range of 5 to 65 degrees relative to the surface normal. This requires that the slanted plane 5405 not be parallel to the flat surface portion to which the phosphor member 5403 is attached. In addition, the apertures of the one or more laser diodes 5402 are positioned at a higher elevation than the top surface of the phosphor member 5403. Of course, top or bottom or surface normal are relative terms depending on the particular package geometry and are not limited to a particular orientation.
In an embodiment of an integrated white light source, heat may be extracted from the bottom of the shaped support member 5401. For example, by attaching the shaped support member 5401 (itself selected from a good thermally conductive material) to a PCB or heat sink by means of soldering, brazing, mechanical fasteners, or using a highly thermally conductive adhesive, this can efficiently transfer away the heat generated by the laser diode 5402. The heat dissipation path from the bottom of the laser diode 5402 to the bottom of the shaped support member 5401 is optimized under the constraints of the overall size of the integrated white light source and the relative positions of the laser diode 5402 and the phosphor member 5403. The cross-section of the contoured support member 5401 increases with increasing distance from the heat source. The primary heat source is a ridge located on top of the laser diode 5402. In one embodiment, the functional relationship of the cross-section as a function of distance from the heat source is: the cross-section is greater than or substantially equal to the distance of the square from the heat source.
Alternatively, the molding support 5401 is made of a material having high thermal conductivity. Alternatively, the shaped support member 5401 is made of Cu or a Cu-containing alloy. In certain embodiments, the shaped support member 5401 is made of a single piece of material without joints, as this provides the lowest thermal resistance from the heat source to the heat sink. Alternatively, the molded support member 5401, which includes a flat surface portion and one or more wedge portions, may be manufactured as a single-piece substrate structure for a Surface Mount Device (SMD) package through a stamping process or through a material reduction machining process. In an alternative embodiment, the shaped support member 5401 includes two or more separate pieces joined using a welded, brazed, or sintered material. For example, the flat surface portion belongs to the primary substrate structure as a separate component. The flat surface portion serves to support the phosphor member 5403. The primary substrate structure also has a flat bottom for mounting to a heat sink. The mounting material is optimized by heat conducting bonds or materials. Also, one or more wedge-shaped portions may be formed as several inclined planes 5405 from a single piece of complex shape as one or more auxiliary substrate structures for supporting the laser diode 5402. Optionally, the one or more wedge portions are attached to the planar portion of the primary baseplate structure. The attachment between the secondary substrate structure and the primary substrate structure may then be thermally conductive. For example, the height of the phosphor member 5403 can be adjusted by inserting a thermally conductive thin riser (not shown) between the flat bottom portion of the shaped support member 5401 and the phosphor member 5403.
Optionally, the geometry of the shaped support members 5401 is optimized to minimize blocking of light emitted from the top of the phosphor members 5403. During the design of the encapsulated white light source, any volume of the molded support member 5401 that is likely to block light while substantially not contributing to heat extraction from the laser diode 5402 is removed. In a particular embodiment, a relief feature is provided to the inclined plane 5405. Any shape of mitigating features is possible.
For example, one or more relief features 5406, 5407 are formed in a planar shape for the purpose of allowing wire bonds 5410 to extend unobstructed between laser diode 5402 and electrical terminal 5408. Shaped support member 5401 is typically made of bare metal, with bonding wires 5410 being bare metal without electrical insulation. In order to prevent short circuits, the bonding wires 5410 must therefore not contact the support members 5401. Wire 5410 can be assembled with a certain amount of loop height with limited ability of the loop to hinder features. However, in subsequent process steps, the rings may sag and require a certain amount of vertical gap margin to account for process variations. For the reasons described above, the mitigating features 5406 and 5407 are critical parts of the program support member 5401 design. For purposes of comparison, fig. 55 shows the results for a shaped support member 5501 designed without a mitigating feature. To achieve an unobstructed bond wire 5510 between laser diode 5502 and electrical terminal 5508, the height of electrical terminal 5508 has been increased. This is not a preferred embodiment because the increased height places the electrical terminals 5508 in the path of light emitted from the phosphor member 5503, which results in a reduction in light output from a white light source.
Optionally, the shaped support member for supporting the one or more laser diodes and the phosphor member is made of a single piece of thermally conductive material. Optionally, the shaped support member is configured to support a phosphor member having a flat surface portion, and to support a plurality of laser diodes having a plurality of wedge-shaped portions comprising inclined faces having different wedge angles with respect to a surface normal of the flat surface portion. According to an embodiment, each wedge portion further comprises a plurality of mitigation members associated with the ramps. Fig. 56 illustrates one embodiment of a shaped support member 5601. This embodiment has two tilted planes 5604 and 5605 for supporting two laser diodes (not shown), and each tilted plane has a respective mitigation feature 5607 or 5608.
Fig. 57 shows some additional elements of a laser-based integrated white light source according to an embodiment of the present invention. As shown, the integrated white light source 5700 includes a shaped support member substantially similar to the shaped support member 5601 illustrated in fig. 56. It has two inclined faces 5705 and 5706 for supporting two laser diodes 5703 and 5704, respectively. Furthermore, the integrated white light source 5700 includes one phosphor member 5702 disposed in a flat region between two inclined planes 5705 and 5706. Furthermore, the integrated white light source 5700 includes several electrical terminals 5708, 5709. A plurality of wires 5710 form an electrical connection between electrical terminal 5708 or 5709 and laser diode 5703 or 5704. Further, the integrated white light source 5700 includes a frame member 5701. Optionally, the frame member 5701 includes a base and a peripheral edge for providing a pocket for housing all of the elements of the integrated white light source described above. It will be appreciated that more additional elements may be included in this integrated white light source.
In another embodiment, an integrated white light source package includes a cover member coupled with a frame member. Fig. 58 illustrates an integrated laser-based white light source package, according to another embodiment of the present invention. As shown, the integrated white light source 5800 includes a cover member 5801 disposed on top of the integrated white light source 5700 of fig. 57. In particular, the cover member 5801 is attached to the top surrounding edge of the frame member 5701 to form a fully assembled package. Optionally, a cover member 5801 is sealed to the frame member 5701 to prevent the cavity in the assembled package from being disturbed by the external environment. Optionally, the cover member 5801 includes at least one transparent region that enables light emitted by the phosphor member to exit the package. Fig. 58 shows a perspective view of an embodiment of an integrated white light source package in which a transparent cover member 5801 is assembled with a solid frame of a white light source 5700, the embodiment having a partial view within a cavity in which two laser diodes are supported by a shaped support and connected to electrical terminals by wire bonds and configured to emit laser light to induce excitation of the phosphor member to re-emit electromagnetic radiation to substantially form white light. The material of the transparent region of the cover member 5801 can be a material that transmits at least 50% white light in at least a portion of the visible spectrum. Examples of such materials include soda lime glass, borosilicate glass, quartz, and sapphire. In addition, the material may be coated with a thin optical coating on one or more sides to change the transmission characteristics of the transparent region. Examples of coatings include broadband antireflective coatings.
Referring to fig. 58, the transparent region of the cover member 5801 includes one or more patterned regions 5805. The transmission characteristics of the patterned region 5805 can be modified to improve light emission quality. In one embodiment, the one or more patterned regions 5805 absorb and/or reflect light having an excitation wavelength of the laser light from the laser diode and are spatially configured to prevent laser light that experiences fresnel reflections at the phosphor member surface from exiting the package. In this embodiment, the design of the patterned region 5805 takes into account the known divergence of the laser diode along the slow and fast axes. In combination with information about the relative positions and angles of the laser diode, the phosphor member surface and the cover member, the partial area on the cover member where the fresnel reflected laser light intersects the cover member can be calculated. The calculated area may be expanded by an appropriate amount to account for variations in laser divergence, as well as variations in lateral alignment of the cover member 5801 relative to the laser diode position. The calculated area including the optional magnification may then constitute the patterned area 5805.
In another embodiment, the patterned region 5805 on the cover member 5801 is designed to prevent other unwanted light from exiting the package. The unwanted light includes stray light reflected from bonding wires on the laser diode, as well as light from the back side of the laser diode (including low level light emitted during normal operation or higher level light emitted in case of failure of the laser diode). For example, degradation of the back-side coating may produce some undesirable light. Patterned regions 5805 can serve as safety features for the white light source, as they can prevent potentially harmful laser light from exiting the package. With this design, the patterned region 5805 can be located near the laser diode, along the length of the laser diode, particularly near the back of the laser emission.
Alternatively, the patterned region 5805 shown in fig. 58 is configured according to a design satisfying the above two embodiments. Thus, the patterned regions 5805 on the cover member 5801 are designed to prevent unwanted light from several different sources from escaping the package: 1) laser light that undergoes Fresnel reflections at the phosphor member surface, 2) stray light reflected from bonding wires on the laser diode, and 3) light from the back of the laser diode.
Optionally, the patterned region 5805 may include a coating on one or both sides of the cover member 5801. The coating may be a thin film metal coating, including single or multiple layers of metal. The coating may also include organic or inorganic pigments printed on the surface by screen printing, ink jet printing, or other processes. The printed material may be heat treated after printing to obtain the desired material properties.
Alternatively, the patterned region 5805 may also include a tab portion that is separate from the cover member 5801 but located adjacent to the cover member 5801. For example, the patterned region 5805 may be a separate part made of a thin metal sheet of a specific shape, and placed in a position as shown in fig. 58. The individual components may be fabricated by methods commonly used to fabricate metal stencils, including laser cutting, photochemical etching, or electroforming. Additional mechanical operations, such as stamping and metal forming operations, may be employed to create the three-dimensional structure. In an assembled package incorporating a white light source 5800, individual portions of the patterned region 5805 can be held in place by compression between a cover member 5801 and one or more interior surfaces of the package (e.g., a molded support member or frame member).
Since lasers are sensitive to dust/contamination, it is important that the design of the laser-based integrated white light source package ensures a clean environment for the laser to work throughout the life of the product. This is typically accomplished by sealing the device from the environment and backfilling the encapsulated space with a controlled environment (e.g., N2 or CDA gas). A partial or hermetic seal is required at the sealing interface, for example between the cover and the frame, to limit and control the ingress of unwanted contaminants (dust, moisture, corrosives) into the cavity in which the laser is located. Epoxy is one possible partial hermetic sealing technique for such devices, but Volatile Organic Compounds (VOCs) released by the epoxy during the curing/sealing process can eventually enter the cavity and cause unwanted organic residues to remain on the laser facet and in operation cause charring of these residues, ultimately resulting in damage to the laser device operation and early failure of the device.
In one embodiment, the present invention provides a method of sealing a member in an assembled package of an integrated white light source as described herein. Optionally, the method includes sealing the interface of the assembled package with a B-stage epoxy to reduce VOC contamination inside the package. In particular, the method includes first applying a B-staged epoxy to a first surface of a first member to be encapsulated. Optionally, as shown in fig. 59A, the first member comprises a cover member 5901. Optionally, the first member is a window member. Optionally, the first surface is a bottom surface of the window member. Optionally, a B-stage epoxy 5902 may be applied to a peripheral edge region of the bottom surface of window member 5901.
The method also includes curing the B-stage epoxy applied to the first member isolated from the second member to be packaged. Optionally, as shown in fig. 59A, partial curing of the B-stage epoxy 5902 substantially releases the VOCs 5909 therein to form a low outgassing state. Optionally, as shown in fig. 59B, the second member comprises a support member 5900 to hold a laser diode 5910 having a face. Optionally, the support member 5900 is a frame member having a second surface configured to attach with the first surface of the first member. Optionally, the second surface is a top surface of a wall ridge or a peripheral edge of the frame member. Additionally, the method includes attaching the first member to the second member by attaching the first surface to the second surface via a partially cured B-stage epoxy. Further, the method includes final curing the B-stage epoxy in a low outgassing state to seal the joint between the first surface and the second surface. Alternatively, as shown in fig. 59B, the release of VOCs 5919 is significantly reduced during the final cure. Alternatively, the B-staged epoxy may be one of a class of epoxy materials that have high thermal conductivity and can be cured in a two-step process to greatly reduce VOCs, or a combination of the above.
In another embodiment, the method includes sealing an interface of the component package with a sintered nanometal to reduce exhaust gas contamination inside the package. In particular, sintered nanometals may be used to seal the first and second members of the integrated white light source to reduce or eliminate the need for an epoxy seal. Optionally, the sintered nanometals provide a solid sealed joint between the two surfaces of the cover and the frame. Optionally, the sintered nanometal is manufactured at a temperature low enough to allow manufacturability of the sealing device. There are many possible nanometal sintered solders that can be used, including Ag and Cu nanometals.
In one embodiment, the sintered nanometal sealing technique may be applied to hermetic packaging, slug (slug) attachment, and window attachment. In one example, the sintered nanometal encapsulation technology is essentially a high power semiconductor packaging technology. Fig. 60 is a schematic diagram illustrating a hermetically sealed package with a window attachment and an insert attachment, in accordance with an embodiment of the present invention. The metal insert 6002 may be bonded to the ceramic frame 6001 by various processes, depending on the application requirements. For high power, sealing applications, this is typically achieved by brazing the metal insert 6002 to the ceramic frame 6001 in a very high temperature process in the range of 650-850 ℃. Due to the high temperature process, the accuracy of the placement of the insert 6002 within the frame 6001 is difficult to control and can result in misalignment of the block strip 6002 and frame 6001 after brazing.
For light emitting device packages, lasers typically require a sealed environment for good reliability. As shown in fig. 60, a window member 6005 is typically made of soda lime glass, borosilicate glass, quartz, and sapphire, and is attached to a surface of an encapsulation frame 6001 by a related process, and the encapsulation frame 6001 is sealed by some sealing material 6004. For example, hermetic sealing of an integrated white light source package may be achieved by attaching a window member to a surface of the package frame using an epoxy and metal alloy solder to form a joint 6004 between the window member 6005 and the frame member 6001. Alternatively, joint 6004 may be made using one or more epoxy resins selected from B-stage epoxy resins suitable for performing the two-stage curing process described earlier. Alternatively, the joint 6004 may be made using a solder such as AuSn, in, pbSn, SAC305, or the like. Conventional epoxy bonding is unsuitable because it outgases during the curing process, and these outgassed materials are ultimately encapsulated within the package. Soldering the window to the package can reduce outgassing problems, but can raise the process temperature required for good bond sealing.
Optionally, the attachment of window member 6005 to ceramic package frame member 6001 using solder may provide a hermetic seal between the window and the package, making the cavity space a well controlled environment for laser operation. In order for most solders to make good sealing contact, the ceramic surface of the frame member 6001 and the glass surface of the window member 6005 will need to be coated with a coating that typically comprises an inert metal layer (such as Au, pd, ag, os, or Pt) in preparation for reflow soldering. These metal coatings provide a smooth, wetted surface for the solder alloy.
In one embodiment, sintered nanometals may be used as a soldering technique that may improve the joint between the window member and the frame member of an assembled package incorporating a white light source. Sintered nanometals used as solders may provide a lower temperature thermal process and provide better control and placement accuracy for the final package. There are many possible nanometal sintered solders that can be used, including Ag and Cu based nanometals. These nanometal materials can form solid state junctions with high thermal conductivity ranging from 75W/mK to-300W/mK. The manufacturable process flow for these materials includes paste dispensing and 250 ℃ curing to form joints. These joints can be sealed when sufficient paste is used to form a strong, continuous joint. Since the nano metal material is sintered in this process, it is difficult to further reflow the material because its melting point is close to that of the pure metal after sintering (Ag-960 ℃, cu-1085 ℃), and there is great flexibility in the thermal process after this process. Standard solders such as SAC, pbSn do not sinter and therefore can maintain a very low melting point, which can limit subsequent process steps below this melting point, thereby limiting the temperature of each process step to lower and lower in order.
In another embodiment, sintered nanometal sealing techniques may be applied to both laser attachment and phosphor attachment. Fig. 61 is a schematic diagram illustrating an integrated white light source with a laser and phosphor attached to a package support member according to one embodiment of the invention. As shown, the laser subassembly used in the integrated white light source needs to have very good thermal conduction to the package support member 6106 due to the relatively high thermal power dissipated by the laser. The laser subassembly 6103 typically employs a multilayer structure, consisting of a GaN laser structure bonded to a substrate. The laser subassembly 6103 is then soldered to the wedge-shaped substrate 6101 formed on the package support member 6106. The laser diode 6103 and the phosphor member 6104 are attached to a mounting surface that covers the package support member 6106, where the non-parallel geometry is determined by the offset angle (α), and the attachment heights are different such that the excitation beam emitted by the laser diode 6103 exits the laser diode at a height greater than the top surface of the phosphor member 6104. The wedge shaped substrate 6101 is used to lift and tilt the laser into place in the package such that the output beam from the laser diode 6103 is incident on the phosphor member 6104 at a predetermined spatial location, a predetermined angle of incidence (α), and a predetermined excitation spot diameter, all of which determine the performance of the laser-based light source.
Typically, laser subassemblies are soldered to the wedge-shaped substrate using standard solders (e.g., snAgCu-SAC, pbSn, auSn, etc.). These conventional solders are common thermal conductors (typically 50W/m-K) and may also be a limiting factor in removing heat from the laser subassembly, thereby limiting device efficiency, light output, and reliability.
In this embodiment, sintered nanometals can be used as a soldering technique to form an attachment joint 6102 between the laser subassembly 6103 and the wedge shaped substrate 6101, just as we form an attachment joint 6105 between the phosphor 6104 and the encapsulating support member 6106. The sintered nanometals can increase the thermal conductivity of the attachment joints 6102 or 6105, providing an improved thermal conduction path for the laser subassembly 6103 and phosphor 6104. This allows for lower laser operating temperatures, improved laser excitation or phosphor re-emitted light output and efficiency, and higher reliability of the integrated white light source. There are many types of nanometal sintered solders available, including sintered nanometals based on Ag and Cu. These materials form solid joints with thermal conductivities from 75W/m-K to 300W/m-K and can be made by simple manufacturable processes requiring paste dispensing and curing at 250 ℃. Since the material is sintered in this process, it is difficult to further reflow the material because its melting point is close to that of the pure metal after sintering (Ag-960 deg.C, cu-1085 deg.C), and there is great flexibility in the thermal process after this process. Standard solders such as SAC, pbSn do not sinter and therefore can maintain a very low melting point, which can limit subsequent process steps below this melting point, thereby limiting the temperature of each process step to lower and lower in order.
In some embodiments, the solder may take a variety of forms, including a paste, a preform, or a composite preform. Fig. 62 shows an example of a composite preform in which a metal frame 6201 is sandwiched between welding materials 6202. The metal frame 6201 may be pre-formed into a desired shape suitable for the integrated white light source package shown in fig. 60. The metal frame 6201 is made of Cu, kovar, steel, etc., specifically selected to improve temperature coefficient matching between the window member and the package as the temperature drifts during processing or operation.
Hermetic sealing will be accomplished using semiconductor processes suitable for solder. Fig. 63 shows a typical flow chart of the process starting with a paste, preform or composite preform. This flow will use typical reflow conditions for the solder, but alternative methods of causing reflow, such as die bonding, localized laser heating of the solder, IR heating of the solder, resistive heating of the solder, may also be used to minimize thermal excursions of other package portions that have been completed. In one embodiment, when the solder is provided as a paste, the soldering process to attach the window to the package includes cleaning the package and the window, and performing paste dispensing on the package or the window. Alternatively, the paste template may also be printed onto the package or window. Alternatively, the paste may be screen printed onto the package or window. In addition, the welding process includes setting up the desired ambient environment and attaching the window to the package. Finally, the soldering process includes reflowing the window onto the package. Alternatively, the reflow step is simply a die attach reflow process.
In another embodiment, when the solder is provided as a preform or composite preform, the soldering process to attach the window to the package includes cleaning the package and the window and securing the preform or composite preform to the window or package. In addition, the welding process includes setting up the desired ambient environment and attaching the window to the package. Finally, the soldering process includes reflowing the window onto the package. Alternatively, the reflow step is simply a die attach reflow process.
In a preferred configuration of the integrated white light source, the window is attached to the frame member using die attach or thermal oven reflow techniques using solders including AuSn solder, SAC solder (e.g., SAC 305), leaded solder, or indium, but may be others. In an alternative embodiment, a sintered silver paste or film may be used for the attachment process at the interface.
In an alternative preferred configuration of the integrated white light source, the window is comprised in a composite metal cover member, and the cover member is fixed to the SMD package using a soldering process. The soldering process is a desirable option for ensuring the hermetic sealing of the package because it is a common method of sealing conventional laser diode product packages such as TO can packages, butterfly packages, and others. In this configuration, the window would be attached to a metal member compatible with the welding process, such that the cover member is a composite member consisting of a glass or sapphire window area and a metal area suitable for welding. In one embodiment of this configuration, the cover member will be welded to the frame member, where the frame member will be constructed of a metal suitable for the welding process. In another configuration of this embodiment, the cover member may be soldered to the base member or the support member of the SMD package. In this configuration, no frame is required. In one example, the lid member would be similar TO a TO can lid member.
SMDs consist of a blue chip on board (CoS) edge emitting laser diode and a broad band yellow phosphor, can emit a color temperature greater than-6300K, and varies with the choice of material and laser wavelength. In order to emit warmer white with a lower Correlated Color Temperature (CCT), a red light source may be added. The red light source may be a solid state device with the addition of another phosphor material, quantum dots, photo-excited quanta, well structures or with the addition of red light such as LEDs, lasers, OLEDs or similar. The addition of a red LED is also not suitable for addition to warm white light emitting devices based on high-brightness lasers because its emitting area is 10 to 100 times larger than that of cold white light emitting devices based on high-brightness lasers. If uniform mottling is desired, it is not sufficient to incorporate these red emission solutions into a warm white emitting device based on a high brightness laser.
In order to maintain high brightness capability of laser-based white emitters in warm white devices, red laser diodes may be used as red emitting sources. The cold white version of these devices contains blue laser emission to excite a 100 to 300 μm diameter spot on a broad band yellow emitting phosphor material. The effective emission point of these devices is the excitation point on the yellow phosphor. Warm white devices can be made by adding a red laser diode. Red laser emission can be projected onto the blue excitation spot of the phosphor material to maintain the high brightness characteristics of the laser-based white emitter. Furthermore, color uniformity can be maintained by presenting red light to the same spot area as the blue excitation spot on the phosphor material. The choice of the wavelength of the red laser has a significant impact on the CCT of the white light emitted. The ability to effectively emit warm white is also affected by the choice of wavelength of the red laser. Fig. 64 shows the warm white spectrum obtained in the simulation when a 630nm or 650nm emitting red laser diode is combined with a blue laser diode and a yellow phosphor. In these emission spectra, the total blue and yellow components of the emission are nearly identical. The red laser emission of a 650nm laser diode may contain more than 2 times the optical power to achieve a warm white light of 3000K compared to a 630nm red laser diode. Fig. 65 shows the radiant luminous efficiency (LER, luminous flux per radiant flux of emitted light) of simulated laser-based warm white light emission at various CCTs incorporating 630nm or 650nm red laser diodes.
A large number of white light applications require high luminous flux and high brightness light sources in order to optimally illuminate a subject or target object from a distance and/or in a very specific pattern. For example, high brightness light sources with total luminous flux values of greater than 2000 lumens, greater than 10000 lumens, greater than 100000 lumens, greater than 1,000,000 lumens, and high brightness light sources with beam ranges of greater than 1 kilometer, greater than 5 kilometers, greater than 10 kilometers, greater than 50 kilometers, and greater than 100 kilometers, may be desirable to replace existing technologies, such as mercury vapor lamps, xenon lamps, sodium vapor lamps, and luminescent plasma sources, and/or to provide light sources with unprecedented capabilities and functions. The beam range may be in the range below 0.25 lux. The light emission can occur at a brightness of greater than 100 candelas per square millimeter, at a brightness of greater than 500 candelas per square millimeter, or at a brightness of greater than 1000 candelas per square millimeter. The electromagnetic radiation emission (light emission) may be in the visible range of 400nm to 700nm, or in the ultraviolet range of 200nm to 400nm, or in the infrared range of 700nm to 1100nm, or in the infrared range of 1100nm to 2500nm, or 2500nm to 15000nm, or a combination of these. Each SMD package may emit at one or more wavelengths onto the same device, which may be achieved by a single control of both wavelengths, or by separate addressable electronic control of the devices within the SMD package. The emission of each SMD package may occur at one or more intensities for the same package, which may be produced by individually addressable electronic control of the devices within the SMD package. In a set of preferred embodiments according to the invention, the laser-based white light source is configured to form a high luminous flux and high brightness white light source to address a wide range of applications. These applications may include, but are not limited to, spotlights, signals, and/or beacons for entertainment, architectural, entertainment, avionics, automotive, marine, military, search and rescue, and other applications; lighting of large structures or objects, such as natural environments like high-rise buildings, bridges, tunnels, signage in urban skylines, statues, national monuments or other important landmarks, as well as mountains or hills; developing applications in any lighting application, such as gardening, epoxy or resin or other curing, hardening or material processing, cleaning or other anti-corrosion or anti-bacterial or anti-fungal applications, advertising, pattern or image projection, signaling or other forms of communication; dynamic illumination comprising dynamic beam shaping optics and a display; high speed wireless communications, such as LiFi or Visible Light Communications (VLC); sensing, such as light imaging and detection and ranging (LIDAR).
One approach to achieving a high-flux, high-brightness white light source is to configure a plurality of individual high-brightness laser-based white light sources to aggregate the luminous flux from each individual high-brightness light source into a single luminaire or light source. Such aggregation of a plurality of individual laser-based white light sources may be achieved in a variety of different arrangements of light sources, including one-dimensional (1D) arrays, two-dimensional (2D) arrays or matrices, or even three-dimensional (3D) array configurations. The device may be driven in a series, parallel or series-parallel configuration to control all elements by one electrical driver. Alternatively, the elements or subsets of elements may be driven independently, thereby dynamically creating and adjusting a light pattern by adjusting the relative light output of each element of the subset of elements.
In some embodiments of the present invention, a one-dimensional or two-dimensional array of laser-based light sources may be configured to aggregate the power of a plurality of individual laser-based light sources. In a preferred embodiment, the Surface Mount Device (SMD) based laser light sources are arranged in one dimension. For example, SMDs capable of producing about 500 lumens of white light may be arranged into N one-dimensional arrangements of SMDs, where the total output power of the array would be about 500 lumens by N, which may range from 2 to 100 or more, with a total luminous flux of about 1,000 lumens to about 50,000 lumens or more. In another example, each SMD may be capable of producing 1,000 lumens, such that the total luminous flux of the one-dimensional array may amount to 2,000 lumens to about 100,000 lumens. In yet another example, each SMD may be capable of producing 2,000 lumens, such that the total luminous flux of the one-dimensional array may amount to 4,000 lumens to about 400,000 lumens. Of course, these descriptions are for illustration, but other configurations and lumen levels are possible.
Fig. 66 shows a schematic top view of a high-luminous-flux laser-based white light source composed of a 1D array of SMD packages as an example. As shown in this figure, one or more laser diodes are located in the SMD package and configured with a phosphor member. Upon application of a current to the laser diode, an electromagnetic radiation output emission is generated from the laser diode and excites the phosphor. The combined emission from the laser diode, and the wavelength converted emission from the phosphor member, produces a white light emission. In this example, individual SMD laser based light sources are arranged in a one-dimensional array to create N SMD light source "lines" placed side-by-side. The total luminous flux of this configuration is approximately equal to the average luminous flux of a single SMD multiplied by the number N of SMDs in the one-dimensional array.
In a second preferred embodiment, the SMD based laser light sources are arranged in a two-dimensional manner. For example, SMDs capable of producing about 500 lumens of white light may be arranged into N by M two-dimensional arrangements of SMDs, where the total output power of the array would be about 500 lumens by N times M, where N may range from 2 to 100 or more, and the total luminous flux is about 2,000 lumens to about 5,000,000 lumens or more. In another example, each SMD may be capable of producing 1,000 lumens, such that the total luminous flux of the two-dimensional array may amount to 4,000 lumens to about 10,000,000 lumens. In yet another example, each SMD may be capable of producing 2,000 lumens, such that the total luminous flux of the two-dimensional array may amount to 8,000 lumens to about 20,000,000 lumens or more. Of course, these descriptions are for illustration, but other configurations and lumen levels are possible.
Fig. 67 shows a schematic top view of a high-flux laser based white light source made up of a 2D array of SMD packages as an example. As shown in this figure, one or more laser diodes are located in the SMD package and configured with a phosphor member. Upon application of a current to the laser diode, an electromagnetic radiation output emission is generated from the laser diode and excites the phosphor. The combined emission from the laser diode, and the wavelength converted emission from the phosphor member, produces a white light emission. In this example, individual white light sources based on SMD lasers are arranged in a two-dimensional array to create a white light source "zone" consisting of N by M SMDs located in a row and column matrix. The total luminous flux of such a configuration is approximately equal to the average luminous flux of a single SMD multiplied by the number of SMDs in the two-dimensional array (N × M). Of course, such a square or rectangular matrix arrangement of rows and columns is merely an example of a two-dimensional array configuration. There are many other possible arrangements such as forming circular or elliptical regions, triangular regions, discontinuous regions and custom geometric illumination regions.
Optical means for shaping or directing the white light may be coupled to the output emissions from the respective laser-based white light sources, including the high-luminous-flux laser-based white light source. In a preferred embodiment, the optical member comprises one or more collimating optics configured to collect and focus white light emissions in a collimated and/or directed emission pattern. The collimating optics may be configured as a lens such as an aspheric lens, a reflector optic such as a parabolic reflector, total internal reflector optics, diffractive or refractive optics, or may be a combination optic using two or more optics to achieve a desired beam shaping effect. In some embodiments, a template for image and/or pattern projection or beam shaping optics is included. Such patterning or beam shaping optics may enable high definition projection of the illumination pattern. Such patterned projection illumination may be used to accurately illuminate a particular object or area while leaving adjacent areas unlit, or may be used to project shapes, objects, text, and other means of communication or advertising.
The optical member configured to collimate, focus and/or shape the white light emission from the laser-based white light source may be configured in a variety of ways. In one exemplary embodiment, each individual white light source has one or more dedicated individual optical components coupled to the white light emission. In this embodiment, one or more optical members may be individually aligned with each individual white light source member, which may provide benefits for the performance and efficiency of the high-luminous-flux white light source, as this may optimize the optical alignment to achieve maximum luminous flux efficiency and optimal beam quality for each emitter, thereby ensuring optimal overall performance of the white light source array. Fig. 68 shows an example schematic of a high lumen 2D array of laser-based white light SMDs where each SMD has one or more designated optical elements coupled to its white light emission. In this example, the optics are collimating optics, such as reflector optics, total internal reflector optics, or other types of collimating optics, but it should be understood that other types of optical elements may also be included.
In another exemplary embodiment, a plurality of individual laser-based white light sources may share a common optical element, wherein the output white light emissions from the individual sources will be coupled to the one or more common optical elements. In this embodiment, one or more common optical elements may be configured as a lens array, where the lens array would contain a dedicated lens element for each white light emitter. For example, for an N x M array of laser-based white light emitters, an N x M lens array would be configured to be coupled to the emitter array. If the spatial and optical alignment of the white light emitters is controlled to within predetermined specified tolerances, and the lens array is designed and manufactured to within acceptable predetermined tolerances, then the common optical component and the emitter array may be configured together in the same optical alignment step. Such a configuration may provide benefits to the cost and throughput of the optical coupling process because only one alignment and attachment process is required. Fig. 69 shows an example schematic of a high lumen 2D array of laser-based white light SMDs where the array of nxm SMDs share a common optical element. In this example, the common optic may be an array of collimating optics, such as reflector optics, total internal reflector optics, or may also be a single large optic. It should be understood that other types of optical elements may also be included, and that this figure is merely an example. The rectangular arrangement is shown in fig. 74 and the circular arrangement is shown in fig. 75.
In some embodiments according to the inventionWhite light emission from a high luminous flux source is shaped or patterned. High brightness (e.g., greater than 100cd// mm) of laser-based light sources 2 Greater than 500 cd/mm 2 Greater than 1000cd/mm 2 Greater than 2000cd/mm 2 Greater than 5000cd/mm 2 Or larger) enable precise patterning of white light that is not possible with low brightness light sources, such as LED-based light sources. In one embodiment, the dedicated optics are coupled to one or more individual sources, including a high luminous flux source. The dedicated optics are configured to shape the light into a predetermined pattern during static operation of the light source. For example, a pattern may be selected from one or more of a circular pattern, a square or rectangular pattern, a vertical and/or horizontal line pattern to generate a line source, a grid pattern, a pattern representing a particular shape or symbol of an object or message, a character or text pattern for communication, or any other one-or two-dimensional pattern. Such static patterning example optics for the light source may include diffractive optical elements, nanostructured optical elements, templates or patterns for basic pattern projection, or others.
In one embodiment, the active optical element is coupled to one or more individual sources including a high luminous flux source. The active optical element is configured to dynamically shape the light into a predetermined pattern during operation of the light source such that the pattern can be changed and modified as a function of time. In one example, the active optical element is a tunable optical lens that modulates the resulting beam divergence from a laser-based white light source. In one example of this embodiment, liquid crystal display technology is used to change the optical lens characteristics to enable the white light beam divergence to be adjusted between a divergence of about 1 to 5 degrees to about 60 to 120 degrees, but other are possible. In another example of this embodiment, the active optical element is coupled to one or more separate high brightness sources, which may comprise micro-display type elements. For example, a Digital Light Processing (DLP) chip may be included. In another example, liquid crystal type display technology, such as LCOS microdisplay chips, is included. In another example, transmissive liquid crystal type beam shaping techniques are included. In another example, an acousto-optic or electro-optic modulator is included. In yet another example, a MEMS scanning mirror or mirror array is included. In all of these examples of active optical elements, the light output pattern from one or more individual high brightness laser based sources may be dynamically controlled. The desired temporal dynamic spatial pattern output may be controlled based on a predetermined timing, such as projecting certain patterns or images in sequence based on a predetermined sequence, may be controlled based on manual input to a control interface such as a button or touch screen interface, or may be controlled according to the general time of day. In a preferred embodiment, the time-dynamic illumination pattern may be feedback controlled by a sensor. For example, cameras, radar, lidar, microphones, photovoltaics, gyroscopes, accelerometers, and any other sensor type may be integrated with the dynamic light source. Feedback from the sensor will trigger the dynamic light source to respond to the environment and change the static or active pattern sequence to the desired configuration depending on the environment. The feedback loop may be arranged as an interactive feedback loop. See, e.g., U.S. patent publication No. 2019/0097722, filed on 2017, 9, 28, the entire contents of which are incorporated herein by reference for all purposes. In some configurations, multiple dedicated optics or active optical elements are included, where each individual high brightness source may have its own dedicated optical element, such that there may be 2 to N or 2 to nxm elements coupled to 1 to N or 1 to nxm individual high brightness light sources.
In one embodiment according to the present invention, a high luminous flux white light source comprised of a separate high brightness laser based white light source is configured for high speed wireless data transmission in LiFi or VLC applications. In this example, at least one laser diode within a laser-based white light source is modulated to encode the laser emission with a predetermined data pattern to generate a signal. In one example, a blue laser diode is modulated to generate a data pattern signal at a blue wavelength. The receiver is configured to detect this modulated blue emission and decode the pattern to provide the desired data to the receiver. The receiver may be deployed on a smart device, a laptop, a display, an audio source, any device connected to the internet of things network, or any device or location where data is needed. Since according to the utility model discloses a high luminous flux laser based source comprises solitary high brightness source, therefore every solitary source can both act as solitary data channel. For example, in a one-dimensional array, an array of N sources may have a potential data rate of up to N x 10Gb/s if each source is capable of transmitting data at a speed of 10Gb/s. In a two-dimensional array, the data rate may be increased to N x M x 10Gb/s. In some embodiments of the present invention, data transmission is combined with static or dynamic beamforming. In such a configuration, the various data streams from the high luminous flux sources may have unique patterns to achieve greater power or selectivity of the data transmission path. See, for example, U.S. patent publication No. 2019/0097722, filed on 28/9/2017.
In an embodiment of a high luminous flux, high brightness white light source according to the invention, the light source is structured such that a plurality of individual laser-based light sources are mounted on a common electronic board member, which is in turn mounted on a common heat sink member. The electronic board member is electrically coupled to an electronic driver member configured to provide a current and a voltage to drive the laser-based light source. A single high brightness white light source may be electrically coupled in series to create high voltage and low current drive conditions, or may take a parallel electrical coupling configuration to create high current and low voltage drive conditions, or may take a series-parallel electrical configuration with multiple series-connected power packs connected in parallel. The driver component is electrically coupled to a power source, such as a battery component or an AC power source having an AC to DC converter. The heat sink may be a passive or active cooling heat sink, including convective cooling, light pipes, conductive cooling such as with water, or the use of cooling elements such as thermoelectric coolers. Fig. 70 shows a schematic diagram of an exemplary high luminous flux high brightness light source, where the single high brightness light source consists of an SMD laser based white light source. The individual SMD light sources are mounted on a common electronic board member, while the electronic board member is mounted on a heat sink member.
In an alternative embodiment of the invention, each single high brightness source has its own dedicated electronic board member mounted to a common heat sink member. The electronic board members are optionally coupled to a common electronic board member. The electronic driver means will be configured to provide current and voltage to drive the laser-based light source. A single high brightness white light source may be electrically coupled in series to create high voltage and low current drive conditions, or may take a parallel electrical coupling configuration to create high current and low voltage drive conditions, or may take a series-parallel electrical configuration with multiple series-connected power packs connected in parallel. The driver component is electrically coupled to a power source, such as a battery component or an AC power source having an AC to DC converter. The heat sink may be a passive or active cooling heat sink, including convective cooling, conductive cooling such as with water, or using a cooling element such as a thermoelectric cooler. Fig. 71 shows a schematic diagram of an exemplary high luminous flux high brightness light source, where the single high brightness light source consists of an SMD laser based white light source. The individual SMD light sources are mounted on a dedicated individual electronic board member, while the electronic board members are mounted on a common heat sink member.
In yet another alternative embodiment of the present invention, each individual high intensity source is mounted directly on a common heat sink member. Such a configuration would provide the benefit of improved thermal performance without the need for intermediate electronic board components, as this would increase the thermal resistance of the stack. The electronic driver means will be configured to provide current and voltage directly to the laser-based light source means. A single high brightness white light source may be electrically coupled in series to create high voltage and low current drive conditions, or may take a parallel electrical coupling configuration to create high current and low voltage drive conditions, or may take a series-parallel electrical configuration with multiple series-connected power packs connected in parallel. The driver component is electrically coupled to a power source, such as a battery component or an AC power source having an AC to DC converter. The heat sink may be a passive or active cooling heat sink, including convective cooling, conductive cooling such as with water, or the use of cooling elements such as thermoelectric coolers. Fig. 72 shows a schematic diagram of an exemplary high luminous flux high brightness light source, where the single high brightness light source consists of an SMD laser based white light source. The individual SMD light sources are mounted directly on a common heat sink member.
In a preferred embodiment of the invention, the high-luminous-flux, high-brightness white light source is configured in the housing member to contain a single high-brightness light source, an optical member, a heat sink member and optionally an electronic member. The housing member is configured to incorporate all components of the high luminous flux source into one stand-alone device ready for integration into a larger system or operation as a stand-alone light source. The housing member may be configured to prevent damage to the light source by providing protection from mechanical shock, handling or transport, and to provide safety for the person using, handling or exposed to the light source. The housing may be configured with an optically transparent "window" member to allow high luminous flux white light to exit the housing. The housing member may be configured to contain a battery member so that the white light source will not be dependent on an external power source. Alternatively, the housing member may be configured with an electrical interface, e.g. with a plug or wire, to electrically couple the high-flux light source to a power supply. In one embodiment, the high luminous flux white light source is equipped with internal battery components and an interface for connection to an external power source. The housing member may be provided with a charging member which functions to charge the battery of the light source when it is plugged into an external power supply. The high luminous flux source housing member may include a handle member for ease of carrying and transport and may incorporate a mechanical mounting member for mechanically positioning the light source to align the light output in a desired direction. Fig. 73 shows a schematic diagram of an exemplary high luminous flux high brightness light source consisting of a white light source based on 30 individual high brightness SMD lasers. The light source is arranged in the housing member according to the invention. In this example, the light source is capable of generating light having a divergence of about 2 degrees and about 12,000 lumens to provide a range of about 600 kilo candelas and about 5 kilometers (or about 3 miles).
While the above is a complete description of certain embodiments, various modifications, alternative constructions, and equivalents may be used. Accordingly, the above description and illustrations should not be taken as limiting the scope of the invention which is defined by the appended claims.

Claims (20)

1. A high-luminous-flux laser-based white light source, comprising:
a plurality of Surface Mount Device (SMD) packages; and
a plurality of electronic board members arranged in an array pattern and each electrically coupled to one of the plurality of electronic board members, each of the plurality of SMD packages comprising:
one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source;
a phosphor member configured as a wavelength converter and an emitter and coupled to the one or more laser diode devices;
at least one common support member configured to support the one or more laser diode devices, the at least one common support member comprising one or more angled portions, and a planar portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the planar portion, and an upper surface of each angled portion is arranged between and at an inverted angle relative to an upper surface of a buffer feature, wherein the buffer features are arranged on an upper surface side of each angled portion in a direction perpendicular to a length of the cavity member of a laser diode device supported by the angled portion;
An output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm;
a free space extending from the output face on each of the one or more laser diode devices to the phosphor member, having a non-guiding characteristic capable of transmitting the laser beam from the output face to an excitation surface of the phosphor member;
a range of incident angles between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off normal incidence to the excitation surface, and a beam spot is configured to a particular geometric size and shape;
wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength longer than the first wavelength; and is provided with
Characterizing a reflection pattern of the phosphor member such that the laser beam from each of the one or more laser diode devices is incident on a beam spot area on the excitation surface of the phosphor member and a white light emission is output from the same beam spot area, the white light emission comprising a mixture of wavelengths characterized by at least the emitted electromagnetic radiation having the second wavelength.
2. The high-fluence laser based white light source of claim 1 wherein the electronic board member comprises a heat sink and the plurality of SMD packages are configured to transfer thermal energy from the one or more laser diode devices and from the phosphor member to the heat sink.
3. The high-fluence laser based white light source as claimed in claim 1, wherein the plurality of SMD packages are arranged on the electronic board member in at least one of a one-dimensional (1D) array pattern or in a two-dimensional (2D) array pattern.
4. The high-fluence laser based white light source of claim 1 further comprising a plurality of optical components, wherein one or more of the plurality of optical components is coupled to the white light emission output from the phosphor component of each of the plurality of SMD packages.
5. The high-fluence laser based white light source of claim 4 wherein the plurality of optical components comprises collimating optics configured to collect the white light emission and focus the white light emission in a collimating and/or directional emission pattern.
6. The high-luminous-flux-laser-based white light source of claim 1, further comprising one or more common optical members coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages.
7. The high-fluence laser based white light source of claim 6 wherein the one or more common optical components comprise a lens array having dedicated lens elements associated with the white light emission output from the phosphor component of each of the plurality of SMD packages.
8. The high-luminous-flux laser-based white light source of claim 1, further comprising optics coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the optics are configured to shape the white light emission into a predetermined pattern.
9. The high-fluence laser based white light source of claim 1 further comprising active optics coupled to the white light emission output from the phosphor member of each of the plurality of SMD packages, wherein the active optics are configured to dynamically shape the white light emission into different predetermined patterns.
10. The high-fluence laser based white light source of claim 1 wherein the laser beam from at least one of the one or more laser diode devices is modulated in a predetermined data pattern to generate signals for wireless data transmission.
11. The high-luminous-flux-laser-based white light source of claim 1, further comprising a single electronic board member other than the plurality of electronic board members, and each of the plurality of electronic board members is coupled to the single electronic board member.
12. The high-luminous-flux laser-based white light source of claim 1, wherein the phosphor member includes a plurality of scattering centers to scatter the electromagnetic radiation having the first wavelength in the laser beam incident on the phosphor member.
13. A high-luminous-flux laser-based white light source, comprising:
a power source; and
a plurality of laser packages arranged in an array pattern and electrically coupled to the power supply, each of the plurality of laser packages comprising:
one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source;
A phosphor member configured as a wavelength converter and an emitter and coupled to the one or more laser diode devices;
at least one common support member configured to support the one or more laser diode devices, the at least one common support member comprising two or more angled portions, and a planar portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the planar portion, and an upper surface of each angled portion is disposed between and at an inverted angle relative to an upper surface of a buffer feature, wherein the buffer features are disposed on an upper surface side of each angled portion in a direction perpendicular to a length of the cavity member of a laser diode device supported by the angled portion;
an output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm;
A free space between the output face on each of the one or more laser diode devices and the phosphor member having a non-guiding characteristic capable of transmitting the laser beam from the output face to an excitation surface of the phosphor member;
a range of angles of incidence between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that, on average, the laser beam is off-normal incident to the excitation surface, and a beam spot is configured to a particular geometric size and shape;
wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength; and is
Characterizing a reflection pattern of the phosphor member such that the laser beam from each of the one or more laser diode devices is incident on a beam spot area on the excitation surface of the phosphor member, and a white light emission is output from the same beam spot area, the white light emission comprising a mixture of wavelengths characterized at least by the emitted electromagnetic radiation having the second wavelength.
14. The high-luminous-flux-laser-based white light source of claim 13, wherein the plurality of laser packages comprise at least one of can-type packages, surface mount-type packages, or flat-type packages.
15. The high-luminous-flux-laser-based white light source of claim 13, wherein the power supply comprises a plurality of electronic board components, wherein each of the plurality of laser packages is electrically coupled to one of the plurality of electronic board components.
16. A high-luminous-flux laser-based white light source, comprising:
a power source; and
a plurality of Surface Mount Device (SMD) packages arranged in an array pattern and electrically coupled to the power supply, each of the plurality of SMD packages comprising:
one or more laser diode devices, each comprising a cavity member of gallium and nitrogen containing material and configured as an excitation source;
a phosphor member configured as a wavelength converter and an emitter and coupled to the one or more laser diode devices;
at least one common support member configured to support the one or more laser diode devices, the at least one common support member comprising two or more angled portions, and a planar portion, each angled portion for supporting a laser diode device of the one or more laser diode devices, wherein an upper surface of each angled portion is at an obtuse angle relative to an upper surface of the planar portion, and an upper surface of each angled portion is arranged between and at an inverted angle relative to an upper surface of a buffer feature, wherein the buffer features are arranged on an upper surface side of each angled portion in a direction perpendicular to a length of the cavity member of a laser diode device supported by the angled portion;
An output face configured on each of the one or more laser diode devices to output a laser beam comprising electromagnetic radiation selected from violet and/or blue light emission having a first wavelength ranging from 400nm to 485 nm;
a free space between the output face on each of the one or more laser diode devices and the phosphor member having a non-guiding characteristic capable of transmitting the laser beam from the output face to an excitation surface of the phosphor member;
a range of angles of incidence between the laser beam from each of the one or more laser diode devices and the excitation surface of the phosphor member such that a beam spot is configured to a particular geometric size and shape;
wherein the phosphor member converts a portion of the electromagnetic radiation from each of the one or more laser diode devices into emitted electromagnetic radiation having a second wavelength that is longer than the first wavelength;
a plurality of scattering centers associated with the phosphor member to scatter the electromagnetic radiation having the first wavelength incident on the phosphor member; and is
Wherein a white light emission is output from the phosphor member, the white light emission being characterized by at least the emitted electromagnetic radiation having the second wavelength.
17. The high-fluence laser based white light source of claim 16,
the laser beam from each of the one or more laser diode devices is incident on a same beam spot area on the excitation surface of the phosphor member, and the white light emission is output from the same beam spot area.
18. The high-luminous-flux-laser-based white light source of claim 16, wherein the laser beam from each of the one or more laser diode devices is incident on a different beam spot region on the excitation surface of the phosphor member, and the white light emission is output from the different beam spot region, the white light emission comprising a same wavelength characterized by a same of the emitted electromagnetic radiation.
19. The high-luminous-flux laser-based white light source of claim 16, wherein the laser beam from each of the one or more laser diode devices is incident on a different beam spot region on the excitation surface of the phosphor member, and the white light emission is output from the different beam spot regions, the white light emission comprising a mixture of wavelengths.
20. The high-luminous-flux-laser-based white light source of claim 16, wherein the power supply comprises a plurality of electronic board components, wherein each of the plurality of SMD packages is electrically coupled to one of the plurality of electronic board components.
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