Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
  • H01L33/08—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
  • G02B19/0028—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0061—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a LED
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0071—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source adapted to illuminate a complete hemisphere or a plane extending 360 degrees around the source
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0095—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with ultraviolet radiation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
  • H01L33/58—Optical field-shaping elements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
  • H01L33/50—Wavelength conversion elements
  • H01L33/501—Wavelength conversion elements characterised by the materials, e.g. binder
  • H01L33/502—Wavelength conversion materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
  • H01L33/52—Encapsulations
  • H01L33/54—Encapsulations having a particular shape
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
  • H01L33/58—Optical field-shaping elements
  • H01L33/60—Reflective elements

Definitions

• the present invention relates to light sources. More particularly, the present invention relates to light sources that include a light emitting diode (LED), a re-emitting semiconductor construction, and an optical element such as an extractor as described herein.
• LED light emitting diode
• an optical element such as an extractor as described herein.
• LEDs may additionally contain one or more quantum wells at the pn junction which capture high concentrations of both electrons and holes, thereby enhancing light-producing recombination.
• Several investigators have attempted to produce an LED device which emits white light, or light which appears white to the 3 -color perception of the human eye.
• the optical element preferably also has a relatively high refractive index, e.g., at least 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, or 2.4 or more, at the wavelength of light emitted by the LED.
• the optical element may be an encapsulant that is formed in place over the LED component and substantially surrounds the LED component (or portions thereof), or it may be an "extractor" that is made separately and then brought into contact or close proximity with a surface of an LED component to couple or extract light therefrom and reduce the amount of light trapped within the component.
• the extractor or other optical element may have a diverging shape, to partially collimate light collected at the input surface, or a converging shape, to direct light collected at the input surface into a side-emitting pattern.
• the light source additionally comprises a patterned low index layer in optical contact with a first portion of the emitting surface, the patterned layer having a first refractive index; and the input surface of the optical element is in optical contact with a second portion of the emitting surface, the optical element having a second refractive index higher than the first refractive index.
• the optical element has a base, an apex, and a converging side joining the base and the apex, and the base is optically coupled to the emitting surface, and the optical element comprises a first section including the base and that is composed of a first material, and a second section including the apex and that is composed of a second material.
• the optical element has a first index of refraction and having a base, an apex residing over the emitting surface, and a converging side joining the base and the apex, the base being optically coupled to the emitting surface, the light source also comprising a second optical element encapsulating the LED component and the first-named optical element, the second optical element having a second index of refraction lower than the first index of refraction.
• a second optical element encapsulating the LED component and the first optical element provides an increase in power extracted from the LED component compared to the power extracted by first optical element alone.
• the optical element has a base, an apex, and a side joining the base and the apex, the base being optically coupled to and mechanically decoupled from the emitting surface.
• “pseudomorphic” means, with reference to a first crystalline layer of given thickness and a second crystalline layer, such as an epitaxial film and a substrate, that each layer taken in isolation has a lattice constant, and that these lattice constants are sufficiently similar so that the first layer, in the given thickness, can adopt the lattice spacing of the second layer in the plane of the layer substantially without misfit defects.
• FIGS. 7 and 8 are schematic sectional views of more LED packages having brightness enhancing layers, and tapered optical elements;
• FIG. 9 is a graph showing modeled brightness and luminous output of an LED component as a function of the footprint size of the tapered element on the front emitting surface of the LED component;
• FIGS. 10-12 are schematic sectional views showing LED packages utilizing compound taper elements, and FIG. 12 further shows multiple taper elements coupled to an LED component;
• FIG. 13 is a schematic sectional view of another LED package having a brightness enhancing layer and multiple optical elements
• FIG. 14 is a schematic side view illustrating an optical element and LED component configuration
• FIGS. 15a-c are perspective views of additional optical elements
• FIG. 16 is a perspective view of a light source having another optical element
• FIGS. 17a-i are top views of additional optical elements
• FIGS. 18a-c are schematic front views illustrating alternative optical elements
• FIGS. 19a-e are schematic side views of additional light sources that incorporate optical elements and LED components
• FIGS. 20a-d are bottom views of optical element/LED component combinations
• FIG. 21 is a perspective view of an optical element and an LED component array; and FIG. 22 is partial side view of another optical element/LED component combination.
• the present application discloses illumination devices that comprise an LED component, which component includes an LED in combination with a re-emitting semiconductor construction, and an optical element in optical contact with, or optically coupled to, an emitting surface of the LED component.
• the optical element is preferably of relatively high refractive index to enhance light coupling out of the LED component, and preferably is or includes an extractor but may also be or include an encapsulant.
• the LED is capable of emitting light at a first wavelength and the re-emitting semiconductor construction is capable of absorbing light at that first wavelength and re- emitting light at a second wavelength.
• the re-emitting semiconductor construction comprises a potential well not located within a pn junction. The potential wells of the re- emitting semiconductor construction are typically but not necessarily quantum wells.
• the LED emits photons in response to an electric current and the re-emitting semiconductor construction emits photons in response to the absorption of a portion of the photons emitted from the LED.
• the re-emitting semiconductor construction can additionally comprise an absorbing layer closely or immediately adjacent to the potential well. Absorbing layers typically have a band gap energy less than or equal to the energy of photons emitted by the LED and greater than the transition energy of the potential well(s) of the re-emitting semiconductor construction. In typical operation the absorbing layers assist absorption of photons emitted from the LED.
• the re-emitting semiconductor construction may additionally comprise at least one second potential well not located within a pn junction having a second transition energy not equal to the transition energy of the first potential well.
• the LED is a UV- emitting LED.
• the re-emitting semiconductor construction comprises at least one first potential well not located within a pn junction having a first transition energy corresponding to blue-wavelength light, at least one second potential well not located within a pn junction having a second transition energy corresponding to green- wavelength light, and at least one third potential well not located within a pn junction having a third transition energy corresponding to red- wavelength light.
• the LED is a visible light-emitting LED, typically a green, blue, or violet LED, more typically a green or blue LED, and most typically a blue LED.
• the re-emitting semiconductor construction comprises at least one first potential well not located within a pn junction having a first transition energy corresponding to yellow- or green-wavelength light, more typically green-wavelength light, and at least one second potential well not located within a pn junction having a second transition energy corresponding to orange- or red-wavelength light, more typically red- wavelength light.
• the re-emitting semiconductor construction may comprise additional potential wells and additional absorbing layers.
• the LED has only one pn junction, and the re-emitting semiconductor construction has only one potential well not located within a pn junction, the potential well having a transition energy corresponding to, for example, green- wavelength light. In such cases the LED emits light at a wavelength shorter than green, e.g., blue, violet, or UV.
• the LED and the re-emitting semiconductor construction may be grown using known semiconductor processing techniques in a single fabrication step or process on a single wafer, in which case the LED and re-emitting semiconductor construction preferably utilize the same material combinations, e.g., ZnSe.
• the LED and the re-emitting semiconductor construction may be grown or fabricated in separate processes and then joined together with a bonding agent or otherwise, and then diced into individual die (either before or after the application of an optical element or array of optical elements corresponding to an array of LEDs formed in an LED wafer).
• the LED and re-emitting semiconductor construction may be kept separate, for example, bonded or otherwise joined or coupled to different surfaces of an extractor or other optical element.
• any suitable LED may be used.
• Elements of the disclosed devices, including the LED and the re-emitting semiconductor construction may be composed of any suitable semiconductors, including Group IV elements such as Si or Ge (other than in light- emitting layers), III-V compounds such as InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, and alloys thereof, II-VI compounds such as ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS and alloys thereof, or alloys of any of the above.
• Group IV elements such as Si or Ge (other than in light- emitting layers)
• III-V compounds such as InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, and alloys thereof
• II-VI compounds such as ZnSe, CdS
• the semiconductors may be n-doped or p-doped by any suitable method or by inclusion of any suitable dopant.
• the LED is a III-V semiconductor device and the re-emitting semiconductor construction is a II-VI semiconductor device.
• compositions of the various layers of a component of the device are selected in accordance with the following considerations.
• Each layer typically will be pseudomorphic to the substrate at the thickness given for that layer or lattice matched to the substrate. Alternately, each layer may be pseudomorphic or lattice matched to immediately adjacent layers.
• Potential well layer materials and thicknesses are typically chosen so as to provide a desired transition energy, which will correspond to the wavelength of light to be emitted from the quantum well. For example, the points labeled 460 nm, 540 nm and 630 nm in FIG.
• thicknesses for quantum well layers are between 1 nm and 100 nm, more typically between 2 nm and 35 nm.
• the quantization energy translates into a reduction in wavelength of 20 to 50 nm relative to that expected on the basis of the band gap energy alone.
• Strain in the emitting layer may also change the transition energy for potential wells and quantum wells, including the strain resulting from the imperfect match of lattice constants between pseudomorphic layers.
• Techniques for calculating the transition energy of a strained or unstrained potential well or quantum well are known in the art, e.g., in Herbert Kroemer, Quantum Mechanics for Engineering, Materials Science and Applied Physics (Prentice Hall, Englewood Cliffs, New Jersey, 1994) at pp. 54 -63; and Zory, ed., Quantum Well Lasers (Academic Press, San Diego, California, 1993) at pp. 72-79; both incorporated herein by reference.
• any suitable emission wavelengths may be chosen, including those in the infrared, visible, and ultraviolet bands.
• the emission wavelengths are chosen so that the combined output of light emitted by the device creates the appearance of any color that can be generated by the combination of two, three, or more monochromatic light sources, including white or near-white colors, pastel colors, magenta, cyan, and the like.
• the device emits light at an invisible infrared or ultraviolet wavelength and at a visible wavelength as an indication that the device is in operation.
• the LED emits photons of the shortest wavelength, so that photons emitted from the LED have sufficient energy to drive the potential wells in the re-emitting semiconductor construction.
• the LED is a III -V semiconductor device, such as a blue-emitting GaN-based LED, and re-emitting semiconductor construction is a II- VI semiconductor device.
• FIG. 1 is a band diagram representing conduction and valence bands of semiconductors in a re-emitting semiconductor construction. Layer thickness is not represented to scale. Table I indicates the composition of layers 1-9 in this embodiment and the band gap energy (Eg) for that composition. This construction may be grown on an
• Layer 3 represents a single potential well which is a red-emitting quantum well having a thickness of about 10 nm.
• Layer 7 represents a single potential well which is a green-emitting quantum well having a thickness of about 10 nm.
• Layers 2, 4, 6 and 8 represent absorbing layers, each having a thickness of about 1000 nm.
• Layers 1, 5 and 9 represent support layers. Support layers are typically chosen so as to be substantially transparent to light emitted from quantum wells 3 and 7 and from a short- wavelength LED. Alternately, the device may comprise multiple red- or green-emitting potential wells or quantum wells separated by absorbing layers and/or support layers.
• blue wavelength photons emitted by the LED and impinging upon the re-emitting semiconductor construction may be absorbed and re-emitted from the green-emitting quantum well 7 as green- wavelength photons or from the red-emitting quantum well 3 as red- wavelength photons.
• the absorption of a short- wavelength photon generates an electron-hole pair which may then recombine in the quantum wells, with the emission of a photon.
• the polychromatic combination of blue-, green-, and red- wavelength light emitted from the device may appear white or near- white in color.
• the intensity of blue-, green-, and red- wavelength light emitted from the device may be balanced in any suitable manner, including manipulation of the number of quantum wells of each type, the use of filters or reflective layers, and manipulation of the thickness and composition of absorbing layers.
• FIG. 3 represents a spectrum of light emitted from one embodiment of the device.
• absorbing layers 2, 4, 5 and 8 may be adapted to absorb photons emitted from the LED by selecting a band gap energy for the absorbing layers that is intermediate between the energy of photons emitted from the LED and the transition energies of quantum wells 3 and 7. Electron-hole pairs generated by absorption of photons in the absorbing layers 2, 4, 6, and 8 are typically captured by the quantum wells 3 and 7 before recombining with concomitant emission of a photon.
• Absorbing layers may optionally have a gradient in composition over all or a portion of their thickness, so as to funnel or direct electrons and/or holes toward potential wells.
• the LED and the re-emitting semiconductor construction are provided in a single semiconductor unit, i.e., the LED and re-emitting semiconductor construction can be grown in a series of fabrication steps on the same wafer.
• This semiconductor unit typically contains a first potential well located within a pn junction and a second potential well not located within a pn junction.
• the potential wells are typically quantum wells.
• the unit is capable of emitting light at two wavelengths, one corresponding to the transition energy of the first potential well (i.e., light emitted by the LED) and a second corresponding to the transition energy of the second potential well (i.e., light emitted by the re-emitting semiconductor construction).
• the first potential well emits photons in response to an electric current passing through the pn junction and the second potential well emits photons in response to the absorption of a portion of the photons emitted from the first potential well.
• the semiconductor unit may additionally comprise one or more absorbing layers surrounding or closely or immediately adjacent to the second potential well. Absorbing layers typically have a band gap energy which is less than or equal to the transition energy of the first potential well and greater than that of the second potential well. In typical operation the absorbing layers assist absorption of photons emitted from the first potential well.
• the semiconductor unit may comprise additional potential wells, located within the pn junction or located not within the pn junction, and additional absorbing layers.
• FIG. 4 is a band diagram representing conduction and valence bands of semiconductors in such a semiconductor unit. Layer thickness is not represented to scale. Table II indicates the composition of layers 1-14 in this embodiment and the band gap energy (E 2 ) for that composition.
• Layers 10, 11, 12, 13 and 14 represent a pn junction, or, more specifically, a pin junction, since intermediate undoped ("intrinsic" doping) layers 11, 12, and 13 are interposed between n-doped layer 10 and p-doped layer 14.
• Layer 12 represents a single potential well within the pn junction which is a quantum well having a thickness of about 10 nm. Alternately, the device may comprise multiple potential or quantum wells within the pn junction.
• Layers 4 and 8 represent second and third potential wells not within a pn junction, each being a quantum well having a thickness of about 10 nm. Alternately, the device may comprise additional potential or quantum wells not within the pn junction.
• the device may comprise a single potential or quantum well not within the pn junction.
• Layers 3, 5, 7, and 9 represent absorbing layers, each having a thickness of about 1000 nm.
• Electrical contacts, not shown, provide a path for supply of electrical current to the pn junction. Electrical contacts conduct electricity and typically are composed of conductive metal. The positive electrical contact is electrically connected, either directly or indirectly through intermediate structures, to layer 14. The negative electrical contact is electrically connected, either directly or indirectly through intermediate structures, to one or more of layers 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.
• this embodiment operates according to the following principles: when an electrical current passes from layer 14 to layer 10, blue-wavelength photons are emitted from quantum well (12) in the pn junction. Photons traveling in the direction of layer 14 may leave the device. Photons traveling in the opposite direction may be absorbed and re-emitted from the second quantum well (8) as green- wavelength photons or from the third quantum well (4) as red- wavelength photons. The absorption of a blue -wavelength photon generates an electron- hole pair which may then recombine in the second or third quantum wells, with the emission of a photon. Green- or red- wavelength photons traveling in the direction of layer 14 may leave the device.
• the polychromatic combination of blue-, green-, and red- wavelength light emitted from the device may appear white or near- white in color.
• the intensity of blue-, green- and red- wavelength light emitted from the device may be balanced in any suitable manner, including manipulation of the number of potential wells of each type and the use of filters or reflective layers.
• FIG. 3 represents a spectrum of light emitted from one embodiment of the device.
• absorbing layers 3, 5, 7, and 9 may be especially suitable to absorb photons emitted from the first quantum well (12), since they have a band gap energy that is intermediate between the transition energy of the first quantum well (12) and those of the second and third quantum wells (8 and 4). Electron-hole pairs generated by absorption of photons in the absorbing layers 3, 5, 7, and 9 are typically captured by the second or third quantum wells 8 and 4 before recombining with concomitant emission of a photon.
• Absorbing layers may optionally be doped, typically like to surrounding layers, which in this embodiment would be n-doping.
• Absorbing layers may optionally have a gradient in composition over all or a portion of their thickness, so as to funnel or direct electrons and/or holes toward potential wells.
• the layers of the re-emitting semiconductor construction may be partially transparent to the light emitted from the LED.
• one or more of the layers of re-emitting semiconductor construction may block a greater portion or substantially or completely all of the light emitted from the LED, so that a greater portion or substantially or completely all of the light emitted from the device is light re-emitted from the re-emitting semiconductor construction.
• the re-emitting semiconductor construction may include red-, green- and blue- emitting quantum wells.
• the device may comprise additional layers of conducting, semiconducting, or nonconducting materials.
• Electrical contact layers may be added to provide a path for supply of electrical current to the LED.
• the electrical contact layers may be disposed such that the electrical current energizing the LED also passes through the re-emitting semiconductor construction.
• a portion of the re-emitted semiconductor construction can be etched away to define a hole or aperture through which electrical contact can be made to the p or n layer of the LED.
• Light filtering layers may be added to alter or correct the balance of light wavelengths in the light emitted by the adapted LED.
• the disclosed light source provides white or near-white light by emitting light at four principal wavelengths in the blue, green, yellow and red bands.
• the light source generates white or near-white light by emitting light at two principal wavelengths in the blue and yellow bands.
• the light source emits in substantially a single visible color, e.g., green.
• the device may comprise additional semiconductor elements comprising active or passive components such as resistors, diodes, zener diodes, capacitors, transistors, bipolar transistors, FET transistors, MOSFET transistors, insulated gate bipolar transistors, phototransistors, photodetectors, SCR's, thyristors, triacs, voltage regulators, and other circuit elements.
• the device may comprise an integrated circuit.
• the device may comprise a display panel or an illumination panel.
• the LED and the re-emitting semiconductor construction which are included in the disclosed light sources may be manufactured by any suitable method, which may include molecular beam epitaxy (MBE), chemical vapor deposition, liquid phase epitaxy and vapor phase epitaxy.
• the elements of the device may include any suitable substrate.
• Typical substrate materials include Si, Ge, GaAs, InP, sapphire, SiC, and ZnSe.
• the substrate may be n-doped, p-doped, or semi-insulating, which may be achieved by any suitable method or by inclusion of any suitable dopant.
• the elements of the device may be without a substrate.
• elements of the device may be formed on a substrate and then separated from the substrate. The elements of the device may also be joined together by any suitable method, including the use of adhesive or welding materials, pressure, heat or combinations thereof.
• Such methods can be used to bond, for example, the LED (such as an LED die) to the re-emitting semiconductor construction, or the LED to the optical element (such as an extractor), or the re-emitting semiconductor construction to the optical element.
• Useful semiconductor wafer bonding techniques include those described in chapters 4 and 10 of the text Semiconductor Wafer Bonding by Q.-Y. Tong and U. G ⁇ sele (John Wiley & Sons, New York, 1999). Wafer bonding methods described in U.S. Patents 5,915,193 (Tong et al.) and 6,563,133 (Tong) may also be used.
• a method for wafer bonding GaN to ZnSe is described in Murai et al., Japanese Journal of Applied Physics 43 No.
• a bonding layer is present between the LED and the re-emitting semiconductor construction.
• the bonding layer may include, for example, a transparent adhesive layer, inorganic thin films, fusable glass frits, or other suitable bonding agents. Additional examples of bonding layers are described in US Pat. Pub. No. 2005/0023545 (Camras et al.). Typically, the bond created is transparent. Bonding methods may include interfacial bonding, or techniques that join the elements (such as the LED and the re- emitting semiconductor construction) only at the edges, i.e., edge bonding. Optionally, refractive index matching layers or interstitial spaces may be included.
• LEDs are typically sold in a packaged form that includes an LED die or chip mounted on a metal header.
• An LED die is an LED in its most basic form, i.e., in the form of an individual component or chip made by semiconductor wafer processing procedures.
• the component or chip can include electrical contacts suitable for application of power to energize the device.
• the individual layers and other functional elements of the component or chip are typically formed on the wafer scale, the finished wafer finally being diced into individual piece parts to yield a multiplicity of LED dies.
• the metal header has a reflective cup in which the LED die is mounted, and electrical leads connected to the LED die.
• the package further includes a molded transparent resin that encapsulates the LED die.
• the encapsulating resin typically has a nominally hemispherical front surface to partially collimate light emitted from the LED die.
• An LED component can be or comprise an LED die or an LED die in combination with a re-emitting semiconductor construction or other elements.
• the optical element discussed above can be made separately and then brought into contact or close proximity with a surface of an LED component may be used to couple or "extract" light therefrom and reduce the amount of light trapped within the component.
• Such an element is referred to as an extractor.
• Extractors normally have an input surface sized and shaped to substantially mate with a major emitting surface of the LED component.
• Extractors can be used to provide high brightness LED packages or light sources.
• the LED component of such packages may be an LED/ re-emitting semiconductor construction combination, either as separate elements or as a semiconductor unit, as described above or in currently pending U.S. patent applications USSN 11/009217 or USSN 11/009241, incorporated herein by reference.
• an LED package 10 includes an LED component 12 mounted on a header or other mount 14.
• the LED component and mount are depicted generically for simplicity, but the reader will understand that they can include conventional design features as are known in the art and re-emitting layers as described above.
• the primary emitting surface 12a, bottom surface 12b, and side surfaces 12c of the LED component are shown in a simple rectangular arrangement, but other known configurations are also contemplated, e.g., angled side surfaces forming an inverted truncated pyramid shape. Electrical contacts to the LED component are also not shown for simplicity, but can be provided on any of the surfaces of the LED component as is known.
• the LED component has two contacts both disposed at the bottom surface 12b of the LED component, such as is the case with "flip chip” LED component designs.
• mount 14 can serve as a support substrate, electrical contact, heat sink, and/or reflector cup.
• LED package 10 also includes a transparent optical element 16 that encapsulates or surrounds the LED component 12.
• the optical element 16 has a refractive index intermediate that of the LED component (more precisely, the outer portion of the LED component proximate emitting surface 12a) and the surrounding medium, which is ordinarily air.
• Optical element 16 has a curved output surface, which can help ensure that light is transmitted out of the LED package to the surrounding medium, and can also be used to focus or collimate, at least partially, light emitted by the LED component.
• Optical elements having other shapes can also be used to collimate light, including tapered shapes discussed further below.
• Optical element 16 may be an encapsulant, formed in place over the LED component, in which case it is typical for the encapsulant to be or comprise a light transmissive epoxy or silicone.
• LED package 10 is further provided with a patterned low refractive index layer 18 between the optical element 16 and the LED component, which has the effect of selectively preserving some light entrapment in the LED component in order to enhance the brightness in a localized aperture or area 20 at the emitting surface 12a.
• Patterned low index layer 18 is in substantial optical contact with side surfaces 12c and the portion of emitting surface 12a exclusive of aperture 20, while the optical element 16 is in optical contact with the portion of emitting surface 12a over the area of the aperture 20.
• optical contact refers to the surfaces or media being spaced close enough together, including but not limited to being in direct physical contact, that the refractive index properties of the low index layer or transparent element, for example, control or substantially influence total internal reflection of at least some light propagating within the LED component.
• the surfaces or media are within an evanescent wave of each other, e.g., separated by a gap of 100, 50, or 25 nm or less, including no gap at all.
• Patterned low index layer 18 has a refractive index substantially lower than both the refractive index of the LED component and the refractive index of transparent element 16. Layer 18 is also optically thick in those places where it is intended to promote light trapping.
• optically thick we mean that its thickness is great enough to avoid frustrated total internal reflection, or that the refractive index properties of the medium on one side of the layer (such as the optical element 16) do not control or substantially influence total internal reflection of at least some light propagating in the medium on the other side of the layer (such as the LED 12).
• the thickness of the patterned low index layer is greater than about one-tenth, more preferably one-half, more preferably about one wavelength for the energy of light of interest in vacuum.
• patterning of layer 18 we also mean to encompass embodiments where layer 18 is continuous over the LED emitting surface, but made to be extremely thin (hence ineffective to maintain total internal reflection) in the aperture 20 and optically thick elsewhere.
• layer 18 is advantageous for layer 18 to be a transparent dielectric material, or to at least comprise a layer of such a material at the surface of the LED component.
• These materials have advantages over reflective coatings made by simply applying a layer of metal to the LED, for example, because dielectric materials can provide 100% reflection (by TIR) for much of the light within the LED component, while simple metal coatings have substantially less than 100% reflectivity, particularly at high incidence angles.
• Patterned low index layer 18 enhances the brightness of some portions of the LED (e.g., in the aperture 20) at the expense of reducing the brightness of other portions of the LED (e.g., the portions of emitting surface 12a beyond aperture 20).
• This effect relies on the LED component having low enough internal losses during operation to support multiple bounce reflections of the emitted light within the LED component.
• losses from surface or volumetric absorption can be expected to decrease, internal quantum efficiency can be expected to increase, and brightness-enhancing effect described herein can be expected to provide steadily increasing benefits.
• Bulk absorption can be reduced by improving substrates and epitaxial deposition processes.
• the majority of the bottom surface 12b is a highly reflective material such as a metal or a dielectric stack.
• the reflector has greater than 90% reflectivity, more preferably 95%,most preferably 99% reflectivity at the LED emission wavelength.
• an arbitrary emitting point source 22 for example, emits light ray 24.
• the refractive indices of LED component 12 and transparent element 16 are such that the ray on its first encounter with the emitting surface 12a at the LED/optical element interface would be transmitted into and refracted by element 16. Patterned layer 18, however, changes the interface at that location to be totally internally reflecting for ray 24. The ray travels through the thickness of the LED component, reflects off the back surface 12b, and again encounters the emitting surface 12a, this time escaping into transparent element 16 because of the absence of layer 18 as shown in FIG. 5. The portion of emitting surface 12a at aperture 20 is thus made brighter (more luminous flux per unit area and per unit solid angle) at the expense of the portion of emitting surface 12a covered by the low index layer 18.
• the low index layer 18 can be overcoated with a good normal- incidence reflector such as a reflective metal or an interference reflector to increase recycling of light in the LED component and further enhance the brightness at aperture 20, without losing the benefit of TIR provided by low index layer 18.
• a good normal- incidence reflector such as a reflective metal or an interference reflector to increase recycling of light in the LED component and further enhance the brightness at aperture 20, without losing the benefit of TIR provided by low index layer 18.
• an interference reflector can be positioned between the outer LED component surface and the low index layer 18.
• Suitable low index layers 18 include coatings of magnesium fluoride, calcium fluoride, silica, sol gels, fluorocarbons, and silicones. Aerogel materials are also suitable, as they can achieve extremely low effective refractive indices of about 1.2 or less, or even about 1.1 or less. Aerogels are made by high temperature and pressure critical point drying of a gel composed of colloidal silica structural units filled with solvents. The resulting material is an underdense, microporous media. Exemplary thicknesses for the low index layer 18 are from about 50 to 100,000 nm, preferably from about 200 to 2000 nm, depending on the refractive index of the material.
• the refractive index of layer 18 is below the refractive index of the optical element 16, which can be a molded resin or other encapsulant material, and below the refractive index of the LED component, or that portion of the LED component proximate the emitting surface(s).
• the refractive index of layer 18 is less than about 1.5, more preferably less than 1.4.
• Low index layer 18 can be a solid layer of dielectric material, or a vacuum or gas-filled gap between the LED component and transparent element 16.
• the outer surfaces of the LED component can be optically smooth, i.e., having a surface finish R A of less than about 20 nm. Some, all, or portions of the outer LED surfaces may also be optically rough, i.e., having a surface finish R A greater than about 20 nm. Portions of the edges or the top surface can also be at non-orthogonal angles relative to the base of the LED component. These angles can range from 0-45 degrees from orthogonality. Further, major or minor surfaces of the LED component need not be flat. For example, a raised portion or portions of the emitting surface of the LED component can contact a generally flat bottom surface of the optical element to define at least the apertures 20, 20a, and 34 in FIGS. 5-7.
• the shape of aperture 20, defined by the substantial absence of the low index layer 18, can be circular, rectangular, square, or more complex shapes, whether polygonal or non-polygonal, regular or irregular. Multiple apertures are also contemplated, as discussed in more detail below.
• the aperture shape(s) will typically be selected as a function of the intended application, and can be tailored to optimize the overall system performance. It is also contemplated to pattern the surface of the aperture with a continuous or discontinuous pattern or network of low index coated areas, or provide the low index layer with a gradient in thickness or refractive index or both to modify the distribution of light output over the surface of the aperture.
• the aperture can also cover the entire top emitting surface 12a, where at least portions of the side surfaces 12c are covered with low refractive index layers.
• an LED package 10a is shown there similar to LED package 10, but where low index layer 18 has been modified by including a network of low index coated areas within the central aperture.
• the modified low index layer is thus labeled 18a, and the modified central aperture is labeled 20a.
• Other elements retain the reference numbers used in FIG. 5.
• the network of low index areas can be arranged in a pattern that is relatively dense near the edges of the aperture so that transmission is relatively low in that region.
• the ability to tailor the transmission through the aperture is useful in high brightness LEDs where a specific spatial uniformity or output distribution is required for the system design.
• Such an arrangement of low refractive index medium within an aperture can likewise be applied to other disclosed embodiments, including without limitation the embodiments of FIGS. 7, 8, and 10-12.
• the aperture can be coated with a low index material having a different thickness or different refractive index or both relative to the low index material defining the aperture (referred to as the "surrounding low index material" for convenience).
• a low index material having a different thickness or different refractive index or both relative to the low index material defining the aperture
• the aperture 20 or 20a can be coated with a material that has a refractive index between that of the optical element 16 and the surrounding low index material. This will cause light that would ordinarily be emitted at high angles to be recycled within the LED component, and increase the output of light in a range of angles that can be more efficiently used by the associated optical system.
• collection optics used in electronic projection systems do not efficiently use light that is outside the commonly used F/2 to F/2.5 acceptance design angles.
• an LED package 30 includes a transparent optical element 32 in partial optical contact with LED component 12 and partially spaced apart from the LED component to define a substantial air gap 34 therebetween.
• Transparent element 32 has an input surface 32a and an output surface 32b, the input surface 32a being: smaller than output surface 32b; smaller than emitting surface 12a of the LED component; and in optical contact with a portion of the emitting surface to define aperture 34.
• the input surface is "smaller" than the output surface because it has a smaller surface area, and the output surface is accordingly larger than the input surface because it has a larger surface area.
• the difference in shape between the optical element 32 and the emitting surface 12a produces an air gap 36 which forms a patterned low refractive index layer around the area of contact (aperture 34). Light generated by the LED component can thus be efficiently extracted at the aperture 34 by the transparent element 32 with a high brightness.
• the optical element 32, and other optical elements disclosed herein can be bonded to the LED component at the point of contact by any suitable means, or it can be held in position without being bonded to the LED component emitting surface. Further discussion regarding non-bonded optical elements in LED packages can be found in commonly assigned U.S. Patent Application Publication US 2006/0091784 (Connor et al.), "LED Package With Non-Bonded Optical Element", which is incorporated herein by reference in its entirety.
• the range of angles of light emitted by the LED emitting surface 12a into optical element 32 over the aperture 34 can be reduced by interposing a layer of material whose refractive index is between that of the LED component 12 and transparent element 32.
• Another approach for reducing the range of angles of collected light — or for collimating (at least partially) the collected light — is to use a transparent element having one or more tapered side walls, as shown in FIG. 8.
• LED package 40 is similar to LED package 30, but optical element 42 is substituted for optical element 32.
• Element 42 has an input surface 42a and an output surface 42b, the input surface 42a being: smaller than output surface 42b; smaller than emitting surface 12a of the LED component; and in optical contact with a portion of the emitting surface to define aperture 44.
• the difference in shape between the optical element 42 and the emitting surface 12a produces an air gap 46 which forms a patterned low refractive index layer around the area of contact (aperture 44).
• optical element 42 includes tapered side surfaces 42c, 42d, which are reflective in order to collimate some of the highly oblique light entering input surface 42a from the LED component. Reflectivity of the side surfaces 42c, 42d can be provided by a low refractive index medium that supports TIR, or by application of a reflective material such as a metal layer or interference reflector, or combinations thereof.
• optical element 42 can be in optical contact with the emitting surface of the LED component through fluids, thermally bound inorganic glasses, plastic inorganic glasses, or by providing the surfaces with an optically smooth finish (surface roughness R A less than about 50 nm, preferably less than about 20 nm) and then holding the surfaces in close proximity to each other.
• optical element 42 can be compound in structure, where the lower tapered portion comprising surfaces 42a, 42c, 42d is made separately from the upper lens-shaped portion comprising surface 42b, and the two portions adhered or otherwise joined together by conventional means. The broken line is provided to show the two portions more clearly. More discussion of compound optical elements, design considerations, and associated benefits is provided below.
• a model was used to determine the potential increase in brightness for a packaged LED that utilized a patterned low index layer and a tapered optical element coupled to the output aperture.
• An LED die was modeled with the material properties of silicon carbide (index 1.55) having an emitting region, an absorptive region, and angled edge facets such as to represent the optical behavior of a typical LED die.
• An inverted truncated pyramid- shaped tapered optical element was optically coupled to the front facet or emitting surface of the LED die.
• the material properties of the optical element were those of silicon carbide.
• the LED die had a square shape as viewed from the front, as did the input and output surfaces of the optical element.
• the model further coupled the output surface of the optical element to a half-sphere lens with the material properties of BK7 glass, where the diameter of the lens was ten times the width of the square LED die emitting surface, and the radius of curvature of the lens was five times the width of the LED die emitting surface.
• the size of the input surface of the optical element was incrementally changed from 100% of the LED die emitting area to 4%, while keeping the aspect ratio of the height of the optical element 2.2 times the width of the output surface of the optical element, and keeping the width of the output surface 2 times the width of the input surface.
• the patterned low index layer of disclosed embodiments can comprise a gap or a coating of low index material applied to the LED component.
• Suitable methods for coating the LED component with a low index material — or with individual layers that will form an interference reflector — from a liquid include spin coating, spray coating, dip coating, and dispensing the coating onto the LED component.
• Liquid coatings can be composed of monomers that are subsequently cured, solvents, and polymers, inorganic glass forming materials, sol gels, and Aerogels.
• Suitable methods of coating the low index material from a gas state include chemical vapor deposition or condensing a vapor on the LED component.
• the LED component can also be coated with a low index material by sputtering, vapor deposition, or other conventional physical vapor deposition methods.
• the coatings can be applied to a multitude of LEDs at the wafer level (before dicing), or after the wafer is diced but before mounting, after the LED component is mounted on the header or other support, and after electrical connections are made to the LED component. Coatings can also be applied after bonding a re-emitting semiconductor construction wafer to an LED wafer containing an array of individual LEDs.
• the aperture can be formed before or after the low index coating is applied.
• the choice of post-coating patterning method may depend on the particular low index material(s) chosen, and its compatibility with semiconductor processing. For example, a wafer can be covered with photoresist and patterned to create openings where the apertures are desired, a suitable low index coating deposited, and then liftoff performed using suitable solvent.
• a low index material can be deposited first over the entire wafer or LED component, a patterned photoresist layer can be applied as an etch mask, and the low index material removed using a suitable technique such as reactive ion etching.
• the photoresist layer can optionally be stripped using a suitable solvent.
• Other techniques for patterning the low index material include laser ablation and shadow masking, which may be particularly useful with materials that are soluble in typical photolithography stripping or development solvents.
• Suitable methods for lifting the unwanted coating off of the low adhesion areas include first applying a bonding material and then removing the bonding material, where the bonding material is able to remove the coating from the aperture area but allow the surrounding coating to remain intact.
• Low index coatings can also be patterned to form areas where electrical connections can be made to the LED component. See, for example, U.S. Patent Publication US 2003/0111667 Al (Schubert), incorporated herein by reference.
• Metal reflective layers can be applied by conventional processes, and patterned as needed to provide an aperture and appropriate electrical isolation.
• optical element 62 also has a compound construction, i.e., it comprises at least two sections 64, 66 joined together.
• the sections have input surfaces 64a, 66a, output surfaces 64b, 66b, and reflective side surfaces 64c, 64d, 66c, 66d as shown.
• the tapered side surfaces of element 62 redirect or collimate (at least partially) light from closely positioned LED emitting surface 12a in a non-imaging way.
• the side surfaces need not be planar. They can be conical, curved (including parabolic) or any suitable combination depending on the intended application and design constraints.
• the disclosed taper elements can have the shape of elements known in the art as CPCs ("compound" parabolic concentrators).
• the optical tapered element It is desirable in many situations to form the optical tapered element from high refractive index materials to reduce reflections at the LED emitting surface 12a over the aperture defined by input surface 64a, so that light is more efficiently coupled out of, or extracted from, the LED component 12. It is also desirable in many situations to fabricate the optical element using a material having high thermal conductivity and high thermal stability. In this way, the optical element can perform not only an optical function but a thermal management function as well. Further thermal management benefits can be gained by thermally coupling such an optical element to a heat sink, as is described in more detail in commonly assigned U.S. Patent Application Publication 2006/0091414 (Ouderkirk et al.), "LED Package With Front Surface Heat Extractor", which is incorporated herein by reference in its entirety.
• transparent materials that have sufficiently high refractive indices at the LED emission wavelength, e.g., greater than about 1.8, 2.0, or even 2.5, and/or that have thermal conductivities greater than about 0.2 W/cm/K, tend to be expensive and/or difficult to fabricate.
• Materials that have both high refractive index and high thermal conductivity include diamond, silicon carbide (SiC), and sapphire (AI2O3). These inorganic materials are expensive, physically very hard, and difficult to shape and polish to an optical grade finish. Silicon carbide in particular also exhibits a type of defect called a micropipe, which can result in scattering of light. Silicon carbide is also electrically conductive, and as such may also provide an electrical contact or circuit function.
• Scattering within optical tapered elements may be acceptable if the scattering is limited to a position near the input end of the element.
• An additional challenge in making one-piece tapered elements is that the material yield may be relatively low, and the form-factor may force the LED component to be individually assembled with the tapered element. For these reasons, it can be advantageous to divide the tapered element into at least two sections, the sections being made of different optical materials, to reduce manufacturing cost.
• a first section desirably makes optical contact with the LED component, and is made of a first optical material having a high refractive index (preferably about equal to the LED component refractive index at the emitting surface), high thermal conductivity, and/or high thermal stability.
• high thermal stability refers to materials having a decomposition temperature of about 600 0 C or more.
• a second section is joined to the first section and is made of a second optical material, which may have lower material costs and be more easily fabricated than the first optical material.
• the second optical material may have a lower refractive index, lower thermal conductivity, or both relative to the first optical material.
• the second optical material can comprise glasses, polymers, ceramics, ceramic nanoparticle-filled polymers, and other optically clear materials.
• Suitable glasses include those comprising oxides of lead, zirconium, titanium, and barium.
• the glasses can be made from compounds including titanates, zirconates, and stannates.
• Suitable ceramic nanoparticles include zirconia, titania, zinc oxide, and zinc sulfide.
• a third section composed of a third optical material can be joined to the second section to further aid in coupling the LED light to the outside environment.
• the refractive indices of the three sections are arranged such that ni > n 2 > n 3 to minimize overall Fresnel surface reflections associated with the tapered element.
• Oversized lens elements such as the upper portion of optical element 42 shown in FIG. 8, can be advantageously placed or formed at the output end of disclosed simple or compound tapered elements.
• Antireflection coatings can also be provided on the surface(s) of such lens elements and/or on input and output surfaces of disclosed optical elements, including tapered or other collimating elements.
• the LED die can comprise a lmm x 1 mm GaN junction on a 0.4 mm thick slab of SiC.
• the first section 64 of the tapered element 62 can be composed of SiC.
• the width dimensions of the junction between the first and second sections and the output dimensions of the second section can be selected as desired to optimize total light output into the surrounding environment, of refractive index 1.0.
• the edges of the 0.4 mm thick SiC slab can be tapered at a 12 degree negative slope to completely frustrate TIR modes of light reflection at the side surfaces of the LED component.
• This slope can be tailored as desired, since the absorption and scattering within the LED junction and SiC slab will change the integrated mode structure compared to a standard encapsulated LED. For example, it may be desirable to use a positive slope (where the width of the LED junction is less than the width of the SiC slab) in order to direct optical modes away from the absorbing junction.
• the SiC slab may, in this manner, be considered as part of the tapered element.
• the first section 64 can be coupled to a thermal heat sink as mentioned previously.
• the second section 66 can be bonded to the first section 64 using conventional bonding techniques. If a bonding material is used, it can have a refractive index between the two optical materials being joined in order to reduce Fresnel reflections.
• Other useful bonding techniques include wafer bonding techniques known in the semiconductor wafer bonding art. Useful semiconductor wafer bonding techniques include those discussed above.
• a compound tapered element 72 in which a first section 74, having an input surface 74a connected to a larger output surface 74b by tapered reflective side walls, is encapsulated in a second section 76, which also has an input surface 76a (coextensive with output surface 74b) and an even larger output surface 76b.
• the output surface 76a is curved to provide the compound element 72 with optical power useful for further collimation or focusing.
• the tapered side surfaces of section 74 are shown with a coating 78 of low refractive index material to promote TIR at such surfaces.
• the material preferably has a refractive index lower than that of first section 74, second section 76, and LED component 12.
• Such coating 78 can also be applied to the portion of emitting surface 12a not in contact with section 74, and/or to the side surfaces 12c (see FIG. 5) of LED component 12.
• first section 74 can be bonded to (or simply placed upon) the desired aperture zone of emitting surface 12a, and a precursor liquid encapsulating material can be metered out in sufficient quantity to encapsulate the LED component and the first section, followed by curing the precursor material to form the finished second section 76.
• Suitable materials for this purpose include conventional encapsulation formulations such as silicone or epoxy materials.
• the package can also include a heat sink coupled to the sides of first section 76 through coating 78. Even without such a heat sink, use of a high thermal conductivity first section of the tapered element can add significant thermal mass to the LED component, providing some benefit at least for pulsed operation using a modulating drive current.
• Both simple tapered elements and compound tapered elements disclosed herein can be manufactured by conventional means, such as by fabricating the tapered components individually, bonding a first segment to the LED component, and then adding successive segments.
• simple and compound tapered elements can be manufactured using precision abrasive techniques disclosed in commonly assigned U.S. Patent Application Publication 2006/0094340 (Ouderkirk et al.), "Process For Manufacturing Optical And Semiconductor Elements", , and U.S. Patent Application Publication 2006/0094322 (Ouderkirk et al.), “Process For Manufacturing A Light Emitting Array", both of which are incorporated herein by reference in their entirety. Briefly, a workpiece is prepared that contains one or more layers of the desired optical materials.
• the workpiece can be in a large format, such as wafers or fiber segments.
• a precisely patterned abrasive is then brought into contact with the workpiece so as to abrade channels in the workpiece.
• the channels define a multiplicity of protrusions, which can be in the form of simple or compound tapered elements.
• the tapered elements can be removed individually from the workpiece and bonded one-at-a- time to separate LED components, or an array of tapered elements can conveniently be bonded to an array of LED components.
• optical elements such as extractors can be made using the techniques described in commonly assigned U.S. Patent Application 11/381,512 (Attorney Docket No.
• such an approach can be used to reduce the quantity of optical material necessary to couple a given amount of light out of the LED component, by simply replacing a single optical taper element with a plurality of smaller ones.
• the difference in material usage can be particularly important when dealing with expensive and difficult-to- work-with materials such as diamond, SiC, and sapphire.
• replacing a single optical tapered element with a 2x2 array of smaller optical tapered elements can reduce the required thickness for the high index (first) optical material by a factor of more than 2
• a 3x3 array can reduce the required thickness by a factor of more than 3.
• gaps or spaces are formed between the elements that can be utilized for various purposes.
• the gaps or spaces can be filled with high refractive index fluids, metal heat conductors, electrical conductors, thermal transport fluids, and combinations thereof.
• Modeling was performed on an LED package in which the LED die was constructed of SiC and an absorbing layer adjusted such that 30% of the light generated within the LED die was emitted from the LED when immersed in a 1.52 refractive index medium.
• the model used a 3x3 array of optical tapered elements coupled to the LED emitting surface as shown in the LED package 80 of FIG. 12.
• the LED die 12' shown there has angled side surfaces 12c' and front emitting surface 12a', to which three of the optical tapered elements 82, 84, 86 are shown coupled at their input surfaces 82a, 84a, 86a respectively. Note the spaces or gaps 83, 85 formed between the smaller optical elements.
• the output surfaces 82b, 84b, 86b couple to an input surface 88a of larger optical tapered element 88, which has output surface 88b.
• the calculated output power (e.g. in Watts) of the modeled LED package is as follows as a function of the small tapered element optical material (designated “A” in the table) and the ambient material (designated “B” in Table III): Table III
• At least a portion of the space between the optical elements can have metal applied to either distribute current to the LED component, or to remove heat from the LED component, or both. Since metals have measurable absorption of light, it can be desirable to minimize absorptive losses. This can be done by minimizing the contact area of the metal with the LED component, and reducing the optical coupling to the metal by introducing a low refractive index material between the metal and the LED component surface, the optical element, or both.
• the contact area can be patterned with an array of metal contacts surrounded by low index material which are in electrical conduct with an upper metal layer. See e.g. the '667 Schubert publication referenced above. Suitable low index materials include a gas or vacuum, fluorocarbons such as fluorinert, available from 3M Company, St. Paul, Minnesota, water, and hydrocarbons.
• the metal can extend into a media surrounding the optical element where heat can be removed.
• the tapered elements can be attached to the LED emitting surface with a low softening temperature solder glass, a soft inorganic coating such as zinc sulfide, a high index fluid, a polymer, a ceramic filled polymer, or by providing the optical elements and LED with very smooth and flat surfaces, and mechanically holding the LED component against the input surfaces of the optical elements.
• FIG. 13 Another LED package 90 having multiple optical elements 92, 94 and a patterned low index layer 96 is depicted in FIG. 13.
• the patterned low index layer 96 includes two apertures as shown over which optical elements 92, 94 are disposed in optical contact with emitting surface 12a of the LED component.
• Layer 96 is also in optical contact with LED component emitting surface 12a, as well as with LED component side surfaces 12c.
• LED package 90 further includes a metal contact 98 shown atop a portion of low index layer 96.
• patterned layer 96 is also patterned in the vicinity of metal contact 98, and metal contact 98 desirably extends through holes in the layer 96 to provide electrical contact to LED component 12.
• a second electrical contact can be provided at another location on the LED component depending on the chip design.
• Each optical element is optically coupled to the emitting surface an LED component (or LED component array) to efficiently extract light and to modify the emission pattern of the emitted light.
• LED sources that include optical elements can be useful in a variety of applications, including, for example, backlights in liquid crystal displays or backlit signs.
• the side emitting pattern has an intensity distribution with a maximum at a polar angle of at least 30°, as measured in an intensity line plot. In other embodiments the side emitting pattern has an intensity distribution centered at a polar angle of at least 30°. Other intensity distributions are also possible with presently disclosed optical elements, including, for example those having maxima and/or centered at 45° and 60° polar angle.
• Converging optical elements can have a variety of forms. Each optical element has a base, an apex, and at least one converging side.
• the base can have any shape (e.g. square, circular, symmetrical or non-symmetrical, regular or irregular).
• the apex can be a point, a line, or a surface (in case of a blunted apex). Regardless of the particular converging shape, the apex is smaller in surface area than the base, so that the side(s) converge from the base towards the apex.
• a converging optical element can be shaped as a pyramid, a cone, a wedge, or a combination thereof.
• a converging optical element can have a polyhedral shape, with a polygonal base and at least two converging sides.
• a pyramid or wedge-shaped optical element can have a rectangular or square base and four sides wherein at least two of the sides are converging sides.
• the other sides can be parallel sides, or alternatively can be diverging or converging.
• the shape of the base need not be symmetrical and can be shaped, for example, as a trapezoid, parallelogram, quadrilateral, or other polygon.
• a converging optical element can have a circular, elliptical, or an irregularly-shaped but continuous base.
• the optical element can be said to have a single converging side.
• an optical element having a circular base can be shaped as a cone.
• a converging optical element comprises a base, an apex residing (at least partially) over the base, and one or more converging sides joining the apex and the base to complete the solid.
• FIG. 15a shows one embodiment of a converging optical element 200 shaped as a four-sided pyramid having a base 220, an apex 230, and four sides 240.
• the base 220 can be rectangular or square and the apex 230 is centered over the base (a projection of the apex in a line 210 perpendicular to the plane of the base is centered over the base 220).
• FIG. 15a also shows LED component 12 having emitting surface 12a which is proximate and parallel to the base 220 of the optical element 200.
• the LED component 12 and optical element 200 are optically coupled at the emitting surface - base interface.
• Optical coupling can be achieved in several ways, described in more detail below.
• the LED component and optical element can be bonded together.
• the base and the emitting surface of the LED component are shown as substantially matched in size. In other embodiments, the base can be larger or smaller than the LED component emitting surface.
• FIG. 15b shows another embodiment of a converging optical element 202.
• optical element 202 has a hexagonal base 222, a blunted apex 232, and six sides 242. The sides extend between the base and the apex and each side converges towards the apex 232.
• the apex 232 is blunted and forms a surface also shaped as a hexagon, but smaller than the hexagonal base.
• FIG. 15c shows another embodiment of an optical element 204 having two converging sides 244, a base 224, and an apex 234.
• the optical element is shaped as a wedge and the apex 234 forms a line. The other two sides are shown as parallel sides. Viewed from the top, the optical element 204 is depicted in FIG. 17d.
• Alternative embodiments of wedge-shaped optical elements also include shapes having a combination of converging and diverging sides, such as the optical element 206 shown in FIG. 16. In the embodiment of FIG. 16, the wedge-shaped optical element 206 resembles an axe-head.
• the two diverging sides 142 act to collimate the light emitted by the LED component.
• the optical element can also be shaped as a cone having a circular or elliptical base, an apex residing (at least partially) over the base, and a single converging side joining the base and the apex.
• the apex can be a point, a line (straight or curved) or it can be blunted forming a surface.
• FIGS. 17a - i show top views of several alternative embodiments of an optical element.
• FIGS. 17a - f show embodiments in which the apex is centered over the base.
• FIGS. 17g - i show embodiments of asymmetrical optical elements in which the apex is skewed or tilted and is not centered over the base.
• FIG. 17a shows a pyramid-shaped optical element having a square base, four sides, and a blunted apex 230a centered over the base.
• Fig. 17h shows a pyramid-shaped optical element having a square base, four sides, and a blunted apex 23Oh that is off-center.
• FIG. 17b shows an embodiment of an optical element having a square base and a blunted apex 230b shaped as a circle. In this case, the converging sides are curved such that the square base is joined with the circular apex.
• FIG. 17c shows a pyramid-shaped optical element having a square base, four triangular sides converging at a point to form an apex 230c, which is centered over the base.
• FIG. 17i shows a pyramid-shaped optical element having a square base, four triangular sides converging at a point to form an apex 23Oi, which is skewed (not centered) over the
• FIGS. 17d-g show wedge-shaped optical elements.
• the apex 23Od forms a line residing and centered over the base.
• the apex 23Oe forms a line that is centered over the base and partially resides over the base.
• the apex 23Oe also has portions extending beyond the base.
• the top view depicted in FIG. 17e can be a top view of the optical element shown perspective in FIG. 16 and described above.
• FIGS. 17f and 17g show two alternative embodiments of a wedge-shaped optical element having an apex forming a line and four converging sides. In FIG. 17f, the apex 23Of is centered over the base, while in FIG. 17g, the apex 23Og is skewed.
• 18c shows a side view of an alternative optical element having a generally triangular cross section.
• the base 325 and the sides 345 and 347 generally form a triangle, but the sides 345 and 347 are non-planar surfaces.
• the optical element has a left side 345 that is curved and a right side that is faceted (i.e. it is a combination of three smaller flat portions 347a-c).
• the sides can be curved, segmented, faceted, convex, concave, or a combination thereof.
• Such forms of the sides still function to modify the angular emission of the light extracted similarly to the planar or flat sides described above, but offer an added degree of customization of the final light emission pattern.
• FIG. 19c the converging portion 441c is convex.
• FIG. 19d shows an optical element 42Od having two sides 44Od formed by joining portions 441d and 442d.
• the portion 442d near the base 422d converges toward the blunted apex 43Od and the top-most portion 441d is perpendicular to the surface of the blunted apex 63Od.
• FIG. 19e shows an alternative embodiment of an optical element 42Oe having curved sides 44Oe.
• the sides 44Oe are s-shaped, but generally converge towards the blunted apex 43Oe.
• the size of the array at the emitting surface side preferably can be matched to the size of the base of the optical element.
• the shape of the array need not match the shape of the base, as long as they are matched in at least one dimension (e.g. diameter, width, height, or surface area).
• the optical element base can be made having a matching square having a lmm side.
• a square emitting surface could be optically coupled to a rectangular base, the rectangle having one of its sides matched in size to the size of the emitting surface side.
• the non-matched side of the rectangle can be larger or smaller than the side of the square.
• an optical element can be made having a circular base having a diameter equal to the diagonal dimension of the emitting surface. For example, for a lmm by lmm square emitting surface a circular base having a diameter of 1.41 mm would be considered matched in size for the purpose of this application.
• the size of the base can also be made slightly smaller than the size of the emitting surface. This can have advantages if one of the goals is to minimize the apparent size of the light source, as described in commonly owned U.S. Patent Application Publication 2006/0091411 (Ouderkirk et al), "High Brightness LED Package”.
• FIG. 21 shows another embodiment of a light source comprising a converging optical element 624 optically coupled to a plurality of LED components 614a-c arranged in an array 612. This arrangement can be particularly useful when red, green, and blue LEDs are combined in the array to produce white light when mixed.
• the optical element 624 has converging sides 646 to redirect light to the sides.
• the optical element 624 has a base 624 shaped as a square, which is optically coupled to the array of LED components 612.
• the array of LED components 612 also forms a square shape (having sides 616).
• Optical elements disclosed herein can be manufactured by conventional means or by using precision abrasive techniques disclosed in commonly assigned U.S. Patent Application Publication 2006/0094340 (Ouderkirk et al.), "PROCESS FOR MANUFACTURING OPTICAL AND SEMICONDUCTOR ELEMENTS", U.S. Patent Application Publication 2006/0094322 (Ouderkirk et al.), “PROCESS FOR MANUFACTURING A LIGHT EMITTING ARRAY”, and U.S. Patent Application No. 11/288071, "ARRAYS OF OPTICAL ELEMENTS AND METHOD OF
• the disclosed optical elements are transparent and preferably have a relatively high refractive index.
• Suitable materials for the optical element include without limitation inorganic materials such as high index glasses (e.g. Schott glass type LASF35, available from Schott North America, Inc., Elmsford, NY under a trade name LASF35) and ceramics (e.g. sapphire, zinc oxide, zirconia, diamond, and silicon carbide). Sapphire, zinc oxide, diamond, and silicon carbide are particularly useful since these materials also have a relatively high thermal conductivity (0.2 - 5.0 W/cm K).
• Suitable polymers can be both thermoplastic and thermosetting polymers.
• Thermoplastic polymers can include polycarbonate and cyclic olefin copolymer.
• Thermosetting polymers can be for example acrylics, epoxy, silicones and others known in the art.
• Suitable ceramic nanoparticles include zirconia, titania, zinc oxide, and zinc sulfide.
• the index of refraction of the optical element is matched to the index of refraction of the primary emitting surface.
• the index of refraction of the optical element can be higher or lower than the index of refraction of the emitting surface.
• the LED component 12 When made of high index materials, optical elements increase light extraction from the LED component due to their high refractive index and modify the emission distribution of light due to their shape, thus providing a tailored light emission pattern.
• the LED component 12 is depicted generically for simplicity, but can include conventional design features as known in the art in addition to the re-emitting structures described above.
• the LED component can include distinct p- and n-doped semiconductor layers, buffer layers, substrate layers, and superstrate layers.
• a simple rectangular LED component arrangement is shown, but other known configurations are also contemplated, e.g., angled side surfaces forming a truncated inverted pyramid LED component shape.
• Electrical contacts to the LED component are also not shown for simplicity, but can be provided on any of the surfaces of the die as is known.
• the LED component has two contacts both disposed at the bottom surface in a "flip chip" design.
• the present disclosure is not intended to limit the shape of the optical element or the shape of the LED component, but merely provides illustrative examples.
• An optical element is considered optically coupled to, or in optical contact with, an
• FIG. 14 shows a gap 150 between the emitting surface 12a of the LED component 12 and the base 120 of optical element 99.
• the gap 150 is an air gap and is typically very small to promote frustrated total internal reflection.
• the base 120 of the optical element 99 is optically close to the emitting surface 12a of the LED component 12, if the gap 150 is on the order of the wavelength of light in air.
• the thickness of the gap 150 is less than a wavelength of light in air.
• the gap 150 is preferably at most the value of the longest wavelength. Suitable gap sizes include 25 nm, 50 nm, and 100 nm. Preferably, the gap is minimized, such as when the LED component and the input aperture or base of the optical element are polished to optical flatness and wafer bonded together. In addition, it is preferred that the gap 150 be substantially uniform over the area of contact between the emitting surface 12a and the base 120, and that the emitting surface 12a and the base 120 have a roughness of less than 20 nm, preferably less than 5 nm.
• the surface of the base 120 can be shaped to match the emitting surface 12a.
• the emitting surface 12a of LED component 12 is flat, as shown in FIG. 14, the base 120 of optical element 99 can also be flat.
• the emitting surface of the LED component is curved (e.g. slightly concave) the base of the optical element can be shaped to mate with the emitting surface (e.g. slightly convex).
• the size of the base 120 may either be smaller, equal, or larger than LED component emitting surface 12a.
• the base 120 can be the same or different in cross sectional shape than LED component 12.
• the LED component can have a square emitting surface while the optical element has a circular base. Other variations will be apparent to those skilled in the art.
• an LED component can be optically coupled to the optical element without use of any adhesives or other bonding agents between the LED component and the optical element.
• Non-bonded embodiments allow both the LED component and the optical element to be mechanically decoupled and allowed to move independently of each other.
• the optical element can move laterally with respect to the LED component.
• both the optical element and the LED component are free to expand as each component becomes heated during operation.
• optical element and LED component can be encapsulated together using any of the known encapsulant materials, to make a final LED package or light source. Encapsulating the optical element and LED component provides a way to hold them together in the non-bonded embodiments.
• the optical element can be made from a single structure, for example cut from a single block of material, or can be made by joining two or more sections together in a compound construction.
• a first section desirably makes optical contact with the LED component, and is made of a first optical material having a high refractive index (preferably about equal to the LED component refractive index at the emitting surface), and optionally high thermal conductivity, and/or high thermal stability.
• high thermal stability refers to materials having a decomposition temperature of about 600 0 C or more.
• the thickness of the first section is preferably optically thick (e.g. effectively at least 5 microns, or 10 times the wavelength of light).
• Silicon carbide is also electrically conductive, and as such may also provide an electrical contact or circuit function. Scattering within optical elements may be acceptable if the scattering is limited to a position near the input end or base of the optical element. However, it would be expensive and time consuming to make an optical element with sufficient length to efficiently couple light from an LED component. An additional challenge in making one-piece optical elements is that the material yield may be relatively low, and the form- factor may force the LED component to be individually assembled with the optical element. For these reasons, it can be advantageous to divide the optical element into two (or more) sections, the sections being made of different optical materials, to reduce manufacturing cost.
• the disclosed light sources may be a component or the critical component of a graphic display device such as a large- or small-screen video monitor, computer monitor or display, television, telephone device or telephone device display, personal digital assistant or personal digital assistant display, pager or pager display, calculator or calculator display, game or game display, toy or toy display, large or small appliance or large or small appliance display, automotive dashboard or automotive dashboard display, automotive interior or automotive interior display, marine dashboard or marine dashboard display, marine interior or marine interior display, aeronautic dashboard or aeronautic dashboard display, aeronautic interior or aeronautic interior display, traffic control device or traffic control device display, advertising display, advertising sign, or the like.
• a graphic display device such as a large- or small-screen video monitor, computer monitor or display, television, telephone device or telephone device display, personal digital assistant or personal digital assistant display, pager or pager display, calculator or calculator display, game or game display, toy or toy display, large or small appliance or large or small appliance display, automotive dashboard or automotive dashboard display, automotive interior or automotive interior display, marine dashboard or
• the disclosed light sources may be a component or the critical component of a liquid crystal display (LCD), or like display, as a backlight to that display.
• the semiconductor device is specially adapted for use a backlight for a liquid crystal display by matching the colors emitted by the semiconductor device to the color filters of the LCD display.
• the disclosed light sources may be a component or the critical component of an illumination device such as a free-standing or built-in lighting fixture or lamp, landscape or architectural illumination fixture, hand-held or vehicle-mounted lamp, automotive headlight or taillight, automotive interior illumination fixture, automotive or non- automotive signaling device, road illumination device, traffic control signaling device, marine lamp or signaling device or interior illumination fixture, aeronautic lamp or signaling device or interior illumination fixture, large or small appliance or large or small appliance lamp, or the like; or any device or component used as a source of infrared, visible, or ultraviolet radiation.
• an illumination device such as a free-standing or built-in lighting fixture or lamp, landscape or architectural illumination fixture, hand-held or vehicle-mounted lamp, automotive headlight or taillight, automotive interior illumination fixture, automotive or non- automotive signaling device, road illumination device, traffic control signaling device, marine lamp or signaling device or interior illumination fixture, aeronautic lamp or signaling device or interior illumination fixture, large or small appliance or large or small appliance lamp, or the like; or any device or component used as
• a light source includes: (a) an LED that is capable of emitting light at a first wavelength; (b) a re-emitting semiconductor construction that includes a potential well that is not located within a pn junction, where the re-emitting semiconductor construction has an emitting surface; (c) a patterned low index layer in optical contact with a first portion of the emitting surface, where the patterned layer has a first refractive index; and (d) an optical element that has an input surface in optical contact with a second portion of the emitting surface, where the optical element has a second refractive index higher than the first refractive index.
• the patterned low index layer provides total internal reflection at the emitting surface for at least some light generated within the light source.
• a light source includes: (a) an LED component that includes: (i) an LED that is capable of emitting light at a first wavelength; and (ii) a re-emitting semiconductor construction which includes a potential well not located within a pn junction, where the re-emitting semiconductor construction has an emitting surface; (b) means for totally internally reflecting at least some of the light generated by the LED component back into the LED component, where the reflecting means is in optical contact with a first portion of the emitting surface; and (c) an optical element that has an input surface in optical contact with a second portion of the emitting surface different from the first portion.
• a light source includes: (a) an LED component that includes: (i) an LED component that includes: (i) an LED that is capable of emitting light at a first wavelength; and (ii) a re-emitting semiconductor construction which includes a potential well not located within a pn junction, where the re-emitting semiconductor construction has an emitting surface; (b) means for totally internally reflecting
• a light source includes: (a) an LED component that includes: (i) an LED that is capable of emitting light at a first wavelength; and (ii) a re-emitting semiconductor construction which includes a second potential well not located within a pn junction, where the re-emitting semiconductor construction has an emitting surface; and (b) a plurality of optical elements, where each such optical element has an input surface.
• the optical elements are sized such that the input surfaces are spaced apart from each other and are in optical contact with different portions of the emitting surface.
• a light source includes: (a) an LED component that includes a first potential well located within a pn junction and a second potential well not located within a pn junction, where the LED component has an emitting surface; (b) a patterned low index layer that is in optical contact with a first portion of the emitting surface, where the patterned layer has a first refractive index; and (c) an optical element that has an input surface in optical contact with a second portion of the emitting surface.
• the optical element has a second refractive index that is higher than the first refractive index.
• the patterned low index layer provides total internal reflection at the emitting surface for at least some light generated within the light source.
• a light source includes: (a) an LED component that includes a first potential well located within a pn junction and a second potential well not located within a pn junction, where the LED component has an emitting surface; (b) means for totally internally reflecting at least some of the light generated by the LED component back into the LED component, where the reflecting means is in optical contact with a first portion of the emitting surface; and (c) an optical element that has an input surface in optical contact with a second portion of the emitting surface different from the first portion.
• a light source includes: (a) an LED component that includes a first potential well located within a pn junction and a second potential well not located within a pn junction, where the LED component has an emitting surface; and (b) a plurality of optical elements, where each such optical element has an input surface.
• the optical elements are sized such that the input surfaces are spaced apart from each other and are in optical contact with different portions of the emitting surface.
• a light source includes: (a) an LED that is capable of emitting light at a first wavelength and has an emitting surface; (b) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; (c) a patterned low index layer in optical contact with a first portion of the emitting surface, that the patterned layer has a first refractive index; and (d) an optical element that has an input surface in optical contact with a second portion of the emitting surface.
• the optical element has a second refractive index higher than the first refractive index.
• the patterned low index layer provides total internal reflection at the emitting surface for at least some light generated within the light source.
• a light source includes: (a) and LED component that includes: (i) an LED that is capable of emitting light at a first wavelength and has an emitting surface; (b) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; (c) a patterned low index layer in
• a light source includes: (a) an LED component that includes: (i) an LED that is capable of emitting light at a first wavelength and has an emitting surface; and (ii) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; and (b) a collimating optical element that has an input surface and an output surface.
• the input surface is in optical contact with at least a portion of the emitting surface.
• the optical element includes a first portion that includes the input surface and is composed of a first material.
• the optical element includes a second portion that includes the output surface and is composed of a second material.
• the first material has a refractive index greater than that of the second material.
• the first material has a thermal conductivity greater than that of the second material.
• a light source includes: (a) an LED component that includes: (i) an LED that is capable of emitting light at a first wavelength and has an emitting surface; and (ii) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; and (b) a plurality of optical elements, where each optical element has an input surface.
• the optical elements are sized such that the input surfaces are spaced apart from each other and are in optical contact with different portions of the emitting surface.
• a light source includes: (a) an LED that is capable of emitting light at a first wavelength and has an emitting surface; (b) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; and (c) a light extractor that has an input surface in optical contact with the emitting surface.
• a light source includes: (a) an LED that is capable of emitting light at a first wavelength; (b) a re-emitting semiconductor construction that includes a potential well not located within a pn junction and has an emitting surface; and (c) a patterned low index layer in optical contact with a first portion of the emitting surface which is less than all of the emitting surface.
• the patterned layer has a refractive index lower than that of the emitting surface.
• a light source includes: (a) an LED component that includes a first potential well located within a pn junction and a second potential well not located within a pn junction, where the LED component has an emitting surface; and (b) a patterned low index layer in optical contact with a first portion of the emitting surface which is less than all of the emitting surface.
• the patterned layer has a refractive index lower than that of the emitting surface.
• a light source includes: (a) an LED that is capable of emitting light at a first wavelength and has an emitting surface; (b) a re-emitting semiconductor construction that includes a potential well not located within a pn junction; and (c) a patterned low index layer in optical contact with a first portion of the emitting surface which is less than all of the emitting surface.
• the patterned layer has a refractive index lower than that of the emitting surface.
• a graphic display device or an illumination device includes the light source.

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• 2007
  • 2007-06-11 EP EP07798367.4A patent/EP2033236A4/de active Pending
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