WO2013064800A1 - Illumination apparatus - Google Patents

Illumination apparatus Download PDF

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Publication number
WO2013064800A1
WO2013064800A1 PCT/GB2012/000828 GB2012000828W WO2013064800A1 WO 2013064800 A1 WO2013064800 A1 WO 2013064800A1 GB 2012000828 W GB2012000828 W GB 2012000828W WO 2013064800 A1 WO2013064800 A1 WO 2013064800A1
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WO
WIPO (PCT)
Prior art keywords
light emitting
emitting elements
inorganic light
array
elements
Prior art date
Application number
PCT/GB2012/000828
Other languages
French (fr)
Inventor
Graham John Woodgate
Jonathan Harrold
Original Assignee
Optovate Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Optovate Limited filed Critical Optovate Limited
Publication of WO2013064800A1 publication Critical patent/WO2013064800A1/en

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Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V5/00—Refractors for light sources
    • F21V5/007—Array of lenses or refractors for a cluster of light sources, e.g. for arrangement of multiple light sources in one plane
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/20—Light sources comprising attachment means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/90—Methods of manufacture
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V5/00—Refractors for light sources
    • F21V5/10—Refractors for light sources comprising photoluminescent material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
    • H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
    • H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
    • H01L25/16—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof the devices being of types provided for in two or more different main groups of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. forming hybrid circuits
    • H01L25/167—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof the devices being of types provided for in two or more different main groups of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. forming hybrid circuits comprising optoelectronic devices, e.g. LED, photodiodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/15—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components having potential barriers, specially adapted for light emission
    • H01L27/153—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components having potential barriers, specially adapted for light emission in a repetitive configuration, e.g. LED bars
    • H01L27/156—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components having potential barriers, specially adapted for light emission in a repetitive configuration, e.g. LED bars two-dimensional arrays
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/70—OLEDs integrated with inorganic light-emitting elements, e.g. with inorganic electroluminescent elements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V7/00—Reflectors for light sources
    • F21V7/0091—Reflectors for light sources using total internal reflection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2105/00—Planar light sources
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2105/00—Planar light sources
    • F21Y2105/10—Planar light sources comprising a two-dimensional array of point-like light-generating elements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • F21Y2115/15—Organic light-emitting diodes [OLED]

Definitions

  • the present invention relates to an illumination apparatus and a method for fabrication of the illumination apparatus.
  • Such an apparatus may be used for domestic or professional lighting, and for general illumination purposes.
  • LEDs Inorganic light-emitting diodes formed using semiconductor growth onto monolithic wafers can demonstrate significantly higher levels of efficiency compared to incandescent sources.
  • LED refers to an unpackaged LED die (chip) extracted directly from a monolithic wafer, i.e. a semiconductor element. This is different from packaged LEDs which have been assembled into a package to facilitate subsequent assembly and may further incorporate optical elements such as a hemispherical structure that increases light extraction efficiency and size.
  • blue iLED elements are commonly combined with a wavelength converting phosphor material.
  • Such an approach suffers from losses including Stokes losses that reduce the achievable output efficiency and thus increase cost.
  • Such arrangements also advantageously enable colour tuning of the final output to match the lighting user's requirements by adjusting the relative proportion of light in red, green and blue channels of the illuminator.
  • iLED elements can be produced with high quantum efficiency in red and blue output wavelengths but material systems can constrain quantum efficiency in the green part of the spectrum. Thus typically it is desirable to use more green chips than red and blue in order to create a white colour output, increasing cost.
  • OLEDs Organic light-emitting diodes formed using coating of organic materials onto substrates are capable of production with large areas but with luminance levels substantially lower than that achieved by iLEDs.
  • an illumination apparatus refers to an illumination apparatus whose primary purpose is illumination of an environment such as a room or street scene, or as a display backlight such as an LCD backlight.
  • An illumination apparatus is typically capable of significantly higher luminance than 1000 nits. This is opposed to for example displays, whose primary purpose is image display by providing light to a viewing observer's eyes so that an image can be seen.
  • the luminance of a display is very high, for example greater than 1000 nits, then disadvantageously a display can be uncomfortably bright to view.
  • the considerations for an illumination apparatus with a primary illumination purpose and a display apparatus that provides an incidental iltumination purpose are different.
  • an illumination apparatus is used as a backlight in a display apparatus, losses in the spatial light modulator of the display apparatus will reduce the luminance to a level suitable for comfortable viewing.
  • an arrangement has an incidental illumination function that is not generally suitable for the purpose of efficient and bright illumination of an environment.
  • an illumination apparatus whose primary purpose is illumination as opposed to display, comprising: an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in gaps between the organic light emitting elements; and the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively Temoved inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the
  • the illumination apparatus may further comprise at least one further array of inorganic light emitting elements for emitting light at a third wavelength or spectral band, the third wavelength or spectral band being different from the first and second wavelengths or spectral bands.
  • the first wavelength or spectral band may be a green wavelength or is in the green spectral band.
  • An array of wavelength conversion elements may be arranged in alignment with the array or inorganic light emitting elements.
  • the first, second and third spectral bands may be arranged to provide white light output.
  • the illumination apparatus may further comprise a controller arranged to separately control the current in the inorganic light emitting elements and inorganic light emitting elements.
  • a method of manufacturing an illumination apparatus comprising: providing an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and providing an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements and the array of inorganic light emitting elements are provided on a common substrate and arranged such that the inorganic light emitting elements are positioned ((interspersed)) in gaps between the organic light emitting elements; and wherein providing the array of inorganic light emitting elements comprises: forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-
  • an illumination apparatus whose primary purpose is illumination as opposed to display, comprising: at least one organic light emitting element for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the at least one organic light emitting element and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in apertures within the at least one organic light emitting elements; and the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements
  • the current embodiments provide a large area light source that achieves high efficiency in a first spectral band, such as the blue part of the spectrum by means of providing microscopic iLED elements with output in the first spectral band; and high efficiency and lifetime in a second spectral band such as the green part of the spectrum by means of providing macroscopic OLED elements with output in the second spectral band.
  • the microscopic iLED elements are interspersed with the macroscopic regions of OLED elements to achieve a uniform white appearance to an observer, advantageously improving the appearance of the lamp when viewed directly, and to improve the glare characteristics of the apparatus.
  • the present embodiments achieve an efficient, white and colour tuneable large area lighting apparatus with low cost.
  • the present embodiments may advantageously comprise common output coupling optical elements across the array to provide higher output efficiency and low cost of manufacture.
  • Fig. 1 shows in plan view a combination of iLED elements and OLED elements provided on a substrate with a first arrangement
  • Fig. 2 shows a method to provide a combination of iLED elements and OLED elements over a large area
  • Fig.3 shows a further method to provide a combination of iLED elements and OLED elements over a large area
  • Fig.4 shows a further method to provide a combination of iLED elements and OLED elements over a large area
  • Fig.5 shows a method to singulate a mothersheet comprising a combination of iLED elements and OLED elements
  • Fig.6a shows in plan view a further combination of iLED elements and OLED elements provided on a substrate
  • Fig.6b shows in plan view a further combination of iLED elements and OLED elements provided on a substrate
  • Fig.7 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate
  • Fig.8 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate
  • Ftg.9 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate
  • Fig.lO shows in plan view an arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements
  • Fig.ll shows in cross section an arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements
  • Fig.12 shows in cross section a method to provide the optical elements of Figs.20 and 11;
  • Fig.13 shows a catadioptric optical element array
  • Fig.14 shows in cross section a further arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements using the optical element array of Fig.13;
  • Fig.15 shows in cross section an integrated light diffusing arrangement
  • Fig.16 shows in cross section an air spaced light diffusing arrangement.
  • Fig.l shows a first embodiment comprising a substrate 2 provided with an anay of organic light emitting elements 4 comprising regions of green OLED material.
  • An array of inorganic light emitting elements 6 comprising blue iLED elements and array of inorganic light emitting elements 8 comprising red iLED elements are provided in alignment with the array of OLED elements 4.
  • LEDs are one form of light emitting elements.
  • the elements 6 and 8 comprise inorganic LED elements that are formed in steps comprising forming a monolithic array of light-emitting elements; selectively removing a plurality of light-emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed light- emitting elements; forming a non-monolithic array of light-emitting elements with the selectively removed light-emitting elements in a manner that preserves the relative spatial position of the selectively removed light- emitting elements; wherein the plurality of light-emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light- emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction.
  • the inorganic LEDs are formed using the method described in GB24639
  • Electrodes and addressing circuitry are provided to achieve electrical connections to the respective light emitting elements 4, 6 and 8.
  • the addressing circuitry may be arranged to advantageously achieve connection to the respective elements, and may also be used to control the output of at least some of the elements to achieve colour tuning.
  • the advantages of highly efficient blue iLED elements with the efficiency and lifetime of green OLED elements can demonstrate high efficiency for all colours and is colour tunable. Further, such an apparatus can be made at low cost.
  • the luminous emittance (measured in lumen/m 2 ) of OLED elements may be three or more orders of magnitude less than the luminous emittance of iLED elements; thus OLED elements are much larger in size than iLED elements.
  • iLED lamps typically comprise further directional optical elements to increase the effective source size and direct the light into a limited viewing cone, so that the lamp can only be seen directly from a limited range of angles.
  • OLED elements are much larger and so not well suited to directional optics. In operation, OLED elements may thus be easily viewed directly by an observer.
  • OLED lighting and the present hybrid OLED-iLED lighting embodiments consider the glare characteristics for an observer looking directly at the surface of the lighting apparatus during operation. For the glare from such a apparatus to appear uniformly white for an observer, it is desirable that the angular size of the group of light emitting elements comprising respective green regions of array 4, and the blue and red elements of arrays 6 and 8 is smaller than the typical human angular resolvable size, for example 1/2000.
  • a ceiling mounted light is arranged at a distance of 2m from an observer, so the angularly resolvable size will be typically less than 1mm.
  • the luminous efficiency of the elements of the elements 6,8 is the same, and if the luminous emittance of an iLED element is 1000 times greater than for an equivalent OLED element, then each of the iLED element areas is approximately 30x30micromerres (on a pitch of lxlmm) while the green OLED elements will substantially fill the remaining space.
  • Such an arrangement provides a visual colour integration and resulting white appearance of the lamp.
  • the iLED elements are provided at spacing substantially greater than lxlmm then glare from the light source will appear to be green, with interspersed red and blue emitting regions; the output will not appear to be white.
  • the white uniformity of the glare from the apparatus tends to be improved by the use of microscopic iLEDs as described interspersed in small gaps between the relatively very much larger macroscopic OLEDs, compared to hypothetical alternative arrangements in which relatively large macroscopic OLEDs of different colours might be arranged together in an interspersed fashion.
  • iLED elements are preferable.
  • such an element may have an area of approximately 500x500mm 2 and use 250,000 individual elements in each of the arrays of elements 6, 8. If the individual iLED elements were attached by means of element-at-a-time pick-and-place operations then the cost of mounting the elements would be prohibitive. Further the electrode attachment steps (for example by means of wire bonding) would provide very high costs and very low output efficiency.
  • the present embodiments achieve high efficiency operation over large areas by means of selective removal of a plurality of light-emitting elements from a monolithic iLED array in a manner that preserves the relative spatial position of the selectively removed light-emitting elements. Further, such elements can be formed over large area to provide the desired output brightness for a single lamp at low cost.
  • iLED elements are formed as shown in Fig.2, then it is possible to conveniently attach many iLED elements to the substrate 2 in a single mounting operation. Further the electrodes may be provided by means of photolithography operations and as such may have a small area compared to the element area, advantageously achieving high output efficiency.
  • a method to form a hybrid iLED-OLED illumination apparatus is shown in Fig.2.
  • a first step at least one mask 62 mounted on a substrate 63 is used to illuminate a monolithic light-emitting element wafer comprising epitaxial layers 60 and substrate 61.
  • the layer 60 may comprise epitaxial layers that achieve blue light output in operation.
  • monolithic refers to consisting of one piece; solid or unbroken.
  • an array 76 of light-emitting elements is formed in the monolithic wafer 60, 61.
  • Each element has a position and orientation defined by the mask 62.
  • the mask is composed of an array of regions, each region defining the structure of at least one layer of an iLED chip. Regions 65 and 67 represent first and second iLED chips and have separation si as shown.
  • elements 72 and 74 are formed from regions 65 and 67 of the mask.
  • the separation si of the elements 72, 74 is substantially the same as the separation of the mask regions 65, 67 and the orientation of the elements 72, 74 is the same as the orientation of the respective mask regions 65, 67.
  • the integrity of separation si and orientation of elements 72, 74 is preserved through the subsequent processing steps.
  • Multiple masks may be used to photolithographically form the complete iLED structure in the manner described, each with regions with the separation si. Such processes preserve a separation and orientations of elements 72 and 74.
  • the array 76 of light-emitting elements may be cut by means of a cutting device 82, which may for example be a scribe, cutting wheel, laser or saw.
  • the separation s2 of the cut lines for a respective edge of elements 72, 74 would ideally be the same as the separation si. However, in practice such a precise separation is very difficult to achieve.
  • the embodiment does not require the separation s2 to be identical to the separation si.
  • a tool 90 which may for example be an adhesive film is attached to the array 76.
  • a patterned array of UV light is imaged onto the interface of the elements 72,74 with the substrate 61 so that separation of the elements from the substrate 61 is achieved.
  • a fifth step the tool 90 together with elements 72,74 is removed, extracting a sparse array of light emitting elements.
  • the integrity of the separation si and orientation of the elements 72 and 74 is advantageously preserved in this extraction step.
  • Fig.3 shows a method wherein the sparse array of iLED elements, comprising light emitting elements 72,74 are formed on the substrate 2.
  • Substrate 2 may be formed with patterned layer of OLED elements 4 and electrode layers (not shown).
  • Open regions 91 may be formed between the regions 4 of OLED material for example by patterned deposition of the OLED material or by uniform deposition followed by patterning of the material, for example by means of lithography or laser removal.
  • the output colour for example the white point, may be adjusted by trimming, e.g. by laser ablation, the emitting area of the OLED elements 4.
  • this trimming process could be arranged so that groups of emitting areas have similar white points at the same operating current.
  • the sparse array of light emitting elements 72, 74 on tool 90 are aligned with the regions 91 and attached to the substrate 2, for example by means of solder, or conductive adhesive.
  • the tool 90 is then removed and electrode layers 92, 94 deposited to provide electrical connection to iLED elements 72, 74 and OLED elements 4.
  • Further planarization layers 96 and encapsulation layers 98, such as a glass cover layer may be added.
  • layer 2 may be thinned (by known techniques such as grinding and polishing) prior to attachment of heatsinks.
  • an illumination apparatus whose primary purpose is illumination as opposed to display, comprises an array of organic light emitting elements 4 for emitting light at a first wavelength ⁇ spectral band (for example a green spectral band); and an array of inorganic light emitting elements 6 for emitting light at a second wavelength or spectral band (for example a blue spectral band), the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements 4 and the array of inorganic light emitting elements 6 are arranged on a common substrate 2 with the inorganic light emitting elements 6 interspersed in gaps between the organic light emitting elements; and the array of inorganic light emitting elements 6 were formed in steps comprising forming a monolithic array 76 of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements 6 from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements 6; forming a non-
  • Fig.4 shows in plan view, an arrangement comprising a large substrate 2 on which multiple tools 90, each comprising a sparse array of blue iLED elements are aligned. Further tools 100 comprising red iLED elements may also be aligned with the substrate 2.
  • the subsequent layers 92, 94, 6 and 98 may be added across the whole of the mothersheet area so that operations on the respective iLED and OLED elements are performed in parallel.
  • the mothersheet may be cut to different sizes (e.g for a desired light output and/or a specific shape) to suit the application, for example along lines 96 as shown in Fig.5.
  • this enables a large area of hybrid iLED-OLED lamp to be fabricated in parallel, reducing cost.
  • Fig.6a shows an embodiment wherein the iLED elements are arranged in holes 10 in a continuous region, comprising element 4 of OLED material.
  • Wavelength conversion elements 7 may further be provided in alignment with at least some of the inorganic light emitting elements 6 as shown in Fig.6b.
  • red light emitting elements may be provided by a blue light emitting element 6 and a red conversion phosphor wavelength conversion element 7.
  • Fig.7 shows a further embodiment wherein the iLED elements and electrodes (not shown) are formed on the surface of a continuous layer of OLED elements.
  • Advantageously such an arrangement reduces the complexity of the OLED layer and uses a single drive circuit, reducing cost .
  • Fig.8 shows a further embodiment wherein an OLED layer is formed over iLED elements for OLED material structures that are transmissive in the red and blue parts of the spectrum.
  • an OLED layer is formed over iLED elements for OLED material structures that are transmissive in the red and blue parts of the spectrum.
  • the size of the red and blue iLED elements in the present embodiments may be different to compensate for differences in luminous emittance between blue elements 6 and red elements 8 to advantageously achieve a means to colour balance the illumination apparatus.
  • guiding of the light from the iLED elements 6,8 within the OLED layers may be used to increase the area over which light from the iLED elements is emitted.
  • this achieves a reduced density of iLED elements to meet visual colour integration requirements.
  • Such a reduced density means that the iLED elements can be larger, which may improve output efficiency of the devices by achieving a
  • Fig.9 shows a further embodiment wherein regions 12 of red OLED material are combined with regions 4 of green OLED material and an array of blue iLED elements 6.
  • Fig.10 shows in plan view output coupling optical elements to improve output extraction efficiency.
  • the output optic is substantially the same for each of the red, green and blue emitting elements.
  • regions 4 may be provided with the same nominal size and spacing, and optical elements 16 provided in alignment with the elements 4, 6.
  • the optical elements 16 may be hemispherical optical elements.
  • a further protective transparent substrate 18 and diffuser layer 22 may further be provided and attached to the substrate 2 by means of sealing material 20.
  • Such an arrangement provides a protected output surface and further optical characteristics that can be used to blur the appearance of the separate red, green and blue elements with high efficiency.
  • a method to form the hemispherical optical elements 16 is shown in Fig.12.
  • the arrays of elements 4, 6 are provided on substrate 2.
  • a tool 24 is provided in alignment with the elements 4, 6 and filled with a material 26 which is cured.
  • optical elements 16 are formed.
  • Advantageously many optical elements can be formed in parallel over a large area.
  • the optical elements 16 are formed on a separate substrate that is aligned to a large mothersheet substrate 2 suitable for subsequent dicing.
  • hemispherical optical elements 16 are difficult to fabricate reliably on such a substrate if the input surface of the hemisphere is to be brought into contact with the elements 4, 6, 8.
  • a further embodiment is provided in Fig.13 comprising a catadioptric optical element 38 (comprising reflective and refractive optical functions) formed on the surface of a substrate 18 and with an input aperture 37.
  • the elements when assembled with the light emitting elements, the elements comprise an outer wall section 28 to provide a total internal reflection function, a wall section 30 to provide a refractive deflection of light and a central section 32 to direct light from the source to the output.
  • a material 34 with high refractive index can be provided in combination with a material 36 with low refractive index so that the light from the emitting elements comprising elements 4, may be efficiently coupled from the light emitting elements.
  • the area of the substrate 2 covered by the OLED elements 4 is preferably maximised to provide the lowest cost of the elements.
  • the gaps between emitters are preferably minimised. This can be achieved by arranging the optical elements to provide substantially a full 2 * pi steradian output cone angle.
  • the light emitting elements 4, 6, 8 can be aligned with the input aperture 37 of the optical elements.
  • An optional diffuser 22 may be incorporated to further reduce the directionality of the output.
  • OLED elements 4 may be incorporated in the gaps between the optical elements providing further light mixing between the iLED and OLED elements.
  • the optical elements 38 can be formed over a large area on substrate 18 so that substrate 18 can be provided in alignment to substrate 2.
  • Individual lamps may be extracted from the array of aligned substrates by dicing the two elements after attachment as shown in Fig.5. In this manner, low cost with high efficiency may be achieved.
  • diffuser 22 may be provided for example with a +/-30 degree angular spread, spaced a distance 23 of 3mm from the elements 4, 6, 8 would provide an effective light integration area of approximately 3mm width. This advantageously achieves an iLED element size of approximately lOOxlOQmicrometre area. FurtheT the spacing 23 can conveniently be achieved using the thickness of substrate 18 and diffuser 22, thus advantageously providing an integrated structure with good mechanical ruggedness and high transmission efficiency.
  • an air spaced diffuser could be used to provide higher degree of separation of the diffuser, for example 25mm, enabling larger chip sizes that may be more suitable for pick-and -place fabrication.
  • an arrangement disadvantageously suffers from increased light losses from surface reflectivity of the additional interfaces of substrate 18 and diffuser 22 with air, thus reducing efficiency compared to the present embodiments.
  • a wide angle diffuser could be used. However, such high angle diffusers suffer from higher losses and degrade efficiency.

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Abstract

An illumination apparatus comprises an array of inorganic light emitting elements (6 or 8) from a monolithic wafer arranged with an array of organic light emitting elements (4). The inorganic light emitting elements (6 or 8) are provided at reduced density compared to the organic light emitting elements (4), achieving high efficiency, long lifetime and high uniformity for white light illumination over a large area.

Description

ILLUMINATION APPARATUS
The present invention relates to an illumination apparatus and a method for fabrication of the illumination apparatus. Such an apparatus may be used for domestic or professional lighting, and for general illumination purposes.
Inorganic light-emitting diodes (iLEDs) formed using semiconductor growth onto monolithic wafers can demonstrate significantly higher levels of efficiency compared to incandescent sources. In this specification LED refers to an unpackaged LED die (chip) extracted directly from a monolithic wafer, i.e. a semiconductor element. This is different from packaged LEDs which have been assembled into a package to facilitate subsequent assembly and may further incorporate optical elements such as a hemispherical structure that increases light extraction efficiency and size.
To provide white light output, blue iLED elements are commonly combined with a wavelength converting phosphor material. However, such an approach suffers from losses including Stokes losses that reduce the achievable output efficiency and thus increase cost. It would be desirable to combine highly efficient red, green and blue LEDs in order to overcome losses in the phosphor materials. Such arrangements also advantageously enable colour tuning of the final output to match the lighting user's requirements by adjusting the relative proportion of light in red, green and blue channels of the illuminator. iLED elements can be produced with high quantum efficiency in red and blue output wavelengths but material systems can constrain quantum efficiency in the green part of the spectrum. Thus typically it is desirable to use more green chips than red and blue in order to create a white colour output, increasing cost.
Organic light-emitting diodes (OLEDs) formed using coating of organic materials onto substrates are capable of production with large areas but with luminance levels substantially lower than that achieved by iLEDs.
In this specification, an illumination apparatus refers to an illumination apparatus whose primary purpose is illumination of an environment such as a room or street scene, or as a display backlight such as an LCD backlight. An illumination apparatus is typically capable of significantly higher luminance than 1000 nits. This is opposed to for example displays, whose primary purpose is image display by providing light to a viewing observer's eyes so that an image can be seen. By way of comparison, if the luminance of a display is very high, for example greater than 1000 nits, then disadvantageously a display can be uncomfortably bright to view. Thus the considerations for an illumination apparatus with a primary illumination purpose and a display apparatus that provides an incidental iltumination purpose are different. If an illumination apparatus is used as a backlight in a display apparatus, losses in the spatial light modulator of the display apparatus will reduce the luminance to a level suitable for comfortable viewing. Thus such an arrangement has an incidental illumination function that is not generally suitable for the purpose of efficient and bright illumination of an environment.
According to a first aspect of the present invention there is provided an illumination apparatus whose primary purpose is illumination as opposed to display, comprising: an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in gaps between the organic light emitting elements; and the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively Temoved inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction. The illumination apparatus may further comprise at least one further array of inorganic light emitting elements for emitting light at a third wavelength or spectral band, the third wavelength or spectral band being different from the first and second wavelengths or spectral bands. The first wavelength or spectral band may be a green wavelength or is in the green spectral band. An array of wavelength conversion elements may be arranged in alignment with the array or inorganic light emitting elements. The first, second and third spectral bands may be arranged to provide white light output. The illumination apparatus may further comprise a controller arranged to separately control the current in the inorganic light emitting elements and inorganic light emitting elements.
According to a second aspect of the present invention there is provided a method of manufacturing an illumination apparatus whose primary purpose is illumination as opposed to display, the method comprising: providing an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and providing an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements and the array of inorganic light emitting elements are provided on a common substrate and arranged such that the inorganic light emitting elements are positioned ((interspersed)) in gaps between the organic light emitting elements; and wherein providing the array of inorganic light emitting elements comprises: forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction.
According to a third aspect of the present invention there is provided an illumination apparatus whose primary purpose is illumination as opposed to display, comprising: at least one organic light emitting element for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the at least one organic light emitting element and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in apertures within the at least one organic light emitting elements; and the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a mann&r that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction.
Further aspects of the invention are as claimed in the appended claims.
Advantageously the current embodiments provide a large area light source that achieves high efficiency in a first spectral band, such as the blue part of the spectrum by means of providing microscopic iLED elements with output in the first spectral band; and high efficiency and lifetime in a second spectral band such as the green part of the spectrum by means of providing macroscopic OLED elements with output in the second spectral band. The microscopic iLED elements are interspersed with the macroscopic regions of OLED elements to achieve a uniform white appearance to an observer, advantageously improving the appearance of the lamp when viewed directly, and to improve the glare characteristics of the apparatus. Advantageously the present embodiments achieve an efficient, white and colour tuneable large area lighting apparatus with low cost. Further, the present embodiments may advantageously comprise common output coupling optical elements across the array to provide higher output efficiency and low cost of manufacture.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Fig. 1 shows in plan view a combination of iLED elements and OLED elements provided on a substrate with a first arrangement;
Fig. 2 shows a method to provide a combination of iLED elements and OLED elements over a large area; Fig.3 shows a further method to provide a combination of iLED elements and OLED elements over a large area; Fig.4 shows a further method to provide a combination of iLED elements and OLED elements over a large area; Fig.5 shows a method to singulate a mothersheet comprising a combination of iLED elements and OLED elements;
Fig.6a shows in plan view a further combination of iLED elements and OLED elements provided on a substrate; Fig.6b shows in plan view a further combination of iLED elements and OLED elements provided on a substrate; Fig.7 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate; Fig.8 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate; Ftg.9 shows in plan view a further combination of iLED elements and OLED elements provided on a substrate; Fig.lO shows in plan view an arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements; Fig.ll shows in cross section an arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements;
Fig.12 shows in cross section a method to provide the optical elements of Figs.20 and 11;
Fig.13 shows a catadioptric optical element array;
Fig.14 shows in cross section a further arrangement of coupling optical elements arranged to efficiently extract light from the array of light emitting elements using the optical element array of Fig.13;
Fig.15 shows in cross section an integrated light diffusing arrangement; and
Fig.16 shows in cross section an air spaced light diffusing arrangement.
Fig.l shows a first embodiment comprising a substrate 2 provided with an anay of organic light emitting elements 4 comprising regions of green OLED material. An array of inorganic light emitting elements 6 comprising blue iLED elements and array of inorganic light emitting elements 8 comprising red iLED elements are provided in alignment with the array of OLED elements 4. LEDs are one form of light emitting elements. The elements 6 and 8 comprise inorganic LED elements that are formed in steps comprising forming a monolithic array of light-emitting elements; selectively removing a plurality of light-emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed light- emitting elements; forming a non-monolithic array of light-emitting elements with the selectively removed light-emitting elements in a manner that preserves the relative spatial position of the selectively removed light- emitting elements; wherein the plurality of light-emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light- emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction. In this embodiment the inorganic LEDs are formed using the method described in GB2463989 (which is incorporated herein by reference) except where described otherwise below.
Electrodes and addressing circuitry (not shown) are provided to achieve electrical connections to the respective light emitting elements 4, 6 and 8. The addressing circuitry may be arranged to advantageously achieve connection to the respective elements, and may also be used to control the output of at least some of the elements to achieve colour tuning.
It is desirable to combine the advantages of highly efficient blue iLED elements with the efficiency and lifetime of green OLED elements to provide white light illumination. Advantageously such an arrangement can demonstrate high efficiency for all colours and is colour tunable. Further, such an apparatus can be made at low cost. However, the luminous emittance (measured in lumen/m2) of OLED elements may be three or more orders of magnitude less than the luminous emittance of iLED elements; thus OLED elements are much larger in size than iLED elements. To avoid glare, iLED lamps typically comprise further directional optical elements to increase the effective source size and direct the light into a limited viewing cone, so that the lamp can only be seen directly from a limited range of angles. However, OLED elements are much larger and so not well suited to directional optics. In operation, OLED elements may thus be easily viewed directly by an observer. In comparison with iLED only lighting, OLED lighting and the present hybrid OLED-iLED lighting embodiments consider the glare characteristics for an observer looking directly at the surface of the lighting apparatus during operation. For the glare from such a apparatus to appear uniformly white for an observer, it is desirable that the angular size of the group of light emitting elements comprising respective green regions of array 4, and the blue and red elements of arrays 6 and 8 is smaller than the typical human angular resolvable size, for example 1/2000.
In one example, a ceiling mounted light is arranged at a distance of 2m from an observer, so the angularly resolvable size will be typically less than 1mm. Assuming the luminous efficiency of the elements of the elements 6,8 is the same, and if the luminous emittance of an iLED element is 1000 times greater than for an equivalent OLED element, then each of the iLED element areas is approximately 30x30micromerres (on a pitch of lxlmm) while the green OLED elements will substantially fill the remaining space. Such an arrangement provides a visual colour integration and resulting white appearance of the lamp. By way of comparison, if the iLED elements are provided at spacing substantially greater than lxlmm then glare from the light source will appear to be green, with interspersed red and blue emitting regions; the output will not appear to be white. Thus it will be appreciated that the white uniformity of the glare from the apparatus tends to be improved by the use of microscopic iLEDs as described interspersed in small gaps between the relatively very much larger macroscopic OLEDs, compared to hypothetical alternative arrangements in which relatively large macroscopic OLEDs of different colours might be arranged together in an interspersed fashion.
To provide desired output illumination, large numbers of iLED elements are preferable. In order to provide a 1 klm white light source, such an element may have an area of approximately 500x500mm2 and use 250,000 individual elements in each of the arrays of elements 6, 8. If the individual iLED elements were attached by means of element-at-a-time pick-and-place operations then the cost of mounting the elements would be prohibitive. Further the electrode attachment steps (for example by means of wire bonding) would provide very high costs and very low output efficiency. Advantageously, the present embodiments achieve high efficiency operation over large areas by means of selective removal of a plurality of light-emitting elements from a monolithic iLED array in a manner that preserves the relative spatial position of the selectively removed light-emitting elements. Further, such elements can be formed over large area to provide the desired output brightness for a single lamp at low cost.
If the iLED elements are formed as shown in Fig.2, then it is possible to conveniently attach many iLED elements to the substrate 2 in a single mounting operation. Further the electrodes may be provided by means of photolithography operations and as such may have a small area compared to the element area, advantageously achieving high output efficiency. A method to form a hybrid iLED-OLED illumination apparatus is shown in Fig.2. In a first step at least one mask 62 mounted on a substrate 63 is used to illuminate a monolithic light-emitting element wafer comprising epitaxial layers 60 and substrate 61. The layer 60 may comprise epitaxial layers that achieve blue light output in operation. For the purposes of the present specification, the term monolithic refers to consisting of one piece; solid or unbroken.
In a second processing step, an array 76 of light-emitting elements is formed in the monolithic wafer 60, 61. Each element has a position and orientation defined by the mask 62. The mask is composed of an array of regions, each region defining the structure of at least one layer of an iLED chip. Regions 65 and 67 represent first and second iLED chips and have separation si as shown. During exposure through the mask onto the wafer 60, elements 72 and 74 are formed from regions 65 and 67 of the mask. The separation si of the elements 72, 74 is substantially the same as the separation of the mask regions 65, 67 and the orientation of the elements 72, 74 is the same as the orientation of the respective mask regions 65, 67. The integrity of separation si and orientation of elements 72, 74 is preserved through the subsequent processing steps.
Multiple masks may be used to photolithographically form the complete iLED structure in the manner described, each with regions with the separation si. Such processes preserve a separation and orientations of elements 72 and 74.
In a third step, the array 76 of light-emitting elements may be cut by means of a cutting device 82, which may for example be a scribe, cutting wheel, laser or saw. The separation s2 of the cut lines for a respective edge of elements 72, 74 would ideally be the same as the separation si. However, in practice such a precise separation is very difficult to achieve. Advantageously the embodiment does not require the separation s2 to be identical to the separation si.
In a fourth step, a tool 90 which may for example be an adhesive film is attached to the array 76. A patterned array of UV light is imaged onto the interface of the elements 72,74 with the substrate 61 so that separation of the elements from the substrate 61 is achieved.
In a fifth step the tool 90 together with elements 72,74 is removed, extracting a sparse array of light emitting elements. The integrity of the separation si and orientation of the elements 72 and 74 is advantageously preserved in this extraction step.
Fig.3 shows a method wherein the sparse array of iLED elements, comprising light emitting elements 72,74 are formed on the substrate 2. Substrate 2 may be formed with patterned layer of OLED elements 4 and electrode layers (not shown). Open regions 91 may be formed between the regions 4 of OLED material for example by patterned deposition of the OLED material or by uniform deposition followed by patterning of the material, for example by means of lithography or laser removal. The output colour, for example the white point, may be adjusted by trimming, e.g. by laser ablation, the emitting area of the OLED elements 4. Advantageously this trimming process could be arranged so that groups of emitting areas have similar white points at the same operating current. In a second step, the sparse array of light emitting elements 72, 74 on tool 90 are aligned with the regions 91 and attached to the substrate 2, for example by means of solder, or conductive adhesive. The tool 90 is then removed and electrode layers 92, 94 deposited to provide electrical connection to iLED elements 72, 74 and OLED elements 4. Further planarization layers 96 and encapsulation layers 98, such as a glass cover layer may be added. To improve the heatsinking performance of the apparatus, layer 2 may be thinned (by known techniques such as grinding and polishing) prior to attachment of heatsinks.
Thus an illumination apparatus whose primary purpose is illumination as opposed to display, comprises an array of organic light emitting elements 4 for emitting light at a first wavelength οτ spectral band (for example a green spectral band); and an array of inorganic light emitting elements 6 for emitting light at a second wavelength or spectral band (for example a blue spectral band), the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements 4 and the array of inorganic light emitting elements 6 are arranged on a common substrate 2 with the inorganic light emitting elements 6 interspersed in gaps between the organic light emitting elements; and the array of inorganic light emitting elements 6 were formed in steps comprising forming a monolithic array 76 of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements 6 from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements 6; forming a non-monolithic array of inorganic light emitting elements 6 with the selectively removed inorganic light emitting elements 6 in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements 6; wherein the plurality of inorganic light emitting elements 6 that are selectively removed from the monolithic array 76 are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements 6 in the ai least one direction, for each respective pair there is at least one respective inorganic light emitting element 6 that is not selected that was positioned in the monolithic array 76 between the pair of selectively removed inorganic light emitting elements 6 in the at least one direction.
Fig.4 shows in plan view, an arrangement comprising a large substrate 2 on which multiple tools 90, each comprising a sparse array of blue iLED elements are aligned. Further tools 100 comprising red iLED elements may also be aligned with the substrate 2. The subsequent layers 92, 94, 6 and 98 may be added across the whole of the mothersheet area so that operations on the respective iLED and OLED elements are performed in parallel. In a subsequent processing step the mothersheet may be cut to different sizes (e.g for a desired light output and/or a specific shape) to suit the application, for example along lines 96 as shown in Fig.5. Advantageously, this enables a large area of hybrid iLED-OLED lamp to be fabricated in parallel, reducing cost.
Fig.6a shows an embodiment wherein the iLED elements are arranged in holes 10 in a continuous region, comprising element 4 of OLED material. Advantageously such an arrangement provides separation of the iLED and OLED addressing and optical output. Wavelength conversion elements 7 may further be provided in alignment with at least some of the inorganic light emitting elements 6 as shown in Fig.6b. For example, red light emitting elements may be provided by a blue light emitting element 6 and a red conversion phosphor wavelength conversion element 7.
Fig.7 shows a further embodiment wherein the iLED elements and electrodes (not shown) are formed on the surface of a continuous layer of OLED elements. Advantageously such an arrangement reduces the complexity of the OLED layer and uses a single drive circuit, reducing cost .
Fig.8 shows a further embodiment wherein an OLED layer is formed over iLED elements for OLED material structures that are transmissive in the red and blue parts of the spectrum. Advantageously, such an arrangement can achieve simplified processing steps, reducing cost. Further, the size of the red and blue iLED elements in the present embodiments may be different to compensate for differences in luminous emittance between blue elements 6 and red elements 8 to advantageously achieve a means to colour balance the illumination apparatus.
Further, guiding of the light from the iLED elements 6,8 within the OLED layers may be used to increase the area over which light from the iLED elements is emitted. Advantageously, this achieves a reduced density of iLED elements to meet visual colour integration requirements. Such a reduced density means that the iLED elements can be larger, which may improve output efficiency of the devices by achieving a
proportionately smaller electrode size compared to iLED size.
Fig.9 shows a further embodiment wherein regions 12 of red OLED material are combined with regions 4 of green OLED material and an array of blue iLED elements 6. Such an arrangement advantageously achieves the advantages of efficiency and large area coating from OLED element processing while achieving the high efficiency of blue iLED elements.
The arrangements described above achieve substantially Lambertian output characteristics. However, if a cover substrate is used, light may he trapped in the layers of OLED material and encapsulation layers. Fig.10 shows in plan view output coupling optical elements to improve output extraction efficiency. Advantageously, the output optic is substantially the same for each of the red, green and blue emitting elements. Thus, regions 4 may be provided with the same nominal size and spacing, and optical elements 16 provided in alignment with the elements 4, 6.
As shown in cross section in Fig.ll the optical elements 16 may be hemispherical optical elements. A further protective transparent substrate 18 and diffuser layer 22 may further be provided and attached to the substrate 2 by means of sealing material 20. Such an arrangement provides a protected output surface and further optical characteristics that can be used to blur the appearance of the separate red, green and blue elements with high efficiency.
A method to form the hemispherical optical elements 16 is shown in Fig.12. The arrays of elements 4, 6 are provided on substrate 2. A tool 24 is provided in alignment with the elements 4, 6 and filled with a material 26 which is cured. On release of the tool 24, optical elements 16 are formed. Advantageously many optical elements can be formed in parallel over a large area.
To further reduce cost, it would be desirable that the optical elements 16 are formed on a separate substrate that is aligned to a large mothersheet substrate 2 suitable for subsequent dicing. However, hemispherical optical elements 16 are difficult to fabricate reliably on such a substrate if the input surface of the hemisphere is to be brought into contact with the elements 4, 6, 8. A further embodiment is provided in Fig.13 comprising a catadioptric optical element 38 (comprising reflective and refractive optical functions) formed on the surface of a substrate 18 and with an input aperture 37.
As shown in Fig.14, when assembled with the light emitting elements, the elements comprise an outer wall section 28 to provide a total internal reflection function, a wall section 30 to provide a refractive deflection of light and a central section 32 to direct light from the source to the output. A material 34 with high refractive index can be provided in combination with a material 36 with low refractive index so that the light from the emitting elements comprising elements 4, may be efficiently coupled from the light emitting elements.
Advantageously, the area of the substrate 2 covered by the OLED elements 4 is preferably maximised to provide the lowest cost of the elements. Thus, the gaps between emitters are preferably minimised. This can be achieved by arranging the optical elements to provide substantially a full 2 * pi steradian output cone angle. The light emitting elements 4, 6, 8 can be aligned with the input aperture 37 of the optical elements. An optional diffuser 22 may be incorporated to further reduce the directionality of the output. To further increase OLED brightness, OLED elements 4 may be incorporated in the gaps between the optical elements providing further light mixing between the iLED and OLED elements. Advantageously, the optical elements 38 can be formed over a large area on substrate 18 so that substrate 18 can be provided in alignment to substrate 2.
Individual lamps may be extracted from the array of aligned substrates by dicing the two elements after attachment as shown in Fig.5. In this manner, low cost with high efficiency may be achieved.
It would be desirable to increase the iLED element size preferably to more than 50 micrometres, more preferably to more than 100 micrometres in order to increase light output by using proportionately smaller electrode sizes. However, this may achieve loss of visual colour integration as described previously. As shown in Fig.15 diffuser 22 may be provided for example with a +/-30 degree angular spread, spaced a distance 23 of 3mm from the elements 4, 6, 8 would provide an effective light integration area of approximately 3mm width. This advantageously achieves an iLED element size of approximately lOOxlOQmicrometre area. FurtheT the spacing 23 can conveniently be achieved using the thickness of substrate 18 and diffuser 22, thus advantageously providing an integrated structure with good mechanical ruggedness and high transmission efficiency.
By way of comparison, an air spaced diffuser could be used to provide higher degree of separation of the diffuser, for example 25mm, enabling larger chip sizes that may be more suitable for pick-and -place fabrication. However such an arrangement disadvantageously suffers from increased light losses from surface reflectivity of the additional interfaces of substrate 18 and diffuser 22 with air, thus reducing efficiency compared to the present embodiments. Alternatively by way of comparison, a wide angle diffuser could be used. However, such high angle diffusers suffer from higher losses and degrade efficiency.

Claims

Claims
1. An illumination apparatus whose primary purpose is illumination as opposed to display, comprising: an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band;
wherein the array of organic light emitting elements and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in gaps between the organic light emitting elements; and
the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction.
2. An illumination apparatus according to claim 1 comprising at least one further array of inorganic light emitting elements for emitting light at a third wavelength or spectral band, the third wavelength or spectral band being different from the first and second wavelengths or spectral bands.
3. An illumination apparatus according to claim 1 or claim 2 wherein the first wavelength or spectral band is a green wavelength or is in the green spectral band.
4. An illumination apparatus according to any of claims 1 to 3 wherein an array of wavelength conversion elements is arranged in alignment with the array or inorganic light emitting elements.
5. An illumination apparatus according to any of claims 1 to 4 wherein the first, second and third spectral bands are arranged to provide white light output.
6. An illumination apparatus according to any of claims 1 to 5 further comprising a controller arranged to separately control the current in the inorganic light emitting elements and inorganic light emitting elements.
7. A method of manufacturing an illumination apparatus whose primary purpose is illumination as opposed to display, the method comprising:
providing an array of organic light emitting elements for emitting light at a first wavelength or spectral band; and providing an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band; wherein the array of organic light emitting elements and the array of inorganic light emitting elements are provided on a common substrate and arranged such that the inorganic light emitting elements are positioned ((interspersed)) in gaps between the organic light emitting elements;
and wherein providing the array of inorganic light emitting elements comprises:
forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction.
8. An illumination apparatus whose primary purpose is illumination as opposed to display, comprising: at least one organic light emitting element for emitting light at a first wavelength or spectral band; and an array of inorganic light emitting elements for emitting light at a second wavelength or spectral band, the second wavelength or spectral band being different from the first wavelength or spectral band;
wherein the at least one organic light emitting element and the array of inorganic light emitting elements are arranged on a common substrate with the inorganic light emitting elements interspersed in apertures within the at least one organic light emitting elements; and
the array of inorganic light emitting elements were formed in steps comprising forming a monolithic array of inorganic light emitting elements; selectively removing a plurality of the inorganic light emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; forming a non-monolithic array of inorganic light emitting elements with the selectively removed inorganic light emitting elements in a manner that preserves the relative spatial position of the selectively removed inorganic light emitting elements; wherein the plurality of inorganic light emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed inorganic light emitting elements in the at least one direction, for each respective pair there is at least one respective inorganic light emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed inorganic light emitting elements in the at least one direction.
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