Blue converter for micro-LEDs

Abstract

A photocurable composition includes a blue photoluminescent material, one or more monomers, and a photoinitiator that initiates polymerization of the one or more monomers in response to absorbing ultraviolet light. The blue photoluminescent material is selected to absorb ultraviolet light having a maximum wavelength in the range of about 300 nm to about 430 nm and emit blue light. The blue photoluminescent material also has an emission peak in the range of about 420 nm to about 480 nm. The full width at half maximum of the emission peak is less than 100 nm, and the photoluminescence quantum yield is in the range of 5% to 100%.

Description

Technical Field

[0001] The present disclosure generally relates to methods of manufacturing blue converters for micro-LEDs (micro-LEDs) mounted by self-aligned in-situ curing, and systems and devices including blue converters.

[0002] background

[0003] Light emitting diode (LED) panels use an array of LEDs, where individual LEDs provide individually controllable pixel elements. Such LED panels can be used in computers, touch panel devices, personal digital assistants (PDAs), cell phones, television monitors, and the like.

[0004] Compared to OLED, LED panels (also called micro-LEDs) using micron-scale LEDs based on III-V semiconductor technology will have various advantages, such as higher energy efficiency, brightness, and longer life, as well as fewer material layers in the display stack, which can simplify manufacturing. However, there are challenges in the manufacture of micro-LED panels. Micro-LEDs with different color emissions (e.g., red, green, and blue pixels) need to be manufactured on different substrates via separate processes. Integrating micro-LED devices of multiple colors onto a single panel typically requires a pick-and-place step to transfer the micro-LED device from its original donor substrate to a target substrate. This often involves modifying the LED structure or manufacturing process, such as introducing a sacrificial layer to simplify die release. In addition, strict requirements for placement accuracy may limit production, final yield, or both.

[0005] An alternative approach to bypass the pick and place step is to selectively deposit a color conversion agent (e.g., quantum dots, nanostructures, photoluminescent materials, or organic substances) at specific pixel locations on a substrate fabricated with a monochromatic LED. The monochromatic LED can produce relatively short wavelength light, e.g., violet or blue light, and the color conversion agent can convert this short wavelength light to longer wavelength light, e.g., red or green light for a red or green pixel. Selective deposition of the color conversion agent can be performed using a high resolution shadow mask or controllable inkjet or aerosol jet printing.

[0006] However, shadow masks are prone to alignment accuracy and scalability issues, while inkjet and aerogel jetting technologies suffer from resolution (inkjet), accuracy (inkjet), and throughput (aerogel jetting) issues. To manufacture micro-LED displays, new technologies are needed to accurately and cost-effectively deliver color conversion agents for different colors to different pixels on a substrate, such as a large area substrate or a flexible substrate. Summary of the invention

[0007] The present disclosure generally relates to methods of manufacturing blue converters for micro-LEDs mounted by self-aligned in-situ curing, and systems and devices including blue converters.

[0008] In a general aspect, a photocurable composition includes a blue photoluminescent material, one or more monomers, and a photoinitiator that initiates polymerization of the one or more monomers in response to absorbing ultraviolet light. The blue photoluminescent material is selected to absorb ultraviolet light having a maximum wavelength in the range of about 300 nm to about 430 nm and emit blue light. The blue photoluminescent material also has an emission peak in the range of about 420 nm to about 480 nm. The full width at half maximum of the emission peak is less than 100 nm, and the photoluminescence quantum yield is in the range of 5% to 100%.

[0009] In another aspect, the photocurable composition includes a polymer matrix, a blue photoluminescent material mixed in the polymer matrix, and a photoinitiator, the photoinitiator initiating polymerization to form the polymer matrix. The blue photoluminescent material is selected to absorb ultraviolet light having a maximum wavelength in the range of about 300 nm to about 430 nm and emit blue light having an emission peak in the range of about 420 nm to about 480 nm, wherein the full width at half maximum of the emission peak is less than 100 nm, and the photoluminescent quantum yield is in the range of 5% to 100%.

[0010] In another aspect, a method of manufacturing a light emitting device includes: dispensing a first photocurable fluid over a display having a backplane and an array of ultraviolet light emitting diodes electrically integrated with backplane circuitry of the backplane; activating a first plurality of light emitting diodes in the array of light emitting diodes to illuminate and polymerize one or more monomers to form a first color conversion layer over each of the first plurality of light emitting diodes for converting light from the first plurality of light emitting diodes into blue light, each color conversion layer comprising a blue photoluminescent material mixed in a polymer matrix; and removing an uncured remaining portion of the first photocurable fluid. The first photocurable fluid includes a blue photoluminescent material selected to absorb ultraviolet light having a maximum wavelength in a range of about 300 nm to about 430 nm and emit blue light having an emission peak in a range of about 420 nm to about 480 nm (wherein the full width at half maximum of the emission peak is less than 100 nm and the photoluminescent quantum yield is in a range of 5% to 100%), one or more monomers, and a photoinitiator that initiates polymerization of the one or more monomers in response to absorbing the ultraviolet light.

[0011] Implementations of these aspects may include one or more of the following features.

[0012] The composition typically includes about 0.1 wt % to about 10 wt % of a blue photoluminescent material, about 0.5 wt % to about 5 wt % of a photoinitiator, and about 1 wt % to about 90 wt % of one or more monomers. In some cases, the composition includes a solvent. The composition with a solvent typically includes about 0.1 wt % to about 10 wt % of a blue photoluminescent material, about 0.5 wt % to about 5 wt % of a photoinitiator, about 1 wt % to about 90 wt % of one or more monomers, and about 10 wt % to about 90 wt % of a solvent.

[0013] The blue photoluminescent material can be an organic material, an organometallic material, or a polymeric material. In some cases, the blue photoluminescent material is an organic material, and the organic material is a free radical. The blue photoluminescent material can be fluorescent or phosphorescent.

[0014] Advantages of blue converters and systems and devices comprising blue converters include high photoluminescence quantum yield, long lifetime and long shelf life.

[0015] The details of one or more embodiments of the object of the present disclosure are set forth in the drawings and the specification. Other features, aspects, and advantages of the object will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A The diagram shows the structural formula of a blue fluorescent molecule. Figure 1B The diagram shows the structural formula of a blue thermally activated delayed fluorescent molecule. Figure 1C The structural formulas of blue phosphorescent organic and organometallic complexes are shown.

[0017] Figure 2 is a schematic top view of a micro LED array that has been integrated with a backplane.

[0018] Figure 3A is a schematic top view of a portion of a micro-LED array. Figure 3B Is from Figure 3A Schematic cross-sectional view of a portion of a micro-LED array.

[0019] 4A to 4H A method of selectively forming a color conversion layer over a micro-LED array is shown.

[0020] FIG. 5A to FIG. 5C The formulation of the photocurable composition is shown.

[0021] FIG. 6A to FIG. 6E A method of manufacturing a micro LED array and isolation walls on a backplane is shown.

[0022] FIG. 7A to FIG. 7DAnother method of fabricating the micro LED array and isolation walls on the backplane is shown.

[0023] Like reference numbers in the various drawings indicate like elements. DETAILED DESCRIPTION

[0024] Quantum dots can be dispersed in acrylate formulations for inkjet printing. After UV curing, quantum dots locked in the polyacrylate matrix can be used as a color conversion layer for advanced displays. However, although red and green light can be achieved by quantum dots, quantum dots that convert UV light into blue light (e.g., ZeS / Se / Te quantum dots) generally suffer from low photoluminescence quantum yield (PLQY), short working life, and short shelf life.

[0025] Techniques that may address the problems associated with the lack of blue color converters for micro-LEDs with UV backlights include using materials other than quantum dots for blue color converters. These blue color converters may be included in the formulation for the micro-LED blue color conversion layer formed by self-aligned curing as described in the present disclosure.

[0026] The formulation for the blue color conversion layer of micro-LEDs generally includes a blue color conversion agent (e.g., without quantum dots), a reactive component, and a photoinitiator. The formulation may optionally include one or more of the following: a solvent, a functional component (e.g., a high refractive index additive, a surfactant, a stray light absorber, or a UV blocker).

[0027] Suitable blue color conversion agents include fluorescent and phosphorescent organic molecules, organic free radicals, organometallic complexes, and polymers including one or more of these color conversion agents. The blue color conversion agent is selected to have a maximum wavelength (λ) in the range of about 300 nm to about 430 nm. max ) and emits blue light having an emission peak in the range of about 420 nm to about 480 nm. The full width at half maximum (FWHM) of the emission peak is generally less than 100 nm, and the photoluminescence quantum yield (PLQY) is generally in the range of 5% to 100%.

[0028] Examples of suitable blue color converters include LUMILUX Blue CD 310, LUMILUX Blue CD 710, and LUMILUX Dispersion Blue CD 910 (available from Honeywell International Inc., USA). Figure 1AThe diagram shows the structural formulas of blue fluorescent molecules 4P-NPD, Bepp2, TPA-SBFF, DPAFVF, Ban-(3,5)-CF3, TBPe, DBzA, BITPI, BiPI-1, 4PF, TPI-Py, and PhImA. Figure 1B The structural formulas of blue thermally activated delayed fluorescence (TADF) molecules v-DABNA, DMAC-DPS, CZ-PS, DMTDAc, DMAC-TRZ, Cab-Ph-TRZ, Ca-TRZ2, Cz-TRZ3, Cz-TRZ4, BCC-TPTA, DDCzTrz, DPCC-TPTA, DCzTrz, BDPCC-TPTA, Phen-TRZ, TCzTrz, Cz-VPN, CPC, 2PXZ-TAZ and CC2BP are shown. Figure 1C Structural formulas of blue phosphorescent organic and organometallic complexes including metalloids (boron) and metals (beryllium and iridium) are shown.

[0029] The formulations for the red and green color conversion layers of micro-LEDs generally include a red color converter, a reactive component and a photoinitiator or a green color converter, a reactive component and a photoinitiator, respectively. The formulations may optionally include one or more of the following: solvents, functional components (e.g., high refractive index additives, surfactants, stray light absorbers, or UV blockers).

[0030] The red and green color converters are materials that emit visible radiation in a first visible wavelength band in response to absorbing UV radiation or visible radiation in a second visible wavelength band. The UV radiation typically has a wavelength in the range of 200 nm to 400 nm. The visible radiation typically has a wavelength or wavelength band in the range of 500 nm to 800 nm. The first visible wavelength band is different (e.g., has greater energy) than the second visible wavelength band. That is, the color converter is a material that can convert shorter wavelength light from the micro-LEDs into longer wavelength light.

[0031] The red and green color converters may include photoluminescent materials (such as organic or inorganic molecules), nanomaterials (e.g., nanoparticles, nanostructures, quantum dots), or other suitable materials. Suitable nanomaterials typically include one or more III-V compounds. Examples of suitable III-V compounds include CdSe, CdS, InP, PbS, CuInP, ZnSeS, and GaAs. In some cases, the nanomaterials include one or more elements selected from the group consisting of: cadmium, indium, copper, silver, gallium, germanium, arsenic, aluminum, boron, iodine, bromine, chlorine, selenium, tellurium, and phosphorus. In some cases, the nanomaterials include one or more perovskites.

[0032] The quantum dots can be homogeneous or can have a core-shell structure. The quantum dots can have an average diameter in the range of about 1 nm to about 10 nm. One or more organic ligands are typically coupled to the outer surface of the quantum dots. The organic ligands promote the dispersion of the quantum dots in the solvent. Suitable organic ligands include aliphatic amines, thiols or acid compounds, wherein the aliphatic portion typically has 6 to 30 carbon atoms. Examples of suitable nanostructures include nanosheets, nanocrystals, nanorods, nanotubes and nanowires.

[0033] Reactive component includes monomer, such as (meth) acrylate monomer, and can include one or more mono (meth) acrylate, di (meth) acrylate, tri (meth) acrylate, tetra (meth) acrylate or aforesaid combination.Reactive component can be provided by negative photoresist, for example, SU-8 photoresist.The example of suitable mono (meth) acrylate includes isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, trimethylcyclohexyl (meth) acrylate, diethyl (meth) acrylamide, dimethyl (meth) acrylamide and tetrahydrofurfuryl (meth) acrylate.Reactive component can include crosslinking agent or other reactive compounds.The example of suitable crosslinking agent includes polyethylene glycol di (meth) acrylate (for example, diethylene glycol di (meth) acrylate or tripropylene glycol di (meth) acrylate), N, N '-methylene bis-(meth) acrylamide, pentaerythritol tri (meth) acrylate and pentaerythritol tetra (meth) acrylate. Examples of suitable reactive compounds include polyethylene glycol (meth)acrylate, vinyl pyrrolidone, vinyl imidazole, styrene sulfonate, (meth)acrylamide, alkyl (meth)acrylamide, dialkyl (meth)acrylamide, hydroxyethyl (meth)acrylate, morpholine ethyl acrylate, and vinyl formamide.

[0034] Photoinitiators initiate polymerization in response to radiation, such as UV radiation, UV-LED radiation, visible radiation, and electron beam radiation. In some cases, the photoinitiator responds to UV or visible radiation. Suitable photoinitiators include free radical photoinitiators, such as bulk curing photoinitiators and surface curing photoinitiators.

[0035] Bulk curing photoinitiators cleave upon exposure to UV radiation, thereby generating free radicals that can initiate polymerization. Bulk curing photoinitiators can be used for surface and through- or bulk curing of dispensed droplets. Bulk curing photoinitiators include benzoin ethers, benzyl ketals, acetophenones, alkyl phenones, phosphine oxides, diphenyl ketone compounds, and thiane compounds.

[0036] Surface curing photoinitiators are activated by UV radiation and form free radicals by abstracting hydrogen from a second compound, which become the actual initiating free radicals. This second compound is often called a co-initiator or polymerization synergist, and can be an amine synergist. Amine synergists are used to reduce oxygen inhibition, and thus, surface curing photoinitiators can be used for rapid surface curing. Surface curing photoinitiators include diphenyl ketone compounds and thioxanthone compounds. Amine synergists are amines with active hydrogen. Amine synergists (such as amine-containing acrylates) can be combined with diphenyl ketone photoinitiators in the resin precursor composition formula to: a) limit oxygen inhibition, b) quickly cure the droplet or layer surface to fix the size of the droplet or layer surface, and c) increase the layer stability in the curing process.

[0037] Examples of suitable photoinitiators include 1-hydroxycyclohexyl phenyl ketone, 4-isopropylphenyl-2-hydroxy-2-methylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propyl-1-one, 2,2-dimethyl-2-hydroxy-acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropionophenone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4 ,6-trimethylphenylphosphine oxide, 2-methyl-1-1[4-(methylthio)phenyl]-2-morpholino-propyl-1-one, 3,6-bis(2-methyl-2-morpholino-propionyl)-9-octylcarbazole, 2-benzyl-2-(dimethylamino)-1-(4-morpholino)phenyl)-1-butanone, benzophenone, 2,4,6-trimethylbenzophenone, isopropylthioxanthone, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1phenyl-1-propanone. Suitable mixtures of commercially available photoinitiators include Darocur 4265, Irgacure 184, Irgacure 250, Irgacure 270, Irgacure 295, Irgacure 369, Irgacure 379, Irgacure 500, Irgacure 651, Irgacure 754, Irgacure 784, Irgacure 819, Irgacure 907, Irgacure 1173, Irgacure 2100, Irgacure 2022, Irgacure 4265, Irgacure TPO, Irgacure TPO-L, Esacure KT37, Esacure KT55, Esacure KTO046, Omnicat 250, and Omnicat 550. Suitable amine synergists include secondary and tertiary amine compounds with or without acrylic groups, such as diethanolamine, triethanolamine, and Genomer 5142.

[0038] Depending on the circumstances, the light-curable composition may include a solvent. The solvent may be organic or inorganic. Examples of suitable solvents include water, ethanol, toluene, dimethylformamide, methyl ethyl ketone, or a combination thereof. The solvent may be selected to provide the desired surface tension or viscosity of the light-curable composition. The solvent may also improve the chemical stability of other components.

[0039] Optionally, the photocurable composition may include a stray light absorber or a UV blocker. Examples of suitable stray light absorbers include Disperse Yellow 3, Disperse Yellow 7, Disperse Orange 13, Disperse Orange 3, Disperse Orange 25, Disperse Black 9, Disperse Red 1 Acrylate, Disperse Red 1 Methacrylate, Disperse Red 19, Disperse Red 1, Disperse Red 13, and Disperse Blue 1. Examples of suitable UV blockers include benzotriazolyl hydroxyphenyl compounds.

[0040] Optionally, the first photocurable composition may include one or more other functional ingredients. As an example, the functional ingredients may affect the optical properties of the color conversion layer. For example, the functional ingredients may include nanoparticles having a sufficiently high refractive index (e.g., at least about 1.7) so that the color conversion layer serves as an optical layer that adjusts the light path of the output light, for example, to provide a microlens. Examples of suitable nanoparticles include TiO2, ZnO2, ZrO2, CeO2, or a mixture of two or more of these oxides. Alternatively or additionally, the nanoparticles may have a selected refractive index so that the color conversion layer serves as an optical layer that reduces total reflection losses, thereby improving light extraction. As another example, the functional ingredient may include a dispersant or surfactant to adjust the surface tension of the photocurable composition. Examples of suitable dispersants or surfactants include siloxanes and polyethylene glycol. As yet another example, the functional ingredient may include a photoluminescent pigment that emits visible radiation. Examples of suitable photoluminescent pigments include zinc sulfide and strontium aluminate.

[0041] In some cases, the photocurable composition includes about up to about 90 wt % reactive ingredients (e.g., about 10 wt % to about 90 wt %), about 0.5 wt % to about 5 wt % photoinitiator, and about 0.1 wt % to about 10 wt % (e.g., about 1 wt % to about 2 wt %) color conversion agent. The photocurable composition may also include a solvent (e.g., up to about 10 wt % solvent).

[0042] The photocurable composition may optionally include up to about 5 wt % of a surfactant or dispersant, about 0.01 wt % to about 5 wt % (eg, about 0.1 wt % to about 1 wt %) of a stray light absorber, or any combination of the foregoing.

[0043] The viscosity of the photocurable composition is generally in the range of about 10 cP (centipoise) to about 2000 cP at room temperature (e.g., about 10 cP to about 150 cP). The surface tension of the photocurable composition is generally in the range of about 20 millinewtons per meter (mN / m) to about 60 mN / m (e.g., about 40 mN / m to about 60 mN / m). After curing, the elongation at break of the cured photocurable composition is generally in the range of about 1% to about 200%. The tensile strength of the cured photocurable composition is in the range of about 1 megapascal (MPa) to about 1 gigapascal (GPa). The photocurable composition can be applied in one or more layers, and the thickness of the cured photocurable composition is generally in the range of about 10 nm to about 100 microns (e.g., about 10 nm to about 20 microns, about 10 nm to about 1000 nm, or about 10 nm to about 100 nm).

[0044] The photocurable compositions described in the present disclosure are useful in displays (such as those related to Figure 2 To the micro LED display described in Figure 7) is implemented as a color conversion layer.

[0045] Figure 2 The backplane 16 includes individual micro-LEDs 14 (see Figure 3A and Figure 3B ) of the micro-LED display 10. The micro-LEDs 14 have been integrated with a backplane circuit 18 so that each micro-LED 14 can be individually addressed. For example, the backplane circuit 18 may include a TFT active matrix array having a thin film transistor and a storage capacitor (not shown) for each micro-LED, column address and row address lines 18a, column and row drivers 18b, etc., for driving the micro-LEDs 14. Alternatively, the micro-LEDs 14 may be driven by a passive matrix in the backplane circuit 18. The backplane 16 may be manufactured using a conventional CMOS process.

[0046] Figure 3A and Figure 3B A portion 12a of a micro-LED array 12 with individual micro-LEDs 14 is shown. All micro-LEDs 14 are manufactured using the same structure so as to produce the same wavelength range (this may be referred to as a "monochromatic" micro-LED). For example, the micro-LEDs 14 may produce light in the ultraviolet (UV) (e.g., near-ultraviolet) range. For example, the micro-LEDs 14 may produce light in the range of 365 to 405 nm. As another example, the micro-LEDs 14 may produce light in the violet or blue range. The micro-LEDs may produce light having a spectral bandwidth of 20 to 60 nm.

[0047] Figure 3BA portion of a micro-LED array that can provide a single pixel is shown. Assuming that the micro-LED display is a three-color display, each pixel includes three sub-pixels, one sub-pixel for each single color (each color), for example, one sub-pixel for blue, green, and red channels, respectively. Therefore, the pixel can include three micro-LEDs 14a, 14b, 14c. For example, the first micro-LED 14a can correspond to a blue sub-pixel, the second micro-LED 14b can correspond to a green sub-pixel, and the third micro-LED 14c can correspond to a red sub-pixel. However, the technology discussed below can be applied to micro-LED displays using a larger number of colors (e.g., four or more colors). In this case, each pixel can include four or more micro-LEDs, each of which corresponds to a corresponding color. In addition, the technology discussed below can be applied to micro-LED displays using only two colors.

[0048] Generally speaking, a monochromatic micro-LED 14 can generate light in a wavelength range having a peak, where the wavelength is no greater than the wavelength of the highest frequency color desired for the display (e.g., violet or blue light). A color conversion agent can convert this short wavelength light to longer wavelength light, e.g., red or green light for red or green sub-pixels. If the micro-LED generates UV light, a color conversion agent can be used to convert the UV light to blue light for a blue sub-pixel.

[0049] Vertical partition walls 20 are formed between adjacent micro-LEDs. The partition walls provide optical isolation to help localize polymerization and reduce optical crosstalk during in-situ polymerization discussed below. The partition walls 20 can be photoresist or metal and can be deposited by conventional lithographic processes. Figure 3A As shown, walls 20 may form a rectangular array, with each micro-LED 14 in an individual recess 22 bounded by wall 20. Other array geometries (e.g., hexagonal or offset rectangular arrays) are also possible. Possible processes for backplane integration and isolation wall formation are discussed in more detail below.

[0050] The wall may have a height H of about 3 to 20 μm. The wall may have a width W of about 2 to 10 μm. The height H may be greater than the width W, for example, the wall may have an aspect ratio of 1.5:1 to 5:1. The height H of the wall is sufficient to block light from one micro LED from reaching an adjacent micro LED.

[0051] 4A to 4H A method for selectively forming a color conversion layer on a micro-LED array is shown. Initially, as Figure 4AAs shown, the first photocurable composition 30a is deposited over the array of micro-LEDs 14 that have been integrated with the backplane circuitry. The first photocurable composition 30a may have a depth D that is greater than the height H of the partition walls 20.

[0052] See also FIG. 5A to FIG. 5C , the photocurable composition (e.g., first photocurable composition 30a, second photocurable composition 30b, third photocurable composition 30c, etc.) includes a polymerizable component 32, a photoinitiator 34 for triggering polymerization under illumination corresponding to the wavelength of emission of the micro-LEDs 14, and a color conversion agent 36a. The polymerizable component 32 includes a reactive component and an antioxidant inhibitor additive as described herein.

[0053] After curing the photocurable composition, components of the photoinitiator 34 may be present in the cured photocurable composition (photopolymer), wherein the components are fragments of the photoinitiator formed during the cleavage of bonds in the photoinitiator during the photoinitiation process.

[0054] Back to Figure 4A The first photocurable composition 30a can be deposited on the display above the micro LED array by spin coating, dipping, spraying, or ink jetting. The ink jetting process can consume the first photocurable composition 30a more efficiently.

[0055] Next, if Figure 4B As shown, the circuit system of the backplane 16 is used to selectively activate the first plurality of micro-LEDs 14a. This first plurality of micro-LEDs 14a corresponds to sub-pixels of a first color. In particular, the first plurality of micro-LEDs 14a corresponds to sub-pixels of the color of light that will be produced by the color conversion agent in the photocurable composition 30a. For example, assuming that the color conversion agent in the fluid 30a converts the light from the micro-LEDs 14 to blue light, only those micro-LEDs 14a corresponding to the blue sub-pixels are turned on. Because the micro-LED array has been integrated with the backplane circuit 18, power can be supplied to the micro-LED display 10 and control signals can be applied by the microprocessor to selectively turn on the micro-LEDs 14a.

[0056] See also Figure 4B and Figure 4C , start the first plurality of micro-LEDs 14a to generate illumination A (see Figure 4B ), which results in in-situ curing of the first photocurable composition 30a to form a first solidified color conversion layer 40a above each activated micro-LED 14a (see Figure 4C). In short, the fluid 30a is cured to form a color conversion layer 40a, but only on selected micro-LEDs 14a. For example, a color conversion layer 40a for converting to blue light can be formed on each micro-LED 14a.

[0057] In some implementations, the illumination from the selected micro-LED 14a does not reach the other micro-LEDs 14b, 14c. In this case, the partition wall 20 may not be necessary. However, if the spacing between the micro-LEDs 14 is small enough, the partition wall 20 can positively block the illumination A from the selected micro-LED 14a from reaching the area above the other micro-LEDs that is otherwise within the penetration depth of the illumination from those other micro-LEDs. The partition wall 20 can also be included, for example, simply as insurance to prevent the illumination from reaching the area above the other micro-LEDs.

[0058] The driving current and driving time for the first plurality of micro-LEDs 14a can be selected for an appropriate photon dose of the photocurable composition 30a. The power per sub-pixel used to cure the fluid 30a is not necessarily the same as the power per sub-pixel in the display mode of the micro-LED display 10. For example, the power per sub-pixel used in the curing mode can be higher than the power per sub-pixel used in the display mode.

[0059] See also Figure 4D When curing is complete and the first solidified color conversion layer 40a is formed, the remaining uncured first photocurable composition is removed from the display 10. This exposes the other micro-LEDs 14b, 14c for the next deposition step. In some implementations, the uncured first photocurable composition 30a is rinsed from the display using only a solvent (e.g., water, ethanol, toluene, dimethylformamide, or methyl ethyl ketone, or a combination of the foregoing). If the photocurable composition 30a includes a negative photoresist, the rinse fluid may then include a photoresist developer for the photoresist.

[0060] See also Figure 4E and Figure 5B , repeating the above about FIG. 4A to FIG. 4D The process described above is repeated, but using a second photocurable composition 30b and activating a second plurality of micro-LEDs 14b. After rinsing, a second color converting layer 40b is formed over each of the second plurality of micro-LEDs 14b.

[0061] The second photocurable composition 30b is similar to the first photocurable composition 30a, but includes a color conversion agent 36b to convert the shorter wavelength light from the micro-LEDs 14 to longer wavelength light of a different second color. For example, the second color may be green.

[0062] The second plurality of micro-LEDs 14b correspond to sub-pixels of a second color. Specifically, the second plurality of micro-LEDs 14b correspond to sub-pixels of the color of light that will be produced by the color conversion agent in the second photocurable composition 30b. For example, assuming that the color conversion agent in the fluid 30a converts light from the micro-LEDs 14 into green light, only those micro-LEDs 14b corresponding to the green sub-pixels are turned on.

[0063] See also Figure 4F and Figure 5C , repeat the above about FIG. 4A to FIG. 4D The process described above is repeated, but using a third photocurable composition 30a and activating a third plurality of micro-LEDs 14c. After rinsing, a third color converting layer 40c is formed over each of the third plurality of micro-LEDs 14c.

[0064] The third photocurable composition 30c is similar to the first photocurable composition 30a, but includes a color conversion agent 36c to convert the shorter wavelength light from the micro-LEDs 14 to longer wavelength light of a different third color. For example, the third color may be red.

[0065] The third plurality of micro-LEDs 14c correspond to sub-pixels of a third color. Specifically, the third plurality of micro-LEDs 14c correspond to sub-pixels of the color of light to be produced by the color conversion agent in the third photocurable composition 30c. For example, assuming that the color conversion agent in the fluid 30c converts light from the micro-LEDs 14 into red light, only those micro-LEDs 14c corresponding to red sub-pixels are turned on.

[0066] exist 4A to 4F In the specific example shown in , the color conversion layers 40a, 40b, 40c are deposited for each color sub-pixel. This step is required, for example, when the micro-LEDs generate ultraviolet light.

[0067] However, the micro-LEDs 14 may generate blue light instead of UV light. In this case, coating the display 10 with a photocurable composition containing a blue color conversion agent may be skipped, and the process may be performed using photocurable compositions for the green and red sub-pixels. This leaves a plurality of micro-LEDs without a color conversion layer, such as Figure 4E Not implemented Figure 4FFor example, the first photocurable composition 30a may include a green CCA and the first plurality of micro-LEDs 14a may correspond to green sub-pixels, and the second photocurable composition 30b may include a red CCA and the second plurality of micro-LEDs 14b may correspond to red sub-pixels.

[0068] Assuming that the fluid 30a, 30b, 30c includes a solvent, some of the solvent may be trapped in the color conversion layer 40a, 40b, 40c. Figure 4G This solvent may be evaporated, for example, by exposing the micro LED array to heat, such as by an IR lamp. Evaporation of the solvent from the color conversion layers 40a, 40b, 40c may cause the layers to shrink, making the final layer thinner.

[0069] Removing the solvent and shrinking the color conversion layer 40a, 40b, 40c can increase the concentration of the color conversion agent (e.g., quantum dots), thereby providing a higher color conversion efficiency. On the other hand, including a solvent allows for greater flexibility in the chemical formulation of other components of the photocurable composition, for example, greater flexibility in the color conversion agent or cross-linkable components.

[0070] Depending on the situation, Figure 4H As shown, a UV blocking layer 50 can be deposited on top of all micro-LEDs 14. The UV blocking layer 50 can block UV light that is not absorbed by the color conversion layer 40. The UV blocking layer 50 can be a Bragg reflector, or can simply be a material that selectively absorbs UV light (e.g., a benzotriazolyl hydroxyphenyl compound). The Bragg reflector can reflect UV light back toward the micro-LEDs 14, thereby increasing energy efficiency. Other layers (such as stray light absorbing layers, photoluminescent layers, and high refractive index layers) include materials that can also be deposited on the micro-LEDs 14 as appropriate.

[0071] Thus, as described herein, a photocurable composition includes a color conversion agent selected to emit radiation in a first wavelength band in the visible range in response to absorbing radiation in a second wavelength band in the UV or visible range, a reactive ingredient (e.g., one or more monomers), and a photoinitiator that initiates polymerization of the reactive ingredient in response to absorbing radiation in the second wavelength band, the second wavelength band being different from the first wavelength band.

[0072] In some implementations, a light emitting device includes a plurality of light emitting diodes, and a cured composition in contact with a surface through which radiation in a first wavelength band in the UV or visible range is emitted from each of the light emitting diodes. The cured composition includes a nanomaterial selected to emit radiation in a second wavelength band in the visible range in response to absorbing radiation in the first wavelength band from each of the light emitting diodes, a photopolymer, and a component (e.g., a fragment) of a photoinitiator that initiates polymerization of the photopolymer in response to absorbing radiation in the first wavelength band. The second wavelength band is different from the first wavelength band.

[0073] In certain implementations, the light emitting device includes an additional plurality of light emitting diodes and an additional cured composition in contact with a surface through which radiation in a first wavelength band is emitted from each of the additional light emitting diodes. The additional cured composition includes ingredients selected to emit radiation in a third wavelength band in the visible range in response to absorbing radiation in the first wavelength band from each of the light emitting diodes, an additional photopolymer, and an additional photoinitiator that initiates polymerization of the photopolymer in response to absorbing radiation in the first wavelength band. The third wavelength band may be different from the second wavelength band.

[0074] FIG. 6A to FIG. 6E A method for manufacturing a micro LED array and isolation walls on a backplane is shown. Fig. 6A , the process starts with a wafer 100, which will provide a micro LED array. The wafer 100 includes a substrate 102, such as a silicon or sapphire wafer, on which a first semiconductor layer 104 having a first doping, an active layer 106, and a second semiconductor layer 108 having an opposite second doping are disposed. For example, the first semiconductor layer 104 can be an n-type doped gallium nitride (n-GaN) layer, the active layer 106 can be a multi-quantum well (MQW) layer 106, and the second semiconductor layer 107 can be a p-type doped gallium nitride (p-GaN) layer 108.

[0075] 6B, the wafer 100 is etched to separate the layers 104, 106, 108 into individual micro-LEDs 14, including first, second, and third pluralities of micro-LEDs 14a, 14b, 14c corresponding to first, second, and third colors. In addition, conductive contacts 110 may be deposited. For example, p-contacts 110a and n-contacts 110b may be deposited on n-GaN layer 104 and p-GaN layer 108, respectively.

[0076] Similarly, the backplane 16 is fabricated to include the circuit 18, and the electrical contacts 120. The electrical contacts 120 may include a first contact 120a (eg, a drive contact), and a second contact 120b (eg, a ground contact).

[0077] See also Figure 6C , the micro LED wafer 100 is aligned and placed in contact with the backplane 16. For example, the first contact 110a can contact the first contact 120a, and the second contact 110b can contact the second contact 120b. The micro LED wafer 100 can be lowered into contact with the backplane, or vice versa.

[0078] Next, see Fig.6D , removing the substrate 102. For example, the silicon substrate can be removed by polishing away the substrate 102, for example, by chemical mechanical polishing. As another example, the sapphire substrate can be removed by a laser lift-off process.

[0079] Finally, see Fig. 6E , the isolation wall 20 is formed on the backplane 16 (the micro LEDs 14 are already attached to the backplane 16). The isolation wall can be formed by a conventional process, such as depositing a photoresist, patterning the photoresist by photolithography, and developing to remove the portion of the photoresist corresponding to the recess 22. The resulting structure can then be used as a display 10 for displaying a display device 10. 4A to 4H Describe the general treatment.

[0080] FIG. 7A to FIG. 7D Another method of manufacturing a micro LED array and a partition wall on a backplane is shown. This process can be similar to the above for FIG. 6A to FIG. 6E The processes discussed are except as mentioned below.

[0081] See also Fig. 7A , the process begins with a process similar to that described above, where the wafer 100 will provide the micro LED array and the backplane 16.

[0082] 7B , the isolation walls 20 are formed on the substrate 16 (the micro LEDs 14 are not yet attached to the backplane 16 ).

[0083] In addition, the wafer 100 is etched to separate the layers 104, 106, 108 into individual micro-LEDs 14, including first, second, and third pluralities of micro-LEDs 14a, 14b, 14c. However, the recesses 130 formed by this etching process are deep enough to accommodate the isolation walls 20. For example, etching can continue so that the recesses 130 extend into the substrate 102.

[0084] Next, if Figure 7C As shown, the micro LED wafer 100 is aligned with and placed in contact with the back plate 16 (or vice versa). The spacer walls 20 fit into the recesses 130. In addition, the contacts 110 of the micro LEDs are electrically connected to the contacts 120 of the back plate 16.

[0085] Finally, see Fig.7D, removing substrate 102. This leaves micro-LEDs 14 and spacer walls 20 on backplane 16. The resulting structure can then be used as display 10 for 4A to 4H Describe the general treatment.

[0086] Terms such as vertical and lateral have been used. However, it should be understood that these terms refer to relative positioning, not absolute positioning with respect to gravity. For example, lateral is a direction parallel to the substrate surface, while vertical is a direction orthogonal to the substrate surface.

[0087] Those skilled in the art will appreciate that the foregoing examples are illustrative and not limiting. For example:

[0088] • Although the above description focuses on micro-LEDs, the technology can be applied to other displays with other types of light emitting diodes, particularly displays with other micro-light emitting diodes, for example, LEDs smaller than about 10 microns.

[0089] Although the above description assumes that the order of forming the color conversion layers is blue, then green, then red, other orders are possible, for example, blue, then red, then green. In addition, other colors are possible, for example, orange is followed by yellow.

[0090] It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.

Claims

1. A photocurable composition comprising: a blue photoluminescent material selected to absorb ultraviolet light having a maximum wavelength in the range of 300 nm to 430 nm and emit blue light having an emission peak in the range of 420 nm to 480 nm, wherein the full width at half maximum of the emission peak is less than 100 nm, and the photoluminescent quantum yield is in the range of 5% to 100%; one or more monomers; and A photoinitiator initiates polymerization of the one or more monomers in response to absorbing the ultraviolet light.

2. The composition of claim 1, wherein the composition comprises: 0.1 wt % to 10 wt % of the blue photoluminescent material; 0.5 wt % to 5 wt % of said photoinitiator; and 1 wt % to 90 wt % of the one or more monomers.

3. The composition of claim 1, wherein the composition further comprises a solvent.

4. The composition of claim 3, wherein the composition comprises: 0.1 wt % to 10 wt % of the blue photoluminescent material; 0.5 wt % to 5 wt % of the photoinitiator; 1 wt % to 90 wt % of said one or more monomers; and 10% to 90% by weight of the solvent, The sum of the weight percentages of the above components in the composition is not greater than 100%.

5. The composition of claim 1, wherein the blue photoluminescent material is an organic material.

6. The composition of claim 1, wherein the blue photoluminescent material is an organic metal material or a polymer material.

7. The composition of claim 5 or 6, wherein the blue photoluminescent material is fluorescent.

8. The composition of claim 7, wherein the blue photoluminescent material comprises blue thermally activated delayed fluorescence (TADF) molecules.

9. The composition of claim 5 or 6, wherein the blue photoluminescent material is phosphorescent.

10. The composition of claim 1, wherein the one or more monomers comprise a (meth)acrylate monomer.

11. A photocurable composition comprising: a polymer matrix formed from one or more monomers; a blue photoluminescent material mixed in the polymer matrix, the blue photoluminescent material being selected to absorb ultraviolet light having a maximum wavelength in the range of 300 nm to 430 nm and emit blue light having an emission peak in the range of 420 nm to 480 nm, wherein the full width at half maximum of the emission peak is less than 100 nm, and the photoluminescent quantum yield is in the range of 5% to 100%; and A photoinitiator component that initiates polymerization in response to absorbing the ultraviolet light to form the polymer matrix.

12. The composition of claim 11, wherein the polymer matrix comprises a polyacrylate.

13. The composition of claim 11, wherein the blue photoluminescent material is an organic material.

14. The composition of claim 11, wherein the blue photoluminescent material is an organic metal material or a polymer material.

15. The composition of claim 11, wherein the blue photoluminescent material is fluorescent.

16. The composition of claim 11, wherein the blue photoluminescent material is phosphorescent.

17. A method of manufacturing a light emitting device, comprising: Include: Dispensing a first photocurable fluid over a display having a backplane and an array of ultraviolet light emitting diodes electrically integrated with backplane circuitry of the backplane, the first photocurable fluid comprising a blue photoluminescent material selected to absorb ultraviolet light having a maximum wavelength in the range of 300 nm to 430 nm and emit blue light having an emission peak in the range of 420 nm to 480 nm, wherein the full width at half maximum of the emission peak is less than 100 nm, and the photoluminescent quantum yield is in the range of 5% to 100%, one or more monomers, and a photoinitiator that initiates polymerization of the one or more monomers in response to absorbing the ultraviolet light; activating a first plurality of light emitting diodes in the array of light emitting diodes to illuminate and polymerize the one or more monomers to form a first color conversion layer over each of the first plurality of light emitting diodes for converting light from the first plurality of light emitting diodes into blue light, each color conversion layer comprising the blue photoluminescent material mixed in a polymer matrix; and Uncured remaining portions of the first photocurable fluid are removed.

18. The method of claim 17, wherein the one or more monomers comprise a (meth)acrylate monomer.

19. The method of claim 17, wherein the first photocurable fluid comprises: 0.1 wt % to 10 wt % of the blue photoluminescent material; 0.5 wt % to 5 wt % of said photoinitiator; and 1 wt % to 90 wt % of the one or more monomers.

20. The method of claim 17, wherein the first photocurable fluid further comprises a solvent, and the method comprises evaporating the solvent.

21. The method of claim 17, wherein the blue photoluminescent material is an organic material.

22. The method of claim 17, wherein the blue photoluminescent material is an organometallic material or a polymeric material.

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