Micro-LED display for reducing sub-pixel crosstalk and method for manufacturing the same

Abstract

A method of manufacturing a micro LED display includes depositing a first material on a substrate having a plurality of micro LEDs such that the plurality of micro LEDs are covered by the first material and the first material fills gaps laterally separating the micro LEDs, removing portions of the first material from the gaps laterally separating the plurality of micro LEDs to form trenches extending to or below a light emitting layer of the micro LEDs, depositing a second material on the substrate such that the second material covers the first material and extends into the trenches, and removing portions of the first and second materials over the plurality of micro LEDs such that a top surface of the plurality of micro LEDs is exposed and a separating wall extends vertically higher than a top surface of the first material. The second material is an opaque material.

Description

Technical Field

[0001]

[0001] This specification relates to the manufacture of micro-LED displays, and more particularly to micro-LED displays that use an opaque material between sub-pixels.

Background Art

[0002]

[0002] Light-emitting diode (LED) panels use an array of LEDs, where each individual LED provides a pixel element that can be individually controlled. Such LED panels can be used in computers, touch panel devices, PDAs (Personal Digital Assistants), mobile phones, television monitors, and the like.

[0003]

[0003] LED panels that use micron-scale LEDs (also called micro-LEDs) based on III-V semiconductor technology have various advantages compared to OLEDs. For example, they have higher energy efficiency, brightness, and longer lifetimes, and manufacturing can be simplified because there are fewer material layers in the display stack. However, there are challenges in manufacturing micro-LED panels. Micro-LEDs having different colors of light emission (e.g., red, green, and blue pixels) need to be fabricated on different substrates through separate processes. To integrate multiple-color micro-LED devices onto a single panel, a pick-and-place step is required to transfer the micro-LED devices from the original donor substrate to the target substrate. This often involves changes to the LED structure and manufacturing process, such as the introduction of a sacrificial layer to facilitate die removal. Additionally, strict requirements for placement accuracy (e.g., less than 1 um) limit throughput, final yield, or both.

[0004]

[0004] An alternative approach to avoiding the pick-and-place step is to selectively deposit a color conversion agent (e.g., quantum dots, nanostructures, fluorescent materials, or organic substances) at specific pixel positions on a substrate fabricated with monochromatic micro-LEDs. The monochromatic micro-LEDs can generate light of a relatively short wavelength, such as violet or blue light, and the color conversion agent can convert this short-wavelength light into light of a longer wavelength, such as red or green light for red or green pixels. For example, the micro-LEDs can emit light in the ultraviolet wavelength range (UV micro-LEDs), and light-emitting quantum dot (QD) particles can be overlaid on the UV micro-LEDs to form sub-pixels that convert the UV backlight into primary colors (e.g., red, green, blue). An array of four QD / UV micro-LED sub-pixels that emit red, green, blue, and white light respectively forms one pixel of the display.

Summary of the Invention

[0005]

[0005] In one aspect, a method of manufacturing a micro-LED display includes depositing a first material on a substrate having a plurality of micro-LEDs such that the plurality of micro-LEDs are covered by the first material and the first material fills gaps that laterally separate the micro-LEDs; removing a portion of the first material from the gaps that laterally separate the plurality of micro-LEDs to form trenches in the first material that extend up to or below the light-emitting layer of the micro-LEDs; depositing a second material on the substrate such that the second material covers the first material and extends into the trenches in the first material; and removing portions of the first and second materials on the plurality of micro-LEDs such that the upper surfaces of the plurality of micro-LEDs are exposed and a plurality of separating walls of the second material disposed in the gaps between the plurality of micro-LEDs extend vertically higher than the upper surface of the first material. The second material is an opaque material.

[0006]

[0006] Embodiments can include one or more of the following features. The first material can be a photoresist material or a redistribution layer material. The third material can be a metal, and the fourth material can be a photoresist material. The fourth material can provide a mask over the separation wall while removing the third material over the micro-LEDs.

[0007]

[0007] In another aspect, a method of manufacturing a micro-LED display includes depositing a first material on a substrate having a plurality of micro-LEDs such that the plurality of micro-LEDs and the substrate exposed between the plurality of micro-LEDs are covered with a first conformal layer of the first material; depositing a second material on the substrate such that the second material covers the first material and fills a gap that laterally separates the micro-LEDs; removing a portion of the second material from the gap that laterally separates the plurality of micro-LEDs to form a trench in the second material that extends to a conformal layer of the first material covering the substrate exposed between the plurality of micro-LEDs; depositing a third material on the second material such that the exposed surfaces of the second material and the first material are covered with a second conformal layer of the third material; depositing a fourth material on the third material such that the fourth material extends into the trench in the third material; and removing a portion of the fourth material and the third material over the micro-LEDs such that the upper surface of the micro-LEDs is exposed and the separation walls of the third material and the fourth material disposed in the gap between the micro-LEDs extend vertically higher than the upper surface of the first material. The fourth material is an opaque material.

[0008]

[0008] Embodiments can include one or more of the following features. The first material can be a dielectric material having a dielectric constant greater than 4. The third material can be a metal. The fourth material can be opaque or transparent.

[0009]

[0009] In another aspect, the display screen includes a backplane, an array of light-emitting diodes electrically integrated with the backplane, and a plurality of partition walls. The light-emitting diodes are configured to emit UV light (ultraviolet light) in a first wavelength range. The plurality of partition walls are formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes. The partition walls are spaced apart from the light-emitting diodes by a gap and extend above the light-emitting diodes. The plurality of partition walls are formed of an opaque material having a transmittance of light in the first wavelength range of less than 1%.

[0010]

[0010] Embodiments can include one or more of the following features. The first wavelength range can be from 320 nm to 400 nm. The plurality of partition walls may be in contact with the backplane. The filling material can be a positive photoresist. The opaque material can be a photoresist. The filling material can be a positive photoresist. The first material can be a photoresist. The first material can be a negative photoresist. The first material can be a metal.

[0011]

[0011] In another aspect, the display screen includes a backplane, an array of light-emitting diodes electrically integrated with the backplane, and a plurality of partition walls. The light-emitting diodes are configured to emit UV light in a first wavelength range. The plurality of partition walls are formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes. The partition walls are spaced apart from the light-emitting diodes and extend above the light-emitting diodes. The plurality of partition walls include a core of a first material and a coating covering at least a portion of the core that extends above the light-emitting diodes. The coating is an opaque second material having a transmittance of light in the first wavelength range of less than 1%.

[0012]

[0012] Embodiments can include one or more of the following features. The coating may not extend below the upper surface of the array of light-emitting diodes. The coating may extend below the upper surface of the array of light-emitting diodes. The dielectric layer can include silicon nitride.

[0013]

[0013] In another aspect, a display screen includes a backplane, an array of light-emitting diodes electrically integrated with the backplane, and a plurality of separation walls. The light-emitting diodes are configured to emit UV light in a first wavelength range. The plurality of separation walls are formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes, the plurality of separation walls are spaced apart from the light-emitting diodes, and extend above the light-emitting diodes. The plurality of separation walls include a lower portion below the upper surface of the light-emitting diodes having substantially vertical sides and an upper portion above the upper surface of the light-emitting diodes having inclined sides.

[0014]

[0014] Embodiments can include one or more of the following features. The plurality of separation walls can include a core of a first material and a coating covering at least a portion of the core extending above the array of light-emitting diodes. The coating can be an opaque second material with a transmittance of light in the first wavelength range of less than 1%.

[0015]

[0015] Advantages of embodiments can include one or more of the following, but are not limited thereto. By reducing light loss, color crosstalk between sub-pixels, and deposition accuracy of the color conversion layer, the overall brightness and color gamut of the display can be improved. This process can increase the possible range of the thickness of the opaque material to increase the opacity between sub-pixels. Additional materials such as metal, dielectric, or photoresist layers can be laminated before or after the opaque material to improve the performance of the opaque layer. Note that the opaque material can include both reflective and absorptive materials.

[0016] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will be apparent from the description, the drawings, and the claims.

Brief Description of the Drawings

[0017]

Figure 1A

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DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0026] Like reference numerals and names in the various drawings indicate like elements.

[0019]

[0027] One technique for manufacturing a micro-LED display involves curing a color conversion layer over a UV micro-LED element. The combination of the separated color conversion layer and the underlying micro-LED forms a sub-pixel, and an array of two or more sub-pixels, such as three or four sub-pixels, that emit different colors of visible light, such as red, green, blue, and / or white (or other primary colors), forms a visible pixel.

[0020]

[0028] To block the light emitted from the micro-LED of one sub-pixel so as not to stimulate light emission within the color conversion layer of adjacent sub-pixels and cause optical crosstalk of the sub-pixels and color shift within the displayed image, an opaque material can separate the sub-pixels. Also, the opaque material can prevent the curing of adjacent color conversion layers during the sub-pixel formation step. Specifically, a "sub-pixel / pixel separation" architecture is required to maintain color purity (e.g., R is only R, G is only G, B is only B). Such color purity is impaired in a display architecture using UV micro-LEDs with color conversion layers by (1) the UV micro-LED irradiating within adjacent color sub-pixels and causing unintended photoluminescence of different color converters (color conversion parts), (2) B emission causing photoluminescence in adjacent R and G sub-pixels, and similarly, G emission causing photoluminescence in adjacent R sub-pixels, and finally, (3) during the manufacturing step of self-aligned curing, adjacent sub-pixels being contaminated with the wrong color converter due to the unintended curing of the color converter distributed within adjacent sub-pixels.

[0021]

[0029] It is desirable to use a micro-LED that emits UV light and a color conversion layer that converts the emitted UV light into primary colors (e.g., red, green, blue). Although the opaque materials currently used in the manufacture of micro-LED displays have a low transmittance in the visible range (e.g., less than 1%), this low transmittance does not necessarily extend to the UV range. As a result, the use of LED displays using UV-emitting micro-LEDs and color conversion layers may still be affected by crosstalk. Further, when UV-emitting micro-LEDs are used for self-aligning curing of the color conversion layer, i.e., without such an "opaque" material to achieve optical separation between pixels / sub-pixels, color conversion materials of a certain color (e.g., red) inadvertently deposited on adjacent sub-pixels (e.g., green) may cure, causing color mixing and potentially changing the color gamut perceived in the finished display.

[0022]

[0030] To adapt the use of existing opaque materials while preventing emission crosstalk between sub-pixels, additional manufacturing steps can be used to reduce the transmission of visible and UV light between sub-pixels. As a base process, an initial coating of an opaque material is deposited to a thickness higher than the underlying UV micro-LEDs on the substrate. The opaque material is then removed by lithography in the regions above the UV micro-LEDs, after which the color conversion layer is sequentially deposited within the sub-pixels. The opaque material can extend over the deposited color conversion layer to further separate the emission profiles of each sub-pixel.

[0023]

[0031] FIG. 1A depicts an exemplary portion of a UV micro - LED (micro - LED) array 100 that includes 16 sub - pixels 102 separated by an opaque wall 104. An array of 4 sub - pixels 102 emits light of different colors, e.g., red, green, blue, and / or white (or other primary colors), to form a pixel 101. However, the techniques described below are applicable to displays using fewer numbers of colors, e.g., 2 or 3 colors, or more colors, or different color gamuts. Further, the techniques described below are applicable to displays of any type of pixel and sub - pixel architecture.

[0024]

[0032] An opaque wall 104 is formed between adjacent sub - pixels 102 to provide optical (e.g., light) separation in order to localize the curing of the color - conversion layer 108 within the sub - pixel 102 during manufacturing and to reduce optical crosstalk between the separated color - conversion layers 108 during operation. The opaque wall 104 can be a wall made of a polymer (e.g., photoresist), metal, or other material (e.g., polymer) with a metal coating. In addition to being opaque, the wall 104 can be reflective with respect to the light emitted by the underlying micro - LED and the light emitted by the color - conversion layer 108, e.g., can have a reflectivity greater than 50%, e.g., greater than 90%. In this case, the wall 104 should be made of metal or a wall made of other material (e.g., polymer) with a metal coating. It can also be made of an optically absorptive material instead of being reflective.

[0025]

[0033] For example, the opaque wall 104 can be composed of a black negative photoresist material (e.g., Daxin Black Matrix) having a high optical density (e.g., 0.3 μm-1 to 0.5 μm-1) in the wavelength range of light (e.g., 380 nm to 780 nm). As shown in FIG. 1A, the opaque wall 104 can form a rectangular array together with each sub-pixel 102, but generally, other array shapes, such as a hexagonal array or an offset rectangular array, are also possible. FIG. 1A includes a line 106 indicating the cross-sectional view of FIG. 1C.

[0026]

[0034] FIG. 1B is a cross-sectional view showing the individual components of the micro-LED sub-pixel 102 supported on an electrical connection portion to a backplane 120 (e.g., a substrate). Each sub-pixel 102 includes a micro-LED 110 and a color conversion layer 108 on the micro-LED 110. Each micro-LED 110 includes a light-emitting layer 112 (e.g., a semiconductor layer), an active layer 114, and conductive contacts 116a, b. The light-emitting layer 112 can be an n-doped semiconductor layer (e.g., n-doped gallium nitride (n-GaN)), and the active layer 114 can be a p-doped semiconductor layer (e.g., p-doped gallium nitride (n-GaN)). In some embodiments, the active layer 114 may further include a multiple quantum well (MQW) layer. The contacts 116a, 116b of each micro-LED 110 are electrically connected to the backplane 120 fabricated to include electrical contacts with a circuit for controlling each micro-LED 110.

[0027]

[0035] FIG. 1C is a cross-sectional view showing three sub-pixels 102 separated by an opaque wall 104 composed of an opaque material 105, and the wall 104 has a solid rectangular cross-section. Generally, when activated by the control circuit of the backplane 120, the micro-LED 110 generates UV light (e.g., between 365 nm and 405 nm) that is emitted into the color conversion layer 108. The color conversion layer 108 can include color conversion agents, such as quantum dots, nanostructures, fluorescent materials, or organic substances, to absorb the emitted UV light of the first wavelength and re-emit light of a second, longer wavelength. For example, the color conversion layer 108 can include color conversion agents that re-emit in a specific color spectrum. For example, in a red sub-pixel, it is a red wavelength spectrum (e.g., 620 nm to 750 nm, or 590 nm to 620 nm), or in a green sub-pixel, it is a green wavelength spectrum (e.g., 495 nm to 570 nm, or 510 nm to 550 nm).

[0028]

[0036] As shown in FIG. 1C, the opaque wall 104 laterally separates adjacent sub-pixels 102 and protrudes above the upper surface of each color conversion layer 108. Assuming that a material that is sufficiently opaque in the UV light region is available, the lateral width of the opaque wall 104 can be sufficient to block the transmission of UV light emitted from one sub-pixel 102 from stimulating the color conversion layer 108 of an adjacent sub-pixel 102 while meeting the requirements of the sub-pixel pitch. The manufacture of the opaque wall 104 consists of coating the micro-LED 110 and the backplane 120 with one or more layers of the opaque material 105 to a depth higher than the upper surface of the micro-LED 110, and then performing exposure that depends on temperature or light to cure the opaque material 105. The portion of the opaque material 105 above the light-emitting layer 112 of the micro-LED 110 is removed, leaving only the wall 104 of the opaque material 105.

[0029]

[0037] Forming the wall 104 from a polymer, such as a photoresist, is advantageous for the manufacturing process. However, considering the constraints on the sub-pixel pitch (e.g., ~10 μm), and thus the thickness of the wall 104, the opaque polymer material 105 available for forming the opaque wall 104 may not completely block the transmission of the UV light emitted by the micro-LED 110 (e.g., <1% transmittance through the width of the opaque wall 104).

[0030]

[0038] The thickness of the wall 104 can also depend on the properties of the material 105 used to form the wall 104. The wall 104 in FIG. 1C is shown as a rectangular partition wall with right-angled (e.g., 90°) corners, which represents a "vertical" profile. Alternatively, the material 105 can form a trapezoidal wall 104 having an aspect ratio defined by the width (wb) of the bottom of the partition wall closest to the substrate and the width (wp) of the top of the partition wall above the micro-LED 110. A wall 104 with wp > wb (the top is wider than the bottom) is said to form a "negative re-entrant" profile, and a wall with wp < wb (the top is narrower than the bottom) is said to form a "positive re-entrant" (or tapered) profile. A wall 104 with a vertical or positive re-entrant profile can further reduce the transmission between the wells by increasing the thickness of the wall 104 near the light-emitting layer 112 of the micro-LED sub-pixel 102.

[0031]

[0039] Disclosed herein is a method of manufacturing an array 100 of micro-LED sub-pixels 102, utilizing additional manufacturing methods and materials to further separate the light emission of each sub-pixel 102.

[0032]

[0040] Figures 2A - 2E illustrate a method of using an underfill material (e.g., a first material) in addition to an opaque material (e.g., a second material) to beneficially reduce crosstalk between adjacent sub - pixels 102 and increase the durability of the electrical contacts 116a,b of the micro - LEDs 110 with the backplane 120. As shown in Figure 2A, following the connection of an exemplary micro - LED 210 to a backplane 220, an underfill layer 230 is deposited over the micro - LED 210 to fill the gaps that laterally separate the micro - LEDs 210 and cover the light - emitting layer of the micro - LED 210 to a certain depth. For example, the exposed surface of the light - emitting layer of the micro - LED 210 can have a height of 10 μm from the substrate, and the material of the underfill layer 230 can be deposited to a depth of 20 μm, thereby covering the micro - LED 210. The underfill layer 230 can also flow into the vertical gaps between the micro - LED 210 and the backplane 220, for example, by surrounding the bonding region on the bottom surface of the micro - LED 210, stabilizing the connection with the backplane 220 and reducing the thermal stress during operation. The underfill layer 230 can be deposited by spin - coating, slot - die coating, spray - coating, or a combination thereof. The deposition method can depend on the composition of the material.

[0033]

[0041] In some embodiments, the width of the micro - LED 210 is 30 μm and the height is 10 μm from the upper surface of the backplane 220. The distance between adjacent micro - LEDs 210 can be 10 μm, and the total pitch of the micro - LEDs 210 is 40 μm. The underfill layer 230 can be deposited to a depth of 20 μm, thereby covering the micro - LED 210 to a depth of 10 μm.

[0034]

[0042] In some embodiments, the underfill layer 230 is a photoresist material (a photosensitive material used in photolithography to form a patterned coating on a surface). In some embodiments, the photoresist material is a positive photoresist material, e.g., a photosensitive material that is removed by a developer in the areas exposed to light after exposure. Another advantage of using a positive photoresist material as the underfill layer 230 is its low coefficient of thermal expansion, which improves the durability of the electrical connection between the micro-LED 210 and the backplane 220 during operation while the micro-LED 210 is generating heat. Further, the air trapped under the micro-LED 210 expands when heated during operation, which may damage the contact with the backplane 220. The underfill layer 230 moves the air away from under the micro-LED 210 and prevents damage due to thermal expansion. In some embodiments, the underfill layer 230 can block at least a portion of the UV light emitted by the micro-LED 210. This can reduce the UV exposure of the backplane 220 components such as thin-film transistors.

[0035]

[0043] In some embodiments, the underfill layer 230 is a redistribution layer (RDL) material such as a polymer dielectric material (e.g., a positive photoresist).

[0036]

[0044] As depicted in FIG. 2B, a portion of the underfill layer 230 is then removed. The removal method may vary depending on the deposited material, but generally, a photoresist can be removed using photolithography. For example, a positive photoresist material can be used (e.g., SPR (trademark) 220, AZ (registered trademark) 10XT, AZ (registered trademark) 40XT, or AZ (registered trademark) 9260). UV light can be directed through a mask to expose the photoresist, and the mask can block light in the regions corresponding to the micro-LEDs 210 (excluding the gaps between the micro-LEDs 210), and a developer can remove the exposed portions. For example, the mask can be made of a transparent wafer such as glass or quartz and coated with a patterned metal layer covering the regions corresponding to the micro-LEDs 210. Alternatively, a negative photoresist material can be used, and the mask can block light in the regions corresponding to the lateral gaps (excluding the micro-LEDs 210), and a developer can remove the unexposed portions. When a portion of the underfill layer 230 is removed, trenches are formed in the lateral gaps between the micro-LEDs 210 that extend up to or below the light-emitting layer 212 of the micro-LEDs 210. In some embodiments, the trenches can extend to a portion of the backplane 220 and expose them.

[0037]

[0045] Next, referring to FIG. 2C, an opaque material 205 is deposited using the method disclosed above to cover the underfill layer 230, fill the trenches, and cover the exposed backplane 220 up to a height above the upper surface of the underfill layer 230. The opaque material 205 is the material used for the opaque wall 104 in FIG. 1B and is, for example, a black negative photoresist. The opaque material 205 is cured by means depending on the material, such as thermal curing or mask UV curing.

[0038]

[0046] Following the hardening step, as shown in FIG. 2D, a portion of the opaque material 205 on the micro-LED 210 is removed until the upper surface 230a of the underfill layer 230 on the micro-LED 210 is exposed. The remaining opaque material 205 forms a vertical separation wall 205a of the opaque material 205 in the lateral space between adjacent covered micro-LEDs 210. These separation walls 205a of the opaque material 205 extend to a height above the upper surface 230a of the underfill layer 230. The separation walls can have a homogeneous composition. For example, the opaque material 205 can have a homogeneous composition.

[0039]

[0047] As shown in FIG. 2E, in some embodiments, by optionally removing the remaining underfill layer 230 covering the upper surface of the light-emitting layer 212, the light extraction from the underlying micro-LED 210 can be increased. At this point, the color conversion material can be deposited within the well 240 defined by the space above the underfill layer 230 and between the walls 205a.

[0040]

[0048] FIGS. 3A - 3E show another method of manufacturing the underfill layer 230 and the opaque material 205. The process of FIGS. 3A - 3E is the same as the process of FIGS. 2A - 2E except as described below. As shown in FIGS. 3A and 3B, the underfill layer 230 is deposited above the backplane 220 to have a thickness equal to the desired total height of the walls of the opaque material. After trenches 232 are formed in the underfill layer 230, the opaque material 205 is deposited to fill the trenches. The opaque material above the height of the underfill layer 230, i.e., above both the underfill layer 230 and the trenches filled with the opaque material, is removed by a planarization process, such as plasma etching, until the upper surface of the underfill layer 230 is exposed, thereby forming a well 240 on the micro-LED 210. Thereafter, the portion of the underfill layer 230 remaining on the micro-LED 210 can be removed using photolithography techniques before depositing the color conversion material.

[0041]

[0049] In some embodiments, as shown in FIGS. 4A-4C, after removal of the second material 204, a layer 302 of an opaque material can be added to further reduce optical crosstalk between the micro LEDs 210. FIG. 4A shows the arrangement of FIGS. 2D or 3D after removing the material 205 from the top surface of the underfill layer 230. The opaque material is deposited to cover the underfill layer 230 and the exposed surfaces of the second material 205.

[0042]

[0050] The opaque material of layer 302 can have a higher opacity than the second material 205. Specifically, if this third material is sufficiently opaque, the material 205 of the pillar 205a does not particularly need to be opaque, which can greatly expand the range of compatible materials and thus improve manufacturing ease. For example, if the opaque material is opaque (e.g., light transmittance < 1%), the second material 205 may be substantially transparent (e.g., transmittance > 95%). In some embodiments, the opaque material is reflective with respect to the wavelength of light. In some embodiments, the opaque material is a metal (e.g., a metal layer) such as aluminum, gold, silver, platinum, or an alloy thereof.

[0043]

[0051] Layer 302 can be deposited as a conformal layer (e.g., having a generally uniform depth across the exposed surface) and can be made relatively thin (e.g., 50 nm to 300 nm) compared to the separation wall 205a and the underfill layer. This layer can be deposited using metal deposition techniques such as plasma-assisted chemical vapor deposition (PCVD), thermal evaporation, or electron beam deposition. Depending on the deposition technique used, the layer 302 covering the vertical surface of the separation wall 205a can be thinner than the layer 302 covering the top of the separation wall 205a. The opaque material increases the light reflectivity, which increases the emission rate of the deposited color conversion layer 108 and reduces UV transmission through the width of the separation wall separating the micro LEDs 110.

[0044]

[0052] Figure 4B depicts the deposition of a photoresist layer 304 (e.g., a fourth material), such as a photoresist material (e.g., a positive or negative photoresist material) for covering the layer 302 of the opaque material. The photoresist layer 304 provides a mask when removing a portion of the layer 302 of the opaque material. The photoresist layer 304 is exposed to UV light through the mask and developed to define the regions of the opaque material to be removed. These regions correspond to the covered micro-LEDs 210 (except for the separation walls or the walls between the micro-LEDs 210). The opaque material of the layer 302 is removed using an appropriate technique such as wet etching or dry etching. Figure 4C shows the final configuration after the removal of the unmasked portions of the layer 302 and the photoresist layer 304 above the light-emitting layer 212 of the micro-LED 210. The layer 302 provides additional protection for the second material 204 (e.g., an underfill layer) and further reduces the optical crosstalk between adjacent micro-LEDs 210. If any, the portion of the photoresist layer 304 at the top of the separation wall can also help reduce the optical crosstalk. However, in some embodiments, the portion of the photoresist layer 304 at the top of the separation wall is completely removed.

[0045]

[0053] In some embodiments, an additional protective material can be deposited prior to the underfill layer 230 of FIG. 2A to coat the backplane 220 and the electrically connected micro-LEDs 210, preventing damage to the connections and further electrically insulating the electrical contacts of the individual micro-LEDs 210. For example, a dielectric coating can electrically insulate a metal layer deposited to form part of the optical barrier from the backplane. FIGS. 5A - 5H show an example process of laminating an additional protective material in a process different from the process described in FIGS. 2A - 2E.

[0046]

[0054] Figure 5A depicts the deposition of an undercoat dielectric material 406 layer (e.g., a dielectric layer) to coat the top and side surfaces of the micro-LED 410, as well as the exposed surfaces of the conductive contacts 416a,b and the backplane 420. For example, the dielectric material 406 can be composed of a nitride material such as silicon nitride (SiN) or aluminum nitride (AlN), or an oxide material such as silicon dioxide (SiO2) or aluminum oxide (Al2O3). The dielectric material 406 can have a dielectric constant of 5 or more (e.g., 5 or more, 6 or more, or 7 or more). The dielectric material 406 is conformal with the features of the micro-LED 410 and can be deposited as a thin layer (e.g., between 100 nm and 500 nm) that wraps around the features. Next, as shown in Figure 5B, an underfill material 430 is deposited to cover the light-emitting layer 412 and fill the lateral gaps between adjacent micro-LEDs 410. The underfill material 430 can be any material as described above.

[0047]

[0055] Figure 5C shows a state in which a part of the underfill material 430 is removed to form trenches in the gaps between adjacent micro-LEDs 410 and expose the dielectric material 406 that coats the backplane 420. The underfill material 430 is removed by the method described above.

[0048]

[0056] As shown in Figure 5D, an opaque layer 402, e.g., a reflective layer, is deposited to cover the top and side surfaces of the exposed underfill material 430 and the dielectric material 406 on the backplane 420. The opaque layer 402 does not need to fill the gaps between the micro-LEDs 410 and can leave trenches to be filled by additional material coatings. The opaque layer 402 can be conductive. The opaque layer 402 can be a metal, e.g., aluminum, gold, silver, platinum, or an alloy thereof.

[0049]

[0057] As shown in FIG. 5E, the trench is filled with an opaque wall material 404, and the excess material 404 on the opaque layer 402 is removed as shown in FIG. 5F, for example, by plasma etching, whereby the opaque layer 402 on the light emitting surface of the micro-LED 410 is exposed. Following the removal of the material 404, the opaque wall material 404 is cured using thermal curing or UV curing.

[0050]

[0058] The exposed opaque layer 402 on the micro-LED 410 is removed by an etching technique, and as a result, as shown in FIG. 5G, the underfill material 430 is exposed. A part of the underfill material 430 is removed, and a well 440 is formed on the micro-LED 410. As shown in FIG. 5H, the underfill material 430 can be removed to a depth that exposes the protective dielectric material 406 on the light emitting surface of the micro-LED 410. Below the upper surface of the micro-LED 410, for example, the underfill material 430 between the LED and the backplane does not need to be removed.

[0051]

[0059] Removal of the underfill material 430 can leave a portion of the fill material 430 as a coating 430a on the vertical surface of the opaque layer 402 that extends above the micro-LED 410. For example, the coating 430a on the vertical surface of the opaque layer 402 can have a horizontal depth in the range of 0.5 μm to 2 μm. This coating 430a can enhance the structural stability of the opaque layer 402. In some embodiments, the dielectric material 406 on the micro-LED 410 can be optionally removed to increase light extraction from the micro-LED 410. Alternatively, the underfill material 430 may be removed without leaving a coating on the vertical surface of the opaque layer 402. In some embodiments, as shown in FIG. 5I, additional dielectric material 406 is deposited on the upper and side surfaces of the separation wall.

[0052]

[0060] As an alternative to the dielectric material 406, an additional layer of the first metal layer 402a can be deposited. In some embodiments, as shown in FIG. 5J, the opaque material 402 is removed from the side surfaces of the isolation walls of FIG. 5H. Next, as shown in FIG. 5K, an additional layer of the first metal layer 402a is deposited on the exposed surfaces including the upper and side surfaces of the isolation walls and on the light-emitting layer of the micro-LED 410. As shown in FIG. 5L, a photoresist layer 405 can be deposited in the well 440 region of FIG. 5K to cover the upper surface of the opaque material 402 layer to a certain depth. In some embodiments, the material of the photoresist layer 405 can be the same as the material of the underfill material 430.

[0053]

[0061] A portion of the photoresist layer 405 can be removed using the method described to form the well 440 region over the micro-LED 410 (FIG. 5M). The well 440 region defines a mask for removing the portion of the opaque material 402 over the light-emitting region of the micro-LED 410. The opaque material 402 can be removed (e.g., etched), and the remaining portion of the photoresist layer 405 can be removed (e.g., developed). In some embodiments, a portion of the photoresist layer 405 may remain on the vertical isolation wall surface coated with the opaque material as described with respect to FIG. 5H. FIG. 5N depicts the final arrangement where the opaque layer 402 covers the upper and side surfaces of the wall material 404, further reducing the optical crosstalk between adjacent micro-LEDs 210.

[0054]

[0062] Alternatively, in some embodiments, the void-filling material 404 of FIGS. 5E - 5N can be a transparent or translucent material, such as a material having a transmittance greater than 1% (e.g., a transmittance of 1 - 50%), instead of an opaque wall material, to reduce the number of exposure and development steps in the lithographic removal of the materials involved. For example, the void-filling material 404 can be a photoresist material such as SU-8.

[0055]

[0063] As an alternative process to the steps depicted in FIGS. 5A - 5N, FIGS. 6A - 6H depict a process in which an additional protective layer can be deposited before forming a separation wall in the gap between adjacent micro - LEDs 210. Following the deposition of the undercoat dielectric material 406 (e.g., dielectric layer) shown in FIG. 5A, as shown in FIG. 6A, a metal layer 402b, e.g., a reflective layer, is deposited to cover the upper and side surfaces of the dielectric material 406 on the backplane 420.

[0056]

[0064] As shown in FIG. 6B, the trenches separating the micro - LEDs 410 are filled with the wall material 404, and the micro - LEDs 410 are covered to a certain depth by the wall material 404 in the same manner as the process of FIG. 5B. In addition, the opaque layer 404 can underfill the gap between the micro - LEDs 410 and the backplane 420, thereby providing additional protection for the electrical contact connection between the micro - LEDs 410 and the backplane 420, while the undercoat dielectric material 406 maintains the electrical insulation of the individual contacts.

[0057]

[0065] Referring to FIG. 6C, while maintaining the metal layer 402b along the side and upper surfaces of the micro - LED 410, a portion of the material 404 is removed as described above to form the separation wall of the wall material 404 and the well 440 over the micro - LED 410. As depicted in FIG. 6D, an additional metal layer 402c is deposited on the side and upper surfaces of the separation wall of the wall material 404 and on the upper surface of the micro - LED 410, thereby covering the exposed surfaces. The additional metal layer 402c (the second metal layer) can have the same composition as the metal layer 402b or can have a different composition from the metal layer 402b.

[0058]

[0066] Similar to the processes depicted in FIGS. 5K - 5N, FIGS. 6D - 6H depict the formation of a second metal layer on the separation wall. In FIG. 6D, an additional metal layer 402c is deposited on the exposed surface of the separation wall of the wall material 404 and on the dielectric material 406 covering the micro - LED 410. By depositing the additional metal layer 402c, the wall material 404 is separated and a separation wall core is formed. A photoresist layer 405, for example a positive photoresist, is deposited on the second metal layer 402c to a depth covering the top of the separation wall as shown in FIG. 6E.

[0059]

[0067] FIG. 6F shows that the photoresist layer 405 is developed, the area above the micro - LED 410 is removed, and a well 440 is formed. Next, using the remaining photoresist layer 405 as a mask, the metal layer 402b / c above the micro - LED 410 can be removed to expose the light - emitting surface as shown in FIG. 6G. Thereafter, as shown in FIG. 6H, the remaining photoresist layer 405 is removed, leaving the first metal layer 402a and the second metal layer 402b covering the separation wall of the wall material 404 extending above the light - emitting surface of the micro - LED 410.

[0060]

[0068] In various embodiments, the separation wall material 404 extending above the light - emitting surface of the micro - LED 410 may be inclined, for example, at an angle other than 90° with respect to the backplane 420. FIGS. 7A - 7F show the metallization process of FIGS. 6A - 6H where the separation wall material 404 is inclined. However, this technique can also be applied to the other processes described above.

[0061]

[0069] FIG. 7A shows the process following FIG. 6B, where the wall material 404 is deposited to fill the trench between the micro - LEDs 410 formed by the first metal layer 402a to a certain depth and underfill the electrical contacts. The wall material 404 is exposed and developed such that the portion below the light - emitting layer (e.g., the upper surface) of the micro - LED has a substantially vertical side surface, and the portion above the light - emitting layer (e.g., the top) forms an inclined side surface.

[0062]

[0070] A process including the second metal layer 402b, application (coating) of a photoresist layer 405 deeper than the isolation wall, formation of a metal etching mask by exposure and development of the photoresist layer 405, removal of the second metal layer 402b over the micro-LED 410, and final removal of the remaining photoresist layer 405 is depicted in FIGS. 7B-7F.

[0063]

[0071] Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. Operations are depicted in the drawings in a particular order and recited in the claims, but this is not to be construed as requiring that such operations be performed in the particular order shown or sequentially, or that all of the operations shown be performed, in order to obtain a desirable result. For example, the acts recited in the claims may be performed in a different order and still achieve a desirable result. As an example, the processes shown in the accompanying figures do not necessarily require the particular or sequential order shown to achieve a desirable result.

Claims

1. A method for manufacturing a micro-LED display, comprising: covering a plurality of micro-LEDs with a first material, and depositing the first material on a substrate having the plurality of micro-LEDs such that the first material fills gaps separating the micro-LEDs laterally; removing a portion of the first material from the gaps separating the plurality of micro-LEDs laterally to form trenches in the first material that extend to or below the light-emitting layer of the micro-LEDs; depositing a second material on the substrate such that the second material covers the first material and extends into the trenches in the first material; removing a portion of the first material and the second material on the plurality of micro-LEDs such that the upper surfaces of each of the plurality of micro-LEDs are exposed and a plurality of separation walls of the second material disposed in the gaps between the plurality of micro-LEDs extend vertically higher than the upper surface of the first material; including wherein the first material is a positive photoresist material; wherein the second material is a negative photoresist material.

2. The method according to claim 1, wherein removing a portion of the first material and the second material on the micro-LEDs to expose the upper surface of the micro-LEDs further includes removing the portion of the second material on the micro-LEDs.

3. The method according to claim 1, wherein removing a portion of the first material and the second material on the micro-LEDs to expose the upper surface of the micro-LEDs includes removing the second material over an area on the micro-LEDs and an area over the gaps between the micro-LEDs until the first material is exposed.

4. depositing a third material on the substrate such that the third material covers the exposed upper surfaces of the separation walls of the second material and the exposed upper surfaces of the micro-LEDs; depositing a fourth material on the third material such that the third material is covered and the area between the separation walls of the second material coated with the third material is filled; removing a portion of the third material and the fourth material on the micro-LEDs to expose the upper surface of the micro-LEDs; further including The third material is a metallic material selected from any one of aluminum, gold, silver, platinum, or an alloy thereof, The fourth material is a photoresist material, the method according to claim 1. **Claim 5** A method of manufacturing a micro LED display, depositing the first material on the substrate having the plurality of micro LEDs such that the plurality of micro LEDs and the substrate exposed between the plurality of micro LEDs are covered with a first conformal layer of the first material; depositing the second material on the substrate such that the second material covers the first material and fills a gap that laterally separates the micro LEDs; removing a part of the second material from the gap that laterally separates the plurality of micro LEDs to form a trench in the second material that extends to the first conformal layer of the first material covering the exposed substrate between the plurality of micro LEDs; depositing the third material on the second material such that the exposed surfaces of the second material and the first material are covered with a second conformal layer of the third material; depositing the fourth material on the third material such that the fourth material extends into the trench in the third material, wherein the fourth material is an opaque material; exposing the upper surfaces of the micro LEDs and removing a part of the fourth material and the third material on the micro LEDs such that the separation walls of the third material and the fourth material disposed in the gap between the micro LEDs extend vertically higher than the upper surface of the first conformal layer of the first material; comprising the first material is a positive photoresist material, the second material is a negative photoresist material, the third material has a higher opacity than the second material and is a metallic material selected from any one of aluminum, gold, silver, platinum, or an alloy thereof, the fourth material is a photoresist material, the method. **Claim 6** A backplane, an array of light emitting diodes electrically integrated with the backplane, the array of light emitting diodes configured to emit UV light in a first wavelength range A plurality of partition walls formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes, wherein the partition walls are spaced apart from the light-emitting diodes by a gap and extend above the light-emitting diodes, and the plurality of partition walls are formed of an opaque material having a transmittance of light in the first wavelength range of less than 1%, the plurality of partition walls A color conversion layer on each light-emitting diode for converting light in the first wavelength range into visible light in a second wavelength range, and A filling material filling the lateral gap between each light-emitting diode of the array of light-emitting diodes and the color conversion layer on each light-emitting diode and the plurality of partition walls, Comprising The opaque material is a photoresist material, The filling material is a positive photoresist material, a display screen.

7. The display screen according to claim 6, wherein each of the plurality of partition walls has a solid rectangular cross-section.

8. A backplane, An array of light-emitting diodes electrically integrated with the backplane, the array of light-emitting diodes configured to emit UV light in a first wavelength range, and A plurality of partition walls formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes, the partition walls being spaced apart from the light-emitting diodes and extending above the light-emitting diodes, the plurality of partition walls, Comprising, the plurality of partition walls A core of a first material, A coating covering at least a portion of the core extending above the light-emitting diodes, the coating being an opaque second material having a transmittance of light in the first wavelength range of less than 1%, A color conversion layer on each light-emitting diode for converting light in the first wavelength range into visible light in a second wavelength range, and A filling material filling the lateral gap between each light-emitting diode of the array of light-emitting diodes and the color conversion layer on each light-emitting diode and the plurality of partition walls, Including The first material is a photoresist material, The second material is a metal material selected from any one of aluminum, gold, silver, platinum, or an alloy thereof, a display screen.

9. The display screen according to claim 8, wherein the coating covers the side surface of the core.

10. The display screen according to claim 9, wherein the coating covers the horizontal upper surface of the core.

11. The display screen according to claim 9, wherein the coating extends below the bottom surface of the core.

12. The display screen according to claim 11, wherein the coating extends across the upper surface of the core.

13. The display screen according to claim 8, further comprising a dielectric layer that conformally coats the array of light-emitting diodes.

14. The display screen according to claim 13, wherein the dielectric layer conformally coats a portion of the backplane between adjacent light-emitting diodes, and each core of the plurality of separation walls is separated from the backplane by the dielectric layer.

15. The display screen according to claim 8, wherein the coating extends to a side surface of the core below the upper surface of the filling material.

16. The display screen according to claim 8, comprising a dielectric layer that conformally covers the coating of the separation wall.

17. Backplane, An array of light-emitting diodes electrically integrated with the backplane, the array of light-emitting diodes being configured to emit UV light in a first wavelength range, A plurality of separation walls formed on the backplane between adjacent light-emitting diodes of the array of light-emitting diodes, the plurality of separation walls being spaced apart from the light-emitting diodes and extending above the light-emitting diodes, the plurality of separation walls including a lower portion having a substantially vertical side surface and below the upper surface of the light-emitting diodes, and an upper portion having an inclined side surface and above the upper surface of the light-emitting diodes. A color conversion layer on each light-emitting diode for converting light in the first wavelength range to visible light in a second wavelength range, and A filling material filling a lateral gap between each light-emitting diode of the array of light-emitting diodes and the color conversion layer on each light-emitting diode and the plurality of separation walls. A display screen comprising.

18. The display screen according to claim 17, wherein the upper portion of the plurality of separation walls extends over a part of the upper surface of the array of light-emitting diodes.

19. The display screen according to claim 17, wherein the upper portions of the plurality of separation walls are wider than the lower portions of the plurality of separation walls on the upper surface of the array of light-emitting diodes.

20. The display screen according to claim 19, wherein the upper portions of the plurality of separation walls are narrower than the lower portions of the plurality of separation walls at the tops of the plurality of separation walls.

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