Micro-led displays for reducing subpixel crosstalk and manufacturing method thereof

Abstract

To improve brightness and color gamut of a display by reducing color crosstalk between subpixels.SOLUTION: A method of manufacturing micro-LED displays includes: depositing a first material over a substrate including a plurality of micro-LEDs in such a manner that the plurality of micro-LEDs is covered with the first material and a gap separating the micro-LEDs in a lateral direction is filled with the first material; removing a part of the first material from the gaps separating the plurality of micro-LEDs in the lateral direction to form trenches extending to or below light-emitting layers of the micro-LEDs; depositing a second material over the substrate in such a manner that the second material covers the first material and extends into the trenches; and removing a part of the first and second materials over the plurality of micro-LEDs to expose a top face of each of the plurality of micro-LEDs and such that isolation walls extend higher than a top face of the first material in a vertical direction. The second material is an opaque material.SELECTED DRAWING: Figure 2E

Description

[Technical Field]

[0001] This specification relates to the fabrication of micro LED displays, and in particular to micro LED displays that use opaque materials between sub-pixels. [Background technology]

[0002]

[0002] Light-emitting diode (LED) panels use arrays of LEDs, each of which provides an individually controllable pixel element. Such LED panels can be used in computers, touch panel devices, personal digital assistants (PDAs), mobile phones, television monitors, etc.

[0003]

[0003] LED panels using micron-scale LEDs (also called micro-LEDs) based on III-V semiconductor technology offer various advantages over OLEDs, such as higher energy efficiency, brightness, and lifetime, as well as simplified manufacturing due to fewer material layers in the display stack. However, manufacturing micro-LED panels presents challenges. Micro-LEDs with different color emissions (e.g., red, green, and blue pixels) need to be fabricated on different substrates through separate processes. Integrating multi-color micro-LED devices onto a single panel requires a pick-and-place step to transfer the micro-LED devices from the original donor substrate to the destination substrate. This often involves modifications to the LED structure or manufacturing process, such as the introduction of sacrificial layers to facilitate die removal. Furthermore, stringent requirements for placement accuracy (e.g., less than 1 μm) limit throughput, final yield, or both.

[0004]

[0004] An alternative approach that avoids the pick-and-place step is to selectively deposit color conversion agents (e.g., quantum dots, nanostructures, fluorescent materials, or organic materials) at specific pixel locations on a substrate fabricated with monochromatic microLEDs. Monochromatic microLEDs can emit relatively short wavelength light, e.g., violet or blue light, and color conversion agents can convert this short wavelength light to longer wavelength light, e.g., red or green light for red and green pixels. For example, microLEDs can emit in the ultraviolet wavelength range (UV microLEDs), and luminescent quantum dot (QD) particles can be layered on top of the UV microLEDs to form subpixels that convert the UV backlight to basic colors (e.g., red, green, and blue). An array of four QD / UV microLED subpixels, emitting red, green, blue, and white light, respectively, forms one pixel of the display. Summary of the Invention

[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 laterally separating the micro LEDs, removing portions of the first material from the gaps laterally separating the plurality of micro LEDs to form trenches in the first material extending to or below light emitting layers 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 over the plurality of micro LEDs to expose a top surface of each of the plurality of micro LEDs, such that a plurality of separation walls of the second material disposed in the gaps between the plurality of micro LEDs extend vertically higher than a top surface of the first material. The second material is an opaque material.

[0006]

[0006] Implementations may include one or more of the following features: The first material may be a photoresist material or a redistribution layer material; The third material may be a metal, and the fourth material may be a photoresist material; The fourth material may provide a mask over the isolation walls during removal of 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 the gaps laterally separating the micro LEDs; and removing portions of the second material from the gaps laterally separating the plurality of micro LEDs to remove the conformal layer of the first material covering the exposed substrate between the plurality of micro LEDs. forming a trench in the second material extending to the first conformal layer, depositing a third material over the second material such that 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 over 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 to expose top surfaces of the micro LEDs and such that a separation wall of the third material and the fourth material disposed in the gap between the micro LEDs extends vertically higher than the top surface of the first material, where the fourth material is an opaque material.

[0008]

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

[0009] 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 (ultraviolet 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 separation walls being spaced apart from and extending above the light emitting diodes by gaps. The plurality of separation walls are formed of an opaque material having a transmittance of less than 1% for light in the first wavelength range.

[0010]

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

[0011] 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 in the array of light-emitting diodes, the separation walls being spaced apart from and extending above the light-emitting diodes. The plurality of separation walls include a core of a first material and a coating covering at least a portion of the core extending above the light-emitting diodes. The coating is an opaque second material having a transmittance of less than 1% for light in the first wavelength range.

[0012]

[0012] Implementations may include one or more of the following features: The coating may not extend below a top surface of the array of light emitting diodes. The coating may extend below a top surface of the array of light emitting diodes. The dielectric layer may include silicon nitride.

[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 being spaced apart from and extending above the light emitting diodes. The plurality of separation walls include a lower portion below a top surface of the light emitting diodes having substantially vertical sides and an upper portion above the top surface of the light emitting diodes having sloping sides.

[0014]

[0014] Implementations may include one or more of the following features: The plurality of separating walls may 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 may be an opaque second material having a transmittance of less than 1% for light in the first wavelength range.

[0015] Advantages of embodiments may include, but are not limited to, one or more of the following: Improved overall display brightness and color gamut by reducing light loss, color crosstalk between subpixels, and deposition accuracy of the color conversion layer. This process can increase the possible range of opaque material thickness to increase opacity between subpixels. 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 absorbing materials.

[0016]

[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 become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1 is a diagram of a QD / UV microLED (microLED) array containing 16 subpixels. [Figure 1B] 1B is a cross-sectional view of a subpixel of the array of FIG. 1A, detailing the components of a micro LED. [Figure 1C] 1B is a cross-sectional view of three subpixels of the array of FIG. 1A. [Figure 2A] 1 illustrates a first process for creating opaque walls between subpixels in a microLED display. [Figure 2B] 1 illustrates a first process for creating opaque walls between subpixels in a microLED display. [Figure 2C] 1 illustrates a first process for creating opaque walls between subpixels in a microLED display. [Figure 2D] 1 illustrates a first process for creating opaque walls between subpixels in a microLED display. [Figure 2E] 1 illustrates a first process for creating opaque walls between subpixels in a microLED display. [Figure 3A] 1 illustrates a second process for creating opaque walls between subpixels in a microLED display. [Figure 3B] 1 illustrates a second process for creating opaque walls between subpixels in a microLED display. [Figure 3C] 1 illustrates a second process for creating opaque walls between subpixels in a microLED display. [Figure 3D] 1 illustrates a second process for creating opaque walls between subpixels in a microLED display. [Figure 3E]1 illustrates a second process for creating opaque walls between subpixels in a microLED display. [Figure 4A] 1 illustrates a third process for creating opaque walls between subpixels in a microLED display. [Figure 4B] 1 illustrates a third process for creating opaque walls between subpixels in a microLED display. [Figure 4C] 1 illustrates a third process for creating opaque walls between subpixels in a microLED display. [Figure 5A] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5B] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5C] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5D] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5E] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5F] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5G] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5H] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5I] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5J] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5K]1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5L] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5M] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 5N] 1 illustrates a fourth process for creating opaque walls between subpixels in a microLED display. [Figure 6A] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6B] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6C] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6D] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6E] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6F] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6G] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 6H] 10 illustrates a fifth process for creating opaque walls between subpixels in a microLED display. [Figure 7A] 10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. [Figure 7B] 10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. [Figure 7C]10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. [Figure 7D] 10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. [Figure 7E] 10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. [Figure 7F] 10 illustrates a sixth process for creating opaque walls between subpixels in a microLED display. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0026] Like reference numbers and designations in the various drawings indicate like elements.

[0019]

[0027] One technique for manufacturing microLED displays involves UV curing a color conversion layer over the microLED elements. The combination of the isolated color conversion layer and the underlying microLEDs forms a subpixel, and an array of two or more subpixels, e.g., three or four subpixels, emitting different colors of visible light, e.g., red, green, blue, and / or white (or other primary colors), forms a pixel visible to the eye.

[0020]

[0028] An opaque material can separate subpixels to block light emitted from the micro-LED of one subpixel from stimulating light emission in the color conversion layer of an adjacent subpixel, resulting in subpixel optical crosstalk and color shifts in the displayed image. The opaque material can also prevent curing of adjacent color conversion layers during the subpixel formation step. In particular, a "subpixel / pixel separation" architecture is required to maintain color purity (e.g., R is only R, G is only G, B is only B). In display architectures using UV microLEDs with color conversion layers, such color purity can be compromised by: (1) UV microLEDs irradiating adjacent color subpixels and causing unintended photoluminescence of different color converters; (2) B emission causing photoluminescence in adjacent R and G subpixels, and similarly, G emission causing photoluminescence in adjacent R subpixels; and finally, (3) unintended curing of color converters distributed within adjacent subpixels during the self-aligned curing manufacturing step, resulting in contamination of the adjacent subpixels with the wrong color converter.

[0021]

[0029] It is desirable to use micro LEDs that emit UV light and color conversion layers that convert the emitted UV light into basic colors (e.g., red, green, blue). While opaque materials currently used in the manufacture of micro LED displays have low transmittance in the visible range (e.g., less than 1%), this low transmittance does not necessarily extend into the UV range. As a result, the use of LED displays using UV-emitting micro LEDs and color conversion layers can still be susceptible to crosstalk. Furthermore, when UV-emitting micro LEDs are used for self-aligned curing of color conversion layers, i.e., without such an "opaque" material to achieve optical separation between pixels / subpixels, color conversion material of one color (e.g., red) unintentionally deposited on an adjacent subpixel (e.g., green) can be cured, resulting in color mixing and altering the perceived color gamut of the finished display.

[0022]

[0030] To accommodate the use of existing opaque materials while preventing emission crosstalk between subpixels, additional fabrication steps can be used to reduce the transmission of visible and UV light between subpixels. As a base process, an initial coating of opaque material is deposited on a substrate to a thickness greater than the underlying UV micro-LEDs. The opaque material is then lithographically removed in the areas above the UV micro-LEDs, after which color conversion layers are sequentially deposited within the subpixels. The opaque material can extend over the deposited color conversion layers to further separate the emission profiles of each subpixel.

[0023]

[0031] 1A depicts an exemplary portion of a UV micro LED (micro LED) array 100 including 16 subpixels 102 separated by opaque walls 104. An array of four subpixels 102 emits light of different colors, e.g., red, green, blue, and / or white (or other primary colors), forming a pixel 101. However, the techniques described below are also applicable to displays using fewer colors, e.g., two or three colors, or more colors, or different color gamuts. Furthermore, the techniques described below are applicable to displays of all types of pixel and subpixel architectures.

[0024]

[0032] Opaque walls 104 are formed between adjacent subpixels 102 to provide optical (e.g., optical) isolation to localize the curing of the color conversion layer 108 within the subpixels 102 during fabrication and to reduce optical crosstalk between the separated color conversion layers 108 during operation. The opaque walls 104 can be a metal coating on an underlying wall made of a polymer (e.g., photoresist), a metal, or another material (e.g., a polymer). In addition to being opaque, the walls 104 can be reflective to light emitted by the underlying micro-LEDs and light emitted by the color conversion layer 108, e.g., greater than 50% reflectivity, e.g., greater than 90% reflectivity. In this case, the walls 104 should be metal or a metal coating on an underlying wall made of another material (e.g., a polymer). Instead of being reflective, the walls 104 can also be optically absorptive.

[0025]

[0033] For example, the opaque walls 104 can be made of a black negative photoresist material (e.g., Daxin Black Matrix) with 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 walls 104 can form a rectangular array with each subpixel 102, although other array shapes, such as a hexagonal array or an offset rectangular array, are generally possible. FIG. 1A includes a line 106 that illustrates a cross-section of FIG. 1C.

[0026]

[0034] FIG. 1B is a cross-sectional view showing individual components of a micro LED subpixel 102 supported on electrical connections to a backplane 120 (e.g., a substrate). Each subpixel 102 includes a micro LED 110 and a color conversion layer 108 overlying 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 can further include a multiple quantum well (MQW) layer. The contacts 116a, 116b of each micro LED 110 are in electrical communication with a backplane 120, which is fabricated to include circuitry and electrical contacts for controlling each micro LED 110.

[0027]

[0035] FIG. 1C is a cross-sectional view showing three subpixels 102 separated by opaque walls 104 composed of an opaque material 105, the walls 104 having a solid rectangular cross-section. Generally, when activated by control circuitry on the backplane 120, the micro LEDs 110 generate UV light (e.g., between 365 nm and 405 nm) that is emitted into a color conversion layer 108. The color conversion layer 108 can include a color conversion agent, such as quantum dots, nanostructures, fluorescent materials, or organic materials, to absorb the emitted UV light at a first wavelength and re-emit light at a second, longer wavelength. For example, the color conversion layer 108 can include a color conversion agent that re-emits at a specific color spectrum, such as a red wavelength spectrum (e.g., 620 nm to 750 nm, or 590 nm to 620 nm) for a red subpixel, or a green wavelength spectrum (e.g., 495 nm to 570 nm, or 510 nm to 550 nm) for a green subpixel.

[0028]

[0036] As shown in FIG. 1C , opaque walls 104 laterally separate adjacent subpixels 102 and protrude above the top surface of their respective color conversion layers 108. Assuming that a material sufficiently opaque in the UV range is available, the lateral width of the opaque walls 104 may be sufficient to block the transmission of UV light emitted from one subpixel 102 from stimulating the color conversion layers 108 of adjacent subpixels 102 while still meeting the subpixel pitch requirements. Fabrication of the opaque walls 104 involves coating the microLEDs 110 and backplane 120 with one or more layers of opaque material 105 to a depth above the top surfaces of the microLEDs 110, followed by temperature- or light-dependent exposure to cure the opaque material 105. Portions of the opaque material 105 above the light-emitting layers 112 of the microLEDs 110 are removed, leaving only the walls 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 separation 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 separation wall closest to the substrate and the width (wp) of the top of the separation 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 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] 2A-2E illustrate the use of an underfill material (e.g., a first material) in addition to an opaque material 105 (e.g., a second material) to beneficially reduce crosstalk between adjacent subpixels 102 and increase the durability of the micro LEDs 110's electrical contacts 116a,b with the backplane 120. As shown in FIG. 2A, following connection of the exemplary micro LEDs 210 to the backplane 220, an underfill layer 230 is deposited over the micro LEDs 210 to fill the gaps laterally separating the micro LEDs 210 and to cover the light emitting layers of the micro LEDs 210 to a depth. For example, the exposed surface of the light emitting layer of the micro LEDs 210 may have a height of 10 μm from the substrate, and the material of the underfill layer 230 may be deposited to a depth of 20 μm, thereby covering the micro LEDs 210. The underfill layer 230 can also flow into the vertical gap between the micro LEDs 210 and the backplane 220, for example, by surrounding the bonding area on the bottom surface of the micro LEDs 210 to stabilize the connection with the backplane 220 and reduce 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 material composition.

[0033]

[0041] In some implementations, the micro LEDs 210 have a width of 30 μm and a height of 10 μm from the top surface of the backplane 220. The distance between adjacent micro LEDs 210 may be 10 μm, resulting in a total pitch of the micro LEDs 210 of 40 μm. The underfill layer 230 may be deposited to a depth of 20 μm, thereby covering the micro LEDs 210 to a depth of 10 μm.

[0034]

[0042] In some embodiments, the underfill layer 230 is a photoresist material (a light-sensitive 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 light-sensitive 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 LEDs 210 and the backplane 220 during operation while the micro LEDs 210 generate heat. Furthermore, air trapped under the micro LEDs 210 can expand when heated during operation and damage the contact with the backplane 220. The underfill layer 230 displaces air from under the micro LEDs 210, preventing damage from thermal expansion. In some embodiments, the underfill layer 230 can block at least a portion of the UV light emitted by the micro LEDs 210. This can reduce UV exposure of backplane 220 components, such as thin-film transistors.

[0035]

[0043] In some implementations, the underfill layer 230 is a redistribution layer (RDL) material, such as a polymeric dielectric material (eg, a positive photoresist).

[0036]

[0044] As depicted in FIG. 2B , a portion of the underfill layer 230 is then removed. While the removal method may vary depending on the deposited material, photolithography techniques are typically used to remove the photoresist. For example, a positive photoresist material can be used (e.g., SPR™ 220, AZ® 10XT, AZ® 40XT, or AZ® 9260). UV light can be directed through a mask to expose the photoresist, which can block the light in areas 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 that covers the areas corresponding to the micro LEDs 210. Alternatively, a negative photoresist material can be used, which can block the light in areas corresponding to the lateral gaps (excluding the micro LEDs 210), and a developer can remove the unexposed portions. Removing portions of the underfill layer 230 forms trenches in the lateral spaces between the micro LEDs 210 that extend down to or below the light emitting layer 212 of the micro LEDs 210. In some implementations, the trenches may extend down to and expose portions of the backplane 220.

[0037]

[0045] 2C, an opaque material 205 is deposited using the methods disclosed above to cover the underfill layer 230, filling the trenches and covering the exposed backplane 220 to a height above the top surface of the underfill layer 230. The opaque material 205 is the material used for the opaque walls 104 in FIG. 1B, e.g., a black negative photoresist. The opaque material 205 is cured by material-dependent means, such as thermal curing or masked UV curing.

[0038]

[0046] Following the curing step, portions of the opaque material 205 over the micro LEDs 210 are removed until the top surface 230a of the underfill layer 230 over the micro LEDs 210 is exposed, as shown in FIG. 2D . The remaining opaque material 205 forms vertical separation walls 205a of opaque material 205 in the lateral spaces between adjacent covered micro LEDs 210. These separation walls 205a of opaque material 205 extend to a height above the top surface 230a of the underfill layer 230. The separation walls may have a homogeneous composition, e.g., the opaque material 205 may have a homogeneous composition.

[0039]

[0047] 2E, in some implementations, the remaining underfill layer 230 covering the top surface of the light-emitting layer 212 can be optionally removed to increase light extraction from the underlying micro LEDs 210. At this point, a color conversion material can be deposited above the underfill layer 230 and into the wells 240 defined by the spaces between the walls 205a.

[0040]

[0048] 3A-3E illustrate another method for fabricating the underfill layer 230 and the opaque material 205. The process of FIGS. 3A-3E is similar to the process of FIGS. 2A-2E, except as noted below. As shown in FIGS. 3A and 3B, the underfill layer 230 is deposited above the backplane 220 to a thickness equal to the desired total height of the opaque material walls. 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., both above the underfill layer 230 and above the trenches filled with the opaque material, is removed by a planarization process, e.g., plasma etching, until the top surface of the underfill layer 230 is exposed, thereby forming wells 240 above the micro-LEDs 210. The remaining portions of the underfill layer 230 above the micro-LEDs 210 can then be removed using photolithography techniques before depositing the color conversion material.

[0041]

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

[0042]

[0050] The opaque material of layer 302 can have a higher opacity than the second material 205. In particular, as long as this third material is sufficiently opaque, the material 205 of pillars 205a need not be particularly opaque, which can significantly expand the range of compatible materials and thus improve manufacturability. For example, if the opaque material is opaque (e.g., light transmittance <1%), the second material 205 can be nearly transparent (e.g., transmittance >95%). In some implementations, the opaque material is reflective to wavelengths of light. In some implementations, the opaque material is a metal (e.g., a metal layer) such as aluminum, gold, silver, platinum, or alloys thereof.

[0043]

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

[0044]

[0052] FIG. 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), to cover the layer of opaque material 302. The photoresist layer 304 provides a mask for removing portions of the layer of opaque material 302. The photoresist layer 304 is exposed to UV light through the mask and developed to define areas of the opaque material to be removed. These areas correspond to the covered micro LEDs 210 (but excluding any separation walls or walls between the micro LEDs 210). The opaque material of layer 302 is removed using an appropriate technique, such as wet or dry etching, and FIG. 4C shows the final configuration after removal of the unmasked portions of layer 302 and photoresist layer 304 above the light-emitting layer 212 of the micro LEDs 210. Layer 302 provides additional protection for the second material 204 (e.g., an underfill layer) and also reduces optical crosstalk between adjacent micro LEDs 210. The portions of photoresist layer 304 on top of the isolation walls, if any, can also help reduce optical crosstalk, however, in some embodiments, the portions of photoresist layer 304 on top of the isolation walls are completely removed.

[0045]

[0053] In some implementations, an additional protective material may be deposited before the underfill layer 230 of FIG. 2A to coat the backplane 220 and the electrically connected micro LEDs 210 to prevent damage to the connections and to further electrically insulate the electrical contacts of the individual micro LEDs 210. For example, the dielectric coating may electrically insulate a metal layer deposited to form part of the optical barrier from the backplane. FIGS. 5A-5H illustrate an example process for depositing the additional protective material in a process separate from that described in FIGS. 2A-2E.

[0046]

[0054] FIG. 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 LEDs 410, as well as the exposed surfaces of the conductive contacts 416a,b and 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 (SiO) or aluminum oxide (AlO). The dielectric material 406 can have a dielectric constant of 5 or greater (e.g., 5 or greater, 6 or greater, or 7 or greater). The dielectric material 406 can be deposited in a thin layer (e.g., between 100 nm and 500 nm) that conforms to and encapsulates the features of the micro LEDs 410. Next, as shown in FIG. 5B, an underfill material 430 is deposited, covering the light-emitting layer 412 and filling the lateral gaps between adjacent micro LEDs 410. The underfill material 430 can be any material as described above.

[0047]

[0055] 5C shows that a portion of the underfill material 430 has been removed to form trenches in the gaps between adjacent micro LEDs 410 and expose the dielectric material 406 coating the backplane 420. The underfill material 430 is removed as described above.

[0048]

[0056] As shown in FIG. 5D, an opaque layer 402, e.g., a reflective layer, is deposited to cover the exposed underfill material 430 and the top and side surfaces of 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 with an additional material coating. The opaque layer 402 may be electrically conductive. The opaque layer 402 may be a metal, e.g., aluminum, gold, silver, platinum, or an alloy thereof.

[0049]

[0057] As shown in Figure 5E, the trenches are filled with opaque wall material 404, and excess material 404 above the opaque layer 402 is removed, as in Figure 5F, for example by plasma etching, thereby exposing the opaque layer 402 above the light-emitting surface of the micro-LEDs 410. Following removal of material 404, the opaque wall material 404 is cured using temperature or UV curing.

[0050]

[0058] The exposed opaque layer 402 above the micro LED 410 is removed by an etching technique, resulting in the exposure of the underfill material 430, as shown in Figure 5G. A portion of the underfill material 430 is removed to form a well 440 above the micro LED 410. As shown in Figure 5H, the underfill material 430 can be removed to a depth that exposes the protective dielectric material 406 above the light-emitting surface of the micro LED 410. The underfill material 430 below the top surface of the micro LED 410, for example, between the LED and the backplane, does not need to be removed.

[0051]

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

[0052]

[0060] As an alternative to the dielectric material 406, an additional layer of the first metal layer 402a can be deposited. In some implementations, the opaque material 402 is removed from the sides of the isolation walls of FIG. 5H, as shown in FIG. 5J. Next, an additional layer of the first metal layer 402a is deposited on the exposed surfaces, including the top and side surfaces of the isolation walls, and on the light-emitting layer of the micro LEDs 410, as shown in FIG. 5K. As shown in FIG. 5L, a photoresist layer 405 can be deposited in the well 440 region of FIG. 5K to cover the top 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] Portions of the photoresist layer 405 can be removed using the described methods to form well 440 regions above the micro LEDs 410 (FIG. 5M). The well 440 regions define a mask for removing portions of the opaque material 402 over the light-emitting regions of the micro LEDs 410. The opaque material 402 can be removed (e.g., etched), and the remaining portions of the photoresist layer 405 are removed (e.g., developed). In some embodiments, portions of the photoresist layer 405 may remain on the vertical separation wall surfaces coated with the opaque material, as described with respect to FIG. 5H. FIG. 5N depicts the final arrangement, in which the opaque layer 402 covers the top and side surfaces of the wall material 404, further reducing optical crosstalk between adjacent micro LEDs 210.

[0054]

[0062] Alternatively, in some embodiments, the gap fill material 404 in Figures 5E-5N can be a transparent or semi-transparent material, such as a material with a transmittance greater than 1% (e.g., 1-50% transmittance), 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 gap fill material 404 can be a photoresist material such as SU-8.

[0055]

[0063] 5A-5N, Figures 6A-6H depict a process in which an additional protective layer may be deposited before forming separation walls in the gaps between adjacent micro LEDs 210. Following the deposition of the undercoat dielectric material 406 (e.g., a dielectric layer) shown in Figure 5A, a metal layer 402b, e.g., a reflective layer, is deposited to cover the top and side surfaces of the dielectric material 406 on the backplane 420, as shown in Figure 6A.

[0056]

[0064] 6B, the trenches separating the micro LEDs 410 are filled with wall material 404, and the micro LEDs 410 are covered to a certain depth by wall material 404, similar to the process of FIG. 5B. Additionally, 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 connections between the micro LEDs 410 and the backplane 420, while the undercoat dielectric material 406 maintains electrical isolation of the individual contacts.

[0057]

[0065] 6C, portions of the material 404 are removed as described above to form separation walls of the wall material 404 and wells 440 above the micro LEDs 410, while maintaining the metal layer 402b along the side and top surfaces of the micro LEDs 410. As depicted in FIG. 6D, an additional metal layer 402c is deposited on the side and top surfaces of the separation walls of the wall material 404, as well as on the top surface of the micro LEDs 410, thereby covering the exposed surfaces. The additional metal layer 402c (being a second metal layer) can have the same composition as the metal layer 402b, or can have a different composition than the metal layer 402b.

[0058]

[0066] Similar to the process depicted in Figures 5K-5N, Figures 6D-6H depict the formation of a second metal layer on the isolation walls. In Figure 6D, an additional metal layer 402c is deposited on the exposed surfaces of the isolation walls of the wall material 404 and on the dielectric material 406 covering the micro LEDs 410. By depositing the additional metal layer 402c, the wall material 404 is separated and an isolation wall core is formed. A photoresist layer 405, e.g., a positive photoresist, is deposited on the second metal layer 402c to a depth that covers the tops of the isolation walls, as shown in Figure 6E.

[0059]

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

[0060]

[0068] In various embodiments, the separation wall material 404 extending above the light emitting surface of the micro LEDs 410 may be angled, for example, at an angle other than 90° relative to the backplane 420. Figures 7A-7F show the metallization process of Figures 6A-6H with the separation wall material 404 angled. However, this technique is also applicable to the other processes mentioned above.

[0061]

[0069] 7A shows a process following that of FIG. 6B in which a wall material 404 is deposited to fill the trenches 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 so that the portion of the micro LED below the light emitting layer (e.g., top surface) has substantially vertical sides and the portion above the light emitting layer (e.g., top) forms sloped sides.

[0062]

[0070] The process is depicted in Figures 7B-7F, including the application of a second metal layer 402b, a photoresist layer 405 deeper than the isolation walls, exposing and developing the photoresist layer 405 to form a metal etching mask, removing the second metal layer 402b over the micro LEDs 410, and finally removing the remaining photoresist layer 405.

[0063]

[0071] Certain embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. Although operations are depicted in the figures and claimed in a particular order, this should not be understood as requiring such operations to be performed in the particular order shown, or in a sequential order, or that all of the operations shown be performed, to achieve desirable results. For example, the operations recited in the claims can be performed in a different order and still achieve desirable results. As an example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or in a sequential order, to achieve desirable results.

Claims

1. 1. A method of manufacturing a micro LED display, comprising: depositing a first material over a substrate having a plurality of micro LEDs such that the plurality of micro LEDs are covered by the first material, the first material filling 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 in the first material that extend down to or below light emitting layers of the micro LEDs; depositing a second material over the substrate such that the second material covers the first material and extends into the trench in the first material, the second material being an opaque material; removing a portion of the first material and the second material above the plurality of micro LEDs to expose a top surface of each of the plurality of micro LEDs and such that a plurality of separation walls of the second material disposed in the gaps between the plurality of micro LEDs extend vertically higher than a top surface of the first material; A method comprising:

2. 10. The method of claim 1, wherein removing a portion of the first material and the second material over the micro LED to expose a top surface of the micro LED further comprises removing the portion of the second material over the micro LED.

3. 10. The method of claim 1, wherein removing portions of the first material and the second material over the micro LEDs to expose top surfaces of the micro LEDs comprises removing the second material over areas over the micro LEDs and areas over gaps between the micro LEDs until the first material is exposed.

4. depositing a third material onto the substrate such that the third material covers the exposed top surfaces of the separation walls of the second material and the exposed top 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 separating walls of the second material coated with the third material is filled; removing a portion of the third material and the fourth material over the micro LED to expose a top surface of the micro LED; The method of claim 1 further comprising:

5. 1. A method of manufacturing a micro LED display, comprising: depositing a first material over 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 a second material over the substrate such that the second material covers the first material and fills gaps laterally separating the micro LEDs; removing portions of the second material from the gaps laterally separating the plurality of micro LEDs to form trenches in the second material extending to the first conformal layer of the first material overlying the exposed substrate between the plurality of micro LEDs; depositing the third material over the second material such that exposed surfaces of the second material and the first material are covered with a second conformal layer of a third material; depositing a fourth material over the third material such that the fourth material extends into the trench in the third material, the fourth material being an opaque material; removing a portion of the fourth material and the third material above the micro LEDs to expose top surfaces of the micro LEDs and such that separation walls of the third material and the fourth material disposed in the gaps between the micro LEDs extend vertically higher than a top surface of the first conformal layer of the first material; A method comprising:

6. 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 separation walls formed on the backplane between adjacent light emitting diodes of the array of light emitting diodes, the separation walls being spaced apart from and extending above the light emitting diodes by gaps, the plurality of separation walls being formed of an opaque material having a transmittance of light in the first wavelength range of less than 1%; and a filler material filling the gaps between each light emitting diode of the array of light emitting diodes and the plurality of separation walls; A display screen comprising:

7. 7. The display screen of claim 6, further comprising 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.

8. 7. The display screen of claim 6, wherein the opaque material provides the separation wall with a homogeneous composition.

9. 7. The display screen of claim 6, wherein each separation wall of the plurality of separation walls has a solid rectangular cross section.

10. 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 separation walls formed on the backplane between adjacent light emitting diodes of the array of light emitting diodes, the separation walls being spaced apart from and extending above the light emitting diodes; The plurality of separation walls are a core of a first material; and a coating covering at least a portion of the core extending above the light emitting diode, the coating being an opaque second material having a transmittance of less than 1% for light in the first wavelength range; a display screen.

11. 11. The display screen of claim 10, further comprising 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.

12. The display screen of claim 10 , wherein the coating covers sides of the plurality of separation walls.

13. 13. The display screen of claim 12, wherein the coating covers a top horizontal surface of the core.

14. 13. The display screen of claim 12, wherein the coating extends below a bottom surface of the core.

15. 15. The display screen of claim 14, wherein the coating extends over an upper surface of the core.

16. 11. The display screen of claim 10, further comprising a dielectric layer conformally coating the array of light emitting diodes.

17. 17. The display screen of claim 16, wherein the dielectric layer conformally coats a portion of the backplane between adjacent light emitting diodes, and wherein each core of the plurality of separation walls is separated from the backplane by the dielectric layer.

18. 11. The display screen of claim 10, further comprising a filler material filling gaps between the array of light emitting diodes and the plurality of separation walls.

19. 20. The display screen of claim 18, wherein the coating extends to a side of the core below a top surface of the filler material.

20. 11. The display screen of claim 10, comprising a dielectric layer conformally covering the coating of the separation wall.

21. 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 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 and extending above the light emitting diodes, the plurality of separation walls including a lower portion below a top surface of the light emitting diodes having substantially vertical sides and an upper portion above the top surface of the light emitting diodes having sloping sides; A display screen comprising:

22. 22. The display screen of claim 21, wherein the upper portions of the plurality of separation walls extend over a portion of the top surface of the array of light emitting diodes.

23. 22. The display screen of claim 21, wherein the upper portions of the plurality of separation walls are wider than the lower portions of the plurality of separation walls at the top surface of the array of light emitting diodes.

24. 24. The display screen of claim 23, wherein the upper portions of the plurality of separator walls are narrower at the top of the plurality of separator walls than the lower portions of the plurality of separator walls.

Images