High density micro LED array with reflective sidewalls

Abstract

The micro LED structure includes an LED epitaxial layer, which may be formed prior to the micro LED structure being coupled to the backplane substrate. To prevent light leakage and maximize light output, the sidewalls and other surfaces of the LED epitaxial layer may be coated with reflective coatings. For example, the reflective coating may include a metal layer electrically insulated from the micro LED electrodes between the dielectric layers. The reflective coating may also be formed using multiple layers in a distributed Bragg reflector configuration. The reflective coating may be formed during an LED manufacturing process prior to the micro LED structure being coupled to the backplane. The pixel isolation structure on the backplane may also include a reflective coating applied over the LED epitaxial layer.

Description

Technical Field

[0001] The present disclosure relates to micro-light-emitting diode (LED) structures. More specifically, the present disclosure describes a micro-LED array with reflective sidewalls to prevent light leakage and improve LED efficiency. Background Art

[0002] High-resolution light-emitting diode (LED) displays may include millions of micron-sized pixels arranged to form a viewing screen. For example, micro-LEDs represent an emerging display technology for flat-panel displays that offer high contrast, response time, and greater energy efficiency than other display types. Micro-LED displays are driven by an array of microscopic LEDs arranged to form individual pixel elements. Summary of the invention

[0003] In some embodiments, a micro-light-emitting diode (micro-LED) structure may include a first electrode configured to be coupled to a corresponding second electrode on a backplane, the backplane comprising an array of micro-LED structures; an LED epitaxial layer comprising a first side coupled to the electrode and a sidewall extending in a direction away from the backplane; and a reflective coating applied to the sidewalls of the LED epitaxial layer.

[0004] In some embodiments, a method of manufacturing a micro-LED structure may include forming an LED epitaxial layer on a substrate, wherein the LED epitaxial layer may include a first side, a second layer opposite the first side and adjacent to the substrate, and a sidewall. The method may also include forming a reflective coating on the sidewall of the LED epitaxial layer and forming a first electrode coupled to the first side of the LED epitaxial layer.

[0005] In some embodiments, a micro LED array may include a backplane substrate, a plurality of micro LED structures mounted to the backplane substrate, wherein the plurality of micro LED structures may include an LED epitaxial layer. The array may also include a plurality of pixel isolation structures formed between the plurality of micro LED structures. The plurality of pixel isolation structures may extend above the height of the LED epitaxial layer of the plurality of micro LED structures. The plurality of pixel isolation structures may include a reflective coating on a portion of the plurality of pixel isolation structures extending above the height of the LED epitaxial layer of the plurality of micro LED structures.

[0006] In any embodiment, any one and / or all of the following features may be included in any combination and are not limited. The reflective coating may substantially cover the sidewalls of the LED epitaxial layer to prevent light leakage from the sidewalls of the LED epitaxial layer. The reflective coating may further cover a portion of the first side of the LED epitaxial layer. The reflective coating may leave an opening on the first side of the LED epitaxial layer, and the first electrode is coupled to the first side. The micro-LED structure may also include a first dielectric layer between the LED epitaxial layer and the reflective coating. The micro-LED structure may also include a second dielectric layer on the reflective coating. The first dielectric layer and the second dielectric layer may surround the reflective coating to electrically isolate the reflective coating from the first electrode. The reflective coating may include a metal layer. The reflective coating may include a material of a group consisting of: Al, Rh, Pt, Ag, Au, and Cr. The reflective coating may include a multilayer of a distributed Bragg reflector (DBR). The multilayer of the DBR may include alternating layers of SiO2 and TiO2. The reflective coating may be formed to leave an opening at a position where the first electrode on the first side of the LED epitaxial layer is coupled to the first side of the LED epitaxial layer. A mesa etch may be performed on the LED epitaxial layer to form a first level including p-doped gallium nitride (GaN) and a second level including n-doped GaN. A first electrode may be coupled to the n-doped GaN. A second electrode coupled to the p-doped GaN may be formed. A dielectric layer may be formed between the reflective coating and the LED epitaxial layer, and the dielectric layer may be etched to expose the LED epitaxial layer at a location where the first electrode is coupled to a first side of the LED epitaxial layer. Multiple micro-LED structures may include a light emitting region formed on the LED epitaxial layer, wherein the reflective coating may be between the light emitting region and multiple pixel isolation structures. The reflective coating on the portion of the multiple pixel isolation structures that extends above the height of the LED epitaxial layer may not extend below the height of the LED epitaxial layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A further understanding of the nature and advantages of the various embodiments may be realized by reference to the remainder of the specification and drawings, wherein the same reference numerals are used throughout the several drawings to represent the same elements. In some cases, a sub-label is associated with a reference numeral to represent one of multiple similar elements. When a reference numeral is referenced without specifying the presence of a sub-label, the reference numeral is intended to represent all such multiple similar elements.

[0008] 1 illustrates a top plan view of one embodiment of a processing system of deposition, etch, bake, and cure chambers in accordance with some embodiments.

[0009] 2 illustrates a simplified process for building a micro-LED structure that can be mounted to a backplane, according to some embodiments.

[0010] 3A-3D illustrate various stages in a process for fabricating a micro LED array from a mounted micro LED structure, according to some embodiments.

[0011] FIG. 4 illustrates an array of micro LEDs mounted on a backplane according to some embodiments.

[0012] 5 illustrates a cross-sectional view of adjacent micro LED structures in an array with light leakage between adjacent structures according to some embodiments.

[0013] 6 illustrates LED epitaxial layers including a reflective coating according to some embodiments.

[0014] 7A-7H illustrate a series of processing steps that may be used to form LED epitaxial layers and reflective coatings according to some embodiments.

[0015] 8 illustrates a graph of the percentage of reflection of different materials used as a reflective coating, according to some embodiments.

[0016] 9A-9E illustrate a process for applying a reflective coating including a distributed Bragg reflector (DBR) according to some embodiments.

[0017] 10 illustrates a graph showing the performance of different numbers of alternating material pairs used in a DBR of a reflective coating, according to some embodiments.

[0018] FIG. 11 illustrates a micro LED array according to some embodiments.

[0019] FIG. 12 illustrates a completed micro LED array according to some embodiments.

[0020] 13 illustrates a flow chart of a method for fabricating a micro LED structure according to some embodiments. DETAILED DESCRIPTION

[0021] The micro-LED structure includes an LED epitaxial layer, which can be formed before the micro-LED structure is coupled to the backplane substrate. To prevent light leakage and maximize light output, the sidewalls and other surfaces of the LED epitaxial layer can be coated with a reflective coating. For example, the reflective coating can include a metal layer that is electrically insulated from the micro-LED electrodes between dielectric layers. The reflective coating can also be formed using multiple layers in a distributed Bragg reflector configuration. The reflective coating can be formed during the LED manufacturing process before the micro-LED structure is coupled to the backplane. The pixel isolation structure on the backplane can also include a reflective coating applied above the LED epitaxial layer.

[0022] FIG. 1 illustrates a top plan view of one embodiment of a processing system 100 of deposition, etching, baking, and curing chambers according to some embodiments. In the figure, a pair of front-opening standard chambers 102 supply substrates of various sizes, which are received by a robot 104 and placed into a low pressure holding area 106 before being placed into one of the substrate processing chambers 108a to 108f located in the serial sections 109a to 109c. A second robot 110 can be used to transfer substrate wafers from the holding area 106 to the substrate processing chambers 108a to 108f and back. Each substrate processing chamber 108a to 108f can be equipped to perform a plurality of substrate processing operations, including dry etching processes as described herein, as well as cyclic layer deposition, atomic layer deposition, chemical vapor deposition, physical vapor deposition, etching, pre-cleaning, annealing, plasma treatment, degassing, orientation, and other substrate processing.

[0023] The substrate processing chambers 108a to 108f may include one or more system elements for depositing, annealing, curing and / or etching material films on substrates or wafers. In one configuration, two pairs of processing chambers (e.g., 108c-108d and 108e-108f) may be used to deposit materials on substrates, and a third pair of processing chambers (e.g., 108a-108b) may be used to cure, anneal or process deposited films. In another configuration, all three pairs of chambers (e.g., 108a to 108f) may be configured to deposit and cure films on substrates. Any one or more of the described processes may be performed in additional chambers separated from the manufacturing systems shown in different embodiments. It should be understood that the processing system 100 contemplates additional configurations for deposition, etching, annealing and curing chambers for material films. Additionally, any number of other processing systems may be used for the present technology, which may be incorporated into chambers for performing any of the specific operations. In some embodiments, a chamber system that can provide access to multiple processing chambers while maintaining a vacuum environment in various sections (such as the holding and transfer areas described) can allow operations to be performed in multiple chambers while maintaining a specific vacuum environment between discrete processes.

[0024] The processing system 100, or more specifically, the chambers incorporated into the processing system 100 or other processing systems, can be used to produce structures according to some embodiments of the present technology. For example, the processing system 100 can be used to produce micro-LED arrays by performing operations such as deposition, etching, sputtering, polishing, cleaning, etc. in each substrate processing chamber 108.

[0025] 2 illustrates a simplified process for building a micro LED structure 200 that can be mounted to a backplane 220 according to some embodiments. As described in more detail below, the micro LED structure can be fabricated on a substrate 210. LED epitaxial layers 212 can be formed on the substrate 210 to serve as electrical elements that generate light for the micro LED structure 200. The LED epitaxial layers 212 can be composed of a number of different individual layers as described below.

[0026] One or more electrodes may be mounted to the LED epitaxial layer 212 to provide electrical connections for the micro LED structure 200. For example, a first electrode 214 and a second electrode 216 may be coupled to the LED epitaxial layer 212 on the same side of the LED epitaxial layer 212. As used herein, the side of the epitaxial layer 212 to which the first electrode 214 is coupled may be generally referred to as the "first side" of the LED epitaxial layer 212. Although FIG. 2 illustrates a micro LED structure 200 having two electrodes mounted to the first side of the LED epitaxial layer 212 in a lateral chip or "flip chip" configuration, other embodiments may mount the first electrode 214 to the first side of the epitaxial layer 212 while mounting the second electrode 216 to the opposite side of the epitaxial layer 212, which is generally referred to as the "second side" of the LED epitaxial layer 212 opposite the first side. This may be referred to as a "vertical chip" orientation, which is compatible with all embodiments described herein that use a reflective coating on the LED epitaxial layer 212.

[0027] Separately, the substrate 221 can be used to form the backplane 220 of the micro LED array. A plurality of electrodes can be coupled to the substrate 221. These electrodes can be configured to receive electrodes on a plurality of different micro LED structures to form an electrical connection between the backplane 220 and the micro LED structures. For example, the first electrode 224 and the second electrode 226 on the substrate 221 can be configured to be electrically coupled to the first electrode 214 and the second electrode 216 on the LED epitaxial layer 212 of the micro LED structure 200.

[0028] The micro LED structure 200 can be mounted to the backplate 220 by flipping the orientation of the micro LED structure 200 and connecting the first electrode 214 and the second electrode 216 on the micro LED structure with the corresponding first electrode 224 and the second electrode 226 on the substrate 221. The substrate 210 with the LED epitaxial layer 212 formed thereon can be removed to expose the LED epitaxial layer 212 on top of the backplate 220. Although FIG. 2 only illustrates a single micro LED structure 200 mounted to a single pair of electrodes on the backplate 220, it should be understood that the backplate 220 can be configured to mount multiple micro LED structures as a micro LED array. Therefore, the substrate 210 can include multiple LED epitaxial layers forming multiple micro LED structures, which can be mounted together on the backplate 220, and the substrate 221 can include multiple mounting locations for multiple micro LED structures in an array that are not explicitly shown in FIG. 2.

[0029] 3A-3D illustrate various stages in a process for manufacturing a micro LED array from mounted micro LED structures according to some embodiments. These figures illustrate cross-sectional views of the structures described above in FIG. 2 . In FIG. 3A , pixel isolation structures 333 may be formed between each of the micro LED structures in the array. These pixel isolation structures 333 may extend above the height of the LED epitaxial layer 212 of each of the micro LED structures. The pixel isolation structures 333 may be made of reflective and / or conductive materials (e.g., metals), and the pixel isolation structures 333 may be surrounded by an electrically insulating passivation layer to prevent the pixel isolation structures 333 from shorting any of the electrodes of the micro LED structures.

[0030] The light emitting region 302 may be formed above the LED epitaxial layer 212 between the pixel isolation structures 333. The light emitting region 302 may include a photoluminescent material. For example, FIG. 3B illustrates how the light emitting region 302 may include a quantum dot material 304 operable to emit light of different wavelengths. For example, a single pixel may include multiple micro-LED structures, each of which may use a different quantum dot material to produce red light, blue light, green light, etc. The light emitting region 302 may be formed using hot imprint lithography, which may include depositing a sub-pixel isolation material on the micro-LED structure and hot imprinting the light emitting region 302 on the sub-pixel isolation material. Alternatively, the light emitting region 302 may be formed using a series of operations including deposition, mask patterning, etching, and mask removal.

[0031] FIG3C illustrates an optional inclusion of an ultraviolet (UV) filter 306 that may be formed on the micro-LED array. The UV filter 306 may absorb ultraviolet light generated by the micro-LED structures in the array. In some embodiments, the UV filter 306 may also absorb other wavelengths, such as blue light types generated by the micro-LED structures in the array, while passing visible light emitted from the light emitting region of each micro-LED structure.

[0032] FIG. 3D illustrates an embodiment including micro lenses 308 that may be formed on top of each of the micro LED structures.

[0033] FIG4 illustrates a micro-LED array 410 mounted on a backplane according to some embodiments. The backplane may also include electronic circuitry to condition electrical signals and initiate illumination of the micro-LEDs in the micro-LED array 410. For example, the backplane may include complementary metal oxide semiconductor (CMOS) circuitry that includes transistors operable to turn on and / or off current flowing to each of the micro-LED structures in the micro-LED array 410. The micro-LED array 410 may be used to manufacture display screens and other display technologies.

[0034] Each "pixel" 412 in the micro LED array 410 may include multiple individual micro LED structures. For example, some embodiments may include three or four individual micro LED structures in each pixel 412. FIG. 4 illustrates a pixel 412 that includes four micro LED structures. A first micro LED structure 414 may be configured to produce red light, a second micro LED structure 416 may be configured to produce green light, a third micro LED structure 418 may be configured to produce blue light, and a fourth micro LED structure 420 may be configured as a backup in the event that one of the other micro LED structures in the pixel 412 fails.

[0035] Each of the four micro LED structures in pixel 412 may be referred to as a sub-pixel in pixel 412. In some embodiments, the pixel isolation structure 333 described above may be configured as a sub-pixel isolation structure to isolate each sub-pixel from each other within pixel 412. In this example, each of the sub-pixels is arranged in a 2x2 grid array in each pixel 412, although other embodiments may use different arrangements for the sub-pixels within a pixel.

[0036] 5 illustrates a cross-sectional view 500 of adjacent micro-LED structures in an array according to some embodiments, wherein light leakage exists between adjacent structures. In existing architectures, light may leak from different regions in a micro-LED structure in an array, thereby causing interference with other adjacent micro-LED structures and reducing the light output efficiency of the micro-LED structures in the array.

[0037] One particular area where light leakage may occur in the micro-LED structure is from the LED epitaxial layer 212. Ideally, in FIG. 5, all light generated by the micro-LED structure should be directed vertically and directly out of the micro-LED array. However, as shown in FIG. 5, light can leak from various locations in the LED epitaxial layer 212 instead of leaving through the second side of the LED epitaxial layer. This light leakage may be inadvertently transmitted to adjacent micro-LED structures and cause interference. For example, light from a micro-LED structure configured to produce blue light may leak into an adjacent micro-LED structure configured to produce red light, thereby changing the light output of the pixel or adjacent pixels. In addition, when light leaks from the LED epitaxial layer 212, this reduces the total light output of the micro-LED structure, resulting in reduced clarity / brightness of the micro-LED display.

[0038] In this example, light 502 may leak out of the sidewalls of the LED epitaxial layer 212. As shown in FIG. 5, the "sidewalls" of the LED epitaxial layer 212 may represent the sides of the LED epitaxial layer extending in a direction away from the backplane. It should be noted that the sidewalls need not extend in a pure vertical direction (e.g., 90°), but may extend away from the backplane at a certain angle. In some embodiments, the angle may be adjusted to maximize the light output efficiency of the micro-LED structure, as described in more detail below. The sidewalls of the LED epitaxial layer 212 may extend around the LED epitaxial layer 212, even though only a cross-sectional view is shown in FIG. 5.

[0039] In addition, light 504 may also leak out from the first side of the LED epitaxial layer 212 coupled to the electrode. This leakage of light 504 may occur between the electrodes as shown in FIG. 5 , as well as on the sides of the electrodes. Between the light 502 leaking from the sidewalls of the LED epitaxial layer 212 and the light 504 leaking from the first side of the LED epitaxial layer 212, there is a need to improve the design of the micro-LED structure to minimize this leakage, minimize interference with adjacent micro-LED structures, and increase the efficiency of light output.

[0040] FIG. 6 illustrates an LED epitaxial layer 212 including a reflective coating 602 according to some embodiments. To address the issue of light leakage and other technical issues, some embodiments may form a reflective coating 602 around the LED epitaxial layer 212 to reduce the aforementioned light leakage. Rather than relying on a pixel isolation structure or other structure formed after the micro-LED structure is formed, these embodiments integrate the reflective coating 602 on the surface of the LED epitaxial layer 212 during the manufacture of the micro-LED structure itself. For example, simply returning to FIG. 2 , the reflective coating 602 may be formed on the LED epitaxial layer 212 while the LED epitaxial layer 212 is still coupled to the substrate 210 and before the first electrode 214 and / or the second electrode 216 are formed on the LED epitaxial layer 212. The reflective coating 602 may also be characterized in that the reflective coating 602 is formed on the LED epitaxial layer 212 before the micro-LED structure 200 is mounted to the backplane 220. Therefore, these embodiments greatly simplify the process during the LED processing step itself, rather than using a reflective layer or an absorption layer that is subsequently inserted between the micro-LED structures on the backplane using complex processing.

[0041] In some embodiments, the reflective coating 602 can be formed on the sidewalls 622 of the LED epitaxial layer 212. Optionally, some embodiments can also apply the reflective coating 602 so that the reflective coating 602 covers a portion of the first side 620 of the LED epitaxial layer 212. For example, the reflective coating 602 can cover a portion of the first side 620 of the LED epitaxial layer 212 between the first electrode 214 and / or the second electrode 216, while leaving an opening in which a portion of the LED epitaxial layer 212 can be exposed, wherein the first electrode 214 and / or the second electrode 216 can be butted or coupled with the LED epitaxial layer 212 at this portion to avoid interfering with the electrical connection.

[0042] In some embodiments, the reflective coating 602 can substantially cover the sidewalls 622 of the LED epitaxial layer 212 to prevent light from leaking out of the sidewalls 622. For example, substantially covering the sidewalls 622 can include covering greater than or about 80% of the surface area of ​​the sidewalls 622. In other embodiments, the reflective coating 602 can cover about 100% of the surface area, greater than or about 90% of the surface area, greater than or about 70% of the surface area, greater than or about 60% of the surface area, greater than or about 50% of the surface area, greater than or about 40% of the surface area, and so forth.

[0043] 7A to 7H illustrate a series of processing steps that may be used to form the LED epitaxial layer 212 and the reflective coating 708 according to some embodiments. FIG. 7A illustrates a substrate 210 on which the LED epitaxial layer 212 is formed. The substrate 210 may include silicon or sapphire, among other substrate materials. These steps may be referred to as micro-LED manufacturing steps, and may be different from the other steps described above in FIG. 3 in which the micro-LEDs are mounted to a backplane, arranged in pixels, surrounded by pixel isolation structures, covered by luminescent materials, and the like.

[0044] Although the LED epitaxial layer 212 is shown as a single layer in these figures, it should be understood that the LED epitaxial layer 212 can actually be formed using multiple continuous layers created on the substrate 210. For example, the LED epitaxial layer 212 can include an LED structure containing gallium and nitrogen. The LED epitaxial layer 212 can be a gallium nitride (GaN) LED structure epitaxially formed on the substrate 210. The LED epitaxial layer 212 can include an n-doped GaN layer and a p-doped GaN layer. A multiple-quantum-well (MQW) region can be formed between the n-doped and p-doped GaN layers, in which light emitted by the LED epitaxial layer 212 is generated.

[0045] 7B illustrates how a mesa etching process can be used to expose two different surfaces in the LED epitaxial layer 212, which can be coupled to corresponding electrodes or electrical contacts. For example, the mesa process can expose a p-doped GaN surface 702 on a portion of the LED epitaxial layer 212. By etching away a portion of the p-doped GaN surface (along with any intermediate layers, such as the MQW region), a portion of the underlying n-doped GaN layer can be exposed to form an n-doped GaN surface 704. Any type of etching process can be used to expose these surfaces, including photolithography, reactive ion etching, and the like.

[0046] 7C illustrates the results of a die singulation process for forming the sidewalls of the LED epitaxial layer 212. In some embodiments, the sidewalls may be formed at an angle. The angle may be configured such that light generated by the micro-LED structure incident on the sidewalls of the LED epitaxial layer 212 may be maximally reflected from the sidewalls of the LED epitaxial layer via microlenses associated with the micro-LED structure. When a reflective coating 708 is added, the sidewalls may reflect light inward that would otherwise escape from the LED epitaxial layer 212. The angle of the sidewalls may be configured such that the reflected light leaves the microlenses with maximum efficiency. The precise angle of the sidewalls may depend on the specific physical characteristics of each individual micro-LED design. For example, compared to a purely vertical sidewall of 90°, some embodiments may alternatively use sidewall angles greater than or about 85°, greater than or about 80°, greater than or about 75°, greater than or about 70°, greater than or about 65°, greater than or about 60°, greater than or about 55°, greater than or about 50°, greater than or about 45°, and / or any intervals within these ranges.

[0047] 7D illustrates a first dielectric layer 706 that may be formed on the first surface and sidewalls of the LED epitaxial layer 212. The first dielectric layer 706 may be formed of any dielectric material, such as silicon dioxide or other oxide materials. The first dielectric layer 706 may form an insulating layer that isolates the reflective coating 708 from the first electrode 214 and the second electrode 216. The first dielectric layer 706 may be formed using a variety of different deposition processes, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), and / or any other deposition process. The first dielectric layer 706 shown in these figures substantially covers the exposed portions of the LED epitaxial layer 212 that are exposed above the substrate 210.

[0048] FIG. 7E illustrates the application of a reflective coating 708. The reflective coating 708 may be formed of any reflective material. Some embodiments may specifically use metals to implement the reflective coating 708. For example, metals such as aluminum (Al), rhodium (Rh), platinum (Pt), silver (Ag), gold (Au), chromium (Cr), and / or other similar metals may be used to form the reflective coating 708. The reflective coating 708 may be formed using sputtering or other deposition processes.

[0049] As shown in these figures, a reflective coating 708 can be formed on top of the first dielectric layer 706. The reflective coating 708 can cover some and / or substantially all of the sidewalls of the LED epitaxial layer 212 and / or the first dielectric layer 706. In addition, the reflective coating 708 can cover a portion of the first surface or top surface of the LED epitaxial layer 212. In some embodiments, the reflective coating 708 can be applied so that the openings 722, 724 can expose a portion of the first dielectric layer 706 above the p-doped GaN surface 702 and the n-doped GaN surface 704. As will be described below, the first dielectric layer 706 can be etched away from these openings 722, 724 to expose the p-doped GaN surface 702 and the n-doped GaN surface 704 for electrical connection to the first electrode 214 and the second electrode 216.

[0050] 7F illustrates how a second dielectric layer 710 may be applied over the reflective coating 708. The second dielectric layer 710 may be applied in a manner similar to that described above for the first dielectric layer 706. The second dielectric layer 710 may cover substantially all of the reflective coating 708. Thus, the second dielectric layer 710 and the first dielectric layer 706 may insulate or surround the reflective coating 708 such that the reflective coating 708 does not contact the first electrode 214 and / or the second electrode 216.

[0051] 7G illustrates how the first dielectric layer 706 and the second dielectric layer 710 are etched or otherwise removed to expose the p-doped GaN surface 702 and the n-doped GaN surface 704. Any etching process may be used to remove the first dielectric layer 706 and the second dielectric layer 710. It should be noted that the reflective coating 708 remains enclosed in the first dielectric layer 706 and the second dielectric layer 710.

[0052] 7H illustrates how the first electrode 214 and the second electrode 216 may be formed on the micro LED structure. For example, the first electrode 214 and the second electrode 216 may be formed during a metallization process, where metal is deposited on the p-doped GaN surface 702 and the n-doped GaN surface 704. In some embodiments, the mask used to deposit the metal for the first electrode 214 and the second electrode 216 may expose the p-doped GaN surface 702 and the n-doped GaN surface 704, as well as a portion of the second dielectric layer 710. This may allow the first electrode 714 and / or the second electrode 716 to extend above the height of the second dielectric layer 710 and be formed on top of a portion of the second dielectric layer 710.

[0053] The electrical first electrode 214 forms a conductive path for passing current through the p-doped GaN layer of the LED epitaxial layer 212. Similarly, the second electrode 216 forms a conductive path for passing current through the n-doped GaN layer. The first electrode 214 and the second electrode 216 can be later connected to the control circuit system of the backplane. The electrical signal from the control circuit system generates a current through the micro-LED structure, which causes light emission from the MQW region of the structure. The MQW region can be formed to emit light characterized by a repeatable peak intensity wavelength and a quantum efficiency of the applied electrical signal (e.g., current and / or voltage).

[0054] FIG8 illustrates a graph 800 of the percentage of reflection of different materials used as a reflective coating according to some embodiments. The y-axis represents the percentage of reflection of some of the many materials that can be used for the reflective coating, while the x-axis represents the wavelength (μm) of light that the reflective coating can reflect at the corresponding percentage shown on the y-axis. Graph 800 can be used to select materials for the reflective coating based on the requirements of a particular design. For example, based on the wavelength and design requirements of a particular micro-LED structure, graph 800 can be used to select materials such as Al-VUV (curve 802), Al (curve 804), Rh (curve 806), Pt (curve 808), Cr (curve 810), Au (curve 812), Ag (curve 814), and / or other materials. Note that the materials describing graph 800 are provided by way of example only and are not meant to be limiting. Any reflective material or metal can be used.

[0055] 9A and 9E illustrate a process for applying a reflective coating including a distributed Bragg reflector (DBR) according to some embodiments. A DBR may include a structure formed of multiple layers of alternating materials with different reflective indices. Each layer boundary may cause partial reflection of the light wave so that the multiple layers act as high-quality reflectors. Some embodiments may replace the reflective coating with the above-mentioned metallic material to use the multiple layers forming the DBR as the reflective coating instead.

[0056] The processing to produce the structure shown in Figures 9A to 9C can be performed as described above with respect to Figures 7A to 7C to form an LED epitaxial layer 212 having an exposed p-doped GaN surface 702 and an exposed n-doped GaN surface 704 on the substrate 210, and to form sidewalls of the LED epitaxial layer 212.

[0057] However, instead of forming the first dielectric layer 706 and / or the second dielectric layer 710, the process may alternatively form a plurality of individual layers constituting the DBR as the reflective coating 902. It should be noted that the plurality of individual layers constituting the DBR may be made non-conductive. This may limit the need to insulate the reflective coating 902 using the first dielectric layer 706 and / or the second dielectric layer 710. Instead of etching away the plurality of individual layers constituting the DBR, these layers may alternatively be selectively formed on the LED epitaxial layer 212 to expose the p-doped GaN surface 702 and the n-doped GaN surface 704. Electrical isolation between the reflective coating 902 and the first electrode 214 and the second electrode 216 may not be necessary.

[0058] Various materials may be used to form the multiple individual layers that make up the DBR for the reflective coating 902. For example, some embodiments may use alternating layers of silicon dioxide (SiO2) 912 and titanium dioxide (TiO2) 914. FIG. 10 illustrates a graph 1000 showing the performance of different numbers of alternating material pairs used in the DBR of the reflective coating 902 according to some embodiments. The reflectivity of various layer counts is represented on the vertical axis for different wavelengths of light represented on the horizontal axis. A graph or data table (such as graph 1000) may be used to select the number of DBR layers that should be used based on the operating conditions of different embodiments in order to achieve the desired reflectivity level as needed. For example, curve 1010 may represent a single pair of DBR layers of SiO2 and TiO2 (where λ Bragg =400 nm, n siO2 =1.47, n TiO2 =2.47, and n GaN =2.50) to achieve a reflectivity of about 50% at 400nm. Curve 1008 may represent two pairs of DBR layers to achieve a reflectivity of about 80%. Curve 1006 may represent three pairs of DBR layers to achieve a reflectivity of about 90%. Curve 1004 may represent four pairs of DBR layers to achieve a reflectivity of about 95%. Curve 1002 may represent five pairs of DBR layers to achieve a reflectivity of about 98%. It should be noted that these curves in graph 1000 are provided by way of example only and are not meant to be limiting. Other DBR layer materials, layer organizations, and / or wavelength ranges may be used without limitation.

[0059] 11 illustrates a micro LED array 1100 according to some embodiments. As described above, a plurality of micro LED structures may be mounted to a backplane substrate, wherein each of the micro LED structures includes an LED epitaxial layer 212 formed as described above. These LED epitaxial layers 212 may include a reflective coating covering at least a portion of the sidewalls and / or first side of the LED epitaxial layer.

[0060] In addition, each micro LED structure may include a pixel isolation structure 1104, which may also be referred to as a "sub-pixel" isolation structure, depending on the arrangement of the micro LED structure relative to the pixel isolation structure 1104. The pixel isolation structure 1104 may extend above and / or around the micro LED structure. In some embodiments, the sidewalls of the pixel isolation structure 1104 do not need to be in a purely vertical direction (e.g., 90°). o ) but can be greater or less than 90 o , so that the direction of light emission from the micro LED structure can be directed into a desired pattern so that light is formed and contained in the photoluminescent material in these areas. The pixel isolation structure 1104 may extend near and below the contact area for the electrode of the micro LED structure, and may extend further downward to the backplane of the micro LED array 1100. The sub-pixel isolation structure may include dielectric materials as well as other types of materials. The dielectric material may include one or more of silicon oxide, silicon nitride, silicon carbide, photoresist materials, or dielectric organic polymer materials, as well as other dielectric materials. The pixel isolation structure 1104 may have a height greater than or about 2.5 μm, greater than or about 5 μm, greater than or about 7.5 μm, greater than or about 10 μm, greater than or about 12.5 μm, greater than or about 15 μm, greater than or about 17.5 μm, greater than or about 20 μm, or more. The pixel isolation structure 1104 may have a width of greater than or about 1 μm, greater than or about 2 μm, greater than or about 3 μm, greater than or about 4 μm, greater than or about 5 μm, greater than or about 6 μm, greater than or about 7 μm, greater than or about 8 μm, greater than or about 9 μm, greater than or about 10 μm, or more. The pixel isolation structure 1104 may have an aspect ratio of greater than or about 1.5:1, greater than or about 2:1, greater than or about 2.5:1, greater than or about 3:1, greater than or about 3.5:1, greater than or about 4:1, greater than or about 4.5:1, greater than or about 5:1, or greater.

[0061] In contrast to prior designs, some embodiments may further include a reflective coating 1102 formed on the pixel isolation structure 1104. The reflective coating 1102 may be formed as described above for any of the reflective coatings that may also be present on the LED epitaxial layer 212. It should be noted that because a separate reflective coating is pre-applied to the LED epitaxial layer 212 during a separate micro-LED manufacturing process, the reflective coating 1102 on the pixel isolation structure 1104 does not need to extend below the top or surface layer of the LED epitaxial layer 212. Instead, the pixel isolation structure 1104 may include the reflective coating 1102 on a portion of the pixel isolation structure 1104 that extends above the height of the LED epitaxial layer 212. Thus, the pixel isolation structure 1104 may omit or eliminate any reflective material or coating that would otherwise be applied or used below the height of the LED epitaxial layer 212. Thus, some embodiments are characterized in that a portion of the pixel isolation structure 1104 below the height of the LED epitaxial layer 212 does not include a reflective material, a reflective surface, and / or a reflective coating.

[0062] The use of a reflective coating on the LED epitaxial layer 212 and a reflective coating 1102 on the pixel isolation structure 1104 provides a number of technical advantages and improvements. For example, a dielectric or non-reflective material may be used to form the pixel isolation structure 1104, rather than a metal or other reflective surface or material. The pixel isolation structure 1104 may be formed of a single material, rather than a core metal pillar surrounded by an insulating material. The reflective coating 1102 may also be applied in a simple process after the pixel isolation structure 1104 is formed. For example, a mask may be applied over the LED epitaxial layer 212, and the reflective coating 1102 may be applied (e.g., by sputtering or other deposition process) over the exposed portions of the pixel isolation structure 1104. This process is much simpler than attempting to apply a reflective coating 1102 that extends below the height of the LED epitaxial layer 212.

[0063] FIG. 12 illustrates a completed micro-LED array 1200 according to some embodiments. As described above, the light-emitting region 302 may be formed based on the desired light output of each of the micro-LED structures. Forming the light-emitting region 302 may include depositing a photoluminescent precursor in the region between the pixel isolation structures 1104. The photoluminescent precursor may be a mixture or slurry including a photocurable fluid and one or more photoluminescent particles or compounds. The one or more photoluminescent compounds may include quantum dot materials that are operable to emit light having specific color characteristics when excited by a light source. These quantum dot materials may include nanoparticles made of one or more inorganic semiconductor materials, such as indium phosphide, zinc selenide, zinc sulfide, silicon, silicates, and graphene, as well as doped inorganic oxides, and other semiconductor materials. The photocurable fluid may include one or more crosslinkable compounds, photoinitiators, and color converters. The crosslinkable compound may include a monomer that forms a polymer when cured. The monomer may include an acrylate monomer, a methacrylate monomer, and an acrylamide monomer. The crosslinkable compound may include a negative photoresist material, such as SU-8 photoresist. Photoinitiators may include phosphine oxide compounds and ketone compounds, as well as other types of photoinitiator compounds that generate free radicals that initiate the curing of unsaturated compounds when excited by ultraviolet light. Commercially available photoinitiator compounds include Irgacure 184, Irgacure 819, Darocur 1173, Darocur 4265, Darocur TPO, Omnicat 250, and Omnicat 550, as well as other photoinitiators. Forming the photoluminescent material may include curing the photoluminescent precursor to form the photoluminescent material in the light emitting region 302. The curing operation may include selectively exposing the photoluminescent precursor in one of the photoluminescent regions to a curing light that converts the photoluminescent precursor into a photoluminescent material. Subsequently, an ultraviolet filter may be formed on top of the light emitting region 302 and the pixel isolation structure, and a microlens 308 may be formed for each sub-pixel to complete the micro LED array 1200.

[0064] 13 illustrates a flow chart 1300 of a method for manufacturing a micro-LED structure according to some embodiments. The method may include forming an LED epitaxial layer (1302) on a substrate. The LED epitaxial layer may be formed as described above in FIG. 2, FIGS. 7A to 7H, and elsewhere in the present disclosure. For example, the LED epitaxial layer may include a first side coupled to one or more electrodes, a second side opposite the first side and adjacent to the substrate on which the LED epitaxial layer is formed. The LED epitaxial layer may also include sidewalls extending away from the first side (or away from the backplane when mounted to the backplane). As described above, the LED epitaxial layer may be formed from a series of internal layers, including various n-doped or p-doped GaN layers and MQW regions.

[0065] The method may also include forming a reflective coating on the sidewalls of the LED epitaxial layer (1304). The reflective coating may be formed using a reflective material such as a metal between one or more dielectric layers as described above in FIGS. 7A to 7H. Alternatively, the reflective material may be formed using one or more pairs of layers to form a DBR, as described above in FIGS. 9A and 9E.

[0066] The method may further include forming a first electrode coupled to the first side of the LED epitaxial layer (1306). Optionally, the method may include forming a second electrode also coupled to the first side of the LED epitaxial layer. Other embodiments may form the second electrode on an opposite side of the LED epitaxial layer.

[0067] It should be understood that the specific steps shown in Figure 13 provide a specific method of manufacturing a micro-LED structure according to various embodiments. According to alternative embodiments, other sequences of steps may also be performed. For example, alternative embodiments may perform the steps outlined above in a different order. In addition, each step shown in Figure 13 may include multiple sub-steps, which may be performed in various orders suitable for each step. In addition, additional steps may be added or removed depending on the specific application. Many variations, modifications and alternatives also fall within the scope of the present case.

[0068] As used herein, the term “about” or “approximately” or “substantially” may be interpreted as being within the range expected by those skilled in the art based on the description.

[0069] In the above description, for the purpose of explanation, specific details are set forth to provide a thorough understanding of various embodiments. However, it is apparent that some embodiments may be practiced without these specific details. In other cases, well-known structures and devices are shown in block diagram form.

[0070] The foregoing description provides only exemplary embodiments and is not intended to limit the scope, applicability or configuration of the present invention. On the contrary, the foregoing description of various embodiments will provide a feasible disclosure for implementing at least one embodiment. It should be understood that various changes may be made to the function and arrangement of the elements without departing from the spirit and scope of some embodiments set forth in the appended claims.

[0071] Specific details are given in the foregoing description to provide a thorough understanding of the embodiments. However, it should be understood that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, and other elements may be shown as elements in block diagram form so as not to obscure the embodiments with unnecessary details. In other cases, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary details in order to avoid obscuring the embodiments.

[0072] In addition, it should be noted that various embodiments may be described as processes, which are shown as flow charts, flow charts, data flow diagrams, structure diagrams, or block diagrams. Although a flow chart may describe operations as sequential processes, many operations may be performed in parallel or concurrently. In addition, the order of operations may be rearranged. A process terminates when its operations are completed, but may have other steps not included in the accompanying drawings. A process may correspond to a method, function, program, routine, subroutine, etc. When a process corresponds to a function, its termination may correspond to the function returning to the calling function or the main function.

[0073] In the foregoing description, features are described with reference to specific embodiments thereof, but it should be appreciated that not all embodiments are limited thereto. Various features and aspects of some embodiments may be used alone or in combination. Furthermore, the embodiments may be used in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. Accordingly, the description and drawings are to be regarded as illustrative rather than restrictive.

[0074] In addition, for ease of explanation, the method is described in a specific order. It should be understood that in alternative embodiments, these methods can be performed in an order different from the described order. It should also be understood that the methods described above can be formed by hardware elements, or can be implemented by a sequence of machine executable instructions, which can be used to make a machine (such as a general or special processor or logic circuit) programmed with instructions perform these methods. These machine executable instructions can be stored on one or more machine-readable media, such as CD-ROM or other types of optical disks, floppy disks, ROM, RAM, EPROM, EEPROM, magnetic cards or optical cards, flash memory or other types of machine-readable media suitable for storing electronic instructions. Alternatively, these methods can be performed by a combination of hardware and software.

[0075] The term "computer-readable medium" includes, but is not limited to, portable or fixed storage devices, optical storage devices, wireless channels, and various other media capable of storing, containing, or carrying instructions and / or data. A code segment or machine executable instruction may represent any combination of a process, function, subroutine, program, routine, subroutine, module, software package, class, or instruction, data structure, or program statement. A code segment may be coupled to another code segment or hardware circuit by passing and / or receiving information, data, actual parameters, parameters, or memory contents. Information, actual parameters, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means, including memory sharing, information passing, token passing, network transmission, etc.

[0076] In addition, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description language, or any combination thereof. When implemented in software, firmware, middleware, or microcode, program code or code segments for performing the necessary tasks may be stored in a machine-readable medium. A processor may perform the necessary tasks.

Claims

1. A micro-light emitting diode (micro-LED) structure comprising: a first electrode configured to be coupled to a corresponding second electrode on a backplane, the backplane comprising an array of micro-LED structures; an LED epitaxial layer, the LED epitaxial layer comprising a first side coupled to the electrode and a sidewall extending in a direction away from the back plate; and A reflective coating applied to the sidewalls of the LED epitaxial layers. 2 . The micro LED structure according to claim 1 , wherein the reflective coating substantially covers the sidewall of the LED epitaxial layer to prevent light leakage from the sidewall of the LED epitaxial layer. 3 . The micro LED structure of claim 1 , wherein the reflective coating further covers a portion of the first side of the LED epitaxial layer. 4 . The micro LED structure of claim 3 , wherein the reflective coating leaves an opening on the first side of the LED epitaxial layer, the first electrode being coupled to the first side. 5 . The micro LED structure of claim 1 , further comprising a first dielectric layer between the LED epitaxial layer and the reflective coating. The micro-LED structure of claim 5 , further comprising a second dielectric layer over the reflective coating. 7 . The micro LED structure of claim 6 , wherein the first dielectric layer and the second dielectric layer surround the reflective coating to electrically isolate the reflective coating from the first electrode. The micro-LED structure of claim 1 , wherein the reflective coating comprises a metal layer.

9. The micro-LED structure of claim 1, wherein the reflective coating comprises a material from the group consisting of: Al, Rh, Pt, Ag, Au, and Cr.

10. The micro-LED structure of claim 1, wherein the reflective coating comprises multiple layers of distributed Bragg reflectors (DBRs).

11. The micro-LED structure of claim 10, wherein the multiple layers of the DBR comprise alternating layers of SiO2 and TiO2.

12. A method for manufacturing a micro LED structure, the method comprising the following steps: forming an LED epitaxial layer on a substrate, wherein the LED epitaxial layer comprises a first side, a second side opposite to the first side and adjacent to the substrate, and a sidewall; forming a reflective coating on the sidewalls of the LED epitaxial layer; and A first electrode is formed coupled to the first side of the LED epitaxial layer.

13. The method of claim 12, further comprising the step of selectively forming the reflective coating to leave an opening on the first side of the LED epitaxial layer, wherein the first electrode is coupled to the first side of the LED epitaxial layer at the opening.

14. The method of claim 12, further comprising the step of performing a mesa etch on the LED epitaxial layer to form a first level comprising p-doped gallium nitride (GaN) and a second level comprising n-doped GaN. The method of claim 14 , wherein the first electrode is coupled to the n-doped GaN.

16. The method of claim 15, further comprising the step of forming a second electrode coupled to the p-doped GaN.

17. The method according to claim 12, further comprising the steps of: forming a dielectric layer between the reflective coating and the LED epitaxial layer; and The dielectric layer is etched to expose the LED epitaxial layer at a location where the first electrode is coupled to the first side of the LED epitaxial layer.

18. A micro LED array comprising: backplane substrate; a plurality of micro LED structures mounted to the backplane substrate, wherein the plurality of micro LED structures include LED epitaxial layers; and A plurality of pixel isolation structures are formed between the plurality of micro-LED structures, wherein the plurality of pixel isolation structures extend above a height of the LED epitaxial layers of the plurality of micro-LED structures, and wherein the plurality of pixel isolation structures include a reflective coating on a portion of the plurality of pixel isolation structures extending above the height of the LED epitaxial layers of the plurality of micro-LED structures.

19. The micro LED array of claim 18, wherein the plurality of micro LED structures further comprise a light emitting region formed on the LED epitaxial layer, wherein the reflective coating is located between the light emitting region and the plurality of pixel isolation structures.

20. The micro LED array of claim 18, wherein the reflective coating on the portions of the plurality of pixel isolation structures extending above the height of the LED epitaxial layer does not extend below the height of the LED epitaxial layer.

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