High density micro LED array with reflective sidewalls

Abstract

The micro LED structure includes an LED epi layer that may be formed before the micro LED structure is bonded to the backplane substrate. To prevent light leakage and maximize light output, the sidewalls and other surfaces of the LED epi layer may be coated with a reflective coating. For example, the reflective coating may include a metal layer electrically isolated between the dielectric layer from the micro LED electrodes. The reflective coating may also be formed using multiple layers of a distributed Bragg reflector configuration. This reflective coating may be formed during the LED fabrication process before the micro LED structure is bonded to the backplane. The pixel isolation structure on the backplane may further include a reflective coating applied over the LED epi layer.

Description

[Technical field]

[0001] The present technology 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 technology]

[0002] High-resolution light-emitting diode (LED) displays can contain 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 offers high contrast, response times, and greater energy efficiency than other display types. Micro-LED displays are driven by an array of tiny LEDs arranged to form individual pixel elements. Summary of the Invention

[0003] In some embodiments, a micro light emitting diode (microLED) structure can include a first electrode configured to be coupled to a corresponding second electrode on a backplane including an array of micro LED structures, an LED epilayer including a first side coupled to the electrode and a sidewall extending away from the backplane, and a reflective coating applied to the sidewall of the LED epilayer.

[0004] In some embodiments, a method of fabricating a micro LED structure can include forming an LED epilayer on a substrate, the LED epilayer can include a first side, a second side opposite the first side and adjacent the substrate, and a sidewall. The method can further include forming a reflective coating on the sidewall of the LED epilayer and forming a first electrode coupled to the first side of the LED epilayer.

[0005] In some embodiments, the micro LED array can include a backplane substrate and a plurality of micro LED structures mounted on the backplane substrate, where the plurality of micro LED structures can include an LED epi layer. The array can further include a plurality of pixel isolation structures formed between the plurality of micro LED structures. The plurality of pixel isolation structures can extend above a height of the LED epi layer of the plurality of micro LED structures. The plurality of pixel isolation structures can include a reflective coating on a portion of the plurality of pixel isolation structures that extend above a height of the LED epi layer of the plurality of micro LED structures.

[0006] In any embodiment, any and / or all of the following features may be included, in any combination, without limitation: The reflective coating may substantially cover the sidewalls of the LED epilayer to prevent light leakage from the sidewalls of the LED epilayer. The reflective coating may further cover a portion of the first side of the LED epilayer. The reflective coating may leave an opening in the first side of the LED epilayer to which the first electrode is coupled. The micro LED structure may further include a first dielectric layer between the LED epilayer and the reflective coating. The micro LED structure may further include a second dielectric layer over the reflective coating. The first and second dielectric layers may surround the reflective coating to electrically insulate the reflective coating from the first electrode. The reflective coating may include a metal layer. The reflective coating may include a material from the group consisting of Al, Rh, Pt, Ag, Au, and Cr. The reflective coating may include multiple layers of a distributed Bragg reflector (DBR). The multiple layers of the DBR may include alternating layers of SiO2 and TiO2. The reflective coating can be formed to leave an opening on a first side of the LED epilayer, and a first electrode is bonded to the first side of the LED epilayer. A mesa etch can be performed on the LED epilayer to form a first level including p-type doped gallium nitride (GaN) and a second level including n-type doped GaN. The first electrode can be bonded to the n-type doped GaN. A second electrode can be formed that is bonded to the p-type doped GaN. A dielectric layer can be formed between the reflective coating and the LED epilayer, and the dielectric layer can be etched to expose the LED epilayer, and the first electrode is bonded to the first side of the LED epilayer. The multiple micro LED structures can include a luminescent region formed on the LED epilayer, and the reflective coating can be between the luminescent region and the multiple pixel isolation structures. The reflective coating on a portion of the multiple pixel isolation structures that extends above the height of the LED epilayer may not extend below the height of the LED epilayer.

[0007] A further understanding of the nature and advantages of the various embodiments can be realized by reference to the remaining portions of the specification and the drawings, in which like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sub-label is associated with a reference numeral to represent one of multiple similar components. When a reference numeral is made without specifying an existing sub-label, it is intended to refer to all of such multiple similar components. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 illustrates a top view of one embodiment of a processing system consisting of a deposition chamber, an etch chamber, a bake chamber, and a curing chamber, in accordance with some embodiments. [Diagram 2] 1 illustrates a simplified process for creating a micro LED structure that can be mounted to a backplane, according to some embodiments. [Figure 3A] 1A-1D illustrate stages in a process for fabricating a micro LED array from mounted micro LED structures according to some embodiments. [Figure 3B] 1A-1D illustrate stages in a process for fabricating a micro LED array from mounted micro LED structures according to some embodiments. [Figure 3C] 1A-1D illustrate stages in a process for fabricating a micro LED array from mounted micro LED structures according to some embodiments. [Figure 3D] 1A-1D illustrate stages in a process for fabricating a micro LED array from mounted micro LED structures according to some embodiments. [Figure 4] FIG. 1 illustrates a micro LED array mounted on a backplane according to some embodiments. [Diagram 5] 1 is a cross-sectional view of adjacent micro LED structures in an array with light leakage between adjacent structures according to some embodiments. [Figure 6] FIG. 2 illustrates an LED epilayer including a reflective coating according to some embodiments. [Figure 7A] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7B] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7C] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7D] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7E] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7F] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7G] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 7H] FIG. 2 illustrates a sequence of processing steps that can be used to form LED epilayers and reflective coatings according to some embodiments. [Figure 8] FIG. 2 illustrates a graph of the reflectance percentage of different materials used as a reflective coating, according to some embodiments. [Figure 9A] 1A-1C illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR) according to some embodiments. [Figure 9B]1A-1C illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR) according to some embodiments. [Figure 9C] 1A-1C illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR) according to some embodiments. [Figure 9D] 1A-1C illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR) according to some embodiments. [Figure 9E] 1A-1C illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR) according to some embodiments. [Figure 10] FIG. 13 shows a graph illustrating the performance of alternating pairs of different numbers of materials used in the DBR of a reflective coating according to some embodiments. [Figure 11] FIG. 1 illustrates a micro LED array, according to some embodiments. [Figure 12] FIG. 1 illustrates a completed micro LED array according to some embodiments. [Figure 13] FIG. 1 illustrates a flowchart of a method for manufacturing a micro LED structure, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The micro LED structure includes an LED epi layer that may be formed before the micro LED structure is bonded to the backplane substrate. To prevent light leakage and maximize light output, the sidewalls and other surfaces of the LED epi layer may be coated with a reflective coating. For example, the reflective coating may include a metal layer electrically isolated between the dielectric layer from the micro LED electrodes. The reflective coating may also be formed using multiple layers of a distributed Bragg reflector configuration. This reflective coating may be formed during the LED fabrication process before the micro LED structure is bonded to the backplane. The pixel isolation structure on the backplane may further include a reflective coating applied over the LED epi layer.

[0010] FIG. 1 is a plan view of one embodiment of a processing system 100 consisting of a deposition chamber, an etch chamber, a bake chamber, and a cure chamber, according to some embodiments. In the figure, a pair of front-opening unified pods 102 supply substrates of various sizes, which are received by a robot arm 104 and placed in a low pressure holding area 106, and then placed in one of the substrate processing chambers 108a-108f located in tandem sections 109a-109c. A second robot arm 110 can be used to transfer the substrate wafer from the holding area 106 to the substrate processing chambers 108a-108f and back. Each substrate processing chamber 108a-108f can be equipped to perform several substrate processing operations, including cyclic layer deposition, atomic layer deposition, chemical vapor deposition, physical vapor deposition, etching, pre-cleaning, annealing, plasma treatment, degassing, orientation, and other substrate processes, as well as the dry etching processes described herein.

[0011] The substrate processing chambers 108a-108f may include one or more system components for depositing, annealing, curing, and / or etching a material film on a substrate or wafer. In one configuration, two pairs of processing chambers, e.g., 108c-108d and 108e-108f, may be used to deposit material on a substrate, and a third pair of processing chambers, e.g., 108a-108b, may be used to cure, anneal, or treat the deposited film. In another configuration, all three pairs of chambers, e.g., 108a-108f, may be configured to both deposit and cure a film on a substrate. Any one or more of the described processes may be performed in additional chambers remote from the illustrated fabrication system in different embodiments. It will be appreciated that additional configurations of deposition, etch, anneal, and cure chambers for material films are contemplated by the processing system 100. Additionally, any number of other processing systems may be utilized with the present techniques, and these other processing systems may incorporate chambers for performing any of the specific operations. In some embodiments, a chamber system that can access multiple processing chambers while maintaining a vacuum environment in various sections, such as the holding and transfer areas mentioned, can make it possible to perform operations in multiple chambers while maintaining a specific vacuum environment between separate processes.

[0012] The processing system 100, or more specifically, the chambers incorporated into the processing system 100 or other processing systems, may be used to produce structures according to some embodiments of the present technology. For example, the processing system 100 may be used to produce micro LED arrays by performing operations such as deposition, etching, sputtering, polishing, cleaning, etc. in the various substrate processing chambers 108.

[0013] 2 shows a simplified process for creating a micro LED structure 200 that may be mounted to a backplane 220, according to some embodiments. As described in more detail below, the micro LED structure may be fabricated on a substrate 210. An LED epi layer 212 may be formed on the substrate 210 and function as the light-generating electrical component of the micro LED structure 200. The LED epi layer 212 may be composed of several different individual layers, as described below.

[0014] One or more electrodes may be attached to the LED epi layer 212 to provide electrical connections for the micro LED structure 200. For example, the first electrode 214 and the second electrode 216 may be bonded to the LED epi layer 212 on the same side of the LED epi layer 212. As used herein, the side of the epi layer 212 to which the first electrode 214 is bonded may be collectively referred to as the "first side" of the LED epi layer 212. While FIG. 2 illustrates the micro LED structure 200 with both electrodes attached to the first side of the LED epi layer 212 in a side-chip or "flip-chip" configuration, other embodiments may attach the first electrode 214 to the first side of the epi layer 212 while attaching the second electrode 216 to an opposing side of the epi layer 212, collectively referred to as the "second side" of the LED epi layer 212, opposite the first side. This is sometimes referred to as a “vertical chip” orientation, and it is compatible with all embodiments described herein that utilize a reflective coating on the LED epilayer 212.

[0015] Separately, a substrate 221 may be used to form the backplane 220 of the micro LED array. A number of electrodes may be coupled to the substrate 221. These electrodes may be configured to receive electrodes of a number of different micro LED structures and form electrical connections between the backplane 220 and the micro LED structures. For example, a first electrode 224 and a second electrode 226 on the substrate 221 may be configured to be electrically coupled with a first electrode 214 and a second electrode 216 on the LED epi layer 212 of the micro LED structure 200.

[0016] The micro LED structure 200 may be mounted to the backplane 220 by flipping the orientation of the micro LED structure 200 and bonding the first electrode 214 and the second electrode 216 on the micro LED structure 200 with the corresponding first electrode 224 and the second electrode 226 on the substrate 221. The substrate 210 on which the LED epi layer 212 is formed may be removed to expose the LED epi layer 212 on the backplane 220. Although FIG. 2 shows only a single micro LED structure 200 mounted to a single pair of electrodes on the backplane 220, it should be understood that the backplane 220 may be configured to mount multiple micro LED structures as an array of micro LEDs. Thus, the substrate 210 may include multiple LED epi layers forming multiple micro LED structures that may be mounted together on the backplane 220, and the substrate 221 may include multiple mounting locations for multiple micro LED structures in an array not explicitly shown in FIG. 2.

[0017] 3A-3D show stages in a process for fabricating a micro LED array from mounted micro LED structures according to some embodiments. These figures show cross-sectional views of the structure described above in FIG. 2. In FIG. 3A, pixel separating structures 333 may be formed between each of the micro LED structures in the array. These pixel separating structures 333 may extend above the height of the LED epi layer 212 of each of the micro LED structures. The pixel separating structures 333 may be fabricated from a reflective and / or conductive material (e.g., metal) and may be surrounded by an electrically insulating passivation layer to prevent the pixel separating structures 333 from shorting any of the electrodes of the micro LED structures.

[0018] The luminescent region 302 may be formed on the LED epilayer 212 between the pixel separating structures 333. The luminescent region 302 may include a photoluminescent material. For example, FIG. 3B shows how the luminescent region 302 may include a quantum dot material 304 operable to emit different wavelengths of light. For example, a single pixel may include multiple micro LED structures, each of which may use a different quantum dot material to generate red light, blue light, green light, etc. The luminescent region 302 may be formed using thermal imprint lithography, which may include deposition of a subpixel separating material onto the micro LED structures and thermal imprinting of the luminescent region 302 onto the subpixel separating material. Alternatively, the luminescent region 302 may be formed using a sequence of operations including deposition, mask patterning, etching, and mask removal.

[0019] 3C illustrates the optional incorporation of an ultraviolet (UV) light filter 306 that may be formed on the micro LED array. The UV light filter 306 may absorb UV light generated by the micro LED structures in the array. In some embodiments, the UV light filter 306 may also absorb other wavelengths, such as some blue light, generated by the micro LED structures in the array while passing visible light emitted from the luminescent region of each micro LED structure.

[0020] FIG. 3D illustrates the incorporation of microlenses 308 that may be formed over each of the micro LED structures.

[0021] 4 illustrates a micro LED array 410 mounted to a backplane, according to some embodiments. The backplane may further include electronic circuitry for conditioning electrical signals and actuating the illumination of the micro LEDs in the micro LED array 410. For example, the backplane may include CMOS circuitry including transistors operable to turn on and / or off the flow of current 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.

[0022] 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 including four micro LED structures. A first micro LED structure 414 may be configured to generate red light, a second micro LED structure 416 may be configured to generate green light, a third micro LED structure 418 may be configured to generate blue light, and a fourth micro LED structure 420 may be configured as a backup in case one of the other micro LED structures in the pixel 412 fails.

[0023] Each of the four micro LED structures within a pixel 412 may be referred to as a sub-pixel within the pixel 412. In some embodiments, the pixel separating structure 333 described above may be configured as a sub-pixel separating structure to separate each of the sub-pixels from each other within the pixel 412. In this example, each of the sub-pixels are arranged in a 2×2 grid array within each pixel 412, although other embodiments may use different arrangements for the sub-pixels within a pixel.

[0024] 5 shows a cross-sectional view 500 of adjacent micro LED structures in an array with light leakage between adjacent structures according to some embodiments. In existing architectures, light can leak from various areas of the micro LED structures in the array, thereby causing interference with other adjacent micro LED structures and reducing the light output efficiency of the micro LED structures in the array.

[0025] One particular area where light leakage may occur in a micro LED structure is from the LED epi layer 212. Ideally, all of the light generated by the micro LED structure should be directed straight out of the micro LED array in the vertical direction in FIG. 5. However, as shown in FIG. 5, light may leak from various locations in the LED epi layer 212 instead of exiting through the second side of the LED epi layer 212. This light leakage may be mis-transmitted to adjacent micro LED structures and cause interference. For example, light from a micro LED structure configured to generate blue light may leak into an adjacent micro LED structure configured to generate red light, thereby changing the light output of the pixel or adjacent pixels. Additionally, when light leaks from the LED epi layer 212, this reduces the total light output of the micro LED structure, thereby causing a reduction in the clarity / brightness of the micro LED display.

[0026] In this example, light 502 may leak out of the sidewalls of the LED epilayers 212. As shown in FIG. 5, the "sidewalls" of the LED epilayers 212 may refer to the sides of the LED epilayers 212 that extend away from the backplane. Note that the sidewalls need not extend in a purely vertical direction (e.g., 90°) but may instead extend away from the backplane at an angle. This angle can be adjusted in some embodiments to maximize the efficiency of the light output of the micro-LED structure, as described in more detail below. The sidewalls of the LED epilayers 212 may extend around the periphery of the LED epilayers 212, although only a cross-sectional view is shown in FIG. 5.

[0027] In addition, light 504 may also leak out of the first side of the LED epilayer 212 to which the electrodes are bonded. This leakage of light 504 may occur between the electrodes as well as at the sides of the electrodes as shown in Figure 5. With light 502 leaking out of the sidewalls of the LED epilayer 212 and light 504 leaking out of the first side of the LED epilayer 212, improvements are needed in the design of the micro LED structure to minimize this leakage, minimize interference with adjacent micro LED structures, and improve the efficiency of light output.

[0028] FIG. 6 illustrates an LED epilayer 212 including a reflective coating 602, according to some embodiments. To solve the light leakage problem along with other technical problems, some embodiments may form a reflective coating 602 around the LED epilayer 212 to reduce the light leakage described above. Instead of relying on pixel separation structures or other structures formed after the micro LED structure is formed, these embodiments instead integrate the reflective coating 602 on the surface of the LED epilayer 212 during the fabrication of the micro LED structure itself. For example, returning briefly to FIG. 2, the reflective coating 602 may be formed on the LED epilayer 212 while the LED epilayer 212 is still bonded to the substrate 210 and before the first electrode 214 and / or second electrode 216 are formed on the LED epilayer 212. The reflective coating 602 may also be characterized in that the reflective coating 602 is formed on the LED epilayer 212 before the micro LED structure 200 is attached to the backplane 220. Therefore, instead of using a reflective or absorbing layer that is subsequently inserted between the micro LED structures on the backplane using a complex process, these embodiments greatly simplify this process during the LED processing step itself.

[0029] In some embodiments, the reflective coating 602 can be formed on the sidewalls 622 of the LED epilayer 212. Optionally, some embodiments can also apply the reflective coating 602 such that it covers a portion of the first side 620 of the LED epilayer 212. For example, the reflective coating 602 can cover the portion of the first side 620 of the LED epilayer 212 between the first electrode 214 and / or the second electrode 216, but leave an opening that can expose a portion of the LED epilayer 212 to interface or couple the first electrode 214 and / or the second electrode 216 with the LED epilayer 212 without interfering with this electrical connection.

[0030] In some embodiments, the reflective coating 602 can substantially cover the sidewalls 622 of the LED epilayer 212 to prevent light leakage from 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, etc.

[0031] 7A-7H illustrate a sequence of processing steps that may be used to form the LED epilayer 212 and reflective coating 708, according to some embodiments. FIG. 7A shows a substrate 210 on which the LED epilayer 212 is formed. The substrate 210 may include silicon or sapphire, among other substrate materials. These steps may be referred to as micro-LED fabrication steps, and may be distinguished from the other steps described above in FIG. 3, where micro-LEDs are attached to a backplane, positioned within pixels, surrounded by pixel separating structures, covered with luminescent material, etc.

[0032] Although the LED epilayer 212 is shown as a single layer in these figures, it should be understood that the LED epilayer 212 may actually be formed using multiple successive layers fabricated on the substrate 210. For example, the LED epilayer 212 may include a gallium and nitrogen containing LED structure. The LED epilayer 212 may be a gallium nitride (GaN) LED structure epitaxially formed on the substrate 210. The LED epilayer 212 may include an n-type doped GaN layer and a p-type doped GaN layer. A multiple quantum well (MQW) region may be formed between the n-type doped GaN layer and the p-type doped GaN layer where the light emitted by the LED epilayer 212 occurs.

[0033] 7B illustrates how a mesa etch process can be used to expose two different surfaces of the LED epilayers 212 that can be bonded to corresponding electrodes or electrical contacts. For example, the mesa process can expose the p-doped GaN surface 702 of one portion of the LED epilayers 212. A portion of the p-doped GaN surface can be etched away (along with any intervening layers such as MQW regions) to expose a portion of the underlying n-doped GaN layer to form the n-doped GaN surface 704. Any type of etching process can be used to expose these surfaces, including photolithography, reactive ion etching, etc.

[0034] FIG. 7C shows the result of a die singulation process to form the sidewalls of the LED epilayer 212. In some embodiments, the sidewalls can be formed at an angle. This angle can be configured such that light generated by the micro LED structure that is incident on the sidewalls of the LED epilayer 212 can be maximally reflected back to the sidewalls of the LED epilayer 212 through the microlenses associated with the micro LED structure. With the addition of a reflective coating 708, the sidewalls can internally reflect light that would otherwise escape the LED epilayer 212. The angle of the sidewalls can be configured such that this reflected light exits the microlenses with the highest efficiency. The exact angle of the sidewalls can 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 instead use sidewall angles of greater than or about 85°, greater than or about 80°, greater than or about 75°, greater than or about 70°, greater than or about 70°, greater than or about 65°, greater than or about 60°, greater than or about 60°, greater than or about 55°, greater than or about 50°, greater than or about 45°, and / or any interval within these ranges.

[0035] FIG. 7D illustrates a first dielectric layer 706 that may be formed on the first surface and sidewalls of the LED epilayer 212. The first dielectric layer 706 may be formed from any dielectric material, such as silicon dioxide or other oxide material. The first dielectric layer 706 may form an insulating layer that insulates the reflective coating 708 from the first electrode 214 and the second electrode 216. The first dielectric layer 706 may be formed using a number 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 illustrated in these figures substantially covers the exposed portions of the LED epilayer 212 that are exposed above the substrate 210.

[0036] 7E illustrates the application of a reflective coating 708. The reflective coating 708 can be formed from any reflective material. Some embodiments may specifically use a metal 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.

[0037] As shown in these figures, a reflective coating 708 can be formed over the first dielectric layer 706. The reflective coating 708 can cover the sidewalls of the LED epilayers 212 and / or a portion and / or substantially all of 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 epilayers 212. In some embodiments, the reflective coating 708 can be applied such that openings 722, 724 can remain exposed portions of the first dielectric layer 706 over the p-type doped GaN surface 702 and the n-type doped GaN surface 704. As described below, the first dielectric layer 706 can be etched away from these openings 722, 724 to expose the p-type doped GaN surface 702 and the n-type doped GaN surface 704 for electrical connection with the first electrode 214 and the second electrode 216.

[0038] 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 similar manner as 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.

[0039] 7G shows how the first dielectric layer 706 and the second dielectric layer 710 may be etched or otherwise removed to expose the p-type doped GaN surface 702 and the n-type doped GaN surface 704. The first dielectric layer 706 and the second dielectric layer 710 may be removed using any etching process. Note that the reflective coating 708 remains surrounded by the first dielectric layer 706 and the second dielectric layer 710.

[0040] 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 in which metal is deposited on the p-type doped GaN surface 702 and the n-type doped GaN surface 704. In some embodiments, a mask for depositing the metal of the first electrode 214 and the second electrode 216 may expose the p-type doped GaN surface 702 and the n-type 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 a portion of the second dielectric layer 710.

[0041] Electrically, the first electrode 214 forms a conductive path for current to pass through the p-type doped GaN layer of the LED epilayer 212. Similarly, the second electrode 216 forms a conductive path for current to pass through the n-type doped GaN layer. The first electrode 214 and the second electrode 216 can later be connected to control circuitry on the backplane. An electrical signal from the control circuitry creates a current flow through the micro-LED structure that causes light emission from the MQW region of the micro-LED structure. The MQW region can be formed to emit light characterized by a repeatable peak intensity wavelength and quantum efficiency versus an applied electrical signal (e.g., current and / or voltage).

[0042] FIG. 8 illustrates a graph 800 of the reflectance percentages of different materials used as reflective coatings, according to some embodiments. The y-axis represents the reflectance percentages of some of the many materials that can be used for the reflective coating, while the x-axis represents the wavelengths (μm) of light that the reflective coating can reflect at the corresponding percentages shown on the y-axis. Graph 800 can be used to select materials that can be used for the reflective coating based on the requirements of a particular design. For example, 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 based on the wavelength and design requirements of a particular micro LED structure. It should be noted that the materials describing graph 800 are provided merely as examples and are not meant to be limiting. Any reflective material or metal may be used.

[0043] 9A-9E illustrate a process for applying a reflective coating that includes a distributed Bragg reflector (DBR), according to some embodiments. A DBR can include a structure formed from multiple layers of alternating materials with different refractive indices. Each layer boundary can cause partial reflection of the light waves, so that the multiple layers act as a high quality reflector. Some embodiments may replace the metallic materials mentioned above for the reflective coating by instead using the multiple layers that form the DBR as the reflective coating.

[0044] The process resulting in the structure shown in Figures 9A-9C can be carried out as described above in connection with Figures 7A-7C to form LED epilayer 212 on substrate 210 having an exposed p-type doped GaN surface 702 and an exposed n-type doped GaN surface 704, and to form sidewalls of LED epilayer 212.

[0045] However, instead of forming the first dielectric layer 706 and / or the second dielectric layer 710, the process can instead form the individual layers that make up the DBR as the reflective coating 902. Note that the individual layers that make up the DBR can be non-conductive. This can limit the need for the first dielectric layer 706 and / or the second dielectric layer 710 to insulate the reflective coating 902. Rather than etching away the individual layers that make up the DBR, they can instead be selectively formed on the LED epilayer 212 to leave the p-type doped GaN surface 702 and the n-type doped GaN surface 704 exposed. Electrical insulation between the reflective coating 902 and the first and second electrodes 214 and 216 may not be required.

[0046] Various materials can be used to form the multiple individual layers that make up the DBR for the reflective coating 902. For example, some embodiments can use alternating layers of silicon dioxide (SiO2) 912 and titanium oxide (TiO2) 914. FIG. 10 shows a graph 1000 illustrating the performance of alternating pairs of different numbers of materials used in the DBR of the reflective coating 902, according to some embodiments. The reflectivity of the various layer numbers is represented on the vertical axis against different wavelengths of light represented on the horizontal axis. A graph such as graph 1000 or a data table can be used to select the number of DBR layers to be used to achieve a desired level of reflectivity as needed based on the operating conditions of different embodiments. For example, curve 1010 can represent a single pair of DBR layers of SiO2 and TiO2 to achieve approximately 50% reflectivity at 400 nm (where λBragg=400 nm, nSiO2=1.47, nTiO2=2.47, and nGaN=2.50). Curve 1008 may represent two pairs of DBR layers to achieve approximately 80% reflectivity. Curve 1006 may represent three pairs of DBR layers to achieve approximately 90% reflectivity. Curve 1004 may represent four pairs of DBR layers to achieve approximately 95% reflectivity. Curve 1002 may represent five pairs of DBR layers to achieve approximately 98% reflectivity. Note that these curves in graph 1000 are provided merely as examples and are not meant to be limiting. Other DBR layer materials, layer configurations, and / or wavelength ranges may be used without limitation.

[0047] 11 illustrates a micro LED array 1100, according to some embodiments. As described above, a plurality of micro LED structures may be mounted on a backplane substrate, each of the micro LED structures including an LED epi layer 212 formed as described above. These LED epi layers 212 may include a reflective coating covering at least a portion of the sidewalls and / or first side of the LED epi layer 212.

[0048] Additionally, individual micro LED structures may include pixel separating structures 1104, which may also be referred to as "sub-pixel" separating structures depending on the arrangement of the micro LED structure relative to the pixel separating structures 1104. The pixel separating structures 1104 may extend above and / or around the micro LED structure. In some embodiments, the sidewalls of the pixel separating structures 1104 need not extend in a purely vertical direction (e.g., 90°), but may instead extend at an angle greater than or less than 90°, such that the direction of light emission from the micro LED structure may be directed in a desired pattern to shape and confine the light of the photoluminescent material in these regions. The pixel separating structures 1104 may extend adjacent to and below the contact areas for the electrodes of the micro LED structure, and may further extend down to the backplane of the micro LED array 1100. The sub-pixel separating structures may include dielectric materials, among other types of materials. The dielectric material may include one or more of silicon oxide, silicon nitride, silicon carbide, a photoresist material, or a dielectric organic polymer material, among other dielectric materials. The pixel separation structure 1104 may have a height of 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 separating structure 1104 can 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 separating structure 1104 can have a height-to-width 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 more.

[0049] In contrast to existing designs, some embodiments may further include a reflective coating 1102 formed on the pixel separating 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 epi layer 212. It is noted that the reflective coating 1102 on the pixel separating structure 1104 does not need to extend below the top or surface level of the LED epi layer 212, since a separate reflective coating was previously applied to the LED epi layer 212 during a separate micro LED fabrication process. Instead, the pixel separating structure 1104 may include the reflective coating 1102 on a portion of the pixel separating structure 1104 that extends above the height of the LED epi layer 212. As a result, the pixel separating structure 1104 may omit or remove a reflective material or coating that would otherwise be applied or used below the height of the LED epi layer 212. Thus, some embodiments may be characterized in that a portion of the pixel separation structure 1104 below the level of the LED epilayer 212 does not include a reflective material, reflective surface, and / or reflective coating.

[0050] The use of a reflective coating on the LED epilayer 212 in conjunction with a reflective coating 1102 on the pixel separating structure 1104 provides several technical advantages and improvements. For example, a dielectric or non-reflective material may be used to form the pixel separating structure 1104 instead of a metal or otherwise reflective surface or material. The pixel separating structure 1104 may be formed of a single material rather than a core metal post surrounded by an insulating material. The reflective coating 1102 may also be applied in a simple process after the pixel separating structure 1104 is formed. For example, a mask may be applied over the LED epilayer 212 and the reflective coating 1102 may be applied (e.g., by sputtering or other deposition process) to the exposed portions of the pixel separating structure 1104. This process is significantly simpler than attempting to apply a reflective coating 1102 that extends below the height of the LED epilayer 212.

[0051] FIG. 12 illustrates a completed micro LED array 1200 according to some embodiments. As mentioned above, the luminescent regions 302 can be formed based on the desired light output of each of the micro LED structures. Forming the luminescent regions 302 can include depositing a photoluminescent precursor in the region between the pixel separating structures 1104. The photoluminescent precursor can be a mixture or slurry including a light curable fluid and one or more photoluminescent particles or compounds. The one or more photoluminescent compounds can include quantum dot materials operable to emit light having specific color characteristics when excited by the source light. These quantum dot materials can include nanoparticles fabricated from one or more types of inorganic semiconductor materials such as indium phosphide, zinc selenide, zinc sulfide, silicon, silicates, and graphene, as well as doped inorganic oxides, among other semiconductor materials. The light curable fluid can include one or more crosslinking compounds, photoinitiators, and color conversion agents. The crosslinking compounds can include monomers that form polymers when cured. The monomers can include acrylate monomers, methacrylate monomers, and acrylamide monomers. The crosslinking compounds can include negative photoresist materials, such as SU-8 photoresist. The photoinitiators can include phosphine oxide compounds and keto compounds, among other types of photoinitiator compounds, which generate radicals that initiate the curing of the unsaturated compounds when excited by UV light. Commercially available photoinitiator compounds include Irgacure 184, Irgacure 819, Darocur 1173, Darocur 4265, Darocur TPO, Omnicat 250, and Omnicat 550, among other photoinitiators. Forming the photoluminescent material can include curing a photoluminescent precursor to form a photoluminescent material in the luminescent regions 302. The curing operation can include selectively exposing the photoluminescent precursor in one of the photoluminescent regions to a curing light that converts the photoluminescent precursor to a photoluminescent material.A UV light filter may then be formed over the luminescent region 302 and pixel separating structures, and a microlens 308 may be formed for each sub-pixel to complete the micro LED array 1200.

[0052] FIG. 13 shows a flowchart 1300 of a method for fabricating a micro LED structure, according to some embodiments. The method can include forming an LED epi layer on a substrate (1302). The LED epi layer can be formed as described above in FIG. 2, 7A-7H, and elsewhere in this disclosure. For example, the LED epi layer can include a first side to which one or more electrodes are coupled and a second side opposite the first side and adjacent to the substrate on which the LED epi layer is formed. The LED epi layer can further include a sidewall extending away from the first side (or away from the backplane when attached to the backplane). As described above, the LED epi layer can be formed by a series of internal layers including various n / p type doped GaN layers and MQW regions.

[0053] The method can further include forming a reflective coating on the sidewalls of the LED epilayer (1304). The reflective coating can be formed using a reflective material such as a metal between one or more dielectric layers, as described above in Figures 7A-7H. Alternatively, the reflective material can be formed using one or more layer pairs to form a DBR, as described above in Figures 9A-9E.

[0054] The method may additionally include forming 1306 a first electrode coupled to a first side of the LED epilayer. Optionally, the method may include forming a second electrode further coupled to the first side of the LED epilayer. Other embodiments may form a second electrode on an opposing side of the LED epilayer.

[0055] It should be appreciated that the specific steps illustrated in FIG. 13 provide a particular method of fabricating a micro LED structure according to various embodiments. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in FIG. 13 may include multiple sub-steps that may be performed in various sequences depending on the individual step. Furthermore, additional steps may be added or removed depending on the particular application. Many variations, modifications, and alternatives also fall within the scope of the present disclosure.

[0056] The terms "about" or "approximately" or "substantially" as used herein can be interpreted to be within the range of what would be expected by one of ordinary skill in the art in light of the present specification.

[0057] In the foregoing description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. It will be apparent, however, that some embodiments may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form.

[0058] The above description provides only exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the above description of various embodiments will provide an enabling disclosure for implementing at least one embodiment. It should be understood that various modifications may be made in the function and arrangement of elements without departing from the spirit and scope of the several embodiments as set forth in the appended claims.

[0059] Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments can be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may be shown as components in block diagram form so as not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail so as not to obscure the embodiments.

[0060] Further, it is noted that the particular embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe operations as a sequential process, many of the operations may be performed in parallel or simultaneously. Additionally, the order of operations may be rearranged. A process terminates when its operations are completed, but may have additional steps not included in the diagram. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, and the like. When a process corresponds to a function, its termination may correspond to a return of the function to the calling function or the main function.

[0061] In the foregoing specification, features are described with reference to specific embodiments, but it should be appreciated that not all embodiments are limited thereto. Various features and aspects of the several embodiments may be used individually or jointly. Moreover, the embodiments may be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. Accordingly, the specification and drawings should be regarded as illustrative rather than restrictive.

[0062] In addition, for purposes of illustration, the method has been described in a particular order. It should be appreciated that in alternative embodiments, the method may be performed in an order different from that described. It should also be appreciated that the above-described method may be executed by hardware components or embodied in a sequence of machine-executable instructions that can be used to cause a machine, such as a general-purpose or special-purpose processor or logic circuitry programmed with the instructions, to perform the method. These machine-executable instructions may be stored on one or more machine-readable media, such as a CD-ROM or other type of optical disk, a floppy diskette, a ROM, a RAM, an EPROM, an EEPROM, a magnetic or optical card, a flash memory, or any other type of machine-readable medium suitable for storing electronic instructions. Alternatively, the method may be performed by a combination of hardware and software.

[0063] 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 that can store, contain, or carry instructions and / or data. A code segment or machine-executable instructions can represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or communicated via any suitable means including memory sharing, message passing, token passing, network transmission, etc.

[0064] Furthermore, the embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform 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 including an array of micro LED structures; an LED epilayer including a first side coupled to the electrode and a sidewall extending away from the backplane; a reflective coating applied to the sidewalls of the LED epilayer; A micro LED structure comprising:

2. 10. The micro LED structure of claim 1, wherein the reflective coating substantially covers the sidewalls of the LED epilayer to prevent light leakage from the sidewalls of the LED epilayer.

3. 10. The micro LED structure of claim 1 , wherein the reflective coating further covers a portion of the first side of the LED epilayer.

4. 4. The micro LED structure of claim 3, wherein the reflective coating leaves an opening on the first side of the LED epilayer to which the first electrode is bonded.

5. 10. The micro LED structure of claim 1 further comprising a first dielectric layer between the LED epilayer and the reflective coating.

6. 6. The micro LED structure of claim 5 further comprising a second dielectric layer over the reflective coating.

7. 7. The micro LED structure of claim 6, wherein the first and second dielectric layers surround the reflective coating to electrically insulate the reflective coating from the first electrode.

8. 10. The micro LED structure of claim 1, wherein the reflective coating comprises a metal layer.

9. 10. 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. 10. The micro LED structure of claim 1, wherein the reflective coating comprises multiple layers of distributed Bragg reflectors (DBRs).

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

12. 1. A method of manufacturing a micro LED structure, the method comprising: forming an LED epilayer on a substrate, the LED epilayer including a first side, a second side opposite the first side and adjacent the substrate, and a sidewall; forming a reflective coating on the sidewalls of the LED epilayer; forming a first electrode coupled to the first side of the LED epilayer; A method comprising:

13. 13. The method of claim 12, further comprising selectively forming the reflective coating to leave an opening on the first side of the LED epilayer, the first electrode being coupled to the first side of the LED epilayer.

14. 13. The method of claim 12, further comprising performing a mesa etch on the LED epilayers to form a first level comprising p-type doped gallium nitride (GaN) and a second level comprising n-type doped GaN.

15. The method of claim 14 , wherein the first electrode is coupled to the n-type doped GaN.

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

17. forming a dielectric layer between the reflective coating and the LED epilayer; etching the dielectric layer to expose the LED epilayer, the first electrode being bonded to the first side of the LED epilayer; The method of claim 12 further comprising:

18. A backplane board; a plurality of micro LED structures mounted on the backplane substrate, the plurality of micro LED structures including an LED epilayer; a plurality of pixel isolation structures formed between the plurality of micro LED structures, the plurality of pixel isolation structures extending above a height of the LED epilayer of the plurality of micro LED structures, the plurality of pixel isolation structures including a reflective coating on a portion of the plurality of pixel isolation structures that extends above the height of the LED epilayer of the plurality of micro LED structures; 1. A micro LED array comprising:

19. 20. The micro LED array of claim 18, wherein the plurality of micro LED structures further comprises a luminescent region formed on the LED epilayer, and the reflective coating is between the luminescent region and the plurality of pixel separating structures.

20. 20. The micro LED array of claim 18, wherein the reflective coating on the portions of the plurality of pixel separation structures that extend above the height of the LED epilayer does not extend below the height of the LED epilayer.

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