High-density micro-led arrays with reflective sidewalls

Abstract

Micro-LED structures include an LED epilayer that may be formed before the micro-LED structure is coupled to a backplane substrate. In order to prevent light leakage and maximize light output, the sidewalls and other surfaces of the LED epilayer may be coated with a reflective coating. For example, the reflective coating may include a metal layer that is electrically insulated between dielectric layers from the micro-LED electrodes. The reflective coating may also be formed using multiple layers in a distributed Bragg reflector configuration. This reflective coating may be formed during the LED fabrication process before the micro-LED structure is coupled to the backplane. The pixel isolation structures on the backplane may also include a reflective coating that is applied above the LED epilayers.

What is claimed is: 
     
         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 comprising an array of micro-LED structures;   an LED epilayer comprising a first side coupled to the electrode and sidewalls extending in a direction away from the backplane; and   a reflective coating applied to the sidewalls of the LED epilayer.   
     
     
         2 . The micro-LED structure of  claim 1 , wherein the reflective coating substantially covers the sidewalls of the LED epilayer to prevent light leakage out of the sidewalls of the LED epilayer. 
     
     
         3 . The micro-LED structure of  claim 1 , wherein the reflective coating further covers a portion of the first side of the LED epilayer. 
     
     
         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 coupled. 
     
     
         5 . The micro-LED structure of  claim 1 , further comprising a first dielectric layer between the LED epilayer and the reflective coating. 
     
     
         6 . 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 enclose the reflective coating to electrically isolate the reflective coating from the first electrode. 
     
     
         8 . 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 a plurality of layers of a Distributed Bragg Reflector (DBR). 
     
     
         11 . The micro-LED structure of  claim 10 , wherein the plurality of layers of the DBR comprises alternating layers of SiO 2  and TiO 2 . 
     
     
         12 . A method of fabricating a micro-LED structure, the method comprising:
 forming an LED epilayer on a substrate, wherein the LED epilayer comprises a first side, a second side opposite the first side and adjacent to the substrate, and sidewalls;   forming a reflective coating on the sidewalls of the LED epilayer; and   forming a first electrode coupled to the first side of the LED epilayer.   
     
     
         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 where the first electrode is coupled to the first side of the LED epilayer. 
     
     
         14 . The method of  claim 12 , further comprising performing a mesa etch on the LED epilayer to form a first level comprising p-doped Gallium Nitride (GaN) and a second level comprising n-doped GaN. 
     
     
         15 . The method of  claim 14 , wherein the first electrode is coupled to the n-doped GaN. 
     
     
         16 . The method of  claim 15 , further comprising forming a second electrode coupled to the p-doped GaN. 
     
     
         17 . The method of  claim 12 , further comprising:
 forming a dielectric layer between the reflective coating and the LED epilayer; and   etching the dielectric layer to expose the LED epilayer where the first electrode couples to the first side of the LED epilayer.   
     
     
         18 . A micro-LED array comprising:
 a backplane substrate;   a plurality of micro-LED structures mounted to the backplane substrate, wherein the plurality of micro-LED structures comprise LED epilayers; and   a plurality of pixel isolation structures formed between the plurality of micro-LED structures, wherein the plurality of pixel isolation structures extend above a height of the LED epilayers of the plurality of micro-LED structures, and wherein the plurality of pixel isolation structures comprise reflective coatings on a portion of the plurality of pixel isolation structures that extends above the height of the LED epilayers of the plurality of micro-LED structures.   
     
     
         19 . The micro-LED array of  claim 18 , wherein the plurality of micro-LED structures further comprises luminescence regions formed on the LED epilayers, wherein the reflective coatings are between the luminescence regions and the plurality of pixel isolation structures. 
     
     
         20 . The micro-LED array of  claim 18 , wherein the reflective coatings on the portion of the plurality of pixel isolation structures that extends above the height of the LED epilayers does not extend below the height of the LED epilayers.