Micro assembled LED displays and lighting elements
The disclosed technology provides micro-assembled micro-LED displays and lighting elements using arrays of micro-LEDs that are too small (e.g., micro-LEDs with a width or diameter of 10 μm to 50 μm), numerous, or fragile to assemble by conventional means. The disclosed technology provides for micro-LED displays and lighting elements assembled using micro-transfer printing technology. The micro-LEDs can be prepared on a native substrate and printed to a display substrate (e.g., plastic, metal, glass, or other materials), thereby obviating the manufacture of the micro-LEDs on the display substrate. In certain embodiments, the display substrate is transparent and/or flexible.
1. A method of forming a display, the method comprising:
depositing a first metal layer on and in direct contact with a surface of a display substrate;
patterning the first metal layer to form a first patterned metal layer;
depositing a layer of dielectric on and in direct contact with the first patterned metal layer to create an electrically insulating layer;
applying an uncured polymer layer on and in direct contact with the dielectric layer, the uncured polymer layer comprising a material different from the dielectric layer;
micro-transfer printing a plurality of light emitters from a native substrate onto and in direct contact with a surface of the uncured polymer layer, wherein the native substrate is native to at least a portion of the plurality of light emitters and the light emitters each have an anode and a cathode for providing power to the light emitters;
exposing the polymer to ultraviolet light to cure the polymer;
forming a plurality of vias through the cured polymer and dielectric layer to expose a portion of the first patterned metal layer;
depositing a second metal layer, wherein the second metal layer contacts an anode and a cathode of each light emitter of the plurality of light emitters; and
patterning the second metal layer to form the second patterned metal layer, wherein the second patterned metal layer comprises a plurality of anode interconnections and a plurality of cathode interconnections, each anode interconnection electrically connecting the anode of a corresponding light emitter of the plurality of light emitters to the first patterned metal layer through a corresponding via of the plurality of vias and each cathode interconnection electrically contacting the cathode of a corresponding light emitter of the plurality of light emitters.
2. The method of claim 1 , wherein the plurality of light emitters comprises a plurality of inorganic light emitting diodes.
3. The method of claim 1 , comprising:
cutting the display substrate into a plurality of displays.
4. The method of claim 3 , comprising:
prior to cutting the non-native wafer into the plurality of displays, coating the wafer with a protective photoresist layer; and
after cutting the display substrate into the plurality of displays, removing the protective photoresist layer from each display of the plurality of displays after cutting the display substrate into the plurality of displays.
5. The method of claim 1 , comprising:
providing a passive-matrix driver integrated circuit on receiving pads on a surface of the non-native wafer.
6. The method of claim 1 , comprising:
burning-in each light emitter of the plurality of light emitters.
7. The method of claim 1 , wherein the anode and cathode of a respective light emitter are horizontally separate by a horizontal distance, wherein the horizontal distance is 100 nm to 100 microns.
8. The method of claim 7 , comprising removing one or more solvents from the polymer using one or more heat treatments.
9. The method of claim 7 , wherein micro-transfer printing the plurality of light emitters comprises micro-transfer printing the plurality of light emitters using a print tool.
10. The method of claim 9 , wherein the print tool comprises a viscoelastic elastomer stamp.
11. The method of claim 1 , wherein the polymer is a photosensitive negative-acting semiconductor-grade epoxy.
12. The method of claim 1 , wherein the first metal layer is deposited using metal physical vapor deposition.
13. The method of claim 1 , wherein the first metal layer is patterned using photolithography.
14. The method of claim 1 , wherein patterning the first metal layer comprises:
prior to depositing the first metal layer, applying a negative-acting photoresist to the first metal layer, selectively exposing the photoresist to light, and developing the photoresist to form a lift-off template; and
after depositing the first metal layer, removing the lift-off template, thereby forming the first patterned metal layer.
15. The method of claim 1 , wherein the first metal layer comprises a metal stack of Titanium on Aluminum on Titanium.
16. The method of claim 1 , wherein depositing the first metal layer comprises depositing the first metal layer using e-beam evaporation.
17. The method of claim 1 , wherein patterning the second metal layer comprises:
patterning a lift-off mask in a negative acting photoresist;
depositing a metal stack; and
lifting-off of the photoresist mask to leave behind the second patterned metal layer.
18. The method of claim 1 , wherein the second metal layer comprises a metal stack.
19. The method of claim 18 , wherein the metal stack comprises Ti/Al/Ti.
20. The method of claim 1 , wherein micro-transfer printing the plurality of light emitters comprises using kinetically tunable adhesion between the plurality of light emitters and the viscoelastic elastomer surface.
21. The method of claim 1 , wherein micro-transfer printing the plurality of light emitters comprises:
picking up at least a portion of the plurality of light emitters from the native substrate by contacting a viscoelastic elastomer stamp to a first surface of each of the light emitters in the portion of the plurality of light emitters and moving the viscoelastic elastomer stamp away from the native substrate at a first rate leading to an effective increase in the adhesion between the elastomer and the portion of the plurality of light emitters; and
printing the portion of the plurality of light emitters to the non-native substrate by contacting a second surface of each of the light emitters picked up by the viscoelastic elastomer stamp to the polymer and moving the viscoelastic elastomer stamp away from the display substrate at a second rate, thereby leaving the light emitters picked up by the viscoelastic elastomer stamp on the polymer, wherein the second rate is less than the first rate.
22. The method of claim 1 , comprising laterally shearing the stamp during the micro transfer printing process.
23. The method of claim 1 , wherein the plurality of light emitters comprises a plurality of red light emitters that emit red light, a plurality of green light emitters that emit green light, and a plurality of blue light emitters that emit blue light.
24. The method of claim 1 , wherein the resolution of the display is 120×90, 1440×1080, 1920×1080, 1280×720, 3840×2160, 7680×4320, or 15360×8640.
25. The method of claim 1 , wherein micro-transfer printing the plurality of light emitters from a native substrate onto the polymer comprises performing at least two micro transfer printing operations.
26. The method of claim 1 , wherein micro-transfer printing the plurality of light emitters from a native substrate onto the polymer comprises:
micro-transfer printing a plurality of red light emitters that emit red light from a red light emitter native substrate;
micro-transfer printing a plurality of green light emitters that emit green light from a green light emitter native substrate; and
micro-transfer printing a plurality of blue light emitters that emit blue light from a blue light emitter native substrate, wherein the plurality of light emitters comprises the plurality of red light emitters, the plurality of green light emitters, and the plurality of blue light emitters.
27. The method of claim 1 , wherein the display substrate is flexible.