Process flow for hybrid TFT-based micro display projector
Disclosed herein are techniques for forming a thin-film circuit layer on an array of light-emitting diodes (LEDs). LEDs in the array of LEDs can be singulated by various processes, such as etching and ion implantation. Singulating LEDs can be performed before or after forming the thin-film circuit layer on the array of LEDs. The array of LEDs can be bonded to a transparent or non-transparent substrate.
1. A method comprising:
obtaining an epitaxial structure, wherein the epitaxial structure is a layered structure including a first doped semiconductor layer, a second doped semiconductor layer, and a light-emitting layer between the first doped semiconductor layer and the second doped semiconductor layer;
applying a thin-film circuit layer to the epitaxial structure;
isolating portions of the first doped semiconductor layer, portions of the second doped semiconductor layer, or portions of both the first doped semiconductor layer and the second doped semiconductor layer for forming a plurality of light emitting diodes (LEDs);
bonding the thin-film circuit layer to a transparent substrate after applying the thin-film circuit layer to the epitaxial structure; and
bonding a backplane to the transparent substrate, wherein:
the backplane is electrically coupled with the thin-film circuit layer; and
the thin-film circuit layer and the backplane are on a same side of the transparent substrate.
2. The method of claim 1 , wherein isolating portions of the first doped semiconductor layer, portions of the second doped semiconductor layer, or portions of both the first doped semiconductor layer and the second doped semiconductor layer for forming a plurality of LEDs is performed before or after applying the thin-film circuit layer to the epitaxial structure.
3. The method of claim 1 , wherein isolating portions of the first doped semiconductor layer, portions of the second doped semiconductor layer, or portions of both the first doped semiconductor layer and the second doped semiconductor layer for forming a plurality of LEDs comprises etching or implanting ions in the first doped semiconductor layer, the second doped semiconductor layer, or both the first doped semiconductor layer and the second doped semiconductor layer.
4. The method of claim 1 , wherein:
the transparent substrate includes a plurality of traces that are transparent and conductive; and
bonding the thin-film circuit layer to the transparent substrate includes bonding the thin-film circuit layer to the plurality of traces, wherein each trace of the plurality of traces is electrically connected to a group of LEDs of the plurality of LEDs through the thin-film circuit layer.
5. The method of claim 4 , wherein:
the transparent substrate includes a plurality of pads, each pad of the plurality of pads electrically coupled to a trace of the plurality of traces; and
bonding the backplane to the transparent substrate includes bonding the backplane to the plurality of pads.
6. The method of claim 1 , wherein bonding the backplane to the transparent substrate includes bonding one or more backplanes to one, two, three, or more sides of the plurality of LEDs.
7. The method of claim 1 , wherein bonding the backplane to the transparent substrate includes bonding one or more backplanes to one or more peripheral regions of the transparent substrate such that the one or more backplanes are not in a field of view of a user.
8. The method of claim 1 , wherein applying the thin-film circuit layer to the epitaxial structure comprises:
depositing a thin-film layer on the epitaxial structure; and
forming, in the thin-film layer, a plurality of transistors for controlling operations of the plurality of LEDs.
9. The method of claim 1 , further comprising forming light extraction elements on the epitaxial structure to couple light out of the light-emitting layer.
10. The method of claim 1 , further comprising, after isolating portions of the first doped semiconductor layer, portions of the second doped semiconductor layer, or portions of both the first doped semiconductor layer and the second doped semiconductor layer for forming the plurality of LEDs:
forming a passivation layer on sidewalls of the plurality of LEDs; and
forming a metal reflector layer on the passivation layer.
11. An apparatus comprising:
a transparent substrate;
a plurality of light emitting diodes (LEDs);
a thin-film circuit layer comprising a plurality of transistors electrically coupled with the plurality of LEDs, wherein:
the plurality of transistors is configured to control operations of the plurality of LEDs; and
the thin-film circuit layer is physically bonded to the transparent substrate; and
a backplane physically bonded to the transparent substrate, wherein:
the backplane is electrically coupled with the thin-film circuit layer; and
the backplane is on a same side of the transparent substrate as the thin-film circuit layer.
12. The apparatus of claim 11 , further comprising a frame of an augmented-reality system, the frame holding the plurality of LEDs, wherein the plurality of LEDs is part of a display for the augmented-reality system.
13. The apparatus of claim 11 , further comprising a trace in the thin-film circuit layer or on the transparent substrate, the trace electrically coupling a pad on the transparent substrate to multiple transistors of the plurality of transistors for controlling operations of multiple LEDs of the plurality of LEDs.
14. The apparatus of claim 13 , wherein the backplane is bonded to the pad on the transparent substrate.
15. The apparatus of claim 13 , wherein the trace includes indium tin oxide (ITO).
16. The apparatus of claim 11 , wherein the backplane includes one or more backplanes at one, two, three, or more sides of the plurality of LEDs.
17. The apparatus of claim 11 , wherein the backplane includes one or more backplanes bonded to one or more peripheral regions of the transparent substrate such that the one or more backplanes are not in a field of view of a user of the apparatus.
18. The apparatus of claim 11 , further comprising light extraction elements on the plurality of LEDs and configured to couple light out of the plurality of LEDs.
19. The apparatus of claim 11 , wherein the thin-film circuit layer and the backplane, alone or in combination, include a multiplexor, memory circuits, modulation circuits, or a combination thereof.
20. The apparatus of claim 11 , wherein each LED of the plurality of LEDs includes:
a mesa structure including a first doped semiconductor layer, a second doped semiconductor layer, and a light-emitting layer between the first doped semiconductor layer and the second doped semiconductor layer;
a passivation layer on sidewalls of the mesa structure; and
a metal reflector layer on the passivation layer.