Package-integrated thin film LED
View Patent ↗LED epitaxial layers (n-type, p-type, and active layers) are grown on a substrate. For each die, the n and p layers are electrically bonded to a package substrate that extends beyond the boundaries of the LED die such that the LED layers are between the package substrate and the growth substrate. The package substrate provides electrical contacts and conductors leading to solderable package connections. The growth substrate is then removed. Because the delicate LED layers were bonded to the package substrate while attached to the growth substrate, no intermediate support substrate for the LED layers is needed. The relatively thick LED epitaxial layer that was adjacent the removed growth substrate is then thinned and its top surface processed to incorporate light extraction features. There is very little absorption of light by the thinned epitaxial layer, there is high thermal conductivity to the package because the LED layers are directly bonded to the package substrate without any support substrate therebetween, and there is little electrical resistance between the package and the LED layers so efficiency (light output vs. power input) is high. The light extraction features of the LED layer further improves efficiency.
1. A method comprising:
growing light emitting diode (LED) layers on a growth substrate, the LED layers comprising a first epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type, and an active layer disposed between the first and second epitaxial layers, wherein a primary emission surface on a first side of the first epitaxial layer is substantially parallel tothe active layer, the LED layers forming at least one individual LED;
providing a package substrate wherein a lateral extent of the package substrate exceeds that of an individual LED, the package substrate comprising a support surface having one or more electrical contact pads thereon for electrical connection to the first and second epitaxial layers, the contact pads being electrically connected to metal leads for connection to package terminals;
placing the LED layers attached to the growth substrate on the package substrate such the second epitaxial layer is facing a first contact pad on the package substrate;
bonding the second epitaxial layer to the first contact pad using a metal interface disposed between the package substrate and the second epitaxial layer, wherein a nearest distance between the primary emission surface and a portion of the package substrate is not more than 50 microns;
removing the growth substrate; and
further processing the LED layers after the growth substrate has been removed, wherein further processing the LED layers comprises forming at least one light extraction feature in the primary emission surface.
2. The method of claim 1 wherein the growth substrate is sapphire, and removing the growth substrate comprises performing a laser liftoff process.
3. The method of claim 1 wherein the growth substrate comprises silicon, and removing the growth substrate comprises performing an etching process.
4. The method of claim 1 wherein the LED layers comprise AlInGaP, and the growth substrate comprises GaAs or Ge.
5. The method of claim 1 further comprising mounting the LED portion and package substrate in a housing surrounding the LED portion and package substrate, and electrically connecting metal leads extending from the housing to contact areas on the package substrate.
6. The method of claim 1 wherein placing the LED layers comprises placing a plurality of LEDs on the package substrate.
7. The method of claim 1 further comprising:
depositing a protective layer over the package substrate after the LED layers have been placed on the package substrate to protect the package substrate; and
etching a portion of the first epitaxial layer.
8. The method of claim 7 wherein etching a portion of the first epitaxial layer comprising etching at least 50% of the thickness of the first epitaxial layer.
9. The method of claim 1 further comprising providing an electrical connector between the first epitaxial layer and a contact pad on the package substrate.
10. The method of claim 9 wherein the electrical connector is a wire.
11. The method of claim 9 wherein the electrical connector is a metal bridge.
12. The method of claim 9 wherein the LED is a flip-chip, wherein providing the electrical connector comprises bonding the first epitaxial layer to a contact pad on the package substrate.
13. The method of claim 1 further comprising dicing the package substrate after the growth substrate has been removed, each package substrate die having one or more LEDs mounted on it.
14. The method of claim 1 wherein growing LED layers comprises growing gallium-nitride based LED layers.
15. The method of claim 1 further comprising dicing the LED layers and growth substrate prior to placing the LED layers on the package substrate.
16. The method of claim 1 wherein placing the LED layers on the package substrate comprises placing the LED layers on the package substrate prior to dicing the LED layers and the growth substrate, wherein removing the growth substrate comprises removing the entire growth substrate intact, and further comprising dicing the package substrate after removing the growth substrate.
17. The method of claim 1 wherein the first epitaxial layer comprises a plurality of epitaxial layers of the first conductivity type, and wherein the second epitaxial layer comprises a plurality of epitaxial layers of the second conductivity type.
18. The method of claim 1 further comprising etching the first epitaxial layer after removing the growth substrate, such that the LED layers have a thickness less than 3 microns.
19. The method of claim 1 further comprising etching the first epitaxial layer after removing the growth substrate, such that the LED layers have a thickness less than 10 microns.
20. The method of claim 1 wherein further processing the LED layers comprises forming light extraction features in the primary emission surface.
21. The method of claim 20 wherein forming light extraction features consists of roughening the primary emission surface, patterning the primary emission surface, dimpling the primary emission surface, or forming a photonic crystal.
22. The method of claim 1 wherein further processing the LED layers comprises thinning the first epitaxial layer.
23. The method of claim 1 further comprising providing an underfill between the LED layers and the package substrate.
24. The method of claim 23 wherein said providing an underfill occurs prior to removing the growth substrate.
25. The method of claim 1 further comprising disposing a wavelength converting layer in a path of light emitted from the primary emission surface.
26. A method comprising:
providing a growth substrate comprising a first layer connected to a second layer;
growing light emitting diode (LED) layers on the first layer of the growth substrate, the LED layers comprising a first epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type, and an active layer disposed between the first and second epitaxial layers, and
bonding the LED layers to a package substrate; and
removing at least a portion of the growth substrate by wet etching.
27. The method of claim 26 wherein the first layer is SiC.
28. The method of claim 26 wherein the second layer is an insulator.
29. The method of claim 28 wherein removing at least a portion of the growth substrate by wet etching comprises etching away the second layer.
30. The method of claim 29 further comprising after etching away the second layer, removing off the first layer.
31. The method of claim 26 wherein a nearest distance between a primary emission surface of the LED layers and a surface of the package substrate is not more than 50 microns, and wherein a lateral extent of the package substrate exceeds that of the LED layers.
32. The method of claim 26 wherein a lateral extent of the package substrate exceeds that of the LED layers.