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 light emitting device comprising:
a light emitting diode (LED) portion comprising:
a first epitaxial layer of a first conductivity type;
a second epitaxial layer of a second conductivity type;
an active layer disposed between the first and second epitaxial layers;
a primary emission surface on a first side of the first epitaxial layer substantially parallel to the active layer;
a package substrate on which the LED portion is mounted; and
a metal interface, disposed between the package substrate and the second epitaxial layer, electrically connecting a conductor on the package substrate to the second epitaxial layer with no support substrate therebetween;
wherein a nearest distance between the primary emission surface and a portion of the package substrate is not more than 50 microns, a lateral extent of the package substrate exceeds that of the LED portion and that of the metal interface, and the primary emission surface incorporates a light extraction feature.
2. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises a solder bond between the metal layer and the conductor on the package.
3. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises an ultrasonic weld of the metal layer to the conductor on the package.
4. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises a thermocompression bond of the metal layer to the conductor on the package.
5. The device of claim 1 further comprising a metal layer deposited over the second epitaxial layer, wherein the metal interface comprises an interdiffusion bond of the metal layer to the conductor on the package.
6. The device of claim 1 further comprising an electrical connector between the first epitaxial layer and a contact pad on the package substrate.
7. The device of claim 6 wherein the electrical connector is a wire.
8. The device of claim 7 wherein the electrical connector is a wire ribbon.
9. The device of claim 6 wherein the electrical connector is a metal bridge.
10. The device of claim 6 wherein the LED is a flip-chip, and wherein the electrical connector comprises a metal bond bonding the first epitaxial layer to a contact pad on the package substrate.
11. The device of claim 1 wherein the LED is a flip-chip, and the metal interface is formed in a pattern.
12. The device of claim 1 wherein the LED is formed of gallium-nitride or gallium phosphide based materials.
13. The device of claim 1 further comprising a plurality of LED portions on the package substrate, each LED portion being grown on a growth substrate having its growth substrate removed and having no support substrate other than the package substrate.
14. The device of claim 1 further comprising a plurality of LED portions on the package substrate, each LED portion being grown on a growth substrate, having its growth substrate removed and having no support substrate other than the package substrate, the plurality of LEDs being arranged in groups of arrays.
15. The device 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.
16. The device of claim 1 further comprising a phosphor over the LED portion.
17. The device of claim 16 wherein the phosphor is formed by electro-phoretic deposition.
18. The device of claim 16 wherein the phosphor is formed by screen printing.
19. The device of claim 1 further comprising an optical element over the LED portion.
20. The device of claim 1 wherein the package substrate is thermally conductive to act as a heat sink for the LED portion.
21. The device of claim 1 wherein the LED layers have a thickness less than 3 microns.
22. The device of claim 1 wherein the LED layers have a thickness less than 10 microns.
23. The device of claim 1 further comprising a housing surrounding the LED portion and package substrate, the housing containing metal leads extending from the housing and electrically coupled to the package substrate.
24. The device of claim 1 further comprising an underfill disposed between the LED portion and the package substrate.
25. The device of claim 1 further comprising a photonic crystal formed in at least a portion of the primary emission surface.
26. The device of claim 1 further comprising a lens disposed over the LED portion.
27. The device of claim 1 further comprising a mirror stack disposed over the primary emission surface.
28. The device of claim 1 wherein:
the first epitaxial layer, active layer, and second epitaxial layer are grown over a growth substrate; and
the growth substrate is removed from the LED portion.
29. The device of claim 28 wherein the first epitaxial layer has been thinned after the growth substrate has been removed and after the LED portion has been mounted on the package substrate.
30. The device of claim 1 wherein the light extraction feature comprises a rough surface.
31. The device of claim 1 wherein the light extraction feature comprises a patterned surface.
32. The device of claim 1 further comprising an underfill disposed between the LED portion and the package substrate.
33. A light emitting device comprising:
a light emitting diode (LED) portion comprising:
a first epitaxial layer of a first conductivity type;
a second epitaxial layer of a second conductivity type;
an active layer disposed between the first and second epitaxial layers;
a primary emission surface on a first side of the first epitaxial layer substantially parallel to the active layer;
a package substrate on which the LED portion is mounted;
a metal interface, disposed between the package substrate and the second epitaxial layer, electrically connecting a conductor on the package substrate to the second epitaxial layer with no support substrate therebetween; and
a wavelength converting layer over the LED portion;
wherein a nearest distance between the primary emission surface and a portion of the package substrate is not more than 50 microns, and wherein a lateral extent of the package substrate exceeds that of the LED portion and that of the metal interface.
34. The device of claim 33 wherein the wavelength converting layer comprises a phosphor layer.
35. The device of claim 33 wherein the LED is mounted as a flip-chip.
36. The device of claim 33 wherein the LED is formed of gallium-nitride or gallium phosphide based materials.
37. The device of claim 33 further comprising an optical element over the LED portion.
38. The device of claim 33 wherein the package substrate is thermally conductive to act as a heat sink for the LED portion.
39. The device of claim 33 wherein the LED layers have a thickness less than 3 microns.
40. The device of claim 33 wherein the LED layers have a thickness less than 10 microns.