Composite high reflectivity layer

• US 8,680,556 B2
• Filed: 03/08/2012
• Issued: 03/25/2014
• Est. Priority Date: 03/24/2011
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Ibbetson, James, Keller, Bernd, Li, Ting
• Primary Examiner(s): YUSHIN, NIKOLAY K
• Application Number:
  US13/415,626
• Publication Number:
  US 20120280263A1
• Time in Patent Office: 747 Days
• Field of Search: 257/98, 257/99, 257/100, 438/22, 438/26, 438/29
• US Class Current: 257/98
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0061 the light source comprising a LED semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission H01L33/00
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/48 characterised by the semiconductor body packages
• CPC Class Codes: H01L 33/56 Materials, e.g. epoxy or silicone resin

Abstract

A high efficiency light emitting diode with a composite high reflectivity layer integral to said LED or package to improve emission efficiency. One embodiment of a light emitting diode (LED) chip comprises a LED and a composite high reflectivity layer integral to the LED to reflect light emitted from the active region. One embodiment of a LED package comprises a LED mounted on a substrate with an encapsulant over said LED and a composite high reflectivity layer arranged to reflect emitted light. The composite layer comprises a plurality of layers such that at least one of said plurality of layers has an index of refraction lower than the encapsulant and a reflective layer on a side of said plurality of layers opposite the LED. In some embodiments, conductive vias are included through the composite layer to allow an electrical signal to pass through the layer to the LED.

Claims

1. A light emitting diode (LED) package, comprising:

an LED mounted on a substrate;

an encapsulant over said LED; and

a composite high reflectivity layer arranged to reflect light emitted from said LED, said composite high reflectivity layer comprising;

a plurality of layers such that at least one of said plurality of layers has an index of refraction lower than said encapsulant, wherein said plurality of layers comprises a dielectric material; and

a reflective layer on a side of said plurality of layers opposite said LED.

2. The LED package of claim 1, wherein said plurality of layers comprise first and second layers.

3. The LED package of claim 2, wherein said first layers have an index of refraction different from said second layers.

4. The LED package of claim 2, wherein said first and second layers alternate, and each of said second layers having different thicknesses compared to the other of said second layers.

5. The LED package of claim 2, wherein said one or more first layers comprises two layers having different thicknesses.

6. The LED package of claim 2, wherein said one or more first layers comprises one layer between said plurality of second layers.

7. The LED package of claim 2, wherein said one or more first layers and said plurality of second layers comprise incomplete first and second layer pairs.

8. The LED package of claim 1, further comprising an adhesion layer between said plurality of layers and said reflective layer.

9. The LED package of claim 1, wherein said reflective layer is on said substrate.

10. The LED package of claim 9, further comprising an adhesion layer between said reflective layer and said substrate.

11. The LED package of claim 1, wherein said composite high reflectivity layer further comprises conductive vias.

12. The LED package of claim 1, further comprising conductive traces to provide an electrical connection to said LED.

13. The LED package of claim 12, wherein said conductive traces at least partially pass over said composite high reflectivity layer.

14. The LED package of claim 1, further comprising wire bonds to provide an electrical connection to said LED.

15. The LED package of claim 14, wherein said wire bonds at least partially pass over said composite high reflectivity layer.

16. The LED package of claim 1, wherein said composite high reflectivity layer formed such that stress is reduced between each of said plurality of layers and reflective layer.

17. The LED package of claim 1, wherein the reflectivity of said composite high reflectivity layer is approximately 100%.

18. The LED package of claim 1, wherein the reflectivity of said composite high reflectivity layer is greater than the reflectivity of a similarly situated Ag layer.

19. The LED package of claim 1, wherein said composite high reflectivity layer comprises an angle averaged reflectivity greater than a quarter wavelength distributed Bragg reflector having the same number of layers.

20. The LED package of claim 1, wherein said composite high reflectivity layer is internal to said LED package.

21. The LED package of claim 1, wherein said at least one of said plurality of layers with an index of refraction lower than said encapsulant has a thickness of at least 0.25 μ

m.

22. The LED package of claim 1, wherein said composite high reflectivity layer is optically smooth.

23. The LED package of claim 1, further comprising a thermal path between said LED and said substrate.

24. A method for fabricating a light emitting diode (LED) package, comprising:

providing a substrate;

providing an LED;

providing a composite high reflectivity layer, arranged to reflect light emitted from said LED, on said substrate, wherein said composite high reflectivity layer comprises a plurality of layers and a reflective layer, wherein said plurality of layers comprises a dielectric material;

mounting said LED on said composite high reflectivity layer; and

providing an encapsulant over said LED.

25. The method of claim 24 wherein providing said composite high reflectivity layer further comprises:

providing said reflective layer on said substrate; and

providing said plurality of layers over said reflective layer such that at least one of said plurality of layers has an index of refraction lower than said encapsulant.

26. The method of claim 25, wherein said plurality of layers comprise first and second layers.

27. The method of claim 26, wherein said first layers have an index of refraction different from said second layers.

28. The method of claim 26, wherein said first and second layers alternate, and each of said second layers having different thicknesses compared to the other of said second layers.

29. The method of claim 25, further comprising providing an adhesion layer between said plurality of layers and said reflective layer.

30. The method of claim 25, further comprising providing an adhesion layer between said reflective layer and said substrate.

31. The method of claim 25, wherein providing said composite high reflectivity layer further comprises reducing layer stress between each of said plurality of layers and reflective layer.

32. The method of claim 26, wherein said one or more first layers comprises two layers having different thicknesses.

33. The method of claim 26, wherein said one or more first layers comprises one layer between said plurality of second layers.

34. The method of claim 26, wherein said one or more first layers and said plurality of second layers comprise incomplete first and second layer pairs.

35. The method of claim 24, further comprising providing an at least one conductive via within said composite high reflectivity layer.

36. The method of claim 24, further comprising providing an at least one conductive trace to provide an electrical connection to said LED.

37. The method of claim 36, wherein said conductive trace at least partially passes over said composite high reflectivity layer.

38. The method of claim 24, further comprising providing an at least one wire bond to provide an electrical connection to said LED.

39. The method of claim 38, wherein said wire bonds at least partially pass over said composite high reflectivity layer.

40. The method of claim 24, wherein the reflectivity of said composite high reflectivity layer is approximately 100%.

41. The method of claim 24, wherein the reflectivity of said composite high reflectivity layer is greater than the reflectivity of a similarly situated Ag layer.

42. The method of claim 24, wherein said composite high reflectivity layer comprises an angle averaged reflectivity greater than a quarter wavelength distributed Bragg reflector having the same number of layers.

43. The method of claim 24, wherein said composite high reflectivity layer is internal to said LED package.

44. The method of claim 24, wherein said at least one of said plurality of layers with an index of refraction lower than said encapsulant has a thickness of at least 0.25 μ

m.

45. The method of claim 24, wherein said composite high reflectivity layer is provided such that it is optically smooth.

46. The method of claim 24, further comprising providing a thermal path between said LED and said substrate.