Low index spacer layer in LED devices

• US 20090236621A1
• Filed: 03/19/2008
• Published: 09/24/2009
• Est. Priority Date: 03/19/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chakraborty, Arpan
• Granted Patent: US 8,637,883 B2
• Time in Patent Office: Days
• US Class Current: 257/95
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/507 the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body

Abstract

A light emitting diode (LED) device having a low index of refraction spacer layer separating the LED chip and a functional layer. The LED chip has a textured light emission surface to increase light extraction from the chip. The spacer layer has an index of refraction that is lower than both the LED chip and the functional layer. Most of the light generated in the LED chip passes easily into the spacer layer due to the textured surface of the chip. At the interface of the spacer layer and the functional layer the light sees a step-up in index of refraction which facilitates transmission. A portion of the light that has passed into the functional layer will be reflected or scattered back toward the spacer layer where some of it will experience total internal reflection. Total internal reflection at this interface may increase extraction efficiency by reducing the amount of light that re-enters the spacer layer and, ultimately, the LED chip where it may be absorbed. The spacer layer also provides a thermal buffer between the LED chip and the functional layer. Thus, the functional layer, which may be a wavelength conversion layer comprising phosphors, for example, is insulated from direct thermal transfer from the LED chip. The spacer layer can also function as a passivation layer.

Claims

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

an LED chip disposed on a mount surface, said LED chip having a textured light emission surface and a first index of refraction;

a spacer layer disposed on said LED chip and covering said light emission surface, said spacer layer having a second index of refraction that is smaller than said first index of refraction; and

at least one functional layer disposed on said spacer layer.

2. The LED device of claim 1, said at least one functional layer comprising a wavelength conversion layer.

3. The LED device of claim 2, said wavelength conversion layer comprising:

a binder material having a third index of refraction that is larger than said second index of refraction; and

a plurality of phosphor particles distributed throughout said binder material.

4. The LED device of claim 3, wherein said second index of refraction is approximately 1.5 and said third index of refraction is approximately 1.8.

5. The LED device of claim 2, said wavelength conversion layer comprising a single crystalline phosphor material.

6. The LED device of claim 2, said wavelength conversion layer comprising a nano-crystalline phosphor dispersed throughout a binder material.

7. The LED device of claim 2, said at least one functional layer further comprising a filter layer that is transmissive to light of a first range of wavelengths and reflective to light of a second range of wavelengths, wherein said filter layer is interposed between said spacer layer and said wavelength conversion layer.

8. The LED device of claim 2, wherein said LED chip is configured to emit blue light and said wavelength conversion layer is configured to convert a portion of said blue light into yellow light such that said LED device emits said blue and yellow light in a combination that appears white.

9. The LED device of claim 2, wherein said at least one functional layer comprises a light scattering element.

10. The LED device of claim 9, wherein said light scattering element comprises light scattering particles.

11. The LED device of claim 1, wherein said spacer layer comprises a substantially planar surface opposite said LED chip.

12. The LED device of claim 1, wherein said functional layer comprises an anti-reflective coating layer.

13. The LED device of claim 1, wherein said spacer layer has a thickness of approximately 1-25 micrometers.

14. The LED device of claim 1, further comprising a hemispherical encapsulant disposed on said mount surface and covering said LED chip.

15. The LED device of claim 14, said encapsulant having an index of refraction of approximately 1.5.

16. The LED device of claim 1, wherein said mount surface is reflective.

17. The LED device of claim 1, wherein said LED chip comprises aluminum gallium indium nitride (AlGaInN) semiconductor layers.

18. The LED device of claim 1, wherein said spacer layer thermally insulates said functional layer from said LED chip.

19. The LED device of claim 1, wherein said spacer layer passivates said LED chip.

20. The LED device of claim 1, said LED chip comprising a reflective element disposed opposite said textured light emission surface.

30. The LED device of claim 18, said LED chip comprising a reflective element opposite said textured light emission surface.

21. A light emitting diode (LED) device, comprising:

an LED chip disposed on a mount surface and having a textured light emission surface and a first index of refraction, said LED emitting blue light;

a spacer layer disposed on said LED chip and covering said light emission surface, said spacer layer having a planar surface opposite said LED chip and a second index of refraction that is smaller than said first index of refraction;

a wavelength conversion layer disposed on said spacer layer, said wavelength conversion layer converting a portion of said blue light and emitting yellow light; and

an encapsulant disposed on said mount surface and covering said LED chip;

wherein said light emitting diode (LED) device is constructed to emit a combination of said blue and yellow light such that said combination appears white.

22. The LED device of claim 21, further comprising a filter layer that is transmissive to light of a first range of wavelengths and reflective to light of a second range of wavelengths, wherein said filter layer is interposed between said spacer layer and said wavelength conversion layer.

23. The LED device of claim 21, said wavelength conversion layer comprising:

a silicone binder material having a third index of refraction that is larger than said second index of refraction; and

a plurality of phosphor particles distributed throughout said binder material.

24. The LED device of claim 23, wherein said third index of refraction is approximately 1.8.

25. The LED device of claim 21, wherein said first index of refraction is approximately 2.5.

26. The LED device of claim 21, wherein said second index of refraction is approximately 1.5.

27. The LED device of claim 21, wherein said spacer layer has a thickness of approximately 1-25 micrometers.

28. The LED device of claim 21, said wavelength conversion layer comprising light scattering particles.

29. The LED device of claim 21, said encapsulant comprising light scattering particles.

31. The LED device of claim 21, wherein said LED chip comprises aluminum gallium indium nitride (AlGaInN) semiconductor layers.

32. The LED device of claim 21, wherein said spacer layer thermally insulates said wavelength conversion layer from said LED chip.

33. A method of fabricating a light emitting diode (LED) device, comprising:

providing an LED chip having a first index of refraction and a textured light emission surface;

disposing a spacer layer with a second index of refraction on said LED chip, wherein said second index of refraction is smaller than said first index of refraction;

disposing a functional layer with a third index of refraction on said spacer layer, wherein said second index of refraction is smaller than said third index of refraction, and said second index of refraction is chosen to maximize light extraction efficiency.

34. The method of claim 33, wherein said function layer comprises a wavelength conversion layer.

35. The method of claim 33, further comprising dispersing light scattering particles throughout said functional layer.

36. The method of claim 33, further comprising encapsulating said LED chip with an encapsulant.

37. The method of claim 36, further comprising dispersing light scattering particles throughout said encapsulant.

38. The method of claim 33, wherein said spacer layer has a thickness of approximately 1-25 micrometers.

39. The method of claim 33, wherein said second index of refraction is approximately 1.5 and said third index of refraction is approximately 1.8.

40. The method of claim 33, wherein said LED chip comprises aluminum gallium indium nitride (AlGaInN) semiconductor layers.