Color correction for wafer level white LEDs

• US 7,897,419 B2
• Filed: 12/23/2008
• Issued: 03/01/2011
• Est. Priority Date: 12/23/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Donofrio, Matthew
• Primary Examiner(s): Picardat; Kevin M
• Application Number:
  US12/317,528
• Publication Number:
  US 20100155750A1
• Time in Patent Office: 798 Days
• Field of Search: 438/22, 438/26, 438/27, 438/28, 438/29, 438/39, 257/79, 257/88, 257/89, 257/98, 257/99, 257/100
• US Class Current: 438/27
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/005 Processes
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/508 having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material

Abstract

A method for fabricating a plurality of LED chips comprises providing a plurality of LEDs and forming a plurality of spacers each of which is on at least one of the LEDs. Coating the LEDs with a conversion material, each of the spacers reducing the amount of conversion material over its one of the LEDs. This reduction causes the plurality of LED chips to emit a wavelength of light in response to an electrical signal that is within a standard deviation of a target wavelength. LEDs, LED chips and LED chip wafers are fabricated using the method according to the present invention. One embodiment of an LED chip wafer according to the present invention comprises a plurality of LEDs on a wafer and a plurality of a spacers, each of which is on a respective one of the LEDs. A conversion material at least partially covers the LEDs and spacers, with at least some light from the LEDs passing through the conversion material and is converted. The spacers cause the LED chips to emit light having a wavelength within a standard deviation compared to the similar LED chips without the spacers where at least some of the LED chips emit light a wavelength of light outside the standard deviation.

Claims

1. A method for fabricating a plurality light emitting diode (LED) chips, comprising:

providing a plurality of LEDs;

forming a plurality of spacers each of which is on at least one of said LEDs;

coating said LEDs with a conversion material, each of said spacers reducing the amount of conversion material over its one of said LEDs such that each of said plurality of LED chips emits a wavelength of light in response to an electrical signal, said wavelength being within a standard deviation of a target wavelength.

2. The method of claim 1, wherein the volume of each said spacer over its one of said LEDs is related to the emission wavelength of its one of said LEDs and said target wavelength.

3. The method of claim 1, wherein said spacer comprises a material that is substantially transparent to light from said LEDs.

4. The method of claim 1, wherein said standard deviation comprises a MacAdam ellipses.

5. The method of claim 1, wherein said standard deviation corresponds to a chromaticity region on a CIE curve.

6. The method of claim 1, wherein light from each of said LED chips comprises emission from said conversion material and said LED.

7. The method of claim 1, wherein said LED chips emit white light.

8. The method of claim 1, wherein said conversion material comprises a phosphor.

9. The method of claim 1, wherein said conversion material coating comprises a phosphor in a binder.

10. The method of claim 1, further comprising measuring the emission characteristics of at least some of said LEDs prior to forming said spacer, said emission characteristics of each of said LEDs determining the volume of said spacer on that one of the LEDs.

11. The method of claim 1, wherein the volume of each of said spacers corresponds to the amount of reduction of said conversion material to cause said LED chip to emit a wavelength within said standard deviation.

12. The method of claim 1, wherein said plurality of LEDs are provided on a wafer and said LED chips are formed from said wafer.

13. The method of claim 1, further comprising singulating said LEDs from said wafer as individual LED chips or groups of LED chips.

14. The method of claim 1, further comprising planarizing said coating over said LEDs.

15. The method of claim 1, wherein one of said spacers is on a plurality of LEDs.

16. The method of claim 1, wherein each of said spacers can comprise a shape from the group consisting of uniform layer, non-uniform layer, conical, pyramid, hemispheric and columned.

17. A light emitting diode (LED) chip wafer, comprising:

a plurality of LEDs on a wafer;

a plurality of a spacers, each of with is on a least one of said LEDs; and

a conversion material at least partially covering said LEDs and spacers, with at least some light from said LEDs passing through said conversion material and is converted, wherein said spacers cause said LED chips to emit light having a wavelength within a standard deviation compared to the similar LED chips without said spacers where at least some LED chips emit light having a wavelength outside said standard deviation.

18. The LED chip wafer of claim 17, wherein the volume of each said spacer over said LEDs is related to the emission wavelength of its said LEDs and the amount reduction in said conversion material over said LEDs to cause said LED chips to emit within said standard deviation.

19. The LED chip wafer of claim 17, wherein said conversion material comprises a phosphor.

20. The LED chip wafer of claim 17, wherein said conversion material comprises a phosphor loaded binder.

21. The LED chip wafer of claim 17, further comprising a plurality of pedestals, each of which is in electrical contact with one of said LEDs, each of said pedestals exposed at the surface of said coating.

22. The LED chip wafer of claim 21, wherein electrical contact is made to said LEDs chips through said pedestals.

23. The LED chip wafer of claim 17, capable of being separated into LED chips.

24. The LED chip wafer of claim 23, wherein said LED chips comprise one of said LEDs and a portion of said conversion material, said LED chips emitting a white light combination of light from its said LED and said conversion material.

25. The LED chip wafer of claim 17, further comprising a submount, wherein said LEDs are flip-chip mounted on a surface of said submount.

26. The LED chip wafer of claim 17, wherein said spacers are transparent to light from said LEDs.

27. An light emitting diode (LED) chip, comprising:

an LED;

a spacer on said LED; and

a phosphor coating on said spacer and at least partially covering said LED so that at least some of the light emitted by said LED is converted by said phosphor, said spacer being transparent to light from said LED having a volume that consumes space that would otherwise be occupied by said conversion material, said spacer reducing the amount of phosphor coating over said LED so that said LED chip emits light at a desired wavelength.

28. The LED chip of claim 27, wherein said LED emits within a standard deviation on a CIE curve.

29. The LED chip of claim 27, emitting a white light combination of light from said LED chip and from said conversion material.

30. The LED chip of claim 27, further comprising a contact and a pedestal formed on said contact, said pedestal extending to and exposed at the surface of said coating.

31. The LED chip of claim 30, wherein an electrical signal can be applied to said LED through said pedestal.

32. The LED chip wafer of claim 27, further comprising a submount, wherein said LED is flip-chip mounted on a surface of said submount.

33. The LED chip of claim 27, wherein said coating comprises a phosphor loaded binder.

34. A light emitting diode (LED) package comprising:

an LED chip comprising an LED with a contact and a spacer, wherein said spacer is transparent to light from said LED;

a conversion coating at least partially covering said LED and spacer, said spacer having a volume that reduces the amount of phosphor coating over said LED so that said LED chip emits light at a desired wavelength;

a package lead in electrical connection with said contact; and

encapsulation surrounding said LED chip and electrical connections.

35. The LED package of claim 34, wherein said spacer is transparent to light from said LED.

36. The LED package of claim 34, wherein said desired wavelength is within a standard deviation on a CIE curve.

37. The LED package of claim 34, emitting a white light combination of light from said LED chip and from said conversion material.

38. The LED package of claim 34, further comprising a pedestal formed on said contact, said pedestal extending to and exposed at the surface of said coating.

39. The LED package of claim 34, wherein an electrical signal can be applied to said LED through said pedestal.

40. The LED package of claim 34, wherein said coating comprises a phosphor loaded binder.