LOW PROFILE SIDE EMITTING LED WITH WINDOW LAYER AND PHOSPHOR LAYER

• US 20080315228A1
• Filed: 12/12/2007
• Published: 12/25/2008
• Est. Priority Date: 06/09/2006
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Inventors: Harbers, Gerard, Mueller, Gerd, Krames, Michael R., Mueller-Mach, Regina, Epler, John E., Pugh, Mark, Shchekin, Oleg Borisovich, Bierhuizen, Serge
• Granted Patent: US 8,080,828 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 2224/0554 External layer
• CPC Class Codes: H01L 2224/0555 Shape
• CPC Class Codes: H01L 2224/0556 Disposition
• CPC Class Codes: H01L 2224/05568 the whole external layer protruding from the surface
• CPC Class Codes: H01L 2224/05573 Single external layer
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/05624 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/05639 Silver [Ag] as principal constituent
• CPC Class Codes: H01L 2224/13 of an individual bump connector
• 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 2924/013 Alloys
• CPC Class Codes: H01L 33/385 the electrode extending at least partially onto a side surface of the semiconductor body
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

Low profile, side-emitting LEDs are described that generate white light, where all light is emitted within a relatively narrow angle generally parallel to the surface of the light-generating active layer. The LEDs enable the creation of very thin backlights for backlighting an LCD. In one embodiment, the LED emits blue light and is a flip chip with the n and p electrodes on the same side of the LED. Separately from the LED, a transparent wafer has deposited on it a red and green phosphor layer. The phosphor color temperature emission is tested, and the color temperatures vs. positions along the wafer are mapped. A reflector is formed over the transparent wafer. The transparent wafer is singulated, and the phosphor/window dice are matched with the blue LEDs to achieve a target white light color temperature. The phosphor/window is then affixed to the LED.

Claims

1. A method of fabricating a side-emitting light emitting device comprising:

providing a transparent wafer for use as a window layer over at least one light emitting diode (LED);

coating a surface of the wafer with at least one phosphor layer for wavelength conversion of light emitted by the at least one LED;

providing a reflector overlying a surface of the wafer;

singulating the wafer to form phosphor/window dice;

providing a blue or UV LED die, the LED die having an active layer that emits light, the active layer having a major surface;

affixing one of the phosphor/window dice to the LED die overlying the major surface of the active layer, with the window layer and phosphor layer between the reflector and LED, such that light emitted by the major surface of the active layer energizes the at least one phosphor layer, and the reflector substantially blocks light exiting the light emitting device normal to the major surface of the active layer such that a majority of light is emitted from sides of the light emitting device, light from the LED die and the at least one phosphor layer creating white light.

2. The method of claim 1 wherein the at least one phosphor layer and reflector are located on opposite surfaces of the transparent wafer.

3. The method of claim 1 wherein the reflector is provided directly over the at least one phosphor layer.

4. The method of claim 1 further comprising:

energizing areas of the at least one phosphor layer with light prior to singulating the wafer;

detecting an emitted color characteristic for each area energized;

mapping data reflecting the emitted color characteristic versus area;

after singulating the wafer, grouping together those phosphor/window dice having similar color characteristics;

wherein providing a blue or UV LED comprises providing a plurality of LEDs, the method further comprising;

testing the LEDs for color emission;

grouping together those LEDs having similar color characteristics; and

matching the phosphor/window dice with the LEDs to achieve a target color temperature.

5. The method of claim 4 wherein energizing areas of the at least one phosphor layer with light comprises energizing the areas with a beam from a blue laser.

6. The method of claim 4 wherein each area energized substantially corresponds to an area of a phosphor/window die after singulating the wafer.

7. The method of claim 1 wherein singulating the wafer to form phosphor/window dice comprises singulating the wafer such that edges of each phosphor/window die extend over edges of each LED die.

8. The method of claim 1 wherein the transparent wafer contains light scattering particles.

9. The method of claim 1 wherein the at least one phosphor layer comprises a single layer of mixed red and green phosphors.

10. The method of claim 1 wherein the at least one phosphor layer comprises a first layer of red phosphor and a second layer of green phosphor.

11. The method of claim 1 wherein the at least one phosphor layer comprises red, green, and blue phosphors.

12. A side-emitting light emitting device comprising:

a light emitting diode (LED) die comprising;

a first semiconductor layer of a first type;

a second semiconductor layer of a second type;

and active layer between the first semiconductor layer and the second semiconductor layer, the active layer having a major surface;

a first electrode in contact with the first semiconductor layer; and

a second electrode in contact with the second semiconductor layer, the first electrode and the second electrode being on a first side of the LED for being directly connected to electrodes on a submount, the LED being a flip chip;

the light emitting structure further comprising;

a window layer affixed to the LED die overlying the major surface of the active layer;

at least one phosphor layer coating a surface of the window layer for wavelength conversion of light emitted by the LED die; and

a reflector overlying a surface of the window layer, with the window layer and the at least one phosphor layer between the reflector and LED die, such that light emitted by the major surface of the active layer energizes the at least one phosphor layer, and the reflector substantially blocks light exiting the light emitting device normal to the major surface of the active layer such that a majority of light is emitted from sides of the light emitting device, light from the LED die and the at least one phosphor layer creating white light.

13. The device of claim 12 wherein the at least one phosphor layer and reflector are located on opposite surfaces of the window layer.

14. The device of claim 12 wherein the reflector is provided directly over the at least one phosphor layer.

15. The device of claim 12 wherein the window layer contains embedded light scattering features.

16. The device of claim 12 wherein the at least one phosphor layer comprises a single layer of mixed red and green phosphors.

17. The device of claim 12 wherein the at least one phosphor layer comprises a first layer of red phosphor and a second layer of green phosphor.

18. The device of claim 12 wherein the at least one phosphor layer comprises red, green, and blue phosphors.

19. The device of claim 12 wherein the LED die emits blue light.

20. The device of claim 12 wherein the LED die emits UV light.

21. The device of claim 12 wherein the window layer has a thickness greater than 100 microns, and the at least one phosphor layer has a thickness less than 50 microns.

22. The device of claim 12 wherein the at least one phosphor layer comprises at least two color phosphors in a transparent binder.

23. The device of claim 12 wherein the window layer has edges that extend over edges of the LED die.

24. The device of claim 12 wherein the window layer has scattering features in a surface adjacent the reflector.

25. The device of claim 12 wherein the LED die active layer is rectangular, and the window layer is non-rectangular and has edges that extend over edges of the LED die.

26. The device of claim 12 wherein the window layer has a concave surface adjacent the reflector.

27. The device of claim 12 further comprising a dichroic mirror between the LED die and the window layer, the dichroic mirror allowing light emitted from the LED die to pass and reflecting light emitted by the at least one phosphor layer.

28. The device of claim 12 wherein the at least one phosphor layer is within a tub formed in the window layer.

29. The device of claim 12 wherein sides of the window layer are roughened.

30. The device of claim 12 wherein the reflector is a diffusive reflector.

31. The device of claim 30 wherein the reflector is a substantially opaque layer comprising TiO₂.