White LED for backlight with phosphor plates

• US 20070215890A1
• Filed: 03/17/2006
• Published: 09/20/2007
• Est. Priority Date: 03/17/2006
• 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, Pugh, Mark, Bierhuizen, Serge
• Granted Patent: US 7,682,850 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133614 using photoluminescence, e.g. phosphors illuminated by UV or blue light
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A white light LED for use in backlighting or otherwise illuminating an LCD is described where the white light LED comprises a blue LED over which is affixed a preformed red phosphor platelet and a preformed green phosphor platelet. In one embodiment, to form a platelet, a controlled amount of phosphor powder is placed in a mold and heated under pressure to sinter the grains together. The platelet can be made very smooth on all surfaces. A UV LED may also be used in conjunction with red, green, and blue phosphor plates. The LED dies vary in color and brightness and are binned in accordance with their light output characteristics. Phosphor plates with different characteristics are matched to the binned LEDs to create white light LEDs with a consistent white point for use in backlights for liquid crystal displays.

Claims

1. A light emitting device for use in a display device comprising:

a white light LED (light emitting diode) comprising;

an LED die that emits light with a peak wavelength less than approximately 480 nm;

a phosphor layer emitting green or yellow-green light having a peak wavelength between 510 and 570 nm when energized by the light emitted by the LED die; and

at least one substantially flat, phosphor plate emitting at least orange-red or red light having a peak wavelength between 590-660 nm when energized by the light emitted by the LED die, the phosphor plate being affixed over the LED die, the at least one phosphor plate having been preformed prior to affixing to the LED die,

the white light LED emitting white light by the combination of the orange-red or red light, the green or yellow-green light, and blue light, the blue light having a peak wavelength between 430 and 480 nm; and

an illumination module containing at least one of said white light LED, the module illuminating a pixelated light modulator, the modulator controlling at least red, green, and blue color subpixels, peak wavelengths of the orange-red or red, green or yellow-green, and blue light components emitted by the white light LED approximately matching maximum light output requirements of the red, green, and blue subpixels within a certain range of wavelengths.

2. The device of claim 1 wherein the LED emits UV light, the device further comprising a substantially flat, phosphor plate emitting blue light when energized by the UV light, the phosphor plate emitting blue light being affixed over the LED die, the phosphor plate emitting blue light having been preformed prior to affixing to the LED die.

3. The device of claim 2 wherein the phosphor plate emitting blue light is the same plate as the phosphor plate emitting at least orange-red or red light, wherein the phosphor plate emitting at least orange-red or red light contains blue emission phosphor.

4. The device of claim 1 wherein the phosphor layer emitting green or yellow-green light when energized by the light emitted by the LED die is a YAG phosphor.

5. The device of claim 1 wherein the phosphor layer emitting green or yellow-green light when energized by the light emitted by the LED die comprises a substantially flat, phosphor plate affixed over the LED die, the phosphor plate emitting green or yellow-green light having been preformed prior to affixing to the LED die.

6. The device of claim 5 wherein the phosphor plate emitting green or yellow-green light is the same plate as the phosphor plate emitting at least orange-red or red light, wherein the phosphor plate emitting at least orange-red or red light contains green or yellow-green emission phosphor.

7. The device of claim 1 wherein the LED die emits blue light, the at least one phosphor plate allowing light emitted by the LED die to leak through the at least one phosphor plate.

8. The device of claim 1 wherein the at least one phosphor plate has a bottom surface approximately matching dimensions of a top surface of the LED die.

9. The device of claim 1 wherein the orange-red or red, green or yellow-green, and blue light components of the white light LED have peak wavelengths within 610 to 660 nm for orange-red or red, 520 to 570 nm for green or yellow-green, and 430 to 480 nm for blue.

10. The device of claim 1 wherein the LED emits blue light, wherein the at least one phosphor plate comprises a flat, preformed first phosphor plate emitting orange-red or red light affixed over the blue LED, and wherein the phosphor layer emitting green or yellow-green light comprises a flat, preformed second phosphor plate emitting green or yellow-green light affixed over the blue LED.

11. The device of claim 10 wherein the second phosphor plate is affixed over the first phosphor plate.

12. The device of claim 10 wherein the first phosphor plate is coplanar with the second phosphor plate over the LED.

13. The device of claim 1 wherein the at least one phosphor plate is affixed to the LED die by an adhesive.

14. The device of claim 13 wherein the adhesive includes one of silicone and glass.

15. The device of claim 1 wherein the at least one phosphor plate comprises a mixture of green and red emission phosphors, wherein the at least one phosphor plate comprises the layer of phosphor emitting green or yellow-green light.

16. The device of claim 1 wherein the at least one phosphor plate has a substantially rectangular shape.

17. The device of claim 1 wherein the at least one phosphor plate comprises phosphor grains sintered together under heat and pressure.

18. The device of claim 1 wherein the illumination module has a plurality of other white light LEDs substantially identical to the white light LED.

19. The device of claim 18 wherein the illumination module comprises mixing optics for mixing the light from the plurality of white light LEDs to create a substantially uniform light at an output of the backlight.

20. The device of claim 1 wherein the light modulator modulates the light from the illumination module to create an image at the output of the light modulator formed of red, green, and blue color components.

21. The device of claim 20 further comprising an LED controller for modulating a brightness of white light LEDs in the illumination module such that a light output of some white light LEDs in the illumination module is different from a light output of other white light LEDs in the backlight.

22. The device of claim 21 wherein the LED controller modulates the brightness of the white light LEDs based on an image displayed by the pixelated light modulator.

23. The device of claim 1 wherein the at least one phosphor plate has a bottom surface that extends over outer edges of the LED die.

24. The device of claim 1 wherein the at least one phosphor plate has a bottom surface that does not extend over outer edges of the LED die.

25. The device of claim 1 wherein the at least one phosphor plate is affixed over the LED die by a mechanical device.

26. The device of claim 1 further comprising a lens encapsulating the at least one phosphor plate and the LED die.

27. The device of claim 26 wherein the lens supports the at least one phosphor plate over the LED die.

28. The device of claim 1 further comprising a submount on which the white light LED is mounted.

29. The device of claim 1 wherein the illumination module is a backlight, and the pixelated light modulator is a liquid crystal layer in a liquid crystal display (LCD).

30. The device of claim 1 wherein the peak wavelengths approximately matching maximum light output requirements of the red, green, and blue subpixels comprises the peak wavelengths of the orange-red or red, green or yellow-green, and blue light components emitted by the white light LED being within approximately 10% of the wavelengths corresponding to the maximum light output requirements of the red, green, and blue subpixels.

31. A light emitting device for use in a display device comprising:

a white light LED (light emitting diode) comprising;

an LED die that emits light with a peak wavelength less than approximately 480 nm;

a YAG phosphor layer emitting green or yellow-green light with a peak wavelength between 510 and 570 nm when energized by the light emitted by the LED die; and

at least one substantially flat, phosphor plate emitting at least orange-red or red light having a peak wavelength larger than 590 nm when energized by the light emitted by the LED die, the phosphor plate being affixed over the LED die, the at least one phosphor plate having been preformed prior to affixing to the LED die,

the white light LED emitting white light by the combination of the orange-red or red light, the green or yellow-green light, and blue light, the blue light having a peak wavelength between 430 and 480 nm; and

an illumination module containing at least one of said white light LED, the module illuminating a pixelated light modulator, the modulator controlling at least red, green, and blue color subpixels, peak wavelengths of at least the orange-red or red and blue light components emitted by the white light LED approximately matching maximum light output requirements of the red and blue subpixels within a certain range of wavelengths.

32. The device of claim 31 wherein the YAG phosphor layer comprises a substantially flat, phosphor plate affixed over the LED die.

33. The device of claim 31 wherein the illumination module is a backlight, and the pixelated light modulator is a liquid crystal layer in a liquid crystal display (LCD).

34. The device of claim 31 wherein the LED die emits blue light, the YAG phosphor layer and the at least one phosphor plate allowing light emitted by the LED die to leak through the YAG phosphor layer and the at least one phosphor plate.

35. The device of claim 31 wherein the peak wavelengths approximately matching maximum light output requirements of the red and blue subpixels comprises the peak wavelengths of the orange-red or red and blue light components emitted by the white light LED being within approximately 10% of the wavelengths corresponding to the maximum light output requirements of the red and blue subpixels.

36. A method of forming a light emitting device comprising:

testing LED dies that emit light with a peak wavelength less than approximately 480 nm and determining light emission characteristics of the LED dies;

binning the LED dies in accordance with their light emission characteristics;

forming a variety of plates of a phosphor that emit at least orange-red or red light with a peak wavelength larger than 590 nm when energized by light from the LED dies, the plates being formed separate from the LED dies, the plates having different characteristics associated with different bins of LED dies;

matching a plate having a particular characteristic to a binned LED die to generate a white light having a target white point; and

affixing a matched plate over an LED die to form a white light LED emitting orange-red or red, green or yellow-green, and blue light components, wherein a combination of the orange-red or red, green or yellow-green, and blue light components produces white light having the target white point.

37. The method of claim 36 further comprising mounting at least one said white light LED in an illumination module for a pixelated light modulator, the modulator controlling at least red, green, and blue color subpixels, wherein the plates are matched to the binned LED dies to generate orange-red or red and blue light components whose peak wavelengths are within approximately 10% of the wavelengths corresponding to maximum light output requirements of the red and blue subpixels within a certain range of wavelengths.

38. The method of claim 36 wherein the LED dies emit blue light.

39. The method of claim 36 wherein the LED dies emit UV light.

40. The method of claim 36 wherein binning the LED dies comprises separating the LED dies based on a peak wavelength output.

41. The method of claim 36 wherein forming a variety of plates of a phosphor that emit at least orange-red or red light with a peak wavelength larger than 590 nm when energized by light from the LED dies comprises forming a variety of plates of a phosphor that emit at least orange-red or red light and green or yellow-green light when energized by light from the LED dies.

42. The method of claim 36 wherein forming a variety of plates of a phosphor that emit at least orange-red or red light when energized by light from the LED dies comprises forming a variety of plates of a phosphor that emit orange-red or red light, green or yellow-green light, and blue light when energized by light from the LED dies.

43. The method of claim 36 wherein forming the variety of plates of a phosphor comprises:

forming a substantially flat first phosphor plate emitting red light; and

forming a substantially flat second phosphor plate emitting green light.

44. The method of claim 43 wherein affixing a matched plate over an LED die comprises affixing the second phosphor plate over the first phosphor plate.

45. The method of claim 36 wherein the matched plate is affixed to the LED die by an adhesive.

46. The method of claim 45 wherein the adhesive includes one of silicone and glass.

47. The method of claim 36 wherein forming the variety of plates of a phosphor that emit at least orange-red or red light comprises mixing green and red emission phosphors together to form a single plate of phosphor.

48. The method of claim 36 wherein the plates have a substantially rectangular prism shape.

49. The method of claim 36 wherein forming the variety of plates of a phosphor that emit at least orange-red or red light comprises sintering phosphor grains under heat and pressure.

50. The method of claim 36 further comprising providing the white light LED, along with a plurality of other white light LEDs substantially identical to the white light LED, in a backlight for a liquid crystal display (LCD).

51. The method of claim 50 further comprising operating the LCD to create images from red, green, and blue pixels.

52. The method of claim 51 further comprising modulating a brightness of white light LEDs in the backlight such that a light output of some white light LEDs in the backlight box is different from a light output of other white light LEDs in the backlight.

53. The method of claim 36 wherein the matched plate has a bottom surface that extends over outer edges of the LED die.

54. The method of claim 36 wherein the matched plate has a bottom surface that does not extend over outer edges of the LED die.

55. The method of claim 36 wherein the matched plate is affixed over the LED die by a mechanical device.