LED with particles in encapsulant for increased light extraction and non-yellow off-state color

• US 7,791,093 B2
• Filed: 09/04/2007
• Issued: 09/07/2010
• Est. Priority Date: 09/04/2007
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.), Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Haque, Ashim Shatil, Chen, Ching-hui, West, Robert Scott, Basin, Grigoriy, Martin, Paul
• Primary Examiner(s): Nguyen; Dao H
• Assistant Examiner(s): NGUYEN, TRAM HOANG
• Application Number:
  US11/849,930
• Publication Number:
  US 20090057699A1
• Time in Patent Office: 1,099 Days
• Field of Search: 257/88, 257/512, 257/117, 257432-437, 257/749, 257E33056-E33059, 257/E25.032, 250/336.1, 313/503, 313/512, 438 25- 28
• US Class Current: 257/98
• 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 2224/05624 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/05639 Silver [Ag] as principal constituent
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• 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 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/56 Materials, e.g. epoxy or silicone resin

Abstract

In one embodiment, sub-micron size granules of TiO₂, ZrO₂, or other white colored non-phosphor inert granules are mixed with a silicone encapsulant and applied over an LED. In one experiment, the granules increased the light output of a GaN LED more than 5% when the inert material was between about 2.5-5% by weight of the encapsulant. Generally, a percentage of the inert material greater than 5% begins to reduce the light output. If the LED has a yellowish YAG phosphor coating, the white granules in the encapsulant make the LED appear whiter when the LED is in an off state, which is a more pleasing color when the LED is used as a white light flash in small cameras. The addition of the granules also reduces the variation of color temperature over the view angle and position over the LED, which is important for a camera flash and projection applications.

Claims

1. A light emitting device comprising:

a semiconductor light emitting diode (LED);

a layer of phosphor over the LED; and

an encapsulant over the LED and phosphor directly contacting the phosphor, the encapsulant comprising a substantially transparent material containing only inert non-phosphor, the particles being between 0.5%-5% by weight of the encapsulant, the particles having a substantially white color under white ambient light

an average diameter of the particles is less than one micron.

2. The device of claim 1 wherein the particles comprise TiO_x.

3. The device of claim 2 wherein the particles comprise TiO₂.

4. The device of claim 1 wherein the particles comprise ZrO_x.

5. The device of claim 4 wherein the particles comprise ZrO₂.

6. The device of claim 1 wherein the particles comprise between 2.5% and 5% of the encapsulant.

7. The device of claim 1 wherein the encapsulant comprises silicone.

8. The device of claim 1 wherein the encapsulant has a substantially flat surface over the LED.

9. The device of claim 1 wherein the phosphor is over at least a top surface of the LED, the phosphor having a yellowish color under white ambient light, the encapsulant, containing the particles, whitening an appearance of the phosphor when the LED is in an off state.

10. The device of claim 9 wherein the phosphor comprises a yttrium aluminum oxide garnet (YAG) phosphor.

11. The device of claim 1 wherein the particles increase light output power out of the encapsulant when the LED is in an on state, compared to the encapsulant having 0% of the particles.

12. The device of claim 1 wherein the particles lower a color temperature of light output from the encapsulant when the LED is in an on state, compared to the encapsulant having 0% of the particles.

13. The device of claim 1 wherein the particles lower a deviation of color temperature versus viewing angle of light output from the encapsulant when the LED is in an on state, compared to the encapsulant having 0% of the particles.

14. The device of claim 1 wherein the particles lower a deviation of color temperature versus position normal to a top surface of the LED when the LED is in an on state, compared to the encapsulant having 0% of the particles.

15. The device of claim 1 wherein the LED and encapsulant comprise a flash light source in a camera.

16. The device of claim 1 wherein a semiconductor portion of the LED emits blue light.