Method of Making White Light LEDs and Continuously Color Tunable LEDs

• US 20080023715A1
• Filed: 07/19/2007
• Published: 01/31/2008
• Est. Priority Date: 07/28/2006
• Status: Abandoned Application

• Current Assignee: Versitech Limited (Government of Hong Kong Special Administrative Region)
• Original Assignee: Versitech Limited (Government of Hong Kong Special Administrative Region)
• Inventors: CHOI, Hoi Wai
• Application Number:
  US11/780,082
• Publication Number:
  US 20080023715A1
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials

Abstract

A light emitting diode comprising of a fluorescent microsphere coating is proposed. The coating consists of fluorescent microspheres which fluoresce at green and red wavelengths, excited by a shorter wavelength LED. Due to the micron-scale dimension of the spheres, they are non-resolvable to the human eye and the overall optical output appears as color mixed. By varying the proportions of green and red fluorescent microspheres and the wavelength of the excitation source, the color of the optical output can be tuned. If the optical output has of blue, green and red components in the correct proportions, white color emission can be achieved. The light emitting diode can be sectioned into multiple individually-addressable regions. Each section can emit at a different wavelength according to the type of fluorescent microspheres coated. By varying the intensity of the blue, green and red regions by changing the bias voltage, the output wavelength (color) can be continuously tuned (varied).

Claims

1. A method for making a white light emitting light emitting diode (LED), comprising:

providing an LED base pump having a light emitting surface that emits light having a wavelength of about 400 nm to about 480 nm;

depositing red and green fluorescent microspheres on the light emitting surface of the LED base pump with;

spreading the red and green microspheres on the light emitting surface of the LED base pump to produce a microsphere layer; and

affixing the microsphere layer with a protective dielectric layer or coating.

2. A method according to claim 1, wherein the dielectric layer or coating is silicon dioxide applied by electron beam evaporation.

3. A method according to claim 1, wherein the red and green microsphere layer on the LED base includes several monolayers of red and green microspheres organized into a hexagonal array.

4. A method according to claim 1, additionally comprising encapsulating the white light emitting LED with an encapsulant to protect the white light emitting LED.

5. A method according to claim 1, wherein the fluorescent microspheres are spread in an even layer using tilting or spinning.

6. A method according to claim 1 wherein the red and green fluorescent microspheres are suspended in deionized water before application to the light emitting surface of the base LED base pumpby tilting or spinning.

7. A method according to claim 1, wherein the red and green fluorescent microspheres are mixed with an encapsulating agent and then applied to the light emitting surface of the LED base pump.

8. A method according to claim 1, wherein the encapsulating agent is an epoxy based resin.

9. A method according to claim 1, wherein the red and green fluorescent microspheres are located in distinct regions to form red and green pixels, and the red and green pixels are interconnected with a gold metal interconnection layer.

10. A method for making a mixed color, tunable light emitting diode (LED), comprising:

providing an LED base pump light source having a light emitting surface that emits light having a wavelength of about 400 nm to about 480 nm;

forming a plurality of green pixels on a region of the LED base pump by coating the region with green fluorescent microspheres;

forming a plurality of red pixels on a region of the LED base pump by coating the region with red fluorescent microspheres;

connecting the plurality of green pixels to one another and the plurality of red pixels to one another using a thin layer of gold metal;

permitting a region of the light emitting surface to remain uncoated to create blue pixels,

depositing a thin layer of silicon dioxide on inactive regions to prevent shorting of p-n junctions on the base LED pump; and

depositing a thin layer of silicon dioxide on the pixels to form a protective cover on the mixed color, tunable light emitting diode.

11. A white light emitting diode (LED), comprising:

an LED base that emits light in the shorter wavelength region (about 400 nm to about 480 nm) as a pump source for the white light emitting LED;

at least one layer of red and green fluorescent microspheres adhered to the LED base that emit red and green colored light in microscale regions when excited by the light emitted by the LED base such that the microscale regions are not resolvable by the unaided human eye and thus appear to emit white light.

12. A white light emitting diode (LED) according to claim 11, wherein the ratio of red and green microspheres can be altered to produce a different color.

13. A white light emitting diode (LED) according to claim 11, wherein the at least one layer of fluorescent red and green microspheres include multiple individually addressable microscale regions or pixels which emit one of blue, red or green colored light.

14. A white light emitting diode (LED) according to claim 11, wherein the LED base emits blue colored light and the fluorescent microspheres emit red or green light.

15. A white light emitting diode (LED) according to claim 13, wherein the blue, green, and red light each have intensity that is individually adjustable.

16. A white light emitting diode (LED) according to claim 11, wherein output wavelength of the base LED and the red and green microspheres is continuously tunable.

17. A color mixed, color tunable light emitting diode (LED), comprising:

an LED base pump source having a light emitting surface that emits light having a wavelength of about 400 nm to about 480 nm;

a plurality of green pixels provided on a region of the LED base pump by coating green fluorescent microspheres onto the region;

a plurality of red pixels provided on a region of the LED base pump by coating red fluorescent microspheres onto the region;

a plurality of blue pixels on an uncoated region of the LED base pump;

the green pixels connected to one another and the red pixels connected to one another using a thin layer of gold metal;

a thin layer of silicon dioxide on inactive regions of the gold metal layer to prevent shorting of p-n junctions on the base LED pump; and

a thin layer of silicon dioxide on the pixels to form a protective cover on the color tunable light emitting diode.