U.S. patent application number 09/751405 was filed with the patent office on 2002-07-04 for light emitting diode with light conversion by dielectric phosphor powder.
This patent application is currently assigned to Airma Optoelectronics Corporation. Invention is credited to Huang, Wen-Chieh, Wang, Wang-Nang.
Application Number | 20020084745 09/751405 |
Document ID | / |
Family ID | 25021830 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020084745 |
Kind Code |
A1 |
Wang, Wang-Nang ; et
al. |
July 4, 2002 |
Light emitting diode with light conversion by dielectric phosphor
powder
Abstract
The invention provides a light emitting diode (LED) comprising a
light emitting component and dielectric phosphor powder (DPP) which
absorb a part of light emitted by the light emitting component and
emits light of a wavelength that is different from that of the
absorbed light. In a preferred embodiment according to the
invention, the LED includes a crystalline semiconductor chip
serving as the light emitting component. The dielectric phosphor
powder is made of a mixture of phosphor particles and microscopic,
nearly spherical dielectric particles with a band gap larger than 3
eV (which do not absorb blue light in the spectrum). The DPP can
also include phosphor particles, and bubbles (or voids) instead of
the dielectric particles. The bubbles of the DPP have a band gap
larger than 3 eV which do not absorb blue light in the spectrum.
The bubbles can be air bubbles, N2 bubbles, noble gas bubbles.
Furthermore, the DPP can also be a mixture of the bubbles,
dielectric particles, and the phosphor particles. According to
another embodiment, the invention provides a light emitting diode
(LED) comprising a light emitting component (such as a crystalline
semiconductor chip) and dielectric phosphor powder (DPP) made of a
mixture of crystalline phosphor particles and microscopic, nearly
spherical dielectric particles. According to yet another
embodiment, the invention provides a light emitting diode (LED)
comprising a light emitting component (such as an AlInGaN
crystalline semiconductor chip) encapsulated into dielectric
phosphor powder (DPP). The DPP is made of a mixture of microscopic,
nearly spherical dielectric particles of microcrystalline AlN. The
LED according to this particular embodiment can also be a white
LED. An exemplary structure of an LED according to a preferred
embodiment of the invention comprises a crystalline semiconductor
chip encapsulated into epoxy, wires connected to the semiconductor
chip, metallic leads connected to the wires, and an epoxy
encapsulation covered with dielectric phosphor powder (DPP). The
DPP is made of a mixture of nearly spherical dielectric particles
with crystalline phosphor particles embedded into the epoxy.
Inventors: |
Wang, Wang-Nang; (Bath,
GB) ; Huang, Wen-Chieh; (Taoyuan, TW) |
Correspondence
Address: |
DARBY & DARBY P.C.
805 Third Avenue
New York
NY
10022
US
|
Assignee: |
Airma Optoelectronics
Corporation
|
Family ID: |
25021830 |
Appl. No.: |
09/751405 |
Filed: |
December 29, 2000 |
Current U.S.
Class: |
313/498 ;
313/502; 313/512 |
Current CPC
Class: |
H01L 2924/181 20130101;
H01L 33/504 20130101; H01L 2224/8592 20130101; Y02B 20/181
20130101; H01L 2224/48247 20130101; H01L 2933/0091 20130101; Y02B
20/00 20130101; H01L 33/502 20130101; C09K 11/7774 20130101; H01L
2224/48257 20130101; H01L 2224/48091 20130101; H01L 2224/48091
20130101; H01L 2924/00014 20130101; H01L 2924/181 20130101; H01L
2924/00012 20130101 |
Class at
Publication: |
313/498 ;
313/512; 313/502 |
International
Class: |
H01J 001/62; H01J
063/04 |
Claims
We claim:
1. A light emitting diode (LED) comprising: a light emitting
component emitting a light; and a dielectric phosphor powder (DPP)
which absorbs a part of the light emitted by the light emitting
component and emits light of a wavelength that is different from
that of the absorbed light; wherein the dielectric phosphor powder
(DPP) is made of a mixture of crystalline phosphor particles and
microscopic, nearly spherical dielectric particles.
2. The LED of claim 1 wherein concentration of the phosphor
particles are generally 2% to 25% of total volume of the dielectric
phosphor powder (DPP).
3. The LED of claim 1 wherein the light emitting component is one
selected from the group consisting of a crystalline semiconductor
chip, nitride compound semiconductor chip, a gallium nitride
compound semiconductor, InGaN crystalline semiconductor chip, and
AlInGaN crystalline semiconductor chip.
4. The LED of claim 1 wherein the light emitted by the dielectric
phosphor powder (DPP) is a white light.
5. The LED of claim 1 wherein the dielectric particles have a band
gap larger then 3 eV.
6. The LED of claim 1 wherein the dielectric particles do not
absorb blue light.
7. The LED of claim 1 wherein the dielectric particles are selected
from the group consisting of microcrystalline AlN, amorphous
Si.sub.3N.sub.4, amorphous GaN, and amorphous SiO.sub.2.
8. The LED of claim 1 wherein the dielectric particles are selected
from the group consisting of amorphous Si.sub.3N.sub.4 with radii
generally between 50 and 5000 nm, amorphous SiO.sub.2 with radii
generally between 50 and 5000 nm, and amorphous GaN with radii
generally between 50 and 5000 nm.
9. The LED of claim 1 wherein the phosphor particles are
micro-crystals of a garnet fluorescent material with radii
generally between 1000 and 10,000 nm.
10. The LED of claim 1 wherein the phosphor particles are selected
from the group consisting of Gd, Y, Ce and Nd-based phosphors.
11. The LED of claim 1 wherein the phosphor particles include
phosphors of garnet fluorescent material activated with cerium
containing at least one element selected from the group consisting
of Y, Lu, Sc, La, Gd and Sm, and at least one element selected from
another group consisting of Al, Ga and In.
12. The LED of claim 1 wherein the mixture of the DPP further
comprises bubbles having a band gap larger than 3 eV.
13. The LED of claim 12 wherein the mixture of the DPP further
comprises bubbles which do not absorb blue light.
14. The LED of claim 1 wherein the mixture of the DPP further
comprises voids selected from the group consisting of air bubbles,
N2 bubbles, and noble gas bubbles.
15. A light emitting diode (LED) comprising: a light emitting
component emitting a light; and a dielectric phosphor powder (DPP)
which absorbs a part of the light emitted by the light emitting
component and emits light of a wavelength that is different from
that of the absorbed light; wherein the dielectric phosphor powder
(DPP) is made of a mixture of crystalline phosphor particles and
light scattering media particles wherein the light scattering media
particles have a band gap larger than 3 eV.
16. The LED of claim 15 wherein the media particles do not absorb
blue light.
17. The LED of claim 15 wherein the media particles are dielectric
particles.
18. The LED of claim 15 wherein concentration of the phosphor
particles are generally 2% to 25% of total volume of the dielectric
phosphor powder (DPP).
19. The LED of claim 15 wherein the light emitting component is one
selected from the group consisting of a crystalline semiconductor
chip, nitride compound semiconductor chip, a gallium nitride
compound semiconductor, InGaN crystalline semiconductor chip, and
AlInGaN crystalline semiconductor chip.
20. The LED of claim 15 wherein the light emitted by the dielectric
phosphor powder (DPP) is a white light.
21. The LED of claim 15 wherein the light scattering media
particles are selected from the group consisting of
microcrystalline AlN, amorphous Si.sub.3N.sub.4, amorphous GaN, and
amorphous SiO.sub.2.
22. The LED of claim 15 wherein the light scattering media
particles are selected from the group consisting of amorphous
Si.sub.3N.sub.4 with radii generally between 50 and 5000 nm,
amorphous SiO.sub.2 with radii generally between 50 and 5000 nm,
and amorphous GaN with radii generally between 50 and 5000 nm.
23. The LED of claim 15 wherein the phosphor particles are
micro-crystals of a garnet fluorescent material with radii
generally between 1000 and 10,000 nm.
24. The LED of claim 15 wherein the phosphor particles are selected
from the group consisting of Gd, Y, Ce and Nd-based phosphors.
25. The LED of claim 15 wherein the phosphor particles include
phosphors of garnet fluorescent material activated with cerium
containing at least one element selected from the group consisting
of Y, Lu, Sc, La, Gd and Sm, and at least one element selected from
another group consisting of Al, Ga and In.
26. The LED of claim 15 wherein the mixture of the DPP further
comprises bubbles having a band gap larger than 3 eV.
27. The LED of claim 26 wherein the mixture of the DPP further
comprises bubbles which do not absorb blue light.
28. The LED of claim 15 wherein the mixture of the DPP further
comprises voids selected from the group consisting of air bubbles,
N2 bubbles, and noble gas bubbles.
29. The LED of claim 15 wherein the light scattering media
particles include voids wherein the voids are selected from the
group consisting of air bubbles, N2 bubbles, and noble gas
bubbles.
30. The LED of claim 29 wherein the bubbles do not absorb blue
light.
31. The LED of claim 15 further comprising: a crystalline
semiconductor chip wherein the crystalline phosphor particles are
embedded into epoxy; wires connected to the semiconductor chip;
metallic leads connected to the wires for transferring an
electrical current to the semiconductor chip; and an epoxy
encapsulation covered with the dielectric phosphor powder
(DPP).
32. The LED of claim 15 further comprising: a crystalline
semiconductor chip encapsulated into the dielectric phosphor powder
(DPP) wherein the crystalline phosphor particles are embedded into
epoxy; wires connected to the semiconductor chip; metallic leads
connected to the wires for transferring an electrical current to
the semiconductor chip; and an epoxy encapsulation covered with the
dielectric phosphor powder (DPP).
33. A light emitting diode (LED) comprising: a crystalline
semiconductor chip; a dielectric phosphor powder (DPP) made of a
mixture of microscopic, nearly spherical dielectric particles with
crystalline phosphor particles embedded into epoxy; wires connected
to the semiconductor chip; metallic leads connected to the wires
for transferring an electrical current to the semiconductor chip;
and an epoxy encapsulation covered with the dielectric phosphor
powder (DPP).
34. The LED of claim 33 wherein concentration of the phosphor
particles are generally 2% to 25% of total volume of the dielectric
phosphor powder (DPP).
35. The LED of claim 33 wherein the semiconductor chip is one
selected from the group consisting of a nitride compound
semiconductor chip, a gallium nitride compound semiconductor, InGaN
crystalline semiconductor chip, and AlInGaN crystalline
semiconductor chip.
36. The LED of claim 33 wherein the light emitted by the dielectric
phosphor powder (DPP) is a white light.
37. The LED of claim 33 wherein the dielectric particles have a
band gap larger then 3 eV.
38. The LED of claim 33 wherein the dielectric particles do not
absorb blue light.
39. The LED of claim 33 wherein the dielectric particles are
selected from the group consisting of microcrystalline AlN,
amorphous Si.sub.3N.sub.4, amorphous GaN, and amorphous
SiO.sub.2.
40. The LED of claim 33 wherein the dielectric particles are
selected from the group consisting of amorphous Si.sub.3N.sub.4
with radii generally between 50 and 5000 nm, amorphous SiO.sub.2
with radii generally between 50 and 5000 nm, and amorphous GaN with
radii generally between 50 and 5000 nm.
41. The LED of claim 33 wherein the phosphor particles are
micro-crystals of a garnet fluorescent material with radii
generally between 1000 and 10,000 nm.
42. The LED of claim 33 wherein the phosphor particles are selected
from the group consisting of Gd, Y, Ce and Nd-based phosphors.
43. The LED of claim 33 wherein the phosphor particles include
phosphors of garnet fluorescent material activated with cerium
containing at least one element selected from the group consisting
of Y, Lu, Sc, La, Gd and Sm, and at least one element selected from
another group consisting of Al, Ga and In.
44. The LED of claim 33 wherein the mixture of the DPP further
comprises bubbles having a band gap larger than 3 eV.
45. The LED of claim 44 wherein the mixture of the DPP further
comprises bubbles which do not absorb blue light.
46. The LED of claim 33 wherein the mixture of the DPP further
comprises voids selected from the group consisting of air bubbles,
N2 bubbles, and noble gas bubbles.
47. A light emitting diode (LED) comprising: a crystalline
semiconductor chip encapsulated into a dielectric phosphor powder
(DPP) made of a mixture of microscopic, nearly spherical dielectric
particles with crystalline phosphor particles embedded into epoxy;
wires connected to the semiconductor chip; metallic leads connected
to the wires for transferring an electrical current to the
semiconductor chip; and an epoxy encapsulation covered with the
dielectric phosphor powder (DPP).
48. The LED of claim 47 wherein concentration of the phosphor
particles are generally 2% to 25% of total volume of the dielectric
phosphor powder (DPP).
49. The LED of claim 47 wherein the semiconductor chip is one
selected from the group consisting of a nitride compound
semiconductor chip, a gallium nitride compound semiconductor, InGaN
crystalline semiconductor chip, and AlInGaN crystalline
semiconductor chip.
50. The LED of claim 47 wherein the light emitted by the dielectric
phosphor powder (DPP) is a white light.
51. The LED of claim 47 wherein the dielectric particles have a
band gap larger then 3 eV.
52. The LED of claim 47 wherein the dielectric particles do not
absorb blue light.
53. The LED of claim 47 wherein the dielectric particles are
selected from the group consisting of microcrystalline AIN,
amorphous Si.sub.3N.sub.4, amorphous GaN, and amorphous
SiO.sub.2.
54. The LED of claim 47 wherein the dielectric particles are
selected from the group consisting of amorphous Si.sub.3N.sub.4
with radii generally between 50 and 5000 nm, amorphous SiO.sub.2
with radii generally between 50 and 5000 nm, and amorphous GaN with
radii generally between 50 and 5000 nm.
55. The LED of claim 47 wherein the phosphor particles are
micro-crystals of a garnet fluorescent material with radii
generally between 1000 and 10,000 nm.
56. The LED of claim 47 wherein the phosphor particles are selected
from the group consisting of Gd, Y, Ce and Nd-based phosphors.
57. The LED of claim 47 wherein the phosphor particles include
phosphors of garnet fluorescent material activated with cerium
containing at least one element selected from the group consisting
of Y, Lu, Sc, La, Gd and Sm, and at least one element selected from
another group consisting of Al, Ga and In.
58. The LED of claim 47 wherein the mixture of the DPP further
comprises bubbles having a band gap larger than 3 eV.
59. The LED of claim 58 wherein the mixture of the DPP further
comprises bubbles which do not absorb blue light.
60. The LED of claim 47 wherein the mixture of the DPP further
comprises voids selected from the group consisting of air bubbles,
N2 bubbles, and noble gas bubbles.
61. A light emitting diode (LED) comprising: a light emitting
component emitting a light; and a mixture of phosphor particles and
voids wherein the mixture absorbs a part of the light emitted by
the light emitting component and emits light of a wavelength that
is different from that of the absorbed light.
62. The LED of claim 61 wherein the voids are selected from the
group consisting of air bubbles, N2 bubbles, and noble gas
bubbles.
63. The LED of claim 61 wherein the voids have a band gap larger
than 3 eV.
64. The LED of claim 61 wherein the voids do not absorb blue
light.
65. The LED of claim 61 further comprising: a crystalline
semiconductor chip wherein the phosphor particles are embedded into
epoxy; wires connected to the semiconductor chip; metallic leads
connected to the wires for transferring an electrical current to
the semiconductor chip; and an epoxy encapsulation covered with the
mixture.
66. The LED of claim 61 further comprising: a crystalline
semiconductor chip encapsulated into the mixture wherein the
phosphor particles are embedded into epoxy; wires connected to the
semiconductor chip; metallic leads connected to the wires for
transferring an electrical current to the semiconductor chip; and
an epoxy encapsulation covered with the mixture.
Description
FIELD OF THE INVENTION
[0001] The invention generally relates to a light emitting diode
(LED), and more particularly, to the fabricating of LEDs with light
wavelength conversion using dielectric phosphor powder (DPP).
DESCRIPTION OF THE RELATED ART
[0002] A light emitting diode (LED) is a well known form of solid
state illuminator. LEDs have been widely used as indicators,
displays and light sources. As a semiconductor element, an LED is
characterized by good burn-out rates, high vibration resistance,
and durability in enduring repetitive ON and OFF operations.
[0003] Conventional LEDs generally emit light in the red portion of
the light spectrum. For light wavelength conversion, e.g., shifting
the wavelength of the light emitted from the red portion, the LED
is doped using various impurities. Such a technique in the art of
doping the LED with impurities cannot, however, provide feasibly
efficient light emission across the entire range of the visible
spectrum.
[0004] As opposed to red light, blue is at the short-wavelength end
of the visible spectrum. Techniques have developed in the art to
exploit the blue portion of the spectrum in generating a wider
range of light emission from an LED. The relatively short
wavelength of the blue light permits the shifting of the light
emitted from a blue LED to the light emission of other colors in
the spectrum, including a white light. This is accomplished through
fluorescence or light wavelength conversion, which is a process
where a light of relatively short wavelength is absorbed and
re-emitted as a longer-wavelength light.
[0005] FIG. 1a is a diagram illustrating an LED with light
wavelength conversion in the art. The LED includes a semiconductor
chip 1, wires 2 and 3, leads 4 and 5, wavelength converting
substance 6 and epoxy encapsulation 7. Semiconductor chip 1,
serving as the light emitting component in the LED, generates
primary light when an electrical current is applied to the chip 1
through wires 2 and 3, which are electrically connected to leads 4
and 5. The wavelength converting substance 6, containing a
specified phosphor, covers the light emitting component (i.e.,
semiconductor chip 1) and is molded in resin. An n electrode and p
electrode of the semiconductor chip 1 are connected to leads 4 and
5, respectively, by means of wires 2 and 3.
[0006] For light wavelength conversion, the active element of the
LED is the wavelength converting substance 6 that partly absorbs
the initial light from the semiconductor chip 1 and generates the
secondary light. Part of the light generated from the semiconductor
chip 1 (hereinafter referred to as the LED light) excites the
phosphor contained in the wavelength converting substance 6 for
generating a fluorescent light having a wavelength different from
that of the LED light. The fluorescent light emitted by the
phosphor and the LED light (which is output without contributing to
the excitation of the phosphor) are mixed and output for emission.
Consequently, the LED outputs a light having a wavelength different
from that of the LED light emitted by the light emitting component,
i.e., the semiconductor chip 1.
[0007] The phosphor included in the wavelength converting substance
6 can be fluorescent materials known in the art, or micro-crystals
of garnet fluorescent material available in the art. For
ultraviolet (UV) primary light emission, the wavelength converting
substance 6 includes dense phosphor powder. FIG. 1b is a diagram
illustrating, in conjunction with FIG. 1a, an LED with light
wavelength conversion in the art using dense phosphor powder. The
phosphor powder is embedded in epoxy 9 and densely deposited as a
thin covering layer on the surface of the light emitting component
(i.e., semiconductor chip 1). For blue primary light emission, the
wavelength converting substance 6 includes dilute phosphor powder.
FIG. 1c is a diagram illustrating, in conjunction with FIF. 1a, an
LED with light wavelength conversion in the art using dilute
phosphor powder. The phosphor powder is embedded in epoxy 9 and
deposited, in a dilute proportion, on the surface of the light
emitting component, as a thick cover, distant spherical or plan
layer or as a lens molded to the semiconductor chip 1.
[0008] For light wavelength conversion, LEDs in the art (such as
the LED disclosed in FIGS. 1a, 1b and 1c) have problems in
controlling color uniformity in light emission. The primary light
generated by semiconductor chip 1 is partially blocked by the
electrode formed on the chip 1 which results in a particular
emission pattern where light is not emitted uniformly in every
direction or angle. The inclusion of the phosphor powder in the
wavelength converting substance 6, however, causes the emission of
the light in a uniform manner. The two conflicting phenomena in
emission uniformity (or lack thereof) create substantial
difficulties in controlling the light color uniformity over
emission angles or directions that results in uncontrolled
variation of the color of the light emission.
[0009] There is therefore a general need in the art for an improved
LED with light wavelength conversion, and more particularly for an
LED that overcomes the aforementioned problems in the art.
SUMMARY OF THE INVENTION
[0010] The invention provides a light emitting diode (LED)
comprising a light emitting component and dielectric phosphor
powder (DPP) which absorb a part of light emitted by the light
emitting component and emits light of a wavelength that is
different from that of the absorbed light. The employment of light
scattering media or dispersion media such as dielectric particles
(or any particles with a band gap larger than 3 eV, which do not
absorb blue light in the spectrum) in an LED significantly improves
the light uniformity of a light emitted by the LED.
[0011] In a preferred embodiment according to the invention, the
LED includes a crystalline semiconductor chip serving as the light
emitting component. The dielectric phosphor powder is made of a
mixture of microscopic, nearly spherical dielectric particles and
phosphor particles. The spherical dielectric micro-particles can be
made of wide-band-gap semiconductors or transparent dielectrics.
The DPP forms scattering optical media, whose refractive index,
scattering properties and light conversion properties are
controlled by the refractive index and radii of the dielectric
particles. Using DPP in the LED allows effective light extraction
from the light emitting component of the LED (e.g., the crystalline
semiconductor chip), effective light wavelength conversion, and
substantially uniform color distribution over emission angles, and
wider emission angle of the light generated by the LED with DPP, in
contrast to conventional LEDs with light conversion without
DPP.
[0012] The DPP can also include phosphor particles, and bubbles (or
voids) instead of the dielectric particles. The bubbles of the DPP
have a band gap larger than 3 eV which do not absorb blue light in
the spectrum. The bubbles can be air bubbles, N2 bubbles, noble gas
bubbles. Furthermore, the DPP can also be a mixture of the bubbles,
dielectric particles, and the phosphor particles.
[0013] According to another embodiment, the invention provides a
light emitting diode (LED) comprising a light emitting component
(such as a crystalline semiconductor chip) and dielectric phosphor
powder (DPP) made of a mixture of crystalline phosphor particles
and microscopic, nearly spherical dielectric particles.
[0014] According to yet another embodiment, the invention provides
a light emitting diode (LED) comprising a light emitting component
(such as an AlInGaN crystalline semiconductor chip) encapsulated
into dielectric phosphor powder (DPP). The DPP is made of a mixture
of microscopic, nearly spherical dielectric particles of
microcrystalline AlN. The LED according to this particular
embodiment can also be a white LED.
[0015] According to a further embodiment, the invention provides an
LED comprising a light emitting component such as an InGaN
semiconductor chip encapsulated into dielectric phosphor powder
(DPP). The DPP is made of a mixture of nearly spherical dielectric
particles of amorphous Si.sub.3N.sub.4 with radii generally between
50 and 5000 nm, and micro-crystals of garnet fluorescent material
with radii generally between 1000 and 10,000 nm. The LED according
to this particular embodiment can also be a white LED.
[0016] According to an additional embodiment, the invention
provides an LED comprising a light emitting component such as an
InGaN semiconductor chip encapsulated into dielectric phosphor
powder (DPP). The DPP is made of a mixture of nearly spherical
dielectric particles of amorphous SiO.sub.2 with radii generally
between 50 and 5000 nm, and micro-crystals of garnet fluorescent
material with radii generally between 1000 and 10,000 nm. The LED
according to this particular embodiment can also be a white
LED.
[0017] According to a yet additional embodiment, the invention
provides an LED comprising a light emitting component such as an
AlInGaN semiconductor chip encapsulated into dielectric phosphor
powder (DPP). The DPP is made of a mixture of nearly spherical
dielectric particles of amorphous GaN with radii generally between
50 and 5000 nm, and micro-crystals of garnet fluorescent material
with radii generally between 1000 and 10,000 nm. The LED according
to this particular embodiment can also be a white LED.
[0018] An exemplary structure of an LED according to a preferred
embodiment of the invention comprises a crystalline semiconductor
chip encapsulated into epoxy, wires connected to the semiconductor
chip, metallic leads connected to the wires, and an epoxy
encapsulation covered with dielectric phosphor powder (DPP). The
DPP is made of a mixture of nearly spherical dielectric particles
with crystalline phosphor particles embedded into the epoxy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The foregoing and other advantages and features of the
invention will become more apparent from the detailed description
of the preferred embodiments of the invention given below with
reference to the accompanying drawings in which:
[0020] FIG. 1a is a diagram illustrating an LED with light
wavelength conversion in the art;
[0021] FIG. 1b is a diagram illustrating, in conjunction with FIG.
1a, an LED with light wavelength conversion in the art using dense
phosphor powder;
[0022] FIG. 1c is a diagram illustrating, in conjunction with FIG.
1a, an LED with light wavelength conversion in the art using dilute
phosphor powder;
[0023] FIG. 1d is a diagram illustrating light wavelength
conversion using dielectric phosphor powder (DPP) in accordance
with the invention;
[0024] FIGS. 2a and 2b are diagrams that illustrate another
embodiment of an LED with light wavelength conversion using the
dielectric phosphor powder (DPP) in accordance with the invention;
and
[0025] FIGS. 3a and 3b are diagrams that illustrate yet another
embodiment of an LED with light wavelength conversion using the
dielectric phosphor powder (DPP) in accordance with the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1d is a diagram that illustrates light wavelength
conversion using dielectric phosphor powder (DPP) in accordance
with the invention, as applied to the LED shown in FIG. 1a. The
wavelength converting substance 6 of FIG. 1a is replaced with a
dielectric phosphor powder or DPP. The DPP according to the
invention is made of a mixture of microscopic, nearly spherical
dielectric particles and crystalline phosphor particles embedded in
the epoxy 9d. The employment of light scattering media or
dispersion media such as dielectric particles (or any particles
with a band gap larger than 3 eV) in an LED significantly improves
the light uniformity of a light emitted by the LED. The weight or
volume concentration of the crystalline phosphor particles embedded
in the epoxy 9d depends on the thickness of the epoxy layers and
the size and distribution of the phosphor particles. The
concentration of the phosphor particles are generally 2% to 25% of
the total volume of the dielectric phosphor powder (DPP). Phosphor
particles that can be used according to the invention include Gd,
Y, Ce or Nd-based phosphors.
[0027] The dielectric phosphor powder (DPP) is made of a mixture of
microscopic, nearly spherical dielectric particles and phosphor
particles. The spherical dielectric micro-particles can be made of
wide-band-gap semiconductors or transparent dielectrics. The DPP
forms scattering optical media, whose refractive index, scattering
properties and light conversion properties are controlled by the
refractive index and radii of the dielectric particles. Using DPP
in the LED allows effective light extraction from the light
emitting component of the LED (e.g., the crystalline semiconductor
chip), effective light wavelength conversion, and substantially
uniform color distribution over emission angles, and wider emission
angle of the light generated by the LED with DPP, in contrast to
conventional LEDs with light conversion without DPP.
[0028] The DPP can also include phosphor particles, and bubbles (or
voids) instead of the dielectric particles. The bubbles of the DPP
have a band gap larger than 3 eV. The bubbles are spherical in
nature because of surface tension thereof, which function as light
scattering media for light wavelength conversion in accordance with
the invention. The bubbles can be air bubbles, N2 bubbles, noble
gas bubbles. The bubble are disposed onto the epoxy 9d by
introducing gas corresponding to the bubbles during molding of the
epoxy 9d. Furthermore, the DPP can also be a mixture of the
bubbles, dielectric particles, and the phosphor particles.
[0029] The structure of the LED according to this particular
embodiment of the invention includes a crystalline semiconductor
chip, a dielectric phosphor powder (DPP) made of a mixture of
microscopic, nearly spherical dielectric particles with crystalline
phosphor particles embedded into the epoxy 9d, wires connected to
the semiconductor chip, metallic leads connected to the wires for
transferring an electrical current to the semiconductor chip, and
an epoxy encapsulation covered with the dielectric phosphor powder
or DPP.
[0030] In another embodiment according to the invention, the DPP is
made of a mixture of microscopic, nearly spherical dielectric
particles of microcrystalline AlN. According to yet another
embodiment, the DPP is made of a mixture of nearly spherical
dielectric particles of amorphous Si.sub.3N.sub.4 with radii
generally between 50 and 5000 nm, and micro-crystals of garnet
fluorescent material with radii generally between 1000 and 10,000
nm. In an additional embodiment, the DPP is made of a mixture of
nearly spherical dielectric particles 10d of amorphous SiO.sub.2
with radii generally between 50 and 5000 nm, and micro-crystals of
garnet fluorescent material 8d with radii generally between 1000
and 10,000 nm embedded into the epoxy 9d. According to a further
embodiment, the DPP is made of a mixture of nearly spherical
dielectric particles 10d of amorphous GaN with radii generally
between 50 and 5000 nm, and micro-crystals of garnet fluorescent
material 8d with radii generally between 1000 and 10,000 nm
embedded into the epoxy 9d.
[0031] FIGS. 2a and 2b are diagrams illustrating another embodiment
of an LED with light wavelength conversion using dielectric
phosphor powder (DPP) according to the invention. The invention
provides an LED comprising a light emitting component and
dielectric phosphor powder (DPP) which absorb a part of light
emitted by the light emitting component and emits light of a
wavelength that is different from that of the absorbed light. In a
preferred embodiment according to the invention, the LED includes a
crystalline semiconductor chip (InGaN crystalline semiconductor
chip 10) serving as the light emitting component. The DPP is made
of a mixture of nearly spherical dielectric particles with
crystalline phosphor particles embedded into the epoxy 70. The
weight or volume concentration of the crystalline phosphor
particles embedded in the epoxy encapsulation 90 depends on the
thickness of the epoxy layers and the size and distribution of the
phosphor particles. The concentration of the phosphor particles can
be 2% to 25% by volume. Phosphor particles that can be used
according to the invention include Gd, Y, Ce or Nd-based phosphors.
In particular, the DPP wavelength converting substance 60 is made
of the mixture of nearly spherical dielectric particles 110 of
amorphous Si.sub.3N.sub.4 with radii generally between 50 and 1000
nm and micro-crystals 120 of garnet fluorescent material with radii
generally between 1000 and 10000 nm embedded into the epoxy 90.
Semiconductor chip 10, serving as the light emitting component in
the LED, generates primary light when an electrical current is
applied to the chip 10 through wires 20 and 30, which are
electrically connected to metallic leads 40 and 50. The wavelength
converting substance 60, containing DPP, covers the light emitting
component (i.e., semiconductor chip 10) and is molded in resin. An
n electrode and p electrode of the semiconductor chip 10 are
electrically connected to the metallic leads 40 and 50,
respectively, by means of the wires 20 and 30.
[0032] The DPP can also include phosphor particles, and bubbles (or
voids) instead of the dielectric particles. The bubbles of the DPP
have a band gap larger than 3 eV. The bubbles are spherical in
nature because of surface tension thereof, which function as light
scattering media for light wavelength conversion in accordance with
the invention. The bubbles can be air bubbles, N2 bubbles, noble
gas bubbles. The bubble are disposed onto the epoxy 90 by
introducing gas corresponding to the bubbles during molding of the
epoxy 90. Furthermore, the DPP can also be a mixture of the
bubbles, dielectric particles, and the phosphor particles.
[0033] The structure of the LED according to this particular
embodiment of the invention includes a crystalline semiconductor
chip 10 encapsulated into a dielectric phosphor powder (DPP) made
of a mixture of microscopic, nearly spherical dielectric particles
with crystalline phosphor particles embedded into the epoxy 90, the
wires 20 and 30 connected to the semiconductor chip 10, the
metallic leads 40 and 50 connected to the wires for transferring an
electrical current to the semiconductor chip, and an epoxy
encapsulation 90 covered with the dielectric phosphor powder or
DPP.
[0034] The light emitting component used in the LED is a gallium
nitride compound semiconductor capable of efficiently exciting the
garnet fluorescent material in the DPP. The light emitting
component of the LED is made by forming a light emitting layer of
InGaN on a substrate in a semiconductor process. The structure of
the light emitting component can be a homostructure,
heterostructure or double heterostructure.
[0035] In this particular embodiment according to the invention, as
an electrical current is applied to the crystalline semiconductor
chip 10, it generates a primary blue-green light with wavelength
.lambda..sub.p in region from 400 to 500 nm. The DPP wavelength
converting substance 60 absorbs the primary blue-green light and
generates the secondary yellow-orange light with wavelength
.lambda..sub.s in region from 550 to 660 nm. The resulting light
coming out of the LED with the DPP is the sum of the blue-green
light with wavelength .lambda..sub.p and the yellow-orange light
with wavelength .lambda..sub.s, which appears white to human
eyes.
[0036] The color quality of the resulting white light is determined
by the distribution over the emission angle of the ratio of the
intensities of the primary blue-green light and the secondary
yellow-orange light, and is controlled by the DPP wavelength
converting substance 60. The DPP wavelength converting substance 60
is made of the mixture of near spherical dielectric particles 110
of amorphous Si.sub.3N.sub.4 with radii R.sub.s in the region
R.sub.s=50 to 1000 nm and micro-crystals 120 of garnet fluorescent
material with radii in the region R.sub.m=1000 to 10000 nm embedded
into the epoxy 90. The light scattering properties of the spherical
dielectric particles of amorphous Si.sub.34.sub.4 strongly depend
on their radii R.sub.s, where R.sub.s=.lambda..sub.p/2.lambda.n.su-
b.e, and n.sub.e=1.3 to 1.5 which is the refractive index of the
epoxy encapsulation 70. This allows the control of the angle
distribution of the ratio in the intensities of the primary
blue-green light and the secondary yellow-orange light, and the
quality of the white light emitted by the LED by controlling the
radii R.sub.s of the nearly spherical dielectric particles of
amorphous Si.sub.34.sub.4.
[0037] Since the refractive index of Si.sub.34.sub.4 spherical
particles n.sub.s=2.05 is close to square root of the product of
the refractive index of InGaN crystalline semiconductor chip 10
(where n.sub.c=2.3 to 2.8) and refractive index epoxy encapsulation
70 (where n.sub.e=1.3 to 1.5), using the DPP in the LED in
accordance with the invention significantly improves the primary
light extraction from the semiconductor chip 10.
[0038] According to another embodiment, the invention provides a
light emitting diode (LED) comprising a light emitting component
(such as an AlInGaN crystalline semiconductor chip 10) encapsulated
into dielectric phosphor powder (DPP). The DPP wavelength
converting substance 60 is made of a mixture of microscopic, nearly
spherical dielectric particles of microcrystalline AIN embedded
into the epoxy 90. According to yet another embodiment, the
invention provides an LED comprising a light emitting component
such as an AlInGaN semiconductor chip 10 encapsulated into
dielectric phosphor powder (DPP). The DPP wavelength converting
substance 60 is made of a mixture of nearly spherical dielectric
particles of amorphous GaN with radii generally between 50 and 5000
nm, and micro-crystals of garnet fluorescent material with radii
generally between 1000 and 10,000 nm embedded into the epoxy
90.
[0039] FIGS. 3a and 3b are diagrams that illustrate a further
embodiment of an LED with light wavelength conversion using
dielectric phosphor powder (DPP) according to the invention. The
invention provides an LED comprising a light emitting component and
dielectric phosphor powder (DPP) which absorb a part of light
emitted by the light emitting component and emits light of a
wavelength that is different from that of the absorbed light. In
another preferred embodiment according to the invention, the LED
includes a crystalline semiconductor chip (InGaN crystalline
semiconductor chip 31) serving as the light emitting component. The
DPP is made of a mixture of nearly spherical dielectric particles
with crystalline phosphor particles embedded into the epoxy 37. The
weight or volume concentration of the crystalline phosphor
particles embedded in the epoxy 39 depends on the thickness of the
epoxy layers and the size and distribution of the phosphor
particles. The concentration of the phosphor particles can be 2% to
25% by volume. Phosphor particles that can be used according to the
invention include Gd, Y, Ce or Nd-based phosphors. In particular,
the DPP wavelength converting substance 36 is made of the mixture
of nearly spherical dielectric particles 311 of amorphous SiO.sub.2
with radii generally between 50 and 1000 nm and micro-crystals 312
of garnet fluorescent material with radii generally between 1000
and 10000 nm embedded into the epoxy 39. Semiconductor chip 31,
serving as the light emitting component in the LED, generates
primary light when an electrical current is applied to the chip 31
through wires 32 and 33, which are electrically connected to
metallic leads 34 and 35. The wavelength converting substance 36,
containing DPP, covers the light emitting component (i.e.,
semiconductor chip 31) and is molded in resin. An n electrode and p
electrode of the semiconductor chip 31 are electrically connected
to the metallic leads 34 and 35, respectively, by means of the
wires 32 and 33.
[0040] The DPP can also include phosphor particles, and bubbles (or
voids) instead of the dielectric particles. The bubbles of the DPP
have a band gap larger than 3 eV. The bubbles are spherical in
nature because of surface tension thereof, which function as light
scattering media for light wavelength conversion in accordance with
the invention. The bubbles can be air bubbles, N2 bubbles, noble
gas bubbles. The bubble are disposed onto the epoxy 39 by
introducing gas corresponding to the bubbles during molding of the
epoxy 39. Furthermore, the DPP can also be a mixture of the
bubbles, dielectric particles, and the phosphor particles.
[0041] The structure of the LED according to this particular
embodiment of the invention includes a crystalline semiconductor
chip 31 encapsulated into the epoxy 37, the wires 32 and 33
connected to the semiconductor chip, the metallic leads 34 and 35
connected to the wires for transferring an electrical current to
the semiconductor chip 31, and an epoxy encapsulation 39 covered
with the dielectric phosphor powder (DPP) made of a mixture of
microscopic, nearly spherical dielectric particles with crystalline
phosphor particles embedded into the epoxy 37.
[0042] In this particular embodiment according to the invention, as
an electrical current is applied to the crystalline semiconductor
chip 31, it generates a primary blue-green light with wavelength
.lambda..sub.p in region from 400 to 500 nm. The DPP wavelength
converting substance 36 absorbs the primary blue-green light and
generates the secondary yellow-orange light with wavelength
.lambda..sub.s in region from 550 to 660 nm. The resulting light
coming out of the LED with the DPP is the sum of the blue-green
light with wavelength .lambda..sub.p and the yellow-orange light
with wavelength .lambda..sub.s, which appears white to human
eyes.
[0043] The color quality of the resulting white light is determined
by the distribution over the emission angle of the ratio of the
intensities of the primary blue-green light and the secondary
yellow-orange light, and is controlled by the DPP wavelength
converting substance 36. The DPP wavelength converting substance 36
is made of the mixture of near spherical dielectric particles 311
of amorphous SiO.sub.2 with radii R.sub.s in the region R.sub.s=50
to 1000 nm and micro-crystals 312 of garnet fluorescent material
with radii in the region R.sub.m=1000 to 10000 nm embedded into the
epoxy 39.
[0044] The light scattering properties of the spherical dielectric
particles of amorphous SiO.sub.2 strongly depend on their radii
R.sub.s, where R.sub.s=.lambda..sub.p/2.lambda.n.sub.e, and
n.sub.e=1.3 to 1.5 which is the refractive index of the epoxy
encapsulation 37. This allows the control of the angle distribution
of the ratio in the intensities of the primary blue-green light and
the secondary yellow-orange light, and the quality of the white
light emitted by the LED by controlling the radii R.sub.s of the
nearly spherical dielectric particles of amorphous SiO.sub.2.
[0045] Other materials that can be used for the garnet fluorescent
material (e.g., 120 of FIG. 2b and 312 of FIG. 3b) include phosphor
of garnet fluorescent material activated with cerium which contains
at least one element selected from Y, Lu, Sc, La, Gd and Sm, and at
least one element selected from Al, Ga and In. For example,
materials such as yttrium-aluminum-garnet fluorescent material (YAG
phosphor) activated with cerium can be used in the DPP according to
the invention.
[0046] Although the discussions herein are in the context of an
LED, it is understood that other light sources (e.g., a planar
light source, laser diodes) will benefit from the methodology
according to the invention. Moreover, although some of the
discussions herein are in the context of a white LED, it is also
understood that other light wavelength emitters will benefit from
the methodology according to the invention. The fields of
application for an LED with DPP according to the invention include
at least electronics, instrumentation, electrical appliances,
displays for automobiles, aircraft, as well as outdoor displays, or
any other illumination applications.
[0047] Although the invention has been particularly shown and
described in detail with reference to the preferred embodiments
thereof, the embodiments are not intended to be exhaustive or to
limit the invention to the precise forms disclosed herein. It will
be understood by those skilled in the art that many modifications
in form and detail may be made without departing from the spirit
and scope of the invention. Similarly, any process steps described
herein may be interchangeable with other steps to achieve
substantially the same result. All such modifications are intended
to be encompassed within the scope of the invention, which is
defined by the following claims and their equivalents.
* * * * *