Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2002-10-29
2004-05-11
Hoang, Huan (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S082000, C257S084000
Reexamination Certificate
active
06734466
ABSTRACT:
The invention relates to a coated phosphor filler for an optical device (e.g., a light emitting diode (LED)), a method for forming a coated phosphor filler and a method for forming a LED making use of that coated phosphor filler.
BACKGROUND OF THE INVENTION
In the prior art, phosphor fillers including phosphor particles are used in a broad field of applications, ranging from electro-luminescence to photo-luminescence devices. This rich applicability is due to the favourable physical properties of phosphor such as a high luminescence efficiency and lifetime as well as due to the presence of suitable emission colours in the optical emission spectrum.
A technological application of such phosphor fillers with increasing importance is the light emitting diode (LED), which comprises a LED-chip being electrically connected to a electrically conducting contact base. The LED-chip usually comprises a semiconducting p-n-junction, in which electrons and holes, which have been injected via a supply voltage, recombine under light emission. In order to direct the light emission into the operational direction of the LED-Chip, the LED-Chip is usually encapsulated by an optical dome made of transparent resin which, in turn, may include a phosphor filler by which the light emitting spectrum of the LED-Chip can be converted as necessary.
In particular, due to the development of blue emitting LED-chips and the use of such phosphor fillers, LED-devices providing a wide colour range can be obtained, including the so-called “white LED”, which can compete with conventional types of light sources in a broad field of applications such as traffic lights and signboards.
Generally speaking, such phosphor fillers may be based on different types of phosphor compounds, namely stable and unstable phosphor compounds. Stable phosphor compounds may e.g. comprise members of the garnet family, preferably (YGd)
3
Al
5
O
12
including Ce
3+
-impurities. Unstable phosphor compounds may e.g. comprise SrGa
2
S
4
:Eu
2+
, SrS:Eu
2+
, (Sr,Ca)S:Eu
2+
, ZnS:Ag.
The advantage of a phosphor filler in the form of stable phosphor compound particles is that it is not sensitive to moisture which would, in turn, reduce the reliability of the electrical device, like an LED-Chip encapsulated in an epoxy dome comprising such a phosphor filler.
However, it is also known in the prior art that the performance of devices with unstable phosphor compound can be improved, too, by coating the phosphor compound material, i.e. the outer surface of the individual unstable phosphor compound particles, with a protective coating film. In particular, said unstable phosphor compound particles may be coated with an inorganic coating film including a moisture-proof barrier material such as aluminium oxide (Al
2
O
3
), zinc sulphide (ZnS), silicon nitride (Si
4
N
3
) or the like. In case of such fillers based on unstable phosphor compounds, the inorganic coating film on the individual phosphor compound particles provides for a chemical and photochemical degradation protection of the phosphor compound.
In the light of the foregoing explanations, the term “phosphor filler” refers, in the following description, to a plurality of phosphor filler particles which are either stable phosphor compound particles or unstable phosphor compounds particles coated with an inorganic moisture-proof coating film.
From U.S. Pat. No. 4,585,673, a method for forming a protective coating film on unstable phosphor compound particles is known, wherein the protective coating film is formed by a gas-phase chemical vapour deposition (MOCVD=“metal organic chemical vapour deposition”) on the phosphor compound particles which are suspended in a fluidised bed which is maintained in a temperature gradient, said protective coating being a refractory oxide such as aluminium oxide.
U.S. Pat. No. 6,001,477 discloses a method for providing on the surface of individual unstable phosphor compound particles a continuous, non-particulate coating of a metal or metalloid compound such as silicon or boron by means of a reaction between the metal or metalloid and a polymer capable of chelating ions of the metal or metalloid. The resulting coating (e.g. a BA-PVM/MA coating) is chemically adhered to the phosphor compound particles which exhibits improved lumen maintenance when applied to the inner surface of a lamp envelope.
U.S. Pat. No. 5,985,175 discloses a method for providing on individual unstable phosphor compound particles a continuous, non-particulate coating of boron oxide to enhance the quantum efficiency of the phosphor compound particles under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The method involves reacting a boron-containing precursor with an oxidizing gas in a fluidised bed of phosphor particles.
Furthermore and more generally, EP 0 539 211 B1 discloses a method for production of a microcapsule type conductive filler, wherein this conductive filler is dispersed in an epoxy type one-component adhesive agent.
A possible structure of a phosphor filler
100
according to the prior art is schematically illustrated in
FIG. 2
a
. The phosphor filler
100
comprises a plurality of unstable phosphor compound particles
101
, each of the phosphor compound particles
101
being coated with an inorganic coating film
102
. The inorganic coating film
102
consists of a suitable moisture-proof barrier material such as e.g. aluminium oxide (Al
2
O
3
) and has a thickness in the range of about 3 to 4 &mgr;m.
If the thickness of the coating film
102
is large, the coating film
102
provides a significant deterioration of the optical transmissibility. On the other hand, if the thickness of the coating film
102
is low, the spacing between neighbouring phosphor compound particles
101
is relatively small. Consequently, the probability of light symbolized by light beams
103
, which is e.g. emitted by a LED as described below with reference to
FIG. 2
b
, to be re-absorbed by surrounding phosphor compound particles
101
is high and, therefore, the brightness obtained in a LED using this kind of phosphor filler is low.
A typical LED
200
, as schematically illustrated in
FIG. 2
b
, comprises a LED-chip
201
, which is mounted on a first electrically conducting frame
202
. Said first electrically conducting frame
202
is provided with a reflector cup
202
a
including a recess in which the LED-chip
201
is mounted. At least two electrodes (not shown), which may be surface mounted electrodes, are attached on said LED-chip
201
, one being electrically connected by means of a first wiring
203
to the first electrically conducting frame
202
, and the other being electrically connected by means of a second wiring
204
to a second electrically conducting frame
205
.
The LED-chip
201
is covered by a drop
206
containing a mixture consisting of epoxy and a phosphor filler dispersed therein, said drop
206
filling almost the whole recess of the reflector cup
202
a
. The phosphor compound particles of the phosphor filler may be coated with a coating film including a moisture-proof barrier material such as aluminium oxide (Al
2
O
3
), i.e. they may form a structure as described above with respect to
FIG. 2
a.
Furthermore, the major upper part of the first and second electrically conducting frames
202
and
205
as well as the whole arrangement formed by the LED-chip
201
covered by the drop
206
and the wirings
203
and
204
are encapsulated by an optical dome (or optical lens)
207
formed of transparent epoxy.
The LED
200
can e.g. be operated as a white light emitting diode, wherein phosphor compound particles in the drop
206
re-emit a broad band of yellow, yellow-green or red-green light with unabsorbed blue light from the LED-chip
201
.
Two common methods for forming a LED device are schematically illustrated in FIG.
3
. These methods are generally referred to as the “pre-mix method” (
FIG. 3
a
) and the “pre-dep method” (
FIG. 3
b
).
In the so-called “pre-dep method”, as can be seen in
FIG. 3
b
, a LED-chip
301
of a LED devic
Agilent Technologie,s Inc.
Nguyen Thinh T
LandOfFree
Coated phosphor filler and a method of forming the coated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coated phosphor filler and a method of forming the coated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coated phosphor filler and a method of forming the coated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3253272