U.S. patent application number 11/920757 was filed with the patent office on 2009-08-20 for luminescence conversion led.
Invention is credited to Daniel Becker, Herbert Brunner, Tim Fiedler, Jorg Strauss, Martin Zachau.
Application Number | 20090206352 11/920757 |
Document ID | / |
Family ID | 36698821 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090206352 |
Kind Code |
A1 |
Becker; Daniel ; et
al. |
August 20, 2009 |
Luminescence conversion led
Abstract
A luminescence conversion LED having a radiation emitting chip
that is connected to electrical connections and is surrounded by a
housing that comprises at least a basic body and a cap, the chip
being seated on the basic body, in particular in a cutout of the
basic body, and the primary radiation of the chip being converted
at least partially into longer wave radiation by a conversion
element, wherein the cap is formed by a vitreous body, the
conversion means being contained in the vitreous body, the
refractive index of the vitreous body being higher than 1.6,
preferably at least n=1.7.
Inventors: |
Becker; Daniel; (Augsburg,
DE) ; Brunner; Herbert; (Sinzing, DE) ;
Fiedler; Tim; (Munchen, DE) ; Strauss; Jorg;
(Regensburg, DE) ; Zachau; Martin; (Geltendorf,
DE) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE LLP
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Family ID: |
36698821 |
Appl. No.: |
11/920757 |
Filed: |
May 11, 2006 |
PCT Filed: |
May 11, 2006 |
PCT NO: |
PCT/DE2006/000823 |
371 Date: |
November 19, 2007 |
Current U.S.
Class: |
257/98 ;
257/E21.001; 257/E33.001; 438/26 |
Current CPC
Class: |
H01L 2224/48247
20130101; H01L 2224/48091 20130101; H01L 33/505 20130101; H01L
2224/48091 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
257/98 ; 438/26;
257/E33.001; 257/E21.001 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H01L 21/00 20060101 H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2005 |
DE |
10 2005 023 134.9 |
Claims
1. A luminescence conversion LED having a radiation emitting chip
that is connected to electrical connections and is surrounded by a
housing that comprises at least a basic body and a cap, the chip
being seated on the basic body, in particular in a cutout of the
basic body, and the primary radiation of the chip being converted
at least partially into longer wave radiation by a conversion
element, wherein the cap is formed by a vitreous body, the
conversion means being contained in the vitreous body, the
refractive index of the vitreous body being higher than 1.6,
preferably at least n=1.7.
2. The LED as claimed in claim 1, wherein the vitreous body is
formed from crown or flint glasses.
3. The LED as claimed in claim 2, wherein the vitreous body is
formed from barite flint, boron crown or lanthanum crown glass.
4. The LED as claimed in claim 1, wherein the phosphor is a highly
stable phosphor of the garnet or oxinitride type.
5. The LED as claimed in claim 1, wherein the vitreous body is
largely free from lead oxide.
6. The LED as claimed in claim 1, wherein the vitreous body is
based on a bismuth containing borate glass.
7. The LED as claimed in claim 1, wherein the vitreous body is
based on a phosphate glass.
8. The LED as claimed in claim 4, wherein the vitreous body is
based on a glass whose main component is Al.sub.2O.sub.3.
9. The LED as claimed in claim 1, wherein the vitreous body
contains at least one of the ions Pb.sup.2+, Bi.sup.3+, Ba.sup.2+,
Li.sup.+ and Ti.sup.4+ in a quantity sufficient to implement a
refractive index of at least n.gtoreq.1.6, in particular
n.gtoreq.1.7.
10. A method for producing a luminescence conversion LED as claimed
in claim 1, wherein the following method steps are used during
production: a) sintering a mixture of phosphor and glass powder, in
particular pressed so as to minimize air inclusions, to a
temperature in the vicinity of the softening point of the
glass.
11. A method for producing a luminescence conversion LED as claimed
in claim 1, wherein the following method steps are used during
production: a) producing a liquid melt from glass, or suitable
precursor materials with phosphor powder suspended therein; b)
spraying the liquid melt.
12. A method for producing a luminescence conversion LED as claimed
in claim 1, wherein the following method steps are used during
production: a) producing a layer of defined thickness from phosphor
and optionally glass powder, binder and other additives on a glass
substrate; b) optionally repeating step a) until the desired layer
thickness is achieved; and c) sintering at a temperature close to
the softening point of the glass.
13. A method for producing a luminescence conversion LED as claimed
in claim 1, wherein the following method steps are used during
production: a) applying a phosphor layer made from particles to a
substrate, in particular directly to a chip; b) depositing glass or
glass precursors from the gas phase into the interspaces between
the phosphor grains.
14. A method for producing a luminescence conversion LED as claimed
in claim 1, wherein the following method steps are used during
production: a) producing a liquid melt from glass, b) precipitating
phosphor particles from the glass melt.
Description
TECHNICAL FIELD
[0001] The invention proceeds from a luminescence conversion LED in
accordance with the preamble of claim 1. What is concerned here in
particular is an LED with a high efficiency of conversion.
PRIOR ART
[0002] US-A 2003/025449 has already disclosed a luminescence
conversion LED in which the phosphor is embedded in an environment
made from glass containing material. This exhibits higher stability
than the usual resins or silicones, above all in the case of chips
that emit shortwave primary radiation in the UV or blue spectral
region. Glass, glass ceramic or silica glass is to be regarded as
suitable in this case.
[0003] U.S. Pat. No. 6,417,019 discloses converting the phosphor by
the use of an environment with as high a refractive index as
possible, namely of at least 1.5, preferably more than 2.1.
However, no particular implementation is specified therefor.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a
luminescence conversion LED in accordance with the preamble of
claim 1 that has a high conversion efficiency.
[0005] This object is achieved by means of the characterizing
features of claim 1. Particularly advantageous refinements are to
be found in the dependent claims.
[0006] The present invention is based on the idea of minimizing the
losses in the LED through jumps in the refractive index of the
various materials. The phosphors are usually embedded in a cladding
material. Primary and secondary radiation is scattered on the
powder particles of the phosphor, and this leads to scattering
losses. This cladding material also surrounds the chip and
constitutes an optical path
for coupling of the light beam from the LED. Known cladding
materials are epoxy resins, silicones and hybrids of these material
classes. The refractive index of these materials, and also of
conventional glass materials, is typically at n=1.4 to 1.6.
[0007] By making targeted use of glasses with as high a refractive
index as possible of more than 1.6, preferably at least n=1.7, it
is possible to reduce the losses attending them. Furthermore, it is
advantageous that the material exhibits good transparency in the
range of 400 to 750 nm.
[0008] In order to minimize the losses owing to jumps in refractive
index and scattering at the phosphor, the refractive index of the
glass should, on the one hand, come as close as possible to that of
the phosphor. On the other hand, in order to maximize the exit
efficiency of the blue light from the semiconductor chip into a
glass/phosphor converter composition, the refractive index of this
converter should come as close as possible to that of the
semiconductor chip. In the exemplary case of the phosphor YAG:Ce
and a blue emitting semiconductor LED of type InGaN, the refractive
indices are approximately n=1.8 and n=2.2.
[0009] A further boundary condition is, of course, that the
emission wavelength of the chip is suitable for exciting the
phosphor to emission, and that the cladding material and this
primary emission, as well as the secondary emission of the
phosphors absorb as little as possible.
[0010] Consequently, it is a basic requirement to clad the phosphor
with high index glass. Many phosphors have a refractive index of
from 1.7 to more than 2. In these cases, the phosphor is to be
embedded in a medium with as high an index as possible. Losses
owing to scattering and jumps in refractive index at the particles
of the phosphor and total reflection, and therefore higher losses
owing to absorption, can thereby be minimized in the phosphor
particles.
[0011] A further advantage of glasses as against the known cladding
materials such as epoxy resins, silicones or hybrids of these two
material classes is their higher resistance to heat, something
which is chiefly important for so called high power LEDs with
"junction" temperatures substantially above 140.degree. C.
[0012] Garnet phosphors, above all, are suitable for such a mode of
procedure: firstly, because they have a high refractive index
(about n=2) in any case, and secondly
because they are stable against relatively high processing
temperatures such as can occur during embedding in glass. Again, a
few oxinitride phosphors are particularly well suited therefor.
[0013] The use of a glass matrix in conjunction with nanophosphors
is particularly advantageous, since the transparency of the glass
is maintained in this case completely or at least to a large
extent. Nanophosphors are phosphors with a mean particle size of
clearly below 1 .mu.m, particularly between 10 and 500 nm.
[0014] The phosphor can be enclosed in particle form by glass, and
subsequently dispersed in a glass or polymer. However, the phosphor
can also be dispersed directly in the glass and subsequently be
brought into the desired form by shaping. The phosphor particles
can also be synthesized directly in the glass melt. If appropriate,
it is also advantageous to machine the surfaces after this, for
example by polishing, in order to obtain desired surfaces or
shapes. Dispersion of the phosphor particles in a glass is
performed, for example, by heating a mixture of phosphor and ground
glass powder. Melting is performed, for example, in a crucible of
Pt in a muffle furnace up to a temperature at which a vitreous body
is produced. Subsequently, the crucible is quenched in a water
bath, and the cooled glass body is removed from the crucible. In
this case, a transparent, vitreous body is produced only starting
from a specific temperature, to be precise, not until the glass
component has partially melted.
[0015] Various methods are possible for producing the phosphor
glass composition converter:
[0016] 1st method: Sintering a mixture of phosphor and glass
powder, and optionally further additives for the more effective
dispersion of the phosphor particles, to a temperature in the
vicinity of the softening point of the glass. In particular, the
mixture can be previously pressed in order to minimize air
inclusions. It is possible with the aid of this method to achieve a
relatively homogeneous distribution of the phosphor in the glass as
long as the temperature is not so high that reaction occurs between
phosphor particles and glass and the viscosity of the glass drops
sharply and the phosphor sediments in the glass. The rate of
cooling will depend on the type of glass and can, if appropriate,
take place quickly in order to avoid crystallization of the glass.
For cooling purposes, the glass can be cast into a mold and
optionally be pressed
immediately or subsequently. This method can be effectively used in
order to simultaneously impart optical properties. A lens can be
formed, for example. As a general rule, in this case an
agglomeration of the phosphor particles is reliably avoided. The
phosphor particles are tightly enclosed by glass in this
method.
[0017] 2nd method: Spraying a liquid melt made from glass or
suitable precursor materials with phosphor powder suspended
therein. In the event of spraying and expansion caused thereby,
cooling occurs immediately and phosphor grains enclosed by a glass
cladding are formed. These can subsequently be sintered to form a
compact vitreous body.
[0018] 3rd method: Producing a layer of defined thickness from
phosphor, and optionally glass powder as well as binder and other
additives on a glass substrate, with subsequent sintering at a
temperature at which no chemical reactions yet occur between glass
material and phosphor. A thin layer is formed in this case in which
the phosphor grains are tightly enclosed by a glass matrix. The
above steps can be repeated until the desired layer thickness is
achieved. In particular, it is possible to use a specifically
shaped, for example plane, and even polished substrate. This method
has the advantage that the shape of the converter, in particular
the planarity, can be largely defined before the introduction of
the phosphor, because it is scarcely influenced by the introduction
of the phosphor. It follows that cost effective standard
substrates, or at least standard shaping techniques, can be used. A
further advantage is that the phosphor penetrates into the
substrate only on one side, and so the averted side remains largely
undisturbed and largely retains its original properties, in
particular the higher mechanical stability of a glass substrate
without inclusions. A glass/phosphor layer can advantageously be
sintered on a glass substrate by supplying energy on one side. In
addition to conventional heating methods, this purpose is also
served by electromagnetic irradiation. In particular, one sided
heating by means of a laser (for example CO.sub.2 laser) or a
microwave transmitter are on offer.
[0019] 4th method: Applying a phosphor layer to a substrate,
preferably directly to the semiconductor substrate, and depositing
glass or suitable glass precursors from the gas phase into the
interspaces between the phosphor grains. The production of glass
from the gas phase is known per se.
[0020] 5th method: The synthesis of the phosphor particles is
performed in the glass melt. The precipitation of YAG:Ce crystals
from a Y.sub.2O.sub.3--Al.sub.2O.sub.3--SiO.sub.2--CeO.sub.2 glass
melt is known, see S. Tanabe (Graduate School of Human and
Environmental Sciences, Kyoto University, Kyoto, Japan): "Glass
ceramic phosphors for solid-state lighting", 79th Glass Conference,
Wurzburg, May 2005. This method can be used with particular
advantage to produce phosphor particles in the nanometer and
submicrometer range that are dispersed in glass, since the
agglomeration of these phosphor particles is effectively
prevented.
[0021] Glasses with a high refractive index of typically 1.6, in
particular 1.7 or more, are fundamentally suitable. Particularly
suitable are barite crown glasses, lanthanum crown glass and dense
flint glasses. A high refractive index is achieved by the inclusion
of specific ions, Pb.sup.2+, Bi.sup.3-, Ba.sup.2+, Li.sup.+ and
Ti.sup.4+ being particularly suitable.
[0022] The advantage of Pb is, for example, the low processing
temperature and the low tendency to devitrification. A typical lead
glass is 15-30% PbO, 3 to 7% Na2O and/or K2O, residue SiO2. These
glasses have a low softening point (approximately 300 to
500.degree. C.), a high coefficient of thermal expansion, a high
refractive index of approximately n=1.8 and a good transparency in
the range of 300 to 3000 nm. A typical processing temperature here
is 720 to 880.degree. C.
[0023] In the case of the class of high index glasses that do not
contain lead, bismuth-containing borate glasses and phosphate
glasses, in particular, prove to be suitable, in addition to a low
processing temperature these also have high refractive indices in
the region of 2.0 to 2.3.
[0024] Finally, such glasses, in particular, can themselves be
especially well shaped directly to the production of optical
properties, for example as dome with lens properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The aim below is to explain the invention in more detail
with the aid of a number of exemplary embodiments. In the
drawings:
[0026] FIG. 1 shows a semiconductor component that serves as light
source (LED) for white light;
[0027] FIG. 2 shows an REM picture of a phosphor glass composition
produced according to method 1;
[0028] FIG. 3 an REM picture of a phosphor glass composition
produced according to method 3; and
[0029] FIG. 4 shows a further exemplary embodiment of an LED.
PREFERRED EMBODIMENT OF THE INVENTION
[0030] A design such as is described in U.S. Pat. No. 5,998,925,
for example, is employed for use in a white LED together with an
InGaN Chip. The design of such a light source for white light is
shown explicitly in FIG. 1. The light source is a semiconductor
component (chip 1) of type InGaN with a peak emission wavelength of
460 nm and having a first and second electrical connection 2, 3
that is embedded in an opaque basic housing 8 in the region of a
cutout 9. One of the connections 3 is connected to the chip 1 via a
bonding wire 14. The cutout has a wall 17 that serves as reflector
for the blue primary radiation of the chip 1. The cutout 9 is
filled with a casting compound 5 that contains the components of
glass and phosphor pigments 6. The phosphor pigments are, for
example, a mixture of a number of pigments, including YAG:Ce. An
alternative is TbAG:Ce. Production takes place according to one of
methods 1 and 2.
[0031] The REM picture in FIG. 2 shows a cross section of a solid
phosphor glass composition. The production took place according to
method 1, more precisely by intensive mixing of glass powder and
phosphor powder and subsequent sintering at 1000.degree. C. for 1
h.
[0032] The REM picture shows, firstly, that the garnet phosphor
grains are tightly coated with glass without air gaps and that,
secondly, it is possible to achieve a high density of YAG particles
in glass without dissolving the YAG particles in the glass, and
that this is possible for phosphor grains of the most varied shape
and grain size. However, the image is only an example and does not
in any way constitute a restriction with regard to the density of
the YAG particles in the glass, the grain size,
the grain distribution or the grain shape of the phosphor
particles. These are generally freely selectable and can be
optimized as a function of design.
[0033] The REM picture of FIG. 3 shows a phosphor glass composition
converter that is produced using method 3. It is to be seen that
this method can be used to produce very thin layers with a high
phosphor content. Here, as well, the phosphor grains are tightly
coated with glass without an air gap. In particular, no air bubbles
are enclosed in the glass.
[0034] A further embodiment is an LED in the case of which a
suitably prepared glass plate is arranged upstream of the chip. In
FIG. 4, the light source is a semiconductor component (chip 1) of
type InGaN with a peak emission wavelength of 460 nm and having a
first and second electrical connection 2, 3 that is embedded in an
opaque basic housing 8 in the region of a cutout 9. One of the
connections 3 is connected to the chip 1 via a bonding wire 14. The
cutout has a wall 17 that serves as reflector for the blue primary
radiation of the chip 1. The cutout 9 is filled with a casting
compound 5 that contains immersion liquid as main component.
Arranged upstream thereof is a glass plate 8 that is prepared on
its underside with pigments, including YAG:Ce, according to one of
methods 3 and 4.
[0035] High index glasses with a low softening temperature and
relatively slight change in viscosity with the temperature at the
softening point are to be preferred as matrix. Starting from a
specific temperature, the phosphor layer diffuses into the glass
plate and can no longer be removed mechanically.
[0036] In order to avoid the inclusion of air bubbles, it is
advantageous to subject the glass powder to a heat treatment before
it is processed. One alternative is to raise the melting process to
temperatures of at least 1200.degree. C. A temperature of 1400 to
1500.degree. C. is recommended for very good homogenization.
Typical homogenizing and refining methods are [0037] thermal
refining: raising the temperature as far as 1590.degree. C.; [0038]
mechanical stirring or ultrasound; [0039] introducing additional
gases into the bottom of the trough; and [0040] chemically refining
by deliberately producing large gas bubbles; a typically refining
agent is Na.sub.2SO.sub.4 in this case; here, a temperature of at
least 1300.degree. C. is to be approached. In general, the aim
should be always to apply the method requiring as little an
increase in temperature as possible.
[0041] Examples of particularly suitable glasses are lanthanum
crown, lanthanum heavy flint, barite heavy flint and, in
particular, lanthanum flint and barite flint.
[0042] The following table 1 shows two particular examples. The
composition is specified in percent.
[0043] A first exemplary embodiment is as follows: a YAG:Ce powder
(d.sub.50 approximately 2 .mu.m) and Schott 8532 glass powder are
mixed at a mass ratio of 1:3 in a centrifugal rotary mixer at 3000
rpm. The mixture is heated for 30 min in a platinum crucible at
780.degree. C. in air and then quenched in a water bath to room
temperature. A glass body with a yellow body color is formed. Its
surface is ground flat.
[0044] A second exemplary embodiment is as follows: a YAG:CE powder
(d.sub.50 approximately 2 .mu.m) and a bismuth-borate glass powder
(30% Bi.sub.2O.sub.3) are mixed at a mass ratio of 1:3 in a
centrifugal rotary mixer at 3000 rpm. The mixture is heated at
700.degree. C. in a platinum crucible for 30 min and then quenched
in a water bath to room temperature. Its surface is ground
flat.
[0045] A third exemplary embodiment YAG:Ce powder (d.sub.50
approximately 6 .mu.m) and Schott 8532 glass powder are mixed at a
mass ratio of 1:3 in a centrifugal rotary mixer at 2700 rpm. The
mixture is slurried in ethanol. Consequently, a thin, flat glass
plate of Schott 8532 glass is coated. The ethanol is vaporized to
air at 50.degree. C. The coated glass plate is heated in a Pt
crucible at 780.degree. C. for 30 min and subsequently cooled
slowly to room temperature. An REM picture of the cross section is
to be seen in FIG. 3.
TABLE-US-00001 TABLE 1 Component Boron crown glass Lanthanum crown
glass SiO2 65-75 -- B2O3 5-11 34-41 K2O 16-23 -- CaO 1.5-3.8 -- BaO
-- 11.5-16 Al2O3 1.6-3.5 -- SrO -- 3.9-8.2 La2O3 -- 15-32 ThO2 --
5-25 Refractive index 1.7-1.75 1.7-1.85 at 590 nm
* * * * *