U.S. patent application number 15/270657 was filed with the patent office on 2018-03-22 for methods for fabricating devices containing red line emitting phosphors.
The applicant listed for this patent is General Electric Company. Invention is credited to William Winder Beers, Fangming Du, Florencio Garcia, James Edward Murphy, Digamber Gurudas Porob, Anant Achyut Setlur, Srinivas Prasad Sista.
Application Number | 20180079955 15/270657 |
Document ID | / |
Family ID | 61617892 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180079955 |
Kind Code |
A1 |
Porob; Digamber Gurudas ; et
al. |
March 22, 2018 |
METHODS FOR FABRICATING DEVICES CONTAINING RED LINE EMITTING
PHOSPHORS
Abstract
Methods for fabricating coated semiconductor elements are
presented. The methods include the steps of combining a phosphor of
formula I and a polymer binder to form a composite material,
providing a semiconductor wafer including
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and a sum of i, j and k is equal to 1, coating the
composite material on a surface of the semiconductor wafer to form
a coated semiconductor wafer, and dicing the coated semiconductor
wafer using a cutting fluid apparatus to form one or more coated
semiconductor elements. A cutting fluid of the cutting fluid
apparatus includes a C.sub.1-C.sub.20 alcohol, a C.sub.1-C.sub.20
ketone, a C.sub.1-C.sub.20 acetate compound, acetic acid, oleic
acid, carboxylic acid, a source of A, silicic acid, or a
combination thereof.
Inventors: |
Porob; Digamber Gurudas;
(Bangalore, IN) ; Murphy; James Edward;
(Niskayuna, NY) ; Garcia; Florencio; (Schenectady,
NY) ; Sista; Srinivas Prasad; (Altamont, NY) ;
Setlur; Anant Achyut; (Niskayuna, NY) ; Beers;
William Winder; (Chesterland, OH) ; Du; Fangming;
(Hudson, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
61617892 |
Appl. No.: |
15/270657 |
Filed: |
September 20, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/0095 20130101;
H01L 33/502 20130101; C09K 11/02 20130101; C09K 11/617 20130101;
H01L 33/32 20130101; H01L 2933/0041 20130101 |
International
Class: |
C09K 11/61 20060101
C09K011/61; H01L 33/00 20060101 H01L033/00; H01L 33/06 20060101
H01L033/06; H01L 33/32 20060101 H01L033/32; H01L 33/56 20060101
H01L033/56; H01L 33/50 20060101 H01L033/50; H01L 33/62 20060101
H01L033/62; H01L 25/075 20060101 H01L025/075 |
Claims
1. A method, comprising: combining a phosphor of formula I and a
polymer binder to form a composite material, wherein the phosphor
of formula I is represented as: A.sub.x[(M,Mn)F.sub.y] (I)
providing a semiconductor wafer comprising
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and wherein a sum of I, j and k is equal to 1; coating
the composite material on a surface of the semiconductor wafer to
form a coated semiconductor wafer; and dicing the coated
semiconductor wafer using a cutting fluid apparatus to form one or
more coated semiconductor elements, wherein a cutting fluid of the
cutting fluid apparatus comprises a C.sub.1-C.sub.20 alcohol, a
C.sub.1-C.sub.20 ketone, a C.sub.1-C.sub.20 acetate compound,
acetic acid, oleic acid, carboxylic acid, a source of A, silicic
acid, or a combination thereof, wherein A independently at each
occurance is Li, Na, K, Rb, Cs, or a combination thereof, M is Si,
Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a
combination thereof, x is an absolute value of a charge of an [(M,
Mn)F.sub.y] ion; and y is 5, 6, or 7.
2. The method according to claim 1, wherein the cutting fluid
comprises ethanol, acetone, isopropyl alchohol, tertiary butyl
alcohol, tertiary butyl acetate, or a combination thereof.
3. The method according to claim 1, wherein the source of A
comprises KF, KCl, KBr, CaF.sub.2, a compound of formula II, or a
combination thereof, A.sub.x[(M, Mn)F.sub.y] (I)
4. The method according to claim 1, wherein the step of combining
the phosphor of formula I and the polymer binder comprises mixing
the phosphor of formula I and the polymer binder homogeneously with
a stirring rate less than 500 rpm.
5. The method according to claim 4, wherein the stirring rate is
less than 300 rpm.
6. The method according to claim 1, wherein the polymer binder is
substantially free of water, substantially free of a base, or
substantially free of water and the base.
7. The method according to claim 1, wherein the polymer binder
comprises a silicone or a silicone derivative, an epoxy or a low
temperature glass.
8. The method according to claim 1, further comprising
heat-treating the coated semicondutor wafer prior to dicing the
coated semiconductor wafer, wherein the step of heat-treating is
carried out at a tempertaure less than 200 degrees Celsius.
9. The method according to claim 8, wherein the tempertaure is less
than 150 degrees Celsius.
10. The method according to claim 1, further comprising coupling
electrical leads to the one or more coated semicondutor elements to
form one or more LED chips.
11. The method according to claim 1, wherein A is K and M is
Si.
12. A lighting apparatus comprising one or more LED chips
fabricated by a method, the method comprising: combining a phosphor
of formula I and a polymer binder to form a composite material,
wherein the phosphor of formula I is represented by: A.sub.x[(M,
Mn)F.sub.y] (I) providing a semiconductor wafer comprising
comprising In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i;
0.ltoreq.j; 0.ltoreq.k, and wherein a sum of I, j and k is equal to
1; coating the composite material on a surface of the semiconductor
wafer to form a coated semiconductor wafer; dicing the coated
semiconductor wafer to form one or more coated semiconductor
elements using a cutting fluid apparatus, wherein a cutting fluid
of the cutting fluid apparatus comprises a C.sub.1-C.sub.20
alcohol, a C.sub.1-C.sub.20 ketone, a C.sub.1-C.sub.20 acetate,
acetic acid, oleic acid, carboxylic acid, a source of A, silicic
acid, or a combination thereof; and coupling electrical leads to
the one or more coated semiconductor elements to form one or more
LED chips wherein A independently at each occurance is Li, Na, K,
Rb, Cs, or a combination thereof, M is Si, Ge, Sn, Ti, Zr, Al, Ga,
In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof, x is
an absolute value of a charge of an [(M, Mn)F.sub.y] ion; and y is
5, 6, or 7.
13. The lighting apparatus according to claim 12, wherein the
lighting apparatus includes a backlight device.
14. A method, comprising: combining K.sub.2[SiF.sub.6]:Mn.sup.4+
and a polymer binder to form a composite material; providing a
semiconductor wafer comprising comprising
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and wherein a sum of I, j and k is equal to 1; coating
the composite material on a surface of the semiconductor wafer to
form a coated semicondutor wafer; dicing the coated semiconductor
wafer using a cutting fluid apparatus to form one or more coated
semiconductor elements, wherein a cutting fluid of the cutting
fluid apparatus comprises K.sub.2[SiF.sub.6]; and coupling
electrical leads to the one or more coated semiconductor elements
to form one or more LED chips.
Description
BACKGROUND
[0001] Red-emitting phosphors based on complex fluoride materials
activated by Mn.sup.4+, such as those described in U.S. Pat. No.
7,358,542, U.S. Pat. No. 7,497,973, and U.S. Pat. No. 7,648,649,
can be utilized in combination with yellow/green emitting phosphors
such as YAG:Ce or other garnet compositions to achieve warm white
light (CCTs<5000 K on the blackbody locus, color rendering index
(CRI>80)) from a blue LED, equivalent to that produced by
current fluorescent, incandescent and halogen lamps. These
materials absorb blue light strongly and efficiently emit between
about 610-635 nanometers (nm) with little deep red/NIR emission.
Therefore, luminous efficacy is maximized compared to other red
phosphors that have significant emission in the deeper red where
eye sensitivity is poor. Quantum efficiency can exceed to 85% under
blue (440-460 nm) excitation.
[0002] While the efficacy and CRI of lighting systems using
Mn.sup.4+ activated (or doped) complex fluoride materials can be
quite high, one potential limitation is material's susceptibility
to degradation under fabrication and use conditions, for example
high temperature and humidity (HTHH) conditions. It may be possible
to reduce the degradation of the material using post-synthesis
processing steps, as described in U.S. Pat. No. 8,252,613. However,
development of improved methods for reducing or preventing
degradation of the materials is desirable.
BRIEF DESCRIPTION
[0003] Briefly, in one aspect, the present disclosure relates to
methods for fabricating coated semiconductor elements for use in
forming one or more LED chips. The methods include the steps of
combining a phosphor of formula I: A.sub.x [(M, Mn)F.sub.y] and a
polymer binder to form a composite material, providing a
semiconductor wafer including In.sub.iGa.sub.jAl.sub.kN, wherein
0.ltoreq.i; 0.ltoreq.j; 0.ltoreq.k, and a sum of i, j and k is
equal to 1, coating the composite material on a surface of the
semiconductor wafer to form a coated semiconductor wafer, and
dicing the coated semiconductor wafer using a cutting fluid
apparatus to form one or more coated semiconductor elements. A
cutting fluid of the cutting fluid apparatus includes a
C.sub.1-C.sub.20 alcohol, a C.sub.1-C.sub.20 ketone, a
C.sub.1-C.sub.20 acetate compound, acetic acid, oleic acid,
carboxylic acid, a source of A, silicic acid, or a combination
thereof. A independently at each occurrence is Li, Na, K, Rb, Cs,
or a combination thereof, M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc,
Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof, x is an
absolute value of a charge on an [(M, Mn)F.sub.y] ion, and y is 5,
6, or 7.
[0004] In another aspect, the present disclosure relates to a
lighting apparatus. The lighting apparatus includes one or more LED
chips fabricated by a method including the steps of combining a
phosphor of formula I and a polymer binder to form a composite
material, providing a semiconductor wafer including
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and where a sum of i, j and k is equal to 1, coating
the composite material on a surface of the semiconductor wafer to
form a coated semiconductor wafer, dicing the coated semiconductor
wafer using a cutting fluid apparatus to form one or more coated
semiconductor elements, and coupling electrical leads to the one or
more coated semiconductor elements to form one or more LED chips. A
cutting fluid of the cutting fluid apparatus includes a
C.sub.1-C.sub.20 alcohol, a C.sub.1-C.sub.20 ketone, a
C.sub.1-C.sub.20 acetate compound, acetic acid, oleic acid,
carboxylic acid, a source of A, silicic acid, or a combination
thereof.
[0005] In yet another aspect, the present disclosure relates to a
method for fabricating one or more LED chips. The method includes
the steps of combining K.sub.2[SiF.sub.6]:Mn.sup.4+ and a polymer
binder to form a composite material, providing a semiconductor
wafer including In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i;
0.ltoreq.j; 0.ltoreq.k, and a sum of i, j and k is equal to 1,
coating the composite material on a surface of the semiconductor
wafer to form a coated semiconductor wafer, dicing the coated
semiconductor wafer using a cutting fluid apparatus to form one or
more coated semiconductor elements, and coupling electrical leads
to the one or more coated semiconductor elements to form one or
more LED chips. A cutting fluid of the cutting fluid apparatus
includes K.sub.2[SiF.sub.6].
DRAWINGS
[0006] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawing, wherein:
[0007] FIG. 1 is a schematic cross-sectional view of an LED chip,
in accordance with one embodiment of the present disclosure;
and
[0008] FIG. 2 shows a flow chart of a method for fabricating one or
more LED chips, in accordance with another embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0009] In the following specification and the claims, the singular
forms "a", "an" and "the" include plural referents unless the
context clearly dictates otherwise. As used herein, the term "or"
is not meant to be exclusive and refers to at least one of the
referenced components being present and includes instances in which
a combination of the referenced components may be present, unless
the context clearly dictates otherwise.
[0010] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about" and
"substantially" is not limited to the precise value specified. In
some instances, the approximating language may correspond to the
precision of an instrument for measuring the value.
[0011] As used herein, the terms "phosphor", "phosphor
composition", and "phosphor material" may be used to denote both a
single phosphor as well as blends of two or more phosphors. As used
herein, the terms "lamp", "lighting apparatus", and "lighting
system" refer to any source of visible and ultraviolet light, which
can be generated by at least one light emitting element producing a
light emission when energized, for example, a phosphor material or
a light emitting diode.
[0012] As used herein, the term "coating" refers to a material
disposed on at least a portion of an underlying surface in a
continuous or discontinuous manner. Further, the term "coating"
does not necessarily mean a uniform thickness of the disposed
material, and the disposed material may have a uniform or a
variable thickness. As used herein, the term "coated on" refers to
coatings or materials disposed directly in contact with each other
or indirectly by having intervening coatings or materials or
features there between, unless otherwise specifically
indicated.
[0013] As used herein, the term "semiconductor wafer" refers to a
wafer or a substrate of a semiconductor material such as a growth
substrate. A growth substrate is typically grown from a
semiconductor material, and includes one or more device structures
having a light emitting region disposed between an n-type region
and a p-type region. In some embodiments, the semiconductor wafer
includes one or more light emitting device (LED) structures.
[0014] Some embodiments of the present disclosure are directed to
methods for fabricating one or more coated semiconductor elements
to form LED chips for use in lighting apparatus, for example LED
devices. A coated semiconductor element as described herein may
include a semiconductor substrate including an LED device structure
and a coating of a composite material including a phosphor of
formula I. A coated semiconductor element may also be referred to
as a phosphor coated semiconductor element. In a lighting
apparatus, electrical leads may be coupled to the one or more
coated semiconductor elements to form one or more LED chips.
[0015] FIG. 1 illustrates a configuration of an LED chip 12. The
LED chip 12 includes a coated semiconductor element 14 and
electrical leads 16 and 18 coupled to the coated semiconductor
element 14. The coated semiconductor element 14 includes a
semiconductor substrate 20 including an LED device structure and a
coating 22 of a composite material disposed on a portion of a
surface 21 of the semiconductor substrate 20. In some embodiments,
electrical leads 16 and 18 form electrical connections to the
semiconductor substrate 20.
[0016] In some embodiments, a method for fabricating coated
semiconductor elements is described. The method includes combining
a phosphor of formula I and a polymer binder to form a composite
material, providing a semiconductor wafer including
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and a sum of I, j and k is equal to 1, coating the
composite material on a surface of the semiconductor wafer to form
a coated semiconductor wafer, and dicing the coated semiconductor
wafer using a cutting fluid apparatus to separate one or more
coated semiconductor elements. A cutting fluid of the cutting fluid
apparatus includes a C.sub.1-C.sub.20 alcohol, a C.sub.1-C.sub.20
ketone, a C.sub.1-C.sub.20 acetate compound, acetic acid, oleic
acid, carboxylic acid, a source of A, where A is Li, Na, K, Rb, Cs,
or a combination thereof, silicic acid, or a combination thereof.
The method further includes coupling electrical leads to the one or
more coated semiconductor elements to form one or more LED chips,
for example the LED chip 12 (FIG. 1).
[0017] The semiconductor wafer including In.sub.iGa.sub.jAl.sub.kN
as described herein may include a plurality of LED device
structures. In some embodiments, each LED device structure includes
a p-type region, an active region, and an n-type region. The active
region may include a multi-quantum well. Each LED device structure
of the plurality of LED device structures may emit light in a
wavelength range from about 250 nanometers (nm) to about 550 nm
when the LED device structure is forward biased. In some
embodiments, the semiconductor wafer includes GaN, and the LED
device structures emit blue light having a peak emission wavelength
from about 400 nm to about 500 nm.
[0018] Although in the description herein, the lighting apparatus
for example, LED devices are nitride-based LEDs that emit blue or
UV light, semiconductor light emitting devices besides LEDs such as
laser diodes and semiconductor light emitting devices made from
other materials such as other III-V semiconductor materials,
III-phosphide, III-arsenide, II-VI semiconductor materials, ZnO, or
Si-based materials may be used.
[0019] The phosphor of formula I is a complex fluoride. In one
embodiment, the phosphor of formula I is a manganese (Mn.sup.4+)
doped complex fluoride. Complex fluorides have a host lattice
containing one coordination center, surrounded by fluoride ions
acting as ligands, and charge-compensated by counter ions (A) as
required. For example, in K.sub.2[SiF.sub.6], the coordination
center is Si and the counter ion is K. Complex fluorides are
generally represented as a combination of simple, binary fluorides.
The square brackets in the chemical formula for the complex
fluorides (occasionally omitted for simplicity) indicate that the
complex ion present in that complex fluoride is a new chemical
species, different from the simple fluoride ion. In the phosphor of
formula I, the Mn.sup.4+ dopant or activator acts as an additional
coordination center, substituting a part of the coordination
center, for example, Si, forming a luminescent center. The
manganese doped phosphor of formula I: A.sub.2(M,Mn)F.sub.6 may
also be represented as A.sub.2[MF.sub.6]:Mn.sup.4+. The host
lattice (including the counter ions) may further modify the
excitation and emission properties of the activator ion. As used
herein, the terms "phosphor of formula I" and "manganese doped
phosphor" may be used interchangeably throughout the
specification.
[0020] The counter ion A in formula I is Li, Na, K, Rb, Cs, or a
combination thereof, and y is 6. In certain embodiments, A is Na,
K, or a combination thereof. The coordination center M in formula I
is an element selected from the group consisting of Si, Ge, Ti, Zr,
Hf, Sn, Al, Ga, In, Sc, Y, Bi, La, Gd, Nb, Ta, and combinations
thereof. In certain embodiments, M is Si, Ge, Ti, or a combination
thereof. In some embodiments, A is K and M is Si. Examples of the
phosphors of formula I include K.sub.2[SiF.sub.6]:Mn.sup.4+,
K.sub.2[TiF.sub.6]:Mn.sup.4+, K.sub.2[SnF.sub.6]:Mn.sup.4+,
Cs.sub.2[TiF.sub.6]:Mn.sup.4+, Rb.sub.2[TiF.sub.6]:Mn.sup.4+,
Cs.sub.2[SiF.sub.6]:Mn.sup.4+, Rb.sub.2[SiF.sub.6]:Mn.sup.4+,
Na.sub.2[TiF.sub.6]:Mn.sup.4+, Na.sub.2[ZrF.sub.6]:Mn.sup.4+,
K.sub.3[ZrF.sub.7]:Mn.sup.4+, K.sub.3[BiF.sub.6]:Mn.sup.4+,
K.sub.3[YF.sub.6]:Mn.sup.4+, K.sub.3[LaF.sub.6]:Mn.sup.4+,
K.sub.3[GdF.sub.6]:Mn.sup.4+, K.sub.2[NbF.sub.7]:Mn.sup.4+ and
K.sub.2[TaF.sub.7]:Mn.sup.4+. In certain embodiments, the phosphor
of formula I is K.sub.2[SiF.sub.6]:Mn.sup.4+.
[0021] Other manganese doped phosphors that may be used in forming
the composite material for coating the semiconductor wafer to
subsequently form one or more LED chips, include: [0022] (A)
A.sub.2[MF.sub.5]:Mn.sup.4+, where A is selected from Li, Na, K,
Rb, Cs, and combinations thereof; and where M is selected from Al,
Ga, In, and combinations thereof; [0023] (B)
A.sub.3[MF.sub.6]:Mn.sup.4+, where A is selected from Li, Na, K,
Rb, Cs, and combinations thereof; and where M is selected from Al,
Ga, In, and combinations thereof; [0024] (C)
Zn.sub.2[MF.sub.7]:Mn.sup.4+, where M is selected from Al, Ga, In,
and combinations thereof; [0025] (D) A[In.sub.2F.sub.7]:Mn.sup.4+
where A is selected from Li, Na, K, Rb, Cs, and combinations
thereof; [0026] (E) E[MF.sub.6]:Mn.sup.4+, where E is selected from
Mg, Ca, Sr, Ba, Zn, and combinations thereof; and where M is
selected from Ge, Si, Sn, Ti, Zr, and combinations thereof; [0027]
(F) Ba.sub.0.65Zr.sub.0.35F.sub.2.70:Mn.sup.4+; and [0028] (G)
A.sub.3[ZrF.sub.7]:Mn.sup.4+where A is selected from Li, Na, K, Rb,
Cs, and combinations thereof.
[0029] The phosphor of formula I for use in forming the composite
material may have a particle size distribution having a D50
particle size of less than 50 microns. In some embodiments, the
phosphor of formula I has a D50 particle size in a range from about
1 micron to about 50 microns. In some embodiments, the phosphor of
formula I has D50 particle size in a range from about 10 microns to
about 40 microns. In particular embodiments, the phosphor of
formula I has a D50 particle size in a range from about 20 microns
to about 35 microns. In some embodiments, it may be desirable to
use particles having smaller particle size, for example a D50
particle size of less than 1 micron.
[0030] The polymer binder may include a material that is optically
transparent to light emitted by the LED device structure, the
phosphor of formula I, an additional luminescent material
(described below) or combinations thereof of a resulting LED chip.
Further, the polymer binder may be chemically and optically
compatible with the phosphor of formula I and any surrounding
materials or layers used in the LED chip or a lighting apparatus
including the LED chip. Suitable examples of the polymer binders
for use in forming the composite material may include epoxies,
silicones and silicones derivatives including, but not limited to,
amino silicone (AMS), polyphenylmethylsiloxane,
polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane,
silsesquioxanes, fluorinated silicones, and vinyl and hydride
substituted silicones; a low temperature glass, or combinations
thereof. In some embodiments, the polymer binder is substantially
free of water, substantially free of a base, or substantially free
of water and the base. As used herein, the terms "substantially
free of water" and "substantially free of a base" are used in
context of a polymer binder that may include less than 1 weight
percent water, less than 1 weight percent of the base, or less than
1 weight percent of water and the base.
[0031] As noted, the method includes the step of combining the
phosphor of formula I and the polymer binder to form a composite
material. For example, a slurry of the composite material may be
prepared by mixing the phosphor of formula I to the polymer binder.
The phosphor of formula I may be dispersed uniformly or
non-uniformly in the polymer binder. In some embodiments, the
combining step includes stirring a combination of the phosphor of
formula I and the polymer binder homogeneously with a stirring
rate. In some embodiments, the combining step may be performed by
stirring the combination of the phosphor of formula I and the
polymer binder with a stirring rate less than 500 rpm. In some
embodiments, the combining step may be performed by stirring the
combination with a stirring rate less than 400 rpm. In certain
embodiments, the combining step may be performed by stirring the
combination with a stirring rate in a range from about 100 rpm to
about 300 rpm. The stirring of the combination of the phosphor of
formula I and the polymer binder in the combining step may be
carried out for a duration of time depending on a selected stirring
rate to achieve the desired properties. A low stirring rate (less
than 500 rpm) may reduce the cleavage of the particles of the
phosphor of formula I as compared to that of a high stirring rate
(higher than 500 rpm). The reduced cleavage of particles may help
in maintaining their shape and retaining their surfaces without any
damage, deformation and erosion during the combining step for
forming the composite material. Further, the combining step may be
carried out at a temperature less than 200 degrees Celsius. In some
embodiments, the combining step is carried out at room temperature.
In some other embodiments, the combining step is carried out at a
temperature less than 150 degrees Celsius. In some embodiments, the
combining step is carried out at a temperature less than 100
degrees Celsius.
[0032] After forming the composite material, the method includes
coating the composite material on a surface of the semiconductor
wafer to form a coated semiconductor wafer. In some embodiments,
prior to coating the composite material, the method further
includes forming electrical contacts on the surface of the
semiconductor wafer. In some embodiments, after forming electrical
contacts, a protective material, for example a photoresist may be
applied to the electrical contacts using a suitable method such as
lithography prior to the step of coating the composite material.
Next, the method includes coating the composite material on a
surface of the semiconductor wafer including electrical contacts.
In some embodiments, the method includes coating one or more
portions of the surface of the semiconductor wafer including the
electrical contacts, which are not covered by the photoresist. In
some other embodiments, after forming the electrical contacts on
the surface of the semiconductor wafer, the method includes coating
the composite material across the entire surface of the
semiconductor wafer. That is, the entire surface of the
semiconductor wafer including the electrical contacts may be
covered by a coating of the composite material. In these
embodiments, a protective material such as a photoresist may be
applied on the coating of the composite material using a suitable
method such as lithography, and the protective material may be
removed in regions above the electrical contacts. In some
embodiments, the protective layer may be applied on the coating of
the composite material (or composite material coating) except the
regions above the electrical contacts. After the protective layer
has been applied and treated as required, the composite material
coating on or above the electrical contacts may be removed by any
suitable method such as wet etching or dry etching. After removing
the portions of the composite material coating as required, the
protective layer may be removed completely from the composite
material coating.
[0033] Various methods may be employed for coating the composite
material on a surface of the semiconductor wafer. Non-limiting
examples of methods for coating the composite material may include
spin coating, screen printing, dispensing, spray coating, inject
printing, or dipping method. In certain embodiments, the composite
material coating is applied by spin coating method. A temperature
during the formation of the composite material coating may be
maintained less than 200 degrees Celsius. In some embodiments, a
temperature during the formation of the composite material coating
is maintained less than 150 degrees Celsius. In certain
embodiments, a temperature during the formation of the composite
material coating is maintained less than 100 degrees Celsius.
[0034] After coating the composite material on the semiconductor
wafer, the method may further include heat-treating the composite
material coating. The step of heat-treating the composite material
coating may be carried out prior to or after applying the
protective layer (described above). Various methods, for example
using a heater, an oven, dried air or radiant heat lamp may be
employed to perform the heat-treating of the composite material
coating. In some embodiments, the method includes heat-treating the
composite material coating at a temperature less than 200 degrees
Celsius. In some embodiments, the step of heat-treating the
composite material coating is carried out at a temperature less
than 150 degrees Celsius. In certain embodiments, the step of
heat-treating the composite material coating is carried out at a
temperature less than 100 degrees Celsius. The step of
heat-treating the composite material coating may be carried out for
a duration of time depending on a selected temperature to achieve
desired purpose, for example evaporate the moisture content of the
composite material coating. After completing the step of
heat-treating, the composite material coating may be patterned to
improve light extraction.
[0035] In the next step, the method includes dicing the coated
semiconductor wafer to form one or more coated semiconductor
elements. The dicing step may include dicing the coated
semiconductor wafer using a cutting fluid apparatus to form one or
more coated semiconductor elements. A cutting fluid apparatus
generally uses a non-compressible cutting fluid to generate a
high-pressure pulsating flow of the cutting fluid. Examples of the
cutting fluid apparatus may include a fluid jet or a fluid saw. A
fluid jet typically uses cutting fluids at ultra-high pressures,
for example higher than 30,000 Pounds per square inch (PSI) for
forming an intense cutting fluid stream through a cutting nozzle.
The energy required for cutting a material is obtained by
pressurizing the cutting fluid by a booster pump to a desired level
and channeling the pressurized cutting fluid to the cutting
nozzle.
[0036] According to some embodiments, a cutting fluid of the
cutting fluid apparatus includes a compound selected from the group
consisting of a C.sub.1-C.sub.20 alcohol, a C.sub.1-C.sub.20
ketone, a C.sub.1-C.sub.20 acetate compound, acetic acid, oleic
acid, carboxylic acid, a source of A, silicic acid, and
combinations thereof. Suitable examples of the compound may
include, but are not limited to, ethanol, acetone, isopropyl
alcohol, tertiary butyl alcohol, tertiary butyl acetate, octanol,
acetic acid, oleic acid, carboxylic acid or combinations thereof.
In some embodiments, the cutting fluid may include additional
compounds for example, an alkane having higher than 4 carbon atoms
and an alkene higher than 4 carbon atoms. Suitable examples of
alkanes include hexane, octane, or a combination thereof. In some
embodiments, the cutting fluid includes an aqueous solution of the
compound. The cutting fluid may include an aqueous solution having
a concentration of about 1 to about 50 percent of the compound. In
an example, an aqueous solution of 50 percent acetone may be used
in the cutting fluid apparatus.
[0037] Non-limiting suitable examples of the sources of A include
KCl, KBr, KF, CaF.sub.2, a compound of formula II or combinations
thereof. The compound of formula II is represented as:
A.sub.x[MF.sub.y] II
[0038] wherein A is Li, Na, K, Rb, Cs, or a combination thereof, M
is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd,
or a combination thereof, x is an absolute value of a charge of an
[MF.sub.y] ion; and y is 5, 6, or 7.
[0039] In certain embodiments, A is K and M is Si. In certain
embodiments, the compound of formula II is K.sub.2[SiF.sub.6]. In
certain embodiments, the cutting fluid includes an aqueous solution
of K.sub.2[SiF.sub.6].
[0040] In some embodiments, the dicing step includes using the
cutting fluid from the cutting fluid apparatus at a pressure in a
range from about 36,000 PSI to about 100,000 PSI. In some
embodiments, the cutting fluid apparatus uses the cutting fluid at
a pressure in a range from about 40,000 PSI to about 60,000
PSI.
[0041] Without being bound by any theory, it is believed that using
a cutting fluid apparatus for dicing the coated semiconductor wafer
into one or more coated semiconductor elements may reduce the
degradation of the phosphor of formula I in the coating of the
composite material as compared to the degradation of the phosphor
of formula I when a water jet is used for dicing the coated
semiconductor wafer.
[0042] In addition to the phosphor of formula I, one or more
additional luminescent materials, for example inorganic phosphors,
quantum dot (QD) materials, electroluminescent polymers, and
phosphorescent dyes may be disposed on the semiconductor wafer.
Additional luminescent materials emitting radiation of, for example
green, blue, yellow, red, orange, or other colors may be used to
customize a resulting light such as white light from the LED chip
with correlated color temperature (CCTs) in the range of
2500-10000K and CRIs in the range of 50-99. In certain embodiments,
an additional luminescent material includes a green emitting
phosphor, such as Ce.sup.3+ doped garnet phosphor.
[0043] In some embodiments, the step of combining the phosphor of
formula I and the polymer binder (as described previously) further
includes adding an additional luminescent material in the polymer
binder along with the phosphor of formula I. For example, the
phosphor of formula I may be blended with one or more additional
luminescent material, for example green, blue, yellow, orange, or
red emitting phosphors or QD materials in the polymer binder to
form the composite material. In some other instances, the
additional luminescent material may be disposed separately on the
semiconductor wafer either prior to or after coating the composite
material including the phosphor of formula I on the semiconductor
wafer. The additional luminescent material may be dispersed in any
polymer binder (as described previously), separately, and a layer
may be disposed on the semiconductor wafer.
[0044] Suitable additional phosphors for use in the coated
semiconductor wafer may include, but are not limited to:
((Sr.sub.1-z(Ca, Ba, Mg, Zn).sub.z).sub.1-(x+w)( Li, Na, K, Rb)
.sub.wCe.sub.x).sub.3(Al.sub.1-ySi.sub.y)O.sub.4+y+3(x-w)F.sub.1-y-3(x-w)-
, 0<x.ltoreq.0.10, 0.ltoreq.y.ltoreq.0.5, 0.ltoreq.z.ltoreq.0.5,
0.ltoreq.w.ltoreq.x; (Ca, Ce).sub.3Sc.sub.2Si.sub.3O.sub.12(CaSig);
(Sr,Ca,Ba).sub.3Al.sub.1-xSi.sub.xO.sub.4+xF.sub.1-x:Ce.sup.3+
(SASOF)); (Ba,Sr,Ca).sub.5(PO.sub.4).sub.3(Cl,F,Br,OH):
Eu.sup.2+,Mn.sup.2+; (Ba,Sr,Ca)BPO.sub.5:Eu.sup.2+,Mn.sup.2+;
(Sr,Ca).sub.10(PO.sub.4).sub.6*vB.sub.2O.sub.3:Eu.sup.2+ (wherein
0<v.ltoreq.1);
Sr.sub.2Si.sub.3O.sub.8*2SrCl.sub.2:Eu.sup.2+;(Ca,Sr,Ba).sub.3MgSi.sub.2O-
.sub.8:Eu.sup.2+,Mn.sup.2+; BaAl.sub.8O.sub.13:Eu.sup.2+;
2SrO*0.84P.sub.2O.sub.5*0.16B.sub.2O.sub.3:Eu.sup.2+;
(Ba,Sr,Ca)MgAl.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+;
(Ba,Sr,Ca)Al.sub.2O.sub.4:Eu.sup.2+;
(Y,Gd,Lu,Sc,La)BO.sub.3:Ce.sup.3+,Tb.sup.3+;ZnS:Cu.sup.+,Cl.sup.-;
ZnS:Cu.sup.+,Al.sup.3+; ZnS:Ag.sup.+,Cl.sup.-;
ZnS:Ag.sup.+,Al.sup.3+;
(Ba,Sr,Ca).sub.2Si.sub.1-.xi.O.sub.4-2.xi.:Eu.sup.2+ (wherein
-0.2.ltoreq..xi..ltoreq.0.2);
(Ba,Sr,Ca).sub.2(Mg,Zn)Si.sub.2O.sub.7:Eu.sup.2+;
(Sr,Ca,Ba)(Al,Ga,In).sub.2S.sub.4:Eu.sup.2+;
(Y,Gd,Tb,La,Sm,Pr,Lu).sub.3(Al,Ga).sub.5-.alpha.O.sub.12-3/2.alpha.:Ce.su-
p.3+ (wherein 0.ltoreq..alpha..ltoreq.0.5);
(Ca,Sr).sub.8(Mg,Zn)(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+,Mn.sup.2+;
Na.sub.2Gd.sub.2B.sub.2O.sub.7:Ce.sup.3+,Tb.sup.3+;
(Sr,Ca,Ba,Mg,Zn).sub.2P.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+;
(Gd,Y,Lu,La).sub.2O.sub.3:Eu.sup.3+,Bi.sup.3+;
(Gd,Y,Lu,La).sub.2O.sub.2S:Eu.sup.3+,Bi.sup.3+;
(Gd,Y,Lu,La)VO.sub.4:Eu.sup.3+,Bi.sup.3+;
(Ca,Sr)S:Eu.sup.2+,Ce.sup.3+; SrY.sub.2S.sub.4:Eu.sup.2+;
CaLa.sub.2S.sub.4:Ce.sup.3+;
(Ba,Sr,Ca)MgP.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+;
(Y,Lu).sub.2WO.sub.6:Eu.sup.3+,Mo.sup.6+;
(Ba,Sr,Ca).sub..beta.Si.sub..gamma.N.sub..mu.:Eu.sup.2+ (wherein
2.beta.+4.gamma.=3.mu.);
(Ba,Sr,Ca).sub.2Si.sub.5-xAl.sub.xN.sub.8-xO.sub.x:Eu.sup.2+
(wherein 0.ltoreq.x.ltoreq.2);
Ca.sub.3(SiO.sub.4)Cl.sub.2:Eu.sup.2+;
(Lu,Sc,Y,Tb).sub.2-u-vCe.sub.vCa.sub.1+uLi.sub.wMg.sub.2-wP.sub.w(Si,Ge).-
sub.3-wO.sub.12-u/2 (where 0.5.ltoreq.u.ltoreq.1,
0<v.ltoreq.0.1, and 0.ltoreq.w.ltoreq.0.2);
(Y,Lu,Gd).sub.2-.phi.Ca.sub..phi.Si.sub.4N.sub.6+.phi.C.sub.1-.phi.:Ce.su-
p.3+, (wherein 0.ltoreq..phi..ltoreq.0.5); (Lu,Ca,Li,Mg,Y),
.alpha.-SiAlON doped with Eu.sup.2+ and/or Ce.sup.3+;
(Ca,Sr,Ba)SiO.sub.2N.sub.2:Eu.sup.2+,Ce.sup.3+;
.beta.-SiAlON:Eu.sup.2+,3.5MgO*0.5MgF.sub.2*GeO.sub.2:Mn.sup.4+;
(Sr,Ca,Ba)AlSiN.sub.3:Eu.sup.2+;
(Sr,Ca,Ba).sub.3SiO.sub.5:Eu.sup.2+;
Ca.sub.1-c-fCe.sub.cEu.sub.fAl.sub.1+cSi.sub.1-3N.sub.3, (where
0.ltoreq.c.ltoreq.0.2, 0.ltoreq.f.ltoreq.0.2);
Ca.sub.1-h-rCe.sub.hEu.sub.rAl.sub.1-h(Mg,Zn).sub.hSiN.sub.3,
(where 0.ltoreq.h.ltoreq.0.2, 0.ltoreq.r.ltoreq.0.2);
Ca.sub.1-2s-tCe.sub.s(Li,Na).sub.sEu.sub.tAlSiN.sub.3, (where
0.ltoreq.s.ltoreq.0.2, 0.ltoreq.t.ltoreq.0.2s+t>0); and
Ca.sub.1-.sigma.-.chi.-.phi.Ce.sub..sigma.(Li,Na).sub..chi.Eu.sub..phi.Al-
.sub.1+.sigma.-.chi.Si.sub.1-.sigma.+.chi.N.sub.3, (where
0.ltoreq..sigma..ltoreq.0.2, 0.ltoreq..chi..ltoreq.0.4,
0.ltoreq..phi..ltoreq.0.2).
[0045] In some embodiments, the additional luminescent material
includes a green light emitting quantum dot (QD) material. The
green light emitting QD material may include a group II-VI
compound, a group III V compound, a group IV-IV compound, a group
IV compound, a group I-111-VI.sub.2 compound or a mixture thereof.
Non-limiting examples of group II-VI compounds include CdSe, CdTe,
CdS, ZnSe, ZnTe, ZnS, HgTe, HgS, HgSe, CdSeTe, CdSTe, ZnSeS,
ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS,
CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe,
CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or
combinations thereof. Group III-V compounds may be selected from
the group consisting of GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP,
InAs, GaNP, GaNAs, GaPAs, AlNP, AlNAs, AlPAs, InNP, InNAs, InPAs,
GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP,
InAlNAs, InAlPAs, and combinations thereof. Examples of group IV
compounds include Si, Ge, SiC, and SiGe. Examples of group
I-III-VI.sub.2 chalcopyrite-type compounds include CuInS.sub.2,
CuInSe.sub.2, CuGaS.sub.2, CuGaSe.sub.2, AgInS.sub.2, AgInSe.sub.2,
AgGaS.sub.2, AgGaSe.sub.2 and combinations thereof.
[0046] QD material for use as the additional luminescent material
may be a core/shell QD, including a core, at least one shell coated
on the core, and an outer coating including one or more ligands,
preferably organic polymeric ligands. Exemplary materials for
preparing core-shell QDs include, but are not limited to, Si, Ge,
Sn, Se, Te, B, C (including diamond), P, Co, Au, BN, BP, BAs, AlN,
AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN,
AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS,
CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe,
MnS, MnSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe,
CuF, CuCl, CuBr, Cul, Si.sub.3N.sub.4, Ge.sub.3N.sub.4,
Al.sub.2O.sub.3, (Al, Ga, In).sub.2 (S, Se, Te).sub.3, Al.sub.2CO,
and appropriate combinations of two or more such materials.
Exemplary core-shell QDs include, but are not limited to, CdSe/ZnS,
CdSe/CdS, CdSe/CdS/ZnS, CdSeZn/CdS/ZnS, CdSeZn/ZnS, InP/ZnS,
PbSe/PbS, PbSe/PbS, CdTe/CdS and CdTe/ZnS.
[0047] The QD materials typically include ligands conjugated to,
cooperated with, associated with, or attached to their surface. In
particular, the QDs may include a coating layer comprising ligands
to protect the QDs from environmental conditions including elevated
temperatures, high intensity light, external gasses, and moisture,
control aggregation, and allow for dispersion of the QDs in the
host binder material.
[0048] Examples of electroluminescent polymers may include
polyfluorenes, preferably poly(9,9-dioctyl fluorene) and copolymers
thereof, such as
poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)diphenylamine)
(F8-TFB); poly(vinylcarbazole); and polyphenylenevinylene and their
derivatives. Materials suitable for use as the phosphorescent dye
may include, but are not limited to, tris(1-phenylisoquinoline)
iridium (III) (red dye), tris(2-phenylpyridine) iridium (green dye)
and Iridium (III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue
dye). Commercially available fluorescent and phosphorescent metal
complexes from ADS (American Dyes Source, Inc.) may also be used.
ADS green dyes include ADS060GE, ADS061GE, ADS063GE, and ADS066GE,
ADS078GE, and ADS090GE. ADS blue dyes include ADS064BE, ADS065BE,
and ADS070BE. ADS red dyes include ADS067RE, ADS068RE, ADS069RE,
ADS075RE, ADS076RE, ADS067RE, and ADS077RE.
[0049] The ratio of each of the individual luminescent materials,
for example phosphor of formula I and additional luminescent
materials may vary depending on the characteristics of the desired
resulting light output from the one or more LED chips. The relative
proportions of the individual luminescent materials may be adjusted
such that the light emitted from the one or more LED chips is
visible light of predetermined x and y values on the chromaticity
diagram created by the International Commission on Illumination
(CIE). In certain embodiments, theone or more LED chips emit white
light. In some embodiments, the resulting white light may possess
an x value in a range of about 0.20 to about 0.55, and a y value in
a range of about 0.20 to about 0.55. The exact identity and amount
of each luminescent material as described herein can be varied
according to the needs of the end user.
[0050] In some embodiments, the method further includes the step of
coupling electrical leads to the one or more coated semiconductor
elements to form one or more LED chips, for example the LED chip 12
in FIG. 1. In some embodiments, the electrical leads include
metallic wires. The electrical leads may be coupled to the
electrical contacts formed on the semiconductor wafer (as described
previously) that are present on one or more separated (or diced)
coated semiconductor elements. In some embodiments, the coupling
step is performed while minimizing or avoiding exposure of the
phosphor of formula I in the coating of the composite material to a
temperature higher than 200 degrees Celsius. That is, during the
coupling step, a temperature may be maintained below 200 degrees
Celsius. In some embodiments, the coupling step is performed at a
temperature less than 150 degrees Celsius. In certain embodiments,
the coupling step is performed at a temperature less than 100
degrees Celsius.
[0051] As used herein, the terms "coupling" and "couple" refer to
electrically connecting one element to another element. In some
embodiments, the electrical leads are electrically connected to the
electrical contacts present on the one or more coated semiconductor
elements. Various methods for example, soldering or brazing can be
used for electrically connecting the electrical leads to the
electrical contacts.
[0052] In some embodiments, the coupling step includes soldering
the electrical leads to the electrical contacts on the one or more
coated semiconductor elements. Suitable soldering materials that
can be used at a temperature lower than 200 degrees Celsius are
desirable. Some embodiments include using a soldering material that
can be used at a temperature lower than 150 degrees Celsius.
Suitable soldering materials may include tin, copper, silver, zinc,
indium, bismuth, cadmium, lead or combinations thereof. In some
embodiments, the soldering material may be substantially free of
lead. As used herein, the term "substantially free of lead" refers
to a soldering material that includes less than 10 weight percent
lead. Further, in some embodiments, the coupling step is performed
in an environment that is substantially free of moisture. As used
herein, the term "substantially free of moisture" refers to an
environment that includes less than 1 percent moisture.
[0053] FIG. 2 shows a flow chart of a method 100 for fabricating
one or more one or more LED chips, for example LED chip 12 as shown
in FIG. 1. The method 100 includes the step 102 of combining a
phosphor of formula I, for example K.sub.2SiF.sub.6:Mn.sup.4+ and a
polymer binder to form a composite material, the step 104 of
providing a semiconductor wafer including
In.sub.iGa.sub.jAl.sub.kN, wherein 0.ltoreq.i; 0.ltoreq.j;
0.ltoreq.k, and a sum of I, j and k is equal to 1, the step 106 of
coating the composite material on a surface of the semiconductor
wafer to form a coated semiconductor wafer, the step 108 of dicing
the coated semiconductor wafer using a cutting fluid apparatus to
separate one or more coated semiconductor elements, and the step
110 of coupling electrical leads to the one or more coated
semiconductor elements to form one or more LED chips. A cutting
fluid of the cutting fluid apparatus includes a C.sub.1-C.sub.20
alcohol, a C.sub.1-C.sub.20 ketone, a C.sub.1-C.sub.20 acetate
compound, acetic acid, oleic acid, carboxylic acid, a source of A,
silicic acid, or a combination thereof.
[0054] Some embodiments provide a lighting apparatus including one
or more LED chips (for example, LED chip 12 FIG. 1)) fabricated by
the method as described herein. The lighting apparatus may include
a number of LED chips to generate a desired light output (that is,
luminous flux). A light output from an LED chip may depend, in
part, on a flux emitted from the LED device structure of the
semiconductor substrate. A desired light output from the lighting
apparatus may be achieved using a lesser number of LED chips
including the LED device structure emitting a high flux or using a
higher number of LED chips including the LED device structures
emitting a lower flux. In some embodiments, the lighting apparatus
may include multiple LED chips including the LED device structures
that emit a flux lower than 40 watt/cm.sup.2. In some embodiments,
the lighting apparatus may include multiple LED chips including the
LED device structures that emit a flux lower than 30 watt/cm.sup.2.
In some embodiments, the lighting apparatus may include multiple
LED chips including the LED device structures that emit a flux
lower than 20 watt/cm.sup.2.
[0055] In some embodiments, a method of operating a lighting
apparatus as described herein includes operating multiple LED chips
including the LED device structures emitting a flux lower than 40
watt/cm.sup.2. Operating the lighting apparatus including multiple
LED chips including the LED device structures emitting a flux, for
example less than 40 watt/cm.sup.2 may reduce or prevent
degradation of the phosphor of formula I during the operation of
the lighting apparatus and provide improved performance and lower
cost driver solutions.
[0056] Non-limiting examples of lighting apparatus include devices
for excitation by light-emitting diodes (LEDs) such as fluorescent
lamps, cathode ray tubes, plasma display devices, liquid crystal
displays (LCD's), ultraviolet (UV) excitation devices, such as
chromatic lamps, backlighting devices, liquid crystal displays
(LCD), plasma screens, xenon excitation lamps, and UV excitation
marking systems. The list of these devices is meant to be merely
exemplary and not exhaustive. In some embodiments, the lighting
apparatus includes a backlight device. The backlight device may
include a surface mounted device (SMD) structure. Examples of the
backlight devices include, but are not limited to, televisions,
computers, monitors, smartphones, tablet computers and other
handheld devices.
[0057] The method steps described above may be used in additional
applications besides LED chips. For example, the method steps of
combining and disposing a composite material as described herein
may be used in a fluorescent lamp, a cathode ray tube, a plasma
display device or a liquid crystal display (LCD). The method steps
may also be used for fabricating a scintillator in an
electromagnetic calorimeter, a gamma ray camera, a computed
tomography scanner or a laser. These uses are meant to be merely
exemplary and not exhaustive.
EXAMPLES
Example 1
[0058] To analyze the effect of various fluids on the phosphor of
formula K.sub.2SiF.sub.6:Mn.sup.4+, various sample combinations
were prepared by adding 0.8 gram phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ individually in various fluids 1-7 (10
milliliters) as provided in Table 1. Each sample combination was
magnetically stirred for 30 minutes at 175 rpm. After stirring,
each sample combination was filtered and dried overnight under
vacuum to receive treated samples of phosphor
K.sub.2SiF.sub.6:Mn.sup.4+. Each treated sample of phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ was characterized to measure quantum
efficiency (QE) and absorption (Abs.). Table 1 shows relative QEs
and relative Abs. of the treated samples 1-7 of phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ (corresponding to the fluids 1-7 used in
preparing the sample combinations) with respect to as-prepared
phosphor K.sub.2SiF.sub.6:Mn.sup.4+.
[0059] As shown in Table 1, the performance of the treated sample 1
of phosphor K.sub.2SiF.sub.6:Mn.sup.4+ reduced drastically (50%
drop in QE) when the phosphor K.sub.2SiF.sub.6:Mn.sup.4+ was
exposed to water (fluid 1). As compared to water, the treated
samples 2-7 of phosphor K.sub.2SiF.sub.6:Mn.sup.4+ in fluids 2-7
showed much lower reduction in QEs. This implies that the phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ has higher stability in fluids (2-7)
than the stability of phosphor K.sub.2SiF.sub.6:Mn.sup.4+ in water.
As shown in table 1, QE of the treated sample 7 of phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ decreased only by 7% in aqueous IPA
(50%IPA+50% water).
TABLE-US-00001 TABLE 1 Treated samples Relative Relative S. No.
Fluids of phosphor QE Abs. Fluid 1 Water Treated sample 1 50% 76%
Fluid 2 Isopropyl alcohol (IPA) Treated sample 2 96% 70% Fluid 3
Acetone Treated sample 3 98% 70% Fluid 4 Ethanol Treated sample 4
96% 70% Fluid 5 t-butyl-acetate Treated sample 5 99% 70% Fluid 6 9
ml IPA + 1 ml water Treated sample 5 96% 70% Fluid 7 5 ml IPA + 5
ml water Treated sample 6 93% 70%
Example 2
[0060] Two samples (samples 1 and 2) were prepared using the
phosphor K.sub.2SiF.sub.6:Mn.sup.4+. The sample 1 was prepared by
stirring 1.0 gram phosphor K.sub.2SiF.sub.6:Mn.sup.4+ in 10 ml
water for 3 hours. The sample 2 was prepared by stirring 1.0 gram
phosphor K.sub.2SiF.sub.6:Mn.sup.4+ and 0.1 gram K.sub.2SiF.sub.6
in 10 ml water for 5 hours. As-prepared samples 1 and 2 were yellow
in color. It was observed that sample 1 turned brown after 3 hours,
which showed performance degradation of the phosphor
K.sub.2SiF.sub.6:Mn.sup.4+ in sample 1. On the other hand, sample 2
showed minimal change in the color. The sample 2 remained yellow in
color. The minimal change in the color of sample 2 indicated
improved stability of the phosphor K.sub.2SiF.sub.6:Mn.sup.4+ in
presence of K.sub.2SiF.sub.6 in water.
[0061] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *