U.S. patent application number 14/970615 was filed with the patent office on 2016-04-14 for engineered-phosphor led packages and related methods.
The applicant listed for this patent is Ian ASHDOWN, Henry IP, Tom PINNINGTON, Philippe M. SCHICK, Michael A. TISCHLER. Invention is credited to Ian ASHDOWN, Henry IP, Tom PINNINGTON, Philippe M. SCHICK, Michael A. TISCHLER.
Application Number | 20160104823 14/970615 |
Document ID | / |
Family ID | 50348849 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160104823 |
Kind Code |
A1 |
PINNINGTON; Tom ; et
al. |
April 14, 2016 |
ENGINEERED-PHOSPHOR LED PACKAGES AND RELATED METHODS
Abstract
In accordance with certain embodiments, a phosphor element at
least partially surrounding a light-emitting die is shaped to
influence color-temperature divergence.
Inventors: |
PINNINGTON; Tom; (Vancouver,
CA) ; IP; Henry; (Richmond, CA) ; TISCHLER;
Michael A.; (Vancouver, CA) ; ASHDOWN; Ian;
(West Vancouver, CA) ; SCHICK; Philippe M.;
(Vancouver, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PINNINGTON; Tom
IP; Henry
TISCHLER; Michael A.
ASHDOWN; Ian
SCHICK; Philippe M. |
Vancouver
Richmond
Vancouver
West Vancouver
Vancouver |
|
CA
CA
CA
CA
CA |
|
|
Family ID: |
50348849 |
Appl. No.: |
14/970615 |
Filed: |
December 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14631392 |
Feb 25, 2015 |
9246070 |
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14970615 |
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14185229 |
Feb 20, 2014 |
9000663 |
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14631392 |
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13863926 |
Apr 16, 2013 |
8686625 |
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14185229 |
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13828498 |
Mar 14, 2013 |
8847261 |
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13863926 |
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Current U.S.
Class: |
257/88 ;
257/98 |
Current CPC
Class: |
H01L 33/505 20130101;
H01L 33/32 20130101; H01L 2224/48091 20130101; H01L 33/508
20130101; H01L 33/507 20130101; H01L 27/15 20130101; H01L
2924/07811 20130101; H01L 27/156 20130101; H01L 33/62 20130101;
H01L 2924/00014 20130101; H01L 2224/48091 20130101; H01L 23/495
20130101; H01L 2924/00 20130101; H01L 33/504 20130101; H01L 33/60
20130101; H01L 2924/07811 20130101; H01L 33/56 20130101 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/62 20060101 H01L033/62; H01L 27/15 20060101
H01L027/15; H01L 33/56 20060101 H01L033/56; H01L 33/32 20060101
H01L033/32 |
Claims
1.-35. (canceled)
36. A light-emitting device comprising: a light-emitting die having
(i) a top face and a bottom face opposite the top face, the top
face being configured for emission of light therefrom, and (ii) at
least one sidewall spanning the top and bottom faces; and first and
second phosphor elements disposed over the light-emitting die,
wherein the first phosphor element (i) is disposed over the second
phosphor element, (ii) has a top surface, (iii) has a base opposite
the top surface, and (iv) has a first light-absorption efficiency,
wherein the second phosphor element (i) is disposed over
substantially all of the top face of the light-emitting die, (ii)
has a base, (iii) has a top surface opposite the base, (iv) has a
second light-absorption efficiency, and (v) comprises (a) a binder
and (b) disposed within the binder, one or more
wavelength-conversion materials for absorbing at least a portion of
light emitted from the light-emitting die and emitting converted
light having a different wavelength, converted light combining with
unconverted light emitted from the light-emitting die to form
substantially white light, and wherein (i) the second
light-absorption efficiency is greater than the first
light-absorption efficiency and (ii) a divergence of color
temperature of the substantially white light emitted from the
device varies, over an angular range of 10.degree. to 85.degree.,
no more than 0.01 in terms of .DELTA.u'v' deviation from a
spatially weighted averaged chromaticity.
37. The light-emitting device of claim 36, wherein the divergence
of color temperature of the substantially white light emitted from
the device varies, over an angular range of 0.degree. to
85.degree., no more than 0.01 in terms of .DELTA.u'v' deviation
from a spatially weighted averaged chromaticity.
38. The light-emitting device of claim 36, wherein the divergence
of color temperature of the substantially white light emitted from
the device varies, over an angular range of 0.degree. to
85.degree., no more than 0.005 in terms of .DELTA.u'v' deviation
from a spatially weighted averaged chromaticity.
39. The light-emitting device of claim 36, wherein at least a
portion of the top surface of the second phosphor element is
curved.
40. The light-emitting device of claim 39, wherein a vertical
distance between the top surface of the second phosphor element and
the top face of the light-emitting die has a minimum at
approximately a center of the top face of the light-emitting
die.
41. The light-emitting device of claim 39, wherein a vertical
distance between the top surface of the second phosphor element and
the base of the first phosphor element has a maximum between the
center of the top face of the light-emitting die and an outer edge
of the base of the second phosphor element.
42. The light-emitting device of claim 36, wherein (i) the base of
the first phosphor element is disposed on the top surface of the
second phosphor element and (ii) the top surface of the first
phosphor element is curved.
43. The light-emitting device of claim 36, wherein the second
phosphor element has an index of refraction substantially the same
as an index of refraction of the first phosphor element.
44. The light-emitting device of claim 36, wherein an angular
intensity distribution of unconverted light emitted through an
outer surface of the first phosphor element substantially matches
an angular distribution of phosphor-converted light emitted through
the outer surface of the first phosphor element.
45. The light-emitting device of claim 36, wherein the binder
comprises at least one of silicone or epoxy.
46. The light-emitting device of claim 36, wherein the one or more
wavelength conversion materials comprise one or more phosphor
particles.
47. The light-emitting device of claim 36, further comprising,
disposed beneath at least one of (i) at least a portion of the
light-emitting die or (ii) the second phosphor element, a mounting
surface reflective to at least one of converted light or
unconverted light emitted by the light-emitting die.
48. The light-emitting device of claim 47, wherein the mounting
surface has a reflectivity to visible light of approximately 95% to
approximately 98%.
49. The light-emitting device of claim 36, wherein the
light-emitting die is a bare light-emitting diode die.
50. The light-emitting device of claim 36, wherein the
light-emitting die comprises a GaN-based semiconductor
material.
51. The light-emitting device of claim 36, further comprising at
least one additional light-emitting die at least partially
surrounded by the second phosphor element.
52. The light-emitting device of claim 36, further comprising a
second device that comprises: a second light-emitting die having
(i) a top face and a bottom face opposite the top face, the top
face being configured for emission of light therefrom, and (ii) at
least one sidewall spanning the top and bottom faces; and third and
fourth phosphor elements disposed over the second light-emitting
die, wherein the third phosphor element (i) is disposed over the
fourth phosphor element, (ii) has a top surface, (iii) has a base
opposite the top surface, and (iv) has a third light-absorption
efficiency, wherein the fourth phosphor element (i) is disposed
over substantially all of the top face of the second light-emitting
die, (ii) has a base, (iii) has a top surface opposite the base,
(iv) has a fourth light-absorption efficiency, and (v) comprises
(a) a second binder and (b) disposed within the second binder, one
or more second wavelength-conversion materials for absorbing at
least a portion of light emitted from the second light-emitting die
and emitting converted light having a different wavelength, and
wherein the fourth light-absorption efficiency is greater than the
third light-absorption efficiency.
53. The light-emitting device of claim 52, wherein a divergence of
color temperature of the substantially white light emitted from the
second device varies, over an angular range of 10.degree. to
85.degree., no more than 0.01 in terms of .DELTA.u'v' deviation
from a spatially weighted averaged chromaticity.
54. The light-emitting device of claim 52, wherein converted light
combines with unconverted light emitted from the second
light-emitting die to form substantially white light.
55. The light-emitting device of claim 52, wherein the second
phosphor element and the fourth phosphor element are separated by a
web therebetween, the web comprising at least one of the binder or
the second binder.
56. The light-emitting device of claim 36, wherein the first
phosphor element comprises a second binder and no
wavelength-conversion material.
57. The light emitting-device of claim 36, further comprising a
substrate having a plurality of conductive elements disposed
thereon, wherein the light-emitting die has at least two contacts
(i) on the bottom face and (ii) each electrically coupled to a
different conductive element on the substrate.
58. The light-emitting device of claim 57, wherein the at least two
contacts are each electrically coupled to a different conductive
element via at least one of a conductive adhesive, an anisotropic
conductive adhesive, a wire bond, or solder.
59. The light-emitting device of claim 57, wherein the substrate is
flexible.
60. The light-emitting device of claim 36, wherein an outer surface
of the first phosphor element at least partially defines a
substantially cubic or rectangular solid shape.
61. The light-emitting device of claim 36, wherein the top surface
of the second phosphor element defines a first shape and an outer
surface of the first phosphor element defines a second shape
different from and not conforming to the first shape.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/863,926, filed Apr. 16, 2013, which is a
continuation of U.S. patent application Ser. No. 13/828,498, filed
Mar. 14, 2013, the entire disclosure of each of which is hereby
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] In various embodiments, the present invention generally
relates to light-emitting diodes (LEDs) and, in particular, to LED
dies packaged with engineered phosphor layers and lighting systems
incorporating such LED dies.
BACKGROUND
[0003] An increasing number of light fixtures utilize LEDs as light
sources due to their lower energy consumption, smaller size,
improved robustness, and longer operational lifetime relative to
conventional filament-based light sources. Conventional LEDs emit
quasi-monochromatic radiation ranging from infrared through the
visible spectrum to ultraviolet. Conventional LEDs emit light at a
particular wavelength, ranging from, for example, red to blue or
ultraviolet (UV) light. However, for purposes of general
illumination, the relatively narrow spectral width of light emitted
light by LEDs is generally converted to broad-spectrum white
light.
[0004] Traditionally, there are two ways of obtaining white light
from LEDs. One approach utilizes two or more LEDs operating at
different wavelengths, where the different wavelengths are chosen
such that their combination appears white to the human eye. For
example, one may use LEDs emitting in the red, green, and blue
wavelength ranges. Such an arrangement typically requires careful
control of the operating currents of each LED, such that the
resulting combination of wavelengths is stable over time and
different operating conditions, for example temperature. Because
the different LEDs may be formed from different materials,
different operating parameters may be required for the different
LEDs; this complicates the LED circuit design. Furthermore, such
systems typically require some form of light combiner, diffuser or
mixing chamber, so that the eye sees white light rather than the
distinct colors of each of the different LEDs. Such light-mixing
systems typically add cost and bulk to lighting systems and may
reduce their efficiency.
[0005] White light may also be produced in LED-based systems for
general illumination via the utilization of wavelength-conversion
materials (also called light-conversion materials) such as
phosphors, sometimes called phosphor-converted LEDs. For example,
an LED combined with a wavelength-conversion material generates
white light by combining the short-wavelength radiant flux (e.g.,
blue light) emitted by the semiconductor LED with long-wavelength
radiant flux (e.g., yellow light) emitted by the wavelength
conversion material. The chromaticity (or color), color
temperature, and color-rendering index are determined by the
relative intensities of the component colors. For example, the
light color may be adjusted from "warm white" with a correlated
color temperature (CCT) of 2700 Kelvin or lower to "cool white"
with a CCT of 6500 Kelvin or greater by varying the type or amount
of phosphor material. White light may also be generated solely or
substantially only by the light emitted by the one or more
wavelength conversion materials.
[0006] In isolation, bare LED dies generally exhibit a Lambertian
luminous intensity distribution pattern, as shown in FIG. 1A, that
is a consequence of the light being uniformly emitted from a planar
surface. (That is, the projected area of its light-emitting region
decreases according to the cosine of the viewing angle with respect
to the surface normal.)
[0007] The wavelength-conversion material is generally one or more
phosphor particles. Such particles emit with a substantially
isotropic distribution. In a phosphor-converted LED, the phosphor
particles are generally embedded into a transparent matrix, for
example a silicone, and typically have a substantially
hemispherical shape surrounding the die with the die positioned at
the equator and in the center of the hemisphere. The hemispherical
shape is used because it generally results in relatively high light
extraction efficiency because of reduced total internal reflection
(TIR) at the phosphor/air interface. The intensity distribution of
isotropic emitting phosphor particles in a hemispherical
transparent matrix is shown in FIG. 1B.
[0008] As may be seen by comparing FIGS. 1A and 1B, the intensity
distributions of a bare-die LED and embedded phosphor particles are
different. This difference results in the chromaticity of the
combined light varying with viewing angle, resulting in a
non-uniform color distribution as seen by the human eye. For
example, a phosphor-coated blue LED may be typically perceived as
being cool white when viewed head-on, but warm white when viewed
obliquely. Thus, while the hemispherical shape provides relatively
high efficiency, it suffers from relatively poor color temperature
uniformity with angle.
[0009] In order to mitigate the relatively poor angular color
uniformity of conventional phosphor-converted LEDs, illumination
systems incorporating such phosphor-converted LEDs often require
additional elements, such as diffusers, mixing chambers, or the
like, to homogenize the color characteristics. Such homogenization
often degrades the light-intensity distribution pattern, however,
resulting in the need for secondary optics to attempt to
re-establish the desired light-intensity distribution pattern. The
addition of these elements typically requires undesirable
additional space or volume, adds cost and expense, and reduces
output efficiency.
[0010] Accordingly, there is a need for structures, systems and
procedures enabling LED-based illumination systems to generate
uniform color distribution of emitted light and operate with high
extraction efficiency while utilizing low-cost integration of
phosphors with the LEDs.
SUMMARY
[0011] In accordance with certain embodiments, one or more phosphor
elements at least partially surrounding a light-emitting element
(LEE) are shaped to improve uniformity of chromaticity of light
emitted from the LEE as a function of viewing angle. The phosphor
element may be formed of a single structure or multiple discrete
portions that may be optically coupled and at least a portion of
the surface of the phosphor element may be roughened (i.e.,
textured) to improve light-extraction efficiency from the device.
Various embodiments of this invention engineer (1) the angular
intensity distribution of the light emitted from the LEE as it
exits the surrounding phosphor and (2) the angular intensity
distribution of light emitted from the phosphor to achieve a
desired angular characteristic of one or more optical parameters,
for example to achieve a relatively uniform color temperature with
viewing angle.
[0012] As utilized herein, the term "light-emitting element" (LEE)
refers to any device that emits electromagnetic radiation within a
wavelength regime of interest, for example, visible, infrared or
ultraviolet regime, when activated, by applying a potential
difference across the device or passing a current through the
device. Examples of LEEs include solid-state, organic, polymer,
phosphor-coated or high-flux LEDs, microLEDs (described below),
laser diodes or other similar devices as would be readily
understood. The emitted radiation of a LEE may be visible, such as
red, blue or green, or invisible, such as infrared or ultraviolet.
A LEE may produce radiation of a spread of wavelengths. A LEE may
feature a phosphorescent or fluorescent material for converting a
portion of its emissions from one set of wavelengths to another. A
LEE may include multiple LEEs, each emitting essentially the same
or different wavelengths. In some embodiments, a LEE is an LED that
may feature a reflector over all or a portion of its surface upon
which electrical contacts are positioned. The reflector may also be
formed over all or a portion of the contacts themselves. In some
embodiments, the contacts are themselves reflective.
[0013] A LEE may be of any size. In some embodiments, a LEE has one
lateral dimension less than 500 .mu.m, while in other embodiments a
LEE has one lateral dimension greater than 500 um. Exemplary sizes
of a relatively small LEE may include about 175 .mu.m by about 250
.mu.m, about 250 .mu.m by about 400 .mu.m, about 250 .mu.m by about
300 .mu.m, or about 225 .mu.m by about 175 .mu.m. Exemplary sizes
of a relatively large LEE may include about 1000 .mu.m by about
1000 .mu.m, about 500 .mu.m by about 500 .mu.m, about 250 .mu.m by
about 600 .mu.m, or about 1500 .mu.m by about 1500 .mu.m. In some
embodiments, a LEE includes or consists essentially of a small LED
die, also referred to as a "microLED." A microLED generally has one
lateral dimension less than about 300 .mu.m. In some embodiments,
the LEE has one lateral dimension less than about 200 .mu.m or even
less than about 100 .mu.m. For example, a microLED may have a size
of about 225 .mu.m by about 175 .mu.m or about 150 .mu.m by about
100 .mu.m or about 150 .mu.m by about 50 .mu.m. In some
embodiments, the surface area of the top surface of a microLED is
less than 50,000 .mu.m.sup.2 or less than 10,000 .mu.m.sup.2. The
size of the LEE is not a limitation of the present invention, and
in other embodiments the LEE may be relatively larger, e.g., the
LEE may have one lateral dimension on the order of at least about
1000 .mu.m or at least about 3000 .mu.m.
[0014] As used herein, "phosphor" refers to any material that
shifts the wavelengths of light irradiating it and/or that is
fluorescent and/or phosphorescent, and is utilized interchangeably
with the term "light-conversion material" or "phosphor-conversion
element." As used herein, a "phosphor" may refer to only the powder
or particles (of one or more different types) or to the powder or
particles with the binder. The light-conversion material is
incorporated to shift one or more wavelengths of at least a portion
of the light emitted by LEEs to other desired wavelengths (which
are then emitted from the larger device alone or color-mixed with
another portion of the original light emitted by the die). A
light-conversion material may include or consist essentially of
phosphor powders, quantum dots, organic dye or the like within a
transparent matrix. Phosphors are typically available in the form
of powders or particles, and in such case may be mixed in binders.
An exemplary binder is silicone, i.e., polyorganosiloxane, which is
most commonly polydimethylsiloxane (PDMS). Phosphors vary in
composition, and may include lutetium aluminum garnet (LuAG or
GAL), yttrium aluminum garnet (YAG) or other phosphors known in the
art. GAL, LuAG, YAG and other materials may be doped with various
materials including for example Ce, Eu, etc. The specific
components and/or formulation of the phosphor and/or matrix
material are not limitations of the present invention. As used
herein, a "phosphor chip" is a discrete piece or layer of phosphor
that has been fabricated and cured while unattached to any LEE, and
that may be later coupled to an LEE by, e.g., optical bonding or
via an optical adhesive.
[0015] The binder may also be referred to as an encapsulant or a
matrix material. In one embodiment, the binder includes or consists
essentially of a transparent material, for example silicone-based
materials or epoxy, having an index of refraction greater than
1.35. In one embodiment the phosphor includes or consists
essentially of other materials, for example fumed silica or
alumina, to achieve other properties, for example to scatter light,
or to reduce settling of the powder in the binder. An example of
the binder material includes materials from the ASP series of
silicone phenyls manufactured by Shin Etsu, or the Sylgard series
manufactured by Dow Corning.
[0016] Herein, two components such as light-emitting elements,
optical elements, and/or phosphor chips being "aligned" or
"associated" with each other may refer to such components being
mechanically and/or optically aligned. By "mechanically aligned" is
meant coaxial or situated along a parallel axis. By "optically
aligned" is meant that at least some light (or other
electromagnetic signal) emitted by or passing through one component
passes through and/or is emitted by the other.
[0017] In an aspect, embodiments of the invention feature a light
emitting device that includes or consists essentially of a
light-emitting die having (i) a top face and a bottom face opposite
the top face, the top and/or bottom face being configured for
emission of light therefrom, and (ii) a sidewall spanning the top
and bottom faces, and at least partially surrounding the
light-emitting die, a phosphor element including or consisting
essentially of (i) a binder and (ii) disposed within the binder,
one or more wavelength-conversion materials for absorbing at least
a portion of light emitted from the light-emitting die and emitting
converted light having a different wavelength. The phosphor element
has an outer contour having a curved region that defines only a
portion of a hemisphere having a hemisphere radius, and a planar
base of the phosphor element has a non-zero centroid z-offset
within the hemisphere.
[0018] Embodiments of the invention may include one or more of the
following in any of a variety of different combinations. The ratio
of the centroid z-offset to the hemisphere radius may be a value
ranging from 0.3 to 0.8. The bottom face of the light-emitting die
may be substantially coplanar with the base of the phosphor
element. The ratio of the centroid z-offset to the hemisphere
radius may be a value ranging from 0.5 to 0.77. The ratio of the
centroid z-offset to the hemisphere radius may be a value ranging
from 0.3 to 0.5. The outer contour of the phosphor element may have
a planar region disposed over the light-emitting die and
substantially parallel to the top face of the light-emitting die.
The ratio of a z-offset value of the planar region within the
hemisphere to the hemisphere radius may have a value ranging from
0.02 to 0.15. The ratio of a z-offset value of the planar region
within the hemisphere to the hemisphere radius may have a value
ranging from 0.04 to 0.12. The radius (or other lateral dimension
such as width) of the planar region may be a value ranging from 50
.mu.m to 1000 .mu.m. The radius (or other lateral dimension such as
width) of the planar region may be a value ranging from 200 .mu.m
to 800 .mu.m. The ratio of the centroid z-offset to the hemisphere
radius may be approximately defined by -1.9.times.F+0.67, where F
is a ratio of the z-offset value of the planar region within the
hemisphere to the hemisphere radius. The centroid z-offset value
may be approximately defined by 1.41.times.R-0.8, where R is the
hemisphere radius.
[0019] The hemisphere radius may be a value ranging from about 0.2
mm to about 20 mm. The hemisphere radius may be a value ranging
from about 0.5 mm to about 5 mm. The hemisphere radius may be a
value ranging from about 0.7 mm to about 1.5 mm. The base radius
(or width) of the phosphor element may be a value ranging from 0.6
mm and 1.0 mm. The outer contour of the phosphor element may have a
planar region disposed over the light-emitting die and
substantially parallel to the top face of the light-emitting die.
The radius (or width) of the planar region may be a value ranging
from about 0.15 mm to about 0.45 mm. The height (distance) from the
base of the phosphor element to the planar region may be a value
ranging from about 0.15 mm to about 0.5 mm. The outer contour of
the phosphor element may have a region defined by a cylindrical
cutoff within the hemisphere. The ratio of the length (e.g.,
dimension parallel to the base of the phosphor element and/or
bottom face of the light-emitting die) of the cylindrical cutoff to
the hemisphere radius may be a value ranging from 0.75 to 0.95. The
length of the cylindrical cutoff may be a value ranging from 50
.mu.m to 500 .mu.m.
[0020] Light emitted from the light-emitting die may have a
Lambertian distribution. The converted light may have an isotropic
distribution. The converted light may combine with unconverted
light emitted from the light-emitting die to form substantially
white light. The divergence of color temperature of the
substantially white light emitted from the device may vary, over an
angular range of 0.degree. to 85.degree., no more than 0.01 in
terms of .DELTA.u'v' deviation from a spatially weighted averaged
chromaticity. The divergence of color temperature of the
substantially white light emitted from the device may vary, over an
angular range of 0.degree. to 85.degree., no more than 0.005 in
terms of .DELTA.u'v' deviation from a spatially weighted averaged
chromaticity. The one or more wavelength conversion materials may
include or consist essentially of one or more phosphor particles.
The phosphor particles may each include or consist essentially of
garnet and a rare-earth element. The device may include, disposed
beneath (i) at least a portion of the light-emitting die and/or
(ii) the phosphor element, a mounting surface reflective to
converted light and/or unconverted light emitted from the
light-emitting die. The mounting surface may have a reflectivity to
visible light of approximately 95% to approximately 98%. At least a
portion of the outer contour of the phosphor element may have a
surface texture for reducing total internal reflection. The
light-emitting die may be a bare light-emitting diode die. The
light-emitting die may include or consist essentially of a
GaN-based semiconductor material (e.g., a material including GaN,
AlN, and/or InN and/or combinations or alloys thereof). The
semiconductor material may include In. The light-emitting die may
emit blue and/or ultraviolet light.
[0021] In another aspect, embodiments of the invention feature a
light-emitting device that includes or consists essentially of a
light-emitting die having (i) a top face and a bottom face opposite
the top face, the top and/or bottom face being configured for
emission of light therefrom, and (ii) a sidewall spanning the top
and bottom faces, and at least partially surrounding the
light-emitting die, a phosphor element including or consisting
essentially of (i) a binder and (ii) disposed within the binder,
one or more wavelength-conversion materials for absorbing at least
a portion of light emitted from the light-emitting die and emitting
converted light having a different wavelength. The phosphor element
has an outer contour having (i) a curved region that defines only a
portion of a hemisphere having a hemisphere radius and (ii) a
planar region disposed over the light-emitting die and
substantially parallel to the top face of the light-emitting
die.
[0022] Embodiments of the invention may include one or more of the
following in any of a variety of different combinations. The bottom
face of the light-emitting die may be substantially coplanar with a
base of phosphor element opposite the planar region. The ratio of a
z-offset of the planar region within the hemisphere to the
hemisphere radius may be a value ranging from 0.02 to 0.15. The
ratio of a z-offset of the planar region within the hemisphere to
the hemisphere radius may be a value ranging from 0.04 to 0.12. The
outer contour of the phosphor element may have a region defined by
a cylindrical cutoff within the hemisphere. The ratio of a length
of the cylindrical cutoff to the hemisphere radius may be a value
ranging from 0.75 to 0.95. The length of the cylindrical cutoff may
be a value ranging from 50 .mu.m to 500 .mu.m. The length of the
cylindrical cutoff may be a value ranging from about 0.2 mm to
about 20 mm. The hemisphere radius may be a value ranging from
about 0.7 mm to about 5 mm. Light emitted from the light-emitting
die may have a Lambertian distribution. The converted light may
have an isotropic distribution. The converted light may combine
with unconverted light emitted from the light-emitting die to form
substantially white light. The divergence of color temperature of
the substantially white light emitted from the device may vary,
over an angular range of 0.degree. to 85.degree., no more than 0.01
in terms of .DELTA.u'v' deviation from a spatially weighted
averaged chromaticity. The divergence of color temperature of the
substantially white light emitted from the device may vary, over an
angular range of 0.degree. to 85.degree., no more than 0.005 in
terms of .DELTA.u'v' deviation from a spatially weighted averaged
chromaticity.
[0023] The one or more wavelength conversion materials may include
or consist essentially of one or more phosphor particles. The
phosphor particles each may include or consist essentially of
garnet and a rare-earth element. The light-emitting device may
include, disposed beneath (i) at least a portion of the
light-emitting die and/or (ii) the phosphor element, a mounting
surface reflective to converted light and/or unconverted light
emitted by the light-emitting die. The mounting surface may have a
reflectivity to visible light of approximately 95% to approximately
98%. At least a portion of the outer contour of the phosphor
element may have a surface texture for reducing total internal
reflection. The light-emitting die may be a bare light-emitting
diode die. The light-emitting die may include or consist
essentially of a GaN-based semiconductor material. The
semiconductor material may include In. The light-emitting die may
emit blue and/or ultraviolet light.
[0024] In yet another embodiment, aspects of the invention feature
a light-emitting device that includes or consists essentially of a
light-emitting die having (i) a top face and a bottom face opposite
the top face, the top and/or bottom face being configured for
emission of light therefrom, and (ii) a sidewall spanning the top
and bottom faces, and at least partially surrounding the
light-emitting die, a phosphor element including or consisting
essentially of (i) a binder and (ii) disposed within the binder,
one or more wavelength-conversion materials for absorbing at least
a portion of light emitted from the light-emitting die and emitting
converted light having a different wavelength, converted light and
unconverted light emitted by the light-emitting die combining to
form substantially white light. The phosphor element includes or
consists essentially of (i) a first region having a sidewall
substantially parallel to the sidewall of the light-emitting die
and (ii) disposed over the first region, a second region having a
top surface defining a portion of an oblate ellipsoid.
[0025] Embodiments of the invention may include one or more of the
following in any of a variety of different combinations. The second
region may define a portion of an oblate ellipsoid described by the
equation
z ( r ) = r 2 R ( 1 + 1 - ( 1 + K ) ( r 2 / R 2 ) ) ,
##EQU00001##
where z is a height of the second region above a top surface of the
light-emitting die, r is a radius of the oblate ellipsoid, R is
approximately 2.38, and K is approximately 6.0. The first region of
the phosphor element may be discrete from and optically bonded to
the second region of the phosphor element. The second region of the
phosphor element may be disposed over the top surface of the
light-emitting die. A reflective surface may be disposed below the
bottom surface of the light-emitting die. The distance between the
sidewall of the first region and the sidewall of the light-emitting
die may be a value ranging from 0.2 mm to 20 mm. The distance
between the sidewall of the first region and the sidewall of the
light-emitting die may be a value ranging from 0.4 mm to 5 mm.
Light emitted from the light-emitting die may have a Lambertian
distribution. The converted light may have an isotropic
distribution. The divergence of color temperature of the
substantially white light emitted from the device may vary, over an
angular range of 0.degree. to 85.degree., no more than 0.01 in
terms of .DELTA.u'v' deviation from a spatially weighted averaged
chromaticity. The divergence of color temperature of the
substantially white light emitted from the device may vary, over an
angular range of 0.degree. to 85.degree., no more than 0.005 in
terms of .DELTA.u'v' deviation from a spatially weighted averaged
chromaticity.
[0026] The one or more wavelength conversion materials may include
or consist essentially of one or more phosphor particles. The
phosphor particles may each include or consist essentially of
garnet and a rare-earth element. The light-emitting device may
include, disposed beneath (i) at least a portion of the
light-emitting die and/or (ii) the phosphor element, a mounting
surface reflective to converted light and/or unconverted light
emitted by the light-emitting die. The mounting surface may have a
reflectivity to visible light of approximately 95% to approximately
98%. The top surface of the second region of the phosphor element
may have a surface texture for reducing total internal reflection.
The light-emitting die may be a bare light-emitting diode die. The
light-emitting die may include or consist essentially of a
GaN-based semiconductor material. The semiconductor material may
include In. The light-emitting die may emit blue and/or ultraviolet
light.
[0027] These and other objects, along with advantages and features
of the invention, will become more apparent through reference to
the following description, the accompanying drawings, and the
claims. Furthermore, it is to be understood that the features of
the various embodiments described herein are not mutually exclusive
and can exist in various combinations and permutations. Reference
throughout this specification to "one example," "an example," "one
embodiment," or "an embodiment" means that a particular feature,
structure, or characteristic described in connection with the
example is included in at least one example of the present
technology. Thus, the occurrences of the phrases "in one example,"
"in an example," "one embodiment," or "an embodiment" in various
places throughout this specification are not necessarily all
referring to the same example. Furthermore, the particular
features, structures, routines, steps, or characteristics may be
combined in any suitable manner in one or more examples of the
technology. The term "light" broadly connotes any wavelength or
wavelength band in the electromagnetic spectrum, including, without
limitation, visible light, ultraviolet radiation, and infrared
radiation. Similarly, photometric terms such as "illuminance,"
"luminous flux," and "luminous intensity" extend to and include
their radiometric equivalents, such as "irradiance," "radiant
flux," and "radiant intensity." As used herein, the terms
"substantially," "approximately," and "about" mean.+-.10%, and in
some embodiments, .+-.5%. The term "consists essentially of" means
excluding other materials that contribute to function, unless
otherwise defined herein. Nonetheless, such other materials may be
present, collectively or individually, in trace amounts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0029] FIGS. 1A and 1B are plots of the simulated spectral radiant
intensity distribution of blue and yellow light, respectively,
emitted from a light-emitting element and phosphor particles;
[0030] FIG. 2 is a schematic cross-section of a light-emitting
device in accordance with various embodiments of the invention,
illustrating refraction and total internal reflection of light;
[0031] FIGS. 3A, 3B, and 4A are schematic cross-sections of
light-emitting devices having shaped phosphor elements in
accordance with various embodiments of the invention;
[0032] FIGS. 4B-4D are, respectively, plots of the lighting-device
emission spectrum, phosphor-transmission spectrum, and
phosphor-emission spectrum for the lighting-devices of FIG. 4A;
[0033] FIG. 4E is a schematic cross-section of a light-emitting
device having a shaped phosphor element in accordance with various
embodiments of the invention;
[0034] FIGS. 5A and 5B are plots of simulated chromaticity
uniformity for a light-emitting device according to FIG. 4A;
[0035] FIG. 5C is a plot of simulated luminance flux for a
light-emitting device according to FIG. 4A;
[0036] FIGS. 6A and 6B are plots of simulated chromaticity
uniformity and luminance flux for a light-emitting device according
to FIG. 4A;
[0037] FIGS. 6C and 6D are plots showing design guidelines for a
light-emitting device according to FIG. 4A;
[0038] FIGS. 7A and 7B are plots of simulated chromaticity
uniformity for a light-emitting device according to FIG. 4A;
[0039] FIG. 7C is a plot of simulated luminance flux for a
light-emitting device according to FIG. 4A;
[0040] FIGS. 8A and 8B are plots of simulated chromaticity
uniformity and luminance flux for a light-emitting device according
to FIG. 4A;
[0041] FIGS. 8C and 8D are plots showing design guidelines a
light-emitting device according to FIG. 4A;
[0042] FIG. 9 is a plot of chromaticity deviation for
light-emitting devices incorporating a hemispherical phosphor
element or an engineered phosphor element in accordance with
various embodiments of the invention;
[0043] FIG. 10 is a plot of measured chromaticity deviation for
light-emitting devices incorporating an engineered phosphor element
in accordance with various embodiments of the invention;
[0044] FIG. 11 is a schematic cross-section of a light-emitting
device incorporating multiple phosphor regions in accordance with
various embodiments of the invention;
[0045] FIGS. 12A and 12B are plots of the simulated spectral
radiant intensity distribution of blue and yellow light,
respectively, that exit the phosphor regions of FIG. 6;
[0046] FIG. 12C is a plot of chromaticity deviation for the
light-emitting device of FIG. 6;
[0047] FIGS. 13A-13C are schematic cross-sections of portions of
light-emitting devices incorporating color equalization layers in
accordance with various embodiments of the invention;
[0048] FIG. 14 is a schematic cross-section of a portion of a
light-emitting device in accordance with various embodiments of the
invention;
[0049] FIG. 15A-15E are schematic cross-sections of light-emitting
devices in accordance with various embodiments of the
invention;
[0050] FIGS. 16A and 16B are schematic cross-sections of arrays of
phosphor elements in accordance with various embodiments of the
invention;
[0051] FIG. 16C is a schematic cross-section of a singulated
phosphor element in accordance with various embodiments of the
invention; and
[0052] FIGS. 17A-17C are schematic cross-sections of pick-and-place
tools interacting with light-emitting devices in accordance with
various embodiments of the invention.
DETAILED DESCRIPTION
[0053] Various embodiments of the present invention engineer (1)
the angular intensity distribution of the light emitted from the
LEE as it exits the surrounding phosphor and (2) the angular
intensity distribution of light emitted from the phosphor to
achieve a desired angular characteristic of one or more optical
parameters, for example to achieve a relatively uniform color
temperature with viewing angle. For example if the light from the
two sources, for example blue from an LEE and yellow from a
phosphor, are engineered to have the same or substantially the same
angular intensity distribution, then the combination, when viewed
or projected externally to the phosphor, has the same or
substantially the same chromaticity as a function of angle. Thus,
preferred embodiments of the invention control the angular
intensity distribution of the light emitted from the LEE and the
light-conversion material as it exits the surrounding phosphor.
Various optical processes occur within the phosphor (for example
absorption and scattering) and at the phosphor/air interface (for
example TIR and refraction) that modify the LEE angular intensity
distribution from what it would be in the absence of an associated
phosphor, and embodiments of the invention account for such
processes, as will be detailed herein.
[0054] In one embodiment of the present invention, a combination of
refraction from the top surface of the phosphor element and TIR
from the interface between the phosphor element and the surrounding
air are used to preferentially redirect both (i) the light from the
LEE that is not absorbed by the phosphor particles and (ii) the
light emitted by the phosphor particles in specific directions to
achieve one or more desired angularly dependent optical
characteristics. In other words, the phosphor element is used not
only to mechanically support the phosphor around a portion of the
LEE, but it is also used as a lens structure that is optically
coupled to the LEE and uses both TIR and refraction to redirect the
pump light (e.g., blue light from the LEE) within the lens
structure such that the chromaticity of the emitted light (e.g.,
white light, being a combination of the blue pump light and the
phosphor emissions) does not appreciably vary with the angle of
emission. FIG. 2 is a schematic of an exemplary system 200 of the
present invention featuring an LEE 130 and that utilizes both
refraction (to produce, for example, light 220) and TIR (to
produce, for example, light 230) from the surface of a phosphor
element 210.
[0055] FIGS. 3A and 3B depict two embodiments of the present
invention, each featuring a LEE 130 over which is disposed a
phosphor element 140. In FIG. 3A, phosphor element 140 has a
single-curve shape, i.e., a smooth curve with no intermediate
discontinuities. FIG. 3B shows another example of phosphor element
140 having a two-curve shape, where the two portions are identified
as portions 330 and 340. In this case, portion 340 is perpendicular
to the bottom surface 315 of LEE 130; however, this is not a
limitation of the present invention, and in other embodiments
portion 340 may form an acute or obtuse angle with the bottom
surface of LEE 130. Various embodiments of this invention control
the shape of phosphor element 140, and in particular the shape of
surfaces 330 and/or 340. While FIGS. 3A and 3B show phosphor
element 140 having one and two surface curvatures respectively,
this is not a limitation of the present invention, and in other
embodiments phosphor element 140 may have more than two such
curvatures. As discussed herein, the shape and size of phosphor
element 140 is an important aspect of embodiments of the present
invention.
[0056] Various factors, such as the dimensions of LEE die, mirrored
active area, phosphor matrix, phosphor particle concentration,
and/or the diffuse and specular reflection properties of the LEE
substrate, may significantly affect the TIR and refraction of both
blue and yellow (for example) light within the phosphor matrix. In
general, numerical simulation may be utilized to determine optimal
shapes of the top surface for given sets of design parameters. As
detailed herein, TIR and refraction may be used to redirect the
light.
Example 1
[0057] FIG. 4A shows a schematic of one class of embodiments of the
present invention, including or consisting essentially of LEE 130
partially surrounded by a phosphor element 420. In this example LEE
130 is a blue LEE, for example a blue LED, having an emission
spectrum as shown in FIG. 4B. LEE 130 has a length of about 324
.mu.m, a width of about 200 .mu.m, and a height of about 134 .mu.m.
In these simulations the phosphor element 420 is a hemispherical
shape having a radius 410 of about 1 mm. Phosphor element 420 has a
refractive index of about 1.53 while LEE 130 has a refractive index
of about 1.74. These simulations are optimized to produce white
light with a CCT of about 3500K and a color point on the 1931 CIE
chromaticity diagram of about 0.4 chromaticity x value and at about
0.4 chromaticity y value using two phosphors, the emission spectra
of which are shown in FIG. 4D. The combined mean-free-path of
phosphor element 420 is about 137 .mu.m between simulation events
(absorption, scattering, etc.); the phosphor transmission spectrum
is shown in FIG. 4C. Phosphor element 420 is defined as a function
of a hemispherical profile with a radius 410. FIG. 4A also shows
additional optional features of phosphor element 420, including a
centroid z-offset 430, a cylindrical cut-off having diameter 440
that in some embodiments results in a second portion of the shape
of phosphor 140, for example portion 340 shown in FIG. 3B, and a
flat-top z-offset 450 that results in a flat top 460 having a flat
top radius (not identified in FIG. 4A). Any one or all of these
features may be combined in phosphor element 420. The structure of
FIG. 4A may also be described as a hemispherical cap, that is a
portion of a hemisphere cut off by a plane above the base of the
hemisphere, as shown in FIG. 4E (for reference a hemispherical cap
with a centroid z-offset of zero (0) is a hemisphere). FIG. 4E
shows hemisphere 470 having a radius 410 and hemispherical cap 475
with LEE 130 sitting on the plane forming the base 490 of
hemispherical cap 475. The hemispherical cap height is identified
as 480, the centroid z-offset is identified as 430, and the
hemispherical cap radius is identified as 411. The structure in
FIG. 4E does not show optional flat top 460 or the cylindrical
cut-off shown in FIG. 4A.
[0058] FIGS. 5A and 5B show the chromaticity uniformity while FIG.
5C shows the luminous flux for the structure of FIG. 4A, as a
function of centroid z-offset 430 and flat top z-offset 450. FIGS.
5A and 5B show the same data but from different orientations. FIG.
5B also shows a contour plot of chromaticity uniformity. In FIGS.
5A-5C both centroid z-offset and flat top z-offset values are
normalized to the hemisphere radius 410. Chromaticity uniformity
(sum of .DELTA. u' v') is measured as the sum of the deviation of
u'v' from the spatially averaged chromaticity coordinate over
0.degree. to 90.degree. polar angles as defined in IES LM-79-08,
"Electrical and Photometric Measurements of Solid-State Lighting
Products," Illuminating Engineering Society, January 2008 (where
0.degree. is perpendicular to the emitting face of LEE 410), the
entire disclosure of which is incorporated by reference herein.
[0059] As may be seen in FIGS. 5A and 5B, there is an unexpected
minimum in the angular chromaticity uniformity for centroid
z-offset values in the range of about 0.3 to about 0.7. Thus,
instead of positioning LEE 130 at the base or equator of the
hemisphere, as is conventionally done, a significant improvement in
chromaticity uniformity may be realized by positioning LEE 130
above the base or equator of the hemisphere. As may be seen from
FIGS. 5A and 5B, the uniformity relative to an LEE 130 at the base
or equator of the hemisphere may improve by over a factor of three.
FIG. 5C shows that the luminance flux increases essentially
monotonically with an increase in the centroid z-offset. As may be
seen from FIGS. 5A-5C, the flat top z-offset has a relatively
smaller impact on chromaticity uniformity and luminance flux.
However, as will be discussed herein, there may be other reasons
for incorporating a flat top, and FIGS. 5A-5C show that
incorporation of a flat top has relatively little impact on the
chromaticity uniformity and luminance flux.
[0060] FIGS. 6A and 6B show plots of chromaticity uniformity and
luminance flux as a function of centroid z-offset at two flat top
z-offset values, about 0.02 and about 0.12 respectively. In FIGS.
6A and 6B, both centroid z-offset and flat top z-offset values are
normalized to radius 410. As may be seen there is a clear minimum
in chromaticity uniformity (or chromaticity deviation) in the range
of centroid z-offset from about 0.3 to about 0.7. As the flat-top
z-offset value increases, the amount of centroid z-offset required
to minimize the chromaticity variation decreases. For a flat top
z-offset of about 0.02 (almost a hemisphere), the optimal centroid
z-offset is in the range of about 0.57 to about 0.7, or in the
range of about 0.6 to about 0.675. For a larger flat top z-offset
of about 0.12, the optimal centroid z-offset is in the range of
about 0.375 to about 0.5, or in the range of about 0.4 to about
0.475.
[0061] As may be seen from FIGS. 6A and 6B, the luminance flux
increases substantially monotonically with increasing centroid
z-offset. In some embodiments, luminance flux intensity may be
relatively more important than angular chromaticity uniformity, and
in these embodiments a larger centroid z-offset value may be chosen
to increase luminance flux intensity while still maintaining
relatively high angular chromaticity uniformity. For example, for
the embodiment where the flat top z-offset is about 0.02, the
centroid z-offset may be in the range of about 0.65 to about 0.7.
For the embodiment where the flat-top z-offset is about 0.12, the
centroid z-offset may be in the range of about 0.45 to about 0.5.
As may be seen, there is a relatively substantial overlap between
the values of centroid z-offset to achieve minimum angular
chromaticity variation and to achieve high luminous flux.
[0062] FIG. 6C shows a plot of centroid z-offset (normalized to
hemisphere radius 410) as a function of flat top z-offset
(normalized to hemisphere radius 410) to achieve minimum angular
chromaticity variation. In some embodiments, FIG. 6C may be used as
a design guide to achieve minimum angular chromaticity variation.
First the desired flat top z-offset is determined, then FIG. 6C is
used to determine the optimal centroid z-offset to achieve minimum
angular chromaticity variation. A line fitted to the data gives a
relationship of H=-1.90.times.F+0.67, where F is the flat top
z-offset and H is the centroid z-offset. As may be seen from FIGS.
5A and 5B, there is relatively little variation in angular
chromaticity non-uniformity as a function of flat top z-offset,
when a preferred value for centroid z-offset is chosen.
[0063] FIG. 6D shows the same data as FIG. 6C, but with the
addition of luminance flux. The luminance flux data shown in FIG.
6C is the value at the minimum angular chromaticity non-uniformity
for each value of flat top z-offset. As may be seen from FIG. 6D,
smaller flat top z-offset values give a relatively larger luminance
flux, but the total variation in luminance flux in FIG. 6D is
relatively small, on the order of about 10%.
[0064] FIGS. 7A-7C show angular chromaticity uniformity and
luminance flux as a function of centroid z-offset and hemisphere
radius, respectively. In this example, the flat top z-offset is
zero and the hemisphere radius is varied from 0.4 to 1.6 mm. The
size of LEE 130 and other simulation parameters are the same as for
FIGS. 5A-5C and FIGS. 6A-6C. As may be seen from FIGS. 7A and 7B,
varying the hemisphere radius does not change the unexpected result
that the angular chromaticity uniformity is minimized with a
relatively large centroid z-offset. There is a slight improvement
in angular chromaticity uniformity with increasing hemisphere
radius, but as will be seen in connection with FIGS. 8A and 8B,
this is relatively small. Similar to the plot of FIG. 6C, the plot
in FIG. 7C shows that the luminance flux increases with increasing
centroid z-offset and also increases with increasing hemisphere
radius.
[0065] FIGS. 8A and 8B show plots of chromaticity uniformity and
luminance flux as a function of centroid z-offset at two hemisphere
radius values, about 0.90 mm and about 1.5 mm respectively. As may
be seen there is a minimum in angular chromaticity uniformity for
higher values. In comparison to FIGS. 6A and 6B, there is a
relatively stronger correlation between the centroid z-offset
position for minimum angular chromaticity uniformity and hemisphere
radius, than for centroid z-offset position and flat top z-offset.
As the hemisphere radius increases, the required value of centroid
z-offset to minimize chromaticity variation increases. For a
hemisphere radius of about 0.90 mm, the optimal centroid z-offset
is in the range of about 0.5 mm to about 0.6 mm, or in the range of
about 0.525 mm to about 0.575 mm. If these values are normalized to
the hemisphere radius, then the ranges are about 0.55 to about 0.67
and about 0.58 to about 0.64. For a hemisphere radius of about 1.5
mm, the optimal centroid z-offset is in the range of about 0.8 mm
to about 1.15 mm, or in the range of about 0.9 mm to about 1.1 mm.
If these values are normalized to the hemisphere radius, then the
ranges are about 0.53 to about 0.77 and about 0.60 to about
0.73.
[0066] As may be seen from FIGS. 8A and 8B, the luminance flux
increases substantially monotonically with increasing centroid
z-offset. In some embodiments, luminance flux intensity may be
relatively more important than angular chromaticity uniformity, and
in these embodiments a larger centroid z-offset value may be chosen
to increase luminance flux intensity while still maintaining
relatively high angular chromaticity uniformity. For example, for
an embodiment in which the hemisphere radius is about 0.9 mm, the
centroid z-offset may be in the range of about 0.5 to about 0.6. As
may be seen from FIG. 8A, the region of centroid z-offset to
achieve high luminance flux and reduced angular chromaticity
exhibit substantial overlap. For the embodiment where the flat-top
z-offset is about 0.90, the centroid z-offset may be in the range
of about 0.5 to about 0.6.
[0067] FIG. 8C shows a plot of centroid z-offset as a function of
hemisphere radius to achieve minimum angular chromaticity
variation. In some embodiments, FIG. 8C may be used as a design
guide to achieve minimum angular chromaticity variation. First, the
desired hemisphere radius is determined, then FIG. 8C may be used
to determine the optimal centroid z-offset to achieve minimum
angular chromaticity variation. A line fitted to the data gives a
relationship of H=-1.41.times.R-0.80, where R is the hemisphere
radius and H is the centroid z-offset.
[0068] FIG. 8D shows the same data as FIG. 8C, but with the
addition of luminance flux. The luminance flux data shown in FIG.
8C is the value at the minimum angular chromaticity non-uniformity
for each value of hemisphere radius. As may be seen from FIG. 8D,
smaller hemisphere radius values give a relatively larger luminance
flux, but the total variation in luminance flux in FIG. 8D is
relatively small, on the order of about 10%.
[0069] The structural parameters associated with the minimum
angular chromaticity variation region from FIG. 5B are a radius in
the range of about 0.9 mm to about 1.1 mm and a centroid z-offset
of about 0.5 mm to about 0.7 mm, and more particularly a radius of
about 0.93 mm to about 1 mm and a centroid z-offset of about 0.55
mm to about 0.65 mm. In one embodiment, the hemisphere has a radius
in the range of about 0.6 mm to about 1.2 mm and a centroid
z-offset value (normalized to the hemisphere radius) in the range
of about 0.5 to about 0.8. In one embodiment, the hemisphere has a
radius in the range of about 0.8 mm to 1.2 mm and a centroid
z-offset value (normalized to the hemisphere radius) in the range
of about 0.4 to about 0.8 and a flat top z-offset (normalized to
hemisphere radius) in the range of about 0.02 to 0.15. In one
embodiment, the hemispherical cap radius is about 0.6 mm to about
1.0 mm, height 480 is in the range of about 0.15 mm to about 0.5
mm, and the flat top radius is in the range of about 0.15 to about
0.45 mm. In one embodiment, the hemispherical cap radius is about
0.6 mm to about 1.0 mm, the centroid offset is about 0.5 mm to
about 0.6 mm, and the flat top z-offset is about 0.02 mm to about
0.08 mm. In one embodiment, the hemispherical cap radius is about
0.96 mm, the centroid offset is about 0.54 mm, and the flat top
z-offset is about 0.05 mm. In some embodiments, the hemispherical
cap has a base radius of about 0.5 mm to about 1.0 mm; however,
this is not a limitation of the present invention, and in other
embodiments the base of hemispherical cap may have a larger or
smaller base radius. In some embodiments, the diameter of the flat
top is in the range of about 50 .mu.m to about 1000 .mu.m; however,
this is not a limitation of the present invention, and in other
embodiments the flat top may have a larger or smaller diameter. In
some embodiments, the diameter of the flat top is in the range of
about 200 .mu.m to about 800 p.m. In some embodiments, the centroid
z-offset is in the range of about 25 .mu.m to about 300 .mu.m;
however, this is not a limitation of the present invention, and in
other embodiments the centroid z-offset may be larger or smaller.
In some embodiments, the centroid z-offset is in the range of about
50 .mu.m to about 150 p.m. In some embodiments, the hemisphere
radius is in the range of about 100 .mu.m to about 20 mm; however,
this is not a limitation of the present invention, and in other
embodiments the hemisphere radius may be larger or smaller.
[0070] While the discussion with respect to the structures shown
herein have identified a hemisphere radius in the range of about
0.4 mm to about 1.6 mm, this is not a limitation of the present
invention, and in other embodiments hemisphere radius may be
smaller or larger. For example, in some embodiments the hemisphere
radius may be 2 mm in diameter or 5 mm in diameter or larger. In
some embodiments, the hemisphere radius may be smaller than 0.4 mm,
for example 0.2 mm or smaller.
Example 2
[0071] Example 2 is one embodiment of the approach discussed above.
FIG. 9 shows the deviation in chromaticity .DELTA.u'v' from the
spatially averaged chromaticity as a function of angle for an
engineered shape of a phosphor element similar to that shown in
FIG. 3B. The deviation in chromaticity over a variety of angles was
simulated using Monte Carlo ray-tracing techniques with ten million
light rays. In this case, the shape of phosphor element 140 is
defined as a function of a hemispherical profile with a radius of
about 800 centroid depth offset of about 410 .mu.m (measured from
the center of the bottom surface 315 of the LEE 130), circular
flat-top of about 500 .mu.m in diameter, and a cylindrical cut-off
of about 1200 .mu.m diameter. The characteristics of phosphor 140
and LEE 130 are the same as in Example 1. FIG. 9 also shows the
deviation in chromaticity for a hemisphere with a radius of about
800 .mu.m and centroid depth offset of about 0 .mu.m, showing
poorer performance (i.e., greater deviation in chromaticity) of the
hemisphere compared to the engineered shape.
[0072] The discussion above has focused on hemispherical-shaped
phosphor elements 130; however, this is not a limitation of the
present invention, and in other embodiments phosphor element 130
may be defined by other shapes. For example, phosphor element 130
may have a top surface that defines a portion of an oblate
ellipsoid.
Example 3
[0073] FIG. 10 shows the measured deviation in chromaticity
.DELTA.u'v' from the spatially average chromaticity as a function
of angle for an engineered shape of a phosphor element similar to
that shown in FIG. 3B. In this case the shape of portion 330 of the
phosphor element 140 is defined as a function corresponding to an
oblate ellipsoid profile described by the equation:
z ( r ) = r 2 R ( 1 + 1 - ( 1 + K ) ( r 2 / R 2 ) )
##EQU00002##
where r is the horizontal distance measured radially from the
central axis, z is the distance (at r) to the surface, measured
vertically with respect to the horizontal plane that touches the
surface at r=0, R=2.38, and K=6.0. The phosphor element 140 has a
refractive index of about 1.53 with a transmission spectrum shown
in FIG. 4B. The phosphor emission spectrums targets a 3500 K CCT at
about 0.4 chromaticity x value and at about 0.4 chromaticity y
value, the phosphor has the same characteristics as discussed in
Example 1 and LEE 130 has the same dimensions and characteristics
as in Example 1. As may be seen from FIG. 10, the measured
deviation in chromaticity .DELTA.u'v' from the spatially average
chromaticity as a function of angle is significantly lower than
that for the hemisphere (shown in FIG. 9).
[0074] An oblate ellipsoid is mathematically defined by the
quadratic equation:
x 2 a 2 + y 2 b 2 + z 2 c 2 = 1 where a = b ##EQU00003##
and has a shape intermediate between a hemisphere and a paraboloid.
A particular advantage of an ellipsoid over a more complicated
shape (as described for example by a higher order cubic or quatric
equation) is that it has a smoother shape. This smoothness is
preferred order to avoid discontinuities in the spatial
distribution that are visible as caustics. (The rings of light
visible in the projected beams from MR16 halogen lamps are a good
example.)
[0075] As discussed above, preferred embodiments of the invention
position the LEE away from the center of an oblate ellipsoid (such
as, for example, the center of a hemisphere). Positioning the LEE
at the center generally maximizes the symmetry of the LEE such that
all light paths (including scattering and absorption/emission) are
substantially the same, thus preventing the modification of the
light paths to achieve improved angular uniformity. Preferred
embodiments also position the LEE away from the surface of the
oblate ellipsoid. When the LEE is at the surface, there is
typically an insufficient mean free path between the LEE and the
phosphor boundary to adequately balance the ratio of blue light and
phosphor emissions to generate white light. Various embodiments of
the invention feature a rectangular LEE whose length is greater
than approximately twice its width and a phosphor element having
the shape of a tri-axial ellipsoid where c>b>a.
[0076] In another embodiment, LEE 130 may be embedded or partially
embedded in a series of multiple phosphor elements. For example, in
one embodiment, a phosphor element 1110 and a phosphor element 1120
may be formed over or partially formed over LEE 130, as shown in
FIG. 11. In one embodiment, phosphor element 1110 is different from
phosphor element 1120. The differences between phosphor element
1110 and 1120 may include a different binder material, a different
type of phosphor particle (1170, 1180) or particles, a different
index of refraction, different concentrations of phosphor
particles, or the like.
[0077] In some embodiments, a reflective surface, for example
surfaces 1160 and/or 1165, may be formed below all or a portion of
LEE 130 and/or phosphors 1110, 1120. In some embodiments, surface
1160 may include or consist essentially of a diffuse or specular
reflector. In one embodiment, surface 1160 may include or consist
essentially of a metal, for example aluminum, copper, silver, gold
or the like. In some embodiments, surface 1160 may include or
consist essentially of a diffuse reflector, such as a white
surface, for example a white ink, or material such as multicellular
polyethylene terephthalate (MCPET) or polyester. In some
embodiments, reflective surface 1165, as shown in FIG. 11, may be
incorporated into LEE 130.
[0078] More generally, the two or more phosphor element binders may
have different refractive indices. If, for example, a first
phosphor element binder 1140 has a lower refractive index than a
second phosphor element binder 1130, TIR may occur at their
boundary, thereby increasing the amount of blue light redirected to
the sides of the first phosphor element. Alternatively, if the two
or more optical elements are adhered with a glue or adhesive, the
optical glue material may have a higher refractive index, thereby
increasing the TIR at the boundary. In addition, the boundary
between the first and second phosphor elements may include a
dichroic mirror that is transparent to blue light but which
reflects longer wavelengths.
Example 4
[0079] FIG. 11 depicts an LEE die 130 that has a length of about
325 .mu.m, a width of about 200 um and a height of about 135 .mu.m,
as well as a mirror or reflective surface 1165 having dimensions of
about 205 .mu.m long and 150 .mu.m wide. In this example, mounting
surface 1160 (on which the LEE die 130 is mounted) has a
reflectivity of about 95% to about 98% over the visible wavelength
range, and may include or consist essentially of a material such as
MCPET. Phosphor element 1110, disposed around the LEE die 130,
includes binder 1130 into which are dispersed phosphor particles
1170. In this example, binder 1130 includes or consists essentially
of a silicone and has a refractive index of about 1.57. Phosphor
element 1110 is about 1200 .mu.m long, about 1200 .mu.m wide and
about 165 .mu.m tall.
[0080] Second phosphor element 1120, which is disposed over the top
surface of the LEE die 130, includes or consists essentially of, in
this example, a silicone binder 1140 with a refractive index of
about 1.57 and containing phosphor particles 1180 with a density
that is about 33% greater than that of the phosphor element 1110.
The phosphor element 1120 may be optically bonded to the top
surface of phosphor element 1110. Phosphor element 1120 is about
1200 .mu.m long and about 1200 .mu.m wide with a maximum height of
about 435 .mu.m.
[0081] A curved upper surface 1190 of the phosphor element 1120 has
an oblate ellipsoid profile described by the equation:
z ( r ) = r 2 R ( 1 + 1 - ( 1 + K ) ( r 2 / R 2 ) )
##EQU00004##
where r is the radius, z is the height (measured from the center of
the top surface), R=2.38 and K=6.0. The profile was determined by
iterative numerical simulations to provide an optimal distribution
of blue and yellow light that minimizes chromaticity variations
with respect to the viewing angle .theta..
[0082] FIGS. 12A and 12B show the simulated spectral radiant
intensity distribution of the blue and yellow light, respectively,
that exit both the first and second phosphor matrices. As shown,
the radiant intensity distributions of blue and yellow light in
FIGS. 12A and 12B are quite similar to each other, indicating that
this system has relatively uniform chromaticity over a large range
of viewing angles. FIG. 12C shows the deviation in chromaticity
.DELTA.u'v' from the spatially average chromaticity as a function
of angle for Example 4.
[0083] In another embodiment of the present invention, a color
equalization layer (CEL) is interposed between the LEE and the
phosphor. The CEL refers to a structure located between the LEE and
the phosphor that includes or consists essentially of a material of
lower absorption coefficient than the phosphor. The shape or
absorption properties of the CEL are designed to provide angular
modulation of the absorption of the LEE light, in such a way that
the angular distribution of the LEE light intensity after passing
through the phosphor is more closely matched to the angular
distribution of the converted light. The CEL and the surrounding
phosphor are typically index matched or substantially index matched
to eliminate or substantially eliminate TIR at their interface. In
one embodiment, the CEL may include or consist essentially of a
substantially optically transparent material (the binder) or a
material having a lower absorption efficiency than the phosphor
element. In one embodiment, the CEL may also be a phosphor material
(e.g., a binder having therewithin a plurality of phosphor or other
wavelength-conversion particles) and have a lower absorption
efficiency than that of the outer phosphor element. Preferred
embodiments of the invention provide an interface adjacent to two
or more index-matched or nearly index-matched regions, which may be
shaped as required to optimize color uniformity while minimizing
TIR or other effects that may impact extraction efficiency or other
performance characteristics of the phosphor-converted package.
[0084] FIGS. 13A-13C depict exemplary illumination systems 1300,
1301, and 1302, respectively, in accordance with embodiments of the
present invention, although alternative systems with similar
functionality are also within the scope of the present invention.
As may be seen from FIGS. 13A-13C, a CEL 1341 is disposed between
LEE 130 and phosphor 140. In various embodiments, the optical
properties of CEL 1341 may be homogeneous and the shape of CEL may
be varied to provide the desired modification of the angular
intensity distribution of light emitted by the LEE, as shown in
FIGS. 13B and 13C. As may be seen schematically in FIGS. 13B and
13C, the exterior shape of phosphor 140 may be varied as well, and
the shape of CEL 1341 is preferably modified accordingly.
Procedures for determining the shape of CEL 1341 are provided
herein. In other embodiments, CEL 1341 may have a relatively
arbitrary shape, for example conformably similar to LEE 130 and/or
phosphor 140 and have inhomogeneous optical properties, for example
absorption or scattering, to provide the desired modification of
the angular intensity distribution of light emitted by the LEE, as
shown in FIG. 13A.
[0085] The inventors have found that a key aspect of the shapes of
the CEL 1341 is that the thickness of the CEL measured vertically
from the plane parallel to and intersecting the bottom surface of
LEE 130, has a maximum thickness at a position intermediate between
the center of LEE 130 and the outer edge of the CEL 1341 or
phosphor 140. In some embodiments, the thickness of the CEL 1341 is
zero or substantially zero at the center of LEE 130 (as shown in
FIGS. 13B and 13C). Thus, the shape of CEL 1341 may be described as
optionally starting on the surface of LEE 130 at the center of LEE
130, increasing monotonically towards the edge of LEE 130, reaching
a maximum thickness after passing the edge of LEE 130, and then
decreasing monotonically until reaching the plane parallel to the
bottom surface of LEE 130. Note that this description is for
one-half of the rotationally symmetric shape, starting at the
center of the structure. The full three-dimensional shapes of CEL
1341 and phosphor 140 are realized by rotating the cross-section
about the y-axis.
Example 5
[0086] Example 5 is based on the structure shown in FIG. 13B.
Phosphor 140 has a cylindrical shape with the axis of the cylinder
aligned with the center of LEE 130. Phosphor 140 has a height of
about 0.5 mm and a diameter of about 1 mm. In this embodiment, CEL
1341 is optically transparent and is substantially the same as the
binder in phosphor 140. LEE 130 is a cylindrical disk having a
height of about 0.1 mm and a radius of about 0.2 mm. The shape of
the interface between CEL 1341 and phosphor 140 is engineered to
minimize the difference in (1) the angular intensity distribution
of the light emitted from LEE 130 as it exits phosphor 140 and (2)
the angular intensity distribution of wavelength-converted light
emitted from phosphor 140 such that they are the same or
substantially the same.
Example 6
[0087] Example 6 is based on the structure shown in FIG. 13C.
Phosphor 140 has a hemispherical shape with the axis of the
hemisphere aligned with the center of LEE 130. The hemispherical
shape may result in increased light output power because of reduced
TIR at the interface between phosphor 140 and air. Phosphor 140 has
a radius of about 1 mm. In this embodiment, CEL 1341 is optically
transparent and is substantially the same as the binder in phosphor
140. LEE 130 is a cylindrical disk having a height of about 0.1 mm
and a radius of about 0.2 mm. The shape of the interface between
CEL 1341 and phosphor 140 is engineered to minimize the difference
in (1) the angular intensity distribution of the light emitted from
LEE 130 as it exits phosphor 140 and (2) the angular intensity
distribution of wavelength-converted light emitted from phosphor
140 such that they are the same or substantially the same.
[0088] Using these principles, the shape of CEL 1341 may be
determined without undue experimentation by one skilled in the art
by first determining the radiant flux distribution pattern of LEE
130 as a function of angle, simulating the entire structure to
determine the angular intensity distribution of blue light emitted
from the outer surface of phosphor 140 and then adjusting the
boundary between CEL 1341 and phosphor 140 such that the angular
intensity distribution of blue light emitted through the outer
surface of the phosphor 140 substantially matches the angular
distribution of the phosphor-converted light emitted from phosphor
140.
[0089] In some embodiments, the interior and/or exposed surfaces of
the phosphor and/or binder may be smooth or textured, depending on
the desired intensity distribution. Additionally, these surfaces
may be intentionally roughened or textured, for example, to further
control the desired intensity distribution. Such modification of
the various surfaces may also be used to increase the
light-extraction efficiency by reducing TIR. FIG. 14 shows an
example of one embodiment of a structure in which the outer surface
of phosphor 140 is roughened or textured, identified as surface
1410 in FIG. 14. While FIG. 14 shows all of the curved surface of
phosphor 140 as being roughened or textured this is not a
limitation of the present invention, and in other embodiments only
a portion of phosphor 140 may be textured or roughened. Texturing
or roughening of phosphor 140 may be accomplished by a variety of
means, for example using ablation or etching, or phosphor 140 may
be formed with a roughened or textured surface, for example by
molding or casting. In some embodiments, the texturing or
roughening may be random, while in other embodiments the texturing
or roughening may be periodic. In some embodiments, the texturing
or roughening may have a feature size in the range of about 0.1
.mu.m to about 5 .mu.m; however, the size and extent and density of
texturing or roughening is not a limitation of the present
invention.
[0090] In some embodiments, the structures described herein,
including or consisting essentially of an LEE and a phosphor
element, herein identified as an LEE/phosphor element, may be
incorporated into packages to produce packaged LEEs with improved
angular chromaticity uniformity. For example, FIGS. 15A-15E show
examples of embodiments of LEE 130 and phosphor 140 incorporated
into packaged devices.
[0091] FIG. 15A depicts an LEE/phosphor element 1500, and FIG. 15B
depicts an LEE/phosphor element 1501. Each LEE/phosphor element may
be mounted on a base or substrate, as identified as 1565 and 1592
in FIGS. 15A and 15B respectively; however, this is not a
limitation of the present invention, and in other embodiments
LEE/phosphor elements within the scope of this invention may be
unmounted or unpackaged, for example as shown in FIG. 15C. FIG. 15C
shows an example of a structure identified as a white die 1502 that
includes or consists essentially of an LEE 130 and a phosphor 140.
White die 1502 is described in U.S. patent application Ser. No.
13/748,864, filed on Jan. 24, 2013, the entire disclosure of which
is herein incorporated by reference.
[0092] In some embodiments of the present invention, contacts 1580,
1585 of LEE 130 may be electrically coupled and/or attached to
conductive traces or conductive elements, as identified as 1560 or
1590 in FIGS. 15A and 15B respectively. Contacts 1580, 1585 of LEE
130 may be electrically coupled and/or attached to conductive
traces 1560 or 1590 using a variety of means; the method of
electrical coupling and/or attachment is not a limitation of the
present invention. In some embodiments, contacts 1580, 1585 of LEE
130 may be electrically coupled and/or attached to conductive
traces 1560 or 1590 using a conductive adhesive, a conductive
paste, an anisotropic conductive film, or another type of
anisotropic conductive adhesive (ACA), as shown in FIG. 15A. In
some embodiments, contacts 1580, 1585 of LEE 130 may be
electrically coupled and/or attached to conductive traces 1560 or
1590 using wire bonds 1591 as shown in FIG. 15B, in which the
phosphor 140 forms a dome 1510 enclosing wire bonds 1591. In some
embodiments, LEE 130 may be attached to conductive traces 1560 or
1590 using a conductive adhesive and/or a non-conductive adhesive.
In some embodiments, contacts 1580, 1585 of LEE 130 may be
electrically coupled and/or attached to conductive traces 1560 or
1590 using a solder process, eutectic solder process, wave solder
process, or a solder reflow process. In some embodiments, LEE 130
may be electrically coupled and/or attached to conductive traces
1560 or 1590 in a flip-chip orientation, for example as shown in
FIGS. 15A and 15D. The method of electrical coupling and/or
attachment of contacts 1580, 1585 to conductive traces 1560 or 1590
is not a limitation of the present invention.
[0093] The structures shown in FIGS. 15A-15C include one LEE 130;
however, this is not a limitation of the present invention, and in
other embodiments the structure may include multiple LEEs 130, as
shown in FIG. 15D. FIG. 15D shows a structure 1503 that includes a
substrate 1592 over which has been formed conductive elements 1560
and to which contacts 1580 and 1585 (not shown for clarity) of LEEs
130 have been electrically coupled. The structure shown in FIG. 15D
may also be referred to as a chip-on-board structure. Contacts 1580
and 1585 may be attached using a variety of means, for example wire
bonding, solder, adhesive, and the like. Exemplary structure 1503
includes four LEEs 130; however, this is not a limitation of the
present invention, and in other embodiments structure 1503 may
include any number of LEEs 130, e.g., 10 or 20. Structure 1503 also
includes package contacts 1591, 1593 to which conductive elements
1560 are electrically coupled and which are typically electrically
connected to an external power source. FIG. 15E shows a structure
1506 including more than one LEE/phosphor element structure,
featuring a line or array of LEE/phosphor element structures formed
over a substrate 1594. As shown, each LEE/phosphor element
structure includes an LEE 1531 and a phosphor element 1532. In some
embodiments, phosphor element 140 may have a radius of at least 2
mm, or at least 5 mm. In some embodiments, for example where
phosphor element 140 encompasses more than one LEE 130 (for example
as shown in FIG. 15D), phosphor element 140 may have a relatively
larger radius, for example over 5 mm or over 10 mm or over 30
mm.
[0094] Substrates 1565 and 1592 may be composed of a wide range of
materials. In some embodiments, substrates 1565 and 1592 may have
relatively low thermal conductivities. In some embodiments,
substrates 1565 and 1592 may have relatively high thermal
conductivities. In some embodiments, substrates 1565 and 1592 may
be flexible, while in others they may be substantially rigid.
Substrate 1565 may include or consist essentially of a
semicrystalline or amorphous material, e.g., polyethylene
naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate,
polyethersulfone, polyester, polyimide, polyethylene, and/or paper.
Substrate 1565 may include or consist essentially of multiple
layers, e.g., a deformable layer over a rigid layer, for example, a
semicrystalline or amorphous material, e.g., PEN, PET,
polycarbonate, polyethersulfone, polyester, polyimide,
polyethylene, and/or paper formed over a rigid substrate
comprising, e.g., acrylic, aluminum, steel, and the like. Depending
upon the desired application for which embodiments of the invention
are utilized, substrate 1565 may be substantially optically
transparent, translucent, or opaque. For example, substrate 1565
may exhibit a transmittance or a reflectivity greater than 70% for
optical wavelengths ranging between approximately 400 nm and
approximately 600 nm. In some embodiments, substrate 1565 may
exhibit a transmittance or a reflectivity of greater than 70% for
one or more wavelengths emitted by LEE 130 and or phosphor 140.
Substrate 1565 may also be substantially insulating, and may have
an electrical resistivity greater than approximately 100 ohm-cm,
greater than approximately 1.times.10.sup.6 ohm-cm, or even greater
than approximately 1.times.10.sup.10 ohm-cm. In some embodiments,
substrates 1565 or 1592 may include or consist essentially of
materials such as fiberglass, FR4, metal, ceramic materials such as
silicon carbide, aluminum nitride, aluminum oxide, combinations of
these materials, and the like. In some embodiments, substrate 1565
or 1592 may include or consist essentially of a metal, for example
a metal leadframe. In some embodiments, substrate 1565 or 1592 may
include or consist essentially of a metal-core printed circuit
board. The material and form of substrates 1565 or 1592 is not a
limitation of the present invention.
[0095] Conductive elements 1560 and 1590 may be formed via
conventional deposition, photolithography, and etching processes,
plating processes, lamination, lamination and patterning,
evaporation sputtering, chemical vapor deposition or the like, or
they may be formed using a variety of printing processes. For
example, conductive elements 1560 and 1590 may be formed via screen
printing, flexographic printing, ink-jet printing, and/or gravure
printing. Conductive elements 1560 and 1590 may include or consist
essentially of a conductive ink, which may include one or more
elements such as silver, gold, aluminum, chromium, copper, and/or
carbon. Conductive elements 1560 and 1590 may include or consist
essentially of a conductive material, which may include one or more
elements such as silver, gold, aluminum, chromium, copper, and/or
carbon. Conductive elements 1560 and 1590 may have a thickness in
the range of about 50 nm to about 500 .mu.m; however, the thickness
of conductive elements 1560 and 1590 is not a limitation of the
present invention. In some embodiments, all or a portion of
conductive elements 1560 and 1590 may be covered or encapsulated.
In some embodiments, a layer of material, for example insulating
material, may be formed over all or a portion of conductive
elements 1560 and 1590. Such a material may include or consist
essentially of, for example, a sheet of material such as that used
for substrate 1565, a printed layer, for example using screen, ink
jet, stencil or other printing techniques, a laminated layer, or
the like. Such a layer may include or consist essentially of, for
example, an ink, a plastic and oxide or the like. The covering
material and/or the method by which it is applied is not a
limitation of the present invention.
[0096] In one embodiment, conductive traces 1560 may be formed so
as to have a gap between adjacent conductive traces 1560, and LEEs
130 are electrically coupled to conductive traces 1560 using
conductive adhesive, e.g., an isotropically conductive adhesive
and/or an ACA 1561, for example as shown in FIG. 15A. ACAs may be
utilized with or without stud bumps and embodiments of the present
invention are not limited by the particular mode of operation of
the ACA. For example, the ACA may utilize a magnetic field rather
than pressure (e.g., the ZTACH ACA available from SunRay Scientific
of Mt. Laurel, N.J., for which a magnetic field is applied during
curing in order to align magnetic conductive particles to form
electrically conductive "columns" in the desired conduction
direction). Furthermore, various embodiments utilize one or more
other electrically conductive adhesives, e.g., isotropically
conductive adhesives, non-conductive adhesives, in addition to or
instead of one or more ACAs.
[0097] In some embodiments, the shape of phosphor element 140 is
formed by casting or molding. In some embodiments, multiple
phosphor elements may be formed separately. In some embodiments,
multiple phosphor elements may be formed simultaneously. In some
embodiments where multiple phosphor elements are formed
simultaneously, each element 140 may be separated from adjacent
shapes by a web 1610, for example as shown in FIG. 16A. In some
embodiments, the elements may be formed in a merged fashion, for
example as shown in FIG. 16B, where adjacent phosphor elements 140
are merged at an interface 1620. In some embodiments, the structure
in FIG. 16B permits the manufacture of a larger number of phosphor
elements 140 in a fixed area, as compared to the structure of FIG.
16A. In a subsequent manufacturing step, phosphor elements 140
shown in FIG. 16A or 16B may be separated or singulated. For
example, the structure of FIG. 16B may be singulated at a cut line
1630. After singulation the structure may look like the example
shown in FIG. 16C, having a cylindrical cutoff 440, as described in
reference to FIG. 4A, and a removed portion having extent 1640, as
shown in FIG. 16C. In some embodiments, the ratio of dimension 440
to the hemisphere diameter (which is two times the hemisphere
radius) is in the range of about 0.95 to about 0.75. In some
embodiments the cut-off portion is in the range of about 50 .mu.m
to about 500 .mu.m.
[0098] During the manufacture of structures described herein, for
example structures shown in FIGS. 15A-15E, it may be necessary to
move or pick up structures such as those shown in FIGS. 3A and 3B.
In some embodiments, pick-and-place equipment may be used.
Pick-and-place tools are conventionally used to pick up
semiconductor dies. These may operate at very high speeds, for
example at least 5000 units per hour or at least 10,000 units per
hour. The pick-and-place equipment may have a vacuum tip that is
applied to the flat top of each semiconductor die. When vacuum is
applied to the vacuum tip, the semiconductor die is temporarily
attached to the tip, and thus may be moved from one location to the
next. A schematic of this is shown in FIG. 17A, showing vacuum tool
1710 and semiconductor die 1720. However, the curved top surface of
phosphor element 140 may render it difficult to achieve a good seal
between vacuum tool 1710 and phosphor element 140 as shown in FIG.
17B. In some embodiments, a flat top may be formed on the top of
phosphor element 140, as shown in FIG. 17C, to provide a flat
surface for sealing of vacuum tool 1710 to phosphor element 140. In
some embodiments, the flat top may have a diameter in the range of
about 50 .mu.m to about 1000 .mu.m; however, this is not a
limitation of the present invention, and in other embodiments the
flat top may be larger or smaller.
[0099] In an exemplary embodiment, LEE 130 represents a
light-emitting element such as an LED or a laser, but other
embodiments of the invention feature one or more semiconductor dies
with different or additional functionality, e.g., processors,
sensors, detectors, control elements, and the like. Non-LEE dies
may or may not be bonded as described herein, and may have contact
geometries differing from those of the LEEs; moreover, they may or
may not have semiconductor layers disposed over a substrate as
discussed below. LEE 130 may be composed of one or more layers, for
example semiconductor layers formed over a substrate. The substrate
may, for example, include or consist essentially of one or more
semiconductor materials, e.g., silicon, GaAs, InP, GaN, and may be
doped or substantially undoped (e.g., not intentionally doped). In
some embodiments, the substrate includes or consists essentially of
sapphire or silicon carbide; however, the composition of the
substrate is not a limitation of the present invention. The
substrate may be substantially transparent to a wavelength of light
emitted by the LEE 130. For a light-emitting element, the
semiconductor layers may include first and second doped layers
which preferably are doped with opposite polarities (i.e., one
n-type doped and the other p-type doped). One or more
light-emitting layers e.g., or one or more quantum wells, may be
disposed between the first and second doped layers. Each of these
layers may include or consist essentially of one or more
semiconductor materials, e.g., silicon, InAs, AlAs, GaAs, InP, AlP,
GaP, InSb, GaSb, AlSb, GaN, AIN, InN, and/or mixtures and alloys
(e.g., ternary or quaternary, etc. alloys) thereof. In preferred
embodiments, LEE 130 is an inorganic, rather than a polymeric or
organic, device.
[0100] In some embodiments, substantially all or a portion the
substrate is removed from LEE 130. Such removal may be performed
by, e.g., chemical etching, laser lift-off, mechanical grinding
and/or chemical-mechanical polishing or the like. In some
embodiments, all or a portion of the substrate is removed and a
second substrate--e.g., one that is transparent to or reflective of
a wavelength of light emitted by LEE 130--is attached to the
substrate or semiconductor layers prior to or after the bonding of
LEE 130 as described below. In some embodiments, the substrate
includes or consists essentially of silicon and all or a portion of
the silicon substrate may be removed prior to or after the bonding
of LEE 130 to a conductive element or other system. Such removal
may be performed by, e.g., chemical etching, laser lift off,
mechanical grinding and/or chemical-mechanical polishing or the
like.
[0101] Electrical contact to LEE 130 may be achieved through
contacts which may make contact to the p- and n-layers
respectively. LEE 130 may optionally feature a mirror or reflective
surface formed over all or portions of the semiconductor layers and
optionally other portions of LEE 130. The mirror may act to direct
light emitted from the light emitting layer back towards and out
the substrate, particularly in a flip-chip configuration, where LEE
130 is mounted contact-side down.
[0102] In some embodiments, the LEE 130 has a square shape, while
in other embodiments LEE 130 has a rectangular shape. In some
preferred embodiments, to facilitate bonding) LEE 130 has a shape
with a dimension in one direction that exceeds a dimension in an
orthogonal direction (e.g., a rectangular shape), and has an aspect
ratio of the orthogonal directions (length to width, in the case of
a rectangular shape) of LEE 130 greater than about 1.2:1. In some
embodiments, LEE 130 has an aspect ratio greater than about 2:1 or
greater than 3:1. The shape and aspect ratio are not critical to
the present invention, however, and LEE 130 may have any desired
shape.
[0103] While the discussion herein has mentioned blue LEDs and
phosphors, that when combined produce white light, the concepts may
be used with respect to LEDs emitting at any wavelength and
phosphors or wavelength-conversion materials with any emission
wavelengths that may in combination or alone be used to produce any
color.
[0104] The terms and expressions employed herein are used as terms
and expressions of description and not of limitation, and there is
no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described or
portions thereof. In addition, having described certain embodiments
of the invention, it will be apparent to those of ordinary skill in
the art that other embodiments incorporating the concepts disclosed
herein may be used without departing from the spirit and scope of
the invention. Accordingly, the described embodiments are to be
considered in all respects as only illustrative and not
restrictive.
* * * * *