U.S. patent application number 13/920925 was filed with the patent office on 2014-12-18 for led light pipe.
The applicant listed for this patent is LuxVue Technology Corporation. Invention is credited to Andreas Bibl, Kelly McGroddy.
Application Number | 20140367711 13/920925 |
Document ID | / |
Family ID | 52018470 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140367711 |
Kind Code |
A1 |
Bibl; Andreas ; et
al. |
December 18, 2014 |
LED LIGHT PIPE
Abstract
A light emitting device and method of manufacture are described.
In an embodiment, the light emitting device includes a micro LED
device, a light pipe around the micro LED device to cause internal
reflection of incident light from the micro LED device within the
light pipe, and a wavelength conversion layer comprising phosphor
particles over the light pipe. Exemplary phosphor particles include
quantum dots that exhibit luminescence due to their size, or
particles that exhibit luminescence due to their composition.
Inventors: |
Bibl; Andreas; (Los Altos,
CA) ; McGroddy; Kelly; (San Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LuxVue Technology Corporation |
Santa Clara |
CA |
US |
|
|
Family ID: |
52018470 |
Appl. No.: |
13/920925 |
Filed: |
June 18, 2013 |
Current U.S.
Class: |
257/89 |
Current CPC
Class: |
H01L 33/58 20130101;
H01L 24/73 20130101; H01L 2924/12044 20130101; H01L 25/0753
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2924/12041 20130101; H01L 24/24 20130101; H01L 2224/14 20130101;
G02B 6/0096 20130101; H01L 33/507 20130101; H01L 2924/12041
20130101; H01L 2924/12044 20130101 |
Class at
Publication: |
257/89 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/08 20060101 H01L033/08 |
Claims
1. A light emitting device comprising: a micro LED device mounted
on a substrate; a light pipe around the micro LED device; and a
wavelength conversion layer over the light pipe, the wavelength
conversion layer comprising phosphor particles; wherein the light
pipe is designed to allow refraction of incident light from the
micro LED device out of the light pipe toward the wavelength
conversion layer, and to cause internal reflection and lateral
spreading of incident light from the micro LED device within the
light pipe.
2. The light emitting device of claim 1, wherein the micro LED
device has a maximum width of 1 .mu.m-100 .mu.m.
3. The light emitting device of claim 1, wherein the light pipe is
elongated dome shaped.
4. The light emitting device of claim 1, wherein a lateral length
of the light pipe is greater than a thickness of the light
pipe.
5. The light emitting device of claim 1, wherein the phosphor
particles are quantum dots.
6. The light emitting device of claim 1, wherein the phosphor
particles exhibit luminescence due to their composition and do not
qualify as quantum dots.
7. The light emitting device of claim 1, wherein the phosphor
particles are dispersed in a polymer or glass matrix.
8. The light emitting device of claim 1, wherein a refractive index
of the light pipe is within 0.1 of a refractive index of the
wavelength conversion layer.
9. The light emitting device of claim 8, wherein the light pipe and
the wavelength conversion layer comprise the same matrix
material.
10. The light emitting device of claim 1, wherein the light pipe is
around a plurality of micro LED devices to cause internal
reflection of incident light from the plurality of micro LED
devices within the light pipe.
11. The light emitting device of claim 1, further comprising a
reflective layer directly over the micro LED device.
12. The light emitting device of claim 11, wherein the reflective
layer is over the wavelength conversion layer.
13. The light emitting device of claim 11, wherein the reflective
layer is between the light pipe and the wavelength conversion
layer.
14. The light emitting device of claim 1, further comprising a
reflective layer beneath the micro LED device and the light
pipe.
15. The light emitting device of claim 14, wherein the micro LED
device is within a reflective bank structure.
16. The light emitting device of claim 1, comprising an array of
micro LED devices, a corresponding array of light pipes around the
array of micro LED devices, and an array of wavelength conversion
layers over the array of light pipes.
17. The light emitting device of claim 16 wherein the array of
wavelength conversion layers comprises multiple groups of
wavelength conversion layers, with each group designed to emit a
different color emission spectrum.
18. The light emitting device of claim 17, further comprising a
plurality of pixels, each pixel comprising at least one wavelength
conversion layer from each of the multiple groups of wavelength
conversion layers.
19. The light emitting device of claim 1, further comprising: an
array of pixels, each pixel comprising a plurality of subpixels
designed for different color emission spectra, wherein the
plurality of subpixels comprises: a first subpixel including: a
first micro LED device; a first light pipe around the first micro
LED device; a first wavelength conversion layer comprising first
phosphor particles over the first light pipe; and a second subpixel
including: a second micro LED device; a second light pipe around
the second micro LED device; a second wavelength conversion layer
comprising second phosphor particles over the second light pipe;
and wherein the first and second micro LED devices have the same
composition for the same emission spectrum, and the first and
second phosphor particles are designed for different color emission
spectra.
20. The light emitting device of claim 1, further comprising: an
array of pixels, each pixel comprising a plurality of subpixels
designed for different color emission spectra, wherein the
plurality of subpixels comprises: a first subpixel including: a
first micro LED device; a first light pipe around the first micro
LED device; a first wavelength conversion layer comprising first
phosphor particles over the first light pipe; and a second subpixel
including: a second micro LED device; a second light pipe around
the second micro LED device; wherein a wavelength conversions layer
comprising phosphor particles is not formed over the second light
pipe.
21. The light emitting device of claim 1, further comprising: an
array of pixels, each pixel comprising a plurality of subpixels
designed for different color emission spectra; an array of light
pipes corresponding to the array of pixels, each light pipe
spanning the plurality of subpixels of a corresponding pixel.
22. The light emitting device of claim 21, further comprising a
micro LED device mounted within each subpixel in each pixel.
23. The light emitting device of claim 21, further comprising a
micro LED device within each light pipe, wherein a micro LED device
is not mounted within every subpixel corresponding to a light
pipe.
24. The light emitting device of claim 21, further comprising a
plurality of different wavelength conversion layers designed for
different color emission spectra formed over each light pipe where
it spans over the plurality of subpixels of a corresponding pixel.
Description
BACKGROUND
[0001] 1. Field
[0002] The present invention relates to micro LED devices. More
particularly embodiments of the present invention relate to a
method and structure for integrating micro LED devices on a
substrate with increased fill factor and tunable color emission
spectrum.
[0003] 2. Background Information
[0004] Quantum dots are semiconductor nanocrystals that can be
tuned to emit light throughout the visible and infrared spectrum.
Due to the small size of 1 to 100 nm, more typically 1 to 20 nm,
quantum dots display unique optical properties that are different
from those of the corresponding bulk material. The wavelength, and
hence color, of the photo emission is strongly dependent on the
size of a quantum dot. For an exemplary cadmium selenide (CdSe)
quantum dot, light emission can be gradually tuned from red for a 5
nm diameter quantum dot, to the violet region for a 1.5 nm quantum
dot. There are generally two types of schemes for quantum dot (QD)
excitation. One uses photo excitation, and the other uses direct
electrical excitation.
[0005] One proposed implementation for quantum dots is integration
into the backlighting of a liquid crystal display (LCD) panel.
Current white light emitting diode (LED) backlight technology for
LCD panels utilizes a cerium doped YAG:Ce (yttrium aluminum garnet)
down-conversion phosphor layer over a plurality of blue emitting
LED chips. The combination of blue light from the LED chips and a
broad yellow emission from the YAG:Ce phosphor results in a near
white light. It has been proposed to replace the YAG:Ce phosphor
with a blend of quantum dots to achieve the white backlighting.
U.S. Pat. No. 8,294,168 describes arranging a quantum dot sealing
package over a package including a row of light emitting device
chips in an edge-type backlight unit light source module. The light
source module is positioned at an edge of the LED display panel so
that it emits light through a side surface of a light guide plate
behind the LED display panel, where the light is reflected toward
the LCD display panel.
SUMMARY OF THE INVENTION
[0006] Light emitting devices for lighting or display applications
are disclosed. In an embodiment a light emitting device includes a
micro LED device mounted on a substrate. A light pipe is formed
around the micro LED device, and a wavelength conversion layer
comprising phosphor particles is formed over the light pipe. The
light pipe in accordance with embodiments of the invention is
designed to allow refraction of incident light form the micro LED
device out of the light pipe toward the wavelength conversion
layer, as well as to cause internal reflection and lateral
spreading of incident light from the micro LED device within the
light pipe. Exemplary micro LED devices may have a maximum width of
1 .mu.m-100 .mu.m. The light pipe may assume a variety of
configurations. For example, the light pipe may have an elongated
dome shape characterized by a lateral length that is greater than a
thickness. The light pipe may also be thicker than the micro LED
device around which it is formed. In some embodiments the light
pipe may be formed around a plurality of micro LED devices.
[0007] Exemplary phosphor particles may include quantum dots, as
well as phosphor particles that exhibit luminescence due to their
composition and do not qualify as quantum dots. In some embodiments
the phosphor particles are dispersed in a polymer or glass matrix.
The light pipe likewise may be formed of a polymer or glass
material, which may be the same or different than the wavelength
conversion layer matrix material. In some embodiments the
refractive indices of the light pipe and wavelength conversion
layer may be closely matched, such as within 0.1.
[0008] Reflective layers may additionally be formed over the micro
LED devices. For example, a reflective layer can be formed over the
wavelength conversion layer. Alternatively, a reflective layer is
formed between the light pipe and wavelength conversion layer. A
separate reflective layer can be formed beneath the micro LED
device and the light pipe. For example, the micro LED device can be
mounted within a reflective bank structure.
[0009] A variety of combinations of light emission spectra for the
micro LED devices and wavelength conversion layers are possible to
achieve a specific color emission spectrum for a light emitting
device including an array of micro LED devices, a corresponding
array of light pipes around the array of micro LED devices, and an
array of wavelength conversions layers over the array of light
pipes. For example, a light emitting device may have a plurality of
pixels, with each including subpixels that have different color
emission spectra. Color emission spectra of a subpixel can be
determined by the emission spectrum of a micro LED device, a
wavelength conversion layer, or both. Accordingly, a pixel may
include different groups of micro LED devices designed for
different color emission spectra, different wavelength conversion
layers designed for different color emission spectra, or both,
separated into the different subpixels. For example, a light
emitting device can include a first subpixel including a first
micro LED device and a first light pipe, and a second subpixel
including a second micro LED device and a second light pipe. In one
embodiment, a first wavelength conversion layer (including first
phosphor particles) is formed over the first light pipe and a
second wavelength conversion layer (including second phosphor
particles) is formed over the second light pipe, where the first
and second micro LED devices have the same composition for the same
emission spectrum, and the first and second wavelength conversion
layers (first and second phosphor particles) are designed for
different color emission spectra. In another embodiment, a first
wavelength conversion layer is formed over the first light pipe,
and a wavelength conversion layer is not formed over the second
light pipe.
[0010] In an embodiment the light emitting device includes an array
of pixels, with each pixel including a plurality of subpixels
designed for different color emission spectra. An array of light
pipes are formed corresponding to the array of pixels such that
each light pipe spans the plurality of subpixels for a
corresponding pixel. For example, in an RGB pixel arrangement, the
light pipe could span the R, G, and B subpixels. A micro LED device
may or may not be mounted within each subpixel over which a light
pipe is formed. In one application, a micro LED device is mounted
within each subpixel and within the light pipe. In another
application, one or more of the subpixels may not include a micro
LED device. Likewise, a wavelength conversion layer may or may not
be formed over light pipe where it spans over the multiple
subpixels. In these manners, light from a micro LED device in an
adjacent subpixel can pass through the light pipe where it is
refracted out and through the wavelength conversion layer in an
adjacent subpixel. Different wavelength conversion layers of
designed for different color emission spectra can be formed over
each light pipe where it spans over the plurality of subpixels of a
corresponding pixel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is combination view illustration of a light pipe
around a micro LED device and a wavelength conversion layer over
the light pipe in accordance with an embodiment of the
invention.
[0012] FIG. 1B is combination view illustration of a light pipe
around a micro LED device and a wavelength conversion layer over
the light pipe in accordance with an embodiment of the
invention.
[0013] FIG. 1C is combination view illustration of a light pipe
around a plurality of micro LED devices and a wavelength conversion
layer over the light pipe in accordance with an embodiment of the
invention.
[0014] FIG. 1D is a cross-sectional side view illustration of a
light pipe around a micro LED device and a wavelength conversion
layer over the light pipe in accordance with an embodiment of the
invention.
[0015] FIGS. 1E-1F are cross-sectional side view illustrations of a
light pipe having a tapered profile in accordance with an
embodiment of the invention.
[0016] FIG. 2A is a combination view illustration of a light
emitting device including a plurality of micro LED devices and a
plurality of light pipes and wavelength conversion layers around
the plurality of micro LED devices in accordance with an embodiment
of the invention.
[0017] FIG. 2B is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0018] FIG. 2C is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0019] FIG. 2D is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0020] FIG. 2E is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0021] FIG. 3A is a combination view illustration of a light
emitting device including a plurality of micro LED devices and a
plurality of light pipes and wavelength conversion layers around
the plurality of micro LED devices in accordance with an embodiment
of the invention.
[0022] FIG. 3B is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0023] FIG. 3C is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0024] FIG. 3D is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0025] FIG. 3E is a schematic side view illustration of a pixel in
accordance with an embodiment of the invention.
[0026] FIG. 4A is combination view illustration of a light pipe
around a micro LED device and a reflective layer over the light
pipe in accordance with an embodiment of the invention.
[0027] FIG. 4B is a cross-sectional side view illustration of a
reflective layer over a wavelength conversion layer and light pipe
in accordance with an embodiment of the invention.
[0028] FIG. 4C is a cross-sectional side view illustration of a
reflective layer over a light pipe and underneath a wavelength
conversion layer in accordance with an embodiment of the
invention.
[0029] FIG. 5A is combination view illustration of a light pipe
around a plurality of micro LED devices and a plurality of
reflective layers over the light pipe in accordance with an
embodiment of the invention.
[0030] FIG. 5B is a cross-sectional side view illustration of a
plurality of reflective layers over a wavelength conversion layer
and light pipe in accordance with an embodiment of the
invention.
[0031] FIG. 5C is a cross-sectional side view illustration of a
plurality of reflective layers over a light pipe and underneath a
wavelength conversion layer in accordance with an embodiment of the
invention.
[0032] FIG. 6A is combination view illustration of a light pipe
around a micro LED device and a reflective layer and plurality of
wavelength conversion layers over the light pipe in accordance with
an embodiment of the invention.
[0033] FIGS. 6B-6C are cross-sectional side view illustrations of a
reflective layer and a plurality of wavelength conversion layers
over the light pipe in accordance with embodiments of the
invention.
[0034] FIGS. 7A-7B are schematic top view illustrations of light
emitting devices including a plurality of micro LED devices in
light pipes, or alternatively pixels of micro LED devices in light
pipes, in accordance with embodiments of the invention.
[0035] FIGS. 8A-8B are cross-sectional side view illustrations of a
light pipe around a micro LED device with top and bottom contacts
and a wavelength conversion layer over the light pipe in accordance
with embodiments of the invention.
[0036] FIGS. 8C-8D are cross-sectional side view illustrations of a
light pipe around a micro LED device with bottom contacts and a
wavelength conversion layer over the light pipe in accordance with
embodiments of the invention.
[0037] FIGS. 9A-9B are cross-sectional side view illustrations of a
light pipe around a plurality of micro LED devices with top and
bottom contacts within a reflective bank structure, and a
wavelength conversion layer over the light pipe in accordance with
embodiments of the invention.
[0038] FIG. 9C is a cross-sectional side view illustration of a
light pipe around a plurality of micro LED devices with top and
bottom contacts within a plurality of reflective bank structures,
and a wavelength conversion layer over the light pipe in accordance
with an embodiment of the invention.
[0039] FIGS. 9D-9E are cross-sectional side view illustrations of a
light pipe around a plurality of micro LED devices with bottom
contacts within a reflective bank structure, and a wavelength
conversion layer over the light pipe in accordance with embodiments
of the invention.
[0040] FIG. 9F is a cross-sectional side view illustration of a
light pipe around a plurality of micro LED devices with bottom
contacts within a plurality of reflective bank structures, and a
wavelength conversion layer over the light pipe in accordance with
an embodiment of the invention.
[0041] FIG. 10 is an illustration of a single side manner for
applying wavelength conversion layers over light pipes, and a black
matrix between micro LED devices in accordance with an embodiment
of the invention.
[0042] FIG. 11 is an illustration of a top press down manner for
applying wavelength conversion layer over light pipes, and a black
matrix between micro LED devices in accordance with an embodiment
of the invention.
[0043] FIGS. 12-16 are top view schematic illustrations for various
top and bottom electrode configurations for lighting or display
applications in accordance with embodiments of the invention.
[0044] FIG. 17 is a schematic illustration of a display system in
accordance with an embodiment of the invention.
[0045] FIG. 18 is a schematic illustration of a lighting system in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] Embodiments of the present invention describe light emitting
devices which incorporate a light pipe around a micro LED device
and a wavelength conversion layer over the light pipe. The light
emitting devices in accordance with embodiments of the invention
may include a plurality of micro LED devices, a plurality of light
pipes, and a plurality of wavelength conversion layers. The light
emitted from the configuration of micro LED devices, light pipes,
and wavelength conversion layers may be the observable light
emitted from the light emitting devices, such as a display or light
source. In accordance with embodiments of the invention, the light
pipes may increase the fill factor for the micro LED devices,
pixels, or subpixels including the micro LED devices, by both
allowing refraction of incident light from the micro LED devices
out of the light pipes toward the wavelength conversion layers, and
causing internal reflection and lateral spreading of the incident
light from the micro LED devices within the light pipes.
Furthermore, a variety of color emission spectra and patterns can
be accomplished by selection of emission spectrum combinations for
the micro LED devices and the wavelength conversion layers, where
present, in the light emitting devices. In an embodiment, the
wavelength conversion layer includes phosphor particles (e.g.
quantum dots that exhibit luminescence due to their size and shape
in addition to their composition, or particles that exhibit
luminescence due to their composition). In this manner, the light
emission can be accurately tuned to specific colors in the color
spectrum, with improved color gamut.
[0047] In some embodiments, a light pipe also functions as a
portion of a micro lens formed around one or more micro LED devices
where incident light from the micro LED devices is refracted out of
the light pipe. Each micro lens structure may include a variety of
configurations and optionally include a number of different layers
in addition to the light pipe including a matching layer, the
wavelength conversion layer, oxygen barrier, and color filter. In
some embodiments, a lateral length of the light pipe is greater
than a thickness of the light pipe. In some embodiments, the light
pipe can be dome shaped. In an embodiment, the light pipe is
elongated dome shaped. The dome shape profile may be hemispherical,
flattened, or narrowed. Flattening or narrowing of the dome profile
can be used to adjust viewing angle for the light emitting device.
In accordance with embodiments of the invention, the thickness and
profile the layers forming the micro lens structure can be adjusted
in order to change the light emission beam profile from the micro
LED device, as well as color over angle characteristics of the
light emitting device which can be related to edge effects.
[0048] In one aspect, the incorporation of micro LED devices in
accordance with embodiments of the invention can be used to combine
the performance, efficiency, and reliability of wafer-based LED
devices with the high yield, low cost, mixed materials of thin film
electronics, for both lighting and display applications. The term
"micro" LED device as used herein may refer to the descriptive size
scale of 1 to 100 .mu.m. For example, each micro LED device may
have a maximum width of 1 to 100 .mu.m, with smaller micro LED
devices consuming less power. In some embodiments, the micro LED
devices may have a maximum width of 20 .mu.m, 10 .mu.m, or 5 .mu.m.
In some embodiments, the micro LED devices have a maximum height of
less than 20 .mu.m, 10 .mu.m, or 5 .mu.m. Exemplary micro LED
devices which may be utilized with some embodiments of the
invention are described in U.S. Pat. No. 8,426,227, U.S.
Publication No. 2013/0126081, U.S. patent application Ser. No.
13/458,932, U.S. patent application Ser. No. 13/711,554, and U.S.
patent application Ser. No. 13/749,647. The light emitting devices
in accordance with embodiments of the invention may be highly
efficient at light emission and consume very little power (e.g.,
250 mW for a 10 inch diagonal display compared to 5-10 watts for a
10 inch diagonal LCD or OLED display), enabling reduction of power
consumption of an exemplary display or lighting application
incorporating the micro LED devices.
[0049] In another aspect, embodiments of the invention describe
light pipe configurations that can increase the fill factor for
micro LED devices, or pixels including micro LED devices.
Wafer-based LED devices can be characterized as point sources,
where light emission occupies a small area and has a concentrated
output. If wafer-based LED devices are secured far enough apart
that they can be perceived by the human eye (e.g. approximately 100
.mu.m or more) it may be possible that the light emitted from the
individual LED devices is perceived as small dots. The light pipe
configurations described in accordance with embodiments of the
invention can be used to increase the fill factor for micro LED
devices, pixels, or sub-pixels including micro LED devices, so that
the individual micro LED devices are not distinguishable by the
human eye, and small dots are not perceived.
[0050] In another aspect, embodiments of the invention provide for
configurations that allow phosphor particles of different emission
spectra to be separated from one another while still providing good
color mixing of the light as perceived by the viewer. Separating
the phosphor particles from each other in each subpixel can prevent
secondary absorption of light emitted from a phosphor particle
emitting a different spectrum (e.g. absorption of green light
emitted from a green emitting phosphor particle by a red emitting
phosphor particle). This may increase efficiency and reduce
unintended color shift. In the micro LED device systems in
accordance with embodiments of the invention the spatial color
separation between different color emitting areas (e.g. subpixels)
can be small enough (e.g. approximately 100 .mu.m or less) that it
will not be perceived by the human eye. In this manner, the "micro"
LED device scale enables the arrangement of micro LED devices,
light pipes, and wavelength conversion layers including phosphor
particles with small enough pitch (e.g. approximately 100 .mu.m or
less) between adjacent micro LED devices or subpixels that the
spatial color separation is not perceived by the human eye. In such
a configuration, spatially non-uniform color of the light source
often associated with non-micro LED device systems can be
avoided.
[0051] In various embodiments, description is made with reference
to figures. However, certain embodiments may be practiced without
one or more of these specific details, or in combination with other
known methods and configurations. In the following description,
numerous specific details are set forth, such as specific
configurations, dimensions and processes, etc., in order to provide
a thorough understanding of the present invention. In other
instances, well-known semiconductor processes and manufacturing
techniques have not been described in particular detail in order to
not unnecessarily obscure the present invention. Reference
throughout this specification to "one embodiment" means that a
particular feature, structure, configuration, or characteristic
described in connection with the embodiment is included in at least
one embodiment of the invention. Thus, the appearances of the
phrase "in one embodiment" in various places throughout this
specification are not necessarily referring to the same embodiment
of the invention. Furthermore, the particular features, structures,
configurations, or characteristics may be combined in any suitable
manner in one or more embodiments.
[0052] The terms "spanning", "over", "to", "between" and "on" as
used herein may refer to a relative position of one layer with
respect to other layers. One layer "spanning", "over" or "on"
another layer or bonded "to" another layer may be directly in
contact with the other layer or may have one or more intervening
layers. One layer "between" layers may be directly in contact with
the layers or may have one or more intervening layers.
[0053] Referring now to FIG. 1A a combination view is provided of a
light pipe around a micro LED device and wavelength conversion
layer over the light pipe in accordance with an embodiment of the
invention. FIG. 1A is referred to as a combination view because it
includes characteristics of an isometric view, plan view for
location of the micro LED device, and cross-sectional view of the
layers. In the particular embodiment illustrated, the micro LED
devices 100 include a vertical micro p-n diode between a bottom
contact 104 and top contact 102. In an embodiment, the micro p-n
diode is several microns thick, such as 30 .mu.m or less, or even 5
.mu.m or less, with the top and bottom contacts 104, 102 being 0.1
.mu.m-2 .mu.m thick. The micro p-n diode may include a n-doped
layer 109, a p-doped layer 105, and one or more quantum well layers
108 between the n-doped layer and p-doped layer. In the particular
embodiment illustrated in FIG. 1A the n-doped layer 109 is
illustrated as being above the p-doped layer 105. Alternatively,
the p-doped layer 105 may be above the n-doped layer 109. The micro
LED devices 100 may have straight or tapered sidewalls 106 (from
top to bottom). The top and bottom contacts 102, 104 may include
one or more layers and can be formed of a variety of electrically
conducting materials including metals, conductive oxides, and
conductive polymers. The top and bottom contacts 102, 104 may be
transparent or semi-transparent to the visible wavelength spectrum
(e.g. 380 nm-750 nm) or opaque. The top and bottom contacts 102,
104 may optionally include a reflective layer, such as a silver
layer. In an embodiment, a conformal dielectric barrier layer 107
may optionally be formed along the sidewalls 106 of the p-n diode
to electrically passivate the quantum well 108, and optionally
along the top or bottom surface of the micro p-n diode. The
conformal dielectric barrier layer 107 may be thinner than the p-n
diode so that it forms an outline of the topography of the p-n
diode it is formed on. For example, the conformal dielectric
barrier layer 107 may be approximately 50-600 angstroms thick
aluminum oxide.
[0054] In an embodiment, the micro LED device 100 is secured over a
reflective layer 309. The reflective layer 309 may assume a number
of different configurations. As described in further detail below,
the reflective layer can be a stand-alone layer, an electrode, an
electrode line, or a reflective bank layer. Reflective layer 309
may also function as an anode, cathode, or ground, or an electrical
line to anode, cathode, or ground. In an embodiment, the reflective
layer is a bottom electrode. In an embodiment, reflective layer 309
comprises a reflective metallic film such as aluminum, molybdenum,
titanium, titanium-tungsten, silver, or gold, or alloys thereof. In
application, the reflective layer may include a stack of layers or
metallic films.
[0055] A bonding layer 314 may optionally be formed between the
micro LED device 100 and the bottom electrode or reflective layer
309 to facilitate bonding of the bottom contact 104 of micro LED
device 100 to the reflective layer 309, or other intervening layer.
In an embodiment, bonding layer 314 includes a material such as
indium, gold, silver, molybdenum, tin, aluminum, silicon, or an
alloy or alloys thereof.
[0056] It is to be appreciated, that the specific vertical micro
LED device 100 illustrated in FIG. 1A is exemplary and that
embodiments of the invention may also be practiced with other micro
LED devices. For example, FIG. 1B illustrates an alternative micro
LED device 100 in a light pipe configuration similar to that in
FIG. 1A. Similar to the micro LED device of FIG. 1A, the micro LED
device in FIG. 1B includes a micro p-n diode including doped layers
105, 109 opposite one or more quantum well layers 108. Unlike the
micro LED device of FIG. 1B, the micro LED device in FIG. 1B
includes bottom contacts to both the doped layers 105, 109. For
example, bottom contact 104 and bottom bonding layer 314A are
formed on doped layer 105, and bottom contact 103 and bottom
bonding layer 314B are formed on doped layer 109. A conformal
dielectric barrier layer 107 may also be optionally formed on the
micro LED device of FIG. 1B, particularly to protect sidewalls 106
including the quantum well layer(s) 108. Since the micro LED device
100 of FIG. 1B includes bottom contacts for both the n-doped and
p-doped layers, the bottom electrode or reflective layer 309 may
also be separated into two electrically separate layers 309A, 309B
to make electrical contact with bottom contacts 104, 103,
respectively. Accordingly, the micro LED device of FIG. 1B may be
implemented within embodiments of the invention where it is not
required to have top and bottom contacts, and the micro LED devices
can be operably connected with bottom contacts.
[0057] As shown in FIGS. 1A-1B a light pipe 120 is formed around
the micro LED device 100. Referring now to FIG. 1C combination view
illustration is shown of a light pipe around a plurality of micro
LED devices and a wavelength conversion layer over the light pipe
in accordance with an embodiment of the invention. As described
herein a layer "around" a micro LED device may be formed laterally
to, over, or below the micro LED device. Thus, the term "around" a
micro LED device does not require the layer to be located at all
directions from the micro LED device. Rather, the term "around" is
intended to refer to a neighboring area through which the light
emission beam path from the micro LED device is designed to pass
through. In the particular embodiments illustrated in FIGS. 1A-1C,
the light pipe around the micro LED devices 100 is both lateral to
and over the micro LED devices.
[0058] The light pipe 120 may be shaped to both allow refraction of
incident light from the micro LED device 100 out of the light pipe
and toward a wavelength conversion layer 110, and to cause internal
reflection and lateral spreading of incident light form the micro
LED device 100 within the light pipe 120. The light pipe 120 may be
thicker than the micro LED device 100. In an embodiment, the light
pipe 120 is 1 .mu.m-100 .mu.m thick. The lateral length/width of
the light pipe may be greater than the thickness of the light pipe
in order to support lateral spreading of the incident light. In an
exemplary embodiment, considering a 100 .mu.m.times.100 .mu.m wide
subpixel, a light pipe 120 may have a lateral length of 100 .mu.m,
a lateral width of 100 .mu.m and a height that is equal to or less
than the maximum lateral length or width.
[0059] The light pipe 120 may also be dome shaped to create radial
spreading of the light refracted out of the light pipe. In some
embodiments, the light pipe 120 is elongated dome shaped. The dome
shape profile may be hemispherical. The dome shape may also be
flattened to create a wider emission profile, or narrowed to create
a narrower emission profile. In an embodiment, the thickness and
profile of the light pipe 120 provides a base structure upon which
a micro lens structure is formed in order to change the light
emission beam profile from the micro LED device 100, as well as
color over angle characteristics of the light emitting device which
can be related to edge effects. Light pipe 120 may be formed of a
variety of transparent materials such as epoxy, silicone, and
acrylic, which have the following reported refractive indices (n)
at nominal 590 nm wavelength: n=1.51-1.57 (epoxy), n=1.38-1.58
(silicone), n=1.49 (acrylic).
[0060] In an embodiment, light pipe 120 is formed by ink jet
printing. In an embodiment, the light pipe 120 is formed by
application of a molten glass. Glass compositions can range from a
variety of compositions ranging from acrylic grass, crown glass,
flint glass, and borosilicate glasses that possess indices of
refraction that can be matched to those of epoxy, silicone, or
acrylic above. The particular profile of the light pipe can be
created through several processing techniques. One way is by
tailoring surface tension on in ink printed materials. Lithography
or other wafer-level optics techniques such as those used to form
micro lenses may also be used. Physical techniques such as moulding
or imprint lithography may also be used.
[0061] FIG. 1D is a cross-sectional side view illustration of a
light pipe around a micro LED device and a wavelength conversion
layer over the light pipe in accordance with an embodiment of the
invention. As shown in FIG. 1D, incident light emitting from the
micro LED device 100 can both be refracted out of the light pipe
120 and into the wavelength conversion layer 110, and also
reflected internally within the light pipe to cause lateral
spreading of the incident light from the micro LED device where the
reflected light is eventually refracted out of the light pipe 120
and into the wavelength conversion layer 110. FIGS. 1E-1F are
cross-sectional side view illustrations of a light pipe having a
tapered profile in accordance with embodiments of the invention. In
the particular embodiment illustrated in FIG. 1E, a micro LED
device is placed in the middle of the light pipe 120, and the light
pipe is tapered toward the lateral edges so that the light pipe is
thinner at the edges than the middle. Tapering the thickness of the
light pipe can result in increase reflection, causing the light to
eventually refract through the top surface of the light pipe rather
than through the edges. In the embodiment illustrated in FIG. 1F, a
micro LED device is placed nearer an edge of the light pipe, which
is tapered from one side to the other. In this manner, the light
pipe 120 can guide the light from one side of the light pipe to the
other where the light is refracted through the top surface rather
than through a side of the light pipe.
[0062] In addition to allowing refraction and reflection of
incident light from the micro LED device 100, light pipe 120 may
also allow the light emitting from the micro LED device 100 to
spread out prior to entering the wavelength conversion layer 110,
which decreases the optical intensity of light entering the
wavelength conversion layer. In one aspect, the internally
reflected light allows for an improved fill factor of the micro LED
device 100, or pixel including the micro LED device. In another
aspect, the spread out light (including incident light not
reflected, as well as reflected light) may result in more even
emission from the wavelength conversion layer 110 to be formed over
the light pipe. In another aspect, the light pipe may function to
increase the length that light travels in the device before being
emitted. This can result in a reduction of the optical density and
reduce thermal degradation of the phosphor particles in wavelength
conversion layer, prolonging lifetime of the light emitting device.
This may also increase the chances of color conversion by the
phosphor particles in the wavelength conversion layer without
having to increase the volume loading of the phosphor particles in
the wavelength conversion layer. In yet another aspect, spreading
out of the light and reduction of the optical intensity may reduce
the amount of back reflection from the wavelength conversion layer
that is reabsorbed by the micro LED device 100. In accordance with
embodiments of the invention, light pipe 120 may increase the fill
factor, increase total light emission, increase emission
uniformity, and increase sharpness of the color spectrum for the
light emitting device. The thickness and profile of the light pipe
may also provide a base structure from which a micro lens structure
is formed in order to change the light emission beam profile from
the micro LED device 100, as well as color over angle
characteristics of the light emitting device which can be related
to edge effects.
[0063] Following the formation of the light pipe 120, a matching
layer 122 may optionally be formed over the light pipe 120 prior to
forming the wavelength conversion layer 110. The matching layer 122
may function to match the indices of refraction for the light pipe
120 and wavelength conversion layer 110 to reduce back reflection
of light. For example, where layers 120, 110 are formed of, for
example, an epoxy, silicone, acrylic, or glass having different
indices of refraction, the matching layer 122 is formed of an
epoxy, silicone, acrylic, or glass having an index of refraction
between that of layers 120, 110. In accordance with embodiments of
the invention, the polymer matrix forming layers 120, 110 is the
same, and layers 120, 110 have an identical index of refraction. In
another embodiment, the index of refraction for layers 120, 110 is
within 0.3, or more particularly within 0.1. In an embodiment,
matching layer is 2 .mu.m or less in thickness. In an embodiment,
curing of the matching layer 122 may be thermal or UV.
[0064] In accordance with embodiments of the invention, a
wavelength conversion layer 110 is formed over the micro LED device
100 and light pipe 120, and around the optional matching layer, if
present. In an embodiment, the wavelength conversion layer includes
phosphor particles to control the light emission spectrum. In one
embodiment, the wavelength conversion layer includes different
phosphor particles (different in designed size or shape, or
composition) for a blended color emission spectrum (e.g. a
combination of any of red, blue, green, yellow, etc). In another
embodiment, the wavelength conversion layer includes phosphor
particles designed for a single color emission spectrum (e.g. red,
blue, green, yellow, etc).
[0065] In an embodiment, the wavelength conversion layer 110 is
formed of phosphor particles. For example, the wavelength
conversion layer is formed of a spray deposition method followed by
removal of solvents. In an embodiment, the wavelength conversion
layer includes a dispersion of phosphor particles in a matrix
material such as a polymer or glass matrix material. Other filler
materials such as pigment, dye, or scattering particles may also be
dispersed within the matrix or among the phosphor particles
themselves if no matrix material is present. In an embodiment,
wavelength conversion layer 110 is formed by ink jet printing, and
UV cured. In an embodiment, the wavelength conversion layer 110 is
formed by application of a molten glass, where the fillers are
thermally and chemically stable within the molten glass. The
thickness of the wavelength conversion layer 110, as well a
concentration of fillers, e.g. phosphor particles, pigment, dye, or
light scattering particles are tuned to achieve the requisite color
spectrum. For example, in an embodiment the thickness and
concentration is tuned to minimize color bleeding from the micro
LED device through the wavelength conversion layer, and maximize
emission from the phosphor particles. Thickness of the wavelength
conversion layer 110 (as well as light pipe 120) may also be partly
determined by the spacing between micro LED devices. For example,
micro LED devices may be spaced more closely together in high
resolution display applications compared to lighting applications.
In an embodiment, the wavelength conversion layer 110 is 5
.mu.m-100 .mu.m thick, or more specifically 30 .mu.m-50 .mu.m thick
for an exemplary 5 .mu.m wide and 3.5 .mu.m tall micro LED device
100. In some embodiments, the thickness of the wavelength
conversion layer and concentration of fillers may be designed to
allow some light from the micro LED device 100 to pass through
resulting a mix of the micro LED device light spectrum and the
converted light spectrum to achieve a blended emission spectrum,
for example, white light. Concentration of the color converting
materials (e.g. phosphor particles, pigment, dye) as well as
thickness of the layers can depend upon the particular application
of the light emitting device, for example, if full color conversion
(e.g. from blue to red, or blue to green, etc.) is to occur, if
leakage or bleeding of light from the underlying micro LED device
is to occur, or if a mixture of converting materials is employed.
In an embodiment where full color conversion (e.g. from blue to
red, or blue to green, etc.) occurs a volume loading percent of
greater than 50% color converting materials may be included in the
wavelength conversion layer. In an embodiment, the wavelength
conversion layer includes greater than 50% volume loading of
phosphor particles. The light pipe can function to increase the
length that light travels in the device before being emitted in
order to increase the chances of color conversion by the phosphor
particles in the wavelength conversion layer without having to
increase the volume loading of the phosphor particles in the
wavelength conversion layer.
[0066] In accordance with embodiments of the invention, the term
"phosphor" may refer to any type of wavelength converting material
that will absorb light at one wavelength and emit light at another
wavelength. One type of phosphor particle is a quantum dot. Quantum
dots are semiconductor materials where the size of the structure is
small enough (less than tens of nanometers) that the electrical and
optical characteristics differ from the bulk properties due to
quantum confinement effects. For example, the emission properties
of quantum dots are related to their size and shape in addition to
their composition. Fluorescence of quantum dots is a result of
exciting a valence electron by absorbing a certain wavelength,
followed by the emission of lower energy in the form of photons as
the excited electrons return to the ground state. Quantum
confinement causes the energy difference between the valence and
conduction bands to change based on size and shape of the quantum
dot meaning that the energy and wavelength of the emitted photons
is determined by the size and shape of the quantum dot. The larger
the quantum dot, the lower the energy of its fluorescence spectrum.
Accordingly, smaller quantum dots emit bluer light (higher energy)
and larger quantum dots emit redder light (lower energy). This
allows size-dependent tuning of the semiconductor photoluminescence
emission wavelength throughout the visible spectrum, with a sharp
emission spectrum and high quantum efficiency.
[0067] Examples of quantum dot materials include, but are not
limited to, groups II-VI, III-V, IV-VI semiconductor materials.
Some exemplary compound semiconductors include CdS, CdSe, CdTe,
ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP,
InSb, AlAs, AlP, AlSb. Some exemplary alloyed semiconductors
include InGaP, ZnSeTe, ZnCdS, ZnCdSe, and CdSeS. Multi-core
structures are also possible. Exemplary multi core configurations
may include a semiconductor core material, a thin metal layer to
protect the core from oxidation and to aid lattice matching, and a
shell to enhance the luminescence properties. The shell may
function to absorb light at a specific spectrum that is different
from the emission spectrum from the quantum dot. The core and shell
layers may be formed of the same material, and may be formed of any
of the exemplary compound semiconductors or alloyed semiconductors
listed above. The metal layer often comprises Zn or Cd.
[0068] In accordance with embodiments of the invention, one type of
phosphor particle is a particle that exhibits luminescence due to
its composition. Some exemplary phosphor particles that exhibit
luminescence due to their composition include sulfides, aluminates,
oxides, silicates, nitrides, YAG (optionally doped with cerium),
and terbium aluminum garnet (TAG) based materials. Other exemplary
materials include yellow-green emitting phosphors:
(Ca,Sr,Ba)Al.sub.2O.sub.4:Eu (green), (Lu,
Y).sub.3Al.sub.5O.sub.12:Ce.sup.3+(LuAG, YAG) (yellow-green),
Tb.sub.3Al.sub.5O.sub.12:Ce.sup.3+(TAG) (yellow-green); orange-red
emitting phosphors: BaMgAl.sub.10O.sub.17:Eu.sup.2+(Mn.sup.2+),
Ca.sub.2Si.sub.5N.sub.8:Eu.sup.2+ (orange-red), (Zn,Mg)S:Mn (green,
red), (Ca,Sr,Ba)S:Eu.sup.2+ (red); uv-deep blue absorbing phosphors
for blue and yellow-green emission:
(Mg,Ca,Sr,Ba).sub.2SiO.sub.4:Eu.sup.2+ (uv-blue excitation, yellow
emission), (Mg,Ca,Sr,Ba).sub.3Si.sub.2O.sub.7:Eu.sup.2+ (uv-deep
blue excitation, blue-green emission),
Ca.sub.8Mg(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+ (uv-deep blue
excitation, blue emission); and phosphors that can emit over the
full visible spectrum depending on composition and processing
(Sr,Ca,Ba)Si.sub.xO.sub.yN.sub.z:Eu.sup.2+ (y>0 green, y=0 red),
Y.sub.2O.sub.2S:Eu.sup.3+ (blue-green),
(Ca,Mg,Y).sub.vSi.sub.wAl.sub.xO.sub.yN.sub.z:Eu.sup.2
(yellow-green-red). In some embodiments the particle size for such
phosphor particles may be from 1 .mu.m to 20 .mu.m. In other
embodiments, the particles size for such phosphor particles can be
nanoparticles from 100 nm to 1 .mu.m. The phosphor particles can
also include a blend of the 1 .mu.m to 20 .mu.m particles and 100
nm to 1 .mu.m nanoparticles. Nanoparticles may be useful, for
example, to reduce the amount of settling when dispersed within a
matrix material of a wavelength conversion layer prior to curing or
solvent removal, which may result in more even distribution of the
nanoparticles and light emission of the light emitting device.
[0069] Other materials may also be dispersed within the wavelength
conversion layer. For example, the other materials may be dispersed
within the matrix material, such as glass or polymer matrix of the
wavelength conversion layer. In an embodiment, a light scattering
agent such as a TiO.sub.2 or Al.sub.2O.sub.3 particles are
dispersed within the wavelength conversion layer. Such light
scattering agents may have the effect of increasing the phosphor
particle efficiency by increasing scattered light within the
wavelength conversion layer. Such light scattering agents may
additionally have the effect of reduced bleeding of the micro LED
device emitted light through the wavelength conversion layer. Light
scattering particles can also be used to control when and where
light is emitted from the micro lens structure. For example, a
higher concentration of light scattering particles can be placed at
the ends of the micro lens structure, e.g. at lateral edges of the
wavelength conversion layer, to direct the light out. In an
embodiment, a pigment or dye may be dispersed within the wavelength
conversion layer 110. This may have the effect of incorporating a
color filter into the wavelength conversion layer. In an
embodiment, the pigment or dye may have a color similar to the
emission wavelength of the phosphor particle. In this manner, the
pigment or die can absorb wavelengths other than those being
emitted from the phosphor particle, further sharpening the emission
spectrum of the assembly. For example, in a particular embodiment,
the micro LED device 100 is a gallium nitride (GaN) based material,
and emits a blue (e.g. 450 nm-495 nm) or deep blue (e.g. 420 nm-450
nm) light. Quantum dots designed for red emission may be dispersed
in the wavelength conversion layer 110 in order to absorb the blue
or deep blue emission from the micro LED device 100 and convert the
emission wavelength to red. In such an embodiment, a red pigment or
dye may also be dispersed within the wavelength conversion layer
110 to also absorb colors other than red. In this manner, the red
pigment or dye may absorb additional blue or deep blue light,
thereby reducing bleeding of the unconverted blue or deep blue
light. Exemplary pigments include lithol rubine (Red), B-copper
thalocyanine (Blue), and diarylide yellow (Yellow). It is to be
appreciated that a blue micro LED device and red phosphor particles
with red pigment or dye is exemplary and a variety of emission
spectrum configurations for the micro LED devices and wavelength
conversion layers, where present, are possible.
[0070] In accordance with some embodiments of the invention, the
polymer matrix forming the wavelength conversion layer 110 may be
permeable to oxygen or moisture. In an embodiment, following the
formation of the wavelength conversion layer 110, an oxygen barrier
film 124 may optionally be formed in order to protect the
wavelength conversion layer 110 from oxygen or moisture absorption.
For example, where wavelength conversion layer 110 includes quantum
dots, the oxygen barrier film 124 can act as a barrier to oxygen or
moisture absorption by the quantum dots, thereby prolonging the
lifetime of the quantum dots in the lighting or display device.
Suitable materials for the oxygen barrier film 124 include, but are
not limited to, Al.sub.2O.sub.3, SiO.sub.2, SiN.sub.x, and glass.
The deposition method for oxygen barrier film 124 may be a low
temperature method in order to not thermally degrade the quantum
dots or other fillers. Exemplary conformal deposition methods
include atomic layer deposition (ALD), sputtering, spin on, and
lamination. The oxygen barrier film may also be blanket deposited
over the entire substrate, or over all of the micro LED devices. In
an embodiment, an Al.sub.2O.sub.3 oxygen barrier film is deposited
by atomic layer deposition (ALD).
[0071] In accordance with embodiments of the invention, the light
emitting device configurations including the micro LED devices,
light pipes, and wavelength conversion layers can be incorporated
into a variety of lighting or display devices. The wavelength
conversion layers that are formed over the light pipes can be
designed to all emit the same color emission spectrum, or the
wavelength conversion layers can be divided into multiple groups of
wavelength conversion layers, with each group designed to emit a
different color emission spectrum. In this manner, the light
emitting devices can emit any color or patterns of colors depending
upon the arrangement and content of the micro LED devices, light
pipes, and wavelength conversion layers. In one embodiment, white
light can be generated by incorporating red (e.g. 620 nm-750 nm)
and green (e.g. 495 nm-570 nm) emitting phosphor particles in a
wavelength conversion layer positioned over a light pipe formed
around a blue emitting (e.g. 450 nm-495 nm) micro LED device. In
another embodiment, white light can be generated by incorporating
multiple micro LED devices into a pixel, with each micro LED device
designed to emit the same emission spectrum (e.g. visible spectrum
or UV spectrum), and different wavelength conversion layers
designed to convert color emission. In this manner, by including
phosphor particles of a single color emission spectrum in each
light pipe wavelength conversion layer, secondary absorption of
light emitted from different emission spectra of different phosphor
particles is avoided. This may increase efficiency and reduce
unintended color shift.
[0072] Referring now to FIG. 2A, a combination view illustration is
provided of a light emitting device including a plurality of micro
LED devices 100 bonded to a substrate 201, a plurality of light
pipes 120 around the plurality of micro LED devices 100, and a
plurality of wavelength conversion layers 110 over the plurality of
light pipes 120. In the particular embodiment illustrated, a pixel
204 includes a plurality of micro LED devices 100 within light
pipes 120 and wavelength conversion layers 110 designed to convert
emission, e.g. in an RGB subpixel arrangement. In an embodiment, a
black matrix material 202 can be formed over the substrate 201 and
between the light pipes 120 to absorb light and prevent color
bleeding into adjacent pixels 204 or subpixels 206. Alternatively,
the black matrix material 202 can be substituted with a white
matrix material to reflect light and prevent color bleeding into
adjacent pixels 204 or subpixels.
[0073] When arranged in a pixel configuration, each subpixel 206
may contain a single phosphor color emission, where present. Each
subpixel may likewise contain a different phosphor color emission,
where present. In this manner, secondary absorption of light
emitted from a phosphor particle emitting a different spectrum
(e.g. absorption of green light emitted from a green emitting
phosphor particle by a red emitting phosphor particle) is avoided.
This may increase efficiency and reduce unintended color shift.
Such pixel and subpixel configurations can be used for the final
output of white light, or any other color of light.
[0074] For example, a pixel 204 may contain 3 micro LED devices in
3 light pipes, or a plurality of micro LED devices in each light
pipe, with all the micro LED devices designed to emit blue light,
with one red emitting wavelength conversion layer over one light
pipe, one green emitting wavelength conversion layer over a second
light pipe, and the third light pipe either not including a
wavelength conversion layer over it or including a blue emitting
wavelength conversion layer over it. In one embodiment, white light
can be generated by incorporating multiple micro LED devices into a
pixel, with each micro LED device designed to emit UV light, with
one red emitting conversion layer over a first light pipe, one
green emitting wavelength conversion layer over a second light
pipe, and one blue emitting wavelength conversion layer over a
third light pipe. In another embodiment, white light can be
generated by incorporating combinations of micro LED devices
designed for different emission spectrum and different wavelength
conversion layers, or no wavelength conversion layers. In another
exemplary embodiment, white light can be generated with a light
pipe around a micro LED device designed for red emission with no
overlying wavelength conversion layer, a light pipe around a micro
LED device designed for blue emission with an overlying wavelength
conversion layer designed for green emission, and a light pipe
around a micro LED device designed for blue emission with no
overlying wavelength conversion layer.
[0075] In the above exemplary embodiments, a red-green-blue (RGB)
subpixel arrangement is obtained, and each pixel includes three
subpixels that emit red, green and blue lights, respectively. It is
to be appreciated that the RGB arrangement is exemplary and that
embodiments are not so limited. Examples of other subpixel
arrangements that can be utilized include, but are not limited to,
red-green-blue-yellow (RGBY), red-green-blue-yellow-cyan (RGBYC),
or red-green-blue-white (RGBW), or other subpixel matrix schemes
where the pixels may have different number of subpixels, such as
the displays manufactured under the trademark name
PenTile.RTM..
[0076] FIG. 2B is a schematic side view illustration of a pixel 204
in accordance with an embodiment of the invention. As illustrated
in FIG. 2B, each micro LED device 100 is designed to emit a deep
blue (DB) color spectrum. In such an embodiment, the different
wavelength conversion layers 110 can be designed to emit red (R),
green (G), and blue (B) in an RGB subpixel arrangement.
[0077] FIG. 2C is a schematic side view illustration of a pixel 204
in accordance with an embodiment of the invention. As illustrated
in FIG. 2C, each micro LED device 100 is designed to emit a blue
(B) color spectrum. In such an embodiment, the different wavelength
conversion layers 110 can be designed to emit red (R) and green
(G). A wavelength conversion layer 110 is not formed over the third
light pipe 120. In this manner an RGB subpixel arrangement is
achieved without having to covert the blue light from the blue
emitting subpixel. In an embodiment, the third light pipe 120 can
be made thicker than the other two light pipes over which
wavelength conversion layers 110 are formed in order to achieve
similar micro lens characteristics. For example, the thickness of
the third light pipe 120 may be similar to the total thickness of
the first light pipe 120, and first red wavelength conversion layer
110 (and any intermediate layers).
[0078] FIG. 2D is a schematic side view illustration of a pixel 204
in accordance with an embodiment of the invention. As illustrated
in FIG. 2D, each micro LED device 100 is designed to emit an
ultraviolet (UV) color spectrum. In such an embodiment, the
different wavelength conversion layers 110 can be designed to emit
red (R), green (G), and blue (B).
[0079] FIG. 2E is a schematic side view illustration of a pixel 204
in accordance with an embodiment of the invention. As illustrated
in FIG. 2E, the pixel 204 includes micro LED devices 100 designed
to emit a red (R) or blue (B) color emission spectrum. As
illustrated, a green (G) emitting wavelength conversion layer 110
is formed over one of the light pipes 120 around one of the blue
emitting micro LED device 100, and a wavelength conversion layer
110 is not required to be formed over the light pipes 120 formed
around the red emitting micro LED device or the other blue emitting
micro LED device. Such a configuration may be implemented, for
example, when it is possible to fabricate and integrate blue
emitting and red emitting micro LED devices that are more efficient
than green emitting micro LED devices. In such an embodiment, it
may be more efficient to convert blue light to green light with a
wavelength conversion layer. Such a configuration may also be
useful when providing a broad spectrum at the visual response peak,
around 555 nm. Such a configuration may allow for controlling the
correlated control temperature (CCT) of the light emitting device,
and hence controlling the warmth, by driving the red emitting micro
LED device independently. Such a configuration may also be useful
for obtaining a good color rendering index (CRI) with the broad
emission spectrum from the green wavelength conversion layer 110,
while using efficient blue emitting micro LED devices and a red
emitting LED device which can increase the CRI R9 without
decreasing efficiency. As described above with regard to FIG. 2C,
the light pipes 120 formed around the red emitting micro LED device
or the other blue emitting micro LED device in FIG. 2E may be made
thicker than the other light pipe over which a wavelength
conversion layer is formed in order to achieve similar micro lens
characteristics.
[0080] Referring now to FIGS. 3A-3E various pixel configurations
are illustrated similar to those illustrated and described above
with regard to FIGS. 2A-2E with one difference being that each
light pipe 120 spans across multiple subpixels within a pixel 204.
For example, the embodiment illustrated in FIG. 3A may be an
exemplary RGB subpixel arrangement in which a light pipe 120 is
formed around a micro LED device in each subpixel of the pixel 204,
however, other subpixel arrangements are possible such as, but not
limited to RGBY, RGBYC, RGBW, or others. In such arrangements the
light pipe spanning across multiple subpixels within a pixel allows
for color mixing between subpixels. Such a configuration may be
used in applications where the micro LED devices or subpixels are
far enough apart that they could otherwise be perceived by the
human eye (e.g. approximately 100 .mu.m or more) and perceived as
small dots. The color mixing associated with the light pipe
configurations of FIGS. 3A-3E may be used to blend the micro LED
device emissions so that they are not perceived by the human eye.
One possible application may be in a heads up display where the
viewing distance is short, and it is more likely that the viewer is
to be capable of perceiving emission spectra from individual
subpixels or micro LED devices.
[0081] Referring to FIGS. 3B-3E, the arrangements of emission
spectra for the micro LED devices 100 and wavelength conversion
layers 110 is similar to that of FIGS. 2B-2E, with one difference
being that the wavelength conversion layers 110 are formed over
only specific portions of the light pipe 120 shared by the micro
LED devices 100 in the pixel 204. Additional modifications can also
be incorporated into the configurations illustrated in FIGS. 3B-3E.
The profile of the light pipe 120 can be altered over certain micro
LED devices 100. For example, the light pipe 120 can be made
thicker over "naked" micro LED devices 100 over which a wavelength
conversion layer 110 is not formed. The light pipes 120 of FIGS.
2A-3E can also be tapered, for example, as previously described
with regard to FIGS. 1E-1F.
[0082] Referring now to FIGS. 4A-4C, combination and
cross-sectional side view illustrations are provided for
embodiments including a reflective layer 130 over the light pipe
120. In an embodiment, the reflective layer 130 may be formed
directly over the micro LED device 100. Reflective layer 130 can be
provided in different locations, which may result in different
effects on the light pipe and wavelength conversion layer
configuration. In one embodiment illustrated in FIG. 4B a
reflective layer 130 is formed over the wavelength conversion layer
110. In this manner, the reflective layer can block incident light
emitted from the micro LED device 100 from bleeding through the
wavelength conversion layer 110 at the closest location to the
micro LED device, where optical intensity may be the greatest.
Reflection of the incident light can also have the effect of
laterally spreading the light thereby improving the fill factor.
Another effect of the reflective layer 130 may also be to increase
the number of passes of the incident light through the wavelength
conversion layer. By way of example, two situations are illustrated
where the incident light passes through the wavelength conversion
layer 110 three times and five times. With each pass, phosphor
particles are excited and emit converted spectra. In this manner,
the efficiency of the phosphor particles in the wavelength
conversion layer 110 can be improved, thereby increasing the
converted spectra light intensity of the system, improving the fill
factor, and reducing the quantity of phosphor needed.
[0083] In another embodiment illustrated in FIG. 4C a reflective
layer 130 is formed between the light pipe 120 and the wavelength
conversion layer 110. In such a configuration, the reflective layer
may influence lateral spreading of incident light, and improve the
fill factor. Such a configuration may also block incident light
from entering the wavelength conversion layer 110 at the closest
location to the micro LED device, where optical intensity may be
the greatest. As such, bleeding of incident light through the
wavelength conversion layer 110 can be reduced. This configuration
may also increase the lifetime of the phosphor particles,
particularly where optical intensity would have been the
greatest.
[0084] FIGS. 5A-5C illustrate embodiments similar to those
illustrated and described with regard to FIGS. 4A-4C. In the
embodiments illustrated in FIGS. 5A-5C, the light pipes 120 are
formed around a plurality of micro LED devices 100, and reflective
layers 130 are formed directly over the micro LED devices. While
embodiments are illustrated including three micro LED devices 100
per light pipe, it is to be appreciated that this is exemplary and
any number of micro LED devices 100 can be located within each
light pipe.
[0085] The reflective layers 130 described above and illustrated in
FIGS. 4A-5C are illustrated as being flat layers. However, it is
not required that the reflective layers 130 are flat. Any
configuration is possible, and the reflective layers 130 may be
shaped to control the direction of light emission. Reflective
layers 130 also are not required to be formed directly above the
micro LED devices, and may be formed at other locations such as
along the lateral edges of the light pipe or wavelength conversion
layer.
[0086] Referring now to FIGS. 6A-6C, combination and
cross-sectional side view illustrations are provided for
embodiments including a reflective layer 130 and a plurality of
wavelength conversion layers over the light pipe 120 in accordance
with embodiments of the invention. For example, these
configurations can be used in a pixel design including a single
light pipe spanning multiple subpixels in the pixel. In the
particular embodiments illustrated, the light pipe configuration is
an RGB configuration. As illustrated in FIG. 6B, a mirror layer 130
is formed over the light pipe 120 over the micro LED device, and a
green emitting wavelength conversion layer 110G and red emitting
wavelength conversion layer 110R are formed over the light pipe 120
along the lateral length of the light pipe. As illustrated in FIG.
6C, a mirror layer 130 is formed over the light pipe 120 and
underneath a blue emitting wavelength conversion layer 110B, with
wavelength conversion layers 110G, 110R being formed similarly as
with FIG. 6B. The particular embodiments illustrated in FIGS. 6A-6C
are exemplary in nature, and represent only one manner for
integrating a light pipe over multiple subpixel areas of a
pixel.
[0087] In accordance with embodiments of the invention, the light
emitting device configuration including the micro LED device, light
pipe, and wavelength conversion layer can be incorporated into a
variety of lighting or display devices. Exemplary lighting
applications include interior or exterior lighting applications,
such as billboard lighting, building lighting, street lighting,
panel lighting, light bulbs, and lamps. Exemplary display
applications include passive matrix display and active matrix
displays, such as, display signage, display panels, televisions,
tablets, phones, laptops, computer monitors, kiosks, digital
cameras, handheld game consoles, media displays, ebook displays, or
large area signage display.
[0088] Referring now to FIGS. 7A-7B, schematic top view
illustrations are provided of light emitting devices including a
plurality of micro LED devices 100, or alternatively pixels 204 of
micro LED devices, arranged with light pipes and wavelength
conversion layers for controlling the light emission spectrum. In
one embodiment, the light emitting device may be a lighting device
700A. For example, each of the micro LED devices 100 or pixels 204
can be addressed together. Alternatively, subsets of the pixels can
be addressed together. For example, blue emitting subpixels can be
addressed together, while red subpixels can be addressed together,
and green emitting subpixels can be addressed together. In another
example, different regions or shapes of micro LED devices 100 or
pixels 204 can be addressed separately. In another embodiment, each
micro LED device, subpixel, or pixel can be selectively addressed.
Referring to FIG. 7B, such a configuration can also be used for a
micro LED display 700B. Any arrangement of light emitting devices
may be made in accordance with embodiments of the invention. For
example, the micro LED devices can be arranged in arrays or
irregular patterns for illumination. Each micro LED device may be
simultaneously addressed, or selectively addressed depending upon
application.
[0089] In the following description, specific examples are
described and illustrated for integrating micro LED devices with
wavelength conversion layers into lighting or display devices. It
is to be appreciated, however, that the following embodiments are
exemplary and are not intended to exclusive of one another, and
that the following embodiments may be combined in certain
situations.
[0090] Referring now to FIGS. 8A-9F, various configurations for
bonding one or more micro LED devices onto a substrate 201 are
described. FIGS. 8A-8B are cross-sectional side view illustrations
of a light pipe around a micro LED device and a wavelength
conversion layer over the light pipe in accordance with embodiments
of the invention, with FIG. 8B illustrating an elongated lateral
length of a light pipe that is greater than a thickness of the
light pipe. In the particular embodiments illustrated in FIGS.
8A-8B the micro LED devices 100 are vertical micro LED devices
including top and bottom contacts 102, 104.
[0091] In an embodiment one or more micro LED devices 100 are
bonded to a bottom electrode 310 on or within a substrate 201. The
micro LED devices 100 can be transferred and bonded to the
substrate 201 as part of an array of micro LED devices 100 using a
variety of techniques including a transfer bonding process,
transfer using elastomeric stamps, or transfer and bonding using an
electrostatic transfer head array, as described in any of U.S. Pat.
No. 8,333,860, U.S. Pat. No. 8,349,116, U.S. Pat. No. 8,415,771,
U.S. Pat. No. 8,415,767, or U.S. Pat. No. 8,415,768.
[0092] Substrate 201 may be a variety of substrates such as, but
not limited to, a display substrate, a lighting substrate, a
substrate with functional devices such as transistors or integrated
circuits (ICs), or a substrate with metal redistribution lines.
Depending upon the particular application, substrate 201 may be
opaque, transparent, or semi-transparent to the visible wavelength
spectrum (e.g. 380-750 nm wavelength), and substrate 201 may be
rigid or flexible. For example, substrate 201 may be formed of
glass, metal foil, metal foil covered with dielectric, or a polymer
such as polyethylene terephthalate (PET), polyethelyne naphthalate
(PEN), polycarbonate (PC), polyethersulphone (PES), aromatic
fluorine-containing polyarylates (PAR), polycyclic olefin (PCO),
and polyimide (PI). In an embodiment, the substrate 201 includes
working circuitry 210. For example substrate 201 may be an active
matrix backplane including working circuitry 210 such as a driving
transistor, switching transistor, and capacitor. In an embodiment,
substrate 201 is a thin film transistor (TFT) substrate including
working circuitry 210.
[0093] Conductive electrodes or electrode lines 310, 330 can be
formed on, within, or over substrate 201. For example, the
electrodes or electrode lines 310, 330 function as an anode,
cathode or ground, or an electrical line to anode, cathode, or
ground. In interests of clarity, 310 is referred to as a bottom
electrode or electrode line and 330 is referred to as a ground line
in the remainder of the description. However, it is to be
appreciated that this is one embodiment, and other configurations
are possible. While the remainder of the description is made with
regard to this designation, it is understood that this is not the
sole embodiment.
[0094] Bottom electrode 310 and ground line 330 can be formed of a
variety of materials, and either may be opaque, transparent, or
semi-transparent to the visible wavelength spectrum. Exemplary
transparent conductive materials include amorphous silicon,
transparent conductive oxides (TCO) such as indium-tin-oxide (ITO)
and indium-zinc-oxide (IZO), carbon nanotube film, or a transparent
conducting polymer such as poly(3,4-ethylenedioxythiophene)
(PEDOT), polyaniline, polyacetylene, polypyrrole, and
polythiophene. In an embodiment bottom electrode 310 is
approximately 100 nm-200 nm thick ITO. In an embodiment, the bottom
electrode 310 includes nanoparticles such as silver, gold,
aluminum, molybdenum, titanium, tungsten, ITO, and IZO. The bottom
electrode 310 or ground line 330 may also be reflective to the
visible wavelength. In an embodiment, a bottom electrode 310 or
ground line 330 comprises a reflective metallic film such as
aluminum, molybdenum, titanium, titanium-tungsten, silver, or gold,
or alloys thereof.
[0095] A bonding layer 314 may optionally be formed between the
micro LED device 100 and the bottom electrode 310 to facilitate
bonding of the bottom contact 104 of micro LED device 100 to the
bottom electrode 310 on substrate 201. In an embodiment, bonding
layer 314 includes a material such as indium, gold, silver,
molybdenum, tin, aluminum, silicon, or an alloy or alloys
thereof.
[0096] Still referring to FIGS. 8A-8B, a sidewall passivation layer
316 can be formed around the sidewalls of the micro LED devices
100. In an embodiment where the micro LED devices 100 are vertical
LED devices, the sidewall passivation layer 316 covers and spans
the quantum well structure 108. In accordance with embodiments of
the invention, the sidewall passivation layer 316 may be
transparent or semi-transparent to the visible wavelength spectrum
so as to not significantly degrade light extraction efficiency from
sidewalls of the micro LED devices 100. Sidewall passivation layer
316 may be formed of a variety of materials such as, but not
limited to epoxy, silicone, acrylic, poly(methyl methacrylate)
(PMMA), benzocyclobutene (BCB), polyimide, and polyester. In an
embodiment, sidewall passivation layer 316 is formed by ink jet
printing around the light emitting devices 100, followed by curing.
In an embodiment, sidewall passivation layer 316 is cured with
ultraviolet (UV) light to minimize volume change as a result of
cure and protect the integrity of the bond between the micro LED
device and the bottom electrode, though thermal curing may also be
performed. Sidewall passivation layer 316 can also be deposited
using other techniques such as slit coating, physical vapor
deposition or chemical vapor deposition of a dielectric material
such as a nitride or oxide, spin on technique such as a spin on
glass, or spray coating followed by solvent evaporation. In an
embodiment, sidewall passivation layer is an a-staged or b-staged
coating already formed over the substrate 201 prior to bonding the
micro LED devices 100 when the micro LED devices punch through the
coating during the transfer and bonding operations, and the coating
is then cured after bonding of the micro LED devices 100.
[0097] In an embodiment the sidewall passivation layer 316 at least
partially covers the bottom electrode 310. The sidewall passivation
layer may completely cover the bottom electrode 310, however, this
is not required. Any combination of other insulating layers can be
used to electrically insulate the bottom electrode 310 from other
electrically conductive layers. For example, insulating layer 317
can be deposited over edges of the reflective bank structure 142.
In accordance with embodiments of the invention, a sidewall
passivation layer 316 may not be required where a conformal
dielectric barrier layer 107 is present along sidewalls of the
micro LED devices 100. Alternatively, a sidewall passivation layer
316 may be formed in combination with an existing conformal
dielectric barrier layer 107.
[0098] In embodiments including a vertical micro LED device,
following the formation of optional sidewall passivation layer 316,
a top electrode layer 318 is formed on the micro LED device 100 and
in electrical contact with the top contact 102 and ground line 330.
Depending upon the particular application, top electrode layer 318
may be opaque, reflective, transparent, or semi-transparent to the
visible wavelength. Exemplary transparent conductive materials
include amorphous silicon, transparent conductive oxides (TCO) such
as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO), carbon
nanotube film, or a transparent conductive polymer such as
poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline,
polyacetylene, polypyrrole, and polythiophene. In an embodiment top
electrode layer 318 is approximately 50 nm-1 .mu.m thick
ITO-silver-ITO stack, with the silver layer thin enough to be
transparent to the visible wavelength spectrum. In a particular
embodiment, the top electrode layer 318 is formed by ink jet
printing. In an embodiment top electrode layer 318 is approximately
50 nm-1 .mu.m thick PEDOT. Other methods of formation may include
chemical vapor deposition (CVD), physical vapor deposition (PVD),
or spin coating depending upon the desired area to be coated and
any thermal constraints. In accordance with embodiments of the
present invention, the top electrode layer 318 may be formed over a
plurality of the micro LED devices 100 on substrate 201,
electrically connecting the plurality of the micro LED devices 100
to ground line 330.
[0099] A light pipe 120, optional matching layer 122, wavelength
conversion layer 110, and optional barrier layer 124 may then be
formed as described above with regard to FIG. 1A. Still referring
to the embodiment illustrated in FIGS. 8A-8B the light pipe is
illustrated as being wider (FIG. 8A) and longer (FIG. 8B) than the
bottom electrode 310. However, this is not required. Referring
again to the embodiment illustrated in FIG. 1A, the reflective
layer 309, which can be a bottom electrode 310 or reflective bank
structure is illustrated as being wider and longer than both the
light pipe 120 and wavelength distribution layer 110. In some
embodiments, the reflective layer 309 or bottom electrode 310 can
be formed underneath all or some of the micro LED devices 100 on
substrate 201. In one embodiment, the reflective layer 309 or
bottom electrode layer 310 is not wider (FIG. 8A) or longer (FIG.
8B) than the wavelength distribution layer 110 so that light that
passes through the light pipe 120 also passes through the
wavelength distribution layer 110, and color bleeding is
prevented.
[0100] Referring briefly back to FIG. 2A a black matrix (or
alternatively white matrix) material 202 is illustrated between the
micro LED devices 100 and light pipes 120 in order to block light
transmission, and to separate bleeding of light between adjacent
micro LED devices 100. Black (or white) matrix 202 can be formed
from a method that is appropriate based upon the material used, and
composition of layers already formed. Manner of formation may also
be determined by whether the black (or white) matrix is formed in a
single side manner (see FIG. 10) or a top press down manner (see
FIG. 11). For example, black (or white) matrix 202 can be applied
using ink jet printing, sputter and etching, spin coating with
lift-off, or a printing method. In some embodiments, black (or
white) matrix 202 is formed by ink jet printing and UV cured in
order to not thermally degrade the phosphor particles in a
wavelength conversion layer 110 already formed. Exemplary black
matrix materials include carbon, metal films (e.g. nickel,
aluminum, molybdenum, and alloys thereof), metal oxide films (e.g.
chromium oxide), and metal nitride films (e.g. chromium nitride),
organic resins, glass pastes, and resins or pastes including a
black pigment or silver particles. Exemplary white matrix materials
include metal particles or TiO.sub.2 particles loaded win a
polymer, organic resin, or glass paste, for example. In the
embodiments illustrated in FIGS. 6A-8, a black (or white) matrix
202 is formed on the substrate 201 in a single side manner--prior
to forming a cover over the light emitting device. In the
embodiment illustrated in FIG. 9, the black (or white) matrix
material can be formed in a top press down manner--in which the
black (or white) matrix is formed on the cover prior attaching to
the substrate 201.
[0101] Referring again to FIGS. 8A-8B a color filter layer 328 may
optionally be formed over the wavelength conversion layer 110 to
filter out colors emitting through the wavelength conversion layer
110 other than those desired and to sharpen the emission spectrum
of the light emitting device. By way of example, a red color filter
layer 328 may be placed over a wavelength conversion layer 110
including red emitting phosphor particles in order to filter out
colors other than red, a green color filter layer 328 may be placed
over a wavelength conversion layer 110 including green emitting
phosphor particles in order to filter out colors other than green,
and a blue color filter layer 328 may be placed over a wavelength
conversion layer 110 including blue emitting phosphor particles in
order to filter out colors other than blue. Referring back to FIG.
2B, in an embodiment, a blue color filer may not be necessary over
a blue wavelength conversion layer 110 wherein the underlying micro
LED device 100 is deep blue emitting. Referring back to FIG. 2C, in
an embodiment, a blue color filer may not be necessary over naked
(e.g. no wavelength conversion layer) blue emitting underlying
micro LED device 100. It is to be appreciated that these
configurations are exemplary and a variety of configurations are
possible depending upon desired light emission spectrum. Suitable
materials for the color filter include pigments or dyes as
previously described above. In an embodiment, color filter layer
328 includes a pigment or dye dispersed in a transparent matrix
material. In an embodiment, the matrix material is the same polymer
used for the wavelength conversion layer 110, such as epoxy,
silicone, or acrylic. Likewise, the color filter may be formed
using similar techniques, such as ink jet printing with UV cure. In
an embodiment, the wavelength conversion layer 110 has an index of
refraction within 0.3, or more particularly within 0.1, of the
index of refraction for the wavelength conversion layer 110. In the
embodiments illustrated in FIGS. 8A-8B the color filter layer 328
is formed after the black matrix 202. In other embodiments, the
color filter layer 328 is formed before the black matrix 202.
[0102] FIGS. 8C-8D are cross-sectional side view illustrations of a
light pipe around a micro LED device with bottom contacts and a
wavelength conversion layer over the light pipe in accordance with
embodiments of the invention. FIGS. 8C-8D are similar to those of
FIGS. 8A-8B with one difference being that the micro LED devices
100 include bottom contacts 104, 103 rather than both a bottom and
top contact. As a result, it may not be required to form a top
electrode layer to contact the ground line 330. Sidewall
passivation layer 316 also may be omitted, and the light pipe 120
or other layers can electrically insulate the bottom electrodes
310A, 310B and quantum well structure 108. As illustrated, bottom
electrodes 310A, 310B are electrically insulated from one another,
and may resemble the configuration of the bottom reflective layers
309A, 309B in FIG. 1B.
[0103] FIGS. 9A-9B are cross-sectional side view illustrations of a
light pipe around a micro LED device within a reflective bank
structure, and a wavelength conversion layer over the light pipe in
accordance with embodiments of the invention, with FIG. 9B
illustrating an elongated lateral length of a light pipe that is
greater than a thickness of the light pipe. In such an embodiment,
a patterned bank layer 304 can be formed over the substrate, and a
reflective layer 312 formed within the openings and along sidewalls
of the openings of the patterned bank layer 304. In this manner,
light emitting laterally from the micro LED devices 100 and through
the light pipe 120 can be reflected out and through the layers
designed to tailor color emission (e.g. 110, 328) rather than being
absorbed by the black matrix 202 or other layers. In addition, back
reflection of light from overlying layers such as the wavelength
conversion layer 110 is not absorbed by the substrate and instead
reflected out of the light emitting device. The patterned
reflective layer may additionally increase efficiency of the
phosphor particles, since they emit light in all directions, light
that is emitted downward can be reflected out of the light emitting
device. In an embodiment, top contact 102 includes a reflective
layer. Where top contact 102 is reflective, light emission from the
micro LED device 100 will become largely dependent upon sidewall
emission. A reflective top contact 102 may additionally reduce the
amount of back reflection of light from overlying layers that is
absorbed by the micro LED device. In addition, the reflective top
contact 102 may increase efficiency of the phosphor particles,
since they emit light in all directions, light that is emitted
downward can be reflected out of the light emitting device.
[0104] In an embodiment, patterned bank layer 304 is formed of an
insulating material and may be formed by a variety of techniques
such as lamination, spin coating, CVD, and PVD. Patterned bank
layer 304 may be may be opaque, transparent, or semi-transparent to
the visible wavelength. Patterned bank layer 304 may be formed of a
variety of materials such as, but not limited to, photodefinable
acrylic, photoresist, silicon oxide (SiO.sub.2), silicon nitride
(SiN.sub.x), poly(methyl methacrylate) (PMMA), benzocyclobutene
(BCB), polyimide, acrylate, epoxy, and polyester. In an embodiment,
patterned bank layer is formed of an opaque material such as a
black matrix material. The patterned bank layer openings may be
formed using a suitable technique such as lithography, and may
expose the bottom electrode 310.
[0105] A reflective layer 312 is then formed over the patterned
bank layer 304 and within the openings spanning the sidewalls and
bottom surface of each of the openings. The reflective layer may be
electrically conducting. In an embodiment, the reflective layer 312
functions as the bottom electrode and a separate bottom electrode
310 is not required. The reflective layer 312 may be formed of a
number of conductive and reflective materials, and may include more
than one layer. In an embodiment, a reflective layer 312 comprises
a metallic film such as aluminum, molybdenum, titanium,
titanium-tungsten, silver, or gold, or alloys thereof. The
reflective layer 312 may also include a conductive material which
is not necessarily reflective, such as amorphous silicon,
transparent conductive oxides (TCO) such as indium-tin-oxide (ITO)
and indium-zinc-oxide (IZO), carbon nanotube film, or a transparent
conducting polymer such as poly(3,4-ethylenedioxythiophene)
(PEDOT), polyaniline, polyacetylene, polypyrrole, and
polythiophene. In an embodiment, the reflective layer includes a
stack of a conductive material and a reflective conductive
material. In an embodiment, the reflective layer includes a 3-layer
stack including top and bottom layers and a reflective middle layer
wherein one or both of the top and bottom layers are transparent.
In an embodiment, the reflective layer includes a conductive
oxide-reflective metal-conductive oxide 3-layer stack. The
conductive oxide layers may be transparent. For example, the
reflective layer 312 may include an ITO-silver-ITO layer stack. In
such a configuration, the top and bottom ITO layers may prevent
diffusion and/or oxidation of the reflective metal (silver) layer.
In an embodiment, the reflective layer includes a Ti--Al--Ti stack.
In an embodiment, the reflective layer includes an ITO-Ti-ITO
stack. In an embodiment, the reflective layer includes an
ITO-Ti--Al--Ti-ITO stack. In an embodiment, the reflective layer is
1 .mu.m or less in thickness. The reflective layer may be deposited
using a suitable technique such as, but not limited to, PVD.
[0106] In the embodiment illustrated the sidewall passivation layer
316 spans sidewalls of the micro LED device 100 and covers the
quantum well structure 108. In the embodiment illustrated the
sidewall passivation layer 316 also covers the bottom surface of
the reflective layer 312. The sidewall passivation layer 316 may
also cover the reflective layer 312 on top of the patterned bank
layer 304, however, this may also be aided by the formation of an
intermediate insulating material 317. As shown, the sidewall
passivation layer 316 may function in part to electrically insulate
the top electrode layer 318 from the reflective layer 312.
[0107] Still referring to FIGS. 9A-9B, the light pipe 120 may be
wider than the opening in the patterned bank layer 304 in which the
micro LED device 100 is bonded. Likewise, the wavelength conversion
layer 110 is wider than the opening in the patterned bank layer
304. Such a configuration may be used to ensure that light emitting
above substrate 201 passes through the layers designed to tailor
color emission (e.g. 110, 328).
[0108] FIG. 9C is a cross-sectional side view illustrations of a
light pipe around a plurality of micro LED devices with top and
bottom contacts within a plurality of reflective bank structures,
and a wavelength conversion layer over the light pipe in accordance
with embodiments of the invention. The configuration illustrated in
FIG. 9C is similar to that of FIG. 9B, with the difference being
that the light pipe 120 is formed over multiple subpixels in a
pixel, with each reflective layer 312 corresponding to a separate
subpixel that is independently addressable by its own underlying
circuitry 210. Similar to the configuration in FIGS. 9A-9B, the
wavelength conversion layer 110 may be wider than the openings in
the patterned bank layer 304 including the multiple reflective
layers 312.
[0109] FIGS. 9D-9E are cross-sectional side view illustrations of a
light pipe around a plurality of micro LED devices with bottom
contacts within a reflective bank structure, and a wavelength
conversion layer over the light pipe in accordance with embodiments
of the invention. FIG. 9F is a cross-sectional side view
illustrations of a light pipe around a plurality of micro LED
devices with bottom contacts within a plurality of reflective bank
structures, and a wavelength conversion layer over the light pipe
in accordance with embodiments of the invention. FIGS. 9D-9F are
similar to those of FIGS. 8D-8F with one difference being that the
micro LED devices 100 include bottom contacts 104, 103 rather than
both a bottom and top contact. As a result, it may not be required
to form a top electrode layer to contact the ground line 330.
Sidewall passivation layer 316 also may be omitted, and the light
pipe 120 or other layers can electrically insulate the reflective
layers 312A, 312B and quantum well structure 108. As illustrated,
reflective layers 312A, 312B are electrically insulated from one
another, and may resemble the configuration of the bottom
reflective layers 309A, 309B in FIG. 1B.
[0110] Referring now to FIGS. 10-11, alternative cover designs are
described and illustrated for packaging the light emitting devices
in accordance with embodiments. FIG. 10 is an illustration a single
side fabrication manner for applying wavelength conversion layers
and a black (or white) matrix between micro LED devices and light
pipes in accordance with an embodiment. As illustrated, the
wavelength conversion layers 110 and matrix 202 are formed on
substrate 201 prior to applying a cover 500 over the light emitting
devices and light pipes. Top cover 500 can be rigid or flexible,
and can be applied in a variety of manners. In an embodiment, top
cover 500 is a transparent plastic material and is laminated onto
the light emitting device configuration. In an embodiment, top
cover 500 is a rigid glass plate that is applied over the light
emitting device configuration, and sealed around the peripheral
edges of the substrate 201 with a sealant. A getter material may
optionally be placed inside the sealed region containing the micro
LED devices and the wavelength conversion layer 110 to absorb
moisture, particularly if the wavelength conversion layer includes
quantum dots.
[0111] FIG. 11 is an illustration of a top press down manner for
applying wavelength conversion layers and a black (or white) matrix
between micro LED devices and light pipes in accordance with an
embodiment. In the embodiment illustrated in FIG. 11, the matrix
202, wavelength conversion layer 110, oxygen barrier film 324, and
optional color filter layer 328 are formed on the top cover 500 and
pressed down over the array of micro LED devices 100 and light
pipes 120. In an embodiment, the top cover 500 of FIG. 11 is a
rigid glass plate, and is sealed around the peripheral edges of the
substrate 201 with a sealant. A getter material may optionally be
placed inside the sealed region containing the micro LED devices
and the wavelength conversion layer 110 to absorb moisture,
particularly if the wavelength conversion layer includes quantum
dots. Either of the top cover configurations of FIGS. 10-11 can be
used when forming the lighting or display devices described and
illustrated herein.
[0112] Referring now to FIGS. 12-16 top view schematic
illustrations are provided for various top and bottom electrode
configurations for lighting or display applications. It is to be
appreciated, that the configurations are exemplary and that
embodiments of the invention may be practiced using other
configurations for incorporating micro LED devices and light pipes
into light emitting devices. For example, each subpixel 206 is
illustrated as including three micro LED devices 100, which may be
within a light pipe. However, each subpixel may contain any number
of micro LED devices within a light pipe. Alternatively, the micro
LED devices 100 within a pixel 204 may be within a light pipe
spanning multiple subpixels 206, or all subpixels within the pixel.
A number of light pipe configurations are available. Referring now
to FIG. 12, in an embodiment a plurality of micro LED devices 100
are bonded to bottom electrode lines 310. In the embodiment
illustrated, ground lines 330 run perpendicular to the bottom
electrode lines 310, separated by an insulating layer.
Alternatively, the ground lines 330 and bottom electrode lines 310
are parallel to one another. In an embodiment, individual top
electrode layers 318 can be formed over the micro LED devices 100
within a single light pipe connecting those micro LED devices 100
to ground lines 330. In other embodiments, a single top electrode
layer 318 can connect a plurality of micro LED devices 100 from a
plurality of light pipes to a single ground line 318. Depending
upon the particular application, the lighting or display device may
include an array of pixels 204. In the particular embodiment,
illustrated each pixel 204 includes three subpixels 206, though
such an arrangement is exemplary.
[0113] Referring to FIG. 13, in an embodiment, the micro LED
devices 100 are bonded to electrode electrode traces 311 connected
with a bottom electrode line 310. Such a configuration may be
suitable for reducing likelihood of shorting between the ground
line 330 and bottom electrode line 310 with the top electrode
layers 318. In an embodiment, individual top electrode layers 318
can be formed over the micro LED devices 100 in a single light pipe
connecting those micro LED devices 100 to ground lines 330. In
other embodiments, a single top electrode layer 318 can connect a
plurality of micro LED devices 100 from a plurality of light pipes
to a single ground line 318.
[0114] Referring to FIG. 14, in an embodiment, micro LED devices
100 are placed on the bottom electrode lines 310, and the ground
lines 330 are formed over the micro LED devices 100, removing the
requirement to form top electrode lines 310 to connect the micro
LED devices to the ground lines 330. In this manner, the ground
lines 330 are also the top electrode lines. In an embodiment, a
plurality of ground lines 330 are formed over rows or columns of
micro LED devices and light pipes. In other embodiments, a single
ground plane 330 is formed over a plurality of rows/columns of
micro LED devices and light pipes.
[0115] FIGS. 15-16 differ from the embodiments illustrated in FIGS.
12-14 in that the bottom electrodes 310 are in the form of separate
pads. For example, rather than applying an operating current
through an end of an electrode line, the operating current can be
applied from below, which may be an electrode line or alternative
working circuitry such as TFT circuitry. In this manner, it may be
possible to address micro LED devices 100 within light pipes
individually, or as a single group within a light pipe, rather in
rows or columns. In the embodiment illustrated in FIG. 15 the micro
LED devices are placed on the bottom electrodes 310, and the ground
lines 330 are formed over the micro LED devices, removing the
requirement to form top electrode lines 310 to connect the micro
LED devices to the ground lines 330. In this manner, the ground
lines 330 are also the top electrode lines. In an embodiment, a
plurality of ground lines 330 are formed over rows or columns of
micro LED devices. In other embodiments, a single ground plane 330
is formed over a plurality of rows/columns of micro LED devices. In
the embodiment illustrated in FIG. 16 the micro LED devices are
placed on the bottom electrodes 310, and the top electrode layer
318 connect the micro LED devices to one or more ground lines 330.
In an embodiment, a single top electrode layer 318 connects a
plurality of micro LED devices 100 in a single light pipe to a
single ground line 330. In an embodiment, a single top electrode
layer 318 connects a row or column of micro LED devices 100 to a
ground line 330. In an embodiment, a top electrode layer 318 is
formed over a plurality of rows/columns of micro LED devices to
connect the plurality of micro LED devices and light pipes to a
ground line 330.
[0116] FIG. 17 illustrates a display system 1700 in accordance with
an embodiment. The display system houses a processor 1710, data
receiver 1720, a display 1730, and one or more display driver ICs
1740, which may be scan driver ICs and data driver ICs. The data
receiver 1720 may be configured to receive data wirelessly or
wired. Wireless may be implemented in any of a number of wireless
standards or protocols including, but not limited to, Wi-Fi (IEEE
802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term
evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS,
CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any
other wireless protocols that are designated as 3G, 4G, 5G, and
beyond. The one or more display driver ICs 1740 may be physically
and electrically coupled to the display 1730.
[0117] In some embodiments, the display 1730 includes one or more
micro LED devices 100 that are formed in accordance with
embodiments of the invention described above. For example, the
display 1730 may include a plurality of micro LED devices, a
plurality of light pipes around the micro LED devices, and a
plurality of wavelength conversion layers over the light pipes.
[0118] Depending on its applications, the display system 1700 may
include other components. These other components include, but are
not limited to, memory, a touch-screen controller, and a battery.
In various implementations, the display system 1700 may be a
television, tablet, phone, laptop, computer monitor, kiosk, digital
camera, handheld game console, media display, ebook display, or
large area signage display.
[0119] FIG. 18 illustrates a lighting system 1800 in accordance
with an embodiment. The lighting system houses a power supply 1810,
which may include a receiving interface 1820 for receiving power,
and a power control unit 1830 for controlling power to be supplied
to the light source 1840. Power may be supplied from outside the
lighting system 1800 or from a battery optionally included in the
lighting system 1800. In some embodiments, the light source 1840
includes one or more micro LED devices 100 that are formed in
accordance with embodiments of the invention described above. For
example, the light source 1840 may include a plurality of micro LED
devices, a plurality of light pipes around the micro LED devices,
and a plurality of wavelength conversion layers over the light
pipes. In various implementations, the lighting system 1800 may be
interior or exterior lighting applications, such as billboard
lighting, building lighting, street lighting, panel lighting, light
bulbs, and lamps.
[0120] In utilizing the various aspects of this invention, it would
become apparent to one skilled in the art that combinations or
variations of the above embodiments are possible for integrating
micro LED devices, light pipes, and wavelength conversion layers
into lighting and display application. Although the present
invention has been described in language specific to structural
features and/or methodological acts, it is to be understood that
the invention defined in the appended claims is not necessarily
limited to the specific features or acts described. The specific
features and acts disclosed are instead to be understood as
particularly graceful implementations of the claimed invention
useful for illustrating the present invention.
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