U.S. patent application number 16/228211 was filed with the patent office on 2019-06-27 for iii-nitride multi-color on wafer micro-led enabled by tunnel junctions.
This patent application is currently assigned to Lumileds LLC. The applicant listed for this patent is Lumileds LLC. Invention is credited to Robert Armitage, Parijat Pramil Deb, Isaac Harshman Wildeson.
Application Number | 20190198709 16/228211 |
Document ID | / |
Family ID | 66950675 |
Filed Date | 2019-06-27 |
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United States Patent
Application |
20190198709 |
Kind Code |
A1 |
Wildeson; Isaac Harshman ;
et al. |
June 27, 2019 |
III-NITRIDE MULTI-COLOR ON WAFER MICRO-LED ENABLED BY TUNNEL
JUNCTIONS
Abstract
A device may include a first light emitting diode (LED) on a
first surface of a substrate, a first tunnel junction on the first
LED a first semiconductor layer on the first tunnel junction, and a
conformal dielectric layer on at least a sidewall of the LED and
the first surface of the substrate.
Inventors: |
Wildeson; Isaac Harshman;
(San Jose, CA) ; Deb; Parijat Pramil; (San Jose,
CA) ; Armitage; Robert; (Los Altos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumileds LLC |
San Jose |
CA |
US |
|
|
Assignee: |
Lumileds LLC
San Jose
CA
|
Family ID: |
66950675 |
Appl. No.: |
16/228211 |
Filed: |
December 20, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62609359 |
Dec 22, 2017 |
|
|
|
62609447 |
Dec 22, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/007 20130101;
H04B 10/116 20130101; H01L 31/02019 20130101; H01L 2933/0016
20130101; H04B 10/572 20130101; H01L 31/02327 20130101; H01L 27/156
20130101; H01L 31/167 20130101; H01L 33/32 20130101; H01L 33/62
20130101; H05B 47/19 20200101; H01L 33/06 20130101; H01L 33/50
20130101; H01L 33/38 20130101; H01L 33/0075 20130101; H01L 27/153
20130101; H01L 33/08 20130101; H05B 45/20 20200101 |
International
Class: |
H01L 33/06 20060101
H01L033/06; H01L 33/00 20060101 H01L033/00; H01L 33/32 20060101
H01L033/32; H01L 33/62 20060101 H01L033/62; H01L 33/50 20060101
H01L033/50; H01L 27/15 20060101 H01L027/15 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2018 |
EP |
18163287.8 |
Mar 26, 2018 |
EP |
18163994.9 |
Claims
1. A device comprising: a first light emitting diode (LED) on a
first surface of a substrate; a first tunnel junction on the first
LED; a first semiconductor layer on the first tunnel junction; and
a conformal dielectric layer on at least a sidewall of the LED and
the first surface of the substrate.
2. The device of claim 1, further comprising: a first contact on a
layer of the first LED; and a second contact on the first
semiconductor layer.
3. The device of claim 1, further comprising: a second LED on the
first tunnel junction, the second LED comprising the first
semiconductor layer; a second tunnel junction on the second LED;
and a second semiconductor layer on the second tunnel junction.
4. The device of claim 3, further comprising: a third contact on a
layer of the second LED; and a fourth contact on the second
semiconductor layer.
5. The device of claim 3, further comprising: a third LED on the
second tunnel junction, the third LED comprising the second
semiconductor layer.
6. The device of claim 5, further comprising: a fifth contact on a
first layer of the third LED; and a sixth contact on a second layer
of the third LED.
7. The device of claim 5, further comprising the conformal
dielectric layer on the first tunnel junction, the second LED, the
second tunnel junction, and the third LED.
8. A light emitting diode (LED) array comprising: a first pixel and
a second pixel on a substrate, the first pixel and the second pixel
comprising one or more tunnel junctions on one or more LEDs; and a
first trench between the first pixel and the second pixel, the
trench extending to the substrate.
9. The LED array of claim 8, wherein the first pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; and a first semiconductor layer on the tunnel junction.
10. The LED array of claim 9, further comprising: a first contact
on a layer of the first LED; and a second contact on the first
semiconductor layer.
11. The LED array of claim 8, wherein the second pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; a second LED on the first tunnel junction; a second tunnel
junction of the second LED; and a second semiconductor layer on the
second tunnel junction.
12. The LED array of claim 11, further comprising: a second contact
on a layer of the second LED; and a second contact on the second
semiconductor layer.
13. The LED array of claim 8, further comprising: a third pixel on
the substrate, the third pixel comprising one or more tunnel
junctions formed on one or more LEDs; and a second trench between
the second pixel and the third pixel, the second trench extending
to the substrate.
14. The LED array of claim 13, wherein the third pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; a second LED on the first tunnel junction; a second tunnel
junction on the second LED; and a third LED on the second tunnel
junction.
15. The LED array of claim 14, further comprising: a fifth contact
on a first layer of the third LED; and a sixth contact on a second
layer of the third LED.
16. A method comprising: forming one or more LEDs and one or more
tunnel junctions on a substrate; and forming a first trench through
the one or more tunnel junctions and the one or more LEDs to define
a first pixel and a second pixel, the first trench extending to the
substrate.
17. The method of claim 16, wherein the first pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; and a first semiconductor layer on the tunnel junction.
18. The method of claim 16, wherein the second pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; a second LED on the first tunnel junction; a second tunnel
junction of the second LED; and a second semiconductor layer on the
second tunnel junction.
19. The method of claim 16, further comprising: forming a second
trench through the one or more tunnel junctions and the one or more
LEDs to define the second pixel and a third pixel, the second
trench extending to the substrate.
20. The method of claim 19, wherein the third pixel comprises: a
first LED on the substrate; a first tunnel junction on the first
LED; a second LED on the first tunnel junction; a second tunnel
junction on the second LED; and a third LED on the second tunnel
junction.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/609,447 filed on Dec. 22, 2017, U.S. Provisional
Application No. 62/609,359 filed on Dec. 22, 2017, European Patent
Application No. 18163287.8 filed on Mar. 22, 2018, and European
Patent Application No. 18163994.9 filed on Mar. 26, 2018, the
contents of which are hereby incorporated by reference herein.
BACKGROUND
[0002] Micro-LEDs (uLEDs) may be small size LEDs (typically
.about.50 um in diameter or smaller) that can be used to produce
very high-resolution color displays when uLEDs of red, blue and
green wavelengths may be aligned in close proximity. Manufacture of
an uLED display typically involves picking singulated uLEDs from
separate blue, green and red WL wafers and aligning them in
alternating close proximity on the display. Due to the small size
of each uLED, this picking, aligning, and attaching assembly
sequence is slow and failure prone. Even worse, since improving
resolution generally requires decreasing uLED size, the intricacy
and difficulty in pick and place operations needed to populate a
high resolution uLED display can make them too expensive for
widespread use.
SUMMARY
[0003] A device may include a first light emitting diode (LED) on a
first surface of a substrate, a first tunnel junction on the first
LEDa first semiconductor layer on the first tunnel junction, and a
conformal dielectric layer on at least a sidewall of the LED and
the first surface of the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] A more detailed understanding can be had from the following
description, given by way of example in conjunction with the
accompanying drawings wherein:
[0005] FIG. 1A shows a multiple quantum well light emitting diode
(LED);
[0006] FIG. 1B shows etching a first LED, a second LED, a third
LED, a first tunnel junction, and second tunnel junction to form
one or more channels;
[0007] FIG. 1C shows removing different portions of the first LED,
the first tunnel junction, the second LED, the second tunnel
junction, and the third LED;
[0008] FIG. 1D shows a third etching step may to further define
pixels;
[0009] FIG. 1E shows forming a blanket conformal dielectric
layer;
[0010] FIG. 1F shows forming openings in the conformal dielectric
layer;
[0011] FIG. 1G shows forming contacts in the openings;
[0012] FIG. 1H shows forming another contact in an opening to form
an LED array;
[0013] FIG. 1I shows attaching the LED array to an LED device
attach region;
[0014] FIG. 1J shows another example of an LED array;
[0015] FIG. 1K shows the LED array forming a part of a visible
light communication (VLC) system;
[0016] FIG. 1L shows a VLC receiver;
[0017] FIG. 1M is a flowchart illustrating a method of use;
[0018] FIG. 1N is a flowchart illustrating a method of forming a
device;
[0019] FIG. 2A is a diagram showing an Light Emitting Diode (LED)
device;
[0020] FIG. 2B is a diagram showing multiple LED devices;
[0021] FIG. 3 is a top view of an electronics board for an
integrated LED lighting system according to one embodiment;
[0022] FIG. 4A is a top view of the electronics board with LED
array attached to the substrate at the LED device attach region in
one embodiment;
[0023] FIG. 4B is a diagram of one embodiment of a two channel
integrated LED lighting system with electronic components mounted
on two surfaces of a circuit board; and
[0024] FIG. 5 is a diagram of an example application system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Examples of different light illumination systems and/or
light emitting diode implementations will be described more fully
hereinafter with reference to the accompanying drawings. These
examples are not mutually exclusive, and features found in one
example may be combined with features found in one or more other
examples to achieve additional implementations. Accordingly, it
will be understood that the examples shown in the accompanying
drawings are provided for illustrative purposes only and they are
not intended to limit the disclosure in any way. Like numbers refer
to like elements throughout.
[0026] It will be understood that, although the terms first,
second, third, etc. may be used herein to describe various
elements, these elements should not be limited by these terms.
These terms may be used to distinguish one element from another.
For example, a first element may be termed a second element and a
second element may be termed a first element without departing from
the scope of the present invention. As used herein, the term
"and/or" may include any and all combinations of one or more of the
associated listed items.
[0027] It will be understood that when an element such as a layer,
region, or substrate is referred to as being "on" or extending
"onto" another element, it may be directly on or extend directly
onto the other element or intervening elements may also be present.
In contrast, when an element is referred to as being "directly on"
or extending "directly onto" another element, there may be no
intervening elements present. It will also be understood that when
an element is referred to as being "connected" or "coupled" to
another element, it may be directly connected or coupled to the
other element and/or connected or coupled to the other element via
one or more intervening elements. In contrast, when an element is
referred to as being "directly connected" or "directly coupled" to
another element, there are no intervening elements present between
the element and the other element. It will be understood that these
terms are intended to encompass different orientations of the
element in addition to any orientation depicted in the figures.
[0028] Relative terms such as "below," "above," "upper,", "lower,"
"horizontal" or "vertical" may be used herein to describe a
relationship of one element, layer, or region to another element,
layer, or region as illustrated in the figures. It will be
understood that these terms are intended to encompass different
orientations of the device in addition to the orientation depicted
in the figures.
[0029] Semiconductor light emitting devices or optical power
emitting devices, such as devices that emit ultraviolet (UV) or
infrared (IR) optical power, are among the most efficient light
sources currently available. These devices may include light
emitting diodes, resonant cavity light emitting diodes, vertical
cavity laser diodes, edge emitting lasers, or the like (hereinafter
referred to as "LEDs"). Due to their compact size and lower power
requirements, for example, LEDs may be attractive candidates for
many different applications. For example, they may be used as light
sources (e.g., flash lights and camera flashes) for hand-held
battery-powered devices, such as cameras and cell phones. They may
also be used, for example, for automotive lighting, heads up
display (HUD) lighting, horticultural lighting, street lighting,
torch for video, general illumination (e.g., home, shop, office and
studio lighting, theater/stage lighting and architectural
lighting), augmented reality (AR) lighting, virtual reality (VR)
lighting, as back lights for displays, and IR spectroscopy. A
single LED may provide light that is less bright than an
incandescent light source, and, therefore, multi-junction devices
or arrays of LEDs (such as monolithic LED arrays, micro LED arrays,
etc.) may be used for applications where more brightness is desired
or required.
[0030] The present disclosure generally relates manufacture of
micro light emitting diode (uLED) displays and of multi-wavelength
light emitters with large bandwidth for free-space visible light
communications. Epitaxial tunnel junctions may be used to combine
multiple emission wavelengths within a single LED device.
[0031] Manufacturing uLEDs could be simplified if two or more
active regions emitting different wavelengths may be integrated
within a single wafer. Such an approach may be possible within the
AlInGaN materials system since it has been demonstrated that blue,
green and red LEDs can be all made in this system. However, use of
a multi-color chip in a uLED display requires not only stacking
multiple layers able to emit at different wavelengths within a
single epitaxial growth run, but also requires an ability to change
respective emission intensity ratios between the emitters of
different wavelengths.
[0032] One possible way to make a multicolor uLED chip may be to
form multiple quantum wells (MQW) able to emit red, green, and blue
light within a single active region, i.e. between the p- and
n-layers of one p-n junction. With an optimized growth order of the
multiple quantum wells, an LED with one predominant color that can
be changed depending on the driving current, e.g., it may appear
predominantly red at low current, predominantly green at
intermediate current, and predominantly blue at high current.
However, this type of color control mechanism makes it difficult to
adjust the surface radiance and dominant wavelength of the LED
independently of each other, and consequent color purity can be
poor.
[0033] As an alternative, two or more pixels of different
wavelengths in the same device footprint can be formed by growing
an LED of several p-n junctions within the same epitaxial wafer. A
multi-level mesa etching procedure can be executed to make
independent electrical contacts to each of the p-n junctions. One
or more emitter layers of different wavelengths can be embedded in
separate p-n junctions with separate current paths so the
wavelength and radiance can be controlled independently.
Unfortunately, given current post-epitaxial device processing
limitations it may be difficult to manufacture such multiple
wavelength uLEDs. Dry etching may be usually needed to open vias
for contacting buried layers. The dry etch process introduces
atomic-level damage to the crystal that changes its conductivity
type from p-type to n-type. Due to this conductivity type
conversion it may not be possible to obtain an ohmic contact of low
resistance to a buried p-type nitride surface that has been exposed
by dry etching. In effect, creating a non-ohmic contact to an
etched p-GaN surface can result in a forward voltage penalty of one
volt or more for some of the active regions. Such a large forward
voltage may not be considered practical with respect to the power
consumption requirements of micro-displays.
[0034] In accordance with other embodiments of the invention, a
multiple quantum well LED suitable for wafer-scale uLEDs can
include a first LED including a group of quantum wells able to emit
light of a first wavelength. A second LED including a group of
quantum wells may also be formed, with the second LED able to emit
light of a second wavelength distinct from the wavelength emitted
by the first LED. A tunnel junction layer may be formed to separate
the first and second LEDs. The quantum wells in the LEDs may be
caused to emit light injecting current from independent electrical
contacts that extend to each of the first and second LEDs. In some
embodiments, three or more LEDs can be defined to allow for RGB
uLEDs.
[0035] In another embodiment, a method of manufacturing a multiple
quantum well LED includes forming a first LED including a group of
quantum wells on a substrate. A tunnel junction layer may be formed
on the first LED, and a second LED may be formed on the tunnel
junction layer. At least one channel with sidewalls may be etched
through the first LED to define at least two light emission regions
in the multiple quantum well LED. Metal contacts can be applied to
provide independent electrical contacts to each of the first and
second groups of quantum wells. The p-GaN layers can be activated,
at least in part, after an anneal promoting hydrogen diffusion
through the sidewall of an etch channel. In some embodiments, the
channel with sidewalls may be etched through to the substrate,
while in other embodiments etching only proceeds to a n-GaN layer
positioned on the substrate.
[0036] FIG. 1A illustrates multiple LEDs formed on a substrate that
may be used to form an LED. The LED may have multiple quantum
wells, multiple defined channels separating the LED into different
pixels, and/or discrete wavelength emitter sites for visual light
communication (VLC). The uLED device may include a mesa structure
and independent electrical contacts.
[0037] In the following description, it will be understood that the
terms light emission, color, red/green/blue, and RGB may include
any light mostly composed of, centered upon, or predominantly
having a specified wavelength. In some embodiments, light emission
may also include non-visible light, including near IR and UV light.
In other embodiments, multiple quantum wells can support closely
matched but still distinct emission wavelengths (e.g.,
independently modulated dual blue emitters having respective 430 nm
and 460 nm peak wavelengths).
[0038] Referring now to FIG. 1A, a multiple quantum well LED may
include a substrate 106 which may be formed from patterned or
unpatterned sapphire. In some embodiments the substrate 106 may be
polished and used to form at least a portion of a display. The
substrate 106 may support light emitting LEDs that can include
multiple p and n-layers sandwiching one or more groups of quantum
wells, with at least some of the quantum wells forming active
regions capable of light emission. For example, the substrate 106
may support a first group of quantum wells positioned between n-GaN
and p-GaN layers to form a first LED 101 able to emit light of a
first wavelength (e.g., blue). A second group of quantum wells may
be positioned between n-GaN and p-GaN layers to form a second LED
103 able to emit light of a second wavelength (e.g., green)
distinct from the first wavelength, with a first tunnel junction
102 separating the first LED 101 and the second LED 103. A second
tunnel junction layer 104 may be formed on the second LED 103 and a
third group of quantum wells may be positioned between n-GaN and
p-GaN layers to form a third LED 105 able to emit light of a third
wavelength (e.g., red) distinct from the first and second
wavelengths. As described below, independent electrical contacts
may be formed as contact pairs to provide sufficient voltage and
current to induce light emission from each of the first LED 101,
the second LED 103, and the third LED 105 from a suitable printed
circuit board. In some embodiments, each of the first LED 101, the
second LED 103, and the third LED 105 may be independently voltage
biased.
[0039] Advantageously, as compared to a uLED display made from
conventional single-wavelength uLEDs, the number of epitaxial
growth runs required to produce source die for uLED displays may be
reduced to one third (or one half if stacking only two wavelengths)
of the number or runs required with existing methods, reducing cost
and improving throughput at the epi manufacturing stage. In
addition, the number of pick and place operations required to
populate a display may be halved or cut to a third, since two or
three pixels may be transferrable in each pick and place
operation.
[0040] For even more efficient manufacture, in wafer scale
embodiments that allow for all required wavelengths to be
efficiently grown on one epi wafer, there may be no required pick
and place. The display uLEDs can remain on a continuous polished
sapphire support/substrate that can form a part of the packaging of
the uLED display.
[0041] As another advantage, since all contacts to buried layers
can be made to n-GaN surfaces, the disclosed structures and methods
avoid problems associated with making an ohmic electrical contact
to etched p-GaN surfaces, making possible lower operating voltage
and higher wall-plug efficiency. The number of etching steps to
make all necessary electrical contacts may be also reduced, and
restrictions on control of the etching rate may be relaxed since
all etched contacts in the tunnel junction invention may be made to
thick n-GaN layers (versus generally thinner p-GaN layers), even
while maintaining high LED efficiency.
[0042] As seen in FIG. 1A, multiple LEDs of quantum wells capable
of light emission of various wavelengths may be formed on a
substrate 106. The substrate 106 may be capable of supporting
epitaxial III-nitride film growth. The substrate 106 may compose,
for example, sapphire, patterned sapphire, or silicon carbide. A
first LED 101 may be formed on the substrate 106. The first LED may
compose any Group III-V semiconductors, including binary, ternary,
and quaternary alloys of gallium, aluminum, indium, and nitrogen,
also referred to as III-nitride materials. In an example, the first
LED 101 may compose GaN. The first LED 101 may be formed using
conventional deposition techniques, such as metal-organic chemical
vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other
epitaxial techniques. In an epitaxial deposition process, chemical
reactants provided by one or more source gases may be controlled
and the system parameters may be set so that depositing atoms
arrive at a deposition surface with sufficient energy to move
around on the surface and orient themselves to the crystal
arrangement of the atoms of the deposition surface. Accordingly,
the first LED 101 may be grown on the substrate 106 using
conventional epitaxial techniques.
[0043] The first LED 101 may be formed from any applicable material
to emit photons when excited. More specifically the first LED 101
may be formed from III-V semiconductors including, but not limited
to, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs,
InSb, II-VI semiconductors including, but not limited to, ZnS,
ZnSe, CdSe, CdTe, group IV semiconductors including, but not
limited to Ge, Si, SiC, and mixtures or alloys thereof.
[0044] The first LED 101 may include a first semiconductor layer
107, an active region 108 on the first semiconductor layer 107, and
a second semiconductor layer 109 on the active region 108. The
first semiconductor layer 107 may be an n-type layer and one or
more layers of semiconductor material that include different
compositions and dopant concentrations including, for example,
preparation layers, such as buffer or nucleation layers, and/or
layers designed to facilitate removal of the growth substrate.
These layers may be n-type or not intentionally doped, or may even
be p-type device layers. The layers may be designed for particular
optical, material, or electrical properties desirable for the light
emitting region to efficiently emit light. The active region 108
may be between the first semiconductor layer 107 and the second
semiconductor layer 109 and may receive a current such that the
active region 108 emits light beams. The second semiconductor layer
109 may be a p-type layer and may include multiple layers of
different composition, thickness, and dopant concentrations,
including layers that may not be intentionally doped, or n-type
layers. An electrical current may be caused to flow through the p-n
junction (e.g., via contacts) in the active region 108 and the
active region 108 may generate light of a first wavelength
determined at least in part by the bandgap energy of the materials.
The first LED 101 may include one more quantum wells.
[0045] A first tunnel junction 102 may be formed on the first LED
101. The first tunnel junction 102 may be a barrier layer, such as
a thin insulating layer or electric potential. The first tunnel
junction may be between two electrically conducting materials.
Electrons (or quasiparticles) may pass through the first tunnel
junction 102 by the process of quantum tunneling. The first tunnel
junction 102 may be formed using conventional deposition
techniques, such as MOCVD), MBE, or other epitaxial techniques.
[0046] A second LED 103 may be formed on the first tunnel junction
102. The second LED 103 may be similar to the first LED 101 and may
be composed of similar layers. The second LED 103 may be formed
using similar techniques as those described above with reference to
the first LED 101.
[0047] A second tunnel junction 104 may be formed on the second LED
103. The second tunnel junction 104 may be similar to the first
tunnel junction and may be composed of similar layers. The second
tunnel junction 104 may be formed using similar techniques as those
described above with reference to the first tunnel junction
102.
[0048] A third LED 105 may be formed on the second tunnel junction
104. The third LED 105 may be similar to the first LED 101 and may
be composed of similar layers. The third LED 105 may be formed
using similar techniques as those described above with reference to
the first LED 101.
[0049] The first semiconductor layer 107, the active region 108,
and the third semiconductor layer 109 of each LED may be composed
of different materials, such that one or more of the first LED 101,
the second LED 103, and the third LED 105 emit a light of a
different wavelength. For example, the first LED 101, the second
LED 103, and the third LED 105 may emit different red, green, and
blue light. In another example, the first LED 101, the second LED
103, and the third LED 105 may emit light of different wavelengths
(e.g., separated by approximately 10-30 nm) within a specific color
range (e.g., 420-480 nm).
[0050] While any order of arranging different LEDs may be possible,
in one embodiment a LED having an active region that emits the
shortest wavelength may be the first one grown in the sequence.
This arrangement may avoid or minimize internal absorption of the
blue emission by the active regions of longer wavelengths.
[0051] Epitaxial growth conditions can be similar to those required
for a conventional blue LED growth run using patterned or
non-patterned sapphire substrates. After completing sequential
growth of a n-GaN layer, blue-emitting multiple quantum wells, and
a p-GaN layer that collectively form the LED 101 capable of
emitting blue light, growth conditions may be changed to grow the
first tunnel junction 102.
[0052] After formation of the first tunnel junction 102, the second
LED 103 capable of emitting green light may be formed. The second
LED 103 may be also grown in a manner similar to that of a
conventional green LED. The thickness and/or growth conditions of
an n-contact layer may be further modified. After completing the
second semiconductor layer 109 of the second LED 103, a second
tunnel junction 104 may be grown.
[0053] The third LED 105 may be a red light emitting InGaN LED.
Growth of the third LED 105 may be similar to that of a
conventional red LED, but the thickness and/or growth conditions of
an n-contact layer can be further modified.
[0054] As will be appreciated, various designs for the first tunnel
junction 102 and the second tunnel junction 104 or LED active
regions can be used. The first tunnel junction 102 and the second
tunnel junction 104 may aid in lateral current spreading, and may
include any layer of different Group III elemental composition
and/or different doping concentration to both the first
semiconductor layer 107 and the second semiconductor layer 109. The
first tunnel junction 102 and the second tunnel junction 104 may
utilize polarization dipoles which naturally occur at interfaces
between nitride layers of different Group III elemental
compositions. The first tunnel junction 102 and the second tunnel
junction 104 may be created by forming layers of low resistance
p-type confinement in conjunction with various impurities able to
generate mid gap states.
[0055] Referring now to FIG. 1B, the first LED 101, the second LED
103, and the third LED 105, each having multiple quantum wells, and
the first tunnel junction 102 and the second tunnel junction 104
may be etched. The etching may include conventional
photolithography and dry etch processes to define one or more
channels. A first channel 111 may define a first pixel 113 and a
second pixel 114. A second channel 112 may define the second pixel
114 and a third pixel 115.
[0056] Conventional dry etching processes may be used, but various
combinations of masks and etch depths may be required. The
conventional photoresist exposure, develop, strip and clean steps
may be understood in the art and have been omitted from the figure.
Layers of a conventional photoresist 116 may be formed on the first
pixel 113, the second pixel 114, and the third pixel 115.
[0057] The first channel 111 and the second channel 112 may be
formed by leaving portions of the LEDs unmasked during the etching.
A deep etch down to the substrate 106 may be desired for these
locations. A first etching process may effectively stop on the
sapphire due to its very slow etching rate relative to epitaxial
layers of the LEDs.
[0058] A surface of the first semiconductor layer 107 in the first
LED 101 may be left during the etching process to serves as an
n-contact 110 for the first pixel.
[0059] Referring now to FIG. 1C, different portions of the first
LED 101, the first tunnel junction 102, the second LED 103, the
second tunnel junction 104, and the third LED 105 may be removed in
a second etching process to further define the different
pixels.
[0060] Each of the first channel 111 and the second channel 112 may
be extended to expose the substrate 106. The first pixel 113 may be
etched to expose an upper surface 117 of the first semiconductor
layer 107 in the second LED 103. The surface 117 may serve as a
p-type contact for the first pixel 113 The second pixel 114 may be
etched to expose the upper surface 117 of the first semiconductor
layer 107 in the second LED 103 as well. The surface 118 may serve
as an n-type contact for the second pixel 114.
[0061] Referring now to FIG. 1D, a third etching step may be
performed to further define the pixels. The second pixel 114 may be
etched to expose an upper surface 119 of the first semiconductor
layer 107 in the third LED 105. The surface 119 may serve as a
p-type contact for the second pixel 114.
[0062] The third pixel 115 may be etched to expose the upper
surface 120 of the first semiconductor layer 107 in the third LED
105. The surface 120 may serve as an n-type contact for the third
pixel 115. The unetched second semiconductor layer 109 in the third
LED 105 may serve as an n-contact 120 for the third pixel 115. In
effect, etches to the p-contact for the first pixel 113 and the
second pixel 114 may remove light absorbing layers for those pixels
(e.g., green and red LEDs may absorb light emitted from a blue
LED).
[0063] It should be noted that the first pixel 113, the second
pixel 114, and the third pixel 115 may be formed in any combination
and in any configuration. For example, more than one of the first
pixel 113, the second pixel 114, and the third pixel 115 may be
adjacent to one another. In addition, the first pixel 113, the
second pixel 114, and the third pixel 115 may be arranged such that
the first pixel 113 is adjacent to the third pixel 115. In
addition, a device may be formed that includes one type of pixel,
two types of pixels, or all three types of pixels. In addition, the
number of LEDs and tunnel junctions described above is not meant to
be limiting.
[0064] In an example, p-GaN activation may be accomplished by
facilitating lateral diffusion of hydrogen through sidewalls of the
etched channels, an anneal can be done following photoresist strip
and cleaning (i.e. after completion of the third dry etch shown in
FIG. 1D). It may be advantageous to anneal at this time, rather
than earlier in the process, because the defined channels between
the pixels may provide an efficient path for lateral diffusion and
escape of hydrogen from the p-GaN layers. Activation anneal process
conditions promoting hydrogen diffusion may be similar to, or
different from, those of a conventional LED and no special
annealing conditions may be claimed here. Alternatively, epitaxial
processes with minimal hydrogen (e.g., MBE or RPCVD) could be used
for growing the tunnel junctions and an anneal to remove hydrogen
by lateral diffusion would not be required.
[0065] After the p-GaN activation anneal, various additive
processing steps may be needed to define electrical connections to
the pixels.
[0066] As seen in FIG. 1E, a conformal dielectric layer 122 may be
formed on the first pixel 113, the second pixel 114, and the third
pixel 115. The conformal dielectric layer 122 may be formed using a
conventional deposition process, such as plasma-enhanced chemical
vapor deposition. The conformal dielectric layer 122 may compose
dielectric material such as silicon dioxide. The conformal
dielectric layer 122 may be formed The electrically insulating
conformal dielectric layer 122 may passivate mesa sidewalls and
isolate from each other the metal contact pads that will be
deposited in later process steps.
[0067] Referring now to FIG. 1F, openings may be formed in the
conformal dielectric layer 122. Portions of the conformal
dielectric layer 122 may be masked with the resist 116 as shown
above with reference to FIG. 1D and portions may remain exposed.
The exposed portions may be removed using a conventional etching
process, such as dry action. A first opening 123 may be formed on
the first pixel 113 to expose the first semiconductor layer 107 of
the first LED 101. A second opening 124 may be formed on the first
pixel 113 to expose the first semiconductor layer 107 of the second
LED 103. A third opening 125 may be formed on the second pixel 114
to expose the first semiconductor layer 107 of the second LED 103.
A fourth opening 126 may be formed on the second pixel 114 to
expose the first semiconductor layer 107 of the third LED 105. A
fifth opening 127 may be formed on the third pixel 115 to expose
the first semiconductor layer 107 of the third LED 105. A sixth
opening 128 may be formed on the third pixel 115 to expose the
second semiconductor layer 109 of the third LED 105.
[0068] Referring now to FIG. 1G, a metal, for example an
aluminum/gold bilayer may be evaporated for metallization and
patterned by lift-off to form one or more of a first contact 129a,
a second contact 129b, a third contact 129c, a fourth contact 129c,
and fifth contact 129d. The lift-off mask openings may coincide
with openings in the dielectric as shown in FIG. 1G. The first
contact 129a may be formed in the first opening 123 and may be on
the first semiconductor layer 107 of the first LED 101. The first
contact 129a may be an n-type contact for the first pixel 113. The
second contact 129b may be formed in the second opening 124 and may
be on the first semiconductor layer 107 of the second LED 103 in
the first pixel 113. The second contact 129b may be a p-type
contact for the first pixel 113.
[0069] The third contact 129c may be formed in the third opening
125 and may be on the first semiconductor layer 107 of the second
LED 103 in the second pixel 114. The third contact 129c may be an
n-type contact for the second pixel 114. The fourth contact 129d
may be formed in the fourth opening 126 and may be on the first
semiconductor layer 107 of the third LED 105 in the second pixel
114. The fourth contact 129d may be a p-type contact for the second
pixel 114.
[0070] The fifth contact 129d may be formed in the fifth opening
127 and may be on the first semiconductor layer 107 of the third
LED 105 in the third pixel 115. The fifth contact 129d may be an
n-type contact for the third pixel 115.
[0071] As shown in FIG. 1H, a sixth contact 130 may be formed in
the sixth opening 128 on the third pixel 115 using a metallization
process. The sixth contact 130 may compose silver and may be
similarly evaporated and patterned onto the second semiconductor
layer 109 of the third LED 105 to form an LED array 121 as shown in
FIG. 1H.
[0072] As seen with respect to FIG. 1I, after wafer singulation,
the LED array 121 may be attached to a LED device attach region
318, as described in further detail below. In an example, the LED
device attach region 318 may be a complementary metal oxide
semiconductor (CMOS) integrated circuit (IC) array having metal
interconnect bonding corresponding to the contacts formed on the
LED array 121. A first surface of the LED device attach region 318
may have one or more interconnect bumps corresponding to the
contacts on the pixels. The interconnect bumps may have different
heights defined to match the first pixel 113, the second pixel 114,
and the third pixel 115, allowing use of substantially same size
interconnect bonding structures. In other variations, the first
surface of the LED device attach region 318 may be substantially
flat, and interposers or connecting pillars of differing height can
be used. Driver circuitry as described below with FIG. 4B may be
coupled to the LED device attach region 318 to allow each contact
pair of the first pixel 113, the second pixel 114, and the third
pixel 115 to be biased independently at a desired voltage. For
example, the driver circuitry may include a driver configured to
provide a first driving current to a first pair of electrodes 152
coupled to the first pair of contacts (129a and 129b), a second
pair of electrodes 154 coupled to the second pair of contacts (129c
and 129d), and a third pair of electrodes 156 coupled to the third
pair of contacts (129e and 130).
[0073] For example, the LED device attach region 318 may be
configured to provide a voltage to only the first contact 129a and
the second contact 129b of the first pixel 113 (collectively
referred to as a first pair of contacts), a voltage to only the
third contact 129c and the fourth contact 129d of the second pixel
114 (collectively referred to as a second pair of contacts), and a
voltage to only the fifth contact 129e and the sixth contact 130 of
the third pixel 115 (collectively referred to as a third pair of
contacts). The LED device attach region 318 may be configured to
provide voltages in any combination of those described above. The
LED device attach region 318 may be coupled to the LED device
attach region 318 described below with reference to FIG. 3.
[0074] Light of a first wavelength be emitted from the first pixel
113, light of a second wavelength may be emitted from the second
pixel 114, and light of a third wavelength may be emitted from the
third pixel through the substrate 106.
[0075] Referring now to FIG. 1J, another example of an LED array
138 is shown. The LED array 138 may be formed using the same or
similar epitaxial growth processes and wafer processing steps as
described above, but using a different mask set to etch the
different layers. The masks used for this embodiment may be
modified to prevent etching of a channel down to the substrate
106.
[0076] The channels 136, 137, and 139 may be masked for all etching
steps, but may be left unmasked for the metal deposition steps
described above. This may result in an LED array 138 having a first
common electrode 132 that may be used for the p-contact of the
first pixel 113 and the n-contact of the second pixel 114 and a
second common electrode 133 that may be used for the p-contact of
the second pixel 114 and the n-contact of the third pixel 115. It
may be possible to generate electroluminescence from any one of the
individual active regions or any combination thereof (including all
three) by applying appropriate bias to the driving electrodes 132,
133, or 135 relative to a ground electrode 134. For example, the
driving voltage may be a combination of 3/6/9V that results in the
illumination of the first pixel 113, the second pixel 114, and the
third pixel 115 together. A combination of 3/3/6V may result in the
illumination of the third pixel 115 and the first pixel 113 without
passing any current through the second pixel 114.
[0077] While potentially requiring greater voltages when the first
LED 101, the second LED 103, and the third LED 105 may be
simultaneously emitting light, the LED array 138 may support higher
pixel resolution due to reduction of overall footprint of the LED
array 138 (i.e., a single uLED may produce all wavelengths which
previously required 3 uLEDs to produce). The smaller footprint may
be a result of the smaller required electrical contact area, and
the lack of isolating gaps between the pixels of separate
wavelengths. Complexity of the printed circuit board may also be
reduced.
[0078] To support an ever-increasing volume of data traffic
transmitted using wireless communications, development of Gbit/sec
class communication systems is necessary. However, there is
currently insufficient available radio spectrum to develop
radio-frequency wireless systems with speeds in the Gbit/sec range.
One alternative to radio-frequency wireless is provided by visible
light communications (VLC) that use wavelengths in the visible
region of the spectrum. VLC is a data communications variant which
uses visible light between 140 and 800 THz (780-375 nm). VLC is a
subset of optical wireless communications technologies. VLC may use
fluorescent lamps (e.g., ordinary lamps, not special communications
devices) to transmit signals at 10 kbit/s, or LEDs for up to 112
Mbit/s over short distances. Systems may be able to transmit at
full Ethernet speed (10 Mbit/s) over distances of 1-2 kilometres
(0.6-1.2 mi).
[0079] Specially designed electronic devices generally containing a
photodiode may receive signals from light sources, although in some
cases conventional cell phone cameras or digital cameras may be
sufficient. The image sensor used in these devices may be an array
of photodiodes (i.e., pixels) and in some applications, the use of
LED arrays may be preferred over a single photodiode. Such a sensor
may provide either multi-channel (e.g., 1 pixel=1 channel) or a
spatial awareness of multiple light sources.
[0080] VLC may potentially provide on the order of THz/sec of
unlicensed band-width, support a high degree of spatial reuse, and
allow for higher security due to inherent difficulties in
intercepting. Furthermore, VLC can use existing infrastructure
designed for illumination which can make possible an additional
wireless transmission capacity with comparatively small capital
investment.
[0081] The data transmission rates possible with conventional
phosphor-converted white LEDs may be generally limited to under 100
MBps due to the slow temporal response of the phosphor among other
factors. On the other hand, a white light source that mixes
wavelengths emitted from two or more independently modulated LED
sources has increased bandwidth and is capable of data transmission
rates up to 5 GBps.
[0082] A white light source comprised of three separate blue,
green, and red LED chips could satisfy the requirements for both
illumination and high bandwidth VLC applications. Alternatively,
multiple blue chips (each with a phosphor to make white light) with
peak wavelengths (WLs) differing by 20 nm or more could be put into
a single package to increase bandwidth with filters used on each
detector to prevent cross-talk between the different blue sources.
Unfortunately for both these alternatives, the significant amount
of space required for assembly of multiple separate chips prevents
design of compact, highly directional VLC systems.
[0083] The devices described above may support VLC applications.
The first contact 129a, the second contact 129b, the third contact
129c, the fourth contact 129c, the fifth contact 129d, and the
sixth contact 130 may be independently drivable to define light
emission from each of the first pixel 113, the second pixel, 114,
and the third pixel 115 to support VLC protocols.
[0084] Referring now to FIG. 1K, a diagram illustrating a combined
display and VLC system 140 is illustrated. A smartphone 402 having
a display 141, VLC emitter 142, and VLC receiver 143 (shown as not
to scale magnified cartoon) may be used to interact with other
devices such as ceiling mounted LED light 144 or another smartphone
145 that support VLC protocols such as Li-Fi.
[0085] The VLC emitter 142 may also be capable of acting as a
display, but the display and VLC functionality may be separate. The
VLC emitter 142 may include the LED array 121 and the LED array 138
described above.
[0086] The VLC receiver 143 may include an avalanche photodiode, or
when more sensitive operation is required, a single photon
avalanche diode (SPAD). The smartphone 402 may include circuitry to
convert data needing transmission into a suitable driving
modulation of the selected VLC emitters. The smartphone 402 may
also include circuitry to convert received light modulations from
the VLC receiver into available data. The VLC receiver 143 may be
the sensor module 314 described below with reference to FIG. 3.
[0087] Referring now to FIG. 1L, a diagram illustrating the VLC
receiver 143 is shown. The VLC receiver 143 may include an
amplification circuit 149 and an optical filter and optical
concentrators 146. Beam divergence may occur in LEDs due to
illuminating large areas results in attenuation. The optical
concentrator 146 may be used to compensate this type of
attenuation. In addition, VLC may be vulnerable to interference
from other sources such as sunlight and other illumination.
Therefore, the optical filters 146 may be used mitigate the DC
noise components present in the received signal.
[0088] In the VLC receiver 143, light may be detected using a
photodiode 147 and may be converted to photo current. The
photodiode may include one or more of a silicon photodiode, a PIN
diode, and avalanche photodiode. The photodiode 451 may include one
or more of the first pixel 113, the second pixel 114, and the third
pixel 115. The photo current may be received by a clock and data
recovery (CDR) unit 148. The CDR unit 148 may provide an output to
one or more circuits in the VLC system 140.
[0089] Light may pass through optical filter and optical
concentrators 146 and be detected by the photodiode 147. The
amplification circuit 149 may amplify the signal and provide it to
the CDR unit 148, which may decode and process the signal.
[0090] Independent electrical connections may be made to the first
pixel 113, the second pixel 114, and the third pixel 115 to allow
for high speed light intensity modulation and data transfer using
IEEE 802.15.7 or other suitable wireless protocols. Since multiple
wavelengths may be supported, improved protocols based on optical
orthogonal frequency-division multiplexing (O-OFDM) modulation may
be used. A VLC signal may be directed to an LED array having
stacked active regions emitting light of different wavelength. Each
pixel may emit different wavelengths or alternatively, each pixel
can emit more than one wavelength.
[0091] Use of a multiple wavelength system such as the LED array
121 and the LED array 138 may deliver connections having a data
transfer rate up to about 5 Gbps, comparing favorably to phosphor
coated white LEDs only able deliver up to about 100 Mbps.
[0092] Color shift keying (CSK), outlined in IEEE 802.15.7, is an
intensity modulation based modulation scheme for VLC. CSK is
intensity-based, as the modulated signal takes on an instantaneous
color equal to the physical sum of three RGB LED instantaneous
intensities. This modulated signal jumps instantaneously, from
symbol to symbol, across different visible colors. Accordingly, CSK
may be construed as a form of frequency shifting. However, this
instantaneous variation in the transmitted color may not be humanly
perceptible, because of the limited temporal sensitivity in the
human vision. A critical flicker fusion threshold (CFF) and a
critical color fusion threshold (CCF), may limit humans from
resolving temporal changes shorter than 0.01 second. Transmissions
from the LED array 121 and the LED array 138 may be preset to
time-average (over the CFF and the CCF) to a specific time-constant
color. Humans may perceive only the preset color that seems
constant over time, but cannot perceive the instantaneous color
that varies rapidly in time. In other words, CSK transmission may
maintain a constant time-averaged luminous flux, even as its symbol
sequence varies rapidly in chromaticity.
[0093] Referring now to FIG. 1M, a flowchart illustrating a method
for use of an LED array is shown. In step 180, a first voltage may
be provided to a first pixel of the LED array. In step 182, a
second voltage may be provided to a second pixel of the LED array.
The first pixel and the second pixel may be separated by a first
trench extending to a substrate. In step 184, a third voltage may
be provided to a third pixel of the LED array. The second pixel and
the third pixel may be separated by a second trench extending to
the substrate.
[0094] Referring now to FIG. 1N, a flowchart illustrating a method
of forming a device is shown. In step 190, one or more LEDs and one
or more tunnel junctions may be formed on a substrate. In step 192,
a first trench may be formed through the one or more tunnel
junctions and the one or more LEDs to define a first pixel and a
second pixel. The first trench may extend to the substrate. In an
optional step 194, a second trench may be formed through the one or
more tunnel junctions and the one or more LEDs to define the second
pixel and a third pixel.
[0095] An LED may include a first pixel having a first pair of
contacts, a second pixel having a second pair of contacts, and a
third pixel having a third pair of contacts, a first trench
separating the first pixel and the second pixel, the first trench
extending to a substrate, and a second trench separating the first
pixel and the second pixel, the first trench extending to a
substrate.
[0096] The first pair of contacts may be configured to receive a
first voltage independent of the second pixel and the third
pixel.
[0097] The second pair of contacts may be configured to receive a
second voltage independent of the first pixel and the third
pixel.
[0098] The third pair contacts may be configured to receive a third
voltage independent of the first pixel and the second pixel.
[0099] The first pixel may be configured to emit a light of a first
wavelength, the second pixel may be configured to emit a light of a
second wavelength, and the third pixel may be configured to emit a
light of a third wavelength.
[0100] The first pixel may include a first LED on the substrate, a
first tunnel junction on the first LED, and a first semiconductor
layer on the tunnel junction.
[0101] The second pixel may include a first LED on the substrate, a
first tunnel junction on the first LED, a second LED on the first
tunnel junction, a second tunnel junction of the second LED, and a
second semiconductor layer on the second tunnel junction.
[0102] The third pixel may include a first LED on the substrate a
first tunnel junction on the first LED, a second LED on the first
tunnel junction, a second tunnel junction on the second LED, and a
third LED on the second tunnel junction.
[0103] A system may include a light emitting diode (LED) array
comprising a first pixel, a second pixel, and a third pixel
separated by one or more trenches extending to a substrate, an LED
device attach region having a first pair of electrodes coupled to a
first pair of contacts on the first pixel, a second pair of
electrodes coupled to a second pair of contacts on the second
pixel, and a third pair of electrodes coupled to a third pair of
contacts on the third pixel, and driver circuity configured to
provide independent voltages to one or more of the first pair of
electrodes, the second pair of electrodes, and the third pair of
electrodes.
[0104] The first pixel may include a first LED on the substrate, a
first tunnel junction on the first LED, and a first semiconductor
layer on the tunnel junction.
[0105] The second pixel may include a first LED on the substrate, a
first tunnel junction on the first LED, a second LED on the first
tunnel junction, a second tunnel junction of the second LED, and a
second semiconductor layer on the second tunnel junction.
[0106] The third pixel may include a first LED on the substrate a
first tunnel junction on the first LED, a second LED on the first
tunnel junction, a second tunnel junction on the second LED, and a
third LED on the second tunnel junction.
[0107] The first pixel may be configured to emit a light having a
first wavelength, the second pixel may be configured to emit a
light having a second wavelength, and the third pixel may be
configured to emit a light having a third wavelength.
[0108] The system may include a VLC receiver configured to convert
a received light into data signals, the VLC receiver comprising an
amplification circuit, an optical filter and concentrator, a
photodiode, and a clock and data recovery (CDR) unit.
[0109] The photodiode may include one or more of the first pixel,
the second pixel, and the third pixel.
[0110] A method may include providing a first voltage to first a
pixel of a light emitting diode (LED) array, providing a second
voltage to a second pixel of the LED array, the first pixel and the
second pixel separated by a first trench extending to a substrate,
and providing a third voltage to a third pixel of the LED array,
the second pixel and the third pixel separated by a second trench
extending to the substrate.
[0111] The first voltage, the second voltage, and the third voltage
may be independent from one another.
[0112] The first voltage may cause the first pixel to emit a light
of a first wavelength, the second voltage may cause the second
pixel to emit a light of a second wavelength, and the third voltage
may cause the third pixel to emit light of a third wavelength.
[0113] One or more of the light of the first wavelength, the light
of the second wavelength, and the light of the third wavelength may
travel through the substrate.
[0114] The LED array may be coupled to an LED device attach region
through one or more contacts.
[0115] FIG. 2A is a diagram of an LED device 200 in an example
embodiment. The LED device 200 may include a substrate 202, an
active layer 204, a wavelength converting layer 206, and primary
optic 208. In other embodiments, an LED device may not include a
wavelength converter layer and/or primary optics.
[0116] As shown in FIG. 2A, the active layer 204 may be adjacent to
the substrate 202 and emits light when excited. Suitable materials
used to form the substrate 202 and the active layer 204 include
sapphire, SiC, GaN, Silicone and may more specifically be formed
from a III-V semiconductors including, but not limited to, AlN,
AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, II-VI
semiconductors including, but not limited to, ZnS, ZnSe, CdSe,
CdTe, group IV semiconductors including, but not limited to Ge, Si,
SiC, and mixtures or alloys thereof.
[0117] The wavelength converting layer 206 may be remote from,
proximal to, or directly above active layer 204. The active layer
204 emits light into the wavelength converting layer 206. The
wavelength converting layer 206 acts to further modify wavelength
of the emitted light by the active layer 204. LED devices that
include a wavelength converting layer are often referred to as
phosphor converted LEDs ("POLED"). The wavelength converting layer
206 may include any luminescent material, such as, for example,
phosphor particles in a transparent or translucent binder or
matrix, or a ceramic phosphor element, which absorbs light of one
wavelength and emits light of a different wavelength.
[0118] The primary optic 208 may be on or over one or more layers
of the LED device 200 and allow light to pass from the active layer
204 and/or the wavelength converting layer 206 through the primary
optic 208. The primary optic 208 may be a lens or encapsulate
configured to protect the one or more layers and to, at least in
part, shape the output of the LED device 200. Primary optic 208 may
include transparent and/or semi-transparent material. In example
embodiments, light via the primary optic may be emitted based on a
Lambertian distribution pattern. It will be understood that one or
more properties of the primary optic 208 may be modified to produce
a light distribution pattern that is different than the Lambertian
distribution pattern.
[0119] FIG. 2B shows a cross-sectional view of a lighting system
220 including an LED array 210 with pixels 201A, 201B, and 201C, as
well as secondary optics 212 in an example embodiment. The LED
array 210 includes pixels 201A, 201B, and 201C each including a
respective wavelength converting layer 206B active layer 204B and a
substrate 202B. The LED array 210 may be a monolithic LED array
manufactured using wafer level processing techniques, a micro LED
with sub-500 micron dimensions, or the like. Pixels 201A, 201B, and
201C, in the LED array 210 may be formed using array segmentation,
or alternatively using pick and place techniques.
[0120] The spaces 203 shown between one or more pixels 201A, 201B,
and 201C of the LED devices 200B may include an air gap or may be
filled by a material such as a metal material which may be a
contact (e.g., n-contact).
[0121] The secondary optics 212 may include one or both of the lens
209 and waveguide 207. It will be understood that although
secondary optics are discussed in accordance with the example
shown, in example embodiments, the secondary optics 212 may be used
to spread the incoming light (diverging optics), or to gather
incoming light into a collimated beam (collimating optics). In
example embodiments, the waveguide 207 may be a concentrator and
may have any applicable shape to concentrate light such as a
parabolic shape, cone shape, beveled shape, or the like. The
waveguide 207 may be coated with a dielectric material, a
metallization layer, or the like used to reflect or redirect
incident light. In alternative embodiments, a lighting system may
not include one or more of the following: the wavelength converting
layer 206B, the primary optics 208B, the waveguide 207 and the lens
209.
[0122] Lens 209 may be formed form any applicable transparent
material such as, but not limited to SiC, aluminum oxide, diamond,
or the like or a combination thereof. Lens 209 may be used to
modify the a beam of light input into the lens 209 such that an
output beam from the lens 209 will efficiently meet a desired
photometric specification. Additionally, lens 209 may serve one or
more aesthetic purpose, such as by determining a lit and/or unlit
appearance of the p 201A, 201B and/or 201C of the LED array
210.
[0123] FIG. 3 is a top view of an electronics board 310 for an
integrated LED lighting system according to one embodiment. In
alternative embodiments, two or more electronics boards may be used
for the LED lighting system. For example, the LED array may be on a
separate electronics board, or the sensor module may be on a
separate electronics board. In the illustrated example, the
electronics board 310 includes a power module 312, a sensor module
314, a connectivity and control module 316 and an LED attach region
318 reserved for attachment of an LED array to a substrate 320.
[0124] The substrate 320 may be any board capable of mechanically
supporting, and providing electrical coupling to, electrical
components, electronic components and/or electronic modules using
conductive connecters, such as tracks, traces, pads, vias, and/or
wires. The power module 312 may include electrical and/or
electronic elements. In an example embodiment, the power module 312
includes an AC/DC conversion circuit, a DC/DC conversion circuit, a
dimming circuit, and an LED driver circuit.
[0125] The sensor module 314 may include sensors needed for an
application in which the LED array is to be implemented.
[0126] The connectivity and control module 316 may include the
system microcontroller and any type of wired or wireless module
configured to receive a control input from an external device.
[0127] The term module, as used herein, may refer to electrical
and/or electronic components disposed on individual circuit boards
that may be soldered to one or more electronics boards 310. The
term module may, however, also refer to electrical and/or
electronic components that provide similar functionality, but which
may be individually soldered to one or more circuit boards in a
same region or in different regions.
[0128] FIG. 4A is a top view of the electronics board 310 with an
LED array 410 attached to the substrate 320 at the LED device
attach region 318 in one embodiment. The electronics board 310
together with the LED array 410 represents an LED system 400A.
Additionally, the power module 312 receives a voltage input at Vin
497 and control signals from the connectivity and control module
316 over traces 418B, and provides drive signals to the LED array
410 over traces 418A. The LED array 410 is turned on and off via
the drive signals from the power module 312. In the embodiment
shown in FIG. 4A, the connectivity and control module 316 receives
sensor signals from the sensor module 314 over trace 4180.
[0129] FIG. 4B illustrates one embodiment of a two channel
integrated LED lighting system with electronic components mounted
on two surfaces of a circuit board 499. As shown in FIG. 4B, an LED
lighting system 400B includes a first surface 445A having inputs to
receive dimmer signals and AC power signals and an AC/DC converter
circuit 412 mounted on it. The LED system 400B includes a second
surface 445B with the dimmer interface circuit 415, DC-DC converter
circuits 440A and 440B, a connectivity and control module 416 (a
wireless module in this example) having a microcontroller 472, and
an LED array 410 mounted on it. The LED array 410 is driven by two
independent channels 411A and 411B. In alternative embodiments, a
single channel may be used to provide the drive signals to an LED
array, or any number of multiple channels may be used to provide
the drive signals to an LED array.
[0130] The LED array 410 may include two groups of LED devices. In
an example embodiment, the LED devices of group A are electrically
coupled to a first channel 411A and the LED devices of group B are
electrically coupled to a second channel 411B. Each of the two
DC-DC converters 440A and 440B may provide a respective drive
current via single channels 411A and 411B, respectively, for
driving a respective group of LEDs A and B in the LED array 410.
The LEDs in one of the groups of LEDs may be configured to emit
light having a different color point than the LEDs in the second
group of LEDs. Control of the composite color point of light
emitted by the LED array 410 may be tuned within a range by
controlling the current and/or duty cycle applied by the individual
DC/DC converter circuits 440A and 440B via a single channel 411A
and 411B, respectively. Although the embodiment shown in FIG. 4B
does not include a sensor module (as described in FIG. 3 and FIG.
4A), an alternative embodiment may include a sensor module.
[0131] The illustrated LED lighting system 400B is an integrated
system in which the LED array 410 and the circuitry for operating
the LED array 410 are provided on a single electronics board.
Connections between modules on the same surface of the circuit
board 499 may be electrically coupled for exchanging, for example,
voltages, currents, and control signals between modules, by surface
or sub-surface interconnections, such as traces 431, 432, 433, 434
and 435 or metallizations (not shown). Connections between modules
on opposite surfaces of the circuit board 499 may be electrically
coupled by through board interconnections, such as vias and
metallizations (not shown).
[0132] According to embodiments, LED systems may be provided where
an LED array is on a separate electronics board from the driver and
control circuitry. According to other embodiments, a LED system may
have the LED array together with some of the electronics on an
electronics board separate from the driver circuit. For example, an
LED system may include a power conversion module and an LED module
located on a separate electronics board than the LED arrays.
[0133] According to embodiments, an LED system may include a
multi-channel LED driver circuit. For example, an LED module may
include embedded LED calibration and setting data and, for example,
three groups of LEDs. One of ordinary skill in the art will
recognize that any number of groups of LEDs may be used consistent
with one or more applications. Individual LEDs within each group
may be arranged in series or in parallel and the light having
different color points may be provided. For example, warm white
light may be provided by a first group of LEDs, a cool white light
may be provided by a second group of LEDs, and a neutral white
light may be provided by a third group.
[0134] FIG. 5 shows an example system 550 which includes an
application platform 560, LED systems 552 and 556, and secondary
optics 554 and 558. The LED System 552 produces light beams 561
shown between arrows 561a and 561b. The LED System 556 may produce
light beams 562 between arrows 562a and 562b. In the embodiment
shown in FIG. 5, the light emitted from LED system 552 passes
through secondary optics 554, and the light emitted from the LED
System 556 passes through secondary optics 558. In alternative
embodiments, the light beams 561 and 562 do not pass through any
secondary optics. The secondary optics may be or may include one or
more light guides. The one or more light guides may be edge lit or
may have an interior opening that defines an interior edge of the
light guide. LED systems 552 and/or 556 may be inserted in the
interior openings of the one or more light guides such that they
inject light into the interior edge (interior opening light guide)
or exterior edge (edge lit light guide) of the one or more light
guides. LEDs in LED systems 552 and/or 556 may be arranged around
the circumference of a base that is part of the light guide.
According to an implementation, the base may be thermally
conductive. According to an implementation, the base may be coupled
to a heat-dissipating element that is disposed over the light
guide. The heat-dissipating element may be arranged to receive heat
generated by the LEDs via the thermally conductive base and
dissipate the received heat. The one or more light guides may allow
light emitted by LED systems 552 and 556 to be shaped in a desired
manner such as, for example, with a gradient, a chamfered
distribution, a narrow distribution, a wide distribution, an
angular distribution, or the like.
[0135] In example embodiments, the system 550 may be a mobile phone
of a camera flash system, indoor residential or commercial
lighting, outdoor light such as street lighting, an automobile, a
medical device, AR/VR devices, and robotic devices. The integrated
LED lighting system shown in FIG. 3, LED System 400A shown in FIG.
4A, illustrate LED systems 552 and 556 in example embodiments.
[0136] In example embodiments, the system 550 may be a mobile phone
of a camera flash system, indoor residential or commercial
lighting, outdoor light such as street lighting, an automobile, a
medical device, AR/VR devices, and robotic devices. The LED System
400A shown in FIG. 4A and LED System 400B shown in FIG. 4B
illustrate LED systems 552 and 556 in example embodiments.
[0137] The application platform 560 may provide power to the LED
systems 552 and/or 556 via a power bus via line 565 or other
applicable input, as discussed herein. Further, application
platform 560 may provide input signals via line 565 for the
operation of the LED system 552 and LED system 556, which input may
be based on a user input/preference, a sensed reading, a
pre-programmed or autonomously determined output, or the like. One
or more sensors may be internal or external to the housing of the
application platform 560.
[0138] In various embodiments, application platform 560 sensors
and/or LED system 552 and/or 556 sensors may collect data such as
visual data (e.g., LIDAR data, IR data, data collected via a
camera, etc.), audio data, distance based data, movement data,
environmental data, or the like or a combination thereof. The data
may be related a physical item or entity such as an object, an
individual, a vehicle, etc. For example, sensing equipment may
collect object proximity data for an ADAS/AV based application,
which may prioritize the detection and subsequent action based on
the detection of a physical item or entity. The data may be
collected based on emitting an optical signal by, for example, LED
system 552 and/or 556, such as an IR signal and collecting data
based on the emitted optical signal. The data may be collected by a
different component than the component that emits the optical
signal for the data collection. Continuing the example, sensing
equipment may be located on an automobile and may emit a beam using
a vertical-cavity surface-emitting laser (VCSEL). The one or more
sensors may sense a response to the emitted beam or any other
applicable input.
[0139] In example embodiment, application platform 560 may
represent an automobile and LED system 552 and LED system 556 may
represent automobile headlights. In various embodiments, the system
550 may represent an automobile with steerable light beams where
LEDs may be selectively activated to provide steerable light. For
example, an array of LEDs may be used to define or project a shape
or pattern or illuminate only selected sections of a roadway. In an
example embodiment, Infrared cameras or detector pixels within LED
systems 552 and/or 556 may be sensors that identify portions of a
scene (roadway, pedestrian crossing, etc.) that require
illumination.
[0140] Having described the embodiments in detail, those skilled in
the art will appreciate that, given the present description,
modifications may be made to the embodiments described herein
without departing from the spirit of the inventive concept.
Therefore, it is not intended that the scope of the invention be
limited to the specific embodiments illustrated and described.
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