U.S. patent application number 16/254342 was filed with the patent office on 2019-05-23 for light emitting device and method of forming the same.
The applicant listed for this patent is EPISTAR CORPORATION. Invention is credited to Min-Hsun HSIEH, Chih-Chiang LU, Ching-Pu TAI.
Application Number | 20190157498 16/254342 |
Document ID | / |
Family ID | 38321383 |
Filed Date | 2019-05-23 |
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United States Patent
Application |
20190157498 |
Kind Code |
A1 |
HSIEH; Min-Hsun ; et
al. |
May 23, 2019 |
LIGHT EMITTING DEVICE AND METHOD OF FORMING THE SAME
Abstract
A light-emitting device includes a transparent substrate, a
transparent adhesive layer on the transparent substrate, a first
transparent conductive layer on the transparent adhesive layer, a
multi-layer epitaxial structure and a first electrode on the
transparent conductive layer, and a second electrode on the
multi-layer epitaxial structure. The multi-layer epitaxial
structure includes a light-emitting layer. The transparent
substrate has a first surface facing the transparent adhesive layer
and a second surface opposite to the first surface, wherein the
area of the second surface is larger than that of the
light-emitting layer, and the area ratio thereof is not less than
1.6.
Inventors: |
HSIEH; Min-Hsun; (Hsinchu,
TW) ; LU; Chih-Chiang; (Hsinchu, TW) ; TAI;
Ching-Pu; (Hsinchu, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EPISTAR CORPORATION |
Hsinchu City |
|
TW |
|
|
Family ID: |
38321383 |
Appl. No.: |
16/254342 |
Filed: |
January 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14100999 |
Dec 9, 2013 |
10224455 |
|
|
16254342 |
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|
12717558 |
Mar 4, 2010 |
8602832 |
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|
14100999 |
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|
11626742 |
Jan 24, 2007 |
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12717558 |
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13730130 |
Dec 28, 2012 |
8932885 |
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|
14100999 |
|
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|
13114384 |
May 24, 2011 |
8344353 |
|
|
13730130 |
|
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|
11724310 |
Mar 15, 2007 |
RE42422 |
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13114384 |
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09683959 |
Mar 6, 2002 |
6867426 |
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11724310 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/10 20130101;
H01L 33/005 20130101; H01L 33/42 20130101; Y10T 156/1062 20150115;
H05B 33/26 20130101; H01L 33/0093 20200501; Y10T 29/49995
20150115 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H05B 33/26 20060101 H05B033/26; H01L 33/10 20060101
H01L033/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2001 |
TW |
090115871 |
Jan 27, 2006 |
TW |
95103659 |
Claims
1. A light-emitting device, comprising: an epitaxial structure
comprising an active layer; a substrate, passable to light from the
epitaxial structure, and having a top surface being not less than
1.6 times an area of the active layer; a first transparent layer,
directly connected to the substrate and comprising a widest width
smaller than that of the substrate and larger than that of the
epitaxial structure; a second transparent layer, made of oxygen and
only one metallic element, arranged between the first transparent
layer and the epitaxial structure; and a first electrode arranged
on the first transparent layer and the second transparent layer
which are not covered by the active layer, wherein the second
transparent layer and the substrate have outmost sidewalls which
are not coplanar with each other.
2. The light-emitting device of claim 1, wherein the substrate
comprises an inclined side surface.
3. The light-emitting device of claim 1, wherein the substrate has
a bottom surface being not less than 1.6 times the area of the
active layer.
4. The light-emitting device of claim 3, wherein the top surface
and the bottom surface have different widths.
5. The light-emitting device of claim 3, wherein the top surface
and the bottom surface substantially have the same width.
6. The light-emitting device of claim 1, wherein the active layer
is narrower than the second transparent layer.
7. The light-emitting device of claim 1, wherein the substrate is
made of a non-semiconductor material.
8. The light-emitting device of claim 1, wherein the second
transparent layer comprises a metal oxide.
9. The light-emitting device of claim 1, wherein the first
transparent layer has a thickness is smaller than that of the
second transparent layer.
10. The light-emitting device of claim 1, wherein the first
electrode is separated from the active layer.
11. The light-emitting device of claim 1, further comprising a
second electrode arranged on the epitaxial structure.
12. The light-emitting device of claim 11, wherein the first
electrode and the second electrode disposed on an opposite side of
the second transparent layer corresponding to the first transparent
layer.
13. The light-emitting device of claim 11, wherein the first
electrode and the second electrode have different width.
14. The light-emitting device of claim 1, further comprising a
reflective layer associated with the substrate and has a width
greater than the epitaxial structure.
15. The light-emitting device of claim 14, wherein the reflective
layer is a distributed Bragg reflector (DBR).
16. The light-emitting device of claim 1, further comprising a
reflective layer arranged under the active layer.
17. The light-emitting device of claim 1, wherein the substrate has
a thickness between 50 to 200 microns.
18. The light-emitting device of claim 1, wherein the first
transparent layer comprising the silicone.
19. The light-emitting device of claim 1, further comprising a
trench between the first electrode and the active layer.
20. The light-emitting device of claim 1, wherein the first
transparent layer has a thickness which is smaller than that of the
substrate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of co-pending application
Ser. No. 14/100,999, filed on Dec. 9, 2013, which is a divisional
of application Ser. No. 12/717,558 filed on Mar. 4, 2010 and which
issued as U.S. Pat. No. 8,602,832 on Dec. 10, 2013, which is a
divisional of application Ser. No. 11/626,742 filed Jan. 24, 2007
and now abandoned. Application Ser. No. 14/100,999 is also a
continuation-in-part of application Ser. No. 13/730,130 filed on
Dec. 28, 2012 and which issued as U.S. Pat. No. 8,932,885 on Jan.
13, 2015, which is a divisional of application Ser. No. 13/114,384
filed on May 24, 2011 and which issued as U.S. Pat. No. 8,344,353
on Jan. 1, 2013, which is a continuation of application Ser. No.
11/724,310 filed on Mar. 15, 2007 and which issued on Jun. 7, 2011
as RE42,422, which is a reissue of application Ser. No. 09/683,959
filed on Mar. 6, 2002 and which issued as U.S. Pat. No. 6,867,426
on Mar. 15, 2005.
TECHNICAL FIELD
[0002] The present invention relates to a light-emitting device,
and more particularly to a light-emitting device having a
multi-layer epitaxial structure and a method of forming the
same.
BACKGROUND
[0003] Light-emitting diodes have different light-emitting
principles and structures from conventional light sources and
advantage of small volume and high reliability, hence they can have
versatile applications. For example, light-emitting diodes may form
a variety of large-scale components on demand to apply to indoor or
outdoor displays. Therefore, the brightness enhancement is always
an important issue in the manufacture of light-emitting diodes.
[0004] FIG. 1A is a schematic diagram of a conventional
light-emitting diode. As shown in FIG. 1A, the light-emitting diode
includes a substrate 110, a multi-layer epitaxial structure 130
having a light-emitting layer 131 on the substrate 110, and a
reflective layer 150 between the multi-layer epitaxial structure
130 and the substrate 110. The reflective layer 150 is configured
to reflect the light downward from the light-emitting layer 131
back above the light-emitting layer 131. However, the light beams
with larger incident angles, such as light R1 and light R2, would
be gradually absorbed by the light-emitting layer 131 after passing
back and forth through the light-emitting layer 131 due to the
total internal reflection, and consequently the brightness and the
luminous efficiency of the light-emitting diode would be reduced.
FIG. 1B is a schematic diagram of another conventional
light-emitting diode. As shown in FIG. 1B, the light-emitting diode
includes a transparent substrate 120 and a multi-layer epitaxial
structure 130 having a light-emitting layer 131. When the light
from the light-emitting layer 131 is reflected at the bottom of the
transparent substrate 120 and travels to the sides of the
transparent substrate 120, some light beams (such as light R3)
would be reflected back inside the light-emitting diode because its
incident angle 81 is larger than the critical angle Sc, and have
more chances of being absorbed by the light-emitting layer 131.
Therefore the brightness and the luminous efficiency of the
light-emitting diode are reduced.
[0005] Consequently, it is necessary to provide a light-emitting
diode and a method of forming the same capable of reducing the
times the light passing through the light-emitting layer.
SUMMARY OF THE INVENTION
[0006] The present invention provides a light-emitting device
having a transparent adhesive layer, including a transparent
substrate capable of improving the brightness and a first and a
second electrodes on the same side.
[0007] In one embodiment, the present invention provides a
light-emitting device including a transparent substrate, a
transparent adhesive layer on the transparent substrate, a
multi-layer epitaxial structure on the transparent adhesive layer,
the multi-layer epitaxial structure including a light-emitting
layer, a first electrode on the transparent adhesive layer, and a
second electrode on the multi-layer epitaxial structure. The
transparent substrate has a first surface facing the transparent
adhesive layer and a second surface opposite to the first surface,
and the ratio of the area of the second surface to the area of the
light-emitting layer is not less than 1.6.
[0008] In another embodiment, the present invention provides a
light-emitting device including a transparent substrate, a
transparent adhesive layer on the transparent substrate, a
multi-layer epitaxial structure on the transparent adhesive layer,
a first electrode on the transparent adhesive layer, and a second
electrode on the multi-layer epitaxial structure, wherein the
transparent substrate has a first surface contacting the
transparent adhesive layer and a second surface opposite to the
first surface, and the area of the second surface is larger than
that of the first surface.
[0009] The present invention further provides a method of forming a
light-emitting device. The multi-layer epitaxial structure is
attached to the transparent substrate through the transparent
adhesive layer and then diced to obtain light-emitting devices with
improved brightness.
[0010] In one embodiment, the method includes a step of providing a
temporary substrate having a multi-layer epitaxial structure and a
first transparent conductive layer formed on the temporary
substrate, and a step of cutting the temporary substrate to form a
first die, the first dice including a portion of the multi-layer
epitaxial structure, a portion of the first transparent conductive
layer, and a portion of the temporary substrate. The method also
includes the step of providing a transparent substrate having a
transparent adhesive layer formed on the transparent substrate, and
a step of attaching the first die on the transparent adhesive
layer. The transparent substrate is then cut to form a second die,
the second die includes at least one of the first die, a portion of
the transparent adhesive layer, and a portion of the transparent
substrate. The transparent substrate of the second die has a first
surface contacting the transparent adhesive layer and a second
surface opposite to the first surface, and the ratio of the area of
the second surface to that of a light-emitting layer of the
multi-layer epitaxial structure is not less than 1.6.
[0011] In another embodiment, the method includes the step of
providing a transparent substrate having a light-emitting element
on the transparent substrate. The light-emitting element includes a
transparent adhesive layer on the transparent substrate, a
multi-layer epitaxial structure on the transparent adhesive layer,
a first electrode on the transparent adhesive layer, and a second
electrode on the multi-layer epitaxial structure. The transparent
substrate is then cut to make the ratio of the area of a second
surface of the transparent substrate distant from the transparent
adhesive layer to the area of a light-emitting layer of the
multi-layer epitaxial structure is not less than 1.6.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1A-1B are schematic diagrams of conventional light
emitting diodes;
[0013] FIGS. 2A-2C are schematic diagrams of light emitting devices
according to the present invention;
[0014] FIGS. 3-6 are schematic diagrams showing the steps of
forming a light emitting devices according to the present
invention; and
[0015] FIGS. 7A-7C are schematic diagrams showing different cutting
methods implemented in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The preferred embodiments of the present invention would be
illustrated with reference to the appended drawings. It should be
noticed that, to present this invention clearly, the layers and
elements in the drawings are not depicted to scale, and the known
components, materials, and processing techniques would be omitted
below to avoid obscuring the teachings of the present
invention.
[0017] FIGS. 2A-2C show preferred embodiments of the present
invention. A light-emitting device 200 according to the present
invention includes a transparent substrate 210, a transparent
adhesive layer 220 on the transparent substrate 210, and a first
transparent conductive layer 230 on the transparent adhesive layer
220. The material of the transparent substrate 210 includes but not
limited to glass, sapphire, SiC, GaP, GaAsP, and ZnSe. The
transparent adhesive layer 220 can have a material including but
not limited to spin-on glasses, silicone, Benzocyclobutene (BCB),
Epoxy, polyimide, and Perfluorocyclobutane (PFCB). The first
transparent conductive layer 230 can be made of a material
including but not limited to indium tin oxide, cadmium tin oxide,
zinc oxide, and zinc tin oxide.
[0018] Moreover, as shown in FIGS. 2A-2C, the light-emitting device
200 according to the present invention further includes a
multi-layer epitaxial structure 240 and a first electrode 250 on
the first transparent conductive layer 230, and a second electrode
260 on the multi-layer epitaxial structure 240. A trench 270 may be
optionally formed between the first electrode 250 and the
multi-layer epitaxial structure 240. The multi-layer epitaxial
structure 240 includes a first contact layer 241, a first
confinement layer 242, a light-emitting layer 243, a second
confinement layer 244, and a second contact layer 245. To form a
good ohmic contact with the second electrode 260, a second
transparent conductive layer 261 capable of spreading currents may
be optionally formed between the second electrode 260 and the
second contact layer 245. The second transparent conductive layer
261 can be made of a material including but not limited to indium
tin oxide, cadmium tin oxide, zinc oxide, and zinc tin oxide. The
first contact layer 241 and the second contact layer 245 can be
independently made of materials including but not limited to GaP,
GaAs, and GaAsP. The first confinement layer 242, the first
light-emitting layer 243, and the second confinement layer 244 can
be made of materials including AlGaInP. The first electrode 250 and
the second electrode 260 can be respectively made of a material
including but not limited to Au, Al, Pt, Cr, and Ti. In the
structures shown in FIGS. 2A-2C, the transparent substrate 210 has
a first surface 211 contacting with the transparent adhesive layer
220 and a second surface 212 opposite to the first surface 211.
However, it should be noticed that, the area of the second surface
212 is larger than that of the light-emitting layer 243.
[0019] In the exemplary embodiment of FIG. 2A, the area of the
second surface 212 is larger than that of the light-emitting layer
243. As shown in FIG. 2A, the second surface 212 of the transparent
substrate has an area essentially equal to that of the first
surface 211, and the areas of the first surface 211 and the second
surface 212 are larger than the area of the light-emitting layer
243. Therefore, the first surface 211 of the transparent substrate
would form an exposed portion, "A", not covered with the
light-emitting layer 243. The exposed portion, "A", should at least
not be covered with the light-emitting layer 243. For example, the
exposed portion, "A", in the figure is not covered with the
multi-layer epitaxial structure 240, the first transparent
conductive layer 230, and the transparent adhesive layer 220. The
size of the exposed portion "A" can be decided upon the area ratio
of the first surface 211 to the light-emitting layer 243, the
second surface 212 to the light-emitting layer 243, or both of
them, and a preferred area ratio is not less than 1.6. The
structure having the exposed portion, "A", can increase the
brightness of the light-emitting device 200. As shown in FIG. 2A,
the light R4 traveling from the second surface 212 upward to the
transparent substrate 210 leaves the light-emitting device 200
through the exposed portion, "A", without passing through the
light-emitting layer 243, hence the brightness is increased.
[0020] In another exemplary embodiment of FIG. 2B, the area of the
second surface 212 is larger than that of the light-emitting layer
243. As shown in the FIG. 2B, the area of the second surface 212 is
greater than that of the first surface 211. More specifically, the
cross-section of the transparent substrate 210 is like a trapezoid.
This structure can increase the brightness of the light-emitting
device 200, because the incident angle S2 of the light Rs traveling
from the second surface 212 to a side 213 of the transparent
substrate 210 is smaller than the critical angle Sc. In detail, a
shown in FIG. 2B is the angle that the side 213 tilts to the
multi-layer epitaxial structure 240. The angle, "a", changes the
incident angle S2 of the light Rs from S1 in FIG. 1B to S2 (namely
S2=S1-a), and makes it smaller the critical angle Sc. Consequently,
the light Rs leaves the transparent substrate 210 through the side
213, rather than be reflected back into the multi-layer epitaxial
structure 240. Those who are skilled in the art should understand
that the critical angle Sc mentioned above depends on the material
of the transparent substrate 210 and the environmental medium.
Therefore, if the environmental medium is set, Sc can be determined
by choosing an suitable transparent substrate 210, and the tilt
angle, "a" is adjusted by changing the ratio of the area of the
second surface 212 to the area of the first surface 211 of the
transparent substrate 210. Taking the transparent sapphire
substrate 210 for example, the ratio of the area of the second
surface 212 to that of the first surface 211 is not less than 1.6,
and preferably ranges between 4 and 20. The thickness of the
transparent substrate 210 is preferably between 50 to 200 microns,
more preferably between 80 to 150 microns.
[0021] In a further exemplary embodiment of FIG. 2C, the area of
the second surface 212 is larger than that of the light-emitting
layer 243. In this embodiment, the second surface 212 is larger
than the first surface 211, and the first surface 211 has an
exposed portion, "A". The ratio of the second surface 212 to the
first surface 211 and the ratio of the second surface 212 to the
light-emitting layer 243 are similar to those mentioned above.
[0022] Additionally, the light-emitting device 200 may further
include a reflective layer 280 on the second surface 212 of the
transparent substrate 210 in view of demand. The reflective layer
280 shown in FIGS. 2A-2C is, but not limited to, attached directly
to the second surface 212. The reflective layer 280 can be made of
a material including but not limited to Sn, Al, Au, Pt, An, Ge, Ag
and the like. The reflective layer 280 can also be a distributed
Bragg reflector (DBR) consisting of oxides, and the oxides can be
Ab03, Si02, or Ti02.
[0023] FIGS. 3-7 show preferred embodiments of forming the light
emitting devices according to the present invention.
[0024] As shown in FIG. 3, a temporary substrate 310 is provided,
and a multi-layer epitaxial structure 240 is formed on the
temporary substrate 310. The steps of forming the multi-layer
epitaxial structure 240 includes sequentially forming a second
contact layer 245, a second confinement layer 244, a light-emitting
layer 243, a first confinement layer 242, and a first contact layer
241 on the temporary substrate 310. Then a first transparent
conductive layer 230 covering the multi-layer epitaxial structure
240 is formed. As shown in FIG. 3, an etch stop layer 320 is
provided between the multi-layer epitaxial structure 240 and
temporary substrate 310 to prevent the multi-layer epitaxial
structure 240 from damages caused by over etching in subsequent
removal of the temporary substrate 310. Preferably, the etch stop
layer 320 has an etching rate lower than that of the temporary
substrate 310.
[0025] After forming the multi-layer epitaxial structure 240 and
the first transparent conductive layer 230 on the temporary
substrate 310, the temporary substrate 310 is cut to form a
plurality of first dices 400. As shown in FIG. 4, the first dice
400 includes a portion of the multi-layer epitaxial structure 240,
a portion of the first transparent conductive layer 230, and a
portion of the temporary substrate 310. The cutting step can be
performed by use of a diamond tool or a laser tool.
[0026] Then, as shown in FIG. 5, the first dice 400 is attached to
the transparent substrate 210. A transparent adhesive layer 220 is
formed in advance on the first surface 211 of the transparent
substrate 210 for bonding the first dice 400 to the transparent
substrate 210. Moreover, a reflective layer 280 may be optionally
disposed on the second surface 212 of the transparent substrate
210. The material of the reflective layer 280 is similar to those
mentioned above.
[0027] Subsequently, as shown in FIG. 6, the surplus transparent
adhesive layer 220 exposed on the transparent substrate 210 is
removed, and the temporary substrate 310 is then removed. If the
temporary substrate 310 is made of GaAs, it can be removed by a
chemical etchant solution such as
5H.sub.3P0.sub.3:3H.sub.20.sub.2:3H.sub.20 or
NH.sub.40H:35H.sub.20.sub.2. After removing the temporary substrate
310, the etch stop layer 320 is further removed.
[0028] Then, structures as shown in FIGS. 7A-7C can be formed by
conventional processes, such as deposition, lithography and
etching. In detail, the multi-layer epitaxial structure 240 is
selectively etched to expose the underlying first transparent
conductive layer 230. Subsequently, a trench 270 as shown in FIGS.
7A-7C is formed, a first electrode 250 is formed on the first
transparent conductive layer 230, and a second electrode 260 is
formed on the multi-layer epitaxial structure 240. The trench 270
isolates the multi-layer epitaxial structure 240 from the first
electrode 250. The first electrode 250 and the second electrode 260
are formed on the same side of the transparent substrate 210.
Additionally, a second transparent conductive layer 261 capable of
spreading currents may be optionally formed between the second
electrode 260 and the second contact layer 245. The second
transparent conductive layer 261 forms a good ohmic contact with
the second electrode 260. The second transparent conductive layer
261 can be made of a material of the first transparent conductive
layer 230 as mentioned above.
[0029] Next, the transparent substrate 210 is cut to form a
plurality of second dice 200 (namely the light-emitting devices
200). The dotted lines in FIGS. 7A-7C respectively illustrate
different cutting manners for obtaining the light-emitting devices
200 shown in FIGS. 2A-2C. After cutting, the second dice 200
includes the first dice 400, a portion of the transparent adhesive
layer 220, and a portion of the transparent substrate 210. During
cutting, it should be noticed that, the transparent substrate 210
of thus formed second dice 200 has a first surface 211 contacting
with the transparent adhesive layer 220 and a second surface 212
opposite to the first surface 211, and the area of the second
surface 212 is larger than that of the light-emitting layer 243.
The cutting manner of FIG. 7A exposes a portion, "A", of the
transparent substrate 210 of the second dice 200. The cutting
manner of FIG. 7B makes the second surface 212 of the transparent
substrate 210 of the second dice 200 be larger than the first
surface 211 without the portion, "A". The cutting manner of FIG. 7C
creates the feature that the second surface 212 of the transparent
substrate 210 of the second dice 200 is larger than the first
surface 211 with the portion, "A". The cutting can be performed by
wafer dicing equipments with a diamond tool or a laser tool. To
reduce the heat produced by cutting and take away the debris, water
with a constant amount at a given pressure may be laterally
introduced along the rotating direction of the diamond tool during
the cutting step.
[0030] The detailed description of the above preferred embodiments
is to describe the features and spirit of the present invention
more clearly, and is not intended to limit the scope of the present
invention. The scope of the present invention should be most
broadly explained according to the foregoing description and
includes all possible variations and equivalents.
* * * * *