U.S. patent application number 11/308015 was filed with the patent office on 2007-07-05 for pixel structure of active matrix organic light-emitting diode and method for fabricating the same.
Invention is credited to Yi-Hsun Huang, Chih-Ming Lai, Yung-Hui Yeh.
Application Number | 20070152217 11/308015 |
Document ID | / |
Family ID | 38223455 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070152217 |
Kind Code |
A1 |
Lai; Chih-Ming ; et
al. |
July 5, 2007 |
PIXEL STRUCTURE OF ACTIVE MATRIX ORGANIC LIGHT-EMITTING DIODE AND
METHOD FOR FABRICATING THE SAME
Abstract
A pixel structure of an active matrix organic light-emitting
diode (AMOLED) includes an organic light-emitting diode (OLED), a
data line, at least one scan line, at least one switch thin film
transistor (TFT), at least one driving TFT and at least one storage
capacitor with two transparent electrodes. Since both the
electrodes of the transparent storage capacitor are formed by
transparent material, the aperture ratio of the pixel and the area
of the capacitor largely increase and can reach 50%.about.95% of a
pixel area. Thus, the display quality of an AMOLED panel can be
improved.
Inventors: |
Lai; Chih-Ming; (Changhua
County, TW) ; Yeh; Yung-Hui; (Hsinchu City, TW)
; Huang; Yi-Hsun; (Tainan County, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
38223455 |
Appl. No.: |
11/308015 |
Filed: |
March 3, 2006 |
Current U.S.
Class: |
257/59 ;
438/149 |
Current CPC
Class: |
H01L 29/7869 20130101;
H01L 27/322 20130101; H01L 27/3265 20130101; H01L 27/1225
20130101 |
Class at
Publication: |
257/059 ;
438/149 |
International
Class: |
H01L 29/04 20060101
H01L029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2005 |
TW |
94147154 |
Claims
1. A pixel structure of an active matrix organic light-emitting
diode (AMOLED), disposed on a transparent substrate and comprising:
an organic light-emitting diode (OLED); a data line; at least one
scan line; at least one switch thin film transistor (TFT), having a
first gate, a first source and a first drain, wherein the first
gate is coupled to the scan line, while the first source is coupled
to the data line; at least one driving thin film transistor (TFT),
having a second gate, a second source and a second drain, wherein
the second gate is coupled to the first drain, while the second
drain is coupled to the OLED; and at least one storage capacitor
having a first transparent electrode, a second transparent
electrode and a dielectric layer, wherein the first transparent
electrode is electrically connected to the first drain and the
second gate.
2. The pixel structure of the AMOLED of claim 1, wherein the first
transparent electrode is a transparent semiconductor layer, while
the second transparent electrode is a transparent metal layer.
3. The pixel structure of the AMOLED of claim 2, wherein the
material of the transparent metal comprises indium-tin-oxide (ITO)
or indium zinc oxide (IZO).
4. The pixel structure of the AMOLED of claim 2, wherein the
material of the transparent semiconductor comprises ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO).
5. The pixel structure of the AMOLED of claim 1, wherein the area
of the storage capacitor is about 50%.about.95% of the pixel
area.
6. The pixel structure of the AMOLED of claim 1, wherein the first
gate of the switch TFT is formed by an opaque metal layer or by a
transparent metal layer and an opaque metal layer, wherein the
resistance of the opaque metal layer is smaller than the
transparent metal layer.
7. The pixel structure of the AMOLED of claim 1, wherein the second
gate of the driving TFT is formed by an opaque metal layer or by a
transparent metal layer and an opaque metal layer, wherein the
resistance of the opaque metal layer is smaller than the
transparent metal layer.
8. The pixel structure of the AMOLED of claim 1, wherein the first
source and the first drain of the switch TFT are formed in a
channel layer and the material of the channel layer is opaque doped
semiconductor or transparent doped semiconductor.
9. The pixel structure of the AMOLED of claim 1, wherein the second
source and the second drain of the driving TFT are formed in a
channel layer and the material of the channel layer is opaque doped
semiconductor or transparent doped semiconductor.
10. The pixel structure of the AMOLED of claim 1, wherein the OLED
includes a white organic light-emitting layer and the pixel
structure of the AMOLED further comprises a color filter disposed
between the transparent substrate and the OLED.
11. The pixel structure of the AMOLED of claim 10, further
comprising a transparent cover plate and another color filter,
wherein the transparent cover plate is disposed on and covers the
OLED, while the another color filter is disposed between the OLED
and the transparent cover plate.
12. A storage capacitor of an AMOLED pixel structure, comprising: a
first transparent electrode connected to a drain of a switch TFT of
the pixel and a gate of a driving TFT of the pixel; a second
transparent electrode; and a dielectric layer between the first
transparent electrode and the second transparent electrode.
13. The storage capacitor of an AMOLED pixel structure of claim 12,
wherein the first transparent electrode is a transparent
semiconductor layer, while the second transparent electrode is a
transparent metal layer.
14. The storage capacitor of an AMOLED pixel structure of claim 13,
wherein the material of the transparent metal comprises
indium-tin-oxide (ITO) or indium zinc oxide (IZO).
15. The storage capacitor of an AMOLED pixel structure of claim 13,
wherein the material of the transparent semiconductor comprises
ZnO, Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO).
16. The storage capacitor of an AMOLED pixel structure of claim 12,
wherein the area of the storage capacitor is about 50%.about.95% of
the pixel area.
17. A method for fabricating the pixel of an AMOLED, comprising:
forming a patterned transparent semiconductor layer on a substrate
to form at least one first channel layer of a switch TFT, at least
one lower electrode of a storage capacitor and at least one second
channel layer of a driving TFT, wherein the area of the storage
capacitor lower electrode is about 50%.about.95% of the pixel area;
forming a first dielectric layer over the substrate to serve as a
first gate dielectric layer of the switch TFT, a dielectric layer
of the storage capacitor and a second gate dielectric layer of the
driving TFT; forming a first opaque metal gate of the switch TFT, a
second opaque metal gate of the driving TFT and at least one scan
line on the first dielectric layer; forming a first source and a
first drain of the switch TFT in the first channel layer and
forming a second source and a second drain of the driving TFT in
the second channel layer; forming a patterned transparent metal
layer on the first dielectric layer to serve as an upper electrode
of the storage capacitor, wherein the area of the upper electrode
is about 50%.about.95% of the pixel area; forming a data line over
the substrate electrically connected to the first source of the
switch TFT; and forming an OLED over the substrate electrically
connected to the second drain of driving TFT.
18. The method for fabricating the pixel of an AMOLED of claim 17,
wherein the material of the transparent semiconductor comprises
ZnO, Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO).
19. The method for fabricating the pixel of an AMOLED of claim 17,
wherein the material of the transparent metal comprises
indium-tin-oxide (ITO) or indium zinc oxide (IZO).
20. The method for fabricating the pixel of an AMOLED of claim 17,
wherein the step for forming the patterned transparent metal layer
on the first dielectric layer includes forming the upper electrode
of the storage capacitor, a first transparent metal gate of the
switch TFT and a second transparent metal gate of the driving
TFT.
21. The method for fabricating the pixel of an AMOLED of claim 20,
wherein the step for forming the patterned transparent metal layer
on the first dielectric layer is performed prior to the step for
forming the first opaque metal gate of the switch TFT, the second
opaque metal gate of the driving TFT and the scan line on the first
dielectric layer.
22. The method for fabricating the pixel of an AMOLED of claim 20,
wherein the step for forming the patterned transparent metal layer
on the first dielectric layer is performed after the step for
forming the first opaque metal gate of the switch TFT, the second
opaque metal gate of the driving TFT and the scan line on the first
dielectric layer.
23. The method for fabricating the pixel of an AMOLED of claim 17,
wherein the OLED includes a white organic light-emitting layer and
the step of the method further comprises forming a color filter on
the substrate prior to forming the data line and the OLED but after
forming the upper electrode of the storage capacitor.
24. The method for fabricating the pixel of an AMOLED of claim 23,
further comprising a step for forming another color filter to cover
the OLED after the step of forming the OLED.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application serial no. 94147154, filed on Dec. 29, 2005. All
disclosure of the Taiwan application is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to an organic light-emitting
diode (OLED) and the method for fabricating the same, and
particularly to an active matrix organic light-emitting diode
(AMOLED) and the method for fabricating the same.
[0004] 2. Description of the Related Art
[0005] An organic light-emitting diode (OLED) is a semiconductor
device capable of converting electrical energy into optical energy.
Since OLEDs have advantages of high conversion efficiency, no angle
of view (AOV) concern, simpler process, low cost, high response
rates, broader operation temperature range and full colorization,
OLEDs meet the requirements of multi-media age today and are
broadly applied in indicator lights, luminance devices of display
panels etc.
[0006] The earlier generation of OLED display is mainly driven by
low-end passive matrix drive. However, the luminance efficiency and
the lifetime of a passive driving device are largely declined along
with the increase of display size and resolution. Instead, the
active matrix OLED display (AMOLED display) featuring high
brightness, low electricity-consumption and long lifetime plays an
exceptional role in the current development of OLED displays.
[0007] An active matrix organic light-emitting diode (AMOLED) is a
device using a thin film transistor (TFT) to drive a light emitting
diode, wherein each pixel structure thereof includes an organic
light-emitting diode (OLED), a switch TFT, a driving TFT, a storage
capacitor, a scan line and a data line. The gray-level of an AMOLED
pixel structure depends on the data line voltage. When a scan line
turns on a switch TFT, the data line voltage drives the gate of the
TFT via the switch TFT, so as to drive a required current to the
OLED. Depending on a different voltage level, a corresponding
different gray-level of display is produced. On the other hand,
when the switch TFT is turned on, the storage capacitor begins with
a charging action in order to store the input voltage. Therefore,
after the switch TFT is turned off, the storage capacitor still
remains the input voltage until the next time to turn on the switch
TFT. In this way, the driving TFT remains on-state, so that the
OLED keeps the original display brightness.
[0008] In a typical bottom emitting AMOLED, to keep a required
frame quality, the storage capacitor is designed with a sufficient
capacitance, and therefore the electrodes of the storage capacitor
need to have enough area. However, the electrodes of the storage
capacitor and the TFT gate are fabricated by opaque materials, and
only an aperture ratio of approximate 30% is given. Thus, when a
color filter is integrated into an OLED panel, the luminance
brightness of the pixel array of a bottom emitting AMOLED is
obviously not as good as a top emitting AMOLED.
SUMMARY OF THE INVENTION
[0009] The present invention is to provide a pixel structure of an
active matrix organic light-emitting diode (AMOLED) and the method
for fabricating the same, capable of improving the pixel aperture
ratio.
[0010] The present invention is to provide a pixel structure of an
active matrix organic light-emitting diode (AMOLED) and the method
for fabricating the same, having sufficient luminance
brightness.
[0011] The present invention provides a pixel structure of an
active matrix organic light-emitting diode (AMOLED). The pixel
structure includes an OLED, a data line, at least one scan line, at
least one switch TFT, at least one driving TFT and at least one
storage capacitor. The switch TFT has a first gate, a first source
and a first drain, wherein the first gate is coupled to the scan
line and the first source is coupled to the data line. The driving
TFT has a second gate, a second source and a second drain, wherein
the second gate is coupled to the first drain and the second drain
is coupled to the OLED. The storage capacitor has a first
transparent electrode, a second transparent electrode and a
dielectric layer, wherein the first transparent electrode is
electrically connected to the first drain and the second gate.
[0012] According to the embodiment of the present invention, the
first transparent electrode of the storage capacitor is a
transparent semiconductor layer, while the second transparent
electrode is a transparent metal layer. The material of the
transparent metal includes indium-tin-oxide (ITO) or indium zinc
oxide (IZO). The material of the transparent semiconductor includes
ZnO, Mg.sub.xZn.sub.1-x, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO). In addition, the area of the
storage capacitor can be 50%.about.95% of a pixel area.
[0013] According to the embodiment of the present invention, the
first gate of the switch TFT and the second gate of the driving TFT
can be formed by an opaque metal layer, respectively, or by a
transparent metal layer and an opaque metal layer, wherein the
resistance of the opaque metal layer is smaller than that of the
transparent metal layer.
[0014] According to the embodiment of the present invention, the
first source and the first drain of the switch TFT and the second
source and the second drain of the driving TFT are formed in a
channel layer, respectively. The material of the channel layer is
opaque doped semiconductor or transparent doped semiconductor.
[0015] According to the embodiment of the present invention, when
the organic light-emitting layer of the OLED is made of white
organic light-emitting material, the pixel structure thereof
further includes a color filter disposed between the transparent
substrate and the OLED. In addition, another color filter can be
further included so that the OLED is between two color filters.
[0016] The present invention further provides a storage capacitor
of the OLED pixel structure, and the capacitor includes a first
transparent electrode, a second transparent electrode and a
dielectric layer. The first transparent electrode is electrically
connected to a drain of a switch TFT of the pixel and a gate of a
driving TFT of the pixel.
[0017] According to the embodiment of the present invention, the
first transparent electrode is a transparent semiconductor layer,
while the second transparent electrode is a transparent metal
layer. The material of the transparent metal includes
indium-tin-oxide (ITO) or indium zinc oxide (IZO). The material of
the transparent semiconductor includes ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZ.sub.1-xO or CdO, or ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZn.sub.1-xO or CdO that have been doped with (a) an element
that can be univalent or (b) Ni; or indium gallium zinc oxide
(InGaZnO). In addition, the area of the storage capacitor can be
50%.about.95% of a pixel area.
[0018] The present invention also provides a method for fabricating
a AMOLED pixel. First, a transparent semiconductor layer is formed
on a substrate. By patterning the transparent semiconductor layer,
a first channel layer of the switch TFT, a lower electrode of a
storage capacitor and a second channel layer of a driving TFT are
formed, wherein the lower electrode area of the storage capacitor
is 50%.about.95% of the pixel area. Next, a first dielectric layer
is formed over the substrate and the dielectric layer is served as
a first gate dielectric layer, a dielectric layer of the storage
capacitor and a second gate dielectric layer of the driving TFT. A
first opaque metal gate of the switch TFT, a second opaque metal
gate of the driving TFT and a scan line are formed on the first
dielectric layer. A first source and a first drain of the switch
TFT are formed in the first channel layer and a second source and a
second drain of the switch TFT are formed in the second channel
layer. A patterned transparent metal layer is formed on the first
dielectric layer and the patterned transparent metal layer is
served as a upper electrode of the storage capacitor, wherein the
area of the storage capacitor upper electrode is 50%.about.95% of a
pixel area. Afterwards, a data line is formed over the substrate to
connect to the first source of the switch TFT. Further, an OLED is
formed over the substrate to electrically connect to the second
drain of driving TFT.
[0019] According to the embodiment of the present invention, the
material of the transparent semiconductor includes ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO). The material of the
transparent metal includes indium-tin-oxide (ITO) or indium zinc
oxide (IZO).
[0020] According to the embodiment of the present invention, the
step of forming and patterning the transparent metal layer on the
first dielectric layer is to form the upper electrode of the
storage capacitor and simultaneously to form the first transparent
metal gate of the switch TFT and the second transparent metal gate
of the driving TFT. In addition, the step for forming and
patterning the transparent metal layer can be performed prior to or
after the step of forming the first opaque metal gate of the switch
TFT, the second opaque metal gate of the driving TFT and the scan
line.
[0021] According to the embodiment of the present invention, when
an organic light-emitting layer of the OLED is made of white
organic light-emitting material, a color filter is further formed
over the substrate prior forming the data line and the OLED but
after forming the upper electrode of the storage capacitor.
Furthermore, after the step of forming the OLED, another color
filter can be formed on the OLED.
[0022] Since the present invention takes two transparent electrodes
to form a storage capacitor in the AMOLED pixel structure, the
entire capacitor is transparent, which enables to largely increase
the aperture ratio of a pixel and allows the capacitor area to be
50%.about.95% of a pixel area for improving the frame quality. On
the other hand, since the capacitor area in a pixel area can reach
50%.about.95%, the frame quality will not be deteriorated even if
the size of the pixel is shrunken. Thus, pixel size can be further
minimized.
[0023] Note that the gate, the scan line and the data line of the
pixel structure are made of low-resistance metal, which contributes
to a shorter RC time delay. Hence, the present invention is
applicable to fabricate an active matrix panel with high
resolution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve for explaining the principles of the invention.
[0025] FIG. 1A is a schematic circuit drawing of an active matrix
organic light-emitting diode (AMOLED) pixel structure.
[0026] FIG. 1B is a schematic top view of an AMOLED pixel structure
of the present invention.
[0027] FIG. 2A to FIG. 2E are schematic cross-sectional drawings of
an AMOLED pixel structure of the present invention.
[0028] FIG. 3A to FIG. 3E are schematic top views of the AMOLED
pixel structure of the present invention corresponding to FIG. 2A
to FIG. 2E, respectively.
DESCRIPTION OF THE EMBODIMENTS
[0029] FIG. 1A is a schematic circuit drawing of an active matrix
organic light-emitting diode (AMOLED) pixel structure. Referring to
FIG. 1A, an AMOLED is disposed on a transparent substrate and the
pixel structure thereof includes an OLED, a data line Yn, a scan
line Xn, a switch TFT T1, a driving TFT T2 and a storage capacitor
C.sub.st. The gate of the switch TFT T1 is coupled to the scan line
Xn, while the source thereof is coupled to the data line Yn and the
drain thereof is coupled to the gate of the driving TFT T2 and the
storage capacitor C.sub.st. The drain of the driving TFT T2 is
coupled to the OLED, while the source thereof is coupled to a power
line Vdd. The storage capacitor C.sub.st is formed by two
transparent electrodes and a dielectric layer between the two
electrodes. The lower electrode of the storage capacitor C.sub.st
is electrically connected to the drain of the switch TFT T1 and the
gate of the driving TFT T2 and is a transparent semiconductor
layer. The material of the transparent semiconductor layer can be
ZnO, Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO, or ZnO,
Mg.sub.xZn.sub.1-xO, Cd.sub.xZn.sub.1-xO or CdO that have been
doped with (a) an element that can be univalent or (b) Ni; or
indium gallium zinc oxide (InGaZnO). The upper electrode of the
storage capacitor C.sub.st is electrically connected to a common
line Vcom and is a transparent metal layer. The material of the
transparent metal layer can be indium-tin-oxide (ITO) or indium
zinc oxide (IZO). Since both electrodes of the storage capacitor
C.sub.st are made of transparent material, thus, the whole storage
capacitor C.sub.st is transparent and can be made of big area. The
area thereof reaches 50%.about.95% of the whole pixel area, which
leads an aperture ratio of storage capacitor C.sub.st to
50%.about.95% of a pixel area accordingly. In an embodiment, the
layout of the components in a pixel structure is shown in FIG.
1B.
[0030] The gate of the switch TFT T1 and the gate of the driving
TFT T2 can be formed either by opaque metal layers, or by a
transparent metal layer and an opaque metal layer, wherein the
resistance of the opaque metal layer is smaller than the resistance
of the transparent metal layer. The layer contacting the gate
dielectric layer of the switch TFT T1 or the gate dielectric layer
of the driving TFT T2 can be either transparent metal layer or
opaque metal layer. Furthermore, to select an appropriate opaque
metal layer, the work function matching issue between the gate
metal and the transparent semiconductor should be taken account of,
so that the TFT possesses the optimum threshold voltage and the
optimum transistor characteristic. The material of the opaque metal
layer can be one of chromium (Cr), aluminum (Al), molybdenum (Mo)
or titanium (Ti). The material of the transparent metal can be
indium-tin-oxide (ITO) or indium zinc oxide (IZO). When the gate of
the switch TFT T1 and the gate of the driving TFT T2 are formed by
a transparent metal layer and an opaque metal layer, the
transparent metal layer can be formed simultaneously with forming
the transparent upper electrode of the storage capacitor
C.sub.st.
[0031] Both the source and the drain of the switch TFT T1 and the
source and the drain of the driving TFT T2 can be made of opaque
polysilicon. To simplify the process, the channel layer in the
switch TFT T1 for forming the source and the drain thereof and the
channel layer in the driving TFT T2 for forming the source and the
drain thereof can be made of a same material as of the lower
electrode of the storage capacitor C.sub.st, which is a transparent
semiconductor layer and can be ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZn.sub.1-xO or CdO, or ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZn.sub.1-xO or CdO that have been doped with (a) an element
that can be univalent or (b) Ni; or indium gallium zinc oxide
(InGaZnO).
[0032] The organic light-emitting layer of the OLED can be made of
a white organic light-emitting material. When the OLED is made of
the white organic light-emitting material, a color filter can be
disposed between the transparent substrate and the OLED for
coloring images.
[0033] Since the present invention uses two transparent electrodes
to form a storage capacitor in the AMOLED pixel structure and the
entire capacitor area reaches 50%.about.95% of a pixel area, the
scheme of the present invention can advance the frame quality and
allows to further downsize the pixel without deteriorating the
frame quality. Besides, such designed electrodes can be applicable
to fabricate a two-side emitting OLED panel.
[0034] The AMOLED pixel structure of the present invention can be
fabricated by the following method. However, the method described
hereinafter is intended to be as an example only, and the present
invention should not be limited by it.
[0035] FIG. 2A to FIG. 2E are schematic cross-sectional drawings of
an AMOLED pixel structure of the present invention and FIG. 3A to
FIG. 3E are schematic top views of the AMOLED pixel structure of
the present invention corresponding to FIG. 2A to FIG. 2E,
respectively. Referring to FIG. 2A and FIG. 3A, first, a substrate
100 is provided and the substrate 100 is, for example, a glass
substrate or a plastic substrate. Next, a buffer layer 102 is
formed on the substrate 100, wherein the buffer layer 102 is an
insulation layer and is, for example, a silicon oxide layer.
Afterwards, a transparent semiconductor layer is formed on the
buffer layer 102, followed by patterning the transparent
semiconductor layer to form a channel layer 104 of the switch TFT,
a lower electrode 106 of the storage capacitor and a channel layer
108 of the driving TFT. The material of the transparent
semiconductor layer can be ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZn.sub.1-xO or CdO, or ZnO, Mg.sub.xZn.sub.1-xO,
Cd.sub.xZn.sub.1-xO or CdO that have been doped with (a) an element
that can be univalent or (b) Ni; or indium gallium zinc oxide
(InGaZnO). In another embodiment, the transparent semiconductor
layer is used for forming the lower electrode 106 of the storage
capacitor only, while the channel layer 104 of the switch TFT and
the channel layer 108 of the driving TFT can be formed by
depositing and patterning an opaque semiconductor layer. The
material of the opaque semiconductor layer is, for example,
polysilicon. In another embodiment, the transparent semiconductor
layer is used for forming the lower electrode 106 of the storage
capacitor and one of the channel layer 104 of the switch TFT and
the channel layer 108 of the driving TFT; and the rest one, either
the channel layer 108 of the driving TFT or the channel layer 104
of the switch TFT can be formed by depositing and patterning an
opaque semiconductor layer.
[0036] Further, referring to FIG. 2B and FIG. 3B, a dielectric
layer 110 is formed over the substrate 100, which serves as a gate
dielectric layer 110a of the switch TFT, a dielectric layer 110b of
the storage capacitor and a gate dielectric layer 110c of the
driving TFT. The material of the dielectric layer 110 is, for
example, silicon oxide (SiO.sub.2), tantalum oxide
(Ta.sub.2O.sub.5), titanium oxide (TiO.sub.2), yttrium oxide
(Y.sub.2O.sub.3), calcium zirconium oxide (CaZrO.sub.3) or indium
gallium zinc oxide (InGaZnO). Furthermore, an opaque metal layer
with low resistance is formed and patterned on the dielectric layer
110 to form an opaque metal gate 112 of the switch TFT, a scan line
113, an opaque metal gate 114 of the driving TFT and a power line
116. Subsequently, taking the opaque metal gate 112 of the switch
TFT and the opaque metal gate 114 of the driving TFT as masks, an
ion implanting process is performed to form a source 120 and a
drain 122 of the switch TFT in the channel layer 104 and a source
124 and a drain 126 of the driving TFT in the channel layer 108,
respectively.
[0037] In succession, referring to FIG. 2C and FIG. 3C, a
transparent metal layer is formed and patterned over the substrate
100 to form an upper electrode 128 of the storage capacitor, a
transparent metal gate 130 of the switch TFT and a transparent
metal gate 132 of the driving TFT. The transparent metal gate 130
of the switch TFT and the transparent metal gate 132 of the driving
TFT can be a mono-gate structure (as shown in FIG. 2C) or a dual
gate structure (as shown in FIG. 3C). In another embodiment, after
patterning the transparent metal layer, only the upper electrode
128 of the storage capacitor is formed without forming the
transparent metal gate 130 of the switch TFT and the transparent
metal gate 132 of the driving TFT. In further another embodiment,
after patterning the transparent metal layer, the upper electrode
128 of the storage capacitor and one of the transparent metal gate
130 of the switch TFT and the transparent metal gate 132 of the
driving TFT are formed.
[0038] The characteristic of the above-described method is forming
a patterned opaque metal layer first and then forming a patterned
transparent metal layer. In another embodiment, however, the method
can be forming a patterned transparent metal layer first and then
forming a patterned opaque metal layer, which is shown in FIG.
2CC.
[0039] After that, referring to FIG. 2D and FIG. 3D, a dielectric
layer 134 is formed over the substrate 100. The material of the
dielectric layer 134 is, for example, silicon oxide. When the
organic light-emitting layer of the OLED is made of a white organic
light-emitting material, the dielectric layer 134 can be a color
filter. Then, contact openings 136, 138, 140, 141 and 142 are
formed in the dielectric layer 134. The contact openings 136, 138,
140, 141 and 142 expose the source 120 of the switch TFT, the drain
122 of the switch TFT, the source 124 of the driving TFT, the gate
114 or 132 of the driving TFT, the upper electrode 128 of the
storage capacitor and the drain 126 of the driving TFT,
sequentially. Then, an opaque metal layer is formed and patterned
over the substrate 100 and in the contact openings 136, 138, 140,
141 and 142 to form contacts 144, 146, 148, 149, 150 and a scan
line 143. The material of the opaque metal layer is, for example,
titanium, tungsten, molybdenum tungsten alloy or aluminum.
[0040] Referring to FIG. 2E and FIG. 3E, a protection layer 152 is
formed to cover the substrate 100, and a contact opening 154 is
formed in the protection layer 152 to expose the contact 148. Then,
an anode layer 156 of the OLED is formed in the contact opening 154
and on the protection layer 152, wherein the anode layer 156 is
electrically connected to the drain 124 of the driving TFT. The
anode layer 156 is a transparent conductive material, for example,
indium-tin-oxide (ITO) or indium zinc oxide (IZO). Then, another
protection layer 158 is formed over the substrate 100, and an
organic light-emitting layer 160 of the OLED is formed to cover the
anode layer 156. Then, a cathode layer 162 of the OLED is formed on
the organic light-emitting layer 160 to finally form an AMOLED. The
material of the cathode layer 162 can be a transparent conductive
material or an opaque conductive material. In an embodiment, the
material of the cathode layer 162 is, for example, a metal, such as
calcium or aluminum. Then, a cover plate 166 is formed on the
cathode layer 162 to cover the cathode layer 162. The material of
the cover plate 166 is, for example, transparent glass or
transparent plastic. When the organic light-emitting layer 160 of
the OLED is made of a white organic light-emitting material, a
color filter 134 can be disposed between the transparent substrate
100 and the anode layer and another color filter 164 can be
disposed between the cathode layer 162 and the cover plate 166
covering the surface of the cathode layer 162 to obtain
light-emitting effects on both sides of the display panel.
[0041] Though a pixel structure comprised of a switch TFT, a
driving TFT and a capacitor is disclosed hereinabove, however, the
disclosed pixel structure does not limit the present invention. Any
skilled in the art can make various modifications and variations to
the structure of the present invention without departing from the
scope or spirit of the invention. For example, the pixel layout of
an AMOLED can be of a plurality of switch TFTs, a plurality of
driving TFTs and a plurality of capacitors associated with a
plurality of scan lines, which is still protected by a true scope
and spirit of the invention being indicated by the following claims
and their equivalents.
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