Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2003-01-08
2004-08-31
Louie, Wai-Sing (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S151000, C438S153000, C438S157000, C438S161000, C438S164000, C438S197000
Reexamination Certificate
active
06784032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix organic light emitting display (AM-OLED) with an amorphous silicon thin film transistor (a-Si:H TFT) as a driving device and, more particularly, to an AM-OLED with a light-shielding structure that isolates parasitic OLEDs outside a display area and prevents damage to an amorphous silicon layer from subsequent surface treatments.
2. Description of the Related Art
In accordance with driving methods, an organic light emitting display (OLED) can be an active matrix type or a positive matrix type. The active matrix organic light emitting display (AM-OLED) is driven by electric currents, in which each of the matrix-array pixel areas has at least one thin film transistor (TFT), serving as a switch, to modulate the driving current based on the variation of capacitor storage potential so as to control the brightness and gray level of the pixel areas. At present, the AM-OLED is driven by two TFTs in each pixel area, and, alternatively, the AM-OLED is driven by four TFTs in each pixel area.
Concerned with the luminescent principle of the AM-OLED, an electric current is applied to a specific organic lamination to change electricity into luminescence. The AM-OLED has panel luminescence with thin-type and light-weight characteristics, spontaneous luminescence with high luminescent efficiency and low driving voltage, and advantages of view angle, high contrast, high-response speed, full color and flexibility. As for the fabrication of the TFTs in the AM-OLED, an amorphous silicon (a-Si:H) TFT process that has been popularly applied to the fabrication of large-size liquid crystal displays (LCDs) is integrated into the AM-OLED process.
Use of two a-Si:H TFTs in each pixel area is an example to describe the conventional a-Si:H TFT process.
FIG. 1
is a top view showing an a-Si:H TFT of an AM-OLED according to prior art. The AM-OLED comprises a plurality of pixel areas
10
arranged in a matrix form that are constituted by a plurality of data lines
12
extending along a Y direction and a plurality of source lines (also called V
dd
lines)
14
extending along an X direction. Also, each pixel area
10
comprises two scanning lines
16
extending along the X direction, two a-Si:H TFTs
18
respectively disposed over the two scanning lines
16
, a pixel electrode
20
of rectangular-shaped transparent conductive material disposed between the two scanning lines
16
, and a capacitor
22
.
In general, the a-Si:H TFT process can be an etching stopper type and a back channel type. Hereinafter, use of the etching stopper type is an example to describe the a-Si:H TFT process of the prior art.
FIG. 2A
is a sectional diagram along line A-A′ of
FIG. 1
to show the a-Si:H TFT
18
. First, a first metal layer is deposited on a transparent substrate
30
and then patterned as the source line
14
, the scanning line
16
and a bottom electrode of the capacitor
22
. Next, a first insulating layer
32
, a second insulating layer
34
and an a-Si:H layer
36
are successively deposited on the entire surface of the transparent substrate
30
. Then, using photolithography and etching to remove parts of the second insulating layer
34
and the a-Si:H layer
36
, an island structure is patterned over the predetermined area of the a-Si:H TFT
18
. Also, the second insulating layer
34
and the a-Si:H layer
36
disposed over the source line
14
are completely removed. Thereafter, an etch stopper
38
is formed on the island structure over the predetermined area of a gate electrode. After a doped amorphous silicon layer
40
and a second metal layer
42
are successively deposited on the entire surface of the transparent substrate
30
, photolithography and etching are used to remove pars of the doped amorphous silicon layer
40
and the second metal layer
42
, thus the second metal layer
42
is patterned as the data line
12
and an upper electrode of the capacitor
22
. It is noted that the doped amorphous silicon layer
40
and the second metal layer
42
disposed on the island structure remain, and the doped amorphous silicon layer
40
and the second metal layer
42
disposed on the source line
14
are completely removed. Next, using photolithography and etching to form an opening on the island structure over the predetermined area of a gate electrode, the second metal layer
42
is separated as source/drain electrodes
42
A and
42
B and the doped amorphous silicon layer
40
is separated as source/drain diffusion regions
40
A and
40
B. Thus, the amorphous silicon layer
36
serves as a channel region.
Next, a protection layer
44
is deposited on the entire surface of the transparent substrate
30
and then patterned to form at least a first via
45
I, a second via
45
II and a third via
45
III. The first via
45
I and the second via
45
II respectively expose parts of the source/drain electrodes
42
A and
42
B. The third via
45
III passes through the first insulating layer
32
to expose a part of the source line
14
. Finally, a transparent-conductive ITO layer
46
is deposited and patterned on the entire surface of the transparent substrate
30
to serve as the rectangular-shaped pixel electrode
20
. Also, the ITO layer
46
covers the exposed areas of the first via
45
I, the second via
45
II and the third via
45
III to provide electrical connections.
FIG. 2B
is a sectional diagram along line A-A′ of
FIG. 1
to show a parasitic OLED according to the prior art. When the above-described a-Si:H TFT process is completed, a surface treatment is required before the vapor deposition of a organic/polymer luminescent layer
47
and a cathode metal layer
48
. However, the surface treatment normally employs a rinsing process with UV/O
3
light or O
2
plasma that damages the amorphous silicon layer
36
, causing an increased threshold voltage or leakage current. To solve this problem, for the ordinary TFT-LCD process, an annealing treatment additionally applied to the amorphous silicon layer
36
can restore the damaged surface. Nevertheless, for the a-Si:H TFT process, because of the limitation of the subsequent vapor deposition of a organic/polymer luminescent layer
47
, it is impossible to use the annealing treatment to restore the damaged surface.
In addition, with regard to the conventional five-mask a-Si:H TFT process, the ITO layer
46
not only serves as the pixel electrode
20
, but also serves as an electrical bridge between the second metal layer and the second metal layer or between the second metal layer and the first metal layer. Thus, the ITO layer
46
outside the pixel electrode
20
forms a parasitic OLED area
49
that provides luminescence causing unnecessary power consumption and visual interference.
SUMMARY OF THE INVENTION
The present invention provides an AM-OLED with an a-Si:H TFT as a driving device and, more particularly, in which a light-shielding structure electrically isolates parasitic OLEDs outside a display area and prevents damage to an amorphous silicon layer from subsequent surface treatments.
The active matrix organic light emitting display (AM-OLED) has a plurality of pixel areas arranged in a matrix form. Each pixel area has at least two amorphous silicon TFTs, a display area and a light-shielding layer. The amorphous silicon TFT has an amorphous silicon layer serving as a channel region. The display area is formed by a transparent-conductive layer. The light-shielding layer covers at least the amorphous silicon layer of the amorphous silicon TFT and exposes the display area.
For a method of forming the AM-OLED, a first metal layer is formed on a transparent substrate and then patterned as a first scanning line extending along a X direction, a second scanning line extending along the X direction and an bottom electrode of a capacitor, wherein the bottom electrode of the capacitor is between the two scanning lines. Next, a first insulating layer is formed on the entire surface of the transparent substrate. Next, an island structure is formed on
Lee Hsin-Hung
Sung Chih-Feng
Au Optronics Corp.
Ladas & Parry
Louie Wai-Sing
LandOfFree
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