Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2003-04-29
2004-11-09
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S042000, C349S110000, C349S155000, C438S149000
Reexamination Certificate
active
06816210
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a method for forming pixel electrodes of a liquid crystal display (LCD), and more particularly, to a self-aligned method for forming the pixel electrodes of a thin-film transistor LCD (TFT-LCD).
2. Description of the Prior Art
Since the LCD has the advantages of portability, low power consumption, and low radiation, the LCD has been widely used in various portable information products, such as notebooks, personal digital assistants (PDA), and etc.
A color filter formed on an array (COA) is a new technology and has been commonly used to form a COA type TFT-LCD. In order to maintain the thickness of a liquid crystal layerin the TFT-LCD, namelya cell gap, plastic beads, glass beads, or glass fibers are normally interposed between two substrates of the TFT-LCD and used as spacers to precisely control the cell gap to a specific value to ensure the performance of the display. In the conventional TFT-LCD process, the spacers are positioned by spraying, and tend to be mal-distributed. Consequently, the contrast of the TFT-LCD is affected due to light scattering by the spacers that are present in the light transmitting regions, generating white point defects and reducing yield rates and the display performance. For this reason, photo spacers formed by a photolithographic process have been developed to replace the conventional plastic beads to control the dimensions and positions of the spacers and the uniformity of the cell gap to accurately raise the display performance. Moreover, the photo spacers positioned in the light opaque regions can be used to prevent the light leakage problem caused by the plastic beads.
Please refer to
FIG. 1
to
FIG. 3
, which are schematic diagrams of a method for forming a COA type TFT-LCD
10
. As shown in
FIG. 1
, a plurality of scan lines and a plurality of signal lines perpendicular to the scan lines (not shown in
FIG. 1
) are formed on a surface of a bottom glass substrate
12
of the TFT-LCD
10
. The signal lines and the scan lines define a plurality of adjacent pixel electrode regions
14
on the bottom glass substrate
12
. Each pixel electrode region
14
includes a TFT structure
16
comprised of a polysilicon layer, a top gate conductive layer, a gate dielectric layer, a channel layer, a source electrode, and a drain electrode (not shown in FIG.
1
).
Then, a planarizing layer
18
is formed on the TFT structures
16
, and a black photoresist layer (not shown in
FIG. 1
) is formed on the planarizing layer
18
. Next, a photo-etching process (PEP) is performed to form a plurality of black matrix (BM) layers
20
in the black photoresist layer corresponding to the underlying TFT structures
16
respectively, so as to improve the contrast of the TFT-LCD
10
, prevent the TFT structures
16
from generating the light leakage current, and shade the oblique leaking light during operation of the TFT-LCD
10
. Thereafter, a red color filter layer (not shown in
FIG. 1
) is formed on the bottom glass substrate
12
, and another PEP is performed to form a red color filter array (CFA)
22
in the red color filter layer. The red color filter layer is composed of a photoresist containing a red dye in an amount of 10 to 50 wt % (dry weight) or a photosensitive resin. Afterwards, a green CFA
24
and a blue CFA
26
are formed on the bottom glass substrate
12
by repeating the above-mentioned processes with dyes of different colors. Thus, an R/G/B CFA comprises the red CFA
22
, the green CFA
24
, and the blue CFA
26
.
An overcoat layer
28
and a photoresist layer (not shown in
FIG. 1
) are formed on the R/G/B CFA, respectively, and a PEP is performed to form a plurality of contact holes (not shown in
FIG. 1
) in the overcoat layer
28
, the R/G/B CFA
22
,
24
,
26
, the BM layer
20
, and the planarizing layer
18
. Next, a transparent conductive layer
30
with low impedance, such as indium tin oxide (ITO), is deposited on the bottom glass substrate
12
and fills the contact holes to form a plurality of contact plugs
32
for connecting the transparent conductive layer
30
and the drain electrodes of the TFT strictures
16
. Afterwards, another PEP is performed to remove portions of the transparent conductive layer
30
, and an orientation film
34
is formed on the transparent conductive layer
30
.
As shown in
FIG. 2
, another transparent conductive layer
38
is formed on a top glass substrate
36
of the TFT-LCD
10
, and a plurality of protrusions
40
with a thickness of approximately 3 micrometers (&mgr;m) are formed on the transparent conductive layer
38
. Then, a plurality of spacers
42
with a thickness of approximately 5 &mgr;m are formed on the protrusions
40
. The spacers
42
are composed of photosensitive polyimide (PI) materials. Further, a spin-coating process is performed to form an orientation film
44
on the top glass substrate
36
.
As shown in
FIG. 3
, the top glass substrate
36
and the bottom glass substrate
12
are positioned face to face, so that each protrusion
40
corresponds to a side of the pixel electrode regions
14
, and each spacer
42
corresponds to an intersection of each signal line and each scan line. Then, a liquid crystal layer
46
is formed between the top glass substrate
36
and the bottom glass substrate
12
to complete the fabrication of the conventional TFT-LCD
10
.
However, the conventional method for forming the TFT-LCD
10
has to utilize the PEP many times to form the BM layer
20
, the R/G/B CFA
22
,
24
,
26
, the transparent conductive layer
30
of the bottom glass substrate
12
, the protrusions
40
, and the spacers
42
of the top glass substrate
36
, respectively, consequently leading to a complicated process and a raised production cost. In addition, due to a misalignment phenomenon caused by performing the PEP many times, the BM layer
20
may not shield the underlying TFT structures
16
perfectly, generating light leakage, and affecting the normal operation of the TFT-LCD
10
.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a self-aligned method for forming pixel electrodes of the LCD to simply the process and reduce the production cost.
It is another object of the claimed invention to provide a method for forming a TFT-LCD, with spacers formed between two substrates of the TFT-LCD also functioning as a black matrix layer of the TFT-LCD.
According to the preferred embodiment of the claimed invention, a method for forming a self-aligned pixel electrode of a TFT-LCD is disclosed. The TFT-LCD is formed on a substrate that comprises a plurality of scan lines and a plurality of signal lines perpendicular to the scan lines. The scan lines and the signal lines define a plurality of adjacent pixel electrode regions on the substrate. First, a photosensitive material layer is formed on the substrate and portions of the photosensitive material layer inside the pixel electrode regions are removed to leave a residual photosensitive material layer on the scan lines and the signal lines. The residual photosensitive material layer is used as a spacer and a top surface area of the spacer is larger than a bottom surface area of the spacer. Then, a transparent conductive layer is formed on the substrate to cover the spacer and the pixel electrode regions. The transparent conductive layer that covers the pixel electrode regions is separated from the spacer so as to form the self-aligned pixel electrode.
In the claimed invention, the residual photosensitive material layer having an undercut profile formed on the scan lines and the signal lines functions as the spacer of the TFT-LCD. Therefore, the transparent conductive layer formed in a subsequent process is separated from the spacer. Therefore, the present invention has the advantages of simplifying the process, reducing cost, and solving the misalignment problem caused by performing the PEP many times.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary sk
Chowdhury Tarifur R.
Hsu Winston
Toppoly Optoelectronics Corp.
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