Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-11-06
2004-07-06
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S139000, C257S059000, C257S072000, C345S092000
Reexamination Certificate
active
06760082
ABSTRACT:
BACKGROUND OF THE INVENTION
(A) Field of the Invention
The present invention relates in general to a thin film transistor (TFT) array substrate. In particular, the present invention relates to a TFT array substrate with high aperture ratio pixel structure.
(B) Description of Related Art
Currently, liquid crystal display (LCD), having the advantages of low power consumption, being thin type, light weight and having low driving-voltage, has been put to practical use, such as in personal computers, archival treatments, navigation systems, projectors, view finders and portable machines (watches, electronic calculators and televisions). The applied electric field on the LCD changes the alignment of liquid crystals that possess the characteristics of dielectric anisotropy and conducting anisotropy, and then the accompanied optical effects will be transformed into visional variation. A LCD employing a thin film transistor (TFT) as an active device is named TFT-LCD, which is good for low power consumption, is thin type, light weight and has low driving-voltage.
FIG. 1A
is a top view showing a pixel structure of conventional TFT-LCD. The scanning lines
110
and the signal lines
120
are arranged in a matrix form. Thin film transistor (TFT)
130
is disposed over the scanning line
110
, and a pixel electrode
140
is electrically connected to the TFT
130
. A black matrix
150
(as shown in
FIG. 1B
) has a window
152
pervious to light.
FIG. 1B
is a sectional view showing the structure along the line A-A′ of FIG.
1
A. The scanning line
110
(not shown in FIG.
1
B), signal lines
120
and pixel electrode
140
are formed on the lower substrate
102
. The black matrix
150
and the window
152
are formed on the upper substrate
104
. Because the light passing through the edge of the pixel electrode
140
is shielded by the black matrix
150
to avoid light leakage, the transmittance area I is only just as broad as the window
152
. In other words, the aperture ratio is reduced. Therefore, another proposal of improved pixel structure is disclosed.
FIG. 2A
is a top view showing another pixel structure of conventional TFT-LCD. Two floating electrodes
160
are disposed on the lower substrate
102
(as shown in
FIG. 2B
) to shield the leakage light passing through from the edge of the pixel electrode
140
near the signal lines
120
.
FIG. 2B
is a sectional view showing the structure along the line B-B′ of FIG.
2
A. Therefore, the window
154
of the black matrix
150
is broader than the window
152
shown in FIG.
1
B. In another word, the transmittance area II is bigger than the transmittance area I (as shown in
FIG. 1B
) so the aperture ratio of pixel structure is improved. Moreover, the aperture ratio of the pixel structure shown in
FIG. 2A
is increased about 3% comparing to the pixel structure shown in FIG.
1
A.
However, the aperture ratio of
FIG. 2A
is still decreased under a misalignment assembly process.
FIG. 3
is a sectional view showing a state of misalignment assembly of conventional TFT-LCD. The upper substrate
104
is shifted along the direction of an arrow
180
under the misalignment assembly process, and the black matrix
150
following the upper substrate
104
is also shifted. Therefore, the transmittance area is decreased from II to II′, and the improved aperture ratio is reduced again. According to actual experiment result, shifting the black matrix
150
1 &mgr;m decreases the aperture ratio 1% the aperture ratio 1%. For this reason, if the black matrix
150
is shifted more than 3 &mgr;m, the aperture ratio will be reduced more than 3%. Consequently, the improved aperture ratio will be canceled out completely.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a TFT array substrate with high aperture ratio pixel structure to solve the problems caused by above conventional TFT-LCD.
This TFT array substrate with high aperture ratio pixel structure comprises a plurality of signal lines and a plurality of scanning lines formed on the substrate. Each paired and adjacent signal lines and each scanning line are arranged in a matrix form to define each pixel unit, each pixel unit includes at least two pixels, and the two pixels are abreast the paired and adjacent signal lines. Each pixel includes at least a thin film transistor disposed on the scanning line. A first floating electrode is disposed parallel to the signal lines and located on a side of the pixel adjacent to the signal line. A second floating electrode is located on the opposite side of the pixel and stretches over to the adjacent pixel. A pixel electrode is formed partially overlapping the first floating electrode and the second floating electrode, and is electrically connected to the thin film transistor.
According to this TFT array substrate of the present invention, each paired and adjacent signal lines and each scanning line are arranged in a matrix form to define each pixel unit, and each pixel unit includes at least two pixels. Therefore, at least one of the aperture ratios of the two pixels is fixed under a misalignment assembly process. For this reason, the whole aperture ratio of each pixel unit is still improved under the misalignment assembly process.
The other object of the present invention is to provide a thin film transistor liquid crystal display using above TFT array substrate, comprising a first substrate and a second substrate. A liquid crystal layer is disposed between the first substrate and the second substrate. A plurality of pixel units are formed on the first substrate, and includes a plurality of signal lines and a plurality of scanning lines. Each paired and adjacent signal lines and each scanning line are arranged in a matrix form to define each pixel unit. Each pixel unit includes at least two pixels, and the two pixels are abreast the paired and adjacent signal lines. Each pixel at least comprises a thin film transistor disposed on the scanning line. A first floating electrode is disposed parallel to the signal lines, and located on a side of the pixel adjacent to the signal line. A second floating electrode is located on the opposite side of the pixel and stretches over to the adjacent pixel. A pixel electrode is formed partially overlapping the first floating electrode and the second floating electrode, and is electrically connected to the thin film transistor. A plurality of black matrixes are formed on the second substrate, wherein the plurality of black matrixes have a plurality of windows, and each window corresponds to a space between the first two floating electrodes in each the pixel units.
REFERENCES:
patent: 5457553 (1995-10-01), Mori
patent: 5701166 (1997-12-01), Fedorovish et al.
patent: 5844647 (1998-12-01), Maruno et al.
patent: 6028577 (2000-02-01), Sakamoto
Chowdhury Tarifur R.
HannStar Display Corp.
Morris Manning & Martin
Nguyen Hoan Chau
Tingkang Xia, Esq. Tim
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