Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-07-10
2001-07-10
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06259502
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an in-plane switching mode liquid crystal display device.
B. Description of the Related Art
Recently, the thin film transistor liquid crystal display device (TFT LCD) has been used as a display device of many applications such as a portable television and a notebook computer, but such TFT LCD has a small viewing angle.
In order to solve this problem, twisted nematic LCDs having optical compensation plates and a multi-domain LCD, and so forth, have been introduced. In these LCDs, however, the color of the image is shifted because the contrast ratio depends on the viewing angle direction.
For a wide viewing angle, an in-plane switching mode LCD is disclosed, for example, in JAPAN DISPLAY 92 p547, Japanese Patent Unexamined Publication No. 7-36058, Japanese Patent Unexamined Publication No. 7-225388, and ASIA DISPLAY 95 P707.
FIG. 1
a
and
FIG. 1
b
are respectively plane and sectional views showing the conventional in-plane switching mode liquid crystal display device (IPS mode LCD).
FIG. 1
b
is a sectional view taken along line A-A′ of
FIG. 1
a
. As shown in these figures, a gate bus line
1
and a data bus line
2
are formed on a first substrate
10
, defining a pixel. Although only one pixel is drawn in the figures, a liquid crystal display device generally has a plurality of pixels. A common bus line
3
is aligned in the pixel, being parallel to gate bus line
1
. A thin film transistor (TFT) is disposed at the cross of gate and data bus lines
1
and
2
. As shown in
FIG. 1
b
, the TFT comprises a gate electrode
5
, a gate insulator
12
, a semiconductor layer
15
, an ohmic contact layer
16
and source/drain electrodes
6
and
7
. In the pixel, a data electrode
8
and a common electrode
9
are formed parallel to data bus line
2
. A portion of data electrode
8
which overlaps common bus line
3
is formed to obtain a storage capacitor which functions as maintaining a grey level voltage applied into data electrode
8
. Common electrode
9
is connected to common bus line
3
. Data electrode
8
is formed on gate insulator
12
and is connected to drain electrode
7
. The TFT, data electrode
8
and gate insulator
12
are covered with a passivation layer
20
. Thereon, a first alignment layer
23
a
is coated to impart an alignment direction.
On a second substrate
11
, a black mask
28
is formed to prevent a leakage of light through the regions of the TFT and gate, data and common bus lines
1
,
2
, and
3
. Thereon, a color filter layer
29
and a second alignment layer
23
b
are formed. Between first and second substrates
10
and
11
, a liquid crystal layer
30
is formed.
When a voltage is applied to the conventional IPS mode LCD, an electric field parallel to substrates
10
and
11
is generated between data and common electrodes
8
and
9
. Liquid crystal molecules in the pixel are rotated according to the electric field, controlling the amount of light passing through liquid crystal layer
30
.
However, the conventional IPS mode LCD has the following problems. First, because the area for storage capacitor occupies quite a portion of the pixel region, and the data and common electrodes are made of opaque metals, the aperture ratio is lowered. Second, because the electric field applied to the LC layer is weakened by both gate insulator
12
and passivation layer
20
formed over two electrodes
8
and
9
, the driving speed of the LC molecules is decreased, and consequently the driving voltage is increased. Third, because data bus line
2
should be apart from the pixel region to the extent of not generating the crosstalk problem, the pixel region is decreased, thereby lowering the aperture ratio.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an in-plane switching mode liquid crystal display device having a low driving voltage.
Another object of the present invention is to provide an in-plane switching mode liquid crystal display device having an improved aperture ratio.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises: a substrate; a common bus line over the substrate; a first insulator over the common bus line; a first electrode over the first insulator, the first electrode at least partially covering the common bus line to form a first storage capacitor between the first electrode and the common bus line; a second insulator over the first electrode; and a second electrode over the second insulator, the second electrode at least partially covering the first electrode to form a second storage capacitor between the first and second electrodes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
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S. Matsumoto, et al., “LP-A: Display Characteristics of In-Plane-Switching (IPS) LCDs and a Wide-Viewing-Angle 14.5-in. IPS TFT-LCD,” Euro Display '96, pp. 445-448.
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Finnegan Henderson Farabow Garrett & Dunner L.L.P.
LG Electronics Inc.
Malinowski Walter J.
LandOfFree
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