Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-12-28
2004-07-13
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S139000, C345S063000, C313S582000
Reexamination Certificate
active
06762819
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-68074, filed on Dec. 31, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device with electrodes on barrier ribs that is adaptive for widening a viewing angle and improving an aperture ratio.
2. Discussion of the Related Art
Generally, an active matrix liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT's) as switching devices to display a natural moving picture. Since such a liquid crystal display can be made into a smaller-size device than the Brown tube or cathode ray tube (CRT), it is commercially available for a monitor such as a portable television or a lap-top personal computer, etc.
The active matrix LCD displays a picture corresponding to video signals, such as television signals, on a pixel (or picture element) matrix having pixels arranged at each intersection between gate lines and data lines. Each pixel includes a liquid crystal cell for controlling a quantity of transmitted light in accordance with a voltage level of a data signal from a data line. The TFT is installed at an intersection between the gate line and the data line to switch a data signal to be transferred to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line.
Such a liquid crystal display device (LCD) can be largely classified into a twisted nematic (TN) mode, in which a vertical electric field is applied, and an in-plane switching (IPS) mode, in which a horizontal electric field is applied to have a wide viewing angle, depending on a direction of an electric field driving a liquid crystal.
In a TN mode LCD as shown in
FIG. 1
, a TFT
30
is provided at an intersection between a data line
22
and a gate line
24
, and pixel electrodes
20
are arranged in a matrix type at a pixel area between the data line
22
and the gate line
24
. As shown in
FIG. 2
, the TFT
30
is provided on a rear substrate
2
. The TFT
30
includes a gate electrode
4
connected to the gate line
24
, a source electrode
14
connected to the data line
22
, and a drain electrode
16
connected to the pixel electrode
20
. A gate insulating film
6
made from SiN
X
or SiO
X
, etc. is entirely deposited on the rear substrate
2
in which the gate electrode
4
is patterned. A semiconductor layer
8
made from amorphous silicon (a-Si) and an ohmic contact layer
10
made from a-Si doped with n+ions are sequentially disposed on the gate insulating film
6
in such a manner to cover the gate insulating film
6
on the gate electrode
4
. A source electrode
14
and a drain electrode
16
made from a metal are formed on the ohmic contact layer
10
. The source and drain electrodes
14
and
16
are patterned in such a manner to be spaced by a predetermined channel width from each other. Subsequently, the ohmic contact layer
10
is etched along a channel defined between the source electrode
14
and the drain electrode
16
to expose the semiconductor layer
8
. A protective film
18
made from SiN
X
or SiO
X
, etc. is entirely deposited on the rear substrate
2
to cover the TFT
30
. The protective film
18
on the drain electrode
16
is etched away to define a contact hole
12
. The contact hole
12
and the pixel area are deposited with indium tin oxide (ITO) to connect the pixel electrode
20
to the drain electrode
16
.
As, shown in
FIG. 3
, the rear substrate
2
provided with the TFT array is opposed to a front substrate
62
provided with black matrices
64
, color filters
66
, and a common electrode
68
of ITO with having a liquid crystal layer
70
therebetween. A gate high pulse is applied to the gate electrode
4
of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode
20
and the common electrode
68
opposed vertically to each other during a scanning interval when a channel is defined between the source electrode
14
and the drain electrode
16
. The liquid crystals of the liquid crystal layer
70
is driven with the vertical electric field to control a quantity of light input from a back light.
Such a TN mode LCD has a drawback in that, since liquid crystal within the pixel cell has a large difference in refractive index and transmissivity depending on an observed angle, the viewing angle is limited. On the other hand, the IPS mode LCD has an advantage in the viewing angle since liquid crystal within the pixel cell is rotated on a basis of horizontal direction by a horizontal electric field.
In an IPS mode LCD as shown in
FIG. 4
, a TFT
50
is provided at an intersection between a data line
52
and a gate line
54
, and pixel electrodes
48
are arranged in a matrix type at a pixel area between the data line
52
and the gate line
54
. As shown in
FIG. 5
, the TFT
50
is provided on a rear substrate
32
. The TFT
50
includes a gate electrode
34
connected to the gate line
54
, a source electrode
42
connected to the data line
52
, and a drain electrode
44
connected to the pixel electrode
48
. The gate electrode
34
and a common electrode
35
are formed on the rear substrate
32
by depositing a metal such as chrome (Cr), etc. and then patterning it. Herein, the common electrode
35
is patterned into a stripe shape within a pixel cell area. A gate insulating film
36
made from SiN
X
or SiO
X
, etc. is entirely deposited on the rear substrate
32
provided with the gate electrode
34
and the common electrode
35
. A semiconductor layer
38
made from amorphous silicon (a-Si) and an ohmic contact layer
40
made from a-Si doped with n+ions are sequentially disposed on the gate insulating film
36
in such a manner as to cover the gate insulating film
36
on the gate electrode
34
. The source electrode
42
and the drain electrode
44
made from a metal are formed on the ohmic contact layer
40
. The source and drain electrodes
42
and
44
are patterned in such a manner as to be spaced by a predetermined channel width from each other. Then, ITO is deposited on the drain electrode
44
and the gate insulating film
36
and thereafter patterned to form the pixel electrode
48
. Herein, the pixel electrode
48
is connected to the drain electrode
44
and is patterned into a stripe shape in such a manner as to be alternated with the common electrode
35
within the pixel cell area. Subsequently, the ohmic contact layer
40
is etched along a channel defined between the source electrode
42
and the drain electrode
44
to expose the semiconductor layer
38
. A protective film
46
made from SiN
X
or SiO
X
, etc. is entirely deposited on the rear substrate
32
to cover the TFT
50
.
As shown in
FIG. 6
, the rear substrate
32
provided with the TFT array is opposed to a front substrate
72
provided with black matrices
74
and color filters
76
, with a liquid crystal layer
78
therebetween. A gate high pulse is applied to the gate electrode
34
of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode
48
and the common electrode
35
opposed horizontally to each other during a scanning interval when a channel is defined between the source electrode
42
and the drain electrode
44
. A liquid crystal of the liquid crystal layer
78
is driven with the horizontal electric field to control a quantity of a light input from a back light.
However, the IPS mode LCD has an advantage in that it can achieve a wide viewing angle, but has a disadvantage in that, since the area occupied by the electrodes within the pixel cell area, particularly the common electrode
35
made from a metal is large, it has a low aperture ratio and transmissivity. The IPS mode LCD, as well as the TN mode LCD, has s
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Ngo Julie
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