Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-08-01
2002-03-12
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S042000, C349S122000, C349S187000, C257S059000, C257S072000
Reexamination Certificate
active
06356319
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 1999-31744, filed on Aug. 2, 1999, under 35 U.S.C. § 119, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same.
2. Description of Related Art
In general, LCD devices have various advantages that they are thin in thickness and low in power consumption, and so on, in comparison with CRT (cathode ray tube) display devices. Therefore, such LCD devices might be expected to be substituted for CRT display devices and have been a matter of great interest in some industry fields.
A typical LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed therebetween. The upper substrate has a color filter, and the lower substrate has a thin film transistor (TFT) as a switching element. An upper polarizer is arranged on the upper substrate of the liquid crystal panel, and a lower polarizer is arranged between the lower substrate of the liquid crystal panel and the backlight device.
FIG. 1
is a plan view illustrating a portion of a conventional liquid crystal display (LCD) device corresponding to one pixel. As shown in
FIG. 1
, the lower substrate includes gate lines
6
and
8
arranged in a transverse direction, data lines
2
and
4
arranged in a longitudinal direction perpendicular to the gate lines
6
and
8
, and thin film transistors “T” (TFTs) formed near the cross point of the gate and data lines
2
and
8
. Each of the TFTs “T” has a gate electrode
18
, a source electrode
12
and a drain electrode
14
. The gate electrode
18
is extended from the gate line
8
, and the source electrode
12
is extended from the data line
12
and spaced apart from the drain electrode
14
. The lower substrate further includes a pixel electrode
10
formed on a region defined by the gate lines
6
and
8
and the data lines
2
and
4
. The pixel electrode
10
is electrically connected with the drain electrode
14
through a contact hole (not shown) and is usually made of a transparent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO).
FIG. 2
is a cross sectional view taken along line—of FIG.
1
. As shown in
FIG. 2
, a gate insulating layer
20
is formed on the substrate
1
, and the data line
2
is formed on the gate insulating layer
20
. A passavation film
22
is formed on the exposed surface of the gate insulating layer
20
while covering the data line
2
. The pixel electrodes
10
are spaced apart from each other. This is to prevent a cross talk due to an electric field generated around the data line when electrical signals are applied to the data line. In other words, the data line
2
is located at a distance of &Dgr;L from the pixel electrode
10
.
The conventional LCD device having such a structure can reduce an affection of the cross talk, but has a disadvantage that an aperture ratio is reduced as long as &Dgr;L plus an alignment margin because a black matrix has to cover a portion of &Dgr;L.
In order to overcome such a problem, an another conventional LCD device having a structure shown in
FIG. 3
is introduced. The two adjacent pixel electrodes
30
overlap both end portions of the data line
2
, respectively. Thus, because the black matrix needs not be arranged to cover a portion in which the pixel electrodes
30
are distant from the data line
2
, the LCD device can have a high aperture ratio.
However, a parasitic capacitor may be formed vertically between the pixel electrode
30
and the data line
2
, leading to causing a cross talk. As the parasitic capacitance “Cdp” between the pixel electrode
30
and the data line
2
increases, display distortion due to a cross talk gets worse. In addition, when the step and repeat method type exposure is employed in manufacturing process of the LCD device, because the mask having the same pattern is used several times during one process, an alignment error of about 0.4 &mgr;m to about 0.5 &mgr;m may occurs centering on an imaginary boundary line between adjacent two portions to be exposed to light. Due to an alignment error, areas of the parasitic capacitors may become to differ and thus a capacitance difference may occur between the adjacent two parasitic capacitors. Such a capacitance difference affects brightness and a display distortion may be displayed near the imaginary boundary line between adjacent two portions to be exposed to light.
Such a capacitance of the parasitic capacitor depends on a vertical distance between the pixel electrode
30
and the data line
2
. In other words, as a vertical distance between the pixel electrode
30
and the data line
2
become large, the capacitance of the parasitic capacitor becomes small.
FIG. 4
is a plan view illustrating an another conventional LCD device disclosed in Japanese Patent Application No. 10-274782. The LCD device is also introduced to prevent such a cross talk.
FIG. 4
is a cross sectional view taken along line—of
FIG. 4
, and
FIG. 6
is a cross sectional view taken along line—of FIG.
4
. As shown in
FIG. 4
, the conventional LCD device includes a gate line
50
arranged in a transverse direction, a data line
60
arranged in a longitudinal direction perpendicular to the gate line
50
, and thin film transistors
74
(TFTs) formed near the cross point of the gate and data lines
50
and
60
. Each of the TFTs “T” has a gate electrode
51
, a source electrode
61
, and a drain electrode
63
. The gate electrode
51
is extended from the gate line
50
, and the source electrode
61
is extended from the data line
60
and spaced apart from the drain electrode
63
. The conventional LCD device further includes a pixel electrode
70
formed on a region defined by the gate line
50
and the data line
60
. The pixel electrode
70
is electrically connected with the drain electrode
63
through a contact hole
67
. At this point, except for a cross portion of the data line
60
and the gate line
50
, the data line
60
is formed directly on the substrate
1
.
Method of manufacturing the conventional LCD device described above is as follows. As shown in
FIG. 5
, a gate insulating layer
20
is formed on the substrate
1
, and a portion
72
of the gate insulating layer
20
that the data line
60
will be formed is etched, except for a cross portion of the gate line
50
and the data line
60
. Then, the data line
60
is formed at the portion
72
and the passivation film
22
is formed covering the data line
60
and the gate insulating layer
20
. The pixel electrode
70
is formed on the passivation film
22
, overlapping a portion of the passivation film
22
corresponding to an end portion of the data line
60
. The tow adjacent pixel electrodes
70
are spaced apart from each other. In other words, a spaced distance between the adjacent two pixel electrode
30
is narrower than a width of the data line
72
.
Since such a structure can have a lengthy vertical distance between the pixel electrode
70
and the data line
60
, a capacitance of a parasitic capacitor vertically formed between the pixel electrode
70
and the data line
60
can be reduced effectively, leading to reducing an affection of a cross talk. In other words, since a portion
72
of the gate insulating layer
20
is etched and thus the data line
60
is formed directly on the substrate
1
, a thickness of the passivation film
22
over the data line
60
can increase as much as a thickness of the gate insulating layer
20
. Therefore, the capacitance of a parasitic capacitor can be reduced. For example, if a thickness of the gate insulating layer
20
and a vertical distance between the substrate
1
and the pixel electrode
70
are 3000 and 5000 angstrom, respectively, the parasitic capacitance of 60% can be reduced.
However, the conventional LCD device having such a structure requires an additional process th
Park Jae-Deok
Yeo Ju-Cheon
Chowdhury Tarifur R.
LG.Philips LCD Co. , Ltd.
Long Aldridge & Norman LLP
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