Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-06-01
2003-10-28
Whitehead, Jr., Carl (Department: 2813)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S049000, C349S139000
Reexamination Certificate
active
06639633
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 2000-30189, filed on Jun. 1, 2000, 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 (LCD) device, and more particularly, to a capacitor electrode of a storage capacitor for use in a LCD device.
2. Description of Related Art
In general, LCD devices have various advantages including being 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.
FIGS. 1A and 1B
are schematic views illustrating a typical liquid crystal display (LCD) device. As shown in
FIG. 1A
, the LCD device
11
includes first and second substrates
5
and
22
, and an interposed liquid crystal layer
14
having liquid crystal molecules therebetween. The first substrate
5
as an upper substrate includes a color filter
7
and a transparent common electrode
18
formed against the color filter
7
. The second substrate
22
as a lower substrate includes pixel regions “P”, pixel electrodes
17
formed on the pixel regions “P”, gate lines
13
arranged in a transverse direction, data lines
15
arranged in a perpendicular direction to the gate lines
13
, and thin film transistors (TFTs) “T” arranged near crossing points of the gate and data lines
13
and
15
.
Each TFT “T” includes an active layer
36
, a gate electrode
35
, and source and drain electrodes
31
and
33
. The gate electrode
35
contacts with the gate line
13
and the source electrode contacts
31
with the data lines
15
. Also, the drain electrode
33
contacts with the pixel electrode
17
. The pixel electrode
17
, an insulating layer (not shown) and the gate line
13
, which are stacked in the above-described order, form a storage capacitor (not shown).
Further, the storage capacitor may be formed by adding a capacitor electrode
37
. In other words, as shown in
FIG. 2
, the pixel electrode
17
, the insulating layer (not shown) and the capacitor electrode
37
, which are stacked in above-described order, form the storage capacitor “C”. The capacitor electrodes
17
are equidistantly arranged in a direction parallel to the gate line
13
.
FIG. 3
shows a conventional in-plane switching (IPS) type LCD device. As shown in
FIG. 3
, in the conventional IPS type LCD device, the pixel electrode
17
and the common electrode
18
are arranged on the same substrate, i.e., the lower substrate, and branches
17
a
of the pixel electrode
17
are interposed between branches
18
a
of the common electrode
18
. Further, the pixel electrode
17
, an insulating layer (not shown) and the gate line
13
, which are stacked in the above-described order, form a storage capacitor “C”. When a voltage is applied to the pixel electrode
17
and the common electrode
18
, a parallel electric field is formed. The parallel electric field operates liquid crystal molecules.
FIG. 4
shows a conventional LCD device having a storage capacitor shown in FIG.
2
. The storage capacitor having a structure shown in
FIG. 2
is formed on the pixel region and usually uses a separate capacitor electrode line to apply a voltage. A voltage that is applied to the storage capacitor is obtained by using a common voltage that is applied to the upper substrate or by supplying a separate capacitor voltage. The storage capacitor shown in
FIG. 4
does not use a separate voltage and uses a common voltage as a capacitor voltage by connecting the capacitor electrode line with the common electrode line.
As shown in
FIG. 4
, the upper substrate
5
has a common electrode (reference
18
of FIG.
1
), and the lower substrate
22
includes the gate lines
13
arranged in a transverse direction and the data lines (not shown) arranged in a direction perpendicular to the gate lines
13
. The lower substrate
22
further includes the capacitor electrode lines
37
equidistantly arranged in a direction parallel to the gate lines
13
. Both terminals of the capacitor electrode lines
37
are electrically connected with each other, respectively. The gate lines
13
are connected with a gate driver
57
transferring signals through a gate pad
41
. The data lines (not shown) are connected with a data driver
59
transferring signals through a data pad (not shown).
The gate and data drivers
57
and
59
, in
FIG. 4
are mounted on the tape carrier package (TCP), and the TCP having the gate driver is referred to as a gate TCP and the TCP having the data driver is referred to as a data TCP. A capacitor voltage may be usually supplied through either the gate TCP or the data TCP.
In
FIG. 4
, a capacitor voltage is supplied through the data TCP. The gate line
13
has an electrostatic circuit
62
at an end portion opposite to the gate pad
41
. Though the electrostatic circuit
62
is connected with the capacitor electrode line
37
, the gate line
13
is electrically independent of the capacitor electrode line
37
under a normal condition. However, when an overcurrent flows along the gate line
13
due to the static electricity, the gate line
13
and the capacitor electrode line
37
are electrically connected with each other by a static electricity across the electrostatic circuit
62
. As a result, an equipotential is formed between the gate line
13
and the capacitor electrode line
37
, thereby preventing a line open of the gate line
13
due to the static electricity.
The capacitor electrode line
37
is electrically connected with dot patterns
63
made of Ag paste, which are located at four corners of the lower substrate
22
for connection with the common electrode (not shown) of the upper substrate. Further, the capacitor electrode lines
37
are connected with an auxiliary capacitor electrode line
38
, which is connected with the data drivers
59
via connecting lines
39
.
In a storage capacitor having such a capacitor electrode line
37
, when a capacitor voltage is applied to the capacitor electrode line
37
through the data drivers
59
respectively arranged on upper and lower regions of the lower substrate
22
, a current flows in two direction, i.e., from both end portions to a central portion. A capacitor voltage level gets to be lowest at a central portion of the capacitor electrode line
37
due to a line resistance of the capacitor electrode line
37
, and therefore a gray level becomes lowest at the central portion of the capacitor electrode line
37
, whereby a central portion of a screen looks white or dark. That is, display characteristics of the LCD device vary according to the pixel position on the pixel matrix being considered.
FIG. 5
shows the IPS type LCD device shown in FIG.
3
. As shown in
FIG. 5
, common electrode lines
18
of the IPS type LCD device are arranged in a direction parallel to the gate lines
13
just like the capacitor electrode line
37
of the LCD device shown in FIG.
4
. When a capacitor voltage is applied to the common electrode line
18
from the data drivers
59
respectively arranged on upper and lower regions of the lower substrate
22
, a current flows in two directions, i.e., from both end portions to a central portion. A capacitor voltage level gets to become lowest at a central portion of the common electrode line
18
due to its line resistance, a gray level becomes lowest at the central portion of the common electrode line
18
, whereby a central portion of a screen looks white or dark. That is, display characteristics of the IPS type LCD device vary according to the pixel position being considered on the pixel matrix.
In other words, in case of a normally white state that a screen shows a black state when a voltage is applied to the liquid crystal layer, since a low voltage is applied to the central portions of the capacitor or common electrode lines, a arrangement state of the liquid crysta
Kim Geon-Tae
Song In-Duk
Birch & Stewart Kolasch & Birch, LLP
Jr. Carl Whitehead
LG. Philips LCD Co. LTD
Nguyen Thanh
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