Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-12-11
2003-06-24
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000, C349S139000, C349S143000, C349S146000, C345S087000, C257S059000
Reexamination Certificate
active
06583841
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-56020, filed on Dec. 9, 1999, 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 liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, low power consumption characteristics have been used in office automation (OA) equipments and video units and the like. Typically there are two types of LCDs—a twist nematic (TN) mode and a super twist nematic (STN) mode. Although TN-LCDs and STN-LCDs have been in wide use, they have a drawback of a very narrow viewing angle. In order to solve the problem, IPS-LCD devices have been proposed. An IPS-LCD device includes a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having no electrode and a liquid crystal is interposed between the upper and lower substrates.
As shown in
FIG. 1
, lower and upper substrates
1
a
and
1
b
are spaced apart from each other, and a liquid crystal “LC” is interposed therebetween. The lower and upper substrates are called array and color filter substrates, respectively. On the lower substrate
1
a,
pixel and common electrodes
15
and
14
are disposed. The pixel and common electrodes
15
and
14
are parallel with and spaced apart from each other. On a surface of the upper substrate
1
b,
a color filter
25
is disposed facing the lower substrate
1
a.
The pixel and common electrodes
15
and
14
apply an electric field “E” to the liquid crystal “LC”. The liquid crystal “LC” has a negative dielectric anisotropy, and thus it is aligned parallel with the electric field “E”.
FIGS. 2
to
5
conceptually illustrate operation modes of a typical IPS-LCD device. When the electric field is not generated between the pixel and the common electrodes
15
and
14
, the long axes of the LC molecules “LC” maintain an angle relative to a perpendicular line to the parallel pixel and common electrodes
15
and
14
. For example, the angle is 45 degrees.
When the electric field is generated between the pixel and common electrodes
15
and
14
, because both of the pixel and common electrodes
15
and
14
are formed on the lower substrate
1
a,
the in-plane electric field “E”, which is parallel to the surface of the lower substrate
1
a
, is generated between the pixel and common electrodes
15
and
14
. Accordingly, the LC molecules “LC” move to coincide the long axes thereof with the electric field direction, and the LC molecules “LC” become aligned such that the long axes thereof is parallel with the perpendicular line to the pixel and common electrodes
15
and
14
.
By the above-mentioned operation modes and with additional elements such as polarizers and alignment layers, the IPS-LCD device displays images. The IPS-LCD device has wide viewing angles, low color dispersion qualities, and the fabricating processes thereof are simpler as compared to other LCD devices. But, since the pixel and common electrodes are disposed on the same plane of the lower substrate, the transmittance and aperture ratio are low.
For the sake of discussing the above-mentioned problem of the IPS-LCD device in detail, the structure of the IPS-LCD device will be described in detail with reference to
FIGS. 6A and 6B
.
FIG. 6A
is a plan view illustrating in detail the structure of one pixel region in the IPS-LCD device, specifically, a unit pixel region
10
. In addition, a cross-sectional view taken along a line “B—B” in
FIG. 6A
is illustrated in FIG.
6
B.
On the surface of the transparent substrate
1
A adjacent to the liquid crystal layer, a gate line (or scan signal line)
2
made of, for example, aluminum (Al) is formed extending along the x-direction. In addition, a common line (or reference signal line)
4
is formed extending along the x-direction, close to the gate line
2
on the +y-direction side thereof. The common line
4
is also made of, for example, Al. A region surrounded by the gate line
2
, the common lines
4
, and the data lines
3
constitutes a pixel region, as previously described.
In addition, the pixel region
10
includes a common electrode
14
formed by the common line
4
, and another common electrode
14
formed adjacent to the gate line
2
. The pair of horizontally extending common electrodes
14
are positioned adjacent to one of a pair of data lines
3
(on the right side of FIG.
6
A), and are electrically connected to each other through a conductive layer
14
A which is formed simultaneously with the common electrodes
14
.
In the structure described above, the pair of common electrodes
14
extend in the direction parallel with the gate line
2
. In other words, the common electrodes
14
take the form of a strip extending in a direction perpendicular to the data lines
3
.
On the surface of the lower substrate
1
a
on which the gate lines and other lines discussed above are formed, a first insulating film
11
(see
FIG. 6B
) made of, for example, silicon nitride is formed overlying the gate line
2
, the common lines
4
, and the common electrodes
14
. This first insulating film
11
functions as an inter-layer insulating film for insulating the gate line
2
and the common lines
4
from the data lines
3
as a gate-insulating layer for a region in which a thin film transistor “TFT” including a drain electrode
3
a
and a source electrode
15
a
is formed. The first insulating film
11
also acts as a dielectric film for a region in which a capacitor Cstg is formed. A semiconductor layer
12
for the TFT is formed near a cross point of the gate and data lines
2
and
3
. On the other surface of the lower substrate
1
a,
a first polarization layer
18
is formed.
On the first insulating film
11
, a pixel electrode
15
is formed parallel with the common electrode
14
. An end portion thereof is electrically connected with the conductive layer
14
a,
and the other portion thereof is electrically connected with the source electrode
15
a
. A first planar film
16
is formed on the first insulating film
11
to cover the pixel electrode
15
, and on the first planar film
16
, a first alignment film
17
is formed.
FIG. 6B
illustrates a cross-sectional view of the upper substrate
1
b
on which a black matrix
300
is formed. In the opening of the black matrix
300
, a color filter
25
is formed to fill the opening. Then, a second planar film
27
is formed to cover the color film
25
and the black matrix
300
, and a second alignment layer
28
is formed on the surface of the second planar film
27
facing the liquid crystal layer.
The color filter
25
is formed to define three sub-pixel regions adjacent to and extending along the data line
3
and including a red (R) filter, a green (G) filter, and a blue (B) filter, for example, from the top of the three sub-pixel regions. The three sub-pixel regions constitute one pixel region for a color display.
A second polarization layer
29
is arranged on the surface of the upper substrate
1
b
opposite to the surface adjacent to the liquid crystal layer on which various films are formed as described above.
In
FIG. 6B
, a voltage applied between the common electrodes
14
and the pixel electrode
15
causes an electric field E to be generated in the liquid crystal layer LC in parallel with the respective surfaces of the lower and upper substrates
1
a,
1
b
. This is the reason why the illustrated structure is referred to as in-plane switching.
As shown in
FIG. 7
, if a distance “L” between the common and pixel electrodes
14
and
15
becomes longer, the aperture ratio problem can be solved. However, a larger “L” causes the threshold voltage to drive the liquid crystal to be higher. That is to say, the threshold voltage “V
th
” is proportional to “L/d”, where “d” is t
Chung In-Jae
Youn Won-Gyun
Chowdhury Tarifur R.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
LandOfFree
In-Plane switching LCD panel wherein pixel electrodes and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with In-Plane switching LCD panel wherein pixel electrodes and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and In-Plane switching LCD panel wherein pixel electrodes and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3163816