Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-27
2001-11-20
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S144000
Reexamination Certificate
active
06320637
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a liquid crystal display (LCD) with a wide viewing angle, and more particularly to a LCD being capable of obtaining a wide viewing angle by simultaneously generating electric fields parallel and perpendicular to a surface of a substrate within an unit pixel area.
An in plane switching (IPS) mode LCD is developed by Hitachi, Ltd., in Japan so as to compensate the viewing angle of a TN mode LCD, which is disclosed in Asia display '95, p 577-850, “Principle and characteristic of electro-optical behaviour with in-plane switching mode”. In the IPS mode LCD, as shown in
FIG. 1
, electrodes
2
a
and
2
b
being spaced with each other are arranged on the same front surface of the substrate
1
. An homogeneous alignment layer (not shown) is formed over the front surface of the substrate where the electrodes
2
a
and
2
b
are arranged. The homogeneous alignment layer is rubbed to make a predetermined angle, for example an angle of 45 degrees with the electrons
2
a
and
2
b
. Although not shown in
FIG. 1
, a first polarizer which has the same polarization axis as a rubbing direction of the homogeneous alignment layer, is disposed over a rear surface of the substrate and a second polarizer which has a polarization axis parallel to the polarization axis of the first polarizer, is disposed over a rear surface of an opposite substrate.
The operation of the IPS mode LCD will be described as follows. First, if a voltage is not applied to the electrodes
2
a
and
2
b
, liquid crystal (LC) molecules
3
are arranged to make the longitudinal axes of LC molecules
3
to be in parallel to the rubbing direction of the homogeneous alignment layer. Accordingly, the picture of the LCD becomes dark state.
On the other hand, if a voltage is applied to the electrodes
2
a
and
2
b
, an electric field is generated between the electrodes
2
a
and
2
b
. Because the electrodes
2
a
and
2
b
are disposed over the same substrate, the direction of the electric field is in parallel to the surface of the substrate. According to this, LC molecules which are arranged in the rubbing direction of the homogeneous alignment layer, are twisted in the clockwise direction to make the longitudinal axes of the LC molecules to be in parallel to the direction of the electric field, if LC molecules are positive dielectric anisotropy. Therefore, the picture of the LCD becomes white state.
However, when an electric field is generated, that is when it is a white state, color of the picture in the prior IPS mode LCD becomes different according to the viewing angle due to the anisotropy of reflection index of the LC molecules. More detailedly speaking, when one views the picture of the IPS mode LCD in the X direction of
FIG. 1
, the one views the short axes of the LC molecules so that the picture of the LCD brings out blue color having a short wavelength rather than white color.
On the other hand, when one views the picture of the IPS mode LCD in the Y direction, the one views the longitudinal axes of the LC molecules
3
b
so that the picture of the LCD brings out yellow color having a long wavelength rather than white color. Therefore, the picture quality of the IPS mode LCD becomes degraded due to the color shift phenomenon. The above color shift phenomenon is detailedly disclosed in SID '97, p 929-932.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a LCD with a wide viewing angle being capable of preventing the color shift in a white state.
According to an aspect of the present invention, there is provided to a wide viewing angle liquid crystal display, comprising: a lower and an upper substrates being opposed with interleaving a liquid crystal layer; a data bus line and a gate bus line being arranged over the lower substrate and being arranged to be perpendicularly crossed with each other to form an unit pixel region, the unit pixel region being divided into a first region and a second region; a switching devices being arranged at an intersection of the data bus line and the gate bus line; first and second counter electrodes; and a pixel electrodes being arranged in the unit pixel region, which a display signal is applied thereto, wherein when the switching device is turned on, the liquid crystal molecules in the unit pixel region twistedly arranged and when the switching device is turned off, an electric field perpendicular to a surface of the lower surface is generated in the first region of the unit pixel region and at the same time, an electric field parallel to the surface of the lower substrate is generated in the second region of the unit pixel region.
There is also provided to a wide viewing angle liquid crystal display, comprising: a lower and an upper substrates being opposed with interleaving a liquid crystal layer; a data bus line and a gate bus line being arranged over a front surface of the lower substrate and being arranged to be perpendicularly crossed with each other to form an unit pixel region, the unit pixel region being divided into a first region and a second region; a switching device being arranged at an intersection of the data bus line and the gate bus line; a pixel electrode being connected to the switching device, which a display signal is applied thereto in turning the switching device on; and first and second counter electrodes forming electric fields with the pixel electrode, wherein in the first region of the unit pixel region, the pixel electrode and the first counter electrode are disposed in the lower and upper substrates, respectively to be opposed with interleaving the liquid crystal layer and in the second region of the unit pixel region, the pixel electrode and the second counter electrode are alternatively disposed over the same substrate.
There is further provided to a wide viewing angle liquid crystal display, comprising: a lower and an upper substrates being opposed with interleaving a liquid crystal layer; a data bus line and a gate bus line being arranged over a front surface of the lower substrate and being arranged to be crossed with each other to form an unit pixel region, the unit pixel region being divided into first region and the second region; a switching device being arranged at an intersection of the data bus line and the gate bus line; a first counter electrode being arranged in the unit pixel region over the front surface of the lower substrate, the first counter electrode having a frame structure; a pixel electrode being arranged in the unit pixel region over the first counter electrode, the pixel electrode including a sheet portion being formed in the first region of the unit pixel region and a rod portion being formed in the second region of the unit pixel region; a second counter electrode disposed over a portion of the upper substrate corresponding to the unit pixel region, the second counter electrode including a sheet portion being formed at the portion of the upper substrate corresponding to the first region and a frame portion being formed at the portion of the upper substrate corresponding to the second region; first and second alignment layers disposed over the lower and upper substrates, respectively; and first and second polarizers disposed over rear surfaces of the lower and upper substrates, respectively, wherein an electric field perpendicular to the surface of the substrate is generated between the sheet portion of the pixel electrode and the sheet portion of the second counter electrode and at the same time, an electric field parallel to the surface of the substrate is generated between the rod portion of the pixel electrode and the first counter electrode of the frame structure.
There is further still provided to a wide viewing angle liquid crystal display, comprising: a lower and an upper substrates being opposed with interleaving a liquid crystal layer;
a data bus line and a gate bus line being arranged over a front surface of the lower substrate and being arranged to be crossed with each other to form an unit pixel region, the unit pixel regio
Kim Hyang Yul
Lee Seung Hee
Dudek James A.
Hyundai Electronics Industries Co,. Ltd.
Ladas & Parry
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