Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-04-16
2001-09-04
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S099000, C349S123000
Reexamination Certificate
active
06285428
ABSTRACT:
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 in-plane switching mode.
2. Description of the Related Art
Of the various liquid crystal display (LCD) devices, those using the twisted nematic mode (TN mode) have low operation voltage and low power consumption, and in recent years have been widely used. A TN mode cell has a liquid crystal layer interposed between first and second glass substrates on which transparent electrodes are formed. The longitudinal axis of molecules of the liquid crystal are parallel to the planes of the substrates. The first and second glass substrates are arranged for a twist angle of almost 90°.
A problem associated with the TN mode-LCD described above, is that the best angle of view cannot be set in the direction normal to the plane of the glass substrate. If the direction of the best angle of view from the glass substrate is defined as upward, the angle of view is symmetric in the horizontal direction whereas the angles of view are unsymmetric in the vertical direction.
To solve the problem, liquid crystal display device with In-Plane Switching (IPS) mode (refer to Principle and Characteristics of Electro-optical Behaviour with In-Plane Switching mode; Asia Display '95, pp 578-580, Hitachi, Japan) is proposed.
FIG. 1
shows a liquid crystal cell with a IPS mode when a voltage is not applied to the cell.
FIG. 2
shows the liquid crystal cell shown in
FIG. 1
when the voltage is applied to the cell. In
FIG. 1
, on the outsides of first and second substrates
22
a
and
22
b,
a polarizer
21
a
and a analyzer
21
b
are arranged, respectively. The polarization axes of the polarizer
21
a
and analyzer
21
b
are orthogonal to each other. On the first substrate
22
a,
a pixel electrode
23
and a counter electrode
24
are formed so that they are spaced to a selective space and are parallel to each other. On a surface of the first substrate
22
a
having the electrodes formed thereon is formed a homogeneous alignment film (not shown). On a surface of the second substrate
22
b
is also formed a homogeneous alignment film (not shown). Both alignment films are anti-parallel to each other. A liquid crystal layer
25
having liquid crystal molecules
25
a
is interposed between the first and second substrates
22
a
and
22
b.
As shown in
FIG. 1
, when the voltage is not applied to the cell, the arrangement of the liquid crystal molecules
25
a
are homogeneous and their optical axes are in good agreement with the polarization axis of the polarizer
21
a.
Therefore, incident light becomes linearly polarized light at the polarizer
21
a
to reach the analyzer
21
b
due to the homogeneous arrangement of the liquid crystal molecules
25
a
, and a dark state exists because the linearly polarized light is not in good agreement with the polarization axis of the analyzer
21
b
through which the light must exit. On the other hand, as shown in
FIG. 2
, when the voltage is applied to the electrodes
23
and
24
, electric field E direction of which is parallel to the plane of the first substrate
22
a,
is formed between the pixel and counter electrode
23
and
24
. Therefore, the longitudinal axes of the liquid crystal molecules
25
a
are arranged so that they parallel to the electric field E. Under the influence of the electric field E, the optical axes of the liquid crystal molecules
25
a
deviate by an angle of about 45° from the polarization axis of the polarizer
21
a.
As a result, the incident light which have been changed to linearly polarized light at the polarizer
21
a,
changes to elliptically polarized light, and a bright state exists because most of the incident light passes through the analyzer
21
b.
This IPS mode-LCD above described has wide view-angle characteristic which are better than the TN mode-LCD while the former has a longer response time than the latter, since the liquid crystal molecules turn in keeping their longitudinal axis parallel to the plane of the substrate and switch light transmission. Furthermore, since the electrodes are formed only on the first substrate, the electric field E becomes fringe field as close to the second substrate. As a result, the liquid crystal molecules which close to the second substrate have a further slow response time, and their the optical axes deviate within about 45° from the polarization axis of the polarizer, thereby decreasing transmittance.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a liquid crystal display device with an IPS mode having wide view angle characteristic and capable of improving response time and transmittance.
To accomplish this above object, a liquid crystal display device with an in-plane switching mode according to the present invention includes a first substrate having first and second electrodes formed thereon. A second substrate is disposed opposite to the first substrate with a selected distance. On a surface of the second substrate are also formed third and fourth electrodes. When a voltage is applied to the respective electrodes, a first electric field which is parallel to the planes of the substrates is generated between the first electrode and the second electrode, and a second electric field which is parallel to the planes of the substrates and is orthogonal to the first electric field is generated between the third electrode and the fourth electrode. A polarizer is arranged on the outside of the first substrate and a analyzer is arranged on the outside of the second substrate. A first homogeneous alignment film is applied to the first substrate. A second homogeneous alignment film is also applied to the second substrate. A liquid crystal layer having liquid crystal molecules is interposed between the both substrates, wherein the arrangement of the liquid crystal molecules is homogeneous when the voltage is not applied to the electrodes, and is twisted when the voltage is applied to the electrodes.
In this embodiment, the axes of the polarizer and analyzer are orthogonal to each other. When the electric fields are applied to the electrodes, the liquid crystal molecules which are substantially close to the first substrate deviate by an angle of about 45° from the polarization axis of the polarizer, and those which are substantially close to the second substrate deviate by an angle of about 45° from the polarization axis of the analyzer. It is preferable that the alignment direction of the first homogeneous alignment film is in good agreement with the polarization axis of the polarizer. The first and second homogeneous alignment films are anti-parallel to each other and the first and second homogeneous alignment films are rubbed in a direction of 45° with respect to the electrodes, respectively. It is preferable that the liquid crystal molecules have a pretilt angle of about 1° to about 5°. It is also preferable that the first electrode is a first pixel electrode, the second electrode is a first counter electrode, the third electrode is a second pixel electrode, and the fourth electrode is a second counter electrode.
Additional object, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 5249070 (1993-09-01), Takano
patent: 5886762 (1999-03-01), Lee et al.
patent: 5926244 (1999-07-01), Takeda et al.
patent: 6097465 (2000-01-01), Hiroki et al.
Kim Hyang Yul
Lee Seung Hee
Park Han Jun
You Jae Geon
Hyundai Electronics Industries Co,. Ltd.
Jacobson & Holman PLLC
Ton Toan
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