Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-12
2004-05-25
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000, C349S124000, C349S177000
Reexamination Certificate
active
06741310
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to liquid crystal display devices and more particularly to an in-plane switching liquid crystal display device. An in-plane switching liquid crystal display device is a device driven by an electric field acting parallel to the liquid crystal layer forming the liquid crystal display device.
Conventionally, driving of a liquid crystal display device has been achieved by applying an electric field to a liquid crystal layer confined by a pair of substrates such that the electric field acts perpendicularly to the liquid crystal layer. On the other hand, there is a proposal of a so-called in-plane switching (IPS) liquid crystal display device, in which an electric field is applied to the liquid crystal layer such that the electric field acts in the direction parallel to the substrates. In such an IPS liquid crystal display device, an interdigital electrode is provided on one of the foregoing substrates.
FIGS. 1A and 1B
show the principle of such an IPS liquid crystal display device.
Referring to
FIG. 1A
, a liquid crystal layer
13
containing therein liquid crystal molecules is confined between a pair of mutually opposing glass substrates
11
and
12
in such a manner that the liquid crystal layer makes an intimate contact with a molecular alignment film
11
A covering the substrate
11
and also an intimate contact with a molecular alignment film
12
A covering the substrate
12
. Further, polarizers
11
B and
12
B are disposed at respective outer sides of the glass substrates
11
A and
11
B in a crossed Nicol state. Further, a pair of electrodes
14
A and
14
B are provided on the glass substrate
11
in a state that the electrodes
14
A and
14
B are covered by the molecular alignment film
11
A.
In the non-activated state of
FIG. 1A
, there is no driving voltage applied across the electrodes
14
A and
14
B and the liquid crystal molecules
13
A of the liquid crystal layer
13
are aligned in a predetermined direction in a plane generally parallel to the substrates
11
and
12
.
In the activated state of
FIG. 1B
, on the other hand, a driving voltage is applied across the electrodes
14
A and
14
B, and an electric field is induced in the liquid crystal layer
13
in the direction generally parallel to the liquid crystal layer
13
. As a result of the electric field, the direction of the liquid crystal molecules
13
A, or molecular orientation, is changed. An IPS liquid crystal display device achieves the desired optical switching by using such a change of the molecular orientation of the liquid crystal molecules
13
A. Due to the fact that the change of the molecular orientation occurs in the plane parallel to the liquid crystal layer
13
, an IPS liquid crystal display device generally provides a superior viewing angle as compared with the conventional twist-nematic (TN) liquid crystal display devices.
On the other hand, such an IPS liquid crystal display device, lacking an electrode on the opposing substrate
12
contrary to a conventional TN liquid crystal display device, tends to induce polarization in the molecular alignment film
12
A, while such a polarization induced in the molecular alignment film
12
A tends to cause the problem of image sticking or afterimage, in which the represented image tends to remain after the image has been changed. This problem of image sticking becomes particularly acute when the liquid crystal display device is used to display an image for a prolonged time period.
In order to eliminate the problem of image sticking, it is necessary to use a low-resistance liquid crystal having a resistance lower than the resistance of the liquid crystal used in a conventional TN liquid crystal display device, for the liquid crystal layer
13
. However, such a liquid crystal having a low resistance generally has a large dielectric constant and tends to dissolve impurities. In other words, a low-resistance liquid crystal is vulnerable to contamination. Such a contamination may come from the sealing material of the liquid crystal display device or from the molecular alignment film. Once the liquid crystal is contaminated, the representation performance of the liquid crystal display device is severely deteriorated.
Further, it should be noted that the electric field
13
B induced in the liquid crystal layer
13
in the driving state of the liquid crystal display device is not exactly parallel to the plane of the liquid crystal layer
13
in the vicinity of the electrode
14
A or
14
B. This means that the electric field component parallel to the plane of the liquid crystal layer
13
becomes small and the response speed of the liquid crystal molecules
13
A becomes accordingly small in the vicinity of the electrodes
14
A and
14
B.
Thus, there is an acute demand of improved performance for the conventional IPS liquid display device.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a liquid crystal display device wherein the foregoing problems are eliminated.
The present invention provides a liquid crystal display device, comprising:
first and second, mutually opposing substrates;
a liquid crystal layer confined between said first and second substrates;
an electrode formed on said first substrate so as to create an electric field acting generally parallel to a plane of said liquid crystal layer; and
a plurality of pixels being defined in said liquid crystal layer,
each of said plurality of pixels including therein a plurality of domains having respective orientations for liquid crystal molecules, such that said orientation is different between a domain and another domain within said plane of said liquid crystal layer.
According to the present invention, it is possible to improve the response speed of the IPS liquid crystal display device, by providing domains in each of the pixels in the liquid crystal layer such that the molecular orientation is different between a domain and another domain when compared in the plane of the liquid crystal layer. More specifically, the present invention achieves the desired improvement of response by twisting the liquid crystal molecules, in the non-activated state of the liquid crystal display device, such that the molecular orientation of the liquid crystal molecules in the domain adjacent to the electrode is closer to the molecular orientation in the activated state of the liquid crystal display device, as compared with the molecular orientation of the liquid crystal molecules in the domain far from the electrode. As a result, the liquid crystal molecules adjacent to the electrode are aligned in the activated direction immediately upon application of the driving voltage to the electrode, in spite of the fact that the electric field component included in the plane of the liquid crystal layer is small in the vicinity of the electrode.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.
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Mayama Takatoshi
Nakanishi Yohei
Tanuma Seiji
Duong Tai
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Kim Robert H.
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