Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-20
2002-05-21
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S111000, C349S028000, C349S034000
Reexamination Certificate
active
06392732
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display apparatus, wherein an electric field is supplied in a direction parallel to the surface of the substrate, and more particularly to an active matrix type liquid crystal display apparatus which provides a wide viewing angle compatible with a high image quality.
In a conventional liquid crystal display apparatus, an electrode for driving a liquid crystal is formed on the surface of each of two substrates, respectively, so that the electrodes are facing each other across the liquid crystal. The above conventional liquid crystal display apparatus uses a method which is represented by a twisted nematic display mode, wherein the liquid crystal is driven by supplying an electric field in a vertical direction with respect to the two substrates. In such case, transparent electrodes, such as ITO (Indium Tin Oxide), are used.
On the other hand, another mode of operation, wherein the liquid crystal is driven by supplying an electric field in a direction approximately parallel to the substrate using comb shaped electrodes provided on one substrate, is disclosed in JP-B-63-21907 (1988), and U.S. Pat. No. 4,345,249. In this case, the electrodes need not necessarily be transparent, and opaque metallic electrodes having a high electric conductivity can be used.
However, in the display mode wherein the electric field is supplied to the liquid crystal in a direction approximately parallel to the substrate using active elements (hereinafter called an in-plane switching mode), any method to supply an adequate electric field to the liquid crystal without causing interference between the electric fields supplied in a direction parallel to the substrate in a condition where a large amount of wiring exists, and any means to concurrently improve the image quality, have not been disclosed entirely.
Generally speaking, in the in-plane switching mode, the electric fields interfere with each other, because a large amount of wiring is formed on only one of the substrates through which electric signals are transmitted. Accordingly, the electric field supplied to the liquid crystal is influenced by unnecessary electric fields, and so an adequate electric field can not be supplied to the liquid crystal.
Furthermore, an unnecessary electric capacitance is formed between the electrodes, which sometimes causes the voltage supplied to the liquid crystal to fluctuate. The above described phenomena will cause deterioration of the image quality of the liquid crystal display apparatus. Especially, an electric field generated by an image signal electrode for transmitting signals to respective pixels having an active element, such as a TFT and the like, influences the electric field between a pixel electrode for operating the liquid crystal and the common electrode.
The potential of the image signal electrode varies always during the frame period in the course of transmitting signals. It has been known that, if the pixel electrode (its potential is in a floating condition when the active element is in an off condition) is located close to the image signal electrode, a nonuniformity appearing like shadow stripes referred to as a smear, similar to a cross talking phenomenon, is generated in parallel with the image signal electrode depending on the varying potential of the image signal electrode. In order to suppress this phenomenon, a technique to arrange the common electrode, which is always supplied with a potential from an external source, as the closest electrode to the image signal electrode has been developed by the present inventor (U.S. patent application Ser. No. 08/374,531).
However, in accordance with the above technique, the shielding effect for the electric field is not necessarily sufficient, and the problem caused by generation of the smear phenomenon still exists. Although the smear phenomenon could be suppressed by increasing the shielding effect with broadening of the width of the common electrode, the broadening of the width of the common electrode causes another problem in which the aperture ratio of the liquid crystal display apparatus is decreased.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to solve the above problems, and to provide an active matrix type liquid crystal display apparatus of the in-plane switching mode type, which is capable of providing a wide viewing angle and a high image quality without generating the smear phenomenon.
The gist of the present invention to achieve the above object is as follows.
An active matrix type liquid crystal display apparatus, comprises a plurality of electrodes, which are formed on a substrate so that an electric field in parallel to the substrate can be supplied to a liquid crystal layer, and a polarizer is provided, which changes its optical characteristics based on an alignment condition of the liquid crystal layer, wherein a shielding layer formed on the substrate in parallel to the image signal electrodes has a specific resistivity of less than 10
8
&OHgr;.cm.
The shielding layer formed on the substrate in parallel to the image signal electrodes is desirably further coated with an insulator of at least 10
8
&OHgr;.cm.
The specific resistivity of the shielding layer formed in parallel to the scanning electrode is also desirably at least 10
8
&OHgr;.cm.
A counterpart to an image signal electrode of the shielding layer formed in parallel to the image signal electrodes is preferably an electric conductor, and the potential of the shielding layer formed in parallel to the image signal electrodes is preferably set at the same level as the potential of the common electrode.
This means that a member for absorbing an electric field is used as the shielding layer concurrently, so that the electric field generated from the image signal electrode is shielded so as to exert no influence on the electric field supplied to the liquid crystal layer. Further, the member for absorbing the electric field may be arranged at only a counterpart to the image signal electrode, and a high shielding effect is generated by arranging the shielding layer made of a high insulating material, such as a metal, so as to cover the member.
The member for absorbing the electric field can be made of an electric conductor, such as a metal. In this case, the shielding effect for the electric field can be increased by arranging the member for absorbing the electric field at only the counterpart to the image signal electrode, providing the member so as to have the same potential as the potential of the common electrodes, and arranging the shielding layer having a high specific resistivity so that it covers the member.
As the insulating and shielding layer, an organic polymer material mixed with conductive particles, such as metallic particles and/or carbon particles, is used, and its specific conductivity can be controlled by adjusting the mixing amount of the conductive particles.
A theory of operation of the in-plane switching mode will be explained hereinafter.
FIG. 1
indicates a schematic structure of an active matrix type liquid crystal display apparatus of the in-plane switching mode type, relating to the present invention. A feature is that the composition of the black matrix
22
a
, which is parallel to the image signal electrodes, differs from the composition of the black matrix
22
b
which is parallel to the scanning electrodes.
FIGS.
2
(
a
) and
2
(
b
) are schematic vertical cross sections indicating the operation of the liquid crystal in the liquid crystal panel of the present invention, and FIGS.
2
(
c
) and
2
(
d
) are their schematic elevations. A vertical cross section of the cell when no voltage is supplied is indicated in FIG.
2
(
a
), and its elevation is indicated in FIG.
2
(
c
). Active elements are omitted in these figures. In accordance with the present invention, plural pixels are formed by forming plural stripe shaped electrodes, but only a part of the pixels are shown in FIGS.
2
(
a
) and
2
(
b
).
FIG. 3
indicates a relationship between an a
Aratani Sukekazu
Asuma Hiroaki
Kinugawa Kiyoshige
Matsuyama Shigeru
Oh-e Masahito
Antonelli Terry Stout & Kraus LLP
Chung David
Parker Kenneth
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