Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-02-04
2002-08-20
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S128000, C349S156000, C349S160000
Reexamination Certificate
active
06437845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter, referred to as an “LCD”) device which is suitable to uses requiring a large viewing angle and to realize large-screen display, and a plasma-addressed LCD device using such an LCD device.
2. Description of the Related Art
(1) ASM Mode
Conventional LCD devices, as represented by TN (twisted nematic) mode LCD devices, cause liquid crystal molecules in the vicinity of two substrates to be aligned in one direction. Accordingly, as shown in
FIG. 17
, the liquid crystal molecules are tilted in one uniform direction when a voltage is supplied. As a result, the apparent phase difference of the liquid crystal molecules is significantly different when the LCD device is seen in a direction of arrow A and when being seen in a direction of arrow B. Therefore, the transmittance is different when the LCD device is seen in the direction of arrow A and when being seen in the direction of arrow B. Thus, the conventional LCD devices have anisotropy in the viewing angle characteristic.
In order to solve the problem, Japanese Laid-Open Publication No. 6-301015 discloses an ASM (axially symmetrically aligned microcell) mode for realizing a large viewing angle, by which liquid crystal molecules are aligned in an axially asymmetrical manner in each pixel. The ASM mode uses a p-type liquid crystal material. In a vertical plane, the liquid crystal molecules in the vicinity of the substrates are aligned substantially parallel to the substrates. In a horizontal plane, the liquid crystal molecules are aligned in an axially symmetrical manner in each of a top portion (FIG.
18
A), an intermediate portion (FIG.
18
B), and a bottom portion (FIG.
18
C). By applying avoltage to the liquid crystal layer in this state, the liquid crystal molecules are tilted vertically to the substrates, and thus black display is provided.
Japanese Laid-Open Publication No. 7-120728, for example, discloses a method for producing an LCD device of the ASM mode. According to this method, a structure having a wall in a lattice pattern is formed on one of the two substrates, and the liquid crystal molecules are aligned in an axially asymmetric manner by interaction of the wall with the liquid crystal molecules.
These LCD devices of the ASM mode require a technology for polymerizing a photo-curable monomer in order to stably maintain the liquid crystal molecules.
Liquid crystal molecules of an n-type liquid crystal material can also be aligned in an axially asymmetrical manner. For example, Japanese Laid-Open Publication No. 10-133206 discloses realizing the ASM mode by using an n-type liquid crystal material together with a vertical alignment layer.
An LCD device of the ASM mode is produced in the following manner. A substrate is formed so as to have convex or concave portions in a lattice pattern on a surface thereof, and a vertical alignment layer is provided thereon. The substrate is assembled with another substrate having a vertical alignment layer provided thereon. A mixture of an n-type liquid crystal material and a photo-curable monomer is injected into a space between the two substrates to produce a cell. A voltage is applied to the n-type liquid crystal material to align liquid crystal molecules of the n-type liquid crystal material in an axially symmetrical manner. Then, the cell is irradiated with ultraviolet light to cure the photo-curable monomer. Thus, the axial symmetrical alignment is secured. Due to the secured axial symmetrical alignment, the direction in which the liquid crystal molecules are tilted when a voltage is applied is determined, which raises the response speed. As can be appreciated, the AMS mode using the n-type liquid crystal material also indispensably requires the technology for polymerizing a photo-curable monomer in order to stably maintain the liquid crystal molecules.
Japanese Laid-Open Publication No. 7-318940 discloses another method for producing an LCD device of an AMS mode. According to this method, a structure having a wall in a lattice pattern is provided on a substrate having electrodes, and a vertical alignment layer or a horizontal alignment layer is provided thereon. A stable axially symmetrical alignment is obtained by the function of the structure. Japanese Laid-Open Publication No. 7-318940 also discloses a hybrid-type axially symmetrical alignment realized by using a vertical alignment layer together with a horizontal alignment layer.
However, the method disclosed in this publication has a problem that since a transparent electrode is below the structure having a wall, a voltage is unlikely to be applied to a portion of the liquid crystal molecules which is above the wall of the structure. Thus, the contrast is lowered.
In the above-mentioned AMS mode LCD devices, a phase plate having a negative anisotropy is provided between the cell and a polarizer in order to further improve the viewing angle characteristic in a direction of 45 degrees relative to the polarization axis of the polarizer.
(2) PALC
For example, Japanese Laid-Open Publication No. 1-217396 discloses a plasma-addressed liquid crystal (PALC) display device. The PALC display device includes a plasma substrate. The plasma substrate is defined by a substrate and a thin dielectric layer. A space between the substrate and the thin dielectric layer accommodates ribs for dividing the space into a plurality of plasma chambers. The plasma chambers each accommodate an anode electrode and a cathode electrode. A change in the plasma state of a noble gas contained in the plasma chamber provides a switching function. The PALC display device further includes a counter substrate having a counter electrode. The counter substrate and the dielectric layer interpose a liquid crystal layer. A voltage is applied to the liquid crystal layer to perform display.
The PALC technology is favorably expected to be applied to large-screen display due to a simple structure realized by the technology, but has a problem in the viewing angle characteristic since the liquid crystal material is used as an optical switch for display.
In order to solve the problem, Japanese Laid-Open Publication Nos. 9-19738 and 10-186331 disclose applying an AMS mode to a PALC display device.
Hereinafter, the problems of the above-described conventional LCD devices will be described.
(1) Contrast
The hybrid ASM mode described in Japanese Laid-Open Publication No. 7-318940 includes a structure having a wall in a lattice pattern on an electrode. Accordingly, the alignment of a portion of the liquid crystal molecules which is above the wall is not sufficient in response to the voltage application. Thus, the transmittance of the corresponding area is not lowered. As a result, a sufficiently high contrast is not provided. As a solution to the problem, a structure having a black wall in a lattice pattern (black matrix) is provided to shield the area from light. In an LCD device of an axially symmetrical alignment mode, the alignment of the liquid crystal molecules is determined by the alignment force provided by the wall of the structure. Since an alignment force cannot regulate the alignment of the liquid crystal molecules in a large pixel area of 200 &mgr;m or greater, such a large pixel area is divided into smaller regions and the structure having a black wall in a lattice pattern is formed in correspondence with the smaller regions. As a result, the numerical aperture is reduced.
(2) Response Speed
In the conventional ASM mode LCD devices, two substrates are both covered with a horizontal alignment layer or a vertical alignment layer. Since the alignment is stable when no voltage is applied, the response speed of the liquid crystal molecules when a voltage is applied is significantly lower than the response speed when the voltage is dropped. Moreover, a portion of the liquid crystal layer on the wall is less likely to be supplied with a voltage than the rest of the liquid crystal layer. Accordingly, when a voltage is applied to the entire liquid cr
Kume Yasuhiro
Yamada Nobuaki
Ngo Julie
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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