Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-17
2002-05-28
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S155000
Reexamination Certificate
active
06396559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device for use in a personal computer, a word processor, an amusement apparatus, a television, or the like, a method for producing such a display device, and a resist for use in such a method. More particularly, the present invention relates to a liquid crystal display device in which liquid crystal molecules are oriented in axial symmetry in each of liquid crystal regions which are partitioned from one another by a polymer wall and a method for producing such a display device.
2. Description of the Related Art
Conventionally, a nematic liquid crystal display device such as a TN (twisted nematic) or STN (super twisted nematic) liquid crystal display device has been known in the art as a display device for displaying images based on an electrooptical effect. Since, this type of liquid crystal display device has a limited viewing angle, considerable effort has been put forth in the art in order to increase the viewing angle.
For example, Japanese Laid-Open Publication No. 6-301015 and Japanese Laid-Open Publication No. 7-120728 disclose a so-called “ASM (Axially Symmetrically aligned Microcell) mode TN liquid crystal display device (hereinafter “Conventional Example 1”) in which liquid crystal molecules are oriented in axial symmetry in each of liquid crystal regions which are partitioned from one another by a polymer wall. Typically, each liquid crystal region substantially surrounded by the polymer wall is corresponds to one pixel.
In the ASM mode liquid crystal display device, the polymer wall substantially surrounding the liquid crystal region is provided on a side of at least one of a pair of substrates facing a liquid crystal layer. In the presence of an applied voltage, the liquid crystal molecules in each liquid crystal region are oriented in axial symmetry, thereby reducing the viewing angle dependency.
An operation principle of this liquid crystal display device will be described below with reference to
FIGS. 22A
to
22
D.
FIG. 22A
is a cross-sectional view illustrating the liquid crystal display device in the absence of an applied voltage,
FIG. 22B
illustrates polarization microscopy (in a crossed Nicols state) of the liquid crystal display device in the absence of an applied voltage,
FIG. 22C
is a cross-sectional view illustrating the liquid crystal display device in the presence of an applied voltage, and
FIG. 22D
illustrates polarization microscopy (in a crossed Nicols state) of the liquid crystal display device in the presence of an applied voltage.
The liquid crystal display device includes a pair of substrates
14
and
18
, and a liquid crystal layer
16
interposed therebetween. The liquid crystal layer
16
includes liquid crystal molecules
11
having a negative dielectric anisotropy. Transparent electrodes
19
and
10
are provided on the substrates
14
and
18
, respectively, on the side facing the liquid crystal layer
16
. Vertical alignment films
21
and
22
are provided on the transparent electrodes
10
and
19
, respectively. A tapered polymer wall
17
is provided on the side of the substrate
18
facing the liquid crystal layer
16
. Apillar-like protrusion
20
is provided selectively on the tapered polymer wall
17
. The tapered polymer wall
17
substantially defines a liquid crystal region
15
. As will be described later with reference to
FIG. 22C
, the liquid crystal molecules
11
within each liquid crystal region
15
are oriented in axial symmetry about a central axis
12
.
In the absence of an applied voltage, the liquid crystal molecules
11
are aligned in a direction substantially perpendicular to the substrates
14
and
18
, as illustrated in
FIG. 22A
, by the anchoring force of the vertical alignment films
21
and
22
. When observed by a polarization microscope in a crossed Nicols state, the liquid crystal region
15
in this state exhibits a dark field (normally black mode), as illustrated in FIG.
22
B.
When a voltage is applied across the liquid crystal layer
16
, a force acts upon the liquid crystal molecules
11
with a negative dielectric anisotropy and orients the molecules
11
so that the long axis of the molecules
11
is perpendicular to the direction of the electric field. As a result, the molecules
11
incline from a direction substantially perpendicular to the substrate, as illustrated in
FIG. 22C
(gray-level display state). When observed by a polarization microscope in a crossed Nicols state, the liquid crystal region
15
in this state exhibits an extinction pattern along the polarization axis, as illustrated in FIG.
22
D.
As described above, the liquid crystal display device according to Conventional Example 1 operates in a normally black mode. In the normally black mode, the liquid crystal molecules
11
are oriented in a direction perpendicular to the substrate (thereby producing a black display) in the absence of an applied voltage, whereas the liquid crystal molecules
11
are oriented in axial symmetry about the central axis
12
formed for each liquid crystal region
15
(thereby producing a white display) in the presence of an applied voltage.
The term “axially symmetrical orientation” as used herein refers to an orientation of liquid crystal molecules where the liquid crystal molecules are oriented in a spiral pattern as illustrated in
FIGS. 23B and 23C
, for example, but also includes other orientations such as a concentric orientation or a radial orientation. Typically, the central axis for the axially symmetrical orientation substantially coincides with the direction normal to the substrate.
FIGS. 23A
to
23
C are schematic diagrams of a modeled liquid crystal region
15
, illustrating an orientation of the liquid crystal molecules
11
in the liquid crystal region
15
.
FIG. 23A
illustrates a plurality of liquid crystal regions
15
defined by the polymer wall
17
,
FIG. 23B
illustrates an orientation of the liquid crystal molecules
11
in one liquid crystal region
15
, and
FIG. 23C
illustrates the respective orientations of the liquid crystal molecules
11
in a top layer
15
T, an intermediate layer
15
M and a bottom layer
15
B of the liquid crystal region
15
.
With such an ASM mode axially symmetrical orientation, the viewing angle characteristic of the liquid crystal display device can be improved as follows.
In the TN mode, the liquid crystal molecules in each liquid crystal region are oriented in a single direction as illustrated in
FIGS. 24D
to
24
F. When the liquid crystal display device in a gray-level display state, as illustrated in
FIG. 24E
, is viewed from directions A and B, the gray-level display is properly perceived only in one of the directions A and B, but not in the other.
On the contrary, in an axially symmetrical orientation, the liquid crystal molecules are oriented in two or more orientations as illustrated in
FIGS. 24A
to
24
C. Thus, the apparent refractive index of the liquid crystal molecules as viewed from the direction A is averaged with that from the direction B, so that the light transmission from the direction A is substantially equal to that from the direction B, thereby realizing a desirable viewing angle characteristic even in a gray-level display state as illustrated in FIG.
24
B.
As described above, in an ASM mode liquid crystal display device, the liquid crystal molecules are oriented in axial symmetry, so that there is little change in the contrast even when the observer changes its viewing direction, thereby realizing a wide viewing angle characteristic.
The ASM mode liquid crystal display device according to Conventional Example 1 may be produced through a polymerization-induced phase separation of a mixture containing a polymerizable material and a liquid crystal material.
A method for producing the liquid crystal display device according to Comparative Example 1 will be described below with reference to
FIGS. 15A
to
15
I.
First, referring to
FIG. 15A
, a glass substrate
908
is provided (step a). Althou
Hamada Kenji
Kishimoto Katsuhiko
Yamada Nobuaki
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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