Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-17
2001-12-11
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C399S155000, C399S130000
Reexamination Certificate
active
06330049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and in particular to a liquid crystal display device having a wide viewing angle characteristic.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 7-120728 discloses a display mode called “ASM mode” (Axially Symmetric Aligned Microcell Mode), where liquid crystal molecules are oriented in axial symmetry in each pixel, in order to improve the viewing angle characteristic of the display. In a display device of this mode, a plurality of liquid crystal regions are formed by phase separation from a mixture of a liquid crystal material with a positive dielectric anisotropy and a photocurable resin, so that the liquid crystal molecules in each liquid crystal region are oriented in axial symmetry.
Japanese Laid-open Patent Publication No. 8-341590 discloses a liquid crystal display device including: a pair of substrates; and a liquid crystal layer interposed between the pair of substrates, wherein: the liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy; the liquid crystal layer includes a plurality of liquid crystal regions; the liquid crystal molecules are oriented in a direction substantially perpendicular to the pair of substrates in the absence of an applied voltage; and the liquid crystal molecules in each liquid crystal region are oriented in axial symmetry in the presence of an applied voltage. This liquid crystal display device operates in a normally black mode, and provides a higher contrast ratio than that of an ASM mode liquid crystal display device which operates in a conventional normally white mode. Moreover, the liquid crystal display device can be produced relatively easily.
FIGS. 1A and 1B
illustrate a liquid crystal display device of Japanese Laid-Open Patent Publication No. 8-341590, wherein
FIG. 1A
is a cross-sectional view and
FIG. 1B
is a plan view thereof. In the liquid crystal display device, a pair of substrates (e.g., a glass substrates
4
and
8
) are provided to oppose each other with a predetermined gap therebetween. A liquid crystal layer
6
of liquid crystal molecules with a negative dielectric anisotropy is interposed between the glass substrates
4
and
8
. A signal electrode
9
of a transparent conductive film (e.g., ITO) is formed in a stripe pattern on the inner surface (closer to the liquid crystal layer
6
) of the glass substrate
4
. A vertical alignment layer
22
of polyimide, or the like, is provided over the signal electrode
9
so as to cover substantially the entire surface of the glass substrate
4
. A color filter (not shown) and a black matrix (not shown) are provided on the inner surface (closer to the liquid crystal layer
6
) of the glass substrate
8
. A signal electrode
10
of a transparent conductive film (e.g., ITO) is formed in a stripe pattern over the color filter and the black matrix. The striped signal electrode
10
is arranged to cross the striped signal electrode
9
, thereby forming a pixel at each intersection therebetween. The color filter (not shown) includes RGB color layers for each pixel. The black matrix (not shown) has a pattern to cover the gap between adjacent color layers of the color filter (not shown). A plurality of partition walls
17
are provided on the glass substrate
8
, with pillar-like spacers
20
being provided selectively and regularly on some of the partition walls
17
, thereby defining a plurality of liquid crystal regions
15
. A vertical alignment layer
21
of polyimide, or the like, is provided on the side surfaces of the pillar-like spacers
20
and on a portion of the glass substrate
8
on which the pillar-like spacer
20
is not provided. Thereafter, the pair of substrates are attached together with the predetermined gap therebetween into which a liquid crystal material is injected, thereby producing a display cell.
FIG. 2
is a schematic cross-sectional view showing a part of the liquid crystal display device of Japanese Laid-Open Patent Publication No. 8-341590.
FIG. 2
illustrates the orientation of liquid crystal molecules
11
(
11
a,
11
b
and
11
c
) in the liquid crystal layer
6
in the vicinity of the partition wall
17
along the periphery of the liquid crystal region
15
in the absence of an applied voltage. The partition wall
17
is provided on the signal electrode
10
which is provided on the glass substrate
8
. The vertical alignment layer
21
covers the top and side surfaces of the partition wall
17
and the surface of the signal electrode
10
.
In the absence of an applied voltage, the liquid crystal molecules
11
a
along the side surface of the partition wall
17
are subject primarily to the anchoring force of the part of the vertical alignment layer
21
along the side surface of the partition wall
17
, and thereby oriented in a direction substantially perpendicular to the side surface of the partition wall
17
. The liquid crystal molecules
11
b
along the signal electrode
10
are subject primarily to the anchoring force of the part of the vertical alignment layer
21
along the signal electrode
10
, and thereby oriented in a direction substantially perpendicular to the substrate
8
. The liquid crystal molecules
11
a
at the corner of the side surface of the partition wall
17
and the substrate
8
are subject to both the anchoring force from the part of the vertical alignment layer
21
along the side surface of the partition wall
17
and the anchoring force from the part of the vertical alignment layer
21
along the signal electrode
10
. Consequently, the liquid crystal molecules
11
c
may suffer from disturbance in their orientation, which results in the liquid crystal molecules not being uniformly oriented in a single direction. Due to the disturbance in the orientation of the liquid crystal molecules, the liquid crystal molecules
11
c
may produce birefringence, leading to light leakage. The light leakage may cause the contrast ratio of the display device to decrease in a black display, thereby deteriorating the display quality.
As will be discussed later in greater detail, the partition walls
17
define the position and the size of the respective liquid crystal regions
15
of the liquid crystal layer. Based on the anchoring force from the side surface of the partition wall
17
, the liquid crystal molecules
11
in each liquid crystal region
15
are controlled to exhibit axially symmetric orientation in the presence of an applied voltage (white display). Conventionally, the partition wall
17
requires a sufficient height with respect to the thickness of the liquid crystal layer (or the cell gap) in order for the side surface of the partition wall
17
to provide the anchoring force and thereby to maintain a stable axially symmetric orientation of the liquid crystal molecules
11
in the liquid crystal region
15
. With an insufficient height of the partition wall
17
, the axially symmetric orientation of the liquid crystal molecules
11
may not be controlled sufficiently, thus failing to obtain the stable axially symmetric orientation. In such a case, the axially symmetric orientation may be destroyed, resulting in non-uniformity in a produced display.
The presence of the partition wall
17
in the liquid crystal layer
6
has presented the following problems. First, the partition wall
17
may present an obstruction to a liquid crystal injection process, thereby increasing the injection time and thus the production cost of the display device. Particularly, in a large-screen liquid crystal display device, there may occur a distribution in the composition ratio of the liquid crystal material across the liquid crystal panel, due to a phenomenon called “chromatographic phenomenon”, thereby resulting in non-uniformity in a produced display.
When the display is viewed from an angle inclined from the direction normal to the display panel, some or all of incident light having passed through the liquid crystal region
15
may be blocked by the par
Himeshima Katsuyuki
Kishimoto Kazuyuki
Kondo Masahiko
Kume Yasuhiro
Yamada Nobuaki
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Ton Toan
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