Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-11-24
2001-07-24
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S187000
Reexamination Certificate
active
06266121
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display element for use in a flat panel display, etc., and to a method of manufacturing the same, and more particularly relates to a liquid crystal display element having excellent resistance to impact and desirable display quality.
BACKGROUND OF THE INVENTION
Conventionally known display devices include liquid crystal display devices adopting a liquid crystal display element which includes a liquid crystal sandwiched between a pair of substrates, each having at least electrodes, wherein a display is performed based on an optical response of the liquid crystal by selectively applying a voltage to the electrodes. For beneficial feature which enables a thin structure, earnest researches have been made on such liquid crystal display devices as the best candidate for the flat panel display in practical applications.
A ferroelectric liquid crystal as an example of such liquid crystal has excellent characteristics in its memory effect, high speed response, wide viewing angle, etc., which permits high precision and large capacity display using a simple matrix system [N. A. Clark and S. T. Lagerwall: Appl. Phys. Lett., vol. 36(1980)899].
FIG. 30
is a cross-sectional view schematically showing one example of the conventional structure of a ferroelectric liquid crystal display device.
Conventional ferroelectric liquid crystal display device includes two glass substrates
122
a
and
122
b.
On the surface of the glass substrate
122
a,
a plurality of transparent signal electrodes
123
a
made of indium tin oxide (generally abbreviated as ITO), etc., are formed in parallel. Further, a transparent insulating layer
124
a
is formed on the entire surface of the glass substrate
122
a
so as to coat the plurality of transparent signal electrodes
123
a.
On the other hand, on the surface, facing the signal electrodes, of the other glass substrate
122
b,
a plurality of transparent scanning electrodes
123
b
made of ITO, etc., are formed in parallel in a direction orthogonal to the signal electrodes
123
a.
These scanning electrodes
123
b
are also coated with a transparent insulating layer
124
b
made of SiO
2
, etc.
On the transparent insulating layers
124
a
and
124
b,
alignment layers
125
a
and
125
b
having applied thereto uniaxial alignment treatment by the rubbing process, etc., are formed respectively. For these alignment layers
125
a
and
125
b,
organic polymeric layers such as polyimide layers, nylon layers, polyvinyl alcohol layers, etc., or SiO oblique vaporation layers, etc., may be used. In the case of adopting the organic polymeric layers for the alignment layers
125
a
and
125
b,
respective alignment treatments are applied in such a manner that liquid crystal molecules are aligned parallel to electrode substrates.
Hereinafter, the glass substrate
122
a
having formed thereon the signal electrodes
123
a,
the transparent insulating layer
124
a,
and the alignment layer
125
a
in this order is defined as an electrode substrate
120
. Similarly, the glass substrate
122
b
whereon the scanning electrodes
123
b,
the transparent insulating layer
124
b
and the alignment layer
125
b
are laminated in this order is defined to be an electrode substrate
121
.
The electrode substrates
120
and
121
are connected together by a sealing agent
126
except for a part which serves as an injection opening, to allow a ferroelectric liquid crystal
127
to be injected therethrough into the spacing formed between the alignment layers
125
a
and
125
b.
After the ferroelectric liquid crystal
127
has been injected, the injection opening is sealed with a sealing agent
130
.
The electrode substrates
120
and
121
thus connected are sandwiched between polarization plates
128
a
and
128
b.
The polarization plates
128
a
and
128
b
are placed such that respective polarizing axes cross at right angle. In the case of a large display area, peripheral spacers
129
are dispersed so that the electrode substrates
120
and
121
are placed in parallel opposing each other with a predetermined cell thickness.
As shown in
FIG. 31
, a molecule
30
of the ferroelectric liquid crystal has a spontaneous polarization
27
perpendicular to a major molecule axis. Therefore, the molecule
30
of the ferroelectric liquid crystal rotates on a conical locus
28
by receiving a force in proportion to a vector product of (1) an electric field generated from a voltage applied across the signal electrodes
123
a
and the scanning electrodes
123
b
and (2) the spontaneous polarization
27
.
Therefore, when seen from an observer, the molecule
30
of the ferroelectric liquid crystal switches between the position A and the position B of the axes of the conical locus
28
. Here, for example, by arranging such that one polarization axis of the polarization plates
128
a
and
128
b
coincides with a major molecular axis direction
29
a
in the state the molecule
30
is switched to the position A, and the other polarization axis coincides with a direction
29
b,
a dark view can be achieved. On the other hand, when the molecule
30
is switched to the position B, a bright view can be achieved by birefringence.
The respective alignment states of the molecule
30
of the ferroelectric liquid crystal in the positions A and B are equivalent in terms of elastic energy. Therefore, even after the electric field is removed by the signal electrodes
123
a
and the scanning electrodes
123
b,
the alignment state and the optical state of the molecule
30
can be maintained, which is known as a memory effect of the ferroelectric liquid crystal. The described memory effect cannot be achieved from the conventional nematic liquid crystal, and the memory effect and the high speed response characteristic by the spontaneous polarization enable the ferroelectric liquid crystal display device to offer high precision and large capacity display by the simple matrix method.
In general, in the large-size liquid crystal display device, a deformation of the substrate is likely to occur due to externally applied forces such as a buckling due to a weight of the substrate itself, an impact, etc. When a thickness between the substrates opposing one another varies by a deformation of the substrates due to externally applied pressure, the alignment of the liquid crystal molecules is disturbed, and irregularities in threshold voltage are likely to occur due to a leakage of the electrode, thereby presenting a problem that a desirable display is difficult to be achieved.
In order to counteract the described problems, either one of the following methods adopting a spacer for maintaining a uniform spacing between the substrates has been adopted: (1) A method of dispersing spherical particles; and (2) A method of forming a wall in a pillar shape of an organic or inorganic series.
However, the described method (1) has the following drawbacks. Firstly, as the agglomeration of the fine particles is likely to occur, it is difficult to disperse fine particles uniformly on the substrate, which, in turn, makes it difficult to achieve a uniform cell thickness. Secondly, as it is difficult to control the position of the particles, the disturbance of alignment is likely to occur due to the particles dispersed in the pixel region, which results in the deterioration of the display quality. Thirdly, in the method (1), the substrate is supported only by a fulcrum of the spacer, and the substrates are not connected together by the spacer, a precise control of the spacing between the substrates is difficult to be achieved, and a sufficient strength for maintaining a spacing between the substrates against the externally applied pressure cannot be obtained.
As an example of the method (1), a method of dispersing adhesive particles and spacer beads simultaneously has been proposed (for example, by Japanese Unexamined Patent Publication No. 174726/1987 (Tokukaisho 62-174726)). However, in order to ensure sufficient adhesiveness for practical applications, it
Kido Masami
Miyoshi Shuji
Shigeta Mitsuhiro
Tamai Kazuhiko
Uchida Hideki
Parker Kenneth
Renner , Otto, Boisselle & Sklar, LLP
Sharp Kabushiki Kaisha
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