Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-15
2002-08-20
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S156000, C349S157000, C349S106000, C349S110000
Reexamination Certificate
active
06437847
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and especially relates to a liquid crystal display device comprising liquid crystal regions divided by polymer walls and having axially symmetrically aligned liquid crystal molecules within said liquid crystal regions.
DESCRIPTION OF THE RELATED ART
Heretofore, a TN (twisted nematic)-type liquid crystal display or an STN (super twisted nematic)-type liquid crystal display utilizing nematic liquid crystal materials is known as a display device utilizing electrooptical effect.
In order to widen the viewing angle of the liquid crystal display, for example, Japanese Patent Application Laid-Open Publication Nos. 6-301015 and 7-120728 disclose a liquid crystal display having liquid crystal molecules axially symmetrically aligned within each of a plurality of liquid crystal regions divided by a polymer wall, or so-called ASM (axially symmetrically aligned microcell)-mode liquid crystal display device (prior art example 1). The liquid crystal regions each substantially surrounded by a polymer wall are typically formed corresponding to each pixel element. Since the liquid crystal molecules are axially symmetrically aligned in the ASM-mode liquid crystal display device, the viewer can observe the liquid crystal display device from any direction without the contrast being varied greatly, or in other words, the ASM-mode display device has a wide viewing angle characteristic.
The ASM-mode liquid crystal display device disclosed in the above publications is manufactured by providing polymerize-induction-phase-separation to the mixture including a polymerized material and a liquid crystal material.
The method for manufacturing the liquid crystal display device according to prior art example 1 is explained in detail with reference to FIG.
10
. First, as shown in FIG.
10
(
a
), a substrate is prepared having color filters and electrodes (not shown) formed on one surface of a glass substrate
11
′ (step a).
Next, as shown in FIG.
10
(
b
), on the surface of the glass substrate
11
′ equipped with the electrodes and color filters, a polymer wall
13
′ for axially symmetrically aligning the liquid crystal molecules is formed, for example in a lattice-shape (step b). Actually, after spin-coating a photosensitive resin material on the surface of the glass substrate
11
′ equipped with the color filters and electrodes, the material is exposed through a photo-mask having a predetermined pattern and then developed, in order to form a lattice-shaped polymer wall
13
′. The photosensitive material utilized in this step could either be negative or positive. According to another example, the polymer wall may also be formed using a resin material without photosensitivity. In that case, however, a step for forming a separate resist layer must be added to the process.
Next, as shown in FIG.
10
(
c
), by exposing/developing the photosensitive resin material, pillar-like protrusions
17
′ are separately formed, through patterning, on some areas of the top of the polymer wall
13
′ selectively (step c).
Next, as shown in FIG.
10
(
d
), the surface of the glass substrate equipped with the polymer wall
13
′ and the pillar-like protrusions
17
′ is covered with a vertical alignment film
18
′ made for example of polyimide (step d).
On the other hand, the surface of an opposing glass substrate
21
′ shown in FIG.
10
(
e
) equippedwith electrodes (not shown) is covered with a vertical alignment film
28
′ (step f).
Next, as shown in FIG.
10
(
g
), the two substrates
11
′ and
21
′ are bonded together with the surfaces equipped with electrodes facing each other, in order to form a liquid crystal cell (step g). The gap between the two substrates is defined by the sum of the heights of the polymer wall
13
′ and the pillar-like protrusion
17
′. Therefore, the thickness of the liquid crystal layer (cell gap) could be adjusted to a preferred value.
Next, as shown in FIG.
10
(
h
), liquid crystal material
32
′ is injected by a vacuum injection method and the like, to the liquid crystal region
31
′ formed within the liquid crystal cell (step h).
Lastly, as shown in FIG.
10
(
i
), voltage is applied to the pair of electrodes arranged in opposed positions, in order to axially symmetrically align the liquid crystal molecules
32
′ within the liquid crystal region
31
′ (step i). The liquid crystal molecules within each of the liquid crystal regions divided by the polymer wall
13
′ are axially symmetrically aligned with a center axis
33
′ shown by a broken line that is perpendicular to the pair of substrates.
The cross-sectional structure of a conventional color filter
12
′ is shown in FIG.
11
. The color filter
12
′ includes a black matrix (BM)
13
′ for blocking the gap formed between colored patterns, and a colored resin layer
14
′ colored to red, green and blue (R, G, B) corresponding to each pixel element, which are formed on the glass substrate
11
′. An overcoat (OC) layer
19
′ formed of acrylic resin, epoxy resin and the like having a thickness of approximately 0.5-2.0 &mgr;m is formed on the colored resin layer, so as to improve the smoothness of the surface. On top of the overcoat layer is formed a transparent electrode
15
′ formed of indium tin oxide (ITO) film. The BM film
13
′ is typically formed of a metal chromium film having a thickness of approximately 100-150 nm. The colored resin layer
14
′ is formed by coloring a resin material with dyestuff or pigment, with a typical thickness of approximately 1-3 &mgr;m.
In order to form the color filter, a colored resin layer having photosensitivity formed on a substrate is patterned through photolithography method. For example, three photosensitive resin materials each colored to red (R), green (G) or blue (B) are utilized, and through coating/exposing/developing of each colored photosensitive resin material, a color filter having R, G, B colors is manufactured. The method for forming the photosensitive colored resin layer includes applying the liquid-state photosensitive colored resin material diluted by a solvent onto the substrate by a spin-coating method and the like, or transferring the photosensitive colored resin material in dry-film form onto the substrate. By providing a color filter to the ASM-mode liquid crystal display device, a colored liquid crystal display device having a wide viewing angle characteristic could be obtained.
However, the ASM-mode liquid crystal display device and the method for manufacturing the same according to the above-mentioned prior art example 1 have the following problems. That is, according to the prior art liquid crystal display device, there is a need to form a separate polymer wall in order to axially symmetrically align the liquid crystal molecules. The existence of such polymer wall increases the resist existing when injecting the liquid crystal material, and as a result, increases the injection time greatly. Therefore, in order to reduce the resist during liquid crystal material injection, the height of the polymer wall is minimized. However, in such case, the height of the pillar-like protrusion made of resin material formed to define the thickness of the cell has to be relatively increased. Especially, when manufacturing a large-scale liquid crystal display device, it is difficult to form pillar-like protrusions made of a thick-film resin having the same height throughout the whole area of the large-sized substrate. As a result, the thickness of the cell becomes uneven within the display region of the liquid crystal display device, which causes unevenness of the brightness, the color, and the viewing angle characteristic of the display, deteriorating the display quality.
SUMMARY OF THE INVENTION
The present invention aims at solving the problems of the conventional method and device. The object of the present invention is to pro
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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