Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-30
2002-07-23
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S110000
Reexamination Certificate
active
06424402
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display and method for manufacturing the same, and especially, to a liquid crystal display and method for manufacturing the same having liquid crystal molecules axially symmetrically aligned within each liquid crystal region of a liquid crystal layer divided into plural regions by a wall-like structure.
DESCRIPTION OF THE RELATED ART
Heretofore, TN (twisted nematic)-type liquid crystal displays and STN (super twisted nematic)-type liquid crystal displays including nematic liquid crystal molecules were used as display devices utilizing electrooptical effect. Techniques aimed at widening the viewing angle of these liquid crystal displays are being developed actively.
One example of the technique for widening the viewing angle of the TN-type liquid crystal display is disclosed in Japanese Patent Application Laid-Open Publication Nos. 6-301015 and 7-120728. The applications disclose a liquid crystal display having liquid crystal molecules axially symmetrically aligned within each liquid crystal regions of a liquid crystal layer divided into plural regions by a polymer wall, the display so called the ASM (axially symmetrically aligned microcell)-mode liquid crystal display. According to the disclosure, the typical liquid crystal display has each liquid crystal region substantially surrounded by a polymer wall formed to correspond to each pixel basis. The ASM-mode liquid crystal display has liquid crystal molecules aligned axially symmetrically. Therefore, no matter what direction the observer views the liquid crystal display, the contrast will not vary greatly. In other words, the liquid crystal display has a wide viewing angle characteristic. The ASM-mode liquid crystal display disclosed in the above-mentioned patent publications is manufactured by performing a polimerization induction—phase separation to a mixture of polimerized material and liquid crystal material.
The conventional method for manufacturing the ASM-mode liquid crystal display is explained with reference to
FIG. 6
(prior art). First, a substrate manufactured by forming a color filter and an electrode on one surface of a glass substrate
21
a
′ is prepared (step (a)). For simplicity, the electrode and the color filter formed on the upper surface of the glass substrate
21
a
′ are not shown in the drawing. The method for manufacturing the color filter is explained later. Next, a polymer wall
6
′ for axially symmetrically aligning liquid crystal molecules are formed, for example in a lattice-shape, on the surface of the glass substrate
21
a
′ equipped with the electrode and color filter (step (b)). In this step, a photosensitive resin material is spin-coated on the glass substrate
21
a
′ to which the electrode and color filter are formed. Then, the substrate is exposed through a photo-mask having a predetermined pattern, and then developed. Thereby, a lattice-shaped polymer wall
6
′ is formed. The photosensitive resin material can either be negative or positive. Further, a resin material having no photosensitivity can also be used, though a step for forming a resist film must be added to the manufacturing steps.
On portions of the top of the polymer wall
6
′ are formed pillar-like protrusions
8
′, which are selectively formed on areas of the wall by patterning (step (c)). In the present step, photosensitive resin material is spin-coated, and then a photo-mask having a predetermined pattern is used to expose and develop the substrate and to form pillar-like protrusions
8
′.
The surface of the glass substrate
21
a
′ to which are formed polymer wall
6
′ and pillar-like protrusions
8
′ is coated with a vertical alignment agent
9
′ formed of polyimide and the like (step (d)).
On the other hand, an opposing glass substrate
21
b
′ to which is formed an electrode is also coated with the vertical alignment agent
9
′ (steps (e) and (f)).
The two substrates
21
a
′ and
21
b
′ formed as above are adhered together, with the surfaces equipped with electrodes facing the inner direction, to form a liquid crystal cell (step (g)). The distance between the two substrates (cell gap; thickness of the liquid crystal layer) is defined by the sum of the height of the polymer wall
6
′ and the height of the pillar-like protrusion
8
′.
Liquid crystal material is injected to the gap formed to the obtained liquid crystal cell through vacuum injection and the like (step (h)).
Lastly, the liquid crystal molecules within each liquid crystal region
31
′ are axially symmetrically aligned, for example, by applying voltage to the pair of electrodes being opposed (step (i)). The liquid crystal molecules
32
′ within each liquid crystal region separated by the polymer wall
6
′ are axially symmetrically aligned with a center axis
33
′ (perpendicular to both substrates) shown by the broken line of FIG.
6
(i).
The cross-sectional structure of the conventional color filter will now be explained with reference to FIG.
7
. On the glass substrate
21
a
′ are formed a black matrix (BM)
4
′ for shading the space (blocking light) between colored patterns, and a colored resin layer
5
′ colored to red (R), green (G) and blue (B) corresponding to each pixel basis. An overcoat (OC) layer
51
′ having a thickness of approximately 0.5 to 2.0 &mgr;m made of acrylic resin or epoxy resin is formed above the colored resin layer
5
′ so as to improve the surface smoothness. Moreover, a transparent signal electrode indium-tin oxide (ITO) film
7
a
′ is formed on the overcoat layer. The BM layer
4
′ is typically formed of a metallic chromium film having a thickness of approximately 100 to 150 nm. Resin materials colored by dyes and pigments are used to form the colored resin layer
5
′, and the thickness of the layer is typically approximately 1 to 3 &mgr;m.
The color filter can be manufactured by utilizing a method of patterning, through photolithography method, the photosensitive colored resin layer
5
′ formed on the substrate
21
a
′. For example, by utilizing photosensitive resin materials each colored to red (R), green (G) or blue (B), and performing formation/exposure/development for each of the three photosensitive colored resins (three times in total), an R/G/B color filter can be manufactured. The methods for forming the photosensitive colored resin layer
5
′ include applying liquid-phase photosensitive colored resin material (diluted with solvent) onto the substrate
21
a
′ through spin-coating method, or transferring the photosensitive colored resin material in the form of a dry film to the substrate. By using the color filter formed as above to manufacture the ASM-mode liquid crystal display, a color liquid crystal display having a wide viewing angle characteristic is obtained.
However, the present inventors have discovered that the ASM-mode liquid crystal display and the method for manufacturing the same according to the prior art have the following problems. That is, though a wide viewing angle characteristic is obtained according to the conventional ASM-mode liquid crystal display, the structure of the ASM-mode display is complicated compared to the conventional TN or STN-type liquid crystal display. Therefore, the manufacturing steps and the manufacturing cost according to the ASM-mode display is increased, and relatively, the yield factor is decreased. Moreover, since the transmission rate of the panel directly above the polymer wall
6
′ (for axially symmetric alignment) is low compared to that of regions where the polymer wall
6
′ does not exist, it causes the brightness of the display to be reduced when the overlapping area of the polymer wall
6
′ is dislocated from the black matrix
4
′ (positioned to shade the space between the colored resin layers
5
of the color filter) and the pattern of the polymer wall
6
′ does
Chung David
Sharp Kabushiki Kaisha
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