Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-11-08
2003-03-18
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S110000, C349S122000
Reexamination Certificate
active
06535264
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
The present application is related to and claims priority from Japanese Patent Application No. 11-319599, filed Nov. 10, 1999.
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device which is provided with a novel spacer arrangement for keeping constant the distance between a pair of substances which seal therebetween liquid crystal compounds which constitute a liquid crystal layer.
BACKGROUND OF THE INVENTION
Liquid crystal display devices are widely used as display devices capable of providing high-resolution and color display for notebook type computers or computer monitors.
These kinds of liquid crystal display device basically include a so-called liquid crystal panel in which liquid crystal compounds are interposed between at least two opposed substrates at least one of which is made of transparent glass or the like, and are generally divided into a type using a liquid crystal panel (simple matrix type: STN type) which selectively applies voltages to various kinds of pixel-forming electrodes formed over the substrates of the liquid crystal panel and turns on and off predetermined pixels, and a type using a liquid crystal panel(active matrix type) in which the various kinds of electrodes and pixel-selecting active elements are formed to turn on and off predetermined pixels by making selection from these active elements.
The active matrix type liquid crystal display devices are represented by a type which uses thin film transistors (TFTs) as active elements which constitute its liquid crystal panel. Liquid crystal display devices using thin film transistors have been widely spread as monitors for display terminals of OA equipment because of their thin sizes and light weights as well as their high picture qualities which compare with those of Braun tubes.
Liquid crystal panels for use in such an active matrix type liquid crystal display device are generally divided into the following two types on the basis of the difference between their liquid crystal driving methods. One of the types includes liquid crystal compounds interposed between two substrates on which transparent electrodes are formed, and the liquid crystal compounds are operated by voltages applied to the transparent electrodes and light which passes through the transparent electrodes and enters the layer of the liquid crystal compounds is modulated to display a picture (TN type).
The other type is constructed to operate a liquid crystal by an electric field which is formed between two electrodes formed on the same substrate, nearly in parallel with the surface thereof, and modulate light which enters the layer of liquid crystal compounds through the gap between the two electrodes, thereby displaying a picture. This type of liquid crystal display device has the feature of a remarkably wide viewing angle and is an extremely promising active matrix type liquid crystal display device. The feature of this type is described in, for example, International Patent Publication No. 505247/1993, Japanese Patent Publication No. 21907/1988 and Japanese Patent Laid-Open No. 160878/1994. This type of liquid crystal display device will be hereinafter referred to as the lateral electric field type (ISP type) of liquid crystal display device.
FIG. 14
is a diagrammatic cross-sectional view illustrating the essential portion of an example of the construction of a TN type of liquid crystal panel. In
FIG. 14
, symbols SUB
1
and SUB
2
denote transparent glass substrates. Thin film transistors TFT are formed over the inner surface of the transparent substrate SUB
1
, while color filters FIL (FIL(R), FIL(G) and FIL(B)) for three colors: red, green and blue are formed over the inner surface of the transparent substrate SUB
2
. Incidentally, the blue filter FIL(B) is not shown.
The thin film transistors TFT formed over the transparent substrate SUB
1
are each made of a gate electrode GT, a gate insulating film GI, an insulating film AOF, a semiconductor layer AS, a drain electrode SD
2
and a source electrode SD
1
, and a pixel electrode ITO
1
is connected to the source electrode SD
1
. Incidentally, two thin film transistors TFT are formed per pixel for the purpose of improving the yield factor of products, but
FIG. 14
shows one of the thin film transistors TFT (TFT
1
).
A protective film PSV
1
is deposited as a layer which overlies these thin film transistors TFT, and an alignment layer (alignment control layer) ORI
1
which is in contact with a liquid crystal (liquid crystal layer) LC is formed as the uppermost layer.
The shown liquid crystal panel has a light shield film, i.e., a so-called black matrix BM, at the boundary between each of the three color filters FIL (FIL(R), FIL(G) and FIL(B)) which are formed over the inner surface of the transparent substrate SUB
2
, and a protective film PSV
2
is formed as a layer which overlies the black matrix BM. A common electrode (also called a counter electrode) ITO
2
is formed over the protective film PSV
2
, and an alignment layer (alignment control layer) ORI
2
which is in contact with the liquid crystal (liquid crystal layer) LC is formed as the uppermost layer. Polarizers POL
1
and POL
2
are stacked on the outer surfaces of the respective substrates SUB
1
and SUB
2
.
This type of liquid crystal panel turns on/off each pixel by changing the alignment direction of the liquid crystal LC by means of an electric field generated between the common electrode ITO
2
and the pixel electrode ITO
1
which is driven by the thin film transistor TFT.
FIG. 15
is a diagrammatic cross-sectional view illustrating the essential portion of one example of the construction of an IPS type of liquid crystal panel. In
FIG. 15
, the same symbols as those shown in
FIG. 14
denote the same functional portions as those shown in FIG.
14
. In this liquid crystal panel, a video signal line (drain line) DL, a counter electrode CT (which corresponds to the common electrode ITO
2
shown in FIG.
14
), and a pixel electrode PX (which corresponds to the pixel electrode ITO
1
shown in
FIG. 14
) are formed over one transparent substrate SUB
1
, and the alignment control layer ORI
1
is formed at the interface between the layer of the liquid crystal LC and the protective film PSV which is deposited over the video signal line DL, the counter electrode CT and the pixel electrode PX. Color filters FIL for three colors (the three color filters are generally denoted by the common symbol FIL) which are separated from one another by the black matrix BM are formed over the other transparent substrate SUB
2
, and an overcoat layer OC (which corresponds to the protective film PSV
2
shown in
FIG. 14
) is deposited to cover the black matrix BM and the color filters FIL so that the constituent materials of the color filters FIL and the black matrix BM are prevented from affecting liquid crystal compounds which constitute the liquid crystal LC. The alignment control layer ORI
2
is formed at the interface between the overcoat layer OC and the liquid crystal LC.
The gate insulating film GI and the insulating film AOF which overlie the transparent substrate SUB
1
are made of an insulating film, and the video signal line (drain line) DL is made of two layers: conductive films d
1
and d
2
. The counter electrode CT is made of a conductive film g
1
, and the pixel electrode PX is made of a conductive film g
2
.
This IPS type of liquid crystal panel turns on/off each pixel by controlling the alignment direction of liquid crystal molecules by means of an electric field (shown as lines of electric force in
FIG. 15
) which is generated in a lateral direction (in a direction parallel to the substrates SUB
1
and SUB
2
) between the pixel electrode PX and the counter electrode CT.
Incidentally, it is general practice to restrict the distance between the pair of substrates SUB
1
and SUB
2
(or the thickness of the layer of the liquid crystal compounds, or the gap between both substrates SUB
1
and
Hasegawa Shinji
Imabayashi Makiko
Iwakabe Yasushi
Akkapeddi P. R.
Hitachi , Ltd.
Kim Robert H.
Townsend and Townsend / and Crew LLP
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