Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-19
2003-03-11
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S038000, C349S125000, C349S129000, C349S178000
Reexamination Certificate
active
06532054
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid crystal display and a method for fabricating the liquid crystal display, more specifically to a liquid crystal display of vertical alignment mode, which controls tilt directions of the liquid crystal molecules upon application of voltages, and a method for fabricating the liquid crystal display.
BACKGROUND ART
As a liquid crystal display (LCD: Liquid Crystal Display) using an active matrix, a liquid crystal display of TN (Twisted Nematic) mode, in which a liquid crystal material having positive dielectric anisotropy is aligned horizontal to the substrate face and is capable of being twisted by 90° between the opposed substrates is widely used. However, the liquid crystal display of TN mode has a serious disadvantage of poor viewing angle characteristics. To improve the viewing angle characteristics, various proposals have been made.
Recently, in place of TN mode there has been proposed MVA (Multi-domain Vertical Alignment) mode, in which a liquid material having negative dielectric anisotropy is vertically aligned, and tilt directions of the liquid molecules upon application of voltages are restricted by projections provided on the faces of the substrates.
As shown in
FIG. 25
, a liquid crystal display of MVA mode, which is a VA (Vertically Aligned) mode liquid crystal display, wherein a liquid crystal material having negative dielectric anisotropy is vertically aligned, comprises projections
128
,
150
on substrates
110
and
140
so as to restrict directions in which the liquid crystal molecules
164
are obliquely inclined upon application of voltages to be plural in one picture element, whereby the viewing angle characteristics are improved.
However, in the above-described conventional MVA mode-liquid crystal display, an electric field is extended from a region near the end of a picture element electrode
126
toward a region outside the picture element electrode
126
, and lines of electric force
166
are extended as shown in FIG.
25
. Accordingly, abnormal domains take place, and disclinations take place as indicated by the shaded portions in
FIG. 26
, which reduces luminance.
A result of a simulation of transmittance characteristics of the conventional MVA mode liquid crystal display shown in
FIG. 25
will be explained with reference to FIG.
27
.
FIG. 27
is a graph of the result of the simulation of transmittance characteristics of the conventional MVA mode-liquid crystal display.
As shown in
FIG. 27
, disclinations are present between a projection
128
and the end portion of a picture element electrode
126
, which results in transmittance decrease. Thus, the conventional MVA mode-liquid crystal display has found it difficult to provide high luminance.
To improve this problem, it has been proposed to place a projection
188
on a counter electrode
148
in a region near the end portion of a picture element electrode
126
, as shown in
FIG. 28
, so as to decrease abnormal domains. Because of projection
188
, the disclinations in the display region disappear as shown in
FIG.29
, but the projection
188
disposed on the counter electrode
148
reduces luminance by an area of the projection
188
.
It is considered to form the projection
188
as outwardly of a picture element electrode as possible, so as to increase luminance. However, when an offset, i.e., a length over which the picture element electrode
126
and the projection
188
overlap each other is 6 &mgr;m, the occurrence of disclinations can e prevented as shown in
FIG. 29
, but when an offset is 5 &mgr;m as shown in
FIG. 30
, the occurrence of disclinations cannot be prevented. When an offset is, e.g., 10 &mgr;m as shown in
FIG. 31
, it is substantially equal to addition of one conventional projection and luminance is further decreased.
In a conventional liquid crystal display which is not of MVA mode, abnormal domains occur in the regions as shaded in
FIG. 32
due to transverse electric fields between picture element electrodes
126
and drain bus lines
122
. The same problem as in the liquid crystal display of MVA mode takes place.
An object of the present invention is to provide a liquid crystal display having good display characteristics, and a method for fabricating the liquid crystal display.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention, there is provided a liquid crystal display comprising a first substrate with a picture element electrode formed on, a second substrate with a counter electrode opposed to the picture element electrode, and a liquid crystal sealed between the first substrate and the second substrate, a distance between the picture element electrode and the counter electrode in a vicinity of the end portion of the picture element electrode is larger than a distance between the picture element electrode and the counter electrode in a region except the vicinity of the end portion of the picture element electrode. Transverse extension of an electric field from a vicinity of the end portion of the picture element electrode can be prohibited to thereby preclude occurrence of abnormal domains, whereby occurrence of disclinations can be suppressed. Accordingly, the liquid crystal display can have high luminance.
In the liquid crystal display, it is preferable that the distance between the picture element electrode and the counter electrode in the vicinity of the end portion of the picture element electrode is gradually increased toward a region where the picture element electrode and the counter electrode are not opposed to each other.
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Kataoka Shingo
Ohmuro Katsufumi
Sasaki Takahiro
Tashiro Kunihiro
Yoshimi Takuya
Akkapeddi P. R.
Fujitsu Limited
Greer Burns & Crain Ltd.
Sikes William L.
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