Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-08-16
2004-12-28
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S124000, C349S156000, C349S157000
Reexamination Certificate
active
06836308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device used in TV receivers, monitors, etc., a substrate for such a liquid crystal display device, and a manufacturing method of such a substrate.
2. Description of the Related Art
In general, a liquid crystal display device is composed of two substrates each having a transparent electrode(s) and a liquid crystal layer that is interposed between the two substrates. The display is controlled by driving the liquid crystal by applying voltages between the transparent electrodes and thereby changing the light transmittance. In recent years, the demand for liquid crystal display devices has increased and requirements for liquid crystal display devices have diversified. In particular, improvement in viewing angle characteristic and display quality is desired strongly and the vertically aligned (VA) liquid crystal display device is considered promising as a means for realizing such requirements.
The VA liquid crystal display device is characterized in that vertical alignment films are formed on the opposite surfaces of two substrates and a liquid crystal layer having negative dielectric anisotropy is interposed between the two substrates. In the VA liquid crystal display device, linear domain regulating means (protrusions or slits) are provided on the two substrates and domain division is performed by the domain regulating means. With these measures, the VA liquid crystal display device attains superior viewing angle characteristic and display quality.
At present, the interval (cell thickness) between the two substrates of a liquid crystal display device is kept by means of spherical or rod-shaped spacers made of plastics or glass. Usually, the spacers are sprayed on one of the two substrates in a spacer spraying process that is executed before attaching the substrates. Then, the two substrates are attached with each other and pressed against each other so that the cell thickness is kept close to the diameter of the spacers.
FIG. 35
is a plan view showing the configuration of a conventional VA liquid crystal display device, and specifically shows three pixels in which color filters of R (red), G (green), and B (blue) are arranged in order on a color filter (CF) substrate
106
. A light shield film (BM) is formed on the CF substrate
106
so as to extend in the top-bottom direction and the right-left direction in FIG.
35
and thereby defines individual pixel regions. Protrusions
102
as linear alignment regulating structures are formed in each pixel region obliquely with respect to its end portions. On an array substrate (not shown in
FIG. 35
) that is opposed to the CF substrate
106
, linear protrusions
103
are formed obliquely with respective to the sidelines of each pixel region so as to be deviated from the protrusions
102
by a half pitch.
FIG. 35
does not show a storage capacitor bus line that traverses pixel regions at the center.
FIG. 36
is a sectional view of the VA liquid crystal display device taken along line C—C in
FIG. 35
, and shows a state of a liquid crystal LC when no voltage is applied. The array substrate
104
has pixel electrodes
110
that are formed on a glass substrate
108
in the respective pixel regions. The protrusions
103
are formed on the pixel electrodes
110
. A vertical alignment film (not shown) is formed on the entire surfaces of the pixel electrodes
110
and the protrusions
103
. On the other hand, the CF substrate
106
has a BM that is formed on a glass substrate
108
. The color filters R, G, and B are formed in the respective pixel regions that are defined by the BM that is formed on the glass substrate
108
. A common electrode
112
is formed on the color filters R, G, and B and the protrusions
102
are formed on the common electrode
112
. A vertical alignment film (not shown) is formed on the entire surfaces of the common electrode
112
and the protrusions
102
. The liquid crystal LC is sealed between the array substrate
104
and the CF substrate
106
.
As shown in
FIG. 36
, liquid crystal molecules (indicated by cylinders in
FIG. 36
) are oriented approximately perpendicular to the substrates
104
and
106
. The liquid crystal molecules in the regions where the protrusions
102
and
103
are formed are oriented approximately perpendicular to the surfaces of the protrusions
102
and
103
and are slightly inclined against the substrates
104
and
106
. Since polarizers (not shown) are disposed outside the respective substrates
104
and
106
in the crossed Nichols state, black display is obtained when no voltage is applied.
FIG. 37
is a sectional view, similar to
FIG. 36
, of the VA liquid crystal display device taken along line C—C in
FIG. 35
, and shows a state of the liquid crystal LC when voltages are applied. Broken lines indicate electric field lines extending between the pixel electrode
110
and the common electrode
112
. As shown in
FIG. 37
, when a voltage is applied between the pixel electrode
110
and the common electrode
112
, the electric field is distorted near the protrusions
102
and
103
which are made of a dielectric, whereby the inclination direction of liquid crystal molecules having the negative dielectric anisotropy is regulated. Gradation display can be attained by controlling the inclination angle in accordance with the electric field strength.
Where the protrusions
102
and
103
are formed in a linear manner as shown in
FIG. 35
, when a voltage is applied, the liquid crystal molecules in the vicinity of the protrusions
102
and
103
fall in the two directions that are perpendicular to the extending direction of the protrusions
102
and
103
, with the protrusions
102
and
103
being as boundaries. Since the liquid crystal molecules in the vicinity of the protrusions
102
and
103
are slightly inclined from the direction perpendicular to the two substrates
104
and
106
even when no voltage is applied, they fall quickly in response to electric field strength. The inclination directions of the liquid crystal molecules around the above liquid crystal molecules are determined in order according to the behavior of the above liquid crystal molecules, and the liquid crystal molecules around the above liquid crystal molecules fall in accordance with the electric field strength. In this manner, the domain division is realized in which the protrusions
102
and
103
as the alignment regulating structures serve as boundaries.
Incidentally,
FIGS. 36 and 37
do not show spacers that determine the cell thickness. How spacers are arranged will be described with reference to
FIG. 38
, which is a sectional view taken along line A—A in FIG.
35
. Together with the liquid crystal LC, spacers
114
for maintaining the cell thickness between the array substrate
104
and the CF substrate
106
are sealed between the two substrates
104
and
106
.
In the VA liquid crystal display device shown in
FIG. 38
, the protrusions
102
and
103
are formed on the two substrates
104
and
106
. Therefore, the cell thickness is determined in one case by spherical spacers
114
that are placed on a protrusion
102
or in another case by spacers
114
that are not placed on any protrusion
102
. As such, it is difficult to obtain a uniform cell thickness distribution. To obtain a uniform cell thickness distribution, it is preferable that the number of asperities on the surface of the two substrates
104
and
106
is as small as possible.
FIG. 39
is a sectional view, taken along line C—C in
FIG. 35
, of a VA liquid crystal display device that is obtained by replacing the protrusions
103
on the array substrate
104
with slits
118
in the VA liquid crystal display device of
FIG. 35
, and shows a state of the liquid crystal LC when a voltage is applied. As shown in
FIG. 39
, in the regions where the slits
118
are formed, approximately the same electric field lines are formed as in the regions in
FIG. 37
where the protrusions
103
are formed. In this manner, domain division in
Sawasaki Manabu
Takagi Takashi
Tanose Tomonori
Duong Tai
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Ton Toan
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