Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-29
2003-06-24
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S001000, C349S139000
Reexamination Certificate
active
06583837
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device comprising a first substrate having a pixel electrode and a first alignment film, and a second substrate having a common electrode and a second alignment film.
2. Prior Art
Recently, as liquid crystal display devices in which a light transmissivity and a viewing angle can effectively be improved, liquid crystal display devices adopting a multiple domain vertical alignment (or SVA; Super Vertical Alignment) method have come into wide use. As an example of such conventional liquid crystal display devices in which the SVA method has been adopted, a liquid crystal display device having a TFT substrate with a TFT (thin film transistor) formed thereon and a color filter substrate with a color filter formed thereon will hereinafter be described.
FIGS. 6 through 9
are schematic explanatory views of a conventional liquid crystal display device adopting the SVA method.
FIG. 6
includes an enlarged plan view (A) of a portion of the TFT substrate in this conventional liquid crystal display device which corresponds to one pixel, and a cross-sectional view (B) of the portion taken along line A—A. FIG.
6
(A) shows only a gate bus, source buses and a pixel electrode, and a TFT is omitted from the drawing.
As shown in FIG.
6
(A), this TFT substrate
10
is formed with a gate bus
11
and source buses
12
. Further, the TFT substrate
10
is formed with a pixel electrode
13
and a TFT (not shown) correspondingly to each pixel. Slits
13
b
(portions indicated by multiple dots) are formed at the central part of the pixel electrode
13
. Further, slits
13
a
and slits
13
c
(portions indicated by multiple dots) are formed at the upper and lower portions (in the drawing) of the pixel electrode
13
, respectively. Gaps
14
are provided between the source buses
12
and the pixel electrode
13
.
As shown in FIG.
6
(B), the surface of the TFT substrate
10
is covered with an alignment film
15
. This alignment film
15
is omitted in FIG.
6
(A). The TFT substrate
10
is opposed to a color filter substrate via a liquid crystal layer.
FIG. 7
includes a plan view (A) of the TFT substrate and the color filter substrate opposed to each other via the liquid crystal layer as viewed from the color filter substrate side, and a cross-sectional view (B) of these two substrates taken along line B—B. To illustrate characteristic portions of this conventional liquid crystal display device in a simplified manner, FIG.
7
(A) shows only the gate bus, the source buses, the pixel electrode and protrusions (or ridges).
As shown in FIG.
7
(B), the TFT substrate
10
is opposed to the color filter substrate
20
via the liquid crystal layer
30
. This liquid crystal layer
30
is constituted of negative liquid crystal molecules having properties to be aligned perpendicularly to electric force lines.
The color filter substrate
20
is provided with a color filter (not shown). Further, the color filter substrate
20
is provided with a common electrode
21
on which protrusions (or ridges)
22
are formed. As shown in FIG.
7
(A), these projections
22
are formed on the right-hand and left-hand sides of the slits
13
b
in parallel thereto. A material for these protrusions
22
may be selected, for example, from phenolic resins, novolac resins, and acrylic resins. Further, as shown in FIG.
7
(B), the common electrode
21
and the protrusions
22
are covered by an alignment film
23
. In this way, protrusions
22
are formed between the common electrode
21
and the alignment film
23
, so that the surface of the color filter substrate
20
is formed with portions
24
which are projected toward the liquid crystal layer
30
caused by the protrusions
22
. Since the protrusions
22
are formed in parallel to the slits
13
b
as shown in FIG.
7
(A), the projected portions
24
are formed also in parallel to the slits
13
b.
The alignment films
15
and
23
formed on the TFT substrate
10
and the color filter substrate
20
, respectively, are adapted to align liquid crystal molecules perpendicularly to these alignment films
15
and
23
, when no voltage is applied to the liquid crystal layer
30
.
Description will now be made on the behavior of the liquid crystal molecules when a voltage is applied between the substrates
10
and
20
with reference to FIG.
8
and
FIG. 9
showing the liquid crystal molecules more distinctly.
FIG. 8
is a cross-sectional view of the device taken along line C—C when no voltage is applied between the substrates
10
and
20
in
FIG. 7
, and
FIG. 9
is the same cross-sectional view when a voltage is applied between the substrates
10
and
20
in FIG.
7
. The liquid crystal molecules are indicated by ellipses.
As shown in
FIG. 8
, when no voltage is applied (hereinafter referred to as “voltage non-applied period”), the liquid crystal molecules in the liquid crystal layer
30
are oriented perpendicularly to the alignment film
23
(i.e., to each of the substrates
10
and
20
). In the state that the liquid crystal molecules are perpendicularly oriented, when a voltage is applied, electric force lines as represented by broken lines develop. As the liquid crystal molecules constituting the liquid crystal layer
30
are negative liquid crystal molecules, they start to be inclined perpendicularly to the electric force lines (horizontally with respect to the substrates
10
and
20
). In this case, the electric force lines develop substantially perpendicularly to the substrates
10
and
20
. However, as the slits
13
b
(See
FIG. 6
) are provided in the pixel electrode
13
, and the gap
14
(See
FIG. 6
) is provided between the pixel electrode
13
and the source bus
12
, the electric force lines around the slit
13
b
and the gap
14
are slightly bent and enter/leave the pixel electrode
13
. Accordingly, immediately after the development of these electric force lines, the electric force lines enter/leave those liquid crystal molecules present in positions away from the slit
13
b
and the gap
14
substantially in parallel thereto, but enter/leave at a slightly inclined angle those liquid crystal molecules present in positions around the slit
13
b
and the gap
14
under the influence of the slit
13
b
and the gap
14
. Therefore, the liquid crystal molecules
31
and
32
present around the slit
13
b
and the gap
14
start to be inclined horizontally to the substrates
10
and
20
earlier than the liquid crystal molecules present in the positions away from the slit
13
b
and the gap
14
. When the liquid crystal molecules
31
and
32
start to be inclined, the other liquid crystal molecules sequentially start to be inclined from the liquid crystal molecules
31
and
32
as their starting points. In this case, when considering the directions of the electric force lines that enter/leave the respective liquid crystal molecules
31
and
32
, the liquid crystal molecule
31
starts to be oriented perpendicularly to the electric force line while being inclined in the clockwise direction T, whereas the liquid crystal molecule
32
starts to be oriented perpendicularly to the electric force line while being inclined in the counterclockwise direction T′. Accordingly, the liquid crystal molecules positioned in a region A closer to the slit
13
b
than the gap
14
are greatly influenced by the liquid crystal molecule
31
inclined in the clockwise direction T, and sequentially become inclined in the clockwise direction T. On the other hand, the liquid crystal molecules existing in a region B closer to the gap
14
are greatly influenced by the liquid crystal molecule
32
inclined in the counterclockwise direction T′, and sequentially become inclined in the counterclockwise direction T′. As a result, during the voltage-applied period, the directions of inclination of the liquid crystal molecules in the regions A and B are opposite to each other, and the liquid crystal molecules are oriented as shown in FIG.
9
.
PROBLEMS
Chapman Jeffrey Alan
De Boer Dirk Kornelis Gerhardus
Fukumoto Masakazu
Johnson Mark Thomas
Nieuwkerk Armanda Cinderella
Chowdhury Tarifur R.
Koninklijke Philips Electronics , N.V.
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