Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-01-21
2002-08-13
Shankar, Vijay (Department: 2773)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C349S038000
Reexamination Certificate
active
06433764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display for displaying pictures and the like, having an appropriate capacity, capable of ensuring the accurate operation of thin-film transistors and having a high aperture ratio.
2. Description of the Related Art
Because of advantages in weight reduction, device miniaturization and thickness reduction, liquid crystal displays have come into wide use. As is generally known, a twist nematic mode (TN mode) active matrix liquid crystal display, in particular, requires a relatively low driving voltage, dissipates power at a relatively low rate, and is capable of displaying pictures in high contrast and high quality.
A general TN mode liquid crystal display of this kind is formed by disposing two glass substrates each provided with a polarizer, a transparent electrode and an alignment layer opposite to each other with a space therebetween and with the respective directions of orientation of the alignment layers perpendicular to each other, and filling up the space between the two glass substrates with a twist nematic liquid crystal so that molecules of the twist nematic liquid crystal can be twisted through and angle of 90°.
Recently, the dependence of the visibility, i.e., viewing angle characteristic, of a general TN mode liquid crystal display of this kind on viewing angle has become a problem.
FIG. 7
shows the viewing angle characteristic of a general TN mode liquid crystal display, in which shaded region corresponds to a viewing angle range in which contrast (CR) is 10 or above. As is obvious from
FIG. 7
, the visibility from lateral viewing directions of the TN mode liquid crystal display is satisfactory, the visibility from vertical viewing directions is not satisfactory, and the visibility from upper vertical viewing directions is very bad.
The applicant of the present patent application proposed a liquid crystal display element of a structure capable of solving such a problem in Japanese Patent Application No. 7-306276. In this previously proposed liquid crystal display element, spaced linear electrodes
12
and
13
of different polarities are formed only on the lower substrate
11
as shown in FIG.
8
and any electrode is not formed on an upper substrate
10
as shown in
FIG. 9
instead of forming liquid crystal driving electrodes on both the upper substrate
10
and the lower substrate
11
disposed on the opposite sides of a liquid crystal layer, and a voltage is applied across the linear electrodes
12
and
13
to align liquid crystal molecules
36
in the direction of a lateral electric field created between the linear electrodes
12
and
13
.
More specifically, the linear electrodes
12
are connected to a base line
14
to form a comblike electrode
16
, the linear electrodes
13
are connected to a base line
15
to form a comblike electrode
17
, the comblike electrodes
16
and
17
are disposed so that the linear electrodes
12
and
13
are arranged alternately at intervals, and the base lines
14
and
15
are connected to a power supply
18
and a switching device
19
.
As shown in
FIG. 10A
, an upper alignment layer is formed on a surface of the upper substrate
10
contiguous with the liquid crystal, the upper alignment layer is treated so as to align the liquid crystal molecules
36
in the direction of the arrow &bgr;, lower alignment layer is formed on a surface of the lower substrate contiguous with the liquid crystal so as to align the liquid crystal molecules in the direction of the arrow &ggr; parallel to the direction of the arrow &bgr;, an upper polarizer film having a polarizing direction in the direction of the arrow &bgr; in
FIG. 10A
is laminated to the upper substrate
10
, and a lower polarizer film having a polarizing direction parallel to the direction of the arrow &agr; is laminated to the lower substrate
11
. When any voltage is not applied across the linear electrodes
12
and
13
, the liquid crystal display element remains dark. When a voltage is applied across the linear electrodes
12
and
13
, the liquid crystal display element turns bright.
FIGS. 12 and 13
show a configuration of an actual active matrix liquid crystal driving circuit employing the structure of a liquid crystal display provided with the foregoing linear electrodes
12
and
13
.
As shown in
FIGS. 12 and 13
, in which only a portion of the active matrix liquid crystal driving circuit corresponding to one pixel is shown, a gate electrode
21
and spaced, parallel, linear electrodes
22
are formed by patterning a conductive film on a transparent substrate
20
, such as a glass substrate, a gate insulating layer
24
is formed over the gate electrode
21
and the linear electrodes
22
, and a thin-film transistor T is formed by forming a semiconductor film
26
in an area on the gate insulating layer
24
corresponding to the gate electrode
21
, and forming a source electrode
27
and a drain electrode
28
on the opposite sides of the semiconductor film
26
, and a second linear electrode
29
is formed by processing a conductive film in an area on the gate insulating film
24
corresponding to the middle between the first linear electrodes
22
.
As shown in plan view in
FIG. 12
, gate lines
30
and signal lines
31
are formed on the transparent substrate
20
to define rectangular pixel regions arranged in a matrix, the gate electrode
21
, i.e., a portion of the gate line
30
, is formed in a corner of the pixel region, the second linear electrode
29
is extended in parallel to the signal line
31
and is connected through a capacity electrode
33
to the drain electrode
28
overlying the gate electrode
21
, and the first linear electrodes
22
are extended in parallel to and on the opposite sides of the second linear electrode
29
.
Ends of the first linear electrodes
22
on the side of the gate line
30
are connected to a connecting line
34
extended in parallel to the gate line
30
in the pixel region, and the other ends of the first linear electrodes
22
are connected to a common electrode
35
extended in parallel to the gate line
30
. The common electrode
35
is extended in parallel to the gate line
30
through a plurality of pixel regions to apply the same voltage to the linear electrodes
22
of all the pixel regions. One end portion of the second linear electrode
29
is extended to a position over the common electrode
35
, a capacity electrode
36
′ is formed at the end of the second linear electrode
29
so as to overlie a portion of the common electrode
35
in the pixel region, the capacity electrode
33
formed at the other end of the second linear electrode
29
overlies the connecting line
34
. The capacity electrodes
33
and
36
′ form capacitors together with the connecting line
34
and the common electrode
35
underlying and separated by the insulating layer
24
from the capacity electrodes
33
and
36
′, respectively, to stabilize the operation of the thin-film transistor T when driving the liquid crystal.
Although this liquid crystal display of the foregoing configuration provided with a liquid crystal driving circuit is advantageous in its wide viewing angle, the same has a problem that its aperture ratio is liable to be small.
The capacitor consisting of the capacity electrode
33
and the connecting line
34
formed on the opposite sides of the insulating layer
24
and the capacitor consisting of the capacity electrode
36
′ and the common electrode
35
formed on the opposite sides of the insulating film
24
shown in
FIGS. 12 and 13
need to have capacities on an appropriate level to stabilize the operation for driving the thin-film transistor T. Therefore, the common electrode
33
, the connecting electrode
34
, the common electrode
35
and the capacity electrode
36
′ must be formed in widths as shown in
FIG. 14
greater than those shown in FIG.
12
. If the common electrode
33
, the connecting line
34
, the common electrode
35
and the capacity electrode
36
&pr
Hebiguchi Hiroyuki
Sung Chae Gee
Brinks Hofer Gilson & Lione
Frenel Vanel
LG. Philips LCD Co. Ltd.
Shankar Vijay
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