Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-12-22
2001-08-28
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06281958
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a matrix liquid crystal display panel which is used for, for example, television sets, personal computers, word processors, and other office automation(OA) equipments.
BACKGROUND OF THE INVENTION
A liquid crystal display panel has been widely used for, for example, television sets, personal computers, and display sections of other office automation equipment thanks to its thinner structure and lighter weight as compared with a display device using a cathode-ray tube, etc.
As a display system of the liquid crystal display panel, the twisted nematic(TN)type has been conventionally used in many cases. In the TN type, nematic liquid crystal is sealed into a gap between transparent electrode substrates, and liquid crystal molecules are disposed between the two substrates with each of the major axes being twisted by 90° in succession, and a vertical electric field driving system, which carries out an image display by driving the liquid crystal molecules using an electric field arranged vertical to the transparent electrode substrate. However, in the above-mentioned liquid crystal display panel which uses the vertical electric field driving system such as the above-mentioned TN type, the actual anisotropy of refractive index varies for each viewing angle. Namely, this system has high dependency upon the viewing angle.
Here, a horizontal electric field driving system has been developed in earnest for improving viewing angle property, that is, for realizing a wide viewing angle in response to recent needs for a large-size display, etc. The horizontal electric field driving system is a system in which liquid crystal molecules are rotated by using a horizontal electric field in the in-plane direction to the substrate so as to provide an image display. Since the major axis of the liquid crystal molecule is always arranged in parallel with the substrate, the optical property inherently does not vary for each viewing angle.
Japanese Laid-Open Patent Publication No.36058/1995 (Tokukaihei 7-36058) discloses some kinds of electrode structures which use the horizontal electric field driving system. Referring to figures, the following explanation describes one example of a conventional liquid crystal display panel disclosed in the aforementioned Patent Publication which uses the horizontal electric field driving system.
FIG. 7
is a top view illustrating one pixel of the conventional liquid crystal display panel which uses the horizontal electric field driving system. This liquid crystal display panel is arranged in a manner so as to have liquid crystal sealed into a gap between two insulating substrates(not shown) opposing each other.
In
FIG. 7
, on a first insulating substrate (not shown), gate lines
91
and a common line
92
are formed so as to be in parallel with each other. A source line
93
is provided in the direction orthogonal to the gate line
91
and the common line
92
. A thin film transistor (TFT)
94
is provided on the gate line
91
, and a pixel electrode
95
, which is connected with the source line
93
via the TFT
94
, is arranged in parallel with the source line
93
. Further, in the vicinity of a source line
93
′ which is disposed on the other end of the pixel, a common electrode
96
, which branches out from the common line
92
, is arranged in parallel with the source line
93
′. Incidentally, an area which is surrounded by a pair of the gate lines
91
and a pair of the source lines
93
and
93
′ corresponds to one pixel.
These electrode wires are coated with an alignment film(not shown) which is provided on the insulating substrate. This substrate is arranged so as to oppose a second insulating substrate which is provided with an alignment film on the surface thereof in the same manner as the first insulating substrate. Liquid crystal is sealed between these two substrates. Further, this liquid crystal is subjected to an optical modulation in a display section
97
disposed between the pixel electrode
95
and the common electrode
96
which are arranged in parallel with each other.
Moreover, the alignment film is subjected to an aligning operation by using a rubbing method, etc. The aligning operation differs depending upon the dielectric-constant anisotropy of the liquid crystal molecule to be used. For example, in the case when a liquid crystal molecule
98
with positive dielectric-constant anisotropy is driven, as shown in
FIG. 7
, an initial aligning direction of a liquid crystal molecule
98
is arranged virtually in parallel with both the pixel electrode
95
and the common electrode
96
, and is arranged so as to be inclined somewhat clockwise when viewed from the side of the second insulating substrate. Moreover, as shown in
FIG. 7
, each broken line passing one end of the liquid crystal molecule
98
indicates the direction in parallel with the pixel electrode
95
and the common electrode
96
. With this arrangement, when voltage is applied between the pixel electrode
95
and the common electrode
96
, the liquid crystal molecule
98
rotates so as to achieve the optical modulation.
However, in and around the display section
97
, the gate line
91
, the common line
92
, and the source lines
93
and
93
′ are provided in addition to the pixel electrode
95
and the common electrode
96
which apply voltage for driving the liquid crystal molecule
98
; therefore, it is very difficult to apply a uniform horizontal electric field to the substrate in the in-plane direction. The reason why is that voltage is applied to each of the electrodes and wires that are disposed in the vicinity of the display section
97
so that electric fields newly appear and affect one another.
The following explanation describes the relationship between the state of electric lines of force in the above-mentioned uneven horizontal electric fields and the aligning directions of the liquid crystal molecule.
As shown
FIG. 7
, during a writing period, to the gate line
91
is inputted a signal with electric potential which is relatively positive based on the electric potential of the common line
92
and the common electrode
96
; meanwhile, electric potential, which is relatively negative, is applied during the other period(holding period).
Therefore, in the case when the pixel electrode
95
is applied a signal with electric potential which is relatively positive based on the electric potential of the common line
92
and the common electrode
96
, during the holding period, as shown in the model of
FIG. 7
, an electric line of force
99
extends from the pixel electrode
95
in any one of directions of the common electrode
96
, the common line
92
, or the gate line
91
.
Incidentally, in the case of the liquid crystal molecule with positive dielectric constant anisotropy, upon applying voltage, torque is exerted in the major axis direction of the liquid crystal molecule along the electric line of force.
Namely, as shown in
FIG. 7
, in the case of the liquid crystal molecule
98
with positive dielectric constant anisotropy, upon applying voltage, torque is exerted to in the major axis direction of the liquid crystal molecule
98
along the electric line of force
99
. Therefore, as shown in
FIG. 7
, in an area A in which the electric line of force
99
virtually orthogonal to the pixel electrode
95
and the common electrode
96
, during the holding period, when to the pixel electrode
95
is applied a signal with electric potential which is relatively positive based on the electric potential of the common line
92
and the common electrode
96
, a liquid crystal molecule
98
a
, which exists close to the pixel electrode
95
in the area A, rotates in the direction of an arrow(to the right) in accordance with the initial aligning direction shown in FIG.
7
. At this time, in an area B of the same pixel as well, when voltage is applied, a liquid crystal molecule
98
b
rotates in the direction of an arrow(to the right) in accordance with the initial aligning direction; however, in an area C
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Dudek James A.
Hartnell, III George W.
Schechter Andrew
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