Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-07-27
2003-09-09
Niebling, John F. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06618109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus of IPS (In-Plane Switching) system in which liquid crystal is made to drive within a surface approximately parallel to a TFT (Thin Film Transistor) substrate by applying a voltage to a pixel electrode and a common electrode therebetween formed on the TFT substrate.
2. Description of the Related Art
An active matrix type liquid crystal display apparatus, having a picture quality of high dignity, uses a thin film transistor (hereinafter referred to TFT) as a switching element of pixels, and is widely used as space-saving designed monitor of a desktop computer and so forth. Generally, in the operating mode of the liquid crystal display apparatus, there are two systems of Twisted Nematic: TN system which allows direction of directors of oriented liquid crystal molecules to be rotated in the perpendicular direction to a transparent substrate and In-Plane Switching: IPS system which allows liquid crystal molecules to be rotated in the direction parallel to a transparent substrate.
The IPS system liquid crystal display apparatus alternately forms pixel electrode and common electrode on the first transparent substrate constituting the TFT, wherein the teeth of a comb of the pixel electrode is parallel to the teeth of a comb of the common electrode with each other, and a light transmission quantity is controlled by changing the direction of the director of the liquid crystal molecule with forming electric field parallel to the substrate by applying a voltage to the pixel electrodes and the common electrodes therebetween. Consequently, because the director rotates within the substrate surface in this display system, the problem that a relationship between the light transmission quantity and the voltage application quantity in the case of TN system, when watching in the direction of the director and in the direction of normal of the substrate has a large difference, does not occur, then it is possible to obtain good picture while watching from very wide angle of vision.
However, in the conventional IPS system of liquid crystal display apparatus, there is a problem that the pixel electrodes and the common electrodes are formed in the straight-line shape mutually, and the liquid crystal molecules perform one directional rotation, in this case of watching from an oblique direction in white indication condition, colored condition occurs. Accordingly, a multi domain structure is proposed for solving the problem, which forms the pixel electrodes and the common electrodes in such a way as to bend the pixel electrodes and the common electrodes at bending point more than one to form a plurality of domains in which orientation direction thereof is different within one pixel.
As to the aforementioned conventional technique, it is explained with referring to
FIG. 1A
, FIG.
1
B and FIG.
2
.
FIG. 1
is a view illustrating a structure of a conventional IPS system liquid crystal display apparatus.
FIG. 1A
is a plan view and
FIG. 1B
is a sectional view along E—E line of FIG.
1
A. Further,
FIG. 2
is a view schematically illustrating electric field between electrodes and rotational direction of the liquid crystal molecules. This liquid crystal display apparatus is constituted by a first transparent substrate
1
on which TFT is formed, a second transparent substrate
2
on which a color filter (CF) is formed, and liquid crystal
17
that is sandwiched therebetween, and in the first transparent substrate
1
forms a gate line
2
and a signal line
6
at approximately right angle, and TFT
5
is arranged in the shape of matrix at an intersection thereof. Furthermore, the pixel electrode
7
and the common electrode
3
are alternately formed in parallel with each other at the respective pixels, bending at the bent point more than one. Moreover, a black matrix
12
for shading extra light, color layer
13
for performing color indication of three RGB colors and flattening film
14
for covering them are formed on the second transparent substrate
11
.
Then, orientation film
18
is coated to opposite surfaces of these first transparent substrate
1
and second transparent substrate
11
, and the liquid crystal
17
, homogeneously oriented in approximately parallel with extended direction of the signal line
6
, is sandwiched between both substrates
1
,
11
. A polarization plate
16
a
is affixed to outside of the substrate
1
. A conductive film
15
is formed at outside of the substrate
11
, and a polarization plate
16
b
is affixed to outside of the conductive film
15
. A polarization axis of both polarization plate
16
a
,
16
b
are at right angles with each other, one polarization axis is set in parallel with oriented direction of the liquid crystal molecule
17
a
. Then, write of electric potential is made to execute to the pixel electrode
7
through the TFT
5
to give lateral electric field to the bent pixel electrodes
7
and the bent common electrodes
3
therebetween, thus indication is made to control so that operation allows the liquid crystal
17
to be subjected to twist deformation within a surface parallel to the substrates
1
,
11
.
According to this method, when the voltage is applied to the pixel electrodes
7
and the common electrodes
3
therebetween, as illustrated in
FIG. 2
, the electric field
25
is generated in each different direction at two regions (upper region and lower region of
FIG. 2
) that are divided by the line which links top of the bent sections, therefore, the liquid crystal
17
a
which is initially oriented in the upper direction and the lower direction of
FIG. 2
is twisted in two directions. Then, when watching from an oblique direction in the white indication condition, since the liquid crystal molecules
17
a
of the two regions compensate with each other, effect is obtained that colored condition is reduced. Furthermore, an equipotential surface
24
is formed in parallel with both the pixel electrodes
7
and the common electrodes
3
.
However, in the conventional multi-domain liquid crystal display apparatus, since the initially oriented direction of molecules
17
a
is approximately right angle to the electric field direction in a adjacent area close to the line which joins tops of bent sections of the pixel electrode
7
or common electrode
3
, rotational direction of the liquid crystal molecules
17
a
depends on whether the liquid crystal molecules
17
a
rotate in which direction depends on shape of the bent section, and when shapes of the bent sections are fluctuated depending on manufacturing errors, irregularities occur in connection with its orientation direction of the liquid crystal molecules
17
a
, resulting in, thus, the problem that disclination occurs. Furthermore, since the liquid crystal molecules
17
a
of the domain of both sides of the bent section rotate in the opposite direction mutually, motion of the liquid crystal molecules
17
a
close to the line joining top of the bent section is inhibited by the liquid crystal molecules
17
a
of the both sides, as a result, there is the problem that delay of response occurs.
Explained the circumstances referring to
FIG. 2
, the liquid crystal molecules
17
a
placed at upper section of
FIG. 2
rotates clockwise because left-down electric field
25
acts to upper and lower initial orientation direction of this liquid crystal molecules
17
a
, on the other hand, the liquid crystal molecules
17
a
placed at lower section of
FIG. 2
rotate counterclockwise because left-up electric field
25
acts to the liquid crystal molecules
17
a
, however, the liquid crystal molecules
17
a
existing in the region
23
of unstable orientation direction close to the line which joins tops of bent sections rotate in the direction without intention in response to the shape of the bent section sensitively, as a result, rotating in unexpected direction depending on slight shape irregularity or deviation of the
Hidehira Masanobu
Kuroha Syouichi
Watanabe Makoto
Isaac Stanetta
NEC LCD Technologies Ltd.
Niebling John F.
Scully Scott Murphy & Presser
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