Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-02-12
2003-10-07
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S146000
Reexamination Certificate
active
06630979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an In-Plane Switching mode LCD (IPS-LCD) and, more particularly, to an electrode array structure of an IPS-LCD.
2. Description of the Related Art
Liquid crystal displays (LCDs) may be classified by the orientation of the liquid crystal molecules between the spaced apart substrates. In a conventional twisted nematic LCD (TN-LCD), the liquid crystal molecules are twisted between the two substrates. In contrast, in an in-plane switching mode LCD (IPS-LCD), common electrodes and pixel electrodes are formed on a lower glass substrate (TFT substrate) and an in-plane electric field therebetween is generated to rearrange the liquid crystal molecules along the in-plane electric field. Accordingly, the IPS-LCD has been used or suggested for improving viewing angle, contrast ratio and color shift.
In the IPS-LCD, the display characteristics of the view angle with respect to the invert luminance are superior. However, as shown in
FIG. 1
, when the liquid crystal molecules
1
are rotated to an angle 45° with respect to the in-plane electric field, the observed image from the direction crossing at 45 degrees or 135 degrees against the lengthwise direction of the common electrodes
2
and the pixel electrodes
3
is colored blue or yellow. This is a problem to be solved in the image quality of the IPS-LCD.
Seeking to solve the coloring phenomenon, a herringbone-shaped electrode structure is developed for modifying the rotating angle of the liquid crystal molecules. As shown in
FIG. 2
, in the conventional IPS-LCD, a TFT substrate
10
has a plurality of parallel data lines
12
extending along Y-axis and a plurality of parallel gate lines
14
extending along X-axis, which are arranged in a manner to form a matrix of pixel areas
24
. Also, a comb-shaped pixel electrode
18
and a herringbone-shaped common electrode
20
are disposed in each pixel area
24
, and at least one TFT device
16
is disposed at a cross point of the data line
12
and the gate line
14
. In addition, an orientation layer (not shown) is spread on the entire surface of the TFT substrate
10
, and the orientation layer is rubbed in a direction shown by arrow A so as to make liquid crystal molecules
22
arrange along the direction A before an external voltage is applied to the TFT substrate
10
.
The comb-shaped pixel electrode
18
has a bar
18
a
transversely disposed over the gate line
14
to form a capacitor, and a plurality of continuous saw-toothed teeth
18
b
,
18
c
extending along Y-axis from the bar
18
a
. The herringbone-shaped common electrode
20
has a center wiring portion
20
a
extending along X-axis, and a plurality of saw-toothed bones
20
b
,
20
c
bent at the center wiring portion
20
a
and respectively extending along a first Y-axis and a second Y-axis. For example, the bones
20
b
extending along the first Y-axis are parallel to the teeth
18
b
,
18
c
and the bones
20
b
arrange at intervals between the teeth
18
b
,
18
c.
When external voltage is applied to the TFT substrate
10
, an in-plane electric field is formed between the bones
20
a
,
20
b
and the teeth
18
b
,
18
c
, resulting in a rotation of the liquid crystal molecules
22
toward the in-plane electric field. Using the center wiring portion
20
a
of the common electrode
20
as the discrimination, the pixel area
24
is divided into a first sub-pixel area
241
and a second sub-pixel area
242
, and the liquid crystal molecules
22
a
and
22
b
positioned adjacent to the center wiring portion
20
a
respectively rotate in counterclockwise direction and in clockwise direction. In the first sub-pixel area
241
, since the bones
20
b
,
20
c
and the teeth
18
b
,
18
c
have the same saw-toothed sidewalls, the liquid crystal molecules
22
a
and
22
a
′ positioned adjacent to the tip of the saw-toothed sidewall respectively rotate in counterclockwise direction and in clockwise direction. Therefore, two domains are formed within the first sub-pixel area
241
. Similarly, the liquid crystal molecules
22
b
and
22
b
′ also form two domains within the second sub-pixel area
242
. Furthermore, the saw-toothed sidewalls lead to a specific tilted degree of the in-plane electric field which corresponds to the rotation angle of the major axes of the liquid crystal molecules
22
. It is preferable that the rotation angle &thgr; of the liquid crystal molecules
22
satisfy the formula 0°<&thgr;≦+60° or −60° &thgr;<0° to solve the coloring phenomenon.
However, the liquid crystal molecules
22
positioned at the peaks of the saw-toothed sidewall, that is, the parting of the two domains of the sub-pixel area, are jostled by surrounding molecules
22
that rotate in a different direction, thus the liquid crystal molecules
22
on the parting of the two domains are stopped from rotating. Due to both the stopped rotation and the common electrode
20
and the pixel electrode
20
non-transparent nature, the liquid crystal molecules
22
positioned at the peaks of the saw-toothed sidewall present as dark lines after voltage is applied to the TFT substrate
10
, as shown by dotted lies I—I and II—II. This decreases the aperture ratio of the IPS-LCD. Especially when the number of peaks of the saw-toothed sidewall is increased, the number of dark lines is correspondingly increased and thereby the aperture ratio is further decreased. Thus, a novel electrode array structure of the IPS-LCD eliminating the aforementioned problems is called for.
SUMMARY OF THE INVENTION
The present invention provides an electrode array structure to modify the rotation angle of the liquid crystal molecules, and achieve increased aperture ration and decreased driving voltage.
An electrode array structure in a pixel area of an in-plane switching mode LCD (IPS-LCD). A comb-shaped common electrode has a bar extending transversely and a plurality of teeth extending in a first lengthwise direction from the bar, in which each tooth of the common electrode has a continuous ∠-shaped sidewall. A comb-shaped pixel electrode has a bar extending transversely and a plurality of teeth extending in a second lengthwise direction from the bar, in which each tooth has a continuous ∠-shaped sidewall and parallel is disposed between adjacent teeth of the common electrode. An electric-field gradient is generated between the tooth of the common electrode and the adjacent tooth of the pixel electrode to form a non-uniform electric field.
Accordingly, it is a principle object of the invention to provide the ∠-shaped sidewall of the electrode to modify the rotation angle of liquid crystal molecules.
It is another object of the invention to make the rotation angle &thgr; of the liquid crystal molecules satisfy the formula 0°<&thgr;≦+60° or −60°≦&thgr;<0°.
Yet another object of the invention is to solve the coloring phenomenon.
It is a further object of the invention to increase the aperture ratio of the IPS-LCD.
Still another object of the invention is to provide an electric-field gradient between the tooth of the common electrode and the adjacent tooth of the pixel electrode to form a non-uniform electric field.
It is a further object of the invention to reduce the starting voltage, the driving voltage and the switching time of the IPS-LCD.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.
REFERENCES:
patent: 5745207 (1998-04-01), Asada et al.
patent: 6266116 (2001-07-01), Ohta et al.
patent: 6538713 (2003-03-01), Yanagawa et al.
Duong Tai
Hannstar Display Corp.
Thomas Kayden Horstemeyer & Risley
Ton Toan
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