Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-12-10
2001-06-05
Malinowski, Walter J. (Department: 2164)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06243154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device (hereinafter LCD), more particularly to an LCD having a wide viewing angle without color shift.
2. Background of the Invention
An LCD has the characteristics of light weight, thin thickness and low power consumption. It has been used in various information display terminals or visual equipment. The major operating mode for the LCD can be the twisted nematic(“TN”) and the super twisted nematic(“STN”). Though they are presently commercially used in various LCD means, the characteristic of narrow viewing angle has still remained unsolved.
An In-Plane Switching(IPS) mode LCD has been suggested to solve the foregoing problems.
FIG. 1
is a plane view showing a general IPS mode LCD. A common electrode
11
is formed on the substrate
10
in the form of comb. A pixel electrode
13
is also formed on the substrate
10
in the form of comb, the comb-like electrodes
11
and
13
form a teeth shape. When an external voltage is applied between the common electrode
11
and the pixel electrode
13
, an electric field F
1
is formed therebetween and the liquid crystal molecules
15
are moved such that their long axes are parallel to the electric field F
1
.
There is a color shift in the direction of long and short axes due to the optical anisotropy since the long and short axes of liquid crystal molecule are different from each other in length.
As well known, the refractive anisotropy(or birefringence, &Dgr;n) has occurred due to the difference of the lengths of the long and the short axes. The refractive anisotropy(&Dgr;n) is also varied from the observer's viewing directions. Therefore a predetermined color is appeared on the region where the polar angle if 0 degree and the azimuth angles range of degrees 0, 90, 180 and 270 in spite of the white state. This results in color shift and more detailed description thereof is attached with reference to the equation 1.
T≈T
0
sin
2
(2&khgr;)·sin
2
(&pgr;·&Dgr;nd/&lgr;) equation 1
wherein,
T : transmittance;
T
0
: transmittance to the reference light;
&khgr;: angle between an optical axis of liquid crystal molecule and a polarizing axis of the polarizing plate;
&Dgr;n: birefringence;
d: distance or gap between the upper and lower substrates(thickness of the liquid crystal layer); and
&lgr;: wavelength of the incident light.
So as to obtain the maximum transmittance T, the &khgr; should be &pgr;/4 or the &Dgr;nd/&lgr; should be &pgr;/2 according to the equation 1. As the &Dgr;nd varies with the birefringence difference of the LC molecules from viewing directions, the &lgr; value is varied in order to make &Dgr;nd/&lgr; to be &pgr;/2. According to this condition, the color corresponding to the varied wavelength &lgr; appears.
Accordingly, as the value of &Dgr;n relatively decreases at the viewing direction “a” toward the short axes of the LC molecules, the wavelength of the incident light for obtaining the maximum transmittance relatively decreases. Consequently a blue color having shorter wavelength than a white color is emerged.
On the other hand, as the value of An relatively increases at the viewing direction “b” toward the short axes of the LC molecules, the wavelength of incident light relatively increases. Consequently a yellow color having a longer wavelength than the white color is emerged. This causes deterioration to the resolution of IPS-LCDs.
To prevent the above disadvantages caused by color shift, a method for forming multi-domain within a unit pixel has been suggested. According to this method, one portion of an alignment layer is rubbed to a first direction, the other portion of the alignment layer is rubbed to second direction symmetrized the first direction. This method, however, is required additional masks compared to the conventional process of liquid crystal molecules alignment.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a LCD having wide viewing angle without color shift occurrence.
Another object of the present invention is to provide a method for fabricating such LCD mentioned above.
So as to accomplish the objects for the present invention, an LCD, comprising: a substrate; and a common electrode and a pixel electrode having same spiral shape formed on the substrate and being opposed each other, wherein an electric field formed between the common electrode and the pixel electrode is radial shape.
Further, the present invention provides an LCD having an electric field formed in parallel to surface of a substrate, comprising; a common electrode formed on the substrate with annular shape whose both edges are spaced each other; and pixel electrode formed on the substrate with annular shape whose both edges are spaced each other corresponding to the shape of the common electrode, wherein an electric field formed between the common electrode and the pixel electrode is radial shape and symmetric shape which is based on the kernel of respective electrode.
Also, to accomplish the above objects, the present invention provides a method for fabricating an LCD comprising the step of: forming a common electrode of spiral shape on a substrate; forming a pixel electrode of spiral shape to be opposed the common electrode; and coating an alignment layer on the surface of the substrate where the common electrode and the pixel electrode are disposed thereon, wherein a radial electric field is formed when a voltage is applied between the common electrode and the pixel electrode.
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Park Jang Sick
Rho Bong Gyu
You Jae Geon
Hyundai Electronics Industries Co,. Ltd.
Ladas & Parry
Malinowski Walter J.
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