Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-26
2002-06-18
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000
Reexamination Certificate
active
06407791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly to a multi-domain liquid crystal display device being excellent in viewing angle characteristics.
2. Description of the Related Art
A conventional Twisted Nematic (TN) type liquid crystal display device being widely used is so constructed that, as a liquid crystal molecule changes a direction of its director (orientation vector) toward an electric field in response to a voltage applied thereto, a state displaying a “bright” color appearing at a time of applying no voltage, in which the liquid crystal molecule is in a twisted state being parallel to a substrate surface, is gradually changed to a state displaying a “black” color. However, the conventional TN-type liquid crystal device has a problem in that its viewing angle is small due to a limitation associated with behaviors of the liquid crystal molecule activated by the applied voltage. The small viewing angle is remarkable in a rising direction of the liquid crystal molecule f or displaying gray shades in particular.
A method of improving viewing angle characteristic of the liquid crystal display device is disclosed in Japanese Patent Application Laid-open No. Hei6-43461.
FIG. 47
is a partial schematic cross-sectional view showing a pixel of the conventional multi-domain liquid crystal display device disclosed in the above patent application. In the disclosed technology, viewing angle characteristic is improved by obtaining a liquid crystal cell by orientating a liquid crystal molecule
22
having negative dielectric constant anisotropy in a homeotropic direction and then putting it between two polarizers (not shown) in which polarization axes are intersected at right angles and using common electrodes
81
having an aperture section
74
to concentrate an electric field on a skew in each pixel and to cause each pixel to be divided into more than two domains, that is, multi-domains. Moreover, in this technology, the viewing angle for the black color can be improved by using an optical compensating plate as necessary. Furthermore, the viewing angle characteristic is improved in not only the liquid crystal cell obtained by homeotropic orientation of the liquid crystal but also in the liquid crystal cell obtained by TN orientation of a liquid crystal by using the common electrodes
81
having the aperture section
74
, by causing a skew electric field to be generated and by dividing each pixel into more than two domains.
Another technology to try to improve a viewing angle characteristic is disclosed in Japanese Patent Application Laid-open No. Hei7-199190. In the disclosed technology, the liquid crystal domain is stabilized by providing a common electrode with an aperture section (serving as an orientation control window), by mounting an orientation control electrode in a manner that it surrounds a pixel electrode and by enhancing a skew electric field in an area surrounding the pixel.
Additionally, Japanese Patent Application Laid-open No. Hei7-230097 also discloses a technology to improve a viewing angle characteristic in which an orientation control electrode formed integrally with a gate bus line is provided on each pixel and each pixel is divided into more than two liquid crystal domains by a skew electric field generated by the orientation control electrode.
Furthermore, in technology disclosed in Japanese Patent Application Laid-open No. Hei10-20323, a pixel is provided with an aperture section and a control electrode is placed at a position of the aperture section to form a plurality of liquid crystal domains.
Also, in technology disclosed in Japanese Patent Application Laid-open No. Hei10-301114, in a liquid crystal cell obtained by orientating a liquid crystal having a negative dielectric constant in a homeotropic direction, an orientation film is provided with a protrusion and a tilt direction of the liquid crystal is controlled by the protrusion at a time of applying a voltage to divide each pixel into more than two domains.
However, the technology disclosed in the Japanese Patent Application Laid-open No. Hei6-43461,in which the common electrodes
81
are provided with the aperture section
74
, has a problem in that microfabrication processes such as a “photoresist process for the common electrode” or a like are required to fabricate a pixel, which are not required in the production processes of an ordinarily used mono-domain type TN liquid crystal display device, and further highly sophisticated technology of laminating upper and lower substrates is also required. This problem presents a serious problem especially in a case of fabricating an ordinary active matrix liquid crystal display device using a switching device such as a TFT (Thin Film Transistor). That is, in the ordinary active matrix liquid crystal display device, when the switching device (active device) such as the TFT is mounted on one transparent substrate (TFT substrate), the microfabrication processes including the photoresist process or the like is required only on the TFT substrate side and is not required by an electrode on an other transparent substrate (opposed substrate) side usually called a “common electrode”. However,in the conventional technology in which the common electrode is provided with the aperture section, the microfabrication processes such the photoresist process as not required in the ordinary cases is required for fabricating the above common electrode, thus causing increased numbers of processes for production of the device and highly sophisticated technology of laminating upper and lower substrates to be required.
To solve this problem, one would think of a technology in which an orientation of the liquid crystal can be controlled by mounting an aperture section or a slit on the pixel electrode formed on a TFT-formed substrate side in which a switching device such as the TFT or a like is mounted to make the pixel electrode generate a skew electric field. This is because the fabrication of the pixel electrode on the TFT substrate side originally requires a patterning process and therefore does not require additional further processes. However, it is impossible to control a liquid crystal domain in a stable manner by such methods. A reason is that, although a tilt direction of an electric field in an area surrounding the aperture section occurring when the aperture section is mounted on the common electrode as disclosed in the Japanese Patent Application No. Hei6-43461, is matched to a tilt direction of the electric field in an area surrounding the pixel electrode
71
(see FIG.
19
), a tilt direction of the electric field in the area surrounding the aperture section occurring when the aperture section is mounted on the pixel electrode formed on the TFT substrate side is not matched to the tilt direction of the electric field in the area surrounding the pixel electrode.
If the control electrode is disposed in the area surrounding the picture electrode as shown in the Japanese Patent Application Laid-open No. Hei7-199190, although skewing of the electric field in the area surrounding the pixel electrode can be enhanced, since it is necessary to mount the aperture section on the common electrode in the substrate existing on the opposite side, the above problem cannot be solved.
If the control electrode is disposed on the picture electrode and a potential of the control electrode is set to an appropriate level as shown in the Japanese Patent Application Laid-open No. Hei7-230097, it is possible to generate the required skew electric field. However, since state of occurrence of the skew electric field is also changed by a change in polarity of the pixel electrode potential at a time of driving in an inverted manner when the polarity of the pixel electrode potential is inverted at a predetermined period, stable and reliable control on the liquid crystal domain is impossible. Moreover, since the control electrode is so constructed integrally with a gate bus line and the control electrod
Hayama Hiroshi
Ikeda Naoyasu
Ishii Toshiya
Kanoh Hiroshi
Nose Takashi
NEC Corporation
Scully Scott Murphy & Presser
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