Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-13
2002-10-22
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S141000
Reexamination Certificate
active
06469765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a liquid crystal display, and more particularly to a liquid crystal display in which display operation is performed by driving liquid crystal molecules in a plane parallel to a substrate of the liquid crystal display.
BACKGROUND OF THE INVENTION
Such type of liquid crystal display is disclosed, for example, in “Field effects in nematic liquid crystals obtained with interdigital electrodes”, by R. A. Soref, Journal of Applied Physics, vol. 45, No. 12, December 1974, which liquid crystal display is hereafter referred to as Prior Art Example 1. In the Prior Art Example 1, there are described basic principles of driving liquid crystal molecules, such as what electric field should be applied to the liquid crystal molecules to rotate the liquid crystal molecules within a plane parallel to a substrate and the like.
Also, taking the basic principles described in the Prior Art Example 1 into consideration, Japanese examined patent publication No. 63-21907 discloses a liquid crystal display in which there is provided a switching element for each pixel, which liquid crystal display is hereafter referred to as Prior Art Example 2.
However, in these two Prior Art Examples, only basic principles, operation and the like are described, and there are still various problems in practicability. Therefore, taking these basic principles into consideration, various research have been done aiming at an electrode structure, alignment direction of liquid crystal molecules, contrast characteristic, and the like.
For example, there is known a liquid crystal display disclosed in Japanese patent laid-open publication No. 1-1200528 which aims at improving a switching characteristic and enabling a high speed operation, which liquid crystal display is hereafter referred to as Prior Art Example 3. In this liquid crystal display, a pair of electrodes are provided in each of an upper substrate and a lower substrate. These electrodes are switched to produce two kind of electric fields and, thereby, alignment direction of liquid crystal molecules is switched at high speed. However, in the structure of the Prior Art Example 3, it is necessary to individually control respective electrode pairs disposed on the upper substrate and the lower substrate, and there are many other problems.
On the other hand, there is known a liquid crystal display disclosed in Japanese patent publication No. 2743293, which liquid crystal display is hereafter referred to as Prior Art Example 4. In this patent publication, there is described a result of research on an initial alignment direction, and relationship between a twist angle and a distribution of contrast characteristic, taking alignment direction of liquid crystal molecules into consideration. However, in the liquid crystal display of the Prior Art Example 4, a conventionally proposed interdigital electrode structure is used and no improvement is made on the electrode structure. In other words, in the Prior Art Example 4, statistics were obtained on electric field caused by the conventional interdigital electrode structure and relationship between the initial alignment direction of liquid crystal molecules and contrast characteristic, and confirmation was made on the effect obtained by such structure. Therefore, the Prior Art Example 4 is valuable as a research result, but does not propose a new technology for liquid crystal display. In the Japanese patent publication No. 2743293, although it is described that an active matrix type liquid crystal display is realizable by using this structure, no proposition is made on a structure of an electrode therefore.
Thereafter, in Japanese patent laid-open publication No. 6-148596, there is proposed an active matrix type liquid crystal display with a concrete electrode structure, which liquid crystal display is hereafter referred to as Prior Art Example 5. In the liquid crystal display of the Prior Art Example 5, thin film transistors (TFT's) are use as active elements, and a structure of electrodes including the active elements is described in this publication. More particularly, in the Prior Art Example 5, basically, two electrodes disposed parallel with each other are used in each pixel. Between the two electrodes, an electric field is produced and, thereby, liquid crystal molecules are rotated in a plane parallel with a substrate. However, in the Japanese patent laid-open publication No. 6-148569, a description is included which refers to the merit of not using transparent electrodes and, therefore, consideration is not given on aperture ratio and the like.
In the Prior Art Example 1 through Prior Art Example 5 mentioned above, liquid crystal molecules are driven such that the liquid crystal molecules rotate in a plane parallel with a substrate to perform display operation. Therefore, when compared with TN mode and the like in which liquid crystal molecules are driven between horizontal condition and vertical condition to perform display operation, it is expected that better viewing angle characteristics can be obtained by the liquid crystal displays of the Prior Art Examples 1 through 5. Hereafter, an operating mode in which liquid crystal molecules are rotated in a plane parallel to the substrate to perform display operation is called In-Plain Switching (IPS).
However, the Prior Art Example 1 through Prior Art Example 5 have various problems to be solved such as low aperture ratios and the like caused by the interdigital electrode structure, and it is difficult obtain such superior performance in practical use as to completely replace liquid crystal displays having TN mode with such IPS type liquid crystal displays.
After a proposition of the Prior Art Example 5, various IPS mode liquid crystal displays are proposed in which merits of the TN mode and the like are retained and demerits of the IPS mode are improved and which have high display characteristics not only in theory but also in practical use.
For example, considering an electrode structure and an electrode material and aiming at improving brightness of a displayed image, Japanese patent laid-open publication No. 9-61842 discloses a liquid crystal display, which is hereafter referred to as Prior Art Example 6. As mentioned above, a conventional electrode structure for IPS mode generally had a pair of interleaved sets of parallel strip-shaped fingers to constitute an interdigital structure. As a result thereof, when a liquid crystal display panel is viewed from the front of the panel, the proportion of the area where the electrodes are not disposed to the total pixel area becomes inevitably small. Also, chromium (Cr) generally used as a material of the electrodes shades light, and therefore it was impossible to obtain high aperture ratio. On the other hand, in the Prior Art Example 6, a transparent material, for example, ITO and the like, which is used as a material of a common electrode of a conventional liquid crystal display of TN mode and the like is used as a material for electrodes. Thereby, unnecessarily shaded area in each pixel area can be decreased and the aperture ratio of each pixel is substantially increased. However, in the Prior Art Example 6, the structure of the electrodes themselves is not changed, and new technology is not proposed except that the transparent material is used as a material of the electrodes.
To improve both a response speed and a transmittance of liquid crystal display, there are proposed liquid crystal displays in Japanese patent laid-open publication No. 11-64892, which is hereafter referred to as Prior Art Example 7, and in “High-Transmittance, Wide-Viewing-Angle Nematic Liquid Crystal Display Controlled by Fringe-Field Switching”, by S. H. Lee, et al., ASIA DISPLAY '98 INTERNATIONAL DISPLAY RESEARCH CONFERENCE, pp. 371-374, Sep. 28-Oct. 1, 1998, which is hereafter referred to as Prior Art Example 8. Each of these Prior Art Example 7 and Prior Art Example 8 discloses a technology somewhat similar to that of the Prior Art Example 6, and proposes ratios of various
Hirai Yoshihiko
Kobayashi Kazumi
Matsuyama Hiroaki
Okamoto Mamoru
Sakamoto Michiaki
Michael Best & Friedrich LLC
Nguyen Dung
Sikes William L.
Whitesel J. Warren
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