Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-04-21
2004-06-15
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S122000, C349S130000
Reexamination Certificate
active
06750933
ABSTRACT:
FIELD OF THE INVENTION
Invention is related to the field of electronics and can be used for making information displays, in particular, liquid crystal (LC) indicators, screens, panels etc.
PRIOR ART
The drawback of the majority of crystal displays is a strong dependence of their transmission on the angle of light incidence [S. T. Wu, C. S. Wu, SID Digest 27, 763 (1996-1] and, as a result, decrease of contrast and even inversion of transmission levels at some observation angles. For improving these characteristics of displays in many cases a set of retardation plates is used [N. Yamag H. Watanabe, K. Yokoyana, ‘Japan Display 89’, 316 (1989)-2], which increases the cost of the device and does not resolve the problem of color inversion.
The most promising from this point of view are multi-domain LC displays, in which a single pixel contains areas with various orientations of the liquid crystal in the plane of substrates [M. Schadt, Proc. SID'97, 24.1 (1997-3].
There is an information display [K-H. Kim, S.-B. Park, J.-U. Shim, J.-H. Souk, J.Chen, SID 98 DIGEST, 1085 (1998)-4], which consists of two plane and parallel substrates with electrodes deposited at least on one of them, the said substrates are overlaid with the electrodes facing each other. The space between the substrates is filled with a homeotropically aligned liquid crystal mixture possessing positive anisotropy. From the outside the substrates are surrounded by two crossed polaroids. In the off state this display does not transmit the light. After electric voltage of the opposite polarity is applied to the neighboring electrodes at one of the substrates, a parabolic electric field is created between the said electrodes, which reorients the liquid crystal parallel to it. In this way it is possible to orient LC molecules between the electrodes in two different directions (the so-called two-domain structure) and as the rest, the viewing angle of such display is improved considerably. To maximize the brightness polaroids are oriented at 45° to the electrodes. Nevertheless, low bless is the drawback of this display, as well as of other displays based on director re-switching in the plane of the substrates [M. Ohta et al, Asia Display'95, 707 (1995)-5]. Another drawback is that it is impossible to have more than two domains in a pixel.
There is display [S.-C. A.Lien, R. A.John, Patent U.S. Pat. No. 5,309,26
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-6], [S.-C. A. Lien, R. A. John, et al, SID 98 DIGEST, 1123 (1998)-7] in which two principles are used to have domain structure: fringe field, which arises at the edge of the electrode after applying electric field, and ridge field at the opposite slopes of the protrusions formed lithographically at the opposite substrates with color filters. Protrusions act as element which incline LC director from the normal to the substrate. The space been the substrates is filled with homeotropically aligned liquid crystal possessing negative dielectric anisotropy. Liquid crystal molecules are aligned perpendicularly to the substrates surface and in the off state this display does not transmit the light (crossed polaroids) and only on the slopes of protrusions the molecules deviate from the normal to the angle which equals the angle between the slope of the protrusion and the substrate. At the slopes the molecules are per-tilted in different directions, but pre-tilt is not high and therefore it does not perturb optical parameters of display in the off state. Within the pixel protrusions are oriented so that the pre-tilt direction coincides with the direction of the fringe field which arises at the long edge of the pixel (the pixel has elongated rectangular shape). In such display co-action of the fringe electric field and protrusions result in reorienting LC molecules within the pixel in different directions relative to the long axes of the protrusions. The drawback of such device is that although it is possible to have four domains within a pixel (this number of domains is optimal for equalizing optical characteristics in different directions), but in a real display these domains have different area and it is difficult to equalize optical characteristics completely. Besides this, the fringe field which arises around the pixel after applying electric voltage is distorted by connecting buses and this results in non-uniform switching of various domains within a pixel.
The closest to the proposed devices and method is technical reference [A. Takeda et al, SID 98 DIGEST, 1077 (1998)-8]. This display consists of two substrates with the pattern of electrodes deposited on them, on the said electrodes protrusions are deposited photolithographically with the slopes in different directions. These protrusions like similar elements in [
7
] tilt the LC director from the normal of the substrate. The space between the substrates if filled with homeotropically aligned liquid crystal possessing negative dielectric anisotropy. In the off state the LC molecules are orthogonal to the substrates except those in the areas where the protrusions are displaced. At the slopes of the protrusions the molecules are pre-tilted to the angle, which equals the angle between the slope and the substrate This pre-tilt is not high and does not perturb optical characteristics of the display in the off state and in crossed polaroids display does not transit the light. When the voltage is applied to the electrodes at the opposite substrates this pre-tilt is sufficient to initiate molecular reorientation in different directions within the pixel area. This leads to appearing domains and makes viewing angle more uniform The drawback of this display is low brightness (30% of conventional single-domain display) because of two factors: protrusions occupy more than 30% of the display area and to realize four domains very specific pattern of the protrusions is required, which leads to additional losses of light. Besides this to make this display two additional photolithographies are required
SUMMARY OF THE INVENTION
Present invention is aimed to make displays with wide viewing angle possessing higher brightness in transmission mode and to develop more simple method for making such displays.
This target is achieved by making in display with multiple pixels deflecting elements of dielectric material and depositing them over the electric conductive coating at least on one of the substrates the space between which is occupied by liquid crystal. Dielectric elements can have profile as from the liquid crystal side, so from the side of the substrate. They can be deposited on both, as well as only on one substrate. Dielectric deflecting elements may be displaced along the perimeter of the pixel as well as across its area. After applying electric voltage to the electrodes at the opposite substrates at the interface LC-dielectric deflecting element distortions of the electric field appear with the component of electric field parallel to the substrates. Direction of this in-plane component is determined by the configuration of the dielectric deflecting elements. The value of this component is sufficient to reorient liquid crystal in different directions and hence to generate different domains within the pixel area and to make optical properties of display independent of the viewing angle. Unlike in the known display [8], dielectric elements take not more than 5-10% of the pixel area and proposed display has higher brightness. At the same time configuration of the dielectric elements is capable of obtaining two-as well as four domain displays for any real pixel shape.
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Konovalov Victor A
Muravsky Anatoly A
Timofeev Sergey N
Yakovenko Sergey E.
Dudek James A.
LG.Phillips LCD Co., Ltd.
McKenna Long & Aldridge LLP
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