Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-02-02
2001-03-06
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000
Reexamination Certificate
active
06198520
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a color liquid crystal display having a wide angle of visibility and also having no unevenness of luminance, and particularly to a color liquid crystal display intended to improve productivity upon production using a large-sized substrate.
BACKGROUND ART
In a prior art matrix type color liquid crystal display, at least part of electrodes for driving liquid crystal are formed on one of a pair of opposed substrates and color filters and black matrixes are formed on the other one of the opposed substrates. In a thin film transistor (TFT) type liquid crystal display, which is a typical liquid crystal display, thin film transistors and a group of interconnection electrodes are formed on one substrate, and color filters and black matrixes are formed on the other substrate.
In such a prior art display in which thin film transistors and color filters are respectively formed on a pair of opposed substrates, when a cell is formed by superimposing the pair of substrates to each other, it is required to accurately align a large number of corresponding pixels to each other. However, as a substrate size becomes larger, there may easily occur offset of pixels between the two substrates due to thermal expansion of the substrates or the like. For this reason, alignment of the pixels must be performed for a long period of time using a high precision aligner, to thereby significantly degrade productivity.
On the other hand, to solve such a problem on alignment of pixels, a technique has been proposed, for example, in Japanese Patent Laid-open Nos. Hei 2-54217 and Hei 2-302727, wherein thin film transistors, a group of interconnection electrodes, color filters, and black matrixes are formed on one substrate. In the technique disclosed in the above documents, however, planar pixel electrodes and a counter electrode are formed on the substrates in such a manner as to hold liquid crystal therebetween. Accordingly, the color filters on the pixel electrodes act as capacitance elements connected in series to the liquid crystal, to thereby significantly reduce a voltage applied to the liquid crystal. In general, liquid crystal has a dielectric constant being as very high as about 10 (average value), while a resin material forming the color filters has a dielectric constant being as low as about 3 to 6. As a result, even if the color filter is formed to a thickness smaller than that of the liquid crystal, it exerts a large effect on a drop in voltage applied to the liquid crystal.
Further, WO91/10936, U.S. Pat. No. 4,345,249, and EPO588562A2 propose a method of applying an electric field to liquid crystal in the direction substantially parallel to a substrate plane (horizontal electric field applying method). In this method, since major axes of liquid crystal molecules are substantially in parallel to the substrate plane and thereby they are not raised, the visibility is not dependent on a viewing angle, that is, the angle of visibility becomes wider. The method disclosed in the above documents fails to examine a reduction in unevenness of luminance, improvement of numerical aperture, and improvement of productivity.
An object of the present invention is to provide a color liquid crystal display having a high productivity.
Another object of the present invention is to provide a color liquid crystal display having no unevenness of luminance.
A further object of the present invention is to provide a color liquid crystal display having a high numeral aperture.
DISCLOSURE OF INVENTION
One substrate of a color liquid crystal display of the present invention may include a plurality of common electrodes, a plurality of pixel electrodes disposed between the plurality of common electrodes, color filters disposed between the common electrodes and the pixel electrodes, and an orientation control layer for controlling orientation of liquid crystal molecules in a liquid crystal layer disposed on the color filters. When a voltage is applied between the common electrodes and the pixel electrodes, an electric field in parallel to the substrate is generated in the liquid crystal layer.
According to one embodiment of the present invention, the one substrate further includes black matrixes for shading boundaries of the color filters. A planarizing film may be formed between the orientation control film and the color filters. Further, the color filers may be formed in such a manner as to cover the pixel electrodes.
According to another embodiment of the present invention, letting d be a thickness of the liquid crystal layer and &Dgr;n be an anisotropy in refractive index, the product &Dgr;n×d is in a range of 0.21 to 0.37 &mgr;m. The orientation control layer is preferably formed of an organic polymer film, and at least one of the color filter, orientation control layer, and planarizing film is preferably made from a photosensitive polymer.
Further, one substrate of a color liquid crystal display of the present invention may include a plurality of scanning interconnections, a plurality of signal interconnections crossing said scanning interconnections in a matrix, and a plurality of thin film transistors formed in such a manner as to correspond crossing points between said scanning interconnections and said signal interconnections. Pixels can be defined by regions surrounded by said plurality of scanning interconnections and said plurality of signal interconnections.
Each of said pixels may include a plurality of common electrodes connected to a common interconnection for connecting a number of said pixels to each other, and at least one pixel electrode disposed between said common electrodes and connected to a corresponding one of said thin film transistors.
Adjacent ones of said plurality of common electrodes may be disposed in such a manner as to surround a corresponding one of said signal interconnections between adjacent ones of said pixels. Each color filter may be formed between said plurality of common electrodes and said pixel electrode, and an orientation control layer may be disposed on said color filters for controlling orientation of liquid crystal molecules of said liquid crystal layer.
Each black matrix may be formed on one of said plurality of signal interconnections and ones of said common electrodes adjacent to said one signal interconnection.
According to the color liquid crystal display of the present invention, the active matrix elements for switching liquid crystal, all of the group of electrodes, the color filters for color display, and the black matrixes for improving a color purity and contract ratio are formed on one substrate. To drive liquid crystal, there is adopted a horizontal electric field applying method of applying an electric field to the liquid crystal in the direction substantially parallel to a substrate plane.
First, since the color filters are disposed between the electrodes, irregularities of the liquid crystal orientation control layer formed on the color filters are moderated, to establish a uniform cell gap, thereby improving unevenness of luminance.
Further, according to the horizontal electric field applying method of the present invention, the electrodes for driving liquid crystal are all in linear shapes and are formed on one substrate. Accordingly, capacitance components of all of the elements formed through the adjacent electrodes are formed in a pattern in which equivalent circuits arranged in parallel are mixed with equivalent circuits arranged in series. However, the capacitance components of the equivalent circuits of the insulators arranged in series to the capacitance component of the liquid crystal are made significantly small. The reason for this is dependent on the facts that in the general design, the interval (about 10 to 30 &mgr;m) between the adjacent electrodes is significantly wider than the thickness (about 2 to 6 &mgr;m) of the liquid crystal layer; that lines of electric force are almost horizontal components; and that the dielectric constant of the liquid crystal is larger than that of the resin mate
Inoue Keiko
Kondo Katsumi
Matsuyama Shigeru
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Parker Kenneth
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