Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-07-21
2003-04-22
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S153000
Reexamination Certificate
active
06552764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display element to be used as a display device for, e.g., television sets, personal computers, word processors, and OA (Office Automation) apparatuses. In particular, the present invention relates to a liquid crystal display element which has a reflection type display mode.
2. Description of the Related Art
As disclosed, for example, in Japanese Laid-Open Publication No. 9-311351, a conventional liquid crystal display element has a pair of insulative substrates usually made of glass. Active elements such as TFTs (thin film transistors) are placed on one of the substrates as switching elements for controlling the electro-optical characteristics of the liquid crystal. Gate signal lines receiving a driving signal for driving the switching elements and source signal lines receiving a display signal are disposed in such a manner that they intersect each other.
Furthermore, on the substrate having TFTs (hereinafter, referred to as an “active matrix substrate”), an inter-layer insulation film is formed over the TFTs and both signal lines, and pixel electrodes are further placed on the insulation film so that the pixel electrodes overlap with the TFTs and the signal lines. By constructing such a structure, light entering any region in which a signal voltage is not applied to the liquid crystal is blocked by both signal lines. Therefore, it becomes unnecessary to provide a black matrix (hereinafter, referred to as a “BM”) which has been conventionally provided in a display region of the other substrate (hereinafter, referred to as a “CF substrate”) on which a color filter is provided. Moreover, it is known that, in this structure, the entire portion excluding the gate signal lines, source signal lines, and TFTs can be utilized as display pixels, thereby improving the opening ratio of the liquid crystal display element.
Japanese Laid-Open Publication No. 10-62768 discloses a structure, as an implementation of the liquid crystal display element disclosed in the above mentioned Japanese Laid-Open publication No. 9-311351, in which a light-blocking member is provided between gate signal lines and source signal lines on an active matrix substrate so as to block light without providing a BM in a frame region on the outer periphery of a display region. In this structure, an increase in production steps resulting from the light-blocking member can be avoided by forming the portion of the light-blocking member between the source signal lines from the same material that is used for the gate signal lines, and the portion of the light-blocking member between the gate signal lines from the same material that is used for the source signal lines. Furthermore, color layers of a color filter on a CF substrate are formed so as to extend to the frame region, thereby concealing the wiring pattern and the like on the active matrix substrate.
In accordance with the above-described conventional technique, it is possible to produce a CF substrate from only three layers of R (red color), G (green color), and B (blue color), instead of the conventionally-required four layers, namely R, G, B and a BM (black matrix) thereby enabling a significant reduction in the production cost of the CF substrate.
The active matrix substrate and the CF substrate are usually attached together with a sealing material. When attaching, spacers are placed within the sealing material and on either one of the active matrix substrate and the CF substrate in order to provide a predetermined gap between the active matrix substrate and the CF substrate. In the case of a TN-mode liquid crystal display element, the gap between the two substrates is usually about 4 &mgr;m to about 6 &mgr;m, with a variation of about ±10%. Then a liquid crystal is injected by vacuum injection through an injection hole provided in a portion of the sealing material. By closing the injection hole with an UV setting resin, the liquid crystal display element is accomplished.
The above-described conventional technique, which is directed toward transmission type liquid crystal display elements having pixel electrodes formed of a transparent conductive material (i.e., a conductive material having a relatively high transmittance), provides a method for producing a CF substrate having only three layers of R, G, and B, while a BM is provided on the active matrix substrate. As a result, the production cost of the liquid crystal display element is significantly reduced.
However, in the case of a reflection type liquid crystal display element, pixel electrodes made of a reflective conductive material (i.e., a conductive material having a relatively high reflectance) are formed on the active matrix substrate, and images are displayed by controlling the reflection of light entering the surface of the liquid crystal display element. For this reason, it is necessary to suppress the reflection of light in the region which is irrelevant to the display function. Conventionally, suppression of such reflection of light has been accomplished by providing a BM which is composed of a light absorption film or a low-reflectance film on the CF substrate. Thus, in order to construct a CF substrate which does not include a BM but only includes three layers of R, G, and B, or complementary colors of C (cyan), M (magenta), and Y (yellow), it is essential to consider how to suppress the reflection of light in the regions irrelevant to the display function.
In the display region, gate signal lines receiving a driving signal for driving TFTs and source signal lines receiving a display signal are inevitably noticeable between adjacent pixel electrodes. Thus, the first problem to be solved is how to suppress light reflection on these signal lines.
The second problem to be solved is how to suppress light reflection on each signal line in the frame region on the outer periphery of the display region.
The third problem to be solved is how to protect the TFT elements from external light. If light energy enters a channel layer of a TFT element, a leakage current (photo-leakage current) is generated in an off-state of the TFT. This prevents a sufficient voltage from being applied to liquid crystal layer, and prevents the TFT element from displaying images properly. However, a reflection type liquid crystal display element is expected to operate under a maximum illuminance of 100,000 lx in the direct sunlight. In other words, a reflection type liquid crystal element may be subjected to light having a maximum of one hundred fold energy as compared to the 10,000 lx which a conventional transmission type liquid crystal display element may be subjected to, or the 1,000 lx (light energy commonly observed in an office during the daytime) which most-widely-used notebook type PCs may be subjected to. Thus, the TFT elements must be protected from light by a material whose ability to block light is equal to or greater than that of a conventional BM.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a liquid crystal display element includes an active matrix substrate; a color filter substrate; a sealing material for attaching the active matrix substrate and the color filter substrate with a predetermined gap maintained therebetween; and liquid crystal injected in the gap between the active matrix substrate and the color filter substrate. The active matrix substrate includes a pixel electrode comprising a reflective conductive material; a switching element connected to the pixel electrode; a gate signal line receiving a driving signal for driving the switching element; and a source signal line receiving a display signal. A plurality of said pixel electrodes and a plurality of said switching elements are arranged in a matrix, and a plurality of said gate signal lines and a plurality of said source signal lines are arranged so as to intersect each other. The color filter substrate includes a color filter having a plurality of color layers corresponding to a plurality of colors; a display re
Fujioka Kazuyoshi
Shimada Takayuki
Yoshimura Youji
Kim Robert H.
Nixon & Vanderhye P.C.
Schechter Andrew
Sharp Kabushiki Kaisha
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