Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Patent
1997-09-04
1999-12-14
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
349156, G02F 11333, G02F 11339
Patent
active
060024631
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a substrate for liquid crystal devices, a method for making the same, a liquid crystal device and an electronic device.
2. Description of Related Art
An active matrix type color liquid crystal display comprises an active matrix substrate, an opposite substrate (a color filter substrate) and a liquid crystal interposed between both substrates.
Since a liquid crystal display device represents given images by means of control of light transmitting the liquid crystal, the light transmission must be strictly controlled. Thus, a light blocking layer, known as a black matrix, is generally provided on the opposite substrate (color filter substrate) in order to prevent transmission and influx of undesired light.
In more detail, the black matrix prevents a decrease in display contrast due to back light transmission between a transparent pixel electrode of indium tin oxide (ITO) and its circumferential wiring and the like, and a decrease in display quality due to leakage current excited by incident light at the channel region of a thin film transistor (TFT). Chromium (Cr) is a material generally used for black matrices.
However, since chromium (Cr) has a high light reflectance in spite of excellent light blocking characteristics, reflected light may adversely affect the display.
Further, when a black matrix is provided at the opposite substrate (color filter substrate) side, two substrates formed in different steps are connected to each other. A layout clearance of, for example, approximately 10 mm, thus, must be considered in design of active matrix substrates depending on alignment accuracy. Such a clearance is one of factors inhibiting a higher aperture ratio.
For the purpose of resolving such a problem, black matrices, in which black resinous materials having low reflectance are used instead of conventional black matrices of thin metal film having high reflectance represented by chromium (Cr), have been studied.
Black matrices using both thin metal films and black resinous materials have also been investigated in order to secure excellent alignment control and light blocking characteristics, as well as low reflectance ((1) Japanese Unexamined Patent Publication No. 5-80320, and (2) "Series Optronics Searchlight No. 12", OPTRONICS July 1995, No. 7, p. 218-219).
However, according to the present inventors' investigation, it has been found that black matrices using black resinous materials also have problems.
In detail, since black resinous materials are inferior to thin metal films in light blocking characteristics in spite of low reflectance, the film thickness of the black matrix should be increased for satisfactory light blocking characteristics. The increased film thickness of the black matrix causes a large bump between a position in which a black matrix is present and a position in which a black matrix is not present, and alignment control at the bump section by means of alignment treatment (rubbing treatment) is difficult.
The present inventors have also investigated a thinner film black matrix using both a metal and a black resinous material, and found that it is not practically useful since production is complicated due to increased production steps and cost increases, and thus it is desirable to form the black matrix using a single material.
On the other hand, there is a proposal in which a black matrix is provided at the active matrix substrate side with no layout clearance from the viewpoint of problems of the black matrix provided at the opposite substrate (color filter substrate) side (International Patent Application No. PCT/JP92/01562, International Laid-Open No. WO93/11455).
The present inventors have investigated a black matrix formed from a black resinous material and provided at the active matrix substrate side. As a result, a new problem of conductivity of the black matrix has been found in addition to the above-mentioned increased film thickness.
In detail, when a black matrix is formed at the active matrix substrate side,
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patent: 5585951 (1996-12-01), Noda et al.
patent: 5691788 (1997-11-01), Kim
patent: 5789761 (1998-08-01), Ihara et al.
patent: 5818558 (1998-10-01), Ogishima
patent: 5854663 (1998-12-01), Oh et al.
"Series Optronics Searchlight No. 12", OPTRONICS Jul. 1995, No. 7, p. 218-219.
Horney Kari M.
Seiko Epson Corporation
Sikes William L.
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