Method of fabricating high-dielectric color filter

Details Method of fabricating high-dielectric color filter Method of fabricating high-dielectric color filter

2001-06-14

2004-04-13

McPherson, John A. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Screen other than for cathode-ray tube

C205S091000

Reexamination Certificate

active

06720119

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology for forming a color filter used in various kinds of display elements and color sensors such as a CCD (charge coupled device) camera and a liquid crystal display element, and more particularly to a method of fabricating a colored layer and a black matrix. Specifically, the present invention relates to a new color filter in which the colored layer and the black matrix are formed simply and with high resolution.
2. Description of the Prior Art
Presently, as color filter fabricating methods, the following are known: (1) dying method, (2) pigment dispersion method, (3) printing method, (4) ink jet method, (5) electrodeposition method, and (6) micelle electrolysis method. Of these methods, although the (1) dying method and the (2) pigment dispersion method are high in technical completion level and are often used for color solid state imaging elements (CCD), because of the need for patterning through a photolithography process, they are problematic in terms of the large number of processes and a high cost.
In contrast, although the (3) printing method and the (4) ink jet method do not require the photolithography process, the (3) printing method, which prints thermosetting resins in which pigments are dispersed for hardening, is inferior in terms of resolution and the uniformity of film thickness. The (4) ink jet method forms a specific ink receiving layer, carries out hydrophilicity and hydrophobicity processing, and then sprays ink into produced hydrophilic portions to obtain color filter layers. This method is problematic in terms of resolution, the tendency to cause color mixing in adjacent filter layers, and position precision.
A color filter produced by each of the above-mentioned methods is generally formed on the side of an ITO substrate that opposes a TFT substrate. However, if the filter is formed in that location, after a liquid crystal is encapsulated, the TFT substrate and a color filter substrate must be aligned. This involves difficulty to obtain high precision, causing a rise in cost.
The (5) electrodeposition method, in an electrolytic solution in which pigments are dispersed in water-soluble polymers, applies the high voltage of about 70 V to a transparent electrode patterned beforehand to form electrodeposition film for electrodeposition coating. By repeating this process three times, red, green, and blue color filter layers are obtained of R.G.B. This method is disadvantageous in that, since the transparent electrode must be patterned beforehand by photolithography for use as an electrodeposition electrode, it cannot be used for TFT liquid crystals because of the limited pattern shapes. Also, although patterning need not be performed if a color filter cannot be formed integrally with pixel electrodes of a TFT liquid crystal substrate by electrodeposition, with conventional electrodeposition methods, electrodeposition by use of TFT pixel electrodes has been impossible, because of the high electrodeposition voltage and the difficulty of causing electrodeposition in transparent pixel electrodes by an active matrix circuit. Also, the TFT pixel electrodes cannot be used for the reason that a liquid crystal voltage increases because a color filter layer becomes insulative, and other reasons.
Therefore, it is necessary to additionally provide a conductive film as a liquid crystal driving electrode on colored films of a color filter, causing an increase in the number of processes and a rise in cost. Especially, a TFT integrated color filter requires the complicated process of forming a through-hole between a conductive film and TFT pixel electrodes on colored films.
A color filter fabricating method is disclosed in Japanese Published Unexamined Patent Application No. Hei 7-333595. According to this method, a color filter transfer substrate on which an adhesive layer containing a ferroelectric substance as well as a color filter layer containing a ferroelectric substance such as barium titanate, etc., are provided on a transfer substrate is mounted on a TFT liquid crystal display substrate after alignment, and the color filter layer is transferred together with the adhesive layer. By containing a ferroelectric substance in the color filter layer and the adhesive layer, the capacitance of both layers is increased and a voltage drop is restrained. However, this method requires the very complicated process of fabricating in advance a color filter transfer substrate on which a color filter layer and an adhesive layer are provided on a transfer substrate, and transferring it after alignment with a TFT liquid crystal display substrate. Also, this method involves many processes and is unsuitable for fabrication of a high-resolution TFT integrated color filter at low cost. Furthermore, the official bulletin does not describe at all how the color filter layer containing a ferroelectric substance is formed on the transfer substrate.
Also, a color filter of a simple matrix style type crystal display apparatus is disclosed in Japanese Published Unexamined Patent Application No. Hei 2-60164. The color filter is reduced in the electric impedance of a color filter layer on which colored films containing high-dielectric material particles are deposited from an electrodeposition liquid containing electrodeposition high polymers, pigments, the high-dielectric material particles.
By the way, in a liquid crystal display apparatus, an orientation film such as polyimide formed on a color filter layer is usually formed by applying an orientation film resin dissolved in an organic solvent onto the color filter layer. However, generally, since the color filter layer does not have solvent resistance, if a resin solution is applied directly onto the color filter layer, the color filter layer will be dissolved by the organic solvent. Therefore, usually, an orientation film is formed before applying a solution of orientation film resin and after providing a protective film made of polymeric materials thermally cross-linked and improved in solvent resistance provided on the color filter layer.
However, since the protective film generally has a low dielectric constant, it must be avoided to form the protective film on a high-dielectric color filter as mentioned above.
Also, there is a problem in that, if high-dielectric material particles are contained in the color filter layer, light transparency decreases. It is described in Japanese Published Unexamined Patent Application No. Hei 5-5874 that a color filter is provided on ITO electrodes on a TFT substrate by the electrodeposition method.
Therefore, when a TFT integrated color filter is considered including R, G, and B layers and a black matrix, there is not yet provided a method of fabricating a TFT integrated color filter which has high resolution and excellent color purity, is high in terms of controllability, has high transparency, requires no use or a minimum amount of use of photolithography, does not require the formation of through-holes and conductive films, has high yields, and is inexpensive.
SUMMARY OF THE INVENTION
The present invention has been made in view of the abovementioned problems, and provides a method of fabricating a color filter, with a small number of processes and at low cost, for which a transparent conductive film for liquid crystal driving need not be formed, a voltage drop during liquid crystal driving is restrained, and a black matrix is easily formed; an apparatus for fabricating the color filter; the color filter, and a liquid crystal display apparatus.
A color filter fabricating method according to an aspect of the present invention includes the steps of: placing a color filter forming substrate formed by providing a transparent conductive film and a transparent thin semiconductor film on a transparent substrate in this order so that at least the thin semiconductor film of the color filter forming substrate contacts an aqueous electrodeposition liquid which contains a colorant, a transparent, high-dielectric material

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