Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-02-07
2002-04-02
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C106S001050, C349S112000, C349S106000
Reexamination Certificate
active
06366333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a thin metal film and also to a method for fabrication of a reflector for liquid crystal display (“LCD”) devices utilizing the film-forming method.
2. Description of Related Art
In manufacturing processes of semiconductors and LCD devices, conductive electrodes, wiring and the like are occasionally provided in the form of a thin metal film. Such a thin metal film is generally deposited by thin film-forming processes, including vacuum evaporation, sputtering and CVD (chemical vapor deposition). Since these thin film-forming processes are generally performed under a reduced pressure, a substrate and the like must be placed interior of a reactor such as a vacuum chamber. The larger the size of an object onto which a thin metal film is deposited, the larger volume of vacuum chamber is required in order to accommodate the large-size object. This has constrained applicable size of the object.
Also, the difficulty has been encountered when the object has a complex surface profile, such as a curved surface. Other problems have arisen when the object has at its surface recesses or cavities such as contact or bier holes. Since the above-described film-forming processes characteristically produce a metal film having a uniform thickness, the film thickness must be made larger enough to fill up those recesses. Also, the shapes and configurations of the recesses are reflected on a surface of the deposited metal film, resulting in formation of craters thereon.
In Japanese Patent Laying-Open No. Hei 3-281783, a method is disclosed which applies a paste containing ultrafine metal particles for subsequent calcining into a thin metal film. Since the application of the paste results in the formation of thin metal films, this method is suitable for use in the formation of a thin metal film on very large surface areas or on a substrate having a complex surface profile.
Also, the use of such a paste containing a dispersion of ultrafine metal particles results in provision of a thin metal film having a metallic luster as if by plating, and the application of the paste containing a dispersion of ultrafine metal particles is a possible substitute of metal plating. With the use of this method, the metallic luster as if provided by plating can thus be readily imparted to articles having very large surface areas, as well as to nonconductive articles such as plastics.
However, the ultrafine metal particles used in the above-identified reference are prepared by vaporizing a metal at a vacuum atmosphere. This adds to a manufacturing cost to thereby make them expensive. The high cost of the ultrafine metal particles thus limits their practical uses.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method by which a thin metal film is formed in a cost-effective way and by a simple process that involves applying a coating composition.
Another object of the present invention is to provide a method by which a reflector for reflective LCD devices can be fabricated in a simple way and by a simple process involving application of a coating composition.
A method of forming a thin metal film, according to the present invention, includes the steps of applying a coating composition containing colloidal particles of noble metal or copper, to form a coating film, and heating the coating film so that the colloidal particles in the coating film are allowed to fuse together to form a thin metal film.
In the present invention, the aforementioned colloidal particles of noble metal or copper can be prepared by reducing a compound of the noble metal or copper in the presence of a polymeric dispersant. A specific example is as follows: A noble metal or copper compound is dissolved in a medium to which a polymeric dispersant is added. The subsequent reduction of the compound to noble metal or copper leads to the production of colloidal particles of noble metal or copper surrounded or protected by the polymeric dispersant. Removal of the aforementioned medium results in obtaining a solid sol of noble metal or copper. The aforementioned coating composition can be formulated by adding a medium, and a binder resin, if necessary, to the solid sol. The colloidal particles of noble metal or copper, as prepared in the manner as stated above, have ultrafine particle sizes from about several nanometers to about several tens nanometers. In the present invention, the coating composition containing such colloidal particles of noble metal or copper is applied in the form of a film which is subsequently heated so that the colloidal particles in the coating film are allowed to fuse together to form a thin metal film. The solid sol of noble metal or copper, as well as a colloidal solution prepared by adding a solvent to the solid sol, will be later discussed in more detail.
In the present invention, a thin metal film is formed by applying a coating composition to form a coating film and then heating the coating film. The coating composition is prepared by adding a solvent, alone or in combination with a binder resin, to the aforementioned solid sol of noble metal or copper. In the present invention, the solvent is dry removed prior to application of the coating composition, preferably prior to heating of the coating film. A drying temperature is suitably adjusted depending upon the type and amount of the solvent used. After the drying, the coating film is heated to allow the colloidal particles present therein to fuse together to form a thin metal film. A heating temperature is not particularly specified, so long as it is sufficient to allow the formation of a thin metal film. It is generally preferred, however, that heating is effected in the 100-500° C. temperature range. If the heating temperature is excessively low, the colloidal particles may be prevented from fusing together to result in the failure to form a thin metal film. On the other hand, if the heating temperature is excessively high, the polymeric dispersant present in the coating film, when heated, may escape therefrom by evaporation to leave holes in the resulting thin metal film. For uses where the formation of such holes is permitted, heating may be effected at a further elevated temperature.
In accordance with the present invention, a thin metal film can be formed having a good electrical conductivity. Such conductive, thin metal films can be utilized to constitute conductive circuit elements, such as electrodes and wiring, on semiconductor substrates, printing substrates, or for thermal heads, electronic parts and the like. They can also be utilized to constitute electrodes, electric wiring and the like for display devices such as LCD devices.
Also in accordance with the present invention, a thin metal film can be formed having a metallic luster as if by plating. Such thin metal films can be utilized to impart the metallic luster to article surfaces for decorative or ornamental purposes.
Also, in accordance with the present invention, a thin metal film can be formed having a good electromagnetic wave shielding property. Accordingly, such thin metal films can be utilized as electromagnetic wave shielding films.
A thickness of the thin metal film, as formed according to the present method, is not particularly limited. In accordance with the present invention, a thin metal film can be formed to a thickness within the range of 0.01 &mgr;m-200 &mgr;m, for example. The use of colloidal particles having fine particle sizes permits the formation of an about 0.1 &mgr;m thick metal film.
In accordance with the present invention, a thin metal film can be formed having a good light reflectance. Such a highly reflective, thin metal film can be utilized to constitute a reflecting layer of a reflector for use in reflective LCD devices.
A method for fabrication of a reflector for reflective LCD devices, according to the present invention, utilizes the above-described film-forming method in fabricating the reflector. This fabricating method thus includes the ste
Ohata Masashi
Seio Mamoru
Yamamoto Akira
Chowdhury Tarifur R.
Olson & Hierl Ltd.
Sharp Kabushiki Kaisha
Sikes William L.
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