Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1996-12-13
2002-02-26
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C428S917000
Reexamination Certificate
active
06351068
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a transparent conductive laminate in which a transparent conductive a film mainly comprising tin, indium and oxygen is formed on a transparent substrate, and more specifically, it relates to a transparent conductive laminate using an amorphous film as a transparent conductive film and having excellent moist heat resistance and scuff resistance, and an electroluminescence (EL) light-emitting element using this transparent conductive laminate.
(ii) Description of the Prior Art
In recent years, devices and equipments regarding optical electronics have remarkably progressed and prevailed with the increasing demand of information in society. In such circumstance, transparent conductive laminates have widely been used as electrodes of I/O devices such as transparent touch panels, electrodes of display devices such as liquid crystal displays, and electroluminescence displays and electrochromic displays. Further, they have been uses as window electrodes of photoelectric conversion elements such as solar batteries and the like, and electromagnetic shielding films of electromagnetic wave shields.
The transparent conductive laminate is usually constituted of a transparent substrate and a transparent conductive layer formed thereon. Examples of the transparent conductive layer include metallic thin films of gold, silver, platinum, palladium and the like, oxide semiconductor thin films of indium oxide, tin (IV) oxide, zinc oxide and the like, and multi-layer thin films comprising a laminate of a metallic oxide and a metal. The metallic thin films are excellent in conductivity but poor in transparency. On the contrary, the oxide semiconductor thin films are slightly poor in conductivity in general but excellent in transparency. Of these oxide semiconductor thin films, the thin films comprising indium, tin and oxygen, which are also called ITO (indium tin oxide) films, are excellent in conductivity and transparency, and in addition, and can easily be formed into electrode patterns by etching. For these features, the ITO films have widely been utilized. The resistivity and the light transmittance of the ITO films are usually in the range of about 5×10
−5
to 1×10
−3
&OHgr;·cm and in the range of 80 to 90%, respectively.
As factors for the performance evaluation of the transparent conductive laminate, there are chemical stability such as moist heat resistance and physical strength such as scuff resistance in addition to the electric resistance and the light transmittance. With regard to the ITO film formed at a low temperature, its electric resistance usually changes depending on the amount of oxygen in the film, so that the electric resistance noticeably changes by a heat treatment or a moist heat treatment. Accordingly, the thus formed ITO film has the problem of chemical stability. The transparent conductive laminate having the thus formed ITO film is finally used as a transparent electrode of a product such as a liquid crystal display or a transparent touch panel, but in this case, if the performance of the transparent conductive laminate changes, a trouble might occur in the product. Moreover, the ITO film formed at a low temperature is liable to be scuffed, and when the ITO film is used in contact with other members as in the transparent touch panel, mechanical strength such as scuff resistance is required to be improved. Furthermore, such an ITO film is chemically unstable, and when the ITO film is coated with another organic substance as in an electroluminescence light-emitting element, the quality of the ITO film itself changes with time. Thus, it is necessary to obtain the chemically stable ITO film.
As means for solving the above-mentioned problem, there usually are a method which comprises heating a substrate at the time of the formation of the ITO film to obtain the crystalline ITO film, and another method which comprises subjecting the ITO film formed at room temperature to a heat treatment to obtain the crystalline ITO film [e.g., Japanese Patent Publication 15536/1991 (JP, B2, 3-15536), and Japanese Patent Application Laid-open Nos. 100260/1989 (JP, A, 1-100260), 194943/1990 (JP, A, 2-194943) and 276630/1990 (JP, A, 2-276630)]. Both of these methods take the means for obtaining the crystallized ITO film by the heat treatment. In the methods, it is utilized that the crystallization of the ITO film permits the formation of the film stable to heat and moisture and hence the improvement of the moist heat resistance and the scuff resistance.
A temperature at which the ITO film is crystallized depends upon the method and the conditions of the film formation, but it is usually 180° C. or more.
The crystalline ITO film formed by the heating film formation or the heat treatment after the film formation usually comprises crystallites (or grains) having a diameter of from several &mgr;m to several tens &mgr;m. If the size of the crystallites is small, a large number of boundaries between the crystallites are in the film, and therefore a gas in the atmosphere easily permeates through the boundaries, so that the moist heat resistance deteriorates. In order to prevent this permeation, the size of the crystallites is required to be enlarged, and for this enlargement, it is necessary to increase the temperature of the film formation or the temperature of the heat treatment after the film formation. For sake of the improvement of moist heat resistance, it is effective that the film formation or the heat treatment after the film formation is carried out at a temperature of about 400° C.
One of the products which requires transparent electrodes is an electroluminescence light-emitting element. The known electroluminescence light-emitting element can be manufactured by forming a light-emitting layer and a back surface electrode in turn on a transparent conductive laminate in which the transparent conductive layer is formed on the transparent substrate. For the purpose of effectively applying an electric field to the light-emitting layer to improve a light-emitting luminance, a dielectric layer having a high dielectric constant is usually inserted between the light-emitting layer and the back surface electrode. Further, in order to prevent the light-emitting layer from deteriorating due to water vapor contained in the atmosphere, all or a part of the light-emitting surface of the electroluminescence light-emitting element is usually covered with a moisture barrier film. In this case, usually, the transparent conductive layer is made of the ITO film or the like, and the light-emitting layer is made of zinc sulfide, cadmium sulfide or zinc selenide, and the back surface electrode is made of aluminum or carbon.
Since the electroluminescence light-emitting element can be obtained in the form of a thin sheet, there is expected its application to a use in which such a shape is required, for example, a back light of a liquid crystal display or an emitting element of the dial of a watch.
The electroluminescence light-emitting element is characterized by being obtained in the form of the thin sheet, but its light-emitting durability is poorer as compared with a fluorescent tube which is a conventional light source. For this reason, the electroluminescence light-emitting element has not actually been prevailed so far. Thus, it has been desired to develop the electroluminescence light-emitting element by which the above-mentioned problem can be solved. In particular, the electroluminescence light-emitting element in which a polymeric film is used as the transparent substrate can be applied in a wide utilization range, because it can emit the light while curved.
As one factor by which the luminance of the electroluminescence light-emitting element deteriorates during the continuous light emission, there is the deterioration of the ITO film of the transparent conductive layer used as the transparent electrode as described above. The transparent conductive layer for the transparent electrod
Fukuda Nobuhiro
Fukuda Shin
Okamura Tomoyuki
Yamazaki Fumiharu
Burns Doane Swecker & Mathis L.L.P.
Mitsui Chemicals Inc.
Patel Ashok
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