Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-09-29
2004-11-02
Jones, Deborah (Department: 1775)
Metal working
Method of mechanical manufacture
Electrical device making
C029S025010, C029S025030, C029S622000, C428S469000, C428S472100, C428S701000
Reexamination Certificate
active
06810575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a functional element for use in an electric, an electronic or an optical device. More particularly, the present invention is concerned with a functional element for use in an electric, electronic or an optical device, comprising a substrate having on an upper surface thereof a plurality of metal oxide needles extending upwardly of the upper surface of the substrate, with their respective central axes arranged substantially in parallel with each other, wherein the metal oxide needles have a specific weighted average circle-based diameter and a specific weighted average aspect ratio, and wherein the metal oxide needles are present at a specific density at the upper surface of the substrate. The present invention is also concerned with a method for producing the above-mentioned functional element. The functional element of the present invention has an advantage in that, although the metal oxide structure therein comprised of the needles has a very large surface area, the metal oxide structure has a very small thickness. Therefore, the functional element of the present invention can be very advantageously used as a component for an electric, an electronic or an optical device.
2. Prior Art
Metal oxides have various functional properties. By virtue of such various functional properties, metal oxides have been used in various fields. For example, metal oxides are used as components for an electric or an electronic device, such as a ceramic capacitor (making use of ferroelectric properties), a gas sensor (making use of resistance properties), and a magnetic tape and a magnetic head (making use of magnetic properties). Further, in recent years, studies have been being made for using metal oxides as components for optical devices, for example, an optical switch (making use of optical waveguide properties) and an ultraviolet laser emission element (making use of light emission properties).
In general, the metal oxides used as components for an electric, an electronic or an optical device have a morphology containing a flat surface. For example, in a ceramic capacitor, a metal oxide having ferroelectric properties (such as barium titanate) is used in the form of a laminate wherein the metal oxide is sandwiched between two flat electrodes. Further, in a magnetic tape, a metal oxide (such as chromium oxide) is used in the form of a film formed on a polymer film. With respect to the various uses of the metal oxides, it should be noted that, in some uses, the performance of the component employing a metal oxide can be greatly improved by increasing the surface area of the metal oxide employed. For example, in the case of a ceramic capacitor mentioned above, the most important property thereof is its capacitance. In the capacitor, a larger capacitance means an improved performance of the capacitor. The capacitance of the capacitor is proportional to the surface area of the metal oxide used therein, and inversely proportional to the thickness of the metal oxide. That is, the larger the surface area of the metal oxide, the larger the capacitance of the capacitor, and, in addition, the thinner the metal oxide, the larger the capacitance of the capacitor. Because of these characteristics of a metal oxide, most of the conventional ceramic capacitors on the market are prepared by laminating approximately 100 layers comprising electrode layers and metal oxide layers. That is, in a conventional capacitor, a high capacitance is obtained by a method in which the surface area of a metal oxide is increased by increasing the number of metal oxide layers, whereas the thicknesses of the electrode layers and the metal oxide layers are reduced to as small a value as possible. However, in the preparation of a capacitor, lamination of a large number of electrode layers and metal oxide layers is very difficult from the viewpoint of productivity and economy.
Such a problem would be able to be solved if it becomes possible to realize, for example, a capacitor containing only one metal oxide layer, wherein the metal oxide layer, on one hand, has a small thickness not larger than the total thickness of the large number of metal oxide layers of a conventional capacitor, and, on the other hand, has a large surface area (and hence a large capacitance) which is the same as or larger than the total surface area of the metal oxide layers of the conventional capacitor. Such a capacitor containing only one metal oxide layer is advantageous not only in that the productivity of the capacitor becomes high and the production cost becomes low, as compared to those of a conventional capacitor containing a large number of metal oxide layers, but also in that the capacitance of the capacitor can be easily increased.
As explained hereinabove by taking as one example the case of the capacitor, the development of a metal oxide structure having a large surface area while maintaining a small thickness will enable the production of an improved component for an electric, an electronic or an optical device. In addition, such a metal oxide structure is also expected to enable the development of new types of devices which can be used for producing new types of equipment.
As a method for producing a metal oxide structure having a large surface area, there is known a method in which whiskers comprised of metal oxide needles are formed. For example, Unexamined Japanese Patent Application Laid-Open Specification No. 50-6597 discloses a method for producing zinc oxide whiskers, in which a zinc alloy (comprising zinc and a metal having a boiling point higher than that of zinc) or a mixture of these two metals is heated under an oxygen-containing atmosphere in the presence of a substrate, to thereby form whiskers comprised of zinc oxide needles on the surface of the substrate. In this prior art technique, the formed zinc oxide whiskers are cut off from the substrate and provided for use as reinforcements for resins, ceramics and the like, and as semiconductors. However, in this prior art document, there is no disclosure suggesting that a structure comprising a substrate and whiskers formed thereon is used as a component for an electric or an electronic device or a component for an optical device.
In addition, there is a report that nanocrystals of ZnO formed on the surface of a substrate are used as an ultraviolet laser emission element (see “Kotai Butsuri (Solid State Physics)”, vol. 33, no. 1, pp. 59-64 (1998)). The nanocrystals of ZnO formed on the surface of a substrate each have a height of 5 nm and a circle-based diameter of 100 nm. That is, the ratio of the length of the crystal to the circle-based diameter of the cross-section thereof (length/circle-based diameter of cross-section) is as small as 0.05. Therefore, in this technique, the surface area of a metal oxide cannot be greatly increased unless the thickness of the metal oxide is greatly increased.
SUMMARY OF THE INVENTION
In this situation, the present inventors have made extensive and intensive studies with a view toward developing a functional element for use in an electric, an electronic or an optical device, which comprises a substrate having a metal oxide structure formed on a surface thereof, wherein the metal oxide structure, on one hand, has a large surface area and, on the other hand, has a small thickness. As a result, the present inventors have successfully developed a functional element, which has been found to have excellent characteristics in that, although the metal oxide structure comprised of the needles has a very small thickness, the metal oxide structure has an extremely large surface area. Specifically, the functional element comprises a substrate having on an upper surface thereof a plurality of metal oxide needles extending upwardly of the upper surface of the substrate, with their respective central axes arranged substantially in parallel with each other, wherein the needles have a weighted average circle-based diameter of from 0.01 to 10,000 &mgr;m and a weighted average as
Kinoshita Hideo
Saito Hidetoshi
Sato Minoru
Ueda Yoshikazu
Asahi Kasai Chemicals Corporation
Birch & Stewart Kolasch & Birch, LLP
Savage Jason
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