Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-06-09
2002-08-06
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S321400, C361S330000, C361S308100, C438S240000
Reexamination Certificate
active
06430026
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel electrode material for capacitors having a large capacitance per unit weight, a capacitor using the electrode material and a method for manufacturing the capacitor.
BACKGROUND OF THE INVENTION
Capacitors used for electronic instruments such as portable telephone and personal computer are demanded to have a small size and a large capacitance. Among these capacitors, a tantalum capacitor is preferred because it has a large capacitance for the size and exhibits good performance. In this tantalum capacitor, a sintered body of powdered tantalum is generally used for the anode moiety. Also, a sintered body using niobium is being studied as a material having a larger dielectric constant than that of tantalum. On such a sintered body, an oxide layer to work as a dielectric material is formed by an electrolytic oxidation process commonly used in conventional techniques to obtain a capacitor.
On the other hand, in JP-A-63-34917 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes a method for manufacturing a capacitor having a large capacitance, where a metal foil or bar having pores or empty spaces is reacted in an alkali solution to form a perovskite oxide layer directly on the metal electrode material (hereinafter referred as a “direct reaction method”), and also describes a capacitor using the oxide layer as a dielectric material.
These capacitors manufactured by a conventional method using an electrode material such as tantalum or niobium, or capacitors using as a dielectric material a perovskite acid compound formed by a direct reaction method have the following problems and cannot satisfactorily respond to the requirement for a larger capacitance.
In the case where a dielectric material oxide film of a capacitor is formed by an electrolytic oxidation method commonly used in conventional techniques, the oxide film for the dielectric material must be formed as an “ultra”-thin film so as to obtain a larger capacitance. However, when an “ultra”-thin film is formed, a leakage current is generated as a serious problem in the thinner film part, therefore, the “ultra”-thin film cannot be used in practice and in turn a larger capacitance cannot be obtained.
The direct reaction method of forming an acid compound film as a dielectric material having a larger dielectric constant cannot produce an acid compound of tantalum or niobium.
Furthermore, when an acid compound film is directly formed using other metals as an electrode material by the direct reaction method commonly used in conventional techniques, the dielectric film formed is uneven in the thickness and the thin part gives rise to the generation of leakage current, therefore, the thickness of this part must be increased as large as to reduce the leakage current to a predetermined value or lower. As a result, the average layer thickness of the film as a whole increases and a larger capacitance cannot be obtained.
In addition, as a problem in the production, when this reaction method is contained in the production process, the raw material solution for the reaction is entirely reacted, therefore, a batch processing of exchanging the raw material solution on each operation is enforced and the productivity decreases.
The present invention has been made to solve the above-mentioned problems. By using the electrode material for capacitors disclosed in the present invention, a capacitor having a large capacitance per unit weight can be obtained without worsening the leakage current characteristic value of the capacitor.
SUMMARY OF THE INVENTION
As a result of extensive investigations, the present inventors have succeeded in developing an electrode material for capacitors having an extremely large capacitance per unit weight without particularly reducing the entire thickness of the dielectric material, and have accomplished the present invention. More specifically,
1) the first invention to solve the above-described problems is an electrode material for capacitors, comprising a tantalum metal and/or a niobium metal having on the surface thereof a tantalic acid compound and/or a niobic acid compound formed by reacting an oxide of the tantalum metal and/or niobium metal formed on the surface of the metal in an alkali solution (for example, an alkali solution containing an alkali metal compound and/or an alkaline earth metal compound); the “tantalum metal and/or niobium metal” as used herein include tantalum metal, niobium metal and tantalum-niobium composite metal and the “oxide of a tantalum metal and/or a niobium metal” as used herein include an oxide of tantalum, an oxide of niobium and an oxide of tantalum-niobium composite metal;
2) the second invention to solve the above-described problems is the electrode material for capacitors as described in 1), wherein the oxide on the surface of a tantalum metal and/or a niobium metal is formed by the electrolytic oxidation using the tantalum metal and/or niobium metal as an anode;
3) the third invention to solve the above-described problems is an electrode material for capacitors, comprising a tantalum metal and/or a niobium metal having on the surface thereof a tantalic acid compound and/or a niobic acid compound formed by the electrolytic oxidation of the tantalum metal and/or niobium metal in an alkali solution (for example, an alkali solution containing an alkali metal compound and/or an alkaline earth metal compound); the “tantalum metal compound and/or niobium metal compound” as used herein include a tantalic acid compound, a niobic acid compound and a composite material of a tantalic acid compound and a niobic acid compound;
4) the forth invention to solve the above-described problems is an electrode material for capacitors, comprising a tantalum metal and/or a niobium metal having on the surface thereof a dielectric layer comprising an oxide of the tantalum metal and/or niobium metal, and a tantalic acid compound and/or a niobic acid compound;
5) the fifth invention to solve the above-described problems is the electrode material for capacitors as described in any one of 1) to 4), wherein the metal is a sintered body;
6) the sixth invention to solve the above-described problems is the electrode material for capacitors as described in any one of 1) to 4), wherein the tantalum metal and/or niobium metal is an alloy consisting of tantalum and/or niobium and at least one element selected from the group consisting of Group 3A elements, Group 4A elements, Group 3B elements, Group 4B elements and Group 5B elements in the Periodic Table;
7) the seventh invention to solve the above-described problems is an electrode material for capacitors, comprising an alloy having on the surface thereof a dielectric layer comprising an oxide of the elements constituting the alloy and a tantalic acid compound and/or a niobic acid compound, the alloy consisting of tantalum and/or niobium and at least one element selected from Group 3A elements, Group 4A elements, Group 3B elements, Group 4B elements and Group 5B elements in the Periodic Table;
8) the eighth invention to solve the above-described problems is the electrode material for capacitors as described in 6) or 7), wherein the alloy is a sintered body;
9) the ninth invention to solve the above-described problems is a capacitor comprising the electrode material described in any one of 1) to 8) as one part electrode having formed thereon a dielectric layer, and the other part electrode.
DETAILED DESCRIPTION OF THE INVENTION
The dielectric layer of the electrode material for capacitors of the present invention is a dielectric material containing at least a tantalic acid compound and/or a niobic acid compound, which, for example, (1) comprises a tantalic acid compound and/or a niobic acid compound or (2) has a two-layer structure consisting of an oxide of a tantalum metal and/or a niobium metal or an alloy thereof, and a tantalic acid compound and/or a niobic acid compound.
In the latter case, the two-layer structure of the dielectric material can be
Nagato Nobuyuki
Naito Kazumi
Ha Nguyen
Reichard Dean A.
Showa Denko K.K.
Sughrue & Mion, PLLC
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