The present invention relates to a powdered niobium for a capacitor having a large capacity per unit weight and good specific leakage current property, a sintered body using the powdered niobium, a capacitor using the sintered body and production method of the capacitor.
Capacitors used for electronic instruments such as portable telephone and personal computer are demanded to be compact and have a large capacity. Among these capacitors, a tantalum capacitor is preferably used because it has a large capacity for the size and exhibits good performance. In this tantalum capacitor, a sintered body of powdered tantalum is generally used for the anode moiety. In order to increase the capacity of the tantalum capacitor, it is necessary to increase the weight of sintered body or to use a sintered body increased in the surface area by pulverizing the powdered tantalum.
The former method of increasing the weight of sintered body is naturally accompanied by enlargement of the capacitor size and the requirement for downsizing cannot be satisfied. On the other hand, in the latter method of pulverizing the powdered tantalum to increase the surface area, the pore size of tantalum sintered body is reduced or closed pores are increased at the stage of sintering, therefore, a cathode agent can be difficultly impregnated in the after process. As a means for solving these problems, a capacitor using a sintered body of a powdered material having a dielectric constant larger than the tantalum is being studied. Examples of such a material having a larger dielectric constant include niobium and titanium.
However, conventional capacitors using a sintered body of such a material are disadvantageous in that the specific leakage current property is greatly dispersed and not satisfied by any means. Using a powdered tantalum makes a sintered body. When a sintered body is electrolytically oxidized and then combined with counter electrode to manufacture a capacitor, it is nothing to satisfy the basis which the specific leakage current as a practical value is 10 nA/xcexcFxc2x7V and less. However, in capacitors using conventional powdered niobium and titanium, the specific leakage current values are greatly dispersed and there are many cases which exceed this value.
Furthermore, conventional capacitors using a sintered body of such a material are deficient in the high-temperature property and are not put into practical use. Because, when a sintered body is electrolytically oxidized and then combined with counter electrode to manufacture a capacitor, the high-temperature property usually falls within xc2x120% in the case of a sintered body using powdered tantalum, however, in some sintered bodies using conventional powdered niobium, the high-temperature property does not fall within xc2x120%.
Therefore, capacitors using a niobium sintered body and a titanium sintered body must be estimated to have low reliability also at room temperature and are duly judged deficient in the service life, thus cannot be used in practice.
As a result of extensive investigations, the present inventors have developed a powdered niobium for a niobium sintered body capable of providing a capacitor having a small dispersion in the specific leakage current value, and accomplished the present invention.
Furthermore, the present inventors have accomplished the present invention by findings which a capacitor having good high-temperature property is obtained when a crystal of a given niobium compound is comprised in a niobium sintered body.
Namely, the present invention relates to the following powdered niobium for capacitor, sintered body thereof, capacitor using the same and production method of the capacitor.
(1) A powdered niobium for a capacitor, containing elements such as iron, nickel, cobalt, silicon, sodium, potassium and magnesium, wherein an amount of each element is about 100 ppm by weight or less.
(2) A powdered niobium for a capacitor, containing elements such as iron, nickel, cobalt, silicon, sodium, potassium and magnesium, wherein the total amount of the elements is about 350 ppm by weight or less.
(3) A powdered niobium for a capacitor, containing elements such as iron, nickel, cobalt, silicon, sodium, potassium and magnesium, wherein an amount of each element is about 100 ppm by weight or less and the total amount of the elements is about 350 ppm by weight or less.
(4) The powdered niobium for a capacitor described in any one of the (1) to (3), which contains at least one of niobium nitride, niobium carbide and niobium boride.
(5) A sintered body for a capacitor using a powdered niobium described in any one of the (1) to (4).
(6) A niobium sintered body for a capacitor, comprising at least one of niobium monoxide crystal and a diniobium mononitride crystal.
(7) The niobium sintered body for a capacitor according to the (6), wherein the content of niobium monoxide crystal is from about 0.1 wt % to about 20 wt %.
(8) The niobium sintered body for a capacitor according to the (6), wherein the content of diniobium mononitride crystal is from about 0.1 wt % to about 20 wt %.
(9) A capacitor comprising one party electrode assigned to the niobium sintered body described in any one of the (5) to (8), other party electrode and a dielectric material interposed between two electrodes.
(10) The capacitor according to the (9), wherein the dielectric material is tantalum oxide, niobium oxide, polymer material, or ceramics compound.
(11) The capacitor according to the (10), wherein the dielectric material is niobium oxide formed by chemical forming on a niobium sintered body.
(12) A process for producing a capacitor, comprising preparing the second electrode opposing on the dielectric material, after forming the dielectric material on the niobium sintered body (first electrode) described in any one of the (5) to (8).
(13) The process for producing a capacitor according to the
(12), wherein the dielectric material is tantalum oxide, niobium oxide, polymer material, or ceramics compound.
(14) The process for producing a capacitor according to the
(13), wherein the dielectric material is niobium oxide formed on a niobium sintered body by chemical forming.