JPH05311275A - Porous intermetallic compound for capacitors - Google Patents

Abstract

(57) [Summary] [Purpose] A capacitor having a large capacity is obtained by using a porous body of an intermetallic compound having no deviation in composition range. [Configuration] Any one or two of Zr and Hf and Al
A porous intermetallic compound obtained by forming a powder of an intermetallic compound consisting of (1) and (2) in contact with each other and firing and oxidizing the surface thereof is used as a material for a capacitor. The particle size of these powders is preferably 0.05 μm to 10 μm. [Effect] As a result, the capacitance of the capacitor is
The value was about 2 to 30 times that of the electrolytic capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material for capacitors.

[0002]

2. Description of the Related Art Anode materials for conventional electrolytic capacitors include
A so-called valve metal is used which electrochemically produces a very thin oxide film and uses it as a dielectric.
The most used metal in aluminum electrolytic capacitors is usually Al having a purity of 99.99% or more. The biggest problem of the aluminum electrolytic capacitor at present is to improve its capacitance. The method usually adopted for increasing the capacity is to increase the surface area by etching. However, at present, the surface area expansion rate has reached the limit, and further expansion will increase the difficulty in terms of cost and quality control.

Further, in Ta capacitors, Ta powder is sintered to increase the surface area, but Ta sintering requires a vacuum treatment at about 2000 ° C., which is very costly. I was holding. Furthermore, electric double layer capacitors using carbon powder have been widely used for backing up semiconductor memories. This is a few m ²
/ G to several hundred m ² / g of large surface area of carbon powder is used, but since the part used as a capacitor is an electrolytic solution and is different from the conventional capacitor using oxide of valve action metal, the operating voltage Was as low as 1 to 2 V and could not be applied to ordinary electronic component fields. In addition, an invention using an aluminum-titanium based alloy porous sintered body using a metal of a composite layer has been proposed for the purpose of aiming at both good points of a Ta capacitor and an Al electrolytic capacitor. However, in this case, in our study,
It was found that the leakage current was large and could not be improved even with some improvement. As described above, in the conventional technique, there is no optimum method for expanding the capacity beyond this.

[0004]

SUMMARY OF THE INVENTION The present invention provides a new anode foil for further increasing the capacity of capacitors, which has reached its limit.

[0005]

As described above, the electrolytic capacitor has its capacity improved by improving the etching, and the metal having a large dielectric constant such as Ta is used. It is at its technical limit. On the other hand, an invention using an aluminum-titanium alloy porous sintered body has been proposed (JP-A-60-147110).
However, since the metal species are Al and Ti, there is a drawback that the leakage current is large and cannot be improved even if some improvements are made.

The present invention has been completed as a result of various studies in order to fundamentally improve the above-mentioned problems, and the present invention has been completed, and the particle diameter of the powder is 0.05 μm to 10 μm.
Porous intermetallic compound for a capacitor, which is obtained by forming a powder of an intermetallic compound consisting of one or two of r and Hf and Al in contact with each other, followed by firing, and oxidizing the surface. Is used as an electrode material.

[0007]

The present invention will be described in detail below. The intermetallic compound in the present invention is, for example, in the case of Al and Hf,
AlHf ₂ , AlHf, etc., and in the case of Al and Zr, Al ₃ Zr, AlZr, Al ₃ Zr ₂ , AlZr ₃
And the like, and the composition ratio thereof does not deviate from the integer ratio. Examples of intermetallic compounds that deviate from the integer ratio include:
AlTi and AlNb ₂ are available. To be precise, Al _1-X Ti
_{1 + X} , Al _1-X Nb _{2 + X} (-1.0 <X <1.0). In the present invention, it has been revealed that a combination of metals forming an intermetallic compound having these ranges cannot be a capacitor. For example, Al
In the case of and Ti, an intermetallic compound called AlTi having a composition range is formed, so that it cannot be a capacitor. It has been clarified from various experiments that even if Al ₃ Ti which is an intermetallic compound having no composition range is used, the leakage current is large and a capacitor cannot be formed.

Therefore, the powder that can be used as the capacitor is Z
It is a powder of an intermetallic compound consisting of Al and one or two of r and Hf. For example, Al and Hf are AlHf ₂ and AlHf, and Al and Zr are Al ₃ Zr, AlZr, Al ₃ Zr ₂ and AlZr ₃
Etc. That is, it has been found from the results of the study conducted by the present inventors that the combinations of metals that can be used are only those in which the intermetallic compound has no deviation from the composition ratio, and specifically, Al and Zr, Only Al and Hf or a mixture thereof. Further, in the present invention, Al was used as a base for study, but similar discussions can be made with other metals, but an intermetallic compound with Al is optimal in terms of cost and the like.

In the present invention, since the powder of the intermetallic compound having the same composition ratio as described above is used, the composition ratio of the metal species is naturally determined. That is, A
In Al ₃ Zr, Al is 75 atomic% and Zr is 25 atomic%, and in AlHf, Al is 50 atomic% and Hf is 50 atomic%.
It is atomic%.

It has also been found that there is an optimum range for the particle size of the powder. That is, when the thickness is 0.05 μm or less, the withstand voltage is low and the capacitor cannot be used. Also,
The electrolytic solution impregnation step also takes time and is not industrially advantageous. On the other hand, when the particle size is 10 μm or more, the capacity does not increase, and the shape retention ability of the molded body is not good, so that the shape is deformed during handling.

Next, the intermetallic compound powder having the above particle size is
Pressure is applied by a uniaxial press molding machine or the like. Then 1000
Bake for several hours at a temperature of ℃ to 1300 ℃. The atmosphere is preferably in vacuum. Further, chemical conversion treatment is performed to form the oxide on the surface of the intermetallic compound. The voltage at this time is
It depends on the specifications of the capacitor used, but it is 10V-30
It is 0V. The chemical conversion liquid is the same as the chemical conversion of a normal aluminum electrolytic capacitor. The dielectric constant of the oxide film formed by the above method is 15 to 30, and both are Al ₂ O ₃
It is large as compared with the dielectric constant of 8.5 to 10. Further, in the process of the aluminum electrolytic capacitor, the process of etching the aluminum plate which is the original foil is required before the formation, but in the present invention, since powder is used, of course, etching is not required. However, in order to further increase the surface area of the molded product, etching may be carried out, but an extra step is required and it is better to adjust the grain size from the beginning.

The present invention provides a very large capacitor capacity by combining the large surface area of the powder and the high dielectric constant of the oxide film. The porosity after molding is
Although it is about 40% to 95%, it is preferably about 55% considering the characteristics as a capacitor.

FIG. 1 is an enlarged view of a porous intermetallic compound according to the present invention, which has been subjected to post-molding and chemical conversion. The shaded area is an intermetallic compound. Although there is a problem in strength due to point contact at the time of pressurization, after the chemical conversion, the oxide can coat the shape sufficiently.

[0014]

【Example】

(Example 1) The powder is Al ₃ Hf having an average particle size of 0.3 μm.
Was used. Using a uniaxial molding press, this is 10mmφ
A coin-shaped molded body of × 3 mmH was formed. The pressure during molding was 1.2 t / cm ² . Then, it was baked in vacuum at 1200 ° C. for 1 hour. A lead was attached to this, an insulating paste was applied to the unnecessary portion for chemical conversion, and it was dried. Next, chemical conversion treatment was performed. The treatment voltage was DC 15 V and ammonium phosphate solution was used. Next, MnO ₂ was subjected to cathodic baking by a manganese nitrate method that is often used in ordinary Ta capacitors, and then graphite and silver paste were baked to obtain capacitors. Table 1 shows the results of four prototype capacitors.

[0015]

[Table 1]

(Example 2) The powder is A having an average particle size of 3 μm.
l ₃ Zr was used. Using a uniaxial molding press,
A coin-shaped molded body of 10 mmφ × 3 mmH was formed. The pressure during molding was 1.5 t / cm ² . Then at 1200 ° C for 2
Burned for hours. A lead was attached to this, an insulating paste was applied to the unnecessary portion for chemical conversion, and it was dried. Next, chemical conversion treatment was performed. The treatment voltage was 25 V AC, and ammonium phosphate solution was used. Next, MnO ₂ was subjected to cathodic baking by the manganese nitrate method, which is often performed in a normal Ta capacitor, followed by baking of graphite and silver paste, and resin molding to obtain a capacitor. Table 2 shows the results of four prototype capacitors.

[0017]

[Table 2]

Reference Example As described above, AlTi could not be used as a capacitor, but an example will be shown. The powder is
AlTi having an average particle size of 1 μm was used. A coin-shaped molded body of 10 mmφ × 3 mmH was formed from this using a uniaxial molding press. All the subsequent treatments were performed in the same manner as in Example 2. Four
Table 3 shows the results of the capacitors that were prototyped.

[0019]

[Table 3]

[0020]

As described above, according to the present invention, it becomes possible to produce a large capacity capacitor by a simple method.

[Brief description of drawings]

FIG. 1 shows an enlarged view of a porous intermetallic compound of the present invention.

Claims (1)

[Claims] 1. The particle size of the powder is 0.05 μm to 10 μm.
Powder of an intermetallic compound consisting of Al and any one of Zr and Hf and Al, and molded into a porous state and sintered, and the surface of the void portion of the porous body is oxidized. Porous intermetallic compound for capacitors.