JPH0513281A - Electrode material for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain an electrode material for an electrolytic capacitor, having a high electrostatic capacity value, no variation in an electrostatic capacity value for a long period and a low leakage current value. CONSTITUTION:A niobium vapor-deposited layer having a high purity of 99.99% or more, is formed on a surface of an aluminum or aluminum alloy base material as an anode or cathode material of an 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 used as an anode or a cathode of an electrolytic capacitor.

[0002]

2. Description of the Related Art Electrolytic capacitors use a valve metal such as aluminum for their electrodes. With the valve metal, an insulating metal oxide thin film layer can be formed on the metal surface by an operation such as anodic oxidation treatment. This thin film functions as a dielectric layer, and since it is an extremely thin film (about a dozen angstroms per 1V), it is possible to increase the capacitance value per electrode area and obtain a compact and large-capacity capacitor. .

Also for the cathode side electrode, the same valve metal as that on the anode side is used because of the problem of reactivity with the electrolytic solution impregnated inside the capacitor and measures against corrosion. For this reason, especially in the aluminum cathode, a natural oxide film formed by oxygen in the atmosphere is formed on the surface, and this has a capacitance, which forms a combined capacitance in series with the anode side electrode, and the electrostatic capacitance of the anode only. The capacity value will be lower than the capacity.

In order to reduce the size and increase the capacity of electrolytic capacitors, it has been attempted to electrochemically etch the electrodes in order to increase the surface area by roughening the electrode surface. In recent years, this etching has been performed. There is a limit to the increase in surface area due to, and new measures to increase the capacitance are required.

To increase the capacitance of the electrodes,
It has been proposed to form layers of different metals or metal compounds on the aluminum surface. As such a thing, for example, Japanese Patent Publication No. 31-5022 and Japanese Patent Laid-Open No. 59-167.
No. 009 and Japanese Patent Laid-Open No. 2-61039,
It is known that a niobium layer is formed on the surface of the base material of the electrode by means such as vapor deposition. A material obtained by vapor-depositing niobium on aluminum or a material obtained by oxidizing a part or all of this niobium by a treatment such as anodic oxidation generally obtains a higher capacitance than aluminum itself, and is suitable as an electrode material for electrolytic capacitors. It is something.

However, while such an electrode material has a high capacitance value, it has problems such as long-term stability of the capacitance value and a high leakage current value when used on the anode side. Yes, there was a need for this improvement.

[0007]

DISCLOSURE OF THE INVENTION The present invention is an improvement over the above-mentioned problems, in which the purity of the niobium layer formed on the surface of the electrode base material affects the stability and leakage current characteristics of the electrode. It was made with a focus on that, with the aim of obtaining an electrode material for an electrolytic capacitor, which has a high capacitance value, can maintain a stable capacitance value for a long period of time, and has little leakage current. There is.

[0008]

The electrode material of the present invention comprises:
It is characterized in that it is made of aluminum or an aluminum alloy as a base material and niobium is vapor-deposited on the surface thereof, and the vapor-deposited niobium layer has a purity of 99.99% or more.

Aluminum used as the base material can be selected from high-purity aluminum used for the anode to aluminum alloy materials having a relatively low purity used for the cathode and the like. The shape of the substrate is not limited, but generally, it is a foil, a thin plate, a wire, a porous block, or the like. The surface of the base material may be roughened by etching or the like.

There are various means for forming a thin film layer of niobium on the surface of the substrate, but physical means such as ion plating method, sputtering method, vacuum vapor deposition method and cathodic arc plasma vapor deposition method, Chemical means such as the CVD method can be selected.

In the present invention, it is necessary that the formed niobium thin film layer has a high purity of 99.99% or more. Therefore, it is necessary to pay attention to the purity of the target material of niobium used during vapor deposition, the cleanliness of the substrate surface, and the like.

The electrode material on which the niobium layer is formed may be anodized to convert the metal niobium to niobium oxide to improve the insulating property and be used as the electrode material on the anode side.
As a result, a strong insulating film layer serving as a dielectric is formed on the surface.

[0013]

According to the present invention, a niobium thin film having a purity of 99.99% or higher can maintain a high capacitance value for a long period of time without being deteriorated as compared with a niobium thin film having a purity lower than this purity. . Similarly, the leakage current is reduced.

[0014]

EXAMPLES The present invention will now be described based on examples. First, a high-purity aluminum foil (purity 9
A roughened surface was prepared by electrochemically etching the surface of 9.99%, 90 μm thick).

A niobium thin film layer was formed on this aluminum foil. The cathodic arc plasma vapor deposition method was used for vapor deposition of the niobium thin film. In the cathodic arc plasma deposition method, a metal target material is used as a cathode under substantially vacuum to cause arc discharge, and the target metal is ionized and evaporated by the energy of the arc current. This ionized metal gas adheres to the material to be processed to which a bias voltage has been applied, and a dense metal thin film layer is obtained. The cathodic arc plasma deposition method is
Since a high temperature ionized metal gas is deposited, it is suitable for forming a high purity metal thin film layer.

In the experiment, the purity of the niobium thin film to be formed was changed by changing the purity of the metal (niobium) target material. Comparative examples are those of the purity of the niobium thin film outside the scope of the present invention,
A target material having a niobium purity of 99.0% was used, and as a result, the purity of the deposited thin film was 99.85%.

In the example 1 of the present invention, a target material having a purity of 99.9% was used. As a result, the purity of the deposited thin film was 99.99%. Further, in Invention Example 2, a target material having a purity of 99.995% was used. As a result, the purity of the deposited thin film was 99.999%. The purity of the deposited thin film can be measured by SIMS (Secondary Ion).
Mass Spectrum) method.

Other vapor deposition conditions are common to the comparative example and the present invention, and are as follows. Chamber pressure: 2 × 10 ⁻³ (Torr) Arc current: 150 (A) Substrate bias voltage: −20 (V) Deposition time: 90 (seconds)

The capacitance value of the vapor deposition foil thus obtained was measured. The capacitance was measured by immersing the electrode foil in an electrolytic solution in which tetramethylammonium was dissolved in γ-butyrolactone (25% by weight solution). Also, for the stability test, the capacitance value after leaving the foil at a high temperature (110 ° C.) for 500 hours was also examined.

Further, in order to use this electrode material on the anode side, the magnitude of leakage current was also measured in a state of being anodized. Conditions for the anodic oxidation, the aqueous solution phosphoric acid (0.1 N, 60 ° C.) foil was subjected to the applied 20 minutes anodic peroxidation voltage of 6V as the anode side in, niobium oxide and metallic niobium layer (Nb ₂ O ₅ ). On this foil
Leak current (2 minutes value) was measured by applying 2V. The results of these measurements are shown in Table 1.

[0021]

[Table 1]

As can be seen from these results, the electrode material of the present invention has a higher capacitance value than the conventional ones,
Moreover, there is little change in capacitance value after being left at a high temperature. Further, the leakage current value measured after the anodic oxidation was also extremely low, indicating that a dense and highly insulating vapor deposition film was obtained.

[0023]

As described above, according to the present invention, it is possible to obtain a stable electrode material having a high electrostatic capacity and little change over a long period of time, and an electrolytic capacitor using this material can be made compact and large. The capacity can be increased.

Moreover, although the electrode material having the thin film formed has a drawback that the leakage current characteristic is inferior, the electrode material of the present invention has a low leakage current value and an electrolytic capacitor having excellent electric characteristics can be obtained.

Claims (1)

Claim: What is claimed is: 1. An electrode material for an electrolytic capacitor obtained by vapor deposition of niobium on the surface of an aluminum or aluminum alloy substrate, wherein the vapor deposition niobium layer has a purity of 99.99%.
The above is an electrode material for electrolytic capacitors characterized by the above.