JPH0414809A - Manufacture of aluminum electrode for electrolytic capacitor use - Google Patents

Abstract

PURPOSE:To obtain an electrode whose electrostatic capacitance value is high and to sharply shorten the treatment time by a method wherein a vapor-deposition layer composed of an oxide of tungsten is formed, by using a cathode arc vapor-deposition method, on the surface of high-purity aluminum in an atmosphere whose total pressure including oxygen is a specific value. CONSTITUTION:High-purity aluminum is used as a material to be treated; the surface of the aluminum is cleaned in advance by a degreasing treatment or the like. Since a very small amount of oxygen exists in an atmosphere to form a vapor-deposition layer, an oxide of tungsten is formed on the surface of the high-purity aluminum. Especially, an oxide having a WO3 structure out of oxides of tungsten increases the permeability on the surface of the aluminum and contributes toward increasing capacitance. Consequently, in order to form the vapor-deposition layer mainly of the oxide having the WO3 structure, a vapor-deposition treatment is executed in such a way that a very small amount of oxygen exists inside a chamber. The amount of oxygen gas inside the chamber is set to a range in which an oxidation reaction is executed sufficiently and which does not prevent extricated metal ions from being vapor- deposited and formed on the surface of the material to be treated; a total pressure including oxygen is set at 1X10<-2> to 1X10<-4>Torr.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method of manufacturing an aluminum electrode used in an electrolytic capacitor, and more particularly to a method of manufacturing a high-purity aluminum electrode used as an anode electrode having a dielectric layer formed on the surface.

[Conventional technology]

Electrolytic capacitors are small, large-capacitance, inexpensive, and have excellent characteristics for applications such as smoothing rectified output, and are one of the important components of various electrical and electronic devices. Electrolytic capacitors generally use a so-called valve metal such as aluminum on which an insulating oxide film can be formed as an anode, the insulating oxide film is used as a dielectric layer, and an electrolyte is placed between the cathode electrode for current collection. It has a structure in which a capacitor element is created by interposing it, this element is housed in an outer container, and lead wires are provided for electrically connecting the electrodes to the outside. As mentioned above, the anode materials used include aluminum, tantalum, niobium, and titanium. Further, the same type of metal as the anode material is usually used as the cathode electrode material for current collection. The valve metal for the anode needs to have a high capacitance value per unit electrode area in order to miniaturize and increase the capacity of electrolytic capacitors. Conventionally, in order to increase the capacitance value of an electrode, there is a method of enlarging the surface area by etching the electrode surface. However, although this technique for increasing surface area is now highly sophisticated, it is becoming increasingly difficult to dramatically increase the capacitance of electrolytic capacitors using this technique alone. Therefore, in order to increase the capacitance, it is possible to increase the dielectric constant of the dielectric oxide film formed on the electrode surface. However, normally, the value is determined by the specific dielectric constant of the oxide of the valve metal that is the anode material, and there is little room for change. In order to increase the dielectric constant of the dielectric oxide film layer on the anode surface, a substance with a high dielectric constant different from that of the base anode metal is formed in place of part or all of the anode's insulating oxide film. It is possible to do so. In order to form a substance different from the base material on the base material, for example, as disclosed in Japanese Patent Application Laid-open No. 1-175714, strontium titanate is formed on the surface of the dielectric film by methods such as vapor deposition, sputtering, and plasma CVD. Those that form a thin film, those that perform chemical conversion treatment after vapor deposition of metal in an inert gas as in JP-A-59-167009, and those that form aluminum-titanium by ion blating as in JP-A-63-306,614. A method has been proposed in which an alloy layer is formed and anodized (chemical conversion) treatment is performed. However, with the method described above, the adhesion of the thin film to the aluminum surface is not necessarily sufficient, and there is still room to improve the vapor deposition technique to produce a better aluminum anode electrode for an electrolytic capacitor. Further, the method using the above-mentioned vapor deposition technique requires a long processing time, and therefore is insufficient in terms of production efficiency.

[Problem to be solved by the invention]

Tungsten oxides or composite oxides thereof are known to exist as inorganic materials with a high dielectric constant. Therefore, the present invention aims to form a tungsten oxide film on the surface of high-purity aluminum by vapor deposition, and use this as a dielectric layer. The aim is to significantly shorten the processing time by improving the method for forming a deposited film, and to obtain an anode aluminum electrode for an electrolytic capacitor that has high capacitance based on a high dielectric constant.

[Means to solve the problem]

In manufacturing an aluminum electrode for an electrolytic capacitor, the present invention applies a total pressure containing oxygen to the surface of high-purity aluminum in the range of lXl0-'' to 1.
This method of manufacturing an aluminum electrode for an electrolytic capacitor is characterized in that a deposited layer of tungsten oxide is formed by cathodic arc deposition in an atmosphere of 4 Torr. The cathodic arc evaporation method utilizes the cathodic arc discharge phenomenon with the target side as the cathode to locally melt and evaporate the target material and deposit it on the surface of the material to be processed. A very small cathode bright spot is created on the side (target), and as a large arc current flows into this small spot, the area near the cathode spot is heated to an extremely high temperature, instantly melting and vaporizing high melting point materials such as tungsten. . The target material that is melted and evaporated simultaneously turns into metal ions and is released into a vacuum. At this time, by applying a bias voltage to the material to be processed, the metal ions, together with the accelerated reaction gas particles, adhere to the surface of the material to be processed, producing a dense vapor deposited film. According to the normal cathodic arc evaporation method, the evaporation process is carried out in an atmosphere in which a small amount of inert gas such as argon or nitrogen is present in the chamber, but in this invention, tungsten is oxidized, Since it is necessary to form a vapor deposited film as a product, the vapor deposition process is performed with a trace amount of oxygen gas present in the chamber. The amount of oxygen gas in the chamber is such that the oxidation reaction is sufficient.
Moreover, it should be selected within a range that does not prevent free metal ions from being deposited on the surface of the material to be treated, and the preferable range is I x 10-'' to I x at the total pressure including oxygen.
It is 10-2 to 1×10-4 Torr. According to the present invention, as the material to be treated, high-purity foil-like or plate-like aluminum, which is used for the cathode of an ordinary electrolytic capacitor, can be used. It is desirable that the aluminum surface be cleaned in advance by degreasing or the like. Further, the aluminum surface may be subjected to an etching treatment or may be left blank. In the present invention, other preferable conditions for cathodic arc evaporation include that the pressure in the chamber is such that the total pressure including oxygen gas is 1X10-2 to IX10 as described above.
The pressure may be set within the range of -2 to 1.times.10.sup.-4 Torr, but within the above range, inert gas such as argon, helium, nitrogen gas, etc. may be mixed in addition to oxygen to adjust the pressure. Also, the evaporation distance is 50 to 400 m1
However, it depends on the device structure and is not necessarily limited to this range. Further, the thickness of the deposited film is 0.05 to 5 μm, and the deposition rate is 0.01 to 0.
．． The deposition time may be 5 μm/min and the deposition time may be about 0.05 to 30 minutes. In addition, in this invention, in order for the oxidation reaction of the tungsten to be vapor-deposited to occur smoothly on the surface of the high-purity aluminum that is the material to be treated, it is also preferable to heat the material to be treated to promote the oxidation reaction on the evaporation surface. That's true. From the viewpoint of promoting the oxidation reaction, a relatively high temperature is preferable, but since the material to be treated is high-purity aluminum, the range is up to about 450°C.

[For production]

By the cathodic arc deposition method of the present invention, a tungsten deposited layer can be formed on the surface of high-purity aluminum. At this time, since a trace amount of oxygen exists in the atmosphere in which the vapor deposition layer is formed, tungsten oxide is formed on the surface of the high-purity aluminum. Tungsten oxide is W2C, WOz, WO3
In addition to these, there are other substances called homologous oxides. Two or more types of structures may coexist depending on the deposition conditions. Especially W.O.
3 structure exhibits a high dielectric constant of about 10' at room temperature, increases the dielectric constant of the aluminum surface, and contributes to an increase in capacitance. Therefore, it is preferable to select vapor deposition conditions such that an oxide having a WO3 structure is mainly formed in the vapor deposited layer. However, tungsten oxide has a high dielectric constant and at the same time exhibits relatively high electrical conductivity, including the above-mentioned WO3 structure. Therefore, after forming the vapor deposition layer of tungsten oxide, it is desirable to perform oxidation treatment such as anodization treatment on the aluminum base material to form an insulating aluminum oxide layer. According to the method of the present invention, since the ionization rate of the particles is high, the ion bombardment effect is strong, and the bias effect during coating is also strong, resulting in a film that has extremely high adhesion to the treated material. The following table shows a comparison of the ionization rate and particle energy of the cathodic arc evaporation method of the present invention and the conventional ion blating method and sputtering method on a metal to be treated. As described above, the cathodic arc deposition method has a significantly higher ionization rate and higher ion energy than other methods, which improves reaction efficiency and improves the adhesion between the aluminum electrode and the deposited metal or its oxide. In addition, the density can be significantly improved. Regarding the processing time, according to the cathodic arc evaporation method of the present invention, the processing can be completed in about IO minutes at the longest.
The ion blasting method takes about 20 minutes, and the sputtering method takes about 50 minutes, both of which take a considerable amount of time compared to the method of the present invention.

【Example】

The present invention will be explained below based on Examples. (Example) First, as an example of the present invention, high-purity aluminum foil (purity 99, 95%) that had been electrochemically etched using alternating current and cut into 50 x 100 mm pieces was used as the material to be treated. Then, tungsten oxide was deposited on this surface. The drawings schematically illustrate an apparatus used for cathodic arc deposition. In this invention, when an arc discharge is caused by using the apparatus shown in the drawings as a metal target (evaporation source) made of tungsten and a cathode of 10 cm, the arc is caused by a metal target (evaporation source).
An arc spot is formed on the surface of -10, and the energy of the arc current concentrated on four arc points causes the surface of the metal target 10 to instantaneously melt and evaporate into metal ions 12, which are emitted into the vacuum. At this time, 5, the material to be treated 14 made of high-purity aluminum
By applying a bias voltage to the metal ion 12, the metal ions 12, together with the accelerated reaction gas particles 16, adhere to the surface of the material to be treated 14, forming a dense film. In the drawings, 18 and 20 are arc power sources, 22 is a bias power source, 24 is a rotary table, 26 is a gas inlet L], 28 is a gas outlet, and 30 is a vacuum chamber. In the example, aluminum as the material to be treated was heated to 400°C. The pressure horn in the chamber containing oxygen gas is
X 101 to iox 1O-3 Torr, firing distance 200m, arc t#i current value 10, OA, evaporation rate 0°05μm/min, cathodic arc evaporation for 4 minutes, 0 A tungsten oxide smoked film with a vapor deposition thickness of .2 μm was formed. In addition, after forming the vapor deposited film, 8
Anodic oxidation treatment was performed at a voltage of (2). This result 1. The resulting film had a breakdown voltage of 8 .mu. and a capacitance of 0.102 m F /cd. (Comparative example) The high-purity aluminum used as the material to be treated was the same as in the example.5 In this comparative example, a vapor-deposited film was formed on the surface, and the surface of the full-minilum foil was anodized by a conventional method. After treatment, a film of aluminum oxide was formed. The capacitance of the film obtained by setting the anodic oxidation voltage to 8■ is O,
It was 043rn F/cd. It is clear from these results that high capacitance can be obtained by using the electrode prepared by the method of the present invention in electrolysis.

【Effect of the invention】

As described above, according to the present invention, high static electricity can be achieved by improving the manufacturing method in which tungsten is deposited on the surface of an aluminum electrode for an electrolytic capacitor in an atmosphere containing oxygen gas to form a °C vapor-deposited film. Since an electrode having a capacitance value can be obtained, the processing time can be significantly shortened.

[Brief explanation of drawings]

The drawing is an explanatory diagram showing the outline of the cathode a'' vapor deposition apparatus used in the present invention. 10... Metal target (evaporation source) 12... Metal ions 14... Material to be treated 16. ...Reactive gas particles 18...Arc power source 20...Arc power source
22...Bias power supply 24...Rotary table
26...Gas population 28...Gas output 1 unit 30
...Vacuum chamber 18, Noah~ri 1;;! χ1ノ! 1

Claims (1)

[Claims] (1) On the surface of high-purity aluminum, the total pressure including oxygen is 1
A method for producing an aluminum electrode for an electrolytic capacitor, comprising forming a deposited layer of tungsten oxide by cathodic arc deposition in an atmosphere of x10^-^2 to 1 x 10^-^4 Torr.