JPH03131013A - Manufacture of aluminum electrode for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To reduce treatment time drastically and obtain an anode aluminum electrode for an electrolytic capacitor with a high electrostatic capacity by forming a deposition layer consisting of an oxide of titanium and strontium within an environment which includes oxygen at a specific Torr onto the surface of a highly pure aluminum surface by the cathode arc deposition method. CONSTITUTION:When an arc discharge is generated with a first metal target 10 consisting of titanium and a second metal target 11 consisting of strontium, the arc forms an arc spot on the surface of the targets 10 and 11 and then the target material 10 and the target material 11 are instantly fluxed and evaporated by the arc current energy and at the same time become a metal ion 12 emitted into vacuum. In this case, by applying a bias voltage to a material to be treated 14 consisting of a highly pure aluminum, this metal ion 12 is made contact onto the surface of the material to be treated 14 along with an accelerated reaction gas particle 16, thus generating an intricate film. Entire pressure including oxygen gas within the chamber is to be set to the range of 1X10<-1>-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. Titanium, strontium oxides, or composite oxides thereof are known to exist as inorganic materials with a high dielectric constant. To form such a material on a different material, for example, as described in Japanese Patent Application Laid-Open No. 1-175714, a thin film of strontium titanate is formed on the surface of a dielectric film by methods such as vapor deposition, sputtering, and plasma CVD. It is proposed that. 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. Furthermore, in order to use the deposited metal as a dielectric layer, it was necessary to oxidize the formed thin film to impart insulation properties.

[Problem to be solved by the invention]

This invention was made by focusing on the fact that oxides of titanium and strontium exhibit a higher dielectric constant than aluminum, and both titanium and strontium are deposited as oxide films on the surface of high-purity aluminum by vapor deposition. The idea is to form this layer and use it as a dielectric layer. At this time, the aim is to significantly shorten the processing time by improving the method of forming the 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 aluminum electrodes for electrolytic capacitors, this invention involves vapor deposition of titanium and strontium oxides on the surface of high-purity aluminum in an atmosphere containing oxygen and having a total pressure of I Xl0-' to I Xl0-4 Torr. This is a method for producing an aluminum electrode for an electrolytic capacitor, characterized in that the layer is formed by cathodic arc evaporation. Another feature of this invention is that high-purity aluminum, which is the material to be treated, is heated to 200°C to 450°C. 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 a large arc current flows into this small spot, so the area near the cathode spot is heated to an extremely high temperature, and even high melting point materials such as titanium and strontium melt instantly. Evaporate. The target material that is melted and evaporated simultaneously turns into metal ions and is released into the 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, titanium and strontium are oxidized. Since it is necessary to form a vapor deposited film as an oxide, 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, the selection should be made within a range that does not prevent free metal ions from being deposited on the surface of the treated material, and the range is from lXl0-' to Ixl0-4 Tor at the total pressure including oxygen.
The range is r. In this invention, two metals, titanium and strontium, are used as target materials. However, in the cathodic arc evaporation method, multiple target electrodes can be installed in the processing chamber, so titanium and strontium can be deposited from different targets using the arc. Titanium and strontium are converted into gas particles by electric discharge, and titanium and strontium are mixed in the gas particle state.
It can be deposited on the surface of high-purity aluminum, which is the material to be treated. According to this method, the amounts of titanium and strontium deposited can be set under different deposition conditions, so it is easy to set the composition ratio of titanium and strontium in the deposited film within a desired range. Of course, it is also possible to use a titanium-strontium alloy with a desired composition ratio in advance as a single target electrode, without placing titanium and strontium separately on different targets. 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 etched or left plain. In the present invention, the preferred conditions for cathodic arc evaporation are that the pressure in the chamber is such that the total pressure including oxygen gas is 1Xl0-' to IXl0-4T, as described above.
It is sufficient to set it within the range of orr. Furthermore, in order to adjust the pressure within the above range, in addition to oxygen, argon, helium, nitrogen gas, etc. may be mixed as an inert gas. It is preferable that the evaporation distance is 100 to 500 rrm, the target evaporation rate is IXl0-' to lXl0-'/d·sec, and the deposition amount is lXl0 to 1/d. Further, the thickness of the deposited film is 0.005 to 3 pm, and the deposition time is 0.05 to 30 minutes. In addition, in this invention, in order for the oxidation reaction of titanium or strontium to be vapor-deposited to occur smoothly on the surface of the high-purity aluminum that is the material to be treated, the material to be treated is heated to promote the oxidation reaction on the evaporation surface. is also desirable. From the viewpoint of promoting the oxidation reaction, this temperature is preferably relatively high, but since the material to be treated is high-purity aluminum, it is preferably carried out within the range of 200°C to 450°C.

[For production]

By the cathodic arc deposition method of the present invention, a deposited layer of titanium and strontium 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, a thin film of titanium or strontium oxide, or a composite oxide of both, is formed on the surface of the high-purity aluminum. Since this thin film is insulating and has a higher dielectric constant than aluminum oxide, an aluminum electrode for an anode with a large capacitance value per unit area can be obtained. 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 10 minutes at the most.
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. - As an example of the present invention, a high-purity aluminum foil (purity 99.95%) that has been electrochemically etched using alternating current is cut into 50×10 OffliII pieces as the material to be treated. titanium and strontium were deposited on this surface. The drawings schematically illustrate an apparatus used for cathodic arc deposition. The present invention uses the apparatus shown in the drawings to provide a first metal target (evaporation source) 10 made of titanium and a second metal target (evaporation source) 11 made of strontium.
When an arc discharge is caused by using and as a cathode, the arc forms an arc spot on the surfaces of targets 10 and 11,
Due to the energy of the arc current concentrated at the arc spot, the target materials 10 and 11 are instantaneously melted and evaporated, simultaneously turning into metal ions 12 and being emitted into the vacuum. At this time, by applying a bias voltage to the material to be processed 14 made of high-purity aluminum, the metal ions 12, together with the accelerated reaction gas particles 16, adhere to the surface of the material to be processed 14, forming a dense film. generate. 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, 28 is a gas outlet, and 30 is a vacuum chamber. In the example, aluminum, which is the material to be treated, is heated to 400°C, and the pressure inside the chamber containing oxygen gas is increased to 2 to 10°C.
Set in the range of X 10-” Torr, evaporation distance 2
The current value of the arc power source was 100 A, the evaporation rate was 0.05 μm/min, and cathodic arc deposition was performed for 4 minutes to form a titanium and strontium deposited film with a thickness of 0.2 μm. As a result, the obtained film has a breakdown voltage of 8■ and a capacitance of 0.
．． It was 113m F/c. -Top 1- The same high-purity aluminum as the material to be treated was used as in the example. In this comparative example, no vapor deposited film was formed on the surface.
The aluminum foil surface is anodized using a conventional method.
An aluminum oxide film was formed. Anodizing voltage 8
The capacitance of the film obtained by setting ■ is 0.043 m
It was F/ci. As is clear from these results, it can be seen that high capacitance can be obtained by using the electrode produced by the method of the present invention in an electrolytic capacitor.

【Effect of the invention】

As described above, according to the present invention, by improving the manufacturing method of depositing titanium and strontium on the surface of an aluminum electrode for an electrolytic capacitor in an atmosphere containing oxygen gas to form a deposited film, high capacitance can be achieved. It is possible to obtain an electrode having a high value and to significantly shorten the processing time.

[Brief explanation of the drawing]

The drawing is an explanatory diagram schematically showing a cathodic arc evaporation apparatus used in the present invention.

Claims (2)

[Claims] (1) On the surface of high-purity aluminum, the total pressure including oxygen is 1
A method for manufacturing an aluminum electrode for an electrolytic capacitor, which comprises forming a vapor deposition layer made of titanium and strontium oxides by cathodic arc evaporation in an atmosphere of ×10^-^1 to 1 × 10^-^4 Torr. . (2) High purity aluminum to be treated at 200℃~450℃
2. The method for producing an aluminum electrode for an electrolytic capacitor according to claim 1, wherein the vapor deposition is carried out by heating to .