JPH042110A - Manufacture of aluminum electrode for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve an electrostatic capacitance value per a unit area by forming a deposit composed of the nitride of tungsten onto the surface of aluminum having high purity through a cathode arc evaporation method in an atmosphere including nitrogen. CONSTITUTION:A deposit consisting of the nitride of tungsten is formed onto the surface of aluminum having high purity through a cathode arc evaporation method in an atmosphere including nitrogen. A nitriding reaction is executed sufficiently and the quantity of nitrogen gas in a chamber in cathode arc evaporation must be selected within a range, in which evaporation-formation on the surface of a material to be treated of free metallic ions is not prevented, in the quantity of nitrogen gas, and the range is kept within a range of 1X10<-1>-1X10<-4>Torr at total pressure containing nitrogen. Accordingly, the surface of metallic aluminum, on which a natural oxide film is hardly formed and which has high conductivity, is protected stably by a tungsten nitride thin- film as it is, thus acquiring high electrostatic capacitance as the whole electrode.

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 a cathode 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 rectifying and smoothing output, and are 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, quantal, niobium, and titanium. Further, the same type of metal as the anode material is usually used as the cathode electrode material for current collection. However, valve metals generally have an oxide film layer formed on their surfaces due to natural oxidation. This tendency is particularly noticeable in aluminum. Since this natural oxide film is an extremely thin insulating layer, capacitance is also formed on the cathode side, and an electrolytic capacitor is a composite capacitance in which the capacitance on the anode side and the capacitance on the cathode side are connected in series. , the desired capacitance cannot be obtained.Also, if you try to obtain the desired capacitance,
It is necessary to increase the capacitance on the anode side more than necessary. In order to reduce this effect, the capacitance value on the cathode side can be made significantly higher than the capacitance value on the anode side (then the effect of the capacitance on the cathode side can be almost ignored, but
The electrostatic capacitance on the anode side of a low-voltage electrolytic capacitor is quite high, and it is difficult to increase it even higher, and it is inevitable that the capacitance value will decrease due to the combined capacitance. Therefore, in order to increase the capacitance value of the cathode side electrode, there is a method of enlarging the surface area by etching the surface of the cathode electrode. 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. Rather, in order to solve the problem of the decrease in capacitance due to the combined capacitance with the cathode, it is necessary to either prevent the formation of a natural oxide film with a capacitance value on the surface of the cathode, or to prevent the natural oxide film from forming on the surface of the cathode. It is desirable to have a form that is extremely thin and can maintain a high capacity. For this reason, if a metal other than the valve metal is used on at least the surface of the cathode material, an insulating oxide film will not be formed. Therefore, as a means to solve this problem, for example,
As disclosed in Japanese Patent No. 1826, it is known that various conductive metals are vacuum-deposited on the surface of aluminum. Further, in order to form a thin film, in addition to the above-mentioned method of vacuum evaporation, there are various physical methods such as an ion blasting method, a sputtering method, or a plasma CVD method. However, electrolytic capacitors are impregnated with an electrolyte, and problems such as corrosion can occur due to reactions with the electrolyte. Therefore, it is difficult to use materials other than valve metal as the cathode material (the only materials that can be used are platinum, gold, etc.). However, it is almost impossible to use these precious metals as cathodes for current collection due to economic reasons.Moreover, with the above method, the metal vapor deposition film on the aluminum surface is The adhesion was not necessarily sufficient, and there remained room to manufacture better aluminum cathode electrodes for electrolytic capacitors by improving the selection of the material to be deposited and the deposition technique.Furthermore, with the existing deposition techniques mentioned above, Since the processing time was long, production efficiency was also insufficient.

[Problem to be solved by the invention] This invention improves the above-mentioned drawbacks, and improves the capacitance by improving the manufacturing method of aluminum electrodes for electrolytic capacitors, which consists of attaching metal nitride to the surface of high-purity aluminum by vapor deposition. The purpose is to increase the adhesion and density of the deposited film, protect the electrode surface from deterioration, and significantly shorten the processing time. [Means to solve the problem]

In manufacturing aluminum electrodes for electrolytic capacitors, this invention applies a cathodic arc to a vapor-deposited layer of tungsten nitride on the surface of high-purity aluminum in a nitrogen-containing atmosphere with a total pressure of 1X10-1X10-4 Torr. This is a method for manufacturing an aluminum electrode for an electrolytic capacitor, characterized in that it is formed by a vapor deposition method. 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. . According to the usual cathodic arc evaporation method, the evaporation process is carried out in an atmosphere in which a small amount of inert gas such as helium, argon, neon, etc. is present in the chamber, but in this invention, tungsten is nitrided, Since it is necessary to form a deposited film as a nitride, the deposition process is performed with a trace amount of nitrogen gas present in the chamber. The target material that has been melted and vaporized simultaneously becomes metal ions and is emitted into the vacuum. At this time, by keeping the inside of the chamber for vapor deposition at a predetermined pressure atmosphere containing nitrogen gas and applying a bias voltage to the material to be processed, these metal ions are transferred to the material to be processed along with the accelerated reaction gas particles. is deposited as a nitride on the surface of the substrate to form a dense thin film. According to the present invention, as the material to be treated, high-purity foil-like or plate-like aluminum used for the cathode of ordinary electrolytic capacitors 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 may remain plain. In this invention, the preferred conditions for cathodic arc evaporation are such that the amount of nitrogen gas in the chamber is within a range that allows the nitriding reaction to occur sufficiently and does not prevent free metal ions from being deposited on the surface of the material to be treated. should be selected, the range being from lXl0-' to Ix10- at total pressure including nitrogen.
It is in the range of 4 Torr. Further, within the above range, in addition to nitrogen, gases such as argon, helium, and neon can be mixed as an inert gas in order to adjust the pressure. In addition, in this invention, in order for the nitriding reaction of tungsten to be vapor-deposited to occur smoothly on the surface of high-purity aluminum, which is the material to be treated, it is also preferable to heat the material to be treated to promote the nitriding reaction on the evaporation surface. That's true. From the viewpoint of promoting the nitriding reaction, a relatively high temperature is preferable, but since the material to be treated is high-purity aluminum, it is preferably carried out within a range of approximately 450°C.

[For production]

By the cathodic arc deposition method of the present invention, a thin film of tungsten nitride can be formed on the surface of high-purity aluminum. Tungsten nitride has Wz depending on the valence of tungsten.
It can take the form of N, WZ N3, WNZ, etc.
All of them are hard compounds with properties similar to interstitial compounds or intermetallic compounds, and have high electrical conductivity. Since it also has good reactivity with aluminum, a dense thin film with high conductivity is formed on the aluminum surface. As a result, the aluminum electrode has an extremely thin natural oxide film with high capacitance formed on its surface, or in certain minute areas, the surface of metal aluminum, which has high conductivity and almost no natural oxide film is formed, is made of tungsten nitride. It is thought that the thin film provides stable protection and that a high capacitance can be obtained as a whole electrode. Furthermore, tungsten nitride is less likely to react with the electrolytic solution and maintains the electrical characteristics of the electrolytic capacitor stably over a long period of time. Furthermore, according to the method of this invention, since the ionization rate of particles is high, the ion bombardment effect is strong, and the bias effect during coating is also strong.
Coupled with the fact that tungsten nitride has good reactivity with aluminum, this results in a film that has extremely high adhesion to the treated material. Table 1 below 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 the reaction efficiency and improves the adhesion between the aluminum electrode and the nitride of the deposited metal. 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 40 minutes, and the sputtering method takes about 60 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. The drawings schematically illustrate an apparatus used for cathodic arc deposition. According to the present invention, when an arc discharge is caused using a metal target (evaporation source) 10 made of tungsten as a cathode using the apparatus shown in the drawings, the arc forms an arc spot on the surface of the target 10, and the energy of the arc current concentrated on the arc spot causes the arc discharge to occur. The target material 10 instantaneously melts and evaporates, turning into metal ions 12 and being released into a vacuum. At this time, by applying a bias voltage to the treated material 14 made of high-purity aluminum, the metal ions 12 adhere to the surface of the treated material 14 together with the accelerated reaction gas particles 16°, forming a dense Produces a membrane. 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. Then, electrodes for electrolytic capacitors according to the following examples were created using the cathodic arc evaporation apparatus shown in the drawings. (Example) High-purity aluminum foil (purity 99.95%) subjected to electrochemical etching treatment using alternating current was placed in a 50×1
A piece cut into 00 mm was used as a material to be treated, and tungsten nitride was vapor-deposited on the surface. In the example, aluminum as the material to be treated is heated to 300°C, and the total pressure inside the chamber containing nitrogen gas is increased to 5
Set in the range of 10-3 Torr, evaporation distance in order of 200, arc power supply current value of 200 A, evaporation rate of 1000.
person/min, cathodic arc deposition for 2 minutes, 0.2 μm
A tungsten nitride vapor deposited film with a thickness of . (Comparative Example 1) The same high-purity aluminum as in the example was used as the material to be treated, and tungsten was used as the evaporation source in an atmosphere containing nitrogen gas with a total pressure of 2 x IF 3 Torr, with an evaporation distance of 200 mm. Tungsten nitride deposition was performed using the ion blating method for 40 minutes at a speed of 50 people/min.
A 0.2 μm thick tungsten nitride vapor deposited film was formed. (Comparative Example 2) The same high-purity aluminum as in the example was used as the material to be treated. Therefore, in this treated material, the surface was only subjected to electrochemical etching treatment using alternating current. Among these Examples and Comparative Examples, the adhesion force of the vapor-deposited tungsten nitride was measured and the adhesion was examined for those subjected to vapor deposition treatment, and the adhesion force of the Example was 3.3 Kgm5. On the other hand, in Comparative Example 1, 2
．． 4 Kgn+s, which indicates that the thin film obtained by the cathodic arc evaporation method of the present invention has good adhesion. Next, Table 2 shows the results of measuring the capacitance values per unit area of these Examples and Comparative Examples. (Table 2) As can be seen from these results, the capacitance of a conventional aluminum electrode with only an etched surface is significantly lower than that of an electrode with a tungsten nitride layer formed by vapor deposition. I understand that. In addition, all of the tungsten nitride thin films formed by the vapor deposition method show high capacitance values, but the one formed by the cathodic arc vapor deposition method of the present invention achieves almost the same level of capacitance in a shorter time than the conventional method of Comparative Example 1. It can be seen that a thin film can be obtained and the manufacturing efficiency is excellent. Next, in order to investigate the stability of the formed thin film, we created an electrolytic capacitor using these treated materials as actual cathodes.
A lifespan test was conducted to examine changes in characteristics. The electrolytic capacitor we created is an electrolytic capacitor with lead wires in the same direction.The element is made by winding foil electrodes together with a separator and is impregnated with electrolyte.The electrolytic capacitor is housed in a metal case, and the opening is sealed with a rubber seal. be. All of the materials constituting the electrolytic capacitors were common, except that the cathode foil used in the above examples and comparative examples was used. The assembly method is also the same. The electrolytic capacitor has a rated voltage of 6.3 mm, a rated capacitance of 47 μF, and an external dimension of 5 mm in diameter and 7 mm in length. The composition of the electrolytic solution used was 1% by weight of 78% ethylene glycol, 10% by weight of ammonium adipate, and 12% by weight of water, which had a higher water content than the normally used electrolytic solution. be. This is to make the occurrence of hydration deterioration of the electrode foil due to water more noticeable. A rated voltage was applied to this electrolytic capacitor, and a life test was conducted at 110° C. for 500 hours, and the capacitance value and the rate of change between the initial capacitance value and the capacitance value were examined. The results are shown in Table 3. (Table 3) As can be seen from the results, the aluminum electrodes of the present invention are not only those that have been subjected to only etching treatment, but also
It can be seen that compared to those using other vapor deposition methods, there is less surface deterioration and change over time, and the characteristics are stable over a long period of time.

【Effect of the invention】

As described above, according to the present invention, as an electrode for an electrolytic capacitor, it is possible to increase the capacitance value per unit area. A capacitor is obtained. Furthermore, since the electrode surface is protected by tungsten nitride, stable electrical characteristics can be maintained over a long period of time, improving the reliability of the electrolytic capacitor. Further, according to the present invention, since the electrode processing time can be shortened, there is an advantage that production efficiency is improved.

[Brief explanation of drawings]

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

Claims (1)

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