JPH0682587B2 - Solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor having excellent capacitor characteristics, particularly high frequency characteristics.

2. Description of the Related Art In recent years, along with the digitization of electric device circuits, the capacitors used therein have low impedance in the high frequency region, and there is an increasing demand for small and large capacity capacitors.

Conventionally, plastic film capacitors, mica capacitors, and monolithic ceramic capacitors have been used as capacitors for the high frequency region.However, film capacitors and mica capacitors are difficult to increase in capacity due to their large size. The capacitor has the drawback that the smaller the size and the larger the capacity, the worse the temperature characteristics and the cost becomes very high.

On the other hand, known as large-capacity type capacitors include an aluminum dry electrolytic capacitor or an aluminum or tantalum solid electrolytic capacitor. These capacitors can realize a large capacity because the anodic oxide film that serves as a dielectric can be made very thin, but on the other hand, damage to the oxide film is likely to occur, so damage between the oxide film and the cathode can be repaired. It is necessary to provide an electrolyte for this purpose. In an aluminum dry electrolytic capacitor, an etched positive and negative aluminum foil is wound around a paper separator and a liquid electrolyte is impregnated into the separator to be used. For this reason, there is a decrease in capacitance and an increase in loss (tan δ) over time due to electrolyte leakage and evaporation, and at the same time, high-frequency characteristics and low-temperature characteristics are markedly deteriorated due to the ionic conductivity of the electrolyte. It has drawbacks.

For aluminum and tantalum solid electrolytic capacitors,
Manganese dioxide is used as a solid electrolyte in order to improve the drawbacks of the aluminum dry electrolytic capacitors. This solid electrolyte is obtained by immersing an anode element in an aqueous solution of manganese nitrate and thermally decomposing it at a temperature of around 350 ° C.
In the case of this capacitor, since the electrolyte is a solid, there are no drawbacks such as electrolyte outflow at high temperature and deterioration of performance caused by solidification at low temperature, and it has better frequency and temperature characteristics than a capacitor using a liquid electrolyte. However, due to the damage of the oxide film due to the thermal decomposition of manganese nitrate and the high specific resistance of manganese dioxide, the impedance or loss in the high frequency range is higher than that of monolithic ceramic capacitors or plastic film capacitors by one digit or more. It is a value.

In order to solve the above-mentioned problems, an organic semiconductor (7, 7,
It has been proposed to use (8,8-tetracyanoquinodimethane complex). This organic semiconductor can be dissolved in an organic solvent or can be impregnated and applied to the oxide film by means such as melting by heating to prevent damage to the oxide film due to thermal decomposition that occurs when impregnating MnO _2. You can TC
NQ complex has high conductivity and excellent anodizing property.
High-frequency characteristics are good and large-capacity capacitors are possible.

For example, an invention using an organic semiconductor composed of N-n-propyl or N-iso-propylisoquinoline and TCNQ as a solid electrolyte has been filed (Japanese Patent Laid-Open No. 58-17609). According to the invention, the wound aluminum electrolytic capacitor is impregnated with the TCNQ salt by heating and melting the TCNQ salt, whereby a strong bond between the TCNQ salt and the oxide film is achieved, and the high conductivity of the TCNQ salt is achieved. It is said that the aluminum capacitor having significantly improved frequency characteristics and temperature characteristics will be manufactured with the help of the above. The use of such an organic semiconductor based on TCNQ salt as a solid electrolyte has already been filed by the same applicant (Japanese Patent Laid-Open No. 58-176).
09), the TCNQ salt has higher conductivity and higher anodic oxidation ability (repairing action) than manganese dioxide, and therefore has a frequency characteristic higher than that of a solid electrolytic capacitor using manganese dioxide. And excellent temperature characteristics. According to the present invention, the TCNQ salt having cation of isoquinolium whose N-position is substituted with an alkyl group is impregnated by heating and melting the oxide film.

Furthermore, in recent years, proposals have been made to form a polymer of a heterocyclic compound such as pyrrole or thiophene on an anode body and use it for solid electrolysis.

However, in the electrolytic polymerization reaction, a polymerized film cannot be attached without destroying the film on the oxide film serving as a dielectric by the reaction process of electrolytic oxidation of monomers. Further, before forming the oxide film, the electrolytic polymerization film can be applied on the valve metal and then the oxide film can be formed by the chemical conversion reaction. In this case, the chemical conversion reaction is performed through the electrolytic polymerization film. As a result, the electropolymerized film is deteriorated and the adhesion to the valve metal is reduced. Therefore, until now, a method for forming a good electrolytic polymerized film on a valve metal has been difficult.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a solid electrolytic capacitor having excellent high-frequency characteristics, small variations in leakage current and withstand voltage characteristics, and high yield.

Means for Solving the Problems The present invention achieves the above object, and its technical means is to provide a first layer of manganese dioxide formed on a valve metal via an anodized film, and the first layer. Comprising an electrolytically reduced polymerized polymer formed on at least a part of the layer of
And a third layer made of a conductive electrolytically oxidized and polymerized polymer.

Action The present invention treats the oxide film on the valve metal such as Al or Ta with manganese dioxide, then forms the electrolytically reduced polymerized polymer on the defective portion of the oxide film, and then oxidizes the electrolytically oxidized polymerized film. By forming it on the entire surface of the film, it is possible to obtain a solid electrolytic capacitor having high frequency characteristics and low leakage current and high withstand voltage.

The electrolytic reduction polymer of the present invention is preferably acrylic acid ester, metacrylic acid ester, acrylonitrile, or acrylamide, and the conductive electrolytic oxidation-polymerization polymer is obtained from monocor selected from pyrrole, thiophene, or a derivative thereof. It is desirable that the polymer is a polymer.

Examples Examples of the present invention will be described below.

FIG. 1 shows a manufacturing schematic diagram for explaining the structure of the solid electrolytic capacitor in one embodiment of the present invention. As shown in FIG. 1 (a), a foil 1 made of Al, which is a valve metal, having a capacitor anode lead electrode 2 attached thereto is prepared, and first, an etching treatment is performed to increase the surface area. Next, FIG. 1 (b)
To form an oxide film 3 made of Al ₂ O ₃ with an aqueous solution of adipic acid as shown in. The oxide film 3 is formed by a usual method by electrochemical means. Then, it is immersed in an aqueous solution of manganese nitrate and subjected to a thermal decomposition treatment in air at 250 to 300 ° C. to form the MnO ₂ film 4. Next, an electrolytically polymerized film is formed on this surface, but even if a voltage is applied using the anode 2 of the capacitor as a polymerizing electrode, the dielectric film intervenes, so that electrolytic polymerization does not occur and the film does not grow. .
Therefore, as shown in FIG. 2, an electrolytic polymerization electrode 5 for initiating polymerization is provided outside so as to contact the MnO ₂ film 4, and an electrolytic polymerization counter electrode 6 is provided separately from the electrolytic polymerization electrode 5. It was However, if there is a defect in the oxide film, a polymerized film grows from it or the film grows deep in the etching pits. Then, such a portion causes an increase in leakage current and a decrease in breakdown voltage. Therefore, in this embodiment, the electrolytic reduction polymerization polymer film is formed in advance on this defect before the electrolytic oxidation polymerization polymer having excellent conductivity is formed. That is, in the polymerization reaction container 7 shown in FIG. 2, acrylic acid ester, methacrylic acid ester, methaclucentryl,
A polymerization solution 8 made of methacrylamide, acrylonitrile, or acrylamide is prepared, and the Al foil 1 on which the MnO ₂ film 4 is formed is immersed in this solution, and a positive potential is applied to the counter electrode 6 for electrolytic polymerization, and an electrode 5 for electrolytic polymerization is used. By applying a negative potential, the electrolytically reduced polymerized polymer film grows and is doped with cations.

Next, in a polymerization reaction container 7 as shown in FIG. 2, a polymerization solution 8 composed of a supporting electrolyte and a solvent was placed in an electropolymerizable monomer selected from pyrrole, thiophene and their derivatives. The Al foil 1 was immersed in this as shown in the figure, and a voltage higher than the polymerization potential was applied between the counter electrode 6 for electrolytic polymerization and the electrode 5 for electrolytic polymerization. First, a polymerized film is gradually grown in the direction of the surface of the manganese dioxide film 4 starting from this. After the polymerized film completely covers the surface of the manganese dioxide film 4, the electrolytic polymerization reaction is completed. In this process, cations are dedoped from the electrolytically reduced polymer, and the electrical conductivity is increased. Therefore, an electropolymerized film having excellent conductivity is formed at the defective portion of the oxide film, and the increase in leakage current and the decrease in withstand voltage are greatly reduced. Finally,
The surface of the polymer film is washed and dried. Then, although not shown, the lead electrode of the cathode for the capacitor is attached to the polymer film by using a carbon paste and a silver paste. Finally, exterior processing is performed using epoxy and resin. Plural electrodes 5 for electrolytic polymerization may be provided. Further, the counter electrode 6 for electrolytic polymerization may be located at any position apart from the electrode 5 for electrolytic polymerization.
Is preferably smaller than the counter electrode 6 for electrolytic polymerization.

Further details will be described below.

Al foil is normally etched and rated at 16
The one for V, 16 μF was used. After forming a chemical conversion film with an adipic acid aqueous solution, it was immersed in a 30% aqueous solution of manganese nitrate and subjected to thermal decomposition treatment in air at 270 ° C for 15 minutes.

An electrolytic reduction polymerization solution was prepared from methyl methacrylate (0.5M / l), tetraethylammonium perchlorate (0.1M / l) and acetonitrile. The electrolytic oxidation polymerization solution was prepared from pyrrole (0.5 M / l), tetraethylammonium paratoluene sulfonate (0.1 M / l), and acetonitrile.

First, an electrolytic reduction polymerization reaction was carried out for 5 minutes by applying a voltage of 7 V between the electrodes using a platinum wire as an electrode at the starting point of electrolytic polymerization and a platinum plate as a counter electrode. Then, after washing with alcohol, an electrolytic oxidative polymerization reaction was carried out for 30 minutes with the same electrode configuration. Then, it is washed with alcohol and dried. Next, a cathode lead electrode is attached using aqua duck and silver paste. Finally, the exterior was covered with epoxy resin. Then 80
An etching treatment of applying 20 V for 2 hours at 0 ° C. was performed.

Next, the characteristics of this capacitor are shown in the table. The results in the table show the average value of 10 samples, and the liquid volume is 10 μF (120H
z).

As is clear from the table, for example, the capacitance value at 120Hz is
Very high at 9.5 μF (normal solid capacitors such as TCN
7μF for Q salt), series resistance at 500KHz (E
SR) is as small as 30mΩ among Al electrolytic capacitors and has excellent high frequency characteristics. Also, the leakage current is 0.2μ
It was a very small value as A or less. Furthermore, when the electrolytic reduction polymer is not treated, there are 2 to 3 out of 10 leakage currents that are in the order of mA or more, and some even break down at a withstand voltage of 16V or less. However, by performing the treatment, such defects were not seen and the yield was improved.

EFFECTS OF THE INVENTION In summary, the present invention provides a first layer formed by manganese dioxide treatment on an oxide film, a second layer formed of an electrolytic reduction polymer provided so as to cover at least a part of the first layer, And a solid electrolytic capacitor provided with a third layer made of an electro-oxidatively polymerized polymer having excellent conductivity, which is excellent in high frequency characteristics, low in leakage current, and high in withstand voltage. Have.

[Brief description of drawings]

1 and 2 are explanatory views showing the procedure of the method for manufacturing a solid electrolytic capacitor in one embodiment of the present invention. 1 ... Al foil, 2 ... Anode lead electrode, 3 ... Oxide film,
4 ... MnO ₂ film, 5 ... Electropolymerization electrode, 6 ... Electropolymerization counter electrode, 7 ... Polymerization reaction vessel, 8 ... Polymerization solution.

Claims (2)

[Claims] 1. A first layer made of manganese dioxide formed on a valve metal via an anodic oxide film, and a second layer made of an electrolytically reduced polymer provided on at least a part of the first layer. And a third layer made of a conductive electrolytically oxidatively polymerized polymer. 2. A polymer obtained from a monomer selected from acrylic acid ester metal acid ester, acrylonitrile, acrylamide as the electrolytic reduction polymer, and conductive electrooxidative polymerization polymer such as pyrrole, thiophene, or a derivative thereof. The solid electrolytic capacitor according to claim 1, wherein