JPH0563009B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a solid electrolytic capacitor, and particularly to a method for forming a semiconductor layer in a capacitor in which the semiconductor layer is a polymer film of a solid electrolyte. [Prior Art] Conventionally, in a solid electrolytic capacitor whose anode body is made of a valve-acting metal such as aluminum or tantalum, inorganic semiconductor manganese dioxide MnO 2 and organic semiconductor manganese dioxide MnO ₂ are used as the solid electrolyte of the semiconductor layer.
A method using TCNQ (tetracyanoquinodimethane) complex salt is well known. The above two types of solid electrolytes are
Both are created by repeated soaking and heating solidification. Since such a process is repeated, the process is complicated and it is difficult to control the thickness of the semiconductor layer. Manufacturing small-capacity capacitors is difficult because the process is complicated and productivity is low, and when manufacturing large-capacity capacitors, heating is done at high temperatures, so the effect of thermal distortion is large and it is difficult to obtain a good semiconductor layer. I couldn't do it. Since the above two types of solid electrolytes are immersed and solidified by heating at a considerably high temperature, it is difficult to carry out a process in which a pattern is formed on the surface of the anode body using a resist member and a semiconductor layer is locally formed.
Furthermore, since the solid electrolyte is a granular material, a process of separating and cutting the solid electrolyte into chips after forming it cannot be carried out. As described above, the degree of freedom as a process is low, and it is not possible to form a large pattern and then disassemble it into chips, and currently only medium-capacity capacitors can be realized. However, if a conductive polymer membrane is used as the solid electrolyte, most of the above problems can be solved.
With a large degree of freedom in process selection and appropriate processes, it is possible to manufacture a wide range of products from chip-type small capacitance capacitors to large capacitance capacitors. [Problems to be solved by the invention] Polymer films are formed by electrolytic oxidative polymerization of heterocyclic compounds such as pyrrole and thiophene. Although it can be formed well on metal surfaces, it is not good to form it on the anode body. Although the reason for this is not clear, it is inferred as follows. The electrolytic oxidation polymerization reaction is carried out via an insulating anodic oxide film provided on the surface of the metal anode body, which has a valve effect.At the same time as the polymerization reaction, an oxidation reaction occurs on the anode body surface, and due to competition between both reactions, polymerization This is thought to be due to the effect that when the polymer has a low molecular weight during the reaction, it cannot stay near the anode surface and diffuses into the electrolyte. Note that it is not possible to directly determine whether the semiconductor layer formation is good or bad, so by verifying the capacitor characteristics,
Determined by withstand voltage and equivalent series resistance. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method for forming a polymer film of a solid electrolyte that provides good characteristics as a capacitor on a valve metal anode body whose surface is anodized. . [Means for Solving the Problems] In the present invention, pyrrole, which is a heterocyclic compound, and a specific derivative thereof are used as the polymer membrane of the solid electrolyte. That is, the following heterocyclic compounds (X: H, -CH ₃ or -CH ₂ CH ₃ Y: H, -CH ₃ or -CH ₂ CH ₃ ) and a supporting salt within the temperature range of -25°C to -45°C. Electrolytic oxidation polymerization is performed to form a solid electrolyte polymer membrane. [Operation] As will be explained in the examples below, a capacitor using a semiconductor layer formed by the above method provides good electrical characteristics. This is because by lowering the temperature of the electrolyte, the molecular movement of monomers or low polymers on the surface of the anode body slows down, and they do not diffuse into the solution but remain near the surface, which prevents the formation of a polymer film. It is presumed that this is because the process is carried out smoothly and a good, uniform semiconductor layer is obtained. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. In the following example, aluminum was used as the anode body. Aluminum etched foil with a roughened surface was cut into 10 mm x 50 mm pieces, and constant-voltage chemical conversion was performed in an adipic acid-based chemical solution at each voltage shown in Table 1. Then, an anodic oxide film is formed on the surface of the foil.

[Table] Next, anodic oxidation polymerization of a polypyrrole film was carried out in an electrolytic solution in which 0.05 mol (3.0 g) of pyrrole and about 0.02 mol (6.0 g) of ammonium borodisalicylate as a supporting salt were dissolved in acetonitrile 1 as a solvent. Do this. FIG. 1 schematically shows the situation in which this process is carried out. An oxidized aluminum etched foil 1 is impregnated with the electrolyte 2, connected to the anode of a battery 4, and the aluminum etched foil 1 is impregnated with the electrolytic solution 2. two stainless steel plates 3 facing each other on both sides of
and connect it to the cathode of battery 4. Electrolyte 2 is cooled to -40°C and kept constant during this process. The polymerization reaction is carried out by continuously flowing a current of about 30 mA for 10 minutes. After completing the reaction, the foil coated with the polypyrrole film is washed with pure water, and then reconversion is carried out in the same adipic acid-based conversion solution at a voltage that is about 3/4 of the conversion voltage shown in Table 1. This is to prevent defects from occurring in the oxide film, and to prevent such accidents. Next, the reconstituted foil is washed with pure water, dried, and silver is deposited by vacuum evaporation, and a cathode lead is drawn out with silver paste to form a capacitor. Figure 2 is a cross-sectional view of the capacitor, and 6 is an aluminum etched foil whose tip becomes an anode lead. The capacitor component part is formed of an aluminum oxide film 9, a polypyrrole film 8, a silver vapor deposited film 7, and a silver paste 10.
The cathode lead 5 is connected by. The electrical characteristics of the capacitor are shown in Table 2. This data indicates that Cap is the capacitance per unit area (μF/
cm ² ), the loss angle tan δ is measured at a frequency of 120 Hz, and an applied voltage
Measured value of 1.0v (AC), leakage current is 1/2 of formation voltage
The value when applied for 2 minutes, ESR is equivalent series resistance and is the measured value at 100KHz.

[Table] Figure 3 shows the frequency/impedance (f-Z) characteristics, and is the data for the 20V chemical products in Table 2. The ideal line determined as pure capacitance and the actual measured value match up to approximately 300KHz. At a rated voltage of 10V with a similar capacity value using the conventional method
The improvement effect is remarkable when compared with an aluminum electrolytic capacitor with a cap of 22μF. In the above example, the electrolyte temperature was about -40°C, but Table 3 shows the results of a second example in which a capacitor was manufactured at -30°C and all other steps were the same. The measurement characteristics are the same, and almost the same results are obtained. In addition, when a methyl group or the like is introduced into the 3rd and 4th positions of a heterocyclic compound, the polymerization reaction positions are fixed at the 2nd and 5th positions, and the molecular structure of the resulting polymer becomes more conductive.

[Table] [Effects of the Invention] As explained in detail above, a metal with a valve action is used as an anode body, and the oxide film surface of the anode body is exposed to a low temperature in an electrolytic solution containing the heterocyclic compound pyrrole or a pyrrole derivative. A polymer film of a solid electrolyte is formed by an electrolytic oxidation polymerization reaction, and a capacitor with good characteristics can be obtained by using this polymer film as a semiconductor layer. Electrolytic oxidation polymerization is performed at a temperature range of -25°C to -45°C to obtain a polymer film with good properties. Regarding the temperature range, temperatures below the lower limit slow the reaction rate, and temperatures above the upper limit inhibit polymer film formation. Although ammonium borodisalicylate was used as the supporting salt in the electrolytic solution in the examples, any commonly used supporting salt may be used.

[Brief explanation of drawings]

The drawings relate to examples, and FIG. 1 is a diagram showing the state of the semiconductor layer forming process of a solid electrolytic capacitor according to the present invention, FIG. 2 is a cross-sectional view of an example of an aluminum solid electrolytic capacitor, and FIG. 3 is a diagram showing the f-
FIG. 3 is a diagram showing Z characteristics. 1...Anodized aluminum etched foil, 2...
...Electrolyte, 3...Stainless steel plate, 4...Battery, 5
... Cathode lead, 6 ... Aluminum etched foil, 7 ... Silver vapor deposition film, 8 ... Polypyrrole film, 9
...Aluminum oxide film, 10...Silver paste.

Claims (1)

[Scope of Claims] 1. In manufacturing a solid electrolytic capacitor, in the step of forming a semiconductor layer on the anodic oxide film on the surface of the anode body, a heterocyclic compound represented by the following (X: H, -CH ₃ or -CH ₂ CH ₃ Y: H, -CH ₃ or -CH ₂ CH ₃ ) and a supporting salt within the temperature range of -25°C to -45°C. A method for forming a semiconductor layer of a solid electrolytic capacitor, which comprises performing electrolytic oxidation polymerization to form a polymer film of a solid electrolyte.