Recently, a solid electrolytic capacitor is often used in a power supply circuit or around a central processing unit (CPU) of a personal computer or the like, and reduction in equivalent series resistance (ESR) is demanded in response to the miniaturization thereof and increase in frequency. One example of electrical characteristics of the solid electrolytic capacitor is a withstand voltage characteristic. The withstand voltage characteristic depends on the thickness of the dielectric film of the solid electrolytic capacitor. When an aluminum solid electrolytic capacitor where the dielectric film is formed by anode oxidation is used, for example, the thickness of the dielectric film is proportional to the voltage of anode oxidation. Therefore, thickness increase of the dielectric film also increases the withstand voltage.
Such a conventional solid electrolytic capacitor basically includes an anode formed of a valve metal having a porous layer, a dielectric film formed on a surface of the porous layer of the valve metal, and a solid electrolyte layer of a conductive polymer formed on the dielectric film. In the conventional solid electrolytic capacitor, as disclosed in Japanese Patent Unexamined Publication No. 2003-158043 for example, a single layer of conductive polymer is used as the solid electrolyte layer.
When a defect occurs in the dielectric film of the conventional solid electrolytic capacitor, leakage current generates heat in the defect part. Generally, a conductive polymer is made insulated by the heat generation caused by the leakage current, but electric short circuit may occur because the withstand voltage of the formed insulator is low. Especially, in an electronic circuit requiring high rated voltage, the short circuit causes a serious problem.