1. Field of the Invention
The present invention relates to an electrolytic capacitor and a fabrication method therefor, the electrolytic capacitor in which a dielectric layer is formed by anodically oxidizing an anode on a surface of the anode. More particularly, the invention relates to an electrolytic capacitor characterized in that anodic oxidation is easily carried out in forming a dielectric layer by anodically oxidizing an anode of titanium or titanium alloy on a surface of the anode.
2. Description of the Related Art
Recently, miniaturization of electronic machines has been bringing about a demand for a small-sized capacitor of large capacity. As such a capacitor, an electrolytic capacitor in which a dielectric layer is formed by anodically oxidizing an anode on a surface of the anode is being developed.
A capacitor employing tantalum or niobium as an anode is known as such a capacitor. However, such a capacitor has a problem in its high cost as a result of tantalum or niobium being expensive. Also, there is a limit to get a small-sized capacitor of large capacity because dielectric constant of a dielectric layer which is formed by anodically oxidizing an anode of tantalum or niobium is not always high.
Therefore, more recently, an electrolytic capacitor employing titanium as an anode and forming a dielectric layer of titanium oxide by anodically oxidizing the anode is proposed as disclosed in JP-A-5-121275.
The dielectric layer of titanium oxide which is formed by anodically oxidizing the anode employing titanium has remarkably high dielectric constant in comparison with a dielectric layer formed by anodically oxidizing an anode employing tantalum or niobium. Consequently it is possible to obtain a smaller-sized capacitor of larger capacity.
However, when said anode employing titanium is anodically oxidized, it takes exceedingly long time to form a dielectric layer of titanium oxide. The reason is that a speed of anodic oxidation goes down because titanium oxide is crystallized in anodic oxidation and electrical insulation is reduced.