Formation and Capacitance of Nb2O5 Thin Film on Aluminum Foil by Sol-Gel Process.

Abstract

Nb2O5 thin films were formed on aluminum foils by a sol-gel process in order to increase the capacitance of the aluminum foils which are used as aluminum electrolytic capacitors. Investigations focussed on the preparation and characterization of the coating solution, the formation of Nb2O5 thin films on aluminum foils, and the heat treatment and anodization of the films. The phase transition and electrical properties, such as capacitance, leakage current, and withstand voltage of the Nb2O5 thin films were also measured. The Nb2O5 thin films annealed at temperatures below 550°C were found to be amorphous, but they were crystallized to the orthorhombic phase by annealing at temperatures higher than 580°C. The capacitance of the coated samples increased with an increase in the thickness of the formed Nb2O5 thin films, but an increase in leakage current and a decrease in withstand voltage were also observed in those samples. The product of capacitance and withstand voltage of the aluminum foils coated with Nb2O5 thin film increased by 30 to 70% compared with those of the non-coated foils.