Preparation and characterization of Nb2O5–Al2O3 composite oxide formed by cathodic electroplating and anodizing

Al foil was coated with niobium oxide by cathodic electroplating and anodized in a neutral boric acid solution to achieve high capacitance in a thin film capacitor. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed the niobium oxide layer on Al to be a hydroxide-rich amorphous phase. The film was crystalline and had stoichiometric stability after annealing at temperatures up to 600 °C followed by anodizing at 500 V, and the specific capacitance of the Nb2O5–Al2O3 composite oxide was approximately 27% higher than that of Al2O3 without a Nb2O5 layer. The capacitance was quite stable to the resonance frequency. Overall, the Nb2O5–Al2O3 composite oxide film is a suitable material for thin film capacitors.