Anodically formed oxide films on niobium: Microstructural and electrical properties

The electrical and structural properties of nanoscale niobium pentoxide (Nb₂O₅) dielectric layers in niobium-based solid electrolyte capacitors were studied. The Nb₂O₅ layers are formed by anodic oxidation of Nb-powder compacts. Capacitance measurements show a strong bias-voltage dependence of the capacitance after anodization. Heat treatments at temperatures up to 320 °C, which are applied in the capacitor-production process, lead to an increase of the capacitance and a reduction of the bias dependence. Based on the electrical and structural properties, which are characterized by electron microscopic techniques, a model is presented which explains the behavior of the specific capacitance after the various processing steps.