Growth Laws of Bilayer Anodized Tantalum Oxide Films Formed in Phosphoric Acid

Experimentally determined growth laws of bilayer tantalum oxide films formed by anodizing sputter-deposited tantalum anodes in a 0.1 M phosphoric acid electrolyte are reported. Transmission electron microscopy, Fourier transform IR reflectance spectroscopy, and wet capacitance measurements are used to measure the growth rates of the inner layer, the outer layer, and the total bilayer oxide thickness in the time domain of . The anodization constants for 250 mV/s potentiodynamic growth in 0.1 M followed by a 50 min hold at the formation voltage are , , and for the total oxide, the inner layer, and the outer layer, respectively. After several days of anodization, the oxide continues to grow, thus confirming the lack of significant tantalum oxide dissolution in nonfluorinated electrolytes. Parametrization of the growth laws allows the ionic currents that are due to the generation of oxygen vacancies and tantalum interstitials to be separately calculated.