EIS Study of Oxide Layer in Porous Tantalum

Electrochemical impedance spectroscopy is used to study the effect of potential (E) on capacitance (C) of porous tantalum coated with a layer of amorphous Ta₂O₅. It is shown that there is a positive linear dependence 1/C² in a wide range of potentials, and its slope can be used to control an oxide layer in porous tantalum. It is established that the transformation of the oxide layer during annealing in the temperature range 100–700°C strongly affects 1/C²(E)-graphics. Annealing at temperatures of 100–500°C raises the concentration of oxygen vacancies in the oxide layer due to partial transfer of oxygen into tantalum, resulting in lower slope of the 1/C²(E) plots as compared with initial non-annealed sample. After annealing at temperatures of 600 and 700°C, a TaO phase forms in the oxide film, accompanied by a strong increase in capacitance and a weak dependence on potential due to the emergence of a high concentration of donors in the oxide film. The promise is shown of using 1/C²(E) dependences to control a layer of oxide in porous tantalum, which could be useful in tantalum capacitor technology.