DC BIAS VOLTAGE DEPENDENCE OF THE CAPACITANCE OF ANODISED NIOBIUM

摘要

The capacitance dependence on bias voltage of the oxidised Nb anode bodies was studied after each technological step: the first preforming, the heat treatment, the second preforming, the MnO_2 coverage and on the finished capacitors. The bias voltage dependence occurs by diminution of the polarisation charge caused by neutral oxygen vacancies (V_o~x) which ionise under the effect of the electric field. The bias dependence for anodes in wettest experiments is significant after the preforming, but it becomes negligible after the MnO_2 coverage. This can be explained by the several improving preforming and annealing steps during the MnO_2 coverage, when further healing of the oxide layer takes place.