D‐C Field Dependence of Tantalum Film Capacitors

The capacitance of tantalum film capacitors changes on the order of 1 percent when a field of a few MV/cm is applied. It is shown that the C(E) dependence of anodic Ta/sub 2/O/sub 5/ is produced by at least three separate physical processes. An equation for C(E) is given in which each process is represented by one term. The effects on each process of oxide thickness, anodization soak time, counterelectrode material, nitrogen doping, heat treatment, measurement frequency and temperature, and the rate of rise of bias voltage during measurement are discussed. It is shown that one of the processes affects the capacitance through a field-dependent bulk polarizability. The other two processes may also involve field-dependent polarizability, but there is evidence that one or perhaps both of them are produced by a change in the oxide thickness with field. A physical model for the asymmetry in C(E) is proposed. 9 figures. (auth)