Properties and Performance of Tantalum Oxide Thin Film Capacitors

Tantalum oxide ~hin film capacitors of approximately 10* ~f were prepared by anodization of sputtered tantalum films and vacuum evaporation of gold counterelectrodes. Initial leakage currents at 75 v d.c. were obtained and the capacitors were placed on a constant voltage life test. The variables studied were anodization voltage (100v-300v), life test voltage (lOv-65v) and life test temperature (RT-110°C). The proportion of test samples meeting a 0.01 ~A leakage current measurement at 75 volts varied from about 90% for films formed at 130 volts to about 100% for films formed at > 165 volts. Marked improvement In life test performance with increasing anodization voltage was observed. For films produced at 165-300 volts no failures were observed in ~ 400 samples for 2500 hours at 50 volts and 85°C. The behavior of leakage current, reverse and forward breakdown voltages, capacitance and dielectric loss as a function of anodization voltage was examined. The data obtained from the former two measurements demonstrate a maximum in these properties in the region of 200 volts and indicate that higher anodization voltages do not lead to any significant improvement in capacitor properties.