Anomalous Currents in Low Voltage Polymer Tantalum Capacitors

Low voltage Polymer Ta capacitors fabricated with porous Ta anodes, anodic oxide films of Ta as a dielectric, and poly(3,4ethylenedioxythiophene) (PEDOT) cathodes were investigated. The polymer cathodes were formed by either pure in-situ polymerization or hybrid polymerization, with in-situ PEDOT inside the porous anodes and a pre-polymerized PEDOT cathode on the external surface of the anodes. Anomalous transient current, DC leakage, and breakdown voltage were observed and investigated at normal and reverse polarities in a broad range of temperatures and voltages. Anomalously high transient current in the ampere range was observed when a pulse of rated voltage at normal polarity (+ on the Ta anode) was applied to the capacitors, and anomalous DC current was observed when rated voltage was applied at low temperature. This effect was significantly more pronounced in the hybrid devices, but significantly decreased in all cases with humidification. The anomalous currents were explained by the presence of dipoles, charged polymer chains, in the conducting polymer cathode at its interface with the dielectric.