Electrical Characterization of High Voltage Polymer Tantalum Capacitors

Current-voltage measurement results on high voltage Ta capacitors with pre-polymerized intrinsically conductive polymer cathodes are reported in this paper. The Ta/Ta2O5/polymer capacitors exhibited relatively low leakage currents in the range of −50 to 125 V at room temperature. Typical leakage current at 125 V normal polarity (+ on the Ta anode) was less than 2 nA/cm2 while at −50 V the leakage was less than 1 μA/cm2. These low leakage currents over such a large range of applied bias were observed in polymer Ta capacitors for the first time. The leakage current mechanism at inverse bias (− on the Ta anode) was found to be consistent with field-assisted thermal emission, the Poole-Frenkel effect, while the mechanism at normal bias was consistent with ohmic hopping. These results are shown to be essentially due to the potential barrier formed at the interface between the dielectric and the pre-polymerized polymer cathode, which is polarity dependent. Such devices have potential applications as high working voltage Polymer Ta capacitors.