The Capacitance Recovery Phenomenon in the Ta/PEDOT Capacitor System

The capacitance recovery of Ta capacitor using poly(3,4-ethylenedioxythiophene) (PEDOT) was evaluated. Capacitance recovery is defined as the ratio of the capacitance of Ta/oxide/PEDOT/Ag to that of Ta/oxide measured in aqueous electrolyte solution. The capacitance recovery was strongly dependent on the oxide formation voltage. From the analysis of this dependence we found an additional capacitance in series with the oxide capacitance which was independent of oxide formation voltage, and was present at the oxide/PEDOT interface. This additional capacitance was postulated by the presence of a depletion layer and poor contact because of the presence of polymerization byproduct at the oxide/PEDOT interface. However, the phenomenon of the additional series capacitance did not match well with the depletion layer capacitance calculated from semiconductor theory assumption.