Non-linear conduction and dispersion in conducting polymers

The conductivity of thin films of conducting polymer deposited between lithographically-fabricated microelectrodes was measured between 100 Hz and 40 MHz. The inter-electrode spacing of 10 μm gave field strengths up to 50 kV/m within the film in response to applied voltages up to 0.5 V. The conductance and capacitance of the films exhibited sample- and counter-ion-dependent degrees of voltage-dependency at frequencies below 1 MHz, but became essentially voltage-independent above about 30 MHz (at room temperature). The disappearance of the voltage sensitivity coincides with a dispersion in the 1-30 MHz range. These results suggest that the low-frequency conductivity of the films is determined by the difficulty involved in inter-granular or inter-domain charge transport