Thermally assisted tunnelling in polyimide film under steady-state and transient conditions

Electrical conduction in `Kapton' polyimide film is studied under both transient and steady-state conditions. An exponential dependence of the current on the square root of the applied voltage is reported under fast transient conditions (80 μs-2 ms). The coefficient of this dependence is found to be temperature- and time-independent over the range 150-275°C. The DC conduction shows a similar field dependence, but the coefficient is expressed as two factors, one of which is temperature-independent. Evidence is presented to suggest that the DC conduction could be associated with a mechanism of thermally assisted tunnelling, and that the transient conduction could involve tunnelling of electrons between conduction-band-tail states in the insulator.