Measured and simulated transient current in polyethylene terephthalate films below and above the glass transition temperature

Charging and discharging current were measured in polyethylene terephthalate films (25 μm) with electrical field ranging from 24 to 72 MV/m and temperature between 40 and 140°C. At temperatures far below the glass transition, the current behaviour was interpreted in term of dipolar mechanisms. While, in rubber state, the current deviate from the well-known Curie-Von Schweidler law. This behaviour was explained, assuming an additional current, due to charge injection at the metal-insulator interface. Numerical simulation, when taking into account these two components, can reproduce the change in the current-time shape. Comparison between measured and calculated current gave a good agreement.