Thermally stimulated current in polypropylene films charged in strong electric fields

Abstract

We have observed a unique feature of the thermally stimulated depolarization (TSD) current in polypropylene (PP) films polarized in strong electric fields (up to 1–2 MV/cm). The direction of the TSD current is the same as the direction of the charging (polarizing) current, and the shape of the TSD current curve is much different from the standard curve. We show by computer model that these features can be explained by charge carrier injection in the film by charging from both electrodes. Both the charging curve shape and TSD current direction are explained by a model in which injected carriers form charged regions inside the film at a distance from the electrodes of one-fourth the thickness of the dielectric.