Trap capture properties of space charge and void breakdown charge in a cellular polypropylene electret film

Abstract

The following aspects have been indicated by systematic studies on the cellular polypropylene (PP) electret film. Trap capture properties of space charges changed with their injected amount or surface potential of the sample. The space charges were captured largely in the deep traps of the sample surface and the second-deep traps of the near-surface region at small amount of charge injection. They would fill these traps in the surface layer (surface and near-surface region) and the shallow traps in bulk at the same time in the case of greater amount of charge injection. The charge detrapping temperatures of the three kinds of trap centers are about 160℃，138℃ and 92℃，respectively. The charges formed due to void breakdown (called the void breakdown charges) were captured not only in the surface layers of voids which have similar traps as the surface layer of the sample，but also there were numerous void breakdown charges which penetrated the void surface layer，entered into the bulk，and were captured by the shallow bulk traps.