Thermal depolarization current study of polypyromellitimide

Abstract

Thermal depolarization current (TDC) of polypyromellitimide film was measured in order to obtain knowledge of the charging and discharging mechanisms of carriers in polypyromellitimide. Two peaks are observed at 173 (α) and 50 °C (β) in the dried film. The β peak attributed to dipole orientation polarization is probably associated with residual reactive groups in polypyromellitimide. The α peak shows nonlinear dependence on polarization electric field Ep. The sign of the current changes with small collecting electric field Ec which is applied during the TDC measurement. The α peak depends on electrode materials. The α peak is considered to be attributed to space-charge polarization due to trapping of electrons injected from the cathode in the vicinity of the polymer film surface. The nonlinear Ep dependence of the α peak can be described by a two-site hopping model.