Field-induced thermally stimulated currents in Kapton-H polyimide films

Thermally stimulated polarization current (TSPC) is investigated in Kapton-H thin films in the temperature region 303 to 523K under various polarizing fields ranging from 10 to 200 kV cm−1; and different heating rates. The TSPC spectra reveal the presence of a single peak (P1) around 400 K and a steady rise in current at high temperatures where ohmic conduction begins to predominate. During the successive cooling, the current retained its positive polarity, while in the second TSPC cycle a negative current is obtained in low temperature region. This can be accounted for the temperature dependence of saturation polarization. In a few cases the corresponding thermally stimulated depolarization current (TSDC) characteristics are also recorded, which are found to consist of two peaks P1 and P2 located nearly at 390 and 480 K, respectively. McKeever's analysis implies the association of the maxima P1, P2, respectively, with dipole and space charge origins. The thermal variation in dielectric constant of the material is also deduced from the TSPC curves. The experimental observations are in general agreement with the theoretical predictions. The difference is presumably caused by the fact that the TSPC technique is subject to several limitations like interference of conduction phenomena.