Relaxation processes in aromatic polyimide

Electrical conduction in non-conjugated insulating polymers such as Kapton(R) films was studied as a function of temperature, T (15-500 K) and electric field F (not greater than 16 kV/cm). The time dependent isothermal transient currents (ITCs) were also studied at different temperatures (15 K < T < 500 K). Thermally stimulated discharge current (TSDC) studies were carried out as a function of initial poling conditions. A distinct change in the conduction mechanism as a function of T was observed at T not less than 300 K from DC conductivity, ITC and TSDC measurements. The origin of this behavior is discussed in terms of transition of dipolar at low T to space charge mechanism at high T, which can be attributed to carrier trapping and release of charge carriers from the trap states. The effective barrier energy for transport and hopping parameter are estimated for Kapton on the basis of these studies. The results obtained for Kapton suggest that, for T < T(g) at low or moderate fields, the transient currents are essentially governed by dipolar relaxation mechanisms. (Author)