Metal Contact Effect on the Dielectric Relaxation Processes in Polypyromellitimide Film

Experiments have been conducted to study the effect of electrode materials (Cu, Al, Pb & Ag) on various relaxation processes in Kapton® film using thermally stimulated discharge current technique. Thermoelectrets were prepared at 80°C(E_p =133.3 kV/cm) and 200°C(E_p =133.3 kV/cm and 280.6 kV/cm). Samples were depolarized from room temperature to 300°C at a linear heating rate of 2°C/min. TSDC spectra consist of three peaks, termed as β, α and ρ. The peak which appears around 108°C is seen to be unaffected by the nature of electrode material and therefore has been attributed to the dipole orientation polarization, associated with the residual reactive groups in polypyromellitimide. The α and ρ peaks appearing around 200°C and 250°C have been attributed to the transference of intrinsic space charge and to the surface charge injected from the electrodes, respectively. For both α and ρ peaks, the peak temperature and peak current is seen to be dependent on the work function of the electrode material. The values of activation energy and relaxation times were also calculated for these peaks. Further, analysis of these relaxation processes has been done by means of M₁-I-M₂ structure.