Measurement of Electric Field Distribution in Thin Polyimide Film

Polyimide films are widely used in various industries because of their excellent thermal, electrical and mechanical properties and environmental stability. Space charge is generally reported as a triggering mechanism for the degradation of insulations. In this report, space charge distribution and electric field distortion associated with the charge accumulation have been investigated for thin PI film with thicknesses of about 8$\mu$m under different DC electric fields from 25 kV/mm to 100 kV/mm for 2 hours at 313 K, using Thermal Pulse Method (TPM). It is shown that the distortion factor of the internal electric field in PI film is negligibly small for applied fields less than 25 kV/mm. However, it can be observed that the electric field distortion is especially pronounced on both sides of the film because the space charge emitted by the electrodes accumulates on both sides of the film, and both positive and negative charges migrate to the interior of the film at higher applied fields. The results show that the increase of the applied electric field will obviously increase the accumulation of space charge and lead to the distortion of the electric field inside the film, which may be one of the reasons for the dielectric breakdown.