Photo-stimulated discharge current in polyimide films

Abstract

Photo-stimulated discharge (PSD) method is one of the ways to measure the trap level of space charge in the dielectric materials. Compared with the thermally stimulated discharge (TSD) method, it has no observable destroy to the sample's microstructure during the procedure of the light scanning and can therefore be considered to be a more accurate measuring method. However, the light scanning procedure may possibly lead to the occurrence of the external photoelectric effect between the electrode-dielectric interfaces or the internal photoelectric effect in the sample bulk, where the extra current due to the two photoelectric effects can seriously distort the PSD current. In this paper, the total current excited by the scanning light on the polarized or being polarized polyimide films are studied. The influence of the applied field intensity, the electrode structures, the evaporated electrode thickness and the isothermal decaying current of the polarized films on the stimulated current is evaluated, which is comprehensively analyzed to extract the space charge dependent PSD current from the distorted current. The charge trap level based on the PSD method is finally obtained.