Breakdown and space charge distribution in polyimide film

We have been studying the breakdown characteristics of polyimide (PI) films. The purpose of this study is to clarify the effect of space charge and heat treatment on breakdown mechanism of PI films in room temperature region. The space charge distribution in a 125 μm thick PI film was measured up to electrical breakdown with a semi-conducting and Al plate electrode under dc voltage by using pulsed electroacoustic (PEA) method. In room temperature region, hetero - charges were formed near the cathode, when the electric field approached the breakdown field. The conduction current shows large increase with increase of electric field near breakdown field. These results show a thermal breakdown process where the high-field conduction current is modified by the space charge effect is considered as a possible breakdown mechanism of PI films; in room temperature region.