Effect of space con conduction current and breakdown of polyimide films

We have been studying the breakdown characteristics of polyimide (PI) films. The purpose of this study is to clarify the effect of space charge on conduction current and breakdown of PI films. The space charge distributions and external circuit current (lex) just before the breakdown of a 125 μm thick PI films were simultaneously measured by using pulsed electro-acoustic (PEA) method in 363 K (90 °C). We tried to observe the change of space charge distribution just before the breakdown of PI films obtained by very short period interval (2 ms) measurement. lex showed a large increase, however the remarkable change of space charge distribution just before the breakdown did not show. These results showed that the breakdown of PI films is not directly caused by the distortion of the electric field, but is caused by a thermal breakdown process due to the conduction current by the temperature rise of the sample. The simultaneous measurement of transient space charge profiles and lex must contribute to the investigation of conduction and breakdown phenomena of PI films.