Space charge distribution before breakdown of polyimide film by short interval measurement with PEA method

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 conduction current on breakdown mechanism of PI. The space charge distributions and external circuit current (lex) were simultaneously measured just before the breakdown of a 125 /spl mu/m thick PI film by using pulsed electro-acoustic (PEA) method in 90/spl deg/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. The space charge distribution just before the breakdown did not show a noticeable change. These results showed that the breakdown of PI films is not directly caused by the distortion of the electric field before 2 ms at the breakdown, but is caused by a thermal breakdown process due to the conduction current by the temperature rise of sample. The simultaneous measurement of transient space charge profiles and lex must contribute to the investigation of conduction and breakdown phenomena of PI films.