The breakdown mechanism of poly-p-xylylene film. Prestress effectson the breakdown strength

Impulse and dc breakdown strengths of 4 μm thick poly-p-xylylene (PPX) films were 5.9 and 4.1 MV/cm, respectively. They were independent of temperature in the temperature range from -60 to 60°C. dc prestressing for a long time (t_p=60 s) reduced impulse breakdown strength for both the same and the opposite polarity. But dc prestressing for a short time (t_p<1 s) increased impulse breakdown strength for the same polarity. These results were explained by positive space charge in PPX film. It was also concluded that positive charge carrier injected from the anode, spread in a 4 μm thick PPX film during a short time