Electrical breakdown and space charge of polyphenylene sulfide films

The electrical breakdown of PPS (polyphenylene sulfide) films of three different thicknesses was investigated. Impulse breakdown strength was almost constant in the temperature range from -60 to 150 degrees C, but showed a negative thickness dependence, suggesting electron avalanche breakdown. Assuming single electron avalanche breakdown, the mean free path was estimated to be about 9 AA. The DC breakdown strength was lower than the impulse breakdown strength, which suggested space charge effects on the DC breakdown or the thermal breakdown. The impulse breakdown strength was also measured with DC prestress superposed. The results can be explained by the formation of homospace charge in PPS during the DC prestress. For the thinner film, the homospace charge was found to act like heterospace charge for the counterelectrode, which causes an enhancement of the electric field there, resulting in the lower breakdown strength.>