Electrical properties of plasma-polymerized silicon-incorporated polyethylene films under very high electric fields

The current-voltage characteristics and the breakdown strengths of silicon-incorporated polyethylene films fabricated by plasma polymerization have been measured under very high electric fields using linear ramp voltages. The results show that electric conduction is mainly due to the flow of holes injected from the anode by a tunneling process, and that electric breakdown is initiated by thermal instability caused by local high current density in one major conduction filament, and followed with the provision of large mean free paths for subsequent impact ionization, leading to a rapid increase in the current and final breakdown. The incorporation of silicon in polyethylene introduces additional hole traps and the amount of these hole traps increases with increasing silicon content. The trapped hole space charge at a fixed silicon content increases with increasing magnitude and duration of the applied field. The major role played by the silicon in polyethylene is to reduce the conduction current and to increase the breakdown strength