HIGH-FIELD HOLE INJECTION, CONDUCTION, AND BREAKDOWN IN POLYETHYLENE FILMS FABRICATED BY PLASMA POLYMERIZATION

The current-voltage (I-V) characteristics of polyethylene films fabricated by plasma polymerization have been measured at very high electric fields using linear ramp voltages. Experimental results show that at average fields higher than 1 MV/cm, electric conduction is mainly due to the Fowler-Nordheim-type tunneling injection of holes from the anode and the high hole mobility. There is no evidence of impact ionization at fields close to the breakdown strength. High-field conduction is filamentary and governed by the trapped hole space charge. Internal discharges such as electrical treeing and breakdown are initiated by thermal instability within high-current density regions of main conduction filaments (or channels), and then followed by the creation of low-density domains to provide large mean free paths for subsequent impact ionization which leads to an indefinite increase in carrier multiplication and final destruction of the material inside the filaments.