Relation between Electrostatic Capacity of Polyethylene and Electronic Space Charges Induced by High Field Application

The electrostatic capacitance of polyethylene (PE) is changed after a high dc electric field is applied to a metal-PE-metal capacitor. The capacitance increases with increasing applied field above the threshold field of about 30 MV/m. This change in the capacitance is explained in terms of the polarization of trapped electronic space charges. These charges are injected from a metal electrode over the Schottky barrier of about 1.3 eV and captured by electron traps. From the measurement of the relaxation time when the capacitance comes back to the initial value under the short-circuited condition, the trap depth associated with polarization is estimated to be about 1.2 eV. This trap depth agrees with the activation energy for the conduction current in the low field region. A new method is proposed for detecting the space charge in PE by measuring the charge in the capacitance.