ADMITTANCE SPECTROSCOPY AND TRAPPING PHENOMENA OF ZNO BASED VARISTORS

Abstract

Electrical properties of ZnO varistors are investigated through admittance spectroscopy. The observed ac admittance dispersion is caused by the existence of two deep bulk trap levels, which are 0.31 eV and 0.245 eV, respectively, below the conduction band. The 0.31 eV level is associated with the oxygen vacancy while the origin of the 0.245 eV level is not yet clear. An equivalent circuit model for ZnO varistors is proposed that is based on the existence of deep bulk traps.