Abnormal conduction properties of ZnO varistor fabricated by 3-composition seed grain

A method for making low-voltage ZnO varistors having extra large grain size with the contents of 3-composition seed grain is reported. The conduction mechanism for a non-ohmic ZnO varistor fabricated by the 3-composition seed grain method was investigated. The knee voltage and nonlinear coefficient α of a sample with 3-composition seed grain of 5 wt.% are 5 V and 18, respectively. The conduction mechanism is mainly governed by thermionic emission below the knee voltage and the field emission of the double Schottky model above the knee voltage. The activation energy and trap level of those regions are calculated to be about 0.367 and 0.513 eV, respectively. The conduction mechanism for the nonlinear region above the knee voltage can be analyzed by the Fowler-Nordheim tunneling effect. The barrier height of the model in this region is about 0.32 eV