Capacitance-vs-voltage characteristics of ZnO varistors

Abstract

Studies were made on the capacitance-vs-voltage characteristics of ZnO varistors which contain rare-earth metal oxides and cobalt oxide. On the basis of the symmetrical Schottky-barrier model of the grain-boundary region, the barrier height φ and donor concentration Nd of ZnO grains were obtained by the modified 1/C2-V plot reduced from observed C-V relations. φ and Nd were obtained as 0.72 V and 1.6×1018 cm−3, respectively, for a ZnO-Pr6O11-Co3O4 system and 1.00 V and 0.76×1018 cm−3, respectively, for a ZnO-Pr6O11-La2O3-Co3O4 system. These results support the validity of this model and the treatment.