Conductivity of Bulk Zinc Oxide Varistors under Dc and Pulsed Bias

Zinc oxide (ZnO) varistors is widely used in over voltage protection of various circuits for its advantages of excellent nonlinear, fast response time and low power consumption. Commercial ZnO varistors was selected and its dc and pulse conductivity was tested. Based on ZnO grain boundary barrier model, the dc conductivity was analyzed in the Breakdown and Pre-breakdown regions. At the pulsed bias, the capacitive current and conduction current of ZnO varistors was obtained. The growth ratio of conduction current is greater than that of the capacitive current. The tunneling electric field coefficient of ZnO grain boundary barrier, the permittivity of boundary and the proportion of boundary thickness were calculated.