Boundary breakdown time of ZnO varistors under nanosecond pulse current

Conductive properties of zinc oxide (ZnO) varistor ceramics depend on the boundary barrier structure. By using the photoconductivity switches (PCSS) technology, the boundary breakdown characteristics of ZnO varistors for nanosecond electric pulse response was measured under bias voltage 700 - 1600 V and the relationship between conductance and material structure was analyzed. Charging time of grain boundary capacitor was ∼ 100 ns and shortened with the increase of the bias electric field. The barrier height of ZnO grain boundary was influenced by bias electric field and the grain boundary capacitance was changed accordingly. The calculating numerical results are in agreement with the measured values.