High-frequency capacitance resonance of ZnO-based varistor ceramics

Capacitance resonance of ZnO varistor ceramics can be shifted from gegahertz to a few megahertz frequency region with increasing amounts of specific secondary phases. The observed resonance is due to the total inductance of the varistor ceramics wherein the grain boundaries are shorted at high frequencies, which arises from the dynamic exchange of charge carriers at the grain interiors and the trap states that are formed at the depletion regions around the grain boundaries. This is applicable to ZnO/ZnO grain boundaries as also to ZnO/secondary phase boundaries. The capacitance-voltage studies show direct correlation between the magnitude of capacitance resonance and the nonlinearity coefficient in current-voltage relations. (C) 1996 American Institute of Physics.