AVERAGING EFFECT ON CURRENT-VOLTAGE CHARACTERISTICS OF ZNO VARISTORS

Surface electrode patterns with systematic changes of electrode gap distances and widths have been developed to investigate the averaging effect in the current-voltage (I-V) measurements of ZnO varistors. Varistor breakdown voltages, V-B, and the nonlinear exponent, alpha, were obtained from the I-V measurements. The alpha vs voltage plots showed multiple breakdown peaks when the gap distances were greater than 2.5 x the average grain diameter. A decrease in alpha due to the lower-voltage breakdowns was also observed. The same effect was obtained when single-junction I-V results were used in simulating the junction network on a computer. The broad distribution of grain size is considered as the main cause of multiple breakdowns. The small amount non-switching and short-circuited junctions also play an important role in the device I-V characteristics.