The Behavior of the ZnO-Bi2O3-Based Varistor Capacitance

The nature of the capacitance of the well-formed ZnO-Bi2O3 based varistors reflecting back-to-back Schottky barriers across the grain boundaries is addressed. Existing reports and models have been used in understanding the origin of the terminal capacitance in conjunction with the postulated capacitance of the simplistic equivalent circuit model proposed by earlier investigators. The capacitor of the R-C (i.e., R-P - C-P) parallel equivalent circuit combination does not portray the total concept of the Schottky barrier capacitance. This response is attributed to the extraneous contributions originated from multiple frequency-dependent trapping and de-trapping capacitances in addition to the frequency-independent geometric capacitance that exist within the grain boundary (GB) electrical barriers. These GB electrical barriers correspond to the electrical field falling regions between the two electrodes of the device for which the terminal capacitance is accounted for.