High-frequency terminal resonance in ZnO-Bi2O3-based varistors

Abstract

The negative terminal capacitance at high frequencies (usually f≫10 6 Hz) in ZnO-Bi2O3-based varistor systems is attributed to two possible sequential and/or combined sources: (a) piezoelectric grain resonance; and (b) electrode-lead or contact impedance. These sources are examined using a variation in the geometry of the varistor material and its electrode-lead configuration. The approximate values of the resonating parameters, designated by an equivalent series lumped inductance-capacitance- resistance (Lr-Cr-Rr) circuit in parallel with materials' characteristic capacitance C0, are extracted employing lumped parameter/complex plane analysis technique for these ac electrical data. At the resonating frequency, the lumped reactance of this series circuit nullifies yielding a resistance Rr referred to the lumped ZnO grains.