HIGH-FREQUENCY TERMINAL RESONANCE IN ZNO-BI2O3-BASED VARISTORS

The negative terminal capacitance at high frequencies (usually f much greater than 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 (L(r)-C(r)-R(r)) 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 R(r) referred to the lumped ZnO grains.