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

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Abstract
The negative terminal capacitance at high frequencies (usually f≫106 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.

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