RELAXATION EFFECTS IN HIGH-VOLTAGE BARIUM-TITANATE NONLINEAR CERAMIC DISK CAPACITORS

Room-temperature capacitance-voltage-frequently measurements are reported for an 85-nF barium titanate high-voltage ceramic-disk nonlinear capacitor, intended for use in a power electronics turnoff snubber circuit. Bias-voltage excursions are from 0 to 1500 Vdc, while the frequency responses are measured from quasi-dc to 1000 Hz. The observed C-V-frequency responses are modeled in terms of series-capacitance contributions from ferroelecttic grains and p-n junction grain-boundaries, involving 16 parameter variables. The ferroelectric capacitance terms are given by a modified Langevin function, while the grain-boundary capacitances are modeled by back-to-back p-n junction diodes on either side of an insulator boundary. The observed frequency dependence of the C-V response is attributed here to a Debye-type relaxation of the compensation regions at the grain boundaries, with time constant tau almost-equal-to 15 ms. Good agreement between theory and experiment is obtained over the 0 to 1500 V bias range.