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

Room-temperature capacitance-voltage-frequently measurements are repor ted for an 85-nF barium titanate high-voltage ceramic-disk nonlinear c apacitor, intended for use in a power electronics turnoff snubber circ uit. Bias-voltage excursions are from 0 to 1500 Vdc, while the frequen cy responses are measured from quasi-dc to 1000 Hz. The observed C-V-f requency responses are modeled in terms of series-capacitance contribu tions from ferroelecttic grains and p-n junction grain-boundaries, inv olving 16 parameter variables. The ferroelectric capacitance terms are given by a modified Langevin function, while the grain-boundary capac itances 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 compen sation regions at the grain boundaries, with time constant tau almost- equal-to 15 ms. Good agreement between theory and experiment is obtain ed over the 0 to 1500 V bias range.