Conduction mechanism and flicker noise in zinc oxide varistors

Journal of Applied Physics (1), - Measurements were performed on the power spectral density Sv of the flicker noise in ZnO varistors as a function of temperature (from 110 to 370 K), bias voltage (from 10 to 90% of the varistor voltage), and frequency (from 0.1 Hz to 2 kHz). Capacitance-voltage (C-V) curves and current-voltage (I-V) characteristics as a function of temperature were also measured. The picture resulting from these measurements is very self-consistent when the data are interpreted on the basis of a Schottky emission model and flicker island models. In particular, the temperature and frequency dependences of Sv provide direct experimental evidence of the thermally activated emission of electrons from localized states, distributed over a large spectrum of energy levels, at the ZnO grain boundaries. Both I-V, C-V curves and Sv data enable one to obtain reliable information on the intergranular barrier height, its dependence on temperature and bias voltage