PREBREAKDOWN CONDUCTION IN ZINC-OXIDE VARISTORS - THERMIONIC OR TUNNEL CURRENTS AND ONE-STEP OR 2-STEP CONDUCTION PROCESSES

This letter is aimed at understanding the intergranular conduction in zinc oxide varistors. In particular, we have studied current-voltage a nd Arrhenius plots of the resistive current for the prebreakdown condu ction. A current-temperature (I-T) relation has been found to present two breaks at approximately 370 and approximately 240 K. Although this result can be interpreted as a consequence of distinct regimes, we fo und that experimental I-T curves can be theoretically reproduced by ca lculating currents for a double Schottky barrier. Experimental results were fitted with one- and two-step transport process models. It was f ound that a two-step model better reproduces the electrical properties of these devices.