Electrical conduction in SnO2 varistors

This paper outlines some details of the conduction mechanism in SnO2-based ceramic varistors. It is shown that the activation energy of electrical conduction EσEσ (the barrier height ϕ) in SnO2 varistor is weakly decreased at low electric field E   and strongly decreased at high fields. The strong decrease in Eσ(E)Eσ(E) at high fields is conditioning factor of highly nonlinear current–voltage characteristic. The conduction process is thermally activated not only at low (Eσ≅0.8–1eV) but also at high electric fields (Eσ≅0.3–0.5eV). The “negative capacitance” phenomenon at high fields in highly nonlinear SnO2 varistor is observed. The relation between the high nonlinearity, the high slope of Eσ(E)Eσ(E) dependence at high fields, the “negative capacitance” and possible generation of the minority carriers (holes) at high fields is discussed.