The AC aging characteristics of high voltage gradient ZnO varistors doped with different content of Bi2O3

In this paper, ZnO varistors with high voltage gradient, which were doped with 0.75 mol% Y₂O₃ and different ratio of Bi₂O₃, were prepared by classic ceramic fabricating method. The obtained samples were degraded under accelerated AC aging stresses of 0.85 V_1mA /135°C/168 h. The electrical properties and Schottky barrier parameters of these samples before and after the aging tests were measured and compared. The leakage current obviously increases after the aging test and the aging rate increases with the Bi₂O₃ content, too. Meanwhile, the linearity of these samples reduces after the aging test and the variation rate increases as the Bi₂O₃ doping ratio increased. The decrease of the donor density and the interface state density after aging leads to the decrease of barrier height.