Fabrication of ZnO-based thick film varistors with high potential gradient

ZnO-based thick film varistors have been fabricated by Y₂O₃ doping and low-temperature sintering, of which the sample with the best electrical properties has a high potential gradient value of 3159.4 V/mm. The effects of Y₂O₃ doping concentration and sintering temperature on the potential gradient of the samples were systematically investigated. The results show that the sample with the best electrical properties can be obtained by doping 0.08 mol% Y₂O₃ and sintering at 725°C. Under these optimum preparation conditions, the leakage current and the nonlinear coefficient are found to be 36.4 μA and 13.1. The sample with the best electrical properties has a grain size of 1.290 μm, a single grain boundary voltage of 4.08 V, a barrier height of 0.81 eV, and a depletion layer width of 10.2 nm, which are determined by thermionic emission. Small grain size with good grain boundary characteristics is beneficial to improve the electrical properties of varistors and promote the potential gradient.