Electrical and microstructural characterization of doped ZnO based multilayer varistors

Abstract

Purpose The purpose of this study was to develop fabrication procedure of multilayer varistors based on doped ZnO and to investigate their microstructure and electrical properties. Design/methodology/approach Two ceramic compositions based on ZnO doped with Bi2O3, Sb2O3, CoO, MnO, Cr2O3, B2O3, SiO2 and Pr2O3 were used for tape casting of varistor tapes. Multilayer varistors were prepared by stacking of several green sheets with screen printed Pt electrodes, isostatic lamination and firing at 1,050-1,100°C. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) studies were carried out to examine the microstructure and elemental composition of the varistors. Current-voltage characteristics were measured in the temperature range from −20 to 100°C. Findings The desired compact and fine-grained microstructure of multilayer varistors and nonlinear current-voltage characteristics were attained as a result of the applied fabrication procedure. The breakdown voltage of the varistors is 33-35 V and decreases slightly in the temperature range from −20 to 100°C. The nonlinearity coefficient changes from 14 to 23 with rising measurement temperature. Originality/value New improved formulations of varistor ceramic foils based on doped ZnO were developed using tape casting method and applied for fabrication of multilayer varistors with good electrical characteristics. The influence of temperature in the range from −20 to 100°C on the varistor parameters was studied.