ELECTRICAL-PROPERTIES AND DEGRADATION PHENOMENA OF GLASS-DOPED ZNO CHIP VARISTORS

Several glass additives with compositions in the PbO-B2O3-ZnO-SiO2 system were applied to multilayer type ZnO ceramic chip varistors which had been manufactured using the ceramic green-sheet lamination technique. Measurements of capacitance-voltage (C-V), current-voltage (I-V) and degradation behavior, as well as microstructural observations, were performed. It was found that specimens into which the above-mentioned glasses were incorporated had good surge-withstanding capability, with the exception of samples including Zn-B-Si glass. The electrical properties of specimens deteriorated gradually with increasing glass content. The addition of glasses improved the thermal stability of ZnO varistors except for G4 glass-doped sample (60 w/oPbO-12w/oB2O3-6.5w/oSiO2-21.5w/oZnO). Stable varistors with good nonlinearity parameters were obtained by combining the glass compositions and other additives.