High-performance Bi-based Multilayer Chip Zinc Oxide Varistor

In this paper, wide application of Zinc Oxide Varistor esp. MultiLayer Varistors(MLV) in advanced electronics technology field was discussed. The ceramic materials used for MLV, inner electrode and preparing process were present and systematic researched through abundant experiments. Theory analyses were also explored to explain the phenomenon and law of the relative experiments.For the ceramic materials, the effects of additives such as PbO, B2O3, Co2O3, MnO2, Cr2O3, Sb2O3 on the electrical properties of Bismuth-free ZnO-glass varistor were studied. The glass phase formed mainly by PbO and B2O3 during sintering process could decrease the sintering temperature, improve grain uniform growth and inhibit grain second growth. Nonlinear property could be improved by properly adding Co2O3, MnO2, and Cr2O3. Synthetic properties could be improved by the spinel phase formed by ZnO, Sb2O3 in the calcinations process. The basic composition of this kind of ceramic materials could be expressed as the following formula0.98ZnO+αPbO+βB2O3+γSb2O3+x(Co2O3?aMnO2?bCr2O3)+y(TiO2?ZrO2)Where 0.01≤α≤0.1 0≤β≤0.04 0≤γ≤0.020≤x≤0.04 0≤y≤0.01 0≤a≤1 0≤b≤1The optimum composition expressed by 0.98ZnO+0.05PbO+0.02B2O3+ 0.01Sb2O3+0.012 (Co2O3?0.6MnO2?0.8Cr2O3)+ 0.005 (TiO2?ZrO2) was obtained by abundant experiments and scientific analyses.For preparing process, The ZnO ceramic disc samples with Φ10mm×1mm exhibited good characteristic with α>50, V1mA < 400V and IL <1μA and Tsintering<1100℃ were obtained by optimum sintering temperature, holding time and firing atmosphere, using proper and silver electrode.MLV was prepared in a process used for MLCC manufacturing, by adopting Pd30/Ag70 inner electrode. MLV samples with V1mA <30V, α >30, IL<1μA, Ip>40A,Tsintering<1050℃ were obtained and could be used to shunt voltage spike away from sensitive IC, to absorb lighting current surge from electronics equipment and to impede transient pulse from loading switch.