Processing And Electrical Characterization Of A Novel Varistor-Capacitor Multilayer Ceramic Device

In this paper, novel multilayer varistor-capacitor ceramic devices (MLVCs) werefabricated from ZnO-based ceramic and Pb(Mg)(1/3)Nb_2/3)O₃(PMN)-based ceramic, usingmultilayer ceramic capacitor (MLC) technology. And the microstructure and electricalcharacterization of MLVCs were investigated systemically. Firstly, ZnO-Bi2O3 based materials and PMN-based materials were chosen as therespective varistor and capacitor component materials. Their microstructures andelectrical properties were improved with different material ratios and sinteringconditions by traditional ceramic preparation technology. The results showed thatZnO-Bi2O3 based ceramic could be sintered at a lower temperature ( 960℃,1.5h),exhibited good I-V characteristics with V1mA of 701.4 V/mm and α of 32.0. ThePMN-based capacitor having ε value in excess of 9000 can be sintered in the same conditionand its tan δ and R are 10-2 1012?·mm, respectively. To cofire the chosen systems successfully, a comprehensive analysis was made todetermine if their thermal expansion coefficients and shrinkage rates would matchand if interfacial reactions would occur during sintering. The results indicated thatPMN6# dielectric provided the closest match in sintering behavior to that of ZnO2^#and no interfacial reaction was found, which confirmed the cofireability of two systems. Theprototype MLVCs with Ag/Pd and Pt internal electrodes were fabricated using conventionaltape-rolling techniques by simulating MLC processing. The results showed that V1mA ofMLVC with Ag/Pd internal electrodes decreased from 250V to 200V by increasing layernumber and α kept constant of 20. At the same stacking style and layer number, MLVCs withPt internal electrodes had a slightly higher V1mA and same α value, because of differentmicrostructural ZnO2^# ceramic/electrode interfaces. I-V measurements demonstrated thatstacking style did not appreciably affect the non-ohmic characteristics of MLVCs, however, ithad an important effect on capacitance of MLVCs. Non-crossbedded MLVC had muchhigher capacitance(about decades nF) than crossbedded MLVCs did. Microstructural analysisrevealed solid ceramic/ceramic and ceramic/electrode interfaces with little evidence ofinteraction, and interfacial microstructure characteristics were coherent with electricalproperties of MLVCs. According to sintering behavior of PMN1^#, MLVCs can also be prepared withcombination of PMN1#-based MLC and ZnO2#-based MLV, which were fabricatedrespectively. These MLVCs had a higher V1mA (between 250V and 370V) and similar α value(about 20), and they also had a high capacitance, compared to once-off MLVCs above.This study demonstrates that MLVCs fabricated in our work were dual functionaldevices and it improved the development of low-voltage varistor-capacitor dual functionaldevices or materials.