Integrated varistor-capacitor ceramics

There exists a continued trend of ceramic integration in electronic components. In the last decade inductor-capacitors, resistor-capacitors have all successfully undergone integration into surface mount components. There exists a need to integrate varistors and capacitors to suppress high frequency transient voltage surges beyond >0.5 ns. The successful co-firing of a varistor and capacitor depends on the careful matching of thermal expansion co-efficients, total densification and shrinkage rates of the respective materials. It is also important that interfacial reactions be reduced or eliminated through design or materials selection. Hence, this work describes attempts to co-fire a ZnO-Bi₂O₃-CoO based varistor and a relaxor based Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3) O₃ capacitor. Both compositions share similar thermal expansion co-efficients which significantly reduces the potential for cracking on cooling. By careful control of the composition the total densification and shrinkage rates were matched to that of the varistor. The interfacial microstructures, relevant I-V and dielectric measurements are also discussed.