Processing and electrical characterization of a varistor-capacitor cofired multilayer device

A comprehensive study of the materials selection, processing, cofiring, and electrical characterization of a multilayer varistor/capacitor (MLVC) device has been presented. The goal was to achieve component miniaturization and provide superior high-frequency and high-amplitude transient-voltage protection. A ZnO-based material and 0.75Pb-(Mg_1/3Nb_2/3)O₃-0.25Pb(Zn _2/3Nb_2/3)O₃ (PMN-PZN) were chosen as the respective varistor and capacitor components. Using a controlled-profile furnace, PMN-PZN with excess PbO resulted in an optimum cofiring with a complex varistor composition. The sintering study made it clear that the ability to cofire is dependent not only on matching sintering temperatures and final densities but also sintering rates. Composite-pellet studies assured the mechanical and electrical integrity of the device and indicated that interaction between the respective components was minimal. Prototype MLVC devices were fabricated using standard tape-casting techniques. Microstructural analysis of the MLVCs revealed solid ceramic/ceramic and ceramic/electrode interfaces with little evidence of interaction. Current-voltage and dielectric measurements both indicated good electrical properties that can be specifically tailored by changing the layer thickness.