Preparation and electrical properties of multilayer ZnO varistors with water-based tape casting

Multilayer ZnO varistors were prepared by water-based tape casting with water-soluble acrylic as binders. Zeta potentials of the doped ZnO suspensions as a function of pH with and without dispersant were measured. Viscosity measurements were used to find the optimum dispersant concentration needed to prepare a stable slurry. Viscosity properties of the tape casting slurry were investigated. The results showed that aqueous acrylic binders have shear thinning properties suitable for tape casting of ceramic powders. Scanning electron microscopy (SEM) studies revealed that the green sheets have a smooth defect-free surface and that the multilayer varistor (MLV) ceramics prepared by water-based tape casting have a fine grain microstructure with a uniform grain size and dopant distribution. The multilayer ZnO varistors prepared by water-based tape casting display comparable good electrical properties to those prepared by solvent-based tape casting. This is believed to be attributed to the well dispersed water-based slurry, which makes more uniform dopant distribution throughout the multilayer ZnO varistors. Therefore, water-based tape casting is suitable for the manufacture of high performance multilayer ZnO varistors.