Improved non-linear behaviour of ZnO-based varistor thick films prepared by tape casting and screen printing

Thick films of ZnO-based varistors have been prepared by screen printing and tape casting techniques. The manufacture of varistor thick films by screen printing shows two critical problems; the excessive volatilization of Bi2O3 during the sintering step, due to the exaggerated area–volume ratio of these devices and the lack of density of the green compacts, problem inherent to screen printing technology. Tape casting improves compact density and it is also possible to include an additional press step before sintering. An electrical and microstructure comparison between thick films prepared by both technologies has been carried out for a wide range of sintering temperatures. Although far from the electrical response of bulk ceramics, the results obtained show good varistor behavior when sintering the films at low temperatures.