INFLUENCE OF PROCESSING PARAMETERS ON THE MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF MULTILAYER-CHIP ZNO VARISTORS

Multilayer-chip varistors based on ZnO with lead zinc borosilicate glass instead of Bi2O3 were prepared by tape casting and green-sheet lamination processes using a non-aqueous slurry system. The influences of slurry composition and the degassing process on the microstructure and non-ohmic properties of multilayer-chip varistors were studied. The electrical properties of chip varistors can be influenced substantially by the pore defects resulting from an unsuitable slurry formulation for the tape-casting process. The sintering temperature of the chip varistors was lowered to 1100 degrees C and silver-palladium alloys were employed as internal electrodes. The non-linear coefficients of 27-32 and breakdown voltages of 7.6-24.5 V were achieved by controlling the green-sheet thickness and sintering temperatures in the present study. The Delta V-br/V-br values for the chip varistors lie within +/-10%, indicating excellent surge-withstanding capability.