LOW-TEMPERATURE SINTERING OF HIGH VOLTAGE GRADIENT ZnO-BASED THICK FILM VARISTORS

High voltage gradient ZnO-based thick film varistors were fabricated by low-temperature sintering. The effect of sintering temperature on electrical properties of thick film varistors was investigated. The voltage gradient of thick film varistors increased significantly to 3159.4 V/mm after sintering at 725°C for 30 min. The small average grain size with good grain boundaries was the origin for the increase in voltage gradient. Sample sintered at 725°C exhibited excellent electrical properties, with a leakage current of 36.4 μA, a nonlinear exponent of 13.1 and the maximum resistivity difference between ZnO grain and grain boundary. Moreover, it possessed high permittivity and low dissipation factor in the low frequency range for the sample sintered at 725°C. Therefore, ZnO-based thick film varistors with high voltage gradient and good nonlinear properties could be obtained under the given experimental conditions and qualified as excellent candidates for high voltage varistor application.