Electrical characteristics and stability of low voltage ZnO varistors doped with Al

The nonlinear electrical characteristics and stability against AC accelerated aging stress of Al-doped low voltage ZnO varistors were investigated as a function of Al content. The varistors with Al exhibited a high nonlinear coefficient above 30, compared with that without Al. The varistors with 200 ppm Al3+ exhibited a highest nonlinearity, with a nonlinear coefficient of 42.9 and a leakage current of 9.5 μA. But the varistor without Al showed high stability, in which the variation rate of varistor voltage, of nonlinear coefficient and of leakage current are −4.1, −4.3 and +20.7%, respectively, under AC accelerated aging stress (1.0 V1 mA/125 °C/24 h).