Highly nonlinear varistors from oxygen-deficient zinc oxide thin films by hot-dipping in Bi2O3: Influence of temperature

Abstract

Highly nonlinear varistors were fabricated by hot-dipping oxygen-deficient zinc oxide (ZnO1−x, x<1) thin films in Bi2O3. The ZnO1−x films were deposited on conducting silicon chips by radio frequency magnetron sputtering of a sintered zinc oxide ceramic target. Then the films were hot-dipped at a temperature from 200 to 600°C in Bi2O3. With the increase in hot-dipping temperature, the nonlinear coefficient (α) of the film varistors increases first and then decreases, and the leakage current (IL) correspondingly decreases initially and then increases, owing mainly to the formation and destroying of complete ZnO1−x/Bi2O3 grain boundaries and the roundness change of the ZnO1−x grains; and the varistor voltage (E1mA) decreases from 0.0268 to 0.0137V/nm, due to the decreased number of effective grain boundaries in the materials. The film varistors prepared by hot-dipping at 400°C exhibit the optimum nonlinear properties with the highest α=15.1, lowest IL=0.0223mA/cm2, and E1mA=0.0176V/nm. Such nanoscaled film varistors will be very promising in electrical/electronic devices working in low-voltage.