High-performance varistors simply by hot-dipping zinc oxide thin films in Pr(6)O(11): Influence of temperature

High-performance ZnO-Pr(6)O(11) thin-film varistors were fabricated simply by hot-dipping oxygen-deficient zinc oxide thin films in Pr(6)O(11) powder. The films had a composition of ZnO(0.81) and a thickness of about 200 nm, which were deposited by radio frequency magnetron sputtering a sintered zinc oxide ceramic target. Special attention was paid on the temperature dependence of the varistors. In 50 min with hot-dipping temperature increased from 300–700 °C, the nonlinear coefficient (α) of the varistors increased, but with higher temperature it decreased again. Correspondingly, the leakage current (I(L)) decreased first and then increased, owing mainly to the formation and destroying of complete zinc oxide/Pr(6)O(11) grain boundaries. The breakdown field (E(1mA)) decreased monotonously from 0.02217 to 0.01623 V/nm with increasing temperature (300–800 °C), due to the decreased number of effective grain boundaries in the varistors. The varistors prepared at 700 °C exhibited the optimum nonlinear properties with the highest α = 39.29, lowest I(L) = 0.02736 mA/cm(2), and E(1mA) = 0.01757 V/nm. And after charge-discharge at room temperature for 1000 times, heating at 100 or 250 °C for up to 100 h, or applying at up to 250 °C, the varistors still performed well. Such nanoscaled thin-film varistors will be very promising in electrical/electronic devices working at low voltage.