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

High-performance ZnO-Pr6 O11 thin-film varistors were fabricated simply by hot-dipping oxygen-deficient zinc oxide thin films in Pr6 O11 powder. The films had a composition of ZnO0.81 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 (IL ) decreased first and then increased, owing mainly to the formation and destroying of complete zinc oxide/Pr6 O11 grain boundaries. The breakdown field (E1mA ) 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 IL  = 0.02736 mA/cm2 , and E1mA  = 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.