Humidity sensing properties of La3+/Ce3+-doped TiO2−20 wt.% SnO2 thin films derived from sol-gel method

The humidity sensing properties of La3+/Ce3+-doped TiO2-20 wt.%SnO2 thin films were studied. Sol-gel method was employed to prepare the films on alumina substrates. By constructing a humidity-impedance measuring system, the sensing behaviors were inspected for the films sintered at different temperatures. Experimental results showed that, 0.5 wt.% of La2O3 or Ce2O3 doped films sintered at 500 °C for 2 h had the best humidity sensing properties, the impedance decreasing from 109 Ω to below 104 Ω in the humidity range of 15–95 RH%. Moreover, Ce3+-doping had better humidity sensing properties than La3+-doping. The doping mechanism was discussed in terms of phase composition, granularity of crystalline and segregation of rare earth ions at grain boundaries.