Humidity sensing properties of La3+ and K+ co-doped Ti0.9Sn0.1O2 thin films

The humidity sensing properties of La3+ and K+ co-doped Ti0.9Sn0.1O2 thin films were investigated. The humidity sensitive thin ?lms were prepared by sol-gel method on alumina substrates. The sensing behaviors of thin ?lms were inspected at different sintering temperatures by constructing a humidity-impedance measuring system. It was found that the addition of rare earth ion La3+ and alkali ion K+ was beneficial for improving the humidity sensitive properties of the samples and La0.003K0.5Ti0.9Sn0.1O2 sintered at 500 °C for 4 h showed the best humidity sensing properties. The impedance of this thin ?lm decreased from 109 to 104 Ω with excellent linearity in the humidity range of 11%–95%. Narrow hysteresis loop, prominent stability and high sensitivity were obtained. The effects of dopant content and doping mechanism on humidity sensitivity were also discussed in terms of segregation of rare earth ions at grain boundaries and granularity of crystalline and influence of K+ on the decrease in the intrinsic resistance of the materials, and increase in the number of water adsorption sites.