Sol–gel BaTiO3 thin film for humidity sensors

BaTiO3 ceramic thin films were prepared by sol–gel processing and their humidity sensitive characteristics have been investigated. The films were formed on Al2O3 substrates with comb type Au electrodes by spin coating. It was found that the impedance of the thin films decreases with increasing relative humidity (RH). The humidity sensitivity of the sensor depends on the applied frequency of the electric signal and the activation energy for conduction is reduced with water adsorption. The BaTiO3 thin films show a negligible hysteresis under cyclic humidity changes with a good long-term stability and fast response time. It appears that the sol–gel process produces films that can be used as efficient humidity sensors.