Humidity sensing with ultrathin LTA-type molecular sieve films grown on piezoelectric devices

LTA-type zeolite films on mass sensors (quartz crystal microbalances) were prepared using secondary growth on a precursor seed layer. Zeolite seeds with a mean size of 40 nm were obtained at room temperature and used to form precursor layers via several identical adsorption steps on silane-modified sensor surfaces. Oriented LTA-type films with thicknesses in the range of 65-980 nm were prepared after additional hydrothermal treatment of the precursor seed layers at elevated temperature (100 degreesC) for different crystallization times (from 3 to 24 h). The application of LTA-type zeolite films in humidity microsensors is presented. The importance of film thickness, type of zeolite structure, and the preparation parameters of the sensor layers with respect to the sensitivity of the humidity sensors at different water vapor concentrations are discussed. The zeolite films are hydrophilic and thermally stable and show reproducible response. On the basis of these results, it was concluded that the above LTA zeolite films can be used effectively as humidity sensor materials for water vapor sensing purposes. High sensitivity, good reversibility, and long life were demonstrated for thin LTA-type zeolite films at low water concentrations.