Highly sensitive humidity sensor based on quartz crystal microbalance coated with ZnO colloid spheres

Different sizes of ZnO colloid spheres were coated on quartz crystal microbalance (QCM) by the self-assembly method. The device exhibits excellent humidity sensing properties in the whole humidity range from 11% to 95%, such as high sensitivity, good linearity, and fast response/recovery time. The results showed that the humidity sensitivity of these sensors increased with increasing relative humidity (RH). Furthermore, the humidity sensitivity enhanced with increasing size of ZnO colloid spheres. We also discussed the adsorption and desorption of water molecules on different sizes of ZnO colloid spheres in different humidity.