Humidity Sensor Based on Polymer Coated Quartz Crystal Microbalance (QCM)

Humidity sensors featured by the combination of a quartz crystal microbalance (QCM) and polyvinylpyrrolidone (PVP) film were fabricated. PVP films were distributed onto the electrode surfaces of quartz crystal by drop-coating. The electrical characteristics of the devices as a function of relative humidity (RH %) measured in the airtight testing chamber to generate the controlled humidity were tested. The change in frequency of QCM with sensitive film was in situ monitored. Result shows when the polymer-coated QCM exposed to certain humidity circumstance, the change of mass on crystal sensitive surface results in the decrease of resonant frequency. It was found that the increase of shift frequency is proportional to the thickness of polymeric film. In low humidity range less than 50% RH, all of the sensors showed linear characteristics to humidity and mild frequency shift. In high humidity, the frequency shift changed dramatically.