A humidity sensor based on AlN Lamb wave resonator coated with graphene oxide of different concentrations

A high-performance humidity sensor based on an AlN (aluminum nitride) Lamb wave resonator coated with graphene oxide (GO) is presented in this paper. With the porous structure and oxygen-containing groups of GO as the sensing layer, the humidity sensor exhibits a high sensitivity of 26kHz/%RH at 10%-90% relative humidity. However, more than half of the frequency variation occurs in the range of 70%RH to 90%RH. In this paper, we propose a vacuum film-coating method to improve the performance of the GO film. With this GO film, the sensitivity is increased by 160% in the humidity range between 10% to 60%RH compared to conventional ones. The sensor also demonstrates a low temperature coefficient of frequency, small hysteresis, and short response (similar to 9s)/recovery (similar to 11s) time. Therefore, the humidity sensor with GO shows great potential in practical applications.