Surface acoustic wave humidity sensors based on uniform and thickness controllable graphene oxide thin films formed by surface tension

Graphene oxide (GO) is a promising candidate for humidity sensing, and the uniformity and thickness of GO films are important for the reproducibility and test signal strength of humidity sensors. In this paper, uniform and thickness-controllable GO films are first formed by the surface tension of different concentrations of GO solution and then transferred to surface acoustic wave (SAW) humidity sensors. This GO film formation and transfer process has very good repeatability and stability, as evidenced by the humidity response of the sensors. With the help of the uniform and highly oxidized GO film, the humidity sensors show a significantly high sensitivity (absolute sensitivity of 25.3 kHz/%RH and relative sensitivity of 111.7 p.p.m./%RH) in a wide test range from 10%RH to 90%RH with very little hysteresis (<1%RH). The sensors achieve good reversibility, excellent short-term repeatability and stability. Moreover, the humidity sensors also show a fast response and recovery time of <10 s.