Graphene Decorated Shear Horizontal Surface Acoustic Wave Resonator as Humidity Sensor

In this article, we reported a surface acoustic wave (SAW) resonator as a humidity sensor. Graphene thin film was decorated on the SAW resonator as a humidity sensing layer. Relative humidity (RH) was varied (17%–80%RH range) and the desired humidity content was established in the process chamber using controlled water vapors. As the humidity level increases, water molecules adsorb onto the graphene surface, causing increases in surface density leading to a change in shear acoustic wave properties that can be measured and correlated with the humidity level. A new design of a Colpitts oscillator has been proposed using the SAW device in the feedback network for the SAW resonator for operating frequency stability. In order to understand the electrical behavior of the SAW resonator, a modified Butterworth-Van Dyke (mBVD) equivalent circuit model is developed using advanced design system (ADS) software. The results show that the motional arm is mainly influenced by the graphene decoration and humidity level exposure. In addition, it is observed that the static arm remains unaffected by the humidity level and only the motional arm is responsible for water vapor sensing behavior. The highest sensitivity (S) is 206.27 ppm/%RH, and the limit of detection (LOD) is 0.269%RH. This novel type of humidity sensor stands out for its cost-effectiveness, stability, reliability, and robustness. It proves to be highly beneficial for applications requiring humidity sensing at room temperature.