Gas Sensors Based on 1 & 2-Dof Piezoelectric Baw MEMS Resonators with Coated ZIF-8

This paper studies ethanol gas sensing applications for 1 and 2-degree-of-freedom (DoF) coupled bulk acoustic wave (BAW) resonators. Zeolitic imidazolate framework-8 (ZIF-8) was coated on the backside of the resonators to adsorb and desorb ethanol molecules, thereby introducing mass changes. For the 1-DoF device, the frequency shift was tracked, similar to conventional quartz crystal microbalance (QCM) gas sensors. In contrast, for the 2-DoF device, the amplitude ratio (AR) change was chosen as the output metric with enhanced sensitivity. Compared with the state-of-the-art gas sensor based on coupled resonators, the presented devices achieved better resolution with a lower ethanol vapor concentration and yielded a higher Q factor in air.