Multi-DoF AlN-on-SOI BAW MEMS resonators with coated ZIF-8 for gas sensing application
Linlin Wang, Yuan Wang, Max L. Tietze, Bernardo Pereira Madeira, Rui P. Martins, Pui‐In Mak, Nicolas Chanut, Divya Bharathi Rajagopal, Masaya Sugihara, Rob Ameloot, Chen Wang
Abstract
This paper explored the practical utility of gas sensing applications based on the multi-degree-of-freedom (Multi-DoF) bulk acoustic wave (BAW) resonant sensors, including 1, 2, and 3-DoF devices, where piezoelectric actuation and sensing methods were adopted. Zeolitic imidazolate framework-8 (ZIF-8) was chosen for the adsorption and desorption of the ethanol vapor, thereby facilitating the gas sensing mechanism and introducing the external mass changes to the multi-DoF resonating system. Similar to conventional quartz crystal microbalance (QCM) gas sensors, the frequency shift of all the devices (1, 2, and 3-DoF devices) was tracked to characterize the sensitivity. Besides, for the 2 and 3-DoF devices, the amplitude ratio (AR) change was also recorded and observed with an enhancement in performance. Compared with the state-of-the-art gas sensor based on 2-DoFcapacitively coupled resonators, the presented devices achieved better Q factor in air, stability, and resolution in terms of both frequency shifts and AR changes. The dominant mass change (dominant stiffness change in the state-of-the-art) of the proposed resonant devices matched well with the theoretical mass sensing principle, which is both predictable and crucial for the accurate modeling of the practical mass sensor. Furthermore, a lower ethanol vapor concentration from 0.1% to 2% was successfully detected by the proposed 2-DoF device, demonstrating even better sensing performance than that of the state-of-the-art.