Square-extensional mode piezoelectric-on-silicon resonator for physical measurements of liquids

In this paper, we report a square-extensional (SE) mode MEMS resonator fabricated in piezoelectric thin film Aluminium Nitride (AlN) on Silicon technology. We demonstrate that the resonator can be used to perform physical measurements of various known organic liquids in addition to deionized water. It is well known that operating a MEMS resonator in liquid inevitably introduces viscous damping. The AlN provides strong electromechanical coupling using piezoelectric transduction, which in the SE mode results in a low insertion loss. We are able to achieve higher quality factors (Qs) using this vibration mode compared to out-of-plane modes. We have found that Qs can vary widely between values of 33 to 181 for different liquids used. Furthermore, we have found that the level of feedthrough for different liquids are linearly correlated with the dielectric properties of the different liquid samples measured. These promising results are beneficial for the detection of chemicals.