Resonant tuning fork strain gauge operating in air with decoupled piezoelectric transducers

We report a unique MEMS resonant force sensor design that provides both reduced motional resistance and greatly enhanced strain gauge factor to target operation under ambient conditions. The proposed device has been realized in an Aluminum Nitride (AlN) on Silicon (Si) process, where the piezoelectric-AlN transducers are uniquely decoupled from a force sensitive triple beam tuning fork (TBTF) resonator to improve transduction and gauge factor together. The experimentally calibrated fractional force sensitivity of the fabricated device is 24.75 ppm/μN, which has been measured under ambient conditions where the quality factor is 550 and the motional resistance is 556 kΩ. In terms of the strain gauge factor, the proposed device has a strain sensitivity, which is reasonably higher compared to previous piezoelectric tuning forks without having to be operated in vacuum.