Electrostatic charge sensor based on a micromachined resonator with dual micro-levers

Abstract

This paper describes an electrostatic charge sensor based on a microelectromechanical systems (MEMS) resonator with dual micro-levers to improve sensitivity. The device comprises a double-ended tuning fork resonant element working at out-of-phase mode with a quality factor (Q) of about 4900 under operating pressure of 40 mTorr. The resonant frequency shifts in proportion to an axial force induced by charge additions and then transformed by dual micro-levers with an amplification factor over 8. The measured responsivity is 1.3×10−3 Hz/fC2, which matches well with the results from analytical models and finite element method. The sensitivity of the charge sensor is 21 fC under 4 ppm frequency fluctuation. Additionally, electrostatic spring softening and nonlinear feature of the resonator are also investigated.