Theoretical study of an electrostatically actuated torsional microsensor for biological applications

Abstract

MEMS mass sensors can operate in different regimes. The static method is the classical technique to measure physical quantities, and it is based on measuring the static deflection of the microstructure upon mass binding (Schmid et al. 2010;Wu et al. 2001). The dynamic method is considered as the most sensitive technique for mass sensing (Park et al. 2011; Bouchaala et al. 2016a, b, c;Gupta et al. 2004). The fundamental principle of the dynamic MEMS mass sensor is to excite the microstructure near one of its natural frequencies, which is a function of the structure stiffness and mass. By adding a small mass on the top of the resonator, the natural frequency downshifts. Based on analytical and experimental techniques, the sensitivity of the MEMS resonator can be calculated, and hence the frequency shift can be transformed into a measurable mass quantity.Different investigations have been conducted to measure the sensitivity of MEMS mass sensors. Ilic et al. (2001) fabricated nanoelectromechanical oscillators for mass sensing applications. An analytical model is developed to investigate the effect of the added mass on the nano-cantilever beam. Subattogram sensitivity is demonstrated under vacuum conditions. Burg et al. (2006) designed and fabricated an electrostatically actuated biomolecular mass sensor. The transducer is a vacuum packaged suspended microchannel for mass sensing in liquid. Schmid et al. ( 2010) developed a real-time approach for mass and position determination by using a resonant micro string. It consists of measuring the frequency shift of the first two bending modes. Electrostatically actuated torsional microsensor is a very promising structure for mass sensing due to the ability to be actuated from one side and exposed for sensing in the other side. In