Exploiting nonlinearities to improve the linear region in an electrostatic MEMS demodulator

This paper presents a technique whereby the overall nonlinear behavior of an electrostatically actuated and sensed MEMS is linearised for most of its usable range. The nonlinear characteristics are first analysed theoretically. This analysis reveals that the nonlinearity can be ‘neutralised’ by replacing the spring with a nonlinear - cubic stiffness - spring. Finding a feasible solution requires finding a compromise between a large number of geometric dimensions and constraints; this was achieved by making extensive use of MATLAB’s optimization toolbox. The device having optimal dimensions was manufactured using the SOIMUMPs process and lab measurements confirmed that the overall nonlinearity was practically eliminated for actuation voltages of 4 volts and upwards.