Sensitivity Enhancement of a Lorentz Force MEMS Magnetometer With Frequency Modulated Output

This paper presents a frequency output micromachined silicon magnetometer comprised of a low stiffness thermalpiezoresistive electromechanical resonator coupled to a Lorentz force generator. The Lorentz force generator utilizes a leverage mechanism amplifying the force by ~ 55X. Upon application of a magnetic field perpendicular to the device, the leveraged Lorentz force deflects the resonator central beam changing its resonance frequency. Furthermore, different structures for the piezoresistive beam have been explored and the design has been modified to enhance the sensitivity by ~ 950X (from 7.73 to ~7200 ppm/mA.T). Frequency shifts as high as 0.123ppm/μT have been demonstrated, for the best-case design operating at a Lorentz force current of 17 mA, which is in good agreement with its simulated values. The drift in the resonance frequency has been experimentally measured for various operating bias currents to get an insight into the noise floor for such devices. The noise floor for the best-case design is measured to be 14 μT/√ Hz, which is in the same order when compared with the prior state-of-the-art frequency modulated Lorentz force MEMS magnetometers.