Frequency Modulated Piezoelectric MEMS Magnetometer Based on Mechanically-Coupled Cantilevers

This study presents a novel frequency modulated (FM) MEMS Lorentz force magnetometer that utilizes two mechanically-coupled cantilevers. By implementing a phase-controlled force-feedback loop across the cantilevers, variations in the magnetic field strength are transformed into changes in the mechanical coupling stiffness. This modulation results in relative shifts of the resonant frequencies, thereby enabling an intrinsic differential FM sensing mechanism. The magnetometer is designed and fabricated on an AlN/Si thin-film piezoelectric-on-substrate (TPoS) MEMS platform, operating at 259.03 kHz and 259.9 kHz for the in-phase and out-of-phase modes, respectively. In the prototype, high differential sensitivities of 1957, 3700, and$6570\ \text{Hz} / \mathrm{T}$are achieved at atmospheric pressure with bias currents of 6.25, 12.5, and 18.75 mA, respectively, using phased feedback implemented via a high-frequency dual channel lock-in amplifier (HF2LI). The experimental results demonstrate a high current-normalized differential sensitivity up to$350\ \text{Hz} / \mathrm{T} / \text{mA}$and therefore validate the proposed differential FM sensing concept.