A piezoelectric-on-silicon width-extensional mode Lorentz force resonant MEMS magnetometer

Abstract

In this paper, we present a unique micromachined magnetometer based on a width-extensional (WE) mode thin-film piezoelectric-on-silicon (TPoS) resonator for detection of magnetic fields applied normal to the plane of fabrication. The reported device targets operation in ambient pressure rather than vacuum, which should simplify packaging requirements. To compensate for a lower quality (Q) factor when operating in ambient pressure, the strong electromechanical coupling provided by the piezoelectric Aluminium Nitride (AlN) transducer has the advantage of greatly enhancing the sensitivity performance of the device. The reported device is based on a rectangular plate that is driven into the WE resonance mode by an in-plane Lorentz force pair that results from an external out-of-plane magnetic field. Two design generations of the proposed device topology are presented herein, with the latter design generation showing a substantial improvement over the former. The resonant frequency of the most recent design generation is 18MHz, and its associated Q-factor was 1500 under ambient conditions. We have experimentally calibrated the sensitivity of the device, which was found to be 63.27mV/T under ambient conditions. The measured result agrees well with both our analytical and finite element model.