Off-Resonance Low-Pressure Operation of Lorentz Force MEMS Magnetometers

This paper demonstrates bandwidth extension for Lorentz force microelectromechanical systems magnetometers operated at a frequency slightly lower than the mechanical resonance. This off-resonance mode of operation also minimizes the critical tradeoff between maximum sensing bandwidth and minimum measurable field, enabling low-pressure operation and the associated resolution improvement. The experimental verification is obtained using two identical devices packaged at two different pressures and tested with a suitable low-noise board-level electronics. The first device, packaged at 1 mbar, has a (mechanical) sensing bandwidth of ~50 Hz, and a resolution per unit bandwidth and driving current of 290 nT · mA/√Hz. With the second device, packaged at 0.25 mbar and operated off-resonance, roughly twice better resolution (160 nT · mA/√Hz) and four times larger bandwidth (>200 Hz) are obtained.