Off-resonance operation of a MEMS Lorentz force magnetometer with improved thermal stability of the scale factor

This paper presents a new method for improving thermal stability of the scale factor in resonator-based microelectromechanical systems (MEMS) Lorentz force magnetometers. The method uses two nominally-identical magnetometers. The first is operated off-resonance in open-loop to measure magnetic field, and the second is operated as a closed-loop oscillator to provide a frequency reference for driving current generation. The proposed operation significantly reduces the effect of the resonator's temperature coefficient of frequency (TCF) on the output, improving the sensor's temperature coefficient from 12177 ppm/°C to 508 ppm/°C in a temperature range of 10-60 °C. The sensor operated with a 50 Hz frequency split exhibits a resolution of 0.36 μT/√Hz and measurement bandwidth of 38 Hz, independent from the O-limited mechanical sensor's bandwidth of 3.2 Hz.