Dual-resonator MEMS Lorentz force magnetometer based on differential frequency modulation

This paper presents a new dual-resonator MEMS magnetic sensor utilizing the Lorentz force. Sensor operation is demonstrated using quadrature frequency modulated (QFM) readout, where the magnetic field strength is measured by monitoring the change in oscillation frequency. The Lorentz force sensor, comprising of a matched pair of differentially operated closed-loop resonators on the same silicon die, produces two similar oscillation frequencies with nearly identical temperature sensitivities, providing a temperature-compensated FM output. The frequencies of the two oscillators are experimentally demonstrated to track each other over temperature, reducing the maximum drift error by a factor of 27 to ±2.2 µT, improving the sensor's bias instability from 170 nT to 63 nT, and increasing the averaging time to reach the bias instability from 0.3 s to 1.1 s. With 1 mA bias current, the device has a measured sensitivity of 2180 Hz/T and Brownian-noise-limited resolution of 60 nT/√Hz which is comparable to, or even better than, that of Hall-effect sensors available today.