Dual-resonator MEMS magnetic sensor with differential amplitude modulation

We report a new Lorentz force magnetic sensor employing a matched pair of silicon micromechanical resonators on the same die. The two resonators are operated as closed-loop oscillators, where the change in oscillation amplitude is used as a measure of the magnetic field strength. The magnetometer, consisting of the two identical oscillators having opposing axes of field sensitivity, produces two similar oscillation amplitudes with nearly identical temperature sensitivities, providing continuous temperature compensation. Differential amplitude modulated (AM) output from the two oscillators reduces the sensor's offset by a factor of 12 to 26 μT, and suppresses the effect of the resonator's temperature coefficient of quality factor (TCQ) on the output, reducing the maximum drift error by a factor of 15 to ±0.49 μT, improving the sensor's bias instability from 86 nT to 26 nT, and increasing the averaging time to reach the bias instability from 1 s to 10 s. With 44-μW power dissipation, the sensor achieves a resolution of 50 nT/√Hz, limited by Brownian noise.