Area-Efficient Three Axis MEMS Lorentz Force Magnetometer

A micro-electromechanical-systems (MEMS) three-axis Lorentz force magnetometer based on a 0.24 x 0.4 mm(2) MEMS resonator that is the smallest Lorentz force sensor reported to date is presented in this paper. A magnetic field can be detected in two axes using a single MEMS structure. Placing two structures perpendicular to each other in a single die makes three-axis sensing possible. Sensing is performed by exciting the MEMS resonator at its in-plane and out-of-plane mechanical resonant frequencies of 40.5 and 107.4 kHz, respectively. A modest die-level vacuum packaging results in in-plane and out-of-plane mechanical quality factors of 110 and 310, respectively. The sensor has a bandwidth of 184 Hz for z-axis and 189 Hz for x/y-axis magnetic field. With an excitation power of 2 mW, the sensor resolution is 285 nT/root Hz for z-axis magnetic field inputs and 344 nT/root Hz for x/y-axis magnetic field inputs. The resolution is limited by Brownian noise in the z-axis whereas the x/y-axis resolution is limited by electronic noise. With an averaging time of 288 s, the sensor shows an offset stability of 23 nT.