Off-resonance Operation of In-plane Torsional MEMS Magnetometers

The work presents a MEMS magnetometer for compass applications, which measures magnetic fields along an in-plane direction. The magnetometer is built with the surface micromachining process used for consumer gyroscopes, accelerometers, and recently proposed out-of-plane magnetometers. The magnetometer is based on the Lorentz force principle, it has an area of 282x1095μm2, and it is packaged at low pressure (0.25 mbar). Operation is demonstrated at- and off-resonance: in both situations the measured resolution per unit bandwidth and current consumption is about 120 nT·mA/√Hz, but the maximum sensing bandwidth is extended from 4Hz (at resonance) to 42Hz in off-resonance mode. Within magnetic fields of ±5 mT, the device shows measured linearity errors <2% and a cross-axis rejection of ∼50dB.