Area-efficient three-axis micromechanical magnetic sensor

Demonstrated here is a 3-axis Lorentz force magnetic sensor based on a 0.24×0.4 mm² MEMS resonator that is the smallest Lorentz force magnetic sensor reported to date. Using a single MEMS structure the sensor can detect magnetic field in two axes. By placing two of these sensors perpendicularly in a single die, three axis field measurement can be performed. The sensor is a MEMS resonator and sensing is performed using excitation current at the device´s in-plane and out-of-plane mechanical natural frequencies which are 40.5 kHz and 107.4 kHz respectively. Die-level vacuum packaging results in in-plane and out-of-plane mechanical quality factors of 117 and 220, respectively. With a drive power of 2 mW, the sensor´s noise is equivalent to 285 nT/√Hz for z-axis magnetic field inputs and 344 nT/√Hz for x- and y-axis fields, comparable to the performance of 3-axis Hall-effect sensors currently used in smart phones.