A sub-μW micromachined magnetic compass

A low-power micromachined magnetic compass has been designed, fabricated and tested. Sensing of the external magnetic field is achieved by incorporating a permanent magnet into a micro mechanical resonator. The shift of the fundamental resonant frequency of the device is used to determine the amplitude or the direction of the external field. The resonator fabrication follows a CMOS-compatible, low temperature process, mainly based on surface micromachining of polymer layers. The fabricated device has been successfully demonstrated as an electronic compass, exhibiting a resolution of 45 degrees at 30μT, for a 10V resonator excitation voltage. The power consumed by the resonator is on the order of 20nW. A theoretical model of the device was developed using vibration analysis and nonlinear deflection theory. Good agreement was observed between the predicted and observed behavior of the magnetic field sensor.