Surface Micromachined Combined Magnetometer/Accelerometer for Above-IC Integration

This paper presents a combined magnetometer/accelerometer sharing a single surface micromachined structure. The device utilizes electrical current switching between two perpendicular directions on the structure to achieve a 2-D in-plane magnetic field measurement based on the Lorentz force. The device can concurrently serve as a 1-D accelerometer for out-of-plane acceleration, when the current is switched off. Accordingly, the proposed design is capable of separating magnetic and inertial force measurements, achieving higher accuracy through a single compact device. The sensor supports static operation at atmospheric pressure, precluding the need for complex vacuum packaging. It can alternatively operate at resonance under vacuum for enhanced sensitivity. The device is fabricated using a low-temperature surface micromachining technology, which is fully adapted for above-IC integration on standard CMOS substrates. The resonance frequency of one of the fabricated structures is measured to be 6.53 kHz with a quality factor of ~30 at a 10-mTorr ambient vacuum level. The magnetic field and acceleration sensitivities of the device are measured using discrete electronics to be 1.57 pF/T and 1.02 fF/g, respectively, under static operation.