Ultra-sensitive magnetic field sensor based on a low-noise magnetoelectric MEMS-CMOS oscillator

This paper reports on the first demonstration of a high performance magnetic field sensor (sub-10 nT/Hz^1/2 resolution) based on a high frequency (168.2 MHz), compact and low-power consumption (~3 mW), self-sustained magnetoelectric MEMS-CMOS oscillator. For the first time, a high electromechanical performance (quality factor Q = 1101 and electromechanical coupling coefficient k_t² = 1.16%) AlN/FeGaB nano-plate (250 nm / 250 nm) resonator working at a higher order lateral-extensional mode of vibration was connected to a CMOS chip-based self-sustaining oscillator loop for direct frequency read-out. Because of the large value of the resonator figure of merit (FOM = k_t²·Q~13), direct wire-bonding of the magnetoelectric MEMS resonator to a Pierce oscillator taped out in the ON Semiconductor 0.5-μm CMOS process was made possible. This first prototype was characterized for DC magnetic field from -200 Oe to 200 Oe, showing high sensitivity (221.4 Hz/μT) and low detection limit (9.3 nT/Hz^1/2) when the magnetic field was applied along the length of the resonator, representing the first demonstration of a high resolution MEMS magnetoelectric resonant sensor interfaced to a compact and low power, self-sustained oscillator as direct frequency readout.