MEMS Surface Acoustic Wave Resonator Based on AlN/Si/Fe-Co-Si-B Structure for Magnetic Field Sensing

While various magnetic sensors have been developed over the years, the capability of passive wireless magnetic field detection is still lacking. Magnetic surface acoustic wave (MSAW) devices, combining magnetostrictive with piezoelectric materials, may be one of the candidates for wireless magnetic field sensing. This work proposes a novel microelectromechanical system (MEMS) MSAW resonator based on the AlN/Si/(Fe90Co10)(78)Si12B10 structure. The frequency responses of the resonator were measured when applying a dc magnetic field along the magnetic easy and hard axes. The results indicate that the resonator has higher magnetic sensitivity along the hard axis, with a maximum magnetic sensitivity of 11 kHz/Oe. When performing a magnetic field loop measurement for the hard axis, the resonator's quality factor and resonance frequency showed almost the same variation tendency against the magnetic field. Moreover, the quality factor can attain about 3700 at the position of maximum magnetic sensitivity, which could simultaneously meet the needs of wireless interrogation and high sensitivity. Our work reveals that such an MEMS MSAW resonator has clear potential in the realization of wireless magnetic field sensors with miniaturization, low power, and high complementary metal-oxide-semiconductor (CMOS) compatibility for the future development of the Internet of Things (IoT).