Highly sensitive spintronic strain-gauge sensor and Spin-MEMS microphone

Strain-gauge sensors consisting of magnetic tunnel junctions (MTJs) have attracted attention because of their high strain sensitivity based on a novel strain sensing scheme different from the piezoresistive effect. To maximize the strain sensitivity of these spintronic strain-gauge sensors (Spin-SGSs), we previously developed an MTJ film with magnetostrictive material that acutely rotates with strain. This review presents a Spin-SGS with a high gauge factor in excess of 5000, which was achieved by adopting an amorphous FeB-based sensing layer with high magnetostriction and low coercivity in a high magnetoresistance Mg-O barrier MTJ. We also investigated the feasibility of using this Spin-SGS in microelectromechanical system (MEMS) sensor devices. This review also describes the properties of a "Spintronic MEMS (Spin-MEMS) microphone," in which Spin-SGSs are integrated onto a bulk micromachined diaphragm.