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This review provides the spintronic strain‐gauge sensor (Spin‐SGS) based on a magnetic tunnel junction (MTJ) with a high gauge factor in excess of 5000, which was realized by adopting a novel amorphous Fe‐B‐based sensing layer with high magnetostriction and low coercivity in a high magnetoresistance Mg‐O barrier MTJ. This review also provides a demonstration of novel "Spintronic MEMS (Spin‐MEMS) microphone," in which a series of Spin‐SGSs are integrated onto a bulk micromachined diaphragm. The Spin‐MEMS microphone exhibits a signal‐to‐noise ratio (SNR) of 57 dB(A) due to the high strain sensitivity of the Spin‐SGSs. [ABSTRACT FROM AUTHOR]

We investigated spintronic strain-gauge sensors (Spin-SGSs) based on magnetic tunnel junctions (MTJs). To enhance the strain sensitivity of Spin-SGSs, which is defined as the gauge factor = (ΔR/R)/Δε, we investigated MgO-MTJs with an amorphous CoFeB sensing layer that exhibits high magnetostriction and soft magnetic properties. To maintain the amorphous structure of the CoFeB sensing layer even after post annealing, we applied a MgO capping layer (MgO-cap) to the CoFeB sensing layer and compared it with a Ta capping layer (Ta-cap). After post annealing at 320 °C, the CoFeB sensing layer with a MgO-cap maintained a low coercivity of 3 Oe, whereas that with a Ta-cap exhibited a high coercivity of 25 Oe. Microstructure analysis revealed that the CoFeB sensing layer with the MgO-cap has an amorphous structure because boron remains in the CoFeB sensing layer even after post annealing. The gauge factor for the Spin-SGS with the MgO-cap was 4016, which was four times larger than 942 for the Spin-SGS with the Ta-cap. [ABSTRACT FROM AUTHOR]