Basic Study of Fabricating High Sensitive Strain Sensor Using Magnetostrictive Thin Film on Si Wafer

We tried to fabricate a strain sensor element using magnetostrictive film on a Si wafer for realizing microelectromechanical systems (MEMS) applications. The principle of the sensor is based on the inverse-magnetostriction effect. In our previous study, the same sensor element on thin conventional glass substrate exhibited ultrahigh sensitivity as a strain sensor due to well-induced uniaxial magnetic anisotropy to the width direction of rectangular FeSiB layers. The uniaxial anisotropy was realized by residual stress among FeSiB, molybdenum as conductive layer, and the substrate after field annealing. However, contrary to the previous results, in this paper, by utilizing Si wafer for the substrate, it was found that uniaxial anisotropy of the rectangular FeSiB layer was induced to the longitudinal direction. The reason of the result was due to the large difference of the coefficient of thermal expansion between the thin glass substrate and Si wafer. Therefore, rotation of magnetic moment of the FeSiB layer from the longitudinal direction to the width direction by applying compressive stress was observed by magnetic Kerr effect microscopy. The results indicate that the sensor element on the Si wafer will have suitable properties as MEMS-type strain sensor.