Strain-impedance properties of a CoSiB/Cu/CoSiB layered film

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Abstract
A type of strain sensor element utilizing the magnetostrictive effect and the magneto-impedance effect was presented and the strain-impedance properties of the element were evaluated. The strain-impedance (SI) element constructed from a CoSiB/Cu/CoSiB layered film was prepared on a Corning No. 0313 glass substrate by magnetron sputtering under a magnetic field. The element was composed of an inner copper conductive layer and outer magnetostrictive layers which covered the conductive layer. The Co73Si12B15 negative magnetostriction films (λ=−6×10−6) were adopted as magnetostrictive layers and magnetic anisotropy was induced perpendicular to the applied strain direction. Impedance Z drastically changed with applied compressive strain ε up to −2×10−3 and exhibited a good reversibility and reproducibility. The impedance change ratios ΔZ/Z0=(Zmax−Z[ε=0])/Z[ε=0] of the element were 40% at 15 MHz and 24% at 1 MHz. The maximum gauge factor Gmax defined as the maximum fractional change in impedance to strain (ΔZ/Z)/ε was 960–1910 in low frequency ranges from 1 to 15 MHz. These values were much larger than those of the single layer SI element constructed from only a CoSiB film and ten times larger than those of conventional semiconductor strain gauges. Therefore, the layered SI element will be very useful for the application of sensing small amounts of strain.