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

A type of strain sensor element utilizing the magnetostrictive effect and t he magneto-impedance effect was presented and the strain-impedance properti es of the element were evaluated. The strain-impedance (SI) element constru cted 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 magnetostrictiv e layers which covered the conductive layer. The Co73Si12B15 negative magne tostriction films (lambda=-6x10(-6)) were adopted as magnetostrictive layer s and magnetic anisotropy was induced perpendicular to the applied strain d irection. Impedance Z drastically changed with applied compressive strain e psilon up to -2x10(-3) and exhibited a good reversibility and reproducibili ty. The impedance change ratios Delta Z/Z(0)=(Z(max)-Z([epsilon=0]))/Z([eps ilon=0]) of the element were 40% at 15 MHz and 24% at 1 MHz. The maximum ga uge factor G(max) defined as the maximum fractional change in impedance to strain (Delta Z/Z)/epsilon was 960-1910 in low frequency ranges from 1 to 1 5 MHz. These values were much larger than those of the single layer SI elem ent constructed from only a CoSiB film and ten times larger than those of c onventional semiconductor strain gauges. Therefore, the layered SI element will be very useful for the application of sensing small amounts of strain. (C) 2000 American Institute of Physics. [S0021-8979(00)33108-5].