Micro-strain sensors using the magnetostrictive properties of FeCeSiB films were investigated. To avoid the effects of the rigidity of the substrate on the stress sensitivity, a sensor was formed on thin polyimide ribbons (50 μm thick), which have superior heat resistance, wide elastic region, and excellent flexibility. By using the large difference in the coefficient of thermal expansion between FeCoSiB and polyimide, the residual stress in the magnetostrictive FeCoSiB patterned film was controlled. The sensor was formed under optimized conditions, and had an extremely high value of the figure of merit F = (ΔZ/Z)/Δε (change in film impedance Z per unit ε) of about 1500 at a carrier current frequency of 700 MHz. In addition, the point of stress representing the largest sensitivity of the sensor was controlled by controlling the field annealing conditions.
