Ferromagnetic / Metal / Ferromagnetic Sandwich Multilayer Stress Impedance Effect

The amorphous magnetic alloy films exhibit obvious stress-impedance effect when external stress is applied on the ferromagnetic material, the impedances of the ferromagnetic materials change remarkably. This characteristic of amorphous alloy is very significant to the development of strain or stress sensor. So it's important to study the stress-impedance effect of amorphous alloy. Since the ferromagnetic/metal/ferromagnetic sandwiched films have a more remarkable stress-impedance effect than that of single layer ferromagnetic films, the stress-impedance effect of ferromagnetic/metal/ ferromagnetic sandwiched films have been studied both in theory and experiment in this thesis.The physic model of ferromagnetic/metal/ferromagnetic sandwiched film has been established firstly. By solving the Maxwell equation we get the relationship between the impedance and the permeability. Later we solve the Landau-Lifshitz-Gilbert equation to get the relationship between the permeability and applied stress. At last we use the permeability of ferromagnetic materials to link the applied stress and the impedance, which gives the formula of stress impedance effect. Based on the model, the influences of geometric and physic parameters on the impedance and stress impedance effect have been studied. The results show that the stress-impedance effect increases with the increase of the thickness of the ferromagnetic layer and metal layer. The stress-impedance effect can be improved by using metal layer with high conductivity and magnetic layer with high saturation magnetization. As the frequency increases, the stress-impedance effect increases firstly and decreases later. There is a best frequency range does exist, and around the best frequency the sandwiched films keep a high stress-impedance effect.FeCoSiB/Cu/FeCoSiB sandwiched films have been prepared on the Kapton substrate. The impedances of the multilayers have been measured when external stress has been applied. The results show that the stress-impedance effect increases with the increase of the thickness of the ferromagnetic layer and the metal layer. When the thickness of FeCoSiB layer keeps 1μm and the thickness of Cu layer varies from 0.25 μm to 1μm, the stress-impedance effect of the sandwiched films increases from 0.3% to 20.5%. When the thickness of Cu layer keeps 0.25μm and the thickness of FeCoSiB layer varies from 0.5μm to 1.5μm, the stress-impedance effect of the sandwiched films increases from 0.5% to 8.6%. Different metal layers exhibits different stress-impedance effect. The stress-impedance effects of the multilayers with Cu metal layer and with Ag metal layer are 3.1% and 13.3%, respectively. The stress-impedance effect of the FeCoSiB/Cu/FeCoSiB sandwiched films increases and decreases later with the increase of the frequency. The maximum effect occurs at 1MHz. The theory results are verified well by the experiment results.FeCoSiB/Cu/FeCoSiB sandwiched films of 3mm×4mm size have been fabricated on Kapton substrate by lithography and lift-off technology. The results show that the impedance increases from 118.7? to 140.3?, with an impedance change of 18.2% and a strain sensitivity more than 100 when the deformation changes from 990ppm to 2700ppm. When the deformation of the strain gauge changes from 990ppm to 2700ppm, the impedance of the samples varies lineally.