Pressure Dependence of the High-Frequency Impedance of NiFe/Cu/NiFe/Cu/Cr Multilayer Films

A large pressure-impedance effect was measured in soft ferromagnetic NiFe/Cu/NiFe/Cu/Cr multilayer films carrying high-frequency alternating currents. Experimental results show that two pressure-impedance sensors consisting of multilayer films were highly sensitive to vertical mechanical pressures at high frequency (>50 MHz) and were capable of measuring small mechanical pressures of 0.1-0.9 gf. The resistance of the pressure-impedance sensors was greatly decreased at high frequency due to the presence of the pressures, and underwent a significant variation of -14% at 113 MHz. Large resistance variation is related to the permeability variation caused by the presence of internal stresses induced by use of mechanical pressures on NiFe films. Magnetic moment rotation caused by the mechanical pressures is probably the origin of the large variation of magnetic permeability at high frequency. The adopted pressure-impedance sensors hold great promise for sensitive measurements of mechanical pressures, such as for monitoring slight vibration, motion, and displacement.