Development of Surface Acoustic Wave Magnetic Field Sensor Incorporating with FeCo Dot Film

To suppress the hysteresis of the magnetostrictive thin-film coated surface acoustic wave (SAW)magnetic field sensor, dotted-design was proposed for magnetostrictive FeCo thin-film in this paper to fully release the magnetostrictive effect and reduce its coercivity. The developed sensor was composed of a sensor chip made by differential delay line-oscillators consist of two oscillation loops, the differential oscillation frequency is collected to evaluate the applied magnetic field. A FeCo dot film was deposited along the SAW propagation path of the sensing device by photolithography and overlay technologies. The size of the FeCo dot element was 3λX4λ (λ: wavelength). The patterned FeCo film produced magnetostrictive effect and ΔE effect generated by the applied magnetic field, resulting in changes in the SAW phase velocity and the corresponding oscillation frequency. Using the Helmholtz coil system, the developed SAW magnetic field sensor with 500 nm FeCo dot film were evaluated. The measured results indicated the dotted pattern design on the FeCo thin-film improved effectively its sensitivity (10.7 KHz/mT)and linearity, and also the hysteresis error reduced significantly up to 0.85%.