Low-temperature annealing regulates magneto-acoustic coupling for enhanced FeCoSiB/Ti SAW magnetic field sensor performance

Abstract

Utilising low-temperature annealing processes to regulate the magneto-acoustic coupling effect in surface acoustic wave (SAW) magnetic field sensors significantly enhances the sensitivity and temperature stability of sensors. This study employs FeCoSiB/Ti multilayer composite soft magnetic alloys as magneto-sensitive films, combining theoretical modelling with experimental validation to elucidate the multifaceted mechanisms by which low-temperature annealing processes (100 °C) influence the magneto-acoustic coupling effect. Through the Arrhenius magnetic domain reorientation model and the modified Stoney equation, we clarified the use of low-temperature annealing to regulate magnetic parameters such as the saturation magnetostrictive coefficient and internal stress relaxation, thereby enhancing the magnetostrictive thin film ΔE effect, and ultimately establishing a quantitative relationship between the annealing temperature and the sensitivity of the SAW magnetic sensor. Theoretical analysis demonstrates that after 100 °C annealing, the saturated magnetostrictive coefficient increases to λ_s = 46.9 × 10⁻⁶, internal stress is significantly reduced, the ΔE effect improves to 49.5%, and the sensitivity of the SAW magnetic field sensor can be enhanced by 51%. The experimental results verified the theoretical analysis results. After annealing at 100 °C, the sensor sensitivity increased from 156.34° per mT to 236.19° per mT, the temperature drift coefficient decreased by 62.5%, and the insertion loss of the sensor device remained almost unchanged. In contrast, high-temperature annealing at 200 °C/300 °C caused significant lattice distortion and increased acoustic propagation loss, leading to a sharp deterioration in sensitivity (8.67° per mT). This study provides theoretical guidance and experimental evidence for the preparation of SAW magnetic field sensors with high sensitivity and excellent stability.