Increasing the sensitivity of Love wave MSAW sensors by magnetoelastic layer thickness variation

Increasing the magnetic field sensitivity is one of the major challenges in the study of magnetic surface acoustic wave (MSAW) sensors. In this paper, Love wave MSAW sensors are investigated in a Transmissive Single Port Delay Line (TSP-DL) configuration, on ZnO (700 nm)/Y-X LiNbO₃. CoFeB (100 nm) or CoFeB(100 nm)/SiO₂(3 nm)/CoFeB(100 nm) sensitive magnetoelastic layers are placed in the acoustic path between two electrically connected interdigital transducers. The fundamental Love wave on ZnO(700 nm)/ Y-X LiNbO₃ presents a high electromechanical coupling coefficient (K²), resulting in a high signal amplitude, which is favorable for delay lines performances. Additionally, shear waves are highly sensitive to the magnetic field due to the large ΔG effect in the magnetoelastic layers. A maximum frequency shift of 0.36% was achieved using a CoFeB(100 nm)/SiO₂(3 nm)/CoFeB(100 nm) stack as the sensitive layer, with a high maximum magnetic sensitivity of 3630 ppm mT⁻¹ (1482 kHz mT⁻¹ at 410 MHz). This sensitivity is among the highest reported in the literature on magnetic SAW sensors.