Enhancing Magnetoelastic Coupling in Shear Surface Acoustic Waveguide Based on ST-Cut Quartz Substrate and Ni Thin Films With Uniaxial Magnetic Anisotropy Induced by Thermal Annealing

In this study, we conduct a comprehensive investigation to enhance the performance of shear surface acoustic wave (SAW) magnetic sensors. We explore the interaction between SAW and a nickel film deposited on ST-cut quartz in a delay line configuration. The nickel film, measuring
$2\ \text{mm}$
in width and
$100\ \text{nm}$
in thickness, undergoes vacuum annealing at
$500\ ^\circ \text{C}$
to induce magnetic anisotropy through the anisotropic thermal properties of ST-cut quartz. Our research combines theoretical and experimental approaches to evaluate the
${S}_{21}$
phase shift in response to an applied magnetic field. The results demonstrate a remarkable agreement between theoretical predictions and experimental data. To interpret the sensor's response behavior, we introduce a custom piezomagnetic model. Notably, we observe a phase shift difference between minimum and maximum of approximately
$30^\circ $
for a propagation path of
$2\ \text{mm}$
. We further investigate the impact of incorporating an SiO
₂
layer on top of the magnetic thin film. This addition doubles the phase shift difference, as shear SAWs become more confined near the surface or entirely waveguided within the SiO
₂
layer. In addition, we explore an innovative approach for modifying the sensor's response behavior by manipulating the magnetic thin film's anisotropy. These findings contribute to the advancement of SAW magnetic sensor technology, offering enhanced sensitivity and performance through the integration of magnetic thin films and SiO
₂
layers.