Enhancing Pressure Sensitivity of Langasite Membrane-Based High-Temperature Pressure Sensor Using Shear Horizontal SAW

Langasite (LGS)-based surface acoustic wave (SAW) pressure sensors have been extensively validated as a promising solution for high-temperature applications. However, mainly the Rayleigh mode SAW has been employed in previous research on LGS membrane-based pressure sensors. In this study, shear horizontal mode SAW (SH-SAW) is employed for its higher normalized pressure sensitivity (NPS) and bigger electromechanical coupling coefficient (K-2) than the Rayleigh wave. To comprehensively calculate the SAW properties of rotated Y-cut LGS, a novel weak-form nonlinear finite element method (FEM) simulation model is applied so that the nonlinear electroelastic wave equations with reduced symmetry can be solved by the commercial FEM software directly. Meanwhile, absolute pressure sensors are fabricated and characterized on one of the well-selected optimal pressure-sensitive cuts with Euler angles of (0 degrees, 0 degrees, 90 degrees). The NPS is 9.14 ppm/MPa at room temperature (RT) and 9.63 ppm/MPa at 400 degrees C, resulting in a total variation of 4.9%. The NPS achieved by the SH-SAW-based sensor surpasses previous research findings and is consistent with simulation results. In addition, prototypes of differential pressure sensors with temperature compensation have been developed as well. The pressure sensitivity reaches a maximum of 435 ppm/MPa with a thinned membrane. Furthermore, a SiO2 cladding layer has been demonstrated to exhibit exceptional device protection and remarkable manipulation of temperature characteristics. This study demonstrates the evident enhancement of SAW pressure sensor performance through SH-SAW utilization, providing valuable guidance for future optimization of SAW sensors.