Numerical Design and Optimization of High Performance Langasite and Hetero-Acoustic Layer-Based Surface Acoustic Wave Device

La3Ga5SiO14 (langasite, LGS)-based surface acoustic wave (SAW) devices are widely used for industrial health monitoring in harsh high-temperature environments. However, a conventional LGS-based SAW structure has a low quality factor (Q) due to its spurious resonant peaks. A hetero-acoustic layer (HAL)-based structure can effectively enhance the Q factor and the figure of merit (FOM) of SAWs due to its better energy confinement of SAWs. In this work, a HAL-based structure is proposed to achieve a high FOM and high-temperature resistance at the same time. Based on the finite element method (FEM) and coupling-of-model (COM) combined simulation, a systematic numerical investigation was conducted to find the optimal materials and structural parameters considering the viability of an actual fabricating process. After optimizing the layer number, an intermediate-layer material choice and structural parameters, Pt/(0°, 138.5°, 27°) LGS/YX-LGS/SiC HAL structure were chosen. The proposed structure achieves a Q factor and FOM improvement of more than 5 and 2.6 times higher than those of conventional SAW structures, which is important for the development of high temperature SAW sensors. These findings pave a viable method for improving the Q factor and FOM of LGS-based SAW and can provide material and device structural design guidance for fabrication and high-temperature applications in the future.