Thermally stable SiO2/AlN/SiO2 Lamb wave resonators utilizing the lowest-order symmetric mode at high temperatures

Thermal compensation at high temperatures for Lamb wave resonators utilizing the lowest symmetric (S₀) mode in a SiO₂/AlN/SiO₂ sandwiched structure is theoretically investigated in this work. When temperature raises from room temperature to 600°C, the deformation and displacement caused by the thermal expansion mismatch in the SiO₂/AlN/SiO₂ symmetric composite plate is much less than a conventional temperature compensation plate, i.e. the AlN/SiO₂ composite plate. Acoustic characteristics of the SiO₂/AlN/SiO₂ symmetric membrane with three main electrode configurations are investigated, exhibiting higher phase velocity and larger electromechanical coupling coefficient than the common AlN/SiO₂ layered structure since the symmetric sandwiched plate traps more acoustic waves in the AlN layer. In addition, with proper thicknesses of the AlN and SiO₂ layers, the S₀ mode can simultaneously achieve a turnover temperature at high temperatures and a large intrinsic k² in the SiO₂/AlN/SiO₂ sandwiched structure.