In Situ Packaged LiNbO3 SAW Resonators for Strain and Temperature Sensing Under Wide-Range Thermal Conditions

Surface acoustic wave (SAW) devices have a wide range of application prospects in ultralow-temperature environments. This article uses COMSOL software simulation to realize the preparation of Y128° LiNiO3 SAW resonator (SAWR) and uses silicon oxide wafers to prepare the packaging cap. The in situ packaged SAWR preparation is completed by adhesive bonding. The tensile strength of the packaged structure can reach 7.49 MPa. A normal temperature strain experimental platform and a high- and low-temperature experimental platform are built to experimentally explore the strain characteristics of the resonator at room temperature and the temperature sensing characteristics of low and high temperatures. The experimental results show that the mounting structure will affect the range of strain sensing, and the in situ packaged SAWR is not suitable for large strain test environments. In the range of 0– $1000~\mu \varepsilon $ , its frequency is basically linear with strain, the linear sensitivity (SSF) is −161 Hz/ $\mu \varepsilon $ , and the strain frequency coefficient (SCF) is 0.49 ppm/ $\varepsilon $ . The in situ packaged SAWR can work normally at $- 196~^{\circ }$ C. Its frequency-temperature relationship in the range of $- 196~^{\circ }$ C to $- 150~^{\circ }$ C is not completely linear, and there is a high-order temperature sensitivity. The frequency–temperature relationship in the temperature range of $- 150~^{\circ }$ C to $140~^{\circ }$ C has a strong linear characteristic, and its linear temperature sensitivity is −26.8 kHz/°C. It has good application prospects in wide temperature band wireless passive temperature sensors across zero degrees and normal temperature strain sensing.