Modal Shift Characterization of LiNbO3 Thick-Film Surface Acoustic Wave Temperature Sensor

Surface acoustic wave (SAW) sensors have obtained significant attention due to their small size, high sensitivity, passive wireless operation, and ability to measure temperature under extreme conditions. Based on these characteristics, this study proposes a dual-mode SAW temperature sensor, utilizing a $128^{\circ} \mathrm{~XY} \mathrm{~LiNbO}_{3}$ substrate to fabricate a SAW resonator-based temperature sensor. The sensor operates within the temperature range of $27.94^{\circ} \mathrm{C}$ to $68.3^{\circ} \mathrm{C}$, with a corresponding frequency shift from 317.629 MHz to 316.531 MHz. At $36.57^{\circ} \mathrm{C}$, the sensor transitions from Mode 1 to Mode 2, causing a mode shift that introduces a breakpoint in the frequency-temperature curve, splitting the linear trend into two distinct sections. This transition results in a downward shift in the frequency-temperature curve by 0.039 MHzS