Research On High-performance SAW Low Temperature Sensors

With the advancements in life sciences and deep space exploration,there has been an increasing demand for real-time wireless temperature monitoring in low-temperature environments.Conventional electrical temperature sensors are inadequate for long-term use in such environments due to their susceptibility to power supply and transmission line interference.In contrast,surface acoustic wave（SAW）temperature sensors have demonstrated great potential for low-temperature measurement,thanks to their small size,high sensitivity,and wireless and passive features.The main work of this article is as follows:（1）The propagation mechanism of SAW and the structural types of SAW sensors were studied,and the core parameters affecting the performance of SAW sensors and the temperature-sensitive mechanism of SAW temperature sensors were analyzed.（2）Theoretical analysis models of SAW sensors were studied,and a two-dimensional model of a single interdigital transducer（IDT）period of SAW sensors was established using the finite element simulation software COMSOL.Meanwhile,combined with an equivalent circuit model,the electrode thickness,aperture,number of IDT fingers,and reflector gratings were optimized.The design of double electrode transducers was introduced to further improve the performance of the SAW temperature sensor.The frequency-temperature characteristics of the SAW sensor were simulated,confirming the feasibility of the designed SAW temperature sensor for low temperature sensing.（3）Research on the micro-nanofabrication process of SAW low temperature sensors was conducted,and SAW low temperature sensors with single electrode transducers and double electrode transducers were prepared respectively.Quality control was performed on the prepared samples.（4）The scattering parameter test at room temperature and low temperature test of the prepared SAW low temperature sensors were performed,and the device performance was characterized using S11 parameters.Among them,the S11 minimum value of the SAW temperature sensor with single electrode transducers was-19.423 d B,with a quality factor of2955.60.The S11 minimum value of the SAW temperature sensor with double electrode transducers was-25.156 d B,with a quality factor of 5757.18.The results indicated that the design of double electrode transducers could significantly enhance the performance of SAW temperature sensors while reducing the insertion loss.The temperature test range was-100～150℃.As the temperature decreased,the resonance frequency increased continuously.The temperature sensitivities of the SAW temperature sensors with single and double electrode transducers were measured to be 11.64 k Hz/℃and 11.84 k Hz/℃,respectively,and the frequency temperature coefficients were-71.09 ppm/℃and-73.7 ppm/℃,respectively.Both sensors exhibited good linearity within the test range,confirming the feasibility of preparing SAW low temperature sensors on 128°YX Li Nb O₃ substrates.