LiNbO₃-Based SAW Temperature Sensor With Improved Sensitivity

A surface acoustic wave (SAW) temperature sensor is presented in this article. Based on the thermal expansion and sound velocity variation of lithium niobate under temperature change, the resonant frequency shifts are used for ambient temperature measurement. After the parameter design of the SAW resonator, the device is fabricated on a 128° YX LiNbO₃ crystal substrate through micro-electro-mechanical system (MEMS) technology, which mainly includes liftoff and wet etch processes. To improve the stability and portability of the sensor, the oscillator is built based on the application of the operational amplifiers and the characters of the fabricated SAW resonator. The closed-loop characterization is carried out to characterize the oscillation frequency, the phase noise, and the frequency short-term stability of the oscillator, and the test results show that the oscillation frequency occurs at 45.28 MHz, the noise floor at 1 MHz offset is −125.13 dBc/Hz, the short-term stability is achieved in terms of the Allan deviation of 27.84 ppb at the measurement time of 1 s, and the lowest deviation is at measurement time of 0.2 s with value of 14.54 ppb. Finally, the temperature sensitivity of the designed SAW temperature sensor is characterized, and the value is up to 3503.14 Hz/°C (77.37 ppm/°C).