Ultralow-Temperature Sensing Characteristics of SAW Resonator With Double-Hammer Weighted LN/LT Substrate

Surface acoustic wave (SAW) temperature sensors have wireless passive characteristics that could solve problems with cable transmission, installation, and high signal requirements in ultralow-temperature sensing for space exploration and exploration of superconducting materials. This work focused on exploring the temperature sensing characteristics of SAW resonators of LiNbO3 and LiTaO3 piezoelectric substrates in the range of $- 196~^{\circ }$ C to $20~^{\circ }$ C and the influence of ultralow-temperature environment on the characteristics of the resonators. This work first designed and prepared an SAW resonator (SAWR) with double-hammer weighted interdigit transducers (IDTs) structures on 128°YX-LN, 64°YX-LN, and 42°YX-LT piezoelectric substrates. It was verified that the double-hammer weighted structure was also suitable for the suppression of the spurious modes of SAWRs on LN and LT piezoelectric substrates. After that, it was carried out the ultralow-temperature experimental investigation by utilizing the ultralow-temperature constant temperature radio frequency (RF) test platform. ${K}^{{2}}$ of SAWR changes little at $196~^{\circ }$ C compared with that at room temperature, and ${Q}_{\text {value}}$ of SAWR is significantly improved compared with that at room temperature. In the range of $- 196~^{\circ }$ C to $20~^{\circ }$ C, the frequency-temperature relationship of the SAWR of LN and LT is nonlinear, the sensitivity of the SAWR of 42°YX-LT as a temperature sensor is relatively small, but its linear frequency-temperature characteristics of the temperature range is $- 160~^{\circ }$ C to $20~^{\circ }$ C, and the SAWR of 128°YX-LN has good linear frequency-temperature characteristics and high-temperature sensitivity in the temperature range greater than $- 120~^{\circ }$ C, which can be applied to the development of wireless low-temperature sensor.