Advanced Surface Acoustic Wave Resonators on LiTaO₃/SiO₂/Sapphire Substrate
Jinbo Wu, Shibin Zhang, Yang Chen, Pengcheng Zheng, Liping Zhang, Hulin Yao, Zhongxu Li, Xiaomeng Zhao, Kai Huang, Tao Wu, Xin Ou
Abstract
The shear horizontal surface acoustic wave (SH-SAW) resonators with excellent quality factor and temperature stability were fabricated on 42°YX-LiTaO3/SiO2/sapphire substrate. For comparison, the 4-inch LiTaO3/SiO2/sapphire (fully insulating LiTaO3-on-insulator, FI-LTOI) and LiTaO3/SiO2/poly-Si/Si (trap-rich layer assisted LiTaO3-on-insulator, TR-LTOI) substrates are prepared by ion-cutting process. The GHz acoustic delay lines (ADLs) built on FI-LTOI exhibit a propagation loss of only 2.95 dB/mm, which is 37.5% smaller than the 4.72 dB/mm of the ADLs on TR-LTOI. The demonstrated SH-SAW resonators on FI-LTOI exhibit higher <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -values than those on TR-LTOI. Among them, a FI-LTOI based resonator with the resonant frequency of 1.76 GHz exhibits a maximum Bode- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{{\mathrm {max}}}$ </tex-math></inline-formula> ) of 4,421, an effective electromechanical coupling coefficient of 13.34%, an excellent figure of merit of 589.8, and a well-compensated temperature coefficient of frequency of −9.1 ppm/°C. More importantly, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{{\mathrm {max}}}$ </tex-math></inline-formula> of the FI-LTOI based resonator is maintained well (2,791) even at 200 °C whereas that of the TR-LTOI based resonator decreased to 674. Overall, the FI-LTOI substrate may serve as an advanced material platform of SAW devices for 5G-FR1 bands.