Comparative study of lithium niobate thin films-based surface acoustic wave resonators including temperature characterization

Abstract

This Letter presents a comparative study of surface acoustic wave (SAW) resonators on two different piezo-on-insulator (POI) substrates, 30° YX-LiNbO3/SiO2/sapphire and 30° YX-LiNbO3/SiO2/poly-Si/Si. The dispersion relationships between the resonant frequencies and wavelengths for the resonators, including the shear horizontal (SH) and Rayleigh modes, are investigated. The theoretical and experimental results showed that the main SH mode provides a larger coupling coefficient (K2) and that the spurious Rayleigh mode can be shifted from the passband and away from the main SH mode. Although the proposed POI SAW resonators on two different substrates have comparable frequencies for the same wavelength, the sapphire-based substrate exhibits a larger K2 of 28% and a higher fitted Bode-Qmax of 977 at 1.4 GHz. The temperature behavior of the SAW resonators is measured over a temperature range from −25 to 250 °C. The findings indicated that the resonator with the Si-based substrate has better temperature stability, with a temperature coefficient of frequency (TCF) of −16.99 ppm/°C and a turning point at 150 °C. In contrast, the one with the sapphire-based substrate provides a moderate TCF of −22.15 ppm/°C and remains linear for temperatures above 200 °C. This study reveals the impact of different substrate structures on the performance of SAW resonators, providing guidance for the design of desired SAW devices and their applications.