Thin-film lithium niobate-on-insulator (LNOI) shear horizontal surface acoustic wave resonators

Abstract

This work investigates the design methodology to obtain large electromechanical coupling factor ( keff2 ) and high quality factor (Q) of shear-horizontal surface acoustic wave (SH-SAW) resonators based on the thin-film lithium niobate-on-insulator (LNOI) technology. The guided SH wave can be excited through interdigital transducers and propagate at the very surface of the material stackings. Such a guided SH wave in LN/SiO2 double layer structure is expected to offer high keff2 by confining the elastic strain energy in the piezoelectric thin film. To capture the optimum design window for high-performance LNOI SH-SAW devices, the impact of electrode material and its thickness on the keff2 dispersive characteristics are intensively investigated by finite element method (FEM). In this study, various one-port resonators with wavelengths from 2.8 μm to 8 μm were fabricated on a LNOI wafer with LN and SiO2 thickness of 0.7 and 2 μm, respectively. The 100 nm thick gold film was chosen as the electrode of the devices, which demonstrate a similar keff2 dispersive behavior to the FEM simulation with small discrepancy. Among the measurement results over several tested samples, a high- keff2 of 25.5% and Q of 960 was recorded at a resonance frequency of 581 MHz (FOM = keff2⋅Q = 245), revealing great potential for the application of wide-band frequency selection in telecommunications.