Low Loss and Wideband Surface Acoustic Wave Devices in Thin Film Lithium Niobate on Insulator (LNOI) Platform

In this work, we demonstrate high performance shearhorizontal surface acoustic wave (SH-SAW) resonators and delay lines based on a thin film lithium niobate on insulator (LNOI) fabrication platform. To attain large effective electromechanical coupling (k
_eff
²
) and low bulk wave radiation, a SiO
₂
layer with subwavelength thickness is inserted between the lithium niobate thin film and the silicon substrate to form a simple and compact acoustic waveguide. The implemented LNOI resonators with wavelengths (λ) of 4, 6, and 8 μm achieve large keff 2 of 28%, 25%, and 16% with corresponding maximum quality factor (Q) of 380, 560, and 980, respectively, featuring excellent figure of merit (FOM) up to 157. Moreover, the low loss acoustic delay line is also demonstrated to achieve a low insertion loss around 8.5 dB at 640MHz with a model-fitted wide fractional bandwidth around 4.5 % based on a conventional bidirectional transducer.