Acoustic Loss in Thin-Film Lithium Niobate: An Experimental Study
Ruochen Lu, Yansong Yang, Songbin Gong
Abstract
This work reports an experimental study of acoustic loss in thin-film lithium niobate (LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) using acoustic delay lines (ADLs). Unlike prior resonator-based quality factor ( Q) studies, this approach directly extracts the damping in thin-film LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , avoiding the influence of other intricate loss mechanisms, e.g., anchor loss and electrode-induced loss. Acoustic attenuation of fundamental symmetric (S0) and shear horizontal (SH0) waves are studied in suspended LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films of different thicknesses. The attenuation is significantly higher in thinner LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films, suggesting the LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal degradation during the microfabrication as the primary loss origin. Nevertheless, the extracted equivalent Q in thin-film LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is still higher than reported values, suggesting that anchor design and electrode quality remain the bottlenecks for higher Q. The proposed loss extraction framework is readily extendable to other acoustic thin-film structures.