Wideband and High Quality Factor Shear Horizontal SAW Resonators with Improved Temperature Stability in LNOI Platform

Abstract

In this work, the relation between temperature coefficient of frequency (TCF) and wavelength (λ) of a shear horizontal surface acoustic wave (SH-SAW) resonator in lithium niobate-on-insulator (LNOI) platform is investigated numerically and experimentally. Proposed device achieves a low TCF of -18.5 ppm/K, quality factor (Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> ) of 1360, and effective electromechanical coupling factor $\left({k_{{\text{eff}}}^2}\right)$ of 21.2%, yielding a high figure-of-merit $\left({{\text{FOM1}} = k_{{\text{eff }}}^2\cdot{Q_{\max }}}\right)$ of 288. The dispersive behavior of the TCF was first analyzed based on finite element method (FEM), which reveals the strong correlation between TCF and the thickness of LN (h <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LN</inf> ) and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (h <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiO2</inf> ) thin films. To confirm our observations, three prototyped SH-SAW devices with λ of 2.8, 4, and 6 μm were fabricated and characterized, showing TCFs approximately -86, -45, and -18.5 ppm/K, respectively, for both series and parallel resonance frequencies. The results captured through experiments fits well with the trends predicted in the FEM simulations. Furthermore, the proposed resonator (λ = 6 μm, TCF = -18.5ppm/K, FOM1 = 288) exhibits a very competitive performance among state-of-the-art thin film LN/LT resonators.