Narrowband Longitudinal Leaky Surface Acoustic Wave Devices on LiTaO3/SiO2/SiC Hetero-Structure With Q Over 2000

Abstract

In the rapidly evolving fifth-generation (5G) communication system, there is an urgent need for high-performance surface acoustic wave (SAW) filters to address challenges such as frequency band congestion and smaller gaps between adjacent frequency bands. In this study, we focused on investigating longitudinal leaky SAW (LLSAW) devices based on the LiTaO3/SiO2/SiC hetero-structure, specifically designed for narrowband applications. A comprehensive analysis of the intrinsic electromechanical coupling coefficients ( ${K} ^{{2}}_{\textit {ij}}$ ) of shear horizontal SAW (SH-SAW) and LLSAW on LiTaO3 (LT) thin films was conducted. Via carefully adjusting the LT cut angle $\theta $ and propagation angle $\psi $ , strong excitation of LLSAWs was achieved. Through elaborated parameter optimization, LLSAW resonators were fabricated based on a $50^{\circ }{Y}$ - ${45}^{\circ }{X}$ LT/SiO2/SiC platform, demonstrating excellent performance on frequencies and quality factors (Q). These resonators exhibited small effective electromechanical coupling coefficients ( ${K}_{\text {eff}}^{{2}}$ ) ranging from 4.6% to 5.9% and scalable resonance frequencies ranging from 2887 to 6050 MHz. In addition, a high maximum Bode-Q of 2121 was attained. Finally, filters were numerically simulated using LLSAW resonators and a narrowband filter with fractional bandwidth (FBW) of 2.3% and minimum insertion loss (ILmin) of 1.4 dB was successfully fabricated. The developed LT/SiO2/SiC structure emerges a great prospect of high-performance narrowband applications in the 5G era.