SV-SAW RF filters based on low-cost 128°Y LiNbO3/SiO2/poly-Si/Si substrate for 6G cmWave wireless communications.

Abstract

Recent advancements in mobile communication have escalated the demand for faster data rates, requiring higher carrier frequencies and compact, high-performance, and low-cost radio frequency (RF) filters. Micro-acoustic resonators offer significant advantages in mobile phone filtering due to their low loss and compact size. Addressing the need for low-cost filter solutions for higher frequencies, this study presents a silicon-substrate-based surface acoustic wave (SAW) technology platform to enable high-performance resonators and filters for 6G X-band (7-12 GHz) centimeter-wave (cmWave) wireless communications. Based on a silicon (Si) substrate, we propose a novel design scheme to excite shear vertical surface acoustic waves (SV-SAW) on a 128°Y LiNbO₃/SiO₂/poly-Si/Si layer stack and realize high-frequency resonators above 6 GHz with high-performance: electromechanical coupling coefficient (k²) of 7.6% ~ 8.9% and high-quality factor (Q) ranging from 193-679. The synthesized filters based on those high-performance resonators show low insertion loss (1.47 to 2.20 dB) and 3-dB bandwidth from 308 to 373 MHz. Especially, the demonstrated filter with a center frequency (f_c) at 8.63 GHz exhibits a low insertion loss of only 1.5 dB, which is the best when compared to all other LiNbO₃ acoustic filters in this frequency range, 3-dB bandwidth of 373 MHz, and decent out-of-band rejection across the entire 1-15 GHz range. These results mark a significant step forward for the microwave acoustics field and pave the way for enabling solidly-mounted, low-cost, and miniature-size SAW filters for emerging 6G cmWave wireless communications.