High-Performance Surface Acoustic Wave Devices Using LiNbO₃/SiO₂/SiC Multilayered Substrates

The rapid development of the fifth-generation (5G) wireless system is driving strong demand for high-performance radio frequency filters. This work studies shear horizontal surface acoustic wave (SAW) devices using 15°-rotated Y-cut X-propagating (15°Y-X) LiNbO ₃ /SiO ₂ /SiC multilayered substrates. Single-crystalline 15°Y-X LiNbO ₃ films are bonded to SiO ₂ /SiC handling substrates by the smart cut technology. On the basis of accurate finite-element-method simulations, LiNbO ₃ /SiO ₂ /SiC wafer configurations are optimized to suppress spurious resonance due to Rayleigh-mode and transverse-mode responses, and one-port resonators with a clean spectrum, a high electromechanical coupling coefficient of 22.00%, and an admittance ratio (impedance ratio) over 65 dB are successfully implemented. Based on the characteristics of the resonators, high-performance filters with a center frequency of 1.28 GHz, a large 3-dB fractional bandwidth of 16.65%, and a low minimum insertion loss of 1.02 dB are successfully designed and fabricated. Furthermore, no ripples in the passband of the filters are observed. Additionally, the filters exhibit a temperature coefficient of center frequency of -63.8 ppm/°C and a large power durability of 33.2 dBm. This work confirms the high performances of the SAW devices using the 15°Y-X LiNbO ₃ /SiO ₂ /SiC multilayered substrate, and this type of SAW device exhibits a prospect of commercial applications in the 5G wireless system.