Single-crystalline LiNbO3 film based wideband SAW devices with spurious-free responses for future RF front-ends

Abstract

This work demonstrates super-high frequency wave-guided surface acoustic wave (SAW) devices based on LiNbO3/SiO2/Si layered substrates. SAW resonators with fundamental operating frequency to the 7-GHz range were developed, and wave modes like the Rayleigh, Shear-horizontal (SH), Pseudo-Bulk, etc., were observed. Furthermore, effective coupling coefficients (k2eff) and quality factor (Q) of the devices have been investigated systematically. Specifically, spurious-free SAW resonators with the SH wave frequency over 7.40 GHz and the high k2eff value of ∼7.8% were obtained at a nanoscale wavelength of 480 nm. Finally, high-performance filters with a bandwidth over 300 MHz were achieved. The demonstrated filters show sharp roll-off and spurious-free responses within the passband with insertion loss <−5 dB and a small temperature coefficient of frequency of ∼−45.8 ppm/K at a super-high frequency of 7.17 GHz. Upon further optimizations, high-performance SAW devices built on a single crystalline LiNbO3 film can potentially enable the low-loss and wideband signal processing functions, promising for the next-generation radio frequency front-end system applications.