High-Performance LLSAW Devices on X-Cut LiNbO₃ Thin Film With Bragg Reflector for n78 Band Applications

In this work, a range of high-performance longitudinal leaky surface acoustic wave (LLSAW) devices based on a composite substrate structure are designed and fabricated, specifically aimed at the 5G new radio (NR) n78 band. The substrate comprises an X-cut lithium niobate (LN) thin film and a Bragg reflector composed of alternating layers of SiO2 and Ta2O5. The fabricated LLSAW resonators exhibit exceptional performance with high admittance ratio (AR) and large electromechanical coupling coefficient (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {k}_{\text {t}}^{{2}}$ </tex-math></inline-formula>) over a frequency range of 3.2–3.7 GHz. Specifically, a resonator centered at 3.317 GHz achieved an AR of 67 dB, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {k}_{\text {t}}^{{2}}$ </tex-math></inline-formula> of 20.4%, and a Bode-Qmax of 1219. Additionally, the fabricated filter with a center frequency of 3.4 GHz shows a minimum insertion loss (IL) of 1.35 dB, a 3-dB bandwidth of 433 MHz, and an attenuation of 43 dB in the n41 band. The filter also exhibits a low temperature coefficient of frequency (TCF) of −35.6/−40.2 ppm/°C. The filter demonstrates a 1-dB compression point (P1dB) of 15.2 dBm and an input third-order intercept point (IIP3) of 52.3 dBm, making it suitable for high-linearity, medium-power RF applications. These results demonstrate the potential of LLSAW technology based on X-cut LN thin film and SiO2/Ta2O5 reflectors for advanced 5G communication applications.