A Temperature-Compensated Dual-Band Passdand Filter Based on Lithium Niobate Thin Films

In this study, we proposed a dual-passband filter based on temperature-compensated laterally excited bulk acoustic resonators with scattering vias (TC-SVBARs), using a 358 nm Z-cut LiNbO₃ thin film and an 836 nm SiO₂ layer. After introducing the SiO2 layer, the even order modes (S2, S4, S6…) are stimulated because the coupled electrical mechanical domain (mutual energy) is non-zero, leading to a non-zero electromechanical coupling coefficient $\left({{K_{\text{t}}}^2}\right)$. Among these, the A3 and S4 modes, with high resonant strength and $\left({{K_{\text{t}}}^2}\right)$, are selected to construct the dual-passband filter. Simultaneously, the SiO₂ film acts as a temperature compensation layer, significantly reducing the temperature coefficient of frequency (TCF). The influence of SiO₂ thickness on the TC-SVBAR is investigated via COMSOL finite element analysis (FEA). The fabricated filter achieves center frequencies (fc) of 4.676 GHz (A3 mode, 3-dB BW of 101 MHz, FBW of 2.16%) and 5.911 GHz (S4 mode, 3-dB BW of 219 MHz, FBW of 3.70%), with low TCF of 7.303 ppm/°C and -4.328 ppm/°C, demonstrating its potential for high-frequency, high-stability RF front-end applications.