Low-Loss and Ultra-Wideband SAW Filters Using LiNbO 3 /Si Structure

Wideband devices are increasingly needed with the development of wireless communication. To simplify the structures of wideband SAW devices and further explore the bandwidth limit, this work researches on ultra-wideband SAW devices using simplified bilayer structures.$X$-cut LiNbO3/Si structure is proposed and resonators with different propagation directions are simulated.$X$-$175^{\circ }Y$LiNbO3/Si is the optimized design when strengthening the main mode and suppressing the spurious mode are well balanced. SAW resonators with different thicknesses of LiNbO3and Cu electrodes are theoretically investigated, and resonators with different wavelengths are fabricated. Results show that the electromechanical coupling factor of the resonators can reach about 29% and the admittance ratio can be larger than 70dB. Meanwhile, the spurious mode is sufficiently suppressed. Ultra-wideband and low-loss SAW filters are designed and fabricated. An ultra large bandwidth of 31.92% is achieved. Atotally flat passband and a minimum insertion loss of 0.99dB prove that the filters have high performances but not only a large bandwidth. This work further extends the bandwidth limit of SAW devices and reveals the application possibility of simplified bilayer structure$X$-$175^{\circ }Y$LiNbO3/Si, effectively and economically developing the technology of wideband SAW devices. [2025-0244]