Over GHz bandwidth SAW filter based on 32° Y-X LN/SiO2/poly-Si/Si heterostructure with multilayer electrode modulation

Abstract

Enhancing the central frequency (fc) and bandwidth (BW) and reducing insertion loss (IL) are essential steps in surface acoustic wave (SAW) filter applications in the 5G era. With this in mind, we construct a 32° Y-X LiNbO3(300 nm)/SiO2(300 nm)/poly-Si(1 μm)/Si heterostructure to avoid both acoustic leakage through the waveguide effect and electrical loss through the introduction of a poly-Si layer. By separately modulating the electrode thicknesses of series and parallel resonators, the spurious modes can be mitigated out of the filter passband, preventing them from negatively impacting the filter characteristics. Moreover, to reduce Ohmic loss, an optimized design for an Al/Cu/Ti multilayer electrode is proposed as a replacement for the Cu/Ti electrode resonators built on Al/Cu/Ti electrodes provide a high resonance frequency of 3.76 GHz, a large electromechanical coupling coefficient of 23%, and a maximum quality factor of 1510 (twice that of the Cu/Ti electrodes). Finally, SAW filters with an fc of 3728 MHz and a 3-dB BW of 1052 MHz are implemented, with IL of 0.92 dB. The achieved specifications demonstrates that one-chip SAW filter is expected to become n77 band filtering solution.