Heterogeneous Interface-Enhanced Thin-Film SAW Devices Using Lithium Niobate on Si

Abstract

Lithium niobate (LiNbO3) on silicon wafer has emerged as a promising candidate for high-performance filter construction in an ultrawide frequency range. However, the direct bonding of these two materials has proven challenging due to the large contrast in their thermal expansion coefficient (TEC) and the parasitic layer in thermal treatment. This article proposes utilizing an amorphous silicon layer to improve the interface quality between LiNbO3 and the supporting substrate, thereby preventing potential losses and enhancing interface reflection. In addition, this work modifies the electrical field distribution and adjusts the power flow angle to align it with the propagation direction of the targeted acoustic wave to suppress spurious modes. By leveraging the enhanced heterogeneous interface and the corresponding design method, the fabricated filter exhibits a low insertion loss (IL) of 1.2 dB, a 3-dB fractional bandwidth (FBW) of 8.9%, a clean rejection band response, and a flat passband without significant ripples. The well-balanced performance has delivered a valid methodology of the LiNbO3-on-silicon heterostructure for building radio frequency (RF) spurious-free and low-loss filters.