Design and fabrication of lithium niobate asymmetrical mode resonators toward C-band and Ku-band

Abstract

This work presents a laterally excited bulk wave resonator (XBAR) based on the suspended Z-cut lithium niobate thin film. In order to systematically analyze the influence of geometric structure on the performance of resonators, including electromechanical coupling coefficient (kt2) and quality factor (Q), the pitch of inter-digital transducers (IDTs) and lateral reflective boundary width (D) were optimized via finite element analysis (FEA) simulation. Besides, the XBARs with the broadband piston mode structure (BPM-XBARs) were further studied, and the transverse displacement was weakened after optimization, hence enhancing the Q value of the targeted mode. Consequently, the fabricated devices exhibited first order asymmetrical (A1) mode resonance at 5.87 GHz with kt2 of 12.98% and Q of 218, a nearly 70% increase in Q value. The third order asymmetrical (A3) mode resonance occurred at 17.18 GHz with kt2 of 7.91%. The above devices have the potential to construct large bandwidth and low loss filters toward the C-band and Ku-band.