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 ( k t 2 ) and quality factor ( Q ), the pitch of inter-digital transducers and lateral reflective boundary width ( D ) were optimized via finite element analysis simulation. Besides, the XBARs with the broadband piston mode structure (BPM-XBAR) 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 k t 2 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 k t 2 of 7.91%. The above devices have the potential to construct large bandwidth and low loss filters toward the C-band and Ku-band.