A 15.8 GHz A6 Mode Resonator with Q of 720 in Complementarily Oriented Piezoelectric Lithium Niobate Thin Films

We present a 15.8 GHz sixth-order antisymmetric (A6) mode resonator in thin-film lithium niobate (LiNbO3). The device shows a high quality factor (Q) of 720 and an extracted electromechanical coupling (k²) of 0.62%. The simultaneously high frequency and high Q are enabled by a unique complementarily oriented bi-layer acoustic resonator (COBAR) design. The device employs a 1.2 µm complementarily oriented piezoelectric (COP) X-cut thin-film LiNbO3. The measured loaded Q at resonance (720) and f∙Q product (1.14×10¹³) are among the highest for piezoelectric acoustic resonators beyond 6 GHz. The thickness-extensional (TE) COBAR technology can potentially facilitate various 5G frequency synthesis applications upon optimization.