5 GHz A1 Mode Lateral Overtone Bulk Acoustic Resonators in Thin-Film Lithium Niobate

This work presents the first demonstration of the first-order antisymmetric (A1) mode lateral overtone bulk acoustic resonators (LOBAR) in thin-film lithium niobate (LiNbO3). Thanks to the fast phase velocity, large coupling, and low loss of A1 in LiNbO3, equally spaced tones around 5 GHz are achieved using a large feature size of 500 nm. Electromechanical coupling (k
²
) around 0.4 % and high Q over 1000 are observed in more than 20 tones, surpassing the reported overtone resonators at 5 GHz. Meanwhile, the highest Q of 2725, and the highest fQ product of 1.4·10
¹³
are measured at 5.16 GHz. Upon further optimizations, A1 LOBARs can facilitate novel 5G signal processing functions.