Toward Ka Band Acoustics: Lithium Niobate Asymmetrical Mode Piezoelectric MEMS Resonators

Abstract

This work presents a new class of micro-electro-mechanical system (MEMS) resonators toward Ka band (26.5-40 GHz) for fifth-generation (5G) wireless communication. Resonant frequencies of 21.4 and 29.9 GHz have been achieved using the fifth and seventh order asymmetric (A5 and A7) Lamb-wave modes in a suspended Z-cut lithium niobate (LiNbO3) thin film. The fabricated device has demonstrated an electromechanical coupling (kt 2 ) of 1.5% and 0.94% and extracted mechanical Qs of 406 and 474 for A5 and A7 respectively. The quality factors are the highest reported for piezoelectric MEMS resonators operating at this frequency range. The demonstrated performance has shown the strong potential of LiNbO3 asymmetric mode devices to meet the front-end filtering requirements of 5G.

5-GHz Antisymmetric Mode Acoustic Delay Lines in Lithium Niobate Thin Film

“…Thus, the amplitude decays during the propagation towards the output transducers. Below fc_open, the section with the input transducer is equivalent to an A1 mode resonator [57]- [60]. The acoustic impedance difference caused by different electrical boundary conditions acts as reflective boundaries [7], [41].…”

“…Recently, acoustic devices using the first-order antisymmetric (A1) mode in Z-cut LiNbO3 have been reported with high k 2 and low loss above 4 GHz [57]- [59]. Different from SH0 and S0, A1 is higher-order in the thickness direction, thus significantly enhancing vp in in-plane dimensions [60] and improving frequency scalability. However, the highly dispersive nature of A1 presents new challenges in designing ADL.…”

“…Moreover, the notable cut-off in A1 confines acoustic waves between the input transducers and prevents their propagation towards the output port. Such effects are especially pronounced in the presence of metallic electrodes [60], and thus has to be analyzed and circumvented for successful implementation of A1 ADLs. Finally, A1 devices demonstrated so far are analyzed for mostly standing wave structures (e.g., resonators [60]) where the A1 propagation characteristics have not been systematically studied.…”

10–60-GHz Electromechanical Resonators Using Thin-Film Lithium Niobate

“…A multiresonance modified Butterworth-Van Dyke (MBVD) model, in which each resonance is captured by a motional branch of R m , L m , and C m , is used to interpret the measurement results [44], [54], [55]. As shown in Fig.…”

“…Therefore, A1 mode devices are being considered as an alternative resonator technology for sub-6-GHz applications [41]- [43]. Due to the promising performances of the A1 mode devices, higher order antisymmetric modes can be scaled up with the great performance for the resonant frequencies beyond 6 GHz [44].…”