Sub-GHz X-Cut Lithium Niobate S₀ Mode MEMS Resonators

This paper reports on the design, fabrication, and characterization of
$S_{0}$
mode X-cut Lithium Niobate Laterally Vibrating Resonators (LVRs) operating between 100 MHz and 1 GHz. In the first Section of this work, analytical and numerical models are implemented to investigate the impact of topology and geometrical features on the Electromechanical Coupling (
$k_{t}^{2}$
) and Quality Factor (
$Q_{s}$
) of this class of devices. The models are used to define the design of experiments aimed at characterizing the resonator performance. The resonators are fabricated and tested in atmospheric, vacuum, and cryogenic (
$T$
= 10 K) conditions to assess their performance and identify the main sources of discrepancies in
$k_{t}^{2}$
and
$Q_{s}$
with respect to the analytical and numerical models. Under vacuum quality factors exceeding a few thousands are recorded across the investigated spectrum, with measured
$k_{t}^{2}$
as high as 28.9%. At 100 MHz, measured
$Q_{s}$
and
$k_{t}^{2}$
of 8,279 and 28.5%, respectively, combine into a record-breaking Figure of Merit (
$FOM$
) of 2,688, while cryogenic testing highlighted
$Q_{s}$
as high as 26,511. In the last section, by analyzing the differences in
$k_{t}^{2}$
and
$Q_{s}$
between experiments and models, best design approaches to maximize the
$FOM$
and minimize spurious modes responses are reported, with a focus on the 100 to 550 MHz range. [2022-0081]