Complementary-Switchable Dual-Mode SHF Scandium Aluminum Nitride BAW Resonator

This article presents a bulk acoustic wave (BAW) resonator with complementary switchable operation in the first and second thickness extensional modes (TE
₁
and TE
₂
) at 7.04 and 13.4 GHz. Two ferroelectric scandium aluminum nitride (Sc
_0.28
Al
_0.72
N) layers are alternatively stacked with three molybdenum electrodes, creating a laminated BAW resonator with independent switchability of polarization in constituent transducers. This enables intrinsic switchability of the resonator in TE
₁
and TE
₂
modes, when the ferroelectric Sc
_0.28
Al
_0.72
N layers are poled in the same or opposite directions, respectively. A generalized analytical proof of complementary switchable operation, extended to laminated BAW resonators consisting of arbitrary number of Sc
_x
Al
_1-x
N layers, is presented. For the demonstrated prototype, electromechanical coupling coefficients (
${k}_{t}^{2}$
) of 10.1% and 10.7%, and quality factors (
${Q}$
) of 115 and 151, are measured for TE
₁
and TE
₂
modes, respectively, when the resonator is configured in the corresponding operation states. Besides showing intrinsically configurable operation in super-high-frequency regime with high
${k}_{t}^{\textbf {2}}$
and
${Q}$
, a laminated Sc
_0.28
Al
_0.72
N BAW resonator exhibits repeatable operation under switching cycles.