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 (TE1 and TE2) at 7.04 and 13.4 GHz. Two ferroelectric scandium aluminum nitride (Sc0.28Al0.72N) 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 TE1 and TE2 modes, when the ferroelectric Sc0.28Al0.72N 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 ScxAl1-xN layers, is presented. For the demonstrated prototype, electromechanical coupling coefficients ( k2t ) of 10.1% and 10.7%, and quality factors ( Q ) of 115 and 151, are measured for TE1 and TE2 modes, respectively, when the resonator is configured in the corresponding operation states. Besides showing intrinsically configurable operation in super-high-frequency regime with high k2t and Q , a laminated Sc0.28Al0.72N BAW resonator exhibits repeatable operation under switching cycles.