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

This article presents a bulk acoustic wave (BAW) resonator with complementary\nswitchable operation in the first and second thickness extensional modes (TE1\nand TE2) at 7.04 and 13.4 GHz. Two ferroelectric scandium aluminum nitride\n(Sc0.28Al0.72N) layers are alternatively stacked with three molybdenum\nelectrodes, creating a laminated BAW resonator with independent switchability\nof polarization in constituent transducers. This enables intrinsic\nswitchability of the resonator in TE1 and TE2 modes, when the ferroelectric\nSc0.28Al0.72N layers are poled in the same or opposite directions,\nrespectively. A generalized analytical proof of complementary switchable\noperation, extended to laminated BAW resonators consisting of arbitrary number\nof ScxAl1-xN layers, is presented. For the demonstrated prototype,\nelectromechanical coupling coefficients ( k2t ) of 10.1% and 10.7%, and quality\nfactors ( Q ) of 115 and 151, are measured for TE1 and TE2 modes, respectively,\nwhen the resonator is configured in the corresponding operation states. Besides\nshowing intrinsically configurable operation in super-high-frequency regime\nwith high k2t and Q , a laminated Sc0.28Al0.72N BAW resonator exhibits\nrepeatable operation under switching cycles.\n