A mm-Wave Trilayer AlN/ScAlN/AlN Higher Order Mode FBAR

Modern wireless communication systems are increasingly complex with greater functionality and imposes new challenges on the RF front end design. One of the major challenges involves filtering beyond the sub-6 GHz regime with increased FBW. To the best of the authors’ knowledge, this work presents the first demonstration of an FBAR with a composite ferroelectric/piezoelectric transduction layer (consisting of AlN – Sc0.3Al0.7N – AlN) that is capable of selectively operating at higher order resonant modes without compromising kt2 for applications in the millimeter wave (mm-Wave) spectrum. The resonator exhibits a fundamental mode at 9 GHz with kt2 of 5.2%, but can switch to a higher order response at 31 GHz through reversing the polarization direction in the ScAlN layer (kt2 of 5.5%).