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

Modern wireless communication systems are increasingly complex with greater functionality and impose new challenges on the radio frequency (RF) front-end design. One of the major challenges involves filtering beyond the sub-6-GHz regime with increased fractional bandwidth (FBW). To the best of our knowledge, this work presents the first demonstration of a film bulk acoustic wave resonator (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 <inline-formula> <tex-math notation="LaTeX">$k_{t}^{2}$ </tex-math></inline-formula> for applications in the millimeter wave (mm-Wave) spectrum. The resonator exhibits a fundamental mode at GHz with <inline-formula> <tex-math notation="LaTeX">$k_{t}^{2}$ </tex-math></inline-formula> of 5.2% but can switch to a higher order response at 31 GHz by reversing the polarization direction in the ScAlN layer (<inline-formula> <tex-math notation="LaTeX">$k_{t}^{2}$ </tex-math></inline-formula> of 5.5%).