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Lamb wave microresonators with wavelengths λ of 5–8 μm, vibrating in the S0 mode, and having 75 electrode pairs were fabricated and characterized. The results were compared to theoretical predictions obtained by finite element simulation. The active material was a 1 μm-thick Al0.85Sc0.15N thin film. Two types of acoustic isolation solutions were implemented: the first one with freestanding plates fixed by two bridges to a device frame [freestanding Lamb wave resonator (FS-LWR)] and the second one containing an acoustic W/SiO2 5-layer reflector [solidly mounted Lamb wave resonator (SM-LWR)]. All devices showed excellent agreement with FEM predictions, regarding resonance frequency and piezoelectric coupling. The quality factors of the SM-LWR devices were 5–6 times larger than the ones of the freestanding structures fabricated by the same Al0.85Sc0.15N deposition process: we achieved a figure of merit of 12–18 (Qp = 771, Qs = 507, k2 = 2.29%) at an operation frequency of 1430 MHz, which is so far the best performance realized with a MEMS Lamb wave resonator having a large number of electrode fingers. This performance opens up perspectives for filter applications. [ABSTRACT FROM AUTHOR]

Accurate property determination of the piezoelectric thin film material Al(1−x)Sc(x)N is necessary for designing the next generation of radio frequency resonators in mobile communication, and for testing results of ab initio calculations. Sound velocity and piezoelectric coupling of both longitudinal and shear mode are evaluated from a single dual mode resonator. This assures a compatible set of coefficients. It is observed that AlScN thin films grew differently on small, isolated bottom electrodes. The investigated film starts growing with a slightly tilted, c‐textured microstructure, and switches after 200 nm to a polycrystalline film with irregularly oriented grains having c‐axis tilt angles in the range of 35°–70°, as revealed by transmission electron microscope nanodiffraction mapping. Based on this information, a finite element model (FEM) is constructed that properly reproduces the resonance behavior of the resonator. The relevant elastic and piezoelectric constants are derived by curve fitting and yield somewhat lower stiffness and higher piezoelectric coefficients than ab initio calculations published in the literature. The FEM modeling results show that the upper film part with the abnormally oriented grains is overall piezoelectric, i.e., the misoriented grains maintain the polarity projected onto the growth direction from the starting layer. [ABSTRACT FROM AUTHOR]