Material Parameter Extraction for Complex AlScN Thin Film Using Dual Mode Resonators in Combination with Advanced Microstructural Analysis and Finite Element Modeling

Abstract

rocksalt ScN, exhibits extraordinarily high piezoelectric coefficients for a nitride material. [1,2] Since its discovery by Akiyama and co-workers, many researchers confirmed the increase of piezoelectricity in AlScN with increasing Sc content, [3][4][5][6][7][8][9][10][11] reaching a maximum at the limit of the wurtzite stability somewhere between 40% and 50% of Sc on the cation site. [2,12] The piezoelectric coefficients increase by about a factor of 4 for the case of charge per stress coefficients (d-tensor), and about a factor 2.5 for the case of charge per strain coefficients (e-tensor). Computational modeling in the frame of density functional theory (DFT) confirmed well the increase of the piezoelectric coefficients, accompanied by a decrease of the stiffness with increasing Sc content. [13,14] Even though the obtained piezoelectric coefficients are small as compared to the ones of ferroelectric thin films, AlScN may reach superior performance wherever the dielectric constant (ε) is relevant as well. This is the case for sensors, [15,16] in energy harvesting, [4,17] and in some of the applications governed by a piezoelectric coupling coefficient. [3,5] This is the case in radio frequency (RF) filters for mobile phone communication operating in the lower GHz frequency range. On the market since 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. Thin FilmsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Design and Optimization of the Dual-Mode Lamb Wave Resonator and Dual-Passband Filter

“…The thickness of one array is fixed at 100 nm, while the thickness of the other array is set as 100 nm, 200 nm and 300 nm. Finite Element Analysis (FEA) is used in this paper, and the material constants of Sc 0.2 Al 0.8 N used in the simulation are shown as the following [32,33]:…”

Evaluation of the impact of abnormal grains on the performance of Sc0.15Al0.85N-based BAW resonators and filters

“…These abnormal grains have been studied and confirmed as misoriented grains with the polar axis (c-axis) departing from the normal direction to the substrate surface [21][22][23], which is intuitively believed to reduce the material's piezoelectric response [24,25]. Moreover, in mass production, the non-uniform distribution of the abnormal grains will lead to wafer level yield loss.…”