In this work, we present a method for growing highly c-axis oriented aluminum scandium nitride (AlScN) thin films on (100) silicon (Si), silicon dioxide (SiO₂) and epitaxial polysilicon (poly-Si) substrates using a substrate independent approach. The presented method offers great advantages in applications such as piezoelectric thin-film-based surface acoustic wave devices where a metallic seed layer cannot be used. The approach relies on a thin AlN layer to establish a wurtzite nucleation layer for the growth of w-AlScN films. Both AlScN thin film and seed layer AlN are prepared by DC reactive magnetron sputtering process where a Sc concentration of 27% is used throughout this study. The crystal quality of (0002) orientation of Al_0.73Sc_0.27N films on all three substrates is significantly improved by introducing a 20 nm AlN seed layer. Although AlN has a smaller capacitance than AlScN, limiting the charge stored on the electrode plates, the combined piezoelectric coefficient d_33,f with 500 nm AlScN is only slightly reduced by about 4.5% in the presence of the seed layer.

This paper presents progress towards the large-scale manufacturability of piezo- and ferroelectric Al_1−x Sc _x N thin films with very high Sc content. Al_0.6Sc_0.4N layers were deposited by pulsed DC reactive sputtering from a 300 mm diameter Al_0.6Sc_0.4 target on standard 200 mm Si wafers with Pt bottom- and Mo top-electrodes. The deposited films were analyzed in depth with x-ray diffraction, reciprocal space mapping, scanning electron microscopy and energy dispersive x-ray spectroscopy showing well oriented c-axis growth over the full wafer with slight variation in the film thickness and Sc content over the wafer radius. An overall low density of abnormally oriented grains was found. Further wafer mapping for piezoelectric and dielectric properties showed a piezoelectric performance increase by 40% in comparison to Al_0.7Sc_0.3N while only moderately increasing the permittivity and loss factor. Switching measurements revealed ferroelectric behavior of the film on all measured positions with an average remanent polarization of 88.36 µC cm⁻² and an average coercive field of 244 V µm⁻¹. This successful demonstration opens new opportunities for MEMS applications with demands for high forces like microspeakers or quasi static micromirrors.

Photocatalysis In article number 1800898, Salih Veziroglu, Franz Faupel, Oral Cenk Aktas, and co-workers present a facile method to prepare Ag nanoparticles (NPs) decorated TiO2 thin film by photocat...