Ion-beam-induced in-plane a-axis oriented (0001) AlN and ScAlN thin film BAW resonators

High-Q RF bulk acoustic wave filters are still required for mobile communication applications. However, the in-plane orientation of commercial AlN films is random, despite their excellent out-of-plane c-axis orientation. We proposed combining two different orientation control techniques: self-texture for out-of-plane alignment and ion beam irradiation for in-plane alignment. To demonstrate the effectiveness of this approach, both in-plane a-axis and out-of-plane c-axis aligned AlN and ScAlN films were grown on Ti/silica glass substrates using 0.3–0.5 keV grazing ion-beam-assisted RF sputtering technique without using epitaxial growth. The clear six symmetry in the pole-figure observed in AlN and ScAlN thin films indicates the single-crystal-like in-plane a-axis orientation. The ion beam direction corresponded to the in-plane 〈101̄0〉 axis. In-plane x-ray diffraction ϕ-scan curve and ω-scan curve FWHM were measured to be 25° and 2.2°.