Atomic layer deposition of AlN for thin membranes using trimethylaluminum and H 2 /N 2 plasma

•AlN films grown at 150°C by ALD using trimethylaluminum and H2/N2-plasma.•Nearly stoichiometric AlN films (ratio Al:N=0.938), polycrystalline by XRD/TEM.•Refractive index of n=1.908 and low thermal conductivity of κ=1.66W/(mK).•Free-standing AlN membranes mechanically stable and buckling free (tensile strain).•Membrane patterning by focused ion beam etching possible.