Aluminum nitride (AlN) thin films with thicknesses from 25 to 100 nm were deposited on silicon and amorphous silica by plasma enhanced atomic layer deposition (PE-ALD). Trimethylaluminum (TMA) and a H2 / N2 - plasma mixture were used as precursors. We investigated the influence of deposition temperature and plasma parameters on the growth characteristics and the film properties of AlN. Stable ALD growth conditions were obtained from 150°C to the highest tested temperature of 300°C. The growth rate, refractive index, and thickness homogeneity on 4" wafers were determined by spectroscopic ellipsometry. With X-ray diffraction and Rutherford backscattering spectrometry the crystallinity and composition of the films were analyzed. Furthermore the thermal conductivity and the film stress were determined. The stress was sufficiently low to fabricate mechanically stable free-standing AlN membranes with lateral dimensions of up to 2.2 x 2.2 mm2. The membranes were patterned with focused ion beam etching. Thus, these AlN membranes qualify as dielectric support material for a variety of potential future applications.