Polycrystalline AIN thick films were deposited on Si(001) and Si(Ill) substrates by reactive radio frequency sputtering technique at low temperature. The structure and the morphology of the films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy techniques. These measurements showed that the AIN films were highly c-axis oriented, with low surface roughness. The surface acoustic wave (SAW) properties of the films were investigated: a mean value of 3.8 x 10(-12) C/N was estimated for the piezoelectric strain constant d(33); the phase velocities of SAWs propagating in polycrystalline AlN/(001)[110]Si and AlN/(111)[1-10]Si structures, for different film thicknesses, were calculated and found to be in good agreement with the theoretical velocities evaluated for SAWs propagating in single crystal AlN/Si structures. (C) 2003 Elsevier B.V. All rights reserved.