Thin film bulk acoustic wave (BAW) resonators and filters are well suited for mobile communication systems operating at high frequencies between 0.5 and 10 GHz. Piezoelectric thin film materials investigated for BAW devices within Philips include AlN thin films. The relationship between sputter deposition conditions, AlN film structure, electromechanical coupling factor k(t), and relevant electrical parameters of BAW devices are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.