A piezoelectric thin film sandwiched between two conductors is the basic structure for high frequency bulk acoustic wave devices. For that purpose, AlN thin films deposited by DC reactive sputtering on various electrode materials were investigated, Highly c-axis oriented thin films as thick as 2.5 mu m were grown on various substrates and analyzed. Intrinsic stress values ranging from strong compression to high tension were observed and piezoelectric d(33,f) coefficients up to 3.9 pm/V were measured. The first fabricated acoustic resonators showed a pronounced resonance peak centered at 2 GHz with a very high Q factor.