Aluminum nitride (AIN) thin films were deposited on silicon wafers and glass substrates by an unbalanced magnetron (UBM) sputtering system equipped with a pulse dc power supply. Microstructure and chemistry of the AIN-coated specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The optical transmission properties of the AIN-coated glass were investigated using an ultraviolet/visible (UV/VIS) spectrophotometer. It was found that the thin films are polycrystalline and have a hexagonal wurtzite structure with (002) preferred orientation, as revealed by XRD and TEM. AFM analysis indicates that the surface of the thin films is smooth, with an average roughness R-a = 6.464 nm, which is suitable for application in surface acoustic wave devices. XPS analysis gives the chemical composition of the coatings as well as the bonding states of the elements. In addition, the AIN thin films are transparent in the visible region with an average transmittance of 60%. (C) 2004 The Electrochemical Society.