Highly c-axis oriented AlN films deposited on LiNbO3 substrates for surface acoustic wave devices

Highly c-axis oriented aluminum nitride (AlN) films were deposited on z-cut LiNbO₃ substrates by reactive rf magnetron sputtering. Growth behaviors of the AlN films deposited at various deposition conditions such as sputtering pressure, nitrogen concentration and substrate temperature were investigated. The crystalline orientation of the AlN film was determined by x-ray diffraction (XRD) which was sensitive to the deposition conditions. A dense pebble-like surface texture of c-axis oriented AlN film was obtained by scanning electron microscopy (SEM). The cross section of c-axis oriented AlN film showed a high degree of alignment of the columnar structure. A network analyzer was used to measure the surface acoustic wave (SAW) characteristics. The phase velocity and the electromechanical coupling coefficient were calculated to be about 4200 m/sec and 1.5%, respectively