Synthesis of c-axis-oriented aluminum nitride films by reactive RF magnetron sputtering for surface acoustic wave

C-axis-oriented aluminum nitride (AIN) films were deposited on SiO2-coated Si substrates by reactive rf magnetron sputtering. The crystallization of t he AIN films, identified by X-ray diffraction (XRD), was dependent on the d eposition conditions. Highly c-axis-oriented AIN films, for fabricating AlN /SiO2/Si-based surface acoustic wave (SAW) devices, were obtained under an rf power of 300 W, substrate temperature of 350 degreesC, sputtering pressu re of 7.5 mTorr and N-2 concentration of 75%. A dense pebblelike surface te xture of the c-axis-oriented AIN films with an average grain size of about 100 nm was observed by scanning electron microscopy (SEM). The phase veloci ty showed a tendency to decrease with increasing kh, where k = 2 pi/lambda is the wavenumber and h is the AIN film thickness. In partucular, the phase velocity and the electromechanical coupling coefficient of the sample at k h = 0.4 were calculated to be about 6080 m/s and 1.1%, respectively.