||In this study, surface acoustic wave (SAW) devices were fabricated by aluminum nitride (AlN) thin films deposited on lithium tantalite (LiTaO3) substrates. The highly c-axis oriented AlN thin films could be obtained by controlling the sputtering parameters and their crystalline characteristics and surface morphologies were measured by SEM, XRD, AFM and rocking curve analysis. The optimal deposition conditions of AlN thin films were RF power of 270W, sputtering pressure of 5mTorr, substrate temperature of 300°C and nitrogen concentration (N2/N2+Ar) of 60%, respectively.|
In addition, the SAW devices with various thicknesses of AlN thin films were studied. Experimental results revealed that, the central frequency increased from 129.88 MHz (Vp=4156.2 m/sec) to 131.275 MHz (Vp=4200.1 m/sec), and the temperature coefficient of frequency (TCF) also changed from -43.21 ppm/°C to -54.65 ppm/°C as the thickness of AlN thin films increased. With thickness of AlN thin films increasing, the acoustic velocity of SAW devices were improved, but TCF became worse. Therefore, the balance should be found between these two tendencies.