Temperature coefficients of SAW velocity for AlN thin film sputtered on ST-X quartz

Highly c-axis prefer-oriented aluminum nitride (AlN) thin films deposited on the Y-rotated, X-propagating, (ST-X), cut of quartz substrates were obtained by reactive rf magnetron sputtering to investigate the temperature coefficient of frequency (TCF) for surface acoustic wave (SAW) devices. The experimental results show that the slope of the temperature dependence of the center frequency of the SAW device on ST-X quartz substrate was doubtless zero and the TCF was calculated to be 0 ppm/°C. As compared, with AlN film on ST-X quartz, the TCF was measured to be about 16 ppm/°C with h/λ=0.05, where h was the AIN film thickness and λ was the wavelength of SAW. The AlN/ST-X quartz based structure could also improve the acoustic wave velocity of SAW devices.