Aluminum nitride thin film based surface acoustic wave sensors

Surface Acoustic Wave (SAW) devices have drawn increasing interest in the field of sensor devices for the accurate detection of gases and liquids. In order to detect a range of gases and liquids, of which some will be capable of attacking the active material of the SAW device, a robust material is desired for fabrication. Aluminum Nitride (A1N) acts as a piezoelectric SAW material that can withstand both high temperatures and harsh environments. SAW devices have been fabricated by reactively sputtering an A1N film directly on silicon as well as on a freestanding SiO₂/Si diaphragm. The selective absorption of the gases or liquids modifies the mechanical properties of the surface of the device which can be detected as a change in resonance and phase velocity of the surface waves. Experimental analysis has been conducted to observe dispersion curves, Rayleigh velocities, and resonance frequencies and the results were found to qualitatively agree with those modeled by theoretical simulation. These results indicate the ability of further analyses to optimize the design and sensitivity of SAW sensors for medicine, engineering, and basic biology and chemistry sciences.