Encapsulated Aluminum Nitride SAW devices for liquid sensing applications

Very low-stress and good crystallinity Aluminum Nitride (AlN) thin films deposited on (100) Silicon substrates are optimized for surface acoustic wave (SAW) devices. We developed a simplified process to fabricate AlN SAW devices suitable for fast screening of liquid substances as needed for health and environmental monitoring. By encapsulating the interdigital transducer (IDT) with a very thin SiN layer, a sufficiently large sensing area is available between the electrodes. This allows direct and fast loading of the liquid drops on the device surface as well as cleaning, for repeated use. Moreover, the amount of layers on top of the piezoelectric AlN is minimized to avoid reduction of the signal. The fabricated devices are tested by using different buffer solutions typical in biological research (NaCl and phosphate buffered saline) and the possibility to operate these SAW devices for liquid sensors is demonstrated.