Piezoelectric aluminum nitride thin film for ultrasonic transducers

Piezoelectric aluminum nitride (AIN) thin films have been developed to realize ultrasonic transducers. AIN up to 1.5 mum is deposited at low temperature (140 degreesC) by reactive DC magnetron sputtering of an Al target in argon and nitrogen on Si, Si/SiO2/Al, and Si/Al substrates, and is wet etched (rates from 0.1 mum/min to 0.2 mum/min and selectivity of 1:10 with Al, and no etching with Si). SiO2/Al/AlN/Al, Al/AlN/Al and Si/AlN/Al square and circular membranes, from 10 mum to 1.5mm size are fabricated using silicon deep reactive ion etching (DRIE), which gives etch profiles about 90 degrees, and allows larger integration density than wet anisotropic etching for ultrasonic transducers arrays. By varying size and thickness of membranes, resonance frequencies from 10kHz to 20MHz are expected, acoustic and electrical measurements are in progress. Ultrasonic transducers using this technology will be used to measure flows velocity by Doppler method. Other potential applications for ultrasonic transducers include medical ultrasounds and sonar. Other structures are also in progress such as Thin Film Bulk Acoustic Resonator (TFBAR), and Lamb wave devices using this technology.