Structure and properties of piezoelectric aluminum nitride thin films deposited by radio-frequency magnetron sputtering for surface acoustic wave applications

Aluminum nitride (AlN) is a promising piezoelectric material for surface acoustic wave (SAW) devices due to its high acoustic velocity and thermal stability. Achieving high-performance SAW devices requires highly c-axis-oriented, columnar AlN thin films with low surface roughness and high Young’s modulus. In this work, [002]-oriented AlN thin films were deposited by radiofrequency sputtering using a ceramic AlN target. Key deposition parameters, including substrate temperature, chamber pressure, and gas composition, were optimized to enhance film quality. Characterization via atomic force microscopy, x-ray diffraction, and scanning electron microscopy confirmed the films’ low surface roughness (0.71 nm), columnar structure with c-axis orientation, and strong crystallinity. The films exhibited a high Young’s modulus of up to 325 GPa. Optimized AlN layers were used to fabricate SAW devices, whose performance was strongly influenced by the AlN thickness and the geometry of the interdigital transducer, including electrode number and device aperture.