High quality sputtered crystalline AlN piezoelectric films on Mo buffered substrates for MEMS applications

High-quality AlN piezoelectric films, particularly when deposited on molybdenum (Mo) electrodes buffered substrates, are crucial for transducers and other micro-electromechanical systems (MEMS) devices for Internet of Things (IoT). However, the crystallographic and electrical properties of AlN films are difficult to control due to the impact of multiple factors. A comprehensive and subtle regulation of buffer layers and fabrication processes is still required to further improve the film quality. In this work, high-quality AlN/Mo/AlN multilayer structures were prepared on Al 2 O 3 (0001) and Si (001) substrates using reactive magnetron sputtering. Epitaxial AlN (002) films with smooth surfaces and high crystalline quality were successfully grown on Al 2 O 3 (0001) substrates by carefully adjusting the AlN seed layer thickness, nitrogen gas concentration, and substrate bias voltage. Using the optimized depositing process, textured (002)-oriented AlN films were further prepared on 4-inch Si (001) wafers. The dielectric and piezoelectric properties of AlN films were characterized compared in detail. These results highlight the impacts of sputtering processing on the AlN film properties and lay a solid technical foundation for the development of MEMS devices.