Scandium and Boron co-alloyed AlN thin films with improved piezoelectric and ferroelectric properties

• Main Author: Wu, Cheng Lung
• Other Authors: Nripan Mathews
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Piezoelectricity; Ferroelectricity; Aluminium scandium nitride; MEMS device; Thin film deposition; PVD reactive sputtering
• Online Access: https://hdl.handle.net/10356/175965
• Institution: Nanyang Technological University

This study explores the optimization of piezoelectric and ferroelectric properties of doped aluminum nitride (AlN) films, specifically investigating the effects of scandium (Sc) and boron (B) doping. The experimental setup involves depositing a Metal-Ferroelectric-Metal (MFM) thin film stack on 200mm silicon wafers and characterizing the samples using various techniques such as scanning electron microscopy (SEM) for morphology analysis, X-ray diffraction (XRD) for crystal orientation measurement, piezotest for piezoresponse measurement, and electrical testing for ferroelectric switching field assessment. The deposition process begins with the deposition of an AlN seed layer on the silicon wafer, followed by the deposition of a molybdenum (Mo) bottom electrode. Subsequently, co-sputtering from aluminum-scandium (AlSc) and boron (B) targets in a nitrogen (N2) atmosphere to form the AlScBN ferroelectric film. Finally, a top metal electrode, doped with aluminum, is deposited using a shadow mask to define its pattern on the wafer, completing the MFM structure. The SEM analysis revealed that the addition of B reduced the presence of abnormal grains in the film. Additionally, the wurtzite crystal structure of AlN is well retained with the addition of B, as indicated by the theta-2theta XRD analysis. Piezotest results indicate that the addition of B does not significantly affect the piezoresponse of AlScN. A similar trend was also observed in electrical tests where the change in switching field is insignificant, but there is an increase in current leakage associated with adding B dopants. In summary, the study highlights the potential of B doping of AlScN films while also indicating a trade-off with increased current leakage. These findings may provide valuable insights for the optimization of piezoelectric and ferroelectric materials for various applications.