Impact of Rapid Thermal Annealing on the Structural and Piezoelectric Properties of AlN Thin Films

Abstract

Aluminum nitride (AlN) is a biocompatible piezoelectric material with energy harvesting properties. This study examines the effects of post‐deposition rapid thermal annealing (RTA) on AlN thin films used in microelectromechanical systems (MEMS) resonators. RTA is performed in a N 2 ‐purged chamber at temperatures ranging from 200°C to 1000°C on AlN thin films deposited via DC reactive magnetron sputtering. The effects of RTA temperature on the crystallinity, morphology, composition, and piezoelectric properties of AlN are systematically analysed. A practical temperature threshold is established at 400°C for AlN, above which the material properties change markedly due to rapid oxidation of the material. Up to that temperature, the grain size decreases, and the grains reorient toward the c‐axis of the wurtzite phase. The piezoelectric coefficient ( d 33 ) increased approximately 160%, and AlN/Si based MEMS showed an amplification of the electromechanical properties to 400 pm/V altogether with an output power density of ∼0.12 µW/cm 3 . Furthermore, this work identifies the thermal stability within the CMOS‐compatible temperature range. Devices employing Ti/Pt electrodes exhibit a degradation threshold between 400°C and 600°C, where the metals undergo diffusion and form undesired bonds and structures. Meanwhile, the AlN/Ta/Nb devices remained stable for temperatures up to 600°C, indicating their suitability for integration into high‐temperature MEMS fabrication.