Oxidation Layer Formation on Aluminum Substrates with Surface Defects using Molecular Dynamics Simulation

Aluminum oxide layer affects the integrity of electrical contact and can contribute adversely to passive intermodulation (PIM) behavior in radio frequency (RF) devices, necessitating a need for understanding its formation mechanism and realistic estimation of its thickness. Using ReaxFF molecular dynamics simulation technique, this study investigated the impact of surface defects on aluminum oxide layer formation. Results reveal that crystallographic orientation did not affect the kinetics of oxidation process of aluminum. However, the reaction kinetics increased significantly with surface inhomogeneities such as cracks, scratches, and grain boundaries. A non-uniform oxide layer with thickness variation in the range of 72-77% was observed due to surface imperfections. Concurrent crack healing and oxidation was observed, where the crack tips acted as sites for oxygen diffusion, thus increasing oxidation kinetics. The observations from this simulation agree with experimental reports and have important implications for optimizing the contact integrity in RF devices and for PIM control.