Reducing the adhesion and friction forces of Si by coating ultra-thin Al2O3 films

Abstract

Si-based microelectromechanical system (MEMS) devices cannot run reliably because of their poor tribological performance. Ultra-thin alumina (Al₂O₃) films are promising candidates to solve the tribological problem. In this study, adhesion and friction forces between a probe tip and ultra-thin alumina (Al₂O₃) films were studied using an atomic force microscope (AFM). The Al₂O₃ films with thickness of 0.8–5.0 nm were prepared on a Si (100) substrate by atomic layer deposition (ALD) using trimethyl aluminum (TMA) and water as precursors. The results show that both the adhesion and friction forces of the Al₂O₃ films are smaller than those of the Si (100) substrate. We attribute the low adhesion force of the Al₂O₃ films to their low surface energy and hydrophobic nature, and the low friction force of the Al₂O₃ films to their low adhesion force. We also calculated the adhesion force between an AFM tip and the samples. The theoretical adhesion force agrees well with the measured result.