Effect of atomic layer deposited Al₂O₃ and subsequent annealing on the nanomechanical properties on various substrates

This paper studies the effect of atomic layer deposited Al₂O₃ and consequent annealing on the mechanical properties on different substrates. Uniform Al₂O₃ thin film with a thickness of ~ 100 nm was deposited on different substrates including Si (100), Al₂O₃ (0001), and yttria-stabilized zirconia (100). Nanoindentation results indicate that the deposition of Al₂O₃ layer reduces the film-substrate system mechanical properties including hardness (from ~ 9.6–24.5 to ~ 9.1–17.0 GPa), elastic modulus (from ~ 140.7–254.0 to ~ 132.5–240.4 GPa), and fracture toughness (from ~ 0.87–1.26 to ~ 0.36–0.98 MPa√m) for each substrate. Meanwhile, peeling and fracturing of the thin film can also be observed after nanoindentation. Subsequent 10 min annealing at 1000 °C in argon leads to the crystallization of the deposited Al₂O₃ thin film, therefore, enhance the film-substrate system mechanical properties (hardness ~ 15.9–24.8 GPa, elastic modulus ~ 228.0–356.8 GPa). The annealing process can also increase the adhesion force between the thin film and consequently no cracks after nanoindentation.