Thermal Stability and Phase Transformations of <i>γ</i>‐/Amorphous‐Al₂O₃ Thin Films

Abstract

Abstract Magnetron‐sputtered Al 2 O 3 thin films were annealed in ambient air. The phase compositions of the as‐deposited Al 2 O 3 films were (i) fully amorphous, (ii) nanocrystalline γ ‐Al 2 O 3 in an amorphous Al 2 O 3 matrix, and (iii) fully crystalline γ . For all samples, annealing to 1 100–1 150 °C resulted in a transformation to α ‐alumina. The transformation paths depend on the phase fraction of γ in the as‐deposited films. For amorphous films and films with low initial γ fraction, the intermediate phase θ ‐Al 2 O 3 appeared in the range of 1 000–1 100 °C. For predominantly crystalline γ ‐Al 2 O 3 as‐deposited films no intermediate Al 2 O 3 phases were observed, indicating a direct γ ‐to‐ α phase transformation at ∼1 100 °C.