Substrate hardness dependency on properties of Al2O3 thick films grown by aerosol deposition

Abstract

The effects of substrate hardness on the growth of Al2O3 films using an aerosol deposition (AD) process were investigated. Substrates with different hardness, such as glass, Cu, Al2O3, and sapphire were used to examine the effects of the deposition rate, microstructure, and mechanical properties of Al2O3 films. As the substrate hardness increased, the deposition rate and the hardness of the films rapidly decreased, but the surface roughness was increased. The adhesive properties of Al2O3 films deposited on sapphire substrates deteriorated compared to those deposited on Cu substrates. To clarify the causes for this behavior, the relationship between the thickness of films and substrate hardness was investigated, and the microstructures of Al2O3 particles at the initial stages were observed. It was revealed that it was difficult to make anchoring layers with Al2O3 particles deposited on hard sapphire substrates. This is the main cause for the lower deposition rate and the more pronounced deterioration of the mechanical properties. In order to improve the deposition rate of Al2O3 films when growing them on hard substrates, two methods were attempted to increase the kinetic energy of particles. The first method involved the use of larger Al2O3 particles, and the second involved increasing the impact velocity of the particles by using specially designed nozzles. Consequently, dense and hard Al2O3 thick films could be successfully fabricated on hard sapphire substrates at room temperature by the AD process through increasing the impact velocity using the acceleration nozzle.