Effect of temperature and deposition power on microstructure and properties of magnetron sputtered thin AlN coatings

This paper demonstrates the influence of deposition parameters (temperature, power and time) and stoichiometric composition of thin aluminum nitride (AlN) coatings, the thickness of which varied from 320 to 1100nm deposited by DC reactive magnetron sputtering on their microstructure, mechanical and microtribological properties. The investigation revealed that high-deposition power (150 W) and temperature (200°C) lead to sputtering of coatings with high roughness, low mechanical and high microtribological properties. Such a phenomenon occurred due to the formation of a coarse-grained structure, high porosity and dendritic growth of the coating, which was observed on their cross-sections. Reducing the deposition temperature to 20°C and power to 80-100 W allowed to obtain a fine-crystalline structure demonstrating low-roughness values with crystallites evenly and compactly distributed over the surface. Such coatings showed higher mechanical and low microtribological properties. Surface resistivity was lower on coatings with a fine crystalline structure and correlated with the nitrogen content of the coating. In the course of the research, it was demonstrated that the optimal combination of microstructure, mechanical, microtribological properties and electrical resistivity for practical use in micro- and nanosensory applications may be achieved for the AlN coating with the thickness of 320nm and 29.71 at.% N, deposited at 20°C, 100 W and 20 min. Such a coating possesses the highest values of mechanical properties, low roughness and specific surface resistance, as well as low coefficient of friction and specific volumetric wear compared to all coatings under study.