Influence of high power impulse magnetron sputtering pulse parameters on the properties of aluminum nitride coatings

• We deposit six crystalline over-stoichiometric AlN coatings using HIPIMS technique under an ionization rate of 55%.
• The peak power density increases to 1.60 kW cm− 2 as duty cycle reaches to 3.5%.
• The hardness increases with decreasing duty cycle and reaches to 28.0 GPa at a frequency = 1000 Hz and duty cycle = 3.5%.
• Increasing repetition frequency and increasing duty cycle can enhance the thin film adhesion property.
• AlN coating grown at a frequency of 1250 Hz and a duty cycle of 3.5% exhibits both high hardness and adequate adhesion.

The aluminum nitride thin film has recently gained importance due to its unique properties, which include good thermal and chemical stabilities as well as dielectric property. In this work, aluminum nitride thin films were fabricated using the high power impulse magnetron sputtering (HIPIMS) technique. Effects of duty cycle and pulse frequency of HIPIMS power on the microstructure and mechanical property evolution of AlN coatings were explored. The ionization ratio of Al+ species in HIPIMS plasma was characterized to be around 55%. The peak power density increased to 1.60 kW cm− 2 as duty cycle decreased to 3.5%. The deposition rate increased from 1.74 to 4.50 nm/min as repetition frequency reached to 833 Hz at a fixed duty cycle of 3.5%. Strong preferred orientation of hcp-AlN (002) was discovered for AlN films with lower oxygen contamination. In addition to the hcp-AlN phase, the α-Al2O3 phase was found when the oxygen concentration was higher than 3.0 at.%. The hardness enhancement effect was brought by the HIPIMS technique. The hardness increased with decreasing duty cycle and increasing peak power density. Greater hardness of around 26.5 to 28.0 GPa was achieved for the crystalline over-stoichiometric AlN thin film when the coating was fabricated using a 3.5% duty cycle. Meanwhile, the adhesion property was improved with increasing duty cycle and frequency. The AlN coating with both high hardness of 27 GPa and adequate adhesion property was fabricated at a repetition frequency of 1250 Hz and duty cycle of 3.5%.