Production of compositionally gradient Al-AlN films by reactive sputtering and their mechanical and electrical properties

The application of reactive sputtering in a mixed gas of argon (Ar) and nitrogen (N₂) to Al metal resulted in the formation of compositionally gradient film consisting of Al and AlN phases. By changing the mixing gas ratio of N₂ to N₂+Ar so as to be 0, 0.05, 0.1, and 0.2 in a total gas pressure of 1 Pa, the resulting phase changes in the order of Al, Al+AlN, AlN+Al, and AlN and the thickness of each phase is 14, 23, 18, and 8 μm, respectively, after sputtering for 3.6, 5.4, 7.2, and 10.8 ks, respectively. The Al concentration along the sample thickness changes from 100% to about 50% with an increase of mixing ratio from 0 to 0.2. The lattice parameters of Al and AlN phases remain constant along the sample thickness. The Knoop hardness and the electrical resistivity increase steeply from 100 to 3900 and from 3×10^-8 Ω m to an infinite value, respectively, with the phase transition from Al to AlN through Al+AlN and AlN+Al. The load leading to an exfoliation among the layers was measured to be 16 N. Thus, the sputtered Al-AlN film is concluded to possess functionally gradient characteristics resulting from the compositional and structural gradients.