Very-high-rate reactive sputtering of alumina hard coatings

A very-high-rate reactive magnetron sputtering deposition process for alumina hard coatings at substrate temperatures ≤250 °C has been developed. Utilizing pulsed DC power to sputter Al + AlO _x off the target surface and partial pressure control of the reactive gas to maintain a certain partial pressure value (accuracy of better than 0.005 mtorr), fully dense, transparent alumina coatings could be produced at 76% of the metal deposition rate. The coatings have an elastic modulus of 140 GPa, a hardness of 12 GPa, a chemical composition close to stoichiometric, and a refractive index of 1.65. The influence of the O ₂ partial pressure on the deposition rate, optical and mechanical properties is discussed.