Tribological and optical properties of crystalline and amorphous alumina thin films grown by low-temperature reactive magnetron sputter-deposition

Amorphous and crystalline alumina thin films were grown by reactive magnetron sputtering. A pulsed d.c. bias was applied to both the aluminum target and the substrate to maintain a stable deposition process and high deposition rate. An external solenoid coil was placed underneath the substrate to form a magnetic trap between the substrate and the target, thus enhancing ion bombardment of the growing film. Effects of substrate bias and magnetic trap on film properties were investigated. Under optimum conditions, crystalline alumina films were obtained at substrate temperatures of ∼340°C, with hardness ∼25 GPa and refractive index 1.65–1.85 in the visible region. Friction and wear properties of crystalline and amorphous alumina thin films were compared.