Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

Abstract

The properties of sol–gel derived ZrO2 thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO2 thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO2 coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO2 coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO2 coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO2 thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm2 (1,064 nm, 10 ns) and 14.6 J/cm2 (1,064 nm, 10 ns) are obtained for ZrO2 coating and ZrO2/SiO2 multilayer coatings respectively.