Jincheng Qian1, Bill Baloukas1, Etienne Bousser1, Carlo A. Kosik-Williams2, James J. Price2, Charles A. Paulson2, Shandon D. Hart2, Karl W. Koch2, Robert A. Bellman2, Jolanta Klemberg-Sapieha1, Ludvik Martinu1 1
1Department of Engineering Physics, Polytechnique Montreal, Montreal, Quebec H3C 3A7, Canada
2Corning Inc., Corning, NY 14830, USA
J.C. Qian1, B. Baloukas1, E. Bousser1, C.A. Kosik-Williams2, J.J. Price2, C.A. Paulson2, S.D. Hart2, K.W. Koch2, R.A. Bellman2, J.E. Klemberg-Sapieha1, L. Martinu1 1Department of Engineering Physics, Polytechnique Montreal, Montreal, Quebec H3T 1J4, Canada 2Corning Inc., Corning, NY 14830, USA
ZrO2 optical coatings with high toughness were deposited by low duty cycle pulsed DC magnetron sputtering. The effect of O2 partial pressure, substrate bias, substrate heating, and pulse length on the microstructure, stress, and optical and mechanical properties were studied. By increasing the O2 partial pressure, the extinction coefficient and the deposition rate decreased, while the crystalline structure changed from a tetragonal to a monoclinic phase. The energy of the bombarding ions can be increased by adding substrate bias, by increasing substrate temperature, or by decreasing the pulse length. As a result of high energy of bombarding ions, the crystalline structure of ZrO2 films shifted from a mixture of monoclinic and tetragonal phases to a monoclinic phase with a preferred (111) crystallographic plane growth, accompanied by a high compressive stress. Toughness has been assessed by indentation measurements for ZrO2 coatings with similar mechanical properties but different thicknesses and different stress levels. It was found that reliable toughness measurements could be obtained for films with a thickness above 2 µm. Higher compressive stress level gave rise to a higher toughness and a higher radial fracture resistance. In contrast, higher compressive stress led to higher Lc1 but lower Lc2 values during the scratch tests. In summary, the ZrO2 coatings synthesized in this work exhibit low absorption, low compressive stress, a hardness of ~14 GPa, a toughness of more than 3 MPa∙m-2, and a good scratch resistance – as such, the ZrO2 films are good candidates for protective optical coatings for touch screens or other optical devices.