Recent Developments In Reactively Sputtered Optical Thin Films

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Abstract
Highlights of a multiyear effort to develop new or improved thin-film, optical-coating materials through the use of reactive sputtering techniques are presented. Reactive sputtering is shown to be an extremely versatile technique capable of straightforward synthesis of broad classes of materials. The exceptional utility of sputtering for preparation of hard coatings such as oxides, nitrides and novel materials based on Si and Ge is described. Some of these coating materials cannot be made by conventional evaporative techniques. Reactive sputtering allows precise control of coating composition, microstructure and the resulting optical properties. Supporting data are presented for TiO2, for which record high damage thresholds were obtained, and for Si-based coatings, for which record low infrared absorptance was achieved. Transparent conductive indium tin oxide (ITO) coatings with low sheet resistance and high visible and near infrared transmission can also be made. These coatings have many electro-optic contact and electromagnetic shielding applications. Examples of multilayer coatings such as all-dielectric and dielectric-enhanced mirrors made from reactively sputtered materials are included, and simple yet elegant fabrication techniques are introduced. The reactive sputtering technique and equipment used specifically for optical coatings are briefly described, and comparison is made with the conventional evaporative approach.

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