Optical and electrical properties of sputtered Ag films on PET webs

Optical and electrical properties of Ag films deposited onto PET webs by sputtering are studied in dependence on the process parameters during deposition. The Ag layers were deposited onto a commercially available PET substrate (Melinex® 400) by DC magnetron sputtering. The optical properties of the samples were analyzed by ellipsometry and VIS/NIR spectroscopy. The electrical properties of the thin Ag films were characterized by four-point-probe measurements. The optical constants for bulk Ag were found to describe the thin films accurately only above a critical thickness dc. This critical thickness depends on the process parameters during deposition and is found to vary between 12 and 18 nm. The results indicate, that the critical thickness marks a transition in the growth mode of Ag thin films from well separated islands to a continuous film.