Optical and electrical properties of sputtered Ag films on PET webs

Optical and electrical properties of Ag films deposited onto polymer 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 dispersion relation for bulk Ag was found to describe the thin films accurately only above a critical thickness d(c). This critical thickness depends on the process parameters during deposition and is found to vary between 12 nm and 18 nm. Our results indicate, that the critical thickness marks a transition in the growth mode of Ag thin films from well separated islands to a continuous films.