Electrical properties of Ag films on polyethylene terephthalate deposited by magnetron sputtering
Ag films with a thickness between 2 nm and 20 nm were analyzed with regard to their sheet resistance. The films were all deposited in one batch, but the Ar pressure, sputtering power as well as the duty cycle were varied between the depositions of the individual samples. The sheet resistance was determined as a function of film thickness. It could be shown that a certain minimum film thickness dec is needed that the films show a measurable conductivity. This minimum film thickness is correlated with the percolation threshold of the Ag films. The coalescence of previously isolated islands leads to a steep increase of the conductivity with increasing film thickness until a fully closed film is formed. The minimum film thickness dec depends especially on the sputtering power and the Ar pressure. An increased Ar pressure leads to an increase of dec from 3.5 nm at 0.35 Pa to 9.2 nm at 7 Pa. For an increasing sputtering power dec is reduced from 4.2 nm at 1.18 W/cm2 to 3.6 nm at 4.74 W/cm2. The model of Mayadas and Shatzkes is used to describe the conductivity in dependence on the film thickness. This model takes into account the influence of the film surfaces as well as the influence of the grain boundaries on the scattering of the electrons.