Resistance Change in Thin Ag Film on Si (100)

Abstract

We have been involved in studying the resistance change of thin Ag film formed on Si substrate at room temperature and at 473 K in UHV. In those studies, using a four terminal method, we measured the periodic resistance change in Ag thin film while film thickness was increased up to 2 nm. Recently, we have been studying film resistance in more detail, namely, how it changes in relation to increase in Ag film thickness at room (300 K) and low (50 K) temperatures. In the former case it was found that film resistance maintained a constant value for Ag thicknesses up to 20 nm and that thereafter resistance decreased monotonously with increase in film thickness. This suggests that electron conduction is mainly limited to Si substrate and is not caused by an increase in the size of Ag islands, consequently, a Schottky barrier which is electrically separated appears between the Ag islands and Si surface. After enough film thickness the islands become connected with each other and make electrical paths. In the case of low temperature, film resistance could not measured until the film thickness reached 2 nm because Si substrate showed too high resistance. When film thickness was greater than 2 nm, resistance was found to decrease monotonously with increase in film thickness. It is suggested that the Ag particles tend to stay where they initially precipitated. After a large amount of Ag particles have precipitated on to the Si surface, they form a lot of very small islands and, consequently, electrical conduction appears in very thin film.