PROPERTIES OF RF-SPUTTERED NIOBIUM THIN-FILMS FOR METROLOGICAL APPLICATIONS

Niobium superconductive films for metrological applications (refractor y Josephson tunnel junctions, superconductive bolometers and radiation sensors), have been fabricated via r.f. magnetron sputtering. Their e lectrical and structural properties have been measured on a wide range of film thicknesses (10-1000 nm). The data indicate the growth of a f irst layer at the substrate interface, which has a different behaviour with respect to the remaining of the film. The electrical data of res istivity at various temperatures show the relevant role of this layer at thicknesses < 200 nm and the effect of pre-deposition treatments on the reduction of this interfacial layer. Experimental resistivity dat a can be fitted for these thicknesses only using a modified version of the Mayadas-Shatzkes model, which keeps into account not only the ref lection at grain boundaries but also the altered composition layer.