Superconducting transition temperature versus thickness of Nb film on various substrates

Dependence of superconducting transition temperature on the thickness of Nb films deposited upon several kinds of substrates by means of rf sputtering was studied in search of rudimental data necessary in fabricating variable thickness microbridge type Josephson junctions. The transition temperature was found to lower with the decrease of Nb film thickness. The lowering characteristics of the transition temperature were found to vary in accordance with whether the substrate surface was amorphous or crystalline. The cause of the variance was studied on thin films with the aid of x-ray diffraction pattern analysis and measurement of film resistance.