ENLARGEMENT OF KINETIC INDUCTANCE OF NBN SUPERCONDUCTING THIN-FILMS FOR DEVICE APPLICATIONS

Experimental studies to enlarge kinetic inductance of NbN thin films using the effects of quality and thickness of the film are made by measuring Fiske current steps in the current-voltage (I-V) characteristics of NbN/Pb-In Josephson junctions. Experiments demonstrate that the specific kinetic inductance L(K) can be enlarged over a wide range by changing stoichiometry of the film, as well as by making the film thickness thin, and that this enlargement becomes larger by both effects when the film thickness is in an ultra thin regime. This inductance is shown to be well fitted to L(K) = mu-0-lambda-2/d, where mu-0 is the vacuum permeability, d is the thickness, and lambda is the magnetic penetration depth in the dirty limit. In the present experiment we attained the inductance as high as L(K) = 130 pH by the combined effects of impurity and thickness for a film with d = 30 nm.