Fabrication of niobium titanium nitride thin films with high superconducting transition temperatures and short penetration lengths

We report a systematic study of the superconducting and normal state properties of reactively sputtered Nb/sub 0.62/Ti/sub 0.38/N thin films deposited on thermally oxidized Si wafers. The superconducting transition temperature (T/sub c/) was found to increase from 12 K for films prepared on unheated substrates to over 16 K for films prepared on substrates maintained at 450/spl deg/C. A Nb buffer layer was found to improve T/sub c/ by /spl sim/0.5 K for growths at lower substrate temperatures. The films fabricated at 450/spl deg/C have an amply smooth surface (1.5/spl plusmn/0.25 nm root mean square roughness), a sufficiently high T/sub c/, and sufficiently small penetration depth (200/spl plusmn/20 nm at 10 K) to be useful as ground planes and electrodes for current-generation 10 K rapid single-flux quantum circuit technology.