The role of the substrate temperature on superconducting properties of sputtered Nb films

• Nb films deposited directly on Si (100) substrate kept at different temperatures TS.
• No significant change of superconducting properties of the Nb films for TS ≤ 373 K
• Internal stress and/or Si/Nb interdiffusion favor degradation of superconductivity
• Determination of the optimum TS value responsible for the highest critical current

The influence of the substrate temperature TS on the superconducting properties of 100 nm sputtered Nb films, prepared directly onto orientated Si (100) substrate, was systematically investigated by measuring their structural, morphological and magnetic properties. Within the TS interval 293–373 K no significant change is observed either in the Nb lattice parameter or in the superconducting transition temperature TC. For TS > 373 K, a degradation of the Nb superconducting properties was observed concomitantly with an increase of the Nb lattice parameter. This effect was attributed to an interdiffusion at the Si/Nb interface and/or an enhancement of the internal stress caused by high temperature deposition. The temperature dependence of the critical current density JC(T) was estimated from magnetization measurements and its behavior is explained based on the granular morphology of Nb films. This work provides some insights on the optimum TS responsible for the highest JC value. It also brings information on how TS affect the superconducting properties of Nb films sputtered directly on Si (100) by DC magnetron sputtering.