Normal Metal-Insulator-Superconductor Tunnel Junctions With Pulsed Laser Deposited Titanium Nitride as Superconductor

Here we report the fabrication of normal metal - insulator - superconductor (NIS) tunnel junctions using superconducting titanium nitride grown by pulsed laser deposition (PLD). The films for NIS junction fabrication were deposited on two different substrates: silicon nitride film and magnesium oxide. TiN films were characterized by means of electrical transport measurements, and films with superconducting transition temperatures above the liquid helium boiling point were chosen for fabrication of NIS junctions. Tunnel junction devices were successfully fabricated using electron beam lithography and shadow evaporation techniques. The insulator layer formation was performed using two different approaches: the tunnel barrier was either formed by direct oxidation of TiN, or by fabrication of an additional aluminum oxide layer. Devices fabricated by direct oxidation showed much more transparent barriers and slightly higher subgap currents, but both types of devices could be used for thermometry. Further optimization of the direct oxidation process may allow electric cooling applications in the future.