Normal-Metal–Insulator–Superconductor Tunnel Junction With Atomic-Layer-Deposited Titanium Nitride as Superconductor

We report the fabrication of 70-350-nm-thick superconducting titanium nitride (TiN
_x
) films using the atomic layer deposition (ALD) technique and the subsequent fabrication of normal metal-insulator-superconductor (NIS) tunnel junction devices from the ALD films. The films were deposited on a variety of substrates: silicon, silicon nitride, sapphire, and magnesium oxide. Superconductivity, with transition temperatures (T
_C
) ranging from 1.35 to 1.89 K, was observed in all films. TC was found to depend on both the substrate type as well as film thickness. Cu-TiO
_x
-TiN
_x
NIS tunnel junction devices were fabricated from the TiN film deposited on silicon, using electron beam lithography and shadow angle evaporation techniques. These devices exhibit temperature-dependent current-voltage characteristics and good thermometric response from 0.1 K to slightly above T
_C
. Nonlinearity in the current-voltage characteristics was observed even at temperatures as high as 5T
_C
, indicating the presence of a pseudogap in these TiNx films.