Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions

We report the development of superconducting tantalum nitride (TaN${}_x$) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlO${}_x$ and TaO${}_x$ (Cu-AlO${}_x$-Al-TaN${}_x$ and Cu-TaO${}_x$-TaN${}_x$), with both devices exhibiting temperature dependent current-voltage characteristics which follow the simple one-particle tunneling model. The superconducting gap follows a BCS type temperature dependence, rendering these devices suitable for sensitive thermometry and bolometry from the superconducting transition temperature $T_{\text{C}}$ of the TaN${}_x$ film at $\sim 5$ K down to $\sim$ 0.5 K. Numerical simulations were also performed to predict how junction parameters should be tuned to achieve electronic cooling at temperatures above 1 K.