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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.