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

Abstract: 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.