Nitridized aluminum thin films for superconducting quantum technologies*

Building quantum technologies with superconducting qubits puts stringent requirements on the choice of materials, as their quality and properties ultimately limit the circuit performance. In this work, we propose a novel superconducting material attractive for superconducting quantum circuits: thin-film nitridized aluminum fabricated by magnetron sputtering in nitrogen-argon flows. At room temperature, the samples behave as a normal conductor (low N₂ partial pressures), and as an insulator (high N₂ partial pressures), finding the limit between both regimes in the sample processed with 15% N₂. Measurements at low temperature show that the thin films display superconductivity for 0% - 15% N₂, with critical temperatures that vary non-monotonically from hundreds of mK for the most resistive samples up to more than 3K for samples fabricated with 5-10% N₂. We also report an important decrease in the critical current density for the most resistive samples and qualitative differences of the resistance behavior as a function temperature. These results indicate that nitridized aluminum may be used in a variety of applications, ranging from a superinductor in the highly resistive regime to a larger-gap material in the low resistance regime.