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.