Growth and Characterization of Thin-film A15 Nb-Al Intermetallics for Superconducting Quantum Electronics: Part 1

Recent developments in qubit technology have underscored the need for superconducting materials with high critical temperatures and critical magnetic fields. Devices such as hybrid superconductor-semiconductor, fluxonium, and hot qubits require superconducting materials resilient to external excitations. A15 intermetallic compounds may provide an avenue for such devices, with critical temperatures and critical magnetic fields exceeding that of more commonly used qubit materials such as Nb and Al. Here, we revisit A15 Nb₃Al as a candidate material for superconducting quantum circuits. We synthesize thin films of Nb-Al alloys via a co-sputtering process followed by rapid post-deposition annealing to realize the Nb₃Al A15 phase. Through energy-dispersive X-ray spectroscopy and X-ray diffractometry, we determine the composition and crystalline structure of the films. By tuning the deposition parameters and rapid annealing, we achieved critical temperatures above 15 K in 200-300 nm thick films.