ArXiv · 2026
In this work, we have presented S-I-S Josephson junctions with rmα-Ta electrodes and a rm TaOₓ barrier. We grew base and top α-Ta electrodes using seed layer engineering, showing both Nb and rm TaNₓ are viable seed layer choices, and particularly emphasize that at room temperature a re-seed layer is required to nucleate rmα-Ta for the top electrode. However, we note that the choice of seed layer can have subtle implications on the electrical tunneling behavior of the junctions. We used room-temperature probing of variable junction areas, combined with Ambegaokar-Baratoff physics, to characterize the wafer scale critical current densities. For 0.4 μm² junctions, we found junction spreads as low as 2.0% across the 20 x 20 mm chip relevant for device performance. The entire process was carried out using standard industry foundry processing using 150 mm wafer tooling, which is an important step towards proving that Ta-based junctions can be implemented at scale. We have successfully fabricated and tested junctions with rmα-Ta electrodes and a rm TaOₓ insulating tunnel barrier, demonstrating that this is a material platform which merits further investigation and studies for potential application in classical and quantum superconducting technologies.
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