Ta/MgO/Ta tunneling junctions for circuit quantum electrodynamics applications

Tantalum (Ta) is a promising material for circuit QED applications since it has a longer coherence time and a higher critical temperature compared to Al. While the results of the superconductivity in Ta has been well documented, there is not much work on Ta-based Josephson junctions because of the difficulty in achieving the superconducting tantalum phase on insulators. In this work, we investigate Ta/MgO/Ta trilayer structures deposited by physical vapor deposition. Using different seed layers such as Si, TaN, MgO, and Pt for the Ta deposition, different Ta phases are formed. We observed the superconducting phase in Ta at 3.4 K on MgO, 2.1 K on TaN, and 0.48 K on Pt, while no superconducting phase was observed on Si. We also demonstrate a normal metal-insulator-superconductor junction on the Ta/MgO/Ta trilayer structure at 3.4 K. This heterostructure structure is promising for its compatibility with magnetic random access memory (MRAM) applications, enabling integration of qubit and classical memory devices on the same material platform.