Cryogenic growth of tantalum thin films for low-loss superconducting circuits

2024/05/20 by Teun A. J. van Schijndel, Anthony McFadden, van Schijndel, Teun A. J. +13 · 4 citations
Engineering · Physics and Astronomy · #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Physics of Superconductivity and Magnetism #Superconducting Materials and Applications #Superconductivity (cond-mat.supr-con) #Superconductivity in MgB2 and Alloys

paper · pdf · doi:10.48550/arxiv.2405.12417

openalex publication_date 2024/05/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

Motivated by recent advancements highlighting Ta as a promising material in low-loss superconducting circuits and showing long coherence times in superconducting qubits, we have explored the effect of cryogenic temperatures on the growth of Ta and its integration in superconducting circuits. Cryogenic growth of Ta using a low temperature molecular beam epitaxy (MBE) system is found to stabilize single phase α-Ta on several different substrates, which include Al₂O₃(0001), Si(001), Si(111), SiN_x, and GaAs(001). The substrates are actively cooled down to cryogenic temperatures and remain < 20 K during the Ta deposition. X-ray θ-2θ diffraction after warming to room temperature indicates the formation of polycrystalline α-Ta. The 50 nm α-Ta films grown on Al₂O₃(0001) at a substrate manipulator temperature of 7 K have a room temperature resistivity (\mathrmρ_{300 K}) of 13.4 μΩcm, a residual resistivity ratio (RRR) of 17.3 and a superconducting transition temperature (T_C) of 4.14 K, which are comparable to bulk values. In addition, atomic force microscopy (AFM) indicates that the film grown at 7 K with an RMS roughness of 0.45 nm was significantly smoother than the one grown at room temperature. Similar properties are found for films grown on other substrates. Results for films grown at higher substrate manipulator temperatures show higher \mathrmρ_{300 K}, lower RRR and Tc, and increased β-Ta content. Coplanar waveguide resonators with a gap width of 3 \mathrmμm fabricated from cryogenically grown Ta on Si(111) and Al₂O₃(0001) show low power Q_i of 1.9 million and 0.7 million, respectively, indicating polycrystalline α-Ta films may be promising for superconducting qubit applications even though they are not fully epitaxial.

Cited by

• Fabrication and Structural Analysis of Trilayers for Tantalum Josephson Junctions with Ta₂O₅ Barriers
• Cryogenic growth of aluminum: structural morphology, optical properties, superconductivity and microwave dielectric loss
• In situ Al₂O₃ passivation of epitaxial tantalum and aluminum films enables long-term stability in superconducting microwave resonators
• Origins of microwave losses in superconducting circuits made with silicon-on-insulator substrates

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