Superconductor Science and Technology

Room temperature pure α-phase tantalum films on sapphire for superconducting qubits

Kunliang Bu, Zhiwen Zong, Zhenxing Zhang, Xingyu Ma, Ming Shao, Dengfeng Li, Yuan Li, Jingjing Hu, Sainan Huai, Shuoming An, Tianqi Cai, Xiaopei Yang, Maochun Dai, Yi-Cong Zheng, Shengyu Zhang

Published Jan 15, 2025• 1 citation

Publisher

Abstract

Abstract Tantalum (Ta) films with a body-centered cubic α-phase play a crucial role in high-performance Ta-based superconducting quantum processors. The growth of pure α-Ta at low temperatures has been a long-term goal. Existing experience with Ta growth on silicon substrates has led to the belief that α-Ta can only be stabilized at high temperatures. In this study, we systematically analyzed the growth mechanism of Ta films on sapphire substrates using first-principles calculations, revealing a narrow growth energy window for pure α-Ta at room temperature (RT). This finding indicates the feasibility of obtaining pure α-Ta at significantly lower temperatures. Experimentally, we successfully achieved pure α-Ta at RT via magnetron sputtering by meticulously adjusting the growth parameters. The resulting superconducting resonators based on the developed RT α-Ta exhibit an internal quality factor ( Q i ) of approximately 2.1 × 10 6 at single-photon levels, comparable to those fabricated at high temperatures. Additionally, fixed-frequency transmon qubits fabricated using the RT α-Ta film demonstrate a coherence time exceeding 280 µs, underscoring the film’s high quality. The RT α-Ta without a seed layer simplifies the fabrication process, offering a more efficient and flexible approach for producing Ta-based superconducting quantum processors.

DOI: 10.1088/1361-6668/adaaa8

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