Superconducting quantum technology has just taken a significant step toward becoming easier to manufacture at scale. Researchers have demonstrated that tantalum thin films suitable for superconducting qubits and microwave resonators can be produced on silicon at temperatures as low as 200 °C by replacing the conventional argon sputtering gas with krypton. The advance addresses one of the most persistent challenges in tantalum-based quantum-device fabrication: obtaining the desirable body-centred cubic, or bcc, phase without exposing substrates to temperatures that are incompatible with advanced semiconductor manufacturing. In experiments reported in Nature Materials, the resulting films supported high-performance microwave circuits and transmon qubits with quality factors reaching 16.9 million.
Tantalum has become one of the most closely watched materials in superconducting quantum computing because devices made from it have recently shown unusually strong performance. Superconducting circuits must preserve fragile quantum states while limiting energy loss to their surroundings, and the choice of metal can strongly influence that balance. Tantalum is attractive because its surface and interface properties can reduce some sources of microwave dissipation, the unwanted absorption of electromagnetic energy that shortens the lifetime of resonator and qubit states. Yet tantalum is not a single uniform material. Its crystal structure, impurities, defects and interaction with the underlying substrate all depend on how the film is deposited, making fabrication conditions central to device performance.
The key structural target is the bcc phase of tantalum, often called alpha tantalum. This phase is metallic and superconducting, while other tantalum phases can have less desirable electrical and structural properties. Direct sputter deposition of bcc tantalum on silicon has generally required substrate temperatures above 400 °C. Such temperatures may be practical for some standalone laboratory processes, but they create serious difficulties for back-end-of-line manufacturing, where new materials must be integrated after sensitive electronic structures, interconnects and insulating layers have already been formed. A lower-temperature route could allow tantalum to be introduced much later in the fabrication sequence, potentially making high-performance superconducting circuitry more compatible with established semiconductor processing.
The researchers found that krypton changes the sputtering environment in a way that promotes bcc tantalum growth at substantially lower temperatures. In sputtering, energetic ions from a plasma strike a tantalum target and eject atoms that travel toward the silicon wafer, where they condense into a thin film. The gas used to sustain that plasma affects the energy and momentum delivered to the arriving atoms, as well as the conditions under which they settle into a crystal lattice. Krypton is heavier than argon, the gas most commonly used in comparable deposition systems. That difference alters ion bombardment and film-growth dynamics, helping tantalum atoms form the desired bcc structure even when the substrate is held at only 200 °C. The result is a wider and more practical processing window rather than a narrow high-temperature route.
The importance of the discovery is not limited to crystal structure. For quantum circuits, a film can appear superconducting and still perform poorly if its interfaces contain defects, disordered regions or unwanted chemical mixtures. Microwave photons moving through a resonator interact with the surfaces and boundaries of the device, so even a thin layer of loss-producing material can degrade the quality factor. The quality factor describes how efficiently a resonator stores electromagnetic energy: a higher value means that energy remains confined for more oscillation cycles. In superconducting qubits, reduced microwave loss generally supports longer-lived quantum states, although the final performance also depends on geometry, materials surrounding the circuit and the details of device fabrication.
To assess the new films, the team fabricated coplanar-waveguide resonators, a standard type of microwave circuit in which a central conducting strip is separated from surrounding ground planes by narrow gaps. These structures provide a sensitive test of material loss because their electromagnetic fields extend into the tantalum, the silicon substrate and the interfaces between them. Resonators made from krypton-sputtered tantalum showed an excellent tight distribution of microwave performance, indicating that the process produced films with consistent properties across the tested devices. Such reproducibility is crucial for manufacturing: a process that creates one exceptional resonator but a broad spread of results would be difficult to use in large quantum processors.
The experiments also revealed a clear warning about increasing the growth temperature. Films deposited at higher temperatures exhibited greater microwave losses, and those losses correlated with the degree of tantalum–silicon intermixing. At the interface, atoms from the film and substrate can diffuse or become incorporated into a mixed chemical region. This intermixing may introduce defects or electronic environments that absorb microwave energy, providing a pathway for dissipation even when the bulk tantalum remains superconducting. The observation suggests that simply raising the temperature to improve crystallinity is not necessarily beneficial. In this system, the lower-temperature krypton process can produce the required crystal phase while limiting the interface reactions that compromise microwave performance.
The researchers then used the films to build transmon qubits, one of the leading architectures for superconducting quantum computers. A transmon stores quantum information in the quantized energy levels of a superconducting circuit containing Josephson junctions and capacitive elements. Its capacitor geometry determines important electrical properties, while the surrounding materials and surfaces can introduce loss. The devices in this study used a compact capacitor gap of just 20 micrometres, a dimension relevant to efforts to pack more circuits into a limited area. Despite the compact geometry, the krypton-sputtered tantalum films enabled qubit quality factors as high as 16.9 million, demonstrating that lower-temperature deposition did not prevent the material from supporting highly coherent quantum hardware.
The combination of low-temperature compatibility, controlled bcc-phase formation, reproducible resonator behaviour and high qubit quality factors makes krypton-sputtered tantalum a promising candidate for scalable quantum-device manufacturing. The work does not remove every challenge facing superconducting processors: qubit performance is governed by many interacting sources of noise and loss, and integrating any new material into a complex fabrication stack requires further testing. Nevertheless, the study offers a practical solution to a major bottleneck. By changing a single part of the deposition environment, researchers have shown that high-quality tantalum can be formed at temperatures compatible with back-end-of-line standards, while avoiding the interface damage associated with hotter growth. As quantum processors move from laboratory demonstrations toward larger and more manufacturable systems, that kind of process innovation could prove as important as improvements to the qubits themselves.
Subject of Research: Krypton-sputtered tantalum thin films for superconducting quantum devices
Article Title: Krypton-sputtered tantalum films for scalable high-performance quantum devices
Article References: Olszewski, M.W., Kong, L., Reinhardt, S. et al. Krypton-sputtered tantalum films for scalable high-performance quantum devices. Nature Materials (2026). https://doi.org/10.1038/s41563-026-02718-z
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41563-026-02718-z
Keywords: superconducting qubits, tantalum thin films, krypton sputtering, quantum computing, microwave resonators, bcc tantalum, transmon qubits, semiconductor fabrication, superconductivity, quantum devices
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