Cornell University researchers have developed a fabrication method that could make tantalum easier to use in superconducting quantum computers. By replacing argon with krypton gas during thin-film deposition, the team reduced the temperature needed to deposit high-quality tantalum on silicon from more than 400°C to about 200°C.
Tantalum is attractive for quantum hardware because it resists corrosion and offers stable surface properties. However, manufacturing it has presented difficulties. At lower deposition temperatures, tantalum can form a crystal phase with undesirable characteristics. Raising the temperature above 400°C can solve this problem, but many semiconductor fabrication systems are not designed for such conditions. Excessive heat can also cause tantalum to mix with the silicon substrate, creating a layer that contributes to information loss.
The Cornell team addressed this limitation by modifying the sputtering process used to create tantalum films. During sputtering, ionized gas knocks atoms from a source material so they can settle onto a substrate. The researchers previously used argon for similar work with niobium. For tantalum, lead author Maciej Olszewski proposed krypton because its ions could transfer greater momentum to tantalum atoms. This additional energy helped stabilize the desired crystal phase at substantially lower temperatures.
The lower temperature creates a wider processing window for semiconductor fabrication facilities, potentially making tantalum easier to integrate into established manufacturing lines. The resulting thin films also showed substantially higher electronic conductivity.
Researchers then incorporated Josephson junctions, essential components that enable quantum tunneling and qubit operation. The resulting devices produced high-quality qubits and strong performance. The team found that as material quality improves, subtle variations in Josephson junction fabrication increasingly influence device behavior.
The research suggests that a relatively simple change in processing gas could help combine high-performance superconducting materials with manufacturing methods better suited to industrial quantum chip production.
