Cornell researchers developed a krypton-based sputtering process that deposits high-quality superconducting tantalum films on silicon at 200 degrees Celsius. Announced in August 18, the method cuts standard deposition temperatures by about half, expanding the manufacturing window for superconducting quantum chips and addressing key nanofabrication bottlenecks.
The Low-Temperature Tantalum Breakthrough at Cornell
Commercializing quantum computing demands high-performance superconducting materials alongside reliable, sustainable manufacturing processes. Tantalum has long attracted hardware designers because it is a corrosion-resistant metal with stable surface properties, carrying electrical current with little to no energy loss. Yet, turning that potential into microchips has faced severe roadblocks. Traditional methods require depositing tantalum on a substrate at temperatures exceeding 400 degrees Celsius, a threshold that pushes past the limits of standard semiconductor foundry tools.
A research team led by Valla Fatemi, assistant professor in the Duffield College of Engineering at Cornell University, shifted the paradigm by altering the physical deposition process using krypton gas to slash the deposition temperature down to 200 degrees Celsius on silicon. The findings were published in Nature Materials, detailing work led by postdoctoral researcher Maciej Olszewski.
“Tantalum as a material has been shown to be very exciting from a device performance perspective, but its manufacturability had some question marks because of integration challenges such as required process temperatures.”
Valla Fatemi, Cornell Duffield College of Engineering
How Krypton Sputtering Replaces Argon
In standard microchip manufacturing, researchers build thin metallic films through sputtering—bombarding a source material with ions from a noble gas to knock atoms loose so they settle onto a substrate. Previous laboratory work on niobium-based materials utilized argon as the ionized gas. When the Cornell team swapped niobium for tantalum, however, they ran into a stubborn materials science barrier. Depositing tantalum at lower temperatures leaves the metal stuck in an undesirable crystal phase.
To fix that flaw previously, engineers had to either blast the substrate past 400 degrees Celsius or seed the surface with extra materials. Unfortunately, overheating tantalum causes it to mix with the underlying silicon, forming a thick layer that ruins chip performance and triggers information loss. The breakthrough arrived when Olszewski hypothesized that using krypton as the ionized gas instead of argon would transfer more momentum, kicking off tantalum atoms with greater energy and stabilizing the correct crystal phase at 200 degrees Celsius.
“There’s this whole set of tooling and fabrication lines that don’t really go above 400 Celsius, and they’re built for that. And tantalum on silicon, when you use the old method, was right on the border of that.”
Maciej Olszewski, postdoctoral researcher
Airbridges, Crosstalk, and Processor Architecture
Beyond foundational deposition chemistry, recent quantum processor designs have incorporated advanced tantalum structures to clean up signal routing. Researchers exploring tunable coupling quantum architectures have turned to fully-capped tantalum airbridges to shield delicate control lines. Because tantalum resists both acid and alkaline solutions, manufacturing teams can immerse the processor chip into piranha and HF solution after airbridge fabrication to strip away residual photoresist and clear out oxygen layers from the substrate—a cleaning step typically unavailable with aluminum airbridges.
This robust processing yields notable performance metrics across multi-qubit architectures. In characterization testing of a 13-qubit flip-chip processor, most qubits exhibit a median T1 exceeding 100 μs, providing the extended coherence necessary for deep quantum circuits. Furthermore, incorporating fully-capped tantalum airbridges over control lines provides physical shielding against unwanted microwave and flux crosstalk, reducing interference without requiring complex, resource-heavy calibration matrices.
Manufacturing Realities and Commercial Integration
Quantum hardware development is choked by the difficulty of scaling high-performance materials to industrial foundries. Qubits store and process information by leveraging fragile quantum states, but maintaining those states requires minimizing microscopic defects across every manufacturing layer. When deposition temperatures drop below the 400-degree ceiling, commercial fabrication lines can adopt tantalum processes without retooling their core infrastructure.
The Cornell team emphasizes that their academic process yields leading-edge performance while remaining fully compatible with existing nanofabrication systems. By proving that high-conductivity, high-coherence tantalum films are achievable at 200 degrees Celsius on standard silicon wafers, the research provides a clear manufacturing blueprint for scaled quantum processor development moving forward.
