Cornell researchers have lowered the temperature required to deposit tantalum, a promising material for quantum computing, by 200°C to 200°C, using krypton gas during nanofabrication. This process allows for deposition on silicon, a standard substrate, and results in thin films with substantially higher electronic conductivity.
“Tantalum as a material has been shown to be very exciting from a device performance perspective, but its manufacturability had some question marks,” said Valla Fatemi, assistant professor at the Cornell Duffield College of Engineering, who led the project. This advance addresses a key bottleneck in scaling quantum computing by making tantalum compatible with more existing semiconductor manufacturing tools.
Krypton Gas Lowers Tantalum Deposition Temperature to 200°C
A deposition temperature of 200°C is now achievable for tantalum, a significant reduction from the typical 400°C previously required, thanks to a novel process developed by researchers at Cornell. This lowered threshold expands compatibility with existing semiconductor manufacturing infrastructure, potentially accelerating the scaling of quantum computing hardware. The team’s work, detailed in the August 18 issue of Nature Materials, centers on utilizing krypton gas during the deposition process to achieve stable thin films of tantalum on silicon substrates.
Previously, depositing tantalum presented a manufacturability challenge; while the material exhibits promising characteristics for superconducting qubits, its deposition demanded high temperatures that strained existing fabrication capabilities. This approach circumvented the need for either excessively high heat or surface seeding with additional materials, both of which were previously necessary to achieve optimal film properties.
Maciej Olszewski, the study’s lead author and a postdoctoral researcher, explained that the use of krypton created a wider margin for reliable fabrication. “There’s this whole set of tooling and fabrication lines that don’t really go above 400 Celsius, and they’re built for that,” Olszewski said. “There was little margin to do things reliably.
Using krypton brought that threshold down to 200 Celsius, so you now have a large window to be able to do reliable fabrication.” This is particularly important given the limitations of current nanofabrication systems, many of which are designed to operate within a 400°C temperature range. The resulting tantalum films not only demonstrate lower deposition temperatures but also exhibit substantially higher electronic conductivity, a critical factor for improving qubit performance.
The team’s earlier work with niobium, utilizing argon gas for sputtering, provided foundational insights into surface science and its impact on film quality. “That work got the ball rolling for us in understanding a lot of the surface science and how that correlates with improving performance,” Fatemi noted.
Building on this knowledge, the researchers were able to refine the process for tantalum, achieving a level of control over the material’s properties that was previously unattainable. A crucial component of the process is the formation of a Josephson junction, an overlap of two metals separated by an insulator that enables quantum tunneling and the creation of qubits.
Fatemi emphasized the sensitivity of device performance to this step, stating, “The performance of the devices in our lab is very sensitive to that step now.” Historically, this was not necessarily obvious, but our devices are at a level of performance that we’re able to see big differences based on subtle changes that we make to the formation of the Josephson junction. This heightened sensitivity underscores the importance of precise control over the deposition process and the impact of even minor adjustments to material properties.
The team’s advancements position Cornell as a leader in superconducting quantum information device development. “We’re right at the world-leading edge,” Fatemi said. “This is a big step forward not only for our group but also Cornell’s efforts in superconducting quantum information devices.” The combination of a lower deposition temperature, improved film conductivity, and enhanced qubit quality represents a leap toward realizing practical, scalable quantum computers.
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, Ph
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