QCBRIEF
Cornell's Fatemi group shows that swapping argon for krypton during tantalum deposition lets high quality superconducting qubits form at 200°C, well within the heat ceiling of standard chip fabs, with coherence matching higher temperature processes.
A Cornell team has shown that swapping argon for krypton during tantalum deposition lets high-quality superconducting qubits be made at 200°C, inside the thermal budget of standard commercial chip fabs. The work, led by Assistant Professor Valla Fatemi, appears in Nature Materials.
Superconducting qubits, the basic units of a quantum computer, need a high-conductivity form of tantalum called α-phase, which traditionally required heating silicon substrates above 400°C during deposition. That heat is incompatible with the back-end-of-line (BEOL) wiring stage of standard chipmaking, where temperatures must stay low to avoid damaging underlying CMOS control circuits.
Krypton ions are heavier than argon, so during magnetron sputtering they transfer more momentum to the tantalum atoms as they land. That extra momentum lets the film crystallize into the body-centered cubic α-phase even at 200°C, the Cornell news release explains. The lower temperature also eliminates the tantalum-silicon intermixing layer that previously degraded qubit coherence.
Transmon qubits built with 20-micrometer capacitor gaps from the krypton-sputtered films reached internal quality factors up to 16.9 million, the paper reports, comparable to qubits made at much higher temperatures. The arXiv preprint supplies the full fabrication detail. The process fits the BEOL thermal ceiling on standard silicon lines; it does not put a quantum computer on store shelves.