Kavli Affiliate: Oskar Painter
| First 5 Authors: Guillaume Marcaud, David Perello, Cliff Chen, Esha Umbarkar, Conan Weiland
| Summary:
The use of $alpha$-tantalum in superconducting circuits has enabled a
considerable improvement of the coherence time of transmon qubits. The standard
approach to grow $alpha$-tantalum thin films on silicon involves heating the
substrate, which takes several hours per deposition and prevents the
integration of this material with wafers containing temperature-sensitive
components. We report a detailed experimental study of an alternative growth
method of $alpha$-tantalum on silicon, which is achieved at room temperature
through the use of a niobium seed layer. Despite a substantially higher density
of oxygen-rich grain boundaries in the films sputtered at room temperature,
resonators made from these films are found to have state-of-the-art quality
factors, comparable to resonators fabricated from tantalum grown at high
temperature. This finding challenges previous assumptions about correlations
between material properties and microwave loss of superconducting thin films,
and opens a new avenue for the integration of tantalum into fabrication flows
with limited thermal budget.
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