Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits
By J. Kreikebaum, Kevin P. O'Brien, A. Morvan, Irfan Siddiqi. Superconductors Science and Technology, 2019
141 citations recorded by the source corpus.
Quantum bits, or qubits, are an example of coherent circuits envisioned for next-generation computers and detectors. A robust superconducting qubit with a coherent lifetime of O(100 µs) is the transmon: a Josephson junction functioning as a non-linear inductor shunted with a capacitor to form an anharmonic oscillator. In a complex device with many such transmons, precise control over each qubit frequency is often required, and thus variations of the junction area and tunnel barrier thickness must be sufficiently minimized to achieve optimal performance while avoiding spectral overlap between neighboring circuits. Simply transplanting our recipe optimized for single, stand-alone devices to wafer-scale (producing 64, 1x1 cm dies from a 150 mm wafer) initially resulted in global drifts in room-temperature tunneling resistance of ± 30%. Inferring a critical current Ic variation from this resistance distribution, we present an optimized process developed from a systematic 38 wafer study that results in < 3.5% relative standard deviation (RSD) in critical current ( ≡σIc/Ic) for 3000 Josephson junctions (both single-junctions and asymmetric SQUIDs) across an area of 49 cm2. Looking within a 1x1 cm moving window across the substrate gives an estimate of the variation characteristic of a given qubit chip. Our best process, utilizing ultrasonically assisted development, uniform ashing, and dynamic oxidation has shown σIc/Ic = 1.8% within 1x1 cm, on average, with a few 1x1 cm areas having σIc/Ic < 1.0% (equivalent to σf/f < 0.5%). Such stability would drastically improve the yield of multi-junction chips with strict critical current requirements.
Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics
View Paper: https://www.semanticscholar.org/paper/7912dd4f59a1771dc00607d26053ba03f96078e4
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Citations in the corpus
- The future of quantum computing with superconducting qubits (2022, methodology): “We can take advantage of these statistical correlations wherever they exist for rapid progress in parts of our process 112 or in post-process tuning 113 .”
- Materials challenges and opportunities for quantum computing hardware (2021, background): “Traditional approaches include building probe stations for higher-throughputmeasurements (121, 122, 347) and cluster tools with in situ processing (297, 298, 300, 302).”