TOF-SIMS Analysis of Decoherence Sources in Nb Superconducting Resonators

Abstract

Superconducting qubits have emerged as a potentially foundational platform technology for addressing complex computational problems deemed intractable with classical computing. Despite recent advances enabling multiqubit designs that exhibit coherence lifetimes on the order of hundreds of $\mu$s, material quality and interfacial structures continue to curb device performance. When niobium is deployed as the superconducting material, two-level system defects in the thin film and adjacent dielectric regions introduce stochastic noise and dissipate electromagnetic energy at the cryogenic operating temperatures. In this study, we utilize time-of-flight secondary ion mass spectrometry (TOF-SIMS) to understand the role specific fabrication procedures play in introducing such dissipation mechanisms in these complex systems. We interrogated Nb thin films and transmon qubit structures fabricated by Rigetti Computing and at the National Institute of Standards and Technology through slight variations in the processing and vacuum conditions. We find that when Nb film is sputtered onto the Si substrate, oxide and silicide regions are generated at various interfaces. We also observe that impurity species such as niobium hydrides and carbides are incorporated within the niobium layer during the subsequent lithographic patterning steps. The formation of these resistive compounds likely impact the superconducting properties of the Nb thin film. Additionally, we observe the presence of halogen species distributed throughout the patterned thin films. We conclude by hypothesizing the source of such impurities in these structures in an effort to intelligently fabricate superconducting qubits and extend coherence times moving forward.

7 pages, 4 figures

References in corpus (6)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Decoherence benchmarking of superconducting qubits
• Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
• Proximity breakdown of hydrides in superconducting niobium cavities
• Discovery of Nb hydride precipitates in superconducting qubits
• Characterization of the Chemical and Electrical Properties of Defects at the Niobium-Silicon Interface

Cited by in corpus (9)

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• Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits
• Modelling dielectric loss in superconducting resonators: Evidence for interacting atomic two-level systems at the Nb/oxide interface
• Characterization of process-related interfacial dielectric loss in aluminum-on-silicon by resonator microwave measurements, materials analysis, and imaging
• Characterization of Nb films for superconducting qubits using phase boundary measurements
• Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits
• Low-loss Nb on Si superconducting resonators from a dual-use spintronics deposition chamber and with acid-free post-processing
• Fabrication effects on Niobium oxidation and surface contamination in Niobium-metal bilayers using X-ray photoelectron spectroscopy