High-RRR thin-films of NB produced using energetic condensation from a coaxial, rotating vacuum ARC plasma (CEDTM)

Valderrama, E.; James, C.; Krishnan, M.; Zhao, Xin; Phillips, L.; Reece, Charles; Seo, Kang Deuk

doi:10.1063/1.4707012

Cited by 8 publications

(6 citation statements)

References 15 publications

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“…Figure 8(b) clearly shows that the NbH − intensity in Nb thin film varied by four orders from 10 4 counts on surface to zero counts near the Nb-Si interface. A similar hydrogen profile of Nb deposited on wafers has been observed earlier [58].…”

Section: Hydrogen In Nbsupporting

confidence: 82%

Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

Bose

Joshi

2015

Supercond. Sci. Technol.

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The performance of Superconducting radio frequency cavities (SRF) is strongly influenced by various impurities within the penetration depth (~50nm) of Nb, which in turn depends on the applied surface treatments. The effect of these surface treatments on the impurities of Nb has been explored using various surface analytical treatments.But, the results are still inadequate in many aspects and the effect of sequential SRF treatments on the impurity distribution has not been explored. The present study analyses various impurities within the penetration depth of Nb samples, treated by SRF cavity processing techniques like colloidal silica polishing (simulating centrifugal barrel polishing), buffer chemical polishing (BCP), high pressure rinsing (HPR) and degassing under high vacuum (HV) condition at 600°C for 10hrs. Static, dynamic and slow sputtering modes of Time of flight secondary ion mass spectrometry (TOFSIMS) technique was employed to study the effect of the above treatments on interstitial impurities, hydrocarbons, oxides, acidic residuals, reaction products and metallic contaminations. The study confirms that the impurity distribution in Nb is not only sensitive to the surface treatment, but also to their sequence. Varying the treatment sequence prior to HV degassing treatments affected the final impurity levels in HV degassed bulk Nb samples. BCP treated samples, exhibited minimum hydrocarbon and metallic contamination but, led to extensive contamination of the oxide layer with residuals and reaction products of acids used in BCP solution. HPR treatment, on the other hand was effective in reducing the acidic impurities on the top surface. The study also establishes the application of TOFSIMS technique to analyze and evolve SRF treatments.

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Section: Hydrogen In Nbsupporting

confidence: 82%

Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

Bose

Joshi

2015

Supercond. Sci. Technol.

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“…RRR has long been used as a gauge of the quality of Nb films for the construction of superconducting radiofrequency cavities 51,52 , capturing the impact of impurities, defects and other factors such as grain boundaries on the bulk resistivity. The impact of bulk resistivity and other, surface or intergranular oxide-specific mechanisms such as TLS, on microwave loss is determined by the field penetration into the film and can be described by an effective surface resistance [14].…”

Section: Discussionmentioning

confidence: 99%

Microscopic relaxation channels in materials for superconducting qubits

et al. 2021

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Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we combine measurements of transmon qubit relaxation times (T1) with spectroscopy and microscopy of the polycrystalline niobium films used in qubit fabrication. By comparing films deposited using three different techniques, we reveal correlations between T1 and intrinsic film properties such as grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Qubit and resonator measurements show signatures of two-level system defects, which we propose to be hosted in the grain boundaries and surface oxides. We also show that the residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.

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“…We observe correlations between T 1 , RRR, grain size, and suboxide concentration near the surface, as shown by the data in Table I. RRR has long been used as a gauge of the quality of superconducting Nb films for the construction of superconducting radio-frequency (RF) cavities [42,43]. Further, seminal studies of RF cavities with Nb walls have shown that residual surface resistance limits the cavity quality factor at low temperatures [44][45][46][47][48].…”

Section: Discussionmentioning

confidence: 60%

Microscopic Relaxation Channels in Materials for Superconducting Qubits

Premkumar¹,

Hwang²,

Jaeck³

et al. 2020

Preprint

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Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we perform measurements of transmon qubit relaxation times T1 in parallel with spectroscopy and microscopy of the thin polycrystalline niobium films used in qubit fabrication. By comparing results for films deposited using three techniques, we reveal correlations between T1 and grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Physical mechanisms connect these microscopic properties to residual surface resistance and T1 through losses arising from the grain boundaries and from defects in the suboxides. Further, experiments show that the residual resistance ratio can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.

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High-RRR thin-films of NB produced using energetic condensation from a coaxial, rotating vacuum ARC plasma (CEDTM)

Cited by 8 publications

References 15 publications

Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

Microscopic relaxation channels in materials for superconducting qubits

Microscopic Relaxation Channels in Materials for Superconducting Qubits

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