Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Torres‐Castanedo, Carlos G.; Goronzy, Dominic P.; Pham, Thang; McFadden, Anthony; Materise, Nicholas; Masih Das, Paul; Cheng, Matthew; Lebedev, Dmitry; Ribet, Stephanie M.; Walker, Mitchell J.; Garcia‐Wetten, David A.; Kopas, Cameron J.; Marshall, Jayss; Lachman, Ella; Zhelev, Nikolay; Sauls, James A.; Mutus, Joshua Y.; McRae, Corey Rae H.; Dravid, Vinayak P.; Bedzyk, Michael J.; Hersam, Mark C.

doi:10.1002/adfm.202401365

Cited by 4 publications

(1 citation statement)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Regarding H – counts, we observe a clear increase in the signal close to the oxide and metal interface for both samples. As previously reported, , this may arise due to the infiltration of hydrogen atoms into the niobium metal before the formation of the surface oxide or during nanofabrication processes such as wet etching. Interestingly, the H – counts are found to be an order of magnitude higher in the uncapped film compared with that in the Ta-capped film.…”

Section: Resultsmentioning

confidence: 72%

Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits

Oh,

Zaman,

Murthy

et al. 2024

ACS Nano

Self Cite

View full text Add to dashboard Cite

Improving the qubit's lifetime (T 1 ) is crucial for fault-tolerant quantum computing. Recent advancements have shown that replacing niobium (Nb) with tantalum (Ta) as the base metal significantly increases T 1 , likely due to a less lossy native surface oxide. However, understanding the formation mechanism and nature of both surface oxides is still limited. Using aberration-corrected transmission electron microscopy and electron energy loss spectroscopy, we found that Ta surface oxide has fewer suboxides than Nb oxide. We observed an abrupt oxidation state transition from Ta 2 O 5 to Ta, as opposed to the gradual shift from Nb 2 O 5 , NbO 2 , and NbO to Nb, consistent with thermodynamic modeling. Additionally, amorphous Ta 2 O 5 exhibits a closer-to-crystalline bonding nature than Nb 2 O 5 , potentially hindering H atomic diffusion toward the oxide/metal interface. Finally, we propose a loss mechanism arising from the transition between two states within the distorted octahedron in an amorphous structure, potentially causing two-level system loss. Our findings offer a deeper understanding of the differences between native amorphous Ta and Nb oxides, providing valuable insights for advancing superconducting qubits through surface oxide engineering.

show abstract

Section: Resultsmentioning

confidence: 72%

Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits

Oh,

Zaman,

Murthy

et al. 2024

ACS Nano

Self Cite

View full text Add to dashboard Cite

show abstract

Enhanced superconducting qubit performance through ammonium fluoride etch

Kopas,

Goronzy,

Pham

et al. 2024

Mater. Quantum. Technol.

View full text Add to dashboard Cite

The performance of superconducting qubits is often limited by dissipation and two-level systems (TLS) losses. The dominant sources of these losses are believed to originate from amorphous materials and defects at interfaces and surfaces, likely as a result of fabrication processes or ambient exposure. Here, we explore a novel wet chemical surface treatment at the Josephson junction-substrate and the substrate-air interfaces by replacing a buffered oxide etch (BOE) cleaning process with one that uses hydrofluoric acid followed by aqueous ammonium fluoride. We show that the ammonium fluoride etch process results in a statistically significant improvement in median T1 by ~22% (p=0.002), and a reduction in the number of strongly-coupled TLS in the tunable frequency range. Microwave resonator measurements on samples treated with the ammonium fluoride etch after niobium deposition and etching also show ~33% lower TLS-induced loss tangent compared to the BOE treated samples. As the chemical treatment primarily modifies the Josephson junction-substrate interface and substrate-air interface, we perform targeted chemical and structural characterizations to examine materials differences at these interfaces and identify multiple microscopic changes that could contribute to decreased TLS.

show abstract

Fabrication-related impurity study of thin superconducting Al films using x-ray absorption spectroscopy

Bhandari,

Stevenson,

Barrentine

et al. 2024

Journal of Vacuum Science &Amp; Technology A

View full text Add to dashboard Cite

Superconducting aluminum thin films are integral to many astrophysics detector applications. Using x-ray absorption spectroscopy (XAS), we have studied the residues and adsorbates created during various standard lithography and etch steps, which are commonly used to pattern thin aluminum films into device structures. We have observed the formation of aluminum oxide as α-Al2O3 and aluminum fluoride as β-AlF3. We have observed correlations between these XAS signatures and the Al film’s microwave loss due to two-level systems. This study, which guides the way for future device optimization, further explores the chemical impact of different process steps, including standard silicon substrate wafer cleaning processes, sulfur-hexa-fluoride plasma etching, passivation with a fluorocarbon, and exposure to photoresist adhesion promoters during the lithography process with the help of control samples.

show abstract

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Cited by 4 publications

References 38 publications

Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits

Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits

Enhanced superconducting qubit performance through ammonium fluoride etch

Fabrication-related impurity study of thin superconducting Al films using x-ray absorption spectroscopy

Contact Info

Product

Resources

About