Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1706.06424 · Applied Physics Letters

An argon ion beam milling process for native AlOx layers enabling coherent superconducting contacts

Lukas Grünhaupt, Uwe von Lüpke, Daria Gusenkova, Sebastian T. Skacel, Nataliya Maleeva, Steffen Schlör, Alexander Bilmes, Hannes Rotzinger, Alexey Vladimirovich Ustinov, Martin Weides, Ioan M. Pop

Published Aug 14, 2017• 27 citations
arXivHTMLPDF

Abstract

We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits. From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50 mΩ μm2 at a frequency of 4.5 GHz. Resonators for which only 6% of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic fields, showed quality factors above 106 in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing.

DOI
10.1063/1.4990491

Related papers

Argon-Milling-Induced Decoherence Mechanisms in Superconducting Quantum Circuits

Jacques Van Damme, Ts. Ivanov, Paola Favia +12 more

The fabrication of superconducting circuits requires multiple deposition, etching, and cleaning steps, each possibly introducing material property changes and microscopic defects. In this work, we specifically investigate the process of argon milling, a potentially coherence-limiting step, using niobium and aluminum superconducting resonators as a proxy for the surface-limited behavior of qubits. We find that niobium microwave resonators exhibit an order of magnitude decrease in quality factors after surface argon milling, while aluminum resonators are resilient to the same process. Extensive analysis of the niobium surface shows no change in the suboxide composition due to argon milling, while two-tone spectroscopy measurements reveal an increase in two-level system electrical dipole moments, indicating a structurally altered niobium oxide. However, a short dry etch can fully recover the argon-milling-induced losses on niobium, offering a potential route towards state-of-the-art overlap Josephson junction qubits with niobium circuitry.

arXiv:2302.03518•Physical Review Applied•Jul 17, 2023•14 citations

Native-oxide-passivated trilayer junctions for superconducting qubits

Pankaj Sethi, Om Prakash, Jukka-Pekka Kaikkonen +15 more

Superconducting qubits in today's quantum processing units are typically fabricated with angle-evaporated aluminum--aluminum-oxide--aluminum Josephson junctions. However, there is an urgent need to overcome the limited reproducibility of this approach when scaling up the number of qubits and junctions. Fabrication methods based on subtractive patterning of superconductor--insulator--superconductor trilayers, used for more classical large-scale Josephson junction circuits, could provide the solution but they in turn often suffer from lossy dielectrics incompatible with high qubit coherence. In this work, we utilize native aluminum oxide as a sidewall passivation layer for junctions based on aluminum--aluminum-oxide--niobium trilayers, and use such junctions in qubits. We design the fabrication process such that the few-nanometer-thin native oxide is not exposed to oxide removal steps that could increase its defect density or hinder its ability to prevent shorting between the leads of the junction. With these junctions, we design and fabricate transmon-like qubits and measure time-averaged coherence times up to 30 $μ$s at a qubit frequency of 5 GHz, corresponding to a qubit quality factor of one million. Our process uses subtractive patterning and optical lithography on wafer scale, enabling high throughput in patterning. This approach provides a scalable path toward fabrication of superconducting qubits on industry-standard platforms.

arXiv:2504.03481•Physical Review Applied•Nov 26, 2025•2 citations

Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques

Simon Lang, Alexandra Schewski, I. Eisele +2 more

This work focuses on the manufacturing of Al/AlOx/Al Josephson junctions (JJs), which are essential components of many quantum circuits. Two processes were studied to understand the oxidation of the aluminum surface. Static oxidation was performed by removing native AlOx in a cluster system with Ar-ion beam milling and controlling the final tunneling oxide by applying a specific O2 pressure in the chamber. Controlled plasma oxidation was performed by removing native AlOx with a H2 plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm and their electrical properties were analyzed on wafer level, providing insight into the structure and composition of the aluminum oxides and their applicability for Qubits. This work is crucial for reliable industrial manufacturing on full-scale 200 mm wafers with a very high uniformity level.

ECS Transactions•May 19, 2023•4 citations

Shadow-Masked Angled Ion Milling for Junction Integration in Silicon-based Tantalum Superconducting Qubits

Yi Zhao, Wei Xin, Zhenchuan Zhang +6 more

Abstract Surface dielectric loss remains a primary bottleneck limiting the energy relaxation time ( T 1 ) of super-conducting qubits. In particular, the amorphization damage introduced by in-situ argon ion milling on silicon (Si) substrates during junction fabrication constitutes a critical local loss channel. Addressing the vulnerability of the junction substrate in the conventional Manhattan process, we propose a bandage-free, shadow-masked angled ion milling technique that is fully compatible with existing mask layouts to enhance the coherence of Ta-on-Si transmons. This process leverages the geometric masking effect of a high-aspect-ratio bilayer resist, combined with a 45° azimuthal ion beam alignment, to isolate the sensitive cross-junction region from direct ion bombardment while ensuring reliable superconducting interconnections under gentle milling conditions. Cryogenic characterization across three independent cooldowns demonstrates that the 45° angled milling effectively enhances qubit performance, with the sample-average T 1 improving from 67.4 μs in the standard 0° process to 98.7 μs, and the average quality factor ( Q ) increasing from 2.0×10 6 to 2.5 × 10 6 . This work offers a practical nanofabrication strategy to suppress junction-region processing loss, providing a viable pathway for high-coherence silicon-based quantum processors.

Chinese Physics B•Sep 15, 2026•0 citations

Postfabrication resistance trimming of a superconducting tunnel junction using a focused ion beam

Z. H. Barber, Mark G. Blamire, Nick Dawes

A high current density NbN/MgO/Nb superconducting tunnel junction has been modified using a focused ion beam to trim the junction area following fabrication and measurement. After milling, the exposed edge of the junction was cleaned of resputtered material using a low current ion beam combined with gas assisted etching. Some remaining shorts across the barrier were then removed by anodization. The modified junction showed a resistance increase correlating exactly with the decrease in area and very little change in quality. This technique may be used on fully fabricated circuits to trim accurately the resistance of selected junctions in order to overcome variations in barrier conductance and junction area.

Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena•Mar 1, 1995•2 citations

Towards Fabrication of Sub-Micrometer Cross-Type Aluminum Josephson Junctions

Stephan Mechold, Katja Peiselt, Matthias Schmelz +5 more

The performance of superconducting electronic devices such as superconducting quantum bits (qubits) and superconducting quantum interference devices (SQUIDs) strongly relies on high-quality Josephson junctions (JJ) and their integration into surrounding circuit elements. Therefore, a corresponding fabrication technology should allow for the fabrication of all required elements including the JJs, inductances, capacitances and waveguides. For a long time, shadow evaporation technique was the state of the art for the implementation of sub-μ m sized JJs based on aluminum for qubits of high coherence times. Although, the use of a single lithographic step represents a major advantage of this technique. However, shadowing effects limit sample size, device complexity, and thus scalability of the circuitry. To overcome these limitations and to meet the demands of next generation scalable quantum circuits, in this work we introduce our cross -type JJ aluminum technology, where JJs are defined by the overlap of two narrow perpendicular stripes. We discuss the technological challenges, with a focus on our newly developed dry etching process for patterning of the aluminum thin film. Compared to a lift-off based process, this advanced wafer-scale fabrication technology offers a high integration density and the required design flexibility. We will present first results on cross -type aluminum JJs.

IEEE Transactions on Applied Superconductivity•Dec 18, 2023•2 citations
We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits. From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50 mΩ μm2 at a frequency of 4.5 GHz. Resonators for which only 6% of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic fields, showed quality factors above 106 in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing.
The fabrication of superconducting circuits requires multiple deposition, etching, and cleaning steps, each possibly introducing material property changes and microscopic defects. In this work, we specifically investigate the process of argon milling, a potentially coherence-limiting step, using niobium and aluminum superconducting resonators as a proxy for the surface-limited behavior of qubits. We find that niobium microwave resonators exhibit an order of magnitude decrease in quality factors after surface argon milling, while aluminum resonators are resilient to the same process. Extensive analysis of the niobium surface shows no change in the suboxide composition due to argon milling, while two-tone spectroscopy measurements reveal an increase in two-level system electrical dipole moments, indicating a structurally altered niobium oxide. However, a short dry etch can fully recover the argon-milling-induced losses on niobium, offering a potential route towards state-of-the-art overlap Josephson junction qubits with niobium circuitry.
Superconducting qubits in today's quantum processing units are typically fabricated with angle-evaporated aluminum--aluminum-oxide--aluminum Josephson junctions. However, there is an urgent need to overcome the limited reproducibility of this approach when scaling up the number of qubits and junctions. Fabrication methods based on subtractive patterning of superconductor--insulator--superconductor trilayers, used for more classical large-scale Josephson junction circuits, could provide the solution but they in turn often suffer from lossy dielectrics incompatible with high qubit coherence. In this work, we utilize native aluminum oxide as a sidewall passivation layer for junctions based on aluminum--aluminum-oxide--niobium trilayers, and use such junctions in qubits. We design the fabrication process such that the few-nanometer-thin native oxide is not exposed to oxide removal steps that could increase its defect density or hinder its ability to prevent shorting between the leads of the junction. With these junctions, we design and fabricate transmon-like qubits and measure time-averaged coherence times up to 30 μμμs at a qubit frequency of 5 GHz, corresponding to a qubit quality factor of one million. Our process uses subtractive patterning and optical lithography on wafer scale, enabling high throughput in patterning. This approach provides a scalable path toward fabrication of superconducting qubits on industry-standard platforms.
This work focuses on the manufacturing of Al/AlOx/Al Josephson junctions (JJs), which are essential components of many quantum circuits. Two processes were studied to understand the oxidation of the aluminum surface. Static oxidation was performed by removing native AlOx in a cluster system with Ar-ion beam milling and controlling the final tunneling oxide by applying a specific O2 pressure in the chamber. Controlled plasma oxidation was performed by removing native AlOx with a H2 plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm and their electrical properties were analyzed on wafer level, providing insight into the structure and composition of the aluminum oxides and their applicability for Qubits. This work is crucial for reliable industrial manufacturing on full-scale 200 mm wafers with a very high uniformity level.
Abstract Surface dielectric loss remains a primary bottleneck limiting the energy relaxation time ( T 1 ) of super-conducting qubits. In particular, the amorphization damage introduced by in-situ argon ion milling on silicon (Si) substrates during junction fabrication constitutes a critical local loss channel. Addressing the vulnerability of the junction substrate in the conventional Manhattan process, we propose a bandage-free, shadow-masked angled ion milling technique that is fully compatible with existing mask layouts to enhance the coherence of Ta-on-Si transmons. This process leverages the geometric masking effect of a high-aspect-ratio bilayer resist, combined with a 45° azimuthal ion beam alignment, to isolate the sensitive cross-junction region from direct ion bombardment while ensuring reliable superconducting interconnections under gentle milling conditions. Cryogenic characterization across three independent cooldowns demonstrates that the 45° angled milling effectively enhances qubit performance, with the sample-average T 1 improving from 67.4 μs in the standard 0° process to 98.7 μs, and the average quality factor ( Q ) increasing from 2.0×10 6 to 2.5 × 10 6 . This work offers a practical nanofabrication strategy to suppress junction-region processing loss, providing a viable pathway for high-coherence silicon-based quantum processors.
A high current density NbN/MgO/Nb superconducting tunnel junction has been modified using a focused ion beam to trim the junction area following fabrication and measurement. After milling, the exposed edge of the junction was cleaned of resputtered material using a low current ion beam combined with gas assisted etching. Some remaining shorts across the barrier were then removed by anodization. The modified junction showed a resistance increase correlating exactly with the decrease in area and very little change in quality. This technique may be used on fully fabricated circuits to trim accurately the resistance of selected junctions in order to overcome variations in barrier conductance and junction area.
The performance of superconducting electronic devices such as superconducting quantum bits (qubits) and superconducting quantum interference devices (SQUIDs) strongly relies on high-quality Josephson junctions (JJ) and their integration into surrounding circuit elements. Therefore, a corresponding fabrication technology should allow for the fabrication of all required elements including the JJs, inductances, capacitances and waveguides. For a long time, shadow evaporation technique was the state of the art for the implementation of sub-μ m sized JJs based on aluminum for qubits of high coherence times. Although, the use of a single lithographic step represents a major advantage of this technique. However, shadowing effects limit sample size, device complexity, and thus scalability of the circuitry. To overcome these limitations and to meet the demands of next generation scalable quantum circuits, in this work we introduce our cross -type JJ aluminum technology, where JJs are defined by the overlap of two narrow perpendicular stripes. We discuss the technological challenges, with a focus on our newly developed dry etching process for patterning of the aluminum thin film. Compared to a lift-off based process, this advanced wafer-scale fabrication technology offers a high integration density and the required design flexibility. We will present first results on cross -type aluminum JJs.