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Nanofabrication of Superconducting Circuits

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A special issue of Electronics (ISSN 2079-9292). This special issue belongs to the section "Microelectronics".

Deadline for manuscript submissions: closed (31 March 2023) | Viewed by 10551

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Prof. Dr. Michael I. Faley

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Guest Editor

Forschungszentrum Jülich, Jülich, Germany
Interests: nanofabrication of superconducting circuits; oxide heterostructures; novel Josephson junctions; superconducting quantum interferometers (SQUIDs)
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Dear Colleagues,

Superconducting circuits exhibit unique characteristics that are not attainable by conventional semiconductor electronics: quantum limited low noise detection and amplification, dispersion- and losses-free interconnections, as well as the energy efficient ultra-high frequency operation of analog and digital circuits, and the realization of a scalable quantum computer. The miniaturization of superconducting circuits follows the trend towards the miniaturization of semiconductor electronics, but with significant delay and a specificity related to the spatial variations in the macroscopic wave function of phase-correlated Cooper pairs in superconductors. In contrast to semiconductors and normal metals, for example, a nanometer-sized constriction transforms superconductors into a Josephson junction, which serves as an active component of superconductor electronics. Today's superconducting components must be manufactured on scales comparable to, or even smaller than, the superconducting coherence length and London penetration depth, which creates difficulties in the manufacturing, operation, and theoretical interpretation of the properties of the devices.

The need to develop specific methods for nanofabrication, to minimize or exploit the kinetic inductance of ultra-thin superconducting structures, and the need to squeeze a quantum of magnetic flux into nanoscale superconducting cells with Josephson junctions are some of the main obstacles to the miniaturization of superconducting circuits. They should be addressed in a comprehensive manner for specific applications.

The most popular superconducting materials that are used in superconducting electronics are Nb, Al, NbN, NbTiN, TiN, MoRe and YBa₂Cu₃O_7-x. Electron beam lithography, direct writing by laser, focused ion beam milling, and self-aligned nanofabrication are the most frequently used methods for the creation of nanoscale superconducting devices. Superconducting bolometers, single photon detectors, SIS detectors, Josephson junctions, SQUIDs, RSFQ circuits, qubits and their readouts are just some of the established applications of the superconducting circuits that require fabrication with nanometer resolutions.

The objective of this Special Issue is to present studies in the field of nanoscale superconducting devices, with emphasis on their nanofabrication, testing and theoretical modelling. Therefore, researchers are invited to submit their manuscripts to this Special Issue and contribute their theoretical models, technology development, reviews, and studies.

Prof. Dr. Michael I. Faley
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Electronics is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

nanostructuring
Josephson junctions
SQUIDs
superconducting single photon detectors
SIS detectors, superconducting bolometers
qubits

Related Special Issue

Nanofabrication of Superconducting Circuits, 2nd Edition in Electronics

Published Papers (6 papers)

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Research

11 pages, 454 KiB

Open AccessArticle

Designing Large Two-Dimensional Arrays of Josephson Junctions for RF Magnetic Field Detection

by Denis Gérard Crété, Sarah Menouni, Juan Trastoy, Salvatore Mesoraca, Julien Kermorvant, Yves Lemaître, Bruno Marcilhac and Christian Ulysse

Electronics 2023, 12(15), 3239; https://doi.org/10.3390/electronics12153239 - 26 Jul 2023

Cited by 1 | Viewed by 872

Abstract

This paper discusses improved design of two-dimensional (2D) arrays, potentially pushing the present state of the art of the high-Tc (and low-Tc) magnetic field detectors to a larger scale, i.e., higher sensitivity. We propose a two-plate geometry for parallel (and two-dimensional) arrays of Josephson junctions (JJs) for application in magnetic field detection. The arrays can be realized either by integration in the same substrate with a multilayer technology or on two different substrates. In the latter case, the substrates can be assembled in a flip-chip or piggyback configuration. A suggestion would be to divide a 2D array in two (equal) parts and to distribute each part on a different layer, one above the other. We model the current distribution in arrays connected in series so that the bias current flowing through the device flows in opposite direction in the layers. We demonstrate that this geometry greatly improves the uniformity of the bias current distribution across the width of the array, thereby restoring the critical current and, in principle, improving the Josephson array response. From the model, we conclude that the alignment of the arrays is not critical and that the realization of the devices requires only conventional techniques. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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14 pages, 10031 KiB

Open AccessFeature PaperArticle

TiN-NbN-TiN and Permalloy Nanostructures for Applications in Transmission Electron Microscopy

by Michael I. Faley, Joshua Williams, Penghan Lu and Rafal E. Dunin-Borkowski

Electronics 2023, 12(9), 2144; https://doi.org/10.3390/electronics12092144 - 8 May 2023

Cited by 1 | Viewed by 1563

Abstract

We fabricated superconducting and ferromagnetic nanostructures, which are intended for applications in transmission electron microscopy (TEM), in a commercial sample holder that can be cooled using liquid helium. Nanoscale superconducting quantum-interference devices (nanoSQUIDs) with sub-100 nm nanobridge Josephson junctions (nJJs) were prepared at a distance of ~300 nm from the edges of a 2 mm × 2 mm × 0.05 mm substrate. Thin-film TiN-NbN-TiN heterostructures were used to optimize the superconducting parameters and enhance the oxidation and corrosion resistance of nJJs and nanoSQUIDs. Non-hysteretic I(V) characteristics of nJJs, as well as peak-to-peak quantum oscillations in the V(B) characteristics of the nanoSQUIDs with an amplitude of up to ~20 µV, were obtained at a temperature ~5 K, which is suitable for operation in TEM. Electron-beam lithography, high-selectivity reactive ion etching with pure SF₆ gas, and a naturally created undercut in the Si substrate were used to prepare nanoSQUIDs on a SiN membrane within ~500 nm from the edge of the substrate. Permalloy nanodots with diameters down to ~100 nm were prepared on SiN membranes using three nanofabrication methods. High-resolution TEM revealed that permalloy films on a SiN buffer have a polycrystalline structure with an average grain dimension of approximately 5 nm and a lattice constant of ~0.36 nm. The M(H) dependences of the permalloy films were measured and revealed coercive fields of 2 and 10 G at 300 and 5 K, respectively. These technologies are promising for the fabrication of superconducting electronics based on nJJs and ferromagnetic nanostructures for operation in TEM. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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16 pages, 8476 KiB

Open AccessArticle

Phase Diffusion in Low-E_J Josephson Junctions at Milli-Kelvin Temperatures

by Wen-Sen Lu, Konstantin Kalashnikov, Plamen Kamenov, Thomas J. DiNapoli and Michael E. Gershenson

Electronics 2023, 12(2), 416; https://doi.org/10.3390/electronics12020416 - 13 Jan 2023

Cited by 3 | Viewed by 1410

Abstract

Josephson junctions (JJs) with Josephson energy

E_{J} ≲ 1

K are widely employed as non-linear elements in superconducting circuits for quantum computing operating at milli-Kelvin temperatures. In the qubits with small charging energy

E_{C}

( [...] Read more.

Josephson junctions (JJs) with Josephson energy

E_{J} ≲ 1

K are widely employed as non-linear elements in superconducting circuits for quantum computing operating at milli-Kelvin temperatures. In the qubits with small charging energy

E_{C}

(

E_{J} / E_{C} ≫ 1

), such as the transmon, the incoherent phase slips (IPS) might become the dominant source of dissipation with decreasing

E_{J}

. In this work, a systematic study of the IPS in low-

E_{J}

JJs at milli-Kelvin temperatures is reported. Strong suppression of the critical (switching) current and a very rapid growth of the zero-bias resistance due to the IPS are observed with decreasing

E_{J}

below 1 K. With further improvement of coherence of superconducting qubits, the observed IPS-induced dissipation might limit the performance of qubits based on low-

E_{J}

junctions. These results point the way to future improvements of such qubits. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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12 pages, 4447 KiB

Open AccessArticle

A Self-Flux-Biased NanoSQUID with Four NbN-TiN-NbN Nanobridge Josephson Junctions

by M. I. Faley and R. E. Dunin-Borkowski

Electronics 2022, 11(11), 1704; https://doi.org/10.3390/electronics11111704 - 27 May 2022

Cited by 3 | Viewed by 1687

Abstract

We report the development of a planar 4-Josephson-junction nanoscale superconducting quantum interference device (nanoSQUID) that is self-biased for optimal sensitivity without the application of a magnetic flux of Φ₀/4. The nanoSQUID contains novel NbN-TiN-NbN nanobridge Josephson junctions (nJJs) with NbN current leads and electrodes of the nanoSQUID body connected by TiN nanobridges. The optimal superconducting transition temperature of ~4.8 K, superconducting coherence length of ~100 nm, and corrosion resistance of the TiN films ensure the hysteresis-free, reproducible, and long-term stability of nJJ and nanoSQUID operation at 4.2 K, while the corrosion-resistant NbN has a relatively high superconducting transition temperature of ~15 K and a correspondingly large energy gap. FIB patterning of the TiN films and nanoscale sculpturing of the tip area of the nanoSQUID’s cantilevers are performed using amorphous Al films as sacrificial layers due to their high chemical reactivity to alkalis. A cantilever is realized with a distance between the nanoSQUID and the substrate corner of ~300 nm. The nJJs and nanoSQUID are characterized using Quantum Design measurement systems at 4.2 K. The technology is expected to be of interest for the fabrication of durable nanoSQUID sensors for low temperature magnetic microscopy, as well as for the realization of more complex circuits for superconducting nanobridge electronics. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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11 pages, 5969 KiB

Open AccessArticle

Fabrication of Superconducting Nb–AlN–NbN Tunnel Junctions Using Electron-Beam Lithography

by Mikhail Yu. Fominsky, Lyudmila V. Filippenko, Artem M. Chekushkin, Pavel N. Dmitriev and Valery P. Koshelets

Electronics 2021, 10(23), 2944; https://doi.org/10.3390/electronics10232944 - 26 Nov 2021

Cited by 9 | Viewed by 1940

Abstract

Mixers based on superconductor–insulator–superconductor (SIS) tunnel junctions are the best input devices at frequencies from 0.1 to 1.2 THz. This is explained by both the extremely high nonlinearity of such elements and their extremely low intrinsic noise. Submicron tunnel junctions are necessary to realize the ultimate parameters of SIS receivers, which are used as standard devices on both ground and space radio telescopes around the world. The technology for manufacturing submicron Nb–AlN–NbN tunnel junctions using electron-beam lithography was developed and optimized. This article presents the results on the selection of the exposure dose, development time, and plasma chemical etching parameters to obtain high-quality junctions (the ratio of the resistances below and above the gap R_j/R_n). The use of a negative-resist ma-N 2400 with lower sensitivity and better contrast in comparison with a negative-resist UVN 2300-0.5 improved the reproducibility of the structure fabrication process. Submicron (area from 2.0 to 0.2 µm²) Nb–AlN–NbN tunnel junctions with high current densities and quality parameters R_j/R_n > 15 were fabricated. The spread of parameters of submicron tunnel structures across the substrate and the reproducibility of the cycle-to-cycle process of tunnel structure fabrication were measured. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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11 pages, 1477 KiB

Open AccessFeature PaperArticle

Fabrication of NIS and SIS Nanojunctions with Aluminum Electrodes and Studies of Magnetic Field Influence on IV Curves

by Mikhail Tarasov, Aleksandra Gunbina, Mikhail Fominsky, Artem Chekushkin, Vyacheslav Vdovin, Valery Koshelets, Elizaveta Sohina, Alexei Kalaboukhov and Valerian Edelman

Electronics 2021, 10(23), 2894; https://doi.org/10.3390/electronics10232894 - 23 Nov 2021

Cited by 2 | Viewed by 1937

Abstract

Samples of superconductor–insulator–superconductor (SIS) and normal metal–insulator–superconductor (NIS) junctions with superconducting aluminum of different thickness were fabricated and experimentally studied, starting from conventional shadow evaporation with a suspended resist bridge. We also developed alternative fabrication by magnetron sputtering with two-step direct e-beam patterning. We compared Al film grain size, surface roughness, resistivity deposited by thermal evaporation and magnetron sputtering. The best-quality NIS junctions with large superconducting electrodes approached a resistance R(0)/R(V_2Δ) factor ratio of 1000 at 0.3 K and over 10,000 at 0.1 K. At 0.1 K, R(0) was determined completely by the Andreev current. The contribution of the single-electron current dominated at V > V_Δ/2. The single-electron resistance extrapolated to V = 0 exceeded the resistance R(V₂_Δ) by 3 × 10⁹. We measured the influence of the magnetic field on NIS junctions and described the mechanism of additional conductivity due to induced Abrikosov vortices. The modified shape of the SINIS bolometer IV curve was explained by Joule overheating via NIN (normal metal–insulator–normal metal) channels. Full article

(This article belongs to the Special Issue Nanofabrication of Superconducting Circuits)

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