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:1705.06166 · Superconductor Science and Technology

Nearly quantum limited nanoSQUIDs based on cross-type Nb/AlO x /Nb junctions

Matthias Schmelz, V Zakosarenko, Thomas Schönau, S Anders, S Linzen, Ronny Stolz, H-G Meyer

Published Nov 2, 2016• 22 citations
arXivHTMLPDF

Abstract

Abstract We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlO x /Nb Josephson junctions offer large I C R N -products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 μ m exhibit white flux noise levels as low as 45 nΦ 0 Hz −1/2 corresponding to an energy resolution ε of about 1 h at 4.2 K, with h being Planck’s constant. Moreover, the large usable voltage swings of the devices of about 300 μ V allow highly sensitive and easy single-stage operation while exploring nearly the intrinsic noise of the SQUIDs, beneficial e.g. for sensor arrays in SQUID microscopy.

DOI
10.1088/0953-2048/30/1/014001

Related papers

Investigation of all niobium nano-SQUIDs based on sub-micrometer cross-type Josephson junctions

Matthias Schmelz, Y Matsui, Ronny Stolz +6 more

We report on the development of highly sensitive SQUIDs featuring sub-micrometer loop dimensions. The integration of high quality and low capacitance SIS Nb/AlO x /Nb cross-type Josephson tunnel junctions results in white flux noise levels as low as 66 n Φ 0 Hz −1/2 , well below state-of-the-art values of their Nb-based counterparts based on constriction type junctions. Estimation of the spin sensitivity of the best SQUIDs yield S μ 1/2 < 7 μ B Hz −1/2 in the white noise region, suitable for the investigation of small spin systems. We discuss fabrication challenges, show results on the electrical characterization of devices with various pickup loops, and describe options for further improvement, which may push the sensitivity of such devices even to single spin resolution.

arXiv:1501.00958•Superconductor Science and Technology•Nov 26, 2014•27 citations

Fabrication and Evaluation of Superconducting Quantum Interference Devices with Nb/Al–AlOx–Al/Nb Edge Junctions

Naoki Mizutani, Shuichi Yamasaki, Youichi Takada +2 more

We have fabricated superconducting quantum interference devices (SQUIDs) with an inductance of 140 pH by using sub- µm Nb/Al–AlO x –Al/Nb edge junctions. The small capacitance of the junction resulted in the very large voltage swing of 210 µV and gradient dV/ dΦ of 940 µV/Φ0. Consequently, the very low flux noise of 0.61 µΦ0/ Hz0.5 corresponding to the energy sensitivity ε of 8.6h at the white noise level was obtained by using a conventional flux-locked loop configuration. The low-frequency noise was also very low, 2.7 µΦ0/ Hz0.5 corresponding to ε= 170 h at 1 Hz. We could obtain very low flux noise for the SQUID which had the practical inductance using only a conventional readout circuit.

Japanese Journal of Applied Physics•May 1, 1994•5 citations

Multiloop Superconducting Quantum Interference Devices with Nb/Al-AlOx-Al/Nb Edge Junctions

Naoki Mizutani, Gen Uehara, Youichi Takada +2 more

We have fabricated multiloop superconducting quantum interference devices (SQUIDs) of 4×4 mm2 total size using sub-µ m Nb/Al-AlO x -Al/Nb edge junctions. We obtained very large voltage swing and gradient ∂V/∂Φ of 0.95-1.53 mV/Φ0, because it was possible to increase the shunt resistance due to the small junction capacitance. This advantage enabled us to achieve very low flux density noise of 1.9 fT/Hz0.5 for white noise by using a readout circuit in which the voltage noise of the amplifier was 1.4 nV/Hz0.5. The low-frequency noise was also very low (7.3 fT/Hz0.5 at 1 Hz). These noise results are half and one-third, respectively, compared with noise before the improvement achieved by this study. We obtained very low flux density noise for the small SQUID using only an inexpensive, compact readout circuit.

Japanese Journal of Applied Physics•Sep 1, 1995•0 citations

3D nanoSQUID based on tunnel nano-junctions with an energy sensitivity of 1.3 h at 4.2 K

Matthias Schmelz, Antonio Vettoliere, V. Zakosarenko +4 more

We report the performance of a reliable three-dimensional nanometer-sized Superconducting QUantum Interference Device (SQUID). The use of superconductor-isolator-superconductor Nb/Al-AlOx/Nb Josephson tunnel junctions together with small SQUID loop dimensions permits a high modulation depth of the SQUID's critical current and thus leads to very low intrinsic flux noise of the device. In particular, we present electrical characterization including detailed noise investigations. At 4.2 K, two-stage noise measurements with a SQUID as a low noise preamplifier result in a white flux noise of 51 nΦ0/Hz1/2, which is equivalent to an energy resolution of 1.3 h, with h being Planck's constant. Simulation of spin sensitivities results in about 1 μB/Hz1/2 for an electron spin positioned directly above the SQUID ring.

Applied Physics Letters•Jul 17, 2017•18 citations

Octagonal washer DC SQUIDs and integrated susceptometers fabricated in a planarized sub- mu m Nb-AlO/sub x/-Nb technology

M. B. Ketchen, Dale J. Pearson, Kevin G. Stawiasz +9 more

The authors have designed, fabricated, and measured a number of Nb-AlO/sub x/-Nb octagonal washer DC superconducting quantum interference devices (SQUIDs) and miniature DC SQUID susceptometers having minimum feature size down to 0.5 mu m. With SQUID inductance values on the order of 100 pH, typical noise performance is better than 1 mu Phi /sub 0// square root Hz. The small minimum feature size of input coils and pickup loop structures will facilitate tight coupling to a wide variety of systems ranging from submicron particles and structures to conventional approximately mu H input circuits. A single-washer SQUID with an 80-turn 0.5- mu m-linewidth, 630-nH input coil has user-friendly V- Phi (voltage-flux) curves and a coupled energy sensitivity of 20 h at 4.2 K. Susceptometers with pickup loops ranging from 20- mu m to 0.8- mu m across have very user-friendly V- Phi curves and a resolution of order 100 mu /sub B// square root Hz at 4.2 K for devices with the smallest loops.>

IEEE Transactions on Applied Superconductivity•Mar 1, 1993•27 citations

Anodization-free fabrication process for high-quality cross-type Josephson tunnel junctions based on a Nb/Al-AlO x /Nb trilayer

F Adam, C. Enss, Sebastian Kempf

Abstract Josephson tunnel junctions form the basis for various superconductor electronic devices. For this reason, enormous efforts are routinely taken to establish and later on maintain a scalable and reproducible wafer-scale manufacturing process for high-quality Josephson junctions. Here, we present an anodization-free fabrication process for Nb/Al-AlO x /Nb cross-type Josephson junctions that requires only a small number of process steps and that is in general intrinsically compatible with wafer-scale fabrication. We show that the fabricated junctions are of very high quality and, compared to other junction types, exhibit not only a significantly reduced capacitance but also an almost rectangular critical current density profile. Our process hence enables the usage of low capacitance Josephson junctions for superconductor electronic devices such as ultra-low noise dc-superconducting quantum interference devices (SQUIDs), microwave SQUID multiplexers based on non-hysteretic rf-SQUIDs and RFSQ circuits.

arXiv:2403.01806•Superconductor Science and Technology•Jul 8, 2024•5 citations
Abstract We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlO x /Nb Josephson junctions offer large I C R N -products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 μ m exhibit white flux noise levels as low as 45 nΦ 0 Hz −1/2 corresponding to an energy resolution ε of about 1 h at 4.2 K, with h being Planck’s constant. Moreover, the large usable voltage swings of the devices of about 300 μ V allow highly sensitive and easy single-stage operation while exploring nearly the intrinsic noise of the SQUIDs, beneficial e.g. for sensor arrays in SQUID microscopy.
We report on the development of highly sensitive SQUIDs featuring sub-micrometer loop dimensions. The integration of high quality and low capacitance SIS Nb/AlO x /Nb cross-type Josephson tunnel junctions results in white flux noise levels as low as 66 n Φ 0 Hz −1/2 , well below state-of-the-art values of their Nb-based counterparts based on constriction type junctions. Estimation of the spin sensitivity of the best SQUIDs yield S μ 1/2 < 7 μ B Hz −1/2 in the white noise region, suitable for the investigation of small spin systems. We discuss fabrication challenges, show results on the electrical characterization of devices with various pickup loops, and describe options for further improvement, which may push the sensitivity of such devices even to single spin resolution.
We have fabricated superconducting quantum interference devices (SQUIDs) with an inductance of 140 pH by using sub- µm Nb/Al–AlO x –Al/Nb edge junctions. The small capacitance of the junction resulted in the very large voltage swing of 210 µV and gradient dV/ dΦ of 940 µV/Φ0. Consequently, the very low flux noise of 0.61 µΦ0/ Hz0.5 corresponding to the energy sensitivity ε of 8.6h at the white noise level was obtained by using a conventional flux-locked loop configuration. The low-frequency noise was also very low, 2.7 µΦ0/ Hz0.5 corresponding to ε= 170 h at 1 Hz. We could obtain very low flux noise for the SQUID which had the practical inductance using only a conventional readout circuit.
We have fabricated multiloop superconducting quantum interference devices (SQUIDs) of 4×4 mm2 total size using sub-µ m Nb/Al-AlO x -Al/Nb edge junctions. We obtained very large voltage swing and gradient ∂V/∂Φ of 0.95-1.53 mV/Φ0, because it was possible to increase the shunt resistance due to the small junction capacitance. This advantage enabled us to achieve very low flux density noise of 1.9 fT/Hz0.5 for white noise by using a readout circuit in which the voltage noise of the amplifier was 1.4 nV/Hz0.5. The low-frequency noise was also very low (7.3 fT/Hz0.5 at 1 Hz). These noise results are half and one-third, respectively, compared with noise before the improvement achieved by this study. We obtained very low flux density noise for the small SQUID using only an inexpensive, compact readout circuit.
We report the performance of a reliable three-dimensional nanometer-sized Superconducting QUantum Interference Device (SQUID). The use of superconductor-isolator-superconductor Nb/Al-AlOx/Nb Josephson tunnel junctions together with small SQUID loop dimensions permits a high modulation depth of the SQUID's critical current and thus leads to very low intrinsic flux noise of the device. In particular, we present electrical characterization including detailed noise investigations. At 4.2 K, two-stage noise measurements with a SQUID as a low noise preamplifier result in a white flux noise of 51 nΦ0/Hz1/2, which is equivalent to an energy resolution of 1.3 h, with h being Planck's constant. Simulation of spin sensitivities results in about 1 μB/Hz1/2 for an electron spin positioned directly above the SQUID ring.
The authors have designed, fabricated, and measured a number of Nb-AlO/sub x/-Nb octagonal washer DC superconducting quantum interference devices (SQUIDs) and miniature DC SQUID susceptometers having minimum feature size down to 0.5 mu m. With SQUID inductance values on the order of 100 pH, typical noise performance is better than 1 mu Phi /sub 0// square root Hz. The small minimum feature size of input coils and pickup loop structures will facilitate tight coupling to a wide variety of systems ranging from submicron particles and structures to conventional approximately mu H input circuits. A single-washer SQUID with an 80-turn 0.5- mu m-linewidth, 630-nH input coil has user-friendly V- Phi (voltage-flux) curves and a coupled energy sensitivity of 20 h at 4.2 K. Susceptometers with pickup loops ranging from 20- mu m to 0.8- mu m across have very user-friendly V- Phi curves and a resolution of order 100 mu /sub B// square root Hz at 4.2 K for devices with the smallest loops.>
Abstract Josephson tunnel junctions form the basis for various superconductor electronic devices. For this reason, enormous efforts are routinely taken to establish and later on maintain a scalable and reproducible wafer-scale manufacturing process for high-quality Josephson junctions. Here, we present an anodization-free fabrication process for Nb/Al-AlO x /Nb cross-type Josephson junctions that requires only a small number of process steps and that is in general intrinsically compatible with wafer-scale fabrication. We show that the fabricated junctions are of very high quality and, compared to other junction types, exhibit not only a significantly reduced capacitance but also an almost rectangular critical current density profile. Our process hence enables the usage of low capacitance Josephson junctions for superconductor electronic devices such as ultra-low noise dc-superconducting quantum interference devices (SQUIDs), microwave SQUID multiplexers based on non-hysteretic rf-SQUIDs and RFSQ circuits.