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

IEEE Transactions on Applied Superconductivity

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, C.‐K. Hu, Alan W. Kleinsasser, Timothy A. Brunner, Cyril Cabral, V. Chandrashekhar, Mark A. Jaso, M. P. Manny, K. Stein, Manjul Bhushan

Published Mar 1, 1993• 27 citations
Publisher

Abstract

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.>

DOI
10.1109/77.233334

Related papers

Ultra-low-noise tunnel junction dc SQUID with a tightly coupled planar input coil

M. B. Ketchen, J. M. Jaycox

We present a new superconducting quantum interference device (SQUID) that combines ultra-low-noise performance with tight coupling to a useable input coil. The inductive loop of the SQUID consists of a superconducting square washer that is slit in a low inductance fashion from its central hole to an outside edge where two Josephson tunnel junctions are incorporated. The inductance of the SQUID is about 90 pH, and each junction has a critical current of 15 μA and a resistive shunt of 4.5 Ω. The 190-nH input coil is a planar spiral of 50 turns situated immediately above the washer and coupled to the SQUID with a coupling constant k2 of 0.86. The SQUID has a minimum coupled energy sensitivity of 19h at 4.2 K and 8h at 1.5 K, in good agreement with theory. The crossover between white and low frequency noise occurs at ∼250 Hz.

Applied Physics Letters•Apr 15, 1982•248 citations

Sub-μm linewidth input coils for low T c integrated thin-film dc superconducting quantum interference devices

M. B. Ketchen, Kevin G. Stawiasz, Dale J. Pearson +6 more

We have, for the first time, demonstrated integrated dc superconducting quantum interference devices (SQUIDs) with input coils of linewidth down to 0.5 μm. The SQUID inductance L consists of a single octagonal washer or two or four such washers configured in parallel. The input coil of inductance Li, which couples to L with a mutual inductance of Mi, consists of fine-line octagonal spiral(s) fabricated in close proximity to the washer(s). For a two-washer SQUID with twin 80-turn, 0.5 μm spirals, Li=2.5 μH, Mi=12.7 nH, L=109 pH, and the coupling constant k2=0.85. This entire device occupies an area of less than 0.2 mm2.

Applied Physics Letters•Jul 20, 1992•23 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

Design considerations for DC SQUIDs fabricated in deep sub-micron technology

M. B. Ketchen

Practical SQUIDs with well-coupled input coils of usable inductance have generally been fabricated at the 2-5 mu m level of lithography. Other technologies, silicon in particular, are now routinely practised at the 0.5 mu m level of lithography with impressive demonstrations at the 0.1-0.25 mu m level not uncommon. The implications of applying such a fabrication capability to advance DC SQUID technology are explored. In particular, the issues of scaling practical DC SQUIDs down to the 0.1-0.25 mu m regime are examined, using as a prototype design the basic washer SQUID with a spiral input coil. A technical path is mapped out that leads to a practical SQUID less than 0.05 mm/sup 2/ in area with a tightly coupled 2- mu H input coil, user-friendly voltage-flux characteristics, minimal flux creep related hysteresis, and coupled energy sensitivity approaching the quantum limit at 4.2 K.

IEEE Transactions on Magnetics•Mar 1, 1991•64 citations

Low noise DC SQUIDs fabricated in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology

M. B. Ketchen, Manjul Bhushan, Steven B. Kaplan +1 more

The authors have designed, fabricated and tested all-refractory DC SQUIDs in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology that have noise performance comparable to the best previously reported for any technology. A variety of SQUID designs were incorporated as part of a trilayer process development test vehicle. SQUID inductance, junction area, and resistive shunt geometry were varied in matrix fashion to give SQUIDs with near-optimum parameter values for a factor of five range in Josephson current density and shunt sheet resistance. The devices were fabricated using a selective niobium anodization with a minimum feature size of 2 mu m. The base electrode and Nb wiring were patterned with dry etching, and the junction areas were defined by anodization: the Ti resistors were patterned with a lift-off process. Current density on different wafers was varied from 400 to 1000 A/cm/sup 2/ with typical junction V/sub m/'s of 60 mV. The shunt sheet resistance was varied in the 1-5- Omega / Square Operator range. The noise was measured with an RF SQUID direct small-signal readout scheme. A 50-pH SQUID with 3- mu m/sup 2/, 16- mu A junctions and 14- Omega shunt resistors was shown to have an ideally low white noise of 1*10/sup -13/ Phi /sub 0//sup 2//Hz, a white to 1/f crossover frequency at 7 Hz, and a noise level less than 6*10/sup -12/ Phi /sub 0//sup 2//Hz at 0.1 Hz.

IEEE Transactions on Magnetics•Mar 1, 1991•24 citations

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
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.>
We present a new superconducting quantum interference device (SQUID) that combines ultra-low-noise performance with tight coupling to a useable input coil. The inductive loop of the SQUID consists of a superconducting square washer that is slit in a low inductance fashion from its central hole to an outside edge where two Josephson tunnel junctions are incorporated. The inductance of the SQUID is about 90 pH, and each junction has a critical current of 15 μA and a resistive shunt of 4.5 Ω. The 190-nH input coil is a planar spiral of 50 turns situated immediately above the washer and coupled to the SQUID with a coupling constant k2 of 0.86. The SQUID has a minimum coupled energy sensitivity of 19h at 4.2 K and 8h at 1.5 K, in good agreement with theory. The crossover between white and low frequency noise occurs at ∼250 Hz.
We have, for the first time, demonstrated integrated dc superconducting quantum interference devices (SQUIDs) with input coils of linewidth down to 0.5 μm. The SQUID inductance L consists of a single octagonal washer or two or four such washers configured in parallel. The input coil of inductance Li, which couples to L with a mutual inductance of Mi, consists of fine-line octagonal spiral(s) fabricated in close proximity to the washer(s). For a two-washer SQUID with twin 80-turn, 0.5 μm spirals, Li=2.5 μH, Mi=12.7 nH, L=109 pH, and the coupling constant k2=0.85. This entire device occupies an area of less than 0.2 mm2.
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.
Practical SQUIDs with well-coupled input coils of usable inductance have generally been fabricated at the 2-5 mu m level of lithography. Other technologies, silicon in particular, are now routinely practised at the 0.5 mu m level of lithography with impressive demonstrations at the 0.1-0.25 mu m level not uncommon. The implications of applying such a fabrication capability to advance DC SQUID technology are explored. In particular, the issues of scaling practical DC SQUIDs down to the 0.1-0.25 mu m regime are examined, using as a prototype design the basic washer SQUID with a spiral input coil. A technical path is mapped out that leads to a practical SQUID less than 0.05 mm/sup 2/ in area with a tightly coupled 2- mu H input coil, user-friendly voltage-flux characteristics, minimal flux creep related hysteresis, and coupled energy sensitivity approaching the quantum limit at 4.2 K.
The authors have designed, fabricated and tested all-refractory DC SQUIDs in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology that have noise performance comparable to the best previously reported for any technology. A variety of SQUID designs were incorporated as part of a trilayer process development test vehicle. SQUID inductance, junction area, and resistive shunt geometry were varied in matrix fashion to give SQUIDs with near-optimum parameter values for a factor of five range in Josephson current density and shunt sheet resistance. The devices were fabricated using a selective niobium anodization with a minimum feature size of 2 mu m. The base electrode and Nb wiring were patterned with dry etching, and the junction areas were defined by anodization: the Ti resistors were patterned with a lift-off process. Current density on different wafers was varied from 400 to 1000 A/cm/sup 2/ with typical junction V/sub m/'s of 60 mV. The shunt sheet resistance was varied in the 1-5- Omega / Square Operator range. The noise was measured with an RF SQUID direct small-signal readout scheme. A 50-pH SQUID with 3- mu m/sup 2/, 16- mu A junctions and 14- Omega shunt resistors was shown to have an ideally low white noise of 1*10/sup -13/ Phi /sub 0//sup 2//Hz, a white to 1/f crossover frequency at 7 Hz, and a noise level less than 6*10/sup -12/ Phi /sub 0//sup 2//Hz at 0.1 Hz.
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.