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

IEICE Transactions on Electronics

Design and Evaluation of Magnetic Field Tolerant Single Flux Quantum Circuits for Superconductive Sensing Systems

Yuki Yamanashi, Nobuyuki Yoshikawa

Published Jan 1, 2014• 6 citations
Publisher

Abstract

A promising application of a single-flux quantum (SFQ) circuit is read-out circuitry for a multi-channel superconductive sensor array. In such applications, the SFQ read-out circuit is expected to operate outside a magnetic shield. We investigated an SFQ circuit structure, which is tolerant to an external magnetic field, using the AIST 2.5kA/cm2 Nb standard 2 process, which has four Nb wiring layers including the ground plane. By covering the entire circuit using an upper Nb wiring layer called the control (CTL) layer, the influences of the external magnetic field on the SFQ circuit operation can be avoided. We experimentally evaluated the sheet inductance of the wiring layer underneath the CTL shielding layer to design a magnetic-field-tolerant SFQ circuit. We implemented and measured test circuits comprising toggle flip-flops (TFFs) to evaluate their magnetic field tolerances. The operating margin and maximum operating frequency of the designed TFF did not deteriorate with increases in the magnetic field applied to the test circuit, whereas the operating margin of the conventional TFF was reduced by applying the magnetic field. We have also demonstrated the high-speed operation of the designed TFF operated in an unshielded environment at a frequency of up to 120GHz with a wide operating margin.

DOI
10.1587/transele.e97.c.178

Related papers

Characterization of an On-Chip Magnetic Shielding Technique for Improving SFQ Circuit Performance

Romain Collot, Pascal Febvre, J. Kunert +3 more

An on-chip magnetic shielding technique was characterized on several DC-SQUIDs to prepare the next generation of complex digital RSFQ circuits designed by the FLUXONICS foundry. The maximal frequency of operation of a toggle flip-flop cell was used as a criteria to validate the concept. It goes from a simulated value of 52 GHz (46 ± 2 GHz experimentally), for a McCumber parameter βc= 1 with JC= 1 kA/cm2 in the absence of external magnetic field, down to 29 GHz in the presence of an external field of 88 μT. The shielding technique consists of surrounding a circuit by one or several superconducting niobium loops with the same layers as for the SFQ circuit. The loops are connected to the ground plane with vias. It is shown experimentally that the local magnetic field is reduced by a factor of 4 for the best shielded configuration, which limits the reduction of the maximal frequency of operation in presence of external magnetic field.

IEEE Transactions on Applied Superconductivity•Mar 15, 2016•5 citations

Development of Program counter through the optimization of RSFQ Toggle Flip-Flop

Baek Seung Hun, Kim Jin Young, Kim Se Hoon +1 more

We has designed, fabricated, and measured a Single flux quantum (SFQ) toggle flip-flop (TFF). The TFF is widely used in superconductive digital electronics circuits. Many digital devices, such as frequency counter, counting ADC and program counter be used TFF Specially, a program counter may be constructed based on TFF We have designed the newly TFF and obtained high bias margins on test. In this work, we used two circuit simulation tools, WRspice and Julia, as circuit optimization tools. We used XIC for a layout tool. Newly designed TFF had minimum bias margins of +/- and maximum bias margins of +/-(enhanced from +/- ). The designed circuits were fabricated by using Nb technology The test results showed that the re-optimized TFF operated correctly on 100kHz and had a very wide bias margins of +/- .

Progress in Superconductivity and Cryogenics•Jan 1, 2005•1 citation

A single flux quantum circuit with a ferromagnet-based Josephson π-junction

M. Khabipov, D Balashov, F. Maibaum +5 more

We report on the functionality of a Nb-based superconducting single flux quantum (SFQ) toggle flip-flop (TFF) circuit, comprising a complementary superconductor–ferromagnet–superconductor (SFS) Josephson π-junction. The SFS junction was used as a phase shifting element inserted in the storage loop of the TFF. The fabricated circuits demonstrated correct functionality with the operation parameter ranges of ± 20%. The application of SFS π-junctions makes the SFQ circuits very compact, may substantially improve their stability, and may also be suitable for integration with Josephson quantum circuits (qubits).

Superconductor Science and Technology•Mar 19, 2010•66 citations

Analysis of a Shielding Approach for Magnetic Field Tolerant SFQ Circuits

Rodwell S. Bakolo, Johannes A. Delport, Pascal Febvre +1 more

The operating margins of unshielded SFQ circuits are influenced by external magnetic fields, and earlier research showed experimental results of operating region versus bias current for circuits with in-plane and perpendicularly applied magnetic fields. Here, we report a method that can be used to analyze shields to protect SFQ circuits from external magnetic fields. To validate the approach, we investigated a grid-patterned shield of varying spacing. The analysis was done with cell layouts made according to the Hypres' 4.5 kA/cm2process, in which the top-most layer, M3, was used to implement the shields. It was calculated that a grid shield of 2.5 μm grid bar width and spacing of 5 μm offered a good compromise at both providing shielding and causing a relatively small drift in circuit inductance. In order to make SFQ circuits more tolerant to magnetic fields, we have simulated with circuit parameter alterations to realize the best bias and higher operating held margins, due to external magnetic fields. The external magnetic fields are modeled through three orthogonal coils that generate roughly a uniform magnetic held density throughout the cell under test.

IEEE Transactions on Applied Superconductivity•Feb 15, 2017•5 citations

HTS SFQ T-flip flop with directly coupled readout

A. G. Sun, D.J. Durand, James M. Murduck +4 more

The authors report the design, fabrication, and test results of single flux quantum (SFQ) toggle flip flop circuits. These circuits, investigated as building blocks of an HTS counting ADC, feature a directly coupled readout junction stack similar to those used in LTS RSFQ circuits. The directly coupled circuit delivers higher readout voltage, hence potentially higher operating speed than magnetically coupled alternatives. The circuits were fabricated using two multilayer HTS SNS junction integrated circuit technologies (one at Northrop Grumman and the other at TRW) featuring three YBCO depositions. Initial testing demonstrated toggling of a T-flip flop in response to SFQ pulses generated by integrated dc/SFQ converters. The readout voltage is shown to approach 40% of the junction I/sub C/R/sub N/ product, and as high as 100 /spl mu/V at 65K. Test results are compared with predicted fabrication process parameter requirements. To increase margins and tolerance to process parameter variations, improvements to the design have been made using JSpice and MALT.

IEEE Transactions on Applied Superconductivity•Jun 1, 1999•14 citations

30GHz Operation of Single-Flux-Quantum Arithmetic Logic Unit Implemented by Using Dynamically Reconfigurable Gates

Yuki Yamanashi, Shohei Nishimoto, Nobuyuki Yoshikawa

A single-flux-quantum (SFQ) arithmetic logic unit (ALU) was designed and tested to evaluate the effectiveness of introducing dynamically reconfigurable logic gates in the design of a superconducting logic circuit. We designed and tested a bit-serial SFQ ALU that can perform six arithmetic/logic functions by using a dynamically reconfigurable AND/OR gate. To ensure stable operation of the ALU, we improved the operating margin of the SFQ AND/OR gate by employing a partially shielded structure where the circuit is partially surrounded by under- and over-ground layers to reduce parasitic inductances. Owing to the introduction of the partially shielded structure, the operating margin of the dynamically reconfigurable AND/OR gate can be improved without increasing the circuit area. This ALU can be designed with a smaller circuit area compared with the conventional ALU by using the dynamically reconfigurable AND/OR gate. We implemented the SFQ ALU using the AIST 2.5kA/cm2 Nb standard process 2. We confirmed high-speed operation and correct reconfiguration of the SFQ ALU by a high-speed test. The measured maximum operation frequency was 30GHz.

IEICE Transactions on Electronics•Jan 1, 2016•1 citation
A promising application of a single-flux quantum (SFQ) circuit is read-out circuitry for a multi-channel superconductive sensor array. In such applications, the SFQ read-out circuit is expected to operate outside a magnetic shield. We investigated an SFQ circuit structure, which is tolerant to an external magnetic field, using the AIST 2.5kA/cm2 Nb standard 2 process, which has four Nb wiring layers including the ground plane. By covering the entire circuit using an upper Nb wiring layer called the control (CTL) layer, the influences of the external magnetic field on the SFQ circuit operation can be avoided. We experimentally evaluated the sheet inductance of the wiring layer underneath the CTL shielding layer to design a magnetic-field-tolerant SFQ circuit. We implemented and measured test circuits comprising toggle flip-flops (TFFs) to evaluate their magnetic field tolerances. The operating margin and maximum operating frequency of the designed TFF did not deteriorate with increases in the magnetic field applied to the test circuit, whereas the operating margin of the conventional TFF was reduced by applying the magnetic field. We have also demonstrated the high-speed operation of the designed TFF operated in an unshielded environment at a frequency of up to 120GHz with a wide operating margin.
An on-chip magnetic shielding technique was characterized on several DC-SQUIDs to prepare the next generation of complex digital RSFQ circuits designed by the FLUXONICS foundry. The maximal frequency of operation of a toggle flip-flop cell was used as a criteria to validate the concept. It goes from a simulated value of 52 GHz (46 ± 2 GHz experimentally), for a McCumber parameter βc= 1 with JC= 1 kA/cm2 in the absence of external magnetic field, down to 29 GHz in the presence of an external field of 88 μT. The shielding technique consists of surrounding a circuit by one or several superconducting niobium loops with the same layers as for the SFQ circuit. The loops are connected to the ground plane with vias. It is shown experimentally that the local magnetic field is reduced by a factor of 4 for the best shielded configuration, which limits the reduction of the maximal frequency of operation in presence of external magnetic field.
We has designed, fabricated, and measured a Single flux quantum (SFQ) toggle flip-flop (TFF). The TFF is widely used in superconductive digital electronics circuits. Many digital devices, such as frequency counter, counting ADC and program counter be used TFF Specially, a program counter may be constructed based on TFF We have designed the newly TFF and obtained high bias margins on test. In this work, we used two circuit simulation tools, WRspice and Julia, as circuit optimization tools. We used XIC for a layout tool. Newly designed TFF had minimum bias margins of +/- and maximum bias margins of +/-(enhanced from +/- ). The designed circuits were fabricated by using Nb technology The test results showed that the re-optimized TFF operated correctly on 100kHz and had a very wide bias margins of +/- .
We report on the functionality of a Nb-based superconducting single flux quantum (SFQ) toggle flip-flop (TFF) circuit, comprising a complementary superconductor–ferromagnet–superconductor (SFS) Josephson π-junction. The SFS junction was used as a phase shifting element inserted in the storage loop of the TFF. The fabricated circuits demonstrated correct functionality with the operation parameter ranges of ± 20%. The application of SFS π-junctions makes the SFQ circuits very compact, may substantially improve their stability, and may also be suitable for integration with Josephson quantum circuits (qubits).
The operating margins of unshielded SFQ circuits are influenced by external magnetic fields, and earlier research showed experimental results of operating region versus bias current for circuits with in-plane and perpendicularly applied magnetic fields. Here, we report a method that can be used to analyze shields to protect SFQ circuits from external magnetic fields. To validate the approach, we investigated a grid-patterned shield of varying spacing. The analysis was done with cell layouts made according to the Hypres' 4.5 kA/cm2process, in which the top-most layer, M3, was used to implement the shields. It was calculated that a grid shield of 2.5 μm grid bar width and spacing of 5 μm offered a good compromise at both providing shielding and causing a relatively small drift in circuit inductance. In order to make SFQ circuits more tolerant to magnetic fields, we have simulated with circuit parameter alterations to realize the best bias and higher operating held margins, due to external magnetic fields. The external magnetic fields are modeled through three orthogonal coils that generate roughly a uniform magnetic held density throughout the cell under test.
The authors report the design, fabrication, and test results of single flux quantum (SFQ) toggle flip flop circuits. These circuits, investigated as building blocks of an HTS counting ADC, feature a directly coupled readout junction stack similar to those used in LTS RSFQ circuits. The directly coupled circuit delivers higher readout voltage, hence potentially higher operating speed than magnetically coupled alternatives. The circuits were fabricated using two multilayer HTS SNS junction integrated circuit technologies (one at Northrop Grumman and the other at TRW) featuring three YBCO depositions. Initial testing demonstrated toggling of a T-flip flop in response to SFQ pulses generated by integrated dc/SFQ converters. The readout voltage is shown to approach 40% of the junction I/sub C/R/sub N/ product, and as high as 100 /spl mu/V at 65K. Test results are compared with predicted fabrication process parameter requirements. To increase margins and tolerance to process parameter variations, improvements to the design have been made using JSpice and MALT.
A single-flux-quantum (SFQ) arithmetic logic unit (ALU) was designed and tested to evaluate the effectiveness of introducing dynamically reconfigurable logic gates in the design of a superconducting logic circuit. We designed and tested a bit-serial SFQ ALU that can perform six arithmetic/logic functions by using a dynamically reconfigurable AND/OR gate. To ensure stable operation of the ALU, we improved the operating margin of the SFQ AND/OR gate by employing a partially shielded structure where the circuit is partially surrounded by under- and over-ground layers to reduce parasitic inductances. Owing to the introduction of the partially shielded structure, the operating margin of the dynamically reconfigurable AND/OR gate can be improved without increasing the circuit area. This ALU can be designed with a smaller circuit area compared with the conventional ALU by using the dynamically reconfigurable AND/OR gate. We implemented the SFQ ALU using the AIST 2.5kA/cm2 Nb standard process 2. We confirmed high-speed operation and correct reconfiguration of the SFQ ALU by a high-speed test. The measured maximum operation frequency was 30GHz.