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

Applied Physics Letters

Josephson single-flux-quantum logic circuits using niobium weak links

Hiroyuki Tamura, Yoji Okabe, T. Sugano

Published Nov 1, 1981• 16 citations
Publisher

Abstract

Josephson logic circuits using fluxoid quantization in a one-junction interferometer to represent logical states have been fabricated from thin films of Nb by means of photolithography, electron beam lithography, and reactive ion etching. A variable thickness bridge is used as a Josephson junction in the one-junction interferometer. The logic circuits have shown AND and OR logic functions.

DOI
10.1063/1.92845

Related papers

Fabrication of Josephson Weak Links using Electron Beam Lithography and Ion Etching and Proposal of a New Single Flux Quantum Logic

Hiroshi Tamura, Y. Okabe, T. Sugano

A new single flux quantum device is proposed, and, in conjunction with it, fabrication process of Josephson weak links using electron beam lithography and ion-etching is reported. Two types of niobium weak links, microbridges and thick-thin-thick type bridges, have been fabricated. They showed dc supercurrent, but microwave-induced steps were observed for thick-thin-thick type bridge only. The proposed logic device is constructed with a magnetically coupled rf-SQUID cells. These cells behave in the similar manner as Domino-toppling, and basic logic operations, AND, OR and NOT, are demonstrated by numerical calculations. Switching delay of about 10ps is expected to be practical.

International Conference on Solid State Devices and Materials (SSDM)•Aug 28, 1979•0 citations

Weak link nanobridges as single flux quantum elements

Connor D. Shelly, Patrick See, Jane Ireland +2 more

This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV -characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM .

Superconductor Science and Technology•Jul 19, 2017•15 citations

Proposal of unilateral single-flux-quantum logic gate

Hidetaka MIYAKE, N. Fukaya, Yoji Okabe +1 more

A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.

IEEE Transactions on Magnetics•Mar 1, 1985•4 citations

High speed logic operations of all refractory Josephson integrated circuits

S. Kosaka, Akira Shoji, Masahiro Aoyagi +4 more

A chain circuit of four-junction logic gates consisting of all refractory junctions with niobium nitride (NbN)-niobium (Nb) double-layered electrodes has been fabricated with a 2.5-μm minimum feature. A reactive ion etching technique has been used for patterning every layer such as junction electrodes, molybdenum resistors, and insulation layers. The minimum logic delay of 18 ps/gate has been obtained in the experimental circuit.

Applied Physics Letters•Jul 15, 1983•16 citations

Digital circuits using self-shunted Nb/NbxSi1−x/Nb Josephson junctions

David I. Olaya, Paul D. Dresselhaus, Samuel P. Benz +5 more

Superconducting digital circuits based on Josephson junctions with amorphous niobium-silicon (a-NbSi) barriers have been designed, fabricated, and tested. Single-flux-quantum (SFQ) shift registers operated with ±30% bias margins, confirming junction reproducibility and uniformity. Static digital dividers operated up to 165 GHz for a single value of bias current, which was only marginally slower than circuits fabricated with externally shunted AlOx-barrier junctions having a comparable critical current density of 4.5 kA/cm2. In comparison, self-shunted a-NbSi junctions enabled a doubling in circuit density. This and their relatively thick 10 nm barriers could increase the yield of complex SFQ circuits.

Applied Physics Letters•May 24, 2010•25 citations

TECHNOLOGIES FOR THE FABRICATION OF NANOSCALE SUPERCONDUCTING CIRCUITS

道生 渡部

Researches on the fabrication of ~ 0.1 × 0.1 μ m 2 superconductor–insulator–superconductor (SIS) Josephson junctions are reviewed. Today, a typical dimension is 1–10 μm for Josephson junctions in superconducting integrated circuits. These Josephson junctions are defined by well-established photolithographic technology with reactive ion etching (RIE), and for the superconductor, Nb is almost always used. The merits of Nb include the facts that the superconducting transition temperature Tc of Nb (9.2 K ) is higher than the boiling point of He (4.2 K ), and that Nb has excellent stability against thermal cycling between room temperature and liquid- He temperature. For the fabrication of ~ 0.1 × 0.1 μ m 2 junctions, on the other hand, there is a standard process with electron-beam lithography, shadow evaporation, and lift-off. This process works well for Al (Tc = 1.2 K ), however, it is not ideal for Nb . The scope of this brief review is the nanoscale junction with Nb electrodes. We will look at the efforts of optimizing the standard lift-off process for Nb , electron-beam-lithographic versions of the Nb Josephson-junction technology, focused-ion-beam (FIB) etching as a convenient alternative to electron-beam lithography and RIE, etc. In order to characterize nanoscale tunnel junctions, the single-charge transistor has been often fabricated. Therefore, a summary of its theoretical transport properties is also included.

Modern Physics Letters B•Apr 30, 2005•3 citations
Josephson logic circuits using fluxoid quantization in a one-junction interferometer to represent logical states have been fabricated from thin films of Nb by means of photolithography, electron beam lithography, and reactive ion etching. A variable thickness bridge is used as a Josephson junction in the one-junction interferometer. The logic circuits have shown AND and OR logic functions.
A new single flux quantum device is proposed, and, in conjunction with it, fabrication process of Josephson weak links using electron beam lithography and ion-etching is reported. Two types of niobium weak links, microbridges and thick-thin-thick type bridges, have been fabricated. They showed dc supercurrent, but microwave-induced steps were observed for thick-thin-thick type bridge only. The proposed logic device is constructed with a magnetically coupled rf-SQUID cells. These cells behave in the similar manner as Domino-toppling, and basic logic operations, AND, OR and NOT, are demonstrated by numerical calculations. Switching delay of about 10ps is expected to be practical.
This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV -characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM .
A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.
Superconducting digital circuits based on Josephson junctions with amorphous niobium-silicon (a-NbSi) barriers have been designed, fabricated, and tested. Single-flux-quantum (SFQ) shift registers operated with ±30% bias margins, confirming junction reproducibility and uniformity. Static digital dividers operated up to 165 GHz for a single value of bias current, which was only marginally slower than circuits fabricated with externally shunted AlOx-barrier junctions having a comparable critical current density of 4.5 kA/cm2. In comparison, self-shunted a-NbSi junctions enabled a doubling in circuit density. This and their relatively thick 10 nm barriers could increase the yield of complex SFQ circuits.
Researches on the fabrication of ~ 0.1 × 0.1 μ m 2 superconductor–insulator–superconductor (SIS) Josephson junctions are reviewed. Today, a typical dimension is 1–10 μm for Josephson junctions in superconducting integrated circuits. These Josephson junctions are defined by well-established photolithographic technology with reactive ion etching (RIE), and for the superconductor, Nb is almost always used. The merits of Nb include the facts that the superconducting transition temperature Tc of Nb (9.2 K ) is higher than the boiling point of He (4.2 K ), and that Nb has excellent stability against thermal cycling between room temperature and liquid- He temperature. For the fabrication of ~ 0.1 × 0.1 μ m 2 junctions, on the other hand, there is a standard process with electron-beam lithography, shadow evaporation, and lift-off. This process works well for Al (Tc = 1.2 K ), however, it is not ideal for Nb . The scope of this brief review is the nanoscale junction with Nb electrodes. We will look at the efforts of optimizing the standard lift-off process for Nb , electron-beam-lithographic versions of the Nb Josephson-junction technology, focused-ion-beam (FIB) etching as a convenient alternative to electron-beam lithography and RIE, etc. In order to characterize nanoscale tunnel junctions, the single-charge transistor has been often fabricated. Therefore, a summary of its theoretical transport properties is also included.