arXiv:1205.3372 · Applied Physics Letters

Ferromagnetic Josephson switching device with high characteristic voltage

Timofei I. Larkin, Vitaly V. Bol’ginov, Vasily S. Stolyarov, Valery V. Ryazanov, I. V. Vernik, Sergey K. Tolpygo, Oleg A. Mukhanov

Published May 28, 2012• 170 citations

arXiv HTML PDF

Abstract

We develop a fast magnetic Josephson junction (MJJ)—a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient single flux quantum (SFQ) circuits. We present experimental results for superconductor-insulator-ferromagnet-superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 μV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ∼30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.

DOI: 10.1063/1.4723576

Related papers

Magnetic Josephson Junctions With Superconducting Interlayer for Cryogenic Memory

I. V. Vernik, V. V. Bol'ginov, Sergey V. Bakurskiy +4 more

We investigate a Magnetic Josephson Junction (MJJ) - a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energy-efficient single flux quantum (SFQ) circuits. The superconductor-insulator-superconductor-ferromagnet-superconductor (SIS'FS) MJJs are analyzed both experimentally and theoretically. We found that the properties of SIS'FS junctions fall into two distinct classes based on the thickness of S'layer. We fabricate Nb-Al/AlOx-Nb-PdFe-Nb SIS'FS MJJs using a co-processing approach with a combination of HYPRES and ISSP fabrication processes. The resultant SIS'FS structure with thin superconducting S'-layer is substantially affected by the ferromagnetic layer as a whole. We fabricate these type of junctions to reach the device compatibility with conventional SIS junctions used for superconducting SFQ electronics to ensure a seamless integration of MJJ-based circuits and SIS JJ-based ultra-fast digital SFQ circuits. We report experimental results for MJJs, demonstrating their applicability for superconducting memory and digital circuits. These MJJs exhibitIcRnproduct only ~ 30% lower than that of conventional SIS junctions co-produced in the same fabrication. Analytical calculations for these SIS'FS structures are in a good agreement with the experiment. We discuss application of MJJ devices for memory and programmable logic circuits.

arXiv:1212.0815IEEE Transactions on Applied SuperconductivityDec 10, 2012150 citations

Magnetic Josephson Junction Technology for Digital and Memory Applications

V. V. Ryazanov, V. V. Bol’ginov, Danila S. Sobanin +4 more

The lack of dense, fast, energy efficient memory has been the main detractor for multiple superconducting digital projects in the past. Recently, fundamental physics research in superconductor-ferromagnet thin-film tunnel structures created a new opportunity to solve this long-standing problem. Superconductivity and ferromagnetism, two deeply antagonistic electronic properties, can co-exist in form of Magnetic Josephson Junctions (MJJs). The superconducting-ferromagnetic MJJs are electrically compatible with traditional superconductor-insulator-superconductor (SIS) Josephson junctions (JJs) used for digital energy-efficient single flux quantum (eSFQ/ERSFQ) circuits. Both MJJ and JJ circuits have similar fabrication process and can be integrated on a single chip. As a result, a combination of MJJs and JJs can be used to form addressable memory cells, energy-efficient memory periphery circuits and programmable logic elements. In this paper, we present the test results of superconductor-insulator-ferromagnet-superconductor (SIFS) MJJs showing their applicability for superconducting spintronic memory and digital circuits.

Physics ProcediaJan 1, 2012120 citations

Shunt-free cryogenic memory using ferromagnetic insulator-based Josephson junctions

Pramod K. Sharma, Avradeep Pal

Magnetic Josephson junctions are the preferred candidate devices for designing fast and scalable cryogenic memory elements. This is especially the case for rapid single-flux quantum-based superconducting electronics, where the speed mismatch between logic and memory elements have remained a long-standing challenge. In this Letter, we demonstrate a simple tri-layer Josephson memory device using ferromagnetic insulating (FI) GdN-based S/FI/S vertical mesa-type junctions, with reliable nonvolatile memory operation without the need of a shunt resistor at 4.2 K. The characteristic frequency of our devices is approximately 90 GHz, corresponding to an IcRn product of 177 μV. We demonstrate a thorough study of the parameter spaces required for designing these devices and identify the scope for future improvements that can lead to further miniaturization and higher operating speed of these devices.

Applied Physics LettersJul 29, 20249 citations

High-Speed Memory Driven by SFQ Pulses Based on 0-π SQUID

Yuto Takeshita, Feng Li, Daiki Hasegawa +4 more

We propose a new cryogenic high-speed and low-power matrix memory required for achieving a high-performance superconductor computing system. The memory cell is based on the 0-π SQUID with conventional Josephson junctions (0-junctions) and a π-shifted ferromagnetic Josephson junction (π-junction). The memory state is stored in the form of two stable states in the 0-π SQUID. The π shift feature of the π-junction eliminates the need for any bias current or magnetic field for the formation of two states, i.e., the memory is non-volatile. In this memory, an impulse-shaped voltage signal generated in single-flux-quantum (SFQ) circuits is used for the write and read operations of the memory state. By using the pulses propagating in passive transmission lines, high-speed and low-power operation can be achieved because a recharging process determining the operation speed and the dominant energy consumption can be eliminated. We fabricated the 0-π SQUID-based pulse-driven memory cells with an SFQ driver. From the static characteristics, we confirmed that the current needed for rewriting can be sufficiently reduced. In addition, we successfully demonstrated the correct write operation in the memory cell by the SFQ pulse train transmitted from the SFQ driver via the passive transmission line.

IEEE Transactions on Applied SuperconductivityFeb 20, 202126 citations

Nonvolatile memory cell using a superconducting-ferromagnetic π Josephson junction

Junwen Zeng, Lei Chen, Xianghai Zhong +8 more

Abstract Storage of a single magnetic flux quantum in a superconducting loop containing a Josephson junction represents a promising unit cell configuration for construction of a cryogenic memory of superconducting digital circuits. However, application of a DC bias current is required for operation of such a memory cell to maintain trapping of the flux quantum in the storage loop. In this work, we present a superconducting memory cell that uses a superconducting-magnetic π junction. The cell characteristics show flux quantum hysteresis centering at the zero-bias current. We develop a fabrication process that combines superconductor–ferromagnet–superconductor (SFS) junctions with superconductor–normal metal–superconductor (SNS) junctions. The critical current density of the SFS junctions shows a 0–π oscillation as a function of the ferromagnetic layer thickness. The formation of the π junction is confirmed further by the flux modulation curves of a superconducting quantum interference device made from SNS junctions with an additional SFS junction.

Superconductor Science and TechnologyJul 13, 20229 citations

Superconductor digital circuits with π junctions alone

Feng Li, Yuto Takeshita, Masamitsu Tanaka +1 more

We adopt superconductor/ferromagnet/insulator/superconductor (SFIS) Josephson junctions (JJs) as both switching JJs and intrinsic π phase shifters in superconductor digital circuits. The critical current density (Jc) and characteristic voltage (Vc) of the SFIS junctions are about 22 A/cm2 and 22 μV, respectively. The intrinsic π phase shift is confirmed by measuring the suppressed nominal critical current Icn and half-period-shifted modulation pattern of a π–π–π superconducting quantum interference device (SQUID) that contains three π-JJs in a superconducting loop. A single-flux-quantum (SFQ) circuit composed of a DC/SFQ, Josephson transmission line (JTL), and SFQ/DC converter based on SFIS JJs alone is demonstrated at 4.2 K. The energy dissipation of the SFQ/DC converter decreases by 80% because some JJs are self-biased by the π phase shifter. The intrinsic circulating currents induced by the π phase shifters lead to a narrow bias margin (±5%) and even error function, which can be solved by parameters optimization or circuit initialization in the future. The half-modulation period (Φ0/2) of a half-flux-quantum (HFQ) SQUID (a partial HFQ JTL) exhibits propagation of HFQ between π–π–π SQUIDs, indicating that more complex HFQ circuits can be developed with π-JJs alone in the future.

Applied Physics LettersApr 17, 202310 citations