Magnetic Josephson Junctions on Nb Four-layer Structure for Half Flux Quantum Circuits

Hasegawa, Daiki; Takeshita, Yuto; Sano, Kôkichi; Tanaka, Masamitsu; Yamashita, Taro

doi:10.1109/isec46533.2019.8990908

Cited by 5 publications

(6 citation statements)

References 4 publications

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“…Use of a non-tunneling ferromagnetic junction with a superconductor/ferromagnet/superconductor (SFS) structure allows a large K to be easily achieved. Experimentally, K ranged from 100 to 1000 [24]. Even if the π-junction has a relatively small McCumber-Stewart parameter (β c ≪ 1), the operating frequency of the HFQ circuit is not affected.…”

Section: Currently Available Hfq Circuitsmentioning

confidence: 99%

“…Previously, we proposed a half-flux-quantum (HFQ) circuit that utilized I nominal to reduce basic power consumption and provide a phase jump of π, rather than 2π, during a switching event [23]. Experimentally, we showed that there is no hysteresis in the current-voltage characteristics of 0-0-π SQUIDs [24]. Thus, HFQ circuits can be operated over a wide bias voltage range without any need for shunt resistors parallel to the junctions.…”

Section: Introductionmentioning

confidence: 99%

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Low-power high-speed half-flux-quantum circuits driven by low bias voltages

Takeshita

Hasegawa

et al. 2021

Supercond. Sci. Technol.

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Half-flux-quantum (HFQ) circuits store and propagate half-flux quanta. The basic circuit element is a 0-π SQUID, which is a superconducting quantum interference device with a conventional Josephson junction (0-junction) and a π-shifted ferromagnetic junction (π-junction). A 0-π SQUID achieves a small critical current in the absence of an external magnetic field, thus reducing power consumption. It is easy to set up 0-0-π SQUIDs with two 0-junctions and a π-junction which serves as a π phase-shifter. We simulated 0-0-π SQUID-based HFQ circuits driven by low bias voltages, referred to as LV-HFQ circuits. In these circuits, shunt resistors are not required for switching junctions because there is no hysteresis in the current–voltage characteristics of 0-0-π SQUIDs. We estimated the power consumption and maximum operating frequency of an HFQ Josephson transmission line based on 0-0-π SQUIDs. When operating at 43.5 GHz, the power dissipation of a single element composed of a 0-0-π SQUID and a bias resistor fell to about 0.165 nW when biased at 60 μV. The LV-HFQ circuit is potentially more power-efficient than all other currently available superconducting logic circuits.

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Section: Currently Available Hfq Circuitsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Low-power high-speed half-flux-quantum circuits driven by low bias voltages

Takeshita

Hasegawa

et al. 2021

Supercond. Sci. Technol.

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“…Therefore, choosing the correct materials and fabrication method for reducing J C spread, controlling I C value, and superconductor film quality are the main challenges in fabrication. Recently, many attempts at large-scale fabrication have shown progress in this regard [32,33].…”

Section: All-jj Circuits 21 2f-junctionmentioning

confidence: 99%

High-density superconductive logic circuits utilizing 0 and π josephson junctions

Razmkhah,

Pedram

2024

Eng. Res. Express

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Superconductor Electronics (SCE) is a fast and power-efficient technology with great potential for overcoming conventional CMOS electronics' scaling limits. Nevertheless, the primary challenge confronting SCE today is its integration level, which lags several orders of magnitude behind CMOS circuits. In this study, we have innovated and simulated a novel logic family grounded in the principles of phase shifts occurring in 0 and π Josephson junctions. The fast phase logic (FPL) eliminates the need for large inductor loops and shunt resistances by combining the half-flux and phase logic. Therefore, the Josephson junction (JJ) area only limits the integration density. The cells designed with this paradigm are fast, and the clock-to-Q delay for logic cells is about 4ps. While maintaining over 50% parameter margins for wiring cells. This logic is power efficient and can increase the integration by at least 100 times in the SCE chips.

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“…2.1. 0-0-π SQUIDs 0-0-π SQUIDs were fabricated using a hybrid process [23,24] that comprised a high-speed standard process (HSTP) and a π-junction process. The underlying 0-junction structures were prepared using the HSTP of the National Institute of Advanced Industrial Science and Technology.…”

Section: Preparationmentioning

confidence: 99%

“…Nb/PdNi/Nb-sandwich MJJs were formed on the top layer of the underlying structures. The PdNi layer was 30 nm-thick and was expected to form π-junctions [24]. Figure 2 The 0-0-π SQUID schematic is shown in figure 2(b).…”

Section: Preparationmentioning

confidence: 99%

Direct observations of π-leaps of superconducting phase differences in π-junction-based SQUIDs

Takeshita

Higashi

et al. 2023

Supercond. Sci. Technol.

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We directly observed π-leaps of superconducting phase differences in π-junction-based superconducting quantum interference devices (SQUIDs). The SQUIDs studied here are formed by introducing a π-junction to a conventional-junction (0-junction)-based direct current (DC)-SQUID, which is referred to as the 0-0-π SQUID. Either clockwise- or counter-clockwise-circulating current flows in the 0-0-π SQUID spontaneously because of a π-phase shift of the π-junction. In other words, the 0-0-π SQUID has a bistable state corresponding to the directions of circulating currents. π-leaps are generated in transiting between the two states of the bistable state. π-leaps are an ultra-fast phenomenon and are difficult to be observed as are. We prepared a half-flux quantum (HFQ)-SQUID that comprised two 0-0-π SQUIDs. π-leaps are reflected in a static characteristic, that is, a modulation pattern of the critical current in the HFQ-SQUID. We formed π-junctions with the PdNi layer on 0-junction-based circuits supplied by the National Institute of Advanced Industrial Science and Technology. The modulation pattern of the HFQ-SQUID had a period corresponding to π-leaps as expected, although some microstructures were observed. We demonstrated that the microstructures originated from the asymmetry inside each 0-0-π SQUID by analysing the relationship between the phase change of 0-0-π SQUIDs and the modulation patterns.

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Magnetic Josephson Junctions on Nb Four-layer Structure for Half Flux Quantum Circuits

Cited by 5 publications

References 4 publications

Low-power high-speed half-flux-quantum circuits driven by low bias voltages

Low-power high-speed half-flux-quantum circuits driven by low bias voltages

High-density superconductive logic circuits utilizing 0 and π josephson junctions

Direct observations of π-leaps of superconducting phase differences in π-junction-based SQUIDs

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