Experimental Demonstration of a Josephson Magnetic Memory Cell With a Programmable $\pi$-Junction

Dayton, Ian; Sage, Tessandra; Gingrich, Eric C.; Loving, Melissa; Ambrose, T.; Siwak, Nathan; Keebaugh, Shawn; Kirby, Christopher; Miller, Donald L.; Herr, Anna; Herr, Q.P.; Naaman, Ofer

doi:10.1109/lmag.2018.2801820

Cited by 80 publications

(53 citation statements)

References 26 publications

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“…Our interest in Josephson junction memories was inspired in part by a recent burst of interest to programmable magnetic πjunctions and their use in "magnetic" junction memories; see, for example, MJRAM [36] and references therein. It could be noted that the equivalent circuit of a MJRAM cell in [36] is somehow similar to the schematics of a VT cell shown in Fig. 1a.…”

Section: Discussionmentioning

confidence: 99%

Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories

Семенов

Polyakov

Tolpygo

2019

IEEE Trans. Appl. Supercond.

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Arrays of Vortex Transitional (VT) memory cells with functional density up to 1 Mbit/cm 2 have been designed, fabricated, and successfully demonstrated. This progress is due to recent advances in design optimization and in superconductor electronics fabrication achieved at MIT Lincoln Laboratory.As a starting point, we developed a demo array of VT cells for the 100-μA/μm 2 MIT LL fabrication process SFQ5ee with 8 niobium layers. The studied two-junction memory cell with a twojunction nondestructive readout occupied 168 μm 2 , resulting in an over 0.5 Mbit/cm 2 functional density. Then, we reduced the cell area down to 99 μm 2 (corresponding to over 0.9 Mbit/cm 2 functional density) by utilizing self-shunted Josephson Junctions (JJs) with critical current density, Jc of 600 µA/μm 2 and eliminating shunt resistors. The fabricated high-Jc memory cells were fully operational and possessed wide Read/Write current margins, quite close to the theoretically predicted values. We discuss approaches to further increasing the integration scale of superconductor memory and logic circuits: a) miniaturization of superconducting transformers by using soft magnetic materials; b) reduction of JJ area by using planar high-Jc junctions similar to variable thickness bridges.

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Section: Discussionmentioning

confidence: 99%

Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories

Семенов

Polyakov

Tolpygo

2019

IEEE Trans. Appl. Supercond.

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“…The first experimental report by Bell et al used a Co/Cu/Permalloy PSV to control the critical current of the junction 28 . Promising electrical engineering architectures which integrate the ferromagnetic Josephson junction bits into scalable memory cells compatible with current technology exists, and recently PSV devices have been demonstrated by several groups [29][30][31][32][33][34][35][36][37][38] . To date, all experimental works on PSV Josephson junctions have considered in-plane F layers as used by Bell et al.…”

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confidence: 99%

Spin-valve Josephson junctions with perpendicular magnetic anisotropy for cryogenic memory

Satchell

Shepley

Algarni

et al. 2020

Applied Physics Letters

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We demonstrate a Josephson junction with a weak link containing two ferromagnets, with perpendicular magnetic anisotropy and independent switching fields in which the critical current can be set by the mutual orientation of the two layers. Such pseudospin-valve Josephson junctions are a candidate cryogenic memory in an all superconducting computational scheme. Here, we use Pt/Co/Pt/CoB/Pt as the weak link of the junction with d Co = 0.6 nm, d CoB = 0.3 nm, and d Pt = 5 nm and obtain a 60% change in the critical current for the two magnetization configurations of the pseudospin-valve. Ferromagnets with perpendicular magnetic anisotropy have advantages over magnetization in-plane systems which have been exclusively considered to this point, as in principle the magnetization and magnetic switching of layers in the junction should not affect the in-plane magnetic flux.Josephson junctions containing ferromagnetic weak links have been of interest over the last twenty years due to the additional physics present when pair correlations from the superconductor (S) interact with the exchange field of the ferromagnet (F) 1-5 . Examples include the tuning of the ground state phase difference across a junction from 0 to π by changing the thickness of the F layer 6-9 . The additional physics can also drive the generation of m s = ±1 spin-triplet pair correlations with spin projection along the magnetization axis of the F layer in the junction 10 , leading to pair propagation through the F layer over much longer distances than the singlet component [11][12][13][14][15][16][17]

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“…Several alternatives have been proposed [6]. This paper focuses on a memory concept developed by workers at Northrop Grumman Corporation called Josephson Magnetic Random Access Memory or JMRAM [7]. The active element in a JMRAM memory cell is a Josephson junction containing two or more ferromagnetic layers, whose characteristics depend on the magnetic configuration of those layers.…”

Section: Introductionmentioning

confidence: 99%

“…( not consider so-called "φ 0 -junctions" here, which can have an arbitrary ground-state phase difference across the terminals.) This digital aspect of the readout provides greater margins for the properties of the active element, hence more robust performance of a large-scale memory array [7].…”

Section: Introductionmentioning

confidence: 99%

Spin-Singlet and Spin-Triplet Josephson Junctions for Cryogenic Memory

Birge¹,

Houzet²

2019

IEEE Magn. Lett.

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Due to the ever increasing power and cooling requirements of large-scale computing and data facilities, there is a worldwide search for low-power alternatives to CMOS. One approach under consideration is superconducting computing based on single-flux-quantum logic. Unfortunately, there is not yet a low-power, high-density superconducting memory technology that is fully compatible with superconducting logic. We are working toward developing cryogenic memory based on Josephson junctions that contain two or more ferromagnetic (F) layers. Such junctions have been demonstrated to be programmable by changing the relative direction of the F layer magnetizations. There are at least two different types of such junctions -those that carry the innate spin-singlet supercurrent associated with the conventional superconducting electrodes, and those that convert spin-singlet to spin-triplet supercurrent in the middle of the device. In this paper we compare the performance and requirements of the two kinds of junctions. Whereas the spin-singlet junctions need only two ferromagnetic layers to function, the spin-triplet junctions require at least three. In the devices demonstrated to date, the spin-singlet junctions have considerably larger critical current densities than the spin-triplet devices. On the other hand, the spin-triplet devices have less stringent constraints on the thicknesses of the F layers, which might be beneficial in large-scale manufacturing.

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Experimental Demonstration of a Josephson Magnetic Memory Cell With a Programmable $\pi$-Junction

Cited by 80 publications

References 26 publications

Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories

Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories

Spin-valve Josephson junctions with perpendicular magnetic anisotropy for cryogenic memory

Spin-Singlet and Spin-Triplet Josephson Junctions for Cryogenic Memory

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