Niobium Josephson junctions with doped amorphous silicon barriers

Kröger, H.; Potter, C.N.; Jillie, D. W.

doi:10.1109/tmag.1979.1060117

Cited by 29 publications

(10 citation statements)

References 7 publications

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“…By inspecting the published I-V characteristics of junctions with doped Si barriers, we noted that IcRN products reported for nonhysteretic JJs with various barrier thicknesses, doping types and levels in [10]- [12], [34]- [37] and other publications do not exceed 0.36 mV, the same value as the IcRN of critically damped Nb/AlOx-Al/Nb junctions at Jc = 10 μA/μm 2 . Therefore, it appears to be not possible to optimize junctions with doped Si barriers by varying d and x to produce nonhysteretic junctions with values of Jc in the practical range, Jc ≤ 2 mA/μm 2 , and IcRN products comparable to values obtained in self-shunted tunnel junctions, about πΔNb/2 ≈ 2 mV.…”

Section: B Nb/si:nb/nb Josephson Junctionsmentioning

confidence: 84%

“…Some promise was shown by Nb-based JJs with amorphous Si (a-Si) barriers doped by Nb, W, or other dopants forming deep impurity levels close to the middle of Si band gap. They were proposed and investigated a long time ago; see, e.g., [10], [34], and references therein to even earlier work. Recently, JJs with a-Si:Nb barriers [35], [36] found applications in programmable Josephson voltage standards and waveform synthesizers developed at NIST USA and PTB Germany.…”

Section: B Nb/si:nb/nb Josephson Junctionsmentioning

confidence: 99%

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Superconductor Electronics Fabrication Process with MoNx Kinetic Inductors and Self-Shunted Josephson Junctions

Tolpygo

Bolkhovsky

Oates

et al. 2018

IEEE Trans. Appl. Supercond.

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Recent progress in superconductor electronics fabrication has enabled single-flux-quantum (SFQ) digital circuits with close to one million Josephson junctions (JJs) on 1-cm 2 chips. Increasing the integration scale further is challenging because of the large area of SFQ logic cells, mainly determined by the area of resistively shunted Nb/AlOx-Al/Nb JJs and geometrical inductors utilizing multiple layers of Nb. To overcome these challenges, we are developing a fabrication process with self-shunted high-Jc JJs and compact thin-film MoNx kinetic inductors instead of geometrical inductors. We present fabrication details and properties of MoNx films with a wide range of Tc, including residual stress, electrical resistivity, critical current, and magnetic field penetration depth λ0. As kinetic inductors, we implemented Mo2N films with Tc about 8 K, λ0 about 0.51 μm, and inductance adjustable in the range from 2 to 8 pH/sq. We also present data on fabrication and electrical characterization of Nb-based self-shunted JJs with AlOx tunnel barriers and Jc = 0.6 mA/μm 2 , and with 10-nm thick Si1-xNbx barriers, with x from 0.03 to 0.15, fabricated on 200-mm wafers by cosputtering. We demonstrate that the electron transport mechanism in Si1-xNbx barriers at x < 0.08 is inelastic resonant tunneling via chains of multiple localized states. At larger x, their Josephson characteristics are strongly dependent on x and residual stress in Nb electrodes, and in general are inferior to AlOx tunnel barriers.

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Section: B Nb/si:nb/nb Josephson Junctionsmentioning

confidence: 84%

Section: B Nb/si:nb/nb Josephson Junctionsmentioning

confidence: 99%

Superconductor Electronics Fabrication Process with MoNx Kinetic Inductors and Self-Shunted Josephson Junctions

Tolpygo

Bolkhovsky

Oates

et al. 2018

IEEE Trans. Appl. Supercond.

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“…Among devices with direct conduction, relatively high values of V c required for digital applications have been demonstrated by Nb-based junctions with amorphous Si barriers doped by various impurities creating deep levels near the middle of the band gap, like Nb, W, etc. ; see [128] and references therein, [129-[131], and many older works, e.g., [132]- [134]. From the author's point of view, their only advantage is that, at large levels of doping (~ 10%), selfshunting and nonhysteretic behavior is obtained.…”

Section: Vlsi Technology Developmentmentioning

confidence: 99%

Superconductor digital electronics: Scalability and energy efficiency issues (Review Article)

Tolpygo¹

2016

Low Temperature Physics

178

115

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Abstract-Superconductor digital electronics using Josephson junctions as ultrafast switches and magnetic-flux encoding of information was proposed over 30 years ago as a sub-terahertz clock frequency alternative to semiconductor electronics based on complementary metal-oxide-semiconductor (CMOS) transistors. Recently, interest in developing superconductor electronics has been renewed due to a search for energy saving solutions in applications related to high-performance computing. The current state of superconductor electronics and fabrication processes are reviewed in order to evaluate whether this electronics is scalable to a very large scale integration (VLSI) required to achieve computation complexities comparable to CMOS processors. A fully planarized process at MIT Lincoln Laboratory, perhaps the most advanced process developed so far for superconductor electronics, is used as an example. The process has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm, and a thin superconducting layer for making compact high-kineticinductance bias inductors. All circuit layers are fully planarized using chemical mechanical planarization (CMP) of SiO 2 interlayer dielectric. The physical limitations imposed on the circuit density by Josephson junctions, circuit inductors, shunt and bias resistors, etc., are discussed. Energy dissipation in superconducting circuits is also reviewed in order to estimate whether this technology, which requires cryogenic refrigeration, can be energy efficient. Fabrication process development required for increasing the density of superconductor digital circuits by a factor of ten and achieving densities above 10 7 Josephson junctions per cm 2 is described.

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“…High speed sensors within the gas stream at several places allow us to measure the instantaneous T, P, and m for frequencies up to [20][21][22][23][24][25][26][27][28][29][30] Slow speed germanium thermometers on the i sothermal izers are used to measure their temperature. Temperature control of the isothermal izers is critical to the operation of the system.…”

Section: Description Of Present Methodsmentioning

confidence: 99%

“…The Naval Research Laboratory has a joint effort with Sperry Research Center to fabricate all refractory superconducting tunnel devices with CVD deposited polysilicon barrier [23], [24].…”

mentioning

confidence: 99%

Refrigeration for cryogenic sensors and electronic systems

Zimmerman¹,

Sullivan²,

McCarthy³

1981

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There are, of course, some applications where lower temperatures are required in any case.In short, the purpose of the first conference was to define the problem.The present conference was organized quite differently.It was open to all interested participants, and most papers were contributed.Invited papers are those by Roubeau and by Nisenoff, the former being a rather free-ranging discussion of some unconventional approaches to cryogenic technology, and the latter a comprehensive review of recent developments in high-T superconducting devices and materials.The contributed papers are on refrigeration concepts, systems and components suited to the support of cryogenic sensors and electronic systems below 20 K. Techniques and components developed for higher temperatures that are applicable to low-temperature refrigeration are included.In reviewing the progress that has been made during the last three years, it is apparent that the desired goals have not been achieved.Nevertheless, there have been some notable developments.Several funding agenices, in particular the Office of Naval Research and Wright-Patterson Air Force Base, are now supporting conceptual studies and developments of low-power cryocoolers for superconducting instruments, and a number of such projects are underway. As described in this report, a helium 1 iquefier-cryocooler for a superconducting computer has been built and is being tested. Also in this report are papers demonstrating increasing interest and emphasis on gas refrigerators using resonant mechanical systems driven by linear reciprocating electric motors and supported by gas bearings or magnetic suspensions. These systems offer the potential of ultimate simplicity, freedom from contamination, long life, and (eventually) low cost. Although the operation of such systems may at ftrst glance appear somewhat subtle, we might point out the obvious, namely that the mathematical description of a resonant reciprocating cryocooler is identical (except for non-linearities) in all essentials to that of coupled electrical resonant circuits with a sinusoidal driving force, a system as familiar as sunrise to most electronic engineers (Probably even the non-linearities are analogous to a considerable extent).Finally, a book by Prof. Q. Walker, Stirling Machines, has just been published by Plenum Press, and a companion book, Cryocoolers, is in press. These books are a very comprehensive source of information and references on the whole technology.• 1 Approximatley one-half (57) of the participants at this meeting returned a questionnaire, distributed during the meeting, with answers to three questions. To the question "Has the conference been worthwhile?", 56 said yes and 1 said somewhat.To "Should it be held again?", the answer was yes, unanimously.To "At what interval?" 11 said 1 year, 33 said 2 years, 12 said 3 years, and 1 said 4 years.There were several useful comments and criticisms. One was to allow more lead time and to provide for distribution of reprints at the meeting.Some comments concern...

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Niobium Josephson junctions with doped amorphous silicon barriers

Cited by 29 publications

References 7 publications

Superconductor Electronics Fabrication Process with MoNx Kinetic Inductors and Self-Shunted Josephson Junctions

Superconductor Electronics Fabrication Process with MoNx Kinetic Inductors and Self-Shunted Josephson Junctions

Superconductor digital electronics: Scalability and energy efficiency issues (Review Article)

Refrigeration for cryogenic sensors and electronic systems

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