Niobium oxide-barrier tunnel junction

Broom, R. F.; Raider, S. I.; Oosenbrug, A.; Drake, R.E.; Walter, W.

doi:10.1109/t-ed.1980.20137

Cited by 114 publications

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“…The native oxides and sub oxides of transition metals often show poor insulating properties [12], which are undesirable for many electronic applications. These problems have also been experienced in, for example, superconducting Nb/NbO x /Nb tunnel junctions [13]. Some of the Nb suboxides showed metallic properties and lead to microshorts.…”

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confidence: 95%

Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Gronckel

Kohlstedt

Daniels

2000

Applied Physics A: Materials Science & Processing

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Aluminum films with thicknesses ranging from 1 nm to 12 nm have been sputtered on 20 nm thick Co layers. The properties of the Co/Al bilayers were studied by X-ray photoemission spectroscopy (XPS) and spin-echo nuclear magnetic resonance (NMR). Both methods show independently that a 1 nm Al film covers the Co surface completely. XPS and NMR also showed that layers thicker than 1 nm Al are not oxidized completely in ambient air. Similarities to and deviations from niobium with Al overlayers (Nb/Al) are described. Prerequisites for the fabrication of tunneling magnetoresistance devices based on Co or NiFe ferromagnets and an aluminum oxide barrier are discussed. PACS: 82.80.Ch; 82.80.Pv; 68.55.-aResearch on magnetoresistance has been particularly active since the discovery of the giant magnetoresistance (GMR) effect in layered magnetic systems [1,2]. In recent years magnetic tunnel junctions (MTJ) have emerged as another source of large magnetoresistance effects [3][4][5][6]. Such devices consist of a ferromagnetic (FM) top and bottom electrode separated by an insulating layer (I) and show large changes in resistance when a magnetic field turns the relative orientation of the magnetization of the ferromagnetic electrodes from parallel to anti-parallel.Although the phenomenon of tunneling magnetoresistance (TMR) in ferromagnetic junctions was already identified more than two decades ago by Julliere [7], it is only recently that one has been able to grow junctions with reproducible characteristics and significant changes in the magnetoresistance (20%) at room temperature [3,5]. The (compared to GMR systems) inherent high absolute resistance -because of the tunneling effect -and the therefore easily measurable magnetoresistance give them a high potential for low-power * Present address: magnetic field sensors [8,9] and nonvolatile magnetic random access memory (MRAM) [10,11].The quality of tunnel junctions and the reproducibility in fabrication in general depend critically on the properties of the, typically, 1 nm to 2 nm thin insulating tunnel barrier. Tunneling is moreover extremely surface sensitive in that it displays the band structure of the electrode surface very close to the barrier insulator. Good barrier uniformity without pinholes is the key aspect to obtain current-voltage (I-V ) characteristics with low leakage currents. These conditions are not fulfilled for all barrier materials. It tends to be difficult to form high-quality and highly insulating tunnel barriers in many cases, especially if a transition metal is used as the base electrode. The native oxides and sub oxides of transition metals often show poor insulating properties [12], which are undesirable for many electronic applications. These problems have also been experienced in, for example, superconducting Nb/NbO x /Nb tunnel junctions [13]. Some of the Nb suboxides showed metallic properties and lead to microshorts. A decade ago, 'artificial' barriers were demonstrated to be a successful solution [14]. Artificial refers in this context to tunne...

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confidence: 95%

Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Gronckel

Kohlstedt

Daniels

2000

Applied Physics A: Materials Science & Processing

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“…(27), Josephson penetration length 5.5 μm, normalized gap frequency k = 3.3, and surface damping parameter β = 0.02. We took the pair current suppression parameter α supp = 0.7 as a reasonable estimate for the strong coupling correction for Nb junctions [20,21] (the proximity effect [19,22] is expected to have a smaller effect in our junctions, not exceeding 10% [18]). To improve computation of dc voltage we used the optimum filtration procedure for a sinusoidal signal, introduced in Ref.…”

Section: Comparison To Experimental Resultsmentioning

confidence: 99%

“…Influence of the idle region on the dynamics of FFO has been neglected in our theoretical treatment (except for the renormalization of Josephson penetration length on which it has an effect [115,116]). The proper account of the idle region requires upgrading the model (21) to the full 2D problem (15) coupled to the Maxwell equations inside the idle region. On the other hand, value of MFFCs may also be influenced by coupling to the load and affected by the losses in the matching circuitry.…”

Section: Comparison To Experimental Resultsmentioning

confidence: 99%

“…Equation (26) should be solved alongside the integrodifferential equation (21). We employ the same approach for evolving Eq.…”

Section: Model Of Josephson Flux-flow Oscillatormentioning

confidence: 99%

“…It was later suggested that, in fact, either sign is possible, while the disagreement between the theory and experiments can be explained by broadening mechanisms which result in smearing of the Riedel peaks [16,17]. The MTT has also been found to overestimate the value of the critical current, which in real junctions turns out to be depressed by strong coupling and/or proximity effects [18][19][20][21][22]. In practice, one can account for this discrepancy by a phenomenological suppression parameter [23].…”

Section: Introductionmentioning

confidence: 99%

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Josephson flux-flow oscillator: The microscopic tunneling approach

2017

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Citation: GULEVICH, D.R., KOSHELETS, V.P. and KUSMARTSEV, F.V., 2017.Josephson flux-flow oscillator:The microscopic tunneling approach.Physical Review B, 96 (2), 024515-1 -024515-12.Additional Information:• We elaborate a theoretical description of large Josephson junctions which is based on Werthamer's microscopic tunneling theory. The model naturally incorporates coupling of electromagnetic radiation to the tunnel currents and, therefore, is particularly suitable for description of the self-coupling effect in Josephson junction. In our numerical calculations we treat the arising integro-differential equation, which describes temporal evolution of the superconducting phase difference coupled to the electromagnetic field, by the Odintsov-Semenov-Zorin algorithm. This allows us to avoid evaluation of the time integrals at each time step while taking into account all the memory effects. To validate the obtained microscopic model of large Josephson junction we focus our attention on the Josephson flux-flow oscillator. The proposed microscopic model of flux-flow oscillator does not involve the phenomenological damping parameter, rather the damping is taken into account naturally in the tunnel current amplitudes calculated at a given temperature. The theoretically calculated current-voltage characteristics is compared to our experimental results obtained for a set of fabricated flux-flow oscillators of different lengths.

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Edge‐junction type nanometer bridge

Yamashita

Hamasaki

Matsumoto

et al. 1985

Electron Comm Jpn Pt II

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An edge‐junction type nm (nanometer) bridge is fabricated which has bridges on the joint of the edges of two Nb films. Each nm bridge has an effective length of less than 50 nm, width about 2 μm, and thickness from 30 to 60 nm. To make a good edge‐junction type nm bridge, it is necessary to form a sharp edge on an Nb film. For this purpose, dry‐etching with a teflon holder in an He gas was used. Voltage steps up to about about 100 μV induced by a microwave were observed in the fabricated device, and the value of IORn greater than 50 μV was obtained. By measuring the threshold characteristic of a DC‐SQUID consisting of this nm bridge, it was confirmed that the current‐phase relation of the bridge is sinusoidal. The temperature range in which this sinusoidal relation is kept is as wide as 4 to 6 K approximately.

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Niobium oxide-barrier tunnel junction

Cited by 114 publications

References 0 publications

Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Josephson flux-flow oscillator: The microscopic tunneling approach

Edge‐junction type nanometer bridge

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