Temperature dependence of Nb penetration depth measured by a resistive method

Besides the conventional method of measuring the penetration depth of Nb superconductors in Nb/AlO_x/Nb Josephson junction, a simple resistive method is applied in this study. With the applied magnetic field parallel to the junction plane, resistive measurement of resistance–temperature characteristics in a given magnetic field or resistance–magnetic field curves at a fixed temperature show resistance peaks whenever the total magnetic flux through the junction equals an integral multiple of the flux quantum. We demonstrate how to determine the penetration depth from such measurements and discuss its temperature dependence in terms of fundamental film properties.     

Josephson junction with an amorphous silicon barrier

A Josephson junction Nb/Si/Nb with a 10 nm thick amorphous silicon barrier is studied. The upper electrode contains a 2 nm thick sublayer of amorphous phase adjacent to the barrier, as revealed by cross-sectional TEM. Thus, the junction can be considered as a S-I-N-S system with the N layer represented by amorphous niobium. Peculiarities in the I–V and Δ(T) dependencies are observed and explained as a consequence of a proximity effect present in the upper electrode.     

Nonequilibrium phenomena in nonsymmetrical superconducting double-barrier structure Nb/NbOx/Al/AlOx/Nb

Tunneling structure Nb/NbO_x/Al/AlO_x/Nb with thin barrier in the Nb/NbO_x/Al junction and 4–6 nm thick Al interlayer was prepared and experimentally studied. Pair breaking at the tunneling processes in one junction produces nonequilibrium state of quasiparticle density in Al interlayer and consequently nonequilibrium tunneling processes in the whole structure. All joined effects, namely gap voltage suppression, presence of negative differential resistance at gap voltage and effects induced by applying of microwave radiation are similar to those observed on stacked Nb/Al/AlO_x/Nb tunnel junction current-voltage characteristics. Results may be used for the interpretation of behavior of high current density SNS or SIS type multilayers of low and high temperature superconductor structures.     

Tantalum and niobium as a diffusion barrier between copper and silicon

The efficiency of Ta and Nb films as diffusion barriers between thin Cu film and Si substrate has been studied using Auger electron spectroscopy, X-ray diffraction, optical microscopy, scanning electron microscopy and sheet resistance measurements. Two kinds of system were prepared by electron-beam evaporation: Cu/Ta (or Nb)/Si and Cu/Ta (or Mb) SiO₂/Si. The samples were annealed at temperatures from 400 to 800C in a vacuum of 1 × 10^–7 torr (13 Pa) for 30 min. In the Cu/Ta (or Nb)/Si system, the thermal stability was determined by interdiffusion at local sites, forming suicides, whereas the Cu/Ta (or Nb)/SiO₂/Si system degraded by interdiffusion at the interface between Ta (or Nb) and Cu. It appears that Ta is a more effective diffusion barrier than Nb for both kinds of system. This difference in the barrier effect of the transition metals is attributed to differences between oxygen segregation at grain boundaries of barrier layers and differences between diffusion coefficients through barrier layers. It is suggested that the driving force for interdiffusion may play a major role in the reaction that determines the thermal stability of a given contact system; this suggestion is based on the fact that the interdiffusion in Cu/barrier/Si systems is suppressed by interposing an SiO₂ layer in the Si substrate.     

约瑟夫森结阵器件的研究进展

介绍了约瑟夫森效应在电压基准方面的应用,综述了目前国内外对用于电压基准的约瑟夫森结阵的研究和发展过程,重点介绍了国内用于电压基准的Nb/NbxSi1-x/Nb单结的研究进展。     

Josephson semiconductor interface circuit

This paper describes an output interface circuit which allows Josephson circuits to communicate with semiconductor circuits. The circuit combines Josephson and GaAs drivers to drive a 50 μ load at a signal level of semiconductor circuits. The output voltage of 2.8 mV (usual for Josephson gates using Nb/AlO_x/Nb junctions) was increased to 1.7 V. The interface circuit has been operated up to 800 MHz.     

The influence of lanthanum doping position in ultra-thin HfO2 films for high-k gate dielectrics

Lanthanum dopant positioning at HfO₂ ultra-thin films was achieved by the co-sputtering method. The physical properties of graded doping HfO₂/HfLaO/p-Si and HfLaO/HfO₂/p-Si structures after 850 °C postannealing were compared. The thickness of the monolayer was analyzed by X-ray reflectivity and confirmed by the multiple beam interference model. The HfO₂ and silicate phases were characterized by X-ray diffraction patterns. It is found that crystallization depends on the ratio of stacked film thicknesses, and the HfLaO/HfO₂/Si structure has more silicate formation at the interface than the HfO₂/HfLaO/Si structure. Metal-insulator-semiconductor capacitors were fabricated. The electrical properties including leakage current, conduction mechanism, flatband voltage shift, and barrier height were studied.     

The role of Ar+, CH+4, O+2and backscattered Pb+ ions during Nb/Oxide/PbAuIn edge junction fabrication

A study has been made of the correlation between energetic positive plasma ions and the resulting Josephson tunnel barriers fabricated in an RF plasma. Typical edge junction current densities of 4000 Amp/cm²and Vm's of 25 mV were achieved. An in-situ mass spectrometer system was designed to extract, energy analyze, and identify the positive ion species incident on the RF cathode/sample surface. The argon positive ion measurements are correlated to Nb sputter rates and back scattered Pb and Nb rates - required for a clean Nb interface. The CH4positive ions are correlated to the growth of niobium carbide which reduces sub-oxide formation while optimizing junction quality. Finally the niobium oxide growth is correlated to the O2positive ion measurements. A simple model for oxide growth consisting of a time dependent O+2ion induced term and a time independent or very fast initial state term accounts for the known junction tunnel current dependencies on the RF plasma parameters of pressure, voltage, frequency, time, and ion to substrate angle.     

Theoretical and experimental investigation of phase coherence in shorted 2D arrays of high-T c Josephson junctions

Phase coherence in shorted 2D Josephson junction arrays shunted by resistive load in presence of disorder and magnetic field are investigated theoretically and experimentally. Using computer simulation it is shown that magnetic field negatively influences radiation properties of such arrays. Similarly to XY-type of 2D arrays maximal spread in junction parameters which allows stable phase-locking state is ±11%. 2D arrays with topology of those investigated theoretically were fabricated using high-T_c superconductor junction technology. The phase-coherence (voltage locking) between rows was observed experimentally.     

Microstructure of interfacial reaction zone in SCS-6 SiC fibre reinforced super α2 composites

Abstract

The microstructure of the interfacial reaction zone in SCS-6 SiC/super α2 composites heat treated at 700°C for 3000 h was investigated by means of analytical transmission electron microscopy. The very fine grained reaction layer adjacent to the carbon coating of the SiC fibre was found to consist of two sub layers, determined to be (Ti, V)C and (Ti, V,Nb)₅Si₃. The second layer is (Ti,Nb)C with large equiaxed grainsfollowed by the third layer consisting of the (Ti,Nb)₃(Al,Si)C phase. This layer is separated from the matrix by a fourth layer with the phase composition (Ti,Nb)₅(Si,Al)₃. At some interface positions, the two layers of(Ti,Nb)C and (Ti,Nb)₃(Al,Si)C are separated by an additional layer of the (Ti,Nb)₃(Si,Al) phase. The thickening of the interfacial reaction zone at 700°C is mainly due to the layers of (Ti, Nb)₃(Al,Si)C and (Ti,Nb)₃(Si,Al). The growth of these two layers is probably responsible for the degradation of the mechanical properties of the composites.     

Phase selection in rapidly solidified niobium-silicon alloys

X-ray diffraction analysis of rapidly solidified Nb-10 at.% Si and Nb-15 at.% Si alloy ribbons produced by electron beam melting and splat quenching shows that the phases present are primarily Nb + Nb₃Si, rather than the stable Nb + Nb₅Si₃ structure. The level of Nb₅Si₃ phase present is a function of the cooling rate and degree of undercooling.     

Analysis of magnetic field patterns of single Josephson tunnel junctions with large idle regions

We have experimentally investigated the effect of a combined lateral and longitudinal idle region on the magnetic field dependence of the critical current of Nb/Al−AlO_x/Nb Josephson junctions. All the samples were high quality devices with a good uniformity and reproducibility of the electrical parameters. An excellent agreement has been found with calculations of the magnetic field patterns made using a simple model of junction with idle region. A comparison with the magnetic field response of the same devices after a proper trimming of the idle region has also been done.     

Static Magnetic Flux Dynamics in One-Dimensional (1D) Josephson Lattices

We investigated static magnetic flux dynamical properties of one-dimensional lattices of Josephson junctions. The discretized wave equations of the Josephson junction lattice were solved using a generalized relaxation iteration algorithm. Numerical simulations indicated that transitions between periodic state and chaotic state will occur as the physical parameters and geometric parameters such as external current y _n, magnetic field h ₀, h, and the length of Josephson junction _n and d _n , varied. A shot length of the Josephson junction favors stable periodic states.     

Laser additive processing of functionally-graded Fe–Si–B–Cu–Nb soft magnetic materials

Laser additive manufacturing is a novel tool for processing compositionally-graded alloys that are challenging to process via a conventional route. This article discusses a novel combinatorial approach for assessing composition–microstructure–magnetic property relationships, using laser deposited compositionally-graded Fe–Si–B–Nb–Cu alloys (by changing the silicon to boron ratios). The microstructure of Fe–Si–B–Nb–Cu alloys with a lower Si to B ratio consists of dendritic α-Fe₃Si grains, with B and Nb partitioning to the inter-dendritic regions, resulting in the formation of Fe₃B grains. As the Si/B ratio increases, the (Fe, Nb) enriched eutectic phase was observed along with α-Fe₃Si grains; and no Fe₃B was observed. These microstructural changes with varying Si/B ratios significantly affect the magnetic properties of these laser-deposited soft magnetic alloys.     

约瑟夫森结Nb电极的实验研究

通过溅射Nb膜张力与氩（Ar）压强的关系，超导转变温度Tc，室温阻扰与液氮温度阻抗比RRT／RLN2，沉积中Ar浓度CAr与负偏压关系的测量和扫描电子显微镜的观察分析，对约瑟夫森结Nb电极作了研究。发现Ar压强在1．1Pa时，Nb膜呈现无应力状态；低负偏压下沉积的Nb膜晶粒结构是由致密膜到圆柱状。在偏压Ub＝－50V时，获得表面致密均匀、晶粒结构合适的Nb膜。对Nb膜用阳极氧化电压谱图（AVS）分析，证实沉积的Nb膜内不存在氧化物、寄生结和分层界面。     

Design and fabrication of thin-film resistive SQUIDs

A partly resistive superconducting quantum interference device, or, RSQUID, is a device utilizing the nonstationary Josephson effect. The resistive part of the device makes it possible to apply a voltage to the Josephson junctions and, in this way, to convert it into frequency. The transconductance ratio of this conversion is defined by the physical constants: 1/ø₀ = 2e/h (ø₀ is the flux quantum). Five different types of thin-film RSQUIDs are described in this paper. They are: an rf RSQUID with an rf pump and one Josephson junction, a dc RSQUID with dc bias and two Josephson junctions, and three topologically different double RSQUIDs with an rf pump, two Josephson junctions and two quantization loops. All five types were successfully fabricated. The resistive part of all devices was an S-N-S sandwich with Nb as the superconductor (S) and Cu as the normal metal (N). Such a design of the resistive part sets its resistance on the order of a few tens of .On leave from the Omsk State Technical University, Mir Prospect 11, 644050, Omsk, Russia.     

Josephson device for voltage measurement

This paper describes a new Josephson device with microwave integrated circuit for voltage standard. The circuit is essentially made of a resonator (Nb), the Josephson junction (Nb, NbOx, Pb-In) and a capacitive microstrip section (Pb-In) which ends the rf part; the dc connections are through Cauer Filters (Nb or Pb-In). A niobium film is deposited on the opposite side of the fused quartz substrate as a ground plane. The circuit is enclosed in a special package with outside dc and rf connections. The technology ensures very good cyclability and lifetime with storage at room temperature. In liquid helium (4.2 K) with a very weak rf power less than 0.5 milliwatts at the frequency resonance (11.5 GHz), 100 μ A high current steps were obtained near a polarization of 4.5 mV. These devices allows a precision of 1 × 10^?7 on the volt standard when used with a series-parallel divider of fixed value (ratio 225). The precise adjustment of the voltages is made by a slight drift of the rf frequency of the source, allowed by the high rf coupling factor of the device and the band width of its resonance.     

Effect of phosphorus on the copper diffusion barrier properties of electroless CoWP films

The properties of electroless CoWP barrier films with different phosphorus contents in Cu/CoWP/Si stacked samples were explored. The Cu/CoWP/Si stacked samples with 30 nm CoWP films, contained about 5.7, 8.2 and 10.8 at.% P, were prepared by electroless deposition, and then annealed in a rapid thermal annealer at a temperature between 300 and 700 °C. The effect of phosphorus content in CoWP film on the barrier properties in preventing copper diffusion and the failure of the Cu/CoWP/Si stacked samples after thermal annealing were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES), and sheet resistance measurement. Increasing the phosphorus content in the electroless CoWP film markedly improves the barrier properties. The failure temperature of Cu/CoWP/Si increased from 500 to 600 °C with the phosphorus content in CoWP film increasing from 5.7 to 10.8 at.%, and the failure of the Cu/CoWP/Si has mainly arisen from the interdiffusion of copper and cobalt during thermal annealing.     

Comparison of epitaxial growth of CoSi2 among Co/Ti, Co/Hf, and Co/Nb bilayers on (100)Si

Formation of epitaxial cobalt silicide film on (100)Si using Co/Ti, Co/Hf, and Co/Nb bilayers has been investigated. The degree of easiness in the epitaxial growth of CoSi₂ by annealing the metal bilayers on (100)Si at 800°C was found to strongly depend upon what thin metal layer was used as an epitaxy promoter. Perfect epitaxy of CoSi₂ was obtained using Co/Ti/(100)Si. Local epitaxy of CoSi₂ was obtained using Co/Ti/(100)Si, while epitaxy of CoSi₂ was not obtained for the Co/Nb/(100)Si system. Epitaxial growth of CoSi₂ in these Co/metal/Si systems seems to be related to the formation and decomposition of stable reaction barriers like Co–Ti–O and Hf–Si–O compounds at high temperatures. These stable reaction barriers formed at high temperatures make uniform diffusion of Co atoms possible, resulting in the growth of epitaxial CoSi₂.     

Nb multilayer planarization technology for a subnanosecondJosephson 1K-bit RAM

A fabrication process for a Josephson 1-kb RAM (random access memory) has been developed using a Nb multilayer planarization technology. The technology consists of an etchback technique using 2000-molecular-weight polystyrene and SiO₂ for the junction layer and wiring layers, and a tapered edge etching technique for contact between individual wiring layers. Excellent planarity, wherein level differences in all step areas were reduced to less than 1/20th of their original values, was achieved. Appropriate RAM operation with 570-ps minimum access time and 13-mW power dissipation, were confirmed