A high-Tc 4-bit periodic threshold analog-to-digital converter

Using ramp-type Josephson junctions a 4-bit periodic threshold ADC has been designed, fabricated and tested. Practical design constraints will be discussed in terms of noise immunity, flux flow, available technology, switching speed etc. In a period of four years we fabricated about 100 chips in order to bring the technology to an acceptable level and to test various designs and circuit layouts. This resulted in a basic comparator that is rather insensitive to the stray field generated by the analog input signal or variations in mask alignment during fabrication. The input signal is fed into the comparators using a resistive divider network. Full functionality at low frequencies has been demonstrate

The Detection of Defects in a Niobium Tri-layer Process

Niobium (Nb) LTS processes are emerging as the technology for future ultra high-speed systems especially in the digital domain. As the number of Josephson Junctions (JJ) per chip has recently increased to around 90000, the quality of the process has to be assured so as to realize these complex circuits. Until now, very little or no information is available in the literature on how to achieve this. In this paper we present an approach and results of a study conducted on an RSFQ process. Measurements and SEM inspection were carried out on sample chips and a list of possible defects has been identified and described in detail. We have also developed test-structures for detection of the top-ranking defects, which will be used for yield analysis and the determination of the probability distribution of faults in the process. A test chip has been designed, based on the results of this study, and certain types of defects were introduced in the design to study the behavior of faulty junctions and interconnections

Transistor performance of high-Tc three terminal devices based on carrier concentration modulation

Electric field effect devices and quasiparticle injection effect devices are good candidates for the realization of three terminal devices from high-T/sub c/ materials, since they take explicit advantage of the low carrier concentration in these compounds. We describe the fabrication and operation of both types of devices, and discuss their performance as transistor-like element

An HTS Quasi-One junction SQUID-based periodic threshold comparator for a 4-bit superconductive flash A/D converter

An all high-Tc periodic threshold comparator for application in a 4-bit superconductive A/D converter has been realized and tested. The theoretical threshold curve of the comparator is calculated and compared to the measured results. Furthermore, the thermal noise immunity and the influence of flux-flow are considered, resulting in practical design constraints for the comparator circui

The propagation characteristics of wave-guiding structures with very thin superconductors:application to coplanar waveguide YBa₂Cu₃O_7-<i>x</i> resonators

The propagation characteristics of waveguiding structures with superconductors which are thin compared to the magnetic penetration depth are analyzed. The complex propagation constant is evaluated within the framework of the modified spectral domain method without the need for numerical calculations in the complex plane. Good agreement is found with the results of other methods. The numerical analysis is instrumental in deducing results for the penetration depth and the surface resistance of YBa2Cu3O7-x thin films on sapphire with a PrBa2Cu3O7-x buffer layer. Recent observations of a non-single-gap BCS temperature dependence are confirme

Test structures and their application in structural testing of digital RSFQ circuits

As the niobium (Nb) LTS RSFQ processes advance being the technology for future ultrahigh-speed systems in the digital domain, the quality of the process should be maintained high for a successful realization of these complex circuits. A defect-oriented testing (DOT) approach is essential so as to increase the yield of the process. Little information is available in this area and the recent increase of Josephson junctions to around 90,000 per chip requires a detailed study on this topic. In this paper we present how DOT can be applied to RSFQ circuits. As a result of a study conducted on an RSFQ process, a list of possible defects has been identified and described in detail. We have also developed test-structures for detection of the top-ranking defects, which will be used for the probability distribution of faults in the process. One of the highly probable defects will be used to elaborate the DOT technique for fault modeling and simulation purposes

The Origin of Medical Terms

In order to prepare planar junctions, multilayers were sputtered, using YBa2Cu3O7-δ as superconductor and PrBa2Cu3O7-δ as barrier material. The sandwiches are a-axis oriented. Out of these, single junctions were etched, planarized with CeO2. Finally gold contacts were sputtered. The junctions are squares of size 20x20 to 100x100 μm2. A prerequisite for successful preparation of junctions from a-axis oriented multilayers is a study of such films. Films deposited by RF off-axis sputtering were characterized electrically, Their morphology was investigated by XRD, AFM and TEM. The films are very smooth and have a grain size of below 100x100 nm2. To improve Tc and crystal quality, template layers were used. The Tc of a single film is about 62 K; by using a template layer up to 78 K can be reached. For α-axis oriented growth not only a reduction of the deposition temperature is important, but also the growth rate must be high enough. Best results were obtained at rates higher than 150 nm/h. The first planar junctions show a supercurrent, but otherwise rounded I-V curves

Metallomacrocycles: Synthesis, X-ray Structure, Electrochemistry, and ESR Spectroscopy of Mononuclear and Heterodinuclear Complexes

A number of novel heterodinucleating ligands have been synthesized by Ba2+-templated (1:1) macrocyclization of the dialdehydes 7, 8, and 20 with the diamines 9 and 21. The ligands have both a cavity suitable for complexation of transition-metal cations and a cavity for complexation of alkali- or alkaline-earth-metal cations. The resulting barium complexes could be converted into the heterodinuclear complexes 1–3, 10–13, 23–25, and 28 upon reaction with nickel, copper, or zinc acetate. The mono-transition-metal complexes 14–17, 26, 27, and 29 could be obtained by removing the barium salt from the polyether cavity. Their 1H NMR, IR, and mass spectra are discussed, and four heterodinuclear complexes have been analyzed by X-ray crystallography. The nickel/barium complex 3•MeOH (C35H44BaCl2NiO19) crystallizes in the monoclinic system, space group P21/n, with a = 15.096 (4) Å, b = 20.278 (4) Å, c = 13.818 (4) Å, β= 93.61 (1)°, and Z = 4. The nickel/barium complex 10-H2O crystallizes in the triclinic system, space group P1, with a = 9.096 (3) Å, b = 11.491 (7) Å, c = 17.119 (5) Å, a = 92.38 (2)°, β = 102.27 (1)°, γ = 98.63 (2)°, and Z = 2. The nickel/sodium complex 14.sodium picrate crystallizes in the monoclinic system, space group P21/c, with a = 14.697 (5) Å, b = 14.574 (7) Å, c = 14.782 (3) Å, β = 96.08 (1)°, and Z = 4. The zinc/barium complex 25.3DMF crystallizes in the monoclinic system, space group C2/c, with a = 24.301 (5) Å, b = 26.232 (4) Å, c = 22.468 (7) Å, β= 119.06 (2)°, and Z = 8. In the complexes 3.MeOH, 10.H2O, and 14-sodium picrate the coordination of the nickel cation is square planar. The zinc cation in 25.3DMF has a square-pyramidal coordination with a DMF molecule at the axial position. The distance between the two metal ions in the complexes 3•MeOH, 10-H2O, 14.sodium picrate, and 25.3DMF is 3.63-3.70 Å. The electrochemical properties of the complexed transition-metal cations in the heterodinuclear complexes and mono-transition-metal cation complexes have been investigated by polarography and cyclic voltammetry. The half-wave potential is dependent on the nature of the transition-metal cation and the mode of coordination. Complexation of alkali-metal (Li+, Na+, and K+) or alkaline-earth-metal (Ba2+) cations in the polyether cavity resulted in anodic shifts of the half-wave potential up to 213 mV; the bivalent Ba2+induced the largest shifts. The shifts of the half-wave potential are also dependent on the ring size and rigidity of the polyether cavity. Cyclic voltammetry of the nickel/barium complex 10 and the copper/barium complex 12 revealed a chemically reversible but electrochemically irreversible reduction at scan rates of 0.5-6 and 1–6 V/s, respectively. A relatively slow adsorption process was observed for the nickel complex 15, and the reduction was chemically reversible but electrochemically irreversible at scan rates of 50 mV /s to 2 V/s. The zinc/barium complex 25 undergoes an irreversible two-electron reduction at E1/2= -1.466 V, whereas the nickel and copper complexes 10–17, 23, 24, 28, and 29 undergo a one-electron reduction. The ESR spectra of a number of copper containing and heterodinuclear complexes are in line with the redox properties