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A superconducting high-order cascaded lowpass sigma-delta modulator is proposed. This cascaded type modulator eliminates the difficulty of designing a feedback driver in a double-loop type modulator.

A proposed multi-input with multistage (MIMS) AND gate is presented involving a three-junction interferometer and a single junction for each stage of the construction. Results show that the number of inputs does not influence the bias margin of the MIMS-AND gate. The bias margin is recorded at plus or minus 20% while the minimum gate delay is at 130 ps. A better test chip is expected to improve the delay time.

The annealing stability of Nb/AlOx-Al/Nb Josephson junctions is investigated via a study of variations in the current-voltage characteristics. Since it is known that the junction degradation is caused by barrier composition changes and oxygen diffusion form the counter electrode, surface plasma nitridation is conducted on the Nb counter electrode to determine whether the process deters oxygen diffusion from occuring. A quantitative comparison between the junction stability of AlNx and AlOx barrier junctions is also presented.

An Nb Josephson junction with a Hf/HfN double overlayer structure was fabricated and presented. The characteristics of the device were not affected by annealing at temperatures up to 350 degrees celsius. The Hf layer acted as a layer for the tunneling barrier formation and as an effective etch stop for a reactive ion etching process during the fabrication of the junction. The HfN layer acted as a stop for grain boundary diffusion between the Nb and Hf layers.

X-ray photoelectron spectroscopy and anodization profile were used to determine the surface coverage of thin aluminum films deposited on niobium layers at variable sputtering parameters. Observations showed superior adhesion between Al and Nb over Al on silicon due to the features of the Nb layers beneath. The testing of prototype b/AlOx-Al/Nb Josephson junctions substantiated the view that the performance of the junction depends on the surface coverage between the films.

An experiment to assess the morphology and superconducting characteristics of the Nb/AlOx-Al/Nb junction using direct current (DC) and radio frequency (RF) magnetron sputtering adjudged DC sputtered niobium (Nb) films as better for Josephson-junction electrode applications. Further investigations also revealed the cathode voltage to be the most significant paraneter controlling film properties. Beyond a threshold voltage, 250 volts, premium quality Nb film occurs. However, film characteristics are still subject to change due to fabrication processes like annealing, anodization and patterning.

Presents a study that developed and tested a triode with a niobium/AlO[subx]/niobium Josephson junction emitter and an n-InSb collector. Background on superconducting transistors; Examination of the control of the collector current of the triode; Analysis of the calculated characteristics of the triode.

Presents a study that investigated the characteristics of a type of field-effect transistor (FET) whose channel consists of ultrafine metal particles between the source and drain electrodes. Background on tunneling for transistor applications; Examination of the semiconductor-like properties that should appear in the idealized discontinuous film used in the study; Analysis of activated tunneling FET characteristics.

Deals with a study which detailed the voltage-charge relation in a small tunnel junction using a model similar to the one employed by Neugebauer and Webb in an analysis of conduction in discontinuous metal films. Consideration in the calculation of the static voltage-charge relation in the junction; Area in which a field effect is possible; Factor similar to a Josephson junction.

Presents a study which investigated the fabrication process of niobium/aluminum-aluminum oxide[sub x]/niobium (Nb/Al-AlO[sub x]/Nb) Josephson junctions. Fabrication of the Nb/Al-AlO[sub x]/Nb; Junction defined by a reactive ion etching technique; Influence of Nb deposition condition on the junction characteristics; Optimization of the Al film thickness.

Presents a study that examined memory operation from the viewpoint of the thermal fluctuation of the potential energy of the cell. Origin of the gray zone; Description of the gray zone; Probability of transition to the voltage state.

Presents a study that examined Nb/AlO[subx] and Al/Nb interfaces in Nb/AlO[subx]-Al/Nb junctions made by varying certain process parameters. Background on the Josephson junction; Analysis of the anodization of basic structures; Assessment of the annealing effects.

Focuses on a study which derived the characteristics of a superconducting-base transistor. Information on the injection of quasiparticles; Flow of quasiparticles in the base; Treatment of electron current and quasiparticle at the collector.

Presents information on a study which described a selective plasma oxidation method for use in making superconducting patterns in nonsuperconducting deoxygenated YBa[sub2]Cu[sub3]O[sub7-x] (YBCO) thin films. Electrical properties of the thin films; Description of the selective plasma oxidation of YBCO films using a metal mask; Effects of plasma oxidation on polycrystalline YBCO films; Conclusions.

Presents a study that investigated plasma nitridation process for superconducting niobium wiring to improve their annealing stability. Method of the study; Results and discussion; Conclusion.

Presents information on a study which fabricated niobium (Nb)/AlO[subx]Nb Josephson junctions which showed excellent current-voltage characteristics. Deposition of Nb and aluminum layers to get a clear junction interface; Fabrication of 10[sup4] junctions connected in series; Estimation of the yield.

Presents a study that calculated and obtained an approximate expression for the thermal noise-limited sensitivity of the pulse-biased SQUID sensor used in the integrated magnetometer. Function of SQUID magnetometers; Description of the magnetometers; Discussion on the real magnetic flux noise.

Presents a study which fabricated high-quality, submicrometer niobium/aluminum oxide[subx]/niobium Josephson junctions. Information on the junction area; Importance of using stress-free niobium for the junction electrodes; Construction of the trilayer structure of the junction.

Reports on the transistor characteristics of a three-terminal structure having YBa[sub2]Cu[sub3]O[sub7-x] electrodes on an insulating SrTiO[sub3] substrate with an intervening NdGaO[sub3] barrier. Illustration of the device structure; Schematic band diagrams of emitter-grounded dielectric-base transistor.

We propose a superconducting high-order cascaded lowpass sigma-delta modulator. The second-order cascaded modulator consists of two single-loop modulators. A part of an integrating inductor of the first-stage modulator forms a primary coil of a transformer. The secondary coil of the transformer forms an integrating inductor of the second-stage modulator. Output of the first integrator is thus magnetically fed to the second integrator through the transformer. Digital outputs from both modulators are input to a delay and a digital differentiator. The quantization noise of the first-stage modulator is canceled by choosing proper transfer functions for the delay and differentiator. This cascaded type modulator eliminates the difficulty of designing a feedback driver in a double-loop type modulator. Analytical calculation of the transfer function showed that the signal-to-noise ratio is comparable to an ideal second-order lowpass sigma-delta modulator at a given sampling frequency. [ABSTRACT FROM AUTHOR]

Previously, a capacitively coupled Josephson memory cell was proposed in which an rf-SQUID device couples capacitively with a single junction. Binary data stored in an rf-SQUID device can be read through a flux change which generates a pulse signal to be detected. The pulse has a very narrow width, i.e., an order of picoseconds. The current would be different in the time before and after the pulse is applied, which is superimposed by an oscillating current after the application of a pulse. The bias current margin of the memory cell is determined by the way in which a memory is read by using such a pulse. When a memory cell of Josephson junction devices is used, the bias current margin of a sense junction would govern the overall margin of the memory circuit. This bias current margin must be made large for the present study. Therefore, by assuming the read mode of a capacitively coupled memory cell, the response of a single junction has been studied for a very narrow-width pulse current which varies with fluxons. The minimum pulsewidth and amplitude required to switch a junction and a bias current dependence before and after the pulse is applied are calculated analytically on the basis of the coupling energy reported by Dong and Van Duzer [18]. The relation between a minimum pulsewidth and amplitude and a switching time for a sense junction, which cannot be solved analytically, is calculated by computer simulation. Further, the influence of a sinusoidal current superimposed over a bias current also is studied by computer simulation. [ABSTRACT FROM AUTHOR]

This paper describes a probing system to test a wafer immersed in liquid helium. This system is intended to improve the following three functions in comparison with conventional systems: (1) measurement of fast rise-time electrical signals, (2) quick release of flux trapping with small loss of liquid helium, (3) facility in exchanging wafers. It was observed that signals with 2-ns rise time could transmit through the system, the release of flux trapping could be achieved in several minutes with negligible helium loss using a cryoinsert with a closable hole at its bottom, and wafers could be exchanged similarly. [ABSTRACT FROM AUTHOR]

Josephson integrated circuit technology has progressed remarkably since the introduction of the reliable niobium junction. Josephson microprocessors and memory circuits that were once considered impracticable have been demonstrated. All the functions required for a Josephson computer can now be fabricated, although integration densities are still much lower than those achievable with semiconductor devices. The next step is to demonstrate a small-scale special-purpose Josephson computer system. [ABSTRACT FROM AUTHOR]

Focuses on the fabrication of an all refractory Josephson junction in which ytterbium (Yb) oxide is used as a tunneling barrier. Application of self-aligned contact process; Advantage of using Yb oxide over aluminum oxide; Background temperature for the sputtering and the oxidation.

High quality Nb/Al-AlOx/Nb Josephson junctions have been fabricated by a novel process named the self-aligned contact process. After the definition of the junction area by a reactive ion etching (RIE) technique, the exposed Nb layer and the junction edge are anodized to protect against electrical shorts and an Al film is deposited as the etching stopper layer. After base electrode patterning by RIE, an insulation layer is deposited. The contact hole, with the diameter of the junction, for connecting a counter electrode and a wiring layer, can be made without registration because of the deposited Al film. The junctions fabricated by this process have exhibited excellent current-voltage characteristics (Vm =70 mV at the critical current density jJ =1.8 kA/cm2, Vm =11 mV at jJ =20 kA/cm2). [ABSTRACT FROM AUTHOR]

Reports on a study of microstructure of Nb/AlO[sub x]-Al/Nb Josephson junctions by cross-sectional transmission electron microscopy that yielded information regarding the junction barrier region. Formation of polycrystalline films with columnar structures by both thick Nb and Al; Current-voltage characteristics of the junctions.

Using anodization profiles, we have analyzed the thin AlOx-Al tunneling barrier in a Nb/AlOx-Al/Nb Josephson junction. We measured the voltage width at the AlOx-Al barrier in the profiles and found that it is closely related to the AlOx-Al thickness. We proposed a way to evaluate this thickness from the voltage width. The anodization profile is useful in diagnosing the 4.2 K critical current density of Josephson junctions even at room temperature. [ABSTRACT FROM AUTHOR]

Investigates the interfaces of niobium (Nb) Josephson junctions with an overlayer structure using cross-sectional transmission electron microscopy. Factors attributing the interface roughness between aluminum (Al) and Nb; Application of McMillan's proximity theory for Al/Nb interface analysis; Impact of thermal annealing on interface roughness.

Examines the use of secondary ion mass spectrometry in observing niobium (Nb) Josephson junction structure changes. Significance of the absorbed water vapor layers in the junction structure; Comparison between the annealing changes of Nb base electrode and Nb counterelectrode; Effect of grain boundary diffusion on the interface.

Focuses on the transistor characteristics of a three-terminal structure on an insulating strontium titanium oxide substrate. Fabrication of a superconducting YBa[sub 2]Cu[sub 3]O[sub 7-x] emitter; Construction of the three-terminal structures on crystals; Formation of base leads by silver paste.

Examines a transistor based on electrical potential control through high-dielectric-constant insulators. Fabrication of ultrafast superconducting transistors; Production of base leads with silver paste; Control of the collector current.

Describes the improvement of the annealing stability in superconducting Nb wiring with nitrogen plasma treatment. Measurement of the critical current of the Nb wiring before and after annealing; Decrease in critical current after annealing; Use of secondary-ion mass spectroscopy profiles.

Plasma polymerization using CHF3 gas, which prevents the degradation of high Tc oxide superconductors due to moisture and annealing, was developed. The resistive transitions of Y1Ba2Cu3Ox thin films, coated by plasma polymerization, did not change before and after soaking in 20 °C water for 60 min. In addition, the critical temperature of those films was unchanged after annealing at 200 °C for 30 min in air, and then soaking in 90 °C water for 10 min. We confirmed that the polymer film grown by this method was dense, and the Y1Ba2Cu3Ox film reacted with the fluorine at the interface using x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]