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Sputter deposition of Co,A1 and NiFe on oxidized Si wafers was used to process tunnel magnetoresistance devices.

A study fabricated and tested a three-dimensional, rapid single flux quantum logic circuit based on a new type of superconducting, stacked, three-terminal device called the stackron. The junctions in the study were used as active devices. The stackrons with overdamped junctions ought to increase the packaging capability and perhaps the maximum clock frequency of a rapid single flux quantum logic circuit. Experiments results are discussed.

A study used electron beam lithography to fabricate the properties of high-quality, ultra-narrow long Josephson junctions with gradually decreasing width down to less than 0.3 microns. Analysis of these Josephson transmission lines indicated a strong dependence of the junction characteristic parameters on the junction width. The data are described in a consistent manner by considering a general-type width dependence of the phase gradient on the magnetic field.

Research was conducted to examine high temperature Josephson mixers and high temperature hot-electron bolometric effect mixers. The Josephson mixers were fabricated and the noise, conversion efficiency and receiver bandwidth calculations were carried out in the frequency range between 90 and 550 GHz. Results illustrate that low-noise mixing is possible with high temperature superconducting Josephson mixers at temperatures above 20 K.

A sub-millimeter wavelength oscillator based on high temperature superconducting step-edge Josephson junctions coupled on-chip with detector Josephson junction-mixer was fabricated and tested. A new type of 2D arrays of Josephson junctions, namely, a shorted 2D array biased in parallel, was considered. The best results such as the steep Shapiro steps up to the 4th order and significant depression of the critical current were obtained from 150 GHZ and 200 GH z.

Research was conducted to fabricate and test a high temperature superconducting Josephson mixer in submm-wave range. Mixer noise temperature of approximately 1100 K was established at 430 GHz. Its performance was enhanced with the use of junctions with low-inductance resistive shunt. A new method for the calculation of Josephson radiation linewidth from the IF noise dependence is proposed.

Research was conducted to examine a new class of superconducting microwave oscillators based on Cherenkov radiation from Josephson vortices. The current-voltage curves and radiation calculations can be explained in terms of Cherenkov radiation of the direct and backward plasma waves in a space-periodical structure and annular structures. Theoretical predictions for the radiation frequencies based on the Cherenkov radiation concept agree with the experimental results.

The design of double junction ring oscillator employing two shunted, stacked junction devices that function as active ring switching nodes is presented. The proposed double junction ring oscillator has an rf detection circuitry that can be used in measuring Shapiro steps and broadband rf. In addition, the device can be used to study multiple flux quantum state, which is a distinct, transient dynamical states associated with the synchronous switching of nodal junction in the circuit.

Research was conducted to examine new microwave circuits for voltage standard application containing 256 bicrystal junctions. Results illustrate successful series dc and parallel ac biasing in such a meandered array. On each of the 8 subarrays, the first current step was achieved at liquid nitrogen temperature at a frequency f = 27332 MHz and for a constant microwave power. Possible ways to increase uniformity of the relative ac current and, correspondingly, the bias frequency were demonstrated.

Research was conducted to examine the properties of gold shunted bicrystal YBCO junctions on yttria-stabilized zirconia and sapphire substrates. Three important properties related to the problem of parameter spreads were noted. First was th control of the shunt resistance. SEcond was the impact of the shunt resistance and the spread in junction resistance on the tolerable junction size. Third was the realization of series arrays with a high packing density of junctions using electron-beam-patterning.

A double-junction stacked Josephson flux-flow oscillator on-chip coupled to a superconductor-insulator-superconductor detector was subjected to radiation measurements. A broad band coupling circuit was employed for impedance matching between the detector and the oscillator. The detector exhibited radiation power of up to 10 nW in the 170 and 410 GHz frequency range. Two stacked junctions emitted coherent radiation at the fundamental Josephson frequency and at its second harmonic.

A study was conducted on the magnetic field dependence of 7-layer stacked Nb/AlAlOx/Nb long Josephson junctions' current voltage characteristics. The common superconducting electrodes with thicknesses less than the London penetration depth provide the magnetic coupling in the junctions. A complex structure of cavity-like resonances modulate the flux-flow characteristics. Pronounced resonant modes with large voltage spacing were observed in the intermediate magnetic field range.

Two basic elements of high-temperature Josephson receivers were fabricated and operated. The elements are a single gain boundary junction, which functions as a mixer, and a Josephson array oscillator based on a multijunction superconducting loop topology. Direct-current measurements were also conducted to determine the phase-locking of all junctions. Results reveal the possible integration of Josephson oscillator and mixer into a single circuit.

Fluxon resonances known as zero-field steps in current-voltage characteristics of long Nb/A1-A1Ox/Nb Josephson junctions made in a window of a stripline is measured with battery-powered current sources for the bias current and magnetic field. Results indicate the appearance of fine structure resonances in fluxon resonant steps and an increase in the effective fluxon propagation velocity. The findings are in agreement with previous measurements.

Double-barrier, long-stacked Josephson tunnel junctions of overlap geometry and with external electric contract to their middle electrodes are developed with the use of Nb-A1/A1Ox-Nb technology. Thicknesses of 90 nm were achieved with the use of a planarization technique. Equal voltage across the top and bottom junctions, which are both of high quality, were observed by biasing the junctions.

The flux-flow dynamic behavior of vertically stacked long Josephson tunneling junctions fabricated via an in situ process is studied by current-voltage and magnetic measurements. The measured data shows the presence of two different mutually phase-locked regimes in the junctions, the lower-velocity anti-phase mode and the high velocity in-phase mode. These modes can be tuned by the magnetic field in a broad voltage range.

The phase-locking behavior of three-dimensional, stacked all-niobium Josephson junction arrays subjected to external resonant frequency irradiation is studied by current-voltage measurements. Results show that the phase-locking range of the arrays decreases under external microwave irradiation as the number of stacks increases. This can be attributed to the increase in the resonant frequency loss in the vertical direction.

The fabrication of superconducting Nb/Al-AlOx/Nb tunnel junctions is discussed. Magnetron sputtering techniques were employed to deposit Nb/Al-AlOx/Nb multilayers on silicon substrates. The internal mechanical stress acting on the niobium films and the morphology of the interfaces were determined by the X-ray stress evaluation method and anodization spectroscopy. The junctions' current-voltage characteristics and Fraunhofer patterns were also measured. Results show that the Fraunhofer patterns are strongly dependent on the surface roughness of the individual junctions.