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The preliminary tests of a microwave frequency-division multiplexed readout of SQUID amplifiers that could help to estimate the number of SQUIDs that could be multiplexed is reported.

Solid-state refrigerators based on normal metal/insulator/superconductor (NIS) tunnel junctions are used to demonstrate the cooling of the electrons and phonons of silicon nitride (Si-N) membranes. A temperature reduction of the Si-N membrane from 260 mK to 240 mK is reported and mechanism for cooling an isolated membrane is explained.

Noise performance of a SQUID multiplexer ( MUX) is examined and discussed.

Far-infrared transmission and reflection of YBa(sub.2)Cu(sub.3)O(sub.7-delta) (YBCO) films on silicon substrates are discussed. Measurements show the feasibility of using thin high-temperature superconducting (HTSC) films deposited on transparent substrates as radiation modulators. Frequency and temperature-dependent refractive indexes for the HTSC films found can be helpful for design of potential far-infrared devices based on YBCO films on Si substrates.

The properties of low-power nonlinear effects in high-temperature superconducting microwave devices were studied by measuring third harmonic generation at 76 K in coplanar waveguide transmission lines of various geometries manufactured from YBa2Cu3O7-delta thin films. The measured power in the third-harmonic signal was observed to change systematically with film thickness, center conductor linewidth and line length. Findings offer a way to set a lower limit for the expected nonlinear response of superconducting components of arbitrary geometry at microwave frequencies.

A study investigated the impact of oxygen pressure on the properties of yttrium barium copper oxide films during pulsed laser deposition. It especially focused on the low power of the films. At the lowest oxygen pressures used in the study, a significant suppression of the critical temperature of the films was observed, with a corresponding increase in the c-axis lattice parameter. This finding is consistent with the introduction of some kind of disorder into the films. Experimental implications are also discussed.

A systematic study was conducted of the microwave frequency, power dependent impedance of yttrium barium copper oxide grain boundaries as a function of grain boundary mis-orientation angle from two degrees to 24 degrees. A unique stripline-resonator method, which is also presented, enabled the effects of the background film to be separated from those of the grain boundary. Results of the experiment including new findings on harmonic generation are discussed.

Junction interactions between bicrystal Josephson junctions in a multilayer structure were examined. Results indicate that the nearness of the junctions produces a large number of effects that include voltage locking and current locking. Voltage locking was found to be influenced by the alternating current provided by a SrTiO3 layer between the stacked junctions while current locking appears to be caused by a Josephson vortex interaction.

Research was conducted to develop YBa2Cu3O(sub 7-x) (YBCO) thermometers for large area bolometers that include a heater for calibration by the electrical substitution of power. YBCO was observed to be electrically sensitive to its passivation layer. Results are competitive with those obtained with smaller thermometers using the inhibit fabrication process and passivation by PtO(sub X).

Research was conducted to examine the wavelength dependent photoresponse in yttrium barium copper oxide (YBCO) thin-film systems. The photoresponse of the systems were explored as a function of temperature, bias current and power at wavelengths of 0.670, 0.850 adn 10.6 microns and at frequencies from 3 to 10 to the 5th power Hz at 0.670 micron. Results suggest that the secondary response observed inn the broad-transition films may be related to the photodoping of underdoped elements of the film.

A systematic study of the effect of film deposition temperature on both the linear and nonlinear microwave response of high temperature superconductor (HTS) materials fabricated by pulsed-laser deposition was conducted. The objective was to make an initial effort at the simultaneous optimization of linear and nonlinear microwave properties of HTS thin films. Results indicate that the increase in defects resulting from film growth at lower deposition temperatures leads to a smaller low-temperature surface resistance.

A study was conducted on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa2Cu3O7-delta. The results indicate that resistively shunted junction-like focused electron-beam junctions can be written in large numbers in any geometry. Moreover, these junctions are quasistable and can be described within a conventional framework as superconductor/normal/superconductor junctions.

An enhanced multi-layer fabrication approach is proposed for circuits based on YBa2Cu3O7-x. A combined HF wet-etching and ion-milling technique was utilized in developing YBa2Cu3O7-x/SrTiO3/YBa2Cu3O7-x multilayers with via connected structures. The via has a critical current density as large as 2x10(super 6) A/cm2 at 76 K, and is controlled by edge contacts in the ab-plane.

YBCO films with widths of 0.1, 1 and 5 mm were subjected to electrical noise measurements at 10 Hz. Results show that increasing the thermometer area by a factor of 2500 will enhance the noise equivalent temperature by a factor of 10. Results also reveal that thermometers can be fabricated using YBCO films with thicknesses not exceeding 50 nm despite the presence of mechanical strains.

A study was conducted on the responsivity of a simple, unoptimized narrow-line YBCO thin film device to a mid-infrared radiation level of 25 micro m. A calibrated HgCdTe detector revealed that pulsed diode-laser sources generate light. Results reveal a conservative upper limit of R - 1000 V/W on low frequency responsivity. Further studies of optimized systems at various wavelengths and configurations are advised.

A step-edge superconductor-normal-superconductor weak link is fabricated using YBCO and Au. A variety of a high-temperature superconducting Josephson junction, the weak link is measured for its critical current and normal resistance dependencies. Results show that junction parameters can be adjusted over orders of magnitude. This indicates that junctions can be designed for specific applications.

The feasibility of using YBa2Cu3O7-pi superconductor-normal-superconductor Josephson junctions as mixers of 30 THz radiation is investigated. CO2 laser difference frequencies of up to 27 GHz are observed when a third microwave signal is added to the junctions. Results indicate that the direct current (DC) bias dependence of the difference frequency signal is caused by either hot-electron mixing in the junction banks at high DC biases and bolometric Josephson mixing at low DC biases.

The electrical transport characteristics of superconductor-normal metal-superconductor step-edge YBCO/Au junctions were studied using the resistively shunted junction model. The Au is deposited at 100 degrees and 600 degrees Celsius. Results show that critical currents are similar for the Au at the two deposit sites while the normal resistance at 100 degrees is consistently higher by 25% than the resistance at 600 degrees. The critical current's low magnetic field modulation indicates either a Fraunhofer-like pattern or a double-junction modulation for the devices.

Nonmagnetic, nondestructive pressure contacts characterized by high current and low resistances are fabricated. The contact resistance consists of the lead/Ag pad interface, the Ag pad/YBCO interface and the bulk resistance of the contact material which determines power dissipation during critical current measurement. Pressure contacts supply lower contact resistance than soldered contacts.

Superconductor-normal metal-superconductor (SNS) Josephson junctions were fabbricated by a step-edge technique commonly used in many high-temperature superconductor processes. The technique enabled the production of SNS junctions with very short normal metal bridges and low contact resistance by in situ pulsed laser deposition. The SNS junctions fabricated using this technique were found to be highly suitable for the production of high-quality individual junctions and superconducting quantum interference devices.

An experiment on the effect of deposition conditions on the structural and superconducting characteristics of laser-ablated YBa2Cu3O(7-delta) films grown on LaAlO3, SrTiO3, MgO and ZrO2 substrates is presented. It interprets the observed morphological and superconducting properties of the films as a function of the substrate material, substrate temperature and oxygen pressure utilized during the fabrication process. It also reveals the films on LaAlO3 to be the best in terms of reproducibility and sensitivity to deposition parameters.

Pulsed laser deposition enables the growth of YBa2Cu3O(7 - delta)-normal metal-YBa2Cu3-O(7 - delta) step-edge junctions, which show ideal resistively shunted Josphson junction behavior, and the observed noise is less than the Johnson-Nyquist noise. These observations prove that superconducting shorts longer than the superconducting coherence length are not predominant in these junctions.

The feasibility of using substrate etching and annealing methods for use on superconducting multilayers and devices was examined. The structural quality and direct current of YBa2Cu3O7-gamma thin films were evaluated by examining their room temperature resistivities, critical current densities, c-axis rocking curve full width-half maximum and inhomogenous strains. It was concluded that damage to the films caused by etching could be repaired by using a preanneal of LaAlO3 in O2 at 950 degrees celsius.