We have studied the magnetic interference of the critical currents of synthetic planar thin-film grain-boundary Josephson junctions. We find that the effective area of these junctions scales as the square of the width w in contrast to the usual w(2λ+d) dependence of sandwich-type Josephson junctions. This behavior is a simple consequence of the magnetic response of thin-film superconductors to perpendicular applied fields. A model based on the London theory yields the observed behavior. In addition, we find the correction to the interference pattern due to the effect of the corners.

Growth conditions for YBaCuO thin films are investigated. Films have been made by reactive e-beam coevaporation using three metal sources. In the best cases, as-made films are superconducting with Tc's (R = 0) up to 90 K and Jc's (at 4.2 K) above 107 A/cm2. Oxygen pressure, deposition temperature, as well as compositional dependencies of the films are presented. It is found that in conditions of lower oxygen, pressure films with average composition off the 1–2–3 stoichiometry have higher Tc's. For pressure <10 mTorr, the highest Tc obtained is for Ba/Y deposition ratio ⋚1.4. The morphology and impurity phases of these films are examined. The Ba-deficient films have oriented CuYO2 and CuO as the dominant impurity phases. C-axis lattice parameters (c0) are also examined. It is found that for a given Tc, films made at lower pressure have c0's which are expanded compared to the films made at higher pressures (>100 mTorr). The expanded c0's for these films cannot be reduced by a low temperature oxygen anneal. We suggest that metal-atom point-like defects are quenched into these films and we discuss a particular Ba-for-Y substitution model.

We have studied the far infrared behavior of high-T, superconductor-normal metal-superconductor (SNS) microbridges with T, > 85 K and critical current-resistance products (I,RN) as high as 10 mV at 4 K. These are the highest I,RN products reported to date for microfabricated Josephson junctions of any material. The junctions were integrated at the feeds of planar log-periodic antennas made from Au thin films. The junctions had dc normal state resistances RN between 6 and 38 Q, reasonably well matched to the antenna's estimated RF impedance of 53 0. Far infrared laser radiation at 404, 760, and 992 GHz induced distinct Shapiro steps (i.e. constant voltage steps at voltages n ( h f / 2 e ) , n = 1, 2, . . .) in the current voltage characteristics as well as modulation of the critical current.Steps were observed at voltages up to 17 mV and 6 mV, at temperatures of 9 K and 57 K, respectively. This corresponds to maximum Josephson oscillation frequencies of 8 and 3 THz at these temperatures. These are the first far infrared measurements performed on high T, junctions. Measurements of the power, frequency, and temperature dependence of the Shapiro steps are presented and discussed in the context of a resistively and capacitively shunted junction (RCSJ) model. A value of 4.5 fF for the junction capacitance is inferred from the hysteresis of the slightly underdamped current-voltage characteristics.

A design analysis is given for a bolometric infrared detector that uses the resistive transition of a high-temperature superconductor as the temperature sensing element, and liquid nitrogen (LN) as the coolant. It is shown that for highly oriented c-axis films, the measured lowfrequency noise causes little or no degradation of the performance. With the incoming radiation chopped at 10 Hz, noise equivalent powers (NEP) in the range (1-20) X 10 \2 W Hz -\12 should be achievabk These values compare favorably with the NEP of other detectors operating at or above LN temperatures for wavelengths greater than 20 pm.

Thin films of the high Tc superconductor YBa2Cu3O7−δ were prepared and characterized. The films made on SrTiO3 showed epitaxial growth and high critical current densities in excess of 9×104 at 78 K and 2×106 at 4.2 K. Also, surface pinning in the parallel direction was found to be very high. The measurements put a lower limit on the depairing critical current density of 5×107 A/cm2.