We have used both electron-beam vapor deposition and sputtering systems to deposit superconducting thin films of the compound YBa₂C_u30_y. In the e-beam deposition system the three metals are individually evaporated in an oxygen partial pressure while the sputtering system uses composite targets. After a high temperature furnace anneal in flowing oxygen these films can have transition temperatures as high as 91 K. The films in thicknesses ranging from 0.07 to several microns are deposited on a variety of substrates such as alumina, Si, MgO, zirconia and SrTiO3. The epitaxial films which are grown on polished SrTiO₃ single crystals generally show the highest critical current density, around 101A/cm² observed at 4 K. Device applications of these films such as SQUIDs and transmission lines will be discussed with particular reference to the processing and patterning techniques used in their fabrication. These techniques include photo-and e-beam lithography, ion implantation and milling and laser ablation.

The development of superconductivity near 100 K allows hybrid superconductor/semiconductor electronic devices to be experimentally investigated as a means of realizing improved ultra high speed very large scale integration (VLSI) electronics. Incorporating superconductors into conventional semiconductor structures will be the most likely approach to developing hybrid VLSI devices. The analysis of passive hybridization (using superconductive interconnects) of semiconductor devices concludes that this approach might produce significant benefits in at least some cases. Active hybridization of semiconductor devices, in which the inclusion of superconductors in a semiconductor device significantly alters device operation, is treated briefly. Such devices might be a means of achieving revolutionary rather than evolutionary improvement of electronic systems. The hybridization schemes are illustrated with a proposed ultra high speed resonant tunneling transistor (RTT) structure and with hybrid MOSFET structures. From the processing perspective, rapid isothermal processing (RIP) based on incoherent light sources is a promising technology for the fabrication of hybrid devices.

The optical response of granular films of Y-Ba-Cu-O and NbN/BN to pulsed and modulated steady-state optical radiation has been investigated. It is shown that the two materials exhibit qualitatively similar responses to steady-state (blackbody or HeNe laser) radiation, but exhibit important differences in their response to pulsed (lOns) radiation.

In Y-Ba-Cu-O systems high yield superconducting devices can be made from the top-quality bulk materials. We report here the stability of bulk oxide compounds in order to search a unique method to produce high Tc and hopefully shorten the period of processing. Systematic measurements of resistivity, magnetization, composition, and X-ray diffraction have been made on samples that have the same chemical prescription (pre-heating)but different heat processing. The processing was varied to find the optimum combination of the calcining time, sintering time, and annealing time at 650 C. We have found that the Tc is stable if the dominant phase remains. A ratio of Meissner: Shielding magnetizations of 61:100 was found under optimum conditions. The intensity and position of the X-ray diffraction peak for (103) was independent of elapsed time but strongly dependent on processing. Long-time annealing should not improve the properties of superconductors if either calcining or sintering time is not long enough. In some cases, it will not enhance the superconducting phase and the stability shows no further improvement. The magnetizations due to Shielding and Meissner effects definitely change with aging time but their ratio remains the same. A correlation between the peak intensity at (103) with the value of FC (Field-Cooling)/ZFC (Zero-Field-Cooling) has been found and corroborates the commonly held view in the significance of the amount of superconducting phases on superconductivity. Based on this study, the stability and degradation of superconducting devices associated with bulk materials will be further investigated.

We have developed a high pressure reactive evaporation (HPRE) process that has proven successful for the in-situ formation of the superconducting phase of YBa2Cu307 thin films at relatively low temperatures, T = 625 C. The process involves the evaporation of the three metallic components in a relatively high pressure oxygen atmosphere, P = 0.65 mTorr. When the deposition is followed by a cool-down anneal in a high pressure oxygen ambient, P~20 Torr, the result is a film with a relatively sharp superconducting transition. The best films, which have been obtained on yttria-stabilized zirconia substrates, have a zero resistance Tc of 86 K. The HPRE process generally results in a highly oriented growth habit, usually with the c-axis of the film being predominantly normal to the substrate plane. This result has been obtained both for (100) zirconia and (100) MgO substrates. Measurements of critical current densities on 20 gm constrictions have yielded values greater than 105 A/cm2 at 77 K and greater than 10⁶ A/cm² at 4.2 K on zirconia substrates. The constrictions were formed by photolithography and ion beam etching.

In the preparation of superconducting oxide films, one frequently observes crack formation, crystal orientation, phase seperation, and chemical reaction, all of which involve interactions between superconductors and substrate. Quantitative verification of these phenomena is expected to provide useful information for the preparation and microprocessing of high Tc films. Thermal expansion behavior of representative superconductors and substrate materials has been measured by a dilatometric method. The superconductors have far greater mean thermal expansion coefficients than conventional substrate materials and the difference correspond well with the crack size observed in some of the films. The non-linear expansion of BLnCO also contain information on the kinetics of oxygen uptake and secession as well as on the phase transition temperature. The effect of lattice matching has been investigated on Ba-Yb-Cu-O films. The films were deposited by sputtering on (100) and (110) SrTiO3 and some other ceramic substrates and their orientation was measured by SEM. Furthermore, chemical interaction has been examined by heating mixed powders of superconductors and substrate materials at various temperatures. The structural variation and the reduction in superconducting volume fraction were analyzed by X-ray diffraction and ac-susceptibility measurements, respectively.

Thick film pastes were manufactured from YBa2Cu3O7-8 superconducting powders prepared by the mixed oxide route. Thick films were printed onto A1203 and stabilized ZrO₂ substrates. Experimentally determined one or two step profiles in the range of 750 to 1000°C in oxygen or air were used to fire the pastes. The two step profile gave better results as the formation of adverse phases was hindered and the adhesion to the substrate was better. X-ray studies revealed that the top layer of the films on A1203 contained ca 90% of YBa2Cu307_8 phase and a minor amount mainly of the Y2BaCuO5 phase. SEM micrographs showed liquid phase sintering to have occurred on A1203 substrates but not on the ZrO2 substrates. SEM micrographs of the cross-section revealed BaAl2O4-phase at the A1203/thick film interface and some CuO and Y2BaCuO5 phases outside of it in addition to the major superconductive YBa2Cu307_5 phase. On ZrO2, the top layer of the films also contained 80 to 90% of YBa2Cu307_δ phase and, when short firing was used, minor amounts of Y2BaCuO5 and Y2Cu2O5. On longer firing the minor phase was Y2BaCuO5. Resistance measurements of films on both substrate materials showed the transition onset above 85 K.

We have demonstrated proximity effect coupling between a high transition temperature superconductor and a normal metal. A device with a 1 Am long gold microbridge coupling two evaporated films of YBa2Cu3O7 has a dc supercurrent and exhibits the ac Josephson effect when irradiated with microwaves. These high quality S-N interfaces should have application to fundamental studies of the superconductor as well as to electronic devices.

We report our experimental results of the surface chemistry and the electronic structure of YBa2Cu307_δthin film by photoemission study. An experimental technique has been successfully used to clean superconducting thin films for photoemission experiments, while still preserving the superconducting properties of the films. The photoemission spectra obtained are consistent with our earlier results from bulk ceramic samples. This technique is then applied to study the surface chemistry of thin films under different annealing conditions. The films which have been ex situ post annealed and the films which have not been ex situ post annealed have been studied and compared. It is found that the oxidation of copper in the film strongly depends on the history of the thermal treatment of the film. On the other hand, Ba seems very stable in its doubly ionized state under all annealing conditions.

Pulsed laser deposition (PLD) from a single target is simple, easy, and inexpensive compared to most of the other techniques employed for preparation of high Tc superconducting thin films. We present the results of Rutherford Backscattering study of the PLD process and identify the parameters which are critical in controlling the deposited film stoichiometry. Also, by using mass spectrometry the nature of the laser deposition process has been investigated. The PLD technique enables us to get films with stoichiometry close to that of the target. High Tc superconducting thin films of R-Ba-Cu oxide (R,Y, Eu, Gd, Sm, Tm, Er) have been prepared using PLD. Films deposited in vacuum at 450 C were not superconducting and post-annealing at over 850 C in oxygen was necessary to achieve high zero resistance temperatures. Detailed analyses of the films were carried out using RBS, TEM, XRD, Raman, Auger, SIMS, X-ray absorption and resistivity measurements. Recently, we were able to obtain superconducting thin films of Y-Ba-Cu Oxide with zero resistance temperature over 80 K at and below 650 C (processing temperature). The critical current densities in the films prepared at low temperature on SrTiO3 were on the order of 5x105 A/cm2 at 77 K. These films exhibited minimal interface reaction and were very smooth. We will also show that PLD can be utilized to prepare high Te superconducting thin films of Bi-Sr-Ca-Cu oxide.

The remarkable discovery of high Tc superconducting ceramics[1] has been followed by intense efforts to realize their potential in the form of devices, films, and wires. A number of techniques have been shown to be effective for growing thin films of these superconductors including electron beam/thermal co-evaporation,[2-41 RF and DC sputtering, [5-8] laser [11-12] evaporation,[9-10] and spin-on/pyrolysis. Of all of these techniques, the e-beam/thermal co-evaporation methods have been shown to give the best electrical characteristics in Ba2YCu3O7 films, particularly with respect to the critical currents which have reached 106 A/cm2 at 77K. [6,13]

We describe here the deposition of superconducting thin films by the laser evaporation technique. The characterization of this process, and optimization with respect to wavelength and pulse duration of the laser will be discussed. Results of laser interaction experiments will also be described. It was shown that the superconducting thin films could be used as room temperature bolometers with a microsecond response time.

High Tc YBaCuO thin films have been deposited by dc magnetron sputtering from two metal alloy targets. Oxygen was sprayed directly onto the film to be chemically incorporated into the film. Since most of the oxygen was absorbed by the film directly, low oxygen partial pressure was achieved to avoid target oxidation. Epitaxial and polycrystalline films with onsets at 92 K having 1 K transition widths have been produced. Films have been deposited on a variety of substrates including LiNbO₃ and LiTa0₃. For potential application in electronic devices and for many electrical measurements, it is important to pattern the films. Laser patterning has been demonstrated successfully with no degradation of the film properties. The advantages of laser processing are short turn around time and no wet processing associated with conventional lithography. Using this technique, lines as narrow as 1 micron have been fabricated.

Surfaces of Y1Ba2Cu3O7 (YBCO) are known to react with H₂O and CO₂ in the ambient atmosphere. The in-situ approach to thin film fabrication and characterization in a closed system makes it possible to investigate the near-surface properties of superconducting YBCO films in the absence of such deleterious reactions. We have fabricated and analyzed superconducting, epitaxial YBCO films entirely or partly in-situ. Oxygen partial pressures during deposition ranged from < 10-9 torr to > 3 X 10^-4 torr and temperatures from 400 to > 650°C, producing either amorphous or crystalline deposits. We found that annealing of oxygen-deficient amorphous deposits in oxygen caused atomic segregation of Ba and Y to the surface with a corresponding depletion in Cu. This effect made near-surface layers nonsuperconducting even in the absence of H2O or CO₂. Fast heating to crystallization temperature minimized the segregation. Measurements of dc contact resistance, R , and I-V characteristics in cross-strip junctions of YBCO/Au/Nb and YBCO/Au/MgO/Nb indicated near-zero Rc and weak-link I-V characteristics which proved that the in-situ approach permits one to obtain superconducting YBCO film surfaces. In the case of crystalline film deposition at 650°C, the in-situ electron-diffraction of SrTiO₃ substrates and 40 to 100 Å thick YBCO films revealed epitaxial crystallization only on clean substrates.

By using ion beam sputtering, the high quality Y-Ba-Cu-O superconducting films were successfully prepared. The superconducting behavior of the films strongly depended on the annealing temperature. The extensive characterization of the prepared films were carried out by measuring the temperature dependence of the resistivity, X-ray diffractometry, electron diffractometry, SEM image, EPMA spectra and XPS spectra.