The various deposition processes for preparing high-T superconducting thin flints are compared. The focus is on both the key film properties produced by each technique as well as the advantages and disadvantages of the specific deposition process. Emphasis is placed on the issues relating to film manufacturability and consequently centers on the YBaCu3O7 superconductor. Innovative solutions allowing in-situ fabrication of thin films are also covered along with the leading post-anneal processes. The specific techniques examined include sputtering (single-target and multi-target), electron-beam co-evaporation, MBE, laser ablation, ion-beam deposition, and CVD.

Thin-film oxide superconductor, Y1B a2Cu307.delta was prepared onto singlecrystal MgO (100) substrates by facing-targets sputtering (FTS) deposition technique. Throughout the various preparation conditions, little deviation of the compositional ratios of the metallic elements in the as-prepared films from those of the targets: i.e. Y:Ba:Cu = 1 :2:3 was observed. The atomic structures and properties of superconductivity of the as-prepared films largely depended on the substrate temperature, T. They were classified as the following five regions. Region I: 720 °C > T > 670 °C. The films had c-axis oriented Y1Ba2Cu3O7 structure having T0 > 70 K. Region II: 670 °C > T5 > 630 °C and 770 °C > Ts > 720 °C. The polycrystalline Y1Ba2Cu3O7 having T0 - 40 K was observed. Region III: 800 °C > T > 770 °C and 530 °C > T > 400 °C. A different crystalline structure having ca. 1/3 periodicities of the c-axis length of Y 1B a2Cu307.8 appeared. It had semiconductor-like temperature dependence of the electric resistivity. Region IV: 630 °C > T > 530 °C. A transition region between Regions I & III. The polycrystalline Y1 B a2 C u 0 and the "1/3 periodicity" structures coexisted. Region V: 400 °C > T > R.T. The films were amorphous and electrically insulating. The dependence of the structure on T will be explained by two factors which govern the crystal growth process: One is the surface mobility of the depositing atoms on the surface of the films; the other, configurational entropy of each crystal structure grown in the films.

In this report we present a systematic study of epitaxial YBa2Cu3O films laser ablated on Y-cut LiNbO3 substrates. X-ray diffraction pattern indicates that the c-axis is perpendicular to the substrate plane and the (110) direction of the film is parallel to the [11.0] of the substrate with two domains with the (1 10) as a mirror plane. Resistivity of the film shows a typical metallic behaviour in the normal state with a sharp transition at 92K. The effects of oxygen deficiency on the resistivity are also studied. Oxygen content is controlled by annealing the sample either in low oxygen pressure or in vacuum and estimated from the c-axis lattice parameter determined by X-ray diffraction. As oxygen is depleted gradually, the film resistivity shows metallic, semiconducting, and eventually insulating behaviors. Superconducting percolation phenomenon is observed for the semiconducting sample at low temperatures.

Strained multilayer thin films of YBa2Cu3O76/Nd1.83Ceo.i7CuO have been prepared by laser ablation deposition. For individual layers below a critical layer thickness of about 250A, coherency strain compresses the Nd1.83Ceo.17CuO lattice and expands the YBa2Cu3O75 lattice. The orthorhombic distortion in the YBa2Cu3O75 layers is also removed. Depending on their oxygen content, either the YBa2Cu3O75, or the Nd1.83Ce0.17CuO layers are superconducting in these multilayers. The strain-induced structural modification has a significant influence on the superconducting transition temperature and critical current density of the YBa2Cu3O75 layers. Zero field critical current densities as high as 1.lxlO7A/cm2 at 77K have been measured for the YBa2Cu3O7 -, layers.

Thin films of quaternary metal oxides, that are superconducting at temperatures above 77°K, were prepared by electrodeposition of the cations from aqueous electrolytes. The resulting deposits were thermally annealed . We will report the procedure for the electrodeposition of YBa2Cu3O7_delta (The "1-2-3" compound). X-ray diffraction demonstrates clearly the predominant presence of the 1-2-3 phase with minor contamination from other oxides. Conductivity measurements show a transition to the superconducting state around 98°K. Magnetic susceptibility measurements show a transition to a diamagnetic phase around 50°K. Scanning Electron Microscopy shows that the films are porous.

A new x-ray technique, called lotal reflection -ay fluorescence (TXRF) analysis, may be able to compare the surface versus bulk stoichiometry for heavy elements (excluding oxygen) in HiTC films. The opportunity in TXRF is that the glancing incident angle of the x-ray source can be varied from below, to above, the critical angle for total external reflectance and thereby can change the analyte depth from a few monolayers to several hundreds of monolayers. The work presented here is a preliminary study of this approach as applied to three films: ErBaCuO/YSZ, YBaCuO/YSZ, and YBaCuO/MgO. The results show little change in relative stoichiometry, but the results are inconclusive because the sample dimensions were too small to allow an accurate determination of the glancing angle for this instrument configuration and the glancing angle may have always been above the angle for total external reflection. Larger area samples are needed to evaluate the concept.

Thin films of YBa2Cu3O7_ deposited by ion-beam sputtering on yttria-stabilised zirconia (YSZ) substrates at room temperature have been lithographically patterned to form dc SQUID structures. Weak links are formed by naturally-occurring grain boundaries during annealing f the previously patterned films. These devices function either by he collective action of an array of weak links or by the action of a few dominating ones. Using a flux-locked-loop feedback circuit, we have obtained an upper limit for the SQUID noise of 1.5 x iO of the flux quantum per root Hz at 100 Hz in a SQUID of inductance 60 pH perating in liquid nitrogen. Critical currents averaged over the weak link cross-section are greater than iO" A/cm2 at 77 K. The performance of these devices is strongly dependent on temperature in the range 64-80 K. In this paper, we describe the preparation and properties of YBa2Cu3O7_ thin ifims and SQUID devices, and discuss further developments needed to improve the operating characteristics of these devices.

We have studied the superconducting critical current 1. of Y1Ba2Cu3O7,-Ag/M-Pb proximity junctions. The current-voltage (I.V) characteristics are typically those of a superconductor-normal metal-superconductor (S-N-S) junction. The Y1Ba2Cu3O7.-Ag/Al-Pb junctions show sharp Shapiro steps in a microwave field. The dependence of step height on microwave power is well described by the Resistively Shunted Junction (RSJ) model, assuming a IC cx: Sin ( Josephson behaviour, where ço is the pha difference of the superconducting order parameter across the junction. The Josephson current shows an interference pattern in a magnetic field applied parallel to the junction plane.

The coherence length in Si is estimated by the measurements of the Nb-Si bilayer superconducting transition temperature and the Nb-Si-Nb weak link superconducting critical current. The coherence length is shown to increase with an increase in the carrier concentration n as a function of n"3 . This result agreed with the numerical result derived from the Seto-Van Duzer's theory. The change in pair potential for the Al-Nb proximity system can be reconstructed by measuring the dependence of differential resistance on incident energy and the bound state levels using lithographic point-contact on Al-Nb bilayer.

In this paper we present the preliminary analytical and experimental results of a novel low temperature metal impregnation method to increase the critical currents in thick film and bulk HTSC materials. The method described results in a structurally more controllable and effective microcomposite than the ones obtained with metal- and metal-oxide precursors. The physical procedure involves the infiltration of the interstices of the porous, fully treated superconductor with low-melting point, low T superconductor under high pressure. Deep penetration of the metal into the granular superconducting matrix creates large surface areas of strong Proximity Effect. Improved intergrain coupling increases the DC Josephson current and therefore J, the critical current. Prior to the experimental work a theoretical study was conducted. Indium was chosen as the impregnation material. Computations showed.that the infiltrated system should have at least a four orders higher critical current (4.47 x 104 A/cm2) as compared to the same array with vacuum barriers of 20A thickness between the grains (0.31 A/cm2). On the experimental side, high T, porous, 1-2-3 samples impregnated with gallium exhibited very low contact resistance (2. 1 x 10-6 cm2) at 85°K, a value about two orders of magnitude better than the 1-2-3 systems containing intergranular silver. Further experiments with indium impregnated samples are planned. This new low temperature method allows the manufacture of highly flexible wires and films when used with suitable substrates.

We have sthdied the ability of high Te supereonduotors to operate as electrical switches or current limiters . For this purpose, we have usi YBaCuO films, deposit&I on polycrystalline zirconia slabs by various techniques: conventional two-step processes as well as rapid thermal annealing have been consider&1 . The main results are that with a Tc(onset) of 91 K, the variation of the critical current density versus fruency shows that it will be possible to use the films at 50-60 Hz, although we ne&i to improve our low current density films to demonstrate this.

Single target in situ sputter deposition using 9O off-axis geometry has made it possible to study various physical properties of superconducting films of YBaCu3O'x under well controlled conditions. The superconducting DC and high frequency properties, and the normal state properties can all be optimized under conditions which do not necessarily produce the highest Tc's. Surface resistances at 4.2 K and 10 GHz are reproducibly less than 20 iQ. Correlations between the processing parameters, DC properties, microstructures and high frequency properties of these films as they are presently known are summarized.

High critical transition temperature (high Tc) superconducting thin films of Tl-Ca-Ba-Cu-O (TlCaBaCuO) were fabricated on LaAlO3 substrates in an rf magnetron sputtering system. As-deposited thin films were sintered and annealed in a thallium rich ambient to obtain superconductivity with a zero resistance critical temperature (Tc) at 103 K. X-ray diffraction (XRD) results showed that the thin films were highly c-axis oriented with both Tl2Ca2Ba2Cu3O (2223) and Tl2CalBa2Cu2Ox (2122) phases present. A wet chemical etching process was used for patterning the as-deposited TlCaBaCuO thin films. Linewidths as small as 25 m were patterned using standard photolithography and wet chemical etching techniques. A ring resonator designed for a center frequency of 30 GHz has been fabricated.

Thin films of YBCO were used as the active element in an optically triggered fast-opening switch. These epitaxial films, up to 1 .tm thick, were deposited either by coevaporation or by if magnetron sputtering. A patterned switch structure was current-biased and subjected to 150 ps pulses from a Nd:YAG laser. Switching from the superconducting to the normal state was observed to occur as fast as 1 ns. A model is presented that can account for the observed switching characteristics in terms of the thermal and electrical times of the films; the results clearly indicate substantial film heating above the ambient temperature. Results are encouraging for potential application to a high-current opening switch.

High-temperature superconducting (HTS) thin films exhibit a change in their electrical properties when exposed to optical radiation. The spectral characteristics of this electrical response were investigated by exposing HTS thin films to radiation from laser sources with wavelengths in the visible and infrared spectra. Experimental results are interpreted with regard to bolometric and/or nonequilibrium detection mechanisms.

Superconducting YBa2C u 3 0 7 (YBCO) thin films were grown on Si with transparent, conducting Indium Tin Oxide (ITO) buffer layers The onset temperature at 92K and zero resistance at 68K were measured. Both, ITO and YBCO films were deposited by ion beam co-deposition. The YBCO/ITO films exhibit metallic resistivity with positive slopes (r0.055 1K). The YBCO is uniform, textured and polycrystalline. The relevance for hybrid opto-electronic device structures is briefly discussed.

High T 1-2-3 superconductor thin films have been deposited on (001) single crystal Si with and without oxide barrier by pulsed excimer laser evaporation technique. The oxide barrier of Zi02 was also deposited by the same laser technique. It is shown that the quality of superconductor film and the corresponding transition depend on the quality of the barrier layer. Low angle X-ray diffraction and IR transmission results have been used to identify the structural quality of the barrier layer. The superconducting films have been characterized using X-ray diffraction and resistivity-temperature measurements. T of 87K has been achieved in O.7p,m thick high T films on Si with O.3p.m thick Z1O2 bather deposited at 600°C.

In order to optimize the performances of YBaCuO thin films, elaborated by a two step process on SiO2/SiN4/Si substrates, we have studi&1 the effect of rapid thermal annealing (EA) conditions on low temperature (i.e. < 200°C) sputter&i layers, in the thickness range 0.3 - 1.5 m. Both the superconducting properties and the surface quality of the layers have been investigated. One of the advantages of this process is to allow the use of a very thin nitride layer (i.e. 45 A), to avoid the harmful diffusion of silicon from the wafer. This fast technique is also efficient to prevent interdiffusion between the silica and YBaCuO layers . Our first results show that an onset temperature in the 87-91K range can been obtained, with T(R.o) 60 K and 'c 500 A. Clii (at T(R.o /2) . It is also shown that these figures might be improved by repeated RTA cycles.

We present in situ real-time monitoring of emission lines from rf induced plasma of elemental and ionized species from target of YBaCu3O7 compounds during the sputtering growth. Abundances of the ionized and/or neutral species rather than clusters were observed while relative composition of the species was varied by target composition, applied rf power, gas pressure, and location of substrate. We discuss usefulness of real time monitoring of ejected species which depend on rf power and gas pressure during the sputtering deposition of high Tc superconducting thin films.

The molecular beam epitaxial growth of layered Bi-Sr-Ca-Cu-O films is reported. The advantage of using ozone rather than molecular oxygen for the growth of cuprate superconductors by molecular beam epitaxy (MBE) is discussed. Molecular beams of the constituent metals were shuttered on an atomic layer-by-layer basis to grow Bi2Sr2Ca..1CuO phases for n=1 to 5, and ordered superlattices of these phases. Using these techniques an as-grown superconducting film with rf.nset near 100 K and T (p=O) of 84 K was achieved. The films are smooth on an atomic scale. The results demonstrate the ability of shuttered MBE to grow custom layered combinations of Bi2Sr2Ca..1CuO layers. This shuttered MBE growth technique seems quite capable of synthesizing artificially layered epitaxial structures consisting of layers of oxides that are superconducting, non-superconducting metals, semiconducting, or insulating, with control of layer thickness and abruptness on an atomic scale.

Barium silicate and barium aluminate films were studied for use as chemical reaction and diffusion barrier layers for Y1Ba2CuO7 (YBC) deposited on sapphire and fused silica substrates by the sol-gel technique. Depth profiling by secondary ion mass spectrometry (SIMS) was used to characterize the abruptness of the interfaces between the barrier layer and the YBC film as well as the barrier layer and the substrate. We found that barium aluminate films reacted with fused silica substrates forming a coarse-grained barium silicate phase. Barium silicate, BaSiO3, also reacted with silica substrates forming a broad, amorphous reaction zone containing some BaSi2O5. Although barium silicate and barium aluminate deposited on sapphire formed a BaA112O19 phase, they provided a barrier to barium diffusion from sol-gel deposited YBC. Crystalline barium aluminate grown on c-cut sapphire was the most effective barrier layer for the growth of YBC films; compositionally uniform YBC films were made similar to that grown on strontium titanate substrates. These data show that chemically stable, crystalline films are more effective barrier layers than amorphous films.