In a superconductor/semiconductor structure, superconducting electron pairs in the superconductor diffuse into the semiconductor because of the proximity effect. This structure has been applied to novel superconducting devices like superconducting transistors and superconducting electron wave devices. These devices are operated by controlling the superconducting wave function in the semiconductor. The physics, fabrication process and operation of the devices are described.

Superconducting YBa2Cu3O7-delta (YBCO) thin films have been grown in situ by ion beam sputtering on Si and GaAs substrates with intermediate, conducting Indium Tin Oxide (ITO) buffer layers. Uniform, textured YBCO films on ITO exhibit Tc onset at 92K and Tc0 at 68K and 60K on Si and GaAs substrates respectively, the latter value is the highest Tc reported on GaAs. YBCO/ITO films exhibit metallic resistivity behavior. In situ YBCO films on SrTiO3 show Tc onset = 92K and Tc0 = 90.5K, transition widths are less than 1K. A simple optical bolometer has been constructed from YBCO films on SrTiO3. Tunnelling measurements have also been carried out using the first YBCO-Pb window-type tunnel junctions.

This paper discusses established electronics technology with prospects for incorporation of high critical temperature (Ta) superconductors, the projected results of introducing superconductors into conventional semiconductor electronics, and processing issues in the construction of hybrid devices.

The reasons for the failure to develop a successful Josephson tunnel junction made from high-temperature superconducting cuprates is discussed. The difficulties in developing a theoretical analysis of even simple-to-make cuprate Josephson devices are pointed out. The development of alternative Josephson devices based on the fabrication of engineered microbridges is addressed, and an overview is given of successful YBCO microbridges. Emphasis is given to focused ion beam and step-edge microbridges.

Planar S/N/S Josephson junctions were successfully fabricated by multi-layered thin films of Bi-based high-Tc oxide superconductors. Two Bi2Sr2Ca1Cu2O(x) films and Bi2Sr2Cu1O(y) film were successively layered as superconducting electrodes and normal conducting buffer layer, respectively. These films were epitaxially deposited on (100) MgO substrate by in situ process of RF magnetron sputtering. Microjunction areas were defined by photolithography and Ar ion milling. These S/N/S type junctions clearly exhibited the AC Josephson effect under the irradiation of radio frequency waves of 12 GHz. More than 20th Shapiro steps were observed and those step heights were oscillated according to the irradiation power. These characteristics were stable and reproducible for different configuration of function area.

Fabrication and testing of planar and edge geometry YBaCuO/Au/Nb superconductor/normal-metal/superconductor (SNS) device structures is described. Weak-link devices of this type serve as sensitive probes of the electrical quality of the YBaCuO/Au interface. The devices are fabricated using laser-ablated, in situ, c-axis-oriented YBaCuO thin films, with both annealed and unannealed YBaCuO/Au interfaces. The planar SNS structures are formed by sequential, in situ deposition of YBaCuO, Au, and Nb, followed by etching, planarization, and wiring electrode definition to produce junctions ranging from 5 to 20 micron on a side. Resulting RnA products are 1-10 x 10 to the -8th ohm-sq cm with critical current densities up to 5 kA/sq cm. For the edge geometry devices, the YBaCuO film edges are patterned using Ar ion milling, followed by a low energy ion cleaning step and in situ deposition of Au and Nb. Devices with areas in the 10 to the -7th to 10 to the -8th sq cm range have been fabricated with RnA products lower than 10 to the -8th ohm-sq cm and critical current densities up to 3kA/sq cm. Both types of devices show ac Josephson steps under microwave irradiation. The best results have been obtained with annealed YBaCuO/Au interfaces.

In exploring the feasibility of fabricating high Tc SNS Josephson junctions with well-defined and clean SN interfaces, have been cleaved epitaxial thin films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O of various crystal orientations in vacuum while the evaporation of a noble metal is taking place. The samples had structures which allowed in situ formation of SNS junctions when the films were cleaved together with substrate with the area of the SN interfaces defined by the revealed cross-sectional edge surfaces of the films. Electrical measurements of the resulting junctions show that oxide/metal interfaces possess contact resistance in the order of 10 to the 9th to 10 to the 8th ohm-sq cm which is at least two orders of magnitude larger than that of similarly made SN interfaces with metallic superconductors. The nature of this interface and the factors influencing and giving rise to the contact resistance are discussed.

The Naval Research Laboratory (NRL) is exploring the feasibility of deploying high temperature superconductivity (HTS) devices and components in space. A variety of devices, primarily passive microwave and millimeter wave components, have been procured and will be integrated with a cryogenic refrigerator system and data acquisition system to form the space package, which will be launched late in 1992. This Space Experiment will demonstrate that this technology is sufficiently robust to survive the space environment and has the potential to significantly improved space communications systems. The devices for the initial launch (HTSSE-I) have been received by NRL and evaluated electrically, thermally and mechanically and will be integrated into the final space package early in 199 1 . The performance of the devices will be summarized and some potential applications of HTS technology in space system will be outlined.

Progress being made on space application technology research on film fabrication, passive microwave circuits, and semiconductor devices for cryogenic circuits is reviewed. Achievements in YBCO and TCBCO films are addressed along with circuit evaluations of microstrip resonators, phase shifters, microstrip filters, dielectric resonator filters, and superconducting antennas.

Recent technological advances have made it possible to form arrays of small thin-film-based bolometric pixels integrated onto Si substrates containing both array addressing and readout electronics. These advances have made bolometer technology a potentially low-cost, high-sensitivity, high-yield staring detector technology for the near future. In this paper, the basic performance aspects of an IR microbolometer are described. The design of a high-performance pixel and the performance measurements on some initial devices are presented. The potential performance of two-dimensional arrays is discussed.

TlCaBaCuO films using e-beam evaporation with subsequent sintering and annealing that have critical current densities of at least several hundred kA/sq cm, critical temperatures over 100 K, and surface resistance better than that of gold at 77 K and 8 GHz. Processing techniques have been developed for making microwave passive elements and a four-terminal active device called the superconducting flux flow transistor (SFFT) for microwave applications. The techniques include contacting, dielectric, normal layer deposition, and controlled HTS film etching. The SFFT shows promise as a microwave amplifier, oscillator, and active impedance converter and may also have many other applications. The advantages of the device include high speed, potentially low noise, and, for some applications, useful impedance levels.

The pulsed-laser deposition method has been used to fabricate epitaxial, nonsymmetric M(Y) x N(Pr) superlattices in which YBa2Cu3O7 (YBCO) layers either M = 1, 2, 3, 4, 8, or 16 c-axis unit cells thick are separated by insulating PrBa2Cu3O7 (PBCO) layers N unit cells thick (N = I to -32). The zero-resistance superconducting transition temperature, Tc0, initially decreases rapidly with increasing PBCO layer thickness, but then saturates at TcO 19 K, 54 K, 71 K, or 80 K, for structures containing 1-, 2-, 3-, or 4-cell-thick YBCO layers, respectively. Critical current density measurements carried out on structures with 16- or 32-cell thick YBCO layers show that the magnitude of Jc(H 0) 12 MA/cm2, as well as the magnetic field dependence and the anisotropy of Jc(H) all are in good agreement with corresponding measurements on thicker, single-layer YBCO films. Thus, there is no evidence of an enhanced Jc(H) due to the multi-layered structure, for the layer thicknesses investigated to date. The systematic variation of Tc0, as a function of the YBCO and PBCO layer thicknesses, is discussed in light of other recent experiments and theoretical model calculations. The superlattices' structural and compositional order are characterized using x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy, and details of the pulsed-laser deposition process are reported.

Heterostructures of non-magnetic/magnetic high T_c superconductors have been grown by laser ablating pur YBaCuO and Ni doped YBaCuO. Superconducting properties of the composite are dependent on the amount of doping and the thickness of the doped layers. The critical temperatures of 87K and critical current densities in excess of 10⁶ A/cm² at 77K in 0.85 Tesia magnetic fields have been obtained for structures grown on ZrO₂ substrates.

In this work, we detail the basic mechanisms and potential applications of the Laser Induced Forward Transfer (LIFT) for the rapid deposition and patterning in a clean environment, of high Tc superconducting thin films. With the LIFT technique, a stoichiometric oxide superconductor compound is initially deposited in a thin layer on an optically transparent support. By irradiating, under vacuum or in air, this precoated layer with a strongly absorbed single laser pulse through the transparent support, we are able to remove the film from its support to be transferred onto a selected target substrate, held in contact or close to the original film. The mechanisms for transferring YBaCuO and BiSrCaCuO thin films, with a pulsed UV excimer laser are described using a thermal melting model based on the resolution of the heat flow equation. The various possibilities given by the LIFT technique for patterning high Tc films (mask and direct patterning) are also examined.

Very high critical current densities are exhibited by epitaxial thin films of the high-temperature superconductors (on single-crystal substrates). Can similar high-current densities be achieved in the form of thin films on large-area polycrystalline substrates? If so, high-current superconducting tapes can be fabricated. We examine the arguments for and against this approach and briefly review the progress to date, in our laboratory and elsewhere, toward achieving flexible high-current tapes.

We have optimized the properties of Ba2YCu3O7 (BYCO) ifims grown by co-evaporation of Y, Cu, and BaF2 followed by a two stage anneal. We find that control of the stoichiometry of the film to 1% is critical to the optimization of both structural and electrical properties. The temperature and time of the high temperature annealing stage are vital to the optimization of the crystallinity and morphology of the ifim; deviations of as little as 25°C can have profound effects on both. The low temperature annealing stage parameters are important for the oxygenation of the film, and hence its superconducting properties. Using our optimized annealing conditions on 100 nm films of correct stoichiometry grown on LaAlO3(001), we obtain Tc(RO)=9OK AT(10-90%)0.5K, and J(77K)1<106Ncm2 in essentially zero magnetic field. The morphology of these films is smooth, and the crystallinity is excellent as measured by Rutherford backscattering/channeling 1 %).

Ninety six percent grain-orientation was achieved in YBa2Cu3O(7-x) ceramics using the hot-forging technique. X-ray diffraction measurements show that the c-axis is oriented parallel to the direction of pressing while the a and b axes are in the plane perpendicular to the pressing direction. Optical and electron microscopy fully support the X-ray results. Highly grain-oriented samples show a sharp Tc at 92 K and in some samples, Jc was found to be close to 10,000 A/sq cm.

The speed of optically controlled superconducting devices is discussed. The results of experimental measurements on the speed of nonequilibrium carrier recombination are reviewed. These results indicate that a voltage change can be induced in YBCO samples by a short laser pulse. It is shown that high-Tc superconducting devices can potentially operate in the subpicosecond regime.

Efforts to grow high quality films of YBCO on Si have been complicated by factors discussed in Ref. 1, chief among them being the reaction between YBCO and Si, which is damaging even at 550 C. This is well below the customary temperatures for YBCO film growth. To avoid the reaction problem, epitaxial YBCO films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ).2 Both layers are grown via an entirely in situ process by pulsed laser deposition (PLD). Although the buffer layer prevents reaction, another problem arises; the large difference in thermal expansion coefficients between silicon and YBCO causes strain at room temperature. Thin (<500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Thicker films are cracked and have poorer electrical properties. The thermal strain may be reduced by growing on silicon-on-sapphire (SOS) rather than silicon.3 This allows the growth of films of arbitrary thickness. Ion channeling reveals a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12% on either silicon or SOS. The normal state resistivity is 250-300 i-cm at 300 K; the critical temperature, Tc (R=0), is 86-88 K with a transition width (ATc) of I K. Critical current densities (J)°f 2x107 A/cm2 at 4.2 K and >2x106 A/cm2 at 77 K have been achieved. In addition, the surface resistance of a YBCO film on SOS was measured against Nb at 4.2 K. At 10 GHz, a value of 45 was obtained. This compares favorably to values reported for LaAlO3. Application of this technology to produce reaction patterned microstrip lines has been tested.4 This was done by ion milling away portions of the YSZ buffer layer prior to the YBCO deposition. YBCO landing on regions of exposed Si reacts to form an insulator. This technique was used to make 3 micron lines 1.5 mm long. The resulting structure had a Jc of l.6xl06 A/cm2 at 77 K. Isolation of separate structures exceeded 20 M. Several advantages of this technique are that no solvents, etchants or photoresist come into contact with the YBCO, hence this technique has a potential for operational-asgrown devices. In summary, it is now possible to produce YBCO films with structural and DC electrical properties which rival the most optimized c-axis epitaxial YBCO films on MgO, SrTiO3 and LaAlO3. Preliminary measurements of microwave properties appear promising. We thank Bruce Lairson for help obtaining magnetization data and Richard Johnson, Steve Ready and Lars-Erik Swartz for technical assistance. This work benefits from AFOSR (F49620-89-C-0017). DBF received support from NSF (DMR- 8822353). DKF acknowledges the AT&T scholarship.

The superconducting properties of YBa2Cu3O7 thin films subjected to controlled pulsed nanosecond laser irradiation were investigated. Irradiated films on (100) LaAlO3 substrates showed excellent thermal stability with the temperatures for zero resistance of approximately 90 K even after irradiation with energy densities greater than 250 mH/sq cm. The critical current density Jc of the films showed an enhancement at low energy densities, followed by a drastic decrease in Jc above a certain energy threshold. This decrease has been correlated with the melting threshold. Similar results are observed for YBa2Cu3O7 films on (100) yttria-stabilized zirconia substrates; however, the energy density was found to be much smaller.

Critical current density above 10,000 A/sq cm at 77 K and zero magnetic field have been achieved for both YBa2Cu3O6.8(YBCO) thin films on metallic substrates. A transition buffer, consisting of sub-buffers deposited at different temperatures, was used to enhance the crystallinity and the transport properties of YBCO films on metallic substrates. YBCO films were fabricated, using in situ laser deposition, and they were strongly c-axis oriented. Critical temperature of 87 K and critical current density of 30,000 A/sq cm at 77 K were obtained for a 0.5 micron-thick YBCO film. This Jc value is the highest reported for YBCO films on metallic substrates. Also, the magnetic field dependence of Jc and the mechanical properties could be improved by using Pt-coated metallic substrates.

One and two inch diameter wafers of (100) LaAlO3 have been coated with thin films of YBa2Cu3O7_ by a pulsed laser deposition technique. Deposition parameters have been optimized to produce uniform, 90 K films which have surface resistance values between 0.4 and 0.8 mμ at 4 K and 22 GHz.

We have grown thin films of YBa2Cu3O7jj in an oxygen atmosphere by pulsed-laser deposition using two synchronized lasers, separated by a variable delay (lps-10 ms). The ablated fragments from the first laser leads to the formation of a blast wave in 02, leaving behind a rarefied ambient. If the second laser is triggered before the 02 pressure returns to equilibrium, the resulting films show a decrease in transition temperature with an expanded c-lattice parameter caused by defects in the non-chain sites of YBa 2Cu3076. This demonstrates that a sufficiently high concentration of oxygen is needed during the time period that the fragments travel and deposit on the substrate. Based on the above understanding, we have been able to grow YBa2Cu3O76 films in a low pressure background (10-10 Ton) by using a pulsed, high intensity jet of 02. The oxygen source is provided by a pulsed molecular beam valve, and the opening of the valve and the triggering of the laser are synchronized with appropriate delay so that the supersonic gas jet and the ablated fragments arrive at the substrate at the same time. This provides the necessary oxygen to form the YBCO phase while maintaining a low oxygen background. The YBCO phase is not formed if the oxygen pulse is provided either before or after the arrival of the ablation fragments at the substrate. The ability to grow superconducting films at low background pressures should allow usage of in situ analysis techniques, such as reflection high-energy electron diffraction, during pulsed laser deposition.

High-Ta superconducting Bi-Sr-Ca--Cu-0 thin films have been prepared by low pressure organometallic chemical vapor deposition (ONCVD). Factors which influence texture and morphology of the OMCVD derived films have been examined, including the effects of precursors, doping and substrates. Under optimal conditions, high quality films with a high degree of preferred orientation are obtained. Initial experiments on in-situ formation of superconducting films are also described.

The effects of plasma -enhancement on MOCVD for growing superconducting YBa2 Cu3 OX thin films is studied. It is revealed that plasma-enhancement accelerates crystal I ization of YBa 2 Cu 0 so that growth temperatures of superconducting fi Ims can be decreased by about 150 °C . Thin fi Ims grown by plasma-enhanced MOCVD at 515°C and 580°C indicate zero-resistivity temperatures of 60K and 84K, respectively. Critical current density in the film grown by plasma-enhanced MOCVD at 580 °C is 1O A/cm2 at 77K. Infrared absorption spectroscopy and ultraviolet and visible emission spectroscopy clarify that plasma excite the metalorganic compounds and that this excitation promotes oxidization of metalorgan ic compounds and crystal I izat ion of YBa2Cu3O.

Highly c-axis-oriented Tl2Ba2CaCu2O(x) thin films were grown on MgO(100) by MOCVD and post annealing processes. Resistive transitions of 105 K, critical current densities as high as 100,000 Amps/sq cm (4 K) and surface resistivities 1/2 to 1/5 that of a gold standard at 17 GHz (77 K) were obtained with unpatterned films. Thin TlBaCaCuO films functioned as bolometric detectors over a spectral range of 1.5 to 20 micron; no quantum or nonequilibrium effects were observed between 4 and 125 K. Fine features were delineated in the BaCaCuO thin films by wet chemical etching. After Tl incorporation, resistive transitions exceeding 103 K were observed in the patterned films.

YBCO films, having critical current densities in excess of 10 to the 6th A/sq cm at 77 K and transition temperatures of about 89 K, successfully deposited on close lattice matched substrate materials at substrate temperature in the range from 720 to 740 C, are presented. The critical current densities are 10,000 A/sq cm at 70 K and the critical temperatures are 82 K for the films deposited on sapphire substrates. Successful deposition of c-axis oriented YBCO films with a transition temperature of 85 K was also achieved on silver substrates. Detailed analyses of the films were carried out by X-ray diffraction, EDS, SEM, resistivity measurements, critical current density measurements, and magnetization susceptibility measurements.

Metal organic chemical vapor deposition (MOCVD) has the potential of emerging as a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of high temperature superconductors, and related materials. As a reduced thermal budget processing technique, rapid isothermal processing (RIP) based on incoherent radiation as the source of energy can be usefully coupled to conventional MOCVD. In this paper we report on the deposition and characterization of high quality superconducting thin films of Y-Ba-Cu-O (YBCO) on MgO, SrTiO3, and YSZ substrates by RIP assisted MOCVD. Some preliminary results are also presented for the deposition of BaF2, Y203 and MgO on silicon substrates. It is envisaged that high energy photons from the incoherent light source and the use of a mixture of N2O and 02 as the oxygen source, assist chemical reactions and lower the overall thermal budget for processing of YBCO films.

Abstract not available.

In the current worldwide technology environment, it is essential for the U.S. microelectronics industry. and especially for the integrated circuit portion of that industry, that precompeutive cooperative research alliances be formed and funded at a level that emables them to be effective in rapidly advancing technology. It is important to realize that technology advances with or without our direct participation. If we do not aggressively participate we are quickly left behind. Increasing complexity and miniaturization have been the themes in semiconductor technology. Many are aware that what began in the early 60's with a few masking steps and minimum dimensions measured in mils. has now evolved to a level of sophistication requiring a 100 MW workstation for IC design and the investment of nearly S400 million dollars in fab cost to produce today's microchips. The leading nations of the world have come to realize that their future well-being is closely tied to their ability to compete in this hi-tech environment. Industry coalitions have been formed to exploit the early ramifications of emeging technologies. Improvements in overseas manufacturing have been made and continue unabated with new producLs, new processes, and new services being introduced at an increasing rate. Many foreign governments are now actively involved in formulating and conducting industrial and technology policies to aid their hi-tech industry. To meet these challenges, U.S. firms, with U. S. government cooperation, must respond.