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Highly selective high-temperature superconducting band-pass filters based on spiral meander line structures have been developed for base transceiver station applications of digital cellular communication systems. The filter comprised 12-pole microstrip line resonators with a circuit size of 0.5 × 17 × 41 mm3. The filter was designed to have a bandwidth of 25 MHz at a centre frequency of 834 MHz. Particularly, the physical size of each resonator was chosen not only to reduce far-field radiation, but also to have reasonable tunability in the filter. Device characteristics exhibited a low insertion loss of 0.4 dB with a 0.2 dB ripple and a return loss better than 10 dB in the pass-band at 65 K. The out-of-band signals were attenuated better than 60 dB at about 3.5 MHz from the lower band edge, and 3.8 MHz from the higher band edge.

We report on the effects of electromigration of basal plane oxygen vacancies on SNS ramp edge Josephson junctions where the N-layer is YBa 2 Cu 2.79 Co 0.21 O 7− δ , a doped version of the YBCO electrodes. Through the application of a 4–10 mA (∼2–5 MA/cm 2 ) current bias at room temperature, the basal plane oxygen order and content in the N and S layers were improved. This is demonstrated by an increase in I c R n from μ V, to as much as 205 μ V. The implications of these results on SNS junction fabrication, and the nature of tunneling in such devices are discussed.

The microstructures of YBCO/N/YBCO ramp-edge junctions have been studied by transmission electron microscopy and related to supercurrent transport properties which depend on the barrier layer N, the interfacial structures and defect structures in the multilayer epitaxial devices. Three different types of junction materials were investigated: Metallic oxide barriers, CaRuO{sub 3} and SrRuO{sub 3}; barriers isostructural to YBCO, Co-doped YBCO and Co-doped PrBa{sub 2}Cu{sub 3}O{sub 7}; and 'interface engineered' barriers, formed by plasma treatment of the YBCO ramp-edge. Metallic oxide barriers are characterized by high steps and strong variations in local barrier width. The observed topologies are consistent with an island growth mode for both CaRuO{sub 3} and SrRuO{sub 3}. The metallic oxide barriers are associated with interfacial strain fields that are believed to be the cause for interfacial oxygen depletion in YBCO and the observed excess normal-state resistance. A number of structural defects and deviations from perfect epitaxy have been observed. Most disruptive to the integrity of the multilayer structures and transport properties is the nucleation of a-axis YBCO grains at steep barrier steps and within the YBCO layers. The barrier layers in isostructural junctions are well structured with a high degree of interfacial coherence and for the most part,more » Cu-O planes are continuous across the interfaces. In contrast to heterostructured metallic oxide barriers, isostructural junctions contain few extraneous defects, such as a-axis grains at the barrier layer, moreover, the second YBCO layer is of good quality due to the perfect epitaxy between the materials. Among the junctions investigated the interface engineered junctions have shown the best electromagnetic properties. Their structure is characterized by narrow (2-3 nm) barriers that are continuous and crystalline. No significant interfacial strains and structural disorder were observed. This and a constant barrier thickness appear responsible for obtaining good uniformity of electric transport properties. The narrow pinhole-free barrier, coupled with excellent epitaxy and few defects, yields good reproducibility and a range of properties suitable for practical applications.« less

We have fabricated all YBCO edge junctions which do not require the deposition of an interlayer or barrier material. Rather, through appropriate high-temperature vacuum annealing and in-situ ion plasma treatments, we have modified the junction interface in such a way as to lead to reliable weak link behavior. These devices display RSJ-type I-V characteristics with excellent magnetic field modulation. I/sub c/R/sub n/ values over the range 0.5 to 3 mV and corresponding R/sub n/A values of 6/spl times/10/sup -8/ to 1.2/spl times/10/sup -9/ /spl Omega/-cm/sup 2/ at 20 K are easily attained by varying the process, which is not possible in most high-T/sub c/ junction technologies. These junctions can also be very uniform and appear to be quite stable. We have observed an unusual response to applied microwave radiation. We have investigated the microstructure of these junctions using transmission electron microscopy (TEM). Results of these analyses lead us to believe these junctions are feasible as the basic components of a high-T/sub c/ circuit technology.

A process is provided for fabricating YBa 2 Cu 3 O 7 thin-film edge junctions in which no deposited barrier is employed. These devices display excellent RSJ-type I-V characteristics with values of I c and R n tunable over a useful range for operation of digital circuits.

Secondary ion mass spectrometry (SIMS) has been used to carry out in-depth analysis of a superconducting multilayer thin film. The film was a multilayer composed of YBa 2 Cu 3 O 7- δ /10% cobalt-doped YBa 2 Cu 3 O 7- δ /YBa 2 Cu 3 O 7- δ (YBCO/Co–YBCO/YBCO) which had been laser-ablated on LaAlO 3 . Optimum conditions for SIMS depth profiling have been sought for the highest resolution of the position and width of the buried Co–YBCO layer. The margins of the Co–YBCO layer are characterised by the Co secondary ion decay length. This parameter has been measured for both oxygen and xenon primary ion beam sources and with respect to the angle of incidence of the primary ion beam on the sample. It has been found for both Xe + and O 2 + ion beam bombardment that the decay length of the leading edge of the Co-doped layer is invariant at 68±3 nm/decade for Xe + and 53±3 nm/decade for O 2 + . The decay length of the trailing edge, however, gets progressively worse as the angle of incidence is increased above 30°. This effect has been attributed, through the use of atomic force microscopy (AFM), to the development of topography in the crater base as the analysis proceeds.

YBa 2 Cu 3−x Co x O 7−δ goes through a metal-insulator transition near x = 0.4. When these doped YBCO materials are used as barriers in SNS junctions, a clean interface can be formed due to their excellent match of lattice constants and thermal expansion coefficients. By using three doping levels, x = 0.12, 0.21 and 0.42, we have estimated the effects of the dopant from the temperature and thickness dependences of I c and R n . In the framework of conventional de Gennes proximity effect theory, we have observed a crossover from the clean limit to the dirty limit as the doping level approaches the metal-insulator transition. In the case of x = 0.42, which no longer superconducts on its own, we had to invoke a pair-breaking mechanism by a cutoff scattering rate in order to explain the slower increase of the critical currents at low temperatures than the standard proximity effect would predict. Several ideas on the possible origins of such a cutoff scattering rate will be discussed. By adding Pr dopants in the Co-doped barrier, we were able to deduce the elastic scattering effect of Pr dopants, which results in smaller diffusion constants. The interfaces YBCO forms with other barriers such as (CaSr)RuO 3 and (LaSr)CoO 3 have been investigated in detail. The defect states on the surface of YBCO seem responsible for the observed zero bias conductance anomaly.

We report on the micro-Raman spectroscopy study of thin films of YBa/sub 2/Cu/sub 3-x/Co/sub x/O/sub 7-/spl delta// grown by laser ablation. Depending on the growth pressure, the films are found to be either homogenous or inhomogeneous on a scale /spl Gt/2 /spl mu/m. In either case the films are, on average, oxygen deficient, but this deficit can be substantially improved, yielding /spl delta/ less than zero in thin film microstructures treated by oxygen electromigration. This indicates that the Co addition to such films impedes, but does not forbid the attainment of a relatively optimal degree of occupancy of the dopant, chain oxygen sites.

Based on a single-level YBCO thin film topology and seven bicrystal grain-boundary junctions, a high temperature superconductor delta modulator for analog-to-digital converters has been designed, fabricated, and tested. A single bit quantizer based on a quantum flux parametron (QFP) comparator is used for the modulator. A large superconducting inductor is used both for the signal input and for the feedback. A small resistor is chosen for connecting the comparator to the read-out section. The oversampling provides large input signal bandwidth with high dynamic range. Circuit simulations prove the concept of the design. The effective LSB and MSB of the modulator are discussed in terms of input inductance, junction critical current, and QFP noise current. The density of latched output pulses is proportional to the change of input amplitude. Au wires were employed to make crossover of bias lines. Although this modulator did not function as expected for low-speed measurements, it shows the proper latching behaviour of the output section at 4.2 K and 35 K.

A superconducting multilayer structure (YBCO/3% Co-doped YBCO/YBCO/LaAlO3) has been studied using secondary ion mass spectrometry (SIMS). Under xenon ion beam bombardment at a range of angles of incidence it has been found that the Co leading edge interface width is invariant at 68 nm/decade. This broadening cannot be solely explained in terms of beam induced mixing or the topography present at that depth, suggesting that some diffusion or segregation has taken place during the growth of the sample. The trailing edge Co interface width, however, gets progressively worse as the angle of incidence of the ion beam is increased. This is believed to be a SIMS artefact and is attributed to the development of topography in the crater base as the analysis proceeds.

The microstructure of YBCO/SrRuO3/YBCO junctions in the edge geometry have been studied by high resolution electron microscopy. Various defects in the YBCO and SrRuO3 films are observed and analyzed. The most striking defects in the c-axis-oriented YBCO film are a-axis particles, which cause bending and interruption of lattice planes as well as high steps and cracks in the subsequent layers. The SrRuO3 layer in the ramp-edge junction region consists of small domains with slightly different orientations. This leads to the formation of steps on its surface and large variation in SrRuO3 thickness. Mechanisms for forming this defective layer are suggested based on the growth mode and the crystal structure of SrRuO3. We find evidence for strain fields at the SrRuO3/YBCO interface. The oxygen deficiency in YBCO caused by this interface strain may to a large part be responsible for the excess resistivity of this junction. In addition to the defective SrRuO3 layer, the occurrence of various defects in the junction area, including Y2O3 and a-axis YBCO particles, seem to be the cause for the wide scatter in the junction electrical characteristics. The formation of steps and large thickness variation in the barrier layer may be the reason for the rather large critical thickness of the SrRuO3 superconductor-normal-superconductor (SNS) junction. In addition to the junction interfaces, the microstructure of SrRuO3/LaAlO3 and SrRuO3/SrTiO3 interfaces have also been studied.

Miniature robots especially miniature flying robots or vehicles are very fast gaining popularity among researchers. They are versatile in design, very compact and lightweight to carry a few grams of camera or any other payload to do the assigned task or inspection routine in given time frame and can come back to the base station. Miniature robots can be of help in many disaster mitigation, search and rescue operations because of their ability to fly in bad weather conditions as well as difficult to access passages without risking human lives. When flying in such conditions, it is essential to have a air vehicle that can easily fit through small openings and maneuver around pillars and destructed wall structure. To complete the given tasks effectively and in given time is the biggest challenge in designing any such vehicles. In this paper our approach is mainly to design the MAV which will maneuver without any disturbance created by the atmosphere. In brief, a kinematic model of the arrangement of MAV is studied keeping in view different aspects like thrust forces, lift co-efficient, basic maneuvering operations, etc. Another aim is to analyze the deflection in structure of MAV in certain loading conditions.

We report on ferroelectric field effect experiments on Pb(Zr0.52Ti0.48)O3/SrCuO2 and Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures with an emphasis on the material characterization. Upon reversing the polarization of the Pb(Zr0.52Ti0.48)O3 ferroelectric layer, we measured a nonvolatile change in the resistivity of ultrathin layers of SrCuO2 and SrRuO3. In thin SrRuO3 films (30 A) up to a 9% resistivity change has been observed at room temperature.

A set of 45° [001] bi-epitaxial YB2Cu3O7−x thin film grain boundaries was studied to compare the effects of the microstructure on transport properties. The grain boundaries were made using two different deposition techniques: pulsed laser deposition (PLD) and pulsed organometallic beam epitaxy (POMBE). The transport properties were highly dependent on the specific growth conditions used, resulting in both fully resistive and superconducting grain boundaries. Subsequent microstructural analysis of the measured boundaries showed that both types (superconducting and resistive) meandered on the length scale of hundreds of nanometers. The major structural difference between the boundaries was at the atomic scale where the resistive boundary had a 1 nm wide disordered region. The direct correlation of microstructure to transport properties demonstrates the importance of the atomic scale structure in the resulting transport behavior.

Superconductor-normal-superconductor (SNS) edge junctions consisting of YBa2Cu3O7/YBa2Cu2.79Co0.21O7−x/YBa2Cu3O7 were fabricated on (001) YSZ substrates using laser deposition. In contrast to other SNS junctions, e.g., with La0.5Sr0.5CoO3, CaRuO3, or SrRuO3 as the barrier layer, these devices do not display an excess normal-state resistance. High-resolution and conventional transmission electron microscopy (TEM) techniques were employed to investigate the SN interface structure and possible interface defects. Results are compared to recent TEM investigations of CaRuO3 SNS junctions.

Superconductor-normal-superconductor (SNS) edge junctions consisting of YBa 2 Cu 3 O 7 /CaRuO 3 /YBa 2 Cu 3 O 7 were fabricated on (001) LaAlO 3 substrates using laser deposition. These devices display an excess resistance which may be related to the SN interface and normal layer structure or composition. High-resolution and conventional transmission electron microscopy were employed to investigate the SN interface structure to determine the degree of interface matching and possible interfacial defects. Energy-loss spectroscopy and energy dispersive X-ray analysis were performed on the CaRuO 3 film and near interface regions to determine the normal layer composition and to quantify the extent of interdiffusion between the CaRuO 3 and YBCO films. Results are compared to recent investigations of SNS edge junctions consisting of YBa 2 Cu 3 O 7− x /YBa 2 Cu 2.79 Co 0.21 O 7− x /YBa 2 Cu 3 O 7− x .

Interfaces between metal oxides have not been studied as extensively as metal or semiconductor interfaces. Even in magnetic metallic systems, new phenomena are still being discovered, such as giant magnetoresistance, which has been attributed to an interface phenomenon. As general interest in metal oxides increases, researchers are studying a large variety of heterostructures consisting of superconducting oxides, conducting oxides, ferroelectric oxides, magnetic oxides, and optical oxides. As the complexity and level of integration increase, scientists need a better understanding of the interfaces in metal oxide systems. For example, interface issues in grain boundaries in high Tc oxides and in Josephson junctions of the superconductor/normal material/superconductor (SNS) type have been identified as important technological barriers. In heterostructures based on ferroelectric materials, fatigue problems are believed to be associated with the interface between the conducting electrodes and the ferroelectric metal oxides, and with grain boundaries in the ferroelectric materials.In this article we will focus on the interface issues related to YBCO superconductors. We will describe interface phenomena observed in several systems, such as YBCO/metal contacts, YBCO/YBCO grain boundaries, and YBCO/epitaxial metal oxides. From their seemingly universal behavior, we will try to identify the origin of the interface phenomena and will describe some recent efforts to control such phenomena.

Shift registers have been demonstrated in YBaCuO operating at 77 K using from 64 to over 1000 junctions. These are some of the larger scale integrated circuits demonstrated to date using YBaCuO Josephson technology. The circuit is a modified rapid single flux quantum design in which a single trigger pulse causes a one bit shift of the entire word of 32-512 b in length. Two different junction technologies, electron-beam defined nanobridges and epitaxial edge junctions, have been used with parameter spreads ranging from 11% to 22%. Correct operation has been verified with low speed random word tests and circulating data tests while pseudo random bit sequence demonstrations are underway. A practical amount of time to shift between cells has been measured to be about 10 ps. >

We fabricated an epitaxial Au/SrTiO3(001)/SrRuO3 (or CaRuO3)(001)/SrTiO3 (or LaAlO3)(001) heterostructure to investigate the effect of the strain on the epitaxial tunable dielectric thin films. SrTiO3 thin films showed very different dielectric properties depending on the bottom electrode with an opposite lattice mismatch. The SrTiO3 thin films grown on the CaRuO3 bottom electrodes showed nearly a two times larger tunability than that on SrRuO3. We think this is due to the different strain on the SrTiO3 thin films. The tensile strain along the applied electric field in the parallel plate capacitor enhances the dielectric constant and the tunability, while the compressive strain decreases them. We believe this is consistent with the hardening of the soft mode phonon due to the compressive strain.

We have synthesized superconducting YBa2Cu3Ox thin films in situ using magnetron cosputtering with three metallic targets (Y, Ba, Cu). We present details of the sputtering chamber, as well as the growth conditions necessary to obtain superconducting films. We discuss the effects of oxygen and ozone partial pressure, differential pumping, O2–Ar plasma deposition and Ba–Cu alloy targets. We elaborate on our ozone condensing and delivery system. Finally, we describe the difficulties encountered with the deposition system and provide details of possible improvements.

We have created YBCO thin film ramp edge Josephson junctions by modification of the edge surface prior to counterelectrode deposition. No deposited interlayer or barrier layer is employed. These devices are uniform and reproducible, and they display resistively shunted junction current-voltage characteristics with excellent magnetic field modulation. IcRn values over the range 0.5–3 mV and corresponding RnA values of 6×10−8–1.2×10−9 Ω cm2 at 20 K are easily attained by varying the process. We believe these junctions offer significant promise as the building blocks of a high Tc electronics technology.

All thin‐film YBCO/Pb Josephson tunnel junctions have been fabricated. The junctions showed a well‐defined Pb gap, Pb phonon structures, and very low leakage current. In addition, a higher bias spectroscopy revealed identical structures as have been seen in junctions made with single‐crystal YBCO. A thin uniform Ag diffusion barrier at the junction interface lowers the junction resistance enough to study the Josephson effct in YBCO/Pb tunnel junctions. Both the temperature and the magnetic field dependencies of the magnitude of the Josephson current displayed conventional behavior. The junctions were very reproducible and uniform as indicated by the Ic(B) pattern.

The fine scale microstructure of YBa2Cu3O7−x (YBCO)/CaRuO3 (CRO)/YBCO edge junctions has been characterized using transmission electron microscopy. The results showed that the damages due to ion beam milling during fabrication of the YBCO edges annealed out during heating to higher temperatures for deposition of additional layers. No contamination due to the ex situ processing of the edges was detected. The CRO grew epitaxially on the YBCO edge and small insulating Y2O3 particles nucleated on the CRO giving rise to inhomogeneous electrical properties along the junction. The nucleation of Y2O3 particles was enhanced by the microscopically rough morphology of the YBCO edge. The results stress the importance of the morphology of the YBCO edge and show that general conclusions about the interface structure cannot be drawn from corresponding planar geometries.

A novel effect from microwave radiation near 9.3 GHz applied to high‐TcYBa2Cu3O7−δ single grain boundary junctions was observed. In addition to the usual Shapiro steps resulting from the ac Josephson effect, constant voltage steps with voltages halfway between the voltages of the Shapiro steps were present. The widths of these ‘‘half‐integral’’ steps were measured as a function of microwave power, and the influence of a magnetic field was investigated. From previous results on high‐Tc grain boundary junctions and a comparison of the results presented here with single‐ and multiple‐junction effects in low‐Tc materials, we conclude that the half‐integral steps are likely to be a result of grain boundaries being composed of multiple junctions in parallel.

We describe the fabrication of a free‐standing YBa2Cu3C7−δ air bridge for useful applications of microstructures and microcircuits integration. We have used a sacrificial dielectric layer, which was subsequently etched, to produce the air gap between top and bottom layers. We have used conventional photolithographic processing, ion‐beam dry etching, and selective wet etching with HF to create the novel microstructures. Step coverage of epitaxial bridge layers have been achieved without significant degradation of the superconducting properties of YBa2Cu3O7−δ layers.

The molecular orientation within a surface liquid crystalline layer made up of semifluorinated side-groups [-CO-(CH2)x−x-(CF2)yF] (SF groups) attached to the isoprene block of a styrene-isoprene diblock copolymer was determined by analyzing the partial electron yield Cedge NEXAFS signal. The results show that in contrast to the bulk, where the SF groups lie parallel to the diblock copolymer lamellae and thus parallel to the surface, the surface SF groups make an average angle with the surface normal of between 29 and 46° depending on x and y.

A well-controlled, high-yield Josephson junction process in high temperature superconductors (HTS) is necessary for the demonstration of ultra-high-speed devices and circuits which exceed the capabilities of conventional electronics. The authors developed nanobridge Josephson junctions in high quality thin-film YBaCuO with dimensions below 100 nm fabricated using electron-beam nanolithography. They characterized this Josephson junction technology for process yield, junction parameter uniformity, and overall applicability for use in high-performance circuits. To facilitate the determination of junction parameters, they developed a measurement technique based on spectral analysis in the range of 90--160 GHz of phase-locked, oscillating arrays of up to 2,450 Josephson junctions. Because of the excellent yield and uniformity of the nanobridge junctions, they successfully applied the junction technology to a wide variety of circuits. These circuits included transmission-line pulse formers and 32 and 64-bit shift registers. The 32-bit shift register was shown to operate at clock speeds near 100 GHz and is believed to be one of the faster and more complex digital circuit demonstrated to date using high temperature superconductor technology.

We report recent measurements of flux quantisation in a hybrid ring formed from niobium and the newly discovered heavy fermion superconductor UPd2Al3 (Tc ~ 2K) providing an unambiguous demonstration of quantum coherence of the superconducting wave function between the heavy fermion and the conventional BCS superconductor. I/V characteristics of the edge-contacts formed across the UPd2Al3/Nb contact regions suggest a relatively weak coupling of the heavy fermion/niobium superconducting wave functions. In the second experiment, a novel method for measuring noise in superconducting circuits is illustrated by measurements on a Conductus do SQUID incorporating two bi-epitaxial weak-link junctions. The noise is shown to arise from fluctuations in critical currents across the two junctions, as independently determined by noise measurements on the junctions themselves after physical isolation from the SQUID. There was no evidence for any increase in noise in either SQUID device or constituent junctions associated with thermally induced motion of flux trapped within the device on cooling.

YBa2Cu3Oy thin films have been deposited in-situ on several substrate materials using pulsed excimer laser deposition. On the substrates, SrTiO3, MgO, LaA103, and yttrium-stabilized zirconia (YSZ), excellent films were obtained. These films had high superconducting transition temperatures (91K) with narrow transition widths (≈0.5K), metallic conductivity in the normal state, low room-temperature resistivity ( ~250 µΩ-cm), high critical currents (~3x107 A/cm2 at 4.2K), c-axis orientation perpendicular to the plane of the film, and epitaxial alignment with the substrate. On the more technologically relevant substrates of A12O3 and Si, less optimal results were obtained. The transition temperatures were high (86-88K) and metallic conductivity way obtained in the normal state. However, the room-temperature and microwave surface resistivities were higher and the critical currents were lower than for the above benchmark substrates. These diminished transport properties correlate with the imperfect alignment and epitaxy of the YBCO and substrate. For A12O3 substrates, a narrow substrate-temperature window was found for the best in-situ YBCO films. The poorer transport properties correlate with the lack of registry of the YBCO a-b plane with the sapphire r-plane. For Si substrates, a buffer layer is required due to high reactivity even at substrate temperatures as low as 550 C. YSZ provides a good buffer, and our best results were obtained on clean, hydrogen-terminated surfaces rather than oxidized Si. The amount of Y2O3 in ZrO2 was varied, and the best films were obtained with x near 0.1 where (ZrO2)1-x(Y2O3)x is cubic. Epitaxial alignment of the YBCO with the Si was achieved, but there was a substantial spread in orientations, accounting for the diminished transport properties.

The electrical characteristics of metal-oxide-semiconductor capacitors with ultrathin fluorinated SiO2 formed by a plasma fluorination technique have been studied and correlated with the chemical properties. Our study showed that the fluorination of conventional SiO2 results in a reduction of leakage current and a small amount of fluorine doping can increase the oxide capacitance. From the analysis of electrical properties and x-ray photoelectron spectroscopy, the increase and decrease of capacitance for small and large amounts of F doping were attributed to filling up the dangling bonds with fluorine at the surface and the formation of fluorine-rich oxyfluoride in the bulk, respectively. The reduction of leakage current can be explained by the removal of hopping states or trap states originating from the Si dangling bonds and Si–H bonds and the resulting higher-energy barrier for the tunneling process.

We report on the growth and the properties of Sr(Ru1−xTix)O3 thin films deposited by laser ablation. By substituting Ti for Ru in SrRuO3, we observe a continuous change of the magnetic and electrical properties of the perovskite. The Curie temperature is reduced from 150 K (x=0) to zero with increasing amount of Ti. The resistivity as a function of temperature shows a crossover from metallic to semiconducting behavior. A comparison with Ca substitution for Sr is presented.