This paper reviews recent work at DuPont to develop high performance Tl2Ba2CaCu2O8 and YBa2Cu3O7 thin films for microwave and electronic device applications. The YBa2Cu3O7 thin films are produced by off-axis magnetron sputtering onto radiatively heated substrates and have surface roughness levels of less than 1 nm over 2 in. diameter wafers as determined by atomic force microscopy. Double-sided Tl2Ba2CaCu2O8 films are produced on 3 in. diameter CeO2 buffered sapphire substrates with excellent uniformity of structural and electrical properties. These films have low microwave surface resistance up to high microwave power levels. We also report on the establishment of a Six Sigma manufacturing capability for Tl2Ba2CaCu2O8 films. These films are used to fabricate a compact high performance eight-pole bandpass filter operating at 1.85 GHz and 80 K.

The use of a high-temperature superconducting probe for in vivo magnetic resonance microscopy at 2 T is described. To evaluate the performance of the probe, a series of SNR comparisons are carried out. The SNR increased by a factor of 3.7 compared with an equivalent copper coil. Quantitative measures of the SNR gain are in good agreement with theoretical predictions. A number of issues that are unique to the application of HTS coils are examined, including the difficulty in obtaining homogenous excitation without degrading the SNR of the probe. The use of the HTS probe in transmit-receive mode is simple to implement but results in nonuniform excitation. The effect of using the probe in this mode of operation on the T1 and T*2 contrast is investigated. Methods for improving homogeneity are explored, such as employing a transmit volume coil. It is found that the cost of using an external transmit coil is an increased probe noise temperature and a reduced SNR by ∼30%. Other important aspects of the probe are considered, including the effect of temperature on probe stability. Three-dimensional in vivo imaging sets are acquired to assess the stability of the probe for long scans. High-resolution images of the rat brain demonstrate the utility of the probe for microscopy applications. Magn Reson Med 41:72-79, 1999. © 1999 Wiley-Liss, Inc.

This paper describes recent work at DuPont to extend the high power microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ high T/sub c/ superconducting (HTS) films on 2 inch diameter MgO and sapphire substrates. The YBa/sub 2/Cu/sub 3/O/sub 7/ films were produced by in-situ off-axis sputtering with radiant substrate heating. The Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films were produced by off-axis sputtering followed by annealing in oxygen and Tl/sub 2/O vapor. The microwave surface resistance and power handling of these films was measured over a wide range of temperature (20 K to 85 K) using an HTS-sapphire resonator technique. At 70 K, the surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7/ films on sapphire remained below 250 /spl mu//spl Omega/ (@8.1 GHz) for microwave surface current densities up to 1.7/spl times/10/sup 6/ A/cm/sup 2/. At 70 K, the surface resistance of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films on MgO remained below 230 /spl mu//spl Omega/ (@8.1 GHz) with microwave current densities up to 2/spl times/10/sup 6/ A/cm/sup 2/.

Research News: High-quality films of several superconducting materials are finding increasing applications. Thin films of materials such as YBa2Cu3O7 (YBCO), Tl2Ba2CaCu2O8 (TBCCO), and (Tl,Pb)Sr2CaCu2O7 (TPSCCO) can be made by a variety of methods, including sputtering and pulsed laser deposition. Magnetron sputtering is now used exclusively by the authors, because it is reproducible, robust, amenable to scale-up, and practised throughout the semiconductor industry. Additionally, sputtered films have proven to have desirable properties in terms of microstructure, surface resistance, and power handling.

We consistently observe a magnetic-field-dependent conductance peak at zero-bias voltage in a wide range of superconductor/noble-metal junctions fabricated from oxide superconductors (YBa2Cu3O7-delta and Tl2Ba2CaCu2O) that have been reported to exhibit d-wave pairing behavior; however, no measurable peak appears in similar junctions made from an s-wave oxide superconductor (Nd1.85Ce0.15CuO4) Explanations of this correlation are considered in terms of the Appelbaum-Anderson model for magnetic interface scattering and the midgap-state model for d-wave interface states.

The focus of High Temperature Superconducting (HTS) microwave circuit development has now shifted to improving the high power handling capability. This paper reviews our latest results in this area including: HTS material improvement; new concepts and rules for HTS high power circuit design; and the latest high power filter test results. For HTS materials, the surface resistance versus rf magnetic field test results and the third harmonic test results for both YBa2Cu307 and T12Ba2CaCuz08 thin films are presented. For HTS microwave circuits, novel design concepts and rules for high power HTS filters are discussed. Several compact planar HTS filters were designed, fabricated, packaged and tested. The performance o f a 3-pole, 1.3% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 74 watts at 77 K. The performance of a 2-pole, 1% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 115 watts at 77 K. To our knowledge, these test results represent the highest power handling o f compact planar HTS filters operating at 77 K, sufficient for use in t e 1 e co mmuni c a ti o n transmitters.

This paper describes recent work at DuPont to extend the high power microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ high-T/sub c/ superconducting (HTS) films. The YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by in-situ off-axis magnetron sputtering using are produced by in-situ off-axis sputtering with radiant substrate heating. The Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films are produced by off-axis sputtering followed by annealing in oxygen and Tl/sub 2/O vapor. The microwave surface resistance and power handling of these films has been measured over a wide range of temperature (20 K to 100 K) using a HTS-sapphire resonator technique. At 70 K, the surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7/ films remains below 65 /spl mu//spl Omega/ (@5.56 GHz) with microwave surface current densities up to 5/spl times/10/sup 6/ A/cm/sup 2/. At 70 K, the surface resistance of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films remains below 200 /spl mu//spl Omega/ (@8.1 GHz) with microwave current densities up to 2/spl times/10/sup 6/ A/cm/sup 2/.

The paper focuses on the latest progress of the power handling capability of HTS thin film materials and microwave circuits particularly filters. The surface resistance vs. rf magnetic field data measured at 8.14 GHz and different temperatures for YBa2Cu3O7−δ and Tl2Ba2CaCu2O8 films are presented. A 3-pole 6.04 GHz 1.3% filter with polygon-shape resonators and back-side coupling circuits were designed, fabricated and tested up to 74 watts transmitting power at 77 K, which is suitable for applications in the transmitters.

The focus of High Temperature Superconducting (HTS) microwave circuit development has now shifted to improving the high power handling capability. This paper reviews our latest results in this area including: HTS material improvement; new concepts and rules for HTS high power circuit design; and the latest high power filter test results. For HTS materials, the surface resistance versus rf magnetic field test results and the third harmonic test results for both YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films are presented. For HTS microwave circuits, novel design concepts and rules for high power HTS filters are discussed. Several compact planar HTS filters were designed, fabricated, packaged and tested. The performance of a 3-pole, 1.3% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 74 watts at 77 K. The performance of a 2-pole, 1% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 115 watts at 77 K. To our knowledge, these test results represent the highest power handling of compact planar HTS filters operating at 77 K, sufficient for use in telecommunication transmitters.

We present the results from sodium magnetic resonance imaging (MRI) experiments using high-temperature superconducting (HTS) receiver coils. Sodium imaging has been shown to have great potential for the assessment of cell integrity but suffers from a substantially lower signal-to-noise ratio (SNR) than that of hydrogen imaging. The use of an HTS receiver coil was found to significantly increase the SNR relative to an equivalent copper receiver coil at room temperature. The SNR gains afforded by HTS coils can also be used to decrease the imaging time.

The nonlinearity or microwave surface resistance of high temperature superconductors (HTS) is of considerable interest. We report the first measurement of the 3rd order intercept (TOI) from harmonic generation for HTS. The nonlinearities were measured for a series of coplanar transmission lines composed of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ or YBa/sub 2/Cu/sub 3/O/sub 7/. At a fundamental frequency of 1.4 GHz, the TOI for a 28 /spl mu/m wide by 5 mm long Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ transmission line was: +52 dBm at 100 K; +68 dBm at 90 K; +72 dBm at 80 K; and +80 dBm at 50 K. This narrow transmission line handled up to 4 Watts of cw power at 80 K which corresponds to an average rf current density of 2.2/spl times/10/sup 6/ A/cm/sup 2/. The 3rd harmonic exhibited the expected slope 3 on a log log scale at both low and high powers and a shift of the TOI was observed at some intermediate power. The scaling rules for power handling from changes of a Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ coplanar transmission line width, length and temperature were also derived. These data suggest a redistribution of the rf current within the transmission line across its width at high powers. A pronounced TOI shift was not observed for YBa/sub 2/Cu/sub 3/O/sub 7/ coplanar transmission lines.<>

We report the growth of c-axis oriented, epitaxial thin films of (Tl,Pb)Sr/sub 2/CuO/sub 5/ on (100) oriented LaAlO/sub 3/ substrates by off-axis sputter deposition in the presence of thallium oxide vapor. These films display a resistivity which crosses over from metallic to semiconducting behavior at low temperature. In addition, we have shown that multiple layers of superconducting (Tl,Pb)Sr/sub 2/Ca/sub 0.8/Y/sub 0.2/Cu/sub 2/O/sub 7/ (1212) and nonsuperconducting (Tl,Pb)Sr/sub 2/CuO/sub 5/ (1201) can be deposited sequentially without compromise of the superconducting properties of the 1212 layer. Bilayers of both 1212 on 1201 and of 1201 on 1212 have been fabricated. In either case, both materials grow with their c-axis normal to the substrate surface and with their a-axes aligned to each other and to the major axes of the substrate. Technologically interesting trilayer structures of 1212/1201/1212 have also been fabricated. Both 1212 layers are superconducting with transition temperatures of up to 94 and 93 K for the upper and lower layers respectively. We believe that this is an important step towards the development of thallium cuprate-based multilayer technology.< >