William L. Holstein

Tl2Ba2CaCu2O8 films with very low microwave surface resistance up to 95 K

Very low surface resistance Tl2Ba2CaCu2O8 films of thickness 1.0 μm on (100) LaAlO3 were fabricated and characterized. The films are highly c‐axis oriented (x‐ray diffraction rocking curve full width half maximum of 0.68°) with good in‐plane epitaxy with respect to the substrate. The Tc of the films was 107.6±0.5 K as measured by ac magnetic susceptibility. The surface resistance at 10 GHz was measured with the parallel plate resonator technique and found to be 23±5 μΩ at 4.2 K, 130±20 μΩ at 77 K, and 300±60 μΩ at 95 K. Using a 20 GHz TE011 end‐wall replacement copper cavity, the surface resistance was found to be comparable to that of copper, about 18 mΩ, at 104±1 K. The surface resistance of the films is significantly lower than that of all films reported to date at temperatures above 70 K and only slightly higher than the best high‐temperature superconductor films reported to date at 4.2 K.

5 GHz high-temperature-superconductor resonators with high Q and low power dependence up to 90 K

The authors have fabricated high-temperature superconducting films made of TlBaCaCuO (2212) and YBaCuO

Surface resistance of large-area Tl2Ba2CaCu2O8 thin films at microwave and millimeter wave frequencies measured by three noncavity techniques

The surface resistanceRs of Tl2Ba2CaCu2O8 films fabricated on LaAlO3 wafers up to 3 inches (7.6 cm) in diameter through a post-deposition anneal process was measured over the frequency range 5.55–94.1 GHz by the following techniques: 5.55 and 27.5 GHz high-temperature superconductor (HTS)-sapphire resonators, 10 GHz parallel plate resonator, and 94.1 GHz scanning confocal resonator.Rswas found to exhibit a quadratic dependence on frequencyf at 77 K:Rs∝f2.0±0.1. The highest-quality films yieldRs=145±15μΩ at 10 GHz and 77 K. Scanning confocal resonator mapping ofRsacross a 2-inch (5.1 cm) diameter wafer yielded a base value forRsof 16±1 mΩ at 77 K and 94.1 GHz (equivalent to 180±10μΩ at 10 GHz) and good uniformity inRsacross the wafer. HTS-sapphire resonator measurements ofRsfor fifteen 1.2 cm square parts cut from a 3-inch diameter wafer yieldedRsvalues scaled to 10 GHz of 196±10μΩ at 80 K. Similar values were measured for Tl2Ba2CaCu2O8 films prepared on both sides of a 2-inch diameter wafer.Rs values at 10 GHz and 80 K of 147−214μΩ were maintained over the course of 40 independent and successive deposition runs and corresponding anneals under nominally identical film fabrication conditions. Surface resistance at 5.55 GHz remained below 80μΩ for maximum rf magnetic fields up to 85 Oe at 4.2 K and 7 Oe at 80 K, respectively. Results are compared with predictions of the two-fluid model. The relative advantages and disadvantages of the different techniques for measuring surface resistance are discussed.

Design and modeling of chemical vapor deposition reactors

Abstract The performance of chemical vapor deposition (CVD) reactors is strongly dependent on fluid flow, heat transport and mass transport. The optimized design of CVD reactors requires an understanding of how these phenomena influence the uniformity in growth rate, composition, and doping. This article will review recent developments in the study of CVD reactors. The focus will be on understanding how the interplay of physical properties and reactor geometries influences fluid flow and growth uniformity. Both numerical models and flow visualization studies of transport phenomena are reviewed. Despite the considerable power of these computational and experimental tools, the greatest asset in reactor design is the ability to conceptualize the interplay and relative significance of different transport phenomena. With this in mind, the underlying goal of this review is to provide a conceptual framework of the fundamental transport phenomena at work in CVD reactors, the conditions under which each of these phenomena plays a roll, and their combined impact on reactor design.

Superconducting epitaxial Tl2Ba2CaCu2O8 films on sapphire with cerium oxide buffer layers

Epitaxial Tl2Ba2CaCu2O8 films were prepared on (1102)Al2O3 with (100) CeO2 buffer layers. The Tl2Ba2CaCu2O8 was epitaxially oriented with its c axis perpendicular to the substrate surface and [100] Tl2Ba2CaCu2O8 aligned with [100] CeO2 and [2201] Al2O3. The films exhibited Tc of 97–98 K as measured both inductively and by ac magnetic susceptibility. Direct transport critical current density Jc at 75 K was 2.8×105 A/cm2.

High performance superconducting thin films on large area substrates

The first fabrication of 3-in-diameter, thin films of thallium-based superconductors is reported. (Tl/sub 0.5/Pb/sub 0.5/)Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9/ thin films on LaAlO/sub 3/ are found to display the best surface resistance (R/sub s/) properties of any superconductor at higher temperatures and show approximately 50* better performance than copper at 100 K and 10 GHz. A Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin film, processed as a 1.8-m-long, 10- mu m-wide meander line carries about 1*10/sup 7/ A/cm/sup 2/ at 4.2 K and 2*10/sup 6/ A/cm/sup 2/ at 80 K. The thallium-based superconductors are compared to YBa/sub 2/Cu/sub 3/O/sub 7/ with respect to T/sub c/, R/sub s/, and Q.<<ETX>>

Preparation and characterization of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films on

A two-step process for the fabrication of 0.12-1.20- mu m-thick Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films on

High T/sub c/ superconductor and III-V solid state microwave hybrid circuits

Several high-temperature superconductor (HTS)/III-V solid-state hybrid microwave circuits were designed, fabricated, and tested. The I-V curves, S-parameters, and noise behavior for several solid-state devices at cryogenic temperatures were measured. Several high-electron-mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) C-band low-noise amplifiers were fabricated and tested at cryogenic temperatures with an additional gain of 3 dB when compared to their room-temperature gain. These amplifiers were also used in low-phase-noise oscillators stabilized by a HTS lambda /2 microstrip line resonator with a loaded Q-value of 3*10/sup 3/ or a sapphire-HTS resonator with a loaded Q-value of 1.2*10/sup 6/, both measured at 80 K. Preliminary measurement at 70 K indicates that the phase noise of an oscillator stabilized with a sapphire-HTS resonator was below -125 dBc/Hz at 10-kHz offset and limited by the test setup.<<ETX>>

Microstructural and electronic properties of highly oriented Tl/sub 0.5/Pb/sub 0.5/Sr/sub 2/Cu/sub 2/O/sub 7/ films on LaAlO/sub 3/

Epitaxial Tl/sub 0.5/Pb/sub 0.5/Sr/sub 2/CaCu/sub 2/O/sub 7/ films produced by RF magnetron sputtering followed by annealing in the presence of thallium oxide vapor have been produced on

Fabrication of Tl-Ba-Ca-Cu-O films by annealing rf-sputtered Ba-Ca-Cu-O films in thallium oxide vapors

Thin, superconducting Tl‐Ba‐Ca‐Cu‐O films were grown using a two‐step fabrication process which involved the growth of Ba‐Ca‐Cu‐O films by reactive magnetron sputtering followed by ex situ high‐temperature crystallization and thallination under thallium oxide vapors. Films were thallinated with both Tl2O3 and Tl2Ba2CuO6 as the source for thallium oxide vapors. Highly oriented films were obtained with the c axis perpendicular to the surface of the film. Best films had a Tc (R=0) of 104 K and a critical current density of 5×104 A/cm2 at 77 K.