THIN-FILMS FOR SUPERCONDUCTING ELECTRONICS - PRECURSOR PERFORMANCE ISSUES, DEPOSITION MECHANISMS, AND SUPERCONDUCTING PHASE FORMATION-PROCESSING STRATEGIES IN THE GROWTH OF TL2BA2CACU2O8 FILMS BY METAL-ORGANICCHEMICAL-VAPOR-DEPOSITION

Epitaxial Tl2Ba2CaCu2O8 thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organ ic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followe d by a postanneal in the presence of Tl2O vapor. Vapor pressure charac teristics of the recently developed liquid metal-organic precursors Ba (hfa)(2) . mep (hfa = hexafluoroacetylacetonate, mep = methylethylpent aglyme), Ca(hfa)(2) . tet (tet = tetraglyme), and the solid precursor Cu(dpm)(2) (dpm = dipivaloylmethanate) are characterized by low pressu re thermogravimetric analysis. Under typical film growth conditions, t ransport is shown to be diffusion limited. The transport rate of Ba(hf a)(2) . mep is demonstrated to be stable for over 85 h at typical MOCV D temperatures (120 degrees C). In contrast, the vapor pressure stabil ity of the commonly used Ba precursor, Ba(dpm)(2), deteriorates rapidl y at typical growth temperatures, and the decrease in vapor pressure i s approximately exponential with a half-life of similar to 9.4 h. Thes e precursors are employed in a low pressure (5 Torr) horizontal, hot-w all, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO3 substrates. From the dependence of film deposition rate on subs trate temperature and precursor partial pressure, the kinetics of depo sition are shown to be mass-transport Limited over the temperature ran ge 350-650 degrees C at a 20 nm/min deposition rate. A Ligand exchange process which yields volatile Cu(hfa)(2) and Cu(hfa)(dpm) is also obs erved under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl2Ba2CaCu2O8 at temperature s of 720-890 degrees C in flowing atmospheres ranging from 0-100% O-2. The resulting Tl2Ba2CaCu2O8 films are shown to be epitaxial by x-ray diffraction and transmission electron microscopic (TEM) analysis with the c-axis normal to the substrate surface, with in-plane alignment, a nd with abrupt him-substrate interfaces. The best films exhibit a T-c = 105 K, transport-measured J(c) = 1.2 x 10(5) A/cm(2) at 77 K, and su rface resistances as low as 0.4 m Omega (40 K, 10 GHz).