Thin films for superconducting electronics: Precursor performance issues, deposition mechanisms, and superconducting phase formation-processing strategies in the growth of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} films by metal-organic chemical vapor deposition
- Department of Chemistry and the Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208-3113 (United States)
- Department Electrical Engineering and Computer Science and the Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208-3118 (United States)
- Materials Science Division and the Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
Epitaxial Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followed by a postanneal in the presence of Tl{sub 2}O vapor. Vapor pressure characteristics of the recently developed liquid metal-organic precursors Ba(hfa){sub 2}{center_dot}mep (hfa=hexafluoroacetylacetonate, mep=methylethylpentaglyme), Ca(hfa){sub 2}{center_dot}tet (tet=tetraglyme), and the solid precursor Cu(dpm){sub 2} (dpm=dipivaloylmethanate) are characterized by low pressure thermogravimetric analysis. Under typical film growth conditions, transport is shown to be diffusion limited. The transport rate of Ba(hfa){sub 2}{center_dot}mep is demonstrated to be stable for over 85 h at typical MOCVD temperatures (120{degree}C). In contrast, the vapor pressure stability of the commonly used Ba precursor, Ba(dpm){sub 2}, deteriorates rapidly at typical growth temperatures, and the decrease in vapor pressure is approximately exponential with a half-life of {approximately}9.4 h. These precursors are employed in a low pressure (5 Torr) horizontal, hot-wall, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO{sub 3} substrates. From the dependence of film deposition rate on substrate temperature and precursor partial pressure, the kinetics of deposition are shown to be mass-transport limited over the temperature range 350{endash}650{degree}C at a 20 nm/min deposition rate. A ligand exchange process which yields volatile Cu(hfa){sub 2} and Cu(hfa)(dpm) is also observed under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} at temperatures of 720{endash}890{degree}C in flowing atmospheres ranging from 0{endash}100{percent}O{sub 2}. (Abstract Truncated)
- OSTI ID:
- 508967
- Journal Information:
- Journal of Materials Research, Journal Name: Journal of Materials Research Journal Issue: 5 Vol. 12; ISSN JMREEE; ISSN 0884-2914
- Country of Publication:
- United States
- Language:
- English
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