Organometallic Chemical Vapor Deposition of Superconducting YBaCuO Films and Post-Deposition Processing

Abstract

Since the recent discovery of materials that exhibit superconductivity above 90K, there has been much interest in the preparation of thin films and coatings of these materials for numerous electronic applications. To date, most of the effort in thin film preparation has centered on physical vapor deposition techniques. However, chemical vapor deposition (CVD), although not yet widely investigated for preparation of these materials, may offer several important advantages. These advantages could include simplified deposition apparatus, excellent film uniformity and compositional control, high deposition rates, and the ability to coat complex shapes. As an example, these advantages suggest that CVD would be particularly well-suited for the large-scale preparation of wires and ribbons. Despite the attractions of CVD for the fabrication of high T_c superconducting films, very few experiments have actually been reported. This situation reflects, in large part, a paucity of suitably volatile, stable barium sources. However, recent reports have shown that metal-organic complexes, especially β-diketonate complexes, are suitable sources of barium. Thus, Ba(dpm)2 (dpm = dipivaloylmethanate) has been successfully used in the CVD of YBa2Cu3O7-δ films.^l–3 Indeed, films with the onset of superconductivity at 90K and zero resistance as high as 80K have been recently prepared.⁴ While these deposition experiments utilizing Ba(dpm)2 have yielded encouraging preliminary results, there are alternative Ba precursors which may yield films with improved properties at lower deposition temperatures and/or with higher deposition rates and yields. A strategy for increasing the vapor pressure of a precursor is to form complexes that involve bulky fluorocarbon ligands.^5,6 The introduction of fluorinated precursors also provides a source of BaF2 which has been previously shown to promote epitaxy in other types of YBa²Cu³O₇-δ deposition processes and ultimately leads to sharpening of the transition to the superconducting state.⁷