Synthesis of superconductors from metal neodecanoates
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Synthesis of superconductors from metal neodecanoates T. N. Bowmer and F. K. Shokoohi Bellcore, Red Bank, New Jersey 07701
(Received 16 April 1990; accepted 21 December 1990) Metal-organic precursors can facilitate the production of superconducting thin films on large area substrates for microelectronic device applications. This paper describes the chemistry that occurs during the thermal processing of yttrium-, barium-, and copper-neodecanoate mixtures into a superconducting material, YBa2Cu3O7-x. Intermediates such as metal carbonates and oxides are identified by combining thermogravimetry with infrared spectral and x-ray diffraction analysis. Changing from argon to oxygen atmospheres increased decomposition rates and metal oxide formation. We found that (1) a low temperature (500-600 °C) decomposition in an oxygen-poor atmosphere, (2) a high temperature (>925 °C) annealing step in an oxygen-rich atmosphere, and (3) slow cooling to 50 °C are all required to produce uniform superconducting films.
I. INTRODUCTION
High temperature superconductors are needed in various physical forms (wires, films, coils, etc.) for applications in microelectronics. Efficient devices will require uniform superconducting films with high transition temperatures and large critical currents.1'2 Among the existing methods, casting a film from solution is a simple and inexpensive technique to cover large area substrates. Solutions of metal nitrates, acetates, hydroxides, ethylhexanoates, or carboxylates have been cast into films which, after high temperature (>900 °C) treatment, can form superconducting materials.3"13 The main advantages of metalorganic precursors are in their spin coating and pattern writing capabilities that may be useful in production of superconducting interconnects. Large area substrates can be spin coated from solutions in volatile organic solvents. Using high energy beams, patterns can be written in these precursors since the large organic ligands absorb the energy and form an insoluble crosslinked network. For example, Hamdi et al.9'w showed that superconducting films of YBa2Cu3O7-J; can be formed on a single crystal of SrTiO3 substrates by thermal decomposition of Y, Ba, and Cu neodecanoates and rapid-thermal-annealing of the decomposition products. They demonstrated superconducting fine-line patterns can be formed by rapid-thermal-annealing of the patterns written in the metalorganics by a laser or ion beam.11"13 To produce superconducting films after thermal processing, precursor mixtures need to form homogeneous coatings (i.e., precursor components must be compatible) as well as decompose simply with minimal residual impurities. We have used Y, Ba, and Cu neodecanoates to form large area superconducting films in various chemical ambient. The electrical properties of 670
J. Mater. Res., Vol. 6, No. 4, Apr 1991
the films are sensitive to their stoichiometry and morphology, which are in turn determined by the chemistry of the precursors.9"13 The precursor film is thermally decomposed to produce metal oxides th
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