Spray Pyrolysis Technique for the Deposition of Superconducting Films
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SPRAY PYROLYSIS TECHNIQUE FOR THE DEPOSITION OF SUPERCONDUCTING FILMS MARC SOLLER*, LARRY P. MOY*, MICHAEL R. SQUILLANTE* AND JAMES MARZIK** *Radiation Monitoring Devices, Inc., 44 Hunt St. Watertown, MA 02172 "**U.S.Army Materials Technology Laboratory, Arsenal St., Watertown, MA 02172
ABSTRACT Research has been performed on the use of chemical spray pyrolysis for depositing films of YBCO. The effects of reagent concentration, deposition rate, substrate temperature and substrate type were investigated. Films from less than 2 to more than 10 microns thick were deposited on single crystal strontium titanate, polycrystalline alumina and type 304 stainless steel.
INTRODUCTION Since the discovery of superconductivity at high temperatures in copper containing ceramics researchers have been exploring a wide variety of technologies to try to realize the commercial potential of the high Tc materials. Since many applications for high Tc superconductors require the use of thin films, the technology to produce them is a particularly important area for research. This paper reports on an investigation of the use of a proven, low cost process to deposit very large area superconductor films: chemical spray pyrolysis. The ultimate success of any large scale commercial application of high temperature ceramic superconductors requires the attainment of several goals: 1) high performance characteristics, 2) reproducibility, 3) long term stability and 4) low production costs. Our program is based on modifying and improving the spray pyrolysis deposition technique. Chemical spray pyrolysis is a well established deposition method which has been used to produce films of a variety of materials over areas of many square meters.1"2' 3' 4' 5 It is a one step process which consists of spraying a solution containing appropriate salts of the desired elements directly onto a heated substrate. The collective advantages of this spray process are 1) large area films are easy to make, 2) the process is low cost, 3) high throughput is achievable, 4) deposition parameters are easy to control.
EXPERIMENTAL RESULTS Many important aspects of film deposition were addressed including the spray chemistry, deposition parameters and post deposition annealing procedures. A variety of substrate materials were tested.
Spray Deposition An ultrasonic humidifier was modified to perform as a sprayer. The diameter of the delivery hose, its length, and the design of the spray head were varied to adjust the deposition rate and area of coverage. The area ranged from 10 to 80 cm2. Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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The chemical requirements of the spray solution are that the components be sufficiently soluble and stable, that they be compatible with each other, and all other end products be volatile such that no other materials are left on the substrates. To meet these requirements we used nitrates of Y, Ba and Cu. After spraying a film, a temperature dependent loss of yttrium and barium from the film (compared to the starting
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