Production of Y-Ba-Cu-0 Superconducting Thin Films by an Aerosol Chemical Vapor Deposition Process
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PRODUCTION OF Y-BA-CU-O SUPERCONDUCTING THIN FILMS BY AN AEROSOL CHEMICAL VAPOR DEPOSITION PROCESS
A. DRIESSEN, Q. TANG, L. HILDERINK AND TH.J.A. POPMA University of Twente, Faculty of Applied Physics, P.O.Box 217, 7500 AE Enschede, The Netherlands
Abstract Thin film production by aerosol deposition is a simple, non-vacuum method, which under certain conditions of the process parameters, can be considered as a chemical vapor deposition (CVD) process. In this paper we describe the formation of superconducting thin films by aerosol deposition in the CVD regime by using metal-organic precursors. The best results were obtained with the metal f-diketonates of Y, Ba and Cu dissolved in butylacetate. This solution was nebulized and sprayed on a heated Si-substrate with a ZrO2 -buffer layer at a temperature of 450 C. After deposition a final heat treatment at a temperature of 800 °C was applied. The resulting superconducting film has a Tczero of 75 K. Introduction There is a continuous progress In the preparation of superconducting thin films of the perovsklte YBa 2 Cu 3 07_,. Many of the methods used like sputtering, laser ablation and co-evaporation demand special and rather complex equipment. As there is a lot of experience in our group with the simple, non-vacuum process of chemical aerosol deposition [I], we decided to apply this method to the formation of high T. superconducting thin films. In this way a cheap, non-vacuum method for the formation of large area superconducting films should be available. Aerosol deposition of superconducting thin films have been described by several groups; as a precursor they used nitrates [2-4] or metal-organic compounds [5]. In this paper we present our work on the aerosol deposition in the Chemical Vapor Deposition CVD regime with metal P-dlketonates as precursors (6]. Thin film preparation In the process of chemical aerosol deposition, a start is made by forming a solution of those metals in a suitable compound, which are required for the thin film formation. This solution is then nebulized and transferred by a carrier gas, e.g. a mixture of N2 and 02, to the warmed substrate. When approaching the substrate surface, the fine aerosol droplets are warmed up and the solvent starts evaporating and a precipitate is formed. With further heating of the precipitate, vapor is formed by sublimation, which by diffusion reaches the substrate surface and undergoes a reaction there. In this way a thin film is formed in a controlable way. Aerosol deposition under such circumstances can be considered as a form of CVD [7]. In order to obtain a good control over the aerosol CVD (ACVD) process, small droplets having a homogenous diameter are necessary. An ultrasonic nebulizer working at high frequency (in our case 3 MHz) will give the best results. problem to be solved in the ACVD process is to find suitable The first precursors, which are soluble in a solvent with good spraying characteristics. We tried several metal-organic precursors and different organic solvents, see
Mat. Res. Soc. Symp. Pro
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