Novel yttrium-stabilized zirconia polymeric precursor for the fabrication of thin films
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An acetate-based polymeric precursor for producing yttrium-stabilized zirconia (YSZ) was developed. The precursor was prepared under ambient conditions and contains only yttrium and zirconium cations. Dense, crack-free films were fabricated with this precursor on alumina substrates at a rate of 60 nm per deposition, producing polycrystalline YSZ at temperatures as low as 600 °C. Grain growth in thin YSZ films followed Arrhenius equation with an activation energy approximately 0.45 eV. The residual strain in YSZ films decreased with increasing annealing temperature from 600 to 900 °C. I. INTRODUCTION
Thin film technology, a process that produces coatings less than 1 m thick, is used extensively to fabricate such items as microelectronic1 and piezoelectric2 devices, insulate high temperature parts as thermal-barrier coatings,3 generate wear resistant coatings,4 or produce solidoxide fuel cells.5,6 Thin films can be deposited by a number of techniques. Some techniques, such as sputtering7 and ion plating,8 use vacuum deposition. Sputtering uses high voltages to produce plasma around a solid target in a high vacuum. Ions from the target are then deposited onto a grounded substrate. Ion plating uses a vapor phase created by evaporation in a vacuum. The source is heated with an electron beam in a vacuum until a sufficiently high vapor pressure is achieved to cause the material to condense on a nearby substrate. Chemical vapor deposition (CVD)9 produces a solid material on the surface of a heated substrate through a chemical reaction in the gas phase caused by heating a solid, liquid, or gas. Wet-chemical processes are also used to produce thin films. In these processes, chemical solution is produced, containing the desired cations in the desired ratios along with a large amount of organic species. The organics in the solution serve as a backbone to keep the cations in a homogenous solution and to help control viscosity.10 This solution is either then spun onto a substrate, known as spin-coating,11 or the substrate is dipped into the solution, referred to as dip-coating.11 When producing films with multiple cations, wetchemistry techniques use a chemical solution in which stoichiometry can be controlled, and thus tend to produce a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0352 2708
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 9, Sep 2004 Downloaded: 13 Mar 2015
homogenous coatings. Vacuum deposition techniques require evaporation of a source. Evaporating multiple cations simultaneously is complex since the rate of evaporation for the different cations may not be the same under a given set of conditions, making control of the stoichiometry difficult. Wet-chemistry based processes can take a variety of forms. Sol-gels10 are often associated with thin films. A sol-gel is produced by first generating a stable colloidal solution, or sol, of metal or metalloid cations surrounded by various ligands in a solvent. Additional monomer species are then added to initiate
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