Wet Chemical Derived Films For Electrical Applications
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WET CHEMICAL DERIVED FILMS FOR ELECTRICAL APPLICATIONS D.R. Uhlmann, G. Teowee, J.M. Boulton and B.J.J. Zelinski Department of Materials Science & Engineering, University of Arizona, Tucson, Arizona 85721 ABSTRACT Wet chemical methods have been used with success to synthesize films for a variety of electrical applications. After first reviewing the important microstructural features of films, the present paper focuses attention on ferroelectric (FE) films. The present state of and critical issues facing wet chemically derived FE films are considered. The needs for more extensive microstructural characterization and for more systematic exploration of electrical behavior are emphasized. I.
INTRODUCTION
Wet chemical or sol-gel deposition of films is a rapidly advancing technology. Coatings can be formed from solution by a number of methods, including spin, dip, spray and roller coating; a wide range of compositions can be synthesized, including multicomponent materials; and doping can readily be effected. The application of sol-gel methods to forming films is natural in that maximal advantage of the wet chemical approach can be taken, while cracking can be avoided - at least for coatings of up to 0.5 Am in thickness. Thicker coatings can be prepared by using several coat-and-fire steps or organic modification. Further, the inherently high raw material cost of wet chemical processing is relatively unimportant in the case of coatings. The use of coatings in electrical applications is an area of considerable importance. Such coatings include: ferroelectric (FE) thin films, spin-on glasses, tantalum oxide, silicon oxynitride, high temperature superconductors, fast ion conductors, electrochromic films and transparent conductive coatings. For reasons of space, the present paper will focus attention exclusively on FE films. The characteristics of such films prepared by wet chemical methods will be compared with those of films prepared using vapor deposition methods; and critical issues which must be addressed for the implementation of wet chemical FE films are considered. It seems clear, however, that most thin film efforts including FE thin films - are property driven. Definition of a desired combination of properties leads to specification of a composition; and variations in properties are effected by changes in chemistry and processing. In such developments, relatively little attention is directed to microstructure despite the key role played by microstructure in the development of materials science and engineering as a discipline. For this reason, it seems appropriate to consider the important
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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microstructural features of films, whether deposited by wet chemical methods or by physical deposition (as sputtering). The importance of microstructure in thin film technology has been emphasized in a recent review [1]; and this importance seems destined to grow during the coming decade. II.
MICROSTRUCTURE OF FILMS
The important microstructural chara
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