Thin film deposition technologies, and structure/property relationships applied to solid state ionic conductors

Abstract

The purpose of this work is to introduce the area of Materials Science known colloquially as “Thin Films”, and to discuss the various process/property/applications relationshiops which have been developed in this field. Thin film technology will be exsamined from the interrelated viewpoints of product application, materials structure/property relationships, and manufacturing (deposition) methods. Special emphasis will be given to the thin film materials properties of metal oxides such as zirconia which are likely to have an impact on electrochemical device performance, coupled with the various fabrication techniques employed to control those properties. Over the last few decades, thin films have moved out of the laboratory, finding application in a virtually unlimited number of product areas: in the tool industry, integrated circuitry, optics, space and communication, architecture, and the food packaging industries, to name a few. In many of these, thin films form an integral part of products which cannot be made using only “bulk” components. For some, this is because the films themselves posses unique properties which cannot be duplicated in bulk - transparent electrical conductors made from indium tin oxide are one example. In still others, the thinness of a material may impart special functional advantages. The use of thin film solid oxide electrolytes in low temperature fuel cells is one such potential example. The materials properties of thin films usually differ substantially from their bulk counterparts. While in some cases this is the result of the increased importance of surface effects over bulk phenomena, it is more often related to the fabrication methods used to produce the films. A large body of knowledge exists which relates deposition processes to such relevant properties as porosity, crystallinity, chemistry, adhesion, etc. These will be reviewed especially in relation to ceramic oxide materials such as zirconia. Finally, there is the issue of manufacturability. Thin films today are produced in volumes measured in millions of square feet. While most thin film depositipon methods in use4 today would probably not be applicable to high volume production of solid state ionic conductors, enough is known about high volume manufacturing applied to physical vapor deposition to provide some guidelines to the future development of thin film electrochamical devices. Several candidates scenarios will be examined.