have still not been extensively studied and evaluated for their applicability to MEMS.

Conclusion. The specialized materials and processes discussed in this chapter all require further research to make them compatible with IC-based materials and processes or to permit them to be at the back end or off line in special process areas that will not add prohibitive costs or processing penalties to products. Extending the list of materials for MEMS that can be processed using lithography-based, IC-compatible techniques will be beneficial to MEMS development, provided that a thorough understanding of the properties of these materials is developed. Materials and techniques that might be able to be incorporated into IC-based MEMS in the nearer term include polyimides, magnetic thin-films, HEXSIL, and piezoelectrics.

Recommendation. Research and development should be encouraged to develop new materials that extend the capabilities of MEMS. The new materials should be capable of being integrated, at some level, with conventional IC-based processing.

Recommendation. Research should be encouraged to develop techniques to produce repeatable, high-quality, batch-processed thin-films of specialized materials and to determine the dependence of their properties on film preparation techniques. For some materials, it may be advisable to establish "foundries" that can be used by the entire MEMS community and can serve as repositories for equipment and know-how.

Recommendation. The characterization and testing of MEMS materials should be an area of major emphasis. Studies that address fundamental mechanical properties (e.g., Young's modulus, fatigue strength, residual stress, internal friction) and the engineering physics of long-term reliability, friction, and wear are vitally needed. It is important that these studies take into account process, scaling, temperature, operational environment (i.e., vacuum, gaseous, or liquid), and size dependencies. Studies of the size effects of physical elements, on a scale comparable to the crystallite regions in a polycrystalline material, are required.



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