| Summary: | Metal-based high-aspect-ratio microscale structures (HARMS) are fundamental building blocks for functional metallic micro devices. This dissertation focuses on addressing several problems in fabrication and assembly of metal based microchannel devices. First, the materials responses to mechanical deformation at micro & nano scales, namely the mechanical size effect, have been explored by molding single crystal Al with long rectangular diamond punches and long wedge shaped indenters. It is noticed that the contact pressure of rectangular punches pressed into single crystal Al strongly depends on the punch width, while that of long wedge shaped indenters depends on the included wedge angle. We observed large discrepancies between characteristic lengths obtained from predictions based on the Nix-Gao model and those derived from experimental results. Our results suggest that the characteristic length maybe dependent on the deformation geometry.
The mold inserts are coated with hard ceramic thin films, which could reduce friction and act as barriers for surface chemical reactions during molding at elevated temperatures. The adhesion between thin film and substrate, a persisting topic in thin film technologies and surface engineering, remains critical in the present case. Therefore, nominal shear strength of the interface between TiN thin film and Si substrate was evaluated through customized compression test of micro cylinders containing inclined film/substrate interfaces. Non-tapered micro cylinders with diameters ranging from 5µm to 1µm were prepared by focused ion beam lathe milling, which was realized by a script based ion milling program. As compared to previous procedures for testing film/substrate interfacial mechanical integrity, results obtained by following this new microscale testing protocol have less scatter and are more conducive to correlating interfacial structure/chemistry to interfacial failure.
Appropriate bonding technology is critical to forming functional micro devices. Cu based HARMS were bonded by sandwiching an Al thin foil in between a Cu sheet metal containing HARMS features and a flat Cu sheet metal counterpart, utilizing formation of a eutectic interfacial liquid. Phase and structure evolution of the Cu/Al/Cu interface, as well as the interfacial mechanical properties, were characterized.
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