Carbon-Nanotube-Templated Metallic Microstructures for MEMS: Preparation and Characterization,

We discuss a materials breakthrough for MEMS. In contrast with conventional electromechanical devices, whose constituents are chosen from a vast range materials and alloys to optimize fabrication, performance
and cost, MEMS have traditionally been made using the same materials and methods as those used in the silicon-based microelectronics industry. In order to make MEMS out of a much richer suite of materials, including metals, semiconductors and ceramics, we have developed a process termed carbon-nanotube-templated microfabrication (CNT-M). In CNT-M we employ patterned, vertically aligned carbon nanotube forests as a scaffold to create precise, high-aspect-ratio (~100:1) microstructures. The “as grown,” low density (0.009 g/cc) CNT structures are not useful as mechanical materials because they are extremely fragile, consisting mostly of air. However, when we replace the air spaces between tubes in the forest with a filler material by atomistic deposition, the infiltrated CNT framework becomes a robust microstructure consisting mostly of the filler material. Thus, by patterning the CNT microstructure and limiting the deposition of the filler material, CNT-M allows control over structural features on both the nano and microscales (nanoscale porosity and microscale structure). In the past, we deposited semiconductors (Si and a-C) or dielectrics (SiO2 and SiNx) within the CNT framework by chemical vapor infiltration. But many existing MEMS applications would be benefited, and many contemplated applications such as remotely read (via RF), high-temperature accelerometers would be enabled, by the right metals. We now report on the use of chemical vapor infiltration and electrodeposition to create metallic microstructures composed of tungsten, molybdenum or nickel by CNT-M. These materials are desirable in MEMS applications because of their high conductivity, high melting temperatures, resistance to corrosion, low thermal expansion, and their high Young’s moduli, hardness and yield strength. We will present electrical, mechanical and structural properties of the metal microstructures and discuss deviations from bulk properties.