Material Properties of Carbon-Infiltrated Carbon Nanotube-Templated Structures for Microfabrication of Compliant Mechanisms

Abstract

Carbon nanotubes can be grown vertically from a substrate to form dense forests hundreds of microns tall. The space between the nanotubes can then be filled with carbon using chemical vapor deposition to create solid structures. These infiltrated structures can be detached from the substrate and operated as single-piece MEMS. To facilitate the design of compliant microdevices using this process, we explored the influence of two fabrication parameters—iron layer thickness and infiltration time—on the material’s mechanical properties, using the fracture strain to judge suitability for compliance. We prepared samples of a simple meso-scale cantilever beam pattern at various levels of these parameters, applied vertical loads to the tips of the beams, and recorded the forces and deflections at brittle failure. These data were then used in conjunction with a nonlinear FEA model of the beams to determine Young’s modulus and fracture stress for each experimental setting. From these data the fracture strains were obtained. The highest fracture strain observed was 2.48%, which is approximately 3.5 times that of polycrystalline silicon. This was obtained using an iron layer thickness of 10 nm and an infiltration time of 30 minutes. We used a test device—a compliant gripper mechanism for holding mammalian egg cells—to demonstrate the use of this material in compliant MEMS design.