Synthesis and Characterization of Nanocomposite Thin Films for MEMS Applications

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Synthesis and Characterization of Nanocomposite Thin Films for MEMS Applications Kaushik Das1, Cheol Park2, 3, Rosemary Le Faive1, Pascal Hubert1, and Srikar Vengallatore1 1

Department of Mechanical Engineering, McGill University, Montreal, QC, Canada. National Institute of Aerospace, Hampton, VA, USA. 3 Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, USA. 2

ABSTRACT Reinforcement with nanotubes, nanofibers, and nanoparticles is an attractive option for enhancing the properties of micromachined polymeric structures employed in microelectromechanical systems (MEMS). Calculations based on Eshelby-Mori-Tanaka micromechanics predict that the elastic modulus and wave velocity can be increased by over an order of magnitude by reinforcing polymers with 10 vol% of aligned, dispersed, single-walled carbon nanotubes (SWNT). Motivated by this prediction, we measured the elastic moduli of polyimide films reinforced with SWNT at volume fractions ranging from 0.05% to 10%. For dilute composites, the elastic modulus increased with increasing nanotube loading from 2.5 GPa for the neat polymer to 3.5 GPa for a nanocomposite containing 0.5 vol% of SWNT. However, with further increase in the nanotube content, the elastic modulus remained essentially constant even for high loadings of 10 vol% of SWNT. In addition, significantly different elastic moduli were measured for specimens containing the same volume fraction (0.5 vol%) of SWNT produced by two different processes.

INTRODUCTION Development of the next-generation of microdevices requires the utilization of advanced multifunctional materials as structural components. Polymer-matrix nanocomposites with nanoparticles, nanotubes, and nanofibers as reinforcement have attracted considerable attention as structural materials for MEMS applications [1, 2]. A recent theoretical study based on Eshelby-Mori-Tanaka micromechanics predicts an increase in elastic modulus and longitudinal wave velocity by an order of magnitude for polymers reinforced with 10 vol% of well-dispersed and aligned single-walled carbon nanotubes (SWNT) [3]. Motivated by these predictions, a systematic study has been undertaken to measure the elastic modulus of polyimide thin films with varying SWNT concentrations, using a modified nanoindenter-based plate bending test.

MATERIALS Eight samples having 2,6-bis(3-aminophenoxy) benzonitrile/4,4-oxydiphthalic anhydride [(β-CN)APB/ODPA] polyimide as matrix, with 0, 0.05, 0.1, 0.2, 0.5, 1, 2 and 10 vol% HiPCO (High Pressure CO, Carbon Nanotechnologies, Inc., Houston, TX) SWNT were fabricated. The nanocomposite synthesis primarily consisted of in-situ polymerization with simultaneous

sonication and mechanical shear. The complete synthesis procedure is described in detail elsewhere [4]. To study the effect of SWNT synthesis and associated dispersion on the mechanical property of nanocomposites, a thin film having the same matrix but with 0.5 vol% LA (Laser ablated, Rice University) SWNT was synthesized. The synt