CNT-based thin-film structures create new MEMS/NEMS

May 12, 2011 — Researchers from the Technology Integration and Advanced Nano/microsystems (TIAN) Lab at the Department of Mechanical Engineering, University of Minnesota used IC assembly processes to fabricate single-walled carbon nanotube (SWCNT) composite thin film micropatterns and suspended beams. The stiff CNT-polymer composite thin film micropattern and suspended beam have potential applications to novel physical sensors, nanoelectromechanical switches, and other MEMS/NEMS devices.

Lithography-compatible layer-by-layer (LbL) nano-self-assembly was used to assemble negatively charged SWCNTs with a positively charged polydiallyldimethylammonium chloride.

The resultant composite thin film was patterned by oxygen plasma etching with a masking layer of photoresist, resulting in a feature size of 2µm.

The SWCNT nanocomposite stripe pattern with a metal clamp on both ends was released by etching a sacrificial layer of silicon dioxide in the hydrofluoric acid vapor. I-V measurement reveals that the resistance of SWCNT nanocomposite film decreases by 23% upon release, presumably due to the effect of reorientation of CNTs caused by the deflection of about 50nm. A high Young’s modulus is found in a range of 500-800GPa based on the characterization of a fixed-fixed beam using nanoindentation. This value is much higher than those of other CNT-polymer composites due to self-assembly and higher CNT loading.

The group was led by Tianhong Cui at the University of Minnesota. They have studied the lithography-compatible layer-by-layer nano self-assembly process in detail, and has previously configured nanomaterials as thin-film transistors and biosensors. The current work lends itself to nano-switches due to the thin films’ stiffness and electrical conductivity.

Dr Dongjin Lee was a PhD student when the study was conducted. He is currently a postdoctoral associate at the Korea Advanced Institute of Science and Technology (KAIST), Korea. The research group, TIAN Lab, is led by Prof. Tianhong Cui. The research goal of the group is to investigate the fundamental electrical and mechanical principles of new materials for MEMS/NEMS and low-cost micro/nanomanufacturing approaches, utilizing nanotechnology to effectively enhance the performance of micro/nanosystems. Learn more at http://www.me.umn.edu/labs/tianlab/.

Additional information including a detailed version of the fabrication procedure is available in the journal Nanotechnology. Access the article, "Suspended carbon nanotube nanocomposite beams with a high mechanical strength via layer-by-layer nano-self-assembly," here: http://iopscience.iop.org/0957-4484/22/16/165601

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