Microtech 2011

Parallel Fabrication of Single-Walled Carbon Nanotube based Piezoresistive Pressure Sensors

B.R. Burg, T. Helbling, C. Hierold, D. Poulikakos
ETH Zurich, CH

Keywords: pressure sensor, piezoresistivity, carbon nanotubes, dielectrophoresis, parallel integration


A major obstacle in the realization of commercially viable single-walled carbon nanotube (SWNT) based devices, hindering the functionality of this uniquely interesting type of material, is their type and site selective integration. In this work, dielectrophoresis is used in the purely parallel fabrication of extremely small SWNT-based piezoresistive pressure sensors. The quasi 1 dimensional transducer elements have a diameter of 1-3 nm and a length of 0.8-1 um, emphasizing the scaling potential of the sensors. Superior strain sensitivity to state-of-the-art silicon based piezoresistive pressure sensors is achieved through the highly selective integration of individual small band gap semiconducting (SGS)-SWNTs by dielectrophoretically guided assembly. Dielectrophoresis further allows precise individual carbon nanotube positioning on the designated membrane edges, ultimately the positions of highest strain. The pressure sensors have a membrane diameter of 120 um and thickness of 190 nm. Highest sensitivity of the long-term stable devices is measured in the off-state of SGS carbon nanotube transistors (CNFETs). The SWNTs are encapsulated by a protective alumina coating to ensure long-term stability and avoid environmental influences. The CNFETs can be modulated by a metallic top gate above the high k dielectric. Low contact resistances and high transmission are essential for good sensor resolution. The scale-up of the introduced robust and reliable fabrication process is straight-forward and provides very promising avenues toward successful realization of functional, commercially viable SWNT sensors.

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