Clean Technology 2008
N.N. Mishra, P. Winterrowd, R. Nelson, W.C. Maki, S.K. Rastogi, E. Cameron, B. Filanoski, G. Maki
University of Idaho, US
nanowire, nano-transistor, nano-biosensor, impedance spectroscopy, bio detection
5x5 arrays of six nano-transistor devices were fabricated on p-type silicon/silicon oxide (200nm) wafers with resistivity 1-100 -cm. 50nm of doped polysilicon were deposited and annealed to make nanowires. All nanowires were made with direct writing of pattern with electron beam lithography (EBL) and unwanted polysilicon were etched with chlorine plasma. The size of each nano-wire was ~50nm in all devices. The nano-wires were connected with 250nm wide gold source and drain electrode with 150nm separation between these contact pads using EBL and metal lift-off. Device characteristics were tested with electrochemical impedance spectroscopy (EIS) using potentiostatic Bode, Nyquist and Schottky-spectra. The device was also tested with varying gate voltage using digital voltammeter. The device was stable in the voltage range 0.0-0.5V and able to pass 100 µA current smoothly. All devices were found sensitive to light during measurements. Most devices have field effect transistor behaved and some other devices were like diodes. Finally various capture molecules for specific bio-detection were immobilized on nano-device sensing surface by using simple adsorption approach as well as covalent linkage chemistry. All modified device surfaces were verified using fluorescent microscopic method. The modified nano-biosensor was incubated with ~300nL biological sample containing 1 nM to 10 fM target molecules and measured with EIS. The detection sensitivity of nano-FET biosensor was found in the range of 40fM-100fM with 50-70% of reproducibility. Further investigation in integrated microelectronic intelligent system on nano-FET device will be carried on.