Integrated CNT sensors in polymer microchannel for gas-flow shear-stress measurement

We have developed CNT sensors for gas-flow shear stress measurement inside a polymethylmethacrylate (PMMA) microchannel. An array of sensors is fabricated by using dielectrophoretic (DEP) technique to manipulate bundled single-walled carbon nanotubes (SWNTs) across the gold microelectrodes on a PMMA substrate. The sensors are then integrated in a PMMA microchannel, which is fabricated by SU-8 molding/hot-embossing technique. Since the sensors detect gas-flow by thermal transfer principle, we have first examined the I-V characteristics of the sensors and confirmed that self-heating effect occurs when the input voltage is above ~1V. We then performed the flow sensing experiment on the sensors using constant temperature (CT) configuration. The voltage output of the sensors increases with the increasing flow rate in the microchannel. We also found that the power of the sensors has a linear relation with 1/3 power of the shear stress. Moreover, measurements of sensors with different overheat ratios were compared and results showed that sensor is more sensitive to the flow with a higher overheat ratio.