Bulk carbon nanotubes as sensing element for temperature and anemometry micro sensing

Bulk multi-walled carbon nanotubes (MWNT) were successfully and repeatably manipulated by AC electrophoresis to form resistive elements between Au microelectrodes and were demonstrated to potentially serve as novel temperature and anemometry sensors. We have measured the temperature coefficient of resistance (TCR) of these MWNT bundles and also integrated them into hot-film anemometry constant current configuration for dynamic characterization. It was discovered that the resulting device could be operated in μW range, which is three orders of magnitude lower than conventional MEMS polysilicon based shear stress sensors. For example, to achieve a resistance overheat ratio in the magnitude of 0.1, only 10 μA of current is needed to heat these MWNT bundle elements compare to mA current range for polysilicon-based sensors. Moreover, the device exhibited very fast frequency response (>100 kHz) in constant current mode, which is higher than its reported MEMS polysilicon counterparts in this mode of operation. Our current processing technology is scalable in producing these MWNT sensing elements ranging from 5 μm to 15 μm in length.