MEMS flow sensors for nano-fluidic applications

This paper presents micromachined thermal sensors for measuring liquid flow rates in the nanoliter-per-minute range. The sensors use a boron-doped pol ysilicon thin-film heater that is embedded in the silicon nitride wall of a microchannel. The boron doping is chosen to increase the heater's temperat ure coefficient of resistance within tolerable noise limits, and the microc hannel is suspended from the substrate to improve thermal isolation. The se nsors have demonstrated a flow rate resolution of 0.4 nl/min, as well as th e capability for detecting micro bubbles in the liquid. Heat transfer simul ation has also been performed to explain the sensor operation and yielded e xcellent agreement with experimental data. (C) 2001 Elsevier Science B.V. A ll rights reserved.