Flow rate sensors for in situ gas or liquid monitoring typically comprise multiple transducer elements, including a heater and one or more temperature sensors to measure the rate of heat energy removal by the flowing fluid. The need for multiple transducer elements limits feasibility of shrinking these sensors to microfluidic flow channels and their integration into standard CMOS processes. In this work, a thermal flow sensor architecture is presented, which is integrated into a CMOS IC without additional post-processing.
The architecture uses a single, resistive transducer element to measure fluid flow with a two-phase control and measurement algorithm. Experimental results demonstrate feasibility of the flow sensor architecture using a discrete micron-scale resistor structure, and using an integrated resistor structure for measuring air flow. By separating heating and temperature measurement in time, instead of in space, this method significantly decreases required transducer area and allows for the architecture to be scaled down to an integrated CMOS thermal flow sensor.