White paper from Integrated Device Technology on the emergence of MEMS thermal mass flow sensors. Link here (PDF)
Flow meters represent the instrumentation of flow sensors and are used to measure the amount of flow that passes through them. There are in principal five different flow meter types: velocity flow, positive displacement flow, differential pressure flow, open channel flow, and mass flow. Mass flow meters are one of the dominant types in the market due to their faster response and better accuracy than other flow meters. They can also be effectively miniaturized and manufactured on silicon wafers. The emergence of MEMS has already revolutionized the consumer electronics market for motion, pressure, and other sensors, and similar micro-machining processes are now being adapted to fabricate flow sensors. Flow sensing applications are typically high-mix and low-to-medium volume compared, for example, to motion sensors that have become ubiquitous in hundreds of millions of smartphones. This paper will focus on the emergence of thermally-based MEMS mass flow sensors and how they match up with existing and more traditional flow sensor technologies.