Microfluidic Thermal Flow Sensor with Extended Linear Range and Reduced Heat Dissipation Using a Shunt

This paper reports an inline microfluidic thermal flow sensor with extended linear range via a thermal shunt between the up- and downstream branch. The shunt is realised by refilling a 3 $\mu \mathrm{m}$ wide trench, such that the up-and downstream branch are thermally short-circuited. Additionally, the fabrication technology allows for the integration of highly-doped silicon heaters in the sidewalls of the freely-suspended microchannel. The sensor is characterised using nitrogen, isopropanol, and water. The shunt extends the linear range 30 times to 0.3 g/h. The heaters dissipate 3.5 mW of power resulting in a maximum temperature of 303 K, suitable for lab-on-a-chip applications. Furthermore, the fabrication technology is compatible with other inline sensors enabling further on-chip integration.