Fabrication and testing of a SU-8 thermal flow sensor

In this work, a microthermal flow sensor integrated in a completely polymeric based microfluidic chip is presented. The fabrication process is based on photolithography of SU-8 layers to pattern the fluidic channels, surface treatment processes in order to improve adhesion of metal layer on top of the polymer, and the use of an adhesive bonding of two patterned SU-8 layers, allowing an easy packaging and integration with other SU-8 based devices like micropumps, microvalves, etc. Characterization of the device shows its successful performance detecting flows in the order of tens of μl/min, working at heater temperatures from 60 °C down to 40 °C. Moreover, the sensor exhibits a linear response at flows below 25 μl/min and the detection of volumes in the range of nanoliters. Such characteristics of the sensor are of great interest for its use in biological applications.