Thermoelectric flow sensors on flexible substrates and their integration process

A thermoelectric mass flow rate sensor on a 10 μm thick polyimide foil and its integration process on planar as well as non-planar surfaces has been developed. Flow sensors, fabricated by MEMS technology, usually have a height which is directly coupled to the wafer thickness (typically 525 μm or 380 μm). They are not bendable and an integration process is always complex when steps in flow channels have to be avoided. A fabrication process has been developed where the functional layers were removed from the silicon substrate and transferred onto a 10 μm thick polyimide foil. The resulting flexible flow sensor has been integrated on different materials by means of flip chip mounting and tested on its electrical and mechanical characteristics. It could be shown that thermoelectric flow sensors on polymer foils have comparable characteristics to flow sensors on silicon substrates but higher diversity in system integration.