Thick film flow sensor for biological microsystems

An anemometer for the in situ control of the flow rates in fluidic systems is designed, manufactured and characterized. For the first time, a flow sensor according to the boundary layer principle is manufactured with exclusive use of thick film technologies. This principle enables the application of the sensor for low fluid temperatures as required in biological fluid systems. The sensor is integrated in a retention module consisting of Low Temperature Cofired Ceramics (LTCC), which allow the cost-effective realisation of complex fluidic microsystems with integrated electronics by only using thick film technologies. Thermistor compositions are printed on a free-standing bridge and encapsulated to ensure biological compatibility. The encapsulation becomes possible by using an adapted technology. At the same time the design facilitates a maximal heat-insulation of the sensor element from the substrate. The control of the stress influences on the free-standing sensor bridge due to shrinking mismatch, TCE mismatch, density gradients and deformation during the lamination is investigated using design of experiments (DoE), resulting in an adapted design and fabrication process. The presented anemometer has a linear sensor characteristic for flow rates up to 80 μl/min. Compatibility investigations of LTCC with biological substances will be presented.