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Investigations for non-destructive characterization of MEMS (Micro-Electro-Mechanical-Systems) are presented that can be applied in production monitoring in early stages. Different aspects and experimental results are shown for quadratic and circular silicon membrane structures with artificial structural defects. The quadratic membranes were manufactured with three variations of notches at the edges. The circular membranes had residues on the backside of the membrane resulting from the etching process. The dynamic properties of the structures were measured non-destructively by scanning laser-Doppler vibrometry. The consequences of the generated defects were investigated using the resonant frequencies and mode shapes of the membrane structures in comparison to the dynamic properties of accurate membranes. The results show that the generated defects lead to a variation of the dynamic properties depending on size and position of the defect

A novel impedimetric and thermal flow sensor chip with perforated membrane for the inline chemical process analysis in micro residence time reactors were developed. Sensors were optimized for reactors made of stainless steel with a hydraulic diameter in the range of ~1 mm. The impedimetric sensor chip consists of capacitively coupled interdigital electrodes made of MoSi 2 on a silicon substrate. The thermal flow sensor consists of a heater in between two thermocouples on a thin membrane containing small holes for pressure compensation. CFD simulations were conducted to study the influence of medium flow in the cavity below the membrane. A micro fluidic flow cell with sensor electronics was developed for the characterization of both sensors. Experimental results revealed that changes of less than 1% in the thermal and electrical properties of the liquid can be detected. Insofar, the combination of the impedimetric and thermal flow sensor chip enables the analysis of reactive mixtures in overpressure regime by means of 4 independent physical parameters.

In micro-plants, as used in chemical micro-process engineering, an integrated inline analytics is regarded as an important factor for the development and optimization of chemical processes. Up to now, there is a lack of sensitive, robust and low-priced micro-sensors for monitoring mixing and chemical conversion in micro-fluidic channels. In this paper a novel sensor system combining an impedimetric sensor and a novel pressure stable thermoelectric flow sensor for monitoring chemical reactions in micro-plants is presented. The CMOS-technology-based impedimetric sensor mainly consists of two capacitively coupled interdigital electrodes on a silicon chip. The thermoelectric flow sensor consists of a heater in between two thermopiles on a perforated membrane. The pulsed and constant current feeds of the heater were analyzed. Both sensors enable the analysis of chemical conversion by means of changes in the thermal and electrical properties of the liquid. The homogeneously catalyzed synthesis of n-butyl acetate as a chemical model system was studied. Experimental results revealed that in an overpressure regime, relative changes of less than 1% in terms of thermal and electrical properties can be detected. Furthermore, the transition from one to two liquid phases accompanied by the change in slug flow conditions could be reproducibly detected.