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Multi-layer SU-8 lift-off technology for microfluidic devices

This paper reports on a novel multilayer SU-8 lift-off technology which allows for low cost rapid prototyping of microfluidic devices. The process presented is based on a multi-layer structure of SU-8 which can be released from the substrate after processing and enables the creation of through holes. The lift-off is accomplished during the development by making use of the volume shrinkage of the SU-8 during postbaking and by modification of the adhesion to the substrate. To demonstrate the technology, prototypes of a multichannel microdispenser according to the Dispensing Well Plate (DWP™) principle (Koltay et al 2004 Sensors Actuators A 116 472, 483) were fabricated. The samples contain 24 parallel dispensing units with 100 µm through holes and a dosage volume of 60 nl. For the first time all functional structures such as reservoirs, channels and through holes (nozzles) of the DWP™ were realized exclusively in the photodefinable epoxy SU-8. To assess the quality of the SU-8 process the geometry of the presented prototypes is characterized by profiler measurements and scanning electron microscopy. Furthermore, the dispensing performance is studied experimentally by gravimetrical measurements. A reproducibility of the dosage volume of 1% and a homogeneity within individual droplet arrays of 3.6% were achieved.