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 (TM)) principle (Koltay et al 2004 Sensors Actuators A 116 472, 483) were fabricated. The samples contain 24 parallel dispensing units with 100 mu m 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 (TM) 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.