Fabrication of normally-closed bidirectional micropumps in silicon–polymer technology featuring photopatternable silicone valve lips

This publication presents novel, normally-closed, bidirectional micropumps. Their main innovation is a fabrication process that combines traditional silicon micromachining with innovative, multifunctional polymer technologies. Therefore a flexible and robust wafer-level bonding technology, based on a laminable permanent dry-film photoresist from Ordyl SY300 Series is utilized. Moreover, using the photolithographic capabilities of Ordyl, 3D MEMS fluidic structures such as micro-channels or, in this study, the pump and valve chambers are simultaneously fabricated. To establish and integrate two flexible and particle tolerant normally-closed microvalves into the micropump, a commercially available photopatternable spin-on silicone (Dow Corning WL5150) is introduced into the manufacturing process. The definition of a reproducible mechanical pre-deformation (2.8 μm) of the silicone material was obtained within the Ordyl wafer-bonding procedure. This combination of features yields the normally-closed character and results in an extremely small leakage-flow in the closed-state up to 500 mbar of applied backpressure. Furthermore, the usage of a multilayer piezo-actuator technology demonstrates the ability of considerably decreasing the piezo driving voltage from formerly applied 360 V p–p (peak-to-peak) down to 30 V p–p. The designed micropumps work bidirectionally by simply applying a reversed actuation scheme. Due to the increased compression ratio of up to 0.512, the presented micropumps are self-priming and can pump water and air. Peak flowrates of 1.65 ml × min −1 and a sustainable backpressure of 600 mbar for water are measured in the pumping mode. In the normally-closed state, a leak-rate of 291 nl × min −1 is measured under 500 mbar of applied backpressure. The overall size of the micropump is 30.65 mm × 13.35 mm × 1 mm. The combination of traditional silicon MEMS and silicone–polymer microfabrication technologies reduces the manufacturing costs and boosts the device performance. Possible applications of the micropumps are the field of microfluidics in general, and micro dosing for biological and chemical applications (e.g. drug delivery).