Fabrication of a normally-closed microvalve utilizing lithographically defined silicone micro O-rings

摘要

The focus of this work is on the development of a simple and variable process chain for the integration of flexible silicone material into silicon-based microfluidic devices. A normally-closed microvalve is chosen as a demonstrator device, as it combines features that are not easily obtained from silicon devices alone, especially, a high leak tightness of up to 1 bar pressure difference in the closed state and a high forward flow of several mL min~(-1) in the open state. For this purpose, a photopattemable silicone is used as a deformable circular valve lip between a piezoelectrically actuated membrane and a valve seat, similar to a micro O-ring with a width of 50 μm. The microvalve is piezo actuated by monolayer piezo actuators with a peak-to-peak driving voltage of V_(p_p) = 200 V. The micro O-ring is pre-deformed by 2.8 μm during the valve fabrication process to yield the normally-closed behavior. A dry film resist lamination technology is developed for this critical process step to mate the two silicon wafers with the actuation membrane, the valve seat and the silicone O-ring in between at a well-defined distance. The dry film resist is used in a multifunctional way, not only to pre-deform the valve lip, but also to define the geometry of the valve chamber and to ensure a leak-tight connection of both wafers. Altogether, a peak value for the on- to off-ratio of the normally-closed microvalve higher than 30 000 is measured. This opens a wide range of potential applications, e.g. in micro-dosing, drug delivery, μ-TAS and microfluidics for biological or chemical applications in general.