Fabrication of a cantilever-based microfluidic flow meter with nL min(-1) resolution

A microfluidic flow meter based on cantilever deflection is developed, showing a resolution down to 3 nL min(-1) for flows in the microliter range. The cantilevers are fabricated in SU-8 and have integrated holes with dimensions from 5 x 5 to20x 20 mu m(2). The holes make it possible to measure in a liquid environment.

With a lithography optimization, holes as small as 3 x 3 mu m(2) can be opened. Further on, an isotropic Si etch step is inserted into the fabrication sequence to ensure a high release yield of the devices (percentage of usable/not broken chips compared to the amount of released chips). With this etch the cantilever structures are under-etched before they are released by tweezers and the release yield is enhanced from 41.5% to 84.0%.

In a continuous flow mode, the deflection of the cantilevers is directly proportional to the flow rate. By tuning the design of the integrated grid (hole size, hole-to-hole distance, amount of holes, etc) the sensitivity of the sensor can be changed.