Design of microfluidic channels separated by an ultra-thin free-standing dielectric membrane

A microfluidic (MF) surface plasmon polariton sensor featuring a gold Mach–Zehnder interferometer on an ultra-thin (20–35 nm) dielectric membrane is described. While the presence of the membrane is required to maintain a near mirror symmetry of the dielectric properties of the medium on either side of the interferometer, it is a source of unique challenges in the MF system design. The pressure required to drive the fluid flow in microchannels causes deflection whose value depends on the membrane’s residual stress in the low pressure range and on its modulus at the higher pressure range. Depending on the empirical membrane strength which would meet the required equipment reliability, narrow fluidic channels may require tight dimensional tolerances to maintain the pressure difference across the membrane below a critical value. With wider channels (≥100 μm) dimensional tolerances are relaxed even with relatively weak membranes.