Macroporous silicon is a type of porous silicon that has ordered arrays of channels with high aspect ratio. Macroporous silicon with ordered 3-D structures have a variety of applications such as filters for a particle separation, photonic crystals and optical shortpass filters because of their spatially periodic structures [1–3]. These structures can be prepared by the electrochemical etching (ECE) of silicon wafers in hydrofluoric acid (HF). We report here a way to fabricate macroporous silicon membranes with ordered 3D structures that have controlled periodicity and dimensions appropriate for cell sorting. The silicon 3D structures have pores with variable diameters to modulate the flow behavior and optimize cell sorting efficiency. The silicon membranes were fabricated by wet etching of n-type (100) silicon substrate (40–60 W cm) in potassium hydroxide (KOH) solution with isopropyl alcohol at 80 °C. The 3-D structures were prepared by the electrochemical etching (ECE) of the membranes in diluted HF using the backside illumination with modulated intensity. The thickness of the fabricated membrane has been varied from 20 to 200 mm to optimize filtration of the cells by MEMS (Micro-ElectroMechanical Systems) chips designed for biological cell sorting and cell positioning. The software packages IntelliSuite and ANSYS FLOWTRAN were used to study the mechanical strength of the membrane as well as the velocity profile and flow behavior of Newtonian fluids inside the macroporous silicon membrane.
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