Fabrication of silicon and glass devices for microfluidic bioanalytical applications

Kai Kolari
Abstract & Cover

This thesis introduces important improvements in fabrication of microfluidic devices on silicon and glass. With the main aim in surface and volume manipulation of aqueous solutions for subsequent biochemical analysis, the backbone of the work has been the development of plasma etching processes for silicon and glass. As the silicon microfabrication technologies are combined with deep anisotropic etching of glass, the processability of microfluidic applications with surface and volume manipulation of fluid is diversified. Several mask materials have been studied with respect to deep plasma etching of glass. As the demand for depth of microfluidic devices extends past 150 µm, the number of usable masking schemes becomes limited. To reach an etch depth beyond 350 µm with aspect ratio of over 3:1 including the mask, silicon shadow mask was used. The results of process development on Al2O3, AlN and TiO2 masks show that a very high etching selectivity on glass can be achieved with these mask materials. The described masking technologies enable e.g. high density of through-a-wafer holes or nearly vertical structuring of glass with great depth. Also, a silicon shadow mask was used for local tuning of hydrophobicity of C4F8 polymer on silicon and glass surfaces by pattering the polymer with O2 plasma through the shadow mask. For both purposes, one silicon shadow mask wafer can be re-used to enable lower processing costs. Thermal manipulation of fluid allows polymerase chain reaction on silicon and glass microchips, but also triggering of capillary action. However, the results of a novel method indicate possible lack of biocompatibility of oxidized silicon surfaces, which may limit the usable microchip surface materials. Microfluidic components with hydrophilic patterning for controlled capillary action can be combined with microphotonics through excitation of fluorescence with evanescent field, which has been characterized with a grating-coupled laser beam. 

Source of Information
FinALD40 exhibition material, http://www.aldcoe.fi/events/finald40.pdf
VTT Technical Research Centre of Finland / Helsinki University of Technology
(Espoo, Finland)
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