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POROUS SILICON FORMATION WITH APPLICATIONS TO BIOSENSING MICROELECTROMECHANICAL SYSTEMS Formation of porous silicon (PSi) by electrochemical processing was investigated with future plans to use the PSi as part of biosensing MEMS devices. An electrolytic cell was designed and manufactured to suit our specific needs. The electrochemical process we used had four variables, these being; wafer resistivity, concentration of chemical solution used as electrolyte, current density, and process time. These variables were manipulated such that we experienced everything from electro-polishing to the formation of PSi to our only roughing the surface of our samples. Processing was done with a 50/50 (volume) mixture of 50% Hydrofluoric Acid and 90% Ethanol. We used p-type Boron doped wafers with risistivties ranging from .02-.1 cm up to 10-15 cm. Current densities from 2.4 mA/cm2 up to 50 mA/cm2 were used during processing of PSi. Processing times ranged from 10-30 minutes. Future plans include using PSi on biosensing devices where the material would be used to attach analyte particles to its surface. PSi would be used specifically because of it extremely high specific area which can reach several hundred square meters per cubic centimeter.
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