Development of Porous-Silicon-Based Active Microfilters

With a goal of preparing silicon-based interactive filters in the micropore range, we have developed the first single-step etch-liftoff procedure (one-step separation) based on the formation and removal of macroporous silicon layers. With silicon wafers whose resistivities are in the range from 14 to 22 Ω cm, we are able to create, in a surprisingly controlled manner, films whose pore diameters range from 1-2 μm and whose thickness ranges from 3 to 70 μm. These silicon-based films (filters), which carry a polarizing negative charge, represent an alternative to porous alumina (films) filters (pore diameter not yet in the 1-2 μm range) both in terms of their size range and potential interaction-reaction at elevated temperature. Preliminary experiments demonstrate that platinum and copper can be introduced to these filters using electroless solutions with a goal to creating an effective reductive surface. Using these and alternate material combinations, interactive-reactive filters in the 1 μm size range that operate at temperatures well in excess of porous polymer films can be realized.