ABSTRACT
Due to the intensive research of electrochemical etching and development of stable and wellcontrollable silicon anodization processes, research activities since the 1990s show a growing interest in fabrication and application of porous silicon (PSi)-based membranes. Application of PSi membranes offers many advantages compared to conventional membrane materials: low cost fabrication process (in comparison to other microtechnology processes), precise control of pore size and pore size distribution depending on the fabrication conditions (e.g., doping, electrolyte concentration, anodization current density, light intensity), high chemical and temperature stability, applicability at high transmembrane pressure, high permeability, high selectivity, sterilizability, easy system and process integration in silicon-based MEMS/NEMS, smart sensors, Lab-on-a-Chips (LOC) or micro total analysis systems (μTAS). PSi is perfectly suited for formation of channels with different properties in nanometer as well as in micrometer scale. Flexible electrochemical and micromachining processes allow the control of membrane properties and realization of complex membrane architectures, including pore size and pore form variations. PSi membranes exhibit high surface-to-volume ratio resulting in a large inner surface, which can be activated in a postprocessing step for catalytic, immobilization, or functionalization purposes. However, the membrane properties are considerably changing due to the anodization and postprocessing process. Investigation of PSi membrane properties is a key issue for proper membrane design and for applications. Low cost processes, access to both membrane sides and compact system integrations open new applications of PSi-based membranes, especially in filtration and separation technology, fuel cells, fluidic systems, smart sensors, optical sensors, biosensors, and miniaturized LOC and μTAS systems.
