Formation of channel silicon for integrated membranes

The morphological features of porous layers obtained on low doped n-type silicon without illumination in a double tank electrochemical cell using electrolytes based on HF and oxidizing agents: formic and hydrochloric acids are studied. The pore sizes in the layers obtained are in the range from 0.16 to 1.4 µm. At a current density of 200-400 mA/cm2 and the addition of formic acid to the electrolyte, the pore diameters do not change with the depth of the porous layer and lie within 0.16-0.21 µm. While without an oxidizing agent or with the addition of hydrochloric acid and at low current densities (10 mA/cm2), the pore diameter at the surface is greater than in depth (0.7-1.4 µm and 0.3-0.5 µm, respectively). When silicon is etched, pore branching is observed in both types of electrolytes. On the base of the obtained porous layers, a single-crystal silicon substrate was removed by mechanical grinding, and membranes with through channels were formed. To test these membranes for gas transmission of nitrogen dioxide NO2, the response of a gas sensor located in the measuring chamber, into which gas was admitted through the membrane or directly. A correlation between the diameters of the channels and the gas transmission of nitrogen dioxide was found.