Electrical porous silicon chemical sensor for detection of organic solvents

A novel electrical sensor platform containing a porous silicon (PSi) layer on a crystalline silicon substrate has been developed in which the electrical contacts are made exclusively on the backside of the substrate allowing complete exposure of the surface to the sensing molecules. The PSi layers were 20 μm thick with an average pore diameter of 1 μm. Real-time measurements of capacitance (C) and conductance (G) were performed and the response produced by the addition of different organic solvents was evaluated. The observed response is attributed to the combined effect of a change in dielectric constant inside the porous matrix and a modification in the depletion layer width in the crystalline silicon structure. A space charge region modulation model was used to explain the effect induced by molecules of different dipole moments, dielectric constants, polarizabilities and water solubilities.