Influence on moisture sensor performances, and characterization of different specific area porous silicon layers

This paper presents results obtained for characterization of porous silicon (PS) layers having different nanostructures, and the influence of this parameter on moisture sensor performances. Two PS layers have been studied, both present the same porosity of 45% and differ in their specific area: 330 m²/g for PS₁ and 223 m²/g for PS₂. Sorption isotherms were measured; the results justify the use of adsorption theories used to characterize mesoporous materials. Average values of pore diameter computed from adsorption theories and images processing show that PS₂ presents smaller pores than PS₂. Pore size distributions have been estimated, showing the wider distribution of PS₂ compared with PS₁. We measured resistivity of PS layers as a function of relative humidity (RH). We found that PS₂ presents higher resistivity and higher relative variation of resistivity. Exposed to moisture step, PS₂ sensor presents faster response time, showing a second advantage among performances criteria.