ABSTRACT
Porous silicon layers are very attractive for applications in humidity sensors because of a unique combination of crystalline structure; a large internal surface area of up to 200–500 m2/cm2, which able to enhance the adsorbate effects; and high activity in surface-chemical reactions. It was established that electrical and optical characteristics of porous semiconductors may change considerably upon adsorption of water molecules to their surfaces and/or by water filling the pores. Analysis carried out in this chapter shows that due to unique properties, porous silicon is a universal humidity-sensitive material suitable for developing all types of humidity sensors, including capacitive, resistive, photoluminescence, micromachined, and multiparameters sensors. Features of silicon porosification, as well as limitations of application and approaches to optimization of PSi-based humidity sensors, are discussed as well. In particular, suggestions are given on how to improve sensitivity, selectivity, kinetics of response, linearity of sensing characteristics and stability, and also to reduce hysteresis.
