ABSTRACT
Al2O3 is one of the most favorable ceramic humidity-sensing materials. Moreover, porous Al2O3 was one of the first ceramics to be used in humidity-capacitance-type sensors. Today this material is being used in many commercial impedance humidity sensors. In this chapter, one can find a description of the structure of such sensors, the principles of their operation, and features of their manufacture. It is shown that the sensor parameters of Al2O3-based devices (sensitivity, humidity range, response time, stability, etc.) strongly depend on the thickness, the density of the porous layer, and the size of the pores. Features of Al anodization used to form the humidity-sensitive layer are also discussed in this chapter. It has been shown that other methods, such as electron-beam evaporation, reactive evaporation, spray pyrolysis, and reactive-ion plating, can also be used to deposit Al2O3 thin films intended for use in humidity sensors. A discussion of the limitations of the Al2O3-based humidity sensors and approaches designed for resolving this problem is also included in this chapter.
