ABSTRACT
According to band theory, in semiconductors, two distinct bands must exist: a conduction band and a valence band. The separation between these two bands is a function of energy, particularly the Fermi level, defined as the highest available electron energy levels at a temperature. In metal oxide semiconductor (MOS) gas sensors, the target gas interacts with the surface of the metal oxide film, typically through reaction with surface-adsorbed oxygen ions. Screen-printing is widely used in industry and the most widely used method for producing MOS gas sensors commercially. The various zeolite layers produced very different responses. The addition of a zeolite layer will primarily act to increase the response time, dependent on the diffusion of gas through the layer, which will vary for different gas–zeolite combinations because of the molecular-shaped pores. This chapter shoes that by using particular combinations of gas-sensitive material and zeolite, it is possible to distinguish between similar target gases.
