Surface state model for conductance responses during thermal-modulation of SnO2-based thick film sensors:: Part I -: Model derivation

Metal oxide gas sensors (MOXs) are widely used in olfactory electronic systems for their high sensitivity and low-cost. These sensors modify their conductivity in presence of oxidizing and reducing gases, and their performance is strictly dependent on the measurement technique adopted. In particular, it was already established by many works that a noticeable improvement in selectivity can be obtained by operating MOXs with a variable temperature. The temperature profile, however, must be tailored to the specific application, and the shape of the "optimum" profile for a given application depends both on the specific sensor and on the tested chemicals. In this context, there exists a strong interest in developing simplified models able to predict the sensor response, and aiming at a better comprehension of the mechanisms involved in sensing operations. In this paper, three simple gray-box models able to predict the behavior of some commercial thick film SnO2-based sensors in presence of oxygen and a reducing gas (CO) are proposed and discussed, whereas in a second paper the experimental validation of the model is presented.