A mobility and free carriers density fluctuations based model of adsorption–desorption noise in gas sensor

Abstract

Noise spectroscopy has been proposed as a means of extracting a more selective response from metallic oxide gas sensors. In this paper, we complete our previous models of adsorption–desorption (A–D) noise by taking into account the effect of the fluctuation of the adsorbed molecule's density, not only on the density of free carriers but also on their mobility. Using Wolkenstein's isotherm, combined with the electroneutrality and the fluctuation of both free electron density and mobility, we derive an exact expression for the A–D noise in the case of dissociative and non-dissociative chemisorption. The model shows that the power density spectrum of the fluctuation of the sensor's conductance has a cut-off frequency and a low frequency magnitude which are specifics of the adsorbed gas. The cut-off frequency is four orders of magnitude lower than the one we obtained without considering mobility fluctuations.