Noise Modeling in MOX Gas Sensors

Abstract

In this paper, we propose a new model of adsorption–desorption (AD) noise in chemoresistive gas sensors by taking into account the polycrystalline structure of the sensing layer and the effect of the adsorbed molecule’s density fluctuation on the grain boundary barrier height. Using Wolkenstein’s isotherm, in the case of dissociative and non-dissociative chemisorption, combined with the electroneutrality, we derive an exact expression for power density spectrum (PDS) of the AD noise generated around one grain. We show that the AD noise generated in the overall sensing layer is a combination of multi-Lorentzian components. The parameters of each Lorentzian depend on the nature of the detected gas, the grain size, and the gas concentration. Moreover, we show that, according to the sensing layer microstructure (distribution of grain sizes in the sensing layer), this combination can lead to a [Formula: see text] spectrum, and in this case the noise level of the [Formula: see text] spectrum depends on the nature of the detected gas. The noise modeling presented in this paper confirms that noise spectroscopy is a useful tool for improving the gas sensor selectivity.

A New Gases Identifying Method With MOX Gas Sensors Using Noise Spectroscopy

“…However below this frequency, the overall spectrum of the gas sensor noise is a combination of multi Lorentzians. This result was shown in our previous paper [25]. Moreover, in the model presented in our previous paper [25], we have shown that the number of lorentzians is independent of the nature of the detected gas.…”

“…In our previous work [25], we have developed a model of noise in metallic-oxide gas micro sensors. We have shown that the adsorption-desorption (A-D) noise generated in the overall sensing layer is a combination of multi-Lorentzian components.…”

“…The calculation of the PSD of the gas sensor noise done in [25] has resulted in the following expression:…”

“…On the basis of our previous work [25], we propose, in this section, to calculate the theoretical expression of the first derivative of the PSD of the gas sensor noise, and to show that it admits a minimum which depends on the nature of the detected gas.…”

“…These parameters are the various noise levels (H i ) 1<i<g and cut off frequencies ( f ci ) 1<i<g which are involved in the expression of the PSD of the gas sensor noise (see "(2)" and "(3)"). Bearing in mind that all these parameters depend on the nature of the detected gas (see [25]), it is clear that the output of each input by this function depends on the nature of the detected gas. Using "(9)", we can easily see that the…”