Tuning the bias sensing layer: A new way to greatly improve Metal-Oxide gas sensors selectivity

The effects of bias current in the sensing layer of resistive Metal-Oxide (MOX) sensors toward gases have been investigated. The behavior of a WO
3
thin film deposited by sputtering has been studied. In a first time, while the working temperature is kept constant, it has been found that tuning the polarization of the MOX layer induces changes on its sensitivity. Besides, the behavior of sensitivity versus bias current depends on the nature of the gas. For example, the response to NH
3
-10ppm hugely increases with the bias rise; at the opposite, the polarization has no effect on NO
2
-10ppm responses. In a second time, the effect of the working temperature changing added to the polarization has been studied. Thus, an optimized temperature-modulated profile has been established and it has been associated with a multivariate analysis in order to quickly and easily discriminate several gases and mixtures. It has been shown this method allows discriminating two gases (NH
3
and NO
2
) at two concentrations (5 and 10 ppm) alone and mixed. These results open a new way to increase the selectivity of MOX sensors.