Impedance spectroscopy on WO3 gas sensor

Tungsten trioxide (WO3) is considered as one of the most interesting materials in the field of gas sensors based on metals oxides semiconductors. We have shown in previous papers [K. Aguir, C. Lemire, D.B.B. Lollman, Electrical properties of reactively sputtered WO3 thin films as ozone gas sensor, Sens. Actuators B 84 (2002) 1-5; C. Lemire, D.B.B. Lollman, A.A. Mohammad, E. Gillet, K. Aguir, Sens. Actuators B 84 (2002) 43-48 [2]; M. Bendahan, R. Boulmani, J.-L. Seguin, K. Aguir, Characterization of ozone sensors based on WO3 reactively sputtered films: influence of O2 concentration in the sputtering gas and working temperature, Sens. Actuators B 100 (2004) 320-324] that structural and surface morphology of tungsten trioxide (WO3) thin films, prepared by RF sputtered, plays an important role in the gas detection mechanism. In this paper we have studied the impedance evolution of WO3 sensors versus time and working temperature, under dry air or/and ozone. The AC impedance spectroscopy is a powerful method to understand the nature of conduction processes and the mechanism of gas/solid interactions. The Nyquist response of the sample, as well as under dry air as well as under 0.1 ppm of O3, have been decomposed on R-C parallel circuits. Then, we have shown, that the adsorption of oxygen mainly affects the characteristics of the space charge region at the grain boundaries.