Impedance spectroscopy on WO3 gas sensor

Abstract Tungsten trioxide (WO 3 ) 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 WO 3 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 WO 3 reactively sputtered films: influence of O 2 concentration in the sputtering gas and working temperature, Sens. Actuators B 100 (2004) 320–324] that structural and surface morphology of tungsten trioxide (WO 3 ) 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 WO 3 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 O 3 , 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.