In recent years, hybrid structures have attracted wide consideration because they generate new very interesting properties. In this study, a hybrid gas sensor was developed using a simple fabrication process from the combination of porous silicon (PSi) and polythiophene (PTh). The study of the effect of electropolymerization rate and film thickness of PTh on the sensitivity and the stability of sensor was realized at room temperature. PSi was formed by electrochemical anodization, and it is an

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... nteresting material for sensing applications due to its high surface area. However, to avoid its degradation and to preserve its properties over the time, PSi surface was functionalized electrochemically with PTh subsequently to thermal oxidation. PTh as a conductive polymer is known for its high sensitivity and stability to environmental change. Several thicknesses of PTh have been electropolymerized onto the oxidized PSi surface to determine the best conditions for developing a sensitive and stable sensor. PTh thickness was controlled by the number of applied voltammogram cyclic. The characterizations of the different elaborated surfaces were carried out by Fourier transform infrared spectroscopy, scanning electron microscopy, cyclic voltammetry, contact angle, and secondary ion mass spectrometry. Finally, we studied the sensitivity, the response time, and the stability of PSi/PTh structures with different PTh thicknesses in the presence of CO2 gas and under cigarette smoke, by performing electrical characterizations, at room temperature.