Semiconductor gas sensors are widely used for qualitative and quantitative analysis of gaseous samples. Typical examples of their applications includes detection of fire, land mine and chemical warfare agents, food quality assessment, disease diagnosis, environmental monitoring, air ratio adjustment in combustion engines and industrial process monitoring. The underlying principles of operation in gas sensors are gas dependent physicochemical processes that change the electrical properties of the sensing material. In metal-oxide gas sensors the resistance of the sensing layer is altered by the oxidation/reduction interaction in the grain boundaries. These gas sensors operate at elevated temperatures and their behavior is hence temperature dependent. In this project the effect of gas type and working temperature on the step responses of resistive gas sensors is investigated experimentally and theoretically. An experimental setup was fabricated to measure the transient responses of gas sensors. Many experiments were carried out to record a data set of transient responses. Gas type, gas concentration, sensor temperature and timing profile were the adjustable parameters of experiments. The results show that the curvature and speed of transient responses both are highly temperature dependent. For example the step responses to the vapor of 4 butanol isomers were clearly distinct at 200 o C while they were similar at 300 o C. The transient behavior of gas sensor is governed by the diffusion-reaction process in the porous sensing layer. Based on these processes the differential equations were extracted and a mathematical model was derived that could successfully model the experimental results. The results of this project provide a more in-depth insight toward the operation of semiconductor gas sensors. Also it can be the basis of a new gas diagnosis method in which the operating temperature is adjusted for obtaining the optimum gas-dependent patterns. Keywords: Metal oxide gas sensor, transient response, thermal dependency, diffusion-reaction
