New Materials for Gas Sensitive Field-Effect Device Studies

Gas sensor control is potentially one of the most important techniques of tomorrow for the environment. All over the world cars are preferred for transportation, and accordingly the number of cars increases, unfortunately, together with pollutants. Boilers and powerplants are other sources of pollutants to the environment. Metal-Insulator-Silicon Carbide (MISiC) Field-effect sensors in car applications and boilers have the potential to reduce the amount of pollutants. These devices are sensitive to several gases in exhaust and flues gases, such as hydrogen, hydrocarbons, and ammonia (for the selective catalytic reduction (SCR) application). These applications require specific and long term stable sensors. The car industry for instance wants sensors that will stand at least 240 000 km. This thesis presents studies of the active layers in MIS Fieldeffect gas sensors. Fundamental studies of the sensor mechanism has been performed in ultra high vacuum, UHV, to understand the gas response mechanism in more detail, and to find out how the sensing mechanism is affected by the catalytic active gate material. The influence of four different insulating layers was studied at atmospheric pressure. The catalytic layer has also been altered to metal oxide nanoparticles with or without impregnation of catalytic metals. Nanoparticles are potential candidates to be used as the gate material for high temperature, long-term stable FET sensor devices. The combination of catalytic metals and metal oxides may prevent reconstruction of the metal. The use of nanoparticles will increase the number of triple points (catalytic material and insulator in contact with gas), which are crucial e.g. for the ammonia sensitivity. Another challenging aspect of nanoparticles is the possibility to get selectivity to different gases based on the particle size.