Approaches and mechanisms to solid state based sensing

A brief survey of different approaches to gas sensing with solid state devices is given. It is pointed out that many physical phenomena can be coupled to chemical reactions on the surface of or within the sensing material. One of the new directions in solid state based chemical sensing is then described in some detail. It concerns the development of fast sensors, e.g. for combustion monitoring at high temperatures. This is first exemplified by the development of semiconducting metal oxides, like strontium titanate, for high operating temperatures. Sensors based on silicon carbide devices with catalytic metal (platinum) gates are described in some detail. A general discussion is given about the fundamental limits of the time response of chemical sensors. It is concluded that, from a chemical point of view, time constants much smaller than presently observed experimentally should be possible.