Semiconducting oxides as gas-sensitive resistors

Some recent advances in technology and basic scientific understanding of gas-sensitive resistors based on semiconducting oxides are described. Highlights are: new materials which have greatly improved performance especially against variations of relative humidity and which have led to new applications, ozone measurement being an example; fabrication methods which have made repeatable and reliable devices available in very large numbers at very low cost; new concepts, including self-diagnostic multiple-electrode array devices and two phase, transducer-detector systems, leading to room-temperature operation; deliberate surface modification, either by gases, or by chemical grafting, or by surface segregation; a general response model which allows systematic discussion of the behaviour of a wide range of materials and separation of the different influences upon response; more detailed understanding of elementary reaction processes on the surface; and the application of computational modelling methods to support interpretations and suggest new lines of development. (C) 1999 Elsevier Science S.A. All rights reserved.