Semiconductors in Gas Sensors

The history of electrochemical sensors began in the thirties of the twentieth century, when the pH-sensitive glass electrode was deployed, but no noteworthy development was carried out till the middle of that century. In 1956, Clark invented his oxygen-sensor based on a Ft electrode in 1959, the first piezoelectric mass-deposition sensor (a quartz crystal microbal-ance) was produced. In the sixties, the first biosensors (Clark and Lyons, 1962) and the first metal oxide semiconductor-based gas sensors (Taguchi, 1962) started to appear. 

M. (1997) A novel electronic nose based on semiconductor films gas sensor to distinguish different types of milk. In Authenticity and Adulteration of Food the Analytical Approach, Proceedings of Euro-FoodChem IX, Interlaken, Switzerland, 24-26 September 1997, pp 89-94. 

Lantto, V. (1992) Semiconductor gas sensors based on Sn02 thick films. In Gas Sensors, G. Sberveglieri (ed.), Kluwer Academic Publishers, Dordrecht, pp. 117-67. 

Multicompositional films can be produced (Fig. 12.1d). The catalytic materials in semiconductor-type gas sensors are usually added after forming a sensing layer through impregnation,55 sputtering,56 and vapor deposition,57 even though it can be... 

The outputs of some mixed potential-type chemical sensors correlate with the type of electronic defect (i.e., n-type versus p-type), so the response has been attributed to the semiconducting behavior of the electrode material [314]. LaFeO3, which has been used as a semiconductor-type gas sensor ] 315, 316], has also been used as an electrode with YSZ [255, 263, 317] or NASICON ]317, 318] electrolytes for potentiometric NO, sensors. Strontium (i.e., (La,Sr)FeO3 ]255, 256, 284]) or strontium and cobalt (i.e., (La, Sr)(Co,Fe)O3 ]275, 280, 309]) have been added to LaFeO3 to improve electrode performance. (La,Ca)MnO3 doped with either cobalt or nickel on the manganese site has been used as the electrode for N O, sensors ]319]. The outputs of some NO, sensors with perovskite electrodes are shown in Figure 13.26 ]255, 256, 264, 275, 309, 312]. 

Because individual droplets evaporate and react quickly, grain sizes are very small, usually less than 0.1 pm. The small grains are a disadvantage for most semiconductor applications but not necessarily for sensor applications e.g. in gas sensors, where surface area is important. 

The aim of this chapter is to describe and review the interface chemistry and transition theory of the electrode-oxide semiconductor layer in gas sensor operation. Section 3.2 deals with criteria for selecting the metal and semiconductor materials used in the fabrication of gas sensors.The chemistry and... 

Recent advances in wide bandgap semiconductor-based gas sensors... 

Various materials and fabrication methods have been investigated to produce metal oxide semiconductor CO2 gas sensors. The most widely-used materials based on tin dioxide have largely been found to be insuffident for the task. Typically, poor response behaviour to CO2 and high cross-sensitivity are major problems for tin dioxide-based materials. Examples are work conducted by Patel et al. (1994) and Hoefer et al. (1994). The sensors in the study by Hoefer et al showed a marked response in the concentration range of 1000-10000 ppm CO2 at an operating temperature of 270°C. The most significant responses were above CO2 concentrations of 5000 ppm but. 

Fig. 10.7 The variation in the sensitivity of semiconductor Sn02 gas sensor as a function of PdO particle size, which is present on the Sn02 particle surface as a surface modifier (From Seal and Shukla (2002). Copyright 2002 The Minerals, Metals and Materials Society)...

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