Working principle, semiconductor sensors

Working Principles and Theory. The mechanisms responsible for semiconductor gas-sensor operation can be divided into two classes. The first class involves changes in bulk conductance (transducer function), while the second relies on changes in surface conductance (receptor func-... 

Electrochemical transducers work based on either an amperometric, potentio-metric, or conductometric principle. Further, chemically sensitive semiconductors are under development. Commercially available today are sensors for carbohydrates, such as glucose, sucrose, lactose, maltose, galactose, the artificial sweetener NutraSweet, for urea, creatinine, uric acid, lactate, ascorbate, aspirin, alcohol, amino acids and aspartate. The determinations are mainly based on the detection of simple co-substrates and products such as 02, H202, NH3, or C02 [142]. 

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

In this section orrly conductometric sensors are discussed in which the ionic conductivity of the material plays a role. An example includes TiO, which exhibits a variable stoichiometry as a function of the oxygen pressme. Semiconductor materials, like SnOj or similar ones used in Figaro sensors for analysis of reducing species, work on principles of heterogeneous catalysis, without exhibiting ionic conduction in the bulk of the material, and therefore are not considered here. - ... 

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