Organic Field Effect Transistors principles

In an active device, like an organic field-effect transistor, chemical tailoring can be applied not only to the semiconductor but also to metallic and insulating layers, thus allowing different localizations of the device-sensing area. This possibility broadens the set of sensing principles exploitable for these devices. In addition, from the electrical characterization of an active device it is possible to simultaneously extract different parameters, which correlate to the identification of a chemical species in a mixture. In this way it is possible to obtain a sort of fingerprint of a compound [5]. 

In addition to applications as functional materials in OLEDs and OSCs, semiconducting polymers are needed for other (opto)electronic devices as well. With regard to displays, sensors, and radio-frequency identification tags (RFIDs) for example, it is a challenge to create polymer-based organic transistors (thin-film transistors, OTFT field-effect transistors, OFETs). Figure 6.7 sketches an optional OFET design, and additionally shows schematically its principle of operation. 

There has recently been considerable interest in the detection and identification of air-borne volatile compounds in such diverse areas as quality control of perfume to detection of toxic gases. Miniaturization, the potential low cost of sensors and the variety of applications promise an enormous market (29, 30), Chemical sensors (29) for volatile compounds operate on varied principles and can be classified according to the method of functioning into basic groups such as electrical (field-effect transistors, metal oxide semiconductors and organic semiconductors), optical (spectrophotometric, luminescence, optothermal) and sensors that are sensitive to a change of mass (piezoelectric and acoustosurface). 

A ChemFET, a chemical field-effect transistor, is a type of FET that is a chemical sensor where the charge on the gate electrode is due to a chemical process. In principle, it may be used to detect atoms, molecules and ions in liquids and gases. For example, the SiOa gate material has Si-OH groups on the surface, which can be used for covalent attachment of organic molecules and polymers. 

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