Insulated gate field-effect transistor IGFET

IGFET insulated-gate field effect transistor... 

Fig. 6.31 Insulated gate field-effect transistor (IGFET) with electronically conducting, chemically selective gate...

According to the IEEE standard test methods for the characterisation of OFETs [26], the Shockley equations for insulated gate field effect transistors (IGFETs) are used to approximate the field-indueed drain eurrent in the organic material between the drain and source contaets. It should be reeom-mended that the following assumptions form the basis of the applieability of the equations ... 

The key issue in these sensors is the interface between the ion selective membrane and the contact. The most convenient way to present this problem is in the form of the equivalent electrical circuit in which the resistances and capacitances have their usual electrochemical meaning (Fig.2). It is necessary to include the electrometer (or at least its input stage) in the analysis of these sensors. In most modern instruments the amplifier is an insulated gate field-effect transistor (IGFET) which has the input dc resistance of greater than 10 and the input capacitance on the order of picofarads. 

CHEMFET devices or chemically sensitive field-effect transistors are potentiometric devices in which the metal layer of a solid-state insulated gate field-effect transistor (IGFET) f29] is replaced with a chemically sensitive electroconductive polymer membrane film. Changes in polymer membrane potential modulate the drain impedance of the space-charge region beneath the insulator. The result is a change in drain current /o under a fixed drain voltage Vd- The potential of the membrane may be modulated in the standard way (as in po-tentiometry, above) or may be modulated by an inert electrode placed beneath the film (but isolated from both the source and drain electrodes) and connected to an efficient electrode for the candidate analyte [30]. 

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