Chemically sensitive field-effect transistors CHEMFETs

Chemically modified waxes, 26 220 Chemically resistant fibers, 13 389 Chemically sensitive field-effect transistors (ChemFETs), 22 269. See also Field effect transistors (FETs)... 

Electrochemical sensors, among them voltammetric and potentiometric devices, chemically sensitized field effect transistor (CHEMFET) and potentiometric soHd electrolyte gas sensors... 

The first example of chemically modified field-effect transistors (CHEMFETs) was reported by Janata et al. [15] in 1978 for ion-sensitive field-effect transistors (ISFETs) in which the gate oxide was covered with a PVC membrane containing... 

CHEMFET Chemically sensitive field effect transistor... 

Another important class of sensors is constituted by inorganic field-effect gas sensors, known as chemically sensitive field-effect transistors (CFIEMFETs) [28,31-35]. Their most successful application is in highly sensitive hydrogen sensors commercialized by Sensistor AB (Sweden) more than 15 years ago as leak detectors. They have proven over the years to be very reliable. A CHEMFET is essentially a... 

Chemically sensitive field effect transistors are called CHEMFETs. If the coating of the gate of the FET is gas-sensitive, the term GASFET is used instead. When the polymer acts as an ion exchanger with protons or other ions, it results in a pH-sensitive or ion-sensitive device called a pH-FET or ISFET. For instance, a potassium-sensitive device is called a K-ISFET. 

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]. 

Figure 3. Ionic leakage paths in chemfet structures a.Schematic illustration of ionic leakage paths around the chemically sensitive membrane. Leakage through the membrane also occurs but is not illustrated b. Schematic illustration of leakage at the surface of a standard ion sensitive field effect transistor.

The membrane potentials can also be measured indirectly, if the membrane is fixed on the surface of a field-effect transistor (FET) from which the metallic gate has been removed. The electric current passing between the source and drain of the EET is then controlled by the membrane potential. The first sensor of this type [ion-selective FET (ISFET) or chemically sensitive FET (CHEMFET, CSFET)] was described by Bergveld in 1970 and the field has been developed primarily by Janata and co-workers and Japanese researchers. 

Field effect transistor, FET an electronic device in which the conductivity of the semiconductor material is controlled by the electrical field at a particular part of its surface, known as the gate . This electrical field may be varied by attachment (and subsequent reaction) of enzymes (ENZFET) or antibodies (IM-MUNOFET) to the gate. The gate may also be sensitized to specific ions (ISFET) or other chemicals (CHEMFET). 

Another approach to eliminate the inner filling solution of conventional ISEs was introduced also in the 1970s and is based on the use of field effect transistors (FETs). These devices are referred to as ISFETs, that is, ion-sensitive FETs, and belong together with enzyme FETs (EnFETs) and gas sensitive FETs to the larger category of ChemFETs (chemically sensitive FETs). In the case of the ISFET, the ISE membrane is applied to the Si3N4... 

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