Metal oxide semiconductor field effect transistors, MOSFETs

The ISFET is an electrochemical sensor based on a modification of the metal oxide semiconductor field effect transistor (MOSFET). The metal gate of the MOSFET is replaced by a reference electrode and the gate insulator is exposed to the analyte solution or is coated with an ion-selective membrane as illustrated in Fig. 

The operation principle of these TFTs is identical to that of the metal-oxide-semiconductor field-effect transistor (MOSFET) [617,618]. When a positive voltage Vg Is applied to the gate, electrons are accumulated in the a-Si H. At small voltages these electrons will be localized in the deep states of the a-Si H. The conduction and valence bands at the SiN.v-a-Si H interface bend down, and the Fermi level shifts upward. Above a certain threshold voltage Vth a constant proportion of the electrons will be mobile, and the conductivity is increased linearly with Vg - Vih. As a result the transistor switches on. and a current flows from source to drain. The source-drain current /so can be expressed as [619]... 

Metal oxide semiconductor field-effect transistors (MOSFETs) are field effect transistors with a thin film of silicon dioxide between the gate electrode and the semiconductor. The charge on the silicon dioxide controls the size of the depletion zone in the polype semiconductor. MOSFETs are easier to mass produce and are used in integrated circuits and microprocessors for computers and in amplifiers for cassette players. Traditionally, transistors have been silicon based but a recent development is field-effect transistors based on organic materials. 

Ion-Selective Field Effect Transistors [22b,c,d] An ion-selective field effect transistor (ISFET) is a hybrid of an ion-selective electrode and a metal-oxide semiconductor field effect transistor (MOSFET), the metal gate of the MOSFET being replaced by or contacted with a thin film of a solid or liquid ion-sensitive material. The ISFET and a reference electrode are immersed in the solution containing ion i, to which the ISFET is sensitive, and electrically connected as in Fig. 5.37. A potential which varies with the activity of ion i, o(i), as in Eq. (5.38), is developed at the ion-sensitive film ... 

Metal oxide semiconductor field-effect transistor (MOSFET)... 

MOSFETs. The metal-oxide-semiconductor field effect transistor (MOSFET or MOS transistor) (8) is the most important device for very-large-scale integrated circuits, and it is used extensively in memories and microprocessors. MOSFETs consume little power and can be scaled down readily. The process technology for MOSFETs is typically less complex than that for bipolar devices. Figure 12 shows a three-dimensional view of an n-channel MOS (NMOS) transistor and a schematic cross section. The device can be viewed as two p-n junctions separated by a MOS capacitor that consists of a p-type semiconductor with an oxide film and a metal film on top of the oxide. 

A variety of chemical gas sensors are or could be used in electronic nose instruments. So far, successful results have been reached with conductive polymer (CP) sensors, metal oxide semiconductor (MOS) sensors, metal oxide semiconductor field effect transistor (MOSFET) sensors, quartz crystal microbalance (QCM) sensors, and infrared sensors. 

Nevertheless, the first functional working TFT was demonstrated by Weimer in 1962 (Ref 2). He used thin films of polycrystalline cadmium sulfide, similar to those ones developed for photodetectors. The simplified structure is shown in Fig. 1(b). Other TFT semiconductor materials like CdSe, Te, InSb and Ge were investigated, but in the mid-1960 s the emergence of the metal oxide semiconductor field effect transistor (MOSFET) based on the crystalline silicon technology and the possibility to perform integrated circuits, led to a decline in TFT development activity by the end of the 1960s. 

The basic building block of all CHEMFETs is the ion-sensitive field effect transistor (ISFET), introduced in 1970 by Bergveld [4]. In an ISFET the gate metal of a metal oxide semiconductor field effect transistor (MOSFET) is removed and the resulting gate oxide surface (2) is directly exposed to the electrolyte solution (Figure 1). 

Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) used in microelectionics. 

Metal oxide semiconductor field effect transistors (MOSFETs) constitute other materials with applicability in the development of biosensors. Usually, a MOSFET structure consists of a metal gate on top of an oxide layer, tyqjically Si02 [189]. The catalytic properties of these sensors depend upon the type of the gate metal as well as the temperature at which the MOSFET is operated. The most used catalytic metals used as gate materials are Pd (is a good... 

One of the easiest ways to visualize the material and device characteristics that need to be measured is to consider a semiconductor device. For this I have chosen in Figure 1 a metal-oxide-semiconductor field-effect transistor (MOSFET) as representative of a typical semiconductor device. Indicated on it are the important material and device parameters that need to be measured. Only some of them are addressed in this chapter. Other devices could have been chosen, but the MOSFET incorporates most ot the parameters of interest and is the most coismon integrated circuit device. 

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