Metal-insulator-semiconductor MIS capacitor

Metal inert gas (MIG) welding, 27 369 Metal-insulator-semiconductor (MIS) capacitor, 29 140-143 Metal-insulator-semiconductor devices, 22 191, 192... 

Field-effect transistors (Appendix C) are miniature cousins of the Kelvin probe. The most common is the insulated gate field-effect transistor. The heart of the insulated gate field-effect transistor is the Metal-Insulator-Semiconductor (MIS) capacitor. Let us form this capacitor from palladium (to be modulated by hydrogen), silicon dioxide (insulator), and p-type silicon (semiconductor), and examine the energy levels in this structure (Fig. 6.32). 

In field-effect transistors (FET) a potential is applied via metal contacts between two -type semiconductor areas - called source and drain - in a bulk of otherwise /7-type semiconductor material. A metal layer - called the gate - in contact with a thin insulating layer placed on top of the semiconductor (between source and drain) forms a metal/insulator/semiconductor (MIS) capacitor. If the gate is charged, the semiconductor region below the insulator is influenced by the electric field. The electric field thus affects the current flowing between source and drain. In ion-sensitive FETs (iSFETs) the metal layer on top of the insulating layer is replaced by an ion-sensitive material. This ion-sensitive layer is in contact with the analyte solution, and a reference electrode is placed close to it. 

The MIS capacitor represents the heart of most field effect sensor devices, and the physics of MIS capacitors is of importance and is treated in semiconductor physics and other sensor books (Sze, 1981 Lundstrom, 1995 Dimitrijev, 2000). Here, we will only give the basic physical principles regarding the metal insulator semiconductor field effect transistor (MISFET), since this is the ultimate transducer for commercial sensor devices. 

Analytical approximations are helpful in order to estimate achievable device properties and to analyze measured current-voltage characteristics. Although MIS (metal insulator semiconductor) capacitors are also of interest, here only the basic analytical dependencies for OFETs, more specifically for TFTs, are compiled. 

---