MOSFET - MOS Field Effect Transistors

This three-terminal semiconductor devices are far more useful than two-terminal ones (ie: diode) because they can be used in a multitude of applications, ranging from signal amplification to digital logic and memory. The basic principle involved is the use of the voltage between two terminals to control the current flowing in the third terminal. In this way a three-terminal device can be used to realize a controlled source.

 

Metal-Oxide Semiconductor Field Effect Transistor, commonly known as MOS. The transistor is fabricated on a p-type substrate, which is a single-crystal silicon wafer that provide physical support for the device. Two heavily doped n-type regions, indicated in the figure as the n+ source and the n+ drain regions, are created in the substrate. A thin layer of silicon dioxide (SiO2) of thickness tox, which is an excellent electrical insulator, is grown on the surface of the substrate, covering the area between the source and drain regions. Metal is deposited on top of the oxide layer to form the gate electrode of the device. Metal contacts are made to the source region, the drain region, and the substrate, also known as the body.

 

An N‐channel enhancement‐mode MOSFET shall be denoted as nMOS and a P‐channel enhancement‐mode MOSFET shall be denoted as pMOS.

 

4 Terminals:-

   a) Source (S)

   b) Gate (G)

   c) Drain (D)

   d) Body (B)

 

The Body (B) has no effect on device operation,  so the MOSFET is usually treated as a 3 terminal device in most of the circuit analysis.