MOSFET:

The acronym MOSFET (pronounced as "MOSS-fet") stands for metal-oxide-semiconductor field-effect transistor. An easy cross-sectional drawing of an n-channel MOSFET and its schematic symbol is shown in figure (a) and (b). And the p-channel device is shown at figure (c) and (d).

Whenever the MOSFET was first build up, it was known as an insulated-gate FET or IGFET. This is possibly more expressive of the device than the presently accepted name. The gate electrode is really insulated, by a thin layer of dielectric, from the channel. As an outcome of this, the input resistance (and therefore the impedance) is tremendously high. The MOSFET draws necessarily no current from the input signal source. This is a benefit in weak-signal amplifiers.

Figure: (a) Pictorial diagram of an n-channel MOSFET, (b) schematic symbol for an n-channel MOSFET, (c) pictorial diagram of a p-channel MOSFET, and (d) schematic symbol for a p-channel MOSFET.

THE MAIN PROBLEM:

The problem with MOSFETs is that they can be damage easily by electrostatic discharge. Whenever building or servicing circuits have MOS devices, technicians should use special equipment to ensure that their hands do not carry electrostatic charges that may ruin the components. When a static discharge takes place through the dielectric of a MOS device, the component will be damaged permanently. The humid environment does not give important protection against this hazard.