MOSFET Tutorial

- overview or tutorial about the basics and essential details of the MOSFET, its structure, MOSFET operation, MOSFET circuits and circuit design, and its applications.

This overview of the different types of field effect transistor, FET is split into several pages, each addressing a differnet type of field effect transistor and its technology:

FETs of all types are widely used electronics components today. Even though MOSFETs have been in use for many years, these electronics components are still a vary important element in today's electronics scene. Not only are MOSFETs found in many circuits as discrete components, but they also form the basis of most of today's integrated circuits. MOSFETs are able to be used in very low current circuits and this is particularly important for integrated circuit technology where power limitations are a major consideration.

MOSFET history

The term MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor, and the name gives a clue to its construction. The devices had been known about for several years but only became important in mid and late 1960s. Initially semiconductor research had focussed in developing the bipolar transistor, and problems had been experienced in fabricating MOSFETs because process problems, particularly with the insulating oxide layers. Now the technology is one of the most widely used semiconductor techniques, having become one of the principle elements in integrated circuit technology today. Their performance has enabled power consumptions in ICs to be reduced. This has reduced amount of heat being dissipated and enabled the large ICs we take for granted today to become a reality. As a result of this the MOSFET is the most widely used form of transistor in existence today.

MOSFET basics

Like the junction FET there are two categories of MOSFET, namely p-channel and n-channel types. The principle of operation is similar, but has some significant differences. Whilst the channel area, and hence its conductivity of a JFET is controlled by the depletion layer of a reverse biased diode, for the MOSFET, the gate is placed on an insulating oxide layer. Voltages applied to the gate control the conductivity of the channel as a result of the electric field induced capacitively across the insulating dielectric layer. There are also two further categories of MOSFET: enhancement and depletion types. As the name suggests the depletion mode MOSFET acts by depleting or removing the current carriers from the channel, whereas the enhancement type increases the number of carriers according to the gate voltage.

Further pages from this tutorial
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