MOSFET Metal oxide field-effect transistor is a semiconductor. A MOS transistor or MOS transistor is a type of insulated gate field effect transistor made by the controlled oxidation of a semiconductor. The MOSFET is a very efficient switching device.


It was first manufactured in 1938 by J.C. Mosley and has been an industry standard ever since. It is a very common power supply used in just about every electronic device you can think of. From the small voltage requirement of radio to the large power requirements of your computer, the FET can handle it all.

MOSFET was invented to overcome the disadvantages of EFETs, such as high drain resistance, moderate input blocking, and slow operation. The voltage determines the conductivity of the device at the gate of the case. This ability to change conductivity depending on the applied voltage can be used to amplify or switch electronic signals.

MOSFETs are also known as IGFET (Insulated Gate Field Effect Transistors). In practice, the MOSFET is a voltage-controlled device, which means that when the rated voltage is applied to the gate terminal, the MOSFET starts to operate through the drain and source terminals.

The main difference between a MOSFET and a FET is that a MOSFET consists of a metal oxide gate electrode electrically connected to a semiconductor N-channel or P-channel through a thin layer of silicon dioxide or glass. With the isolation of the control gate, the price in megaohms is very high.


The construction of a MOSFET is like a FET. It is a four-pin device with source (S), gate (G), drain (D), and body (B) leads. The enclosure is often connected to a source terminal, which reduces the number of terminals to three. It works by changing the width of the channel through which charge carriers (electrons or holes) flow.

A thin layer of silicon dioxide (SiO2) is grown over the entire surface, and holes are made for the ohmic contacts for the drain and source leads. A conductive aluminum layer is deposited along the entire channel on this SiO2 layer from source to drain, which constitutes the gate. The SiO2 substrate is connected to a common terminal or a ground terminal.

MOSFET structure, MOSFET functionality depends on electrical changes occurring in the channel width and the flux of carriers (holes or electrons). Charge carriers enter the channel through the source terminal and exit through the drain. In the MOSFET design, the lightly doped substrate is scattered by the heavily doped region. They are called P-type and N-type MOSFETs, depending on the substrate used.

Charge carriers enter the channel through the source and exit the drain. The width of the channel is controlled by the voltage across an electrode called a gate, which is located between the source and the groove. This metal is insulated from the channel by a very thin oxide layer.

The Metallic Semiconductor Field Effect Transistor or MISFET is a term that is almost synonymous with MOSFET. Another synonym is the gate conductor IGFET field-effect transistor.

Working Principle OF MOSFET

The working principle of MOSFET depends on the MOS capacitor. . The lower oxide layer is located between the surface semiconductor source and the lower terminal. It can be converted from P-type to N-type by applying a positive or negative gate voltage. The MOSFET acts as a switch, controlling the flow of voltage and current between the source and drain of the MOSFET.

It works by adjusting the width of the channel through which charge carrier (an electron for the N channel and a hole for the P channel) from the source to the groove. A gate terminal is a conductor whose voltage regulates the conductivity of the device.

When a drain-source voltage (VDS) is applied between the drain and the source, a positive voltage applied to the drain and a negative voltage. Here, the drain PN junction is biased, and the PN junction is forward biased at the source. At this point, there will be no current between drain and source.

When we apply a positive gate voltage, the holes under the oxide layer have a bending force. The hole is pushed downward—reducing the area of ​​the population due to negative charges associated with acceptors. Electrons reaching the channel are generated.

The positive voltage also attracts electrons from the N + source and carries lines into the channel. If the voltage applied between the channel and the source, the current flows freely between the source and the channel and drives the electrons in the gate voltage channel. While giving a negative voltage is applied, a hole channel is formed under the oxide layer.

When no voltage is applied to the gate terminal, no current will flow except for a small amount of current due to minority carriers. The minimum voltage at which the MOSFET starts is called the threshold voltage.

Depletion-mode MOSFET

The Depletion-mode MOSFET is equivalent to a “normally ” close switch. The absence of transistors requires a source gate voltage (VGS) to turn off the device. The Depletion-mode, which is less common than magnification mode types, usually operates “on” without using the gate base voltage.


The same channel works when VGS = 0 makes it a “normally closed” device. The scaled-down MOSFET circuit designation above typically uses a solid channel line to indicate a closed conductive channel. In this MOSFET depletion mode, a thin layer of silicon is deposited under the gate terminal. The conductivity of the channel in depletion is less compared to the enhancement type.

When there is no voltage at the gate pin, the channel shows its maximum current. However, when the voltage at the gate pin is either positive or negative, channel transmission is reduced. Reducing the N-channel will eliminate the conduction channel (hence its name) of the MOSFET gate, negative source gate voltage, its free electrons are turned off. Likewise, the positive source gate voltage for the POS down-channel MOSFET, + VGS, will “turn off” its open-hole channel.

In other words, for the N-channel reduction mode, MOSFET: + VGS means more electrons and more current. At the same time, A-VGS means less electrons and less current. It’s the same with the P-channel types. The decrease mode is then equivalent to a normally-off switch.

Enhancement-Mode MOSFET

An Enhancement Mode MOSFET MOSFET is equivalent to a “normally open” switch, and this type of transistor requires a source gate voltage to switch the device. In the absence of voltage at the gate terminal, the device does not work. When the gate terminal is at maximum voltage, the device shows increased conductivity. In this case, this oxide layer is called the “reverse layer”.


A channel is formed between a channel and a source in a type as opposed to a substrate. For example, an N-channel is formed with a P-type substrate and a P-channel with an N-type substrate. The movement of the channel due to electrons or holes depends on the N-type or P-type channels, respectively.

Here we can notice a dotted line between the source and the groove, indicating the type of surge mode. In Enhancement mode, conductivity is increased by increasing the oxide layer through which the channel passes.
This oxide layer is commonly referred to as the “back layer”. This channel is formed between the drain and the opposite-type substrate between the lower source,

For example, the N-channel is formed from the P-type substrate, and the P-channel is formed from the N-type substrate. Channel transfer due to electrons or holes depends on the channel type N or P, respectively.

Symbol of MOSFET

There are different MOSFET schematic symbols, and many different MOSFET types are represented between different symbols that represent the same thing. Typically, a MOSFET is a four-terminal device with drain (D), source (S), gate (G), and body (B) / substrate leads. The terminal on the case will always be connected to the source terminal so that the MOSFET will act as a three-pin device.


Describes an electrical symbol for use in IEE circuit diagrams. However, there are many variations of the FET, JFET and MOSFET symbols. As technology improves, manufacturers often try to represent the component better. American standards are certainly very simple and easy to remember.

The amplifier is easy to read with a schematic mirror transistor symbolizing the symmetrical output phase of the complement as a result. They reflect the P-channel symbol on the horizontal axis, and as a result, the source terminal ends at the top. If this symbol was not labeled, then the source terminal is very easy to identify because the gate is close to it.

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