A Field-Effect Transistor (FET) is a type of semiconductor device used in electronic circuits to control the flow of current. It belongs to the family of transistors and is widely used in various applications due to its ability to amplify and switch electronic signals with high efficiency.
FETs work based on the principle of an electric field controlling the conductivity of a semiconductor channel. The conductivity of the channel between the source and drain terminals is controlled by the voltage applied to the gate terminal, hence the name "field-effect" transistor.
There are several types of FETs, but the most common ones are:
Metal-Oxide-Semiconductor FET (MOSFET):
Metal-Oxide-Semiconductor Field-Effect Transistor is the most widely used type of FET in modern electronics.
It consists of a metal gate separated from the semiconductor channel by a thin insulating layer, typically made of silicon dioxide (hence, MOSFET).
The most common subtypes of MOSFETs are:
Enhancement-mode MOSFET (normally-off): Requires a positive voltage at the gate to turn it on and allow current flow between the source and drain terminals.
Depletion-mode MOSFET (normally-on): Conducts current by default and requires a negative voltage at the gate to reduce the current flow.
Junction Field-Effect Transistor (JFET):
Junction Field-Effect Transistors have a semiconductor channel with a pn-junction acting as a diode between the gate and the channel.
The gate voltage controls the depletion region's width, which influences the conductivity of the channel.
JFETs can be of two types:
N-channel JFET: The channel is made of N-type semiconductor material.
P-channel JFET: The channel is made of P-type semiconductor material.
Insulated Gate Bipolar Transistor (IGBT):
An IGBT is a combination of a MOSFET and a bipolar transistor (BJT).
It has a gate like a MOSFET but also exhibits conductivity modulation like a BJT.
IGBTs are commonly used in high-power applications such as motor drives and power inverters.
Each type of FET has its own advantages and applications, but all of them are essential components in modern electronics, enabling various functionalities like amplification, switching, and voltage regulation in electronic circuits.