A Field-Effect Transistor (FET) is a type of transistor that uses an electric field to control the flow of current between its source and drain terminals. It belongs to the family of transistors, which are semiconductor devices used for amplification and switching of electronic signals. FETs have a distinct advantage over bipolar transistors like BJTs (Bipolar Junction Transistors) because they have very high input impedance, low noise, and consume less power.
There are three main types of Field-Effect Transistors:
MOSFET (Metal-Oxide-Semiconductor FET): This is the most common type of FET and is widely used in various electronic devices. It has three terminals: source, drain, and gate. The MOSFET has a thin insulating layer (oxide) between the gate electrode (usually made of metal) and the semiconductor material (usually silicon). MOSFETs are further classified into two types based on the arrangement of the semiconductor material:
N-channel MOSFET (NMOS): In this type, the majority carriers (electrons) flow between the source and drain terminals. A positive voltage applied to the gate relative to the source creates an electric field that allows the flow of electrons from source to drain.
P-channel MOSFET (PMOS): Here, the majority carriers (holes) flow between the source and drain terminals. A negative voltage applied to the gate relative to the source creates an electric field that allows the flow of holes from source to drain.
JFET (Junction Field-Effect Transistor): JFETs are less common than MOSFETs but still find applications in specific areas. They have a single-channel, unlike the dual-channel configuration of MOSFETs. JFETs are further divided into two types:
N-channel JFET: In this type, the majority carriers (electrons) flow between the source and drain terminals. A reverse-biased PN junction is created between the gate and the channel to control the flow of electrons.
P-channel JFET: Here, the majority carriers (holes) flow between the source and drain terminals. Similarly, a reverse-biased PN junction is formed between the gate and the channel.
DE-MOSFET (Depletion-Enhancement MOSFET): This is a less common type of FET that combines the characteristics of both depletion-mode and enhancement-mode MOSFETs. It can operate in both enhancement and depletion modes by controlling the voltage applied to the gate.
Each type of FET has its own set of characteristics and applications. MOSFETs, in particular, dominate the field due to their versatility and compatibility with modern integrated circuit fabrication processes. They are crucial components in various electronic devices, such as microprocessors, memory chips, power amplifiers, and more.