FET Transistor

Fet Transistor stands for Field-Effect transistor. The function of this transistor is to facilitate conductivity and the form of the charge carrier in a semiconductor through an electric field. The first patent for FET transistors was filed by Julias Edgar in 1926. Since then much development has taken place. Another patent was filed by Oskar Heil in 1934. The junction gate that is used in field-effect transistors was created at the Bell Labs by William Shockley. Many other advancements in FET Transistors have been made over the years. Moreover, there are two types of FET transistor:

  • Junction Field Effect Transistor (JFET)

  • Metal oxide Semiconductor Field Effect Transistor (MOSFET)


Working of FET Transistor

The Fet transistor is a voltage-operated device in which the voltage applied is used to control the current flowing. It is also known by the name unipolar transistor as they undergo an operation of a single-carrier type. The input impedance is high in all forms and types of FET. The conductivity is always regulated with the help of applied voltage from the field-effect transistor’s terminal. Moreover, the density of the carrier charge affects conductivity. 

A FET transistor is a device with three major components: Source, Drain, and Gate. The source is one of the terminals of the FET transistor through which most of the carriers enter the bar. The Drain is the second terminal through which majority carriers lead the bar. The Gate has two terminals which are internally connected with each other. 

Since the gate in a FET transistor is in reverse biased, the gate current is practically zero. The drain supply is connected to the source terminal leading the electrons flow which provides the necessary carriers.  


FET Transistor 

There is another subdivision of FET Transistors. In one of the types, the current is taken up primarily by the majority carriers and is therefore called majority charge carrier devices. There are minority charge carrier devices, as well,  in which the current flow is primarily due to minority carriers. 

The two terminals, source, and gate have a potential between them which in turn has the conductivity of the channel as a function of it. The three terminals i.e. source, drain, and gate are there for every FET Transistor. The function of the gate terminal is similar to the gate in real-life as the gate can open and close and can either choose to permit the passage of electrons or stop them altogether. 

The main difference between the two major types of FET transistors - JFET and MOSFET- is that JFET (Junction Field Effect Transistor) is a three-terminal semiconductor device while MOSFET (Metal oxide semiconductor field-effect transistor) is a four-terminal semiconductor device. JFET can only operate in the depletion mode. While MOSFET can operate in the enhancement as well as the depletion mode. The input impedance is higher in MOSFET making them more resistive. In comparison to the price, MOSFET is more expensive than JFET. 

Due to high input impedance, FET transistors are commonly used in and as input amplifiers in electronic voltmeter, oscilloscopes, and other measuring devices. They also occupy little space which makes them more efficient for other devices. 


Difference Between FET and MOSFET

Field Effect Transistors can be of various types such as JFET and MOSFET. The functions and applications of these also differ but they all have three terminals common: source, drain, and gate. Each terminal has an application for regulating the current and voltage of the transistor. Both the two types of FET Transistors are commonly used as input amplifiers as they create high input impedance. These are some important and key characteristics of FET Transistors. This foundational knowledge can be further used in understanding more concepts related to electricity and current. The definition of FET, types of FET, and how it regulates the circuits are the key highlights from this article. 

FAQ (Frequently Asked Questions)

1. What is a Junction Field Effect Transistor (JFET)?

There are two major types of FET Transistors. JFET  is a device that is a unipolar semiconductor with three terminals and is voltage controlled. Furthermore, there are two major configurations of JFET, the N-Channel JFET, and the P-Channel JFET. The N-Channel JFET has better conductivity as compared to the P-Channel JFET as the electrons have higher mobility through a conductor. The P-Challenge JFET has the tendency because of which the flow of current through the channel is positive. One of the applications of JFET is an amplifier. The JFET Transistor can amplify weak signals. Moreover, JFET transistors are also used in voltage regulators, analog switches, and amplifying circuits. 

2. What is a Metal Oxide Semiconductor Field Effect Transistor (MOSFET)?

The second common type of FET is Metal Oxide Semiconductor Field Effect Transistor (MOSFET). The gate terminal of this FET Transistor is electrically isolated from the conductive channel. The gate electrode is made of a  “Metal Oxide” and the insulating material is common “silicon oxide”. It is further subdivided into DE-MOSFET and E only MOSFET. The DE-MOSFET can work in both, duplication and enhancement mode. E only MOSFET works in one mode only and that is enhancement mode. Some of the applications of MOSFET are TV receiver, computer circuits, high-frequency amplifier, electronic voltmeter, and other measuring and testing equipment.