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Field-effect transistors
(FETs)
Page 2


Field-effect transistors
(FETs)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
l In 1945, Shockley had an idea for making a solid state
device out of semiconductors.
l He reasoned that a strong electrical field could cause the
flow of electricity within a nearby semiconductor.
l He tried to build one, but it didn't work.
l Three years later, Brattain & Bardeen built the first
working transistor, the germanium point-contact
transistor, which was designed as the junction (sandwich)
transistor.
l In 1960 Bell scientist John Atalla developed a new
design based on Shockley's original field-effect theories.
l By the late 1960s, manufacturers converted from
junction type integrated circuits to field effect devices.
Page 3


Field-effect transistors
(FETs)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
l In 1945, Shockley had an idea for making a solid state
device out of semiconductors.
l He reasoned that a strong electrical field could cause the
flow of electricity within a nearby semiconductor.
l He tried to build one, but it didn't work.
l Three years later, Brattain & Bardeen built the first
working transistor, the germanium point-contact
transistor, which was designed as the junction (sandwich)
transistor.
l In 1960 Bell scientist John Atalla developed a new
design based on Shockley's original field-effect theories.
l By the late 1960s, manufacturers converted from
junction type integrated circuits to field effect devices.
l Field effect devices are those in which current is
controlled by the action of an electron field, rather
than carrier injection.
l Field-effect transistors are so named because a
weak electrical signal coming in through one
electrode creates an electrical field through the rest
of the transistor.
l The FET was known as a “unipolar” transistor.
l The term refers to the fact that current is transported
by carriers of one polarity (majority), whereas in the
conventional bipolar transistor carriers of both
polarities (majority and minority) are involved.
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
Page 4


Field-effect transistors
(FETs)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
l In 1945, Shockley had an idea for making a solid state
device out of semiconductors.
l He reasoned that a strong electrical field could cause the
flow of electricity within a nearby semiconductor.
l He tried to build one, but it didn't work.
l Three years later, Brattain & Bardeen built the first
working transistor, the germanium point-contact
transistor, which was designed as the junction (sandwich)
transistor.
l In 1960 Bell scientist John Atalla developed a new
design based on Shockley's original field-effect theories.
l By the late 1960s, manufacturers converted from
junction type integrated circuits to field effect devices.
l Field effect devices are those in which current is
controlled by the action of an electron field, rather
than carrier injection.
l Field-effect transistors are so named because a
weak electrical signal coming in through one
electrode creates an electrical field through the rest
of the transistor.
l The FET was known as a “unipolar” transistor.
l The term refers to the fact that current is transported
by carriers of one polarity (majority), whereas in the
conventional bipolar transistor carriers of both
polarities (majority and minority) are involved.
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
The family of FET devices may be divided into :
l Junction FET
l Depletion Mode MOSFET
l Enhancement Mode MOSFET
Page 5


Field-effect transistors
(FETs)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
l In 1945, Shockley had an idea for making a solid state
device out of semiconductors.
l He reasoned that a strong electrical field could cause the
flow of electricity within a nearby semiconductor.
l He tried to build one, but it didn't work.
l Three years later, Brattain & Bardeen built the first
working transistor, the germanium point-contact
transistor, which was designed as the junction (sandwich)
transistor.
l In 1960 Bell scientist John Atalla developed a new
design based on Shockley's original field-effect theories.
l By the late 1960s, manufacturers converted from
junction type integrated circuits to field effect devices.
l Field effect devices are those in which current is
controlled by the action of an electron field, rather
than carrier injection.
l Field-effect transistors are so named because a
weak electrical signal coming in through one
electrode creates an electrical field through the rest
of the transistor.
l The FET was known as a “unipolar” transistor.
l The term refers to the fact that current is transported
by carriers of one polarity (majority), whereas in the
conventional bipolar transistor carriers of both
polarities (majority and minority) are involved.
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
The Field Effect Transistor (FET) The Field Effect Transistor (FET)
The family of FET devices may be divided into :
l Junction FET
l Depletion Mode MOSFET
l Enhancement Mode MOSFET
Junction FETs (JFETs) Junction FETs (JFETs)
l JFETs consists of a piece of high-resistivity
semiconductor material (usually Si) which
constitutes a channel for the majority carrier
flow.
l Conducting semiconductor channel between two
ohmic contacts – source & drain
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FAQs on PPT: Field Effect Transistors - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is a field effect transistor (FET)?
Ans. A field effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current. It is a three-terminal device with a source, gate, and drain. The electric field generated by the voltage applied to the gate terminal determines the conductivity of the channel between the source and drain, thus regulating the flow of current.
2. How does a field effect transistor work?
Ans. A field effect transistor (FET) works by utilizing the electric field generated by the voltage applied to its gate terminal. When a positive voltage is applied to the gate, it creates an electric field that attracts negatively charged carriers (electrons) towards the gate, depleting the channel between the source and drain. This effectively cuts off the flow of current. Conversely, when a negative voltage is applied, it repels the electrons, allowing current to flow through the channel.
3. What are the advantages of field effect transistors?
Ans. Field effect transistors (FETs) offer several advantages over other types of transistors. Firstly, they have a high input impedance, which means that they draw very little current from the input source. This makes them suitable for use in amplifiers and other high-impedance circuits. Secondly, FETs have a very high switching speed, allowing them to operate at high frequencies. Additionally, FETs can be made smaller in size compared to other transistor types, making them ideal for miniaturized electronic devices.
4. What are the different types of field effect transistors?
Ans. There are mainly two types of field effect transistors (FETs): junction field effect transistors (JFETs) and metal-oxide-semiconductor field effect transistors (MOSFETs). JFETs are made of a single semiconductor material and have a simple structure, while MOSFETs have an additional insulating layer between the gate and channel, providing better control over the current flow.
5. What are the applications of field effect transistors?
Ans. Field effect transistors (FETs) find applications in various electronic devices and systems. They are commonly used in amplifiers, oscillators, and voltage regulators due to their high input impedance and low noise characteristics. MOSFETs are extensively used in digital logic circuits, microprocessors, and memory devices. They are also employed in radio frequency (RF) applications, such as wireless communication systems and radar systems, due to their high switching speed and frequency capabilities.
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