Introduction to Field-Effect Transistors (FETs)

Summary

This lecture introduces Field Effect Transistors (FETs), comparing them to Bipolar Junction Transistors (BJTs). FETs are three-terminal, voltage-controlled devices, unlike BJTs which are current-controlled. FETs can be either n-channel or p-channel, used for amplification and switching. The lecture outlines the history of FETs, from early patents to modern MOSFETs, and discusses their high input impedance, temperature stability, smaller size, and lower sensitivity compared to BJTs.

Takeaways

• 🔬 Field Effect Transistors (FETs) and Bipolar Junction Transistors (BJTs) are both three-terminal devices, but FETs are voltage-controlled while BJTs are current-controlled.
• 🌐 FETs can be used for both amplification and switching, similar to BJTs.
• 🔋 FETs are unipolar devices, meaning they rely solely on either electrons or holes, unlike BJTs which are bipolar.
• 📡 There are two types of FETs: Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
• 🧬 JFETs can be further divided into n-channel and p-channel types, just like NPN and PNP BJTs.
• 🏗️ MOSFETs are also divided into two types: depletion mode (D-MOSFET) and enhancement mode (E-MOSFET), each with n-channel and p-channel variants.
• 📚 The concept of FETs was patented by Julius Edgar Lilienfeld in 1926 and Oscar Heil in 1934, but the actual devices were developed later.
• 🔎 The first JFET was made in the late 1950s, and the MOSFET, an improvement over JFET, was invented by Dawon Kahng in 1959.
• 🔌 FETs have a high input impedance compared to BJTs, which is an advantage in certain applications.
• 🌡️ FETs are more temperature stable than BJTs, making them suitable for environments with varying temperatures.
• 🏞️ FETs are smaller in size compared to BJTs, which is beneficial for miniaturization in electronic devices.
• 📡 BJTs are more sensitive to the applied signal than FETs, which can be a consideration in signal processing applications.

Q & A

What is the main focus of the new chapter introduced in the lecture?

The main focus of the new chapter is Field Effect Transistors (FETs).

How are Field Effect Transistors (FETs) similar to Bipolar Junction Transistors (BJTs) in terms of terminals?

Both FETs and BJTs are three-terminal devices. In BJTs, the terminals are base, collector, and emitter, whereas in FETs, they are gate, drain, and source.

What is the main difference between BJTs and FETs in terms of control mechanism?

BJTs are current-controlled devices, with the output current (IC) being a function of the input current (IB). In contrast, FETs are voltage-controlled devices, where the output current (ID) is a function of the voltage between the gate and source (V_GS).

Why are Field Effect Transistors referred to as 'unipolar' devices?

FETs are called 'unipolar' because they depend solely on either electrons or holes for conduction, unlike BJTs which are 'bipolar' and involve both types of charge carriers.

What are the two types of Field Effect Transistors discussed in the lecture?

The two types of Field Effect Transistors discussed are Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).

Who is credited with the initial patent of the Field Effect Transistor concept?

The initial patents for concepts similar to FETs were by Julius Edgar Lilienfeld in 1926 and by Oscar Heil in 1934.

How do FETs compare to BJTs in terms of input impedance?

FETs have a higher input impedance compared to BJTs.

What is the significance of the term 'Field Effect' in the name of Field Effect Transistors?

The term 'Field Effect' refers to the electric field developed by charges that controls the conduction path of the output circuit in FETs.

Are FETs more temperature stable than BJTs?

Yes, FETs are more temperature stable than BJTs.

How do the size and area occupied by FETs compare to those of BJTs?

FETs are smaller in size and occupy less area than Bipolar Junction Transistors.

Which type of transistor is more sensitive to the applied signal, BJTs or FETs?

BJTs are more sensitive to the applied signal compared to FETs.

Outlines

00:00

📚 Introduction to Field Effect Transistors

This paragraph introduces the topic of Field Effect Transistors (FETs), comparing them with Bipolar Junction Transistors (BJTs). The lecturer explains that both FETs and BJTs are three-terminal devices, with the terminals being the gate, drain, and source for FETs, and the base, collector, and emitter for BJTs. The paragraph also discusses the applications of FETs, which are similar to those of BJTs, and highlights the main difference between the two: BJTs are current-controlled devices, while FETs are voltage-controlled.

05:00

🔬 Characteristics of Field Effect Transistors

The second paragraph delves into the characteristics of FETs, emphasizing that they are unipolar devices, meaning they rely either on electrons or holes, unlike BJTs which are bipolar. It also explains the concept of n-channel and p-channel FETs, analogous to npn and PNP transistors. The paragraph mentions that FETs can be used for both amplification and switching. The hierarchy of FETs is outlined, distinguishing between Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), with further classification into n-channel and p-channel types. The history of FETs is briefly touched upon, mentioning the initial patents and the evolution leading to the invention of the MOSFET by D. Kong in 1959.

10:02

🔍 Further Insights into Field Effect Transistors

The final paragraph provides additional insights into FETs, explaining the term 'Field Effect' and how it pertains to the electric field that controls the conduction path in FETs. It also compares the input impedance of FETs to that of BJTs, stating that FETs have a higher input impedance. The paragraph discusses the temperature stability of FETs, noting that they are more stable than BJTs. It also mentions the smaller size of FETs compared to BJTs and concludes with a comparison of sensitivity between BJTs and FETs, stating that BJTs are more sensitive to applied signals. The lecture concludes with an invitation for questions and a预告of the next presentation, which will discuss the construction and characteristics of JFETs.

Keywords

💡Field Effect Transistors (FETs)

Field Effect Transistors (FETs) are a type of semiconductor device that uses an electric field to control the flow of current. They are the main focus of the lecture, as the instructor aims to introduce them and compare them with Bipolar Junction Transistors (BJTs). FETs are three-terminal devices, with the terminals being gate, drain, and source. The script mentions that FETs can be used for both amplification and switching, similar to BJTs.

💡Bipolar Junction Transistors (BJTs)

Bipolar Junction Transistors (BJTs) are another type of semiconductor device that differs from FETs in that they are current-controlled devices. In the script, BJTs are compared to FETs, highlighting their three terminals: base, collector, and emitter. The lecture emphasizes the differences in control mechanisms between BJTs and FETs.

💡Terminals

Terminals refer to the points of connection in a transistor. The script explains that both BJTs and FETs are three-terminal devices, with specific functions for each terminal. For BJTs, these are base, collector, and emitter, while for FETs, they are gate, drain, and source. Understanding the function of each terminal is crucial for comprehending how these devices operate.

💡Current Control

Current control refers to the mechanism by which the output current in a device is controlled by the input current. The script uses BJTs as an example of current-controlled devices, where the output current (IC) is dependent on the input current (IB) through a current gain factor (Beta).

💡Voltage Control

Voltage control is the method by which the output current in a device is controlled by the input voltage. FETs are described as voltage-controlled devices in the script, where the drain current (ID) is dependent on the gate-source voltage (VGS). This is a key distinction between FETs and BJTs.

💡Unipolar

Unipolar devices, such as FETs, rely on either electrons or holes for conduction, but not both, unlike bipolar devices like BJTs. The script mentions that FETs are unipolar, which means they can be either n-channel (electrons) or p-channel (holes).

💡n-channel FET

An n-channel FET is a type of Field Effect Transistor that conducts current primarily via electrons. The script mentions that when FETs depend solely on electrons, they are referred to as n-channel FETs, analogous to NPN transistors in BJTs.

💡p-channel FET

A p-channel FET is a type of Field Effect Transistor that conducts current primarily via holes. In the script, p-channel FETs are mentioned as the counterpart to n-channel FETs, relying on holes for conduction, similar to PNP transistors in BJTs.

💡Junction Field Effect Transistor (JFET)

Junction Field Effect Transistors (JFETs) are a type of FET where the conducting channel is formed between two reverse-biased PN junctions. The script outlines that JFETs are one of the two broad classifications of FETs, the other being MOSFETs.

💡Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

MOSFETs are a type of FET that uses a metal gate electrode insulated from the semiconductor by a layer of oxide. The script indicates that MOSFETs are superior to JFETs and are the second broad classification of FETs discussed in the lecture.

💡Input Impedance

Input impedance refers to the measure of opposition to alternating current (AC) at the input of a device. The script highlights that FETs have a high input impedance compared to BJTs, which is an important characteristic when considering their use in circuits.

Highlights

Introduction to Field Effect Transistors (FETs) and their comparison with Bipolar Junction Transistors (BJTs).

FETs and BJTs are both three-terminal devices.

BJT is a current-controlled device, while FET is a voltage-controlled device.

BJT is a bipolar device, whereas FET is a unipolar device.

FETs can be either n-channel or p-channel, similar to NPN and PNP transistors.

FETs can be used for amplification and switching, just like BJTs.

Classification of FETs into Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).

JFETs are further divided into n-channel and p-channel types.

MOSFETs are also divided into n-channel and p-channel types.

History of Field Effect transistors, starting with patents by Julius Edgar Lilienfeld in 1926 and Oscar Heil in 1934.

The first FET was made in the 1950s, and MOSFET was invented by Dawon Kahng in 1959.

Field Effect transistors derive their name from the electric field that controls the conduction path.

FETs have a high input impedance compared to BJTs.

FETs are more temperature stable than BJTs.

FETs are smaller in size compared to Bipolar Junction Transistors.

BJTs are more sensitive to the applied signal than FETs.

Next lecture will discuss the construction and characteristics of Junction Field Effect Transistors (JFETs).

Transcripts

from this lecture we will start a new

chapter that is Field Effect transistors

and in this lecture I will give a small

introduction about the Field Effect

transistors I will give a small

introduction about the Field Effect

transistors we will try to understand

what are fs and also compare them with

bjts we will compare f

with bipolar Junction transistors so

this is what we will do in this lecture

now we will move to the first point and

in this point we will talk about

terminals we already know BJT is a three

terminal device

BJT is a

three terminal device and like BJT f is

also a three terminal device Fe

is also a three terminal device in this

figure you can see the first box is

representing the BJT and the second box

is representing the F and in case of BJT

we have three terminals this terminal is

the base terminal this terminal is the

collector terminal and this terminal is

the Amer terminal the

current IB is the input current and the

current I is the output current in case

of BJT and in case of F this terminal

here is the gate terminal this terminal

is the drain terminal this terminal here

is the source terminal and the potential

difference between these two

terminals is equal to V GS v subscript

GS this is the potential difference

between the gate terminal and the source

terminal and the current in this branch

that is the output current is equal to I

subscript D so BJT and F both are three

terminal devices now we will talk about

applications to a larger extent the

application of f is same as application

of BJT the application of

Fe is nearly same as application of

application of

BJT so we are done with the first point

now we will move to the second point and

in this point we will talk about what

type of device is f BJT is current

control device you can see here the

output current is IC and I is equal to

Beta time IB where IB is the input

current so the output current is

dependent on the input current so we say

BJT is a current

controlled

device on the other hand the current ID

is dependent on the voltage

vgs so f e is a voltage

controlled device and this is the main

difference

main difference between BJT and F BJT is

a current control device and F is a

voltage control device IC is a function

of current IB current

IC is the function of input current IB

on the other hand in case of f current

ID is the function of voltage VG s and

you can see in both the cases the output

currents are the functions of input

parameters so we can say that the output

currents in both the cases are

controlled by parameters of input

circuit vgs is the input voltage in case

of F and IB is the input current in case

of BJT so we are done with the second

point which is very important point

because this is the main difference

between BJT and F let's discuss the

third point if you remember the first

presentation on BJT then I told you BJT

is a bipolar device BJT is a bipolar

device and this word bipolar is

reflected in the name BJT b stands for

bipolar on the other hand the Field

Effect

transistor is unipolar is uni

polar this means F depends solely on

either electrons or holes so f is a

unipolar device because it depends

either on electrons or on holes so this

is all for the third point now we will

move to the fourth point and in case of

f we have

n channel f and

P channel f p channel f like npn

transistor and PNP transistor when the f

is dependent on electrons only then we

call the f n channel f and when F

depends only on holes we call that f p

channel f f can be used for

amplification as well as switching the

fourth point is f

can be used for

amplification and also for switching

like BJT we can use f for amplification

and for switching let's move to the

fifth point and the fifth point is

related to the hierarchy we are going to

follow in this

chapter the Field Effect

transistors can be broadly classified

into two types the first one is jat the

Junction Field Effect transistor and the

second one is Mos

fat metal oxide semiconductor Field

Effect transistor in this chapter we

have to focus on these two Field Effect

transistors we can further classify J

fat into two types the first one is n

Channel J fat and the second one is p

Channel J fat MOS fat we can classify in

into two types the first one is

dfat D mosfet and the second one is e

mosfet and again we can classify D

mosfet into two types n

Channel P Channel oset we can classify

into two types n Channel and P channel

so this is all about the hierarchy we

are going to follow in this chapter now

let's talk about the history of Field

Effect transistors this is the sixth

point the history of Field Effect

transistors the Field Effect transistor

was first patented by Julius Edgar

Lilian field

Julius

Edgar

Lilian field in

1926 and by Oscar hail by Oscar

hail in

1934 and this patents were not for the

actual F but for the concepts and f-

like devices in 1947 William shlay and

his team tried to make AF but failed

while they were trying to diagnose the

reasons for failures they discovered the

first transistor or Point contact

transistor and after one decade the

first jet was made and Mos fat which is

better than J fat was invented by D Kong

D Kong in

1959 so this was the history of Field

Effect transistors now we will move to

the next point and in this point we will

try to understand meaning of Field

Effect meaning of

field

effect in the name Field Effect

transistor in case of Field Effect

transistors an electric field is

developed by the charges present an

electric field is developed by the

charges present and this electric field

controls the conduction path of the

output circuit this electric field

controls controls the

conduction

path of the out output circuit so there

is an effect due to electric field and

because of this reason we call the

device Field Effect transistor now let's

move to the next point and in this point

we will talk about input impedance Field

Effect

transistors Field Effect

transistors have high input impedance

high input impedance as compared to bjts

in the next point we will talk about

temperature stability FS

FS are more temperature stable FS

are

more

temperature stable as compared to bjts

in the next point we will talk about

area occupied or the size of fets Field

Effect

transistors are smaller are

smaller than bipolar Junction

transistors the last point the last

point is related to

sensitivity bjts

bjts are more sensitive to the applied

signal as compared to the fets so this

is all for this lecture if you have any

doubt you may ask in the comment section

in the next presentation we will discuss

the construction and characteristics of

G fets Junction Field Effect transistors

so see you in the next presentation