Lecture 01 Introduction and applications of Electronics & SemiConductors.pdf

Engr. Athar Baig
Lecturer
athar.baig@uoc.edu.pk
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Lecture 1
Introduction to Electronics & Semiconductors
Department of Electronics Engineering
University of Chakwal
Digital Logic Design

Introduction (Applications)
 We are living in an electronic era where machine robots are capable to do
human work with more ease and high efficiency. Capsules and tablets
contain wireless sensors that collect information from the body to diagnose.
Transparent smartphones will exist in the coming days, we can see through
them and they may lead to the use of windows or mirrors in our home to be
used as PC screens and TV monitors. Sensors are placed on the plants to
detect the shortage of water and alert the farmers.
 Electronic devices are made up of active & passive elements and smaller IC
memories. The ICs, diodes, and transistor are made of semiconductor materials
and their working is dependent on current flow through them.
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Department of Computer Science

Introduction
 “Electronics”, as the name implies relating to electrons. The word electronics
arrived from electron mechanics (Behavior of the electron when it is subjected
to externally applied fields).
 The definition of electronics technically says “Electronics is an engineering
branch that concerns with the flow of current through semiconductor, gas
or any form of matter”.
 The world is growing at a fast rate and it is relevant for the technology
enthusiast to upgrade with latest changes happening in the society. Moreover,
it is difficult to spend few hours without electronics gadgets and they had
become an important part of our everyday routine.
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Applications
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History of Electronics
 Vacuum Tubes
 The invention of Vacuum tube – Invented by John Ambrose Fleming in
1897 brought in the age of electronics. The basic working principle of a
vacuum tube is a phenomenon called thermionic emission. It works like
this: you heat up a metal, and the thermal energy knocks some electrons
loose. Fleming’s device consisted of two electrodes, a cathode and an anode,
placed on either end of an encapsulated glass tube. When the cathode is
heated, it gives off electrons via thermionic emission. Then, by applying a
positive voltage to the anode (also called the plate), these electrons are
attracted to the plate and can flow across the gap. By removing the air from
the tube to create a vacuum, the electrons have a clear path from the cathode
to the anode, and a current is created.
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 A simplified diagram of a vacuum tube diode. When the cathode is heated,
and a positive voltage is applied to the anode, electrons can flow from the
cathode to the anode. Note: A separate power source (not shown) is required
to heat the cathode.
 This type of vacuum tube, consisting of
only two electrodes, is called a diode.
 Diodes are commonly used for
rectification, that is, converting from
an alternating current (AC) to a direct
current (DC).
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 In 1907, American inventor Lee de Forest added a third electrode to the
mix, creating the first triode tube. This third electrode, called the control
grid, enabled the vacuum tube to be used not just as a rectifier, but as an
amplifier of electrical signals.
 Further enhancements of vacuum tubes placed an additional grid (called the
screen grid) and yet another (called the suppressor grid) even closer to the
anode, creating a type of vacuum tube called a tetrode and a pentode,
respectively. These extra grids solve some stability problems and address
other limitations with the triode design, but the function remains largely the
same.
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 Transistors
 In 1947, the trio of physicists William Shockley, Walter Brattain and
John Bardeen created the world’s first transistor, and marked the
beginning of the end for the vacuum tube. The transistor could replicate all
the functions of tubes, like switching and amplification, but was made out of
semiconductor materials.
 Transistors are much more durable (vacuum tubes, like light bulbs, will
eventually need to be replaced), much smaller (imagine fitting 2 billion tubes
inside an iPhone), and require much less voltage than tubes in order to
function (for one thing, transistors don’t have a filament that needs heating).
They had better reliability and probably most importantly, their
characteristics were far more linear and stable.
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 Vacuum tubes are still used in high power RF transmitters, as they can
generate more power than modern semiconductor equivalents. For this
reason, you’ll find vacuum tubes in particle accelerators, MRI scanners, and
even microwave ovens.
 The real development started with the invention of the transistor in 1948 in
Bell Laboratories. Large Bulky Vacuum diodes are replaced with junction
transistor.
 Transistors are initially made with germanium material, later on, silicon BJT
(Bipolar Junction Transistor) are grown up. Most of the devices developed
today are made up of silicon only due to its low cost.
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 IC (Integrated Circuit) – Jack Kilby
 To reduce the size and cost of the entire circuit Jack Kilby introduced a new
concept. This idea entirely changed the world. The complete interconnected
circuit is placed on a single chip commonly called VLSI (Very Large Scale
Integrated). Computer processors used today are made up of billions of
transistors integrated on a single IC.
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The miniaturization that has occurred in recent years
leaves us to wonder about its limits. Complete systems
now appear on wafers thousands of times smaller than the
single element of earlier networks.
Today, the Intel® 𝐶𝑜𝑟𝑒𝑇𝑀 i7 extreme edition processor
has 731 million transistors in a package that is only
slightly larger than a 1.67 sq. inches.
 In 1965, Dr. Gordon E. Moore presented a paper
predicting that the transistor count in a single IC chip
would double every two years.
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All ICs used in Electronics are fabricated
with Semiconductors.
OR
All Electronics depends upon the
semiconductors.
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Materials
Before moving towards semiconductors let’s see how
many major types of materials exist.
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Materials
Insulators
Semi
Conductors
Conductors

Conductors
Materials allows charges to flow easily.
High Conductivity – low resistivity.
No energy band gap, Positive temp. coefficient.
Valence electron is loosely bound with nucleus.
Examples are Copper, Silver, Gold, Aluminum etc. and
Copper is very cheap among all.
Vastly used in Electrical Engineering (Generation,
Transmission and distribution).
Some special conductors turn into super conductors at 0K.
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Insulators
Materials do not allow to flow of charges.
low conductivity – high resistivity.
Huge energy band gap (5eV), Negative temp. coefficient
Valence electron is tightly bound with nucleus as it has
stable orbit (8 electrons).
Examples are mica, glass, wood, rubber etc.
Vastly used in Electrical Engineering (Transmission and
distribution side).
Resistance increases when cooled down.
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Semiconductor Materials (Ge, Si, & GaAs)
The construction of every discrete (individual) solid-state (hard
crystal structure) electronic device or integrated circuit begins
with a semiconductor material of the highest quality.
 Semiconductors are a special class of elements having a
conductivity between that of a good conductor and that of an
insulator, having negative temp. coefficient, Energy band gap of
1eV, behaves as insulator at absolute zero temp (0K, - 273 °C).
They have four valence electrons.
Backbone of Electronics.
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Semiconductor Materials (Ge, Si, AND GaAs)
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Semiconductor Materials
Single Crystal Compound Crystal
repetitive crystal structure
(Si, Ge)
constructed of two or more
semiconductor materials of
different atomic structures (GaAs,
CdS, GaN, GaAsP)
The three semiconductors used most frequently in the construction of electronic devices are Ge, Si, and GaAs

In the early few decades (1940s -1950s), Ge was used for
the fabrication of diodes and transistors because
 easy to find
 available in fairly large quantities
 easy to refine (to obtain very high levels of purity)
But
 suffered from low levels of reliability due primarily to its
sensitivity to changes in temperature
High reverse saturation current
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 At the time, scientists were aware that another material, silicon, had
improved temperature sensitivities with low reverse saturation
current
But
 The refining process for manufacturing silicon of very high levels
of purity was still in the development stages.
 Finally, however, in 1954 the first silicon transistor was introduced,
and silicon quickly became the semiconductor material of choice.
 Not only is silicon less temperature sensitive, but it is one of the
most abundant materials on earth, removing any concerns about
availability.
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 As time moved on, however, the field of electronics became
increasingly sensitive to issues of speed and communication
systems were operating at higher levels of performance.
 A semiconductor material capable of meeting these new needs
had to be found. The result was the development of the first
GaAs transistor in the early 1970s.
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GaAs Si
i. Speeds of operation up to five times that
of Si
i. Speeds of operation is less than GaAs
ii. More expensive (Difficult to manufacture) ii. Cheaper to manufacture
iii. Little design support iii. Highly efficient design strategies

However, in time the demand for increased speed
resulted in more funding for GaAs research, to the
point that today it is often used as the base material
for new high-speed, very large scale integrated
(VLSI) circuit designs.
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This brief review of the history of semiconductor materials is not
meant to imply that GaAs will soon be the only material
appropriate for solid-state construction.
Germanium devices are still being manufactured, although for a
limited range of applications. Even though it is a temperature-
sensitive semiconductor, it does have characteristics that find
application in a limited number of areas. Given its availability
and low manufacturing costs, it will continue to find its place in
product catalogs.
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Ge
Germanium is in limited production
due to its temperature sensitivity and
high reverse saturation current. It is
still commercially available but is
limited to some high-speed
applications (due to a relatively high
mobility factor) and applications that
use its sensitivity to light and heat
such as photodetectors and security
systems.
Si
Without question the
semiconductor used most
frequently for the full range of
electronic devices. It has the
advantage of being readily
available at low cost and has
relatively low reverse saturation
currents, good temperature
characteristics, and excellent
breakdown voltage levels. It also
benefits from decades of enormous
attention to the design of large-scale
integrated circuits and processing
technology.
GaAs
Since the early 1990s the interest in
GaAs has grown in leaps and
bounds, and it will eventually take a
good share of the development from
silicon devices, especially in very
large scale integrated circuits. Its
high-speed characteristics are in
more demand every day, with the
added features of low reverse
saturation currents, excellent
temperature sensitivities, and high
breakdown voltages.
More than 80% of its applications
are in optoelectronics with the
development of light-emitting
diodes, solar cells, and other
photodetector devices, but that will
probably change dramatically as its
manufacturing costs drop and its use
in integrated circuit design continues
to grow; perhaps the semiconductor
material of the future.
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As noted earlier, Si has the benefit of years of
development, and is the leading semiconductor
material for electronic components and ICs. In fact,
Si is still the fundamental building block for Intel’s
new line of processors.
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Conductors have a positive temperature coefficient i.e. the
resistance increases with an increase in heat. This is because
the numbers of carriers in a conductor do not increase
significantly with temperature, but their vibration pattern about
a relatively fixed location makes it increasingly difficult for a
sustained flow of carriers through the material
While
Semiconductor materials have a negative temperature
coefficient i.e. they exhibit an increased level of conductivity
with the application of heat.
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Thank You

Lecture 01 Introduction and applications of Electronics & SemiConductors.pdf

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Lecture 01 Introduction and applications of Electronics & SemiConductors.pdf