Semiconductor Devices and
Microelectronics
A subtopic of Basic Electronics
First Electronic Devices
• Contain several hundred
vacuum tubes occupying one
large room
• Vacuum tubes consume
several thousand watts of
electrical power
Semiconductors/
Transistors
• Occupies a small side table
• Uses only several watts
• Small-sized and more
efficient
Microelectronics
Microelectronics is the branch of
electronics which deals with small,
miniaturized components
Diodes
•The simplest semiconductor device
•has many applications, from simple
indicators and AC/DC conversion to
voltage regulation and appliance
protection.
Kinds of Diodes
A diode is forward-biased
when the voltage on the
positive leg is higher than on
the negative leg then
current flows through the
diode (the resistance Is very
low)
Kinds of Diodes
A diode is reverse-biased
when the voltage is lower
on the positive leg than on
the negative leg then the
current does not flow (the
resistance is very high).
Cathode and Anode
Types of Diodes
Junction Diode
• the first type of diode
developed
• Name derived from the
principle of the diode,
the positive-negative or
p-n “junction”
Types of Diodes
Zener Diode
• Might be called as a voltage
reference diode.
• used to provide a certain voltage
to a circuit, determined by the
rating of the zener diode.
• If the zener is forward-biased,
then the voltage will just be
equal to the forward biased
voltage of an ordinary diode.
Types of Diodes
Light Emitting Diode
• LED is a special kind of diode.
• When current flows through
from the anode to the cathode,
it lights up
• The higher the current passing
through the LED, the brighter
the light
Types of Diodes
Photodiode s
• The current flow depends on
whether the diode is exposed to
light within a given range of
wavelength
• Absence of light turns the diode in
reverse-biased mode
• usually paired with a light source,
which could be as simple as
ordinary or ambient light, to as
restrictive as an infrared LED, to as
state-of-the-art as lasers.
Other Diodes
• Optoisolators
• Tunnel diodes
• Power diodes
• Varactor or tuning diodes
• Schottky Barrier diodes
Rectification
• the process of making a signal flow in
one direction only
• the converting of a signal from an
alternating current (AC) to direct
current (DC).
Two ways of rectifying a signal
a) Half –wave Rectification
•
the process of converting of
a signal with both positive
and negative phases to a DC
signal with a single phase
only, either positive or
negative (not both). The
other phase is clipped or
removed.
Two ways of rectifying a signal
b) Full –wave Rectification
•
also converts an AC signal to a single
phase but this time instead of
clipping the other phase, it cpnverts
it to the opposite phase.
•
Two ways of creating a full-wave
rectifier
a) By using two diodes, with a center
top as ground reference,
b) via a diode bridge
The Transistor
Transistors are basic components in all of today’s
electronics. They are simple switches that can turn
things on and off.
It is another semiconductor with a wide range of
applications, from simple switching states to amplifying
signals.
Three types of transistors:
a) Bipolar Junction Transistors (BJTs)
b) Unipolar Junction Transistors (UJTs)
c) Field Effect Transistors (FETs)
Bipolar Junction Transistors
The BJT is a three-terminal device.
Parts of a Transistor:
a) Base
b) Collector
c) Emitter
Two basic transistor configurations
a) n-p-n transistor
- a p-type semiconductor
is sandwiched between
two n-type
semiconductors.
b) p-n-p transistor
- a n-type semiconductor
is sandwiched between
two p-type
semiconductors.
Basic Circuit
The Base (B) is the On/Off switch for the transistor. If
a current is flowing through the Base, there will
be a path from the Collector (C) to the Emitter (E)
where current can flow (The Switch is On). If
there is no current flowing to the Base, then no
current can reach the Emitter from the Collector
(The Switch is Off)
Basic Circuit
Basic Circuit
We will use Ohm’s Law to find the current in the path from
the Input to the Base of the transistor and the current
flowing through the LED. To do this we need to use two
basic facts about the transistor.
1. If the transistor is on, then the Base voltage is 0.6 volts
higher than the Emitter voltage VBE = 0.6V
2. If the transistor is on, the Collector voltage is 0.2 volts
higher than the Emitter voltage VCE = 0.2V
Basic Circuit
So the base current ib (current flowing through the 2.2K
resistor) similar to this circuit.
And is given by
ib = VB/Rb = (9 – 0.6)/2200 = 0.0038 A = 3.8 mA
The current flowing through the 330-ohm resistor can be
derived from this circuit,
Basic Circuit
So the base current ib (current flowing through the 2.2K
resistor) similar to this circuit.
And is given by
ib = VC/RC = (9 – 0.6)/2200 = 0.0038 A = 26.7 mA
The current flowing through the 330-ohm resistor can be
derived from this circuit,
Basic Circuit
Mathematically,
ic = Vc/RC = (9 – 0.2)/330 = 0.0224 A = 26.7 mA
If we want more current flowing through the collector, we
can use a smaller resistor (instead of 330). This means we
can control things that use a lot of power with cheap,
low power circuits. The is called current driving