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DMT 121/3 : ELECTRONIC I
DMT 121/3
Electronic 1
Pn. Shariffah Zarihan bt Syed Zaharim Helmi
04-9853337 / 012-4539120
[email protected]
DMT 121/3 : ELECTRONIC I
Contents
•
•
•
•
•
Ch 01 – Introduction to Semiconductor
Ch 02 – Diode Applications
Ch 03 – Bipolar Junction Transistors (BJTs)
Ch 04 – DC BJT Biasing
Ch 05 – Field – Effects Transistors (FETs)
TEXT BOOK : Robert L. Boystead & Louis
Nashelsky, ELECTRONIC DEVICES AND CIRCUIT
THEORY, Ninth Edition, 2006
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Lab Modules
•
•
•
•
•
•
Lab 1 : Introduction to Basic Laboratory
Equipment
Lab 2: Introduction to Diode
Lab 3: Diode as Rectifier
Lab 4: Limiter and Clamper Circuits
Lab 5: Current & Voltage Characteristics
of BJT
Lab 6: Voltage Divider Biasing
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Evaluation Contribution
•
•
Final Examination : 50 %
Course Works : 50 %
Details of course work contribution
•
Lab works
: 30 %
•
Test
: 10 %
•
Lab Test
: 10 %
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Time Table
• Lecture – Monday (8.00 am – 10.00 am),
BKS 1
• Lab – Thursday (8.00 am – 10.00 am),
MMS
• Attendance – Compulsory, attendance will
be recorded.
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Semiconductor Materials
History of Semiconductor Devices
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Semiconductor Materials
Definition :
Semiconductors are a special class of
elements having a conductivity between
that of a good conductor and that of an
insulator
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Semiconductor Materials
• Single crystal – Germanium (Ge) and
Silicon (Si)
• Compound Semiconductor – Gallium
Arsenide (GaAs), Cadmium Sulfide (CdS),
Gallium Nitride (GaN) and Gallium
Arsenide phosphide (GaAsP).
• Mostly used : Ge, Si and GaAs
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Semiconductor Materials
• Ge – First discovered. Used as Diode in 1939,
transistor in 1947. Sensitive to changes in
temperature – suffer reliability problem.
• Si – Introduced in 1954 (as transistor), less
sensitive to temperature. Abundant materials on
earth. Over the time – its sensitive to issue of
speed.
• GaAs – in 1970 (transistor), 5x speed faster
than Si. Problem – difficult to manufacture,
expensive, had little design support at the early
stage.
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H
Li Be
Metal
Nonmetal
Intermediate
accept 2e
accept 1e
inert gases
give up 1e
give up 2e
give up 3e
THE
PERIODIC
TABLE
• Columns: Similar Valence Structure
He
Ne
O
F
Na Mg
S
Cl Ar
K Ca Sc
Se Br Kr
Rb Sr
Te
Y
Cs Ba
I
Xe
Po At Rn
Fr Ra
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
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Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
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Semiconductors, Conductors, and Insulators
Conductors
 material that easily conducts electrical current.
 The best conductors are single-element material (e.g copper,silver,gold,aluminum,ect.)
 One valence electron very loosely bound to the atom- free electron
Insulators
 material does not conduct electric current
 valence electron are tightly bound to the atom – less free electron
Semiconductors
 material between conductors and insulators in its ability to conduct electric current
 in its pure (intrinsic) state is neither a good conductor nor a good insulator
 most commonly use semiconductor- silicon(Si), germanium(Ge), and carbon(C).
 contains four valence electrons
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Covalent Bonding & Intrinsic
Materials
• Atom = electron + proton + neutron
• Nucleus = neutrons + protons
Protons
(positive charge)
Neutrons
(uncharged)
Electrons
(negative charge)
Nucleus
(core of atom)
ATOM
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Atomic Structure
No. of electron in each shell
Ne = 2(n)2
n = no of shell.
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Covalent Bonding
Covalent bonding of the Silicon atom
Covalent bonding of the GaAs crystal
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Intrinsic Carriers
Table 1.1
Intrinsic Carriers
Semiconductor
Intrinsic Carriers
(per cubic centimeter)
GaAs
1.7 x 106
Si
1.5 x 1010
Ge
2.5 x 1013
Intrinsic (pure) carriers – The free electrons in a material due to only external
causes
Ge has the highest number of carriers and GaAs has the lowest intrinsic
carriers.
The term intrinsic (pure) is applied to any semiconductor material that has
carefully refined to reduce the number of impurities to a very low level –
essentially as pure as can be made available through modern technology
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Relative Mobility Factor µn
Table 1.2
Relative Mobility Factor
Semiconductor
µn (cm2/V-s)
Si
1500
Ge
3900
GaAs
8500
Relative mobility – the ability of the free carriers to move throughout the
material.
GaAs has 5X the mobility of free carriers compared to Si, a factor that results
in response times using GaAs electronic devices is 5X those of the same
device made from Si.
Ge has more than twice the mobility of electrons in Si, a factor that results in
the continued of Ge in high-speed radio frequency applications.
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Interesting difference between
Semiconductors and Conductors
• Conductors – Resistance increases with the increase in
heat, because their vibration pattern about relatively fixed
location makes it increasingly difficult for a sustained flow
of carriers through the material – positive temperature
coefficient.
• Semiconductors – Exhibit an increased level of
conductivity with the application of heat. As the
temperature rises, an increasing number of valence
electron absorb sufficient thermal energy to break the
covalent bond and contribute to the number of free
carriers – negative temperature effects
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Energy Levels
Fig. 1.6 Energy levels: conduction and valence bands of an insulator, a semiconductor, and a conductor.
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Extrinsic Materials : n-Type and PType Materials
• The characteristics of a semiconductor material
can be altered significantly by the addition of a
specific purity atoms to relatively pure
semiconductor materials – this process is known
as doping process
• A semiconductor that has been subjected to the
doping process is called an extrinsic materials.
• Extrinsic Materials are n-type material [five
valence electrons (pentavalent)] and p-type
material [three valence electrons atom
(trivalent)]
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n-Type Material
• n-Type material is created by introducing the impurity
(bendasing) elements that have five valence electrons
(pentavalent).
• There are antimony (Sb), Arsenic (As) and phosphorous (P).
Diffused impurities with five
valence electrons are called
donor atoms
Fig. 1.7 Antimony impurity in n-type material
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n-Type Material
• The effect of this doping cause the energy level (called the donor
level) appears in the forbidden band with Eg significantly less
than intrinsic material.
• This cause less thermal energy to move free electron (due to
added impurity) into conduction band at room temperature.
Fig. 1.8 Effect of donor impurities on the energy band structure
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n-Type Material
• Pentavalent atoms is an n-type semiconductor (n stands for the
negative charge on electrons).
• The electrons are called the majority carrier in n-type materials.
• In n-type material there are also a few holes that are created when
electrons-holes pairs are thermally generated
• Holes in n-type materials are called minority carrier
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p-Type Material
• Si or Ge doped with impurities atoms having three
valence electrons.
• Mostly used are boron (B), gallium (Ga) and indium (In).
• The void (vacancy) is called ‘hole’ represented by small
circle or a ‘+’ sign.
Diffused impurities with three
valence electrons are called
acceptor atoms
Fig. 1.9
Boron impurity in p-type material.
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Electron versus Hole Flow
• With sufficient kinetic energy to break its covalent bond,
the electron will fills the void created by a hole, then a
vacancy or hole, will be created in the covalent bond that
released the electron.
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p-Type Materials
• In p-type materials the hole is the majority carrier
and the electron is the minority carrier.
• Holes can be thought as +ve charges because
the absence of electron leaves a net +ve charge
on the atom.
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Semiconductor Diode
Diode
• Simple construction of electronic device,
• it a joining between n-type and p-type
material (joining one with majority carrier
of electron to one with a majority carrier of
holes)
Diode @ No Applied
Bias (VD=0)
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Reverse Bias (VD < 0 V)
Fig. 1.13 Reverse-biased p–n junction. (a) Internal distribution of charge under reverse-bias conditions; (b)
reverse-bias polarity and direction of reverse saturation current.
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Forward Bias (VD > 0 V)
(b)
Fig. 1.14 Forward-biased p–n junction. (a) Internal distribution of charge under forward-bias conditions; (b)
forward-bias polarity and direction of resulting current.
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Diode Characteristics Curve
Fig. 1.15 Silicon semiconductor diode
characteristics.
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Ge, Si and GaAs
Fig. 1.18 Comparison of Ge, Si, and
GaAs diodes.
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Temperature Effects
Fig. 1.19 Variation in Si diode characteristics
with temperature change.
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Ideal Vs Practical
Fig. 1.21 Ideal semiconductor diode: (a) forward-biased;
(b) reverse-biased.
Fig. 1.22
Ideal versus actual semiconductor characteristics.
RF 
VD
0V

 0
ID 5mA
(Short circuit equivalent –fwd bias, actual case R ≠ 0)
RR 
VD 20V

 
ID 0mA
(Open circuit equivalent – Reverse bias, actual case
saturation current Is ≠ 0)
DMT 121/3 : ELECTRONIC I
Ideal Vs Practical
• Semiconductor diode behaves in a
manner similar to mechanical switch that
can control the current flow between it’s
two terminal
• However, semiconductor diode different
from a mechanical switch in the sense that
it permit the current flow in one direction
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Approximate Diode
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Resistance Levels
DC or Static Response
• Application of dc voltage will result in an operating point on the
characteristic curve will not change with time.
VD
RD 
ID
In general, the higher the current
through a diode, the lower is the
dc resistance level.
Fig. 1.23 Determining the dc resistance of a diode at a
particular operating point.
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Resistance Levels
AC or Dynamic Response
Fig. 1.25
Defining the dynamic or ac resistance.
Vd 26mV
rd 

Id
Id
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Resistance Levels
Average AC Response
Vd
rav 
Id
Fig. 1.28
Determining the average ac resistance between indicated limits.
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Diode Equivalent Model
VF  0.7V  IFrd
VBIAS  IF RLIMIT  rd   0.7V
VBIAS  0.7V
IF 
RLIMIT  rd
VBIAS  IF[rR  RLIMIT ]
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Example
Determine the forward voltage (VF) and forward current [IF]. Also
find the voltage across the limiting
resistor. Assumed rd’ = 10 at the determined value of forward.
IF 
1.0kΩ
VBIAS  0.7V 10V  0.7V

 9.21mA
'
RLIMIT  rd
1k  10
VF  0.7V  I F rd'  0.7V  (9.21mA)(10)  792mV
VRLIMIT  I F RLIMIT  (9.21mA)(1k)  9.21V
10V
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Example
Determine the Reverse voltage (VR). Also
find the voltage across the limiting resistor. Assumed IR = 1 µA.
Answer:
VRLIMIT =1mV
VR=4.999V
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Diode Testing
• Analog MM (or Ohm meter testing)
Fig. 1.42
Checking a diode with an ohmmeter.
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Diode Testing
• Digital MM
FIGURE 1-38
DMM diode test on a properly functioning diode.
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Diode Testing
• Digital MM (Testing Defective Diode)
FIGURE 1-39
Testing a defective diode.
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Diode Notation
Fig. 1.38
Semiconductor diode notation.
Robert L. Boylestad
Electronic Devices and Circuit Theory, 9e
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
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Zener Diode
Fig. 1.46 Conduction direction: (a) Zener diode;
(b) semiconductor diode; (c) resistive element.
Fig. Characteristics of Zener region.
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Zener Region
The Zener region is in the diode’s
reverse-bias region.
At some point the reverse bias voltage
is so large the diode breaks down and
the reverse current increases
dramatically.
•
•
This maximum voltage is called
avalanche (runtuhan) breakdown voltage
The current is called avalanche current.
48
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