Bridging Theory in Practice
Transferring Technical Knowledge
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Introduction to Semiconductors
Introduction to Semiconductors
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Introduction to Semiconductors
Intended Audience:
• Engineers with little or no semiconductor background
• A basic understanding of electricity is assumed
Topics Covered:
•
•
•
•
What is a semiconductor?
What is a diode?
What is a bipolar transistor?
What is a MOSFET transistor?
Expected Time:
• Approximately 1 Hour
Introduction to Semiconductors
•
•
•
•
•
What is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
Silicon Crystal Structure
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–
–
–
–
–
–
–
• A crystal is a solid composed of atoms in a single,
UNIFIED array
• Notice each silicon atom is “connected” to its four
nearest neighboring silicon atoms
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–
–
–
–
–
–
–
– Si – Si – Si – Si –– Si – Si – Si – Si –
–
–
–
–
–
–
–
–
– Si – Si – Si – Si –– Si – Si – Si – Si –
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
– Si – Si – Si – Si –– Si – Si – Si – Si –
– Si – Si – Si – Si –– Si – Si – Si – Si –
Sharing Electrons
• Many atoms (including silicon) like to have EIGHT electrons in
their outer “orbit”
• But, silicon only has FOUR outer electrons
• Solution: Silicon atoms share electrons with each other
Silicon Atoms Sharing Electrons
in a Crystal
Si
Si
Si
Si
Si
Si
Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si
Si
Si
Si
Si
Si
Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si Si
Si
Si
Si
Si
Si
Si
Si
Semiconductor Silicon
• A conductor is a material which “conducts”
electricity easily (such as metals)
• An insulator is a material which is a very poor
conductor of electricity (such as glass)
• A semiconductor (silicon) is a material which acts
like an insulator, but behaves like a conductor when
it is combined with other materials
Introduction to Semiconductors
•
•
•
•
•
What is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
N-Type Silicon Charge Neutrality
• Adding Phosphorous to silicon creates a semiconductor
with additional mobile Negative charges (electrons)
Phosphorous
Phosphorous added to
Silicon
+5
+5
Plus 1 Mobile Electron (-)
P-Type Silicon Charge Neutrality
• Adding boron to silicon creates a semiconductor with additional
mobile Positive charges (absence of electrons)
Boron
Boron added to Silicon
+3
+3
Plus 1 Mobile Hole (+)
Boron and Phosphorous Atoms
in a "Sea of Silicon"
Boron
Phosphorous
Introduction to Semiconductors
•
•
•
•
•
What is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
Boron and Phosphorous Mobile Charge
in a Sea of Silicon
Boron
Phosphorous
Boron and Phosphorous Mobile
Charge in a Sea of Silicon
Boron
Diffusing positive
charge leaves
behind a
stationary
negative charge
Boron and Phosphorous Mobile
Charge in a Sea of Silicon
Boron
Diffusing negative
charge leaves
behind a
stationary
positive charge
Phosphorous
Boron and Phosphorous Mobile
Charge in a Sea of Silicon
Boron
Phosphorous
Diode Under Forward Bias
• Before the forward bias is applied…
Positive
P
Electrons
Negative
Holes
"Built In Voltage" ~ 0.7V
N
Diode Under Forward Bias
P
Positive
+
Negative
• As the forward bias is applied, it overcomes the
built in voltage and current can flow....
"Built In Voltage" ~ 0.0V
0.7V
0.6V
0.5V
0.4V
0.3V
0.2V
0.1V
0.0V
0.7V
0.6V
0.5V
0.4V
0.3V
0.2V
0.1V
N
-
Diode Under Forward Bias
• As the forward bias is applied, it overcomes the
built in voltage and current can flow....
+
P
N
"Built In Voltage" ~ 0.0V
0.7V
-
Diode Under Forward Bias
Current (I)
• As the forward bias is applied, it overcomes the
built in voltage and current can flow....
~0.7
Voltage (V)
Diode Under Reverse Bias
• Before the reverse bias is applied…
Positive
P
Electrons
Negative
Holes
"Built In Voltage" ~ 0.7V
N
Diode Under Reverse Bias
• As reverse bias is applied…
P
Positive
-
Electrons
Negative
Holes
"Built In Voltage" ~ 1.7V
1.0V
N
+
Diode Under Reverse Bias
• As reverse bias is applied…
P
Positive
-
Electrons
Negative
Holes
N
"Built In Voltage" ~ 1.7V
1.0V
+
P
Positive
Negative
Ideal Diode Current-Voltage
(I-V) Characteristics
N
Current (I)
V
Voltage (V)
0.7
Ideal
Current (I)
Actual Diode Current-Voltage
(I-V) Characteristics
0.7
Actual
Voltage (V)
Diode I-V Temperature Characteristics
Current (I)
+125C +25C -40C
-40C
0.7
+25C
+125C
Voltage (V)
Introduction to Semiconductors
•
•
•
•
•
What Is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
Bipolar Junction Transistor (BJT)
Positive
P
Negative
Negative
N
Positive
• Formed by back-to-back n-type and p-type
semiconductor regions
P-type region is very narrow
N
NPN Bipolar Junction Transistor (BJT)
Collector (will collect electrons)
N
Base
(of operations,
i.e. the
control center)
Positive
Negative
P
Negative
Positive
N
Emitter (will emit electrons)
NPN Bipolar Junction Transistor (BJT)
Collector
VCollector > VBase
N
Positive
Negative
Base
Current tries to flow
P
Negative
Positive
N
Emitter
VCE
Reverse
Biased
No Current
Flows
NPN Bipolar Junction Transistor (BJT)
Collector
N
VBase > VEmitter
Base
VBE
VCE
Positive
Negative
P
Negative
Positive
N
Emitter
Forward
Biased
Current
Can
Flow
NPN Bipolar Junction Transistor (BJT)
We now have an
excessively large
number of electrons
in the base.
VBase > VEmitter
Base
VBE
Collector
N
VCE
Positive
Negative
P
Negative
Positive
Current
Flows
Electrons near basecollector interface
are pulled across
creating a current.
N
Emitter
Forward
Biased
Current
Can
Flow
NPN Bipolar Junction Transistor (BJT)
Collector (will collect electrons)
N
Base
(of operations,
i.e. the
control center)
C
Positive
Negative
B
P
Negative
Positive
E
N
Emitter (will emit electrons)
Bipolar Junction Transistor (BJT)
Invented in 1947 by:
William Shockley (1910-1989)
Walter Brattain (1902-1987)
John Bardeen (1908-1991)
• “Point contact” transistor
used a single physical
contact as the base
• Consisted of a
germanium crystal and
two “whiskers”
Introduction to Semiconductors
•
•
•
•
•
What Is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
Metal Oxide Semiconductor Field Effect
Transistor (MOSFET)
True of False:
The transistor was first conceived and
patented
by W.Shockley, J.Bardeen, and W.Brattain
at Bell
Labs in the late 1940’s…
Metal Oxide Semiconductor Field Effect
Transistor (MOSFET)
FALSE!
The concept of a field effect transistor was first
developed and patented by J.Lilienfeld in Canada and
the United States in the years 1924-1928.
In fact, the Bell Labs engineers’ first patent was
written to reflect Lilienfeld’s prior work.
n-Channel MOSFET Cross Section (nMOS)
“Sea of Silicon with Mobile Holes”
P-Type Silicon Substrate
n-Channel MOSFET Cross Section (nMOS)
SiO2 (An Excellent Insulator)
P-Type Silicon Substrate
n-Channel MOSFET Cross Section (nMOS)
N-Type Silicon
“Sea of Silicon with Mobile Electrons”
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
n-Channel MOSFET Cross Section (nMOS)
Metal Contacts
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
n-Channel MOSFET Cross Section (nMOS)
“Gate” (or Door) between
Electrons will come
source and drain
from here Source
Gate
Electrons will
Drain come out
out here
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
n-Channel MOSFET Cross Section (nMOS)
Source
Gate
Drain
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
Gate
Source
Drain
n-Channel MOSFET Biasing
Source
Gate
Drain
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
Back-to-Back Diodes
n-Channel MOSFET Biasing
Current wants to flow
Source
Gate = 0V
Drain
SiO2
N-Type Si
N-Type Si
Reverse Bias
No Current Flows
P-Type Silicon Substrate
n-Channel MOSFET Mobile Carriers
• Above 0 degK, a few mobile electrons will exist in the
substrate
Source
Gate
Drain
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
Diodes Still Exist
n-Channel MOSFET Biasing
Source
Gate > 0V
Drain
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
n-Channel MOSFET Biasing
Current
Flows
Source
Gate > 0V
Drain
SiO2
N-Type Si
N-Type Si
P-Type Silicon Substrate
Introduction to Semiconductors
•
•
•
•
•
What Is a Semiconductor?
What is a N-Type and a P-Type Semiconductor?
What is a Diode?
What is a Bipolar Junction Transistor (BJT)?
What is a Field Effect Transistor (MOSFET)?
Introduction to Semiconductors
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Thank you!
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