Field-Effect Transistors (2) Notes | EduRev

: Field-Effect Transistors (2) Notes | EduRev

 Page 1


1
Chapter 5
Field-Effect Transistors
Chapter Goals
• Describe operation of MOSFETs and JFETs.
• Define MOSFET characteristics in operation regions of cutoff, 
triode and saturation.
• Discuss mathematical models for i-v characteristics of MOSFETs
and JFETs.
• Introduce graphical representations for output and transfer 
characteristic descriptions of electronic devices.
• Define and contrast characteristics of enhancement-mode and 
depletion-mode MOFETs.
• Define symbols to represent MOSFETs in circuit schematics.
• Investigate circuits that bias transistors into different operating 
regions.
• MOSFET and JFET DC circuit analysis
• Explore MOSFET modeling in SPICE
Types of Field-Effect Transistors
• MOSFET (Metal-Oxide Semiconductor Field-Effect 
Transistor)
– Primary component in high-density VLSI chips such 
as memories and microprocessors
• JFET (Junction Field-Effect Transistor)
– Finds application especially in analog and RF circuit 
design
Page 2


1
Chapter 5
Field-Effect Transistors
Chapter Goals
• Describe operation of MOSFETs and JFETs.
• Define MOSFET characteristics in operation regions of cutoff, 
triode and saturation.
• Discuss mathematical models for i-v characteristics of MOSFETs
and JFETs.
• Introduce graphical representations for output and transfer 
characteristic descriptions of electronic devices.
• Define and contrast characteristics of enhancement-mode and 
depletion-mode MOFETs.
• Define symbols to represent MOSFETs in circuit schematics.
• Investigate circuits that bias transistors into different operating 
regions.
• MOSFET and JFET DC circuit analysis
• Explore MOSFET modeling in SPICE
Types of Field-Effect Transistors
• MOSFET (Metal-Oxide Semiconductor Field-Effect 
Transistor)
– Primary component in high-density VLSI chips such 
as memories and microprocessors
• JFET (Junction Field-Effect Transistor)
– Finds application especially in analog and RF circuit 
design
2
The MOS Transistor
Polysilicon
Aluminum
The NMOS Transistor Cross Section
n areas have been doped with donor ions 
(arsenic) of concentration N
D
- electrons 
are the majority carriers 
p areas have been doped with acceptor
ions (boron) of concentration N
A
- holes 
are the majority carriers 
Gate oxide
n+
Source Drain
p substrate
Bulk (Body)
p+ stopper
Field-Oxide
(SiO
2
) n+
Polysilicon
Gate
L
W
MOS Capacitor Structure
• First electrode - Gate : 
Consists of  low-resistivity
material such as highly-doped 
polycrystalline silicon,
aluminum or tungsten
• Second electrode -
Substrate or Body: n-or p-
type semiconductor
•Dielectric - Silicon dioxide: 
stable high-quality electrical 
insulator between gate and 
substrate.
Substrate Conditions for Different 
Biases
Accumulation
V
G 
<< V
TN
Depletion
V
G 
< V
TN
Inversion
V
G 
> V
TN
Page 3


1
Chapter 5
Field-Effect Transistors
Chapter Goals
• Describe operation of MOSFETs and JFETs.
• Define MOSFET characteristics in operation regions of cutoff, 
triode and saturation.
• Discuss mathematical models for i-v characteristics of MOSFETs
and JFETs.
• Introduce graphical representations for output and transfer 
characteristic descriptions of electronic devices.
• Define and contrast characteristics of enhancement-mode and 
depletion-mode MOFETs.
• Define symbols to represent MOSFETs in circuit schematics.
• Investigate circuits that bias transistors into different operating 
regions.
• MOSFET and JFET DC circuit analysis
• Explore MOSFET modeling in SPICE
Types of Field-Effect Transistors
• MOSFET (Metal-Oxide Semiconductor Field-Effect 
Transistor)
– Primary component in high-density VLSI chips such 
as memories and microprocessors
• JFET (Junction Field-Effect Transistor)
– Finds application especially in analog and RF circuit 
design
2
The MOS Transistor
Polysilicon
Aluminum
The NMOS Transistor Cross Section
n areas have been doped with donor ions 
(arsenic) of concentration N
D
- electrons 
are the majority carriers 
p areas have been doped with acceptor
ions (boron) of concentration N
A
- holes 
are the majority carriers 
Gate oxide
n+
Source Drain
p substrate
Bulk (Body)
p+ stopper
Field-Oxide
(SiO
2
) n+
Polysilicon
Gate
L
W
MOS Capacitor Structure
• First electrode - Gate : 
Consists of  low-resistivity
material such as highly-doped 
polycrystalline silicon,
aluminum or tungsten
• Second electrode -
Substrate or Body: n-or p-
type semiconductor
•Dielectric - Silicon dioxide: 
stable high-quality electrical 
insulator between gate and 
substrate.
Substrate Conditions for Different 
Biases
Accumulation
V
G 
<< V
TN
Depletion
V
G 
< V
TN
Inversion
V
G 
> V
TN
3
Low-frequency C-V Characteristics for MOS Capacitor 
on P-type Substrate
• MOS capacitance is non-
linear function of voltage.
• Total capacitance in any 
region dictated by the 
separation between 
capacitor plates.
• Total capacitance modeled 
as series combination of 
fixed oxide capacitance
and voltage-dependent 
depletion layer
capacitance.
NMOS Transistor: Structure
• 4 device terminals: 
Gate(G), Drain(D),
Source(S) and Body(B).
• Source and drain regions 
form pn junctions with 
substrate.
• v
SB
, v
DS
and v
GS
always 
positive during normal 
operation.
• v
SB
must always reverse 
bias the pn junctions
Read More
Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!