数字集成电路第三章

Devices
The Body Effect
0.9 0.85 0.8 0.75 0.7
V (V)
T
0.65 0.6 0.55 0.5 0.45 0.4 -2.5 -2 -1.5 -1 -0.5 0
V
BS
(V)
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Devices
Current-Voltage Relations A good ol’ transistor
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Devices
A model for manual analysis
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Devices
Current-Voltage Relations The Deep-Submicron Era
2.5 x 10
-4
Early Saturation
2
VGS= 2.5 V
VGS= 2.0 V
1.5
ID (A)
1
VGS= 1.5 V
Linear Relationship
0.5
VGS= 1.0 V
0
0
0.5
1 VDS (V)
1.5
2
2.5
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Goal of this chapter
Present intuitive understanding of device operation Introduction of basic device equations Introduction of models for manual analysis Introduction of models for SPICE simulation Analysis of secondary and deep-submicron effects Future trends
Diode Model
RS + VD ID CD
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Devices
SPICE Parameters
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Devices
What is a Transistor?
A Switch!
-0.8
VGS = -2.5V
-1 -2.5
-2
-1.5
VDS (V)
-1
-0.5
0
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Devices
Transistor Model for Manual Analysis
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Devices
The Transistor as a Switch
VGS V T Ron S
ID V GS = VD D Rmid R0 V DS VDD/2 VDD
D
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Devices
The Transistor as a Switch
ID versus VDS
6 5 4 ID (A) 3 2 1 0 0 x 10
-4
VGS= 2.5 V
x 10 2.5
-4
VGS= 2.5 V
2
Resistive Saturation VDS = VGS - VT
VGS= 1.5 V
0.5 ID (A)
VGS= 2.0 V
VGS= 2.0 V
1.5
Saturated
1 1.5 2 2.5
VDS (V)
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Devices
A PMOS Transistor
0 x 10
-4
VGS = -1.0V
-0.2
VGS = -1.5V -0.4
ID (A)
-0.6
VGS = -2.0V
Assume all variables negative!
Al A
Mostly occurring as parasitic element in Digital ICs
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Depletion Region
hole diffusion electron diffusion p hole drift electron drift Charge Density + x Distance (b) Charge density. n (a) Current flow.
Devices
Forward Bias
pn (W2)
pn0 Lp np0
p-region
-W1 0
W2
n-region
x
diffusion
Typically avoided in Digital ICs
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Reverse Bias
Diffusion Capacitance
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Devices
Secondary Effects
0.1
ID (A)
0
–0.1 –25.0
–15.0 VD (V)
–5.0
0
5.0
Avalanche Breakdown
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1
VGS= 1.5 V
VGS= 1.0 V
0.5 1 1.5 2 2.5 0 0 0.5 1 VDS(V) 1.5
VGS= 1.0 V
2 2.5
VDS(V)
Long Channel © Digital Integrated Circuits2nd
Short Channel Devices
A unified model for manual analysis
Digital Integrated Circuits
A Design Perspective
Jan M. Rabaey Anantha Chandrakasan Borivoje Nikolic
The Devices
July 30, 2002
© Digital Integrated Circuits2nd Devices
6 x 10
-4
VGS= 2.5 V
5
Resistive
4
ID (A)
Saturation
VGS= 2.0 V
3
VDS = VGS - VT
VGS= 1.5 V
Quadratic Relationship
2
1
VGS= 1.0 V
0
0
0.5
1
1.5
2
2.5
VDS (V)
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Threshold Voltage: Concept
S + VGS G D
n+
n+
n-channel p-substrate B
Depletion Region
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Devices
The Threshold Voltage
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pn0
np0
p-region
-W1 0
W2
x n-region
diffusion
The Dominant Operation Mode
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Models for Manual Analysis
ID = IS(eV D/T – 1) VD – – ID + + – VDon
Devices
Transistor in Linear
VGS S G n+ – VDS D n+ L x ID
V(x)
+
p-substrate B
MOS transistor and its bias conditions
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Devices
G
S
D
B
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Devices
Simple Model versus SPICE
2.5 x 10
-4
VDS=VDSAT
2
1.5
Velocity Saturated Linear
ID (A)
1
VDSAT=VGT
0.5
VDS=VGT
0 0 0.5
7 x 10
5
6 5
(Ohm) R
4
eq
3
2 1
0 0.5
1
1.5
2
2.5
V
DD
(V)
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Devices
The Transistor as a Switch
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Devices
MOS Capacitances Dynamic Behavior

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Devices
The Diode
B Al A
SiO2
p n Cross-section of pn -junction in an IC process A p n B One-dimensional representation B diode symbol
ID
Long-channel device VGS = VDD Short-channel device
V DSAT
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VGS - V T
VDS
Devices
ID versus VGS
6 5 2 4
I D (A)
x 10
-4
x 10 2.5
Transistor in Saturation
VGS VDS > VGS - VT D
G
S n+
-
VGS - VT
+
n+
Pinch-off
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Devices
Current-Voltage Relations Long-Channel Device
Devices
Velocity Saturation
u n (m/s)
usat = 105
Constant velocity
Constant mobility (slope = µ)
c = 1.5
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(V/µm)
Devices
Perspective
VGS V T Ron S D
An MOS Transistor
|VGS|
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Devices
The MOS Transistor
Polysilicon
Aluminum
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Devices
Electrical Field
x (c) Electric field.
V Potential -W 1 W2 x (d) Electrostatic potential.
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Devices
Diode Current
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+ VD
(a) Ideal diode model
(b) First-order diode model
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Devices
Junction Capacitance
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DLeabharlann Baiduvices
-4
quadratic
linear
1.5
ID (A)
3 2 1 0 0
1
0.5
quadratic
0.5 1
VGS(V)
1.5
2
2.5
0 0
0.5
1
VGS(V)
1.5
2
2.5
Long Channel
Short Channel
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Devices
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Devices
Dynamic Behavior of MOS Transistor
G
CGS S
CGD D
CSB
CGB
CDB
B
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MOS Transistors Types and Symbols
D D G
G S
S
NMOS Enhancement NMOS Depletion
D D
G
G
B
S
S
PMOS Enhancement
NMOS with Bulk Contact Devices
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