This document discusses transistors and their properties. It describes the basic structure and operation of MOS transistors, including how threshold voltage and body bias affect behavior. It also compares the current-voltage characteristics of long-channel versus short-channel transistors, noting how short-channel devices exhibit velocity saturation and earlier transition to saturation. Finally, it briefly introduces the concept of a PMOS transistor.

1. Digital Integrated
Circuits
A Design Perspective
Jan M. Rabaey
Anantha Chandrakasan
Borivoje Nikolic
The Devices
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2. What is a Transistor?
A Switch! An MOS Transistor
VG S ≥ V T |VGS|
R on
S D
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3. The MOS Transistor
Polysilicon Aluminum
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4. Threshold Voltage: Concept
+
S VGS D
G
-
n+ n+
n-channel Depletion
Region
p-substrate
B
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5. The Body Effect
0.9
0.85
0.8
0.75
0.7
V (V)
0.65
T
0.6
0.55
0.5
0.45
0.4
-2.5 -2 -1.5 -1 -0.5 0
V (V)
BS
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6. Current-Voltage Relations
A good ol’ transistor
-4
x 10
6
VGS= 2.5 V
5
Resistive Saturation
4
VGS= 2.0 V
ID (A)
3 Quadratic
VDS = VGS - VT Relationship
2
VGS= 1.5 V
1
VGS= 1.0 V
0
0 0.5 1 1.5 2 2.5
VDS (V)
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7. Transistor in Linear
VGS VDS
S
G ID
D
n+ –
V(x)
+ n+
L x
p-substrate
B
MOS transistor and its bias conditions
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8. Transistor in Saturation
VGS
VDS > VGS - VT
G
D
S
- +
n+ VGS - VT n+
Pinch-off
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9. Current-Voltage Relations
Long-Channel Device
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10. Current-Voltage Relations
The Deep-Submicron Era
-4
x 10
2.5
VGS= 2.5 V
Early Saturation
2
VGS= 2.0 V
1.5
ID (A)
Linear
1
VGS= 1.5 V Relationship
0.5 VGS= 1.0 V
0
0 0.5 1 1.5 2 2.5
VDS (V)
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11. Velocity Saturation
υ n (m/s)
υsat = 105
Constant velocity
Constant mobility (slope = µ)
ξc = 1.5 ξ (V/µm)
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12. Perspective
ID
Long-channel device
VGS = VDD
Short-channel device
V DSAT VGS - V T VDS
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13. ID versus VGS
-4
x 10 x 10
-4
6 2.5
5
2
4 linear
quadratic 1.5
ID (A)
ID (A)
3
1
2
0.5
1
quadratic
0 0
0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5
VGS(V) VGS(V)
Long Channel Short Channel
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14. ID versus VDS
-4 -4
x 10 x 10
6 2.5
VGS= 2.5 V
VGS= 2.5 V
5
2
Resistive Saturation
4 VGS= 2.0 V
VGS= 2.0 V 1.5
ID (A)
ID (A)
3
VDS = VGS - VT 1 VGS= 1.5 V
2
VGS= 1.5 V
0.5 VGS= 1.0 V
1
VGS= 1.0 V
0 0
0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5
VDS(V) VDS(V)
Long Channel Short Channel
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15. A PMOS Transistor
-4
x 10
0
VGS = -1.0V
-0.2
VGS = -1.5V
-0.4
ID (A)
VGS = -2.0V
-0.6 Assume all variables
negative!
-0.8
VGS = -2.5V
-1
-2.5 -2 -1.5 -1 -0.5 0
VDS (V)
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