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Chapter 2
MOS Transistors
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Figure 2-1
Here is a simplified view of an n-channel MOS transistor. In simple terms, there are two operating modes for this transistor:on and off. We must use the terminals provided on the device to place it in these two possible conditions. The four terminals are the gate, drain, source, and bulk ( or body, or substrate). The schematic for the NMOS device is shown on the right.
L between 350nm to 90 nm, tox < 5nm, xj between 70nm to 150nm
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Figure 2-2
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Figure 2-3
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Figure 2-4
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Figure 2-5
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The Threshold Voltage
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The Body Effect
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Figure 2-6
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Figure 2-7
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Figure 2-8
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12. Current-Voltage Relations A good ol’ transistor
0.5 1
1.5 2
2.5 3 4 5 6
x 10 -4 V DS
(V) I D
(A)
VGS= 2.5 V
VGS= 2.0 V
VGS= 1.5 V
VGS= 1.0 V
Resistive
Saturation
VDS = VGS - VT
Quadratic
Relationship
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Transistor in Linear
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14. Transistor in Saturation
Pinch-off
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15. Current-Voltage Relations Long-Channel Device
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16. A model for manual analysis
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17. Current-Voltage Relations The Deep-Submicron Era-4 V DS
(V)
0.5 1
1.5 2
2.5
x 10 I D
(A)
VGS= 2.5 V
VGS= 2.0 V
VGS= 1.5 V
VGS= 1.0 V
Early Saturation
Linear
Relationship
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Velocity Saturation u n ( m / s ) u
sat
= 10 5
Constant velocity
Constant mobility (slope = µ) x c
= 1.5 x
(V/µm)
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Perspective I D
Long-channel device V
= V GS DD
Short-channel device V V
- V V
DSAT GS T DS
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ID versus VGS
0.5 1
1.5 2
2.5 3 4 5 6
x 10 -4 V GS
(V) I D
(A)
0.5 1
1.5 2
2.5
x 10 -4 V GS
(V) I D
(A)
linear
quadratic
quadratic
Long Channel
Short Channel
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ID versus VDS
0.5 1
1.5 2
2.5 3 4 5 6
x 10 -4 V DS
(V) I D
(A)
VGS= 2.5 V
VGS= 2.0 V
VGS= 1.5 V
VGS= 1.0 V
Resistive
Saturation
VDS = VGS - VT -4 V DS
(V)
0.5 1
1.5 2
2.5
x 10 I D
(A)
VGS= 2.5 V
VGS= 2.0 V
VGS= 1.5 V
VGS= 1.0 V
Long Channel
Short Channel
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22. A unified model for manual analysisG B
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23. Simple Model versus SPICE
0.5 1
1.5 2
2.5
x 10 -4
Velocity Saturated
Linear
Saturated
VDSAT=VGT
VDS=VDSAT
VDS=VGT
(A) I D V
(V) DS
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A PMOS Transistor
-2.5 -2
-1.5 -1
-0.5
-0.8
-0.6
-0.4
-0.2
x 10 -4 V DS
(V) I D
(A)
VGS = -1.0V
VGS = -1.5V
VGS = -2.0V
Assume all variables
negative!
VGS = -2.5V
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25. Transistor Model for Manual Analysis
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26. The Transistor as a Switch
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27. The Transistor as a Switch
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Figure 2-9
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Figure 2-10
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Figure 2-11
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Figure 2-12
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Figure 2-13
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Figure 2-14
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Figure 2-15
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Figure 2-16
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Figure 2-17
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37. Dynamic Behavior of MOS Transistor
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The Gate Capacitance x d L
Polysilicon gate
Top view
Gate-bulk
overlap
Source n +
Drain W t ox n +
Cross section L
Gate oxide
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Figure 2-18
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Figure 2-19
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Figure 2-20
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Figure 2-21
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Figure P2-4
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Figure P2-5
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Figure P2-6
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Figure P2-7
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Figure P2-8
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TA 2-1, p. 83
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