The document covers the fundamental physics and characteristics of MOS devices, including their structure, I/V characteristics, and operation in various regions such as triode and saturation. It also discusses important concepts like transconductance, second-order effects such as body effect and channel length modulation, and includes layout and capacitance considerations. Additionally, it touches on small signal models and SPICE models for MOS simulation.

1. Basic MOS Device Physics
Chapter 1
Basic MOS Device Physics

2. Basic MOS Device Physics
MOS Device Structure
Fig: Simple MOS Device
1. MOSEFT as a SWITCH
2. MOSFET Structure
Fig1: Structure of a MOS Device

3. Basic MOS Device Physics
NMOS and PMOS with Well
Fig2: (a): Simple PMOS device and (b): PMOS inside an n-well

4. Basic MOS Device Physics
MOS Symbols
Fig: MOS Symbols

5. Basic MOS Device Physics
MOS I/V Characteristics
1. Threshold Voltage

6. Derivation of I/V Characteristics
)
1
(






  v
Q
I d

7. Basic MOS Device Physics
I/V Characteristics

8. Basic MOS Device Physics
I/V Characteristics
)
2
(
)
( 






 TH
GS
ox
d V
V
WC
Q
)
1
(






  v
Q
I d
)
3
(
)
)
(
(
)
( 






 TH
GS
ox
d V
x
V
V
WC
x
Q

9. Basic MOS Device Physics
I/V Characteristics (cont.)
)
4
(
]
)
(
[ 






 v
V
x
V
V
WC
I TH
GS
ox
D
)
6
(
]
)
(
[
0
0






 
 

VDS
V
TH
GS
n
ox
L
x
D dV
V
x
V
V
WC
dx
I 
Given v  E and E(x)  
dV (x)
dx
)
5
(
)
(
]
)
(
[ 







dx
x
dV
V
x
V
V
WC
I n
TH
GS
ox
D 
)
7
(
]
2
1
)
[( 2






 DS
DS
TH
GS
L
W
ox
n
D V
V
V
V
C
I 
From eq(1) the current is given by
Using Boundary conditions V(0)=0 and V(L)=Vds

10. Basic MOS Device Physics
I/V Characteristics (cont.)
ID  nCox
W
L
[(VGS  VTH)VDS 
1
2
VDS
2
]

11. Basic MOS Device Physics
Operation in Triode Region
)
8
(
2
)
[(
2
1




 TH
GS
L
W
ox
n
D V
V
C
I 
)
9
(
)
( 



 DS
TH
GS
L
W
ox
n
D V
V
V
C
I 
)
10
(
)
(
1




TH
GS
L
W
ox
n
ON
V
V
C
R

If Vds=Vgs-Vth
)
(
2 TH
GS
DS V
V
V 

In eqn 7

12. Basic MOS Device Physics
Operation in Active (Saturation) Region

13. 11
)
)
(
(
)
( 






 TH
GS
ox
d V
x
V
V
WC
x
Q
Using Boundary conditions for saturated device
)
12
(
]
)
(
[
0
0






 
 

VDS
V
TH
GS
n
ox
L
x
D dV
V
x
V
V
WC
dx
I 
)
13
(
]
)
(
[
0
0






 





VTH
VGS
V
TH
GS
n
ox
L
x
D dV
V
x
V
V
WC
dx
I 
Limits of left hand side from eqn (12) x=0 to x=L’ and right
hand side frrom V(x)=0 to V(x)=Vgs- Vth

14. Basic MOS Device Physics
Active Region (cont.)
)
14
(
)
( 



 
DS
TH
GS
L
W
ox
n
D V
V
V
C
I 

15. Basic MOS Device Physics
Transconductance, gm
gm 
ID
VGS VDS cons tan t
 nCox
W
L
(VGS  VTH)
gm  2nCox
W
L
ID

2ID
VGS  VTH

16. Basic MOS Device Physics
Triode and Active Region Transition
Active Active

17. Basic MOS Device Physics
Second Order effects
1.Body Effect

18. Basic MOS Device Physics
Threshold Voltage and Body Effect (cont.)
VTH  VTH0  2F  VSB  2F
 ,  
2qsiNsub
Cox
No Body Effect With Body Effect
,
2
,
ox
dep
F
MS
TH
C
Q
V
Where 



 MS  gat e  sili con
 ,
ln
i
sub
F
n
N
q
kT 






 Qdep  4qsi F Nsub

19. Basic MOS Device Physics
2. Channel Length Modulation
L'  L L 1/ L' 
1
L
(1  L/ L)
1/ L' 
1
L
(1  VDS), VDS  L/ L
ID 
nCox
2
W
L
(VGS  VTH)2
(1  VDS)
L L’

20. Basic MOS Device Physics
Channel Length Modulation (cont.)
gm  nCox
W
L
(VGS  VTH)(1  VDS)
gm 
2nCox W
LID
(1  VDS)
gm 
2ID
VGS  VTH
, (unchanged)

21. Basic MOS Device Physics
3. Subthreshold Conduction
ID  I0 exp
VGS
 kT
q







22. Basic MOS Device Physics
MOS Layout

23. Basic MOS Device Physics
MOS Device Capacitances

24. Basic MOS Device Physics
Layout for Low Capacitance

25. Basic MOS Device Physics
G-S and G-D Capacitance
Different regions of MOS device capacitance

26. Basic MOS Device Physics
2. MOS Small Signal Models

27. Basic MOS Device Physics
Bulk Transconductance, gmb
gmb 
ID
VBS

nCox
2
W
L
(VGS  VTH)
VTH
VBS




gmb  gm

2 2F VSB
 gm
Also,
VTH
VBS

VTH
VSB
 

2
(2F  VSB)1/ 2
ro 
VDS
ID

1
ID /VDS

1
nCox
2
W
L
(VGS  VTH)2


1
ID

28. Basic MOS Device Physics
MOS Small Signal Model with Capacitance

29. MOS SPICE MODELS