small-signal model (very preliminary) bulk cmos process …class.ece.iastate.edu/ee330/lectures/ee...
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EE 330Lecture 18
Small-signal Model (very preliminary)
Bulk CMOS Process Flow
How many models of the MOSFET do we have?
Switch-level model (2)
Square-law model (with λ and bulk additions)
α-law model (with λ and bulk additions)
BSIM model
Square-law model
BSIM model (with binning extensions)
BSIM model (with binning extensions and process corners)
Review from Last Lecture
ID
VDS
VGS1
VGS2
VGS3
Actual
Modeled with one model
Local Agreement
with Any Model
(and W/L variations or
Process Variations)
(and W/L variations or
Process Variations)
(and W/L variations or
Process Variations)
(and W/L variations or
Process Variations)
The Modeling Challenge
VDS
VBS = 0
VGS
ID
IG
IB
D 1 GS DS
G 2 GS DS
B 3 GS DS
I = f V ,V
I = f V ,V
I = f V ,V
Difficult to obtain analytical functions that
accurately fit actual devices over bias, size, and
process variations
Review from Last Lecture
Model Status
Simple dc Model
Small
Signal
Frequency
Dependent Small
Signal
Better Analytical
dc Model
Sophisticated Model
for Computer
Simulations
Simpler dc Model
Square-Law Model
Square-Law Model (with extensions for λ,γ effects)
Short-Channel α-law Model
BSIM Model
Switch-Level Models
• Ideal switches
• RSW and CGS
Review from Last Lecture
D D
S S
G G
D
BG
S
D
BG
S
VDS
VGSVBS
ID
IG IB
0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5
VDS
ID
VGS1
VGS2
VGS4
VGS3
GS4 GS3 GS2 GS1V V V V > 0
VDS
GS Tn
DS
D n OX GS Tn DS GS DS GS Tn
2
n OX GS Tn GS Tn DS GS Tn
G B
0 V V
VWI μ C V V V V V V V V
L 2
Wμ C V V V V V V V
2L
I =I =0
Tn
D D
S S
G G
D
BG
S
D
BG
S
VDS
VGS
VBS
ID
IG IB
GS Tp
DS
D p OX GS Tp DS GS Tp DS GS Tp
2
p OX GS Tp GS Tp DS GS Tp
G B
0 V V
VWI -μ C V V V V V V V V
L 2
W-μ C V V V V V V V
2L
I =I =0
n-channel …. p-channel modeling
Models essentially the
same with different signs
and model parametersRev
iew
fro
m L
ast
Lect
ure
Model Relationships
Determine RSW and CGS in the switch-level model for an n-channel MOSFET
from square-law model in the 0.5u ON CMOS process if L=1u, W=1u
(Assume μCOX=100μAV-2, COX=2.5fFu-2,VT0=1V, VDD=3.5V, VSS=0)
GS T
DS
D OX GS T DS GS DS GS T
2
OX GS T GS T DS GS T
0 V V
VWI μC V V V V V V V V
L 2
WμC V V V V V V V
2L
T
when SW is on, operation is “deep” triode
Review from Last Lecture
VGS
RSWn
CGSn
S
DG
Model Relationships
(Assume μCOX=100μAV-2, COX=2.5fFu-2,VT0=1V, VDD=3.5V, VSS=0)
DS
D OX GS T DS OX GS T DS
VW WI μC V V V μC V V V
L 2 L
14
14 3 5 1
1
K
E
GS DD
GS
DS
SQ
D V =VOX GS T
V =3.5V
V 1R =
WIμC V V ( ) .
L
CGS= COXWL = (2.5fFµ-2)(1µ2) = 2.5fF
Determine RSW and CGS for an n-channel MOSFET from square-law model
in the 0.5u ON CMOS process if L=1u, W=1u
When on operating in deep triode
VGS
RSWn
CGSn
S
DG
Review from Last Lecture
Model Relationships
( COX=2.5fFu-2,VT0=1V, VDD=3.5V, VSS=0)
GS T
DS
D OX GS T DS GS DS GS T
2
OX GS T GS T DS GS T
0 V V
VW-I μC V V V V V V V V
L 2
WμC V V V V V V V
2L
T
When SW is on, operation is “deep” triode
Determine RSW and CGS for an p-channel MOSFET from square-law model
in the 0.5u ON CMOS process if L=1u, W=1u
Observe µn\ µp≈3
VGS
RSWp
CGSp
S
DG
Review from Last Lecture
Model Relationships
DS
D p OX GS T DS p OX GS T DS
VW W-I μ C V V V μ C V V V
L 2 L
112
1 14 3 5 1
3 1GS DD
GS
DS
SQ
D V =Vp OX GS T
V =3.5V
-V 1R =
W-Iμ C V V ( ) .
L
K
E
CGS= COXWL = (2.5fFµ-2)(1µ2) = 2.5fF
Determine RSW and CGS for an p-channel MOSFET from square-law model
in the 0.5u ON CMOS process if L=1u, W=1u
( COX=2.5fFu-2,VT0=1V, VDD=3.5V, VSS=0)
Observe µn\ µp≈3
Observe the resistance of the p-channel device is approximately 3 times
larger than that of the n-channel device for same bias and dimensions !
Review from Last Lecture
VGS
RSWp
CGSp
S
DG
Modeling of the MOSFET
Drain
Gate Bulk
ID
ID IB
VDS
VBS
VGS
Goal: Obtain a mathematical relationship between the
port variables of a device.
Simple dc Model
Small
Signal
Frequency
Dependent Small
Signal
Better Analytical
dc Model
Sophisticated Model
for Computer
Simulations
Simpler dc Model
BSDSGS3B
BSDSGS2G
BSDSGS1D
V,,VVfI
V,,VVfI
V,,VVfI
Small-Signal Model
Goal with small signal model is to predict performance of circuit or device in the vicinity of an operating point
Operating point is often termed Q-point
Small-Signal Modely
x
Q-point
XQ
YQ
Analytical expressions for small signal model will be developed later
Technology Files
• Design Rules
• Process Flow (Fabrication Technology)
• Model Parameters
n-well
n-well
n-
p-
Bulk CMOS Process Description• n-well process
• Single Metal Only Depicted
• Double Poly− This type of process dominates what is used for high-volume “low-
cost” processing of integrated circuits today
− Many process variants and specialized processes are used for lower-
volume or niche applications
− Emphasis in this course will be on the electronics associated with the
design of integrated electronic circuits in processes targeting high-
volume low-cost products where competition based upon price
differentiation may be acute
− Basic electronics concepts, however, are applicable for lower-volume
or niche applicaitons
Components Shown
• n-channel MOSFET
• p-channel MOSFET
• Poly Resistor
• Doubly Poly Capacitor
A A’
B’B
C
C’
D
D’
Consider Basic Components Only
Well Contacts and Guard Rings Will be Discussed Later
A A’
B’B
A A’
B’B
A A’
B’B
n-channel MOSFET
S
D
G
S
D
BG
Metal details hidden to reduce clutter
A A’
B’B
S
D
BG
W L
A A’
B’B
n-channel MOSFET
Capacitor
p-channel MOSFET
Resistor
n-well
n-well
n-
p-
A A’
B’B
N-well Mask
A A’
B’B
N-well Mask
Detailed Description of First Photolithographic Steps Only
• Top View
• Cross-Section View
~
Blank Wafer
p-doped Substrate
ExposeDevelop
Photoresistn-well Mask
Implant
A A’
B’B
Will use positive photoresist(exposed region soluble in developer)
A-A’ Section
B-B’ Section
PhotoresistN-well MaskExposureDevelop
A-A’ Section
B-B’ Section
Implant
N-well Mask
A-A’ Section
B-B’ Sectionn-well
n-well
n-well
n-
p-
A A’
B’B
Active Mask
A A’
B’B
Active Mask
Active Mask
A-A’ Section
B-B’ Section
Field Oxide Field Oxide Field Oxide
Field Oxide
n-well
n-well
n-
p-
A A’
B’B
Poly1 Mask
A A’
B’B
Poly1 Mask
A A’
B’B
n-channel MOSFET
Capacitor
P-channel MOSFET
Resistor
Poly plays a key role in all four types of devices !
Poly 1 Mask
A-A’ Section
B-B’ Section
Gate Oxide Gate Oxide
n-well
n-well
n-
p-
A A’
B’B
Poly 2 Mask
A A’
B’B
Poly 2 Mask
Poly 2 Mask
A-A’ Section
B-B’ Section
n-well
n-well
n-
p-
A A’
B’B
P-Select
A A’
B’B
P-Select
P-Select Mask – p-diffusion
A-A’ Section
B-B’ Section
p-diffusion
Note the gate is self aligned !!
n-Select Mask – n-diffusion
A-A’ Section
B-B’ Section
n-diffusion
n-well
n-well
n-
p-
A A’
B’B
Contact Mask
A A’
B’B
Contact Mask
Contact Mask
A-A’ Section
B-B’ Section
n-well
n-well
n-
p-
A A’
B’B
Metal 1 Mask
A A’
B’B
Metal 1 Mask
Metal Mask
A-A’ Section
B-B’ Section
A A’
B’B
A A’
B’B
n-channel MOSFET
Capacitor
P-channel MOSFET
Resistor
Should now know what you can do in this process !!
Can poly be connected to active under gate?
Can poly be connected to active any place?
Can metal be placed under poly to isolate it from bulk?
Can metal connect to active?
Can metal connect to substrate when on top of field oxide?
How can metal be connected to substrate?
Can metal 2 be connected directly to active?
Could a process be created that will result in an answer of YES to most of above?
Can metal 2 be connected to metal 1?
Can metal 2 pass under metal 1?
Semiconductor and
Fabrication Technology
CAD Tools
Device Operation
and Models
Circuit Structures and
Circuit Design
How we started this course
Semiconductor and
Fabrication Technology
CAD Tools
Device Operation
and Models
Circuit Structures
and Circuit Design
Thanks for your patience !!
The basic concepts should have now come together
How does the inverter delay compare between a 0.5u
process and a 0.18u process?
VIN VOUT
VDD
VSS
VIN VOUT
How does the inverter delay compare between a 0.5u process and a 0.18u process?
VIN
VOUT
Assume n-channel and p-channel devices with L=Lmin, W=1.5Lmin
tHL=RpdCL
tLH=RpdCL
n
pd
n OX n DD TN
LR
C W V V
p
pu
p OX p DD TP
LR
C W V V
L OX n n p pC C W L W L
Note 0.18u process is much faster than 0.5u process
Feature 0.5 0.18 Units
Vtn 0.81 0.5 V
Vtp -0.92 -0.53 V
uCoxn 109.6 344 uA/V^2
uCoxp 39.4 72.6 uA/V^2
Cox 2.51 8.5 fF
Vdd 5 1.8 V
fosc-31 94.5 402.8 MHz
Feature 0.5 0.18 Units
CL 1.88 0.83 fF
Rpd 1452 1491 ohms
Rpu 2858 3941 ohms
THL 2.73 1.23 psec
TLH 5.38 3.26 psec
f 123 223 GHz
End of Lecture 18