Transcript High Frequency MOSFET Model

High Frequency MOSFET Model
Models for Computer Simulation
Simple dc Model
Small Signal
Model
Frequency-Dependent
Small Signal Model
Better Analytical
dc Models
Sophisticated Model
for Computer Simulations
Better Models
for Predicting
Device Operation
Strategy
• Identify and include relevant parasitic
capacitors that inherently exist in a MOS
transistor
Question
• Are the parasitic capacitors relevant?
Observation
• Parasitic Capacitors are Small
Consider a minimum-sized transistor
2l
3l
4l
Process Parameters from AMI 0.5u Process
PR OC ESS PAR AMETERS
Sheet Resistance
C ontact R esistance
Gate Oxide Thickness
PR OC ESS PAR AMETERS
Sheet Resistance
C ontact R esistance
N +ACTV P+AC TV
81.5
101.9
64.6
141.9
140
MTL 3
0.06
0.65
N \PLY
822
POLY
21.6
15.8
PLY2_ H R POLY2 MTL1
1120
41
0.09
26.8
MTL2
0.09
0.8
N W ELL
812
U NITS
ohms/sq
ohms
angstrom
ohms/sq
ohms
C OMMEN TS: N\POLY is N -well under poly silicon.
C APACITAN CE PAR AMETER S
Area (substrate)
Area (N+activ e)
Area (P+activ e)
Area (poly )
Area (poly 2)
Area (metal1)
Area (metal2)
Fringe (substrate)
Fringe (poly )
Fringe (m etal1)
Fringe (m etal2)
Ov erlap (N +activ e)
Ov erlap (P+activ e)
l=.35 microns
N +ACTV P+AC TV
424
731
424
315
POLY
87
2473
2473
2382
247
POLY2
M1
32
36
M2
16
16
M3
10
12
969
56
50
15
10
31
13
39
38
28
34
55
72
57
195
239
58
39
48
N _W ELL U NITS
39
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um
aF/um
aF/um
aF/um
aF/um
aF/um
Size of Capacitances
Gate-Channel Capacitance = 6l2 x 2.47fF/m2 = 1.82fF
Source Diffusion-Substrate Capacitance =
12l2 x .424fF/m2 + 14l x .315fF/m =
.624fF + 1.54fF =2.16fF
Are these negligible?
Process Parameters from AMI 0.5u Process
Vth
Vth
Vth
Gamma
Uo*Cox
Low-field Mobility
W/L
3.0/0.6
20/0.6
50/50
50/50
N-Channel P-Channel Units
0.79
-0.91 volts
0.67
-0.9 volts
0.73
-0.94 volts
0.46
0.58 V^0.5
117.6
-38.8 uA/V^2
476.79
157.31 cm^2/V*s
Size of Capacitances
Gate-Channel Capacitance = 6l2 x 2.47fF/m2 = 1.82fF
Source Diffusion-Substrate Capacitance =
12l2 x .424fF/m2 + 14l x .315fF/m =
.624fF + 1.54fF =2.16fF
Are these negligible?
Impedance of Triode Region Device
RFET = L/(mCOXW[VGS-VT]) = 2/(118E-6 x 3 x 1)=5.6K
Time Constant
RFETCGC = 1.82E-15 x 5.6K = 10.2psec
Are these negligible?
These small capacitors play the dominant role in the speed
limitations of most digital circuits
These small capacitors play a major role in the performance
of many linear circuits
It is essential that these capacitors
(parasitic capacitors) be considered and
managed when designing most integrated
circuits today!
Types of Capacitors
1. Fixed Capacitors
a. Fixed Geometry
b. Junction
2.
Operating Region Dependent
a. Fixed Geometry
b. Junction
Parasitic Capacitors in MOSFET
Parasitic Capacitors in MOSFET
Fixed Capacitors
CGSO
Overlap Capacitors: CGDO, CGSO
CGDO
Parasitic Capacitance Summary
D
CGD
B
G
CGS
S
CGS
CGD
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
Parasitic Capacitors in MOSFET
Fixed Capacitors
CBS1
Junction Capacitors: CBS1, CBD1
CBD1
Parasitic Capacitors in MOSFET
Fixed Capacitors
CGSO
CBS1
Overlap Capacitors: CGDO, CGSO
Junction Capacitors: CBS1, CBD1
CGDO
CBD1
Parasitic Capacitance Summary
D
CBD
CGD
B
G
CBS
CGS
CGS
CGD
CBG
CBS
CBD
S
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CBS1 = CBOTAS+CSW PS
CBS1 = CBOTAS+CSW PS
CBS1 = CBOTAS+CSW PS
CBD1 = CBOTAD +CSW PD
CBD1 = CBOTAD +CSW PD
CBD1 = CBOTAD +CSW PD
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Cutoff
CGBCO
Cutoff Capacitor: CGBCO
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Cutoff
CGBCO
Note: A depletion region will form under the gate if a positive
Gate voltage is applied thus decreasing the capacitance density
Cutoff Capacitor: CGBCO
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Cutoff
CGSO
CBS1
CGDO
CGBCO
Overlap Capacitors: CGDO, CGSO
Junction Capacitors: CBS1, CBD1
Cutoff Capacitor: CGBCO
CBD1
Parasitic Capacitance Summary
D
CBD
CGD
G
B
CBS
CGS
S
CGS
CGD
CBG
CBS
CBD
CBG
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CoxWLD
CBOTAS+CSW PS
CBS1 = CBOTAS+CSW PS
CBS1 = CBOTAS+CSW PS
CBOTAD +CSW PD
CBD1 = CBOTAD +CSW PD
CBD1 = CBOTAD +CSW PD
CoxWL (or less)
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Ohmic
CGCH
CBCH
Note: The Channel is not a node in the lumped device model
so can not directly include this distributed capacitance in existing
models
Note: The distributed channel capacitance is usually lumped
and split evenly between the source and drain nodes
Ohmic Capacitor: CGCH , CBCH
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Ohmic
CGSO
CGCH
CGDO
CBCH
CBS1
Overlap Capacitors: CGDO, CGSO
Junction Capacitors: CBS1, CBD1
Ohmic Capacitor: CGCH , CBCH
CBD1
Parasitic Capacitance Summary
D
CBD
CGD
G
B
CBS
CGS
S
CGS
CGD
CBG
CBS
CBD
CBG
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CBOTAS+CSW PS
CBOTAS+CSW PS+0.5CBCH
CBS1 = CBOTAS+CSW PS
CBOTAD +CSW PD
CBOTAD +CSW PD +0.5CBCH
CBD1 = CBOTAD +CSW PD
CoxWL (or less)
Parasitic Capacitance
Summary
D
CBD
CGD
G
B
CBS
CGS
CBG
S
CGS
CGD
CBG
CBS
CBD
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CoxWL (or less)
0
CBOTAS+CSW PS
CBOTAS+CSW PS+0.5WLCBOTCH
CBS1 = CBOTAS+CSWPS
CBOTAD+CSW PD
CBOTAD +CSW PD +0.5WLCBOTCH
CBD1 = CBOTAD+CSWPD
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Saturation
CGCH
CBCH
Note: Since the channel is an extension of the source when in saturation, the
distributed capacitors to the channel are generally lumped to the source node
Saturation Capacitors: CGCH , CBCH
Parasitic Capacitors in MOSFET
Operation Region Dependent -- Saturation
CGSO
CGCH
CGDO
CBCH
CBS1
Overlap Capacitors: CGDO, CGSO
Junction Capacitors: CBS1, CBD1
Saturation Capacitors: CGCH , CBCH
CBD1
Parasitic Capacitance
Summary
D
CBD
CGD
G
B
CBS
CGS
S
CGS
CGD
CBG
CBS
CBD
CBG
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD +(2/3)COXWL
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CoxWL (or less)
0
0
CBOTAS+CSW PS
CBOTAS+CSW PS+0.5WLCBOTCH
CBS1 + (2/3)CBC
CBOTAD +CSW PD
CBOTAD +CSW PD +0.5WLCBOTCH
CBOTAD +CSWPD
Parasitic Capacitance
Summary
D
CBD
CGD
G
B
CBS
CGS
CBG
S
CGS
CGD
CBG
CBS
CBD
Cutoff
Ohmic
Saturation
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD +(2/3)COXWL
CoxWLD
CoxWLD + 0.5COXWL
CoxWLD
CoxWL (or less)
0
0
CBOTAS+CSW PS
CBOTAS+CSW PS+0.5WLCBOTCH CBOTAS+CSW PS +(2/3)WLCBOTCH
CBOTAD +CSW PD
CBOTAD +CSW PD +0.5WLCBOTCH
CBOTAD +CSW PD
Process Parameters from AMI 0.5u Process
PROCESS PARAMETERS
Sheet Resistance
Contact Resistance
Gate Oxide Thickness
PROCESS PARAMETERS
Sheet Resistance
Contact Resistance
N+ACTV P+ACTV
81.5
101.9
64.6
141.9
140
MTL 3
0.06
0.65
N\PLY
822
POLY
21.6
15.8
PLY2_ HR POLY2 MTL1
1120
41
0.09
26.8
MTL2
0.09
0.8
N W ELL
812
UNITS
ohms/sq
ohms
angstrom
ohms/sq
ohms
COMMENTS: N\POLY is N-well under poly silicon.
CAPACITANCE PARAMETERS
Area (substrate)
Area (N+activ e)
Area (P+activ e)
Area (poly )
Area (poly 2)
Area (metal1)
Area (metal2)
Fringe (substrate)
Fringe (poly )
Fringe (metal1)
Fringe (metal2)
Ov erlap (N+activ e)
Ov erlap (P+activ e)
N+ACTV P+ACTV
424
731
315
POLY
87
2473
2382
POLY2
M1
32
36
M2
16
16
M3
10
12
969
56
50
15
10
31
13
39
38
28
34
55
247
72
57
195
239
l=.35 microns
58
39
48
N_W ELL UNITS
39
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um
aF/um
aF/um
aF/um
aF/um
aF/um
Small Signal Model Summary
D
CBD
G
CGD
B
CBS
CGS
S
CBG
Small Signal Model Summary
CGD
G
CGB
VGS
CBD
B
CGS
VBS
D
CBS
gmVGS
gmBVBS
gO
S
Equivalent circuit showing dependent sources
In many applications simpler small signal model is adequate
Small Signal Model Summary
G
D
VGS
gmVGS
CGS
gO
CBD
B
S
Simplified Equivalent Circuit Adequate for Many
Applications When Source is Grounded
(CBS need not be shown when source connected to ground)
That’s all folks!