high frequency mosfet model. models for computer simulation simple dc model small signal model...

High Frequency MOSFET Model

Models for Computer Simulation

Simple dc Model

Small SignalModel

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

2

3

4

Process Parameters from AMI 0.5u ProcessUNITSMTL2 MTL1 HR POLY2 PLY2_POLY P+ACTV N+ACTV PROCESS PARAMETERS

ohms/sq0.090.0941112021.6101.981.5Sheet Resistance ohms0.826.815.8141.964.6Contact Resistance

angstrom140Gate Oxide Thickness

N WELLN\PLYMTL 3PROCESS PARAMETERS ohms/sq8128220.06Sheet Resistance ohms 0.65Contact Resistance

COMMENTS: N\POLY is N-well under polysilicon.

UNITSN_WELL M3 M2 M1 POLY2 POLY P+ACTV N+ACTV CAPACITANCE PARAMETERS aF/um^23910163287731424Area (substrate) aF/um^21216362473Area (N+active) aF/um^22382Area (P+active) aF/um^2101556969Area (poly) aF/um^250Area (poly2) aF/um^21331Area (metal1) aF/um^239Area (metal2) aF/um385872247315Fringe (substrate) aF/um283957Fringe (poly) aF/um3448Fringe (metal1) aF/um55Fringe (metal2) aF/um195Overlap (N+active) aF/um239Overlap (P+active)

=.35 microns

2473

424

Size of Capacitances

Gate-Channel Capacitance = 62 x 2.47fF/2 = 1.82fF

Source Diffusion-Substrate Capacitance = 122 x .424fF/2 + 14 x .315fF/ = .624fF + 1.54fF =2.16fF

Are these negligible?

W/L N-Channel P-Channel UnitsVth 3.0/0.6 0.79 -0.91 voltsVth 20/0.6 0.67 -0.9 voltsVth 50/50 0.73 -0.94 voltsGamma 50/50 0.46 0.58 V^0.5Uo*Cox 117.6 -38.8 uA/V^2Low-field Mobility 476.79 157.31 cm^2/V*s

Process Parameters from AMI 0.5u Process

Size of Capacitances

Gate-Channel Capacitance = 62 x 2.47fF/2 = 1.82fF

Source Diffusion-Substrate Capacitance = 122 x .424fF/2 + 14 x .315fF/ = .624fF + 1.54fF =2.16fF

Are these negligible?Impedance of Triode Region Device

RFET = L/(COXW[VGS-VT]) = 2/(118E-6 x 3 x 1)=5.6KTime Constant

RFETCGC = 1.82E-15 x 5.6K = 10.2psec

Are these negligible?

These small capacitors play the dominant role in the speedlimitations 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 integratedcircuits 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 MOSFETFixed Capacitors

Overlap Capacitors: CGDO, CGSO

CGDOCGSO

Parasitic Capacitance Summary

D

S

G B

CGS

CGD

Cutoff Ohmic SaturationCGS CoxWLD CoxWLD CoxWLD

CGD CoxWLD CoxWLD CoxWLD


CBS1 CBD1

Junction Capacitors: CBS1, CBD1



CGDOCGSO

CBS1 CBD1


Parasitic Capacitance SummaryD

S

G B

CGS

CGD

CBS

CBD



CBG

CBS CBS1 = CBOTAS+CSWPS CBS1 = CBOTAS+CSWPS CBS1 = CBOTAS+CSWPS

CBD CBD1 = CBOTAD+CSWPD CBD1 = CBOTAD+CSWPD CBD1 = CBOTAD+CSWPD

Parasitic Capacitors in MOSFETOperation Region Dependent -- Cutoff

CGBCO

Cutoff Capacitor: CGBCO


CGBCO


Note: A depletion region will form under the gate if a positiveGate voltage is applied thus decreasing the capacitance density




CGDOCGSO

CBS1 CBD1

CGBCO



S

G B

CGS

CGD

CBS

CBD

CBG



CBG CoxWL (or less)

CBS CBOTAS+CSWPS CBS1 = CBOTAS+CSWPS CBS1 = CBOTAS+CSWPS

CBD CBOTAD+CSWPD CBD1 = CBOTAD+CSWPD CBD1 = CBOTAD+CSWPD

Parasitic Capacitors in MOSFETOperation Region Dependent -- Ohmic

Ohmic Capacitor: CGCH , CBCH

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 lumpedand split evenly between the source and drain nodes

Parasitic Capacitors in MOSFETOperation Region Dependent -- Ohmic



CGDOCGSO

CBS1 CBD1

Ohmic Capacitor: CGCH , CBCH

CGCH

CBCH


Cutoff Ohmic SaturationCGS CoxWLD CoxWLD + 0.5COXWL CoxWLD

CGD CoxWLD CoxWLD + 0.5COXWL CoxWLD

CBG CoxWL (or less)

CBS CBOTAS+CSWPS CBOTAS+CSWPS+0.5CBCH CBS1 = CBOTAS+CSWPS

CBD CBOTAD+CSWPD CBOTAD+CSWPD+0.5CBCH CBD1 = CBOTAD+CSWPD

D

S

G B

CGS

CGD

CBS

CBD

CBG


CGS CoxWLD CoxWLD + 0.5COXWL CoxWLD


CBG CoxWL (or less) 0

CBS CBOTAS+CSWPS CBOTAS+CSWPS+0.5WLCBOTCH CBS1 = CBOTAS+CSWPS

CBD CBOTAD+CSWPD CBOTAD+CSWPD+0.5WLCBOTCH CBD1 = CBOTAD+CSWPD

D

S

G B

CGS

CGD

CBS

CBD

CBG

Parasitic Capacitors in MOSFETOperation Region Dependent -- Saturation

Saturation Capacitors: CGCH , CBCH

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

Parasitic Capacitors in MOSFETOperation Region Dependent -- Saturation



CGDOCGSO

CBS1 CBD1

Saturation Capacitors: CGCH , CBCH

CGCH

CBCH


Cutoff Ohmic SaturationCGS CoxWLD CoxWLD + 0.5COXWL CoxWLD+(2/3)COXWL


CBG CoxWL (or less) 0 0

CBS CBOTAS+CSWPS CBOTAS+CSWPS+0.5WLCBOTCH CBS1 + (2/3)CBC

CBD CBOTAD+CSWPD CBOTAD+CSWPD+0.5WLCBOTCH CBOTAD+CSWPD

D

S

G B

CGS

CGD

CBS

CBD

CBG


S

G B

CGS

CGD

CBS

CBD

CBG

Cutoff Ohmic SaturationCGS CoxWLD CoxWLD + 0.5COXWL CoxWLD+(2/3)COXWL


CBG CoxWL (or less) 0 0

CBS CBOTAS+CSWPS CBOTAS+CSWPS+0.5WLCBOTCH CBOTAS+CSWPS +(2/3)WLCBOTCH

CBD CBOTAD+CSWPD CBOTAD+CSWPD+0.5WLCBOTCH CBOTAD+CSWPD

Process Parameters from AMI 0.5u ProcessUNITSMTL2 MTL1 HR POLY2 PLY2_POLY P+ACTV N+ACTV PROCESS PARAMETERS

ohms/sq0.090.0941112021.6101.981.5Sheet Resistance ohms0.826.815.8141.964.6Contact Resistance

angstrom140Gate Oxide Thickness

N WELLN\PLYMTL 3PROCESS PARAMETERS ohms/sq8128220.06Sheet Resistance ohms 0.65Contact Resistance

COMMENTS: N\POLY is N-well under polysilicon.

UNITSN_WELL M3 M2 M1 POLY2 POLY P+ACTV N+ACTV CAPACITANCE PARAMETERS aF/um^23910163287731424Area (substrate) aF/um^21216362473Area (N+active) aF/um^22382Area (P+active) aF/um^2101556969Area (poly) aF/um^250Area (poly2) aF/um^21331Area (metal1) aF/um^239Area (metal2) aF/um385872247315Fringe (substrate) aF/um283957Fringe (poly) aF/um3448Fringe (metal1) aF/um55Fringe (metal2) aF/um195Overlap (N+active)

=.35 microns

Small Signal Model Summary

CGS

CGD

CBD

CBS

CBG

G

D

B

S


S

G B D

VBSVGSgmVGS

gmBVBS

gOCGS

CBS

CGD

CGB CBD

Equivalent circuit showing dependent sources

In many applications simpler small signal model is adequate


Simplified Equivalent Circuit Adequate for Many Applications When Source is Grounded

S

G D

VGS

gmVGS

gOCGS

CBD

B

(CBS need not be shown when source connected to ground)

That’s all folks!

high frequency mosfet model. models for computer simulation simple dc model small signal model...

Documents

c gso c gdo c gso slide

c bd1 slide

c gbco slide

c bch c gch c bch note

c gso junction capacitors

c gbco note

mosfet slide

small capacitors