ee141 © digital integrated circuits 2nd wires 1 digital integrated circuits a design perspective...

EE1411

© Digital Integrated Circuits2nd Wires

Digital Integrated Digital Integrated CircuitsCircuitsA Design PerspectiveA Design Perspective

The WireThe Wire

Jan M. RabaeyAnantha ChandrakasanBorivoje Nikolic

July 30, 2002

EE1412


The WireThe Wire

transmitters receivers

schematics physical

EE1413


Interconnect Impact on ChipInterconnect Impact on Chip

EE1414


Wire ModelsWire Models

All-inclusive model Capacitance-only

EE1415


Impact of Interconnect ParasiticsImpact of Interconnect Parasitics

Interconnect parasitics reduce reliability affect performance and power

consumption Classes of parasitics

Capacitive Resistive Inductive

EE1416


10 100 1,000 10,000 100,000

Length (u)

No

of

ne

ts(L

og

Sc

ale

)

Pentium Pro (R)

Pentium(R) II

Pentium (MMX)

Pentium (R)

Pentium (R) II

Nature of InterconnectNature of Interconnect

Local Interconnect

Global Interconnect

SLocal = STechnology

SGlobal = SDie

So

urc

e:

Inte

l

EE1417


INTERCONNECTINTERCONNECT

EE1418


Capacitance of Wire InterconnectCapacitance of Wire Interconnect

VDD VDD

VinVout

M1

M2

M3

M4Cdb2

Cdb1

Cgd12

Cw

Cg4

Cg3

Vout2

Fanout

Interconnect

VoutVin

CL

SimplifiedModel

EE1419


Capacitance: The Parallel Plate ModelCapacitance: The Parallel Plate Model

Dielectric

Substrate

L

W

H

tdi

Electrical-field lines

Current flow

WLt

cdi

diint

LLCwire SSS

SS

1

EE14110


PermittivityPermittivity

EE14111


Fringing CapacitanceFringing Capacitance

W - H/2H

+

(a)

(b)

EE14112


Fringing versus Parallel PlateFringing versus Parallel Plate

(from [Bakoglu89])

EE14113


Interwire CapacitanceInterwire Capacitance

fringing parallel

EE14114


Impact of Interwire CapacitanceImpact of Interwire Capacitance

(from [Bakoglu89])

EE14115


Wiring Capacitances (0.25 Wiring Capacitances (0.25 m CMOS)m CMOS)

EE14116



EE14117


Wire Resistance Wire Resistance

W

L

H

R = H W

L

Sheet ResistanceRo

R1 R2

EE14118


Interconnect Resistance Interconnect Resistance

EE14119


Dealing with ResistanceDealing with Resistance

Selective Technology Scaling Use Better Interconnect Materials

reduce average wire-length e.g. copper, silicides

More Interconnect Layers reduce average wire-length

EE14120


Polycide Gate MOSFETPolycide Gate MOSFET

n+n+

SiO2

PolySilicon

Silicide

p

Silicides: WSi 2, TiSi2, PtSi2 and TaSi

Conductivity: 8-10 times better than Poly

EE14121


Sheet ResistanceSheet Resistance

EE14122


Modern InterconnectModern Interconnect

EE14123


Example: Intel 0.25 micron ProcessExample: Intel 0.25 micron Process

5 metal layersTi/Al - Cu/Ti/TiNPolysilicon dielectric

EE14124



EE14125


InterconnectInterconnectModelingModeling

EE14126


The Lumped ModelThe Lumped Model

Vout

Driver

cwire

VinClum pe d

RdriverVout

EE14127


The Lumped RC-ModelThe Lumped RC-ModelThe Elmore DelayThe Elmore Delay

EE14128


The Ellmore DelayThe Ellmore DelayRC ChainRC Chain

EE14129


Wire ModelWire Model

Assume: Wire modeled by N equal-length segments

For large values of N:

EE14130


The Distributed RC-lineThe Distributed RC-line

EE14131


Step-response of RC wire as a Step-response of RC wire as a function of time and spacefunction of time and space

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

0.5

1

1.5

2

2.5

time (nsec)

volta

ge (V

)

x= L/10

x = L/4

x = L/2

x= L

EE14132


RC-ModelsRC-Models

EE14133


Driving an RC-lineDriving an RC-line

Vi n

Rs Vo ut

(rw,cw,L)

EE14134


Design Rules of ThumbDesign Rules of Thumb

rc delays should only be considered when tpRC >> tpgate of the driving gate

Lcrit >> tpgate/0.38rc rc delays should only be considered when the

rise (fall) time at the line input is smaller than RC, the rise (fall) time of the line

trise < RC when not met, the change in the signal is slower

than the propagation delay of the wire

© MJIrwin, PSU, 2000

ee141 © digital integrated circuits 2nd wires 1 digital integrated circuits a design perspective...

Documents

intel slide

interconnect resistance

permittivity slide

interconnectmodeling

cmos slide

chip slide

poly slide

modern interconnect