Chp 13 Electrical Properties

8/3/2019 Chp 13 Electrical Properties

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ISSUESTOADDRESS...

CHAPTER13:

ELECTRICALPROPERTIES

Howareelectricalconductanceandresistance

characterized?

Whatarethephysicalphenomenathatdistinguish

conductors,semiconductors,andinsulators?

Formetals,howisconductivityaffectedby

imperfections,T,anddeformation?

Forsemiconductors,howisconductivityaffected

byimpurities

(doping)

and

T?

ScanningelectronmicroscopeimagesofanIC:

Al

Si

(a)(d)

VIEW

OF

AN

INTEGRATED

CIRCUIT

AdotmapshowinglocationofSi(asemiconductor):

Sishowsupaslightregions.

0.5mm45m

(doped)

(b)

Alshowsupaslightregions.

Fig.(a),(b),(c)fromFig.18.0,

Callister6e.

Fig.(d)fromFig.18.25,Callister6e.(Fig.18.25iscourtesy

NickGonzales,NationalSemiconductorCorp.,WestJordan,

UT.)

(c)


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Ohm's Law:V

=

I R

voltagedrop(volts) resistance(Ohms)

current(amps)

ELECTRICALCONDUCTION

VIe-

A(crosssect.area)

L

Resistivity, andConductivity,:geometryindependentformsofOhm'sLaw(recallnormalizationwith)

V IE:electric resistivit

LA

field

intensity

(Ohmm)

J:currentdensity

I

conductivity

Resistance:

R

L

A

L

A

Silver 6.8 x 107

METALS

Soda-lime glass 10-10

CERAMICSconductors

RoomTvalues(Ohmm)1

CONDUCTIVITY: COMPARISON

-14

Copper 6.0 x 107

Iron 1.0 x 107

-4

SEMICONDUCTORS

Concrete 10-9

Aluminum oxide


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100m

Cu wire I = 2.5A- +e-

EX: CONDUCTIVITYPROBLEM

Whatistheminimumdiameter(D)ofthewiresothat

V


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Metalsaregoodconductors

sincetheirvalencebandisonly

partiallyfilled.

Metals: Thermalenergyputs

manyelectronsinto

a hi her ener state.

+-

-

CONDUCTION&ELECTRONTRANSPORT

eeeqn ne =#ofe

qe =Chargeofe

=E mobility

EnergyStates:

thecasesbelow

formetalsshow

thatnearby

energystates

Energy

filled

emptyband

s

Energy

partlyfilled

emptyband

GAPMylevel

highest

filledstate

are

access ebythermal

fluctuations.

filledband

valenceband

filledstate

filledband

va enceband

filledstates

Fermihttp://www.bayarea.net/~kins/

AboutMe/GIFs/Fermi_2.jpg


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Insulators:Higherenergystatesnot

accessible dueto a .

Semiconductors:Higherenergystates

separatedbyasmallergap.

ENERGYSTATES: INSULATORSAND

SEMICONDUCTORS

Energy

filled

emptyband

es

GAP

Energy

filled

emptyband

es

GAP?Engineered

material:Gaps

aretunable

moretocome

filledband

band

filled

sta

filledband

va enceband

filled

stat

Insulators: Aparallelplatecapacitorinvolvesaninsulator,ordielectric,between

two

metal

electrodes.

The

charge

density

buildup

at

the

capacitor

surface

is

related

to

thedielectricconstant ofthematerial

E,Electricfieldstrength(V/m)

o

D,charge

density(C/m2)

o electricpermittivityinvacuum,

constant 8.9x1012C Vm

k,dielectricconstant

(materialproperty)

ko electricpermittivity


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Imperfectionsincreaseresistivitygrainboundaries

dislocations

impurityatoms

Theseacttoscatterelectronssothatthey

takealessdirectpath.

METALS: RESISTIVITYVST,IMPURITIES

vacancies

Cu+3

.32at%

Ni

Cu+2

.16at%

Ni

eforme

dCu+

1.12a

t%Ni

3

4

5

6

esistivity,

0-8Ohm-m)

at%Ni

)](1[ rto TT temperaturecoefficient ofresistivity,o is

intrinsic(noimpurity)resistivity

T (C)-200 -100 0

1R(1

0

Cu+.

Pure

Cu

increaseswith:temperature

wt%impurity

%CWAdaptedfromFig.18.8,Callister 6e. (Fig.18.8adaptedfromJ.O.Linde,

Ann.Physik5,p.219(1932);andC.A.WertandR.M.Thomson,Physicsof

Solids,2nded.,McGrawHillBookCompany,NewYork,1970.)

Why????


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Variationinelectricalresistivitywithcompositionforvariouscopperalloyswithsmalllevelsof

elementaladditions.AlldataareatfixedT(20C).

xo 1o resistivityofpuremetal

slope

x amtofalloy(impurity)addition

DataforPureSilicon:

increaseswithT

oppositetometalsundoped e

Egap /kT

Energy

PURESEMICONDUCTORS: CONDUCTIVITYVST

Arrheniuseq.!

filled

filledvalenceband

emptyband

filledstates

GAP?

electrons

cancross

gapat

higherT

e ec r ca con uc v y,

(Ohm-m)-1

100

101

102

103

104

pure

material

Si

Ge

GaP

CdS

bandgap(eV)

1.11

0.67

2.25

2.40

AdaptedfromFig.19.15,Callister5e. (Fig.19.15adapted

fromG.L.PearsonandJ.Bardeen,Phys.Rev.75,p.865,

1949.)

SelectedvaluesfromTable

18.2,Callister6e.

50 100 100010-2

10-1(undoped)

T(K)


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CONDUCTIONINTERMSOFELECTRONANDHOLEMIGRATION

Light(shown),heat,

ElectricalConductivitygivenby:3

toexcitee from

valencebandto

conductionband

Conductioncanbeeitherbynegativecarriers,

nee peh

#electrons/m 3 electronmobility

holemobility

electrons(ntype)and/orpositivecarriers,holes(ptype).

Electronsmovetowards(+)potentialandholesmoveto()potential

kT

Eg

oe 2

Arrheniusequation;Why2? Producetwo

chargecarriers electronandhole

mxBy

Tk

E

e

g

o

Tk

E

o

g

1

2lnln

1

2

Determiningtheactivationenergyforconduction


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Intrinsicsemiconductors: #ofthermallygeneratedelectrons=

#of

holes

(broken

bonds)

INTRINSICVSEXTRINSICCONDUCTION

x r ns csem con uc ors: mpur esa e o esemiconductorthatcontributetoexcesselectronsorholes.Doping=intentionalimpurities

Siisthemainmaterialinsemiconductors Largebandgap(1.1eV);allowsSitooperateatwarmertemperatures(150oC) Canformanativeoxide,SiO2,forinsulatingbarriers(importantinfabrication)

Sicanbemadeintolarge(12inchdia.),highpurity,singlecrystalingots. Czochralski method. Wafersarecutfromtheingot

DopingofSi Sihas4outershellelectrons ntype:Phosphorous,arsenic(groupV),donateextraelectron ptype:boron(groupIII)forSi

ntype

4valenceelectronsofAsallowittobondlikeSi,butthefifthelectronisleftorbitingAs

site theenergytoreleasethefifthelectronintotheCBissmall

nee kT

EEg

o

d

e)(

Eg isbottomofconductionband

Ed isthedonorlevelArrheniusequation,again!


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ptype

Boron

has

only

3

valance

electrons.

When

it

substitutes

for

a

Si

atoms,

one

of

its

bonds

haveamissingelectron(hole)

Holetunnelsaround,andcanbelibratedbythermalvibrationofSiatoms,fromtheB

siteintotheVB.

p eh

kTE

o

a

e

ptype

ntype

?type

?type


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Arrheniusplotofelectricalconductivityforanntype

semiconductoroverawide

temperaturerange.Atlowtemperatures(high1/T),thematerialisextrinsic.Athightemperatures(low1/T),thematerialisintrinsic.Inbetweenistheexhaustion

range,inwhichallextra

electronshavebeenpromoted

why?

why?

CompoundSemiconductors

GroupIIIVandIIVcompoundsnominallyhave

theZincBlendstructureandareintrinsic

semiconductors.Can

be

doped,

like

Si,

to

change

conduction(extrinsic)

MXCompounds:GroupIII3+valence,GroupV

5+valence avg.of4+valenceperatom//

GroupII2+valence,GroupVI6+valence avg.4

valenceperatom

Applications:

Solarcells

Lightemittingdiodes(occurswith

electronholerecombination)

Higheroperationspeeds,etc.


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Allowsflowofelectronsinonedirectiononly (e.g.,useful

toconvert

alternating

current

to

direct

current).

Processing: diffusePintoonesideofaBdopedcrystal.

Results: - -

ICDEVICES:PNRECTIFYINGJUNCTION

Noappliedpotential:

nonetcurrentflow.

Forwardbias: carrier

flowthroughptypeand

ntyperegions;holesand

electronsrecombineat

++

+

+

-

-

--

-

++

++

+

---

--

p-type n-type+ -

14

.

Reversebias: carrier

flowawayfrompnjunction;

carrierconc.greatlyreduced

atjunction;littlecurrentflow.

+++

+

+

--- --

p-type n-type- +

PN

Rectifying

Junction


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LightEmittingDiode(LED)

http://electronics.howstuffworks.com/led.htm/printable

http://spie.org/Images/Graphics/Newsroom/Importe

d/0695/0695_fig4.jpg

Bandgapdetermines

light,viaDeBoglie

equation=h/(mv)

TheTransistor

InventedbyShockley,Bardeen,

andBrattainin1948.Nobelprize

in1956.

Athreeterminaldevicethatacts

likeasimpleonoffswitch.

ThebasisofIntegratedCircuits(IC)

technology

Computers,cellphones,

automotivecontrol,etc.

Ifvoltage(potential)appliedto

the ate,currentflowsbetween

thesource

and

the

drain.

On/offswitch logicswitch,

go/nogo


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Howtodoweprocessthematerials?

Features?

Controlling

oxide

thickness?

MakingSintype?MakingSiptype?

FabricatingSingleCrystal,HighPuritySi

Czochralski method Zonerefining

http://www.mindfiesta.com/images/article/Metallurgy_clip_image003_0002.gif

ls CCK /K=segregationcoefficient

C=concentrationofimpuritiesinsolidand

liquidMoresoluterejected asTdecreases


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Cleanrooms

Featuresbeingmadeare

submicron

DUST

is

your

enemy! Candestroyentire

waferofmulti le rocessors

Cleanroomclassification

http://docs.engineeringtoolbox.com/documents/933/cleanroomclass

particlesizediagramISO.png

http://zedomax.com/blog/wp

content/uploads/2009/12/silico

nwafer.jpg

http://philip.greenspun.com/images/pcd0094/microdisplaycleanroom

31.3.jpg

Turbulentflow Laminarflowhttp://en.wikipedia.org/wiki/Cleanroom

Oxidation

Oxidation =growthofanoxidelayerbythereactionofoxygenwiththesubstrate

Providesdopant maskinganddeviceisolation

ICtechnologyuses

Thermalgrownoxidization(dry)

O2richenvironment,7501100oC,

largebatchprocess(150+wafers)

Si+O2 SiO2 Wetoxidation

Si+H O SiO +2H

Highergrowthrates,lowoxidedensity(lowerdielectricproperties)

Selectiveoxidation:Useofsiliconnitridetopreventoxidationinspecificregions

http://www.semi.org/cms/groups/pu

blic/documents/web_content/~expor

t/CTR_032685~1~000086~DC_SNIPPE

T_LAYOUT/866811.jpg


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Lithography

Lithography =processbywhich

geometricpatternsaretransferredfromamask(reticle)

toasurfaceofachiptoformthe

.

Mooreslaw(1965)

Linewidth =widthofsmallest

featureobtainableonSisurface

(dependent)

Photoresist (PR)=lightsensitivepolymermaterial Patternsareimprintedusingphotoresist

Positiveresist =the

portion

of

the

photoresist that

is

exposedtolightbecomessolubletothephotoresistdeveloperandtheportionofthephotoresist thatisunexposedremainsinsolubletothephotoresistdeveloper(exposed,removed)

Negativeresist =unexposed(uncrosslinked)portionofthephotoresist isdissolvedbythephotoresistdeveloper (exposed,staysput)

Whytheyellowlight?ICFeatureMaking

(1) PRspunontowaferandprebaked(driveoffsolvents)(2) Alignmask,usingastepper,overthesubstrate(PR).Maskis

steppedoverthewaferandexposedtoUV makingseveralpatterns(devices)onasinglewafer(registration)

(3) Postbake hardenedtheresistthatisexposedtoUV.Regionnotcoveredbyresistisimplantedoretchedaway.

(4) ResistisstrippedawaybyawetstripperorO2 plasma(ashing).Lithographypatternedmanytimeswithdifferentmasks.

http://www.anl.gov/Media_Center/ArgonneNow/Fall_2006

/Center_for_Nanoscale_Materials.html


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Etching

Wet:isotropic,undercut Dry:anisotropic,directional

(Cl andFbasedgasremoval)

IonImplantation(Doping)


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pnDiodeFab Steps

p

n

Diode


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Metallization

Metallization =growing

interconnectionsto

(a)

connec ev ces

Lowelectricalresistance,

goodadhesionto

dielectricinsulators

Electromigration =rocessb whichmetal

atomsdiffusebecauseof

apotential.

Not

good

a

materialsresearcharea!

FilmDeposition

Tobuildadevice,variousthinmetalorinsulatingfilmsaregrownontopofeachother

Evaporation

Sputtering

Evaporation

MBE

Sputtering

CVD(ALD)

CVD

http://www rpl.stanford.edu/user/files/www/ald1.gif

MBEhttp://www.sandia.gov/media/NewsRel/NR2000/images/jpg/MBE.jpg


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WireBondingandPackaging

(a) (b) (c)

LargelydeterminestheoverallcostofIC

Massproduced,notindividuallypackaged

Packages:polymers,metals,ceramics

Yieldand

Reliability

Yield=ratiooffunctionalchipstototal#ofchips ,

processing

ReliabilityNodevicehasinfinitelifetime.Statisticalmethodsto

predictexpectedlifetime

Failuremechanisms

Oxidelayers(dielectricbreakdown)

Lithography(unevenfeaturedefintion)

Metallayers(poorconnections)

Lossofpackagehermeticity


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Electricalconductivity andresistivity are:

material

parameters.

geometryindependent.

Electrical resistance is:

SUMMARY

ageometryandmaterialdependentparameter.

Conductors,semiconductors, andinsulators...

differentinwhetherthereareaccessibleenergy

statesforconductanceelectrons.

Formetals,conductivityisincreasedby

reducingdeformation

reducingimperfections

decreasingtemperature.

Forpuresemiconductors,conductivityisincreasedby

increasingtemperature

doping(e.g.,addingBtoSi(ptype)orPtoSi(ntype).

Chp 13 Electrical Properties

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