jbean thermionic

8/9/2019 JBean Thermionic

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University of Notre DameDepartment of Electrical Engineering

ThermionicRefrigeration

Jeffrey A. Bean

EE666 – Advanced Semiconductor Devices


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University of Notre Dame

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Outline

Types of refrigerationTypes of refrigerationApplication of eac type in electronicsApplication of eac type in electronics

!y te "fuss# a$out cooling%!y te "fuss# a$out cooling%

Termionic refrigeration &T'() in detailTermionic refrigeration &T'() in detail

*urrent Devices*urrent Devices

'mprovements'mprovements

+ossi$le uses+ossi$le uses


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Types of Refrigeration

*ompressive*ompressive

Utili,es a refrigerant fluid and a compressorUtili,es a refrigerant fluid and a compressorEfficiency- /01203 of *arnot valueEfficiency- /01203 of *arnot value

TermoelectricTermoelectric

Utili,es materials 4ic produce a temperatureUtili,es materials 4ic produce a temperaturegradient 4it potential across devicegradient 4it potential across device

Efficiency- 21503 of *arnot valueEfficiency- 21503 of *arnot value

TermionicTermionic

Utili,es parallel materials separated $y a smallUtili,es parallel materials separated $y a smalldistance &eiter vacuum or oter material)distance &eiter vacuum or oter material)

Efficiency- 501/03 of *arnot valueEfficiency- 501/03 of *arnot value

Saouri7 A. and Bo4ers7 J. E.7 8eterostructure 'ntegrated Termionic (efrigeration7 56t 'nt. *onf. on Termoelectrics7 pp. 6/67 599:

c

cT

T ∆=η


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Compressive Refrigeration

5) (efrigerant fluid is compressed &ig5) (efrigerant fluid is compressed &igpressure – temperature increases)pressure – temperature increases)

;)


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Thermoelectric Refrigeration (TER)

A temperature difference $et4een teA temperature difference $et4een te

>unctions of t4o dissimilar metal 4ires>unctions of t4o dissimilar metal 4iresproduces a voltage potentialproduces a voltage potential&no4n as te See$ec Effect)&no4n as te See$ec Effect)

+eltier cooling forces eat+eltier cooling forces eatflo4 from one side to teflo4 from one side to teoter $y applying anoter $y applying ane=ternal electric potentiale=ternal electric potential

Termoelectric generationTermoelectric generationis utili,ed on deep spaceis utili,ed on deep spacemissions using a plutoniummissions using a plutoniumcore as te eat sourcecore as te eat source

ttp-??444.dts1generator.com?main1e.tm


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Thermionic Refrigeration (TIR)

'nvestigation into termionic energy'nvestigation into termionic energy

conversion $egan in te 5920sconversion $egan in te 5920sUtili,es fact tat electrons 4it igUtili,es fact tat electrons 4it ig

termal energy &greater tan te 4ortermal energy &greater tan te 4or

function) can escape from te metalfunction) can escape from te metal@eneral idea-@eneral idea-

A ig 4or functionA ig 4or function

metal catode in contactmetal catode in contact4it a eat source 4ill4it a eat source 4ill

emit electrons to a lo4eremit electrons to a lo4er

4or function anode4or function anode

φm8 φm*

*atode Anodeacuum

Barrier


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Impact of Each Type on Electronics

*ompressive*ompressive+ros- efficient7 ig cooling po4er from am$ient+ros- efficient7 ig cooling po4er from am$ient

*ons- $uly7 e=pensive7 noisy7 po4er consumption7 scaling*ons- $uly7 e=pensive7 noisy7 po4er consumption7 scaling

TermoelectricTermoelectric

+ros- ligt4eigt7 small footprint+ros- ligt4eigt7 small footprint*ons- lousy efficiency7 lo4 cooling po4er from am$ient7*ons- lousy efficiency7 lo4 cooling po4er from am$ient7

can#t $e integrated on '* cips7 po4er consumptioncan#t $e integrated on '* cips7 po4er consumption

TermionicTermionic+ros- integration on '*s using current tecnology7 lo4 po4er+ros- integration on '*s using current tecnology7 lo4 po4er

*ons- only support locali,ed cooling7 lo4 cooling po4er*ons- only support locali,ed cooling7 lo4 cooling po4er

from am$ient temperaturefrom am$ient temperature


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Why the ‘fuss’ about cooling

+o4er dissipation in electronics is+o4er dissipation in electronics is

$ecoming a uge issue$ecoming a uge issue

'ntel

+rocessor *ip +o4er Density


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Under an applied $ias7 "ot#Under an applied $ias7 "ot#

electrons flo4 to te ot sideelectrons flo4 to te ot sideof te >unctionof te >unction

(emoving te ig energy(emoving te ig energyelectrons from te cold side ofelectrons from te cold side of

te >unction cools itte >unction cools it

*arge neutrality is maintained*arge neutrality is maintained$y adding electrons$y adding electronsadia$atically troug an omicadia$atically troug an omiccontactcontact

Amount of eat a$sor$ed inAmount of eat a$sor$ed incatode is total current timescatode is total current timeste average energy of electronste average energy of electronsemitted over te $arrieremitted over te $arrier

!o" Thermionic Refrigerators Wor#

φm8 φm*

*atode Anode

Structure under termal eCuili$rium

Structure under $ias

φm8

φm*

*atode

Anode

E

e1 flo4

tunneling

termionic

emission


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TER vs$ TIR

Termoelectric (efrigerationTermoelectric (efrigerationElectrons a$sor$ energy from te latticeElectrons a$sor$ energy from te latticeBased on $ul properties of te semiconductorBased on $ul properties of te semiconductor

Electron transport is diffusiveElectron transport is diffusive

Termionic (efrigerationTermionic (efrigeration

Electron transport is $allisticElectron transport is $allistic

Selective emission of ot carriers from catodeSelective emission of ot carriers from catode

to anode yields iger efficiency tan TE(to anode yields iger efficiency tan TE(

Tunneling of lo4er energy carriers reduces efficiencyTunneling of lo4er energy carriers reduces efficiency


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Thermionic Refrigeration

Termionic devices are $ased on (icardson#sTermionic devices are $ased on (icardson#s

eCuationseCuationsdescri$es current per unit area emitted $y a metaldescri$es current per unit area emitted $y a metal

4it 4or function4it 4or function φφ and temperature Tand temperature T

*atode $arrier eigt as a function of current*atode $arrier eigt as a function of current

)(*),( 12 η φ F T AT J E =

aan7 @. D.7 Termionic (efrigerationF7 J. Appl. +ys7 ol. :6 &:) 7 pp. G/6;7 599G.

−

= )ln(

2

*ln),(32

22

I T k qm

q

T k I T B Bcπ

φ

[ ])()(2*),( 122 η η η φ F F q

kT T AT J Q −=

3

2*4*

h

k qm A

π =

kT

qC

φ η =


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+ractical termionic refrigerators sould emit at least+ractical termionic refrigerators sould emit at least

5 A?cm5 A?cm;; from te catodefrom te catode


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Thermionic Refrigerator IssuesIo4ering te $arrier eigt to provide for roomIo4ering te $arrier eigt to provide for room

temperature coolingtemperature coolingetal1acuum1etal termionic refrigerators onlyetal1acuum1etal termionic refrigerators only

operate at ig temperatures &:00H)operate at ig temperatures &:00H)

Anode?*atode spacingAnode?*atode spacing

Uniformity of electrodesUniformity of electrodes

+ro=imity issues+ro=imity issues

Space carges in te vacuum regionSpace carges in te vacuum region

'mpedes te flo4 of electrons from te anode to te'mpedes te flo4 of electrons from te anode to tecatode $y introducing an e=tra potential $arriercatode $y introducing an e=tra potential $arrier

Termal conductivity &in semiconductor devices)Termal conductivity &in semiconductor devices)


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!eterostructure Cooling o"er

Effective mass affectsEffective mass affects

te cooling performancete cooling performance$y canging te density$y canging te density

of supply electrons andof supply electrons and

electrons in te $arrierelectrons in te $arrier

Tis cooling po4erTis cooling po4er

reduces at lo4erreduces at lo4er

temperatures $ecausetemperatures $ecause

te


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!eterostructure Refrigeration

Electron mean free patElectron mean free pat λλ atat/00H is assumed to $e 0.;/00H is assumed to $e 0.;µµmm

Barrier ticness I must $e MBarrier ticness I must $e M λλ

φm8

φm*

I

Saouri7 A. and Bo4ers7 J. E.7 8eterostructure 'ntegrated Termionic (efrigeration7 56t 'nt. *onf. on Termoelectrics7 pp. 6/67 599:


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ultilayer (*uperlattice) !eterostructuresLverall termal conductivity reduced to 503 of teLverall termal conductivity reduced to 503 of te

individual materials tat compose itindividual materials tat compose it

Efficiency increases 2150 times over single $arrier structuresEfficiency increases 2150 times over single $arrier structures

aan7 @. D.7 J. L. Sofo7 and . Barto4ia7 ultilayer termionic refrigerator and generatorF7 J. Appl. +ys.7 ol. / No. 97 pp. G6/7 599

Efficiency of a single $arrier T'( 4ere

T8O/00H and T*O;60H as a function of φEfficiency of a multiple $arrier T'( 4ere

T8O/00H and T*O;60H as a function of φ


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*i+e,*i icrocoolers

;00 repeated layers of /nmSi?5;nmSi;00 repeated layers of /nmSi?5;nmSi

0.:20.:2@e@e

0.;20.;2 superlattice &/superlattice &/µµm tic)m tic)

@ro4n on Si@ro4n on Si0.0.@e@e0.;0.; $uffer layer on Si su$strate$uffer layer on Si su$strate

esa etc to define devicesesa etc to define devicesSaouri7 A. and Pang7 Q.7 Ln1*ip Solid1State *ooling for '*s Using Tin1


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*i+e,*i icrocoolers

Lptimum device si,e- 20=20 60=60Lptimum device si,e- 20=20 60=60µµmm;;Autor reports ma=imum cooling of ;01/0R* andAutor reports ma=imum cooling of ;01/0R* andseveral tousands of !?cmseveral tousands of !?cm;; cooling po4er densitycooling po4er density4it optimi,ed Si@e superlattic structures4it optimi,ed Si@e superlattic structures

Saouri7 A. and Pang7 Q.7 Ln1*ip Solid1State *ooling for '*s Using Tin1


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University of Notre Dame-

-&vantages of !eterostructure TIR

*ompared to $ul termoelectric*ompared to $ul termoelectric

refrigeratorsrefrigerators5) very small si,e and standard tin1film5) very small si,e and standard tin1film

fa$rication 1 suita$le for monoliticfa$rication 1 suita$le for monolitic

integration on '* cipsintegration on '* cips+ossi$le to put refrigerator near active devices and+ossi$le to put refrigerator near active devices and

cool ot spots directlycool ot spots directly

;) iger cooling po4er density;) iger cooling po4er density

/) transient response of Si@e?Si superlattice/) transient response of Si@e?Si superlatticerefrigerators is several orders of magnituderefrigerators is several orders of magnitude

faster &50faster &5022 for tese Si@e?Si microrefrigerators)for tese Si@e?Si microrefrigerators)


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.urther Improvement(educe termal(educe termal

conductivity &materials)conductivity &materials)Te current limitation inTe current limitation insuperlattice coolers issuperlattice coolers iste contact resistancete contact resistance

$et4een te metal and$et4een te metal andcap layercap layer

Lmic contacts to aLmic contacts to atermionic emissiontermionic emissiondevice &$allistic transport)device &$allistic transport)

4ill ave a non1,ero4ill ave a non1,eroresistance due to >ouleresistance due to >ouleeating from te largeeating from te largecurrent densitiescurrent densities

a=imum cooling for

contact resistance of-

0 Ωcm;

501 Ωcm;

501: Ωcm; 5016

Ωcm;Ulric7 . D.7 +. A. Barnes7 and *. B. ining7 Effect of contact resistance in solid1state termionic emissionF7 J. Appl. +ys.7 ol. 9; No. 57 pp. ;G27 ;00;


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ore Improvements

+acaging is also an important aspect of+acaging is also an important aspect of

te device optimi,ationte device optimi,ation

Addition of a pacage $et4een cip and eatAddition of a pacage $et4een cip and eat

sin adds anoter termal $arriersin adds anoter termal $arrier

Use of Si or *u pacages aided in reducing tisUse of Si or *u pacages aided in reducing tistermal resistancetermal resistance

Lptimi,ing lengt of 4ire $ondsLptimi,ing lengt of 4ire $onds

Tese improvements ave resulted in aTese improvements ave resulted in ama=imum cooling increase of 5003ma=imum cooling increase of 5003


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Conclusions

Small area7 locali,ed cooling7 can $eSmall area7 locali,ed cooling7 can $e

implemented 4it current '* fa$ricationimplemented 4it current '* fa$ricationtecniCuestecniCues

!it optimi,ation7 current devices could!it optimi,ation7 current devices could

provide-provide-*ooling of ;01/0R* for 20=20*ooling of ;01/0R* for 20=20 µµmm;; areasareas

Several tousands of !?cmSeveral tousands of !?cm;; cooling po4ercooling po4erdensitydensity

jbean thermionic

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