1、第27卷第2期2006年2月半導(dǎo)體學報CHINESEJOURNALOFSEMICONDUCTORSVol.27No.2Feb.,2006MonolithicallyIntegratedOptoelectronicReceiversmMS/RFCMOS3Implementedin0.25ChenHongda,GaoPeng1,󰂍,MaoLuhong,andHuangJiale22(1StateKeyLaboratoryofIntegratedOptoelectronics,InstituteofSemiconductors,ChineseAcademyofSciences,Bei

2、jing100083,China)(2SchoolofElectronicInformationEngineering,TianjinUniversity,Tianjin300072,China)Abstract:Amonolithicallyintegratedoptoelectronicreceiverispresented.Asilicon2basedphoto2diodeandreceiv2ercircuitsareintegratedonidenticalsubstratesinordertoeliminatetheparasiticsinducedbyhybridpackaging

3、.Implementedinthepresentdeepsub2micronMS/RF(mixedsignal,radiofrequency)CMOS,thismonolithicallyOEICtakesadvantageofseveralnewfeaturestoimprovetheperformanceofthephoto2diodeandeventuallythewholeOEIC.Keywords:monolithicallyintegrated;OEIC;CMOSprocessEEACC:4250;2560BCLCnumber:TN303Documentcode:AArticleI

4、D2()1IntroductionThedemadatatransmis2sioninashorttiinhepresentageofinforma2tionhasbroughtonahugeneedforopticalinter2connection,whichhasbeenproventobethebestwaytotransmitdataatextremelyhighspeeds.Nowadays,theareaofoptoelectronicdevicesisdominatedbycompoundsemiconductormaterials,duetotheirintrinsiccha

5、racteristics.Sincemosttransmitteddataareprocessedonsiliconchips,chipsondifferentmaterialshavetobepackagedtogethertorealizethewholeopticalinterconnec2tionsystem.Hybridpackagingeitherbywirebondingorbyflip2chipbondinghasintroducedseveralundesiredeffects,whichinevitablylimittheutilityandperformanceofthe

6、system.Becauseofthedisadvantagesmentionedabove,theindus2tryhasbeenrelentlessinitsquesttointegratethefunctionsofoptoelectronicsystemsontoasinglechip.Monolithicintegrationoncompoundsemi2conductorsubstratehasbeenputintopracticaluse1formanyyears,butintegrationonsiliconingeneralICprocessesispreferredbeca

7、useofitslarge2scaleintegration,especiallyin(localareanetwork)andVSR(veryshortreach)applications.ThemotivationandpotentialtorealizesuchfullintegrationinCMOShasin2creasedmarkedlyasthespeedofCMOScircuitshasmadethemviablecandidatesforGbitrateda22,3tacommunication.Inthispaper,wereviewtheissuesassociatedw

8、ithfabricatingphoto2diodesinCMOS.SomenewfeaturesofferedbypresentMS/RFCMOSareemployedtoimprovetheperform2anceofsuchphoto2diodes.Thefront2endcircuitsoffibercommunicationsareintegratedwiththisnovelphoto2diode,includingTIAs(trans2imped2anceamplifiers)andLAs(limitingamplifiers).2Designofphoto2diodesinMS/

9、RFCMOSFabricatingahighperformancephoto2diodeinCMOSisregardedasthebottleneckinrealizingamonolithicallyintegratedreceiver,becausethedesigntechniqueofsuchanoptoelectronicdeviceisrestrictedtoanarrowspacenotonlybytheop2ticalpropertiesofthematerialbutalsobythetechnologyprocess.Fortunately,CMOSprocesses3Pr

10、ojectsupportedbytheNationalHighTechnologyResearchandDevelopmentProgramofChina(Nos.2002AA312240,2003AA312040)andtheNationalNaturalScienceFoundationofChina(No.60536030)󰂍Correspondingauthor.Email:gaopengReceived12October2005,revisedmanuscriptreceived31October20052006ChineseInstituteofElectronic

11、s© 1994-2006 China Academic Journal Electronic Publishing House. All rights reserved. 324半導(dǎo)體學報第27卷themselvesarecontinuallyprogressing.Manynewfeatureshavebeenaddedtothebasicprocessinordertoexpandtheavailablefunctions.Theycanalsobetakenadvantageofinthedesignofphoto2diodes.Inthissection,weframethe

12、problembydescribingimportantfeaturesofthesiliconmate2rialsandsemiconductorprocesstechnologiesastheyrelatetotheproblemofrealizingphoto2di2odes.Theopticalpropertiesofsiliconarewellknown.Inparticular,theabsorptioncoefficient()withagradualonsetowingtosiliconsindi2rectbandgapstructureisofprimaryimportanc

13、e.Incontrast,theabsorptiononsetsofdirectbandgapmaterialsaremoreabrupt.Thisunique)tovaryfeaturecausestheabsorptionlength(1/significantlywithwavelength,andtobemuchlar2gerthanthatofdirectbandgapmaterialsforwavelengthsinthevicinityofthebandgap.photonabsorptionprocesscreates2pairsinthebulksilicon;neinare

14、gionofftdif2fuseintothentotheoutputphoto2current.Ot,theywilleventuallyre2combineintheabsenceofanelectricfield.Com2paredwiththefield2aideddriftcomponent,diffu2sion2basedcarriersaretransportedatamuchslo2wervelocity,whichwillsignificantlyaffectthetime2responseofthephoto2diode.Thebasicphoto2diodeisasimp

15、lepnjunctionwithadepletionregionwidthW.Foranincidentopticalpower(Popt),thephoto2generatedcurrent(Ig)isrelatedtotheresponsivity(R)by(1)Ig=RPoptR=thanthejunctiondepththatcanbeachievedinanormalCMOSprocess.Therefore,thediffusivecomponentwillcontributealargeparttothepho2to2generatedcurrentandwillconseque

16、ntlyintro2duceanundesiredeffectonthetime2responseofthephoto2diode.2.1Doublephoto2diodeinCMOSAsmentionedabove,ifthegeneratedcurrentpurelycontaineddriftingcarriers,abettertime2responsewouldbeattained.Butunfortunately,CMOSprocessesarespecializedforthefabrica2tionofelectriccircuits.Thesource/drainimplan

17、tprocessweusuallyusetomakethephoto2diodecanonlyformadepletionwithadepthofm,foritshighlevelofabout1016about5-3cm.Theore,willbeinevi2tabyheortingofthedif2inthebulksilicon.Meth2fngthespeedofCMOScompatiblepo2diodesfocusonhowtoeliminatethesedif2fusivecarriers.Suchamethodisillustratedin4Fig11.Fig.1Crossse

18、ctionofinterdigitatedphoto2diode=Popthc-d-W(2)=(1-Pref)e(3)1-1+Lwhereistheexternalquantumefficiency,andListheminoritycarrierdiffusionlengthinthere2gionwitharelativelylowdopingrate.Asde2scribedinEqs.(13),Land1/arecharacteris2ticlengthsassociatedwithphoto2generatedcarri2ers.ForWontheorderof1/,mostphot

19、o2gener2atedcarriersarecollectedbytheelectricfield,andthediffusivecomponentcanbeignored.Withthecarriersdriftingwiththeaidofthefield,thephoto2diodecanoperateataveryhighspeed.Un2mfortunately,theabsorptionlengthisabout14forawavelengthof850nm,whichismuchdeeperAsshowninFig.1,aphoto2diodeisimple2mentedina

20、processidenticaltotheformationofa+p2typeMOSFET.Apregionwithaninterdigita2tedlateralstructureisdesignedastheanodeofthephoto2diode,whichisoriginallyimplantedtoformthesourceanddrainoftheMOSFET.Anin2terdigitatedstructureisemployedtobroadenthedepletionregion,andmakesasmanyofthephoto2generatedcarriersaspo

21、ssibledrifting.Anotherdi2odeformedbyann2wellandp2substratealsoplaysanimportantroleinthisstructure.Calledascreeningdiode,thisdiodeprohibitsthediffusivecarriersgeneratedinthebulkfromcontributingtothetotalgeneratedcurrent.Thiskindofscreeningschemeobviouslytradesresponsivityforspeed,becausealargepartofp

22、hoto2generatedcarriershavebeendiscarded.Fortunately,thede2generationofresponsivityisnotaseriousprobleminLANandVSRapplications,wherethepower© 1994-2006 China Academic Journal Electronic Publishing House. All rights reserved. 第2期ChenHongdaetal.:MonolithicallyIntegratedOptoelectronicReceivers325fa

23、deinthefiberismuchlessthaninlong2haultransmissionapplications.2.2Novelphoto2diodeimplementedinMS/RFCMOSvariationinthen2wellwillincreasethephoto2di2odecapacitance,whichmaydegeneratetheband2widthofthereceivercircuit.ThankstotherapiddevelopmentofCMOStechnology,wehavemanynewwaystoinventnewphoto2diodes.H

24、avingbeenpredominantindigitalcircuitfabricationformanyyears,CMOSprocessesareattractingmoreandmoreattentionintheareaofMS/RFcircuits.Thedeep2n2wellisaddedtomitigatetheinfluenceofswitchingnoisegeneratedbydigitalcircuitsonthefriableanalogorRFpartonthesamechip.InconjunctionwithnewlydevelopedSTI(shallowtr

25、enchisolation)technology,thisnewfeaturecansignificantlyim2provetheperformanceofCMOS2compatiblepho2to2diodes.OneexampleofnovelstructuresbasedonMS/RFCMOSisgiveninFig.2,whereatrationalDPD(doublephoto2diode)isanSTIcircleandthenia23ReceivercircuitdesignThefront2endofanopticalreceivercircuitu2suallyconsis

26、tsofaTIAandanLA.Aregulatedcascode(RGC)configurationisemployedtorealizetheTIA.IthasbeenprovedthatRGCcanmoreeffectivelyisolatethephoto2diodecapacitancefromthebandwidthdetermina26tionthanotherstructures.AsshowninFig.3(a),M1andM2makeuptheRGCinputstage,significantlyenhancingtheiutgm,andconse2quentlypulli

27、ngthepolebythephoto2di2odecapncetmpedanceoutofTheorRfisappliedft(M4)tothedrainofM1,booststheoutputgmbutalsoeffi2ntlybuffersthecurrentattheinput.Fig.2Crosssectionofnovelphoto2diodeinMS/RFCMOSComparedwithconventionalDPDs,thisno2velstructurehasimprovementsinmanyas25pects.(1)Darkcurrent:Somedarkcurrenti

28、sinevi2tablebecauseitisimpossibletogetaperfectlyde2fect2freesiliconsubstrate.However,thedarkcur2rentcanbemitigatedbyisolatingthelaterallydif2fusiverandomcarriers.ThroughtheuseofSTIandthedeep2n2well,themagnitudeofthedarkcurrentisonlyabout1/5ofthatinDPDswithoutthesenewfeatures.(2)Responsivity:Poorresp

29、onsivityhasbeenregardedasthemainshortcomingofDPDs.ItcanbeenhancedwhenanSTIwallisintroduced,sincethephoto2generatedcarriersarerestrictedinsidethecircle,wheretheycanbeefficientlyused.Theexperimenthasshownthattheresponsivityofthenovelstructureis0.066A/W,comparedtoonly501017A/WinconventionalDPDs.Ontheot

30、herhand,theconcentrationindexFig.3(a)SchematicdiagramofanRGCTIA;(b)SchematicdiagramofonestageofanLATheLAconsistsofaninputstage,again2stageandanoutputbuffer.Thegainstageiscom2posedof6seriallyconnecteddifferentialampli2© 1994-2006 China Academic Journal Electronic Publishing House. All rights res

31、erved. 326半導(dǎo)體學報第27卷fiers,oneofwhichisgiveninFig.3(b).Allthesedifferentialamplifiersareloadedbyactiveinduc2torsconsistingofann2MOSFEToperatinginsatu2rationplusagateresistor,inordertobroadenthebandwidth.bandwidthhasbeenachieved.Thedegenerationofthebandwidthcanbeattributedtotheincre2mentofthephoto2diod

32、ecapacitance.MoreeffortshouldbedevotedtothedesignoftheTIAcircuitinfuturework.4Chipdesignandmeasurementre2sultsAmonolithicallyintegratedoptoelectronicmMS/RFreceiverisimplementedinTSMC0.25CMOStechnology.AchipphotographisshowninFig.4.Thephoto2diodeisdesignedwithanoctag2onallateralconfiguration,whichint

33、roduceslesscapacitancethanasquareone.Fig.6FrequencyoftheOEICwouldliketothankProf.LiZhiqun,andXueZha2InstituteofRF&OEIC,SoutheastUni2fortheirsupportinthisproject.ReferencesFig.4Amonolitintegratedoptoelectronicre2ceiver1ChoiJ,SheuBJ,ChenOTC.AmonolithicGaAsreceiverforopticalinterconnectsystems.IEEE

34、JSolid2StateCircuits,1994,29(3):3282ZimmermannH.Integratedhigh2speed,high2sensitivitypho2todiodesandoptoelectronicintegratedcircuits.SensorsandMaterials,2001,13(4):1893WoodwardTK,KrishnamoorthyAV.1Gbit/sCMOSphoto2receiverwithintegrateddetectoroperatingat850nm.Elec2tronLett,1998,34(12):12524MaoLuhong

35、,ChenHongda,WuRonghan,etal.SimulationanddesignofaCMOS2process2compatiblehigh2speedSi2pho2todetector.ChineseJournalofSemiconductors,2002,23(2):193(inChinese)毛陸虹,陳弘達,吳榮漢,等.與CMOS工藝TheOEICwastestedwithasinusoidalmodu2latedopticalinputwithanincidentpowerofWatawavelengthof850nm.Themeasured600transientresp

36、onseisshowninFig.5.Anampli2tudeofnearly20mVisachievedattheoutputoftheOEIC,whichmeansthatatrans2impedanceofisattainedbythefront2endcir2about56dBcuits.兼容的硅高速光電探測器的模擬與設(shè)計.半導(dǎo)體學報,2002,23(2):1935HuangJiale,MaoLuhong,ChenHongda,etal.ResearchofCMOS2process2compatiblephotodetector.ChineseJournalofSemiconductors,2005,26(10):1995(inC