1/Process/ManufacturingElectronicsfollowcurvesPosted:03Nov2008Inelectronics,rigidandflatisnormal.Intherealworld,notsomuch.Therearemanyapplicationsinwhichitwouldbeusefulforelectronicstoconformtocurvilinearsurfacesortodeformwithuse,especiallyinsensing.Adetectorarraycouldbemadetoencircletheheart,stretchingwitheachbeat.Anartificialskincouldbestretchedaroundthewingofanaircraft,relayingdetailedlocalinformationwhileinflight.Anartificialretinacouldfitinthecurvedspaceatthebackoftheeyelikethebiologicalsensoritreplaced.Thusfar,however,flexibletechnologieshavelackedtheperformance,manufacturabilityor,well,theflexibilitytomakesuchapplicationsfeasible.ButanewtechnologydemonstratedattheUniversityofIllinoisatUrbana-Champaign(UIUC)maybeabletofillthisnicheonethatiscertaintowidenonceengineersareallowedtothinkbeyondflatandrigid.Thenewcircuitsaredesignedtohavelong,thininterconnects,fabricatedusingstandardsemiconductors(silicon,galliumarsenideandsoon)andconventionaltechniques,andthentransferredontoastretchedelasticsheet.Oncethesubstrateisrelaxed,theinterconnectswhicharethinenoughtobendwithoutbreakingbuckleunderthestrain.Ifdesignedcorrectly,theycanthenbucklefurtherifcompressedorflattenifstretched.Thus,anelasticcircuitfabriccanbecreatedusingmore-or-lessordinaryelectronics.Alternatively,theelasticfabriccanbeusedtoformtheelectronicsinto3Dshapesthatcanbetransferredontoarigidsubstrate.ThisishowtheUIUCteamwasabletocreatethefirsthemisphericalsiliconcamera.BiggestbenefitWhetherflexibilityorshapeisthegoal,theapproachhastheadvantageofleveragingconventionalmicrolithographyandsemiconductorprocessing.John2Rogers,wholedtheUIUCresearch,hassetupSempriusInc.tocommercializethetechnology.Themostimportantadvantage,Rogerssaid,isthatweuseknown,establishedmaterialsandprocessingtechniquestoachievelevelsofperformanceinthecircuitsashighascomparablydesignedwafer-basedsystems,butwithlevelsofstretchabilityapproachingthatofarubberbandupto100percentstrainsandevenlarger.Anassociatedadvantageisthatwecanfullyexploitallexistingelectronicsknowledgeandfabricationfacilities.BobReuss,anindependentconsultantandformerDARPAprogrammanagerandMotorolaseniortechnologist,alsosuggeststhetechnologywill,attheveryleast,findaniche.Toachieveconformaland/orflexibleelectronicswithatleastmoderatefunctionality,Ibelievethetechnologywillbevaluable,ifnotessential.Sosuccesswillmeancreationofanewmarketsegment,hesaid.Further,headded,ElasticSisinmyopinionanexampleofmorethanMoore.ItisnotontheInternationalTechnologyRoadmapforSemiconductorsandperhapsneverwillbe.Rather,itisoneofavarietyoftechnologiesbeingcreatedeithertomoreeffectivelyutilizeICtechnologyforapplicationsbeyondcomputingandcommunications,ortoactuallyreplacetheexistingICinfrastructurewherecostandformfactorarenotcompetitivefortheintendedapplication.ElasticisnotplasticsThebest-knownwaytocreateflexibleelectronicsistoprintcircuitsdirectlyontocarbon-basedplastics.Onetargetapplicationforthistechnologyistheelectronicnewspaper,whichisintheprocessofbeingrealizedcommercially.Althoughthetechnologyismaturing,ithasinherentproblems:Itreliesonorganicmaterialsthathavemuchpoorerelectronicperformancethansemiconductors.Worse,thedevelopmentofthesematerialsdoesnotcomefreeasabyproductofprogressintheelectronicsindustry.Finally,althoughthesematerialsareflexible,theyarenotelastic:Theybend,buttheydontstretch.Anotherapproachistofabricateconventionalchipsandthenthinthewaferstomakethemlighterandlessrigid.Again,stretchingisnotanoption,andevenbendingabilityislimited.Yetanotheroptionistoattachsmallchips3toanelasticsurfaceandcreatewirestoconnectthemafterthefact.Thoughthisoffersbothperformanceandmechanicalflexibility,therearemanynon-conventional(and,therefore,expensive)fabricationstepsinvolved.ThinisflexibleTheUIUCapproachdependsonthefactthatsilicon,GaAsandothersemiconductorsallbasicallybrittlebecomeflexiblewhendepositedinverythinlayers.MaxLagally,amaterialsscienceandengineeringprofessorattheUniversityofWisconsin-Madison,worksintheareaofnanostructuresforelectronics,amongotherthings.Thin,flexibleSiandothersemiconductors,includingGehastremendouspotential,hesaid.Thereistheflexibility,theabilitytotakeadvantageofthethirddimension.Onecanalsostrainthemandthustakeadvantageofbetterelectronicpropertiesonecanstackthemetc.TheUIUCapproach,infact,takeslittleadvantageoftheseproperties,asthecarrieriswhatisflexible,Lagallysaid.Thisisincontrasttoresearcherscreatingfarmoresophisticatedmicro-andnano-mechanicaldevicesbyengineeringthestraininfabricatedlayersso,whenreleased,theyformcomplexthree-dimensionalstructures.Rather,heexplained,thegroupsmostimportantachievement,isthetransfertechnologytheabilitytotransferthesiliconpiecesandconnecttheminsuchawaythattheyendupinthehemisphericalpattern.Itisreallythefirstexampleofahemisphericalphotodetectorinsilicon.However,accordingtoRogers,theUIUCteamwithcolleaguesatNorthwesternUniversityandelsewherehasalsomadeanimportantcontributiontotheunderstandingofmechanicsinsilicon.Thebucklingmechanicsandthemodesofdeformationpushintotheforefrontoftheoreticalmechanics,Rogerssaid.Infact,ourverycarefulexperimentalstudiesofelasticsiliconrevealedaflawedassumptionineverypreviousknowntheoreticaltreatmentofbucklinginstiffmaterialsoncompliantsubstrates.Further,heseesthefutureofelectronicsastakingmechanicsintoaccount.Ithinkthesekindsofsystemsbringmechanicaldesigntotheforefrontofsystemdefinition,atalevelthatmightbeasimportantascircuitdesign,hesaid.Weenvision,infact,akindofmechanicsequivalenttoPspicethatcouldaidinthelayoutofacircuitforoptimalperformanceinanelasticconfiguration.Acombinedmechanics/electronicsdesigntoolmightbe4theultimate.Weworkcloselywiththeoreticalmechaniciansandanalogcircuitdesignerstopursuethistypeofoutcome.PotentialapplicationThereisanentire,untappedworldofapplicationsforelectronicsthatdemandpropertiesunachievablewithconventionaltechnologiesbasedonsemiconductorwafers,Rogerssaid.Themostprominentexamplesfallintotwocategories:bio-inspireddevicesandbiomedicaldevices.Bothrelyonsystemsthathavethelayoutsofbiologicalsystems,noneofwhichhavetherigid,planarnatureofasemiconductorwafer.Inthebiomedicalarea,Rogerssaid,Weareworkingonelectronicsensorpatchesthatconformallyintegratewiththecomplex,curvilinearsurfaceofthehumanbrain.Ourgoal,incollaborationswithProfessorBrianLittinthemedicalschoolatUniversityofPennsylvania,istoprovideasystemthatcandetecttheonsetofaseizureinapersonwhosuffersfromepilepsy,beforetheseizureactuallyoccurs.Thetechnologyhasagoodchanceofsucceedingintheseareas,concursReuss,whobelievesitwillprovelucrativeforinvestors.Whethertoaugment,replaceormonitorbiologicalfunction,flexible/stretchableelectronicswillbeneededtoeffectivelyandcomfortablyachievehumaninterface,hesaid.Giventheagi