29-Microwave-Dielectric-Properties-of-Li2WO4-Ceram

MicrowaveDielectricPropertiesofLi2WO4CeramicwithUltra-LowSinteringTemperatureDiZhou,w,z,yCliveA.Randall,yLi-XiaPang,zHongWang,zJingGuo,zGao-QunZhang,zXin-GuangWu,zLiShui,zandXiYaozzElectronicMaterialsResearchLaboratory,KeyLaboratoryoftheMinistryofEducation,Xi’anJiaotongUniversity,Xi’an710049,ChinayCenterforDielectricStudies,MaterialsResearchInstitute,ThePennsylvaniaStateUniversity,UniversityPark,Pennsylvania16802zMicro-optoelectronicSystemsLaboratories,Xi’anTechnologicalUniversity,Xi’an710032,ChinaAnewultra-low-temperaturefiringmicrowavedielectricceramic,Li2WO4withthephenacitestructure,waspreparedviasolid-statereactionmethod.TheLi2WO4ceramiccanbewellsinteredat6401–6601C,withamicrowaverelativepermit-tivityB5.5,aQfvalueabout62000GHz,andanegativetemperaturecoefficientof146ppm/1Cat15.7GHz.FromanX-raydiffractionanalysis,theLi2WO4ceramicwasfoundtobechemicallycompatiblewithbothsilverandaluminumpowdersat6401C.AlltheresultsindicatethattheLi2WO4ceramicisapromisingcandidateforultra-lowtemperaturecofiredceramictechnology,especiallyfordielectricsubstrateapplication.I.IntroductionLOW-temperaturecofiredceramic(LTCC)technologyplaysanimportantroleinthemodernmicrowavecircuitfabrica-tionandintegrationduetothecofiringbetweenactivelayers,electrodesandsubstrates.ManymicrowavedielectricceramicshavebeendevelopedforuseintheLTCCfieldinthepastde-cadeswithlowmeltingpointoxideandfluorideglassestopro-videsinteringtemperaturesdesignedforcofiringwithanelectrodeofAg(9611C).1,2About10yearsago,anumberofresearchersmovedtheirattentiontoobtainingmicrowavedi-electricceramicswithintrinsiclowfiringtemperatures.3TherearemanygoodexamplesinTeO2-rich,Bi2O3-rich,andMoO3-richsystems.4–9Themicrowavedielectricceramicsthatcanbedensifiedatultra-lowtemperatures(usuallybelowthemeltingpointofAl6601C)arecalledultra-lowfiringceramics(ULTCC).Ifachemicallycompatibleelectrodecanbefound,theso-calledULTCCtechnologycanbeachieved.Thesearchfornewultra-lowfiringmicrowavedielectricceramicshasat-tractedmoreandmoreattention.Inourpreviouswork,10aseriesofcompoundsintheLi2O–Bi2O3–MoO3ternarysystemswerereportedtopossessgoodmicrowavedielectricpropertiesandultra-lowfiringtemperature.Amongalltheceramicsinthatwork,Li2MoO4ceramichasthelowestsinteringtemperatures,about5401C(toourknowledgeitisthelowestsinteringtemperaturereportedintheliteratureformicrowavedielectricceramics),witharelativepermittivityB5.5,aQfvalueof46000GHz,andatemperaturecoefficientofresonantfrequency(TCF)B160ppm/1Cat13GHz.Inthiswork,thesinteringbehavior,microwavedielectricproperties,andchemicalcompatibilitywithAgandAlofLi2WO4ceramicareintroducedasnewULTCCmaterials.II.ExperimentalProcedureTheLi2WO4compositionwerepreparedbymixed-oxideap-proachusingproportionateamountsofreagent-gradestartingmaterialsofLi2CO3andWO3(499%,AlfaAesar,WardHill,MA).Powdersweremixedandballmilledwithstabilizedzir-coniamedia(TosohCeramics,Tokyo,Japan)for24h.Thepowdermixturewasthencalcinedat5001Cfor4h.Thecalcinedpowderswerevibratorymilledfor24htoincreasereactivityandbetterhomogeneityandthengranulatedwith2–5wt%acryloidpolymerbinder(acrylicresin,RohmandHassCo.,Philadel-phia,PA),pulverized,andsievedthroughameshscreenwith180mmopenings.Thenthepowderswerepressedintocylinders(12mmindiameterand6mminheight)inasteeldieunderauniaxialpressureof200MPa.Afterdebinding,thesamplesweresinteredatvarioustemperaturesrangingfrom5801to6601Cfor2hundertheairatmosphere.Toinvestigatethechemicalcom-patibilityofthesecompoundswithelectrodemetalpowders,20wt%Agand20wt%Alweremixedwiththedifferentcom-poundsandheldatthesinteringtemperaturesfor4h.PhasedeterminationwasmadeusinganX-raydiffraction(XRD)(ScintagPADVandX2diffractometers,ScintagInc.,Cupertino,CA)withCuKaradiation(l51.54A˚).Beforeexamination,sinteredpelletswerecrushedinamortarandpestletopowder.TheapparentdensitiesofsinteredceramicsweremeasuredbyArchimedes’method.Microstructuresofcofiredceramicswereobservedonthefracturesurfacewithscanningelectronmicroscopy(SEM)(HitachiS-3000H,HitachiHigh-TechnologiesCo.,Tokyo,Japan).Thedielectricpropertiesweremeasuredatmicrowavefre-quencybythepostresonatormethod,assuggestedbyHakkiandColeman,11withanetworkanalyzer(HP8510NetworkAna-lyzer,Agilent,Hewlett-Packard,Loveland,CO).TheTCFwasdeterminedusingazerothermalexpansioncavitywithpro-grammabletemperaturechamber(Delta9023,DeltaDesign,M.Valant—contributingeditorThisworkwasfinanciallysupportedbytheNational973-projectofChina(2009CB623302),NationalProjectofInternationalScienceandTechnologyCollaboration(2009DFA51820)andNSFCprojectsofChina(109790365,60871044,and50835007).TheNationalScienceFoundationI/UCRCprogram,aspartoftheCenterforDielectricStudiesunderGrantNo.0628817,forpartialsupport.wAuthortowhomcorrespondenceshouldbeaddressed.e-mail:[e-mail]18,2010;approvedNovember2,2010.JournalJ.Am.Ceram.Soc.,94[2]348–350(2011)DOI:10.1111/j.1551-2916.2010.04312.xr2011TheAmericanCeramicSociety348Poway,CA)inthetemperaturerangeof251–851C.TheTCFwascalculatedbythefollowingformula:tf¼f85f25f25ð8525Þ106(1)wheref85andf25weretheTE01