An approach for embedding high-K dielectric thin films into polymer packages has been developed. Pb{sub 0.85}La{sub 0.15}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.96}O{sub 3} thin films were prepared by chemical solution deposition on 50 {micro}m thick Ni-coated Cu foils. Sputter deposited Ni top electrodes completed the all base-metal capacitor stack. After high temperature N{sub 2} crystallization anneals, the PLZT composition showed reduction resistance while the base-metal foils remained flexible. Capacitance density and Loss tangent values range between 300 and 400 nF/cm{sup 2} and 0.01 and 0.02 from 1 to 1,000 kHz respectively. These properties represent a 2 to 3 order of magnitude improvement over available embedded capacitor technologies for polymeric packages

Cheek, K.

Dunn, G.

Kim, S. H.

Kingon, A. I.

Maria, J. P.

Streiffer, S. K.

UNT Digital Library

LEAD ZIRCONATE TITANATE ON BASE METAL FOILS: AN APPROACHFOR EMBEDDED HIGH-K PASSIVE COMPONENTS*J-P. Marial, Kevin Cheekl, S. K. Streiffe#, S-H. Kiml, G. Dunn3, and A.I. KingonllDepartment of Materials Science&EngineeringNorth Carolina State University “Raleigh, NC 27695-79192Argonne National Laboratory +Materials Science Division‘@9700 S. Cass Ave.o%4 *>Argonne, IL 60439-4838 Q G’> ~~3Motorola Materials Research Laboratory “q’ @@ @)Corporate Manufacturing CenterSchaumburg,, IL 60196$9Januarv 2000mGovernment retains for itself. and othersdacting on its behalf, a paid-up, nonexclusive, irrevomble worldwide license inworks, dmnbute mpm to the pbhc. andpa-formpublicly and display publicly,by or-.This paper was submitted to the US-Japan Seminar on Dielectric and Piezoelectric Ceramics,Okinawa, Japan, held on November 3-5, 1999.*we wish to ac~owledge support from the U. S. Department of Energy, BES-MaterialsSciences, under Contract W-31 -109-ENG-38.tLead Zirconate Titanate thin films on base-metal foils: An approach for embeddedhigh-K passive componentsJ-P. Maria, Kevin Cheek, S. K. Streiffer, S-H. Kim, G. Dunn$, and A. I. KingonNorthCarolinaStateUniversity,Departmentof MaterialsScienceandEngineering,Raleigh,NC27695,fax:011-919-515-5055,emsil: jpmaxia@unity.ncsu.eduMaterialsScienceDivision,‘ArgonneNationrdLaboratory,Argonne,IL 60439.fax 011-630-252-4289,email:streiffer@anl.gov‘MotorolaAdvancedTechnologyCenter,Shaumburg,IL 60196,fax:011-847-576-2111,email:AGDO10@lmpsi102.comm.mot.comABSTRACTAn approach for embedding high-Kdielectric thin films into polymer packages has beendeveloped. Pb0.g5L%.ls(fiOszTb.M)0.gsOsthin filmswere prepared by chemical solution deposition on50 pm thick Ni-coated Cu foils. Sputter depositedNi top electrodes completed the all base-metalcapacitor stack. After high temperature N2crystallization anneals, the PLZT compositionshowed reduction resistance while the base-metalfoils remained flexible. Capacitance density andLoss tangent values range between 300 and 400nF/cm2 and 0.01 and 0.02 from 1 to 1000 kHzrespectively. These properties represent a 2 to 3order of magnitude improvement over availableembedded capacitor technologies for polymericpackages.lINTRODUCTIONEmbedding thin film high-permittivitydielectrics into low temperature processed polymerpackages offers advantages in electronicsminiaturization and manufacturing cost reduction.Miniaturization potential stems from replacement ofsurface mount components and the subsequentreduction of the required wiring board real estate.Cost reductions are associated with the ability toproduce packaging substrates with capacitiveJayerspre-embedded. Such layers remove the need forpick-and-place assembly operations which cancomprise an appreciable fraction of themanufacturing cost.1 Photolithographic methodscoupled with etching and metallization steps canconceivably be used synthesize the necessarycombinations of capacitive elements andinterconnects rapidly and in large quantity.We present here a strategy to produce highpermittivity capacitive layers compatible with lowtemperature processed polymer packages. To avoidtraditional temperature limitations, all hightemperature processing steps required by the oxidedielectric would be performed prior to theembedding process. This goal was achieved throughfilm deposition onto metal foils which could besubsequently embedded using standard laminationmethods. Unlike other commonly used substrates,metal foils are thin enough as not to add appreciablethickness to the subsequent package. Such metalfoils are, however, thick enough to support the brittleas deposited oxides. In this study, composite basemetal foils (comprised of 50 pm Cu coated with 4pm of electroless Ni) were used as the carriersubstrates to minimize cost. This work followsseveral previous investigations of high-K films onmetal foils, and/or with base-metal electrodes.2-7La-doped Pb(Zr,Ti)03 was used as the highpermittivity dielectric. The La doping drives theCurie transition below room temperature leaving alarge K and non-hysteretic electrical properties. Thiscomposition is tolerant of the non-stoichiometryexpected after processing in the inert atmospheresrequired to preserve the base metal foil. Resultingoxygen vacancy populations can be ionicallycompensated by controlled Pb-deficiency.EXPERIMENTAL PROCEDURE50 pm thick Cu-foil substrates (0.5 oz.gage) were obtained from Motorola. 4 pm ofautocatalytic (i.e., electroless) NI (abbreviated as e-Ni) was deposited on each side of the metal foil byMacDermid Inc. from a NiC12- Na(HzPQ)” solutionbath. The foils were obtained in 12 “ x 14” sheets.Sections of foil 2.5 cm x 5 cm were cut from thelarge sheets and used as the standard substrate size.Prior to depositions, the foils were cleaned by rinsingin acetone and isopropanol. AFM surface imaging ofthe as-received foils revealed - 2pm rms roughness,with 1-3 pm diameter e-Nl clusters.PLZT was prepared by chemical solutiondeposition. The precursor solution was methanol-based, incorporating lead acetate trihydrate, titaniumisopropoxide, lanthanum isopropoxide, andzirconium N-butoxide chemical sources.8 After spin-on deposition, the films were dried on a hot plate at250 “C for 5 rein, then pyrolyzed in air @ 450 “C(tube furnace) for 10 minutes. This procedure wasDISCLAIMERThis report was prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.,repeated 6 times to achieve the desired thickness of-6000 ~. After deposition, drying, and pyrolysis,the films were crystallized in an N2 tube furnace at600 “C for 30 minutes. Capacitor structures werecompleted by ion beam deposition of Pt or Ni topelectrodes.The film surface topography, crystallinity,and microstructure, were characterized using atomicforce microscopy, X-ray diffraction, andtransmission electron microscopy. Frequency andelectric field dependent dielectric properties weremeasured using an HP 4192A impedance analyzer.0.1OurnRESULTS AND DISCUSSIONFig. 1 shows an 0-2e x-ray diffractionpattern respective of thin film PLZT samplesdeposited on e-Nl substrates under the optimizedprocessing conditions. As seen in the figure, peaksare present from Ni, Cu, Ni~P,and PLZT. Under theoptimal processing conditions, no evidence is foundsuggesting the presence of pyrochlore crystals. It isalso apparent from the diffraction pattern that thereducing anneal conditions are effective inpreventing oxide formation in the composite basemetal foil. The N13Pphase forms via a precipitationreaction in the as-deposited e-Ni which containsbetween 9 and 11% dissolved phosphorus.g1 ...8....8,. I1000800~“~ 600G40020025 30 35 40 45 50 55213(degrees) -.Fig. 1: (3-20x-ray diffractionpatternof 6 layer (-6000 Athick) PLZT thin film deposited on an e-Nl coated foilsubstrate. In the figure, p = perovskitePLZT, np = Ni3P,andPt refersreflectionsfromR topelectrodes.Of some concern was the large surfaceroughness of the as-received e-Ni surfaces (- 10 xgreater than the dielectric thickness). The largeundulations could potentially lead to shorting orpremature electrical breakdown. AFM analysis wasperformed on the final PLZT thin films, a typicalresult is given in Fig. 2.Fig. 2: Tapping mode AFM image of 6 layer (-6000 Athick) PLZT thin film deposited on an e-Ni coated foilsubstrate.Note that on the scale of this image, the surfaceappears quite smooth. If, however, an image is takenover a larger area (10 pm x 10 pm), the roughness issimilar to that of the e-Ni substrate prior todeposition, i.e., - 2pm rms. This surface topographysuggests a typical lateral grain size between 20 and100 nrn, and relatively conforrnal coverage.In this report, electrical characterization islimited to room temperature measurements. Fig. 3shows a capacitance-voltage curve typical of thePLZT the non-hysteretic response indicates theeffectiveness of La-doping to temperature-shift theferroelectric transition below room temperature.ElectricField(kV/cm)~-E400~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-160 -80 0 80 160 10.05“~ 100~ 0.0,8 -15 -10 -5 0 5 10 15Bias(V)Fig. 3: Voltage dependence of the permittivity anddielectricloss tangent for a 6 layer (-6000A thick) PLZTthin filmdepositedon an e-Nicoatedfoil substrate.Fig. 3 also demonstrates the limited dielectrictunability - the combination of a small grain size andrelatively low-temperature processing likelycontributes to this condition. (The lack of tunabilityis desired for the targeted applications.).0.120.100.080.060.040.020.00iiiw4: Frequency dependence of the permittivity-anddielectric loss tangent for a 6 layer (-6000A thick)PLZTthin filmdepositi- on an e-Ni coatedCu foil substrate.Fig, 4 gives the frequency dependence of thepermittivity and loss tangent for a typical PLZTsample. In Flg.4, 10 curves aregiven and indicatethe degree of variability among test capacitorstructures. Typically, the yield of functionalcapacitors (500 pm diameter circles defined with ashadow mask) is -80 %. This data is presented ascapacitance/unit area since these units can be readilycompared to other capacitor technologies. (Theaverage dielectric constant at 10 kHz was 240.) Thedielectric constant was found to drop approximately1 % per decade.One likely influence producing therelatively low dielectric constant of this PLZT (whencompared to bulk values exceeding 10,000)10 is theformation of a Iow-permittivity layer at the PLZT /e-Ni interface. Cross-sectional TEM images weretaken to investigate this possibility, Fig. 5 gives theresult. In this image an interracial layer between 35and 40 nm in thickness becomes appment.-.Fig. 5: Cross-sectional TEM image of a foil-basedcapacitor detailing the dielectric layers and interfaceformationbehveenPLZTande-Nlbottomelectrode.At this point it remains unclear as to theexact composition of this layer. However, the size ofthe structural features is on the order of those foundin the PLZT and peaks from CU02 or NIO were notseen in xrd scans. These results suggest that theregion may be comprised of reacted or poorlycrystallized PLZT. Though this layer is present inthe as-deposited films, with the exception of areduced total permittivity, it appears not to stronglyinfluence the frequency dependent electricalproperties. As such, structures containing theseinterface layers may be appropriate for a functionaldevice application in the frequency rangeinvestigated. The influence of these interfaces maybecome more important if applications are gearedtowards microwave frequencies.Foil samples were qualitatively tested afterdeposition to roughly determine handle-ability. Ingeneral, the foils could be repeatedly wrapped around3 cm diameter mandrels without cracking ordelamination. This type of resilience is important asit will facilitate handling and storage on rolls.Moreover, it suggests that these structures willsurvive the potentially ag~essive conditions requiredfor lamination into polymer packages.CONCLUSIONS.A method has been developed whichproduces high-K capacitors on base-metal foilsubstrates suitable for embedding into polymer-based printed wiring boards. Depositing thedielectric on e-Nl coated Cu foils allows all hightemperature processing steps necessary for structureand property development to be isolated from thetemperature sensitive organic-based packages. Thehigh-permittivity layers were produced by chemicalsolution deposition. The specific startingcomposition and firing temperatures were chosensuch that high-quality material could be achieveddespite the reducing Nz atmospheres used duringcrystallization anneals. Shadow mask definedcapacitors (Ni or Pt metal) typically exhibitedpermittivities and loss tangents of 240 and <0.017in the frequency range between 0.1 and 100 kHz.Dispersion was” limited to approximately 1% /decade in this range. Transmission electronmicroscopy revealed the presence of a - 35 nminterface layer between the PLZT and e-Nl substrate.This layer and its effects on film properties is undercontinued investigation. Even with the existence ofthis interface region, the electrical properties appearto be appropriate for capacitor applications.ACKNOWLEDGEMENTSThe authors would like to acknowledge thesupport of DARPA/Wright Lab Cooperativeagreement F33615-96-2-1838 “Low Cost MixedSignal Modules Using Embedded Mass FormedPassives”.REFERENCES1 Personal communication, Greg Dunn, MotorolaCorporate Manufacturing Research Center (1999).2 K. B. Lee, B. R. Rhee, and S. K. Cho, Mat. Res.Sot. Symp. Proc. 433,181-186 (1996).3 S. A. Myers and E. R. Myers, Mat. Res. JSQC.Symp. Proc., 107-112 (1992).4 T. Ogawa, S. Shindou, A. Sends, and T.Kasanami, Mat. Res. Sot. Symp. Proc., 93-99(1992).5 T. Ogawa, S. Saitoh, O. Sugiyarna, A. Kondoh, T.Mochizuka, and H. Masuda, Proc. 9th Int. Symp.Application of Ferroelectrics, 399-403 (1994).6 T. Ogawa, N. Ujie, and K. Hukuta, Proc. 10th Int.Symp. Application of Ferroelectrics, 459-462(1996).7 K. Saegusa, Jpn. J. Appl. Phys. 30 Pt. 1 (11),6888-6893 (1997).8 S.-H. Kim, D.-J. Kim, J. Hong, S. K. Streiffer, andA. I. Kingon, J. Mater. Res. 14 (4), 1371-1377(1999).9 J. K. Dennis and T. E. Such, Nickel and chromiumplating, Thiid ed. (ASM International, The MaterialsInformation Society, Materials Park, OH, 1993).10 B. Jaffe, W. R. COOIGand H. Jaffe, PiezoelectricCeramics (R. A. N. Publishers, Marietta, OH, 1971).

Lead zirconate titanate on base metal foils: An approach for embedded high-K passive components

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Lead zirconate titanate on base metal foils: An approach for embedded high-K passive components

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