Binder, J.R.

Hausselt, J.

Jakoby, R.

Kohler, C.

Sazegar, M.

Stemme, F.

Zhou, X.

English

Binder, J. R.

KITopen

Institute for Applied Materials – Materials Process Technology (IAM-WPT)1 KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association www.kit.eduThe effect of ZnO-B2O3 addition on thedielectric properties and microstructure of screen-printed low-sintered BST thick filmsC. Kohler, X. Zhou, M. Sazegar,R. Jakoby, F. Stemme, J. Hausselt, J.R. BinderInstitute for Applied Materials – Materials Process Technology (IAM-WPT)Electronic Materials and Applications 2012, Orlando, FloridaInstitute for Applied Materials – Materials Process Technology (IAM-WPT)2MotivationTunable capacitors (varactors) are essential elements of tunablemicrowave components23.01.2012 Christian Kohler et al.Institute for Applied Materials – Materials Process Technology (IAM-WPT)3RF components based on BST thick-filmsTunable filter Tunable matching networkCPW basedphase shifterLeft-handedphase shifterPhase shifterMultiband antenna RF-ID modulatorAntennaµCMicrowave Engineering,  Technical University Darmstadthttp://www.mwe.tu-darmstadt.de/de/fachgebiete/mikrowellentechnik/forschung/ferroelectrics/ferroelectrics.htmlChristian Kohler et al.23.01.2012Institute for Applied Materials – Materials Process Technology (IAM-WPT)4Restrictions of BST thick films• Sintering temperature (~1200°C) not compatible with LTCC technology (Tm of silver = 962°C) Processing of low-fired electrodes (e.g. Ag, Au) after firing of BST thick film  Co-fired MIM devices only possible with high fireable electrodes (e.g. Pt)• Porosity of BST thick films lowered mechanical stability adsorbed water causes extrinsic dielectric loss23.01.2012Additives for: 1.) Lowering sintering temperature2.) Reduction of porosity3.) Adjusting of dielectrical performance (low loss)Christian Kohler et al.Institute for Applied Materials – Materials Process Technology (IAM-WPT)5Requirements Additives• Lowering sintering temperature of BST• No or limited formation of secondary phases• Low permittivity and dielectric loss• Low softening point and wetability23.01.2012SiO2 B2O3 Li2O+++ ++---±-± ±Christian Kohler et al.Focus on  binary borate systemSystem: ZnO – B2O3 1:1(based on Leonov,1958)Institute for Applied Materials – Materials Process Technology (IAM-WPT)6Dilatometry (pellets)Christian Kohler et al.23.01.2012900°C/2hTemperature(C)-0,20-0,15-0,100,00-0, 0540060010008002000ShrinkagedL/L0(%)Temp.BST+30%Time (min)100 200 30001000°C/2h-0,20-0,15-0,100,00-0, 0540060010008002000Temp.Time (min)100 200 3000ZnO/H3BO3 addition in vol.% Densification at lower sintering temperaturesInstitute for Applied Materials – Materials Process Technology (IAM-WPT)7ProcessingSolPrecursorCalcinded powderSpray-dryingCalcination (900°C)Reactants:(Ba / Sr / Co)-AcetatesTi(IV)- Isopropoxidein Acetic acid + water≈ 10 µmPasteAddition of ZnO-H3BO, MillingDispersingThick film (green)Screen-Printing, DryingPowder mixtures Addition of ZnO-H3BO3:5, 10, 20 vol%(1.85, 3.84, 8.24 wt%)Sintering(800 – 1000°C)Thick filmTesting structures/devicesMetallization23.01.2012 Christian Kohler et al.Institute for Applied Materials – Materials Process Technology (IAM-WPT)8 23.01.2012 Christian Kohler et al.Microstructure of thick films800°C 900°C 1000°C5%10%20%Institute for Applied Materials – Materials Process Technology (IAM-WPT)9Thick films – phase content23.01.20122-Theta - Scale15 20 30 40 50 60 70 8020%800°C900°C1000°C2-Theta - Scale15 20 30 40 50 60 70 8010%800°C900°C1000°C Low formation of secondary phases no obvious shift of BST reflexes; Ba/Sr ratio constantChristian Kohler et al.(310)2-Theta - Scale15 20 30 40 50 60 70 805%800°C900°C1000°C(100)(110)(111) (200)(210)(211)(220)* * ****** *(221)(hkl) : BST* : Al2O3 :  Secondary phasesInstitute for Applied Materials – Materials Process Technology (IAM-WPT)10Dielectric characterisation of thick filmsChristian Kohler et al.23.01.2012Analytical modelScattering paramters Sijw = 300 µmg = 10 - 20 µms = 10 µmh2 = 4 - 8 µmPermittivity r(f = 2 - 20 GHz)Dielectric loss tan(f = 2 - 20 GHz)Tunability (E) (E = 0 - 10 V/µm)Processing of Coplanar Wave Guides (CPW)UV lightMaskPhoto resinStart metallizationBSTSubstratePhoto resinStart metallizationBSTSubstrateGoldStart metallizationBSTSubstrateInstitute for Applied Materials – Materials Process Technology (IAM-WPT)11Permittivity23.01.2012 Christian Kohler et al.BST pure (1200°C)20%10%5%800 900 1000100150200250Relative PermittivitySintering temperature ( C)@ 10GHz, 0VPermittivity vs. Sintering temperature5 10 15 20Frequency (GHz)20 vol% additives100150200250800°C900°C1000°CPermittivity vs. FrequencyInstitute for Applied Materials – Materials Process Technology (IAM-WPT)12Dielectric loss23.01.2012Dielectricloss0,040,050,060,07800 900 1000Sintering temperature ( C)20%10%5%BST pure (1200°C)@ 10GHz, 0VDielectric loss vs. Sintering temperatureBST pure (1200°C)5 10 15 20Frequency (GHz)0,000,020,040,0620 vol% additives800°C 900°C1000°CDielectric loss vs. Frequency0,08Christian Kohler et al.Institute for Applied Materials – Materials Process Technology (IAM-WPT)13Tunability23.01.2012800 900 10000,150,200,250,30TunabilitySintering temperature20%10%5%Tunability vs. Sintering temperatureBST pure (1200°C)@ 10GHz, 10V/µm10E (V/µm)500,150,200,250,3020 vol% additivesTunability vs. E-Field800°C900°C1000°C@ 10GHzChristian Kohler et al.Institute for Applied Materials – Materials Process Technology (IAM-WPT)14Summary• Lowering sintering temperature achieved• Low formation of secondary phases• Trends in microstructure and dielectric properties• Comparable dielectric data to undoped BST thick film without addition(sintered at 1200°C)Outlook • (Co-)Doped BST thick films with ZnO/H3BO3-additions• Compatibility with LTCC substrates?• Co-sintered MIM-Devices23.01.2012 Christian Kohler et al.

The effect of ZnO-B₂O₃ addition on the dielectric properties and microstructure of screen-printed low-sintered BST thick films

https://publikationen.bibliothek.kit.edu/230086136/3815998

The effect of ZnO-B₂O₃ addition on the dielectric properties and microstructure of screen-printed low-sintered BST thick films

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