Binder, J.R.

Friederich, A.

Jakoby, R.

Kohler, C.

Nikfalazar, M.

Sazegar, M.

Wang, D.

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.edu Microstructure and microwave properties of low  temperature sintered BST (Ba0.6Sr0.4TiO3) thick-films  and their applicability to co-firing processes C. Kohler, A. Friederich, D. Wang, M. Nikfalazar,  M. Sazegar, R. Jakoby, J.R. Binder Institute for Applied Materials– Materials Process Technology(IAM-WPT) 10th Pacific Rim Conference on Ceramic and Glass Technology 2013, San Diego  Institute for Applied Materials – Materials Process Technology (IAM-WPT) 2 Outline • Introduction    - Ba1-xSrxTiO3  - Microwave components  • Low temperature sintered BST thick-films  - Experimental route  - Additive system  - Microstructure and phase content  • Dielectric characterisation  - Co-Firing of MIM structures  - CPW vs. MIM  • Summary and Outlook  Christian Kohler et al. 03.06.2013 Institute for Applied Materials – Materials Process Technology (IAM-WPT) 3 Ba0.6Sr0.4TiO3    bulk ceramic Tc tetragonal cubic 5 10 15 20 25 0 -200 -100 0 50 100 150 Temperature [°C] -50 -150 rel. Permittivity [x1000] System Ba1-xSrxTiO3 (BST) Ferroelectric Phase Paraelectric Phase Tetragonal Crystal Structure Cubic Crystal Structure For microwave applications: • usage of paraelectric phase • application  at RT Ba0.6Sr0.4TiO3  Jeon, J., J. Eur. Ceram. Soc., 2004, 24, 1045 – 1048 03.06.2013 Curie Temperature Temperatur Christian Kohler et al. Institute for Applied Materials – Materials Process Technology (IAM-WPT) 4 Ba0.6Sr0.4TiO3 as tuneable dielectric material Displacement of Ti4+-ion through an external electric field • no power consumption • high linearity  • fast tuning speed -20 -15 -10 -5 0 5 10 15 20100200300rE [V/µm]BST shows a non-linear dependancy of the permittivity on a static E-field Dielectric tunability 03.06.2013 Christian Kohler et al. Institute for Applied Materials – Materials Process Technology (IAM-WPT) 5 Microwave components based on BST thick-films Tunable filter Tunable matching network CPW based  phase shifter Left-handed  phase shifter Phase shifter Multiband antenna RF-ID modulator Antenna µC Microwave Engineering,  Technical University Darmstadt http://www.mwe.tu-darmstadt.de/de/fachgebiete/mikrowellentechnik/forschung/ferroelectrics/ferroelectrics.html Christian Kohler et al. 03.06.2013 Institute for Applied Materials – Materials Process Technology (IAM-WPT) 6 Motivation Restriction: High sintering temperature of BST thick film (~1200°C) •  co-firing with silver/gold electrodes not possible (melting point of silver = 962°C) •  co-fired MIM devices only feasible by using high temperature fireable electrodes (e.g. Pt) •  not compatible with LTCC technology (firing range 865-900°C) BST varactors •  so far: fabrication of electrodes after firing         of BST thick-films via fotolithography •  coplanar varactors (IDC, CPW) Objectives   development of low-temperature sintered BST-thick films   fabrication of co-fired MIM devices 03.06.2013 Christian Kohler et al. BST Au 200 µm CPW IDC MIM Institute for Applied Materials – Materials Process Technology (IAM-WPT) 7 Experimental route Christian Kohler et al. 03.06.2013 Spray drying + Calcination (900°C)addition ZnO/H3BO3 + co-millingPressingDispersingSinteringScreen-printing+(Co-)Firing(850-900°C)SolBST powderComposite powderPastePelletBST thick-film on Al2O3MIM structureon Al2O3BST Ag Al2O3DilatometryInstitute for Applied Materials – Materials Process Technology (IAM-WPT) 8 Choice of additive system Christian Kohler et al. 03.06.2013 500 600 700 800 900 1000 1100 1200 1300 1400-0.15-0.10-0.050.00 BST-0ZB BST-5ZB BST-10ZB BST-20ZBShrinkage [dL/L0]Temperature [°C] Dilatometry Ag-MIM LTCC Pt-MIM CPW Requirement additive system • lowering of sintering temperature of BST • no or limited formation of secondary phases • low permittivity and dielectric loss   ZnO-B2O3 (molar ratio1:1)     (εr = 6.9, tan δ = 9.4×10−3 (16 GHz), Surendran 2004)   mixing with BST via co-milling  Samples  1.) BST-5ZB (5 vol.% ZnO-H3BO3) 2.) BST-10ZB (10 vol.% additive)_ 3.) BST-20ZB (20 vol.% additive)_      Reducing of sintering temperature  (further details: Kohler et al., IJAC 2013, doi: 10.1111/ijac.12116) Institute for Applied Materials – Materials Process Technology (IAM-WPT) 9 03.06.2013 Microstructure & phase content of thick films BST-10ZB (P = 41.5%) BST-20ZB (Porosity P = 34.8%)  BST-5ZB (P = 45.0%) Higher additive amount  lower grain sizes  clustering of particles BST-5ZB BST-10ZB BST-20ZB Ba0.6Sr0.4TiO3 Substrate BST-20ZB BST-10ZB BST-5ZB    no significant formation of (crystalline) secondary phases  shift of BST main (110) reflex (Ba0.6Sr0.4TiO3 Ba0.5Sr0.5TiO3) Ti Ba TEM BST-10ZB Distribution Titanium Distribution Barium    dissolution of barium      in amorphous phase Christian Kohler et al.  (Kohler et al., IJAC 2013) Institute for Applied Materials – Materials Process Technology (IAM-WPT) 10 Dielectric characterization – CPW vs. MIM Christian Kohler et al. 03.06.2013 /Au e Concept coplanar waveguides (CPW) Fabrication Realized Structures 1. Screen-printing BST-ZB paste on Al2O3  2. Drying and firing (900°C/1h) of thick-films 3. Fotolithography of gold electrodes  E-field lines (Gevorgian et al., 2009) Concept Metal-Insulator-Metal (MIM) structure Fabrication Al2O3AgBSTRealized Structures 1. Screen-printing of silver electrodes as well as BST-ZB pastes  2. Drying and co-firing (865°C/1h) of multilayer E-field lines (Gevorgian et al., 2009) Institute for Applied Materials – Materials Process Technology (IAM-WPT) 11 Dielectric characterization - CPW Christian Kohler et al. 03.06.2013 BST-10ZB 100 nm BST-20ZB BST-5ZB 5 10 15 200.000.020.040.060.080.10Dielectric LossFrequency (GHz)    BST-5ZB BST-10ZB BST-20ZB  0 2 4 6 8 100.00.10.20.310 GHzTunabilityVoltage (V/µm) BST-5ZB BST-10ZB BST-20ZB  5 10 15 20100120140160180Effective PermittivityFrequency (GHz)  BST-5ZB BST-10ZB BST-20ZB   decrease of ε, tan δ, τ with     increasing additive amount Due to microstructure • lower grain sizes • clustering of particles • higher content amorphous phase • change in ratio of Ba:Sr   Institute for Applied Materials – Materials Process Technology (IAM-WPT) 12 Fabricated MIM structures (co-fired at 865°C/1h) Christian Kohler et al. 03.06.2013 + good adhesion between layers - quality of silver electrodes (edges, roughness) + no reaction (proved by XRD, REM) - cracks in BST-20ZB thick-film  + no infiltration of Ag in porous BST + dielectric characterization possible   BST-20ZB BST-10ZB Ag Al2O3 BST BST-5ZB Al2O3 BST Ag BST Ag Al2O3 Institute for Applied Materials – Materials Process Technology (IAM-WPT) 13 Dielectric characterization – CPW vs. MIM (2GHz) Christian Kohler et al. 03.06.2013 CPW vs. MIM   similar trends for permittivity and tunability    different for Q-values     (due to loss of rough electrodes for MIM)    values of tunability for MIM lower than     expected (printing quality has to be optimized)   5 10 15 20501001502 GHz CPW MIMZnO/H3BO3 addition (Vol.%)Permittivity 5 10 15 200.150.200.250.302 GHz, 10 V/µm CPW MIMZnO/H3BO3 addition (Vol.%)Tunability  5 10 15 200204060801002 GHz CPW MIMZnO/H3BO3 addition (Vol.%)Q-factor (1/tan ) Institute for Applied Materials – Materials Process Technology (IAM-WPT) 14 Summary and Outlook Christian Kohler et al. 03.06.2013 CuF BST-5ZB (τ = 45%, 80V, 2GHz) • material system BST-ZnO/B2O3   - lowering of sintering temperature achieved  • low temperature sintered BST thick films  - dependancy of additive amount on the microstructure and phase content     grain sizes     clustering of particles     content of amorphous phase     Ba-Sr ratio  • Co-firing of MIM structures  - good adhesion and compatibility of multilayers  • Outlook  - optimizing printing quality  fully printed RF component  - usage of CuF-coped BST with ZnO/B2O3  Institute for Applied Materials – Materials Process Technology (IAM-WPT) 15      Thank you for your kind attention! Christian Kohler et al. 03.06.2013 

Microstructure and microwave properties of low temperature sintered BST (Ba₀̣₆Sr₀̣₄TiO₃) thick-films abd their applicability to co-firing processes

https://publikationen.bibliothek.kit.edu/230091807/3816297

Microstructure and microwave properties of low temperature sintered BST (Ba₀̣₆Sr₀̣₄TiO₃) thick-films abd their applicability to co-firing processes

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