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Soft Magnetic Nanocrystalline Materials for Inductors and Shielding Applications Optimized for Higher Frequencies.

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Plenary lecture given by Christian Polak (Vacuumschmelze GmbH) at the XVII B-MRS Meeting, in Natal (Brazil), on September 17, 2018.

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Soft Magnetic Nanocrystalline Materials for Inductors and Shielding Applications Optimized for Higher Frequencies.

  1. 1. MRS-2018 Brazil Sept. 2018 1 Christian Polak Soft Magnetic Nanocrystalline Materials for Inductors and Shielding Applications Optimized for Higher Frequencies Rapid Solidification Technology VACUUMSCHMELZE GmbH & Co. KG, D-63450 Hanau, Germany ®
  2. 2. MRS-2018 Brazil Sept. 2018 2 VACUUMSCHMELZE VACUUMSCHMELZE is one of the world's leading manufacturers of advanced magnetic materials and value added products. In 1914 the first vacuum melting furnace laid the foundation for today's VACUUMSCHMELZE. Melting alloys under vacuum went into production on an industrial scale in 1923. The Company / Portrait Vacuum melting furnace 1914 - 1917
  3. 3. MRS-2018 Brazil Sept. 2018 3 VACUUMSCHMELZE The Company / Portrait VACUUMSCHMELZE offers the entire range of magnetic products: Today VACUUMSCHMELZE manufactures a broad spectrum of high quality materials & parts, components and systems for numerous markets, from Swiss watch manufacturers to the aircraft industry. Materials and Parts 33 % Permanent Magnets 31 % Cores and Components 36 %
  4. 4. MRS-2018 Brazil Sept. 2018 4 VACUUMSCHMELZE The Company / Locations VAC worldwide VACUUMSCHMELZE is present in more than 50 countries on all five continents, in order to be able to provide you with competent service wherever you are.
  5. 5. MRS-2018 Brazil Sept. 2018 5 VACUUMSCHMELZE million Euro 2015 2016 2017 Sales 379 363 400 Capital Expenditure 19 16 20 R & D 16 16 17 Employees 4,300 4,300 4,400 The Company / Facts and Figures Headquarter an R&D Center located in Hanau, Germany. Active on a global basis: with approx. 4,400 employees in more than 50 countries annual sales 400 million Euro Headquarter: Hanau, Germany
  6. 6. MRS-2018 Brazil Sept. 2018 6 Applications of Amorphous and Nanocrystalline Alloys Established Products: Industrial applications: • Chokes, transformers and power sensors for power supplies and rectifiers Transportation: • Chokes, transformers and current sensors The frequency converter permits efficient control of motors in which complex semi- conductor technology is used. Current-compensated chokes made of nanocrystalline materials have excellent attenuation characteristics combined with high temperature resistance (150 C) and a smaller volume for the design.
  7. 7. MRS-2018 Brazil Sept. 2018 7 Applications of Amorphous and Nanocrystalline Alloys Established Products: Installation: • Total current converters for earth fault current protection switches • Current converters for electronic energy meters Current sensors using a magnetic probe provide high accuracy and excellent temperature stability.
  8. 8. MRS-2018 Brazil Sept. 2018 8 Applications of Amorphous and Nanocrystalline Alloys Established Products: Installation:Automotive: • Chokes and transformers for the power management • Current-Compensated chokes • Current sensors • Flexible antennas, e.g. Keyless-Entry Current-compensated chokes made of nanocrystalline materials have excellent attenuation characteristics combined with high temperature resistance (150 C) and a smaller volume for the design. Cost-optimised chokes and transformers for power control units such as gas or diesel direct injection systems. Current sensors using a magnetic probe provide high accuracy and excellent temperature stability. VAC manufactures transmission antennas for 19-kHz KEYLESS-ENTRY-Systems.
  9. 9. MRS-2018 Brazil Sept. 2018 9 Nanocrystalline Alloys - Differentiation Target: High Frequency Range: up to MHz • Cores • Planar Inductors • Shielding material • Sensors smaller size less weight less electrical losses improved energy efficiency high precision wide range of service temperature • Energy efficiency and Renewable energy • Electrical safety and Smart grids • Automotive and e-Mobility New Markets and Applications LED Technology www.audi.de Wireless Charging Brick-Type Converter (DC/DC)
  10. 10. MRS-2018 Brazil Sept. 2018 10 Amorphous Materials – Rapid Solidification Technology rapid solidification (106K/s) Amorphous structure → no long range order T70-85M15-30 (at%) T = Fe, Co, Ni ... M= Si, B, C, Nb, Mo ... Typical Composition • thin ribbon (d ~ 20 m) • high electrical resistivity Properties • mechanically hard • magnetically soft Video
  11. 11. MRS-2018 Brazil Sept. 2018 11 •Fe73.5Cu1Nb3Si13.5B9 (Yoshizawa & Yamauchi, 1988) •Fe86(Cu1)Zr7B6 •Fe84Nb7B9 (Suzuki et al., 1990, 1991) nanocrystalline state for special compositions like: Annealing above TxRapid Solidification (106K/s) Amorphous structure → no long range order Large scale production as: • FINEMET® (Hitachi) • VITROPERM® (Vacuumschmelze) • AT&M VITROPERM® (nanocrystalline) Bs high; ⇒⇒⇒⇒ low and high brittle; Tapp ≤≤≤≤ 200°C; Nanocrystalline Materials – Rapid Solidification Technology
  12. 12. MRS-2018 Brazil Sept. 2018 12 Alloy System Nano-Crystalline Fe74.5Cu1Nb3Si15.5B7 basic ferromagnetic properties glass forming elements enhances nucleation of bcc-FeSi crystallites •impedes grain growth alternatives: Au, Ag (?) Cr < V < Mo < Nb ≈≈≈≈ Ta < Zr, Hf •inhibits formation of Fe-B compounds
  13. 13. MRS-2018 Brazil Sept. 2018 13 magneto-crystalline 10 102 103 104 J/m3 excellent soft magnetic properties excellent soft magnetic properties Magnetic Anisotropies with regard to Annealing Process customizing magnetic properties HEATTREATMENT nanocrystalline Fe-based alloys Lex D K1 1K K N = Hc (A/m) 1nm 1µm 1mm 0.1 1 10 100 1 000 10 000 perm- alloy 50NiFe FeSi6.5 Grain Size, D Fe-base amorphous Co-base 1/D crystalline nano- crystalline D6 Herzer, G.,1997, Handbook of Magnetic Materials, Vol.10, Capter 3
  14. 14. MRS-2018 Brazil Sept. 2018 14 Tailoring Hysteresis Loop: Induced Magnetic Anisotropies annealing induced ⇒ Magnetic Field Annealing 10 102 103 104 J/m3 HA H B F Z HA [A/cm] µ 0.096 100 000 0.32 30 000 HA [A/cm] µ 0.096 100 000 0.32 30 000 2 u02µ sB µ K = transverse anisotropy H B Ku magnetization rotation applied magnetic field H applied magnetic field H ( )u Fe 3/ 2 ˆK P f B ∆ ∝ ⋅ H B longitudinal anisotropy domain wall displacement excellent soft magnetic properties excellent soft magnetic properties
  15. 15. MRS-2018 Brazil Sept. 2018 15 Nanocrystalline Alloys – NEW Products longitudinal transverse perpendicular NEW Products: for the higher frequency range: up to MHz • Cores & Components • Planar Inductors • Shielding material • Sensors LED Technology www.audi.de Photovoltaic Battery Charger Brick-Type Converter (DC/DC) Wireless Charging DC/DC Converter Tape wound Cores Low permeability material for DC/DC Converter (e.g. Ćuk – Converter) M.Christoph, C. Dick, RWTH Aachen Low permeability material for CT’s (current transformer for electronic watt hour meter) Flux guiding and shielding foils (wirleless charging, NFC, RFID) E. Waffenschmidt, PHILIPS Research ®
  16. 16. MRS-2018 Brazil Sept. 2018 16 1. Topic: Shielding & Flux Guiding Wireless Charging Requirements: Highly soft magnetic material Flux guiding: high power transfer efficiency @ 120 …200 kHz 13.6 MHz Shielding: protection of electronics and battery from inductive heating Shape: as thin as possible consumer electronic market Materials: Competitive material: Hard and Flexible Ferrites Thin and flexible 2/4 layered Composite Material of nanocrystalline VITROPERM® of mobile electronic devices… PET foil + adhesive (20 m) VP 800 (20 m) PET foil + adhesive (30 m) VP 800 (20 m) adhesive (15 m) 2-layered composite VITROPERM® Prof. E. Waffenschmidt, PHILIPS Research, Fachhochschule Köln – Elektrische Netze
  17. 17. MRS-2018 Brazil Sept. 2018 17 Wireless Power Transmission Systems Application: Technology & Electrical Circuit Prof. E. Waffenschmidt, PHILIPS Research, Fachhochschule Köln – Elektrische Netze Principle & Background
  18. 18. MRS-2018 Brazil Sept. 2018 18 Shielding / Flux Guiding ? ReceiverTransmitter mobile device electronic, battery pack, metallic cover … eddy current “free” area shielding material flux guide Advantages: • more closed magnetic circuit • higher coupling factor k ⇒ 1 • reduced losses and heat generation in all other metallic parts • improved electro-magnetic compatibility (EMC) Required material: • High quality factor Q • Ability of creating a higher coupling factor k • Low losses at high frequencies: up to MHz shielding / flux guiding material
  19. 19. MRS-2018 Brazil Sept. 2018 19 Optimization Process for Efficiency Responsible for efficiency for wireless power transmission ࢑ ∙ ࡽ Our consideration: optimize the product of coupling factor k and the average quality factor Q Inductance L: characteristic of assembly of coil + shielding material Quality factor Q: indicator of energy loss Coupling factor k: indicator of energy transfer Power loss: no suitable indicator of performance Parameters [1] C.P. Dick, C. Polak, and E. Waffenschmidt. Proposal of a Figure of Merit for the characterization of soft-magnetic shielding material used in inductive wireless power transmission systems IEEE Journal of Emerging and Selected Topics in Power Electronics 2015, Vol 3, Page 272 [2] C.P. Dick, A.Krause, E. Waffenschmidt and C. Polak. Qualification of Soft-Magnetic Shielding Materials Used in Inductive Wireless Power Transmission Systems APEC 2015: Applied Power Electronics Conference and Exposition 2015, Proceedings of; Charlotte, North Carolina, USA; 15-19 Mar 2015
  20. 20. MRS-2018 Brazil Sept. 2018 20 Shielding / Flux Guiding Material - Optimization sheets and packetssheets and packets planar windings Sheet, e.g. nanocrystalline material Measurement of Quality Factor Q )( )( fµ fµ Q imag real = imagreal iµµµ += flossesµimag @∝ in amorphous and nanocrystalline alloys power losses are mainly determined by excess losses: 2/3 )(BfKu∝ Example of a planar coil used in electronic power transfer systems
  21. 21. MRS-2018 Brazil Sept. 2018 21 “Zero” Anisotropy ⇒⇒⇒⇒ Planar Inductivities sheets and packetssheets and packets planar windings Sheet, e.g. nanocrystalline material 0 10 20 30 40 50 60 10 100 1000 10000 Frequency, f [kHz] QualityFactor,Q[1] amorphous material VITROPERM® Fe73.5 Cu1Nb3Si15.5B7 nanocrystalline material; almost completely reduced anisotropies ≈≈≈≈ isotropic higher Q, lower losses theory: Q ⇑ for ⇓ anisotropy (excess losses: ) VITROPERM® Fe73.5 Cu1Nb3Si15.5B7 nanocrystalline material; almost completely reduced anisotropies ≈≈≈≈ isotropic higher Q, lower losses theory: Q ⇑ for ⇓ anisotropy (excess losses: )( ) 2/3 BfKu∝ Measurement of Quality Factor Q VITROPERM®®®® (nanocrystalline) ⇒ preferred material Further Quality Enhancement: (loss reduction) by structuring by inducing small, directed anisotropies
  22. 22. MRS-2018 Brazil Sept. 2018 22 Composite layered Structure - Samples PET foil + adhesive (20 m) VP 800 (20 m) PET foil + adhesive (30 m) VP 800 (20 m) adhesive (15 m) 2-layered composite VITROPERM® Nanocrystalline VITROPERM® Samples of homogeneous VITROPERM® sheet: „disc“ shaped and rectangular Samples of slit VITROPERM® sheet (2mm strips): „disc“ shaped and rectangular
  23. 23. MRS-2018 Brazil Sept. 2018 23 Cracked / Crashed – Samples, Flake – Samples Samples: VITROPERM® sheet cracked / crashed material: rectangular cracks Samples: VITROPERM® Flakes on adhesive: rectangular 450 m 185 m
  24. 24. MRS-2018 Brazil Sept. 2018 24 Planar Inductivities – Measurement of Quality Factor 0 10 20 30 40 50 60 70 80 90 100 10 100 1000 10000 Frequency f [kHz] QualityFactorQ[1] VITROPERM® sheet cracked / crashed 2 layers, 30x30mm VITROPERM® sheet: homogeneous 2 layers, 30x30mm VITROPERM® sheet: Slit (2mm) 2 layers, 30x30mm VITROPERM® Flakes on adhesive 30x30mm
  25. 25. MRS-2018 Brazil Sept. 2018 25 Loss Reduction by Structuring Domain structure determined by magneto-optical Kerr microscopy Domain structure determined by magneto-optical Kerr microscopy 100 µµµµm planar windings nanocrystalline material sample: VITROPERM® „R“ nanocrystalline, 20 x 20 mm sample: VITROPERM® „R“ nanocrystalline, 20 x 20 mm domain width: 220 µmdomain width: 220 µm 100 µµµµm Domain structure determined by magneto-optical Kerr microscopy Domain structure determined by magneto-optical Kerr microscopy domain width: 50 µmdomain width: 50 µm 0 10 20 30 40 50 60 10 100 1000 10000 Frequency, f [kHz] QualityFactor,Q[1] structured un-structured wall displacement eddy currents eddy current field external magnetic field
  26. 26. MRS-2018 Brazil Sept. 2018 26 2. Topic: High induced Anisotropy - Cores for DC/DC Converters or CT’s tape wound corestape wound cores high frequencies .... 10 100 1000 10000 100000 Frequency, f [MHz] Permeability,µ' 0.001 0.01 0.1 1 10 100 µDC fg [MHz] 100 000 0.03 30 000 0.1 d = 20 µm ρel = 120 µΩcm 30 kHz fg µ‘ µ‘VAC: conventional cores and components VAC: conventional cores and components Limitation of High Permeability Materials 2 0 4 d f DC el g µµ ρ π =
  27. 27. MRS-2018 Brazil Sept. 2018 27 Limitation of High Permeability Materials 2 0 4 d f DC el g µµ ρ π = DCelQ µρ /∝ high frequencies .... 10 100 1000 10000 100000 Frequency, f [MHz] Permeability,µ' 0.001 0.01 0.1 1 10 100 µDC fg [MHz] 100 000 0.03 10 000 0.3 1 000 3 100 30 d = 20 µm ρel = 120 µΩcm 3 MHz 30 MHz fg fg µ‘ µ‘
  28. 28. MRS-2018 Brazil Sept. 2018 28 H B 0.5 1.0 1.5 10 3 10 4 10 5 10 6 nanocrystalline (Fe-base) amorphous (Co-base) permalloys MnZn- Ferrites Permeability,µi Saturation Induction, Bs (T) µ 2 u02 sB µ K = µ 2 u02 sB µ K = WANTED nanocrystalline Fe-base alloy low - Alloy - Mech. Processing - Heat Treatment Typical Permeabilities after Transverse Field Annealing of Tape Wound Cores
  29. 29. MRS-2018 Brazil Sept. 2018 29 Low Permeability Solution: Stress Annealing Annealing under Tensile Stress (1999) ribbon tensile stress σa kg weight furnace annealing furnace supply reel tensile force control winding unitinline control furnace Annealing under Tensile Stress (2011) Reel-to-Reel Process σa First experiments: G. Herzer, Nanocrystalline soft magnetic alloys, Handbook of Magnetic Materials Vol 10 ©1999 Elsevier Science
  30. 30. MRS-2018 Brazil Sept. 2018 30 10 102 103 104 J/m3 annealing induced ⇒ stress annealing (without magnetic field) H J HA Ku= HAJs/2 (induced anisotropy) HA [A/cm] µ 3.21 3 000 9.63 1 000 96.3 100 HA [A/cm] µ 3.21 3 000 9.63 1 000 96.3 100 Induced Magnetic Anisotropies
  31. 31. MRS-2018 Brazil Sept. 2018 31 VITROPERM®, Fe73.5Cu1Nb3Si15.5B7 0 2 4 6 8 10 12 14 0 200 400 600 800 InducedAnisotropy,Ku(kJ/m 3 ) Annealing Stress, σa (MPa) stress annealed 4s 600°C 4s 655°C 4s 690°C field annealed K1 (Fe80Si20) furnace ribbon tensile stress σa Induced Anisotropy vs. Annealing Stress, Hystereses, Magnetostriction Herzer, Budinsky, Polak, 2011 J. Phys.: Conf. Ser. 266 012010
  32. 32. MRS-2018 Brazil Sept. 2018 32 Nano-Crystallization under Tensile Stress: Domain Structure and Coercivity Field zigzag domain walls 10 µm Kerr sensitivity Herzer, Budinsy, Polak, 2011 J. Phys.: Conf. Ser. 266 012010 easy magnetic plain Herzer, Budinsy, Polak, 2011 J. Phys.: Conf. Ser. 266 012010 Herzer, Budinsy, Polak, 2011 J. Phys.: Conf. Ser. 266 012010 0 2 4 6 8 10 0 5 10 15 Induced Anisotropy, K u (kJ/m3 ) Coercivity,Hc(A/m) K1 (Fe80Si20)K1/3 4s 600°C 4s 655°C 4s 690°C field annealed stress annealedFe73.5Cu1Nb3Si15.5B7 ∝c uH K
  33. 33. MRS-2018 Brazil Sept. 2018 33 Industrial Production Process Creep Induced Anisotropy Advantages: … continuous process highly linear hysteresis loops permeability: 3000 to 100 (60) vanishing magnetostriction (λs ≈ 0) positive temperature coefficient of permeability (Tk > 0) very good aging stability -200 -150 -100 -50 0 50 100 150 200 -20 -15 -10 -5 0 5 10 15 20 Magnetic Field H [A/cm] MagneticFluxΦΦΦΦ[nVs] annealing 600°C to 700°C magnetic measurement tensile stress along the ribbon axis
  34. 34. MRS-2018 Brazil Sept. 2018 34 “Stress” Annealing – Production Process annealing 600°C to 700°C magnetic measurement tensile stress along the ribbon axis Permeability = 500 feedback control system Continuous Process: Stress-Annealing, Quality inspection, Core Production Nanocrystalline, low permeability, cores outstanding low scattering of magnetic properties
  35. 35. MRS-2018 Brazil Sept. 2018 35 “Very High” Anisotropy Requirements: Highly soft magnetic material Shape: as flat as possible, height 1mm Low power losses Inductivity in the range of H Quality factor > 20 Applicable at high frequencies (MHz range) Material & Production Process: VITROPERM®, VP800 FF, nanocrystalline Stress Annealing =100 Conventional PCB Embedded Components Application of nanocrystalline low permeability cores: Embedded Tape Wound Cores for DC/DC Converter
  36. 36. MRS-2018 Brazil Sept. 2018 36 Tape Wound Cores: DC-Permeability -1.5 -1 -0.5 0 0.5 1 1.5 -200 -150 -100 -50 0 50 100 150 200 Magnetic Field, H [A/cm] Magnetization,J[T] VITROPERM®, Fe73.5 Cu1Nb3Si15.5B7 nanocrystallization under tensile stress; annealed at 695°C; 4s; stresses up to 700 MPa VITROPERM®, Fe73.5 Cu1Nb3Si15.5B7 nanocrystallization under tensile stress; annealed at 695°C; 4s; stresses up to 700 MPa µ ~ 2000 µ ~ 1000 µ ~ 400 µ ~100 µ ~ 60 tape wound cores: 7.5 x 3.5 x 1.0mm tape wound cores: 7.5 x 3.5 x 1.0mm
  37. 37. MRS-2018 Brazil Sept. 2018 37 Tape Wound Cores: Permeability at high Frequencies 0 0.2 0.4 0.6 0.8 1 1.2 0.01 0.10 1.00 10.00 100.00 Frequency, f [MHz] NormalizedPermeability,µ'/µ'max VITROPERM®, Fe73.5 Cu1Nb3Si15.5B7 nanocrystallization under tensile stress; annealed at 695°C; 4s; stresses up to 700 MPa VITROPERM®, Fe73.5 Cu1Nb3Si15.5B7 nanocrystallization under tensile stress; annealed at 695°C; 4s; stresses up to 700 MPa µ ~ 2000 µ ~ 60 µDC d [µm] fg [MHz] 1 750 19.3 1.9 1 070 19.2 3.2 396 18.8 9.1 99 17.8 45.2 58 15.3 95.0 ρel = 120 µΩcm
  38. 38. MRS-2018 Brazil Sept. 2018 38 Recent Developments High Bs Alloys Coercivity Hc [A/m] SaturationPolarisation,Js[T] 0.1 1 10 100 1000 0.5 2.0 1.0 2.5 1.5 0.0 50% CoFe Fe3% SiFe 40-50% NiFe 70-80% NiFe (Permalloy) MnZn NiZn Soft Ferrites amorphous Co-base FeSiAl (Sensust) amorphous FeNi-base amorphous Fe-base nano- crystalline High Bs Nano-Crystalline Fe-base alloys with high saturation induction
  39. 39. MRS-2018 Brazil Sept. 2018 39 High Bs Alloys Fe-content (at.%) (Liu et al., 2014) Suzuki et al (1991 – 1993): Fe84Nb7B9, Fe86Zr7B6Cu1: Js = 1.5 T, λs ~ 0 ppm Fe91Zr7B2 : Js = 1.7 T, λs ~ - 1 ppm Older approaches:
  40. 40. MRS-2018 Brazil Sept. 2018 40 High Bs Alloys Fe-content (at.%) (Liu et al., 2014) Older approaches: Vacuumschmelze (1991 – 2001): Magnetization: Magnetostriction: ?
  41. 41. MRS-2018 Brazil Sept. 2018 41 High Bs Alloys Fe-content (at.%) (Liu et al., 2014) Hitachi, Ohta et al 2009: Fe82.5 Si2 B14 Cu1.5 : Js = 1.85 T, λs ~ 14 ppm (enhanced Cu content) IMR, Makino et al 2009: Fe85.3 Si4 B8 P4 Cu0.7 : Js = 1.80 T, λs ~ 14 ppm (combined action of Cu+P) More recent approaches:
  42. 42. MRS-2018 Brazil Sept. 2018 42 Recent Developments “under development” • Laboratory Caster width: 50mm, thickness: 22 m • Co addition: improvement of casting behavior • Short time, continuous annealing! established heat treatments like batch annealing not feasible, need for high heating/cooling rate • Hc < 10 A/m • Bs about 1.8T • λs about 15 to 20ppm Fe-base Co0 or 4 /Nb free /P high Bs alloy: annealing 600°C to 700°C magnetic measurement tensile stress along the ribbon axis M. Kuhnt, M. Marsilius, T. Strache, C. Polak, and G. Herzer, “Magnetostriction of nanocrystalline (fe,co)-si-b-p-cu alloys,” Scripta Materialia, vol. 130, pp. 46 – 48, 2017
  43. 43. MRS-2018 Brazil Sept. 2018 43 Conclusions: Nanocrystalline Fe-base Alloys recent developments for high frequency applications zero induced anisotropy wireless charging high induced anisotropy Ku (low ) size reduction, CT’s & chokes high saturation induction (Bs ≈ 1.8 T ) further size reduction • excellent soft magnetic properties (due to vanishingly small K1 and near-zero λs ) • customizable to the needs of application (by annealing induced anisotropies) • low losses even at high frequencies (thin ribbons ~20 m, high resistivity ~120 Ωcm, shift fg to high f growing market for nanocrystalline materials further progress needs more sophisticated casting and annealing technologies

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