thin amorphous core material for power applications...•objective is to replace ferrite cores with...
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Thin Amorphous Core Material for Power Applications
Paul McCloskey, Santosh Kulkarni, Ansar Masood, Cian O’Mathuna
Integrated Magnetics, Micro-Nano Systems Center, Tyndall National Institute, Cork, Ireland
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Outline
• Motivation
• Analysis of magnetic core losses
• Review of soft magnetic thin films
• Material performance comparison
• Post-processed nanocrystalline thin film
• New low loss alloy systems
• Conclusions
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• Desired performance: high efficiency and high power density
• Advances in power switches & controllers, GaN, SiC…
– frequency , inductance required
• Magnetic materials key challenge for advancing power conversion technology
Motivation
• Key Applications: o Power Factor Correctiono Flybacko Buck
• Complements advances in semiconductor technologies including wide-band gap devices.
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Kolar et al*
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Ferrite Performance
Performance Bench Mark:
700 kW/m3 @500kHz & 100 mT Bpeak
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Bsat = 420 mT at 100 OC
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Anomalous Loss–Inconsistencies in domain wall motion during magnetization reversal
–Variations in localized flux densities
– Model for estimating anomalous loss proposed by Bertotti (Book- Hysteresis in Magnetism)
Magnetic Core Losses
• Magnetic core losses can be broadly classified
Eddy Current Loss-Eddy currents resist change in applied magnetic field
-Skin depth, thickness at which the current density drops to (1/e) Js
- Skin depth, d = (2r /wmr)0.5
Where; r = resistivity, mr =
relative permeability, w =
angular frequency (=2pf )
-Eddy current loss (thickness less than one skin depth)
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• Commercial magnetic thin film alloys
o Very high permeability (typically > 20,000)
=> Lower skin depth & hence high eddy current losses at high frequencies
• Electrodeposited crystalline thin films
o Crystalline structure in plated NiFe alloys impedes domain wall motion
=> coercive fields (20-80 A/m)
• Electrodeposited amorphous thin films
o Elimination of magnetocrystalline anisotropy
=> low coercive fields (10-20 A/m)
• Nanocrystalline thin films
o Randomly oriented crystalline anisotropies cancelled by ferromagnetic exchange
o Opposite direction of magnetostriction of nanocrystalline and amorphous phases can => reduction or elimination of magnetostrictive anisotropy
=> Ultra-low coercivity (<2 A/m)
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Review of Soft Magnetic thin films
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Review of Soft Magnetic thin films
Materials Research
polycrystalline
thin films (NiFe)
Research
Amorphous thin
films (CoP)
Nanocrystalline
thin films (Vitroperm,
MT, etc)
Thickness (um) 3~5 3~5 >16
Coercivity
(A/m)
20 ~ 80 10-20 <3
Resistivity
(W.m)
25 ~ 45 x10-8 >100 x10-8 ~110 x10-8
Saturation
Flux Density
(T)
0.8 ~ 1.5 0.8 ~ 1.2 1.2
Relative
Permeability
<1000 <1000 >15000
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• Objective is to replace ferrite cores with high flux density thin film material with improved performance
• Three different soft magnetic thin films evaluated:-o Electrodeposited research based thin films (NiFe, CoP etc)- thickness <5 µmo High permeability commercial thin film alloys (NiFe-Esong, Goodfellows)- thickness
<5 µmo Nanocrystalline thin films (Vacuumschmelze, Toshiba) - thickness >21 µm
• Wound core samples prepared with OD- 7.7 mm, ID- 7.5 mm along with 25 turn copper primary & secondary windings
• Performance of thin films compared to ferrite (3c90) at 100 kHz
Material performance comparison
Commercial magnetic thin films Amorphous and nanocrystaline tape-wound cores
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Magnetic Core loss measurement set-up
• Test samples characterized as toroidal transformers• Current sensor measures primary current (I)• Oscilloscope measures secondary voltage (U)• Power loss, P= U.I• Air-core contribution compensated for accurate core loss measurement
sample
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Material performance comparison
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Measurement & Discussion
• Thinned nanocrystalline films produced by post-processing of commercial ribbons• Assembled into wound core transformers • Similar air-core transformer for air core compensation
Magnetic Core
Air-Core3F35(datasheet)
Test Frequency 500 kHz
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Measurement Results
Eddy current
Anomalous
Hysteresis
Losses 21 µm 5 µm
Eddy Current 1650 kW/m3 93 kW/m3
Hysteresis 31 kW/m3 31 kW/m3
Anomalous 419 kW/m3 76 kW/m3
Total Loss-2100 kW/m3
Total Loss-200 kW/m3
80 %
46 %
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Potential Impact on magnetic components
• Lower loss density Higher efficiencySmaller core sizeShorter conductor lengthHigher power density
• Higher Bsat Greater design flexibility
40% reduction in device volume
25% reduction in magnetic loss
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LM22679 Evaluation Board
Wurth inductor:
o 4.8 μH
o DCR 12mΩ
Tyndall gapped inductor:
o 4.7 μH
o DCR 15 mΩ
Efficiency the same at currents > 2 A
Tyndall Inductor
Performance evaluation- Tyndall vs Wurth
• Input Voltage : 5 V
• Output Voltage: 3.3V
• Output Current Range: 1 A to 3.5 A
• Frequency of Operation: 500 kHz
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84
86
88
90
92
94
96
0 1 2 3 4
Eff
icie
ncy (
%)
IOUT (A)
Wurth
Tyndall litz+solid wire
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Key Summary points
• Very low loss density achieved using post-processing of nanocrystalline thin film material:
o 200 kW/m3 @500kHz & 0.1T Bpeak vs. 700 kW/m3 for 3F35 o 30 kW/m3 @ 100kHz & 0.1T Bpeak vs. 70 kW/m3 for 3C90
• Demonstrated performance of post-processed nanocrystalline thin film material
o 40% reduction in device volumeo 25% reduction in magnetic loss
• Challenge still exist in relation to costs:-o Elemental costso Processing costs
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New Alloy Systems
Tyndall’s low loss material systems
VitroVAC alloy: Co67Fe4B11Si16Mo2
Alloy # 1: CoFe- alloy- New elemental mixture to minimize
cost & also achieve in-situ film thinning
Alloy # 2: CoFe- alloy- New CoFe alloy system to minimize
elemental costs
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New alloy systems
100 kHz
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Key Conclusions
• Ultra-low loss performance demonstrated with as-deposited magnetic thin film
• Further, loss performance improvements under investigation
o In-situ magnetic field induction
o Creep & Magnetic Anneal
• Alloy 1 shows a power loss density of 200 kW/m3 at 100 KHz (same as Vitrovac and ferrite); significant volume and cost reduction
• Tyndall looking for partners to develop this technology further
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Acknowledgements
- Dr. George Young, Dr. Trong Tue Vu - Icergi Ltd.
- Mr. Diarmuid Hogan, Mr. J J Wilkinson - Excelsys Ltd
- Mr. Hugh McCafferty - Nuvotem Talema Ltd
- Dr. Plamen Stamenov, Trinity College, Dublin
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The authors would like to acknowledge European Union, Enterprise Ireland,
Icergi Ltd & Competence Center for Applied Nanotechnology (CCAN) in
funding this work.
The authors also acknowledge the support from Vacuumschmelze, Toshiba
and E-song in providing thin film material for this work.