Why is the Ferrite Material Development for GaN so Difficult?

JC SunBs&T Frankfurt am Main GmbH

04. December 2018power electronics conference in München

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content

• Introduction Bs&T• Demand on ferrite material development• Need for GaN application• High Bs material for high power and high

frequency application• Conclusion (roadmap of material development)

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Bs & T Analyzer

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Sinus Magnetization AC Pulse Magnetizationhigh excitation low excitation fast transit of magnetic state

IEC 62044-3 IEC 62044-2 dB/dt

loss, µa driven by B mode

Bpeak, loop driven by H mode

DC superposition

BsT-Pro BsT-Pulse

loss map (f, B, T, HDC) µrev differential and amplitude L

major, and biased minor loop energetic L, power loss

Bs & T Analyzer

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Square Wave

PCIM 2018

Demand on ferrite material

• Driving forces for development of ferrite material

information and communication technologyenergy digitalization

• High power and power density application require new materials outside of the conventional power ferrite material map

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Soft magnetic behaviour

• Good soft magnetic behaviour:large magnetization changes as a result of very smallapplied magnetic fields ~ high permeability

easy rotation of magnetization vectoreasy motion of domain wallhigh versatility

• „Ideal“ soft magnetic material:magnetically isotropic and structurally homogeneous, no crystallographic easy axis, no defects, no grainboundary, no internal stress, no magnetostriction

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Design consideration of softmagnetic materials

• Intrinsic material properties, depend only on material composition (unaffected by the microstructure), are:Tc, Bs and crystalline anisotropy K1, λsselective choice of the material composition

• Structure sensitive properties are:Hc, permeability µ and Brproper processing route

The most important microstructural parameters are: grain size, crystallographic texture, lattice defects, volumefraction as well as the size and chemical nature of non-magneticinclusion and internal stresses

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R+D

M

Performance factor 300 mW/cm3 @ 100°C materialmap

nanocrystalline

Alex Goldman: modern ferrite technology

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Consideration for material choice

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GaN for high voltage application

• P = U I• High U; U = dB/dt• Large I; low permeable (powdered) cores• Need for magnetic component is high flux

linkage, corresponding to accessible saturation flux density

• High Bs material

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How to achieve the highest Bs MnZnFerrite material ?

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State of art methodology

GaN for high frequency application

• High switching frequency requires high resonance frequencySnoek’s fR ~ Ms / µ

Ms/Bs should be as high as possible, at same timeµ should be as low as possible

• Key issue is heat dissipation @ MHzresistivity and permittivity investigation are necessary

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Resistivity for high frequency

the dc resistivity roughly scales as the resistivity of the grain boundaryRg:V2O5, Nb2O5 Rb: SnO2 , SiO2, CaOCb: Ta2O5

IEEE TRANSACTIONS ON MAGNETICS, VOL. 50, NO. 1, JANUARY 2014 13Bs&T Frankfurt am Main GmbH

Low frequency

High frequency

Chemistry dopants for high resistivity

Resistivity on grain 3F3

Resistivity on boundary 3F4

Number of publication ICF 6 /7 about dopants are available

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High Bs ferrite material for GaN application

• Highest Bs ferrite material for high voltage application. The benefit in combination with the largest possible size as monolith in favor of high power magnetic component design (core height 5 inch, and length of 8 inch)*, commercially available

• Highest Bs ferrite material is essential for highest possible resonance frequency: trade-off MnZnFerrite vs. NiZnFerrite

• High resistivity with comprehensive investigation with number of dopants at expense of Bs has been studied since decades, the chemical composition is just only one consideration, the morphological optimization is process related

• Resistivity @ applied frequency and operation temperature have to be firstly specified as material properties

* IEEE September 2018Recent Ferrite material development for high power application

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Conclusion

• MnZnFerrite material for high voltage GaN is commercial available, its power magnetic component can be charaterized by BsT-pulse (thyristor based technology enables bipolar excitation) funded by EU H2020 and VDE DIN-Connect, dB/dt provides useful assignments of magnetization inductance and current

• MnZnFerrite for high frequency GaN is still vague, and under development, the most critical part is experimental approval by suitable measuring technique due to problem with thermal inequilibrium, BsT-SQ can be a help (GaN based loss tester)

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Annex 1 measuring data for simulation

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BsT-Pro 2016

BsT-SQ 2018BsT-Pulse 2017

BsT-ProBsT-SQ

BsT-Pulse

Annex 2 BsT-Pulse

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1. assignment inductance vs. current NOT unique

2. Voltage decay pending on DUT

Annex 3 BsT-SQ with Herbert Curve

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mW

µs

Annex 4 Diverse D.U.T.s

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Power ferrite Fe amorphous

metal alloyed powder “HF” ferrite