Why is the Ferrite Material Development for GaN so Difficult?

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Rudolf Burke
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1 Why is the Ferrite Material Development for GaN so Difficult? JC Sun 04. December 2018 power electronics conference in München 1

2 content Introduction Bs&T Demand on ferrite material development Need for GaN application High B s material for high power and high frequency application Conclusion (roadmap of material development) 2

3 Bs & T Analyzer Sinus Magnetization AC Pulse Magnetization high excitation low excitation fast transit of magnetic state IEC IEC db/dt loss, µ a driven by B mode B peak, loop driven by H mode DC superposition BsT-Pro BsT-Pulse loss map (f, B, T, H DC ) µ rev differential and amplitude L major, and biased minor loop energetic L, power loss 3

4 Bs & T Analyzer Square Wave PCIM

5 Demand on ferrite material Driving forces for development of ferrite material information and communication technology energy digitalization High power and power density application require new materials outside of the conventional power ferrite material map 5

6 Soft magnetic behaviour Good soft magnetic behaviour: large magnetization changes as a result of very small applied magnetic fields ~ high permeability easy rotation of magnetization vector easy motion of domain wall high versatility Ideal soft magnetic material: magnetically isotropic and structurally homogeneous, no crystallographic easy axis, no defects, no grain boundary, no internal stress, no magnetostriction 6

7 Design consideration of softmagnetic materials Intrinsic material properties, depend only on material composition (unaffected by the microstructure), are: T c, B s and crystalline anisotropy K 1, λ s selective choice of the material composition Structure sensitive properties are: H c, permeability µ and B r proper processing route R+D M The most important microstructural parameters are: grain size, crystallographic texture, lattice defects, volume fraction as well as the size and chemical nature of non-magnetic inclusion and internal stresses 7

8 Performance factor 300 mw/cm 100 C material map nanocrystalline Alex Goldman: modern ferrite technology 8

9 Consideration for material choice 9

10 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 B s material 10

11 How to achieve the highest B s MnZnFerrite material? State of art methodology Zaspalis

12 GaN for high frequency application High switching frequency requires high resonance frequency Snoek s f R ~ M s / µ M s /B s should be as high as possible, at same time µ should be as low as possible Key issue is heat MHz resistivity and permittivity investigation are necessary 12

O 5, Nb 2 O 5 R b : SnO 2, SiO 2, CaO High frequency C b : Ta 2

13 Resistivity for high frequency Low frequency the dc resistivity roughly scales as the resistivity of the grain boundary R g :V 2 O 5, Nb 2 O 5 R b : SnO 2, SiO 2, CaO High frequency C b : Ta 2 O 5 IEEE TRANSACTIONS ON MAGNETICS, VOL. 50, NO. 1, JANUARY

14 Chemistry dopants for high resistivity Resistivity on boundary 3F4 Resistivity on grain 3F3 Number of publication ICF 6 /7 about dopants are available 14

15 High B s ferrite material for GaN application Highest B s 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 B s has been studied since decades, the chemical composition is just only one consideration, the morphological optimization is process related applied frequency and operation temperature have to be firstly specified as material properties * IEEE September 2018 Recent Ferrite material development for high power application 15

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)

16 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) 16