Research On DC-Bias-Superposition NiCuZn Ferrite And High Power Inductor

In recent years,multi-layer chip inductors have gradually occupied the mainstream market because of their high integration and good magnetic shielding effect.In this paper,the preparation and application of key substrate materials are urgently needed for high current laminated chip inductors.The influence mechanism of multi composite doping on the microstructure,DC bias resistance and comprehensive magnetic properties of power NiCuZn ferrite materials is studied.Firstly,the effects of Bi₂O₃ and Al₂O₃ binary doping system on the electromagnetic properties and DC bias resistance of NiCuZn ferrite are analyzed.It is found that the appropriate proportion of binary doping can promote the growth of the grains,which can increase the material density,permeability,magnetic induction strength and other parameters;At the same time,the demagnetization introduced by the non-magnetic phase Al₂O₃ is beneficial to reduce the effect of the external magnetic field and improve the DC bias resistance of the material.When the doping concentration of Bi₂O₃ is0.16wt%,the properties of the materials change.It is also noted that the addition of ultrafine Al₂O₃ can improve the DC bias resistance of the material and increase the density.The reason is that Al₂O₃ powder has better dispersion in ferrite,enhances the demagnetization field and improves the DC bias resistance of the material;Moreover,Al₂O₃ powder has higher surface activity and is conducive to improve the density of the material.Next,in order to improve the DC bias resistance of the material,BZB-Al₂O₃-Bi₂O₃ternary doping system is introduced.In this scheme,the fine grain matrix can be formed by proper doping of BZB glass.The low melting point Bi₂O₃ can promote the growth of grains and increase the filling density.Non-magnetic Al₂O₃ can enhance the demagnetization field and inhibit the growth of abnormal grains.The experimental results show that the fine adjustment of ferrite microstructure by ternary composite doping is expected to improve the DC bias resistance of the material and maintain good electromagnetic properties.The samples doped with 0.45wt%BZB+0.16wt%Bi₂O₃+0.32wt%Al₂O₃ have special multi microstructure and obtain the best comprehensive properties.The test results show that the DC bias resistance performance parameters H_70%>600A/m（@1MHz）,saturated magnetic induction strength B_s>350m T（@5000A/m）,initial permeabilityμ_i>70。In addition,the density of the material is 4.69g·cm^-3.Finally,based on the power ferrite material,the simulation design of high power laminated chip inductor is carried out.Based on the optimization of the chip inductor structure,the number of layers and the distribution position of the air gap layer,the design of the high power laminated chip inductor is realized by using the air cavity and sacrificial layer structure.The inductance size is 0805 type,and the inductance L=1.06μH at 1MHz.The saturation current I_sat=2.26A and the self resonance frequency is greater than 150MHz,which lays a foundation for the next step of the production of inductor.