Study On Low Power Loss And Low-temperature-fired NiCuZn Ferrite Materials And Its Application

Miniaturization,lightweight,and intergration are the inevitable trend of the development of modern electronic products,so the miniaturization of switching mode power supply,as an important internal energy supply module,has become a hot research topic.The key to the miniaturization of switching mode power supply lies in the miniaturization of its internal magnetic components as inductors or transformers.LTCF（LTCC）technology,as the mainstream technology of passive integration,provides the possibility for its miniaturization.The magnetic components made by LTCF technology can not only realize the function of inductor or transformer,but also can be used as a substrate for power module,which provides a way to further reduce the cost of the whole power module.For the application of LTCF transformer in DC-DC switching power supply in the thesis,low loss and low-temperature-fired NiCuZn ferrite material should be developed.In order to develop this material,it is necessary to realize low-temperature-fired NiCuZn ferrite about 900℃at first.In the thesis,two kinds of low melting point oxide flux V₂O₅ and Bi₂O₃ were selected to try to reduce the sintering temperature of NiCuZn ferrite to about 900℃.The results showed that the sintering temperature of NiCuZn ferrite can be reduced by doping appropriate amount of V₂O₅ or Bi₂O₃,but the power loss of NiCuZn ferrite can not be improved by V₂O₅.0.2wt%Bi₂O₃ could not only realize low-temperature-fired NiCuZn ferrite about 900℃,but also improved its power loss.Therefore,WO₃,Co₂O₃ and Nb₂O₅ oxides were selected as binary dopants with0.2wt%Bi₂O₃ to compare their effects on the power loss of NiCuZn ferrites.It was found that the density,initial permeability and saturated magnetic induction of NiCuZn ferrite can be increased and the coercivity can be reduced by trace WO₃ below 0.04wt%,thus its power loss could be improved to some extent;Although the density,initial permeability,saturated magnetic induction could be reduced and the coercivity could be increased by Co₂O₃,appropriate amount of Co₂O₃ could improve the power loss of NiCuZn ferrite in a certain range of maximum magnetic induction intensity;the doping of Nb₂O₅ below 0.1wt%not only increased the density,initial permeability,saturated magnetic induction and reduced the coercivity of NiCuZn ferrite,but also obviously improved the power loss under all test conditions.By comparing all the doped samples,the samples doped with 0.2wt%Bi₂O₃ and 0.1wt%Nb₂O₅ not only had almost the highest density（5.32g/cm³）,initial permeability（about 710）,saturated magnetic induction（360.96mT）and the lowest coercivity（75.96A/m）,but also had almost the lowest power loss under all test conditions.Finally,based on NiCuZn ferrite material doped with 0.2wt%Bi₂O₃ and 0.1wt%Nb₂O₅,the simulation of LTCF transformer was carried out by Maxwell software.By structural improvement of opening"Open"type air cavity,a LTCF transformer simulation model with coupling coefficient always greater than 0.97 was obtained.The three-dimensional dimension of the LTCF transformer model was 20mm×20mm×1mm,and the primary and secondary saturation currents were about 0.28A and 0.84A,respectively.