Reseach On Resistance To Bias Low Temperature Sintering NiCuZn Ferrites And Applied In Power Multilayer Chip Inductor

In recent years, with the development tendency of the electronic equipment to be the direction of portable, integrated and multi-functional, passive components such as multilayer chip high-power inductors develop rapidly. Multilayer chip high-power inductors are widely used in the low-noise amplifier, switching power supply etc. devices. On the one hand, it require the multilayer chip high-power inductors to be miniaturization and high-performance, on the other hand, the multilayer chip high-power inductors need to be stable and reliable under the working condition of DC-bias-superposition. Usually, the DC-bias-superposition characteristics of the multilayer chip high-power inductors are based on its ferrite materials and structure. Therefore, in this paper, DC-bias superposition characteristics of low-temperature-fired ferrites have been investigated for the stability of multilayer chip high-power inductors. Then we designed and produced multilayer chip high-power inductors based on the ferrite which we had prepared.In the first part of the thesis, different amount of SnO2 and SiO2 were doped respectively into low-temperature-fired NiCuZn ferrites to investigate the DC-bias superposition characteristics. The results indicated that all XRD patterns of SnO2 doping exhibited single spinel phase, while the SnO2 doping had obvious influence on the Q factor, incremental permeability, saturation magnetic flux density(Bs) and coercivity(Hc) and the DC-bias superposition characteristics. With the increasing of SnO2 content, the average grain size gradually decreased, while the sintered density gradually increased. The sample with 0.75 wt% SnO2 favored to obtain a better DC-bias-superposition characteristic on incremental permeability, its initial permeability is 120 and H70% is 568A/m. Similarly, SiO2 doped the low-temperature-fired NiCuZn ferrites also had obvious influence on the typical microstructure and magnetic properties. The initial permeability of sample decreased continuously with the increase of SiO2 content. In the experiment, little SiO2 doped low-permeability-composition(group A) and moderate more SiO2 doped low-permeability-composition(group B). The results indicated that the Bs、ΔB、Hc of sample had influence on the DC-bias-superposition characteristics. We found that 0.35 wt% SiO2 doped ferrite A possessed similar permeability with 0.75 wt% SiO2 doped ferrite B. The latter sample presented a better DC-bias-superposition characteristic owing to the higher coercivity. The declining rate of incremental permeability under high superposition magnetic fields was slower for the sample with higher coercivity under higher DC-bias superposition. Therefore we could conclude higher coercivity benefit for better DC-bias-superposition characteristic. According to the initial permeability and H70%, the sample 0.75 wt% SiO2 doped ferrite B obtained a better DC-bias-superposition characteristic, its initial permeability is 57.3 and H70% is 866A/m.From viewpoint of multilayer chip high-power inductors, the purpose of produced multilayer chip high-power inductors was to verify the practicability of B0.75 material. In our experiment, the ferrites material of B0.75 was used for the matrix of multilayer chip high-power inductors, which was produced by Low Temperature Co-Fired Ceramic technology. Then we tested the properties of multilayer chip high-power inductors, and all test performances have been met the design target. The inductance value met 1.0±20% μH, the self-resonant was more than 50 MHz, the direct-current resistance met 0.06±25% ?, and the ranted current surpassed 1000 mA. The test results indicated that the ferrites material of B0.75 was suitable for the the matrix of multilayer chip high-power inductors, which promote the high-power inductors to be the direction of Super-Current and miniaturization.