Preparation Of NiZn Ferrite Thin Films By Sputtering Method And Brillouin Function Temperature Characteristics Of Magnetization

As one of the three most important passive components in the circuit structure,the inductor is widely used in power supplies,filters,oscillators,low noise amplifiers,impedance matching networks and other components.NiZn ferrite film has high saturation magnetization,magnetic permeability and high resistivity,which is very suitable for the development of high frequency magnetic devices.In this paper,the NiZn ferrite film was prepared by RF magnetron sputtering.The effects of the formulation and process parameters on the microstructure and magnetic properties of the film were studied systematically.Based on the Néel molecular field theory,the Brillouin function temperature characteristics of the magnetization of the film were studied.Firstly,Ni_0.91-xCu_0.09Zn_xFe_1.998O₄（x=0.62⁰.70）target was prepared by Solid phase reaction.The phase structure,microstructure and magnetic properties of NiZn ferrite target were studied.influences.The results show that:（1）ZnO acts as a co-solvent,and the grain size and density of NiZn ferrite increase with the increase of ZnO content;（2）Influence of the occupancy distribution,NiZn ferrite material The saturation magnetic induction intensity is slightly reduced;（3）The increase of non-magnetic ion Zn²⁺can significantly reduce the magnetocrystalline anisotropy constant and magnetostriction coefficient,increase the initial permeability and reduce the coercive force.Secondly,based on the prepared targets,different compositions of thin films were prepared by sputtering method,and the Brillouin function temperature characteristics of the magnetization of the films were studied.The results show that:（1）With the increase of ZnO content,the grain size of the sample increases,and the saturation magnetization and resonance frequency decrease.（2）Using the Brillouin function to fit the M^T curve of the sample,with the increase of Zn content The molecular field coefficientsω_ab=ω_baa andω_bb decreases,andω_aa increase.At the same substitution amount,the value ofω_ab=ω_ba is always the largest compared to the other two molecular field coefficients,indicating that the super-exchange effect between the A-B lattices is the largest.Then,the effects of sputtering pressure,sputtering power,substrate temperature and annealing temperature on the properties of the film were investigated.The following conclusions were obtained by XRD,SEM,VSM and other tests on the film:（1）The grain size of the film deposited at 1.5Pa is the most uniform,the M_s of the film is up to 175kA/m,and the H_c is the smallest;（2）the grain size of the NiZn ferrite film increases with the increase of sputtering power.When 140W,the saturation magnetization M_s is the largest and the coercive force H_c is gradually increased.（3）The increase of the substrate temperature promotes the grain growth of the film,the saturation magnetization M_s increases,the defect concentration decreases,and the coercive force decreases.When the substrate temperature continues to rise,the film structure deteriorates and M_s decreases.（4）The annealing process promotes the crystallization of the film,the grain size increases,and the saturation magnetization M_s of the film increases remarkably after annealing,and the annealing temperature increases.The M_s of the film gradually increased.Finally,in order to solve the problem that the ferrite film is compatible with the semiconductor process in subsequent device applications,the NiZn ferrite bilayer film prepared by the combination of the magnetron sputtering method and the spin coating method is used.The results show that:（1）The introduction of the seed layer promotes the crystallization and grain growth of the NiZn ferrite bilayer film spinel phase under low temperature conditions,and increases the film density,the saturation magnetization M_s increases from 74kA/m to 420kA/m and the magnetic permeabilityμ’（300MHz）increased from 90 to 202;（2）Due to the rough surface of the seed layer,the internal stress of the film is increased,so that the coercive force H_c of the sample increases,and the introduction of the seed layer increases the film.The effective anisotropy field,the cutoff frequency f_r rises.