Preparation Of NiZn Ferrite Film By Spin Spraying Method And Its Study On Application Technology

With the rapid development of electronic information products towards high frequency,miniaturization and integration,inductor,as one of the three major passive components,limits its integrated development in circuit system due to the huge volume and quality of traditional magnetic materials.Therefore,the development of high-performance and Integrable soft magnetic films becomes more and more urgent.In this paper,NiZn ferrite thin films were prepared by spin spraying method.The heating temperature in the reaction process is not more than 150°C,and the process flow is compatible with semiconductor process.Therefore,on the basis of low-temperature deposition of NiZn ferrite thin film,the planar thin film inductor is designed by simulation,and the thin film inductor which can be applied to system on chip is fabricated by microelectronic technology.In this paper,NiZn ferrite thin films were prepared by spin spraying method.The effects of main formula（Fe content,Zn content and Co content）and process conditions（deposition time and substrate type）on the microstructure and magnetic properties of the films were investigated.（1）With the decrease of Fe content(mainly Fe²⁺)in the main formula,the grain size of NiZn ferrite film is gradually refined and uniform,and the saturation magnetization M_sdecreases.At the same time,the decrease of Fe²⁺content leads to the decrease of the magnetocrystalline anisotropy constant K₁,which significantly increases the permeabilityμ’of the NiZn ferrite film,decreases the coercive force H_c,and decreases the cut-off frequency f_r.（2）With the increase of the Zn content in the main formula,the grains of the NiZn ferrite film increase and become more uniform;when the Zn content increases to a certain level,the grains agglomerate and the density of the film decreases.As the content of Zn increases,the crystal grain and density of the film change,causing its saturation magnetization M_s and permeabilityμ’to increase first and then decrease.The coercivity H_c and cut-off frequency f_r of the films decrease monotonously due to the decrease of magnetic anisotropy.（3）With the introduction of the Co component in the main formula,the grains of the NiZn ferrite film become fine and uniform,and the saturation magnetization Ms decreases.The appropriate amount of Co²⁺is introduced to reduce the magnetic anisotropy of the film through the compensation of the positive and negative magnetocrystalline anisotropy constants,so that the permeabilityμ’is significantly increased,the coercive force H_cdecreases,and the cut-off frequency f_r Will be reduced.（4）With the increase of deposition time,the film thickness increases gradually,the deposition rate first increases and then decreases,the coercivity decreases,and the other magnetic properties change little.（5）Compared with the NiZn ferrite film on the Si O₂ substrate and the PI substrate,the film on the Glass substrate and the Si₃N₄ substrate has fine and uniform crystal grains,high density,and greater saturation magnetization M_s.At the same time,the coercivity H_cof the Glass substrate and the Si₃N₄ film is also lower,the permeabilityμ’is relatively higher,and the cut-off frequency fr is relatively reduced.Through the optimization of the main experimental formula and process conditions,the NiZn ferrite film was prepared on glass substrate Ni_0.41Zn_0.18Co_0.02Fe_2.39O₄.The magnetic film has the following excellent magnetic properties:permeabilityμ’≥120（100MHz）,cut-off frequency f_r≥200 MHz,saturation magnetization 4πM_s≥4800 G_s,coercivity H_c≤10.7 O_e.Two kinds of thin film inductors,planar solenoid type and planar spiral type,are designed by Comsol software.The influences of geometric parameters（turns,line width,line spacing and coil thickness）,magnetic film characteristic parameters（magnetic film thickness,magnetic film width and permeability）and different substrates on the performance of thin film inductors are studied.The simulation results show that,compared with the planar solenoid thin film inductor,the planar spiral inductor can reduce the substrate loss more effectively by using the substrate with high resistivity and low dielectric constant PI transition layer,so as to significantly improve the quality factor of the thin film inductor.The simulation parameters of planar helix thin film inductor are optimized as follows:turns 30,line width 30μm,line spacing 30μm,coil thickness 13μm,magnetic film thickness 1μm,permeability real part 80,substrate PI layer thickness50μm,single inductor size 3.95 mm×3.95 mm,inductance L is 1.291μH（100 MHz）,quality factor Q is 20.85（100 MHz）,resonance frequency f₀≥160 MHz.4×4 planar helix thin film inductors were fabricated on 35 mm×35 mm substrate by microelectronic technology.The thin film inductors were tested by microwave probe and network vector analyzer.The test results show that the inductance L is 0.96μH（100MHz）,the quality factor Q is-3.5（100 MHz）,and the resonant frequency f₀≥140 MHz.