Preparation And Microwave Characteristics Of Fe-based High Frequency Soft Magnetic Films

With the development of electronic information technology towards high integration,miniaturization,and high frequency,more and more components are required to be integrated in a smaller substrate.In order to reduce the overall size and weight of the electric system,developing thin film components is practical way to satisfy the requirement above.Microwave soft magnetic films?SMFs?exhibit good magnetic performances,such as high saturation magnetization 4?Ms,high permeability ?,and low damping constant a.The inductance of SMFs-covered inductors will be dramatically enhanced,and then their occupying area in monolithic microwave integrated circuits?MMICs?is drastically reduced.On the other hand,the magnetic field generators,which usually have a heavy weight and/or large power consumption,should be removed from MMICs for satisfying the miniaturization,light weight and low power consumption.Therefore,metal SMFs with endogenous magnetic anisotropy draw an increasing attention.According to the Kittel's equation,fFMR decided by saturation magnetization 4?Ms and the in-plane uniaxial anisotropy field H_K of the magnetic thin films.The in-plane uniaxial anisotropy field H_K as an extrinsic parameter is more sensitive to preparation conditions,defects and so on.It is easier to be increased by 1-2 orders of magnitude.So major research has been focused on improving the uniaxial anisotropy field of the soft magnetic thin films.In this dissertation,we emphasized on the fabrication of soft magnetic films with uniaxial magnetic anisotropy under an Integrated Circuits?IC?compatible process,and the improvement of the microwave soft magnetic performances.The detailed investigation are listed as follows:Firstly,we prepared various stripe permalloy films with composition of Ni₈₀Fe₂₀ by pulsed laser deposition and photolithography.As a control,a continuous permalloy film was also prepared at the same deposition condition.The microstructures and uniaxial anisotropy of Ni₈₀Fe₂₀ thin films with a same stripe length of 5 mm and various stripe width of 20?m,30?m and 40?m stripe were investigated.Comparing with the continuous magnetically isotropic permalloy film,the anisotropy fields H_K increase with the decrease of the FM strips' width.As a result,the ferromagnetic resonance frequency fFMR is enhanced from 1.71 GHz of continuous film to 2.1 GHz of patterned film with FM strip width of 20?m.The comparison of fFMR and the anisotropy field H_K for all samples demonstrates that the enhancement of fFMR can be attributed to the shape anisotropy of permalloy stripe films.Secondly,a series of Fe₅₆Co₂₄B₂₀ amorphous thin films with 65 nm in thickness but different compressive stresses were prepared by pulsed laser deposition method using a stress fixture.The effects of compressive stress on the domain structure and unixial anisotropy of the films were investigated.It was revealed that the easy axis is perpendicular to the direction of stress,and with the increase of compressive stress,the uniaxial magnetic field H_K increases from 54 Oe to over 191 Oe.As a result,the ferromagnetic resonance fFMR is enhanced from 3.41 to 4.03 GHz.It was also found that the stripe domain structures and the contrast of magnetic domain of films are more apparent with the increase of compressive stress.The stress deposition method can not only increase the ferromagnetic resonance frequency of soft magnetic thin films,but also reduce the magnetic loss.