Study On The Preparation Of Magnetic-Dielectric Composite Films And Its Electromagnetic Wave Absorption Properties

In the current days,the emergence of all kinds of wireless communication technology and electronic digital products has brought great convenience to our life.However,when people use these electronic products,the harm caused by electromagnetic radiation to human body and surrounding environment cannot be ignored.Therefore,electromagnetic radiation and protection technology has become a research popular topic of the researchers.The absorbing film material has the advantages of small space,light weight,flexible adjustment of film composition to change the absorbing characteristics of the film,and can meet the special requirements of impedance matching through the structure design of gradual change or gradient film system,so this kind of material has a very broad application prospect in the GHz frequency band.The absorption efficiency of the electromagnetic wave absorbing material is the result of the interaction of the magnetic and dielectric properties of the absorbing body.Therefore,it is generally required that the material should have a large complex permeability,especially the imaginary part should be as large as possible,and a lower real part of the dielectric constant,so as to achieve a good impedance matching effect.In this way,when the incident electromagnetic wave acts on the surface of the absorbing material,most of the electromagnetic wave can be incident into the absorber,and the energy of electromagnetic wave can be absorbed through the dissipation of the film to achieve the purpose of attenuation or even completely shielding of the electromagnetic wave.In this thesis,FeCoB-SiO₂ nano-composite films were deposited on polyimide?PI?substrates by magnetron sputtering double target co-sputtering.The effects of composition and process conditions on the physical properties and electromagnetic wave absorption properties of the films were studied.X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,atomic force microscopy?AFM?were used to characterize and analyze the composition,microstructure and morphology of the film.VSM,VNA and short-circuit micro-strip line were used to measure the static magnetic properties of the film.The absorption property of electromagnetic wave is studied.The results show that the effect of increasing sputtering power on the deposition rate of FeCoB and SiO₂ films is linear increasing.The composition of FeCoB and SiO₂ films is close to the target composition or stoichiometric ratio.When the volume ratio of FeCoB to SiO₂ in the composite film changes from 0.9:0.1 to 0.4:0.6,that is to say,with the decrease of the volume fraction of the magnetic medium in the FeCo B-SiO₂ composite film,the complex permeability and the electromagnetic wave absorption property of the film decrease gradually.The volume ratio of 0.7:0.3 is the critical value of the obvious wave absorption property of the FeCoB-SiO₂ composite film.The complex permeability and microwave absorption of FeCoB-SiO₂ composite film can be improved to a certain extent by sticking different amount of pure Fe sheets on the surface of FeCoB target to change the ratio of Fe and Co.For example,when the volume ratio of FeCoB-SiO₂ is 0.9:0.1,with the increase of the number of Fe sheets,the resonance frequency fr of the composite films moves to the high frequency direction,and the absorption band moves to the high frequency direction both the width and the absorption properties are improved.The initial frequency when the absorption efficiency reaches more than 90%is about 1.5 GHz,and the highest resonance frequency is 2.34 GHz.In the deposition process of the composite films,the application of bias magnetic field can significantly affect the in-plane uniaxial anisotropy of the composite films,and then change the absorption properties of the films.For example,under the action of 180 Oe and 380 Oe bias magnetic fields,the resonance frequency of FeCoB-SiO₂?volume ratio of 0.9:0.1?films can be increased from 2.7 GHz of the former to 4.1 GHz of the latter,the high-frequency absorption characteristics of the composite films are significantly enhanced under the strong bias magnetic field.