Study On Fabrication And Magnetic Properties Of High-density Fe-based Nanoparticle Films For GHz Band

In recent years,with the rapid development of electronic information industry and internet of things?Io T?,the need of miniaturization,high operation frequency and integration of electronic devices and higher requirements for soft magnetic materials as the core of electronic devices have been raised.The traditional bulk magnetic material can not have both high permeability and GHz operating frequency due to the limitation of itself properties.To satisfying applied demands,a great deal of research effort has been devoted to exploring magnetic granular films with GHz microwave performance.The basic requirements for soft magnetic films include high saturation magnetization,high electric resistivity,high stability,low coercivity and suitable in-plane magnetic anisotropy field.In addition,with the films trend toward to miniaturization and pattern,the changing on electromagnetic performances of films must be considered.Many technical methods,such as traditional sputtering,molecular beam epitaxy,and thermal evaporation,have been employed for the preparation of soft magnetic nanoparticle films.But,these nanoparticle films usually exhibit low saturation magnetization due to their super-paramagnetic characteristic.In this work,Fe-based alloy soft magnetic thin films were prepared by electric field assisted deposition technique.Conventional ultra-violet photolithography and lift-off methods were used to fabricate the strip-patterns.The microstructure,magnetic properties,microwave characteristics of the samples were investigated systematically.The main results were carried out as follows:?1?A systematic study about the effects of preparation conditions on the microstructure and magnetic properties of FeNi films has been done.The microstructure characteristics indicate that the application of the EF during deposition is a very promising method to prepare Fe₅₀Ni₅₀ nanoparticle films with higher stacking density.The Ms of Fe₅₀Ni₅₀ nanoparticle films prepared at 20 k V is about1.32 T,which is nearly 85%of the one for bulk fcc–Fe₅₀Ni₅₀ alloy.The 200 nm-thick sample annealed under a vacuum environment exhibits a higher ferromagnetic resonance frequency 3.2 GHz.?2?The high-density Fe₅₀Ni₅₀ nanoparticle films with strip structures were prepared by electric field-assisted deposition technique with no external magnetic field applied on substrates.It is found that application of EF during deposition induces the double increase of in-plane uniaxial magnetic anisotropy and saturation magnetization for our samples.?3?The experimental results have confirmed that the samples exhibit a considerable enhancement of in-plane uniaxial magnetic anisotropy and excellent soft magnetic properties as temperature increases from 200 to 400°C.From the perspective of practical application,there are many processing steps finished at around 400°C in modern CMOS and MEMS technique.Therefore,the nanoparticle films prepared in this study have a broad application prospect in the GHz electron magnetic devices which are processed by CMOS and MEMS technology.?4?The patterned FeCoB-SiO₂ nanoparticle films have the basic demands for soft magnetic films operated in the GHz range including high resistivity,high saturation magnetization,low coercivity and appropriate anisotropy field,making it possible for high permeability???and high resistivity???in same materials.More importantly,excellent microwave magnetic properties were obtained in a wide v?v=11⁵5%?range by carefully controlling the strip width of SiO₂.