The Preparation And Magnetic Properties Studies Of High-Frequency Magnetic Thin Films

With the advance of information technology and digital electronic products,there has been an increasing demand for electronic devices and basic materials used in them. Up to now,SIP(system in package)technolgoy is still the main technology in fabrication of monolithic integrated circuits(MICs)technology due to 2D inductors occupy too large area in MICs boards.In order to miniaturize the size,to reduce the power,to enhance the reliability of electromagnetic devices,and to increase the data transmission rate,MICs technology must be converted from SIP to SOC(system on chip).The key fator,which affects this conversion,is the size of inductors.The inductor should exhibit large enough inductance and should be small enough to be integrated into circuit.Ferromagnetic materials give rise to an increase of inductance so that it can effectively miniaturize the size of inductors.Therefore,the ferromagentic inductors are widely employed in SOC technology.Wireless communications utilize increasingly high working frequencies reaching MHz and GHz now.For example,2.4 and 5.8 GHz are typical frequencies for bluetooth technology.Therefore,it is desire to prepare the magnetic materials with ferromagnetic resonance frequencies higher than the corresponding working frequencies. In this dissertation,Fe-based and FeCo-based high-frequency ferromagnetic thin films were prepared and studied.The high-frequency ferromagnetic properties and theoretical interpretation for high uniaxial magnetic anisotropy of the films were investigated.The investigation details were summarized as follows:Firstly,Fe-based FeNdBO films were deposited by dc magnetron sputtering.The film annealed at 350℃for 1 hour exhibits the ferromagnetic resonance frequency in excess of 3 GHz and the relative permeability of 100.The good high-frequency ferromagnetic properties can be attributed to the high values of Ms(15.7 kG),H_k,(over 1000 Oe),and,ρ(more than 10Ωm).These results demonstrate that the annealed FeNdBO thin film is a potential candidate for high-frequency applications.Secondly,FeCo-based thin films(FeCoHf,FeCoZr)were prepared by a rf gradient sputtering(GS)method at room temperature.The anisotropy fields of GS annealed films were great larger than that of co-sputtered films.A distinct uniaxial magnetic anisotropy (UMA)up to 300 Oe,and high resonance frequency over 3 GHz was achieved in the magnetic annealed films.Experimental results reveal that doping element Hf/Zr atoms was introduced into FeCo sublattice,giving riseg to a lattice expansion and stress enhancement.GS FeCoHf(FeCoZr)displayed evident unixial magnetic anisotropy,with its easy axis perpendicular to the direction of gradient composition in the plane.The uniaxial stress distribution along composition gradient of dopping elements results into the ordered arrangement of magnetic moments.In other words,the uniaxial magnetic anisotropy in the GS films can be attributed to the uniaxial Hf/Zr composition distribution. As a result,high-frequency ferromagnetic properties can be obtained in GS thin films. The gradient sputtering is an effective way to prepare for good high-frequency ferromagnetic films.