Investigation On Electronic And Magnetic Properties Of Soft Granular Films And Its Application Basis In GHz Frequency Band

With the rapid development of the electronic industry, a remarkable tendency inelectronic device is the continued increase in the operational frequency and degree ofintegration in order to reduce volume and to enhance the data transfer rates. As one ofthe key part of the electronic components, magnetic components must adapting thetendency and development towards high frequency and miniaturization. The highpermeability magnetic material with operating frequency above1GHz is a bottleneckfor development the magnetic components and then realization the finally integration ofthe electronic systems. The traditional bulk magnetic material can not have both highpermeability and excess of1GHz operating frequency due to the limitation of itselfproperties. To satisfying applied demands, a great deal of research effort has beendevoted to exploring magnetic granular films with high frequency performance. Thinfilms electromagnetic noise suppressors are one of the proposed applications.The fundamental requirements for these films characteristics are excess of1GHzoperating frequency, high permeability, favorable electromagnetic matching andperformance control in the nanometer scale. Based on the above requirements, softmagnetic FeCoHfO, NiFe-NiZnFe2O4and FeCo-SiO2thin films are fabricated usingradio frequency (rf) magnetron sputtering, the electrical and magnetic properties ofthese thin films are studied. The films with optimal performance will be used in theresearch of the electromagnetic noise suppressors.Granular FeCoHfO thin films are fabricated using rf magnetron reactive sputtering,influences of partial pressure of oxygen (PO₂=O₂/O₂+Ar), sputtering power andannealing on the magnetic properties of films have been investigated. The saturationmagnetization (4MS) decreases with increasing PO2and the electrical resistivity of thefilms monotonically increases with the increasing of PO2at fixed sputtering power andpressure. The coercivity (Hc) of films decreases with the increase of PO2when PO2＜5.1%, increases with the increase of PO2when PO2＞5.1%. The change of in-planeuniaxial anisotropy field (Hk) has a contrary trend compared with coercivity. The films show optimal properties of high saturation magnetization4Ms¹8.3kG, high electricalresistivity²675cm and high natural ferromagnetic resonant frequency fr³.1GHzwhen PO2=5.1%. The permeability spectra of films display relaxation character whenPO2deviation from5.1%in a large range. The average size of-FeCo particle is9nm.The sputtering power has an important effect on structure and composition of films, andthen modifies the film magnetic properties in the case of fixed PO2=5%. Thenonmagnetic content of films decreases with the increase of sputtering power and themagnetic FeCo atoms have an inverse trend. With the increase of sputtering power from50W to300W, films decreases steeply and the frranged from0.92GHz to3.2GHz.The best soft magnetic properties with4Ms20.5kG, Hc1Oe, fr3.2GHz and2500cm are obtained at200W sputtering powers. In the condition of fixedsputtering power of200W, fr,4Msand Hkdecrease with the increases of sputteringpressure, Hcand have an opposite trend.For the typical sample of x0.13, the (Ni80Fe20)1-x(Ni_0.5Zn_0.5Fe₂O₄)xfilms withdesired properties of Hc².5Oe,4Ms⁹.8kG,¹500cm and fr².9GHz areobtained. The sputtering power has a significant effect on electronic and magneticproperties of films. For the FeCo-SiO₂films, with the increases of SiO2volume ratio,4Msdecrease and increase, the frof films changed from2.86GHz to4.05GHz. Thetypical films with fr⁴.05GHz,4Ms¹6.4kG, Hc².5Oe, Hk¹08Oe and¹600cm are obtained. With the film thickness increasing from50nm to1200nm,effective damping factor effand the full width at half maximum f of the imaginarypart increase in a large range, indicating presence the extrinsic damping contributions,but the films still has favourable properties. The average size of-FeCo particle is3nmin FeCo-SiO₂flames. The influences of Cu underlayer on the FeCo-SiO2properties arealso investigated. The results show that different thickness Cu underlayer can notobviously improve the soft magnetic properties of films, but have a significant effect onthe dynamic magnetic properties of films.The FeCo-SiO₂films possess optimal comprehensive performance, itselectromagnetic noise suppression characteristic are studied. The results show that withthe increase of film thickness the signal attenuation increases. The maximum value ofsignal attenuation is close to60dB when film thickness is1200nm. In the condition offixed film thickness, the signal attenuation decreases with the increase of thickness of SiO₂dielectric layers while the resonance frequency have no obviously change. Theresonance frequency of noise suppression is closely related to film natural resonancefrequency which indicates ferromagnetic resonant is responsible for the loss generation.The main mechanism of the loss generation is found to be the ferromagnetic resonance,not L-C resonance which induced by distributed inductor (L) and distributed capacitor(C).