Electromagnetic And Microwave Properties Of NiFe-based Soft Magnetic Films

With the rapidly development of GHz electromagnetic microwave communication technology, the electromagnetic interference between the electronic components become more and more serious, which is threat to the information security seriously; The permeability drops rapidly and unstable performance for some electromagnetic devices such as inductors, transformers and other microwave devices under the condition of high frequency; As the development of military reconnaissance technology, the traditional stealth materials are no longer meet the demand of modern and future military confrontation. Due to the permeability attenuation of traditional magnetic materials under high frequency, all aspects of the traditional magnetic materials performance have been cannot satisfy the requirement of developing new electromagnetic devices, it requires to develop the high frequency magnetic materials that suitable for GHz frequency band, miniaturization, low loss and new anti-interference needed for the high frequency. At present, the high frequency electromagnetic devices are development toward to miniaturization and chip. As a result, the new type of metal soft magnetic thin film can satisfy this requirement, today it is occupied a pivotal position and become the research focus in the modern wireless communication, radar, electronic countermeasures,stealth technology, bluetooth, mobile phones, satellite television, instrument measurement, electromagnetic shielding, microwave dark room, and computer storage. The permalloy Ni Fe-based soft magnetic thin film has a good performance: low coercive force, high saturation magnetization, high Curie temperature, high magnetic permeability and excellent magnetic properties such as magnetic anisotropy characteristic, which is suitable for application in high frequency, so it is used widely.The topic is depositing the Ta/Ni Fe/Ta monolayer、 [Ni Fe(x nm) /Ni Fe O(y nm)]10 and Ta/[Ni Fe(8 nm)/Ni Fe O(y nm)]10/Ta multilayer film on the surface of the(100) Si based wafer by DC magnetron sputtering method at room temperature. In the whole process of sputtering, there is always an extra magnetic field about 120 Oe that parallel to the substrate surface which is used toinduce the in-plane uniaxial anisotropy.X-ray diffraction(XRD) analysis the crystal structure of the thin films;Energy Dispersive Spectrometry(EDS) was used to determine the composition of the elements in the films. Transmission electron microscope used to observe structure of the multilayer; Using four point probe method to measure the resistivity of the samples; Vibrating sample magnetometer to draw the hysteresis loop of the sample, which can analyze the static magnetic of the thin films,including saturation magnetization, the coercive force and anisotropy field; The magnetic spectrum of all samples from 0.2 to 5 GHz measurement by a single port of short-circuit method(microstrip method) in the vector network analyzer.All the samples exhibit a single diffraction peak relative to the(111) plane of the fcc Ni Fe phase. Ni Fe monolayer film possess excellent soft magnetic properties, such as high saturation magnetization, low coercive force, and an obvious anisotropy, but the change of film thickness can’t make contributions to the anisotropy, all the resonance frequencies are very low, about in 1 GHz. The multilayer films mixed Ni Fe O layer are more excellent in high-frequency performance than the monolayer films, the multilayer film of [Ni Fe(x nm)/Ni Fe O(y nm)]10 which is a single cycle of Ni Fe/Ni Fe O total thickness of 10 nm, the resisitivity and high frequency performance increase with the rising of the y. when y > 5 nm, the resonant frequency will be higher, but the permeability will continue to decrease, which is too small to used in microwave devices, when the single cycle Ni Fe O is 5 nm, the resonance frequency and magnetic permeability is large enouph to used in microwave devices. For the structure of[Ni Fe(8 nm)/Ni Fe O(y nm)]10 multilayer film, the single cycle of Ni Fe layer thickness remain 8 nm, to regulate the microwave electromagnetic properties by change the Ni Fe O layer thickness, because of the y value also cannot too large,otherwise the permeability is too small that can not to used in the actual application, the excellent microwave and electromagnetic properties can be obtained when the single cycle Ni Fe O layer is 6 nm, the resistivity is 268.8μΩ·cm, the resonance frequency is 2.85 GHz, the real part( ? ’) of the complex permeability is larger than 100 in the range of 0.2~1.9 GHz and the damping coefficient increases to 0.078 for y = 6 nm. The comprehensive performance is more outstandingthan the [Ni Fe(5 nm)/Ni Fe O(5 nm)]10 film.