Chemical Synthesis And Application Explorations Of Iron-Based Magnetic Nanomaterials In Microelectronic Packaging

With the development of nanotechnology,the preparation and characterization techniques of magnetic nanomaterials have also made great progress.Nowadays,magnetic nanomaterials have played an indispensable role in the fields related to microelectronics,such as magnetoelectric sensors,high-frequency thin film inductors,thermal conducting composite materials and so on.However,there are still some problems in the preparation and application of FeCo alloy nanomaterials and amorphous FeNiP nanoparticles.As for the synthesis of FeCo alloy nanoparticles,it is difficult to control the morphology and size of the FeCo nanoparticles.What's more,the formation mechanism of FeCo nanocubes and the effect of PEG-400 or cyclohexane on the synthesis of the FeCo nanocubes should be clarified.At the same time,amorphous FeNiP materials are always prepared by electrodeposition which have been reported by other researchers.There is few research works focusing on the chemical preparation.Moreover,the thermal stability of amorphous FeNiP nanoparticles is vital for the application,such as in the field of embedded thin film inductance.The temperature change of the substrate can have a significant impact on the application of amorphous FeNiP nanoparticles.As for the present application of the FeCo alloy nanoparticles,according to the related literatures,the composite films with magnetic fillers used for magneto-electric sensors own low sensitivity and poor mechanical properties.So,the properties of the composite films should be modified.At present,magnetic field-assisted aligned thermal conducting composite materials have poor orientation.What's more,superparamagnetic or soft magnetic nanoparticles which coated on the surface of the thermal conducting materials will impede the direct contact,in which case the interfacial thermal resistance will increase.Therefore,the thermal conductivity of the composite films is low which can not meet the needs of heat dissipation in the field of microelectronics.Therefore,it is urgent to fabricate composite films with perfect aligned structure and high thermal conductivity.In this paper,FeCo and amorphous FeNiP nanoparticles have been prepared firstly,and the controllable syntheses of the morphology and composition of the FeCo nanoparticles were successfully conducted.Crystallization process of amorphous FeNiP nanoparticles was investigated in detail.Then PDMS composite films with anisotropic FeCo chain were fabricated by magnetic field-assisted assembly method.Moreover,by using spray coating method,the composite films with vertically aligned FeCo/hBN structure were obtained which can be used for microelectronic encapsulation or flexible thermal conducting substrate.First,by varying the molar ratio of Fe2+/Co2+ and the concentration of PEG-400 and cyclohexane,as well as the reaction temperature and time,FeCo alloy nano particles with different morphologies have been synthesized successfully,in which the iron content could be adjusted in the range of 17-84 at%.Accompanying the decrease of the Fe2+/Co2+ molar ratio from 5:1 to 1:5,the shapes of FeCo alloy nanoparticles change from sheets,cubes and spheres to flower-like particles.While the Fe2+/Co2+molar ratio is 3:1,the perfect FeCo nanocubes can be obtained in the presence of 2.752g PEG-400 as well as 0.32ml cyclohexane.The FeCo nanocubes have a cubic structure exposing{100}surface facets.It is found that combined action of PEG-400 and cyclohexane plays a vital role in regulating the growth rate of different crystal facets.Their addition effects were discussed,and a growth mechanism was proposed to illustrate the formation of the FeCo nanocubes.While the reaction temperature is 160?,the FeCo nanocubes have the highest saturation magnetization(Ms),which is measured to be 250 emu g-1.And it is higher than that of the FeCo bulk alloy(Fe70Co30-245 emu g-1).To further understand the thermal stability of the amorphous FeNiP nanoparticles,the amorphous FeNiP nanoparticles(70nm)were synthesized by chemical reduction.The crystallization process of FeNiP nanoparticles from room temperature to 800°C were cofirmed by DSC,SEM,XRD and TEM.The involved crystallization behavior can be summarization as:amorphous FeNiP ? Ni + FcNi3 + Ni3P ? Ni +(Ni,Fe)3[PO4]2.And the sintered nanoparticles show varied magnetic properties due to the phase transformation and proportion change among different phases involved in.On the basis of stable preparation of homogenous FeCo nanocubes,flexible and anisotropic FeCo nanochain-PDMS composite films are successfully fabricated by magnetic field induced self-assembly.The embedded nanochains are controllable in average length(<200?m)and width(<2?m)through optimizing the filler mass fraction and the magnetic field intensity,and an ultra-high aspect ratio of 150 can be obtained.The composite films are anisotropic along the directions parallel or perpendicular to the aligned nanochains or nanobundles.The highest tensile strength in the tension direction perpendicular to the nanochains is 3.20 MPa for the composite film fabricated at 60 mT with 1.0 wt%of filler.And different tensile models are proposed to discuss the fracture mechanism.VSM measurements indicate that the nanochains are easier to be magnetized in parallel geometry.By controlling fabrication,one can tune the mechanical performance and magnetic anisotropy of the thin polymer nanocomposite films synchronously.Considering the anisotropic thermal conductivity of hBN nanosheets,composite films containing FeCo/hBN vertically aligned structure were preparaed by spray coating technology and magnetic field-assisted assembly method.Exfoliated negatively charged BNNs and positively charged FeCo nanocubes self-assemble to form complex nanomaterials by strong electrostatic interactions.Then the BNNs can orient with FeCo nanocubes in magnetic field,of which the {001} facets of BNNs adsorb on the{100}facets of FeCo nanocubes.The large scale range and high-density FeCo/hBN aligned structures are observed by SEM,which can act as thermal dissipation channels by conveying more phonons through a preponderant thermally conductive direction.In this way,it can solve the inferior thermal conductivity of composite films encountered by other researcher.The thermal conductivity of the composite films with 30 wt%FeCo and 50 wt%BN filler is 2.25 W m-1 K-1,which is seven times higher than that of the films with 50 wt%randomly distributed hBN filler(0.33 W m-1 K-1).Apart from the surprising thermal conductivity,FeCo-BNNs composite films also exhibt superb flexibility and low moisture absorption.