Ultra Low Dielectric Material Inspired By The Concept Of Nanocomposite

With the rapid development of microelectronics industry,the corresponding electronic devices and integrated circuits are developing toward the direction of miniaturization and high density.The improvement of the component density and function,more and higher requests are needed for low dielectric technology.The introduction of nanopores into the material can reduce the dielectric constant(k).But each decrease of 0.1 of k,at least 10% of the porosity is needed to introduce.So a large number of pore structure is often needed to get ultralow dielectric constant,what sacrifice the mechanical properties of the material.In recent decades,nanocomposite as a means of modification of polymer materials,has been widely used.The prominent feature of nanocomposite is that it can significantly change the mechanical,thermal,optical and electrical properties of polymers by extremely small amounts of nanoparticles.The internal mechanism of action is that the polymer chains are arranged on the surface of the nanoparticles through the large specific surface area and strong interface of the nanoparticles,which can change the properties of the polymers to a great extent.The effect of nanocomposite is expected to play an important role in the regulation of low dielectric properties.At the same time,the preparation of low dielectric materials with nanocomposite technology can further improve the mechanical properties of materials and is more simple and efficient than traditional chemical or porous methods,Showing a significant performance advantage.Based on the above ideas,this paper uses several typical nanocomposite systems to study the effect of nanocomposite effect on the low dielectric properties of materials and obtain the ultralow dielectric constant(k = 1.77)and low loss(10-3)Nanocomposites.The effects of nanocomposites on the dielectric properties were studied by using typical nanocomposite systems,linear low density polyethylene(PE)/silica nanoparticles(SNP)composites.A series of nanocomposite materials(PE/SNP)with different volume fraction of silica were obtained by hot-press forming using SNP with diameter of 20 nm as nanofiller particles.Dielectric test found that the dielectric constant of the composites was reduced from 2.45 to k = 1.93(10 MHz)when the volume fraction of silica was 3.58%.At this test frequency(well above 1000 Hz),the dielectric constant is mainly determined by Electron and molecular polarization,slightly by directional polarization and the interface polarization,so dielectric constant is mainly related to the quantity and arrangement of dipole.With the increase of SNP content,the dielectric constant decreased first and then increased.Scanning electron microscopy and density test results showed that there were only a few holes or defects in PE/SNP nanocomposites,which precluded the effect of porous structure on the dielectric properties of the composites.DSC and XRD results showed that SNP had the nucleation effect in PE,but SNP content had little effect on nucleation,and it was difficult to explain the change of dielectric constant.The phase structure of nanocomposites was analyzed by SEM,and it was found that PE exhibited an anisotropic layered crystal structure under hot pressing.The introduction of SNP would lead to the nucleation of the PE around the SNP.The resulting PE/SNP aggregates would be further agglomerated to form a spherical phase structure,which reduced the anisotropy of the material.The results also show that the regularity and content of the spherical structure are directly related to the dielectric properties,revealing the influence of the phase structure and the intrinsic polymer chain arrangement on the dielectric properties and the regulation mechanism.The effect of nanocomposite on the dielectric properties of the nanocomposites was further investigated by adjusting the nanocomposite structure(modification of nanoparticles,molding pressure and temperature,filler size,type and dimension).Firstly,the interface effect was directly controlled by the surface grafting of nanoparticles and changing the size and type of the filler.It was found that the dielectric constant of nanocomposite containing the SNP grafted polystyrene(G-SNP)and PE(PE/G-SNP)was 2.02 when the volume fraction of silica was 3.58%,which was slightly higher than that of PE / SNP.The dielectric constant of nanocomposite system is relatively higher with the larger filler size.The effect of spherical nanoparticles on reducing the dielectric constant is more obvious than that of nanorods.The above results show that the interfacial effect of nanoparticles has an important effect on the dielectric properties.The larger the interface area,the stronger the effect and the lower the dielectric constant.Another important finding is that the dielectric properties and phase structure of PE/SNP are directly related to the hot pressing pressure.Under certain molding pressure,SNP can produce significant interfacial induction and produce regular spherical phase structure and so resulting in a low dielectric effect.This result further confirms the mechanism of the effect of nanocomposite on the dielectric properties.Through the molding process,the ideal molding conditions were obtained.When the molding temperature was 155 oC and the forming pressure was 2MPa,the dielectric constant of the composites was the lowest,reaching 1.77,which achieved good ultralow dielectric properties.