Structure Design And Performance Study Of Three-layer PI/TiO₂Composite Films

Polymer/inorganic nanometer composite dielectric films have good mechanical,electrical and thermal property, which are applied to electrical engineering andmicroelectronic technique field extensively. TiO₂has a wide bandgap, high dielectricconstant, strong ability to absorb uv light and strong ability of heat conduction inoptical, electrical and thermal properties. And with the unique physical and chemicalproperties of nanoparticles, the research of nano TiO₂composite film based onpolyimide has been widely concerned.The three-layer PI/TiO₂-PI-PI/TiO₂composite films（30μm） with differentcomponents and different interlayer（PI） thickness are prepared by in-situpolymerization method. The interlayer thickness are5μm（A1），10μm（A2），15μm（A3），20μm（A4）, respectively. And the doping content are separately2%,3%,4%,5%,6%and7%. The structure performance of the composite films arecharacterized by SEM, XRD, SAXS and ultraviolet spectrum. And thecomprehensive performance of composite films are studied through thermalweightlessness, dielectric spectrum, corona resistance time by usingthermo-gravimetric apparatus, dielectric spectrometer and corona equipment. Theinfluences induced by component and interlayer thickness on the performance of thecomposite films are studied by comparing the related experimental data of themonolayer and three-layer composite films.The experimental results point out that: sectional morphology of the three-layerfilms shows that thickness of the interlayer meets the design requirements.Nanoparticles are dispersed evenly in the polyimide substrate. The dopingnanoparticles don’t affect the polymerization of PI. The XRD spectrum shows notonly the PI characteristic spectrum but also several characteristic peaks of the TiO₂powder, but the later are weaker than the pure TiO₂powder, which shows that thereare strong interaction between the PI matrix and the nanoparticles. The absorbance ofcompound films on the same wavelength range becomes stronger with the increaseof the doping content, which show that nanoparticles introduced a number of localenergy state, which change the microstructure of composite films. The interface layerand the transition layer between doping layer and PI layer exist in the composite films, and the thickness of the interface layer is around3.5nm; The spatial structureof the film becomes more compact and homogenized with the increase of thecomponents. The layer structure can makes composite films more compact and theinterface layer more smooth.At the same time, the thermal stability of three-layer films become stronger firstand then weaker with the increase of the doping content, in which A2series with4%wt content has the strongest thermal stability, which are stronger than that ofmonolayer films. Moreover, component and layer structure can both change thedielectric parameters, which shows that they can significantly influence on dielectricproperties of the films. When the layer structure is fixed, the corona resistance timeof three-layer composite films increase first and then decrease. The4%wt dopingcontent has the longest time. And that time first increases then decreases and increaselater again with the increase of the interlayer thickness when the doping content iscertain. The A2series films have the longest corona resistance time, which is higherthan that of monolayer film under the same doping content. So there is a optimalvalue that can maximize the corona resistant performance for the layer structure aswell as component. And this paper established the films structure and the bandstructure model of three layers of PI/TiO₂composite films and explained themechanism of corona resistant.