In-situ Photochemical Synthesis of Novel Silver Nanoparticles/Polymer Composites as High K Polymer Matrix for Embedded Passives Applications

Abstract

Considerable attention has been devoted to the synthesis and application of nanoparticles because of their unusual physical and chemical properties resulted from the ultra-fine size and ultra-large surface area. Polymer composite materials based on metal nanoparticles provide a potential solution to meet the present and future technological demand in virtue of the good processibility and mechanical properties of polymers combined with the unique electrical, magnetic or dielectric properties of nanoparticles. Conductive filler-polymer composite materials have been extensively investigated as conductor-insulator percolative system to achieve high dielectric constant (K). Additionally, the effective dielectric constant of conductive filler/polymer composite can be dramatically enhanced by increasing the dielectric constant of polymer matrix according to scaling theory. However, the high dielectric loss of this type of material at high filler loading levels has been a challenging issue, which is originated from the high conductivity and excessive polarized interface induced by the fillers. In this study, an in-situ formed metal nanoparticles/polymer resin compound was developed as a high k polymer matrix by adopting a relatively low concentration of conductive filler to obtain high k retaining low dielectric loss simultaneously. Nano-sized metal particles are preferred because they achieve thinner dielectric films leading to a higher capacitance density. Compared to an ex-situ blending technique by incorporating and dispersing pre-synthesized nanoparticles into polymers, the in-situ synthesis method can offer more advantages such as much more uniform dispersion in polymers and easy size control of nanoparticles. This study explores the in-situ nanoparticle synthesis method by photochemical conduction of a metallic precursor within the polymer matrix. Crystal structure analysis and morphology characterisation of the as-prepared nanocomposites by X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively demonstrated the success of the in-situ formation of silver (Ag) nanoparticles in various polymer-matrices by the photochemical method. Uniform dispersion of nano Ag particles with size of less than 10 nm in polymer matrices were observed. The effects of reducing agent types, concentrations of a metal precursor epoxy matrix types, additives etc., on the morphology of nanoparticles are discussed. Based on the results of UV-Vis and FT-IR study, the proposed reaction mechanism of reduction of silver ion to silver is presented. Aluminum particles were incorporated into the in-situ formed nano Ag/epoxy compounds and the dielectric properties of the composite materials were also investigated. The composites showed a more than 50% increase in K values compared with an Al/neat epoxy composite with the same filler loading of Al. Moreover, the dielectric loss was maintained below 0.05. The results suggested that the in-situ formed Ag-polymer nanocomposites via photochemical approach can be employed as a high-k polymer matrix to host various fillers such as conductive metal or high dielectric constant ceramic fillers. The dielectric behavior of the composite materials at various frequency, their morphology, physical properties and their correlations is discussed