Nanofiller Dispersion in Polymer Dielectrics

Nanodielectric composites have been developed in recent years attempting to improve the dielectric properties such as dielectric constant, dielectric strength and voltage endurance. Among various investigations, nanoparticle dispersion was particularly emphasized in this work. General Electric Global Research Center in Niskayuna NY USA has investigated various nanoparticles, nanocomposites and nanocomposite synthesis methods intending to understand particle dispersion and their impact on the nanocomposite dielectric properties. The breakdown strength and microstructures of the nanocomposites containing different particles were studied for projects related to capacitor and electrical insulation technologies. The nanocomposite synthesis methods either employed commerical nanoparticles or utilized nanoparticles that were self-assembled (in-situ precipitation) in a matrix. Our investigations have shown that nanocomposites prepared with solution chemistry were more favorable for producing uniform dispersion of nanoparticles. Structural information of nanocomposites was studied with transmission electron microscopy and the interection between particles and matrix polymers were tentatively probed using dielectric spectroscopy. In these new class of materials high energy densities on the order of 15J/cc were achievable in nanocomposites.

Change in dielectric relaxation with the presence of water in highly filled composites

It is important to determine the dielectric characteristics of semiconductor encapsulation materials based on epoxy resins.We employed the dielectric spectroscopy technique to investigate the dielectric relaxation in the presence of water and how it changes the relaxation.It was observed that the dielectric relaxation of the material was significantly influenced by absorbed water,the local segmental motion(also known as Johari-Goldstein(β)relaxation)was influenced most by the presence of the water,it was modified by the wet sample compared to dry one,and required high activation energy.The relaxation related to the glass transition was contributed by the cooperative motion(the a-relaxation)of the epoxy resin system.The a-relaxation was shifted to a low temperature in the wet sample compared to dry one.The relaxation was modeled with a clear Vogel-Fulcher-Tammann-Hesse(VFTH)behavior;the Vogel temperature of the wet sample was 8 K lower than the dry sample.The presence of water acts as a plasticizer for the molecular relaxation,and speed-up the cooperative process.The measured data were also used to estimate the electrical properties of the resin system by employing an effective-medium model together with a porous media continuum model by taking into account the physical properties of the system.It is already known that the influence of water in semiconductor packaging is important in sensitive applications.The presented measurements and the analysis method would be appreciated within the semiconductor packaging community to improve material selection and performance evaluation efforts.