Dielectric properties of Ag@SiO2/epoxy composite for embedded capacitor applications

Nano-sized Ag particles were prepared through a wet chemical reduction route and treated with tetraethoxysilane (TEOS) to form an amorphous SiO₂ thin layer on the particles surface (Ag@SiO₂). Ag@SiO₂/Epoxy composite film was fabricated via coating process. The experimental results showed that the dielectric constant k increased gradually with Ag@SiO₂ content before reaching the percolation threshold. The value of dielectric constant k was 28 at 100 Hz for the composite containing 20 vol% Ag@SiO₂, which was 5 times larger than that of the pure epoxy resin. In contrast, the value of loss tanδ remained at a low level (<;0.02) before reaching the threshold. Tanδ was 0.014 for the composite containing 20 vol% Ag@SiO₂, which was even lower than that of the pure epoxy resin (0.018). When the Ag@SiO₂ content reached 25 vol%, both of the k and tanδ values increased substantially, indicating formation of conducting pathway between Ag particles. The results implied that when Ag@SiO₂ content was at a low level, the insulating SiO₂ shell served as electrons barrier layer between Ag cores and prevented electrons from transferring from one Ag core to another under an external field. As a result, the measured k value increased with Ag@SiO₂ content, while the tanδ remained low. However, when Ag@SiO₂ filler loading reached a higher level and was in the vicinity of critical concentration, Ag cores was so close to each other and the conducting pathway could be developed in the amorphous SiO₂ shell, leading to remarkable growth of k and tanδ.