Micro-structural and interfacial effects on the dielectric properties of High-k aluminum/epoxy composites for embedded capacitors

Electrically percolative composites have attracted much attention because they exhibit a high dielectric constant at a critical concentration of the conductive fillers. Aluminum (Al) is well known as a fast self-passivation and low-density metal. The thin and dense passivation layer forms an insulating boundary layer outside the metallic spheres (core-shell) which lowers the dielectric loss and realizes high filler loading levels. In this article, the influences of the content of Al, the size of Al core, the thickness of Al₂O₃ shell, and the two interfaces of polymer-Al₂O₃ and Al₂O₃-Al on the dielectric behaviors of the resulting percolative composites have been systematically analyzed and interpreted. For the composite containing 70 vol.% of 1.0 mum aluminum, a dielectric constant of 95.49 and a low dielectric loss of about 0.05 over a frequency range of 100 Hz~10 MHz was achieved. The broad peak over a wide volume fraction range of the percolation threshold concentration makes the material reproducible for use.