A study on grain boundary barrier layer solid aluminum capacitors

This study employs solid-state and chemical plating methods to fabricate aluminum grain boundary capacitors using Al@CuO composite materials. The materials were prepared under varying compaction pressures (200 psi, 500 psi, and 700 psi) and thermal treatments (450 °C, 500 °C, and 550 °C). The dielectric layer structure, consisting of aluminum oxide and copper oxide, was successfully synthesized, as evidenced by the crystal structures and chemical bonds of the constituent materials. XRD and XPS analyses confirmed the composition of the aluminum grain boundary capacitors. SEM and STEM data revealed a layered grain boundary structure. Observations of thermite reactions and solid-state diffusion mechanisms contributed to the formation of this layered structure. Each grain exhibited a core-shell configuration (aluminum core / aluminum oxide grain boundary layer / cuprous oxide shell layer / copper oxide grain boundary layer), effectively functioning as an equivalent capacitor. AC impedance analysis revealed two semicircles for Al coated with CuO, compacted under 200 psi and thermally treated at 550 °C, respectively representing the grain boundary resistance of the Al₂O₃ dielectric with a 30 nm thickness and the grain boundary resistance of the CuO dielectric with a 376 nm thickness. Consequently, two grains form three equivalent capacitors, resulting in a solid-state aluminum grain boundary capacitor with promising dielectric properties, including a dielectric constant of 4059, a dielectric loss of 0.02, and an insulation resistance of 9.41 × 10⁴ kΩ.