Excellent Dielectric Properties and Finite Element Simulation of Al-Epoxy Composites with Constructed Ultrathin Al₂O₃...

Metal-polymer dielectric composites show promising potential as embedded capacitors, whereas it remains a great challenge to achieve a high dielectric constant (ε_r) and low dielectric loss (tan δ) simultaneously. This work demonstrates a strategy for overcoming this challenge. Al nanoparticles with self-passivated ultrathin Al₂O₃ shells are compacted under the uniaxial pressure (P), and Al-epoxy composites are prepared by curing the liquid epoxy monomer that infiltrates into Al compacts. The contacting regions between adjacent Al nanoparticles are flattened and enlarged during the compacting process, so that the ultrathin Al₂O₃ parallel-plate microcapacitors are constructed by the insulating Al₂O₃ shells and conductive Al cores. The composite with P of 100 MPa and Al volume fraction (υ_Al) of 53.7% exhibits the ε_r of 189 at 10 kHz, which is much higher than the ε_r (48-102) of 0-3 type Al-polymer composites with similar υ_Al and even higher than the highest ε_r (160) reported in the Al-polymer composite with υ_Al > 80%. Furthermore, the present composites show low tan δ (<0.03) and good frequency and temperature stability of ε_r. The finite element simulation proves that the construction and enlargement of ultrathin Al₂O₃ parallel-plate microcapacitors dramatically increase the electric energy stored in Al₂O₃ and therefore greatly improve the ε_r.