Atomic doping of Alumina-based dielectric with high permittivity and breakdown field strength

Abstract

High specific capacitance anode aluminum foils fabricated by introducing TiO₂ to improve the permittivity (ε_r) of Al₂O₃ is one of the most effective ways to reduce the size and weight of aluminum electrolytic capacitors (AECs). However, the underlying mechanism by which the introduction of TiO₂ causes capacity enhancement remains unclear. Here, a proposition is claimed that TiO₂ is not directly responsible for the capacity enhancement but Al-doping TiO₂ (AOT) actually. An atomically doping strategy based on atomic thermal diffusion and ionic electromigration is proposed to realize the fabrication of AOT via modulating the thermal and electric fields. Results show that the doping behavior of Al³⁺ induces the displacement of neighboring Ti⁴⁺ ions, which enhances the dipole polarization resulting in an increase of ε_r (25). Meanwhile, the diffusion of O₂ and migration of O^2– effectively removes the oxygen vacancy, enhancing the breakdown field strength (> 6 MV·cm⁻¹) of dielectrics. Ultimately, the specific capacitance of anode foils is increased by about 50 % compared to those without AOT. On a brighter note, this work deepens the understanding of the capacity enhancement mechanism and will contribute to further facilitating the miniaturization of AECs.