MnO₂ Thin Film Electrodes for Enhanced Reliability of Thin Glass Capacitors

Many dielectric thin films for energy storage capacitors fail by thermal breakdown events under high-field drive conditions. The lifetime of the device can be improved under conditions where the current path within the defect regions in dielectrics is eliminated. Self-healing electrodes were developed by depositing a manganese dioxide (MnO₂) thin film between the glass substrate and an aluminum film. For this purpose, thin films of MnO₂ on boroaluminosilicate glass were fabricated via chemical solution deposition and heat-treated at temperatures in the range 500°C-900°C. The α-MnO₂ structure was stabilized by Ba²⁺ insertion to form the hollandite structure. The phase transition temperature of α-MnO₂ to Mn₂O₃ is strongly dependent on the Ba concentration, with transition temperatures of 600°C and 675°C with Ba concentrations of [Ba]/[Mn] = 0.04 and 0.1, respectively. The electrical resistivity increased from 4.5 Ω·cm for MnO₂ to 10⁵ Ω·cm for Mn₂O₃. Both dielectric breakdown strength and the associated cleared aluminum electrode area increased with an MnO₂ interlayer between Al electrodes and the borosilicate glass. The enhancement in dielectric strength was related with self-healing. The associated redox reaction between MnO₂ and Mn₂O₃ was also proved by RAMAN spectroscopy following dielectric breakdown.