Solid-state thin-film supercapacitor with ruthenium oxide and solid electrolyte thin films

Direct current reactive sputtering deposition of ruthenium oxide thin films (bottom and top electrodes) at 400°C are performed to produce a solid-state thin-film supercapacitor (TFSC). The supercapacitor has a cell structure of RuO₂/Li_2.94PO_2.37N_0.75 (Lipon)/RuO₂/Pt. Radio frequency, reactive sputtering deposition of an Li_2.94PO_2.37N_0.75 electrolyte film is performed on the bottom RuO₂ film at room temperature to separate the bottom and top RuO₂ electrodes electrically. The stoichiometry of the RuO₂ thin film is investigated by Rutherford back-scattering spectrometry (RBS). X-ray diffraction (XRD) shows that the as-deposited RuO₂ thin film is an amorphous phase. Scanning electron microscopy (SEM) measurements reveal that the RuO₂/Lipon/RuO₂ hetero-interfaces have no inter-diffusion problems. Charge-discharge measurements with constant current at roo m temperature clearly reveal typical supercapacitor behaviour for a RuO₂/Lipon/RuO₂/Pt cell structure. Since the electrolyte thin film has low ionic mobility, the capacity and cycle performance are inferior to those of a bulk type of supercapacitor. These results indicate that a high performance, TFSC can be fabricated by a solid electrolyte thin film with high ionic conductivity.