Thin film supercapacitor with ruthenium oxide electrode and solid electrolyte

It is possible to fabricate all solid-state thin film supercapacitor (TFSC) with an amorphous Li_xPO_yN_z (LiPON), Ta ₂O₅ thin film electrolytes and ruthenium oxide film electrodes, which has the full cell structure of RuO₂/LiPON/RuO ₂/Pt, RuO₂/Ta₂O₅/RuO₂/Pt. The TFSC will be very useful to drive a microelectronic device if it can be hybrid with thin film battery (TFB). The ruthenium oxide thin films were grown on Pt/TiO₂/SiO₂/Si substrates by using direct current (d.c.) reactive magnetron sputtering at room temperature. Both LiPON and Ta ₂O₅ electrolyte films were grown on the RuO₂ films by using radio frequency (r.f.) magnetron sputtering at room temperature. After the deposition of amorphous LiPON and Ta₂O₅ electrolyte films, RuO₂ top electrode films were grown on the as-deposited electrolyte films by using d.c. reactive sputtering system. Room temperature charge-discharge measurements of the RuO₂/LiPON/RuO ₂/Pt TFSC at a constant current clearly revealed a typical supercapacitor behavior, even though the capacity of as-fabricated TFSC showed much lower than the bulk one and relatively fast decreased. However, room temperature charge-discharge curves of RuO₂/Ta₂O ₅/RuO₂ supercapacitor did not show the same pattern as above one. Electric double layer capacitance was prominent due to high dielectric constant of Ta₂O₅ material.