CHARGING EFFECT IN PARTIALLY OXYGEN-DEPLETED SUPERCONDUCTING Y-BA-CU-O THIN-FILMS

We report our studies on the charging effect in metal-insulator-superconductor, thin-film structures with thick (approximately 100 nm), partially oxygen-depleted YBa2CU3Oy (YBCO) channels. The devices were fabricated in YBCO-on-SrTiO3 films with a laser-writing patterning technique. The SrTiO3 Substrates were used as gate insulators. A number of test structures, consisting of the oxygen-deficient (superconducting at 10-60 K) channel and fully oxygenated (superconducting above 85 K) source and drain electrodes, were measured. We found that the electric field applied to our as-fabricated structures complexly affected their superconducting properties, causing both reversible and irreversible modifications of the channel's critical temperature and critical current. The channel sensitivity to the electric field disappeared in our samples after several days of room-temperature aging; however, it could be subsequently recovered, again only temporarily, by hydrogen doping. The charging effect was particularly pronounced in structures with the lowest critical temperatures of the channel. We associate the behavior observed in our samples with charge-transfer effects related to electric-field-enhanced changes of the crystalline order in oxygen-deficient YBCO.