High critical current density ultrathin YBa2Cu3Ox films made by a modified rf-magnetron sputtering technique

Abstract

High‐quality ĉ‐axis oriented thin films have been grown in situ on (100) surfaces of ZrO₂ , SrTiO₃ , and MgO. Sharp transitions to superconductivity were observed with T_c,off of 87–89.5 K for films thicker than 70 Å. The critical current density at 77.3 K was found to be strongly dependent on the film thickness. A maximum value was found for a 100‐Å film with 8×10⁶ A/cm² at 77.3 K. On atomically flat single‐crystal MgO substrates, films as thin as 15 Å revealed a full transition to superconductivity above 45.5 K. The superconducting properties of the films turned out to be quite insensitive to the deposition parameters, such as substrate temperature, oxygen partial pressure, sputter power, etc.