Growth of c-axis oriented superconducting Bi2Sr2CaCu2O8+δ films suitable for device fabrication

Abstract

We report the growth of c-axis oriented, superconducting Bi₂Sr₂CaCu₂O_8+δ films from stoichiometric and non-stoichiometric BSCCO melts via Liquid Phase Epitaxy. The melt consists of Bi-Sr-Ca-Cu-O powder (solute) and an appropriate amount of KCl (flux) for a solute to flux ratio of 1:7. The films are grown on MgO substrates at a temperature of 1000°C for 3 minutes with and without substrate rotation. The films are then annealed in air at 830°C for five hours to induce crystallization.
Surface morphology evaluation reveals that films grown from a (Bi-2201 + 0.5 Ca₂CuO₃ + 0.5 CuO) melt are completely covered, opaque, relatively homogenous, flat and free of deposited bulk materials. X-ray diffractometry scans, on the other hand confirm that the formation of highly crystalline, c-axis oriented Bi-2212 films is enhanced using (a) the Bi-2223 melt and (b) the (Bi-2201 + 0.5 Ca₂CuO₃ + 0.5 CuO) melt. Resistivity measurements confirm the superconductivity of the films grown from a (Bi-2201 + 0.5 Ca₂CuO₃ + 0.5 CuO) melt, exhibiting a transition temperature of 81 K. With these results in hand, we choose the films from the (Bi-2201 + 0.5 Ca₂CuO₃ + 0.5 CuO) melt as the films most suitable for device fabrication.
The suitability of the films for device fabrication is demonstrated with the fabrication of a rough superconductor-insulator-normal metal (SIN) tunnel junction. The IV measurements show an ohmic behavior at room temperature. At liquid nitrogen temperature, the IV trace shows a smoothly varying characteristic with a flattening of the current at low biases. These behaviors are expected of an SIN tunnel junction.