In-situ deposition and processing of YBa2Cu3O 7-x films and multilayers for optoelectronic devices

In situ direct deposition at ~700°C of thin YBa₂Cu ₃O_7-x superconductive films and multilayers has been done by three techniques using stoichiometric YBa₂Cu₃O_7-x sintered targets. Excimer laser ablation in a DC magnetron system with hollow and planar targets leads to 0.5-, 1.2-, and 2.5-in diameter uniformly superconductive layers under static conditions. High critical current densities (>10 ⁶ A cm² at 77 K) associated with low resistivity and good epitaxial behavior are achieved on top of MgO, SrTiO₃, LaAlO₃, and YSZ single-crystal wafers. High-quality c-oriented films (T_c>80 K) are routinely obtained by means of a DC magnetron on large sapphire (>2 in) substrates covered by a YSZ RF sputtered buffer layer. The infrared properties of such films have been checked at 1.15-μm wavelength. In order to achieve active devices (such as optical detectors and high-frequency mixers), small (<10-μm²) YBa₂Cu₃O₇-YSZ-Ag tunnel junctions and arrays have been successfully patterned in the superconductor/insulator/normal-metal trilayers using SNOP (selective niobium overlap process)