Fabrication of a-axis Oriented Y B a₂ C u₃ O _x /P r G a O₃/a-axis Oriented Y B a₂ C u₃ O _x Trilayer Films

This paper reports the fabrication of a-axis oriented YBa₂Cu₃O _x /PrGaO₃ insulating barrier/a-axis oriented YBa₂Cu₃O _x trilayer films by in-situ pulsed-laser deposition. A cross sectional transmission electron microscopy (XTEM) analysis of the junctions verifies that the ultrathin PrGaO₃ insulating barrier does not form islands between the base and the counter electrode of YBa₂Cu₃O _x films and the a-axis oriented YBa₂Cu₃O _x grows right on the insulating PrGaO₃ ultrathin (30 Å) film without any c-axis oriented or disordered YBa₂Cu₃O _x layer. Excellent surface coverage of the base electrode of the YBa₂Cu₃O thin film is considered to result from lattice matching and the similarity of the crystal structure. Lattice matching perovskite insulators with the same thermal expansion coefficient are attractive for use as the insulating barrier for superconductor/insulating barrier/superconductor (SIS) junctions.