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We deposited SmBCO thin films on BaZrO3 (BZO)-buffered MgO(100) substrates by an off-axis magnetron sputtering method. SmBCO films were deposited at a fixed condition on stoichiometric and Zr-rich BZO-buffered MgO substrates. We found that the crystal orientation of SmBCO films changed from a-axis to c-axis orientation by using Zr-rich BZO. We speculate that the reaction between excess Zr oxides on the buffered substrates and deposited species at the initial stage of the SmBCO deposition is important in inducing these phenomena.

We have studied the fabrication process for c-axis-oriented Pr1.4Ba1.6Cu3Oy (P4) thin films as non-superconducting layers in HTS electronic devices. The P4 films were deposited by a pulsed laser deposition method. We found that gas control is a key factor for successful fabrication. Deposition in 200 mTorr oxygen, which was a suitable condition for deposition of c-axis-oriented YBCO thin films, resulted in c-axis-oriented P4 films containing BaPrO3 impurities. It seemed that oxygen stabilized Pr4+ and promoted the formation of BaPrO3. Pinholes were observed in the films. Energy loss of the ablated species by collision with excess atoms in the deposition chamber possibly brought about insufficient migration of the deposited atoms on the substrate and imperfect connection of the P4 grains. It was found that deposition in 40 mTorr oxygen yields P4 films without impurity phases or pinholes. Feasibility of the P4 film as an insulating layer in ramp-edge Josephson junctions and a buffer layer for Hg-based superconducting films is preliminarily studied.

We have developed a multilayer structure with a smooth surface and fabrication processes for HTS single-flux-quantum (SFQ) circuits. The multilayer structure with surface roughness Ra less than 2 nm, composed of a La0.2–Y0.9Ba1.9Cu3Ox ground plane and base electrode layer, and SrSnO3 insulating layers, was deposited by off-axis magnetron sputtering. We have fabricated interface-engineered junctions based on the multilayer structure using an La0.2–Yb0.9Ba1.9Cu3Ox counter-electrode layer prepared by pulsed laser deposition. The fabricated junctions exhibited excellent Josephson characteristics with a 1-σ spread in Ic as low as 8% for 1000 junctions. The sheet inductance values below 50 K were 0.8–1.0 pH per square. Operation of several elementary SFQ circuits including a toggle flip-flop, a confluence buffer, a set–reset flip-flop and other SFQ elements has been successfully demonstrated at 30–60 K.

(Hg0.9Re0.1)Ba2CaCu2Oy [(Hg, Re)-1212] grain boundary Josephson junctions have been fabricated on SrTiO3 (STO) [001]-tilt bicrystal substrates with thin CeO2 and Y0.9La0.2Ba1.9Cu3Oy (YLBCO) buffer layers. These buffer layers effectively suppressed the formation of undesirable precipitates, which existed along the grain boundaries in (Hg, Re)-1212 films directly fabricated on STO bicrystal substrates without a buffer layer. The junctions on both the buffer layers exhibited resistively shunted junction (RSJ)-type current–voltage (I–V) characteristics and more homogeneous current distribution than those for the junctions on the STO bicrystal substrate. For the junctions on the YLBCO buffer layers, RSJ-type I–V curves were observed at temperatures up to 112–114 K, being very close to the film Tc of 115–117 K, while a substantially lower junction Tc was observed for those on the CeO2 buffer layers. The junctions on YLBCO exhibited more systematic variations of junction parameters with the misorientation angle θ than those for the junctions on STO. These results and the reduction of the critical current density with θ apparently smaller than that for the junctions on STO are probably attributed to no inclusion of precipitates and superior crystallinity near the grain boundaries. The junctions on the YLBCO buffer layers with θ = 36.8° were found to have a magnitude of Ic suitable for applications to superconducting quantum interference devices (SQUIDs) at temperatures higher than 77 K. The dc SQUIDs fabricated using such junctions exhibited voltage–flux modulation at temperatures up to 110 K.