Superconductive circuits

993,225. Superconducting devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 26, 1963 [June 28, 1962], No. 25349/63. Heading H1K. In an arrangement in which a deposited superconductor has a tapered edge, the edge is arranged to have a higher concentration of an impurity as compared with the rest of the superconductor whereby the critical temperature of the edge is lowered. The device is then operated at a temperature such that the edge is resistive, but the remainder is superconducting. This improves the sharpness of the transition characteristics under applied magnetic field. In one embodiment, Fig. 1A (not shown), a substrate is coated with silicon monoxide upon which a thin film of gold is deposited, followed by the deposition (through a mask) of indium, resulting in a layer having tapered edges. The gold tends to alloy with the indium to produce gold impurities in the latter, the gold concentration being higher in the tapered portions, whereby the critical temperature thereat is lowered. Moreover in the region of the gold the indium on deposition agglomerates into discrete particles and so become non- conductive, this effect being prominent at the tapered edges. In a second embodiment, Fig. 2 (not shown), the indium is first deposited and the gold layer then deposited thereon. The agglomeration effect is absent in this embodiment. In a third embodiment, Fig. 3 (not shown), gold films are on both sides of the indium. In fourth and fifth embodiments, Figs. 4 and 5 (not shown), the gold is applied only in the vicinity of the tapered edges of the indium. In further embodiments, Figs. 6 and 8 (not shown), a layer of silicon monoxide is placed between the gold and the main portion of the indium to prevent interaction of the gold with the indium thereat, interaction taking place at the tapered edges where the silicon monoxide is absent. In these embodiments separate masks are used for vapour deposition of the silicon monoxide and the indium. In preferred embodiments, Figs. 7 and 9, the same mask is used. Thus in Fig. 7 the substrate 75 having a silicon monoxide layer 74 is first exposed through a mask to an indium vapour source at a distance of eight inches, the shade effect producing the tapered edges 73a, 73b in the indium layer 73. The surface is then exposed to a silicon monoxide vapour source at a distance of nine inches. The shade effect is thereby less due (a) to the smaller solid angle subtended at the source, and (b) due to the fact that the s