Patent GB-993225-A (GB)
Title: Method of manufacturing a superconductor device and the superconductor device manufactured thereby
IPC: C23F1/02
Filed: 1963-06-26
Abstract: 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 silicon monoxide film is thinner than the indium layer. Thus the silicon monoxide film 72 does not cover the tapered edges allowing them to interact with the gold layer 71 when the latter is applied. A similar technique is applied in Fig. 9 where the gold film 93 lies below the indium 91. In a modified technique, after deposition of indium through a slit in a mask, a heavy deposit of indium on the mask itself narrows the slit, through which the silicon monoxide is then passed. Fig. 10c shows the invention applied to a conventional cross film cryotron. A gold film strip 105 is first deposited followed by a perpendicular insulating film 106. The indium is then deposited as a strip parallel and overlying the strip 105. Gold alloys with the indium in the regions 109, 110 in the manner previously described. This has the additional effect of restricting the area of the superconductor in the neighbourhood of the control conductor 102<SP>1</SP> whereby the superconducting current/control current characteristic is improved. Other superconductors such as tin or tin-indium alloy may be used. Mention is also made of the deposition of the indium in the presence of oxygen.