Patent GB-1098703-A (GB)
Title: Improvements in and relating an information store comprising a superconductor memory cell
Inventor: BALDWIN JOHN PATRICK
IPC: G11C11/44
Filed: 1963-07-05
Abstract: 1,098,703. Super conductor devices. MULLARD Ltd. July. 2, 1964 [July. 5, 1963], No. 26749/64. Heading H1K. [Also in Divison H3] An information store or matrix comprises a thin sheet (film) of superconductive material one or more areas of which each form memory cells in which as described in Specification 1,002,398 the superconductor film is switched out of the superconductive state by a constant magnetic field and an applied switching magnetic field acting together, is switched back to the superconductive state by reversing the applied switching magnetic field and is maintained or permitted to remain in the superconductive or resistive state to which it has previously been switched, by the constant field acting alone which latter field has a value falling between the two field values at which switching into and out of the resistive state takes place. Fig. 1 of the Complete Specification shows a matrix having series connected conductors Y, Y<SP>1</SP> on opposite sides of a superconductive (tin) film 2 and similar series connected conductors X, X<SP>1</SP> which sandwich the film 2 at the information storage locations. A constant magnetic field is applied parallel to the plane of film and together with the fields produced at any storage location by coincident half-write pulses in X, X<SP>1</SP> and Y, Y<SP>1</SP> switches an area of film 2 at this location from the superconductive to the resistive state. Coincident pulses in X, X<SP>1</SP> and Y, Y<SP>1</SP> in the opposite direction at this location oppose the constant field and switch the area of film back to the superconductive state. The constant field may be produced by a superconductive solenoid or by a steady current in a switching conductor. The existence of a resistive state in any area can be sensed by applying a half-write pulse to the appropriate X conductor and sensing the induced pulse in the associated X<SP>1</SP> conductor. If the X<SP>1</SP> conductors are replaced by a conductive ground plane between the Y<SP>1</SP> conductors and the substrate, the Y<SP>1</SP> conductors can be used for the interrogating pulse which will then induce pulses in the X and Y conductors at the switched (resistive) areas. The matrix may be shielded from the earth's field and is immersed in liquid helium. Details of the method of manufacture of the matrix and of its materials and their thicknesses as well as of the applied field strengths, are given. The coincident current superconductive memory cell (Figs. 5 and 6 of Provisional Specification, not shown) may have the switching conductors at right angles and may have its superconductive film maintained normally in the resistive state and switched to the superconductive state. The storage film may be of tin, indium, mercury, thallium or lead, the conductors of copper, gold, silver or of superconductive material, e.g. lead, the insulation of silicon monoxide and the substrate of quartz or other materials. To produce the matrix the substitute is put in an evaporation chamber which is then pumped to 10<SP>-9</SP> torr, the system being then baked for at least 10 hours at 350‹ C. A molybdenum getter in a chamber between the evaporation chamber and the vacuum tap is heated and an ion gauge coupled to the tap and bombarded. After the ion gauge has been at 5 x 10-8 torr for 30 minutes the tap is closed and a second ion gauge is set pumping, the getter temperature being raised to give a slight evaporation. The conductors, the silicon monoxide layers and the superconductor film (tin) are then laid down by evaporation the depositing temperature being raised to 1050‹ C. when starting deposition of the tin.