Patent GB-1221998-A (GB)
Title: Magnetic memory devices
IPC: G11C5/02
Filed: 1968-03-20
Abstract: 1,221,998. Magnetic data storage apparatus. NIPPON ELECTRIC CO. Ltd. 20 March, 1968 [20 March, 1967 (3); 23 March, 1967; 25 May, 1967 (2)], No. 13574/68. Heading H3B. [Also in Division H1] A memory matrix comprising intersecting groups of non-magnetic conductors and conductors coated with thin magnetic-film has a magnetic flux keeper disposed adjacent thereto, the keeper being of a composition comprising magnetic particles (e.g. of ferrite) in an insulating (e.g. organic) binder. In Fig. 1 the non- magnetic conductors 12 comprise upper and lower structures 13, 13<SP>1</SP> including copper wires 14 embedded in polyethylene tape 15. The wires are interconnected at each end of the structure to form a two-turn coil surrounding coated conductors 11. The magnetic keeper composition consists of a Ni-Zn ferrite ground and dispersed in a solution of a copolymer of acrylic ester and acrylonitrile, the solvent being toluene. A slurry of this composition is poured over the matrix and the solvent is then driven off by heating to 50‹ to 60‹ C. The resulting structure is rubbery and flexible and has a permeability of about 6 and a dielectric constant of about 5. Since the magnetic flux paths in the axial direction of the coated conductors 11 are closed through the keeper the spacing between adjacent conductors 12 and the magnitude of the driving currents can be reduced. Instead of separate polyethylene strips 15 all the component conductors 14 for the drive conductors may be embedded in a pair of polyethylene sheets, one on each side of the coated conductors. Alternatively the drive conductors may be flat copper strips, having the same shape as the tapes 15, coated with polyethylene for insulation and to enable the upper and lower strips to be bonded together by thermal adhesion. In Fig. 10 (not shown) a single copper wire is wound several times around each coated conductor and synthetic resin is deposited on each wound portion to prevent the keeper composition from flowing between the drive conductors and the coated conductors during construction. A similar procedure is adopted in the construction of a woven memory, the resin in this case also fixing the woven conductors in position and avoiding the necessity for spacers. Fig. 13 shows an embodiment in which the coated conductors 11 are pre-assembled by disposing wire formers in a plastics sheet, removing the formers and replacing them by the coated conductors to form assembly 90. In the remaining embodiments a prefabricated keeper is used. Parallel strip conductors are formed on such a keeper, which is in the form of a flat sheet. Grooves 103 are then formed by pressure in the surface of the sheet, between the conductors and extending perpendicularly thereto. Further grooves 104 of slightly larger radius are subsequently formed in conductors 102 and the conductors themselves are pressed into the ferrite sheet so that they are at or below its surface. Two such structures are arranged faceto-face with the coated conductors between them to form the matrix. Alternatively, the ferrite sheet may be moulded to the shape shown in Fig. 15 prior to hardening, and the conductors may be preformed to the correct shape and secured in position. The regions on which the conductors will be secured may be formed as deep rectilinear channels, deeper than grooves 103, in which channels flat strip conductors are secured. The binder for the ferrite powder may be an epoxy resin or a thermoplastic resin.