GB1143775A - - Google Patents

Abstract

1,143,775. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES Ltd. 7 April, 1966 [13 April, 1965], No. 15678/65. Heading H3B. [Also in Division H1] Each row and column line of a magnetic storage matrix comprises a conductive loop, Fig. 18, the crossing points of the loops being contained between an isotropic magnetic storage film and a layer of high permeability magnetic material. The film and layer are in contact at all regions except those where the conductors are located so that each storage location provides a plurality of flux paths. Fig. 14 shows the flux paths produced when a binary one is stored by pulsing a horizontal digit loop and a vertical word loop simultaneously. The flux pattern for a binary zero is shown in Fig. 15, in this case the half-current pulse in the digit loop being of reversed polarity. When read out is effected by a full current pulse in a vertical read loop, an output pulse is induced in a horizontal sense loop and the flux pattern is charged to that shown in Fig. 16. The storage film consists of a 97% Fe, 3% Ni film deposited on a copper substrate, the matrix of conductors being formed by a printing process on the storage film. The magnetic paths are completed by a plate of high permeability ferrite, Fig. 10 (not shown), which has two orthogonal sets of parallel slots which leave a series of rectangular posts. The plate fits over the substrate, film and conductor matrix assembly with the posts in contact with the storage film; the contacting surfaces being plane polished. Instead of a ferrite plate a similar grooved copper plate may be used which is coated with a high permeability magnetic material such as nickel-cobalt alloy. Alternatively the nickel cobalt alloy may be directly plated on the matrix assembly to avoid the use of a slotted plate. The matrix assembly may be formed by electroplating the copper substrate 1, Fig. 2, with the magnetic film 2, followed by an oxalate conversion coating 3 and a layer of metal etch resist 4. A strip 5 of the etch resist along the required path of a conductor and of greater width is exposed to ultra-violet light, the whole surface being then copper plated. The copper layer 6 is coated with a layer 7 of photo resist, a strip 8 of the same width as a conductor to be formed being exposed to ultra violet light. The unwanted parts of the layers 4, 6 and 8 are removed by developing and etching, Fig. 4. A second overlying conductor is then applied by coating the structure with metal etch resist 15, Fig. 5, followed by layers of copper 19, photo resist 18 and metal etch resist 20, strips of the resists being exposed as for the first phase of construction. Finally the unwanted portions of the assembly are removed by etching, this etching process removing the oxalate coating 3 from the regions of the magnetic film not covered by conductors.