Development of Magnetic Thin Film Memory

Structural detail of Fine Striped Memory

Fig.1 Structural detail of Fine Striped Memory

    “Fine Stripe Memory”, a magnetic thin film memory of closed flux path, was developed by S. Oshima, T. Kobayashi, T. Kamibayashi and the others of magnetic thin film memory study group.

 Three important factors are considered to fabricate this memory. 1) Digit lines must be completely surrounded by magnetic film: 2) Magnetic characteristics of the memory film must be excellent: 3) Flux keeper, by which the word driving field effectively drives the memory film, and whose structure reduces a capacitive coupling between the word line and the digit line, must be developed.

 A structural detail of F. S. M. is illustrated. Permalloy, copper and permalloy were laminated, in turn, by evaporation on the whole area of a flat glass substrate, to the thicknesses of 2000Å, 5000Å and 300Å, respectively. Permalloy films were evaporated in a magnetic field. Stripes of 50 micron wide and 50 micron spacing shaped by photoetching were electroplated with permalloy in a magnetic field to form the digit lines of closed flux path structure. The word lines are formed by inserting copper wires into the grooves on the ferrite sheet. The width of the grooves is 100 microns, depth 200 microns and 100 micron spacing.

 The base plate on which the digit lines are fabricated by the above-mentioned way and the flux keeper sheet in which the word lines are inserted are combined to form these lines crossing. It could be observed that the read-out voltages were higher than those of semi-closed flux path structure as the flux path on the digit line was completely closed by electroplating, and that its memory operation was extremely stable. This assures that stripes narrower than 50 microns are enough to use.

 The compositional uniformity into the normal direction of the electroplated film on the evaporated permalloy on copper was better than that of directly plated on the copper stripe. Interferences from adjacent word lines are extremely low since the ferrite keeper completely attached to the magnetic film. The noise induced by capacitive coupling is exceedingly low because of the enough spacing between the word lines and the digit lines.

 The manufacturing process for F. S. M. is very simple and is suitable to make a high density memory. A small sized high density memory over 5000bits/cm2 can be fabricated with low cost.

    For these achievements, the Institute of Electronics, Information and Communication awarded S. Ohshima, T. Kobayashi and T. Kamibayashi an Achievement Award in 1972.


[1] S. Ohshima, T. Kobayashi, T. Kamibayashi, A. Okada, Y. Komazawa and K. Komuro、On Fine Striped Memory、1969、IEICE Technical Report on Electronic Computer, EC69-7, 1969-05
[2] S. Ohshima, T. Kobayashi, T. Kamibayashi, A. Okada, Y. Komazawa and K. Komuro、Improvement on magnetic properties of Fine Striped Memory、1970、IEEE Trans., Mag-6, 725 (1970)

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