GB1156192A - Thin Magnetic Film Storage Element - Google Patents

Abstract

1,156,192. Magnetic storage elements. INTERNATIONAL BUSINESS MACHINES CORP. 20 Oct., 1966 [2 Nov., 1965], No. 46893/66. Heading H1T. [Also in Division H3] In a magnetic anisotropic thin film store an electrically conducting non-magnetic screen is placed between a thin film element of the store and a word drive line so as to shield part of the element. A single thin film element 21, Fig. 3c, having an easy axis in the direction parallel to the word line 26 is positioned on a ground plane 23 and to prevent flux being trapped within the ground plane ferromagnetic layer 24 is provided. Part of the film 21 is covered by a copper screen 25, which in the arrangement shown lies in the same plane as sense line 28 and bit line 27. To write information into the film a word write pulse is applied to word drive line 26, to rotate the vector of magnetization into the hard axis, coincidently with a bit pulse of the required polarity applied to bit line 27. The duration and amplitude of the word pulse is such that the whole of film 21 is switched and this pulse terminates before the bit pulse. Information is read out by applying only a word pulse which is of shorter duration than the write pulse, the resulting rotation of the magnetization vector of the thin film producing eddy currents within the screen which generate an opposing field between screen 25 and ground plane 23. This field causes the magnetization in the part of the film covered by the screen to rotate slowly compared with that outside the screen so that the part of the film under the screen 25 acts as a store region and the part outside as a read region. When the read pulse ceases the slowly rotating part of the film returns to the easy axis and generates a magnetic field strong enough to cause the fast switching part of the film to return to its original position in the easy direction. The rotation of the magnetization vector in the fast switching part induces an output signal in sense line 28. A plurality of the elements may be arranged in a matrix, Fig. 6a, with the word 26, bit 27, and sense 28 lines arranged as shown with part of the films 21, being screened by 25. In the arrangement of Fig. 6b (not shown), one screen 25 partly covers film elements in two adjacent columns.