1. Field of the Invention
The present invention relates to magnetic storage devices generally, and in particular to a crosstie random access memory element and circuitry, for reading and/or writing at a application Ser. No. 386,388 filed Jun. 8, 1982 with respect to which the present application is a continuation. This application is also related to U.S. Pat. No. 4,962,477 to Schwee, which in turn refers to other related copending applications, including Ser. No. 386,389 of Schwee et al filed Jun. 8, 1982 (abandoned in favor of its continuing application, Ser. No. 07/615,728, filed Nov. 19, 1990) naming Paul E. Hunter as coinventor who is not a coinventor of subject matter covered by the present application.
2. Description of the Prior Art
Electronic computers and other data processing devices, to a great extent, are limited by the speed, capacity, and reliability of their memory systems. Memory systems currently in use include tiny ring shaped ferrite cores strung on a mesh of fine wires (core memories) and semiconductor memories comprising transistor circuits laid down on tiny chips of silicon. At the present time the most common nonvolatile random access memory (RAM) in use is core memory. However, core memories having large storage capacity become bulky, heavy and extremely expensive compared to memories which can be fabricated using photolithographic techniques such as the aforementioned semiconductor memories. Unfortunately, for the most part, dense and light weight semiconductor memories are volatile. The exception is MNOS semiconductor memories which take a relative long time to write and read and have limited retentivity Consequently, there is a need in the prior art to configure by use of photolithographic techniques a nonvolatile random access memory in association with read/write circuitry, which is fast, but light in weight and low in cost.
In the prior art, as an alternative to the foregoing memories data bits are stored in the form of magnetic bubbles which move in thin films of magnetic material These magnetic bubbles are actually cylindrical magnetic domains whose polarization is opposite to that of the thin magnetic film in which they are embedded The magnetic bubbles are stable over a considerable range of conditions and can be moved from point to point at high velocity. Magnetic bubble memories are substantially cheaper than the core memories aforementioned, and much faster than magnetic disk memory systems which are widely used for high capacity storage. Magnetic bubble memories are analogous to magnetic disk memories in that both systems store data as states on, or in, a thin magnetic film. In a disk memory, the film is moved mechanically at high speeds while in a magnetic bubble memory, the magnetic bubbles move at high speeds throughout the thin magnetic film. Since magnetic bubble memories are nonvolatile, logical operations can be performed without reading or writing the stored data out/in again so that magnetic bubble memories do not have moving parts and therefore may operate reliably for long periods of time. However, a drawback of magnetic bubble memory devices is that single crystals with minimal defects are required for fabrication. Moreover, it is difficult to produce large single crystals for high storage devices. Even the attempted use of amorphous materials does not eliminate the problem of high eddy currents which reduce the speed of the magnetic bubble domains. Even so, magnetic bubble memories have many advantages. Nevertheless, there is a need in the prior art to configure a nonvolatile random access memory using thin magnetic film technology and yet provide rapid access time while utilizing only polycrystalline material.
As further background, the present invention is an out growth of the crosstie memory technology disclosed primarily in U.S. Pat. Nos.: 3,846,770 to Schwee et al., entitled "Serial Access Memory Using Magnetic Domains in Thin Film Strips," filed Jul. 11, 1973, patented Nov. 5, 1974; 3,868,659 to Schwee, entitled "Serial Access Memory Using Thin Magnetic Films," filed Apr. 10, 1973, patented Feb. 25, 1975; 3,868,660 to Schwee, entitled "Detector for Cross-tie Memory," filed Apr. 10, 1973, patented Feb. 25, 1975; 4,100,609 to Schwee, et al., entitled "Magnetoresistance Detector for Crosstie Memories," filed Sep. 3, 1976, patented Jul. 11, 1978; 4,192,012 to Schwee et al., entitled "Crosstie Memory Bit Stretcher Detector," filed Nov. 8, 1978, patented Mar. 4, 1980; and 4,231,107 to Schwee et al., entitled "Serriform Strip Crosstie Memory," filed Feb. 14, 1978, patented Oct. 28, 1980, all patents being assigned to the same assignee as the present invention.
Briefly, Schwee et al., '770 disclose a polycrystalline thin film strip for storing digital information serially in the form of reversal domains. The reversal domains are propagated along the thin film strip, e.g., of permalloy, and then sensed to detect the stored digital information.
Schwee, '659, discloses a serial access memory based on the propagation of crosstie walls and Bloch lines along domain walls in thin magnetic films. Variation of the current through conductors placed above the domain walls changes the fields along the walls causing the relocation of Bloch lines and crossties in the walls which causes propagation of the information contained in inverted Neel walls along the domain walls.
Schwee et al., '107, discloses a crosstie memory using a plurality of permalloy thin film strips of uniform thickness each strip having parallel denticulated margins etched to align with the oblong axis thereof. Each pair of opposite denticles defines a distinct memory cell.
The other Patents listed above are cited to show additional prior art of crosstie memory development, and the development of certain types of detectors for use therewith. All of the listed patents are incorporated herein by reference.
The cited and discussed Patents do disclose certain versions and particular aspects of crosstie memories. But they do not disclose or teach, inter alia, the placing of magnetic domain walls into a matrix or array configuration using "wiggle" patterns thereby creating a random access memory element (memory array). Nor do the Patents teach a scheme to read and/or write in this memory array.
The prior art, as indicated hereinabove, teach some advances in crosstie memories including devices for detecting or reading-out binary information therefrom. However, insofar as can be determined, no prior art device or process incorporates the features and advantages of the present invention.