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Memory effects observed on GaAs thin films that were evaporated on tungsten substrates have been studied. If metallic films are evaporated on the GaAs thin films, a polarized memory effect is found between the tungsten substrate and the metallic film. A nonpolarized memory effect is found if a metallic wire point contact is made to the GaAs film. These memory effects were only slightly dependent on counterelectrode, point contact, and substrate materials used and originated from the properties of the GaAs evaporated film itself.

This paper considers the propagation of waves in a transmission line loaded with thin permalloy films. Since the films are driven to saturation, the transmission line equations which are derived to describe the wave propagation are nonlinear. The nonlinearity requires the use of shock wave analyses, and a derivation of the appropriate shock relations is included. The problems of a line loaded with a single film and a line loaded with a periodic array of films are both treated. The saturation front moving along a string of films is shown to be the shock front. The shock speed, which is determined in terms of the parameters of the circuit, is then the operational speed limit of a thin film memory.

The hard axis magnetic field distribution within the uniaxial magnetic film element of a thin film memory device is calculated. In the memory device considered, the driving stripline and magnetic film are located between a magnetic keeper and a conducting ground plane. The difficulty encountered in the keeper-ground plane problem arises from the requirement of satisfying boundary conditions at the keeper and ground plane surfaces simultaneously, or in other words, from considering an infinite set of film and stripline images. A method of solution using Fourier transforms proves satisfactory. The dependence of the magnetic field distribution on the relative position of the elements and on variations in material properties is assessed.

The 256-word, 200-bit NDRO memory utilizes magnetic films deposited in arrays of discrete spots on thin glass substrates. Sandwiching of conductors between two substrates provides partial coupling to film pairs. The magnetic films exhibit both uniaxial and biaxial anisotropy and are interrogated by word fields of less than H k amplitude. Word currents of 15-ns duration and 5-ns rise time produce sense signals in excess of 1 mV with a 7- to 10-ns duration. A single compact assembly houses the stack and its associated circuitry. Circuits are packaged employing hybrid techniques where electroless plating produces resistors from a nickel-phosphide solution onto copper-clad glass-epoxy laminates.

A three-layer device is proposed which uses temperature-dependent exchange coupling between two magnetic layers. One layer is composed of a magnetically "hard" material, the other is uniaxial Permalloy. The coupling layer is an alloy that has a Curie temperature near room temperature. A brief pulse of heat applied by means of an optical or electron beam can raise the temperature of the device above its lowest Curie temperature, and the film will change its magnetic state under the influence of an external bias field. An energy calculation for the single-domain case leads to a family of critical curves with exchange coupling as a parameter. An alloy of Ni-Fe-Cr is proposed for use in the coupling layer. Measurements of saturation magnetization versus temperature are reported for sputtered films of the alloy. Although the desired properties are observed for some samples, the alloy appears to be metallurgically unstable.

The Soniscan ferroacoustic memory is a new all-electronic mass storage system which utilizes a propagating sonic pulse to access a batch-fabricated film storage medium. The storage element consists of two magnetostrictive film layers with a conductor sandwiched between them. They are deposited on a thin glass substrate and etched into a suitable pattern. A piezoelectric transducer is bonded to one edge of the substrate. The switching behavior of the magnetic storage element is described by a modified Stoner-Wohlfarth model and the sonic wave generation and propagation by a one-dimensional transmission-line analog. The fabrication and operation of the storage elements are discussed. The design of a 107bit memory system is presented. A 2048-bit experimental model of a Soniscan memory has been constructed. It has an access time of less than 2μs, a data rate of 7 Mbit/s/line, and a storage density of 4000 bit/in2A Soniscan bulk store will be relatively inexpensive, since memory planes are batch fabricated; a single electronic unit, the transducer driver switch, half-selects tens of thousands of bits during reading and writing; and sense and recording electronics are shared among many planes by the series stringing of write-sense lines. It is expected that Soniscan will present an attractive alternative to electromechanical units in many applications.

Results of an investigation of flexible keepers are reported. The parameters studied include the composition, preparation, and particle size of the ferrite and the thickness and binder content of the sheet. The optimization of these parameters improved the performance of the keeper by 10 percent. The use of the improved keeper in thin film memory arrays results in reducing the increase of bit drive current due to worst case effects by a substantial amount.

A new thin film memory has been developed. The memory plane is comprised of an NDRO storage array with fully integrated structure and the peripheral integrated circuits on the same substrate. The distinctive feature of this memory is the multilayered structure of a metal substrate, digit lines, and word lines covered by thin Permalloy keeper stripes with thin polyimide resin as the intermediate insulative layers. In order to realize a superior building block unit adaptable to any memory structure requirement, the memory plane is mounted on a printed circuit board whose physical dimensions are identical with those of the logic IC board.

Since Pohm introduced the concept of multiturn windings as a means for improving the efficiency of planar thin film memory elements and thereby lowering the cost, very little, work has been published on memories using this technique. Planar thin film memory elements typically require word currents on the order of 500 ma and bit currents on the order of 150 ma while signals are in the range of 1 to 2 mv. Multiturn windings can be used for sense lines and/or word lines to improve the efficiency of planar film elements because the drive requirements are inversely proportional to the number of turns while the signal output is theoretically directly proportional to the number of turns. This paper describes the design of a 74000 bit planar thin film memory using a multiturn sense-digit structure but using single lines for word drive.

In a previous paper, a ferromagnetic film memory was described having a complex structure of evaporated magnetic, dielectric and conducting materials. The multiple plane geometry was designed to enhance the characteristics which are desirable in practical digital computer memories without requiring extreme uniformity and control of the magnetic properties.This paper describes the electrical characteristics of prototype memory elements, and discusses their application in computer memory systems. A short review of the basic magnetic structure and mode of operation is given first to provide a common reference for discussion.

A high performance computer memory must operate at high speed, require a minimum amount of power, and be capable of operating under extreme environmental conditions. Thin film memories meet these requirements, however, anyone who expected them to become the primary memory technology was certainly premature. Despite its superior performance features, the thin film memory has encountered producibility problems which have prevented it from becoming cost competitive. Univac has developed the MATED FILM memory concept and a continuous vacuum deposition system which together have overcome previous producibility obstacles and now make the evaporated film memory a serious contender for main store applications. The features which are new and unique to this approach are:1. Economical continuous deposition for 16-hour periods with all deposition parameters maintained in equilibrium.2. The closed-flux path design has wide operating margins and provides an exceptionally low susceptibility to process variations.3. Changing the film array organization from a word-bit matrix to a bit-slice array has greatly reduced the number of connections and process steps required to fabricate the memory stack.

Memories in today's high-performance systems are typically made up of memory modules of capacity comparable to the new memory to be described here. Cycle times are 500 nsec to 1 μsec with access times of 300 to 500 nsec. This paper presents the design of a thin-film main memory with a capacity of 8,192 words of 72 bits each. The cycle time of this memory is 120 nsec with an access time of 60 nsec. Thus, this memory design represents a 4-to-8-times improvement in main memory performance over the present state of the art.

The computer in a B8500 modular data processing system may be equipped with as many as 16 memory modules, each of which has a capacity of 16,000 words of 52 bits each. The modules are self-contained with power supplies, logic circuits, and receiving and transmitting circuits which communicate with the computers.

An experimental prototype memory with 32 ten bit words has been designed, built, and tested. Circular spots 116 in. in diameter about 600 A thick are used. These are evaporated on two pieces of glass each comprising a 16×16 spot array. An operating cycle time of less than one‐half microsecond appears possible.The circuitry for driving and sensing is transistorized and the memory uses external register selection from a core‐diode matrix. Word selection is provided by a transverse field, and a digit winding conditions the information written by applying a longitudinal field in the “one” or “zero” direction.Extension to sizes of the order of 1000 words is planned using these techniques. The memory constructed here will soon be installed in the control element of the TX‐2 computer.

The concept of sharp films results from a study of the behavior of the magnetization vector at the edge of a thin film. In that study it was shown that many of the effects of the demagnetizing field at the edge of a film can be predicted by assuming a local shape edge‐anisotropy field, whose easy axis lies parallel to the edge of the film. According to this theory, square films have a low nucleation threshold because the edges of the film perpendicular to the easy axis have an edge anisotropy that subtracts from the ordinary field‐induced anisotropy yielding a region of low resultant anisotropy. Sharp films are memory elements in which the angle between the film edge and the easy axis is everywhere small. Consequently, the resultant anisotropy field along the edge is the sum instead of the difference of the two anisotropy fields, and the nucleation threshold is high. In fact, reverse domains in these films generally form in the center rather than at the edge. Sharp films have typical Hc values of 3 Oe for films of 4½ to 5 Oe Hk , while the reversible limit (creep threshold for zero easy axis field) will be 0.1 Oe less than Hk . Since magnetization creep is the principle limitation of thin film memory elements and since sharp films have creep thresholds far larger than films of ordinary shape deposited on the same substrate at the same time, new fast, low‐power NDRO memory modes are possible with sharp films. These modes involve rotationally switching the films from one saturated state to another and use fields that are ⅔ Hc and ⅔ Hk so that no unselected films are disturbed.