JPS5947378B2 - Magnetoresistive cylindrical domain detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is an improved invention of Patent Application No. 103893 of 1975 (Japanese Patent Publication No. 58-46787), and is a magnetic resistance device for reading out information stored in a cylindrical domain transfer memory. Concerning effect type domain detectors.

When applying an external supporting or holding magnetic field in an appropriate direction and magnitude to a ferromagnetic single crystal thin film with uniaxial anisotropy, a cylindrical magnetic domain, a so-called cylindrical domain, is generated perpendicular to the plane of the thin film. , whose magnetization direction is opposite to the surrounding magnetization and the magnetization of the holding field.

The cylindrical domain has a magnetic field rotating in the plane of the film and an associated operating pattern provided on the memory film, each element of which is made of a magnetizable material, e.g. a Ni-Fe alloy,
(provided in layers and rectangularly on one membrane plane) can be moved at high speeds and is therefore suitable for the construction of shift registers that can be integrated into serial memories. The memory operation is then directed to the detector as to the presence or absence of a cylindrical domain at a predetermined location within the memory, and the detector is capable of converting the magnetic field generated by the cylindrical domain into an electrical signal at the detector location. is necessary.

Detectors are known that make use of various physical effects, such as the Faraday effect during magneto-optical readout, the Hall effect in a magnetic field or the change in resistance of ferromagnetic materials. For reasons of technically simple construction, magnetoresistive domain detectors, ie detectors utilizing the last-mentioned effect, have generally been implemented. In this case, a thin film-like detection strip is used as the detector element, which runs preferably perpendicularly to the domain domain and is made of a particularly magnetostrictive Ni--Fe alloy, for example deposited by vapor deposition on the storage plane. If the detection strip is not exposed to the stray field of the cylindrical domain, there is a magnetization MD of the detection strip parallel to the direction of the current iD flowing through the detector during memory operation.

When the cylindrical domain passes along the sensing strip, its stray field rotates the magnetization by an angle θ from the current direction. This results in the resistance R of the detection strip. changes by the value ΔR.
This resistance change causes a voltage drop ΔU=iD・ΔR(
θ), which can be further processed as a readout signal.

That is, the readout signal at a predetermined detection current ID is higher as the resistance change ΔR of the detection element exerted by the cylindrical domain is larger.

ΔR is a function of the change in intrinsic magnetoresistance of the sensing material. It initially increases linearly with the magnetic field strength, but then tends to reach a saturation value. The detection strip is the leakage magnetic field H of the cylindrical domain.
In order to be completely saturated by D, this leakage field must be combined with the anisotropic field Hk of the detector material (in which a ferromagnetic Ni-FeJ alloy is used) and the demagnetizing field of the detection strip. He
It must be larger than the sum of n. However, the resistance change can also be increased by making the detection strip as long as possible. However, this is only meaningful if the detection strip is captured by the leakage field of the cylindrical domain over its entire length, and therefore the cylindrical domain is replaced by a domain extender (which is generally made of magnetostrictive ferromagnetic Ni-Fe). (a suitable thin film-like pattern made of a metal alloy) is extended stepwise to the predetermined length of the detection strip, i.e. stretched into long strip-like domains, thereby being detected. The leakage field of the power cylindrical domain is significantly expanded. For domain extension, a domain extender as shown in FIG. It is formed by an equal number of 90" chevron bars 3, each of which overlaps the detection strip in an area 4 and makes metal contact with it. A cylindrical domain not shown in FIG. 1 and exclusively indicated by arrow A In the direction of the transfer path, parallel to and parallel to the illustrated chevron columns, other chevron columns are arranged.In this known magnetoresistive domain detector, the saturation value of the relative magnetoresistive change of the sensing element is below the value of , so that for signal detection the magnetoresistive properties of the sensing material are only partially utilized, resulting in only a relatively small readout signal.

The object of the invention of Patent Application No. 103,893 of 1975 is to provide an improved readout compared to known magnetoresistive domain detectors due to an improvement in the resistance change of the detection strip caused by the leakage field of the cylindrical domain. The objective is to obtain a magnetoresistive domain detector with a signal.

The original invention is based on the recognition that the above-mentioned drawbacks are caused by the overlap of the domain expander with the detection strip of the magnetic bar.

Starting from this recognition, according to the original invention, a magnetoresistive domain detector is provided which has a membrane-like detection strip of magnetoresistive material and a domain extender, which runs particularly perpendicular to the cylindrical domain path. A conductive separation of the detection strip and the domain extender was proposed. For this purpose, the end of the domain extender pointing towards the detection strip, ie the limit line of each bar pointing towards the detection strip, is arranged, for example, at a distance from the detection strip. The part of the domain extender directed towards the detection strip and the detection strip overlap, so that the conductive separation is provided, for example, by an insulating interlayer, eg SiO. This can be done in layers. In a domain detector configured in this way, the magnetization MD of the detector material is equal to the detection current I.

A readout signal occurs when parallel to the direction of (
The MD changes direction in synchronization with the rotating magnetic field used to transfer the cylindrical domain). The aim of the invention is to further develop the domain detector of the original invention, to increase the signal sensitivity of the detector and to improve the signal-to-noise ratio.

a thin film-like sensing strip of magnetoresistive material and a domain extender running particularly perpendicular to the cylindrical domain transfer path, which are electrically conductively separated for reading out the cylindrical domain transfer memory; In a magnetoresistive domain detector, the invention provides a further improvement in that the central longitudinal axis of the sensing strip is offset parallel to the axis of symmetry of adjacent chevron columns of domain stretchers.

Since magnetoresistance is a function of COs2θ (where θ represents the angle between magnetization MD and detection current ID), the highest signal sensitivity is obtained when the directions of magnetization and detection current form an angle of 45°. It will be done.

This requirement for optimal signal sensitivity is met by the above-described asymmetrical arrangement of the domain stretchers and detection conditions according to the invention. An advantageous configuration of the domain detector is such that the domain extender has at least one chevron column on each side of the detection strip, the detection strip and one of the two chevron columns adjacent to the detection strip having The parts facing towards the strips are superimposed so that the insulating intermediate layer e.g.
They are electrically conductively separated by an iO2 layer.

The invention will now be explained with reference to the drawings.

FIG. 1 diagrammatically and partially shows a known domain detector as described above, FIG. 2 shows an embodiment of the domain detector of the present invention, and FIGS. shows a diagram highlighting the advantages of the domain detector of the present invention.

In the embodiment of FIG. 2, the axis of symmetry of the domain extender 5 is
The end of the chevron column 2, which is offset parallel to the intermediate longitudinal axis of the detection strip 1 and is present on the detection strip 1 and is shown on the left in the plane of the figure, is not shown. Insulating layer e.g. SiO
It is electrically conductively separated from the sensing strip by two layers.

In the diagram of FIG. 3, the read signal USlg for the domain detectors of FIGS. , 5 μm.

Here, 1'' and 2'' indicate the readout signal-detection current curves for the domain detectors of FIGS. 1 and 2. The signal sensitivities for the domain detectors of Figures 1 and 2 are 1.3, mVmA and 2mV/MA, respectively, i.e., with the axis of symmetry of the domain extender offset relative to the central long axis of the detection strip. By this, 50% of the signal sensitivity
improvement can be obtained. An undisputed electronic distinction between the 2, original value ``1'''' when the cylindrical domain passes along the detector, and the binary value ``0'''' when the domain does not pass along the domain detector. Therefore, in addition to the absolute value of the readout signal, the signal-to-noise ratio is particularly important.

During electronic processing of the readout signal, it is evaluated only during a fraction of the time between two consecutive signals. That is, a distinction should be made between (S/N) Max, which relates to the maximum protection signal, and (S/N) Fenster, which relates to the interference signal appearing during the evaluation window. (S/N)Max=(S/N)Fen for the domain detector with the symmetrical configuration in Fig. 1
It's a star. This is because the read signal and the maximum disturbance signal appear at approximately the same time within one read cycle. Due to the asymmetrical arrangement according to the invention of the domain detector of FIG. 2, in particular the readout signal moves in time within one readout cycle, but the maximum signal does not;
In this case (S/N) Max (S/N) Fens
It is achieved that ter. In the diagram of FIG. 4, for the domain detectors of FIGS. 1 and 2,
Detect the amount (S/N) Max and (S/N) Fenster current 1.

for the domain detector of FIG. 1, with (S/N)Max=(S/N)Fenster (curve 1''''). In this case, a time interval having 20% of one readout cycle with respect to the signal maximum is selected as the evaluation window. In the domain detector in Figure 2 (S/N)
Fenster (curve 2″″) is (S/
It can be seen that it is significantly larger than N) Max (curve 2″″). The difference in (S/N) Max of both domain detectors is responsible for the different signal sensitivities. For a typical 3 mA detection current in memory operations, the improvement in S/N Fenster of the domain detector of FIG. 2 is nearly 400%.

[Brief explanation of drawings]

FIG. 1 diagrammatically and partially shows a known domain detector, FIG. 2 shows an embodiment of the domain detector of the present invention, and FIGS. Figure 3 shows a dymagram demonstrating the advantages of the domain detector of the invention. In the figure, 1 is the detection strip, 2 is the chevron column, 3 is the chevron bar, 1'' is the signal-detection current curve of the domain detector of FIG. 1, and 1'' is the S/N of the detector of FIG. 1. ratio curve, 2″ is the second
The signal-detection current curve of the detector in the figure, 2'' is the (S/N) Fenster's curve of the detector in Figure 2, 2'' is the same (S/N) Max curve, and MO is the detection strip. magnetization, I
D is the detection current.

Claims (1)

Claims: 1. A magnetoresistive device running specifically perpendicular to the cylindrical domain transfer path, characterized in that the central long axis of the detection strip is offset parallel to the axis of symmetry of adjacent chevron columns of domain extenders. A magnetoresistive domain detector for reading stored information of a cylindrical domain transfer memory by means of a thin film-like detection strip of material and a domain extender with conductively separated chevron columns. 2. The domain stretcher has at least one chevron column on each side of the detection condition, comprising a detection strip and a portion of the chevron columns adjacent to each side of the detection strip directed toward said detection strip. 2. A domain detector according to claim 1, wherein the domain detectors are superimposed and electrically conductively separated by an insulating intermediate layer.