JPH0312092A - Magnetic storage element - Google Patents

Abstract

PURPOSE:To improve stability and to reduce power consumption by superimposing a high coercive force ferromagnetic film pattern and a low coercive force ferromagnetic film pattern by interposing a superconductor layer. CONSTITUTION:A first conductor wire 1 is arranged on a substrate via an insulating layer. A superconductor pattern 6 having micro-Josephson junction for information readout, a second magnetic film pattern 3, and the thin film 8 of a superconductor having a critical magnetic field with the same degree as that of the superconductor used in a lead wire are provided via the insulating layer 5, and a first magnetic film pattern 4 is arranged. A second conductor wire 2 is arranged so as to cross with the position 1 of the magnetic film pattern via an insulating layer 9. The write of information is performed by supplying a pulse shape current to the conductor wires 1 and 2. Readout is performed by using a conductor pattern for information readout, a lead wire 7, and the conductor wire 2. Thus, no magnetic flux of the pattern 3 is inputted to the pattern 4 according to magnetic inversion, and instead of that, it is inputted to the pattern 6, and breaks the superconducting state of the pattern 6, then, it goes to a stationary conducting state, and a detection ratio can be heightened by utilizing the output of a voltage and detecting it with the conductor pattern for information readout.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to nonvolatile high-density solid-state magnetic storage elements.

(Prior Art) Solid-state magnetic memory has high reliability because it does not have a mechanical drive unit and is a nonvolatile memory. Solid-state magnetic memory can be broadly classified into random access type memory and serial access type memory. Core memory is a typical example of the former, and bubble memory is a typical example of the latter. When aiming for high-density storage elements, the random access type requires a detector for each bit, which limits the ability to reduce the cell size. On the other hand, in the serial access type, it is relatively easy to increase the density, but the increase in access time accompanying the increase in density is a major problem. Furthermore, devices such as bubble memories that require the movement of bubbles, which are information carriers, have the disadvantage that the stability of information retention deteriorates as the bubbles move. Considering this situation, we have developed a detector using random access memory as a non-volatile solid-state magnetic memory.
It is desirable to achieve high density.

The basic operation of a random access memory using a magnetic material will be explained using a magnetic thin film memory as an example. As the magnetic thin film, for example, 19% Fe-, which is a soft magnetic material with a magnetostriction constant λ20, is used.
Using an 81% Ni alloy, as shown in Figure 9,
It is deposited in a disk shape on the substrate. The film thickness is about 1oooA. By applying a magnetic field during vapor deposition, uniaxial magnetic anisotropy is imparted within the film plane. In this case, it is attached so that the Y-axis direction is the axis of easy magnetization.

When reversing magnetization, a magnetic field HY in the opposite direction to the magnetization direction is applied parallel to the easy axis. - At the same time, the magnetic field HxIYo- is applied by a line in the perpendicular direction to prevent magnetization reversal due to domain wall movement, and the magnetization is reversed in a short time on the order of Ions by using the simultaneous rotation mode of the magnetic moment. . On the other hand, in the magnetic film pattern 12 to which only HY is added, magnetization reversal occurs due to domain wall movement, but since the reversal time is long, the short time width of HY actually used for writing is No reversal occurs. That is, only when a magnetic field is simultaneously applied by the conductor wire in the X direction and the conductor wire in the Y direction, the magnetization reversal of the magnetic film pattern 12 occurs as shown at 12'. magnetic field H
x and HY are created by applying current to conductor wires arranged vertically and horizontally close to the deposited film. However, with this element, the magnetization of the magnetic film pattern gradually returns to its original orientation due to interaction with adjacent cells, resulting in poor stability of information storage. As time goes on, the detection output becomes smaller, making it difficult to read out information.

(Problems to be Solved by the Invention) In order to solve these problems and realize high-density storage, the present invention has developed an element using a double-layer magnetic film pattern, which had already been devised in the 1960s. We are proposing an improved device that enables high-density, large-capacity storage. conventionally,
The double-layer structure has a sense line sandwiched between magnetic films to detect the induced electromotive force generated from changes in magnetic flux caused by magnetization reversal in the magnetic film pattern. This method was not suitable for miniaturizing the cell size. In addition, the magnetoresistive memory element proposed by the present inventor (Japanese Patent Application No. 63-42089,
-61493), magnetic film patterns for reading arranged in pairs with magnetic film patterns for information storage are coupled adjacently to each other and used as read lines for stored information. However, with this method, as the pattern becomes smaller, the pattern film thickness also becomes thinner, and the electrical resistance of the write line, readout (detection) line increases rapidly, and power consumption increases and the detection output decreases. It has some drawbacks and is difficult to use as a high-density memory element.

The present invention enables a high-density, large-capacity magnetic memory element that suppresses the increase in electrical resistance of the readout line due to miniaturization of cell size, which was a problem with conventional methods, and reduces the demagnetizing magnetic field of the information storage film pattern. It presents a cell structure for

(Means for Solving the Problems) The present invention adopts a method for reading out stored information using oxide superconductors, which has been attracting attention recently, and unlike conventional elements, the magnetic film pattern is We are proposing a cell structure that does not allow direct current flow. The new structure allows for 1) stabilization of written information and 2) efficient detection of information.
High coercive force ferromagnetic film pattern and low coercive force ferromagnetic film pattern, or magnetic film pattern with large uniaxial magnetic anisotropy in the film plane and magnetic film with small uniaxial magnetic anisotropy Incorporating a structure that combines a film structure in which the pattern is layered with a diamagnetic superconductor layer and an oxide superconductor pattern with negative magnetic permeability to simplify the device structure and improve operational stability. We also present a high-density solid-state magnetic memory element with reduced power consumption. Conventional devices also use magnetoresistive effect instead of electromagnetic induction voltage for readout in order to miniaturize the cell size. Materials with a large magnetoresistive effect were limited to ferromagnetic films or semiconductor films. Semiconductors have inherently high electrical resistance, so they were not an option for miniaturization.

Out of necessity, I ended up using the former. In terms of usage, a structure was adopted in which, because of its high magnetic permeability, in addition to serving as a readout pattern, it also played the role of reducing the demagnetizing magnetic field of the information storage film pattern. However, in this structure, as the cell is miniaturized, the line width and film thickness are reduced accordingly to keep the magnetization suppressed within the film plane and maintain detection efficiency. For this reason, there was a limit to miniaturization due to the increase in electrical resistance.

In contrast, when oxide superconductors, which have been attracting attention recently, are used in a state where the electrical resistance is zero, that is, in a superconducting state, the magnetic permeability is negative. Moreover, there is no problem with superconductivity even if the film thickness is about 500 people. The readout superconductor film pattern has a structure with micro-Josephson coupling so that the superconductor film changes to a normal conduction state in response to a magnetic field. A three-layer structure in which two magnetic films differing in at least either in-plane uniaxial magnetic anisotropy or coercive force are stacked with an exchange interaction separation layer formed of an oxide superconductor layer interposed therebetween. The structural film is patterned, the above-mentioned superconductor film pattern for information reading is attached to the outside thereof, and first and second superconductor lines are provided above and below the pattern and intersect with each other at the position of the pattern, and the structure has a three-layer structure. A lead wire for applying current is attached to the superconductor film pattern outside the pattern, which is a magnetic memory element. In this way, a high-density solid-state magnetic memory element with improved information stability, improved operational stability, and reduced operating time is provided.

(Example 1) FIG. 1 shows an example of the structure of a unit cell used in this memory element.

First, X
- arranging a first conductor wire 1 extending in the axial direction; A superconductor pattern 6 having a micro-Josephson junction for information reading is placed on top of that via an insulating layer 5, a second magnetic film pattern 3 is placed on top of that, and a lead wire is placed on top of that. A superconductor with a critical magnetic field comparable to that of the superconductor used (
A thin layer 8 of a non-magnetic material is placed, and a first magnetic film pattern 4 is placed thereon. A second conductor wire 2 is placed thereon with an insulating layer 9 in between so as to intersect with wire 1 at the position of the magnetic film pattern. Information is written by applying a pulsed current to the conductor wire 1.2. Reading is performed using the information reading conductor pattern, its leads 7, and the conductor wire 2. By doing this, the magnetic film pattern 4 for reading information is
With the magnetization reversal of , the magnetic flux of 3 no longer enters 4, and instead enters 6, breaking the superconducting state of 6 and becoming a normal conductive state, and using the fact that a voltage is generated, it can be used as a conductive pattern for information reading. The detection efficiency can be kept high.

The feature of the present invention is that by using an oxide superconductor film pattern with micro-Josephson bonds in the conductor pattern for information reading, the storage information is created by the double film structure of the magnetic film, which was adopted for information stabilization. It enables stable reading of stored information without compromising the stability of the device, improves the stability of device operation, and shortens operation time. The point is that the thickness of the superconductor thin film 8 can be controlled arbitrarily.

This device has large uniaxial magnetic anisotropy within the film plane,
A ferromagnetic film pattern 3 that satisfies at least one of a high coercive force and a ferromagnetic film pattern that satisfies at least one of a small uniaxial magnetic anisotropy in the film plane and a low coercive force. In the double membrane structure pattern combining the former 3, information is written and stored in the former 3. The latter pattern 4 is used for reading written information and stably maintaining written information. In addition, the information reading superconductor film pattern 6 used here normally has negative magnetic permeability and does not serve as a path for magnetic flux, but since it has a micro-Josephson junction, it can pass magnetic flux when a magnetic field is applied. As a result, it transitions to a normal conduction state and exhibits electrical resistance. Therefore, when no magnetic field is applied, it has the characteristic that it is maintained in a state where it is almost not magnetically coupled to the upper and lower magnetic film patterns. FIG. 2 shows the unit cells shown in FIG. 1 arranged in a matrix. The part surrounded by the dotted line indicated by A in FIG. 2 is the unit cell.

FIG. 3 shows the relationship between the electrical resistance R of the superconductor thin film that can be used in pattern 6 and the externally applied magnetic field H, .

H,,,,> At HcrIt, the superconducting state is broken and electrical resistance appears.

FIG. 4 shows an example of magnetization curves 3' and 4' in reversal mode due to simultaneous magnetization rotation of the magnetic film pattern 3.4 when no magnetic field HT is applied in the direction of difficult magnetization. The horizontal axis is the external magnetic field HY applied in the direction of easy magnetization, and the vertical axis is the magnetic flux density B.
represents. People and HK each have a pattern of 3.4.
is the uniaxial anisotropic magnetic field in the plane of - Shows that the magnitude of the magnetic field HY applied in the direction of easy magnetization (Y-axis direction) when magnetization reversal occurs due to simultaneous magnetization rotation differs depending on the magnitude of the uniaxial anisotropic magnetic field in the film plane. ing. This difference in switching magnetic fields is utilized in the present invention. The material used for the element of the present invention is gold, aluminum, etc. as a conductor, and pb-based, Nb-based, or Ba-Y-Cu- as a superconductor.
0 series, B1-8r-Ca-Cu-0 series, Tl-Ba-C
Ceramics such as a-Cu-0 series, SiO2, etc. can be used as the insulator. Furthermore, suitable materials selected from a wide range of materials can be used for the magnetic film. Known techniques can be used for forming the thin film. The ceramic can be formed by sputtering or laser evaporation, and the etching can be, for example, dry etching.

Explain how to write information. As an initial state, the direction of magnetization of the ferromagnetic film pattern 3 used for information storage is saturated in a predetermined direction (for example, Y-axis direction, negative direction) and "0" is defined. Figures (a) to (d) are cross-sectional views of the unit cell. Figure 5(a) shows the paper surface normal and
- It is a sectional view of the cell when cut along a plane including the center line of the conductor wire 1 parallel to the axis. The direction of magnetization is shown in Figure 5(a).
The direction along the Y-axis direction shown by is defined as the positive direction. The write operation is performed as follows. By applying a pulse current to the conductor wire 1 running in the X-axis direction and the conductor wire 2 running in the Y-axis direction, the conductor wires 1 and 2 are connected in the magnetic film pattern 3 at each position. The direction of magnetization (Y-axis direction, negative direction) of the magnetic film pattern 3 existing at the intersecting position is the fifth
It is reversed in the positive direction as shown by 10 in Figures (a) and (b).

In order to clearly illustrate this situation, FIG. 5(b) shows a cell cross section when the unit cell is formed on a plane including the normal to the plane of the paper and the center line of the conductor wire 2 parallel to the Y-axis. It is a view seen from the left side of FIG. 5(a). Below (b), (C),
All drawings in (d) are views viewed from this direction. The direction of magnetization of the magnetic film pattern 4 is as shown in Fig. 5 (
As shown in FIG. 5(b), the magnetization is combined with the magnetization of the magnetic film pattern 3 and is magnetized in the opposite direction to the magnetization direction of the magnetic film pattern 3. However, during writing, as shown in FIG. 5(c), , it becomes the same direction as the magnetization of 3, which is reversed and reversed to the direction of the Y-axis direction pressure. In order to reach the stable holding state from this state in the shortest possible time, the current in the conductor wire 2 running in the Y-axis direction is held for a longer time than the current in the conductor wire 1 running in the X-axis direction. put. Then, the magnetization of the magnetic film pattern 4 is caused by the magnetic field from the magnetic film pattern 3 and the Y
- In combination with the magnetic field from the axial superconductor wire,
- It is reversed in the simultaneous magnetization rotation mode and quickly reaches the final state (stable holding state) shown in FIG. 5(d). This rotation speed becomes faster as the interaction between the two magnetic film patterns becomes stronger. What is important is that the magnetization state of the magnetic film pattern for information storage is large enough so that it does not change as a result of changing the magnetization state of the magnetic film pattern for reading during reading. The objective is to provide magnetic anisotropy of . The maximum value of the write current is determined by the magnitude of this magnetic anisotropy. In the information retention state, closed circulation magnetic flux lines are formed between the ferromagnetic film pattern 4 and the ferromagnetic film pattern 3, reducing the demagnetizing magnetic field.

Figures 6(a) and (b) indicate information ``0'' or +, respectively.
This corresponds to the stabilization state showing 1111. Note that the time required to write one bit of data using this method is on the order of several tens of ns. In addition, when overriding,
Prior to writing information, the current polarity of the Y-axis direction conductor wire 2 is kept the same as during writing, and only the current applied to the X-axis direction conductor wire is supplied with a reset pulse magnetic field whose polarity is reversed from that during writing. or if the written information is “′′
A method is used in which external control is performed so that inverted magnetic fields with opposite polarities corresponding to 0'' or 11111 are applied to the magnetic film pattern for information storage.

Next, an example of how to read the written information will be described. When information is written, the magnetization of the ferromagnetic film pattern 4 and the ferromagnetic film pattern 3 are in opposite directions, so most of the magnetic flux flows through the two magnetic film patterns, which have low magnetic flux resistance. is taking. As a result, almost no magnetic flux passes through the detection superconductor pattern 6).

In this state, when a predetermined current is applied to the conductor wire 7, magnetization reversal due to the simultaneous magnetization rotation mode does not occur in the magnetic film pattern 3 for information storage, and on the other hand, the magnetic film pattern for reading The current applied to the conductor wire 2 is adjusted to tilt the direction of magnetization from the easy magnetization direction (Y-axis) so that only the magnetization of the conductor wire 2 can be reversed in the simultaneous rotation mode. In other words, using conductor wires running in the Y-axis direction, the magnetic field H
x is added in the direction of difficult magnetization (X-axis). Figure 7 (a
) to (C) show the state in which two magnetic film patterns are combined. FIGS. 7(b) and 7(d) show simultaneous rotation magnetization reversal curves for each of the two film patterns at that time. The fact that the magnetization reversal curve shown by the solid line is asymmetrical with respect to the vertical axis indicates the magnetostatic coupling effect between the magnetic thin film patterns 3.4. Figure 7(a) shows the information “
The state corresponding to 0'' is shown in FIG. 7(c), and the state corresponding to 1' is shown in FIG. Now, when reading 1'', the detection superconductor film pattern 6 transitions to normal conduction, and when reading 0°', it indicates that it does not transition to normal conduction. For easy explanation, Figure 8(a) is an enlarged version of Figure 7.
Use (b).

At the time of reading, first, the conductor pattern 2 applies a magnetic field HT in the direction in which the magnetic film pattern is difficult to magnetize.

Then, the magnetization of the magnetic film pattern 4 rotates from the easy magnetization direction to the difficult magnetization direction. Due to this magnetization rotation, the critical value of the magnetic field in the easy direction of magnetization required for the magnetization-simultaneous rotation mode changes from H to H', from the magnetization reversal curve shown by the solid line to the magnetization reversal curve shown by the dashed line in FIG. 8(b). decreases to In cells to which no magnetic field is applied in the direction of hard magnetization, this critical value remains at H, so the effect of the magnetic field in the direction of easy magnetization on simultaneous magnetization reversal is determined between cells to which HT is applied and cells to which HT is not applied. It will be automatically controlled. In this state, the conductor wire 6 moves H'<H in the direction of easy magnetization.
Apply a magnetic field H in the range <H. Then, the magnetization is temporarily reversed only in the magnetic film pattern 4 whose magnetization is tilted in the difficult direction. In other words, by rotating the magnetization of the magnetic film pattern 4 from the easy magnetization direction to the difficult magnetization direction,
Cells are specified by making a difference of HH' from the critical value of the magnetic field in the direction of easy magnetization required for the simultaneous rotation mode of magnetization.

When magnetization reversal occurs, the magnetic flux leaving the magnetic film pattern 3 that has been flowing through the magnetic film pattern 4 enters the superconductor pattern 6 connected to the conductor wire 7, causing 6 to transition to a normal conduction state. and generates electrical resistance. Since a current is applied to the conductor wire 7, a voltage is inevitably generated. In the state of "0", the direction of magnetization of the magnetic film pattern 4 is opposite to that in the case of "1", so the magnetic field applied in the direction of easy magnetization to read out "1" is as shown in Fig. 6(a). As is clear from this, it is attracted to the direction of easy magnetization and does not cause magnetization reversal.
No magnetic flux enters the conductor pattern 6. In other words, no voltage is generated. Therefore, with this method, “T” of the stored information
, "011" can be discriminated. After reading, the current in the conductor wire 6 is first cut off. Then, the magnetization of the ferromagnetic film pattern 4 is divided by the magnetic field from the ferromagnetic film pattern 3 and the magnetic field from the Y-axis direction conductor wire. In combination with - simultaneous rotation mode,
The stable bonding state of the two magnetic film patterns is quickly restored.

Note that the magnetization reversal curve shown by the dotted line in the figure is a curve when the magnetic film patterns 3 and 4 are not magnetostatically coupled to each other. The magnetic film pattern 4 has unidirectional magnetic anisotropy due to the magnetic field Δ generated from the magnetostatic coupling with the magnetic film pattern 3, and the simultaneous rotation magnetization reversal curve of the pattern 4 has a right-hand direction as shown in FIG. It's off.

The characteristics of this readout are that the magnetic field applied during readout is made small so as not to affect the magnetization state of the ferromagnetic film pattern 3 that stores information, and the readout line 7
By using its own sense current to generate the magnetization reversal magnetic field, noise from the magnetic field applied to the detection signal is minimized, making it possible to completely non-destructively read out stored information.

(Effects of the Invention) The present invention provides high-performance, high-density magnetism that has significantly improved both the instability of the magnetization state after magnetization reversal, which has been a problem in the past, and the instability of information readout due to improved storage density. A memory element can be realized.

[Brief explanation of the drawing]

FIG. 1 is an external view of an example of the basic cell structure of the present invention. FIG. 2: A diagram showing an example in which the basic cells of FIG. 1 are arranged in a matrix to form a memory element. Fig. 3 is a diagram showing the relationship between the electrical resistance of the superconductor film pattern 6 used for reading information of this device and the applied magnetic field, and Fig. 4 is a diagram showing the relationship between the electrical resistance and the applied magnetic field of the superconductor film pattern 6 used for reading information of this device. The magnetization curves of a low coercive force ferromagnetic film pattern with a magnetic anisotropy of figure. Figure 5(a)-(
d) is a cross-sectional structural diagram of a basic cell and a diagram illustrating an information writing process. FIGS. 6(a) and 6(b) are diagrams showing an example of a state in which information has been written. FIGS. 7(a) to 7(d) are diagrams showing the magnetization state of a stabilized cell and the corresponding magnetization curve. FIGS. 8(a) and 8(b) are diagrams showing the principle of read operation. FIG. 9 is a diagram showing an example of a conventional memory using a magnetic film pattern. In the figure, 1... superconductor wire, 2... superconductor wire, 3... has large uniaxial magnetic anisotropy in the film plane,
or a ferromagnetic film pattern with a large coercive force, 4.
...Ferromagnetic film pattern with small uniaxial magnetic anisotropy in the film plane or low coercive force, 3', 4'...
- Magnetization curves of patterns 3 and 4, 5... insulating layer, 6
. . . Superconductor film pattern for reading information, 7 . . Lead wire of conductor film pattern 6, 8 . . . Superconductor thin layer, 9
...Insulating layer, 10...Y-axis direction positive direction, 11.
...Y-axis direction, 12...magnetic film pattern,
12'...Magnetic film pattern with reversed magnetization.

Claims (1)

[Claims] The direction of uniaxial magnetic anisotropy in the film plane is the same on the substrate,
Two magnetic film patterns having different sizes or coercive forces are placed one on top of the other with a nonmagnetic layer interposed therebetween, and the first magnetic film pattern has an in-plane uniaxial magnetic anisotropy constant, Alternatively, a magnetic film with a small coercive force or a magnetic film with a large in-plane uniaxial magnetic anisotropy constant or a large coercive force is used as the second magnetic film pattern, respectively. The superconductor pattern No. 3 is in contact with the second magnetic film pattern, and the three-layer structure pattern is stacked on the side opposite to the side where the first magnetic film pattern is. A magnetic memory element characterized in that conductor wires are arranged so as to cross each other at the position of the magnetic film pattern, and a lead wire for applying a current is attached to the third superconductor pattern.