JP2001256773A - Access method of magnetic memory cell, and magnetic memory cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that in magnetic memory using conventional magnetic tunnel junction(MTJ) elements, a ferro-magnetic layer forming a memory layer is magnetized in the direction of the surface inside, therefore, demagnetizing influence by the magnetic poles at both end parts increases with micronizing of the element and magnetization of the memory layer becomes unstable. SOLUTION: A bit line 12 is arranged within a closed magnetic path of a magnetic memory cell 11 having a closed magnetic path structure, and a word line 13 is arranged to be orthogonal to the bit line 12 on the magnetic memory cell 11 via an insulating layer 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic memory cell access method and a magnetic memory cell.

[0002]

2. Description of the Related Art In recent years, a magnetic tunnel junction (MTJ) element has a larger output than conventional anisotropic magnetoresistive (AMR) elements or giant magnetoresistive (GMR) elements, and has been used for HDDs. Applications to read heads and magnetic memories are being considered.

[0003] In particular, a magnetic memory is a solid-state memory having no moving parts like a semiconductor memory, does not lose information even when power is cut off, and has an infinite number of repetitions.
It is more useful than a semiconductor memory, for example, there is no danger of erasing recorded contents even when radiation is incident.

FIG. 4 shows a configuration example of a conventional MTJ element.
Such a structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-10651.
No. 4 discloses this.

The MTJ element shown in FIG. 4 has an antiferromagnetic layer 41, a ferromagnetic layer 42, an insulating layer 43, and a ferromagnetic layer 44 laminated. The magnetizations of the ferromagnetic layer 42 and the ferromagnetic layer 44 are both in the plane of the film and have an effective uniaxial magnetic anisotropy such that they are parallel or antiparallel. And the ferromagnetic layer 4
The magnetization of No. 2 is substantially fixed in one direction by exchange coupling with the antiferromagnetic layer 41, and the recording is held in the direction of the magnetization of the ferromagnetic layer 44.

The antiferromagnetic layer 41 is made of FeMn, NiM
Alloys such as n, PtMn, and IrMn are used, and the ferromagnetic layers 42 and 44 are made of Fe, Co, Ni, or an alloy thereof. Various oxides and nitrides have been studied for the insulating layer 43, but Al ₂ O ₃ is currently used.
It is known that the highest magnetoresistance (MR) ratio can be obtained in the case of an O ₃ film.

[0007] In addition, there has been proposed an MTJ element having a configuration excluding the antiferromagnetic layer 41 and utilizing a coercive force difference between the ferromagnetic layers 42 and 44.

FIG. 5 is a schematic diagram showing a case where the MTJ element having the structure shown in FIG. 4 is used in a magnetic memory that can be accessed randomly. The transistor 51 has a role of selecting the MTJ element 52 at the time of reading. The information of “0” and “1” is recorded by the magnetization direction of the ferromagnetic layer 44 of the MTJ element shown in FIG. 4, and the magnetization direction of the ferromagnetic layer 42 is fixed. Information is read using the magnetoresistance effect that the resistance value is low when the magnetizations of the ferromagnetic layers 42 and 44 are parallel and high when the magnetizations are antiparallel. on the other hand,
Writing is realized by reversing the direction of magnetization of the ferromagnetic layer 44 by a combined magnetic field formed by the bit line 53 and the word line 54. In addition, 55 is a plate line.

[0009]

By the way, in the MTJ element having the above structure, the magnetization of the ferromagnetic layers 42 and 44 is in the in-plane direction, so that magnetic poles are generated at both ends. To increase the density of the magnetic memory, it is necessary to miniaturize the MTJ element. However, as the element is miniaturized, the influence of the demagnetizing field due to the magnetic poles at both ends increases.

Since the ferromagnetic layer 42 is exchange-coupled with the antiferromagnetic layer 41, the influence of the above-described demagnetizing field is small, and as disclosed in US Pat. No. 5,841,692. By configuring 42 with two ferromagnetic layers that are antiferromagnetically coupled, the magnetic pole generated at the end can be made substantially zero.

On the other hand, since the same method cannot be used for the ferromagnetic layer 44 serving as a memory layer, the magnetization becomes unstable due to the influence of the end magnetic poles as the pattern becomes finer, and the recording can be maintained. It will be difficult.

Therefore, it is conceivable to reduce the influence of the end magnetic pole by forming the ferromagnetic layer 44 serving as a memory layer into a closed magnetic circuit structure. At this time, if both the bit line and the word line pass through this closed magnetic path, the effect of efficiently reversing the magnetization of the ferromagnetic layer 44 at the time of writing can be obtained. Therefore, it is difficult to obtain a simple orthogonal arrangement as shown in FIG. An example of a closed magnetic circuit structure is disclosed in JP-A-10-302456.
However, there is no disclosure of an optimal method for accessing the magnetic memory cells at that time.

An object of the present invention is to provide a method of accessing a magnetic memory cell in which the cell density of a magnetic memory does not decrease even when a closed magnetic circuit structure is introduced into a ferromagnetic layer 44 serving as a memory layer. With the goal.

[0014]

According to a first aspect of the present invention, there is provided a closed magnetic path layer provided on a magnetic layer for holding a memory of a magnetic memory cell, wherein a closed magnetic path layer is formed by the magnetic layer and the closed magnetic path layer. And a second current line is disposed outside the closed magnetic circuit, and the magnetization of the closed magnetic circuit layer is reversed but the magnetization of the magnetic layer is not reversed in the first current line. A current flows, and the magnetization of the magnetic layer does not reverse by itself on the two current lines, but the combined magnetic field with the bit line changes the magnetization direction of the magnetic layer by passing a current that reverses the magnetization of the magnetic layer. It is characterized by the following.

According to a second aspect of the present invention, there is provided a magnetic memory cell using the access method of the first aspect, wherein the magnetic memory cell comprises a magnetic tunnel junction element in which at least a first magnetic layer, an insulating layer, and a second magnetic layer are sequentially stacked. And providing the closed magnetic path layer at least on the first or second magnetic layer on a side of the magnetic layer different from the insulating layer lamination side, with a central portion separated from the first or second magnetic layer.
A closed magnetic circuit is formed by the magnetic layer and the closed magnetic circuit layer or the second magnetic layer and the closed magnetic circuit layer.

Further, a third invention is a magnetic memory cell using the access method of the first invention, wherein the magnetic memory cell is a magnetic tunnel junction device in which at least a first magnetic layer, an insulating layer, and a second magnetic layer are sequentially stacked. And providing the closed magnetic circuit layer at least on a side of the first or second magnetic layer different from the insulating layer lamination side with a metal layer interposed therebetween and with a central portion separated therefrom, the first magnetic layer and the closed magnetic circuit layer Alternatively, a closed magnetic circuit is constituted by the second magnetic layer and the closed magnetic circuit layer.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a magnetic memory cell access method and a magnetic memory cell according to the present invention;

FIG. 1 shows an embodiment of the present invention. The magnetic memory cell 11 is arranged at the intersection of the bit line 12 and the word line 13. The magnetic memory cell 11 has a closed magnetic circuit structure in the vertical direction in the drawing, and the magnetization is also oriented in the same direction. FIG.
2 is shown in FIG. Only one magnetic memory cell is shown for simplicity.

As shown in FIG. 2, the magnetic memory cell 11 has a closed magnetic circuit layer 25 provided on an MTJ element including an antiferromagnetic layer 21, a ferromagnetic layer 22, an insulating layer 23, and a ferromagnetic layer 24. The antiferromagnetic layer 21 and the ferromagnetic layer 22 are exchange-coupled. The ferromagnetic layer 24 and the closed magnetic circuit layer 25 are joined at both ends, and are separated at the center. The bit line 12 is provided at the centrally separated portion, and is electrically connected to the MTJ element. The word line 13 is provided on the magnetic memory cell 11 via the insulating layer 26.

Therefore, one side of the MTJ element is connected to the bit line 12.
And the other is connected to the collector of a selection transistor (not shown). Also,
The word line is electrically insulated from the MTJ element and is connected to the gate of a select transistor (not shown). As a result, a layout capable of random access shown in FIG. 5 is configured.

The information of the magnetic memory cell is stored in the magnetization direction of the ferromagnetic layer 24. On the other hand, the magnetization direction of the ferromagnetic layer 22 is fixed by exchange coupling with the antiferromagnetic layer 21. Therefore, utilizing the fact that the magnetization directions of the ferromagnetic layers 22 and 24 are parallel and antiparallel and the resistance of the MTJ element changes, the information stored in the magnetic memory cell, that is, the magnetization direction of the ferromagnetic layer is detected. I do.

Rewriting of information in the magnetic memory cell is realized by passing a current through the bit line 12 and the word line 13 and changing the magnetization direction of the ferromagnetic layer 24. At this time, it is necessary that the magnetization directions of the ferromagnetic layers 12 of the magnetic memory cells other than the magnetic memory cell 11 at the intersection of the bit line 12 and the word line 13 through which current flows do not change. This can be achieved as follows.

The ferromagnetic layer 24 has a coercive force that can hold information and can be rewritten with a recording current. On the other hand, the closed magnetic circuit layer 25 is made of a material having a smaller coercive force than the ferromagnetic layer 24. When rewriting the information in the magnetic memory cell 11, a current having a magnitude that reverses the magnetization of the closed magnetic circuit layer 25 but does not reverse the magnetization of the ferromagnetic layer 24 flows to the bit line 12. Further, the combined magnetic field with the bit line 12 causes the current of the ferromagnetic layer 24 to be inverted, but a current of a magnitude that cannot be inverted alone flows through the word line 13. At this time, since the magnetic field from the word line 13 is not applied to cells other than the magnetic memory cell 11 on the bit line 12, the ferromagnetic layer 24
Does not change. On the other hand, since the magnetic field from the bit line 12 is not applied to cells other than the magnetic memory cell 11 on the word line 13, the magnetization direction of the ferromagnetic layer 24 does not change.

As described above, by controlling the magnetic characteristics of the ferromagnetic layer 24 and the closed magnetic circuit layer 25 and the magnitude of the current flowing through the bit line 12 and the word line 13, the intersection between the bit line 12 and the word line 13 is controlled. Can be changed only in the magnetization direction of the magnetic memory cell 11 in FIG.

According to this embodiment, since the bit line 12 is in the closed magnetic circuit structure composed of the ferromagnetic layer 24 and the closed magnetic circuit layer 25, the magnetization of the closed magnetic circuit layer 25 can be reversed with a sufficiently low current. Thus, a magnetic field can be effectively applied to the ferromagnetic layer 24. On the other hand, since the word line 13 is also provided close to the closed magnetic circuit layer 25 via the insulating layer, it is possible to effectively apply a magnetic field to the ferromagnetic layer 24 through the closed magnetic circuit layer 25. Therefore, as compared with the conventional structure shown in FIG.
The magnetization direction of the magnetic memory cell 11 can be changed with a sufficiently low current. Therefore, if the closed magnetic circuit layer 25 is made of a material having a high magnetic permeability, it is effective to reduce the recording current.

FIG. 3 shows another configuration example of the magnetic memory cell 11 shown in FIG. The difference from FIG. 2 is that the ferromagnetic layer 24 and the closed magnetic circuit layer 25 are joined via the metal layer 27.
The thickness of the metal layer 27 depends on the ferromagnetic layer 24 and the closed magnetic circuit layer 25.
Are set to be antiferromagnetically coupled. Therefore,
When the information of the magnetic memory cell 11 is rewritten in the same manner as described above, the magnetization of the ferromagnetic layer 24 and the closed magnetic circuit layer 25 in the cells other than the magnetic memory cell 11 that have not been rewritten is the same as that of the metal layer 27. Due to the interposed antiferromagnetic coupling, a closed magnetic circuit is reliably formed.

In the above embodiment, two examples using the MTJ element as the magnetic memory cell having a closed magnetic circuit structure have been described. However, magnetic memory cells having other closed magnetic circuit structures can be used. . Further, in the above embodiment, the word line is provided above the bit line, but may be provided below the MTJ element. Also,
It is also possible to insulate the bit line from the MTJ element, replace the bit line and the word line, or provide separate bit lines or word lines for recording and reading. It is clear that the closed magnetic circuit structure is not limited to the above embodiment.

[0028]

As described above, according to the method for accessing a magnetic memory cell of the present invention, it is possible to control the magnetic characteristics of the ferromagnetic layer and the closed magnetic circuit layer and the magnitude of the current flowing through the bit line and the word line. Accordingly, only a single magnetic memory cell can be accessed, and the recording current can be reduced. Further, since the influence of the end magnetic pole of the magnetic memory cell can be reduced, a stable magnetization state can be maintained even when the pattern is miniaturized, and a magnetic memory with a higher degree of integration can be realized. Further, since the ferromagnetic layer serving as the memory layer has a closed magnetic circuit structure, the structure is stable against an external leakage magnetic field. Furthermore, according to the present invention, the power consumption of the magnetic memory can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of a magnetic memory cell according to an embodiment of the present invention.

FIG. 3 is another sectional view of the magnetic memory cell according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional MTJ element.

FIG. 5 is a schematic diagram of a conventional magnetic memory.

[Explanation of symbols]

 Reference Signs List 11 magnetic memory cell 12 bit line 13 word line 21, 41 antiferromagnetic layer 22, 24, 42, 44 ferromagnetic layer 23, 43 insulating layer 25 closed magnetic circuit layer 26 insulating layer 27 metal layer 51 transistor 52 MTJ element 53 bit line 54 Word line 55 Plate line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidekazu Hayashi 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka F-term (reference) 5D091 CC05 CC26 HH20 5F083 FZ10 GA11 KA01 KA05

Claims (3)

[Claims] 1. A closed magnetic circuit layer is provided on a magnetic layer holding data stored in a magnetic memory cell, and a first current line is arranged in a closed magnetic circuit formed by the magnetic layer and the closed magnetic circuit layer. A second current line is disposed outside the road, and a current in which the magnetization of the closed magnetic circuit layer is reversed but the magnetization of the magnetic layer is not reversed flows in the first current line, and the second current line is singly applied to the second current line. Wherein the magnetization of the magnetic layer is not reversed, but the combined magnetic field with the first current line changes the magnetization direction of the magnetic layer by passing a current that reverses the magnetization of the magnetic layer. Cell access method. 2. The magnetic memory cell using the access method according to claim 1, wherein said magnetic memory cell comprises at least a magnetic tunnel junction element in which a first magnetic layer, an insulating layer, and a second magnetic layer are sequentially stacked, and at least. The first or second magnetic layer is provided with the closed magnetic path layer on a side different from the insulating layer lamination side of the magnetic layer at a center portion thereof, and the first magnetic layer and the closed magnetic path layer or the second magnetic layer and the closed magnetic layer are provided. A magnetic memory cell, wherein a closed magnetic path is formed by a path layer. 3. The magnetic memory cell using the access method according to claim 1, wherein the magnetic memory cell is formed of a magnetic tunnel junction element in which at least a first magnetic layer, an insulating layer, and a second magnetic layer are sequentially stacked, and at least. A first magnetic layer and a closed magnetic path layer or a second magnetic layer, wherein the closed magnetic path layer is provided on a side of the first or second magnetic layer different from the insulating layer lamination side with a metal layer interposed therebetween and with a central portion separated therefrom; And a closed magnetic circuit layer comprising a closed magnetic circuit layer.