Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
2001-02-17
2002-08-27
Le, Vu A. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S173000
Reexamination Certificate
active
06442064
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic tunnel junction element and a magnetic memory using the same.
Recently, the application of magnetic tunnel junction (MTJ) elements to playback magnetic heads for hard disk drives (HDDs) and to magnetic memories has been considered and discussed because the MTJ elements provides a higher output, compared with conventional anisotropic magnetoresistive (AMR) elements and giant magnetoresistive (GMR) elements.
In particular, magnetic memories, which are solid state memories having no operating parts similar to semiconductor memories, are more useful than the semiconductor memories because of the following characteristics of their own: the information stored therein is not lost even if electric power is disconnected; the number of repetitive rewrites is infinite, namely, an infinite endurance is provided; there is no risk of destroying the recorded contents even if exposed to radioactive rays, etc.
As an example of the constitution of conventional MTJ elements, the one according to the teaching of JP-A-9-106514 is shown in FIG.
12
.
The MTJ element in
FIG. 12
is constituted of an antiferromagnetic layer
41
, a ferromagnetic layer
42
, an insulating layer
43
, and a ferromagnetic layer
44
. As the antiferromagnetic layer
41
, an alloy such as FeMn, NiMn, PtMn or IrMn is used. As the ferromagnetic layers
42
and
44
, Fe, Co, Ni or an alloy thereof is used. Further, as the insulating layer
43
, various oxides and nitrides are being studied, and it is known that the highest magnetoresistance (MR) ratio is obtained when using an Al
2
O
3
film.
In addition to this, there has been proposed an MTJ element with the antiferromagnetic layer
41
eliminated to utilize a difference in coercive force between the ferromagnetic layers
42
and
44
.
FIG. 13
shows the principle of operation of the MTJ element having the constitution shown in
FIG. 12
where the MTJ element is used for a magnetic memory.
The magnetizations of both the ferromagnetic layers
42
and
44
are within a film surface and have effective uniaxial magnetic anisotropy such that the magnetizations of these layers are parallel or antiparallel with each other. The magnetization of the ferromagnetic layer
42
is fixed substantially in one direction by the exchange coupling with the antiferromagnetic layer
41
, and a recorded content is stored according to the direction of magnetization of the ferromagnetic layer
44
.
The resistance of the MTJ element differs depending on whether the magnetization of the ferromagnetic layer
44
to serve as a memory layer is parallel or antiparallel to the direction of magnetization of the ferromagnetic layer
42
. Utilizing the difference in magnetic resistance, information is read from the MTJ element by detecting its magnetic resistance. On the other hand, information is written to the MTJ element by changing the direction of magnetization in the ferromagnetic layer
44
using a magnetic field generated by current lines placed in the vicinity of the MTJ element.
In the MTJ element having the above constitution, the ferromagnetic layers
42
and
44
are magnetized parallel to the layer surfaces, and thus magnetic poles are generated at opposite end portions of these layer surfaces.
For increasing the packing density or integration degree in the magnetic memory, the size reduction of the MTJ elements is required. However, with the size reduction of the elements, an influence of the diamagnetic field due to the magnetic poles at the opposite end portions becomes greater.
Since the ferromagnetic layer
42
is exchange-coupled with the antiferromagnetic layer
41
, the influence of the diamagnetic field upon the ferromagnetic layer
42
is small. Further, it is possible to substantially eliminate magnetic poles at the end portions by constituting the ferromagnetic layer
42
of two ferromagnetic layers that are antiferromagnetically coupled with each other as disclosed in U.S. Pat. No. 5841692.
However, as to the ferromagnetic layer
44
to serve as a memory layer, a similar technique cannot be applied. Thus, with finer patterns, the magnetization of the ferromagnetic layer
44
becomes unstable due to the influence of the magnetic poles at the end portions, which makes it difficult for the ferromagnetic layer
44
to hold a recorded content.
Japanese publication JP-A-11-163436 discloses that in order to realize an increase of output voltage, three ferromagnetic layers and two insulating layers are alternately laid on one another to thereby form two magnetic tunnel junctions in an MTJ element. This MTJ element provides an output that is about twice of that of an MTJ element having a single magnetic tunnel junction. However, since the three ferromagnetic layers are magnetized along their layer surfaces, there arises a problem similar to the above-described problem inherent in the MTJ element of FIG.
12
.
Further, with the reduction in the area of a memory cell in a magnetic thin film memory, it becomes impossible to ignore the diamagnetic field (self-demagnetizing field) that will occur inside the magnetic layer. Due to this, the magnetization of the magnetic layer that stores information is not fixed in one direction, thus becoming unstable. As a solution to this problem, Japanese Patent Publications JP-A-10-302456 and JP-A-10-302457 disclose to provide a laminated film consisting of a first magnetic layer, a non-magnetic layer and a second magnetic layer, which all together form a memory cell, with a third magnetic layer at both sides of the laminated film, so as to form a closed magnetic circuit surrounding the non-magnetic layer by the first, second and third magnetic layers when an external magnetic field is zero.
A magnetic tunnel junction element in which an extremely thin insulating film is formed as the non-magnetic layer of the laminated film exhibits a great change in magnetoresistance, and thus the element is regarded as a promising memory cell having a high output. In this case, the third layer is required to be formed of an insulating material. However, an insulative magnetic layer having a coercive force low enough to realize a closed magnetic circuit structure is extremely difficult to form with a currently available technique. Accordingly, it is unrealistic.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic tunnel junction element that enables a magnetization state recorded in the memory layer to exist stably even if finer patterns are used, and also to provide a magnetic memory using such a magnetic tunnel junction element.
In order to accomplish the above object, a magnetic tunnel junction element according to an aspect of the present invention comprises:
a first magnetic layer and a second magnetic layer acting as a memory layer;
a first insulating layer disposed between the first and second magnetic layers; and
a third magnetic layer provided on a side of the second magnetic layer opposite from the first insulating layer so as to form a closed magnetic circuit together with the second magnetic layer.
According to the present invention, the influence of the end-portion magnetic poles is reduced. Therefore, even if a finer pattern is used for the magnetic tunnel junction (MTJ) element, the magnetized state is retained stably. Further, because the ferromagnetic layer to serve as a memory layer forms a closed magnetic circuit structure, the MTJ element of the present invention becomes stable to an external leakage magnetic field.
Further, since the MTJ element of the present invention can stably retain the magnetized state thanks to the reduced influence of the magnetic poles at the end portions even if a finer patter therefor is used, it is possible to realize a magnetic memory having a higher integration degree and consuming less power.
In one embodiment, the third magnetic layer is joined to the second magnetic layer at opposite ends thereof directly or through fourth magnetic layers, with a central portion of the third magnetic layer spaced from the second
Hayashi Hidekazu
Michijima Masashi
Minakata Ryoji
Conlin David C.
Dike Bronstein Roberts & Cushman IP Group Edwards & Angell LLP
Sharp Kabushiki Kaisha
Tucker David A
LandOfFree
Magnetic tunnel junction element and magnetic memory using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic tunnel junction element and magnetic memory using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic tunnel junction element and magnetic memory using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2901578