Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2001-01-05
2003-09-30
Dinh, Son T. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000
Reexamination Certificate
active
06628542
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistive element or device using a magnetic layer having perpendicular magnetic anisotropy, and also to a magnetic memory using the magnetoresistive devices. The invention further relates to a recording method for such magnetic memories.
GMR (Giant MagnetoResistive) devices and TMR (Tunnel MagnetoResistive) devices obtained by stacking magnetic layers and nonmagnetic layers can be expected to exhibit higher performance as magnetic sensors, by virtue of their having larger rates of change in magnetoresistance as compared with conventional AMR (Anisotropic MagnetoResistive) devices. GMR devices have already been put into practical use as read-use or playback magnetic heads for HDDs (Hard Disk Drives). TMR devices, on the other hand, which have even higher rates of change of magnetoresistance than GMR devices, are under discussion for applications to not only magnetic heads but also magnetic memories.
A fundamental structure of a conventional TMR device as shown in
FIG. 1
is known (see, for example, Japanese Patent Laid-Open Publication HEI 9-106514). Referring now to
FIG. 1
, the TMR device is made up by stacking a first magnetic layer
31
, an insulating layer
32
, a second magnetic layer
33
and an antiferromagnetic layer
34
. In this case, the first magnetic layer
31
and the second magnetic layer
33
are ferromagnetics made of Fe, Co, Ni or alloys of these, the antiferromagnetic layer
34
is made of FeMn, NiMn or the like, and the insulating layer
32
is made of Al
2
O
3
.
Replacing the insulating layer
32
in
FIG. 1
with a nonmagnetic layer having electrical conductivity made of Cu or the like would result in a GMR device.
In conventional GMR devices and TMR devices, since the magnetic layers are magnetized along the layer surfaces, scale-down of the device dimensions as in magnetic heads of narrow track widths or magnetic memories of high integration would cause those devices to be strongly affected by diamagnetic fields generated at end-portion magnetic poles. For this reason, the direction of magnetization of the magnetic layers would become unstable, which in turn makes it hard to maintain uniform magnetization, and eventually leads to occurrence of operating failures of the devices such as the magnetic head and the magnetic memory.
As a solution to this drawback, a magnetoresistive device using a magnetic layer having perpendicular magnetic anisotropy is disclosed in Japanese Patent Laid-Open Publication HEI 11-213650. The device structure as taught in this publication is shown in FIG.
2
. The magnetoresistive device is so structured that a nonmagnetic layer
42
is sandwiched between a first magnetic layer
41
formed of a perpendicularly magnetized film having a low coercive force and a second magnetic layer
43
formed of a perpendicularly magnetized film having a high coercive force. The first and second magnetic layers are provided by using a ferrimagnetic film made of rare earth—transition element alloys, a garnet film, PtCo, PdCo or the like.
In this case, since end-portion magnetic poles occur at the magnetic film surfaces, increases in diamagnetic fields due to the scale-down of devices are suppressed. Accordingly, if perpendicular magnetic anisotropy energy of the magnetic film is substantially larger than the diamagnetic field energy caused by the end-portion magnetic poles, the magnetization can be stabilized along the perpendicular direction regardless of the device dimensions.
However, in the magnetoresistive device using a magnetic layer having perpendicular magnetic anisotropy, end-portion magnetic poles occur at the magnetic film surfaces. Since the nonmagnetic layer to be used for GMR devices and TMR devices is extremely thin, a magnetic pole that occurs at the interface of one magnetic layer and the nonmagnetic layer affects the magnetization of the other magnetic layer so largely that the magnetization may not be reversed. Accordingly, when the magnetoresistive devices are applied to a magnetic memory as an example, there may occur problems that information to be stored cannot be written to the memory or that written information is dissipated.
Therefore, with a view to solving these and other problems, a first object of the present invention is to provide a magnetoresistive device, as well as a magnetic memory using the magnetoresistive device, which allows a magnetic layer to be maintained in a stable magnetized state without being affected by a leakage magnetic field applied from the other magnetic layer through an insulating layer.
In the aforementioned conventional magnetoresistive device, in order that the magnetization within the magnetic layer overcomes the effect of the diamagnetic field energy due to the end-portion magnetic poles so as to be directed perpendicular stably, it is preferable that the perpendicular magnetic anisotropy energy of the magnetic film be as large as possible. However, this normally causes the coercive force to also increase concurrently. Accordingly, when a conventional magnetoresistive device having a sufficiently stabilized perpendicularly magnetized film is applied to a magnetic memory, the coercive force of the recording layer will be excessively increased, which would make it hard to perform magnetization reversal by a magnetic field generated by a recording current.
Therefore, a second object of the present invention is to provide a magnetoresistive device, as well as a magnetic memory using the magnetoresistive device, which has a coercive force of such a magnitude as to allow the magnetization reversal to be performed and which stably holds magnetized information stored in its recording layer.
Now, the recording method for a magnetic memory using a perpendicularly magnetized film is explained by way of an example disclosed in the Japanese Patent Laid-Open Publication HEI 11-213650. The arrangement of magnetoresistive devices and write lines according to the teaching of the publication is shown in FIG.
3
.
The device of
FIG. 3
, as in the case of
FIG. 2
, is made up of a first magnetic layer
21
, a nonmagnetic layer
22
and a second magnetic layer
23
. Assuming that the first magnetic layer
21
is a memory layer, information recording to the device is fulfilled by passing electric currents through write or recording lines
24
,
25
provided on both sides of the device to thereby make the magnetization of the first magnetic layer
21
reversed by the magnetic fields generated from the current lines. For example, to make the first magnetic layer
21
magnetized upward of the device, currents are passed through the recording line
24
frontward of the drawing sheet, namely toward a direction in which a front side of the drawing sheet is facing, and through the recording line
25
backward of the drawing sheet, namely toward a direction in which a reverse side of the drawing sheet is facing. Since the resultant of the magnetic fields
27
generated from these two current lines is directed upward of the device, magnetization of the first magnetic layer
21
can be directed upward of the device.
However, locating the recording lines beside the magnetoresistive device would be disadvantageous for high integration of the device. In the case where the recording lines are located on both sides of the device as shown in
FIG. 3
, with a wiring rule (F) used, the distance between the adjoining devices is
4
F. On the other hand, in the case of an ordinary array pattern with no recording lines provided between devices, the distance between the adjoining devices is
2
F. From the viewpoint that high integration of devices is of importance for memory fabrication, the arrangement of the magnetic memory of
FIG. 3
is disadvantageous to the increase of the integration.
Further, in the wiring pattern shown in
FIG. 3
, although devices located beside a selected device are not recorded, devices located in the anteroposterior direction of the selected device (namely, in a direction perpendicular to the drawing sheet) would be recorded.
Hayashi Hidekazu
Michijima Masashi
Minakata Ryoji
Conlin David G.
Dinh Son T.
Edwards & Angell LLP
Tucker David A.
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