Method for magnetic characteristics modulation and...

Static information storage and retrieval – Systems using particular element – Magnetic thin film

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C365S158000, C365S173000

Reexamination Certificate

active

06625058

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
The present document is based on Japanese Priority Document JP 2001-186045, filed in the Japanese Patent Office on Jun. 20, 2001, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for magnetic characteristics modulation and a magnetically functioning apparatus. More particularly, the present invention is concerned with a magnetic characteristics modulation method for changing the characteristics of a magnetic thin film by changing an electric field generated on the surface of the magnetic thin film, and a magnetically functioning apparatus.
2. Description of the Related Art
As an example of a magnetically functioning apparatus utilized in large scale integrated circuit (LSI), a magnetic random access memory (hereinafter, referred to simply as “MRAM”)
101
diagrammatically shown in
FIG. 30
has been known An MRAM is constituted by a bit line
111
, a word line
121
disposed in a direction perpendicular to the bit line
111
, and a magnetic memory device
131
provided between the bit line
111
and the word line
121
which cross to each other, and a tunnel magnetoresistance device is used in the magnetic memory device
131
.
In the further scaled-down devices, the MRAM
101
suffers inversion of magnetization and therefore, the strength of a magnetic field generated by a current is reduced, that is, the strength of the magnetic field obtained is reduced substantially proportionally to the diameter of a conductor wire. Further, when the device size reaches a so-called deep submicron, writing to a thermally stable memory by such a magnetic field generated by a current is impossible. This situation is described with reference to FIG.
31
.
In
FIG. 31
, a magnetic field is taken as the ordinate, and a conductor wire diameter is taken as the abscissa. The solid line indicates a magnetic field strength that can be created by flowing a current through a conductor wire on the assumption that a current density satisfies the relationship: i<5 MA/cm
2
. The dotted line indicates a coercive force required when the magnetic storage is thermally stable, and the region on the right side of the dotted line is a thermally stable region and the region on the left side of the dotted line is a thermally unstable region.
The MRAM described above with reference to
FIG. 30
has a feature such that writing is conducted using a magnetic field, and has an advantage in that the writing speed is high. However, when the structure of the MRAM is scaled down, the diameter of a conductor wire (for example, a bit line or a word line) used for generating a magnetic field must be reduced. As shown in
FIG. 31
, the smaller the diameter of a conductor wire, the smaller the strength of the magnetic field generated. That is, writing to a device having a high coercive force is difficult. On the other hand, as also shown in
FIG. 31
, in the magnetic memory device
131
(see
FIG. 30
) designed for a small conductor wire diameter, when it has no satisfactorily large coercive force and magnetic anisotropy, it is difficult to keep a magnetic storage against thermal fluctuation. For example, when the conductor wire diameter is about 0.1 &mgr;m, a magnetic field at about 50 Oe is required. This means that writing by a current is difficult.
For removing the above-mentioned problem in driving of the magnetization in a scaled-down device by a magnetic field, several proposals have been made.
One example of driving of magnetization by using heat is described with reference to the diagrammatic view of FIG.
32
. As shown in
FIG. 32
, on a substrate
201
, a CoFe
2
O
4
layer
211
, an Fe—Ag layer
212
, and a NiFe
2
O
4
layer
213
are stacked on one another, and a circuit
221
for applying a voltage to the Fe—Ag layer
212
through the NiFe
2
O
4
layer
213
is provided. The circuit
221
has a construction such that a power source
222
and a switch
223
are connected to each other in series. When a voltage is applied by means of the circuit
221
, the exchange coupling between a magnetic vector M in the CoFe
2
O
4
layer
211
in one fixed direction indicated by the arrow shown in the figure and a magnetic vector of the NiFe
2
O
4
layer
213
through the Fe—Ag layer
212
is broken, so that the magnetic vector of the NiFe
2
O
4
layer
213
is rendered free. When no voltage is applied from the circuit
221
, the magnetic vector of the NiFe
2
O
4
layer
213
is affected so that the direction of its magnetic vector and the direction of the magnetic vector M of the CoFe
2
O
4
layer
211
are the same.
Next, one example of a method for modulating the magnetic anisotropy by using a stress utilizing a magnetostrictive material is described with reference to the diagrammatic view of FIG.
33
. As shown in
FIG. 33
, on an electrode layer
311
, a piezoelectric layer
312
and a distortion-sensitive magnetic thin film (which functions also as an electrode)
313
are stacked on one another, and a circuit
321
for applying a voltage to between the distortion-sensitive magnetic thin film
313
and the electrode layer
311
is provided. The circuit
321
has a construction such that a power source
322
and a switch
323
are connected to each other in series. When a voltage is applied by means of the circuit
321
, a magnetic vector M indicated by the arrow shown in the figure is generated in the distortion-sensitive magnetic thin film
313
.
Next, one example of a method of driving the magnetization by using quantum interference in the multilayer structure is described with reference to the diagrammatic view of FIG.
34
. As shown in
FIG. 34
, on a MgO substrate
401
, a Cu under layer
411
, a Co magnetic layer
412
, a Cu intermediate layer
413
, a Co magnetic layer
414
, a Cu coating layer
415
, a Ge coating layer
416
, and a Cu electrode layer
417
are stacked on one another, and a circuit
421
for applying a voltage to between the Cu electrode layer
417
and the Cu coating layer
415
is provided. The circuit
421
has a construction such that a power source
422
and a switch
423
are connected to each other in series.
However, the construction shown in
FIG. 32
, in which driving of magnetization is conducted using heat, needs a practical method for forming a scaled-down structure which can realize inversion of opposite directions (N/S repeated inversion) of magnetization using only heat.
On the other hand, the construction shown in
FIG. 33
, in which the magnetic anisotropy is changed using a stress, has problems of integration in the growth of the piezoelectric layer
312
and the removal of fatigue caused by the stress from the material.
Further, the construction shown in
FIG. 34
, in which driving of magnetization is conducted using quantum interference in the multilayer structure, requires at least two magnetic layers for practical driving of magnetization, and, in this construction, modulation of the magnetization does not always occur only on the surface of the magnetic layer, leading to a necessity that the whole layer structure containing these layers must be formed with high precision.
SUMMARY OF THE INVENTION
The present invention provides a method of modulating magnetic properties of materials and a magnetically functioning apparatus for alleviating or solving the above-mentioned problems.
An embodiment of the present invention is a method of changing magnetization state of a magnetic thin film in a stacked multilayer structure comprising following layers: a first layer, a second layer having a higher electrical resistivity than that of the first layer, and a third layer having a lower electrical resistivity than that of the second layer. At least one of the three layers is a magnetic layer having an ordering of microscopic magnetic moments. The method comprises changing the magnetization state of the magnetic thin film by utilizing an effect wherein, when a voltage is applied between the first layer and the third layer by means of

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Method for magnetic characteristics modulation and... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method for magnetic characteristics modulation and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for magnetic characteristics modulation and... will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3098082

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.