JP4631372B2 - memory - Google Patents

Description

The present invention relates to a memory using a memory element, and is suitable for use in a nonvolatile memory or the like.

In information devices such as computers, DRAMs with high speed and high density are widely used as random access memories.
However, since DRAM is a volatile memory in which information disappears when the power is turned off, a nonvolatile memory in which information does not disappear is desired.

  As a candidate for a nonvolatile memory, a magnetic random access memory (MRAM) that records information by magnetization of a magnetic material has attracted attention and is being developed.

  The MRAM reverses the magnetization of the magnetic layer of the magnetic memory element at the intersection of the address lines by passing a current through two orthogonal address lines (word lines and bit lines) and by a current magnetic field generated from each address line. Information recording.

However, in order to stably hold the recorded information, a certain coercive force is required in the magnetic layer (storage layer) for recording information.
On the other hand, in order to rewrite the recorded information, a certain amount of current must be passed through the address wiring.
As the elements constituting the MRAM become finer, the address wiring becomes thinner, so that a sufficient current cannot flow.

Thus, attention has been paid to a magnetic memory having a configuration using magnetization reversal by spin injection as a configuration capable of reversing magnetization with a smaller current (see, for example, Patent Document 1 and Non-Patent Document 1).
Magnetization reversal by spin injection is to cause magnetization reversal in another magnetic material by injecting spin-polarized electrons that have passed through the magnetic material into another magnetic material.
Magnetization reversal by spin injection has an advantage that magnetization reversal can be realized with a small current even if the element is miniaturized.

Furthermore, in order to increase the efficiency of magnetization reversal by spin injection, a structure in which a storage layer is sandwiched between two magnetization fixed layers has been proposed (see, for example, Patent Document 2).
JP 2003-17782 A JP 2004-193595 A F. J. et al. Albert et al. Appl Phys. Lett. Vol. 77, 2002, p. 3809

However, as described in Patent Document 2, when the magnetization fixed layers are arranged above and below the storage layer, in order to direct the magnetizations of both the upper and lower magnetization fixed layers in a predetermined direction, It is necessary to provide an antiferromagnetic layer in the magnetization fixed layer.
When the antiferromagnetic layers are provided above and below the storage layer in this way, the entire storage element becomes thick, and it is difficult to finely process and pattern the storage element. For this reason, it becomes difficult to miniaturize the memory element, which is a problem in increasing the density of the memory.
In particular, since the antiferromagnetic layer needs to be formed thicker than the magnetic layer constituting the magnetization fixed layer and the storage layer, when the antiferromagnetic layer is provided above and below, only one of the antiferromagnetic layers is provided. Compared to the case, the entire memory element becomes considerably thicker.

In order to increase the efficiency of magnetization reversal by spin injection, the magnetization direction of the magnetization fixed layer below the storage layer and the magnetization direction of the magnetization fixed layer above the storage layer are opposite to each other. Therefore, the layer structure of the memory element is complicated.
For this reason, an increase in device resistance due to a complicated layer structure, an increase in recording current due to a decrease in spin polarizability, and a decrease in reproduction output occur.

In order to solve the above-described problems, the present invention provides a memory that can increase spin injection magnetization reversal efficiency with a relatively simple layer structure, is easy to be finely processed, and can be integrated at high density. It is.

The memory of the present invention has at least a storage layer that holds information by the magnetization state of a magnetic material, and a magnetization fixed layer that is provided to the storage layer via a nonmagnetic layer and whose magnetization direction is fixed. The information is recorded by reversing the magnetization direction of the storage layer by spin injection by passing a current between the storage layer and the magnetization fixed layer through the nonmagnetic layer, and the magnetization is fixed to the storage layer. A magnetization free layer capable of changing the magnetization direction via a nonmagnetic layer is provided on the opposite side of the layer, and the magnetization direction of the magnetization free layer is reversed by spin injection, so that the magnetization free layer and the storage layer The magnitude of the interaction between the magnetization free layer and the magnetization free layer is such that the magnetization direction of the magnetization free layer is reversed simultaneously with the reversal of the magnetization direction of the storage layer. A storage element that is small enough to be When recording information using a memory cell, first, a current in the film thickness direction is passed through the storage element, so that the relationship between the magnetization direction of the storage layer and the magnetization direction of the magnetization free layer is parallel or opposite. After that, the amount of current in the same direction is increased, and the relationship between the magnetization direction of the storage layer and the magnetization direction of the magnetization free layer is kept parallel or antiparallel, and the magnetization of the storage layer is The direction and the magnetization direction of the magnetization free layer are reversed .

According to the above-described memory configuration of the present invention, a storage layer that holds information according to the magnetization state of the magnetic material, and a magnetization fixed that is provided to the storage layer via a nonmagnetic layer and the magnetization direction is fixed. Since the recording of information is performed by reversing the direction of magnetization of the storage layer by spin injection by passing a current between the storage layer and the magnetization fixed layer through the non-magnetic layer through the non-magnetic layer, By flowing a current between the storage layer and the magnetization fixed layer, information can be recorded by changing the magnetization state (magnetization direction) of the storage layer by so-called spin injection.
A magnetization free layer capable of changing the magnetization direction via a non-magnetic layer is provided on the opposite side of the magnetization fixed layer from the storage layer, and the magnetization direction of the magnetization free layer by spin injection And the interaction between the magnetization free layer and the storage layer has such a magnitude that the magnetization direction of the magnetization free layer is reversed simultaneously with the reversal of the magnetization direction of the storage layer, and The magnetization direction of the magnetization free layer is sufficiently small so that the magnetization direction can be freely moved, so that a current flows in the stacking direction of the storage element, and the magnetization free layer and the magnetization fixed layer respectively Thus, torque by spin injection can be generated and the torque by these spin injections can be strengthened to each other, so that the efficiency of reversing the magnetization direction of the storage layer by spin injection can be improved.
Thereby, the current (recording current) for recording information by reversing the magnetization direction of the storage layer by spin injection can be reduced.

The above-described memory configuration of the present invention improves the efficiency of magnetization reversal by spin injection and reduces the recording current without providing a fixed magnetization layer and an antiferromagnetic layer on both upper and lower sides of the storage layer. Therefore, compared with a configuration in which a fixed magnetization layer and an antiferromagnetic layer are provided on both upper and lower sides of the storage layer, the increase in the thickness of the storage element can be suppressed, and the layer structure of the storage element is simplified. can do.

In the memory of the present invention, the magnetization direction of the magnetization free layer is reversed more than the minimum current value for reversing the magnetization direction of the storage layer when a current in the film thickness direction is passed through the storage element. Therefore, the magnetization direction is reversed with a smaller current in the magnetization free layer than in the storage layer.
Thus, before reversing the magnetization direction of the storage layer, the magnetization direction of the magnetization free layer is made antiparallel to the magnetization direction of the magnetization fixed layer, and the spin injection torque from the magnetization free layer to the storage layer is Further, the spin injection torque from the magnetization fixed layer to the storage layer can be strengthened.

Further, in the memory according to the present invention, the magnetization free layer has a configuration in which the product of the saturation magnetic flux density and the thickness of the magnetization free layer is smaller than the product of the saturation magnetic flux density and the thickness of the storage layer. It becomes magnetically lighter than the layer, and the direction of magnetization is reversed with a smaller current.
Thus, as described above, before the magnetization direction of the storage layer is reversed, the spin injection torque from the magnetization free layer to the storage layer and the spin injection torque from the magnetization fixed layer to the storage layer are intensified with each other. Can be.

According to the memory of the present invention described above, the recording current can be reduced, and information can be recorded with a small amount of current.
Thereby, power consumption can be reduced.

In addition, since increase in the thickness of the memory element can be suppressed, the memory element can be easily miniaturized by microfabrication.
Thus , according to the memory of the present invention, it is possible to easily reduce the size of the memory or increase the storage capacity by increasing the density.
Since the layer structure of the memory element can be simplified, it is possible to suppress an increase in resistance of the memory element, suppress a decrease in spin polarizability, and suppress a decrease in reproduction output. It is considered to be.

  Therefore, according to the present invention, a high-density nonvolatile memory capable of power saving operation can be realized.

  First, an outline of the present invention will be described prior to description of specific embodiments of the present invention.

  As a result of studying the optimum structure to achieve the above-mentioned purpose, that is, the spin injection magnetization reversal efficiency can be increased with a relatively simple layer structure, the microfabrication is easy, and the high density integration is possible. , Sandwiched between at least two magnetic layers, a storage layer that holds the magnetization direction (magnetization state) as information, and a magnetization fixed layer (having a reference layer serving as a reference for information) in which the magnetization direction is fixed In a storage element that includes a nonmagnetic layer and records and reads information by a current flowing through the nonmagnetic layer, the storage element is further on the opposite side of the magnetization fixed layer from the magnetization fixed layer via the nonmagnetic layer. It has been found that the magnetization direction of the memory layer can be reversed with a small amount of current when the magnetization free layer in which the magnetization direction easily changes is provided.

That is, the present invention includes a storage layer that holds the magnetization direction (magnetization state) as information, and a magnetization fixed layer (having a reference layer that serves as a reference for information) in which the magnetization direction is fixed. A nonmagnetic layer (insulating layer or nonmagnetic conductive layer) is provided between the pinned layer and the pinned layer, and the direction of magnetization is compared via the nonmagnetic layer on the opposite side of the pinned layer from the storage layer. A storage element is formed by providing a magnetization free layer that can be changed easily.
In addition, information recording is performed on the storage layer by reversing the magnetization direction of the magnetic layer constituting the storage layer by using the above-described magnetization reversal by spin injection.

Here, as schematically shown in FIG. 1A, the storage layer 3 is formed on the fixed magnetization layer 1 via the nonmagnetic layer 2, and the free magnetization layer is formed on the storage layer 3 via the nonmagnetic layer 4. The memory element in which 5 is formed is configured. The direction of the magnetization M1 of the magnetization fixed layer 1 is fixed to the right.
In this schematic diagram, the magnetization fixed layer 1, the storage layer 3, and the magnetization free layer 5 are all composed of a single-layer magnetic film, and the magnetization direction of the magnetic film is the same as the spin polarization direction of electrons. Shows the case.

And operation | movement at the time of recording information with respect to the memory | storage layer 3 of a memory element of such a structure is shown to FIG. 1A-FIG. 2F.
First, two storage states are shown in FIGS. 1A and 2D, respectively. With these states as initial states, the process of reversing magnetization will be described below. In this initial state, the magnetization M5 of the magnetization free layer 5 may face either the right direction or the left direction.

Next, as shown in FIG. 1A, in the state where the magnetization M3 of the storage layer 3 is rightward, when an upward current 6 of an appropriate amount of current is passed, the storage layer 3 has a magnetization free layer 5 and a magnetization direction. A spin injection torque that works in parallel acts, and as a reaction, the magnetization free layer 5 exerts a force that makes the direction of magnetization antiparallel to the storage layer 3.
Here, if the product of the saturation magnetic flux density and the thickness of the magnetization free layer 5 is smaller than the product of the saturation magnetic flux density and the thickness of the storage layer 3, the magnetization free layer 5 is magnetically lighter. The direction of the magnetization M5 of the magnetization free layer 5 changes, and the magnetization M5 of the magnetization free layer 5 and the magnetization M3 of the storage layer 3 become antiparallel as shown in FIG. 1B.
At this time, the storage layer 3 receives torque from the fixed magnetization layer 1 due to spin injection, but since the storage layer 3 is magnetically heavy, the direction of the magnetization M3 of the storage layer 3 is not reversed.
As described above, when the product of the saturation magnetic flux density and the thickness of the magnetization free layer 5 is smaller than the product of the saturation magnetic flux density and the thickness of the storage layer 3, the direction of the magnetization M5 of the magnetization free layer 5 Is smaller than the minimum current value for reversing the direction of the magnetization M3 of the storage layer 3.

Further, when the amount of the upward current 6 is increased, the storage layer 3 receives a force that is antiparallel to the magnetization fixed layer 1 from the magnetization fixed layer 1 side, and the magnetization free layer 5 receives the magnetization free layer 5 from the magnetization free layer 5. Receives a force that is parallel to As a result, a force that changes the magnetization M3 of the storage layer 3 from right to left in the state of FIG. 1B acts, and the magnetization M3 of the storage layer 3 is reversed leftward.
At this time, since the magnetization free layer 5 is magnetically light, simultaneously with the reversal of the magnetization M3 of the storage layer 3, the magnetization M5 of the magnetization free layer 5 is also reversed from left to right, and finally the state shown in FIG. 1C is obtained.

Similarly, as shown in FIG. 2D, when a downward current 7 of an appropriate amount of current flows when the magnetization M3 of the storage layer 3 in the initial state is leftward, the magnetization free layer 5 and the magnetization of the storage layer 3 The storage layer 3 receives a force such that the direction is parallel, and the storage layer 3 receives a force so that the magnetization direction is parallel to the magnetization fixed layer 1.
Thereby, since the magnetization free layer 5 is magnetically lighter than the storage layer 3, the direction of the magnetization M5 of the magnetization free layer 5 changes, and as shown in FIG. 2E, the magnetization M5 of the magnetization free layer 5 The magnetization M3 of the storage layer 3 is parallel. At this time, the storage layer 3 receives torque from the fixed magnetization layer 1 due to spin injection, but since the storage layer 3 is magnetically heavy, the direction of the magnetization M3 of the storage layer 3 is not reversed.

Further, when the amount of the downward current 7 is increased, the storage layer 3 receives a force parallel to the magnetization fixed layer 1 from the magnetization fixed layer 1 side, and the magnetization free layer 5 Receives anti-parallel force. As a result, a force that changes the magnetization M3 of the storage layer 3 from left to right in the state of FIG. 2E acts, and the magnetization M3 of the storage layer 3 is reversed to the right.
At this time, since the magnetization free layer 5 is magnetically light, simultaneously with the reversal of the magnetization M3 of the storage layer 3, the magnetization M5 of the magnetization free layer 5 is also reversed from left to right, and finally the state shown in FIG. 2F is obtained.

In either state, during the information recording process, as shown in FIGS. 1B and 2E, the directions of the magnetization M1 of the magnetization fixed layer 1 and the magnetization M5 of the magnetization free layer 5 are antiparallel, and each layer 1 , 5 work to strengthen the spin injection torque from the storage layer 3 to the recording layer 3, so that the recording current can be reduced.
In order for this magnetization process to be established, the amount of current (minimum reversal current) necessary for reversing the magnetization M5 of the magnetization free layer 5 needs to be smaller than the minimum reversal current of the storage layer 3. For this purpose, for example, as described above, the product of the saturation magnetic flux density and the film thickness of the magnetization free layer 5 may be made smaller than the product of the saturation magnetic flux density and the film thickness of the storage layer 3.

When a downward current 7 is passed in the initial state of FIG. 1A, or when an upward current 6 is passed in the initial state of FIG. 2D, the spin injection torque and magnetization from the free magnetization layer 5 to the storage layer 3 Since the spin injection torque from the fixed layer 1 to the storage layer 3 cancels out, the direction of the magnetization M3 of the storage layer 3 is not reversed unless a large current is passed. That is, the direction of the magnetization M3 of the storage layer 3 is not reversed at a small current.
In particular, if the spin injection torque from the magnetization fixed layer 1 to the storage layer 3 is larger, this spin injection torque works to maintain the direction of the magnetization M3 of the storage layer 3, so the direction of the magnetization M3 of the storage layer 3 Is never reversed.

From the above description, as shown in FIGS. 1 and 2, in the configuration in which the magnetization fixed layer 1 is in the lower layer of the storage layer 3 and the magnetization M1 of the magnetization fixed layer 1 is rightward, the magnetization M3 of the storage layer 3 The recording current can be reduced by flowing an upward current 6 when the current is directed to the left and a downward current 7 when the magnetization M3 of the storage layer 3 is directed to the right.
To express this generally, when the magnetization of the storage layer is made antiparallel to the magnetization of the magnetization fixed layer, a current flowing from the magnetization fixed layer to the storage layer is passed, and the magnetization of the storage layer is changed to that of the magnetization fixed layer. In the case of being parallel to the magnetization, the recording current can be reduced if a current from the storage layer to the magnetization fixed layer is allowed to flow. The directions of these currents are the same as the directions of currents that flow to reverse the magnetization direction of the storage layer in a configuration in which a normal magnetization free layer is not provided.

As shown in FIGS. 1 and 2, in the configuration in which the magnetization fixed layer 1 is in the lower layer of the storage layer 3 and the magnetization M1 of the magnetization fixed layer 1 is rightward, the magnetization M3 of the storage layer 3 is rightward. Sometimes, when a downward current 7 is applied, or when an upward current 6 is applied when the magnetization M3 of the storage layer 3 is leftward, the orientation of the magnetization M3 of the storage layer 3 is not reversed with a small current.
In general, this can be expressed when the current flowing from the storage layer to the magnetization fixed layer flows when the magnetization direction of the storage layer and the magnetization direction of the magnetization fixed layer are parallel, When a current from the magnetization fixed layer to the storage layer is passed when the magnetization direction and the magnetization direction of the magnetization fixed layer are antiparallel, the magnetization direction of the storage layer is not reversed with a small current.

That is, the magnetization direction of the storage layer is reversed with a small current by combining the relationship between the magnetization direction of the storage layer and the magnetization direction of the fixed magnetization layer (parallel or antiparallel) and the direction of the current flowing through the storage element. (The reversal current is small) and the small current does not reverse the magnetization direction of the storage layer (the reversal current is large). By flowing an amount of current between these large and small reversal currents, Only in the combination where the reversal current is small, the magnetization direction of the storage layer is reversed.
As described above, such a combination that reduces the reversal current is the same as the direction of the current that flows in order to reverse the magnetization direction of the storage layer in the configuration in which the normal magnetization free layer is not provided.

  Therefore, in the same manner as the configuration in which the normal magnetization free layer is not provided, the direction of the current passed through the storage element corresponding to the content of information to be recorded in the storage layer is selected according to the direction of magnetization of the storage layer. When the content of the information to be recorded in the storage layer is different from the content of the information already recorded in the storage layer, the reversal current is reduced so that the magnetization direction of the storage layer is reversed and the information is already recorded in the storage layer. If the information matches the information content, the reversal current increases and the magnetization direction of the storage layer remains unchanged.

  As described above, a magnetization free layer is provided on the opposite side of the storage layer from the magnetization fixed layer with respect to the configuration having the storage layer, the magnetization fixed layer, and the nonmagnetic layer therebetween. Thus, when a current is passed in the stacking direction of these magnetic layers so that a spin torque force acts between the magnetic layers via the nonmagnetic layer, the magnetization free layer and the magnetization fixed layer are magnetized with a relatively weak current. When the directions are antiparallel and the amount of current is further increased, the magnetization direction of the storage layer can be reversed with a relatively small amount of current by the spin torque from both the magnetization fixed layer and the magnetization free layer.

As a material for the storage layer and the magnetization free layer, a material having a suitably high polarizability and a small magnetic braking is desirable. For example, a 3d transition metal element of Fe, Co, Ni, or the 3d transition metal element as a main component. An alloy based on a magnetic material made of such an alloy is desirable.
In particular, it is desirable to use a material having a small saturation magnetic flux density Ms as the material for the magnetization free layer in order to reduce the product of the saturation magnetic flux density and the thickness.

More preferably, the magnetization free layer is configured so as to have as little interaction as possible with the storage layer. This is because if there is interaction with the storage layer, the magnetization direction of the magnetization free layer becomes difficult to move due to the influence of the magnetization direction of the storage layer.
Even if there is an interaction between the magnetization free layer and the storage layer, it is possible to freely move the magnetization direction of the magnetization free layer by canceling the interaction by some method such as an external magnetic field. If the interaction is canceled during recording, it is possible to perform the same operation as the configuration in which there is no interaction or is very small.

  As a material for the nonmagnetic layer, a material that does not lower the spin polarizability is desirable, a metal material such as Cu or Al, a semiconductor material such as Si, a conductive nitride material such as TiN, and a thin tunnel insulating film such as Al oxide Can be used.

Note that the magnetization free layer, the storage layer, and the magnetization fixed layer may each be one layer as described above, or may be formed by laminating a plurality of magnetic layers.
Further, a laminated ferri-coupled film in which a nonmagnetic film is sandwiched between magnetic films and the magnetizations of the magnetic films on both sides are magnetically coupled in antiparallel may be used. In particular, it is desirable to use a laminated ferri-coupled film for the magnetization fixed layer in order to stabilize the magnetization direction.

  In the explanation of the operations in FIGS. 1A to 2F, the magnetization free layer 5, the storage layer 3, and the magnetization fixed layer 1 all use magnetic films in which the polarization direction and the magnetization direction of spin injection electrons are the same. However, even if a magnetic film having different magnetization direction and polarization polarity of spin injection electrons is used, only the magnetization direction of each layer is reversed, and the effect of the present invention is not changed.

  Next, specific embodiments of the present invention that satisfy the above-described configuration of the present invention will be described.

FIG. 3 shows a schematic configuration diagram (cross-sectional view) of a memory element constituting a memory as an embodiment of the present invention.
The storage element 10 includes a base layer 11, an antiferromagnetic layer 12, a magnetic layer 13, a nonmagnetic layer 14, a magnetic layer (reference layer) 15, a tunnel insulating layer 16, a storage layer 17, a nonmagnetic layer 18, The magnetization free layer 19 and the protective layer 20 are laminated.

The storage layer 17 is made of a magnetic material, and is configured to hold information in a magnetization state (magnetization direction).
The three layers of the magnetic layer 13, the nonmagnetic layer 14, and the magnetic layer (reference layer) 15 constitute a magnetization fixed layer 21 having a laminated ferri structure. The magnetic layer 13 has a magnetization direction fixed by the antiferromagnetic layer 12, and the magnetic layer (reference layer) 15 serves as a reference for the magnetization direction with respect to the storage layer 17. The magnetic layer 13 and the magnetic layer (reference layer) 15 are coupled antiparallel to each other by the nonmagnetic layer 14.
The tunnel insulating layer 16 is for injecting spin-polarized electrons and reading the magnetization state of the storage layer 17 by the ferromagnetic tunnel effect.

The storage element 10 of the present embodiment has a configuration in which a nonmagnetic layer 18 and a magnetization free layer 19 are further added on the storage layer 17 in addition to the normal configuration of the storage element in which information is recorded by spin injection. It has become.
The nonmagnetic layer 18 on the storage layer 17 is a nonmagnetic layer for injecting spin-polarized electrons.
As described above, the magnetization free layer 19 is configured so that the product of the saturation magnetic flux density and the thickness is smaller than the product of the saturation magnetic flux density and the thickness of the storage layer 17 and is magnetically lighter than the storage layer 17. Is desirable.

Then, by passing a current between the base layer 11 and the protective layer 20, the magnetization direction of the memory layer 17 can be reversed by spin injection.
When a current is passed from the protective layer 20 toward the base layer 11, that is, from the storage layer 17 to the magnetic layer (reference layer) 15, polarized electrons are injected from the magnetic layer (reference layer) 15 into the storage layer 17, Also, polarized electrons are injected from the storage layer 17 into the magnetization free layer 19. Thus, the spin injection torque is received from the reference layer 15 and the magnetization free layer 19 respectively, and these spin injection torques reinforce each other, so that the magnetization direction of the storage layer 17 is parallel to the magnetization direction of the reference layer 15. become.
When a current is passed from the underlayer 11 to the protective layer 20, that is, from the reference layer 15 to the storage layer 17, polarized electrons are injected from the storage layer 17 to the reference layer 15, and from the magnetization free layer 19 to the storage layer. 17 is injected with polarized electrons. Accordingly, the spin injection torque is received from the reference layer 15 and the magnetization free layer 19 respectively, and these spin injection torques reinforce each other, so that the magnetization direction of the storage layer 17 is opposite to the magnetization direction of the reference layer 15. Become parallel.
In this way, information to be recorded can be selected depending on the direction in which the current flows.

When the magnetization direction of the magnetic layer (reference layer) 15 and the magnetization direction of the storage layer 17 are in parallel, the resistance of the current passing through the tunnel insulating layer 16 is small, and in the antiparallel state, the tunnel insulating layer 16 is The resistance of the current that passes is increased. Utilizing this fact, the content of information recorded in the storage layer 17 can be read from the resistance value.
Note that the current that flows during reading is made smaller than the reversal current so that the magnetization reversal of the memory layer 17 due to spin injection does not occur.

A memory cell can be configured by configuring a memory cell by the memory element 10 of the present embodiment and arranging a large number of the memory cells in a column or matrix.
In such a memory, a wiring or the like is connected to the base layer 11 and the protective layer 20 in order to pass a current to the memory element 10 of each memory cell. When information is recorded or read, a current is supplied from the drive circuit to the memory element 10 of the target memory cell through wiring or the like.

According to the configuration of the storage element 10 of the present embodiment described above, the magnetization free layer 19 is provided on the upper layer (the opposite side to the lower magnetization fixed layer 21) with respect to the storage layer 17 via the nonmagnetic layer 18. By being provided, current flows in the stacking direction of the memory element 10 to generate torque by spin injection from the magnetization free layer 19 and the magnetization fixed layer 21 to the storage layer, respectively. Since the torques can be strengthened each other, the efficiency of reversing the magnetization direction of the storage layer 17 by spin injection can be improved. Thereby, the current (recording current) for recording information by reversing the direction of magnetization of the storage layer 17 by spin injection can be reduced.
Since the current for recording information can be reduced in this manner, information can be recorded with a small amount of current.
Thereby, power consumption can be reduced.

In addition, according to the configuration of the memory element 10 of the present embodiment, the efficiency of magnetization reversal by spin injection can be improved and recording can be performed without providing a magnetization fixed layer and an antiferromagnetic layer on both upper and lower sides of the memory layer 17. Since the current can be reduced, an increase in the thickness of the memory element 10 can be suppressed as compared with the configuration in which the magnetization fixed layer and the antiferromagnetic layer are provided on both upper and lower sides of the memory layer. Ten layer structures can be simplified.
Since an increase in the thickness of the memory element 10 can be suppressed, the memory element 10 can be easily miniaturized by microfabrication.
As a result, it is possible to easily reduce the size of the memory constituting the memory cell by the memory element 10 of the present embodiment or increase the storage capacity by increasing the density.
Since the layer structure of the memory element 10 can be simplified, it is possible to suppress an increase in resistance of the memory element, to suppress a decrease in spin polarizability, and to suppress a decrease in reproduction output. It is thought that it becomes.

  Therefore, if the memory is configured with the memory element 10 of the present embodiment, a high-density nonvolatile memory capable of power saving operation can be realized even with the memory element 10 having a relatively simple layer configuration.

In the memory element 10 of the above-described embodiment, the antiferromagnetic layer 12 and the magnetization fixed layer 21 including the reference layer 15 are provided below the memory layer 17, but with respect to the memory layer, A storage element may be configured by providing a fixed magnetization layer and an antiferromagnetic layer as an upper layer.
Further, a storage element may be configured by providing a nonmagnetic conductive layer instead of the tunnel insulating layer 16 between the storage layer and the magnetization fixed layer.

Here, Oite the storage element constituting the memory of the present invention, by setting the dimensions and composition of the concrete storage layer, was investigated whether characteristics are how.

Then, the material and film thickness of each layer were set as follows, and the memory element 10 having the configuration shown in FIG. 3 was produced.
That is, an underlayer 11 made of a 10 nm thick Ta film, an antiferromagnetic layer 12 made of a 30 nm thick PtMn film, a magnetic layer 13 made of a 2 nm thick CoFe film, and a 0.7 nm thick Ru film. Nonmagnetic layer 14 made of a film, magnetic layer (reference layer) 15 made of a CoFe film having a thickness of 2 nm, tunnel insulating layer 16 made of an aluminum oxide film having a thickness of 0.5 nm, and storage layer made of a NiFe film having a thickness of 6 nm 17. A nonmagnetic layer 18 made of a TiN film with a thickness of 2 nm, a magnetization free layer 19 made of a GdFeCo film (film thickness t [nm]), and a protective layer 20 made of a Ta film with a thickness of 5 nm were sequentially stacked.
In addition, each layer of the memory element 10 was patterned into an elliptical pattern having a major axis of about 200 nm and a minor axis of about 150 nm.

The magnetization free layer 19 uses GdFeCo having a small saturation magnetic flux density in order to reduce the magnetic influence on the storage layer 17.
Then, samples of the memory element 10 were prepared by changing the film thickness t of the magnetization free layer 19.
Further, as a comparative control, a sample of a storage element in which a nonmagnetic layer and a magnetization free layer were omitted and a protective layer was formed on the storage layer was produced.

(Measurement of reverse current Ic)
The resistance of the memory element 10 was measured while sweeping the amount of current flowing between the base layer 11 and the protective layer 20, and the inversion current Ic was obtained from the current value when the resistance changed.
A current value at which the magnetization direction of the storage layer 17 changes from a parallel state to an anti-parallel state and a current value at which the magnetization direction of the reference layer 15 changes from an anti-parallel state to a parallel state; The average of the absolute values of these current values was taken as the value of the reversal current Ic.
The polarity of the current flowing through the storage element 10 is positive when flowing from the lower layer to the upper layer of the storage element 10, that is, from the underlying layer 11 to the protective layer 20, and the magnetization direction of the storage layer 17 is the magnetization of the reference layer 15. Ic ^{+ is} a current in which the resistance value of the memory element 10 changes from a low resistance to a high resistance by changing from a parallel state to an antiparallel state with respect to the direction, and the magnetization direction of the storage layer 17 is the magnetization direction of the reference layer 15. On the other hand, a current that changes from an antiparallel state to a parallel state and the resistance value of the memory element 10 changes from a high resistance to a low resistance is defined as Ic ⁻ .

(Relationship between presence / absence of magnetization free layer and change in resistance of memory element)
In the memory element 10 in which the GdFeCo film having a thickness of 2 nm was formed as the magnetization free layer 19 and the comparative memory element having no magnetization free layer, the change in resistance value of the memory element when current was swept was measured. The measurement results are shown in FIG.

As can be seen from FIG. 4, in the memory element 10 with the magnetization free layer 19, both the positive and negative inversion currents Ic ⁺ and Ic ⁻ are about half of those of the memory element without the magnetization free layer.
That is, it can be seen that the reversal current can be reduced by providing the magnetization free layer 19.
In the memory element 10 having the magnetization free layer 19, a small resistance change is observed in a region where current is small, as indicated by an arrow in FIG. This is a change in resistance due to the magnetization reversal of the magnetization free layer 19.

(Change in thickness and characteristics of the magnetization free layer)
Next, the reversal current was measured for each sample having a different thickness t (nm) of the magnetization free layer 19.
As a measurement result, the relationship between the film thickness of the magnetization free layer 19 and the reversal current is shown in FIG. In FIG. 5, the negative inversion current Ic ⁻ indicates −Ic ^{−, that} is, an absolute value. Further, the portion with a film thickness of 0 nm shows the value of the reversal current of a memory element without a magnetization free layer as a comparison.

From FIG. 5, it can be seen that the reversal current is minimized and the effect is highest in the vicinity of the film thickness of the magnetization free layer 19 of 2 nm.
It can also be seen that the effect of reducing the reversal current is obtained in a relatively wide range of film thickness of 0.5 nm to 4 nm.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

AC is a schematic diagram for explaining a change in magnetization when a current is passed in an example of a memory element constituting the memory of the present invention. DF is a schematic diagram illustrating a change in magnetization when a current is passed in an example of a storage element constituting the memory of the present invention. It is a schematic block diagram (sectional drawing) of the memory element which comprises the memory of one embodiment of this invention. It is a figure which shows the change of the resistance value of the memory element with respect to an electric current comparing the memory element with a magnetization free layer, and the memory element without a magnetization free layer. It is a figure which shows the change of the reversal current when changing the thickness of a magnetization free layer.

Explanation of symbols

  1,21 Magnetization fixed layer, 2, 4, 14, 18 Nonmagnetic layer, 3,17 Storage layer, 5,19 Magnetization free layer, 10 Storage element, 12 Antiferromagnetic layer, 13 Magnetic layer, 15 Magnetic layer (Ref. Layer), 16 tunnel insulation layer

Claims (3)

A storage layer that holds information by the magnetization state of the magnetic material;
A magnetization pinned layer provided to the storage layer via a nonmagnetic layer and having a magnetization direction fixed;
Information is recorded by reversing the magnetization direction of the storage layer by spin injection by passing a current between the storage layer and the magnetization fixed layer through the nonmagnetic layer ,
A magnetization free layer capable of changing the direction of magnetization via a nonmagnetic layer is provided on the opposite side of the magnetization fixed layer with respect to the storage layer ,
Spin injection reverses the magnetization direction of the magnetization free layer,
The interaction between the magnetization free layer and the storage layer has such a magnitude that the magnetization direction of the magnetization free layer is reversed simultaneously with the reversal of the magnetization direction of the storage layer, and , Using a memory element as a memory cell that is small enough to freely move the magnetization direction of the magnetization free layer,
When recording information, first, a current in the film thickness direction is passed through the storage element, and the relationship between the magnetization direction of the storage layer and the magnetization direction of the magnetization free layer is parallel or antiparallel. And then increasing the amount of current in the same direction so that the relationship between the magnetization direction of the storage layer and the magnetization direction of the magnetization free layer is maintained parallel or antiparallel. And the magnetization direction of the magnetization free layer are reversed.
Memory . The minimum current value for reversing the magnetization direction of the magnetization free layer is less than the minimum current value for reversing the magnetization direction of the storage layer when a current in the film thickness direction is passed through the storage element. memory according to a small claim 1. The memory according to claim 1 , wherein a product of the saturation magnetic flux density and the thickness of the magnetization free layer is smaller than a product of the saturation magnetic flux density and the thickness of the storage layer .

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