JP2014116474A - Magnetoresistive element - Google Patents

Abstract

A magnetoresistive element capable of reducing a magnetization reversal current and achieving low power is provided.
An MTJ layer having a storage layer with a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and an insulator layer provided between the storage layer and the fixed layer. And the storage layer 14 is provided between the ferromagnetic layer 41, the perpendicular magnetization holding layer 43, and the ferromagnetic layer 41 and the perpendicular magnetization holding layer 43. And a magnetic coupling control layer 42 for controlling magnetic coupling.
[Selection] Figure 2

Description

  The present invention relates to magnetoresistance of perpendicularly magnetized ferromagnets such as STT-MRAM (Spin Transfer Torque Magnetic Random Access Memory), racetrack memory (Racetrack-memory: magnetic-based non-volatile memory), and HDD read heads. The present invention relates to a magnetoresistive element using an effect.

  A magnetoresistive element that has perpendicular magnetization and performs reading by the magnetoresistive effect has high thermal disturbance resistance against miniaturization, and is expected as a next-generation memory or the like. Ferromagnetic materials with high perpendicular magnetic anisotropy and high spin polarizability are required as the basic constituent material of such next-generation memories, but the material itself has perpendicular magnetic anisotropy and is theoretically The only material with a high spin polarizability is Mn-Ga and other materials, and the material selection range is very narrow, forming a ferromagnetic thin film with high perpendicular magnetic anisotropy. It is difficult to do.

  On the other hand, as a solution, a method of coupling a perpendicular magnetization holding layer to an MTJ (Magnetic Tunnel Junction) layer has been proposed. As such a conventional magnetoresistive element, for example, a magnetization pinned layer having a magnetic film in which the direction of the spin moment is fixed in a direction perpendicular to the film surface, and the spin moment is perpendicular to the film surface. A magnetic recording layer oriented in a direction, a nonmagnetic layer provided between the magnetization fixed layer and the magnetic recording layer, and an antiferromagnetic film provided on at least a side surface of the magnetization fixed layer. is there. (For example, refer to Patent Document 1).

  And a ferromagnetic tunnel junction including a three-layer structure of a first ferromagnetic layer / tunnel barrier layer / second ferromagnetic layer, wherein the first ferromagnetic layer is more than the second ferromagnetic layer. A magnetoresistive element having a large coercive force and a tunnel conductance that changes depending on a relative angle between the magnetizations of the two ferromagnetic layers, wherein the magnetization of the end of the second ferromagnetic layer is the second ferromagnetic layer; A magnetoresistive element fixed in a direction having a component orthogonal to the direction of the easy axis of magnetization is also introduced. (For example, refer to Patent Document 2).

  The first magnetic layer having a variable magnetization direction having an easy axis in the direction perpendicular to the film surface, the second magnetic layer having an invariable magnetization direction having the easy axis in the direction perpendicular to the film surface, and the first magnetic layer. And a first nonmagnetic layer provided between the first magnetic layer and the second magnetic layer, wherein the first magnetic layer is formed by alternately stacking Co and Pd or Co and Pt on an atomically dense surface. It has a CoPd alloy or a CoPt alloy and is made of a ferromagnetic material whose c-axis is oriented in the direction perpendicular to the film surface, and the magnetization direction of the first magnetic layer includes the first magnetic layer, the first nonmagnetic layer, and A magnetoresistive element that is changed by a bidirectional current passing through the second magnetic layer is also introduced. (For example, refer to Patent Document 3).

JP 2005-32878 A JP 2005-150303 A JP 2011-71352 A

  By combining the MTJ layer with the perpendicular magnetization holding layer, the range of materials with high spin polarizability has been expanded to half-metal systems, Heusler systems, etc., but the range of selection has been expanded. Current increases and it is difficult to reduce power consumption.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetoresistive element that can reduce magnetization reversal current and achieve low power.

  To achieve this object, the present invention includes a storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and an insulator layer provided between the storage layer and the fixed layer. A magnetoresistive element including an MTJ layer, wherein the storage layer is provided between a first ferromagnetic layer, a first perpendicular magnetization holding layer, and the first ferromagnetic layer and the first perpendicular magnetization holding layer. And a magnetic coupling control layer for controlling magnetic coupling between the first ferromagnetic layer and the first perpendicular magnetization holding layer.

  In the magnetoresistive element having this configuration, by changing the thickness of the magnetic coupling control layer provided between the first ferromagnetic layer and the first perpendicular magnetization holding layer of the storage layer as appropriate, the resistance change rate, Various parameters such as thermal stability, recording current, and magnetization reversal speed can be optimized. Therefore, the magnetization reversal current can be reduced, and low power can be achieved.

  In the magnetoresistive element according to the present invention, the fixed layer may include a second ferromagnetic layer and a second perpendicular magnetization holding layer. In this configuration, the perpendicular magnetic anisotropy constant of the first and second perpendicular magnetization holding layers (ie, the perpendicular magnetization holding layer of the MTJ layer) is the same as that of the first and second ferromagnetic layers (ie, the MTJ layer). By setting the magnetic layer to be larger than the perpendicular magnetic anisotropy constant of the (ferromagnetic layer), the magnetization reversal current can be reduced more efficiently, and a magnetoresistive element with lower power can be provided.

  In addition, the perpendicular magnetic anisotropy constant of the ferromagnetic layer of the MTJ layer may be set to have 0 or a negative value. By doing in this way, a magnetization reversal current can be reduced more efficiently and the magnetoresistive element which is lower power can be provided.

  The ferromagnetic layer of the MTJ layer can be formed from a half metal or Heusler material having a high polarizability.

  According to the present invention, it is possible to provide a magnetoresistive element in which the magnetization reversal current is reduced and low power is achieved.

It is sectional drawing which shows typically the principal part of the magnetoresistive element which concerns on embodiment of this invention. It is sectional drawing which expands and shows typically the memory | storage layer of the magnetoresistive element shown in FIG. It is a figure which shows the relationship between the current density and inversion probability in the magnetoresistive element which concerns on embodiment of this invention, and the conventional magnetoresistive element. It is a figure which shows the relationship between the anisotropy and inversion current density in the magnetoresistive element which concerns on embodiment of this invention, and the conventional magnetoresistive element.

  Next, a magnetoresistive element according to an embodiment of the present invention will be described with reference to the drawings. In addition, embodiment described below is the illustration for demonstrating this invention, and this invention is not limited only to these embodiment. Therefore, the present invention can be implemented in various forms without departing from the gist thereof.

  FIG. 1 is a cross-sectional view schematically showing a main part of a magnetoresistive element according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view schematically showing a memory layer of the magnetoresistive element shown in FIG. is there. In the drawings, for easy understanding, the thickness, size, enlargement / reduction ratio, etc. of each member are not matched with the actual ones.

  As shown in FIG. 1, the magnetoresistive element according to this embodiment includes a fixed layer 12 formed on a base electrode 11, an insulator layer 13 formed on the fixed layer 12, and an insulator layer 13. A memory layer 14 formed and a cap layer 15 formed on the memory layer 14 are included, and a transistor 16 is connected to the base electrode 11. In this magnetoresistive element, the fixed layer 12, the insulator layer 13, and the memory layer 14 constitute an MTJ layer (magnetic tunnel junction layer).

  The magnetoresistive element performs writing by a spin injection magnetization reversal method. That is, the magnetoresistive element is a magnetoresistive element used for the spin injection writing method. That is, at the time of writing, by passing a current in the direction perpendicular to the film surface from the fixed layer 12 to the storage layer 14 or from the storage layer 14 to the fixed layer 12, electrons that accumulate spin information are transferred from the fixed layer 12. It is injected into the storage layer 14. Then, the spin angular momentum of the injected electrons is transferred to the electrons in the storage layer 14 according to the conservation law of the spin angular momentum, so that the magnetization of the storage layer 14 is reversed. In other words, the relative angles of magnetization of the fixed layer 12 and the storage layer 14 are made parallel or anti-parallel (that is, the resistance is minimum or maximum) according to the direction of the spin-polarized current that flows in the direction perpendicular to the film surface with respect to each layer. Information is stored by changing and associating with binary information “0” or “1”.

  The fixed layer 12 has an easy magnetization axis in a direction perpendicular to the film surface, and the magnetization direction (see the arrow described in the fixed layer 12 shown in FIG. 1) is fixed to the storage layer 14. In FIG. 1, the magnetization direction of the fixed layer 12 is typically upward with respect to the base electrode 11, but may be downward (base electrode 11 side). The pinned layer 12 has a ferromagnetic layer and a perpendicular magnetization holding layer, although not particularly shown. Note that the fixed layer 12 may be referred to as a magnetization fixed layer, a reference layer, a magnetization reference layer, a pinned layer, a reference layer, a magnetization reference layer, or the like.

  As the fixed layer 12, it is preferable to select a material whose magnetization direction does not easily change with respect to the storage layer 14. That is, it is preferable to select a material having a large effective magnetic anisotropy Kueff and saturation magnetization Ms and a large magnetic relaxation constant α. However, the material constituting the fixed layer 12 is not particularly limited, and can be selected from any material depending on various conditions.

  The insulator layer 13 is a tunnel barrier layer and is made of an insulating film such as MgO. In addition, as a material which comprises the insulator layer 13, the oxide which has a NaCl structure is preferable, CaO, SrO, TiO, VO, NbO etc. other than MgO mentioned above are mentioned, The function as the insulator layer 13 is mentioned. There is no particular limitation as long as it does not hinder.

  The memory layer 14 has an easy axis of magnetization in a direction perpendicular to the film surface, and rotates along a surface that intersects the film surface. As shown in FIG. 2, the storage layer 14 includes a ferromagnetic layer 41, a magnetic coupling control layer 42 formed on the ferromagnetic layer 41, and a perpendicular magnetization holding layer 43 formed on the magnetic coupling control layer 42. have. That is, the memory layer 14 has a configuration in which a magnetic coupling control layer 42 that controls the magnetic coupling between the ferromagnetic layer 41 and the perpendicular magnetization holding layer 43 is provided between the ferromagnetic layer 41 and the perpendicular magnetization holding layer 43. Have. The storage layer 14 may be referred to as a free layer, a magnetization free layer, a magnetization variable layer, or the like.

  The ferromagnetic layer 41 is preferably selected from, for example, half metal or Heusler material.

  The magnetic coupling control layer 42 can be made of, for example, Pd, Pt, Ru, MgO, or the like. The magnitude of the magnetic coupling is appropriately changed so that the thickness (film thickness) of the magnetic coupling control layer 42 is 2 nm or less, so that the rate of change in resistance, thermal stability, recording current, and magnetization reversal speed can be obtained. Etc. can be optimized.

Perpendicular magnetization holding layer 43 may be composed of high perpendicular magnetic anisotropy material composed of L1 ₀ type FePd or FePt.

  The cap layer 15 functions mainly as a protective layer, such as for preventing the storage layer 14 from being oxidized.

Next, in the magnetoresistive element according to the present embodiment, the perpendicular magnetic anisotropy constant (Ku ₁ ) of the ferromagnetic layer of the MTJ layer composed of the fixed layer 12, the insulator layer 13, and the storage layer 14, and the MTJ The perpendicular magnetic anisotropy constant (Ku ₂ ) of the perpendicular magnetization retention layer of the layer was measured for the relationship between the current density and the inversion probability for the sample configured to have the value shown in FIG. 3 (Ku ₁ <Ku ₂ ). . The result is shown in FIG.

  The ferromagnetic layer of the MTJ layer is a ferromagnetic layer of the fixed layer 12 and the storage layer 14, and the perpendicular magnetization holding layer of the MTJ layer is the perpendicular magnetization holding layer of the fixed layer 12 and the storage layer 14. That is.

For comparison, the relationship between current density and inversion probability was measured for a conventional MTJ layer having a single layer film (SL) in which a magnetic coupling control layer was not formed in the memory layer. The result is shown in FIG. In the case of the conventional MTJ layer, perpendicular magnetic anisotropy constant of the ferromagnetic layers (Ku ₁₎ and perpendicular magnetic anisotropy constant of perpendicular magnetization holding layer (Ku ₂₎ are the same.

FIG. 3 shows that the reversal current density decreases as the perpendicular magnetic anisotropy constant (Ku ₁ ) of the ferromagnetic layer decreases. It can also be seen that when the perpendicular magnetic anisotropy constant (Ku ₁ ) is negative, the reversal current density is lower than that of the single layer film.

The minimum reversal current density was 7.94 GA / m ² when Ku ₁ was −10.0 Merg / cm ³ . Moreover, it was reduced by about 8% compared with the reversal current density of the conventional MTJ layer having a single layer film (SL).

Next, as shown in FIG. 4, the perpendicular magnetic anisotropy constant (Ku ₁ ) of the ferromagnetic layer and the reversal current are obtained for a conventional MTJ layer having a sample showing five types of A _IL and a single layer film (SL). The relationship with density was measured. The result is shown in FIG. In FIG. 4, when A _IL = 1.00 μerg / cm, the thickness of the magnetic coupling control layer 42 is the thinnest (almost 0), and when A _IL = 0.03 μerg / cm, the magnetic coupling control layer The film thickness of 42 is the thickest. That is, the thickness of the magnetic coupling control layer 42 is thicker A _IL decreases.

FIG. 4 shows that the perpendicular magnetic anisotropy constant (Ku ₁ ) of the ferromagnetic layer at which the reversal current density is minimized changes depending on the value of A _IL . It can be seen that when the A _IL is 0.05 μerg / cm and 0.03 μerg / cm, the reversal current density rapidly increases when Ku ₁ is around 2 Merg / cm ³ . _Also, the _{A IL} is 0.03μerg / cm, when Ku ₁ is negative, it can be seen that the switching current density higher Ku ₁ decreases increases.

  From the above, it was proved that by providing the magnetic coupling control layer 42 in the storage layer 14, the reversal recording current can be reduced and the power can be reduced.

DESCRIPTION OF SYMBOLS 11 Base electrode 12 Fixed layer 13 Insulator layer 14 Memory layer 15 Cap layer 16 Transistor 41 Ferromagnetic layer 42 Magnetic coupling control layer 43 Perpendicular magnetization retention layer

Claims (4)

A magnetoresistive element comprising a magnetic tunnel junction layer having a storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and an insulator layer provided between the storage layer and the fixed layer Because
The storage layer is
A first ferromagnetic layer;
A first perpendicular magnetization retention layer;
A magnetic coupling control layer that is provided between the first ferromagnetic layer and the first perpendicular magnetization holding layer and controls magnetic coupling between the first ferromagnetic layer and the first perpendicular magnetization holding layer;
A magnetoresistive element comprising: The pinned layer includes a second ferromagnetic layer and a second perpendicular magnetization holding layer,
The magnetoresistive element according to claim 1, wherein perpendicular magnetic anisotropy constants of the first and second perpendicular magnetization holding layers are larger than perpendicular magnetic anisotropy constants of the first and second ferromagnetic layers.   3. The magnetoresistive element according to claim 1, wherein perpendicular magnetic anisotropy constants of the first and second ferromagnetic layers have 0 or a negative value. 4. The magnetoresistive element according to any one of claims 1 to 3, wherein the first and second ferromagnetic layers are made of a half metal or a Heusler material.

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