Spin-orbit-torque magnetization rotational element, spin-orbit-torque type magnetoresistance effect element, and magnetic memory

A spin-orbit-torque magnetization rotational element includes: a spin-orbit-torque wiring; and a laminated body laminated on the spin-orbit-torque wiring, wherein the laminated body includes a first ferromagnetic layer, an oxide containing layer, and a second ferromagnetic layer in order from the spin-orbit-torque wiring, wherein the oxide containing layer contains an oxide of a non-magnetic element, and wherein the first ferromagnetic layer and the second ferromagnetic layer are ferromagnetically coupled to each other.

TECHNICAL FIELD

The present invention relates to a spin-orbit-torque magnetization rotational element, a spin-orbit-torque type magnetoresistance effect element, and a magnetic memory. Priority is claimed on Japanese Patent Application No. 2018-105393, filed May 31, 2018, the content of which is incorporated herein by reference.

BACKGROUND ART

A giant magnetoresistance (GMR) element including a multilayer film of a ferromagnetic layer and a non-magnetic layer and a tunnel magnetoresistance (TMR) element using an insulating layer (tunnel barrier layer, barrier layer) for a non-magnetic layer are known. These elements are used in magnetic sensors, high-frequency components, magnetic heads, nonvolatile random access memories (MRAM), and the like.

The MRAM reads and writes data using a characteristic that the element resistance of the TMR element changes when the magnetization directions of two ferromagnetic layers sandwiching the insulating layer change. As a writing method of the MRAM, a writing (magnetization reversal) method using a magnetic field generated by a current or a writing (magnetization reversal) method using a spin transfer torque (STT) generated by flowing a current in a lamination direction of a magnetoresistance effect element is known.

In the magnetoresistance effect element performing writing using an STT, there has been an attempt to decrease the damping constant of the ferromagnetic layer for performing the magnetization reversal. For example, Patent Document 1 describes a method of setting the damping constant to be 0.01 or less. It is known that the critical writing current density using an STT is proportional to the damping constant of the ferromagnetic layer and it is preferable to use a material having a low damping constant from the viewpoint of energy saving, high durability, and high integration. In recent years, it has come to be expected that Mn—Ga and Mn—Ge alloys will be able to the materials having low damping constants. However, when the damping constant of the ferromagnetic layer is low, there is a possibility that erroneous writing may be performed by the reading current. As a result, the problem of lowering the reliability of a device also occurs.

The damping constant is a physical quantity generated from spin-orbit interaction. For that reason, the damping constant has a close relationship with the magnetic anisotropic energy. In general, when the damping constant is small, the magnetic anisotropic energy is also small. When the magnetic anisotropic energy decreases, the magnetization of the ferromagnetic layer is more easily reversed and hence data can be more easily read and written.

Further, Non-Patent Document 1 described that a Co—Fe alloy which is a material generally used in a magnetoresistance effect element has a damping constant of less than 0.01. According to Non-Patent Document 1, a Co—Fe—B alloy manufactured by sputtering also has a damping constant of less than 0.01. Among the Co—Fe—B alloys, those having a damping constant of 0.01 or more are only structures other than a BCC structure which cannot obtain high output characteristics. For that reason, a ferromagnetic material having a damping constant of less than 0.01 is used in the magnetoresistance effect element using an STT.

Meanwhile, in recent years, magnetization reversal using a pure spin current generated by spin-orbit interaction has been gaining attention as means for reducing a reversal current (for example, Non-Patent Document 2). The pure spin current generated by the spin-orbit interaction causes a spin-orbit-torque (SOT). The pure spin current is generated by the same number of upward spin electrons and downward spin electrons flowing in opposite directions. In the pure spin current, since the number of electrons flowing in the opposite direction is the same, the charge flow is canceled. For that reason, the current flowing to the magnetoresistance effect element due to the flow of the pure spin current is zero and the long life of the magnetoresistance effect element is expected.

Also in the magnetization reversal using an SOT, the damping constant is one of the factors affecting the behavior of the magnetization reversal. Non-Patent Document 3 describes that a damping constant of Ni81Fe19increases as the degree of oxidation of a Pt oxide film increases in a laminated body of a Pt oxide film, Ni81Fe19, and an oxide cap layer.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Research on the spin-orbit-torque magnetization rotational element using an SOT has just begun. The magnetization reversal element using an SOT is different from the magnetization reversal element using an STT in the mechanism of magnetization reversal. For that reason, an appropriate configuration for driving the magnetization reversal element using an SOT is not sufficiently known.

The present invention has been made in view of the above-described problems and an object of the present invention is to provide a spin-orbit-torque magnetization rotational element, a spin-orbit-torque type magnetoresistance effect element, and a magnetic memory capable of quickly performing magnetization reversal.

Solution to Problem

The present inventors have carried out an examination in order to solve the above-described problems and found that the magnetization reversal of the ferromagnetic layer (free layer) can be performed quickly by inserting an oxide containing layer into the ferromagnetic layer (free layer) performing the magnetization reversal in a spin-orbit-torque magnetization rotational element.

That is, the present invention provides the following means in order to solve the above-described problems.

(1) A spin-orbit-torque magnetization rotational element of a first aspect includes: a spin-orbit-torque wiring; and a laminated body laminated on the spin-orbit-torque wiring, wherein the laminated body includes a first ferromagnetic layer, an oxide containing layer, and a second ferromagnetic layer in order from the spin-orbit-torque wiring, wherein the oxide containing layer contains an oxide of a non-magnetic element, and wherein the first ferromagnetic layer and the second ferromagnetic layer are ferromagnetically coupled to each other.

(2) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, an easy axis of magnetization of the first ferromagnetic layer may intersect a direction of a spin injected from the spin-orbit-torque wiring into the first ferromagnetic layer.

(3) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, the non-magnetic element of the oxide contained in the oxide containing layer may contain at least one selected from a group consisting of Al, Si, Mg, Ti, Cr, Cu, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Ir, Pt, and Bi.

(4) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, a film thickness of the oxide containing layer may be 1.0 nm or less.

(5) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, the oxide contained in the oxide containing layer may contain insufficient oxygen with respect to a stoichiometric composition.

(6) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, a diffusion preventing layer may be inserted between the oxide containing layer and the second ferromagnetic layer.

(7) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, a film thickness of the first ferromagnetic layer may be thicker than a film thickness of the second ferromagnetic layer.

(8) In the spin-orbit-torque magnetization rotational element according to the above-described aspect, the second ferromagnetic layer may contain at least one element selected from a group consisting of Co, Fe, and B.

(9) A spin-orbit-torque type magnetoresistance effect element according to a second aspect includes: the spin-orbit-torque magnetization rotational element according to the above-described aspect; a non-magnetic layer which is laminated on the side opposite to the spin-orbit-torque wiring in the laminated body; and a third ferromagnetic layer, the laminated body and the non-magnetic layer being sandwiched between the third ferromagnetic layer and the spin-orbit-torque wiring.

(10) A magnetic memory according to a third aspect includes a plurality of the spin-orbit-torque type magnetoresistance effect elements according to the above-described aspect.

Advantage of the Invention

According to the present invention, it is possible to provide a spin-orbit-torque magnetization rotational element, a spin-orbit-torque type magnetoresistance effect element, and a magnetic memory capable of quickly performing magnetization reversal.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred examples of the present invention will be described in detail by appropriately referring to the drawings. In the drawings used in the following description, characteristic parts are enlarged for convenience of description in order to easily understand the characteristics of the present invention and hence the dimensional ratio of each component may be different from the actual one. The materials, dimensions, and the like exemplified in the following description are merely examples and the present invention is not limited thereto and can be implemented with appropriate modifications within a range in which the effects of the present invention are exhibited.

FIG. 1is a cross-sectional view schematically showing an example of a spin-orbit-torque magnetization rotational element according to a first embodiment.FIG. 1shows a cross-section in which a spin-orbit-torque magnetization rotational element is cut along the xz plane passing through a center of a spin-orbit-torque wiring50in the y direction. A spin-orbit-torque magnetization rotational element101shown inFIG. 1includes a laminated body10and the spin-orbit-torque wiring50.

In the present specification, a direction in which a spin-orbit-torque wiring extends is referred to as the x direction, a direction in which the laminated body10is laminated is referred to as the z direction, and a direction which is orthogonal to the x direction and the z direction is referred to as the y direction.

The laminated body10is laminated in the thickness direction of the spin-orbit-torque wiring50. The laminated body10includes a first ferromagnetic layer11, an oxide containing layer12, and a second ferromagnetic layer13in order from the spin-orbit-torque wiring50. The first ferromagnetic layer11and the second ferromagnetic layer13are ferromagnetic ally coupled to each other.

(First Ferromagnetic Layer and Second Ferromagnetic Layer)

A ferromagnetic material, in particular, a soft magnetic material can be applied to the first ferromagnetic layer11and the second ferromagnetic layer13. For example, metals selected from a group consisting of Cr, Mn, Co, Fe, and Ni, alloys containing at least one or more of these metals, and alloys containing these metals and at least one or more elements from B, C and N can be used. Specifically, Co—Fe, Co—Fe—B, and Ni—Fe can be exemplified. When the first ferromagnetic layer11is an in-plane magnetic film, for example, a Co—Ho alloy (CoHo2), a Sm—Fe alloy (SmFe12), or the like can be used.

A Heusler alloy such as Co2FeSi may be used for the first ferromagnetic layer11and the second ferromagnetic layer13. The Heusler alloy contains an intermetallic compound with a chemical composition of XYZ or X2YZ. X in the chemical composition of the Heusler alloy is a transition metal element or a noble metal element of the Co, Fe, Ni, or Cu group in the periodic table. Y in the chemical composition of the Heusler alloy is a transition metal from the Mn, V, Cr or Ti group or an element type of X. Z in the chemical composition of the Heusler alloy is a typical element of Group III to Group V. Examples of the Heusler alloys include, for example, Co2FeSi, Co2FeGe, Co2FeGa, Co2MnSi, Co2Mn1-aFeaAlbSi1-b, Co2FeGe1-cGac, and the like. The second ferromagnetic layer13preferably contains at least one element selected from a group consisting of Co, Fe, and B. The second ferromagnetic layer13is particularly preferably made of Co—Fe—B.

The first ferromagnetic layer11and the second ferromagnetic layer13are ferromagnetically coupled to each other. That is, the magnetization M11of the first ferromagnetic layer11and the magnetization M13of the second ferromagnetic layer13are orientated in the same direction. Whether the magnetization M11and the magnetization M13are ferromagnetically coupled or antiferromagnetically coupled can be controlled by the material and thickness of the oxide containing layer12. In the embodiment, the material and the film thickness of the oxide containing layer12are controlled so that the magnetization M11and the magnetization M13are ferromagnetically coupled to each other.

Further, it is preferable that the film thickness of the first ferromagnetic layer11is thicker than the film thickness of the second ferromagnetic layer13. When the film thickness of the first ferromagnetic layer11is thick, the effect of orienting the magnetization M11the in-plane direction works strongly. Meanwhile, when the film thickness of the second ferromagnetic layer13is thin, the effect of orienting the magnetization M13in the direction perpendicular to the plane works strongly. Since the magnetization M11and the magnetization M13are ferromagnetically coupled to each other, the magnetization M11of the first ferromagnetic layer11is oriented in a direction inclined from the direction perpendicular to the plane. When the magnetization M11of the first ferromagnetic layer11is inclined, the reversal symmetry of the magnetization reversal is broken, the magnetization reversal of the first ferromagnetic layer11easily occurs, and the magnetization reversal without a magnetic field becomes easy. It is preferable that the film thickness of the first ferromagnetic layer11is in a range of 0.3 nm or more and 2.0 nm or less. It is preferable that the film thickness of the second ferromagnetic layer13is in a range of 0.5 nm or more and 3.0 nm or less. It is preferable that the film thickness of the first ferromagnetic layer11is in a range of 150% or more and 200% or less with respect to the film thickness of the second ferromagnetic layer13.

The oxide containing layer12is located between the first ferromagnetic layer11and the second ferromagnetic layer13.

As described in Non-Patent Document 3, when an oxide film is disposed adjacent to the ferromagnetic layer, the damping constant of the ferromagnetic layer increases. The damping constant of the first ferromagnetic layer11and the second ferromagnetic layer13increases as the oxide containing layer12is adjacent to each of the first ferromagnetic layer11and the second ferromagnetic layer13. The magnetization of the ferromagnetic material performs magnetization reversal while performing procession. When the damping constant is large, the force of the magnetization M11in the direction of easy magnetization increases and the magnetization reversal can be performed quickly.

The oxide containing layer12contains an oxide of a non-magnetic element. It is preferable that the non-magnetic element contains at least one selected from a group consisting of Al, Si, Mg, Ti, Cr, Cu, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Ir, Pt, and Bi.

When the non-magnetic element is a light metal (Al, Si, Mg, Ti, Cr, Cu) having an atomic number of 38 or less, a thin and stable oxide containing layer12can be formed. Since the electronegativity of these light elements is relatively small, diffusion of oxygen by heat is unlikely to occur and the light elements are stable as oxides.

When the non-magnetic element is a heavy metal having an atomic number of 39 or more (Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Ir, Pt, and Bi), the oxide containing layer12can reduce a reversal current density for reversing the magnetization M11of the first ferromagnetic layer11. A part of the current also enters the oxide containing layer12. This is because SOT (torque) is also efficiently generated in the oxide containing layer12when a current flows to the oxide containing layer12containing a heavy metal. Then, this contributes to the magnetization reversal of the first ferromagnetic layer11.

It is preferable that the oxide of the ferromagnetic metal element contained in the oxide containing layer12contains insufficient oxygen with respect to the stoichiometric composition. In this case, the spin current supplied from the first ferromagnetic layer11easily passes through the oxide containing layer12and the efficiency of transmitting the spin current to the second ferromagnetic layer13is improved. It is preferable that the oxide of the ferromagnetic metal element contains insufficient oxygen in a range of 5 atomic % to 30 atomic % with respect to the stoichiometric composition.

It is preferable that the film thickness of the oxide containing layer12is 1.0 nm or less. In this case, since the first ferromagnetic layer11and the second ferromagnetic layer13are more strongly ferromagnetically coupled to each other, stability of magnetization against thermal disturbances increases. Further, when the film thickness of the oxide containing layer12is thin, oxygen is scattered and the symmetry of the crystal structure of the first ferromagnetic layer11is easily broken. For this reason, it is preferable that the film thickness of the oxide containing layer12is at least one atomic layer. In the case of one atomic layer, a continuous and uniform layer is not formed and an oxide is scattered. However, in this case, the layer is also treated as an oxide containing layer.

The spin-orbit-torque wiring50extends in the x direction. The spin-orbit-torque wiring50is located on one surface of the ferromagnetic conductor layer11a.The spin-orbit-torque wiring50may be directly connected to the ferromagnetic conductor layer11aor may be connected thereto through other layers.

When a current flows to the spin-orbit-torque wiring50, a spin current is generated due to a spin Hall effect. The spin Hall effect is a phenomenon in which a spin current is induced in a direction orthogonal to the direction of a current based on a spin-orbit interaction when a current flows through a wiring. A mechanism in which a spin current is generated by the spin Hall effect will be described.

As shown inFIG. 1, a current1flows in the x direction when a potential difference is applied to both ends of the spin-orbit-torque wiring50in the x direction. When the current I flows, a first spin S1oriented in the y direction and a second spin S2oriented in the −y direction are respectively bent in a direction orthogonal to the current. The normal Hall effect and the spin Hall effect are common in that the moving charges (electrons) can bend the movement (moving) direction. Meanwhile, the normal Hall effect and the spin Hall effect are different in the conditions required for the moving charge (electrons) to bend the movement (moving) direction. In the normal Hall effect, charged particles moving in a magnetic field are subject to the Lorentz force to bend the moving direction. However, the spin Hall effect is largely different in that the moving direction is bent only by the movement of electrons (only the flow of current) without the presence of a magnetic field. In order to eliminate the uneven distribution of the first spin S1and the second spin S2caused by the spin Hall effect, a spin current is generated in the z direction.

Since the number of electrons of the first spin S1is equal to the number of electrons of the second spin S2in the non-magnetic material (a material that is not a ferromagnetic material), the number of electrons of the first spin S1going upward is equal to the number of electrons of the second spin S2going downward in the drawing. For that reason, a current as a net flow of charge is zero. This spin current without this current is particularly called a pure spin current.

Here, if the electron flow of the first spin S1is represented by J↑, the electron flow of the second spin S2is represented by J↓, and the spin current is represented by Js, this is defined as Js=J↑−J↓. A spin current Jsflows in the z direction of the drawing. InFIG. 1, the first ferromagnetic layer11is present on the surface of the spin-orbit-torque wiring50. Therefore, spin is injected into the first ferromagnetic layer11.

It is preferable that the direction of the spin injected into the first ferromagnetic layer11intersects the easy axis of magnetization of the first ferromagnetic layer11.

For example, when the magnetization M11of the first ferromagnetic layer11is oriented in the +y direction and the direction of the injected spin is the −y direction (the direction of the spin injected into the first ferromagnetic layer11matches the easy axis of magnetization of the first ferromagnetic layer11), the magnetization M11receives a force in which a vector direction is different by 180° due to the injected spin. For that reason, the initial operation of the magnetization M11is slow.

In contrast, for example, when the magnetization M11of the first ferromagnetic layer11is oriented in the +z direction and the direction of the injected spin is the −y direction (the direction of the spin injected into the first ferromagnetic layer11intersects the easy axis of magnetization of the first ferromagnetic layer11), the magnetization M11quickly starts to rotate by receiving a force in which a vector direction is different due to the injected spin. For that reason, the initial operation of the magnetization M11is fast.

When the damping constant of the first ferromagnetic layer11is large, the magnetization reversal of the magnetization M11is fast. When the direction of the injected spin intersects the easy axis of magnetization of the first ferromagnetic layer11, the magnetization reversal of the magnetization M11can be further accelerated. The intersection relationship between the direction of the spin injected into the first ferromagnetic layer11and the easy axis of magnetization of the first ferromagnetic layer11is only for the spin-orbit-torque magnetization rotational element using an SOT.

The spin-orbit-torque wiring50is made of a metal, an alloy, an intermetallic compound, a metal boride, a metal carbide, a metal silicide, or a metal phosphide having a function of generating a spin current by a spin Hall effect when a current flows.

The main configuration of the spin-orbit-torque wiring50is preferably a non-magnetic heavy metal. Here, the heavy metal means a metal having a specific gravity of yttrium or more. It is preferable that the non-magnetic heavy metal is a non-magnetic metal having an atomic number of 39 or more and having a large atomic number, having d electrons or f electrons in the outermost shell. These non-magnetic metals have a large spin-orbit interaction that causes the spin Hall effect.

Electrons generally move in the opposite direction to the current regardless of their spin direction. However, the direction in which electrons of non-magnetic metal having a large atomic number having d electrons or f electrons in the outermost shell move depends on the direction of the electron spin. This is because non-magnetic metal having a large atomic number having d or f electrons in the outermost shell has a large spin-orbit interaction and a strong spin Hall effect. Thus, the spin current Jsis likely to occur in a non-magnetic heavy metal having a large atomic number having d electrons or f electrons in the outermost shell.

Further, the spin-orbit-torque wiring50may contain magnetic metal. The magnetic metal refers to ferromagnetic metal or antiferromagnetic metal. When a small amount of magnetic metal is contained in non-magnetic metal, magnetic metal becomes a spin scattering factor. When the spin is scattered, the spin-orbit interaction is enhanced and the efficiency of generating a spin current with respect to the current increases.

Meanwhile, when the added amount of the magnetic metal is too large, the generated spin current is scattered by the added magnetic metal. As a result, the effect of reducing the spin current may be increased. For that reason, it is preferable that the molar ratio of the magnetic metal to be added is sufficiently smaller than the total molar ratio of the elements constituting the spin-orbit-torque wiring. It is preferable that the molar ratio of the magnetic metal to be added is 3% or less of the whole.

The spin-orbit-torque wiring50may contain a topological insulator. The topological insulator is a substance in which the inside of a substance is an insulator or a high-resistance substance, but a spin-polarized metal state occurs on its surface. An internal magnetic field is generated in the topological insulator due to the spin-orbit interaction. Therefore, a new topological phase appears due to the effect of the spin-orbit interaction even without an external magnetic field. That is, the topological insulator disturbs the symmetry of the magnetization direction of the insulator inside the material or the high-resistance body even without an external magnetic field. The topological insulator can generate a pure spin current with high efficiency due to the strong spin-orbit interaction and the breakage of the reversal symmetry at edges.

Preferred examples of the topological insulator include SnTe, Bi1.5Sb0.5Te1.7Se1.3, TlBiSe2, Bi2Te3, Bi1-xSbx, and (Bi1-xSbx)2Te3. These topological insulators can generate a spin current with high efficiency.

For example, the spin-orbit-torque magnetization rotational element101can be manufactured by laminating the first ferromagnetic layer11, the oxide containing layer12, and the second ferromagnetic layer13in this order from the spin-orbit-torque wiring50. Hereinafter, in the present specification, the layers laminated on the spin-orbit-torque wiring50may be collectively referred to as a laminated body. For example, in the spin-orbit-torque magnetization rotational element101, the first ferromagnetic layer11, the oxide containing layer12, and the second ferromagnetic layer13are collectively referred to as the laminated body10. As a method of laminating the first ferromagnetic layer11and the second ferromagnetic layer13, known methods such as a sputtering method and a chemical vapor deposition (CVD) method can be used. As a method of laminating the oxide containing layer12, for example, a method of forming a ferromagnetic metal film by a sputtering method or a CVD method and then oxidizing the obtained ferromagnetic metal film or a method of co-sputtering a ferromagnetic metal and an oxide can be used.

It is preferable that the obtained laminated body10is subjected to an annealing treatment. When the annealing treatment is performed, the crystallinity of each layer is improved and the MR ratio of the laminated body4can be increased.

As the annealing treatment, it is preferable that the laminated body is heated at a temperature of 300° C. or more and 500° C. or less for 5 minutes or more and 100 minutes or less in the presence of an inert atmosphere such as Ar and then is heated at a temperature of 100° C. or more and 500° C. or less for 1 hour or more and 10 hours or less while a magnetic field of 2 kOe or more and 10 kOe or less is applied thereto.

The spin-orbit-torque magnetization rotational element101with the above-described configuration according to the embodiment can quickly perform the magnetization reversal of the second ferromagnetic layer13. This is because the damping constant of the first ferromagnetic layer11and the second ferromagnetic layer13increases due to the oxide containing layer provided in the laminated body10. Since the force of the magnetization M11of the first ferromagnetic layer11and the magnetization M13of the second ferromagnetic layer13in the easy magnetization direction increases as the damping constant increases, the magnetization reversal can be quickly performed.

FIG. 2is a schematic cross-sectional view of Modified Example 1 of the spin-orbit-torque magnetization rotational element according to the first embodiment.FIG. 2shows a cross-section in which a spin-orbit-torque magnetization rotational element102is cut along the xz plane passing through the center of the spin-orbit-torque wiring50in the y direction. The spin-orbit-torque magnetization rotational element102shown inFIG. 2is the same as the spin-orbit-torque magnetization rotational element101shown inFIG. 1except that a diffusion preventing layer14is provided. For this reason, the same reference numerals will be given to the same components as those of the spin-orbit-torque magnetization rotational element101and a description thereof will be omitted.

The diffusion preventing layer14is inserted between the oxide containing layer12and the second ferromagnetic layer13. For example, the diffusion preventing layer is located between the oxide containing layer12and the second ferromagnetic layer13. For example, in a high-temperature environment such as when an annealing treatment is performed during the manufacturing of the spin-orbit-torque magnetization rotational element102, the diffusion preventing layer14prevents the element contained in the second ferromagnetic layer13from diffusing into the oxide containing layer12.

It is preferable that the diffusion preventing layer14contains a non-magnetic element. The non-magnetic element is, for example, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ti, Pt, or Au. The diffusion preventing layer14may contain one of these elements alone or may contain two or more of these elements in combination. Further, it is preferable that the thickness of the diffusion preventing layer14is twice or more the diameter of the element constituting the diffusion preventing layer14. When the non-magnetic element is formed with such a thickness, the non-magnetic element is strictly scattered like islands. Thus, the diffusion preventing layer14is a mixed layer of a part of the upper layer or the lower layer and a non-magnetic element.

It is preferable that the film thickness of the diffusion preventing layer14is in a range of 0.3 nm or more and 2.0 nm or less.

The spin-orbit-torque magnetization rotational element102can be manufactured similarly to the case of the spin-orbit-torque magnetization rotational element101except that the diffusion preventing layer14is laminated between the oxide containing layer12and the second ferromagnetic layer13. As a method of laminating the diffusion preventing layer14, known methods such as a sputtering method and a chemical vapor deposition (CVD) method can be used.

Since the spin-orbit-torque magnetization rotational element102with the above-described configuration includes the oxide containing layer12, the damping constant of the first ferromagnetic layer11and the second ferromagnetic layer13increases and the magnetization reversal is fast. Further, since the spin-orbit-torque magnetization rotational element102includes the diffusion preventing layer14, elements contained in the second ferromagnetic layer13hardly diffuses into the oxide containing layer12even in a high-temperature environment. For this reason, the oxide containing layer12is stable for a long period of time.

FIG. 3is a schematic cross-sectional view of a preferred example of a spin-orbit-torque type magnetoresistance effect element according to a second embodiment.FIG. 3shows a cross-section in which a spin-orbit-torque type magnetoresistance effect element200is cut along the xz plane passing through the center of the spin-orbit-torque wiring50of in the y direction. The spin-orbit-torque type magnetoresistance effect element200shown inFIG. 3includes the spin-orbit-torque magnetization rotational element101according to the first embodiment, a non-magnetic layer20, and a third ferromagnetic layer30. The same reference numerals will be given to the same components as those of the spin-orbit-torque magnetization rotational element101of the first embodiment and a description thereof will be omitted.

A functional unit40formed by laminating the laminated body10, the non-magnetic layer20, and the third ferromagnetic layer30functions similarly to the normal magnetoresistance effect element. The functional unit40functions by fixing the magnetization M30of the third ferromagnetic layer30in one direction (the z direction) and relatively changing the direction of the magnetization M13of the second ferromagnetic layer13. The magnetization M30of the third ferromagnetic layer30is harder to move than the magnetization M13of the second ferromagnetic layer13when the same external force is applied. In the case of the application to a coercive force difference type (pseudo spin valve type) MRAM, the coercive force of the third ferromagnetic layer30is made larger than the coercive force of the second ferromagnetic layer13. In the case of the application to an exchange bias type (spin valve type) MRAM, the magnetization M30of the third ferromagnetic layer30is fixed by the exchange coupling with the antiferromagnetic layer.

Further, in the functional unit40, when the non-magnetic layer20is made of an insulator, the functional unit40has the same configuration as a tunneling magnetoresistance (TMR) element. Further, when the non-magnetic layer20is made of metal, the functional unit40has the same configuration as a giant magnetoresistance (GMR) element.

As a laminated structure of the functional unit40, a laminated structure of a known magnetoresistance effect element can be adopted. For example, each layer of the functional unit40may include a plurality of layers. For example, the functional unit40may further include a layer other than the laminated body10, the non-magnetic layer20, and the third ferromagnetic layer30, such as an antiferromagnetic layer for fixing the magnetization direction of the third ferromagnetic layer30. The third ferromagnetic layer30may be called a fixed layer or a reference layer and the laminated body10may be called a free layer or a storage layer.

The third ferromagnetic layer30is a known material. For example, the third ferromagnetic layer is a metal selected from a group consisting of Cr, Mn, Co, Fe, and Ni and an alloy containing at least one metal selected from this group and exhibiting ferromagnetism. For the third metal layer30, an alloy containing these metals and at least one or more elements of B, C, and N can also be used in addition to these metals and alloys. For example, Co—Fe or Co—Fe—B can be used for the third ferromagnetic layer30.

Further, a Heusler alloy such as Co2FeSi may be used for the third ferromagnetic layer30. By using the Heusler alloy, the MR ratio of the functional unit40can be made higher. The Heusler alloy contains an intermetallic compound having a chemical composition of XYZ or X2YZ and X in the chemical composition of the Heusler alloy is a transition metal element or a noble metal element of the Co, Fe, Ni, or Cu group in the periodic table. Y in the chemical composition of the Heusler alloy is a transition metal from the Mn, V, Cr or Ti group or an element type of X. Z in the chemical composition of the Heusler alloy is a typical element of Group III to Group V. As the Heusler alloy, for example, Co2FeSi, Co2MnSi, Co2Mn1-aFeaAlbSi1-b, or the like can be used as the third ferromagnetic layer30.

It is preferable that the film thickness of the third ferromagnetic layer30is in a range of 0.5 nm or more and 5.0 nm or less.

In order to further increase the coercive force of the third ferromagnetic layer30with respect to the laminated body10, an antiferromagnetic material such as IrMn or PtMn may be provided in contact with the third ferromagnetic layer30. In order to prevent the leakage magnetic field of the third ferromagnetic layer30from affecting the laminated body10, a synthetic ferromagnetic coupling structure may be used.

Known materials can be used for the non-magnetic layer20.

For example, when the non-magnetic layer20is made of an insulator (in the case of a tunnel barrier layer), the non-magnetic layer20is, for example, Al2O3, SiO2, MgO, MgAl2O4, or the like. In addition, as the non-magnetic layer20, a material in which a part of Al, Si, and Mg is replaced by Zn, Be, or the like can be also used. Among them, when MgO or MgAl2O4is used as the non-magnetic layer20, a coherent tunnel can be realized, so that spin can be injected efficiently. When the non-magnetic layer20is made of metal, the non-magnetic layer20is, for example, Cu, Au, Ag, or the like. Further, when the non-magnetic layer20is made of a semiconductor, the non-magnetic layer20is, for example, Si, Ge, CuInSe2, CuGaSe2, Cu (In, Ga) Se2, or the like.

It is preferable that the film thickness of the non-magnetic layer20is in a range of 0.3 nm or more and 3.0 nm or less.

The functional unit40may further include other layers. For example, an underlayer may be provided between the laminated body10and the spin-orbit-torque wiring50or a cap layer may be provided on the surface opposite to the non-magnetic layer20in the third ferromagnetic layer30.

When a layer is disposed between the spin-orbit-torque wiring50and the first ferromagnetic layer11, it is preferable not to dissipate the spin propagating from the spin-orbit torque wiring50. For example, silver, copper, magnesium, aluminum, and the like are known to have a long spin diffusion length of 100 nm or more and are unlikely to dissipate spin. Accordingly, they can be suitably used. Further, it is preferable that the thickness of the layer disposed between the spin-orbit-torque wiring50and the first ferromagnetic layer11is the spin diffusion length or less of the material constituting this layer. When the thickness of the layer is the spin diffusion length or less, the spin propagated from the spin-orbit-torque wiring50can be sufficiently transmitted to the first ferromagnetic layer11.

The spin-orbit-torque type magnetoresistance effect element200reads or records data using a change in the resistance value of the functional unit caused by a difference in relative angle between the magnetization M13of the second ferromagnetic layer13and the magnetization M30of the third ferromagnetic layer30.

The spin-orbit-torque type magnetoresistance effect element200can be manufactured by laminating the non-magnetic layer20and the third ferromagnetic layer30in this order on the second ferromagnetic layer13of the spin-orbit-torque magnetization rotational element101. As a method of laminating the non-magnetic layer20and the third ferromagnetic layer30, known methods such as a sputtering method and a chemical vapor deposition (CVD) method can be used.

It is preferable that the obtained functional unit40is subjected to an annealing treatment. When the annealing treatment is performed, the crystallinity of each layer is improved and the MR ratio of the functional unit40can be increased.

Since the spin-orbit-torque type magnetoresistance effect element200with the above-described configuration includes the oxide containing layer12, the damping constant of the first ferromagnetic layer11and the second ferromagnetic layer13increases and the magnetization reversal is fast.

FIGS. 4 and 5are schematic cross-sectional views of a spin-orbit-torque type magnetoresistance effect element201according to Modified Example 1.FIG. 4shows a cross-section in which the spin-orbit-torque type magnetoresistance effect element201is cut along the xz plane passing through the center of the spin-orbit-torque wiring50in the y direction.FIG. 5shows a cross-section in which the spin-orbit-torque type magnetoresistance effect element201is cut along the yz plane passing through the center of the functional unit40in the x direction. The spin-orbit-torque type magnetoresistance effect element201shown inFIGS. 4 and 5are the same as the spin-orbit-torque type magnetoresistance effect element200except that the shape of the side surface of the functional unit40and the shape of a first surface50aof the spin-orbit-torque wiring50are different. For this reason, the same reference numerals will be given to the same components as those of the spin-orbit-torque type magnetoresistance effect element200and a description thereof will be omitted.

The functional unit40shown inFIGS. 4 and 5spreads within the xy plane as it goes toward the spin-orbit-torque wiring50when viewed from the z direction. When viewed from the z direction, the outer peripheral length or the outer diameter of the functional unit40increases as it goes toward the spin-orbit-torque wiring50. Further, the side surface40sof the functional unit40is inclined with respect to the xy plane when viewed from the x direction or the y direction. An inclination angle θ of the side surface40swith respect to the xy plane may be different or constant in accordance with the height position in the z direction. The inclination angle θ of the side surface40swith respect to the xy plane decreases, for example, as it goes toward the spin-orbit-torque wiring50.

The side surface40sof the functional unit40includes the side surfaces30s,20s,13s,12s,and11sof the third ferromagnetic layer30, the non-magnetic layer20, the second ferromagnetic layer13, the oxide containing layer12, and the first ferromagnetic layer11. The side surfaces11s,12s,13s,20s,and30sare respectively inclined with respect to the xy plane. The side surfaces11s,12s,13s,20s,and30sare respectively continuous so as to form one side surface40s. Here, “continuous” means that the inclination of a tangent drawn along the side surface40sis constant or changes continuously in a cut plane cut in the xz plane or the yz plane.

Further, the height position of the first surface50aof the spin-orbit-torque wiring50in the z direction is different depending on a location. The first surface50ais a surface near the functional unit40in the spin-orbit-torque wiring50. Hereinafter, a portion overlapping the functional unit40in the z direction in the first surface50ais referred to as a first surface50aA and a non-overlapping portion is referred to as a first surface50aB. The first surface50aA is located at a position in the +z direction in relation to the first surface50aB. That is, the first surface50aA is located at a position separated from a substrate Sub to be described later in relation to the first surface50aB. The first surface50aB may be formed at a position in the −z direction from the first surface50aA by ion milling or the like when the functional unit40is processed into a predetermined shape.

Further, as shown inFIG. 5, the side surface50sof the spin-orbit-torque wiring50is inclined with respect to the xy plane. The side surface50sand the side surface40sare, for example, discontinuous. “Discontinuous” means that the inclination of the tangent drawn along the side surfaces50sand40sdoes not change continuously in the cut plane cut in the xz plane or the yz plane. When processing the functional unit40into a predetermined shape after processing the spin-orbit-torque wiring50into a predetermined shape, the side surface50sand the side surface40smay be discontinuous.

Further,FIGS. 4 and 5simultaneously show insulating layers90and91surrounding the peripheries of the functional unit40and the spin-orbit-torque wiring50. The insulating layers90and91are insulating layers that insulate between multilayer wirings and between elements. The insulating layers90and91are made of, for example, silicon oxide (SiOx), silicon nitride (SiNx), silicon carbide (SiC), chromium nitride, silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al2O3), zirconium oxide (ZrOx), or the like.

In the spin-orbit-torque type magnetoresistance effect element201with the above-described configuration, since the damping constant of the first ferromagnetic layer11increases, the force of the magnetization M11to move in the easy magnetization direction increases and hence the magnetization reversal can be performed quickly. Further, since the side surface11sof the first ferromagnetic layer11is inclined with respect to the xy plane, the flow of the current from the spin-orbit-torque wiring50to the first ferromagnetic layer11is smooth. That is, the spin-orbit-torque type magnetoresistance effect element201can prevent a current loss due to a rapid change in current density.

FIG. 6is a schematic cross-sectional view of a spin-orbit-torque type magnetoresistance effect element202according to Modified Example 2.FIG. 6shows a cross-section in which the spin-orbit-torque type magnetoresistance effect element202is cut along the xz plane passing through the center of the spin-orbit-torque wiring50in the y direction. The spin-orbit-torque type magnetoresistance effect element202shown inFIG. 6is the same as the spin-orbit-torque type magnetoresistance effect element202according to Modified Example 1 except that the shape of the side surface of the functional unit40is different. For this reason, the same reference numerals will be given to the same components as those of the spin-orbit-torque type magnetoresistance effect element202and a description thereof will be omitted.

The functional unit40shown inFIG. 6gradually spreads within the xy plane as it goes toward the spin-orbit-torque wiring50when viewed from the z direction. The outer peripheral length or the outer diameter of each of the third ferromagnetic layer30, the second ferromagnetic layer13, and the first ferromagnetic layer11which are made of metal in the functional unit40shown inFIG. 6increases as it goes toward the spin-orbit-torque wiring50. The outer peripheral length or the outer diameter of each of the non-magnetic layer20and the oxide containing layer12which are made of a material other than metal in the functional unit40shown inFIG. 6decreases as it goes toward the spin-orbit-torque wiring50.

The side surfaces30s,13s,and11sof the third ferromagnetic layer30, the second ferromagnetic layer13, and the second ferromagnetic layer11are inclined by, for example, an inclination angle θ1with respect to the xy plane. The side surfaces20sand12sof the non-magnetic layer20and the oxide containing layer12are inclined by, for example, an inclination angle θ2with respect to the xy plane. The inclination angles θ1and θ2may be different or constant in accordance with the height position in the z direction. The inclination angle θ1and the inclination angle θ2are different from each other. The inclination angle θ1is, for example, less than 90° and the inclination angle θ2is, for example, 90° or more.

The side surface40sof the functional unit40is discontinuous. The side surface40sat the boundary of the side surfaces11s,12s,13s,20s,and30sof the layers is discontinuous. The side surface40shas, for example, a step at the boundary between the third ferromagnetic layer30and the non-magnetic layer20, the boundary between the non-magnetic layer20and the second ferromagnetic layer13, the boundary between the second ferromagnetic layer13and the oxide containing layer12, and the boundary between the oxide containing layer12and the first ferromagnetic layer11.

When forming the functional unit40, ion milling (side milling) or the like may be performed from the x direction or the y direction after processing from the z direction through a mask. When the side milling is performed, the width of the functional unit40in the x direction and the y direction can be decreased and hence the size of the functional unit40can be made fine. The degree of side milling depends on the material of the layer. Metals are often softer than non-metals and side milling may progress more with metals than with non-metals. Due to a difference in the degree of progress of the side milling of each layer, the side surface40sof the functional unit40becomes discontinuous.

A spin-orbit-torque type magnetoresistance effect element203with the above-described configuration can quickly perform the magnetization reversal since the damping constant of the first ferromagnetic layer11increases. Further, since the side surface11sof the ferromagnetic layer11is inclined with respect to the xy plane, the flow of the current from the spin-orbit-torque wiring50to the ferromagnetic conductor layer11is smooth. Furthermore, when the side surface40sis discontinuous, the adhesion to the insulating layer90can be improved.

Further,FIG. 7is a schematic cross-sectional view of an example of a spin-orbit-torque type magnetoresistance effect element according to Modified Example 2.FIG. 7shows a cross-section in which the spin-orbit-torque type magnetoresistance effect element202is cut along the xz plane passing through the center of the spin-orbit-torque wiring50in the y direction. A spin-orbit-torque type magnetoresistance effect element202A is an example when an inclination angle θ2is 90°.

FIG. 8is a schematic cross-sectional view of the spin-orbit-torque type magnetoresistance effect element203according to Modified Example 3.FIG. 8shows a cross-section in which the spin-orbit-torque type magnetoresistance effect element203is cut along the xz plane passing through the center of the spin-orbit-torque wiring50in the y direction. The spin-orbit-torque type magnetoresistance effect element203shown inFIG. 8is the same as the spin-orbit-torque type magnetoresistance effect element202shown inFIG. 6except that the positional relationship between the functional unit40and the spin-orbit-torque wiring50is different. For this reason, the same reference numerals will be given to the same components as those of the spin-orbit-torque type magnetoresistance effect element202and a description thereof will be omitted.

In the spin-orbit-torque type magnetoresistance effect element203, the spin-orbit-torque wiring50is located at a position in the +z direction with respect to the functional unit40. That is, the spin-orbit-torque wiring50is located at a position separated from the substrate Sub to be described in relation to the functional unit40.

The functional unit40includes the third ferromagnetic layer30, the non-magnetic layer20, the second ferromagnetic layer13, the oxide containing layer12, and the first ferromagnetic layer11in this order in the +z direction. The third ferromagnetic layer30is located at a position near the substrate Sub to be described later in relation to the first ferromagnetic layer11. The functional unit40may be called a bottom pin structure.

The spin-orbit-torque wiring50is laminated at the position of the functional unit40and the insulating layer90in the +z direction. The height positions of the first surface50aand the second surface50bof the spin-orbit-torque wiring50in the z direction are different depending on a location. The first surface50ais a surface near the functional unit40in the spin-orbit-torque wiring50and the second surface50bis a surface on the side opposite to the first surface50a. Hereinafter, a portion overlapping the functional unit40in the z direction in the first surface50ais referred to as a first surface50aA and a non-overlapping operation is referred to as a first surface50aB. Hereinafter, a portion overlapping the functional unit40in the z direction in the second surface50bis referred to as a second surface50bA and a non-overlapping portion is referred to as a second surface50bB. The first surface50aB is located at a position in the +z direction in relation to the first surface50aA. The first surface50aA is recessed in the −z direction with respect to the first surface50aB due to a difference in polishing speed when the first surface50ais subjected to, for example, chemical mechanical polishing (CMP). The second surface50aB is located at a position in the +z direction in relation to the second surface50aA. The second surface50breflects the shape of the first surface50a.

The spin-orbit-torque type magnetoresistance effect element203with the above-described configuration can quickly perform the magnetization reversal since the damping constant of the first ferromagnetic layer11increases even in the bottom pin structure.

The characteristic configurations of Modified Examples 1 to 3 can be also applied to the spin-orbit-torque magnetization rotational element according to the first embodiment.

FIG. 9is a schematic view of a magnetic memory300. The magnetic memory300includes a plurality of the spin-orbit-torque type magnetoresistance effect elements200(seeFIG. 3) of the first embodiment.FIG. 3corresponds to a cross-sectional view in which the spin-orbit-torque type magnetoresistance effect element200is cut along a plane A-A ofFIG. 9. In the magnetic memory300shown inFIG. 9, the spin-orbit-torque type magnetoresistance effect elements200are arranged in a 3×3 matrix.FIG. 9is an example of a magnetic memory and the configuration, number, and arrangement of the spin-orbit-torque type magnetoresistance effect element200are optional.

One of word lines WL1to WL3, one of bit lines BL1to BL3, and one of read lines RL1to RL3are respectively connected to the spin-orbit-torque type magnetoresistance effect element200.

When a voltage difference of a predetermined value or more is applied across the word lines WL1to WL3and the bit lines BL1to BL3, a current flows to the spin-orbit-torque wiring50of an arbitrary spin-orbit-torque type magnetoresistance effect element200so that a writing operation is performed. Further, when a voltage difference of a predetermined value or more is applied across the read lines RL1to RL3and the bit lines BL1to BL3, a current flows in the lamination direction of the functional unit40of an arbitrary spin-orbit-torque type magnetoresistance effect element200so that a reading operation is performed. When data of an arbitrary element is read out from the plurality of spin-orbit-torque type magnetoresistance effect elements200, the element can be used as a magnetic memory.

Further,FIG. 10is a cross-sectional view showing a main part of the magnetic memory300shown inFIG. 9when taken along a plane A-A. The magnetic memory300includes the spin-orbit-torque type magnetoresistance effect element200and a plurality of switching elements connected to the spin-orbit-torque type magnetoresistance effect element200.

The switching element shown inFIG. 10is a transistor Tr. The transistor Tr includes a gate electrode G, a gate insulating film GI, and a source region S and a drain region D formed on the substrate Sub. The substrate Sub is, for example, a semiconductor substrate.

Each transistor Tr is electrically connected to the spin-orbit-torque type magnetoresistance effect element200, the word line WL, and the bit line BL via a conductive portion Cw. The conductive portion Cw may be referred to as, for example, a connection wiring or a via wiring. The conductive portion Cw contains a conductive material. The conductive portion Cw extends in the z direction.

Further, the functional unit40of the spin-orbit-torque type magnetoresistance effect element200is provided with an electrode80. The electrode80contains a conductive material. The electrode80is connected to the read line RL. A switching element (for example, a transistor) may be provided between the read line RL and the electrode80. The switching element between the read line RL and the electrode80is located, for example, in the depth direction (−y direction) inFIG. 10.

The storage element100and the transistor Tr are electrically separated by the insulating layer90except for the conductive portion Cw.

The magnetic memory300according to the third embodiment includes a plurality of the spin-orbit-torque type magnetoresistance effect elements200according to the second embodiment. As described above, each spin-orbit-torque type magnetoresistance effect element200can quickly perform magnetization reversal. Thus, the magnetic memory300can be driven quickly.

REFERENCE SIGNS LIST

12Oxide containing layer

200Spin-orbit-torque type magnetoresistance effect element