JPWO2010143248A1 - Tunnel magnetoresistive element and random access memory using the same - Google Patents

Abstract

A magnetoresistive element using a perpendicular magnetization material and having a reduced write current density is provided. In the central portion of the recording layer 10, a region having a thickness smaller than that of the surrounding is formed. Alternatively, a region having an effective film thickness that functions as a ferromagnetic material is formed in the central portion of the recording layer thinner than the surroundings.

Description

  The present invention relates to a tunnel magnetoresistive effect element using a perpendicular magnetization material and a random access memory using the same.

  In recent years, MRAM (Magnetic Random Access Memory) has been developed as a memory using a magnetic material. The MRAM uses MTJ (Magnetic Tunneling Junction) that utilizes a tunneling magnetoresistive (TMR) effect as an element element, and records information by controlling the magnetization direction of a magnetic substance included in the MTJ element. Since the magnetization direction of the magnetic material does not change even when the power is turned off, a nonvolatile operation in which recorded information is retained can be realized. In order to change the magnetization direction (rewrite information) of the MTJ element, in addition to a method of applying a magnetic field from the outside, in recent years, a spin transfer torque magnetization reversal (spin injection magnetization) in which a direct current is passed through the MTJ element to reverse the magnetization. Inversion) method has been found. For example, Patent Document 1 discloses an MTJ element using an in-plane magnetization material as a recording layer and utilizing spin injection magnetization reversal and a memory in which the MTJ element is integrated: SPRAM (SPin-transfer torque Magnetic Random Access Memory).

  In order to improve the degree of integration of SPRAM, it is necessary to miniaturize the MTJ element. At that time, the thermal stability of magnetic information in the MTJ element becomes a problem. When the thermal energy due to the environmental temperature is higher than the magnetic energy necessary for reversing the magnetization direction of the recording layer of the MTJ element, magnetization reversal occurs without applying an external magnetic field or current. Since the magnetic energy of the MTJ element decreases as the size decreases, this thermal stability decreases as the element becomes finer. In order to maintain thermal stability even in a fine region and realize a highly reliable operation, it is effective to increase the magnetocrystalline anisotropy of the recording layer material of the MTJ element. So far, an MTJ element using a perpendicular magnetization material having higher magnetocrystalline anisotropy than an in-plane magnetization material has been disclosed (Patent Document 2). Further, in the MTJ element to which the perpendicular magnetization material is applied, the influence of the demagnetizing field applied in the recording layer is different from the in-plane magnetization MTJ element and works in the direction of reducing the current density required for the magnetization reversal (write current density). Therefore, compared with the in-plane magnetization MTJ element, there is an advantage that the write current density can be reduced and the power consumption can be suppressed.

  In order to further reduce the power consumption of the SPRAM to which the perpendicular magnetization MTJ element is applied, it is necessary to further reduce the write current density. When a perpendicular magnetic thin film forms a multi-domain structure, it is generally known that the magnetization of some magnetic domains is first reversed by current injection, and the magnetization of the entire magnetic thin film is reversed by propagation of the surrounding domain wall. ing. This magnetization reversal mechanism requires less current density for magnetization reversal than the magnetization reversal mechanism in which the magnetization of the ferromagnetic thin film rotates all at once. However, as the MTJ element is further miniaturized, the perpendicular magnetization thin film used for the recording layer has a single domain structure that does not include a domain wall, and the magnetization reversal becomes a simultaneous magnetization reversal mechanism, so that the write current density increases.

On the other hand, regarding a method of reversing the magnetization of the recording layer of the MTJ element by an external magnetic field instead of current injection, a configuration for lowering the write magnetic field is disclosed. For example, in Patent Document 3, a region having a smaller coercive force than the central portion is provided in the outer peripheral portion of the recording layer, and the magnetization of the outer peripheral portion is first reversed when an external magnetic field is applied, and the magnetization reversal of the central portion is performed by the leakage magnetic field. Shows how to assist.
JP 2002-305337 A JP 2003-142364 A JP 2002-299727 A

  In view of the above-described problems, an object of the present invention is to provide a perpendicular magnetization MTJ element that can reduce a write current as compared with the prior art. Further, it is an object of the present invention to provide a perpendicular magnetization MTJ element that can reduce a write current even in a very fine region in which a recording layer has a single magnetic domain structure.

  When the spin injection magnetization reversal method is used, the reversal of the magnetization at the central portion prior to the outer peripheral portion of the recording layer facilitates the propagation of the domain wall described above, so that the efficiency of the magnetization reversal is good. Furthermore, as in Patent Document 3, it is necessary to lower the resistance of the outer peripheral portion from the central portion in order to reverse the magnetization of the outer peripheral portion first, but normally the outer peripheral portion is exposed to an ion beam during the MTJ element shape processing. High resistance. Therefore, it is difficult to reverse the magnetization of the outer peripheral portion before the central portion by current injection.

  In the present invention, a structure in which a part of the magnetic thin film used as the recording layer of the MTJ element is made thinner than the periphery thereof is applied. Alternatively, a structure in which the magnetic moment per unit area of a partial region of the magnetic thin film used as the recording layer is reduced from the surroundings is applied.

  More specifically, the tunnel magnetoresistive element of the present invention includes a recording layer made of a perpendicular magnetization film, a fixed layer made of a perpendicular magnetization film, a nonmagnetic layer disposed between the recording layer and the fixed layer, A pair of electrode layers is formed in contact with each of the recording layer and the fixed layer, and flows a current for reversing the magnetization direction of the recording layer in the element film thickness direction. The recording layer includes at least one of a first region and a second region, and the magnetic moment per unit area in the first region is lower than the magnetic moment per unit area in the second region, and the outer periphery of the recording layer The ratio of the second area to the portion is larger than the ratio of the first area.

  By applying the element structure of the present invention, the write current density in the perpendicular magnetization MTJ element can be further reduced as compared with the prior art. Furthermore, even if the magnetic thin film of the recording layer is a very fine element having a single magnetic domain structure, an increase in write current density can be suppressed.

It is a schematic diagram of the MTJ element of Example 1, (A) is a cross-sectional schematic diagram, (B) is a top schematic diagram. FIG. 5 is a diagram showing a manufacturing process of the MTJ element of Example 1. FIG. 3 is a diagram schematically showing a magnetization reversal mechanism of the MTJ element of Example 1. It is a schematic diagram of the MTJ element of Example 2, (A) is a cross-sectional schematic diagram, (B) is a top schematic diagram. It is a schematic diagram of the MTJ element of Example 3, (A) is a cross-sectional schematic diagram, (B) is a top schematic diagram. It is a schematic diagram of the MTJ element of Example 4, (A) is a cross-sectional schematic diagram, (B) is an upper surface schematic diagram. 6 is a schematic cross-sectional view of an MTJ element of Example 5. FIG. FIG. 10 is a view showing a manufacturing process of the MTJ element of Example 5. 6 is a schematic cross-sectional view of an MTJ element according to Example 6. FIG. It is a cross-sectional schematic diagram which shows the structural example of a magnetic memory cell. It is a schematic diagram which shows the structural example of a random access memory.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the MTJ element described in the embodiment of the present invention, the magnetization of the recording layer is reversed by utilizing the mechanism of spin injection magnetization reversal. That is, a current is passed through the element, and the spin of the spin-polarized current gives a torque to the magnetic moment of the magnetic recording layer, thereby reversing the magnetization of the recording layer.

<Example 1>
FIG. 1 is a schematic diagram of an MTJ element in Example 1. 1A is a schematic cross-sectional view, and FIG. 1B is a schematic top view. The element is configured by laminating a lower electrode layer 21, a ferromagnetic fixed layer 11, a nonmagnetic layer 23, a ferromagnetic recording layer 10, and an upper electrode layer 22 on a substrate 20. The element is circular with a diameter W when viewed from above. The magnetizations of the recording layer 10 and the fixed layer 11 are perpendicular to the film surface. The material and film thickness of the recording layer 10 and the fixed layer 11 are set so that the magnetization of the recording layer 10 is reversed before the magnetization of the fixed layer 11 when a spin-polarized current is passed. In this embodiment, the recording layer 10 and the fixed layer 11 are made of the same ferromagnetic material, and the recording layer 10 is made thinner than the fixed layer 11. Further, a concave region (region 1) having a smaller film thickness than the periphery was formed in the central portion of the recording layer 10. That is, the concave-shaped region 1 has a smaller magnetic moment m ₀ per unit area than the other region 2 (m ₀ = M _S · t, M _S : saturation magnetization, t: film thickness). Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

In Example 1, using the L1 ₀ type Co ₅₀ Pt ₅₀ ordered alloy in the material of the fixed layer 11 and the recording layer 10. Further, a laminated film made of Ta, Ru, Pt was used for the lower electrode layer 21, and a laminated film made of Ta, Ru was used for the upper electrode layer 22. Further, magnesium oxide (MgO) was used for the nonmagnetic layer 23. The recording layer 10 has a thickness t ₀ of 3 nm, the fixed layer 11 has a thickness t ₁ of 10 nm, and the nonmagnetic layer 23 has a thickness of 1 nm. The diameter W of the element was 30 nm, and the diameter D of the concave portion provided in the center of the recording layer 10 was 10 nm.

A method for manufacturing the MTJ element of Example 1 will be described. FIG. 2 shows a manufacturing process of the element. Hereinafter, description will be made in accordance with the order of steps shown in FIGS. 2 (A) to 2 (H). First, a laminated film 25 in which a lower electrode layer 21, a fixed layer 11, a nonmagnetic layer 23, a recording layer 10, and an upper electrode layer 22 were laminated in this order was formed on a substrate 20 (FIG. 2A). A thin film was formed by sputtering, and all layers were formed in-situ. Thereafter, the laminated film 25 was processed into a pillar shape by using electron beam (EB) lithography and ion beam etching (FIG. 2B). Next, Al ₂ O ₃ was deposited as an interlayer insulating layer 52 with the resist pattern 51 remaining on the pillar surface (FIG. 2C). Thereafter, the resist on the pillar surface was removed by lift-off to expose the pillar surface (FIG. 2D).

  Subsequently, a resist was applied from above the exposed pillar, and a resist pattern having an opening at the center upper part of the pillar was formed by EB lithography (FIG. 2E). In this state, the upper electrode layer 21 and part of the recording layer 10 were removed by etching with an ion beam (FIG. 2F). The depth h for etching the central portion of the recording layer 10 was 1 nm. After etching, Ru and Ta to be the additional upper electrode layer 26 were deposited in-situ by sputtering to cover the upper part of the pillar (FIG. 2G). After that, patterning was performed using EB lithography and ion beam etching, leaving only the upper electrode layer 21 above the pillar, thereby completing the MTJ element (FIG. 2 (H)). Finally, the device was annealed at a temperature of 300 ° C. For example, a nanoimprint technique may be used for forming the resist pattern 51 as a technique other than the EB lithography.

  Next, the rewriting operation of the recording layer in the MTJ element of Example 1 will be described. It is assumed that the magnetization of the fixed layer 11 is fixed in the upper direction of the element. When the magnetization of the recording layer 10 has an antiparallel arrangement in the opposite direction to the magnetization of the fixed layer 11, when a current is passed from the upper part to the lower part of the MTJ element, spin-polarized electrons are transferred from the fixed layer 11. The magnetization of the recording layer 10 is reversed by flowing into the recording layer 10 and reversing the spin injection magnetization. That is, the magnetization of the fixed layer 11 and the magnetization of the recording layer 10 are arranged in parallel, and the resistance of the MTJ element is switched from the high resistance state to the low resistance state. On the other hand, when the magnetization of the recording layer 10 has a parallel arrangement in the same direction as the magnetization of the fixed layer 11, when a current is passed from the lower part to the upper part of the MTJ element, spin-polarized electrons are generated. And flows to the fixed layer 11. At that time, only electrons having a spin in the same direction as the spin of the fixed layer 11 flow into the fixed layer 11, and the electrons having a spin in the reverse direction are reflected on the surface of the insulator 23. The reflected electrons act on the magnetization of the recording layer 10, and the magnetization of the recording layer 10 is reversed by spin injection magnetization reversal. That is, the magnetization of the fixed layer 11 and the magnetization of the recording layer 10 become an antiparallel arrangement, and the resistance of the MTJ element is switched from the low resistance state to the high resistance state.

In Example 1, the thickness of the central portion of the recording layer 10 is reduced. Therefore, the magnetization reversal of the recording layer 10 proceeds as follows. First, consider a state in which the magnetization of the recording layer faces the upper side of the film surface (FIG. 3A). When spin-polarized electrons are caused to flow from the upper side to the lower side of the element, first, magnetization reversal occurs in the central region where the film thickness is thin (FIG. 3B). That is, a magnetization reversal nucleus is formed. At that time, a domain wall 35 is formed around the central portion where the magnetization is reversed in the recording layer 10. The formed domain wall 35 propagates toward the outer periphery of the element (FIG. 3C), and finally the magnetization of the entire recording layer is reversed (FIG. 3D). In the conventional MTJ element, the film thickness of the recording layer 10 is uniform, and in the case of the same size as in the first embodiment, a single magnetic domain structure is formed. Therefore, the magnetization rotates all over the entire area of the recording layer 10. In contrast to such a simultaneous rotation mechanism, in the MTJ element of the first embodiment, a region where the magnetization is easily reversed is provided in the central portion, and if the magnetization is reversed, the entire magnetization is reversed by propagation of the domain wall. That is, in the MTJ element of Example 1, the current density (J _C0 ) at which magnetization reversal starts can be reduced as compared with the conventional structure in which no concave region is provided in the recording layer, and power consumption can be reduced. As a result of evaluating the prototype MTJ element of Example 1, it was possible to reduce the write current to about 50% as compared with a perpendicular magnetization MTJ element having a conventional structure in which no concave region was provided in the recording layer.

The width δ of the domain wall depends on the crystal anisotropy energy Ku of the magnetic material and is proportional to 1 / √Ku. In the case of a CoPt ordered alloy having a high crystal anisotropy energy Ku of about 10 ⁷ erg / cm ² , the domain wall width δ is about 5 to 10 nm. In order to form a domain wall in the recording layer 10 by current injection, it is desirable that the diameter D (10 nm) of the concave region is equal to or larger than the domain wall width δ. In Example 1, the diameter D of the concave region of the recording layer is 10 nm. However, in order to obtain the same effect as in this example, it is preferably 5 nm or more at the minimum. Furthermore, in order to perform rewriting utilizing nucleation of magnetization reversal and domain wall propagation, the diameter W of the recording layer is W> D + 2δ using the diameter D of the concave region and the width δ of the domain wall of the ferromagnetic material. It is desirable. In this embodiment, the diameter W of the recording layer is 30 nm, the diameter D of the concave region is 10 nm, and the domain wall width δ is about 5 to 10 nm, which satisfies this relationship.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 1, the film thickness of the central concave region is 2 nm with respect to the film thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in order to obtain a superior J _C0 reduction effect over the MTJ element having the conventional configuration in which the concave region is not provided in the recording layer in consideration of the distribution of the write current density for each device, the film of the concave region in the recording layer 10 is obtained. It is desirable that the thickness be at least about 80% of the circumference.

In Example 1, as a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also in Example 1 by applying other perpendicularly magnetized material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

  In Embodiment 1, a circular concave area is formed in the circular recording layer, but the shape of the concave area may be a square shape other than a circular shape.

  In the first embodiment, an element having an extremely fine size in a region where the recording layer 10 has a single magnetic domain structure is proposed. However, the present invention can be applied to an element having a larger size. For example, in an MTJ element having a diameter of 100 nm when viewed from above, even in a conventional structure in which no concave region is provided in the recording layer, a magnetic domain is formed in the recording layer when the magnetization is reversed by current injection, and the recording layer is propagated by the propagation of the domain wall. The entire magnetization is reversed. Even with such an element size, an MTJ element with a thin film thickness at the central portion of the recording layer to which the present invention is applied can induce the generation of magnetization reversal nuclei, and the write current density is lower than that of a conventional element that does not provide a concave region in the recording layer. Needless to say, it can be further reduced.

<Example 2>
Example 2 proposes a rectangular perpendicular magnetization MTJ element. FIG. 4 shows a schematic cross-sectional view and a top view of the MTJ element of Example 2. The basic structure of the element, the structure and material of the laminated film, and the film thickness of each layer are the same as in Example 1. The element of Example 2 has a square shape when viewed from above, and as shown in FIG. 4, a region having a smaller film thickness than the surroundings is provided in the center of the recording layer 10 (film thickness t ₀ : 3 nm). One side A of the element was 30 nm, one side B of the concave portion provided in the center of the recording layer 10 was 10 nm, and the groove depth h of the concave portion was 1 nm. Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

  The rewriting operation and the magnetization reversal mechanism of the MTJ element of Example 2 are the same as those of Example 1. In the recording layer 10, magnetization reversal occurs from a thin central portion, and magnetization of the entire recording layer 10 is reversed by domain wall movement. Thereby, the write current density can be reduced as compared with a perpendicular magnetization MTJ element having a conventional structure in which no concave region is provided in the recording layer.

  In order to form a domain wall in the recording layer 10 by current injection, it is desirable that one side B of the concave region has a size equal to or greater than the width δ of the domain wall. In Example 2, one side B of the concave region of the recording layer is 10 nm. However, in order to obtain the same effect as in this example, it is desirable that the minimum is 5 nm or more. Further, in order to perform rewriting utilizing nucleation of magnetization reversal and domain wall propagation, one side A of the recording layer is A> B + 2δ using one side B of the concave region and the domain wall width δ of the ferromagnetic material. It is desirable. In this embodiment, one side A of the recording layer is 30 nm, one side B of the concave region is 10 nm, and the domain wall width δ is about 5 to 10 nm, which satisfies this relationship.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 2, the thickness of the central concave region was set to 2 nm with respect to the thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in order to obtain a superior J _C0 reduction effect over the MTJ element having the conventional configuration in which the concave region is not provided in the recording layer in consideration of the distribution of the write current density for each device, the film of the concave region in the recording layer 10 is obtained. It is desirable that the thickness be at least about 80% of the circumference.

In Example 2, as a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also in Example 2 by applying the other perpendicular magnetization material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

  In the second embodiment, the quadrangular concave area is formed in the quadrangular recording layer. However, the concave area may have a shape other than the square, for example, a circle.

<Example 3>
Example 3 proposes a quadrangular perpendicular magnetization MTJ element as in Example 2. FIG. 5 shows a schematic cross-sectional view and a top view of the MTJ element of Example 3. The basic structure of the element, the configuration and material of the laminated film, and the film thickness of each layer are the same as in the first and second embodiments. The element of Example 3 has a quadrangular shape when viewed from above. As shown in FIG. 5, a region having a thinner film thickness than the surroundings is provided in the center of the recording layer 10. As shown in the top view of FIG. 5B, the concave portion region is connected from one side of the element outer periphery to the opposite side. One side A of the element was 30 nm, and the width B of the concave portion provided in the center of the recording layer 10 was 10 nm. Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

  The rewriting operation and the magnetization reversal mechanism of the MTJ element of Example 3 are the same as those of Example 1. In the recording layer 10, magnetization reversal occurs from a thin central portion, and magnetization of the entire recording layer 10 is reversed by domain wall movement. As a result, the write current density can be reduced as compared with a conventional perpendicular magnetization MTJ element in which no concave region is provided in the recording layer.

  In order to form a domain wall in the recording layer 10 by current injection, it is desirable that the width B of the concave region is equal to or greater than the width δ of the domain wall. In Example 3, the width B of the concave region of the recording layer was 10 nm. However, in order to obtain the same effect as in this example, it is desirable that the width be at least 5 nm. Further, in order to perform rewriting utilizing nucleation of magnetization reversal and domain wall propagation, one side A of the recording layer is A> B + 2δ using one side B of the concave region and the domain wall width δ of the ferromagnetic material. It is desirable. In this embodiment, one side A of the recording layer is 30 nm, one side B of the concave region is 10 nm, and the domain wall width δ is about 5 to 10 nm, which satisfies this relationship.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 3, the film thickness of the central concave region was set to 2 nm with respect to the film thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in order to obtain a superior J _C0 reduction effect over the MTJ element having the conventional configuration in which the concave region is not provided in the recording layer in consideration of the distribution of the write current density for each device, the film of the concave region in the recording layer 10 is obtained. It is desirable that the thickness be at least about 80% of the circumference.

In Example 3, as a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also in Example 3 by applying other perpendicularly magnetized material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

<Example 4>
Example 4 proposes a perpendicular magnetization MTJ element having a plurality of concave portions. FIG. 6 shows a schematic cross-sectional view and a top view of the MTJ element of Example 4. The basic structure of the element, the configuration and material of the laminated film, and the film thickness of each layer are the same as in Example 3. In the case of Example 4, a plurality of concave portions are formed. The side A of the element was 100 nm, and the width B of the concave region provided in the recording layer 10 was 10 nm. Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

  The rewriting operation and the magnetization reversal mechanism of the MTJ element of the fourth embodiment are basically the same as those of the first embodiment. Magnetization reversal occurs from the two thin portions provided in the recording layer 10, and magnetization of the entire recording layer 10 is reversed by domain wall movement. As a result, the write current density can be reduced as compared with a conventional perpendicular magnetization MTJ element in which no concave region is provided in the recording layer.

  In order to form a domain wall in the recording layer 10 by current injection, it is desirable that the width B of the concave region is equal to or greater than the width δ of the domain wall. In Example 4, the width B of the concave region of the recording layer is 10 nm. However, in order to obtain the same effect as in this example, it is desirable that the width be at least 5 nm.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 4, the film thickness of the central concave region was 2 nm with respect to the film thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in order to obtain a superior J _C0 reduction effect over the MTJ element having the conventional configuration in which the concave region is not provided in the recording layer in consideration of the distribution of the write current density for each device, the film of the concave region in the recording layer 10 is obtained. It is desirable that the thickness be at least about 80% of the circumference.

In Example 4, as a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also in Example 4 by applying the other perpendicular magnetization material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

<Example 5>
Example 5 proposes an MTJ element that realizes nucleation of magnetization reversal in a recording layer by controlling physical properties, not the shape of the recording layer. FIG. 7 is a schematic cross-sectional view of the MTJ element in Example 5. The basic structure of the element is the same as that of the first embodiment. The recording layer 10 and the fixed layer 11 were made of a Co ₅₀ Pt ₅₀ alloy, which is a perpendicularly magnetized ferromagnetic material, and MgO was used for the nonmagnetic layer 23. In Example 5, as illustrated in FIG. 7, the upper electrode layer 22 includes a first cap layer 41 and a second cap layer 42. The first cap layer 41 is disposed substantially at the center of the recording layer 10, and the second cap layer 42 is disposed around the first cap layer 41. The first cap layer 41 was Ti, and Pt was used for the second cap layer 42. A reaction region 43 is formed in the recording layer 10 by reaction with the first cap layer 41.

The recording layer 10 has a thickness t ₀ of 3 nm, the fixed layer 11 has a thickness t ₁ of 10 nm, and the nonmagnetic layer 23 has a thickness of 1 nm. The diameter W of the element was 30 nm, and the diameter D of the first cap layer 41 was 10 nm. Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

A device manufacturing method of Example 5 will be described. FIG. 8 shows a manufacturing process of the element. Hereinafter, description will be made in accordance with the order of steps shown in FIGS. First, a laminated film 25 in which the lower electrode layer 21, the fixed layer 11, the nonmagnetic layer 23, the recording layer 10, and the first cap layer 41 were laminated in this order was formed on the substrate 20 (FIG. 8A). A thin film was formed by sputtering, and all layers were formed in-situ. Thereafter, the laminated film 25 was processed into a pillar shape by using electron beam (EB) lithography and ion beam etching (FIG. 8B). Next, Al ₂ O ₃ was deposited as an interlayer insulating layer 52 with the resist 51 remaining on the pillar surface (FIG. 8C). Thereafter, the resist on the pillar surface was removed by lift-off to expose the pillar surface (FIG. 8D). Subsequently, a resist was applied from above the exposed pillar, and a resist pattern 51 was formed at a part of the center of the pillar by EB lithography (FIG. 8E). In this state, the first cap layer 41 was etched using the ion beam 53 (FIG. 8F). Thereafter, the resist pattern was removed (FIG. 8G), and Pt as the second cap layer 42 was laminated on the pillar of the laminated film 25 (FIG. 8H). Subsequently, the second cap layer 42 was processed into the shape of the upper electrode layer by using EB lithography and ion beam etching (FIG. 8I). Finally, the device was annealed at a temperature of 400 ° C. to form a reaction region 43 to complete the MTJ device (FIG. 8J). In this embodiment, the EB lithography is used for forming the resist pattern. However, for example, a nanoimprint technique may be used as another pattern technique.

  Since the reaction region 43 in the recording layer 10 does not behave as a ferromagnet, the recording layer 10 is substantially equivalent to a thin central portion as in the first embodiment. Therefore, when a current is passed through the element to reverse the magnetization, the same mechanism as that of the element of Example 1 works. That is, first, the magnetization of the central portion is reversed, the domain wall formed around the center is propagated toward the outer periphery, and the magnetization of the entire recording layer 10 is reversed. With this magnetization reversal mechanism, the current density required for rewriting magnetic information can be reduced as compared with the conventional MTJ element in which the recording layer is not provided with the concave region, as in the first embodiment.

  In order to form a domain wall in the recording layer 10 by current injection, it is desirable that the diameter D of the first cap layer 41 be equal to or greater than the domain wall width δ. In the fifth embodiment, the diameter D of the first cap layer 41 is 10 nm. However, in order to obtain the same effect as that of the present embodiment, it is desirable that the diameter is at least 5 nm.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 5, the depth h of the central reaction region 43 is about 1 nm with respect to the film thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in order to obtain a superior J _C0 reduction effect with respect to the MTJ element having the conventional configuration in which the recording layer is not provided with the concave region in consideration of the variation distribution of the write current density for each element, the reaction is performed in the central portion of the recording layer 10. It is desirable that the film thickness not including the region 43 (t ₀ -h) be at least about 80% of the surrounding film thickness (t ₀ ).

In Example 5, as a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also Example 5 by applying other perpendicularly magnetized material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

  In the fifth embodiment, Ti and Pt are used as a combination of materials for the first cap layer 41 and the second cap layer 42. However, other materials may be used. For example, Ta or Ru may be used as the second cap layer 42.

  In the fifth embodiment, the quadrangular reaction region 43 is formed in the quadrangular recording layer. However, the reaction region 43 may have a shape other than the quadrangle, such as a circle.

<Example 6>
Example 6 proposes an MTJ element that realizes nucleation of magnetization reversal in a recording layer by controlling the crystallinity rather than the shape of the recording layer. FIG. 9 is a schematic cross-sectional view of the MTJ element in Example 6. The basic structure of the element is the same as that of the first embodiment. The recording layer 10 and the fixed layer 11 were made of a Co ₅₀ Pt ₅₀ alloy, which is a perpendicularly magnetized ferromagnetic material, and MgO was used for the nonmagnetic layer 23. In Example 6, a modified region 44 is included in the recording layer 10 as shown in FIG. The modified region 44 is a region made amorphous. The film thickness t ₀ of the recording layer 10 was 3 nm, the film thickness t ₁ of the fixed layer 11 was 10 nm, and the film thickness of the nonmagnetic layer 23 was 1 nm. The diameter W of the element was 30 nm, and the diameter D of the modified region 44 was 10 nm. Although not shown in the drawing, the upper electrode layer 22 and the lower electrode layer 21 are connected to wirings for supplying current to the element.

  A device manufacturing method of Example 6 will be described. The manufacturing method is basically the same as that of the device of Example 1 shown in FIG. However, this is different after the pillars of the laminated film 25 are formed and the resist pattern 51 on the pillar surface is removed by lift-off. In Example 6, with the surface of the pillar exposed (FIG. 2D), a focused ion beam is irradiated from the upper center of the recording layer 10 to modify the crystal structure of the central portion of the recording layer 10. Thereafter, the upper electrode layer 22 was formed and processed by EB lithography and ion beam etching to complete the MTJ element. Finally, heat treatment was performed at a temperature of 300 ° C.

  The modified region 44 in the recording layer 10 has a different crystal structure from the other regions, and the crystal structure is amorphous. Since the amorphous region does not generate perpendicular magnetization, it is substantially equivalent to a reduction in the thickness of the central portion of the recording layer 10 as in the first embodiment. Therefore, when a current is passed through the element to reverse the magnetization, the same mechanism as that of the element of Example 1 works. That is, first, the magnetization of the central portion is reversed, the domain wall formed around the center is propagated toward the outer periphery, and the magnetization of the entire recording layer 10 is reversed. With this magnetization reversal mechanism, the current density required for rewriting magnetic information can be reduced as compared with the conventional MTJ element in which the recording layer is not provided with the concave region, as in the first embodiment.

  In order to form a domain wall in the recording layer 10 by current injection, the diameter D of the modified region 44 is desirably equal to or greater than the domain wall width δ. In Example 6, the diameter D of the modified region 44 is 10 nm. However, in order to obtain the same effect as in this example, it is desirable that the diameter be 5 nm or more at the minimum.

The write current density of the perpendicular magnetization MTJ element is represented by J _C0 ∝ (M _S H _k −4πM _S ² ) · t (M _S : saturation magnetization of the recording layer material, H _k : different of the recording layer material) Isotropic magnetic field, t: film thickness of recording layer). That is, the current density required for magnetization reversal is proportional to the thickness of the recording layer. In Example 6, the thickness h of the central modified region 44 is about 1 nm with respect to the thickness t ₀ = 3 nm of the recording layer 10, but the same effect can be obtained with other dimensions. However, in view of the variation distribution of the write current density for each element, in order to obtain a superior J _C0 reduction effect with respect to the MTJ element having the conventional configuration in which the concave region is not provided in the recording layer, the recording layer 10 is modified in the central portion. It is desirable that the film thickness (t ₀ -h) not including the quality region 44 be at least about 80% or less of the surrounding film thickness (t ₀ ).

In Example 6, a perpendicular magnetization material of the recording layer 10 and the fixed layer 11, L1 ₀ type is applied the Co ₅₀ Pt ₅₀ ordered alloy, the same as also Example 6 by applying the other perpendicular magnetization material Needless to say, an effect can be obtained. Specific materials, for example, L1 ₁ type CoPt ordered alloy, m-D0 ₁₉ type Co ₇₅ Pt ₃₅ ordered alloy, L1 ₀ type ordered alloy such as Fe ₅₀ Pt ₅₀ or,, CoCrPt-SiO _2, FePt- A granular structure material in which a granular magnetic material such as SiO ₂ is dispersed in a non-magnetic matrix, or an alloy containing one or more of Fe, Co, Ni, and Ru, Pt, Rh, Pd, A laminated film in which nonmagnetic metals such as Cr are alternately laminated, or an amorphous alloy containing a transition metal in a rare earth metal such as Gd, Dy, or Tb such as TbFeCo or GdFeCo may be used.

  In Embodiment 6, the quadrangular modified region 44 is formed in the quadrangular recording layer. However, the modified region 44 may have a shape other than the quadrangle, such as a circle.

<Example 7>
The seventh embodiment proposes a random access memory to which the MTJ element according to the present invention is applied. FIG. 10 is a schematic cross-sectional view showing a configuration example of a magnetic memory cell according to the present invention. This magnetic memory cell 100 is equipped with the MTJ element 110 shown in the first to sixth embodiments.

  The C-MOS 111 includes two n-type semiconductors 112 and 113 and one p-type semiconductor 114. An electrode 121 serving as a drain is electrically connected to the n-type semiconductor 112, and is connected to the ground via the electrode 141 and the electrode 147. An electrode 122 serving as a source is electrically connected to the n-type semiconductor 113. Further, 123 is a gate electrode, and ON / OFF of the current between the source electrode 122 and the drain electrode 121 is controlled by ON / OFF of the gate electrode 123. An electrode 145, an electrode 144, an electrode 143, an electrode 142, and an electrode 146 are stacked on the source electrode 122, and the lower electrode 11 of the MTJ element 110 is connected via the electrode 146.

  The bit line 222 is connected to the upper electrode 22 of the MTJ element 110. In the magnetic memory cell of the present embodiment, magnetic information is recorded by rotating the magnetization direction of the recording layer of the MTJ element 110 by the current flowing through the MTJ element 110, that is, the spin transfer torque. The spin transfer torque is not a spatial external magnetic field, but is mainly a principle that spins of a spin-polarized current flowing in the MTJ element give torque to the magnetic moment of the ferromagnetic free layer of the MTJ element. Accordingly, the MTJ element is provided with means for supplying current from the outside, and spin transfer torque magnetization reversal is realized by flowing current using the means. In this embodiment, the direction of magnetization of the recording layer 110 is controlled by passing a current between the bit line 222 and the electrode 146.

  FIG. 11 is a diagram showing a configuration example of a magnetic random access memory in which the magnetic memory cell 100 is arranged. A word line 223 and a bit line 222 connected to the gate electrode 123 are electrically connected to the memory cell 100. By disposing the magnetic memory cell 100 including the MTJ element described in the first to sixth embodiments, the magnetic memory uses the in-plane magnetization MTJ element or the conventional perpendicular magnetization MTJ element in which no concave region is provided in the recording layer. Operation with lower power consumption than memory is possible, and a gigabit-class high-density magnetic memory can be realized.

In writing in this configuration, first, a write enable signal is sent to the write driver connected to the bit line 222 to which a current is to be supplied to boost the voltage, and a predetermined current is supplied to the bit line 222. Depending on the direction of the current, either the write driver 230 or the write driver 231 is dropped to the ground, and the current direction is controlled by adjusting the potential difference. Next, after a predetermined time has elapsed, a write enable signal is sent to the write driver 232 connected to the word line 223 to boost the write driver 232 and turn on the transistor connected to the MTJ element to be written. As a result, a current flows through the MTJ element, and spin torque magnetization reversal is performed. After the transistor is turned on for a predetermined time, the signal to the write driver 232 is disconnected and the transistor is turned off. At the time of reading, only the bit line 222 connected to the MTJ element to be read is boosted to the reading voltage V, only the selection transistor is turned on, and a current is supplied to perform reading. Since this structure is the simplest arrangement of 1 transistor + 1 memory cell, the area occupied by the unit cell can be made highly integrated with 2F × 4F = 8F ² .

  DESCRIPTION OF SYMBOLS 10 ... Recording layer, 11 ... Fixed layer, 20 ... Substrate, 21 ... Lower electrode layer, 22 ... Upper electrode layer, 23 ... Nonmagnetic layer, 25 ... Multilayer film, 26 ... Additional upper electrode layer, 35 ... Domain wall, 41 ... 1st cap layer, 42 ... 2nd cap layer, 43 ... Reaction region, 44 ... Modified region, 51 ... Resist pattern, 52 ... Interlayer insulating layer, 53 ... Ion beam, 100 ... Memory cell, 110 ... MTJ Element, 111... C-MOS, 112, 113... N-type semiconductor, 114... P-type semiconductor, 121... Source electrode, 122... Drain electrode, 123 ... Gate electrode, 141 to 147. Bit line, 223 ... word line, 230, 231, 232 ... write driver

Claims (13)

A recording layer made of a perpendicular magnetization film;
A fixed layer made of a perpendicular magnetization film;
A nonmagnetic layer disposed between the recording layer and the fixed layer;
A pair of electrode layers, formed in contact with each of the recording layer and the fixed layer, for passing a current for reversing the magnetization direction of the recording layer in the element film thickness direction;
The recording layer includes at least one of a first region and a second region, and a magnetic moment per unit area in the first region is lower than a magnetic moment per unit area in the second region,
The tunnel magnetoresistive element according to claim 1, wherein a ratio of the second region to an outer peripheral portion of the recording layer is larger than a ratio of the first region.   2. The tunnel magnetoresistive element according to claim 1, wherein the second region of the recording layer is disposed so as to surround the first region.   2. The tunnel magnetoresistive element according to claim 1, wherein the film thickness of the first region of the recording layer is smaller than the film thickness of the second region of the recording layer. element.   2. The tunnel magnetoresistive effect according to claim 1, wherein the saturation magnetization of the first region of the recording layer is lower than the saturation magnetization of the second region of the recording layer. element.   5. The tunnel magnetoresistive element according to claim 4, wherein the first region of the recording layer includes a region having a crystal structure different from that of the second region.   2. The tunnel magnetoresistive effect element according to claim 1, wherein the minimum side length W of the recording layer is D as the minimum side length of the first region of the recording layer and δ is the width of the domain wall of the material constituting the recording layer. A tunnel magnetoresistive effect element satisfying W> D + 2δ.   2. The tunnel magnetoresistive element according to claim 1, wherein both or one of the perpendicular magnetization films constituting the recording layer and the fixed layer is one of Co, Fe, and Ni, or one or more elements therein. , Pt, Pd is a regular alloy containing one or more elements.   2. The tunnel magnetoresistive effect element according to claim 1, wherein one or both of the recording layer and the perpendicular magnetization film constituting the fixed layer contain Co, and Cr, Ta, Nb, V, W, Hf, Ti, Zr. , Pt, Pd, Fe, Ni, an alloy containing one or more elements, and a tunnel magnetoresistive effect element.   2. The tunnel magnetoresistive effect element according to claim 1, wherein both or one of the perpendicular magnetization films constituting the recording layer and the fixed layer is Fe, Co, Ni, or an alloy containing one or more of them. And a tunnel magnetoresistive effect element characterized by being a laminated film in which nonmagnetic metals such as Ru, Pt, Rh, Pd, and Cr are alternately laminated.   2. The tunnel magnetoresistive element according to claim 1, wherein at least one of the recording layer and the perpendicular magnetization film constituting the fixed layer has a granular structure in which granular magnetic materials are dispersed in a non-magnetic matrix. A tunnel magnetoresistive effect element.   2. The tunnel magnetoresistive element according to claim 1, wherein both or one of the perpendicular magnetization films constituting the recording layer and the fixed layer is an amorphous alloy containing a rare earth metal and a transition metal. Resistive effect element. In tunneling magnetoresistive element according to claim 1, wherein both or one of the recording layer and the perpendicular magnetic film of the pinned layer, m-D0 ₁₉ type CoPt ordered alloy, L1 ₁ type CoPt ordered alloy or, Co-Pt, Co-Pd, Fe-Pt, tunneling magnetoresistive element which is a L1 ₀ type ordered alloy mainly composed of Fe-Pd. In a random access memory comprising a plurality of magnetic memory cells and a selection means for selecting a desired magnetic memory cell,
The magnetic memory cell includes a tunnel magnetoresistive element and a transistor for energizing the tunnel magnetoresistive element,
The selection means includes a first write driver circuit, a second write driver circuit, and a third write driver circuit,
The tunnel magnetoresistive element includes a recording layer made of a perpendicular magnetization film, a fixed layer made of a perpendicular magnetization film, a nonmagnetic layer disposed between the recording layer and the fixed layer, the recording layer and the fixed layer A pair of electrode layers formed in contact with each of the layers for flowing a current for reversing the magnetization direction of the recording layer in the element film thickness direction. The recording layer includes a first region and a second region. At least one of the regions, and the magnetic moment per unit area in the first region is lower than the magnetic moment per unit area in the second region, and the second region is formed on the outer peripheral portion of the recording layer. Is greater than the proportion of the first region,
One end of the transistor is electrically connected to a source line connected to a first write driver circuit;
The electrode layer of the tunnel magnetoresistive element not connected to the transistor is connected to a bit line connected to a second write driver circuit and an amplifier for amplifying a read signal,
A word line for controlling the resistance of the transistor, the word line connected to a third write driver circuit;
Information is written by passing a current in a film thickness direction of a tunnel magnetoresistive element included in the magnetic memory cell selected by the selection unit, and reversing the magnetization of the recording layer of the tunnel magnetoresistive element by spin transfer torque. Random access memory.

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