Magnetoresistive element and method for manufacturing the same

Abstract

To provide a magnetoresistive effect element having a high RA while suppressing a reduction in MR ratio, and a manufacturing method thereof.SOLUTION: A magnetoresistive effect element according to an aspect of the present invention includes a first ferromagnetic layer, a second ferromagnetic layer, and a tunnel barrier layer laminated between the first ferromagnetic layer and the second ferromagnetic layer, and the tunnel barrier layer has an upper surface and a lower surface located on the opposite side of the upper surface, and when a larger maximum height roughness from among the maximum height roughness of the upper surface and the maximum height roughness of the lower surface of the tunnel barrier layer is set to Rz, and the thickness of the tunnel barrier layer is set to t, Rz / t<1 is satisfied, and the tunnel barrier layer includes at least one amorphous region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetoresistive effect element and a method for manufacturing the magnetoresistive effect element.

Background Art

[0002] Since ferromagnetic tunnel junction (MTJ) elements can exhibit a large magnetoresistive effect ratio (MR ratio), they have been used in recent years in magnetic devices such as magnetic heads and nonvolatile random access magnetic memories (MRAMs). An MTJ element is composed of, for example, two ferromagnetic layers and a tunnel barrier layer provided between the two ferromagnetic layers. The ferromagnetic layer contains, for example, Co, Fe, Co alloys, Fe alloys, CoFe alloys, and Co-based Heusler alloys, and the tunnel barrier layer contains, for example, MgAl2O4 having a spinel structure. This produces a coherent tunneling effect, and as a result, a large MR ratio is realized.

[0003] Both Patent Document 1 and Patent Document 2 disclose a ferromagnetic tunnel junction, a magnetoresistive effect element using the same, and a spintronics device. Further, Patent Document 1 discloses a ferromagnetic tunnel junction in which the tunnel barrier layer contains MgAl2O4 having a spinel structure, and Patent Document 2 discloses a ferromagnetic tunnel junction in which the tunnel barrier layer contains (Mg 1-x Al x )-O (0 < x ≦ 1) having an irregular spinel structure. In any of the patent documents, the ferromagnetic tunnel junction has a structure in which a tunnel barrier layer of a crystalline oxide having a spinel structure is directly sandwiched between two ferromagnetic layers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] For MTJ elements used in magnetic devices such as magnetic heads and MRAMs, film development is underway to reduce the area resistance (RA), which is the resistance per unit area of ​​the MTJ element. Meanwhile, for MTJ elements used in magnetic devices such as new types of magnetic field sensors and analog memories that utilize domain wall motion, increasing the RA of the MTJ element is desirable. One known method for increasing the RA of an MTJ element is to increase the thickness of the tunnel barrier layer. However, while this method increases the RA, it also suffers from problems such as a reduction in the MR ratio due to pinholes in the tunnel barrier layer. Therefore, it has been difficult to increase the RA of an MTJ element while suppressing the reduction in the MR ratio.

[0006] The present invention has been made in view of these problems, and aims to provide a magnetoresistive effect element that has a high RA while suppressing a decrease in the MR ratio, and a method for manufacturing such a magnetoresistive effect element. [Means for solving the problem]

[0007] A magnetoresistive effect element according to one embodiment of the present invention comprises a first ferromagnetic layer, a second ferromagnetic layer, and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer, wherein the tunnel barrier layer has an upper surface and a lower surface located opposite the upper surface, and wherein Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is the thickness of the tunnel barrier layer, Rz / t<1, and the tunnel barrier layer includes at least one amorphous region.

[0008] In this magnetoresistive element, the tunnel barrier layer has a maximum height roughness of Rz on its top and / or bottom surface and includes at least one amorphous region, thereby achieving a high RA. Furthermore, since the tunnel barrier layer satisfies Rz / t<1, a reduction in the MR ratio caused by the maximum height roughness being excessive relative to the thickness of the tunnel barrier layer can be prevented.

[0009] In a magnetoresistive effect element according to one embodiment of the present invention, the tunnel barrier layer further includes at least one crystallized region, and in a cross section along the stacking direction, the ratio of the area of ​​the at least one crystallized region to the area of ​​the entire tunnel barrier layer may be greater than 5% and less than 65%.

[0010] In this magnetoresistive element, the proportion of the crystalline region in the cross section along the stacking direction is greater than 5%, which prevents a decrease in the MR ratio due to an excessively large proportion of amorphous region. Furthermore, since the proportion of the crystalline region is less than 65%, the proportion of the amorphous region is sufficiently large, which prevents a decrease in the MR ratio due to deterioration of the ferromagnetic layer that may occur during a process for crystallizing a portion of the tunnel barrier layer, and also ensures a sufficiently high RA.

[0011] In the magnetoresistive element according to one aspect of the present invention, at least one crystallized region may have a crystal structure in which the (001) plane is oriented in the stacking direction.

[0012] This magnetoresistive element can obtain a high coherent tunneling effect due to the crystallized region in which the (001) plane is oriented, and can have a high MR ratio.

[0013] In the magnetoresistive element according to one aspect of the present invention, at least one crystallized region may have a width along an in-plane direction of the tunnel barrier layer, and the maximum value of this width may be less than 8 nm.

[0014] According to this magnetoresistive element, even if a lattice mismatch occurs between the tunnel barrier layer and at least one of the first and second ferromagnetic layers in the crystallized region of the tunnel barrier layer, the region where the lattice mismatch occurs can be reduced, resulting in a higher MR ratio.

[0015] In the magnetoresistive element according to one aspect of the present invention, at least a portion of the at least one crystallized region may be lattice-matched with at least one of the first ferromagnetic layer and the second ferromagnetic layer.

[0016] This magnetoresistive element can achieve a high coherent tunneling effect and has a higher MR ratio.

[0017] In the magnetoresistive element according to one aspect of the present invention, at least one of the first ferromagnetic layer, the second ferromagnetic layer, and the tunnel barrier layer may include a twin crystal.

[0018] In this magnetoresistive element, the twin crystals can alleviate strain that may occur near the interface between the tunnel barrier layer and the first and / or second ferromagnetic layer due to the roughness of the upper and lower surfaces of the tunnel barrier layer, thereby alleviating lattice strain at the interface between the tunnel barrier layer and the first and / or second ferromagnetic layer.

[0019] In the magnetoresistive effect element according to one aspect of the present invention, the twin crystal may have a face-centered cubic lattice structure and the twin crystal plane may be a (111) plane, or the twin crystal may have a body-centered cubic lattice structure and the twin crystal plane may be a (112) plane.

[0020] In this magnetoresistive element, the twin crystal can have an appropriate twin plane depending on the type of the crystalline structure of the twin crystal, which further reduces lattice distortion at the interfaces between the tunnel barrier layer and the first and second ferromagnetic layers, thereby enabling the magnetoresistive element to have a higher MR ratio.

[0021] In the magnetoresistive element according to one aspect of the present invention, the tunnel barrier layer may include an oxide material having a spinel structure represented by formula (1). A 1-x B x O y …(1) In formula (1), A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, and B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Ti, V, Cr, Mn, Fe, Rh, Ir, Ge, and Co, where 0 < x ≦ 1 and 0.35 ≦ y ≦ 1.7.

[0022] According to this magnetoresistive element, in the crystallization region of the tunnel barrier layer, the lattice mismatch with the first and second ferromagnetic layers can be made smaller.

[0023] In the magnetoresistive element according to one aspect of the present invention, in formula (1), A may represent Mg and B may represent Al.

[0024] [[ID=Z22]]According to this magnetoresistive element, with this configuration, the tunnel barrier layer can fully exhibit its function for realizing a large MR ratio.

[0025] In the magnetoresistive element according to one aspect of the present invention, in formula (1), 0 < x < 0.5 may be satisfied.

[0026] According to this magnetoresistive element, in formula (1), the tunnel barrier layer can more fully exhibit its function for realizing a large MR ratio. <000012z3>

[0027] In the magnetoresistive element according to one aspect of the present invention, at least one of the first ferromagnetic layer and the second ferromagnetic layer may have a region consisting of Co z Fe 100-z (0 < z < 80).

[0028] According to this magnetoresistive effect element, the spin polarization rate of the region can be increased, and the lattice mismatch between the region and the tunnel barrier layer can be reduced.

[0029] A method for manufacturing a magnetoresistive effect element according to an aspect of the present invention includes a step of forming a first ferromagnetic layer, a step of forming a MgAl alloy layer on the first ferromagnetic layer, and oxidizing the MgAl alloy layer to form at least one amorphous region and at least one crystallization region having a spinel structure represented by Mg 1-x Al x O y (0 < x ≤ 1, 0.35 ≤ y ≤ 1.7) to form a tunnel barrier layer, and a step of forming a second ferromagnetic layer on the tunnel barrier layer. The tunnel barrier layer has an upper surface and a lower surface located on the opposite side of the upper surface. Among the maximum height roughness of the upper surface and the maximum height roughness of the lower surface of the tunnel barrier layer, when the larger maximum height roughness is Rz and the thickness of the tunnel barrier layer is t, Rz / t < 1.

[0030] According to this method for manufacturing a magnetoresistive effect element, a magnetoresistive effect element having a high RA can be manufactured while suppressing a reduction in the MR ratio.

[0031] In a method for manufacturing a magnetoresistive effect element according to an aspect of the present invention, the step of oxidizing the MgAl alloy layer may include a step of oxidizing the MgAl layer by at least one of radical oxidation, plasma oxidation, ozone oxidation, and natural oxidation.

[0032] According to this method for manufacturing a magnetoresistive effect element, a tunnel barrier layer of a predetermined aspect as described above can be efficiently formed.

Advantages of the Invention

[0033] According to the present invention, it is possible to provide a magnetoresistive effect element having a high RA while suppressing a reduction in the MR ratio, and a method for manufacturing such a magnetoresistive effect element.

Brief Description of the Drawings

[0034] [Figure 1] FIG. 1 is a diagram showing a cross section of a magnetoresistive element according to an embodiment taken along the stacking direction. [Figure 2] FIG. 2 is an enlarged view of an example of the region E1 shown in FIG. [Figure 3] FIG. 3 is an enlarged view of another example of the region E1 shown in FIG. [Figure 4] FIG. 4 is a diagram showing a magnetoresistive device capable of evaluating the MR ratio of the magnetoresistive effect element according to Example 1. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same reference numerals are used for the same elements whenever possible. The dimensional ratios within and between components in the drawings are arbitrary for ease of viewing. In this embodiment, X, Y, and Z axes are set based on a Cartesian coordinate system in FIGS. 1 to 3, but these axes are set for convenience of explanation, with the Z axis being set in the stacking direction of the magnetoresistive effect element.

[0036] 1 is a diagram showing a cross section of a magnetoresistive effect element according to an embodiment taken along the stacking direction. The magnetoresistive effect element 1 includes, for example, a substrate 10, an underlayer 20, a magnetoresistive layer 30, and a cap layer 40, in this order. For ease of understanding, the magnetoresistive effect element 1 is depicted in FIG. 1 with the thickness of each layer enlarged in the stacking direction (Z-axis direction).

[0037] The substrate 10 includes, for example, silicon single crystal, metal oxide single crystal, silicon single crystal with a thermally oxidized silicon film, sapphire single crystal, ceramic, quartz, and glass. The material contained in the substrate 10 is not particularly limited as long as it has appropriate mechanical strength and is suitable for heat treatment and microfabrication. An example of a metal oxide single crystal is MgO single crystal. An epitaxially grown film can be easily formed on a substrate containing MgO single crystal, for example, by sputtering.

[0038] The underlayer 20 is provided to improve the crystallinity of the magnetoresistive layer 30, and can also be used as an electrode for measuring the magnetoresistive characteristics of the magnetoresistive effect element 1. The underlayer 20 includes, for example, a lower electrode layer 21 for the electrode, and a buffer layer 22 provided on the lower electrode layer 21.

[0039] The lower electrode layer 21 may contain at least one metal element selected from the group consisting of Al, Ag, Au, Cu, Cr, Pt, Ru, Ta, V, and W, and may also contain an alloy of these metal elements or a stack of materials consisting of two or more of these metal elements. Examples of alloys of metal elements include cubic AgZn alloys, AgMg alloys, and NiAl alloys. Examples of stacks of materials consisting of two or more metal elements include a stack of materials containing Ta and Ru. Specifically, the lower electrode layer 21 may include a three-layer stack of Ta, Ru, and Ta.

[0040] The lower electrode layer 21 has an upper surface 21a, which can be subjected to CMP (Chemical Mechanical Polishing). CMP polishing involves polishing the upper surface 21a of the lower electrode layer 21 using, for example, a CMP device, until the upper surface 21a has a desired roughness. The roughness of the upper surface 21a can be controlled by the polishing time of the CPM polishing. In one example, the roughness of the upper surface 21a can be reduced as the polishing time of the CPM polishing is increased. Alumina, for example, is used as a slurry for the CPM polishing.

[0041] The thickness of the lower electrode layer 21 in the Z-axis direction is, for example, in the range of 10 nm to 1000 nm, and also in the range of 30 nm to 150 nm.

[0042] A buffer layer 22 can be stacked on the upper surface 21a of the polished lower electrode layer 21, and the buffer layer 22 contains, for example, a metal element, similar to the lower electrode layer 21. The metal element is, for example, at least one of Al, Ag, Au, Cu, Cr, Pt, Ru, Ta, V, and W, and the buffer layer 22 may contain an alloy of these metal elements or a stack of materials consisting of two or more of these metal elements. Examples of the alloy of the metal elements include a cubic AgZn alloy, an AgMg alloy, and an NiAl alloy. Specifically, the buffer layer 22 may include a two-layer stack of Ta and Ru.

[0043] The thickness of the buffer layer 22 in the Z-axis direction is, for example, in the range of 1 nm to 10 nm, and also in the range of 2 nm to 5 nm.

[0044] If necessary, a crystal orientation layer for controlling the crystal orientation of the upper layer may be provided between the underlayer 20 and the substrate 10. The crystal orientation layer contains, for example, at least one of MgO, TiN, and a NiTa alloy.

[0045] The magnetoresistive layer 30 includes a first ferromagnetic layer 31, a second ferromagnetic layer 32, a tunnel barrier layer 33, an antiferromagnetic layer 34, a third ferromagnetic layer 35, and a magnetic coupling layer 36. The tunnel barrier layer 33 is made of an insulating material and is stacked between the first ferromagnetic layer 31 and the second ferromagnetic layer 32. The antiferromagnetic layer 34 is disposed on the side of the second ferromagnetic layer 32 opposite the tunnel barrier layer 33, and in this embodiment, is stacked on the third ferromagnetic layer 35. The first ferromagnetic layer 31 is stacked on, for example, the underlayer 20, and the first ferromagnetic layer 31, tunnel barrier layer 33, second ferromagnetic layer 32, magnetic coupling layer 36, and third ferromagnetic layer 35 are arranged in this order. The first ferromagnetic layer 31 functions as a magnetization free layer, and the second ferromagnetic layer 32, the magnetic coupling layer 36, the third ferromagnetic layer 35 and the antiferromagnetic layer 34 can collectively function as a magnetization fixed layer.

[0046] The first ferromagnetic layer 31 functioning as a magnetization free layer is made of a ferromagnetic material having soft magnetic properties, such as Fe, Co—Fe, Co—Fe—B, and a ferromagnetic Heusler alloy.

[0047] The thickness of the first ferromagnetic layer 31 in the Z-axis direction is, for example, in the range of 0.5 nm to 100 nm, and also in the range of 0.8 nm to 20 nm.

[0048] In this embodiment, the pinned magnetization layer has a structure called a synthetic antiferromagnetic (SAF) structure. That is, the magnetoresistive layer 30 further includes, as the pinned magnetization layer, a third ferromagnetic layer 35 provided between the second ferromagnetic layer 32 and the antiferromagnetic layer 34, and a magnetic coupling layer 36 provided between the second ferromagnetic layer 32 and the third ferromagnetic layer 35. The second ferromagnetic layer 32 and the third ferromagnetic layer 35 are antiferromagnetically coupled to each other through exchange coupling via the magnetic coupling layer 36. The third ferromagnetic layer 35 may have a structure similar to that of the second ferromagnetic layer 32. The magnetic coupling layer 36 is made of a nonmagnetic metal such as Ru, Rh, or Ir, and its thickness in the Z-axis direction is, for example, in the range of 0.3 nm to 2 nm. In this embodiment, the pinned magnetization layer may not have an SAF structure, if necessary. In this case, the magnetization fixed layer does not have the magnetic coupling layer 36 and the third ferromagnetic layer 35 , and the antiferromagnetic layer 34 is stacked directly on the second ferromagnetic layer 32 .

[0049] The magnetization directions of the second ferromagnetic layer 32 and the third ferromagnetic layer 35 of the fixed magnetization layer are less susceptible to external magnetic fields than the magnetization direction of the first ferromagnetic layer 31, which functions as a free magnetization layer. The magnetization directions of the second ferromagnetic layer 32 and the third ferromagnetic layer 35 are preferably substantially fixed with respect to external magnetic fields that may be applied during use, such as the external magnetic field to be measured, and are substantially unaffected by such external magnetic fields. In this embodiment, such magnetization direction configuration of the second ferromagnetic layer 32 and the third ferromagnetic layer 35 is achieved by exchange coupling the antiferromagnetic layer 34 with the third ferromagnetic layer 35 to impart unidirectional magnetic anisotropy directly to the third ferromagnetic layer 35 and indirectly to the second ferromagnetic layer 32. Since such magnetization direction configuration can be achieved without the antiferromagnetic layer 34, the magnetoresistive layer 30 does not need to have the antiferromagnetic layer 34. For the same reason, even if the magnetization fixed layer does not have an SAF structure, the magnetoresistive layer 30 may not have an antiferromagnetic layer 34. On the other hand, the first ferromagnetic layer 31, which functions as the magnetization free layer, is made of, for example, a soft magnetic material, and its magnetization direction is not substantially fixed. Therefore, when an external magnetic field is applied to the magnetoresistive layer 30, the magnetization direction easily changes in that direction. When an external magnetic field is applied to the magnetoresistive layer 30, the relative magnetization directions of the first ferromagnetic layer 31 and the second ferromagnetic layer 32 change, which changes the resistance value of the magnetoresistive layer 30, and the magnetoresistive effect of the magnetoresistive element 1 is exhibited.

[0050] The second ferromagnetic layer 32 and the third ferromagnetic layer 35 can be made of a ferromagnetic material. Ferromagnetic materials for the fixed magnetization layer include, for example, metals or alloys containing at least one element selected from the group consisting of Ni, Fe, Ru, Mn, Ir, and Co. Specific examples of alloys include Co-Fe alloys, Ni-Fe alloys, Co-B alloys, Fe-B alloys, and Co-Fe-B alloys. Examples of alloys include Heusler alloys such as Co-Fe-Al alloys, Co-Fe-Si alloys, Co-Mn-Si alloys, Co-Mn-Ge alloys, Co-Fe-Al-Si alloys, and Co-Fe-Ga-Ge alloys. The second ferromagnetic layer 32 can have a structure in which multilayer films of, for example, Co-Fe-B alloys and Co-Fe alloys are repeatedly stacked.

[0051] The thickness of the second ferromagnetic layer 32 in the Z-axis direction is, for example, in the range of 2 nm to 10 nm. This thickness is also, for example, in the range of 3 nm to 7 nm. The thickness of the third ferromagnetic layer 35 in the Z-axis direction is, for example, in the range of 1 nm to 8 nm. This thickness is also, for example, in the range of 2 nm to 6 nm.

[0052] The antiferromagnetic layer 34 is made of an antiferromagnetic material such as an FeMn alloy, a PtMn alloy, a PtCrMn alloy, a NiMn alloy, an IrMn alloy, NiO, or Fe2O3.

[0053] The thickness of the antiferromagnetic layer 34 in the Z-axis direction is, for example, in the range of 5 nm to 20 nm.

[0054] In the magnetoresistive layer 30, one of the first ferromagnetic layer 31 and the second ferromagnetic layer 32 may function as a magnetization free layer, and the other may function as part of a magnetization fixed layer. Therefore, as a modification of this embodiment, the first ferromagnetic layer 31 may function as part of the magnetization fixed layer, and the second ferromagnetic layer 32 may function solely as a magnetization free layer. In this case, the antiferromagnetic layer 34 is provided on the side of the first ferromagnetic layer 31 opposite the tunnel barrier layer 33, either directly or via the magnetic coupling layer 36 and the third ferromagnetic layer 35 to form an SAF structure, and directly or indirectly imparts unidirectional magnetic anisotropy to the first ferromagnetic layer 31.

[0055] The magnetoresistive element 1 may include a cap layer 40 on the magnetoresistive layer 30. The cap layer 40 is provided to protect the magnetoresistive layer 30. The cap layer 40 may include, for example, one or more metal elements selected from the group consisting of Ru, Ag, Al, Cu, Au, Cr, Mo, Pt, W, Ta, Pd, and Ir, an alloy of these metal elements, or a stack of materials containing two or more of these metal elements. If necessary, an upper electrode may be provided on the cap layer 40 to pass a current through the magnetoresistive element 1 along the Z-axis direction.

[0056] 2 is an enlarged view of an example of region E1 shown in FIG. 1, illustrating an example of a cross section along the stacking direction (Z-axis direction) of the magnetoresistive layer 30. As shown in FIG. 2, the tunnel barrier layer 33 has an upper surface 33a and a lower surface 33b located opposite the upper surface 33a. The upper surface 33a can be located on the second ferromagnetic layer 32 side, and the lower surface 33b can be located on the first ferromagnetic layer 31 side. The upper surface 33a of the tunnel barrier layer 33 has surface roughness. Due to the surface roughness, the upper surface 33a has, for example, one or more protrusions 33c and one or more depressions 33d.

[0057] The upper surface 33a of the tunnel barrier layer 33 has a maximum height roughness Rz1 as the surface roughness. This maximum height roughness Rz1 is defined by the JIS B 0601:2013 standard. According to this standard, the maximum height roughness Rz1 of the upper surface 33a is defined as the sum of the height Rp1 of the highest protrusion 33c from an average line Av1 (the arithmetic mean height of the roughness curve of the upper surface 33a within the reference length Lr1) and the depth Rv1 of the lowest depression 33d from the average line Av1 within the reference length Lr1 of the roughness curve of the upper surface 33a. The roughness curve of the upper surface 33a is measured using, for example, a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), a scanning electron microscope (SEM), or an atomic force microscope (AFM). The reference length Lr1 is a predetermined length along the in-plane direction (XY in-plane direction) of the magnetoresistive layer 30, and is, for example, 4 nm, 8 nm, 10 nm, 20 nm, or 30 nm.

[0058] The lower surface 33b of the tunnel barrier layer 33 has a surface roughness similar to the upper surface 33a, and the surface roughness results in, for example, one or more protrusions 33f and one or more depressions 33g. The maximum height roughness Rz2 of the lower surface 33b, like the maximum height roughness Rz1 of the upper surface 33a, is defined by the JIS B 0601:2013 standard. The maximum height roughness Rz2 is defined as the sum of the height Rp2 of the highest protrusion 33f from the average line Av2 and the depth Rv2 of the lowest depression 33g from the average line Av2 within a reference length Lr2 of the roughness curve of the lower surface 33b. The roughness curve of the lower surface 33b is also measured using a TEM or the like, and the reference length Lr2 is, for example, 4 nm, 8 nm, 10 nm, 20 nm, or 30 nm along the in-plane direction of the magnetoresistive layer 30. Although FIG. 2 illustrates an example in which the reference length Lr1 is the same as the reference length Lr2, the reference length Lr1 may be different from the reference length Lr2.

[0059] In the magnetoresistive element 1, the larger of the maximum height roughness Rz1 of the upper surface 33a of the tunnel barrier layer 33 and the maximum height roughness Rz2 of the lower surface 33b can be Rz. The upper surface 33a of the tunnel barrier layer 33 may have the maximum height roughness Rz, or the lower surface 33b may have the maximum height roughness Rz. When the maximum height roughness Rz1 of the upper surface 33a is the same as the maximum height roughness Rz2 of the lower surface 33b, both the upper surface 33a and the lower surface 33b may have the maximum height roughness Rz. The upper surface 33a and / or the lower surface 33b of the tunnel barrier layer 33 have the maximum height roughness Rz. FIG. 2 shows a case where the upper surface 33a has a larger maximum height roughness Rz than the lower surface 33b.

[0060] When the thickness of the tunnel barrier layer 33 in the Z-axis direction is t, Rz / t<1 is satisfied in at least one cross section of the magnetoresistive layer 30 taken along the Z-axis direction. When the maximum height roughness Rz1 of the upper surface 33a is the maximum height roughness Rz, the thickness t of the tunnel barrier layer 33 in the Z-axis direction can be determined, for example, by arithmetically averaging the thickness of the tunnel barrier layer 33 in the Z-axis direction within a range of a reference length Lr1. The thickness t of the tunnel barrier layer 33 in the Z-axis direction is measured, for example, using a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or a scanning electron microscope (SEM). When the maximum height roughness Rz2 of the lower surface 33b is the maximum height roughness Rz, the thickness t of the tunnel barrier layer 33 in the Z-axis direction can be determined, for example, by arithmetically averaging the thickness of the tunnel barrier layer 33 in the Z-axis direction within a range of a reference length Lr2.

[0061] In this embodiment, it is preferable that Rz / t<1 in at least two mutually perpendicular cross sections of the magnetoresistive layer 30 along the Z-axis direction, and it is even more preferable that Rz / t<1 in substantially all cross sections of the magnetoresistive layer 30 along the Z-axis direction.

[0062] The surface roughness of the upper surface 33a and the lower surface 33b of the tunnel barrier layer 33 is also due to the surface roughness of the upper surface of an element below the tunnel barrier layer 33 of the magnetoresistive element 1 (for example, the upper surface 21a of the lower electrode layer 21 (see FIG. 1)). Therefore, the magnitude of the maximum height roughness Rz of the tunnel barrier layer 33 can be controlled to a predetermined magnitude by controlling the surface roughness (for example, the maximum height roughness) of the upper surface (for example, the upper surface 21a) of the element. The magnitude of the maximum height roughness Rz of the tunnel barrier layer 33 may be similar to, larger than, or smaller than the magnitude of the maximum height roughness of the upper surface of the element.

[0063] The maximum height roughness Rz of the tunnel barrier layer 33 is preferably, for example, 0.2 nm to 3.2 nm, and more preferably 0.6 nm to 1.8 nm. The thickness of the tunnel barrier layer 33 in the Z-axis direction is preferably, for example, 1 nm to 3.2 nm, and more preferably 1.6 nm to 2.2 nm.

[0064] 2, the tunnel barrier layer 33 includes at least one amorphous region 61 and at least one crystallized region 62. The amorphous region 61 and the crystallized region 62 can be separated from each other by, for example, a boundary 33e. The tunnel barrier layer 33 may be substantially composed of only the at least one amorphous region 61 and the at least one crystallized region 62. The amorphous region 61 and the crystallized region 62 may have substantially the same composition, or may have substantially different compositions.

[0065] At least one amorphous region 61 is included in the tunnel barrier layer 33. The number of amorphous regions 61 in the entire tunnel barrier layer 33 may be, for example, two or five. At least one crystallized region 62 is included in the tunnel barrier layer 33. The number of crystallized regions 62 in the entire tunnel barrier layer 33 may be, for example, two or five. In the entire tunnel barrier layer 33, the number of amorphous regions 61 and the number of crystallized regions 62 may be the same as or different from each other.

[0066] The crystalline structure of the tunnel barrier layer 33 can be identified by local electron diffraction using TEM and STEM. Local electron diffraction is sometimes called nanobeam electron diffraction when the electron beam is focused to the nanometer scale, and angstrom electron diffraction when the electron beam is focused to the sub-nanometer scale. If a local region of the tunnel barrier layer 33 is crystallized, the corresponding electron diffraction image will be a spot pattern, and if the local region of the tunnel barrier layer 33 is amorphous, the corresponding electron diffraction image will be a halo pattern. Therefore, local electron diffraction can be used to determine whether a local region of the tunnel barrier layer 33 is crystallized or amorphous.

[0067] In the magnetoresistive effect element 1 described above, the upper surface 33a and / or the lower surface 33b of the tunnel barrier layer 33 have a maximum height roughness Rz. Therefore, compared to when the upper surface 33a and / or the lower surface 33b are substantially flat, the area of ​​the upper surface 33a and / or the lower surface 33b is increased, resulting in a higher RA (resistance per unit area in the XY plane) of the magnetoresistive effect element 1. Furthermore, because the tunnel barrier layer 33 includes at least one amorphous region 61, the RA of the magnetoresistive effect element 1 is higher compared to when the region is crystallized. Furthermore, because Rz / t<1 is satisfied in the tunnel barrier layer 33, a reduction in the MR ratio caused by the maximum height roughness Rz of the upper surface 33a being excessive relative to the thickness t of the tunnel barrier layer 33 can be prevented. As a result, the magnetoresistive effect element 1 of this embodiment can achieve a high RA while suppressing a reduction in the MR ratio.

[0068] In the tunnel barrier layer 33 of the magnetoresistive element 1 of the present embodiment, it is preferable that 0.1 < Rz / t, and it is more preferable that 0.32 < Rz / t. Thereby, since the area of the upper surface 33a sufficiently increases, the RA of the magnetoresistive element 1 can be made sufficiently high. The condition regarding the lower limit value of Rz / t may be satisfied in at least one cross-section of the cross-section of the magnetoresistive layer 30 along the Z-axis direction, similar to the condition regarding the upper limit value of Rz / t described above. Among the cross-sections of the magnetoresistive layer 30 along the Z-axis direction, it is preferably satisfied in at least two cross-sections orthogonal to each other, and it is more preferably satisfied in substantially all cross-sections of the magnetoresistive layer 30 along the Z-axis direction.

[0069] In FIG. 2, an example is shown in which the amorphous region 61 and the crystallization region 62 are arranged in the substantially in-plane direction (XY in-plane direction) of the tunnel barrier layer 33 within the tunnel barrier layer 33. However, the amorphous region 61 and the crystallization region 62 may be arranged in the stacking direction (Z-axis direction). For example, within the tunnel barrier layer 33, the crystallization region 62 may be arranged above the amorphous region 61. For example, the amorphous region 61, the crystallization region 62, and the amorphous region 61 may be arranged in this order in the stacking direction.

[0070] In at least one cross-section (preferably at least two cross-sections orthogonal to each other, more preferably substantially all cross-sections) of the cross-section of the tunnel barrier layer 33 along the Z-axis direction, the ratio of the area of at least one crystallization region 62 to the area of the entire tunnel barrier layer 33 is preferably greater than 5% and less than 65%, and more preferably greater than 20% and less than 50%.

[0071] When the area ratio is greater than 5% (preferably 20%), it is possible to suppress a decrease in the MR ratio due to an excessively large proportion of the amorphous region 61. When the area ratio is less than 65% (preferably 50%), the proportion of the amorphous region 61 is sufficiently large, preventing a decrease in the MR ratio due to deterioration of at least one of the first ferromagnetic layer 31 and the second ferromagnetic layer 32, which may occur during a process for crystallizing a portion of the tunnel barrier layer 33, and achieving a sufficiently high RA. The area ratio of the at least one crystallized region 62 can be controlled, for example, by the annealing temperature in the annealing step performed when forming the tunnel barrier layer 33, and may be greater than, approximately equal to, or smaller than the area ratio of the at least one amorphous region 61.

[0072] In at least one cross section along the in-plane direction, the ratio of the area of ​​the at least one amorphous region 61 to the entire area of ​​the tunnel barrier layer 33 may be larger, approximately equal to, or smaller than the ratio of the area of ​​the at least one crystallized region 62 to the entire area of ​​the tunnel barrier layer 33. In this embodiment, the ratio of the area of ​​the at least one crystallized region 62 is preferably larger than 5% and smaller than 65%, and more preferably larger than 20% and smaller than 50%.

[0073] At least one amorphous region 61 has a width W61 along the in-plane direction of the tunnel barrier layer 33, and at least one crystallized region 62 has a width W62 along the in-plane direction of the tunnel barrier layer 33. The width W61 of the amorphous region 61 is, for example, 1 nm or more and 30 nm or less, and the width W62 of the crystallized region 62 is, for example, 0.15 nm or more and less than 8 nm. In this embodiment, the widths W61 and W62 both indicate the maximum widths defined along the in-plane direction (XY in-plane direction). FIG. 2 shows an example in which the widths W61 and W62 are both the maximum widths along the X-axis direction.

[0074] In the magnetoresistive element 1, the width W62 of the crystallized region 62 may be less than 8 nm. Therefore, even if lattice mismatch occurs between the tunnel barrier layer 33 and at least one of the first ferromagnetic layer 31 and the second ferromagnetic layer 32 in the crystallized region 62 of the tunnel barrier layer 33, the region where the lattice mismatch occurs can be reduced. As a result, the magnetoresistive element 1 can have a higher MR ratio. This effect is more pronounced when the width W62 of the crystallized region 62 is less than 5 nm.

[0075] At least one amorphous region 61 has a height H61 along the Z-axis direction, and at least one crystallized region 62 has a height H62 along the Z-axis direction. The height H61 of the amorphous region 61 is, for example, not less than 0.2 nm and not more than 3 nm, and the height H62 of the crystallized region 62 is, for example, not less than 0.2 nm and not more than 3 nm.

[0076] In this embodiment, at least one crystallized region 62 may have a crystal structure in which the (001) plane is oriented in the Z-axis direction. The magnetoresistive element 1 can obtain a high coherent tunneling effect due to the crystallized region 62 in which the (001) plane is oriented, and as a result, can have a high MR ratio. This effect is particularly pronounced when the crystallized region 62 is made of MgO, MgAl2O4, or γ-alumina.

[0077] At least a portion of at least one crystallized region 62 may be lattice-matched with at least one of the first ferromagnetic layer 31 and the second ferromagnetic layer 32. This allows a high coherent tunneling effect to be obtained. The magnetoresistive element 1 can have a higher MR ratio. In the magnetoresistive element 1, the lattice-matching of the crystallized region 62 with the first ferromagnetic layer 31 and the second ferromagnetic layer 32 can be confirmed, for example, by an image obtained by inverse Fourier transform of a lattice image obtained by structural observation.

[0078] The tunnel barrier layer 33 may include an oxide material having a spinel structure represented by the following formula (1): A 1-xB x O y …(1) In formula (1), A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, and B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Ti, V, Cr, Mn, Fe, Rh, Ir, Ge, and Co. Also, 0 < x ≤ 1 and 0.35 ≤ y ≤ 1.7, and O represents oxygen. Note that the above spinel structure also includes an irregular spinel structure in which the atomic arrangement of A and B in formula (1) is irregularized.

[0079] In this case, in the crystallization region 62 of the tunnel barrier layer 33, the lattice mismatch with the first ferromagnetic layer 31 and the second ferromagnetic layer 32 can be made smaller. This is because the mismatch between the lattice constant of the crystallization region 62 of the tunnel barrier layer 33 and the lattice constants of the first ferromagnetic layer 31 and the second ferromagnetic layer 32 can be reduced.

[0080] In formula (1), A may represent Mg and B may represent Al. With this configuration, the tunnel barrier layer 33 can fully exhibit its function for realizing a large MR ratio.

[0081] Also, in formula (1), 0 < x < 0.5 may be satisfied. Thereby, the tunnel barrier layer 33 can more fully exhibit its function for realizing a large MR ratio.

[0082] Also, in formula (1), 0 < x < 0.5 and 1 ≤ y ≤ 1.33 may be satisfied. In this case, the tunnel barrier layer 33 can more fully exhibit its function for realizing a large MR ratio.

[0083] The tunnel barrier layer 33 can be composed of MgO or γ-alumina in addition to the oxide material having the spinel structure represented by the above formula (1).

[0084] In the magnetoresistive layer 30, at least one of the first ferromagnetic layer 31, the second ferromagnetic layer 32, and the tunnel barrier layer 33 may contain twins. As a result, the strain that may occur in the vicinity of the interfaces of these layers due to the upper surface 33a and the lower surface 33b of the tunnel barrier layer 33 having roughness can be relaxed by these twins. As a result, the lattice strain at the interface between the tunnel barrier layer 33 and the first ferromagnetic layer 31 and / or the second ferromagnetic layer 32 is relaxed.

[0085] The above-mentioned twin has a face-centered cubic lattice structure, and its twin plane may be the (111) plane, or the above-mentioned twin has a body-centered cubic lattice structure, and its twin plane may be the (112) plane. Since the twin can have an appropriate twin plane according to the type of the crystal structure of the twin, the lattice strain at the interface between the tunnel barrier layer 33 and the first ferromagnetic layer 31 and / or the second ferromagnetic layer 32 is further relaxed. The magnetoresistive effect element 1 can have a higher MR ratio.

[0086] At least one of the first ferromagnetic layer 31 and the second ferromagnetic layer 32 may have a region composed of Co z Fe 100-z (0 < z < 80). As a result, the spin polarization rate of the region increases, and the lattice mismatch between the region and the tunnel barrier layer 33 can be reduced.

[0087] FIG. 3 is a diagram showing an enlarged view of another example of the region E1 shown in FIG. 1, and is a diagram showing another example of one of the cross-sections along the stacking direction (Z-axis direction) of the magnetoresistive layer 30.

[0088] 3 differs from the tunnel barrier layer 33 shown in FIG. 2 in that it further includes an intervening region 63 between the amorphous region 61 and the crystallized region 62. The intervening region 63 is made of a material that is neither crystallized nor amorphous, among the materials that make up the tunnel barrier layer 33. The amorphous region 61 and the intervening region 63 can be separated from each other, for example, by a boundary 61a, and the crystallized region 62 and the intervening region 63 can be separated from each other, for example, by a boundary 62a.

[0089] The tunnel barrier layer 33 of FIG. 3 may have a structure similar to that of the tunnel barrier layer 33 of FIG. 2, except that it has an intervening region 63 between an amorphous region 61 and a crystallized region 62. The tunnel barrier layer 33 of FIG. 3 has an upper surface 33a and a lower surface 33b located opposite the upper surface 33a. The upper surface 33a of the tunnel barrier layer 33 has a maximum height roughness Rz1 as surface roughness. The upper surface 33a has, for example, one or more protrusions 33c and one or more depressions 33d due to the surface roughness. The lower surface 33b of the tunnel barrier layer 33 has, like the upper surface 33a, a surface roughness and has, for example, one or more protrusions 33f and one or more depressions 33g due to the surface roughness.

[0090] In this embodiment, the magnetoresistive effect element 1 is fabricated by forming each layer from the underlayer 20 to the cap layer 40 on the substrate 10 by a manufacturing method such as sputtering or electron beam evaporation. When forming each layer, heat treatment may be performed as needed, and further, if necessary, a magnetic field application process may be performed to impart unidirectional magnetic anisotropy. Heat treatment may be performed simultaneously with the magnetic field application process. The magnetoresistive effect element 1 may be microfabricated into a shape that allows evaluation of the magnetoresistive characteristics by lithography using an electron beam or the like and dry etching using Ar ions or the like. The magnetoresistive effect element 1 is a magnetoresistive effect element with a current perpendicular to the plane (CPP) structure in which a detection current flows along the stacking direction (the direction perpendicular to the film surface of each layer, i.e., the Z-axis direction).

[0091] The method for manufacturing a magnetoresistive effect element according to this embodiment includes a step of forming a first ferromagnetic layer 31 on the underlayer 20, a step of forming a tunnel barrier layer 33 on the first ferromagnetic layer 31, and a step of forming a second ferromagnetic layer 32 on the tunnel barrier layer 33.

[0092] The step of forming the first ferromagnetic layer 31 can be carried out by a sputtering method. In this step, a two-layer laminate composed of, for example, a CoFeB layer and a CoFe layer is formed on the underlayer 20.

[0093] The step of forming the tunnel barrier layer 33 includes, for example, a step of forming a MgAl alloy layer on the first ferromagnetic layer 31 by a sputtering method, and a step of oxidizing this MgAl alloy layer to form a tunnel barrier layer 33 including at least one amorphous region 61 and at least one crystallization region 62 having a spinel structure represented by Mg 1-x Al x O y (0 < x ≤ 1, 0.35 ≤ y ≤ 1.7). In the tunnel barrier layer 33 formed by this step, when the larger of the maximum height roughness Rz1 of the upper surface 33a and the maximum height roughness Rz2 of the lower surface 33b is defined as Rz and the thickness of the tunnel barrier layer 33 is defined as t, in a cross section along the stacking direction, Rz / t < 1. <l

[0094] Also, the step of oxidizing the MgAl alloy layer can include a step of oxidizing the MgAl layer by at least one of radical oxidation, plasma oxidation, ozone oxidation, and natural oxidation. In this case, a tunnel barrier layer 33 in a predetermined aspect as described above can be efficiently formed.

[0095] The step of forming the second ferromagnetic layer is carried out, for example, by a sputtering method. In this step, a three-layer laminate composed of, for example, a CoFe layer, a CoFeB layer, and a CoFe layer is formed on the tunnel barrier layer 33.

[0096] According to this method for manufacturing a magnetoresistive element, it is possible to manufacture a magnetoresistive element 1 having a high RA while suppressing a decrease in the MR ratio. [Example]

[0097] The magnetoresistive effect element will be further described below with reference to examples and comparative examples of the present invention, but the present invention is not limited to the following examples.

[0098] Example 1 As Example 1, a magnetoresistive effect element having a configuration similar to that of the magnetoresistive effect element 1 of the embodiment shown in Fig. 1 was fabricated. In the explanation of Example 1, the symbols used to explain the magnetoresistive effect element 1 are used. Note that, in the examples and comparative examples from Example 2 onwards, the symbols used to explain the magnetoresistive effect element 1 are also used.

[0099] In Example 1, the magnetoresistive effect element 1 was fabricated by the following procedure. First, a substrate 10 made of Si was prepared. A thermally oxidized silicon film was provided on the substrate 10. The substrate 10 with the thermally oxidized silicon film provided thereon was placed in a magnetron sputtering device, and a lower electrode layer 21 of the underlayer 20 was formed. The lower electrode layer 21 was a three-layer laminate formed by laminating a Ta layer (5 nm thick), a Ru layer (100 nm thick), and a Ta layer (30 nm thick) in this order. The temperature during the formation of the lower electrode layer 21 was room temperature.

[0100] The substrate 10 on which the lower electrode layer 21 was formed was removed from the magnetron sputtering apparatus and placed in a CMP apparatus. Using the CMP apparatus, the upper surface of the lower electrode layer 21 was polished to a desired roughness. Alumina was used as the polishing slurry. The polishing time was 60 seconds.

[0101] After the CMP polishing, the substrate 10 was placed again in the magnetron sputtering device, and a buffer layer 22 was formed by sputtering on the polished lower electrode layer 21. The buffer layer 22 was a two-layer laminate consisting of a Ta layer (thickness 2 nm) and a Ru layer (thickness 2 nm). The temperature during the formation of the buffer layer 22 was room temperature.

[0102] Next, a magnetoresistive layer 30 was formed on the buffer layer 22 of the underlayer 20 by sputtering. In forming the magnetoresistive layer 30, first, a first ferromagnetic layer 31 was formed as a magnetization free layer. The first ferromagnetic layer 31 was a two-layer laminate consisting of a CoFeB layer (thickness 3 nm) and a CoFe layer (thickness 1 nm). The temperature during formation of the first ferromagnetic layer 31 was room temperature. No heat treatment was performed after forming the first ferromagnetic layer 31.

[0103] Next, a tunnel barrier layer 33 was formed on the first ferromagnetic layer 31. To form the tunnel barrier layer 33, first, an MgAl alloy layer was formed on the first ferromagnetic layer 31, and then the MgAl alloy layer was oxidized. The MgAl alloy layer was formed by sputtering, and the MgAl alloy layer was oxidized by natural oxidation. After annealing (at 300°C) for 15 minutes, the tunnel barrier layer 33 made of MgAl2O4 was formed. The thickness t of the tunnel barrier layer 33 was 1.80 nm.

[0104] Next, a magnetization pinned layer with an SAF structure was formed on the tunnel barrier layer 33. The magnetization pinned layer was a multilayer laminate consisting of a three-layer laminate consisting of a CoFe layer (1 nm thick), a CoFeB layer (3 nm thick), and a CoFe layer (1 nm thick) as the second ferromagnetic layer 32, a Ru layer (0.8 nm thick) as the magnetic coupling layer 36, a CoFe layer (3 nm thick) as the third ferromagnetic layer 35, and an IrMn layer (8 nm thick) as the antiferromagnetic layer 34. The temperature during the formation of the magnetization pinned layer was room temperature. No heat treatment was performed after the formation of the magnetization pinned layer. The magnetoresistive layer 30 was fabricated by forming the magnetization pinned layer.

[0105] After the magnetoresistive layer 30 was formed, a cap layer 40 was formed on the magnetization fixed layer of the magnetoresistive layer 30. The cap layer 40 was a two-layer laminate including a Ru layer (thickness 3 nm) and a Ta layer (thickness 5 nm). The temperature during the formation of the cap layer 40 was room temperature. No heat treatment was performed after the formation of the cap layer 40.

[0106] After the formation of the cap layer 40, a heat treatment in a magnetic field was performed to exchange-couple the IrMn layer serving as the antiferromagnetic layer 34 with the third ferromagnetic layer 35, thereby imparting unidirectional magnetic anisotropy to the three-layer stack consisting of the CoFe layer serving as the third ferromagnetic layer 35 and the CoFe layer, CoFeB layer, and CoFe layer serving as the second ferromagnetic layer 32. In this heat treatment in a magnetic field, the heat treatment temperature was 300°C, the heat treatment time was 3 hours, and the strength of the applied magnetic field was 10 kOe (798 kA / m). This heat treatment in a magnetic field completed the production of the magnetoresistive effect element 1 according to Example 1.

[0107] (MR ratio measurement) FIG. 4 is a diagram showing a magnetoresistive device capable of measuring the MR ratio of the magnetoresistive element according to Example 1. The magnetoresistive device 50 includes a first electrode layer 51 and a second electrode layer 52 that sandwiches the magnetoresistive element 1 together with the first electrode layer 51. The magnetoresistive element 1 is microfabricated into a shape suitable for measuring magnetoresistive characteristics. The first electrode layer 51 is connected to an underlayer 20 on a substrate 10 of the magnetoresistive element 1, and the second electrode layer 52 is connected to a cap layer 40 of the magnetoresistive element 1. The magnetoresistive device 50 further includes a power supply 53 and a voltmeter 54, both of which are connected to the first electrode layer 51 and the second electrode layer 52. A current is applied to the magnetoresistive element 1 in the stacking direction by the power supply 53, and the voltage applied to the magnetoresistive element 1 at this time can be monitored by the voltmeter 54. In this example, a constant current was passed through the magnetoresistive element 1 in the stacking direction, and the resistance change of the magnetoresistive element 1 was measured by monitoring the applied voltage to the magnetoresistive element 1 with a voltmeter 54 while sweeping a magnetic field from the outside to the magnetoresistive element 1.

[0108] In this example, the MR ratio of the magnetoresistive element 1 was calculated from the measurement results of the resistance change. The MR ratio is expressed as a percentage and can be calculated by the following formula (i). MR ratio (%)=((R AP -R P ) / R P )×100(%) …(i) In this formula (i), R APis the magnitude of the resistance of the magnetoresistive element 1 when the magnetization direction of the first ferromagnetic layer 31 and the magnetization direction of the second ferromagnetic layer 32 are antiparallel. P is the magnitude of the resistance of the magnetoresistive element 1 when the magnetization direction of the first ferromagnetic layer 31 is parallel to the magnetization direction of the second ferromagnetic layer 32. In other examples and comparative examples described later, the MR ratio was similarly measured.

[0109] (RA measurement) In Example 1, the magnetoresistive device 50 was used to measure the resistance change of the magnetoresistive element 1, and the RA (area resistance) of the magnetoresistive element 1 was measured from the measurement results. In this example, when the area of ​​the magnetoresistive element 1 in a planar view is A, R p R multiplied by A p A was defined as RA (area resistance). RA is a numerical value obtained by dividing the resistance value obtained by dividing the applied bias voltage by the current flowing in the stacking direction of the magnetoresistive effect element 1 by the reciprocal of the area of ​​the surface where each layer is joined, and normalizing it to the resistance value per unit area. The RA (area resistance) value includes a measurement error of 3% or less. RA was also measured in the other examples and comparative examples described later in the same manner.

[0110] (Measurement of maximum height roughness Rz) In this example, the maximum height roughness Rz1 of the upper surface 33a of the tunnel barrier layer 33 and the maximum height roughness Rz2 of the lower surface 33b were measured by TEM observation of a cross section along the stacking direction. Measurement of these maximum height roughnesses Rz1 and Rz2 was performed in accordance with JIS B 0601:2013, with both reference lengths Lr1 and Lr2 set to 20 nm. In this example, of the maximum height roughness Rz1 of the upper surface 33a of the tunnel barrier layer 33 and the maximum height roughness Rz2 of the lower surface 33b, the maximum height roughness Rz1 of the upper surface 33a exhibited a larger maximum height roughness, so the maximum height roughness Rz1 of the upper surface 33a was designated as the maximum height roughness Rz. Similar measurements of maximum height roughness Rz were also performed in other examples and comparative examples described below. In these other examples and comparative examples, the maximum height roughness Rz1 of the upper surface 33a exhibited a larger maximum height roughness, so the maximum height roughness Rz1 of the upper surface 33a was designated as the maximum height roughness Rz.

[0111] (Estimation of the percentage of crystallized area) In this example, the proportion of the crystallized region 62 in the tunnel barrier layer 33 was estimated by TEM observation of a cross section along the stacking direction. In other examples and comparative examples described later, the proportion of the crystallized region 62 was similarly measured.

[0112] Example 2 In Example 2, a magnetoresistive effect element 1 was fabricated in the same manner as Example 1, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 30 seconds and the thickness t of the tunnel barrier layer 33 was 1.81 nm.

[0113] Example 3 In Example 3, a magnetoresistive effect element 1 was fabricated in the same manner as Example 1, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 15 seconds and the thickness t of the tunnel barrier layer 33 was 1.79 nm.

[0114] Example 4 In Example 4, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 1, except that the thickness t of the tunnel barrier layer 33 was set to 2.00 nm.

[0115] Example 5 In Example 5, a magnetoresistive effect element 1 was fabricated in the same manner as Example 1, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 30 seconds and the thickness t of the tunnel barrier layer 33 was 2.01 nm.

[0116] Example 6 In Example 6, a magnetoresistive effect element 1 was fabricated in the same manner as Example 1, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 15 seconds and the thickness t of the tunnel barrier layer 33 was 1.96 nm.

[0117] Example 7 In Example 7, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 1, except that the material and thickness of the tunnel barrier layer 33 were different.

[0118] The tunnel barrier layer 33 was formed by first forming an Mg layer on the first ferromagnetic layer 31 and then oxidizing the Mg layer. The Mg layer was formed by sputtering, and the Mg layer was oxidized by natural oxidation. After annealing (at 250°C) for 15 minutes, the tunnel barrier layer 33 made of MgO was formed. The thickness t of the tunnel barrier layer 33 was 1.79 nm.

[0119] Example 8 In Example 8, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 7, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 30 seconds and the thickness t of the tunnel barrier layer 33 was 1.82 nm.

[0120] Example 9 In Example 9, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 7, except that the polishing time for CMP polishing the upper surface of the lower electrode layer 21 was 15 seconds and the thickness t of the tunnel barrier layer 33 was 1.81 nm.

[0121] Example 10 In Example 10, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 3, except that the thickness t of the tunnel barrier layer 33 was set to 1.83 nm and the annealing conditions (temperature and treatment time) of the tunnel barrier layer 33 were changed. The annealing temperature was 380°C, and the annealing time was 15 minutes. In this example, the proportion of the crystallized region 62 was changed by changing the annealing temperature compared to Example 3.

[0122] Example 11 In Example 11, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 3, except that the thickness t of the tunnel barrier layer 33 was set to 1.82 nm and the annealing conditions (temperature and treatment time) of the tunnel barrier layer 33 were changed. The annealing temperature was 350°C, and the annealing time was 15 minutes. In this example, the proportion of the crystallized region 62 was changed by changing the annealing temperature compared to Example 3.

[0123] Example 12 In Example 12, a magnetoresistive effect element was fabricated in the same manner as in Example 3, except that the thickness t of the tunnel barrier layer 33 was set to 1.81 nm and the annealing conditions (temperature and treatment time) of the tunnel barrier layer 33 were changed. The annealing temperature was set to 330°C, and the annealing time was set to 15 minutes. In this example, the proportion of the crystallized region 62 was changed by changing the annealing temperature compared to Example 3.

[0124] Example 13 In Example 13, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 3, except that the thickness t of the tunnel barrier layer 33 was set to 1.83 nm and the annealing conditions (temperature and treatment time) of the tunnel barrier layer 33 were changed. The annealing temperature was set to 260°C, and the annealing time was set to 15 minutes. In this example, the proportion of the crystallized region 62 was changed by changing the annealing temperature compared to Example 3.

[0125] Example 14 In Example 14, a magnetoresistive effect element 1 was fabricated in the same manner as in Example 3, except that the thickness t of the tunnel barrier layer 33 was set to 1.84 nm and the annealing conditions (temperature and treatment time) of the tunnel barrier layer 33 were changed. The annealing temperature was set to 220°C, and the annealing time was set to 15 minutes. In this example, the proportion of the crystallized region 62 was changed by changing the annealing temperature compared to Example 3.

[0126] (Comparative Example 1) In Comparative Example 1, a magnetoresistive effect element was fabricated in the same manner as in Example 1, except that the upper surface of the lower electrode layer 21 was not polished by CMP and the thickness t of the tunnel barrier layer 33 was set to 1.82 nm.

[0127] (Comparative Example 2) In Comparative Example 2, a magnetoresistive effect element was fabricated in the same manner as in Example 1, except that the upper surface of the lower electrode layer 21 was not polished by CMP and the thickness t of the tunnel barrier layer 33 was set to 1.98 nm.

[0128] (Comparative Example 3) In Comparative Example 3, a magnetoresistive effect element was fabricated in the same manner as in Example 7, except that the upper surface of the lower electrode layer 21 was not polished by CMP and the thickness t of the tunnel barrier layer 33 was set to 1.84 nm.

[0129] Comparative Example 4 In Comparative Example 4, a magnetoresistive effect element was fabricated by an epitaxial method. First, a substrate 10 made of MgO single crystal was placed in an epitaxial apparatus, and an underlayer 20 was formed. In this Comparative Example, the underlayer 20 consisted of a single Cr layer (thickness: 40 nm). After the underlayer 20 was formed, a heat treatment (temperature: 800°C) was performed for 60 minutes.

[0130] Next, a magnetoresistive layer 30 was formed on the underlayer 20. The magnetoresistive layer 30 had, in this order, a first ferromagnetic layer 31 as a magnetization free layer, a tunnel barrier layer 33, and a magnetization fixed layer. In this comparative example, the magnetization fixed layer did not have an SAF structure.

[0131] First, a first ferromagnetic layer 31 was formed as a magnetization free layer. The first ferromagnetic layer 31 was made of an Fe layer (thickness: 30 nm). After the formation of the first ferromagnetic layer 31, an annealing treatment (temperature: 300°C) was performed for 60 minutes. A tunnel barrier layer 33 made of MgAl2O4 was formed on the first ferromagnetic layer 31. The thickness t of the tunnel barrier layer 33 was set to 1.80 nm. After the formation of this MgAl2O4 layer, an annealing treatment (temperature: 450°C) was performed for 15 minutes.

[0132] Subsequently, a magnetization fixed layer was formed on the tunnel barrier layer 33. The magnetization fixed layer was a multilayer laminate consisting of an Fe layer (thickness 6 nm) as the second ferromagnetic layer 32 and an IrMn layer (thickness 12 nm) as the antiferromagnetic layer 34. After the Fe layer was formed, an annealing treatment (temperature 300°C) was performed for 15 minutes. No heat treatment was performed after the magnetization fixed layer was formed. By forming the magnetization fixed layer, a magnetoresistive layer 30 was produced.

[0133] After fabricating the magnetoresistive layer 30, a cap layer 40 made of a Ru layer (thickness: 10 nm) was formed on the magnetization fixed layer of the magnetoresistive layer 30. After forming the cap layer 40, a magnetic field heat treatment was performed to exchange-couple the IrMn layer serving as the antiferromagnetic layer 34 with the Fe layer serving as the second ferromagnetic layer 32, thereby imparting unidirectional magnetic anisotropy to the Fe layer. The heat treatment temperature in the magnetic field was 300°C, and the heat treatment time was 3 hours. The strength of the applied magnetic field was 10 kOe (798 kA / m). The formation of the magnetoresistive effect element 1 according to this comparative example was completed by the magnetic field heat treatment.

[0134] Table 1 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect elements according to Examples 1 to 3. Table 2 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect elements according to Examples 4 to 6. Table 3 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect elements according to Examples 7 to 9. Table 4 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect elements according to Examples 10 to 12. Table 5 shows the structure, fabrication conditions, and evaluation results of RA and MR ratio of each layer included in the magnetoresistive effect elements according to Examples 13 and 14. Table 6 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect elements according to Comparative Examples 1 to 3. Table 7 shows the structure, fabrication conditions, and measurement results of RA and other properties of each layer included in the magnetoresistive effect element according to Comparative Example 4.

[0135] [Table 1]

[0136] [Table 2]

[0137] [Table 3]

[0138] [Table 4]

[0139] [Table 5]

[0140] [Table 6]

[0141] [Table 7]

[0142] As shown in Tables 1 to 7, the Rz / t of Examples 1 to 14 was Rz / t<1, and the Rz / t of Comparative Examples 1 to 4 was Rz / t>1. Examples 1 to 14 were shown to have high RA while suppressing a decrease in MR ratio compared to Comparative Examples 1 to 4. Furthermore, Examples 1 to 9 and 11 to 13 (proportion of crystallized region greater than 5% and less than 65%) were shown to have particularly high RA while suppressing a decrease in MR ratio compared to Examples 10 and 14 (proportion of crystallized region equal to or less than 5% or equal to or greater than 65%). [Industrial Applicability]

[0143] According to the present embodiment, a magnetoresistive element having a high RA while suppressing a decrease in the MR ratio, and a method for manufacturing such a magnetoresistive element are provided. [Explanation of symbols]

[0144] 1...magnetoresistive effect element, 31...first ferromagnetic layer, 32...second ferromagnetic layer, 33...tunnel barrier layer, 33a...upper surface, 33b...lower surface, 61...amorphous region, 62...crystallized region.

Claims

1. a first ferromagnetic layer; and a second ferromagnetic layer; and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is a thickness of the tunnel barrier layer, Rz / t<1; the tunnel barrier layer includes at least one crystallized region having a composition represented by formula (1), A magnetoresistive element, wherein in a cross section along a stacking direction, the ratio of the area of ​​the at least one crystallized region to the area of ​​the entire tunnel barrier layer is greater than 5% and smaller than 65%. A １－ｘ B ｘ O ｙ …(1) [In the formula, A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Cr, Rh, Ir, Ge, and Co, and 0<x≦1 and 0.35≦y≦1.7.]

2. 2. The magnetoresistive element according to claim 1, wherein said at least one crystallized region has a crystal structure in which the (001) plane is oriented in said stacking direction.

3. A first ferromagnetic layer; a second ferromagnetic layer; and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is a thickness of the tunnel barrier layer, Rz / t<1; the tunnel barrier layer includes at least one crystallized region having a composition represented by formula (1), the at least one crystallized region has a width along an in-plane direction of the tunnel barrier layer, The maximum width of the magnetoresistive element is less than 8 nm. A 1-x B x O y…(1) [In the formula, A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Cr, Rh, Ir, Ge, and Co, and 0<x≦1 and 0.35≦y≦1.7.]

4. 4. The magnetoresistive element according to claim 1, wherein at least a portion of said at least one crystallized region is lattice-matched with at least one of said first ferromagnetic layer and said second ferromagnetic layer.

5. A first ferromagnetic layer; a second ferromagnetic layer; and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is a thickness of the tunnel barrier layer, Rz / t<1; the tunnel barrier layer includes at least one crystallized region having a composition represented by formula (1), At least one of the first ferromagnetic layer, the second ferromagnetic layer, and the tunnel barrier layer includes a twin crystal. A 1-x B x O y…(1) [In the formula, A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Cr, Rh, Ir, Ge, and Co, and 0<x≦1 and 0.35≦y≦1.7.]

6. 6. The magnetoresistive element according to claim 5, wherein the twin crystal has a face-centered cubic lattice structure and the twin crystal plane is a (111) plane, or the twin crystal has a body-centered cubic lattice structure and the twin crystal plane is a (112) plane.

7. A first ferromagnetic layer; a second ferromagnetic layer; and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is a thickness of the tunnel barrier layer, Rz / t<1; the tunnel barrier layer includes at least one crystallized region having a composition represented by formula (1), A magnetoresistive element, wherein in the formula (1), A represents Mg and B represents Al. A 1-x B x O y…(1) [In the formula, A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Cr, Rh, Ir, Ge, and Co, and 0<x≦1 and 0.35≦y≦1.7.]

8. A first ferromagnetic layer; a second ferromagnetic layer; and a tunnel barrier layer stacked between the first ferromagnetic layer and the second ferromagnetic layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, Rz is the larger of the maximum roughness in height of the upper surface and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is a thickness of the tunnel barrier layer, Rz / t<1; the tunnel barrier layer includes at least one crystallized region having a composition represented by formula (1), A magnetoresistive element, wherein in the formula (1), 0<x<0.

5. A 1-x B x O y…(1) [In the formula, A represents at least one element selected from the group consisting of Mg, Zn, Cu, Cd, Li, Ni, Co, Fe, Mn, Cr, Hg, and V, B represents at least one element selected from the group consisting of Al, Ga, In, Sc, Cr, Rh, Ir, Ge, and Co, and 0<x≦1 and 0.35≦y≦1.7.]

9. At least one of the first ferromagnetic layer and the second ferromagnetic layer is a Co layer in contact with the tunnel barrier layer. ｚ Fe １００－z 9. The magnetoresistive element according to claim 1, having a region where (0<z<80).

10. forming a first ferromagnetic layer; forming an MgAl alloy layer on the first ferromagnetic layer; The MgAl alloy layer is oxidized to form Mg １－ｘ Al ｘ O ｙ forming a tunnel barrier layer including at least one crystallized region having a composition expressed by (0<x≦1, 0.35≦y≦1.7); forming a second ferromagnetic layer on the tunnel barrier layer; Equipped with the tunnel barrier layer has an upper surface and a lower surface opposite the upper surface, A method for manufacturing a magnetoresistive effect element, wherein Rz / t<1 is satisfied, where Rz is the larger of the maximum roughness in height of the upper surface of the tunnel barrier layer and the maximum roughness in height of the lower surface of the tunnel barrier layer, and t is the thickness of the tunnel barrier layer.

11. 11. The method for manufacturing a magnetoresistive effect element according to claim 10, wherein the step of oxidizing the MgAl alloy layer includes the step of oxidizing the MgAl alloy layer by at least one of radical oxidation, plasma oxidation, ozone oxidation, and natural oxidation.

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