JP2020027896A - Magnetic tunnel junction element and magnetoresistive memory device - Google Patents

Abstract

To provide a magnetic tunnel junction element which can be simplified in a structure of a fixing layer of a magnetic tunnel junction element and in which the number of laminates of the magnetic tunnel junction element is reduced.SOLUTION: A magnetic tunnel junction element 10 comprises: a free layer 15 in which a magnetization direction can be changeable; a fixing layer 13 that maintains the magnetization direction to a prescribed direction and is formed by a single layer; and an insulation layer 14 that is laminated between the free layer 15 and the fixing layer 13. Any one of at least the free layer 15 and the fixing layer 13 is a L1-type magnetic alloy film, and the insulation layer 14 is a layer having a texture of (111).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic tunnel junction device and a magnetoresistive memory device.

  A magnetoresistive element having perpendicular magnetization and performing reading by the magnetoresistive effect has high thermal agitation resistance to miniaturization, and is expected as a next-generation memory or the like.

  This next-generation memory has a free layer (also called a storage layer) whose magnetization direction is variable, a fixed layer (also called a reference layer) that maintains a predetermined magnetization direction, and a gap between the free layer and the fixed layer. , A magnetic tunnel junction (MTJ) element having an insulating layer provided as a tunnel barrier.

  A ferromagnetic material having high perpendicular magnetic anisotropy and high spin polarizability is required as a material of a spin-polarized magnetic layer that basically constitutes such a next-generation memory. However, there are few reports of a material having a perpendicular magnetic anisotropy and having a high spin polarizability experimentally. In addition, the only material having perpendicular magnetic anisotropy and high spin polarizability is a CoFeB alloy using interfacial magnetic anisotropy, and the material selection range is very narrow in practice. .

  Patent Literature 1 discloses that a spacer layer having a lattice constant smaller than that of a spin-polarized magnetic layer is brought into contact with the spin-polarized magnetic layer, and a spin-polarized magnetic layer is used for spin-polarized magnetic layers. A magnetic tunnel junction device in which the crystal lattice of a magnetic layer is reduced in the x-axis and y-axis directions is described.

However, in Patent Document 1, since the material itself does not have a large perpendicular magnetic anisotropy, a fixed layer in which a perpendicular magnetization holding layer is combined is used. In many studies, the perpendicular magnetization holding layer of L1 ₀ type having a (001) texture FePd, FePt, Co and Pd, or a laminate of Co and Pt in the (001) axially Co / Pd multilayer film, or Co / Pt This is a layer composed of a ferromagnetic material composed of a multilayer film and having an easy axis of magnetization oriented perpendicular to the film surface.

  Further, the fixed layer needs to be formed by combining the perpendicular magnetization holding layer with the ferromagnetic material CoFeB having a high spin polarization. In the magnetic tunnel junction device having a free layer and a fixed layer made of a CoFeB alloy, the (001) texture is required to obtain a high TMR (Tunnel Magneto Resistance) effect due to the band structure of the insulating layer. have.

  For example, as an MTJ stack configuration, there is an example in which an MgO film having a (001) texture is used for an insulating layer, and an underlayer for improving the orientation of the perpendicular magnetization holding layer also has a (001) texture. That is, the MTJ structure and the process are configured based on the (001) texture.

Japanese Patent Application Laid-Open No. 2010-238769

  As described above, the magnetic tunnel junction element described in Patent Document 1 has a problem that the structure of the fixed layer is complicated and the thickness is large.

  In the free layer, there is a problem in thermal stability and high density due to weak perpendicular magnetic anisotropy. On the other hand, Mn—Ge materials such as MnGa and MnGe, which have a large perpendicular magnetic anisotropy, have been studied, but there is a problem that a high tunnel magnetoresistance effect cannot be obtained by experiments.

The magnetic tunnel junction element of one embodiment has a free layer in which the magnetization direction is variable, a magnetization layer that maintains the magnetization direction in a predetermined direction, a fixed layer made of a single layer, and a gap between the free layer and the fixed layer. and an insulating layer laminated are either L1 ₁ type magnetic alloy film of at least the free layer and the fixed layer, the insulating layer was set to be a layer having a texture (111).

  According to the magnetic tunnel junction element of one embodiment, the magnetization direction can be maintained in a predetermined direction by a single spin-polarized magnetic layer without including the perpendicular magnetization holding layer and the spacer layer. Therefore, in the magnetic tunnel junction device of one embodiment, the structure of the fixed layer can be simplified, and the number of stacked magnetic tunnel junction devices can be reduced.

In one embodiment, the insulating layer is preferably made of MgO, MgAl ₂ O _4, MgGa ₂ O ₄ , ZnAl ₂ O ₄ or ZnGa ₂ O ₄ having a texture of (111). You may.

  According to the magnetic tunnel junction device of one embodiment, both a large tunnel magnetoresistance effect and a high perpendicular magnetic anisotropy can be obtained.

  In one embodiment, the magnetic tunnel junction device preferably includes an underlayer having a texture of (111).

  According to the magnetic tunnel junction device of one embodiment, the (111) plane has more coordination numbers (the number of nearest lattice points) and the in-plane coupling is stronger than the (001) plane, so that the crystal structure is stabilized. As a result, atom diffusion can be suppressed.

  In one embodiment of the present invention, the fixed layer preferably does not include a perpendicular magnetization holding layer or a spacer layer.

  According to the magnetic tunnel junction device of one embodiment, the thickness of the magnetic tunnel junction device can be reduced.

The magnetoresistive memory device according to one embodiment includes a free layer having a variable magnetization direction, a magnetization layer maintained in a predetermined direction, a fixed layer including a single layer, and a fixed layer formed between the free layer and the fixed layer. and an insulating layer laminated are either L1 ₁ type magnetic alloy film of at least the free layer and the fixed layer, the insulating layer and the magnetic tunnel junction device is a layer having a texture (111) And an electrode for applying a voltage to the magnetic tunnel junction element.

  According to the magnetoresistive memory device of one embodiment, a single spin-polarized magnetic layer can be used as a layer that maintains the magnetization direction in a predetermined direction without including the perpendicular magnetization holding layer and the spacer layer. Therefore, in the magnetoresistive memory device according to one embodiment, the structure of the fixed layer can be simplified, and the number of stacked magnetic tunnel junction elements can be reduced.

  According to the magnetic tunnel junction device and the magnetoresistive memory device of the present invention, the structure of the fixed layer of the magnetic tunnel junction device can be simplified, and a magnetic tunnel junction device with a reduced number of stacked magnetic tunnel junction devices is provided. be able to.

FIG. 2 is a sectional view illustrating a schematic configuration of a magnetic tunnel junction element according to the first embodiment; It is sectional drawing which shows schematic structure of the reference example of a magnetic tunnel junction element. 4 is a graph showing a band structure of a material NiPt used for a spin-polarized magnetic layer (fixed layer) of the magnetic tunnel junction element according to the first embodiment. 9 is a graph showing a band structure of MgAl ₂ O ₄ used for a barrier layer of the magnetic tunnel junction device according to the second embodiment. FIG. 14 is a perspective view illustrating a main part of an example of a magnetoresistive memory device according to a third embodiment.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a schematic configuration of the magnetic tunnel junction device according to the first embodiment. The magnetic tunnel junction device 10 includes a substrate 11, a buffer layer 12, a fixed layer 13, an insulating layer 14, a free layer 15, and a cap layer 16.

  The substrate 11 is a Si substrate. For example, the substrate 11 is preferably a (111) substrate. Further, the substrate 11 may be a Si substrate with a thermal oxide film or a Si single crystal substrate.

  The buffer layer 12 is a stabilizing layer formed on the substrate 11. Specifically, the buffer layer 12 is a layer containing Ru.

The fixed layer 13 is a layer that maintains the magnetization direction in a predetermined direction. Fixed layer 13 is desirably L1 ₁ type magnetic alloy film. Further, as the fixed layer 13, it is preferable to select a material whose magnetization direction does not easily change with respect to the free layer 15. However, the material forming the fixed layer 13 is not particularly limited, and can be selected from any material according to various conditions.

For example, the fixed layer 13 may be made of an L11 type ₁ alloy. In particular the fixed layer 13 may be composed of L1 ₁ type (Co-Ni) Pt alloy. Specifically, the fixed layer 13 _may be composed of L1 ₁ type alloys of Co _{0.5 Ni} 0.5 Pt. Further, the fixed layer 13 may be made of Fe _0.5 Ni _0.5 Pt, Co _0.5 Fe _0.5 Pt, NiPt, FePt, or CoPt. Further, the atomic ratio in the alloy may be changed. When the fixed layer 13 has any one of the above-described configurations, the fixed layer 13 can be a single layer that maintains the magnetization direction in a predetermined direction. The fixed layer 13 is also called a reference layer.

The insulating layer 14 is a layer containing an insulating substance as a main component. The insulating layer 14 is a layer having a texture of (111). The insulating layer 14 is laminated between the fixed layer 13 having ferromagnetism and the free layer 15. Further, the insulating layer 14 is desirably formed of an insulating film of MgO or MgAl ₂ O ₄ . Then, when a voltage is applied perpendicularly to the junction surface between the fixed layer 13 and the free layer 15, a current flows through the magnetic tunnel junction element 10 by a tunnel effect.

The free layer 15 is a layer whose magnetization direction changes. Free layer 15 is desirably L1 ₁ type magnetic alloy film. For example, the free layer 15 may be composed of L1 ₁ type ordered alloy. Especially the free layer 15 may be composed of L1 ₁ type (Co-Ni) Pt ordered alloy. Specifically, the free layer 15 _may be composed of L1 ₁ type alloys of Co _{0.5 Ni} 0.5 Pt. The free layer 15 may be made of Fe _0.5 Ni _0.5 Pt, Co _0.5 Fe _0.5 Pt, NiPt, FePt or CoPt. Further, the atomic ratio in the alloy may be changed. When the free layer 15 has any one of the above-described configurations, the free layer 15 can be a single layer in which the magnetization direction changes. The free layer 15 is also called a storage layer.

  The cap layer 16 is a stabilizing layer formed on the free layer 15. For example, the cap layer 16 is preferably a layer containing Ru.

  Thus, the magnetic tunnel junction device according to the first embodiment is configured. Next, a comparison with the structure of a conventional magnetic tunnel junction device will be described. FIG. 2 is a sectional view showing a schematic configuration of a reference example of the magnetic tunnel junction element.

  2, the magnetic tunnel junction device 20 includes a substrate 21, a buffer layer 22, a high spin polarization magnetic layer 23A, a perpendicular magnetization holding layer 23B, an insulating layer 24, a free layer 25, a cap layer 26, Is provided. Then, the fixed layer 23 is formed of the high polarizability magnetic layer 23A and the perpendicular magnetization holding layer 23B. The high polarizability magnetic layer 23A is made of a Co-based Heusler alloy or the like, but the material itself has no perpendicular magnetic anisotropy. Therefore, in order to function as the fixed layer 23 of the magnetic tunnel junction device 20, it is necessary to couple the perpendicular magnetization holding layer 23B.

Compared to reference example, the magnetic tunnel junction element 10 of the first embodiment, by using the L1 ₁ type magnetic alloy film to the fixed layer 13, the fixed layer 13, with a high spin polarization of a single layer It can have high perpendicular magnetic anisotropy. Therefore, in the magnetic tunnel junction device 10 of the first embodiment, the fixed layer 23 needs to be formed of a plurality of layers of the high spin polarization magnetic layer 23A and the perpendicular magnetization holding layer 23B, like the magnetic tunnel junction device 20 of the reference example. There is no.

Next, the band structure of the magnetic tunnel junction device 10 according to the first embodiment will be described. FIG. 3 is a graph showing a band structure of a material NiPt used for the spin-polarized magnetic layer (fixed layer 13) of the magnetic tunnel junction device according to the first embodiment. In FIG. 3, the vertical axis indicates the energy level (ev), and the horizontal axis indicates the electron wave vector k. In Figure 3, the band structure is shown in the example with L1 ₁ type magnetic alloy NiPt the fixed layer 13.

FIG. 3 shows the band structure of the L11 type ₁ magnetic alloy NiPt. As a result of first-principles calculations, the L11 type ₁ magnetic alloy NiPt is half metallic (ie, 100% spin polarizability) in the (111) direction, that is, between G and Z in FIG. A resistance effect can be expected. Also as shown in Table 1, L1 ₁ type magnetic alloy NiPt shows a large perpendicular magnetic anisotropy ¹⁰ 6 J / ^{m 3} things.

  As described above, the magnetic tunnel junction device 10 according to the first embodiment has a large perpendicular magnetic anisotropy and a large spin polarizability.

Furthermore, it is desirable to consider lattice constant matching when producing a magnetic tunnel junction device. Table 1 is a table showing the lattice constant and Misfit of the alloy. In Table 1, Misfit is shown at a ratio Ru, the difference in lattice constant NiPt alloy MgO or lattice constants and L1 ₁ structure of MgAl ₂ O _4, divided by the lattice constant of NiPt alloy L1 ₁ structure .

The size of Misfit As shown in Table 1 is a value sufficiently smaller in laminating the _L1 1 NiPt Ru, MgO or MgAl ₂ O _4.

Thus, according to the magnetic tunnel junction device of the first embodiment, by a fixed layer and L1 ₁ type magnetic alloy film, a layer having a texture insulating layer (111), the magnetization of a single layer It can be a layer that maintains the direction in a predetermined direction.

  According to the magnetic tunnel junction device of the first embodiment, a single layer can be used as a layer that maintains the magnetization direction in a predetermined direction without including the perpendicular magnetization holding layer. Therefore, in the magnetic tunnel junction device of the first embodiment, the structure of the fixed layer can be simplified, and the number of stacked magnetic tunnel junction devices can be reduced. Further, according to the magnetic tunnel junction device of the first embodiment, the thickness of the magnetic tunnel junction device can be reduced.

Further, according to the magnetic tunnel junction device of the first embodiment, the free layer and L1 ₁ type magnetic alloy film by a layer having a texture insulating layer (111), the magnetization direction of a single layer It can be a variable layer.

Further, according to the magnetic tunnel junction device of the first embodiment, by a layer having a texture at least either the free layer and the fixed layer and L1 ₁ type magnetic alloy film, an insulating layer (111), more The magnetic tunnel junction element can be configured with a small number of stacked layers, and the crystal structure can be stabilized. As a result, in the magnetic tunnel junction element, the diffusion of atoms can be suppressed.

  In addition, the magnetic tunnel junction device of the first embodiment has good thermal stability, so that the density of the magnetic tunnel junction device can be increased.

  Further, according to the magnetic tunnel junction device of the first embodiment, Ms (saturated magnetization) can be reduced by adjusting the amounts of Ni and Co, and the magnetization direction can be switched at high speed.

(Embodiment 2)
In the second embodiment, an example in which MgAl ₂ O ₄ is used for the insulating layer 14 will be described.
FIG. 4 is a graph showing a band structure of MgAl ₂ O ₄ used for the barrier layer of the magnetic tunnel junction device according to the second embodiment. 4, the vertical axis indicates the energy level (ev), and the horizontal axis indicates the electron wave vector k. FIG. 4 shows a band structure in an example in which MgAl ₂ O ₄ is used for the insulating layer 14.

As shown in FIG. 4, MgAl ₂ O ₄ is a direct gap insulator at point G and filters only electrons that are perpendicularly incident on the insulating layer, ie, travel in the (111) direction. Therefore, the magnetic tunnel junction device using MgAl ₂ O ₄ for the insulating layer has high cost by using a material that is half metallic in the (111) direction as shown in FIG. 3 of the first embodiment for the spin polarization layer. It can be seen that a tunnel magnetoresistance effect and a high spin polarizability can be obtained.

  As described above, according to the magnetic tunnel junction element of the second embodiment, since the lattice mismatch can be reduced, an even larger tunnel magnetoresistance effect can be expected.

(Embodiment 3)
In the third embodiment, a description will be given of a magnetoresistive memory device using the magnetic tunnel junction element of the first or second embodiment.
FIG. 5 is a perspective view illustrating a main part of an example of the magnetoresistive memory device according to the third embodiment.

  In FIG. 5, the magnetoresistive memory device includes a memory cell 30, a bit line 31, contact plugs 35 and 37, and a word line 38.

  The memory cell 30 includes a semiconductor substrate 32, diffusion regions 33 and 34, a source line 36, a gate insulating film 39, and a magnetic tunnel junction device 10. Although the magnetic tunnel junction element 10 corresponds to the magnetic tunnel junction element 10 of the first embodiment, the magnetic tunnel junction element of the second embodiment may be used.

  The magnetoresistive memory device is formed by arranging a plurality of memory cells 30 in a matrix and connecting them to each other using a plurality of bit lines 1 and a plurality of word lines 38. In the MRAM, data write processing is performed using a spin torque injection method.

  The semiconductor substrate 32 has diffusion regions 33 and 34 on the upper surface, and the diffusion region 33 is arranged at a predetermined distance from the diffusion region 34. Diffusion region 33 functions as a drain region, and diffusion region 34 functions as a source region. Diffusion region 33 is connected to magnetic tunnel junction device 10 via contact plug 37.

  The bit line side electrode 31 is arranged above the semiconductor substrate 32 and is connected to the magnetic tunnel junction device 10. The bit line 31 is connected to a write circuit (not shown) and a read circuit (not shown).

  Diffusion region 34 is connected to source line 36 via contact plug 35. The source line 36 is connected to a write circuit (not shown) and a read circuit (not shown).

  Word line 38 is arranged on semiconductor substrate 32 via gate insulating film 39 so as to be in contact with diffusion region 33 and diffusion region 34. The word line 38 and the gate insulating film 39 function as a selection transistor. The word line 38 is activated by being supplied with current from a circuit (not shown), and is turned on as a selection transistor.

  In this magnetoresistive memory device, a voltage is applied to the magnetic tunnel junction device 10 using the bit line 31 and the diffusion region 33 as electrodes, and the spin torque of electrons aligned in a certain direction by the application of the voltage causes the magnetization of the ferromagnetic layer to change. Change direction. By changing the current direction, the value of data recorded in the magnetoresistive memory device can be changed.

  As described above, according to the magnetoresistive memory device of the third embodiment, it is possible to provide a single layer that maintains the magnetization direction in a predetermined direction without including the perpendicular magnetization holding layer. Therefore, in the magnetoresistive memory device according to one embodiment, the structure of the fixed layer can be simplified, and the number of stacked magnetic tunnel junction elements can be reduced.

  Further, according to the magnetoresistive memory device of the third embodiment, since the magnetic tunnel junction element has good thermal stability, it is possible to realize a high density of the magnetoresistive memory device.

It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist. For example, in the magnetic tunnel junction element, the (111) plane junction may be between one of the fixed layer 13 and the free layer 15 and the insulating layer 14. In the magnetic tunnel junction device, both the fixed layer 13 and the insulating layer 14 and the free layer 15 and the insulating layer 14 may have a (111) plane junction. Further _{, the} insulating layer 14 may be made of MgGa ₂ O ₄ , ZnAl ₂ O ₄ or ZnGa ₂ O ₄ having a texture of (111).

10, 20 Magnetic tunnel junction element 11, 21 Substrate 12, 22 Buffer layer 13, 23 Fixed layer 14, 24 Insulating layer 15, 25 Free layer 16, 26 Cap layer 23A Highly polarizable magnetic layer 23B Perpendicular magnetization holding layer 30 Memory cell 31 bit line 32 semiconductor substrate 33, 34 diffusion region 35, 37 contact plug 36 source line 38 word line 39 gate insulating film

Claims (5)

A free layer having a variable magnetization direction;
A fixed layer consisting of a single layer, maintaining the magnetization direction in a predetermined direction,
An insulating layer laminated between the free layer and the fixed layer,
At least one of the free layer and the fixed layer is an L11 type ₁ magnetic alloy film,
The magnetic tunnel junction device, wherein the insulating layer is a layer having a texture of (111). The insulating layer, _MgO having a texture of _{(111), MgAl 2 O 4} , MgGa 2 O 4, the magnetic tunnel junction device according to claim 1 consisting of ZnAl ₂ O ₄ or ZnGa ₂ O _4.   3. The magnetic tunnel junction device according to claim 1, further comprising an underlayer having a texture of (111).   4. The magnetic tunnel junction device according to claim 1, wherein the fixed layer does not include a perpendicular magnetization holding layer. A free layer having a variable magnetization direction, maintaining the magnetization direction in a predetermined direction, a fixed layer formed of a single layer, and an insulating layer laminated between the free layer and the fixed layer, is either L1 ₁ type magnetic alloy film of at least the free layer and the fixed layer, the insulating layer and the magnetic tunnel junction device is a layer having a texture (111),
A magnetoresistive memory device comprising: an electrode for applying a voltage to the magnetic tunnel junction element.

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