JP5441274B2 - Magnetoresistive element and magnetic memory - Google Patents

Description

  The present invention relates to a magnetoresistive effect element capable of recording information by supplying current bidirectionally, and a magnetic memory using the magnetoresistive effect element.

  2. Description of the Related Art A magnetic random access memory (MRAM) using a tunneling magnetoresistive effect (TMR) is characterized in that data is stored according to the magnetization state of an MTJ (Magnetic Tunnel Junction) element. In general, an MTJ element includes a magnetic layer called a storage layer, a magnetic layer called a reference layer, and a tunnel barrier layer provided between these magnetic layers. For magnetic random access memory, a number of technologies have been proposed for practical use. For example, a yoke wiring structure has been proposed for the purpose of reducing the write current. Further, regarding the structure of the MTJ element, there are a structure using a perpendicular magnetization film made of a GdFe alloy (for example, see Non-Patent Document 1), a laminated structure using a perpendicular magnetization film (for example, see Non-Patent Document 2), and the like. Proposed.

  These are magnetic field writing methods that basically reverse the magnetization direction of the magnetic layer using a magnetic field generated by an electric current. As a matter of course, the magnetic field generated by the current can generate a large magnetic field if the current is large, but the current that can be passed through the wiring is limited as the miniaturization progresses. By using a yoke structure that reduces the distance between the wiring and the magnetic layer or concentrates the generated magnetic field, the current value required to reverse the magnetization of the magnetic material can be reduced. Since the magnetic field required for the magnetization reversal of the body increases, it is very difficult to achieve both current reduction and miniaturization.

  The reason why the magnetic field necessary for the magnetization reversal of the magnetic material increases due to the miniaturization is that it requires magnetic energy to overcome the thermal disturbance. Magnetic energy can be increased by increasing the magnetic anisotropy energy density and the volume of the magnetic material, but the volume is reduced by miniaturization. It is common.

  However, as described above, an increase in the magnetic energy of the magnetic material increases the reversal magnetic field, so it is very difficult to achieve both low current and miniaturization. A fully closed magnetic circuit type yoke structure has been proposed in which a perpendicularly magnetized film having a large magnetocrystalline anisotropy energy is introduced and which has an ultimate generation efficiency of a large current magnetic field (see, for example, Patent Document 1). However, in Patent Document 1, since the yoke structure is larger than the magnetic element, the cell area becomes relatively large, and miniaturization, low current, and reduction of the cell area cannot all be satisfied.

  In recent years, magnetization reversal due to spin-polarized current has been theoretically predicted and has been confirmed by experiments, and MRAM using spin-polarized current has been proposed (see, for example, Non-Patent Document 3). According to this MRAM, the magnetization reversal of the magnetic material can be realized by the action of the spin-polarized electrons only by passing a spin-polarized current through the magnetic material. If the volume of the magnetic material is small, the number of spin-polarized electrons injected is small. Therefore, it is expected that both miniaturization and low current can be achieved. Further, since the magnetic field generated by the current is not used, a yoke structure for increasing the magnetic field is not necessary, and the cell area can be reduced.

  However, as a matter of course, even in the magnetization reversal method using the spin-polarized current, the problem of thermal disturbance becomes obvious as the size is reduced. As described above, in order to ensure thermal disturbance resistance, it is necessary to increase the magnetic anisotropic energy density. In the in-plane magnetization type configuration mainly studied so far, it is common to use shape magnetic anisotropy. In this case, since the magnetic anisotropy is ensured by utilizing the shape, the current required for the magnetization reversal becomes sensitive to the shape, and there is a problem that the variation of the reversal current increases with the miniaturization. Moreover, since the aspect of the MTJ cell needs to be at least 1.5 or more, the cell size is also increased. A material having a large magnetocrystalline anisotropy energy density when the magnetic layer of the magnetoresistive effect element is in-plane magnetization type and utilizes magnetocrystalline anisotropy instead of shape magnetic anisotropy, such as a hard disk medium When the Co—Cr alloy material used in the above is used, the crystal axes are greatly dispersed in the plane. For this reason, a decrease in MR ratio (Magneto Resistive) and incoherent precession are induced, resulting in an increase in reversal current.

JP 2005-19464 A

Ikeda et al., “GMR film and TMR film using GdFe alloy perpendicular magnetization film”, Journal of Japan Society of Applied Magnetics, Vol.24, No.4-2, 2000, p.563-566 N.Nisimura, et al., "Magnetic tunnel junction device with perpendicular magnetization films for high-density magnetic random access memory", JOURNAL OF APPLIED PHYSICS, VOLUME 91, NUMBER 8, 15 APRIL 2002 J.C. Slonczewski et al., "Current-driven excitation of magnetic multilayers", JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, VOLUME 159, NUMBER 1-2, L1-7 1996

  As described above, the memory layer and the reference layer constituting the MTJ element are made of a magnetic material and generate a magnetic field to the outside. In general, in the perpendicular magnetization type MTJ element, the leakage magnetic field generated from the reference layer is larger than that in the in-plane magnetization type. In addition, the memory layer having a smaller coercive force than the reference layer is strongly influenced by the leakage magnetic field from the reference layer. Specifically, due to the influence of the leakage magnetic field from the reference layer, the reversal current value required for writing increases, which causes a problem of deteriorating thermal stability.

  As a measure for reducing the leakage magnetic field from the reference layer in the perpendicular magnetization type MTJ element, a SAF (Synthetic Anti-Ferromagnetic) structure, a dual pin structure, and the like have been proposed. For the SAF structure, the leakage magnetic field applied to the storage layer is reduced by providing a film thickness difference. In the case of the in-plane magnetization type SAF structure, the leakage magnetic field applied to the storage layer can be reduced with a film thickness difference of about 1.2 times.

  However, as will be described later, in the case of the perpendicular magnetization type SAF structure, the present inventors cannot sufficiently reduce the leakage magnetic field applied to the memory layer with a film thickness difference of about 1.2 times. I found it.

  Also, in the dual pin structure, the vertical magnitude of the leakage magnetic field applied to the storage layer is reduced, but the leakage magnetic field in the in-plane direction increases conversely, resulting in a decrease in MR, which is necessary for writing. The reverse current value also increases.

As described above, there are several reports on measures for reducing the leakage magnetic field in the perpendicular magnetization type MTJ configuration, but no specific means for reducing the leakage magnetic field applied to the storage layer has been proposed.

The present invention has been made in view of the above circumstances, and provides a magnetoresistive effect element capable of reducing a leakage magnetic field applied to a storage layer as much as possible and a magnetic random access memory using the same. For the purpose.

The magnetoresistive effect element according to the first aspect of the present invention includes a ferromagnetic layer having magnetic anisotropy in a direction perpendicular to the film surface, a first nonmagnetic layer provided on the ferromagnetic layer, and the first Provided on one nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface, having a magnetization antiparallel to the magnetization direction of the ferromagnetic layer, and extending in the stacking direction of the ferromagnetic layer. A reference layer having a thickness of 1 / 2.8 or more and 1 / 1.5 or less of a thickness, a second nonmagnetic layer provided on the reference layer, and provided on the second nonmagnetic layer And a storage layer whose magnetization direction is changed by the action of spin-polarized electrons having a magnetic anisotropy perpendicular to the film surface, the saturation magnetization of the reference layer being Ms ₁ , and the ferromagnetic layer When the saturation magnetization of Ms ₂ is Ms ₂ , the relationship of Ms ₁ <Ms ₂ is satisfied .

According to a second aspect of the present invention, there is provided a magnetoresistive effect element comprising a memory layer having a magnetic anisotropy perpendicular to a film surface and having a magnetization direction changed by the action of spin-polarized electrons, and the memory layer A first nonmagnetic layer provided on the first nonmagnetic layer; a reference layer provided on the first nonmagnetic layer and having a magnetic anisotropy perpendicular to a film surface; and a first layer provided on the reference layer. Provided on the second nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface and having a magnetization antiparallel to the magnetization direction of the reference layer, and A ferromagnetic layer having a film thickness of 1.5 times or more and 2.8 times or less of the film thickness in the stacking direction of the reference layer, the saturation magnetization of the reference layer being Ms ₁ , and the saturation magnetization of the ferromagnetic layer being When Ms ₂ is satisfied, the relationship of Ms ₁ <Ms ₂ is satisfied .

The magnetoresistive effect element according to the third aspect of the present invention includes a first ferromagnetic layer having magnetic anisotropy perpendicular to the film surface, and a first ferromagnetic layer provided on the first ferromagnetic layer. Provided on the first nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface and having a magnetization antiparallel to the magnetization direction of the first ferromagnetic layer. And a first reference layer having a thickness of 1 / 2.8 to 1 / 1.5 of the thickness of the first ferromagnetic layer in the stacking direction, and the first reference layer. A second nonmagnetic layer and a memory provided on the second nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface and having a magnetization direction changed by the action of spin-polarized electrons. A layer, a third nonmagnetic layer provided on the storage layer, and a third nonmagnetic layer provided on the third nonmagnetic layer and having magnetic anisotropy perpendicular to the film surface. A second reference layer having a magnetization antiparallel to the magnetization direction of the first reference layer; a fourth nonmagnetic layer provided on the second reference layer; and the fourth nonmagnetic layer. The film thickness of the second reference layer in the stacking direction is provided, has a magnetic anisotropy perpendicular to the film surface, has a magnetization antiparallel to the magnetization direction of the second reference layer, and And a second ferromagnetic layer having a film thickness of 1.5 times or more and 2.8 times or less of the saturation magnetization of the first and second reference layers, respectively, Ms ₁₁ , Ms ₁₂ , When the saturation magnetizations of the second and second ferromagnetic layers are Ms ₂₁ and Ms ₂₂ , respectively , the relations of Ms ₁₁ <Ms ₂₁ and Ms ₁₂ <Ms ₂₂ are satisfied .

  According to a fourth aspect of the present invention, there is provided a magnetic memory comprising: the magnetoresistive element according to any one of the first to third aspects; and first and second electrodes for energizing the magnetoresistive element. It is characterized by including a memory cell including.

Sectional drawing of the magnetoresistive effect element by 1st Embodiment. Sectional drawing which shows the optimal film thickness in the magnetoresistive effect element of 1st Embodiment. The figure which shows the MH loop in the case of satisfy | filling the conditions which cancel the film surface perpendicular | vertical component of a leakage magnetic field. The figure which shows the relationship between the film thickness of a ferromagnetic layer, and the film thickness of a reference layer when satisfy | filling the conditions which cancel the film surface perpendicular | vertical component of a leakage magnetic field. The figure which shows the film thickness dependence of the nonmagnetic layer regarding the ferromagnetic layer and the reference layer when satisfy | filling the conditions which cancel the film surface perpendicular | vertical component of a leakage magnetic field. Sectional drawing of the magnetoresistive effect element by 2nd Embodiment. Sectional drawing which shows the optimal film thickness in the magnetoresistive effect element of 2nd Embodiment. A circuit diagram showing a magnetic memory of a 3rd embodiment. Sectional drawing which shows the memory cell in the magnetic memory of 3rd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the description, common parts are denoted by common reference symbols throughout the drawings.

(First embodiment)
A magnetoresistive effect element according to a first embodiment of the present invention is shown in FIG. The magnetoresistive effect element of the present embodiment is an MTJ element 1 having a single pin structure. The MTJ element 1 of this embodiment includes a magnetization free layer (storage layer) 2 made of a magnetic layer, a reference layer 6 made of a magnetic layer, a ferromagnetic layer 10 made of a magnetic layer, and a storage layer 2 and a reference layer 6. A laminated structure having a nonmagnetic layer 4 sandwiched between and a nonmagnetic layer 8 sandwiched between a reference layer 6 and a ferromagnetic layer 10 is provided. That is, the MTJ element 1 of the present embodiment has a laminated structure in which the ferromagnetic layer 10, the nonmagnetic layer 8, the reference layer 6, the nonmagnetic layer 4, and the memory layer 2 are laminated in this order (in the order shown in FIG. 1). Or a laminated structure in which the storage layer 2, the nonmagnetic layer 4, the reference layer 6, the nonmagnetic layer 8, and the ferromagnetic layer 10 are laminated in this order (FIG. 1). Or a stacked structure formed in the reverse order of the order shown in FIG.

The MTJ element 1 of the present embodiment is a so-called perpendicular magnetization type MTJ element in which the magnetization directions of the storage layer 2, the reference layer 6, and the ferromagnetic layer 10 are perpendicular to the film surface. That is, the memory layer 2, the reference layer 6, and the ferromagnetic layer 10 have magnetic anisotropy in the direction perpendicular to the film surface. Here, the “film surface” means the upper surface of each layer. The storage layer 2 can be reversed in magnetization direction by the action of spin-polarized electrons. The reference layer 6 and the ferromagnetic layer 10 have an antiparallel magnetization arrangement in which the magnetizations are directed in opposite directions. In the reference layer 6, the peeling of magnetization before and after writing is unchanged. The MTJ element 1 has a TMR effect when the nonmagnetic layer 4 is an insulator, and has a GMR effect when the nonmagnetic layer 4 is a metal. Here, when the nonmagnetic layer 4 is an insulator, MgO (magnesium oxide), AlO (aluminum oxide, such as Al ₂ O ₃ ) or the like is used, and when the nonmagnetic layer 4 is a metal, Cu, Pt, Au, or the like. Is used. In this structure, if the saturation magnetization Ms and the film thickness t of the ferromagnetic layer 10 are made the same as those of the reference layer 6, the leakage magnetic field from the reference layer 6 applied to the storage layer 2 cannot be completely canceled out.

  Therefore, the present inventors sought hard research and determined conditions between parameters necessary for canceling the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2. Here, “cancel” means a case where the area average of the film surface vertical component Hz of the leakage magnetic field applied to the intermediate surface between the upper surface and the lower surface of the storage layer becomes zero.

First, in the case of the MTJ element 1 having a cylindrical single pin structure with a diameter size R of R = 50 nm shown in FIG. 2, the ferromagnetic layer 10 for canceling the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2. The optimum film thickness was determined by analysis (simulation). The values of the parameters used in this analysis are the saturation magnetization Ms, the magnetic anisotropy constant Ku, and the thickness t of the storage layer 2 are Ms = 700 (emu / cm ³ ) and Ku = 4.7, respectively. × 10 ⁶ (erg / cm ³ ), t = 2 nm, and the saturation magnetization Ms ₁ , magnetic anisotropy constant Ku ₁ , and film thickness t ₁ of the reference layer 6 are respectively Ms ₁ = 750 (emu / cm ³ ), Ku ₁ = 20 × 10 ⁶ (erg / cm ³ ), and t ₁ = 7 nm. Here, the thickness of the nonmagnetic layer 4 is 1 nm, and the thickness of the nonmagnetic layer 8 is 5 nm. The saturation magnetization Ms ₂ and the magnetic anisotropy constant Ku ₂ of the ferromagnetic layer 10 are set to Ms ₂ = 1000 (emu / cm ³ ) and Ku ₂ = 20 × 10 ⁶ (erg / cm ³ ), respectively. . In this case, assuming that the optimum film thickness of the ferromagnetic layer 10 for canceling the film surface vertical component Hz of the leakage magnetic field from the reference layer 6 applied to the storage layer 2 is t ₂ , t ₂ = 19.80 nm from the analytical calculation. Met.

Conditions to cancel the leakage magnetic field perpendicular to the film surface component, that is, the M-H loop of the MTJ element 1 in the case of the film thickness _t 2 = _19.80nm ferromagnetic layers in the graph _{g 1} in FIG. The horizontal axis represents the external magnetic field _Hex applied to the MTJ element, and the vertical axis represents the magnetization obtained by normalizing the saturation magnetization M with the magnetization Ms of the storage layer 2. In FIG. 3, a graph _{g 2} shows the M-H loop of the MTJ element having a structure in which remove the ferromagnetic layer 10 from the MTJ device 1 shown in FIG. It can be seen that not only the shift is improved by canceling the film surface vertical component Hz of the leakage magnetic field, but also the coercive force and the square shape are improved.

Here, the film thicknesses of the reference layer 6 and the nonmagnetic layer 8 will be examined. The thickness t ₁ of the reference layer 6 is preferably 5 nm or more. When the thickness of the reference layer 6 is less than 5 nm, the crystallinity is lowered and the perpendicular magnetic anisotropy cannot be maintained. Moreover, it is preferable that the film thickness of the reference layer 6 is 7 nm or less. When the thickness of the reference layer 6 exceeds 7 nm, the roughness at the interface between the reference layer 6 and the nonmagnetic layer 8 increases. Thereby, the crystallinity of the ferromagnetic layer 10 formed via the nonmagnetic layer 8 is lowered, and the perpendicular magnetic anisotropy cannot be maintained. Therefore, the film thickness t ₁ of the reference layer 6 is
5 nm ≦ t ₁ ≦ 7 nm
It is desirable to satisfy this relationship.

The film thickness of the nonmagnetic layer 8 is preferably 1 nm or more. If the film thickness of the nonmagnetic layer 8 is less than 1 nm, the ferromagnetic interlayer coupling between the reference layer 6 and the ferromagnetic layer 10 is strong, making it difficult to create an antiparallel coupling state. The film thickness of the nonmagnetic layer 8 is preferably 5 nm or less. When the thickness of the nonmagnetic layer 8 exceeds 5 nm, the roughness at the interface between the ferromagnetic layer 10 and the nonmagnetic layer 8 increases. Thereby, the crystallinity of the ferromagnetic layer 10 is lowered, and it becomes difficult to maintain the perpendicular magnetic anisotropy. Therefore, the thickness _{t 12} of the non-magnetic layer 8,
1 nm ≦ t ₁₂ ≦ 5 nm
It is desirable to satisfy this relationship.

Next, with respect to the MTJ element 1, the ferromagnetic layer necessary for canceling the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2 when the thickness t ₁ of the reference layer 6 is 5 nm, 6 nm, and 7 nm. the thickness _{t 2} of the layer 10 was determined by analysis.

a) For t ₁ = 5 nm, if t ₁₂ = 1 nm, t ₂ = 7.52 nm is required. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.50.

Further, when t ₁₂ = 3 nm with respect to t ₁ = 5 nm, t ₂ = 8.96 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.79.

Further, when t ₁₂ = 5 nm with respect to t ₁ = 5 nm, t ₂ = 10.9 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 2.18.

Therefore, at t ₁ = 5 nm, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.50 ≦ t ₂ / t ₁ ≦ 2.18.
Meet.

b) Where t ₁₂ = 1 nm for t ₁ = 6 nm, t ₂ = 9.75 nm is required. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.63.

Further, when t ₁₂ = 3 nm with respect to t ₁ = 6 nm, t ₂ = 12.01 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 2.00.

Further, when t ₁₂ = 5 nm with respect to t ₁ = 6 nm, t ₂ = 14.76 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 2.46.

Therefore, at t ₁ = 6 nm, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.63 ≦ t ₂ / t ₁ ≦ 2.46.
Meet.

c) Where t ₁₂ = 1 nm for t ₁ = 7 nm, t ₂ = 12.73 nm is required. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.82.

Further, when t ₁₂ = 3 nm with respect to t ₁ = 7 nm, t ₂ = 15.84 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 2.26.

Further, when t ₁₂ = 5 nm with respect to t ₁ = 7 nm, t ₂ = 19.81 nm is necessary. In this case, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 2.83.

Therefore, at t ₁ = 7 nm, the ratio of the film thickness t ₂ to the film thickness t ₁ (= t ₂ / t ₁ ) is 1.82 ≦ t ₂ / t ₁ ≦ 2.83.
Meet.

The analysis result is shown in FIG. In Figure 4, taking the thickness _{t 12} of the non-magnetic layer 8 between the reference layer 6 and the ferromagnetic layer 10 to the _parameter obtained for the case t 12 = 1 nm, 3 nm, a 5 nm.

Next, FIG. 5 shows a result of considering the MTJ element in which the film thickness t ₁₂ of the nonmagnetic layer 8 is 1 nm, 3 nm, and 5 nm. FIG. 5 shows the product of the magnetization Ms ₂ of the ferromagnetic layer 10 and the film thickness t ₂ of the ferromagnetic layer 10 necessary to cancel the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2 in each case. ratio of (Ms ₂ × _{t 2),} the product of the saturation magnetization Ms ₁ of the reference layer 6 and the thickness _{t 1} of the reference layer 6 and _{(Ms 1 × t 1) (} (Ms 2 × t 2) / (Ms ₁ × t ₁ )) is plotted. In FIG. 5, the thickness t ₁ of the reference layer 6 is used as a parameter, and the case where t ₁ = 5 nm, 6 nm, and 7 nm is obtained.

From the above, in order to cancel the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2, the film thickness of the ferromagnetic layer 10 with respect to the film thickness t ₁ (5 nm ≦ t ₁ ≦ 7 nm) of the reference layer 6. t ₂ is found to be necessary less 2.8 times 1.5 times or more at least.

Furthermore, the value of the ratio ((Ms ₂ × t ₂ ) / (Ms ₁ × t ₁ )) corresponding to this can be seen from FIG.
It is preferable that the relationship of 2.0 ≦ (Ms ₂ × t ₂ ) / (Ms ₁ × t ₁ ) ≦ 3.8 is satisfied.

Further, in order to cancel the film surface vertical component Hz of the leakage magnetic field applied to the memory layer 2, the ratio ((Ms ₂ × t ₂ ) / (Ms ₁ × t ₁ )) is 2.0 or more and 3.8 or less. It is preferable to further satisfy certain conditions.

Further, in order to cancel the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 2, when the Curie temperature of the reference layer 6 is T ₁ and the Curie temperature T ₂ of the ferromagnetic layer 10, T ₁ <T ₂ It is preferable to further satisfy the relationship. This preferably satisfies the relationship of Ms ₁ <Ms _{2 in} order to reduce the film surface vertical component Hz of the leakage magnetic field applied to the memory layer 2. Furthermore, if the Curie temperature T ₂ of the ferromagnetic layer 10 is higher than the Curie temperature T ₁ of the reference layer 6, the magnitude relationship of Ms ₁ <Ms ₂ can always be maintained. Therefore, the relationship between the Curie temperature _{T 2} of the Curie temperature _{T 1} of the ferromagnetic layer 10 of the reference layer 6 preferably _further satisfy the relationship _T 1 <T _2.

(Second Embodiment)
Next, a magnetoresistive effect element according to a second embodiment of the present invention is shown in FIG. The magnetoresistive element of this embodiment is an MTJ element 1 having a dual pin structure. The MTJ element 1 of this embodiment includes a ferromagnetic layer 12, a nonmagnetic layer 14, a reference layer 16, a nonmagnetic layer 18, a storage layer 20, a nonmagnetic layer 22, a reference layer 24, and a nonmagnetic layer. The layer 26 and the ferromagnetic layer 28 have a stacked structure in which they are stacked in this order. In contrast to the case shown in FIG. 6, the MTJ element 1 of the present embodiment includes the ferromagnetic layer 28, the nonmagnetic layer 26, the reference layer 24, the nonmagnetic layer 22, the storage layer 20, and the nonmagnetic layer. The layer 18, the reference layer 16, the nonmagnetic layer 14, and the ferromagnetic layer 12 may have a stacked structure in which they are stacked in this order.

  For the reference layers 16 and 24, the ferromagnetic layers 12 and 28, and the storage layer 20, a perpendicular magnetization material having perpendicular magnetic anisotropy is used. That is, the MTJ element 1 of the present embodiment is a so-called perpendicular magnetization type MTJ element in which the magnetization directions of the storage layer 20, reference layers 16 and 24, and ferromagnetic layers 12 and 28 are perpendicular to the film surface. That is, the memory layer 20, the reference layers 16 and 24, and the ferromagnetic layers 22 and 38 have magnetic anisotropy perpendicular to the film surface. Here, the “film surface” means the upper surface of each layer. The storage layer 20 can reverse the direction of magnetization by the action of spin-polarized electrons. In the case of the dual pin structure, the magnetizations of the reference layer 16 and the reference layer 24 are antiparallel magnetization arrays oriented in opposite directions. Similarly, the magnetizations of the ferromagnetic layer 12 and the ferromagnetic layer 28 have antiparallel magnetization arrangements oriented in opposite directions. The magnetizations of the reference layer 16 and the ferromagnetic layer 12 have an antiparallel magnetization arrangement oriented in opposite directions.

Similarly, the magnetizations of the reference layer 24 and the ferromagnetic layer 28 have antiparallel magnetization arrangements oriented in opposite directions.

The MTJ element 1 has a TMR effect when the nonmagnetic layers 18 and 22 are insulators, and has a GMR effect when the nonmagnetic layers 18 and 22 are metal. Here, when the nonmagnetic layers 18 and 22 are insulators, MgO (magnesium oxide), AlO (aluminum oxide, such as Al ₂ O ₃ ) or the like is used, and when the nonmagnetic layers 18 and 22 are metals, Cu, Pt, Au, etc. are used. In this structure, when the saturation magnetization Ms and the film thickness t of the ferromagnetic layers 12 and 28 are made the same as those of the reference layers 16 and 24, the leakage magnetic field from the reference layers 16 and 24 on the storage layer 20 is completely eliminated. It cannot be countered.

  Therefore, the present inventors sought hard research and determined conditions between parameters necessary for canceling the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 20. Here, “cancel” means a case where the area average of the film surface vertical component Hz of the leakage magnetic field applied to the storage layer becomes zero.

  First, in the case of the MTJ element 1 having a cylindrical dual pin structure with a diameter size R of R = 50 nm shown in FIG. 7, the ferromagnetic layer 12 for canceling the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 20. 28 were determined by analysis (simulation).

The parameter values used in this analysis are the saturation magnetization Ms and the magnetic anisotropy constant Ku of the memory layer 20, and the film thicknesses are Ms = 700 (emu / cm ³ ) and Ku = 4.7 ×, respectively. 10 ⁶ (erg / cm ³ ), t = 2 nm, the saturation magnetizations Ms ₁₁ , Ms ₁₂ , magnetic anisotropy constants Ku ₁₁ , Ku ₁₂ , and film thicknesses t ₁₁ , t ₁₂ of the reference layers 16, 24 are as follows: Ms ₁₁ = Ms ₁₂ = 750 (emu / cm ³ ), Ku ₁₁ = Ku ₁₂ = 20 × 10 ⁶ (erg / cm ³ ), and t ₁₁ = t ₁₂ = 7 nm, respectively. Here, the thickness of the nonmagnetic layers 18 and 22 is 1 nm, and the thickness of the nonmagnetic layers 14 and 26 is 5 nm. The magnitudes of saturation magnetization Ms ₂₁ and Ms ₂₂ , magnetic anisotropy constants Ku ₂₁ and Ku ₂₂ , and film thicknesses t ₂₁ and t ₂₂ of the ferromagnetic layers 12 and 28 are Ms ₂₁ = Ms ₂₂ = 1000 (emu / cm ³ ), Ku ₂₁ = Ku ₂₂ = 20 × 10 ⁶ (erg / cm ³ ). In this case, the optimum film thicknesses t ₂₁ and t ₂₂ of the ferromagnetic layers 12 and 28 for canceling the film surface vertical component Hz of the leakage magnetic field from the reference layers 16 and 24 applied to the storage layer 20 are equal, and t ₂₁ = t ₂₂ = 19.80 nm.

  The above analysis results show that the ferromagnetic layer 12, the nonmagnetic layer 14, the reference layer 16, the nonmagnetic layer 18, and the storage layer 20 constitute one MTJ element, and the storage layer 20, the nonmagnetic layer 22, the reference layer 24, The same result is obtained as when the nonmagnetic layer 26 and the ferromagnetic layer 28 constitute another MTJ element.

For this reason, in order to cancel the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 20, as in the first embodiment, it is strong against the film thickness t ₁₁ (5 nm ≦ t ₁₁ ≦ 7 nm) of the reference layer 16. thickness _{t 21} of the magnetic layer 12 is required below 2.8 times 1.5 times or more at least, of the reference layer 24 thickness _t 12 of (5nm ≦ _{t 12} ≦ 7nm) to the ferromagnetic layer 28 the film thickness _{t 22} is required below 2.8 times 1.5 times or more at least.

Further, the saturation magnetizations of the reference layers 16 and 24 are Ms ₁₁ and Ms ₁₂ , the film thicknesses are t ₁₁ and t ₁₂ , respectively, and the saturation magnetizations of the ferromagnetic layers ₁₂ and 28 are Ms ₂₁ and Ms ₂₂ , respectively. _21, when the _{t 22,}
2.0 ≦ (Ms ₂₁ × t ₂₁ ) / (Ms ₁₁ × t ₁₁ ) ≦ 3.8 and 2.0 ≦ (Ms ₂₂ × t ₂₂ ) / (Ms ₁₂ × t ₁₂ ) ≦ 3.8 Is preferably further satisfied.

Further, in order to cancel the film plane perpendicular component Hz of the leakage magnetic field applied to the storage layer 20, T ₁ and the Curie temperature of the reference layer _16, the Curie temperature T ₂ of the ferromagnetic layer _12, the Curie temperature of the reference layer 24 T _3, when the Curie temperature of the ferromagnetic layers 28 and _{T 4,}
T ₁ <T ₂ and T ₃ <T ₄
This relationship may be further satisfied.

  If the above condition is satisfied, the film surface vertical component Hz of the leakage magnetic field applied to the storage layer 20 can be canceled.

(Third embodiment)
Next, a magnetic memory (MRAM) according to a third embodiment of the present invention will be described with reference to FIGS.

  A circuit diagram of the MRAM of this embodiment is shown in FIG. The MRAM of this embodiment uses the MTJ element 1 of the first embodiment or the second embodiment as a memory element of a memory cell. The MRAM includes a memory cell array 30 having a plurality of memory cells MC arranged in a matrix. The memory cell array 30 is provided with a plurality of bit line pairs BL and / BL so as to extend in the column direction. The memory cell array 30 is provided with a plurality of word lines WL so as to extend in the row direction.

  Memory cells MC are arranged at the intersections between the bit lines BL and the word lines WL. Each memory cell MC includes an MTJ element 1 and a selection transistor 31 including an n-channel MOS transistor. One end of the MTJ element 1 is connected to the bit line BL. The other end of the MTJ element 10 is connected to the drain terminal of the selection transistor 31. The gate terminal of the selection transistor 31 is connected to the word line WL. The source terminal of the selection transistor 31 is connected to the bit line / BL.

  A row decoder 32 is connected to the word line WL. A write circuit 34 and a read circuit 35 are connected to the bit line pair BL, / BL. A column decoder 33 is connected to the write circuit 34 and the read circuit 35. Each memory cell MC is selected by the row decoder 32 and the column decoder 33.

  Data is written to the memory cell MC as follows. First, in order to select a memory cell MC for writing data, the word line WL connected to the memory cell MC is activated. As a result, the selection transistor 31 is turned on.

  Here, a bidirectional write current Iw is supplied to the MTJ element 1 in accordance with the write data. Specifically, when the write current Iw is supplied to the MTJ element 1 from left to right in FIG. 8, the write circuit 34 applies a positive voltage to the bit line BL and applies a ground voltage to the bit line / BL. To do. Further, when the write current Iw is supplied to the MTJ element 1 from right to left in FIG. 8, the write circuit 34 applies a positive voltage to the bit line / BL and applies a ground voltage to the bit line BL. In this way, data “0” or data “1” can be written in the memory cell MC.

  Next, data reading from the memory cell MC is performed as follows. First, in order to select a memory cell MC from which data is read, the word line WL connected to the memory cell MC is activated. As a result, the select transistor 31 of the selected memory cell MC is turned on. The read circuit 35 supplies the MTJ element 1 with, for example, a read current Ir that flows from right to left in FIG. Then, the read circuit 35 detects the resistance value of the MTJ element 1 based on the read current Ir. In this way, data stored in the MTJ element 1 can be read.

  Next, the structure of the MRAM will be described. FIG. 9 is a cross-sectional view showing the configuration of the MRAM centered on one memory cell MC.

  An element isolation insulating layer 41 is provided in the surface region of the p-type semiconductor substrate 40, and the surface region of the semiconductor substrate 40 in which the element isolation insulating layer 41 is not provided becomes an element area (active area) for forming an element. . The element isolation insulating layer 41 is configured by, for example, STI (Shallow Trench Isolation). For example, silicon oxide is used as the STI.

  A selection transistor 31 is formed in the element region of the semiconductor substrate 40. The selection transistor 31 is provided with a source region 32a and a drain region 32b that are separated from each other.

Each of the source region 32 a and the drain region 32 b is composed of an n ⁺ type diffusion region formed by introducing a high concentration N ⁺ type impurity into the semiconductor substrate 40. A gate insulating film 34 is formed on the region of the semiconductor substrate 40 that becomes the channel 33 between the source region 32 a and the drain region 32 b, and a gate electrode 35 is provided on the gate insulating film 34. The gate electrode 35 functions as the word line WL.

  A wiring layer 43 is provided on the source region 32 a via a contact 42. The wiring layer 43 functions as a bit line / BL. On the drain region 32 b, a lead wiring 45 is provided via a contact 44. An MTJ element 1 sandwiched between a lower electrode 36 and an upper electrode 37 is provided on the lead wiring 45. A wiring layer 47 is provided on the upper electrode 37. The wiring layer 47 functions as the bit line BL. The space between the semiconductor substrate 40 and the wiring layer 47 is filled with an interlayer insulating layer 46 made of, for example, silicon oxide.

  As described above in detail, according to the present embodiment, the MRAM can be configured using the MTJ element 1 of the first embodiment or the second embodiment. The MTJ element 1 can be used not only for spin injection type magnetic memories but also for domain wall motion type magnetic memories.

  Next, the magnetic material used for the reference layer having perpendicular magnetization and the ferromagnetic layer having perpendicular magnetization of the above embodiment will be described.

  As the perpendicular magnetization film used for the MTJ element of this embodiment, at least one of Fe (iron), Co (cobalt), Ni (nickel), and Mn (manganese), Pt (platinum), Pd (palladium). ), Ir (iridium), Rh (rhodium), Os (osmium), Au (gold), Ag (silver), Cu (copper) and Cr (chromium). . Furthermore, B (boron), C (carbon), Si (silicon), Al (aluminum) are used for adjusting saturation magnetization, controlling crystal magnetic anisotropy energy, and adjusting crystal grain size and inter-grain bond. ), Mg (magnesium), Ta (tantalum), Zr (zirconium), Ti (titanium), Hf (hafnium), Y (yttrium) and a rare earth element may be added.

Specific examples of the Co-based material include a Co—Cr—Pt alloy, a Co—Cr—Ta alloy, and a Co—Cr—Pt—Ta alloy having an HCP (Hexagonal Closest Packing) structure. It is done. By adjusting the composition of each element, it is possible to adjust the magnetocrystalline anisotropy energy within the range of 1 × 10 ⁵ or more and less than 1 × 10 ⁷ erg / cc. Here, the symbol “-” represents an alloy.

The Co—Pt alloy forms an L1 ₀ -CoPt ordered alloy in a composition range near Co ₅₀ Pt ₅₀ (at (atomic)%). This ordered alloy has an FCT (Face-Centered Tetragonal) structure. When MgO (100) is used as the nonmagnetic layer, the (001) -oriented FCT-CoPt ordered alloy is preferable because the interface misfit with the nonmagnetic layer can be reduced.

Specific examples of the material mainly containing Fe include an Fe—Pt alloy and an Fe—Pd alloy. Among them, Fe-Pt alloy composition is ordered in _{Fe 50 Pt 50 (at%)} , having an L1 ₀ structure as a basic structure FCT structure. Thereby, a large magnetocrystalline anisotropy energy of 1 × 10 ⁷ erg / cc or more can be expressed.

The Fe ₅₀ Pt ₅₀ alloy has an FCC (Face-Centered Cubic) structure before ordering. In this case, the magnetocrystalline anisotropy energy is about 1 × 10 ⁶ erg / cc. Therefore, the crystal magnetic anisotropy is within the range of 5 × 10 ⁵ erg / cc to 5 × 10 ⁸ erg / cc by adjusting the annealing temperature, the composition, controlling the degree of order by the laminated structure, and adding the additive. Energy can be adjusted.

  Specifically, the saturation magnetization (Ms) and magnetocrystalline anisotropy energy (Ku) of the Fe—Pt alloy can be controlled by adding Cu or V (vanadium) to the Fe—Pt alloy. . Further, with respect to V, there is an effect of lowering a damping constant (magnetization braking constant) that is important in spin injection magnetization reversal, and an effect of reducing reversal current.

  The ordered Fe-Pt alloy has an FCT structure, and has an FCC structure before ordering.

Therefore, it is very consistent with MgO (100). More specifically, a (100) -oriented BCC (Body-Centered Cubic) -Fe is grown on the MgO (100) plane, and Pt (100) is laminated thereon, whereby the MgO (100) is laminated. It is possible to form a (100) plane-oriented oriented growth Fe-Pt ordered alloy. Further, when BCC-Cr is formed between the Fe—Pt ordered alloy and MgO (100), the (100) plane orientation of the Fe—Pt ordered alloy is more preferred.

  Further, when forming an Fe—Pt ordered alloy, an Fe—Pt ordered alloy close to an ideal rule can be formed by forming a multilayer structure of [Fe / Pt] n (n is an integer). In this case, the film thicknesses of Fe and Pt are desirably set to be 0.1 nm or more and 1 nm or less. This is indispensable for creating a uniform composition state, and in the case of ordering of the Fe-Pt alloy, this transformation involves a martensitic transformation from the FCC structure to the FCT structure. It is important because it is promoted.

  Further, the ordering temperature of the Fe—Pt alloy is as high as 500 ° C. or more, and is excellent in heat resistance. This point is very preferable because it has resistance to annealing treatment in a later step. Further, the ordering temperature can be lowered by an additive element such as Cu or V.

  Further, as the perpendicular magnetization film used in the MTJ element of the above embodiment, a ferromagnetic material made of a mixed crystal of a metal magnetic phase and an insulating phase may be used. In this case, the metal magnetic phase is at least one of Fe, Co, Ni, and Mn, and at least one of Pt, Pd, Ir, Rh, Os, Au, Ag, Cu, Cr, Ta, and rare earth elements. It is comprised from the ferromagnetic material containing the above. The insulating phase is an oxide, nitride, or oxynitride containing at least one element selected from B, C, Si, Al, Mg, Ta, Cr, Zr, Ti, Hf, Y, and a rare earth element Consists of

  A ferromagnetic material composed of a mixed crystal of a metallic magnetic phase and an insulating phase is separated into a conductive metallic magnetic portion and a non-conductive insulating portion, so that current concentrates on the metallic magnetic portion. The current-carrying area is reduced and the local current density is increased. This has the effect of reducing the required reversal current substantially.

  In order to obtain such an effect, it is necessary to control the crystallinity. As the two-phase separation structure, there are a granular (crystal grain dispersion) type structure, an island (island shape) type structure, and a columner (columnar type) type structure. In the case of the columnar structure, since the metal magnetic body portion vertically penetrates in the magnetic layer, a current confinement effect is easily obtained. In the case of the granular type structure and the island type structure, since the current flows through the path having the smallest tunnel barrier, the current confinement effect can be obtained as in the columnar type structure.

In addition, examples of the perpendicular magnetization film used in the MTJ element of the embodiment include a Mn ferromagnetic alloy or a Cr ferromagnetic alloy. Examples of the Mn-based ferromagnetic alloy include a Mn—Al alloy, a Mn—Au alloy, a Mn—Zn alloy, a Mn—Ga alloy, a Mn—Ir alloy, and a Mn—Pt ₃ alloy. There are features. Examples of the Cr-based ferromagnetic alloy include a Cr—Pt ₃ alloy. This also has a regular lattice.

  DESCRIPTION OF SYMBOLS 1 ... MTJ element, 2 ... Memory layer, 4 ... Nonmagnetic layer, 6 ... Reference layer, 8 ... Nonmagnetic layer, 10 ... Ferromagnetic layer, 20 ... MTJ element, 22 ... Ferromagnetic layer, 24 ... Nonmagnetic layer, Reference numeral 26 ... Reference layer, 28 ... Nonmagnetic layer, 30 ... Memory cell array, 32 ... Nonmagnetic layer, 34 ... Reference layer, 36 ... Nonmagnetic layer, 38 ... Ferromagnetic layer.

Claims (8)

A ferromagnetic layer having magnetic anisotropy perpendicular to the film surface;
A first nonmagnetic layer provided on the ferromagnetic layer;
Lamination of the ferromagnetic layer provided on the first nonmagnetic layer and having magnetic anisotropy perpendicular to the film surface and antiparallel to the magnetization direction of the ferromagnetic layer A reference layer having a thickness of 1 / 2.8 or more and 1 / 1.5 or less of the thickness in the direction;
A second nonmagnetic layer provided on the reference layer;
A storage layer provided on the second nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface and having a magnetization direction changed by the action of spin-polarized electrons;
Equipped with a,
When the saturation magnetization of the reference layer is Ms ₁ and the saturation magnetization of the ferromagnetic layer is Ms ₂ ,
Ms ₁ <Ms ₂
A magnetoresistive effect element satisfying the relationship: A storage layer that has a magnetic anisotropy perpendicular to the film surface and whose magnetization direction is changed by the action of spin-polarized electrons;
A first nonmagnetic layer provided on the storage layer;
A reference layer provided on the first nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface;
A second nonmagnetic layer provided on the reference layer;
A film provided on the second nonmagnetic layer, having a magnetic anisotropy in a direction perpendicular to the film surface, having a magnetization antiparallel to the magnetization direction of the reference layer, and being in the stacking direction of the reference layer A ferromagnetic layer having a thickness of 1.5 to 2.8 times the thickness;
Equipped with a,
When the saturation magnetization of the reference layer is Ms ₁ and the saturation magnetization of the ferromagnetic layer is Ms ₂ ,
Ms ₁ <Ms ₂
A magnetoresistive effect element satisfying the relationship: When the saturation magnetization of the reference layer is Ms ₁ , the film thickness is t ₁ , the saturation magnetization of the ferromagnetic layer is Ms ₂ , and the film thickness is t ₂ ,
3. The magnetoresistive element according to claim 1, wherein a relationship of 2.0 ≦ (Ms ₂ × t ₂ ) / (Ms ₁ × t ₁ ) ≦ 3.8 is satisfied. A first ferromagnetic layer having magnetic anisotropy perpendicular to the film surface;
A first nonmagnetic layer provided on the first ferromagnetic layer;
Provided on the first nonmagnetic layer, having magnetic anisotropy in a direction perpendicular to the film surface, having a magnetization antiparallel to the magnetization direction of the first ferromagnetic layer, and the first A first reference layer having a thickness of 1 / 2.8 to 1 / 1.5 of the thickness of the ferromagnetic layer in the stacking direction;
A second nonmagnetic layer provided on the first reference layer;
A storage layer provided on the second nonmagnetic layer and having a magnetic anisotropy perpendicular to the film surface and having a magnetization direction changed by the action of spin-polarized electrons;
A third nonmagnetic layer provided on the storage layer;
A second reference layer provided on the third nonmagnetic layer, having a magnetic anisotropy perpendicular to the film surface and having a magnetization antiparallel to the magnetization direction of the first reference layer;
A fourth nonmagnetic layer provided on the second reference layer;
The second reference is provided on the fourth nonmagnetic layer, has a magnetic anisotropy perpendicular to the film surface, has a magnetization antiparallel to the magnetization direction of the second reference layer, and the second reference. A second ferromagnetic layer having a thickness of 1.5 times or more and 2.8 times or less of the thickness in the stacking direction of the layers;
Equipped with a,
When the saturation magnetizations of the first and second reference layers are Ms ₁₁ and Ms ₁₂ , respectively, and the saturation magnetizations of the first and second ferromagnetic layers are Ms ₂₁ and Ms ₂₂ , respectively .
Ms ₁₁ <Ms ₂₁ , and
Ms ₁₂ <Ms ₂₂
A magnetoresistive effect element satisfying the relationship: The saturation magnetizations of the first and second reference layers are Ms ₁₁ and Ms ₁₂ , the film thicknesses are t ₁₁ and t ₁₂ , respectively, and the saturation magnetizations of the first and second ferromagnetic layers are Ms ₂₁ and Ms, respectively. _{22 and} when the film thicknesses are t ₂₁ and t ₂₂ respectively,
2.0 ≦ (Ms ₂₁ × t ₂₁ ) / (Ms ₁₁ × t ₁₁ ) ≦ 3.8 and 2.0 ≦ (Ms ₂₂ × t ₂₂ ) / (Ms ₁₂ × t ₁₂ ) ≦ 3.8
The magnetoresistive element according to claim 4 , wherein the relationship is satisfied. Magnetic memory, characterized in that it comprises a magnetoresistive element described in the first and second electrodes for performing energization with respect to the magnetoresistive element, a memory cell including a to any one of claims 1 to 5 . A first wiring electrically connected to the first electrode;
A second wiring electrically connected to the second electrode;
A writing circuit that is electrically connected to the first wiring and the second wiring and that supplies current to the magnetoresistive element in both directions;
The magnetic memory according to claim 6 , further comprising: A select transistor connected between the second electrode of the magnetoresistive element and the second wiring;
A third wiring for controlling on / off of the selection transistor;
The magnetic memory according to claim 7 , further comprising:

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