WO2011078018A1 - 磁気抵抗効果素子及びそれを用いた磁気ランダムアクセスメモリ - Google Patents
磁気抵抗効果素子及びそれを用いた磁気ランダムアクセスメモリ Download PDFInfo
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- WO2011078018A1 WO2011078018A1 PCT/JP2010/072494 JP2010072494W WO2011078018A1 WO 2011078018 A1 WO2011078018 A1 WO 2011078018A1 JP 2010072494 W JP2010072494 W JP 2010072494W WO 2011078018 A1 WO2011078018 A1 WO 2011078018A1
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- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
- G11C11/161—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
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- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
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- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
- G11C11/165—Auxiliary circuits
- G11C11/1653—Address circuits or decoders
- G11C11/1655—Bit-line or column circuits
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- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
- G11C11/165—Auxiliary circuits
- G11C11/1659—Cell access
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- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
- G11C11/165—Auxiliary circuits
- G11C11/1675—Writing or programming circuits or methods
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- G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
- G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
- G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
- G11C19/0808—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation
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- G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
- G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
- G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
- G11C19/0808—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation
- G11C19/0841—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation using electric current
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- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/3254—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
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- H01—ELECTRIC ELEMENTS
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- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/3286—Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
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- H10B—ELECTRONIC MEMORY DEVICES
- H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B61/20—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having three or more electrodes, e.g. transistors
- H10B61/22—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having three or more electrodes, e.g. transistors of the field-effect transistor [FET] type
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- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/70—Resistive array aspects
- G11C2213/74—Array wherein each memory cell has more than one access device
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- G—PHYSICS
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- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
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- G11C2213/79—Array wherein the access device being a transistor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/3295—Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
Definitions
- the present invention relates to a magnetoresistive effect element and a magnetic random access memory using the same.
- Magnetic memory in particular, Magnetic Random Access Memory (MRAM)
- MRAM Magnetic Random Access Memory
- the MRAM uses a magnetic material as a storage element and stores data corresponding to the magnetization direction of the magnetic material.
- the magnetization of the magnetic material is switched to a direction corresponding to the data.
- a current hereinafter referred to as “write current”.
- Non-Patent Document 1 N. Sakimura et al., “MRAM Cell Technology for Over 500-MHz SoC”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 42, No. 4, pp. 830-838) Accordingly, it is shown that the cell area becomes equal to that of an existing embedded SRAM by reducing the write current to 0.5 mA or less.
- the most common method of writing data to the MRAM is to arrange a wiring for writing around the magnetic memory element and generate a magnetic field by flowing a write current through the wiring, and the magnetic field of the magnetic memory element is generated by the magnetic field.
- This is a method of switching the magnetization direction. According to this method, writing in 1 nanosecond or less is possible in principle, which is suitable for realizing a high-speed MRAM.
- the magnetic field for switching the magnetization of the magnetic material that has ensured thermal stability and disturbance magnetic field resistance is generally about several tens of Oe (Yersted). In order to generate such a magnetic field, several A write current of about mA is required.
- the chip area must be increased, and the power consumption required for writing also increases, so that it is inferior in competitiveness compared to other random access memories.
- the write current further increases, which is not preferable in terms of scaling.
- the first is a spin-injection magnetization reversal (Spin Torque Transfer) method.
- the second magnetic layer is composed of a first magnetic layer having reversible magnetization and a second magnetic layer that is electrically connected thereto and whose magnetization direction is fixed.
- a write current is passed between the magnetic layer and the first magnetic layer.
- the magnetization of the first magnetic layer can be reversed by the interaction between the spin-polarized conduction electrons and the localized electrons in the first magnetic layer.
- a magnetoresistive effect developed between the first magnetic layer and the second magnetic layer is used. Therefore, a magnetic memory element using spin injection magnetization reversal is a two-terminal element.
- spin transfer magnetization reversal occurs at a certain current density or higher, the current required for writing is reduced if the element size is reduced. That is, it can be said that the spin injection magnetization reversal method is excellent in scaling.
- an insulating layer is provided between the first magnetic layer and the second magnetic layer, and a relatively large write current must be passed through the insulating layer during writing. Rewriting durability and reliability are issues. Further, since the write current path and the read current path are the same, there is a concern about erroneous writing during reading. Thus, although spin transfer magnetization reversal is excellent in scaleability, there are some barriers to practical use.
- the second method is a current-induced domain wall motion (Current Drive Domain Wall Motion) method.
- An MRAM using current-induced domain wall motion is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2005-191032).
- Patent Document 1 Japanese Patent Laid-Open No. 2005-191032.
- a magnetic layer having reversible magnetization domain wall motion layer for storing data
- the magnetizations at both ends of the domain wall motion layer are substantially antiparallel to each other. Fixed to. With such a magnetization arrangement, the domain wall is introduced into the domain wall moving layer.
- Non-Patent Document 2 (A. Yamaguchi et al., “Real-Space Observation of Current-Drived Domain Wall Motion in Submicron Magnetic Wires.
- TELSOL As reported in, when a current is passed in the direction penetrating the domain wall, the domain wall moves in the direction of conduction electrons. Therefore, by supplying a write current in the in-plane direction to the domain wall moving layer, it is possible to move the domain wall in a direction corresponding to the current direction and write desired data.
- a magnetic tunnel junction including a region where the domain wall moves is used, and reading is performed based on the magnetoresistance effect. Therefore, a magnetic memory element using current-induced domain wall motion is a three-terminal element.
- current induced domain wall motion also occurs when the current density is greater than a certain current density.
- the current induced domain wall motion method is also excellent in scaling.
- the write current does not flow through the insulating layer, and the write current path and the read current path are different. Therefore, the above-mentioned problem in the case of spin injection magnetization reversal is solved.
- Non-Patent Document 2 a current density of about 1 ⁇ 10 8 [A / cm 2 ] is reported as a current density necessary for current-induced domain wall motion.
- Non-Patent Document 3 (S.Fukami et al., “Micromagnetic analysis of current 7, and the current 7 of the current, the current 7 of the current, the current 7 of the current, the current 7 of the current, the current 7 of the current, the 7 of the current, the 7 The utility of perpendicular magnetic anisotropy materials in the system is described. Specifically, it has been found through micromagnetic simulation that the write current can be reduced sufficiently small when the domain wall motion layer where domain wall motion occurs has perpendicular magnetic anisotropy.
- Patent Document 3 International Publication WO / 2009/001706 discloses a magnetoresistive effect element using a magnetic material having perpendicular magnetic anisotropy, and an MRAM provided with the magnetoresistive effect element as a memory cell.
- FIG. 1 is a cross-sectional view schematically showing a magnetoresistive effect element disclosed in International Publication WO / 2009/001706.
- the magnetoresistive effect element 170 includes a domain wall motion layer 110, a spacer layer 120, and a reference layer 130.
- the domain wall motion layer 110 is formed of a ferromagnetic material having perpendicular magnetic anisotropy.
- the domain wall motion layer 110 includes a first magnetization fixed region 111a, a second magnetization fixed region 111b, and a magnetization free region 113.
- the magnetization fixed regions 111 a and 111 b are arranged on both sides of the magnetization free region 113.
- the magnetizations of the magnetization fixed regions 111a and 111b are fixed in opposite directions (antiparallel). For example, as shown in FIG. 1, the magnetization direction of the first magnetization fixed region 111a is fixed in the + z direction, and the magnetization direction of the second magnetization fixed region 111b is fixed in the ⁇ z direction.
- the magnetization direction of the magnetization free region 113 can be reversed by a write current flowing from one of the magnetization fixed regions 111a and 111b to the other, and becomes the + z direction or the ⁇ z direction. Therefore, the domain wall 112 a or the domain wall 112 b is formed in the domain wall moving layer 110 according to the magnetization direction of the magnetization free region 113. Data is stored as the magnetization direction of the magnetization free region 113. It can also be seen that it is stored as the position (112a or 112b) of the domain wall 112.
- the reference layer 130 which is a ferromagnetic material whose magnetization direction is fixed, the spacer layer 120 of the nonmagnetic layer (insulating layer), and the magnetization free region 113 form a magnetic tunnel junction (MTJ).
- the data is read as the magnitude of the MTJ resistance value.
- Patent Document 3 discloses that when the domain wall motion layer 110 has perpendicular magnetic anisotropy, the write current can be reduced.
- domain wall motion layer domain wall motion layer
- domain wall motion layer domain wall motion layer
- domain wall motion can be caused by a smaller write current
- the inventor examined the following points this time. That is, when the domain wall motion layer is formed of a ferromagnetic material having perpendicular magnetic anisotropy, the inventor can further reduce the write current if the spin polarizability of the domain wall motion layer can be further increased. I thought it was. Clarification of the relationship between spin polarizability and perpendicular magnetic anisotropy (anisotropic magnetic field) in ferromagnets, and spin by applying the optimum perpendicular magnetic anisotropy (anisotropic magnetic field) to the domain wall moving layer It is considered that the write current can be further reduced by further increasing the polarizability.
- One object of the present invention is to provide a magnetoresistive effect element using current-induced domain wall motion and a domain wall motion layer having perpendicular magnetic anisotropy that can operate with a lower write current in an MRAM using the magnetoresistive effect device. is there.
- the magnetoresistive effect element of the present invention includes a domain wall motion layer, a spacer layer, and a reference layer.
- the domain wall motion layer is formed of a ferromagnetic material having perpendicular magnetic anisotropy.
- the spacer layer is provided on the domain wall motion layer and is formed of a nonmagnetic material.
- the reference layer is provided on the spacer layer, is formed of a ferromagnetic material, and has a fixed magnetization.
- the domain wall motion layer has at least one domain wall and stores information corresponding to the position of the domain wall.
- the anisotropic magnetic field of the domain wall motion layer is larger than the value at which the domain wall motion layer can maintain perpendicular magnetic anisotropy, and smaller than the value of the original anisotropic magnetic field of the ferromagnetic material of the domain wall motion layer.
- the magnetoresistive effect element of the present invention includes a domain wall motion layer, a spacer layer, and a reference layer.
- the domain wall motion layer is formed of a first laminated film of a Co film and a Ni film having perpendicular magnetic anisotropy.
- the spacer layer is provided on the domain wall motion layer and is formed of a nonmagnetic material.
- the reference layer is provided on the spacer layer, is formed of a ferromagnetic material, and has a fixed magnetization.
- the domain wall motion layer has at least one domain wall and stores information corresponding to the position of the domain wall.
- the anisotropic magnetic field of the domain wall motion layer is greater than 8 kOe and less than 15 kOe.
- the magnetic random access memory of the present invention uses the magnetoresistive effect element according to any one of the above paragraphs as a magnetic memory cell.
- a magnetoresistive effect element using current-induced domain wall motion and an MRAM using the magnetoresistive effect device it is possible to preferably realize a domain wall motion layer having perpendicular magnetic anisotropy that can operate with a lower write current. It becomes possible.
- FIG. 1 is a cross-sectional view schematically showing a magnetoresistive effect element disclosed in International Publication WO / 2009/001706.
- FIG. 2 is a schematic cross-sectional view showing the configuration of the magnetoresistive element according to the embodiment of the present invention.
- FIG. 3 is a schematic circuit diagram showing a configuration example of the magnetic memory cell 80 for 1 bit according to the embodiment of the present invention.
- FIG. 4 is a block diagram showing a configuration example of the magnetic random access memory 90 according to the present embodiment.
- FIG. 5 is a side view showing the configuration of the magnetoresistive effect element 70 to which the underlayer according to the present embodiment is applied.
- FIG. 6 is a table showing the first embodiment of the present invention and its comparative example 1.
- FIG. 7 is a table showing a second embodiment of the present invention and its comparative example 2.
- FIG. 8 is a table showing the third and fourth embodiments of the present invention and the comparative example 3.
- FIG. 9 is a graph summarizing the results of the first to fourth examples and the first to third comparative examples.
- FIG. 2 is a schematic cross-sectional view showing the configuration of the magnetoresistive element according to the embodiment of the present invention.
- the magnetoresistive effect element 70 includes a domain wall motion layer 10, a spacer layer 20, and a reference layer 30.
- the domain wall motion layer 10 is formed of a ferromagnetic material having perpendicular magnetic anisotropy.
- the domain wall motion layer 10 includes a region in which the magnetization direction can be reversed, and stores data according to the magnetization state. More specifically, the domain wall motion layer 10 includes a first magnetization fixed region 11a, a second magnetization fixed region 11b, and a magnetization free region 13.
- the magnetization fixed regions 11a and 11b are provided adjacent to the magnetization free region 13, respectively.
- the magnetizations of the magnetization fixed regions 11a and 11b are fixed in opposite directions (antiparallel).
- the magnetization direction of the first magnetization fixed region 11a is fixed in the + z direction
- the magnetization direction of the second magnetization fixed region 11b is fixed in the ⁇ z direction.
- a magnetization fixing method for example, a method of providing a hard layer (not shown) whose magnetization is fixed in the + z / ⁇ z direction adjacent to each of the magnetization fixed regions 11a and 11b can be considered.
- the magnetization direction of the magnetization free region 13 can be reversed and can be either the + z direction or the ⁇ z direction. Therefore, the domain wall 12 (12 a or 12 b) is formed in the first domain wall motion layer 10 according to the magnetization direction of the magnetization free region 13.
- a domain wall 12b is formed between the magnetization free region 13 and the second magnetization fixed region 11b.
- a domain wall 12a is formed between the magnetization free region 13 and the first magnetization fixed region 11a. That is, the domain wall motion layer 10 has at least one domain wall 12 (12 a or 12 b), and the position of the domain wall 12 corresponds to the magnetization direction of the magnetization free region 13.
- the spacer layer 20 is provided adjacent to the domain wall motion layer 10.
- the spacer layer 20 is provided so as to be adjacent to at least the magnetization free region 13 of the domain wall motion layer 10.
- the spacer layer 20 is made of a nonmagnetic material. More preferably, it is formed of an insulator.
- the reference layer 30 is provided adjacent to the spacer layer 20 on the side opposite to the domain wall motion layer 10. That is, the reference layer 30 is connected to the domain wall motion layer 10 (magnetization free region 13) through the spacer layer 20.
- the reference layer 30 is made of a ferromagnetic material, and its magnetization direction is fixed in one direction.
- the reference layer 30 is also formed of a ferromagnetic material having perpendicular magnetic anisotropy.
- the magnetization direction of the reference layer 30 is fixed in the + z direction or the ⁇ z direction. In the example of FIG. 2, the magnetization direction of the reference layer 30 is fixed in the + z direction.
- the domain wall motion layer 10 (magnetization free region 13), the spacer layer 20, and the reference layer 30 described above form a magnetic tunnel junction (MTJ). That is, the domain wall motion layer 10 (magnetization free region 13), the spacer layer 20, and the reference layer 30 correspond to a free layer, a barrier layer, and a pinned layer in the MTJ.
- MTJ magnetic tunnel junction
- electrode layers are electrically connected to both ends of the domain wall motion layer 10, respectively.
- two electrode layers are provided so as to be connected to the magnetization fixed regions 11a and 11b, respectively. These electrode layers are used for introducing a write current into the domain wall motion layer 10. These electrode layers can be connected to both ends of the domain wall motion layer 10 via the hard layer described above. Further, another electrode layer (not shown) is electrically connected to the reference layer 30.
- the magnetization directions of the magnetization fixed regions 11a and 11b of the domain wall motion layer 10 are fixed in the + z direction and the ⁇ z direction, respectively, and the magnetization direction of the reference layer 30 is fixed in the + z direction.
- the domain wall 12b is formed at the boundary between the magnetization free region 13 and the second magnetization free region 11b.
- the magnetization direction of the magnetization free region 13 and the magnetization direction of the reference layer 30 are parallel to each other. Therefore, the MTJ resistance value is relatively small.
- Such a magnetization state is associated with, for example, a storage state of data “0”.
- the domain wall 12a is formed at the boundary between the magnetization free region 13 and the first magnetization free region 11a.
- the magnetization direction of the magnetization free region 13 and the magnetization direction of the reference layer 30 are antiparallel to each other. Accordingly, the MTJ resistance value is relatively large.
- Such a magnetization state is associated with a storage state of data “1”, for example.
- the domain wall motion layer 10 has at least one domain wall 12 (12 a or 12 b), and the position of the domain wall 12 corresponds to the magnetization direction of the magnetization free region 13. Therefore, the domain wall motion layer 10 stores data corresponding to the position of the domain wall 12.
- data reading is performed by using a tunneling magnetoresistive effect (TMR effect).
- TMR effect tunneling magnetoresistive effect
- a read current is passed in a direction penetrating the MTJ (the magnetization free region 13 of the domain wall motion layer 10, the spacer layer 20, and the reference layer 30). Note that the read current direction is arbitrary.
- the magnetoresistive element 70 is in the data “0” state, the resistance value of the MTJ is relatively small. In the data “1” state, the MTJ resistance value is relatively large. Therefore, data can be read by detecting the resistance value.
- FIG. 3 is a schematic circuit diagram showing a configuration example of the magnetic memory cell 80 for 1 bit according to the embodiment of the present invention.
- the magnetic memory cell 80 has a 2T-1MTJ (2 Transistors-1 Magnetic Tunnel Junction) configuration including a magnetic memory element 70 and two transistors TRa and TRb.
- the magnetoresistive effect element 70 is a three-terminal element, and is connected to the word line WL, the ground line GL, and the bit line pair BLa, BLb.
- the terminal connected to the reference layer 30 is connected to the ground line GL.
- a terminal connected to the first magnetization fixed region 11a of the domain wall motion layer 10 is connected to the bit line BLa via the transistor TRa.
- a terminal connected to the second magnetization fixed region 11b of the domain wall motion layer 10 is connected to the bit line BLb via the transistor TRb.
- the gates of the transistors TRa and TRb are connected to a common word line WL.
- the word line WL is set to the high level, and the transistors TRa and TRb are turned on.
- one of the bit line pair BLa and BLb is set to a high level, and the other is set to a low level (ground level).
- a write current flows between the bit line BLa and the bit line BLb via the transistors TRa and TRb and the domain wall motion layer 10.
- the word line WL is set to the high level, and the transistors TRa and TRb are turned on. Further, the bit line BLa is set to an open state, and the bit line BLb is set to a high level. As a result, the read current Iread flows from the bit line BLb through the MTJ of the magnetoresistive effect element 70 to the ground line GL.
- FIG. 4 is a block diagram showing a configuration example of the magnetic random access memory 90 according to the present embodiment.
- the magnetic random access memory 90 includes a memory cell array 91, an X driver 92, a Y driver 93, and a controller 94.
- the memory cell array 91 is composed of a plurality of magnetic memory cells 80 arranged in an array. As shown in FIG. 3 described above, each magnetic memory cell 80 is connected to the word line WL, the ground line GL, and the bit line pair BLa, BLb.
- the X driver 92 is connected to a plurality of word lines WL, and drives a selected word line connected to the accessed magnetic memory cell 80 among the plurality of word lines WL.
- the Y driver 93 is connected to a plurality of bit line pairs BLa and BLb, and sets each bit line to a state corresponding to a write operation or a read operation.
- the controller 94 controls each of the X driver 92 and the Y driver 93 according to a write operation or a read operation.
- Non-Patent Document 3 when the domain wall motion layer (domain wall motion layer) has perpendicular magnetic anisotropy, in the domain wall motion layer, In comparison, domain wall motion can be caused by a smaller write current.
- Non-Patent Document 4 (A. Thiaville et al., “Domain wall motion by spin-polarized current: a micromagnetic study”, JOURNAL OF APPLIED PHYSICS, VOL. 70. 49. p. Therefore, current-induced domain wall motion is more likely to occur as the parameter: g ⁇ B P / 2eM s increases.
- g Lande g factor
- ⁇ B Bohr magneton
- P spin polarizability
- e elementary charge of electron
- M s saturation magnetization
- the first domain wall motion layer 10 has a laminated structure in which a first layer and a second layer are laminated.
- the first layer contains an alloy made of a plurality of materials selected from any one of Fe, Co, and Ni, or a group thereof.
- the second layer contains an alloy made of a plurality of materials selected from Pt, Pd, Au, Ag, Ni, Cu, or a group thereof.
- Co / Ni has a high spin polarizability. Therefore, it can be said that the Co / Ni laminated film is particularly suitable as the domain wall motion layer 10. In fact, the inventors have confirmed through experiments that domain wall movement with high controllability can be realized by using Co / Ni.
- the magnetic material of the domain wall motion layer 10 as described above has an fcc structure and an fcc (111) -oriented crystal structure in which (111) planes are stacked in the direction perpendicular to the substrate.
- Non-Patent Document 5 (G.H.O. Daaldelop et al., “Prediction and Configuration of Permanent Magnetic Anisotropy in Co / Ni Multilayers”, PHYSIC. 68. REVIEW. , 1992.), the perpendicular magnetic anisotropy of the laminated film as described above is manifested by the interfacial magnetic anisotropy at the interface of these films. Therefore, in order to achieve good perpendicular magnetic anisotropy in the domain wall motion layer 10, it is preferable to provide a “underlayer” that allows the above-described magnetic material to grow with good fcc (111) orientation.
- the domain wall motion layer 10 may have an “underlayer” that can grow with a good fcc (111) orientation and realize a good perpendicular magnetic anisotropy.
- underlayer will be mainly described.
- FIG. 5 is a side view showing the configuration of the magnetoresistive effect element 70 to which the underlayer according to the present embodiment is applied.
- the underlayer 40 is provided on the substrate side of the domain wall motion layer 10.
- the domain wall motion layer 10 is formed on the base layer 40 by using the base layer 40 as a base.
- the underlayer 40 can be a single layer or two layers.
- the material is any one of Group 9 to Group 11 metals having an fcc structure such as Cu, Rh, Pd, Ag, Ir, Pt, Au, or a plurality of materials selected from these groups. Containing an alloy. It should be noted that the present invention can be implemented even if other materials are included within an appropriate range. It is also possible to adjust so as to obtain more desired characteristics by adding an appropriate material.
- the material of the first underlayer contains Group 4 to Group 6 elements. That is, the first underlayer 15A is made of any one of Group 4 to Group 6 metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W, or an alloy made of a plurality of materials selected from these groups. contains.
- the second underlayer upper side (domain wall moving layer 10) side) contains Group 9 to Group 11 elements.
- the second underlayer is made of any one of Group 9 to Group 11 metals having an fcc structure such as Cu, Rh, Pd, Ag, Ir, Pt, and Au, or a plurality of materials selected from these groups
- the present invention can be carried out even if other materials are included within an appropriate range. It is also possible to adjust so as to obtain more desired characteristics by adding an appropriate material.
- the reason why such a combination of the first underlayer and the second underlayer is preferable is as follows.
- the Group 4 to Group 6 metal used as the first underlayer grows in an amorphous state in a region where the film thickness is thin, and its surface energy increases. Accordingly, such a first underlayer can produce a close-packed surface (lowest surface energy surface) orientation of the crystal grown thereon. That is, when a Group 9 to Group 11 metal having an fcc structure is grown on the first underlayer as the second underlayer, the (111) plane orientation which is the most dense surface is realized.
- Such a second underlayer serves as a template for the crystal orientation of the domain wall motion layer 10. As a result, good fcc (111) orientation is also achieved in the domain wall motion layer 10.
- a suitable underlayer 40 structure and material can be obtained when the first underlayer and the second underlayer have a laminated structure. It has been found that suitable characteristics can be obtained with respect to the / Ni laminated film.
- the inventor further examined the following points this time. That is, when the domain wall motion layer is formed of a ferromagnetic material having perpendicular magnetic anisotropy, the inventor can further reduce the write current if the spin polarizability of the domain wall motion layer can be further increased. is there. Clarification of the relationship between spin polarizability and perpendicular magnetic anisotropy (anisotropic magnetic field) in ferromagnets, and spin by applying the optimum perpendicular magnetic anisotropy (anisotropic magnetic field) to the domain wall moving layer It is considered that the write current can be further reduced by further increasing the polarizability.
- the perpendicular magnetic anisotropy is represented by the anisotropic magnetic field of the domain wall motion layer 10.
- the upper limit is an anisotropic magnetic field smaller than the value of the original anisotropic magnetic field of the ferromagnetic material of the domain wall moving layer 10.
- the lower limit is an anisotropic magnetic field in which the domain wall motion layer 10 can maintain perpendicular magnetic anisotropy.
- the anisotropic magnetic field of the domain wall motion layer 10 is smaller than the original anisotropic magnetic field value of the ferromagnetic material of the domain wall motion layer.
- the value of the original anisotropic magnetic field of the material is a value of the anisotropic magnetic field that is theoretically predicted from the inherent physical property (physical property value) of the material. For example, when using an alternate laminated film of transition metal-based tax as the domain wall motion layer 10, considering the physical properties inherent to the transition metal-based material, the structure of the laminated structure, the ideal perpendicular magnetic anisotropy, etc. It is the value of the anisotropic magnetic field theoretically predicted by the theoretical calculation (simulation) to be performed. It is considered that the spin polarizability becomes relatively high when the anisotropic magnetic field of the domain wall motion layer 10 is smaller than the original anisotropic magnetic field of the material. The reason is as follows.
- the origin of perpendicular magnetic anisotropy includes crystal magnetic anisotropy and interfacial magnetic anisotropy.
- interfacial magnetic anisotropy the spin initiation interaction of d electrons having anisotropic electron orbits may play an important role.
- increasing the perpendicular magnetic anisotropy corresponds to lowering the energy level of the d electrons.
- domain wall motion current (write current) is governed by the difference in the number of positive and negative spins of d electrons near the Fermi energy contributing to conduction, that is, the spin polarizability.
- the orbital energy of d electrons is reduced, and the d electrons contributing to conduction are reduced below Fermi energy. Therefore, it is considered that the difference in the number of positive and negative spins is reduced, and as a result, the spin polarizability is reduced. From the above, in such a case, the perpendicular magnetic anisotropy is moderately weakened to increase the d electron energy level and increase the d electrons in the vicinity of the Fermi energy, thereby increasing the spin spin rate. Can be realized.
- the anisotropic magnetic field in the perpendicular magnetic anisotropy of the domain wall moving layer 10 is larger than the minimum value at which the domain wall moving layer 10 can maintain the perpendicular magnetic anisotropy. That is, the anisotropic magnetic field of the domain wall motion layer 10 needs to be sufficiently large to overcome the demagnetizing field described later and direct the magnetization in the vertical direction.
- the minimum value capable of maintaining the perpendicular magnetic anisotropy is the perpendicular magnetic anisotropy in the vicinity of the boundary between the state where the domain wall motion layer 10 has the perpendicular magnetic anisotropy and the state where it does not have the magnetic anisotropy.
- the state having perpendicular magnetic anisotropy means that the magnetization direction of the domain wall motion layer 10 is generally in the ⁇ z direction. Specifically, the ⁇ z direction component of the magnetization direction of the domain wall motion layer 10 is at least larger than the ⁇ x direction component and the ⁇ y direction component (both components in the direction parallel to the substrate surface). It is considered that the fact that the anisotropic magnetic field of the domain wall motion layer 10 takes such a value means that the current-induced domain wall motion type domain wall motion layer 10 has perpendicular magnetic anisotropy. In that case, as described in Patent Document 3 and Non-Patent Document 3, the write current can be reduced.
- FIG. 6 is a table showing the first embodiment of the present invention and its comparative example 1.
- the domain wall motion layer of the magnetoresistive effect element 70 in FIG. 6 is formed by the first film forming apparatus.
- domain wall moving layer indicates the configuration (material, film thickness, number of layers) of the domain wall moving layer 10 used in the experiment.
- Underlayer indicates the configuration (material, film thickness) of the underlayer 40 used in the experiment.
- Hk indicates an actual measurement value of the anisotropic magnetic field of the domain wall motion layer 10. The magnitude of the anisotropic magnetic field Hk substantially indicates the degree of perpendicular magnetic anisotropy.
- Example 1 uses, as the domain wall motion layer 10, a Co / Ni laminated film in which a Co film having a film thickness of 0.3 nm and a Ni film having a film thickness of 0.6 nm are alternately laminated.
- As the underlayer 40 a Ta / Pt laminated film in which a Ta film with a thickness of 4 nm and a Pt film with a thickness of 1.6 nm are laminated in this order is used.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 14.3 kOe.
- the minimum value of the write current that causes domain wall motion was 0.4 mA.
- Comparative Example 1 as the domain wall motion layer 10, a Co / Ni laminated film in which five Co films having a film thickness of 0.3 nm and five Ni films having a film thickness of 0.6 nm are alternately laminated, as in Example 1. Used.
- As the underlayer 40 a Ta / Pt laminated film in which a Ta film with a thickness of 4 nm and a Pt film with a thickness of 2.4 nm are laminated in this order is used.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 15.2 kOe.
- the minimum value of the write current that causes domain wall motion was 0.7 mA.
- Example 1 the thickness of the Pt film of the underlayer 40 is relatively thin (1.6 nm). Therefore, it is considered that the (111) orientation of the Pt film is relatively lowered. As a result, the (111) orientation of the domain wall motion layer 10 is also relatively lowered, and its anisotropic magnetic field Hk (perpendicular magnetic anisotropy) is lower than the original value of the material of the domain wall motion layer 10. The value (about 14.3 kOe) can be considered. At this time, for the reasons described above, it is considered that the minimum value of the write current causing the domain wall movement can be relatively low (0.4 mA).
- the domain wall motion layer 10 When the domain wall motion layer 10 is a Co / Ni laminated film, it needs to be oriented to (111) in order to have perpendicular magnetic anisotropy. For that purpose, it is effective to orient the Pt film of the underlayer 40 in the (111) orientation.
- the Pt film on the Ta film is (111) oriented when the film thickness is sufficiently thick, but is not completely (111) oriented when the film thickness is thin.
- the perpendicular magnetic anisotropy is lowered and the domain wall motion current is reduced.
- Example 1 by reducing the perpendicular magnetic anisotropy of the domain wall motion layer 10 from the original state of the material, the value of the write current that causes domain wall motion can be reduced. That is, the value of the write current causing domain wall motion can be reduced by lowering the value of the anisotropic magnetic field of the domain wall motion layer 10 from the original value of the material.
- FIG. 7 is a table showing the second embodiment of the present invention and its comparative example 2.
- the domain wall moving layer is formed by the second film forming apparatus and the thickness of the Pt film as the underlayer is reduced compared to the case of FIG. This is different from the case of FIG.
- Example 2 uses a Co / Ni laminated film in which five Co films having a film thickness of 0.3 nm and five Ni films having a film thickness of 0.6 nm are alternately laminated as the domain wall motion layer 10.
- a Ta / Pt laminated film in which a Ta film with a thickness of 4 nm and a Pt film with a thickness of 1.0 nm are laminated in this order is used.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 11.4 kOe.
- the minimum value of the write current that causes domain wall motion was 0.4 mA.
- the underlayer 40 a Ta / Pt laminated film in which a Ta film with a thickness of 4 nm and a Pt film with a thickness of 1.6 nm are laminated in this order is used.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 15.4 kOe.
- the minimum value of the write current that causes domain wall motion was 0.8 mA.
- Example 2 and Comparative Example 2 are compared, first, in Comparative Example 2, the thickness of the Pt film of the underlayer 40 is relatively thick (1.6 nm). Therefore, it is considered that the (111) orientation of the Pt film is high. As a result, the (111) orientation of the domain wall motion layer 10 is improved, and the anisotropic magnetic field Hk (perpendicular magnetic anisotropy) is the original value of the material of the domain wall motion layer 10 (about 15.4 kOe). I can think of it. Therefore, for the reasons described above, it is considered that the minimum value of the write current that causes domain wall motion is relatively high (0.8 mA).
- Hk perpendicular magnetic anisotropy
- Example 1 the thickness of the Pt film of the underlayer 40 is relatively thin (1.0 nm). Therefore, it is considered that the (111) orientation of the Pt film is relatively lowered. As a result, the (111) orientation of the domain wall motion layer 10 is also relatively lowered, and its anisotropic magnetic field Hk (perpendicular magnetic anisotropy) is lower than the original value of the material of the domain wall motion layer 10. The value (about 11.4 kOe) can be considered. At this time, for the reasons described above, it is considered that the minimum value of the write current causing the domain wall movement can be relatively low (0.4 mA).
- Example 2 by reducing the perpendicular magnetic anisotropy of the domain wall motion layer 10 from the original state of the material, the value of the write current that causes domain wall motion can be reduced. That is, the value of the write current causing domain wall motion can be reduced by lowering the value of the anisotropic magnetic field of the domain wall motion layer 10 from the original value of the material.
- FIG. 8 is a table showing the third and fourth embodiments of the present invention and the comparative example 3.
- the basic structures of the third and fourth embodiments and the comparative example 3 are the same as those of the first embodiment shown in FIG. However, it differs from the case of Example 1 in FIG. 6 in that it has a structure in which the cap layer is laminated on the surface of the domain wall motion layer 10 opposite to the base layer 40.
- Example 3 a Ru film having a thickness of 2.0 nm is laminated as a cap layer in the configuration of Example 1 in FIG.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 13.4 kOe, which was lower than that in Example 1.
- the minimum value of the write current causing the domain wall movement was 0.3 mA, which was lower than that in the case of Example 1. That is, by using the Ru film as the cap layer, the write current that causes the domain wall movement can be further reduced. This is probably because the influence of the interface magnetic anisotropy changed at the interface between the Ru film and the domain wall motion layer, and the perpendicular magnetic anisotropy was lowered.
- Example 4 a Pt film having a thickness of 2.0 nm is laminated as a cap layer on the configuration of Example 1 in FIG.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 was 14.3 kOe, which was not changed compared to the case of Example 1.
- the minimum value of the write current causing the domain wall motion was 0.4 mA, which was not changed as compared with the case of Example 1. That is, even when the Pt film was used as the cap layer, the write current that caused domain wall movement did not change. This is presumably because the influence of the interfacial magnetic anisotropy did not change at the interface between the Pt film and the domain wall motion layer.
- an MgO film having a film thickness of 1.0 nm is laminated as a cap layer in the configuration of Example 1 in FIG.
- the anisotropic magnetic field Hk of the domain wall motion layer 10 increased to 15.7 kOe compared to the case of Example 1.
- the minimum value of the write current causing the domain wall movement was 0.8 mA, which was increased compared to the case of Example 1. That is, by using the MgO film as the cap layer, the write current that causes the domain wall motion is increased. This is probably because the influence of the interface magnetic anisotropy was changed at the interface between the MgO film and the domain wall motion layer, and the perpendicular magnetic anisotropy was improved.
- Example 3 by laminating the cap layer, the perpendicular magnetic anisotropy of the domain wall motion layer 10 is weakened from the original state of the material, so that the value of the write current that causes domain wall motion is reduced. Further reduction can be achieved. That is, by reducing the value of the anisotropic magnetic field of the domain wall motion layer 10 from the original value of the material, the value of the write current that causes domain wall motion can be further reduced.
- FIG. 9 is a graph summarizing the results of the first to fourth examples and the first to third comparative examples.
- the vertical axis represents the domain wall motion current (the minimum value of the write current that causes domain wall motion), and the horizontal axis represents the anisotropic magnetic field Hk (corresponding to the perpendicular magnetic anisotropy).
- Hk H + 4 ⁇ Ms (about 8 kOe).
- 4 ⁇ Ms is indicated by H S0 .
- Black circles indicate Example 1 and Comparative Example 1
- white squares indicate Example 2 and Comparative Example 2
- black triangles indicate Examples 3, 4 and Comparative Example 3, respectively.
- the domain wall moving current is lowered. This is considered because the perpendicular magnetic anisotropy of the domain wall motion layer 10 is weakened from the original state of the material. As a result, the domain wall motion current can be reduced in a region where the anisotropy magnetic field is smaller than 15 kOe as compared with the case where the magnetic field has the original perpendicular magnetic anisotropy.
- the anisotropic magnetic field needs to be larger than 4 ⁇ Ms (about 8 kOe), so the anisotropic magnetic field needs to be larger than 8 kOe. From the above, it is considered that the anisotropic magnetic field is preferably larger than 8 kOe and smaller than 15 kOe.
- the degree of (111) orientation is about 100% when the anisotropic magnetic field (perpendicular magnetic anisotropy) is the original value. Therefore, it can be seen that in order to weaken the perpendicular magnetic anisotropy of the domain wall motion layer 10 from the original state of the material, the degree of (111) orientation is preferably less than 100%. In that case, it can be seen that the degree of (111) orientation is preferably smaller than 100% for the underlayer 40 as well.
- the degree of (111) orientation needs to be larger than the orientation degree capable of maintaining the perpendicular magnetic anisotropy.
- the degree of orientation that can maintain the perpendicular magnetic anisotropy is such that the proportion of crystals oriented in the (111) direction in the Co / Ni laminated film is oriented in the (111) direction included in the randomly oriented film.
- the degree of orientation is greater than the proportion of crystals.
- the degree of (111) orientation in the underlayer 40 also needs to be larger than the degree of orientation in which the Co / Ni laminated film can maintain perpendicular magnetic anisotropy.
- the degree of orientation is approximately the same as the degree of orientation of the Co / Ni laminated film.
- the degree of (111) orientation in the Co / Ni laminated film is larger than the degree of orientation in which the Co / Ni laminated film can maintain the perpendicular magnetic anisotropy, and more than 100% of the degree of orientation. A small value is considered preferable.
- the method of reducing the perpendicular magnetic anisotropy of the domain wall moving layer 10 from the original state of the material that is, reducing the value of the anisotropic magnetic field of the domain wall moving layer 10 from the original value of the material.
- crystal orientation example: (111) orientation of Co / Ni
- the crystal orientation of the domain wall moving layer 10 is controlled by controlling the crystal orientation of the underlayer 40 by the film thickness.
- the present invention is not limited to this example, and other methods can be used as long as the perpendicular magnetic anisotropy of the domain wall motion layer 10 can be weakened from the original state of the material.
- the underlayer 40 can be made of a material having a long-period structure.
- the long-period structure is defined as a structure having an orientation surface slightly inclined from (111), for example, (664). Thereby, it is considered that the value of the anisotropic magnetic field can be lowered from the original value of the material, for example, the crystal orientation of the domain wall motion layer 10 is lowered.
- a method of adding another element to the domain wall motion layer 10 can be considered. Thereby, it is considered that the value of the anisotropic magnetic field can be lowered from the original value of the material, for example, the crystal orientation of the domain wall motion layer 10 is lowered.
- a trace amount of non-magnetic material can be considered. Examples of such a nonmagnetic material include Ta and Cu.
- the interface magnetic anisotropy is affected by the crystallinity disorder or mutual diffusion at the interface between the domain wall motion layer 10 and the underlayer 40, and the perpendicular magnetic anisotropy decreases.
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Abstract
Description
すなわち、磁壁移動層10は少なくとも一つの磁壁12(12a又は12b)を有し、その磁壁12の位置は磁化自由領域13の磁化方向に対応している。従って、磁壁移動層10は、その磁壁12の位置に対応してデータを記憶している。
きる。すなわち、磁壁移動層10の異方性磁界の値をその材料の本来の値から低下させることで、磁壁移動を起こす書き込み電流の値を更に低減することができる。
Claims (7)
- 垂直磁気異方性を有する強磁性体で形成された磁壁移動層と、
前記磁壁移動層上に設けられ、非磁性体で形成されたスペーサ層と、
前記スペーサ層上に設けられ、強磁性体で形成され、磁化が固定された参照層と
を具備し、
前記磁壁移動層は、少なくとも一つの磁壁を有し、前記磁壁の位置に対応して情報を記憶し、
前記磁壁移動層の異方性磁界は、前記磁壁移動層が垂直磁気異方性を保ち得る値より大きく、前記磁壁移動層の強磁性体本来の異方性磁界の値より小さい
磁気抵抗効果素子。 - 請求項1に記載の磁気抵抗効果素子において、
前記磁壁移動層は、垂直磁気異方性を有するCo膜とNi膜との第1積層膜で形成され、
前記第1積層膜の(111)配向の度合いは、前記第1積層膜が垂直磁気異方性を保ち得る配向度より大きく、100%より小さい
磁気抵抗効果素子。 - 垂直磁気異方性を有するCo膜とNi膜との第1積層膜で形成された磁壁移動層と、
前記磁壁移動層上に設けられ、非磁性体で形成されたスペーサ層と、
前記スペーサ層上に設けられ、強磁性体で形成され、磁化が固定された参照層と
を具備し、
前記磁壁移動層は、少なくとも一つの磁壁を有し、前記磁壁の位置に対応して情報を記憶し、
前記磁壁移動層の異方性磁界は、8kOeより大きく、15kOeより小さい
磁気抵抗効果素子。 - 請求項3に記載の磁気抵抗効果素子において、
前記第1積層膜の(111)配向の度合いは、前記第1積層膜が垂直磁気異方性を保ち得る配向度より大きく、100%より小さい
磁気抵抗効果素子。 - 請求項2又は4に記載の磁気抵抗効果素子において、
前記第1積層膜下に設けられ、Pt膜とTa膜との第2積層膜で形成された下地層を更に具備し、
前記第1積層膜に接する前記Pt膜の(111)配向の度合いは、前記第1積層膜が垂直磁気異方性を保ち得る配向度より大きく、100%より小さい
磁気抵抗効果素子。 - 請求項2又は4に記載の磁気抵抗効果素子において、
前記第1積層膜下に設けられ、Pt膜とTa膜との第2積層膜で形成された下地層を更に具備し、
前記第1積層膜に接する前記Pt膜は、長周期構造を有する
磁気抵抗効果素子。 - 請求項1乃至6のいずれか一項に記載の磁気抵抗効果素子を磁気メモリセルとして用いた磁気ランダムアクセスメモリ。
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JPWO2011078018A1 (ja) | 2013-05-02 |
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