WO2010074130A1 - 磁気メモリ素子及び磁気ランダムアクセスメモリ - Google Patents
磁気メモリ素子及び磁気ランダムアクセスメモリ Download PDFInfo
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- WO2010074130A1 WO2010074130A1 PCT/JP2009/071408 JP2009071408W WO2010074130A1 WO 2010074130 A1 WO2010074130 A1 WO 2010074130A1 JP 2009071408 W JP2009071408 W JP 2009071408W WO 2010074130 A1 WO2010074130 A1 WO 2010074130A1
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- G—PHYSICS
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- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- 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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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- 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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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- 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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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- 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
- G11C11/1673—Reading or sensing circuits or methods
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- 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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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H—ELECTRICITY
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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
Definitions
- the present invention relates to a magnetic memory element and a magnetic random access memory, and more particularly to a domain wall motion type magnetic memory element and a magnetic random access memory.
- Magnetic Random Access Memory Magnetic Random Access Memory
- MRAM Magnetic Random Access Memory
- MRAM Magnetic Random Access Memory
- a magnetoresistive element is integrated in a memory cell, and data is stored as the magnetization direction of the ferromagnetic layer of the magnetoresistive element.
- MRAMs Several types have been proposed corresponding to the method of switching the magnetization direction of the ferromagnetic layer.
- the most common MRAM is a current-induced magnetic field writing type MRAM.
- this MRAM wiring for passing a write current is arranged around the magnetoresistive element, and the magnetization direction of the ferromagnetic layer of the magnetoresistive element is switched by a current magnetic field generated by passing the write current.
- this MRAM can be written in 1 nanosecond or less, and is suitable as a high-speed MRAM.
- the magnetic field for switching the magnetization of the magnetic material in which the thermal stability and the disturbance magnetic field resistance are ensured is generally about several tens [Oe].
- a large write current of about 1 mA to several mA is required.
- the write current is large, the chip area is inevitably increased, and the power consumption required for writing increases.
- the write current further increases and does not scale.
- a technique capable of reducing the write current in response to miniaturization of the memory cell is desired.
- spin transfer method As a write method that can suppress an increase in write current due to miniaturization, a “spin transfer method” has been proposed (for example, Japanese Patent Application Laid-Open No. 2005-93488, “Current-drive excitation of magnetic”. multilayers ”, JC Slonzewski, Journal of Magnetism & Magnetic Materials, 159, L1-L7 (1996)).
- spin injection method a spin-polarized current is injected into the ferromagnetic conductor, and the magnetization is reversed by a direct interaction between the spin of the conduction electron carrying the current and the magnetic moment of the conductor. (Hereinafter referred to as “Spin Transfer Magnetization Switching”).
- the presence or absence of spin injection magnetization reversal depends on the current density (not the absolute value of the current). Therefore, when spin injection magnetization reversal is used for data writing, the write current is reduced if the size of the memory cell is reduced. That is, the spin injection magnetization reversal method is excellent in scaling. When the write current is small, the chip area is small, and high integration and large scale are possible. However, the writing time tends to be longer than that of the current-induced magnetic field writing type MRAM (example: 1 nsec. Or more).
- US Pat. No. 6,834,005 discloses a magnetic shift register using spin injection.
- This magnetic shift register stores data using a domain wall in a magnetic material.
- a current is injected so as to pass through the domain wall, and the domain wall is moved by the current.
- the magnetization direction of each region is treated as recorded data.
- Such a magnetic shift register is used, for example, for recording a large amount of serial data.
- the movement of the domain wall in the magnetic material is described in “Real-Space Observation of Current-Driving Domain Wall Motion in Submicron Magnetic Wires”, A.M. Yamaguchi et al. , Physical Review Letters, Vol. 92, pp. 077205-1-4 (2004).
- MRAM of domain wall motion type utilizing such domain wall motion by spin injection (Domain Wall Motion) is described in Japanese Patent Application Laid-Open No. 2005-191032 and WO 2007/020823.
- An MRAM described in Japanese Patent Application Laid-Open No. 2005-191032 includes a magnetization fixed layer in which magnetization is fixed, a tunnel insulating layer stacked on the magnetization fixed layer, and a magnetization recording layer stacked on the tunnel insulating layer. . Since the magnetization recording layer includes a portion where the magnetization direction can be reversed and a portion where the magnetization direction is not substantially changed, it is referred to as a magnetization recording layer, not a magnetization free layer.
- FIG. 1 is a schematic plan view showing the structure of a magnetic recording layer disclosed in Japanese Patent Application Laid-Open No. 2005-191032. In FIG. 1, the magnetization recording layer 100 has a linear shape.
- the magnetization recording layer 100 includes a junction 103 that overlaps the tunnel insulating layer and the magnetization fixed layer, a constriction 104 adjacent to both ends of the junction 103, and a pair of magnetization fixed regions formed adjacent to the constriction 104. 101, 102.
- the pair of magnetization fixed regions 101 and 102 are given fixed magnetizations in opposite directions.
- the MRAM further includes a pair of write terminals 105 and 106 that are electrically connected to the pair of magnetization fixed regions 101 and 102. Through the write terminals 105 and 106, a current that passes through the junction 103, the pair of constricted portions 104, and the pair of magnetization fixed regions 101 and 102 of the magnetization recording layer 100 flows.
- FIG. 2 is a schematic plan view showing the structure of the magnetic recording layer 120 of WO2007 / 020823.
- the magnetization recording layer 120 has a U-shape.
- the magnetization recording layer 120 includes a first magnetization fixed region 121, a second magnetization fixed region 122, and a magnetization switching region 123.
- the magnetization switching region 123 overlaps the pinned layer 130.
- the first and second magnetization fixed regions 121 and 122 are formed to extend in the Y direction, and their magnetization directions are fixed in the same direction.
- the magnetization switching region 123 is formed so as to extend in the X direction, and has reversible magnetization.
- the domain wall is formed at the boundary B1 between the first magnetization fixed region 121 and the magnetization switching region 123 or at the boundary B2 between the second magnetization fixed region 122 and the magnetization switching region 123.
- the first and second magnetization fixed regions 121 and 122 are connected to current supply terminals 125 and 126, respectively. By using these current supply terminals 125 and 126, a write current can be passed through the magnetization recording layer 120.
- the domain wall moves in the magnetization switching region 123 according to the direction of the write current. By this domain wall movement, the magnetization direction of the magnetization switching region 123 can be controlled.
- the threshold current density for current-induced domain wall motion is smaller in the element using the perpendicular magnetic anisotropy material in which the magnetic anisotropy of the magnetization recording layer is perpendicular to the substrate surface. It has been shown experimentally. For example, “Threshold currents to move domain walls in films with perennial anisotropy”, D.M. Ravelosona et al. , Applied Physics Letters, Vol. 90,072508 (2007), a threshold current density of 10 6 A / cm 2 is observed. Also, “Micromagnetic analysis of current drive domain wall motion in nanostripping with pendular magnetic anisotropy”, S. et al. Fukami et. al.
- Japanese Patent Application Laid-Open No. 2006-73930 discloses a method for changing the magnetization state of a magnetoresistive element using domain wall motion, a magnetic memory element using the method, and a solid magnetic memory.
- This magnetic memory element has a first magnetic layer, an intermediate layer, and a second magnetic layer, and records information in the magnetization directions of the first magnetic layer and the second magnetic layer.
- magnetic domains that are antiparallel to each other and a domain wall that separates these magnetic domains are constantly formed in at least one of the magnetic layers, and the domain walls are moved in the magnetic layer so that adjacent magnetic domains can be moved.
- the information recording is performed by controlling the position.
- the second magnetic layer may have magnetic anisotropy in a direction perpendicular to the film surface.
- the inventor examined reducing the write current by using a perpendicular magnetic anisotropic material as the magnetization recording layer in the MRAM using current-driven domain wall motion, as described below.
- the magnetization recording layer 210 includes a magnetization switching area 213 and a pair of magnetization fixed areas 211a and 211b.
- white circles and dots, white circles and crosses, and white arrows indicate the regions in which they are described (in the case of FIGS. 3A and 3B, the magnetization switching region 213 and the magnetization fixed region 211a. , 211b).
- the magnetization switching region 213 overlaps with the tunnel insulating layer 232 and the pinned layer 230 and functions as a free layer.
- the magnetization switching region 213, the tunnel insulating layer 232, and the pinned layer 230 constitute a magnetic tunnel junction (MTJ).
- the magnetization fixed region 211a is adjacent to one end of the magnetization switching region 213, and the magnetization fixed region 211b is adjacent to the other end of the magnetization switching region 213.
- a constricted portion 215 to which the pin potential forming method disclosed in Japanese Patent Application Laid-Open No. 2005-191032 is applied is provided at the junction between the magnetization switching region 213 and the magnetization fixed regions 211a and 211b.
- the pair of magnetization fixed regions 211a and 211b must be given fixed magnetizations in opposite directions. Further, the constricted portion 215 functions as a pin potential for the domain wall, and the domain wall must be initialized so as to become the domain wall 212a or the domain wall 212b in a region near the constricted portion.
- the magnetization recording layer when the magnetic anisotropy of the magnetization recording layer is in-plane and the magnetization is in the in-plane direction, the magnetization recording layer is made U-shaped to fix the magnetization. It is easy to initialize the magnetization direction and domain wall position of the region to a desired state.
- the shape of the magnetization recording layer can be made U-shaped. It is difficult to perform initialization using an external magnetic field.
- the constriction is smaller than that of the magnetic recording layer 210. Since the size of the part 215 is small, the shape may be disturbed due to manufacturing variations. In that case, since the constricted portion 215 does not have a desired shape, the domain wall 212 cannot be pinned and does not function as a magnetic memory. Furthermore, if the element is further miniaturized and the width of the magnetic recording layer is narrowed, it is very difficult to form a constriction, and there is a possibility that processing exceeding the lithography limit of the semiconductor process may be required.
- An object of the present invention is to easily form a magnetization fixed region and easily form a pinning site of a domain wall in a current-driven domain wall motion type MRAM in which the magnetic anisotropy of the magnetization recording layer is perpendicular.
- a magnetic memory device having a structure and a magnetic random access memory are provided.
- the magnetic memory element of the present invention includes a magnetization recording layer and a magnetic tunnel junction.
- the magnetization recording layer is a ferromagnetic layer having perpendicular magnetic anisotropy.
- the magnetic tunnel junction is for reading information from the magnetic recording layer.
- the magnetization recording layer includes two domain wall motion regions.
- a plurality of magnetic memory cells including the magnetic memory element described in the above paragraph are arranged in a matrix.
- the sensor layer has a magnetic anisotropy in a direction perpendicular to a direction connecting the first domain wall motion region and the second domain wall motion region.
- a magnetic memory element in which a magnetization fixed region can be easily formed and a domain wall pinning site can be easily formed.
- FIG. 1 is a schematic plan view showing the structure of a magnetic recording layer disclosed in Japanese Patent Application Laid-Open No. 2005-191032.
- FIG. 2 is a schematic plan view showing the structure of the magnetic recording layer of WO2007 / 020823.
- FIG. 3A is a plan view of a magnetoresistive element using a perpendicular magnetic anisotropic material that can be assumed.
- FIG. 3B is a cross-sectional view of a magnetoresistive element using a perpendicular magnetic anisotropic material that can be assumed.
- FIG. 4A is a plan view showing the configuration of the magnetization recording layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 1 is a schematic plan view showing the structure of a magnetic recording layer disclosed in Japanese Patent Application Laid-Open No. 2005-191032.
- FIG. 2 is a schematic plan view showing the structure of the magnetic recording layer of WO2007 / 020823.
- FIG. 3A is a plan view of a magnet
- FIG. 4B is a cross-sectional view showing the configuration of the magnetic memory element according to the embodiment of the present invention.
- FIG. 5A is a cross-sectional view illustrating a configuration of a magnetic memory element according to an embodiment of the present invention.
- FIG. 5B is a cross-sectional view showing the configuration of the magnetic memory element according to the embodiment of the present invention.
- FIG. 6A is a cross-sectional view illustrating a method for initializing a magnetic memory device according to an embodiment of the present invention.
- FIG. 6B is a cross-sectional view illustrating a method for initializing a magnetic memory device according to an embodiment of the present invention.
- FIG. 6C is a cross-sectional view illustrating a method for initializing a magnetic memory device according to an embodiment of the present invention.
- FIG. 7 is a cross-sectional view showing the principle of writing to the magnetic memory element according to the embodiment of the present invention.
- FIG. 8A is a cross-sectional view illustrating the principle of reading data from a magnetic memory device according to an embodiment of the present invention.
- FIG. 8B is a cross-sectional view illustrating the principle of reading data from the magnetic memory device according to the embodiment of the present invention.
- FIG. 9 is a circuit diagram showing a configuration example of the memory cell according to the embodiment of the present invention.
- FIG. 10 is a block diagram showing a configuration example of the MRAM according to the embodiment of the present invention.
- FIG. 11 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 12 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 13 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 14 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 15 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 16 is a configuration diagram showing an example of a sensor layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 17 is a configuration diagram showing a variation regarding the positional relationship between the sensor layer and the hard layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 18 is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19A is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19B is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19C is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 20 is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 21 is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19A is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19B is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 19C is a configuration diagram
- FIG. 22 is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 23 is a configuration diagram illustrating an example of a domain wall stopping method according to the embodiment of the present invention.
- FIG. 24 is a configuration diagram illustrating an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 25 is a configuration diagram illustrating an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 26 is a configuration diagram illustrating an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 27A is a configuration diagram illustrating an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 27B is a configuration diagram illustrating an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 28 is a configuration diagram showing an example of a magnetization fixing method according to the embodiment of the present invention.
- FIG. 29 is a plan view showing an example of the magnetic anisotropy direction of the sensor layer according to the embodiment of the present invention.
- FIG. 30 is a plan view showing an example of the magnetic anisotropy direction of the sensor layer according to the embodiment of the present invention.
- FIG. 31 is a cross-sectional view showing the configuration of the magnetic memory element in the reference cell of the MRAM according to the embodiment of the present invention.
- FIG. 32 is a perspective view showing a configuration example of the magnetic memory element according to the embodiment of the present invention.
- FIG. 33 is a perspective view showing a configuration example of the magnetic memory element according to the embodiment of the present invention.
- FIG. 34 is a perspective view showing a configuration example of the magnetic memory element according to the embodiment of the present invention.
- FIG. 4A is a plan view showing an example of the configuration of the magnetization recording layer in the magnetic memory element according to the embodiment of the present invention.
- FIG. 4B is a cross-sectional view showing an example of the configuration of the magnetic memory element according to the exemplary embodiment of the present invention.
- white circles and dots, white circles and crosses, and white arrows indicate the magnetization directions of the regions in which they are written, as is generally used. (Hereinafter, the same in this specification and each drawing).
- the magnetic memory element 1 includes a magnetization recording layer 10 and a magnetic tunnel junction 20.
- the magnetization recording layer 10 is a ferromagnetic layer having perpendicular magnetic anisotropy.
- the magnetization recording layer 10 includes two domain wall motion regions.
- the magnetic tunnel junction 20 is provided in the vicinity of the center of the magnetization recording layer 10 and has a configuration for reading data (information) stored in the magnetization recording layer 10. Details of the magnetic recording layer 10 and the magnetic tunnel junction 20 will be described later.
- the magnetic memory element 1 may further include a contact layer 30 that electrically connects the magnetization recording layer 10 and the magnetic tunnel junction 20.
- the magnetic tunnel junction 20 includes a sensor layer 23, a reference layer 21, and a barrier layer 22.
- the reference layer 21 is a ferromagnetic layer having a fixed magnetization direction and having in-plane magnetic anisotropy.
- in-plane magnetic anisotropy means having magnetic anisotropy in the xy plane in the example of this figure.
- the magnetization direction of the reference layer 21 is preferably the longitudinal direction of the magnetization recording layer 10.
- the magnetization direction of the reference layer 21 is the ⁇ x direction among the ⁇ x directions that are the longitudinal directions of the magnetization recording layer 10. This direction of magnetization may be reversed.
- the reference layer 21 is preferably composed of a plurality of ferromagnetic layers having laminated ferri coupling.
- the reference layer 21 is preferably adjacent to an antiferromagnetic layer such as Pt—Mn. This is because it is preferable that the magnetization of the reference layer 21 is substantially fixed in one direction because the magnetization direction of the reference layer 21 is not changed by writing and reading operations.
- the sensor layer 23 is a ferromagnetic layer having reversible magnetization and having in-plane magnetic anisotropy.
- the sensor layer 23 is magnetically coupled to the magnetization recording layer 10 as will be described later. Therefore, the direction of magnetization of the sensor layer 23 varies in the plane according to the magnetization state (stored data) of the magnetization recording layer 10. In the example of this figure, it rotates in the xy plane according to the magnetization state (stored data) of the magnetization recording layer 10.
- the barrier 22 is a nonmagnetic film or an insulating film provided between the sensor layer 23 and the reference layer 21.
- the reference layer 21, barrier layer 22, and sensor layer 23 constitute a magnetic tunnel junction (MTJ) as a pinned layer, a tunnel insulating layer, and a free layer, respectively.
- the direction of magnetization of the sensor layer 23 rotates according to the state stored in the magnetization recording layer 10.
- the magnetization direction of the reference layer is fixed. Accordingly, the resistance value of the magnetic tunnel junction 20 (MTJ) varies depending on the relative relationship between the magnetization direction of the sensor layer 23 and the magnetization direction of the reference layer 21. Therefore, the data stored in the magnetization recording layer 10 can be read by detecting the resistance value of the magnetic tunnel junction 20.
- the magnetic tunnel junction 20 can be used as a means for reading data stored in the magnetization recording layer 10.
- the sensor layer 23 and the reference layer 21 having in-plane magnetic anisotropy preferably contain at least one material selected from Fe, Co, and Ni.
- B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W , Re, Os, Ir, Au, and the like can be adjusted so that desired magnetic properties are expressed.
- Ni—Fe, Co—Fe, Fe—Co—Ni, Ni—Fe—Zr, Co—Fe—B, Co—Fe—Zr—B and the like are exemplified.
- the barrier layer 22 is preferably made of an insulating material.
- Mg—O, Al—O, Al—N, Ni—O, Hf—O and the like are exemplified.
- the present invention can also be implemented by using a nonmagnetic material such as a semiconductor material or a metal material as the barrier layer 22.
- a nonmagnetic material such as a semiconductor material or a metal material as the barrier layer 22.
- Cr, Al, Cu, Zn and the like are exemplified.
- the magnetoresistance effect ratio corresponding to the SN ratio of the read signal is large.
- the sensor layer 23 and the reference layer 21 are made of a Co—Fe—B material
- the barrier layer 22 is made of an Mg—O material.
- the magnetization recording layer 10 includes a first magnetization fixed region 11b, a zeroth magnetization fixed region 11a, a second magnetization fixed region 11c, a first domain wall motion region 13a, and a second domain wall motion region 13b.
- the first domain wall motion region 13a and the second domain wall motion region 13b are connected to both sides of the 0 th magnetization fixed region 11a, respectively.
- the first magnetization fixed region 11b and the second magnetization fixed region 11c are connected to the outside of the first domain wall motion region 13a and the second domain wall motion region 13b, respectively.
- the first magnetization fixed region 11b, the zeroth magnetization fixed region 11a, and the second magnetization fixed region 11c are ferromagnetic regions having fixed magnetization directions and having perpendicular magnetic anisotropy.
- the perpendicular magnetic anisotropy means having a magnetic anisotropy perpendicular to the xy plane in the example of this figure. The same applies hereinafter.
- the magnetization directions of the first magnetization fixed region 11b and the second magnetization fixed region 11c are substantially the same, and the magnetization direction of the zeroth magnetization fixed region 11a is opposite to that. That is, the magnetizations of the first magnetization fixed region 11b and the second magnetization fixed region 11c are fixed in directions parallel to each other.
- the magnetizations of the first magnetization fixed region 11b, the second magnetization fixed region 11c, and the zeroth magnetization fixed region 11a are fixed in antiparallel directions.
- the magnetization directions of the first magnetization fixed region 11b and the second magnetization fixed region 11c and the magnetization direction of the zeroth magnetization fixed region 11a are directions that can fulfill the function of generating the domain walls 12a and 12b. What is necessary is not to mean the same and the opposite in a strict sense.
- “magnetization is fixed” means that the magnetization direction does not change before and after the write operation. Even if the magnetization direction of a part of the magnetization fixed region changes during the write operation, it returns to the original state after the write operation is completed.
- the magnetization direction of the first magnetization fixed region 11b and the second magnetization fixed region 11c is the + z direction
- the magnetization direction of the zeroth magnetization fixed region 11a is the -z direction.
- the first magnetization fixed region 11b and the second magnetization fixed region 11c are formed substantially the same.
- the reason for this is that it is easiest to form the same from the viewpoint of the manufacturing process, and when holding a write operation and data to be described later, it is highly symmetrical in terms of stability and reliability. It is because it is preferable.
- substantially the same means that the shape and material including the film thickness are the same within a range of errors in the manufacturing process. In this case, the magnetization fixing method (described later) is also the same.
- the first hard layer 40 is preferably formed adjacent to each other.
- the first hard layer 40 uses the coercive force of the first magnetization fixed region 11b and the second magnetization fixed region 11c as the coercive force of the first domain wall motion region 13a, the 0th magnetization fixed region 11a, and the second domain wall motion region 13b. In comparison, it can be effectively increased and initialization can be facilitated.
- the first hard layer 40 is included in each of the first magnetization fixed region 11b and the first hard layer 40, and the second magnetization fixed region 11c and the first hard layer 40.
- the included fixed portions of magnetization are preferably substantially the same in the above sense.
- the first domain wall motion region 13a and the second domain wall motion region 13b are ferromagnetic regions having reversible magnetization, movable domain walls, and perpendicular magnetic anisotropy. Accordingly, combinations of magnetization directions that can be taken by the first domain wall motion region 13a and the second domain wall motion region 13b are (+ z, -z), (-z, + z), (+ z, + z), (-z, -z). ). In the embodiment of the present invention, two magnetization directions (+ z, ⁇ z) and ( ⁇ z, + z) are used according to the data to be stored.
- the magnetic tunnel junction 20 is provided in the vicinity of the 0 th magnetization fixed region 11a.
- the direction of magnetization of the reference layer 21 of the magnetic tunnel junction 20 is directed to the direction of a straight line connecting the first domain wall motion region 13a and the second domain wall motion region 13b.
- the magnetization direction of the reference layer 21 is directed in the ⁇ x direction, which is the direction of a straight line connecting the first domain wall motion region 13a (the center of gravity) and the second domain wall motion region 13b (the center of gravity). Yes.
- the direction of magnetization of the sensor layer 23 will be described later.
- the magnetic recording layer 10 having perpendicular magnetic anisotropy preferably contains at least one material selected from Fe, Co, and Ni. Furthermore, perpendicular magnetic anisotropy can be stabilized by including Pt and Pd.
- B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W , Re, Os, Ir, Au, Sm, and the like can be added so that desired magnetic properties are expressed.
- Co Co, Co—Pt, Co—Pd, Co—Cr, Co—Pt—Cr, Co—Cr—Ta, Co—Cr—B, Co—Cr—Pt—B, Co—Cr—Ta— B, Co-V, Co-Mo, Co-W, Co-Ti, Co-Ru, Co-Rh, Fe-Pt, Fe-Pd, Fe-Co-Pt, Fe-Co-Pd, Sm-Co, Examples thereof include Gd—Fe—Co, Tb—Fe—Co, and Gd—Tb—Fe—Co.
- the magnetic anisotropy in the perpendicular direction can also be expressed by alternately stacking layers containing any one material selected from Fe, Co, and Ni and different layers. Specific examples include a laminated film in which Co / Pd, Co / Pt, Co / Ni, and Fe / Au are alternately laminated.
- the first hard layer 40 can be made of the above ferromagnetic material or an antiferromagnetic material such as PtMn, NiMn, or FeMn.
- FIGS. 5A and 5B are cross-sectional views showing an example of the configuration of the magnetic memory element according to the embodiment of the present invention.
- FIG. 5A shows a case where data “0” is stored (0-state), for example
- FIG. 5B shows a case where data “1” is stored (1-state), for example.
- the magnetization recording layer 10 stores data “0”
- the magnetization of the first domain wall motion region 13a is oriented in the + z direction
- the magnetization of the second domain wall motion region 13b is oriented in the ⁇ z direction. (+ Z, -z).
- the first magnetization fixed region 11b and the first domain wall motion region 13a are magnetized in the + z direction
- the zeroth magnetization fixed region 11a and the second domain wall motion region 13b are the magnetization in the -z direction
- the second magnetization fixed region 11c Has magnetization in the + z direction.
- first magnetization fixed region 11b and the first domain wall motion region 13a, the 0th magnetization fixed region 11a and the second domain wall motion region 13b, and the second magnetization fixed region 11c form separate magnetic domains. That is, domain walls 12a and 12b are formed between the first domain wall motion region 13a and the zeroth magnetization fixed region 11a and between the second domain wall motion region 13b and the second magnetization fixed region 11c, respectively. Is done.
- a magnetic field H from the second domain wall motion region 13b toward the first domain wall motion region 13a is generated below the magnetization recording layer 10 (on the ⁇ z direction side).
- the magnetic field H becomes a magnetic field directed in the ⁇ x direction in the vicinity of the sensor layer 23.
- the magnetization of the sensor layer 23 is oriented in the ⁇ x direction. That is, the data stored in the magnetization recording layer 10 is reflected on the sensor layer 23.
- the magnetization of the sensor layer 23 and the magnetization of the reference layer 21 are parallel. Therefore, this parallel state can be detected by detecting the resistance value of the magnetic tunnel junction 20 in the ⁇ z direction. That is, the data “0” stored in the magnetization recording layer 10 can be read.
- the magnetization recording layer 10 stores data “1”
- the magnetization of the first domain wall motion region 13a is directed in the ⁇ z direction
- the magnetization of the second domain wall motion region 13b is in the + z direction. Facing (-z, + z).
- the first magnetization fixed region 11b is the magnetization in the + z direction
- the first domain wall motion region 13a and the zeroth magnetization fixed region 11a are the magnetization in the -z direction
- the second domain wall motion region 13b and the second magnetization fixed region 11c Has magnetization in the + z direction.
- the first magnetization fixed region 11b, the first domain wall motion region 13a and the 0th magnetization fixed region 11a, and the second domain wall motion region 13b and the second magnetization fixed region 11c form separate magnetic domains. That is, the domain walls 12a and 12b are formed between the first magnetization fixed region 11b and the first domain wall motion region 13a and between the 0th magnetization fixed region 11a and the second domain wall motion region 13b, respectively.
- a magnetic field H directed from the first domain wall motion region 13a to the second domain wall motion region 13b is generated below the magnetization recording layer 10 (on the ⁇ z direction side).
- the magnetic field H is a magnetic field toward the + x direction in the vicinity of the sensor layer 23.
- the magnetization of the sensor layer 23 is oriented in the + x direction. That is, the data stored in the magnetization recording layer 10 is reflected on the sensor layer 23.
- the magnetization of the sensor layer 23 and the magnetization of the reference layer 21 are antiparallel. Therefore, this antiparallel state can be detected by detecting the resistance value of the magnetic tunnel junction 20 in the ⁇ z direction. That is, the data “1” stored in the magnetization recording layer 10 can be read.
- the magnetization recording layer 10 holds data by the mutual relation of the magnetization directions in the domain wall motion regions.
- the magnetization recorded in the sensor layer 23 is caused by the magnetic interaction between the sensor layer 23, the second domain wall motion region 13b, and the first domain wall motion region 13a.
- it has the effect of stabilizing the magnetization state (magnetization direction) of the second domain wall motion region 13b and the first domain wall motion region 13a.
- the domain walls 12a and 12b can be more stably fixed (held) at a desired position. That is, the retention characteristic of the magnetic memory element can be improved.
- 6A to 6C are cross-sectional views illustrating an example of a method for initializing a magnetic memory element according to an embodiment of the present invention.
- the magnetic memory element 1 is heated to a predetermined temperature and cooled while applying a magnetic field H 01 in the ⁇ x direction to the magnetic memory element 1 (step 1). ).
- the reference layer 21 of the magnetic tunnel junction 20 is magnetized in the ⁇ x direction.
- the magnetization recording layer 10 is formed of a material having perpendicular magnetic anisotropy, it is not magnetized in the ⁇ x direction.
- a magnetic field H 02 in the + z direction is applied to the magnetic memory element 1 (step 2).
- the magnetic field H 02 is set larger than the coercive force of the first hard layer 40 and the magnetization recording layer 10.
- the entire magnetization of the first hard layer 40 and the magnetization recording layer 10 is oriented in the + z direction.
- the reference layer 21 of the magnetic tunnel junction 20 is formed of a material having in-plane magnetic anisotropy and is heated and magnetized, so that it is not magnetized in the + z direction.
- the first magnetization fixed region 11b and the second magnetization fixed region 11c have an effective coercive force due to exchange coupling with the first hard layer 40, so that the first domain wall motion region 13a, the zeroth magnetization fixed region 11a, and It becomes larger than the coercive force of the second domain wall motion region 13b.
- a magnetic field H 03 in the ⁇ z direction is applied to the magnetic memory element 1 (step 3).
- this magnetic field H03 is larger than the coercive force of the first domain wall motion region 13a, the 0th magnetization fixed region 11a, and the second domain wall motion region 13b, and the effective of the first magnetization fixed region 11b and the second magnetization fixed region 11c.
- the value is smaller than the typical coercive force.
- the first magnetization fixed region 11b and the second magnetization fixed region 11c having a relatively large coercive force in the magnetization recording layer 10 are not reversely magnetized in the ⁇ z direction. Further, since the reference layer 21 of the magnetic tunnel junction 20 is formed of a material having in-plane magnetic anisotropy and is heated and magnetized, it is not magnetized in the ⁇ z direction.
- a region is formed.
- Domain walls 12a and 12b are formed at the boundary between the first magnetization fixed region 11b and the coupling region and at the boundary between the second magnetization fixed region 11c and the coupling region, respectively.
- FIG. 7 is a cross-sectional view illustrating the principle of writing data to the magnetic memory element according to the embodiment of the present invention.
- Data writing is performed by a domain wall motion method using spin injection.
- the write current Iw flows not in the direction penetrating through the MTJ (magnetic tunnel junction 20) but in the direction penetrating through the domain walls 12a and 12b in the magnetization recording layer 10 in a plane.
- the write current Iw is supplied from one of a current supply terminal (not shown) connected to the first magnetization fixed region 11b and a current supply terminal (not shown) connected to the second magnetization fixed region 11c.
- the magnetic recording layer 10 is supplied.
- the state where the magnetization direction of the first domain wall motion region 13a is in the + z direction and the magnetization direction of the second domain wall motion region 13b is in the ⁇ z direction is data “0”. It is associated. This is as shown in FIG. 5A.
- the first write current Iw1 (solid arrow) is supplied from the current supply terminal on the first magnetization fixed region 11b side. Then, the first magnetization fixed region 11b reaches the zeroth magnetization fixed region 11a through the first domain wall motion region 13a.
- the magnetization direction of the second domain wall motion region 13b is switched to the + z direction by the spin transfer effect.
- the domain wall 12b moves to the boundary between the second domain wall moving region 13b and the zeroth magnetization fixed region 11a.
- spin electrons e ⁇ are injected from the 0 th magnetization fixed region 11a into the first domain wall motion region 13a.
- the spins of the injected electrons e ⁇ drive the domain wall 12a at the boundary between the zeroth magnetization fixed region 11a and the first domain wall motion region 13a in the direction of the first magnetization fixed region 11b.
- the magnetization direction of the first domain wall motion region 13a is switched to the ⁇ z direction by the spin transfer effect.
- the domain wall 12a moves to the boundary of the 1st domain wall movement area
- data “1” is written as shown in FIG.
- the state in which the magnetization direction of the first domain wall motion region 13a is in the ⁇ z direction and the magnetization direction of the second domain wall motion region 13b is in the + z direction is the data “1”. ". This is as shown in FIG. 5B.
- the second write current Iw2 (solid line arrow) is supplied from the current supply terminal on the second magnetization fixed region 11c side. Then, the second magnetization fixed region 11c reaches the zeroth magnetization fixed region 11a through the second domain wall moving region 13b.
- the current flows from the 0th magnetization fixed region 11a to the first magnetization fixed region 11b through the first domain wall motion region 13a and is sent from the current supply terminal on the first magnetization fixed region 11b side.
- the movement of the electron e ⁇ (broken arrow) is opposite to the second write current Iw2.
- spin electrons e ⁇ are injected into the first domain wall motion region 13a from the first magnetization fixed region 11b.
- the spins of the injected electrons e ⁇ drive the domain wall 12a at the boundary between the first magnetization fixed region 11b and the first domain wall moving region 13a in the direction of the 0th magnetization fixed region 11a.
- the magnetization direction of the first domain wall motion region 13a is switched to the + z direction by the spin transfer effect.
- the domain wall 12a moves to the boundary between the first domain wall moving region 13a and the zeroth magnetization fixed region 11a.
- spin electrons e ⁇ are injected into the second domain wall motion region 13b from the zeroth magnetization fixed region 11a.
- the spin of the injected electron e ⁇ drives the domain wall 12b at the boundary between the 0 th magnetization fixed region 11a and the second domain wall moving region 13b in the direction of the second magnetization fixed region 11c.
- the magnetization direction of the second domain wall motion region 13b is switched to the ⁇ z direction by the spin transfer effect.
- the domain wall 12b moves to the boundary between the second domain wall moving region 13b and the second magnetization fixed region 11c.
- data “0” is written as shown in FIG.
- the magnetization directions of the first domain wall motion region 13a and the second domain wall motion region 13b are switched by the write currents Iw1 and Iw2 flowing in the magnetization recording layer 10 in a plane.
- the first magnetization fixed region 11b and the zeroth magnetization fixed region 11a serve as different spin electron supply sources with respect to the first domain wall motion region 13a.
- the zeroth magnetization fixed region 11a and the second magnetization fixed region 11c serve as different spin electron supply sources for the second domain wall motion region 13b.
- the magnetization recording layer 10 is formed of a perpendicular magnetic anisotropic material. Therefore, the magnetization direction of each region of the magnetization recording layer 10 is perpendicular to the write currents Iw1 and Iw2. Therefore, the magnitudes of the write currents Iw1 and Iw2 can be significantly reduced. At this time, the write currents Iw1 and Iw2 may pass anywhere after passing through the domain walls 12a and 12b.
- the data “0” and the data “1” can be written separately according to the direction of the write current flowing in the magnetization recording layer 10. Further, it is clear from the above writing principle that overwriting (writing data “0” to data “0”, writing data “1” to data “1”) is also possible.
- 8A and 8B are cross-sectional views illustrating the data read principle of the magnetic memory device according to the embodiment of the present invention.
- the read current IR is supplied so as to flow through the MTJ of the magnetic tunnel junction 20 (reference layer 21, barrier layer 22, and sensor layer 23). If so supplied, the read current IR may or may not flow through the magnetization recording layer 10.
- the read current IR is supplied from one of the current supply terminal on the reference layer 21 side and the current supply terminal on the second magnetization fixed region 11c side, and is sent from the other.
- the read current IR passes through the MTJ of the magnetic tunnel junction 20 and flows through the zeroth magnetization fixed region 11a, the second domain wall motion region 13b, and the second magnetization fixed region 11c.
- the magnetization of the sensor layer 23 is in the ⁇ x direction.
- the magnetization of the reference layer 21 is fixed in the ⁇ x direction. That is, the directions of both magnetizations are parallel. Therefore, by supplying the read current IR, a low resistance value, that is, “0” is read as data stored in the magnetic memory element.
- the magnetization of the sensor layer 23 is in the + x direction.
- the magnetization of the reference layer 21 is fixed in the ⁇ x direction. That is, the directions of both magnetizations are antiparallel. Therefore, by supplying the read current IR, a high resistance value, that is, data “1” is read as data stored in the magnetic memory element.
- the data stored in the magnetization recording layer 10 of the magnetic memory element 1 can be read.
- a relatively large current required for writing does not flow through the MTJ and only a relatively small current needs to flow through the MTJ when reading data, it is possible to suppress degradation of the MTJ.
- FIG. 9 is a circuit diagram showing a configuration example of a memory cell in which a magnetic memory element according to an embodiment of the present invention is integrated.
- a terminal connected to the reference layer 21 of the magnetic tunnel junction 20 is connected to a ground line GL for reading.
- One of the two terminals connected to the first magnetization fixed region 11b and the second magnetization fixed region 11c of the magnetization recording layer 10 is connected to one of the source / drain of the MOS transistor TRa, and the other is connected to the source / drain of the MOS transistor TRb. Connected to one of the drains.
- the other of the sources / drains of the MOS transistors TRa and TRb is connected to the bit lines BLa and BLb for writing, respectively. Further, the gates of the MOS transistors TRa and TRb are connected to the word line WL.
- the configuration of the memory cell is not limited to this example.
- FIG. 10 is a block diagram showing a configuration example of the MRAM in which the memory cells according to the embodiment of the present invention are integrated.
- the MRAM 90 includes a memory array 91 in which a plurality of memory cells 80 are arranged in a matrix.
- the memory array 91 includes a reference cell 80r that is referred to when data is read, in addition to the memory cell 80 used for data recording described in FIG.
- one column is a reference cell 80r.
- the structure of the reference cell 80r is the same as that of the memory cell 80.
- the MTJ of the reference cell 80r has a resistance R0.5 intermediate between the resistance R0 when data “0” is stored and the resistance R1 when data “1” is stored.
- the resistor 0.5 is created from the reference cell 80r of the resistor R0 and the reference cell 80r of the resistor R1, and used for reading.
- the word line WL and the ground line GL each extend in the X direction.
- One end of the word line WL is connected to the X-side control circuit 92.
- the X-side control circuit 92 selects the word line WL connected to the target memory cell 80 as the selected word line WL during the data write operation and the read operation.
- Each of the bit lines BLa and BLb extends in the Y direction, and one end thereof is connected to the Y-side control circuit 93.
- the Y-side control circuit 93 selects the bit lines BLa and BLb connected to the target memory cell 80 as the selected bit lines BLa and BLb during the data write operation and the read operation.
- the control circuit 94 controls the X-side control circuit 92 and the Y-side control circuit 93 during a data write operation and a read operation.
- the X side control circuit 92 selects the selected word line WL. As a result, the selected word line WL is pulled up to the “high” level, and the MOS transistors TRa and TRb are turned “ON”.
- the Y-side control circuit 93 selects the selected bit lines BLa and BLb. Accordingly, one of the selected bit lines BLa and BLb is pulled up to the “high” level, and the other is pulled down to the “Low” level.
- the X-side control circuit 92, the Y-side control circuit 93, and the control circuit 94 that controls them constitute a “write current supply circuit” for supplying the write current Iw to the memory cell 80.
- the X side control circuit 92 selects the selected word line WL. As a result, the selected word line WL is pulled up to the “high” level, and the MOS transistors TRa and TRb are turned “ON”.
- the Y-side control circuit 93 selects the selected bit lines BLa and BLb. Thereby, one of the selected bit lines BLa and BLb is pulled up to the “high” level, and the other is set to “open” (floating).
- the read current IR is applied from one of the selected bit lines BLa and BLb to, for example, the second magnetization fixed region 11c, the second domain wall motion region 13b, the zeroth magnetization fixed region 11a, the contact layer 30, and the magnetic tunnel junction 20 It flows to the ground line GL via (the MTJ composed of the sense layer 23, the barrier layer 22, and the reference layer 21).
- the potential of the bit line BL through which the read current IR flows or the magnitude of the read current depends on a change in the resistance value of the magnetic memory element 1 (magnetic tunnel junction 20) due to the magnetoresistive effect.
- the X-side control circuit 92, the Y-side control circuit 93, and the control circuit 94 that controls them constitute a “read current supply and sense circuit” for supplying and reading the read current IR to and from the memory cell 80.
- FIG. 11 to FIG. 16 are configuration diagrams showing variations in the position of the sensor layer 23 of the magnetic memory element according to the embodiment of the present invention. 11 to 13 are cross-sectional views, and FIGS. 14 to 16 are plan views.
- FIG. 11 shows the case shown in FIGS. 4A to 8B, and the sensor layer 23 is provided below the magnetization recording layer 10 (on the ⁇ z direction side) via the contact layer 30.
- the magnetic tunnel junction 20 is upside down, that is, the reference layer 21 is the same as the contact layer 30. They may be in contact (not shown).
- the sensor layer 23 may be provided on the upper side (+ z direction side) of the magnetic recording layer 10 via the contact layer 30. Furthermore, if the magnetic field generated by the first domain wall motion region 13 a and the second domain wall motion region 13 b can reverse the magnetization direction of the sensor layer 23, the magnetic tunnel junction 20 is upside down, that is, the reference layer 21 is in contact with the contact layer 30. They may be in contact (not shown).
- the contact layer 30 is not provided in the magnetic memory element 1
- the sensor layer 23 may not be electrically connected to the magnetization recording layer 10.
- current supply terminals 44 and 45 for writing current are provided at both ends of the magnetic recording layer 10
- current supply terminals 46 and 47 for reading current are separately provided at both ends of the magnetic tunnel junction 20.
- FIG. 14 shows the case shown in FIGS. 4A to 8B, in which the sensor layer 23 is provided immediately below the ⁇ 0th magnetization fixed region 11a of the magnetization recording layer 10 (on the ⁇ z direction side) or directly above (on the + z direction side). ing. That is, the projection of the sensor layer 23 onto the magnetization recording layer 10 overlaps the zeroth magnetization fixed region 11a.
- This configuration is preferable because the magnetic field generated by the first domain wall motion region 13a and the second domain wall motion region 13b can more stably reverse the magnetization of the sensor layer 23.
- the sensor layer 23 is the 0th layer of the magnetization recording layer 10. It may be provided on the back side (+ y direction side) or the near side ( ⁇ y direction side) of the magnetization fixed region 11a. At that time, the projection of the sensor layer 23 onto the magnetization recording layer 10 may overlap at least a part of the region in the magnetization recording layer 10 between the first domain wall motion region 13a and the second domain wall motion region 13b. preferable.
- Such a region is a region including a part of the 0 th magnetization fixed region 11a, and may further include at least one of a part of the first domain wall motion region 13a and a part of the second domain wall motion region 13b.
- the sensor layer 23 is the 0th layer of the magnetization recording layer 10. It may be provided on the far side (+ y direction side) or near side ( ⁇ y direction side) and the left side ( ⁇ x direction side) or right side (+ x side) side of the magnetization fixed region 11a. At that time, the projection of the sensor layer 23 onto the magnetization recording layer 10 may overlap at least a part of the region in the magnetization recording layer 10 between the first domain wall motion region 13a and the second domain wall motion region 13b. preferable.
- Such a region includes a part of the zero-th magnetization fixed region 11a and further includes any one of a part of the first domain wall motion region 13a and a part of the second domain wall motion region 13b.
- the positional relationship between the sensor layer 23 and the magnetization recording layer 10 is such that the magnetic field generated by the first domain wall motion region 13a and the second domain wall motion region 13b can reverse the magnetization direction of the sensor layer 23. Any relationship is acceptable. Therefore, the degree of freedom of the sensor layer 23 is high.
- FIG. 17 is a configuration diagram showing a variation regarding the positional relationship between the sensor layer and the hard layer of the magnetic memory element according to the embodiment of the present invention.
- FIG. 17 is a cross-sectional view.
- the positional relationship between the sensor layer 23 and the hard layer 40 with respect to the magnetization recording layer 10 is arbitrary.
- the sensor layer 23 is provided on the lower side ( ⁇ z side) with respect to the magnetization recording layer 10
- the hard layer 40 is provided on the upper side (+ z side) with respect to the magnetization recording layer 10. Also good.
- the sensor layer 23 is provided on the upper side (+ z side) with respect to the magnetic recording layer 10, and the hard layer 40 is provided on the lower side ( ⁇ z side) with respect to the magnetic recording layer 10. Also good.
- the sensor layer 23 is provided on the upper side (+ z side) with respect to the magnetization recording layer 10, and the hard layer 40 is also provided on the upper side (+ z side) with respect to the magnetization recording layer 10. Good.
- the hard layer 40 can realize a predetermined magnetization structure of the magnetization recording layer 10, and the sensor layer 23 reads the magnetization directions of the first domain wall motion region 13a and the second domain wall motion region 13b. As long as it is possible, there are no restrictions on these positional relationships.
- the hard layer 40 is provided adjacent to the upper surface of the magnetization recording layer 10 in order to introduce a domain wall into the magnetization recording layer 10 and easily realize a predetermined magnetization structure. This is because when the hard layer 40 is provided adjacent to the upper surface of the magnetic recording layer 10, the magnetic recording layer 10 and the hard layer 40 can continuously deposit films, so that strong exchange coupling is established between them. This is because it can be obtained.
- the magnetic tunnel junction 20 for reading is provided on the upper side (+ z side) with respect to the magnetization recording layer 10. This is because it is necessary to introduce a write current to the magnetization recording layer 10 via a transistor. At this time, since the write current is supplied from the lower side ( ⁇ z side) of the magnetic memory element 1, This is because it is preferably provided on the upper side (+ z side) of the magnetic memory element 1.
- the read wiring is provided on the upper side (+ z side) of the magnetic memory element 1, it is possible to perform the layout so that the cell area becomes the smallest.
- the embodiment in which both the hard layer 40 and the sensor layer 23 shown in FIG. 17 are arranged on the upper side (+ z side) of the magnetic recording layer 10 is the magnetic memory element 1. It can be said that it is most preferable from the viewpoint of initialization and layout ease.
- the hard layer 40 is preferably formed as follows. As described above, in the present embodiment, the magnetization directions of the first magnetization fixed region 11b and the second magnetization fixed region 11c are fixed in parallel to each other, while the zeroth magnetization fixed region 11a is in an antiparallel direction. Fixed. Therefore, it is desirable to provide a difference in magnetic characteristics between the hard layer 40 adjacent to the first magnetization fixed region 11b and the second magnetization fixed region 11c and the hard layer 40 adjacent to the zeroth magnetization fixed region 11a. This difference in magnetic characteristics can be provided by, for example, a difference in film thickness. As a specific example, as shown in FIG.
- the hard layer 40 adjacent to the first magnetization fixed region 11b and the second magnetization fixed region 11c is compared with the hard layer 40 adjacent to the zeroth magnetization fixed region 11a.
- the magnetic recording layer 10 can be easily initialized so as to have a predetermined magnetization structure.
- FIGS. 18 to 23 are configuration diagrams showing variations of the domain wall stopping method at both ends of the 0 th magnetization fixed region 11a of the magnetic memory device according to the embodiment of the present invention. However, the magnetic tunnel junction 10 is omitted in each figure. 18, FIG. 19A to FIG. 19C, FIG. 21, and FIG. 22 are sectional views, and FIG. 20 and FIG. 23 are plan views.
- FIG. 18 shows an example of a method for stopping the domain wall.
- a material having a lower resistance than the material of the zeroth magnetization fixed region 11 a is used as the material of the contact layer 30.
- examples of such materials include Au, Ag, Cu, Al, Ru, Pt, and Pd.
- the write current Iw that has flowed through the first domain wall motion region 13a (or the second domain wall motion region 13b) flows not only through the 0th magnetization fixed region 11a but also into the contact layer 30. That is, the write current Iw is shunted to the 0 th magnetization fixed region 11a and the contact layer 30.
- the current density in the zeroth magnetization fixed region 11a decreases.
- a current density equal to or higher than a certain threshold is required.
- the current density of the write current Iw becomes equal to or higher than the threshold value in the first domain wall motion region 13a (or the second domain wall motion region 13b), and decreases due to shunting in the zeroth magnetization fixed region 11a.
- the domain wall moves in the first domain wall motion region 13a (or the second domain wall motion region 13b) having a current density equal to or higher than the threshold value, and stops near the end of the 0th magnetization fixed region 11a that is less than the threshold value.
- the write current Iw (electrons) that flows through the first domain wall motion region 13a (or the second domain wall motion region 13b) flows not only through the zeroth magnetization fixed region 11a but also into the contact layer 30. That is, the write current Iw (electrons) is shunted to the 0 th magnetization fixed region 11 a and the contact layer 30. At this time, electrons flowing into the contact layer 30 are spin-scattered by the contact layer 30, and a part of the electrons returns to the zeroth magnetization fixed region 11a.
- the electrons in the zero-th magnetization fixed region 11a are disturbed by the influence of the spin-scattered electrons and become irregular, and the domain wall cannot be moved.
- the electron spins are aligned in the second domain wall motion region 13b (or the first domain wall motion region 13a), but are disturbed in the 0th magnetization fixed region 11a and become uneven. Therefore, the domain wall moves in the first domain wall motion region 13a (or the second domain wall motion region 13b) in which the electron spins are aligned, and stops near the end of the 0th magnetization fixed region 11a in which the electron spin is disturbed. become.
- this stopping method is realized by using a low-resistance material or a material that easily causes spin scattering for the contact layer 30 on the lower side ( ⁇ z direction side) of the 0 th magnetization fixed region 11a.
- the present invention is not limited to the examples. That is, if the auxiliary layer 14 using the low-resistance material or the material that easily causes spin scattering is provided adjacent to the periphery of the zeroth magnetization fixed region 11a, the contact layer 30 may not be used. Moreover, the position is not ask
- FIG. 18 shows an example in which the auxiliary layer 14 (indicated by a broken line) is provided on the upper side (+ z direction side) of the 0 th magnetization fixed region 11a. Also in this case, the same effect as the contact layer 30 shown by the two methods can be obtained.
- the method shown in FIG. 18 described above does not require a special process in manufacturing, and can be carried out only by selecting the material of the contact layer 30, and the process is easy.
- FIGS. 19A to 19C show another example of the domain wall stopping method.
- a step Q is intentionally provided at both ends of the 0 th magnetization fixed region 11a of the magnetization recording layer 10. Therefore, the plane on the upper side (+ z direction side) of the 0th magnetization fixed region 11a is the upper side of the first magnetization fixed region 11b, the first domain wall motion region 13a, the second domain wall motion region 13b, and the second magnetization fixed region 11c. It sticks out from the plane.
- a step Q is formed at the boundary between the zeroth magnetization fixed region 11a and the second domain wall motion region 13b and at the boundary between the zeroth magnetization fixed region 11a and the first domain wall motion region 13a.
- Such a step Q functions as a pin potential for the domain wall and can stop the domain wall at that position.
- FIG. 19A shows a state in which a part of the contact layer 30 protrudes from the bottom surface on the lower side of the magnetic recording layer 10, but a part of the contact layer 30 projects from the bottom surface on the lower side of the magnetic recording layer 10. It does not have to be.
- the contact layer 30 is formed by depositing a film of metal or the like on the interlayer insulating layer 49 provided with holes such as via holes, and polishing by a CMP method.
- polishing by the CPM method it is difficult to avoid the formation of the step P between the surface of the interlayer insulating layer 49 and the surface of the contact layer 30 due to the nature of the process. Therefore, in the example of FIG. 19A, this step P is actively used. That is, as shown in FIG. 19C, a film for the magnetic recording layer 10 is formed so as to cover the interlayer insulating layer 49 and the contact layer 30 while leaving the step P.
- the step Q is also formed in this film by being affected by the step P of the contact layer 30. Therefore, the shape of FIG. 19A can be obtained by forming this film into the shape of the magnetic recording layer 10.
- Such a step may be provided in the first magnetization fixed region 11b or the second magnetization fixed region 11c at both ends of the magnetization recording layer 10 in order to fix the domain wall. This method does not require a special manufacturing process and is easy to implement.
- FIG. 20 shows still another example of the domain wall stopping method.
- the cross-sectional area of the zeroth magnetization fixed region 11a is increased so that the current density in the region of the zeroth magnetization fixed region 11a falls below a threshold necessary for causing domain wall motion ( Example: make the shape thick, wide, etc.).
- the write current Iw that has flowed through the first domain wall motion region 13a (or the second domain wall motion region 13b) flows through the zeroth magnetization fixed region 11a having an increased cross-sectional area.
- the current density of the zeroth magnetization fixed region 11a decreases.
- the width of the 0 th magnetization fixed region 11a is widened by the protrusions 15 and 16 in the ⁇ y direction.
- the current density of the write current Iw is set to be equal to or higher than the threshold value in the first domain wall motion region 13a (or the second domain wall motion region 13b), and is decreased in the zeroth magnetization fixed region 11a to be lower than the threshold value. Is done. Therefore, the domain wall moves in the first domain wall motion region 13a (or the second domain wall motion region 13b) having a current density equal to or higher than the threshold value, and stops near the end of the 0th magnetization fixed region 11a that is less than the threshold value.
- the width of the 0 th magnetization fixed region 11a is wide in the ⁇ y direction, but the present invention is not limited to that example. That is, as long as the cross-sectional area of the 0 th magnetization fixed region 11a can be increased, the width may extend in either the + y direction or the ⁇ y direction, or in the + z direction or the ⁇ z direction. Even in this case, the same effect as in the case of FIG. 20 can be obtained.
- This method is easy to implement because it requires only a partial change in the pattern of the magnetic recording layer 10 and does not require any special manufacturing process.
- FIG. 21 shows still another example of the domain wall stopping method.
- the contact layer 30 is formed of the same perpendicular magnetic anisotropic material as that of the zeroth magnetization fixed region 11a and has the same magnetization direction as that of the zeroth magnetization fixed region 11a.
- the domain wall movement can be made difficult to occur.
- This method does not require a special process in manufacturing, and can be performed only by selecting the material of the contact layer 30 and is easy to process.
- FIG. 22 shows another example of the domain wall stopping method.
- a hard layer (second hard layer 18) is provided also in the 0th magnetization fixed region 11a, similarly to the first magnetization fixed region 11b and the second magnetization fixed region 11c.
- it is not harder than the first hard layer 40 (retaining force is reduced). This is because the above-described initialization method can be used.
- the domain wall movement can be made difficult to occur.
- FIG. 23 shows still another example of the domain wall stopping method.
- a pin for the domain wall is provided at the boundary between the 0th magnetization fixed region 11a and the first domain wall motion region 13a and at the boundary between the 0th magnetization fixed region 11a and the second domain wall motion region 13b.
- a pin site such as a notch 17 that functions as a potential is provided.
- Such pin sites are difficult to manufacture due to the miniaturization of the magnetic recording layer 10, but can be used if the size of the magnetic recording layer 10 is large to some extent. By doing in this way, the notch 17 functions as a pin potential, and the domain wall can be stopped at that position.
- the stopping method described above is not only the stop of the domain wall at the boundary between the 0th magnetization fixed region and the first and second domain wall moving regions, but also the boundary between the first magnetization fixed region and the first magnetization fixed region,
- the present invention can be similarly applied to the boundary between the second magnetization fixed region and the second domain wall motion region.
- FIGS. 24 to 28 are configuration diagrams showing variations of the magnetization fixing method in the first magnetization fixed region and the second magnetization fixed region of the magnetic memory element according to the embodiment of the present invention. However, the magnetic tunnel junction 10 is omitted in each figure. 24 to 26, FIG. 27B, and FIG. 28 are cross-sectional views, and FIG. 27A is a plan view.
- FIG. 24 shows an example of the magnetization fixing method.
- the first hard layer 40 is provided on the upper side (+ z direction side) of the first magnetization fixed region 11b and the second magnetization fixed region 11c.
- the first hard layer 40 may be provided below the first magnetization fixed region 11b and the second magnetization fixed region 11c (on the ⁇ z direction side). This method is preferable when it is desired to provide the lower side due to the convenience of the manufacturing process.
- FIG. 25 shows another example of the magnetization fixing method.
- the first hard layer 40 is provided on both the upper side (+ z direction side) and the lower side ( ⁇ z direction side) of the first magnetization fixed region 11b and the second magnetization fixed region 11c. It may be done.
- this method when it cannot be formed thick on one of the upper and lower sides due to the convenience of the manufacturing process or the like, it is thinly provided on both the upper and lower sides, or the magnetization of the first magnetization fixed region 11b and the second magnetization fixed region 11c. It is preferable when it is desired to fix the material more firmly.
- FIG. 26 shows still another example of the magnetization fixing method.
- the first hard layer 40 is magnetically coupled to the first magnetization fixed region 11b and the second magnetization fixed region 11c, the first magnetization fixed region 11b and the second magnetization fixed region. It is not necessary to be in direct contact with 11c. That is, it is only necessary that the first hard layer 40 be formed on at least one of the upper side and the lower side of the first magnetization fixed region 11b and the second magnetization fixed region 11c as close as possible to magnetic coupling.
- the first hard layer 40 is provided below the first magnetization fixed region 11b and the second magnetization fixed region 11c via another intermediate layer 43. This method is preferable when the first hard layer 40 cannot be provided in direct contact with the magnetic recording layer 10 due to the convenience of the manufacturing process.
- FIG. 27A (plan view) and FIG. 27B (cross-sectional view) show another example of the magnetization fixing method.
- a desired magnetization state can be created by devising the shape without using the first hard layer.
- the width of the first magnetization fixed region 11b near the boundary with the first domain wall motion region 13a and the width of the second magnetization fixed region 11c near the boundary with the second domain wall motion region 13b are Is larger than the width of the first domain wall motion region 13a and the second domain wall motion region 13b.
- the domain wall is less likely to enter the first magnetization fixed region 11b and the second magnetization fixed region 11c, and each boundary functions as a pin potential for the domain wall.
- the magnetizations of the first magnetization fixed region 11b and the second magnetization fixed region 11c are fixed.
- FIG. 28 shows still another example of the magnetization fixing method.
- a desired magnetization state can be created by devising the material without using the first hard layer.
- a material different from the first domain wall motion region 13a and the second domain wall motion region 13b is used as the material of the first magnetization fixed region 11b and the second magnetization fixed region 11c.
- a material having a relatively large coercive force is exemplified.
- FIGS. 29 to 30 are plan views showing variations in the direction of magnetic anisotropy of the sensor layer of the magnetic memory element according to the embodiment of the present invention.
- the solid line arrow in FIG. 29 indicates the easy axis direction 26 a of the reference layer 21
- the solid line arrow in FIG. 30 indicates the hard axis direction 26 b of the reference layer 21.
- the sensor layer 23 is made of a material having in-plane magnetic anisotropy.
- the direction of the magnetic anisotropy of the sensor layer 23 may be in the in-plane ⁇ x direction (FIG. 29) or in the ⁇ y direction (FIG. 30).
- the magnetic anisotropy of the sensor layer 23 may be imparted by shape (shape magnetic anisotropy), may be imparted by crystal structure (crystal magnetic anisotropy), or the magnetostriction may be adjusted appropriately. It may be imparted by stress (stress-induced magnetic anisotropy).
- the operation of reversing the magnetization of the sensor layer 23 is an easy axis operation.
- the maximum MR ratio can be obtained.
- the leakage magnetic field from the magnetization recording layer 10 (the first domain wall motion region 13a and the second domain wall motion region 13b) is small, it may be difficult to reverse.
- the operation of reversing the magnetization of the sensor layer 23 is a difficult axis operation.
- the leakage magnetic field from the magnetization recording layer 10 (the first domain wall motion region 13a and the second domain wall motion region 13b) is small so as not to cause magnetization reversal by easy axis operation, it can be read (magnetization reversal).
- the MR ratio becomes relatively small and tends to vary.
- FIG. 31 is a sectional view showing an example of the configuration of the magnetic memory element in the reference cell of the MRAM according to the embodiment of the present invention.
- the basic configuration of the magnetic memory element of the reference cell is the same as that of a normal magnetic memory element as described in FIG.
- the direction of the magnetic anisotropy of the sensor layer 23 is the ⁇ y direction (difficult axis operation), as in FIG.
- the MTJ magnetic resistance of the magnetic tunnel junction 20 of the reference cell is a resistance R0.5 (an intermediate value between the resistance R1 and the resistance R0).
- the average value of the resistor R0 and the average value of the resistor R1 are The intermediate value resistor R0.5 is generated as a reference level and used for reading. In that case, it is necessary to write “1” or “0” in the reference cell 80r after the MRAM is manufactured. By writing “1” or “0”, the magnetization of the sensor layer is directed in a predetermined direction, but there is some variation in the direction. For this reason, a certain degree of inaccuracy enters the setting of the reference level of the reference cell 80r that stores the resistor R1 and the resistor R0. On the other hand, there is a certain amount of variation similarly in the memory cell 80 in which 1 ”or“ 0 ”is written, in which case the variation in the memory cell 80 and the variation in the reference cell 80r make it difficult to read accurately. Can be considered.
- the reference cell 80r of FIG. 31 when the reference cell 80r of FIG. 31 is used in which the reference cell column is one column and the resistance is R0.5, the resistance of the magnetic memory element in the memory cell 80 Even if R0 and the resistance R1 vary, the reference cell 80r is surely set to the resistance R0.5. Therefore, the reference cell level is accurately determined without variation. That is, even when the magnetic anisotropy of the magnetic memory element varies, the reference level serving as a reference is accurate, so that it is possible to accurately determine (read out) the resistance R0 or the resistance R1.
- the number of necessary reference cells 80r can be reduced. Since only one column of reference cells is obtained, the array area can be reduced particularly in the case of a small-scale array. Further, it is not necessary to provide the Y-side control circuit 93 with a controller for setting the reference cell 80r to the resistors R0 and R1, and the area of the peripheral circuit can be reduced. In addition, a process for setting the reference cell 80r to the resistors R0 and R1 becomes unnecessary, and the manufacturing cost and the manufacturing time can be reduced. Furthermore, a peripheral circuit and a program for calculating the resistance R0.5 from the resistances R0 and R1 of the reference cell 80r are not required, and the area of the peripheral circuit and the program storage area can be reduced.
- FIGS. 32 to 34 are perspective views showing a configuration example of a magnetic memory element according to an embodiment of the present invention.
- the wirings 52, 55, 35, and 56 for writing to the magnetization recording layer 10 are magnetized from the lower side. It is preferable to be connected to the recording layer 10. This is because elements such as MOS transistors TRa and TRb are on the lower side (semiconductor substrate side).
- connection portion between the reference layer 21 and the wiring 51 is It is preferable not to overlap with the barrier layer 22. This is because the following problems occur when the connection portion overlaps the barrier layer 22. That is, the step difference of the via of the wiring 51 (see the description of FIGS. 19A to 19C) is reflected in the reference layer 21, and a defect due to the step occurs in the barrier layer 22 on the reference layer 21, and the reference layer 21 and the sensor This is because the layer 23 is short-circuited.
- the width D of the first domain wall motion region 13a and the second domain wall motion region 13b can be made smaller than the design rule F. This makes it possible to increase the speed of writing to the magnetic memory element. Furthermore, the size of the magnetic memory element can be reduced, and the size of the memory array can be reduced.
- the magnetization can be easily fixed including the magnetization fixed regions on both sides. That is, the magnetization fixed region can be easily formed.
- the boundary between the two domain wall motion regions and the three magnetization fixed regions can be a domain wall pinning site. That is, the domain wall pinning site can be easily formed.
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Abstract
Description
図4Aは、本発明の実施形態に係る磁気メモリ素子のうち磁化記録層の構成の一例を示す平面図である。図4Bは、本発明の実施形態に係る磁気メモリ素子の構成の一例を示す断面図である。ただし、図4A及び図4Bにおいて、白丸と点の記号、白丸とバツの記号、及び白矢印は、一般的に用いられているように、それらが記載された領域の磁化の向きを示している(以下、本明細書及び各図面において同じとする)。
リファレンス層21は、磁化の向きが固定され、面内磁気異方性を有する強磁性層である。ここで、面内磁気異方性とは、この図の例において、xy面内で磁気異方性を有していることである。以下、本明細書において同じである。リファレンス層21の磁化の向きは、磁化記録層10の長手方向であることが好ましい。この図の例では、リファレンス層21の磁化の向きは、磁化記録層10の長手方向である±x方向のうち、-x方向である。この磁化の向きは逆であってもよい。また、リファレンス層21は、積層フェリ結合を有する複数の強磁性層から構成されることが好ましい。及び/又は、リファレンス層21は、Pt-Mnのような反強磁性層が隣接していることが好ましい。リファレンス層21の磁化の向きは書込み、及び、読出し動作によって変化させないため、リファレンス層21の磁化は実質的に一方向に固定されていることが好ましいためであるからである。
図5A及び図5Bは、本発明の実施形態に係る磁気メモリ素子の構成の一例を示す断面図である。図5Aは例えばデータ“0”を記憶した場合(0-state)を示し、図5Bは例えば、データ“1”を記憶した場合(1-state)を示している。
次に、本発明の実施形態に係る磁気メモリ素子の初期化方法について説明する。図6A~図6Cは、本発明の実施形態に係る磁気メモリ素子の初期化方法の一例を示す断面図である。
次に、磁気メモリ素子に対するデータの書込み原理を説明する。
図7は、本発明の実施形態に係る磁気メモリ素子に対するデータの書込み原理を示す断面図である。データ書込みは、スピン注入を利用した磁壁移動方式で行われる。書込み電流Iwは、MTJ(磁気トンネル接合部20)を貫通する方向ではなく、磁化記録層10内を平面的に、磁壁12a、12bを貫通する方向に流れる。その書込み電流Iwは、第1磁化固定領域11bに接続された電流供給端子(図示されず)、及び、第2磁化固定領域11cに接続された電流供給端子(図示されず)のいずれか一方から磁化記録層10に供給される。
次に、磁気メモリ素子に対するデータの読出し原理を説明する。図8A及び図8Bは、本発明の実施形態に係る磁気メモリ素子に対するデータの読出し原理を示す断面図である。データ読出し動作時、読出し電流IRは、磁気トンネル接合部20(リファレンス層21、バリア層22、及びセンサ層23)のMTJを貫通して流れるように供給される。そのように供給されれば、読出し電流IRは磁化記録層10を流れても流れなくてもよい。図8A及び図8Bの例では、読出し電流IRは、リファレンス層21側の電流供給端子、及び、第2磁化固定領域11c側の電流供給端子のいずれか一方から供給され、他方から送出される。それにより、読出し電流IRは、磁気トンネル接合部20のMTJを貫通すると共に、第0磁化固定領域11aと第2磁壁移動領域13bと第2磁化固定領域11cとを流れる。
図9は、本発明の実施形態に係る磁気メモリ素子が集積化されたメモリセルの構成例を示す回路図である。図9に示すように、磁気メモリ素子1において、磁気トンネル接合部
20のリファレンス層21に接続される端子は、読み出しのためのグラウンド線GLに接続される。磁化記録層10の第1磁化固定領域11b及び第2磁化固定領域11cに接続される二つの端子は、一方がMOSトランジスタTRaのソース/ドレインの一方に接続され、他方がMOSトランジスタTRbのソース/ドレインの一方に接続される。また、MOSトランジスタTRa、TRbのソース/ドレインの他方は、それぞれ書き込みのためのビット線BLa、BLbに接続される。更に、MOSトランジスタTRa、TRbのゲートはワード線WLに接続される。ただし、メモリセルの構成はこの例に限定されるものではない。
まず、書き込みを行う場合について説明する。X側制御回路92は、選択ワード線WLを選択する。それにより、選択ワード線WLが“high”レベルにプルアップされ、MOSトランジスタTRa、TRbが“ON”になる。また、Y側制御回路93は、選択ビット線BLa、BLbを選択する。それにより、選択ビット線BLa、BLbのいずれか一方が“high”レベルにプルアップされ、他方が“Low”レベルにプルダウンされる。選択ビット線BLa、BLbのどちらを“high”レベルにプルアップし、どちらを“Low”レベルにプルダウンするかは、当該磁気メモリ素子1に書き込まれるべきデータにより決定される。すなわち、磁化記録層10に流す書込み電流Iwの方向に応じて決定される。以上により、データ“0”とデータ“1”とを書き分けることができる。X側制御回路92とY側制御回路93及びそれらを制御する制御回路94は、メモリセル80に書き込み電流Iwを供給するための「書き込み電流供給回路」を構成している。
図11~図16は、本発明の実施形態に係る磁気メモリ素子のセンサ層23の位置のバリエーションを示す構成図である。ただし、図11~図13は断面図であり、図14~図16は平面図である。
図17は、本発明の実施の形態に係る磁気メモリ素子のセンサ層とハード層の位置関係に関するバリエーションを示す構成図である。ただし、図17は断面図である。
本実施の形態においては、センサ層23とハード層40の磁化記録層10に対する位置関係には任意性がある。例えば図4Bに示されるようにセンサ層23は磁化記録層10に対して下側(-z側)に設けられ、ハード層40は磁化記録層10に対して上側(+z側)に設けられてもよい。また図12に示されるようにセンサ層23は磁化記録層10に対して上側(+z側)に設けられ、ハード層40は磁化記録層10に対して下側(-z側)に設けられてもよい。あるいは図17に示されるように、センサ層23は磁化記録層10に対して上側(+z側)に設けられ、ハード層40も磁化記録層10に対して上側(+z側)に設けられてもよい。このように、本発明においては、ハード層40は磁化記録層10の所定の磁化構造を実現でき、またセンサ層23は第1磁壁移動領域13aと第2磁壁移動領域13bの磁化方向を読み出すことができさえすれば、これらの位置関係には何の制約もない。
図18~図23は、本発明の実施形態に係る磁気メモリ素子の第0磁化固定領域11aの両端での磁壁の停止方法のバリエーションを示す構成図である。ただし、各図において磁気トンネル接合部10は省略されている。また、図18、図19A~図19C、図21、図22は断面図であり、図20、図23は平面図である。
第1の方法では、コンタクト層30の材料として、第0磁化固定領域11aの材料と比較して低抵抗の材料を用いる。そのような材料としては、例えば、Au、Ag、Cu、Al、Ru、Pt、Pdなどが例示される。その場合、第1磁壁移動領域13a(又は第2磁壁移動領域13b)を流れた書き込み電流Iwは、第0磁化固定領域11aを流れるだけでなく、コンタクト層30により多く流れ込む。すなわち、書込み電流Iwは、第0磁化固定領域11aとコンタクト層30とに分流する。このとき、書き込み電流Iwの総量は変わらないことから、第0磁化固定領域11a内の電流密度は低下することになる。ところが、磁壁移動を起こすには、ある閾値以上の電流密度が必要である。この図の例では、書き込み電流Iwの電流密度は、第1磁壁移動領域13a(又は第2磁壁移動領域13b)において上記閾値以上になり、第0磁化固定領域11aにおいて分流により低下して上記閾値未満になるように設定される。そのため、磁壁は、閾値以上の電流密度の第1磁壁移動領域13a(又は第2磁壁移動領域13b)において移動し、閾値未満の第0磁化固定領域11aの端部付近で停止することになる。
図19Aに示される方法では、磁化記録層10の第0磁化固定領域11aの両端に、意図的に段差Qを設ける。そのため、第0磁化固定領域11aの上側(+z方向の側)の平面は、第1磁化固定領域11b、第1磁壁移動領域13a、第2磁壁移動領域13b、及び第2磁化固定領域11cの上側の平面よりも突き出ている。その結果、第0磁化固定領域11aと第2磁壁移動領域13bとの境界、及び、第0磁化固定領域11aと第1磁壁移動領域13aとの境界に段差Qが形成される。このような段差Qは磁壁に対するピンポテンシャルとして機能し磁壁をその位置で停止させることができる。
図20に示される方法では、第0磁化固定領域11aの領域での電流密度が、磁壁移動を起こすのに必要な閾値未満に低下するように、第0磁化固定領域11aの断面積を増大(例示:形状を太く、幅を広く等)させる。その場合、第1磁壁移動領域13a(又は第2磁壁移動領域13b)を流れた書き込み電流Iwは、断面積の増大した第0磁化固定領域11aを流れる。このとき、書き込み電流Iwの総量は変わらないことから、第0磁化固定領域11aの電流密度は低下することになる。この図の例では、第0磁化固定領域11aの幅は±y方向に突出部15、16の分だけ広くなっている。そして、書き込み電流Iwの電流密度は、第1磁壁移動領域13a(又は第2磁壁移動領域13b)において上記閾値以上になり、第0磁化固定領域11aにおいて低下して上記閾値未満になるように設定される。そのため、磁壁は、閾値以上の電流密度の第1磁壁移動領域13a(又は第2磁壁移動領域13b)において移動し、閾値未満の第0磁化固定領域11aの端部付近で停止することになる。
図21に示される方法では、コンタクト層30を、第0磁化固定領域11aと同じ垂直磁気異方性材料で形成し、第0磁化固定領域11aと同じ磁化の向きとする。このようにすることで、第0磁化固定領域11aの磁化が多くなるので、磁壁移動を起こり難くすることができる。その結果、相対的に磁化の少ない第1磁壁移動領域13a(又は第2磁壁移動領域13b)を移動してきた磁壁は、磁化の多い第0磁化固定領域11aの端部付近で停止することになる。この方法は、製造上特別なプロセスが不要であり、コンタクト層30の材料の選択だけで実施できプロセスが容易である。
図22に示される方法では、第0磁化固定領域11aにも、第1磁化固定領域11bや第2磁化固定領域11cと同様に、ハード層(第2のハード層18)を設ける。ただし、第1のハード層40よりもハードでなく(保持力を小さく)する。上述の初期化方法を利用できるようにするためである。このようにすることで、第0磁化固定領域11aの磁化が多くなるので、磁壁移動を起こり難くすることができる。その結果、相対的に磁化の少ない第1磁壁移動領域13a(又は第2磁壁移動領域13b)を移動してきた磁壁は、磁化の多い第0磁化固定領域11aの端部付近で停止することになる。
図22に示される方法では、第0磁化固定領域11aと第1磁壁移動領域13aとの境界部分、及び、第0磁化固定領域11aと第2磁壁移動領域13bとの境界部分に、磁壁に対するピンポテンシャルとして機能するノッチ17のようなピンサイトを設ける。このようなピンサイトは、磁化記録層10の微細化により製造困難となるが、磁化記録層10の大きさがある程度大きければ用いることは可能である。このようにすることで、ノッチ17がピンポテンシャルとして機能し、その位置で磁壁を停止することができる。
図24~図28は、本発明の実施形態に係る磁気メモリ素子の第1磁化固定領域及び第2磁化固定領域での磁化の固定方法のバリエーションを示す構成図である。ただし、各図において磁気トンネル接合部10は省略されている。また、図24~図26、図27B、図28は断面図であり、図27Aは平面図である。
図4A~図8Bに示した例では、第1のハード層40は、第1磁化固定領域11b及び第2磁化固定領域11cの上側(+z方向の側)に設けられている。しかし、図24に示すように、第1のハード層40は、第1磁化固定領域11b及び第2磁化固定領域11cの下側(-z方向の側)に設けられていてもよい。この方法は、製造プロセスの都合等により、下側に設けたい場合などに好ましい。
図25に示すように、第1のハード層40は、第1磁化固定領域11b及び第2磁化固定領域11cの上側(+z方向の側)及び下側(-z方向の側)の両方に設けられていてもよい。この方法は、製造プロセスの都合等により、上側又は下側の一方に厚く形成できないときに上側及び下側の両方に薄く設ける場合や、第1磁化固定領域11b及び第2磁化固定領域11cの磁化をより強固に固定したい場合などに好ましい。
図26に示すように、第1のハード層40は、第1磁化固定領域11b及び第2磁化固定領域11cに磁気的に結合していれば、第1磁化固定領域11b及び第2磁化固定領域11cに直接接触している必要は無い。すなわち、第1磁化固定領域11b及び第2磁化固定領域11cの上側及び下側の少なくとも一方に、磁気的に結合可能な程度に近傍に、第1のハード層40が形成されていればよい。この図の例では、第1磁化固定領域11b及び第2磁化固定領域11cの下側に、他の中間層43を介して第1のハード層40が設けられている。この方法は、製造プロセスの都合等により、磁化記録層10に直接接触して第1のハード層40を設けられない場合などに好ましい。
図27A及び図27Bに示すように、第1のハード層を用いなくても、形状を工夫することにより、所望の磁化状態を作り出すことができる。この図の例では、第1磁化固定領域11bにおける第1磁壁移動領域13aとの境界付近の幅、及び、第2磁化固定領域11cにおける第2磁壁移動領域13bとの境界付近の幅は、いずれも第1磁壁移動領域13a及び第2磁壁移動領域13bの幅よりも大きくなっている。これにより、磁壁は第1磁化固定領域11bや第2磁化固定領域11c内に侵入しにくくなり、それぞれの境界は磁壁に対するピンポテンシャルとして機能する。すなわち、第1磁化固定領域11bや第2磁化固定領域11cの磁化は固定化される。この方法は、第1のハード層を形成する必要がなく、磁化記録層10の形状変更だけで済むので、製造プロセスを簡略化でき、製造コストを削減することができる。
図28に示すように、第1のハード層を用いなくても、材料を工夫することにより、所望の磁化状態を作り出すことができる。この図の例では、第1磁化固定領域11b及び第2磁化固定領域11cの材料として、第1磁壁移動領域13aや第2磁壁移動領域13bと異なる材料を用いている。そのような材料としては、相対的に保磁力の大きい材料が例示される。また、第1磁化固定領域11b及び第2磁化固定領域11cにイオン注入を行い、その部分の磁気特性を変えることで実現することも可能である。
図29~図30は、本発明の実施形態に係る磁気メモリ素子のセンサ層の磁気異方性の方向のバリエーションを示す平面図である。ただし、図29中の実線矢印はリファレンス層21の磁化容易軸方向26a、図30中の実線矢印はリファレンス層21の磁化困難軸方向26bをそれぞれ示している。
図31は、本発明の実施形態に係るMRAMのリファレンスセルにおける磁気メモリ素子の構成の一例を示す断面図である。リファレンスセルの磁気メモリ素子の基本的な構成は、図10の説明にあるように通常の磁気メモリ素子と同じである。ただし、この図の例では、図30と同様に、センサ層23の磁気異方性の方向が±y方向(困難軸動作)である。この場合、リファレンスセルの磁気トンネル接合部20のMTJの磁気抵抗は、抵抗R0.5(抵抗R1と抵抗R0との中間の値)になっている。これをリファレンスレベルとすることで、以下のようなメリットが得られる。
図32~図34は、本発明の実施形態に係る磁気メモリ素子の構成例を示す斜視図である。図32~図34に示すように、磁化記録層10への書き込み用の配線52、55、35、56(第1磁化固定領域11b、第2磁化固定領域11cへの配線)は下側から磁化記録層10へ接続されることが好ましい。MOSトランジスタTRa、TRbなどの素子は下側(半導体基板側)にあるからである。
Claims (17)
- 垂直磁気異方性を有する強磁性層である磁化記録層と、
前記磁化記録層の情報を読み出すための磁気トンネル接合部と
を具備し、
前記磁化記録層は、二つの磁壁移動領域を備える
磁気メモリ素子。 - 請求項1に記載の磁気メモリ素子であって、
前記磁気トンネル接合部は、反転可能な磁化を有し、面内磁気異方性を有する強磁性層であるセンサ層を備える
磁気メモリ素子。 - 請求項1または2に記載の磁気メモリ素子であって、
前記磁化記録層は、
磁化の向きが固定された第1磁化固定領域、第0磁化固定領域、及び第2磁化固定領域と、
反転可能な磁化を有し、磁壁が移動可能であり、前記第1磁化固定領域と前記第0磁化固定領域との間に設けられた第1磁壁移動領域と、
反転可能な磁化を有し、磁壁が移動可能であり、前記第0磁化固定領域と前記第2磁化固定領域との間に設けられた第2磁壁移動領域と
を備える
磁気メモリ素子。 - 請求項3に記載の磁気メモリ素子であって、
前記第1磁化固定領域と前記第2磁化固定領域とは、実質的に同一である
磁気メモリ素子。 - 請求項3に記載の磁気メモリ素子であって、
前記第1磁化固定領域及び前記第2磁化固定領域の磁化の向きは、実質的に同一であり、
前記第0磁化固定領域の磁化の向きは、前記第1磁化固定領域及び前記第2磁化固定領域の磁化の向きと反対である
磁気メモリ素子。 - 請求項3乃至5のいずれか一項に記載の磁気メモリ素子であって、
前記センサ層の前記磁化記録層への射影は、前記第1磁壁移動領域と前記第2磁壁移動領域との間の前記磁化記録層内の領域の少なくとも一部に重なる
磁気メモリ素子。 - 請求項6に記載の磁気メモリ素子であって、
前記磁気トンネル接合部は、磁化の向きが固定され、面内磁気異方性を有する強磁性層であるリファレンス層を更に備え、
前記リファレンス層の磁化の向きは、前記第1磁壁移動領域と前記第2磁壁移動領域とを結ぶ直線の方向である
磁気メモリ素子。 - 請求項6に記載の磁気メモリ素子であって、
前記第0磁化固定領域と前記磁気トンネル接合部との間に設けられ、導電性を有するコンタクト層を更に具備する
磁気メモリ素子。 - 請求項8に記載の磁気メモリ素子であって、
前記コンタクト層は、前記第0磁化固定領域よりも低抵抗である
磁気メモリ素子。 - 請求項3から8のいずれか一項に記載の磁気メモリ素子であって、
前記第0磁化固定領域と、前記第1磁壁移動領域及び前記第2磁壁移動領域との境界に段差を有する
磁気メモリ素子。 - 請求項3から8のいずれか一項に記載の磁気メモリ素子であって、
前記第0磁化固定領域の垂直方向の断面積は、前記第1磁壁移動領域及び前記第2磁壁移動領域の垂直方向の断面積よりも大きい
磁気メモリ素子。 - 請求項8に記載の磁気メモリ素子であって、
前記コンタクト層は磁性体であり、
前記コンタクト層の磁化の向きは、前記第0磁化固定領域の磁化の向きと同じに固定されている
磁気メモリ素子。 - 請求項3乃至12のいずれか一項に記載の磁気メモリ素子であって、
前記第1磁化固定領域及び前記第2磁化固定領域の各々の近傍に設けられ、前記第1磁化固定領域及び前記第2磁化固定領域の各々の磁化の向きを固定する第1のハード層を更に具備する
磁気メモリ素子。 - 請求項3乃至12のいずれか一項に記載の磁気メモリ素子であって、
前記第0磁化固定領域の近傍に、第2のハード層を具備する
磁気メモリ素子。 - 請求項13または14に記載の磁気メモリ素子であって、
前記磁気トンネル接合部と前記第1のハード層、または、前記磁気トンネル接合部と前記第1のハード層及び前記第2のハード層が、前記磁化記録層に対していずれも基板とは反対側に設けられる
磁気メモリ素子。 - 請求項1乃至15のいずれか一項に記載の磁気メモリ素子を備えた複数の磁気メモリセルが行列状に配置された
磁気ランダムアクセスメモリ。 - 請求項16に記載の磁気ランダムアクセスメモリであって、
請求項2乃至15のいずれか一項に記載の磁気メモリ素子と同じ構成を有する磁気メモリ素子を備えた複数のリファレンスセルを更に具備し、
前記複数のリファレンスセルの前記磁気メモリ素子の各々は、前記センサ層が、前記第1磁壁移動領域と前記第2磁壁移動領域とを結ぶ方向に対して垂直な方向に磁気異方性を有する
磁気ランダムアクセスメモリ。
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