WO2009122992A1

WO2009122992A1 - Magnetoresistance storage

Info

Publication number: WO2009122992A1
Application number: PCT/JP2009/056053
Authority: WO
Inventors: 有光加藤
Original assignee: 日本電気株式会社
Priority date: 2008-04-03
Filing date: 2009-03-26
Publication date: 2009-10-08

Abstract

A magnetoresistance storage includes magnetoresistance elements (1). Each magnetoresistance element (1) has a first magnetic layer (10), a second magnetic layer (20), and a third magnetic layer (30). The direction of the magnetization of the first magnetic layer (10) is fixed in a first direction. The second magnetic layer (20) is connected to the first magnetic layer (10) via a nonmagnetic layer (41) and has a first surface (S1) in contact with the nonmagnetic layer (41) and a second surface (S2) opposite to the first surface (S1). The third magnetic layer (30) is formed on the second surface (S2) and magnetically coupled to the second magnetic layer (20). The direction of the magnetization of the third magnetic layer (30) is fixed in a direction different from the first direction. The direction of the magnetization of the second magnetic layer (20) is a second direction neither parallel nor antiparallel to the first direction in the second surface (S2), and varies from the second direction to a direction parallel or antiparallel to the first direction with increasing distance from the second surface (S2) toward the first surface (S1).

Description

Magnetoresistive memory device

The present invention relates to a magnetoresistive storage device including a plurality of magnetoresistive elements. In particular, the present invention relates to a magnetoresistive memory device based on a spin injection method.

MRAM is a promising nonvolatile memory from the viewpoint of high integration and high-speed operation. In the MRAM, a magnetoresistive element exhibiting a “magnetoresistance effect” such as a TMR (Tunnel MagnetoResistance) effect is used. In the magnetoresistive element, for example, a magnetic tunnel junction (MTJ; Magnetic Tunnel Junction) in which a tunnel barrier layer is sandwiched between two ferromagnetic layers is formed. The two ferromagnetic layers are composed of a pinned layer (magnetization pinned layer) whose magnetization direction is fixed and a free layer (magnetization free layer) whose magnetization direction can be reversed (for example, Roy Scheuerlein et al. , “A 10ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, 2000 IEEE International Solid-State Circuits Conference, DIGEST OF TECHNICAL PAPERS, pp.128-129.

The MTJ resistance value (R + ΔR) when the magnetization directions of the pinned layer and the free layer are “antiparallel” should be larger than the resistance value (R) when they are “parallel” due to the magnetoresistance effect. It has been known. The MRAM uses the magnetoresistive element having the MTJ as a memory cell, and stores data in a nonvolatile manner by utilizing the change in the resistance value. Data is written to the memory cell by reversing the magnetization direction of the free layer.

As a method of writing data to the MRAM, an asteroid method is conventionally known (for example, M. Durlam et al., Nonvolatile RAM based on Magnetic Tunnel Junction Elements, ”2000 IEEE International Solid-State Circuits Conference, DIGEST OF TECHNICAL PAPERS, pp. 130-131. According to the asteroid method, the reversal magnetic field necessary for reversing the magnetization of the free layer increases in inverse proportion to the memory cell size. That is, the write current tends to increase as the memory cell is miniaturized.

“Spin injection method” has been proposed as a write method that can suppress an increase in write current due to miniaturization (for example, Yagami and Suzuki, Research Trends in Spin Transfer Magnetization Switching, Journal of Japan Society of Applied Magnetics, Vol. (28, No. 9, 2004.) According to the spin transfer method, a spin-polarized current is injected into a ferromagnetic conductor, and the direct interaction between the spin of the conduction electron carrying the current and the magnetic moment of the conductor Magnetization is reversed (hereinafter referred to as “spin injection magnetization reversal: Spin Transfer Magnetization Switching”). An outline of spin injection magnetization reversal will be described with reference to FIG.

1, the magnetoresistive element includes a free layer 101, a pinned layer 103, and a tunnel barrier layer 102 that is a nonmagnetic layer sandwiched between the free layer 101 and the pinned layer 103. Here, the pinned layer 103 whose magnetization direction is fixed is formed to be thicker than the free layer 101, and plays a role as a mechanism (spin filter) for creating a spin-polarized current. The state where the magnetization directions of the free layer 101 and the pinned layer 103 are parallel is associated with data “0”, and the state where they are anti-parallel is associated with data “1”.

The spin injection magnetization reversal shown in FIG. 1 is realized by the CPP (Current Perpendicular Plane) method, and the write current is injected perpendicularly to the film surface. Specifically, current flows from the pinned layer 103 to the free layer 101 at the time of transition from data “0” to data “1”. In this case, electrons having the same spin state as the pinned layer 103 as a spin filter move from the free layer 101 to the pinned layer 103. Then, the magnetization of the free layer 101 is reversed by a spin transfer (spin angular momentum transfer) effect. On the other hand, at the transition from data “1” to data “0”, the direction of the current is reversed, and the current flows from the free layer 101 to the pinned layer 103. In this case, electrons having the same spin state as the pinned layer 103 as a spin filter move from the pinned layer 103 to the free layer 101. Due to the spin transfer effect, the magnetization of the free layer 101 is reversed.

Thus, in spin injection magnetization reversal, data is written by the movement of spin electrons. The magnetization direction of the free layer 101 can be defined by the direction of the spin-polarized current injected perpendicular to the film surface. Here, it is known that the threshold for writing (magnetization reversal) depends on the current density. Therefore, as the memory cell size is reduced, the write current required for magnetization reversal decreases. Since the write current decreases with the miniaturization of the memory cell, the spin injection magnetization reversal is important for realizing a large capacity of the MRAM.

The magnetoresistive element described in Japanese Patent Application Laid-Open No. 2005-150303 has a ferromagnetic tunnel junction including a three-layer structure of a first ferromagnetic layer / tunnel barrier layer / second ferromagnetic layer. The coercive force of the first ferromagnetic layer is greater than the coercivity of the second ferromagnetic layer. The magnetization of the end portion of the second ferromagnetic layer is fixed in a direction having a component orthogonal to the easy axis direction of the second ferromagnetic layer.

A magnetoresistive element described in Japanese Patent Application Laid-Open No. 2006-128579 includes a storage layer that holds information according to the magnetization state of a magnetic material, a magnetization fixed layer provided to the storage layer via an intermediate layer, and a storage layer And a drive layer provided via a nonmagnetic layer. The direction of magnetization of the drive layer is substantially fixed in the stacking direction.

As described above, in the spin injection method, a write current is injected perpendicularly to the film surface, and the magnetization direction of the free layer is reversed by spin transfer. However, the write current density at this time needs to be about 1 × 10 ⁷ A / cm ² . Since such a large write current flows through the tunnel barrier layer, the tunnel barrier layer may be deteriorated due to heat generation or electron collision. The deterioration of the tunnel barrier layer degrades the reliability and life of the magnetoresistive element.

One object of the present invention is to provide a magnetoresistance storage device of a spin injection system that can reduce a write current.

In one aspect of the present invention, a magnetoresistive memory device is provided. The magnetoresistive storage device includes a plurality of magnetoresistive elements. Each of the plurality of magnetoresistive elements includes a first magnetic layer, a second magnetic layer, and a third magnetic layer. The magnetization direction of the first magnetic layer is fixed in the first direction. The second magnetic layer is connected to the first magnetic layer through the nonmagnetic layer, and has a first surface in contact with the nonmagnetic layer and a second surface facing the first surface. . The third magnetic layer is formed on the second surface side of the second magnetic layer and is magnetically coupled to the second magnetic layer. The magnetization direction of the third magnetic layer is fixed in a direction different from the first direction. The magnetization direction of the second magnetic layer is a second direction that is neither parallel nor anti-parallel to the first direction on the second surface, and is parallel to the first direction from the second direction as it approaches the first surface from the second surface, or Transition in antiparallel direction.

According to the present invention, it is possible to reduce a write current in a magnetoresistance storage device of a spin injection method. As a result, deterioration of the tunnel barrier layer is suppressed, and the reliability of the magnetoresistive element and the magnetoresistive memory device is improved.

The above and other objects, advantages, and features will become apparent from the embodiments of the present invention described in conjunction with the following drawings.

FIG. 1 is a conceptual diagram for explaining data writing by a spin injection method. FIG. 2 is a schematic diagram showing an example of the magnetoresistive element according to the first embodiment of the present invention. FIG. 3 is a schematic view showing another example of the magnetoresistance element according to the first exemplary embodiment of the present invention. FIG. 4 is a cross-sectional view showing the structure of the magnetoresistive element according to the first embodiment. FIG. 5 is a plan view showing the structure of the magnetoresistive element according to the first embodiment. FIG. 6 is a schematic diagram illustrating an example of a magnetoresistive element according to the second embodiment of the present invention. FIG. 7 is a cross-sectional view showing the structure of the magnetoresistive element according to the second embodiment. FIG. 8 is a plan view showing the structure of the magnetoresistive element according to the second embodiment. FIG. 9 is a schematic diagram showing an example of a magnetoresistive element according to the third embodiment of the present invention. FIG. 10 is a circuit block diagram schematically showing the configuration of the MRAM according to the embodiment of the present invention.

A magnetoresistive memory device according to an embodiment of the present invention will be described with reference to the accompanying drawings. The magnetoresistive storage device includes a plurality of magnetoresistive elements. For example, the magnetoresistive memory device is an MRAM that uses a plurality of magnetoresistive elements arranged in an array as memory cells.

1. First Embodiment (Configuration)
FIG. 2 schematically shows the configuration of the magnetoresistive element 1 according to the first exemplary embodiment of the present invention. The magnetoresistive element 1 includes a pinned layer 10 (first magnetic layer), a free layer 20 (second magnetic layer), a twist generation layer 30 (third magnetic layer), and the pinned layer 10 and the free layer 20. A first nonmagnetic layer 41 sandwiched is provided. In FIG. 2, the stacking direction (the direction perpendicular to the film surface) is the Z direction.

The pinned layer 10 is a magnetic layer whose magnetization direction is fixed. In the present embodiment, the magnetization direction of the pinned layer 10 is fixed in a direction perpendicular to the film surface. In the example shown in FIG. 2, the magnetization direction of the pinned layer 10 is fixed in the + Z direction. For example, the pinned layer 10 is formed of a perpendicular magnetization film (perpendicular magnetic field) having perpendicular magnetic anisotropy. In this case, the easy axis direction of the pinned layer 10 is the Z direction perpendicular to the film surface.

The free layer 20 is a magnetic layer for storing data, and its magnetization state changes according to the recording data of the magnetoresistive element 1. The free layer 20 is connected to the pinned layer 10 via the first nonmagnetic material layer 41, and an MTJ is formed by the pinned layer 10, the free layer 20, and the first nonmagnetic material layer 41 (tunnel barrier film). . The easy axis direction of the free layer 20 is substantially parallel to the fixed magnetization direction (Z direction) of the pinned layer 10. More specifically, in the present embodiment, the free layer 20 is formed of a perpendicular magnetization film having perpendicular magnetic anisotropy. Therefore, the easy axis direction of the free layer 20 is a direction perpendicular to the film surface, and is substantially parallel to the magnetization direction of the pinned layer 10. The planar shape of the free layer 20 is arbitrary, for example, rectangular or circular.

As shown in FIG. 2, the free layer 20 has a first surface S1 that contacts the first nonmagnetic layer 41 and a second surface S2 that faces the first surface S1. The free layer 20 includes a “data storage region RD” and a “magnetization transition region RT”. The data storage region RD is a region on the first surface S1 side, and the magnetization transition region RT is a region on the second surface S2 side.

The magnetization direction of the data storage area RD is parallel to the easy axis direction (Z direction) and is allowed to be parallel (+ Z) or antiparallel (−Z) to the magnetization direction of the pinned layer 10. When the magnetization direction of the data storage region RD is the + Z direction, that is, the state in which the magnetization direction of the data storage region RD and the pinned layer 10 is parallel is associated with data “0”. On the other hand, when the magnetization direction of the data storage region RD is the −Z direction, that is, the state where the magnetization directions of the data storage region RD and the pinned layer 10 are antiparallel, the data “1” is associated.

On the other hand, the magnetization direction of the magnetization transition region RT is different from the easy axis direction (Z direction), and is neither parallel nor antiparallel to the magnetization direction of the pinned layer 10. In particular, the magnetization direction of the magnetization transition region RT is most different from the easy axis direction on the second surface S2, and transitions in a direction parallel to the easy axis direction from the second surface S2 toward the first surface S1. Yes. For example, in FIG. 2, the magnetization direction of the magnetization transition region RT is the in-plane direction on the second surface S2, and is substantially orthogonal to the easy axis direction. The magnetization direction of the magnetization transition region RT transitions from the in-plane direction to the easy axis direction (a direction parallel or antiparallel to the magnetization direction of the pinned layer 10) as it approaches the first surface S1 from the second surface S2. .

The twist generation layer 30 is a magnetic layer for forming the above-described magnetization transition region RT in the free layer 20. Therefore, the twist generation layer 30 is formed on the second surface S2 side (side closer to the magnetization transition region RT) of the free layer 20 so as to be magnetically coupled to the free layer 20. Further, the magnetization direction of the twist generation layer 30 is fixed in a direction different from the magnetization direction of the pinned layer 10, that is, the easy magnetization axis direction (+ Z, −Z direction) of the free layer 20. In FIG. 2, the magnetization direction of the twist generation layer is fixed in the in-plane direction orthogonal to the Z direction. For example, the twist generation layer 30 is formed of an in-plane magnetic film having an in-plane magnetic anisotropy. In this case, the easy magnetization axis direction of the twist generation layer 30 is one direction in the plane. A magnetic transition region RT is formed in the free layer 20 by magnetic coupling between the twist generation layer 30 and the free layer 20.

2, the twist generation layer 30 is in contact with the second surface S2 of the free layer 20. For example, the twist generation layer 30 is formed of an antiferromagnetic film, and its magnetization direction is fixed in the + X direction. In this case, the magnetization transition region RT has a magnetization component in the −X direction different from the easy axis direction. FIG. 3 shows a modification of the magnetoresistive element 1 according to the present exemplary embodiment. In the example of FIG. 3, the magnetoresistive element 1 further includes a second nonmagnetic material layer 42 sandwiched between the free layer 20 and the twist generation layer 30, and the twist generation layer 30 includes the second nonmagnetic material layer 42. Is connected to the second surface S2 of the free layer 20. In this case, the twist generation layer 30 is ferromagnetically or antiferromagnetically coupled to the free layer 20 via the second nonmagnetic layer 42. In any case, the magnetization transition region RT is formed in the free layer 20 due to magnetic coupling between the twist generation layer 30 and the free layer 20.

In the example shown in FIGS. 2 and 3, each magnetic layer may have a single-layer structure or a laminated structure in which a plurality of magnetic bodies are laminated. Further, a laminated structure in which a plurality of magnetic bodies are magnetically coupled via a non-magnetic body is also possible.

The free layer 20 may have a laminated structure of a perpendicular magnetization film having perpendicular magnetic anisotropy and an in-plane magnetization film having in-plane magnetic anisotropy. In this case, the perpendicular magnetization film is formed so as to be in contact with the first surface S1, and the in-plane magnetization film is formed so as to be in contact with the second surface S2. That is, the perpendicular magnetization film corresponds approximately to the data recording region RD, and the in-plane magnetization film corresponds approximately to the magnetization transition region RT. The perpendicular magnetization film and the in-plane magnetization film are magnetically coupled. Further, the perpendicular magnetization film and the in-plane magnetization film may be magnetically coupled via a nonmagnetic layer.

The magnetoresistive element 1 further includes a first terminal 51 electrically connected to the pinned layer 10 and a second terminal 52 electrically connected to the twist generation layer 30.

(Write operation)
A data write operation to the magnetoresistive element 1 according to the present exemplary embodiment will be described with reference to FIG. 2 or FIG. Data writing is performed by a spin injection method using a write current that flows perpendicularly to the film surface. That is, the write current flows between the first terminal 51 and the second terminal 52. At this time, the pinned layer 10 whose magnetization direction is fixed in the + Z direction serves as a spin filter, and applies torque to the free layer 20 to reverse the magnetization of the free layer 20 (data storage region RD).

When writing data “0”, a write current flows from the second terminal 52 to the first terminal 51. In this case, the write current flows from the free layer 20 to the pinned layer 10. Therefore, electrons having the same spin state (+ Z) as the pinned layer 10 as the spin filter move from the pinned layer 10 to the free layer 20. Here, it is noted that the torque direction (+ Z) applied to the free layer 20 is almost exactly opposite to the magnetization direction (−Z) of the data storage region RD, but is not exactly opposite to the magnetization direction of the magnetization transition region RT. I want. This is because the magnetization direction of the magnetization transition region RT is neither parallel nor antiparallel to the magnetization direction of the pinned layer 10. Therefore, a change in magnetization direction due to spin transfer is likely to occur in the magnetization transition region RT. In particular, in the vicinity of the second surface S2, the magnetization direction is almost orthogonal to the torque direction (+ Z), and the magnetization direction is most likely to change due to spin transfer. When the magnetization direction in the vicinity of the second surface S2 changes to have a component in the + Z direction, the magnetization in the + Z direction component further assists the change in the magnetization direction on the first surface S1 side. Such a magnetization change is transmitted to the first surface S1 side, and the magnetization of the free layer 20 has components in the + Z direction in order from the vicinity of the second surface S2 toward the first surface S1. Eventually, the magnetization direction of the data storage area RD is reversed from the −Z direction to the + Z direction.

On the other hand, when data “1” is written, a write current flows from the first terminal 51 to the second terminal 52. In this case, the write current flows from the pinned layer 10 to the free layer 20. Therefore, electrons having the same spin state (+ Z) as the pinned layer 10 as a spin filter move from the free layer 20 to the pinned layer 10, while electrons having a spin state (−Z) opposite to the pinned layer 10 are Reflected by the free layer 20. Again, it is noted that the torque direction (−Z) applied to the free layer 20 is almost exactly opposite to the magnetization direction (+ Z) of the data storage region RD, but is not exactly opposite to the magnetization direction of the magnetization transition region RT. I want. Therefore, a change in magnetization direction due to spin transfer is likely to occur in the magnetization transition region RT. As a result, the magnetization of the free layer 20 has a component in the −Z direction in order from the vicinity of the second surface S2 toward the first surface S1. Eventually, the magnetization direction of the data storage area RD is reversed from the + Z direction to the −Z direction.

In the case of FIG. 1 described above, the torque applied to the free layer 101 has only a component opposite to the magnetization direction of the free layer 101, so that magnetization reversal hardly occurs. On the other hand, according to the present embodiment, the magnetization direction of the free layer 20 is neither parallel nor antiparallel to the magnetization easy axis direction on the second surface S2, but is magnetized as it approaches the first surface S1 from the second surface S2. The transition is in a direction parallel or antiparallel to the easy axis direction. Accordingly, a change in magnetization direction due to spin transfer is likely to occur in the magnetization transition region RT (particularly in the vicinity of the second surface S2). And the change of the magnetization direction is transmitted in order toward the 1st surface S1 from the 2nd surface S2 vicinity. Thus, according to the present embodiment, the magnetization direction of the free layer 20 (data storage area RD) can be easily reversed compared to the case of FIG. As a result, data writing can be realized with a smaller write current. According to the Landau-Lifshitz-Gilbert (LLG) simulation by the present inventor, it was confirmed that the write current can be reduced to 0.45 times that in the case of FIG.

As described above, according to the present embodiment, the write current can be reduced in the spin-injection magnetoresistive element. As a result, deterioration of the tunnel barrier layer is suppressed, and the reliability of the magnetoresistive element and the magnetoresistive memory device is improved.

(Read operation)
A data read operation from the magnetoresistive element 1 according to the present exemplary embodiment will be described with reference to FIG. 2 or FIG. When reading data, a read current smaller than the write current is passed between the first terminal 51 and the second terminal 52. Based on the read current, the resistance value of the magnetoresistive element 1 is evaluated, whereby the recording data is determined. For example, the magnitude of the resistance value of the magnetoresistive element 1, that is, the recording data can be determined by comparing the read current or the read voltage corresponding to the read current with a predetermined reference level. Note that the angle formed by the magnetization direction of the free layer 20 and the magnetization direction of the twist generation layer 30 is approximately 90 degrees, regardless of the recording data. That is, the resistance value between the free layer 20 and the twist generation layer 30 is the same regardless of the recording data. Therefore, only a change in resistance value between the pinned layer 10 and the free layer 20 is observed.

(Structural example and manufacturing method thereof)
4 and 5 respectively show an example of a cross-sectional structure and a planar structure of the magnetoresistive element 1 according to the present exemplary embodiment. A cross-sectional structure along line AA ′ in FIG. 5 is shown in FIG. An example of the magnetoresistive element 1 and a manufacturing method thereof will be described with reference to FIGS.

After transistors and wirings are formed on the semiconductor substrate, an interlayer insulating film 60 is formed. A tungsten plug 61 that penetrates the interlayer insulating film 60 and is connected to the lower layer wiring is formed. Subsequently, a Cu film 62 (20 nm), a Ta film 63 (10 nm), a PtMn film 64 (20 nm) as an antiferromagnetic film, a CoFe film 65 (4 nm), a Ru film 66 (0.8 nm), and a CoFe film 67 (4 nm), CoPt film 69 (2 nm), MgO film 70 (1 nm), CoPt film 71 (6 nm), and Ta film 72 (50 nm) are sequentially formed by sputtering.

Among these, the Cu film 62 corresponds to the second terminal 52. The CoFe film 65, the Ru film 66, and the CoFe film 67 correspond to the twist generation layer 30. The two

CoFe films

65 and 67 are antiferromagnetically coupled via the Ru film 66. The CoFe film 65 and the Ru film 66 may be omitted. Alternatively, the CoFe film 65 to the CoFe film 67 may be omitted, and the PtMn film 64 that is an antiferromagnetic film may be used as the twist generation layer 30. The CoPt film 69 corresponds to the free layer 20 and has perpendicular magnetic anisotropy. The MgO film 70 that is a tunnel insulating film corresponds to the first nonmagnetic layer 41. The CoPt film 71 corresponds to the pinned layer 10 and has perpendicular magnetic anisotropy. The Ta film 72 corresponds to the first terminal 51.

Next, in order to set the magnetization directions of the pinned layer 10 and the twist generation layer 30, an annealing process is performed in a magnetic field. The annealing conditions are, for example, temperature: 275 ° C., applied magnetic field: 1 T, and processing time: 2 hours. In addition, the angle of the applied magnetic field with respect to the plane is set to about 45 degrees. Thereby, the

CoFe films

65 and 67 as the twist generation layer 30 are magnetized in the in-plane direction, and the CoPt film 71 as the pinned layer 10 is magnetized in the vertical direction.

Next, the Ta film 72 is processed to have a predetermined planar shape by photolithography and reactive ion etching. After the resist is removed, the laminated film from the CoPt film 71 to the CoPt film 69 is patterned by a milling method using the Ta film 72 as a mask. The planar shape of the laminated film from the CoPt film 69 to the Ta film 72 is a circular shape as shown in FIG. 5, and its diameter is, for example, 0.2 μm. The MTJ is formed by the circular CoPt film 69, MgO film 70, and CoPt film 71.

Next, in order to protect the side wall of the MTJ, a SiN film 73 (30 nm) is formed on the entire surface by the CVD method. Subsequently, the laminated film from the CoFe film 67 to the Cu film 62 is patterned by photolithography and milling. The planar shape of the laminated film from the Cu film 62 to the CoFe film 67 is a rectangular shape as shown in FIG.

Next, a SiN film 74 and a SiO ₂ film 75 (50 nm) are formed on the entire surface by CVD. Further, CMP is performed until the Ta film 72 is exposed. Subsequently, an interlayer insulating film 76 (400 nm) is formed on the entire surface by CVD. Next, the interlayer insulating film 76 on the MTJ is removed by photolithography and reactive ion etching, and a contact hole reaching the Ta film 72 is formed. Further, after the AlCu film 77 is formed on the entire surface, it is processed into a pattern as shown in FIG. Thereby, the upper wiring 77 is formed.

2. Second Embodiment (Configuration)
FIG. 6 schematically shows the configuration of the magnetoresistive element 1 according to the second exemplary embodiment of the present invention. As in the first embodiment, the magnetoresistive element 1 includes a pinned layer 10, a free layer 20, a twist generation layer 30, a first nonmagnetic layer 41, a first terminal 51, and a second terminal 52. . The description overlapping with the first embodiment is omitted as appropriate.

In the present embodiment, the magnetization direction of the pinned layer 10 is fixed in the in-plane direction. In the example shown in FIG. 6, the magnetization direction of the pinned layer 10 is fixed in the + X direction. For example, the pinned layer 10 is formed of an in-plane magnetization film having in-plane magnetic anisotropy. In this case, the magnetization easy axis direction of the pinned layer 10 is the in-plane direction.

In this embodiment, the free layer 20 is formed of an in-plane magnetization film having in-plane magnetic anisotropy. Therefore, the easy axis direction of the free layer 20 is the in-plane direction and is substantially parallel to the magnetization direction of the pinned layer 10. The in-plane magnetic anisotropy of the free layer 20 is realized by shape anisotropy and material anisotropy depending on the planar shape. Therefore, the planar shape of the free layer 20 is preferably an ellipse or a rectangle. Similar to the first embodiment, the free layer 20 according to the present embodiment also includes a data storage region RD on the first surface S1 side and a magnetization transition region RT on the second surface S2 side.

The magnetization direction of the data storage area RD is parallel to the easy axis direction (X direction) and is allowed to be parallel (+ X) or antiparallel (−X) to the magnetization direction of the pinned layer 10. When the magnetization direction of the data storage region RD is the + X direction, that is, the state in which the magnetization direction of the data storage region RD and the pinned layer 10 is parallel is associated with data “0”. On the other hand, when the magnetization direction of the data storage region RD is the −X direction, that is, the state where the magnetization directions of the data storage region RD and the pinned layer 10 are antiparallel, this is associated with data “1”.

On the other hand, the magnetization direction of the magnetization transition region RT is different from the magnetization easy axis direction (X direction), and is neither parallel nor antiparallel to the magnetization direction of the pinned layer 10. In particular, the magnetization direction of the magnetization transition region RT is most different from the easy axis direction on the second surface S2, and transitions in a direction parallel to the easy axis direction from the second surface S2 toward the first surface S1. Yes. For example, in FIG. 6, the magnetization direction of the magnetization transition region RT is substantially the + Z direction on the second surface S2, and is substantially perpendicular to the easy magnetization axis direction. The magnetization direction of the magnetization transition region RT changes from the + Z direction to the easy axis direction (a direction parallel or antiparallel to the magnetization direction of the pinned layer 10) as it approaches the first surface S1 from the second surface S2.

In this embodiment, the magnetization direction of the twist generation layer 30 is fixed in a direction perpendicular to the film surface, and is orthogonal to the easy axis direction (in-plane direction) of the free layer 20. In FIG. 6, the magnetization direction of the twist generation layer 30 is fixed in the + Z direction. For example, the twist generation layer 30 is formed of a perpendicular magnetization film having perpendicular magnetic anisotropy. In this case, the easy axis of magnetization of the twist generation layer 30 is a direction perpendicular to the film surface. The twist generation layer 30 may be in contact with the second surface S2 of the free layer 20, or may be connected to the second surface S2 via a nonmagnetic layer. A magnetic transition region RT is formed in the free layer 20 by magnetic coupling between the twist generation layer 30 and the free layer 20.

In the example shown in FIG. 6, each magnetic layer may have a single layer structure, or may have a stacked structure in which a plurality of magnetic materials are stacked. Further, a laminated structure in which a plurality of magnetic bodies are magnetically coupled via a non-magnetic body is also possible.

The free layer 20 may have a laminated structure of a perpendicular magnetization film having perpendicular magnetic anisotropy and an in-plane magnetization film having in-plane magnetic anisotropy. In this case, the in-plane magnetization film is formed so as to be in contact with the first surface S1, and the perpendicular magnetization film is formed so as to be in contact with the second surface S2. That is, the in-plane magnetization film corresponds approximately to the data recording region RD, and the perpendicular magnetization film corresponds approximately to the magnetization transition region RT. The perpendicular magnetization film and the in-plane magnetization film are magnetically coupled. Further, the perpendicular magnetization film and the in-plane magnetization film may be magnetically coupled via a nonmagnetic layer.

(Write operation)
The data write operation is the same as in the first embodiment. Also in the present embodiment, the magnetization direction of the free layer 20 is neither parallel nor anti-parallel to the magnetization easy axis direction on the second surface S2, but is parallel to the magnetization easy axis direction as approaching the first surface S1 from the second surface S2. Transition to anti-parallel direction. Accordingly, a change in magnetization direction due to spin transfer is likely to occur in the magnetization transition region RT (particularly in the vicinity of the second surface S2). And the change of the magnetization direction is transmitted in order toward the 1st surface S1 from the 2nd surface S2 vicinity. Thus, according to the present embodiment, the magnetization direction of the free layer 20 (data storage area RD) can be easily reversed compared to the case of FIG. As a result, data writing can be realized with a smaller write current. Therefore, deterioration of the tunnel barrier layer is suppressed, and the reliability of the magnetoresistive element and the magnetoresistive memory device is improved.

(Read operation)
The data read operation is the same as that in the first embodiment. It is known that when the pinned layer 10 and the free layer 20 are in-plane magnetic films, the MR ratio of the MTJ is larger than when they are perpendicular magnetic films. For example, in the CoFeB / MgO / CoFeB structure, an MR ratio of 100% or more is obtained. In the second embodiment, such a large MR ratio can be used.

(Structural example and manufacturing method thereof)
7 and 8 respectively show an example of a cross-sectional structure and a planar structure of the magnetoresistive element 1 according to the present exemplary embodiment. A cross-sectional structure along line AA ′ in FIG. 8 is shown in FIG. An example of the magnetoresistive element 1 and a manufacturing method thereof will be described with reference to FIGS.

The structure from the interlayer insulating film 60 to the CoFe film 67 is the same as in the case of FIG. Further, an MgO film 68 (1 nm), a NiFe film 81 (4 nm), a CoPt film 82 (1 nm), and a Ta film 83 (50 nm) are sequentially formed by a sputtering method. In this example, the Cu film 62 corresponds to the first terminal 51. The CoFe film 65, the Ru film 66 and the CoFe film 67 correspond to the pinned layer 10. The two

CoFe films

65 and 67 are antiferromagnetically coupled via the Ru film 66. The MgO film 68 that is a tunnel insulating film corresponds to the first nonmagnetic layer 41. The NiFe film 81 corresponds to the free layer 20 and has in-plane magnetic anisotropy. The CoPt film 82 corresponds to the twist generation layer 30 and has perpendicular magnetic anisotropy. The Ta film 83 corresponds to the second terminal 52.

CoFe films

65 and 67 as the pinned layer 10 are magnetized in the in-plane direction, and the CoPt film 82 as the torsion generation layer 30 is magnetized in the vertical direction.

Next, the Ta film 83 is processed to have a predetermined planar shape by photolithography and reactive ion etching. After the resist is removed, the laminated film from the CoPt film 82 to the NiFe film 81 is patterned by a milling method using the Ta film 83 as a mask. The planar shape of the laminated film from the NiFe film 81 to the Ta film 83 is an elliptical shape as shown in FIG. For example, the major axis of the elliptical shape has a length of 0.4 μm and the minor axis has a length of 0.2 μm. Thereby, shape magnetic anisotropy is realized.

The subsequent steps are the same as those in the first embodiment. As shown in FIG. 8, the planar shape of the laminated film from the Cu film 62 to the MgO film 68 is a rectangle.

3. Third Embodiment FIG. 9 schematically shows a configuration of a magnetoresistive element 1 according to a third embodiment of the present invention. The third embodiment is different from the second embodiment in the direction of the magnetization fixed direction of the twist generation layer 30. A duplicate description with the second embodiment is omitted as appropriate.

In the present embodiment, the magnetization direction of the twist generation layer 30 is fixed in one direction in the plane. However, the in-plane magnetization direction of the twist generation layer 30 is different from the in-plane magnetization direction of the pinned layer 10 (the easy axis direction of the free layer 20). In the example of FIG. 9, the magnetization direction of the pinned layer 10 is the + X direction, while the magnetization direction of the twist generation layer 30 is the + Y direction orthogonal to the magnetization direction. For example, the twist generation layer 30 is formed of an in-plane magnetization film having in-plane magnetic anisotropy. The twist generation layer 30 may be an antiferromagnetic film. The twist generation layer 30 may be in contact with the second surface S2 of the free layer 20, or may be connected to the second surface S2 via a nonmagnetic layer. A magnetic transition region RT is formed in the free layer 20 by magnetic coupling between the twist generation layer 30 and the free layer 20.

Also in the present embodiment, the magnetization direction of the magnetization transition region RT is different from the easy magnetization axis direction (X direction). For example, in FIG. 9, the magnetization direction of the magnetization transition region RT is substantially the −Y direction on the second surface S2, and is substantially orthogonal to the easy axis direction (X direction). The magnetization direction of the magnetization transition region RT changes from the −Y direction to the easy axis direction (a direction parallel or antiparallel to the magnetization direction of the pinned layer 10) as it approaches the first surface S1 from the second surface S2. . Therefore, the same effect as in the second embodiment can be obtained.

In order to realize the magnetoresistive element 1 according to the present embodiment, for example, in the structure shown in FIG. 7 described above, instead of the CoPt film 82, a laminated structure of a CoFe film and an FeMn film which is an antiferromagnetic film Is preferably used as the twist generation layer 30. In this case, after setting the magnetization direction of the pinned layer 10, the magnetization direction of the twist generation layer 30 is set. Specifically, an annealing process is performed in a magnetic field in order to set the magnetization direction of the pinned layer 10. The annealing conditions are, for example, temperature: 275 ° C., applied magnetic field: 1 T, and processing time: 2 hours. The direction of the applied magnetic field is set in a direction parallel to the easy axis direction of the free layer 20, and the

CoFe films

65 and 67 are magnetized in this direction. Furthermore, in order to set the magnetization direction of the twist generation layer 30, an annealing process is performed in a magnetic field. At this time, the temperature is lowered to 150 ° C., for example, and the direction of the applied magnetic field is changed to a direction perpendicular to the easy axis direction of the free layer 20. Thereby, the CoFe film and the FeMn film are magnetized in the direction perpendicular to the easy axis direction of the free layer 20.

4). Circuit Configuration of MRAM FIG. 10 schematically shows a configuration of the MRAM 90 according to the present embodiment. The MRAM 90 includes a plurality of memory cells MC arranged in an array. Each memory cell MC has the magnetoresistive element 1 and the selection transistor 2 described above. The gate of the selection transistor 2 is connected to the word line WL. The first terminal 51 of the magnetoresistive element 1 is connected to the first bit line BL1. The second terminal 52 of the magnetoresistive element 1 is connected to one of the source / drain of the selection transistor 2. The other of the source / drain of the selection transistor 2 is connected to the second bit line BL2.

The word line WL is connected to the word control circuit 91. The first bit line BL1 is connected to the bit control circuit 92. The second bit line BL2 is connected to the bit termination circuit 93. The first bit line BL1 and the second bit line BL2 intersect with the word line WL. The bit control circuit 92 is connected to the sense amplifier 94.

The data write operation to the target memory cell MC is as follows. The word control circuit 91 selects the word line WL connected to the target memory cell MC, and applies a predetermined ON voltage to the selected word line WL. As a result, the select transistor 2 connected to the selected word line WL is turned on. The bit control circuit 92 selects the first bit line BL1 connected to the target memory cell MC, and the bit termination circuit 93 selects the second bit line BL2 connected to the target memory cell MC. The bit control circuit 92 and the bit termination circuit 93 give a predetermined potential difference between the selected first bit line BL1 and the selected second bit line BL2. As a result, a write current flows between the selected first bit line BL1 and the selected second bit line BL2 through the magnetoresistive element 1 of the target memory cell MC. The magnitude of the write current is, for example, about 500 μA. Since a write current flows between the first terminal 51 and the second terminal 52 of the magnetoresistive element 1, the magnetization direction of the free layer 20 can be reversed by spin transfer. The direction of the write current flowing through the magnetoresistive element 1 can be controlled by adjusting the potential difference applied to the selected first bit line BL1 and the selected second bit line BL2. That is, desired data can be written into the target memory cell MC.

The data read operation from the target memory cell MC is as follows. The word control circuit 91 selects the word line WL connected to the target memory cell MC, and applies a predetermined ON voltage to the selected word line WL. As a result, the select transistor 2 connected to the selected word line WL is turned on. The bit termination circuit 93 sets the second bit line BL2 to the ground level. The bit control circuit 92 selects the first bit line BL1 connected to the target memory cell MC, and supplies a read current of about 20 μA to the selected first bit line BL1. The read current flows from the selected first bit line BL1 to the bit termination circuit 93 through the target memory cell MC and the selected second bit line BL2. At this time, the bit control circuit 92 outputs the sense voltage Vs determined from the read current and the resistance value (recording data) of the magnetoresistive element 1 of the target memory cell MC. It is assumed that the sense voltages Vs when the recording data of the target memory cell MC are “0” and “1” are Vs (0) and Vs (1), respectively. The reference voltage Vref is set between the sense voltages Vs (0) and Vs (1). The sense amplifier 94 can determine the recording data of the target memory cell MC by comparing the sense voltage Vs with the reference voltage Vref.

The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

This application claims priority based on Japanese Patent Application No. 2008-097049 filed on Apr. 3, 2008, the entire disclosure of which is incorporated herein.

Claims

A magnetoresistive storage device comprising a plurality of magnetoresistive elements,
Each of the plurality of magnetoresistive elements is
A first magnetic layer whose magnetization direction is fixed in the first direction;
A second magnetic body connected to the first magnetic layer via the first nonmagnetic layer and having a first surface in contact with the first nonmagnetic layer and a second surface opposite to the first surface Layers,
A third magnetic layer formed on the second surface side of the second magnetic layer and magnetically coupled to the second magnetic layer;
The magnetization direction of the third magnetic layer is fixed in a direction different from the first direction,
The magnetization direction of the second magnetic layer is a second direction that is neither parallel nor anti-parallel to the first direction on the second surface, and from the second direction as approaching the first surface from the second surface. A magnetoresistive memory device that transitions in a direction parallel or antiparallel to the first direction.
The magnetoresistive storage device according to claim 1,
The magnetization direction of the third magnetic layer is fixed in a direction orthogonal to the first direction,
The magnetization direction of the second magnetic layer is perpendicular to the first direction on the second surface. Magnetoresistive memory device.
The magnetoresistive storage device according to claim 1 or 2,
The magnetization easy axis direction of the second magnetic layer is parallel to the first direction.
A magnetoresistive storage device according to claim 3,
The second magnetic layer is formed of a perpendicular magnetization film whose easy axis direction is perpendicular to the film surface,
The magnetization direction of the first magnetic layer is fixed in a direction perpendicular to the film surface,
The magnetoresistive memory device, wherein the magnetization direction of the third magnetic layer is fixed in the in-plane direction.
A magnetoresistive storage device according to claim 3,
The second magnetic layer is formed of an in-plane magnetization film in which the easy axis direction is an in-plane direction,
The magnetization direction of the first magnetic layer is fixed in the in-plane direction,
The magnetoresistive memory device, wherein the magnetization direction of the third magnetic layer is fixed in a direction perpendicular to the film surface.
A magnetoresistive storage device according to claim 3,
The second magnetic layer is formed of an in-plane magnetization film in which the easy axis direction is an in-plane direction,
The magnetization direction of the first magnetic layer is fixed in the first direction in the plane,
The magnetoresistive memory device, wherein the magnetization direction of the third magnetic layer is fixed in a third direction in a plane different from the first direction.
The magnetoresistive storage device according to claim 1 or 2,
The second magnetic layer is
A first magnetic film whose easy axis direction is parallel to the first direction and is in contact with the first surface;
A magnetoresistive storage device comprising: a second magnetic film having an easy axis direction perpendicular to the first direction and in contact with the second surface.
A magnetoresistive memory device according to any one of claims 1 to 7,
The third magnetic layer is connected to the second surface of the second magnetic layer through a second nonmagnetic layer. A magnetoresistive storage device.
A magnetoresistive memory device according to any one of claims 1 to 7,
The third magnetic material layer is in contact with the second surface of the second magnetic material layer.
A magnetoresistive storage device according to any one of claims 1 to 9,
Each of the magnetoresistive elements further includes:
A first terminal electrically connected to the first magnetic layer;
A second terminal electrically connected to the third magnetic layer,
A magnetoresistive storage device in which a current flows between the first terminal and the second terminal during data writing.