WO2010071174A1

WO2010071174A1 - Method for initializing magnetoresistive element, and magnetoresistive element

Info

Publication number: WO2010071174A1
Application number: PCT/JP2009/071042
Authority: WO
Inventors: 哲広鈴木; 則和大嶋; 聖万永原; 俊輔深見; 延行石綿
Original assignee: 日本電気株式会社
Priority date: 2008-12-19
Filing date: 2009-12-17
Publication date: 2010-06-24
Also published as: JPWO2010071174A1; JP5472821B2

Abstract

Disclosed is a method for initializing a magnetoresistive element which comprises a magnetization recording layer that is a ferromagnetic layer. The magnetization recording layer comprises a magnetization reversal region having a reversible magnetization, a first magnetization fixed region connected to a first boundary of the magnetization reversal region, and a second magnetization fixed region connected to a second boundary of the magnetization reversal region. The method for initializing a magnetoresistive element comprises: a step wherein the magnetizations of the magnetization reversal region, the first magnetization fixed region and the second magnetization fixed region are directed to a first direction; and a step wherein a first magnetic field having a component in a second direction that is opposite to the first direction is applied to the magnetization recording layer, while passing a current between the first magnetization fixed region and the second magnetization fixed region through the magnetization reversal region.

Description

Method for initializing magnetoresistive element and magnetoresistive element

The present invention relates to a magnetoresistive element and an initialization method thereof, and more particularly, to an initialization method of a magnetoresistive element configured to reverse magnetization by domain wall motion.

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. One of the two ferromagnetic layers is a magnetization fixed layer (pinned layer) whose magnetization direction is fixed, and the other one is a magnetization free layer (free layer) whose magnetization direction can be reversed. ).

The resistance value (R + ΔR) of the MTJ when the magnetization directions of the pinned layer and the free layer are “anti-parallel” is larger than the resistance value (R) when they are “parallel” due to the magnetoresistance effect. It is 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. For example, the antiparallel state is associated with data “1”, and the parallel state is associated with data “0”. Data is written to the memory cell by reversing the magnetization direction of the magnetization free layer.

The most traditional method of writing data to the MRAM is a method of reversing the magnetization of the magnetization free layer by a current magnetic field. However, in this writing method, the reversal magnetic field necessary for reversing the magnetization of the magnetization free layer becomes substantially inversely proportional to the memory cell size. That is, as the memory cell is miniaturized, the write current increases. This is not preferable in providing a highly integrated MRAM.

A “spin transfer method” has been proposed as a write method that can suppress an increase in write current accompanying miniaturization (for example, Japanese Patent Laid-Open No. 2005-93488). In the spin injection method, a spin-polarized current is injected into a ferromagnetic conductor, and the magnetization is reversed by a direct interaction between the spin of conduction electrons carrying the current and the magnetic moment of the conductor. This phenomenon is referred to as spin transfer magnetization switching. Writing by the spin injection method is suitable for realizing a highly integrated MRAM because the write current decreases as the size of the magnetization free layer decreases.

US Pat. No. 6,834,005 discloses a magnetic shift register utilizing spin injection. This magnetic shift register stores information using a domain wall in a magnetic material. In a magnetic material divided into a number of regions (magnetic domains) by constriction or the like, 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.

“Domain wall motion MRAM” using such domain wall motion by spin injection is described in Japanese Patent Laid-Open No. 2005-191032 and WO 2005/069368.

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 shows the structure of the magnetic recording layer. In FIG. 1, the magnetization recording layer 100 has a linear shape. Specifically, 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 units formed adjacent to the constriction 104. 101, 102. The pair of magnetization fixed

portions

101 and 102 are provided with fixed magnetizations in opposite directions. The magnetization of these magnetization fixed portions is fixed by an exchange bias magnetic field formed by laminating an antiferromagnetic layer, for example. The MRAM further includes a pair of

write terminals

105 and 106 that are electrically connected to the pair of magnetization fixed

portions

101 and 102. The

write terminals

105 and 106 allow a write current to pass through the junction portion 103, the pair of constricted portions 104, and the pair of magnetization fixed

portions

101 and 102 of the magnetization recording layer 100. The constricted portion 104 serves as a pin potential with respect to the domain wall, and information is held depending on which of the constricted portions the domain wall is present on the left or right side or the magnetization direction of the joint portion 103. The direction of the domain wall movement is controlled by the direction of the write current.

In the MRAM described in WO2005 / 069368, a step is used as a means for forming a pin potential. FIG. 2 shows the structure of the magnetic recording layer. In FIG. 2, the magnetic recording layer 100 is composed of three regions having different thicknesses. Specifically, the magnetization recording layer 100 is composed of the thickest first magnetization fixed portion 101, the second thickest second magnetization fixed portion 102, and the thinnest bonding portion 103 disposed therebetween. In FIG. 2, the step at the boundary between the junction 103, the magnetization fixed unit 101, and the magnetization fixed unit 102 functions as a pin potential. Therefore, the domain wall 112 moves between the two steps by applying a current. In WO2005 / 069368, a magnetic semiconductor having anisotropy perpendicular to the film surface is used as the magnetization recording layer, and the current for domain wall movement is as small as 0.35 mA. The junction 103 is actually provided with a tunnel insulating layer and a magnetization fixed layer, which are not shown in FIG.

In the domain wall motion type MRAM, the magnetization directions of the two magnetization fixed portions of the magnetization recording layer need to be antiparallel. For example, a process of making the magnetization directions of the two magnetization fixed portions antiparallel by applying an external magnetic field having an appropriate magnitude is hereinafter referred to as “initialization”. Japanese Patent Laid-Open No. 2005-191032 does not mention a method of making the magnetization directions of the two magnetization fixed portions antiparallel.

WO 2005/069368 discloses that initialization is performed by an external magnetic field after film formation by utilizing the coercive force difference between the first magnetization fixed part 101 and the second magnetization fixed part 102. Specifically, WO2005 / 069368 discloses that a coercive force difference is provided by making the thicknesses of the first magnetization fixed portion 101 and the second magnetization fixed portion 102 different. Since the magnetization is less likely to be reversed as the magnetic layer is thicker, a magnetic field is applied so that the magnetization of the second magnetization fixed unit 102 and the junction 103 is reversed and the magnetization of the first magnetization fixed unit 101 is not reversed. Thus, the domain wall can be introduced at the boundary between the first magnetization fixed portion 101 and the joint portion 103.

JP 2005-93488 A US Pat. No. 6,834,005 Japanese Patent Laid-Open No. 2005-191032 WO2005 / 069368

However, if a structure in which the thicknesses of the first magnetization pinned portion 101 and the second magnetization pinned portion 102 are made different as in WO 2005/069368, the number of steps increases and the cost increases. . That is, in order to make the thicknesses of the first magnetization fixed portion 101 and the second magnetization fixed portion 102 different, it is necessary to form two steps having different sizes. In order to form two different types of steps, it is necessary to repeat the exposure process twice. This means that the number of steps increases.

Further, the difference in thickness between the first magnetization pinned portion 101 and the second magnetization pinned portion 102 is magnetically asymmetric, that is, the first magnetization pinned portion 101 and the second magnetization pinned portion 102 are different from each other. It means that the depth of pin potential is different. This means that the current value when the domain wall moves to the left and right may be different values.

Accordingly, an object of the present invention is to provide a magnetically symmetric element structure having a small number of steps and a method for introducing and initializing a domain wall into the structure in a current-driven domain wall motion type magnetoresistive element. is there.

In one aspect of the present invention, a magnetization recording layer that is a ferromagnetic layer is provided, and the magnetization recording layer has a magnetization reversal region having reversible magnetization and a first magnetization connected to a first boundary of the magnetization reversal region. A method of initializing a magnetoresistive element having a fixed region and a second magnetization fixed region connected to a second boundary of the magnetization switching region is provided. The initialization method includes a step of directing magnetization of the magnetization switching region, the first magnetization fixed region, and the second magnetization fixed region in the first direction, and between the first magnetization fixed region and the second magnetization fixed region. Applying a first magnetic field having a component in a second direction opposite to the first direction to the magnetization recording layer while passing a current through the magnetization switching region.

According to the present invention, in a current-driven domain wall motion type magnetoresistive element, there are provided an element structure in which the number of steps is small and a domain wall motion defect does not occur, and a method for introducing and initializing a domain wall into the structure. it can.

FIG. 1 is a plan view showing a configuration of a magnetization recording layer of a conventional magnetoresistive element. FIG. 2 is a perspective view showing another configuration of the magnetization recording layer of the conventional magnetoresistive element. FIG. 3 is a perspective view showing the configuration of the magnetoresistive element according to the embodiment of the present invention. FIG. 4 is a perspective view showing a configuration of a magnetoresistive element according to another embodiment of the present invention. FIG. 5 is a perspective view showing a configuration of a magnetoresistive element according to still another embodiment of the present invention. FIG. 6A is a conceptual diagram illustrating a magnetoresistive element initialization method according to an embodiment of the present invention. FIG. 6B is a conceptual diagram illustrating a magnetoresistive element initialization method according to an embodiment of the present invention. FIG. 6C is a conceptual diagram showing a method of initializing a magnetoresistive element in one embodiment of the present invention. FIG. 6D is a conceptual diagram showing a magnetoresistive element initialization method in one embodiment of the present invention. FIG. 7 is a phase diagram showing the state of the magnetoresistive element after initialization by the magnetoresistive element initialization method of one embodiment of the present invention. FIG. 8 is a perspective view showing the configuration of a magnetoresistive element according to still another embodiment of the present invention. FIG. 9 is a conceptual diagram showing a data writing method of the magnetoresistive element in one embodiment of the present invention. FIG. 10 is a circuit diagram showing an example of the configuration of an MRAM in which magnetoresistive elements according to an embodiment of the present invention are integrated.

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. The present invention can be applied to both the case where the magnetization recording layer of the magnetoresistive element has magnetization in the in-plane direction and the case where the magnetization has magnetization in the vertical direction. A case where the recording layer is used will be described. In order to improve the performance of the magnetoresistive element, it is preferable to use a magnetization recording layer having magnetization in the perpendicular direction.

(Structure of magnetoresistive element)

FIG. 3 is a perspective view showing the structure of the magnetoresistive element 1 according to the embodiment of the present invention. As shown in FIG. 3, the magnetoresistive element 1 includes a magnetization recording layer 10, a magnetization fixed layer 30, and a tunnel barrier layer 32 provided therebetween. The tunnel barrier layer 32 is a nonmagnetic insulating layer, and is composed of a thin insulating film such as an Al ₂ O ₃ film or an MgO film. The tunnel barrier layer 32 is sandwiched between the magnetization recording layer 10 and the magnetization fixed layer 30, and a magnetic tunnel junction (MTJ) is formed by the magnetization recording layer 10, the tunnel barrier layer 32, and the magnetization fixed layer 30.

The magnetization recording layer 10 is a ferromagnetic layer having anisotropy (perpendicular magnetic anisotropy) in a direction perpendicular to the substrate surface. The magnetization recording layer 10 includes at least one material of Fe, Co, and Ni. Further, the perpendicular magnetic anisotropy can be stabilized when the magnetic recording layer 10 contains Pt or Pd. In addition to this, the magnetic recording layer 10 has B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, By adding Hf, Ta, W, Re, Os, Ir, Au, and Sm, adjustment can be made so that desired magnetic properties are expressed. Specifically, the material of the magnetic recording layer 10 includes Co, Co—Pt, Co—Pd, Co—Cr, Co—Pt—Cr, Co—Cr—Ta, Co—Cr—B, and 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 and the like can be mentioned. In addition, a laminated body in which a layer containing at least one material of Fe, Co, and Ni is laminated with different layers can be used as the magnetization recording layer 10 that exhibits magnetic anisotropy in the perpendicular direction. . Specifically, a laminate of Co film and Pd film, a laminate of Co film and Pt film, a laminate of Co film and Ni film, a laminate of Fe film and Au film, etc. can be used as the magnetization recording layer 10. is there.

The magnetization fixed layer 30 is composed of a ferromagnetic layer having a fixed magnetization or a laminated body of a ferromagnetic layer and a nonmagnetic layer. The magnetization fixed layer 30 has perpendicular magnetic anisotropy like the magnetization recording layer 10. In addition, the magnetization fixed layer 30 is configured such that the magnetization direction thereof is not changed by the write and read operations. Therefore, the magnetization fixed layer 30 is configured so that the magnetic anisotropy is larger than that of the magnetization recording layer 10. This can be realized by appropriately selecting materials and compositions of the magnetization recording layer 10 and the magnetization fixed layer 30. The magnetization direction of the magnetization fixed layer 30 is fixed by stacking an antiferromagnetic layer (not shown) on the surface of the magnetization fixed layer 30 opposite to the tunnel barrier layer and pinning the magnetization. Is also feasible. The magnetization fixed layer 30 can also be configured using the same material as the magnetization recording layer 10.

In the present embodiment, as shown in FIG. 3, the magnetization fixed layer 30 is composed of a laminated body including a ferromagnetic layer 34, a nonmagnetic layer 31, and a ferromagnetic layer 33. Here, the magnetization fixed layer 30 is configured such that the

ferromagnetic layers

33 and 34 are antiferromagnetically coupled and the magnetizations of the

ferromagnetic layers

33 and 34 are antiparallel to each other. For example, by using a Ru film or a Cu film as the nonmagnetic layer 31 and appropriately selecting the film thickness, the magnetizations of the two

ferromagnetic layers

33 and 34 can be coupled antiparallel to each other. In this case, if the magnetizations of the two

ferromagnetic layers

34 and 33 are substantially equal, the leakage magnetic field from the magnetization fixed layer 30 can be suppressed.

Further, a material having a large TMR effect such as CoFe or CoFeB may be used for a part of the magnetization recording layer 10 and the magnetization fixed layer 30, particularly a part in contact with the tunnel barrier layer.

Further, a ferromagnetic layer is disposed between the tunnel barrier layer 32 and the magnetic recording layer 10 via a nonmagnetic metal layer, and data is read using the MTJ formed from the ferromagnetic layer and the magnetization fixed layer 30. It can also be taken. In this case, the magnetization direction of the ferromagnetic layer is determined by the leakage magnetic field from the magnetization recording layer, and the magnetization state of the magnetization recording layer is indirectly read out. In this configuration, a material having in-plane anisotropy may be used as the ferromagnetic layer and the magnetization fixed layer.

The magnetoresistive element 1 of the present embodiment is configured to support a write operation by a domain wall motion method. More specifically, the magnetization recording layer 10 of the magnetoresistive element 1 has a first magnetization fixed region 11 a, a second magnetization fixed region 11 b, and a magnetization switching region 13. The magnetization switching region 13 is formed so as to face the magnetization fixed layer 30. In other words, a part of the magnetization switching region 13 of the magnetization recording layer 10 is connected to the magnetization fixed layer 30 via the tunnel barrier layer 32.

By the initialization operation described later, the magnetizations of the first magnetization fixed region 11a and the second magnetization fixed region 11b are fixed in antiparallel directions. Note that “magnetization is fixed” means that the magnetization direction does not change before and after the write operation. That is, 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. In the initialization operation, the magnetization of the second magnetization fixed region 11b is reversed by an external magnetic field or Joule heat as will be described later.

On the other hand, the magnetization direction of the magnetization switching region 13 is reversible and is the + Z direction or the −Z direction. That is, the magnetization of the magnetization switching region 13 is allowed to be parallel or antiparallel to the magnetization of the ferromagnetic layer 34 of the magnetization fixed layer 30. As shown in FIG. 3, when the magnetization direction of the magnetization switching region 13 is the + Z direction, the first magnetization fixed region 11b and the magnetization switching region 13 form one magnetic domain, and the first The magnetization fixed region 11a forms another magnetic domain. That is, a domain wall 12 is formed between the first magnetization fixed region 11 a and the magnetization switching region 13. On the other hand, when the magnetization direction of the magnetization switching region 13 is the -Z direction, the first magnetization fixed region 11a and the magnetization switching region 13 form one magnetic domain, and the second magnetization fixed region 11b forms another magnetic domain. . That is, a domain wall is formed between the second magnetization fixed region 11 b and the magnetization switching region 13.

The first magnetization fixed region 11 a and the second magnetization fixed region 11 b are formed thicker than the magnetization switching region 13. Such a structure can be obtained by etching only the portion corresponding to the magnetization switching region 13 after forming the magnetic recording layer. The reason for making the film thicknesses different is that a pin potential of the domain wall is formed at the boundary between the first and second magnetization fixed

regions

11 a and 11 b and the magnetization switching region 13. Since the domain wall energy is proportional to the film thickness, the domain wall generated in the first and second magnetization fixed

regions

11a and 11b easily moves to the magnetization switching region 13, whereas the domain wall generated in the magnetization switching region 13 is the first. It is difficult to move to the first and second magnetization fixed

regions

11a and 11b. The domain wall is pinned to the boundary between the magnetization switching region 13 and the first and second magnetization fixed

regions

11a and 11b by the static magnetic field from the thick portions of the first and second magnetization fixed

regions

11a and 11b. In addition, by changing the configuration in the thickness direction of the magnetization recording layer 10 in the middle, the portions that remain in common in the magnetization switching region 13 and the first and second magnetization fixed

regions

11a and 11b during etching, The film configuration of the portion remaining only in the second magnetization fixed

regions

11a and 11b may be changed. For example, a Co / Ni laminated film, which is a highly polarized material that easily causes domain wall movement due to current, can be used for the former, and a Co / Pt laminated film having a large magnetic anisotropy can be used for the latter. The latter can be replaced with an antiferromagnetic material such as PtMn, a nonmagnetic metal such as Ru and a laminated structure such as a Co / Pt laminated film, or a magnetic material having in-plane anisotropy such as NiFe. .

Current supply terminals

14a and 14b for applying a write current are connected to the first magnetization fixed region 11a and the second magnetization fixed region 11b, respectively. A domain wall is introduced between the

current supply terminals

14a and 14b by the initialization operation described later, and is driven in accordance with the write current. The portion where the tunnel barrier layer 32 and the magnetization fixed layer 30 are stacked to form the MTJ must include the portion between the

current supply terminals

14 a and 14 b in the magnetization recording layer 10. This is because the direction of magnetization during this time changes as a result of the write operation. Note that the

current supply terminals

14 a and 14 b may be located either above or below the magnetization recording layer 10.

It should be noted in the structure of the magnetization recording layer 10 in FIG. 3 that the first magnetization fixed region 11a and the second magnetization fixed region 11b are magnetically symmetric (except for manufacturing errors), that is, the first magnetization The pin potential depth of the fixed region 11a and the second magnetization fixed region 11b is the same (except for manufacturing errors). This is because the pin potential is the same when the domain wall 12 is at the boundary between the magnetization switching region 13 and the first magnetization fixed region 11a and when the domain wall 12 is at the boundary between the magnetization switching region 13 and the second magnetization fixed region 11b. In operation, this means that the domain wall is driven with substantially equal current. This is desirable not only from the viewpoint of circuit design but also from the viewpoint of pin potential design. In other words, the design of the magnetization fixed region, that is, the pin potential must be designed in consideration of thermal disturbance. However, if the magnetization fixed region is asymmetric, at least one of them has an excessive pin potential. This can lead to current imbalance and increase.

As long as the condition that the first magnetization fixed region 11a and the second magnetization fixed region 11b are magnetically symmetric (excluding manufacturing errors) is satisfied, various other structures are employed as the magnetoresistive element of the present invention. Can be done. 4 and 5 are perspective views showing other structures of the magnetic recording layer 10. 4 and 5, the MTJ portion is not shown, and only the magnetization recording layer 10 is shown.

In the structure of FIG. 4, the first magnetization fixed region 11 a and the second magnetization fixed region 11 b have a wider shape than the magnetization switching region 13. This is because a domain wall pin potential is formed at the boundary between the first and second magnetization fixed

regions

11 a and 11 b and the magnetization switching region 13. Since the energy of the domain wall is substantially proportional to the width of the magnetization recording layer 10, the domain wall generated in the first and second magnetization fixed

regions

11 a and 11 b easily moves to the magnetization switching region 13, whereas in the magnetization switching region 13 The generated domain wall hardly moves to the first and second magnetization fixed

regions

11a and 11b. Further, the domain wall is pinned to the boundary between the magnetization switching region 13 and the first and second magnetization fixed

regions

11a and 11b by a static magnetic field from a portion of the first and second magnetization fixed

regions

11a and 11b protruding from the magnetization switching region 13. Stopped.

On the other hand, in the structure of FIG. 5, the first magnetization fixed region 11 a and the second magnetization fixed region 11 b are wider and thicker than the magnetization switching region 13. This is because a domain wall pin potential is formed at the boundary between the first and second magnetization fixed

regions

11 a and 11 b and the magnetization switching region 13. Since the domain wall energy is substantially proportional to the width and thickness of the magnetization recording layer 10, the domain wall generated in the first and second magnetization fixed

regions

11 a and 11 b easily moves to the magnetization switching region 13, whereas the magnetization switching is performed. The domain wall generated in the region 13 is difficult to move to the first and second magnetization fixed

regions

11a and 11b. In addition, the domain walls of the first and second magnetization fixed

regions

11a and 11b that protrude from the magnetization reversal region 13 and the static magnetic field from the thick portion cause the domain wall to become the magnetization reversal region 13 and the first and second magnetization fixed regions 11a, Pinned to the boundary of 11b.

(Initialization of magnetization fixed region)

As described above, in the present embodiment, the first magnetization fixed region 11a and the second magnetization fixed region 11b are magnetically symmetric (except for manufacturing errors), that is, the first magnetization fixed region 11a and the second magnetization fixed region 11b. The pinned potential depth of the magnetization fixed region 11b is the same (except for manufacturing errors). This is suitable as a characteristic of the magnetoresistive element 1, but is initialized by application of an external magnetic field, that is, the first magnetization fixed region 11a and the second magnetization fixed region 11b are magnetized antiparallel to each other, and the domain wall is obtained. There is also the problem of making it difficult to introduce. That is, simply applying an external magnetic field causes the first magnetization fixed region 11a and the second magnetization fixed region 11b to face in the same direction and cannot be initialized.

Therefore, in the present embodiment, the magnetoresistive element 1 is initialized using a special initialization method. Hereinafter, the initialization process of the magnetoresistive element 1 in the present embodiment, that is, the process of magnetizing the first magnetization fixed region 11a and the second magnetization fixed region 11b antiparallel to each other and introducing the domain wall will be described with reference to FIGS. 6A to 6D. Will be described. 6A to 6D, the configuration of FIG. 3 is assumed, but the initialization method and the principle thereof are common to the elements of FIGS. Further, it is assumed that the coercive force of the magnetization fixed layer 30 is sufficiently larger than the coercivity of the magnetization recording layer 10, and the magnetization direction of the magnetization fixed layer 30 is not changed in the initialization process, and the illustration of the magnetization fixed layer 30 is omitted. Yes.

As shown in FIG. 6A, when a large magnetic field is first applied in the −Z direction, all the magnetizations are directed in the −Z direction (step S1). Next, a current is applied between the current supply terminals while applying a magnetic field in the + Z direction. At this time, if the magnetic field and the current are larger than a certain value, only the magnetization switching region 13 is reversed in magnetization as shown in FIG. 6B, and the boundary between the magnetization switching region 13 and the first and second magnetization fixed regions is obtained. Two domain walls are introduced (step S2a). This is because the cross-sectional area of the magnetization switching region 13 is smaller than the cross-sectional areas of the first and second magnetization fixed regions, and the current density is large. That is, since the temperature rise due to Joule heat in the magnetization switching region 13 is large, the saturation magnetization is preferentially lowered, and only the magnetization switching region 13 is switched. Further, when the magnetic field and current are large, as shown in FIG. 6C, the domain wall 12b depins in the direction of the second magnetization fixed region, and at least a part of the second magnetization fixed region is reversed (step S2b). . This is because the domain wall 12b is pushed in the direction of electron movement by the effect of the spin torque. At this time, whether the domain wall 12b that has entered the second magnetization fixed region 11b stays in the second magnetization fixed region 11b or whether the domain wall falls out of the boundary and the entire second magnetization fixed region 11b is inverted is mainly at this time. Depends on the applied magnetic field. As shown in FIG. 6D, the magnetization reversal of the entire second magnetization fixed region 11b can be more reliably performed by applying a magnetic field in the + Z direction after stopping the current application (step S3). In addition, the magnetic field at this time needs to be more than the propagation magnetic field of the domain wall in the 2nd magnetization fixed area | region 11b.

FIG. 7 shows a phase diagram of the initial magnetization state when the applied current and the applied magnetic field in steps S2a and S2b described above are used as parameters. Here, in step S1, the entire magnetic recording layer 10 is saturated by applying a sufficiently large magnetic field, and step S3 is omitted. When both the magnetic field and the current are small, the magnetization of any region is not reversed, and the magnetization state does not change from step S1 (region A in FIG. 7). When the magnetic field and current become a certain magnitude, a magnetization state in which only the magnetization switching region 13 is reversed is obtained (region B in FIG. 7). When the magnetic field and current are further increased, a magnetization state in which only one magnetization fixed region is reversed in addition to the magnetization reversal region 13 is obtained (region C in FIG. 7). Which magnetization fixed region is inverted can be controlled by the current direction, and the magnetization fixed region on the side where electrons enter from the magnetization inverted region is inverted by the spin torque effect. The state of region C in FIG. 7 is the magnetization state required for the domain wall motion memory. When the magnetic field and current are excessively large, the magnetization of all the regions is reversed (region D in FIG. 7). This is because the influence of the magnetic field and Joule heat becomes relatively larger than the effect of the spin torque.

In order to widen the operation margin of the initialization method of the present invention, it is effective to make one of the first magnetization fixed region 11a and the second magnetization fixed region 11b difficult to reverse magnetization. Thereby, the vertical boundary between the region C and the region D in FIG. 7 can be shifted to the right.

As a method for realizing this without making the magnetic characteristics of the first magnetization fixed region 11a and the second magnetization fixed region 11b asymmetrical, as shown in FIG. 8, the first magnetization fixed region 11a and the second magnetization fixed region 11b. There is a method of laminating a nonmagnetic metal layer 15a on one side of the region 11b. In FIG. 8, the nonmagnetic metal layer 15a is laminated only on the first magnetization fixed region 11a. The nonmagnetic metal layer 15a makes the current density in the first magnetization fixed region 11a smaller than the current density in the second magnetization fixed region 11b in the current application in the initialization process of the magnetoresistive element 1 described above. Accordingly, if the current direction in steps S2a and S2b of FIGS. 6B and 6C is selected so as to invert the second magnetization fixed region 11b (that is, the first magnetization is passed from the second magnetization fixed region 11b through the magnetization switching region 13). If a current is passed through the fixed region 11a), the initialization margin can be increased. In FIG. 8, the method of laminating the nonmagnetic metal layer 15a is applied to the magnetic recording layer 10 having the structure of FIG. 3, but the method is applied to the magnetic recording layer 10 having the structure of FIGS. Applicability will be apparent to those skilled in the art.

It goes without saying that a desired initial state can be obtained even if the magnetic field directions are all set in opposite directions in the initialization operation described above. The magnetic field application direction is not limited to the Z direction, and may have a certain amount of X or Y component.

The initialization method of the present invention can be implemented in an inspection at the end of a wafer process or an inspection after assembling a package. Further, the steps shown in FIGS. 6A to 6D may be performed in different work processes. For example, step S1 can be performed during the wafer process, and steps S2a, S2b, and S3 can be performed after the assembly of the package.

(Write and read operations)

Next, data writing to the magnetoresistive element 1 will be described.

FIG. 9 shows the data writing principle for the structure shown in FIG. Data writing is performed by a domain wall motion method using spin injection. The write current flows in a plane in the magnetization recording layer 10, not in the direction penetrating the MTJ. The write current is supplied to the magnetic recording layer 10 from the

current supply terminals

14a and 14b. In the present embodiment, the state in which the magnetization direction of the ferromagnetic layer 34 of the magnetization fixed layer 30 and the magnetization direction of the magnetization switching region 13 are parallel is associated with data “0”. In the data “0” state, the magnetization direction of the magnetization switching region 13 is the −Z direction, and the domain wall 12 exists at the boundary between the magnetization switching region 13 and the second magnetization fixed region 11 b. On the other hand, the state where the magnetization directions of the magnetization switching region 13 and the ferromagnetic layer 34 are antiparallel is associated with the data “1”. In the data “1” state, the magnetization direction of the magnetization switching region 13 is the + Z direction, and the domain wall 12 exists at the boundary between the magnetization switching region 13 and the first magnetization fixed region 11 a.

When data “1” is written, the write current IW1 flows from the first magnetization fixed region 11a through the magnetization switching region 13 to the second magnetization fixed region 11b. In this case, spin electrons are injected into the magnetization switching region 13 from the second magnetization fixed region 11b. The spin of the injected electrons drives the domain wall at the boundary between the magnetization switching region 13 and the second magnetization fixed region 11b in the direction of the first magnetization fixed region 11a. As a result, the magnetization direction of the magnetization switching region 13 is switched to the + Z direction. That is, due to the spin transfer effect, the magnetization of the magnetization switching region 13 is reversed and the magnetization direction is changed to the + Z direction.

On the other hand, when data “0” is written, the write current IW2 flows from the second magnetization fixed region 11b through the magnetization switching region 13 to the first magnetization fixed region 11a. In this case, spin electrons are injected into the magnetization switching region 13 from the first magnetization fixed region 11a. As a result, the magnetization of the magnetization switching region 13 is reversed and the magnetization direction is changed to the −Z direction. In this way, the magnetization direction of the magnetization switching region 13 is switched by the write currents IW1 and IW2 that flow in the magnetization recording layer 10 in a plane. The first magnetization fixed region 11a and the second magnetization fixed region 11b serve as a supply source of electrons having different spins.

Further, reading of data from the magnetoresistive element 1 is performed according to the following procedure. At the time of data reading, a read current is supplied so as to flow between the magnetization fixed layer 30 and the magnetization switching region 13. For example, the read current flows from one of the magnetization fixed

regions

11 a and 11 b to the ferromagnetic layer 34 of the magnetization fixed layer 30 via the magnetization switching region 13 and the tunnel barrier layer 32. Alternatively, the read current flows from the ferromagnetic layer 34 of the magnetization fixed layer 30 via the tunnel barrier layer 32 and the magnetization switching region 13 to either of the magnetization fixed

regions

11 a and 11 b. Based on the read current or read potential, the resistance value of the magnetoresistive element is detected, and the magnetization direction of the magnetization switching region 13 is sensed.

(Integration into MRAM)

The magnetoresistive element 1 described above can be used by being integrated in an MRAM. FIG. 10 is a conceptual diagram showing the configuration of such an MRAM. The MRAM has a memory cell array 60 in which a plurality of memory cells 61 are arranged in a matrix. In each memory cell 61, a magnetoresistive element 1 and two select transistors TR1 and TR2 are integrated. One of the source / drain of the selection transistor TR1 is connected to the current supply terminal 14a connected to the first magnetization fixed region 11a, and the other is connected to the first bit line BL1. One of the source / drain of the selection transistor TR2 is connected to the current supply terminal 14b of the second magnetization fixed region 11b, and the other is connected to the second bit line BL2. The gates of the selection transistors TR1 and TR2 are connected to the word line WL. The magnetization fixed layer 30 of the magnetoresistive element 1 is connected to a ground line through wiring.

The word line WL is connected to the X selector 62. The X selector 62 selects a word line WL corresponding to a target memory cell 61 (hereinafter referred to as “selected memory cell”) as a selected word line in writing / reading data. The first bit line BL1 is connected to the Y-side current termination circuit 64, and the second bit line BL2 is connected to the Y selector 63. The Y selector 63 selects the second bit line BL2 connected to the selected memory cell as the selected second bit line. The Y-side current termination circuit 64 selects the first bit line BL1 connected to the selected memory cell as the selected first bit line.

The memory cell array 60 includes a reference cell 61r that is referred to when reading data, in addition to the memory cell 61 used for data recording. The structure of the reference cell 61r is the same as that of the memory cell 61. A first reference bit line BL1r and a second reference bit line BL2r are provided along the column of reference cells 61r.

The operation of the MRAM at the time of data writing is as follows: The Y-side current source circuit 65 supplies or draws a predetermined write current (IW1, IW2) to the selected second bit line. The Y-side power supply circuit 66 supplies a predetermined voltage to the Y-side current termination circuit 64 at the time of data writing. As a result, the write currents (IW1, IW2) flow into or out of the Y selector 63. These X selector 62, Y selector 63, Y side current termination circuit 64, Y side current source circuit 65, and Y side power supply circuit 66 are a write current supply circuit for supplying write currents IW 1 and IW 2 to the magnetoresistive element 1. Is configured.

On the other hand, the operation of the MRAM during data reading is as follows: the first bit line BL1 is set to “Open”. The read current load circuit 67 supplies a predetermined read current to the selected second bit line. The read current load circuit 67 supplies a predetermined current to the second reference bit line BL2r connected to the reference cell 61r corresponding to the selected word line. The sense amplifier 68 determines the data stored in the selected memory cell from the potential difference between the second reference bit line BL2r and the selected second bit line, and outputs the data.

Although various embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-324736 for which it applied on December 19, 2008, and takes in those the indications of all here.

Claims

A magnetization recording layer, which is a ferromagnetic layer, wherein the magnetization recording layer has a magnetization reversal region having reversible magnetization, a first magnetization fixed region connected to a first boundary of the magnetization reversal region, and the magnetization An initialization method for a magnetoresistive element having a second magnetization fixed region connected to a second boundary of an inversion region,

Directing the magnetizations of the magnetization switching region, the first magnetization fixed region, and the second magnetization fixed region in the first direction;

A first magnetic field having a component in a second direction opposite to the first direction is applied while applying a current so as to pass through the magnetization switching region between the first magnetization fixed region and the second magnetization fixed region. Step of applying to the magnetic recording layer

With

A method for initializing a magnetoresistive element.
An initialization method for a magnetoresistive element according to claim 1,

After applying the first magnetic field, applying a second magnetic field having a component in the second direction to the magnetization recording layer in a state where the application of the current is stopped

Further comprising

A method for initializing a magnetoresistive element.
An initialization method for a magnetoresistive element according to claim 1 or 2,

The current is passed from the second magnetization fixed region to the first magnetization fixed region through the magnetization switching region,

Magnetization of the second magnetization fixed region and the magnetization switching region is directed in the second direction.

A method for initializing a magnetoresistive element.
An initialization method for a magnetoresistive element according to claim 3,

A nonmagnetic metal layer is laminated on the first magnetization fixed region.

A method for initializing a magnetoresistive element.
An initialization method for a magnetoresistive element according to any one of claims 1 to 4,

The first magnetization fixed region and the second magnetization fixed region are magnetically symmetric.

A method for initializing a magnetoresistive element.
An initialization method for a magnetoresistive element according to claim 5,

The first magnetization fixed region and the second magnetization fixed region are thicker than the magnetization switching region.

A method for initializing a magnetoresistive element.
7. The method of initializing a magnetoresistive element according to claim 5, wherein a width of the first magnetization fixed region and a second magnetization fixed region is wider than a width of the magnetization switching region.

A method for initializing a magnetoresistive element.
A magnetic recording layer that is a ferromagnetic layer;

The magnetization recording layer is

A magnetization reversal region having reversible magnetization;

A first magnetization fixed region connected to a first boundary of the magnetization switching region and having magnetization fixed in a first direction;

A second magnetization fixed region connected to the second boundary of the magnetization switching region and having magnetization fixed in a second direction opposite to the first direction

And

The first magnetization fixed region and the second magnetization fixed region are magnetically symmetric.

Magnetoresistive element.
The magnetoresistive element according to claim 8,

The first magnetization fixed region and the second magnetization fixed region are thicker than the magnetization switching region.

Magnetoresistive element.
10. The magnetoresistive element according to claim 8, wherein a width of the first magnetization fixed region and a second magnetization fixed region is wider than a width of the magnetization switching region.

Magnetoresistive element.
The magnetoresistive element according to any one of claims 8 to 10,

A nonmagnetic metal layer is laminated on the first magnetization fixed region.

Magnetoresistive element.