WO2010013566A1 - Magnetoresistive element, magnetic random access memory, and initialization method thereof - Google Patents

Abstract

A magnetoresistive element includes a first ferromagnetic layer (10), a non-magnetic layer (20), and a second ferromagnetic layer (30).  The first ferromagnetic layer (10) having a prolonged shape in the longitudinal direction on a non-magnetic undercoat (50) includes magnetization fixing units (10a, 10b) at the both ends of the longitudinal direction and a magnetic wall moving portion (10c) between the magnetization fixing units (10a, 10b).  The non-magnetic layer (20) is arranged on the magnetic wall moving portion (10c).  The second ferromagnetic layer (30) is arranged on the non-magnetic layer (10) and magnetization thereof is fixed.  The second ferromagnetic layer (30) has a magnetic anisotropy in the film thickness direction.  The magnetization fixing units (10a, 10b) have a magnetic anisotropy in the in-plane direction.  The magnetic wall moving portion (10c) has a magnetic anisotropy in the film thickness direction.

Description

Magnetoresistive element, magnetic random access memory, and initialization method thereof

The present invention relates to a magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof, and more particularly to a domain wall motion type magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof.

Magnetic random access memory (Magnetic Random Access Memory; MRAM) is expected to be a non-volatile memory capable of high-speed operation and infinite rewriting, and has been actively developed. In the MRAM, a magnetoresistive effect element is used for a memory cell, and data is stored as the magnetization direction of the ferromagnetic layer of the magnetoresistive effect element. Several methods have been proposed as a method for switching the magnetization of the ferromagnetic layer, all of which are common in that current is used. In putting MRAM into practical use, it is very important how much the write current can be reduced. For example, 2006 Symposium on VLSI Circuits, Digest of Technical Papers, p. 136 requires a reduction to 0.5 mA or less, and more preferably to 0.2 mA or less.

The most common method for writing information to the MRAM is the following method. That is, this is a method in which wiring for passing a write current is arranged around the magnetoresistive effect element, and the magnetization direction of the ferromagnetic layer of the magnetoresistive effect element is switched by a current magnetic field generated by passing the write current. This method can be written in 1 nanosecond or less in principle, and is suitable for realizing a high-speed MRAM. For example, Japanese Patent Laid-Open No. 2005-150303 discloses a structure in which the magnetization of the end portion of the magnetization fixed layer is directed in the film thickness direction for an MRAM that performs data writing by a current magnetic field. However, the magnetic field for switching the magnetization of the magnetic material that has ensured thermal stability and disturbance magnetic field resistance is generally about several tens (Oe), and in order to generate such a magnetic field, about several mA. A large write current is required. When the write current is large, the chip area is inevitably increased, and the power consumption required for writing increases, so that it is inferior in competitiveness compared to other random access memories. In addition to this, when the memory cell is miniaturized, the write current further increases, which is not preferable in terms of scaling.

In recent years, the following two methods have been proposed as means for solving such problems. The first method uses spin injection magnetization reversal. In an MRAM using spin injection magnetization reversal, a magnetoresistive element of a memory cell includes a first ferromagnetic layer having a reversible magnetization (often referred to as a free layer) and a second strong magnetic layer having a fixed magnetization. A magnetic layer (often referred to as a pinned layer) and a laminated body including a tunnel barrier layer provided between these ferromagnetic layers. In such MRAM data writing, the interaction between the spin-polarized conduction electrons and the localized electrons in the free layer when a current is passed between the free layer and the pinned layer is used. Magnetization is reversed. The presence or absence of spin injection magnetization reversal depends on the current density (not the absolute value of the current). Therefore, when spin injection magnetization reversal is used for data writing, if the memory cell size is reduced, the write current is also reduced. Reduced. That is, it can be said that the spin injection magnetization reversal method is excellent in scaling.

However, when data is written, a write current must be passed through the thin tunnel barrier layer, and rewriting resistance and reliability become problems. In addition, since the current path for writing and the current path for reading are the same, there is a concern about erroneous writing during reading. Thus, although spin transfer magnetization reversal is excellent in scaling, there are some barriers to practical use.

The second method is a method using a current-driven domain wall motion phenomenon. The magnetization reversal method using the current-driven domain wall motion phenomenon can solve the above-described problems of spin injection magnetization reversal. For example, Japanese Patent Application Laid-Open Nos. 2005-191032, 2006-73930, and 2006-270069 disclose MRAMs that use the current-driven domain wall motion phenomenon. In the most general configuration of an MRAM using a current-driven domain wall motion phenomenon, a ferromagnetic layer (often called a magnetic recording layer) that holds data is provided with a magnetization reversal unit having reversible magnetization and both ends thereof. It is comprised by the two magnetization fixed parts which have the fixed magnetization connected. The data is stored as the magnetization of the magnetization switching unit. The magnetizations of the two magnetization fixed portions are fixed so as to be substantially antiparallel to each other. When the magnetization is arranged in this way, a domain wall is introduced into the magnetic recording layer.

Physical Review Letters, vol. 92, number 7, p. As reported in 077205, (2004), when a current is passed in the direction penetrating the domain wall, the domain wall moves in the direction of conduction electrons, so that data can be written by passing a current through the magnetic recording layer. . Since the presence or absence of current-driven domain wall movement also depends on the current density, it can be said that there is scaling as with spin injection magnetization reversal. In addition, in an MRAM memory cell using current-driven domain wall motion, the write current does not flow through the insulating layer, and the write current path and the read current path are different from each other. The above-mentioned problems that can be solved will be solved.

However, the MRAM using current-driven domain wall motion has a problem that the absolute value of the write current becomes relatively large. In order to reduce the write current below this, the width of the ferromagnetic film may be reduced and the film thickness may be reduced. However, it has been reported that when the film thickness is reduced, the current density required for writing is further increased (for example, Japan Journal of Applied Physics, vol. 45, No. 5A, pp. 3850-3853, (2006)). reference). Moreover, reducing the width of the ferromagnetic film to 100 nm or less is accompanied by great difficulty in terms of processing technology. In addition, when writing is performed using a current density close to 1 × 10 ⁸ [A / cm 2], there is a concern about the effects of electron migration and temperature rise.

It has been proposed to use a perpendicular magnetization film for the domain wall motion element as a method for reducing the write current. Simulations show that the domain wall can be driven with a lower current than the in-plane magnetization film by using the perpendicular magnetization film. Actually, domain wall current drive using a CoCrPt perpendicular magnetization film has been reported.

JP 2005-150303 A Japanese Patent Laid-Open No. 2005-191032 JP 2006-73930 A JP 2006-270069 A

As described above, it is effective to use a domain wall motion element having a perpendicular magnetization film in order to reduce the write current. However, when an attempt is made to apply the domain wall motion element to a memory cell, it is necessary to fix the magnetizations of the two magnetization fixed portions of the magnetic recording layer so as to be substantially antiparallel to each other as described above. Therefore, a complicated manufacturing process is required to realize this. A complicated manufacturing process causes an increase in manufacturing cost.

An object of the present invention is to provide a magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof that have a sufficiently small write current and can be easily manufactured.

The magnetoresistive element of the present invention includes a first ferromagnetic layer, a nonmagnetic layer, and a second ferromagnetic layer. The first ferromagnetic layer has a shape that is long in the longitudinal direction on the nonmagnetic underlayer, the first magnetization fixed portion on one end side in the longitudinal direction, the second magnetization fixed portion on the other end side, and In addition, a domain wall moving unit is provided between the first magnetization fixed unit and the second magnetization fixed unit. The nonmagnetic layer is provided on the domain wall moving part. The second ferromagnetic layer is provided on the nonmagnetic layer and has a fixed magnetization. The second ferromagnetic layer has magnetic anisotropy in the film thickness direction. The first magnetization fixed part and the second magnetization fixed part have magnetic anisotropy in the in-plane direction, and the domain wall moving part has magnetic anisotropy in the film thickness direction.

The magnetic random access memory according to the present invention includes a plurality of magnetic memory cells arranged in a matrix and a control circuit that controls writing and reading to each of the plurality of magnetic memory cells. Each of the plurality of magnetic memory cells includes the magnetoresistive element described above.

The present invention is a method for initializing a magnetic random access memory. Here, the magnetic random access memory includes a plurality of magnetic memory cells arranged in a matrix and a control circuit that controls writing and reading to each of the plurality of magnetic memory cells. However, in each of the plurality of magnetic memory cells, the magnetoresistive element includes a first ferromagnetic layer, a nonmagnetic layer, and a second ferromagnetic layer. The first ferromagnetic layer has a shape that is long in the longitudinal direction on the nonmagnetic underlayer, the first magnetization fixed portion on one end side in the longitudinal direction, the second magnetization fixed portion on the other end side, and In addition, a domain wall moving unit is provided between the first magnetization fixed unit and the second magnetization fixed unit. The nonmagnetic layer is provided on the domain wall moving part. The second ferromagnetic layer is provided on the nonmagnetic layer and has a fixed magnetization. The second ferromagnetic layer has magnetic anisotropy in the film thickness direction. The first magnetization fixed part and the second magnetization fixed part have magnetic anisotropy in the in-plane direction, and the domain wall moving part has magnetic anisotropy in the film thickness direction. The method for initializing a magnetic random access memory includes a step of applying a first external magnetic field having a component in a direction from the first seed layer to the second seed layer to a plurality of magnetic memory cells; And a step of applying a second external magnetic field having a component in the film thickness direction of the first ferromagnetic layer to the plurality of magnetic memory cells. Alternatively, the initialization method of the magnetic random access memory includes a step of flowing a current from one of the first seed layer and the second seed layer to the other through the first ferromagnetic layer, and a step of stopping the current. It comprises.

According to the present invention, it is possible to provide a magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof that have a sufficiently small write current and can be easily manufactured.

FIG. 1A is a plan view showing the structure of the main part of the magnetoresistive element according to the embodiment of the present invention. FIG. 1B is a cross-sectional view showing the structure of the main part of the magnetoresistive effect element according to the exemplary embodiment of the present invention. FIG. 2 is a cross-sectional view showing magnetic anisotropy in the magnetoresistive element of FIG. 1B. FIG. 3A is a cross-sectional view illustrating a method for initializing a magnetoresistive effect element according to an embodiment of the present invention. FIG. 3B is a cross-sectional view for explaining the initialization method of the magnetoresistive effect element according to the embodiment of the present invention. FIG. 3C is a cross-sectional view for explaining the initialization method of the magnetoresistive effect element according to the embodiment of the present invention. FIG. 4A is a cross-sectional view illustrating a method for initializing a magnetoresistive effect element according to an embodiment of the present invention. FIG. 4B is a cross-sectional view for explaining the initialization method of the magnetoresistive effect element according to the embodiment of the present invention. FIG. 4C is a cross-sectional view for explaining the initialization method of the magnetoresistive effect element according to the embodiment of the present invention. FIG. 5A is an xz sectional view showing the magnetization state of the first ferromagnetic layer in a state where the magnetoresistive effect element according to the exemplary embodiment of the present invention stores data. FIG. 5B is an xz sectional view showing the magnetization state of the first ferromagnetic layer in a state where the magnetoresistive effect element according to the exemplary embodiment of the present invention stores other data. FIG. 6A is a cross-sectional view showing the magnetization direction in each configuration of the “0” state in the magnetoresistive effect element according to the exemplary embodiment of the present invention. FIG. 6B is a cross-sectional view showing the magnetization direction in each configuration of the “1” state in the magnetoresistive effect element according to the exemplary embodiment of the present invention. FIG. 7 is a circuit diagram showing a configuration example of a 1-bit circuit of a magnetic memory cell using the magnetoresistive effect element according to the embodiment of the present invention. FIG. 8 is a block diagram showing an example of the configuration of the magnetic random access memory according to the embodiment of the present invention. FIG. 9A is sectional drawing which shows an example of the manufacturing method of the magnetoresistive effect element based on embodiment of this invention. FIG. 9B is sectional drawing which shows an example of the manufacturing method of the magnetoresistive effect element based on embodiment of this invention. FIG. 9C is a cross-sectional view showing an example of a method for manufacturing a magnetoresistance effect element according to the exemplary embodiment of the present invention. FIG. 9D is a cross-sectional view showing an example of a method for manufacturing a magnetoresistance effect element according to the exemplary embodiment of the present invention. FIG. 9E is a cross-sectional view showing an example of a method for manufacturing a magnetoresistance effect element according to the exemplary embodiment of the present invention.

Hereinafter, embodiments of a magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof according to the present invention will be described with reference to the accompanying drawings.

The magnetic random access memory according to the present embodiment has a plurality of memory cells arranged in an array. Each memory cell has a magnetoresistive element. Hereinafter, the configuration of the magnetoresistive effect element (memory cell) will be described.

(Configuration of magnetoresistive element)
FIG. 1A is a plan view showing the structure of the main part of the magnetoresistive effect element according to the present embodiment. FIG. 1B is a cross-sectional view (AA ′ plane of FIG. 1A) showing the structure of the main part of the magnetoresistive effect element according to the present exemplary embodiment. The magnetoresistive effect element 60 includes a first ferromagnetic layer 10, a spacer layer 20, and a second ferromagnetic layer 30. The first ferromagnetic layer 10 is provided extending in the x-axis direction. The second ferromagnetic layer 30 is provided approximately above the central portion (z-axis direction) of the first ferromagnetic layer 10 via the spacer layer 20. The spacer layer 20 is sandwiched between the first ferromagnetic layer 10 and the second ferromagnetic layer 30. The first ferromagnetic layer 10 and the second ferromagnetic layer 30 are formed of a ferromagnetic material. The spacer layer 20 is a nonmagnetic material, and is preferably formed of an insulator. In this case, a magnetic tunnel junction (MTJ) is formed by the first ferromagnetic layer 10, the spacer layer 20, and the second ferromagnetic layer 30. The spacer layer 20 is preferably made of an insulator, but may be made of a nonmagnetic conductor or semiconductor.

The first seed layer 40a and the second seed layer 40b are joined to the surface of the first ferromagnetic layer 10 opposite to the surface to which the spacer layer 20 is joined. The first seed layer 40 a is joined in the vicinity of one end of the first ferromagnetic layer 10, and the second seed layer 40 b is joined in the vicinity of the other end of the first ferromagnetic layer 10.

FIG. 2 is a cross-sectional view showing magnetic anisotropy in the magnetoresistive element of FIG. 1B. In this figure, the directions of magnetic anisotropy of the first ferromagnetic layer 10 and the second ferromagnetic layer 30 are indicated by arrows. As the second ferromagnetic layer 30, a perpendicular magnetization film is used. The first ferromagnetic layer has magnetization in the in-plane direction at portions in contact with the seed layers 40a and 40b, and has magnetization in the direction perpendicular to the film surface at the other portions. The magnetization of the second ferromagnetic layer 30 is fixed in one direction substantially in the direction perpendicular to the film surface. On the other hand, the magnetization of at least a portion of the first ferromagnetic layer 10 facing the second ferromagnetic layer 30 can be reversed. The magnetization of the portion is directed in a direction parallel or antiparallel to the magnetization of the second ferromagnetic layer 30 according to stored data. The second ferromagnetic layer 30 is made of a single layer film formed of a material having perpendicular magnetic anisotropy or a laminate formed of a plurality of films in order to realize magnetic anisotropy in the film thickness direction. Preferably it is formed. The laminated body in this case may be a laminated body composed of a plurality of ferromagnetic films or a laminated body composed of a ferromagnetic film and a nonmagnetic film.

As the material of the first ferromagnet 10, a combination of materials that have in-plane magnetization when stacked on the seed layers 40 a and 40 b and have vertical magnetization when stacked on the nonmagnetic underlayer 50. Select. For example, Cr is a body-centered cubic (bcc) metal. When a Co alloy having a hexagonal close-packed structure (hcp) is formed thereon, the c-axis side of the easy magnetization surface has good consistency with the length of the easy magnetization surface (110) of Cr, and the Co alloy is made of Cr ( 110), it is epitaxially grown so as to lie on the surface, and is thus in-plane oriented. For example, a fourth periodic element of the periodic table such as Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, or Se or an alloy film of these and Cr is used as an element having a body-centered cubic structure other than Cr. Also good.

On the other hand, when a Co alloy is formed on a base having the same hexagonal close-packed structure (hcp) as the Co alloy, the Co alloy film is affected by the atomic arrangement of the nonmagnetic base 50 and the (0001) plane is the base. Since the parallel polycrystalline alignment film grows and the easy magnetization surface faces in the film thickness direction, it becomes a perpendicular magnetization film. As such a base film, Ti, TiCr, Ta, Ru, nonmagnetic CoCr, Ge, Si, C, Au, Al, Pt, Ti / Ge, nonmagnetic CoCr / TiCr, nonmagnetic CoCrRu / TiCr, Pt / Co3O4, A laminated film in which Pt / Ti, Pd / Ti, Ta / MgO, CoCrRu / MgO, Ru / Ru-oxide, Ru / Ta, or the like is used alone or in combination is used.

That is, when a hexagonal close-packed structure (hcp) Co alloy is used as the first ferromagnetic material 10, the material of the seed layers 40a and 40b and the material of the nonmagnetic underlayer 50 are as follows. Examples of the material of the seed layers 40a and 40b include body-centered cubic (bcc) Cr, periodic table fourth periodic elements such as Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. It is an alloy of Cr and the above-mentioned periodic table fourth periodic element. On the other hand, as the material of the nonmagnetic underlayer 50, Ti, TiCr, Ta, Ru, nonmagnetic CoCr, Ge, Si, C, Au, Al, Pt, Ti / Ge, nonmagnetic CoCr / TiCr, nonmagnetic CoCrRu / TiCr Pt / Co ₃ O ₄ , Pt / Ti, Pd / Ti, Ta / MgO, CoCrRu / MgO, Ru / Ru-oxide, Ru / Ta, or a combination thereof.

The materials of the seed layers 40a and 40b and the ferromagnetic layer 10 are preferably adjusted so that the lattice constants of these materials are close to each other. In addition, when there is no base film (nonmagnetic base 50), for example, even when a Co alloy film is formed on a Si oxide film, the easy magnetization surface is oriented in the film thickness direction, but the crystal orientation is uniformly aligned in the film thickness direction. Therefore, it is more preferable to have the base film as described above. When the first ferromagnetic layer 10, the first seed layer 40 a, and the second seed layer 40 b are in the magnetization arrangement as described above, the magnetization of the region of the first ferromagnetic layer 10 that faces the second ferromagnetic layer 30. Depending on the direction, a domain wall is formed in the first ferromagnetic layer 10.

The magnetization directions of the in- plane magnetization regions 10a and 10b at both ends of the first ferromagnetic layer 10 are oriented in the same direction parallel to the x-axis direction. This is effective for facilitating the manufacturing process of the MRAM. In the present embodiment, since the directions in which the magnetizations of the in- plane magnetization regions 10a and 10b should be directed in the manufacturing process are the same, the initialization can be easily performed by applying an external magnetic field. In the example of FIG. 2, the magnetizations of the in- plane magnetization regions 10a and 10b are all directed in the + x direction (right direction in FIG. 2).

In the in-plane magnetization region 10a, which is a portion joined to the first seed layer in the first ferromagnetic layer 10, no magnetization reversal occurs. For this reason, hereinafter, the in-plane magnetization region 10a may be referred to as the first magnetization fixed portion 10a. Similarly, the in-plane magnetization region 10b that is a portion joined to the second seed layer 40b in the first ferromagnetic layer 10 may be referred to as a second magnetization fixed portion 10b. In the perpendicular magnetization region 10c, which is a portion between the first magnetization fixed portion 10a and the second magnetization fixed portion 10b, the domain wall can move. For this reason, hereinafter, the perpendicular magnetization region 10c may be referred to as a domain wall motion unit 10c.

The second ferromagnetic layer 30, the first seed layer 40a, and the second seed layer 40b are electrically connected to different external wirings (not shown). As will be understood from this, the magnetoresistive element 60 is a three-terminal element. Although not shown in FIG. 1A, FIG. 1B, and FIG. 2, the electrode layers for obtaining electrical connection with the wiring are respectively the second ferromagnetic layer 30, the first seed layer 40a, and the second seed layer 40b. It is preferable to be joined to each other.

The spacer layer 20 is preferably made of an insulator. Specifically, Mg—O, Al—O, Al—N, Ni—O, Hf—O, Ti—O, SrTiO 3, etc. can be used as the material of the spacer layer 20. However, it should be noted that the present invention can be implemented even if a semiconductor or a metal material is used for the spacer layer 20. Specific examples of semiconductors and metal materials that can be used as the spacer layer 20 include Cr, Al, Cu, and Zn.

(Initialization method)
Next, a method for initializing the magnetoresistive effect element 60 according to the present embodiment will be described. 3A to 3C and FIGS. 4A to 4C are cross-sectional views illustrating a method for initializing the magnetoresistive effect element according to the present embodiment. In the magnetoresistive effect element 60, it is necessary to introduce a domain wall into the first ferromagnetic layer 10, and FIGS. 3A to 3C and FIGS. 4A to 4C show the domain wall introduction process. 3A to 3C and FIGS. 4A to 4C show only the first ferromagnetic layer 10, the first seed layer 40a, and the second seed layer 40b.

In order to introduce the domain wall into the first ferromagnetic layer 10, first, a uniform and sufficiently large external magnetic field is applied to the magnetoresistive element 60 substantially parallel to the x-axis direction (which is the longitudinal direction of the first ferromagnetic layer 10). Applied in the direction. At this time, as shown in FIG. 3A, all the magnetic moments are aligned and saturated in the direction of the external magnetic field. Next, the external magnetic field is reduced from this state. The rate of decrease of the external magnetic field is preferably moderately slow. When the external magnetic field starts to decrease, magnetization relaxation begins. As shown in FIG. 3B, since the first ferromagnetic layer 10 has magnetic anisotropy in the z-axis direction except for both end portions, first the first seed layer 40a and the second seed layer of the first ferromagnetic layer 10 are first used. Magnetization near the connection surface with 40b starts to rotate in the z-axis direction. The magnetization that has begun to rotate forms a magnetic domain having a magnetization in the film thickness direction, and this magnetic domain grows in the first ferromagnetic layer 10. Here, as shown in FIG. 3C, the two magnetic domains grown in the first ferromagnetic layer 10 have magnetizations in antiparallel directions. Therefore, as shown in FIG. 3C, when two magnetic domains grow and meet, a domain wall is formed there. The above is the first initialization process of the magnetoresistive element 60 in the present embodiment.

The domain wall introduced into the first ferromagnetic layer 10 by the first initialization process is moved to a desired position by the second initialization process as shown in FIGS. 4A to 4C. FIG. 4A shows an example of the magnetization state at the time when the first initialization process is completed. In the state of FIG. 4A, a magnetic field is applied in the film thickness direction (that is, the z-axis direction) of the first ferromagnetic layer 10. This magnetic field is preferably reasonably small. The magnetic field may be applied in either the + z direction or the −z direction. When a magnetic field is applied in the + z direction, the domain wall formed near the center of the first ferromagnetic layer 10 in FIG. 4A is on the right side (ie, the second seed layer 40b) as shown in FIG. 4B. Move to the vicinity). Conversely, when a magnetic field is applied in the −z direction, the domain wall formed near the center of the first ferromagnetic layer 10 is on the left side (ie, the first seed layer as shown in FIG. 4C). Move to the vicinity of 40a). 4B and 4C correspond to states in which different data are stored, respectively. As described above, by applying a small external magnetic field in the z-axis direction (+ z direction or −z direction) in the state of FIG. 4A, initialization to a state in which arbitrary data is stored is possible.

Although an example in which a magnetic field in the x-axis direction is applied in the first initialization process is shown here, the applied magnetic field is a y component (that is, a component that is not parallel to the x-axis direction excluding the z-axis direction). You may have. Although an example in which a magnetic field in the z-axis direction is applied in the second initialization process is shown here, the applied magnetic field has an x component and a y component (that is, a component that is not parallel to the z-axis direction). It may be. Further, as described later with reference to FIGS. 5A and 5B, the memory state may be initialized by passing a write current through the first ferromagnetic layer 10 without using an external magnetic field.

(Data writing)
Next, a method of writing data to the magnetoresistive effect element 60 according to the present embodiment will be described. FIG. 5A shows the magnetization state of the first ferromagnetic layer in a state where the magnetoresistive effect element according to the present embodiment stores data (“0” state storing data “0”). FIG. FIG. 5B shows the magnetization state of the first ferromagnetic layer in a state where the magnetoresistive element according to the present embodiment stores other data (the “1” state storing data “1”). It is xz sectional drawing shown. In the drawing, the second ferromagnetic layer 30 and the spacer layer 20 are omitted. Here, a state in which the magnetization of the central portion (domain wall moving portion 10c) of the first ferromagnetic layer 10 is directed in the −z direction is defined as a “0” state (see FIG. 5A). On the other hand, a state in which the magnetization of the central portion (domain wall moving portion 10c) of the first ferromagnetic layer 10 is directed in the + z direction is defined as a “1” state (see FIG. 5B). However, it goes without saying that the definition regarding the magnetization direction and stored data is not limited to the above case.

When the magnetoresistive effect element 60 has the magnetization state as described above, in the “0” state, the domain wall is formed on the right side of the first ferromagnetic layer 10 (that is, in the vicinity of the second seed layer 40b). On the other hand, in the “1” state, the domain wall is formed on the left side of the first ferromagnetic layer 10 (that is, in the vicinity of the first seed layer 40a). In the present embodiment, data writing is performed by passing a write current through the first ferromagnetic layer 10 in the in-plane direction. By appropriately selecting the direction of the write current, the domain wall is moved to a desired position in the first ferromagnetic layer 10, and thereby, data “0” and data “1” can be written separately.

For example, when the magnetoresistive element 60 is in the “0” state of FIG. 5A, if a write current is passed in the + x direction (right direction in FIG. 5A), conduction electrons in the −x direction (left direction in FIG. 5A). Flow occurs. The domain wall on the right side of the first ferromagnetic layer 10 receives the spin transfer torque due to the conduction electrons and moves to the same direction as the conduction electrons, that is, to the left side of the first ferromagnetic layer 10. As a result, data is written to the “1” state. Similarly, when a write current is passed in the −x direction (left direction in FIG. 5B) when the magnetoresistive element 60 is in the “1” state of FIG. 5B, conduction electrons in the + x direction (right direction in FIG. 5B). Flow occurs. The domain wall on the left side of the first ferromagnetic layer 10 receives the spin transfer torque due to the conduction electrons and moves in the same direction as the conduction electrons, that is, on the right side of the first ferromagnetic layer 10. As a result, data is written to the “1” state. In this way, writing can be performed from the “0” state to the “1” state and from the “1” state to the “0” state.

Further, when a write current is passed in the −x direction when the magnetoresistive effect element 60 is in the “0” state of FIG. 5A, that is, when data “0” is written, the domain wall tends to move in the + x direction. However, since the region of the second magnetization fixed portion 10b of the first ferromagnetic layer 10 has anisotropy in the in-plane direction, it cannot have a large magnetization component substantially in the z-axis direction. The domain wall motion does not occur in the region of the second magnetization fixed portion 10b of the first ferromagnetic layer 10. That is, it is possible to overwrite the data “0” when it is in the “0” state. Alternatively, even if the magnetization of a part of the first ferromagnetic layer 10 is reversed in the + z direction due to the domain wall movement, the magnetization of the part is again directed to the original state, that is, the + x direction when the write current is turned off. If designed to recover to the above, overwriting as described above becomes possible. The same applies when a write current is passed in the + x direction when the magnetoresistive effect element 60 is in the “1” state of FIG. 5B, that is, when data “1” is written. Since the first magnetization fixed portion 10a has magnetic anisotropy in the in-plane direction, it is possible to overwrite the data “1” when the magnetoresistive element 60 is in the “1” state.

In the present embodiment, reducing the film thickness of the first magnetization fixed portion 10a and the second magnetization fixed portion 10b provides anisotropy in the in-plane direction and stably maintains the in-plane magnetization. And more preferable. Further, it is more preferable to increase the thickness of the magnetization moving part 10c from the viewpoint of providing anisotropy in the vertical direction and stably maintaining the perpendicular magnetization. Therefore, it is more preferable to make the film thickness of the first magnetization fixed part 10a and the second magnetization fixed part 10b thinner than the film thickness of the magnetization moving part 10c.

(Data read)
Next, reading of information from the magnetoresistive effect element 60 according to the present exemplary embodiment will be described. As described above, in the present embodiment, data is stored as the magnetization direction of the first ferromagnetic layer 10, while the central portion (domain wall moving portion 10c) of the first ferromagnetic layer 10 is the spacer layer. It is joined to the second ferromagnetic layer 30 via 20. In the magnetoresistive effect element 60, a change in the MTJ resistance value due to the magnetoresistive effect is used for data reading. In other words, the data stored in the first ferromagnetic layer 10 can be read by passing a read current between the first ferromagnetic layer 10 and the second ferromagnetic layer 30.

6A and 6B are cross-sectional views showing the magnetization directions in the respective configurations of the “0” state and the “1” state in the magnetoresistive effect element according to the present embodiment. For example, as shown in FIG. 6A, when the relationship between the magnetization direction of the central portion (domain wall moving portion 10c) of the first ferromagnetic layer 10 and the magnetization direction of the second ferromagnetic layer 30 is parallel (that is, data “0”). ”Is stored), the resistance value of the MTJ formed in the magnetoresistive effect element 60 is relatively low. On the other hand, when the magnetization direction of the central portion of the first ferromagnetic layer 10 and the magnetization direction of the second ferromagnetic layer 30 are antiparallel as shown in FIG. 6B (that is, when data “1” is stored). The resistance value of MTJ becomes relatively high. The data stored in the first ferromagnetic layer 10 can be determined by reading the resistance value of the MTJ as a current signal or a voltage signal.

(Technical advantage of magnetoresistive element of this example)
By using the magnetoresistive effect element 60 according to the present exemplary embodiment, a magnetic random access memory having a reduced write current and an excellent scaling property can be provided by an easy manufacturing process. This is due to the fact that the magnetization direction of the part (domain wall moving part 10c) related to domain wall movement in the first ferromagnetic layer 10 is oriented in the vertical direction.

Furthermore, in the magnetoresistive effect element 60 according to the present exemplary embodiment, the first seed layer 40 a and the second seed layer 40 b are provided adjacent to both ends of the first ferromagnetic layer 10. Thereby, in one first ferromagnetic layer 10, the magnetization directions of both end portions (first magnetization fixed portion 10 a and second magnetization fixed portion 10 b) are in-plane directions, and the magnetization of the central portion (domain wall moving portion 10 c). Can be controlled to be the film thickness direction. Thereby, the domain wall can be easily introduced into the first ferromagnetic layer 10. That is, the in-plane magnetization film and the perpendicular magnetization film can be formed in the same film. As a result, the number of processes is reduced and the manufacturing cost is reduced.

(Circuit configuration)
Next, a circuit configuration for introducing a write current and a read current into the magnetic memory cell 80 having the magnetoresistive effect element 60 according to the present embodiment will be described.

FIG. 7 is a circuit diagram showing a configuration example of a circuit for one bit of the magnetic memory cell 80 using the magnetoresistive effect element 60 according to the present exemplary embodiment. In the example shown in FIG. 7, the magnetic memory element 60 is a three-terminal element, and is connected to the word line WL, the ground line GL, and the bit line pair BLa, BLb. For example, the terminal connected to the second ferromagnetic layer 30 is connected to the ground line GL for reading. A terminal connected to the first magnetization fixed portion 10a is connected to one of the source / drain of the transistor TRa, and the other of the source / drain is connected to the bit line BLa. A terminal connected to the second magnetization fixed portion 10b is connected to one of the source / drain of the transistor TRb, and the other of the source / drain is connected to the bit line BLb. The gates of the transistors TRa and TRb are connected to a common word line WL.

At the time of data writing, the word line WL is set to the high level, and the transistors TRa and TRb are turned on. In addition, one of the bit line pair BLa and BLb is set to a high level, and the other is set to a low level (ground level). As a result, a write current flows between the bit line BLa and the bit line BLb via the transistors TRa and TRb and the first ferromagnetic layer 10.

When reading data, the word line WL is set to a high level, and the transistors TRa and TRb are turned on. Further, the bit line BLa is set to an open state, and the bit line BLb is set to a high level. As a result, a read current flows from the bit line BLb through the transistor TRb and the MTJ of the magnetoresistive element 60 to the ground line GL. This enables reading using the magnetoresistive effect.

FIG. 8 is a block diagram showing an example of the configuration of the magnetic random access memory 90 according to the present embodiment. The magnetic random access memory 90 includes a memory cell array 110, an X driver 120, a Y driver 130, and a controller 140. The memory cell array 110 has a plurality of magnetic memory cells 80 arranged in an array (matrix). Each of the magnetic memory cells 80 has the magnetoresistive element 60 described above. As shown in FIG. 7 described above, each magnetic memory cell 80 is connected to the word line WL, the ground line GL, and the bit line pair BLa, BLb. The X driver 120 is connected to a plurality of word lines WL. Then, the selected word line connected to the magnetic memory cell 80 to be accessed is driven among the plurality of word lines WL. The Y driver 130 is connected to a plurality of bit line pairs BLa and BLb. Each bit line is set to a state corresponding to data writing or data reading. The controller 140 controls each of the X driver 120 and the Y driver 130 in accordance with data writing or data reading. The configuration including the X driver 120, the Y driver 130, and the controller 140 can be regarded as a control circuit that controls writing and reading of each memory cell in the memory cell array 110.

(Description of manufacturing method)
Next, a method for manufacturing the magnetoresistive effect element according to this embodiment will be described. 9A to 9E are cross-sectional views showing an example of a method for manufacturing the magnetoresistive effect element according to the present embodiment.
First, as shown in FIG. 9A, a nonmagnetic underlayer 50 and a seed layer 40 are formed on a CMOS substrate (not shown). As the material of the nonmagnetic underlayer 50, an insulating film such as SiO, SiN, SiCN, or Ti, TiCr, Ta, Ru, nonmagnetic CoCr, Ge, Si, C, Au, Al, Pt, Ti / Ge, nonmagnetic CoCr / TiCr, nonmagnetic CoCrRu / TiCr, Pt / Co3O4, Pt / Ti, Pd / Ti, Ta / MgO, CoCrRu / MgO, Ru / Ru-oxide, Ru / Ta, etc. The material is selected from crystal-oriented materials so that the ferromagnetic film has magnetization in the vertical direction. The seed layer 40 is selected from materials such as Cr or Cr—Mn, which are crystal-oriented so that the ferromagnetic film formed thereon has magnetization in the in-plane direction. At this time, an amorphous material SiO, SiN, Al 2 O 3 or the like may be sandwiched between the nonmagnetic underlayer 50 and the seed layer 40 in order to remove the influence of the crystal orientation from the material of the upper nonmagnetic underlayer 50.

Next, as shown in FIG. 9B, the seed layer 40 is patterned into a predetermined shape. The patterning is performed by physical or chemical etching using a photoresist or a hard mask material as a mask. Subsequently, as shown in FIG. 9C, a ferromagnetic layer 10, a nonmagnetic layer (spacer layer) 20, and a ferromagnetic layer 30 are further stacked thereon. At this time, in order to epitaxially grow the ferromagnetic material on the nonmagnetic layer and the seed layer, it is important to perform film formation after etching impurities such as an oxide film on the surface physically or chemically. Also, it is desirable that these processes be performed consistently in a vacuum.

Next, as shown in FIG. 9D, the ferromagnetic layer 30 and the nonmagnetic layer 20 are patterned. The patterning is performed by physical or chemical etching using a photoresist or a hard mask material as a mask. Finally, as shown in FIG. 9E, the ferromagnetic layer 10 is patterned. The patterning is performed by physical or chemical etching using a photoresist or a hard mask material as a mask. The magnetoresistive effect element 60 can be manufactured like an abnormality.

The magnetoresistive effect element of the present invention is adiabatic in the LLG equation that takes into account the spin-polarized current because the first ferromagnetic layer in which current-driven domain wall motion occurs has magnetic anisotropy in the film thickness direction. The domain wall can be driven with a small current density by the spin torque term. That is, the write current can be reduced.
In addition, when the domain wall is driven, the domain wall can be moved almost without being affected by the threshold magnetic field at which the domain wall is depinned. Therefore, the current required for writing is maintained while maintaining high thermal stability and disturbance magnetic field resistance. Can be reduced.
Furthermore, by providing the first and second seed layers so as to be in contact with the lower portions of both ends of the first ferromagnetic layer, the magnetization of the first ferromagnetic layer is directed in the in-plane direction, and the domain wall is easily introduced at a desired position. can do. Since in-plane magnetization and perpendicular magnetization can be created only with the first ferromagnetic layer, it is not necessary to introduce a new ferromagnetic film, and the manufacturing is facilitated.

In the example of FIG. 2, the first seed layer 40 a and the second seed layer 40 b are formed on the nonmagnetic underlayer 50. However, if the portion of the first ferromagnetic layer 10 in contact with the seed layers 40a and 40b has magnetization in the in-plane direction, and the other portion of the first ferromagnetic layer 10 has magnetization in the direction perpendicular to the film surface, The first seed layer 40 a and the second seed layer 40 b may be embedded in the nonmagnetic underlayer 50. That is, the lower surface of the first ferromagnetic layer 10 may be flat. In that case, as a manufacturing method, another nonmagnetic underlayer is further formed between the above-described FIG. 9B and FIG. 9C, and a flattening process (CMP or etching) is performed, so that the nonmagnetic underlayer 50 can be easily formed. The first seed layer 40a and the second seed layer 40b can be buried.

Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above embodiment. 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 is based on a Japanese patent application filed on July 31, 2008, patent application No. 2008-197252, which claims the benefit of priority from that application, and the disclosure of that application should be cited Is incorporated here as it is.

Claims (8)

1. It has a shape that is long in the longitudinal direction on the nonmagnetic base, and has a first magnetization fixed portion on one end side, a second magnetization fixed portion on the other end side, and the first magnetization fixed portion and the first magnetization fixed portion. A first ferromagnetic layer having a domain wall moving part between the two magnetization fixed parts;
   A nonmagnetic layer provided on the domain wall moving part;
   A second ferromagnetic layer provided on the nonmagnetic layer and having a fixed magnetization;
   The second ferromagnetic layer has magnetic anisotropy in the film thickness direction,
   The first magnetization fixed part and the second magnetization fixed part have magnetic anisotropy in an in-plane direction, and the domain wall moving part has magnetic anisotropy in a film thickness direction.
2. The magnetoresistive effect element according to claim 1,
   A first seed layer provided in contact with the first magnetization pinned portion;
   A magnetoresistive element, further comprising: a second seed layer provided in contact with the second magnetization fixed portion.
3. The magnetoresistive effect element according to claim 2,
   The first seed layer and the second seed layer may be a material selected from a group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se, or Including alloys using the material,
   The first ferromagnetic layer includes a material represented by CoCrX,
   X is Ta, Fe, Zr, WC, Ru, Rh, Ti, W, Mo, O, Mo, Gd, Zn, Cu, Pr, Nb, Pt, Pt—O ₂ , Pt—SiO ₂ , and A magnetoresistive element, which is a substance selected from the group consisting of Pt—TiO ₂ .
4. The magnetoresistive effect element according to claim 2 or 3,
   The nonmagnetic underlayer includes a Ti film, a TiCr film, a Ta film, a Ru film, a CoCr film, a Ge film, a Si film, a C film, an Au film, an Al film, a Pt film, a Ti / Ge film, and a laminate of CoCr and TiCr. Film, CoCrRu and TiCr laminated film, Pt and Co ₃ O ₄ laminated film, Pt and Ti laminated film, Pd and Ti laminated film, Ta and MgO laminated film, CoCrRu and MgO laminated film A magnetoresistive element, which is a film selected from a group consisting of a film, a laminated film of Ru and Ru—O, and a laminated film of Ru and Ta.
5. The magnetoresistive effect element according to any one of claims 2 to 4,
   The first seed layer and the second seed layer are electrically connected to an external wiring. A magnetoresistive effect element.
6. A plurality of magnetic memory cells arranged in a matrix;
   A control circuit for controlling writing and reading to each of the plurality of magnetic memory cells,
   Each of the plurality of magnetic memory cells includes:
   A magnetic random access memory comprising the magnetoresistive effect element according to claim 1.
7. An initialization method for a magnetic random access memory,
   Here, the magnetic random access memory is
   A plurality of magnetic memory cells arranged in a matrix;
   A control circuit for controlling writing and reading to each of the plurality of magnetic memory cells,
   Each of the plurality of magnetic memory cells includes:
   It has a shape that is long in the longitudinal direction on the non-magnetic base, a first magnetization fixed portion on one end side in the longitudinal direction, a second magnetization fixed portion on the other end side, and the first magnetization fixed portion And a first ferromagnetic layer each having a domain wall moving part between the second magnetization fixed part and
   A nonmagnetic layer provided on the domain wall moving part;
   A second ferromagnetic layer provided on the nonmagnetic layer and having a fixed magnetization;
   The second ferromagnetic layer has magnetic anisotropy in the film thickness direction,
   The first magnetization fixed part and the second magnetization fixed part have magnetic anisotropy in the in-plane direction, the domain wall moving part has magnetic anisotropy in the film thickness direction,
   The initialization method of the magnetic random access memory is as follows:
   Applying a first external magnetic field having a component in a direction from the first seed layer to the second seed layer to the plurality of magnetic memory cells;
   Reducing the first external magnetic field at a predetermined rate;
   Applying a second external magnetic field having a component in the film thickness direction of the first ferromagnetic layer to the plurality of magnetic memory cells. An initialization method for a magnetic random access memory.
8. An initialization method for a magnetic random access memory,
   Here, the magnetic random access memory is
   A plurality of magnetic memory cells arranged in a matrix;
   A control circuit for controlling writing and reading to each of the plurality of magnetic memory cells,
   Each of the plurality of magnetic memory cells includes:
   It has a shape that is long in the longitudinal direction on the non-magnetic base, a first magnetization fixed portion on one end side in the longitudinal direction, a second magnetization fixed portion on the other end side, and the first magnetization fixed portion And a first ferromagnetic layer each having a domain wall moving part between the second magnetization fixed part and
   A nonmagnetic layer provided on the domain wall moving part;
   A second ferromagnetic layer provided on the nonmagnetic layer and having a fixed magnetization;
   The second ferromagnetic layer has magnetic anisotropy in the film thickness direction,
   The first magnetization fixed part and the second magnetization fixed part have magnetic anisotropy in the in-plane direction, the domain wall moving part has magnetic anisotropy in the film thickness direction,
   The initialization method of the magnetic random access memory is as follows:
   Passing a current from one of the first seed layer and the second seed layer to the other through the first ferromagnetic layer;
   A method of initializing a magnetic random access memory, comprising: stopping the current.

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