KR102291612B1 - Magnetoresistive Device - Google Patents

Abstract

Disclosed is a magnetoresistive element that realizes low power consumption and improved stability. The magnetoresistive element includes a pinned layer having a predetermined magnetization direction fixed, a free layer having a variable magnetization direction, and an insulating layer provided between the pinned layer and the free layer, wherein the pinned layer, the free layer, and the insulating layer are a magnetic tunnel junction layer to form The free layer includes at least a first magnetic layer and a second magnetic layer having a lower Curie temperature than the first magnetic layer. By setting the Curie temperature of the second magnetic layer to be lower than the Curie temperature of the first magnetic layer, the amount of current that reverses the magnetization direction of the first magnetic layer during a write operation may be reduced.

Description

Magnetoresistive Device

The present invention relates to a magnetoresistive element using a magnetic tunnel junction, for example, a magnetic tunnel element using a spin injection magnetization reversal effect, and a magnetoresistive element used in a magnetoresistive memory (MRAM).

Magnetoresistive random access memory (MRAM) is attracting attention as a high-speed, low-power, large-capacity nonvolatile memory. A magnetoresistive memory uses a magnetoresistive element in which a magnetic tunnel junction (MTJ) is formed as a memory element. Specifically, the magnetoresistive element includes a free layer having a variable magnetization direction, a pinned layer having a fixed magnetization direction perpendicular to the film surface, and a tunnel barrier layer disposed between the free layer and the pinned layer and made of an insulator. The pinned layer, the tunnel barrier layer, and the free layer form a magnetic tunnel junction. A magnetoresistive element is also called a magnetic tunnel junction (MTJ) element.

The magnetoresistive element stores information by using the magnitude of the crystal magnetoresistance as the relative magnetization direction of a pair of magnetic layers with a tunnel barrier layer interposed therebetween. The magnetoresistive element performs read by such a magnetoresistance effect and writes by a spin transfer torque (STT) method.

As the material of the pinned layer and the free layer, ferromagnetic materials with high perpendicular magnetic anisotropy and high spin polarizability are preferred.

The spin injection magnetization reversal method employed as the write method reverses the magnetization direction of the free layer by using a magnetic moment caused by the spin of electrons. The spin injection method is suitable for device miniaturization and low current compared to the conventional wiring current method. In addition, the magnetoresistive element has resistance to thermal disturbance against miniaturization.

Such a magnetoresistive element is expected as a basic component of a next-generation high-integration memory such as, for example, STT-MRAM.

However, the perpendicular magnetic anisotropy of the CoFeB-based material, which is currently being actively developed as a material for the free layer, is small because the interfacial magnetic anisotropy is used. In addition, materials having high spin polarization and high perpendicular magnetic anisotropy are theoretically only materials such as Mn-Ge or Mn-Al, so the material selection range is very narrow.

Meanwhile, as a solution, a method of bonding a perpendicular self-retaining layer to the MTJ has been proposed. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2005-0328878), a magnetization-fixed layer having magnetism in which a spin moment is oriented perpendicular to the film surface and the direction of the spin moment is fixed, and a direction in which the spin moment is perpendicular to the film surface. Disclosed is a magnetoresistive element comprising a magnetic recording layer facing toward the magnetic recording layer, a nonmagnetic layer provided between the magnetization fixing layer and the magnetic recording layer, and an antiferromagnetic film provided on at least a side surface of the magnetization fixing layer.

In addition, Patent Document 2 (Japanese Patent Laid-Open No. 2005-150303) includes a ferromagnetic tunnel junction having a three-layer structure of a first ferromagnetic layer/tunnel barrier layer/second ferromagnetic layer, wherein the first ferromagnetic layer is the second The coercive force is greater than that of the ferromagnetic layer, the tunnel conductance changes according to the relative angles of the magnetizations of the first and second ferromagnetic layers, and the magnetization of the end of the second ferromagnetic layer facilitates the magnetization of the second ferromagnetic layer. A magnetoresistive element fixed in a direction having a component orthogonal to the axial direction is disclosed.

In addition, in Patent Document 3 (Japanese Patent Laid-Open No. 2011-071352), a first magnetic layer having an easy axis of magnetization perpendicular to the film surface but having a variable magnetization direction, an easy axis of magnetization perpendicular to the film surface, but having an invariant magnetization direction a second magnetic layer, and a first non-magnetic layer provided between the first magnetic layer and the second magnetic layer, wherein the first magnetic layer has Co and Pd or Co and Pt alternately in an atomic dense plane. It is composed of a ferromagnetic material including a CoPd alloy or a CoPt alloy to be laminated and having a c-axis in a direction perpendicular to the film surface, and the magnetization direction of the first magnetic layer is the first magnetic layer, the first non-magnetic layer, and the second A magnetoresistive element that changes with a bidirectional current passing through a magnetic layer is disclosed.

By this technique, the range of materials with high spin polarization has been extended to half-metal series and Heusler series. However, there has been a problem in that the magnetization reversal current increases and it is difficult to reduce the power consumption because the film thickness of the device becomes large.

In response to such a problem, for example, Patent Document 4 (Japanese Patent Laid-Open No. 2014-116474) provides a magnetoresistive element that reduces the magnetization reversal current to achieve low power consumption. In the magnetoresistive element of Patent Document 4, the memory layer (free layer) includes a ferromagnetic layer, a perpendicular magnetization holding layer, and a magnetic coupling control layer. A magnetic coupling control layer is provided between the ferromagnetic layer and the perpendicular magnetization holding layer to control the magnetic coupling between the ferromagnetic layer and the perpendicular magnetization holding layer. By appropriately changing the thickness of the magnetic coupling control layer, various parameters such as resistance change rate, thermal stability, write current, and magnetization reversal rate are optimized. Accordingly, it is possible to achieve low power by reducing the magnetization reversal current.

On the other hand, in a recording medium such as a magnetoresistive memory, stability for safely holding recorded information while reducing power consumption is required. For example, recording media are used in environments that are exposed to heat generated by themselves or other devices. Therefore, the magnetoresistive element is required to have magnetization thermal stability in the free layer (storage layer) holding information. However, the magnetoresistive element of Patent Document 1 realizes power reduction, but does not disclose a technique for realizing magnetic stability.

An object of the present invention is to provide a magnetoresistive device with reduced power consumption and improved stability, which has been made in the background of the above-described situation.

The present invention focuses on the relationship between the Curie temperature of the magnetic layer (ferromagnetic layer) constituting the free layer and the element temperature of the magnetoresistive element during write operation. According to the present invention, by appropriately selecting the Curie temperature of the free layer, power consumption during a write operation is lowered and the magnetization direction of the free layer is stably maintained. Specifically, the magnetoresistive element according to the present invention may include the following configuration.

A magnetoresistive device according to an embodiment of the present invention may include a pinned layer having a fixed magnetization direction, a free layer having a variable magnetization direction and having perpendicular magnetic anisotropy, and an insulating layer formed between the pinned layer and the free layer. . The pinned layer, the free layer, and the insulating layer may form a magnetic tunnel junction layer. The free layer may include at least a first magnetic layer and a second magnetic layer having a lower Curie temperature than the first magnetic layer and having perpendicular magnetic anisotropy.

The Curie temperature of the second magnetic layer constituting the free layer may be lower than that of the first magnetic layer. Since the Curie temperature of the second magnetic layer is small, if the device temperature increases during a write operation, the perpendicular magnetic anisotropy of the second magnetic layer may decrease and thermal disturbance may become very large. The first magnetic layer adjusts the magnetization direction of the ferromagnetic layer to be fixed. During the write operation, since the effect of thermal disturbance increases due to the decrease in magnetic anisotropy of the second magnetic layer, the write operation is performed with an amount of current that controls the magnetization direction of the first magnetic layer. After that, as the device temperature is lowered, the effect of thermal disturbance becomes smaller, so that the second magnetic layer changes in the same magnetization direction as that of the first magnetic layer. Power consumption can be reduced by configuring the amount of current for inverting the magnetization direction of the second magnetic layer to be almost unnecessary (a value close to zero) during a write operation. Since the temperature during the read operation is smaller than the Curie temperature, the thermal stability of the magnetoresistive element may be improved by hybridization as in the prior art.

In the magnetoresistive device according to an embodiment of the present invention, the Curie temperature of the second magnetic layer is preferably 350K to 500K. By appropriately selecting the Curie temperature of the second magnetic layer, the range of device temperatures in which the second magnetic layer exhibits large thermal disturbances can be adjusted. Furthermore, in relation to an increase in thermal stability during a read operation, the perpendicular magnetic anisotropy value of the second magnetic layer is preferably 5×10 ⁵ J/m ³ (5×10 ⁶ erg/cc) or more.

As for the first magnetic layer, it is preferable to have any of the following. First, the magnetic anisotropy of the first magnetic layer is in-plane magnetic anisotropy. Second, the first magnetic layer has perpendicular magnetic anisotropy, and the value of the perpendicular magnetic anisotropy is 2×10 ⁵ J/m ³ (2×10 ⁶ erg/cc) to 10 ⁶ J/m ³ (10 ⁷ erg/cc) cc). In this way, since the magnetization direction of the entire free layer is controlled according to the amount of current that reverses the magnetization direction of the first magnetic layer during a write operation, the amount of inversion current in the magnetization direction can be reduced.

A magnetoresistive element according to an embodiment of the present invention includes a magnetic coupling control layer provided between the first magnetic layer and the second magnetic layer to control magnetic coupling between the first magnetic layer and the second magnetic layer. It is preferable to do Controlling the magnetization direction of the second magnetic layer to be the same as that of the first magnetic layer when the second magnetic layer changes from a high thermal disturbance state to ferromagnetic by adjusting (eg, thickness) the magnetic coupling control layer can do. Accordingly, the thermal stability of the magnetoresistive element can be improved.

The second magnetic layer may include a material having a controlled Curie temperature and having high perpendicular magnetic anisotropy. For example, the second magnetic layer preferably includes a magnetic material such as FePtCu, [Co/Pt]n, TbFeCo, Mn ₂ RuGa, or Mn _{2 RuGe or other ferromagnetic material.} The resistance value of the magnetoresistive element (MTJ element) ^{is preferably 30 Ωμm 2} or less. FePtCu, [Co/Pt]n, TbFeCo, Mn ₂ RuGa, and Mn ₂ RuGe are examples of materials having a high perpendicular magnetic anisotropy constant at a low Curie temperature, and may be suitably used for the second magnetic layer.

In addition, it is preferable that the Curie temperature of the second magnetic layer is close to or lower than the device temperature during the write operation and higher than the device temperature of the second magnetic layer during the read operation. Accordingly, when the Curie temperature of the second magnetic layer is close to the device temperature, thermal disturbance increases, and when the Curie temperature of the second magnetic layer is lower than the device temperature, it can be adjusted to exhibit non-magnetism.

According to the embodiments of the present invention, a magnetoresistive device with reduced power consumption and improved stability may be provided.

1 is a perspective view showing a main part of an example of an MRAM employing a magnetoresistive element according to an embodiment of the present invention.
2 is a cross-sectional view illustrating an example of a magnetoresistive device according to an embodiment of the present invention.
3 is a cross-sectional view illustrating a configuration example of a free layer according to an embodiment of the present invention.
4 is a diagram illustrating a concept of an operation example of a free layer when a write operation is performed on a magnetoresistive element according to an embodiment of the present invention.
5 is a view for explaining an example of a free layer used for LLG simulation.
FIG. 6 is a graph showing the effect of reducing the write current using the temperature of the magnetoresistive element during the write operation as a parameter according to the LLG simulation test result of the free layer of FIG. 5 .
7 is a diagram for explaining another example of a free layer used for LLG simulation.
8 is a graph illustrating the relationship between the Curie temperature and the current density according to the LLG simulation test result of the free layer of FIG. 7 .
9 is a graph showing the relationship between the Curie temperature and the amount of current according to the LLG simulation test result of the free layer of FIG. 7 .
10 is a graph illustrating the relationship between a damping constant (α) and a current density according to the LLG simulation test result of the free layer of FIG. 7 .
11 is a graph showing the relationship between the diameter of the free layer and the perpendicular magnetic anisotropy constant according to the LLG simulation test result of the free layer of FIG. 7 .
12 is a view for explaining a configuration example of a free layer in which the first magnetic layer does not have perpendicular magnetic anisotropy, used for LLG simulation.
13 is a graph illustrating the relationship between the Curie temperature and the current density according to the LLG simulation test result of the free layer of FIG. 12 .
14 is a graph showing the relationship between the Curie temperature and the amount of current according to the LLG simulation test result of the free layer of FIG. 12 .
15 is a graph showing the relationship between the diameter of the free layer and the perpendicular magnetic anisotropy constant according to the LLG simulation test result of the free layer of FIG. 12 .
16 is a graph illustrating a relationship between a magnetic exchange stiffness constant and a current density.
17 is a graph illustrating a relationship between an exchange stiffness constant and an amount of current.
18 is a graph illustrating a model of parameter variation according to temperature change in LLG simulation.
19A to 19E are views showing examples of combinations of materials constituting a free layer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For clarity of explanation, the following description and drawings have been appropriately omitted and simplified. In each drawing, the same components or components having the same functions and their substantial portions are denoted by the same reference numerals, and overlapping descriptions are omitted.

The configuration of the MRAM is described.

1 is a perspective view showing a main part of an example of an MRAM employing a magnetoresistive element according to an embodiment of the present invention. 2 is a cross-sectional view illustrating an example of a magnetoresistive device according to an embodiment of the present invention. A magnetoresistive device according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2 .

1 , as main parts of the MRAM, a memory cell 100 , a bit line 1 , contact plugs 5 , 7 and a word line 8 are shown.

The memory cell 100 may include a semiconductor substrate 2 , diffusion regions 3 and 4 , a source line 6 , a gate insulating layer 9 , and a magnetoresistive element 10 .

The MRAM may be formed by arranging several memory cells 100 in a matrix form and connecting the memory cells 100 to each other using a plurality of bit lines 1 and a plurality of word lines 8 . In the MRAM, a data write operation may be performed using a spin torque injection method.

The semiconductor substrate 2 may have diffusion regions 3 and 4 on its upper surface, and the diffusion region 3 may be disposed at a predetermined distance from the diffusion region 4 . The diffusion region 3 may function as a drain region and the diffusion region 4 may function as a source region. The diffusion region 3 may be connected to the magnetoresistive element 10 through a contact plug 7 .

The bit line 1 may be disposed on the semiconductor substrate 2 and may be connected to the magnetoresistive element 10 . The bit line 1 may be connected to a write circuit (not shown) and a read circuit (not shown).

The diffusion region 4 may be connected to the source line 6 through a contact plug 5 . The source line 6 may be connected to a write circuit (not shown) and a read circuit (not shown).

The word line 8 may be disposed on the semiconductor substrate 2 to vertically overlap the diffusion regions 3 and 4 . A gate insulating layer 9 may be interposed between the word line 8 and the semiconductor substrate 2 . The word line 8 and the gate insulating film 9 can function as a selection transistor. The word line 8 may be activated by receiving a current from a circuit (not shown) to be turned on as a selection transistor.

The configuration of the magnetoresistive element is described.

As shown in FIG. 2 , the magnetoresistive element 10 may have a structure in which a pinned layer 11 , an insulating layer 12 , and a free layer 13 are sequentially stacked. Alternatively, they may be stacked in the reverse order. Similarly, in the following description, in the configuration of the magnetoresistive element shown in the other drawings, they may be stacked in the reverse order. The magnetoresistive element 10 may form a magnetic tunnel junction (MTJ) by the pinned layer 11 , the insulating layer 12 , and the free layer 13 . Incidentally, in this specification, unless otherwise specified, "magnetoresistive element" and "magnetic tunnel junction element (MTJ element)" are used without distinction.

A write operation may be performed on the magnetoresistive element 10 by a spin injection magnetization reversal method. That is, the magnetoresistive element 10 may be a magnetoresistive element using a spin injection and write method. In detail, during a writing operation, from the pinned layer 11 to the free layer 13 or from the free layer 13 to the pinned layer 11 in a direction perpendicular to the surfaces of the pinned layer 11 and the free layer 13 . By flowing an electric current, electrons that accumulate spin information can be injected from the pinned layer 11 to the free layer 13 . And, the magnetization of the free layer 13 may be reversed as the spins of the injected electrons move to the electrons of the free layer 13 according to the spin conservation law. That is, depending on the direction of the spin polarization current flowing in the direction perpendicular to the film surface of each layer, the magnetoresistive element 10 sets the relative angles of the magnetizations of the pinned layer 11 and the free layer 13 in a parallel or antiparallel state (that is, (minimum or maximum of resistance) and store information in such a way that binary information "0" or "1" is given.

The pinned layer 11 may be made of a ferromagnetic metal. The ferromagnetic metal may be, for example, Fe, Ni, CoFeB, Co/Pt, Co/Pd, or a combination thereof. The magnetization of the pinned layer 11 may be fixed in a predetermined direction. The predetermined magnetization direction may be a direction perpendicular to the surface of the pinned layer 11 . It is preferable to select a material in which the magnetization direction does not easily change for the pinned layer 11 compared to the free layer 13 . That is, it is preferable to select a material having large effective magnetic anisotropy (Kueff) and saturation magnetization (Ms). However, the material constituting the fixed layer 11 is not particularly limited, and an arbitrary material can be selected according to various conditions. Further, the pinned layer 11 may be referred to as a magnetized pinned layer, a magnetized pinned layer, a reference layer, a magnetized reference layer, a pinned layer, a reference layer, or a magnetized reference layer.

The insulating layer 12 is a tunnel barrier layer and may be an oxide having a NaCl structure. The insulating layer 12 may be made of an insulating film such as MgO. The insulating layer 12 may include CaO, SrO, TiO, VO, NbO, or Al ₂ O ₃ in addition to the aforementioned MgO. However, it is not limited thereto, and is not particularly limited as long as it does not impair the function of the insulating layer 12 . The thickness of the insulating layer 12 may be appropriately changed according to the resistance value of the magnetoresistive element 10 . The insulating layer 12 may be referred to as a tunnel barrier layer or barrier layer.

The free layer 13 can have a magnetization that can change direction. The magnetization of the free layer 13 can be, for example, magnetized perpendicular to the surface of the free layer 13 so that its direction is upward or downward. The free layer 13 may have an easy axis of magnetization in a direction perpendicular to its surface. The thickness of the free layer 13 may be appropriately changed according to a target sheet resistance value of the magnetoresistive element 10 . The free layer 13 may also be referred to as a magnetization free layer, a magnetization variable layer, or a memory layer. The free layer 13 may comprise, for example, CoFeB, a Heusler material, or MnGe.

The configuration of the free layer equipped with the magnetoresistive element is described.

3 is a cross-sectional view illustrating the free layer 13 according to an embodiment of the present invention. The free layer 13 may have a structure in which the first magnetic layer 31 , the magnetic coupling control layer 32 , and the second magnetic layer 33 are sequentially stacked. That is, the free layer 13 may have a configuration in which the magnetic coupling control layer 32 is formed between the first magnetic layer 31 and the second magnetic layer 33 . In the following description, it is assumed that the first magnetic layer 31 of the free layer 13 is disposed adjacent to the insulating layer 12 .

From the viewpoint of thermal stability, the first magnetic layer 31 preferably has perpendicular magnetic anisotropy. From the viewpoint of reducing the write current, it is preferable that the first magnetic layer 31 has magnetization in the perpendicular direction when magnetically coupled with the second magnetic layer 33 . In this case, the first magnetic layer 31 itself does not need to have perpendicular magnetic anisotropy. The first magnetic layer 31 is preferably made of a ferromagnetic material, for example, preferably made of a half-metal or Heusler material.

The magnetic coupling control layer 32 may control magnetic coupling of the first magnetic layer 31 and the second magnetic layer 33 . The magnetic coupling control layer 32 may include, for example, Pd, Pt, Ru, MgO, Ta, or W. In addition, parameters such as resistance change rate, thermal stability, write current, and magnetization reversal rate can be optimized by appropriately changing the size of the magnetic coupling so that the thickness of the magnetic coupling control layer 32 is 2 nm or less.

The second magnetic layer 33 may be made of a material having a lower Curie temperature (Tc) than the first magnetic layer 31 . The second magnetic layer 33 preferably has perpendicular magnetic anisotropy. The second magnetic layer 33 may be made of a material that is ferromagnetic or ferrimagnetic with perpendicular magnetic anisotropy. In addition, the Curie temperature of the material constituting the second magnetic layer 33 is preferably 350K to 500K. Furthermore, as for the upper limit of the said Curie temperature, it is more preferable that it is 450K or less, and it is especially preferable that it is 400K or less.

The second magnetic layer 33 is preferably made of a material having a Curie temperature lower than an expected element temperature when a write operation is performed on the magnetoresistive element. Since the expected device temperature (the device temperature of the free layer or the temperature of the material constituting the free layer) when a write operation is performed on the magnetoresistive device is about 350 K to 400 K, the Curie temperature of the second magnetic layer 33 is higher than 350 K If it is low, the read operation of the magnetoresistive element may be affected by temperature. That is, during a read operation, a problem may occur in thermal stability. The Curie temperature of the second magnetic layer 33 is preferably higher than the device temperature of the second magnetic layer 33 during the read operation. On the other hand, if the Curie temperature of the second magnetic layer 33 is higher than 500K, the temperature range in which the second magnetic layer 33 is greatly affected by thermal disturbance becomes smaller, so it is difficult to obtain the effect of reducing power consumption during the write operation. can Therefore, it is preferable that the Curie temperature of the second magnetic layer 33 is 350K to 500K. In this case, it may have an effect of reducing power consumption during a write operation while securing thermal stability during a read operation.

Furthermore, it is preferable that the element resistance of the magnetoresistive element 10 is 30 Ωμm ^{2 or less. 30 Ωμm 2} is preferable in order to use a device such as an MRAM when an environment such as DRAM is applied.

Incidentally, FIG. 3 shows an example (three-layer structure) in which the free layer 13 is composed of three layers: a first magnetic layer 31 , a magnetic coupling control layer 32 , and a second magnetic layer 33 . has been However, it is also possible when the free layer 13 does not have the magnetic coupling control layer 32, that is, it is composed of two layers of the first magnetic layer 31 and the second magnetic layer 33 (two-layer structure). do. In other words, unlike shown in FIG. 3 , the free layer 13 may have a structure in which the first magnetic layer 31 and the second magnetic layer 33 are stacked.

An operational example of the free layer is described.

Next, an operation example will be described with reference to a specific configuration example of the free layer 13 based on the configuration example of the free layer 13 described above.

4 is a diagram illustrating a concept of an operation example of the free layer 13A when a write operation is performed on a magnetoresistive element. A magnetic coupling control layer (ECC layer) 32A may be disposed between the first magnetic layer 31A and the second magnetic layer 33A. Although Fig. 4 shows a configuration example provided with the magnetic coupling control layer 32A, a configuration without the magnetic coupling control layer 32A is also possible.

In addition, in Fig. 4, the insulating layer 12 is shown in order to facilitate the explanation of the operation of the free layer 13A. 4 shows a case in which the insulating layer 12 is a MgO barrier.

In the following description, unless otherwise specified, the Curie temperature of the first magnetic layer 31A is Tc1, the perpendicular magnetic anisotropy constant is Ku1, the Curie temperature of the second magnetic layer 33A is Tc2, and the perpendicular magnetic anisotropy constant is Ku2. to explain

4 : is demonstrated on the assumption that Curie temperature Tc2 is smaller than Curie temperature Tc1, and is 500 K or less. When the temperature of the second magnetic layer 33A (in particular, the temperature of the material of the second magnetic layer 33A) is lower than the Curie temperature Tc2, it operates as a ferromagnetization (Ferro/Ferri Magnetization), and the second magnetic layer 33A It can be configured to operate paramagnetically when the temperature of is higher than the Curie temperature Tc2.

The perpendicular magnetic anisotropy constants Ku1 and Ku2 are not particularly limited, but it is preferable that the first magnetic layer 31A and the second magnetic layer 33A have perpendicular magnetism. The values of the perpendicular magnetic anisotropy constants Ku1 and Ku2 may be identical or different from each other. The perpendicular magnetic anisotropy constant Ku1 is 0 (zero), that is, the first magnetic layer 31A may be made of a material having no perpendicular magnetic anisotropy. The first magnetic layer 31A and the second magnetic layer 33A may have perpendicular magnetic anisotropy as a whole.

Each of the perpendicular magnetic anisotropy constants is a value indicating the stability of the orientation of the easy axis of magnetization, and the larger the value, the more difficult it is to shake the axis of easy magnetization arranged in the vertical direction.

An example of the operation of the free layer 13A and the decrease in the magnetization reversal current of the magnetoresistive element will be described with reference to FIG. 4 . 4 shows the state of the magnetization direction of the free layer 13A before writing in step 1 (Before writing), during the writing process in step 2 (Writing process), and after writing in step 3 (After writing). The layer 31A and the second magnetic layer 33A are indicated by arrows.

Step 1 indicates the magnetization direction of the free layer 13A before writing, specifically, before a write current flows through the bit line 1 and the word line 8 of FIG. 1 . The first magnetic layer 31A (High Tc layer) and the second magnetic layer 33A (Low Tc layer) have the same magnetization direction and face downward.

Step 2 indicates the magnetization direction of the free layer 13 during a write operation, specifically, when a write current flows through the bit line 1 and the word line 8 of FIG. 1 . The temperature of the free layer 13A may be increased by the write current. For example, the temperature of the second magnetic layer 33A constituting the free layer 13A rises to about 350K to 400K (or, the temperature difference during a read operation during a write operation is 50K to 100K) and the second magnetic When the Curie temperature Tc2 of the layer 33A is less than 500K, the second magnetic layer 33A is affected by strong thermal disturbance and thus the magnetization direction is not determined, so that it may operate like a paramagnetic. That is, when the device temperature is equal to or higher than the Curie temperature Tc2, the second magnetic layer 33A may have a random magnetic moment and become paramagnetic. Meanwhile, the magnetization direction of the first magnetic layer 31A may be reversed by the flow of spin. 4 , the magnetization direction of the first magnetic layer 31A is upward. As described above, according to the configuration of the free layer 13A of FIG. 4 , a complex tunnel junction (freedom) composed of a combination of two magnetic layers (eg, Tc: 700K) whose Curie temperature is much higher than the device temperature during a write operation. layer), the magnitude of the current during the write operation may be reduced. This is because only the magnetization direction of the first magnetic layer 31A is reversed, not the entire free layer 13A.

Step 3 shows the magnetization direction of the free layer 13A after the write operation, specifically when the application of the write current is stopped. The magnetization direction of the first magnetic layer 31A is upward in the same direction as in step 2. As the device temperature decreases, the magnetic moment of the second magnetic layer 33A returns to the property of a ferromagnetic material, and its direction may be directed upward by magnetic interaction with the magnetization of the first magnetic layer 31A. .

During a read operation, the magnetoresistive device can be thermally stable as the device temperature drops to room temperature.

The magnitude of the energy for thermal stability (ie, perpendicular magnetic anisotropy energy) can be very stable because it is related to the perpendicular magnetic anisotropy constants Ku1 and Ku2. Since this formula is a general formula, a detailed description thereof will be omitted. More specifically, since the perpendicular magnetic anisotropy energy is 60 times or more of the thermal energy kT generated by heat, the stability to heat of the magnetoresistive element can be improved. This is because the perpendicular magnetic anisotropy energy is very large compared to the thermal disturbance energy.

Although the magnetic coupling control layer 32A is illustrated in FIG. 4 , the operation of the free layer 13A may be the same as the above-described operation even in the absence of the magnetic coupling control layer 32A.

According to the configuration example of the free layer 13A shown in FIG. 4, it is possible to maintain the thermal stability of magnetization and to reduce the magnetization reversal current. In addition, the magnitude of the magnetic coupling of the first magnetic layer 31A and the second magnetic layer 33A can be optimized by changing the thickness of the magnetic coupling control layer 32A.

The properties of the free layer and the test results are described.

Using LLG (Landau-Liftshitz-Gilbert-Langevin equations) simulation, a first magnetic layer 31 having a high Curie temperature in the free layer 13 and a second magnetism having a lower Curie temperature than the device temperature during a write operation The effect of reducing power consumption during a write operation was confirmed by applying the two-layer structure composed of the layers 33 . The test results will be described together with an example of the configuration of the specific free layer 13 used in the simulation.

The change in the magnetization reversal current (change in the reversal probability due to the current) according to the temperature rise of the second magnetic layer is explained.

5 shows an example of the configuration of the free layer 13B used in the LLG simulation. The free layer 13B includes a first magnetic layer 31B (High Tc Layer), a magnetic coupling control layer 32B (Ecc Layer or Spacer), and a second magnetic layer 33B (Low Tc Layer). The power consumption during the write operation was evaluated by the current density when the magnetization (the first magnetic layer 31 and the second magnetic layer 33) of the free layer 13B was reversed (switched), as an example. .

Descriptions and setting parameters for the first magnetic layer 31 and the second magnetic layer 33 will be described below.

(1) first magnetic layer 31B

Material: MnGe based

Magnetic Moment (Ms1): 150 × 10E3 A/m (150 emu/cc)

Normal magnetic anisotropy constant (Ku1): 10 × 10E5 J/m ³ (10 × 10E6 erg/cc)

Attenuation constant α = 0.005

Curie Temperature (Tc1, High Tc): Above 700K

Polarizability P = 1.0

(2) the second magnetic layer 33B

Material: FePtCu

Magnetic Moment (Ms2): 800 × 10E3 A/m (800 emu/cc)

Normal magnetic anisotropy constant (Ku2): 10 × 10E5 J/m ³ (10 × 10E6 erg/cc) at room temperature

Attenuation constant α = 0.01

Curie Temperature (Tc2, Low Tc): 523.15K

Incidentally, here, the parameters indicated in CGS units in parentheses were used for the above-described LLG simulations. Parameters indicated in SI units can be obtained by using (A) and (B) below as conversion formulas for parameters indicated in CGS units in parentheses.

10 erg/cc = 1 J/m ³ ... (A)

1 G = 1 emu/cc = 1 × 10E3 A/m ... (B)

In other LLG simulations described herein, parameters indicated in CGS units in parentheses are used as in the above-described LLG simulations. The parameters indicated in SI units can be obtained by using the above (A) and (B) as conversion formulas for the parameters indicated in CGS units in parentheses.

The height (thickness) of the first magnetic layer 31B is 2 nm (h1 = 2 nm), the height of the magnetic coupling control layer 32B is 0 nm (hsp = 0), and the height of the second magnetic layer 33B is 2 nm (h2 = 2 nm) ) was made.

The diameter (width) D of the free layer 13B was 20 nm. Here, it is assumed that the free layer 13B has a cylindrical shape, and the cross-sectional diameter D of the free layer 13B is used as a value indicating the size of the free layer 13B. The size of the free layer 13B may be expressed by using a diameter when the cross-section of the free layer 13B is circular, and by using a major axis (length of a major axis) when the free layer 13B has an elliptical cross-section. When the cross-section of the free layer 13B has a different shape, the diameter of a circumscribed circle circumscribing the free layer 13B may be used.

With the temperature rise ΔT as a parameter, the temperature change was set between 10 and 223 °C. The temperature change during write operation was as follows.

The temperature of the first magnetic layer 31B was always 300K. The temperature increase during the write operation occurred only in the second magnetic layer 33B, and the temperature was changed as follows. Even when the temperature rise of the first magnetic layer 31B is taken into consideration, there is no difference in the result.

After applying the write current, the temperature of the second magnetic layer 33B increased and reached the saturation state within 1 ns.

The write current is applied for 10 ns. At this time, the device temperature is in a steady state.

After the write operation, the temperature of the second magnetic layer 33B was lowered to 300K within 5 ns.

6 is a graph showing the effect of reducing the write current using the rising temperature of the magnetoresistive element during the write operation as a parameter according to the LLG simulation result. The graph of FIG. 6 shows the current density (A/m ² ) on the horizontal axis and the reversal probability (switching probability, sw. prob) on the vertical axis. The reversal probability indicates the probability that the magnetization direction of the free layer 13B is reversed at any current density, and FIG. 6 shows the probability in the range of 0 (zero) to 1. When the temperature of the second magnetic layer 33B in the free layer 13B of the embodiment of the present invention is higher than the Curie temperature Tc2, the inversion probability of the free layer 13B is the probability that the first magnetic layer 31B is inverted. can be This is because the magnetization direction of the first magnetic layer 31B is reversed when the second magnetic layer 33B is in a state of large thermal disturbance or paramagnetic during the write operation of the free layer 13B, so that the device temperature after the write operation is lowered. This is because the operation is performed in which the magnetization direction of the ground second magnetic layer 33B is determined.

In FIG. 6 , ΔT (degree C, described as “deg.” in FIG. 6 ) represents the amount of temperature (temperature increase amount) raised during the write operation before the write operation. Here, the amount of temperature increase of the second magnetic layer 33B is indicated.

As shown in the graph of FIG. 6 , as the amount of temperature increase of the second magnetic layer 33B increases, the current density at which the magnetization direction is reversed decreases. That is, the amount of current required for reversing the magnetization direction of the free layer 13B (hereinafter, the amount of current required for reversing the magnetization direction will be referred to as "reversal current") decreases. In the example of FIG. 6 , when the temperature of the second magnetic layer 33B rises adjacent to the Curie temperature Tc2, it can be seen that the amount of inversion current drops to 1/4 or less. Specifically, considering the current density at which the reversal probability is 0.5, compared to the case where ΔT is 0, when ΔT is 223°C (496.15K) close to the Curie temperature Tc2 (close to the Curie temperature Tc2), the current density is 4 min. When is 1, the inversion occurs.

As described above, according to the magnetoresistive element according to the embodiment of the present invention, power consumption during a write operation can be reduced. When the temperature of the device returns to room temperature, the amount of energy for thermal stability is the sum of the effects of the magnetic anisotropy energy Ku1 of the first magnetic layer 31B and the magnetic anisotropy energy Ku2 of the second magnetic layer 33B. Very stable.

As another example, the effect of reducing power consumption during a write operation according to the Curie temperature will be described.

Hereinafter, test results of performing LLG simulation using the free layer 13C configuration shown in FIG. 7 will be described. In this test, a free layer 13C having a two-layer structure consisting of a first magnetic layer 31C having a high Curie temperature and a second magnetic layer 33C having a Curie temperature lower than the device temperature during writing was used. , it was confirmed that the amount of inversion current during the write operation decreased according to the Curie temperature of the second magnetic layer 33C.

Details of the free layer 13C are described below.

(1) first magnetic layer

Material: CoFeB layer

Magnetic Moment (Ms1): 1 × 10E6 A/m (1000 emu/cc)

Normal magnetic anisotropy constant (Ku1): 2 × 10E5 J/m ³ (2 × 10E6 erg/cc)

Attenuation constant α = 0.01

Curie temperature (Tc1): 700K

Polarizability P = 1.0

(2) second magnetic layer

Material: FePtCu layer

Magnetic Moment (Ms2): 600 × 10E3 A/m (600 emu/cc)

Normal magnetic anisotropy constant (Ku2): Ku1 × 2 J/m ³

Attenuation constant α = 0.01

Curie Temperature (Tc2): 700K, 500K, 450K, 400K

(3) Others

The diameter D of the free layer 13C was between 10 nm and 20 nm.

The height (thickness) of the first magnetic layer 31C is 2 nm (h1 = 2 nm), the height of the magnetic coupling control layer 32C is 0 nm (hsp = 0), and the height of the second magnetic layer 33C is 2 nm (h2 = 2 nm) It was. The thickness of the magnetic coupling control layer 32C was set to zero, and the free layer 13C was configured not to include the magnetic coupling control layer 32C.

In the LLG simulation using the configuration of the free layer 13C, the magnetic anisotropy constant Ku value was adjusted so that the increase amount Δ of the device temperature (material) of the second magnetic layer 33C was 60.

Further, as a comparative example, a test was also conducted on a configuration of a general free layer that does not have the above-described two-layer structure.

Material: Co/Ni mulutilayer

Magnetic Moment (Ms): 600 × 10E3 A/m (600 emu/cc)

Normal magnetic anisotropy constant (Ku): 6 × 10E5 J/m ³ (6 × 10E6 erg/cc)

Curie temperature (Tc): values greater than 700K (426.85℃) (> 700K)

8 to 10 show the analysis of the results of the LLG simulation test of the free layer shown in FIG. 8 is a graph showing the relationship between the Curie temperature and the current density, FIG. 9 is a graph showing the relationship between the Curie temperature and the amount of current, and FIG. 10 is a graph showing the relationship between the damping constant α and the current density. 8 to 10 are results of testing on the premise that the device temperature of the free layer rises by 50° C. during the write operation of the magnetoresistive device.

The graph shown in FIG. 8 shows the Curie temperature Tc (K) on the horizontal axis and the current density j _sw (×10 ¹² A/m ² ) on the vertical axis. The graph shown in FIG. 9 shows the Curie temperature Tc (K) on the horizontal axis and the amount of current i _sw (mA) on the vertical axis. 8 and 9 show the values of the Curie temperature Tc2 of the second magnetic layer 33C (Example) as the Curie temperature Tc (Example) and the value of the Curie temperature 700K of the typical free layer (Comparative Example) at each Curie temperature. shows the test results.

The value of the diameter D of the free layer 13C is 10 nm in the solid line and 20 nm in the dotted line.

As can be seen from the graphs shown in FIGS. 8 and 9 , the free layer 13C having a Curie temperature Tc of 500K or less can reduce power consumption compared to a general free layer having a Curie temperature of 700K (or 700K or higher). For example, when the device temperature of the second magnetic layer 33C increases by 50° C., power consumption may be reduced by 40-50%.

The graph shown in FIG. 10 is represented on the horizontal axis using the attenuation sensitivity α of the second magnetic layer as a parameter, and the current density j _sw (×10 ¹² A/m ² ) is represented on the vertical axis. In FIG. 10, the solid line is the test result (Example) when the Curie temperature of the second magnetic layer 33C in the free layer 13C shown in FIG. 7 is 400K, and the dotted line is the normal free layer (the Curie temperature is 700K). ) is the test result (comparative example). Compared to the general free layer, the free layer 13C of FIG. 7 is less affected by the damping constant α. Accordingly, the range of materials constituting the second magnetic layer 33C can be widened. That is, a magnetic material having a relatively large damping constant and a small Tc may be used.

11 is a graph showing the relationship between the diameter of the free layer 13C and the perpendicular magnetic anisotropy constant Ku used for the LLG simulation test of the free layer shown in FIG. 7 . 11 shows the diameter D (nm) of the free layer 13C on the abscissa axis and the perpendicular magnetic anisotropy constant Ku (Merg/cc) on the ordinate axis. As a material constituting the free layer 13C, the solid line is the test result of the FePtCu layer constituting the second magnetic layer 33C, and the dotted line is the test result of the CoFeB layer constituting the first magnetic layer 33A. In addition, for the perpendicular magnetic anisotropy constant Ku, the thermal stability parameter (KuV/Kt) becomes 60 (KuV / Kt = 60), and the perpendicular magnetic anisotropy constant Ku2 value of the FePtCu layer is equal to the perpendicular magnetic anisotropy constant Ku1 value of the CoFeB layer. It was adjusted so that it might become 2 times (Ku2@FePtCu=2*Ku1@CoFeB). During the write operation, the temperature of the second magnetic layer 33C was raised to 300K.

11, when the diameter D of the free layer 13C is 10 nm, the perpendicular magnetic anisotropy constant Ku is large, and as the diameter D increases, the perpendicular magnetic anisotropy constant Ku becomes small. Therefore, when the size (diameter of the free layer) of the magnetoresistive element (magnetic tunnel coupling element) is small, it is necessary to make the perpendicular magnetic anisotropy constant Ku to a large value. In addition, it was confirmed that the need to increase the perpendicular magnetic anisotropy constant Ku according to the size of the magnetoresistive element and/or the material constituting the free layer is different.

Power consumption reduction in the case where the first magnetic layer does not have perpendicular magnetic anisotropy is described.

Hereinafter, test results of performing LLG simulation using the configuration of the free layer 13D shown in FIG. 12 will be described. The free layer 13D has a double structure including the first magnetic layer 31D and the second magnetic layer 33D.

When the first magnetic layer 31D is configured such that the perpendicular magnetic anisotropy constant Ku1 is zero, and the first magnetic layer 31D of the free layer 13D does not have perpendicular magnetic anisotropy, it is consumed during a write operation. It was tested whether the power could be reduced.

The thickness of the magnetic coupling control layer 32D (Spacer) was set to 0 (hsp = 0 nm), so that the free layer 13D did not have the magnetic coupling control layer 32D.

Details of the free layer 13D are described below.

(1) first magnetic layer

Material: CoFeB layer or CFMS layer with in-plane magnetic anisotropy

Magnetic Moment (Ms): 1 × 10E6 A/m (1000 emu/cc)

Normal magnetic anisotropy constant (Ku1): 0 J/m ³ (0 erg/cc)

Attenuation constant α = 0.01

Curie temperature (Tc1): 700K (426.85 ℃)

Polarizability P = 1.0

(2) second magnetic layer

Material: FePtCu layer

Magnetic Moment (Ms): 600 × 10E3 A/m (600 emu/cc)

perpendicular magnetic anisotropy constant (Ku2): when the diameter D of the free layer is in the range of 10 - 20 nm,

so that the value of the thermal stability constant Δ of the free layer is 60

Adjusted the value of the perpendicular moral anisotropy constant Ku2

Damping constant α = 0.01

Curie Temperature (Tc): 360K, 400K, 450K, 500K, 700K

(86.85 ℃, 126.85 ℃, 176.85 ℃, 226.85 ℃, 426.85 ℃)

(3) Others

The diameter D of the free layer 13D was 10-20 nm.

The height (thickness) of the first magnetic layer 31D is 2 nm (h1 = 2 nm), the height of the magnetic coupling control layer 32D is 0 nm (hsp = 0), and the height of the second magnetic layer 33D is 2 nm (h2) = 2 nm).

Several Curie temperatures Tc of the second magnetic layer 33D are parameters, and the case of a Curie temperature Tc of 700K is set to be a typical free layer.

13 to 15 are analyzes of LLG simulation test results of the free layer shown in FIG. 12 . 13 is a graph showing the relationship between the Curie temperature and the current density, FIG. 14 is a graph showing the relationship between the Curie temperature and the amount of current, and FIG. 15 is a graph showing the relationship between the diameter of the free layer and the perpendicular magnetic anisotropy constant.

The graph shown in FIG. 13 represents the Curie temperature Tc (K) on the horizontal axis and the current density j _sw (×10 ¹² A/m ² ) on the vertical axis. The graph shown in FIG. 14 shows the Curie temperature Tc (K) on the horizontal axis and the amount of current i _sw (mA) on the vertical axis. 13 and 14 show the current density or the amount of current when the magnetic direction of the first magnetic layer 31D is reversed at each Curie temperature set as a parameter.

The value of the diameter D of the free layer 13D is 10 nm in the solid line and 20 nm in the dotted line.

13 and 14 , the free layer 13D can significantly reduce power consumption when the Curie temperature is 360K, 400K, and 450K. For example, when the Curie temperature Tc of the second magnetic layer 33D is 400 K or less, when the device temperature is increased by 50° C., 50 to 70% of power consumption may be reduced. From the test results of FIGS. 13 and 14 , it was confirmed that the effect of saving power occurs even when the first magnetic layer does not have perpendicular magnetic anisotropy.

The graph shown in FIG. 15 represents the diameter D of the free layer 13D on the horizontal axis, and the perpendicular magnetic anisotropy constant Ku2 (Merg/cc) of the second magnetic layer 33D on the vertical axis. For the perpendicular magnetic anisotropy constant Ku, the thermal stability parameter (KuV/Kt) was adjusted to be 60 (KuV/Kt = 60), and the Ku1 value of the CoFeB layer or the CFMS layer was adjusted to be zero. During the write operation, the temperature of the second magnetic layer 33C was increased to 300K.

15, when the diameter D of the free layer 13D is 10 nm, the perpendicular magnetic anisotropy constant Ku2 is large, and as the diameter D becomes large, the perpendicular magnetic anisotropy constant Ku2 becomes small. Therefore, when the size (diameter of the free layer) of the magnetoresistive element (magnetic tunnel coupling element) is small, it is necessary to make the perpendicular magnetic anisotropy constant Ku2 of the second magnetic layer 33D a large value. That is, when the first magnetic layer 31D does not have perpendicular magnetic anisotropy, it is preferable that the second magnetic layer 33D has perpendicular magnetic anisotropy, especially when the diameter of the free layer 13D is small (small size). case), the need to increase the perpendicular magnetic anisotropy constant Ku2 becomes higher than in the case where the diameter is large.

A review of the magnetic exchange stiffness constant of the first and second magnetic layers is described.

Hereinafter, the test results of examining the self-exchange stiffness constant after performing the LLG simulation using the configuration of the free layer 13D shown in FIG. 12 will be described. In this test, parameters of the second magnetic layer 33D were changed in the free layer 13D described with reference to FIG. 12 as follows.

Curie temperature (Tc): 400K, 700K (126.85 ℃, 426.85 ℃)

Exchange bond constant A: 0.1 - 2.0 × 10 ^-13 J/cm (0.1 - 2.0 × 10 ^-6 erg/cm)

In this test, it is assumed that the device temperature rises by 50 ℃ during write operation.

When the Curie temperature Tc is 400K, it is a free layer according to an embodiment of the present invention, and when it is 700K, it is a general free layer. The free layer diameter D was tested for a case of 10 nm and a case of 20 nm, respectively.

Figures 16 and 17 show the test results of the exchange binding constant. 16 is a graph showing the relationship between the magnetic exchange stiffness constant (× 10 ⁻⁶ erg/cm) and the current density j _sw (× 10 ¹² A/m ² ), and FIG. 17 is the magnetic exchange stiffness constant A (× 10 ^{−6 )} erg/cm) and the amount of current i _sw (mA). The magnetic exchange stiffness constant A can be adjusted through the thickness of the magnetic coupling control layer 32C. It can be seen that the optimal value of the self-exchange stiffness constant A at which the inversion current becomes small is smaller when the diameter D of the free layer is 10 nm than when it is 20 nm. In addition, when the diameter D of the free layer is the same, it can be confirmed that the inversion current value of the free layer according to the embodiment of the present invention is smaller than that of the general free layer. Accordingly, the magnetoresistive device according to the embodiment of the present invention can reduce the magnetization reversal current without impairing thermal stability. It suggests that the thermal stability of the magnetoresistive device can be improved.

18 shows a model of variation of parameters according to temperature change in LLG simulation.

The graph shown in FIG. 18 corresponds to the Curie temperature Tc on the abscissa axis and the magnetic moment Ms on the ordinate axis, the perpendicular magnetic anisotropy constant Ku, or the transformation parameter A. That is, the ratio (T/Tc) of the Curie temperature Tc and the temperature T of the material when an electric current flows is made to correspond to the value of each parameter. Each parameter is expressed as the ratio of the value of each element (Ms0, Ku0, A0) to the value of each element (Ms, Ku, A) when the material temperature is zero.

Other embodiments are described.

19A shows an example of the configuration of STT-MRAM. FL is the free layer, MgO is the insulating layer, PEL is the reference layer, and Ru is the layer that helps the crystal orientation of the reference layer.

[Co/Pt] ML is the perpendicular self-retaining layer, and seed represents the layer that controls the crystal orientation.

19B to 19E show configuration examples of the free layer FL of FIG. 19A .

19B and 19C , a CoFeB layer may be used for the first magnetic layer of the free layer, and an FePtCu layer or a Fe/Pt/Cu multi-layer may be used for the second magnetic layer. Referring to FIG. 19D , a MnGe layer may be used for the first magnetic layer and a FePtCu layer may be used for the second magnetic layer. Referring to FIG. 19E , a Heusler (CFMS) layer may be used for the first magnetic layer, and a Fe/Pt/Cu multi-layer may be used for the second magnetic layer.

For example, FePtCu is a material having a high perpendicular magnetic anisotropy constant Ku and a low Curie temperature Tc, and is preferable for use as the second magnetic layer. As the second magnetic layer, a material having a controllable Curie temperature Tc and large perpendicular magnetic anisotropy is suitable for use, for example, a magnetic material such as _{FePtCu [Co/Pt]n, TbFeCo, Mn 2} RuGa, or Mn _{2 RuGe.} can be used.

For example, an LLG simulation was performed using a CoFeB layer as the first magnetic layer and a FePtCu layer or Fe/Pt/Cu multi-layer as the second magnetic layer. As a result, the following test results were obtained.

FePtCu layer

Magnetic Moment (Ms): 600 × 10E3 A/m (600 emu/cc)

Normal magnetic anisotropy constant (Ku2): 10 × 10E5 J/m ³ (10 × 10E6 erg/cc) at room temperature

Curie temperature (Tc): 250 ℃ (523.15K)

Attenuation constant α = 0.01

CoFeB layer

Magnetic Moment (Ms): 1 × 10E6 A/m (1000 emu/cc)

Normal magnetic anisotropy constant (Ku1): 2 × 10E5 J/m ³ (2 × 10E6 erg/cc) at room temperature

Curie temperature (Tc): temperature above 250 ℃ (523.15K) (>>> 250 ℃)

Attenuation constant α = 0.01

In the configuration examples of the four types of free layers described above, the magnetic coupling control layer (ECC Layer) may include, for example, Pd, Pt, Ru, MgO, Ta, and/or W.

The second magnetic layer of the free layer may include, for example, MnGeX, [Co/Pt]n, TbFeCo, FePtCu, and/or Mn2RuGa.

As described above, the magnetoresistive element having perpendicular magnetization and performing a read operation by the magnetoresistance effect has high resistance to thermal disturbance due to miniaturization, and thus is expected as a next-generation memory. On the other hand, when it is difficult to form a ferromagnetic thin film having high perpendicular magnetic anisotropy, which is the main component of a magnetoresistive element, and to solve this problem, when a perpendicular magnetization holding layer is combined with a magnetic tunnel junction (MTJ), the magnetization reversal current is increased to reduce power consumption. There was a problem that it was difficult to implement the device. To solve these problems, in the magnetoresistive device according to an embodiment of the present invention, in the magnetoresistive device configured as a magnetic tunnel junction by sandwiching an insulating thin film between two ferromagnetic thin films, the perpendicular magnetization film having a low Curie temperature Tc is perpendicularly magnetized. By including it as a holding layer, it was realized that the magnetization and thermal stability of the free layer (recording layer) was maintained and the magnetization reversal current was reduced. This technology contributes to the practical use of STT-MRAM.

More specifically, the free layer included in the magnetoresistive element according to an embodiment of the present invention has at least a first magnetic layer and a second magnetic layer. By adjusting the Curie temperature of the second magnetic layer to be lower than the Curie temperature of the first magnetic layer, it is possible to reduce the write current due to the effect of raising the temperature during the write operation. For example, compared with a general technique, power consumption during recording operation can be reduced by 50% or more.

The present invention relates to an MTJ device for high-integration STT-MRAM using spin injection magnetization reversal effect, such as STT-MRAM (Spin Transfer Torque Magnetic Random Access Memory) or Racetrack-memory (magnetic-based non-volatile memory). can be used

1: bit line
2: semiconductor substrate
3, 4: diffusion regions
5, 7: contact plugs
6: source line
8: word line
9: gate insulating film
10: magnetoresistive element
11, 21: fixed layer
12: insulating layer
13, 13A, 13B, 13C: free layer
100: memory cell
31, 31A, 31B, 31C: first magnetic layer
32, 32A, 32B, 32C: magnetic coupling control layer
33, 33A, 33B, 33C: second magnetic layer

Claims (9)

a pinned layer with a fixed magnetization direction;
a free layer having a variable magnetization direction and having a first magnetic anisotropy; and
an insulating layer provided between the pinned layer and the free layer;
the pinned layer, the free layer, and the insulating layer form a magnetic tunnel junction;
The free layer is:
a first magnetic layer;
a second magnetic layer having a lower Curie temperature than the first magnetic layer and having a second perpendicular magnetic anisotropy; and
a magnetic coupling control layer provided between the first magnetic layer and the second magnetic layer and controlling magnetic coupling of the first magnetic layer and the second magnetic layer;
The second magnetic layer operates as a paramagnetic during a write operation, and operates as a ferromagnetic during a read operation.
The method of claim 1,
The second magnetic layer has a Curie temperature of 350K or higher and 500K or lower.
The method of claim 1,
The magnitude of the second perpendicular magnetic anisotropy is 5×10E5 J/m ³ (5×10E6 erg/cc) or more.
4. The method according to any one of claims 1 to 3,
The first magnetic anisotropy is in-plane magnetoresistive element.
4. The method according to any one of claims 1 to 3,
the direction of the first magnetic anisotropy is perpendicular to the surface of the free layer,
The magnitude of the first magnetic anisotropy is 2×10E5 J/m ³ (2×10E6 erg/cc) or more and 10E6 J/m ³ (10E7 erg/cc) or less.
4. The method according to any one of claims 1 to 3,
The magnetic coupling control layer includes at least one of Pd, Pt, Ru, MgO, Ta, and W.
4. The method according to any one of claims 1 to 3,
The second magnetic layer is a magnetoresistive element made of FePtCu, [Co/Pt]n, TbFeCo, Mn ₂ RuGa, Mn ₂ RuGe, or other ferromagnetic material.
4. The method according to any one of claims 1 to 3,
A resistance value of the magnetoresistive element is 30 Ωμm ² or less.
4. The method according to any one of claims 1 to 3,
A Curie temperature of the second magnetic layer is lower than a temperature of the second magnetic layer during a write operation, and is higher than a temperature of the second magnetic layer during a read operation.

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