WO2009136454A1

WO2009136454A1 - Spin valve element and storage device

Info

Publication number: WO2009136454A1
Application number: PCT/JP2008/065414
Authority: WO
Inventors: 春雄川上; 泰史荻本
Original assignee: 富士電機ホールディングス株式会社
Priority date: 2008-05-09
Filing date: 2008-08-28
Publication date: 2009-11-12
Also published as: JP2011175987A

Abstract

A spin valve element in which intermediate layers (24, 51) comprising one insulator layer or non magnetic layer and a pair of ferromagnetic layers (23, 25) between which the intermediate layer is sandwiched are provided so as to reduce current for magnetic reverse and speed up operation and the magnetic coercive forces of the pair of ferromagnetic layers are different from each other, or a storage device using the spin valve element. The directions of magnetization facilitating axes (10, 12) of the pair of ferromagnetic layers are set to be different. Further, an angle between the magnetization facilitating axes is desirably set to be in a fixed range.

Description

Spin valve element and storage device

The present invention relates to a spin valve element using a tunnel magnetoresistive effect (TMR) or a giant magnetoresistive effect (GMR) and a memory device using the spin valve element.

In recent years, along with the progress of nanoelectronics, the development of products that apply physical phenomena unique to micro-sized magnetic materials has been promoted. Among them, in particular, a field using the spin property of free electrons of magnetic materials is called a spin electronics field, and energetic technological development is underway.

In this spin electronics field, what is currently considered to have the highest practical applicability is the tunnel magnetoresistance (TMR) effect that occurs in the laminated structure of a ferromagnetic layer, an insulating layer, and a ferromagnetic layer, Alternatively, there is a spin valve element that applies a giant magnetoresistance (GMR) effect generated in a laminated structure of a ferromagnetic layer, a nonmagnetic layer (conductive layer), and a ferromagnetic layer. 11 and 12 show a configuration example of a conventional spin valve element in the present invention.

FIG. 11 is a sectional view showing the basic components of a spin valve element using TMR. This spin-valve element includes a single insulator layer 24 formed on a substrate 5, and a ferromagnetic layer 23 (fixed layer) and a ferromagnetic layer 25 (free layer) forming a pair sandwiching the insulator layer.

Electrode layers

21 and 27, and an antiferromagnetic layer (pinned layer) 22, a capping layer 26, and the like are added as necessary. The magnetization of the fixed layer 23 is fixed by magnetic coupling with the antiferromagnetic layer 22 or the like. The magnetization of the free layer 25 is controlled by spin injection with a polarized current or by an external magnetic field.

In the control by spin injection, when electrons are caused to flow from the fixed layer 23 to this element, torque that tends to be parallel to the magnetization of the fixed layer 23 acts on the magnetization of the free layer 25. Conversely, when electrons flow from the free layer 25 toward the fixed layer 23, a torque that tends to be antiparallel to the magnetization of the fixed layer 23 acts on the magnetization of the free layer 25. By these actions, the magnetization direction of the free layer 25 can be controlled by the direction of current (spin injection magnetization reversal).

FIG. 12 is a sectional view showing the basic components of a spin valve element using GMR. The difference between the spin valve element using GMR and the spin valve element using TMR in FIG. 11 is that the insulator layer 24 is replaced with the nonmagnetic layer 51 in the spin valve element using TMR. The configuration other than is basically the same.

Further, Patent Document 1 discloses an example in which the relationship between the angle of the wiring and the direction of the easy axis is determined in a configuration using a spin valve element that controls magnetization by an external magnetic field (external magnetization reversal).
JP 2005-142299 A

As an application of a spin valve element using spin injection magnetization reversal or external magnetization reversal, a magnetic random access memory (MRAM) has received the most attention, and a conventional DRAM (Dynamic Random Access Memory) or SRAM (SRAM) It is expected as an alternative to Synchronous DRAM. The MRAM potentially exhibits excellent technical characteristics such as high speed operation, low power consumption, low voltage operation, and high rewrite durability. In particular, since the structure is simplified by performing writing by spin injection magnetization reversal as described above, the MRAM can be increased in density. One of the biggest technical problems related to the practical application of MRAM using a spin valve element is to reduce the magnetization reversal current.

Also, as another problem related to the magnetization reversal, there is an increase in the speed of the rewriting operation necessary for operating the MRAM at a high speed. Generally, when the magnetization of the free layer is completely parallel or antiparallel to the magnetization of the fixed layer, the torque in the reversal direction (circumferential direction in FIG. 2) due to the injected spin becomes zero, and reversal is not started. In practice, the free layer magnetization has a finite angle with respect to the fixed layer magnetization due to thermal fluctuations, so inversion is observed in many cases, but there is essentially a stochastic element in the inversion operation and inversion time. is doing. In addition, since the initial reversal torque is small due to the geometric arrangement, it takes time to rotate the magnetization, and therefore the magnetization reversal cannot be accelerated.

In view of the above circumstances, an object of the present invention is to reduce a magnetization reversal current in a spin-injection magnetization reversal spin valve element or to speed up magnetization reversal.

The inventors of the present application have found that the magnetization reversal current can be reduced or the magnetization reversal can be performed at high speed by making the easy axis direction of the free layer different from the easy axis direction of the fixed layer. .

That is, in the present application, there is provided a spin valve element including an intermediate layer made of one insulating layer or a nonmagnetic layer, and a pair of ferromagnetic layers sandwiching the intermediate layer, wherein the pair of ferromagnetic layers There is provided a spin valve element in which the coercive forces of the ferromagnetic layers are different from each other, and the directions of the easy axes of the ferromagnetic layers of the pair of ferromagnetic layers are different from each other.

The easy axis of magnetization can be artificially set by the shape anisotropy, the influence of the adjacent antiferromagnetic layer, the orientation during film formation, and the like. Therefore, it is possible to intentionally change the direction of the easy magnetization axis between the free layer and the fixed layer.

In order to realize a ferromagnetic layer with different coercive force, a pair of ferromagnetic layers whose coercive force is changed by changing the magnetism of the ferromagnetic layer itself, or another layer (for example, a pinned layer). It is possible to use a pair of magnetic layers with a larger effective coercive force in combination with an antiferromagnetic layer, or a pair of ferromagnetic layers with different coercive forces by changing the film thickness. it can.

In the present invention, preferably, the directions of the easy magnetization axes can be different from each other in the plane of the ferromagnetic layer. The state in which the easy axes of the ferromagnetic layer are different from each other in the plane of the ferromagnetic layer typically means a state in which both the easy axes of the ferromagnetic layer are in the plane of the layer and the directions are different from each other. In addition, when the direction vector in the direction of the easy axis of each ferromagnetic layer is projected onto the surface of the ferromagnetic layer, the easy axis of the ferromagnetic layer is oriented so that the projected direction is different. Including those that are.

In the present invention, it is preferable that the angle θ formed by the easy magnetization axes of the pair of ferromagnetic layers is a spin valve element satisfying the following expression (1).
(K × T) / (K _u × V) <sin ² θ <0.25 (1)
Here, _Ku is the magnetic anisotropy constant, k is the Boltzmann constant, T is the operating temperature expressed in absolute temperature, and V is the volume per element of the ferromagnetic layer with the smaller coercive force. When the value obtained by squaring the sine (SIN) component of the angle between the easy magnetization axes is larger than a constant value (formula (1), left side) determined by the physical property value such as magnetic anisotropy constant and coercive force and temperature, A stable angle can be maintained without being affected by thermal fluctuations. On the other hand, the value also has a certain upper limit from the MR ratio, the convergence to a stable point, and the like. The present inventor has found that these technical requirements can be satisfied if the easy axis is set so as to satisfy the above-mentioned conditions.

Also, since the easy axis of magnetization is affected by the shape, it is also preferable to adjust the shape of the ferromagnetic layer. That is, the shape of the periphery of at least one of the pair of ferromagnetic layers has a first direction included in the surface of the ferromagnetic layer and a first direction included in the surface and orthogonal to the first direction. It is preferable that the ranges of the two directions are different from each other. Among the ferromagnetic layers, one direction (for example, the first direction) is perpendicular to the shape of the peripheral edge of either or both of the layer having a high coercive force (fixed layer) and the layer having a low coercive force (free layer). The shape can be larger than the direction (second direction). Examples of this shape include a rectangle and an ellipse.

In the present invention, a storage device using a spin valve element having any of the above-described characteristics as a storage element is also provided.

The present invention has an effect that it is possible to achieve at least one of reducing the magnetization reversal current of the spin valve element and increasing the speed of magnetization reversal of the spin valve element. When the magnetization reversal current is reduced, for example, the reliability of the circuit element for driving the memory element when the spin valve element is used as the memory element of the memory device can be improved, and the size of the circuit element can be reduced. And power consumption during driving can be suppressed. Further, if the magnetic reversal can be performed at high speed, data writing to the memory element when the spin valve element is used can be speeded up, and the operation speed of the memory device can be increased.

Explanatory drawing which shows the relative relationship of the easy axis of a free layer and a fixed layer in the spin valve element of this invention. Explanatory drawing which shows the relative relationship of the magnetization easy axis | shaft of a free layer, and injection | pouring spin torque in the conventional spin valve element. Explanatory drawing which shows the relative relationship of the magnetization easy axis | shaft of a free layer, and injection | pouring spin torque in the spin valve element of this invention. Calculation example 1 of magnetization reversal behavior in a conventional spin valve element. Calculation Example 2 of magnetization reversal behavior in a conventional spin valve element. Calculation Example 1 of magnetization reversal behavior in the spin valve element of the present invention. Calculation Example 2 of magnetization reversal behavior in the spin valve element of the present invention. Calculation Example 3 of magnetization reversal behavior in the spin valve element of the present invention. FIG. 3 is a schematic diagram illustrating a configuration of a memory element of a memory device of the present invention. 1 is a block diagram illustrating a configuration of a storage device of the present invention. Sectional drawing which shows the basic composition part of the spin valve element using TMR. Sectional drawing which shows the basic composition part of the spin valve element using GMR.

Explanation of symbols

5 Substrate 21 Electrode layer 22 Antiferromagnetic layer (pinned layer)
23 Ferromagnetic layer (pinned layer)
24 Insulator layer 25 Ferromagnetic layer (free layer)
26 Capping Layer 27 Electrode Layer 30 Insulating Layer 31 Wiring 51 Nonmagnetic Layer 100 Nonvolatile Memory Device

Embodiments of the present invention will be described below. First, the inventor of the present application examined the reduction of the magnetization reversal current. When a MOS-FET is used as the memory selection element, the magnetization reversal current density J _c is required to be at least 10 ⁶ A / cm ² or less from the viewpoint of ensuring the reliability of the MOS-FET. In general, it is known that the magnetization reversal current density J _c is expressed by the following equation in spin injection magnetization reversal.
J _c ^{P → AP} = −e (VM _s / μ _B ) αγ [+ H _ext + (H _U + M _s / μ ₀ ) / 2] / g (0) (2)
J _c ^{AP → P} = + e (VM _s / μ _B ) αγ [−H _ext + (H _U + M _s / μ ₀ ) / 2] / g (π) (3)
Here, J _c ^{P → AP} and J _c ^{AP → P} are used for reversing the magnetization of the free layer 25 and the fixed layer from the parallel state to the anti-parallel state, and from the anti-parallel state to the parallel state, respectively. E is the elementary charge, V is the volume per element of the free layer, M _s is the saturation magnetization of the free layer, μ _B is the Bohr magneton, α is the Gilbert damping coefficient, γ Is the magnetic gyro constant, H _ext is the externally applied magnetic field, H _U is the anisotropic magnetic field of the free layer, and μ ₀ is the magnetic permeability. Further, g (θ) is a coefficient representing the efficiency of spin transfer, and is expressed by the following equation, where θ is an angle formed by the magnetization of the fixed layer and the free layer, and P is a function of the spin polarization.
g (θ) = [− 4+ (P ^1/2 + P ^−1/2 ) ³ × (3 + cos θ) / 4] ⁻¹
for GMR (4)
g (θ) = P / (1 + P ² cos θ) for TMR (5)
In the case of spin injection magnetization reversal, the externally applied magnetic field H _ext is zero. Further, from the expressions (4) and (5), since g (π)> g (0) is generally satisfied, J _c ^{P → AP} > J _c ^{AP → P.}

According to the expressions (2) and (3), J _c is proportional to the volume V of the free layer, for example. Therefore, if the free layer is made thinner, J _c can be reduced. However, the stability of the memory, i.e. the thermal stability of the free layer magnetization, it is possible to describe the K _u × V a K _u as anisotropy, (small V) thin free layer Then as a memory The stability of is reduced. That is, the thickness of the free layer can be reduced only within the range of the restriction. Further, the other parameters are physical property values of the material. This material development to reduce the magnetization reversal current density J _c by focusing on the physical property values is performed, sufficient characteristics are not obtained heretofore.

The main technical point of the present invention is that the direction of the easy axis of magnetization of the free layer and the fixed layer is made different to reduce J _c ^{P → AP} expressed by the above equation (2) and to invert The purpose is to ensure that the torque due to the injection spin at the start is a finite value and to increase the speed of magnetization reversal.

As shown in FIG. 1, when the angle between the easy axis 10 of the free layer and the easy axis 12 of the fixed layer is θ, the magnetization of the free layer and the fixed layer when there is no injected spin current are also θ Make. Therefore, the threshold current density J _c ^{P → AP} for switching the magnetization of the free layer 25 and the fixed layer 23 from the parallel state to the antiparallel state is
J _cθ ^{P → AP} = −e (VM _s / μ _B ) αγ [+ H _ext + (H _U + M _s / μ ₀ ) / 2] / g (θ)
(6)
Represented by Here, since g (θ)> g (0) in general, J _cθ ^{P → AP} <J _c ^{P → AP} , as compared with the case where θ = 0 expressed by the equation (2) is substituted. It can be seen that the threshold current density can be lowered. Similarly, since g (θ + π) <g (π), J _cθ ^{AP → P} > J _c ^{AP → P} , but when θ <π / 2, J _cθ ^{P → AP} > J _cθ ^{AP → P} Therefore, in that range, there is an effect of substantially lowering the threshold value of the current density.

Further, as shown in FIG. 3, it is clear that the torque at the start of reversal becomes a non-zero value by having an angle θ with respect to the torque caused by the spin into which the magnetization of the free layer is injected. For comparison, FIG. 2 shows a relative relationship between the easy magnetization axis of the free layer and the injection spin torque in a conventional spin valve element. As described above, the angle of the free layer magnetization is distributed in a certain range due to thermal fluctuation. Regardless of thermal fluctuation, in order for the angle of the free layer magnetization to have a finite angle value with respect to the angle of the fixed layer magnetization, it is desirable that the angle θ is larger than the angle caused by the thermal fluctuation. In general, the condition that the anisotropic energy due to the magnetization inclination θ is equivalent to the thermal energy is K _u × V × sin ² θ = kT (where k is the Boltzmann constant and T is the absolute temperature during operation). Temperature).
(K × T) / (K _u × V) <sin ² θ (7)
It is desirable that For example, assuming a CoFe-based material as the material of the free layer, K _u = ⁴ × 10 ⁴ Jm ³ , the shape of the free layer is an ellipse having a major axis of 130 nm × minor axis of 70 nm, a thickness of 2 nm, and a volume per element V = 1 Assuming .4 × 10 ⁻²³ m ³ , θ> 0.035π radians (= 6.3 °) is obtained from Equation (7) using 4.14 × 10 ⁻²¹ J at a temperature of 300 K.

As the tilt angle θ increases, J _c decreases and the magnetization reversal time also shortens. On the other hand, the electrical resistance ratio (MR ratio) of the spin valve element due to magnetization reversal decreases, and as described later, After magnetization reversal, convergence to a stable point tends to be slow. The slow convergence to the stable point is presumed that the two driving forces of the injected spin and the anisotropic magnetic field of the free layer are balanced and the precession along the balance is stable. From these two limiting conditions, it has also been found that if a practical upper limit of θ is determined, it is preferable to set it to about 30 ° (= π / 6 radians).

An example of a procedure for manufacturing a TMR type spin valve element is shown below. The material and film thickness of each layer given below are examples. A Cu thin film (30 nm) is formed as an electrode layer 21 on a substrate 5 such as a silicon wafer with an oxide film, and then CoFeB (20 nm) as a ferromagnetic layer 23, MgO (0.6 nm) as an insulator layer 24, CoFeB (2 nm) is sequentially stacked as the ferromagnetic layer 25 and Cu (2 nm) is sequentially stacked as the capping layer 26. Further, a negative resist is applied, patterning is performed by electron beam irradiation, and an elliptical columnar spin valve element is formed by ion milling or dry etching. Further, an SiO ₂ film is formed by CVD or the like to cover the side surfaces of the elliptical columnar spin valve element, and then the resist on the spin valve element is removed by lift-off to form an upper electrode. Thereafter, annealing is performed at 350 to 500 ° C. in a magnetic field of about several kOe (1 Oe≈79.6 A / m) to determine the easy axis of magnetization of the fixed layer. In the case of a GMR type spin valve element, basically the same manufacturing procedure is used except that a nonmagnetic layer 51 such as Cu is used instead of the insulator layer 24.

As a material constituting the spin valve element of the present invention, the substrate 5 can be a silicon substrate or a glass substrate, and a copper substrate having a high function as a heat sink is also possible. It is also possible to cool by the method. The electrode layers 21, 29, 31 are Ta, Pt, Cu, Au, Ag, Al, Mo, the antiferromagnetic layer 22 is IrMn, PtMn, and the ferromagnetic layer 23 (fixed layer) is CoFe, CoFeB. The insulating layer 24 is MgO, Al oxide, the nonmagnetic layer 51 is Cu, the ferromagnetic layer 25 (free layer) is commonly used CoFe, CoFeB, and the perpendicular easy axis Anisotropy TbFe, TbFeCo, GdFe, GdFeCo, or the like that easily obtains anisotropy or NiFe having a small crystal anisotropy is suitable, but is not limited thereto. Further, Cu and Pd are typical examples of the capping layer 27, but the ferromagnetic layer that can be used in the present invention is not limited to this.

In order to exhibit a function as a spin valve element, it is necessary to make the holding force of the ferromagnetic layer 23 (fixed layer) larger than that of the ferromagnetic layer 25 (free layer). As this method, the material of the ferromagnetic layer 23 (fixed layer) and the ferromagnetic layer 25 (free layer) are made the same, and the former film thickness is made larger than the latter film thickness to give a difference in coercive force. Has been done. Further, an antiferromagnetic layer (pinned layer) 22 is provided, and the retention of the ferromagnetic layer 23 (fixed layer) is increased by antiferromagnetic coupling therewith. If necessary, an antiferromagnetic coupling film such as CoFeB / Ru / CoFeB may be used. The crystallinity and the easy axis direction of each layer including the fixed layer are controlled by annealing in a magnetic field after laminating them.

There are the following methods for making the directions of easy magnetization of the free layer and the fixed layer different from each other. That is, the in-plane shape of the free layer is an ellipse or a rectangle, the aspect ratio is increased to increase the anisotropic magnetic field due to the shape, and the major axis direction is the easy axis of magnetization. On the other hand, since the magnetization easy axis of the fixed layer is determined by the magnetic field application direction in the annealing in the magnetic field, by making the magnetic field application direction different from the long axis direction of the free layer, the magnetization easy axis of the free layer and the fixed layer is determined. Can be different. It is desirable that the in-plane shapes of the free layer and the pinned layer are different (that is, the shape anisotropy imparted to the free layer is not imparted to the pinned layer). Therefore, it can be formed so as not to coincide with the easy axis of magnetization of the free layer. The in-plane shape of the free layer can be processed by normal dry etching using a halogen gas such as Cl ₂ , BCl ₂ , or SiCl ₄ . Also, in order to change the in-plane shape of the free layer and the fixed layer, it is necessary to stop dry etching between the free layer and the fixed layer. For this, for example, an etching end point monitor using plasma emission spectroscopy is used. This is possible.

An example of calculation of free layer magnetization behavior by spin injection is shown below. The calculation was based on the macrospin approximation using the following equations (8) and (9) in which the spin injection term was added to the Landau-Lifschitz-Gilbert equation (LLG equation), and the entire free layer was considered as one magnetization.
dm / dt = γm × H _eff + αm × dm / dt + β _ST (θ) Im × (m × s) (8)
β _ST (θ) = g (θ) μ _B / (M _s × V × e) (9)
Where m and s are unit vectors indicating the magnetization direction of the fixed layer and the fixed layer, γ is a magnetic gyro constant, H _eff is an effective magnetic field, α is a Gilbert damping constant, 1 is a current, θ is s and m The angle formed, μ _B is a Bohr magneton, M _s is the saturation magnetization of the free layer, V is the free layer volume, and e is the electronic charge. Here, m, s, and H _eff are vectors, and therefore, the operation of the “x” symbol acting on the vectors represents an outer product (vector product). As a material for the free layer magnetization, a CoFe-based material was assumed, and a specific calculation was performed assuming that the shape of the free layer is an ellipse having a major axis of 130 nm × minor axis of 70 nm and a thickness of 2 mm. Table 1 shows the parameters used in the calculation and the values of the main physical constants. The time t is normalized by (γM _s ) ⁻¹ , and the unit standardization time based on the physical property values in Table 1 corresponds to about 17 psec. In the following calculation, the xy plane is in the free layer plane, the X axis is the axis of easy magnetization of the fixed layer (= direction of spin injection S), and the Z axis is the direction perpendicular to the film plane.

Examples of calculation of the dynamic behavior of magnetization reversal under the above conditions are shown in FIG. 4 to FIG. 4 by the time change (left figure) of each coordinate of the magnetization unit vector m of the free layer and the three-dimensional display (right figure) of the locus of m. It is shown in FIG. 4 and 5 are calculation examples in the case where the easy axes of the free layer and the fixed layer are parallel in the conventional spin valve element. 4 shows a case where the initial magnetization of the free layer and the fixed layer is exactly parallel, and no magnetization reversal occurs even when a polarized spin current is injected so that the magnetization is antiparallel in this state. FIG. 5 shows the case where the initial magnetization of the free layer is tilted by 6 ° with respect to the fixed layer. The precession around the easy axis of the free layer is repeated and the unit of time is normalized. Magnetization reversal occurs at time (standardization time) 245. The conventional magnetization reversal phenomenon is roughly represented by these two examples.

On the other hand, FIGS. 6 and 7 show the case where the easy axis of magnetization of the free layer and the fixed layer forms an angle of 15 ° (= π / 12 radians) in the spin valve element of the present invention. Among these, FIG. 6 shows the case where the initial magnetization of the free layer is exactly parallel to the magnetization easy axis (X axis) of the fixed layer, and shows that magnetization reversal occurs at the normalization time 179. FIG. 7 shows a case where the initial magnetization of the free layer coincides with the easy axis of the free layer itself and forms an angle of 15 ° with respect to the easy axis (X axis) of the fixed layer. Unlike the conventional case of FIG. 4, since a finite torque exists even in the initial state, magnetization reversal occurs at the normalization time 420. In addition, the initial state in which the magnetization of the free layer in FIG. 6 is different from the easy axis by 15 ° exceeds the thermal fluctuation range of 6 °. However, for comparison with FIG. It is a thing. The direction of initial magnetization is an angle obtained by adding the effect of thermal fluctuation to the easy axis direction (θ) of the free layer. Assuming that the angle after taking into account this thermal fluctuation is β, g (β)> g (0) is satisfied. Therefore, the threshold current density J _c for magnetization reversal in the above case (FIGS. 6 and 7) is the conventional value. Obviously, it is kept smaller than (FIGS. 4 and 5).

FIG. 8 shows a case where the easy axis of the free layer and the fixed layer has an angle of 30 ° (= π / 6 radians), and the initial magnetization of the free layer matches the easy axis of the free layer itself. Show. In this case, the magnetization of the free layer is reversed at the normalized time 370. As can be seen from a comparison between FIG. 7 and FIG. 8, under the condition that the initial magnetization of the free layer coincides with the easy axis of the free layer itself, the magnetization reversal time increases as the tilt angle θ of the easy magnetization axis increases. There is a tendency to shorten. From FIG. 3, it can be easily estimated that the initial torque increases, and this tends to coincide with this. However, as described above, when the tilt angle θ increases, the electric resistance ratio (MR ratio) of the spin valve element due to magnetization reversal decreases, and the tendency to converge to a stable point after magnetization reversal is delayed. This tendency appears as a difference in the attenuation of the vibration of the x component of the magnetization m in FIGS.

Next, a configuration example of a nonvolatile memory device (the device of the present invention) using the spin valve element (magnetic memory device) of the present invention as a memory cell will be described with reference to FIGS.

FIG. 9 schematically shows magnetic memory elements constituting a cross-point type memory cell array, which is an embodiment of the nonvolatile memory device according to the present invention, by a variable resistor 8 symbol. FIG. 10 is a block diagram showing a configuration of a memory array of the nonvolatile memory device 100 driven by word lines and bit lines. As already described, the magnetic memory element of the present invention can be switched by spin transfer magnetization reversal. Therefore, the cross-point type memory is formed by forming the upper electrode and the lower electrode in an array and providing a magnetic memory element connected to both electrodes in the vicinity of the intersection. For example, it is possible to form a wiring on an Si substrate in advance through an appropriate insulating film and form the magnetic memory element of the present invention on the upper part to further form an upper electrode. Thereby, it is possible to perform switching efficiently by applying positive and negative electric pulses from the free layer side.

When the contents of the memory are written, the word line decoder 110 selects a line corresponding to the accessed word from the word lines WLi (i = 1 to n), and is connected to the selected word line. A signal corresponding to data to be written to a row of the memory cells is applied from the bit line decoder 120 to the corresponding memory cells through the bit lines BLj (j = 1 to m). Then, taking the difference from the voltage of the bit line, for each memory cell connected to the accessed word line, a signal that realizes a set operation or a reset operation according to necessary data is transmitted to the bit line. Applied from the decoder 120. Although not shown, each crosspoint is provided with an additional circuit having one or more transistors and a positive and negative power supply line. When the transistors open and close according to the addressed signal, positive and negative pulses are applied to the spin valve element. Application may be made. Regardless of the configuration, the current of the output stage transistor of the word line decoder 110 or the bit line data element 120 or the transistor connected to the spin valve element is the same in the spin valve element having the features of the present invention. Reduced.

When the memory contents are read, a current detection unit (not shown) included in the bit line decoder 120 and provided corresponding to each bit line is selected by a word line decoder that operates in the same manner as in writing. A current flowing through each bit line is detected with respect to the word line to be accessed, and a voltage value corresponding to the resistance of the memory cell 8 corresponding to each bit line is detected in the word line with the word to be accessed. Read the status.

As described above, according to the embodiment of the present invention, in the embodiment of the present invention, the magnetization reversal current in the spin injection magnetization reversal spin valve element is reduced. In the embodiment of the present invention, it is possible to increase the speed of magnetization reversal. The present invention is not limited to the above-described embodiments, and various modifications, changes and combinations are possible based on the technical idea of the present invention.

Claims

A spin valve element comprising an intermediate layer made of one insulating layer or a nonmagnetic layer, and a pair of ferromagnetic layers sandwiching the intermediate layer,
A spin valve element in which coercive forces of the ferromagnetic layers of the pair of ferromagnetic layers are different from each other, and directions of easy magnetization axes of the ferromagnetic layers of the pair of ferromagnetic layers are different from each other.
The spin valve element according to claim 1, wherein directions of easy magnetization axes of the ferromagnetic layers of the pair of ferromagnetic layers are different from each other in a plane of the ferromagnetic layer.
2. The spin valve element according to claim 1, wherein an angle θ formed by an easy axis of each of the pair of ferromagnetic layers satisfies the following expression (1).
(K × T) / (K u × V) <sin 2 θ <0.25
Here, Ku is the magnetic anisotropy constant, k is the Boltzmann constant, T is the operating temperature expressed in absolute temperature, and V is the volume per element of the ferromagnetic layer with the smaller coercive force.
The shape of the periphery of at least one of the pair of ferromagnetic layers is a first direction included in the surface of the ferromagnetic layer and a second direction included in the surface and perpendicular to the first direction. The spin valve element according to any one of claims 1 to 3, wherein the range of the direction is different from each other.
A storage device using the spin valve element according to any one of claims 1 to 3 as a storage element.
A storage device using the spin valve element according to claim 4 as a storage element.