JP2012064624A - Storage element and memory unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage element that can reduce a write current and improve heat stability.SOLUTION: The storage element comprises a dual structure including a storage layer 17 having magnetization perpendicular to a film surface with a magnetization direction varying corresponding to information, insulation layers 16U, 16L provided above and below the storage layer 17, and magnetization fixed layers 15U, 15L provided above and below the insulation layers 16U, 16L, respectively, and each having magnetization perpendicular to the film face. Information is recorded by a magnetization direction of the storage layer 17 varied by injection of an electron spin polarized in a lamination direction. Here, a magnitude of an effective anti-magnetic field applied to the storage layer 17 is adjusted to be smaller than a magnitude of saturation magnetization of the storage layer 17. Further, magnetization directions perpendicular to respective film surfaces of the two magnetization fixed layers 15 are adjusted to be opposite to each other. Still further, a sheet resistivity value of the whole element is adjusted to be from 10 Ωμmto 40 Ωμm, and a sheet resistivity value of the upper insulation layer 16U is adjusted to be higher than a sheet resistivity value of the lower insulation layer 16L.

Description

  The present invention has a storage layer that stores the magnetization state of a ferromagnetic layer as information and a magnetization fixed layer in which the magnetization direction is fixed, and changes the magnetization direction of the storage layer by passing a current. And a memory device including the memory element.

JP 2003-17782 A US Pat. No. 6,256,223 US Pat. No. 7,242,045 JP 2008-227388 A JP 2006-93432 A

PHYs. Rev. B, 54.9353 (1996) J. Magn. Mat., 159, L1 (1996) F. J. Albert et al., Appl. Phy. Lett., 77, 3809 (2000)

In information devices such as computers, DRAMs with high speed and high density are widely used as random access memories.
However, since DRAM is a volatile memory in which information disappears when the power is turned off, a nonvolatile memory in which information does not disappear is desired.

  As a candidate for a nonvolatile memory, a magnetic random access memory (MRAM) that records information by magnetization of a magnetic material has attracted attention and is being developed.

  In the MRAM, current is supplied to two types of address lines (word lines and bit lines) that are substantially orthogonal to each other, and the magnetization of the magnetic layer of the magnetic memory element at the intersection of the address lines is caused by a current magnetic field generated from each address line. Inverted information is recorded.

A schematic diagram (perspective view) of a general MRAM is shown in FIG.
A drain region 108, a source region 107, and a gate electrode 101 constituting a selection transistor for selecting each memory cell are formed in a portion separated by the element isolation layer 102 of the semiconductor substrate 110 such as a silicon substrate. Has been.
A word line 105 extending in the front-rear direction in the figure is provided above the gate electrode 101.
The drain region 108 is formed in common to the left and right selection transistors in the drawing, and a wiring 109 is connected to the drain region 108.
A magnetic storage element 103 having a storage layer whose magnetization direction is reversed is disposed between the word line 105 and the bit line 106 disposed above and extending in the horizontal direction in the drawing. The magnetic memory element 103 is composed of, for example, a magnetic tunnel junction element (MTJ element).
Further, the magnetic memory element 103 is electrically connected to the source region 107 via the horizontal bypass line 111 and the vertical contact layer 104.
By applying current to each of the word line 105 and the bit line 106, a current magnetic field is applied to the magnetic memory element 103, thereby reversing the magnetization direction of the memory layer of the magnetic memory element 103 and recording information. be able to.

In order to stably hold recorded information in a magnetic memory such as MRAM, it is necessary that a magnetic layer (storage layer) for recording information has a certain coercive force.
On the other hand, in order to rewrite the recorded information, a certain amount of current must be passed through the address wiring.
However, as the elements constituting the MRAM become finer, the address wiring becomes thinner, so that a sufficient current cannot flow.

In view of this, attention has been paid to a memory that uses magnetization reversal by spin injection as a configuration that allows magnetization reversal with a smaller current (see, for example, Patent Documents 1, 2, and 4, Non-Patent Documents 1 and 2).
Magnetization reversal by spin injection is to cause magnetization reversal in another magnetic material by injecting spin-polarized electrons that have passed through the magnetic material into another magnetic material.

  For example, when a current is passed through a giant magnetoresistive element (GMR element) or a magnetic tunnel junction element (MTJ element) in a direction perpendicular to the film surface, magnetization of at least a part of the magnetic layer of these elements is performed. Can be reversed.

  Magnetization reversal by spin injection has an advantage that magnetization reversal can be realized without increasing current even if the element is miniaturized.

9 and 10 are schematic views of a memory device configured to use the above-described magnetization reversal by spin injection. 9 is a perspective view, and FIG. 10 is a cross-sectional view.
A drain region 58, a source region 57, and a gate electrode 51 constituting a selection transistor for selecting each memory cell are formed in a portion separated by the element isolation layer 52 of the semiconductor substrate 60 such as a silicon substrate. Has been. Among these, the gate electrode 51 also serves as a word line extending in the front-rear direction in FIG.
The drain region 58 is formed in common to the left and right selection transistors in FIG. 9, and a wiring 59 is connected to the drain region 58.
A storage element 53 having a storage layer in which the direction of magnetization is reversed by spin injection is disposed between the source region 57 and the bit line 56 disposed above and extending in the left-right direction in FIG.
The storage element 53 is configured by, for example, a magnetic tunnel junction element (MTJ element). The storage element 53 has two magnetic layers 61 and 62. Of these two magnetic layers 61 and 62, one magnetic layer is a magnetization fixed layer whose magnetization direction is fixed, and the other magnetic layer is a magnetization free layer, that is, a storage layer whose magnetization direction changes.
The storage element 53 is connected to the bit line 56 and the source region 57 via the upper and lower contact layers 54, respectively. As a result, a current can be passed through the memory element 53 to reverse the magnetization direction of the memory layer by spin injection.

In the case of a memory device configured to utilize such magnetization reversal by spin injection, the device structure can be simplified as compared with the general MRAM shown in FIG. It also has the feature of becoming.
Further, by utilizing magnetization reversal by spin injection, there is an advantage that the write current does not increase even when the element is miniaturized as compared with a general MRAM in which magnetization reversal is performed by an external magnetic field.

  As described in Patent Document 5, a dual-structure in-plane magnetization type magnetic memory element has been proposed.

In the case of an MRAM, a write wiring (word line or bit line) is provided separately from a memory element, and information is written (recorded) by a current magnetic field generated by passing a current through the write wiring. Therefore, a sufficient amount of current required for writing can be passed through the write wiring.
On the other hand, in a memory device configured to utilize magnetization reversal by spin injection, it is necessary to reverse the magnetization direction of the storage layer by performing spin injection with a current flowing through the storage element.
Since the current is directly supplied to the memory element and information is written (recorded) as described above, the memory cell is configured by connecting the memory element to a selection transistor in order to select a memory cell to be written. In this case, the current flowing through the memory element is limited to the magnitude of the current that can flow through the selection transistor (the saturation current of the selection transistor).
Therefore, it is necessary to perform writing with a current lower than the saturation current of the selection transistor, and it is necessary to improve the efficiency of spin injection and reduce the current flowing through the memory element.

Also, in order to increase the read signal, it is necessary to secure a large rate of change in magnetoresistance. To that end, a memory element having a tunnel insulating layer (tunnel barrier layer) as an intermediate layer in contact with both sides of the memory layer is required. The configuration is effective.
When the tunnel insulating layer is used as the intermediate layer as described above, the amount of current flowing through the memory element is limited in order to prevent the tunnel insulating layer from being broken down. From this viewpoint, it is necessary to suppress the current during spin injection.

In order to reduce the current value, the current value is proportional to the film thickness of the memory layer and proportional to the square of the saturation magnetization of the memory layer. Therefore, it is only necessary to adjust these (film thickness and saturation magnetization). It is understood (for example, refer nonpatent literature 3).
For example, Patent Document 3 shows that the current value can be reduced by reducing the amount of magnetization (Ms) of the recording material.

However, on the other hand, if the information written by the current is not stored, it cannot be a nonvolatile memory. That is, it is necessary to ensure the stability (thermal stability) of the storage layer against thermal fluctuation.
In the case of a memory element using magnetization reversal by spin injection, the volume of the memory layer is smaller than that of a conventional MRAM, so that the thermal stability tends to be lowered in a simple way.
If the thermal stability of the storage layer is not ensured, the reversed magnetization direction is reversed again by heat, resulting in a write error.
When the capacity of a storage element that utilizes magnetization reversal by spin injection is increased, the volume of the recording element is further reduced, so ensuring thermal stability becomes an important issue.

  Therefore, thermal stability is a very important characteristic in a memory element using magnetization reversal by spin injection.

  Therefore, in order for a memory element configured to reverse the magnetization direction of the memory layer by spin injection to exist as a memory, the current required for magnetization reversal by spin injection is reduced below the saturation current of the transistor and written. It is necessary to ensure the thermal stability to hold the information firmly.

As described above, in order to reduce the current required for magnetization reversal by spin injection, it is conceivable to reduce the saturation magnetization amount Ms of the storage layer or to make the storage layer thinner. For example, as in Patent Document 3 described above, it is effective to use a material having a low saturation magnetization Ms as the material of the storage layer. However, as described above, when a material having a low saturation magnetization Ms is simply used, it is not possible to ensure thermal stability that holds information firmly.
Accordingly, an object of the present invention is to provide a memory element that can improve thermal stability without increasing a write current, and a memory device having the memory element.

The storage element of the present invention has a storage layer that has magnetization perpendicular to the film surface and whose magnetization direction changes corresponding to information, and a first nonmagnetic material provided in contact with the lower surface side of the storage layer. An insulating layer, a first magnetization fixed layer having a magnetization perpendicular to the film surface, and provided in contact with the upper surface side of the storage layer. A layer structure having a second insulating layer made of a nonmagnetic material and a second magnetization fixed layer provided above the memory layer via the second insulating layer and having magnetization perpendicular to the film surface . This is a so-called dual structure. Then, by injecting spin-polarized electrons in the stacking direction of the layer structure, the magnetization direction of the storage layer is changed, information is recorded on the storage layer, and the storage layer receives The effective demagnetizing field is smaller than the saturation magnetization of the storage layer, and the magnetization directions perpendicular to the film surfaces of the first and second fixed magnetization layers are opposite to each other. Has been.
The ferromagnetic layer material constituting the memory layer is Co—Fe—B, and the composition of Co—Fe—B is 0 ≦ Co _x ≦ 40, 60 ≦ Fe _y ≦ 100, 0 <B _z ≦ 30. in a _{(Co x -Fe y) 100-} z -B z.
Further, the area resistance value of the entire element is 10 Ωμm ² or more and 40 Ωμm ² or less.
The sheet resistance value of the second insulating layer is set higher than the sheet resistance value of the first insulating layer.

  The memory device of the present invention includes a storage element that holds information according to the magnetization state of a magnetic material, and two types of wirings that intersect each other, and the storage element has the configuration of the above-described storage element of the present invention. A memory element is arranged between the two, a current in the stacking direction flows through the memory element through these two types of wiring, and spin-polarized electrons are injected.

According to the configuration of the memory element of the present invention described above, by injecting spin-polarized electrons in the stacking direction, the magnetization direction of the memory layer changes, and information is recorded on the memory layer. Information can be recorded by injecting spin-polarized electrons by passing a current in the stacking direction.
Since the effective demagnetizing field received by the storage layer is smaller than the saturation magnetization of the storage layer, the demagnetizing field received by the storage layer is low, and the magnetization direction of the storage layer is reversed. Therefore, it is possible to reduce the amount of write current required.
On the other hand, since the amount of write current can be reduced without reducing the saturation magnetization amount of the storage layer, it is possible to sufficiently secure the thermal stability of the storage layer by making the saturation magnetization amount of the storage layer sufficient. It becomes possible.
Further, in the dual structure, the perpendicular magnetization of the upper magnetization fixed layer and the lower magnetization fixed layer is opposite.
By using FeCoB having a high Fe ratio for the memory layer and the fixed layer, perpendicular magnetization can be obtained, and at the same time, by having a dual structure, the spin injection efficiency is dramatically improved and the write current is reduced.

Further, according to the configuration of the memory device of the present invention described above, the memory element is arranged between the two types of wirings, current in the stacking direction flows through the memory elements through these two types of wirings, and spin-polarized electrons are injected. Thus, information can be recorded by spin injection by flowing current in the stacking direction of the memory element through two types of wiring.
Further, since it becomes possible to reduce the amount of write current of the storage element without reducing the saturation magnetization amount of the storage layer, it is possible to stably hold the information recorded in the storage element and to consume the memory device. It becomes possible to reduce electric power.

According to the present invention, it is possible to reduce the write current amount of the storage element without reducing the saturation magnetization amount of the storage layer. A memory element having excellent characteristic balance can be configured.
Furthermore, by having a dual structure, the spin injection efficiency is dramatically improved and the write current is reduced.
Therefore, a highly reliable memory device that operates stably can be realized.
In addition, the write current can be reduced, so that power consumption when writing to the memory element can be reduced. Therefore, the power consumption of the entire memory device can be reduced.

It is explanatory drawing of schematic structure of the memory device of embodiment of this invention. It is sectional drawing of the memory element of embodiment. It is explanatory drawing of the sample used in Experiment 1-Experiment 4 of embodiment. It is the figure which showed the relationship between the quantity of Co of the memory | storage layer of 0.09x0.18 micrometer size, and inversion current density. It is the figure which showed the relationship between the quantity of Co of the memory | storage layer of 0.09x0.18 micrometer size, and the parameter | index of thermal stability. It is the figure which showed the relationship between the quantity of Co of a 50 nm diameter size memory layer, and the parameter | index of thermal stability. It is explanatory drawing of the layer structure of the sample of Experiment 5 of embodiment. It is the perspective view which showed the structure of the conventional MRAM typically. It is explanatory drawing of schematic structure of the memory device using the magnetization reversal by spin injection. FIG. 10 is a cross-sectional view of the memory device of FIG. 9.

Hereinafter, embodiments of the present invention will be described in the following order.
<1. Outline of Memory Element of Embodiment>
<2. Configuration of Embodiment>
<3. Experiment>

<1. Outline of Memory Element of Embodiment>

First, an outline of a memory element according to an embodiment of the invention will be described.
In the embodiment of the present invention, information is recorded by reversing the magnetization direction of the memory layer of the memory element by the spin injection described above.
The memory layer is made of a magnetic material such as a ferromagnetic layer, and holds information by the magnetization state (magnetization direction) of the magnetic material.

  As will be described in detail later, the memory element of the present embodiment has a layer structure as shown in FIG. 2A, for example, and includes a memory layer 17 as a magnetic layer and a magnetization fixed layer 15 (15U, 15) as a magnetic layer. 15L) and an insulating layer (tunnel insulating layer) 16 (16U, 16L) as an intermediate layer is employed.

The storage layer 17 has magnetization perpendicular to the film surface, and the magnetization direction is changed in accordance with information.
The magnetization fixed layers 15U and 15L have magnetization perpendicular to the film surface serving as a reference for information stored in the storage layer 17. The magnetization directions perpendicular to the film surfaces of the upper and lower magnetization fixed layers 15U and 15L are opposite to each other.
The insulating layers 16U and 16L are non-magnetic materials and are provided between the storage layer 17 and the magnetization fixed layer 15U and between the storage layer 17 and the magnetization fixed layer 15L.

  Then, by injecting spin-polarized electrons in the stacking direction of the layer structure having the storage layer 17, the insulating layers 16U and 16L, and the magnetization fixed layers 15U and 15L, the magnetization direction of the storage layer 17 is changed. Information is recorded on the storage layer 17.

The basic operation of reversing the direction of magnetization of the magnetic layer (memory layer 17) by spin injection is performed on a memory element composed of a giant magnetoresistive element (GMR element) or a tunnel magnetoresistive element (MTJ element). A current exceeding a certain threshold is passed in a direction perpendicular to the film surface. At this time, the polarity (direction) of the current depends on the direction of magnetization to be reversed.
When a current having an absolute value smaller than this threshold is passed, magnetization reversal does not occur.

  When the magnetization direction of the magnetic layer is reversed by spin injection, a current threshold Ic required is expressed by the following formula (1).

ここで、Ａ：定数、α：スピン制動定数、η：スピン注入効率、Ｍｓ：飽和磁化量、Ｖ：記憶層の体積、Ｈｄ：実効的な反磁界である。

Here, A: constant, α: spin braking constant, η: spin injection efficiency, Ms: saturation magnetization, V: volume of storage layer, Hd: effective demagnetizing field.

  As represented by Equation (1), the current threshold can be arbitrarily set by controlling the volume V of the magnetic layer, the saturation magnetization Ms of the magnetic layer, the spin injection efficiency η, and the spin braking constant α. Is possible.

In the present embodiment, a storage element including a magnetic layer (storage layer 17) capable of holding information depending on the magnetization state and a magnetization fixed layer 15 in which the magnetization direction is fixed is configured.
In order to be able to exist as a memory, it must be able to hold the written information. As an index of the ability to hold information, it is determined by the value of the thermal stability index Δ (= KV / k _B T). This Δ is represented by the following formula (2).

ここで、Ｈｋ：実効的な異方性磁界、ｋ_B：ボルツマン定数、Ｔ：温度、Ｍｓ：飽和磁化量、Ｖ：記憶層の体積である。

Here, Hk: effective anisotropic magnetic field, k _B : Boltzmann constant, T: temperature, Ms: saturation magnetization, and V: volume of the storage layer.

  The effective anisotropy magnetic field Hk incorporates effects such as shape magnetic anisotropy, induced magnetic anisotropy, and magnetocrystalline anisotropy. When a single domain coherent rotation model is assumed, It is equivalent to magnetic force.

  The thermal stability index Δ and the current threshold value Ic often have a trade-off relationship. Therefore, in order to maintain the memory characteristics, it is often a problem to achieve both.

The threshold value of the current for changing the magnetization state of the storage layer 17 is actually, for example, a threshold value on the + side + Ic in a substantially elliptic TMR element having a thickness of the storage layer 17 of 2 nm and a planar pattern of 100 nm × 150 nm. = + 0.5 mA, −side threshold −Ic = −0.3 mA, and the current density at that time is about 3.5 × 10 ⁶ A / cm ² . These are almost in agreement with the above formula (1).

On the other hand, in a normal MRAM that performs magnetization reversal by a current magnetic field, a write current of several mA or more is required.
Therefore, it can be seen that when the magnetization reversal is performed by spin injection, the threshold value of the write current becomes sufficiently small as described above, which is effective in reducing the power consumption of the integrated circuit.
In addition, the current magnetic field generation wiring (wiring 105 in FIG. 8) required in a normal MRAM is not necessary, and this is advantageous in terms of integration compared to a normal MRAM.

When magnetization reversal is performed by spin injection, information is written (recorded) by directly passing a current through the memory element. Therefore, the memory element is connected to a selection transistor in order to select a memory cell to be written. Thus, a memory cell is configured.
In this case, the current flowing through the memory element is limited by the magnitude of the current that can be passed through the selection transistor (the saturation current of the selection transistor).

It can be seen from equation (1) that the saturation magnetization amount Ms of the memory layer 17 can be reduced in order to make the threshold value Ic of the magnetization reversal current by spin injection smaller than the saturation current of the selection transistor.
However, when the saturation magnetization amount Ms is simply reduced (for example, Patent Document 3), the thermal stability of the storage layer 17 is significantly impaired, and the function as a memory cannot be performed.
In order to configure the memory, it is necessary that the thermal stability index Δ is larger than a certain level.

Therefore, as a result of various studies by the inventors of the present application, an effective reaction that the storage layer 17 receives is selected by selecting, for example, a Co—Fe—B composition as the ferromagnetic layer constituting the storage layer 17. It has been found that the magnitude of the magnetic field (Meffective) is smaller than the saturation magnetization amount Ms of the memory layer 17.
By using the above-described ferromagnetic material, the effective demagnetizing field received by the storage layer 17 is smaller than the saturation magnetization Ms of the storage layer 17.
As a result, the demagnetizing field received by the storage layer 17 can be reduced, and the current threshold value Ic represented by the equation (1) is reduced without impairing the thermal stability Δ represented by the equation (2). Effect is obtained.
Furthermore, the inventors have magnetized Co—Fe—B in the direction perpendicular to the film surface in the limited composition range of the selected Co—Fe—B composition, thereby increasing the capacity of the Gbit class. It has been found that sufficient thermal stability can be secured even in a feasible micro-recording element.
Accordingly, it is possible to form a stable memory in which information can be written with a low current while maintaining thermal stability in a Gbit class spin injection memory.

  In the present embodiment, the effective demagnetizing field received by the storage layer 17 is smaller than the saturation magnetization amount Ms of the storage layer 17, that is, the effective demagnetizing field with respect to the saturation magnetization amount Ms of the storage layer 17. The value of the size ratio is made smaller than 1.

Further, in consideration of the saturation current value of the selection transistor, a magnetic tunnel junction is formed by using a tunnel insulating layer (insulating layer 16) made of an insulator as a nonmagnetic intermediate layer between the storage layer 17 and the magnetization fixed layer 15. (MTJ) The element is configured.
By constructing a magnetic tunnel junction (MTJ) element using a tunnel insulating layer, a magnetoresistance change rate (MR ratio) is compared with a case where a giant magnetoresistive effect (GMR) element is constructed using a nonmagnetic conductive layer. This is because the read signal intensity can be increased.

In particular, by using magnesium oxide (MgO) as the material of the tunnel insulating layer 16 (16U, 16L), the rate of change in magnetoresistance is higher than that in the case of using aluminum oxide that has been generally used so far. (MR ratio) can be increased.
In general, the spin injection efficiency depends on the MR ratio, and the larger the MR ratio, the higher the spin injection efficiency and the lower the magnetization reversal current density.
Therefore, by using magnesium oxide as the material of the tunnel insulating layer 16 (16U, 16L) which is the intermediate layer and simultaneously using the memory layer 17, the write threshold current due to spin injection can be reduced and the current can be reduced. Information can be written (recorded). In addition, the read signal intensity can be increased.
As a result, the MR ratio (TMR ratio) can be ensured, the write threshold current by spin injection can be reduced, and information can be written (recorded) with a small current. In addition, the read signal intensity can be increased.

  Thus, when the tunnel insulating layer 16 (16U, 16L) is formed of a magnesium oxide (MgO) film, it is more desirable that the MgO film is crystallized and the crystal orientation is maintained in the 001 direction.

In the present embodiment, the intermediate layer (tunnel insulating layers 16U, 16L) between the storage layer 17 and the magnetization fixed layers 15U, 15L is made of magnesium oxide, for example, aluminum oxide, nitride Various insulators such as aluminum, SiO ₂ , Bi ₂ O ₃ , MgF ₂ , CaF, SrTiO ₂ , AlLaO ₃ , and Al—N—O, dielectrics, and semiconductors can also be used.

The area resistance value of the tunnel insulating layer 16 needs to be controlled to about several tens of Ωμm ² or less from the viewpoint of obtaining a current density necessary for reversing the magnetization direction of the storage layer 17 by spin injection.
In the tunnel insulating layer 16 made of the MgO film, it is necessary to set the film thickness of the MgO film to 1.5 nm or less in order to make the sheet resistance value in the above range.

In addition, it is desirable to make the memory element small so that the magnetization direction of the memory layer 17 can be easily reversed with a small current.
Therefore, preferably, the area of the memory element is 0.01 μm ² or less.

In the present embodiment, the storage layer 17 can be directly laminated with other ferromagnetic layers having different compositions. It is also possible to stack a ferromagnetic layer and a soft magnetic layer, or to stack a plurality of ferromagnetic layers via a soft magnetic layer or a nonmagnetic layer. Even when laminated in this way, the effect referred to in the present invention can be obtained.
In particular, when a configuration in which a plurality of ferromagnetic layers are laminated via a nonmagnetic layer, the strength of the interaction between the ferromagnetic layers can be adjusted. Even if it becomes below, the effect that it becomes possible to suppress so that a magnetization reversal current may not become large is acquired. The material of the nonmagnetic layer in this case is Ru, Os, Re, Ir, Au, Ag, Cu, Al, Bi, Si, B, C, Cr, Ta, Pd, Pt, Zr, Hf, W, Mo. , Nb or their alloys can be used.

It is desirable that the magnetization fixed layer 15 and the storage layer 17 have unidirectional anisotropy.
The film thicknesses of the magnetization fixed layer 15 and the storage layer 17 are preferably 0.5 nm to 30 nm.

  The other configuration of the storage element can be the same as a conventionally known configuration of the storage element that records information by spin injection.

The magnetization pinned layer 15 can be configured to have its magnetization direction fixed by using only the ferromagnetic layer or by using the antiferromagnetic coupling between the antiferromagnetic layer and the ferromagnetic layer.
For example, in the configuration of FIG. 2B, antiferromagnetic layers 19U and 19L are provided adjacent to the magnetization fixed layers 15U and 15L, respectively. Thus, the magnetization fixed layer 15 has unidirectional anisotropy by exchange coupling with the antiferromagnetic layer 19 and the magnetization direction in the absence of an external magnetic field is fixed.
In addition, the magnetization fixed layer 15 can be configured by a single ferromagnetic layer or a laminated ferripin structure in which a plurality of ferromagnetic layers are laminated via a nonmagnetic layer.
Co, CoFe, CoFeB, or the like can be used as the material of the ferromagnetic layer constituting the magnetization fixed layer 15 having the laminated ferripin structure. Moreover, Ru, Re, Ir, Os etc. can be used as a material of a nonmagnetic layer.

Examples of the material of the antiferromagnetic layer 19 include magnetic materials such as FeMn alloy, PtMn alloy, PtCrMn alloy, NiMn alloy, IrMn alloy, NiO, and Fe ₂ O ₃ .
In addition, nonmagnetic elements such as Ag, Cu, Au, Al, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Hf, Ir, W, Mo, and Nb are included in these magnetic materials. Can be added to adjust the magnetic properties and other physical properties such as crystal structure, crystallinity and material stability.

  As a method for reading information recorded in the memory layer 17 of the memory element, a magnetic layer serving as a reference for information is provided on the memory layer 17 of the memory element via a thin insulating film, and the information is recorded via the insulating layer 16. Reading may be performed by a flowing ferromagnetic tunnel current, or may be performed by a magnetoresistive effect.

In the present embodiment, in addition to obtaining perpendicular magnetization by using FeCoB having a high Fe component composition for the memory layer 17 and the magnetization fixed layers 15U and 15L, the above-described dual structure dramatically increases the spin injection efficiency. Improve and reduce write current.
The dual structure itself has also been proposed in the conventional in-plane magnetization type MTJ described in FIGS. 9 and 10 (for example, Patent Document 5).
Since there are two fixed magnetization layers 15 with respect to the storage layer 17 and the spin torque transfer between the fixed magnetization layer 15 and the intermediate layer (insulating layer 16) is doubled, the spin injection efficiency is structurally increased, The inversion current can be reduced.
Here, the present embodiment is a perpendicular magnetization type MTJ. In the perpendicular magnetization type MTJ, the magnetic anisotropy is not the shape magnetic anisotropy but uses the interfacial magnetic anisotropy, which is greatly different from the in-plane magnetization type.
In the perpendicular magnetization type MTJ, since the magnetic anisotropy is mainly interface anisotropy, it is desirable that the memory layer is thin. However, in reality, since various types of thin films are laminated by a sputtering apparatus, roughness and crystal There is a growth disorder, and if the film thickness is 1 nm or less, a problem arises in the homogeneity of the microscopic structure of the memory layer / insulating layer interface. That is, there arises a problem of achieving both a reduction in memory layer thickness and uniform interface anisotropy.
According to the dual structure, since the memory layer 17 is sandwiched between the insulating layers 16U and 16L, the interface anisotropy can be imparted from both the upper and lower surfaces of the memory layer 17, and at the same time as ensuring the film thickness, the memory layer 17 Interfacial anisotropy can be reliably imparted throughout.

Further, for example, in the conventional single-layer structure of the in-plane magnetization type MTJ, that is, the structure in which the pair of the storage layer and the magnetization fixed layer is interposed through the intermediate layer, the bottom structure in which the magnetization fixed layer and the intermediate layer are below the storage layer has In general, even in the case of the in-plane magnetization type dual structure, a structure mainly composed of the lower intermediate layer is common.
In the case of the perpendicular magnetization type dual structure, the interface anisotropy is more in the order of CoFeB / MgO than in the order of MgO (intermediate layer: insulating layer 16) / CoFeB (ferromagnetic layer: storage layer 17). Interfacial anisotropy increases. For this reason, it is necessary to increase the thickness of the upper intermediate layer (insulating layer 16U).
Furthermore, in order to transfer spin torque between the magnetization fixed layer and the storage layer, it is necessary to secure a distance for electrons to move between the storage layers, and specifically, a storage layer thickness of 1 nm or more is required. From this point of view, a dual structure that can ensure the film thickness is preferable.
In the case of a dual structure, MgO (001) growth and a bcc-type FeCo layer (001) having high consistency are grown, so that a more ideal crystal orientation can be obtained. As a result, the spin injection efficiency η This leads to an improvement and leads to further reduction of the write current Ic.

<2. Configuration of Embodiment>

Next, a specific configuration of the embodiment of the present invention will be described.
FIG. 1 shows a schematic configuration diagram (perspective view) of a memory device according to an embodiment of the present invention.
In this memory device, a storage element 3 capable of holding information in a magnetized state is disposed near an intersection of two types of address lines (for example, a word line and a bit line) orthogonal to each other.
That is, the drain region 8, the source region 7, and the gate electrode 1 that constitute a selection transistor for selecting each memory cell in a portion separated by the element isolation layer 2 of the semiconductor substrate 10 such as a silicon substrate, Each is formed. Of these, the gate electrode 1 also serves as one address wiring (for example, a word line) extending in the front-rear direction in the figure.
The drain region 8 is formed in common to the left and right selection transistors in the figure, and a wiring 9 is connected to the drain region 8.

The storage element 3 is disposed between the source region 7 and the other address wiring (for example, bit line) 6 disposed above and extending in the left-right direction in the drawing. The storage element 3 has a storage layer composed of a ferromagnetic layer whose magnetization direction is reversed by spin injection.
The storage element 3 is arranged near the intersection of the two types of address lines 1 and 6.
The storage element 3 is connected to the bit line 6 and the source region 7 through upper and lower contact layers 4, respectively.
As a result, a current in the vertical direction can be passed through the storage element 3 through the two types of address lines 1 and 6, and the magnetization direction of the storage layer can be reversed by spin injection.

  2A and 2B are cross-sectional views of the memory element 3 of the memory device according to the present embodiment.

2A, the memory element 3 includes, in order from the lower layer side, a base layer 14, a lower magnetization fixed layer 15L, a lower insulating layer 16L, a storage layer 17, an upper insulating layer 16U, an upper magnetization fixed layer 15U, A cap layer 18 is laminated.
That is, a dual structure is provided in which the magnetization fixed layers 15U and 15L are provided above and below the storage layer 17 via the insulating layers 16U and 16L.

In this spin injection memory, information “0” and “1” are defined by the relative angle between the magnetization M17 of the storage layer 17 and the magnetization M15L of the lower magnetization fixed layer 15L.
In such a dual structure, it is essential that the magnetization directions of the magnetization fixed layers 15U and 15L do not change (the magnetization M15U of the upper magnetization fixed layer 15U and the magnetization M15L of the lower magnetization fixed layer 15L are reversed). is there.
Insulating layers 16U and 16L serving as tunnel barrier layers are provided as intermediate layers between the storage layer 17 and the magnetization fixed layers 15U and 15L. The storage layer 17 and the magnetization fixed layer 15L, and the storage layer 17 and the magnetization fixed layer 15U constitute an MTJ element.

The memory layer 17 is made of a ferromagnetic material having a magnetic moment in which the direction of the magnetization M17 freely changes in the direction perpendicular to the layer surface. The magnetization fixed layers 15U and 15L are made of a ferromagnetic material having a magnetic moment in which the magnetization M15 is fixed in the direction perpendicular to the film surface.
Information is stored according to the direction of magnetization of the storage layer 15 having uniaxial anisotropy. Writing is performed by applying a current in the direction perpendicular to the film surface to cause spin torque magnetization reversal. Thus, for example, the lower magnetization fixed layer 15L is used as a reference for storage information (magnetization direction) of the storage layer 17 with respect to the storage layer 15 whose magnetization direction is reversed by spin injection.
In the present embodiment, Co—Fe—B is used for the memory layer 17 and the magnetization fixed layers 15U and 15L.

In addition, the area resistance value of the entire element is 10 Ωμm ² or more and 40 Ωμm ² or less.
Furthermore, in the insulating layers 16U and 16L, the area resistance value of the upper insulating layer 16U is higher than that of the lower insulating layer 16L.

FIG. 2B is an example in which antiferromagnetic layers 19U and 19L are added to the configuration of FIG.
The memory element 3 includes a base layer 14, a lower antiferromagnetic layer 19L, a lower magnetization fixed layer 15L, a lower insulating layer 16L, a storage layer 17, an upper insulating layer 16U, an upper magnetization fixed layer 15U, and an upper antiferroelectric layer in order from the lower layer side. A magnetic layer 19U and a cap layer 18 are laminated.
That is, the magnetization fixed layers 15U and 15L are provided above and below the storage layer 17 via the insulating layers 16U and 16L. Antiferromagnetic layers 19U and 19L are stacked on the magnetization fixed layers 15U and 15L.

  In this case, in order to fix the magnetizations of the upper and lower magnetization fixed layers 15U and 15L, the antiferromagnetic layers 19U and 19L such as PtMn and IrMn are brought into contact with the magnetization fixed layers 15U and 15L, respectively. That is, the magnetization fixed layers 15U and 15L have unidirectional anisotropy by exchange coupling with the antiferromagnetic layers 19U and 19L, and the magnetization direction in the absence of an external magnetic field is fixed.

As a result, the magnetization directions of the magnetization fixed layers 15U and 15L in a zero magnetic field with no external magnetic field are fixed, and the stable state is uniquely determined. In this case, even when a magnetic field exceeding the coercive force is applied, after the magnetic field is removed, the magnetizations M15U and M15L of the upper and lower magnetization fixed layers 15U and 15L return to the originally designed directions.
As described above, in the case of the dual structure, the magnetization M15U of the upper magnetization fixed layer 15U and the magnetization M15L of the lower magnetization fixed layer 15L must be opposite to each other, so the antiferromagnetic layers 19U and 19L are provided to stabilize the magnetization The necessity is high compared to the single structure. In other words, in the case of the dual structure, the antiferromagnetic layers 19U and 19L greatly contribute to the operational stability of the memory element 3.

In the embodiment of FIGS. 2A and 2B described above, the storage element is particularly designed so that the effective demagnetizing field received by the storage layer 17 is smaller than the saturation magnetization amount Ms of the storage layer 17. 3 of the memory layer 17 is adjusted.
That is, the composition of the ferromagnetic material Co—Fe—B of the storage layer 17 is selected, and the magnitude of the effective demagnetizing field received by the storage layer 17 is reduced so as to be smaller than the saturation magnetization Ms of the storage layer 17. To.

Further, in the present embodiment, the insulating layers 16U and 16L which are intermediate layers are magnesium oxide (MgO) layers. In this case, the magnetoresistance change rate (MR ratio) can be increased.
By increasing the MR ratio in this way, the efficiency of spin injection can be improved and the current density required to reverse the direction of the magnetization M17 of the storage layer 17 can be reduced.

  The memory element 3 of the present embodiment is manufactured by continuously forming the base layer 14 to the cap layer 18 in a vacuum apparatus and then forming the pattern of the memory element 3 by processing such as etching. Can do.

According to the present embodiment described above, the storage layer 17 of the storage element 3 is configured such that the effective demagnetizing field received by the storage layer 17 is smaller than the saturation magnetization Ms of the storage layer 17. Therefore, the demagnetizing field received by the storage layer 17 is low, and the amount of write current necessary for reversing the direction of the magnetization M17 of the storage layer 17 can be reduced.
On the other hand, since the amount of write current can be reduced without reducing the saturation magnetization amount Ms of the storage layer 17, the thermal stability of the storage layer 17 is sufficient with the saturation magnetization amount Ms of the storage layer 17 sufficient. Can be secured.

As described above, since the thermal stability as the information holding capability can be sufficiently ensured, the memory element 3 having an excellent characteristic balance can be configured.
Further, as shown in FIG. 2B, the magnetization fixed layers 15U and 15L are stacked with the antiferromagnetic layers 19U and 19L, and the magnetization fixed layers 15U and 15L are given unidirectional anisotropy, whereby the magnetization fixed layer 15U. , 15L magnetization is stabilized, which is effective in reducing the recording current, reducing the recording current variation, and improving the holding characteristics.
As a result, an operation error can be eliminated, a sufficient operation margin of the memory element 3 can be obtained, and the memory element 3 can be operated stably.
Therefore, a highly reliable memory device that operates stably can be realized.

In addition, it is possible to reduce the write current and reduce the power consumption when writing to the memory element 3.
The write current Ic is expressed by α · Δ / η. (Α: braking constant, Δ: thermal stability index, η: spin injection efficiency)
By using a dual structure with respect to a single structure, it is possible to improve the spin injection efficiency η, reduce the write current / voltage, and increase the write margin.
In addition, because of the perpendicular magnetization type, the MTJ is circular and can define a radius. Since the conventional in-plane magnetization type has an elliptical shape, that is, it is necessary to make the long axis long because of the shape magnetic anisotropy, in this embodiment, it may be circular and the area is small, so the current is also small.
Furthermore, by controlling the interface structure between the storage layer 17 and the insulating layers 16U and 16L, which are intermediate layers, the perpendicular magnetization type dual structure can increase the spin injection efficiency as compared with the in-plane magnetization type dual structure, so that the write current can be increased. Reduction is possible.
From the above, it is possible to reduce the power consumption of the entire memory device in which the memory cell is configured by the memory element 3 of the present embodiment.
Accordingly, a highly reliable memory device that has excellent information retention characteristics and operates stably can be realized, and power consumption can be reduced in the memory device including the memory element 3.

In the present embodiment, the area resistance value of the entire element is set to 10 Ωum ² or more and 40 Ωμm ² or less as described above.
In this case, a suitable value of the reversal current density Jc0 is obtained.

Furthermore, in the insulating layers 16U and 16L, the area resistance value of the upper insulating layer 16U is higher than that of the lower insulating layer 16L.
The perpendicular magnetic anisotropy of the storage layer 17 is presumed to be governed by the interface anisotropy, and the storage layer / insulation layer lamination state from the lower side than the case of the insulation layer / storage layer lamination state from the lower side. In this case, an interface desirable for perpendicular magnetic anisotropy is formed, and a larger interface anisotropy is obtained. For this reason, it is considered that the upper MTJ having the configuration of the memory layer 17 / upper insulating layer 16U from the lower side should be mainly used as the element resistance.
This is because the upper insulating layer 16U is thick and has sufficient crystallinity to lead to good interface anisotropy, leading to a favorable MR ratio and a reduction in reversal current, and a dual structure effect can be obtained more remarkably. Because.
Furthermore, since the dual structure exhibits a higher insulating layer breakdown voltage when the upper insulating layer 16U is thicker than the lower insulating layer 16L at the same time, it is desirable that the upper insulating layer 16U is thick and has high resistance.

Further, the memory layer 17 does not include a giant element having a braking constant α such as Pt or Pd in order to obtain perpendicular magnetization, and does not require an extremely thin film laminated structure such as a Co / Pd laminated film. The memory layer is composed of Co, Fe and / or B having a small α, and the origin of perpendicular anisotropy is mainly interface anisotropy. That is, it can be made of a material that does not sacrifice MTJ characteristics.
Further, the gate width of the select transistor can be shortened by reducing the write current, and the memory cell size can be drastically reduced.
This is also advantageous for large capacity.

In addition, the memory device having the memory element 3 shown in FIG. 2A or 3A and configured as shown in FIG. 1 can apply a general semiconductor MOS formation process when manufacturing the memory device. Has the advantage.
Therefore, the memory device of this embodiment can be applied as a general-purpose memory.

<3. Experiment>

Here, in the configuration of the memory element of the present embodiment, the magnitude of the effective demagnetizing field received by the memory layer is adjusted by specifically selecting the material of the ferromagnetic layer constituting the memory layer 17. A sample of the memory element was manufactured and its characteristics were examined.

As shown in FIG. 1, an actual memory device includes a semiconductor circuit for switching in addition to the memory element 3. Here, for the purpose of examining the magnetization reversal characteristics of the memory layer 17, only the memory element is used. A study was carried out using a wafer on which the film was formed.
In the following [Experiment 1] to [Experiment 4], a sample having a single structure shown in FIG. That is, the base layer 14, the magnetization fixed layer 15, the insulating layer 16, the memory layer 17, and the cap layer 18 are structured. In [Experiment 1] to [Experiment 4], the ferromagnetic material Co—Fe—B composition of the memory layer 17 is selected, the magnitude of the effective demagnetizing field received by the memory layer 17 is reduced, and the memory layer 17 To make it smaller than the saturation magnetization amount Ms.
In [Experiment 5], a sample corresponding to FIG. 2A was used, and the case of a dual structure was examined.

[Experiment 1]
A thermal oxide film having a thickness of 300 nm was formed on a silicon substrate having a thickness of 0.725 mm, and the memory element 3 having the configuration shown in FIG. 3A was formed thereon.
Specifically, as shown in FIG. 3B, the material and film thickness of each layer were selected.
-Underlayer 14: Laminated film of Ta film with a thickness of 10 nm and Ru film with a thickness of 25 nm-Magnetization fixed layer 15: CoFeB film with a thickness of 2.5 nm-Tunnel insulating layer 16: Magnesium oxide film with a thickness of 0.9 nm Memory layer 17: CoFeB film having the same composition as the magnetization fixed layer Cap layer 18: Laminated film of 3 nm thick Ta film, 3 nm thick Ru film, 3 nm thick Ta film A Cu film (not shown) having a thickness of 100 nm (to be described later) was provided between the base layer 14 and the silicon substrate.
With the above film configuration, the ferromagnetic layer of the memory layer 17 is made of a ternary alloy of Co—Fe—B, and the thickness of the ferromagnetic layer is fixed at 2.0 nm.

Each layer other than the insulating layer 16 made of a magnesium oxide film was formed using a DC magnetron sputtering method.
The insulating layer 16 made of a magnesium oxide (MgO) film was formed using an RF magnetron sputtering method.
Further, after each layer of the memory element 3 was formed, heat treatment was performed in a heat treatment furnace in a magnetic field.

Next, after masking the word line portion by photolithography, the word line (lower electrode) was formed by performing selective etching with Ar plasma on the laminated film other than the word line.
At this time, except for the word line portion, the substrate was etched to a depth of 5 nm.

Thereafter, a mask of the pattern of the memory element 3 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 3. Except for the memory element 3 portion, the etching was performed up to the Cu layer of the word line.
In addition, in order to generate the spin torque necessary for the magnetization reversal, it is necessary to flow a sufficient current through the storage element for the characteristic evaluation storage element, and thus it is necessary to suppress the resistance value of the tunnel insulating layer. Therefore, the pattern of the memory element 3 is an ellipse having a minor axis of 0.09 μm and a major axis of 0.18 μm, and the area resistance value (Ωμm ² ) of the memory element 3 is 20 Ωμm ² .

Next, the portion other than the memory element 3 portion was insulated by sputtering of Al ₂ O ₃ having a thickness of about 100 nm.
Thereafter, a bit line to be an upper electrode and a measurement pad were formed using photolithography.
In this way, a sample of the memory element 3 was produced.

Then, each sample of the memory element 3 was manufactured by changing the composition of the Co—Fe—B alloy of the ferromagnetic layer of the memory layer 17 by the above-described manufacturing method.
The composition of the Co—Fe—B alloy is such that the composition ratio (atomic%) of CoFe and B is fixed at 80:20, and the composition ratio x (atomic%) of Co in CoFe is 90%, 80%, It was changed to 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%.

As described above, the characteristics of each sample of the produced memory element 3 were evaluated as follows.
Prior to the measurement, the storage element 3 was configured to be able to apply a magnetic field from the outside in order to control the positive and negative values of the reversal current to be symmetrical.
Further, the voltage applied to the memory element 3 was set to 1 V within a range where the insulating layer 16 was not broken.

(Measurement of saturation magnetization)
The saturation magnetization amount Ms was measured by VSM measurement using a vibrating sample magnetometer.

(Measurement of effective demagnetizing field)
As a sample for measuring an effective demagnetizing field, a sample in which each layer constituting the memory element 3 was formed separately from the above-described sample of the memory element 3 and formed into a 20 mm × 20 mm square pattern was prepared. .
The effective demagnetizing field magnitude Meffective was determined by FMR (Ferromagnetic Resonance) measurement.
The resonance frequency fFMR obtained by this FMR measurement with respect to an arbitrary external magnetic field Hex is given by the following equation (3).

  Here, Meffective in the formula (3) can be expressed by 4πMeffective = 4πMs−H⊥ (H⊥: an anisotropic magnetic field in a direction perpendicular to the film surface).

(Measurement of reversal current value and thermal stability)
For the purpose of evaluating the writing characteristics of the memory element 3 according to the present embodiment, the inversion current value was measured.
A current having a pulse width of 10 μs to 100 ms was passed through the memory element 3, and the subsequent resistance value of the memory element 3 was measured.
Furthermore, the amount of current flowing through the storage element 3 was changed, and a current value at which the direction of the magnetization M1 of the storage layer 17 of the storage element 3 was reversed was obtained. A value obtained by extrapolating the pulse width dependence of the current value to a pulse width of 1 ns was defined as an inversion current value.
Further, the inclination of the pulse width dependency of the inversion current value corresponds to the above-described thermal stability index (Δ) of the memory element 3. It means that the more the reverse current value does not change with the pulse width (the smaller the slope), the stronger the heat disturbance.
Then, in order to take into account the variation between the storage elements 3, about 20 storage elements 3 having the same configuration were produced, and the above-described measurement was performed to obtain the average value of the inversion current value and the thermal stability index Δ. .
Further, the reversal current density Jc0 was calculated from the average value of the reversal current values obtained by the measurement and the area of the planar pattern of the memory element 3.

  For each sample of the storage element 3, the composition of the Co—Fe—B alloy of the storage layer 17, the measurement result of the saturation magnetization amount Ms and the effective demagnetizing field magnitude Meffective, the saturation magnetization amount and the effective demagnetizing field Table 1 shows the ratio Meffective / Ms with respect to the size. Here, the Co content of the Co—Fe—B alloy of the memory layer 17 shown in Table 1 is shown in atomic%.

Table 1, in the _{(Co x Fe 100-x)} 80 when the amount of Co (x) of B ₂₀ is 70% or less, the level of effective demagnetizing field (Meffective) is smaller than the saturation magnetization amount Ms, that is, The ratio Meffective / when the Co amount x is 70% or less is smaller than Ms, 1.0.
Furthermore, it can be confirmed that the difference between Meffective and Ms increases as the Co amount x decreases.

The measurement result of the reverse current value is shown in FIG. 4, and the measurement result of the thermal stability index is shown in FIG.
FIG. 4 shows the relationship between the Co amount x (content in CoFe; atomic%) of the Co—Fe—B alloy of the memory layer 17 and the reversal current density Jc0 obtained from the reversal current value.
FIG. 5 shows the relationship between the Co content of the Co—Fe—B alloy of the memory layer 17 (content in CoFe; atomic%) and the thermal stability index Δ (KV / k _B T).

FIG. 4 shows that the reversal current density Jc0 decreases as the Co amount x decreases.
This is because when the Co amount x decreases, the saturation magnetization amount Ms increases, but the effective demagnetizing field Meffective decreases, so that the product of both (Ms × Meffective) decreases.

From FIG. 5, as the Co amount x decreases, the thermal stability index Δ (= KV / k _B T) increases, and when the Co amount x decreases to a certain extent, the thermal stability index Δ increases. It turns out to be stable.
This is in good agreement with the change expected from the measurement result of the saturation magnetization amount Ms shown in FIG. 5 and the fact that the thermal stability index Δ is proportional to the saturation magnetization amount Ms from the equation (2).

  From the results of Table 1, FIG. 4, and FIG. 5, the thermal destabilization is sacrificed in the composition in which the effective demagnetizing field Meffective is smaller than the saturation magnetization Ms and the Co content x is 70% or less. It has been clarified that the reversal current value Jc0 can be reduced without using a technique while maintaining high thermal stability.

[Experiment 2]
The Experiment 1 above, found to be reduced in the case of _{(Co x Fe 100-x)} 80 B 20, while the amount of Co (x) had a high thermal stability at greater than 70% composition, the inversion current value Jc0 It was.
Therefore, in [Experiment 2], using the storage layer 17 having a composition of (Co ₇₀ Fe ₃₀ ) ₈₀ B _z and (Co ₈₀ Fe ₂₀ ) ₈₀ B _z , the B amount z is set to the ratio of Co to Fe and Meffective / Ms. We examined what kind of effect it has. The details of the sample are the same as in [Experiment 1].

Table 2 shows the composition of a CoFeB alloy with (Co ₇₀ Fe ₃₀ ) _100-z B _z and a B amount z (atomic%) of 5 to 40%, a saturation magnetization amount Ms, and an effective demagnetizing field magnitude M effective. Further, the ratio Meffective / Ms between the saturation magnetization and the effective demagnetizing field is shown.
Table 3 also shows the composition of the CoFeB alloy in which the amount of B (z) (atomic%) is 5 to 40%, the saturation magnetization Ms, and the effective in the case of (Co ₈₀ Fe ₂₀ ) _100-z B _z. The demagnetizing field magnitude Meffective and the ratio Meffective / Ms are shown.

From the results shown in Table 2, when the ratio of Co and Fe is fixed at 70/30, such as (Co ₇₀ Fe ₃₀ ) _100-z B _z , the saturation magnetization Ms is not obtained for compositions other than B content z = 40 atomic%. It can be confirmed that the value is smaller than the effective demagnetizing field Meffective.

From the results shown in Table 3, when the ratio of Co and Fe is fixed at 80/20 as in (Co ₈₀ Fe ₂₀ ) _100-z B _z , the saturation magnetization Ms is effective demagnetizing field Meffective in any composition. It can be confirmed that it is larger.

From the results of Tables 1 to 3, if the B amount z is in the range of 30 atomic% or less, the magnitude relationship between the saturation magnetization Ms and the effective demagnetizing field Meffective is determined by the ratio of Co and Fe. It was revealed.
Therefore, the composition of the Co—Fe—B alloy in which the saturation magnetization amount Ms of the storage layer 17 is smaller than the effective demagnetizing field Meffective is:
0 ≦ Co _x ≦ 70,
30 ≦ Fe _y ≦ 100,
In 0 <B _z ≦ 30,
It is _{(Co x -Fe y) 100-} z -B z.

[Experiment 3]
In the Gbit class spin injection type memory, the size of the recording element is assumed to be 100 nmφ or less. Therefore, in [Experiment 3], thermal stability was evaluated using a recording element having a size of 50 nmφ.
The composition of the Co—Fe—B alloy is such that the composition ratio (atomic%) of CoFe and B is fixed at 80:20, and the composition ratio x (atomic%) of Co in CoFe is 90%, 80%, It was changed to 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%.
Details of the sample other than the element size are the same as those in [Experiment 1].

FIG. 6 shows the relationship between the Co amount (content in CoFe; atomic%) of the Co—Fe—B alloy and the thermal stability index Δ (KV / k _B T) when the size of the recording element 3 is 50 nmφ. .

  As shown in FIG. 6, when the element size is 50 nmφ, the dependence of the thermal stability index Δ on the Co—Fe—B alloy composition is an elliptical shape with the minor axis 0.09 μm × major axis 0.18 μm shown in FIG. It can be seen that Δ greatly obtained from the Co—Fe—B alloy composition dependency of Δ obtained in the recording element.

According to FIG. 6, high thermal stability is maintained only in the case of a Co—Fe—B alloy composition in which Fe is present at 60 atomic% or more.
As a result of various studies, the reason why the Co—Fe—B alloy having Fe of 60 atomic% or more exhibits high thermal stability Δ in a very small recording element is that the magnetization of the Co—Fe—B alloy is the film surface. It became clear that it was caused by facing in the direction perpendicular to the surface.
The reason why the magnetization of the Co—Fe—B alloy is in the direction perpendicular to the film surface is thought to be due to the fact that the saturation magnetization Ms has a composition that is significantly smaller than the effective demagnetizing field Meffective.
In addition, the reason why the thermal stability is maintained even in a microelement when it is a perpendicular magnetization film is related to Hk [effective anisotropic magnetic field] in the equation (2), and the Hk of the perpendicular magnetization film is Generally, the value is much larger than that of the in-plane magnetization film. That is, in the perpendicular magnetization film, due to the effect of large Hk, high thermal stability Δ can be maintained even in a very small element that cannot secure sufficient thermal stability Δ in the in-plane magnetization film.
From the above experimental results, the _{(Co x Fe 100-x)} 80 Co-Fe-B alloy having the composition of B _20, if the Fe _100-x is 60 or more, the memory device using the spin of Gbit class It can be said that it is preferable.

[Experiment 4]
In the Experiment 3, in the _{(Co x Fe 100-x)} 80 Co-Fe-B alloy having the composition of B _20, if the Fe content is more than 60, preferably in a memory device using the spin of Gbit class It was shown that. In [Experiment 4], a recording element having a size of 50 nmφ was manufactured using a Co—Fe—B alloy having a B content in the range of 5 to 30 atomic%, and thermal stability was evaluated.
Details of the sample other than the element size are the same as those in [Experiment 1].

Co—Fe— having a composition of (Co _x Fe _100-x ) _100-z B _z in the range of Co amount x = 50, 40, 30, 20, 10, 0 and B amount z = 5, 10, 20, 30 Table 4 shows the relationship between the alloy B and the thermal stability index Δ (KV / k _B T).

From Table 4, it can be seen that the thermal stability Δ is largely maintained in all compositions except for the case where the Co amount x = 50 and the B amount z = 5-30.
That is, similarly to the result of [Experiment 4], it is clear that the Co amounts x = 50 and 60 are boundaries for ensuring high thermal stability in a micro device corresponding to a Gbit class spin injection memory. Became.

Therefore, from the above results, the composition of the Co—Fe—B alloy of the memory layer 17 is
0 ≦ Co _x ≦ 40,
60 ≦ Fe _y ≦ 100,
In 0 <B _z ≦ 30,
(Co _x -Fe _y) when a _100-z -B _z, it is suitable for producing a spin injection type memory of Gbit class has been found.

Note that the Co—Fe—B alloy has a large Co and Fe ratio Fe, and the difference between Meffective and Ms becomes large, and it becomes easy to perform perpendicular magnetization, so that it is easy to ensure thermal stability.
Therefore, when the capacity of the magnetic memory is increased and the size of the memory element 3 is reduced, the Co—Fe—B alloy containing a large amount of Fe is more likely to ensure thermal stability.
Thus, for example, considering the situation where a Gbit class spin-injection type magnetic memory can be realized with the storage layer 17 having Fe _y of 60, 70 nmφ, the Co—Fe—B alloy every time the diameter of the storage element 3 decreases by 5 nmφ. It is desirable that the Fe amount y is increased by 5 at a time.
For example Fe amount y, in case of the above _{(Co x -Fe y) 100-} z -B z, atomic% as the content in the CoFe 65%, 70%, 75%, of 80%.. A composition (in terms of Co amount x, 35%, 30%, 25%, 20%,...) Is a more preferable example in accordance with the reduction in the memory element size.

[Experiment 5]
Next, the case of the dual structure was examined.
Also in this experiment, a thermal oxide film having a thickness of 300 nm was formed on a silicon substrate having a thickness of 0.725 mm, and the memory element 3 corresponding to the structure of FIG.
A sample corresponding to the structure of FIG. For the measurement, a sample 3B having a partial layer structure of the sample 3A was also used.

Specifically, for the sample 3A, the material and film thickness of each layer were selected as shown in FIG.
Underlayer 14: Laminated film of 10 nm thick Ta film and 25 nm thick Ru film Lower magnetization pinned layer 15 L: CoFe film having a laminated ferripin structure and 1.5 nm thick CoFe film and 0.8 nm thick Ru film And a lower insulating layer 16L: a magnesium oxide film having a thickness of about 1 nm; a memory layer 17: a FeCoB film having a thickness of 2 nm; and an upper insulating layer 16U: a magnesium oxide having a thickness of about 1 nm. Film / Upper magnetization fixed layer 15U: FeCoB film with a film thickness of 1.5 nm / Cap layer 18: Laminated film of Ta film with a film thickness of 3 nm, Ru film with a film thickness of 3 nm, Ta film with a film thickness of 3 nm

In each sample (samples 1 to 7 described later) corresponding to the sample 3A, the lower insulating layer 16L serving as the lower tunnel barrier layer was a magnesium oxide film, and the thickness was changed around 1 nm to adjust the sheet resistance.
In each sample, the area resistance value was adjusted by changing the film thickness of the upper insulating layer 16U serving as the upper tunnel barrier layer to about 1 nm with a magnesium oxide film.
Further, the leakage magnetic fields of the lower magnetization fixed layer 15L and the upper magnetization fixed layer 15U were adjusted so that the leakage magnetic field to the storage layer 17 was canceled.

  Further, a Cu film (not shown) having a thickness of 100 nm (to be a word line described later) was provided between the base layer 14 and the silicon substrate to form each layer.

A sample 3A of the memory element 3 was produced as follows.
Each layer other than the upper and lower insulating layers 16U and 16L made of a magnesium oxide film was formed by DC magnetron sputtering.
The upper and lower insulating layers 16U and 16L made of a magnesium oxide (MgO) film were formed using an RF magnetron sputtering method.
Further, after each layer of the memory element 3 was formed, heat treatment was performed in a heat treatment furnace in a magnetic field.

Next, after masking the word line portion by photolithography, the word line (lower electrode) was formed by performing selective etching with Ar plasma on the laminated film other than the word line. At this time, except for the word line portion, the substrate was etched to a depth of 5 nm.
Thereafter, a mask of the pattern of the memory element 3 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 3. Except for the memory element 3 portion, the etching was performed up to the Cu layer of the word line.
In addition, in order to generate the spin torque necessary for the magnetization reversal, it is necessary to flow a sufficient current through the storage element for the characteristic evaluation storage element, and thus it is necessary to suppress the resistance value of the tunnel insulating layer. Therefore, the pattern of the memory element 3 is circular with a minor axis of 0.09 μm and a major axis of 0.09 μm, and the area resistance value (Ωμm) of the memory element 3 is adjusted by adjusting the film thickness of the lower and upper insulating layers 16U and 16L. ² ) was set to ⁵ to 100 Ωμm ² .

Next, the portion other than the memory element 3 portion was insulated by sputtering of Al ₂ O ₃ having a thickness of about 100 nm. Thereafter, a bit line to be an upper electrode and a measurement pad were formed using photolithography.
In this way, a sample of the memory element 3 was produced.
The composition of the Co—Fe—B alloys of the magnetization fixed layers 15U and 15L and the memory layer 17 was (Co 30% -Fe 70%) 80% -B 20% (both atomic%).

In addition, a sample 3B corresponding to each sample corresponding to the sample 3A was also prepared for measurement.
The sample 3B has a layer structure from the base layer 14 to the memory layer 17 of the sample 3A as shown in FIG. 7B. This is a sample for measuring the sheet resistance value and the JcO value only on the lower insulating layer 16L side.
That is, for each sample of the sample 3A in which the sheet resistance values of the insulating layers 16U and 16L were adjusted, the sample 3B having the same sheet resistance value of the insulating layer 16L was created.

As described above, the characteristics of the produced samples 3A and 3B were evaluated as follows.
Prior to the measurement, the storage element 3 was configured to be able to apply a magnetic field from the outside in order to control the positive and negative values of the reversal current to be symmetrical. In addition, the voltage applied to the memory element 3 was set to 1 V within a range where the insulating layers 16U and 16L were not broken.

(Measurement of magnetization curve)
The magnetization curve of each sample was measured by VSM measurement using a sample vibrating magnetometer. At this time, not the element after microfabrication but a bulk film portion of about 8 mm × 8 mm specially provided for evaluating the magnetization curve on the wafer was used for the measurement. The measurement magnetic field was applied in the direction perpendicular to the film surface.

(Measurement of reversal current value and thermal stability)
For the purpose of evaluating the writing characteristics of the memory element 3, the inversion current value was measured.
A current having a pulse width of 10 μs to 100 ms was passed through each sample, and then the resistance value of each sample was measured. Further, the amount of current flowing through each sample was changed to obtain a current value at which the direction of the magnetization M17 of the storage layer 17 of each sample was reversed. A value obtained by extrapolating the pulse width dependence of the current value to a pulse width of 1 ns was defined as an inversion current value.
Further, the inclination of the pulse width dependency of the inversion current value corresponds to the above-described thermal stability index (Δ) of the memory element 3. It means that the more the reverse current value does not change with the pulse width (the smaller the slope), the stronger the heat disturbance.
Then, in order to take into account the variation between the samples, about 20 samples each having the same configuration were prepared, the above-described measurement was performed, and the average value of the inversion current value and the thermal stability index Δ was obtained.
Further, the reversal current density Jc0 was calculated from the average value of the reversal current values obtained by the measurement and the area of the planar pattern of the memory element 3.

(Measurement of sheet resistance)
First, the resistance value of the entire memory element was measured.
Further, for the memory element of each sample, a sample 3B of the lower half magnetoresistive element shown in FIG. 7B was separately prepared, and its resistance value and inversion current value were measured.
Then, the lower magnetoresistive effect and the upper magnetoresistive effect were derived separately from the resistance value of the entire memory element, the resistance value of the lower half magnetoresistive element, and the inversion current value, and the effect of the dual structure was obtained.

  The values of the reversal current density Jc0 and the thermal stability index Δ of each sample obtained from the coercive force of each sample obtained by VSM and the results of spin injection magnetization reversal measurement were as follows.

As a memory, Δ needs to be 45 or more. In each sample, since the film thickness of the FeCoB film of the memory layer 17 is 2 nm, the Δ value is 50.
On the other hand, in order to secure a margin between the write voltage and the barrier breakdown voltage, the Jc0 value needs to be 4 MA / cm ² or less. As described above, Δ value and Jc0 value are generally in a trade-off relationship.

  Table 5 shows the values of the reversal current density Jc0, the coercive force Oe, and the thermal stability index Δ for each sample in which the thickness of the insulating layers 16U and 16L is adjusted and the sheet resistance value is adjusted as the sample 3A. As shown in FIG.

In Table 5, the area resistance value of the dual structure is a value measured with the sample 3A of FIG. 7A, and the area resistance value of only the lower side is the sample 3B of FIG. 7B of the corresponding structure. It is the value measured by.
The upper area resistance value is a value obtained by subtracting the lower area resistance value from the area resistance value of the dual structure.
The same applies to the JcO value of the dual structure and the JcO value of the lower side only.
Samples 1 to 7 correspond to the sample 3A described above as a dual structure. Sample 8 corresponds to the single structure sample shown in FIG.

First, the dual structure JcO values of Samples 1-7 are reduced from the JcO value of Samples 1-7 only or the single structure JcO values of Sample 8, and the dual structure is effective in reducing the write current. It can be seen that it is. The decrease in the Jc0 value is due to the improvement of the spin injection efficiency η by the dual structure.
In particular, it was found that Samples 1 to 4 having a total area resistance value of 10 Ωμm ² or more and 40 Ωμm ² or less of the dual-structure memory element 3 are preferable in terms of JcO value.
Sample 5 having a sheet resistance value of 45 Ωμm ² is outside the operating region at a high voltage.
Sample 7 having a sheet resistance value of 8 Ωμm ² could not be measured due to element breakdown.

In samples 1 to 4, the area resistance value of the upper insulating layer 16U is higher than the area resistance value of the lower insulating layer 16L.
On the other hand, in the sample 6, the lower insulating layer 16L has a higher area resistance value. In Sample 6, no improvement in the JcO value is observed.
From this, it can be seen that it is appropriate that the area resistance value of the upper insulating layer 16U is higher than the area resistance value of the lower insulating layer 16L. Since the upper insulating layer 16U is thick and has sufficient crystallinity, it leads to good interface anisotropy, leading to a favorable MR ratio and a reduction in inversion current, and a dual structure effect can be obtained more remarkably.

  In the samples 1 to 6 having the dual structure, the thermal stability index Δ is 60, which is an improvement over the sample 8 having the single structure. Further, in the dual structure samples 1 to 6, the coercive force (Hc) is 600 Oe, which is larger than that of the single structure sample 8 300 Oe, and is based on the dual structure in which both sides of the memory layer 17 are sandwiched between the insulating layers 16U and 16L. The effect of improving the interface anisotropy is obtained.

Although the embodiment has been described above, the present invention is not limited to the layer configuration of the memory element 3 described in the above embodiment, and various layer configurations can be employed.
For example, in the embodiment, the composition of Co—Fe—B of the storage layer 17 and the magnetization fixed layer 15 is the same, but is not limited to the above embodiment, and does not depart from the gist of the present invention. Various other configurations are possible within the scope.
The underlayer 14 and the cap layer 18 may be a single material or a laminated structure of a plurality of materials.
In addition, the magnetization fixed layer 15 (15L, 15U) may be a single layer or a laminated ferri-pin structure including two ferromagnetic layers and a nonmagnetic layer.

  3 memory element, 14 underlayer, 15 magnetization fixed layer, 15U upper magnetization fixed layer, 15L lower magnetization fixed layer, 16 insulation layer, 16U upper insulation layer, 16L lower insulation layer, 17 storage layer, 18 cap layer, 19U Ferromagnetic layer, 19L Lower antiferromagnetic layer

Claims (5)

A storage layer having magnetization perpendicular to the film surface and having the magnetization direction changed in response to information;
A first insulating layer made of a non-magnetic material provided in contact with the lower surface side of the storage layer;
A first magnetization fixed layer provided below the storage layer via the first insulating layer and having magnetization perpendicular to the film surface;
A second insulating layer made of a non-magnetic material provided in contact with the upper surface side of the storage layer;
A second magnetization fixed layer provided above the memory layer via the second insulating layer and having a magnetization perpendicular to the film surface;
A layer structure having
By injecting spin-polarized electrons in the stacking direction of the layer structure, the magnetization direction of the storage layer changes, and information is recorded on the storage layer.
The effective demagnetizing field received by the storage layer is smaller than the saturation magnetization of the storage layer,
Furthermore, the memory element in which the magnetization directions perpendicular to the film surfaces of the first and second magnetization fixed layers are opposite to each other. The ferromagnetic layer material constituting the memory layer is Co-Fe-B,
The composition of the Co-Fe-B is
0 ≦ Co _x ≦ 40,
60 ≦ Fe _y ≦ 100,
0 <B _z ≦ 30
In
The memory element according to claim 1, wherein (Co _x −Fe _y ) _100−z −B _z . The memory element according to claim ² , wherein the area resistance value of the entire element is 10 Ωμm ² or more and 40 Ωμm ² or less.   The memory element according to claim 3, wherein a sheet resistance value of the second insulating layer is higher than a sheet resistance value of the first insulating layer. A storage element that holds information according to the magnetization state of the magnetic material;
Two types of wiring intersecting each other,
The memory element is
A storage layer that has magnetization perpendicular to the film surface and whose magnetization direction is changed according to information; a first insulating layer made of a non-magnetic material provided in contact with the lower surface of the storage layer; A first magnetization fixed layer having a magnetization perpendicular to the film surface, and a nonmagnetic material provided in contact with the upper surface side of the storage layer. A layer structure having an insulating layer and a second magnetization fixed layer provided above the memory layer via the second insulating layer and having a magnetization perpendicular to the film surface; and a stacking direction of the layer structure By injecting spin-polarized electrons into the storage layer, the magnetization direction of the storage layer changes, information is recorded on the storage layer, and the effective demagnetizing field received by the storage layer The size is smaller than the saturation magnetization of the storage layer, and the first, Perpendicular magnetization direction in each of the film surface of the second magnetization pinned layer is a configuration that is the reverse direction,
The memory element is disposed between the two types of wirings,
A memory device in which a current in the stacking direction flows through the memory element through the two types of wirings and spin-polarized electrons are injected.

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