JP2012074716A - Storage element and memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage element which can reduce a current necessary for recording information by improving spin injection efficiency.SOLUTION: A storage element 10 comprises a storage layer 17 holding information by a magnetization state of a magnetic material and a magnetization fixed layer 19 provided above the storage layer 17 via an intermediate layer 16, in which a magnetization direction of the storage layer 17 is changed by a flow of a current in a lamination direction thereby recording information in the storage layer 17. A damping constant of the magnetic material included in the storage layer 17 satisfies the condition α<0.015.

Description

  The present invention relates to a memory element that changes the magnetization direction of a memory layer by passing a current and a memory having the memory element, and is suitable for application to a nonvolatile memory.

With the rapid spread of information communication equipment, especially small personal information equipment such as portable terminals, the elements such as memory and logic that constitute it are further integrated, increased in speed, reduced in power, etc. There is a demand for higher performance.
In particular, the nonvolatile memory is considered to be an indispensable component for enhancing the functionality of the device.
For example, the nonvolatile memory can protect important information of the system and individuals even when the power supply is consumed or troubled or the server and the network are disconnected due to some trouble.
In addition, recent portable devices are designed to reduce power consumption as much as possible by putting unnecessary circuit blocks in a standby state, but realize a non-volatile memory that can serve both as a high-speed work memory and a large-capacity storage memory. If this can be done, power consumption and memory waste can be eliminated.
Furthermore, if a high-speed, large-capacity nonvolatile memory can be realized, an “instant-on” function that can be instantly activated when the power is turned on will be possible.

Examples of the non-volatile memory include a flash memory using a semiconductor and an FRAM (Ferro electric Random Access Memory ; registered trademark ) using a ferroelectric.
However, the flash memory has a drawback in that it is not suitable for high-speed access because the writing speed is as low as the order of microseconds.
On the other hand, the FRAM has a limited number of rewritable times of 10 ¹² to 10 ^14, and therefore, it is pointed out that the durability is small to completely replace the SRAM and DRAM, and that fine processing of the ferroelectric capacitor is difficult. ing.

A magnetic random access memory (MRAM) that records information by magnetization of a magnetic material is attracting attention as a nonvolatile memory that does not have these drawbacks (see, for example, Non-Patent Document 1).
Since this MRAM stores data by rotating the magnetic moment, the number of rewrites is large.
Also, the access time is very high.

Here, 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 current value for reversing the direction of magnetization tends to increase. On the other hand, the address wiring also becomes thinner, so that a sufficient current cannot flow.

Therefore, attention has been paid to a magnetic memory having a configuration using magnetization reversal by spin injection as a configuration capable of reversing magnetization with a smaller current (see, for example, Patent Document 1).
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 with a small current even if the element is miniaturized.

Moreover, the schematic diagram of the magnetic memory of the structure using the magnetization reversal by the spin injection mentioned above is shown in FIG.10 and FIG.11. 10 is a perspective view, and FIG. 11 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. Of 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 with the left and right selection transistors in FIG. 10, and a wiring 59 is connected to the drain region 58.
A storage element 53 having a storage layer whose magnetization direction 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).
In the figure, reference numerals 61 and 62 denote magnetic layers. Of the 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 direction. A changing magnetization free layer, that is, a storage layer is used.
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 magnetic memory element 53 to reverse the magnetization direction of the memory layer by spin injection.

In the case of a memory configured to use such magnetization reversal by spin injection, the wiring for generating a current magnetic field (105 in FIG. 12) is not required as compared with the general MRAM shown in FIG. Another feature is that the structure can be simplified.
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.

JP 2003-17782 A

Nikkei Electronics 2001.1.22 (pages 164-171)

  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 configured to use 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.

In order to increase the read signal, it is necessary to ensure a large magnetoresistance change rate. For this purpose, a storage element in which an intermediate layer in contact with both sides of the storage layer is a tunnel insulating layer (tunnel barrier layer) 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.

  Therefore, in a memory element configured to reverse the magnetization direction of the memory layer by spin injection, it is necessary to improve the spin injection efficiency and reduce the required current.

The write current threshold required for reversing the magnetization direction of the storage layer by spin injection is, for example, a CoFeB alloy with a thickness of 2 nm for the storage layer, and a substantially elliptical shape with a planar pattern of 130 nm × 100 nm. In the giant magnetoresistive effect element (GMR element), the threshold value on the + side + Ic = + 0.6 mA and the threshold value on the negative side −Ic = −0.2 mA. The current density at this time is about 6 × 10 ⁶ A / cm ² (see Rooftop et al., Journal of the Japan Society of Applied Magnetics, Vol. 28, No. 2, p. 149, 2004).
For example, when CoFe which is general as a ferromagnetic layer is used as the material of the memory layer, a current density of about 1 × 10 ⁷ A / cm ² is required to cause magnetization reversal.
When the current density is the value described above, for example, if the size of the memory element is 90 nm × 130 nm, the write current threshold value is approximately 550 μA.

Here, FIG. 13 shows the relationship between the element resistance of the memory element and the element current flowing in the memory element when the general selection transistor and the memory element are connected by the SPICE simulator.
Considering the magnitude of the read signal, the larger the element resistance, the better. However, from FIG. 13, when the element resistance is increased, the current that can be passed through the memory element is reduced.
Considering the case of the element resistance of 2.5 kΩ, which is estimated as the lower limit for sufficiently securing the read characteristics, the upper limit of the current that can be passed through the memory element is about 400 μA from FIG. In addition, the write current threshold must be reduced by 30% or more.
For this reason, in order to sufficiently secure the read characteristics, it is required to further reduce the write current as compared with the case where CoFe or CoFeB is used as the material of the storage layer.

  In order to solve the above-described problems, the present invention provides a memory element that can reduce the current required for recording information by improving the spin injection efficiency, and a memory having the memory element. is there.

  The storage element of the present invention has a storage layer that holds information according to the magnetization state of a magnetic material, and a magnetization fixed layer is provided to the storage layer via an intermediate layer. When the damping constant α satisfies α <0.015 and a current is passed in the stacking direction, the magnetization direction of the storage layer changes, and information is recorded on the storage layer.

According to the configuration of the above-described storage element of the present invention, the storage layer that holds information according to the magnetization state of the magnetic material is provided, and the magnetization fixed layer is provided to the storage layer via the intermediate layer. Since the direction of magnetization of the recording layer changes and information is recorded on the storage layer, by passing a current between the storage layer and the fixed magnetization layer, the magnetization state (magnetization) of the storage layer is caused by so-called spin injection. Information can be recorded by changing the direction of
Since the damping constant α of the magnetic material constituting the storage layer satisfies α <0.015, the damping constant of the storage layer can be reduced, and the magnetization direction of the storage layer proportional to the damping constant can be changed. The threshold value of the current for changing can be reduced. As a result, the amount of current required to record information by reversing the magnetization direction of the storage layer by spin injection can be reduced.

  The memory of the present invention includes a storage element having a storage layer that holds information according to the magnetization state of a magnetic material, and two kinds of wirings that intersect each other, and the storage element is magnetized via an intermediate layer with respect to the storage layer. A fixed layer is provided, the damping constant α of the magnetic material constituting the storage layer satisfies α <0.015, and by passing a current in the stacking direction, the magnetization direction of the storage layer changes, and the storage layer In the configuration in which information is recorded, a memory element is arranged near the intersection of two types of wiring and between the two types of wiring, and the current in the stacking direction flows through the memory element through the two types of wiring. It is.

According to the configuration of the memory of the present invention described above, a memory element having a memory layer that holds information according to the magnetization state of the magnetic material and two kinds of wirings intersecting each other are provided, and the memory element is the memory element of the present invention. (A storage layer damping constant α <0.015), a storage element is disposed near an intersection of two types of wiring and between the two types of wiring, and the stacking direction is passed to the storage element through two types of wiring. Therefore, information can be recorded by spin injection by flowing current in the stacking direction of the memory element through two types of wiring.
In addition, the amount of current necessary for reversing the magnetization direction of the memory layer of the memory element by spin injection can be reduced.

According to the above-described present invention, the amount of current required for recording information can be reduced.
As a result , the power consumption of the entire memory can be reduced.
Therefore, it is possible to realize a memory with low power consumption that has not been conventionally available.

In particular, when an insertion layer made of an oxide or nitride of Al or Mg is arranged between the memory layer and the upper protective layer, the characteristics of the memory element when heat is applied to the memory element Degradation can be suppressed, and information can be recorded and read stably in the memory. A memory element with little characteristic deterioration can be formed even at high temperatures.
As a result, a memory having heat resistance and high reliability can be realized.

It is a schematic block diagram (sectional drawing) of the memory element of one embodiment of this invention. It is the figure which showed the change of the spin polarizability with respect to the addition amount when various elements are added to an AFeNi alloy. It is the figure which showed the change of the average magnetic moment with respect to the addition amount when various elements are added to a B2FeNi alloy. It is the figure which showed the change of the spin polarizability per mean magnetic moment with respect to the addition amount when various elements are added to a FeNi alloy. It is a schematic block diagram (sectional drawing) of the memory element of other embodiment of this invention. A to C are resistance-magnetic field curves of the memory elements of Samples 8 to 10. A, B It is a figure which shows the relationship between the reversal current value of the memory | storage element of sample 9-sample 10, and the magnitude | size of an external magnetic field. This is a change in characteristics depending on the Ni content in the sample of the memory element having the film configuration 5. It is a figure which shows the relationship between ANi content and MR ratio. It is a figure which shows the relationship between BNi content and a magnetization reversal current density. This is a change in characteristics due to the Ni content in the sample of the memory element having the film configuration 6. It is a figure which shows the relationship between ANi content and MR ratio. It is a figure which shows the relationship between BNi content and a magnetization reversal current density. 6 is a diagram showing current-resistance characteristics of a memory element of Sample 11. FIG. It is a schematic block diagram (perspective view) of the magnetic memory using the magnetization reversal by spin injection. It is sectional drawing of the magnetic memory of FIG. It is the perspective view which showed the structure of the conventional MRAM typically. It is a figure which shows the relationship between element resistance and element current at the time of connecting the general selection transistor and storage element by SPICE simulator.

First, an outline of the present invention will be described prior to description of specific embodiments of the present invention.
In the present invention, information is recorded by reversing the magnetization direction of the storage layer of the storage 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.

The basic operation of reversing the magnetization direction of the magnetic layer by spin injection is perpendicular to the film surface of a memory element composed of a giant magnetoresistive element (GMR element) or a tunnel magnetoresistive element (MTJ element). In such a direction, a current exceeding a certain threshold is passed. 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, the required current threshold Ic is phenomenologically expressed by the following equation 1 (JZ Sun, Phys. Rev. B, Vol. 62, p. 570, 2000).

（ただし、α：記憶層のダンピング定数、Ｈ_ｋ：記憶層の面内一軸異方性磁界、Ｍ_ｓ：記憶層の飽和磁化、η：スピン注入係数、a：記憶層の半径、ｌ_ｍ：記憶層の厚さ、Ｈ：外部印加磁界）

(Where, α: damping constant of the storage layer, H _k : in-plane uniaxial anisotropic magnetic field of the storage layer, M _s : saturation magnetization of the storage layer, η: spin injection coefficient, a: radius of the storage layer, l _m : Memory layer thickness, H: externally applied magnetic field)

In order to reduce the write threshold current Ic, various parameters in the above equation 1 may be adjusted.
On the other hand, the above various parameters are restricted from the viewpoint of maintaining the performance as a memory. For example, the term (a ² l _m H _k M _s ) in Equation 1 is known as a term that determines thermal fluctuation, and the long-term stability of written data is ensured by suppressing variations in the write threshold current Ic. In order to do this, a value above a certain value must be maintained, and it cannot be reduced below a certain value. For this reason, there is a lower limit to the size of the storage element and the thickness l _{m of the} storage layer and the saturation magnetization M _s , and the technique for reducing the write current by reducing these parameters is limited in some places.

  It is known that the damping constant α can be measured by ferromagnetic resonance (FMR) or the like. , J. Magn. Magn. Mater., 226-230, p.1640 (2001).

Conventionally, CoFe has been generally used as a material for a memory layer of a memory element by spin injection in order to obtain a large readout signal.
Further, when CoFeB is used as the material for the memory layer, the saturation magnetization M _s is reduced by adding boron B to CoFe that is generally used, so that the write threshold current is smaller than that of CoFe. It is considered that Ic can be reduced.
However, these materials (CoFe, CoFeB) have a large damping constant α of about 0.02. For this reason, the write current density becomes as large as 6 × 10 ⁶ A / cm ² or more, and since the term that determines the above-described thermal fluctuation becomes large, it is adversely affected by the thermal fluctuation.
Therefore, with these materials, it is difficult to reduce the write threshold current Ic while suppressing the influence of thermal fluctuation, and it becomes impossible to write information by forming a memory cell connected to the selection transistor.

As a result of investigating an optimal structure for achieving the above-described purpose, that is, to improve the efficiency of spin injection and to be able to record information with a low current, a storage layer that holds the direction of magnetization (magnetization state) as information And a magnetization fixed layer (having a reference layer serving as a reference for information) having a fixed magnetization direction and a nonmagnetic layer sandwiched between them, and a current flowing through the nonmagnetic layer In a storage element that records and reads information, paying attention to the importance of the damping constant α expressed by the equation (1), the storage layer size and saturation magnetization M _s are reduced by reducing the damping constant α of the storage layer. It has been found that the recording current can be reduced by reducing the saturation magnetic flux density of the storage layer without reducing the recording current.

For example, when a material having a small damping constant such as a NiFe alloy having a damping constant α of about 0.01 is used for the memory layer, the threshold of the write current density is reduced to about 3 × 10 ⁶ A / cm ² or less.
At this time, if the size of the memory element is, for example, 90 nm × 130 nm, the write threshold current Ic is about 280 μA, which can be made smaller than the saturation current (about 400 μA) of the selection transistor described above, and spin injection is used. Thus, a memory for writing information can be realized.

Since the saturation current of the selection transistor is about 400 μA as described above, and the write current threshold value Ic is proportional to the damping constant α from Equation 1, the damping constant α of the magnetic material constituting the storage layer is
α <0.015 (Formula 2)
It is required to satisfy this relationship.

That is, the present invention has a storage layer that holds the direction of magnetization (magnetization state) as information, and a magnetization fixed layer whose magnetization direction is fixed, and a nonmagnetic layer is formed between the storage layer and the magnetization fixed layer. An intermediate layer (insulating layer or nonmagnetic conductive layer) is provided to form a memory element.
In addition, information recording is performed on the storage layer by reversing the magnetization direction of the magnetic layer constituting the storage layer by using the above-described magnetization reversal by spin injection.
Then, a material that satisfies the relationship of the above-mentioned formula 2, such as a NiFe alloy having a damping constant α of about 0.01, is used as a magnetic body constituting the memory layer.
As a result, the damping constant α of the memory layer is reduced, the write threshold current Ic is approximately 280 μA, which can be smaller than the saturation current (approximately 400 μA) of the selection transistor described above, and information writing is performed using spin injection. It is possible to realize a memory that performs the above.

Examples of the material used for the storage layer that satisfy the condition shown in Formula 2 include NiFe alloys and materials containing NiFe as a main component and other materials.
For example, NiFe is the main component, and other elements are B, C, N, Si, P, Al, Ta, Mo, Cr, Nb, Cu, Zr, W, V, Hf, Gd, Mn, and Pd. Can be used.
The addition amounts of these other elements are set so that the damping constant α satisfies Equation 2. More preferably, the initial permeability (μi) is set to be 10,000 or more. By setting the addition amount of other elements so that the initial magnetic permeability is 10,000 or more, the damping constant of the memory layer can be suppressed from becoming large.
In addition, the magnetic material is not limited to NiFe as a main component, and any other magnetic material can be used as long as the damping constant α satisfies the expression (2).

  In addition, the memory layer is made of a material mainly composed of NiFe, and a memory element is formed by sandwiching a CoFe film or CoFeB film having a thickness of 0.5 nm or less between the memory layer and an intermediate layer (tunnel insulating layer or the like). You may do it.

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 fixed layer has a configuration in which the magnetization direction is fixed only by the ferromagnetic layer or by using the antiferromagnetic coupling between the antiferromagnetic layer and the ferromagnetic layer.
In addition, the magnetization fixed layer has a single-layered ferromagnetic layer structure or a laminated ferrimagnetic structure in which a plurality of ferromagnetic layers are stacked via a nonmagnetic layer. When the magnetization pinned layer has a laminated ferrimagnetic structure, the sensitivity of the magnetization pinned layer to the external magnetic field can be reduced. Therefore, unnecessary magnetization fluctuations in the magnetization pinned layer due to the external magnetic field are suppressed, and the memory element operates stably. Can be made.

Examples of the material of each of the other layers constituting the memory element include the following materials.
As the material used for the antiferromagnetic layer, manganese alloys such as iron, nickel, platinum, iridium, and rhodium, cobalt, nickel oxide, and the like can be used.
As a material used for the nonmagnetic layer, ruthenium, copper, chromium, gold, silver or the like can be used. Although the film thickness varies depending on the material, it is used in the range of about 0.4 nm to 2.5 nm.
As a material of the ferromagnetic layer constituting the magnetization fixed layer, a Co or Co—Fe ferromagnetic material, an amorphous material added with 15 to 30 atomic% of boron B, or a ferromagnetic material made of an alloy of Co, Fe, and Ni. Materials can be used.

  Among the ferromagnetic layers constituting the magnetization fixed layer, in particular, the ferromagnetic layer in contact with the antiferromagnetic layer (for example, PtMn film) is made of Co or Co—Fe ferromagnetic material, and its Fe content is set to 0 to 0. It should be 20%. If the Fe content exceeds 20% and becomes too large, it tends to deteriorate due to high-temperature heat treatment.

  Of the ferromagnetic layers constituting the magnetization fixed layer, the ferromagnetic layer in contact with the intermediate layer (tunnel insulating layer or the like) is preferably composed mainly of CoFeB. This is because CoFeB has a higher spin polarizability than CoFe and the like, so that the spin injection efficiency of the memory element is increased and the amount of current required to reverse the magnetization direction of the memory layer can be reduced. Because it becomes.

  In the laminated ferrimagnetic structure, the ferromagnetic layer in contact with the lower side of the nonmagnetic layer (eg, Ru film) is preferably a CoFe layer rather than a CoFeB layer so that sufficient antiferromagnetic coupling can be obtained.

In particular, when the magnetic material constituting the storage layer is configured to add at least one element selected from Cu, Pd, and Zn to a NiFe alloy, the addition of these elements makes a comparison with the NiFe alloy alone. Thus, the saturation magnetic flux density can be further lowered and the spin polarizability can be improved.
By reducing the saturation magnetic flux density, the write threshold current due to spin injection can be reduced, and information can be written (recorded) with a small current.
By improving the spin polarizability, it is possible to increase the magnetoresistance change rate (MR ratio) and increase the read signal intensity when reading information recorded in the storage layer.

Here, the spin polarizability P when the respective elements of Cu, Pd, Cr, Ru, and Zn are added in place of Ni of the standard soft magnetic FeNi alloy composition (Fe ₂₀ Ni ₈₀ ) is obtained by calculation. It was. The relationship between the calculated value of the spin polarizability P and the amount of element added is shown in FIG. 2A.
As shown in FIG. 2A, when Cr and Ru are added, the polarizability is improved by adding a small amount, but the polarizability decreases when the added amount is increased. It can also be seen that when Cu, Pd, and Zn are added, the polarizability increases at a relatively large addition amount.

Similarly, FIG. 2B shows the relationship between the amount of each element added to Fe ₂₀ Ni ₈₀ and the average magnetic moment.
From FIG. 2B, there is a difference in the decrease rate of the average magnetic moment due to the type of element to be added, Cr and Zn have a large decrease rate, and Pd has a small decrease rate. Since the average magnetic moment and the saturation magnetic flux density are substantially proportional, the smaller the average magnetic moment, the smaller the recording current.

Next, in order to consider the spin polarizability and the average magnetic moment, the spin polarizability per average magnetic moment is calculated, and the change of this value with respect to the added amount is calculated and shown in FIG.
FIG. 3 shows that when Zn, Cu, and Pd are added, the polarizability per average magnetic moment is remarkably improved.

In addition, by forming a magnetic tunnel junction (MTJ) element using a tunnel insulating layer as a nonmagnetic intermediate layer between the storage layer and the magnetization fixed layer, a giant magnetoresistive effect ( Compared with the case of configuring a (GMR) element, the magnetoresistance change rate (MR ratio) can be increased, and the read signal intensity can be increased.
As a material for the tunnel insulating layer, for example, an oxide such as aluminum oxide (AlOx) or magnesium oxide (MgO) can be used.

In particular, by using magnesium oxide (MgO) as the material of the tunnel insulating layer, the magnetoresistance change rate (MR ratio) can be made larger than when aluminum oxide is used. In general, the spin injection efficiency depends on the MR ratio, and the higher 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, 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.

  In the case where the tunnel insulating layer is formed of an MgO film, it is desirable that the MgO film is crystallized and the crystal orientation is maintained in the 001 direction.

In order to pass a sufficient write current to the memory element, it is necessary to reduce the area resistance value of the tunnel insulating layer (tunnel barrier layer).
In a memory element that reverses the magnetization direction of the memory layer by spin injection, a current density of approximately 3 to 8 × 10 ⁶ (A / μm ² ) is required to enable magnetization reversal by spin injection. Although depending on reliability such as pinhole density in the tunnel insulating layer, magnetization reversal by spin injection is possible, and the dielectric breakdown voltage of the relatively low resistance tunnel insulating layer is about 1V.
Here, in order to obtain a current density of 3 to 8 × 10 ⁶ (A / μm ² ), assuming that the area of the memory element is 0.06 × 0.167 μm = 0.01 μm ² , The resistance value needs to be smaller than 33.3 to 12.5 (Ωμm ² ).
Note that the smaller the current density required for magnetization reversal, the larger the resistance value of the memory element.
Therefore, the area resistance value of the tunnel insulating layer, from the viewpoint of obtaining a current density required for spin injection is preferably at least 30Omegamyuemu ² or less, and more preferably 15Omegamyuemu ² or less.
When an MgO film is used for the tunnel insulating layer, it is desirable that the thickness of the MgO film be 0.8 nm or less in order to make the sheet resistance value 30 Ωμm ² or less.

In the present invention, when a NiFe alloy or a material containing NiFe as a main component is used for the memory layer, the thickness of the memory layer is further set to 3 nm or more and 4 nm or less, so that the memory element is favorably destroyed. Information can be written (recorded), and a large MR ratio can be obtained.
As the memory layer becomes thinner, the MR ratio becomes smaller and the read signal strength becomes smaller.
On the other hand, when the storage layer is thick, it is necessary to increase the write current for reversing the direction of magnetization, which may destroy the tunnel insulating layer.

  Note that, depending on other configuration conditions of the memory element, even when the film thickness of the memory layer is out of the above range of 3 nm to 4 nm, information can be written (recorded) satisfactorily and a large MR ratio can be obtained. However, by setting the film thickness of the memory layer within the above-described range, the above-described effects can be obtained regardless of other configuration conditions.

In the present invention, when using a NiFe alloy or a material containing NiFe as a main component for the memory layer, the Ni content in at least a part of the memory layer (a part of the memory layer or the entire memory layer) When the atomic ratio is 70 atomic% or more and 90 atomic% or less, the spin injection efficiency can be improved and a large MR ratio can be obtained. Thereby, the write threshold current by spin injection can be reduced, information can be written (recorded) with a small current, and the read signal intensity can be increased.
When the Ni content is small, the MR ratio is small, and the write threshold current by spin injection is also large.
On the other hand, when the Ni content increases to around 100 atomic%, the MR ratio is greatly degraded. In addition, the write threshold current due to spin injection is larger than in the case of 90 atomic% or less.
Note that when the Ni content in the partial region of the storage layer is effective as described above, the region is effective wherever the storage layer is, but the region is in contact with the intermediate layer (such as a tunnel insulating layer). In some cases, the greatest effect is obtained.

In the present invention, when a NiFe alloy or a material containing NiFe as a main component is used for the memory layer, the memory layer has a saturation magnetization of 1 T or less, so that the write threshold current is equal to the saturation magnetization of the memory layer. Since it is proportional to the square, writing threshold current by spin injection can be reduced and information can be written (recorded) with a small current.
When the saturation magnetization of the storage layer exceeds 1T, the write threshold current due to spin injection also increases.

The thickness of the memory layer containing NiFe as a main component is preferably several nm or less, more preferably 3 nm or more and 4 nm or less as described above.
As a process for forming such a thin memory layer, a method of directly forming a thin film having a desired film thickness by a DC magnetron sputtering method or the like can be considered.
Further, for example, after the magnetic thin film constituting the storage layer is formed to be thicker than a desired thickness, the upper portion is changed to a non-magnetic region by a chemical reaction, oxidation, ion implantation, etc. It is also possible to reduce the effective thickness. By using this manufacturing method, it is possible to produce a film in a good state even if it is difficult to form a film directly in a good state.

  Next, specific embodiments of the present invention will be described.

FIG. 1 is a schematic configuration diagram (cross-sectional view) of a memory element as an embodiment of the present invention.
The storage element 10 includes a base layer 11, an antiferromagnetic layer 12, a ferromagnetic layer 13, a nonmagnetic layer 14, a ferromagnetic layer 15, a tunnel insulating layer 16, a storage layer 17, and a cap layer (protective layer) 18 from the lower layer. Are laminated.
The storage layer 17 is made of a magnetic material, and is configured to hold information in a magnetization state (the direction of the magnetization M1 of the storage layer 17).
The ferromagnetic layer 13, the nonmagnetic layer 14, and the ferromagnetic layer 15 constitute a magnetization fixed layer 19 having a laminated ferri structure. Among them, the ferromagnetic layer 13 is fixed to the right direction of the magnetization M13 by the antiferromagnetic layer 12. The direction of the magnetization M15 of the ferromagnetic layer 15 is leftward, which is antiparallel to the direction of the magnetization M13 of the ferromagnetic layer 13.
The ferromagnetic layer 15 is also referred to as a reference layer because it serves as a reference for the direction of magnetization with respect to the storage layer 17.

As a material of the ferromagnetic layers 13 and 15 of the magnetization fixed layer 19, an alloy material composed of one or more of iron, nickel, and cobalt, for example, a CoFe alloy can be used. Furthermore, transition metal elements such as Nb and Zr, and light elements such as B can also be contained.
For example, amorphous (amorphous) CoFeB in which 20 to 30 atomic% of boron B is added to a CoFe alloy can be used.

  In particular, by using CoFeB for the ferromagnetic layer (reference layer) 15 in contact with the tunnel insulating layer 16 of the magnetization fixed layer 19, the spin polarizability can be increased and the spin injection efficiency of the memory element 10 can be improved. Can do. Thereby, the current for reversing the direction of the magnetization M1 of the storage layer 17 can be further reduced.

As a material of the tunnel insulating layer 16, an oxide such as Al, Mg, Hf, or Si, or an insulating material such as another oxide or nitride can be used.
In particular, when magnesium oxide (MgO) is used as the material of the tunnel insulating layer 16, a large magnetoresistance change rate (MR ratio) can be obtained as described above.
For the reason described above, the thickness of the tunnel insulating layer 16 made of MgO is preferably 0.8 nm or less.

By flowing a current between the base layer 11 and the cap layer 18, the magnetization direction of the memory layer 17 can be reversed by spin injection.
When a current is passed from the cap layer 18 toward the base layer 11, that is, from the storage layer 17 toward the ferromagnetic layer (reference layer) 15, polarized electrons are injected from the ferromagnetic layer (reference layer) 15 into the storage layer 17. Thus, the magnetization direction of the storage layer 17 is parallel to the magnetization direction of the reference layer 15.
When a current is passed from the underlayer 11 to the cap layer 18, that is, from the reference layer 15 to the storage layer 17, polarized electrons are injected from the storage layer 17 to the reference layer 15, and the magnetization direction of the storage layer 17 changes. The direction of magnetization of the reference layer 15 is antiparallel.
In this way, information to be recorded can be selected depending on the direction in which the current flows.

When the magnetization direction of the ferromagnetic layer (reference layer) 15 and the magnetization direction of the storage layer 17 are parallel, the resistance of the current passing through the tunnel insulating layer 16 is small, and when the magnetization direction is antiparallel, the tunnel insulating layer 16 The resistance of the current passing through is increased. Utilizing this fact, the content of information recorded in the storage layer 17 can be read from the resistance value.
Note that the current that flows during reading is made smaller than the reversal current so that the magnetization reversal of the memory layer 17 due to spin injection does not occur.

In the present embodiment, in particular, the configuration in which the storage layer 17 is mainly composed of NiFe, or the configuration in which the damping constant α of the magnetic material forming the storage layer 17 satisfies α <0.015 (the above-described formula 2). To do.
As a result, the damping constant of the storage layer can be reduced as described above, and therefore the current threshold value for changing the magnetization direction of the storage layer, which is proportional to the damping constant, can be reduced.

  Further, when the storage layer 17 is configured to have NiFe as a main component, as described above, the initial permeability is set to 10,000 or more. The storage layer 17 is made of at least one selected from Cu, Pd, and Zn as NiFe. The film thickness of the memory layer 17 is 3 nm or more and 4 nm or less, and the Ni content in at least a part of the memory layer 17 is 70 atom% or more and 90 atom% or less. By adding a configuration such that the saturation magnetization of the layer 17 is 1T or less, the characteristics of the memory element 10 can be further improved.

  The memory element 10 of the present embodiment is manufactured by continuously forming the base layer 11 to the cap layer 18 in a vacuum apparatus and then forming a pattern of the memory element 10 by processing such as etching. Can do.

Further, a memory having the same structure as the memory illustrated in FIG. 10 can be formed using the memory element 10 of this embodiment.
That is, the memory element 10 is arranged near the intersection of two types of address lines to constitute a memory, and a current in the vertical direction (stacking direction) is passed through the memory element 10 through the two types of address lines, and the memory layer is formed by spin injection. Information can be recorded in the storage element 10 by reversing the direction of magnetization of 17.

  According to the configuration of the storage element 10 of the present embodiment described above, the storage layer 17 is mainly composed of NiFe, or the damping constant α of the magnetic material forming the storage layer 17 is α <0.015 (described above). With the configuration satisfying the expression 2), the current threshold value for changing the magnetization direction of the storage layer can be reduced. As a result, the amount of current required to record information by reversing the magnetization direction of the storage layer by spin injection can be reduced.

  Accordingly, the amount of current required for writing (recording) information can be reduced, and in a memory having a large number of memory elements 10, the power consumption of the entire memory can be reduced, and a memory with low power consumption that has not been conventionally obtained can be achieved. Can be realized.

In the above-described embodiment, the cap layer 18 is formed directly on the storage layer 17, but an insertion layer made of an oxide or nitride may be provided between the storage layer and the cap layer.
By providing such an insertion layer, even when a high temperature (eg, 400 ° C.) thermal history is received during manufacturing or when a high temperature heat treatment step is performed, the element between the cap layer 18 and the memory layer 17 is not affected. Diffusion can be suppressed by the insertion layer.

Examples of the material of the insertion layer include Al and Mg oxides or nitrides.
The insertion layer using such a material can be formed by, for example, RF magnetron sputtering using an oxide target, reactive sputtering by introducing oxygen gas during film formation, oxygen film formation after forming a metal film. It can be formed by a known method such as natural oxidation by exposure to a gas or oxidation of a metal film by oxygen plasma.

In order to allow a sufficient write current to flow through the memory element, it is desirable that the area resistance value of the insertion layer is smaller than the area resistance value of the tunnel insulating layer.
For example, when the tunnel insulating layer and the insertion layer are both formed of an MgO film, the thickness of the tunnel insulating layer is preferably 0.8 nm or less as described above, so the thickness of the insertion layer is also 0.8 nm. Below. That is, when both the tunnel insulating layer and the insertion layer are formed of the same material, the thickness of the insertion layer is set to be the same as the thickness of the tunnel insulating layer or thinner than the tunnel insulating layer.
An embodiment in which this insertion layer is provided will be described below.

FIG. 4 shows a schematic configuration diagram of a memory element as another embodiment of the present invention.
In the memory element 20 of the present embodiment, in particular, an insertion layer 21 is provided between the memory layer 17 and the upper cap layer (protective layer) 18.
Since other configurations are the same as those of the memory element 10 of the previous embodiment, the same reference numerals are given and redundant description is omitted.

  Specific materials for the insertion layer 21 include the materials described above, for example, oxides such as aluminum oxide and magnesium oxide, and nitrides such as aluminum nitride and magnesium nitride.

  According to the configuration of the memory element 20 of the present embodiment described above, similar to the memory element 10 of the aforementioned embodiment, it is necessary to record information by reversing the magnetization direction of the memory layer by spin injection. The amount of current can be reduced, the power consumption of the entire memory in a memory having a large number of storage elements 20 can be reduced, and an effect of realizing a memory with low power consumption that has never been obtained can be obtained. .

Further, according to the configuration of the memory element 20 of the present embodiment, the insertion layer 21 is provided between the memory layer 17 and the cap layer 18, so that a high-temperature thermal history is received when the memory element 20 is manufactured. In some cases, even when a high-temperature heat treatment step is performed, the diffusion of elements between the memory layer 17 and the cap layer 18 can be suppressed by the insertion layer 21.
As a result, even when the memory layer 17 is thinned, the magnetic characteristics can be maintained, so that a sufficient magnetoresistance change rate (MR ratio) can be maintained. It becomes possible to reduce the current required for recording.

Since deterioration of characteristics due to diffusion of elements when heat is applied to the memory element 20 can be suppressed, information can be recorded and read stably in the memory.
Therefore, a memory having heat resistance and high reliability can be realized.
In particular, when a layer requiring a relatively high heat treatment temperature, such as MgO, is used for the tunnel insulating layer 16 of the memory element 10, the resistance change rate is further increased by the heat treatment and the deterioration of the magnetic characteristics is suppressed. be able to.

(Example)
Here, in the configuration of the memory element of the present invention, the dimensions and composition of the memory layer were specifically set to examine the characteristics.

<Experiment 1>
First, the difference in characteristics depending on the magnitude of the damping constant α of the magnetic material constituting the storage layer was examined.
Actually, as shown in FIG. 10, the memory includes a semiconductor circuit for switching in addition to the memory element. Here, for the purpose of examining the magnetoresistive characteristics of the memory layer, the memory element The wafer was examined using only the wafer.

(Sample 1; comparative example)
First, a thermal oxide film having a thickness of 2 μm was formed on a silicon substrate having a thickness of 0.575 mm, and a memory element similar to the memory element 10 shown in FIG. 1 was formed.
Specifically, in the memory element 10 having the configuration shown in FIG. 1, the underlayer 11 is a Ta film having a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film having a thickness of 20 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19. The layers 13 and 15 are a CoFe film having a thickness of 2 nm, the nonmagnetic layer 14 constituting the magnetization fixed layer 19 having a laminated ferri structure is a Ru film having a thickness of 0.8 nm, and the tunnel insulating layer 16 is an Al film having a thickness of 0.5 nm. An oxide film obtained by oxidizing aluminum, a storage layer 17 of 3 nm-thickness Co ₇₂ Fe ₈ B ₂₀ film, and a cap layer 18 of 5 nm-thickness Ta film are selected, and between the underlayer 11 and the antiferromagnetic layer 12 A Cu film (not shown) having a thickness of 100 nm (to be a word line described later) was provided to form each layer.
That is, the memory element 10 was fabricated with the material and film thickness of each layer as the following configuration (film configuration 1).
Membrane configuration 1:
Ta (3nm) / Cu (100nm) / PtMn (20nm) / CoFe (2nm) / Ru (0.8nm) / CoFe (2nm) / Al (0.5nm) -Ox / Co72Fe8B20 (3nm) / Ta (5nm)
In the above film configuration, the PtMn composition whose alloy composition is not shown is Pt50Mn50 (atomic%).
Each layer other than the tunnel insulating layer 16 made of an aluminum oxide film was formed using a DC magnetron sputtering method.
The tunnel insulating layer 16 made of an aluminum oxide (Al—O _x ) film is formed by first depositing a metal Al film to a thickness of 0.5 nm by a DC sputtering method, and then setting the oxygen / argon flow ratio to 1: 1. The metal Al layer was oxidized by this. The oxidation time was 10 minutes.
Further, after each layer of the memory element 10 was formed, heat treatment was performed at 10 kOe · 270 ° C. for 4 hours in a heat treatment furnace in a magnetic field, and ordered heat treatment was performed on the PtMn film of the antiferromagnetic layer 12.

  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.

After that, a mask of the pattern of the memory element 10 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 10. Except for the memory element 10 portion, 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 10 is an ellipse having a short axis of 90 nm × long axis of 130 nm, and the area / resistance product (RA) of the memory element 10 is 10 Ωμm ² .

Next, the part other than the memory element 10 was insulated by sputtering of Al ₂ O ₃ having a thickness of about 100 nm.
Thereafter, a bit line serving as an upper electrode and a measurement pad were formed by using photolithography to prepare a sample of the memory element, and a sample of the memory element of Sample 1 was obtained.

(Sample 2; Examples)
The memory layer 17 was formed of a Ni ₈₀ Fe ₂₀ film having a thickness of 3 nm, and the other configuration was the same as the film configuration 1 to fabricate the memory element 10.
That is, the memory element 10 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 2).
Membrane configuration 2:
Ta (3nm) / Cu (100nm) / PtMn (20nm) / CoFe (2nm) / Ru (0.8nm) / CoFe (4nm) / Al (0.5nm) -Ox / Ni80Fe20 (3nm) / Ta (5nm)
This was used as a sample of the memory element of Sample 2.

The characteristics of the memory elements of Sample 1 and Sample 2 were evaluated as follows.
Prior to the measurement, the storage element was configured to be able to apply a magnetic field from the outside in order to control the values of the reversal current in the positive and negative directions to be symmetrical.

(Reverse current value measurement)
A current was passed through the memory element, and then the resistance value of the memory element was measured. When measuring the resistance value of the memory element, the temperature was set to room temperature 25 ° C. and the bias voltage applied to the word line terminal and the bit line terminal was adjusted to 10 mV. Further, the resistance value of the memory element was measured by changing the amount of current flowing through the memory element, and a resistance-current curve was obtained from the measurement result. In addition, the measurement which obtains this resistance-current curve was performed about the electric current of both polarities (plus direction and minus direction).
From this resistance-current curve, a current value at which the resistance value changes was obtained, and this was set as an inversion current value for reversing the direction of magnetization. The inversion current value was obtained for the bipolar current. Furthermore, the average value of the absolute values of the inverting current values of both polarities was calculated and used as the inverting current value of each sample.
Further, the reversal current density was obtained by calculation from the reversal current value and the cross-sectional area of the memory element.
Table 1 shows the reversal current density, the reversal current value, and the value of the damping constant α of the magnetic material constituting the storage layer for each sample.

From Table 1, sample 1 using CoFeB having a large damping constant α for the memory layer has a large reversal current value, whereas sample 2 using NiFe having a small damping constant α for the memory layer is inverted. The current value is small.
Here, if the allowable current upper limit of the selection transistor is 400 μA, the inversion current value exceeds the allowable current upper limit in the memory element of Sample 1, and information cannot be recorded by spin injection.
On the other hand, in the memory element of Sample 2, since the magnetization of the memory layer can be reversed with a current value smaller than the allowable current upper limit of the selection transistor, information can be recorded by spin injection.

  Therefore, like the sample 2 of the embodiment, by using the structure of the memory element of the present invention, it is possible to write information to the memory layer with a small amount of current, and an unprecedented low power consumption type. A memory can be realized.

<Experiment 2>
(Membrane structure 3: Sample 3 to Sample 7)
Next, the relationship between the magnitude of the saturation magnetization of the storage layer and the characteristics was examined.
First, a memory element similar to the memory element 10 shown in FIG. 1 was formed on a silicon substrate.
Specifically, in the memory element 10 having the configuration shown in FIG. 1, the underlayer 11 is a Ta film having a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film having a thickness of 30 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19. The layer 13 is a CoFe film having a thickness of 1.8 nm, the nonmagnetic layer 14 constituting the magnetic pinned layer 19 having a laminated ferri structure is the Ru film having a thickness of 0.8 nm, and the ferromagnetic layer constituting the magnetic pinned layer 19 (reference layer) ) 15 is selected as a CoFeB film having a thickness of 2 nm, a tunnel insulating layer 16 having a thickness of 0.7 nm, a memory layer 17 having a thickness of 3 nm, and a cap layer 18 as a Ta film having a thickness of 6 nm. A laminated film of an Al film (not shown) having a film thickness of 60 nm (to be a word line described later) and a Ta film having a film thickness of 3 nm was provided between the magnetic layer 12 and each layer was formed.
That is, the memory element 10 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 3).
Membrane configuration 3:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / CoFe (1.8nm) / Ru (0.8nm) / CoFeB (2nm) / Tunnel insulating layer (0.7nm) / Memory layer (3nm) / Ta (6nm)
Each layer other than the tunnel insulating layer 16 was formed using a DC magnetron sputtering method.
When an aluminum oxide (Al—O _x ) film is formed as the tunnel insulating layer 16, a metal Al film is first deposited by 0.7 nm by DC sputtering, and then the oxygen / argon flow ratio is 1: 1. The metal Al layer was oxidized by a natural oxidation method.
When a magnesium oxide (MgO) film was formed as the tunnel insulating layer 16, a 0.7 nm-thick magnesium oxide film was formed as it was by RF sputtering using MgO as a target.
Further, after each layer of the memory element 10 was formed, heat treatment was performed at 10 kOe · 270 ° C. for 4 hours in a heat treatment furnace in a magnetic field, and ordered heat treatment was performed on the PtMn film of the antiferromagnetic layer 12.

  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.

After that, a mask of the pattern of the memory element 10 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 10. Etching was performed up to the Al layer of the word line except for the memory element 10 portion.
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 10 is an elliptical shape having a minor axis of 80 nm and a major axis of 150 nm.

Next, the part other than the memory element 10 was insulated by sputtering of Al ₂ O ₃ having a thickness of about 100 nm.
After that, a bit line serving as an upper electrode and a measurement pad were formed using photolithography to prepare a sample of the memory element.

Samples of the memory elements of Sample 3 to Sample 7 in which the material of the tunnel insulating layer 16 and the material of the memory layer 17 were respectively changed in the film configuration 3 by the manufacturing method described above were produced.
Sample 3 (Example) used magnesium oxide (MgO) for the tunnel insulating layer 16 and NiFe for the memory layer 17. The saturation magnetization of NiFe in the memory layer 17 was 0.88T.
In Sample 4 (Example), magnesium oxide (MgO) was used for the tunnel insulating layer 16 and NiFeMo was used for the memory layer 17. The saturation magnetization of NiFeMo in the memory layer 17 was 0.85T.
In Sample 5 (Example), aluminum oxide (AlO) was used for the tunnel insulating layer 16 and NiFe was used for the memory layer 17. The saturation magnetization of NiFe in the memory layer 17 was 0.88T.
In sample 6 (comparative example), magnesium oxide (MgO) was used for the tunnel insulating layer 16, and CoFeB was used for the memory layer 17. The saturation magnetization of CoFeB in the storage layer 17 was 1.45T.
In sample 7 (comparative example), aluminum oxide (AlO) was used for the tunnel insulating layer 16, and CoFeB having a composition different from that of the sample 6 was used for the memory layer 17. The saturation magnetization of CoFeB in the storage layer 17 was 0.88T.

The reversal current value was measured in the same manner as in Experiment 1 for the memory elements of Samples 3 to 7.
Table 2 summarizes the material of the intermediate layer (tunnel insulating layer 16), the material of the storage layer 17, the magnitude of the saturation magnetization, and the reversal current value for each sample.

From Table 2, it can be seen that the use of NiFe or NiFeMo having a saturation magnetization of 1T or less for the storage layer can significantly reduce the reversal current value compared to CoFeB having a large saturation magnetization of 1.45T.
Furthermore, it can be seen that CoFeB cannot reduce the reversal current value even when the composition is changed and the saturation magnetization is 1 T or less, and the reversal current value can be greatly reduced only in the case of NiFe or NiFeMo.
Further, it can be seen from the comparison between Sample 3 and Sample 4 and Sample 5 that the effect of reducing the reversal current value is greater when MgO is used as the tunnel insulating layer 16.

From the above results, the recording current can be lowered by using NiFe or a material in which an additive element such as Mo is added to NiFe having a saturation magnetization (Ms) of 1 T or less for the storage layer.
In particular, the recording current can be further reduced by using magnesium oxide (MgO) as the tunnel insulating layer.

<Experiment 3>
(Membrane structure 4; Sample 8 to Sample 10)
Next, when NiFe was used for the memory layer, changes in characteristics due to the film thickness of the memory layer were examined.
First, a 2 μm thick thermal oxide film was formed on a 0.6 mm thick silicon substrate to form the memory element 10 shown in FIG.
Specifically, in the memory element 10 having the configuration shown in FIG. 1, the underlayer 11 is a Ta film having a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film having a thickness of 30 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19. The layer 13 is a CoFe film having a thickness of 1.8 nm, the nonmagnetic layer 14 constituting the magnetization fixed layer 19 having a laminated ferri structure is the Ru film having a thickness of 0.8 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19 (reference layer) ) 15 is a CoFe film having a thickness of 2 nm, the tunnel insulating layer 16 is a magnesium oxide film having a thickness of 0.7 nm, the memory layer 17 is a NiFe film having a thickness of t (nm), and the cap layer 18 is a Ta film having a thickness of 5 nm. A layered film of an Al film (not shown) having a thickness of 60 nm (to be a word line described later) and a Ta film having a thickness of 3 nm is provided between the base layer 11 and the antiferromagnetic layer 12. Formed.
That is, the memory element 10 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 4).
Membrane configuration 4:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / CoFe (1.8nm) / Ru (0.8nm) / CoFe (2nm) / MgO (0.7nm) / NiFe (tnm) / Ta ( 5nm)
Each layer other than the tunnel insulating layer 16 made of a magnesium oxide (MgO) film was formed using a DC magnetron sputtering method.
The tunnel insulating layer 16 made of a magnesium oxide (MgO) film was directly formed to 0.7 nm by RT sputtering using MgO as a target.

  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, an insulating film was formed on the entire surface of the substrate, and then the word line surface was exposed by a lift-off method.
Subsequently, a mask of the pattern of the memory element 10 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film by Ar plasma to form the memory element 10. At this time, the word lines other than the memory element 10 portion were etched to a depth that left PtMn at 15 nm.
Note that the pattern of the memory element 10 was an elliptical shape having a minor axis of 68 nm and a major axis of 195 nm.

Thereafter, an insulating film was formed on the entire surface of the substrate, and then the surface of the memory element 10 was exposed by a lift-off method.
Next, in order to obtain an electrical connection with the word line from a probe needle or the like, after masking other than the word line terminal pad by photolithography, the terminal pad is selectively etched by Ar plasma, and the word under the terminal pad is etched. The line was exposed. Thereafter, the resist mask covering the terminal pad was peeled off.
Subsequently, a metal film made of a laminated film of a Cr film with a thickness of 20 nm, a Cu film with a thickness of 100 nm, and an Au film with a thickness of 100 nm is formed on the entire surface of the substrate, and bit line and bit line terminals are formed on the metal film. After the pad pattern was masked by photolithography, it was selectively etched with Ar plasma to form bit lines and terminal pads. Thereafter, the resist mask covering the bit line and the terminal pad was peeled off.
Finally, in a magnetic field heat treatment furnace, heat treatment was performed for 4 hours at 265 ° C. in a magnetic field of 10 kOe, and ordered heat treatment was performed on the PtMn layer that is an antiferromagnetic layer.
In this way, a sample of the memory element was manufactured.

Samples of the memory elements of Sample 8 to Sample 10 were manufactured by changing the film thickness t (nm) of the memory layer 17 by the manufacturing method described above.
In Sample 8, the thickness t of the memory layer 17 was 2 nm.
In sample 9, the thickness t of the memory layer 17 was 3 nm.
In Sample 10, the thickness t of the memory layer 17 was 4 nm.

The characteristics of the memory elements of Samples 8 to 10 were evaluated as follows.
Prior to the measurement, the storage element was configured to be able to apply a magnetic field from the outside in order to control the values of the reversal current in the positive and negative directions to be symmetrical.

(RH curve)
The resistance value was measured by magnetizing the storage layer with an external magnetic field. That is, first, an external magnetic field for reversing the magnetization of the storage layer of the storage element was applied so as to be parallel to the easy axis of magnetization of the storage layer. The magnitude of the external magnetic field for measurement was 1 kOe.
Next, a positive sweep from −1 kOe to +1 kOe and a subsequent negative sweep from +1 kOe to −1 kOe as seen from one side of the easy axis of the storage layer are performed, and at the same time, the word line terminal pad and bit line A bias current applied to each of the terminal pads was adjusted to 100 mV, and a tunnel current was passed through the ferromagnetic tunnel junction. The resistance value with respect to each external magnetic field at this time was measured, and the RH curve was obtained.

(TMR ratio)
Measure the resistance value when the magnetization of the magnetization fixed layer and the storage layer is antiparallel and the resistance is high, and the resistance value when the magnetization of the magnetization fixed layer and the storage layer is parallel and the resistance is low. From these, the TMR ratio (magnetic resistance change rate) was determined.
From the viewpoint of obtaining good read characteristics, the TMR ratio is preferably 30% or more.

(Coercive force Hc)
The RH curve is measured by the above measurement method, and from the RH curve, the resistance value in the state where the magnetization of the magnetization fixed layer and the storage layer is antiparallel and the resistance is high, the magnetization fixed layer and the storage The average value with the resistance value in the state where the magnetization of the layers is parallel and the resistance is low is obtained, and the value of the external magnetic field when the resistance value of this average value is obtained is defined as the coercive force Hc.

As a measurement result, the resistance-magnetic field curve (RH curve) of each sample is shown in FIGS. 5A to 5C.
5A shows the curve of Sample 8 in which the thickness t of the storage layer 17 is 2 nm, FIG. 5B shows the curve of Sample 9 in which the thickness t of the storage layer 17 is 3 nm, and FIG. 5C shows the thickness t of the storage layer 17. Shows the curve of the sample 10 of 4 nm. The vertical axis of each curve indicates the rate (%) of change in resistance due to the tunneling magnetic effect (TMR), instead of the resistance value.

As shown in FIG. 5A, the sample 8 in which the film thickness t of the storage layer 17 is 2 nm has an RH curve with zero coercive force Hc and no hysteresis. This indicates that the storage layer is so-called superparamagnetic. Then, in the state where there is no external magnetic field, the magnetization direction of the storage layer becomes indefinite, and information can no longer be stored.
As shown in FIGS. 5B and 5C, in the sample 9 having the memory layer 17 having a film thickness t of 3 nm and the sample 10 having the thickness of 4 nm, a high TMR ratio and steep magnetization reversal are realized. The resistance value is 1.4 kΩ and the TMR ratio is 33%.

When the breakdown voltage of another memory element was measured, about 0.9 V was obtained. That is, a maximum current of about 0.9 V / 1.4 kΩ = 0.6 mA can flow through these memory elements.
Further, comparing sample 9 (t = 3 nm) and sample 10 (t = 4 nm), sample 10 (t = 4 nm) has a larger coercive force due to the difference in magnitude of the magnetic moment.
Although not shown, when t <3 nm, there are a large number of superparamagnetic elements.

  Next, for each sample of sample 9 (t = 3 nm) and sample 10 (t = 4 nm), the reversal current value of magnetization reversal by spin injection is measured as follows, and the possibility of writing by current is measured. investigated.

With the external magnetic field fixed at a certain value, a current was passed through the memory element to monitor the resistance value. When the resistance value changed to the same level as the resistance difference obtained from the RH curve at a certain current value, it was considered that the magnetization of the memory layer was reversed, and the current value was set as the inverted current value. Note that the upper limit of the current value that can be passed through the memory element as described above is about 0.6 mA so as not to destroy the tunnel insulating layer. Inverted current values of both polarities, that is, when the memory element is inverted from the low resistance state to the high resistance state, and the memory element is inverted from the high resistance state to the low resistance state with respect to the same external magnetic field. The reversal current value was measured respectively.
Then, since the reversal current when the magnetization reversal by spin injection occurs changes according to the magnitude of the external magnetic field, the above reversal current value was measured under various external magnetic fields.

As a measurement result, the relationship between the reversal current value and the magnitude of the external magnetic field is shown in FIGS. 6A and 6B. FIG. 6A shows the result of sample 9 (t = 3 nm), and FIG. 6B shows the result of sample 10 (t = 4 nm). In the figure, the diamond marks correspond to the inversion from the low resistance state to the high resistance state, and the star marks correspond to the inversion from the high resistance state to the low resistance state. Usually, when operating as a storage element, the external magnetic field is zero.
From FIG. 6A and FIG. 6B, it can be seen that the reversal current value changes monotonously as the external magnetic field changes.
6A shows that in the case of sample 9 (t = 3 nm), the external magnetic field is inverted at a current value smaller than about 0.6 mA under the condition that the external magnetic field is zero. Can be written.
On the other hand, as shown in FIG. 6B, in the case of sample 10 (t = 4 nm), inversion is performed at a current value substantially equal to the upper limit value of about 0.6 mA under the condition that the external magnetic field is zero. Although not shown, when t> 4 nm, the write current is larger than the upper limit of current about 0.6 mA, so the magnetization of the storage layer is not reversed.

Of course, the reversal current value and the upper limit value of the current to flow vary depending on the area of the memory element, but the reversal current density (= reversal current / element area) and the breakdown voltage do not depend on the area of the memory element.
For this reason, when the thickness t> 4 nm of the storage layer, the result that the magnetization of the storage layer does not reverse is effective even if the element area changes.

  Considering the above results, by setting the film thickness of the memory layer to 3 nm or more and 4 nm or less, the magnetization of the memory layer can be stably maintained and the magnetization can be reversed by spin injection within the upper limit of the current. It became clear that it was possible.

<Experiment 4>
Next, when NiFe or a NiFe-based material was used for the memory layer, the change in characteristics depending on the Ni content (composition ratio) of the memory layer was examined.

(Membrane structure 5)
The ferromagnetic layer (reference layer) 15 constituting the magnetization fixed layer 19 is a CoFeB film having a thickness of 2.5 nm, the tunnel insulating layer 16 is a magnesium oxide (MgO) film having a thickness of 0.8 nm, and the NiFe of the storage layer 17 is formed. A memory element 10 was fabricated in the same manner as the film configuration 2 of Sample 2 in Experiment 1 except that the Ni—Fe composition ratio of the film was changed.
That is, the memory element 10 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 5).
Membrane configuration 5:
Ta (3nm) / Cu (100nm) / PtMn (20nm) / CoFe (2nm) / Ru (0.8nm) / CoFeB (2.5nm) / MgO (0.8nm) / NiFe (3nm) / Ta (5nm)
In the above-described film configuration, the composition of the PtMn film whose alloy composition is not shown is Pt50Mn50 (atomic%), and the composition of the CoFe film is Co90Fe10 (atomic%).
The tunnel insulating layer 16 made of a magnesium oxide film (MgO) was formed using an RF magnetron sputtering method.
The pattern of the memory element 10 is an ellipse having a minor axis of 90 nm and a major axis of 180 nm so that the area resistance value (Ωμm ² ) of the memory element 10 is 30Ωμm ² .
Other conditions and manufacturing processes were the same as those in Sample 2 of Experiment 1, and a memory element sample was manufactured.

  In the film configuration 5, the composition of the Ni—Fe alloy of the memory layer 17 is changed so that the Ni content (atomic%) in the Ni—Fe alloy is 0% (Fe film), 20%, 60%. 70%, 80%, 90%, and 100% (Ni film) were prepared in total for seven types of memory element samples.

The reversal current value and the MR ratio (TMR ratio) were measured for each of the seven types of samples of the memory element having the film structure 5 in which the Ni content of the memory layer 17 was changed by the same method as described above. Then, the magnetization reversal current density was calculated from the reversal current value and the cross-sectional area of the memory element 10.
The measurement results are shown in FIGS. 7A and 7B. FIG. 7A shows the relationship between the Ni content (atomic%) and the MR ratio, and FIG. 7B shows the relationship between the Ni content (atomic%) and the magnetization reversal current density.

(Membrane structure 6)
A memory element was fabricated in the same manner as in the film configuration 5 except that a NiFeCo film having a thickness of 3 nm (Co content fixed at 10 atomic%) was formed as the memory layer 17.
That is, the memory element 10 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 6).
Membrane configuration 6:
Ta (3nm) / Cu (100nm) / PtMn (20nm) / CoFe (2nm) / Ru (0.8nm) / CoFeB (2.5nm) / MgO (0.8nm) / NiFeCo (3nm) / Ta (5nm)
The other conditions and manufacturing steps were the same as those of the sample with the film configuration 5.

In the film configuration 6, the composition of the Ni—Fe—Co alloy of the memory layer 17 is changed so that the Ni content (atomic%) in the Ni—Fe—Co alloy is 0% (Fe ₉₀ Co ₁₀ ). 20%, 60%, 70%, 80%, and 90% (Ni ₉₀ Co ₁₀ ), a total of six types of memory element samples were manufactured.

The reversal current value and the MR ratio (TMR ratio) were measured for each of the six types of samples of the memory element having the film structure 6 in which the Ni content of the memory layer 17 was changed by the same method as described above. Then, the magnetization reversal current density was calculated from the reversal current value and the cross-sectional area of the memory element 10.
The measurement results are shown in FIGS. 8A and 8B. FIG. 8A shows the relationship between the Ni content (atomic%) and the MR ratio, and FIG. 8B shows the relationship between the Ni content (atomic%) and the magnetization reversal current density.

7 and 8, in any film configuration, when the Ni content is 70 atomic% or more and 90 atomic% or less, the MR ratio is large, the magnetization reversal current density is small, and excellent magnetization reversal characteristics are obtained. I understand that
In addition, a storage element capable of recording information with a relatively small current value of 0.4 mA or less can be realized, and an unprecedented low power consumption type magnetic memory can be realized. .

<Experiment 5>
Next, as shown in the cross-sectional view of FIG. 4, the effect when the insertion layer 21 made of an oxide was provided between the memory layer 17 and the upper cap layer 18 was examined.

(Membrane structure 7: Sample 11 to Sample 12)
First, a 300 nm thick thermal oxide film was formed on a 0.575 mm thick silicon substrate to form the memory element 20 shown in FIG.
Specifically, in the memory element 20 having the configuration shown in FIG. 4, the underlayer 11 is a Ta film having a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film having a thickness of 30 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19. The layer 13 is a Cu ₉₀ Fe ₁₀ film having a thickness of 2 nm, the nonmagnetic layer 14 constituting the magnetization fixed layer 19 having a laminated ferri structure is the Ru film having a thickness of 0.8 nm, and the ferromagnetic layer constituting the magnetization fixed layer 19 (see Layer) 15 is a CoFeB film having a thickness of 2 nm, tunnel insulating layer 16 is a MgO film having a thickness of 0.8 nm, memory layer 17 is a NiFe film, and insertion layer 21 is an aluminum oxide film obtained by oxidizing an Al film having a thickness of 0.6 nm. The cap layer 18 is selected as a Ta film having a film thickness of 5 nm, and an Al film (not shown) having a film thickness of 60 nm (to be described later) and a film thickness of 3 nm between the underlayer 11 and the antiferromagnetic layer 12. A laminated film with a Ta film of To form a layer.
That is, the memory element 20 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 7).
Membrane configuration 7:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / Co90Fe10 (2nm) / Ru (0.8nm) / CoFeB (2nm) / MgO (0.8nm) / NiFe / Al (0.6nm)- Ox / Ta (5nm)
In the above film configuration, the PtMn composition whose alloy composition is not shown is Pt50Mn50 (atomic%).
Each layer other than the tunnel insulating layer 16 and the insertion layer 21 was formed using a DC magnetron sputtering method. For the tunnel insulating layer 16 made of a magnesium oxide film, an oxide was deposited as it was using an RT sputtering method using an MgO target.
The insertion layer 21 made of an aluminum oxide (Al—O _x ) film is formed by first depositing a metal Al film by 0.6 nm by DC sputtering, and then filling the chamber with oxygen up to 10 Torr and leaving it for a predetermined time. Then, the metal Al layer was oxidized by a natural oxidation method. The oxidation time was 10 minutes. After the oxidation, the cap layer 18 was formed by evacuating again to a high vacuum of 1 × 10 ⁻⁷ to 1 × 10 ⁻⁸ Torr.
Further, after each layer of the memory element 20 was formed, heat treatment was performed at 10 kOe · 300 ° C. for 2 hours in a magnetic field heat treatment furnace, and regularization heat treatment and high-temperature durability heat treatment of the PtMn film of the antiferromagnetic layer 12 were performed. .

  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.

  After that, a mask of the pattern of the memory element 20 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 20. Except for the memory element 20 portion, etching was performed up to just above the Al layer of the word line.

As the size of the memory element is reduced, Δ = KuV / kT (Ku is the anisotropic energy, V is the volume of the magnetic material, k is the Boltzmann constant, and T is the temperature) becomes too small. Due to the problem of the thermal fluctuation resistance of the magnetic material, the magnetization direction becomes unstable and the magnetization direction holding characteristic is insufficient. On the other hand, if the size of the memory element is made too large, the above Δ becomes too large, which increases the spin torque necessary for magnetization reversal, and therefore requires a larger current density and a larger area. It is necessary to pass a large current through the element.
Therefore, the pattern of the memory element 20 is an elliptical shape having a short axis of 70 nm and a long axis of 170 nm.

Next, portions other than the memory element 20 portion were insulated by sputtering of Al ₂ O ₃ having a thickness of about 100 nm.
Further, a contact on the upper surface of the memory element 20 was formed by lift-off.
Next, a metal film composed of a laminated film of a Cr film with a thickness of 20 nm, a Cu film with a thickness of 100 nm, and an Au film with a thickness of 100 nm is formed on the entire surface of the substrate, and bit line and bit line terminals are formed on the metal film. After the pad pattern was masked by photolithography, selective etching was performed with Ar plasma to form a pad portion for bit lines and terminals. Thereafter, the resist mask covering the bit line and the terminal pad was peeled off.
In this way, a sample of the memory element was manufactured.

Samples of the memory elements of Sample 11 and Sample 12 in which the film thickness of the memory layer 17 was changed in the above-described film configuration 7 were manufactured by the above-described manufacturing method.
In Sample 11, the NiFe film thickness of the memory layer 17 was set to 3.0 nm, and in Sample 12, the NiFe film thickness of the memory layer 17 was set to 2.0 nm.

(Membrane structure 8: Sample 13 to Sample 14)
The memory layer 20 was formed of a NiFe film having a thickness of 2.0 nm, the insertion layer 21 was formed of an MgO film, and the other configuration was the same as that of the film configuration 7 to fabricate the memory element 20.
That is, the memory element 20 was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 8).
Membrane configuration 8:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / Co90Fe10 (2nm) / Ru (0.8nm) / CoFeB (2nm) / MgO (0.8nm) / NiFe (2.0nm) / MgO / Ta (5nm)
Similarly to the MgO film of the tunnel insulating layer 16, the MgO film of the insertion layer 21 was formed by RF sputtering using an MgO target. Other manufacturing steps were the same as those of the memory element sample having the film structure 7.
Samples of the memory elements of Sample 13 and Sample 14 in which the thickness of the insertion layer 21 in the film configuration 8 was changed were produced.
In Sample 13, the thickness of the MgO film of the insertion layer 21 was 0.6 nm, and in Sample 14, the thickness of the MgO film of the insertion layer 21 was 0.8 nm.

(Membrane structure 9: Sample 15)
The fixed magnetization layer is composed of a single layer of ferromagnetic layer, and this ferromagnetic layer is formed of a laminated film of a Co ₉₀ Fe ₁₀ film with a thickness of 2 nm and a CoFeB film with a thickness of 2 nm, and the memory layer 17 is formed with a film thickness. A memory element was fabricated by forming a 3.0 nm NiFe film, forming the insertion layer 21 by a 0.6 nm-thick MgO film, and performing the other configuration in the same manner as the film configuration 7.
That is, a memory element was manufactured with the material and film thickness of each layer as the following configuration (film configuration 9).
Membrane configuration 9:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / CoFe10 (2nm) / CoFeB (2nm) / MgO (0.8nm) / NiFe (3.0nm) / MgO (0.6nm) / Ta ( 5nm)
In the film forming method of each layer and the manufacturing process of the memory element, the memory element was manufactured in the same manner as the memory element of the film configuration 8 and used as the sample of the memory element of Sample 15.

(Membrane structure 10: Sample 16 to Sample 17)
A memory element was fabricated in the same manner as Sample 11 and Sample 12 of the film structure 7 except that the insertion layer 21 was not formed and the cap layer 18 was formed directly on the memory layer 17.
That is, a memory element was manufactured with the material and film thickness of each layer as the following configuration (film configuration 10).
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / Co90Fe10 (2nm) / Ru (0.8nm) / CoFeB (2nm) / MgO (0.8nm) / NiFe / Ta (5nm)
Samples 16 and 17 were prepared in which the film thickness of the memory layer 17 in the film configuration 10 was changed.
In Sample 16, the NiFe film thickness of the memory layer 17 was set to 3.0 nm, and in Sample 17, the NiFe film thickness of the memory layer 17 was set to 2.0 nm.

(Membrane structure 11: Sample 18)
A memory element was fabricated in the same manner as Sample 14 except that the thickness of the insertion layer 21 was increased to 1.0 nm.
That is, a memory element was manufactured by setting the material and film thickness of each layer to the following configuration (film configuration 11).
Membrane configuration 11:
Ta (3nm) / Al (60nm) / Ta (3nm) / PtMn (30nm) / CoFe10 (2nm) / Ru (0.8nm) / CoFeB (2nm) / MgO (0.8nm) / NiFe (2.0nm) / MgO ( 1.0nm) / Ta (5nm)
This was designated as the memory element of Sample 18.

The characteristics of each of the above-described memory element samples were evaluated as follows.
Prior to the measurement, a magnetic field was externally applied to the storage element.
Moreover, since each measured sample was produced by the manufacturing method mentioned above, all were heat-processed in a magnetic field at 300 degreeC for 2 hours.

(Measurement of area resistance and resistance change rate)
The bias voltage applied to the word line terminal and the bit line terminal was always adjusted to 10 mV, and the direction of magnetization of the recording layer was reversed by an external magnetic field, and the sheet resistance value of the entire memory element was measured.
Further, the relationship between resistance and external magnetic field was examined.
Then, the resistance change rate is calculated by the formula (high resistance−low resistance) / low resistance from the area resistance value (high resistance) when the resistance is high and the area resistance value (low resistance) when the resistance is low. Was calculated.

(Reverse current value measurement)
The resistance value of the memory element was measured by changing the amount of current passed through the memory element at a measurement temperature of 25 ° C., and a resistance-current curve was obtained from the measurement result. In addition, the measurement which obtains this resistance-current curve was performed about the electric current of both polarities (plus direction and minus direction).
Here, an example of the resistance-current curve of the sample 11 is shown in FIG.
As shown in FIG. 9, when a certain current or more is applied, the state changes from the high resistance state to the low resistance state or vice versa, and it can be confirmed that the magnetization is reversed.

From the obtained resistance-current curve, a current value at which the resistance value changes was obtained, and this was set as an inversion current value for reversing the direction of magnetization. The inversion current value was obtained for the bipolar current.
In the measurement of the reversal current, an offset occurs in which the threshold value at which the magnetization direction is reversed is changed by an external magnetic field. In order to eliminate this offset, (1) in the above-described measurement of the rate of change in resistance, the offset magnetic field of the RH loop is obtained in advance from the relationship between the resistance and the external magnetic field, and the inversion is performed while applying the offset magnetic field from the outside. Two methods are conceivable: measuring the current, and (2) measuring the dependence of the reversal current on the external magnetic field while changing the applied magnetic field from the outside. Here, the measurement was performed by employing the method (1).
Further, although it depends on the resistance value of the memory element, the tunnel insulating layer breaks down at a bias voltage of about 1.0 to 1.2 V in the elliptical memory element of 70 nm short axis × 170 nm long axis fabricated this time. Therefore, the upper limit of the applied current is set to a current value to which a bias voltage of 0.8 V is applied.
And the reversal current density was computed from the average value of the reversal current value (absolute value) of both polarity of + and-.

Table 3 shows the area resistance value and resistance change rate of each sample. Each measured value in Table 3 is an average value of values obtained by measuring 200 memory elements fabricated on each sample wafer.
Table 4 shows the measurement results of the reversal current value and reversal current density of each sample.

First, sample 11 and sample 12, and sample 16 and sample 17 are compared.
In sample 11 and sample 12 in which the insertion layer 21 formed of AlOx is provided between the memory layer 17 and the cap layer 18, the sample 12 in which the NiFe film thickness of the memory layer is 2 nm is also shown in Table 3 Thus, it can be seen that a good resistance change rate can be obtained, and Table 4 shows that the magnetization reversal by spin injection is performed well.
On the other hand, in the sample 17 in which the cap layer 18 is formed directly on the storage layer 17 without providing the insertion layer 21, as compared with the sample 12 in which the thickness of the storage layer 17 is the same 2 nm, from Table 3. Thus, the rate of change in resistance is significantly reduced. Also, from Table 4, the magnetic reversal occurred and the magnetization reversal could not be measured.
The reason why such a difference occurs is not necessarily clear, but by providing the insertion layer 21 between the storage layer 17 and the cap layer (protective layer) 18, the NiFe film of the storage layer 17 and the Ta layer of the cap layer 18 are provided. It is considered that the thermal diffusion at the interface with the film is suppressed, so that the magnetic characteristics of the storage layer 17 are maintained without being adversely affected by the diffusion even when the NiFe film thickness of the storage layer 17 is small. it can.
Therefore, by providing the insertion layer 21 between the memory layer 17 and the cap layer (protective layer) 18, the film thickness of the memory layer 17 can be reduced, which is advantageous for reducing the inversion current.

Next, in Sample 13 and Sample 14 in which the insertion layer 21 is formed of an MgO film, the thickness of the storage layer 17 is 2 nm, as in Sample 12 in which the insertion layer 21 is formed of an AlOx film. Even in this case, the rate of change in resistance is maintained, and magnetization reversal by spin injection is performed well.
Therefore, not only AlOx but also MgO can be used for the insertion layer 21.

Next, the sample 13 and the sample 14 are compared with the sample 18. In these samples, the thickness of the MgO film of the insertion layer 21 is changed to 0.6 nm, 0.8 mm, and 1.0 nm.
From Table 3, a good resistance change rate is obtained in Sample 13 and Sample 14 in which the thickness of the insertion layer 21 is 0.8 nm or less, but in Sample 18 in which the thickness of the insertion layer 21 is 1.0 nm. The rate of change in resistance is reduced to 15%. This is because the area resistance value becomes a value that cannot be ignored as the insertion layer 21 becomes thicker.
That is, it is understood that the thickness of the insertion layer 21 is preferably 0.8 nm or less.
In these samples, the thickness of the MgO film of the tunnel insulating layer 16 is 0.8 nm.
Therefore, it can be seen that the thickness of the insertion layer 21 is preferably the same as the thickness of the tunnel insulating layer 16 or thinner than the tunnel insulating layer 16.
As a result, the area resistance value of the insertion layer 21 becomes equal to or less than the area resistance value of the tunnel insulating layer 16, and as described above, a current for recording information by reversing the magnetization direction of the storage layer is sufficiently supplied to the storage element. It becomes possible to flow in.

Next, in Sample 15 in which the pinned magnetization layer is not a laminated ferrimagnetic structure but a single-layered ferromagnetic layer, from Tables 3 and 4, similar to Samples 11 to 14 in which the pinned magnetic layer is a laminated ferrimagnetic structure. The rate of change in resistance is maintained, and magnetization reversal by spin injection is performed well.
Therefore, even when the pinned magnetization layer is formed of a single ferromagnetic layer, the insertion layer can be applied without any significant adverse effect due to the provision of the insertion layer.

As described above, with the structure in which the insertion layer is provided between the memory layer and the cap layer, the characteristic deterioration is small even after a thermal history at a high temperature of 300 ° C. or higher required in the semiconductor process. A memory element and a memory can be realized.
As a result, the storage layer made of NiFe can be made thinner, and the reversal current value can be reduced by making the storage layer thinner. Therefore, the resistance change rate is high and the current density of magnetization reversal by spin injection is high. A small memory element can be realized.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10,20 Memory element, 11 Underlayer, 12 Antiferromagnetic layer, 13 Ferromagnetic layer, 14 Nonmagnetic layer, 15 Ferromagnetic layer (reference layer), 16 Tunnel insulating layer, 17 Memory layer, 18 Cap layer (protective layer) ), 19 magnetization fixed layer, 21 insertion layer

Claims (2)

It has a storage layer that holds information according to the magnetization state of the magnetic material,
A magnetization fixed layer is provided via an intermediate layer for the storage layer,
The damping constant α of the magnetic material constituting the storage layer satisfies α <0.015,
A storage element that records information on the storage layer by changing a magnetization direction of the storage layer by passing a current in a stacking direction. A storage element having a storage layer for retaining information by the magnetization state of the magnetic material;
Two types of wiring intersecting each other,
The storage element is provided with a magnetization fixed layer via an intermediate layer with respect to the storage layer, and a damping constant α of a magnetic material constituting the storage layer satisfies α <0.015, and is in a stacking direction. By flowing a current, the direction of magnetization of the storage layer changes, and information is recorded on the storage layer.
The storage element is disposed near the intersection of the two types of wiring and between the two types of wiring,
A memory in which a current in the stacking direction flows in the memory element through the two types of wirings.

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