JP2006295000A - Storage element and memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage element in which a current value required for writing can be reduced by enhancing spin injection efficiency. <P>SOLUTION: A magnetization fixing layer 31 is provided for a storage layer 17 holding information by the magnetization state of a magnetic body through an intermediate layer 16 composed of magnesium oxide. Direction of magnetization M1 in the storage layer 17 is changed by feeding a current in the laminating direction and information is recorded for the storage layer 17. At least one of ferromagnetic layers 17, 13, 15 constituting the storage layer 17 or the magnetization fixing layer 31 principally comprises NiFeB wherein the content of Ni is 50-80 atom% and the content of B is 10-30 atom% in the storage element 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a storage layer that stores the magnetization state of a ferromagnetic layer as information, and a magnetization fixed layer whose magnetization direction is fixed, and a storage element that changes the magnetization direction of the storage layer by passing an electric current. The present invention relates to a memory provided with this memory element, and is suitable for application to a nonvolatile memory.

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

  As a candidate for a non-volatile memory, a magnetic random access memory (MRAM) that records information by magnetization of a magnetic material has attracted attention and is being developed (for example, see Non-Patent Document 1).

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

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

In order to stably hold recorded information in a magnetic memory such as MRAM, it is necessary that a magnetic layer (storage layer) for recording information has a certain coercive force.
On the other hand, in order to rewrite the recorded information, a certain amount of current must be passed through the address wiring.
However, as the elements constituting the MRAM are miniaturized, the current value for reversing the direction of magnetization tends to increase. On the other hand, since the address wiring becomes thin, a sufficient current cannot flow.

In view of this, attention has been focused on a memory that uses magnetization reversal by spin injection as a structure that allows magnetization reversal 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 without increasing current even if the element is miniaturized.

6 and 7 are schematic diagrams of a memory having a configuration using the above-described magnetization reversal by spin injection. 6 is a perspective view, and FIG. 7 is a cross-sectional view.
A drain region 58, a source region 57, and a gate electrode 51 constituting a selection transistor for selecting each memory cell are formed in a portion separated by the element isolation layer 52 of the semiconductor substrate 60 such as a silicon substrate. Has been. Among these, the gate electrode 51 also serves as a word line extending in the front-rear direction in FIG.
The drain region 58 is formed in common to the left and right selection transistors in FIG. 6, 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 memory element 53 to reverse the magnetization direction of the memory layer by spin injection.

Such a memory using a magnetization reversal by spin injection has a feature that the device structure can be simplified as compared with the general MRAM shown in FIG.
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.

  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 magnetization reversal by spin injection, it is necessary to reverse the magnetization direction of the storage layer by performing spin injection with a current flowing through the storage element.
Since the current is directly supplied to the memory element and information is written (recorded) as described above, the memory cell is configured by connecting the memory element to a selection transistor in order to select a memory cell to be written. In this case, the current flowing through the memory element is limited to the magnitude of the current that can flow through the selection transistor (the saturation current of the selection transistor).
Therefore, it is necessary to perform writing with a current lower than the saturation current of the selection transistor, and it is necessary to improve the efficiency of spin injection and reduce the current flowing through the memory element.

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

  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.

Therefore, as a solution for suppressing the current at the time of spin injection, the storage element has a structure of a fixed magnetic layer / intermediate layer / memory layer, which is a general magnetic tunnel junction element, and has a fixed magnetization layer / intermediate layer / memory. It has been proposed to change to a configuration having a layered structure of a layer / intermediate layer / magnetization fixed layer, and the magnetization directions of the magnetization fixed layers provided above and below the storage layer being opposite to each other (Patent Document 2). reference).
In Patent Document 2, it is shown that the spin injection efficiency can be doubled by making the magnetization directions of the upper and lower magnetization fixed layers opposite to each other.

Nikkei Electronics 2001.1.22 (pages 164-171) JP 2003-17782 A US Patent Publication No. 2004/0027853

  Certainly, theoretically, it is considered that the spin injection efficiency is doubled by adopting the structure described in Patent Document 2.

  However, as a result of actually producing a memory element having the structure described in Patent Document 2 and investigating the characteristics of this memory element, a theoretical result cannot be obtained and a sufficient improvement in spin injection efficiency is not recognized. It was.

  In order to solve the above-described problems, the present invention provides a memory element that can reduce a current value required for writing by improving spin injection efficiency, and a memory including the memory element. .

  The memory element of the present invention has a memory layer that retains information by the magnetization state of a magnetic material, and a magnetization pinned layer is provided through the intermediate layer with respect to the memory layer, the intermediate layer is made of magnesium oxide, and is laminated. By flowing a current in the direction, the direction of magnetization of the storage layer changes, information is recorded on the storage layer, and at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer contains NiFeB. As a main component, the Ni content is 50 atomic% or more and 80 atomic% or less, and the B content is 10 atomic% or more and 30 atomic% or less.

  The memory according to the present invention includes a memory element having a memory layer that holds information according to the magnetization state of a magnetic material, and two kinds of wirings that intersect each other, and the memory element has the configuration of the memory element according to the present invention. A storage element is arranged near the intersection of two types of wiring and between two types of wiring, and the current in the stacking direction flows through the storage element through the two types of wiring.

According to the configuration of the above-described storage element of the present invention, the storage layer that holds information by the magnetization state of the magnetic material is provided, and the fixed magnetization layer is provided on the storage layer via the intermediate layer. By flowing a current, the direction of magnetization of the storage layer changes and information is recorded on the storage layer. Therefore, it is possible to record information by spin injection by flowing a current in the stacking direction.
The intermediate layer is made of magnesium oxide, and at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer is mainly composed of NiFeB, and the Ni content is 50 atomic% or more and 80 atomic% or less, When the B content is 10 atomic% or more and 30 atomic% or less, the spin injection efficiency can be significantly increased. Thereby, the amount of current (threshold current) required to reverse the magnetization direction of the storage layer by spin injection can be reduced.

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. The memory element is arranged near the intersection of two types of wiring and between the two types of wiring, and current in the stacking direction flows through the memory element through these two types of wiring. Information can be recorded by spin injection by passing a current in the stacking direction of the memory element through the wiring.
In addition, the amount of current (threshold current) required to reverse the magnetization direction of the storage layer of the storage element by spin injection can be reduced.

  According to the above-described present invention, since the amount of current (threshold current) necessary for reversing the magnetization direction of the storage layer can be suppressed, the amount of current necessary for recording information can be reduced. .

Thereby, a sufficient operating margin of the memory element can be obtained, and the memory element can be operated without error.
In addition, since it is not necessary to apply a large voltage, the intermediate layer of magnesium oxide is not destroyed.

Therefore, a highly reliable memory that operates stably can be realized.
In addition, the power consumption of the entire memory can be reduced.

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 storage layer is composed 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 current threshold Ic required is phenomenologically expressed by the following equation 1 (for example, FJAlbert et al., Appl. Phys. Lett. ., 77, p. 3809, 2000, etc.).

In the present invention, as represented by the equation (1), the current threshold controls the volume V of the magnetic layer, the saturation magnetization M _s of the magnetic layer, and the magnitude of the effective magnetic anisotropy, Use that it can be set arbitrarily.
Then, a storage element having a magnetic layer (storage layer) capable of holding information depending on the magnetization state and a magnetization fixed layer in which the magnetization direction is fixed is configured.

The threshold value of the current that changes the magnetization state of the storage layer is actually a substantially elliptical giant magnetoresistive element (GMR element) having a storage layer thickness of 2 nm and a planar pattern of 120 to 130 nm × 100 nm, for example. , The positive threshold value + Ic = + 0.6 mA, the negative threshold value −Ic = −0.2 mA, and the current density at that time is about 6 × 10 ⁶ A · cm ² . These almost agree with the above formula (1) (see Rooftop et al., Journal of Japan Society of Applied Magnetics, Vol.28, No.2, p.149, 2004).

On the other hand, a normal MRAM that performs magnetization reversal by a current magnetic field requires a write current of several mA or more.
On the other hand, when the magnetization reversal is performed by spin injection, the threshold value of the write current becomes sufficiently small as described above, which is effective for reducing the power consumption of the integrated circuit.
Further, since the wiring for generating a magnetic field (105 in FIG. 8) required for a normal MRAM is not necessary, the degree of integration is also advantageous compared to a normal MRAM.

However, as described above, in a memory configured to use magnetization reversal by spin injection, it is necessary to reverse the magnetization direction of the storage layer by performing spin injection with a current flowing through the storage element.
Since the current is directly supplied to the memory element and information is written (recorded) as described above, the memory cell is configured by connecting the memory element to a selection transistor in order to select a memory cell to be written. In this case, the current flowing through the memory element is limited to the magnitude of the current that can flow through the selection transistor (the saturation current of the selection transistor).
Therefore, it is necessary to perform writing with a current lower than the saturation current of the selection transistor, and it is necessary to improve the efficiency of spin injection and reduce the current flowing through the memory element.

  By constructing 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 (GMR) is achieved using the nonmagnetic conductive layer. Compared with the case where the element is configured, the magnetoresistance change rate (MR ratio) can be increased, and the read signal intensity can be increased.

In particular, by using magnesium oxide (MgO) as the material of the tunnel insulating layer, the magnetoresistance change rate (MR ratio) can be increased as compared with the case of using aluminum oxide.
In general, the spin injection efficiency depends on the MR ratio, and the larger the MR ratio, the higher the spin injection efficiency and the lower the magnetization reversal current density.
Therefore, by using magnesium oxide as the material of the tunnel insulating layer which is an intermediate 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.

Therefore, in the present invention, the intermediate layer between the storage layer and the magnetization fixed layer has a configuration (tunnel insulating layer) made of magnesium oxide.
As a result, the MR ratio (TMR ratio) can be increased, 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.

  Note that it is more desirable that the tunnel insulating layer made of a magnesium oxide (MgO) film maintains the crystal orientation in the 001 direction because the MgO film is crystallized.

  In addition, as a result of various studies, the spin injection efficiency is improved by limiting the material of at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer and further defining the composition of this layer. It has been found that the current density required to reverse the magnetization direction of the storage layer is reduced.

Therefore, in the present invention, at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer is mainly composed of NiFeB, and the Ni content is 50 atomic% or more and 80 atomic% or less, The content of B is 10 atomic% or more and 30 atomic% or less.
Thereby, the spin injection efficiency can be improved and the current density required for reversing the magnetization direction of the storage layer can be reduced.

When the content of Ni in the ferromagnetic layer containing NiFeB as a main component is 50 atomic% or more, the feature of Ni element appears well, and the magnetization reversal current density by spin injection can be reduced.
Why is Ni good and why the reversal current density is significantly reduced when the Ni content is 50 atomic% or more (1/2 or more)? As a result, it was confirmed that the reversal current density was reduced.

In order to obtain excellent MR characteristics when magnesium oxide is used for the intermediate layer, it is generally required that the annealing temperature is set to a high temperature of 300 ° C. or higher, desirably 340 ° C. to 360 ° C. This is higher than the annealing temperature range (250 ° C. to 280 ° C.) in the case of aluminum oxide conventionally used for the intermediate layer.
This is considered to be because a high temperature is required to form an appropriate internal structure or crystal structure of magnesium oxide.
For this reason, excellent MR characteristics cannot be obtained unless a ferromagnetic material having heat resistance is used for the ferromagnetic layer of the memory element so as to be resistant to this high-temperature annealing.

  Therefore, in the above-described ferromagnetic layer containing NiFeB as a main component, the Ni content is 50 atomic% or more, and further, the B content is 10 atomic% or more, thereby forming the magnetic layer constituting the ferromagnetic layer. It was found that the heat resistance of the body can be improved, and the effect of suppressing element diffusion between the ferromagnetic layer and the adjacent layer is recognized.

On the other hand, in the above-described ferromagnetic layer containing NiFeB as a main component, when the Ni content exceeds 80 atomic%, the spin injection efficiency is not greatly reduced, but the MR ratio is greatly reduced. Therefore, as a result, the effect of reducing the reversal current density is reduced, and the reversal current density starts to increase.
Therefore, the Ni content is limited to 50 atom% or more and 80 atom% or less.

As for the content of B, in order to ensure the heat resistance up to 400 ° C., 10 atomic% or more is necessary as described above.
On the other hand, if the B content exceeds 30 atomic%, it may exist as a magnetic layer, but the saturation magnetization necessary for constituting the memory element cannot be obtained, so the B content is 30 atomic%. The following.

Note that a Co—Fe alloy is used as a material of a memory layer having a general MRAM configuration. If the Fe content of this Co—Fe alloy increases, the MR ratio certainly increases and the spin injection efficiency increases. There is a tendency to improve.
In practice, however, the decrease in reversal current density as expected from the increase in MR ratio cannot be obtained.

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).
The sheet resistance value of the tunnel insulating layer needs to be controlled to about several tens of Ωμm ² or less from the viewpoint of obtaining a current density necessary for reversing the magnetization direction of the storage layer by spin injection.
In the tunnel insulating layer made of the MgO film, it is necessary to set the film thickness of the MgO film to 1 nm or less in order to make the sheet resistance value in the above range.

In addition, it is desirable to make the memory element small so that the magnetization direction of the memory layer can be easily reversed with a small current.
Accordingly, the area of the memory element is preferably 0.04 μm ² or less.

In the present invention, at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer is configured to have NiFeB having the above composition range as a main component.
That is, one or all of the ferromagnetic layers constituting the storage layer are composed mainly of NiFeB having the above composition range, and one or all of the ferromagnetic layers constituting the magnetization fixed layer. The layer is composed mainly of NiFeB having the composition range described above, one or all of the ferromagnetic layers constituting the storage layer, and one or all of the ferromagnetic layers constituting the magnetization fixed layer. The structure which has NiFeB which has the composition range mentioned above as a main component is mentioned.

  It is also possible to directly laminate a ferromagnetic layer composed mainly of NiFeB having the composition range described above and another ferromagnetic layer having a different material or composition range. However, the effect of the present invention can be obtained.

Usually, the memory layer is mainly composed of a ferromagnetic material such as Co, Fe, Ni, Gd, etc., and the memory layer is formed in one or more laminated states using these two or more kinds of alloys as one layer.
In the case of applying the composition mainly composed of NiFeB having the above-described composition range to the ferromagnetic layer constituting the memory layer, for example, NiFeB alloy or NiFeB as the principal component is used as the ferromagnetic layer. B, C, N, Si, P, Al, Ta, Mo, Cr, Nb, Cu, Zr, W, V, Hf, Gd, Mn, and Pd are added as magnetic elements such as, Gd, and other elements. Materials can be used.

  In addition, the film configuration of the storage element has no problem whether the storage layer is disposed above the magnetization fixed layer or the lower layer.

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

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

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

A cross-sectional view of the memory element 3 of the memory according to the present embodiment is shown in FIG.
As shown in FIG. 2, the storage element 3 is provided with a fixed magnetization layer 31 in the lower layer with respect to the storage layer 17 in which the direction of the magnetization M1 is reversed by spin injection. The antiferromagnetic layer 12 is provided under the magnetization fixed layer 31, and the magnetization direction of the magnetization fixed layer 31 is fixed by the antiferromagnetic layer 12.
An insulating layer 16 serving as a tunnel barrier layer (tunnel insulating layer) is provided between the storage layer 17 and the magnetization fixed layer 31, and the storage layer 17 and the magnetization fixed layer 31 constitute an MTJ element.

  A base layer 11 is formed below the antiferromagnetic layer 12, and a cap layer 18 is formed on the storage layer 17.

The magnetization fixed layer 31 has a laminated ferrimagnetic structure.
Specifically, the magnetization fixed layer 31 has a configuration in which two ferromagnetic layers 13 and 15 are stacked via a nonmagnetic layer 14 and antiferromagnetically coupled.

Since each of the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31 has a laminated ferrimagnetic structure, the magnetization M13 of the ferromagnetic layer 13 is directed to the right, and the magnetization M15 of the ferromagnetic layer 15 is directed to the left. It has become.
Thereby, the magnetic fluxes leaking from the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31 cancel each other.

In the present embodiment, in particular, at least one of the ferromagnetic layers constituting the storage layer 17 and the magnetization fixed layer 31, that is, the storage layer 17 and the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31, NiFeB is the main component, the Ni content is 50 atomic% to 80 atomic%, and the B content is 10 atomic% to 30 atomic%.
Further, the insulating layer 16 which is an intermediate layer is a magnesium oxide layer.

  In the ferromagnetic layer mainly composed of NiFeB having the above composition range, as other elements, in addition to iron, cobalt and gadolin, transition metals such as molybdenum, manganese, copper, niobium and zirconium, and light metals such as boron and carbon are used. An element may be contained.

In the case where the memory layer 17 is not composed of the above-described NiFeB as a main component, the constituent material of the memory layer 17 is not particularly limited.
In this case, for example, an alloy material composed of one or more of cobalt, iron, nickel, and gadolinium can be used. Furthermore, transition metal elements such as molybdenum, manganese, copper, niobium, and zirconium, and light elements such as B can also be included.
In addition, the storage layer 17 may be configured by directly stacking a plurality of films made of different materials, such as a CoFe / NiFe / CoFe stacked film, without using a nonmagnetic layer.

The constituent materials of the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31 are not particularly limited when the ferromagnetic layers 13 and 15 are not composed of the above-described NiFeB as a main component.
In this case, for example, an alloy material composed of one or more of iron, nickel, cobalt, and gadolinium can be used. Furthermore, transition metal elements such as Nb and Zr, and light elements such as B and C can also be included.

As the material of the nonmagnetic layer 14 constituting the laminated ferrimagnetic pinned layer 31, ruthenium, copper, chromium, gold, silver or the like can be used. Although the film thickness of the nonmagnetic layer 14 varies depending on the material, it is preferably used in the range of approximately 0.5 nm to 2.5 nm.
As a material of the antiferromagnetic layer 12, an alloy of a metal element such as iron, nickel, platinum, iridium and rhodium and manganese, an oxide of cobalt or nickel, or the like can be used.

  The film thickness of the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31 is suitably 1 nm or more and 4 nm or less.

  The memory element 3 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 the pattern of the memory element 3 by processing such as etching. Can do.

  According to the above-described embodiment, at least one of the ferromagnetic layers 17, 13, and 15 constituting the storage layer 17 or the magnetization fixed layer 31 of the storage element 3 has NiFeB as a main component and the Ni content. Is 50 atomic% or more and 80 atomic% or less, and the B content is 10 atomic% or more and 30 atomic% or less, a high MR ratio can be secured and the spin injection efficiency is improved. Thus, the current density necessary for reversing the direction of the magnetization M1 of the storage layer 17 by spin injection can be significantly reduced.

In addition, the heat resistance of the ferromagnetic layer is increased, so that it can withstand annealing at 400 ° C. without deterioration of magnetic properties.
This has the advantage that a general semiconductor MOS formation process can be applied when manufacturing a memory including the memory element 3, and the memory including the memory element 3 of the present embodiment is applied as a general-purpose memory. It becomes possible.

Furthermore, according to the present embodiment, the magnetoresistive change rate (MR ratio) can be increased by using the insulating layer 16 as the intermediate layer as the magnesium oxide layer.
By increasing the MR ratio in this way, it is possible to improve the efficiency of spin injection and reduce the current density required to reverse the direction of the magnetization M1 of the storage layer 17.

  Accordingly, a highly reliable memory that operates stably can be realized, and power consumption can be reduced in the memory including the memory element 3.

Next, as another embodiment of the present invention, a cross-sectional view of a memory element constituting a memory is shown in FIG.
In this storage element 30, a magnetization fixed layer 31 is provided in the lower layer and a magnetization fixed layer 32 is provided in the upper layer with respect to the storage layer 17 in which the direction of the magnetization M1 is reversed by spin injection. That is, the upper and lower two magnetization fixed layers 31 and 32 are provided for the storage layer 17.

The upper magnetization pinned layer 32 has only a single ferromagnetic layer 20.
An insulating layer 19 serving as a tunnel barrier layer (tunnel insulating layer) is provided between the storage layer 17 and the upper magnetization fixed layer 32. The storage layer 17 and the magnetization fixed layer 32 constitute an MTJ element. Yes.
The antiferromagnetic layer 21 is provided on the magnetization fixed layer 32, and the direction of the magnetization M <b> 20 of the ferromagnetic layer 20 of the magnetization fixed layer 32 is fixed by the antiferromagnetic layer 21.
A cap layer 18 is formed on the antiferromagnetic layer 21.

In the present embodiment, in particular, the ferromagnetic layers constituting the storage layer 17 and the magnetization fixed layers 31 and 32, that is, the storage layer 17, the ferromagnetic layers 13 and 15 of the magnetization fixed layer 31, and the magnetization fixed layer 32. Among the ferromagnetic layers 20, at least one layer is composed of NiFeB as a main component, the Ni content is 50 atomic% or more and 80 atomic% or less, and the B content is 10 atomic% or more and 30 atomic% or less. And
Further, the insulating layers 16 and 19 as intermediate layers are magnesium oxide layers.

  In the ferromagnetic layer mainly composed of NiFeB having the above composition range, as other elements, in addition to iron, cobalt and gadolin, transition metals such as molybdenum, manganese, copper, niobium and zirconium, and light metals such as boron and carbon are used. An element may be contained.

  Other configurations are the same as those of the memory element 3 shown in FIG.

Further, a memory having a structure similar to that of the memory illustrated in FIG. 1 can be formed using the memory element 30 of this embodiment.
That is, the memory element 30 is arranged near the intersection of two types of address wirings to form a memory, and a current in the vertical direction (stacking direction) is passed through the memory element 30 through the two types of address wirings, and the memory layer is formed by spin injection. Information can be recorded in the storage element 30 by reversing the direction of the magnetization M <b> 1 of 17.

  According to the present embodiment described above, at least one of the ferromagnetic layers 17, 13, 15, and 20 constituting the storage layer 17 or the magnetization fixed layer 31 of the storage element 30 is made of NiFeB as a main component and made of Ni. By adopting a configuration in which the content is 50 atomic% or more and 80 atomic% or less and the B content is 10 atomic% or more and 30 atomic% or less, a high MR ratio can be ensured and the spin injection efficiency can be improved. As a result, the current density required to reverse the direction of the magnetization M1 of the storage layer 17 by spin injection can be significantly reduced.

In addition, the heat resistance of the ferromagnetic layer is increased, so that it can withstand annealing at 400 ° C. without deterioration of magnetic properties.
This has the advantage that a general semiconductor MOS formation process can be applied when manufacturing a memory including the memory element 30, and the memory including the memory element 30 of the present embodiment is applied as a general-purpose memory. It becomes possible.

Furthermore, according to the present embodiment, the magnetoresistive change rate (MR ratio) can be increased by using the insulating layers 16 and 19 as intermediate layers as magnesium oxide layers.
By increasing the MR ratio in this way, it is possible to improve the efficiency of spin injection and reduce the current density required to reverse the direction of the magnetization M1 of the storage layer 17.

  Furthermore, in the present embodiment, the magnetization fixed layers 31 and 32 are provided on the lower layer side and the upper layer side via the insulating layers 16 and 19 with respect to the memory layer 17, respectively. However, the current required to reverse the direction of the magnetization M1 of the storage layer 17 can be reduced.

  Therefore, a highly reliable memory that operates stably can be realized, and power consumption can be reduced in the memory including the memory element 30.

Here, in the structure of the memory element of the present invention, the material and film thickness of each layer were specifically selected, and the characteristics were examined.
Actually, as shown in FIGS. 1 and 6, 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 is stored. The study was performed using a wafer on which only elements were formed.

<Experiment 1>
A thermal oxide film having a thickness of 2 μm was formed on a silicon substrate having a thickness of 0.575 mm, and the memory element 3 having the configuration shown in FIG. 2 was formed thereon.
Specifically, in the memory element 3 having the configuration shown in FIG. 2, the material and thickness of each layer are as follows: the underlayer 11 is a Ta film with a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film with a thickness of 20 nm, and the magnetization The ferromagnetic layer 13 constituting the fixed layer 31 is a CoFe film having a thickness of 2 nm, the ferromagnetic layer 15 is a CoFeB film having a thickness of 2.5 nm, and the nonmagnetic layer 14 constituting the magnetization fixed layer 31 having a laminated ferrimagnetic structure is formed. A 0.8 nm Ru film, an insulating layer (barrier layer) 16 serving as a tunnel insulating layer is a 0.8 nm thick magnesium oxide film, a memory layer 17 is a 3 nm thick NiFeB film, and a cap layer 18 is a 5 nm thick Ta film. The film was selected, and a Cu film (not shown) having a thickness of 100 nm (to be described later) was provided between the base film 11 and the antiferromagnetic layer 12 to form each layer.
In the above film configuration, the composition of the PtMn film was Pt50Mn50 (atomic%), and the composition of the CoFe film was Co90Fe10 (atomic%).
Each layer other than the insulating layer 16 made of a magnesium oxide film was formed using a DC magnetron sputtering method.
The insulating layer 16 made of a magnesium oxide (MgO) film was formed using an RF magnetron sputtering method.
Further, after each layer of the memory element 3 was formed, heat treatment was performed 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, selective etching was performed by Ar plasma on the laminated film other than the word line to form the word line (lower electrode). At this time, except for the word line portion, the substrate was etched to a depth of 5 nm.

Thereafter, a mask of the pattern of the memory element 3 was formed by an electron beam drawing apparatus, and selective etching was performed on the laminated film to form the memory element 3. Except for the memory element 3 portion, the etching was performed up to the Cu layer of the word line.
In addition, in order to generate the spin torque necessary for the magnetization reversal, it is necessary to flow a sufficient current through the storage element for the characteristic evaluation storage element, and thus it is necessary to suppress the resistance value of the tunnel insulating layer. Therefore, the pattern of the memory element 3 is an ellipse having a minor axis of 0.09 μm and a major axis of 0.18 μm, and the area resistance value (Ωμm ² ) of the memory element 3 is set to 30Ωμm ² .

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

Each sample of the memory element 3 was manufactured by changing the Ni—Fe composition by fixing the B content of the NiFeB film of the memory layer 17 to 20 atomic% by the above-described manufacturing method.
That is, the Ni content is 0 atomic% (Fe80B20), 10 atomic%, 20 atomic%, 30 atomic%, 40 atomic%, 50 atomic%, 60 atomic%, 70 atomic%, and 80 atomic% (Ni80B20). Each sample was prepared.

<Experiment 2>
In the memory element 3 having the configuration shown in FIG. 2, the material and thickness of each layer are configured such that the base film 11 is a Ta film with a thickness of 3 nm, the antiferromagnetic layer 12 is a PtMn film with a thickness of 20 nm, and the magnetization fixed layer 31 is configured. The ferromagnetic layer 13 to be formed is a CoFe film having a thickness of 2 nm, the ferromagnetic layer 15 is a NiFeB film having a thickness of 2.5 nm, and the nonmagnetic layer 14 constituting the magnetization fixed layer 31 having a laminated ferri structure is a Ru film having a thickness of 0.8 nm. The insulating layer (barrier layer) 16 serving as a tunnel insulating layer was selected as a 0.8 nm thick magnesium oxide film, the memory layer 17 as a 3 nm thick CoFeB film, and the cap layer 18 as a 5 nm thick Ta film.

  Other configurations and manufacturing methods were the same as those of the memory element 3 of Experiment 1.

Then, each sample of the memory element 3 in which the content of B in the NiFeB film of the ferromagnetic layer 15 of the magnetization fixed layer 31 was fixed to 15 atomic% and the Ni—Fe composition was changed was produced.
That is, the content of Ni is 0 atomic% (Fe85B15), 10 atomic%, 20 atomic%, 30 atomic%, 40 atomic%, 50 atomic%, 60 atomic%, 70 atomic%, 80 atomic%, 85 atomic%. Each sample was made (Ni85B15).

The characteristics of each sample of the memory element 3 produced in Experiment 1 and Experiment 2 were evaluated as follows.
Prior to the measurement, the storage element 3 was configured to be able to apply a magnetic field from the outside in order to control the positive and negative values of the reversal current to be symmetrical. Further, the amount of current flowing through the memory element 3 was set to 1 mA within a range where the insulating layer 16 was not broken.

(Measurement of reversal current and MR ratio)
A current was passed through the memory element 3, and the subsequent resistance value of the memory element 3 was measured. When the resistance value of the memory element 3 was measured, 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. Furthermore, the resistance value of the memory element 3 was measured while changing the amount of current flowing through the memory element 3, 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.
And the average value of the absolute value of the reversal current value of both polarities was calculated, and the magnetization reversal current density (MA / cm ² ) was calculated by dividing this average value by the element area.
Further, the resistance value when the direction of the magnetization M15 of the ferromagnetic layer 15 on the storage layer 17 side of the fixed magnetization layer 31 and the direction of the magnetization M1 of the storage layer 17 are in an antiparallel state and the resistance is high, and A ratio with the resistance value in a state where the directions of the magnetizations M15 and M1 are parallel and the resistance is low is obtained, and this is defined as an MR ratio (TMR ratio).

  The measurement results of each sample in Experiment 1 are shown in FIGS. 4A and 4B, and the measurement results of each sample in Experiment 2 are shown in FIGS. 5A and 5B. 4A and 5A show the relationship between the Ni content (atomic%) and the MR ratio, and FIGS. 4B and 5B show the relationship between the Ni content (atomic%) and the magnetization reversal current density. Show.

From FIG. 4B, in the configuration of the memory element 3 of Experiment 1, when the Ni content of the NiFeB layer of the memory layer 17 is 50 atomic% or more, the magnetization reversal current density is reduced to about 4 MA / cm ² or less. I understand.
4A shows that a high MR ratio can be obtained when the Ni content of the NiFeB layer of the memory layer 17 is in the range of 40 atomic% to 80 atomic%. When the Ni content exceeds 80 atomic%, the MR ratio decreases. I guess it will continue.
That is, by setting the Ni content of the NiFeB layer of the memory layer 17 to 50 atom% or more and 80 atom% or less, the MR ratio can be increased and the magnetization reversal current density can be decreased.

Similarly, from FIGS. 5A and 5B, in the configuration of the memory element 3 of Experiment 2, the Ni content of the NiFeB layer of the ferromagnetic layer 15 of the fixed magnetization layer 31 is set to 50 atomic% or more and 80 atomic% or less. In addition, the MR ratio can be increased and the magnetization reversal current density can be decreased (about 4.5 MA / cm ² or less).

Therefore, it can be seen that excellent magnetization reversal characteristics can be obtained by adopting the configuration of the present invention in which the Ni content of the NiFeB layer is 50 atomic% or more and 80 atomic% or less.
With the structure of the present invention, a memory element capable of writing information with a relatively small current density of 5 MA / cm ² or less can be manufactured, which has an unprecedented low power consumption type. A magnetic memory can be realized.

  The present invention is not limited to the film configuration of the memory elements 3 and 30 shown in the above embodiments, and various film configurations can be employed.

  In each of the embodiments described above, the magnetization fixed layer 31 has a laminated ferrimagnetic structure including the two ferromagnetic layers 13 and 15 and the nonmagnetic layer 14. For example, the magnetization fixed layer is a single-layer ferromagnetic layer. You may comprise by.

  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.

1 is a schematic configuration diagram (perspective view) of a memory according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the memory element in FIG. 1. It is sectional drawing of the memory element of other embodiment of this invention. A It is a figure which shows the relationship between Ni content (atomic%) of each sample of Experiment 1, and MR ratio. B is a diagram showing the relationship between the Ni content (atomic%) and the reversal current density of each sample in Experiment 1. FIG. A It is a figure which shows the relationship between Ni content (atomic%) of each sample of Experiment 2, and MR ratio. B is a diagram showing the relationship between the Ni content (atomic%) and the reversal current density of each sample in Experiment 2. FIG. It is a schematic block diagram (perspective view) of a memory using magnetization reversal by spin injection. It is sectional drawing of the memory of FIG. It is the perspective view which showed the structure of the conventional MRAM typically.

Explanation of symbols

  3,30 Memory element, 11 Underlayer, 12, 21 Antiferromagnetic layer, 13, 15, 20 Ferromagnetic layer, 14 Nonmagnetic layer, 16, 19 Insulating layer, 17 Memory layer, 18 Cap layer, 31, 32 Magnetization Fixed 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 intermediate layer comprises magnesium oxide;
By flowing a current in the stacking direction, the magnetization direction of the storage layer changes, and information is recorded on the storage layer.
At least one of the ferromagnetic layers constituting the memory layer or the magnetization fixed layer is mainly composed of NiFeB, the Ni content is 50 atomic% or more and 80 atomic% or less, and the B content is 10 atomic%. It is 30 atomic% or less. 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,
In the storage element, a magnetization fixed layer is provided via an intermediate layer with respect to the storage layer, the intermediate layer is made of magnesium oxide, and a current flows in the stacking direction, whereby the magnetization direction of the storage layer Changes, information is recorded on the storage layer, and at least one of the ferromagnetic layers constituting the storage layer or the magnetization fixed layer is mainly composed of NiFeB, and the Ni content is 50. The atomic percent is 80 atomic percent or less and the B content is 10 atomic percent or more and 30 atomic percent or less.
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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