JP2007305629A - Spin-injection magnetization inverting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multivalued storage magnetic memory capable of obtaining high output by preventing the number of wires and power consumption from increasing. <P>SOLUTION: In a spin-injection magnetization inverting element; at least a lower electrode, an antiferromagnetic layer, a ferromagnetic pin layer, a first intermediate layer, a first ferromagnetic free layer, a second intermediate layer, a second ferromagnetic free layer, and an upper electrode, are provided on the lower electrode in this order. In the spin-injection magnetization inverting element; the first and second ferromagnetic free layers have a bcc structure, and magnetization inversion critical current density differs between the first ferromagnetic free layer and the second one. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a functional device that controls spin of electrons. In particular, the present invention relates to a spin injection type magnetization reversal element. A large number of elements of the present invention are integrated on a silicon semiconductor substrate together with a CMOS circuit, so that a magnetic random access memory having a large recording capacity and not including a mechanical drive part can be realized.

  2. Description of the Related Art Recently, a giant magneto-resistance (GMR) effect element composed of a ferromagnetic layer / nonmagnetic metal layer / ferromagnetic layer and a tunnel magnetoresistance (TMR: Tunnel) composed of a ferromagnetic layer / insulator layer / ferromagnetic layer. Magneto-Resistance effect elements have been developed and are expected to be applied to new magnetic sensors and magnetic memories (MRAM). For example, see Non-Patent Document 1 for the GMR effect.

  A conventional technique of MRAM as an application example of GMR and TMR effect elements will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing the basic structure of an MRAM. FIG. 1A is an overall view, and FIG. 1B is a cross-sectional view showing the structure of a TMR element. As shown in FIG. 1A, in the MRAM, bit lines and word lines are wired in a matrix, and TMR elements are arranged at intersections of the matrix. In the TMR element, as shown in FIG. 1B, a first ferromagnetic layer 12, an insulating layer 13, and a second ferromagnetic layer 14 are provided between a bit line 11 and a word line 15. Further, a writing word line 16 for writing theoretical information to the TMR element is separately provided. FIG. 1B shows a case where the coercive force of the second ferromagnetic layer 14 is higher than the coercive force of the first ferromagnetic layer 12. The theoretical information is written into the TMR element by causing a current to flow through the write word lead wire 16 to generate a magnetic field. By adjusting the direction and strength of the magnetic field generated at this time, the magnetization directions of the first ferromagnetic layer 12 and the second ferromagnetic layer 14 are made parallel or antiparallel, and information of “1” or “0” is stored. . The stored information is read by passing a current from the word line 15 to the bit line 11 and reading the resistance value of the element generated by the TMR effect. In this way, theoretical information can be recorded / reproduced with respect to the TMR element, but this method can record / reproduce only binary information of “1” and “0”, that is, 1-bit information in one memory cell. There was a problem that it was not sufficient for future demands for higher density.

  As a method for solving this problem, Patent Document 1 discloses a method of storing and reproducing multi-value information of three or more values in one memory cell. This technique will be described with reference to FIG. FIG. 2A is a schematic cross-sectional view showing the structure of a single cell of the element, and FIGS. 2B to 2D show the first ferromagnetic layer 22 and the second ferromagnetic layer when a magnetic field is generated. It is a figure (example) which shows the direction of magnetization of each magnetic layer of 24,25.

  As shown in FIG. 2A, the element has a bit line 21, and a first ferromagnetic layer 22, a tunnel layer 23, and second ferromagnetic layers 24 and 25 sequentially formed thereon. The second ferromagnetic layers 24 and 25 have different coercive forces by changing the film forming conditions of the magnetic material. In addition, this element is provided with a word line 26 and a write word line 27. In addition, it is assumed that the coercive forces A, B, and C of the first ferromagnetic layer 22 and the second ferromagnetic layers 24 and 25 in this element have a relationship of A <B <C. In the figure, the direction of magnetization is referred to as rightward or leftward in accordance with the direction of the arrow (the direction of the magnetic field is also the same).

  When a current is passed through a writing word line installed outside the device to generate a magnetic field (H), the direction and strength of the magnetic field, the first ferromagnetic layer 22 and the second ferromagnetic layers 24 and 25 are generated. The magnetization direction of is as follows. First, assuming that a sufficiently large current is passed through the word line to generate a magnetic field H in the right direction that satisfies A <B <C <H, the first ferromagnetic layer 22 and the magnetic field H are generated by this magnetic field as shown in FIG. The magnetization directions of the second ferromagnetic layers 24 and 25 are all rightward. This state is assumed to be a theoretical value “0”. Next, when a leftward magnetic field H satisfying A <B <H <C is generated in this state, the magnetizations of the first ferromagnetic layer 22 and the second ferromagnetic layer 24 are changed as shown in FIG. Flip left. This state is the theoretical value “1”. When the leftward magnetic field H is further strengthened so that A <B <C <H, all the magnetizations are directed to the left as shown in FIG. This state is assumed to be a theoretical value “2”. The above relationship is shown in Table 1.

  Reproduction of stored information is performed by generating a weak rightward magnetic field satisfying A <H <B <C from the word line 26 for writing and reading a change in element resistance when the magnetization of the first ferromagnetic layer 22 is reversed. In this manner, ternary information can be stored and reproduced for one memory cell.

  Patent Document 2 discloses an example of a memory element that records and reproduces binary information using spin injection having the structure shown in FIG. 3 (in Patent Document 2, this element is referred to as a normal type). ). This magnetic cell includes two magnetic pinned layers C1 and C2 in which the directions of magnetizations M1 and M2 are antiparallel to each other, one magnetic recording layer A having a variable magnetization direction, and between the magnetic recording layer A and the magnetic pinned layer. It has intermediate layers B1 and B2.

  FIG. 4 shows the behavior of electron spin and magnetization in the magnetic layer when electrons flow through the element from the magnetic pinned layer C1 toward the magnetic pinned layer C2. In FIG. 4, the white arrow indicates the magnetization direction of each magnetic layer, the small circled arrow indicates the direction of electron spin, and the thin arrow without a circle indicates the direction of electron flow. Hereinafter, the direction of magnetization is referred to as right or left direction in accordance with the direction of the arrow.

  First, in FIG. 4A, electrons that have passed through the first magnetic pinned layer C1 having the magnetization M1 have a spin in the direction of the magnetization M1, and when this flows into the magnetic recording layer A, The angular momentum is transmitted to the magnetic recording layer A and acts on the magnetization M. On the other hand, the magnetization M2 of the second magnetic pinned layer C2 is opposite to the magnetization M1. For this reason, at the interface where the flow of electrons enters the second magnetic pinned layer C2, electrons having a rightward spin in the same direction as the magnetization M1 are reflected. The reverse spins of the reflected electrons still act on the magnetic recording layer A. That is, since spin electrons in the same direction as the magnetization of the first magnetic pinned layer act twice on the magnetic recording layer A, a substantially double writing effect can be obtained. As a result, writing to the magnetic recording layer A can be performed with a smaller current than in the past.

  FIG. 4B shows a case where the current I is inverted. In this case, the electrons constituting the current I first have a spin in this direction (leftward in the figure) due to the action of the magnetization M2 of the second magnetic pinned layer C2. The spin electrons act on the magnetization M in the magnetic recording layer A. Further, the spin electrons are reflected at the interface with the first magnetic pinned layer C1 having the magnetization M1 opposite to the spin electrons, accumulated in the intermediate layer B2, and once again act on the magnetization M of the magnetic recording layer A.

  In this way, binary information can be written by preparing two magnetic pinned layers having magnetizations in opposite directions and changing the direction of the current flowing through the element.

  A method of performing multilevel recording by laminating a large number of the above elements has also been proposed (see Patent Document 2, paragraph numbers 0095 to 0096). Such an element has a structure as shown in FIG. FIG. 5 is a schematic cross-sectional view showing a magnetic cell provided with two magnetic recording layers. That is, in this magnetic cell, the magnetic pinned layer C1, the intermediate layer B1, the magnetic recording layer A1, the intermediate layer B2, the magnetic pinned layer C2, the intermediate layer B3, the magnetic recording layer A2, the intermediate layer B4, and the magnetic pinned layer C3 They are stacked in order. That is, the magnetic pinned layer C2 is shared, and the magnetic cells illustrated in FIG. 3 are formed in series above and below the magnetic pinned layer C2, respectively. Basically, the element in FIG. 5 is a stack of the elements in FIG. 3, and the critical current density (hereinafter referred to as magnetization reversal) in which the magnetization direction of each layer is reversed by changing the magnetic material or film thickness of each intermediate layer. (Also referred to as current density) to enable multi-value.

JP 2002-42457 A JP 2004-193595 A J. A. Katine, Phys. Rev. Letters, 84 (14), 3149 (2000)

  The element described in Patent Document 1 can store and reproduce multi-valued theoretical information in one memory cell, and is considered to be very effective from the viewpoint of increasing the density of MRAM. . However, in this element, when writing information to the TMR element, a write word line installed outside the TMR element is essential, so the number of wirings increases. Furthermore, the magnetization reversal by the current magnetic field has a problem that the threshold current for the magnetization reversal is very large and the power consumption at the time of writing increases.

  The memory cell described in Patent Document 2 assumes that multi-value recording is performed by stacking a plurality of elements that perform binary recording. Therefore, it is necessary to dispose at least one magnetic pinned layer for each magnetic recording layer for recording magnetization reversal, and the total number of magnetic pinned layers increases as the number of multi-level recordings increases. The magnetic pinned layer needs to have a sufficient film thickness to fix the magnetization so that it does not fluctuate easily. For this reason, when a plurality of magnetic pinned layers are provided, the element resistance increases, Power consumption will increase.

  In addition, since this element records multi-value information by changing the magnetization reversal current of a plurality of magnetic recording layers, a design guideline for setting the magnetization reversal current density to a different value is important. As a design guideline for such a magnetic recording layer, it has been proposed to change the film thickness of each magnetic recording layer. However, an increase in film thickness leads to an increase in resistance value, which in turn leads to an increase in power consumption. is not. In addition, there is no specific method for setting the magnetic material when designing the magnetic recording layer.

  The present invention has been devised to solve such a problem, and an object of the present invention is to provide a multi-value storage magnetic memory that can prevent an increase in the number of wires and power consumption and obtain a high output.

  The present invention relates to a spin-injection type magnetization reversal element, which includes at least a lower electrode, an antiferromagnetic layer, a ferromagnetic pinned layer, a first intermediate layer, a first ferromagnetic free layer, a second intermediate layer, a second strong layer. A spin injection type magnetization reversal element in which a magnetic free layer and an upper electrode are provided in this order on a lower electrode, wherein the first and second ferromagnetic free layers have a bcc structure, and the first ferromagnetic free layer And the second ferromagnetic free layer have different magnetization reversal critical current densities.

In the element of the present invention, the ferromagnetic pinned layer, the first ferromagnetic free layer, and the second ferromagnetic free layer are an alloy containing two or more elements selected from Co, Fe, or Ni. It is preferable that an element selected from Cr, V, Mo, W, Ta, B or Pt is further included, and the composition of the first ferromagnetic free layer and the second ferromagnetic free layer is different. Furthermore, it is preferable that the upper electrode is electrically connected to the lower electrode. The first intermediate layer and the second intermediate layer may be a nonmagnetic metal selected from the group consisting of Cu, Au, Ag, and Al, or the first intermediate layer and the second intermediate layer may be Al _2. An insulator selected from the group consisting of O ₃ , SiO ₂ and MgO may be used.

  In the spin injection magnetization switching element of the present invention, each layer is preferably formed by sputtering, ion beam sputtering, molecular beam epitaxy (MBE), or laser ablation.

  The spin-injection type magnetization reversal element of the present invention can perform multi-value recording of three or more values depending on its configuration. Moreover, the element which shows high MR ratio can be obtained by making the crystal structure of a 1st ferromagnetic free layer and a 2nd ferromagnetic free layer into a bcc structure. As a result, it is possible to provide a multi-value storage magnetic memory that can prevent an increase in the number of wires and power consumption and obtain high output.

The present invention will be described below with reference to the drawings.
FIG. 6 is a conceptual diagram for explaining the basic configuration of the spin-injection magnetization switching element of the present invention. As shown in FIG. 6, the spin injection magnetization reversal element of the present invention includes a lower electrode 30, an antiferromagnetic layer 31, a ferromagnetic pinned layer 32, a first intermediate layer 33, a first ferromagnetic free layer 34, and a second one. The intermediate layer 35, the second ferromagnetic free layer 36, and the upper electrode 37 are included, and these layers are sequentially stacked on the lower electrode. The element of the present invention is characterized in that the first and second ferromagnetic free layers have a bcc structure, and the magnetization reversal critical current densities of the first ferromagnetic free layer and the second ferromagnetic free layer are different. To do.

(Description of each layer of the spin injection type magnetization reversal element of the present invention)
Each layer of the present invention will be described below.
1) Lower electrode 30 and upper electrode 37
The lower electrode 30 and the upper electrode 37 can be made of a material that is normally used as an electrode of a spin injection magnetization switching element. For example, materials such as Cu, Au, Al, and Ag can be suitably used. In the present invention, it is preferable that the upper electrode is electrically connected to the lower electrode so that a current can flow from either the upper electrode side or the lower electrode side.

2) Antiferromagnetic layer 31
The antiferromagnetic layer 31 is a layer used for fixing the magnetization of a ferromagnetic pinned layer, which will be described later, and a material usually used for the same layer of the spin injection type magnetization reversal element can be used. For example, materials such as PtMn, IrMn, PdPtMn, NiMn, NiO can be suitably used. A preferred elemental composition of the material can be Ir20Mn80, for example. The film thickness of the antiferromagnetic layer is preferably 2 to 15 nm.

3) Ferromagnetic pinned layer 32
The ferromagnetic pinned layer 32 is a layer whose magnetization is fixed in one direction. In the spin-injection type magnetization reversal element, the ferromagnetic pinned layer 32 serves as a filter layer that selectively passes either an upspin or a downspin of electrons. The material of the ferromagnetic pinned layer 32 is an alloy including two or more elements selected from Co, Fe, or Ni, and this alloy is further selected from Cr, V, Mo, W, Ta, B, or Pt. It is preferable that the element is included. The film thickness of the ferromagnetic pinned layer is preferably 2 to 50 nm. Further, a preferable combination of materials is FeCoB or FeCoNiB, and a preferable element composition can be, for example, Fe50Co40B10 or Fe50Ni30Co10B10.

4) First intermediate layer 33 and second intermediate layer 35
When the first intermediate layer 33 and the second intermediate layer 35 are used as TMR elements, any one of Al ₂ O ₃ , SiO _{2, and} MgO that is a nonmagnetic insulating material can be used. The film thickness is preferably between 0.5 nm and 3 nm in consideration of productivity and the critical thickness of the tunnel barrier.

  In addition, when the first intermediate layer 33 and the second intermediate layer 35 are used as CPP-GMR elements (here, CPP is an abbreviation for Current Perpendicular to Plane), Cu is a nonmagnetic conductive material. , Au, Ag, or Al can be used. The film thickness is preferably between 1 nm and 7 nm in terms of productivity and the thickness in which exchange coupling does not work between the ferromagnetic pinned layer and the ferromagnetic free layer.

5) First ferromagnetic free layer 34 and second ferromagnetic free layer 36
The first ferromagnetic free layer 34 and the second ferromagnetic free layer 36 have a magnetization direction parallel or antiparallel to the ferromagnetic pinned layer 12 depending on the current density flowing between the lower and upper electrodes and the direction in which the current flows. It is a layer used to change the electrical resistance. The material of the ferromagnetic free layer is an alloy containing two or more elements selected from Co, Fe, or Ni, and this alloy is further selected from Cr, V, Mo, W, Ta, B, or Pt. It is preferable that an element is included. When the element of the present invention is used as a multi-value memory having three or more values, it is preferable that the compositions of the first ferromagnetic free layer and the second ferromagnetic free layer are different.

  Since the critical current of magnetization reversal depends on the saturation magnetization, volume, and shape anisotropy of the magnetic film, for example, the first ferromagnetic free layer and the second ferromagnetic free layer by changing the amount of Cr with respect to FeCo Can be used as In this case, the larger the amount of Cr, the smaller the Ms, and the critical current density for magnetization reversal can be reduced. In order to further increase MR, the structure of the ferromagnetic free layer is preferably a bcc structure. The cause of this is not clear, but the material of the intermediate layer, which will be described later, mainly has the fcc structure, and the crystal structure of the intermediate layer and the ferromagnetic free layer are different, resulting in an increase in spin-dependent interface scattering. It is expected that

  Preferred material combinations for the ferromagnetic free layer include FeCoCr, FeCoCrB, FeCoMo, FeCoMoB, FeCoW, FeCoWB, FeCoPt, and FeCoPtB.

  For example, when the composition ratio of the elements of the preferable material is FeCoCrB, Fe is 70 to 30 atomic%, Cr is 30 to 10 atomic%, Co is 20 to 5 atomic%, and B is 15 to 5 atomic%. be able to. By setting it as such a range, the structure of a ferromagnetic free layer can be made into a bcc structure. The film thicknesses of the first ferromagnetic free layer and the second ferromagnetic free layer can be 1 to 15 nm and 2 to 20 nm, respectively.

  Each of the above layers is formed by sputtering, ion beam sputtering, molecular beam epitaxy (MBE), laser ablation, etc., the lower electrode, antiferromagnetic layer, ferromagnetic pinned layer, first intermediate layer, first ferromagnetic free The layer, the second intermediate layer, the second ferromagnetic free layer, and the upper electrode can be formed in this order.

(Operating principle)
Hereinafter, the operation principle of the spin injection type magnetization reversal element of the present invention will be described with reference to FIG. In the following description, an element having the same configuration as the spin-injection type magnetization reversal element of the present invention shown in FIG. 7A to 7C show the cases of theoretical values “0”, “1”, and “2”, respectively. Also, the reference numerals are respectively 50: lower electrode, 51: antiferromagnetic layer, 52: ferromagnetic pinned layer, 53: first intermediate layer, 54: first ferromagnetic free layer, 55: second intermediate layer, 56: means the second ferromagnetic free layer, and 57: means the upper electrode.

First, the magnetization direction of the ferromagnetic pinned layer 52 is rightward on the paper surface as shown in FIG. 7 (indicated by a white arrow pointing rightward in the drawing. Hereinafter, in FIG. 7, the magnetization direction is indicated by a white arrow. In the first ferromagnetic free layer 54 and the second ferromagnetic free layer 56, the saturation magnetization of the first ferromagnetic free layer 54 is smaller than the saturation magnetization of the second ferromagnetic free layer 56, that is, the first Consider the case where I _c1 <I _c2 , where I _c1 and I _c2 are the magnetization reversal critical current densities in the ferromagnetic free layer 54 and the second ferromagnetic free layer 56, respectively.

First, when a sufficiently large current I (I> I _c2 ) is passed from the upper electrode 57 toward the lower electrode 50, electrons flow from the lower electrode 50 toward the upper electrode 57. Due to the interaction with the magnetization inside, the magnetization directions of the first ferromagnetic free layer 54 and the second ferromagnetic free layer 56 are parallel to the magnetization direction of the ferromagnetic pinned layer 52 (rightward in the drawing). This state is the theoretical value “0” (FIG. 7A). In this state, when a current I of I _c1 <I <I _c2 is passed from the lower electrode 50 to the upper electrode 57, the interaction between the electron spin and the magnetization in the ferromagnetic layer causes the first ferromagnetic free layer 54 to Only the magnetization direction is reversed and turned leftward. On the other hand, the magnetization directions of the second ferromagnetic free layer 56 and the ferromagnetic pinned layer 52 remain rightward in the drawing. This state is assumed to be a theoretical value “1” (FIG. 7B). Further, when a current I of I> I _c2 > I _c1 is passed from the lower electrode 50 to the upper electrode 57 in this state, the second ferromagnetic free layer is caused by the interaction between the electron spin and the magnetization in the ferromagnetic layer. The magnetization direction of 56 is leftward on the page. Therefore, compared with the first state, the magnetization directions of the first ferromagnetic free layer 54 and the second ferromagnetic free layer 56 are reversed to be leftward on the paper surface, and the magnetization direction of the ferromagnetic pinned layer 52 is rightward on the paper surface. Become. This state is assumed to be a theoretical value “2” (FIG. 7C). In this way, ternary information can be recorded for one element by controlling the direction and magnitude of the current flowing through the element. Table 2 shows the relationship between the theoretical value of recorded information and the magnetization direction of each magnetic layer.

Next, a method for reading information recorded in the magnetoresistive element will be described. When information is read, the magnetizations of the first ferromagnetic free layer 54 and the second ferromagnetic free layer 56 do not reverse from the upper electrode 57 toward the lower electrode 50 or from the lower electrode 50 toward the upper electrode 57. A small current I (I <I _c2 <I _c1 ) is passed, and the resistance value of the element is measured. It is known that the resistance value between both electrodes of the element is small when the magnetization directions of the two ferromagnetic free layers are parallel and large when the magnetization directions are antiparallel. Therefore, in the example of this description, the resistance value of the element is the smallest at the theoretical value “0” where the magnetization direction of all the ferromagnetic layers is the right direction on the paper surface, and only the magnetization direction of the first ferromagnetic free layer 54 is the paper surface. The resistance value of the element is the largest at the theoretical value “1” in the left direction, and the theoretical value “2” in which the magnetization directions of the first ferromagnetic free layer 54 and the second ferromagnetic free layer 56 are both in the left direction on the page. The resistance value of the element becomes intermediate. Therefore, it is possible to read information recorded in the element by passing a current through the element and measuring its resistance value.

  The present invention will be described below with reference to examples and comparative examples. However, these examples and comparative examples are merely representative examples for explaining the present invention, and are not intended to limit the present invention.

(Element creation)
In the case of the CPP-GMR element having the structure shown in FIG. 6, the composition and crystal structure of the ferromagnetic free layer are changed, and the following procedures are used for Examples 1 to 3, Comparative Example 1 and Comparative Example 2. A device was created.

Example 1
The lower electrode 30 was formed with a thickness of 100 nm by a DC magnetron sputtering method using Au as a material. Next, an antiferromagnetic layer 31 was formed with a thickness of 15 nm by a DC magnetron sputtering method using IrMn as a material. Next, the ferromagnetic pinned layer 32 was formed with a thickness of 10 nm by a DC magnetron sputtering method using Fe40Co10B as a material. Next, the first intermediate layer 33 was formed with a thickness of 5 nm by a DC magnetron sputtering method using Cu as a material. Next, the first ferromagnetic free layer 34 was formed with a thickness of 3 nm by a DC magnetron sputtering method using Fe30Co20Cr5B as a material. Next, the second intermediate layer 35 was formed with a thickness of 5 nm by a DC magnetron sputtering method using Cu as a material. Next, the second ferromagnetic free layer 36 was formed with a thickness of 3 nm by DC magnetron sputtering using Fe30Co10Cr5B as a material. Next, the upper electrode 37 was formed with a thickness of 100 nm by a DC magnetron sputtering method using Au as a material. Next, a pillar-shaped sample consisting of a rectangle having a side of 300 to 100 nm was prepared by a resist mask method using EB lithography and Ar ion milling. The CPP-GMR element produced in this way was taken as Example 1.

(Comparative Example 1)
Each layer was formed in the same manner as in Example 1 except that the first ferromagnetic free layer 34 was changed to Fe30Co10Cr5B, and an element of Comparative Example 1 was produced.

(Comparative Example 2)
Each layer was formed in the same manner as in Example 1 except that the first ferromagnetic free layer 34 was changed to Ni20Fe20Cr and the second ferromagnetic free layer 36 was changed to Ni20Fe5Cr, and an element of Comparative Example 2 was formed.

(Example 2)
The present embodiment is an example in which a spin injection type magnetization reversal element is TMR. Each layer was formed in the same manner as in Example 1 except that the first intermediate layer 33 and the second intermediate layer 35 were made of Al ₂ O _{3 with} a thickness of 1 nm by RF-sputtering. A device was created.

(Example 3)
In this embodiment, the TMR element is created by MBE. The ferromagnetic pinned layer 32 is Fe20Co10Pt, the first intermediate layer 33 and the second intermediate layer 35 are MgO, the first ferromagnetic free layer 34 is Fe20Co20Ta, and the second ferromagnetic free layer 36 is Fe20Co10Ta. The same procedure as in Example 1 was performed, except that the layer, the ferromagnetic pinned layer, the first intermediate layer, the first ferromagnetic free layer, the second intermediate layer, the second ferromagnetic free layer, and the upper electrode were formed by MBE. The device of Example 3 was created.

(Description of Examples and Comparative Examples)
First, Example 1, Comparative Example 1, and Comparative Example 2 will be described. Example 1, Comparative Example 1 and Comparative Example 2 are examples of CPP-GMR elements. Comparative Example 1 is an example of an element in which two types of ferromagnetic free layers have the same composition as in Example 1. Comparative Example 2 is an example in which the crystal structure of the ferromagnetic free layer is fcc, and is an element having a crystal structure different from that of Example 1.

Next, Example 2 and Example 3 will be described. Examples 2 and 3 are examples of TMR elements. Example 2 is an example of an element in which the intermediate layer is Al ₂ O ₃ . Example 3 is an example of an element formed by MBE with an intermediate layer made of MgO.

(Evaluation)
The magnetoresistance ratio and the average magnetization reversal critical current density were measured for the elements of the examples and comparative examples. The magnetoresistance ratio and the average magnetization reversal critical current density were calculated by measuring the IV curve by the direct current four-terminal method. The average magnetization reversal critical current density was ((Ic ^pap -Ic ^ppp ) / 2) / cell area. Here, Ic ^papp is the case where the first ferromagnetic free layer is antiparallel and the second ferromagnetic free layer is parallel based on the magnetization direction of the ferromagnetic pinned layer, and ^Icppp is the ferromagnetic pinned layer, This is a case where the one ferromagnetic free layer and the second ferromagnetic free layer are all parallel.

In a general spin injection type magnetization reversal element, the average magnetization reversal critical current density is about 10 mA / cm ² , and the magnetoresistance ratio of the CPP-GMR element is generally about 1 to 5%.

  The crystal structure of the ferromagnetic free layer was measured using an X-ray diffractometer, and the tube voltage and tube current were measured at 30 kV and 300 mA, respectively. As a result of confirmation of the structure, the crystal structures of the first and second ferromagnetic free layers were the bcc structure in Examples 1 to 3 and Comparative Example 1, and the fcc structure in Comparative Example 2.

(result)
Table 3 shows the measurement results of the magnetoresistance ratio and the average magnetization reversal critical current density of the elements of Examples 1 to 3, Comparative Example 1 and Comparative Example 3.

The element of Example 1 had a magnetoresistance ratio of 9.5%, an average magnetization reversal critical current density of 0.6 (mA / cm ² ), and had very good characteristics. In contrast, in Comparative Example 1 in which the two types of ferromagnetic free layers have the same composition, although the magnetoresistance ratio is high, the average magnetization reversal critical current density is larger than that in Example 1. This is because the composition of the first ferromagnetic free layer of the element of Comparative Example 1 is the same as that of the second ferromagnetic free layer, so that two layers having the same composition as the ferromagnetic free layer having a low Cr concentration in Example 1 are provided. Therefore, it is considered that Ms is lowered, and therefore magnetization reversal does not occur unless the critical current is high.

  In Comparative Example 2, since the compositions of the first ferromagnetic free layer and the second ferromagnetic free layer are different, the average magnetization reversal critical current density is somewhat lower than that of Comparative Example 1, but Example 1 and Comparative Example Compared to 1, the magnetoresistance ratio is smaller. This is considered to be due to the crystal structure of the ferromagnetic free layer. That is, in Comparative Example 2, it is presumed that the effect of spin-dependent interface scattering was small because the crystal structure of the ferromagnetic free layer was the same fcc structure as that of the intermediate layer and the ferromagnetic pinned layer.

  Next, regarding Example 2 and Example 3, in comparison with Example 1, both of the average magnetization reversal critical current densities were the same as those of Example 1. In addition, the magnetoresistance ratio was much larger than that of Example 1 which is a CPP-GMR element.

  When Example 2 and Example 3 were compared, the average magnetization reversal critical current density was the same, but the magnetoresistance ratio was greater in Example 3 than in Example 2. This is considered to be because the interface between the ferromagnetic free layer and the intermediate layer is flattened by reducing the conduction electron scattering by adopting the MBE method as the film forming method.

  As described above, in the present invention, the multi-value information recording / reproducing is performed by the polarized spin current injection, so that the word line for writing, which has been essential in the past, becomes unnecessary, the number of wirings can be reduced, and the conventional current magnetic field can be reduced. Compared with the recording / reproducing according to the above, it is possible to record / reproduce information with low power consumption.

It is the schematic which shows the basic structure of the conventional MRAM. (A) is a general view and (b) is a cross-sectional view showing the structure of a TMR element. (A) is schematic sectional drawing which shows the structure of the single cell of the conventional multi-value MRAM, (b)-(d) is the 1st ferromagnetic layer and 2nd strong when a magnetic field is generated in this element. It is a figure (example) which shows the direction of magnetization of each magnetic layer of a magnetic layer. It is a figure which shows an example of the memory element which records / reproduces binary information using spin injection by a prior art. (A) And (b) is a figure which shows the behavior of the electron spin and magnetization of the element shown in FIG. It is a figure which shows the structure of the element for performing multi-value recording by laminating | stacking many elements shown in FIG. It is the schematic which shows the structure of the spin injection type | mold magnetization reversal element of this invention. FIG. 7 is a diagram for explaining the operating principle of the spin-injection type magnetization reversal element of the present invention shown in FIG. 6, wherein (a) to (c) are theoretical values “0”, “1”, and “2”, respectively. It is a figure which shows a case.

Explanation of symbols

10, 50 Lower electrode 11, 21 Bit line 12, 22 First ferromagnetic layer 13 Insulating layer 14, 24, 25 Second ferromagnetic layer 15, 26 Word line 16, 27 Write word line 23 Tunnel layer 31, 51 Ferromagnetic layers 32, 52 Ferromagnetic pinned layers 33, 53 First intermediate layers 34, 54 First ferromagnetic free layers 35, 55 Second intermediate layers 36, 56 Second ferromagnetic free layers 37, 57 Upper electrodes A, A2 Magnetic recording layers B1, B2, B3, B4 Intermediate layers C1, C2, C3 Magnetic pinned layer

Claims (6)

  At least the lower electrode, the antiferromagnetic layer, the ferromagnetic pinned layer, the first intermediate layer, the first ferromagnetic free layer, the second intermediate layer, the second ferromagnetic free layer, and the upper electrode were provided on the lower electrode in this order. A spin-injection type magnetization reversal device, wherein the first and second ferromagnetic free layers have a bcc structure, and the first and second ferromagnetic free layers have different magnetization reversal critical current densities. A spin injection type magnetization reversal element characterized by the above.   The ferromagnetic pinned layer, the first ferromagnetic free layer, and the second ferromagnetic free layer are alloys containing two or more elements selected from Co, Fe, or Ni, and these alloys are Cr, V, Mo The spin injection magnetization according to claim 1, further comprising an element selected from W, Ta, B, or Pt, wherein the first ferromagnetic free layer and the second ferromagnetic free layer have different compositions. Inversion element.   The spin injection type magnetization reversal element according to claim 1, wherein the upper electrode is electrically connected to the lower electrode.   4. The spin injection according to claim 1, wherein the first intermediate layer and the second intermediate layer are nonmagnetic metals selected from the group consisting of Cu, Au, Ag, and Al. 5. Type magnetization reversal element. The spin according to any one of claims 1 to 3, wherein the first intermediate layer and the second intermediate layer are insulators selected from the group consisting of Al ₂ O ₃ , SiO _2, and MgO. Injection type magnetization reversal element. 6. The spin-injection type magnetization reversal element according to claim 1, wherein each layer is formed by sputtering, ion beam sputtering, molecular beam epitaxy (MBE), or laser ablation. A spin injection type magnetization reversal element characterized by the above.

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