JP4834834B2 - Tunnel magnetoresistive element, nonvolatile magnetic memory, light emitting element, and three-terminal element - Google Patents

Description

  The present invention relates to a high-power tunnel magnetoresistive element, a nonvolatile magnetic memory equipped with the same, a light-emitting element, and a three-terminal element (device having a three-terminal structure).

The tunnel magnetoresistive element has a basic structure in which an insulating film is sandwiched between two ferromagnetic films. As such a tunnel magnetoresistive element, a tunnel laminated film using aluminum oxide as an insulating film as described in Non-Patent Document 1 is known, but this tunnel laminated film is used industrially. Therefore, a sufficient electrical output signal could not be obtained.
"T.Miyazaki and N. Tezuka, J. Magn. Magn. Mater 139, L231 (1995)"

Recently, it has been reported that by using magnesium oxide as an insulator of a tunnel magnetoresistive element, a magnetoresistance ratio several times larger than that of a tunnel magnetoresistive element using aluminum oxide as an insulating film can be obtained (for example, Non-patent document 2).
Thus, in most cases, a kind of oxide is used as the insulating film of the tunnel magnetoresistive element.
"S.Yuasa et al., Nature Material 3, 868 (2004)"

When a kind of oxide is used as the insulating film of the tunnel magnetoresistive element, if the thickness of the oxide is defined, the characteristics of the tunnel magnetoresistive are determined by the band gap inherent to the oxide. For this reason, it is difficult to artificially manipulate the characteristics of the tunnel magnetoresistance, and it is also difficult to attach new characteristics.
Thus, there has been a strong demand for the development of an insulating film that enables an artificial characteristic manipulation of the tunneling magnetoresistance.

  It is an object of the present invention to propose a tunnel magnetoresistive element that can advantageously meet the above requirements, together with a nonvolatile magnetic memory, a light emitting element and a device having a three-terminal structure.

In order to solve the above-mentioned problems, the inventors have made extensive studies on the material of a tunnel magnetoresistive element, particularly an insulating film, which enables an artificial characteristic manipulation of the tunnel magnetoresistive.
As a result, in a tunnel magnetoresistive element having a basic laminated structure in which an insulating film is sandwiched between ferromagnetic films, the insulating film is expressed by the chemical formula: Mg _1-y X _y O (X: Zn, Ca, Sr, Ba and Cd). By using one or two or more selected oxides represented by 0 <y ≦ 1), new findings have been obtained that the intended purpose is advantageously achieved.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has a chemical formula : Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (excluding y = 1) ) A tunnel magnetoresistive element comprising a material.

2. 2. The tunnel magnetoresistive element according to 1 above, wherein one or both of the ferromagnetic films is a film having a body-centered cubic structure.

3. 3. The tunnel magnetoresistive element according to 1 or 2 above, wherein the insulating film is an oxide having a rock salt structure.

4). It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has two layers. The first insulating layer is MgO, and the second insulating layer is chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd) , 0 <y ≦ 1 (excluding y = 1) ). A tunnel magnetoresistive element characterized by comprising:

5). It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has two layers. And the first insulating layer has a chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (provided that (except y = 1) The oxide represented by ) ) and the second insulating layer are of the chemical formula: Mg _1-z X _z O (X: one or two selected from Zn, Ca, Sr, Ba and Cd) As described above, the tunnel magnetoresistive element is made of an oxide represented by y <z ≦ 1).

6). 6. The tunnel magnetoresistive element according to 4 or 5 above, wherein one or both of the ferromagnetic films is a film having a body-centered cubic structure.

7). It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe, and Ni, while the insulating film has three layers. The first and third insulating layers adjacent to the ferromagnetic film are MgO, and the second insulating layer sandwiched between the first and third insulating layers is a chemical formula: Mg _1-y X _y It is characterized by comprising an oxide represented by O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (excluding y = 1) ) Tunnel magnetoresistive element.

8). 8. The tunnel magnetoresistive element according to 7 above, wherein one or both of the ferromagnetic films is a body-centered cubic film.

9. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe, and Ni, while the insulating film has three layers. The first and third insulating layers adjacent to the ferromagnetic film have a chemical formula: Mg _1-y X _y O (X: one or two selected from Zn, Ca, Sr, Ba and Cd) As described above, the oxide represented by 0 <y ≦ 1 (excluding y = 1) and the second insulating layer sandwiched between the first and third insulating layers have the chemical formula: Mg _1-z X A tunnel magnetoresistive element comprising an oxide represented by _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z ≦ 1).

Ten. 10. The tunnel magnetoresistive element according to 9 above, wherein either one or both of the ferromagnetic films is a film having a body-centered cubic structure.

11． It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has four layers. With the above structure, these insulating layers have the chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 ( However, excluding y = 1) ) and the chemical formula: Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z A tunnel magnetoresistive element, wherein oxides represented by ≦ 1) are alternately laminated.

12． 12. The tunnel magnetoresistive element according to claim 11, wherein one or both of the ferromagnetic films is a film having a body-centered cubic structure.

13. 13. A nonvolatile magnetic memory comprising the tunnel magnetoresistive element according to any one of 1 to 12 above.

14. 13. A light emitting device comprising the tunnel magnetoresistive device according to any one of 7 to 12 above.

15． 11. A three-terminal element having a multilayer insulating film having a three-layer structure according to any one of 7 to 10 as a basic structure, wherein an electrode is provided on the second layer of the multilayer insulating film. Terminal element.

16． 13. A three-terminal element having, as a basic structure, a laminated insulating film having a structure of four or more layers as described in 11 or 12 above, wherein an electrode is provided in an arbitrary layer of the laminated insulating film .

  According to the tunnel magnetoresistive element of the present invention, an artificial characteristic manipulation of the tunnel magnetoresistive can be easily performed. Therefore, by mounting the tunnel magnetoresistive element accompanied by such a novel characteristic, It is possible to obtain a nonvolatile magnetic memory, a light emitting element, and a device having a three-terminal structure that can be easily operated.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a basic structure of a tunnel magnetoresistive element.
In the figure, reference numeral 1 denotes an insulating film, and the insulating film 1 is sandwiched between two ferromagnetic films 2 and 3. Reference numeral 4 is a base film, and 5 is a protective film.
The present invention is characterized in that a special oxide is used as the insulating film 1 in the tunnel magnetoresistive element having the above basic structure.
In other words, in the present invention, such an insulating film 1 has the chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (excluding y = 1) ).
By using an oxide represented by such a chemical formula, it becomes possible to artificially manipulate the tunnel magnetoresistance.

  In addition, as such an oxide, the thing of a rock salt structure adapts more advantageously. Here, the rock salt structure belongs to a cubic system, and means a structure in which different elements are alternately arranged at the corners of a simple cubic lattice. When such a rock salt structure is used, an electron in a specific electronic state is used. (Electrons with s-electron properties with perfect symmetry) have a high tunnel probability, and when the preferentially tunneled electronic state has a high spin polarizability, a huge tunnel magnetoresistance effect appears There is an advantage that you can. For such a rock salt structure, (001) orientation is more advantageous for obtaining a large tunnel magnetoresistance effect.

On the other hand, as the ferromagnetic films 2 and 3, it is necessary to use a material containing at least one selected from Co, Fe and Ni which are ferromagnetic materials. Here, the content of such a ferromagnetic material in the ferromagnetic film is preferably 30 atomic% or more. This is because, if the content is less than 30 atomic%, there arises a problem that the exchange coupling between the magnetic atoms is broken due to the other nonmagnetic atoms contained, resulting in no ferromagnetism.
As such a ferromagnetic film, a film having a body-centered cubic structure is more advantageously adapted. This is because, by using a ferromagnetic film having a body-centered cubic structure, electrons of Δ ₁ band (electronic state having s-electron properties with perfect symmetry) on the (001) plane of the body-centered cubic structure are used. There can preferentially tunnel (001) surface of the insulating film having a rock salt structure, and to its delta ₁ band is completely spin-polarized by the Fermi level E _F, because a large tunnel magnetoresistance effect occurs It is.

The thickness of the insulating film 1 is preferably about 0.4 to 4.0 nm. This is because if the thickness of the insulating film 1 is less than 0.4 nm, a rock salt structure cannot be formed. On the other hand, if the thickness exceeds 4.0 nm, since the resistance is high, a high potential is applied to the insulating film 1 even at a low current. This is because a large tunnel magnetoresistance effect cannot be expected due to the bias. In addition, when the thickness of the insulating film is increased beyond 4.0 nm in a single layer, the film quality tends to deteriorate, and the reduction of the tunnel magnetoresistance effect has been observed.
A more preferable insulating film thickness is in the range of 0.4 to 3.5 nm.

On the other hand, the thickness of each of the ferromagnetic films 2 and 3 is preferably about 0.8 to 20 nm. This is because if the thickness of the ferromagnetic films 2 and 3 is less than 0.8 nm, it becomes non-magnetic due to atomic diffusion between the adjacent insulating film 1 and protective film 5 and the tunnel magnetoresistive effect may not be generated. On the other hand, if the thickness exceeds 20 nm, it becomes difficult to obtain a flat and homogeneous structure due to columnar growth of crystal grains, and the tunnel magnetoresistance effect is reduced.
A more preferable thickness of the ferromagnetic film is in the range of 1 to 10 nm.

Furthermore, in the present invention, the insulating film does not necessarily have to be a single layer, and may be a multilayer of two layers, three layers, or more.
For example, when the insulating film is composed of two layers, any one layer is selected from the chemical formula: Mg _1-y X _y O (X: Zn, Ca, Sr, Ba and Cd selected from two or more types) , 0 <y ≦ 1 (except for y = 1) ) must be used. In addition, MgO can be used for the other layers, but the chemical formula: Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z It is more advantageous to use an oxide represented by ≦ 1).
Then, by forming such a two-layer structure, that is, by adjusting the composition of the first and second insulating films on the ferromagnetic film 2 and depositing them with good lattice matching, a high-quality insulating film 1 is formed and the insulating film 1 is formed. The resistance can be made lower than that when the film 1 is composed of a single layer, and the magnetic coupling between the ferromagnetic films 2 and 3 can be controlled. As a result, device design is facilitated.

Next, when the insulating film is composed of three layers, MgO is used as the first and third insulating layers adjacent to the ferromagnetic film, while the second is sandwiched between the first and third insulating layers. As the insulating layer, the chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (excluding y = 1) It is advantageous to use the oxides represented by ) ).
In addition, by adopting such a three-layer structure, the resistance can be made lower than when the insulating film 1 is composed of a single oxide layer, and the magnetic coupling between the ferromagnetic films 2 and 3 is also controlled. In addition to facilitating device design, the structure of the ferromagnetic film 3 on MgO is in a good state with good crystallinity by making the insulating film 1 have a three-layer structure rather than a two-layer structure. The tunnel magnetoresistance effect can be enhanced.

In the case of such a three-layer structure, the first and third insulating layers adjacent to the ferromagnetic film have chemical formulas: Mg _1-y X _y O (X: Zn, Ca, Sr, Ba and Cd). One or two or more selected from among them, an oxide represented by 0 <y ≦ 1 (excluding y = 1) ), on the other hand, a second insulation sandwiched between the first and third insulation layers As the layer, an oxide represented by the chemical formula: Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba, and Cd, y <z ≦ 1) is used. it can.
Thus, by using an oxide represented by Mg _1-y X _y O for the first and third layers of the three insulating layers and Mg _1-z X _z O for the second layer, Compared with the case, the lattice matching with the ferromagnetic films 2 and 3 can be improved, and the tunnel magnetoresistance effect is further improved.
In the oxides represented by the chemical formulas: Mg _1-y X _y O and Mg _1-z X _z O, the value of z is larger than the value of y because the amount of X in the oxide is smaller There since small lattice mismatch with the ferromagnetic film, the other that X amount to less that that in a homogeneous insulating film of an oxide in contact with the ferromagnetic film can be achieved a large tunnel magnetoresistance obtained, Mg _{1- This is because} the band gap of _z X _z O can be made smaller than the band gap of Mg _1-y X _y O to form a band offset. By adopting such a configuration, the tunnel magnetoresistive effect is also obtained. Application to resonant tunneling effect elements, light-emitting elements, and three-terminal devices can be realized.

Furthermore, in the present invention, the insulating film may have a structure of four or more layers. In this case, as the insulating layer, the chemical formula: Mg _1-y X _y O (X: Zn, Ca, Sr, Ba and Cd One or two or more selected from among the oxides represented by 0 <y ≦ 1 (excluding y = 1) and the chemical formula: Mg _1-z X _z O (X: Zn, Ca, Sr, A structure in which one or more selected from Ba and Cd and oxides represented by y <z ≦ 1) are alternately laminated is preferable.
By adopting such an insulating film having a four-layer structure, it is possible to maintain better matching between the insulating films. As a result, it is easy to improve characteristics such as the tunnel magnetoresistive effect and arbitrarily adjust the characteristics. Because it becomes.

As described above, in accordance with the present invention, as an insulating film for a tunnel magneto-resistance element, the part of the MgO, ZnO and CaO, SrO, BaO, oxides obtained by substituting CdO, etc. _{(Mg 1-y X y O} , Mg 1- by using _z X _z O), the reasons for improving various properties including tunneling magnetoresistance effect, but not been yet elucidated, the inventors presume as follows .
Since the band gap E _g of XO (X: Zn, Ca, Sr, Ba and Cd) is smaller than the band gap E _{g of} MgO, the oxide in which Mg is substituted with X maintains the tunnel magnetoresistance effect. Low resistance can be realized. Due to the effect of reducing the resistance, a device that can be driven at high speed by reducing the resistance of the element can be obtained. When the resistance of the element is constant, the insulating layer is thickened, that is, the interval between the magnetic layers is reduced. Since it can be widened, it is possible to suppress variations between elements due to magnetic coupling between magnetic layers.
In addition, the large tunnel magnetoresistance effect is achieved by aligning the crystal orientations of the rock salt structure of the insulating layer 1 and the body-centered cubic structure of the ferromagnetic layers 2 and 3 to the (001) plane so that the ferromagnetic layers 2 and 3 are completely Since the spin-polarized Δ1 band electrons can preferentially tunnel through the insulating film 1, the composition of X (X: Zn, Ca, Sr, Ba and Cd) in the oxide is adjusted to adjust the insulating layer. Forming the insulating layer 1 by forming a multi-layer 1 with different compositions or improving the lattice matching in the interface between the ferromagnetic layers 2, 3 and the insulating layer 1 or in the insulating layer 1, It improves the tunnel magnetoresistance effect by improving the flatness by suppressing grain growth by addition or multilayering.
Further, by stacking the different oxides added amount of X, if the band offset by the difference in the band gap E _g of the oxide layers of the different compositions resulting sandwich these heterojunctions ferromagnetic films 2 and 3 Therefore, there is a possibility that a quantum well structure with a tunnel magnetoresistive effect can be formed. An increase in the TMR ratio at a potential corresponding to the resonance level of the quantum well structure and the parallel / reverse magnetization of the ferromagnetic films 2 and 3 are possible. It is possible to control the characteristics of the light emitting element and the three-terminal element in the parallel magnetization arrangement state.

Next, in the present invention, a nonvolatile magnetic memory can be manufactured using the tunnel magnetoresistive element as described above.
When the tunnel magnetoresistive element according to the present invention is used in a non-volatile magnetic memory, conventionally, the variation in tunnel magnetoresistance between memory cells due to magnetic coupling of the ferromagnetic films 2 and 3 has been a problem. By increasing the insulating film thickness while maintaining the resistance value, the magnetic coupling between the ferromagnetic films 2 and 3 is weakened, so that variations in tunneling magnetoresistance can be suppressed and the performance of the nonvolatile magnetic memory can be improved.

In the present invention, a light-emitting element can be manufactured using the tunnel magnetoresistive element as described above (however, the insulating film has a three-layer structure or more).
When the tunnel magnetoresistive element according to the present invention is used as a light emitting element, there is an advantage that light emission can be controlled by the magnetization arrangement state of the ferromagnetic films 2 and 3, that is, the light emitting state can be changed by a magnetic field. This makes it possible to directly convert magnetic information into optical information.

Further, in the present invention, the tunnel magnetoresistive element as described above (however, the insulating film has a three-layer structure or more) can also be used for a three-terminal element (device having a three-terminal structure).
First, when the insulating film has a three-layer structure,
MgO is used as the first and third insulating layers adjacent to the ferromagnetic film, while the second insulating layer sandwiched between the first and third insulating layers is represented by the chemical formula: Mg _1-y X _y O ( X: One or more selected from Zn, Ca, Sr, Ba, and Cd, and an oxide represented by 0 <y ≦ 1 (excluding y = 1) ) or a ferromagnetic film As the first and third insulating layers adjacent to each other, the chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 ( However, except for y = 1) ), the second insulating layer sandwiched between the first and third insulating layers has the chemical formula: Mg _1-z X _z O (X: Zn , Ca, Sr, Ba and Cd selected from one or more selected from oxides represented by y <z ≦ 1), and in any case, an electrode is provided on the second layer of the insulating layer Possibly Thus, a three-terminal element can be obtained.

Next, when the insulating film has a structure of four or more layers,
As the insulating layer, chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (except y = 1)) And an oxide represented by the chemical formula: Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z ≦ 1) A three-terminal element can be obtained by alternately stacking layers and providing electrodes on any of these insulating layers.
As described above, by applying the tunnel magnetoresistive element structure according to the present invention to a three-terminal element, characteristics can be obtained in the magnetization arrangement state of the ferromagnetic films 2 and 3 in addition to the conventional control by current or electric field between terminals. There is an advantage that it can be controlled and also has a non-volatile performance capable of maintaining the state immediately after the circuit is cut off without supplying electric charge.

Example 1
FIG. 2 schematically shows a cross section of an example of a tunnel magnetoresistive element according to the present invention.
In FIG. 2, the outline of the configuration of the tunnel magnetoresistive element is the same as that shown in FIG.
The tunnel magnetoresistive element is composed of a base film 4, an orientation control film 6, an antiferromagnetic film 7, a ferromagnetic film (1) 8, a nonmagnetic film 9, a ferromagnetic film (2) 2, an insulating film 1, and a strong film. The magnetic film (3) 3 and the protective film 5 are sequentially laminated. The tunnel magnetoresistance (TRM) ratio is optimized by heat treatment at an appropriate temperature while applying a magnetic field. In the figure, the structure in which the insulating film 1 is sandwiched between the second ferromagnetic film 2 and the third ferromagnetic film 3 is the basic structure of the tunnel magnetoresistive element of the present invention.

In this example, the tunnel magnetoresistive element was produced using a sputtering method. The underlying film 4 is Ta (5 nm) / Ru (50 nm) / Ta (5 nm), the orientation control film 6 is NiFe (5 nm), the antiferromagnetic film 7 is MnIr (8 nm), and ferromagnetic. Co ₅₀ Fe ₅₀ (2.5 nm) was used for the film (1) 8 and Ru (0.8 nm) was used for the nonmagnetic film 9. The ferromagnetic film (2) in _{2 Co 40 Fe 40 B 20 (} 3nm), the ferromagnetic film (3) on _{3 Co 40 Fe 40 B 20 (} 3nm), the protective film 5 Ta (5 nm ) / Ru (15 nm) was used.
Further, as the insulating film 1, three types of MgO (1 nm) single layer, MgO (1.6 nm) single layer, and MgO (1 nm) / ZnO (0.6 nm) double layer structure were used.

For the element processing, a tunnel magnetoresistive element having an area of 0.8 μm × 1.6 μm was fabricated by using photolithography and ion milling.
The tunnel magnetoresistance was measured by a direct current four-terminal method. The TMR ratio is defined as {(R _AP −R _P ) / R _P } × 100, where R _AP and R _P are the magnetizations of the ferromagnetic film 2 and the ferromagnetic film 3 in FIG. The resistance value when parallel and parallel is shown.

FIG. 3 shows a comparison of the magnetic field dependence of the TMR ratio of the tunnel magnetoresistive element in the case where the insulating film is a single layer of MgO (1 nm) and in the case of a double layer structure of MgO (1 nm) / ZnO (0.6 nm). This tunnel magnetoresistive element was heat-treated at 325 ° C. under a magnetic field of 4 kOe.
As shown in the figure, changing the insulating film from MgO (1 nm) monolayer to MgO (1 nm) / ZnO (0.6 nm) bilayer structure not only increases the TMR ratio from 85% to 117%. The amount of shift from the zero magnetic field of the TMR curve corresponding to the magnetization reversal of Co ₄₀ Fe ₄₀ B ₂₀ (3 nm) in the ferromagnetic film 3 is greatly reduced, and symmetric magnetization reversal is exhibited at almost zero magnetic field. It was.
This is because the magnetic interaction between the ferromagnetic film 2 and the ferromagnetic film 3 is reduced by increasing the thickness of the insulating film.

Next, Table 1 shows a product RA of element resistance and element junction area.
As shown in the table, RA is 174Ωμm ² for tunnel magnetoresistive element whose insulating film has MgO (1 nm) / ZnO (0.6 nm) bilayer structure, which is about 1.9 times of 90Ωμm ² obtained with MgO (1 nm). The RA of the MgO (1.6 nm) monolayer with MgO thickened was 795 Ωμm ² , reaching 8.3 times that of MgO (1 nm).

In this embodiment, Co ₄₀ Fe ₄₀ B ₂₀ is used for the ferromagnetic film adjacent to the insulating film, and the structure thereof is a body-centered cubic structure. However, the structure contains one or more of Co, Fe, and Ni, and The composition may include other elements, and one of the ferromagnetic films may have a body-centered cubic structure and the other may have a structure other than the body-centered cubic structure or an amorphous structure.
In addition, the case where the MgO / ZnO bilayer structure is used for the insulating film has been shown, but instead of ZnO, it is replaced with CaO, SrO, BaO, CdO having a band gap Eg smaller than MgO as shown in Table 2. It was confirmed that the same effect can be obtained also in the case of.
Further, Mg _1-y X _y O (X: Zn, Ca, Sr, where Mg is partially or entirely substituted with one or more arbitrary elements of Zn, Ca, Sr, Ba and Cd). One or two or more selected from Ba and Cd, 0 <y ≦ 1 (excluding y = 1) ), the RA or the MgO is smaller than MgO at the same film thickness. It was confirmed that the same effect as the above-mentioned result can be obtained. For example, in Mg _0.5 Zn _0.5 O in which Mg of MgO is replaced with 50 atomic% Zn, RA = 20Ωμm ² in a Mg _0.5 Zn _0.5 O (1.6 nm) monolayer, and MgO (1 nm) / Mg _0.5 Zn _0.5 O (0.6 nm) RA = 200 Ωμm ² for the two-layer structure, which is much smaller than RA = 795 Ωμm ^{2 for} the MgO (1.6 nm) single layer.
Further, Mg _1-y X _y O / Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (where y = In the case of a two-layer structure in which the composition is modulated as in y <z ≦ 1), the same effect of reducing RA was obtained. As an example, Table 1 shows the results when X = Zn, y = 0.1 and z = 0.5: and when X = Zn, y = 0.3 and z = 0.5.

As described above, by composite oxides of substituted or different composition one part of Mg in MgO with another element, simply increasing RA than when thick MgO is effectively suppressed, TMR curve Therefore, it can be seen that the design of the insulating film is extremely effective for device application using tunneling magnetoresistance.
By artificially designing the insulating layer in this way, it is possible to control the magnetic characteristics of the tunnel magnetoresistive element constituting the recording cell of the nonvolatile memory, particularly the MRAM, and the manufacture of the MRAM becomes easy.

Example 2
Next, in the stacked structure of FIG. 2, the insulating film 1 is made of MgO (t _MgO nm) single layer, or MgO (1 nm) / ZnO (t _ZnO nm) double layer structure, or MgO (1 nm) / ZnO (t _ZnO nm). Figure 4 shows the results of investigating the dependence of the TMR ratio on the total barrier thickness (sum of MgO and ZnO thickness) after heat treatment at 325 ° C for a tunnel magnetoresistive element with a three-layer structure of MgO / MgO (1 nm) .
FIG. 5 shows the results of examining the dependence of RA on the total barrier thickness (total thickness of MgO and ZnO) in a similar structure.
Also in this example, Co ₄₀ Fe ₄₀ B ₂₀ was used as the ferromagnetic film, and the structure thereof was a body-centered cubic structure. However, the ferromagnetic film contained one or more of Co, Fe, and Ni and contained other elements. Needless to say, one of the ferromagnetic films may have a body-centered cubic structure and the other may have a structure other than the body-centered cubic structure or an amorphous structure.

As shown in FIGS. 4 and 5, the MgO (1 nm) / ZnO (t _ZnO nm) barrier maintains a lower resistance RA than the MgO single layer barrier, and the TMR ratio increases until t _MgO + t _ZnO = 2. However, the TMR ratio decreased when t _MgO + t _ZnO > 2. The reason for the high TMR ratio in the MgO barrier is that MgO is oriented in the (001) plane of the rock salt structure. Therefore, such deterioration of TMR characteristics is caused by a decrease in (001) orientation and a change in structure because it tries to shift from a structure similar to MgO where MgO becomes thicker on MgO to a structure that is essentially stable in ZnO. Then, it is thought.
On the other hand, by using MgO (1 nm) / ZnO (t _ZnO nm) / MgO (1 nm) as a barrier, the TMR ratio of 212% is the same as that of MgO single layer even in the region of t _MgO + t _ZnO > 2. It was obtained, and a lower resistance RA than that of the MgO single layer was realized.

From the above results, it can be seen that the barrier of the MgO / ZnO / MgO trilayer structure is effective for achieving both a high TMR ratio and a low RA.
In this example, a typical result of the MgO layer having a thickness of 1 nm was shown. However, the same tendency was obtained even when the MgO thickness was changed, and MgO as shown in Table 2 instead of ZnO. It can be obtained the same effect even when the place of CaO or SrO, BaO, a CdO having a smaller band gap E _g than was confirmed.
Further, Mg _1-y X _y O (X: Zn, Ca, Sr, where Mg is partially or entirely substituted with one or more arbitrary elements of Zn, Ca, Sr, Ba and Cd). MgO / Mg _1-y X _y O / MgO composite film composed of one or more selected from Ba and Cd, 0 <y ≦ 1 (except y = 1) ), and Mg _{1 -y X y O / Mg 1-} z X z O / Mg 1-y X y O (X: Zn, Ca, Sr, one or more kinds chosen from among Ba and Cd, 0 <y ≦ 1 ( However, except for y = 1) , in the case of a multi _- layer barrier in which a composition is modulated as in y <z ≦ 1) and a multilayer barrier in which Mg _1-y X _y O / Mg _1-z X _z O is repeatedly laminated In addition, it has been confirmed that the same effect as described above can be obtained.

Example 3
When band offsets are generated by heterojunction of dissimilar insulating materials, sandwiching these heterojunctions with a ferromagnetic film increases the TMR ratio at a potential corresponding to the resonance level of the quantum well or increases the ferromagnetic film It is possible to control the characteristics of the light emitting element and the three-terminal element in the parallel / antiparallel magnetization arrangement state of the magnetization.
For example, as shown in FIG. 6, when the tunnel magneto-resistance element having an intermediate layer of barrier a and quantum well having a three-layer structure between the ferromagnetic layers, and applying a potential V ₁ corresponding to the resonance level epsilon _1, When the magnetizations of the two ferromagnetic layers are parallel, the spin-polarized electrons are not scattered and can tunnel through the barrier. On the other hand, even if the potential V ₁ corresponding to the resonance level ε ₁ is applied, if the magnetizations of the two ferromagnetic layers are antiparallel, the spin-polarized electrons are scattered by one ferromagnetic electrode.

Therefore, as shown in FIG. 7, when the magnetizations of the two ferromagnetic layers are arranged in parallel, a characteristic negative resistance characteristic can be obtained by the resonant tunneling effect.
On the other hand, when the magnetizations of the two ferromagnetic layers are antiparallel, the spin-polarized current is scattered by the ferromagnetic layer, and the negative resistance characteristic is reduced or eliminated.
Therefore, a divergent increase in the TMR ratio is expected at the potential V ₁ corresponding to the resonance level ε ₁ , and a structure in which such an insulator is mixed and combined is expected as a high-power tunnel magnetoresistive device.

FIG. 8 is a band diagram obtained from theoretical calculation in an MgO / ZnO / MgO insulating layered structure sandwiched between Fe ferromagnetic films. From this result, the band offset of the conduction band is 4.5 to 4.7 eV, and the valence band. It can be seen that the band offset is 0.2 eV. Here, MgO and ZnO were used, but the band offset can be changed arbitrarily by combining Mg—X—O containing X = (Zn, Ca, Sr, Ba, Cd) into a heterojunction. As a result, the resonance level of the quantum well can be changed. As a result, the tunnel magnetoresistance ratio can be increased at an arbitrary applied potential, or a light emitting element or a three-terminal element controlled by the tunnel magnetoresistance can be designed.
Note that Mg—X—O may be doped with another impurity element that serves as a donor or an acceptor. Further, the ferromagnetic film may contain other elements as long as it contains one or more kinds of Co, Fe, and Ni in a predetermined amount or more.

It is the schematic diagram which showed the basic structure of the tunnel magnetoresistive element of this invention. It is the schematic diagram which showed an example of the structure of the tunnel magnetoresistive element of this invention. It is the figure which showed an example of the magnetic field dependence of the magnetoresistive ratio of the tunnel magnetoresistive element of this invention. It is the figure which showed an example of the barrier thickness dependence of the magnetoresistive ratio of the tunnel magnetoresistive element of this invention. It is the figure which showed an example of barrier thickness dependence of RA (product of element resistance and junction area) of the tunnel magnetoresistive element of this invention. It is a schematic diagram of the resonant tunnel of the tunnel magnetoresistive element of this invention. It is a schematic diagram of the electric current dependency of the current I-potential V curve and the tunnel magnetoresistance ratio of the tunnel magnetoresistive element of the present invention. It is the figure which showed an example of the band structure of the tunnel magnetoresistive element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating film 2 Ferromagnetic film 3 Ferromagnetic film 4 Base film 5 Protective film 6 Orientation control film 7 Antiferromagnetic film 8 Ferromagnetic film 9 Nonmagnetic film

Claims (16)

It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has a chemical formula : Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (However, y = 1 is excluded.) The tunnel magnetoresistive element characterized by comprising.   2. The tunnel magnetoresistive element according to claim 1, wherein one or both of the ferromagnetic films is a film having a body-centered cubic structure.   3. The tunnel magnetoresistive element according to claim 1, wherein the insulating film is an oxide having a rock salt structure. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has two layers. The first insulating layer is MgO, and the second insulating layer is chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd) , 0 <y ≦ 1 (excluding y = 1) ). A tunnel magnetoresistive element characterized by comprising: It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has two layers. And the first insulating layer has a chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (provided that (except y = 1) The oxide represented by ) ) and the second insulating layer are of the chemical formula: Mg _1-z X _z O (X: one or two selected from Zn, Ca, Sr, Ba and Cd) As described above, the tunnel magnetoresistive element is made of an oxide represented by y <z ≦ 1).   6. The tunnel magnetoresistive element according to claim 4, wherein one or both of the ferromagnetic films are films having a body-centered cubic structure. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe, and Ni, while the insulating film has three layers. The first and third insulating layers adjacent to the ferromagnetic film are MgO, and the second insulating layer sandwiched between the first and third insulating layers is a chemical formula: Mg _1-y X _y It is characterized by comprising an oxide represented by O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 (excluding y = 1) ) Tunnel magnetoresistive element.   8. The tunnel magnetoresistive element according to claim 7, wherein one or both of the ferromagnetic films are films having a body-centered cubic structure. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe, and Ni, while the insulating film has three layers. The first and third insulating layers adjacent to the ferromagnetic film have a chemical formula: Mg _1-y X _y O (X: one or two selected from Zn, Ca, Sr, Ba and Cd) As described above, the oxide represented by 0 <y ≦ 1 (excluding y = 1) and the second insulating layer sandwiched between the first and third insulating layers have the chemical formula: Mg _1-z X A tunnel magnetoresistive element comprising an oxide represented by _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z ≦ 1).   The tunnel magnetoresistive element according to claim 9, wherein either one or both of the ferromagnetic films is a body-centered cubic film. It has a basic structure in which an insulating film is sandwiched between two ferromagnetic films, and the ferromagnetic film has a composition containing at least one selected from Co, Fe and Ni, while the insulating film has four layers. With the above structure, these insulating layers have the chemical formula: Mg _1-y X _y O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, 0 <y ≦ 1 ( However, excluding y = 1) ) and the chemical formula: Mg _1-z X _z O (X: one or more selected from Zn, Ca, Sr, Ba and Cd, y <z A tunnel magnetoresistive element, wherein oxides represented by ≦ 1) are alternately laminated.   12. The tunnel magnetoresistive element according to claim 11, wherein one or both of the ferromagnetic films is a body-centered cubic structure film.   A nonvolatile magnetic memory comprising the tunnel magnetoresistive element according to claim 1.   13. A light emitting device comprising the tunnel magnetoresistive device according to any one of claims 7 to 12.   11. A three-terminal element having, as a basic structure, a laminated insulating film having a three-layer structure according to claim 7, wherein an electrode is provided on a second layer of the laminated insulating film. 3-terminal element.   13. A three-terminal element having, as a basic structure, a laminated insulating film having a structure of four or more layers according to claim 11 or 12, wherein an electrode is provided on an arbitrary layer of the laminated insulating film. element.

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