JP6586872B2 - Magnetoresistive element and method for manufacturing magnetoresistive element - Google Patents

Description

  The present invention relates to a magnetoresistive effect element and a method for manufacturing the magnetoresistive effect element.

  Giant magnetoresistive (GMR) elements composed of a multilayer film of a ferromagnetic layer and a nonmagnetic layer, and tunnel magnetoresistive (TMR) elements using an insulating layer (tunnel barrier layer, barrier layer) as the nonmagnetic layer are known. Yes. In general, although a TMR element has a higher element resistance than a GMR element, the magnetoresistance (MR) ratio of the TMR element is larger than the MR ratio of the GMR element. Therefore, TMR elements are attracting attention as elements for magnetic sensors, high-frequency components, magnetic heads, and nonvolatile random access memories (MRAM).

  TMR elements can be classified into two types according to the difference in the mechanism of electron tunneling. One is a TMR element that uses only the oozing effect (tunnel effect) of the wave function between the ferromagnetic layers. The other is TMR, which is dominated by coherent tunneling (only electrons having a specific wave function symmetry) utilizing the conduction of specific orbits of a nonmagnetic insulating layer that tunnels when tunneling occurs. It is an element. It is known that a TMR element in which a coherent tunnel is dominant can obtain a larger MR ratio than a TMR element using only the tunnel effect.

  In a magnetoresistive element, in order to obtain a coherent tunnel effect, the two ferromagnetic metal layers and the tunnel barrier layer are crystalline with each other, and the interface between the two ferromagnetic metal layers and the tunnel barrier layer is crystallographically continuous. It is necessary to become.

MgO is known as a tunnel barrier layer capable of obtaining a coherent tunnel effect. Patent Documents 1 and 2 describe that a coherent tunnel effect can be obtained even in (MgZn) O in which a part of Mg in MgO is replaced with Zn.
In addition to this, Patent Document 3 reports MgAl ₂ O ₄ having a spinel structure as a material replacing MgO. Patent Document 4 describes that MgAl ₂ O ₄ having an irregular spinel structure is used for a tunnel barrier layer.

US Patent Application Publication No. 2008/0138660 JP 2012-204348 A Japanese Patent No. 5586028 JP 2013-175615 A

  However, although the magnetoresistive effect elements described in Patent Documents 1 to 4 have a high MR ratio, there is a problem that the area resistance RA is large.

  As a result, the magnetoresistive effect elements described in Patent Documents 1 to 4 cannot sufficiently cope with a high frequency response. This problem is particularly noticeable in miniaturized magnetoresistive elements. Moreover, since it has high element resistance, it is necessary to apply a high voltage, and there also exists a problem that noise increases.

  In addition, the tunnel barrier layer using the materials described in Patent Documents 1 and 2 has a problem that the MR ratio is greatly lowered when the bias voltage applied to the TMR element is increased.

Patent Documents 3 and 4 describe that a high MR ratio can be obtained even under a high bias voltage by reducing lattice mismatch in a tunnel barrier layer having a spinel structure represented by MgAl ₂ O ₄ . . However, there is no known TMR element that can obtain a high MR ratio even under a high bias voltage by using a tunnel barrier layer having a crystal structure close to the NaCl structure typified by MgO. When combined with a ferromagnetic material having a BCC structure, a higher MR ratio can be obtained with a tunnel barrier layer having a crystal structure close to a NaCl structure. This is because the coherent tunnel is caused by band symmetry. When the symmetry of the crystal is lowered, an electron band is formed and the number of electrons that cause a coherent tunnel is reduced, leading to a reduction in MR ratio. In the case of MgAl ₂ O ₄ having a spinel structure, the MR ratio is reduced as compared with the tunnel barrier layer having a crystal structure close to the NaCl structure, but it is known that the reduction width is small. On the other hand, in the case of MgAl ₂ O ₄ having a spinel structure, it can be adjusted to an arbitrary lattice constant according to the ferromagnetic material, so that it is considered that the bias dependency of the applied voltage is good.

  In future devices such as magnetic sensors and MRAMs, there is a great need for low-resistance TMR elements. Further, there is a greater need for a TMR element having a low resistance and a high MR ratio.

  For example, magnetic sensors that can observe minute magnetic fields such as geomagnetism and biomagnetism are required. In order to observe such a small magnetic field, the influence of noise cannot be ignored. For this reason, when a low-resistance magnetoresistive element is used, measurement with less noise can be performed. Therefore, a TMR element having a low resistance and a high MR ratio is required.

  Further, for example, in MRAM, high-speed driving is required in the writing operation. The writing operation is performed by changing the magnetization direction of the ferromagnetic layer of the magnetoresistive effect element. The direction of magnetization of the ferromagnetic layer changes as the spin-polarized current acts on the spin of the ferromagnetic layer. That is, in order to perform a writing operation at high speed, a low resistance TMR element is required.

  However, the magnetoresistive effect elements described in Patent Documents 1 to 4 cannot meet such needs.

  The present invention has been made in view of the above problems, and an object thereof is to provide a magnetoresistive element having a small sheet resistance.

The present inventors can obtain a magnetoresistive element having a small area resistance while suppressing a decrease in MR ratio by replacing predetermined ions in the tunnel barrier layer with other ions having different valences. The headline and the present invention were completed.
That is, this invention provides the following means in order to solve the said subject.

(1) A magnetoresistive effect element according to an aspect of the present invention includes a first ferromagnetic metal layer, a second ferromagnetic metal layer, and between the first ferromagnetic metal layer and the second ferromagnetic metal layer. The tunnel barrier layer is expressed by a composition formula A _1-x A ′ _x O (A is a divalent cation, and A ′ is a monovalent cation). It is made of a nonmagnetic oxide having a cubic crystal structure, and the space group of the crystal structure is any one selected from the group consisting of Pm3m, I-43m, and Pm-3m, in the basic lattice of the crystal structure The number of A ions in is greater than the number of A ′ ions.

(2) In the magnetoresistive effect element according to (1), A in the composition formula may be at least one selected from the group consisting of beryllium, magnesium, and zinc.

(3) In the magnetoresistive effect element according to any one of (1) and (2), A ′ in the composition formula may be at least one selected from the group consisting of lithium, sodium, and potassium. .

(4) In the magnetoresistive effect element according to any one of (1) and (2), A ′ in the composition formula is lithium, and x in the composition formula satisfies 0 <x ≦ 0.04 Also good.

(5) In the magnetoresistive effect element according to any one of (1) and (2), A ′ in the composition formula is sodium, and x in the composition formula satisfies 0 <x ≦ 0.03 Also good.

(6) In the magnetoresistive effect element according to any one of (1) and (2), A ′ in the composition formula is potassium, and x in the composition formula satisfies 0 <x <0.02. Also good.

(7) A method of manufacturing a magnetoresistive element according to one aspect of the present invention is the method of manufacturing a magnetoresistive element according to any one of (1) to (6) above, A film forming step for forming a metal or alloy containing ions and the oxide containing the monovalent ions and the divalent ions; and an oxidation step for oxidizing the formed laminate.

(8) In the film forming step of the method of manufacturing a magnetoresistive effect element according to (7), the oxide containing the monovalent ions is simultaneously formed with the oxide containing the monovalent ions and the divalent ions. An object may be further formed into a film.

(9) In the method of manufacturing a magnetoresistive effect element according to (8), the oxide containing monovalent ions is coated with a metal or alloy containing divalent ions, and the film forming step Prior to this, the coating may be removed.

  According to the spintronic device according to one embodiment of the present invention, it is possible to provide a magnetoresistance effect device having a small sheet resistance.

It is a cross-sectional schematic diagram of the magnetoresistive effect element which concerns on 1 aspect of this invention. It is a side surface schematic diagram of a magnetoresistive effect apparatus provided with the magnetoresistive effect element which concerns on 1 aspect of this invention. It is the schematic diagram which planarly viewed the magnetoresistive effect apparatus from the lamination direction. Is a graph showing the change in the area resistance when changing the range ratio 0 of <x <0.06 of Mg and Li in the composition ratio of the tunnel barrier layer _{(Mg 1-x Li x O} ). Is a graph showing the change in the area resistance when changing the ratio of Mg and Li in the range of 0 <x ≦ 0.5 in the composition ratio of the tunnel barrier layer _{(Mg 1-x Li x O} ). Is a view showing a change in the tunnel barrier layer _{(Mg 1-x Li x O} ) 0 ratio of Mg and Li in the composition ratio of <x <0.06 MR ratio when changed in the range of. It is a view showing a change in the tunnel barrier layer _{(Mg 1-x Li x O} ) Mg and Li ratio of 0 <x ≦ 0.5 MR ratio when changing the range of the composition ratio of. Is a graph showing the change in the area resistance when changed in the range ratio of 0 <x <0.05 of Mg and Na in the composition ratio of the tunnel barrier layer _{(Mg 1-x Na x O} ). It is a graph showing the change in the area resistance when changing the ratio of Mg and Na in the range of 0 <x ≦ 0.5 in the composition ratio of the tunnel barrier layer _{(Mg 1-x Na x O} ). Is a view showing a change in the tunnel barrier layer _{(Mg 1-x Na x O} ) 0 ratio of Mg and Na in the composition ratio of <x <0.05 MR ratio when changed in the range of. Is a view showing a change in the tunnel barrier layer _{(Mg 1-x Na x O} ) Mg and Na ratio of 0 <x ≦ 0.5 MR ratio when changing the range of the composition ratio of. Is a graph showing the change in the area resistance when changed in the range ratio of 0 <x <0.03 of Mg and K in the composition ratio of the tunnel barrier layer _{(Mg 1-x K x O} ). Is a graph showing the change in the area resistance when changing the ratio of Mg and K in the range of 0 <x ≦ 0.5 in the composition ratio of the tunnel barrier layer _{(Mg 1-x K x O} ). Is a view showing a change in the tunnel barrier layer _{(Mg 1-x K x O} ) 0 ratio of Mg and K in the composition ratio of <x <0.03 MR ratio when changed in the range of. It is a view showing a change in the tunnel barrier layer _{(Mg 1-x K x O} ) Mg and K ratio of 0 <x ≦ 0.5 MR ratio when changing the range of the composition ratio of.

  Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention.

  FIG. 1 is a schematic cross-sectional view of a magnetoresistive element according to one embodiment of the present invention. A magnetoresistive effect element 10 according to an aspect of the present invention includes a first ferromagnetic metal layer 1, a second ferromagnetic metal layer 2, and a tunnel barrier layer 3. As shown in FIG. 1, the first ferromagnetic metal layer 1 may be laminated on an underlayer 5 provided on the substrate 4 and is in contact with the tunnel barrier layer 3 of the second ferromagnetic metal layer 2. A cap layer 6 may be provided on the surface opposite to the surface.

(Tunnel barrier layer)
The tunnel barrier layer 3 is made of a nonmagnetic insulating material. The film thickness of the tunnel barrier layer 3 is generally 3 nm or less. When the tunnel barrier layer 3 is sandwiched between the metal materials, the electron wave function of the atoms of the metal material spreads beyond the tunnel barrier layer 3, so that a current flows despite the presence of an insulator on the circuit. The magnetoresistive element 10 has a structure in which the tunnel barrier layer 3 is sandwiched between ferromagnetic metal materials (the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2), and the respective magnetization directions of the sandwiched ferromagnetic metals. The resistance value is determined by the relative angle.

  The magnetoresistive effect element 10 includes a device using a normal tunnel effect and a device having a dominant coherent tunnel effect in which a trajectory at the time of tunneling is limited. In the normal tunnel effect, the magnetoresistance effect is obtained by the spin polarizability of the ferromagnetic material, but in the coherent tunnel, the orbit at the time of tunneling is limited. Therefore, in the magnetoresistive effect element in which the coherent tunnel is dominant, an effect higher than the spin polarizability of the ferromagnetic metal material can be expected. In order to exhibit the coherent tunnel effect, the ferromagnetic metal material and the tunnel barrier layer 3 must be crystallized and bonded in a specific orientation.

The crystal structure of the tunnel barrier layer 3 is cubic and has any one space group selected from the group consisting of Pm3m, I-43m, and Pm-3m.
The cubic structure having symmetry of the space group Pm3m is a NaCl structure, and the cubic structure having symmetry of the space groups I-43m and Pm-3m is a structure distorted from the NaCl structure.
The NaCl structure is the same in crystal structure as MgO conventionally used for the tunnel barrier layer 3. Therefore, when the tunnel barrier layer 3 having the NaCl structure is sandwiched between the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2, a coherent tunnel effect can be generated. In addition, it was confirmed that the coherent tunnel effect was exhibited even in a cubic structure having symmetry of space groups I-43m and Pm-3m slightly distorted from the NaCl structure. Whether the tunnel phenomenon is caused by the coherent tunnel effect or not can be estimated from the MR ratio. In the case of TMR using a general ferromagnetic material such as iron, the upper limit of the MR ratio is considered to be about 80%. Therefore, when the MR ratio exceeds about 80%, it can be considered that the coherent tunnel effect is developed.

The tunnel barrier layer 3 is represented by a composition formula A _1-x A ′ _x O (A is a divalent cation and A ′ is a monovalent cation). In addition, the composition formula described in this specification shows the stoichiometric composition formula of the tunnel barrier layer 3, and the shift | offset | difference of the composition of the range which has the effect of invention is accept | permitted. For example, a composition formula A _1-x A ′ _x O _1-δ in which oxygen deficiency or the like that generally occurs is also included in the range of the composition formula A _1-x A ′ _x O.

The tunnel barrier layer represented by the composition formula A _1-x A ′ _x O has a part of divalent ions (A ions: for example, Mg ²⁺ ) compared to MgO widely used as a tunnel barrier layer. The difference is that it is substituted by a monovalent ion (A ′ ion).

When a part of divalent ions (A ions: for example, Mg ²⁺ ) is replaced by monovalent ions (A ′ ions), the area resistance RA of the magnetoresistive effect element 10 is greatly reduced. That is, a low resistance magnetoresistance effect element can be obtained.
Here, since MgAl ₂ O ₄ described in Patent Documents 3 and 4 has Mg and Al introduced into the A site and B site of the spinel structure, it does not replace ions having different valences. The effect of lowering the sheet resistance RA cannot be sufficiently obtained.

  When an ion with a different valence is introduced into the site of a divalent ion, the electronic state (band structure) of the tunnel barrier layer 3 changes. Specifically, an impurity level is formed in the band structure by introducing an ion of another valence into the site of a divalent ion that originally exists. When the impurity level is formed, a detour for electron conduction is formed, and the barrier barrier height (barrier height) in the electronic state between the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 and the tunnel barrier layer 3 is formed. ) Becomes lower. As a result, electrons are easily conducted between the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 and the tunnel barrier layer 3, and the resistance of the magnetoresistive effect element 10 is reduced. This effect is particularly remarkable when monovalent ions are substituted for divalent ions. When divalent is changed to trivalent, the resistance is not easily changed because the amount of oxygen is adjusted along with the distortion of the crystal lattice. However, when divalent is changed to monovalent, the crystal lattice is distorted but the MgO crystal structure is maintained. As a result, the amount of oxygen is hardly adjusted, and the resistance is greatly reduced.

At this time, the maximum value of the MR ratio slightly decreases due to the lower barrier height. However, the decrease in MR ratio is slight, and a magnetoresistance effect element having a high MR ratio and a low resistance can be obtained. There is a strong need for such a low-resistance magnetoresistive element 10 in order to realize a high-frequency response, noise reduction, etc. in a narrow region such as a miniaturized magnetic head.
Here, the maximum value of MR ratio means the maximum value of MR ratio that can be obtained during normal operation of the magnetoresistive effect element, and can maintain a high MR ratio when a high bias voltage is applied. Have different meanings.

In the composition formula A _1-x A ′ _x O of the tunnel barrier layer 3, A is a divalent cation and A ′ is a monovalent cation.

A is preferably a nonmagnetic divalent cation, more preferably at least one selected from the group consisting of beryllium, magnesium and zinc, and more preferably at least magnesium.
Since the metastable crystal structure is the same when the divalent ions are composed only of beryllium and zinc, a tunnel barrier layer having a coherent tunnel can be obtained. Moreover, the thing containing magnesium as a bivalent ion can obtain a coherent tunnel stably, and can raise MR ratio.

  A ′ is preferably a nonmagnetic monovalent cation, and more preferably contains at least one selected from the group consisting of lithium, sodium and potassium.

Specifically, for example, Mg _1-x Li _x O, Be _1-x Li _x O, Zn _1-x Li _x O, (Mg, Zn) _1-x Li _x O, (Mg, Be) _{1- x} Li _x O, and those obtained by substituting at least a part of these lithium sites with sodium and potassium can be used.
As the number of constituent elements is increased, impurity levels are more easily formed, and the resistance is lowered. On the other hand, since the barrier height decreases as the number of constituent elements increases, the MR ratio decreases. Depending on the application, each material can be used properly.

In the crystal structure of the tunnel barrier layer 3, the number of A ions constituting the basic lattice is larger than the number of A ′ ions. That is, in the composition formula A _1-x A ′ _x O, the substitution amount is 0 <x <0.5. If the substitution amount is within this range, the lattice constant can be appropriately adjusted without changing the crystal structure. As a result, the consistency of the crystal structure with the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 described later can be improved, and the magnetoresistive element 10 maintains a sufficient MR ratio even under a high bias voltage. it can. If the substitution amount is 0 <x <0.5 in the composition formula A _1-x A ′ _x O, the sheet resistance of the magnetoresistive element can be sufficiently reduced as described above.

  Although the above-mentioned thing can be used as A 'substituted, the preferable range of substitution amount changes with ionic radii of A' substituted.

  For example, when the element to be substituted is lithium, 0 <x ≦ 0.04 is preferable, and 0.02 <x <0.04 is more preferable.

  For example, when the element to be substituted is sodium, 0 <x ≦ 0.03 is preferable, and 0.01 <x <0.03 is more preferable.

  For example, when the element to be substituted is potassium, 0 <x ≦ 0.02 is preferable, and 0.01 <x <0.02 is more preferable.

  If the substitution amount of each substitution element is within this range, the low-resistance magnetoresistive element 10 can be obtained without greatly reducing the MR ratio.

  Also, replacing some of the divalent ions with monovalent ions reduces the lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer, and a sufficient MR ratio can be obtained even under a high bias voltage. Produces the effect of being able to.

  In general, when the ferromagnetic metal layer is made of Fe and the tunnel barrier layer is made of MgO, it is known that the lattice constants thereof differ by about 3%. When the tunnel barrier layer is made of MgO, the difference in lattice constant between the ferromagnetic metal layer and the tunnel barrier layer can be somewhat relaxed due to oxygen deficiency. However, the difference in lattice constant due to oxygen vacancies is slight, and the lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer cannot be sufficiently reduced.

On the other hand, in the tunnel barrier layer 3 in the magnetoresistive effect element 10 according to one embodiment of the present invention, a part of divalent ions (A ions: for example, Mg ²⁺ ) are monovalent ions (A ′ ions). ). When predetermined ions are replaced with ions having different ionic radii, the lattice constant of the crystal lattice constituting the tunnel barrier layer 3 changes greatly. As a result, lattice mismatch between the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 and the tunnel barrier layer 3 described later can be reduced. Further, by changing the substitution amount and the ion species to be substituted, the lattice constant of the crystals constituting the tunnel barrier layer 3 can be freely controlled, and the ferromagnetic metal layers (the first ferromagnetic metal layer 1 and the first ferromagnetic metal layer 1 and the first ferromagnetic metal layer 1) can be controlled more easily. 2) The lattice mismatch between the ferromagnetic metal layer 2) and the tunnel barrier layer 3 can be reduced.

The magnetoresistive effect element 10 in which the lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer is reduced can obtain a sufficient MR ratio even under a high bias voltage. This is because the lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer is reduced, so that the continuity of crystals at these interfaces is increased and the amount of spin scattering is reduced.
If there is a lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer, spins are scattered at these interfaces. When a high bias voltage is applied, the amount of spin propagating in the magnetoresistive effect element 10 increases, and this influence becomes remarkable.

  As described above, according to the magnetoresistive element 10 according to one aspect of the present invention, lattice mismatch between the ferromagnetic metal layer and the tunnel barrier layer is reduced, spin scattering at these interfaces is suppressed, A sufficient MR ratio can be obtained even under a high bias voltage. As a result, the magnetoresistive effect element 10 according to one embodiment of the present invention can be used for a device to which a high bias voltage is applied, such as a high-sensitivity magnetic sensor, a logic-in memory, and an MRAM.

The amount of decrease in the MR ratio when the bias voltage is applied can be expressed by an index V _half . V _half refers to a bias voltage at which the MR ratio is halved with respect to the MR ratio when a low bias voltage is applied, with a low bias voltage as a reference. The low bias voltage is 1 mV, for example. Further, since the optimum low bias voltage obtained depends on conditions such as the resistance value of the magnetoresistive effect element, the low bias voltage may be at least one-tenth or less of V _half .

(First ferromagnetic metal layer, second ferromagnetic metal layer)
The first ferromagnetic metal layer 1 has a higher holding force than the second ferromagnetic metal layer 2. That is, the magnetization of the first ferromagnetic metal layer 1 is fixed in one direction, and the magnetization direction of the second ferromagnetic metal layer 2 changes relatively, thereby functioning as the magnetoresistive element 10. The first ferromagnetic metal layer 1 is called a fixed layer or a reference layer, and the second ferromagnetic metal layer 2 is called a free layer or a recording layer.

  A known material capable of forming a coherent tunnel can be used for the first ferromagnetic metal layer 1. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni and an alloy that includes one or more of these metals and exhibits ferromagnetism can be used. An alloy containing these metals and at least one element of B, C, and N can also be used. Specifically, Co-Fe and Co-Fe-B are mentioned.

In order to obtain a higher output, it is preferable to use a Heusler alloy such as Co ₂ FeSi. The Heusler alloy includes an intermetallic compound having a chemical composition of X ₂ YZ, where X is a transition metal element or noble metal element of Co, Fe, Ni, or Cu group on the periodic table, and Y is Mn, V It is a transition metal of Cr, Ti or Ti, and can take the elemental species of X, and Z is a typical element of Group III to Group V. Examples thereof include Co ₂ FeSi, Co ₂ MnSi, and Co ₂ Mn _1-a Fe _a Al _b Si _1-b .

  In order to further increase the coercive force of the first ferromagnetic metal layer 1 with respect to the second ferromagnetic metal layer 2, an antiferromagnetic material such as IrMn or PtMn is used as a material in contact with the first ferromagnetic metal layer 1. Also good. Further, in order to prevent the leakage magnetic field of the first ferromagnetic metal layer 1 from affecting the second ferromagnetic metal layer 2, a structure of synthetic ferromagnetic coupling may be used.

Further, when the magnetization direction of the first ferromagnetic metal layer 1 is perpendicular to the laminated surface, it is preferable to use a Co and Pt laminated film. Specifically, the first ferromagnetic metal layer 1 has [Co (0.24 nm) / Pt (0.16 nm)] ₆ / Ru (0.9 nm) / [Pt (0.16 nm) / Co (0.16 nm). )] _{4 /} Ta (0.2 nm) / FeB (1.0 nm).

  As the material of the second ferromagnetic metal layer 2, a ferromagnetic material, particularly a soft magnetic material can be applied. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy containing one or more of these metals, these metals and at least one element of B, C, and N are included. Alloys that can be used can be used. Specific examples include Co—Fe, Co—Fe—B, and Ni—Fe.

  In the case where the magnetization direction of the second ferromagnetic metal layer 2 is perpendicular to the laminated surface, the thickness of the second ferromagnetic metal layer is preferably 2.5 nm or less. Perpendicular magnetic anisotropy can be added to the second ferromagnetic metal layer 2 at the interface between the second ferromagnetic metal layer 2 and the tunnel barrier layer. Further, since the effect of perpendicular magnetic anisotropy is attenuated by increasing the thickness of the second ferromagnetic metal layer 2, it is preferable that the thickness of the second ferromagnetic metal layer 2 is small.

  In order to use the magnetoresistive effect element as the magnetic sensor, it is preferable that the resistance change linearly changes with respect to the external magnetic field. In a general laminated film of ferromagnetic layers, the direction of magnetization tends to be in the laminated plane due to shape anisotropy. In this case, for example, by applying a magnetic field from the outside and making the magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer orthogonal, the resistance change linearly changes with respect to the external magnetic field. However, in this case, a mechanism for applying a magnetic field in the vicinity of the magnetoresistive effect element is necessary, which is not desirable for integration. Therefore, it is preferable that the ferromagnetic metal layer itself has a perpendicular magnetic anisotropy.

(Substrate, base layer)
The substrate 4 is preferably excellent in flatness. In order to obtain a surface with excellent flatness, for example, Si, AlTiC, or the like can be used as a material. For example, in the case of MRAM, a circuit formed of a Si substrate is required. Therefore, when using the magnetoresistive effect element 10 as MRAM, it is preferable to use a Si substrate. Moreover, when using a magnetoresistive effect element as a magnetic head, it is preferable to use the AlTiC board | substrate which is easy to process.

  An underlayer 5 may be formed on the surface of the substrate 1 on the first ferromagnetic metal layer 1 side. When the underlayer 5 is provided, crystallinity such as crystal orientation and crystal grain size of each layer including the first ferromagnetic metal layer 1 laminated on the substrate 4 can be controlled.

The underlayer 5 may be either conductive or insulating, but it is preferable to use a conductive material when energizing the underlayer 5.
For example, as an example, the underlayer 5 has a (001) -oriented NaCl structure, and is selected from the group consisting of Ti, Zr, Nb, V, Hf, Ta, Mo, W, B, Al, and Ce. A nitride layer containing one element can be used.

As another example, the base layer 5 can be a (002) -oriented perovskite conductive oxide layer represented by the composition formula of ABO ₃ . Here, the site A includes at least one element selected from the group of Sr, Ce, Dy, La, K, Ca, Na, Pb, and Ba, and the site B includes Ti, V, Cr, Mn, Fe, and Co. , Ni, Ga, Nb, Mo, Ru, Ir, Ta, Ce, and Pb.

  As another example, the underlayer 5 can be an oxide layer having a (001) -oriented NaCl structure and containing at least one element selected from the group consisting of Mg, Al, and Ce.

  As another example, the underlayer 5 has a (001) -oriented tetragonal structure or cubic structure, and Al, Cr, Fe, Co, Rh, Pd, Ag, Ir, Pt, Au, Mo, W, W A layer containing at least one element selected from the group can be used.

  The underlayer 5 is not limited to a single layer, and a plurality of layers of the above-described examples may be stacked. By devising the configuration of the underlayer 5, the crystallinity of each layer of the magnetoresistive effect element 10 can be increased and the magnetic characteristics can be improved.

(Cap layer)
A cap layer 6 is preferably formed on the surface of the second ferromagnetic metal layer 2 opposite to the tunnel barrier layer 3. The cap layer 6 can suppress element diffusion from the second ferromagnetic metal layer 2. The cap layer 6 also contributes to the crystal orientation of each layer of the magnetoresistive effect element 10. As a result, by providing the cap layer 6, the magnetic resistance of the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 of the magnetoresistive effect element 10 can be stabilized, and the resistance of the magnetoresistive effect element 10 can be reduced. it can.

  The cap layer 6 is preferably made of a highly conductive material. For example, Ru, Ta, Cu, Ag, Au, etc. can be used. The crystal structure of the cap layer 6 is preferably set as appropriate from an fcc structure, an hcp structure, or a bcc structure in accordance with the crystal structure of the adjacent ferromagnetic metal layer. The thickness of the cap layer 6 may be in a range in which a strain relaxation effect is obtained and a decrease in MR ratio due to the shunt is not observed, and is preferably 1 nm or more and 30 nm or less.

(Configuration when using)
FIG. 2 is a schematic side view of a magnetoresistive effect device including the magnetoresistive effect element according to one aspect of the present invention. FIG. 3 is a schematic view of the magnetoresistive effect device viewed in plan from the stacking direction. In the magnetoresistive effect device 20, an electrode layer 11 is formed on the surface of the cap layer 6 opposite to the second ferromagnetic metal layer 2 in the magnetoresistive effect element 10 shown in FIG. A power source 13 and a voltmeter 14 are provided between the electrode layer 11 and the electrode layer 12 provided on the base layer 5. By applying a voltage to the electrode layer 11 and the underlayer 5 by the power source 13, a current flows in the stacking direction of the stacked body including the first ferromagnetic metal layer 1, the tunnel barrier layer 3, and the second ferromagnetic metal layer 2. The applied voltage at this time can be monitored by the voltmeter 14.

  In the magnetoresistive effect device 20 according to one aspect of the present invention, the barrier height is lowered while maintaining the coherent tunnel of the tunnel barrier layer 3 by replacing some of the divalent ions with monovalent ions. Yes. As a result, the sheet resistance RA can be reduced.

Further, in the magnetoresistive effect device 20 according to one aspect of the present invention, crystal lattice mismatch of the first ferromagnetic metal layer 1, the tunnel barrier layer 3, and the second ferromagnetic metal layer 2 is reduced. Therefore, it is possible to prevent spins from being scattered when the first ferromagnetic metal layer 1 passes through the coherent tunnel of the tunnel barrier layer 3 and reaches the second ferromagnetic metal layer 2. That is, the MR ratio can be increased and the reduction of V _half can be suppressed.

(Element shape and dimensions)
The laminated body which consists of the 1st ferromagnetic metal layer 1, the tunnel barrier layer 3, and the 2nd ferromagnetic metal layer 2 which are shown in FIG. 2 is columnar shape. The shape of the laminate in plan view can take various shapes such as a circle, a quadrangle, a triangle, and a polygon, but is preferably a circle from the viewpoint of symmetry. That is, the laminate is preferably cylindrical.

  When the laminate is cylindrical, the diameter in plan view is preferably 80 nm or less, more preferably 60 nm or less, and further preferably 30 nm or less. When the diameter is 80 nm or less, it becomes difficult to form a domain structure in the ferromagnetic metal layer, and it becomes unnecessary to consider a component different from the spin polarization in the ferromagnetic metal layer. Furthermore, if it is 30 nm or less, a single domain structure is formed in the ferromagnetic metal layer, and the magnetization reversal speed and probability are improved. In addition, there is a strong demand for lower resistance in a magnetoresistive element that has been miniaturized.

(Evaluation methods)
A method for evaluating the magnetoresistive effect element will be described with reference to FIGS. As described above, the power supply 13 and the voltmeter 14 are arranged as shown in FIG. 3, and a constant current or a constant voltage is applied to the magnetoresistive effect element. By measuring the voltage or current while sweeping the magnetic field from the outside, the resistance change of the magnetoresistive effect element can be observed.

The MR ratio is generally expressed by the following equation.
MR ratio _{(%) = (R AP -R} P) / R P × 100
R _P is the resistance in the case of parallel first ferromagnetic metal layer 1 and the second magnetization direction of the ferromagnetic metal 2, R _AP is the magnetization of the first ferromagnetic metal layer 1 and the second ferromagnetic metal 2 This is the resistance when the direction is antiparallel.

V _half is obtained, for example, by measuring the MR ratio when a low bias voltage of 1 mV is applied, and specifying the voltage at which the MR ratio is halved while increasing the bias voltage.

In RA, the resistance value obtained by dividing the applied bias voltage by the current flowing in the stacking direction of the magnetoresistive effect element is divided by the area of the surface where each layer is joined, and normalized to the resistance value in unit area. Is. The bias voltage to be applied and the value of the current flowing in the stacking direction of the magnetoresistive effect element can be obtained by measuring with a voltmeter and an ammeter.
In addition, by fitting the electric conduction characteristics obtained from the applied bias voltage and the current density of the current flowing in the stacking direction of the magnetoresistive effect element by the least square method so as to fit the Simons formula based on the WKB approximation, The height of the tunnel barrier (barrier height) can also be calculated.

(Other)
In the above example, the first ferromagnetic metal layer 1 having a large coercive force is provided on the substrate 4 side with respect to the tunnel barrier layer 3. However, the present invention is not limited to this configuration. When the first ferromagnetic metal layer 1 having a large coercive force is on the side opposite to the substrate 4 with respect to the tunnel barrier layer 3, the first ferromagnetic metal layer 1 is on the substrate 4 side with respect to the tunnel barrier layer 3. Although the coercive force is smaller than in the case of the structure, the tunnel barrier layer 3 can be formed taking advantage of the crystallinity of the substrate, so that the MR ratio can be increased.

  As described above, according to the magnetoresistive effect element according to one aspect of the present invention, the impurity level is formed by replacing the divalent ion of the tunnel barrier layer 3 with the monovalent ion, and the magnetoresistive effect element is formed. Can be achieved. Even if impurity levels are formed and the barrier height is lowered, the coherent tunnel is maintained, so that a high MR ratio can be obtained. That is, it is possible to obtain a magnetoresistive element having a high MR ratio and a low resistance.

  In addition, since the crystal lattice matching between the first ferromagnetic metal layer 1 and the second ferromagnetic metal layer 2 and the tunnel barrier layer 3 is enhanced, a sufficient MR ratio can be maintained even under a high bias voltage. Therefore, the magnetoresistance effect element according to one embodiment of the present invention can be used as a memory such as a magnetic sensor or an MRAM. In particular, the magnetoresistive element according to one embodiment of the present invention is effective in a product that is required to be smaller and faster than a conventional magnetic sensor.

(Production method)
The magnetoresistive effect element can be formed using, for example, a magnetron sputtering apparatus. As a film forming method, in addition to a magnetron sputtering method, a thin film forming method such as an evaporation method, a laser ablation method, or an MBE method can be used.
The underlayer, the first ferromagnetic metal layer, the second ferromagnetic metal layer, and the cap layer can be produced by known methods, respectively.

  The tunnel barrier layer includes a film forming step of forming a metal or alloy containing A ions (divalent ions) and an oxide containing A ′ ions (monovalent ions) and A ions (divalent ions). And an oxidation step of oxidizing the deposited film. The film forming process and the oxidation process may be repeated a plurality of times. And a tunnel barrier layer is formed by heat-processing the laminated body after performing the film-forming process and the oxidation process. The oxidation can be performed by plasma oxidation or natural oxidation by introducing oxygen.

  In the film formation step, when an oxide containing A ′ ions (monovalent ions) and A ions (divalent ions) is formed, an oxide containing A ′ ions (monovalent ions) is simultaneously formed. The film may be used as a target. By using an oxide containing A ′ ions (monovalent ions) directly as a target, the amount of substitution of A ′ ions for A ions can be increased.

  When the target is an oxide containing A ′ ions (monovalent ions), the surface of the oxide containing A ′ ions (monovalent ions) is a metal or alloy containing A ions (divalent ions). More preferably, it is coated. For example, monovalent ions such as lithium, sodium, and potassium are difficult to exist stably by themselves. A tunnel barrier layer can be stably produced by coating the surface with a metal or alloy containing A ions in the form of oxides of A ′ ions. The coating can be removed in the deposition chamber before the actual deposition. For example, the coating can be removed by performing a process such as sputtering in a state where no sample is installed.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims. Can be modified or changed.

Example 1
Each layer of the magnetoresistive effect element was produced by film formation using a magnetron sputtering method on a substrate provided with a thermal silicon oxide film.
First, Ta (5 nm) / Ru (3 nm) was formed as a base layer. Thereafter, IrMn (12 nm) / CoFe (10 nm) / Ru (0.8 nm) / CoFe (7 nm) were sequentially laminated as a first ferromagnetic metal layer on the underlayer.

Next, a tunnel barrier layer was produced on the obtained first ferromagnetic metal layer by the following procedure. First, using a Mg target and a Mg _0.985 Li _0.015 O _x alloy composition target, Mg (0.15 nm) / Mg _0.985 Li _0.015 O _x (0.5 nm) / Mg (0. 15 nm) in order. Then, by moving the sample in which the above-described laminate is formed into an oxidation chamber held in an ultrahigh vacuum of 1.0 × 10 ⁻⁸ Pa or less, and introducing Ar and oxygen into the oxidation chamber, Oxidation treatment was performed. The oxidation treatment was performed by natural oxidation, the conditions for natural oxidation were 10 seconds, the partial pressure ratio between Ar and oxygen was 1:10, and the total gas pressure was 0.05 Pa.

The sample is returned to the film formation chamber again, and the oxidized sample is again in order of Mg (0.15 nm) / Mg _0.985 Li _0.015 O _x (0.5 nm) / Mg (0.15 nm). Laminated. And the oxidation process was performed to the sample after re-stacking in the oxidation chamber hold | maintained to the ultrahigh vacuum of 1.0 * 10 <^-8> Pa or less. The oxidation treatment was performed by natural oxidation and inductively coupled plasma oxidation. The natural oxidation time was 30 seconds, the inductively coupled plasma oxidation condition was 5 seconds, the Ar / oxygen partial pressure ratio was 1:20, and the total gas pressure was 0.08 Pa.

In this way, the sample on which the predetermined tunnel barrier layer is formed is moved again to the deposition chamber, and CoFe (5 nm) is formed as the second ferromagnetic metal layer, and Ru (3 nm) / Ta (5 nm) is formed as the cap layer. Filmed.
And the sample in which each layer was laminated | stacked was moved to the annealing apparatus, and it heated for 10 minutes in Ar atmosphere and 450 degreeC environment. Thereafter, heat treatment was performed at 280 ° C. for 6 hours with 8 kOe applied, and a magnetoresistive effect element was manufactured.

(Structural analysis)
The structure of the tunnel barrier layer in the magnetoresistive effect element manufactured in Example 1 was measured by electron diffraction and X-ray diffraction measurements. The tunnel barrier layer in the magnetoresistive element has a ferromagnetic metal layer formed on the top and bottom and cannot be directly measured. Therefore, the tunnel barrier layer was measured before the second ferromagnetic metal layer was laminated. Further, in order to remove the influence of the layer below the tunnel barrier layer, Mg (0.15 nm) / Mg _0.985 Li _0.015 O _x (0.5 nm) / Mg (0.15 nm) are sequentially formed. The film forming process to be sputtered and the oxidation process were repeated 10 times to ensure a sufficient film thickness.

  As a result of X-ray diffraction measurement, the main peak can be indexed due to the symmetry of the space group Pm3m, which is the crystal structure of MgO, and it was confirmed that the structure is similar to that of MgO. Further, in the electron diffraction measurement, a weak peak was confirmed in addition to the peak indexed by the MgO structure. When structural analysis was performed again including the intensity of the newly confirmed weak peak, it was found that the crystal structure of the tunnel barrier layer had a space group I-43m or Pm-3m distorted from the NaCl structure.

(Composition analysis)
The composition ratio of the tunnel barrier layer was determined using the atom probe method. Although the atom probe method is used here, it can also be performed using energy dispersive X-ray analysis (EDS) and electron energy loss spectroscopy (EELS). As a result of analysis, Mg: Li = 0.96: 0.04.

The magnetoresistive effect characteristics (MR ratio) and sheet resistance (RA) of Example 1 thus obtained were measured. The MR ratio when a bias voltage of 0.1 V was applied was 50.6%, and RA was 0.23 Ω · μm ² . At this time, the diameter of the magnetoresistive effect element was 0.1 μm.

The magnetoresistive effect element of Example 1 greatly exceeds the MR ratio (25%) theoretically assumed in the conventional magnetoresistive effect element composed of Fe / MgO / Fe, and has a high MR ratio. is doing. The sheet resistance RA is also less than 1Ω · μm ² required for device application.
That is, in the magnetoresistive effect element of Example 1, low resistance can be realized by substituting a part of divalent magnesium with monovalent lithium. At this time, the MR ratio was not significantly reduced. That is, the magnetoresistive effect element of Example 1 has a high MR ratio and a low resistance.

(Example 2)
The second embodiment is different from the first embodiment only in that the target used when forming the tunnel barrier layer is changed and the composition ratio of the tunnel barrier layer is changed.

In Example 2, a target of Mg _0.8 Zn _0.2 and an alloy target having a composition of Mg _0.77 Zn _0.19 Li _0.04 O _x were used as targets for producing the tunnel barrier layer. Then, Mg ₀ . ₈ Zn _0.2 (0.15 nm) / Mg _0.77 Zn _0.19 Li _0.04 O _x (0.5 nm) / Mg ₀ . Sputtering was performed to obtain ₈ Zn _0.2 (0.15 nm). This film formation step and oxidation step were repeated two sets to produce a tunnel barrier layer. The oxidation process in the tunnel barrier layer and the lamination conditions of the other layers were the same as in Example 1.

(Structural analysis)
The structure of the tunnel barrier layer in the magnetoresistive effect element manufactured in Example 2 was measured by electron beam diffraction and X-ray diffraction measurement. Also in Example 2, as in Example 1, the film forming process and the oxidizing process were repeated 10 times to ensure a sufficient film thickness.

  As a result of X-ray diffraction measurement, the main peak can be indexed due to the symmetry of the space group Pm3m, which is the crystal structure of MgO, and it was confirmed that the structure is similar to that of MgO. Further, in the electron diffraction measurement, a weak peak was confirmed in addition to the peak indexed by the MgO structure. When structural analysis was performed again including the intensity of the newly confirmed weak peak, it was found that the crystal structure of the tunnel barrier layer had a space group I-43m or Pm-3m distorted from the NaCl structure.

(Composition analysis)
As a result of analyzing by the same analysis method as Example 1, it was Mg: Zn: Li = 0.77: 0.19: 0.04.

The magnetoresistance effect characteristics (MR ratio) and sheet resistance (RA) of Example 2 obtained in this way were measured. The MR ratio when a bias voltage of 0.1 V was applied was 38.3%, and RA was 0.16 Ω · μm ² . At this time, the diameter of the magnetoresistive effect element was 0.1 μm.

The magnetoresistive effect element of Example 2 greatly exceeds the MR ratio (25%) theoretically assumed in the conventional magnetoresistive effect element having the structure of Fe / MgO / Fe, and has a high MR ratio. is doing. The sheet resistance RA is also less than 1Ω · μm ² required for device application.
That is, the magnetoresistive effect element of Example 2 has a high MR ratio and a low resistance. Further, compared with Example 1, the sheet resistance RA could be further reduced by adding Zn.

(Example 3)
Example 3 is different from Example 1 only in that the target used when producing the tunnel barrier layer is changed and the composition ratio of the tunnel barrier layer is changed.

In Example 2, an Mg target, an alloy target having a composition of Mg _0.99 Li _0.01 O _x , and a target in which the surface of Li ₂ O was coated with Mg were used as targets for producing the tunnel barrier layer. . Since Li ₂ O easily reacts with moisture in the atmosphere, it was coated with Mg. At the time of actual film formation of the element, Mg coated on the surface of Li ₂ O was removed in a sputtering apparatus. At the time of removal, the inside of the sputtering apparatus was sufficiently high in vacuum, and the Mg on the surface was removed by sputtering treatment. At this time, no sample is installed in the apparatus.
Then, sputtering was performed so that Mg (0.15 nm) / Mg _0.99 Li _0.01 O _x + Li ₂ O (0.5 nm) / Mg (0.15 nm) was achieved in one stacking step. “Mg _0.99 Li _0.01 O _x + Li ₂ O” means that Mg _0.99 Li _0.01 O _x and Li ₂ O were simultaneously sputtered. This film formation step and oxidation step were repeated two sets to produce a tunnel barrier layer. The oxidation process in the tunnel barrier layer and the lamination conditions of the other layers were the same as in Example 1.

(Structural analysis)
The structure of the tunnel barrier layer in the magnetoresistive effect element manufactured in Example 3 was measured by electron beam diffraction and X-ray diffraction measurement. Also in Example 3, as in Example 1, the film forming process and the oxidation process were repeated 10 times to ensure a sufficient film thickness.

  As a result of X-ray diffraction measurement, the main peak can be indexed due to the symmetry of the space group Pm3m, which is the crystal structure of MgO, and it was confirmed that the structure is similar to that of MgO. Further, in the electron diffraction measurement, a weak peak was confirmed in addition to the peak indexed by the MgO structure. When structural analysis was performed again including the intensity of the newly confirmed weak peak, it was found that the crystal structure of the tunnel barrier layer had a space group I-43m or Pm-3m distorted from the NaCl structure.

(Composition analysis)
As a result of analyzing by the same analysis method as Example 1, it was Mg: Li = 0.965: 0.035.

The magnetoresistance effect characteristic (MR ratio) and sheet resistance (RA) of Example 3 obtained in this way were measured. The MR ratio when a bias voltage of 0.1 V was applied was 63.5%, and RA was 0.25 Ω · μm ² . At this time, the diameter of the magnetoresistive effect element was 0.1 μm.

The magnetoresistive effect element of Example 3 greatly exceeds the MR ratio (25%) theoretically assumed in the conventional magnetoresistive effect element having the structure of Fe / MgO / Fe, and has a high MR ratio. is doing. The sheet resistance RA is also less than 1Ω · μm ² required for device application.
That is, the magnetoresistive element of Example 3 has a high MR ratio and a low resistance. Also by including the Li 2 _O is a monovalent oxide target, it is understood that it is possible to increase the amount of substitution Li.

(Example 4)
In Example 4, the MR ratio and RA were measured by changing the target used when producing the tunnel barrier layer and changing the ratio of Mg and Li in the composition ratio. The production conditions other than changing the target were the same as in Example 1.

4 and 5 are diagrams showing changes in sheet resistance when the ratio of Mg and Li in the composition ratio of the tunnel barrier layer is changed. FIG. 4 is an enlarged view of the range of 0 <x <0.06 when the composition formula of the tunnel barrier layer of the magnetoresistive effect element is Mg _1-x Li _x O. FIG. It is measured in the range of x ≦ 0.5. 6 and 7 are diagrams showing changes in the MR ratio when the ratio of Mg to Li in the composition ratio of the tunnel barrier layer is changed. FIG. 6 is an enlarged view of the range of 0 <x <0.06 when the composition formula of the tunnel barrier layer of the magnetoresistive effect element is Mg _1-x Li _x O. FIG. It is measured in the range of x ≦ 0.5.

  As shown in FIG. 4, the sheet resistance (RA) of the magnetoresistive effect element decreases as the amount of Li substitution increases. When x = 0.04, the sheet resistance is hardly reduced. Also, as shown in FIG. 6, the MR ratio of the magnetoresistive element decreases as the amount of Li substitution increases. And when it exceeds x = 0.04, it has fallen significantly. That is, it can be seen that Li functions as an electron or spin scatterer in the substitution region exceeding x = 0.04. Further, as shown in FIG. 5, the sheet resistance can be lowered in the range of 0 <x ≦ 0.5 compared to the case of x = 0. As shown in FIGS. 6 and 7, the MR ratio is also reduced when x ≧ 0.04. However, since the resistance is sufficiently low, it can be applied to various elements. For example, a high frequency element needs impedance matching, and if the resistance is high, sufficient characteristics cannot be obtained. On the other hand, the magneto-optical effect element of Example 4 has an MR ratio higher than that of a general GMR element (about 10%) and realizes a sufficiently low resistance.

(Example 5)
In Example 5, the target used when producing the tunnel barrier layer was changed, the composition formula of the tunnel barrier layer to be formed was Mg _1-x Na _x O, and the ratio of Mg and Na in the composition ratio was changed. MR ratio and RA were measured. The production conditions other than changing the target were the same as in Example 1.

8 and 9 are diagrams showing a change in sheet resistance when the ratio of Mg and Na in the composition ratio of the tunnel barrier layer is changed. FIG. 8 is an enlarged view of the range of 0 <x <0.05 when the composition formula of the tunnel barrier layer of the magnetoresistive effect element is Mg _1-x Na _x O. FIG. It is measured in the range of x ≦ 0.5. 10 and 11 are diagrams showing changes in the MR ratio when the ratio of Mg and Na in the composition ratio of the tunnel barrier layer is changed. FIG. 10 is an enlarged view of the range of 0 <x <0.05 when the composition formula of the tunnel barrier layer of the magnetoresistive element is Mg _1-x Na _x O. FIG. It is measured in the range of x ≦ 0.5.

  As shown in FIG. 8, the sheet resistance (RA) of the magnetoresistive element decreases as the amount of Na substitution increases. And when x = 0.03, the sheet resistance started to increase. Also, as shown in FIG. 10, the MR ratio of the magnetoresistive element decreases as the amount of Na substitution increases. And when it exceeds x = 0.03, it has fallen significantly. That is, it can be seen that Na functions as an electron or spin scatterer in the substitution region exceeding x = 0.03. Further, as shown in FIG. 9, the sheet resistance can be lowered in the range of 0 <x ≦ 0.5 compared to the case of x = 0. Further, as shown in FIGS. 10 and 11, the MR ratio is also decreased when x ≧ 0.03, but since it has a sufficiently low resistance, it can be applied to various elements.

(Example 6)
In Example 6, the target used when forming the tunnel barrier layer was changed, the composition formula of the tunnel barrier layer to be formed was Mg _1-x K _x O, and the ratio of Mg and K in the composition ratio was changed. MR ratio and RA were measured. The production conditions other than changing the target were the same as in Example 1.

12 and 13 are diagrams showing a change in sheet resistance when the ratio of Mg and K in the composition ratio of the tunnel barrier layer is changed. FIG. 12 is an enlarged view of the range of 0 <x <0.03 when the composition formula of the tunnel barrier layer of the magnetoresistive effect element is Mg _1-x K _x O. FIG. It is measured in the range of x ≦ 0.5. 14 and 15 are diagrams showing changes in the MR ratio when the ratio of Mg and K in the composition ratio of the tunnel barrier layer is changed. FIG. 14 is an enlarged view of the range of 0 <x <0.03 when the composition formula of the tunnel barrier layer of the magnetoresistive effect element is Mg _1-x K _x O. FIG. It is measured in the range of x ≦ 0.5.

  As shown in FIG. 12, the sheet resistance (RA) of the magnetoresistive effect element decreases as the K substitution amount increases. Then, when x = 0.02, the sheet resistance started to increase. As shown in FIG. 14, the MR ratio of the magnetoresistive effect element decreases as the K substitution amount increases. And when it exceeds x = 0.02, it will fall significantly. That is, it can be seen that K functions as an electron or spin scatterer in the substitution region exceeding x = 0.02. Further, as shown in FIG. 13, the sheet resistance can be lowered in the range of 0 <x <0.5, compared to the case of x = 0. As shown in FIG. 14 and FIG. 15, when x ≧ 0.02, the MR ratio is also reduced, but since it has a sufficiently low resistance, it can be applied to various elements.

(Comparative Example 1)
Comparative Example 1 is different from Example 1 in that the tunnel barrier layer is MgO. That is, in the film forming process of Example 1, only MgO (0.8 nm) was produced in one sputtering process using a target made of MgO. Other conditions were the same as in Example 1.

(Structural analysis)
The structure of the tunnel barrier layer in the magnetoresistive effect element manufactured in Comparative Example 1 was measured by electron beam diffraction and X-ray diffraction measurement. In Comparative Example 1, as in Example 1, the sputtering process and the oxidation treatment process were repeated 10 times to ensure a sufficient film thickness.

  As a result of X-ray diffraction measurement, the main peak can be indexed due to the symmetry of the space group Pm3m, which is the crystal structure of MgO, and it was confirmed that the structure is similar to that of MgO. Further, in the electron beam diffraction measurement, no peak other than the peak indexed with the MgO structure was confirmed. This shows that MgO was produced as a tunnel barrier layer.

The magnetoresistive effect characteristic (MR ratio) and sheet resistance (RA) of Comparative Example 1 thus obtained were measured. The MR ratio when a bias voltage of 0.1 V was applied was 94.4%, and RA was 0.94 Ω · μm ² . At this time, the diameter of the magnetoresistive effect element was 0.1 μm.

  The MR element of Comparative Example 1 has an extremely high MR ratio. On the other hand, the sheet resistance was high and could not be said to be low resistance.

DESCRIPTION OF SYMBOLS 10 ... Magnetoresistive element, 1 ... 1st ferromagnetic metal layer, 2 ... 2nd ferromagnetic metal layer, 3 ... Tunnel barrier layer, 4 ... Substrate, 5 ... Underlayer, 6 ... Cap layer, 20 ... Magnetoresistive effect Device, 11, 12 ... Electrode layer, 13 ... Power source, 14 ... Voltmeter

Claims (7)

A first ferromagnetic metal layer, a second ferromagnetic metal layer, and a tunnel barrier layer sandwiched between the first ferromagnetic metal layer and the second ferromagnetic metal layer,
The tunnel barrier layer is made of a nonmagnetic oxide having a cubic crystal structure represented by a composition formula A _1-x A ′ _x O (A is a divalent cation, A ′ is a monovalent cation). Become
The space group of the crystal structure is any one selected from the group consisting of Pm3m, I-43m and Pm-3m,
A in the composition formula includes magnesium,
A ′ in the composition formula is at least one selected from the group consisting of lithium, sodium and potassium,
A magnetoresistive element in which the number of A ions in the basic lattice of the crystal structure is larger than the number of A ′ ions. A ′ in the composition formula is lithium,
The magnetoresistive element according to claim 1, wherein x in the composition formula satisfies 0 <x ≦ 0.04. A ′ in the composition formula is sodium,
The magnetoresistive element according to claim 1, wherein x in the composition formula satisfies 0 <x ≦ 0.03. A ′ in the composition formula is potassium,
The magnetoresistive element according to claim 1, wherein x in the composition formula satisfies 0 <x ≦ 0.02. It is a manufacturing method of the magnetoresistive effect element according to any one of claims 1 to 4 ,
A film forming step of forming the metal or alloy containing the divalent ions and the oxide containing the monovalent ions and the divalent ions;
And a method of manufacturing a magnetoresistive element having an oxidation step of oxidizing the deposited laminate. 6. The magnetoresistive element according to claim 5 , wherein in the film forming step, an oxide containing the monovalent ions is further formed simultaneously with the oxide containing the monovalent ions and the divalent ions. Method. The oxide containing monovalent ions is coated with a metal or alloy containing the divalent ions;
The method of manufacturing a magnetoresistive element according to claim 6 , wherein the coating is removed before the film forming step.

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