TUNNEL JUNCTION LAMINATED FILM, MAGNETIC MEMORY ELEMENT, AND MAGNETIC MEMORY

Provided are a tunnel junction stacked film having a high thermal stability, and a magnetic memory element and a magnetic memory using the tunnel junction stacked film. A tunnel junction stacked film 1 includes a recording layer 14 including a first ferromagnetic layer 24 containing boron, a tunnel junction layer 13 adjacent to the recording layer 14, and a reference layer 12 adjacent to the tunnel junction layer 13, wherein the first ferromagnetic layer 24 and the reference layer 12 are magnetized in a perpendicular direction with respect to a film surface, and the recording layer 14 includes a hafnium layer 25 adjacent to the first ferromagnetic layer 24.

TECHNICAL FIELD

The present invention relates to a tunnel junction stacked film, a magnetic memory element, and a magnetic memory.

BACKGROUND ART

A magnetic random access memory (MRAM) using a magnetic tunnel junction (MTJ) element as a memory element has been known as a next-generation nonvolatile magnetic memory in which high-speed properties and high write tolerance can be obtained. A spin transfer torque random access memory (STT-MRAM) element performing magnetization reversal with respect to the magnetic tunnel junction by using spin transfer torque (refer to PTL 1) has been gathering attention as a next-generation magnetic memory element used in the MRAM.

The STT-MRAM element includes a MTJ having a three-layer structure of a ferromagnetic layer (also referred to as a recording layer)/a barrier layer (also referred to as a tunnel junction layer)/a ferromagnetic layer (also referred to as a reference layer). The STT-MRAM element has properties in which the resistance of the element is high in an anti-parallel state in which a magnetization direction of the recording layer and a magnetization direction of the reference layer are antiparallel to each other, and records data by allowing a parallel state and an anti-parallel state to correspond to 0 and 1. In the STT-MRAM element, when a current flows through the MTJ, polarized electron spins flow into the recording layer, and the magnetization direction of the recording layer is reversed by the spin r torque induced by the polarized electron spins. Accordingly, the STT-MRAM element is capable of recording data by switching the parallel state and the anti-parallel state.

Regarding a write current ICOand a thermal stability factor Δ (=E/kBT) of spin injection magnetization reversal in a perpendicular magnetic anisotropy magnetic tunnel junction (perpendicular (p)-MTJ), a relationship is given by the next equation.

In addition, the thermal stability factor Δ is represented by the following formula.

Here, a is a damping constant, e is an elementary charge, h (in the formula, h with a stroke mark) is a Dirac constant, P is a spin polarizability, S is a junction area, KB is a Boltzmann constant, t is a film thickness of the recording layer, T is an absolute temperature, and Keffis an effective magnetic anisotropy constant.

From Formula (1) described above, in order to maintain a high thermal stability factor Δ and to attain a low write current ICO, it is necessary to set a recording layer having high Keffand a low damping constant (a). In general, it is known that the damping constant increases by a material having a large spin orbit interaction. It is known that the spin orbit interaction increases in accordance with an increase in an atomic number.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in a case of miniaturizing the STT-MRAM element as the magnetic memory element in order to attain a magnetic memory having a high density, the thermal stability of the magnetization of the recording layer decreases, the recording layer is less likely to maintain the record of the data, and nonvolatility decreases. For this reason, the thermal stability of the recording layer of the magnetic memory element is required to be improved.

Therefore, the invention has been made in consideration of the problems described above, and an object thereof is to provide a tunnel junction stacked film having a high thermal stability, and a magnetic memory element and a magnetic memory using the tunnel junction stacked film.

Solution to Problem

A tunnel junction stacked film according to the invention includes a recording layer including a first ferromagnetic layer containing boron, a tunnel junction layer adjacent to the recording layer, and a reference layer adjacent to the tunnel junction layer, wherein the first ferromagnetic layer and the reference layer are magnetized in a perpendicular direction with respect to a film surface, and the recording layer includes a hafnium layer adjacent to the first ferromagnetic layer.

A magnetic memory element according to the invention includes the tunnel junction stacked film described above, a first terminal electrically connected to the reference layer, and a second terminal electrically connected to the recording layer, wherein a magnetization direction of the recording layer is reversed by a write current to flow between the first terminal and the second terminal.

A magnetic memory according to the invention includes the magnetic memory element described above.

Advantageous Effects of Invention

According to the invention, the recording layer includes the hafnium layer adjacent to the first ferromagnetic layer, and thus, perpendicular magnetic anisotropy of the first ferromagnetic layer can be improved, and as a result thereof, a thermal stability of the magnetization of the first ferromagnetic layer adjacent to the hafnium layer is improved, and a thermal stability of the recording layer is high. Accordingly, a tunnel junction stacked film having a high thermal stability can be provided, and a magnetic memory element and a magnetic memory having a high thermal stability can be provided.

DESCRIPTION OF EMBODIMENTS

First, the outline of a tunnel junction stacked film of the invention will be described. As illustrated inFIG.1, a tunnel junction stacked film1of the invention is a magnetoresistive effect element including a recording layer14, a tunnel junction layer13adjacent to the recording layer14, and a reference layer12adjacent to the tunnel junction layer13. In the tunnel junction stacked film (hereinafter, also referred to as a MTJ film)1, a resistance value is changed in accordance with whether a magnetization direction of the reference layer12and a magnetization direction of the recording layer14are parallel to each other (a state in which the magnetization directions are approximately the same direction) or antiparallel to each other (a state in which the magnetization directions are different from each other by approximately 180 degrees). In a case of using the MTJ film1in a magnetic memory element, 1-bit data of “0” and “1” is assigned to a parallel state and an anti-parallel state by using the fact that the resistance value of the MTJ film1is different between the parallel state and the anti-parallel state, and thus, data is stored. The MTJ film1is a perpendicular magnetization film in which the recording layer14and the reference layer12are magnetized in a perpendicular direction with respect to a film surface.

The recording layer14includes a first ferromagnetic layer24containing boron, and a hafnium layer (hereinafter, also referred to as a Hf layer)25adjacent to the first ferromagnetic layer24. Further, the recording layer14may include a second ferromagnetic layer, a non-magnetic insertion layer, or the like, described below. The recording layer14is configured such that the first ferromagnetic layer24is magnetized in the perpendicular direction with respect to the film surface, and the magnetization direction can be reversed. The reference layer12includes at least one or more ferromagnetic layers film magnetized in the perpendicular direction with respect to the surface, and is configured such that the magnetization direction is fixed. Note that, herein, in a case where the reference layer12and the recording layer14include a plurality of ferromagnetic layers, the magnetization or the magnetization direction of the reference layer12and the recording layer14simply indicates the magnetization or the magnetization direction of the ferromagnetic layer of each of the layers, which is adjacent to the tunnel junction layer13.

InFIG.1, a case where the first ferromagnetic layer24is magnetized in a vertically upper direction (hereinafter, simply referred to as an upper direction) with respect to a substrate2, and the reference layer12is magnetized in a vertically lower direction (hereinafter, simply referred to as a lower direction) with respect to the substrate2is illustrated as an example. Further, inFIG.1, the magnetization of the first ferromagnetic layer24is represented by a void arrow as magnetization24M, the magnetization of the reference layer12is represented by a black arrow as magnetization12M, and the direction of the arrow indicates a magnetization direction. In the example illustrated inFIG.1, the direction of the magnetization24M of the first ferromagnetic layer24and the direction of the magnetization12M of the reference layer12are antiparallel to each other. Herein, a case where the magnetization directions are antiparallel to each other indicates that the directions of the magnetizations are different from each other by approximately 180 degrees. In addition, the black arrow indicates that the magnetization direction is fixed, and the void arrow indicates that the magnetization direction can be reversed. Note that, in practice, there may be components that are not directed to the magnetization direction (the direction of the arrow). Hereinafter, the same applies to a case where the magnetization is represented by an arrow in the other drawings of this specification.

The tunnel junction stacked film1of the invention includes various variations, and hereinafter, various variations of the tunnel junction stacked film1will be described as an embodiment.

(1) First Embodiment

(1-1) Configuration of Tunnel Junction Stacked Film of First Embodiment

In a tunnel junction stacked film of a first embodiment, the recording layer14of the tunnel junction stacked film1illustrated inFIG.1is configured such that the Hf layer25is interposed between the ferromagnetic layers. As illustrated inFIG.2in which the same reference numerals are applied to the same configurations as those inFIG.1, a MTJ film1aof the first embodiment includes the reference layer12, the tunnel junction layer13, a recording layer14a, and a non-magnetic layer27containing oxygen atoms (hereinafter, simply represented as0) adjacent to the recording layer14a. The recording layer14ais a multi-layer film including the first ferromagnetic layer24, the Hf layer25, and a second ferromagnetic layer26containing boron that is a perpendicular magnetization film, in which the first ferromagnetic layer24is adjacent to the tunnel junction layer13and the hafnium layer25, the hafnium layer25is adjacent to the second ferromagnetic layer26, and the second ferromagnetic layer26is adjacent to the non-magnetic layer27containing O.

The reference layer12includes a multi-layer film including a Co layer, such as a cobalt (Co)/platinum (Pt) multi-layer film, a Co/palladium (Pd) multi-layer film, a Co/nickel (Ni) multi-layer film, and a Co/iridium (Ir) multi-layer film, and a ferromagnetic layer containing a regular alloy such as manganese-gallium (Mn—Ga), Mn-germanium (Ge), and iron (Fe)—Pt, or an alloy containing Co such as Co—Pt, Co—Pd, Co-chromium (Cr)—Pt, Co—Cr—Ta—Pt, CoFeB, FeB, and CoB.

Note that, the reference layer12may include a plurality of ferromagnetic layers, or may have a multi-layer structure of a ferromagnetic layer/a non-magnetic coupling layer/a ferromagnetic layer. In this case, the non-magnetic coupling layer includes a non-magnetic body such as ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os), and rhenium (Re). According to such a multi-layer structure, the magnetizations of two ferromagnetic layers can be antiferromagnetically coupled by an interlayer interaction, and the magnetization direction of the reference layer12can be fixed.

In addition, in order to cause interface magnetic anisotropy on the interface between the reference layer12and the tunnel junction layer13, and to set the magnetization direction of the reference layer12to be perpendicular to the film surface, it is preferable that the ferromagnetic layer (in a case where the reference layer12has a multi-layer structure, the ferromagnetic layer adjacent to the tunnel junction layer13) configuring the reference layer a ferromagnetic material containing boron (B), in particular, CoFeB, FeB, or CoB. In a case where the reference layer12has a multi-layer structure, the reference layer12, for example, has a multi-layer structure such as a ferromagnetic layer/a non-magnetic coupling layer/a ferromagnetic layer/an exchange coupling layer containing tantalum (Ta), tungsten (W), or molybdenum (Mo)/a ferromagnetic layer (adjacent to the tunnel junction layer13) containing CoFeB, FeB, or CoB.

As described above, by inserting the exchange coupling layer containing Ta, W, or Mo, the ferromagnetic layer containing CoFeB, FeB, or CoB that is stacked on the exchange coupling layer can be an amorphous ferromagnetic layer, which is further desirable. Note that, the amorphous ferromagnetic layer indicates a ferromagnetic layer that is dominantly amorphous, and may partly contain crystals. In the reference layer12, the number of laminations, a film thickness, and the like are suitably adjusted in accordance with the size of the MTJ. The thickness of the reference layer12is not particularly limited, and in a case of using perpendicular magnetization caused by the interface magnetic anisotropy, the thickness is preferably 5.0 nm or less, more preferably 3.0 nm or less, and even more preferably 1.6 nm or less.

In addition, in a case where MgO is stacked on an amorphous layer, the tunnel junction layer13containing MgO (100) is easily formed adjacent to the reference layer12by properties in which a MgO layer that dominantly contains monocrystals oriented in a (100) direction is formed, and thus, it is desirable that the layer of the reference layer12that is closest to the tunnel junction layer13side (for example, the uppermost layer) contains CoFeB, FeB, or CoB. As described above, the tunnel junction layer13containing MgO (100) can be epitaxially grown as a (100) highly oriented film on the amorphous ferromagnetic layer even in an in-plane direction by large grains, in-plane homogeneity of the orientation of MgO (100) can be improved, and the homogeneity of a resistance change rate (an MR change rate) can be improved.

Note that, the magnetization direction of the reference layer12may be fixed in the perpendicular direction, and the direction of the magnetization12M may be fixed in the perpendicular direction, by crystal magnetic anisotropy or shape magnetic anisotropy but not by the interface magnetic anisotropy.

In this case, it is desirable that the reference layer12, for example, includes a ferromagnetic layer that contains an alloy containing at least one or more of Co, Fe, Ni, and Mn. In the detailed description, an alloy such as Co—Pt, Co—Pd, Co—Cr—Pt, and Co—Cr—Ta—Pt is desirable as an alloy containing Co, and in particular, it is desirable that such an alloy is so-called Co-rich in which more Co is contained than the other elements. An alloy such as Fe—Pt and Fe—Pd is desirable as an alloy containing Fe, and in particular, it is desirable that such an alloy is so-called Fe-rich in which more Fe is contained than the other elements. An alloy such as Co—Fe, Co—Fe—Pt, and Co—Fe—Pd is desirable as an alloy containing Co and Fe. The alloy containing Co and Fe may be Co-rich or may be Fe-rich. An alloy such as Mn—Ga and Mn—Ge is desirable as an alloy containing Mn. In addition, an element such as boron (B), carbon (C), nitrogen (N), oxygen (O), phosphorus (P), aluminum (Al), and silicon (Si) may be slightly contained in the alloy containing at least one or more of Co, Fe, Ni, and Mn, described above.

The tunnel junction layer13is formed adjacent to the reference layer12. It is desirable that the tunnel junction layer13contains a non-magnetic material containing O, such as MgO, Al2O3, AlN, and MgAlO, in particular, MgO (100). In addition, the thickness of the tunnel junction layer13is 0.1 nm to 2.5 nm, and desirably 0.5 nm to 1.5 nm.

The recording layer14ais a multi-layer film including the first ferromagnetic layer24adjacent to the tunnel junction layer13, the Hf layer25adjacent to the first ferromagnetic layer24, and the second ferromagnetic layer26adjacent to the Hf layer25. The recording layer14ahas a ferromagnetic coupling structure in which the magnetization24M of the first ferromagnetic layer24and magnetization26M of the second ferromagnetic layer26are ferromagnetically coupled. For this reason, the magnetizations of the first ferromagnetic layer24and the second ferromagnetic layer26are ferromagnetically connected by an interlayer interaction, and the magnetization directions are parallel to each other.

In addition, in this embodiment, the material and the thickness of the first ferromagnetic layer24are selected such that the interface magnetic anisotropy occurs on the interface between the first ferromagnetic layer24of the recording layer14athat is closest to the tunnel junction layer13side and the tunnel junction layer13, and the magnetization direction of the first ferromagnetic layer24becomes the perpendicular direction with respect to the film surface. For this reason, the first ferromagnetic layer24is a perpendicular magnetization film that is magnetized in the perpendicular direction with respect to the film surface. Then, the magnetization direction of the second ferromagnetic layer26is parallel to the magnetization direction of the first t ferromagnetic layer24by the interlayer interaction, and thus, the second ferromagnetic layer26is a perpendicular magnetization film that is magnetized in the perpendicular direction with respect to the film surface. The magnetization direction of the first ferromagnetic layer24and the magnetization direction of the second ferromagnetic layer26are not fixed, and the magnetization direction can be reversed between the upper direction and the lower direction with respect to the substrate2. The magnetization direction of the first ferromagnetic layer24and the magnetization direction of the second ferromagnetic layer26are reversed in tandem with each other, and thus, in a case where the magnetization direction of the first ferromagnetic layer24is reversed by spin torque described below, the magnetization direction of the second ferromagnetic layer26is also reversed.

In order to cause the interface magnetic anisotropy in the first ferromagnetic layer24, the first ferromagnetic layer24contains a ferromagnetic material containing B, in particular, CoFeB, FeB, or CoB. In order to cause the interface magnetic anisotropy on the interface with the non-magnetic layer27containing O, described below, and to facilitate the perpendicular magnetization with respect to the film surface, s preferable that the second ferromagnetic layer26contains the ferromagnetic material containing B, such as CoFeB, FeB, or CoB, as with the first ferromagnetic layer24. Alternatively, it is preferable that the second ferromagnetic layer26is a multi-layer film including a layer containing the ferromagnetic material containing B, such as CoFeB, FeB, or CoB, in a position adjacent to the non-magnetic layer27containing O. Note that, the second ferromagnetic layer26, for example, may include a multi-layer film including a Co layer, such as a Co/Pt multi-layer film, a Co/Pd multi-layer film, and a Co/Ni multi-layer film, a regular alloy such as Mn—Ga, Mn—Ge, and Fe—Pt, or an alloy containing Co, such as Co—Pt, Co—Pd, Co—Cr—Pt, Co—Cr—Ta—Pt, CoFeB, and CoB, and the like.

The thicknesses of the first ferromagnetic layer24and the second ferromagnetic layer26are not particularly limited, and in a case of using the perpendicular magnetization caused by the interface magnetic anisotropy, each of the thicknesses is preferably 5.0 nm or less, more preferably 3.0 nm or less, and even more preferably 1.6 nm or less. In particular, it is preferable that the thicknesses of the first ferromagnetic layer24and the second ferromagnetic layer26are a thickness of 0.5 nm to 4.0 nm. In addition, it is preferable that the total thickness of the both thicknesses of the first ferromagnetic layer24and the second ferromagnetic layer26is 2.0 nm or more.

The Hf layer25is provided adjacent to the first ferromagnetic layer24and the second ferromagnetic layer26. The Hf layer25is a thin film containing hafnium. The Hf layer25has a function as a non-magnetic coupling layer in which the recording layer14ahas a ferromagnetic coupling structure (the magnetization24M of the first ferromagnetic layer24and the magnetization26M of the second ferromagnetic layer26are ferromagnetically coupled by the interlayer interaction).

In addition, the recording layer14aincludes the Hf layer25adjacent to the first ferromagnetic layer24containing boron, and thus, perpendicular magnetic anisotropy increases, and magnetization can be easily performed in the perpendicular direction with respect to the film surface. Further, according to the Hf layer25, boron of the first ferromagnetic layer24is less likely to be diffused in the non-magnetic coupling layer, in a heat treatment described below, compared to a case of using a non-magnetic coupling layer containing Ta, W, or an alloy thereof. Accordingly, by using the Hf layer25, the diffusion of boron of the first ferromagnetic layer24due to the heat treatment can be suppressed, an increase in saturation magnetization Ms of the first ferromagnetic layer24adjacent to the Hf layer25due to the heat treatment can be suppressed, and an increase in a diamagnetic field of the first ferromagnetic layer24in the perpendicular direction can also be suppressed. As a result thereof, the degree of perpendicular magnetic anisotropy can be further improved by the heat treatment, and the first ferromagnetic layer24can be easily magnetized in the perpendicular direction, compared to a case of not including the Hf layer25. For this reason, a thermal stability of the first ferromagnetic layer24as the perpendicular magnetization film can be improved. In addition, the first ferromagnetic layer24has thicker perpendicular magnetization, and thus, the thermal stability can be further improved. Further, in the first embodiment, the second ferromagnetic layer26is adjacent to the surface of the Hf layer25facing a surface to which the first ferromagnetic layer24is adjacent, and thus, the same effect also occurs on the second ferromagnetic layer26side, and the thermal stability can be further improved.

In addition, Hf is less likely to cause an atom diffusion of Hf atoms due to heat, compared to Ta or W. For this reason, the Hf layer25is used as the non-magnetic coupling layer for introducing the interlayer interaction, and thus, the atom diffusion of the atoms configuring the non-magnetic coupling layer to the first ferromagnetic layer24and the second ferromagnetic layer26from the non-magnetic coupling layer due to the heat treatment can be suppressed, compared to a case of using the non-magnetic coupling layer containing Ta, W, or an alloy thereof. That is, when a Ta layer or a W layer is inserted instead of the Hf layer25, a large diffusion occurs between CoFeB (the first ferromagnetic layer24and the second ferromagnetic layer26) and Ta or W. In contrast, when the Hf layer25is inserted, a diffusion between CoFeB (the first ferromagnetic layer24and the second ferromagnetic layer26) and Hf decreases. In a diffusion between CoFeB and Ta, W, or Hf, it is known that a damping constant increases when heavy metals such as W, Ta, and Hf with an atomic number greater than an atomic number of Co or Fe are mixed with Co or Fe. It is preferable to select a heavy metal that has a small diffusion amount, that is, decreases the thickness of a magnetic dead layer. When a film thickness t of the non-magnetic coupling layer (the Hf layer, the Ta layer, the W layer) is 0.3 nm or more, the diffusion is further suppressed and an increase in a damping constant α of CoFeB is further suppressed in a case where the Hf layer is inserted than in a case where the Ta layer or the W layer is inserted. For this reason, it is preferable that the Hf layer is inserted since a write current ICOdecreases.

Accordingly, the recording layer14aof the MTJ film1ahas a high thermal stability. For this reason, a magnetic memory element100is prepared by using such a MTJ film1a, and thus, the magnetic memory element100having high nonvolatility can be provided.

Note that, the Hf layer25may contain zirconium (Zr). The Hf layer25is formed to have a thickness of preferably 0.2 nm or more and 0.9 nm or less, preferably 0.3 nm or more and 0.7 nm or less. In order to form the Hf layer25into the shape of a layer, a thickness of approximately 0.2 nm is required. By setting the thickness to 0.3 nm or more, an effect of preventing the diffusion of boron from the first ferromagnetic layer24increases, compared to Ta or W. Thinner total thickness of MTJ is preferable in consideration of etching workability of the MTJ, and even in a case where the thickness of the Hf layer25is thicker than 0.7 nm, the perpendicular magnetic anisotropy of the first ferromagnetic layer24and the second ferromagnetic layer26adjacent to the Hf layer25is not considerably improved, and thus, it is preferable that the film thickness of the Hf layer25is 0.7 nm or less. It is preferable that the film thickness of the Hf layer25is 0.9 nm or less, in consideration of ensuring film thickness homogeneity of the entire wafer.

It is preferable that the non-magnetic layer27containing O includes a non-magnetic body containing oxygen, and for example, contains MgO, MgOTi, MgOTiN, Al2O3, SiO2, MgZnO, and the like. The non-magnetic layer27containing O causes the interface magnetic anisotropy on the interface with the adjacent recording layer14a(in the first embodiment, the second ferromagnetic layer26), and is capable of easily magnetizing the recording layer14ain the perpendicular direction with respect to the film surface. In the first embodiment, a double interface structure in which the recording layer14ais interposed between the tunnel junction layer13containing O and the non-magnetic layer27containing O can be formed. Accordingly, it is possible to cause the interface magnetic anisotropy on each of the interface between the tunnel junction layer13and the recording layer14aand the interface between the recording layer14aand the non-magnetic layer27containing O, and to increase the thermal stability by increasing the film thickness of the recording layer14a. The thickness of the non-magnetic layer27containing O is not particularly limited, and is preferably 10 nm or less, and particularly preferably 5 nm or less. In addition, it is preferable that the non-magnetic layer27containing O has the same thickness as that of the tunnel junction layer13, or has a thickness less than that of the tunnel junction layer13.

The MTJ film1a, for example, is prepared by a general film formation method such as a physical vapor deposition (PVD), a lithography technology, and the like. For example, first, an under layer (not illustrated inFIG.2) is formed on the substrate (not illustrated inFIG.2) on which an electrode or the like is formed, and then, the reference layer12is formed on the under layer. Next, the tunnel junction layer13is formed on the reference layer12. Finally, the first ferromagnetic layer24, the Hf layer25, and the second ferromagnetic layer26are formed on the tunnel junction layer13in this order, and thus, the recording layer14ais prepared, and the non-magnetic layer27containing O is formed on the recording layer14a. After that, the MTJ film1ais prepared through a heat treatment step and a molding step described below.

(1-2) Example of Tunnel Junction Stacked Film of First Embodiment

Hereinafter, a specific example of the tunnel junction stacked film1aof the first embodiment of the invention will be described with reference toFIG.3. In the specific example illustrated inFIG.3, the tunnel junction stacked film1ais formed on the substrate2, and is provided with a first terminal10electrically connected to the reference layer12and a second terminal16electrically connected to the recording layer14a, and thus, configured as a two-terminal magnetic memory element. In addition, in the tunnel junction stacked film1a, a under layer11is provided between the first terminal10and the reference layer12, and a cap layer15is provided between the second terminal16and the non-magnetic layer27containing O.

As described above, the first terminal10is electrically connected to the reference layer12, and the second terminal16is electrically connected to the recording layer14a, and thus, a current can flow between the first terminal10and the second terminal16by flowing through the MTJ film1a. For this reason, the magnetization direction of the recording layer14aof the MTJ film1acan be reversed by the current to flow between the first terminal10and the second terminal16, and the MTJ film1ais transitioned between the parallel state and the anti-parallel state, and thus, can be used as a STT-MRAM element as a magnetic memory element storing data. In addition, the reference layer12is disposed on the substrate2side from the recording layer14a, and thus, a so-called Bottom-pinned structure is formed.

The substrate2, for example, includes a Si substrate in which a SiO2film is formed on the surface, and the like, and has a structure including a transistor, multiple wiring layers, and the like. The first terminal10is formed on the surface of the substrate2, and the second terminal16is formed on the cap layer15. The first terminal10and the second terminal16, for example, are a conductive layer containing metals having conductivity, such as copper (Cu), aluminum (Al), and gold (Au), or a compound of the metals. The thickness of the first terminal10is approximately 20 to 50 nm, and the thickness of the second terminal16is approximately 10 to 100 nm. For convenience, even though it is not illustrated inFIG.3, in this example, the first terminal10formed on the surface of the substrate2is connected to a field effect transistor (FET)111(refer toFIG.4andFIG.5) formed on the substrate2, and the second terminal16is connected to a bit line BL1described below (refer toFIG.4andFIG.5). Note that, the substrate2is also capable of including the first terminal10.

The under layer11is formed on the first terminal10. The under layer11is a layer to be a foundation for laminating the tunnel junction stacked film1a, and includes a surface that is smoothly formed. The under layer11, for example, includes a Ta layer having a thickness of approximately 5 nm. The under layer11may contain a metal material such as Cu, copper nitride (CuN), Au, silver (Ag), and Ru, and an alloy thereof. The under layer11may have a structure in which a plurality of layers of a metal material are stacked, for example, a structure of a Ta layer/a Ru layer/a Ta layer. In addition, the under layer11may not be formed.

The tunnel junction stacked film1aincludes the reference layer12, the tunnel junction layer13, the recording layer14a, and the non-magnetic layer27containing O, which are stacked on the under layer11in this order. In the example illustrated inFIG.3, the reference layer12has a multi-layer structure of a ferromagnetic layer including a [Co/Pt]n/Co multi-layer film/a non-magnetic coupling layer containing Ru/a ferromagnetic layer including a [Co/Pt]m/Co multi-layer film/an exchange coupling layer containing Ta or W/a ferromagnetic layer containing CoFeB. Note that, [Co/Pt]n indicates that a Co/Pt multi-layer film is repeatedly stacked n times, and the [Co/Pt]n/Co multi-layer film indicates that a layer of the lowermost layer and a layer of the uppermost layer are Co. The same applies to the [Co/Pt]m/Co multi-layer film.

In the reference layer12, as described below, the tunnel junction layer13contains MgO, and thus, the ferromagnetic layer containing CoFeB becomes a perpendicular magnetization film by the interface magnetic anisotropy. For this reason, the ferromagnetic layer including the [Co/Pt]m/Co multi-layer film is magnetically connected to the ferromagnetic layer containing CoFeB by the interlayer interaction, and becomes a perpendicular magnetization film. Further, the magnetization of the ferromagnetic layer including the [Co/Pt]m/Co multi-layer film and the magnetization of the ferromagnetic layer including the [Co/Pt]n/Co multi-layer film are antiferromagnetically coupled by the Ru layer, and the magnetization directions are antiparallel to each other.

The tunnel junction layer13contains MgO having a thickness of 1.5 nm.

The recording layer14aincludes the first ferromagnetic layer24containing CoFeB, the Hf layer25, and the second ferromagnetic layer26containing CoFeB, which are stacked on the tunnel junction layer13in this order. For example, the recording layer14acan be CoFeB (1.0 nm)/Hf (0.7 nm)/CoFeB (1.0 nm).

The non-magnetic layer27containing O contains MgO. In this example, the non-magnetic layer27containing O and the tunnel junction layer13contain MgO, and the recording layer14ahas a double interface structure. The thickness of the non-magnetic layer27containing 0, for example, can be 1 nm.

The cap layer15is formed on the non-magnetic layer27containing O. The cap layer15, for example, contains Ta or W, and has conductivity. The thickness of the cap layer15, for example, can be 1.0 nm. Note that, the cap layer15may not be provided.

The magnetic memory element illustrated inFIG.3, for example, is prepared by a general film formation method such as a physical vapor deposition (PVD), a lithography technology, and the like. First, the first terminal10, the under layer11, the MTJ film1a, the cap layer15, and the second terminal16are stacked on the surface of the substrate2in this order, the heat treatment is performed at a temperature of approximately 300° C. to 400° C., and thus, the multi-layer film is prepared. After that, the multi-layer film is etched into a pillar shape by a lithography technology or the like, and thus, the magnetic memory element100is prepared. The pillar shape can be various shapes such as a columnar shape, a quadrangular prism, and a polygonal prism.

(1-3) Write Method and Read Method of Magnetic Memory Element

A write method of the magnetic memory element using the MTJ film1awill be described with reference toFIG.4AandFIG.4Bin which the same reference numerals are applied to the same configurations as those inFIG.2. As illustrated inFIG.4A, the magnetic memory element100is a two-terminal memory including the first terminal10electrically connected to the reference layer12through the under layer11, and the second terminal16electrically connected to the recording layer14through the non-magnetic layer17containing O and the cap layer15. In the magnetic memory element100, a resistance value of the MTJ film1ais changed in accordance with whether the magnetization direction of the recording layer14aand the magnetization direction of the reference layer12are parallel to each other or antiparallel to each other. In a case where the recording layer14aand the reference layer12are a multi-layer film, in the magnetic memory element100, the resistance value of the MTJ film1ais changed in accordance with whether the magnetization directions of the ferromagnetic layers adjacent to the tunnel junction layer13(for example, the first ferromagnetic layer24of the recording layer14aand the reference layer12), in the ferromagnetic layers of the recording layer14aand the reference layer12, are parallel to each other or antiparallel to each other.

Accordingly, herein, a case where the recording layer14aand the reference layer12are in the parallel state indicates a state where the magnetization directions of the ferromagnetic layers adjacent to the tunnel junction layer13are parallel to each other, and a case where the recording layer14aand the reference layer12are in the anti-parallel state indicates a state where the magnetization directions of the ferromagnetic layers adjacent to the tunnel junction layer13are antiparallel to each other.

In the magnetic memory element100, 1-bit data of “0” and “1” is assigned to the parallel state and the anti-parallel state by using the fact that the resistance value of the MTJ film1ais different between the parallel state and the anti-parallel state, and thus, data is stored in the magnetic memory element100. In the magnetic memory element100, the recording layer14ahas a reversible magnetization direction, and thus, the MTJ film1ais transitioned between the parallel state and the anti-parallel state by reversing the magnetization direction of the recording layer14a, “1” is stored in the MTJ film1ain which “0” is stored, and “0” is stored in the MTJ film1ain which “1” is stored. Herein, as described above, changing the resistance value of the MTJ film1aby reversing the magnetization direction of the recording layer14aindicates writing data.

The write method of the magnetic memory element100will be described in more detail. InFIG.4AandFIG.4B, the first terminal10of the magnetic memory element100is connected to a drain of the field effect transistor111, and the second terminal16is connected to a bit line BL1. In the transistor111, a gate is connected to a word line WL1, and a source is connected to a source line SL1. For this reason, in a case where a predetermined voltage is applied to the gate of the transistor111from the word line WL1, and the transistor111is turned on, a write current Iw flowing through the MTJ film1acan be applied to the second terminal16from the first terminal10or to the first terminal10from the second terminal16, in accordance with a potential difference between the bit line BL1and the source line SL1. Note that, inFIG.4AandFIG.4B, for convenience, the substrate2is omitted, but in practice, the transistor111is formed on the substrate2.

First, a case of writing the data “0” in the magnetic memory element100in which the data “1” is stored will be described. Here, as illustrated inFIG.4A, a state where the magnetic memory element100stores the data “1” when the magnetization direction of the recording layer14ais the upper direction, the magnetization direction of the reference layer12is the lower direction, and the MTJ film1ais in the anti-parallel state is set to an initial state. Then, the transistor111is turned off.

First, the bit line BL1is set to a write voltage Vw. After that, the word line WL1is set to a high level, and the transistor111is turned on. At this time, since the voltage of the second terminal16to which the write voltage Vw is applied from the bit line BL1is higher than that of the first terminal10, the write current Iw flows to the first terminal10from the second terminal16by flowing through the MTJ film1a.

Since the write current Iw flows to the reference layer12from the recording layer14a, electrons are injected to the recording layer14afrom the reference layer12. Since the magnetization direction of the reference layer12and the magnetization direction of the recording layer14aare antiparallel to each other, spins antiparallel to the magnetization direction of the recording layer14aflow into the recording layer14aby the flow of the electrons. Since the spins that flow into the recording layer14aare antiparallel to the magnetization direction of the recording layer14a, torque functions such that the magnetization direction of the recording layer14ais reversed by the spins that flow into the recording layer14a. The magnetization direction of the recording layer14ais reversed by the torque, the MTJ film1ais in the parallel state, and the data “0” is stored. In practice, the recording layer14ahas the ferromagnetic coupling structure, and thus, the magnetization direction of the first ferromagnetic layer24adjacent to the tunnel junction layer13is reversed by the spins that flow into the recording layer14a, and accordingly, the magnetization26M of the second ferromagnetic layer26that is ferromagnetically coupled to the magnetization24M of the first ferromagnetic layer24is also reversed. After a predetermined time has elapsed since the transistor111is turned on, the word line WL1is set to a low level, the transistor111is turned off, the bit line BL1is stepped down, and the write current Iw is stopped.

Next, a case of writing the data “1” in the magnetic memory element100in which the data “0” is stored will be described. Here, as illustrated inFIG.4B, a state where the magnetic memory element100stores the data “0” when the magnetization direction of the recording layer14ais the lower direction, the magnetization direction of the reference layer12is the lower direction, and the MTJ film1ais in the parallel state is set to an initial state. Then, the transistor111is turned off.

First, the source line SL is set to the write voltage Vw. After that, the word line WL1is set to a high level, and the transistor111is turned on. At this time, since the voltage of the first terminal10to which the write voltage Vw is applied from the source line SL1is higher than that of the second terminal16, the write current Iw flows to the second terminal16from the first terminal10by flowing through the MTJ film1a.

Since the write current Iw flows to the recording layer14afrom the reference layer12, electrons are injected to the reference layer12from the recording layer14a. Since the magnetization direction of the reference layer12and the magnetization direction of the recording layer14aare parallel to each other, spins parallel to the magnetization direction of the reference layer12flow into the reference layer12by the flow of the electrons. On the other hand, spins not parallel to the magnetization direction of the reference layer12also exist in the recording layer14a, and the spins are scattered on the interface between the tunnel junction layer13and the reference layer12, and flow again into the recording layer14a. Since the spins that flow again into the recording layer14aare directed to a direction different from the magnetization direction of the recording layer14a, torque is applied to the magnetization of the recording layer14a(the magnetization24M of the first ferromagnetic layer24). The magnetization direction of the recording layer14ais reversed by the torque, the MTJ film1ais in the anti-parallel state, and the data “1” is stored. In practice, the recording layer14ahas the ferromagnetic coupling structure, and thus, the magnetization direction of the second ferromagnetic layer26is also reversed in accordance with the magnetization reversal of the first ferromagnetic layer24. After a predetermined time has elapsed since the transistor111is turned on, the word line WL1is set to a low level, the transistor111is turned off, the source line SL1is stepped down, and the write current Iw is stopped.

As described above, in the magnetic memory element100, the write current Iw flowing through the MTJ film1ais applied between the first terminal10and the second terminal16, and thus, the magnetization direction of the recording layer14ais reversed, and the data “0” or the data “1” can be written.

Subsequently, a read method will be described. A case of reading data from the magnetic memory element100in which the data “1” is stored will be described as an example, with reference toFIG.4A. In this case, in the initial state, as illustrated inFIG.4A, the magnetic memory element100stores the data “1” when the magnetization direction of the recording layer14ais the upper direction, the magnetization direction of the reference layer12is the lower direction, and the MTJ film1ais in the anti-parallel state. Then, the transistor111is turned off.

First, the bit line BL1is set to a read voltage Vr. The read voltage Vr is a voltage lower than the write voltage Vw, and is set to a voltage at which the magnetization direction of the recording layer14ais not reversed. After that, the word line WL1is set to a high level, and the transistor111is turned on. At this time, since the voltage of the second terminal16to which the read voltage Vr is applied from the bit line BL1is higher than that of the first terminal10, the read current Ir flows to the first terminal10from the second terminal16by flowing through the MTJ film1a. The read current Ir is detected by a current detector that is not illustrated. Since the size of the read current Ir is changed in accordance with the resistance value of the MTJ, whether the MTJ is in the parallel state or in the anti-parallel state, that is, whether the MTJ stores the data “0” or the data “1” can be read from the size of the read current Ir. Accordingly, the data “1” can be read from the size of the read current Ir. After a predetermined time has elapsed since the transistor111is turned on, the word line WL1is set to a low level, the transistor111is turned off, the bit line BL1is stepped down, and the read current Ir is stopped.

Even in a case where data is read from the magnetic memory element100in which the data “0” is stored, the stored data can be read by the same method, and thus, the description will be omitted. Note that, even in a case where the read current Ir flows to the second terminal16from the first terminal10, similarly, the data stored in the magnetic memory element100can be read from a current value of the read current Ir.

(1-4) Magnetic Memory Including Magnetic Memory Element of Invention

Next, a magnetic memory cell circuit using the magnetic memory element100having the configuration described above as a memory element, and a magnetic memory in which the magnetic memory cell circuit is integrated will be described with reference toFIG.5in which the same reference numerals are applied to the same configurations as those inFIG.4A. A region surrounded by a dotted line illustrated inFIG.5is a magnetic memory cell circuit300of one bit. Such a magnetic memory cell circuit300includes a magnetic memory element100configuring a memory cell of one bit, the bit line BL1, the source line SL1, the word line WL1, and the transistor111. InFIG.5, for convenience, the magnetic memory element100is schematically illustrated.

Next, a magnetic memory200will be described. The magnetic memory200includes a plurality of bit lines, a plurality of source lines, a plurality of word lines, a plurality of magnetic memory cell circuits300, an X driver203, a Y driver202, and a controller201. InFIG.5, for convenience, only two bit lines BL1and BL2, two source lines SL1and SL2, and three word lines WL1, WL2, and WL3are illustrated. The magnetic memory cell circuit300is disposed in the vicinity of each intersection point between the bit line, the source line, and the word line.

The X driver203is connected to the plurality of bit lines (BL1and BL2) and the plurality of source lines (SL1and SL2), decodes an address received from the controller201, and applies the write voltage Vw or the read voltage Vr to the bit line or the source line in a row that is an access target. In addition, the X driver203includes the current detector (not illustrated inFIG.5), and detects the read current Ir that flows to the magnetic memory element100of the selected magnetic memory cell circuit300, and thus, is capable of reading data stored in the magnetic memory element100.

The Y driver202is connected to the plurality of word lines (WL1, WL2, and WL3), decodes an address received from the controller201, and sets the voltage of the word line in a column that is an access target to a high level or a low level.

The controller201controls each of the X driver203and the Y driver202in accordance with data write or data read. The controller201transmits the address of the magnetic memory cell circuit300in which data is to be written to the X driver203and the Y driver202, and transmits a data signal indicating the data to be written to the X driver. The X driver203selects the bit line and the source line on the basis of the received address, and applies the write voltage Vw to any one of the bit line and the source line on the basis of the received data signal. The Y driver202selects the word line on the basis of the received address, and sets the voltage of the word line to a high level. According to the operation of the X driver203and the Y driver202, the write current Iw flows to the magnetic memory element100of the magnetic memory cell circuit300selected by the controller201, and the data is written.

The controller201transmits the address of the magnetic memory cell circuit300from which data is to be read to the X driver203and the Y driver202. The X driver203selects the bit line and the source line on the basis of the received address, and applies the read voltage Vr to any one of the bit line and the source line. The Y driver202selects the word line on the basis of the received address, and sets the voltage of the word line to a high level. According to the operation of the X driver203and the Y driver202, the read current Ir flows to the magnetic memory element100of the magnetic memory cell circuit300selected by the controller201, the read current Ir is detected by the X driver203, and the data is read.

(1-5) Action and Effect

In the configuration described above, the tunnel junction stacked film1aof the first embodiment includes the recording layer14aincluding the first ferromagnetic layer24containing boron, the tunnel junction layer13adjacent to the recording layer14a, and the reference layer12adjacent to the tunnel junction layer13, and is configured such that the first ferromagnetic layer24and the reference layer12are magnetized in the perpendicular direction with respect to the film surface, and the recording layer14aincludes the hafnium layer25adjacent to the first ferromagnetic layer24.

Accordingly, in the tunnel junction stacked film1a, the recording layer14aincludes the hafnium layer25adjacent to the first ferromagnetic layer24, and thus, the perpendicular magnetic anisotropy of the first ferromagnetic layer24can be improved, and as a result thereof, the thermal stability of the magnetization of the first ferromagnetic layer24adjacent to the hafnium layer25is improved, and the thermal stability of the recording layer14ais high. Accordingly, the tunnel junction stacked film1ahaving a high thermal stability can be provided, and the magnetic memory element100and the magnetic memory200having high nonvolatility can be provided by using the tunnel junction stacked film1ahaving a high thermal stability in the magnetic memory element100or the magnetic memory200.

Further, the tunnel junction stacked film1ais configured such that the recording layer14aincludes the second ferromagnetic layer26containing boron, the tunnel junction layer13is adjacent to the first ferromagnetic layer24, the first ferromagnetic layer24is adjacent to the hafnium layer25, the hafnium layer25is adjacent to the second ferromagnetic layer26, and the second ferromagnetic layer26is adjacent to the non-magnetic layer27containing oxygen atoms (O), and thus, the perpendicular magnetic anisotropy of the second ferromagnetic layer26can be improved, the thermal stability of the second ferromagnetic layer26can be improved, and the thermal stability of the recording layer14can be further increased. As a result thereof, the tunnel junction stacked film1ahaving a higher thermal stability can be provided.

(2) Second Embodiment

(2-1) Tunnel Junction Stacked Film of Second Embodiment

A tunnel junction stacked film of the second embodiment is different from the tunnel junction stacked film of the first embodiment in the configuration of the recording layer. The other configurations, the write operation the read operation, and the like are identical to those of the first embodiment, and thus, the configuration of the recording layer14will be mainly described.

As illustrated inFIG.6in which the same reference numerals are applied to the same configurations as those inFIG.1, the recording layer14of a tunnel junction stacked film (MTJ film)1bof the second embodiment includes the first ferromagnetic layer24adjacent to the tunnel junction layer13, and the Hf layer25adjacent to the first ferromagnetic layer24. Further, in the second embodiment, the MTJ film1bincludes the cap layer15adjacent to the Hf layer25of the recording layer14.

The first ferromagnetic layer24is formed on the tunnel junction layer13such that the thickness is approximately 1.0 nm to 4.0 nm, and contains a ferromagnetic material containing B, such as CoFeB, FeB, or CoB. In the second embodiment, the first ferromagnetic layer24may include one ferromagnetic layer, and for example, may have a multi-layer structure such as a ferromagnetic layer/a non-magnetic coupling layer/a ferromagnetic layer or a multi-layer structure in which layers containing different materials are alternately stacked. A void arrow inFIG.6represents the direction of the magnetization24M of the first ferromagnetic layer24. InFIG.6, it is represented that the magnetization24M is directed to the perpendicular direction with respect to the film surface, and the first ferromagnetic layer24is a perpendicular magnetization film. Note that, in a case where the first ferromagnetic layer24has a multi-layer structure, the magnetization24M in FIG.6represents the magnetization direction of the ferromagnetic layer adjacent to the tunnel junction layer13.

In the second embodiment, the Hf layer25is disposed in a position furthest from the tunnel junction layer13to which the recording layer14is adjacent, in the recording layer14of the multi-layer structure, and the face of the Hf layer25facing the surface adjacent to the first ferromagnetic layer24is adjacent to the cap layer15. The thickness of the Hf layer25is 0.2 nm or more and 0.9 nm or less. In order to form the Hf layer25into the shape of a layer, a thickness of approximately 0.2 nm is required. By setting the thickness to 0.3 nm or more, the effect of preventing the diffusion of boron from the first ferromagnetic layer24increases, compared to Ta or W. It is preferable that the total film thickness decreases in consideration of the etching workability of the MTJ, and even in a case where the thickness of the Hf layer25is greater than 0.7 nm, the perpendicular magnetic anisotropy of the first ferromagnetic layer24adjacent to the Hf layer25is not considerably improved, and thus, it is preferable that the film thickness of the Hf layer25is 0.7 nm or less. It is preferable that the film thickness of the Hf layer25is 0.9 nm or less, in consideration of ensuring the film thickness homogeneity of the entire wafer. Further, as with the second embodiment, in a case where the Hf layer25is disposed in the position furthest from the tunnel junction layer13in the recording layer14, it is preferable that the thickness of the Hf layer25is 0.3 nm or more and 5.0 nm or less.

Further, in the second embodiment, the cap layer15, for example, contains Ta, W, or an alloy thereof, having conductivity, and thus, does not increase the resistance of the MTJ film1b. It is possible to decrease the resistance of the MTJ film1b, compared to a case where a non-magnetic layer containing O is used in the cap layer.

Such a MTJ film1bincludes the Hf layer25adjacent to the first ferromagnetic layer24containing boron, and thus, the perpendicular magnetic anisotropy increases, and the magnetization can be easily performed in the perpendicular direction with respect to the film surface. In addition, since the diffusion of B to the Hf layer25or the cap layer15from the first ferromagnetic layer24in the heat treatment can be suppressed, an increase in the saturation magnetization Ms of the first ferromagnetic layer24can be suppressed, and an increase in the diamagnetic field of the first ferromagnetic layer24in the perpendicular direction can also be suppressed. As a result thereof, the degree of perpendicular magnetic anisotropy can be further improved, and the thermal stability of the first ferromagnetic layer24can be improved. Further, since the MTJ film1bincludes the Hf layer25on the interface between the first ferromagnetic layer24of the recording layer14and the cap layer15, the diffusion of atoms configuring the cap layer15to the first ferromagnetic layer24from the cap layer15in the heat treatment is suppressed compared to a case where the Ta layer or the W layer is inserted instead of the Hf layer25or a case where the Hf layer25is not provided, and thus, the saturation magnetization Ms of the first ferromagnetic layer24decreases, and a decrease in the thermal stability can be suppressed. Accordingly, the thermal stability of the MTJ film1bcan be further improved.

Further, the Hf layer25itself adjacent to the first ferromagnetic layer24can also be used as the cap layer15. Even in such a case, similarly, the perpendicular magnetic anisotropy of the first ferromagnetic layer24can be improved, and the thermal stability of the MTJ film can be improved. Since Hf is a metal having conductivity, it is also possible to decrease the resistance of the MTJ film by using the Hf layer25itself as the cap layer15.

Note that, the recording layer14may have a synthetic ferrimagnetic structure, as with the recording layer14aof the first embodiment. For example, the recording layer14has a multi-layer structure of a second ferromagnetic layer/a non-magnetic coupling layer/a first ferromagnetic layer from the tunnel junction layer13side, and the Hf layer is inserted to the interface between the first ferromagnetic layer and the cap layer (in the recording layer14, the Hf layer25is provided to be adjacent to the first ferromagnetic layer disposed in the position furthest from the tunnel junction layer13and to face the tunnel junction layer13through the first ferromagnetic layer). Even in this case, the perpendicular magnetic anisotropy of the first ferromagnetic layer24can be improved.

As described above, the magnetic memory element is prepared by using the MTJ film1b, and thus, the thermal stability of the recording layer32can be improved and a conductive non-magnetic metal can be used in the cap layer, and a magnetic memory element having high nonvolatility and low resistance can be provided.

(2-2) Action and Effect

In the configuration described above, the tunnel junction stacked film1bof the second embodiment includes the recording layer14including the first ferromagnetic layer24containing boron, the tunnel junction layer13adjacent to the recording layer14, and the reference layer12adjacent to the tunnel junction layer13, and is configured such that the first ferromagnetic layer24and the reference layer12are magnetized in the perpendicular direction with respect to the film surface, and the recording layer14includes the Hf layer25adjacent to the first ferromagnetic layer24.

Accordingly, in the tunnel junction stacked film1b, the recording layer14includes the Hf layer25adjacent to the first ferromagnetic layer24, and thus, the perpendicular magnetic anisotropy of the first ferromagnetic layer24can be improved, and as a result thereof, the thermal stability of the magnetization of the first ferromagnetic layer24adjacent to the Hf layer25is improved, and the thermal stability of the recording layer14is high. Accordingly, the tunnel junction stacked film1bhaving a high thermal stability can be provided, and a magnetic memory element and a magnetic memory having high nonvolatility can be provided by using the tunnel junction stacked film1bhaving a high thermal stability in the magnetic memory element or the magnetic memory.

Further, the tunnel junction stacked film1bis configured such that the Hf layer25is disposed in the position furthest from tunnel junction layer13in the recording layer14, and thus, the diffusion of atoms of a material configuring a layer adjacent to the Hf layer25, such as the cap layer15, to the first ferromagnetic layer24from the layer can be suppressed, the saturation magnetization Ms of the first ferromagnetic layer24decreases, and a decrease in the thermal stability can be suppressed. Accordingly, the thermal stability of the MTJ film1bcan be further improved.

(3) Modification Example

Note that, the invention is not limited to the first embodiment and the second embodiment described above, and various modifications can be made within the scope of the gist of the invention.

Modification Example 1

In the first embodiment described above, a case has been described in which the recording layer14aof the MTJ film1ahas a multi-layer structure of the first ferromagnetic layer24, the Hf layer25, and the second ferromagnetic layer26, but the invention is not limited thereto. As with a recording layer14cof a MTJ film1cillustrated inFIG.7, a multi-layer structure including the first ferromagnetic layer24, the Hf layer25, a non-magnetic insertion layer40, and the second ferromagnetic layer26may be formed.

In the recording layer14cof Modification Example 1, the second ferromagnetic layer26is adjacent to the tunnel junction layer13, and the first ferromagnetic layer24is adjacent to the non-magnetic layer27containing O. In the recording layer14c, a multi-layer structure of the non-magnetic insertion layer40and the Hf layer25is used as a non-magnetic coupling layer in order to form a ferromagnetic coupling structure, the non-magnetic insertion layer40is adjacent to the second ferromagnetic layer26, and the Hf layer25is adjacent to the first ferromagnetic layer24. Then, the surface of the Hf layer25facing the surface adjacent to the first ferromagnetic layer24is adjacent to the non-magnetic insertion layer40.

In Modification Example 1, the recording layer14chas a double interface structure in which the recording layer14cis interposed between the tunnel junction layer13containing O and the non-magnetic layer27containing 0, and the interface magnetic anisotropy occurs on each of the interface between the tunnel junction layer13and the recording layer14c(the second ferromagnetic layer26) and the interface between the recording layer14c(the first ferromagnetic layer24) and the non-magnetic layer27containing O. Accordingly, the first ferromagnetic layer24and the second ferromagnetic layer26of the recording layer14care used as a perpendicular magnetization film. In Modification Example 1, the first ferromagnetic layer24and the second ferromagnetic layer26contain a ferromagnetic material containing B, such as CoFeB, FeB, or CoB. The non-magnetic insertion layer40contains Ta, W, Mo, or an alloy thereof, thickness of approximately 0.2 to 1 nm. Note that, the first ferromagnetic layer24and the second ferromagnetic layer26may be a single layer, or may be multiple layers.

It is preferable that the thickness of the Hf layer25is 0.2 nm or more and 0.9 nm or less. In order to form the Hf layer25into the shape of a layer, a thickness of approximately 0.2 nm is required. By setting the thickness to 0.3 nm or more, the effect of preventing the diffusion of boron from the first ferromagnetic layer24increases, compared to Ta or W. It is preferable that the total film thickness decreases in consideration of the etching workability of the MTJ, and even in a case where the thickness of the Hf layer25is greater than 0.7 nm, the perpendicular magnetic anisotropy of the first ferromagnetic layer24adjacent to the Hf layer25is not considerably improved, and thus, it is preferable that the film thickness of the Hf layer25is 0.7 nm or less. It is preferable that the film thickness of the Hf layer25is 0.9 nm or less, in consideration of ensuring the film thickness homogeneity of the entire wafer. Further, as with Modification Example 1, in a case where the second ferromagnetic layer26of the recording layer14cis adjacent to the non-magnetic insertion layer40, the non-magnetic insertion layer40is adjacent to the Hf layer25, the Hf layer25is adjacent to the first ferromagnetic layer24, and the first ferromagnetic layer24is adjacent to the non-magnetic layer27containing 0, it is preferable that the thickness of the Hf layer25is 0.3 nm or more and 0.7 nm or less.

In this case, in the first ferromagnetic layer24adjacent to the Hf layer25, the perpendicular magnetic anisotropy increases by the heat treatment, and the diffusion of atoms configuring the non-magnetic insertion layer40to the first ferromagnetic layer24from the non-magnetic insertion layer40is suppressed, and thus, a decrease in the saturation magnetization Ms of the first ferromagnetic layer24due to the diffusion of the atoms is also small, and the thermal stability can be improved.

On the other hand, in the second ferromagnetic layer26adjacent to the non-magnetic insertion layer40, the Hf layer25is not inserted between the non-magnetic insertion layer40and the second ferromagnetic layer26, and thus, the diffusion of the atoms configuring the non-magnetic insertion layer40to the second ferromagnetic layer26from the non-magnetic insertion layer40occurs, the saturation magnetization Ms of the second ferromagnetic layer26decreases, the thermal stability of the second ferromagnetic layer26further decreases, and the magnetization direction is easily reversed. As a result thereof, spin torque required for the magnetization reversal of the magnetization26M of the second ferromagnetic layer26decreases, and the write current Iw can be reduced. In addition, in the second ferromagnetic layer26adjacent to the non-magnetic insertion layer40, B is absorbed in the non-magnetic insertion layer40by the diffusion of B to the non-magnetic insertion layer40. Accordingly, for example, in a case where the second ferromagnetic layer26contains CoFeB, CoFe is formed on the second ferromagnetic layer26, and a TMR ratio is improved. As described above, there is a merit that B is removed from the second ferromagnetic layer26, and thus, a ferromagnetic body not containing B is partly formed, and the TMR ratio of the MTJ film1cincreases.

For this reason, since the second ferromagnetic layer26that is subjected to the magnetization reversal by the spin torque is easily subjected to the magnetization reversal, the recording layer14cof the MTJ film1cof Modification Example 1 can be easily subjected to the magnetization reversal by the spin torque, and the thermal stability of the first ferromagnetic layer24is high, and thus, the thermal stability of the entire recording layer14ccan also be improved, and the TMR ratio can also be increased.

The magnetic memory element can be prepared by using such a MTJ film1c, and thus, it is possible to provide the magnetic memory element in which the write can be performed at low energy, the nonvolatility is high, and the TMR ratio is large.

Modification Example 2

In the first embodiment, the second embodiment, and Modification Example 1, described above, the tunnel junction stacked film (for example,FIG.1) having a Bottom-pinned structure in which the reference layer is disposed on the substrate side from the recording layer has been described as an example, but the invention is not limited thereto. A tunnel junction stacked film having a Top-pinned structure in which the recording layer is disposed on the substrate side from the reference layer may be formed, and even in this case, the same effects as those of the tunnel junction stacked film having a Bottom-pinned structure are obtained. In a case where the tunnel junction stacked film of the second embodiment has the Top-pinned structure, the Hf layer may be inserted to be adjacent to the under layer.

Modification Example 3

In the first embodiment and Modification Example 1, described above, a case has been described in which the recording layers14aand14cof the tunnel junction stacked films1aand1chave the ferromagnetic coupling structure, but the invention is not limited thereto. As with a tunnel junction stacked film1dillustrated inFIG.8, a recording layer14dmay have a synthetic ferrimagnetic structure in which the magnetization24M of the first ferromagnetic layer24and the magnetization26M of the second ferromagnetic layer26are antiferromagnetically coupled by the interlayer interaction. In the tunnel junction stacked film1dof Modification Example 3, as with the first embodiment, the recording layer14dis a multi-layer film including the first ferromagnetic layer24, the Hf layer25adjacent to the first ferromagnetic layer24, and the second ferromagnetic layer26adjacent to the Hf layer25. In this case, the film thickness of the Hf layer25between the first ferromagnetic layer24and the second ferromagnetic layer26is suitably adjusted, and thus, the recording layer14dhaving a ferromagnetic coupling structure can be set to a synthetic ferrimagnetic structure. The other configurations are identical to those of the tunnel junction stacked film1of the first embodiment. Further, the recording layer14dmay have a multi-layer structure of a ferromagnetic layer/a non-magnetic insertion layer/a Hf layer/a ferromagnetic layer containing B, a multi-layer structure of a ferromagnetic layer containing B/a Hf layer/a ferromagnetic layer containing B/a Hf layer/a ferromagnetic layer containing B, or a multi-layer structure including more layers.

In Verification Experiment 1, in order to check an effect that a recording layer includes a Hf layer adjacent to a ferromagnetic layer, Ta (7.0 nm), a W—Ta alloy (3.0 nm), Hf (0.3 nm or 0.7 nm), CoFeB (1.15 nm to 1.7 nm), MgO (1.5 nm), CoFeB (0.4 nm), and Ta (1.0 nm) were formed on a Si substrate in which SiO2was formed on the surface, in this order, by a sputtering method, a heat treatment was performed at 400° C., and thus, a magnetic memory element was prepared. For comparison, a magnetic memory element having the same structure as described above except that the Hf layer is not provided was prepared. A product of a magnetic anisotropy constant Keffof the prepared magnetic memory element and an effective film thickness t* of the ferromagnetic layer, and saturation magnetization Ms were evaluated by a vibrating sample magnetometer (VSM).

The results of the magnetic anisotropy constant Keffand the saturation magnetization Ms evaluated by the VSM are shown inFIG.9AandFIG.9B. InFIG.9A, a horizontal axis is a film thickness of the Hf layer, and a vertical axis is a value obtained by multiplying the magnetic anisotropy constant Keffby the film thickness t* of the ferromagnetic layer, and is represented by a difference from a value when the Hf layer is not provided. InFIG.9B, a horizontal axis is the film thickness of the Hf layer, and a vertical axis is the saturation magnetization Ms. InFIG.9B, the saturation magnetization Ms of the magnetic memory element is represented by a solid line shown as Ms (CoFeB/Hf/WTa), and the saturation magnetization Ms of bulk CoFeB is represented by a dotted line shown as Ms (CoFeB).

InFIG.9A, it is found that perpendicular magnetic anisotropy increases by including the Hf layer. Accordingly, it was possible to check that perpendicular magnetic anisotropy of the ferromagnetic layer of the recording layer increases, magnetization is easily performed in a perpendicular direction with respect to a film surface, and a perpendicular magnetization film can be prepared up to a region in which the ferromagnetic layer is thicker, by including the Hf layer, and thus, a thermal stability of the ferromagnetic layer can be improved. In addition, inFIG.9B, the saturation magnetization Ms decreases by including the Hf layer. That is, it is found that an increase in the saturation magnetization Ms due to the heat treatment is suppressed. Accordingly, by including the Hf layer, an increase in the saturation magnetization Ms of the ferromagnetic layer of the recording layer can be suppressed, and as a result thereof, an increase in a diamagnetic field of the ferromagnetic layer in the perpendicular direction can also be suppressed, and the degree of perpendicular magnetic anisotropy can be further improved by the heat treatment and the thermal stability can be improved, compared to a case where the Hf layer is not provided. The film thickness of the Hf layer is preferably 0.9 nm or less, and more preferably 0.7 nm or less. It is found that the diffusion of B of CoFeB can be nearly suppressed by interposing the Hf layer of 0.7 nm. It is preferable that the total film thickness decreases in consideration of the etching workability of the MTJ, and even in a case where the thickness of the Hf layer25is greater than 0.7 nm, the perpendicular magnetic anisotropy of the first ferromagnetic layer24adjacent to the Hf layer25is not considerably improved, and thus, it is preferable that the film thickness of the Hf layer25is 0.7 nm or less. It is preferable that the film thickness of the Hf layer25is 0.9 nm or less, in consideration of ensuring the film thickness homogeneity of the entire wafer.

In Verification Experiment 2, a verification experiment for checking an effect that a recording layer includes a Hf layer as a non-magnetic coupling layer adjacent to a ferromagnetic layer, in particular, an effect that an atom diffusion of atoms configuring the non-magnetic coupling layer to the first ferromagnetic layer24and the second ferromagnetic layer26from the non-magnetic coupling layer due to a heat treatment is suppressed, compared to a case where a non-magnetic coupling layer contains other materials (Ta or W), was performed. Specifically, a tunnel junction stacked film having a structure illustrated on the left side ofFIG.10(in the drawing, the thickness of a layer in unit of nm is represented in the parenthesis) was prepared, and the thickness of a magnetic dead layer of a ferromagnetic layer (CoFeB) was measured. The magnetic dead layer is a layer of which magnetic properties disappear by the ferromagnetic layer (CoFeB) of the tunnel junction stacked film having the structure illustrated on the left side ofFIG.10. In Verification Experiment 2, in addition to the tunnel junction stacked film of Example, having a structure in which the Hf layer is inserted between two ferromagnetic layers, a tunnel junction stacked film having a structure in which a Ta layer is inserted between two ferromagnetic layers instead of the Hf layer, and a tunnel junction stacked film having a structure in which a W layer is inserted between two ferromagnetic layers instead of the Hf layer were prepared as a tunnel junction stacked film of Comparative Example, and similarly, the thickness of the magnetic dead layer was measured.

The tunnel junction stacked films of Example and Comparative Example were prepared by laminating each layer of Ta (5.0 nm), CoFeB (0.4 nm), MgO (1.5 nm), CoFeB (1.0 nm), Ta, W, or Hf (0 to 0.7 nm), CoFeB (1.0 nm), MgO (1.1 nm), and Ta (1.0 nm) on a Si substrate in which a SiO2film is formed on the surface, in this order, by a sputtering method, and then, by performing a heat treatment at 400° C. Three tunnel junction stacked films of Example were prepared in which the thickness of the Hf layer was 0.2 nm, 0.35 nm, and 0.7 nm. Three tunnel junction stacked films of Comparative Example were prepared in which the thickness of the Ta layer or the W layer was 0.2 nm, 0.35 nm, and 0.7 nm both in a case where the Ta layer is inserted and a case where the W layer is inserted. The results thereof are shown in a graph on the right side ofFIG.10.

In the graph on the right side ofFIG.10, a horizontal axis is a film thickness t (nm) of the Hf layer, the Ta layer, or the W layer, and a vertical axis is the thickness (nm) of the magnetic dead layer. A solid line and a black circle in the drawing are the result of the W layer, a dashed-dotted line and a void circle in the drawing are the result of the Hf layer, and a dotted line and a void square in the drawing are the result of the Ta layer. In the graph, in a case where the film thickness t of the Hf layer, the Ta layer, and the W layer is 0.2 nm, the thickness of the magnetic dead layer is extremely small in any case where the Hf layer, the Ta layer, or the W layer is inserted. It was obvious that in a case where the film thickness t of the Hf layer, the Ta layer, and the W layer is 0.3 nm or more, the thickness of the magnetic dead layer when the Ta layer or the W layer is inserted is extremely larger than the thickness of the magnetic dead layer when the Hf layer is inserted. This indicates that a considerable diffusion occurs between CoFeB and Ta or W when the Ta layer or the W layer is inserted, whereas a diffusion between CoFeB and Hf when the Hf layer is inserted is suppressed. In a diffusion between CoFeB and Ta, W, or Hf, it is known that a damping constant increases when heavy metals such as W, Ta, and Hf with an atomic number greater than an atomic number of Co or Fe are mixed with Co or Fe. It is preferable to select a heavy metal that has a small diffusion amount, that is, decreases the thickness of the magnetic dead layer. When the film thickness t of the Hf layer, the Ta layer, and the W layer is 0.3 nm or more, the diffusion is further suppressed and an increase in a damping constant α of CoFeB is further suppressed in a case where the Hf layer is inserted than in a case where the Ta layer or the W layer is inserted. For this reason, it is preferable that the Hf layer is inserted since the write current ICOdecreases. The film thickness of the Hf layer is preferably 0.2 nm or more, and more preferably 0.3 nm or more. In order to form the Hf layer into the shape of a layer, a thickness of approximately 0.2 nm is required. In addition, by setting the thickness to 0.3 nm or more, an effect of preventing the diffusion compared to Ta or W increases.

(4-1) Tunnel Junction Stacked Film of Third Embodiment

A tunnel junction stacked film of a third embodiment is different from the tunnel junction stacked film of the first embodiment in the configuration of the recording layer. The other configurations, the write operation the read operation, and the like are identical to those of the first embodiment, and thus, the configuration of the recording layer will be mainly described.

As illustrated inFIG.11in which the same reference numerals are applied to the same configurations as those inFIG.1, a recording layer14eof a tunnel junction stacked film (MTJ film)1eof the third embodiment is configured by laminating the first ferromagnetic layer24adjacent to the tunnel junction layer13, a first Hf layer25aadjacent to the first ferromagnetic layer24, the second ferromagnetic layer26adjacent to the first Hf layer25a, and a second Hf layer25badjacent to the second ferromagnetic layer26in this order. Further, the MTJ film1eincludes the cap layer15adjacent to the second Hf layer25bof the recording layer14e.

The first Hf layer25ais provided adjacent to the first ferromagnetic layer24and the second ferromagnetic layer26. The first Hf layer25ais a thin film containing hafnium. The first Hf layer25ahas a function as a non-magnetic coupling layer in which the recording layer14ehas a ferromagnetic coupling structure, and the recording layer14ehas the ferromagnetic coupling structure in which the magnetization24M of the first ferromagnetic layer24and the magnetization26M of the second ferromagnetic layer26are ferromagnetically coupled. The magnetization of the first ferromagnetic layer24and the magnetization of the second ferromagnetic layer26are ferromagnetically coupled by the interlayer interaction, and the magnetization directions are parallel to each other. InFIG.11, a void arrow represents the direction of the magnetization24M of the first ferromagnetic layer24and the direction of the magnetization26M of the second ferromagnetic layer26. It is represented that the magnetization24M and the magnetization M26are directed to the perpendicular direction with respect to the film surface, and the first ferromagnetic layer24and the second ferromagnetic layer26are a perpendicular magnetization film.

The second Hf layer25bis disposed in a position furthest from the tunnel junction layer13to which the recording layer14eis adjacent, in the recording layer14ehaving a multi-layer structure, and the surface of the second Hf layer25bfacing the surface adjacent to the second ferromagnetic layer26is adjacent to the cap layer15.

In this embodiment, the first ferromagnetic layer24, the first Hf layer25a, and the second ferromagnetic layer26have the same configurations as those of the first ferromagnetic layer24, the Hf layer25, and the second ferromagnetic layer26described in the first embodiment, respectively. In addition, the second Hf layer25bhas the same configuration as that of the Hf layer25described in the second embodiment.

(4-2) Action and Effect

In the configuration described above, the tunnel junction stacked film1eof the third embodiment includes the recording layer14eincluding the first ferromagnetic layer24containing boron, the tunnel junction layer13adjacent to the recording layer14e, and the reference layer12adjacent to the tunnel junction layer13. Here, the recording layer14eincludes the first ferromagnetic layer24adjacent to the tunnel junction layer13, the first Hf layer25aadjacent to the first ferromagnetic layer24, the second ferromagnetic layer26adjacent to the first Hf layer25a, and the second Hf layer25badjacent to the second ferromagnetic layer26. Further, the tunnel junction stacked film1eincludes the cap layer15adjacent to the second Hf layer25bof the recording layer14e. The first ferromagnetic layer24and the reference layer12are magnetized in the perpendicular direction with respect to the film surface.

In the tunnel junction stacked film1e, the perpendicular magnetic anisotropy of the first ferromagnetic layer24can be improved by being adjacent to the first Hf layer25a, the thermal stability of the magnetization of the first ferromagnetic layer24is improved, and a thermal stability of the recording layer14eis high. Accordingly, the tunnel junction stacked film1ehaving a high thermal stability can be provided, and a magnetic memory element and a magnetic memory having high nonvolatility can be provided by using the tunnel junction stacked film1ehaving a high thermal stability in the magnetic memory element or the magnetic memory.

Further, in the tunnel junction stacked film1e, the perpendicular magnetic anisotropy of the second ferromagnetic layer26can be improved by being adjacent to the first Hf layer25aand the second Hf layer25b, the thermal stability of the second ferromagnetic layer26is improved, the thermal stability of the recording layer14ecan be further increased, and the tunnel junction stacked film1ehaving a higher thermal stability can be provided.

Further, the tunnel junction stacked film1eis configured such that the second Hf layer25bis disposed in the position furthest from the tunnel junction layer13in the recording layer14e, and thus, the diffusion of atoms of a material configuring a layer adjacent to the second Hf layer25b, such as the cap layer15, to the second ferromagnetic layer26from the layer can be suppressed, the saturation magnetization Ms of the second ferromagnetic layer26decreases, and a decrease in the thermal stability can be suppressed. Accordingly, the thermal stability of the MTJ film1ecan be further improved.

REFERENCE SIGN LIST