Magnetoresistive element and magnetic memory

The present invention relates to a magnetoresistive element and a magnetic memory, and relates to a magnetoresistive element capable of recording information by supplying an electric current in both directions, and a magnetic memory using the same.

In recent years, many solid-state memories that record information based on a new principle have been proposed. Among them, as a solid-state magnetic memory, a magnetic random access memory (MRAM: Magnetoresistive Random) that utilizes the tunnel magnetoresistive (TMR) effect. Access Memory) is in the limelight. MRAM is characterized in that data is stored according to the magnetization state of the MTJ (Magnetic Tunnel Junction) element.

In a conventional MRAM that writes with a magnetic field generated by a wiring current, the holding force Hc increases when the MTJ element size is reduced, so that the current required for writing tends to increase. Actually, in order to produce MRAM with a large capacity of 256 Mbits or more, it is necessary to reduce the chip size, and in order to realize it, increase the cell array occupancy in the chip and suppress the reduction of MTJ element size. However, it is necessary to reduce the write current to the μA level. The reduction of MTJ element size and the reduction of write current are in a contradictory relationship, and it is difficult for conventional MRAM to achieve both miniaturization of cell size and reduction of current for a large capacity exceeding 256 Mbits. ..

As a writing method that overcomes such problems, MRAM using a spin angular momentum transfer (SMT) writing method has been proposed (for example, Patent Document 1 and Non-Patent Documents 1 and 2). In spin angular momentum transfer (hereinafter referred to as spin injection) magnetization reversal, the reversal current Ic required for magnetization reversal is defined by the current density Jc. Therefore, as the device area becomes smaller, the reversal current Ic for magnetization reversal by spin injection also becomes smaller.

Compared to the conventional magnetic field writing method described above, when writing with a constant current density, the writing current becomes smaller as the MTJ element size becomes smaller, so it is expected to be excellent in scalability. However, in the current spin injection MRAM, the current density Jc required for its magnetization reversal is 10 mA / cm.²Very large above, 100nm²Even when a size MTJ element is used, a write current of about 1 mA is required.

This is because in the case of the spin injection magnetization reversal method, bidirectional energization is required, and the spin injection efficiency differs depending on the energization direction. That is, the spin injection magnetization reversal curve becomes asymmetric. This is a case where the magnetization direction of the free layer is reversed so that the magnetization arrangements of the magnetization free layer (hereinafter referred to as the free layer) and the magnetization reference layer (hereinafter referred to as the pin layer) are parallel to antiparallel. The current is about twice as much as when inverting from antiparallel to parallel.

As a problem associated with this asymmetry, when a tunnel magnetoresistive (TMR) effect film is used, the current threshold is small when energizing and writing in order to reverse the magnetization arrangement of the free layer and the pin layer from antiparallel to parallel. there is no problem. However, when writing with energization to reverse the magnetization arrangement of the free layer and the pin layer from parallel to antiparallel, a large writing current is the cause, and if writing is performed with a constant current density Ia-ap, the TMR effect The element resistance Rap at the time of antiparallel arrangement increases by the amount corresponding to, and as a result, the write voltage Vp-ap increases.

Therefore, if the withstand voltage of the tunnel barrier layer is not sufficiently high, the breakdown voltage Vbd of the tunnel barrier layer is reached before the antiparallel magnetization arrangement is formed, and the tunnel barrier layer has a problem of dielectric breakdown. Further, even if the dielectric breakdown is not broken, there is a problem that the operation reliability under a high voltage cannot be ensured.<patcit num="1"><text>U.S. Pat. No. 6,256,223</text></patcit><nplcit num="1"><text>C. Slonczewski, Current-driven ecitation of magnetic multilayers, JORNAL OF MAGNETISM AND MAGNETIC MATERIALS, VOLUME 159, 1996, pp.L1-L7</text></nplcit><nplcit num="2"><text>L. Berger, Emission of spin waves by a magnetic multilayer traversed by a current, PHYSICAL REVIEW B, VOLUME 54, NUMBER 13, 1996, pp.9353-9358</text></nplcit>

<p> The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetoresistive element capable of further reducing the reversal current at the time of magnetization reversal and a magnetic memory using the same. ..</p>

<p> The magnetic resistance element according to the first viewpoint of the present invention includes a first magnetization reference layer in which the magnetization direction is fixed, a magnetization free layer in which the magnetization direction is changed by the action of spin-polarized electrons, and a magnetization. A second magnetization reference layer having a fixed direction, a first intermediate layer provided between the first magnetization reference layer and the magnetization free layer, and the magnetization free layer and the second magnetization reference. A second intermediate layer provided between the layers is provided, and the easy magnetization direction of the magnetization free layer and the first magnetization reference layer is perpendicular or parallel to the film surface, and the first The easy magnetization directions of the magnetization reference layer 1 and the second magnetization reference layer are orthogonal to each other.</p><p> The magnetic memory according to the second viewpoint of the present invention includes a memory cell including a magnetoresistive element according to the first viewpoint and first and second electrodes for energizing the magnetoresistive element. It is characterized by that.</p>

<p> According to the present invention, it is possible to provide a magnetoresistive element capable of further reducing the reversal current at the time of magnetization reversal and a magnetic memory using the same.</p>

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, elements having the same function and configuration are designated by the same reference numerals, and duplicate explanations will be given only when necessary.

(First Embodiment) FIG. 1 is a cross-sectional view showing the configuration of the MTJ element 10 according to the first embodiment of the present invention. FIG. 1 shows the basic configuration of the MTJ element 10 of the present embodiment. The arrows in the figure indicate the direction of magnetization.

In the MTJ element 10, the first magnetization reference layer (pin layer) 11, the first intermediate layer 12, the magnetization free layer (free layer) 13, the second intermediate layer 14, and the second magnetization reference layer 15 are laminated in this order. It has a laminated structure. In this basic configuration, the stacking order may be reversed.

The direction of magnetization (or spin) of the pin layer 11 and the pin layer 15 is fixed. In the free layer 13, the direction of magnetization changes (inverts). Further, the easy magnetization direction of the pin layer 11 and the free layer 13 is perpendicular to the film surface (or the laminated surface) (hereinafter referred to as perpendicular magnetization), and the easy magnetization direction of the pin layer 15 is parallel to the film surface. (Hereinafter referred to as in-plane magnetization). That is, the pin layer 11 and the pin layer 15 have easy magnetization directions orthogonal to each other.

The easy magnetization direction is the direction in which the internal energy becomes the lowest when the spontaneous magnetization faces that direction in the absence of an external magnetic field, assuming a ferromagnet of a certain macro size. The difficult magnetization direction is the direction in which the internal energy becomes the largest when the spontaneous magnetization points in that direction in the absence of an external magnetic field, assuming a ferromagnet of a certain macro size.

In this embodiment, a perpendicular magnetization film is used as the free layer 13. By using a perpendicular magnetization film for the free layer 13, the aspect ratio Ar (ratio of the short side length to the long side length of the element, that is, Ar = long side length / short side length) of the MTJ element size is designed to be 1. It becomes possible. This is because in the case of an in-plane magnetized film, the anisotropic magnetic field (Hk) required for thermal stability is covered by the shape magnetic anisotropy energy, so the aspect ratio of the MTJ element becomes larger than 1. .. On the other hand, in the case of a vertically magnetized film, the anisotropic magnetic field (Hk) required for thermal stability is covered by the crystalline magnetic anisotropy energy, so that the anisotropic magnetic field (Hk) is This is because it does not depend on the aspect ratio of the MTJ element.

As a result, the MTJ element size can be miniaturized. In this case, if a TMR film with the same current density Jc required for magnetization reversal by spin injection is used, the spin injection reversal current Ic will be perpendicular magnetization between the in-plane magnetization film and the perpendicular magnetization film having the same MTJ element width. Since the aspect ratio Ar of the film is smaller, it is reduced.

In the MTJ element 10 configured in this way, data is written as follows. In this embodiment, the electric current refers to the flow of electrons. First, the MTJ element 10 is energized in both directions in a direction perpendicular to the film surface (or laminated surface).

As a result, the free layer 13 is supplied with electron spins that are polarized to majority and minority. Then, the spin angular momentum of the majority electron spin moves to the free layer 13, so that the spin torque is applied to the free layer 13 and induces the magnetization rotation of the free layer 13. Since the spin torque is represented by the outer product of the unit vector of the magnetization direction of the pin layer and the free layer, the spin torque can be applied to the free layer from both of the two orthogonal pin layers. As a result, the magnetization reversal current due to spin injection can be reduced.

Specifically, when electrons are supplied from the pin layer 11 side (that is, electrons going from the pin layer 11 to the free layer 13), the electrons spin-polarized in the same direction as the easy magnetization direction of the pin layer 11 and the pins Electrons that are spin-polarized in the direction opposite to the direction of easy magnetization of the pin layer 15 by being reflected by the layer 15 are injected into the free layer 13. In this case, the magnetization direction of the free layer 13 is aligned with the easy magnetization direction of the pin layer 11. As a result, the directions of magnetization of the pin layer 11 and the free layer 13 are arranged in parallel. In the case of this parallel arrangement, the resistance value of the MTJ element 10 is the smallest, and this case is defined as data 0.

On the other hand, when electrons are supplied from the pin layer 15 side (that is, electrons going from the pin layer 15 to the free layer 13), the electrons spin-polarized in the same direction as the easy magnetization direction of the pin layer 15 and the pin layer 11 By being reflected, electrons spin-polarized in the direction opposite to the easy magnetization direction of the pin layer 11 are injected into the free layer 13. In this case, the magnetization direction of the free layer 13 is aligned with the direction opposite to the easy magnetization direction of the pin layer 11. As a result, the magnetization directions of the pin layer 11 and the free layer 13 become antiparallel. In the case of this antiparallel arrangement, the resistance value of the MTJ element 10 is the largest, and this case is defined as data 1.

Next, the data is read out as follows. A read current is passed through the MTJ element 10 to detect a change in the resistance value of the MTJ element 10. This read current is set to a value smaller than the write current.

Here, since the easy magnetization direction of the free layer 13 is perpendicular to the membrane surface, a magnetoresistive effect is exhibited between the free layer 13 and the pin layer 11 in which the magnetization arrangement is parallel, but the magnetization arrangement is exhibited. The magnetoresistive effect via the intermediate layer 14 is not exhibited between the pin layer 15 and the pin layer 15 having a vertical value. This is a great merit, and the second problem with magnetoresistive elements having a dual pin layer structure (that is, a structure in which two pin layers are arranged on both sides of a free layer via an intermediate layer). It is possible to avoid deterioration of the read output due to the pin layer of.

That is, in the MTJ element 10 of the present embodiment, the directions of magnetization of the two pin layers (pin layer 11 and pin layer 15) are orthogonal to each other. Therefore, the same material in both the intermediate layer 12 and the intermediate layer 14, for example, MgO (magnesium oxide), AlO_xWhen an insulator such as (aluminum oxide) is used, high spin injection efficiency can be obtained by the two pin layers, and at the same time, the magnetoresistive effect is exhibited only in one intermediate layer.

Therefore, in the conventional dual-pin layer structure, although high spin injection efficiency can be obtained, the TMR ratio required at the time of reading is lowered because the magnetoresistive effects opposite to each other are exhibited in both the intermediate layer 12 and the intermediate layer 14. However, in the present embodiment, this problem can be avoided.

Next, a more detailed specific example of the MTJ element 10 of the present embodiment will be described. FIG. 2 is a cross-sectional view showing a specific example of the MTJ element 10. For example, in a planar shape, the aspect ratio of the free layer 13 is set to approximately 1.

The lowermost layer on the substrate (not shown) side is provided with a base layer 16 for controlling the crystal orientation or crystallinity of the basic configuration. For the base layer 16, for example, a non-magnetic metal layer is used. The uppermost layer is provided with a cap layer 17 for protecting the basic configuration from deterioration such as oxidation and corrosion. For the cap layer 17, for example, a non-magnetic metal layer is used.

FIG. 3 is a cross-sectional view showing another configuration of the pin layer 15. The easy magnetization direction of the pin layer 15 is parallel to the film surface. The pin layer 15 has a laminated structure of pin layer 15C / intermediate layer 15B / pin layer 15A. Further, an antiferromagnetic layer 18 is provided on the pin layer 15C (between the pin layer 15 and the cap layer 17) so as to be in contact with the pin layer 15C. The pin layer 15C is exchanged with the antiferromagnetic layer 18 so that the direction of magnetization is fixed parallel to the film surface.

The easy magnetization direction of the pin layer 15A and the pin layer 15C is parallel to the film surface. Further, the magnetization directions of the pin layer 15A and the pin layer 15C are set to be antiparallel (opposite directions) to each other, and the pin layer 15A and the pin layer 15C are antiferromagnetically coupled with the intermediate layer 15B in between. Synthetic Anti-Ferromagnet (SAF) structure is a laminated structure of the first magnetic layer / intermediate layer (non-magnetic layer) / second magnetic layer whose magnetization directions are antiparallel to each other via the intermediate layer. That is. By using this SAF structure, the magnetization fixing force of the pin layer 15 is enhanced, and the resistance to an external magnetic field and the thermal stability can be improved. Specifically, the temperature dependence of the magnetization fixing force of the pin layer 15 is improved.

In the SAF structure, the saturation magnetization of the first magnetic layer (corresponding to the pin layer 15C) is Ms1, the film thickness is t1, the saturation magnetization of the second magnetic layer (corresponding to the pin layer 15A) is Ms2, and the film thickness is Assuming t2, by setting Ms1 · t1 Ms2 · t2, the product Ms · t of the apparent saturation magnetization of the pin layer 15 and the thickness of the magnetic layer can be made almost zero. As a result, the pin layer 15 is less likely to react to the external magnetic field, and the resistance to the external magnetic field can be further improved.

A metal material such as Ru (ruthenium) or Os (osmium) is used for the intermediate layer 15B in the SAF structure, and the film thickness is set to 3 nm or less. This is to obtain a sufficiently strong antiferromagnetic bond via the intermediate layer 15B. By using such an intermediate layer 15B, the magnetization fixing force of the pin layer 15 is enhanced, and the resistance to an external magnetic field and the thermal stability are improved.

FIG. 4 is a cross-sectional view showing another configuration of the pin layer 11. An antiferromagnetic layer 19 is provided below the pin layer 11 (between the pin layer 11 and the base layer 16) so as to be in contact with the pin layer 11. The pin layer 11 is exchanged with the antiferromagnetic layer 19 so that the direction of magnetization is fixed perpendicular to the film surface. By using this structure, the magnetization fixing force of the pin layer 11 is enhanced, and the resistance to an external magnetic field and the thermal stability are improved.

FIG. 5 is a cross-sectional view showing another configuration of the pin layer 11. The pin layer 11 has a laminated structure of pin layer 11C / intermediate layer 11B / pin layer 11A. That is, the pin layer 11 has a SAF structure.

The easy magnetization direction of the pin layer 11A and the pin layer 11C is perpendicular to the film surface. Further, the directions of magnetization of the pin layer 11A and the pin layer 11C are set to be antiparallel to each other, and the pin layer 11A and the pin layer 11C are antiferromagnetically coupled with the intermediate layer 11B interposed therebetween. By using this SAF structure, the magnetization fixing force of the pin layer 11 is enhanced, and the resistance to an external magnetic field and the thermal stability are improved. In this configuration, an antiferromagnetic layer may be provided under the pin layer 11A so as to be in contact with the pin layer 11A, and the pin layer 11A and the antiferromagnetic layer may be exchanged and coupled.

FIG. 6 is a cross-sectional view showing another configuration of the free layer 13 and the pin layer 11. The free layer 13 has a laminated structure of an interface free layer 13C / a free layer 13B / an interface free layer 13A. As described above, it is preferable that the interface free layer made of a ferromagnet is inserted between the free layer 13B and the intermediate layer 12 or between the free layer 13B and the intermediate layer 14.

Further, as shown in FIG. 6, the pin layer 11 has a laminated structure of the interface pin layer 11E / pin layer 11D. As described above, it is preferable that the interface pin layer 11E made of a ferromagnet is inserted between the pin layer 11D and the intermediate layer 12.

The interface pin layer and the interface free layer have the effect of increasing the magnetoresistive effect, and further have the effect of reducing the write current during spin injection writing. Further, for the interfacial layer that increases the magnetoresistive effect, it is desirable that the bulk polarizability of the material itself is large, and further, the material can be selected so that the interfacial polarizability with the intermediate layer is increased. preferable.

Next, the materials of each layer constituting the MTJ element 10 will be described.

[1] Materials used for the intermediate layer 12 and the intermediate layer 14 In the MTJ element 10 of the present embodiment, an insulator or a semiconductor is used for the intermediate layer 12. In this case, the tunnel magnetoresistive effect is exhibited in the constituent parts of the free layer 13 / intermediate layer 12 / pin layer 11. Therefore, at the time of reading, the magnetization directions of the pin layer 11 and the free layer 13 become parallel or antiparallel, so that the resistance value of the MTJ element 10 becomes low resistance or high resistance, and the respective states are data 0 or Determined as data "1".

On the other hand, in the constituent parts of the pin layer 15 / intermediate layer 14 / free layer 13, the tunnel magnetoresistive effect is not exhibited because the magnetization directions of the free layer 13 and the pin layer 15 are orthogonal to each other. Therefore, any of a metal conductor, an insulator, and a semiconductor may be used for the intermediate layer 14. However, when an insulator or a semiconductor is used, the resistance value of the MTJ element increases, so it is preferable to use a metal conductor.

Here, as the metal conductor used for the intermediate layer 14, Cu (copper), Al (aluminum), Ag (silver), Au (gold) and the like are preferable. Furthermore, in order to improve the spin injection efficiency by using the current concentration effect that locally increased the current density, MgO-Cu and AlO_x-Using a mixed crystal structure material of a conductive metal phase such as Cu and an insulating phase also has the effect of reducing the magnetization reversal current of the free layer.

The film thicknesses of the intermediate layer 12 and the intermediate layer 14 are set to be 3 nm or less when the tunnel magnetoresistive effect is used. This is 1x10 when writing information⁵~1×10⁷A / cm²Since it is necessary to pass a tunnel current of about 100Ωμm, the resistance and area product (RA) of the MTJ element is 100Ωμm.²This is because it is necessary to make it as small as possible.

The insulator used for the intermediate layer 12 and the intermediate layer 14 is Al.₂O₃Oxides such as (aluminum oxide), MgO (magnesium oxide), CaO (calcium oxide), SrO (strontium oxide), TiO (titanium oxide), EuO (eurobium oxide), ZrO (zirconium oxide) and HfO (hafnium oxide) Can be given. As semiconductors, compound semiconductors such as Ge (germanium), Si (silicon), GaAs (gallium arsenide) and InAs (indium arsenide), TiO₂Examples include oxide semiconductors such as (titanium oxide). MgO, CaO, SrO, TiO, and EuO have a NaCl structure.

Among these, MgO having a NaCl structure is a preferable material for the intermediate layer 12. This is because the TMR ratio is the largest when MgO is used. When MgO is used, the RA of the MTJ element is 5Ωμm.²More than 1000Ωμm²It is possible to obtain a TMR ratio of 100% or more within the following range. This MgO has a NaCl structure, and the (100) plane orientation is the most preferable as the crystal orientation from the viewpoint of the TMR ratio. Further, when the MgO layer is formed, the TMR ratio can be further improved by inserting an Mg layer of 1 nm or less in the upper part or the lower part of the MgO.

The MgO layer is formed by sputtering with a noble gas (Ar (argon), Ne (neon), Kr (krypton) or Xe (xenon)) using an MgO target, or O using an Mg target.₂It is formed by an oxidation-reactive sputtering method in an atmosphere. It can also be formed by forming the Mg layer and then oxidizing it with oxygen radicals, oxygen ions, ozone, or the like. Furthermore, it can also be formed by epitaxial growth by a molecular beam epitaxy (MBE) method or an electron beam deposition (electron beam deposition) method using MgO.

Here, in order to obtain a large TMR ratio, it is necessary to improve the degree of orientation of MgO. Based on the plane orientation of MgO, the orientation of the magnetic layer, which is the underlying layer to be selected, is determined. MgO is preferably (100) plane oriented. In order to preferentially orient MgO on the (100) plane, the underlying layer (free layer, pin layer, interface free layer or interface pin layer, etc.) must be BCC (Body-Centered Cubic) structure (100) oriented plane, FCC ( Face-Centered Cubic) structure (100) Orientation plane or amorphous structure is preferable.

As a material for BCC structure, BCC-Fe_100-xCo_x(0 x 70 at (atom)%), BCC-Co of 1 nm or less grow epitaxially on the BCC structure, and the like. Alternatively, BCC-Fe_100-x(CoNi)_x(0 x 70 at%) or the like may be used. In this case, the effect of increasing the TMR ratio of 10 to 20% can be obtained by adding dilute Ni of 10 at% or less. Examples of the amorphous material include Co (cobalt) -Fe (iron) -B (boron) alloy and Fe-Co-Zr alloy.

[2] Magnetic Material Used for Perpendicular Magnetization Free Layer and Perpendicular Magnetization Pin Layer In this embodiment, a perpendicular magnetization film is used for the perpendicular magnetization free layer 13 and the pin layer 11. When the in-plane magnetization free layer is used, the switching magnetic field strongly depends on the size of the MTJ element, but by using the perpendicular magnetization free layer, the dependence on the MTJ element size becomes small.

That is, in the case of in-plane magnetization, the switching magnetic field changes depending on the device shape and device size in order to maintain the stability of magnetization by the shape magnetic anisotropy energy utilizing saturation magnetization. On the other hand, in the case of perpendicular magnetization, in order to reduce the saturation magnetization and maintain the stability of magnetization by the crystalline magnetic anisotropy energy that does not depend on the element shape and element size, the switching magnetic field depends on the element shape and element size. It's less likely to change. Therefore, by using the perpendicular magnetization free layer, the problem of the MTJ element using the in-plane magnetization film that the switching magnetic field of the MTJ element increases when the MTJ element is made smaller is solved, which is preferable for miniaturization of the MTJ element.

The vertical magnetization film used for the MTJ element 10 of the present embodiment includes at least one of Fe (iron), Co (cobalt), Ni (nickel) and Mn (manganese), and Pt (platinum) and Pd (Platinum). Basically contains at least one of palladium), Ir (iridium), Rh (rhodium), Os (osmium), Au (gold), Ag (silver), Cu (copper), and Cr (chromium). And. Furthermore, B (boron), C (carbon), Si (silicon), and Al (aluminum) are used to adjust the saturation magnetization, control the crystal magnetic anisotropy energy, and adjust the crystal grain size and intergranular bond. ), Mg (magnesium), Ta (tantal), Zr (zirconium), Ti (titanium), Hf (hafnium), Y (yttrium), and at least one element selected from rare earth elements may be added. .. By adding these elements, the saturation magnetization Ms and the crystal magnetic anisotropy energy Ku can be reduced without impairing the perpendicular magnetization, and the fragmentation and fineness of the crystal grains can be promoted.

Specific examples of the material containing Co as a main component include a Co-Cr-Pt alloy having an HCP (Hexagonal Closest Packing) structure, a Co-Cr-Ta alloy, and a Co-Cr-Pt-Ta alloy. .. These are 1 × 10 by adjusting the composition of each element.⁵Above 1 × 10⁷It is possible to adjust the crystal magnetic anisotropy energy within the range of less than erg / cc. When these materials are used for the pin layer on the side close to the substrate, it is preferable to use Ru having an HCP structure as the base layer.

Co-Pt alloy is Co₅₀Pt₅₀In the composition range near (at%), L1₀-Forms a CoPt ordered alloy. This ordered alloy has an FCT (Face-Centered Tetragonal) structure. When MgO (100) is used as the intermediate layer 12, the (001) plane-oriented FCT-CoPt ordered alloy is preferable because the interface mismatch with the intermediate layer 12 can be reduced. Further, even when the interface layer is inserted between the intermediate layer and the free layer (or pin layer), the interface layer can be easily oriented in the (100) plane.

Specific examples of the material containing Fe as a main component include Fe-Pt alloy and Fe-Pd alloy. Among them, Fe-Pt alloy has a composition of Fe.₅₀Pt₅₀L1 regularized at (at%) and based on the FCT structure₀Has a structure. The composition of Fe-Pt alloy is Fe.₇₅Pt₂₅L1 regularized at (at%) and based on the FCT structure₂Structure (Fe₃It has a Pt structure). This makes 1x10⁷It is possible to express a large crystal magnetic anisotropy energy of erg / cc or more.

Fe₅₀Pt₅₀Alloy is L1₀Before regularizing into structure, it has an FCC structure. The crystal magnetic anisotropy energy in this case is 1 × 10.⁶It is about erg / cc. Therefore, by adjusting the annealing temperature and composition, controlling the regularity by the laminated structure, and adding additives, 5 × 10⁵erg / cc or more 5 × 10⁸The crystal magnetic anisotropy energy can be adjusted within the range of erg / cc or less. In addition, the saturation magnetization is about 800 to 1100 emu / cc before addition, but it can be reduced to 800 emu / cc or less. This is preferable in terms of low current density Jc when used in the free layer.

Specifically, L1₀Fe-Pt by adding Cu (copper), Ti (titanium), V (vanadium), Mn (manganese), Cr (chromium), etc. to a regular Fe-Pt alloy in the range of 30 at% or less. It is possible to control the saturation magnetization (Ms) of the alloy and the magnetocrystalline anisotrophic energy (Ku). Further, regarding V, it has the effect of lowering the damping constant (magnetization braking constant), which is important in spin injection magnetization reversal, and also has the effect of reducing the reversal current.

L1₀Structure or L1₂The structurally regularized Fe-Pt alloy has an FCT structure and has an FCC structure before regularization. Therefore, it is very consistent with MgO (100). Specifically, by growing BCC-Fe oriented in the (100) plane on the MgO (100) plane and laminating Pt (100) on it, the (100) plane preferential orientation is placed on the MgO (100). Growing L1₀Structure or L1₂It is possible to form Fe-Pt ordered alloys of structure. Further, when BCC-Cr is formed between the Fe-Pt ordered alloy and MgO (100), the (100) plane orientation of the Fe-Pt ordered alloy is further prioritized, which is desirable.

Also, L1₀Structure or L1₂When forming a Fe-Pt ordered alloy of structure, forming a multilayer structure of [Fe / Pt] n (n is an integer of 1 or more) is close to the ideal rule L1.₀Structure or L1₂Fe-Pt ordered alloys of structure can be formed. In this case, it is desirable that the film thicknesses of Fe and Pt are set to be 0.1 nm or more and 3 nm or less. This is essential to create a uniform compositional state, thereby L1.₀Structure or L1₂The regularization of the Fe-Pt alloy in structure is important because it involves a martensitic transformation from the FCC structure to the FCT structure, which promotes this transformation.

Also, L1₀Structure or L1₂The regularized temperature of the Fe-Pt alloy of the structure is as high as 500 degrees or more, and it has excellent heat resistance. This point is highly preferable because it has resistance to annealing treatment in the subsequent step. Further, the regularized temperature can be lowered by the above-mentioned additive elements such as Cu and Pd in the range of 30 at% or less.

Other perpendicularly magnetized films used in the MTJ element 10 of the present embodiment include ferrimagnetic materials containing at least one of Fe, Co, Ni, Mn, Cr and rare earth elements. Rare earth elements include La (lantern), Ce (cerium), Pr (placeodium), Nd (neodymium), Pm (bromethium), Sm (samarium), Eu, Gd (gadolinium), Tb (terbium), Dy (dysprosium). ), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

The ferrimagnetic material containing a rare earth element has an amorphous structure. By adjusting the composition of this ferrimagnetic material, the saturation magnetization is reduced to 400 emu / cc or less, and the crystal magnetic anisotropy energy is 1 × 10.⁶It can be improved to erg / cc or higher.

Further, as the perpendicular magnetization film used for the MTJ element 10 of the present embodiment, a ferromagnet composed of a mixed crystal of a metal magnetic phase and an insulating phase may be used. In this case, the metal magnetic phase is at least one of Fe, Co, Ni, and Mn, and at least one of Pt, Pd, Ir, Rh, Os, Au, Ag, Cu, Cr, Ta, and rare earth elements. It is composed of ferromagnetic materials including one or more types. The insulating phase is an oxide, nitride, and acid nitride containing at least one element selected from B, C, Si, Al, Mg, Ta, Cr, Zr, Ti, Hf, Y, and rare earth elements. Consists of.

Since the ferromagnetic material consisting of a mixed crystal of the metal magnetic phase and the insulating phase is separated into a conductive metal magnetic material part and a non-conductive insulating material part, the current is concentrated in the metal magnetic material part. As a result, the energized area becomes smaller and the local current density increases. This has the effect of reducing the reversal current that is substantially required.

In order to obtain such an effect, it is necessary to control the crystallinity. The two-phase separated structure includes a granular (grain dispersion) type structure, an island (island-like) type structure, and a columnar (columnar) type structure. In the case of the columnar type structure, since the metal magnetic material portion penetrates vertically in the magnetic layer, the current constriction effect can be easily obtained. In the case of the granular type structure and the island type structure, the current energizes the path having the smallest tunnel barrier, so that the current constriction effect can be obtained as in the columnar type structure.

In addition, examples of the perpendicular magnetization film used for the MTJ element 10 of the present embodiment include Mn-based ferromagnetic alloys and Cr-based ferromagnetic alloys. Mn-based ferromagnetic alloys include Mn-Al alloys, Mn-Au alloys, Mn-Zn alloys, Mn-Ga alloys, Mn-Ir alloys, and Mn-Pt.₃There are alloys and the like, which are characterized by having a regular grid. In addition, as a Cr-based magnetic alloy, Cr-Pt₃Examples include alloys. This is L1₀It has a regular lattice and has the characteristics of a ferrimagnetic material.

[3] Magnetic Material Used for In-plane Magnetized Pin Layer In the present embodiment, an in-plane magnetized film is used for the pin layer 15 whose magnetization direction is orthogonal to the pin layer 11.

As the in-plane magnetizing film used for the MTJ element 10 of the present embodiment, a ferromagnetic material containing at least one of Fe, Co, Ni, Mn, and Cr is used. As a material containing Fe, Co, and Ni as main components, specifically, Fe having an FCC structure or a BCC structure._xCo_yNi_zAlloys (x 0, y 0, z 0, x + y + z = 1) can be mentioned.

As the material used for the pin layer, a half-metal material having a large polarizability and capable of achieving 100% polarizability in principle is preferable.

As a material containing Mn, an Mn-based ferromagnetic Whistler alloy can be mentioned as a half metal material. Here, the Mn-based ferromagnetic Whistler alloy is A.₂It is a body-centered cubic system alloy having a ordered lattice represented by MnX. Element A is a material selected from Cu, Au, Pd, Ni, and Co. Element X is a material selected from Al (aluminum), In (indium), Sn (tin), Ga (gallium), Ge (germanium), Sb (antimony), and Si (silicon). Of the Whisler alloys, Co with a BCC structure₂BCC (100) plane orientation of MnAl alloys and the like improves consistency with MgO (100).

The film thickness of the ferromagnetic layer in the pin layer needs to be 1 nm or more. This is because if the film thickness is less than the above, the ferromagnetic layer does not become a continuous film, the characteristics as a magnetic layer are not sufficiently exhibited, and a sufficient magnetoresistive effect ratio (TMR ratio or GMR (Giant Magnetoresistive) ratio) is obtained. I can't. The maximum film thickness is preferably 3 nm or less. This is because when the film thickness exceeds 3 nm, the precession length of the coherent spin is far exceeded, and therefore the current threshold required for spin injection magnetization reversal becomes significantly large.

When the above-mentioned in-plane magnetized pin layer serves as a base layer for the MgO barrier layer, the composition formula Fe_xCo_yNi_zThe material represented by the alloy (x 0, y 0, z 0, x + y + z = 1) preferably has a (100) plane orientation and a BCC structure. Furthermore, the composition formula Fe_xCo_yNi_zB, C, N, etc. can be added to the material represented by the alloy (x 0, y 0, z 0, x + y + z = 1) at a concentration of 30 at% or less to form an amorphous structure. preferable. This is because the MgO film tends to preferentially orient the (100) plane on the film having an amorphous structure.

[4] Materials used for the interface-free layer and the interface-pin layer The interface-pin layer and the interface-free layer (hereinafter, both are referred to as the interface layer) shown in FIG. 6 have the effect of increasing the magnetoresistive effect, and further. , Has the effect of reducing the write current during spin injection writing. For the interfacial layer that increases the magnetoresistive effect, it is desirable that the bulk polarizability of the material itself is large, and further, it is preferable to select the material so that the interfacial polarizability with the intermediate layer is increased.

As the interface layer used in the MTJ element 10 of the present embodiment, a ferromagnetic material containing at least one of Fe, Co, Ni, Mn, and Cr is used. As a material containing Fe, Co, and Ni as main components, specifically, Fe having an FCC structure or a BCC structure._xCo_yNi_zAlloys (x 0, y 0, z 0, x + y + z = 1) can be mentioned. In addition, in order to reduce the saturation magnetization (Ms) of the above Fe-Co-Ni alloy, (Fe_xCo_yNi_z)_100-aX_aAlloys (x 0, y 0, z 0, x + y + z = 1, a (at%)&gt; 0, X is an additive element) are also preferred. By reducing the saturation magnetization (Ms), the inverting current can be significantly reduced. It is preferable that FeCoNi is 50 at% or more, but when x + y + z&gt; 50 at%, the coverage of the FeCoNi magnetic layer at the barrier layer interface is 50% or more, so the TMR phenomenon effect is exhibited. This is because it can be suppressed.

An additive that can be added without destroying the BCC structure and that can reduce saturation magnetization (Ms), that is, an additive having a total solid solution that can be solid-dissolved by a substitution type or a solid solution source to some extent, is V ( Examples include vanadium), Nb (niobium), Ta (tantalum), W (tungsten), Cr (chromium), Mo (molybdenum), Si (silicon), Ga (gallium), and Ge (germanium). Among these, V is also effective because it has the effect of reducing the damping constant (magnetization braking constant).

In addition, by adding intrusive elements such as B, C and N, or by adding Zr, Ta, Ti, Hf, Y, and rare earth elements that have almost no solid solution source, the crystal structure is made amorphous. Saturation magnetization (Ms) can be reduced by changing to. Such a material has, for example, an amorphous structure (Fe)._xCo_yNi_z)_100-bX_{b b}Alloys (x 0, y 0, z 0, x + y + z = 1, b (at%)&gt; 0, X is B, C, N, Zr, Ta, Ti, Hf, Y, and rare earths Additive elements such as elements) can be mentioned. However, in order to obtain a certain TMR ratio, it is important to promote recrystallization partially, that is, at the interface with MgO.

Examples of the material containing Mn include Mn-based ferromagnetic Whistler alloys. Here, the Mn-based ferromagnetic Whistler alloy is A.₂It is a body-centered cubic alloy having a ordered lattice represented by MnX. Element A is a material selected from Cu, Au, Pd, Ni, and Co. Element X is a material selected from Al, In, Sn, Ga, Ge, Sb, and Si. Of the Whisler alloys, Co with a BCC structure₂BCC (100) plane orientation of MnAl alloys and the like improves consistency with MgO (100). Mn-based Whistler alloys may exhibit half-metal-like conductive properties.

Moreover, an oxide material can also be used. As an oxide material, Fe₂O₃Such as half metal can be applied as an interface layer.

The minimum film thickness of the interface layer formed on the metal layer such as the free layer or the pin layer must be 0.5 nm or more, and the minimum film thickness of the interface layer formed on the insulating layer or the semiconductor layer is also required. , 0.5 nm or more is required. This is because if the film thickness is less than the above, the interface layer does not become a continuous film, the characteristics as an interface-free layer or an interface pin layer are not sufficiently exhibited, and a sufficient magnetoresistive effect ratio (TMR ratio or GMR ratio) is obtained. I can't. The maximum film thickness is preferably 5 nm or less. This is because when the film thickness exceeds 5 nm, the precession length of the coherent spin is far exceeded, and therefore the current threshold required for spin injection magnetization reversal becomes significantly large.

As described in detail above, according to the present embodiment, the spin injection efficiency into the free layer 13 can be improved by having two pin layers having magnetization directions perpendicular to each other in a dual pin layer structure. As a result, the switching speed of the MTJ element 10 can be improved. Further, as a result of improving the spin injection efficiency, it is possible to reduce the write current required for magnetization reversal.

Further, the magnetization directions of the free layer 13 and the pin layer 11 are set to be parallel to each other, while the magnetization directions of the free layer 13 and the pin layer 15 are set to be orthogonal to each other. Therefore, the magnetoresistive effect is exhibited in the intermediate layer 12, but the magnetoresistive effect is not exhibited in the intermediate layer 14. As a result, the TMR ratio of the MTJ element 10 can be further increased when reading information.

Further, it becomes possible to use a conductor such as a metal for the intermediate layer 14 in which the magnetoresistive effect is not exhibited. As a result, the resistance value of the MTJ element 10 can be reduced.

In addition, a perpendicular magnetization film is used for the free layer 13. That is, the anisotropic magnetic field (Hk) required for the free layer 13 to be thermally stabilized is covered by the crystalline magnetic anisotropy energy. As a result, the aspect ratio of the free layer 13 can be reduced, so that the MTJ element size can be miniaturized.

Further, an interface free layer made of a ferromagnet is inserted between the free layer 13 and the intermediate layer 12 or between the free layer 13 and the intermediate layer 14. Further, an interface pin layer made of a ferromagnet is inserted between the pin layer 11 and the intermediate layer 12. By using a material having a large bulk polarizability of the material itself for the interface-free layer and the interface pin layer, the magnetoresistive effect can be increased, and further, the writing current at the time of writing can be reduced. ..

More specific laminated structures of TMR films used in MTJ devices include the following. In addition, in Examples 1 to 3, the numerical value described after each layer indicates the film thickness.

(Example 1) Ta5 / PtMn15 / CoFe2.5 / Ru0.85 / CoFe2.5 / Cu3 (intermediate layer 14) / CoFeB0.5 / FePt (L1)₀) 2 / Fe0.5 / MgO0.75 (intermediate layer 12) / CoFeB1 / FePt (L1)₀) 10 / Pt5 / Cr20 / MgO2 / CoFeB2 / Ta5 // Substrate (Example 2) Ta5 / IrMn10 / CoFe2.5 / Ru0.85 / CoFe2.5 / Cu3 (intermediate layer 14) / CoFeB0.5 / CoFeTb3 / CoFeB0 .75 / MgO0.75 (intermediate layer 12) /CoFeB2 / CoFeTb30 / Ru5 / Ta5 // substrate (Example 3) Ta5 / IrMn10 / CoFe2.5 / Ru0.85 / CoFe2.5 / Cu3 (intermediate layer 14) / CoFeB0.5 / CoPt3 / CoFeB0.5 / MgO0.75 (intermediate layer 12) / CoFeB2 / CoPt20 / Ru10 / Ta5 // Substrate In Example 1 and Example 3, 270 ° in an in-plane magnetic field and in a vacuum. C was annealed. Using these MTJ membranes, MTJ elements capable of four-terminal measurement were created, and the current density Jc required for spin injection magnetization reversal was evaluated. The measurement was performed with a pulse width of 1 msec. The MTJ element size is approximately 100 nm x 100 nm, and the aspect ratio is 1. In addition, the resistance x area (RA) of the MTJ element is 15Ωμm, respectively.²The MgO film thickness was adjusted so as to be.

In each of the examples, as a result of comparison with the comparative example in the case where the in-plane magnetizing pin layer was not provided on the intermediate layer 14, the current density Jc was reduced by about 10% to 30%, respectively. Moreover, since Cu was used for the intermediate layer 14 in each example, almost no increase in resistance × area (RA) was observed, and no significant deterioration in the TMR ratio was measured.

(Second Embodiment) In the second embodiment, the MTJ element 10 is configured by using an in-plane magnetizing film on the free layer 13. FIG. 7 is a cross-sectional view showing the configuration of the MTJ element 10 according to the second embodiment of the present invention. FIG. 7 shows the basic configuration of the MTJ element 10 of the present embodiment.

The MTJ element 10 has a laminated structure in which a first pin layer 11, a first intermediate layer 12, a free layer 13, a second intermediate layer 14, and a second pin layer 15 are laminated in this order. In this basic configuration, the stacking order may be reversed.

The easy magnetization direction of the pin layer 11 and the free layer 13 is parallel to the film surface, and the easy magnetization direction of the pin layer 15 is perpendicular to the film surface. That is, the pin layer 11 and the pin layer 15 have easy magnetization directions orthogonal to each other. Therefore, the magnetoresistive effect is exhibited via the intermediate layer 12 between the free layer 13 and the pin layer 11 in which the magnetization arrangements are parallel, but between the free layer 13 and the pin layer 15 in which the magnetization arrangements are vertical. The magnetoresistive effect via the intermediate layer 14 is not exhibited.

FIG. 8 is a cross-sectional view showing a specific example of the MTJ element 10. A cap layer 17 and a base layer 16 are provided on the uppermost layer and the lowermost layer of the basic configuration shown in FIG. 7, respectively. The pin layer 11 has a laminated structure of pin layer 11C / intermediate layer 11B / pin layer 11A. That is, the pin layer 11 has a SAF structure.

The easy magnetization direction of the pin layer 11A and the pin layer 11C is parallel to the film surface. Further, the directions of magnetization of the pin layer 11A and the pin layer 11C are set to be antiparallel to each other, and the pin layer 11A and the pin layer 11C are antiferromagnetically coupled with the intermediate layer 11B interposed therebetween. A metal material such as Ru or Os is used for the intermediate layer in the SAF structure, and the film thickness is set to 3 nm or less. This is to obtain a sufficiently strong antiferromagnetic bond via the intermediate layer.

Further, below the pin layer 11A (between the pin layer 11A and the base layer 16), an antiferromagnetic layer 19 is provided so as to be in contact with the pin layer 11A. The pin layer 11A is exchanged with the antiferromagnetic layer 19 so that the direction of magnetization is fixed parallel to the film surface.

By using this structure, the magnetization fixing force of the pin layer 11 is enhanced, and the resistance to an external magnetic field and the thermal stability can be improved. Further, in order to improve the resistance to an external magnetic field, it is preferable to set the product Ms · t of the apparent saturation magnetization of the pin layer 11 and the magnetic layer film thickness to be substantially zero.

FIG. 9 is a cross-sectional view showing another configuration of the free layer 13. The free layer 13 has a laminated structure of a free layer 13F / an intermediate layer 13E / a free layer 13D. That is, the free layer 13 has a SAF structure. The easy magnetization directions of the free layer 13D and the free layer 13F are parallel to the film surface. Further, the magnetization directions of the free layer 13D and the free layer 13F are set to be antiparallel to each other, and the free layer 13D and the free layer 13F are antiferromagnetically coupled with the intermediate layer 13E interposed therebetween. In the case of the SAF-free layer, it has the effect of promoting precession during magnetization reversal. In the SAF-free layer, the apparent net Ms can be set to zero, so that the demagnetic field can be suppressed in the direction perpendicular to the film surface. Therefore, it has the effect of promoting the precession of the free layer 13 and reducing the spin injection magnetization reversal.

Even when the MTJ element 10 is configured in this way, the same effect as that of the first embodiment can be obtained. As shown in the first embodiment, the interface layer may be inserted into the free layer 13 and the pin layer 11.

Further, the pin layer 15 has an effect of facilitating the precession of the free layer 13 at the time of magnetization reversal when the intermediate layer 14 is thin. In the spin injection magnetization reversal in the in-plane magnetization film, the demagnetic field in the direction perpendicular to the film surface hinders the aging motion of the magnetization and is a factor that increases the spin injection magnetization reversal current. The demagnetic field in the direction perpendicular to the film surface at this time is generated by the generation of a magnetic charge on the film surface of the free layer 13. Therefore, if the magnetic charge generated on the film surface is canceled, the demagnetic field in the direction perpendicular to the film surface decreases, and the magnetization of the free layer 13 becomes easy to precess. As a result, it is possible to reduce the spin injection magnetization reversal current.

In the case of the MTJ element 10 of the present embodiment, the pin layer 15 formed via the intermediate layer 14 is perpendicularly magnetized and exerts a magnetic charge on the film surface. Therefore, when the free layer 13 precesses, the effect of canceling the magnetic charge on the film surface of the free layer 13 works. In order to maximize this effect, the intermediate layer 14 is preferably as thin as possible, preferably 1 nm or less. In the case of the intermediate layer 14 having a thickness of more than 1 nm, the influence of the magnetization of the pin layer 15 is inversely proportional to the distance, so that a considerable part of the leakage magnetic field is attenuated. If only the effect of promoting precession is obtained, it is better not to have the middle layer 14. However, in this case, the portion of the perpendicular magnetization film loses its function as a pin layer and behaves as a part of the free layer 13. That is, the free layer 13 has anisotropy in two directions, the in-plane magnetization direction and the perpendicular magnetization direction.

A Fe-Co-Ni alloy is mainly used for the free layer 13 of the present embodiment. Also, in order to reduce the saturation magnetization (Ms) of the Fe-Co-Ni alloy, (Fe_xCo_yNi_z)_100-aX_aAlloys (x 0, y 0, z 0, x + y + z = 1, a (at%)&gt; 0, X is an additive element) are also preferred. By reducing the saturation magnetization (Ms), the inverting current can be significantly reduced.

Additives that can be added without destroying the BCC structure and that can reduce saturation magnetization (Ms), that is, a total solid solution that can be solid-dissolved in a substitution type or an additive that has a solid solution source to some extent, include V. Examples include Nb, Ta, W, Cr, Mo, Si, Ga and Ge. Among these, V is also effective because it has the effect of reducing the damping constant (magnetization braking constant).

In addition, by adding intrusive elements such as B, C and N, or by adding Zr, Ta, Ti, Hf, Y and rare earth elements that have almost no solid solution source, the crystal structure becomes an amorphous structure. Saturation magnetization (Ms) can be reduced by changing. Such a material has, for example, an amorphous structure (Fe)._xCo_yNi_z)_100-bX_{b b}Alloys (x 0, y 0, z 0, x + y + z = 1, b (at%)&gt; 0, X is B, C, N, Zr, Ta, Ti, Hf, Y, and rare earths Additive elements such as elements) can be mentioned.

Examples of the material containing Mn include Mn-based ferromagnetic Whistler alloys. Whisler alloy is a material that exhibits half-metal-like conductive properties. Here, the Mn-based ferromagnetic Whistler alloy is A.₂It is a body-centered cubic system alloy having a ordered lattice represented by MnX. Element A is a material selected from Cu, Au, Pd, Ni, and Co. Element X is a material selected from Al, In, Sn, Ga, Ge, Sb, and Si. Of the Whisler alloys, Co with a BCC structure₂BCC (100) plane orientation of MnAl alloys and the like improves consistency with MgO (100).

Further, as the material of the other layers constituting the MTJ element 10, the material shown in the first embodiment can be used.

(Third Embodiment) In the third embodiment, the MTJ element 10 is configured by using an in-plane magnetizing film for each of the free layer and the two pin layers. FIG. 10 is a perspective view showing the configuration of the MTJ element 10 according to the third embodiment of the present invention. FIG. 10 shows the basic configuration of the MTJ element 10 of the present embodiment.

The MTJ element 10 has a laminated structure in which a first pin layer 11, a first intermediate layer 12, a free layer 13, a second intermediate layer 14, and a second pin layer 15 are laminated in this order. In this basic configuration, the stacking order may be reversed.

The easy magnetization directions of the pin layer 11, the free layer 13, and the pin layer 15 are parallel to the film surface. That is, it becomes possible to use an in-plane magnetization film as all the magnetic layers, and the MTJ element 10 can be easily formed.

Further, the pin layer 11 and the free layer 13 have parallel easy magnetization directions, and the pin layer 11 and the pin layer 15 have easy magnetization directions orthogonal to each other. Therefore, the magnetoresistive effect is exhibited via the intermediate layer 12 between the free layer 13 and the pin layer 11 in which the magnetization arrangements are parallel, but between the free layer 13 and the pin layer 15 in which the magnetization arrangements are vertical. The magnetoresistive effect via the intermediate layer 14 is not exhibited.

FIG. 11 is a perspective view showing a specific example of the MTJ element 10. A cap layer 17 and a base layer 16 are provided on the uppermost layer and the lowermost layer of the basic configuration shown in FIG. 10, respectively. The pin layer 11 has a laminated structure of pin layer 11C / intermediate layer 11B / pin layer 11A. That is, the pin layer 11 has a SAF structure. The easy magnetization direction of the pin layer 11A and the pin layer 11C is parallel to the film surface. Further, the directions of magnetization of the pin layer 11A and the pin layer 11C are set to be antiparallel to each other, and the pin layer 11A and the pin layer 11C are antiferromagnetically coupled with the intermediate layer 11B interposed therebetween.

Further, below the pin layer 11A (between the pin layer 11A and the base layer 16), an antiferromagnetic layer 19 is provided so as to be in contact with the pin layer 11A. The pin layer 11A is exchanged with the antiferromagnetic layer 19 so that the direction of magnetization is fixed parallel to the film surface. By using this structure, the magnetization fixing force of the pin layer 11A is enhanced, and the resistance to an external magnetic field and the thermal stability are improved.

Further, the pin layer 15 needs to have a clear holding force difference from the free layer 13. Therefore, it is preferable to use an in-plane magnetized hard magnetic layer as the pin layer 15.

As the material of the in-plane magnetized hard magnetic layer, a Co-Pt alloy or a Co-Pt-X alloy (X is at least one element selected from Cr, Ta, Pd, B, Si, and Ru) is used. can give. Further, it is possible to form a SAF structure having a structure of a hard magnetic layer / intermediate layer / hard magnetic layer using an in-plane magnetization type hard magnetic layer. In this case, Ru or Os is used for the intermediate layer.

FIG. 12 is a perspective view showing another configuration of the pin layer 15. An antiferromagnetic layer 18 is provided on the pin layer 15 (between the pin layer 15 and the cap layer 17) so as to be in contact with the pin layer 15. The pin layer 15 is exchanged with the antiferromagnetic layer 18 so that the direction of magnetization is fixed parallel to the film surface.

FIG. 13 is a perspective view showing another configuration of the pin layer 15. The pin layer 15 has a laminated structure of pin layer 15C / intermediate layer 15B / pin layer 15A. That is, the pin layer 15 has a SAF structure. The easy magnetization direction of the pin layer 15A and the pin layer 15C is parallel to the film surface. Further, the directions of magnetization of the pin layer 15A and the pin layer 15C are set to be antiparallel to each other, and the pin layer 15A and the pin layer 15C are antiferromagnetically coupled with the intermediate layer 15B interposed therebetween.

The antiferromagnetic layer 19 and the antiferromagnetic layer 18 shown in FIGS. 12 and 13 differ in the critical temperature of coupling with the ferromagnetic layer, that is, the blocking temperature, and the pin layer 11 and the pin layer 15 are subjected to an annealing sequence. It is possible to easily orthogonalize the magnetization direction with and. More specifically, the antiferromagnetic layer 19 should be made of a material having a high blocking temperature such as PtMn or NiMn, and the antiferromagnetic layer 18 should be made of a material having a relatively low blocking temperature such as FeMn or IrMn. Is preferable.

Further, the free layer 13 may have a laminated structure of a ferromagnetic layer / an intermediate layer / a ferromagnetic layer, that is, a SAF structure. In the SAF structure, the directions of magnetization between the ferromagnetic layers are set to be antiparallel to each other, and antiferromagnetic coupling is performed with the intermediate layer in between.

Even when the MTJ element 10 is configured in this way, the same effect as that of the first embodiment can be obtained. As shown in the first embodiment, the interface layer may be inserted into the free layer 13 and the pin layer 11. Further, as the material of each layer constituting the MTJ element 10, the materials shown in the first and second embodiments can be used.

(Fourth Embodiment) The fourth embodiment shows an embodiment in the case where the MRAM is configured by using the MTJ element 10 described above.

FIG. 14 is a circuit diagram showing a configuration of MRAM according to a fourth embodiment of the present invention. The MRAM includes a memory cell array 20 having a plurality of memory cells MC arranged in a matrix. A plurality of bit lines BL are arranged in the memory cell array 20 so that each of them extends in the column direction. Further, in the memory cell array 20, a plurality of word lines WL are arranged so that each of them extends in the row (row) direction.

The memory cell MC described above is arranged at the intersection of the bit line BL and the word line WL. Each memory cell MC is composed of an MTJ element 10 and a selection transistor 21. One end of the MTJ element 10 is connected to the bit line BL. The other end of the MTJ element 10 is connected to the drain of the selection transistor 21. A word line WL is connected to the gate of the selection transistor 21. The source of the selection transistor 21 is connected to the source line SL.

A power supply circuit 22 is connected to one end of the bit line BL. A sense amplifier circuit 24 is connected to the other end of the bit line BL. A power supply circuit 23 is connected to one end of the source line SL. The other end of the source line SL is connected to the power supply 25 via a switch element (not shown).

The power supply circuit 22 applies a positive potential to one end of the bit line BL. The sense amplifier circuit 24 detects the resistance value of the MTJ element 10 and applies, for example, a ground potential to the other end of the bit line BL. The power supply circuit 23 applies a positive potential to one end of the source line SL. The power supply 25 applies, for example, a ground potential to the other end of the source line SL by turning on the switch element connected to the power supply 25. Each power supply circuit also includes a switch element that controls the electrical connection to the corresponding wiring.

Data is written to the memory cell MC as follows. First, in order to select the memory cell MC to write data to, the word line WL connected to this memory cell MC is activated. As a result, the selection transistor 21 is turned on.

Here, a bidirectional write current Iw is supplied to the MTJ element 10. Specifically, when the write current Iw is supplied to the MTJ element 10 from top to bottom, the power supply circuit 22 applies a positive potential to one end of the bit line BL, and the power supply 25 uses a switch element corresponding to this power supply 25. By turning it on, the ground potential is applied to the other end of the source line SL.

When supplying the write current Iw to the MTJ element 10 from bottom to top, the power supply circuit 23 applies a positive potential to one end of the source line SL, and the sense amplifier circuit 24 applies a ground potential to the other end of the bit line BL. Apply. Here, the switch element corresponding to the power supply 25 is turned off. In this way, data "0" or data "1" can be written to the memory cell MC.

Data reading from the memory cell MC is performed as follows. First, the memory cell MC is selected. Next, the power supply circuit 23 and the sense amplifier circuit 24 supply the MTJ element 10 with the read current Ir flowing from the power supply circuit 23 to the sense amplifier circuit 24. Then, the sense amplifier circuit 24 detects the resistance value of the MTJ element 10 based on the read current Ir. In this way, the information stored in the MTJ element 10 can be read out.

Next, the structure of MRAM will be described. FIG. 15 is a cross-sectional view of the MRAM showing the MTJ element 10 at the center. The MTJ element 10 is formed above a selection transistor 21 formed on a semiconductor substrate (not shown) made of silicon or the like via an interlayer insulating layer.

An MTJ element 10 is provided on the lead-out electrode 32. The lead-out electrode 32 is electrically connected to the drain region of the selection transistor 21 via the via plug 31. A conductive hard mask 33 is provided on the MTJ element 10. A bit line BL is provided on the hard mask 33.

As the bit wire BL, the hard mask 33, and the via plug 31, W, Al, Cu, AlCu, and the like are used. In the case of a metal wiring layer or via plug using Cu, a Cu damascene or Cu dual damascene process is used.

FIG. 16 shows another configuration example of the MRAM centered on the MTJ element 10. The MTJ element 10 is directly provided on the via plug 31. That is, the MRAM of FIG. 16 omits the lead-out electrode 32 as compared with the MRAM of FIG. A hard mask 33 is provided on the MTJ element 10. A bit line BL is provided on the hard mask 33.

The MTJ element 10 may be electrically connected to the via plug 31 by the extraction electrode 32 as shown in FIG. 15, or the MTJ element 10 may be formed directly on the via plug 31 as shown in FIG. is there. When the configuration shown in FIG. 16 is used, it is preferable that the MTJ element size is smaller than the via size.

Assuming that the minimum processing dimension determined by lithography and etching technology is F (Minimum Feature Size), the minimum cell size is 8F when the layout shown in Fig. 15 is used.²Is. On the other hand, when using the layout shown in Fig. 16, the minimum cell size is 4F.²It is possible to reduce to.

In the MRAM configured in this way, the writing speed when writing information to the MTJ element 10 can be improved. Specifically, as the writing speed, spin injection writing can be performed with a current having a pulse width of several nanoseconds to several microseconds.

It is desirable that the read current Ir supplied to the MTJ element 10 at the time of reading has a shorter pulse width than the write current Iw supplied to the MTJ element 10 at the time of writing. As a result, erroneous writing at the read current Ir can be reduced. This is based on the fact that the shorter the pulse width of the write current Iw, the larger the absolute value of the write current value.

The present invention is not limited to the above-described embodiment, and the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be constructed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components disclosed in the embodiment, or components of different embodiments may be combined as appropriate.

<figref num="1">The cross-sectional view which shows the structure of the MTJ element 10 which concerns on 1st Embodiment of this invention.</figref><figref num="2">The cross-sectional view which shows the specific example of the MTJ element 10 which concerns on 1st Embodiment.</figref><figref num="3">FIG. 5 is a cross-sectional view showing another configuration of the pin layer 15 according to the first embodiment.</figref><figref num="4">FIG. 5 is a cross-sectional view showing another configuration of the pin layer 11 according to the first embodiment.</figref><figref num="5">FIG. 5 is a cross-sectional view showing another configuration of the pin layer 11 according to the first embodiment.</figref><figref num="6">FIG. 5 is a cross-sectional view showing another configuration of the free layer 13 and the pin layer 11 according to the first embodiment.</figref><figref num="7">The cross-sectional view which shows the structure of the MTJ element 10 which concerns on 2nd Embodiment of this invention.</figref><figref num="8">FIG. 5 is a cross-sectional view showing a specific example of the MTJ element 10 according to the second embodiment.</figref><figref num="9">FIG. 5 is a cross-sectional view showing another configuration of the free layer 13 according to the second embodiment.</figref><figref num="10">The perspective view which shows the structure of the MTJ element 10 which concerns on 3rd Embodiment of this invention.</figref><figref num="11">The perspective view which shows the specific example of the MTJ element 10 which concerns on 3rd Embodiment.</figref><figref num="12">The perspective view which shows the other structure of the pin layer 15 which concerns on 3rd Embodiment.</figref><figref num="13">The perspective view which shows the other structure of the pin layer 15 which concerns on 3rd Embodiment.</figref><figref num="14">The circuit diagram which shows the structure of MRAM which concerns on 4th Embodiment of this invention.</figref><figref num="15">Sectional drawing of MRAM showing MTJ element 10 as a center.</figref><figref num="16">FIG. 5 is a cross-sectional view showing another configuration example of MRAM showing the MTJ element 10 as the center.</figref>

Code description

10 ... MTJ element, 11 ... 1st magnetization reference layer (pin layer), 11A, 11C, 11D ... pin layer, 11B ... intermediate layer, 11E ... interface pin layer, 12. .. 1st intermediate layer, 13 ... magnetized free layer (free layer), 13A, 13C ... interface free layer, 13B, 13F, 13D ... free layer, 13E ... intermediate layer, 14. .. 2nd intermediate layer, 15 ... 2nd magnetization reference layer (pin layer), 15A, 15C ... pin layer, 15B ... intermediate layer, 16 ... underlayer, 17 ... Cap layer, 18,19 ... anti-conductive layer, 20 ... memory cell array, 21 ... selective transistor, 22,23 ... power supply circuit, 24 ... sense amplifier circuit, 25 ... power supply , 31 ... Via plug, 32 ... Leader electrode, 33 ... Hard mask, MC ... Memory cell, BL ... Bit line, WL ... Word line, SL ... Source line.