JP2004087870A - Magnetoresistive effect element and magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To assure a great margin of selective recording into each memory unit by suppressing variations in inverse magnetic field between the memory units and the deviation of asteroids. <P>SOLUTION: The magnetoresistive effect element comprises a stacked structure which includes at least two ferromagnetic layers 24 and 26 and an insulation layer 25 interposed between the two ferromagnetic layers 24 and 26, with the ferromagnetic layer 26 serving as a free layer which can inverse its magnetization direction and the ferromagnetic layer 24 serving as a fixed layer with no inversion of magnetization direction. The fixed layer 26 serves as a magnetic field application member for applying a static magnetic field to the free layer 24. For the fixed layer 26 to apply the static magnetic field, the intensity of leakage magnetic field from the fixed layer 26 is set to a prescribed value or above. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetoresistive element that generates a so-called MR (MagnetoResistant) effect in which a resistance value changes by an externally applied magnetic field, and a magnetic memory configured as a memory device that stores information using the magnetoresistive element. Related to the device.
[0002]
[Prior art]
In recent years, with the rapid spread of information communication devices, especially personal small devices such as portable terminal devices, devices such as memories and logics are becoming increasingly more integrated, faster, and lower in power. There is a demand for higher performance. In particular, increasing the density and capacity of non-volatile memory is a complementary technology that replaces hard disk devices and optical disk devices that are inherently difficult to miniaturize due to the existence of movable parts (for example, a head seek mechanism and a disk rotating mechanism). It is becoming more and more important.
[0003]
A magnetic memory device called an MRAM (Magnetic Random Access Memory) has attracted attention as a nonvolatile memory that can meet such a demand. The MRAM performs information recording using a giant magnetoresistive (GMR) type or tunnel magnetoresistive (TMR) type storage element. In particular, attention has been paid to the improvement in characteristics of TMR materials in recent years. (Eg, “Naji et al. ISSCC 2001”).
[0004]
Here, the operation principle of the MRAM will be briefly described. The MRAM has magnetoresistive effect type storage elements (cells) arranged in a matrix, and has a conductive line (word line) and a read line crossing these element groups vertically and horizontally for recording information in a specific storage element. (Bit line), and is configured to selectively write information only to elements located in the intersection area. That is, writing to the storage element is performed by controlling the magnetization direction of the magnetic material in each storage element using a combined current magnetic field generated by flowing a current through both the word line and the bit line. Generally, information of either “0” or “1” is stored according to the direction of magnetization. On the other hand, reading of information from a storage element is performed by selecting a storage element using an element such as a transistor, and extracting a magnetization direction of a magnetic body in the storage element as a voltage signal through a magnetoresistance effect. As a film configuration of the storage element, a three-layer structure including a ferromagnetic material / a nonmagnetic material / a ferromagnetic material, that is, a structure called a ferromagnetic tunnel junction (MTJ) has been proposed. In the MTJ structure, by using one ferromagnetic material as a fixed reference layer (pinned / reference layer) and the other as a free layer (free layer), the magnetization direction in the free layer corresponds to the voltage signal through the tunnel magnetoresistance effect. Therefore, the extraction as a voltage signal as described above can be realized.
[0005]
Subsequently, selection of a storage element at the time of writing will be described in more detail. Generally, when a magnetic field opposite to the magnetization direction is applied in the easy axis direction of the ferromagnetic material, the magnetization direction can be reversed to the direction of the applied magnetic field at a certain critical value ± Hsw (hereinafter referred to as “reversal magnetic field”). Are known. The value of the reversal magnetic field can be theoretically obtained from the minimum energy condition. Furthermore, it is known that when a magnetic field is applied not only in the easy axis of magnetization but also in the direction of the hard axis of magnetization, the absolute value of the reversal magnetic field decreases. This can also be obtained from the minimum energy condition. That is, assuming that the magnetic field applied in the direction of the hard axis is Hx, the relation Hx ^(2/3) + Hy ^(2/3) = Hc ^(2/3) is established between the magnetic field and the reversal magnetic field Hy at this time. I do. Hc is the anisotropic magnetic field of the free layer. This curve is called an asteroid curve because it forms an asteroid (star) on the Hx-Hy plane as shown in FIG.
[0006]
The selection of the storage element is easy to explain using this asteroid. Generally, in an MRAM having a configuration in which a magnetic field generated from a word line substantially coincides with the direction of an easy axis of magnetization, information is recorded by reversing magnetization by a magnetic field generated from a word line. However, since there are a plurality of storage elements located at the same distance from the word line, when a current for generating a magnetic field equal to or greater than the reversal magnetic field is applied to the word line, recording is similarly performed for all of the storage elements located at the same distance. Will be done. However, at this time, when a current is applied to a bit line crossing the storage element to be selected to generate a magnetic field in the hard axis direction, the reversal magnetic field in the storage element to be selected is reduced. Therefore, assuming that the reversing magnetic field at this time is Hc (h) and the reversing magnetic field when the bit line magnetic field is “0” is Hc (0), the word line magnetic field H is Hc (h) <H <Hc (0). By setting such that, it becomes possible to selectively perform information recording only on the storage element desired to be selected. This is the method of selecting a storage element when recording information in the MRAM.
[0007]
The MRAM having such a configuration is nonvolatile and can perform nondestructive reading and random access, and has the following features. That is, since the structure is simple, high integration is easy, and the number of rewritable times is large (for example, 10 ¹⁶ times or more) in order to record information by rotating the magnetic moment in the storage element. Furthermore, the access time is expected to be very fast, and it has already been confirmed that the operation can be performed on the order of nanoseconds (for example, 5 ns or less). In addition, since it is formed only in the wiring step after the production of a MOS (Metal Oxide Semiconductor), process consistency is good. In particular, it is superior to a flash memory in the three points of the number of rewritable times, random access, and high-speed operation, and is superior to FeRAM (Ferroelectric Random Access Memory) in terms of process consistency. Further, since it is expected that both high integration similar to DRAM (Dynamic Random Access Memory) and high speed comparable to SRAM (Static Random Access Memory) can be achieved, there is a possibility that the memory device may become the mainstream.
[0008]
[Problems to be solved by the invention]
By the way, for MRAM, instead of other nonvolatile memory such as flash memory or FeRAM or MOS switch such as volatile memory such as DRAM or SRAM, a characteristic writing method of selective recording by orthogonal magnetic field is adopted. Therefore, there is also a technical problem unique to the MRAM. The selective recording using the orthogonal magnetic field has already been described with reference to the asteroid curve in FIG. 11A, but the asteroid curve in the figure is ideal and can be obtained by actually evaluating the MRAM. The asteroid curve has two features as shown in FIG. That is, in the actually obtained asteroid curve, (1) the value of the reversal magnetic field with respect to each hard-axis direction magnetic field differs between the storage elements (hereinafter, this is referred to as “variation of the reversal magnetic field”). (2) The asteroid curve itself is displaced in the easy axis magnetic field direction (vertical direction in the figure) (hereinafter, this is referred to as "asteroid displacement").
[0009]
In the case of the asteroid curve having these two features (1) and (2), the area where the selective recording can be performed by the orthogonal magnetic field is limited to the hatched area in FIG. As compared with the case of the ideal asteroid curve shown in FIG. Therefore, in order to accurately select an element at the time of recording information, it is important to suppress the variation of the reversal magnetic field between the storage elements and to make the deviation of the asteroid close to “0”.
[0010]
However, in reality, it is extremely difficult to control the switching magnetic field variation. In other words, the variation of the switching field is due to a combination of many sources such as the variation and shape of the element dimensions, the magnetic anisotropy and magnetostriction of the free layer, and the interface roughness, and is required from the viewpoint of circuit design. It is generally considered difficult to satisfy the variation specifications. Also, the asteroid displacement is a phenomenon that occurs due to the presence of a magnetic interaction between the fixed reference layer and the free layer. It is its origin. It is extremely difficult to make this magnetostatic interaction "0". Therefore, it is considered that it is not easy to make the shift of the asteroid close to “0”.
[0011]
The present invention has been made in view of the above-described conventional circumstances, and makes it possible to suppress the variation of the inversion magnetic field between the storage elements and easily realize that the deviation of the asteroid is close to “0”. It is an object of the present invention to provide a magnetoresistive element and a magnetic memory device which can secure a large margin for selective recording and realize good recording characteristics.
[0012]
[Means for Solving the Problems]
The present invention is directed to a magnetoresistive element devised to achieve the above object, comprising a laminated structure including at least two ferromagnetic layers and an insulating layer interposed therebetween, and one of the ferromagnetic layers Functions as a free layer whose magnetization direction can be reversed, and the other ferromagnetic layer functions as a fixed layer whose magnetization direction is not reversed. In the magneto-resistance effect element, a magnetic field applying member for applying a static magnetic field to the free layer is provided. It is characterized by having.
[0013]
According to another aspect of the present invention, there is provided a magnetic memory device devised to achieve the above object, comprising a laminated structure including at least two ferromagnetic layers and an insulating layer sandwiched between the two. A magnetoresistive element in which the layer functions as a free layer whose magnetization direction can be inverted and the other ferromagnetic layer functions as a fixed layer whose magnetization direction is not inverted. In the magnetic memory device for recording information by utilizing the change in the magnetic field, a magnetic field applying member for applying a static magnetic field to the free layer is provided.
[0014]
According to the magnetoresistive element and the magnetic memory device having the above configuration, a static magnetic field having a constant strength is applied to the free layer, for example, in the direction of the easy axis of magnetization, by the static magnetic field from the magnetic field applying member. Therefore, in the free layer, by applying the static magnetic field, the imbalance of the reversal threshold value of the magnetization direction can be corrected, and the correction of the asteroid shift can be easily realized. That is, the application of the static magnetic field simplifies the magnetization reversal mechanism, reduces variations in the reversal magnetic field, which has been difficult with the related art, and increases the selective recording margin.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a magnetoresistive element and a magnetic memory device according to the present invention will be described with reference to the drawings. Here, a TMR spin valve element (hereinafter, simply referred to as a “TMR element”) will be described as an example of a magnetoresistive element, and an MRAM having a TMR element will be described as an example of a magnetic memory device.
[0016]
First, a schematic configuration of the entire magnetic memory device according to the present invention will be described. FIG. 1 is a schematic diagram illustrating a basic configuration example of the MRAM. The MRAM includes a plurality of TMR elements 1 arranged in a matrix. Further, mutually intersecting word lines 2 and bit lines 3 are provided so as to vertically and horizontally traverse each group of TMR elements 1 so as to correspond to each of the rows and columns in which these TMR elements 1 are arranged. . Each of the TMR elements 1 is arranged so as to be sandwiched between the word line 2 and the bit line 3 from above and below, and to be located in an intersection region therebetween. The word lines 2 and the bit lines 3 are formed by chemically or physically depositing a conductive material such as Al (aluminum), Cu (copper), or an alloy thereof, and then selectively etching them. It shall be formed using.
[0017]
FIG. 2 is a schematic diagram illustrating an example of a cross-sectional configuration of a single TMR element portion forming the MRAM. In each TMR element portion, a field effect transistor including a gate electrode 5, a source region 6, and a drain region 7 is disposed on a semiconductor substrate 4, and further above the word line 2, the TMR element 1, and the bit line 3 Are arranged in order. As is apparent from this, the TMR element 1 is arranged so as to be sandwiched between the word line 2 and the bit line 3 from above and below at the intersection of the word line 2 and the bit line 3. The TMR element 1 is connected to a field effect transistor via a bypass line 8.
[0018]
With such a configuration, in the MRAM, a combined current magnetic field is generated by applying a current to both the word line 2 and the bit line 3 to the free layer of the TMR element 1, and the free layer is generated using the combined current magnetic field. The information is written by changing the magnetization direction of. The reading of information from the TMR element 1 is performed by selecting the TMR element 1 using a field effect transistor and extracting the magnetization direction of the free layer in the TMR element 1 as a voltage signal.
[0019]
Next, the configuration of the TMR element 1 used in such an MRAM will be described. The TMR element 1 has an MTJ structure. FIG. 3 is a schematic diagram showing a basic configuration example of the MTJ structure. The MTJ structure has a three-layer structure of a ferromagnetic material / insulator / ferromagnetic material. One ferromagnetic layer functions as a free layer (free layer) 11 whose magnetization direction can be reversed, and the other ferromagnetic layer. Function as a fixed reference layer (pinned / reference layer) 12 whose magnetization direction is not reversed. The fixed reference layer 12 is formed by laminating a fixed layer (pinned layer) made of a ferromagnetic layer and an antiferromagnetic reference layer (reference layer) for fixing the magnetization direction of the fixed layer. It is. By changing the magnetization direction of the free layer 11 by a combined current magnetic field generated by the word line 2 and the bit line 3, information is written (recorded), and the magnetization in the free layer 11 is performed through the tunnel MR effect. The direction and the voltage signal correspond. The insulating layer 13 sandwiched between the two ferromagnetic layers, that is, the free layer 11 and the fixed reference layer 12, is made of, for example, Al oxide and functions as a tunnel barrier layer. Other layers such as the underlayer 14 and the protective layer 15 are generally made of a material having no magnetism.
[0020]
FIG. 4 is a schematic diagram for explaining the TMR element having the MTJ structure more specifically. As the TMR element 1, for example, a Ta (tantalum) film 22, a PtMn (platinum manganese) film 23, a CoFe (cobalt iron) film 24a, A Ru (ruthenium) film 24b, a CoFe film 24c, an Al-Ox (aluminum oxide) film 25, a CoFeB (cobalt iron boron) film 26, and a Ta film 27 are sequentially laminated.
[0021]
In such a TMR element 1, the Ta film 22 functions as the underlayer 14. The PtMn film 23 functions as an antiferromagnetic layer, and the stacked ferrimagnetic structure 24 in which CoFe films 24a and 24c are stacked via a Ru film 24b, which is a nonmagnetic layer, functions as a fixed layer. When the magnetization direction of the laminated ferrimagnetic structure 24 is fixed directly or indirectly by the PtMn film 23, these layers 23 and 24 function as the fixed reference layer 12. Further, the Al-Ox film 25 functions as the insulating layer 13, the CoFeB film 26 functions as the free layer 11, and the Ta film 27 functions as the protective layer 15.
[0022]
It is conceivable that the TMR element 1 having the above configuration is manufactured by the following procedure. For example, using a magnetron sputtering apparatus in which the back pressure is evacuated to an ultra-high vacuum region, a Ta film 22 is 3 nm thick, a PtMn film 23 is 30 nm thick, and a CoFe film is formed on a thermally oxidized Si (silicon) substrate 21. 24a is 2.5 nm thick, the Ru film 24b is 0.8 nm thick, the CoFe film 24c is 3.1 nm, and the Al film is 1 nm thick. At this time, the target composition of the CoFe films 24a and 24c may be, for example, Co75Fe25 (atomic%). Then, the Al film is plasma-oxidized in pure oxygen to obtain a uniform Al-Ox film 27. After that, the CoFeB film 26 and the Ta film 27 are sequentially formed with a thickness of 3 nm and a thickness of 5 nm, respectively, again by the magnetron sputtering apparatus. At this time, the target composition of the CoFeB film 26 may be (Co90Fe10) 80B20 (atomic%). Finally, a heat treatment for orderly alloying the PtMn film 23 is performed in a magnetic field at, for example, 280 ° C. for one hour. The TMR element 1 having the above-described configuration can be formed by subjecting the thus obtained TMR laminated film to microfabrication with an outer shape of, for example, 0.8 μm × 1.6 μm. Note that the fine processing may be performed by, for example, a combination of photolithography and ion milling.
[0023]
In the TMR element 1 described in the present embodiment, the total ΔMt including the sign of the product Mt of the thickness t of each of the CoFe films 24 a and 24 c constituting the laminated ferrimagnetic structure 24 and the saturation magnetization M thereof is 750 emunm / There is a great feature in that it is configured to satisfy either cc or more or -2000 emunm / cc or less. Here, the CoFe film 24c is coupled anti-parallel to the CoFe film 24a by exchange interaction, and the CoFe film 24a is fixed by the PtMn film 23 so as to be easily oriented in one direction. It is easy to turn. Here, the sign of Mt indicates that the direction of easy magnetization of the CoFe film 24c adjacent to the Al-Ox film 25 is positive.
[0024]
Specifically, since the thickness of each of the CoFe films 24a and 24c is 2.5 nm and the saturation magnetization of CoFe is 1500 emu / cc, ΔMt in the laminated ferrimagnetic structure 24 is − (1500 × 2.5 nm) + (1500 × 3.1 nm) = 964 emunm / cc.
[0025]
The reason why the laminated ferrimagnetic structure 24 is configured is to apply the leakage magnetic field from the side end face of the laminated ferrimagnetic structure 24 to the CoFeB film 26 functioning as the free layer 11, and furthermore, the leakage magnetic field strength H This is because the product HL of the length L of the element in the direction of the easy axis of magnetization of the element is 15 Oe * μm (Oersted * micron meter) or more. The direction of the magnetic field applied by the laminated ferrimagnetic structure 24 is assumed to be along the easy axis direction of the CoFeB film 26.
[0026]
Here, the relationship between ΔMt and the leakage magnetic field in the laminated ferrimagnetic structure 24 will be described in detail.
[0027]
First, prior to the description of the relationship between ΔMt and the leakage magnetic field, the applied magnetic field to the CoFeB film 26 and the variation in the switching field in the CoFeB film 26 will be described. Here, four types of samples having different thicknesses of the CoFe film 24a in the laminated ferrimagnetic structure 24 are prepared, and the description will be made using the evaluation results of the switching field variation for each sample. As the samples, four types of CoFe films 24a having a thickness of 3.1 nm, a thickness of 2.6 nm, a thickness of 2.1 nm, and a thickness of 1.6 nm were prepared. The element size is 0.8 μm × 1.6 μm. Since a method for evaluating the switching field variation is known, its description is omitted here.
[0028]
FIG. 5 is an explanatory diagram showing the evaluation results of the switching field variation for each sample. As can be seen from the figure, among the four types of samples, the CoFe film 24a having the largest film thickness has the smallest switching field variation in the CoFeB film 26. In order to explain this origin, the relationship between the deviation Hf of the asteroid curve representing the asymmetry of the switching field in each sample in the easy axis direction and the element size will be described.
[0029]
FIG. 6 is an explanatory diagram showing the relationship between the asteroid shift Hf and the element size. It can be seen from the example of the figure that the deviation Hf of the asteroid and the reciprocal 1 / L of the major axis dimension of the element have a linear relationship with each other. The rate of change (inclination) is considered to reflect the leakage magnetic field from the laminated ferrimagnetic structure 24. That is, the larger the rate of change (the steeper the slope), the greater the leakage magnetic field.
[0030]
From the results shown in FIGS. 5 and 6, it can be said that the stronger the leakage magnetic field from the laminated ferrimagnetic structure 24, that is, the stronger the magnetic field applied to the CoFeB film 26, the smaller the switching field variation in the CoFeB film 26.
[0031]
FIG. 7 shows this relationship for more samples. In the example shown in FIG. 5, in addition to the results shown in FIG. 5, the thickness of each of the films 24a and 24c (the reference layer and the pinned layer) in the laminated ferri-structure 24 has a device size of 0.8 μm × 1.2 μm. The results are shown together. As can be seen from the example of this figure, when the absolute value of the change rate with respect to the reciprocal 1 / L of the deviation Hf of the asteroid increases, that is, when the influence of the leakage magnetic field increases, the switching field variation decreases. This is thought to be due to the fact that the existence of the leakage magnetic field stabilizes the magnetization distribution, thereby simplifying the mechanism of reversing the magnetization direction. It is also considered that the leakage magnetic field functions as a bias magnetic field, thereby stabilizing the operation of reversing the magnetization direction.
[0032]
That is, as shown in FIG. 7, the effect of suppressing the switching magnetic field variation of the leakage magnetic field does not greatly depend on the element size if the horizontal axis indicates the rate of change with respect to the reciprocal 1 / L of the asteroid shift Hf. In addition, there is no significant effect until the rate of change of the deviation Hf of the asteroid is about 0 to -15 Oe * μm, and the effect starts to appear from about -15 Oe * μm. That is, in order to obtain the suppression effect, the leakage magnetic field as the rate of change of the asteroid shift Hf needs to be 15 Oe * μm or more in absolute value. The leakage magnetic field is determined by the material and the film thickness distribution of each of the films 24a and 24c of the laminated ferrimagnetic structure 24, and the strength is determined by the sum of the product Mt of the thickness t of each of the films 24a and 24c and its saturation magnetization M ΣMt Is a parameter. Note that, in each of the films 24a and 24c, since the respective magnetization directions are arranged in antiparallel, the total ΣMt is substantially the difference ΔMst between the respective products Mt.
[0033]
FIG. 8 is an explanatory diagram showing the relationship between the difference ΔMst and the leakage magnetic field (change rate of the asteroid shift Hf). According to the example in the figure, in order to make the leakage magnetic field 15 Oe * μm or more in absolute value, the difference ΔMst needs to satisfy either 750 emunm / cc or more or -2000 emunm / cc or less.
[0034]
From this, in the TMR element 1 described in the present embodiment, the difference ΔMst between the CoFe films 24a and 24c constituting the laminated ferri-structure 24 satisfies either 750 emunm / cc or more or -2000 emunm / cc or less. In addition, the thicknesses of the CoFe films 24a and 24c are 2.5 nm and 3.1 nm, respectively, and both are formed of CoFe which is a material having a saturation magnetization of 1500 emu / cc.
[0035]
However, if the difference ΔMst between the films 24a and 24c is too large, the leakage magnetic field can be increased, but at the same time, the exchange coupling via the pin magnetic field (the interaction magnetic field with the PtMn film 23) and the Ru film 24b is performed. Since the magnetic field is also reduced, the anti-parallel arrangement of the CoFeB film 26 and the laminated ferri-structure 24 is destroyed at a low magnetic field, which may lead to variation in the reversal magnetic field. Therefore, it is desirable to set an upper limit on the strength of the leakage magnetic field. Specifically, considering the reduction of the pin magnetic field, the exchange coupling magnetic field, and the like, the change rate of Hf may be set to 50 Oe-um or less. When this is converted into ΔMst based on the relationship shown in FIG. 8, it is desirable that ΔMst be set in a range from −3750 emunm / cc to 3250 emunm / cc.
[0036]
That is, in the CoFe films 24a and 24c in the laminated ferrimagnetic structure 24, the difference ΔMst (or the total ΔMt) between the thickness t of each of the films 24a and 24c and the saturation magnetization M thereof is −3750 emunm / cc or more and −2000 emunm / cc or It is assumed that each is configured to belong to the range of 750 emunm / cc or more and 3250 emunm / cc or less.
[0037]
Since the laminated ferrimagnetic structure 24 is configured as described above, in the TMR element 1, the absolute value of the leakage magnetic field from the laminated ferrimagnetic structure 24, that is, the magnetic field applied to the CoFeB film 26, is 15 Oe * μm or more. , And thereby the variation in the switching field in the CoFeB film 26 can be reduced.
[0038]
Meanwhile, in order to suppress the switching magnetic field variation, it is effective to increase the leakage magnetic field (the magnetic field applied to the CoFeB film 26), but the leakage magnetic field generally tends to act to increase the asteroid shift. That is, the magnetostatic interaction tends to increase between the laminated ferrimagnetic structure 24 and the CoFeB film 26 by suppressing the switching magnetic field variation. However, as described above, it is necessary to make the deviation of the asteroid close to “0” as in the case of suppressing the switching magnetic field variation.
[0039]
In order to make the deviation of the asteroid close to “0” while increasing the leakage magnetic field, another source of the deviation, specifically, the Neel coupling magnetic field may be strengthened. Generally, since the Neel coupling magnetic field takes a positive value, if the leakage magnetic field is set to a negative value and the magnitude of the Neel coupling magnetic field is adjusted, the vector sum can be reduced. The strength of the Neel coupling magnetic field may be adjusted by, for example, the roughness (surface roughness) of the interface between the laminated ferrimagnetic structure 24 and the CoFeB film 26. As described above, if the vector sum with the Neel coupling magnetic field is used, for example, as shown in FIG. 9, even if the asteroid shift tends to increase due to the leakage magnetic field (see FIG. 9A), Can be adjusted so as to bring the deviation closer to “0” (see FIG. 9B).
[0040]
As described above, according to the TMR element 1 described in the present embodiment and the MRAM configured using the TMR element 1, the application of the static magnetic field to the CoFeB film 26 causes the magnetization direction of the CoFeB film 26 to be inverted. It is possible to correct the imbalance of the threshold value, and it is also easy to realize that the deviation of the asteroid is brought close to “0”. That is, since the magnetization reversal mechanism is simplified by the application of the static magnetic field, it is possible to suppress the variation of the reversal magnetic field between the TMR elements 1 and easily realize the deviation of the asteroid to “0”. Become. Therefore, even when an MRAM is configured, it is possible to secure a large selective recording margin and realize good recording characteristics.
[0041]
In the present embodiment, a specific configuration in which a static magnetic field is applied from the laminated ferrimagnetic structure 24 to the CoFeB film 26 has been described as an example. However, the material and the film thickness of the film configuration are merely examples. It is not limited to this. That is, at least the total ΔMt of the product Mt of the thickness t of each film generating the leakage magnetic field and its saturation magnetization M satisfies either 750 emunm / cc or more or -2000 emunm / cc or less. Needless to say, it is not limited to the film configuration described in the present embodiment. Also, the configuration of the portion that generates the leakage magnetic field does not necessarily need to be the laminated ferrimagnetic structure 24, and may be a single fixed layer. Further, the end surface of the PtMn film 23 functioning as a reference layer is exposed, an element shape is formed so that a leakage magnetic field is generated from the PtMn film 23, and the leakage magnetic field from the PtMn film 23 may be used. Conceivable.
[0042]
Further, in the present embodiment, the leakage magnetic field from the laminated ferrimagnetic structure 24 is used as the magnetic field applied to the CoFeB film 26, thereby stabilizing the magnetization distribution in the CoFeB film 26 and simplifying the configuration. However, the applied magnetic field that is the source for stabilizing the magnetization distribution is not limited to the leakage magnetic field, and may be provided with another magnetic field source. . FIG. 10 is a schematic diagram illustrating a configuration example including another magnetic field generation source. As shown in the example of the drawing, as another magnetic field generating source, for example, a CoPt (cobalt platinum) film 31 (see FIG. 10A) made of a high coercive force material laminated on the CoFeB film 26, or an end face of the CoFeB film 26 It is also conceivable to use a CoPt film 32 (see FIG. 10B) individually arranged on both sides and cover the periphery with a buried insulating material 33. Even in this case, if the strength of the applied magnetic field from the CoPt film 31 or the CoPt film 32 to the CoFeB film 26 is equal to or greater than 15 Oe, as in the case of the present embodiment, while suppressing the variation in the switching magnetic field, It is easily feasible to make the asteroid shift close to “0”.
[0043]
In this embodiment, a so-called bottom type TMR element has been described as a preferred specific example of the present invention. However, it is considered that the present invention can be applied to other elements in exactly the same manner. For example, even in a GMR element that generates a giant magnetoresistance effect by sandwiching a non-magnetic layer made of a metal between two ferromagnetic regions, the present invention is applied to improve the variation in the switching field and the asteroid shift. The effect is expected.
[0044]
【The invention's effect】
As described above, according to the magnetoresistive element and the magnetic memory device of the present invention, the magnetization reversal process is simplified by controlling the static magnetic field in the free layer to a certain range, and the variation of the reversal magnetic field is suppressed. It becomes possible. In other words, it is possible to suppress the variation of the inversion magnetic field between the respective magnetoresistive elements, and to easily realize the deviation of the asteroid close to “0”. Therefore, even when the magnetic memory device is configured, it is possible to secure a large margin for selective recording and realize good recording characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a basic configuration example of an MRAM.
FIG. 2 is a schematic diagram showing an example of a cross-sectional configuration of a single TMR element portion forming an MRAM.
FIG. 3 is a schematic diagram showing a basic configuration example of an MTJ structure.
FIG. 4 is a schematic diagram for explaining a TMR element having an MTJ structure more specifically;
FIG. 5 is an explanatory diagram showing evaluation results of switching magnetic field variation for a plurality of types of TMR elements.
FIG. 6 is an explanatory diagram showing a relationship between asteroid displacement and element size in each TMR element of FIG.
FIG. 7 is an explanatory diagram showing an evaluation result of a relationship between an asteroid shift and an element size in a plurality of types of TMR elements.
FIG. 8 is an explanatory diagram showing a relationship between a total ΔMt of a product Mt with a saturation magnetization M and a leakage magnetic field.
FIGS. 9A and 9B are explanatory diagrams showing a specific example of asteroid shift, wherein FIG. 9A is a diagram showing a state before adjustment, and FIG. 9B is a diagram showing a state after adjustment.
10A and 10B are schematic diagrams showing a modification of the magnetoresistive effect element according to the present invention, wherein FIG. 10A is a diagram showing a configuration example having another magnetic field generating source (part 1), and FIG. FIG. 9 is a diagram (part 2) illustrating a configuration example including a magnetic field generation source.
FIG. 11 is an explanatory diagram plotting the deviation Hf of the asteroid in the easy axis direction with respect to the reciprocal of the dimension L in the major axis direction of the TMR element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... TMR element, 11 ... Fixed reference layer, 12 ... Storage layer, 13 ... Insulating layer, 23 ... PtMn film, 24 ... Stacked ferri structure, 24a, 24c ... CoFe film, 24b ... Ru film, 25 ... Al-Ox film , 26 ... CoFeB film, 31, 32 CoPt film

Claims (10)

It has a laminated structure including at least two ferromagnetic layers and an insulating layer sandwiched between them, one ferromagnetic layer functions as a free layer whose magnetization direction can be reversed, and the other ferromagnetic layer functions as a magnetization direction. In the magnetoresistive effect element functioning as a fixed layer that does not invert,
A magnetoresistive element comprising a magnetic field applying member for applying a static magnetic field to the free layer. 2. The magnetoresistance according to claim 1, wherein the absolute value of the product of the strength H of the static magnetic field and the length L of the magnetoresistance effect element in the easy axis direction is 15 [Oersted * micrometer] or more. Effect element. The magnetic field applying member is at least one of the fixed layer or an antiferromagnetic reference layer stacked on a side opposite to the insulating layer side of the fixed layer,
The magnetoresistance effect element according to claim 2, wherein the static magnetic field is a leakage magnetic field from at least one of the fixed layer and the reference layer. The product Mt of the thickness t of the layer that functions as the magnetic field applying member of the fixed layer and the reference layer and the saturation magnetization M satisfies either 750 emunm / cc or more or -2000 emunm / cc or less. The magnetoresistive element according to claim 3, wherein the magnetoresistive element is configured. A layered structure in which CoFe / Ru / CoFe / PtMn is sequentially stacked as the fixed layer and an antiferromagnetic reference layer stacked on the opposite side of the fixed layer from the insulating layer side;
While using a leakage magnetic field from the laminated structure as the static magnetic field,
The total ΔMt including the sign of the product Mt of the thickness t of each layer constituting the laminated structure and the saturation magnetization M satisfies either 750 emunm / cc or more or −2000 emunm / cc or less. 2. The magnetoresistance effect element according to claim 1, wherein: It has a laminated structure including at least two ferromagnetic layers and an insulating layer sandwiched between them, one ferromagnetic layer functions as a free layer whose magnetization direction can be reversed, and the other ferromagnetic layer functions as a magnetization direction. A magnetic memory device that includes a magnetoresistive element that functions as a fixed layer that does not invert, and that records information by using a change in the magnetization direction of a free layer in the magnetoresistive element.
A magnetic memory device comprising a magnetic field applying member for applying a static magnetic field to the free layer. 7. The magnetic memory according to claim 6, wherein the absolute value of the product of the strength H of the static magnetic field and the length L of the magnetoresistive effect element in the easy axis direction is 15 [Oersted * micrometer] or more. apparatus. The magnetic field applying member is at least one of the fixed layer or an antiferromagnetic reference layer stacked on a side opposite to the insulating layer side of the fixed layer,
7. The magnetic memory device according to claim 6, wherein the static magnetic field is a leakage magnetic field from at least one of the fixed layer and the reference layer. The product Mt of the thickness t of the layer that functions as the magnetic field applying member of the fixed layer and the reference layer and the saturation magnetization M satisfies either 750 emunm / cc or more or -2000 emunm / cc or less. 7. The magnetic memory device according to claim 6, wherein the magnetic memory device is configured. A layered structure in which CoFe / Ru / CoFe / PtMn is sequentially stacked as the fixed layer and an antiferromagnetic reference layer stacked on the opposite side of the fixed layer from the insulating layer side;
While using a leakage magnetic field from the laminated structure as the static magnetic field,
The total ΔMt including the sign of the product Mt of the thickness t of each layer constituting the laminated structure and the saturation magnetization M satisfies either 750 emunm / cc or more or −2000 emunm / cc or less. 7. The magnetic memory device according to claim 6, wherein:

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