JP3607609B2 - Magnetoresistive element, magnetic memory, magnetic head, and magnetic reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistive effect element, a magnetic memory, a magnetic head, and a magnetic reproducing apparatus.
[0002]
[Prior art]
The ferromagnetic single tunnel junction has a structure in which a thin insulator layer is sandwiched between a pair of ferromagnetic layers. When a bias voltage is applied using these ferromagnetic layers as electrodes, a tunnel current flows through the ferromagnetic single tunnel junction.
[0003]
In a ferromagnetic single tunnel junction, a tunnel resistance when a tunnel current flows, that is, a tunnel conductance, changes depending on an angle formed by the magnetization direction of one ferromagnetic layer and the magnetization direction of the other ferromagnetic layer. In other words, the magnetoresistance effect obtained in the ferromagnetic single tunnel junction is based on the fact that the tunnel conductance changes according to the angle formed by the magnetization direction between the ferromagnetic layers. For example, when the magnetization direction of one ferromagnetic layer is a first direction parallel to the film surface and the magnetization direction of the other ferromagnetic layer is a second direction opposite to the first direction The tunnel conductance is minimized. Further, when both the magnetization directions of the ferromagnetic layers are the first direction, the tunnel conductance is maximized.
[0004]
Such a ferromagnetic single tunnel junction is expected to be applied to various devices. For example, for a ferromagnetic single tunnel junction in which one ferromagnetic layer is a fixed magnetization layer with a fixed magnetization direction and the other ferromagnetic layer is a free layer whose magnetization direction can be changed in response to an external magnetic field, It has been proposed to use it as a memory cell of a memory (or magnetic random access memory: MRAM), and this MRAM has already been prototyped with a low storage capacity.
[0005]
The MRAM is basically non-volatile, can be written and read at high speed, and has excellent characteristics such as high fatigue resistance against repeated writing and reading. However, as will be described below, in the MRAM, when the size of the memory cell is reduced as the capacity increases, the magnetic field necessary for reversing the magnetization direction of the free layer, the so-called reversal magnetic field, increases. The problem is that a larger write current is required.
[0006]
The reversal magnetic field of the free layer is proportional to 1 / W (W: cell width). Further, this reversal magnetic field is caused by the free layer thickness t and the saturation magnetization M. _s Is also known to be proportional. That is, the reversal magnetic field of the free layer is t · M _s It is proportional to / W. Note that the reversal magnetic field of the free layer is proportional to 1 / W because it exceeds the demagnetizing field generated inside the free layer in order to rewrite the information stored in the MRAM cell by reversing the magnetization direction of the free layer. This is because an external magnetic field needs to be applied, but this demagnetizing field is caused by magnetic poles generated in the width direction of the cell.
[0007]
As is apparent from the above proportional relationship, in order to avoid an increase in the reversal magnetic field when the size of the memory cell is reduced, for example, the film thickness t of the free layer may be reduced. However, when the film thickness t is reduced, a free layer that should be a continuous film cannot be obtained, and a large number of fine particles are dispersed on the base. Since the thin film formed by such a large number of fine particles is not a ferromagnetic material but a paramagnetic material, the magnetoresistance ratio is significantly reduced.
[0008]
Further, in order to avoid an increase in the reversal magnetic field when the memory cell size is reduced, the saturation magnetization M _s Can also be reduced. However, saturation magnetization M _s When a non-magnetic material is added to the material constituting the free layer in order to reduce the resistance, the spin polarization degree of conduction electrons on the Fermi surface is often lowered, leading to a reduction in magnetoresistance ratio.
[0009]
That is, in the prior art, when the size of the memory cell is reduced, an increase in the reversal magnetic field of the free layer cannot be prevented while maintaining a sufficiently high magnetoresistance ratio. The problem described in connection with the MRAM also exists in a magnetic head using a ferromagnetic single tunnel junction. In addition, the above-mentioned problem concerning the ferromagnetic single tunnel junction is the same in the ferromagnetic double tunnel junction.
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems. A magnetoresistive effect element, a magnetic memory, and the like that can maintain a sufficiently high magnetoresistance ratio and prevent an increase in switching magnetic field even when the size is reduced. An object is to provide a magnetic head and a magnetic reproducing apparatus.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a first ferromagnetic layer that retains the direction of magnetization provided when no external magnetic field is applied in a predetermined external magnetic field, and when the external magnetic field is not applied with the external magnetic field. Comprising: a second ferromagnetic layer capable of changing a magnetization direction; and a first tunnel barrier layer interposed between the first ferromagnetic layer and the second ferromagnetic layer, One ferromagnetic layer, the first tunnel barrier layer, and the second ferromagnetic layer form a ferromagnetic tunnel junction; The first tunnel barrier layer is made of an insulator, the second ferromagnetic layer is formed on the first tunnel barrier layer, and the thickness of the second ferromagnetic layer is 0.3 nm to 2. In the range of 5 nm, The composition of the ferromagnetic material contained in the second ferromagnetic layer has the general formula (CoFe) _100-x Y _x Or general formula (CoFeNi) _100-x Y _x Y is at least one element selected from the group consisting of B, Si, Zr, P, Mo, Al, and Nb. X satisfies the relationship expressed by the inequality 3 ≦ x ≦ 16. A magnetoresistive effect element is provided.
[0012]
According to another aspect of the present invention, there is provided a magnetic memory comprising the magnetoresistive element and first and second wirings that intersect with the magnetoresistive element.
[0013]
Furthermore, the present invention provides a magnetic head comprising the magnetoresistive element, a support that supports the magnetoresistive element, and a pair of electrodes connected to the magnetoresistive element. To do.
[0014]
In addition, the present invention includes a magnetic recording medium, the magnetoresistive effect element, a support that supports the magnetoresistive effect element, and a pair of electrodes connected to the magnetoresistive effect element. Provided is a magnetic reproducing apparatus comprising a magnetic head for reading recorded information, and a moving mechanism for moving the magnetic head relative to the magnetic recording medium.
[0016]
In the present invention, the ferromagnetic tunnel junction may be a ferromagnetic single tunnel junction or a ferromagnetic double tunnel junction. In the latter case, the magnetoresistive effect element further includes a third ferromagnetic layer and a second tunnel barrier layer that maintain the magnetization direction provided when no external magnetic field is applied in the external magnetic field, and the third tunnel barrier layer. The second ferromagnetic barrier layer and the second tunnel barrier layer have a second ferromagnetic layer interposed between the two tunnel barrier layers, and the second ferromagnetic layer and the two tunnel barrier layers are the first and third ferromagnetic layers. It arrange | positions so that it may interpose between layers.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, in each figure, the same referential mark is attached | subjected to the same or similar component, and the overlapping description is abbreviate | omitted.
[0018]
FIG. 1 is a cross-sectional view schematically showing a magnetoresistive effect element according to a first embodiment of the present invention. A magnetoresistive effect element 1 shown in FIG. 1 has a ferromagnetic single tunnel junction 2a. The ferromagnetic single tunnel junction 2 a has a structure in which a tunnel barrier layer 6 made of an insulator or the like is interposed between a pair of ferromagnetic layers 3 and 4. The ferromagnetic single tunnel junction 2 a is configured such that a tunnel current flows between the ferromagnetic layers 3 and 4 via the tunnel barrier layer 6.
[0019]
An antiferromagnetic layer 8 is disposed on the back surface of the surface of the ferromagnetic layer 3 in contact with the tunnel barrier layer 6. Thereby, the magnetization direction of the ferromagnetic layer 3 does not change even when an external magnetic field is applied. On the other hand, the magnetization direction of the ferromagnetic layer 4 can be freely rotated in accordance with an external magnetic field. That is, in the magnetoresistive effect element 1 shown in FIG. 1, the ferromagnetic layer 3 is a first ferromagnetic layer whose magnetization direction is fixed, that is, a so-called magnetization fixed layer, and the ferromagnetic layer 4 corresponds to an external magnetic field. A second ferromagnetic layer whose magnetization direction can be changed, a so-called free layer. In other words, the magnetoresistive effect element 1 shown in FIG. 1 is an angle formed between the magnetization direction of the ferromagnetic layer 3 and the magnetization direction of the ferromagnetic layer 4 by reversing or rotating the magnetization direction of the ferromagnetic layer 4 by an external magnetic field. The magnetoresistive effect that the tunnel resistance or the tunnel current changes when the current is changed is utilized.
[0020]
The ferromagnetic single tunnel junction 2a and the antiferromagnetic layer 8 described above are usually formed by sequentially depositing various thin films on one main surface of the substrate 10. In the magnetoresistive effect element 1 of FIG. 1, a diffusion barrier layer 11 and an orientation control layer 12 are sequentially stacked from the substrate 10 side between the substrate 10 and the antiferromagnetic layer 8. A protective layer 13 and a wiring layer 14 are sequentially laminated on the top. Reference numeral 15 is an insulating layer.
[0021]
FIG. 2 is a cross-sectional view schematically showing a magnetoresistive effect element according to the second embodiment of the present invention. The magnetoresistive effect element 1 shown in FIG. 2 has a ferromagnetic double tunnel junction 2b instead of the ferromagnetic single tunnel junction 2a, and is further counteracted between the ferromagnetic double tunnel junction 2b and the protective layer 13. Except for having the ferromagnetic layer 9, the magnetoresistive effect element 1 shown in FIG.
[0022]
In the magnetoresistive element 1 shown in FIG. 2, the ferromagnetic double tunnel junction 2 b has a tunnel barrier layer 6 interposed between the ferromagnetic layers 3 and 4 and a tunnel barrier layer 7 interposed between the ferromagnetic layers 4 and 5. Has a structure. The ferromagnetic double tunnel junction 2 b is configured such that a tunnel current flows between the ferromagnetic layers 3 and 4 and between the ferromagnetic layers 4 and 5 via the tunnel barrier layers 6 and 7.
[0023]
In the magnetoresistive effect element 1 shown in FIG. 2, the ferromagnetic layer 5 is also a magnetization pinned layer whose magnetization direction is fixed by the presence of the antiferromagnetic layer 9 as described with respect to the ferromagnetic layer 3. The magnetoresistive effect element 1 shown in FIG. 2 changes the angle between the magnetization direction of the ferromagnetic layers 3 and 5 and the magnetization direction of the ferromagnetic layer 4 by reversing or rotating the magnetization direction of the ferromagnetic layer 4 by an external magnetic field. This makes use of the magnetoresistance effect that the tunnel resistance or tunnel current changes.
[0024]
The magnetoresistive effect element 1 according to the first and second embodiments described above is characterized in that the ferromagnetic layer 4 is made of the material described below. That is, in the magnetoresistive effect element 1 shown in FIGS. 1 and 2, the composition of the ferromagnetic layer 4 has the general formula (CoFe). _100-x Y _x Or general formula (CoFeNi) _100-x Y _x It is represented by In these general formulas, Y is at least one element selected from the group consisting of B, Si, Zr, P, Mo, Al, and Nb. Further, x is a numerical value that satisfies the inequality 0 <x <100, and preferably a numerical value that satisfies the inequality 3 <x <16.
[0025]
The materials represented by these general formulas have saturation magnetization M as compared with materials having the same composition except that they do not contain the element Y. _s Therefore, even when the size of the magnetoresistive effect element 1 is reduced (or when the width W of the ferromagnetic layer 4 is reduced), the switching magnetic field does not become excessively large. Even when the film thickness t of the ferromagnetic layer 4 is reduced, the crystallization is suppressed according to the material containing the element Y, so that the ferromagnetic layer 4 can be formed as a continuous film. That is, even when the size of the magnetoresistive element 1 is reduced, by using the material represented by the general formula, the formula t · M _s The reversal magnetic field of the ferromagnetic layer 4 proportional to / W can be maintained at a sufficiently small value.
[0026]
FIG. 3 is a graph showing an example of the relationship between the composition of the ferromagnetic layer 4 of the magnetoresistive effect element 1 according to the first and second embodiments of the present invention and the magnetoresistance change rate. This graph shows the general formula (Co ₉ Fe) _100-x B _x Is drawn based on the data obtained for the magnetoresistive effect element 1 using the ferromagnetic layer 4 having a thickness of 1 nm and the horizontal axis indicates the concentration of B in the ferromagnetic layer 4. In the corresponding general formula, x is shown, and the vertical axis shows the magnetoresistance change rate (%).
[0027]
In a normal film formation method at room temperature, B-free Co ₉ The lower limit of the film thickness that can be formed using the Fe film as a continuous film is at most about 1.5 nm. Co ₉ When the Fe film is formed as a discontinuous film, the discontinuous film is composed of an aggregate of fine particles having a diameter of several nm. Each of these fine particles loses ferromagnetism at room temperature, and the magnetization direction is not fixed, so-called superparamagnetism. As a result, the magnetoresistance change rate is significantly reduced within a practical magnetic field strength range.
[0028]
In contrast, Co ₉ When B is added to Fe, a continuous film can be formed up to a film thickness of about 0.5 nm. For example, when the film thickness is 1 nm, x is set to 3 to 16 as shown in FIG. Thus, a sufficiently high magnetoresistance change rate of 10% or more can be obtained, and by setting x to about 5, a magnetoresistance change rate of 20% or more can be obtained.
[0029]
The data shown in FIG. 3 was obtained when B was added as the element Y, but the same tendency was observed when Si, Zr, P, Mo, Al, and Nb were added as the element Y. Is observed.
[0030]
The reason why an extremely thin continuous film can be formed when the element Y is added is that the addition or the element Y suppresses the diffusion or movement of atoms reaching the film formation surface during the film formation process. It is because it is suppressed. In other words, when the element Y is not added, crystallization is likely to occur because diffusion or movement of atoms that have reached the film formation surface is performed relatively freely. For this reason, in the prior art, when the film thickness is reduced, an island-like structure in which the diameter of each island is about several nanometers is formed, and the magnetization direction fluctuates even though each island is a ferromagnetic substance. As a result, the rate of change in magnetoresistance is significantly reduced.
[0031]
In FIG. 3, when x increases beyond 5, the magnetoresistance change rate decreases. The reason is not necessarily clarified, but it is considered that the conduction electron scattering increases as the concentration of the element Y increases, and the spin polarization degree of the Fermi level conduction electrons is remarkably lowered.
[0032]
As described above, according to the material shown in the above general formula, it is possible to form a very thin continuous film, and yet it has a sufficiently high magnetoresistance change rate even though it contains the element Y which is a nonmagnetic material. Can be obtained. That is, by configuring the ferromagnetic layer 4 with a material represented by the above general formula, even when the size of the magnetoresistive element 1 is reduced, a sufficiently high magnetoresistance ratio is maintained and an increase in the reversal magnetic field is prevented. can do.
[0033]
In the magnetoresistive element 1 described above, the material constituting the ferromagnetic layers 3 and 5 is not particularly limited, and examples thereof include NiFe alloys represented by Permalloy, Fe, Co, Ni, and alloys containing them, Half metal such as NiMnSb and Hetler alloy such as PtMnSb, CrO ₂ Uses various ferromagnetic materials from various soft magnetic materials such as oxide half metals and amorphous alloys such as magnetite and Mn perovskite to hard magnetic materials such as CoPt alloy, FePt alloy and transition metal-rare earth alloy can do.
[0034]
In the magnetoresistive element 1 described above, the antiferromagnetic layers 8 and 9 are provided to fix their magnetization directions by exchange coupling with the ferromagnetic layers 3 and 5, respectively. These antiferromagnetic layers 8 and 9 include, for example, antiferromagnetic alloys such as FeMn, IrMn, PtMn, NiMn, NiO, Fe ₂ O ₃ In addition to a thin film made of an antiferromagnetic material such as, an antiferromagnetic exchange coupling film such as Co / Ru / Co or Co / Au / Co may be used.
[0035]
The tunnel barrier layers 6 and 7 may have any potential height and thickness within a range in which a tunnel current can flow between the ferromagnetic layers 3 and 4 and between the ferromagnetic layers 4 and 5. As materials for the tunnel barrier layers 6 and 7, for example, Al, Si, Mg, rare earth elements, and oxides or nitrides of alloys containing these elements can be used. However, the potential barrier of a thin film made of an oxide insulator varies greatly depending on its manufacturing conditions. Since the characteristics of the magnetoresistive element 1 vary greatly depending on the width and height of the potential barrier, when such an oxide insulator is used, the degree of freedom in setting the element characteristics is increased. Accordingly, it is necessary to appropriately set the type and production conditions.
[0036]
In the magnetoresistive effect element 1, as the substrate 10, for example, the surface is SiO. ₂ A silicon single crystal substrate on which an oxide film is formed can be used. The diffusion barrier layer 11 formed on the substrate 10 is for preventing diffusion, and examples of the material include Ta, TaPt, Ti, and TiN. _x And CoSi ₂ Etc. can be used. The orientation control layer 12 formed on the diffusion barrier layer is an underlayer for forming the antiferromagnetic layer 8 having a desired crystal orientation, and is made of, for example, a material such as NiFe, Cu, Ag, and Au. Can be done. Further, as the material of the protective layer 13, for example, Ta or Au can be used, and as the material of the wiring layer 14, for example, Al, Cu, Ag, Au, or the like can be used.
[0037]
Next, a magnetic memory using the magnetoresistive effect element 1 according to the first and second embodiments will be described.
[0038]
FIG. 4 is a cross-sectional view schematically showing a magnetic memory (MRAM) using the magnetoresistive effect element 1 according to the first and second embodiments of the present invention. FIG. 5 is an equivalent circuit diagram of the MRAM shown in FIG.
[0039]
The MRAM 21 shown in FIG. 4 has a silicon substrate 22. A gate electrode 24 is formed on the silicon substrate, and source / drain regions 25 and 26 are formed on the surface region of the silicon substrate 22 so as to sandwich the gate electrode 24. Thereby, the MOS transistor 23 is configured. The gate electrode 24 forms a read word line (WL1). A write word line (WL 2) 28 is formed on the word line (WL 1) 24 via an insulating film 27.
[0040]
One end of a contact metal 29 is connected to the drain region 26 of the MOS transistor 23, and a base layer 30 is connected to the other end of the contact metal 29. A ferromagnetic tunnel junction element (TMR) 31 is formed at a position corresponding to the word line (WL 2) 28 on the underlayer 30, and a bit line 32 is formed on the TMR 31.
[0041]
The cell of the MRAM 21 is configured as described above. 4 has a structure in which, for example, the substrate 10, the protective layer 13, the wiring layer 14, and the insulating layer 15 are excluded from the magnetoresistive effect element 1 shown in FIGS. Equivalent to.
[0042]
The memory cells composed of the MOS transistor 23 and the TMR 31 described above are arranged in an array as shown in FIG. The read word line (WL1) 24, which is the gate electrode of the transistor 23, and the write word line (WL2) 28 are arranged in parallel. Further, the bit line (BL) 32 connected to the upper part of the TMR 31 is disposed so as to be orthogonal to the word line (WL 1) 24 and the word line (WL 2) 28.
[0043]
Since this MRAM 21 uses the magnetoresistive effect element 1 according to the first and second embodiments, the inversion of the free layer while maintaining a sufficiently high magnetoresistance ratio even when the size of the memory cell is reduced. An increase in the magnetic field can be prevented. That is, in the MRAM 21, even when the memory cell size is reduced, information can be written with sufficient current.
[0044]
In the MRAM 21, a diode may be used instead of the transistor 23. For example, the MRAM 21 can be obtained by forming a memory cell made of a stack of a diode and TMR 31 on the word line 24 and forming the bit line 32 on the TMR 31 so as to be orthogonal to the word line 24.
[0045]
Next, a magnetic head using the magnetoresistive effect element 1 according to the first and second embodiments will be described.
FIG. 6 is a perspective view schematically showing a magnetic head assembly having a magnetic head using the magnetoresistive effect element 1 according to the first and second embodiments of the present invention. The magnetic head assembly 41 shown in FIG. 6 includes an actuator arm 42 including a bobbin portion that holds a drive coil, for example. One end of a suspension 43 is attached to the actuator arm 42, and a head slider 44 is attached to the other end of the suspension 43. The magnetoresistive effect element 1 according to the first and second embodiments described above is used in a magnetic reproducing head incorporated in the head slider 44.
[0046]
Signal writing and reading lead wires 45 are formed on the suspension 43, and these lead wires 45 are electrically connected to electrodes of a magnetic reproducing head incorporated in the head slider 44, respectively. In FIG. 6, reference numeral 46 indicates an electrode pad of the magnetic head assembly 41.
[0047]
The magnetic head assembly 41 can be mounted on, for example, a magnetic recording / reproducing apparatus as described below.
FIG. 7 is a perspective view schematically showing a magnetic recording / reproducing apparatus equipped with the magnetic head assembly 41 shown in FIG. In the magnetic recording / reproducing apparatus 51 shown in FIG. 7, a magnetic disk 52 as a magnetic recording medium is rotatably supported by a spindle 53. A motor (not shown) that operates in response to a control signal from a control unit (not shown) is connected to the spindle 53, whereby the rotation of the magnetic disk 52 can be controlled.
[0048]
A fixed shaft 54 is disposed in the vicinity of the circumferential portion of the magnetic disk 52, and the fixed shaft 54 is shown in FIG. 6 through ball bearings (not shown) disposed at two upper and lower positions. 41 is swingably supported. A coil (not shown) is wound around the bobbin portion of the magnetic head assembly 41. The coil, the permanent magnet disposed opposite to the coil, and the opposing yoke form a magnetic circuit and the voice. A coil motor 55 is configured. This voice coil motor 55 enables the head slider 44 at the tip of the magnetic head assembly 41 to be positioned on a desired track of the magnetic disk 52. In the magnetic recording / reproducing apparatus 51, information recording and reproduction are performed in a state where the magnetic disk 52 is rotated and the head slider 44 is floated from the magnetic disk 52.
[0049]
As described above, the magnetoresistive effect element 1 according to the first and second embodiments can be used for a magnetic memory, a magnetic head, a magnetic reproducing apparatus, and a magnetic recording / reproducing apparatus. The magnetoresistive effect element 1 according to the first and second embodiments can also be used for a magnetic sensor and a magnetic field detection device using the same.
[0050]
【Example】
Examples of the present invention will be described below.
(Example)
The magnetoresistive effect element 1 shown in FIG. 2 was produced by the method described below.
First, Si / SiO ₂ The substrate 10 was carried into the sputtering apparatus. Next, the initial degree of vacuum in the apparatus is 2 × 10. ^-7 The pressure is set to less than Torr, and then Ar is introduced into the apparatus so that the pressure is 2 × 10 ^-3 It was. Next, Si / SiO ₂ On one main surface of the substrate 10, a diffusion barrier layer 11 made of Ta having a thickness of 5 nm, an orientation control layer 12 made of NiFe having a thickness of 15 nm, and an Ir having a thickness of 17 nm. ₂₂ Mn ₇₈ The antiferromagnetic layer 8 made of and the ferromagnetic layer 3 made of CoFe having a thickness of 3 nm were successively and sequentially formed.
[0051]
Next, in Ar gas, Al ₂ O ₃ By sputtering the target, Al having a thickness of 1.5 nm is formed on the ferromagnetic layer 3. ₂ O _x Layers were deposited. Subsequently, oxygen plasma is generated by introducing pure oxygen into the apparatus without breaking the vacuum and performing glow discharge, and this oxygen plasma is used to generate Al plasma. ₂ O _x Al ₂ O ₃ The tunnel barrier layer 6 was obtained by oxidation into the above. At this time, Al ₂ O _x To Al ₂ O ₃ The degree of conversion to was adjusted by controlling the power and oxidation time during glow discharge.
[0052]
After exhausting pure oxygen from the apparatus, sputtering is performed under the same conditions as described above, so that a 1.5 nm thick (Co ₉ Fe) _0.95 B _0.5 A ferromagnetic layer 4 comprising: Next, sputtering is performed in Ar gas under the same conditions as described above to form Al on the ferromagnetic layer 4. ₂ O _x The layer is deposited and this Al ₂ O _x Al by plasma treatment of the layer ₂ O ₃ A tunnel barrier layer 7 made of Further, by performing sputtering under the same conditions as described above, a ferromagnetic layer 5 made of CoFe having a thickness of 5 nm and an Ir having a thickness of 17 nm are formed on the tunnel barrier layer 7. ₂₂ Mn ₇₈ An antiferromagnetic layer 9 made of and a protective film 13 made of Ta having a thickness of 5 nm were sequentially formed.
[0053]
Thereafter, using a normal photolithography technique and an ion milling technique, these thin films are patterned so that the width W is 2 to 0.25 μm and the length L is three times the width W, thereby forming a double tunnel. A joint was defined. As described above, the magnetoresistive effect element 1 shown in FIG. 2 was obtained.
[0054]
The magnetization direction of the ferromagnetic layer 3 and the magnetization direction of the ferromagnetic layer 5 were fixed in the same direction parallel to the substrate surface by the antiferromagnetic layers 8 and 9. According to such a configuration, the magnetization directions of the ferromagnetic layers 3 and 5 are not changed by a weak external magnetic field of about several hundred Oe, and the magnetization direction of the ferromagnetic layer 4 is changed in accordance with the external magnetic field. In this magnetoresistive effect element 1, the resistance of the ferromagnetic double tunnel junction 2b is lowest when the magnetization directions of the ferromagnetic layers 3 and 5 and the magnetization direction of the ferromagnetic layer 4 are the same. The highest value is obtained when the magnetization directions of the layers 3 and 5 are opposite to the magnetization direction of the ferromagnetic layer 4.
[0055]
(Comparative example)
The ferromagnetic layer 4 has a thickness of 1.5 nm (Co ₉ Fe) _0.95 B _0.5 3 nm thick Co instead of forming a film ₉ A magnetoresistive effect element 1 shown in FIG. 2 was produced by the same method as described in the above example except that the Fe film was formed.
[0056]
Next, the magnetoresistive ratio (TMR) of the magnetoresistive effect element 1 manufactured in the above examples and comparative examples was examined. TMR is the minimum resistance value of the ferromagnetic double tunnel junction 2b. _min And the maximum value is R _max The following equation:
TMR (%) = [(R _max -R _min ) / R _min ] / 100
Defined by
[0057]
FIG. 8 is a graph showing the magnetoresistance ratio of the magnetoresistive element 1 according to the example of the present invention and the comparative example. In the figure, the horizontal axis is the reciprocal 1 / W (μm of the width W of the tunnel junction. ^-1 The vertical axis represents the magnetic field strength H required to reverse the magnetization direction of the ferromagnetic layer 4. _c (Oe) is shown. Further, in the figure, a curve 61 shows data obtained for the magnetoresistive effect element 1 according to the example of the present invention, and a curve 62 shows data obtained for the magnetoresistive effect element 1 according to the comparative example.
[0058]
As shown in FIG. 8, in the magnetoresistive effect element 1 according to the embodiment of the present invention, the magnetization direction of the ferromagnetic layer 4 can be reversed even if the width W of the tunnel junction is reduced to about 0.25 μm. Required magnetic field strength H _c Is sufficiently small as 40 Oe or less. Moreover, the magnetic field strength H _c Since the rate of change with respect to the width W is small, it can be seen that further miniaturization can be accommodated.
[0059]
On the other hand, in the magnetoresistive effect element 1 according to the comparative example, when the width W of the tunnel junction is about 0.25 μm, the magnetic field strength H necessary for reversing the magnetization direction of the ferromagnetic layer 4 is obtained. _c Exceeded 100 Oe, and it was practically difficult to reverse the magnetization direction of the ferromagnetic layer 4.
[0060]
The magnetoresistive effect element 1 according to the example and the comparative example is manufactured by the same method as described above except that Si, Zr, P, Mo, Al, and Nb are used instead of B as the element Y. When these were compared, the same tendency as the case where B was used as the element Y was seen. Further, as a material of the ferromagnetic layer 4, a general formula (CoFe) _100-x Y _x Instead of the material represented by the general formula (CoFeNi) _100-x Y _x When the same comparison was performed using the material represented by the following, the same tendency as described above was observed.
[0061]
【The invention's effect】
As described above, in the present invention, an extremely thin continuous film can be formed on a ferromagnetic layer whose magnetization direction can be changed according to an external magnetic field, and a sufficiently high magnetoresistance change rate can be obtained. Use materials. Therefore, even when the size is reduced, it is possible to maintain a sufficiently high magnetoresistance ratio and prevent an increase in the reversal magnetic field.
That is, according to the present invention, there are provided a magnetoresistive effect element, a magnetic memory, a magnetic head, and a magnetic reproducing apparatus capable of maintaining a sufficiently high magnetoresistance ratio and preventing an increase in switching magnetic field even when the size is reduced. Is done.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a magnetoresistive effect element according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view schematically showing a magnetoresistive effect element according to a second embodiment of the invention.
FIG. 3 is a graph showing an example of the relationship between the composition of the ferromagnetic layer of the magnetoresistive effect element according to the first and second embodiments of the present invention and the rate of change in magnetoresistance.
FIG. 4 is a cross-sectional view schematically showing a magnetic memory using magnetoresistive elements according to the first and second embodiments of the present invention.
5 is an equivalent circuit diagram of the magnetic memory shown in FIG.
FIG. 6 is a perspective view schematically showing a magnetic head assembly having a magnetic head using the magnetoresistive effect element according to the first and second embodiments of the present invention.
7 is a perspective view schematically showing a magnetic recording / reproducing apparatus on which the magnetic head assembly shown in FIG. 6 is mounted. FIG.
FIG. 8 is a graph showing magnetoresistance ratios of magnetoresistive elements according to examples and comparative examples of the present invention.
[Explanation of symbols]
1 ... magnetoresistive effect element
2a ... Ferromagnetic single tunnel junction
2b ... Ferromagnetic double tunnel junction
3-5 ... ferromagnetic layer
6, 7 ... Tunnel barrier layer
8,9 ... Antiferromagnetic layer
10 ... Board
11 ... Diffusion barrier layer
12 ... Orientation control layer
13 ... Protective layer
14 ... Wiring layer
15 ... Insulating layer

Claims (5)

A first ferromagnetic layer that retains a magnetization direction provided when the external magnetic field is not applied in a predetermined external magnetic field; and a second strong layer that can change a magnetization direction provided when the external magnetic field is not applied in the external magnetic field. A magnetic layer; and a first tunnel barrier layer interposed between the first ferromagnetic layer and the second ferromagnetic layer, wherein the first ferromagnetic layer and the first tunnel barrier are provided. The layer and the second ferromagnetic layer form a ferromagnetic tunnel junction;
The first tunnel barrier layer is made of an insulator;
The second ferromagnetic layer is formed on the first tunnel barrier layer;
The film thickness of the second ferromagnetic layer is in the range of 0.3 nm to 2.5 nm;
The composition of the ferromagnetic material contained in the second ferromagnetic layer is represented by the general formula (CoFe) _100-x Y _x or the general formula (CoFeNi) _100-x Y _x, where Y is B, Si, Zr, P, Mo, Al, and at least one element der selected from the group consisting of Nb is,
The x satisfies the relationship represented by the inequality 3 ≦ x ≦ 16 . The third magnetic layer and the second tunnel are further provided with a third ferromagnetic layer and a second tunnel barrier layer that retain a magnetization direction provided when the external magnetic field is not applied in the external magnetic field. The barrier layer has the second ferromagnetic layer interposed between the first tunnel barrier layer and the second tunnel barrier layer, and the second ferromagnetic layer and the first and second tunnel barriers. A layer disposed between the first ferromagnetic layer and the third ferromagnetic layer, the third ferromagnetic layer, the second tunnel barrier layer, and the second strong layer. 2. The magnetoresistive effect element according to claim 1, wherein the magnetic layer forms a ferromagnetic tunnel junction. 3. A magnetic memory comprising: the magnetoresistive effect element according to claim 1; and first and second wirings intersecting each other with the magnetoresistive effect element interposed therebetween. A magnetoresistive element according to claim 1, a support that supports the magnetoresistive element, and a pair of electrodes connected to the magnetoresistive element. head. Magnetic recording media,
A magnetoresistive effect element according to claim 1, a support that supports the magnetoresistive effect element, and a pair of electrodes connected to the magnetoresistive effect element, and recorded on the magnetic recording medium. A magnetic head for reading out the information, and
A magnetic reproducing apparatus comprising a moving mechanism for moving the magnetic head relative to the magnetic recording medium.

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