JP2000195250A - Magnetic memory device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonvolatile magnetic memory device, using a ferromagnetic tunnel junction stable operative within the cell area of a submicron size. SOLUTION: A plurality of the memory cells are arranged on fine wire-like ferromagnetic metal layers, constituted integrally with bit lines for supplying current to the respective cells. Each memory cell has a magnetic recording layer 21, a tunnel barrier layer 30 and the ferromagnetic metal layer 12 and has a free magnetization region facing an insulating layer in part of the ferromagnetic metallic layer 12. The area of the free magnetization region is smaller than the area of the ferromagnetic metal layer 12. The reading out of the recording information of the respective cells is executed through magnetic wall transfer in the ferromagnetic metal layer 12. Then, the influence of the nonuniform magnetization distribution induced by the self-degaussing magnetic field at the end face and the interlayer magnetostatic bonding of the ferromagnetic metallic layers 12 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonvolatile memory device using a ferromagnetic material, and more particularly, to a magnetic memory device using a ferromagnetic tunnel junction.

[0002]

2. Description of the Related Art Giant MagnetoResistance
stance: Abbreviated below as GMR effect. ) Is a phenomenon in which, in a complex of a certain ferromagnetic material and a non-magnetic material, electric resistance changes depending on the magnetization direction of the ferromagnetic material. As a specific configuration showing such a GMR effect, for example, there is a magnetic artificial lattice film in which ferromagnetic metal layers and non-magnetic metal layers each having a thickness of several nm are alternately laminated. In the magnetic artificial lattice film, a difference of several tens% or more occurs in the electric resistance between the case where the magnetization directions of the ferromagnetic metal layers are parallel in the same direction and the case where they are antiparallel in the opposite directions. GMR in magnetic artificial lattice films
The effect is based on Fe / Cr artificial lattice film (Phys. Rev. Lett., 61,
2472 (1988)), Co / Cu artificial lattice film (J. Magn. M.
agn. Mater., 94, L1 (1991)).

[0003] The realization of the antiparallel state of magnetization in the above-mentioned magnetic artificial lattice film is performed using antiferromagnetic exchange coupling between ferromagnetic layers. However, a film using such antiferromagnetic exchange coupling generally has a problem that the interlayer coupling is strong, so that the saturation magnetic field is large and the hysteresis with respect to an external magnetic field is also large.

Therefore, in a three-layer film composed of a ferromagnetic metal layer 1 / a non-magnetic metal layer / a ferromagnetic metal layer 2 having no interlayer coupling, an antiferromagnetic material is formed in contact with one of the ferromagnetic metal layers 1. After fixing the magnetization direction of the ferromagnetic metal layer 1 by using the method, a ferromagnetic material having a small coercive force is used for the material of the other ferromagnetic metal layer 2 so that the magnetization direction of the ferromagnetic metal layer 2 at a low magnetic field is reduced. There has been reported a spin valve film exhibiting a GMR effect by reversal of physics (Phys. Rev. B43, 1297 (1991)).

In recent years, as an application of such an element exhibiting the GMR effect (hereinafter abbreviated as a GMR element), in addition to a magnetic field sensor and a magnetic head, a magnetic random access memory (Ma
gneticRandom Access Memory. Hereinafter, it is abbreviated as MRAM. ) Has been proposed and is attracting attention. In an MRAM, many elements exhibiting the GMR effect are arranged in a memory array. As the GMR element, the above-described spin valve film is used. Information on the ferromagnetic metal layer that constitutes the spin valve film
Recorded as 1 magnetization direction. Reading of recorded information is performed by passing a current through a word line and a bit line, and detecting a change in element resistance when the magnetization direction of the ferromagnetic metal layer 2 is reversed by a magnetic field generated thereby. At this time, by setting the magnitude of the magnetic field to be smaller than the coercive force of the ferromagnetic metal layer 1, non-destructive reading can be realized. Compared with a conventional semiconductor memory using a dielectric capacitor, the function of the MRAM is (1) nonvolatile, (2) non-destructive read is possible, and the read cycle can be shortened. In addition, (3) the resistance to radiation is higher than that of charge storage type memory cells,
And many other advantages. The degree of integration is, for example, 0.
With a 25 μm rule, it is about 64 MB.

However, the resistance change rate of the spin valve film used in the MRAM is about several percent to about ten and several percent. Further, the sheet resistance of the spin valve film is about several tens Ω / □,
The cell read voltage for a mA sense current is about several mV. On the other hand, for example, the voltage drop in the cell driving transistor increases as the element size becomes smaller, and reaches about 100 mV in the 0.25 μm rule. That is, if there is a variation of 10% in the resistance value of the transistor, a noise of about 10 mV appears. Several compensating circuits for reducing these noises have been proposed, but all of them cause a reduction in the degree of integration.
In other words, with the currently obtained resistance change rate of the GMR element and the sheet resistance, the cell read voltage is small,
There is a problem that it is difficult to achieve both high integration and stable operation.

In order to solve this problem, a GMR element is replaced by an element exhibiting a ferromagnetic tunnel effect (Tunnel MR element;
Abbreviated as TMR element. ) Has been proposed. The TMR element is mainly composed of a three-layer film composed of a ferromagnetic metal layer 1 / an insulating barrier / a ferromagnetic metal layer 2, and a current flows through the insulating barrier. The tunnel conductance changes in proportion to the cosine of the relative angle of the magnetization of both ferromagnetic metal layers, and takes a minimum value when both magnetizations are antiparallel. For example, Fe / Al ₂ O ₃ / Fe tunnel junction (J. Magn. Magn.
Mater., 139, L231 (1995).), A resistance change rate exceeding 20% was found. That is, the TMR element has an advantage that it has a larger rate of resistance change than the GMR element even with the same three-layer structure.

Further, in the TMR element, a current flows through the insulating barrier by tunneling, so that a higher cell resistance can be obtained as compared with the GMR element. Therefore, as compared with the case where the GMR element is used, there is an advantage that a larger cell read voltage can be obtained even with the same sense current.

However, in order to use a GMR element or a TMR element as an MRAM, it is necessary to reduce its plane dimension to several mm or less, which causes a problem peculiar to a microstructured magnetic material. For example, the optimal size of the GMR element for increasing the degree of element integration is about 3 to 5 times the channel length of the transistor, and is about 1 μm square according to the above-mentioned 0.25 μm rule. When such a small ferromagnetic material is magnetized in the film surface, there is a problem that the magnetization state in the film surface becomes non-uniform depending on the shape of the film. For example, it is known that self-demagnetization occurs due to magnetic poles generated on the end face, and a so-called edge domain occurs in which the magnetization direction of the film end face is different from that of the center (J. Ap
pl. Phys. 81, 5471 (1997).). The presence of the edge domain causes a decrease in the hysteresis squareness ratio, and causes a reduction in the effective magnetoresistance change rate. Further, the presence of the edge domain causes a problem that the magnetization process of the film becomes unstable.

Furthermore, in a three-layer film having a minute dimension, the magnetostatic coupling between the ferromagnetic metal layer 1 and the ferromagnetic metal layer 2 has a value that cannot be ignored (IEEE Trans. Mag. MAG-33, 3286 (1997)). .)
That is, the distribution of lines of magnetic force on the film end faces differs between the case where the magnetization arrangement of both metal layers is parallel and the case where the magnetization arrangement is anti-parallel, and a difference occurs in magnetostatic energy. Therefore, when the magnetization of the ferromagnetic metal layer 2 is reversed by an external magnetic field, not only the hysteresis becomes asymmetric, but also the problem that the magnetic field required for the magnetization reversal increases. Further, interlayer magnetostatic coupling has the same effect as the above-described self-demagnetization, and becomes a factor for generating an edge domain.

The problem of the non-uniform magnetization state in the microstructured magnetic material described above is a common problem in both the GMR element and the TMR element. In the future, in order to obtain a degree of integration exceeding 64 MB, it is necessary to reduce the area of each element to 1 mm or less, which causes a problem that it becomes more difficult to control the magnetization state of the element.

[0012]

As described above, by using a TMR element for an MRAM, a cell read voltage can be made higher than when a GMR element is used.
It is possible to realize stable operation as an MRAM.
However, the problem of the non-uniformity of the magnetization state due to the miniaturization of the element remains unsolved. In the future, if the element area is further miniaturized in order to obtain a higher degree of element integration, the magnetization state of the element will be controlled. Has the problem of becoming more difficult.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem, and has provided a TMR element having good uniformity of magnetization state and capable of suitably controlling the magnetization state even in a submicron size element. It is an object to provide a magnetic memory device using the same.

[0014]

In order to solve the above-mentioned problems, the present invention provides a first ferromagnetic layer and a second ferromagnetic layer opposed to the first ferromagnetic layer via an insulating barrier. A magnetic memory device comprising a magnetic memory cell having the following structure, wherein the magnetization state of the first ferromagnetic layer is detected as a change in tunnel conductance obtained by changing the magnetization state of the second ferromagnetic layer. The ferromagnetic layer includes a free magnetic region that is in contact with the insulating barrier and a peripheral portion adjacent to the free magnetic region.

The shape and area of a ferromagnetic tunnel junction are determined by the shape and area of an insulating film constituting an insulating barrier sandwiched between both ferromagnetic layers. In other words, if a ferromagnetic tunnel junction is formed with an insulating barrier and a ferromagnetic electrode larger than its plane dimension, the part that actually acts as a ferromagnetic electrode is the part of the ferromagnetic electrode that is effective at the junction surface. The shape is limited to a portion projected in a direction perpendicular to the bonding surface.
The free magnetization region in the present invention is a portion that effectively functions as a ferromagnetic electrode of such a ferromagnetic tunnel junction. The shape and area of the free magnetization region are determined by changing the shape of the insulating barrier in the direction perpendicular to the junction surface. Is defined by projecting The peripheral portion is adjacent to the free magnetization region.

With such a configuration, since the magnetization distribution of the free magnetization region is a part of the magnetization distribution of the second ferromagnetic layer, an undesired magnetization state is formed around the second ferromagnetic layer. Even if it exists, the free magnetization region can be in a uniform magnetization state as compared with the peripheral portion. Therefore, the magnetization distribution in the ferromagnetic tunnel junction can be made more uniform than before.

In the magnetic memory device of the present invention, it is preferable that the magnetization state of the free magnetization region is reversed by domain wall motion in the second ferromagnetic layer. That is, by applying a magnetic field in a direction opposite to the magnetization direction around the free magnetization region, a reverse magnetic domain is formed in the second ferromagnetic layer, and the reverse magnetic domain and the existing magnetization direction are maintained. When the domain wall between the free magnetic region passes through the free magnetic region and the free magnetic region is included in the reverse magnetic domain, the magnetization state of the free magnetic region can be reversed.

Further, in the magnetic memory device of the present invention,
A second ferromagnetic layer is provided in common for the plurality of magnetic memory cells, and a free magnetization region is provided in each of the magnetic memory cells;
In addition, by making the free magnetization regions of adjacent magnetic memory cells adjacent to each other via the peripheral portion, a highly integrated magnetic memory device can be easily obtained. At this time, the magnetization states of the plurality of free magnetization regions can be reversed by continuous domain wall movement between the adjacent free magnetization regions via the peripheral portion. By doing so, higher-speed data reading becomes possible.

Still further, in the magnetic memory device of the present invention, the peripheral portion has a structure different from the periphery, such as a protrusion, a constriction, and a change in film thickness, for controlling the movement of the domain wall in the adjacent free magnetization region. It is preferable to have different partial areas.
Thus, by changing the shape of the peripheral portion from that of the free magnetization region, the magnetization distribution of the free magnetization region can be suitably controlled, and the more stable control of the magnetization distribution becomes possible.

In an integrated magnetic memory device having a plurality of memory cells, it is preferable that the shape of the second ferromagnetic layer be a thin line. By taking such a fine wire shape, the second ferromagnetic layer has a shape magnetic anisotropy whose easy axis is in the length direction of the fine wire, and the magnetization state of the second ferromagnetic layer is made more uniform and stable. Be transformed into

Further, in the integrated magnetic memory device, it is preferable that the second ferromagnetic layer and a current path for supplying a current to each cell are integrally formed. With such integration, the degree of integration can be further improved.

As the tunnel barrier layer, in addition to a single layer made of a non-magnetic insulator, a laminated film using different non-magnetic insulating layers, a granular structure in which metal fine particles are dispersed in the insulator, and a thickness of several nm A composite structure such as a structure in which an ultrathin metal film is sandwiched between the above-described insulating films is also possible. When these composite structures are used as the barrier layer, the cell resistance can be easily controlled by the structure design, and it can be said that this is a preferable embodiment in practical use.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIGS. 1 and 2 are schematic views for explaining a first embodiment of a magnetic memory device according to the present invention. FIG. 1 shows a cross-sectional structure of two memory cells, and FIG. 2 shows a corresponding planar structure.

The memory cell of this embodiment mainly includes a first metal layer 10, a second metal layer 20, and a tunnel barrier layer 30 made of an insulator in a multilayer structure of memory cells formed on a substrate such as Si. It is provided as a simple configuration. First metal layer 10
Is composed of a nonmagnetic metal layer 11 and a ferromagnetic metal layer 12, while the second metal layer 20 is a magnetic recording layer 2 made of a ferromagnetic material.
1 and a nonmagnetic metal layer 22. And the first
The metal layer 10 and the second metal layer 20 are opposed to each other with a tunnel barrier layer 30 interposed therebetween in a contact hole 50 formed in the interlayer insulating layer 31, and between the two ferromagnetic metal layers via the tunnel barrier. TMR is obtained. Therefore, each TM
The R memory cell is formed in a portion where the first metal layer 10 and the second metal layer 20 overlap, and the vertical projection image and the free magnetization of the tunnel barrier layer 30 where the first metal layer 10 and the second metal layer 20 face each other. Regions 13 overlap. 1 and 2, 2
One memory cell is displayed, and one free magnetization region 13 is formed in each memory cell as shown by a broken line in FIG. In FIG. 2, the free magnetization region 13 is quadrangular, reflecting the shape of the contact hole 50 that substantially defines the tunnel junction surface.

As shown in FIGS. 1 and 2, the first metal layer 10 has a thin line shape having a longitudinal direction and is connected to a plurality of memory cells, and functions as a bit line for supplying a current to each memory cell. I do. The magnetic recording layer 21 constituting the second metal layer 20 has a higher coercive force than the ferromagnetic metal layer 12, and information recorded in the memory cell is recorded as the magnetization direction of the recording layer 21. The nonmagnetic metal layer 22 is made of a CuAu film having a thickness of 100 nm, and is provided for connecting a tunnel junction of a memory cell and a cell transistor.
A well-known technique such as a field-effect transistor such as a MOSFET can be typically used for the cell transistor, and a detailed description and illustration thereof are omitted.

Incidentally, reference numeral 40 in FIGS. 1 and 2 denotes a word line. The word line 40 is formed so that its longitudinal direction and current direction are perpendicular to the longitudinal direction of the first metal layer 10. That is, in FIG. 1 and FIG.
Has a longitudinal direction in a direction perpendicular to the paper surface, and the first metal layer 10 has a longitudinal direction in the paper surface. The magnetic memory device includes peripheral circuits such as a write / read circuit other than a word line. The peripheral circuits include conventional semiconductor technologies, for example, a dynamic random access memory, a random access memory using a ferroelectric as a capacitor dielectric. Various semiconductor circuits used for an access memory, a nonvolatile memory device, and the like can be adopted, and detailed description of the circuit configuration and the like is omitted. A peripheral circuit such as a read / write circuit and a cell region where a large number of memory cells are collected and formed are separated by an interlayer insulating film such as SiO ₂ .

The write operation of the recording information is performed by the word line 40.
In addition, current is supplied to the first metal layer 10 functioning as a bit line. That is, the word line 40 and the first metal layer 1
Each current value is set such that the sum of the current magnetic fields generated from 0 is a value sufficient to reverse the magnetization direction of the magnetic recording layer 21. The magnetization direction of the magnetic recording layer 21 is determined by the direction of the current flowing through the word line 40 and the first metal layer 10. In the present embodiment, the word line 40 and the first
Since the metal layer 10 and the metal layer 10 are perpendicular to each other, the above object can be achieved by changing one of the current directions.

Next, an operation of reading recorded information in the magnetic memory cell of the present invention will be described with reference to schematic plan views shown in FIGS. 3 (a) to 3 (d). 3 (a) to 3
In (d), 51 is the magnetization of the ferromagnetic metal layer 12, 52
Indicates schematically the magnetization of the recording layer 21, and the directions of the arrows indicate the respective magnetization directions.

First, in the initial state, as shown in FIG. 3A, a state in which the magnetizations 51 and 52 of all the regions are in the same direction is defined as a recording state "1". Then figure
As shown in FIG. 3 (b), when an upward current i flows through the word line 40, the ferromagnetic metal layer 12 has an opposite direction of magnetization due to the vertical relationship between the word line 40 and the ferromagnetic metal layer 12. The direction current magnetic field is applied locally. Note that word line 4
If the vertical relationship between 0 and the ferromagnetic metal layer 12 is opposite to that shown in the figure, a current magnetic field in the same direction can be applied to the ferromagnetic metal layer 12 by reversing the current direction of the word line. Here, the current magnetic field from the word line causes the ferromagnetic metal layer 12
In FIG. 3B, a reverse domain having a reverse magnetization 51 ′ surrounded by a domain wall 53 indicated by a double line in FIG. 3B is generated, and the domain wall 53 propagates inside the ferromagnetic metal layer 12, whereby the reverse domain is formed. Spreads.

Further, after a lapse of a predetermined time, FIG.
As shown in (1), the domain wall 53 passes through the region of the free magnetization region 13, and the magnetization reversal of the free magnetization region 13 is completed. Thereby, the relative relationship of magnetization between the magnetic recording layer 21 and the free magnetization region 13 changes from parallel to antiparallel, and accordingly, the resistance value between the two metal layers 10 and 20 via the tunnel barrier increases. . Therefore, if a constant current is passed from the first metal layer 10 to the second metal layer 20, an upward voltage pulse is generated at both ends of the element.

On the other hand, as an initial state, when the magnetization of the magnetic recording layer 21 is antiparallel to the magnetization directions of the ferromagnetic metal layer 12 and the free magnetization region 13, that is, in the recording state "0",
When the read operation shown in FIGS. 3A to 3C is performed, the relative relationship of magnetization between the magnetic recording layer 21 and the free magnetization region 13 changes from antiparallel to parallel. Accordingly, the resistance value between the first and second metal layers 10 and 20 is reduced. Therefore, if a constant current is passed between the first and second metal layers 10 and 20, a downward voltage pulse is generated. Occurs. In this manner, the recording state of the magnetic recording layer 21 can be read by detecting the rising and falling of the voltage pulse separately.

The value of the current i flowing through the word line 40 shown in FIG.
By setting the coercive force to be equal to or less than the non-destructive readout operation, the stored information is not erased. Conversely, the current i is set so that the current magnetic field is equal to or greater than the coercive force of the magnetic recording layer 21.
If the value of is set, destructive reading is performed.

Here, the domain wall 53 generated by the operation shown in FIGS. 3B and 3C is formed in the fine wire longitudinal direction of the ferromagnetic metal layer 12 if the ferromagnetic metal layer 12 is magnetically uniform. Keep going without decay. However, in general, since the ferromagnetic metal layer 12 has roughness of an end face generated at the time of microfabrication or a defect generated at the time of film formation, the domain wall 53 is formed at the position indicated by the pinning position 54 in FIG. Is bound,
Its progress stops.

As described above, since the reading involves movement of the domain wall 53, a refresh operation for returning the magnetization state of the free magnetization region 13 to the initial state is required after the reading. The refresh operation can be easily realized by applying a current to the word line in a direction opposite to that in the read operation.

FIG. 4 shows a cell read voltage (Output Vo) of each magnetic memory cell shown in FIGS. 1 (a) and 1 (b).
ltage) of the magnetic field (Magnetic Field) response. For this measurement, a sample in which the above-described magnetic memory cell was directly formed on a Si substrate whose main surface was coated with SiO ₂ , and in which the semiconductor circuit portion and the word line were not formed, was used.
The magnetic field applied at the time of measurement corresponds to a current magnetic field from a word line. The width of the ferromagnetic metal layer 12 of this sample is 1 mm, and the length is
The contact hole 50 is a rectangle of 0.5 mm square. Twenty-five contact holes 50 were formed in the longitudinal direction of the ferromagnetic metal layer 12 at intervals of 3.5 mm. The magnetic field was applied uniformly to the whole sample, the measured current was a constant value of 10 mA, and the magnetic field response of the output voltage of a single cell was measured. The measurement is
The test was performed after an external magnetic field of 500 Oe was applied to the sample to align the magnetization directions of the ferromagnetic metal layer 12 and the magnetic recording layer 21 in parallel. In this sample, the coercive force of the magnetic recording layer 21 is 23
0 Oe, and the magnetization direction of the magnetic recording layer 21 is kept in the initial state over the magnetic field range shown in FIG.

It can be seen that there are two voltage states in the magnetic field response shown in FIG. These two voltage states are generated when the magnetization of the free magnetization region 13 is reversed by an external magnetic field, and the relative relationship between the magnetizations of the free magnetization region 13 and the magnetic recording layer 21, that is, whether both magnetizations are parallel (large output voltage) or not. It reflects whether it is antiparallel (small output voltage). There is a hysteresis in the magnetic field response, which reflects the magnetization process of the free magnetization region 13.

Next, after briefly describing the sample of the conventional magnetic memory cell shown in FIG. 5, the magnetic field response of the cell read voltage will be described with reference to FIG. The basic structure of this sample is the same as that of the magnetic memory cell of the first embodiment except that the ferromagnetic metal layer 12 is divided and arranged in each cell as shown in the cross section in FIG. . The shape of the ferromagnetic metal layer 12 is a rectangle of 0.5 mm square.

The magnetic response of the conventional memory cell shown in FIG.
Although the same hysteresis as in the first embodiment is shown, the output voltages of the positive magnetic field and the negative magnetic field are obviously asymmetric. further,
The squareness ratio of the hysteresis is smaller than 1. A decrease in the squareness of the hysteresis causes a decrease in the cell output voltage, which is not preferable in practical use. Such asymmetry of hysteresis and reduction of the squareness ratio are caused by the ferromagnetic metal layer 12 as described above.
Of the ferromagnetic metal layer 12 and the magnetic recording layer 21 due to a self-demagnetizing magnetic field generated at the edge of the magnetic recording layer 21. Therefore,
4 and FIG. 6, it can be seen that the hysteresis of the first embodiment is symmetric, and the magnetization reversal of the ferromagnetic metal layer 12 occurs with a smaller magnetic field.

In this embodiment, the squareness ratio of the hysteresis is substantially 1. Thus, the point that a symmetrical output signal waveform is obtained and the magnetic field required for magnetization reversal is sufficiently small
This is a great advantage of the present invention.

The hysteresis of the high squareness ratio in the present embodiment is because the ferromagnetic metal layer 12 has a fine line shape.
This is due to exhibiting strong shape magnetic anisotropy whose easy axis is in the longitudinal direction of the thin wire, and that the magnetization reversal mechanism is performed not by simultaneous rotation but by domain wall motion. Here, in order to obtain the same hysteresis of the squareness ratio 1 as in the present embodiment, it is preferable that the ratio between the length and the width of the thin line, that is, the aspect ratio is at least 10: 1 or more, and the shape is thinner. In the conventional structure of FIG. 5, if the ferromagnetic metal layer 12 having such an aspect ratio is used, an increase in the junction area and thus the element area cannot be avoided, but in the present embodiment, the element area is kept constant. Even if the size is reduced, the ferromagnetic metal layer 12 can be provided with strong shape magnetic anisotropy, and the effective cell output signal can be increased.

Next, a method of manufacturing the magnetic memory device according to the present embodiment will be described in detail. Non-magnetic metal layer 11 of FIG.
Has a two-layer structure in which a 100 nm thick CuAu film and a 20 nm thick Pt are stacked. Here, the former CuAu film is formed as a bit line, and can be replaced with a low-resistance wiring material such as Cu or Al. Pt layer is nonmagnetic metal layer 1
The ferromagnetic metal layer 12 functions as a template for assisting the crystal orientation of the ferromagnetic metal layer 12 grown thereon. The ferromagnetic metal layer 12 shown in FIG. 1A is formed using a Ni ₈₂ Fe ₁₈ alloy having a thickness of 10 nm in the presence of a magnetic field parallel to the longitudinal direction of the electrode.
Is given uniaxial magnetic anisotropy with the longitudinal direction of the electrode as the axis of easy magnetization. As means for imparting such induced magnetic anisotropy, heat treatment in a magnetic field after film formation is effective in addition to the film formation in a magnetic field. An Al oxide film is used as the insulating film 30 in FIG. 1, and after forming an Al film of 2 nm or less on the ferromagnetic metal layer 12, the Al film is then formed.
The film is formed by oxidation using oxygen plasma. The material used for the tunnel barrier layer 30 is required to have a very thin film thickness of 2 nm or less and to have good insulating properties.
As the material, in addition to the plasma oxide film of Al, for example, a natural oxide film of Al, or an Al ₂ O ₃ film directly formed,
AlN films are available. Also, as already explained,
A composite structure such as a laminated film made of different non-magnetic insulators, a granular structure in which metal fine particles are dispersed in an insulator, or a structure in which an ultrathin metal film of several nm is sandwiched between the above-mentioned insulating films is also possible. On the insulating film 30 of FIG. 1, a 10 nm-thick Co is used as the magnetic recording layer 21 in the same manner as the ferromagnetic metal layer 12.

After the formation of the magnetic recording layer 21, a positive resist pattern for forming the contact hole 50 shown in FIG.
Is removed by reactive ion etching until the insulating film 30 is reached. After the etching, an interlayer insulating film 31 made of SiO _{2 having} a thickness of 50 nm is formed on the entire surface, and a lift-off process is performed. Through the above steps, a magnetic memory cell including the free magnetization region 13, the insulating film 30, and the magnetic recording layer 21, in which the tunnel junction area is defined by the contact holes 50 in FIGS. 1 and 2, is formed. Here, the so-called self-alignment method in which the alignment between the magnetic recording layer 21 and the contact hole 50 is self-aligned has been described, but other element forming processes are also possible. As the nonmagnetic metal layer 22, a 100 nm-thick CuAu film or the like was used.

The formation of each of the metal films and the interlayer insulating films described above can be performed using a conventional sputtering technique or CVD technique. Further, the thickness and composition of each metal film and insulating film can be changed in order to improve device characteristics.

After forming the nonmagnetic metal layer 22 and forming the contact 23 to the cell readout transistor, the word line 40 shown in FIGS. 1 and 2 is formed by an interlayer insulating film 41 made of SiO _{2 having} a thickness of 100 nm. , After the interlayer separation from the magnetic memory cell is performed. At this time, it is preferable to flatten the surface of the interlayer insulating film 41 by a method such as chemical mechanical polishing.
Thereafter, as a word line in FIGS.
A CuAu film is formed, and a memory cell portion of the magnetic memory device is completed. The manufacture of the magnetic memory device is completed by connecting the peripheral circuit unit with the peripheral circuit unit before and after the manufacture of the memory cell unit, or in a process that is combined with a part of the process of the memory cell unit.

Next, a modification of the magnetic memory cell structure of the first embodiment will be described with reference to the schematic sectional view of FIG. This modification is, as shown in FIG.
And the second metal layer 20 have a structure in which the vertical relationship is reversed. The free magnetization region of the ferromagnetic metal layer 12 is a contact hole 5 which is a tunnel junction of each memory cell.
The thickness is increased corresponding to 0. However, in order to maximize the effects of the present invention, it is desirable that the ferromagnetic metal layer 12 be as uniform as possible. This is because when the film thickness changes in the free magnetization region, a magnetic pole is generated in the rectangular portion, which causes self-demagnetization.

For the purpose of positively controlling the pinning position of the domain wall, as shown in the schematic plan view of FIG.
The constriction 55 may be formed as a pinning structure at an appropriate location of the second. At the constriction 55, the cross-sectional area of the domain wall 53 is locally reduced, so that the energy of the domain wall is reduced and the domain wall 53 is reduced.
Is pinned at that position. Examples of the structure for pinning the domain wall include, besides constriction, a structure in which the thickness of the ferromagnetic metal layer 12 at the pinning position is made thinner than other regions, or a structure in which a pinhole is inserted. It is possible. In FIG. 8, illustration of the word line 40, the current direction, and the magnetization directions of the ferromagnetic layers 12 and 21 is omitted for convenience of description.

(Second Embodiment) In the first embodiment, in the case of the NiFe alloy used for the free magnetization region 12, the diameter of the domain wall is about several tens nm. Therefore, the ferromagnetic metal layer 12 having a size of a micron size or more in the length direction of the fine wire.
Is formed, the ferromagnetic metal layer 12 hardly behaves as a single magnetic domain. However, if the dimension in the fine line width direction of the ferromagnetic metal layer 12 is set to the submicron size, the formation of the 180 ° domain wall when the reverse magnetic domain is generated is hindered, so that the vortex magnetic domain may be formed early in the magnetization reversal process. . The presence of eddy magnetic domains is a factor that causes the reversal magnetic field to increase, which is not preferable.

In the second embodiment, FIGS. 9A and 9
As shown in the schematic plan view of FIG.
A reverse magnetic domain is formed between the constriction 55 and the free magnetization region 13, whereby it is possible to prevent the occurrence of a vortex magnetic domain. As shown in FIG. 9A, the introduction of the reverse magnetic domain may be achieved by providing a projection 56 on a part of the ferromagnetic metal layer 12.
As shown in FIG. 9B, a hard magnetic material such as CoPt, an antiferromagnetic material such as MnPt, or a magnetic material having an interlayer coupling such as ferromagnetic coupling or antiferromagnetic coupling is formed in a part of the ferromagnetic metal layer 12. By bringing the pinned layer 57 made of an artificial lattice into close contact with the ferromagnetic metal layer 12, a reverse magnetic domain can be introduced by an exchange bias. In the structure shown in FIG. 9B, the domain wall 53 is bound by a constriction 55 as shown.

As shown in FIG. 9B, when a reverse magnetic domain is previously introduced into the ferromagnetic metal layer 12 and the domain wall 53 is pinned, the domain wall 53 is moved from one pinning position to the next pinning position. The critical magnetic field Ho required for this is approximately expressed by the following equation 1.

[0050]

[Number 1] Ho = (r / Is) × (R / L 2) energy of the domain wall per unit area R in this formula, Is
Is the saturation magnetization, L is the width of the ferromagnetic thin wire, and r is the size of the pinning site (it is a hole having a radius r). Fe
Substituting r = 0.2 L and L = 1 mm using γ and Is in the above, Ho becomes a value of about 10 Oe. On the other hand, in the conventional memory cell having the structure shown in FIG.
Is a rectangle of 0.5mm square. In such a rectangular ferromagnetic electrode 12, magnetization reversal is performed by simultaneous rotation, and the coercive force Hc depends on the planar dimensions of the film. Film thickness 10nm, width 0.
For a 5 mm NiFe alloy film with an aspect ratio of 1.5: 1, Hc = 15
It becomes 0 Oe. That is, according to the magnetic memory device of the present embodiment, the magnitude of the magnetic field required for the read operation of the recorded information may be several times smaller than that of the related art. Therefore, it is possible to reduce the word line current required for generating a magnetic field.

(Third Embodiment) In a third embodiment, a domain wall movement is performed in a memory cell array in which a plurality of memory cells having a domain wall pinning control structure as described in the second embodiment are connected. A method of reading recorded information by positively utilizing is described. FIG.
FIGS. 10A to 10C are schematic plan views for explaining this reading method. FIG.
3A to 3D show a state after the recorded information of the memory cell 101 has been read by the read operation shown in FIG. The read operation is performed by applying an upward current pulse i to the word line 401 corresponding to the memory cell 101. After the end of the read operation, the domain wall 53 is bound by a pinning constriction 55 shown in FIG.
Numeral 2 has magnetization in the left direction on the paper, and the ferromagnetic metal layer 12 on the side opposite to the memory cell 101 from the domain wall 53 has magnetization in the right direction on the paper. In this state, as shown in FIG. 10B, an upward current pulse i is applied to the word line 402 corresponding to the memory cell 102 in the same manner as in the read operation of the memory cell 101. By this operation, as shown in FIG. 10B, the domain wall 53 bound to the pinning neck 55 receives pressure by the rightward magnetic field, moves away from the neck 55, and moves to the next neck 55 on the right side thereof. Therefore, the recorded information of the cell 102 is read by the movement of the domain wall 53. Next, as shown in FIG.
By applying the same current pulse i to the word line 403 corresponding to, the domain wall 53 moves to a notch, which is located on the further right side, and the read operation of the cell 103 is completed.

The moving speed of the domain wall is proportional to the strength of the applied magnetic field, and also depends on the magnetization state and the film thickness of the ferromagnetic material. Film thickness
In the case of a 10-nm NiFe alloy fine wire, a speed of about 100 m / Oe · s is observed. Therefore, in the memory cell array having the above-described structure, a magnetic field of 10 Oe is applied, and the distance between the cells is 3.
At 5mm, the read speed is 3.5ns. This value is at least one digit smaller than the access speed determined by the RC constants of the peripheral semiconductor circuit and wiring, and does not pose a practical problem.

That is, according to the above method, the recorded information of the plurality of memory cells connected to the ferromagnetic metal layer 12 is
Reading can be performed by sequentially applying a current pulse to a word line corresponding to each cell. This corresponds to the nibble mode in the conventional memory technology, and has an advantage that high-speed reading is possible as compared with the read / write mode.

In the structure shown in FIGS. 10A to 10C, the magnetic field applied from each word line is required to move the domain wall 53 between the pinning constrictions 55 corresponding to each cell. However, if the ferromagnetic metal layer 12 is magnetically formed with good uniformity, and the domain wall motion is smoothly performed by means other than artificial pinning in the ferromagnetic metal layer 12,
Other types of reading methods are possible. That is, FIG.
As shown in FIG. 11A, after the read operation of the memory cell 401 is performed, as shown in FIG. 11B, the domain wall 53 is propagated as it is, and the current is not applied to the word line 402. Through memory cell 102
Of the free magnetization region 13 is completed. Finally,
The domain wall 53 is bound by the pinning constriction 55, and a series of read operations is completed.

This method corresponds to a reading method conventionally known as a static column mode.
As in the nibble mode, there is an advantage that high-speed reading is possible as compared with the read / write mode. Furthermore, compared to the nibble mode, the number of word line operations can be reduced, and power consumption can be significantly reduced.

[0056]

According to the magnetic memory device of the present invention, it is possible to avoid the self-demagnetizing effect on the end face and the occurrence of non-uniform magnetization distribution due to interlayer magnetostatic coupling between the ferromagnetic electrodes. Even when the dimensions are miniaturized,
Not only can the switching field be prevented from increasing, but also a symmetric magnetization response and a high hysteresis squareness ratio can be maintained, and a stable memory operation can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a magnetic memory device according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view of the magnetic memory device according to the first embodiment of the present invention.

FIG. 3 is a schematic plan view illustrating a read operation of the magnetic memory device according to the first embodiment of the present invention.

FIG. 4 is a diagram (magnetic field-output voltage characteristic) showing a magnetic field response of an output signal of the magnetic memory device according to the first embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a conventional magnetic memory device which is a comparative example with the first embodiment of the present invention.

FIG. 6 shows the magnetic field of the conventional magnetic memory device shown in FIG.
It is an output voltage characteristic.

FIG. 7 is a schematic plan view showing a modification of the first embodiment of the present invention.

FIG. 8 is a schematic plan view of a magnetic memory device having a reverse magnetic domain control structure according to a second embodiment of the present invention.

FIG. 9 is a schematic plan view of a magnetic memory device according to a second embodiment of the present invention.

FIG. 10 is a schematic plan view illustrating a read operation in a magnetic memory device according to a third embodiment of the present invention.

FIG. 11 is a schematic plan view for explaining another example of the read operation of the magnetic memory device according to the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... 1st metal layer 11, 22 ... Non-magnetic metal layer 12 ... Ferromagnetic metal layer 13 ... Free magnetization area 20 ... Second metal layer 21 ... Magnetic recording layer 23 ... Contact to a cell transistor 30 ... Tunnel barrier layer 31, 41 ... interlayer insulating layers 40, 401, 402, 403 ... word lines 50 ... contact holes 51, 51 ', 52 ... magnetization 53 ... domain walls 55 ... constrictions 56 ... protrusions 57 ... pinning layers 101, 102, 103 ... memories cell

Claims (5)

[Claims] 1. A magnetic memory cell comprising: a first ferromagnetic layer; and a second ferromagnetic layer facing the first ferromagnetic layer via an insulating barrier, wherein the first ferromagnetic layer A magnetic state detected as a change in tunnel conductance obtained by changing the magnetization state of the second ferromagnetic layer, wherein the second ferromagnetic layer is free to join with the insulating barrier. A magnetic memory device comprising: a magnetization region; and a peripheral portion adjacent to the free magnetization region. 2. The method according to claim 2, wherein the domain wall motion in said second ferromagnetic layer causes
2. The magnetic memory device according to claim 1, wherein a magnetization state of the free magnetization region is changed. 3. The second ferromagnetic layer is provided in common to a plurality of the magnetic memory cells, and the free magnetization region is provided in each of the non-volatile magnetic memory cells, and the free magnetic region is provided in the adjacent magnetic memory cell. 2. The magnetic memory device according to claim 1, wherein the free magnetization regions of the memory cell are adjacent to each other via the peripheral portion. 4. The magnetic memory according to claim 3, wherein the magnetization states of said plurality of free magnetization regions are changed by continuous domain wall movement between said free magnetization regions adjacent via said peripheral portion. apparatus. 5. The magnetic memory according to claim 4, wherein the peripheral portion has a partial region having a structure different from that of the surrounding region in order to suppress the movement of the domain wall between the free magnetization regions adjacent to each other. apparatus.