JP2005203535A - Magnetic memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a write current and to ensure resistance to heat disturbance. <P>SOLUTION: This magnetic memory comprises a magnetic resistance effect element 6 having a magnetization secured layer composed of a magnetic layer securing a direction of magnetization, a record layer composed of the magnetic layer varying the direction of magnetization, and an unmagnetized layer provided between the magnetization secured layer and the record layer; a write wiring in which an induced magnetic field caused by a current is generated, and the direction of magnetization of the record layer is reversible by the induced magnetic field; a yoke 4 which covers a write wiring, and comprises a gap 5 having a substantially same width as a width of the magnetic resistance effect element on an opposed side of the magnetic resistance effect element; and a read wiring connected electrically to one end of the magnetic resistance effect element. The width of the gap is 0.2 times or less of the width of the write wiring. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic memory.

  In recent years, a magnetic random access memory using a magnetic element exhibiting a giant magnetoresistive effect has been proposed as a solid-state magnetic storage memory. In particular, a magnetic memory using a ferromagnetic tunnel junction as a magnetic element has attracted attention.

  The ferromagnetic tunnel junction is mainly composed of a three-layer film of a first ferromagnetic layer / insulating layer / second ferromagnetic layer, and a current flows through the insulating layer. In this case, the junction resistance value changes in proportion to the cosine of the relative angle of magnetization of the first and second ferromagnetic layers. Therefore, the resistance value takes a minimum value when the magnetizations of the first and second ferromagnetic layers are parallel, and takes a maximum value when the magnetization is antiparallel. This is called the tunnel magnetoresistance (TMR) effect. For example, it has been reported that the change in resistance value due to the TMR effect is 49.7% at room temperature.

  In a magnetic memory element including a ferromagnetic tunnel junction as a memory cell, the magnetization of one of the two ferromagnetic layers is fixed as a reference layer, and the other ferromagnetic layer is used as a memory layer. In this cell, information is stored by associating binary information “0” and “1” with the magnetization arrangement of the reference layer and the storage layer parallel or antiparallel. In writing recorded information, the magnetization of the storage layer is reversed by a magnetic field generated by passing a current through a write wiring provided separately for the cell. Reading is performed by passing a current through the ferromagnetic tunnel junction and detecting a resistance change due to the TMR effect. A magnetic memory is configured as a large-capacity memory by arranging a large number of such memory cells.

  The actual configuration is such that, for example, a switching transistor is arranged for each cell and a peripheral circuit is incorporated so that an arbitrary one cell can be selected. There has also been proposed a method in which a ferromagnetic tunnel junction is incorporated in combination with a diode at a position where a word line and a bit line intersect.

  Now, when considering a magnetic memory using a ferromagnetic tunnel junction as a memory cell, the higher the integration, the smaller the size of the memory cell, and inevitably the size of the ferromagnetic material constituting the cell. Such a magnetic thin film having a finite size generally has a complicated magnetic domain structure composed of a plurality of magnetic domains as a magnetic state. In particular, in the case of a rectangular cell, it is known that there is a so-called edge domain having magnetization oriented in a direction different from the central portion in the region of the end portion in the long axis direction. When there is such an edge domain region, the magnetization of the entire cell is lowered, and as a result, the resistance change rate of the TMR effect is lowered. Moreover, since the change of the magnetic structure pattern in the magnetization reversal is complicated, it not only causes noise, but also increases the coercive force and increases the switching magnetic field.

  Further, considering the high integration of a magnetic memory using a ferromagnetic tunnel junction as a memory cell, the size of the memory cell is reduced, and the size of the ferromagnetic material constituting the cell is inevitably reduced. In general, the smaller the ferromagnetic material, the greater the coercive force. Since the magnitude of the coercive force is a measure of the magnitude of the switching magnetic field necessary for reversing the magnetization, this means an increase in the switching magnetic field. Therefore, when writing bit information, a larger current must be passed through the write wiring, which brings about undesirable results such as an increase in power consumption and a shortened wiring life. Therefore, reducing the coercivity of the ferromagnetic material used in the memory cell of the magnetic memory is an important issue in the practical application of highly integrated magnetic memory.

  In order to solve this problem, a magnetic material-covered wiring is considered as a method for efficiently applying a magnetic field induced by a write current to a storage layer. This is because the write wiring has a structure in which a magnetic material having excellent soft magnetic properties is placed in the vicinity of a surface other than the surface facing the storage layer, and is placed close to the wiring. Since a magnetic material having a high magnetic permeability is used, magnetic flux can be collected. On the other hand, since the magnetic material is not placed on the surface of the memory cell facing the storage layer and a gap structure is formed, the magnetic flux concentrated in the magnetic material is emitted from the tip of the magnetic material toward the storage layer. Distribution as shown. Accordingly, the magnetic field from the magnetic material-coated wiring can be efficiently applied to the storage layer as compared with the wiring without the magnetic material coating.

  A magnetic memory element having a thin film made of a high magnetic permeability material around a write wiring has been proposed (see, for example, Patent Document 1). In these elements, since the magnetic flux generated by the write current can be converged by the high permeability thin film around the write wiring, the magnetic field generated at the time of writing can be strengthened, resulting in a smaller current. With this, bit information can be written.

Further, since the magnetic material covering the wiring concentrates the magnetic flux as described above, it also has a so-called magnetic shield effect that reduces the magnetic flux leaking to the region on the opposite side of the wiring with respect to the coated magnetic body. As a result, the leakage of the magnetic field to the adjacent cell can be minimized, and there is an effect that the occurrence of erroneous writing to the adjacent cell can be suppressed.
US Pat. No. 5,659,499

  As described above, by placing a magnetic material having excellent soft magnetic properties around the write wiring, a magnetic field is efficiently applied to the storage layer of the memory cell, and the write current can be reduced. A memory device with low power consumption can be provided.

  However, since the reversal magnetic field of the memory layer of the memory cell is several tens of Oersted when the width of the memory layer is in the submicron region, a current of, for example, 10 mA or more needs to flow through the write wiring. As described above, it is possible to increase the magnetic field generation efficiency by coating the magnetic material, but the current required to flow through the write wiring is expected to be about 4 mA to 6 mA, and the current value (usually used in DRAM and the like) Compared to a hundred μA), the write current is still large.

  Further, considering that the memory device is highly integrated and miniaturized as the year progresses, the MRAM is also miniaturized without exception. In this case, the width of the memory cell is expected to advance from a submicron to a smaller region. In this case, it is known that the switching magnetic field of the storage layer increases as the demagnetizing field increases as the width of the storage layer decreases.

  Further, there is a problem that the magnetic layer used for the storage layer is reversed in magnetization due to thermal fluctuation due to the miniaturization of the memory cell. This is because the magnetization takes a stable direction so as to minimize the uniaxial anisotropy energy. Usually, thermal energy due to temperature is added randomly, so the magnetization has an amplitude centered on the stable direction. It is vibrating. When the thermal energy becomes larger than the uniaxial anisotropy energy, the amplitude of this vibration increases and eventually peels in the opposite direction. The probability of going in the opposite direction increases when the uniaxial anisotropy energy is small. In general, since the uniaxial anisotropy energy is proportional to the product of the uniaxial anisotropy coefficient and the volume of the magnetic material, the uniaxial anisotropy energy decreases as the memory cell is miniaturized. In order to avoid this, the volume of the magnetic material must be increased or the uniaxial anisotropy coefficient must be increased. In this case, the switching magnetic field inevitably increases. This means that the switching magnetic field cannot be miniaturized to a size that can withstand thermal disturbance, and has a fatal defect that scaling does not work as a memory device.

  Therefore, when the miniaturization of the memory is taken into consideration, the current required for writing information increases more and more. When the write current increases in this way, the utility value as a memory device is halved.

  As described above, reducing the write current, particularly reducing the write current for a minute memory cell, is a very important issue from the viewpoint of device application. In order to reduce the write current, it has been proposed to coat the write wiring with a soft magnetic material as described above, and a certain effect has been recognized. However, the effect is not sufficient particularly in a minute memory cell.

  An object of the present invention is to provide a magnetic random access memory capable of reducing a write current and ensuring thermal disturbance resistance.

  A magnetic memory according to an aspect of the present invention includes a magnetic pinned layer made of a magnetic layer having a fixed magnetization direction, a recording layer made of a magnetic layer having a variable magnetization direction, the magnetic pinned layer, and the recording layer. A magnetoresistive effect element having a non-magnetic layer provided therebetween, a write wiring capable of generating an induced magnetic field by current and reversing the magnetization direction of the recording layer by the induced magnetic field, and covering the write wiring A yoke provided with a gap having substantially the same width as the magnetoresistive effect element on the side facing the magnetoresistive effect element, and a read wiring electrically connected to one end of the magnetoresistive effect element And the width of the gap is 0.2 times or less the width of the write wiring.

  Note that a selection transistor for writing, one end of which is electrically connected to the writing wiring, may be provided.

  The other end of the magnetoresistive effect element may be connected to the write wiring.

  Note that a lead-out line connected to the other end of the magnetoresistive element and a read selection transistor whose one end is electrically connected to the lead-out line may be provided.

The memory layer may be made of a magnetocrystalline anisotropic material having an anisotropy constant greater than 1 × 10 ^{3 and} less than or equal to 1 × 10 ⁶ .

  The nonmagnetic layer may be a tunnel barrier layer.

  According to the present invention, it is possible to reduce the write current and ensure thermal disturbance resistance.

  Hereinafter, embodiments of the present invention will be described in detail.

(First embodiment)
A magnetic memory according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the configuration of the memory cell of the magnetic memory according to the first embodiment. The magnetic memory according to this embodiment is a magnetic random access memory and includes a plurality of memory cells. Each memory cell includes a write wiring 2, a yoke 4 made of a magnetic material covering the write wiring, a magnetoresistive element 6, a read wiring 8, and a selection transistor 20 for selecting the memory cell. Yes.

An insulating film 100 is formed on a substrate (not shown) on which the selection transistor 20 and a drive circuit are formed, and a write wiring 2 is formed on the insulating film 100. The yoke 4 is made of a magnetic material having excellent soft magnetic characteristics, and the yoke 4a that covers the surface of the write wiring 2 on the insulating film 100 side and the side surface of the write wiring 2 and the side of the write wiring 2 opposite to the insulating film 100 are provided. And a yoke 4b covering the surface. The yoke 4 b is provided with a gap 5 for connecting the magnetoresistive effect element 6 directly to the write wiring 2. The width W _G of the gap 5 has a width substantially the same width of the magnetoresistive element 6. Here, have substantially the same width, the width of the extent to which the magnetoresistive element 6 is not in contact with the yoke 4b, in the present embodiment, the width W _G is the width of the magneto-resistive element 6 of the gap 5 It is formed about 10 nm larger than W _MTJ .

  The magnetoresistive element 6 includes two ferromagnetic layers 6a and 6c, a tunnel barrier layer 6b sandwiched between the ferromagnetic layers 6a and 6c, and an electrode layer 6d. One of the two ferromagnetic layers 6a, 6c, for example, the ferromagnetic layer 6a is a magnetization fixed layer with magnetization fixed, and the other, for example, the ferromagnetic layer 6c is a magnetization free layer serving as a storage layer whose magnetization can be reversed. It is. The electrode 6 d electrically connects the magnetization free layer 6 c and the readout wiring 8. Note that an antiferromagnetic layer (not shown) for fixing the magnetization of the magnetization fixed layer 6c is usually provided on the surface of the magnetization fixed layer 6a opposite to the tunnel barrier layer 6b. Note that the magnetization free layer 6 c serving as the storage layer has an easy axis in the magnetic field direction induced by the current flowing through the write wiring 2. In the present embodiment, the magnetization pinned layer 6 a is electrically connected to the write wiring 2. In this embodiment, the magnetoresistive effect element 6 is laminated on the write wiring 2 in the order of the magnetization fixed layer 6a, the tunnel barrier layer 6b, and the magnetization free layer 6c. However, the magnetization free layer 6c and the tunnel barrier layer are stacked. 6b and the magnetization pinned layer 6a may be laminated in this order.

Examples of the magnetic material excellent in soft magnetic characteristics used for the yoke 4 include Fe—Ni, Fe—Si, Fe—Al, Fe—Si—Al alloy called sendust, Fe—Ni alloy, Mo, Cu, Cr, etc. permalloy alloy was added, Ni-Fe-Co alloy, ferrimagnetic oxide mainly composed of Fe ₂ O _3, called soft ferrite, garnet type ferrite such as YIG, etc. are mentioned hexagonal ferrite such BaFeO It is done.

  Moreover, as a wiring material of the read wiring 8 for reading bit information, a commonly used material such as Al, Al—Cu alloy, Cu, or the like may be used. Note that although the reading wiring is used here, writing can also be performed by applying a magnetic field from two directions by supplying a current to the reading wiring during writing. In this case, it is known that the magnetization reversal of the memory layer is represented by a curve called asteroid.

  In the present embodiment, the write wiring 2 is provided with a selection transistor 20 for selecting a bit to be written.

Next, the width W _MTJ of the magnetoresistive element 6, i.e. changing the width W _G of substantially equal gap 5 to the width W _MTJ of the magnetoresistive element 6, the magnetic memory having the above structure, and various manufactured, The experiment was conducted. This will be described below.

The write wiring 2 has a width of 500 nm and a thickness of 400 nm, and the read wiring 8 has a width of 600 nm and a thickness of 500 nm. The magnetoresistive effect element 6 has a magnetization pinned layer 6a made of Co—Fe, a tunnel barrier layer 6b made of alumina, and a memory layer 6c made of Co—Fe—Ni having a thickness of 2 nm. The magnetization pinned layer 6a made of Co—Fe is provided with an antiferromagnetic layer 6e made of Ir—Mn adjacent to the opposite side of the tunnel barrier layer 6b. An exchange interaction acts between the magnetization pinned layer 6a and the antiferromagnetic layer 6e, and the magnetization of the magnetization pinned layer 6a made of Co—Fe is pinned by this exchange interaction. The memory layer 6c is electrically connected to the read wiring 8 via an electrode 6d provided on the surface opposite to the tunnel barrier layer 6b. Width W _G of the gap 5, with respect to the width W _WL of the write wiring 2, were prepared six types of up to from 0.8 to 0.05 times.

The write wiring 2 is covered with a yoke 4 made of a magnetic material made of a Ni—Fe alloy. In particular, the surface and the side of the write wiring 2 not facing the magnetoresistive effect element 6 are completely covered with a yoke 4a having a thickness of 50 nm. In the surface side of the yoke 4b facing the magneto-resistance effect element 6, the gap 5 having a 10nm width greater W _G is provided with respect to the width W _MTJ of the magnetoresistive element 6.

When a write test was performed on this system, results as shown in FIG. 2 were obtained. That is, FIG. 2, with respect to the write wiring 2 with a constant width, plots the magnetic field H induced when a constant current I _W, the horizontal axis represents the write wiring 2 width W _G of the gap 5 The vertical axis is a value obtained by dividing the induction magnetic field H by the write current I _W by the value divided by the width W _WL . Induced magnetic field H is gradually increased as the width W _G of the gap 5 is narrowed from 0.8 times, in particular, it can be seen that rapidly increases to be 0.2 times or less.

  In the above description, it has been described that the easy axis of magnetization of the storage layer of the magnetoresistive element 6 is the direction that coincides with the direction of the magnetic field induced by the current flowing through the write wiring 2. In order to realize this magnetic anisotropy, for example, the planar shape (film surface shape) of the magnetoresistive effect element 6 has an aspect extending in the direction of the induced magnetic field due to the current flowing in the write wiring 2. Good. In this case, the easy magnetization axis is set by the shape magnetic anisotropy of the storage layer.

However, it is known that when the magnetoresistive effect element is miniaturized, the influence of the demagnetizing field increases and the switching magnetic field increases. This is shown in FIG. Figure 3 takes a reciprocal of the width W _G of the gap 5 in the horizontal axis, the switching field the vertical axis, i.e. are taking the minimum magnetic field capable of reversing the magnetization direction of the storage layer. In FIG. 3, the width W _{G of the} gap 5 is 10 nm larger than the width W _MTJ of the magnetoresistive element 6. Graph g ₁ in FIG. 3 shows the characteristics of the switching field of the storage layer. A graph g _2, when the ratio between the width W _G and write wiring 2 of the width of the gap 5 may be 1, i.e. the yoke 4a shown in Figure 1 is present there is no yoke 4b, current density The characteristic of the induction magnetic field induced | guided | derived when the electric current of 10 < ⁶ > A / cm < ² > is sent is shown. Graph g _3, when the ratio between the width W _G and write wiring 2 of the width of the gap 5 is 0.2, the induced magnetic field that the current density is induced when a current of a 10 6 ^{A /} cm ² current The characteristics of When the ratio of the width W _{G of the} gap 5 to the width of the write wiring 2 is set to a predetermined value and the current density of the current flowing through the write wiring 2 is made constant, the width W _MTJ of the magnetoresistive effect element 6 can be reduced. If the width of the gap 5 is narrowed, the width of the write wiring 2 is also narrowed, so that the current flowing through the write wiring 2 is small. Further, if the width of the gap 5 is increased, the width of the write wiring 2 is also increased, so that the current flowing through the write wiring 2 is increased. As a result, the graphs g ₂ and g ₃ are lowered to the right.

The graph g _{1 in} FIG. 3 shows that the switching magnetic field increases almost linearly with respect to the reciprocal of the width of the gap 5. In particular, when the width W _{G of the} gap 5 is smaller than 0.1 μm, it can be seen that the switching magnetic field exceeds 100 Oe. The graph _{g 1} and Graph _{g 2,} when the ratio between the width W _G and write wiring 2 of the width of the gap 5 is 1, a gap width of about 0.13 [mu] m, that is, the width of the write wiring 2 is about 0.13 [mu] m It turns out that it becomes impossible to switch when it becomes smaller. Further, from the graphs g ₁ and g ₃ , in the write wiring 2 in which the ratio of the width W _{G of the} gap 5 to the width of the write wiring 2 is 0.2, switching can be performed when the gap width W _G is smaller than 0.1 μm. I understand that it will disappear.

Even if the gap width W _G is smaller than 0.1 μm, if the width W _WL of the write wiring 2 is increased, that is, if the ratio of the gap width W _G and the width W _WL of the write wiring 2 is smaller than 0.2, as can be seen from the graph shown in FIG. 2, since the induced magnetic field H caused by the current flowing through the write wiring 2 is increased, the graph g ₂ of FIG. 3 showing the characteristics of the magnetic field by the write wirings 2 is made to move to the upper right Thus, the magnetization of the storage layer can be switched more easily.

As described above, in the present embodiment, by setting the ratio of the gap width W _G and the width W _WL of the write wiring 2 to 0.2 or less, the write current can be reduced and the thermal disturbance resistance can be reduced. Can be secured.

  In the above description, the storage layer of the magnetoresistive effect element 6 has a shape magnetic anisotropy. Can also be defined. In this case, by making the planar shape of the magnetoresistive element 6 isotropic, there is no increase in the switching magnetic field due to the miniaturization of the magnetoresistive element as shown in FIG. Therefore, it is effective to use this method for miniaturization. As materials having strong magnetocrystalline anisotropy, Co and its alloys such as Co-Cr, Co-Mn, Co-Fe, Co-Ni, Co-Cu, Mn and its compounds MnSb, MnBi, MnCrSb, Commonly known materials such as MnGe can be used.

Even when the magnetoresistive element 6 has a magneto-crystalline anisotropy, as can be seen from FIG. 2, the ratio of the gap width W _G to the width W _WL of the write wiring 2 is 0.2. The following is preferable.

  In the first embodiment shown in FIG. 1, when memory cells having magnetoresistive elements are arranged in an array, a sneak current is generated during reading. For this reason, the read operation is slow, but since the structure is simple, for example, a large capacity memory can be realized by stacking memory cells.

(Second Embodiment)
Next, a magnetic memory according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view showing the configuration of the memory cell of the magnetic memory according to the second embodiment. In the magnetic memory according to this embodiment, in the magnetic memory according to the first embodiment, the magnetoresistive effect element 6 is directly connected to the read select transistor 40 via the lead wiring 30 instead of being directly connected to the write wiring 2. It is composed. For this reason, the magnetoresistive element 6 is not inserted into the gap 5 of the yoke 4. The width W _G of the gap 5 has a width substantially the same width of the magnetoresistive element 6. Here, have substantially the same width, the width of the extent to which the magnetoresistive element 6 is not in contact with the yoke 4b, in the present embodiment, the width W _G is the width of the magneto-resistive element 6 of the gap 5 It is formed about 10 nm larger than W _MTJ .

As in the first embodiment, the magnetic memory having the above-described configuration in which the width W _{MTJ of} the magnetoresistive effect element 6, that is, the width W _{G of the} gap 5 substantially equal to the width W _MTJ of the magnetoresistive effect element 6 is changed. Various productions and experiments were conducted. This will be described below.

The write wiring 2 has a width of 500 nm and a thickness of 400 nm, and the read wiring 8 has a width of 600 nm and a thickness of 500 nm. The magnetoresistive element 6 includes a magnetization pinned layer 6a made of Co—Fe, a tunnel barrier layer 6b made of alumina, and a memory layer 6c made of Co—Fe—Ni having a thickness of 2 nm. The magnetization pinned layer 6a made of Co—Fe is provided with an antiferromagnetic layer 6e made of Ir—Mn adjacent to the opposite side of the tunnel barrier layer 6b. An exchange interaction acts between the magnetization pinned layer 6a and the antiferromagnetic layer 6e, and the magnetization of the magnetization pinned layer 6a made of Co—Fe is pinned by this exchange interaction. The memory layer 6c is electrically connected to the read wiring 8 via an electrode 6d provided on the surface opposite to the tunnel barrier layer 6b. Width W _MTJ, i.e. the width W _G of the gap 5 of the magnetoresistive element 6, compared width W _WL of the write wiring 2, were prepared six to 0.8 to 0.05 times.

When a writing test was performed on this system, results as shown in FIG. 5 were obtained. That is, FIG. 5, to write wiring 2 with a constant width, plots the magnetic field H induced when a constant current I _W, the horizontal axis represents the write wiring 2 width W _G of the gap 5 The vertical axis represents the value obtained by dividing the induction magnetic field H by the write current I _W. It can be seen that the induction magnetic field H gradually increases as the width WG of the gap 5 becomes narrower from 0.8 times, and particularly, when the width W _G becomes 0.2 times or less, the induction magnetic field H increases rapidly.

  In the above description, it has been described that the easy axis of magnetization of the storage layer of the magnetoresistive element 6 is the direction that coincides with the direction of the magnetic field induced by the current flowing through the write wiring 2. In order to realize this magnetic anisotropy, for example, the planar shape (film surface shape) of the magnetoresistive effect element 6 has an aspect extending in the direction of the induced magnetic field caused by the current flowing through the write wiring 2. Good. In this case, the easy magnetization axis is set by the shape magnetic anisotropy of the storage layer.

In the present embodiment, the switching magnetic field increases as the magnetoresistive effect element is miniaturized as in the first embodiment. This is shown in FIG. In FIG. 6, the horizontal axis represents the reciprocal of the width of the gap 5, and the vertical axis represents the switching magnetic field, that is, the minimum magnetic field that can reverse the magnetization direction of the storage layer. The width W _G of the gap 5 in FIG. 6 is a 10nm great value for the width W _MTJ of the magnetoresistive element 6. Graph g ₁ in FIG. 6 shows the characteristic of the switching field of the storage layer. A graph g _2, when the ratio between the width W _G and write wiring 2 of the width of the gap 5 may be 1, i.e. the yoke 4a shown in FIG. 4, but is present there is no yoke 4b, current density The characteristic of the induction magnetic field induced | guided | derived when the electric current of 10 < ⁶ > A / cm < ² > is sent is shown. Graph g _3, when the ratio between the width W _G and write wiring 2 of the width of the gap 5 is 0.2, the induced magnetic field that the current density is induced when a current of a 10 6 ^{A /} cm ² current The characteristics of As in the case of FIG. 3 described in the first embodiment, the graphs g ₂ and g ₃ have a downward slope.

The graph g _{1 in} FIG. 6 shows that the switching magnetic field increases almost linearly with respect to the width of the gap 5, that is, the reciprocal of the width of the magnetoresistive element 6. In particular, when the width W _{G of the} gap 5 is smaller than 0.1 μm, it can be seen that the switching magnetic field exceeds 100 Oe. The graph g ₁ and Graph g _2, when the ratio between the width W _G and write wiring 2 of the width of the gap 5 is 1, it is understood that not be switched when the gap width is less than about 0.17 .mu.m. Further, from the graphs g ₁ and g ₃ , when the ratio of the width W _{G of the} gap 5 to the width of the write wiring 2 is 0.2, switching cannot be performed if the gap width W _G is smaller than 0.12 μm. I understand.

Even if the gap width W _G is smaller than 0.12 μm, if the width W _WL of the write wiring 2 is increased, that is, if the ratio of the gap width W _G to the width W _WL of the write wiring 2 is smaller than 0.2, as can be seen from the graph shown in FIG. 5, since the induced magnetic field H caused by the current flowing through the write wiring 2 is increased, the graph g ₃ of FIG. 6 showing the characteristics of the magnetic field by the write wirings 2 is made to move to the upper right Thus, the magnetization of the storage layer can be switched more easily.

As described above, in the present embodiment, the write current can be reduced and the thermal disturbance resistance can be achieved by setting the ratio of the gap width W _G and the width W _WL of the write wiring 2 to 0.24 or less. Can be secured.

  In the present embodiment, since there is the lead-out wiring 30, the storage layer of the magnetoresistive effect element 6 is slightly distant from the write wiring, so that the magnetic field application efficiency is somewhat lower than in the first embodiment. However, since the switching transistor 40 is connected to the magnetoresistive effect element 6, the sneak current generated in the first embodiment becomes zero, so that there is an advantage that a high-speed response as a memory is possible. Therefore, it is suitable for applications such as system LSI.

  As described in the first embodiment, it is possible to define the easy axis of magnetization by giving the storage layer of the magnetoresistive element 6 not the shape magnetic anisotropy but the magnetocrystalline anisotropy. is there. In this case, by making the planar shape of the magnetoresistive element 6 isotropic, there is no increase in the switching magnetic field due to the miniaturization of the magnetoresistive element as shown in FIG.

In the first and second embodiments, when a material having magnetocrystalline anisotropy is used for the memory layer, a material having a large magnetocrystalline anisotropy may be used. In particular, the anisotropy constant is preferably larger than 1 × 10 ³ . When the anisotropy constant is 1 × 10 ³ , the coercive force is about 2 Oe to ³ Oe. Therefore, it is preferable to have a larger anisotropy constant for use as a memory element. However, if the anisotropy constant is large, the magnetic field required for inversion becomes too large and the write current increases. For example, when the anisotropy constant is larger than 1 × 10 ⁶ , the coercive force exceeds 1 kOe, which is not practical. Fe ₃ O ₄ , NiFe ₂ O _{4 as} well as Fe, Co, Ni, and alloys thereof as materials having anisotropy constants having appropriate values (values greater than 1 × 10 ^{3 and} less than or equal to 1 × 10 ⁶ ). And ferrite such as MnFe ₂ O ₄ , YIG, GdIG and the like. Also, 4f metals such as Gd, Tb, Dy, Er, and alloys thereof have a larger anisotropy constant, but by controlling the anisotropy constant by making it thin, it has a preferable value. be able to. The anisotropy constant is obtained by measuring a torque curve with a torque magnetometer or a vibrating sample magnetometer (VSM). The anisotropy constant can also be obtained by measuring a magnetization curve by VSM or the like, or by measuring a resonance magnetic field by a resonance method.

Even when the storage layer of the magnetoresistive element 6 has crystal magnetic anisotropy, as can be seen from FIGS . 2 and 5, the ratio between the gap width W _G and the width W _WL of the write wiring 2 is It is preferable to make it 0.2 or less.

1 is a cross-sectional view showing a configuration of a memory cell of a magnetic memory according to a first embodiment of the present invention. The figure which shows the gap dependence of the yoke of the induction magnetic field by the write current of the magnetic memory by 1st Embodiment. The figure which shows the gap dependence of the yoke of the switching magnetic field of the magnetic memory by 1st Embodiment. Sectional drawing which shows the structure of the memory cell of the magnetic memory by 2nd Embodiment of this invention. The figure which shows the gap dependence of the yoke of the induced magnetic field by the write current of the magnetic memory by 2nd Embodiment. The figure which shows the gap dependence of the yoke of the switching magnetic field of the magnetic memory by 2nd Embodiment.

Explanation of symbols

2 writing wiring 4 yoke 4a yoke 4b yoke 5 yoke gap 6 magnetoresistive element 6a magnetic pinned layer 6b tunnel barrier layer 6c magnetization free layer (memory layer)
6d Electrode 8 Read-out wiring 20 Select transistor 30 Lead-out wiring 40 Read-out select transistor 100 Insulating film

Claims (6)

A magnetization pinned layer made of a magnetic layer with a fixed magnetization direction, a recording layer made of a magnetic layer with a variable magnetization direction, and a nonmagnetic layer provided between the magnetization pinned layer and the recording layer; A magnetoresistive element having
A write wiring that generates an induced magnetic field by current and can reverse the magnetization direction of the recording layer by the induced magnetic field;
A yoke that covers the write wiring and is provided with a gap having a width substantially the same as the width of the magnetoresistive element on the side facing the magnetoresistive element;
A read wiring electrically connected to one end of the magnetoresistive element;
The magnetic memory is characterized in that the width of the gap is not more than 0.2 times the width of the write wiring.   2. The magnetic memory according to claim 1, further comprising a write selection transistor having one end electrically connected to the write wiring.   3. The magnetic memory according to claim 1, wherein the other end of the magnetoresistive element is connected to the write wiring.   3. The magnetism according to claim 1, further comprising: a lead wire connected to the other end of the magnetoresistive effect element; and a read selection transistor having one end electrically connected to the lead wire. memory. 5. The magnetic memory according to claim 1, wherein the storage layer is made of a magnetocrystalline anisotropic material having an anisotropy constant greater than 1 × 10 ^{3 and} less than or equal to 1 × 10 ^6. .   The magnetic memory according to claim 1, wherein the nonmagnetic layer is a tunnel barrier layer.

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