JP2009049101A - Magnetic memory element and magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spin injected inverted magnetization MTJ element which is less in failure in writing and has small threshold of write current density by improving transient characteristics during writing, and can be highly integrated, made fast, and reduced in power consumption, and to provide a magnetic memory device using the same. <P>SOLUTION: A magnetic memory element which has a free magnetization layer 5 which is made of a ferromagnetic conductor and changeable in the magnetization direction and stores the magnetization direction as information and a fixed magnetization layer 3 which is made of a ferromagnetic conductor and fixed in magnetization direction, and is configured to write information by magnetizing the free magnetization layer 5 in a predetermined direction with a spin polarization current penetrating those ferromagnetic conductor layers and to read the information by using magnetoresistance effect is provided with a free spin torque layer (magnetized coupler) 13 which is magnetically coupled to the free magnetization layer 5 to suppress change in magnetization direction caused when the magnetization direction of the free magnetization layer 5 is inverted, and prevents the spin polarization current from flowing in the free spin torque layer 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention has a magnetization free layer (memory layer) that can change the magnetization direction and stores this magnetization direction as information, and a magnetization fixed layer in which the magnetization direction is fixed, and these ferromagnetic conductor layers A magnetic memory device that writes and reads information by a current flowing through the memory, and a magnetic memory device including a memory unit that includes the magnetic memory device, for example, a magnetic random access memory (MRAM) The present invention relates to a magnetic memory device.

  With the rapid spread of information communication devices, especially small personal devices such as portable terminals, the elements such as memory and logic that make up these devices have higher performance such as higher integration, higher speed, and lower power consumption. Is required.

  In particular, a nonvolatile memory is indispensable for reducing the power consumption of a device because it can retain information even when the power is turned off, and its large capacity and high speed are strongly desired. A memory device having a mechanical drive portion such as a hard disk device is essentially difficult to reduce in size, increase in speed, and reduce power consumption. Therefore, the semiconductor nonvolatile memory is a memory device complementary to a hard disk device or the like, and a memory device that can realize a new function such as so-called “instant on” that can start the system at the same time as the power is turned on. It is becoming increasingly important.

  As a semiconductor non-volatile memory, a flash memory, a FRAM (Ferroelectric Random Access Memory) using a ferroelectric, and the like have been put into practical use. However, in recent years, a high-speed, large-capacity, low power consumption non-volatile memory has been developed. Magnetic Random Access Memory (MRAM) using the resistance effect has attracted attention and is being developed (see, for example, Nikkei Electronics, February 12, 2001, p.164-171).

  Early MRAM was based on a spin valve using a giant magnetoresistance (GMR) effect or the like. However, in recent years, magnetic memory elements using the TMR effect, that is, MRAMs composed of MTJ elements, have attracted attention due to improved characteristics of materials using the tunnel magnetoresistance (TMR) effect.

  FIG. 7A is an explanatory diagram showing the basic structure of the MTJ element and the reading operation of the stored information. As shown in FIG. 7A, the MTJ element 100 includes a tunnel barrier layer that is a thin nonmagnetic insulating layer between two ferromagnetic layers of a magnetization free layer (storage layer) 105 and a magnetization fixed layer 103. It has a structure sandwiching 104, a so-called magnetic tunnel junction (MTJ). The magnetization free layer (memory layer) 105 is made of a ferromagnetic conductor having uniaxial magnetic anisotropy, can change the magnetization direction, and can store the magnetization direction as information. For example, whether the magnetization direction is “parallel” or “antiparallel” with respect to the magnetization direction of the magnetization fixed layer 103 is stored as information of “0” and “1”, respectively.

  For reading information from the MTJ element 100, the TMR effect is used in which the resistance value with respect to the tunnel current flowing through the tunnel barrier layer 104 varies depending on the relative magnetization direction difference between the two magnetic layers. This resistance value takes a minimum value when the magnetization direction of the magnetization free layer (memory layer) 105 and the magnetization direction of the magnetization fixed layer 103 are parallel, and takes a maximum value when the magnetization direction is antiparallel.

  FIG. 7B is a partial perspective view showing an example of the structure of an MRAM memory cell including the MTJ element 100. In this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, MTJ elements are arranged at the positions of their intersections, and memory cells corresponding to 1 bit are formed. .

  A write bit line 121 and a read bit line 123 are provided above the memory cell with an interlayer insulating film interposed therebetween, and the MTJ element 100 is disposed below and in contact with the read bit line 123. A write word line 122 is disposed under the lead electrode layer 106 of the MTJ element 100 with an insulating layer interposed therebetween.

  On the other hand, a MOS (Metal Oxide Semiconductor) type field effect transistor is provided under the memory cell as a selection transistor 110 for selecting the memory cell in a semiconductor substrate 111 such as a silicon substrate during a read operation. Yes. The gate electrode 115 of the transistor 110 is formed in a band shape connecting cells, and also serves as a read word line. The drain region 114 is connected to the lead electrode layer 106 of the MTJ element 100 via the read connection plug 107, and the source region 116 is connected to the sense line 124 that is a read row wiring.

  In the MRAM configured as described above, when writing information to the MTJ element 100 of a desired memory cell, a write current is supplied to the write bit line 121 in the column including the memory cell and the write word line 122 in the row. And a combined magnetic field of these magnetic fields is generated at the position of the intersection of the two write wirings. By this synthetic magnetic field, the magnetization free layer (storage layer) 105 of the MTJ element 100 of the desired memory cell is “parallel” to a predetermined magnetization direction, that is, the magnetization direction of the magnetization fixed layer 103, or “ Information is written by being magnetized in the direction of “anti-parallel”.

  In reading information from the MTJ element 100, a selection signal is applied to the gate electrode 115 which is a read word line, and all the selection transistors 110 in a row including a desired memory cell are turned on (conductive). To do. In accordance with this, a read voltage is applied between the read bit line 123 and the sense line 124 in a column including a desired memory cell. As a result, only a desired memory cell is selected, and the difference in the magnetization direction of the magnetization free layer (storage layer) 105 of the MTJ element 100 is the difference in the magnitude of the tunnel current flowing through the MTJ element 100 using the TMR effect. Detected as The tunnel current is taken out from the sense line 124 to a peripheral circuit (not shown) and measured.

  The TMR type MRAM is a nonvolatile memory that reads information by utilizing the magnetoresistive effect based on the spin-dependent conduction phenomenon peculiar to nanomagnets, and is rewritten by reversal of the magnetization direction, so that it is practically infinite. It is reported that rewriting is possible and the access time is high (see, for example, R. Scheuerlein et al., ISSCC Digest of Technical Papers, pp.128-129, Feb.2000).

  However, in an MRAM that performs writing using a current magnetic field, it is necessary to pass a large current (for example, about several mA) for rewriting, resulting in an increase in power consumption. Further, when the MTJ element is miniaturized, the current required for rewriting tends to increase. However, since the write wiring becomes thin, it is difficult to pass a sufficient current for rewriting. Further, as the integration density increases, the probability of erroneously writing to another adjacent memory cell increases. Further, since a writing wiring and a reading wiring are required, the structure is complicated. For these reasons, it is difficult to miniaturize memory cells.

  Therefore, attention has been paid to a magnetic memory element using magnetization reversal by spin injection as an element for performing writing to the magnetization free layer (storage layer) of the magnetic memory element based on different principles. Spin injection is a current consisting of a group of electrons whose spin direction is biased in one direction (spin-polarized current) by passing a current through a ferromagnetic conductive layer (magnetization pinned layer) whose magnetization direction is fixed. ) And injecting this current into a magnetic conductive layer (magnetization free layer) whose magnetization direction is not fixed. In this way, when the spin-polarized current flows through the magnetization free layer, a force (torque) is applied to make the magnetization direction of the magnetization free layer coincide with the spin-polarized direction by the spin-polarized electrons. . Therefore, the magnetization direction of the magnetization free layer can be reversed by flowing a spin-polarized current having a current density higher than a certain threshold (for example, L. Berger, “Emission of spin waves by a magnetic multilayer transversed by a current ”, Phys. Rev. B, 54. 9353 (1996), JC Slonczewski,“ Current-driven excitation of magnetic multilayers ”, J. Magn. Magn. Mater., 159 (1996) L1, and the following patent documents 1).

  FIG. 8 shows the structure of an MRAM memory cell composed of an MTJ element (hereinafter, simply referred to as “spin injection magnetization reversal MTJ element”) that utilizes magnetization reversal by spin injection, as described in Patent Document 2 described later. It is a fragmentary sectional view. Also in this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, MTJ elements are arranged at the positions of their intersections, and memory cells corresponding to 1 bit are formed. .

  As shown in FIG. 8, at the center of the memory cell, in order from the lower layer, the underlayer 1, the antiferromagnetic layer 2, the fixed magnetization layer 3a, the intermediate layer 3b, the reference magnetization layer 3c, the tunnel barrier layer 4, and the magnetization free layer. The (memory layer) 5 and the cap layer 6 are laminated to form the spin injection magnetization switching MTJ element 200.

  The pinned magnetization layer 3a, the intermediate layer 3b, and the reference magnetization layer 3c are stacked on the antiferromagnetic layer 2, and constitute the magnetization pinned layer 3 as a whole. The magnetization direction of the fixed magnetic layer 3 a made of a ferromagnetic conductor is fixed by the antiferromagnetic layer 2. Similarly, the reference magnetization layer 3c made of a ferromagnetic conductor forms antiferromagnetic coupling with the fixed magnetization layer 3a via the intermediate layer 3b which is a nonmagnetic layer. As a result, the magnetization direction of the reference magnetization layer 3c is fixed in a direction opposite to the magnetization direction of the fixed magnetization layer 3a. In the example shown in FIG. 8, the magnetization direction of the fixed magnetization layer 3a is fixed to the left, and the magnetization direction of the reference magnetization layer 3c is fixed to the right. According to such a laminated ferrimagnetic structure, there is an advantage that the magnetization states of the fixed magnetization layer 3a and the reference magnetization layer 3c are kept stable, and magnetic fluxes leaking from these cancel each other and become smaller.

  The magnetization free layer (memory layer) 5 is made of a ferromagnetic conductor having uniaxial magnetic anisotropy, can change the magnetization direction, and can store the magnetization direction as information. For example, whether the magnetization direction is “parallel” or “antiparallel” with respect to the magnetization direction of the reference magnetization layer 3 c is stored as information of “0” and “1”, respectively. A tunnel barrier layer 4 which is a nonmagnetic thin insulating layer is provided between the reference magnetization layer 3c and the magnetization free layer (storage layer) 5, and the reference magnetization layer 3c and the magnetization free layer (storage layer) 5 are provided. Thus, a magnetic tunnel junction (MTJ) is formed.

  On the other hand, in the lower part of the memory cell, a gate insulating film 52, a drain electrode 53, a drain as a selection transistor 50 for selecting the memory cell are formed in a well region 51a of the semiconductor substrate 51 such as a silicon substrate. A MOS field effect transistor including a region 54, a gate electrode 55, a source region 56, and a source electrode 57 is provided.

  The gate electrode 55 of the selection transistor 50 is formed in a band shape connecting cells, and also serves as a word line which is a first row wiring. The source electrode 57 is connected to the row wiring 62 as the second row wiring, and the drain electrode 53 is connected to the underlying layer 1 of the MTJ element 200 via the connection plug 7. On the other hand, the cap layer 6 of the MTJ element 200 is connected to a bit line 61 which is a column wiring provided on the upper part of the memory cell.

  As a feature of the spin injection magnetization reversal MTJ element, in writing information to the MTJ element 200 of a desired memory cell, a selection signal is applied to the gate electrode 55 which is a word line to select a row including the desired memory cell. All transistors 50 are turned on (conductive). In accordance with this, a write voltage is applied between the bit line 61 and the row wiring 62 in the column including the desired memory cell. As a result, a desired memory cell is selected, a spin-polarized current flows through the magnetization free layer (memory layer) 5 of the MTJ element 200, and the magnetization free layer (memory layer) 5 is magnetized in a predetermined magnetization direction. Information is written.

  At this time, the magnetization direction of the reference magnetization layer 3 c of the MTJ element 200 is initially in an “anti-parallel” state with respect to the magnetization direction of the magnetization free layer (memory layer) 5. When the magnetization direction of the (layer) 5 is reversed to a state of being “parallel” to the magnetization direction of the reference magnetization layer 3c, a write current having a current density equal to or higher than the threshold is freed of magnetization as shown in FIG. It is made to flow from the layer (storage layer) 5 to the reference magnetization layer 3c. As a result, as a matter of fact, a spin-polarized electron flow having an electron density equal to or higher than the threshold value flows from the reference magnetization layer 3c to the magnetization free layer (memory layer) 5, and magnetization reversal occurs. Hereinafter, this point will be described.

  An electron can take one of two motion states as an internal motion state based on the degree of freedom of spin, and is usually distinguished by calling it an upward spin and a downward spin. Electrons have a spin angular momentum and a magnetic moment corresponding to the direction of spin, and two electrons having different spin directions have the same absolute value of spin angular momentum and magnetic moment, but opposite directions. Therefore, the magnetic moments of two electrons having different spin directions cancel each other.

  In a non-magnetic material, the same number of electrons having upward spins and electrons having downward spins are included in the material, so that the magnetic moments of the individual electrons cancel each other and there is no magnetism in the entire material. On the other hand, in ferromagnets, the number of electrons with upward spins and electrons with downward spins contained in a material is different, so the magnetic moment of individual electrons as a whole does not completely cancel out. As a result, it has magnetism. When a current is passed through such a ferromagnet, the electrons that make up the current interact with the electrons in the material. Therefore, as with the electrons in the ferromagnet, electrons with upward spins and electrons with downward spins are used. There is a difference in the number. This is the spin-polarized electron current, and the current resulting from this is the spin-polarized current.

  Now, in the above write operation, the spin-polarized electron flow by flowing through the reference magnetic layer 3 c that is a ferromagnetic layer flows into the tunnel barrier layer 4. If the thickness of the tunnel barrier layer 4 is sufficiently thick, an upward spin in the electron current is generated by the interaction with the electrons in the tunnel barrier layer 4 while flowing through the tunnel barrier layer 4 which is a non-magnetic material. The number of electrons having the same number of electrons as those having downward spins is the same, and the spin polarization of the electron current is eliminated. However, since the thickness of the tunnel barrier layer 4 is actually thin, the spin-polarized electron current passes through the tunnel barrier layer 4 before the spin polarization is eliminated, and enters the magnetization free layer (memory layer) 5. Inflow.

  The spin-polarized electron current flowing into the magnetization free layer (memory layer) 5 interacts with electrons in the magnetization free layer (memory layer) 5. At this time, since the magnetization direction of the magnetization free layer (storage layer) 5 is opposite to the magnetization direction of the reference magnetization layer 3c, the electrons in the magnetization free layer (storage layer) 5 are the electrons in the electron current until now. Tries to spin-polarize in the opposite direction. For this reason, the spin direction of some of the electrons in the electron flow is reversed by the interaction with the electrons in the magnetization free layer (memory layer) 5. As a reaction, the magnetization free layer (memory layer) 5 is reversed. The electrons inside receive a so-called spin torque from the electrons in the electron stream to reverse the spin. At this time, since the angular momentum of the entire system is preserved, a spin torque proportional to the number of electrons in the electron flow whose spin has been reversed acts on the electrons in the magnetization free layer (memory layer) 5.

  When the electron current density is small and the number of electrons passing through the magnetization free layer (memory layer) 5 per unit time is small, the number of electrons in the electron current that reverses the spin is small, and the reaction causes free magnetization. The spin torque received by the electrons in the layer (memory layer) 5 is also small. Therefore, the magnetization direction of the magnetization free layer (storage layer) 5 is not reversed. This state is nothing but an operating state when reading information from the MTJ element 200.

  On the other hand, as the electron current density increases, the number of electrons in the electron current that reverses the spin per unit time increases, and the spin torque received by the electrons in the magnetization free layer (memory layer) 5 increases as a reaction. Therefore, when the current density exceeds a certain threshold value, the magnetization direction of each magnetic fine particle in the magnetization free layer (storage layer) 5 starts to change all at once, and is stable when rotated 180 degrees by its uniaxial anisotropy. To reach. That is, inversion from the “antiparallel” state to the “parallel” state occurs.

  The above description is a case where the magnetization direction of the reference magnetization layer 3 c in the “antiparallel” state with respect to the magnetization direction of the magnetization free layer (storage layer) 5 is reversed to the “parallel” state. On the other hand, when the magnetization direction of the reference magnetization layer 3 c in the “parallel” state to the magnetization direction of the magnetization free layer (storage layer) 5 is reversed to the “anti-parallel” state, the current density equal to or higher than the threshold value. Is written in the reverse direction, that is, from the reference magnetic layer 3 c to the magnetization free layer (storage layer) 5. As an entity, an electron flow having an electron density equal to or higher than a threshold value is allowed to flow from the magnetization free layer (storage layer) 5 to the reference magnetization layer 3c.

  In this way, the electron flow that flows into the magnetization free layer (storage layer) 5 as an unpolarized electron flow becomes a spin-polarized electron flow from the reference magnetization layer 3c in the magnetization direction of the reference magnetization layer 3c. Leaked. At this time, since the angular momentum of the entire system is preserved and the magnetization direction of the reference magnetization layer 3c is fixed, the number of electrons in the electron current in which the spin is reversed in the magnetization direction of the reference magnetization layer 3c is set. As a reaction, the proportional spin torque acts on the electrons in the magnetization free layer (storage layer) 5 so as to reverse the spin in the direction opposite to the magnetization direction of the reference magnetization layer 3c.

  Also in this case, when the electron current density is small and the number of electrons passing through the magnetization free layer (storage layer) 5 per unit time is small, the number of electrons in the electron current for reversing the spin is small. The reversal of the magnetization direction of the free layer (memory layer) 5 does not occur. However, as the density of the electron current increases, the number of electrons in the electron current that reverses the spin per unit time increases, and as a reaction, the spin torque received by the electrons in the magnetization free layer (memory layer) 5 also increases. Therefore, when the current density exceeds a certain threshold value, the magnetization direction of each magnetic fine particle in the magnetization free layer (storage layer) 5 starts to change all at once, and is stable when rotated 180 degrees by its uniaxial anisotropy. To reach. That is, the inversion from the “parallel” state to the “anti-parallel” state occurs. However, the amount of current required for reversing from the “parallel” state to the “antiparallel” state is greater than when reversing from the “antiparallel” state to the “parallel” state.

  As described above, information is written to the magnetization free layer (storage layer) 5 from the magnetization free layer (storage layer) 5 to the reference magnetization layer 3c, or in the opposite direction, threshold values corresponding to the respective directions. This is done by flowing a current having the above current density.

  Further, reading of information from the MTJ element 200 is performed using the TMR effect, as in the MTJ element 100. Both reading and writing use the interaction between the electrons in the magnetization free layer (memory layer) 5 and the spin-polarized current that flows through this layer, and the current density of the spin-polarized current is read. Writing is performed in a small region, and writing is performed in a region where the current density of the spin-polarized current exceeds the threshold value.

  In the MRAM using the spin injection magnetization reversal MTJ element 200, the current required for the magnetization reversal is reduced by the miniaturization of the magnetic material. Therefore, the MRAM is smaller than the MRAM using the MTJ element 100 that performs writing by the current magnetic field. It is advantageous for high integration. In addition, since information is written to the memory cell selected by the selection transistor 50, unlike the writing by the current magnetic field, there is no possibility of erroneously writing to another adjacent cell. In addition, since the influence of the shape of the magnetic material is small compared to the magnetic field writing, it is easy to increase the yield during manufacturing. Furthermore, since most of wiring can be shared for writing and reading, there is an advantage that the structure is simplified.

  However, since writing is performed using the selection transistor 50, the following problems occur. That is, the current that can be passed through the MTJ element 200 during writing is limited to the current that can be passed through the selection transistor 50 (transistor saturation current). In general, as the gate width or gate length of a transistor decreases, the saturation current of the transistor also decreases. For this reason, if the selection transistor 50 is to be formed with the minimum dimensions for miniaturization and higher density, it is necessary to improve the efficiency of spin injection and reduce the current density threshold of the write current as much as possible. is there.

  In order to prevent the tunnel barrier layer 4 from being broken down, it is necessary to reduce the write current density threshold. In order to reduce the power consumption of the MRAM, it is necessary to reduce the write current density threshold as much as possible.

  The time change of the magnetization of the magnetic material constituting the magnetization free layer (memory layer) 5 is expressed by the following equation (1) and equation (2) called LLG (Landau-Lifshitz-Gilbert) equation. (L. Torres et al., “Micromagnetic computations of spin polarized current-driven magnetization process”, J. Magn. Magn. Mater., 286, (2005)).

Formula (1):

Formula (2):

However, in the equations (1) and (2), an arrow attached to the top of the symbol indicates that the physical quantity to which the arrow is attached is a vector (the same applies hereinafter). M is a unit magnetization vector, m _adj is an adjacent unit magnetization vector, γ is a gyro constant, α is a damping constant that is a material characteristic of the magnetization free layer (storage layer) 5, T is a torque vector, and M _S is a magnetization free Saturation magnetization of the layer (memory layer) 5, H _eff is an effective magnetic field, H _th is a Langevin magnetic field indicating thermal fluctuation, μ _B is a Bohr magneton, g is a coupling constant, e is an elementary charge, J is a spin-polarized current density of current, t _F is the thickness of the magnetization free layer (storing layer) 5.

  The first term in parentheses [] on the right side of the equation (1) acts as a torque for driving the magnetization rotation, and the second term in [] acts as a torque for braking the magnetization rotation. The larger the damping constant α, the greater the braking effect of the second term in []. In addition, the first term and the second term on the right side of the formula (2) are the torque caused by the magnetic field and the spin torque caused by the spin transfer effect caused by the spin-polarized current, respectively.

Further, it is theoretically derived that the threshold value J _c0 of the write current density at which the spin injection magnetization reversal occurs is expressed by the following equation (3) (RH Koch, JA Katine, and JZ Sun, “ Time-resolved reversal of spin-transfer switching in a nanomagnet ”, Phy. Rev. Lett., 92, 27 February 2004).

Formula (3):
However, in Formula (3), _Hk is a uniaxial anisotropic magnetic field of the magnetization free layer (memory layer) 5, and e, α, M _S , t _F , and g are the same as Formulas (1) and (2). It is.

As shown in the equation (3), the write current density threshold value J _c0 depends on the damping constant α, the saturation magnetization M _S , the film thickness t _{F and the} like of the magnetization free layer (storage layer) 5. Whether or not the MRAM comprising the spin injection magnetization reversal MTJ element 200 can be put into practical use depends on the damping constant α, the saturation magnetization M _S and the film thickness while maintaining the thermal stability of the recording magnetization in the magnetization free layer (memory layer) 5. It depends on how much the write current density threshold J _c0 can be reduced by reducing t _F and the like.

Japanese Patent Laid-Open No. 2003-17782 (pages 6 and 7, FIG. 2) Japanese Patent Laying-Open No. 2006-295000 (page 9-11, FIG. 2)

However, the present inventor reduced the damping constant α, the saturation magnetization M _S , the film thickness t _F, etc. of the magnetization free layer (memory layer) 5 to reduce the write current density threshold J _{c0 and the} spin injection magnetization reversal MTJ. When an MRAM composed of the element 200 (see FIG. 8) was manufactured, the frequency of error occurrence during writing was much larger than expected from the thermal fluctuation of the recording magnetization in the magnetization free layer (storage layer) 5, An MRAM with uncertain operation was obtained.

  FIG. 9 is a graph showing an example of a result of a write test performed on the above MRAM by the inventor. In the test shown in FIG. 9A, a write current having a pulse width of 10 ns is applied to the MTJ element 200 whose initial state is in the high resistance state (“anti-parallel” state), and the low resistance state (“parallel” state) is obtained. Inverted. The test was performed several times while gradually increasing the magnitude of the current pulse. In FIG. 9A, the vertical axis indicates the current pulse magnitude, and the results for 21 memory cells are shown separately. In the figure, the case where writing failed is indicated by a hatched rectangle, and the case where writing was successful is indicated by a rectangle without hatching.

  The lower region of FIG. 9A indicates that writing has failed in all the memory cells when the current density of the current pulse does not reach the threshold value, which is natural. The problem is that even in the upper region of FIG. 9A where the current density of the current pulse is larger than the threshold value, failure examples are scattered, and in particular, sufficiently larger than the threshold value. The writing may fail even when a current is passed.

  In the test shown in FIG. 9B, a write current having a pulse width of 10 ns is applied to the MTJ element 10 whose initial state is in a low resistance state (“parallel” state) in the opposite direction to the above, Parallel ”state). The test was performed several times while gradually increasing the magnitude of the current pulse. In FIG. 9B, as in FIG. 9A, the vertical axis indicates the current pulse magnitude, and the results for 21 memory cells are shown separately.

  As in the test shown in FIG. 9A, in the lower region of FIG. 9B where the magnitude of the current pulse does not reach the threshold value, writing has failed in all the memory cells. Even in the upper region of FIG. 9B where the length is larger than the threshold value, failure examples are scattered.

  As a result of examining the write transient characteristics of the spin-injection magnetic reversal MTJ element 200 in detail, the present inventor has found that there is an example in which the path from the initial state to the target end state takes a long time. . In the present specification, hereinafter, this phenomenon is described as “magnetization rotates more than necessary”. The reason why writing may fail even when a current sufficiently larger than the threshold value is passed is that the magnetization of the magnetization free layer (memory layer) 5 on which the spin torque is applied rotates more than necessary, and at least once. It was found that the end state is not determined to be the reverse state even though the reverse condition is satisfied. In the present specification, this phenomenon is hereinafter referred to as “magnetization reinverts”.

  The “re-inversion” phenomenon has characteristics that cannot be solved by devising the writing method, such as being unable to be solved even if the write pulse width is increased, and is difficult to solve. Although it is not impossible to relieve the error of the “re-inverted” memory cell by applying a parallel magnetic field from the outside, this method goes against the flow aimed at reducing the current consumption by the spin injection memory.

Note that “re-inversion” may be observed even in the magnetization free layer (storage layer) 5 having a large α, M _S, or t _F. This is because the end state becomes indefinite as a result of the vortex magnetization state (vortex) acting as a metastable state in the write transient state. Hereinafter, this phenomenon will be described.

In the magnetization free layer (memory layer) 5, in addition to a stable magnetization state uniformly magnetized in a certain direction (a magnetization direction that is “parallel” or “anti-parallel” to the magnetization direction of the reference magnetization layer 3 c). Various vortex magnetization states (vortex) may exist as metastable states. The vortex magnetization state has a property induced by a demagnetizing field or a current magnetic field, the demagnetizing field increases in proportion to M _S × t _F , and the current magnetic field increases in proportion to α which determines the reversal current density. For this reason, when α, M _S, or t _F increases, the vortex magnetization state becomes more energetically stable and tends to appear.

  If this metastable vortex magnetization state exists on the path of the magnetization reversal process, the magnetization free layer (memory layer) 5 may be trapped in this metastable state during the magnetization reversal process. In this state, the resistance value of the magnetization free layer (storage layer) 5 takes an intermediate value between the low resistance in the “parallel” state and the high resistance in the “antiparallel” state. When the transition from the metastable state to the stable magnetization state is completed after the end of the write pulse, it is undefined whether the end state becomes the “parallel” state or the “antiparallel” state. If such magnetization behavior occurs above the write current density threshold, this is recognized as “re-inversion”.

As described above, α, M _S, and t _F that define the threshold value J _c0 of the write current density are physically different that cause “re-inversion” when the values are small and large. There are factors. For this reason, it is extremely difficult to determine the optimum conditions of α, MS, and tF for producing a spin-injection magnetization reversal MTJ element that does not cause “re-inversion” and has few write failures.

  The present invention has been made in view of such a situation, and an object thereof is to improve the transient characteristics at the time of writing, to reduce writing failure, to reduce the threshold of writing current density, and to achieve high integration. An object of the present invention is to provide a spin injection magnetization switching MTJ element suitable for increasing the speed, reducing the power consumption, and a magnetic memory device using the MTJ element.

  As a result of intensive studies, the present inventor has found that the above problem can be solved by appropriately providing a magnetic coupling body that is magnetically coupled to the magnetization free layer (storage layer), and to complete the present invention. Arrived.

That is, the present invention is a magnetization free layer made of a ferromagnetic conductor and capable of changing the magnetization direction and storing the magnetization direction as information; a magnetization fixed layer made of a ferromagnetic conductor and having a fixed magnetization direction; The magnetic free layer is magnetized in a predetermined direction by a spin-polarized current that flows through these ferromagnetic conductor layers, information is written, and the written information is read using the magnetoresistive effect. In the magnetic memory element
A magnetic coupling body that is magnetically coupled to the magnetization free layer and suppresses fluctuations in the magnetization direction that occurs when the magnetization direction of the magnetization free layer is reversed;
The present invention relates to a magnetic memory device, characterized in that the spin-polarized current is prevented from flowing into the magnetic coupling body.

  Further, the present invention relates to a magnetic memory device having a memory unit composed of the magnetic memory element and provided with wiring and a control circuit for writing and / or reading information with respect to a predetermined magnetic memory element.

In the magnetic memory element of the present invention,
A magnetic coupling body that is magnetically coupled to the magnetization free layer and suppresses fluctuations in the magnetization direction that occurs when the magnetization direction of the magnetization free layer is reversed;
Since the spin-polarized current is configured to be suppressed from flowing into the magnetic coupling body, the transient characteristic when the magnetization free layer is reversed has a magnetic coupling body in which the spin-polarizing current does not act directly. The magnetization free layer is promptly and reliably guided to the inverted state. As a result, a spin injection magnetization reversal MTJ element suitable for high integration, high speed, and low power consumption can be realized with few write failures and a low write current density threshold. In addition, the magnetic memory device of the present invention has the same characteristics as described above since it has a memory unit composed of the magnetic memory element.

  In the magnetic memory element of the present invention, an extraction conductive layer is provided between the magnetization free layer and the magnetic coupling body, and the extraction conductive layer is electrically connected to a control circuit that supplies the spin-polarized current. It is good to be.

  Further, a bypass conductive member is provided in parallel to the magnetic coupling body, and the parallel conductive path is electrically connected between the control circuit for supplying the spin-polarized current and the magnetization free layer, It is preferable that the spin-polarized current flow mainly through the bypass conductive member. At this time, the magnetic coupling body is preferably made of a magnetic material having a specific resistance value of 100 μΩcm or more, and the conductive member is preferably made of a conductor having a specific resistance value of 100 μΩcm or less.

  In addition, a spin sink layer that eliminates the spin polarization of the spin polarization current and a cap layer may be provided between the free magnetization layer and the magnetic coupling body. At this time, the spin sink layer has at least one selected from the group consisting of osmium Os, iridium Ir, rhenium Re, platinum Pt, ruthenium Ru, tungsten W, niobium Nb, and zirconium Zr having a short spin diffusion length. It is good to contain an element. The cap layer has a long spin diffusion length, such as silver Ag, copper Cu, chromium Cr, gold Au, vanadium V, titanium Ti, rhodium Rh, thallium Ta, hafnium Hf, cobalt Co, iron Fe, nickel Ni, and It is preferable to contain at least one element selected from the group consisting of manganese Mn.

  The magnetic coupling body preferably contains at least one element selected from the group consisting of cobalt, nickel, iron, and manganese.

  In addition, the magnetization free layer is formed of a multilayer film that is separated by an intermediate layer and ferromagnetically coupled, and the intermediate layer has a long spin diffusion length, silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, and It is preferable to contain at least one element selected from the group consisting of hafnium.

  Further, the magnetic coupling body is formed of a multilayer film that is separated by an intermediate layer and is ferromagnetically coupled, and the intermediate layer has a long spin diffusion length, such as silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, and It is preferable to contain at least one element selected from the group consisting of hafnium.

  Further, the magnetization fixed layer and the magnetization free layer are laminated with a tunnel barrier layer, which is a thin insulating layer, sandwiched therebetween, and configured as a tunnel magnetoresistive element, and by a tunnel current flowing through the tunnel barrier layer, Information should be written and read. The magnetic memory element of the present invention is not limited to a tunnel magnetoresistive effect (TMR) element. For example, when compared with a giant magnetoresistive effect (GMR) element having a nonmagnetic conductive layer interposed therebetween, the magnetoresistive element There are advantages that the rate of change (MR ratio) can be increased and the read signal intensity can be increased.

The magnetic memory device of the present invention is preferably configured as a magnetic random access memory. For example, first row wirings and column wirings are arranged in a matrix, and the magnetic memory elements and selection transistors for selecting the magnetic memory elements are arranged at the positions of their intersections. A cell is formed,
When writing or reading information to or from a predetermined memory cell,
When a selection signal is applied to the first row wiring of the row in which this memory cell is arranged, all the selection transistors in that row are turned on,
A write voltage or a read voltage is applied to the column wiring of the column where the memory cell is arranged,
As a result, writing or reading is performed by the current flowing between the column wiring and the second row wiring through the magnetic memory element and the selection transistor of the memory cell.
It is good to be configured as follows.

  Next, a preferred embodiment of the present invention will be described more specifically with reference to the drawings.

Embodiment 1
In the first embodiment, a spin-injection magnetization reversal MTJ element will be mainly described as an example related to claims 1, 2, 8, and 11, and as an example related to claims 12 to 14, this MTJ element is used as a magnetic memory element. A magnetic memory device configured as an MRAM will be described.

  FIG. 1 is a partial cross-sectional view showing the structure of a memory cell of an MRAM composed of a spin transfer magnetization switching MTJ element according to the first embodiment. In this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, and spin injection magnetization reversal MTJ elements 10 are arranged at the positions of their respective intersections, and a memory cell corresponding to 1 bit. Is formed.

  As shown in FIG. 1, in the central portion of the memory cell, there are an underlayer 1, an antiferromagnetic layer 2, a fixed magnetization layer 3a, an intermediate layer 3b, a reference magnetization layer 3c, a tunnel barrier layer 4, and a magnetization free layer in order from the lower layer. The MTJ element 10 is formed by laminating the (memory layer) 5, the cap layer 6, the lead conductive layer 11, the cap layer 12, the spin torque free layer 13, and the cap layer 14.

  The pinned magnetization layer 3a, the intermediate layer 3b, and the reference magnetization layer 3c are stacked on the antiferromagnetic layer 2, and constitute the magnetization pinned layer 3 as a whole. The magnetization direction of the fixed magnetic layer 3 a made of a ferromagnetic conductor is fixed by the antiferromagnetic layer 2. Similarly, the reference magnetization layer 3c made of a ferromagnetic conductor forms antiferromagnetic coupling with the fixed magnetization layer 3a via the intermediate layer 3b which is a nonmagnetic layer. As a result, the magnetization direction of the reference magnetization layer 3c is fixed in a direction opposite to the magnetization direction of the fixed magnetization layer 3a. In the example shown in FIG. 1, the magnetization direction of the fixed magnetization layer 3a is fixed to the left, and the magnetization direction of the reference magnetization layer 3c is fixed to the right.

  When the magnetization fixed layer 3 has the above laminated ferrimagnetic structure, the sensitivity of the magnetization fixed layer to the external magnetic field can be reduced. Therefore, the magnetization fluctuation of the magnetization fixed layer 3 due to the external magnetic field is suppressed, and the stability of the MTJ element is improved. Can be improved. Further, since the magnetic flux leaking from the fixed magnetic layer 3a and the reference magnetic layer 3c cancel each other, the magnetic flux leaking from the fixed magnetic layer 3 can be minimized by adjusting these film thicknesses.

  The magnetization free layer (memory layer) 5 is made of a ferromagnetic conductor having uniaxial magnetic anisotropy, can change the magnetization direction, and can store the magnetization direction as information. For example, whether the magnetization direction is “parallel” or “antiparallel” with respect to the magnetization direction of the reference magnetization layer 3 c is stored as information of “0” and “1”, respectively. A tunnel barrier layer 4 which is a nonmagnetic thin insulating layer is provided between the reference magnetization layer 3c and the magnetization free layer (storage layer) 5, and the reference magnetization layer 3c and the magnetization free layer (storage layer) 5 are provided. Thus, a magnetic tunnel junction (MTJ) is formed.

  As a feature of the MTJ element based on the first embodiment, the MTJ element 10 is provided with a spin torque free layer 13 above the magnetization free layer (memory layer) 5. The spin torque free layer 13 corresponds to the magnetic coupling body, is magnetically coupled to the magnetization free layer (memory layer) 5, and is a transient magnetization generated when the magnetization direction of the magnetization free layer (memory layer) 5 is reversed. Suppresses direction fluctuations. Cap layers 12 and 14 are provided on the lower surface and the upper surface of the spin torque free layer 13, respectively.

Since the spin torque free layer 13 forms a magnetic pair with the magnetization free layer (storage layer) 5, it is not preferable that the product of the saturation magnetization and the film thickness of both is remarkably different. When the product of the saturation magnetization and the film thickness of the magnetization free layer (memory layer) 5 is expressed by M _s t _F , the product of the saturation magnetization and the film thickness of the spin torque free layer 13 is 0.1 M _s t _{F to} 10 M _s. It is preferably set in the range of t _F.

  As long as the magnetization of the spin torque free layer 13 is not disturbed by the spin torque, the transient instability of the magnetization of the magnetization free layer (memory layer) 5 can be removed by the spin torque free layer 13. In this sense, if the operation is merely stabilized, there is a considerably large allowable range in the magnitude of the magnetic coupling between the spin torque free layer 13 and the magnetization free layer (storage layer) 5.

However, if the reversal current density significantly increases as a result of the magnetic coupling exceeding the appropriate range for stabilization, the practical value of the spin injection magnetization reversal MTJ element is reduced. become. In order not to cause a significant increase in the reversal current density, the torque that the spin torque free layer 13 acts on the magnetization free layer (memory layer) 5 through magnetic coupling is T ₁ , and the current is the magnetization free layer (memory layer). ) When a spin torque acting on the magnetization of 5 to T _2, during current supply period is the essential condition that T ₁ is not exceed T _2. That is, the following formula (4) needs to be satisfied as a condition imposed on the magnitude of the magnetic coupling in order not to cause a significant increase in the reversal current density.
Formula (4):

  Magnetic coupling between the spin torque free layer 13 and the magnetization free layer (memory layer) 5 includes ferromagnetic coupling, antiferromagnetic coupling, and magnetostatic coupling. The magnetostatic coupling works in the direction in which the magnetization of the spin torque free layer 13 is antiparallel to the magnetization of the magnetization free layer (memory layer) 5, as with the antiferromagnetic coupling. Since the strength of the magnetostatic coupling is proportional to the product of the saturation magnetization and the film thickness, the condition of the product of the saturation magnetization and the film thickness as described above is satisfied.

Next, the optimum range of ferromagnetic coupling or antiferromagnetic coupling is determined. When the magnitude of the ferromagnetic coupling or antiferromagnetic coupling is J _N , the interlayer exchange coupling magnetic field H _inter is defined by the following equation (5).
Formula (5):
Here, t _N is the film thickness of the nonmagnetic layer interposed between the spin torque free layer 13 and the magnetization free layer (memory layer) 5. The unit of J _N in the cgs unit system is erg / cm ² .

When the torque T ₁ that the spin torque free layer 13 acts on the magnetization free layer (memory layer) 5 through magnetic coupling is defined using the equation (5), the following equation (6) is obtained.
Formula (6):

Further, the spin torque T ₂ in which the current acts on the magnetization free layer (storage layer) 5 magnetization is expressed by the following equation (7) from the equation (2).
Formula (7):

Substituting Equation (6) and Equation (7) into Equation (4) and rearranging results in the following Equation (8) representing the optimum range for magnetic coupling.
Formula (8):

The current density for reversing the magnetization of the magnetization free layer (storage layer) 5 is set to a value equal to or higher than the threshold value, but does not exceed the current density at which the element is destroyed at the maximum. The current density J and the coupling constant g that the device can withstand vary depending on the material / film thickness of the tunnel barrier layer, resistance value, device cross-sectional area, etching, and other conditions, and there is a considerable range in the optimum condition defined by equation (8). Exists. For this reason, it is difficult to limit the claims with a specific value of J _N , but empirically, it is practical if | J _N | <1 erg / cm ² , regardless of ferromagnetic coupling or antiferromagnetic coupling. It can be said that it is within the range.

  An extraction conductive layer 11 is provided between the magnetization free layer (memory layer) 5 and the spin torque free layer 13. The lead conductive layer 11 is formed to extend to the outside of the MTJ element 10 and is electrically connected to the bit line (column wiring) 61 via the connection plug 15. The bit line (column wiring) 61 is connected to a control circuit that supplies a spin-polarized current to the MTJ element 10 (not shown). The lead conductive layer 11 functions as a part of the column wiring and serves to prevent the spin polarized current from flowing into the spin torque free layer 13.

  With the above configuration, the transient characteristics when the magnetization free layer (memory layer) 5 is inverted are improved by the magnetic coupling with the spin torque free layer 13 to which the spin polarization current does not act directly. As described with reference to FIG. 1, the magnetization free layer (storage layer) 5 is promptly and reliably guided to the inverted state.

  On the other hand, below the memory cell, a gate insulating film 52, a drain electrode 53, a selection transistor 50 for selecting the memory cell is formed in a well region 51a in which a semiconductor substrate 51 such as a silicon substrate is isolated. A MOS field effect transistor including a drain region 54, a gate electrode 55, a source region 56, and a source electrode 57 is provided.

  A gate electrode 55 of the selection transistor 50 is formed in a band shape connecting cells, and also serves as a word line which is the first row wiring. The source electrode 57 is connected to the row wiring 62 as the second row wiring, and the drain electrode 53 is connected to the underlying layer 1 of the MTJ element 10 through the connection plug 7.

  As a constituent material of the spin torque free layer 13, a magnetic material containing at least one element selected from the group consisting of cobalt, nickel, iron, and manganese can be used. The cap layers 12 and 14 are laminated in order to prevent the deterioration of the magnetic characteristics at the interface of the spin torque free layer 13, but the stability of the final magnetization free layer (memory layer) 5 and the write current density threshold. If there is no problem with the value, etc., it can be omitted. As a constituent material of the cap layers 12 and 14, silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, hafnium, cobalt, iron, nickel, manganese, or an alloy containing these elements can be used. As a constituent material of the lead conductive layer 11, the same conductive material as that of the bit line 61 and the like can be used.

  The other layers of the MTJ element 10 can have the same structure as a conventionally known configuration of the spin injection magnetization switching MTJ element.

  The constituent material of the magnetization free layer (memory layer) 5 is not particularly limited, but an alloy material composed of one or more of Fe, Ni, and Co can be used. Further, transition metal elements such as Nb and Zr, and light elements such as boron B can be contained. Further, the magnetization free layer (memory layer) 5 may be configured by directly laminating a plurality of films of different materials (not via a nonmagnetic layer) such as a CoFe / NiFe / CoFe laminated film. .

As a constituent material of the tunnel barrier layer 4, magnesium oxide MgO is preferably used. As a result, the magnetoresistance change rate (MR ratio) can be increased and the spin injection efficiency can be improved as compared with the case of using aluminum oxide which has been generally used conventionally. As a result, the signal intensity can be increased during reading, and the write current density threshold can be decreased during writing. However, the constituent material of the tunnel barrier layer 4 is not limited to this, and aluminum oxide Al ₂ O ₃ , aluminum nitride AlN, aluminum oxynitride AlN _x O _y , silicon dioxide SiO ₂ , bismuth oxide Bi ₂ O ₃ Various insulators, dielectrics, and semiconductors such as magnesium fluoride MgF ₂ , calcium fluoride CaF ₂ , strontium titanate SrTiO ₃ , and aluminum lanthanum AlLaO ₃ can be used.

  As the constituent material of the ferromagnetic conductive layers 3a and 3c of the magnetization fixed layer 3, an alloy material composed of one or more of Fe, Ni, and Co can be used. Further, transition metal elements such as Nb and Zr, and light elements such as boron B can be contained. Further, Ru, Cu, Cr, Au, Ag, or the like can be used as a constituent material of the intermediate layer 3b. The thickness of the intermediate layer 3b is appropriately selected according to the constituent material, but is preferably about 0.5 to 2.5 nm. In the present embodiment, the example in which the magnetization pinned layer 3 has a laminated ferrimagnetic structure has been described. However, the magnetization pinned layer may have a single ferromagnetic layer.

The constituent material of the antiferromagnetic layer 2 includes alloys of metal elements such as Fe, Ni, Pt, Ir, and Rh with Mn, such as FeMn, NiMn, PtMn, PtCrMn, and IrMn, and oxidation of Co and Ni. For example, magnetic materials such as NiO and Fe ₂ O ₃ can be used. Further, by adding a non-magnetic element to these magnetic materials, it is possible to adjust magnetic properties and various physical properties such as substance stability.

  The MTJ element 10 can be manufactured by forming each layer by sputtering, vapor deposition, or the like, and patterning by photolithography and etching.

  In the MRAM configured as described above, in writing information to the MTJ element 10 of a desired memory cell, first, a selection signal is applied to the gate electrode 55 which is a word line, and a row including the desired memory cell is included. All the selection transistors 50 are turned on (conductive). In accordance with this, a write voltage is applied to the bit line 61 in the column including the desired memory cell. As a result, only a desired memory cell is selected, a spin-polarized current flows through the magnetization free layer (memory layer) 5 of the MTJ element 10, and the magnetization free layer (memory layer) 5 is magnetized in a predetermined magnetization direction. Information is written.

  FIG. 2 is a graph showing an example of a result of a write test performed on the MRAM. In the test shown in FIG. 2A, a write current having a pulse width of 10 ns is applied to the MTJ element 10 whose initial state is the high resistance state (“anti-parallel” state), and the low resistance state (“parallel” state) is obtained. Inverted. The test was performed several times while gradually increasing the magnitude of the current pulse. In FIG. 2A, the vertical axis represents the current pulse magnitude, and the results for 21 memory cells are shown separately. In the figure, the case where writing failed is indicated by a hatched rectangle, and the case where writing was successful is indicated by a rectangle without hatching.

  The lower region of FIG. 2A indicates that writing has failed in all the memory cells when the magnitude of the current pulse does not reach the threshold value, which is natural. On the other hand, there is no failure example in the upper region of FIG. 2A where the magnitude of the current pulse is larger than the threshold value. The failure example and the success example are clearly separated by the threshold value, which is a significant difference from the conventional example shown in FIG.

  FIG. 3 is a graph showing the write transient characteristics of the MTJ element 10. FIG. 3 shows the result of writing to the MTJ element 10 (see FIG. 8) as a comparative example, together with the result of writing to the MTJ element 10. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the resistance value indicated by the MTJ element. The high resistance state and the low resistance state respectively correspond to states in which the magnetization direction of the magnetization free layer (storage layer) 5 is “antiparallel” and “parallel” to the magnetization direction of the reference magnetization layer 3c.

The planar shape (top view) of the MTJ element 10 is an ellipse having a major axis length of 300 nm and a minor axis length of 100 nm. The magnetization free layer 5 and the spin torque free layer 13 are formed by laminating a CoFeBTa alloy and both have a thickness of 2 nm. The saturation magnetization is about 400 emu / cm ³ and the damping constant α is 0.01 or less. A rectangular constant current pulse having a size of 2 mA and a pulse width of 10 ns was applied to the device. Time 0 on the horizontal axis is the time when the application of the current pulse starts. A current of 2 mA corresponds to a current density of about 8.5 MA / cm ² in the magnetization free layer (memory layer) 5.

  The transient change of the resistance value of the MTJ element 10 was obtained by the four probe method. A pulse generator DG2040 (Tektronix; trade name) is used as a signal source, and an ultra-high-speed oscilloscope DSA71254 (Tektronix; trade name) is used. It was measured. After the measurement, the resistance value was calculated from the current value and the voltage value.

  As shown in FIG. 3, in the conventional MTJ element 200, the magnetization direction of the magnetization free layer (memory layer) 5 starts reversal almost immediately after the start of application of the current pulse. ”State and the“ parallel ”state continue to fluctuate irregularly, and there is almost no tendency to settle down to the“ parallel ”state that is the inverted state. This is a phenomenon called “magnetization rotates more than necessary” in this specification.

As one method for suppressing such excessive fluctuations in the magnetization direction, it is conceivable to increase the damping constant α of the magnetization free layer (memory layer) 5. However, this is not preferable because the write current density threshold value J _c0 also increases as shown in the equation (3).

  Therefore, in the MTJ element 10 according to the present embodiment, the spin torque free layer 13 is provided in the vicinity of the magnetization free layer (memory layer) 5, and the magnetization free layer (memory layer) 5 is dynamically changed by the magnetic coupling force. Damping to However, if the spin torque due to the spin-polarized current directly acts on the spin torque free layer 13, the magnetization direction itself of the spin torque free layer 13 also changes excessively, and the magnetization of the spin torque free layer 13 serves as a damper. Can no longer be applied. Therefore, the spin torque free layer 13 must be configured so that the spin torque caused by the spin polarized current does not act directly.

  Therefore, in the MTJ element 10, as shown in FIG. 1, the lead conductive layer 11 is provided between the magnetization free layer (memory layer) 5 and the spin torque free layer 13. The spin-polarized current supplied from the bit line 61 flows through the connection plug 15 and the lead conductive layer and is guided to the magnetization free layer (memory layer) 5, and the spin-polarized current flows without passing through the spin torque free layer 13. . For this reason, the spin torque due to the spin-polarized current does not directly act on the spin torque free layer 13.

  In the MTJ element 10 configured in this way, as shown in FIG. 3, the magnetization of the magnetization free layer (memory layer) 5 is completely suppressed from excessive fluctuations by the spin torque free layer 13, and is extremely less than 1 ns. Transition from a high resistance state (“anti-parallel” state) to a low resistance state (“parallel” state) in a short time. At this time, the magnetization free layer (memory layer) 5 and the spin torque free layer 13 undergo magnetization reversal at different timings. As a result, as shown in FIG. 2A, the spin-injection magnetization reversal MTJ element 10 suitable for high speed and low power consumption with few write failures and a very small write current density threshold is obtained. realizable.

  In addition, statically, the spin torque free layer 13 and the magnetization free layer (memory layer) 5 are magnetized in opposite directions and function as a magnetically coupled two-layer film, so that the magnetization free layer (memory layer) The resistance against thermal fluctuation of the recorded magnetization stored in the memory 5 is improved, and the thermal reliability as a memory is greatly improved.

  In the test shown in FIG. 2B, a write current having a pulse width of 10 ns is applied to the MTJ element 10 whose initial state is in the low resistance state (“parallel” state) in the opposite direction to the above state. Parallel ”state). The test was performed several times while gradually increasing the magnitude of the current pulse. In FIG. 2B, as in FIG. 2A, the magnitude of the current pulse is plotted on the vertical axis, and the results for 21 memory cells are shown separately.

  As in the test shown in FIG. 2A, in the lower area of FIG. 2B where the magnitude of the current pulse does not reach the threshold value, writing failed in all the memory cells. There is no failure example in the upper region of FIG. The failure example and the success example are clearly separated by the threshold value, which is a significant difference from the conventional example shown in FIG.

  On the other hand, reading of information from the MTJ element 10 is performed using the TMR effect, as in the MTJ elements 100 and 200. That is, first, a selection signal is applied to the gate electrode 55 that is a word line, and all the selection transistors 50 in a row including a desired memory cell are turned on (conductive). In accordance with this, a read voltage is applied to the bit line 61 in the column including the desired memory cell. As a result, only a desired memory cell is selected, and the difference in magnetization direction of the magnetization free layer (memory layer) 5 of the MTJ element 10 is different in the magnitude of the tunnel current flowing through the MTJ element 10 using the TMR effect. Detected as The tunnel current is taken out from the row wiring 62 to a peripheral circuit (not shown) and measured.

Embodiment 2
In the second embodiment, a spin-injection magnetization reversal MTJ element and an MRAM using this MTJ element will be mainly described as an example relating to claims 1, 3, 4, 8, and 11.

  FIG. 4 is a partial cross-sectional view showing the structure of the memory cell of the MRAM including the spin transfer magnetization switching MTJ element according to the second embodiment. As in the first embodiment, in this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, and MTJ elements 20 are arranged at the positions of their intersections, corresponding to 1 bit. A memory cell is formed.

  As shown in FIG. 4, at the center of the memory cell, in order from the bottom, the underlayer 1, the antiferromagnetic layer 2, the fixed magnetization layer 3a, the intermediate layer 3b, the reference magnetization layer 3c, the tunnel barrier layer 4, and the magnetization free layer. The (memory layer) 5 and the cap layer 6 are laminated, and the cap layer 12, the spin torque free layer 13 and the cap layer 14 surrounded by the bypass conductor 21 are further laminated thereon. The MTJ element 20 is formed.

  The MTJ element 20 according to the second embodiment is different from the MTJ element 10 in that a bypass conductor 21 as the bypass conductive member is provided instead of the lead conductive layer 11 and the connection plug 15. Since the others are the same, avoid duplication and mainly explain the differences.

  In the MTJ element 20, similarly to the MTJ element 10, the spin torque free layer 13 is provided on the magnetization free layer (memory layer) 5. The spin torque free layer 13 is magnetically coupled to the magnetization free layer (memory layer) 5 and suppresses transient fluctuations in the magnetization direction that occur when the magnetization direction of the magnetization free layer (memory layer) 5 is reversed. Cap layers 12 and 14 are provided on the lower surface and the upper surface of the spin torque free layer 13, respectively.

  The laminated body of the cap layer 12, the spin torque free layer 13 and the cap layer 14 is surrounded by a bypass conductor 21. All of these are inserted between the bit line 61 and the cap layer 6. Therefore, the bypass conductor 21 is provided in parallel to the spin torque free layer 13, and this parallel conductive path is provided between the bit line 61 that supplies the spin-polarized current and the magnetization free layer (storage layer) 5. Electrically connected. At this time, the spin torque free layer 13 is made of a magnetic material having a specific resistance value of 100 μΩcm or more, and the bypass conductor 21 is made of a conductor having a specific resistance value of 100 μΩcm or less.

  As a result, in the MTJ element 20, most of the write current supplied from the bit line 61 is guided to the magnetization free layer (memory layer) 5 via the bypass conductor 21, and only a part is slightly spin torque free. It flows to the magnetization free layer (storage layer) 5 via the layer 13. For this reason, the spin-polarized current flowing through the spin torque-free layer 13 is slightly suppressed, and spin torque that causes a practical problem does not act on the electrons in the spin-torque free layer 13.

  In the MTJ element 20 configured as described above, like the MTJ element 10, the transient characteristics when the magnetization free layer (memory layer) 5 is reversed have a spin torque free layer 13 in which a spin-polarized current does not directly act in practice. Thus, the magnetization free layer (storage layer) 5 is promptly and reliably guided to the inverted state.

  In the MTJ element 20, in addition to the effect obtained by the MTJ element 10, the lead conductive layer 11 is not necessary, and thus the area of the memory cell can be reduced. As a result, the MRAM including the MTJ element 20 can be further integrated and increased in capacity.

Embodiment 3
In the third embodiment, a spin-injection magnetization reversal MTJ element and an MRAM using this MTJ element will be mainly described as examples relating to claims 1, 5 to 8, and 11.

  FIG. 5 is a partial cross-sectional view showing the structure of an MRAM memory cell comprising an MTJ element using magnetization reversal by spin injection based on the third embodiment. As in the first embodiment, in this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, and MTJ elements 30 are arranged at the positions of their intersections, corresponding to 1 bit. A memory cell is formed.

  As shown in FIG. 5, at the center of the memory cell, there are an underlayer 1, an antiferromagnetic layer 2, a fixed magnetization layer 3a, an intermediate layer 3b, a reference magnetization layer 3c, a tunnel barrier layer 4, and a magnetization free layer in order from the bottom. (Storage layer) 5, the cap layer 31, the spin sink layer 32, the cap layer 33, the spin torque free layer 13, and the cap layer 14 are laminated to form the TMR magnetic memory element 30. The spin sink layer 32 is a layer that eliminates the spin polarization of the spin polarization current, and the cap layers 31 and 33 are laminated on the upper and lower sides thereof.

  The MTJ element 30 according to the third embodiment is different from the MTJ element 10 or the MTJ element 20 in that a spin sink layer 32 is provided instead of the lead conductive layer 11 and the connection plug 15 or the bypass conductor 21. It is. Since the others are the same, avoid duplication and mainly explain the differences.

  In the MTJ element 30, similarly to the MTJ element 10, the spin torque free layer 13 is provided on the magnetization free layer (memory layer) 5. The spin torque free layer 13 is magnetically coupled to the magnetization free layer (memory layer) 5 and suppresses transient fluctuations in the magnetization direction that occur when the magnetization direction of the magnetization free layer (memory layer) 5 is reversed. A cap layer 33 and a cap layer 14 are provided on the lower surface and the upper surface of the spin torque free layer 13, respectively.

  As a method of preventing the spin torque due to the spin-polarized current from acting on the spin torque free layer 13, there is a method of preventing the current from flowing to the spin torque free layer 13 as in the first and second embodiments. There is a method of flowing the current to the spin torque free layer 13 after eliminating the spin polarization of the spin polarized current. In the third embodiment, this method is adopted, and a spin sink layer 32 is provided between the magnetization free layer (memory layer) 5 and the spin torque free layer 13 to eliminate the spin polarization of the spin polarization current.

  The density of current having an upward spin ↑ and the density of current having a downward spin ↓ flowing through the magnetization free layer (memory layer) 5 are defined as J ↑ and J ↓, respectively. The sum of electrons as charged particles is represented by a load current (J ↑ + J ↓), and the sum of spin particles is represented by a spin current (J ↑ −J ↓). The spin torque acts on the magnetic material because the spin current flows into the magnetic material. The distance at which the magnitude of the spin current is 1 / e is called the spin diffusion length, and the MTJ element uses the fact that the spin diffusion length is longer than the mean free path in the nm size region.

  In other words, even if the load current flows, the spin torque does not act unless the spin current flows. A material with an extremely short spin diffusion length acts as a spin-sink (Y. Tserkovnyak and A. Brataas, “Spin pumping and magnetization dynamics in metallic multilayers”, Phys. Rev. B, 66, 224403 (2002). )reference.). Therefore, in order to attenuate the spin current, the spin sink layer 32 is made of the group consisting of osmium Os, iridium Ir, rhenium Re, platinum Pt, ruthenium Ru, tungsten W, niobium Nb, and zirconium Zr having a short spin diffusion length. A layer containing at least one selected element may be used, and this layer may be sandwiched between the magnetization free layer (memory layer) 5 and the spin torque free layer 13.

  The film thickness of the spin sink layer 32 needs to be long enough to attenuate the spin current, approximately 2 nm or more. When the spin sink layer 32 is brought into direct contact with the magnetization free layer (memory layer) 5 and the spin torque free layer 13, the spin sink layer 32 inhibits the spin current in the magnetization free layer (memory layer) 5 from being adversely affected. May occur. In order to prevent this, it is preferable to sandwich the cap layers 31 and 33 between the spin sink layer 32 and the magnetization free layer (memory layer) 5 and the spin torque free layer 13.

  The cap layers 31 and 33 have at least one selected from the group consisting of silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, hafnium, cobalt, iron, nickel, and manganese having a long spin diffusion length. It is preferable that the layer contains an element. In order to prevent the adverse effect of the spin sink layer 32, the film thickness of the cap layers 31 and 33 needs to be at least 0.1 nm or more.

  In the MTJ element 30 configured as described above, like the MTJ element 10, the transient characteristics when the magnetization free layer (memory layer) 5 is reversed have a spin torque free layer 13 to which a spin-polarized current does not directly act in practice. Thus, the magnetization free layer (storage layer) 5 is promptly and reliably guided to the inverted state.

  In the MTJ element 30, in addition to the effects obtained by the MTJ element 10 or the MTJ element 20, the connection plug 15 and the lead conductive layer 11 or the bypass conductor 21 are not required. For this reason, the mask for these formation is not required and manufacturing cost can be reduced. Further, since the memory cell area can be reduced, the capacity of the MRAM composed of MTJ elements can be further increased.

Embodiment 4
In the fourth embodiment, a spin-injection magnetization reversal MTJ element and an MRAM using this MTJ element will be mainly described as examples relating to claims 1 and 8 to 11.

  FIG. 6 is a partial cross-sectional view showing the structure of a memory cell in an MRAM composed of a spin transfer magnetization switching MTJ element according to the fourth embodiment. As in the first embodiment, in this MRAM, row wirings (word lines) and column wirings (bit lines) are arranged in a matrix, and MTJ elements 40 are arranged at the positions of their intersections, corresponding to 1 bit. A memory cell is formed.

  As shown in FIG. 6, at the center of the memory cell, in order from the bottom, the underlayer 1, the antiferromagnetic layer 2, the fixed magnetization layer 3a, the intermediate layer 3b, the reference magnetization layer 3c, the tunnel barrier layer 4, and the magnetization free layer (Storage layer) 5a, intermediate layer 41, magnetization free layer (storage layer) 5b, cap layer 31, spin sink layer 32, cap layer 33, spin torque free layer 13a, intermediate layer 42, spin torque free layer 13b, and cap The TMR magnetic memory element 40 is formed by laminating the layers 14.

  The TMR magnetic memory element 40 is different from the TMR magnetic memory element 30 of the third embodiment in that the magnetization free layer (memory layer) 5 and the spin torque free layer 13 are provided in a multilayer structure.

  One of the gist of the present invention is to dynamically damp the dynamic behavior of the magnetization of the magnetization free layer (memory layer) 5 with the dynamic behavior of the magnetization of the spin torque free layer 13. For this purpose, the dynamic characteristics of the magnetization of the magnetization free layer (storage layer) 5 and the magnetization of the spin torque free layer 13 must be completely controlled by the process conditions. One method for controlling the basic characteristics of the magnetic material including the damping constant is to configure the magnetic layer not with a single-layer magnetic material but with a multilayer magnetic material with a nonmagnetic intermediate layer interposed therebetween. If the grain size and the coupling constant between grains can be controlled by multilayering, a desired dynamic behavior suitable for a spin injection magnetization switching MTJ element can be realized.

  At this time, the magnetization free layer (memory layer) 5 is composed of the multilayer films 5a and 5b separated by the intermediate layer 41 and ferromagnetically coupled. The intermediate layer 41 has a long spin diffusion length, silver, copper, chromium, gold And at least one element selected from the group consisting of vanadium, titanium, rhodium, thallium, and hafnium.

  The spin torque free layer 13 is composed of multilayer films 13a and 13b separated by an intermediate layer 42 and ferromagnetically coupled. The intermediate layer 42 has a long spin diffusion length, such as silver, copper, chromium, gold, vanadium, titanium, It is preferable to contain at least one element selected from the group consisting of rhodium, thallium, and hafnium.

  In the MTJ element 40 configured as described above, as in the MTJ element 30, the transient characteristics when the magnetization free layer (memory layer) 5 is inverted are substantially the same as the spin torque free layer 13 in which the spin-polarized current does not act directly. Thus, the magnetization free layer (storage layer) 5 is promptly and reliably guided to the inverted state.

  In the MTJ element 40, since the dynamic behavior of the magnetization of the magnetization free layer (storage layer) 5 and the magnetization of the spin torque free layer can be improved, the effect obtained by the MTJ element 30 can be further improved, and the spin injection magnetization reversal is achieved. The MRAM including the MTJ element 40 can further reduce current consumption and speed. A similar improvement method may be applied to the MTJ element 10 of the first embodiment or the MTJ element 20 of the second embodiment.

  As mentioned above, although this invention was demonstrated based on embodiment, it cannot be overemphasized that this invention is not limited to these examples at all, and can be suitably changed in the range which does not deviate from the main point of invention.

  According to the present invention, the spin injection magnetization reversal improves the transient characteristics at the time of writing, reduces the number of write failures, the threshold value of the write current density is small, enables high integration, high speed, and low power consumption. A type MTJ element and a magnetic memory device using the same can be provided and contributed to its practical use.

1 is a partial cross-sectional view showing a structure of a memory cell of an MRAM composed of a spin-injection magnetization switching MTJ element based on Embodiment 1 of the present invention. 4 is a graph showing an example of a result of a write test performed on an MRAM composed of a plurality of memory cells. 4 is a graph showing the write transient characteristics of the spin injection MTJ element. It is a fragmentary sectional view which shows the structure of the memory cell of MRAM which consists of a spin injection magnetization reversal MTJ element based on Embodiment 2 of this invention. It is a fragmentary sectional view which shows the structure of the memory cell of MRAM which consists of a spin injection magnetization reversal MTJ element based on Embodiment 3 of this invention. It is a fragmentary sectional view which shows the structure of the memory cell of MRAM which consists of a spin injection magnetization reversal MTJ element based on Embodiment 4 of this invention. FIG. 2 is an explanatory diagram (a) showing a basic structure of an MTJ element, a read operation of stored information, and a partial perspective view (b) showing an example of a structure of a memory cell of an MRAM comprising an MTJ element. It is a fragmentary sectional view which shows the structure of the memory cell of MRAM which consists of a spin injection magnetization reversal MTJ element shown by below-mentioned patent document 3. FIG. It is a graph which shows an example of the result of which the inventor performed the write test with respect to the conventional spin transfer magnetization reversal MRAM which consists of a plurality of memory cells.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Underlayer, 2 ... Antiferromagnetic layer, 3a ... Fixed magnetization layer, 3b ... Intermediate layer, 3c ... Reference magnetization layer,
4 ... Tunnel barrier layer, 5, 5a, 5b ... Magnetization free layer (memory layer), 6 ... Cap layer,
DESCRIPTION OF SYMBOLS 10 ... Spin injection magnetization reversal MTJ element, 11 ... Lead-out conductive layer, 12 ... Cap layer,
13, 13a, 13b ... spin torque free layer, 14 ... cap layer, 15 ... connection plug,
20 ... Spin injection magnetization reversal MTJ element, 21 ... Bypass conductor,
30 ... Spin injection magnetization reversal MTJ element, 31 ... Cap layer, 32 ... Spin sink layer,
33 ... cap layer, 40 ... spin injection magnetization reversal MTJ element, 41, 42 ... intermediate layer,
50 ... selection transistor, 51 ... semiconductor substrate, 51a ... well region,
52 ... Gate insulating film, 53 ... Drain electrode, 54 ... Drain region, 55 ... Gate electrode,
56 ... Source region, 57 ... Source electrode, 61 ... Bit line, 62 ... Row wiring,
DESCRIPTION OF SYMBOLS 100 ... MTJ element, 103 ... Magnetization fixed layer, 104 ... Tunnel barrier layer,
105 ... free magnetization layer (memory layer), 106 ... extraction electrode layer,
107: Read connection plug, 110: Selection transistor, 111: Semiconductor substrate,
114... Drain region, 115... Gate electrode (read word line),
116: Source region, 121: Write bit line, 122: Write word line,
123: Read bit line, 124 sense line, 200: Spin injection magnetization reversal MTJ element

Claims (14)

A magnetization free layer that can change the magnetization direction and stores the magnetization direction as information; and a magnetization fixed layer that consists of a ferromagnetic conductor and the magnetization direction is fixed. In a magnetic memory element configured to write information by magnetizing the magnetization free layer in a predetermined direction by a spin-polarized current flowing through the ferromagnetic conductor layer, and to read the written information using a magnetoresistive effect,
A magnetic coupling body that is magnetically coupled to the magnetization free layer and suppresses fluctuations in the magnetization direction that occurs when the magnetization direction of the magnetization free layer is reversed;
A magnetic memory element configured to suppress the spin-polarized current from flowing into the magnetic coupling body.   The extraction conductive layer is provided between the magnetization free layer and the magnetic coupling body, and the extraction conductive layer is electrically connected to a control circuit that supplies the spin-polarized current. Magnetic memory element.   A bypass conductive member is provided in parallel to the magnetic coupling body, and the parallel conductive path is electrically connected between the control circuit for supplying the spin-polarized current and the magnetization free layer, and the spin-polarized member is provided. The magnetic memory element according to claim 1, wherein a pole current is configured to flow mainly through the bypass conductive member.   The magnetic memory element according to claim 3, wherein the magnetic coupling body is made of a magnetic material having a specific resistance value of 100 μΩcm or more, and the bypass conductive member is made of a conductor having a specific resistance value of 100 μΩcm or less.   The spin sink layer that eliminates the spin polarization of the spin-polarized current and a cap layer are provided between the magnetization free layer and the magnetic coupling body in a stacked manner. Magnetic memory element.   The spin sink layer contains at least one element selected from the group consisting of osmium Os, iridium Ir, rhenium Re, platinum Pt, ruthenium Ru, tungsten W, niobium Nb, and zirconium Zr having a short spin diffusion length. The magnetic memory element according to claim 5.   The cap layer has a long spin diffusion length, such as silver Ag, copper Cu, chromium Cr, gold Au, vanadium V, titanium Ti, rhodium Rh, thallium Ta, hafnium Hf, cobalt Co, iron Fe, nickel Ni, and manganese Mn. The magnetic memory element according to claim 5, comprising at least one element selected from the group consisting of:   The magnetic memory element according to claim 1, wherein the magnetic coupling body contains at least one element selected from the group consisting of cobalt, nickel, iron, and manganese.   The magnetization free layer is formed of a multilayer film which is separated by an intermediate layer and ferromagnetically coupled, and the intermediate layer is made of silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, and hafnium having a long spin diffusion length. The magnetic memory element according to claim 1, comprising at least one element selected from the group consisting of:   The magnetic coupling body is made of a multilayer film that is separated by an intermediate layer and ferromagnetically coupled, and the intermediate layer is made of silver, copper, chromium, gold, vanadium, titanium, rhodium, thallium, and hafnium having a long spin diffusion length. The magnetic memory element according to claim 1, comprising at least one element selected from the group consisting of:   The magnetization fixed layer and the magnetization free layer are stacked with a tunnel barrier layer, which is a thin insulating layer, sandwiched therebetween, and configured as a tunnel magnetoresistive element, and information is transferred by a tunnel current flowing through the tunnel barrier layer. The magnetic memory element according to claim 1, wherein writing and reading are performed.   It has a memory part which consists of a magnetic memory element given in any 1 paragraph of Claims 1-11, and was provided with wiring and a control circuit for writing in and / or reading out information to a predetermined magnetic memory element , Magnetic memory device.   The magnetic memory device according to claim 12, which is configured as a magnetic random access memory. First row wirings and column wirings are arranged in a matrix, and the magnetic memory elements and selection transistors for selecting the magnetic memory elements are arranged at the positions of their respective intersections. Formed,
When writing or reading information to or from a predetermined memory cell,
When a selection signal is applied to the first row wiring of the row in which this memory cell is arranged, all the selection transistors in that row are turned on,
A write voltage or a read voltage is applied to the column wiring of the column in which the memory cell is arranged,
As a result of the above, writing or reading is performed by the current flowing between the column wiring and the second row wiring through the magnetic memory element and the selection transistor of the memory cell.
The magnetic memory device according to claim 13.