JP2013197518A - Magnetic tunnel junction element and magnetic memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic tunnel junction element having a resistance change function with less degradation.SOLUTION: A magnetic tunnel junction element according to an embodiment includes: first and second ferromagnetic layers; a tunnel barrier layer provided between the first ferromagnetic layer and the second ferromagnetic layer; and a resistance change layer provided between the tunnel barrier layer and the second ferromagnetic layer and having a lamination structure composed of an ion source layer, which contains a metal element functioning as an ion source, and an ion conduction layer, wherein a thickness of the resistance change layer is equal to or less than a spin relaxation length of the metal element.

Description

  Embodiments described herein relate generally to a magnetic tunnel junction device and a magnetic memory.

  A magnetoresistive memory (MRAM (Magnetic Random Access Memory)) that uses a magnetic tunnel junction element (MTJ element) as a memory element can be rewritten indefinitely and has an infinite length of data retention characteristics. Attention has been paid.

  The MTJ element has a structure in which a tunnel barrier layer is sandwiched between ferromagnetic layers, and is a resistance change element in which the resistance changes depending on the magnetization directions of the upper and lower ferromagnetic layers. When the magnetizations of the upper and lower ferromagnetic layers are parallel, the resistance is low, and when the magnetization is antiparallel, the resistance is high. Therefore, “parallel” and “antiparallel” can be distinguished by measuring the resistance of the MTJ element. Since the magnetization of the ferromagnetic layer does not change permanently unless a magnetic field or current is applied from the outside, “parallel” or “antiparallel” does not change permanently. Therefore, the MTJ element can be used as a storage element of a nonvolatile memory.

  As described above, the MTJ element is a so-called two-terminal variable resistance element. A word line in which a plurality of conductive lines are arranged in parallel on a plane and a bit line in which a plurality of conductive lines are arranged in parallel in a direction intersecting the word line are superimposed on the word line, and the intersection of the word line and the bit line In (cross point), a word line and a bit line are connected by a resistance change element having two terminals, whereby a so-called cross point type large capacity memory can be configured. By applying a voltage to the word line (or bit line) and reading the current flowing through the bit line (or word line), the resistance state of the resistance change element at the intersection can be read. A cross-point type memory can be easily densified because conductive lines can be formed in a line and space structure. Therefore, a cross-point type MRAM in which MTJ elements are arranged on a cross point can be expected as a next-generation large-capacity nonvolatile memory.

  However, the cross point type MRAM has the following problems caused by the MTJ element.

  First, the current-voltage characteristics of the MTJ element are symmetric with respect to positive and negative voltages. Further, the ratio (MR) ratio between the resistance in the “parallel” state and the resistance in the “anti-parallel” state is about 600% at the maximum, which is not different by one digit. That is, the current cannot be cut off even in a high resistance state, and a relatively large current flows.

  On the other hand, in a cross-point type large-capacity memory, a resistance is read by applying a voltage between one bit line of a plurality of bit lines and one word line of a plurality of word lines. To read data. In this case, a voltage is applied to all MTJ elements on the same bit line or the same word line.

  As described above, the MTJ element flows regardless of the direction of the voltage, and cannot interrupt the current in the high resistance state. Therefore, the MTJ element is selected between the selected bit line and the selected word line. In addition to the MTJ element, there are many conduction paths, that is, sneak currents, through other bit lines and word lines. For this reason, erroneous reading tends to occur during reading.

In order to avoid this problem, in the MRAM, a selection transistor is provided in series with the MTJ element. Only when it is desired to access the MTJ element, the transistor is opened and the information of the MTJ element is read or written. However, since the area of the transistor is large, if a select transistor is provided in each memory cell in addition to the MTJ element, the area of the memory cell increases and it is difficult to increase the capacity. If the minimum processing dimension is F, an area of 8F ² or more is required per cell.

On the other hand, a method of suppressing a sneak current by connecting a diode to the MTJ element and preventing a current from flowing in the opposite direction is also conceivable. Since the diode can be formed by being stacked on the MTJ element, this method can reduce the size to about 4F ² per cell. However, since the current is one-way in the diode, it is impossible to rewrite the MTJ element using the spin injection writing method. Therefore, the only way to rewrite the magnetization direction of the MTJ element is to generate a magnetic field locally from a separately provided conductive line. However, this greatly increases the power consumption.

  Therefore, it is desirable to have a resistance change switch function that operates as an MTJ element only when a certain voltage is applied to the MTJ element.

  An MTJ element having a resistance change switch function is known. This MTJ element having a resistance change switch function is obtained by adding a resistance change function to a tunnel barrier layer. However, since the resistance change of the tunnel barrier layer is used, the MTJ element may not exhibit the magnetic resistance due to the deterioration of the tunnel barrier layer.

JP 2009-59807 A US Patent Application Publication No. 2009/0179245

  The present embodiment provides a magnetic tunnel junction element and a magnetic memory having a resistance change function with little deterioration.

  The magnetic tunnel junction device according to the present embodiment includes a first and second ferromagnetic layers, a tunnel barrier layer provided between the first ferromagnetic layer and the second ferromagnetic layer, and the tunnel barrier layer. A variable resistance layer provided between the second ferromagnetic layer and having a laminated structure of an ion source layer containing a metal element serving as an ion source and an ion conductive layer, and the thickness of the variable resistance layer is: It is less than or equal to the spin relaxation length of the metal element.

Sectional drawing which shows the magnetic tunnel junction element by 1st Embodiment. Sectional drawing which shows the magnetic tunnel junction element by the modification of 1st Embodiment. The figure which shows the electric current-voltage characteristic of a resistance change layer. FIGS. 3A and 3B are diagrams illustrating reading and writing in a low resistance state and a high resistance state, respectively. 4A and 4B are waveform diagrams illustrating a reading method. 5A and 5B are waveform diagrams illustrating a writing method. Sectional drawing which shows the magnetic tunnel junction element by 2nd Embodiment. FIGS. 7A and 7B are diagrams illustrating a writing method according to the second embodiment. FIGS. 8A and 8B are diagrams illustrating a writing method according to the second embodiment. The figure which shows the electric current-voltage characteristic of a resistance change layer. Sectional drawing which shows the magnetic tunnel junction element by the modification of 2nd Embodiment. The perspective view which shows the magnetic memory by 3rd Embodiment. The perspective view which shows the magnetic memory by the 1st modification of 3rd Embodiment. The perspective view which shows the magnetic memory by the 2nd modification of 3rd Embodiment. The perspective view which shows the magnetic memory by the 3rd modification of 3rd Embodiment. The perspective view which shows the magnetic memory by 4th Embodiment. The perspective view which shows the magnetic memory by the 1st modification of 4th Embodiment. The perspective view which shows the magnetic memory by the 2nd modification of 4th Embodiment.

  Embodiments will be described below with reference to the drawings.

(First embodiment)
A magnetic tunnel junction element (hereinafter also referred to as an MTJ element) according to the first embodiment is shown in FIG. 1A. The MTJ element 1 according to the first embodiment has a structure in which a ferromagnetic layer 11, a tunnel barrier layer 13, an ion conductive layer 15a, an ion source layer 15b, and a ferromagnetic layer 17 are stacked in this order. A structure in which the layers are stacked in the reverse order, that is, a structure in which the ferromagnetic layer 17, the ion source layer 15b, the ion conductive layer 15a, the tunnel barrier layer 13, and the ferromagnetic layer 11 are stacked in this order may be employed. . The ion conductive layer 15 a and the ion source layer 15 b constitute the resistance change layer 15.

The ferromagnetic layer 11 is Co, Fe, Ni, or an alloy containing these. For example, a ferromagnetic material such as CoFeB or CoFe can be used. Here, as an example, it is assumed that the ferromagnetic layer 11 is CoFeB. The tunnel barrier layer 13 is an insulator such as MgO or Al ₂ O ₃ and has a thickness of 1 nm to ₂ nm, for example. Here, as an example, it is assumed that the tunnel barrier layer 13 is a 1 nm MgO layer. Ion conducting layer 15a, for example amorphous silicon (hereinafter, a-Si also called) amorphous _{semiconductors,} SiO 2, HfOx, AlOx, metal oxides, such as TaOx, or GeS, _GeSe, Ag 2 S, chalcogenide such as CuS It is. Here, as an example, it is assumed that the ion conductive layer 15a is a-Si. As will be described below, the ion source layer 15b needs to contain a metal that conducts electron spin. The metal that conducts electron spin is, for example, Ag or Cu. Here, as an example, it is assumed that the ion source layer 15b is Ag or a metal containing Ag. As with the ferromagnetic layer 11, Co, Fe, Ni, or an alloy containing these can be used for the ferromagnetic layer 17. For example, a ferromagnetic material such as CoFeB or CoFe can be used. Here, as an example, it is assumed that the ferromagnetic layer 17 is CoFeB.

  As shown in FIG. 2, the a-Si ion conduction layer 15a connected to the Ag ion source layer 15b transitions from a high resistance state to a low resistance state when a voltage of a certain level or more is applied. At this time, the resistance shows a large change of 3 digits or more. However, when the applied voltage is returned to zero volts, the state transitions to the high resistance state again. This change occurs symmetrically regardless of whether the voltage is positive or negative.

  This resistance change occurs by the following mechanism. The a-Si ion conductive layer 15a is in contact with the Ag ion source layer 15b, and Ag ions exist inside the ion conductive layer 15a. When a voltage higher than a certain level (hereinafter referred to as a set voltage) is applied, Ag ions move to form a conduction path called a filament in which a current flows inside the ion conduction layer 15a. Since Ag inside a-Si easily diffuses, the Ag filament immediately collapses when the application of voltage is stopped. Therefore, when a certain voltage is applied, an Ag filament is formed and the resistance is rapidly lowered. However, when the voltage is returned to zero volts, the Ag filament collapses and the resistance is increased.

  Since the resistance change layer 15 has an asymmetric structure in which the upper layer and the lower layer are different from each other, the current-voltage characteristics may be asymmetrical depending on whether the voltage is positive or negative. Ag supply is performed from all directions by diffusing inside. Therefore, as a result, a current-voltage characteristic that is symmetric with respect to positive and negative voltages can be obtained. In order to further improve the symmetry, Ag, which is a metal of the ion source layer 15b, may be diffused in the ion conductive layer 15a of a-Si by performing heat treatment or the like in advance.

  In the following description, the ferromagnetic layer 11 is a reference layer (fixed layer) whose magnetization direction is fixed, and the ferromagnetic layer 17 is a storage layer (free layer) whose magnetization direction is variable. However, the ferromagnetic layer 17 may be a reference layer (fixed layer) whose magnetization direction is fixed, and the ferromagnetic layer 11 may be a storage layer (free layer) whose magnetization direction is variable. The direction of magnetization being variable means that the direction of magnetization of the ferromagnetic layer 11 serving as the reference layer is unchanged before and after writing when a write current is passed through the MTJ element. The variable magnetization direction means that the magnetization direction of the ferromagnetic layer 17 serving as the storage layer is variable when a write current is passed through the MTJ element. Further, the magnetization directions of the ferromagnetic layer 11 and the ferromagnetic layer 17 may be either parallel to the film surface or perpendicular to the film surface. Here, the film surface means a surface perpendicular to the stacking direction of the elements. A material having high perpendicular magnetic anisotropy is used for the ferromagnetic layer whose magnetization direction is perpendicular to the film surface.

(Reading method)
Next, a reading method will be described.

  Consider a case where the magnetization of the ferromagnetic layer 11 and the magnetization of the ferromagnetic layer 17 are parallel as shown in FIG. When a set voltage is applied between the ferromagnetic layers 11 and 17, an Ag filament 16 is formed in the a-Si ion conductive layer 15a. As described above, electron spin can be conducted in Ag. Accordingly, electrons in the ferromagnetic layer 17 are conducted through the Ag ion source layer 15b and the Ag filament 16 while maintaining the spin, and reach the tunnel barrier layer 13 made of MgO. Electrons that reach the MgO tunnel barrier layer 13 tunnel to the ferromagnetic layer 11. However, since the magnetizations of the ferromagnetic layer 15 and the ferromagnetic layer 11 are parallel, they operate as MTJ elements in a parallel state. The parallel magnetoresistance is low.

  Conversely, as shown in FIG. 3B, consider the case where the magnetization of the ferromagnetic layer 11 and the magnetization of the ferromagnetic layer 17 are antiparallel. In this case, when a set voltage is applied between the ferromagnetic layers 11 and 17, Ag filaments 16 are also formed inside the a-Si ion conductive layer 15a, and electrons in the ferromagnetic layer 17 remain MgO while maintaining spin. Reaches the tunnel barrier layer 13 and tunnels to the ferromagnetic layer 11. At this time, since the magnetization of the ferromagnetic layer 17 is antiparallel to the magnetization of the ferromagnetic layer 11, it operates as an MTJ element in an antiparallel state. The magnetoresistance in the antiparallel state is high.

  As described above, the magnetization directions of the ferromagnetic layer 11 and the ferromagnetic layer 17 can be “read” by the level of resistance.

The reading process described above is shown in FIGS. 4 (a) and 4 (b). FIGS. 4A and 4B are waveform diagrams showing voltages and currents applied between the ferromagnetic layers 11 and 17 in the reading process, respectively. First, a set voltage is applied to form an Ag filament 16 in the a-Si ion conductive layer 15a (time t ₁ ). Since the Ag filament 16 is formed in about several tens of nanoseconds, an application time of about 10 nanoseconds to 100 nanoseconds is sufficient. During application of the set voltage, the current flowing in the MTJ element is limited to a predetermined range (for example, 8 μA to 12 μA) by an external circuit, and the current flows excessively, so that the magnetization of the ferromagnetic layers 11 and 17 This prevents the orientation from changing or the a-Si ion conductive layer 15a from being destroyed.

Next, a voltage for reading is applied (time t ₂ , t ₃ ). In order to prevent the Ag filament 16 from collapsing, it is desirable to continuously apply a voltage (set voltage) for forming the Ag filament 16 after application. This read voltage may be lower than the set voltage. When the read voltage is lower than the set voltage, it is difficult to limit the current flowing through the element during reading, and the reading can be performed more accurately. The current flows to the external readout circuit, and charges are accumulated in the readout circuit and the current is also lowered.

  Regardless of the magnetization directions of the ferromagnetic layer 11 and the ferromagnetic layer 17, the Ag filament 16 is not formed inside the ion conductive layer 15a unless a voltage higher than the set voltage is applied. Therefore, it does not operate as an MTJ element. Therefore, in the cross-point structure, if a set voltage is applied between the selected word line and the selected bit line and a voltage lower than the set voltage is applied to the non-selected word line and the non-selected bit line, The MTJ element of the selected cell remains insulative and no current flows, and the problem of erroneous reading, which is a problem with the cross-point structure, is avoided. Even if the filament is formed by applying a voltage higher than the set voltage, if the voltage application is stopped, the filament collapses and becomes insulating. Therefore, the selected MTJ element also becomes insulating after reading is completed. Then, when reading another MTJ element later, erroneous reading is not caused.

(Writing method)
Next, a writing method will be described with reference to FIGS. 5 (a) and 5 (b). FIGS. 5A and 5B are waveform diagrams showing voltages and currents applied between the ferromagnetic layers 11 and 17 in the writing process, respectively.

Consider a case where the magnetization direction of the ferromagnetic layer 17 is parallel to the magnetization direction of the ferromagnetic layer 11 as shown in FIG. In this case, the writing in which the magnetization direction of the ferromagnetic layer 17 is reversed to be antiparallel to the magnetization direction of the ferromagnetic layer 11 is performed as follows. First, as current flows through the ferromagnetic layer 17 of a ferromagnetic layer 11, applying a set voltage between the ferromagnetic layers 11, 17 (see time _{t 1} in FIG. 5 (a), 5 (b )). Then, an Ag filament 16 is formed in the ion conductive layer 15a. Even after the Ag filament is formed, the set voltage is continuously applied. Then, a write current is passed from the ferromagnetic layer 11 to the ferromagnetic layer 17 via the tunnel barrier layer 13 and the resistance change layer 15 (time t ₂ ). At this time, electrons flow from the ferromagnetic layer 17 to the ferromagnetic layer 11 through the resistance change layer 15 and the tunnel barrier layer 13. The electrons are spin-polarized when passing through the ferromagnetic layer 17. Then, the spin-polarized electrons flow to the ferromagnetic layer 11 through the ion source layer 15b, the Ag filament 16 of the ion conductive layer 15a, and the tunnel barrier layer 13. Electrons having a spin in the same direction as the magnetization of the ferromagnetic layer 11 pass through the ferromagnetic layer 11. Electrons having a spin antiparallel to the magnetization of the ferromagnetic layer 11 are reflected at the interface between the ferromagnetic layer 11 and the tunnel barrier layer 13, and are strongly transmitted through the tunnel barrier layer 13, the Ag filament 16, and the ion source layer 15b. It flows into the magnetic layer 17. Then, the direction of magnetization of the ferromagnetic layer 17 is reversed by the spin transfer torque, and the direction of magnetization of the ferromagnetic layer 17 becomes antiparallel to the direction of magnetization of the ferromagnetic layer 11. Thereafter, the write current is set to 0, and the write is finished (time t ₃ ).

Next, consider a case where the magnetization direction of the ferromagnetic layer 17 is antiparallel to the magnetization direction of the ferromagnetic layer 11 as shown in FIG. In this case, the writing in which the magnetization direction of the ferromagnetic layer 17 is reversed to be parallel to the magnetization direction of the ferromagnetic layer 11 is performed as follows. First, as current flows through the ferromagnetic layer 11 of a ferromagnetic layer 17, applying a set voltage between the ferromagnetic layers 11, 17 (see time _{t 1} in FIG. 5 (a), 5 (b )). Then, an Ag filament 16 is formed in the ion conductive layer 15a. Even after the Ag filament is formed, the set voltage is continuously applied. Then, a write current is passed from the ferromagnetic layer 17 to the ferromagnetic layer 11 through the resistance change layer 15 and the tunnel barrier layer 13. At this time, electrons flow from the ferromagnetic layer 11 to the ferromagnetic layer 17 through the tunnel barrier layer 13 and the resistance change layer 15. These electrons are spin-polarized when passing through the ferromagnetic layer 11. The spin-polarized electrons flow to the ferromagnetic layer 17 via the tunnel barrier layer 13, the Ag filament 16 of the ion conductive layer 15a, and the ion source layer 15b. Electrons having a spin in the same direction as the magnetization of the ferromagnetic layer 17 pass through the ferromagnetic layer 17. The direction of magnetization of the ferromagnetic layer 17 is reversed by the spin transfer torque caused by electrons having spins antiparallel to the magnetization of the ferromagnetic layer 17, and the direction of magnetization of the ferromagnetic layer 17 is changed to the direction of magnetization of the ferromagnetic layer 11. Parallel.

In the MTJ element of this embodiment, the spin is conducted through the filament 16 inside the ion source layer 15b and the ion conductive layer 15a. Therefore, it is desirable that the thickness of the ion source layer 15b and the ion conductive layer 15a is not more than the spin relaxation length. When the ion source layer 15b is Ag, the spin relaxation length is about 300 nm. Therefore, the total thickness of the Ag ion source layer 15b and the a-Si ion conductive layer 15a is preferably 300 nm or less. The resistance change of a-Si / Ag occurs when a-Si is several nm to several tens of nm. When SiO ₂ is used as the ion conductive layer 15a and Ag is used as the ion source layer 15b, the resistance change of the resistance change layer 15 made of SiO ₂ / Ag occurs in the SiO ₂ layer 15a of several nm. When other oxide films and chalcogenides are used as the ion conductive layer, the resistance change is generally about 100 nm or less. On the other hand, the ion source layer 15b is a layer for supplying an ion source for forming filaments such as Ag and Cu, and has almost no sensitivity to the film thickness, and operates without any problem at about several nm. Therefore, the total film thickness of the ion source layer 15b and the ion conductive layer 15a is several tens of nm or less, and can be made sufficiently thinner than the spin relaxation length.

  Usually, it is preferable that the area of the MTJ element is small. This is because the smaller the area, the larger the ratio of the resistance of the MTJ element to the total resistance of the system, so that reading becomes easier. In this embodiment, the electron spin tunnels from the tip of the Ag filament 16 through the MgO tunnel barrier layer 13 to the ferromagnetic layer 11. Since the Ag filament 16 has a width of 10 nm or less, the area of the tunnel junction is extremely small, and the structure is more suitable for MRAM than a conventional MTJ element having a tunnel junction area of about 50 nm.

  In the present embodiment, since the tunnel barrier layer and the resistance change layer of the MTJ element are separate layers, the tunnel barrier layer does not deteriorate as in the conventional case.

  In the first embodiment, as shown in FIG. 1B, the ion conductive layer 15a may be disposed on the ferromagnetic layer 17 side, and the ion source layer 15b may be disposed on the tunnel barrier layer 13 side.

  As described above, according to the present embodiment, a magnetic tunnel junction element having a resistance change function with little deterioration can be obtained.

(Second Embodiment)
An MTJ element according to the second embodiment is shown in FIG. The MTJ element 1A according to the second embodiment is the same as the MTJ element 1 according to the first embodiment shown in FIG. 1A or FIG. 1B or a modification thereof, but on the opposite side of the ferromagnetic layer 17 from the ion source layer 15b. 19 and a nonmagnetic metal layer 18 is provided between the ferromagnetic layer 17 and the ferromagnetic layer 19. In FIG. 6, in the MTJ element of the first embodiment shown in FIG. 1A, a ferromagnetic layer 19 is provided on the opposite side of the ferromagnetic layer 17 from the ion source layer 15b. A nonmagnetic metal layer 18 is provided between the layer 19 and the layer 19. The ferromagnetic layer 19 has a fixed magnetization direction and is antiparallel to the magnetization direction of the ferromagnetic layer 11. The nonmagnetic metal layer 18 prevents magnetic coupling between the ferromagnetic layer 17 and the ferromagnetic layer 19 and has a thickness of about several nm. In the second embodiment, the ion conductive layer 15a may be disposed on the ferromagnetic layer 17 side and the ion source layer 15b may be disposed on the tunnel barrier layer 13 side, as in the first embodiment.

  The separation of the fixed layer and the storage layer can be made simply by changing the material. In the case of the present embodiment, as the material of the ferromagnetic layer 17 serving as the memory layer, a material that is more easily reversed in magnetization than the material of the ferromagnetic layers 11 and 19 serving as the fixed layer, for example, a material having a small coercive force, or a friction coefficient ( Use a material with a small damping factor. Alternatively, the same material can be made as follows. That is, the thickness of the ferromagnetic layers 11 and 19 is set to be thicker than that of the ferromagnetic layer 17. The ease of magnetization reversal of the ferromagnetic layer is determined by the volume of the ferromagnetic layer. When the cross-sectional area is the same, it is determined by the film thickness. For example, when CoFeB is used as the ferromagnetic layers 11, 17, and 19, the ferromagnetic layer 17 has a thickness of 2 nm to 3 nm, and the ferromagnetic layers 11 and 19 have a thickness of 5 nm to 10 nm or more. Preferably there is.

(Writing method)
A method of writing data to the MTJ element of this embodiment will be described with reference to FIGS. 7 (a) to 8 (b). First, it is assumed that the magnetization direction of the magnetization reversible ferromagnetic layer 17 is parallel to the magnetization direction of the ferromagnetic layer 11, that is, antiparallel to the magnetization direction of the ferromagnetic layer 19 (FIG. 7A). When a positive voltage equal to or higher than the set voltage is applied to the ferromagnetic layer 11 with respect to the ferromagnetic layer 19, an Ag filament 16 is formed in the ion conductive layer 15 a, and electrons pass from the ferromagnetic layer 19 through the nonmagnetic metal layer 18. It flows into the ferromagnetic layer 17. Since the direction of magnetization of the ferromagnetic layer 17 is antiparallel to the direction of magnetization of the ferromagnetic layer 19, a spin opposite to the direction of magnetization of the ferromagnetic layer 17 flows from the ferromagnetic layer 19 and receives spin torque. Magnetization is reversed by the principle of the spin transfer torque (FIG. 7B). At this time, electrons having a spin antiparallel to the magnetization direction of the ferromagnetic layer 11 enter the ferromagnetic layer 11 via the ferromagnetic layer 17, the ion source layer 15 b, the Ag filament 16, and the tunnel barrier layer 13. And is reflected at the interface between the tunnel barrier layer 13 and the ferromagnetic layer 11 and flows into the ferromagnetic layer 17 through the tunnel barrier layer 13, the Ag filament 16, and the ion source layer 15b. It acts as a spin transfer torque that reverses the magnetization. That is, in the second embodiment, the ferromagnetic layer 17 receives the spin transfer torque from the ferromagnetic layer 19 and the ferromagnetic layer 11. In this way, the magnetization direction of the ferromagnetic layer 17 can be reversed from “parallel” to “antiparallel” with respect to the magnetization direction of the ferromagnetic layer 11.

  Next, it is assumed that the magnetization direction of the magnetization reversible ferromagnetic layer 17 is antiparallel to the magnetization direction of the ferromagnetic layer 11, that is, parallel to the magnetization direction of the ferromagnetic layer 19 (FIG. 8A). . When a positive voltage equal to or higher than the set voltage is applied to the ferromagnetic layer 11 with respect to the ferromagnetic layer 11, an Ag filament 16 is formed in the ion conductive layer 15 a, and electrons are transferred from the ferromagnetic layer 11 to the tunnel barrier layer 13 and the Ag filament 16. And flows into the ferromagnetic layer 17 through the ion source layer 15b. Since the direction of magnetization of the ferromagnetic layer 17 is antiparallel to the direction of magnetization of the ferromagnetic layer 11, a spin opposite to the direction of magnetization of the ferromagnetic layer 17 flows from the ferromagnetic layer 11 and receives spin torque. Magnetization is reversed by the principle of the spin transfer torque (FIG. 8B). At this time, electrons having a spin antiparallel to the magnetization direction of the ferromagnetic layer 19 reach the ferromagnetic layer 19 via the ferromagnetic layer 17 and the nonmagnetic metal layer 18, and the nonmagnetic metal layer 18. Is reflected at the interface between the magnetic layer 19 and the ferromagnetic layer 19, flows into the ferromagnetic layer 17 through the nonmagnetic metal layer 18, and acts as a spin transfer torque that reverses the magnetization of the ferromagnetic layer 17. That is, in the second embodiment, the ferromagnetic layer 17 receives the spin transfer torque from the ferromagnetic layer 19 and the ferromagnetic layer 11, so that the magnetization of the ferromagnetic layer 17 is smaller than that in the first embodiment. Inversion can be easily performed.

  In this way, the magnetization direction of the ferromagnetic layer 17 can be reversed from “antiparallel” to “parallel” with respect to the magnetization direction of the ferromagnetic layer 11.

  Note that the read operation is performed in the same manner as in the first embodiment.

  In both cases, the read operation and the write operation are exactly the same operation in the sense that a voltage equal to or higher than the set voltage is applied to form a filament and a current flows. However, the current required for writing by magnetization reversal is larger than the current required for reading. Typically, reading can be performed with an order of 10 μA or less, while writing requires a current of about 100 μA. For this reason, when reading is performed, the read current is limited to about 10 μA, and when writing is performed, the writing current and the reading can be distinguished from each other by controlling from the outside so that the write current flows to about 100 μA. .

  The set voltage and write current in the above writing process are performed in the same manner as in the first embodiment shown in FIGS. 5 (a) and 5 (b). For example, a set voltage is applied between the ferromagnetic layer 11 and the ferromagnetic layer 19 in order to form the Ag filament 16 in the ion conductive layer 15 a of a-Si. Since the filament is formed in about several tens of nanoseconds, an application time of about 10 nanoseconds to 100 nanoseconds is sufficient. During application of the set voltage, a current limit of about 100 μA is applied by an external circuit to prevent the a-Si ion conduction layer 15a and the tunnel barrier layer 13 from being destroyed due to excessive current flow.

  Next, a voltage for writing is applied. In order to prevent the filament from collapsing, it is desirable to apply the filament forming voltage after the application. Since sufficient current (about 100 μA) is necessary for writing, a voltage sufficiently higher than that for reading is applied. In order to secure a sufficient current necessary for writing, a constant current is supplied until the writing operation is completed.

  FIG. 9 shows current-voltage characteristics when a voltage is applied to the resistance change layer composed of an Ag ion source layer and an a-Si ion conduction layer while applying a current limit. Changing the current limit value does not change the set voltage value. For this reason, it is not necessary to change the applied voltage itself at the time of reading or writing, and the current limit value on the reading side may be changed. The current limitation can be realized by using, for example, the saturation characteristic of MOSET.

(Modification)
An MTJ element according to a modification of the second embodiment is shown in FIG. The MTJ element 1B of this modification is opposite to the tunnel barrier layer 13 with respect to the ferromagnetic layer 11 in order to fix the magnetization direction of the ferromagnetic layer 11 in the MTJ element 1A of the second embodiment shown in FIG. An antiferromagnetic layer 21 is provided on the side, and an antiferromagnetic layer 22 is provided on the side opposite to the nonmagnetic metal layer 18 with respect to the ferromagnetic layer 19 in order to fix the magnetization direction of the ferromagnetic layer 19. It has become. In this modification, the magnetization directions of the ferromagnetic layers 11, 17, and 19 are parallel to the film surface. In general, when the magnetization directions of the ferromagnetic layers 11, 17, and 19 are perpendicular to the film surface, the antiferromagnetic layers 21 and 22 may not be provided.

  In the ferromagnetic layer joined to the antiferromagnetic layer, magnetization reversal does not occur under a certain magnetic field range due to the exchange bias. In the case of this modification, for example, the magnetization is fixed by bonding antiferromagnetic layers 21 and 22 made of IrMn or PtMn having a thickness of about 10 nm to the CoFeB ferromagnetic layers 11 and 19 having a thickness of about 3 nm, respectively. can do.

  As described above, similarly to the first embodiment, the second embodiment and its modification can provide a magnetic tunnel junction element having a resistance change function with little deterioration. In the second embodiment and its modifications, as in the first embodiment, the total thickness of the ion source layer 15b and the ion conductive layer 15a is equal to or less than the spin relaxation length of the metal constituting the ion source layer. It is preferable. If the ion source layer 15b is Ag, the spin relaxation length is 300 nm.

(Third embodiment)
A magnetic memory according to the third embodiment is shown in FIG. The magnetic memory according to the third embodiment has a configuration in which the MTJ element 1A according to the second embodiment shown in FIG. 6 is provided at the cross point (intersection region) between the word line 30 and the bit line 40 that intersect each other. The ferromagnetic layer 11 of the MTJ element 1A is electrically connected to the word line 30, and the ferromagnetic layer 19 of the MTJ element 1A is electrically connected to the bit line 40. The operation principle is the same as in the second embodiment. The MTJ element in the intersecting region can be manufactured in the same manner as a general MTJ element forming process. Note that the MTJ element according to the first embodiment and its modified example or the modified example of the second embodiment may be used as the MTJ element serving as the memory element.

In addition, as shown in FIG. 12, a plurality of word lines 30 ₁ and 30 ₂ and a plurality of bit lines 40 ₁ and 40 ₂ are arranged in a lattice shape, and any of the first to second embodiments is arranged in an intersection region thereof. By disposing such an MTJ element, a large-capacity nonvolatile memory can be obtained.

Note that the ferromagnetic layer 11 and the ferromagnetic layer 19 may extend along the word line 30 and the bit line 40, respectively, as in the magnetic memory according to the first modification of the third embodiment shown in FIG. . Further, as in the magnetic memory according to the second modification of the third embodiment shown in FIG. 14, the ferromagnetic layer 11 and the ferromagnetic layer 19 extend along the word lines 30 ₁ and 30 ₂ and the bit lines 40 ₁ and 40 ₂ , respectively. May be extended.

  In addition, in order to fix the magnetization directions of the ferromagnetic layer 11 and the ferromagnetic layer 19, the anti-strength shown in FIG. 10 is respectively shown between the word line and the ferromagnetic layer 11 and between the ferromagnetic layer 19 and the bit line. A magnetic layer 21 and an antiferromagnetic layer 22 may be inserted. The antiferromagnetic layer 21 and the antiferromagnetic layer 22 may also extend in the word line and bit line directions, respectively.

  As described above, in the third embodiment, since the MTJ element according to any one of the first and second embodiments and their modifications is used as an MTJ element serving as a memory element, a resistance change function with little deterioration is provided. The provided magnetic memory can be obtained.

(Fourth embodiment)
FIG. 15 shows a magnetic memory according to the fourth embodiment. In the magnetic memory of the fourth embodiment, the first word line 30A and the bit line 40 intersect each other, and a second word line 30B parallel to the first word line 30A is provided on the bit line 40. The first word line 30A, the bit line 40, and the second word line 30B intersect at one point. In this intersection region, the MTJ element 1A of the second embodiment shown in FIG. 6 is provided in the intersection region between the first word line 30A and the bit line 40, and FIG. 6 is provided in the intersection region between the bit line 40 and the second word line 30B. The MTJ element 1A of the second embodiment shown in FIG. In the fourth embodiment, the first word line 30A / the ferromagnetic layer 11 / the tunnel barrier layer 13 / the ion conductive layer 15a / the ion source layer 15b / the ferromagnetic layer 17 / the nonmagnetic metal layer 18 / the ferromagnetic layer. 19 / bit line 40 / ferromagnetic layer 11 / tunnel barrier layer 13 / ion conduction layer 15a / ion source layer 15b / ferromagnetic layer 17 / nonmagnetic metal layer 18 / ferromagnetic layer 19 / bit line 30B. Have a structure. Note that the MTJ element according to the first embodiment and its modified example or the modified example of the second embodiment may be used as the MTJ element serving as the memory element.

In the fourth embodiment, a voltage equal to or higher than the set voltage is applied between the first word line 30A and the bit line 40 to read or write the MTJ element between the first word line 30A and the bit line 40. However, by floating the second word line 30B at that time, the MTJ element between the bit line 40 and the second word line 30B is not applied with a voltage higher than the set voltage, and the insulation state is reduced. Can keep. For this reason, since the upper and lower MTJ elements can be operated independently, the structure can be three-dimensionalized. In addition, as shown in FIG. 16, a plurality of word lines 30A ₁ and 30A ₂ , a plurality of bit lines 40 ₁ and 40 ₂ , and a plurality of second word lines 30B ₁ and 30B ₂ are arranged in a lattice pattern and intersecting them. A large-capacity nonvolatile memory can be obtained if the MTJ element according to any one of the first to second embodiments and their modifications is provided as a storage element in each region.

  As shown in FIG. 17, the MTJ element 1A provided in the intersection region between the first word line 30A and the bit line 40, and the MTJ element 1A provided in the intersection region between the bit line 40 and the second word line 30B. The stacking order may be reversed. For example, first word line 30A / ferromagnetic layer 11 / tunnel barrier layer 13 / ion conducting layer 15a / ion source layer 15b / ferromagnetic layer 17 / nonmagnetic metal layer 18 / ferromagnetic layer 19 / bit line 40 / ferromagnetic Even in a structure in which layer 19 / nonmagnetic metal layer 18 / ferromagnetic layer 17 / ion source layer 15b / ion conductive layer 15a / tunnel barrier layer 13 / ferromagnetic layer 11 / second word line 30B are stacked in this order. Good. That is, the MTJ elements above and below the bit line 40 are stacked symmetrically with respect to the bit line 40.

  As described above, in the fourth embodiment, since the MTJ element according to any one of the first and second embodiments and their modifications is used as the MTJ element serving as the memory element, the resistance change function with little deterioration is provided. The provided magnetic memory can be obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

1, 1A, 1B MTJ element (magnetic tunnel junction element)
DESCRIPTION OF SYMBOLS 11 Ferromagnetic layer 13 Tunnel barrier layer 15 Resistance change layer 15a Ion conduction layer 15b Ion source layer 16 Ag filament 17 Ferromagnetic layer 18 Nonmagnetic metal layer 19 Ferromagnetic layer 21 Antiferromagnetic layer 22 Antiferromagnetic layer 30 Word line 40 Bit line

Claims (9)

First and second ferromagnetic layers;
A tunnel barrier layer provided between the first ferromagnetic layer and the second ferromagnetic layer;
A variable resistance layer provided between the tunnel barrier layer and the second ferromagnetic layer and having a laminated structure of an ion source layer containing a metal element serving as an ion source and an ion conductive layer;
And a thickness of the variable resistance layer is equal to or less than a spin relaxation length of the metal element.   2. The magnetic tunnel junction device according to claim 1, wherein the ion conductive layer is one of an amorphous semiconductor, a metal oxide, and a chalcogenide.   The magnetic tunnel junction element according to claim 1, wherein the ion source layer contains Ag or Cu.   4. The magnetic tunnel junction according to claim 1, wherein the ion source layer is provided on the second ferromagnetic layer side, and the ion conductive layer is provided on the tunnel barrier layer side. element.   4. The magnetic tunnel junction according to claim 1, wherein the ion source layer is provided on the tunnel barrier layer side, and the ion conductive layer is provided on the second ferromagnetic layer side. element. A third ferromagnetic layer provided on the opposite side of the resistance change layer with respect to the second ferromagnetic layer;
A nonmagnetic metal layer provided between the second ferromagnetic layer and the third ferromagnetic layer;
Further comprising
The first ferromagnetic layer is a reference layer having a fixed magnetization direction, the second ferromagnetic layer is a storage layer having a variable magnetization direction, and the third ferromagnetic layer has a magnetization direction of the first magnetization layer. 4. The magnetic tunnel junction element according to claim 1, wherein the magnetic tunnel junction element is antiparallel to the magnetization direction of one ferromagnetic layer. A first antiferromagnetic layer that fixes the magnetization direction of the first ferromagnetic layer;
A second antiferromagnetic layer that fixes the magnetization direction of the third ferromagnetic layer;
The magnetic tunnel junction device according to claim 6, further comprising: A first wiring;
A second wiring crossing the first wiring;
The first magnetic tunnel junction element according to any one of claims 1 to 7, provided in an intersecting region between the first wiring and the second wiring;
A magnetic memory comprising: A third wiring parallel to the first wiring and intersecting the second wiring;
The second magnetic tunnel junction element according to any one of claims 1 to 7, provided in an intersecting region between the second wiring and the third wiring;
The magnetic memory according to claim 8, further comprising:

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