JP2009239135A - Magnetic memory cell and magnetic storage device using same, and magnetic storage method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic memory cell which has low power consumption and high storage density by moving a magnetic domain wall in a magnetic layer with a small current through spin orbit interaction and performing ratchet driving. <P>SOLUTION: The magnetic memory cell 1 has a first magnetic layer 10 whose magnetization state is fixed as a reference layer, a second magnetic layer 30 whose magnetization state changes as a data storage layer, and a tunneling barrier layer 20 sandwiched between the first magnetic layer 10 and second magnetic layer 30. In the magnetic memory cell 1, spin orbit interaction of the second magnetic layer 30 is controlled when the magnetization state of the second magnetic layer 30 is changed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a magnetic memory cell that realizes low power consumption and high memory density by moving the domain wall in the magnetic layer with a low current by controlling the spin-orbit interaction in the magnetic layer and driving the ratchet. And a magnetic storage device using such a magnetic memory cell and a magnetic storage method.

  In memory elements used for computers and electronic devices, intense technological development competition is taking place. The technology advances at an ever-increasing speed, and various new memory devices have been proposed. In recent years, a giant magnetoresistive effect has been discovered in a magnetoresistive film in which a nonmagnetic layer is sandwiched between ferromagnetic layers, and magnetic sensors and memory elements using this phenomenon are attracting attention. Hereinafter, the memory device using the magnetoresistive film is generically referred to as MRAM.

  In the MRAM, a three-layer structure of two ferromagnetic layers and a thin nonmagnetic layer sandwiched between them is a basic structural unit for recording information. By utilizing the phenomenon that the resistance values differ between the two ferromagnetic layers sandwiching the non-magnetic layer when the magnetization directions are aligned and antiparallel, “0”, “1” Record the status of. A predetermined induction magnetic field is applied to change the magnetization direction in one of the magnetic layers.

  When reading the recorded information, apply a weaker alternating magnetic field than at the time of writing, change the direction of the magnetization direction of only one ferromagnetic layer, and measure the resistance value change at that time, Read the status of “0” and “1”. The MRAM has an advantage that it is excellent in radiation resistance because information is magnetically recorded, is non-volatile in principle, and has no limitation on the number of times of writing. By using existing semiconductor technology, high-density recording can be easily performed, so replacement of DRAM is expected in the future.

A technique for realizing magnetization reversal without using the induction magnetic field as described above has also been proposed. For example, a carrier spin injection magnetization reversal magnetoresistive film has been proposed in which magnetization reversal is performed by injecting carrier spins in the stacking direction. In the above carrier spin injection magnetization reversal type magnetoresistive effect film, when spin-polarized carriers are electrically injected from the injection layer to the inversion layer, the torque caused by the carriers to the magnetization of the magnetic material exceeds a certain inversion current. Magnetization rotation of the magnetization switching film occurs. Such a carrier spin injection magnetization reversal type MRAM is disclosed in Patent Document 1, for example.
JP 2005-19561 A

  However, in a magnetic memory cell which is a basic unit of magnetic storage in a conventional MRAM or the like, a large current value is required to move the domain wall in the magnetic layer. If a device is configured using the conventional magnetic memory cell, power consumption is increased. There was a problem that became larger.

  In addition, in the conventional magnetic memory cell, it is difficult to control the movement of the domain wall in the magnetic layer with good reproducibility, which is an obstacle to improving the storage density of the device using the conventional magnetic memory cell. there were.

  In order to solve the above problems, the invention according to claim 1 includes a first magnetic layer whose magnetization state is fixed as a reference layer, a second magnetic layer whose magnetization state changes as a data storage layer, In a magnetic memory cell having a tunnel barrier layer sandwiched between the first magnetic layer and the second magnetic layer, the spin of the second magnetic layer is changed when the magnetization state of the second magnetic layer is changed. It is characterized by controlling orbit interaction.

  According to a second aspect of the present invention, in the magnetic memory cell according to the first aspect, the second magnetic layer is provided with a spin orbit interaction control electrode for applying a voltage for controlling the spin orbit interaction. It is characterized by that.

  According to a third aspect of the present invention, there is provided a magnetic memory device comprising the magnetic memory cells according to the first or second aspect connected in an array.

  According to a fourth aspect of the present invention, there is provided a magnetic storage method for storing information by changing a magnetization state in a magnetic layer, wherein the spin orbit of the magnetic layer is changed when the magnetization state of the magnetic layer is changed. It is characterized by controlling the action.

  According to the magnetic memory cell of the present invention, since the spin-orbit interaction is given to the second magnetic layer, the domain wall can be moved with a lower current than in the prior art.

  According to the magnetic memory cell of the present invention, the domain wall in the second magnetic layer can be ratchet-driven by spin orbit interaction in the second magnetic layer. It becomes possible to record.

  In addition, according to the magnetic memory device of the present invention, the current consumed by each magnetic memory cell when the memory operation is performed is reduced by the spin orbit interaction applied to the second magnetic layer, thereby reducing the power consumption. be able to.

  In addition, according to the magnetic memory device of the present invention, the magnetic wall in the second magnetic layer of each memory cell can be ratchet driven by the spin orbit interaction, so that information is recorded at a higher density. Will be able to.

  In addition, according to the magnetic storage method of the present invention, the magnetic wall can be moved with a lower current and the magnetic wall can be ratchet driven by applying a spin orbit interaction to the magnetic layer, so that low power consumption・ High memory density can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the structure of a magnetic memory cell according to an embodiment of the present invention. In the following, in the present embodiment, information can be read from the magnetic memory cell by a known method such as the giant magnetoresistive effect. Information writing will be described.

In FIG. 1, 1 is a magnetic memory cell, 10 is a first magnetic layer (reference layer), 20 is a tunnel barrier layer, 30 is a second magnetic layer (data storage layer), 51 and 52 are spin injection magnetization reversal control electrodes, Reference numerals 61 and 62 denote spin orbit interaction control electrodes, 70 denotes a spin injection magnetization reversal control current source J1 and 80, spin orbit interaction control voltage sources V2, SW1 and SW2 denote switches, respectively.

As shown in FIG. 1, the magnetic memory cell 1 has a tunnel barrier layer 20 sandwiched between a first magnetic layer (reference layer) 10 and a second magnetic layer (data storage layer) 30 which are two ferromagnetic layers. It has a structure.
The first magnetic layer (reference layer) 10 is provided with a spin injection magnetization reversal control electrode 51, and the second magnetic layer (data storage layer) 30 is provided with a spin injection magnetization reversal control electrode 52 as shown in the figure. By opening / closing the switch SW1, the current J1 from the spin injection magnetization reversal control current source 70 can be passed through the first magnetic layer (reference layer) 10-tunnel barrier layer 20-second magnetic layer (data storage layer) 30. It is like that.

  Further, as shown in the figure, spin orbit interaction control electrodes 61 and 62 are provided so as to sandwich both ends of the second magnetic layer (data storage layer) 30, and the spin orbit interaction control voltage source 80 is opened and closed by opening and closing the switch SW 2. The voltage V <b> 2 can be applied to the second magnetic layer (data storage layer) 30.

  The first magnetic layer (reference layer) 10 constitutes a fixed magnetization layer whose magnetization state cannot be changed, whereas the second magnetic layer (data storage layer) 30 switches the current J1 and the voltage V2. The magnetization free layer which can change a magnetization state by controlling by SW1 and SW2 is comprised.

  In the magnetic memory cell 1, the relationship between the magnetization state between the first magnetic layer (reference layer) 10 and the second magnetic layer (data storage layer) 30 is parallel magnetization state (low resistance) or antiparallel magnetization state (high resistance). ) Is a non-volatile memory cell that reads out the difference in electrical resistance due to the storage information as memory information.

  In the magnetic memory cell 1 of the present embodiment, the second magnetic layer (data storage layer) 30 has a carrier spin injection magnetization reversal magnetoresistance effect in which magnetization reversal is performed by injecting carrier spin. In addition, the second magnetic layer (data storage layer) 30 of the magnetic memory cell 1 of the present embodiment is controlled to give a spin orbit interaction by applying a voltage V2.

  The spin-orbit interaction is an interaction that changes the spin simultaneously with the movement of the electron, and gives the spin-orbit interaction by acting an electric field perpendicular to the direction of the electron movement. be able to. In the present embodiment, spin orbit interaction is applied to the second magnetic layer (data storage layer) 30 by the previous voltage V2.

  It has been clarified by the inventors' earnest study that a characteristic domain wall movement is performed by applying a spin orbit interaction to a predetermined material. The present invention uses the characteristic domain wall motion under spin orbit interaction. Details of the characteristic domain wall movement under spin-orbit interaction are detailed in Kazutoshi Ogura “Current-induced Magnetization in Rashba spin-oribit system” (Tokyo Metropolitan University Master's thesis). The contents will be incorporated.

  FIG. 2 is a diagram showing a type of domain wall movement under the spin-orbit interaction. It is a figure which shows the domain wall position X when the voltage V2 is applied to a predetermined material. FIG. 2 shows one having λ = 0 (no spin orbit interaction) and one showing three different domain wall motion patterns under spin orbit interaction. Those showing these characteristic domain wall motion patterns are defined as Bloch (z), Neel (x), and Bloch (y). Note that FIG. 2 is normalized by assuming that the current at which the domain wall motion starts is 1 for λ = 0.

As a material used for the second magnetic layer (data storage layer) 30, Bloch (z), Neel (
x) and Bloch (y) can be defined by the direction of the easy magnetic axis. FIG. 3 is a diagram showing the correspondence between the easy magnetization axis and the magnetization structure. In the present specification, the structure of each domain wall is referred to as “Bloch (z) wall”, “Nel (x) wall”, “Bloch (y) wall”.

  In FIG. 2, when λ = 0 (no spin-orbit interaction), the domain wall position rises as illustrated with J1 = 1 as the base point, whereas Bloch (z) and Neel (x) both have J1 = At 0.8, the domain wall position rises stepwise, and continues to be flat for a while. When J1 = 1.3, it starts increasing again. In Bloch (y), the domain wall position rises from J1 = 0, shows a peak around J1 = 0.2, then decreases once, and then gradually increases around J1 = 0.4.

  As described above, when the spin orbit interaction is applied, it is possible to move the domain wall with a smaller amount of current than when there is no spin orbit interaction. This is true for any of Bloch (z), Neel (x), and Bloch (y), but is particularly noticeable with Bloch (y) as shown in the figure. In the present invention, this phenomenon is used to reduce the power consumption of the magnetic memory cell 1.

In the case of Bloch (z) and Neel (x), the domain wall position remains constant in the current range of J1 = 0.8 to .1.3. In the present invention, this phenomenon is used for the domain wall control of the magnetic memory cell 1.

  FIG. 4 is a diagram showing an extracted second magnetic layer (data storage layer) 30 in the magnetic memory cell 1 according to the embodiment of the present invention. Here, a Bloch (y) substance that enables domain wall movement at a low current is arranged in a coordinate system as shown in the figure, and the domain wall is moved up and down by a spin injection magnetization reversal control current J1 and a spin orbit interaction control voltage V2. Thus, the magnetization state in the second magnetic layer (data storage layer) 30 is changed to either the parallel magnetization state or the antiparallel magnetization state with the first magnetic layer (reference layer) 10. FIG. 4 shows a state in which the domain wall is moving. An arrow shown in the second magnetic layer (data storage layer) 30 indicates the direction of magnetization.

  According to the magnetic memory cell 1 according to the embodiment of the present invention, since the spin-orbit interaction is applied to the second magnetic layer (data storage layer) 30, the domain wall can be moved with a lower current than in the prior art. It becomes like this.

  FIG. 5 is a diagram showing a magnetic storage device 2 in which such magnetic memory cells 1, 1 ', 1' 'are arranged in an array. In the magnetic memory device 2 according to the present embodiment, the spin injection magnetization reversal control electrode 51 provided so as to be common to the magnetic memory cell 1 and the spin injection magnetization provided independently for each of the magnetic memory cells 1. By the reversal control electrode 52, the spin injection magnetization reversal control current J1 is selectively applied to the memory cell to be stored, and at that time, the spin orbit interaction control voltage V2 is applied to move the domain wall up and down. The magnetization state in the second magnetic layer (data storage layer) 30, 30 ′, 30 ″ is changed.

  According to the magnetic storage device 2 according to the embodiment of the present invention as described above, even when the density is increased, the current consumed by each magnetic memory cell when performing the storage operation becomes small. Can be reduced.

Next, another embodiment of the present invention will be described. FIG. 6 is a diagram showing the structure of a magnetic memory cell according to another embodiment of the present invention. In the embodiment shown in FIG. 1, the magnetization state of the second magnetic layer (data storage layer) 30 was either the parallel magnetization state or the anti-parallel magnetization state, while the second embodiment of the embodiment shown in FIG. The magnetization state of the magnetic layer (data storage layer) 40 is configured to be able to take two or more states.

  FIG. 7 is a diagram showing a second magnetic layer (data storage layer) 30 extracted from a magnetic memory cell 3 according to another embodiment of the present invention, and FIG. 8 shows a magnetic field according to another embodiment of the present invention. 3 is a diagram showing a magnetization pattern of a second magnetic layer (data storage layer) 30 in the memory cell 3. FIG.

  In the magnetic memory cell 3 of the present embodiment, a Bloch (z) substance that can easily control the domain wall motion is arranged in a coordinate system as shown in the figure, and the spin injection magnetization reversal control current J1 and the spin orbit interaction control voltage V2 are arranged. Is applied to move the domain wall up and down by the interval d, and the magnetization state in the second magnetic layer (data storage layer) 30 can take five patterns (A) to (E) shown in FIG. Thus, more than 1 bit of information is stored in one magnetic memory cell 3. In the examples shown in FIGS. 7 and 8, the magnetization state is five patterns, but the present invention is not limited to this number of patterns.

  In the present embodiment, for example, a Bloch (z) material is used as the second magnetic layer (data storage layer) 40, and the domain indicated by F in FIG. (Ie, the domain wall is ratchet driven). In the present embodiment, for example, a Bloch (z) material is used as the second magnetic layer (data storage layer) 40, but Neel (x) can also be used.

  The domain walls of Bloch (z) and Neel (x) exhibit a behavior in which the domain wall stays moving a certain distance. This will be described based on the potential diagram. FIG. 9 is a diagram showing changes in the domain wall potential due to the spin-orbit interaction. FIG. 9A shows the domain wall potential when there is no spin-orbit interaction, and FIG. 9B shows the domain wall potential when there is a spin-orbit interaction. In FIG. 9, φ on the horizontal axis indicates the rising angle of the domain wall, and V (φ) on the vertical axis indicates the potential with respect to the rising angle φ. Also, any figure in any of FIGS. 9A and 9B shows the domain wall potential when J1 = 1.2.

  FIG. 9A shows the domain wall potential when there is no spin orbit interaction. When the spin orbit interaction is applied to this, the vicinity of the figure a is pushed down as shown in FIG. The curve changes so that the vicinity is pushed up, and a recessed portion of the potential V (φ) is formed in the vicinity of d in the figure. Since the domain wall is trapped in the recessed portion, the domain wall can be ratchet-driven.

  FIG. 9C shows the potential of the domain wall when the spin injection magnetization reversal control current J1 is applied while further applying a negative voltage to the spin orbit interaction control voltage in the state shown in FIG. 9B. . At this time, the vicinity of d shown in the figure is pushed down, the curve changes so that the vicinity of e shown in the figure is pushed up, and a recessed portion of potential V (φ) is formed in the vicinity of f shown in the figure. That is, the domain wall has an image that moves to the indented portion. Since the domain wall of the second magnetic layer (data storage layer) 40 can be ratchet-driven by such a spin orbit interaction control voltage, the second magnetic layer (data storage layer) of the magnetic memory cell 3 is used. Forty more information can be written. Further, according to the magnetic memory cell 3 according to another embodiment, there is an advantage that the domain wall can be moved with a low current.

FIG. 10 is a diagram showing a state in which the domain wall position is controlled by applying a spin orbit interaction control voltage with J1 = 1.2. FIG. 10A shows a case where a pulse voltage of 300 ns is applied once. FIG. 10B is a diagram illustrating the movement of the domain wall position when a pulse voltage of 300 ns is applied twice, and FIG. 10C is the diagram illustrating the movement of the domain wall position of FIG. FIG. 10D is a diagram showing the movement of the domain wall position when the pulse voltage is applied three times, and FIG. 10D is a diagram showing the movement of the domain wall position when the pulse voltage of 300 ns is applied four times. In any figure of FIG. 10, the horizontal axis represents time, and the vertical axis represents the domain wall position.

  From FIG. 10, it can be seen that in the second magnetic layer (data storage layer) 40, the domain wall position is ratchet-driven in accordance with the number of times the pulse voltage is applied. FIG. 10 also shows that the domain wall position remains even when the current J1 is stopped after the application of the pulse voltage. Thus, according to the magnetic memory cell 2 according to the present embodiment, the domain wall of the second magnetic layer (data storage layer) 40 can be ratchet-driven by the spin orbit interaction control voltage. For this reason, it becomes possible to write more information than 1 bit in the second magnetic layer (data storage layer) 40 of the magnetic memory cell 3, and the recording density can be improved.

  FIG. 11 is a diagram showing a magnetic storage device 4 in which the magnetic memory cells 3, 3 ', 3' 'as described above are arranged in an array. In the magnetic memory device 4 according to the present embodiment, the spin injection magnetization reversal control electrode 51 provided so as to be common to the magnetic memory cell 3 and the spin injection magnetization provided independently for each of the magnetic memory cells 3. By the reversal control electrode 52, the spin injection magnetization reversal control current J1 is selectively applied to the memory cell to be stored, and at that time, the spin orbit interaction control voltage V2 is applied to move the domain wall up and down. The magnetization state in the second magnetic layer (data storage layer) 40, 40′40 ″ is changed. Since the change in the magnetization state is stepwise, it is possible to store more than 1 bit of information in each second magnetic layer (data storage layer).

  According to the magnetic memory device 4 according to another embodiment of the present invention as described above, the domain wall in the second magnetic layer (data storage layer) of each memory cell can be ratchet-driven. Thus, information can be recorded at a higher density.

  Further, by controlling the spin-orbit interaction, even when the density is increased, the current consumed when each magnetic memory cell performs the storage operation is reduced, so that the power consumption can be reduced.

It is a figure which shows the structure of the magnetic memory cell which concerns on embodiment of this invention. It is a figure which shows the type of the movement of the domain wall under a spin orbit interaction. It is a figure which shows a response | compatibility with a magnetization easy axis | shaft and a magnetization structure. It is a figure which extracts and shows the 2nd magnetic layer (data storage layer) 30 in the magnetic memory cell 1 which concerns on embodiment of this invention. 1 is a diagram showing a structure of a magnetic memory device according to an embodiment of the present invention. It is a figure which shows the structure of the magnetic memory cell based on other embodiment of this invention. It is a figure which extracts and shows the 2nd magnetic layer (data storage layer) 30 in the magnetic memory cell 3 which concerns on other embodiment of this invention. It is a figure which shows the magnetization pattern of the 2nd magnetic layer (data storage layer) 30 in the magnetic memory cell 3 which concerns on other embodiment of this invention. It is a figure which shows the change of the potential of the domain wall by a spin orbit interaction. It is a figure which shows the mode of a movement of the domain wall position when a spin orbit interaction control voltage is applied. It is a figure which shows the structure of the magnetic memory device based on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 3 ... Magnetic memory cell 2, 4 ... Magnetic storage device 10 ... 1st magnetic layer (reference | standard layer)
20 ... Tunnel barrier layer 30, 40 ... Second magnetic layer (data storage layer)
51, 52 ... Spin injection magnetization reversal control electrodes 61, 62 ... Spin orbit interaction control electrode 70 ... Spin injection magnetization reversal control current source J1
80 ... Spin orbit interaction control voltage source V2
SW1, SW2 ... switch

Claims (4)

A first magnetic layer whose magnetization state is fixed as a reference layer;
A second magnetic layer whose magnetization state changes as a data storage layer;
In a magnetic memory cell having a tunnel barrier layer sandwiched between the first magnetic layer and the second magnetic layer,
A magnetic memory cell that controls spin-orbit interaction of the second magnetic layer when changing the magnetization state of the second magnetic layer. The magnetic memory cell according to claim 1, wherein the second magnetic layer is provided with a spin orbit interaction control electrode for applying a voltage for controlling the spin orbit interaction. 3. A magnetic storage device comprising the magnetic memory cells according to claim 1 connected in an array. A magnetic storage method for storing information by changing a magnetization state in a magnetic layer, characterized by controlling a spin-orbit interaction of the magnetic layer when changing the magnetization state of the magnetic layer Memory method.

Images