KR20100104413A - Magnetic memory device using perpendicular magnetic anisotopy - Google Patents

Abstract

The present invention relates to a memory device using perpendicular magnetic anisotropy. More specifically, the present invention relates to a multilayer thin film structure for a current-applied magnetic domain wall moving technique.

Magnetic memory device using the perpendicular magnetic anisotropy according to the present invention includes a nonmagnetic layer, a first magnetic layer formed between the nonmagnetic layer and a second magnetic layer formed between the first magnetic layer, the saturation magnetization value of the second magnetic layer is It is characterized by being less than the saturation magnetization value.

According to the present invention, even when the thickness of the magnetic layer becomes thicker than the conventional Pt / Co / Pt structure, the vertical magnetism can be maintained, and thus, the magnetic domain wall can be moved at a low current density, and thus the magnetic domain movement efficiency can be further improved. In addition, by minimizing the number of interfaces by implementing a simple structure of Pt / Co / Ni / Co / Pt can be improved magnetic domain wall movement efficiency than the existing Co / Ni multilayer thin film structure.

Description

Magnetic memory device using vertical magnetic anisotropy {MAGNETIC MEMORY DEVICE USING PERPENDICULAR MAGNETIC ANISOTOPY}

The present invention relates to a memory device using perpendicular magnetic anisotropy. More specifically, the present invention relates to a multilayer thin film structure for a current-applied magnetic domain wall transfer technique.

Interest in magnetic wall memory devices, first raised by IBM's Stuart Parkin, has recently increased. The magnetic domain wall memory device is attracting attention as an innovative next-generation memory device that combines the advantages of the conventional hard disk and flash memory.

1 is a view showing the conceptual configuration and information storage method of the magnetic domain wall memory device using vertical magnetic anisotropy.

As shown in FIG. 1, a magnetic domain wall memory device using vertical magnetic anisotropy stores information using magnetic domains (magnetic domains, hereinafter referred to as magnetic domains) in vertical magnetic nanowires having a width of several hundred nanometers. By using the spin torque effect by the magnetic domain walls are taken.

In the magnetic domain, there are two stable magnetization directions (or magnetic moment directions, 53), and information processing is possible by providing unit bits of '0' or '1' according to the magnetization direction to operate as a memory element. . In this case, the magnetization directions of the magnetic domains are staggered at the portion where the bit value changes, and a magnetic domain wall 51 is formed thereon. The magnetic domain wall 51 is a boundary portion of magnetic domains having different magnetization directions, and the magnetic domain wall can be moved by an electric current or an external magnetic field applied to the magnetic material. The magnetic domain wall 51 thus formed serves to distinguish information. What is important here is that the magnetic domain walls can be moved by flowing a current through the nanowires, and thus the information can be moved on the magnetic nanowires without losing information. This is the core concept of the magnetic domain wall memory.

Therefore, the magnetic domain wall memory can secure ultra high integration of the size of several hundred nanometers, and the current-based method can solve the speed and stability problems caused by the physical motion, which is a disadvantage of the conventional hard disk.

The key to magnetic domain wall memory devices is that the magnetic domain walls must be moved at the smallest current density possible. Recent research shows that the magnetic domain walls can be moved at a smaller current density in the vertical magnetic material than in the horizontal magnetic material, and many research groups are trying to find a suitable vertical magnetic material for the magnetic domain wall memory.

There are three magnetic domain movement patterns in vertical magnetism: wall-motion, stripe-growth, and nucleation. In order to move the magnetic domain wall by current, it is necessary to maintain the 'wall-motion' pattern. Usually, only the very thin magnetic layer (below 1 nm) maintains the 'wall-motion' pattern. However, in the magnetic domain wall memory, the magnetic layer must be thick to maximize the spin torque effect and to move the magnetic domain at a small current density.

2 is a cross-sectional view illustrating a structure of a conventional magnetic domain wall memory device using vertical magnetic anisotropy.

As shown in Fig. 2, the existing magnetic domain wall memory device has the most typical structure such as Pt (or Pd, 55a) / Co (57) / Pt (or Pd, 55b). This structure has a very large saturation magnetization value (about 1400 emu / cc) of the magnetic layer (57, Co layer), so when the magnetic layer (57, Co layer) becomes thick, volume anisotropy interferes with the perpendicular magnetism, so it is usually only 1 nm or less. It shows a 'wall-motion' pattern, and when it is above 1 nm, the vertical magnetism is rapidly lost. Since the magnetic domain wall movement effect by the current is made in the magnetic layer, if the magnetic layer is too thin, the effect is reduced, requiring a large current density to move the magnetic domain wall. Stacking the magnetic layers repeatedly may increase the overall magnetic layer, but increasing the number of interfacial layers may hinder uniform spin torque.

On the other hand, in the structure of magnetic domain wall memory elements, Co / Ni multilayer films, which are recently attracting attention, are usually vertically formed by magnetocrystalline anisotropy by repeatedly stacking very thin (Co-0.2 nm, Ni-0.4 nm) thin films. Have magnetism. Such a structure usually requires a thick buffer-layer, and the interlaminar interfacial number is more than 10 layers, making it difficult to predict a constant tendency for the wall movement of the domain. Research has been conducted on perpendicular magnetic materials using magnetic crystal anisotropy of various synthetic materials (ex: TbFeCo). However, most composites have very high coercive force and a large crystal state, which impedes the transmission of uniform spin torque.

An object of the present invention is to provide a magnetic memory device that maintains vertical magnetism even in a thick magnetic layer and is formed to minimize the number of interfaces to improve magnetic domain movement efficiency due to current.

Magnetic memory device using the perpendicular magnetic anisotropy according to the present invention includes a nonmagnetic layer, a first magnetic layer formed between the nonmagnetic layer and a second magnetic layer formed between the first magnetic layer, the saturation magnetization value of the second magnetic layer is It is preferable that it is less than saturation magnetization value.

Preferably, the nonmagnetic layer contains Pt or Pd.

The first magnetic layer includes Co or Co-based alloy,

It is preferable that a 2nd magnetic layer contains Ni or Ni type alloy.

The first magnetic layer is

A first upper magnetic layer stacked on the second magnetic layer and a first lower magnetic layer stacked on the lower portion of the second magnetic layer,

The nonmagnetic layer is

It is preferable to include an upper nonmagnetic layer laminated on the upper portion of the first upper magnetic layer and a lower nonmagnetic layer laminated on the lower portion of the first lower magnetic layer.

Magnetic memory device using the perpendicular magnetic anisotropy according to the present invention is formed between a nonmagnetic layer containing Pt or Pd, the nonmagnetic layer, and formed between the first magnetic layer and the first magnetic layer containing Co or Co-based alloy , A second magnetic layer comprising Ni or a Ni-based alloy.

According to the present invention, even when the thickness of the magnetic layer is thicker than the conventional Pt / Co / Pt structure, the vertical magnetism can be maintained, and thus the magnetic domain wall can be moved at a low current density, thereby improving the magnetic domain movement efficiency.

In addition, by minimizing the number of interfaces by implementing a simple structure of Pt / Co / Ni / Co / Pt can be improved magnetic domain wall movement efficiency than the existing Co / Ni multilayer thin film structure.

Hereinafter, a magnetic memory device using vertical magnetic anisotropy according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1. Configuration

3 is a cross-sectional view illustrating a configuration of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

Referring to FIG. 3, a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention may include the first magnetic layers 110a and 110b formed between the nonmagnetic layers 100a and 100b and the nonmagnetic layers 100a and 100b. The second magnetic layer 120 is formed between the first magnetic layers 110a and 110b.

The first magnetic layers 110a and 110b include the first upper magnetic layer 110a stacked on the second magnetic layer 120 and the first lower magnetic layer 110b stacked below the second magnetic layer 120.

The second magnetic layer 120 preferably includes a magnetic material that is less than the saturation magnetization value of the first upper magnetic layer 110a and the first lower magnetic layer 110b. That is, the magnetic material included in the second magnetic layer 120 has a smaller saturation magnetization value than the magnetic material included in the first magnetic layers 110a and 110b. For example, the first upper magnetic layer 110a and the second upper magnetic layer 110b may include a magnetic material made of Co (about 1400 emu / cc) or Co based alloy, and the second magnetic layer 120 may be made of Co. Or a magnetic material made of Ni (about 450 emu / cc) or a Ni-based alloy that is smaller than the saturation magnetization value of the Co-based alloy material.

In addition, the first upper magnetic layer 110a, the second magnetic layer 120, and the second upper magnetic layer 110b may each include a magnetic material whose saturation magnetization value is adjusted according to the alloy composition. That is, the saturation magnetization value of the magnetic material included in the second magnetic layer 120 is configured to have a value smaller than the saturation magnetization value of the magnetic material included in the first upper magnetic layer 110a and the second upper magnetic layer 110b. Can be.

As such a magnetic material, an alloy such as CoFeB, Ni-Fe, Co-Ni, Co-Fe, Co-Cr, Fe-Pt, or Co-Fe-Ni may be applied. For example, when a CoFeB alloy is used as a magnetic material, the saturation magnetization value of CoFeB included in the second magnetic layer 120 is equal to the saturation magnetization of CoFeB included in the first upper magnetic layer 110a and the second upper magnetic layer 110b. It has a value smaller than the value.

The nonmagnetic layers 100a and 100b include an upper nonmagnetic layer 100a stacked on an upper portion of the first upper magnetic layer 110a and a lower nonmagnetic layer 100b stacked on a lower portion of the first lower magnetic layer 110b. The upper nonmagnetic layer 100a and the lower nonmagnetic layer 100b may be formed of platinum (Pt) or palladium (Pd). In addition, the nonmagnetic layers 100a and 100b include osmium (Os), niobium (Nb), ruthenium (Ru), tantalum (Ta), zirconium (Zr), titanium (Ti), boron (B), zinc (Zn), and It may be formed by including any one or more materials of silver (Ag).

2. Characteristics

Prior to the description of the characteristics of the magnetic memory element of the present invention, the characteristics of the existing magnetic domain wall memory element will be described.

There are three magnetic domain movement patterns in vertical magnetism: wall-motion, stripe-growth, and nucleation. In order to move the magnetic domain by the current, the wall-motion pattern must be maintained. Usually, the wall-motion pattern is maintained only in a very thin magnetic layer (1 nm or less). However, in the magnetic domain wall memory, the magnetic layer must be thick to maximize the spin torque effect and to move the magnetic domain with a small current density. Therefore, in the structure of the magnetic domain wall memory device using the perpendicular magnetism, in order to move the magnetic domain more efficiently by using the current, the ratio of the magnetic layer to the entire device must be large.

As shown in Fig. 2, the conventional magnetic domain wall memory device has a basic structure of Pt 55a / Co 57 / Pt 55b. Here, since the magnetic layer, that is, the Co layer 57, has a very large saturation magnetization value of about 1400 emu / cc, when implemented with a thickness of 1 nm or more, the 'volume anisotropy' increases to lose vertical magnetism. That is, in the conventional Pt (55a) / Co (57) / Pt (55b) structure, the thickness of the Co layer 57 that can maintain the vertical magnetism when moving the magnetic domain is up to 1nm.

In the magnetic domain wall memory, the magnetic layer should be thick to maximize the spin torque effect and move the magnetic domain with a small current density.However, in the conventional magnetic domain wall memory device, the magnetic layer that can maintain the vertical magnetization has a maximum thickness of 1 nm. In order to move, a high current density is required, thereby causing a phenomenon in which the magnetic domain moving efficiency is lowered.

Hereinafter, the characteristics of the magnetic domain wall memory device using vertical magnetic anisotropy according to an embodiment of the present invention will be described in detail. Description of the characteristics of the magnetic memory device of the present invention will be described in detail by applying to the magnetic domain wall memory device.

According to the present invention, even if the thickness of the magnetic layer is increased by inserting a second magnetic layer having a saturation magnetization value smaller than that of the first magnetic layer between the first magnetic layers to minimize the phenomenon occurring in the conventional magnetic domain wall memory device described above, It is to be maintained as it is to improve the magnetic domain movement efficiency. That is, even if the thickness of the magnetic layer is formed thicker than the conventional, the surface anisotropy is maintained and the volume anisotropy is reduced to improve the magnetic domain movement efficiency.

3 is a cross-sectional view illustrating a structure of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

As shown in FIG. 3, Pt is used as the upper nonmagnetic layer 100a and the lower nonmagnetic layer 100b, and Co is used as the first upper magnetic layer 110a and the first lower magnetic layer 110b. Ni was used as the second magnetic layer 120. In particular, FIG. 3 is a diagram illustrating the Ni layer, that is, the second magnetic layer 120 having a maximum thickness capable of maintaining vertical magnetism in a wall-motion pattern in the Pt / Co / Ni / Co / Pt structure of the present invention. The Pt layer, that is, the lower nonmagnetic layer 100b, was formed to a thickness of 2 nm or more in order to clean the interface with the first lower magnetic layer 110b, and the Co layer, that is, the first upper magnetic layer 110a and the second lower magnetic layer 110b. Each was formed with a thickness of about 0.3 nm to reduce the total saturation magnetization value.

The thickness of the entire magnetic layer including the first upper magnetic layer (Pt) 110a / the second magnetic layer 120 (Ni) / the second lower magnetic layer (Co) (110b) structure is a conventional magnetic layer (Co) shown in FIG. (57) The thickness is more than four times the thickness, and since the resistance values of the upper and lower nonmagnetic layers (Pt) 100a and 100b are the largest, the current flows in the first upper magnetic layer (Pt) 110a and the second magnetic layer ( (120) (Ni) and the second lower magnetic layer (Co) (110b) flows to be able to maximize the magnetic domain movement effect by the current.

FIG. 4 is a photograph of a magneto-optic kerr effect microscope (MOKE) microscope showing a pattern of magnetic domain shifting in response to a change in magnetic layer thickness of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

As shown in Figure 4, according to an embodiment of the present invention, when the thickness of the Ni layer, that is, the second magnetic layer 120 in the Pt / Co / Ni / Co / Pt structure of the present invention is about 1nm to 4nm In Essence, a long wall, ie, the wall of the domain, appeared to move between the domains. In addition, when the thickness of the Ni layer was about 5 nm to 6 nm, stripe-growth patterns in which the domains extend in the shape of branches appeared. In addition, when the thickness of the Ni layer is about 7 nm or more, the vertical magnetism gradually loses, and a nucleation pattern occurs in which magnetic domains are irregular at various places.

Therefore, the magnetic memory device of the present invention has high magnetic domain movement efficiency since the magnetic layer can maintain the vertical magnetism even if the thickness of the magnetic layer is four times thicker than the thickness of the existing magnetic layer.

FIG. 5 is a graph illustrating a vertical hysteresis curve according to wall-motion, stripe-growth, and nucleation of a magnetic memory device according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the magnetic domain wall memory device of the present invention has a clean magnetization direction even when the Ni layer, that is, the second magnetic layer 120 has a thickness of about 4 nm in the Pt / Co / Ni / Co / Pt structure. It can be seen that the same operation as that of the conventional magnetic domain wall memory device can be performed.

In the conventional structure, when the magnetic layer thickness is 1 nm or more, the wall-motion pattern is lost. However, in the memory structure of the present invention, the wall-motion pattern is maintained even when the total thickness of the magnetic layer including the Ni layer and the Co layer is about 4.6 nm. By maximizing the magnetic domain movement efficiency by the current. That is, compared to the conventional Pt / Co / Pt structure, even if the thickness of the magnetic layer is more than four times thick, the vertical magnet can be maintained, so that the magnetic domain wall can be moved at a low current density, the magnetic domain movement efficiency can be improved.

In addition, by minimizing the number of interfaces by implementing a simple structure of Pt / Co / Ni / Co / Pt can be improved magnetic domain wall movement efficiency than the existing Co / Ni multilayer thin film structure.

As mentioned above, although the present invention has been described in detail by applying to magnetic domain wall memory devices, it is to be understood that the present invention is not limited thereto and may be applied to all magnetic memory devices using vertical magnetic anisotropy. Therefore, the embodiments of the magnetic domain memory device using the perpendicular magnetic anisotropy described above are illustrative in all respects and should not be considered as limiting, and the scope of the present invention is defined by the following claims rather than the detailed description. It should be construed that all changes or modifications shown and derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention.

1 is a diagram conceptually illustrating a configuration of a magnetic domain wall memory device using vertical magnetic anisotropy and a method of storing information;

2 is a cross-sectional view showing the structure of a magnetic domain wall memory device using the conventional perpendicular magnetic anisotropy.

3 is a cross-sectional view illustrating a configuration of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

FIG. 4 is a photograph of a magneto-optic kerr effect microscope (MOKE) microscope showing a pattern of magnetic domain shifting in response to a change in magnetic layer thickness of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

FIG. 5 is a graph illustrating vertical hysteresis curves according to wall-motion, stripe-growth, and nucleation of a magnetic memory device using vertical magnetic anisotropy according to an embodiment of the present invention.

******** Explanation of symbols for the main parts of the drawing ********

100a: upper nonmagnetic layer

100b: lower nonmagnetic layer

110a: first upper magnetic layer

110b: first lower magnetic layer

120: second magnetic layer

Claims (5)

Nonmagnetic layer; A first magnetic layer formed between the nonmagnetic layers; And A second magnetic layer formed between the first magnetic layers, Saturation magnetization value of the second magnetic layer is less than the saturation magnetization value of the first magnetic layer, Magnetic memory device using vertical magnetic anisotropy. The method of claim 1, The nonmagnetic layer includes Pt or Pd, Magnetic memory device using vertical magnetic anisotropy. The method of claim 1, The one magnetic layer includes Co or Co-based alloy, The second magnetic layer comprises Ni or Ni-based alloy, Magnetic memory device using vertical magnetic anisotropy. The method of claim 1, The first magnetic layer is, A first upper magnetic layer stacked on the second magnetic layer; And A first lower magnetic layer stacked below the second magnetic layer, The nonmagnetic layer, An upper nonmagnetic layer stacked on the first upper magnetic layer; And A lower nonmagnetic layer stacked below the first lower magnetic layer, Magnetic memory device using vertical magnetic anisotropy. A nonmagnetic layer comprising Pt or Pd; A first magnetic layer formed between the nonmagnetic layers and comprising Co or a Co-based alloy; And It is formed between the first magnetic layer, comprising a second magnetic layer containing Ni or Ni-based alloy, Magnetic memory device using vertical magnetic anisotropy.

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