JP2002368199A - Magnetic memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-power consumption magnetic memory. SOLUTION: The magnetic memory is provided with a free layer 38 for storing information and a high-resistance soft magnetic layer 41 on the side of a work line 231 or both sides of a bit line 251, which are used for flowing a current to write information in order to lead a magnetic field generated by a current flowing in the word line or the bit line into the free layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic memory cell in a magnetic random access memory, for example.

[0002]

2. Description of the Related Art A magnetoresistive effect whose electric resistance changes depending on the direction of magnetization of a ferromagnetic material can be used for a memory cell of a magnetic random access memory. Until now, anisotropic magnetoresistive (AMR effect) films and giant magnetoresistive (GMR effect) films have been used for memory cells. Since these films are made of metal, the resistance of the cells is reduced. The resistance change is small due to the change in the storage state.

In recent years, it has been reported that a ferromagnetic tunnel magnetoresistance effect (TMR effect) film in which a tunnel barrier layer is sandwiched between two ferromagnetic layers has a large resistance change at room temperature (1995). Journal of Magnetics and Magnetic Materials, Vol. 139, pp. L231-L234, published annually, has attracted attention as a memory cell of a magnetic memory.

Japanese Patent Application Laid-Open No. Hei 10-162326 discloses that T
A magnetic random access memory using an MR effect film as a memory cell is disclosed in Japanese Patent Application Laid-Open No. 11-161919, and a ferromagnetic layer is provided on at least one of a lower magnetic layer and an upper magnetic layer of a TMR effect film. A ferromagnetic tunnel magnetoresistive film using a three-layer film of / intermediate layer / ferromagnetic layer is disclosed.

[0005]

Problems to be solved by the magnetic memory include (1) obtaining a large resistance change, (2) having high stability, and (3) reducing power consumption.

In order to solve the problem (1), a coercive force is larger as a fixed layer of a magnetic tunnel junction memory element than a free layer, which is a magnetic layer for retaining information, as disclosed in Japanese Patent Application Laid-Open No. 10-162326. A structure has been proposed in which a large change in resistance is obtained by using a hard ferromagnetic layer having a multilayer structure.

In order to solve the problem (2), Japanese Patent Application Laid-Open No. 11-161919 discloses a ferromagnetic layer / intermediate layer / ferromagnetic layer in at least one of a lower magnetic layer and an upper magnetic layer. It has been proposed to use a three-layer film. This stabilizes the two magnetization states when the external magnetic field is zero by reducing the net magnetic moment of the ferromagnetic layer and reducing the magnetostatic interaction between the two ferromagnetic layers. is there.

[0008] Regarding the problem (3), it is considered that it is effective to reduce the current flowing through the conducting wire at the time of writing data in the magnetic memory, but it cannot be solved by the above two prior arts.

An object of the present invention is to provide a magnetic memory with low power consumption, particularly a magnetic memory with low power consumption when writing data.

[0010]

According to the present invention, the above object can be attained by providing the following magnetic memory.

That is, there is a cell for storing information magnetically in a region where the first and second plural conductors cross each other, and the cell includes a magnetoresistive effect film. By controlling the direction of magnetization of a magnetic layer that holds information, which is one layer of the magnetoresistive film, by a magnetic field generated by flowing a current through at least one of the first and second conductive wires, Is a magnetic memory capable of writing and reading, a magnetic layer holding information and a side portion of a conducting wire through which a current flows for writing information,
A high-resistance soft magnetic layer for guiding a magnetic field generated by a current for writing information to a magnetic layer holding information is provided.

At this time, an insulating layer may be provided between the high-resistance soft magnetic layer and a conductor through which a current flows for writing information, or between the high-resistance soft magnetic layer and the magnetic layer holding information. Good.

A conventional magnetic memory is, as shown in FIG.
A cell 30 is arranged in a region where a plurality of conductors 21 to 23 and 24 to 26 intersect. When a write current is applied to a conductor for writing data to a magnetic memory, a magnetic field is generated around the conductor in a circumferential direction around the conductor according to Ampere's law. Of the circumferential magnetic field, only the magnetic field passing through the magnetic layer holding information changes its magnetization direction. That is, it acts to rewrite information. As described above, only a small part of the magnetic field generated on the concentric circle around the conductor is used for rewriting information, and the power consumption is high due to low magnetic field utilization efficiency.

From the above, in order to reduce power consumption, it is necessary to increase the efficiency of using a magnetic field for rewriting information so that information can be rewritten with a small current. To achieve this, a magnetic flux guide is provided between the conducting wire for passing the rewrite current and the magnetic layer holding the information, so that the magnetic field does not spread to space and acts efficiently on the magnetic layer holding the information. May be provided.
At this time, use a high-resistance soft magnetic material as a material for the magnetic flux guide, or use a high-resistance soft magnetic layer so that the write current does not flow through the magnetic flux guide to another intersecting conductor. It is preferable that an insulating layer be provided between the conductive layer and a conducting wire through which a current flows for writing information or between the magnetic layer and the magnetic layer. As the high-resistance soft magnetic material, a multilayer film of an oxide film and a magnetic film, or a mixture of an oxide and a magnetic material can be used.

In the case where the cell of the magnetic memory is a magnetoresistive film utilizing the TMR effect in which two magnetic films are stacked via a barrier layer, a conductive material is formed on the side wall of the barrier layer. In such a case, the sense current for detecting the resistance change passes through the conductive material without passing through the barrier layer, and the resistance change does not occur. Therefore, use a high-resistance soft magnetic material for the magnetic flux guide, or use a high-resistance soft magnetic material. It is necessary to provide an insulating layer between the magnetic layer and a conducting wire through which a current flows for writing information, or between the magnetic layer and the magnetic layer holding information.

When the structure of the present invention is used, the next time generated from the conductive wire does not spread spatially, so that the magnetic field leaking to the adjacent memory cell can be reduced, the influence of disturbance at the time of writing is small, and the stability is reduced. A simple magnetic memory can be realized.

[0017]

Embodiments of the present invention will be described with reference to the drawings. First, the operation will be described with reference to the schematic diagram of the magnetic random access memory shown in FIG. In FIG. 1, a ferromagnetic tunnel magnetoresistance effect (TMR effect) film is used as a cell for magnetically storing information.

The parallel conductors 21, 22, 23 in one plane are word lines, and the parallel conductors 2 in another plane are word lines.
4, 25, and 26 are arranged as bit lines, and T is located at a position where the word line and the bit line intersect when viewed from above.
A memory cell 30 utilizing the MR effect is arranged. FIG.
FIG. 3 shows three bit lines, three word lines and nine memory cells.
In a memory, more bit lines, word lines, and memory cells are arranged.

The memory cell 30 includes a diode portion and a ferromagnetic tunnel junction as described later, and a detection current flows in the memory cell 30 in a vertical direction during the operation of the memory. Note that an anisotropic magnetoresistance effect (AMR effect) film or a giant magnetoresistance effect (GMR effect) film can be used as a cell. In this case, a current flows in the in-plane direction of the film.

Although not shown in FIG. 1, the bit line or the word line may be a circuit for selecting an arbitrary bit line or a word line to supply a detection current or a write current, or a detection circuit for detecting a resistance change. A circuit or the like is connected, and a space between the surface where the bit lines are arranged and the surface where the word lines are arranged, and where no memory cell is arranged, an insulating material layer is usually provided. ing.

FIG. 2 shows an example of the structure of the memory cell 30. The memory cell 30 includes a diode part 301 and a ferromagnetic tunnel junction part 302. The diode unit 301
This is a silicon junction diode including an n-type silicon layer 31 and a p-type silicon layer 32. Ferromagnetic tunnel junction 30
2 is a lower electrode layer 33, an underlayer 34, an antiferromagnetic layer 35,
The fixed layer 36, the barrier layer 37, the free layer 38, and the upper electrode layer 39 are stacked.

The lower electrode layer 33 is for electrically connecting the diode portion 301 to the ferromagnetic tunnel junction, and may be made of, for example, Ru, Pt, Hf, Zr, Ta, or the like.

The underlayer 34 is provided mainly for controlling the crystal orientation since the magnetic properties of the antiferromagnetic material and the magnetic material laminated thereon are greatly affected by the crystal orientation. Yes, specifically, a Ni-Fe alloy or an alloy containing at least one element selected from Cr, Ta, Mo, and Nb can be used.

The antiferromagnetic layer 35 is exchange-coupled with the fixed layer 36 made of a ferromagnetic material at its interface. Even when an external magnetic field acts, the magnetization of the fixed layer 36 does not move and always faces a certain reference direction. That's what you want. On the other hand, the free layer 38 is also made of a ferromagnetic material, but has a role of changing the direction of its magnetization and storing information when an external magnetic field of a certain magnitude or more acts thereon. The antiferromagnetic layer 35
Are Pt-Mn alloy, Pt-Pd-Mn alloy, Cr-Mn-Pt alloy, Ni-Mn alloy, Ir
-Mn-based alloys, Ru-Rh-Mn-based alloys, and Fe-Mn-based alloys can be used.

The fixed layer 36 and the free layer 38 are made of Ni, F
e, Co and alloys thereof, and it is desirable to use a material having a large spin polarizability at the interface with the barrier layer 37. The barrier layer 37 is a thin Al oxide, and the upper electrode layer 39 is made of Ru, Pt, Hf,
Zr, Ta, or the like can be used.

The free layer 38 has uniaxial anisotropy, and can take two stable states in the direction of the easy axis of magnetization. Each direction corresponds to stored information of "0" and "1". On the other hand, as described above, the fixed layer 36 has unidirectional anisotropy due to exchange coupling with the antiferromagnetic layer 35. By making the direction of the uniaxial anisotropy of the free layer 38 and the direction of the unidirectional anisotropy of the fixed layer 36 substantially parallel, the magnetizations of the free layer 38 and the fixed layer 36 are substantially parallel and substantially antiparallel. Will be.

In the ferromagnetic tunnel magnetoresistance effect,
Since the conductance is large in the substantially parallel state and the conductance is small in the substantially anti-parallel state, the state becomes a low resistance state and a high resistance state, respectively, and these can be extracted as "0" or "1" signals.

The information stored in the free layer 38 is rewritten by applying a write current of an appropriate magnitude to a word line and a bit line crossing in a memory cell to be rewritten (hereinafter referred to as a selected cell). By applying a magnetic field necessary to cross the hard magnetization axis. The current having the appropriate magnitude refers to a memory cell which is not to be rewritten (hereinafter, referred to as an unselected cell) among memory cells connected to a word line or a bit line through which a current flows.
This is the magnitude of the write current that acts only on the magnetic field that cannot exceed the hard magnetization axis, that is, the magnitude of the write current that does not cause magnetization reversal.

According to the present invention, a magnetic field generated by a write current flowing through a word line or a bit line is efficiently guided to a free layer 38 in a memory cell 30.
In this example, a new structure is adopted in the peripheral portion of 0.

FIG. 3 shows that the magnetic field generated by the write current (indicated by an arrow 54) flowing through the word line 231 is guided from the side surface of the word line 231 to the side surface of the free layer 38 in order to guide the free layer 38 holding information. An example in which a high-resistance soft magnetic layer 41 is provided up to this point is shown. The high-resistance soft magnetic layer 41 and the bit line 251 are not electrically connected. This is because, when reading information, the detection current flows from the bit line 251 to the memory cell 30.
Through the word line 231, if the high-resistance soft magnetic layer 41 and the bit line 251 are in electrical contact at this time, a part of the detection current is shunted to the high-resistance soft magnetic layer 41, This is because the current flowing through the memory cell 30 decreases and the output decreases.

When a write current flows in the direction of arrow 54 in FIG. 3, a magnetic flux flows in the direction of arrow 43 in the high resistance soft magnetic layer 41 and the free layer 38, and the current flows in the opposite directions. The direction of flow of magnetic flux is also in the opposite direction.

As the high-resistance soft magnetic layer 41, Co, N
i, a magnetic thin film containing at least one element of Fe and at least one selected from the group consisting of aluminum oxide, silicon oxide, tantalum oxide, zirconium oxide, hafnium oxide, aluminum nitride, silicon nitride, tantalum nitride, zirconium nitride, and hafnium nitride A stacked film with an oxide or nitride thin film containing
selected from the group consisting of a magnetic metal containing at least one of o, Ni, and Fe and aluminum oxide, silicon oxide, tantalum oxide, zirconium oxide, hafnium oxide, aluminum nitride, silicon nitride, tantalum nitride, zirconium nitride, and hafnium nitride. A mixed film containing at least one oxide or nitride or a spinel ferrite film can be used.

As a typical characteristic of these materials, Co
9 to 11 show characteristics of a laminated film of a ₉₀ Fe ₁₀ (atomic percent) film and an aluminum oxide film.

FIG. 9 shows a Co ₉₀ Fe film having a thickness of 1.5 nm.
A laminated film (hereinafter, referred to as a laminated film) in which a two-layer film of ₁₀ films and an aluminum oxide film having a thickness of 1.0 nm is laminated 20 times as a unit of lamination.
[CoFe (1.5 nm) / aluminum oxide (1.0
nm)] 20). The saturation magnetic flux density 4πMs is 9 kG (0.9T) and the coercive force is 5 Oe
(400 A / m), which is a sufficient property for passing a magnetic flux for reversing the magnetization of the free layer.

FIG. 10 shows the dependency of the specific resistance of the [CoFe / aluminum oxide (0.9 or 1.0 nm)] ultra-thin multilayer film on the CoFe film thickness, and FIG.
nm) / aluminum oxide] is the dependency of the specific resistance of the ultra-thin multilayer film on the thickness of the aluminum oxide film. From these results, it can be seen that a soft magnetic film having a high specific resistance, that is, a high resistance, can be obtained by reducing the CoFe film thickness, increasing the aluminum oxide film thickness, and increasing the number of layers.

These results indicate that using a [CoFe / aluminum oxide] ultra-thin multilayer film, the saturation magnetic flux density 4π
Ms is 9 kG (0.9 T) and coercive force is 5 Oe (400 A
/ M), a characteristic of specific resistance of 10 mΩ · cm or more can be realized,
This indicates that the material is suitable for a high-resistance soft magnetic layer that guides a magnetic flux generated by a current flowing through a word line or a bit line to a free layer.

In FIG. 3, the word line 231 and the memory cell 30 have the same width and the high-resistance soft magnetic layer 41 is provided on each side surface. However, such a structure is not necessarily required. The word line 231 may be wider than the width of the memory cell 30 and the high-resistance soft magnetic layer 41 may be provided above the word line 231 (FIG. 4), or may be provided above and on the side surface (FIG. 5).

Further, as shown in FIG.
When the insulating layer 42 is provided between the word line 231 and the high-resistance soft magnetic layer 41, there is no shunt of the detection current flowing at the time of reading, and a large resistance change can be obtained. Here, when the width 44 of the insulating layer 42 is increased, the magnetic path resistance of the magnetic path including the word line 231, the high-resistance soft magnetic layer 41, and the free layer 38 increases, and the effect of guiding the magnetic flux to the free layer 38 decreases. Therefore, the width 44 is desirably 100 nm or less. However, if the distance between adjacent memory cells is reduced, magnetic flux may enter the adjacent cells and information may be erroneously written. Therefore, the width 44 of the insulating layer 42 should be set to 1/3 or less of the distance between adjacent memory cells. Is desirable.

FIG. 7 shows another embodiment of the magnetic memory of the present invention. In this embodiment, the high-resistance soft magnetic layer 41 is
1 is arranged from the side surface to the side surface of the free layer 38. By applying a magnetic field in a direction orthogonal to the magnetization of the free layer 38, the magnetization of the free layer 38 can be reversed with a small magnetic field. As described above, the bit line 25 is
Power consumption can be reduced even if a current is supplied to the power supply 1.

FIG. 8 shows a structure in which the word line 231 and the free layer 38 are connected as a magnetic circuit, and the bit line 251 and the free layer 38 are further connected.
Are provided with high-resistance soft magnetic layers 411 and 412, respectively, in order to connect them as a magnetic circuit.

The structure shown in FIGS. 6 to 8 is a specific embodiment of the present invention. It is not necessary to provide a high-resistance soft magnetic layer on the side of a word line or a bit line. As described above, it may be provided on the upper or lower surface and the side surface of the word line or the bit line. 7 and 8, an insulating layer may be provided between the memory cell 30 and the word line (bit line) and the high-resistance soft magnetic layer 41.

[0042]

As described above, according to the present invention,
A free layer for holding information, and a high-resistance soft magnetic layer for guiding a magnetic field generated by a current flowing through the word line or the bit line to the free layer on a side of a word line or a bit line through which a current flows for writing information. Is provided, a magnetic memory with low power consumption can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic structure of a magnetic random access memory.

FIG. 2 is a perspective view showing a structure of a memory cell utilizing a ferromagnetic tunnel magnetoresistance effect.

FIG. 3 is a perspective view showing a configuration example of a memory cell provided with a high-resistance soft magnetic layer of the present invention.

FIG. 4 is a perspective view showing another configuration example of the memory cell provided with the high-resistance soft magnetic layer of the present invention.

FIG. 5 is a perspective view showing another configuration example of the memory cell provided with the high-resistance soft magnetic layer of the present invention.

FIG. 6 is a perspective view showing another configuration example of the memory cell provided with the high-resistance soft magnetic layer of the present invention.

FIG. 7 is a perspective view showing another configuration example of the memory cell provided with the high-resistance soft magnetic layer of the present invention.

FIG. 8 is a perspective view showing another configuration example of the memory cell provided with the high-resistance soft magnetic layer of the present invention.

FIG. 9 is a characteristic diagram showing a magnetic hysteresis curve of a [CoFe / aluminum oxide] multilayer film.

FIG. 10 is a characteristic diagram showing the dependency of the specific resistance of the [CoFe / aluminum oxide] multilayer film on the CoFe film thickness.

FIG. 11 is a characteristic diagram showing the dependence of the specific resistance of a [CoFe / aluminum oxide] multilayer film on the thickness of aluminum oxide.

[Explanation of symbols]

21, 22, 23, 231 ... word lines, 24, 25, 2
6, 251 bit line, 30 memory cell, 301 diode section, 302 ferromagnetic tunnel junction, 31 n
Type silicon layer, 32 p-type silicon layer, 33 lower electrode layer, 34 base layer, 35 antiferromagnetic layer, 36 fixed layer,
37: barrier layer, 38: free layer, 39: upper electrode layer, 4
1,411,412: high resistance soft magnetic layer, 42: insulating layer,
43: magnetic flux flow, 44: width of insulating layer, 54, 541,
542: Write current.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E049 AA01 AA04 AA07 AC00 AC05 BA06 CB01 DB12 5F083 FZ10 GA05 JA38 JA39 JA60

Claims (10)

[Claims] 1. A cell for storing information magnetically in a plurality of first and second plurality of conductors forming a plurality of intersection areas, and magnetically storing information in the plurality of intersection areas. Includes a magnetoresistive film, and retains information, which is one layer constituting the magnetoresistive film, by a magnetic field generated by passing a current through at least one of the first and second conductors. In a magnetic memory capable of writing and reading information by controlling the direction of magnetization of a layer, a current for writing the information is provided on a side of a magnetic layer holding the information and a conducting wire through which a current flows for writing the information. A high-resistance soft magnetic layer for guiding a magnetic field generated by the magnetic field to a magnetic layer holding the information. 2. The high-resistance soft magnetic layer is made of Co, Ni, Fe.
And a magnetic thin film containing at least one element selected from the group consisting of aluminum oxide, silicon oxide, tantalum oxide, zirconium oxide, hafnium oxide, aluminum nitride, silicon nitride, tantalum nitride, zirconium nitride, and hafnium nitride. 2. The magnetic memory according to claim 1, wherein the magnetic memory is a laminated film including an oxide or a nitride thin film. 3. The high-resistance soft magnetic layer is made of Co, Ni, Fe.
And at least one element selected from the group consisting of a magnetic metal containing at least one of the following and aluminum oxide, silicon oxide, tantalum oxide, zirconium oxide, hafnium oxide, aluminum nitride, silicon nitride, tantalum nitride, zirconium nitride, and hafnium nitride. 2. The magnetic memory according to claim 1, wherein the magnetic memory is a mixed film with an oxide or a nitride. 4. The magnetic memory according to claim 1, wherein an insulating layer is provided between the high-resistance soft magnetic layer and a conductor through which a current flows for writing the information. 5. The magnetic memory according to claim 1, wherein an insulating layer is provided between the high-resistance soft magnetic layer and the magnetic layer holding the information. 6. A magnetoresistive film constituting a cell for magnetically storing information includes a lower magnetic layer, a non-magnetic intermediate layer,
An upper magnetic layer is laminated, and one of the lower magnetic layer and the upper magnetic layer has its magnetization direction constrained with respect to a magnetic field generated by a current flowing through a conductor for writing the information, and On one side, the direction of the magnetization rotates with respect to the magnetic field generated by the current for writing the information,
2. The magnetic memory according to claim 1, wherein the magnetic memory is a magnetoresistive film whose resistance changes depending on the relative angle of magnetization of the lower magnetic layer and the upper magnetic layer. 7. The magnetic memory according to claim 6, wherein said non-magnetic intermediate layer is an oxide film. 8. The magnetic memory according to claim 6, wherein said non-magnetic intermediate layer is a nitride film. 9. The magnetic memory according to claim 6, wherein said nonmagnetic intermediate layer is a mixed film of an oxide and a nitride. 10. The magnetic memory according to claim 6, wherein said nonmagnetic intermediate layer is a laminated film of an oxide film and a nitride film.