JP2006318983A - Magnetic memory element and memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic memory element wherein enough high MR ratio can be realized and which can be stably manufactured at a low cost. <P>SOLUTION: The magnetic memory element 10 is provided with a memory layer 1, a tunnel insulating film 2, and a magnetization fixed layer 3. A ferromagnetic layer constituting at least either of the memory layer 1 and the magnetization fixed layer 3 contains at least one or more kinds of elements selected from Fe, Co and Ni and a B element, and it is comprised of a compound having a crystal structure. In this case, the period x of the unit crystal structure of crystals of the compound is within 0.19 nm≤x≤0.23 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic memory element and a memory (storage device) including the magnetic memory element.

  With the rapid spread of information communication devices, especially small personal information devices such as mobile terminals, the elements such as memory and logic that make up these devices have higher integration, higher speed, lower power consumption, etc. There is a need for performance. In particular, increasing the density and capacity of non-volatile memory is becoming a complementary technology to magnetic hard disks that are inherently difficult to reduce in size, increase speed, and reduce power consumption due to the presence of moving parts. It is becoming increasingly important.

  As nonvolatile memories, semiconductor flash memories, FeRAMs (ferroelectric nonvolatile memories) and the like have been put into practical use, and active research and development for further enhancement of performance is being performed.

Recently, an MRAM (Magnetic Random Access Memory) using a tunnel magnetoresistive effect has been experimentally produced as a new nonvolatile memory using a magnetic material, and has attracted attention (for example, see Non-Patent Document 1).
This MRAM is superior to the flash memory in that it is easy to perform random access, has a large number of rewritable times, and can be operated at high speed, and also has a large number of rewritable times. It is superior to FeRAM (ferroelectric memory). Furthermore, since it is expected that the high integration level is equivalent to that of a DRAM and the speed is equivalent to that of an SRAM, there is a possibility that all the mixed memories for the system LSI are replaced.

The MRAM has a structure in which minute magnetic memory elements for recording information are regularly arranged, and wirings such as word lines and bit lines are provided so that each of them can be accessed.
Each magnetic memory element includes a storage layer that records information as the magnetization direction of the ferromagnetic material.

  As a configuration of the magnetic memory element, a so-called magnetic tunnel junction (Magnetic Tunnel Junction) including the above-described storage layer, a tunnel insulating film (nonmagnetic spacer film), and a magnetization fixed layer whose magnetization direction is fixed. A structure using MTJ) is employed. The magnetization direction of the magnetization fixed layer can be fixed, for example, by providing an antiferromagnetic layer.

  In such a structure, a so-called tunnel magnetoresistance effect is produced in which the resistance value with respect to the tunnel current flowing through the tunnel insulating film changes depending on the angle between the magnetization direction of the storage layer and the magnetization direction of the magnetization fixed layer. Therefore, information can be written (recorded) by utilizing the tunnel magnetoresistance effect. The magnitude of the resistance value takes a maximum value when the magnetization direction of the storage layer and the magnetization direction of the magnetization fixed layer are antiparallel, and takes a minimum value when they are parallel.

In the magnetic memory element configured as described above, writing (recording) of information to the magnetic memory element is performed on the storage layer of the magnetic memory element by a combined current magnetic field generated by flowing current to both the word line and the bit line. This can be done by controlling the direction of magnetization. In general, the difference in magnetization direction (magnetization state) at this time is stored in association with “0” information and “1” information.
On the other hand, when reading recorded information, a memory cell is selected using an element such as a transistor, and the difference in the magnetization direction of the storage layer is determined by using the tunnel magnetoresistive effect of the magnetic memory element. By detecting as, it is possible to detect the recorded information.

  In the MRAM, in order to reduce the error rate and stably operate the memory, it is important to increase the magnetoresistance change rate (MR ratio) of the magnetoresistive element as much as possible.

Conventionally, a ferromagnetic material such as NiFe or CoFe has been generally used as a material of a ferromagnetic layer (a magnetization free layer and a magnetization fixed layer) of a tunnel magnetoresistive effect element using a magnetic tunnel junction (MTJ). Aluminum oxide (Al—O) has been used as a material for the insulating film.
Various research institutions have reported that the MR ratio of a magnetic tunnel junction element (MTJ element) using these materials is 20 to 50%.

On the other hand, by using an amorphous material in which a B element is added to a CoFe-based ferromagnetic material as the ferromagnetic layer (particularly the magnetization free layer) of the tunnel magnetoresistive effect element, the MR ratio is higher than that of the conventional configuration. (50 to 55%) has been reported to be obtained stably (see Non-Patent Document 2).
In this report, the addition of the B element to the ferromagnetic layer suppresses the diffusion of the O element of the aluminum oxide of the tunnel insulating film into the ferromagnetic layer, resulting in the deterioration of the magnetic polarizability of the ferromagnetic layer. It is considered that a high MR ratio was obtained.

  Further, it is disclosed that an effect of preventing interlayer diffusion and an effect of improving the continuity of the magnetic thin film can be obtained by adding B element to the ferromagnetic layer (see, for example, Patent Document 1 and Patent Document 2). reference).

In the various report examples described above, the ferromagnetic layer is amorphized or microcrystallized by adding the B element to the ferromagnetic layer.
When the ferromagnetic layer is microcrystallized by the addition of B element, the crystal structure of the microcrystalline particles reflects the crystal structure of the base magnetic material (for example, CoFe), and the face-centered cubic lattice (fcc) Alternatively, it has any structure of a body-centered cubic lattice (bcc).
Whether the ferromagnetic layer microcrystallized by adding the B element has an fcc or bcc structure depends on the composition ratio of the constituent elements of the base magnetic material. For example, a CoFe alloy has a bcc structure when the element composition is Fe-rich, and has an fcc structure when it is Co-rich. It has been reported that a CoFe alloy having a Fe composition of 25% or more has a bcc structure, and if the Fe composition is less than 25%, it has an fcc structure (see Patent Document 3).

  In the case of a magnetic material based on a 3d transition metal element such as Co, Fe, or Ni, the unit cell lattice constant is generally 0.28 to 0.29 nm for bcc and 0.35 to 0.36 nm for fcc. It is known that

On the other hand, an MTJ element using magnesium oxide (MgO) as a material for a new tunnel insulating film (nonmagnetic spacer layer) has recently been highlighted.
This is because a higher MR ratio can be realized by using magnesium oxide for the tunnel insulating film as compared with the case of using aluminum oxide.

  For example, in a single crystal MTJ element composed of Fe (001) / MgO (001) / Fe (001) epitaxially grown on a magnesium oxide MgO (001) single crystal substrate, an MR ratio exceeding 100% is reported for the first time at room temperature. (See Non-Patent Document 3 and Non-Patent Document 4).

Further, on the Si substrate having a silicon oxide film formed on the surface, it is made of TaN underlayer / IrMn antiferromagnetic layer / CoFe ferromagnetic pinned layer / MgO spacer layer / CoFe ferromagnetic free layer by sputtering film formation. 100) An oriented polycrystalline MTJ element is produced, and this MTJ element has been reported to have an MR ratio exceeding 200% at room temperature (see Non-Patent Document 5).
It has been reported that the CoFe ferromagnetic layer of the MTJ element having this configuration has a bcc structure. Since this MTJ element has a polycrystalline structure, it can be applied to a magnetic memory.

Wang et al., IEEETrans.Magn. 33, (1997), p4498 Intermag Europe 2002, BB04, April 2002 Jpn. J. Appl. Phys., 43, L588 (2004) Nature material, 3,868 (2004) Nature material, 3,862 (2004) JP 2001-68760 A JP 2002-204004 A JP 2003-124541 A

  However, with the materials and film configurations reported so far, MTJ elements having a sufficiently high MR ratio could not be produced stably and at low cost.

  When the B element is added to the ferromagnetic layer, the MR ratio is higher than that of the conventional configuration as described above, but it is difficult to greatly improve the MR ratio.

  In addition, the material described in Non-Patent Document 3 requires a single crystal substrate in order to produce a single crystal MTJ element, which increases the material cost and is difficult to apply to a magnetic memory.

Since the material described in Non-Patent Document 4 needs to be (100) oriented in the entire region from the lowermost IrMn layer to the uppermost ferromagnetic free layer in the multilayer film constituting the MTJ element, And the choice of antiferromagnetic materials is limited.
For this reason, the freedom degree of design of a film | membrane structure becomes low, and material cost becomes high correspondingly.

  In order to solve the above-described problems, the present invention provides a magnetic memory element that can obtain a sufficiently high MR ratio, can be stably manufactured at low cost, and a memory including the magnetic memory element. To do.

  The magnetic memory element of the present invention has a storage layer that retains information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer whose magnetization direction is fixed. The ferromagnetic layer constituting at least one of them is composed of a compound having at least one element selected from Fe, Co, and Ni and a B element and having a crystalline structure. The period x of the structure is in the range of 0.19 nm ≦ x ≦ 0.23 nm.

  The magnetic memory element of the present invention has a storage layer that retains information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer whose magnetization direction is fixed. The ferromagnetic layer constituting at least one of them is composed of a compound having at least one element selected from Fe, Co, and Ni and a B element and having a crystalline structure. The lattice constant a satisfies the following condition: 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).

  The memory according to the present invention includes a magnetic memory element and two types of wirings that intersect each other, and the magnetic memory element is disposed near the intersection of the two types of wirings. Thus, a magnetic field or current is applied, and the magnetic memory element has the configuration of the magnetic memory element of the present invention.

According to the above-described configuration of the magnetic memory element of the present invention, the ferromagnetic layer having the storage layer, the tunnel insulating film, and the magnetization fixed layer, and at least one of the storage layer and the magnetization fixed layer is Fe, Co. , Ni containing at least one element selected from Ni and B, and having a crystalline structure, a magnetic tunnel junction element comprising a memory layer, a tunnel insulating film, and a magnetization fixed layer is formed. The magnetoresistance change rate (MR ratio) can be increased.
And since the said compound has crystalline structure, MR ratio can be improved compared with the case where it is set as the amorphous structure or microcrystal structure containing the same element.

  Further, the period x of the unit crystal structure of the crystal of this compound is in the range of 0.19 nm ≦ x ≦ 0.23 nm, or the lattice constant a of the unit cell of the crystal of this compound is 0.19 × n By satisfying (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2), the crystal lattice of the tunnel insulating film (oxide film or the like) and the crystal lattice of the compound can be matched. . As a result, the crystal of the compound can be formed in a good state, so that a high MR ratio can be stably obtained with good reproducibility.

According to the present invention described above, a high MR ratio (for example, 200% or more) can be stably obtained with good reproducibility.
Thereby, in the magnetic memory element, the error rate can be lowered and the memory operation can be stably performed.
Moreover, since a high MR ratio can be obtained, the degree of freedom in designing the film configuration of the magnetic memory element is increased, and a magnetic memory can be manufactured at a low cost.

  Therefore, according to the present invention, it is possible to realize a memory that operates stably with few errors and at a low manufacturing cost.

  First, prior to description of specific embodiments of the present invention, an outline of the present invention will be described.

  As described above, in the MRAM, in order to reduce the error rate and stably operate the memory, it is required to increase the magnetoresistance change rate (MR ratio) of the magnetoresistive element as much as possible.

As a result of intensive studies, the present inventor has found a ferromagnetic material having a new structure different from the conventional structure.
This new material is characterized in that it is a compound containing at least one element selected from Fe, Co, and Ni, at least a B element, and having a crystalline structure.

Further, the crystal of this compound is characterized in that it has either of the following constitutions (1) or (2).
(1) The unit crystal structure of the compound crystal has a structure having a periodicity of a period x of 0.19 nm ≦ x ≦ 0.23 nm.
(2) The lattice constant a of the unit cell of the compound crystal satisfies 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).

In the MTJ element constituting the magnetic memory element, the new material having the above-described structure is used for the ferromagnetic layer constituting at least one of the magnetization free layer and the magnetization fixed layer sandwiching the tunnel insulating film.
In other words, one or all of the ferromagnetic layers constituting the memory layer are constructed using the above-described new material, and one or all of the ferromagnetic layers constituting the magnetization fixed layer are described above. The new material described above was used for one or all of the ferromagnetic layers constituting the storage layer and one or all of the ferromagnetic layers constituting the pinned magnetic layer. A configuration is mentioned.

  As a result, the MR ratio of the MTJ element can be made extremely high (for example, around 200%), and the magnetic memory element can be operated stably.

  It is also possible to directly stack a ferromagnetic layer composed of the above-described new material and another ferromagnetic layer having a different material or composition range to form a ferromagnetic layer constituting a memory layer or a magnetization fixed layer. Even in such a case, the effects of the present invention can be obtained.

As described above, when the compound material having the crystalline structure containing the B element is used as the ferromagnetic layer of the MTJ element, the MR ratio is dramatically improved, and an MR ratio exceeding 200% can be obtained. The reason for this is not well understood, but is thought to be due to physical properties unique to the material (for example, physical properties such as magnetic polarizability).
Therefore, if the structure of the compound material constituting the ferromagnetic layer satisfies the above-described conditions, a high MR ratio exceeding 200% can be obtained with good reproducibility without depending on the manufacturing method and the film configuration.

In the compound material described above, the content of B element is preferably 5% to 50% (atomic%).
If the content is 5% or more, the MR ratio can be sufficiently increased.
On the other hand, if the content is less than 5%, the B element may be precipitated at the grain boundaries or the like, and the compound may not be formed.
On the other hand, if the content exceeds 50%, the ferromagnetism disappears and a good MR ratio may not be obtained.

However, when the composition, film configuration, and manufacturing method of the CoFeB compound material are made exactly the same as the conventionally proposed configuration, it becomes amorphous or microcrystalline.
Therefore, in order to obtain a crystalline structure, at least a part of these manufacturing conditions is changed from a conventionally proposed configuration.

For example, the temperature of the substrate at the time of film formation or the temperature of the heat treatment step (including the ordering heat treatment step of the antiferromagnetic layer) after forming the laminated film is set to a range of 350 ° C. to 380 ° C. By applying heat (4 hours), the compound material (such as CoFeB) containing the B element can have a crystalline structure.
In the structure proposed conventionally, since it is only heat processing for a short time or lower temperature, it will be considered that it will become amorphous or a microcrystal.

  In addition, the compound material containing the B element can have a crystalline structure by adjusting the composition ratio and the film configuration of each element.

Subsequently, specific embodiments of the present invention will be described.
First, FIG. 1 shows a schematic configuration diagram (schematic perspective view) of an embodiment of a magnetic memory element of the present invention.
This magnetic memory element 10 shows a portion corresponding to one memory cell of a magnetic memory device such as an MRAM. From the upper layer side, a memory layer 1, a tunnel insulating film 2, and a magnetization fixed layer 3 are laminated. The magnetic tunnel junction MTJ is configured.

The storage layer 1 is made of a magnetic layer and can record the magnetization state, that is, the magnetization direction as information.
The tunnel insulating film 2 is made of an oxide film, a nitride film, or an oxynitride film, and is formed thin to allow a tunnel current to flow.
The magnetization fixed layer 3 is made of a magnetic layer, and the magnetization direction is fixed. For example, by providing an antiferromagnetic layer (not shown) to the magnetization fixed layer 3, the magnetization direction of the magnetization fixed layer 3 can be fixed.

The magnetic tunnel junction MTJ, a bit line (BL) 11, a write word line (WWL) 12, a read word line (RWL) 13, and a MOS transistor Tr for selecting a memory cell are included. Configured.
A bit line (BL) 11 is connected on the magnetic tunnel junction MTJ, and a write word line (WWL) 12 is disposed below the magnetic tunnel junction MTJ.
The read word line (RWL) 13 also serves as the gate G of the MOS transistor Tr.
The source (S) 16 and the drain (D) 17 of the MOS transistor Tr are formed in the semiconductor layer 21.
Further, a buffer wiring 14 is provided to connect the MOS transistor Tr and MTJ. The buffer wiring 14 has one end connected to the magnetic tunnel junction MTJ and the other end connected to the source 16 of the MOS transistor Tr via the contact layer 15.
The write word line (WWL) 12 is insulated from the MTJ, the read word line (RWL) 13 and the drain 17 of the MOS transistor Tr by an insulating layer (not shown).

  Information is written (recorded) in the magnetic memory element 10 by storing a current through both the bit line (BL) 11 and the write word line (WWL) 12 and using a resultant current magnetic field. This can be done by controlling the direction of magnetization of the layer 1.

  On the other hand, the recorded information is read out by selecting a memory cell using the MOS transistor Tr and using the tunnel magnetoresistance effect in the tunnel insulating film 2 of the magnetic memory element 10 to determine the magnetization direction of the storage layer 1. This can be done by detecting the difference as a voltage signal difference.

FIG. 2 is a schematic diagram of an MRAM integrated circuit configured by regularly arranging the magnetic memory elements 10 of FIG. In FIG. 2, the portion surrounded by a broken line corresponds to the magnetic memory element 10 shown in FIG.
A plurality of bit lines (BL) 11 extending in the vertical direction in the figure, and a plurality of write word lines (WWL) 12 and read word lines (RWL) 13 extending in the horizontal direction in the figure are arranged in parallel. A memory cell, that is, the magnetic memory element 10 shown in FIG. 1 is provided near the intersection of the wirings 11, 12, and 13.

  In the integrated circuit 100 having the configuration shown in FIG. 2, when information is written (recorded), the write word line (WWL) 12 and the bit line (BL) 11 corresponding to the memory cell to which information is written. The direction of magnetization of the storage layer 1 of the target memory cell where these wirings 11 and 12 intersect is controlled by a combined current magnetic field generated by flowing current in both.

On the other hand, when reading the information recorded in the memory layer 1 of the memory cell, the target memory cell is selected using the MOS transistor Tr. That is, the read word line (RWL) 13 connected to the target memory cell is set to High (ON state).
Further, by detecting the potential change of the bit line (BL) 11, information recorded in the target memory cell where the bit line (BL) 11 and the read word line (RWL) 13 intersect is read. At this time, the potential of the bit line (BL) 11 shows a value proportional to the magnetic resistance (ΔR) determined by the magnetization direction of the storage layer 1 of the magnetic memory element 10.
In this manner, information can be written and recorded information can be read from the target memory cell.

  Here, FIG. 3 shows a typical film configuration of the magnetic memory element 10 having the magnetic tunnel junction MTJ used in the integrated circuit 100 of FIG.

  FIG. 3 shows a bottom-type film configuration in which the magnetization fixed layer is disposed below the storage layer. That is, similarly to FIG. 1, the storage layer 1, the tunnel insulating film 2, and the magnetization fixed layer 3 are arranged from the upper layer side to form the magnetic tunnel junction MTJ, and the magnetization of the magnetization fixed layer 3 is formed below the magnetization fixed layer 3. An antiferromagnetic layer 4 for fixing the orientation is disposed. In the figure, reference numeral 31 denotes a base layer, an electrode, a buffer wiring for bypass, and the like, 32 denotes a protective layer, a bit line (BL), and the like.

In the present embodiment, in particular, at least one ferromagnetic layer of the storage layer 1 or the magnetization fixed layer 3 includes at least one element selected from Fe, Co, and Ni, and B element, and It is composed of a compound having a crystalline structure.
Moreover, the crystal | crystallization of this compound is set as the structure of either the following (1) or (2).
(1) The unit crystal structure of the compound crystal has a structure having a periodicity of a period x of 0.19 nm ≦ x ≦ 0.23 nm.
(2) The lattice constant a of the unit cell of the compound crystal satisfies 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).

  As described above, by configuring at least one of the ferromagnetic layers of the storage layer 1 or the magnetization fixed layer 3 from the compound having the crystalline structure described above, the MR ratio can be increased.

According to the magnetic memory element 10 of the present embodiment described above, at least one of the ferromagnetic layers of the storage layer 1 or the magnetization fixed layer 3 is made of one or more elements selected from Fe, Co, Ni, and the B element. Therefore, the MR ratio can be increased even when compared with an amorphous structure or a microcrystalline structure containing the same element.
Further, the crystal of this compound has (1) the unit crystal structure of the compound crystal has a structure with a periodicity of a period x of 0.19 nm ≦ x ≦ 0.23 nm. When the lattice constant a satisfies any one of the following conditions: 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2) The crystal lattice of an oxide (for example, magnesium oxide) used for the insulating film 2 can be matched. As a result, the crystal of the compound can be formed in a good state, so that a high MR ratio can be stably obtained with good reproducibility.

Thus, a high MR ratio (for example, 200% or more) can be obtained stably and with good reproducibility, so that the magnetic memory element 10 can be operated stably with a low error rate.
Further, since a high MR ratio can be obtained, the degree of freedom in designing the film configuration of the magnetic memory element 10 is increased, and a magnetic memory can be manufactured at a low cost.

  Therefore, using the magnetic memory 10 of the present embodiment, it is possible to realize a memory (storage device) that operates stably with few errors and at a low manufacturing cost.

In the magnetic memory element of the present invention, film configurations other than those shown in FIG. 3 are possible.
It is also possible to adopt a top type film configuration in which the magnetization fixed layer is disposed in an upper layer with respect to the storage layer, or a dual type film configuration in which the magnetization fixed layer is disposed in an upper layer and a lower layer with respect to the storage layer.
Further, for example, the magnetic layer (the storage layer 1 or the magnetization fixed layer 3) can have a laminated ferrimagnetic structure including two or more ferromagnetic layers with a nonmagnetic layer interposed therebetween. In this case, the number of laminated ferromagnetic layers may be any number depending on the device design, and such a structure is generally (ferromagnetic layer / nonmagnetic layer) _n + (ferromagnetic layer) (n is 0 or more) Integer).
With the film configuration as described above, the magnetic memory element 10 having the magnetic tunnel junction MTJ can be configured. The magnetic memory element 10 can be used to configure the integrated circuit 100 shown in FIG.

In the present invention, a magnetic material made of a compound having a crystalline structure containing B element may be used in at least one of the ferromagnetic layers constituting the memory layer and the magnetization fixed layer.
In addition to a structure using a magnetic material made of this compound for the entire ferromagnetic layer, a ferromagnetic layer made of a magnetic material made of this compound and a ferromagnetic layer made of another magnetic material are directly laminated to form a memory layer Or you may form the ferromagnetic layer which comprises a magnetization fixed layer.

  Subsequently, the magnetic memory element of the present invention was actually fabricated and its characteristics were examined.

  As shown in FIG. 4, the magnetization fixed layer 3 having the film configuration shown in FIG. 3 has a laminated ferrimagnetic structure composed of two ferromagnetic layers 5 and 7 and a nonmagnetic conductive layer 6 therebetween. A magnetic memory element having the film configuration shown was fabricated.

(Example)
In the film configuration shown in FIG. 4, the material and film thickness of each layer are as follows: a Ta film with a film thickness of 3 nm as the base material 31, a PtMn film with a film thickness of 25 nm as the antiferromagnetic layer 4, and the magnetization fixed layer 3 with a laminated ferrimagnetic structure. The ferromagnetic layer 5 is a Co80Fe20 film having a thickness of 1.8 nm, the nonmagnetic conductive layer 6 is a Ru film having a thickness of 0.8 nm, the ferromagnetic layer 7 is a Co64Fe16B20 film having a thickness of 2.0 nm, and the tunnel insulating film 2 is The MgO film having a thickness of 2.0 nm and the Co64Fe16B20 film having a thickness of 3 nm were selected as the memory layer 1.
That is, a Co 64 Fe 16 B 20 alloy having a Co composition of 64%, an Fe composition of 16%, and a B composition of 20% is used for the ferromagnetic layer 7 and the memory layer 1 of the magnetization fixed layer 3. As described above, the ferromagnetic layers (the ferromagnetic layer 7 of the magnetization fixed layer 3 and the memory layer 1) on both sides of the tunnel insulating film (MgO film) are made of Co64Fe16B20 alloy, and therefore, due to the physical properties of this alloy, MR The magnitude of the ratio will be determined.
After forming each of the above layers in sequence, a protective layer 32 made of a Ta film was formed thereon. Each layer was formed by sputtering.
Thereafter, in order to add antiferromagnetism to the PtMn film of the antiferromagnetic layer 4, heat treatment was performed at 360 ° C. for 2 hours.
Thus, the magnetic memory element having the film configuration shown in FIG. 4 was formed.

Since the two ferromagnetic layers 5 and 7 of the pinned magnetization layer 3 are laminated via the nonmagnetic conductive layer 6, the directions of the respective magnetizations are antiparallel, and are strongly antiferromagnetically coupled to each other.
Since the magnetization directions are antiparallel, the magnetic moments of the two ferromagnetic layers cancel each other, and the net magnetic moment of the entire magnetization fixed layer 3 is reduced. Since the pinning magnetic field is inversely proportional to the net magnetic moment, the result is that the pinning magnetic field is amplified.

The cross section of the sample of the magnetic memory element of the example was observed with a high-resolution transmission electron microscope (TEM).
The observation results are shown in FIG. 5A.
FIG. 5B shows a schematic diagram of lattice fringes in which the periodic contrast of the TEM image in FIG. 5A is connected by a straight line.

As shown in FIG. 6, MgO has a NaCl-type crystal structure, and Mg atoms and O atoms are alternately arranged.
The TEM image in FIG. 5A is an image reflecting the arrangement and periodicity of atoms as viewed from the [010] direction in FIG.

From FIG. 5A, the interval between the lattice fringes, that is, the interval between the (002) plane and the (200) plane is estimated to be 0.21 nm.
Further, the lattice constant “a” of the unit cell shown in FIG. 6 is 0.42 nm, which is twice as large as the (002) plane spacing (0.21 nm). The interval between the (002) planes of MgO is affected by the composition ratio of Mg and O in MgO, internal stress, etc., and changes by about 10%.

On the other hand, from FIG. 5A, lattice fringes are also observed in CoFeB (Co64Fe16B20), which indicates that it is crystalline.
The quadrangle formed by the lattice fringes in the lattice fringe schematic diagram of FIG. 5B can be considered as the minimum unit of Co64Fe16B20 crystals.
The quadrangular lattice stripes reflect an atomic arrangement when observed from the [010] direction of a spatial lattice such as cubic, tetragonal, orthorhombic, and monoclinic as shown in FIG.
From the TEM image in FIG. 5A, the interval between one side of the quadrangular shape was estimated as 0.19 (nm) ≦ a ≦ 0.23 (nm). The interval between the lattice fringes is considered to correspond to the lattice constant a. Depending on the composition ratio of B and the ferromagnetic element, there is a possibility that a regular lattice in which B and the ferromagnetic element are regularly arranged with a period twice as long as the lattice fringe may be formed as in the NaCl type crystal structure. In this case, the lattice constant a can be considered to be twice the interval between lattice fringes. Therefore, in general, the lattice constant a can be expressed as 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2). The meaning of multiplying the interval between the lattice fringes by n is a problem of the definition of the basic lattice, and does not mean that the lattice constant becomes large.

Which of the spatial lattices shown in FIG. 7 is taken depends on the local strain distribution, the content ratio (composition) of the B element, etc., but in actual materials, MgO and Co64Fe16B20 Since there are not a few local strains at the interface and fluctuations in the content (composition) of the B element, any of the spatial lattices in FIG. 7 can be taken even in the same film. In any spatial lattice, all of a1, a2, and a3 satisfy 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).
From another point of view, the crystal structure of Co64Fe16B20 is based on a cubic crystal, and the basic lattice is caused by local distortion at the interface between MgO and Co64Fe16B20 and fluctuations in the content (composition) of B element. Can be considered to be deformed.

It should be noted that the lattice constant a of the above-mentioned Co64Fe16B20 is the lattice constant (0.28 to 0.29 nm) of the CoFe alloy having the bcc structure or the lattice constant (0.35 to 0.36 nm) of the CoFe alloy having the fcc structure. It is a different point.
This indicates that this CoFeB material has a different crystal structure from the materials reported so far.

Subsequently, the distribution of each element of Co, O, and B in the magnetic memory element of the sample of the example was analyzed using an analysis method called an energy filter electron microscope method (energy filter TEM method).
This analysis method is also called imaging electron energy loss spectroscopy (imaging EELS method). The present inventor has found that this energy filter electron microscopic method is an indispensable inspection method for manufacturing an MRAM with a high yield, and includes an inspection process using electron energy loss spectroscopy. (See JP 2004-349574 A). Details of the measurement principle are described in the specification of this publication.

The analysis results are shown in FIGS. 8A and 8B.
FIG. 8A is called an energy filter TEM image, and shows a region where Co, O, and B elements exist with white contrast.
FIG. 8B shows the line profile result of the contrast intensity of the energy filter TEM image. The vertical axis indicates the position in the film thickness direction of the laminated film of the magnetic memory element, and the horizontal axis indicates the contrast intensity. The unit of the horizontal axis of the line profile is arbitrary, and the contrast intensity of each element is not quantified. Therefore, the line profile of FIG. 8B shows a relative distribution situation.

From the results of FIGS. 8A and 8B, it can be seen that the B element is uniformly distributed in the CoFeB film disposed on both sides of the MgO film.
This result means that the compound is formed as one element constituting the crystal lattice without the B element being precipitated at the crystal grain boundary.

(Comparative example)
Next, in the film configuration shown in FIG. 4, the ferromagnetic layer 7 and the memory layer 1 of the pinned magnetization layer 3 are the same as in the embodiment except that the Co composition is 80% Co and the Fe composition is 20%. A magnetic memory element was manufactured as a comparative sample.

MR ratio was measured about each sample of the magnetic memory element of an Example and a comparative example.
The measurement results are shown in Table 1.

  From Table 1, the MR ratio is about 45% in the comparative example using Co80Fe20 as the ferromagnetic layer, whereas the MR ratio as high as 220% is obtained in the example using Co64Fe16B20 as the ferromagnetic layer. I understand that.

In Non-Patent Document 5, an MR ratio of 200% or more is also reported for an MTJ element in which a CoFe ferromagnetic layer and an MgO layer are combined, but in this comparative example, only 50% or less MR is obtained. Not.
This suggests that in an MTJ element using CoFe as a ferromagnetic layer, the MR ratio is sensitively influenced by the layer configuration, CoFe composition, and crystal orientation.
Therefore, when a CoFe alloy material is used for a magnetic memory element for the purpose of obtaining a high MR ratio of 200% or more, the degree of freedom in designing the layer configuration of the magnetic memory element is reduced.

In the above-described embodiment, a CoFeB alloy is used as the compound having a crystalline structure containing B element according to the present invention, but the lattice constant does not change greatly even if it is replaced with another 3d transition metal having a close atomic radius.
However, in order to obtain ferromagnetic properties, at least one element selected from Fe, Co, and Ni needs to be included.
Further, the composition ratio of Co and Fe in the CoFeB alloy is not particularly limited, and the influence of the composition ratio of Co and Fe on the crystal structure and lattice constant is small.

(Relationship between heat treatment temperature and properties)
Next, after forming each layer of the magnetic memory element having the same film configuration as the above-described embodiment, a heat treatment step for 2 hours is performed, and the temperature of this heat treatment step is 265 ° C., 340 ° C., 360 ° C., and 380 ° C. Instead, samples of magnetic memory elements were produced.

The MR ratio was measured for each sample.
The measurement results are shown in FIG.

  FIG. 9 shows that the MR ratio increases as the heat treatment temperature increases.

  Further, the cross section of the laminated film of the magnetic memory element was observed by TEM for the sample heat-treated at 265 ° C. and the sample heat-treated at 380 ° C. A TEM image of the sample heat treated at 265 ° C. is shown in FIG. 10, and a TEM image of the sample heat treated at 380 ° C. is shown in FIG.

FIG. 10 shows that in the sample heat-treated at 265 ° C., CoFeB is crystallized only in the vicinity of the interface with the MgO film.
From FIG. 11, it can be seen that in the sample heat-treated at 380 ° C., the crystallization region spreads in the film thickness direction.
Therefore, when the heat treatment temperature is increased, it is presumed that the MR ratio is also increased by expanding the crystallization region.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic configuration diagram (schematic perspective view) of an embodiment of a magnetic memory element of the present invention. FIG. 2 is a schematic diagram of an MRAM integrated circuit in which the magnetic memory elements of FIG. 1 are regularly arranged. FIG. 2 is a cross-sectional view showing a film configuration of the magnetic memory element of FIG. 1. It is sectional drawing which shows the film | membrane structure of a magnetic memory element. A is a TEM image of a cross section of a sample of a magnetic memory element of an example. B is a schematic diagram of lattice fringes created from the TEM image of FIG. 5A. It is a figure which shows the crystal structure of MgO. It is a figure which shows various spatial lattices. It is the result of having analyzed distribution of each element of Co, O, and B in the magnetic memory element of the sample of an Example. A is an energy filter TEM image. B is a line profile of contrast intensity of the energy filter TEM image of FIG. 8A. It is a figure which shows the relationship between heat processing temperature and MR ratio of a magnetic memory element. It is a TEM image of a section of a sample heat-treated at 265 ° C. It is a TEM image of the cross section of the sample heat-processed at 380 degreeC.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Memory layer, 2 Tunnel insulating film, 3 Magnetization fixed layer, 4 Antiferromagnetic layer, 10 Magnetic memory element, 11 Bit line (BL), 12 Write word line (WWL), 13 Read word line (RWL), 14 Buffer Wiring, 100 integrated circuit, MTJ magnetic tunnel junction, Tr MOS transistor

Claims (6)

A storage layer that holds information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer in which the magnetization direction is fixed;
A compound in which at least one of the storage layer and the magnetization fixed layer includes at least one element selected from Fe, Co, and Ni and a B element and has a crystalline structure Consisting of
A magnetic memory element, wherein a period x of a unit crystal structure of the compound crystal is in a range of 0.19 nm ≦ x ≦ 0.23 nm. A storage layer that holds information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer in which the magnetization direction is fixed;
A magnetic layer having at least one of the storage layer and the magnetization fixed layer including at least one element selected from Fe, Co, and Ni and a B element and having a crystalline structure Composed of materials,
A magnetic memory element, wherein a lattice constant a of a unit cell of the compound crystal satisfies 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).   The magnetic memory element according to claim 1, wherein the tunnel insulating film is made of magnesium oxide.   The magnetic memory element according to claim 2, wherein the tunnel insulating film is made of magnesium oxide. A magnetic memory element;
Two types of wiring intersecting each other,
The magnetic memory element is disposed near the intersection of the two types of wiring;
A magnetic field or current is applied to the magnetic memory element by the two types of wirings,
The magnetic memory element includes a storage layer that retains information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer whose magnetization direction is fixed, and the storage layer or the magnetization fixed layer includes: Among them, the ferromagnetic layer constituting at least one is composed of a compound having at least one element selected from Fe, Co and Ni and a B element and having a crystalline structure. A memory characterized in that the period x of the unit crystal structure is in a range of 0.19 nm ≦ x ≦ 0.23 nm. A magnetic memory element;
Two types of wiring intersecting each other,
The magnetic memory element is disposed near the intersection of the two types of wiring;
A magnetic field or current is applied to the magnetic memory element by the two types of wirings,
The magnetic memory element includes a storage layer that retains information according to the magnetization state of the ferromagnetic layer, a tunnel insulating film, and a magnetization fixed layer whose magnetization direction is fixed, and the storage layer or the magnetization fixed layer includes: Among them, the ferromagnetic layer constituting at least one is composed of a compound having at least one element selected from Fe, Co and Ni and a B element and having a crystalline structure. A memory characterized in that a lattice constant a of a unit cell satisfies 0.19 × n (nm) ≦ a ≦ 0.23 × n (nm) (n is 1, 2).