JP2005203701A - Magnetoresistive effect element and magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetoresistive effect element capable of enhancing magnetic characteristics regardless of thermal history. <P>SOLUTION: A pair of ferromagnetic layers 5 and 7 are formed while sandwiching an intermediate layer 6 wherein at least one ferromagnetic layer 7 is arranged to change the direction of magnetization freely with respect to an external field. An underlying layer 3 touching one ferromagnetic layer 7 is a multilayer film of a Ta layer 31 and an Ru layer 32. In the multilayer film, the Ta layer 31 is formed in contact with one ferromagnetic layer 7 thus forming a magnetoresistive effect element 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetoresistive effect element and a magnetic memory device configured to obtain a change in magnetoresistance by flowing a current perpendicular to a film surface.

  With the rapid spread of information communication devices, especially small personal devices such as portable terminals, the elements such as memory and logic that compose this device have higher performance such as higher integration, higher speed, lower power consumption, etc. Is required. In particular, increasing the density and capacity of nonvolatile memory is becoming increasingly important as a technology that replaces hard disks and optical disks that are essentially impossible to miniaturize due to the presence of moving parts.

  Examples of the nonvolatile memory include a flash memory using a semiconductor and an FRAM (Ferro electric Random Access Memory) using a ferroelectric. However, the flash memory has a drawback that the writing speed is on the order of microseconds and is slow. On the other hand, in the FRAM, a problem that the number of rewritable times is small has been pointed out.

  For example, a magnetic memory device called MRAM (Magnetic Random Access Memory) is attracting attention as a non-volatile memory that does not have these drawbacks (see Non-Patent Document 1). Since this MRAM has a simple structure, it can be easily integrated and has a large number of rewritable times in order to store data by rotating a magnetic moment. The access time is also expected to be very high, and it has already been confirmed that it can operate in the nanosecond range.

Here, a configuration of a magnetoresistive effect element used in such an MRAM, for example, a tunnel magnetoresistive effect (Tunnel Magneto Resistance: TMR) element, will be described with reference to FIGS. 13A and 13B.
In the TMR element 60, as shown in FIG. 13A, a tunnel barrier layer 63 is sandwiched between a pair of ferromagnetic layers 61 and 62 to form a ferromagnetic tunnel junction 64. In this TMR element 60, an external magnetic field is applied in a state where a constant current flows between the ferromagnetic layers 61 and 62, so that the magnetoresistive effect depends on the relative angle of the magnetization direction of the ferromagnetic layers 61 and 62. Appears.
As shown in the figure, for example, when the magnetization directions (arrows in the figure) of both the ferromagnetic layers 61 and 62 are antiparallel, the resistance value is maximum, and as shown in FIG. When the magnetization directions (arrows in the figure) of the ferromagnetic layers 61 and 62 are parallel, the resistance value is minimum.

  Thus, the function as a memory element can be obtained by creating an antiparallel and parallel state by an external magnetic field.

  In addition to such a configuration, the TMR element forms an antiferromagnetic layer 65 adjacent to one of the ferromagnetic layers (in the case of FIG. 14A, the ferromagnetic layer 62), as shown in FIGS. 14A and 14B. Thus, by utilizing the antiferromagnetic coupling between the ferromagnetic layer 62 and the antiferromagnetic layer 65, one of the ferromagnetic layers 62 is magnetized with the magnetization direction (arrow in the figure) always fixed. A so-called spin-valve type TMR element is also known in which a fixed layer is used and the other ferromagnetic layer 61 is a magnetization free layer in which magnetization is easily reversed by an external magnetic field or the like.

  14A, the spin valve type TMR element 90 has a bottom layer in which the magnetization fixed layer 62 is formed below the tunnel barrier layer 63 and the magnetization free layer 61 is formed above the tunnel barrier layer 63. 14B, the spin-valve type TMR element shown in FIG. 14B has the magnetization fixed layer 62 formed above the tunnel barrier layer 63 and the magnetic field free layer 61 formed below the tunnel barrier layer 63. A top type TMR element 91 is shown.

When a magnetic memory device (MRAM) is configured using such a magnetoresistive effect element, although not shown, as described above, near the intersection of a bit write line and a word write line orthogonal to the bit write line. This is possible by forming a memory cell by arranging various magnetoresistive elements and forming an MRAM array (memory cell array) by arranging a plurality of such memory cells in a matrix.
When recording is performed in the magnetic memory device having such a configuration, selective writing is performed on the magnetoresistive element using asteroid characteristics (see Patent Document 1).
Wang et al., IEEE Trans Magn. 33 (1997), P.4498 JP 10-116490 A

  By the way, in the magnetic memory device (MRAM) described above, when there is a variation in the magnetic characteristics of the magnetoresistive effect element in each memory cell, or when the same magnetoresistive effect element is repeatedly measured, there is a variation in the magnetic characteristics. In this case, the asteroid characteristic is deviated from the center of the zero magnetic field, and there arises a problem that the selective writing property is deteriorated. That is, selective writing using asteroid characteristics becomes difficult.

  Therefore, an ideal asteroid curve needs to be drawn in the RH (resistance-magnetic field) curve of the resistance change rate (TMR ratio) of the magnetoresistive effect element. For this purpose, for example, in the RH curve, it is required that there is no noise (for example, Barkhausen noise), that the waveform has good squareness, and that there is little variation in coercive force Hc.

  In order to satisfy such a requirement, it is desirable to make the characteristics of each ferromagnetic layer as uniform as possible within the same TMR element or between TMR elements. To this end, each layer adjacent to the ferromagnetic layer is desirable. It is important to suppress compositional deviation caused by mutual diffusion or the like that occurs with (for example, a protective layer or a base layer).

  That is, for example, as shown in FIG. 15A, a protective layer 66 is formed on the magnetization free layer 61 of the bottom type TMR element shown in FIG. 14A, the magnetization free layer 61 is a CoFeB layer, and the protection layer 66 is Ta Consider the case of layers. In this case, the diffusion amount of B element from the magnetization free layer (CoFeB layer) 61 and the diffusion amount of Ta element from the protective layer (Ta layer) 66 when the thermal history is applied in the manufacturing process of the TMR element If there is a difference, a composition shift occurs between the magnetization free layer 61 and the protective layer 66. Since the composition deviation amount varies depending on the thermal history, the magnetic characteristics of the TMR element (for example, the coercive force Hc of the magnetization free layer 61) vary.

  Further, for example, as shown in FIG. 15B, the magnetization free layer 61 of the top type TMR element shown in FIG. 14B is formed on the electrode layer 68 through the base layer 67, and the magnetization free layer 61 is a CoFeB layer. Consider the case where the underlayer 67 is a Ta layer. Also in this case, the diffusion amount of B element from the magnetization free layer (CoFeB layer) 61 and the diffusion amount of Ta element from the underlayer (Ta layer) 67 when a thermal history is applied in the manufacturing process of the TMR element. If there is a difference between the two, a composition shift occurs between the magnetization free layer 61 and the underlayer 67. Since the composition deviation amount differs depending on the thermal history, the magnetic characteristics of the TMR element (for example, the coercive force Hc of the magnetization free layer 61) vary.

  In view of the above, the present invention provides a magnetoresistive effect element and a magnetic memory device having a configuration capable of improving magnetic characteristics regardless of thermal history.

  In the magnetoresistive effect element according to the present invention, a pair of ferromagnetic layers is formed with an intermediate layer interposed therebetween, and at least one of the ferromagnetic layers has a free magnetization direction with respect to an external magnetic field. The underlayer or protective layer in contact with one of the ferromagnetic layers is a laminated film of a Ta layer and a Ru layer, and in this laminated film, the Ta layer is formed in contact with one of the ferromagnetic layers. The configuration is as follows.

  According to the magnetoresistive effect element of the present invention described above, a pair of ferromagnetic layers are formed with an intermediate layer interposed therebetween, and at least one of the ferromagnetic layers is free from an external magnetic field. The magnetization direction is changed, and the underlayer or protective layer in contact with one of the ferromagnetic layers is a laminated film of a Ta layer and a Ru layer. In this laminated film, the Ta layer is in contact with one of the ferromagnetic layers. Therefore, it is possible to suppress a significant change in the amount of composition deviation between one ferromagnetic layer and the underlayer or protective layer due to a difference in thermal history applied in the element manufacturing process. Thereby, for example, variation in coercivity in the magnetization free layer can be suppressed, and the magnetic characteristics of the magnetoresistive element can be stabilized.

  In the magnetic memory device according to the present invention, a pair of ferromagnetic layers are formed with an intermediate layer interposed therebetween, and at least one of the ferromagnetic layers has a magnetization direction freely with respect to an external magnetic field. The underlayer or protective layer in contact with one ferromagnetic layer is a laminated film of a Ta layer and a Ru layer, and in this laminated film, a Ta layer is formed in contact with one ferromagnetic layer. The magnetoresistive effect element is configured to include a word line and a bit line sandwiching the magnetoresistive effect element in the thickness direction.

  According to the magnetic memory device of the present invention described above, since the magnetoresistive effect element has the configuration of the magnetoresistive effect element of the present invention, stable magnetic characteristics can be obtained in the magnetoresistive effect element. Thereby, for example, selective writing can be performed satisfactorily.

  According to the magnetoresistive effect element of the present invention, since the magnetic characteristics can be stabilized regardless of the thermal history, a high-performance and highly reliable magnetoresistive effect element can be obtained.

  In addition, by configuring a magnetic memory device using such a magnetoresistive effect element, for example, a magnetic memory device having excellent write characteristics can be obtained, so that a highly reliable magnetic memory device can be realized. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, an embodiment of a magnetoresistive effect element according to the present invention, for example, a tunnel magnetoresistive effect element, will be described with reference to FIG.
The tunnel magnetoresistive element (hereinafter referred to as a TMR element) 1 includes a substrate 2 made of, for example, silicon, an electrode layer 11, an underlayer 3, a magnetization free layer 7 as a ferromagnetic layer, a tunnel barrier. A layer (intermediate layer) 6, a magnetization pinned layer 5 that is a ferromagnetic layer, an antiferromagnetic layer 4, and a protective layer (topcoat layer) 8 are sequentially stacked.
In this TMR element 1, a ferromagnetic barrier junction 9 is formed by sandwiching a tunnel barrier layer 6 between a magnetization fixed layer 5 and a magnetization free layer 7 which are a pair of ferromagnetic layers. The TMR element 1 is a so-called spin-valve type TMR element in which one of the ferromagnetic layers is a magnetization fixed layer 5 and the other is a magnetization free layer 7. The TMR element 1 is a so-called top type TMR element in which a magnetization free layer 7 is formed below the tunnel barrier layer 6.

  The electrode layer 11 can be formed from a material such as Ta, for example. The electrode layer 11 is formed with a film thickness of 10 nm to 20 nm, for example.

The magnetization free layer 7 can be formed of any one of Fe, Co, and Ni, or an amorphous material containing B or more as a main component and containing B (for example, a CoFeB layer or a FeCoNiB layer).
When the TMR element 1 is used for an MRAM, the magnetization free layer 7 is used as an information storage layer.

  The tunnel barrier layer 6 can be formed by oxidizing or nitriding a metal film formed by sputtering or vapor deposition. The tunnel barrier layer 6 can also be formed by a CVD method using an organic metal and oxygen, ozone, nitrogen, halogen, halogenated gas, or the like.

  For example, as described above, the magnetization fixed layer 5 is coupled to the antiferromagnetic layer 4 so that the magnetization direction is always fixed.

The antiferromagnetic layer 4 can be formed of a material such as an Mn alloy containing Fe, Ni, Pt, Ir, Rh, Co oxide, Ni oxide, or the like.
The antiferromagnetic layer 4 is coupled to the magnetization fixed layer 5 which is one of the ferromagnetic layers, so that the magnetization direction of the magnetization fixed layer 5 is not reversed even when a magnetic field is applied, and the magnetization of the magnetization fixed layer 5 is This is a layer for always fixing the orientation of.

  The protective layer 8 can be formed using a material such as Ta, for example.

  In this embodiment, in particular, the underlayer 3 is a laminated film of the Ta layer 31 and the Ru layer 32, and the side in contact with the magnetization free layer 7 is the Ta layer 31.

  By configuring the underlayer 3 in contact with the magnetization free layer 7 in such a configuration, the amount of composition deviation generated between the magnetization free layer 7 and the underlayer 3 is greatly changed due to the difference in thermal history applied in the element manufacturing process. For example, variation in coercive force Hc in the magnetization free layer 7 can be improved.

  In the present embodiment, in the laminated film of the base layer 3, the side in contact with the magnetization free layer 7 is the Ta layer 31. For example, the side in contact with the magnetization free layer 7 with the lamination order reversed is the Ru layer 32. In this case, the change (variation) in the coercive force Hc in the magnetization free layer 7 is slightly increased. For this reason, the Ta layer 31 is the side in contact with the magnetization free layer 7.

  In addition, although the magnetization free layer 7 is formed as a single layer, for example, when the magnetization free layer 7 is composed of a plurality of ferromagnetic layers, the base layer 3 having the above-described configuration is formed in contact with the outermost layer. Thus, the same action can be obtained.

  Moreover, it is preferable that the film thicknesses of the Ta layer 31 and the Ru layer 32 are both in the range of 1 nm to 5 nm. When the Ta layer 31 and the Ru layer 32 exceed such a film thickness, the amount of mutual diffusion due to heat between the Ta free layer 7 and the magnetization free layer 7 further increases, so that the above-described operation of the present invention is difficult to obtain. .

The film thickness of the amorphous material used for the magnetization free layer 7 is preferably 1 nm or more and 15 nm or less. That is, by defining the film thickness within such a range, good magnetic properties can be ensured.
For example, when the thickness of the magnetization free layer 7 is less than 1 nm, the magnetic characteristics in the TMR element 1 are greatly impaired due to mutual diffusion due to heat.
Further, when the thickness of the magnetization free layer 7 exceeds 15 nm, the coercive force Hc in the TMR element 1 becomes excessively high.

  Here, the TMR element 1 having such a configuration was actually manufactured, and the change in the coercive force Hc in the magnetization free layer 7 after heat treatment was measured in the TMR element 1.

Specifically, the TMR element 1 according to the present embodiment in which the Ta layer 31 and the Ru layer 32 are formed in this order from the side in contact with the magnetization free layer 7 side is subjected to heat treatment from room temperature to 400 ° C. The change in the coercive force Hc in the layer 7 was measured.
Further, in this measurement, as a comparative example, a TMR element having a structure in which only a Ta layer is formed as an underlayer is manufactured, and the TMR element is similarly retained in the magnetization free layer after heat treatment. The change in the magnetic force Hc was measured.
In any case, the composition of the magnetization free layer was Co63Fe7B30 (atomic%). The layer configuration other than the base layer was the same.

The measurement results are shown in FIG.
In FIG. 2, a solid line X indicates a change in the coercive force Hc in the TMR element 1 of the present embodiment, and a broken line Y indicates a change in the coercive force Hc in the TMR element of the comparative example.

As shown in FIG. 2, in the case of the present embodiment in which the base film 3 has a laminated structure composed of the Ta layer 31 and the Ru layer 32, the magnetization free layer 7 at any heat treatment temperature (eg, 340 ° C., 360 ° C., 380 ° C.). It can be seen that the change in the coercive force Hc is suppressed to be small.
That is, this is because the underlying layer 3 is a laminated film of the Ta layer 31 and the Ru layer 32, and when a thermal history is applied, Ta elements and Ru elements that travel from the underlying layer 3 to the magnetization free layer 7 are applied. This is considered to be because the amount of interdiffusion changes, and this change in the amount of interdiffusion has some influence on the characteristics of the magnetization free layer 7.
On the other hand, in the case of the comparative example in which the underlayer is simply a single layer structure including only the Ta layer, the coercive force Hc in the magnetization free layer is greatly increased when the heat treatment temperature exceeds 360 ° C., for example. I understand.

  From these results, it is possible to stabilize the coercive force Hc in the magnetization free layer 7 by forming the underlayer 3 not only with the Ta layer 31 but also with a stacked structure of the Ta layer 31 and the Ru layer 32. I understood.

According to the TMR element 1 of the present embodiment described above, in the top type TMR element 1, the base layer 3 in contact with the magnetization free layer 7 is a laminated film of the Ta layer 31 and the Ru layer 32, and is in contact with the magnetization free layer 7. Since the Ta layer 31 is provided on the side, it is possible to suppress an increase in the composition deviation amount between the magnetization free layer 7 and the underlayer 3 due to a difference in thermal history applied in the element manufacturing process.
Thereby, for example, variation in the coercive force Hc in the magnetization free layer 7 can be suppressed. In addition, for example, the squareness of the RH curve of the TMR element 1 can be improved.
That is, the magnetic characteristics of the TMR element 1 can be improved regardless of the difference in thermal history.

Next, another embodiment of the magnetoresistive effect element according to the present invention will be described with reference to FIG.
In the above-described embodiment, a top-type spin-valve TMR element in which the magnetization free layer 7 is formed on the lower side with the tunnel barrier layer 6 interposed therebetween, and the magnetization fixed layer 5 and the antiferromagnetic layer 4 are formed on the upper side. The case of 1 was described.
In contrast, the present embodiment is a bottom type spin valve type in which the antiferromagnetic layer 4 and the magnetization fixed layer 5 are formed on the lower side with the tunnel barrier layer 6 interposed therebetween, and the magnetization free layer 7 is formed on the upper side. This is the case of the TMR element 10.
Since other configurations are the same as those shown in FIG. 1, the corresponding portions are denoted by the same reference numerals, and redundant description is omitted.

  In this embodiment, in particular, the protective layer 8 on the magnetization free layer 7 is a laminated film of the Ta layer 81 and the Ru layer 82, and the side in contact with the magnetization free layer 7 is the Ta layer 81.

  According to the magnetoresistive effect element 10 of the present exemplary embodiment, since the protective layer 8 in contact with the magnetization free layer 7 is formed as described above, the heat applied in the element manufacturing process is the same as in the case of the above-described exemplary embodiment. It is possible to suppress a large change in the composition shift amount generated between the magnetization free layer 7 and the protective layer 8 due to the difference in the history, and for example, to improve variation in the coercive force Hc in the magnetization free layer 7. it can.

  The specific configurations of the Ta layer 81 and the Ru layer 82 can be the same as those of the Ta layer 31 and the Ru layer 32 in the above-described embodiment. In addition, the configuration of each layer other than this can be the same as in the above-described embodiment.

  According to the present embodiment described above, in the bottom type TMR element 10, the protective layer 8 in contact with the magnetization free layer 7 is the laminated film of the Ta layer 81 and the Ru layer 82, and the layer in contact with the magnetization free layer 7 is the Ta layer. Since it is set to 81, for example, it is possible to suppress a change in the composition shift amount between the magnetization free layer 7 and the protective layer 8 due to a difference in temperature history in the element manufacturing process. Thereby, for example, variation in the coercive force Hc in the magnetization free layer 7 can be suppressed. Further, for example, the squareness of the RH curve of the TMR element 10 can be improved.

  In each of the above-described embodiments, as shown in FIGS. 1 and 3, the TMR elements 1 and 10 having a configuration in which the magnetization fixed layer 5 and the magnetization free layer 7 are each formed as a single layer will be described. However, in the present invention, the magnetization fixed layer 5 and the magnetization free layer 7 may have a laminated ferrimagnetic structure including a plurality of ferromagnetic layers and a nonmagnetic intermediate layer.

  For example, as shown in FIG. 4, in a bottom type TMR element in which a fixed magnetization layer 5 and an antiferromagnetic layer 4 are formed on the lower side of a tunnel barrier layer 6 and a free magnetization layer 7 is formed on the upper side. As in the embodiment shown in FIG. 3, the protective layer 8 is a laminated film of the Ta layer 81 and the Ru layer 82 and the magnetization fixed layer 5 is nonmagnetic between the pair of ferromagnetic layers 51 and 52. A laminated ferrimagnetic structure in which the intermediate layer 53 is sandwiched may be used.

  Further, as shown in FIG. 5, in the top type TMR element in which the magnetization fixed layer 5 and the antiferromagnetic layer 4 are formed on the upper side of the tunnel barrier layer 6 and the magnetization free layer 7 is formed on the lower side. As in the embodiment shown in FIG. 1, the underlayer 3 is a laminated film of a Ta layer 31 and a Ru layer 32, and the magnetization fixed layer 5 is nonmagnetic between the pair of ferromagnetic layers 51 and 52. A laminated ferrimagnetic structure in which the intermediate layer 53 is sandwiched may be used.

In the TMR element shown in FIGS. 4 and 5, the nonmagnetic intermediate layer 53 can be formed using a layer made of a material such as Ru, Rh, Ir, Cu, Cr, Au and Ag, for example. . Further, the nonmagnetic intermediate layer 53 is formed with a film thickness that provides antiferromagnetic coupling.
Since other configurations are the same as those shown in FIGS. 1 and 3, the corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  The laminated ferrimagnetic structure is not limited to the configuration in which the nonmagnetic intermediate layer 53 is sandwiched between the two ferromagnetic layers 51 and 52 as shown in FIGS. Further, a laminated ferrimagnetic structure including three or more ferromagnetic layers in which a nonmagnetic intermediate layer and a ferromagnetic layer are further formed may be used. Even in this case, the same operation as in the above-described embodiment can be obtained.

Next, an embodiment of a magnetic memory device according to the present invention using the TMR element having such a configuration will be described with reference to FIG.
In the present embodiment, a magnetic memory device will be described as an example of an MRAM.

  The magnetic memory device (MRAM) 20 has a plurality of word lines WL and a plurality of bit lines BL orthogonal to the word lines WL. At each intersection of the word lines WL and the bit lines BL, FIG. A TMR element (1, 10) as shown in FIG. 3 is arranged to form a memory cell 21, and a plurality of memory cells 21 are arranged to form an MRAM array 22. FIG. 6 shows an MRAM array 22 having a configuration in which 3 × 3 memory cells 11 are arranged in a matrix.

Next, the configuration of the memory cell 21 described above will be described with reference to FIG.
The memory cell 21 includes, for example, a transistor 27 including a gate electrode 24, a source region 25, and a drain region 26 on a silicon substrate 23. The gate electrode 24 constitutes a read word line WL1. A write word line WL2 is formed on the gate electrode 24 via an insulating layer (not shown). A contact metal 28 is connected to the drain region 26 of the transistor 27, and a base layer 29 is connected to the contact metal 28.

In the magnetic memory device (MRAM) 20 of the present embodiment, the TMR element 1 or 10 having the above-described configuration is formed at a position on the base layer 29 corresponding to the upper side of the write word line WL2.
A bit line BL orthogonal to the word lines WL1 and WL2 is formed on the TMR element 1 or 10.

  According to the magnetic memory device 20 of the present embodiment, by using the TMR element 1 or 10 having the above-described configuration, the magnetic characteristics of the TMR element 1 or 10 are stable. It becomes possible to do.

  In the present embodiment, the case where the TMR element of the present invention is applied to a magnetic memory device (MRAM) has been described. However, the TMR element of the present invention is not limited to such a magnetic memory device. The present invention can be applied to a magnetic head or a hard disk drive equipped with this magnetic head. In addition, the present invention can also be applied to various electronic devices such as integrated circuit chips, personal computers, mobile terminals, and mobile phones, and electrical devices.

(Example)
Next, the TMR elements of the above-described embodiments were actually fabricated and the characteristics were examined.
As described with reference to FIGS. 6 and 7, in the magnetic memory device 20, the switching transistor 27 and the like are formed in addition to the TMR element 1. In this embodiment, the characteristics of the TMR element 1 are as follows. In order to investigate, as will be described later, a characteristic evaluation element (Test Element Group: TEG) in which only a ferromagnetic tunnel junction was formed was prepared, and the characteristic was examined using this characteristic evaluation element.

(Experiment 1)
In the top type TMR element shown in FIG. 1, the thicknesses of the Ta layer 31 and the Ru layer 32 are respectively changed in order to define the optimum film thicknesses of the Ta layer 31 and the Ru layer 32 in the underlayer 3. Thus, the change in the coercive force Hc in the magnetization free layer 7 after the heat treatment was measured.

(Sample 1)
As shown in the plan view of FIG. 8 and the cross-sectional view taken along the line AA of FIG. 8, the word line WL and the bit line BL are orthogonally crossed on the substrate 33 as a characteristic evaluation element (TEG). A structure in which the TMR element 1 is formed in the vicinity of the intersection between the word line WL and the bit line BL is manufactured. The TEG has an elliptical shape with a TMR element having a minor axis of 5 μm and a major axis of 10 μm. Terminal pads 31 and 32 are formed at both ends of the word line WL and the bit line BL, respectively, and the word line WL and the bit line BL are connected to Al _2. The insulating layer 34 made of an O ₃ film is electrically insulated from each other.

Specifically, the TEG shown in FIGS. 8 and 9 was produced as follows.
First, after forming a word line material on the substrate 33 and masking it by photolithography, portions other than the word line WL were selectively etched by Ar plasma to form the word line WL. At this time, regions other than the word line WL were etched to a depth of 5 nm of the substrate 33. As the substrate 33, a silicon substrate having a thickness of 0.6 mm, on which a thermal oxide film having a thickness of 2 μm was formed, was used.

Subsequently, a TMR element having the following layer structure (1) was produced by a known lithography method and etching. In the layer structure (1), the left side of / is the substrate side, and the inside of () indicates the film thickness.
Electrode layer / underlayer (Ru layer 1 nm or 2 nm, Ta layer x nm) / magnetization free layer (6 nm) / Al—Ox / CoFe (2.5 nm) / Ru (0.8 nm) / CoFe (3 nm) / PtMn (30 nm ) / Ta (5 nm)-(1)

  In the layer configuration (1), the composition of the magnetization free layer 7 was Co63Fe7B30 (atomic%), and the composition of the layer made of CoFe other than the magnetization free layer 7 was Co75Fe25 (atomic%). Further, the magnetization fixed layer 5 has a laminated ferri structure.

The Al—Ox layer formed as the tunnel barrier layer 6 is formed by first depositing an Al film with a film thickness of 1 nm on the ferromagnetic layer 51 of the magnetization fixed layer 5 by using a DC sputtering method. The Al film was formed by plasma oxidation using ICP plasma with a flow ratio of 1: 1 and a gas pressure introduced into the chamber of 0.1 mTorr.
Further, although the oxidation time depends on the ICP plasma output, it was set to 30 seconds in the present example.
In addition, each layer other than the Al—Ox layer was formed using a DC magnetron sputtering method.

  After the TMR element 1 is formed on the word line WL in this way, a heat treatment is performed at 10 kOe, 250 ° C. for 5 hours in a magnetic field heat treatment furnace, and an ordered heat treatment of the PtMn layer that is the antiferromagnetic layer 4 is performed. As a result, a ferromagnetic tunnel junction 9 was formed.

Next, for example, an Al ₂ O ₃ film is sputtered to form an insulating layer 34 having a thickness of about 100 nm, and further, a bit line BL and terminal pads 31 and 32 are formed by using a lithography technique. The TEG shown in FIGS. 8 and 9 was obtained and used as the TEG of Sample 1.

In the TEG of Sample 1, after the heat treatment was performed by changing the thickness of the Ru layer 32 in the underlayer 3 to 1 nm or 2 nm and changing the thickness x of the Ta layer 31 within the upper limit of 5 nm. The change in coercive force Hc was measured.
Specifically, as described later, the RH curve was measured, and the coercive force Hc was obtained from the RH curve.

(Measurement of RH curve)
In a normal magnetic memory device such as an MRAM, information is written by reversing the magnetization of the TMR element with a current magnetic field. In this embodiment, the resistance value was measured by reversing the magnetization of the TMR element 1 with an external magnetic field. . That is, first, an external magnetic field for reversing the magnetization of the magnetization free layer 7 of the TMR element 1 was applied so as to be parallel to the easy axis of magnetization of the magnetization free layer 7. The magnitude of the external magnetic field for measurement was, for example, 500 Oe. Next, when sweeping from −500 Oe to +500 Oe, for example, when viewed from one of the easy axes of the magnetization free layer 7, the bias voltage applied to the terminal pad 31 of the word line WL and the terminal pad 32 of the bit line BL is 100 mV. Then, a tunnel current was passed through the ferromagnetic tunnel junction 9. The resistance value with respect to each external magnetic field at this time was measured, and the RH curve was obtained.

(Measurement of change in coercive force Hc)
The coercive force (Hc) is measured by measuring the RH curve using the above-described method of measuring the RH curve, and the magnetization fixed layer 5 and the magnetization free layer 7 are in an antiparallel state and have a high resistance. The external magnetic field value when the resistance value is half of the resistance value and the resistance value in the state where the magnetization fixed layer 5 and the magnetization free layer 7 are parallel and low in resistance is obtained as the coercive force (Hc ).
The coercive force Hc is measured after the heat treatment at 200 ° C. and after the heat treatment at 400 ° C., and the value obtained by subtracting the coercive force Hc after the heat treatment at 200 ° C. from the coercive force Hc after the heat treatment at 400 ° C. is ΔHc, The coercive force Hc after heat treatment at 200 ° C. was defined as Hc ₋ 200, and the change in coercive force depending on the heat treatment temperature was defined as ΔHc / Hc_200.

The measurement result of the change in the coercive force Hc of the TEG of Sample 1 is shown in FIG.
In FIG. 10, the hatched graph indicates the case where the thickness of the Ru layer 32 is 1 nm, and the open graph indicates the case where the thickness of the Ru layer 32 is 2 nm.

From FIG. 10, it can be seen that the change in the coercive force Hc after the heat treatment can be suppressed by using the base layer 3 as a laminated film of the Ta layer 31 and the Ru layer 32 as in the present embodiment described above. However, in this case, the Ru layer 32 needs to be formed with a film thickness of, for example, 2 nm (outlined) or more.
Note that when the Ru layer 32 is formed to a certain extent, grains increase with crystal growth, which causes an undesirable increase in interface roughness in the TMR element. Therefore, the Ru layer 32 is preferably formed with a film thickness of 5 nm or less.

  Further, in such a configuration, when the thickness x of the Ta layer 31 is formed in the range of 2 nm to 5 nm, the change in the coercive force Hc in the magnetization free layer 7 after the heat treatment is further suppressed. I understand.

It can also be seen that the change in the coercive force Hc is suppressed even when the thickness x of the Ta layer 31 is 0 (zero) nm, that is, when the underlayer 3 is formed of only the Ru layer 32.
However, in this case, since the Ru layer 32 is formed directly in contact with the amorphous material layer (CoFeB layer) which is desirable as the material of the magnetization free layer 7, this amorphous material layer is further grown as a crystalline material. This is not preferable when the magnetic characteristics are taken into consideration. Therefore, it is necessary to form the Ta layer 31 between the magnetization free layer 7 and the Ru layer 32.

  From the results of Experiment 1 as described above, in the case of the top type TMR element, the underlayer 3 in contact with the magnetization free layer 7 has a laminated structure of the Ta layer 31 and the Ru layer 32, so that the magnetic field free after the heat treatment is obtained. It was found that the change in the coercive force Hc in the layer 7 can be suppressed. In this case, the Ta layer 31 has a thickness x of 2 to 5 nm and the Ru layer 32 has a thickness of 2 to 5 nm, thereby changing the coercive force Hc in the magnetization free layer 7 after the heat treatment. It was found that can be further suppressed.

(Experiment 2)
In the bottom type TMR element shown in FIG. 3, in order to define the optimum film thickness of one Ru layer 82 in the protective layer 8, the film thickness of this Ru layer 82 is changed and heat treatment is performed. After that, the change of the coercive force Hc in the magnetization free layer 7 was measured.

(Sample 2)
A TMR element 10 having the following layer structure (2) was produced by a known lithography method and etching in the same manner as in Experiment 1 described above. In the layer structure (2), the left side of / is the substrate side, and the inside of () indicates the film thickness.
Ta (3 nm) / PtMn (30 nm) / CoFe (3 nm) / Ru (0.8 nm) / CoFe (2.5 nm) / Al—Ox / magnetization free layer (6 nm) / protective layer (Ta layer 5 nm, Ru layer ynm) -(2)

In the layer configuration (2), the composition of the magnetization free layer 7 was Co63Fe7B30 (atomic%), and the composition of the layer made of CoFe other than the magnetization free layer 7 was Co75Fe25 (atomic%). Further, the magnetization fixed layer 5 has a laminated ferri structure.
Then, the TEG shown in FIGS. 8 and 9 was obtained in the same manner as in Experiment 1 described above, and this was used as the TEG of Sample 2.

In the TEG of the sample 2, the film thickness y of the Ru layer 82 in the protective layer 8 is changed within the upper limit of 3 nm, and the change in coercive force Hc after the heat treatment at 200 ° C. and after the heat treatment at 400 ° C. Measurements were made.
Specifically, as described above, the RH curve was measured, and the coercive force Hc was obtained from the RH curve.

  The measurement result of the change in the coercive force Hc of the TEG of Sample 2 is shown in FIG.

As can be seen from FIG. 11, when the film thickness y of the Ru layer 82 is 0 (zero) nm as the protective layer 8 in contact with the magnetization free layer 7, that is, in the case of a TMR element in which only the Ta layer 81 is formed, It can be seen that the change in the coercive force Hc in the magnetization free layer 7 due to the heat treatment is increased.
On the other hand, when the Ru layer 82 is further formed on the Ta layer 81 to form a laminated film as in the present embodiment, the heat treatment is performed when the Ru layer 82 has a thickness of 1 nm and 3 nm. It turns out that the change of the coercive force Hc in the magnetization free layer 7 after that is suppressed.
However, from FIG. 11, it can be inferred that the change in the coercive force Hc in the magnetization free layer 7 after heat treatment increases as the film thickness y of the Ru layer 81 increases.

  From the results of Experiment 2 as described above, the protective layer 8 is formed by laminating the Ta layer 81 and the Ru layer 82 in this order from the side in contact with the magnetization free layer 7, so that the coercivity in the magnetization free layer 7 after the heat treatment is It was found that variation in Hc variation can be suppressed. Further, in this case, it has been found that if the film thickness y of the Ru layer 82 is too thick, the magnetic characteristics are affected.

(Experiment 3)
In the bottom type TMR element, in order to define the optimum film thickness of the other Ta layer 81 in the protective layer 8, the film thickness of the Ta layer 81 is changed and the magnetization free after the heat treatment is performed. The change in the coercive force Hc in the layer 7 was measured.

(Sample 3)
The TMR element having the layer configuration (3) similar to the layer configuration (2) except that the protective layer (Ta layer znm, Ru layer 1 nm) is changed from the layer configuration (2) of Experiment 2 as described above. Similarly to the case shown in Experiment 1, it was prepared by a known lithography method and etching.
Then, the TEG shown in FIGS. 8 and 9 was obtained in the same manner as in Experiment 1 described above, and this was used as the TEG of Sample 3.

In the TEG of Sample 3, the thickness z of the Ta layer 81 in the protective layer 8 is changed within the range of the upper limit of 5 nm, and the change in coercive force Hc after the heat treatment at 200 ° C. and after the heat treatment at 400 ° C. Measurements were made.
Specifically, as described above, the RH curve was measured, and the coercive force Hc was obtained from the RH curve.

  The TEG measurement result of Sample 3 is shown in FIG.

As can be seen from FIG. 12, by laminating the Ru layer 82 on the Ta layer 81, even if the film thickness z of the Ta layer 81 is changed within the range of 5 nm, the inside of the magnetization free layer 7 after the heat treatment It can be seen that the change in the coercive force is suppressed.
Here, it can be seen that the change in the coercive force Hc is suppressed even when the thickness z of the Ta layer 81 is 0 nm, that is, when the underlayer 3 is formed of only the Ru layer 82. However, in this case, it is known that the rate of change in resistance (TMR ratio) of the TMR element deteriorates, so it is necessary to form the Ta layer 81 between the magnetization free layer 7 and the Ru layer 82.

  From the results of Experiment 3 as described above, as in Experiment 2, the Ta layer 81 and the Ru layer 82 are stacked in this order from the side in contact with the magnetization free layer 7 to form the protective layer 8. It was found that the variation in the change in the coercive force Hc in the magnetization free layer 7 can be suppressed. Further, it has been found that when the protective layer 8 is formed only by the Ru layer 82, the magnetic characteristics of the TMR element are affected. In this case, it was found that it is preferable to form the Ta layer 81 so that the film thickness z is not too thick.

  Therefore, based on the results of Experiment 2 and Experiment 3, in the case of the bottom type TMR element 10, the Ta layer 81 and the Ru layer 82 are stacked in order from the side in contact with the magnetization free layer 7, and the protective layer 8 is formed. It can be seen that good magnetic properties can be obtained by forming the Ta layer 81 with a thickness z of 1 to 5 nm and a Ru layer 82 with a thickness y of 1 to 3 nm.

  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.

It is a schematic sectional drawing which shows one Embodiment of the magnetoresistive effect element which concerns on this invention. It is a graph which shows the change of the coercive force after the heat processing with the structure of this invention and the structure of a comparative example. It is a schematic block diagram which shows other embodiment of the magnetoresistive effect element which concerns on this invention. It is a schematic block diagram (the 1) which shows the other form of the magnetoresistive effect element based on this invention. It is a schematic block diagram (the 2) which shows the other form of the magnetoresistive effect element based on this invention. 1 is a perspective view showing an embodiment of a magnetic memory device according to the present invention. FIG. 7 is an enlarged cross-sectional view of a memory cell of the magnetic memory device shown in FIG. 6. It is a top view of TEG for TMR element evaluation used in an experiment. It is an expanded sectional view on the AA line of TEG shown in FIG. In a top type magnetoresistive effect element, it is a figure which shows the change of the coercive force after heat-processing by changing the film thickness of Ta layer and Ru layer, respectively. In a bottom type magnetoresistive effect element, it is a figure which shows the change of the coercive force after performing the heat processing by changing the film thickness of Ru layer. In a bottom type magnetoresistive effect element, it is a figure which shows the change of the coercive force after performing the heat processing by changing the film thickness of Ta layer. A and B are schematic cross-sectional views showing a main part of a conventional magnetoresistive element. A and B are diagrams for explaining a conventional spin valve magnetoresistive element. It is a figure for demonstrating the magnetoresistive effect element of A and B bottom type and a top type.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 10 ... TMR element, 2 ... Substrate, 3 ... Underlayer, 31 ... Ta layer, 32 ... Ru layer, 4 ... Antiferromagnetic layer, 5 ... Magnetization Fixed layer, 51, 52 ... Ferromagnetic layer, 53 ... Nonmagnetic intermediate layer, 6 ... Tunnel barrier layer, 7 ... Magnetization free layer, 8 ... Protective layer, 81 ... Ta Layer, 82 ... Ru layer, 9 ... ferromagnetic tunnel junction, 11 ... electrode layer, 20 ... magnetic memory device, 21 ... memory cell, 22 ... MRAM array

Claims (14)

A pair of ferromagnetic layers are formed with an intermediate layer in between,
Among the ferromagnetic layers, at least one of the ferromagnetic layers is configured to freely change the magnetization direction with respect to an external magnetic field,
The underlayer or protective layer in contact with the one ferromagnetic layer is a laminated film of a Ta layer and a Ru layer, and in the laminated film, a Ta layer is formed in contact with the one ferromagnetic layer. A magnetoresistive effect element.   2. The magnetoresistive element according to claim 1, wherein the underlayer is the laminated film, and the thicknesses of the Ta layer and the Ru layer are both in the range of 2 nm to 5 nm.   The protective layer is the laminated film, the thickness of the Ta layer is in the range of 1 nm to 5 nm, and the thickness of the Ru layer is in the range of 1 nm to 3 nm. The magnetoresistive effect element as described.   2. The magnetoresistive element according to claim 1, wherein the one ferromagnetic layer in contact with the underlayer or the protective layer has an amorphous or microcrystalline structure.   The magnetoresistive effect element according to claim 1, wherein a tunnel barrier layer is used as the intermediate layer.   2. The magnetoresistive element according to claim 1, wherein the one ferromagnetic layer in contact with the underlayer or the protective layer is a magnetization free layer or a part thereof.   2. The magnetoresistive element according to claim 1, wherein at least one of the pair of ferromagnetic layers has a laminated ferrimagnetic structure. A pair of ferromagnetic layers is formed with an intermediate layer interposed therebetween, and at least one of the ferromagnetic layers is configured to freely change the magnetization direction with respect to an external magnetic field, A magnetoresistive element in which the underlayer or protective layer in contact with the ferromagnetic layer is a laminated film of a Ta layer and a Ru layer, and in the laminated film, the Ta layer is formed in contact with the one ferromagnetic layer;
A magnetic memory device comprising a word line and a bit line sandwiching the magnetoresistive effect element in a thickness direction.   9. The magnetic memory device according to claim 8, wherein the underlayer is the laminated film, and the thicknesses of the Ta layer and the Ru layer are both in the range of 2 nm to 5 nm.   9. The protective layer is the laminated film, the thickness of the Ta layer is in the range of 1 nm to 5 nm, and the thickness of the Ru layer is in the range of 1 nm to 3 nm. The magnetic memory device described.   9. The magnetic memory device according to claim 8, wherein the one ferromagnetic layer in contact with the underlayer or the protective layer has an amorphous or microcrystalline structure.   The magnetic memory device according to claim 8, wherein a tunnel barrier layer is used as the intermediate layer.   9. The magnetic memory device according to claim 8, wherein the one ferromagnetic layer in contact with the underlayer or the protective layer is a magnetization free layer or a part thereof.   9. The magnetic memory device according to claim 8, wherein at least one of the pair of ferromagnetic layers has a laminated ferrimagnetic structure.

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