JP2009004692A - Magnetoresistive element and manufacturing method thereof - Google Patents

Abstract

A tunnel magnetoresistive element (TMR element) having a low element resistance and a high MR ratio is provided.
An underlayer 12, an antiferromagnetic layer 13, a pinned layer 14, a nonmagnetic coupling layer 15, a reference layer 16, a tunnel barrier layer 17, a free ferromagnetic layer 18, and a cap layer 19 are sequentially disposed above a substrate 11. In the formed tunnel magnetoresistive effect element (TMR element 10), the tunnel barrier layer 17 and a crystalline oxide film such as an MgO film are formed under a low oxygen partial pressure (for example, under a high vacuum of about 10 ⁻⁷ Pa). Then, the crystalline oxide film is brought into contact with oxygen gas or a gas containing oxygen. According to the TMR element 10 including the crystalline oxide film formed as described above, an MR ratio higher than the conventional one can be obtained.
[Selection] Figure 1

Description

  The present invention relates to a tunnel magnetoresistive effect element used for a magnetic device such as a magnetic disk device and a magnetic memory device, and a manufacturing method thereof.

  With the recent increase in recording density of magnetic disk devices, magnetic signals from recording media are becoming even smaller. For this reason, an improvement in the S / N ratio of the reading element used in the magnetic head of the magnetic disk device is required. Further, as the recording density of the magnetic disk device is increased, the transfer speed of the magnetic head reading element is also required to be improved.

  A TMR (Tunneling Magneto Resistance) element, which is a type of magnetoresistive effect element, has a higher MR ratio (Magneto Resistive ratio) than a GMR (Giant Magneto Resistance) element, and an S / N ratio. Because of its excellent ratio, it is becoming the mainstream as a reading element for magnetic disk devices currently being produced. Further, the TMR element is expected not only as a reading element of a magnetic disk device but also as a recording element for a magnetic memory device (MRAM: Magnetoresistive Random Access Memory).

  This TMR element has a ferromagnetic tunnel junction (TMJ: Tunneling Magnetic Junction) in which a tunnel barrier film is sandwiched between ferromagnetic films, and the resistance value of the ferromagnetic tunnel junction is changed by a change in magnetization of the ferromagnetic film. Change. This resistance value is low when the magnetic moment of the ferromagnetic film sandwiching the tunnel barrier film is parallel, and is high when the magnetic moment is antiparallel. The rate of change of the resistance value is the MR ratio, and a signal output accompanying a change in the ferromagnetic film is larger from a TMR element having a high MR ratio.

  It is known that characteristics such as the MR ratio of the TMR element are greatly influenced by the tunnel barrier film. TMR elements using AlO (aluminum oxide) film, MgO (magnesium oxide) film, and TiO (titanium oxide) film are known as tunnel barrier films, but when a crystalline MgO film is used as the tunnel barrier film Reported that a high MR ratio can be obtained (for example, Non-Patent Documents 1 to 5). As a method for forming this crystalline MgO film, there are an electron beam evaporation method (for example, Patent Document 3) and a sputtering method (for example, Patent Document 4). In particular, film formation by sputtering is highly mass-productive.

In addition, there is a technique such as Patent Document 1 or Patent Document 2 for forming an AlO film.
JP 2002-314166 A JP 2001-84532 A JP 2006-210391 A JP 2006-80116 A WH Butler et al., Physical Review B, Vol. 63 (2001), p.054416 J. Mathon et al., Physical Review B, Vol. 63 (2001), p.220403 S. Yuasa et al., Nature Materials, Vol. 3 (2004), p.868 SS Parkin et al., Nature Materials, Vol. 3 (2004), p.862 DD Djayaprawira et al., Applied Physics Letter, Vol. 86 (2004), p.92502

  By the way, since the TMR element includes an insulating film as a tunnel barrier layer, the resistance of the element is relatively large. For this reason, when a TMR element having a large element resistance is used in various devices, the time constant due to the resistance of the element and the stray capacitance such as wiring increases, and it becomes difficult to increase the transfer rate of the element. From the viewpoint of improving the transfer rate of the TMR element, it is necessary to reduce the element resistance. As one method for reducing the resistance of the TMR element, a method of making the tunnel barrier film thin and facilitating the flow of the tunnel current can be considered. However, when the thickness of the tunnel barrier film is reduced, a current flow path other than the tunnel current is generated due to a large influence of crystal defects in the tunnel barrier film and non-uniformity of the interface of the tunnel barrier film. There was a problem that the MR ratio was lowered.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a magnetoresistive effect element having a low element resistance and a high MR ratio, and a method for manufacturing the same.

  According to one aspect of the present invention, a first ferromagnetic layer formed above a substrate, a tunnel barrier layer made of a crystalline oxide formed on the first ferromagnetic layer, A magnetoresistive effect element comprising a second ferromagnetic layer formed on the tunnel barrier layer, wherein the tunnel barrier layer is made of a crystalline oxide film subjected to an oxygen exposure treatment. A magnetoresistive effect element is provided.

  According to the above viewpoint, since there are few crystal defects such as oxygen defects in the crystalline oxide constituting the tunnel barrier layer, the scattering of tunnel electrons is difficult to occur. For this reason, tunnel electrons passing through the tunnel barrier film are more greatly affected by the difference in the magnetization directions of the first and second ferromagnetic layers than in the prior art, and the MR ratio can be further improved. In addition, the current flow path other than the tunnel current due to crystal defects in the crystalline oxide is reduced, and the ratio of the tunnel current is increased. For this reason, even a TMR element having a thin tunnel barrier layer can obtain a higher MR ratio than the conventional one. As a result, a TMR element having a low element resistance and a high MR ratio can be obtained.

  In the magnetoresistive effect element according to the above aspect, it is preferable that a high MR ratio is obtained by forming the tunnel barrier film with crystalline MgO.

  According to another aspect of the present invention, a step of forming a first ferromagnetic layer made of a ferromagnetic material above a substrate, and a tunnel barrier made of a crystalline oxide on the first ferromagnetic layer. A step of forming a layer, a step of exposing the tunnel barrier layer to oxygen exposure, and a step of forming a second ferromagnetic layer made of a ferromagnetic material on the tunnel barrier layer. A method of manufacturing a magnetoresistive element is provided.

  According to the method of manufacturing a magnetoresistive effect element of this aspect, after the crystalline oxide layer is formed as the tunnel barrier layer, the crystalline oxide is subjected to oxygen exposure treatment. For this reason, the crystalline oxide can be brought into contact with oxygen without oxidizing and degrading the first ferromagnetic layer serving as a base of the crystalline oxide film. In addition, since oxygen defects (crystal defects) in the tunnel barrier layer are reduced by the oxygen exposure treatment of the crystalline oxide, according to the manufacturing method according to this aspect, tunnel electrons are scattered in the tunnel barrier layer due to oxygen defects, oxygen A magnetoresistive element with less current flow path generation other than the tunnel current due to defects (crystal defects) can be obtained. For this reason, according to this aspect, a high MR ratio can be obtained even when the tunnel barrier film is thin and the element resistance is low, so that a magnetoresistive effect element can be manufactured with a high information transmission speed.

  In the method for manufacturing a magnetoresistive effect element according to the above aspect, it is preferable that the tunnel barrier film is formed by sputtering under high vacuum using MgO as a target. An MgO film having good crystallinity can be formed with high productivity by forming a film by sputtering using MgO as a target. Further, since the film formation is performed under a high vacuum, the crystalline MgO film can be formed without deteriorating the first ferromagnetic layer as a base. Furthermore, since the crystalline MgO film is subjected to oxygen exposure treatment, a crystalline MgO film with few oxygen defects (crystal defects) can be obtained, and a magnetoresistive element having a high MR ratio can be manufactured even if the film thickness is small.

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

(First embodiment)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing a magnetoresistive effect element (TMR element 10) according to a first embodiment of the present invention, and FIG. 2 shows a magnetoresistive effect element according to an experimental example and a comparative example of the first embodiment. It is a graph which shows the relationship between RA (resistance area product) and MR ratio.

  As shown in FIG. 1, the TMR element 10 of this embodiment is a laminated structure, and in order above the substrate 11, an underlayer 12, an antiferromagnetic layer 13, a pinned layer 14, a nonmagnetic coupling layer 15, and a reference layer. 16, a tunnel barrier layer 17, a free ferromagnetic layer 18, and a cap layer 19 are stacked. Hereinafter, these configurations will be described in more detail.

As the substrate 11, for example, a ceramic substrate made of Al ₂ O ₃ —TiC or the like, or a Si single crystal substrate can be used. Further, an insulating film or a conductive film may be formed between the substrate 11 and the base layer 12. For example, in the case of the TMR element 10 used in the magnetic memory device, an interlayer insulating film or a conductive film such as Al or Cu may be formed between the substrate 11 and the base layer 12 (see FIGS. 9), in the case of the TMR element 10 for a magnetic head, a NiFe film or the like may be formed as a magnetic shield material (see FIG. 4 described later).

  The underlayer 12 is a layer formed in order to improve the crystallinity of a film formed thereabove, and is composed of, for example, a Ta film of 5 nm or more, a Ru film, or a laminated film thereof. FIG. 1 shows an example in which the base layer 12 is configured as a laminated film, and the base layer 12 is configured by a substrate-side base layer 12a and an upper base layer 12b. In this case, the substrate-side base layer 12a can be configured as a Ta film having a thickness of 3 nm, for example, and the upper base layer 12b can be configured as a Ru film having a thickness of 2 nm, for example. Both the substrate-side base layer 12a and the upper base layer 12b are formed by sputtering or the like.

  The antiferromagnetic layer 13 is a layer formed on the base layer 12 and is formed to fix the magnetization direction of the pinned layer 14. The antiferromagnetic layer 13 is made of, for example, a TM-Mn alloy having a film thickness of 5 to 30 nm (including at least one of TM = Pt, Pd, Ni, and Ir), such as IrMn, PtMn, and PdPtMn. , Formed by sputtering or the like. The antiferromagnetic layer 13 is regularly alloyed by heat treatment, and antiferromagnetism appears. By performing heat treatment while applying a magnetic field in a predetermined direction, exchange coupling is generated by exchange interaction with the pinned layer 14, and the magnetization direction of the pinned layer 14 can be fixed. This heat treatment can be performed, for example, after forming the cap layer 19 in a vacuum atmosphere at 250 ° C. to 350 ° C., a heating time of 2 hours to 4 hours, and an applied magnetic field of 1.5 T.

  The pinned layer 14 is a layer formed on the antiferromagnetic layer 13 and is composed of a ferromagnetic film such as Fe, Co, Ni, or an alloy thereof (for example, a CoFe alloy) having a thickness of 1 to 30 nm. The The nonmagnetic coupling layer 15 is a layer formed on the pinned layer 14 and has a thickness of about 0.4 to 0.9 nm of Ru (or Ru-based alloy), Rh (or Rh-based alloy), or Ir ( Or an Ir-based alloy). The pinned layer 14 and the nonmagnetic coupling layer 15 can be formed by sputtering or the like.

  The reference layer 16 is a layer formed on the nonmagnetic coupling layer 15 and is composed of a CoFe film, a NiFe film, a CoFeB film, or the like having a thickness of 1 to 30 nm. When the tunnel barrier layer 17 is composed of a crystalline MgO film, it is preferable to use CoFeB for the reference layer 16 because a high MR ratio can be obtained. The reference layer 16 can be formed by a sputtering method or the like. The pinned layer 14, the nonmagnetic coupling layer 15, and the reference layer 16 configured as described above constitute a synthetic ferri-pin layer (exchange coupling film). That is, the reference layer 16 is antiferromagnetically exchange-coupled with the pinned layer 14 via the nonmagnetic coupling layer 15, and the magnetization direction of the reference layer 16 is antiparallel to the magnetization direction of the pinned layer 14. It is fixed to.

  The tunnel barrier layer 17 is a layer made of an insulating film formed on the surface of the reference layer 16 and is composed of a crystalline oxide film that has been subjected to oxygen exposure treatment. This crystalline oxide film is composed of, for example, a crystalline MgO film. The thickness of the crystalline oxide film can be variously selected depending on the application, but it is as much as possible from the viewpoint of obtaining high-speed information transfer speed by lowering element resistance suitable for a reading element such as a magnetic head, in particular, element resistance. It is desirable to form it thinly. For example, when the crystalline oxide film is an MgO film, the thickness can be 1.2 nm or less, more preferably 1 nm or less. This crystalline MgO film can be formed by sputtering using MgO as a target.

Since the crystalline oxide film is formed under a low oxygen partial pressure (for example, a vacuum atmosphere having a total pressure of about 10 ⁻⁷ Pa) in order to prevent oxidative deterioration of the reference layer 16, the crystalline oxidation film immediately after the film formation is formed. The material film contains oxygen defects. In the present embodiment, the tunnel barrier film 17 is configured as a crystalline oxide film having few crystal defects such as oxygen defects by performing an oxygen exposure treatment after forming a crystalline oxide film containing oxygen defects. For example, in the case of a crystalline MgO film, after forming the crystalline MgO film, the MgO film is brought into contact with an oxygen gas having an oxygen partial pressure of 10 ³ Pa or less at room temperature or a gas containing oxygen for a predetermined time. This oxygen exposure treatment can reduce crystal defects such as oxygen defects in the crystalline MgO film. Further, since the oxygen exposure treatment is performed after the formation of the crystalline MgO film, the underlying ferromagnetic film (reference layer 16) is less likely to be oxidized and deteriorated near the interface between the tunnel barrier film 17 and the reference layer 16. Can be suppressed.

  The free ferromagnetic layer 18 is a layer formed on the tunnel barrier film 17 and has a thickness of 1 nm to 30 nm and includes a ferromagnetic material containing at least one of Co, Ni, and Fe, for example, CoFe, CoFeB, NiFe. (Permalloy) or the like, or a laminate of films made of these materials. The material of the free ferromagnetic layer 18 can be appropriately selected according to the application. For example, when CoFeB is used, a high MR ratio can be obtained, so that the TMR element 10 suitable for a recording element such as a magnetic memory can be obtained. Further, by using a ferromagnetic material having a low coercive force such as a CoFe / NiFe laminated film or NiFe, the TMR element 10 suitable for a magnetic head or the like can be obtained. The free ferromagnetic layer 18 may be a laminated free layer using a nonmagnetic layer as an intermediate layer, and may be composed of, for example, CoFeB / Ru / CoFeB. The free ferromagnetic layer 18 is formed by sputtering or the like. The magnetization of the free ferromagnetic layer 18 is directed in the in-plane direction. For example, the magnetization direction changes depending on the magnetic field leaking from the magnetic recording medium or the magnetic field generated by the current flowing through the word line of the magnetic memory device.

  The cap layer 19 is a layer formed on the free ferromagnetic layer 18 and is composed of, for example, a Ta film having a thickness of 3 nm or more, a Ru film, or a laminated film thereof. In the example shown in FIG. 1, the cap layer 19 has a laminated structure of a substrate-side cap layer 19a (for example, a Ta film having a thickness of 5 nm) and an upper cap layer 19b (for example, a Ru film having a thickness of 10 nm). The cap layer 19 (substrate-side cap layer 19a and upper cap layer 19b) is formed by sputtering or the like.

  Hereinafter, a method for manufacturing the TMR element 10 according to the present embodiment will be described using the TMR element 10 shown in FIG. 1 as an example.

A substrate side underlayer 12a, an upper underlayer 12b, an antiferromagnetic layer 13, a pinned layer 14, a nonmagnetic coupling layer 15, and a reference layer 16 are sequentially formed on the substrate by sputtering. In any process, film formation can be performed at room temperature. These steps are performed under high vacuum (about 10 ⁻⁷ Pa), and the substrate is also transferred under high vacuum, thereby preventing oxidative degradation of the metal film constituting the ferromagnetic layer and the like. After the formation of the reference layer 16, the tunnel barrier layer 17 is formed. In the formation process of the tunnel barrier layer 17, a crystalline oxide film is first formed. When forming an MgO film as the crystalline oxide film, the MgO film is formed on the reference layer 16 by sputtering using MgO as a target. By this step, a crystalline MgO film can be formed. In this step, if the oxygen partial pressure during film formation is high, the underlying reference layer 16 is oxidized and deteriorates, and therefore, it is performed under a low oxygen partial pressure (for example, in a vacuum atmosphere with a total pressure of about 10 ⁻⁷ Pa). It is desirable.

  Next, the formed crystalline oxide film is subjected to oxygen exposure treatment. In this case, the substrate on which the crystalline oxide film is formed is transferred from the deposition chamber to the oxygen exposure chamber. This is because when oxygen exposure processing is performed in the film forming chamber, it is necessary to perform processing for lowering the oxygen partial pressure such as decompression or purging before performing the next substrate film forming processing, and the procedure becomes complicated. This is because the ferromagnetic film (reference layer 16) may be oxidized and deteriorated by oxygen remaining in the chamber.

In the oxygen exposure treatment, an oxygen gas or a gas containing oxygen is introduced for a predetermined time while evacuating the chamber for oxygen exposure treatment so that the oxygen partial pressure becomes 10 ³ Pa or less, and a crystal such as a crystalline MgO film is formed. The conductive oxide film is brought into contact with O ₂ . The oxygen exposure treatment can be performed at a substrate temperature of room temperature. The time for bringing the crystalline oxide film into contact with O ₂ (time for introducing oxygen gas into the chamber; hereinafter referred to as oxygen exposure time) is optimal as appropriate according to the thickness of the crystalline oxide film and the oxygen partial pressure. It is necessary to make it. This is because if the oxygen exposure time is too long, the MR ratio of the device decreases. This is because the underlying reference layer 16 is oxidized and deteriorated due to oxygen diffusion through crystal defects or pinholes in the crystalline oxide film. The optimum oxygen exposure time is shorter when the thickness of the crystalline oxide film is thin and longer when the thickness of the crystalline oxide film is thick under a constant oxygen partial pressure. Further, under a certain film thickness, it is short when the oxygen partial pressure is high, and is long when the oxygen partial pressure is low. From the viewpoint of controllability of the oxygen exposure treatment, when an MgO film is used as the crystalline oxide film, it is desirable to perform the oxygen exposure treatment with an oxygen partial pressure of 10 ³ Pa or less. For example, when the crystalline oxide film is an MgO film having a thickness of about 1 nm, the optimum oxygen exposure time is 120 seconds at room temperature and an oxygen partial pressure of 130 Pa. In the above example, the substrate temperature is set to room temperature. However, the present embodiment is not limited to this, and the oxygen exposure treatment may be performed by heating or cooling the substrate. In this case, the highest MR ratio is obtained. In addition, the oxygen partial pressure and the oxygen exposure time may be optimized as appropriate. The formation process of the tunnel barrier film 17 is completed by the formation of the crystalline oxide film and the oxygen exposure treatment of the crystalline oxide film.

Thereafter, the substrate 11 is transferred to a chamber under a low oxygen partial pressure (for example, a vacuum atmosphere having a total pressure of about 10 ⁻⁷ Pa), and the free ferromagnetic layer 18, the substrate side cap layer 19a, and the upper cap layer 19 are sputtered. Sequentially formed. These layers can be formed at room temperature. Thereafter, the magnetization of the pinned layer 14 and the reference layer 16 is performed by heat-treating the substrate 11 under a vacuum atmosphere at a temperature of 250 ° C. to 350 ° C., a heating time of 2 hours to 4 hours, and an applied magnetic field of 1.5 T (Tesla). Fix the direction. The magnetoresistive film thus formed is shaped by a known photolithography method or etching process, and electrodes are formed on the substrate 11 side and the cap layer 19 side by a known film forming method (sputtering method, CVD method, etc.). As a result, the TMR element 10 of the present embodiment is completed.

(Experimental example)
A magnetoresistive effect element according to an experimental example which is an aspect of the present embodiment and a magnetoresistive effect element according to a comparative example were manufactured, and the MR ratio was measured. The magnetoresistive effect element according to the experimental example includes, in order from the substrate side, a 3 nm thick Ta film (substrate side underlayer 12a), a 2 nm thick Ru film (upper underlayer 12b), and a 7 nm thick IrMn film (anti-layer). Ferromagnetic layer 13), 1.8 nm thick CoFe film (pinned layer 14), 0.8 nm thick Ru film (nonmagnetic coupling layer 15), 2.0 nm thick CoFeB film (reference layer 16), Crystalline MgO film (tunnel barrier layer 17) having a thickness of 1.2 nm or less, CoFeB film (free ferromagnetic layer 18) having a thickness of 3.0 nm, Ta film having a thickness of 5 nm (substrate-side cap layer 19a), thickness It consists of a 10 nm Ru film (upper cap layer 19b). These films, including the MgO film, were formed by sputtering at room temperature under high vacuum (about 10 ⁻⁷ Pa). Further, the tunnel barrier layer 17 of this experimental example is made of MgO films whose thickness is changed within a range of 1.2 nm or less, and these MgO films are formed at room temperature and in accordance with the film thickness. Oxygen exposure treatment was performed while appropriately changing the oxygen exposure time and oxygen partial pressure so as to optimize the MR ratio. Among these, the MgO film having a thickness of 1.0 nm was subjected to oxygen exposure treatment at a substrate temperature of room temperature and an oxygen partial pressure of 130 Pa and an oxygen exposure treatment time of 120 seconds.

On the other hand, the magnetoresistive effect element of the comparative example is composed of a laminated film similar to the experimental example except for the tunnel barrier film, and the manufacturing method is the same except for the step of forming the tunnel barrier film 17. The tunnel barrier film of the comparative example was made of a crystalline MgO film, and was formed by sputtering using MgO as a target in a vacuum atmosphere (10 ⁻⁷ Pa) as in the experimental example. However, the comparative example is different from the experimental example in that the tunnel barrier film forming step is completed without performing the oxygen exposure treatment on the crystalline MgO film.

The resistance value and MR ratio of the manufactured TMR element were measured, and the resistance area product RA (Ωμm ² ) of each element was determined based on the results. Here, the resistance area product is a product of an element area (μm ² ) and a resistance value (Ω). For example, when the size of the film surface of the sample element is 0.1 μm × 0.1 μm and the resistance value of the element is 300Ω, the resistance area product is determined to be 3 (Ωμm ² ). The resistance area product RA of the TMR elements of this experimental example and the comparative example depends on the thickness of the MgO film, and in the sample showing RA = 10 (Ωμm ² ), the thickness of the MgO film is about 1.2 nm. The film thickness of the MgO film of the sample showing RA = 3 (Ωμm ² ) was about 1.0 nm.

As shown in FIG. 2, the relationship between the resistance area product RA and the MR ratio of the TMR elements of the present experimental example and the comparative example is as follows. The higher MR ratio was obtained. In particular, in a TMR element having a low resistance area product RA of 1 to 3.5 Ωμm ² suitable for a magnetic head, the element of this experimental example has an MR ratio of 25% to 60%, which is about 20% that of the comparative example. A high MR ratio was exhibited. This is presumably because the tunnel barrier films of the present experimental example and the comparative example are formed by sputtering under a low oxygen partial pressure (high vacuum), so that the MgO film contains many oxygen defects. However, in the case of the tunnel barrier film of this experimental example, oxygen defects (crystal defects) are reduced by the oxygen exposure treatment, the tunnel electron spin scattering based on the oxygen defects is reduced, and the current flow path other than the tunnel current based on the oxygen defects Since the formation is reduced, it is considered that the MR ratio is improved as compared with the TMR element of the comparative example including many oxygen defects.

  As described above, in the magnetoresistive effect element according to the present embodiment, after the crystalline oxide film is formed as the tunnel barrier layer 17, the oxygen defect ( A crystalline oxide (eg, MgO) film with few crystal defects can be obtained. In addition, since the treatment for reducing oxygen defects in the tunnel barrier film is performed after the formation of the crystalline oxide, there is no possibility that the ferromagnetic film on the base side is deteriorated. Furthermore, according to the crystalline oxide film subjected to the oxygen exposure treatment, spin scattering of tunnel electrons due to oxygen defects (crystal defects) and generation of current channels other than tunnel current due to oxygen defects (crystal defects) are reduced. Therefore, a high MR ratio can be obtained even with an element having a thin tunnel barrier film and a low resistance (low resistance area product RA). Furthermore, according to the TMR element 10 of the present embodiment, the information transfer rate can be improved by a low element resistance.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to FIGS. The second embodiment relates to a magnetic head and a magnetic disk apparatus provided with the magnetoresistive effect element of the present invention. FIG. 3 is a cross-sectional view showing a main part of the magnetic head 30 of the second embodiment, and FIGS. 4A to 4C are cross-sections showing a state during the manufacture of the magnetic head 30 of the second embodiment. FIG. 5 is a diagram showing a magnetic disk device 50 according to the second embodiment. In the above drawings, the same reference numerals are given to the same components as those already described, and the description thereof is omitted.

(Magnetic head)
As shown in FIG. 3, the magnetic head 30 includes a TMR element 10 formed above a substrate 31 and an inductive recording element 35 formed above the TMR element 10.

The substrate 31 is a head slider of the magnetic head 30 and is made of a ceramic substrate (altic substrate) such as Al ₂ O ₃ —TiC. A substrate-side magnetic shield layer 32 is formed on the substrate 31. The substrate side shield layer 32 serves as a magnetic shield and a lower electrode of the TMR element 10 and is made of, for example, NiFe or CoFe as a soft magnetic alloy. The TMR element 10 is formed on the substrate side shield layer 32. The film surface of the laminated film of the TMR element 10 extends in a direction perpendicular to the paper surface, and its normal line is formed to be substantially the same as a line extending in the vertical direction of the paper surface in FIG. A magnetic domain control layer 41 is provided on the side of the TMR element 10. The magnetic domain control layer 41 makes the reference layer 16 and the free ferromagnetic layer 18 constituting the TMR element 10 into a single magnetic domain and prevents Barkhausen noise from occurring. An upper magnetic shield layer 34 is formed on the TMR element 10. The upper magnetic shield layer 34 serves as a magnetic shield and an upper electrode of the TMR element 10 and is formed using a soft magnetic alloy material similar to the substrate-side magnetic shield layer 32.

  The inductive recording element 35 includes a main magnetic pole 36 and an auxiliary magnetic pole (also serving as the upper magnetic shield layer 34), a recording gap formed between the magnetic poles, a yoke that magnetically connects the magnetic poles, and an induction coil that winds the yoke. 42.

  Next, a method for manufacturing the magnetic head 30 will be described with reference to FIGS. 4A to 4C show structures when the magnetic head is viewed from the recording medium side.

First, steps required until a structure shown in FIG. An Al ₂ O ₃ film is formed on the substrate 31 (not shown), and a magnetic substrate-side magnetic shield layer 32 is formed on the substrate 31 with a soft magnetic alloy such as NiFe to a thickness of 2 to 3 μm. Then, the underlayer 12 (the substrate side underlayer 12a and the upper underlayer 12b) constituting the TMR element 10, the antiferromagnetic layer 13, the pinned layer 14, the nonmagnetic coupling layer 15, and the reference are formed on the soft magnetic shield layer 32. A magnetoresistive film is formed by sequentially forming the layer 16, the tunnel barrier layer 17, the free ferromagnetic layer 18, and the cap layer 19 (the substrate-side cap layer 19a and the upper cap layer 19b), as shown in FIG. The structure shown is completed. The film thickness, material, and manufacturing method of each layer constituting the magnetoresistive film can be the same as those of the TMR element 10 of the first embodiment.

  Next, the formed magnetoresistive film is processed into a predetermined shape. A resist pattern having a predetermined shape is formed on the magnetoresistive film by a photoresist method, and ion milling is performed using the resist pattern as a mask until the substrate-side magnetic shield layer 32 is exposed, as shown in FIG. The structure (TMR element 10) is completed.

  Next, steps required until a structure shown in FIG. After the magnetoresistive film is processed to a predetermined size as described above, the insulating film 40 having a thickness of 3 to 10 nm is formed on the entire upper surface of the substrate 31 by sputtering while leaving the resist pattern. Thereafter, CoCrPt is deposited on the insulating film 40 by sputtering to form the magnetic domain control layers 41 on both sides of the TMR element 10. Next, the resist pattern is removed.

  Next, after planarizing the surface of the magnetic domain control layer 41, the upper magnetic shield layer 34 made of, for example, NiFe is formed on the surfaces of the TMR element 10 and the magnetic domain control layer 41 to a thickness of 2 to 3 μm. In this way, the structure shown in FIG. 4C is completed.

  Next, an inductive recording element 35 (main magnetic pole, auxiliary magnetic pole, yoke, coil, etc.) is formed on the upper magnetic shield layer 34 by a known method (see FIG. 3). In this way, the magnetic head 30 according to this embodiment is completed.

  In the magnetic head 30, the detection current flowing through the TMR element 10 flows in the direction perpendicular (normal) to the film surface. For example, the detection current flows from the upper magnetic shield layer 34 to the substrate-side magnetic shield 32. The direction of magnetization of the free ferromagnetic layer 18 of the TMR element 10 changes in the in-plane direction perpendicular to the paper surface in FIG. 3 due to the magnetic field leaking from the magnetic recording medium. As a result, the resistance value of the TMR element 10 changes. Information recorded on the magnetic recording medium can be read by electrically detecting the change in the resistance value. Further, since the TMR element 10 used in the magnetic head 30 of the present embodiment exhibits a high MR ratio even when the resistance area product RA is small, even when an element having a small resistance area product RA is used, the S / N ratio is high. The ratio does not decrease. For this reason, the reading speed (transfer speed) of the magnetic recording medium can be improved by using an element having a small resistance area product RA.

(Magnetic disk unit)
Next, the magnetic disk device 50 will be described with reference to FIG. The magnetic disk device 50 according to the present embodiment is characterized by including the magnetic head 30 described above.

  As shown in FIG. 5, the magnetic disk device 50 includes a magnetic recording medium 51 in a housing 54, a head slider (substrate) 31 having a magnetic head 30 at the tip, and a suspension arm 53 that holds the head slider 31. Is housed. The magnetic recording medium 51 is rotated by a spindle motor (not shown), and the magnetic head 30 can be moved to a predetermined track on the recording medium 51 by a head positioning mechanism (not shown) that drives the suspension arm 53.

  The magnetic disk device of this embodiment includes a crystalline oxide (for example, MgO) film subjected to an oxygen exposure process on the reading element (TMR element 10) of the magnetic head 30. Therefore, the output signal of the read signal is higher than that of the conventional read element, the S / N ratio is improved, and a read operation with higher reliability is possible. In addition, an element having a resistance area product RA lower than that of a conventional TMR element can be used as a reading element. As a result, the magnetic disk device 50 of the present embodiment can lower the resistance value of the TMR element and increase the transfer speed of the read signal from the recording medium, so that a faster information reading speed can be achieved. .

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to FIGS. The third embodiment relates to a magnetic memory device using the magnetoresistive effect element of the present invention as a storage element. FIG. 6 is a diagram showing a configuration example 1 of the memory device according to the third embodiment, and FIG. 7 is an equivalent circuit diagram of one memory cell of the magnetic memory device of the configuration example 1. Moreover, FIG. 8 is sectional drawing which shows the structural example 2 of 3rd Embodiment. In addition, in each said figure, the same code | symbol is attached | subjected about the same component as the already demonstrated structure, and the description is abbreviate | omitted. 6 and 8 show orthogonal coordinate axes for indicating directions. Of these, the Y1 and Y2 directions are directions perpendicular to the paper surface, the Y1 direction is the back of the paper surface, and the Y2 direction is the front of the paper surface. In the following description, the X direction may be either the X1 direction or the X2 direction, and the same applies to the Y direction and the Z direction.

(Current magnetic field writing type magnetic memory device)
As shown in FIG. 6, the magnetic memory device 60 includes a plurality of memory cells 61 arranged in a matrix, for example. The memory cell 61 is configured by the TMR element 10 and the FET 62. The FET 62 can be a p-type or n-type MOSFET. In the following description, an n-type MOSFET will be described as an example. The FET 62 includes a p-well (a region into which p-type impurities are introduced) formed in the semiconductor substrate 63 and diffusion regions 65a and 65b provided on the surface of the semiconductor substrate 63 so as to be separated from each other. The diffusion regions 65a and 65b are regions where n-type impurities are diffused, the diffusion region 65a is on the source (S) side, and the diffusion region 65b is on the drain (D) side. A gate (G) is formed above the portion between the diffusion regions 65 a and 65 b through a gate insulating film 66. The source-side diffusion region 65 a of the FET 62 is electrically connected to one of the TMR elements 10 (for example, the substrate-side base layer 12 a) via the vertical wiring 74 and the intra-layer wiring 75. The drain-side diffusion region 65 b is electrically connected to the plate line via the vertical wiring 74. The gate (G) is connected to the read word line 69. In the example of FIG. 6, the word line 69 also serves as the gate (G) electrode of the FET 62.

  The bit line 70 is electrically connected to the other side of the TMR element 10 (for example, the upper cap layer 19b). Below the TMR element 10, a word line 71 for writing is arranged electrically isolated. The TMR element 10 has the same configuration as that of the TMR element 10 shown in FIG. 1, and the tunnel barrier layer is subjected to oxygen exposure treatment. The TMR element 10 sets the direction of the easy axis of magnetization along the Y direction. The direction of the easy magnetization axis may be formed by heat treatment or by shape anisotropy. When the easy magnetization axis is formed in the X direction due to the shape anisotropy, the cross-sectional shape parallel to the film surface of the TMR element 10 (the cross-sectional shape parallel to the XY plane) A rectangle with a long side.

  In the magnetic memory device 60, the surface of the semiconductor substrate 63 and the gate electrode G are covered with an interlayer insulating film 73 such as a silicon nitride film or a silicon oxide film. The TMR element 10, the plate line 68, the read word line 69, the bit line 70, the write word line 71, the vertical wiring 74, and the intra-layer wiring 75 are interlayer insulating films except for the electrical connection described above. 73 are electrically insulated from each other.

  The magnetic memory device 60 holds information in the TMR element 10. Information is held depending on whether the magnetization direction of the free ferromagnetic layer 18 is parallel or antiparallel to the magnetization direction of the reference layer 16.

  Next, write and read operations of the magnetic memory device 60 will be described.

  The operation of writing information to the TMR element 10 of the magnetic memory device 60 is performed by the bit line 70 and the write word line 71 arranged above and below the TMR element 10. The bit line 70 extends in the X direction above the TMR element 10, and a magnetic field in the Y direction is applied to the TMR element 10 by passing a current through the bit line 70. The write word line 71 extends in the Y direction below the TMR element 10, and a magnetic field in the X direction is applied to the TMR element 10 by passing a current through the write word line 71. When the magnetic field is not applied, the magnetization of the free ferromagnetic layer 18 of the TMR element 10 faces the X direction, and the magnetization direction is stable.

  When writing information to the TMR element 10, a current is simultaneously applied to the bit line 70 and the write word line 71. For example, when the magnetization of the free ferromagnetic layer 18 of the TMR element 10 is directed in the X1 direction, a current is supplied to the bit line 70 in the X direction and a current in the Y1 direction is supplied to the write word line 71. A magnetic field in the Y direction is applied to the TMR element 10 by the current flowing through the bit line 70, and the free ferromagnetic layer 18 functions as a part of the magnetic field for exceeding the barrier of the hard axis. The current flowing in the Y1 direction through the write word line 71 applies a magnetic field in the X1 direction to the TMR element 10 and directs the magnetization direction of the free ferromagnetic layer 18 in the X1 direction.

  In this way, information (“0” or “1”) is written according to the direction of magnetization of the free ferromagnetic layer 18 of the TMR element 10. For example, when the magnetization direction of the reference layer 16 of the TMR element 10 is fixed in the X1 direction and the magnetization direction of the free ferromagnetic layer 18 is in the X1 direction, the resistance value of the tunnel barrier film 17 becomes low. For example, it can be detected as “1”. Similarly, when the magnetization direction of the free ferromagnetic layer 18 is the X2 direction, the resistance value of the tunnel barrier film 17 becomes high and can be detected as, for example, “0”. It should be noted that the current value supplied to the bit line 70 and the write word line 71 during the write operation is the same as that of the free ferromagnetic layer 18 even if a current flows only through either the bit line 70 or the write word line 71. Is set to such an extent that no magnetization reversal occurs. Thereby, writing can be performed only to the TMR element 10 located at the intersection of the bit line 70 supplied with the current and the writing word line 71 supplied with the current. Further, the FET 62 is turned off and the source (S) of the FET 62 is set to high impedance so that the current flowing through the bit line 70 does not flow to the TMR element 10 during the write operation.

  In the read operation of the magnetic memory device 60, the bit line 70 is set to a voltage lower than that of the source S, and a voltage higher than the threshold voltage of the FET 62 is applied to the read word line 69 (gate electrode G). As a result, the FET 62 is turned on, and electrons flow from the bit line 70 to the plate line 68 via the TMR element 10, the source S and the drain D. By electrically connecting a current detector 78 such as an ammeter to the plate line 68, it is possible to detect a magnetoresistance value reflecting the relative magnetization direction of the free ferromagnetic layer 18 and the reference layer 16. . Thereby, “1” or “0” information held by the MTR element 10 can be read.

  In the magnetic memory device 10 of the configuration example 1 of the third embodiment configured as described above, the tunnel barrier layer 17 of the TMR element 10 is formed of a crystalline oxide film after forming a crystalline oxide (for example, MgO) film. Since the oxygen exposure treatment is performed, it is made of a crystalline oxide film with few oxygen defects. According to the tunnel barrier film 17 made of a crystalline oxide (eg, MgO) film with few oxygen defects, the MR ratio is large even in an element having a small resistance area product RA. Therefore, in the magnetic memory device 60, when the information is read, the change in the magnetoresistance value with respect to the held “0” and “1” is larger, so that the output change of the TMR element 10 becomes larger and more accurate. Reading is possible. Furthermore, since the element resistance can be lowered, the reading speed from the TMR element 10 can be further increased.

(Polarized spin current injection writing type magnetic memory device)
FIG. 8 shows a magnetic memory device 80 according to Configuration Example 2 of the third embodiment. In FIG. 8, the same components as those in FIG. The magnetic memory device 80 is different from the magnetic memory device 60 of Configuration Example 1 in the mechanism and operation for writing information to the TMR element 10.

  The memory cell of the magnetic memory device 80 has the same configuration as the memory cell shown in FIGS. 6 and 7 except that the write word line 71 is not provided. Hereinafter, a description will be given with reference to FIGS.

  The magnetic memory device 80 injects a polarized spin current into the TMR element 10 and controls the magnetization direction of the free ferromagnetic layer 18 according to the direction of the current. A polarized spin current is an electron flow composed of electrons in one of two possible spin directions. By causing the direction of the polarized spin current to flow in the Z1 direction or the Z2 direction of the TMR element 10, torque is generated in the magnetization of the free ferromagnetic layer 18 to cause so-called spin injection magnetization reversal. The amount of the polarized spin current is appropriately selected according to the film thickness of the free ferromagnetic layer 18, but is 20 mA or less. The amount of the polarized spin current is smaller than the amount of current flowing through the bit line 70 and the write word line 71 in the write operation of the configuration example 1 in FIG. 6, and the power consumption can be reduced.

  The polarized spin current can be generated by causing a current to flow perpendicularly to a laminate in which a Cu film having a configuration substantially similar to that of the TMR element 10 is sandwiched between two ferromagnetic layers. The direction of electron spin can be controlled by setting the magnetization directions of the two ferromagnets to be parallel or antiparallel. The reading operation of the magnetic memory device 80 is the same as that of the magnetic memory device 60 of the configuration example 1 of FIG.

  In addition to the effect of the magnetic memory device 60 of the configuration example 1, the magnetic memory device 80 of the configuration example 2 also has an effect that power consumption can be reduced.

(Other embodiments)
As described above, the TMR element 10 of the present invention has a configuration in which one layer of a crystalline oxide film (for example, MgO film) is formed as a tunnel barrier layer 17 between two ferromagnetic films. In addition to this, the following configuration may be adopted. That is, the present invention can also be applied to a TMR element having a double ferromagnetic tunnel junction in which two tunnel barrier layers are formed between three ferromagnetic films. FIG. 9 is a cross-sectional view showing a configuration of a TMR element 20 having a double ferromagnetic tunnel junction according to another embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the structure similar to the part demonstrated previously, and the description is abbreviate | omitted.

The TMR element 20 includes a base layer 12 having a substrate side base layer 12a and an upper base layer 12b, an antiferromagnetic layer 13, a pinned layer 14, a nonmagnetic coupling layer 15, and a reference layer 16 on a substrate 11. A tunnel barrier layer 17 and a free ferromagnetic layer 18 are provided in order, and an upper tunnel barrier layer 27, an upper reference layer 26, an upper nonmagnetic intermediate layer 25, an upper pinned layer 24, and an upper antiferroelectric layer are further provided thereon. A magnetic layer 23 and a cap layer 19 including a substrate-side cap layer 19a and an upper cap layer 19b are sequentially provided. In another embodiment of the present invention, the tunnel barrier layer 17 and the upper tunnel barrier layer 27 have the same material and film thickness, and are made of a crystalline oxide film such as an MgO film. This crystalline oxide film is formed by sputtering using an oxide (for example, MgO) as a target under a low oxygen partial pressure (for example, under a high vacuum of about 10 ⁻⁷ Pa). Furthermore, the tunnel barrier layers 17 and 27 of the present embodiment are produced through an oxygen exposure treatment in which the formed crystalline oxide is brought into contact with an oxygen gas having an oxygen partial pressure of 10 ³ Pa or less or a gas containing oxygen. .

  In the TMR element 20, the upper reference layer 26 is the reference layer 16, the upper nonmagnetic intermediate layer 25 is the nonmagnetic intermediate layer 15, the upper pinned layer 24 is the pinned layer 14, and the upper antiferromagnetic layer 23 is the antiferromagnetic layer. 13 and the same material, film thickness, and manufacturing method. The substrate 11, the underlayer 12, the antiferromagnetic layer 13, the pinned layer 14, the nonmagnetic coupling layer 15, the reference layer 16, the tunnel barrier layer 17, the free ferromagnetic layer 18, and the cap layer 19 of the present embodiment are shown in FIG. 1 can be configured to be the same as the components to which the corresponding reference numerals of the TMR element 10 already described in FIG.

  Also in the TMR element 20 having the double ferromagnetic tunnel junction configured as described above, the crystalline oxide film is subjected to the oxygen exposure treatment after the formation of the crystalline oxide film. An MR ratio higher than that of a TMR element having a magnetic tunnel junction can be obtained.

FIG. 1 is a cross-sectional view showing a magnetoresistive effect element according to the first embodiment of the present invention. FIG. 2 is a graph showing the relationship between the RA and MR ratio of the magnetoresistive effect element according to the experimental example and the comparative example of the first embodiment. FIG. 3 is a cross-sectional view showing the configuration of the main part of the magnetic head according to the second embodiment of the present invention. 4A to 4C are cross-sectional views showing a state in the middle of manufacturing the magnetic head according to the second embodiment. FIG. 5 is a diagram showing a magnetic disk device including a magnetic head according to the second embodiment of the present invention. FIG. 6 is a cross-sectional view showing a memory cell of a magnetic memory device according to the third embodiment of the present invention. FIG. 7 is a diagram showing an equivalent circuit for a part of the magnetic memory device according to the third embodiment. FIG. 8 is a sectional view showing a modification of the magnetic memory device according to the third embodiment. FIG. 9 is a cross-sectional view showing a configuration of a magnetoresistive effect element according to another embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... TMR element, 11 ... Substrate, 12 ... Underlayer, 12a ... Substrate side underlayer, 12b ... Upper underlayer, 13 ... Antiferromagnetic layer, 14 ... Pinned layer, 15 ... Nonmagnetic coupling layer, 16 ... Reference layer , 17 ... Tunnel barrier layer, 18 ... Free ferromagnetic layer, 19 ... Cap layer, 19a ... Substrate side cap layer, 19b ... Upper cap layer, 20 ... Double tunnel junction TMR element, 27 ... Upper tunnel barrier layer, 26 ... upper reference layer, 25 ... upper nonmagnetic coupling layer, 24 ... upper pinned layer, 23 ... upper antiferromagnetic layer, 30 ... magnetic head, 31 ... substrate (head slider), 32 ... substrate side magnetic shield layer, 34 ... Upper magnetic shield layer, 35 ... inductive recording element, 40 ... insulating film, 41 ... magnetic domain control layer, 50 ... magnetic disk device, 51 ... magnetic recording medium, 52 ... magnetic head, 53 ... suspension , Arm, 54 ... housing, 60 ... magnetic memory device (current magnetic field writing type), 61 ... memory cell, 62 ... FET, 63 ... semiconductor substrate, 64 ... p well, 65a ... source side diffusion region, 65b ... drain side diffusion Area 66... Gate insulating film 68. Plate line 69. Reading word line 70. Bit line 71. Writing word line 73. Interlayer insulating film 74. Vertical wiring 75 75 In-layer wiring 78 ... Current detector, 80 ... Magnetic memory device (polarized spin current injection writing type).

Claims (5)

A first ferromagnetic layer formed above the substrate;
A tunnel barrier layer made of a crystalline oxide formed on the first ferromagnetic layer;
A magnetoresistive effect element comprising: a second ferromagnetic layer formed on the tunnel barrier layer;
2. The magnetoresistive element according to claim 1, wherein the tunnel barrier layer is made of a crystalline oxide film that has been exposed to oxygen.   The magnetoresistive effect element according to claim 1, wherein the tunnel barrier layer is made of an MgO film. Forming a first ferromagnetic layer made of a ferromagnetic material above the substrate;
Forming a tunnel barrier layer made of a crystalline oxide on the first ferromagnetic layer;
A step of exposing the tunnel barrier layer to oxygen;
Forming a second ferromagnetic layer made of a ferromagnetic material on the tunnel barrier layer;
A method for manufacturing a magnetoresistive effect element, comprising:   4. The method of manufacturing a magnetoresistive element according to claim 3, wherein the tunnel barrier layer is formed by a sputtering method.   4. The method of manufacturing a magnetoresistive effect element according to claim 3, wherein the tunnel barrier layer is formed by sputtering under high vacuum using MgO as a target.

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