JP7149055B2 - Ferromagnetic exchange-coupled device and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ferromagnetic exchange-coupled device and a manufacturing method thereof.

Conventionally, it is known that two ferromagnetic thin films formed via a very thin non-magnetic metal thin film are ferromagnetically exchange-coupled by an exchange-coupling magnetic field (see, for example, Patent Document 1). A coercive force difference type TMR (Tunnel MagnetoResistance: tunnel magnetoresistive effect) element can be cited as an element that utilizes this ferromagnetic exchange coupling. In the coercive force difference type TMR element, one of the Co--Fe--B layers having a large MR (magnetoresistive) effect formed at the interface on both sides of the MgO layer is ferromagnetically exchange-coupled with the other ferromagnetic thin film. By controlling the coercive force, a large coercive force difference is obtained between the two Co--Fe--B layers.

It is also known that ferromagnetic exchange coupling occurs by the exchange coupling magnetic field even when magnetic layers having different characteristics are directly superimposed. In this case, there is an effect that the magnetic characteristics obtained by combining the characteristics of each magnetic layer can be obtained. Such an effect is utilized in, for example, composite perpendicular magnetic recording media, spin-valve TMR elements, and the like (see, for example, Patent Documents 2 and 3).

WO2009/110119 JP 2011-114151 A Japanese Patent No. 4039656

By the way, the crystallinity of the MgO intermediate layer, which is often used in TMR elements, can be improved by heat treatment. As a result, the TMR effect is improved, the spin injection efficiency is improved, and the amount of current required for spin injection magnetization reversal can be further reduced. However, when a material having no heat resistance is applied to the magnetization free layer, in the conventional manufacturing method, a layer with heat treatment resistance including an MgO intermediate layer (cross section of a ferromagnetic exchange coupling element according to a second embodiment described later) After forming the film up to the Co--Fe--B layer 65 in FIG. 68, it is necessary to deposit a GdFe layer 69). In this case, the heat treatment requires a heating and cooling time, and the process time is longer than that of the film formation, so it is not practical for mass production equipment or the like.

In addition, in the microfabrication process, it may not be possible to continuously form two ferromagnetic thin films consistently in a vacuum due to the process. Therefore, ferromagnetic exchange coupling between ferromagnetic thin films cannot be achieved in such a microfabrication process.

The present invention has been made in view of the above, and an object of the present invention is to provide a ferromagnetic exchange coupling element that can realize ferromagnetic exchange coupling with a material having no heat resistance with high production efficiency and can be applied to various microfabrication processes. It is to provide a manufacturing method.

(1) In order to achieve the above objects, the present invention provides a first ferromagnetic layer (for example, a first magnetization pinned layer 11 and a second magnetization pinned layer 21 to be described later) made of a ferromagnetic material, and the first ferromagnetic layer. A non-magnetic metal layer (for example, non-magnetic metal layers 12 and 22 to be described later) formed thereon and made of a non-magnetic metal, and a buffer layer made of oxide or nitride (for example, , buffer layers 13 and 23 to be described later), and a second ferromagnetic layer (for example, a light modulation layer 30 to be described later) formed on the buffer layer and made of a ferromagnetic material, and the first ferromagnetic A ferromagnetic exchange-coupled element (eg, ferromagnetic exchange-coupled elements 10 and 20 described below) is provided in which the layer and the second ferromagnetic layer are ferromagnetically exchange-coupled.

( ₂ ) In the ferromagnetic exchange coupling element of (1), the buffer layer may be made of MgO, _{Al2O3 , MgAl2O4} , _TiO2 , ZnO or _RuO2 .

(3) In the ferromagnetic exchange coupling element of (1) or (2), the second ferromagnetic layer may contain Gd or GdFe.

(4) In the ferromagnetic exchange coupling element according to any one of (1) to (3), the second ferromagnetic layer comprises a Gd layer formed on the first ferromagnetic layer and made of Gd; A GdFe layer made of GdFe may be formed.

(5) In the ferromagnetic exchange coupling element according to any one of (1) to (4), the first ferromagnetic layer may be a Co--Fe--B or Co/Pd multilayer film.

(6) In the ferromagnetic exchange coupling element according to any one of (1) to (5), the buffer layer may be made of MgO.

(7) In the ferromagnetic exchange coupling element according to any one of (1) to (6), the nonmagnetic metal layer may be made of Ta.

(8) A method for manufacturing a ferromagnetic exchange coupling element, comprising: a first ferromagnetic layer forming step of forming a first ferromagnetic layer made of a ferromagnetic material; a non-magnetic metal layer forming step of forming a non-magnetic metal layer comprising: a buffer layer forming step of forming a buffer layer made of an oxide or a nitride on the non-magnetic metal layer; 1 a cap layer forming step of forming a cap layer for suppressing oxidation of the ferromagnetic layer, the non-magnetic metal layer and the buffer layer; A treatment step of performing at least one of a lift-off treatment for removing a pattern and a heat treatment for heating a laminate having the cap layer formed thereon, and the cap layer in the laminate subjected to the lift-off treatment or the heat treatment. and a second ferromagnetic layer forming step of forming a second ferromagnetic layer made of a ferromagnetic material on the buffer layer partly removed by the removing step. and a method for manufacturing a ferromagnetic exchange-coupled device.

(9) In the method of manufacturing a ferromagnetic exchange-coupled element of (8), the heat treatment temperature in the treatment step may be 300° C. or higher.

(10) In the method of manufacturing a ferromagnetic exchange coupled element of (8) or (9), ion beam milling or high-density plasma etching may be performed in the removing step.

ADVANTAGE OF THE INVENTION According to this invention, the ferromagnetic exchange-coupling element which can implement|achieve the ferromagnetic exchange coupling with the material without heat resistance with high production efficiency, and can be applied to various microfabrication processes, and its manufacturing method can be provided.

1 is a perspective view showing the configuration of a ferromagnetic exchange coupling element according to a first embodiment; FIG. 1 is a side view showing the configuration of a ferromagnetic exchange coupling element according to a first embodiment; FIG. FIG. 4 is a diagram showing the operation of the ferromagnetic exchange coupling device according to the first embodiment; 1 is a cross-sectional view showing the configuration of an example of a ferromagnetic exchange coupling element according to a first embodiment; FIG. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 1st Embodiment. FIG. 4 is a diagram showing magneto-optical characteristics of the ferromagnetic exchange coupling device according to the first embodiment; FIG. 4 is a diagram showing magneto-optical characteristics of the ferromagnetic exchange coupling device according to the first embodiment; FIG. 4 is a diagram showing magneto-optical characteristics of the ferromagnetic exchange coupling device according to the first embodiment; FIG. 5 is a cross-sectional view showing the configuration of an example of a ferromagnetic exchange coupling element according to a second embodiment; It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 2nd Embodiment. It is a figure which shows the manufacturing method of the ferromagnetic exchange coupling element which concerns on 2nd Embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in the description of the second embodiment, the description of the configuration common to the first embodiment is omitted. For convenience of explanation, the upper, lower, left, and right sides in the drawing will be described as the upper, lower, left, and right sides of the ferromagnetic exchange coupling element.

[First embodiment]
FIG. 1 is a perspective view showing the configuration of a ferromagnetic exchange coupling element according to the first embodiment. FIG. 2 is a side view showing the configuration of the ferromagnetic exchange coupling element according to the first embodiment. FIG. 3 is a diagram showing the operation of the ferromagnetic exchange-coupled device according to the first embodiment. Arrows in FIGS. 1 and 3 indicate directions of magnetization.
As shown in FIGS. 1 to 3, the ferromagnetic exchange coupling element 10 according to the first embodiment constitutes a spatial light modulation element using domain wall motion.

As shown in FIG. 1, the ferromagnetic exchange coupling element 10 is formed on a substrate such as Si (not shown), and includes a first ferromagnetic exchange coupling section 1, a second ferromagnetic exchange coupling section 2, and an optical modulation section 3. and have
The first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are made of general metal electrode materials such as metals (not shown) such as Cu, Al, Au, Ag, Ru, Ta, Cr and alloys thereof. A pulse current can be applied by connecting a pulse current source 9 to this lower electrode.

Although the shape of the ferromagnetic exchange coupling element 10 is not particularly limited, for example, as shown in FIG. A shape in which the second ferromagnetic exchange coupling portion 2 is arranged is exemplified. The upper surfaces of the optical modulation section 3 and the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 are continuously flush with each other. is thicker than the thickness of the light modulating section 3 .

As shown in FIG. 2, the first ferromagnetic exchange coupling section 1 is configured by stacking a first magnetization fixed layer 11, a nonmagnetic metal layer 12, a buffer layer 13, and an optical modulation layer 30 in this order. be.

The first magnetization fixed layer 11 is made of a ferromagnetic material and corresponds to the first ferromagnetic layer of the present invention. The first magnetization fixed layer 11 is a layer whose magnetization direction is fixed in one direction and has a large coercive force. The first magnetization fixed layer 11 has magnetic anisotropy in the same direction as the optical modulation layer 30 described later. When a ferromagnetic material having perpendicular magnetic anisotropy is used for the optical modulation layer 30, A ferromagnetic material having perpendicular magnetic anisotropy is also used for the magnetization fixed layer 11 . Preferably, both the first magnetization fixed layer 11 and the optical modulation layer 30 are made of a ferromagnetic material having perpendicular magnetic anisotropy.

The first magnetization fixed layer 11 is a CPP-GMR (CPP-GMR) structure having perpendicular magnetic anisotropy in which a non-magnetic layer is sandwiched between a magnetization fixed layer whose magnetization is fixed in the perpendicular direction and a magnetization free layer whose magnetization direction can be reversed. Current Perpendicular to the Plane Giant MagnetoResistance (Perpendicular to the Plane Giant MagnetoResistance) elements, TMR elements, etc. can be made of a known ferromagnetic material as a magnetization fixed layer. Specifically, transition metals such as Fe, Co, and Ni and alloys containing them, for example, TbFe-based, TbFeCo-based, CoCr-based, CoPt-based, CoPd-based, and FePt-based alloys can be used. As a result, the coercive force of the first magnetization fixed layer 11 can be increased, and the magnetization direction of the first magnetization fixed layer 11 can be fixed so as not to be easily changed by an external magnetic field.

Also, the first magnetization fixed layer 11 may be composed of a multi-layer laminate in which these transition metal layers and non-magnetic metal layers are alternately laminated. etc. can be used. By using these ferromagnetic materials, the first magnetization fixed layer 11 having strong perpendicular magnetic anisotropy and large coercive force can be obtained.

Here, the multilayer film described above has a characteristic that the coercive force is increased by heat treatment. Therefore, if the first magnetization pinned layer 11 made of the above multilayer film is heat-treated to increase its coercive force, the coercive force of the ferromagnetic exchange coupling portion after being coupled with the optical modulation layer 30 is also increased, resulting in optical modulation. A coercive force difference from the portion 3 can be made larger.

The non-magnetic metal layer 12 and the buffer layer 13 are arranged between the first magnetization pinned layer 11 and the light modulation layer 30 and are arranged so as to maintain the magnetic coupling between the first magnetization pinned layer 11 and the light modulation layer 30 . can do.

The non-magnetic metal layer 12 is laminated on the first magnetization fixed layer 11 described above. The non-magnetic metal layer 12 is provided to prevent the first magnetization fixed layer 11 from being damaged by etching in the manufacturing process described later. The non-magnetic metal layer 12 is made of a non-magnetic metal, and thin film layers of various non-magnetic metals can be used. For example, Ta, Mo, and Ru can be used as the non-magnetic metal layer 12, and among them, Ta is preferably used.

The buffer layer 13 is laminated on the non-magnetic metal layer 12 described above. The buffer layer 13 is required to allow current to flow in both the spatial light modulation element using the domain wall motion and the TMR element. In addition, the buffer layer 13 needs to be a material that has a slow etching rate in the manufacturing process to be described later, contains an element with high detection sensitivity of SIMS (Secondary Ion Mass Spectrometry), and is visible with a SIMS endpoint monitor. . This makes it possible to reliably stop the etching at the buffer layer 13 and avoid damage to the first magnetization fixed layer 11 .

The buffer layer 13 is made of oxide or nitride. More specifically, the buffer layer 13 is preferably composed of _MgO , _{Al2O3 , MgAl2O4} , _TiO2 , ZnO or _RuO2 . Among them, as the buffer layer 13, one made of MgO is preferably used. According to the MgO layer made of MgO, it is possible to form the buffer layer 13 having high conductivity, low etching rate and high SIMS sensitivity.

The light modulation layer 30 is laminated on the buffer layer 13 described above. This light modulation layer 30 is made of a ferromagnetic material and corresponds to the second ferromagnetic layer of the present invention. A known ferromagnetic material can be applied to the light modulation layer 30, and preferably a material with a large magneto-optical effect (Kerr effect) is applied. In order to increase the magneto-optical effect, it is preferable to use a magnetic layer having perpendicular magnetic anisotropy. multi-layered films, or alloys of rare earth metals such as TbFeCo and GdFe and transition metals (RE-TM alloys). Among them, a GdFe layer made of GdFe is preferably used as the light modulation layer 30 .

The optical modulation layer 30 constitutes the second ferromagnetic layer in the second ferromagnetic exchange coupling section 2, which will be described later, and also constitutes the optical modulation section 3 itself.

In the first ferromagnetic exchange coupling section 1 configured as described above, the first magnetization pinned layer 11 and the optical modulation layer 30 are ferromagnetic exchange coupled via the nonmagnetic metal layer 12 and the buffer layer 13 . Due to this ferromagnetic exchange coupling, the magnetization direction of the first magnetization pinned layer 11 and the magnetization direction of the optical modulation layer 30 in the first ferromagnetic exchange coupling portion 1 are simultaneously reversed.

The second ferromagnetic exchange coupling section 2 is configured by laminating a second magnetization fixed layer 21, a nonmagnetic metal layer 22 and a buffer layer 23, and an optical modulation layer 30 in this order.

In addition, in the second ferromagnetic exchange coupling section 2, similarly to the first ferromagnetic exchange coupling section 1, the second magnetization pinned layer 21 and the optical modulation layer 30 are strongly connected via the nonmagnetic metal layer 22 and the buffer layer 23. Magnetically exchange coupled. Due to this ferromagnetic exchange coupling, the magnetization direction of the second magnetization fixed layer 21 and the magnetization direction of the optical modulation layer 30 in the second ferromagnetic exchange coupling section 2 are simultaneously reversed.

The second magnetization fixed layer 21 is selected from materials that can be used for the first magnetization fixed layer 11. Selected from available materials.

Here, the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are arranged so that their coercive forces are different from each other in order to form the domain wall 33 and the optical modulation region 300 as described later in detail. Designed.

Specifically, as will be described later in detail, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 have different shapes (e.g., width, thickness, etc.), or only one of them is heat-treated, Alternatively, it is selected whether the layer configurations are different from each other. Thus, by making the coercive force of the first magnetization fixed layer 11 and the coercive force of the second magnetization fixed layer 21 different from each other, the coercive force of the first ferromagnetic exchange coupling portion 1 and the coercive force of the second ferromagnetic exchange coupling portion 2 have different coercive forces.

As described above, the light modulating layer 30 constitutes the light modulating section 3 . A domain wall 33 and magnetic domains 31 and 32 are formed in the light modulating portion 3 composed of the light modulating layer 30 . This will be detailed later.

Note that the magnetization fixed layers (hereinafter, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 are also simply referred to as magnetization fixed layers), the non-magnetic metal layers, the buffer layers, and the optical modulation layers 30 are inter-layered. Alternatively, a functional layer may be appropriately provided at the interface with the lower electrode. For example, a cap layer containing or consisting of Ta, Ru or SiN may be provided on the light modulating layer 30 to prevent damage to the light modulating layer 30 during the microfabrication process. This cap layer has the function of preventing GdFe and TbFeCo, which are used to form the light modulation layer 30 and are easily oxidized, from being oxidized in the air after the device is completed.

Next, the magnetic characteristics of the ferromagnetic exchange coupling element 10 according to the first embodiment will be described in detail.
As described above, the first ferromagnetic exchange coupling section 1 has the first magnetization pinned layer 11 that is ferromagnetically exchange-coupled with the optical modulation layer 30, and the second ferromagnetic exchange coupling section 2 is similarly coupled with the optical modulation layer 30. It has a second magnetization pinned layer 21 for ferromagnetic exchange coupling. That is, the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 each have a ferromagnetic exchange coupling inside, and their magnetization directions are reversed at the same time. As shown in FIGS. 1 and 3, the magnetization direction of the first ferromagnetic exchange coupling portion 1 is designed downward, while the magnetization direction of the second ferromagnetic exchange coupling portion 2 is designed upward. there is

A domain wall 33 extending in a direction perpendicular to the direction in which the light modulation section 3 extends is formed in the light modulation section 3 . That is, the magnetization directions of the magnetic domains 31 and 32 formed on both sides of the domain wall 33 are opposite to each other. For example, as shown in FIGS. 1 and 3, the magnetization direction of the magnetic domain 31 on the first ferromagnetic exchange coupling portion 1 side of the domain wall 33 is upward, and the magnetic domain on the second ferromagnetic exchange coupling portion 2 side of the domain wall 33 is upward. The magnetization direction of 32 is downward.

By forming the magnetic domains 31 and 32 with different magnetization directions in the optical modulation section 3 via the domain wall 33 in this way, the ferromagnetic exchange coupling element 10 can function as a spatial optical modulation element. More specifically, for example, when the ferromagnetic exchange coupling element 10 is configured as a reflective spatial light modulation element, polarized light is directed from above the ferromagnetic exchange coupling element 10 to the upper surface of the optical modulation section 3 . When incident, the angle of rotation of the plane of polarization of the reflected light varies depending on the direction of magnetization. Therefore, light can be modulated by allocating the reflected lights according to the different rotation angles of the planes of polarization to the brightness of the light through the polarizing filter. However, it is also possible to make the ferromagnetic exchange coupling element 10 function as a transmissive spatial light modulating element by forming the substrate from a translucent material such as glass or sapphire.

Here, the generation mechanism of the domain wall 33 will be described with reference to FIGS. 2 and 3. FIG.
First, in order to form the magnetic domain wall 33 in the optical modulation section 3, the coercive force of the first magnetization pinned layer 11 ferromagnetically exchange-coupled with the optical modulation layer 30 and the second magnetization fixed layer 11 ferromagnetically exchange-coupled with the optical modulation layer 30 It is necessary to make the coercive force of the magnetization fixed layer 21 different from each other. For this purpose, the first magnetization pinned layer 11 and the second magnetization pinned layer 21 may have different shapes (for example, width, thickness, etc.), or only one of them may be subjected to heat treatment, or the layer structures thereof may be different from each other. or , the coercive force of the first magnetization pinned layer 11 and the coercive force of the second magnetization pinned layer 21 can be made different from each other.

For example, the coercive force of the first magnetization fixed layer 11 is designed to be larger than the coercive force of the second magnetization fixed layer 21 by any of the above methods. In this case, as shown in FIG. 2, if the coercive force of the first ferromagnetic exchange coupling portion 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling portion 2 is Hc2, and the coercive force of the optical modulation layer is Hc_m, then A relationship of Hc1>Hc2>Hc_m is established.

Then, a magnetic field having a magnetic field intensity H of H>Hc1 is applied downward to the element having the structure in which the above-described coercive force relationship is established. Then, the magnetization direction is downward in all of the first ferromagnetic exchange coupling portion 1, the second ferromagnetic exchange coupling portion 2, and the optical modulation portion 3. FIG.

Then, a magnetic field having a magnetic field strength H' of Hc1>H'>Hc2 is applied upward to the element. Then, while the magnetization direction of the first ferromagnetic exchange coupling portion 1 remains downward, the magnetization directions of the second ferromagnetic exchange coupling portion 2 and the optical modulation portion 3 are both directed upward. Change.

At this time, initial magnetic domains 31a and 32a are generated at both ends of the light modulation section 3 as shown in FIG. More specifically, at the end of the optical modulation section 3 on the side of the first ferromagnetic exchange coupling section 1, a first strong magnetic field is generated by the leakage magnetic field from the first ferromagnetic exchange coupling section 1 (see the dashed arrow in FIG. 3). An initial magnetic domain 31a having an upward magnetization direction antiparallel to the downward magnetization of the magnetic exchange coupling portion 1 is generated. At the end of the optical modulation section 3 on the side of the second ferromagnetic exchange coupling section 2, the leakage magnetic field from the second ferromagnetic exchange coupling section 2 (see the dashed arrow in FIG. 3) causes the second ferromagnetic exchange An initial magnetic domain 32a having a downward magnetization direction antiparallel to the upward magnetization of the coupling portion 2 is generated.

Next, in this state, a pulse current is applied from the pulse current source 9, and the first ferromagnetic exchange coupling portion 1 to the second ferromagnetic exchange coupling portion 2 or the second ferromagnetic exchange coupling portion 2 to the first ferromagnetic exchange coupling is applied. A pulse current is applied to the portion 1 . Then, the domain wall 33 formed by the generation of the initial magnetic domains 31a and 32a can be moved in the direction opposite to the direction of the pulse current (the same direction as the electron flow). As a result, as shown in FIG. 3, the magnetization direction of the light modulation region 300 excluding both ends of the light modulation section 3 is reversed (in the example of FIG. 3, the magnetization direction of the light modulation region 300 is reversed upward). is possible.

Next, a detailed configuration of the ferromagnetic exchange coupling element 10 according to the first embodiment will be described with reference to FIG.
FIG. 4 is a cross-sectional view showing the configuration of an example of the ferromagnetic exchange coupling element 10 according to the first embodiment. In FIG. 4, the numerical value in parentheses for each layer indicates an example of a preferable thickness (nm) of each layer.

In the example shown in FIG. 4, the ferromagnetic exchange coupling element 10 is formed on a Si backplane 41. In the example shown in FIG.
Each of the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 includes a Ta layer 44, an Ag layer 45, Co/Pd layers 11 and 21, and Ta layers 12 and 22 in this order from the Si backplane 41 side. , MgO layers 13 and 23, and a GdFe layer 3 are laminated.

The Si backplane 41 includes a bottom electrode (not shown). The bottom electrode is made of common metal electrode materials such as metals such as Cu, Al, Au, Ag, Ru, Ta, Cr and alloys thereof.
However, in this embodiment, it suffices if a current can flow. For example, like the Si backplane 41, a TFT backplane may be used as a configuration for active matrix driving. Also, for example, instead of the Si backplane, a simple matrix drive configuration may be employed.

The Ta layer 44 and the Ag layer 45 are base layers provided to improve adhesion to the lower electrode described above. These Ta and Ag are preferable because they do not adversely affect the magnetic properties of the Co/Pd multilayer films 11 and 21 . Note that Ru may be used instead of Ta.

The Co/Pd layers 11 and 21 constitute the above-described first and second magnetization fixed layers, respectively, the Ta layers 12 and 22 constitute the above-described non-magnetic metal layers, and the MgO layers 13 and 23 constitute the above-described buffer layers. Configure.

In this example, the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are made of the same material, but have different shapes. Specifically, as shown in FIG. 4, the width dimension in the direction in which the light modulating portion extends (horizontal direction) is greater than that of the first ferromagnetic exchange coupling portion 2 (the second magnetization fixed layer 21). Part 1 (first magnetization fixed layer 11) is designed to be larger. As a result, the coercive force of the first ferromagnetic exchange coupling portion 1 becomes smaller than the coercive force of the second ferromagnetic exchange coupling portion 2, and domain walls and domains can be formed in the optical modulation portion.

The light modulating portion, that is, the light modulating layer is composed of the GdFe layer 3 . A Ru layer 4 is formed on the GdFe layer 3 as a cap layer.
SiO ₂ layers 42 serving as insulating members are arranged adjacent to both the left and right sides of the first ferromagnetic exchange coupling section 1 and the left and right sides of the second ferromagnetic exchange coupling section 2 .

Next, an example of a method for manufacturing the ferromagnetic exchange coupling element 10 will be described in detail with reference to FIGS. 5A to 5H.
Here, FIGS. 5A to 5H are diagrams showing the manufacturing method of the ferromagnetic exchange coupling element 10 according to the first embodiment.

A method for manufacturing the ferromagnetic exchange coupling element 10 according to the first embodiment includes a first ferromagnetic layer forming step, a nonmagnetic metal layer forming step, a buffer layer forming step, a cap layer forming step, a treatment step, It has a removing step and a second ferromagnetic layer forming step.
Each of these steps will be described below.

First, as shown in FIG. 5A, a first magnetization pinned layer and a second magnetization pinned layer are formed on a SiO ₂ layer 42 of an insulating member formed on a Si back plane 41 using conventionally known electron beam lithography or the like. Resist patterning corresponding to each shape of the layer is performed. That is, a resist layer 40 corresponding to each shape of the first magnetization fixed layer and the second magnetization fixed layer is formed on the SiO ₂ layer 42 . After resist patterning, high-density plasma etching is performed. This high-density plasma etching is superior in anisotropic etching characteristics to ion milling, and is therefore particularly suitable for this step.

Then, as shown in FIG. 5B, the SiO ₂ layer 42 in the region where the resist layer 40 is not formed is removed by etching. The regions from which the SiO ₂ layer 42 has been removed correspond to the shapes of the first magnetization pinned layer and the second magnetization pinned layer, respectively.

Next, as shown in FIG. 5C, a magnetization fixed layer, a non-magnetic metal layer, a buffer layer, and a cap layer for suppressing oxidation of the buffer layer, which constitute the first ferromagnetic layer, are formed in this order (first ferromagnetic layer formation step, non-magnetic metal layer formation step, buffer layer formation step, and cap layer formation step). Specifically, the Ta layer 44, Ag layer 45, Co/Pd layers 11, 21, 51, Ta layers 12, 22, 52, MgO layers 13, 23, 53, and _SiO2 layers 14, 24, 54 are Films are continuously formed in this order. All film formation can be performed by an ion beam sputtering apparatus. This is because the ion beam sputtering method, in which the sputtered particles are highly straight, is particularly preferable because it is necessary to deposit the material in a region having a small nanometer-order aperture size and a relatively deep depth. However, it is not limited to this, and conventionally known methods such as molecular beam epitaxy (MBE) can be used.

Then, as shown in FIG. 5D, lift-off is performed to remove the remaining resist layer 40 (processing step). Specifically, lift-off is performed after the element is taken out from vacuum into the atmosphere. As a result, all layers formed on the resist layer 40 are removed. A conventionally known resist remover can be used to remove the resist layer 40 .

After lift-off, if necessary, heat treatment at 350° C. is performed in an annealing furnace (processing step). This heat treatment increases the coercive force of the Co/Pd layers 11 and 21 constituting each magnetization fixed layer. The heat treatment temperature in the treatment step is preferably 300° C. or higher, for example.

Then, as shown in FIG. 5E, ion beam milling (or high density plasma etching) is performed (removal step). As a result, the SiO ₂ layers 14 and 24 on the outermost surface are all removed, and part of the MgO layers 13 and 23 are also removed. That is, the etching is performed halfway through the MgO layers 13 and 23 . At this time, the MgO layers 13 and 23 have a slow etching rate, and Mg has a characteristic of high SIMS sensitivity. As a result, etching can be reliably stopped in the middle of the MgO layers 13 and 23 .

After completion of ion beam milling (or high-density plasma etching), the device is transported under vacuum (for example, 1×10 ⁻⁶ [Pa]) to a light modulation layer deposition apparatus. Then, as shown in FIG. 5F, the GdFe layer 3 as the light modulating layer is formed by, for example, an ion beam sputtering apparatus in the light modulating layer forming apparatus. In addition, a Ru layer 4 as a cap layer is formed on the GdFe layer 3 by, for example, an ion beam sputtering apparatus.

Next, as shown in FIG. 5G, resist patterning of the light modulating layer is performed by electron beam lithography or the like. That is, a resist layer 40 corresponding to a desired pattern is formed on the Ru layer 4 . After resist patterning, ion beam milling (or high-density plasma etching) is performed.

Then, as shown in FIG. 5H, the GdFe layer 3 and the Ru layer 4 in the regions where the resist layer 40 is not formed are removed by etching. Thereby, the GdFe layer 3 constituting the light modulating layer is formed in a desired pattern shape (second ferromagnetic layer forming step).

Finally, the resist layer 40 remaining on the uppermost layer is removed with a conventionally known resist remover. As described above, the ferromagnetic exchange coupling element 10 shown in FIG. 4 is obtained.

According to the method of manufacturing the ferromagnetic exchange coupling element 10 according to the first embodiment described above, the nonmagnetic metal layer, the buffer layer, and the cap layer for suppressing oxidation of the buffer layer are formed on the first ferromagnetic layer. They are formed in order, and in this state, a lift-off process and, if necessary, a heat treatment are performed. After removing the entire cap layer and part of the buffer layer, the second ferromagnetic layer is formed.

Here, in order to manufacture an optical modulation element using domain wall displacement as in the present embodiment, it is necessary to take the element out into the air once and lift it off before forming the optical modulation layer 30 . Therefore, in the conventional microfabrication process, two ferromagnetic thin films could not be formed continuously in a vacuum, and ferromagnetic exchange coupling could not be achieved. According to this method, the treatment process and the film forming process can be separated, so that the first ferromagnetic layer and the second ferromagnetic layer can be ferromagnetically exchange-coupled. Therefore, the manufacturing method according to this embodiment can be applied to various microfabrication processes.

Further, according to the manufacturing method of the present embodiment, since the cap layer is formed on the buffer layer 13 to suppress the oxidation of the layers below the buffer layer 13, when the device is taken out from the vacuum integrated device, it is removed by another device. Heat treatment can also be performed at about 300°C to 400°C. After the heat treatment, the entire cap layer and the buffer layer 13 are removed by ion beam milling or the like, and a second ferromagnetic layer such as GdFe, Gd, or the like, which does not have heat resistance, is formed. can be exchange coupled.

Next, the magneto-optical characteristics of the ferromagnetic exchange coupling element 10 according to the first embodiment will be described in detail with reference to Kerr rotation angle measurement results using a micro Kerr effect measurement device.
Specifically, a simulated sample of the ferromagnetic exchange coupling element 10 according to the first embodiment is prepared, and the magneto-optical characteristics of the sample are evaluated to confirm the effect of the present embodiment.

In the preparation of the simulated sample, a simple Si substrate was used instead of the Si backplane, and the first magnetization pinned layer 11 and the non-magnetic metal layer 12 of the above-described first ferromagnetic exchange coupling section 1 except for the optical modulation layer 30 were formed. and the buffer layer 13 was formed in a size of 5 μm wide×5 μm long (that is, a square shape). In the second ferromagnetic exchange coupling section 2 described above, the laminate consisting of the second magnetization pinned layer 21, the non-magnetic metal layer 22 and the buffer layer 23 except for the optical modulation layer 30 was formed with a size of 1 μm wide×2 mm long. It was formed in the shape of a line (that is, a line shape).

Here, FIGS. 6 to 8 are diagrams showing magneto-optical characteristics of simulated samples of the ferromagnetic exchange coupling device 10 according to the first embodiment. 6 to 8, the horizontal axis represents the intensity of the external magnetic field (kOe), and the vertical axis represents the Kerr rotation angle (°), that is, the polarization plane of the incident light is rotated by the magnetization direction of the ferromagnetic material. represents the angle of rotation.

In FIG. 6, the thick solid line indicates that a GdFe(9)/Ru(3) layer is formed on a line-shaped magnetization fixed layer of 1 μm wide×2 mm long, which corresponds to the second magnetization fixed layer 21. 6 shows the results of Kerr rotation angle measurement of the region where the grains were formed (indicated as “GdFe on line” in FIG. 6). The dashed line graph shows the curve of the region where the GdFe(9)/Ru(3) layer was formed on the square-shaped magnetization fixed layer of 5 μm×5 μm, which corresponds to the first magnetization fixed layer 11 . This is the rotation angle measurement result (indicated as "GdFe on 5 μ_sq" in FIG. 6). The graph of the thin solid line is the Kerr rotation angle measurement result of the region where the GdFe(9)/Ru(3) layer was deposited on the SiO ₂ layer corresponding to the SiO ₂ layer 42 as the insulating member (Fig. 6, labeled as "GdFe on SiO ₂ ").

From the results of FIG. 6, it can be seen that due to the ferromagnetic exchange coupling between the magnetization pinned layer and the GdFe(9)/Ru(3) layer of the optical modulation layer, two magnetization pinned layers with different coercive forces under the optical modulation layer It was found that three levels of coercive force differences were generated corresponding to the layer and SiO ₂ (insulator layer). This confirms that the ferromagnetic exchange coupling element 10 according to the first embodiment can function as a domain wall motion type optical modulation element.

The thick solid line graph and the dashed line graph have two hysteresis loops. ₂ This is because the measurement results (thin solid line graph) of the region where the GdFe(9)/Ru(3) layer was formed on the (insulator layer) are also added and output.

FIG. 7 shows the Kerr rotation angles before and after forming the light modulating layer on the line-shaped magnetization fixed layer of 1 μm×2 mm, which corresponds to the second magnetization fixed layer 21 . 8 shows the Kerr rotation angles before and after forming the light modulating layer on a square-shaped magnetization fixed layer of 5 μm in width×5 μm in length, which corresponds to the first magnetization fixed layer 11 .
In FIGS. 7 and 8, thin solid line graphs are Kerr rotation angle measurement results in the state corresponding to the state of FIG. "Pin in line" in 7 and "Pin in 5μ_sq" in Fig. 8). The graph of the thick solid line is the measurement result of the Kerr rotation angle of the device in the state corresponding to the state of FIG. line” and “GdFe on 5 μ_sq” in FIG. 8).

In both FIGS. 7 and 8, the thick solid line graph, that is, the coercive force in the ferromagnetic exchange-coupled state, is smaller than the thin solid line graph, that is, the coercive force in the non-ferromagnetic exchange-coupled state. This indicates that the magnetization fixed layer and the optical modulation layer are ferromagnetic exchange coupled. Therefore, from the results of FIGS. 7 and 8, it was confirmed that the magnetization fixed layer and the optical modulation layer are reliably ferromagnetically exchange-coupled.

[Second embodiment]
FIG. 9 is a cross-sectional view showing the configuration of an example of the ferromagnetic exchange coupling element 20 according to the second embodiment. The ferromagnetic exchange coupling element 20 according to the present embodiment is an optical modulation element using a coercive force difference type TMR element, not a domain wall motion type optical modulation element as in the first embodiment.
As shown in FIG. 9, the ferromagnetic exchange coupling element 20 includes a lower electrode 61, a Co/Pt multilayer film 62, a Co--Fe--B layer 63, an MgO layer 64, a Co--Fe--B layer 65, a Ta layer 66, An MgO layer 67, a Gd layer 68, a GdFe layer 69, and a Ru layer 70 are laminated in this order.

Here, the Co/Pt multilayer film 62, the Co--Fe--B layer 63, the MgO layer 64, and the Co--Fe--B layer 65 constitute a conventionally known coercive force difference type TMR element. This TMR element has a characteristic that the MR effect is very large, and the Co--Fe--B layer 65 constitutes the first ferromagnetic layer of the present invention as a magnetization free layer.

The direction of magnetization of the magnetization free layer is, for example, the vertical direction (the thickness direction of the layer), and the direction of magnetization is inverted by supplying a necessary drive current. It is preferable that the magnetization direction of the magnetization free layer is easily reversed by spin injection and that the magneto-optical effect is large. In order to increase the magneto-optical effect, it is preferable to use a magnetic layer having perpendicular magnetic anisotropy.

The Ta layer 66 constitutes the non-magnetic metal layer of the present invention, the MgO layer 67 constitutes the buffer layer of the present invention, and the Gd layer 68 and GdFe layer 69 constitute the second ferromagnetic layer of the present invention for optical modulation. The Ru layer 70 constitutes the cap layer.

The Co--Fe--B layer 65 in the TMR element forming the first ferromagnetic layer and the Gd layer 68 and GdFe layer 69 forming the second ferromagnetic layer are ferromagnetically exchange-coupled. Due to this ferromagnetic exchange coupling, the magnetization direction of the Co--Fe--B layer 65 in the TMR element and the magnetization direction of the optical modulation layer composed of the Gd layer 68 and the GdFe layer 69 are simultaneously reversed. That is, the Gd layer 68 and the GdFe layer 69 are ferromagnetically exchange-coupled with the Co--Fe--B layer 65 of the magnetization free layer, thereby forming one magnetization free layer (=optical modulation layer) as a whole.

Here, the GdFe alloy, when combined with Co--Fe--B or Co--Fe, does not exhibit perpendicular magnetic anisotropy and exhibits in-plane magnetic anisotropy similar to Co--Fe--B or the like. This is probably because Fe such as Co--Fe--B strengthens the influence of the diamagnetic field component of Fe in the GdFe alloy. In this regard, in the present embodiment, by providing the Gd layer 68 between the Co--Fe--B layer 65 and the GdFe layer 69, the effect of Fe due to the Co--Fe--B layer 65 is offset, and the GdFe layer 69 is perpendicular magnetic. It shows anisotropy.

GdFe-based alloys, GdFeCo-based alloys, CoPt-based alloys, CoPd-based alloys, MnBi alloys, MnSb alloys, PtMnSb-based alloys, and the like can be used as the magnetization free layer. Multilayer films such as Co/Pt and Co/Pd can also be used.

For the first ferromagnetic layer, the second ferromagnetic layer, the non-magnetic metal layer, the buffer layer, the cap layer, etc., the constituent materials described in the first embodiment can be appropriately used. Moreover, a functional layer may be appropriately provided at the interface of each layer.

Next, a method for manufacturing the ferromagnetic exchange coupling element 20 according to the second embodiment will be described in detail with reference to FIGS. 10A and 10B.
Here, FIGS. 10A and 10B are diagrams showing a method of manufacturing the ferromagnetic exchange coupling element 20 according to the second embodiment.

The method of manufacturing the ferromagnetic exchange coupling element 20 according to the second embodiment includes a first ferromagnetic layer forming step and a nonmagnetic metal layer forming step, similar to the method of manufacturing the ferromagnetic exchange coupling element 10 according to the first embodiment. It has a process, a buffer layer forming process, a cap layer forming process, a treating process, a removing process, and a second ferromagnetic layer forming process.

First, as shown in FIG. 10A, the above-described lower electrode 61, Co/Pt multilayer film 62, Co--Fe--B layer 63, MgO layer 64, Co--Fe--B layer 65, Ta layer 66, MgO layer 67, and Ru layer 71 are formed in this order by a known method such as sputtering (first ferromagnetic layer forming step, non-magnetic metal layer forming step, buffer layer forming step, cap layer forming step).

Next, the element is taken out from the vacuum consistent apparatus, and heat-treated at about 300° C. to 400° C. in another apparatus such as an annealing furnace (processing step). This improves the crystallinity of the MgO layer 64, resulting in an improved TMR effect.

Next, as shown in FIG. 10B, ion beam milling (or high-density plasma etching) is performed to remove all of the uppermost Ru layer 71 and to etch (remove) the MgO layer 67 of the buffer layer until about 0.3 nm remains. process). At this time, the MgO layer 67 has a slow etching rate and Mg in the MgO layer 67 has a characteristic of high SIMS sensitivity. As a result, etching can be reliably stopped in the middle of the MgO layer 67 .

After the MgO layer 67 has been etched halfway, it is transported to a film forming apparatus in a vacuum, and a Gd layer 68 without heat resistance, a GdFe layer 69, and a Ru layer 70 serving as a cap layer are formed in this order. A film is formed by a film apparatus (second ferromagnetic layer forming step).
As described above, the ferromagnetic exchange coupling element 20 according to the second embodiment is obtained.

The ferromagnetic exchange coupling element 20 according to the second embodiment has the same effect as the ferromagnetic exchange coupling element 10 according to the first embodiment.

Further, the crystallinity of the MgO layer 64 in the ferromagnetic exchange coupling element 20 (TMR element) according to the second embodiment can be improved by heat treatment. As a result, the TMR effect is improved, the spin injection efficiency is improved, and the amount of current required for spin injection magnetization reversal can be reduced. However, GdFe, Gd, etc., which constitute the light modulation layer corresponding to the second ferromagnetic layer, are materials with no heat resistance, and have the characteristic that desired magnetic properties and magneto-optical effects cannot be obtained when heat-treated. . Therefore, in the conventional manufacturing method, after forming the Co--Fe--B layer 65 corresponding to the first ferromagnetic layer to be ferromagnetically exchange-coupled, heat treatment is continuously performed in a vacuum, and then the second ferromagnetic layer is formed. Since it is necessary to deposit the Gd layer 68 and the GdFe layer 69, which require a heating and cooling time, there is a problem that the process time is long.

On the other hand, according to the present embodiment, in order to form a cap layer on the buffer layer 67 to suppress the oxidation of the layers below the buffer layer 67, the device is taken out from the vacuum integrated apparatus and heated to 300° C. to 400° C. in another apparatus. It can be heat treated at about °C. After the heat treatment, the entire cap layer and the buffer layer 67 are removed by ion beam milling or the like, and a second ferromagnetic layer such as GdFe, Gd, or the like having no heat resistance is formed to obtain a ferromagnetic layer. can be exchange coupled.

As described above, according to the manufacturing method of the present embodiment, the heat treatment process and the film formation process can be separated, and the process of performing etching and film formation after mass film formation/mass heat treatment can be adopted, so that efficient production can be achieved. It becomes possible. As a result, it is possible to select a material that does not have heat resistance, thereby increasing the degree of freedom in material selection and improving the performance of the device.

It should be noted that the present invention is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present invention.

1 first ferromagnetic exchange coupling portion 2 second ferromagnetic exchange coupling portion 3 optical modulation portion 9 pulse current source 10, 20 ferromagnetic exchange coupling element 11 first magnetization fixed layer (first ferromagnetic layer)
12, 22 nonmagnetic metal layer 13, 23 buffer layer 21 second magnetization fixed layer (first ferromagnetic layer)
30 light modulation layer (second ferromagnetic layer)
31, 32 magnetic domain 31a, 32a initial magnetic domain 33 domain wall 300 light modulation region

Claims (8)

a first ferromagnetic layer made of a ferromagnetic material;
a non-magnetic metal layer formed on the first ferromagnetic layer and made of a non-magnetic metal;
a buffer layer formed on the non-magnetic metal layer and made of oxide or nitride;
a second ferromagnetic layer formed on the buffer layer and made of a ferromagnetic material;
The first ferromagnetic layer and the second ferromagnetic layer are ferromagnetically exchange-coupled,
The second ferromagnetic layer is formed on the first ferromagnetic layer and is ferromagnetic composed of two layers: a Gd layer made of Gd and a GdFe alloy layer formed on the Gd layer and made of a GdFe alloy Exchange coupling element. _2. The ferromagnetic exchange coupling device according to claim ₁ , wherein said buffer layer is made of MgO, _{Al2O3 , MgAl2O4} , _TiO2 , ZnO or RuO2. 3. A ferromagnetic exchange coupling device according to claim 1, wherein said first ferromagnetic layer comprises a Co--Fe--B or Co/Pd multilayer film. 4. The ferromagnetic exchange coupling device according to claim 1 , wherein said buffer layer is made of MgO. 5. A ferromagnetic exchange coupling device according to claim 1 , wherein said non-magnetic metal layer is made of Ta. A method for manufacturing a ferromagnetic exchange coupling element,
a first ferromagnetic layer forming step of forming a first ferromagnetic layer made of a ferromagnetic material;
a non-magnetic metal layer forming step of forming a non-magnetic metal layer made of a non-magnetic metal on the first ferromagnetic layer;
a buffer layer forming step of forming a buffer layer made of oxide or nitride on the non-magnetic metal layer;
a cap layer forming step of forming a cap layer that suppresses oxidation of the first ferromagnetic layer, the non-magnetic metal layer and the buffer layer on the buffer layer;
At least one of a lift-off process for removing the resist pattern when the laminate having the cap layer formed thereon includes a resist pattern, and a heat treatment for heating the laminate having the cap layer formed thereon. a processing step to be performed;
a removal step of removing all of the cap layer and a portion of the buffer layer in the stack subjected to the lift-off process or heat treatment;
and a second ferromagnetic layer forming step of forming a second ferromagnetic layer made of a ferromagnetic material on the buffer layer partly removed in the removing step. 7. The method of manufacturing a ferromagnetic exchange coupling device according to claim 6 , wherein the heat treatment temperature in said treatment step is 300[deg.] C. or higher. 8. The method of manufacturing a ferromagnetic exchange coupling device according to claim 6 , wherein ion beam milling or high - density plasma etching is performed in said removing step.

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