JP2011060918A - Spin injection magnetization reversal element, magnetic random access memory, optical modulator, display apparatus, holography apparatus, hologram recording apparatus, and method of manufacturing optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spin injection magnetization reversal element which has high perpendicular magnetic anisotropy and moreover does not deteriorate the perpendicular magnetic anisotropy by heat treatment, a magnetic random access memory and an optical modulator constituted by using this spin injection magnetization reversal element, a display device, a holography apparatus, and a hologram recording apparatus constituted by using this optical modulator, and a method of manufacturing the optical modulator. <P>SOLUTION: A spin injection magnetization reversal element 11 has a structure of the spin injection magnetization reversal element formed by layering a foundation layer 21, a fixed magnetized film layer 22, a non-magnetic intermediate film layer 23 and a free magnetized film layer 24, in this order. The magnetization direction in the fixed magnetized film layer 22 and the free magnetized film layer 24 is perpendicular to the film surface, and the foundation layer 21 is a silver film layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a spin injection magnetization reversal element using a change in magnetization direction, a magnetic random access memory and an optical modulator using the spin injection magnetization reversal element, a display device using the optical modulator, a holography device, and a hologram recording The present invention relates to a device and a method for manufacturing the optical modulator.

  Conventionally, a technique applied to a magnetic random access memory (MRAM) using a spin-injection magnetization reversal element configured by sequentially laminating a magnetization fixed layer, a nonmagnetic intermediate layer, and a magnetization reversal layer has been proposed (for example, Patent Document 1). The main problems of the spin injection magnetization reversal element are to increase the density and reduce the magnetization reversal current. Here, a spin-injection magnetization reversal element using a perpendicular magnetization film having a large perpendicular magnetic anisotropy has a large coercive force, and is resistant to thermal fluctuations and disturbances and suitable for miniaturization, and achieves high memory density. It is expected that. It has also been theoretically shown that the magnetization reversal current can be reduced compared to the in-plane magnetization film.

  As an application to an optical element using a spin injection magnetization reversal element, at least one of two electrodes provided on the upper and lower parts of the element is indium zinc oxide (IZO) or indium tin oxide (ITO). A spin injection type spatial light modulator formed by a transparent electrode such as) is proposed (for example, Patent Document 2).

JP 2009-81216 A (paragraphs 0014 to 0067) Japanese Patent Laying-Open No. 2008-83686 (paragraphs 0024 to 0048)

  As conventional spin-injection magnetization reversal elements, in order to form a perpendicular magnetization film with large perpendicular magnetic anisotropy, an alloy of transition metal and rare earth metal, an alloy of transition metal and noble metal, transition metal and There are those using a multilayer film with a noble metal. However, rare earth metals are liable to oxidize, and there are many materials whose magnetic properties deteriorate due to heat in heat treatment for high orientation of element films and heat in microfabrication process. On the other hand, alloys and multilayer films of transition metals and noble metals are difficult to oxidize and have relatively high heat resistance. Here, in order to reduce the magnetization reversal current, it is necessary to improve the MR ratio by using a tunnel insulating layer such as MgO as the nonmagnetic intermediate layer, but it was formed on the tunnel insulating layer such as MgO. Transition metal / noble metal alloys and multilayer films have a problem of deterioration in perpendicular magnetic anisotropy. Therefore, development of a spin injection magnetization reversal element that can maintain high perpendicular magnetic anisotropy is desired.

  The present invention has been made in view of such circumstances, and has a high perpendicular magnetic anisotropy, and the spin injection magnetization reversal element in which the perpendicular magnetic anisotropy does not deteriorate even by heat treatment, and the spin injection magnetization An object of the present invention is to provide a magnetic random access memory and an optical modulator configured using an inverting element, a display device configured using the optical modulator, a holography device and a hologram recording device, and a method for manufacturing the optical modulator. And

A spin injection magnetization reversal element according to the present invention has a spin injection magnetization reversal element structure in which an underlayer, a fixed magnetization film layer, a nonmagnetic intermediate film layer, and a free magnetization film layer are stacked in this order, A spin-injection magnetization reversal element in which the directions of magnetization in the fixed magnetization film layer and the free magnetization film layer are perpendicular to the film surface, wherein the underlayer is a silver film layer.
According to such a configuration, due to the strong crystal orientation of the silver film layer, the crystal orientation of the fixed magnetization film layer formed on the silver film layer is increased, and high perpendicular magnetic anisotropy can be maintained.

In the spin transfer magnetization switching element according to the present invention, the nonmagnetic intermediate film layer is preferably an insulator layer.
According to such a configuration, the magnetoresistance effect ratio (MR ratio) of the spin-injection magnetization switching element is improved, and the magnetization switching current that is inversely proportional to the MR ratio can be reduced.

The spin-injection magnetization reversal element according to the present invention includes a layer made of an alloy of a transition metal and a noble metal, a thin film layer made of the transition metal, and a thin film layer made of the noble metal. And a multilayer film in which a cobalt film layer and a magnetic thin film layer other than the cobalt film layer are alternately stacked.
Furthermore, in the spin-injection magnetization switching element according to the present invention, all or a part of the free magnetization film layer is composed of a layer made of an alloy of a transition metal and a noble metal, a thin film layer made of the transition metal, and the noble metal. A multilayer film in which thin film layers are alternately stacked or a multilayer film in which cobalt film layers and magnetic thin film layers other than the cobalt film layer are alternately stacked is preferable.

  According to such a configuration, the spin-injection magnetization reversal element can be resistant to oxidation and can have high heat resistance. Therefore, the spin-injection magnetization reversal element is high even after the heat treatment for high orientation of the element film and the microfabrication process. The perpendicular magnetic anisotropy can be maintained.

A magnetic random access memory according to the present invention uses the above-described spin-injection magnetization switching element.
Since the spin-injection magnetization switching element according to the present invention has a large coercive force, such a configuration can increase the density of the memory. In addition, the magnetization reversal current can be reduced.

An optical modulator according to the present invention is an optical modulator using the spin injection magnetization reversal element described above, wherein the spin injection magnetization reversal element changes the magnetization state in the free magnetic film layer. It is a light modulation element that changes the polarization direction of reflected or transmitted light with respect to the polarization direction of light incident on the magnetic film layer.
The spin-injection magnetization reversal element (light modulation element) according to the present invention is capable of miniaturization of pixels and has high-speed response, and according to such a configuration, high-definition light modulation can be performed at high speed. . In addition, the magnetization reversal current can be reduced.

A display device according to the present invention includes the above-described optical modulator and a screen that projects light emitted from the optical modulator.
According to such a configuration, high-definition images and video can be expressed with a low current and a high display speed.

The holography device according to the present invention includes an imaging unit that captures interference fringes formed by object light and reference light, and an image reproducing unit that reproduces an image signal recorded in the imaging unit using the optical modulator described above. It is characterized by comprising.
According to such a configuration, a high-definition stereoscopic image can be reproduced with a low current and a high display speed.

  The hologram recording apparatus according to the present invention is a hologram recording apparatus that records predetermined information on a recording medium using two systems of light, and the optical modulator described above and the two systems of light are incident on the recording medium. Imaging means for detecting a change in the state of the recording medium as phase information at the time, and based on the phase information detected by the imaging means, at least one light modulation of the two light systems is performed. This is performed using the above-described optical modulator.

  According to such a configuration, the multiplicity of recording can be remarkably improved, and the multiplicity of recording can be increased by performing optical modulation of the two systems of light using the optical modulator, respectively. Further improvement can be achieved.

An optical modulator manufacturing method according to the present invention is the above-described optical modulator manufacturing method, wherein a lower electrode, an underlayer, a fixed magnetic film layer, a nonmagnetic intermediate film layer, and a free magnetic layer are formed on a substrate. In the element structure, the element structure manufacturing step for forming the element structure by forming the magnetized film layer in this order, the resist forming step for forming a resist pattern on the upper surface of the element structure, A partial removal step of partially removing a portion of the resist pattern where the resist is not formed by etching or milling; and an insulator deposition step of depositing an insulator on the upper surface of the element structure having the partially removed portion; The method includes a resist removing step of removing the resist, and an upper electrode forming step of forming an upper electrode on the upper surface of the element structure from which the resist is removed.
According to such a manufacturing method, the above-described optical modulator can be easily manufactured.

Furthermore, in the partial removal step, it is preferable to perform partial removal so that the nonmagnetic intermediate film layer is exposed on the surface of the element structure.
According to such a manufacturing method, the base layer is not exposed in the manufacturing process and is not exposed to the atmosphere.

  Since the spin-injection magnetization reversal element according to the present invention has high perpendicular magnetic anisotropy, it has high coercive force and is resistant to thermal fluctuations and disturbances and can be miniaturized. Therefore, it is possible to increase the density of the memory and perform high-definition light modulation at high speed. Furthermore, the magnetization reversal current can be reduced. In addition, according to the present invention, a magnetic random access memory having a high density and a low driving current using the characteristics of such a spin injection magnetization reversal element, and a high definition using the characteristics of such a spin injection magnetization reversal element. An optical modulator, a display device, a holography device, and a hologram recording device having light modulation characteristics and high-speed response can be realized.

  The magnetic random access memory according to the present invention uses a spin-injection magnetization reversal element that has a large coercive force and can be miniaturized, so that it is possible to increase the density of the memory. In addition, the drive current can be reduced.

  Since the optical modulator according to the present invention uses an optical modulation element capable of performing high-definition light modulation at high speed, a high-definition and high-speed response can be realized. In addition, the drive current can be reduced.

  In the display device according to the present invention, it is possible to achieve high definition in image / video expression, and to increase the display speed with a low current. In the holography device according to the present invention, high-definition can be achieved in the reproduction of a stereoscopic image, and the display speed can be increased with a low current. In the hologram recording apparatus according to the present invention, the multiplicity of recording can be remarkably improved.

  In the method for manufacturing an optical modulator according to the present invention, the optical modulator can be easily manufactured. Furthermore, by not exposing the underlayer, the underlayer is not exposed to the air during the manufacturing process, so that the silver film layer that is the underlayer is not easily corroded and the resistance value does not increase.

It is sectional drawing which shows typically the specific structure of the spin injection magnetization reversal element which concerns on this invention. It is sectional drawing which shows typically the specific structure of the spin injection magnetization reversal element which concerns on this invention. It is sectional drawing which shows typically the specific structure of the spin injection magnetization reversal element which concerns on this invention. It is sectional drawing which shows typically the specific structure of the spin injection magnetization reversal element which concerns on this invention. (A), (b) is sectional drawing which shows typically the specific structure of the spin-injection magnetization inversion element based on this invention. 1 is a plan view schematically showing a schematic configuration of a recording apparatus including a magnetic random access memory (MRAM) according to an embodiment of the present invention. It is sectional drawing which shows typically 1 cell of MRAM shown in FIG. (A) is a top view which shows typically schematic structure of the optical modulator which concerns on one Embodiment of this invention, (b) is BB sectional drawing shown to (a). It is a figure which shows typically the relationship between the voltage application form to the light modulation element in 1st Embodiment which concerns on this invention, and the Kerr effect of a free magnetic film layer, (a), (b) is a lower electrode and upper part, respectively. It is a schematic diagram at the time of reversing the positive / negative of the voltage applied to an electrode. It is a figure which shows typically the relationship between the voltage application form to the light modulation element in 2nd Embodiment which concerns on this invention, and the Faraday effect of a free magnetic film layer, (a), (b) is a lower electrode and upper part, respectively. It is a schematic diagram at the time of reversing the positive / negative of the voltage applied to an electrode. It is a figure which shows the manufacturing method of an optical modulator typically, and (a)-(f) is the schematic diagram which showed the structure in a respectively predetermined manufacturing stage. (A) is a schematic block diagram of the display apparatus using the optical modulator in 1st Embodiment which concerns on this invention, (b) is a display apparatus using the optical modulator in 2nd Embodiment which concerns on this invention. It is a schematic block diagram. 1 is a schematic structural diagram of a holographic device that supports stereoscopic video using an optical modulator according to the present invention. 1 is a schematic structural diagram of a hologram recording apparatus using an optical modulator according to the present invention. It is a schematic structure figure of the perpendicular magnetic field application microcar effect measuring device used in the example. It is a graph which shows the Kerr loop of the spin-injection magnetization reversal element using the silver film layer of this invention, (a) is after a film forming, (b) is a measurement result after performing 350 degreeC-1h vacuum heat processing. . FIG. 17 is a graph showing the Kerr loop of a spin-injection magnetization reversal element using a conventional copper film layer. (A) is after film formation, and (b) is measured after vacuum heat treatment at 350 ° C. for 1 h. It is a result.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
≪Spin injection magnetization reversal element≫
As shown in FIG. 1, the spin-injection magnetization reversal element 11 includes, from the lower electrode 13 side, an underlayer 21, a fixed magnetization film layer (magnetization fixed layer) 22, a nonmagnetic intermediate film layer (intermediate layer) 23, The free magnetic film layer (magnetization reversal layer) 24 and the protective film layer (protective layer) 25 have a structure (spin injection magnetization reversal element structure) laminated in this order, and an upper electrode is formed on the protective film layer 25. 12 is provided. Here, the spin-injection magnetization reversal element 11 including the base layer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 is illustrated, but the protective film layer 25 may be provided as necessary. The spin injection magnetization reversal element 11 has a so-called CPP-GMR (Current Perpendicular to the Plane Giant MagnetoResistance) type or TMR (Tunneling MagnetoResistance) type structure. Used.
Each configuration will be described below.

[Underlayer]
The underlayer 21 is a layer provided below the fixed magnetization film layer 22, that is, between the fixed magnetization film layer 22 and the lower electrode 13, and is made of a silver film layer (Ag film layer). By using Ag as the base layer material of the fixed magnetization film layer 22, the crystal orientation of the fixed magnetization film layer 22 formed thereon can be enhanced by the strong crystal orientation of the silver film layer. Therefore, high perpendicular magnetic anisotropy can be maintained in the spin transfer magnetization switching element 11. This is because when heat is applied in a heat treatment or microfabrication process for high orientation of the film, in the conventional copper film layer (Cu film layer) using Cu, the crystal of the fixed magnetization film layer 22 is diffused by Cu diffusion. Although the orientation is deteriorated or the crystal orientation of Cu is changed by heat, the crystal orientation of the fixed magnetization film layer 22 is also affected, and the crystal orientation of the fixed magnetization film layer 22 is deteriorated. This is probably because such a situation does not occur when a silver film layer is used. The Ag concentration in the underlayer 21 may be about 99.9%, which is a commonly used Ag concentration. The thickness of the underlayer 21 is preferably 3 to 20 nm. By making the thickness of the underlayer 21 3 nm or more, crystal growth of the Ag (111) plane is likely to occur, and by making it 20 nm or less, the surface roughness does not become too large, and the magnetic characteristics and electrical properties of the element are increased. The physical characteristics do not deteriorate.

  Further, it is preferable to dispose a ruthenium film layer (Ru film layer) between the base of the silver film layer, that is, between the lower electrode 13 and the base layer 21. By providing the ruthenium film layer, the crystal orientation of the fixed magnetization film layer 22 is further enhanced. In addition, the thickness of the ruthenium film layer is preferably 1 to 3 nm. By setting the thickness of the ruthenium film layer to 1 nm or more, crystal growth easily occurs in the ruthenium film layer, and by setting the thickness to 3 nm or less, the surface roughness does not become too large, and the magnetic characteristics and electrical properties of the element are increased. The physical characteristics do not deteriorate.

[Fixed magnetic film layer]
The fixed magnetization film layer 22 is a layer disposed between the underlayer 21 and the nonmagnetic intermediate film layer 23. The fixed magnetization film layer 22 has a filter function for discriminating spins.
The fixed magnetization film layer 22 uses a material having perpendicular magnetic anisotropy together with the free magnetization film layer 24. For example, when the spin-injection magnetization reversal element 11 is a magnetoresistive effect element to be described later, since the coercive force as the element is large, it can be miniaturized strongly against thermal fluctuations and disturbances. In the magnetic random access memory, the density of the memory can be increased. Further, since the magnetization reversal current can be reduced as compared with in-plane magnetization, the performance as a magnetic random access memory can be improved.

  For example, when the spin-injection magnetization reversal element is a light modulation element to be described later, a polar Kerr effect that makes light incident and reflected in a direction perpendicular to the light modulation element constituting the pixel is used. The direction of incident light that can obtain the maximum magnetic Kerr effect is a direction parallel to the direction of magnetization. Therefore, by having perpendicular magnetic anisotropy, the direction perpendicular to the film surface of the free magnetization film layer 24 Therefore, light can be incident and reflected on the light modulation element, and the polar Kerr effect can be increased.

In other words, since the magnitude of the magnetic Kerr effect is proportional to the scalar product of the wave vector of incident light and the magnetization vector of the magnetic material, the polar Kerr effect is generally observed from an oblique direction with respect to the film surface of the spin injection light modulation element. A large Kerr rotation angle (θ _K ) can be obtained as compared with the incident vertical Kerr effect and horizontal Kerr effect. Therefore, as compared with the in-plane magnetization, it is possible to increase the theta _K, it is possible to improve the performance of the optical modulator.

The fixed magnetic film layer 22 is entirely or partially composed of an alloy of transition metal and noble metal, a multilayer film in which thin film layers made of the transition metal and thin film layers made of the noble metal are alternately laminated, or a cobalt film. A multilayer film in which layers (Co film layers) and magnetic thin film layers other than cobalt film layers are alternately stacked is preferable.
That is, the fixed magnetization film layer 22 includes a layer made of an alloy of a transition metal and a noble metal, a multilayer film thereof, or a multilayer film of a cobalt film layer and a magnetic thin film layer other than the cobalt film layer. As shown in FIG. 1, the entire fixed magnetic film layer 22 may be composed of a layer made of an alloy of a transition metal and a noble metal (shown as an alloy film layer in the figure), or as shown in FIGS. These multilayer films may constitute the entire fixed magnetic film layer 22 (shown as a cobalt film layer and a platinum film layer in the figure, the same applies hereinafter), or a magnetic thin film layer other than the cobalt film layer and the cobalt film layer. (The illustration is omitted, but if the platinum film layer is a magnetic thin film layer other than the cobalt film layer, the structure is as shown in FIGS. 2 to 4). Furthermore, as shown in FIGS. 5A and 5B, an alloy film layer, a multilayer film of a transition metal and a noble metal, or a multilayer film of a cobalt film layer and a magnetic thin film layer other than the cobalt film layer is provided. It is good also as a structure included in a part. (In the figure, it is illustrated as a multilayer film composed of an alloy film layer and a multilayer film of a transition metal and a noble metal). In addition to the alloy film layer and the multilayer film of transition metal and noble metal, other metals may be used. Further, the position of the alloy film layer or the multilayer film in the fixed magnetization film layer 22 is not limited to the form of FIGS. 5A and 5B, and is disposed, for example, in the center of the fixed magnetization film layer 22. May be.

  Examples of the transition metal include Fe, Co, Ni, and examples of the noble metal include Au, Ag, Ru, Rh, Pd, Os, Ir, and Pt. Examples of the magnetic thin film layer other than the cobalt film layer include a nickel film layer (Ni film layer) using Ni, and the fixed magnetization film layer 22 can be a Co / Ni multilayer film layer. In the present invention, Fe, Co, and Ni are all equivalent as transition metals, and Au, Ag, Ru, Rh, Pd, Os, Ir, and Pt are all equivalent as noble metals. The same effect can be obtained with any combination of the transition metal and the noble metal. The same applies to the free magnetic film layer 24 described later.

  In the fixed magnetization film layer 22, by including (using) a transition metal and a noble metal, or including (using) a multilayer film in which a cobalt film layer and a magnetic thin film layer other than the cobalt film layer are alternately stacked, Resistant to oxidation and heat resistance can be increased. Therefore, it is possible to obtain an element that retains high perpendicular magnetic anisotropy even after heat treatment for fine orientation of the film or after a fine heat treatment process.

  Here, as an example, the fixed magnetization film layer 22 is a multilayer structure in which thin film layers (cobalt film layer) made of transition metal (Co) and thin film layers (platinum film layer) made of noble metal (Pt) are alternately stacked (hereinafter, A case where it is configured as “Co / Pt multilayer” will be described with reference to FIGS.

Here, the thickness of the cobalt film layer and the platinum film layer and the number of layers of the cobalt film layer and the platinum film layer are not particularly limited, but if the thickness of the cobalt film layer or the platinum film layer is too thin, Further, if the number of stacked layers is too small, the coercive force is lowered. On the other hand, if the thickness of the cobalt film layer or the platinum film layer is too thick, and if the number of stacked layers is too large, the perpendicular magnetic anisotropy is deteriorated. Therefore, the thickness of the cobalt film layer is preferably 0.2 to 0.5 nm, the thickness of the platinum film layer is preferably 0.8 to 1.5 nm, and the number of layers of the cobalt film layer and the platinum film layer is 3-20 are preferable for a cobalt film layer and a platinum film layer as a set. Note that the order of stacking the cobalt film layer and the platinum film layer is not particularly defined, and as shown in FIGS. 2 to 4, the cobalt film layer may be disposed at the lowermost part of the fixed magnetization film layer 22. The film layer may be disposed at the bottom. Further, from the viewpoint of coercive force and perpendicular magnetic anisotropy, the thickness of the fixed magnetization film layer 22 is preferably 10 to 30 nm.
The same applies when a layer other than the cobalt film layer or the platinum film layer is used.

The interface layer (first interface layer) S ₁ , which is a layer disposed at the interface between the fixed magnetization film layer 22 and the nonmagnetic intermediate film layer 23, is a cobalt film layer (Co film layer), a nickel film layer (Ni film). Layer), an iron film layer (Fe film layer), or a layer containing any one of Co, Ni, and Fe (for example, a CoFe alloy layer, a CoFeB alloy layer, a NiFe alloy layer). Is preferred. By using these layers, a non-magnetic intermediate film layer 23, which will be described later, is passed through a tunnel current using an amorphous insulator such as alumina (Al ₂ O ₃ ) or combined with a (100) crystal of magnesia (MgO). By supplying a coherent tunnel current, the drive current can be reduced. In the case of the TMR structure using a very thin insulating layer (film thickness of 0.5 to 1.5 nm) for the nonmagnetic intermediate film layer 23, this is between the fixed magnetization film layer 22 and the nonmagnetic intermediate film layer 23 and freely. This is because the spin polarization between the magnetic film layer 24 non-magnetic intermediate layer 23 (when provided with the second interface layer S ₂ to be described later) contributes significantly to drive current reduction, respectively. For example, in a Co / MgO / Co junction using a cobalt film layer as the interface layer and MgO as the nonmagnetic intermediate film layer 23, the spin polarization between Co and MgO becomes very large, and a theoretically large current Reduction can be achieved. The thickness of the first interface layer S ₁ does not have to be equal to the thickness of one layer of cobalt film layer constituting the pinned magnetic layer 22, be in the range of 0.1 to 1 nm, the fixed magnetization The perpendicular magnetic anisotropy of the film layer 22 does not deteriorate.

[Non-magnetic interlayer]
The nonmagnetic intermediate film layer 23 is a layer disposed between the fixed magnetization film layer 22 and the free magnetization film layer 24. When the spin injection magnetization reversal element 11 is a CPP-GMR type magnetoresistive effect element, a nonmagnetic metal is used as the nonmagnetic intermediate film layer 23. The nonmagnetic intermediate film layer 23 is necessary for separating the magnetization states of the free magnetization film layer 24 and the fixed magnetization film layer 22 and is spin-polarized between the free magnetization film layer 24 and the fixed magnetization film layer 22. It functions as a passage when exchanging electrons.
For example, in an element in which the lower electrode 13, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the upper electrode 12 are stacked in this order, the upper electrode 12 has a positive voltage (current). When a voltage (current) is applied between the lower electrode 13 and the upper electrode 12, electrons injected from the lower electrode 13 align the spin in the magnetization direction of the fixed magnetization film layer 22 inside the fixed magnetization film layer 22 (spin polarization). ), The spin-polarized electrons pass through the nonmagnetic intermediate film layer 23 while maintaining the spin, and are injected into the free magnetic film layer 24. Inside the free magnetic film layer 24, a force called local spin torque is generated by the interaction between the internal electrons that determine the magnetization direction of the free magnetic film layer 24 and the injected spin-polarized electrons. In order to reverse the spins of the internal electrons that determine the internal magnetization direction, the magnetization direction of the free magnetic film layer 24 is inverted as a result. Thus, since the nonmagnetic intermediate film layer 23 functions as a spin path, it is preferable to use a material having a small spin-orbit interaction and a long spin diffusion length (distance for holding spin). In the case of a nonmagnetic metal material, Cu, Al, Ag, Au or the like is preferable, and a semiconductor material such as ZnO may be used. The thickness is preferably 1 to 10 nm so that spin-polarized electrons can flow while maintaining a sufficient spin state.

Further, as the nonmagnetic intermediate film layer 23, an insulator such as magnesia (MgO), alumina (Al ₂ O ₃ ), or MgF ₂ can be used. In that case, the structure of the spin injection magnetization reversal element 11 is a tunnel current type magnetoresistive effect element (TMR element). In the case of a TMR element, the thickness of the nonmagnetic intermediate film layer 23 is preferably about 0.5 to 2 nm. By using the nonmagnetic intermediate film layer 23 as an insulator layer, the magnetoresistance effect ratio (MR ratio) of the spin injection magnetization reversal element 11 can be improved, and the magnetization reversal current inversely proportional to the MR ratio can be reduced. it can.

[Free magnetic film layer]
The free magnetic film layer 24 is a layer disposed between the nonmagnetic intermediate film layer 23 and the protective film layer 25 (upper electrode 12). The free magnetic film layer 24 injects electrons to be injected according to the direction of the voltage applied between the upper electrode 12 and the lower electrode 13 (that is, according to the direction of the current flowing through the spin injection magnetization switching element 11). The direction of magnetization in the free magnetic film layer 24 is reversed by the interaction between the spins and the electron spins in the free magnetic film layer 24. The free magnetic film layer 24 uses a material having perpendicular magnetic anisotropy together with the fixed magnetic film layer 22.

The free magnetic film layer 24 is entirely or partly a layer made of an alloy of a transition metal and a noble metal, a multilayer film in which thin film layers made of the transition metal and thin film layers made of the noble metal are alternately laminated, or A multilayer film in which a cobalt film layer (Co film layer) and magnetic thin film layers other than the cobalt film layer are alternately stacked is preferable.
That is, the free magnetic film layer 24 includes a layer made of an alloy of a transition metal and a noble metal, a multilayer film thereof, or a multilayer film of a cobalt film layer and a magnetic thin film layer other than the cobalt film layer. As shown in FIG. 1, the entire free magnetic film layer 24 may be composed of a layer made of an alloy of a transition metal and a noble metal (shown as an alloy film layer in the figure), or as shown in FIGS. These multilayer films may constitute the entire free magnetic film layer 24 (in the figure, shown as a cobalt film layer and a platinum film layer; the same applies hereinafter), or a magnetic thin film layer other than the cobalt film layer and the cobalt film layer. (The illustration is omitted, but if the platinum film layer is a magnetic thin film layer other than the cobalt film layer, the structure is as shown in FIGS. 2 to 4). Furthermore, as shown in FIGS. 5A and 5B, an alloy film layer, a multilayer film of a transition metal and a noble metal, or a multilayer film of a cobalt film layer and a magnetic thin film layer other than the cobalt film layer is provided. It is good also as a structure included in a part. (In the figure, it is illustrated as a multilayer film composed of an alloy film layer and a multilayer film of a transition metal and a noble metal). In addition to the alloy film layer and the multilayer film of transition metal and noble metal, other metals may be used. Further, the position of the alloy film layer or the multilayer film in the free magnetic film layer 24 is not limited to the form shown in FIGS. 5A and 5B, and is disposed, for example, in the center of the free magnetic film layer 24. May be.

  By including (using) a transition metal and a noble metal, or including (using) a multilayer film in which a cobalt film layer and a magnetic thin film layer other than the cobalt film layer are alternately stacked, Resistant to oxidation and heat resistance can be increased. Therefore, it is possible to obtain an element that retains high perpendicular magnetic anisotropy even after heat treatment for fine orientation of the film or after a fine heat treatment process.

  Here, as an example, the free magnetic film layer 24 is a multilayer structure in which thin film layers (cobalt film layer) made of transition metal (Co) and thin film layers (platinum film layer) made of noble metal (Pt) are alternately stacked (hereinafter, A case where it is configured as “Co / Pt multilayer” will be described with reference to FIGS.

The thickness of the cobalt film layer and the platinum film layer and the number of layers of the cobalt film layer and the platinum film layer are not particularly limited, but if the thickness of the cobalt film layer or the platinum film layer is too thin, If the number is too small, the coercive force is lowered, while if the thickness of the cobalt film layer or the platinum film layer is too thick, or if the number of stacked layers is too large, the perpendicular magnetic anisotropy is deteriorated. Therefore, the thickness of the cobalt film layer is preferably 0.2 to 0.5 nm, the thickness of the platinum film layer is preferably 0.8 to 1.0 nm, and the number of layers of the cobalt film layer and the platinum film layer is 1-8 are preferable for a cobalt film layer and a platinum film layer as a set. From the viewpoint of coercive force and perpendicular magnetic anisotropy, the thickness of the free magnetic film layer 24 is preferably 20 nm or less.
The same applies when a layer other than the cobalt film layer or the platinum film layer is used.

Further, the free magnetic layer 24 and the nonmagnetic intermediate interface layer disposed at the interface of the membrane layer 23 (second interface layer) S ₂ is cobalt film layer (Co layer), a nickel film layer (Ni layer), It is preferable to form a single layer film of an iron film layer (Fe film layer) or a layer containing any one of Co, Ni, and Fe (for example, a CoFe alloy layer, a CoFeB alloy layer, a NiFe alloy layer). As in the case of the fixed magnetization film layer 22, by using these layers, a tunnel current is allowed to flow in the nonmagnetic intermediate film layer 23 using an amorphous insulator such as alumina (Al ₂ O ₃ ) or magnesia (MgO The driving current can be reduced by passing a coherent tunnel current in combination with the (100) crystal. The thickness of the second interface layer S ₂ need not be equal to the thickness of one layer of cobalt film layer constituting the free magnetic layer 24, be in the range of 0.1 to 1 nm, the free magnetization The perpendicular magnetic anisotropy of the film layer 24 does not deteriorate.

[Protective film layer]
The protective film layer 25 is a layer provided above the free magnetic film layer 24, that is, between the free magnetic film layer 24 and the upper electrode 12 as necessary. The protective film layer 25 is a layer that plays a role of preventing damage such as oxidation of the free magnetic film layer 24, and in particular, the free magnetic film layer 24 in heat treatment (described later) when forming the spin transfer magnetization switching element 11. Prevent oxidation. The material constituting the protective film layer 25 is required to have a property that does not react with the material constituting the free magnetic film layer 24 during heat treatment. Further, when the spin injection magnetization reversal element 11 is used as a light modulation element, the protective film layer 25 is excellent in translucency and does not deteriorate the magnetic Kerr effect of the free magnetization film layer 24 (in other words, incident light). It is required to have a characteristic that does not scatter the polarization planes of light and reflected light. Ta, Ru, or the like can be used as a material that satisfies such requirements. In particular, Ru is preferably used for the spin-injection magnetization reversal element 11 of the present invention because the resistivity does not increase even if it is oxidized itself.

  As shown in FIGS. 1 to 5, the spin injection magnetization reversal element 11 is connected to an upper electrode 12 and a lower electrode 13, which are a pair of electrodes, at the top and bottom, and is supplied with a current perpendicular to the film surface. An insulator 15 is embedded in a gap between the upper electrode 12 and the lower electrode 13, that is, in a region adjacent to the side surface of the spin transfer magnetization switching element 11.

<Lower electrode>
The lower electrode 13 is one of a pair of electrodes for applying a voltage (current) to the spin injection magnetization switching element 11. As the material constituting the lower electrode 13, copper (Cu) that is inexpensive and excellent in electrical conductivity is preferably used. However, the material is not limited to this, and noble metals such as gold (Au) and platinum (Pt) are used. It may be used. Moreover, you may use transparent electrode materials, such as IZO and ITO. Note that a spin injection type light modulation element to be described later can be formed by using either or both of the upper electrode 12 and the lower electrode 13 as transparent electrodes such as IZO and ITO. The width of the lower electrode 13 is appropriately determined according to the shape of the spin transfer magnetization switching element 11 formed on the lower electrode 13.

<Upper electrode>
The upper electrode 12 is one of a pair of electrodes for applying a voltage (current) to the spin injection magnetization switching element 11. As the material constituting the upper electrode 12, copper (Cu) that is inexpensive and excellent in electrical conductivity is preferably used. However, the material is not limited to this, and a noble metal such as gold (Au) or platinum (Pt) is used. It may be used. Moreover, you may use transparent electrode materials, such as IZO and ITO.

<Insulator>
The insulator 15 is a member provided between the upper electrode 12 and the lower electrode 13 for insulating between these electrodes. As the insulator 15, a conventionally known insulating material such as SiO ₂ or Al ₂ O ₃ may be used.

  This spin-injection magnetization reversal element 11 can be used for a magnetic random access memory (MRAM) as a magnetoresistive effect element or an optical modulator as an optical modulation element, for example. Hereinafter, an example of the MRAM and the optical modulator using the spin transfer magnetization switching element 11 will be described, but the configuration of the MRAM and the optical modulator is not limited to this.

≪Magnetic random access memory≫
The magnetic random access memory uses the above-described spin-injection magnetization reversal element, and is, for example, arranged in a two-dimensional array or a three-dimensional array.

  As shown in FIG. 6, the MRAM (magnetic random access memory) 100 includes a plurality of cells 101. In the present embodiment, the cells 101 are two-dimensionally arranged in a 4 × 4 matrix shape in a plan view (arranged in a two-dimensional array shape). The MRAM 100 constitutes a recording apparatus R together with the bit line selection unit 102, the gate wiring selection unit 103, the current source 104, and the current control unit 105.

<Control device>
The control device 106 includes a bit line selection unit 102 that selects a bit line 107 that allows current to flow from four bit lines 107, and a gate wiring selection unit 103 that selects a gate wiring 108 that allows current to flow from four gate lines 108. A current source 104 that supplies current to the bit line selection unit 102 and the gate wiring selection unit 103, and a current control unit 105 that controls the bit line selection unit 102, the gate wiring selection unit 103, and the current source 104.

The bit line selection unit 102 selects the cells 101 arranged in the horizontal direction, and the gate line selection unit 103 selects the cells 101 arranged in the vertical direction. One bit 101 is specified by the bit line selection unit 102 and the gate wiring selection unit 103.
The current source 104 supplies a pulse current to the cell 101. In addition, you may comprise so that a direct current may be supplied.
The current control unit 105 controls the bit line selection unit 102, the gate wiring selection unit 103, and the current source 104. The current control unit 105 controls the direction and magnitude of the current flowing in each cell 101 and spin-injects into each cell 101, whereby the magnetoresistive effect element (MR element) 11 in the cell 101 (see FIG. 7). ) Is reversed. The MR element 11 is a spin injection magnetization reversal element, specifically, a CPP-GMR element or a TMR element. The details of the operation mechanism of the control device in the MRAM 100 are the same as those of the control device in the optical modulator 10 described later.

<MRAM>
FIG. 7 is a cross-sectional view schematically showing one cell of the MRAM shown in FIG. As shown in FIG. 7, in the cell 101, the upper surface of the MR element 11 is connected to the bit line 107 through the upper electrode 12. The lower surface of the MR element 11 is connected to the drain region 113 a of the source / drain regions on the surface of the semiconductor substrate 120 through the lower electrode 13, the extraction electrode 111, and the plug 112. The drain region 113a constitutes a selection transistor Tr together with the source region 113b, the gate insulating film 114 formed on the substrate 120, and the gate wiring (gate electrode) 108 formed on the gate insulating film 114. The selection transistor Tr and the MR element 11 constitute one cell 101 of the MRAM 100. The source region 113 b is connected to another bit line (wiring layer) 116 through a plug 115. An insulating material (insulator 15) is disposed around the MR element 11. Instead of using the extraction electrode 111, a plug 112 may be provided below the lower electrode 13, and the lower electrode 13 and the plug 112 may be directly connected.

<Function of current controller>
Next, spin injection performed by the current control unit 105 will be described. The MR element 11 is an element configured to take one of two steady states according to the direction of current flowing through the film surface. By making each steady state correspond to “0” data and “1” data, the MR element 11 can store binary data. The MR element 11 changes the magnetization state by the spin injection writing method, and stores information corresponding to this state. For example, with respect to the MR element 11, when the current flows between the upper electrode 12 and the lower electrode 13 from the upper electrode 12 side to the lower electrode 13 side perpendicularly to the film surface, the free magnetization film The magnetization (spin) direction in the layer 24 is the same as the magnetization direction in the fixed magnetic film layer 22. For this low resistance state, a value of “0” can be assigned to the recording bit. On the other hand, when a current flows perpendicularly to the film surface from the lower electrode 13 side to the upper electrode 12 side, the magnetization direction in the free magnetization film layer 24 is the magnetization direction in the fixed magnetization film layer 22. Vice versa. For this high resistance state, a value of “1” can be assigned to the recording bit.
In this way, the current control unit 105 can control the direction and magnitude of the magnetization direction of the free magnetic film layer 24 by performing spin injection by changing the magnitude and direction of the current flowing through the MR element 11. .

  Since the spin-injection magnetization reversal element 11 of the present invention is used as the MR element 11, the memory can be densified and the magnetization reversal current can be reduced.

  Note that the two-dimensionally arranged cells 101 may be stacked in the height direction to form a three-dimensional array (arranged in a three-dimensional array). By using a three-dimensional array structure, the volume density can be increased and the memory density can be increased.

≪Optical modulator≫
The optical modulator uses the spin-injection magnetization reversal element described above, and the light incident on the free magnetization film layer by the spin-injection magnetization reversal element changing the magnetization state in the free magnetization film layer. The light modulation element changes the polarization direction of the reflected light or transmitted light with respect to the polarization direction of the light. The optical modulator has a mesa structure, for example, by arranging such optical modulation elements in a two-dimensional array (two-dimensional matrix).

[First Embodiment]
The light modulator according to the first embodiment changes the magnetization state in the free magnetic film layer of the light modulation element (spin injection magnetization reversal element), thereby changing the polarization direction of light incident on the free magnetic film layer. The polarization direction of the reflected light is changed.

  As shown in FIGS. 8A and 8B, an optical modulator (spatial light modulator) 10 includes a substrate 14, a strip-like lower electrode 13 provided in parallel on the substrate 14 at regular intervals, and a lower portion. A strip-shaped upper electrode (upper portion) provided in parallel at regular intervals so as to sandwich the optical modulation device 11 between the light modulation device (spin injection magnetization reversal element) 11 provided on the electrode 13 at regular intervals and the lower electrode 13. Transparent electrode) 12. Further, as will be described later, a half mirror 16 and polarizing filters 17 and 18 are disposed above the upper electrode 12, and the reflected light from the light modulation element 11 is reflected by the half mirror 16 to polarize the reflected light. Depending on the angle of the surface, the polarizing filter 18 transmits or blocks the reflected light (see FIG. 9).

<Board>
The substrate 14 serves as a base for forming the lower electrode 13, the light modulation element 11, and the upper electrode 12. As will be described later, since the light modulator 10 uses light reflected after being incident on the light modulation element 11, in the first embodiment, the substrate 14 is not required to transmit light, and the lower electrode 13, What is necessary is just to be able to endure the film forming environment when forming (film forming) the light modulation element 11 and the upper electrode 12. Therefore, a silicon substrate (Si wafer), a plastic substrate, a glass substrate, a ceramic substrate, or the like can be used as the substrate 14.

<Lower electrode>
The lower electrode 13 is one of a pair of electrodes for applying a voltage (current) to the light modulation element 11. In the light modulator 10, here, the light modulation elements 11 are two-dimensionally arranged at regular intervals in the vertical and horizontal directions. Therefore, the lower electrode 13 has a strip shape and is formed on the substrate 14 at a constant width and a constant interval. Is provided. Others are the same as described in the item of the spin injection magnetization switching element.

<Upper electrode>
The upper electrode 12 is one of a pair of electrodes for applying a voltage (current) to the light modulation element 11. In the optical modulator 10, the upper electrode 12 has a belt-like shape with a constant width so that a voltage can be applied to an arbitrary element selected from the light modulation elements 11 that are two-dimensionally arranged at regular intervals in the vertical and horizontal directions. And arranged in parallel at regular intervals so that the longitudinal direction thereof is orthogonal to the longitudinal direction of the lower electrode 13. Others are the same as described in the item of the spin injection magnetization switching element.

<Light modulation element>
When a constant voltage (current) is applied between the lower electrode 13 and the upper electrode 12, the light modulation element 11 rotates the polarization plane of incident light incident on the light modulation element 11 by a Kerr effect. Plays the role of reflection. The size of the light modulation element 11 in plan view (FIG. 8A) is, for example, 100 nm × 300 nm. In the light modulator 10, the light modulation element 11 is in a two-dimensional matrix (vertically and horizontally). Although one light modulation element 11 is one pixel, the light modulation element 11 may be composed of two or more. Further, the shape of the light modulation element 11 is not limited to a rectangle (rectangle). The distance between the light modulation elements 11 depends on the accuracy of the film formation technique (a semiconductor manufacturing process is preferably used) of the upper electrode 12, the lower electrode 13, and the light modulation element 11, and is determined as appropriate.

<Control device>
As shown in FIG. 8A, the drive (operation) of the optical modulator 10 is controlled by the control device 80, and the control device 80 selects the electrode to which the voltage is applied from the plurality of lower electrodes 13. An electrode selection unit 82; an upper electrode selection unit 83 that selects an electrode to which a voltage is applied from the plurality of upper electrodes 12; a power source 81 that supplies power to the lower electrode selection unit 82 and the upper electrode selection unit 83; A lower electrode selection unit 82, an upper electrode selection unit 83, and a control unit 84 that controls operation of the power source 81 are provided.

  The lower electrode selection unit 82 includes a plurality of switching elements provided corresponding to the plurality of lower electrodes 13 respectively. Similarly, the upper electrode selection unit 83 includes a plurality of switching elements provided corresponding to the plurality of upper electrodes 12, respectively. A constant voltage is supplied to each switching element from a power supply 81, and the switching element connected to the light modulation element 11 to be driven via the lower electrode 13 and the switching element connected via the upper electrode 12 However, a voltage is applied to the light modulation element 11 by conducting a conduction operation in response to a command (operation signal) from the control unit 84. Selection of the light modulation element 11 to be driven and operation control of the switching element for driving the light modulation element 11 are performed by the control unit 84.

  The power supply 81 has a voltage inversion function. That is, a positive voltage can be applied to the lower electrode 13 and a negative voltage can be applied to the upper electrode 12. Conversely, a negative voltage can be applied to the lower electrode 13 and a positive voltage can be applied to the upper electrode 12. You can also. The control of the voltage inversion function of the power supply 81 is also performed by the control unit 84. The control unit 84 is a so-called computer, and operation control of the power supply 81, the lower electrode selection unit 82, and the upper electrode selection unit 83 is performed by a central processing unit (not shown) executing a program stored in the ROM.

Here, the deflection filter will be described with reference to FIG.
<Polarizing filter>
9A and 9B, in the light indicated by the deflection axis 70, the deflection axis is directed in a random direction. The polarizing filter 17 serves to align the deflection axes so that light incident on the light modulation element 11 is in a predetermined direction indicated by the polarization axis 71. The polarizing filter 18 plays a role of transmitting or shielding the reflected light from the light modulation element 11 reflected by the half mirror 16 depending on the angle of the polarization axis. The states shown in FIGS. 9A and 9B will be described below with reference to FIG.

<Driving of light modulation element>
FIG. 9 schematically shows the relationship between the voltage application mode to the light modulation element and the magnetic Kerr effect of the free magnetic film layer in the first embodiment. FIGS. 9A and 9B show forms in which the positive and negative voltages applied to the lower electrode 13 and the upper electrode 12 are reversed. The arrows shown in each of the fixed magnetic film layer 22 and the free magnetic film layer 24 shown in FIGS. 9A and 9B indicate the magnetization directions (spin directions). Hereinafter, it is assumed that the magnetization of the fixed magnetization film layer 22 is fixed upward, and the magnetization of the free magnetization film layer 24 is downward in the initial state.

As shown in FIG. 9A, when the current flows between the upper electrode 12 and the lower electrode 13 from the upper electrode 12 side to the lower electrode 13 side perpendicularly to the film layer surface, the free magnetic film The magnetization (spin) direction in the layer 24 is the same as the magnetization direction in the fixed magnetic film layer 22. On the other hand, as shown in FIG. 9B, when the current flows perpendicularly to the film layer surface from the lower electrode 13 side to the upper electrode 12 side, the magnetization direction in the free magnetic film layer 24 is fixed. This is opposite to the magnetization direction in the magnetic film layer 22. Thus, the state of magnetization in the free magnetic film layer 24 changes depending on the direction of the current flowing between the upper electrode 12 and the lower electrode 13. This change in state of magnetization is extremely fast, from several ns to several tens ns (ns: nanoseconds). Although the magnitude of the current to flow varies depending on the area of the light modulation element 11, in the case of a CPP-GMR structure using a metal thin film such as Cu for the nonmagnetic intermediate film layer 23, the current required for magnetization reversal The density is about 10 ⁷ to 10 ⁸ A / cm ² . In addition, in the case of a TMR structure using an extremely thin insulating layer such as MgO for the nonmagnetic intermediate film layer 23, it is expected to be a value that is about an order of magnitude lower than the above value.

  When incident light having a predetermined polarization axis indicated by the polarization axis 71 by passing through the polarization filter 17 is incident on each light modulation element 11 shown in FIGS. 9A and 9B, the free magnetic film layer 24 Due to the Kerr effect, the polarized light is reflected by a predetermined angle and emitted from each light modulation element 11. Here, with respect to the Kerr rotation angle, as in the case of the light modulation element 11 in FIG. 9A, the direction in which the right rotation indicated by the polarization axis 72 occurs is “positive direction (+ direction, + θ)”. As in the case of the light modulation element 11 in (b), the direction in which the left rotation indicated by the polarization axis 73 occurs is defined as “negative direction (−direction, −θ)”.

  Therefore, when the half mirror 16 is arranged in the traveling direction of the reflected light, the reflected light is reflected by the half mirror 16. When a polarizing filter 18 having a polarization axis parallel to the polarization axis 72 is arranged in the traveling direction of the reflected light at the half mirror 16, the reflected light in the case of FIG. 9A passes through the polarizing filter 18. However, the reflected light in the case of FIG. 9B can create a state where it cannot pass through the polarizing filter 18. As described above, the optical modulator 10 can selectively drive (apply voltage) the upper electrode 12 and the lower electrode 13 to allow a current to flow through the desired optical modulation element 11. The direction of magnetization of the free magnetic film layer 24 is controlled for each modulation element 11 (for each pixel) by the direction of current, and reflected depending on whether the reflected light can pass through the polarizing filter 18 or not. Light intensity (contrast) can be controlled.

  The contrast ratio of the reflected light is determined by the magnitude of the magnetic Kerr effect (the magnitude of the Kerr rotation angle) by the free magnetic film layer 24. As shown in FIGS. 9A and 9B, when the reflected light is transmitted or blocked (that is, when the Kerr rotation angle is equal to or larger than a certain angle), a high contrast can be obtained. However, when the Kerr rotation angle is small, the contrast is low. When the magnetization direction of the free magnetic film layer 24 is upward as shown in FIG. 9A, the output of the photodetector becomes “bright state”, and conversely, the free magnetic film as shown in FIG. 9B. When the direction of magnetization of the layer is downward, it becomes a “dark state”.

  Thus, since the magnetization direction of the free magnetic film layer 24 can be controlled by the direction in which the pulse current flows, it can be operated as the light modulation element 11 that controls the polarization plane of the light reflected by the pulse current. . The direction of magnetization after applying the pulse is maintained as it is, and it is not necessary to separately pass a current or apply a voltage. That is, the light modulation element 11 of the present invention has its own memory function.

[Second Embodiment]
The optical modulator according to the second embodiment changes the magnetization state in the free magnetic film layer of the optical modulation element (spin injection magnetization reversal element), thereby changing the polarization direction of light incident on the free magnetic film layer. The polarization direction of the transmitted light is changed. That is, the Faraday effect is used in which incident light is transmitted to the side opposite to the side on which incident light is incident and the polarization of the transmitted light is detected.

In the second embodiment, the polarizing filter 18 is disposed on the side opposite to the side on which incident light is incident (see FIGS. 10A and 10B).
When the light modulation element 11 applies a constant voltage between the lower electrode 13 and the upper electrode 12, the light modulation element 11 transmits the incident light incident on the light modulation element 11 by rotating the polarization plane of the incident light by a fixed angle by the Faraday effect. Take on.

And in order to permeate | transmit incident light, the board | substrate 14 and the lower electrode 13 also need to have transparency. Therefore, as the substrate 14, a substrate having excellent transparency such as quartz glass is used. As the lower electrode 13, a transparent electrode material such as IZO or ITO may be used, and a metal film such as Cu can be used because it has a certain transparency if it is a thin film.
Since other configurations are the same as those in the first embodiment, the description thereof is omitted here.

<Driving of light modulation element>
FIG. 10 schematically shows the relationship between the voltage application mode to the light modulation element and the Faraday effect of the free magnetic film layer in the second embodiment. FIGS. 10A and 10B show forms in which the positive and negative voltages applied to the lower electrode 13 and the upper electrode 12 are reversed.
In addition, since the description about the direction of magnetization in the free magnetic film layer 24 is the same as that of the first embodiment, the description is omitted here.

  When incident light having a predetermined polarization direction indicated by the polarization axis 71 by passing through the polarization filter 17 is incident on each light modulation element 11 shown in FIGS. 10A and 10B, the free magnetic film layer 24 Due to the Faraday effect, the polarized light is transmitted through a predetermined angle and emitted from each light modulation element 11. Here, as in the case of the light modulation element 11 in FIG. 10A, the direction in which the clockwise rotation indicated by the polarization axis 72 occurs is “positive direction (+ direction, + θ)”, and the light in FIG. As in the case of the modulation element 11, the direction in which the left rotation indicated by the polarization axis 73 occurs is defined as “negative direction (−direction, −θ)”.

Therefore, if the polarizing filter 18 having a polarization axis parallel to the polarization axis 72 is arranged in the traveling direction of the transmitted light, the transmitted light in the case of FIG. 10A can pass through the polarizing filter 18. The transmitted light in the case of (b) can create a state where it cannot pass through the polarizing filter 18. Thus, the transmitted light that passes through the polarizing filter 18 is controlled by the direction of the current for each light modulation element 11 (for each pixel) by the direction of the current, and the transmitted light that can pass through the polarizing filter 18. The intensity of the reflected light (contrast) can be controlled depending on whether the transmitted light is transmitted or not transmitted.
Since other explanations are the same as those in the first embodiment, explanations are omitted here.

  Since the spin-injection magnetization reversal element 11 of the present invention is used as the light modulation element 11, high-definition light modulation can be performed at high speed and the magnetization reversal current can be reduced.

≪Method for manufacturing optical modulator≫
Next, an example of a method for manufacturing an optical modulator will be described with reference to FIG. Ag constituting the base layer 21 is a highly corrosive material, and when exposed to the atmosphere, it absorbs moisture and easily corrodes, and the resistance value increases, so that the base layer 21 is not exposed as much as possible. Is preferable. Therefore, here, as an example of a method in which the base layer is not exposed, a case where the mode illustrated in FIG. 4 is manufactured will be described. Here, a case where one pixel (light modulation element) constituting the light modulator is manufactured will be described with reference to the drawings.

An optical modulator manufacturing method is the above-described optical modulator manufacturing method, and includes an element structure manufacturing step, a resist forming step, a partial removal step, an insulator deposition step, and a resist removal step. .
Hereinafter, each step will be described. Here, the case where the protective film layer 25 is provided is illustrated.

<Element structure manufacturing process>
The element structure manufacturing process includes a lower electrode 13, an underlayer 21, a fixed magnetic film layer 22, a nonmagnetic intermediate film layer 23, a free magnetic film layer 24, and a protective film as necessary. In this step, the layer 25 is formed in this order to produce an element structure (light modulation element) C composed of these layers. A ruthenium film layer (not shown) may be provided between the substrate 14 and the lower electrode 13 (ruthenium film layer forming step). In this step, the lower electrode 13, the underlayer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 are sequentially formed on the substrate 14 by a sputtering method (for example, magnetron sputtering, Using a known technique such as ion beam sputtering, a film is consistently formed in a vacuum (FIG. 11A).

  In the formation of the fixed magnetic film layer 22 and the free magnetic film layer 24, for example, a sputtering apparatus having a structure in which a Co sputtering target and a Pt sputtering target can be mounted and a sputtering voltage can be selectively applied to these targets. By using this, a Co / Pt multilayer film can be easily formed. Further, in addition to magnetron sputtering and ion beam sputtering, MBE method capable of controlling one atomic layer can be used.

<Resist formation process>
The resist formation step is a step of forming a resist pattern on the upper surface of the element structure C. In this step, a pixel-sized resist 91 is formed on the layer of the element structure C, and a resist pattern is formed (FIG. 11B). For example, the resist 91 is formed by an EB exposure method or the like so that a resist pattern of 100 nm × 300 nm becomes a mesa pattern.

<Partial removal process>
The partial removal step is a step of partially removing a portion of the element structure C where the resist 91 of the resist pattern is not formed by etching or milling. In this step, the portion is partially removed (predetermined thickness) to a predetermined position in the film thickness direction of the element structure C. Here, the nonmagnetic intermediate film layer 23 is exposed on the surface of the element structure C. First, partial removal is performed (so that the surface of the nonmagnetic intermediate film layer 23 is exposed). That is, partial removal is performed up to the upper surface of the nonmagnetic intermediate film layer 23 (until the surface is exposed) or halfway through the nonmagnetic intermediate film layer 23. That is, the layer of the element structure C is etched up to or before the nonmagnetic intermediate film layer 23, or is milled by an ion beam milling method using Ar ions or the like (FIG. 11C). In this way, Ag of the silver film layer is not exposed to the atmosphere, so that the underlying layer 21 is unlikely to corrode and the resistance value does not increase.

<Insulator deposition process>
The insulator deposition step is a step of depositing the insulator 15 on the upper surface of the element structure C having the part (groove) partially removed. After the partial removal step, an insulating material (insulator 15) such as alumina or silicon oxide is deposited on the entire surface without peeling off the resist 91, and a groove formed by milling or the like is filled with the insulator 15 (FIG. 11 ( d)). The insulator 15 can be formed by a reactive sputtering method, a CVD method, a sol-gel method, or the like. The thickness of the insulator 15 deposited in the groove is equal to or greater than the groove depth. In addition, since the insulator 91 is deposited before the resist 91 is removed, the insulator 15 is also deposited on the resist 91.

<Resist removal process>
The resist removing process is a process of removing the resist 91. After the insulator 15 is deposited, it is immersed in a resist stripping solution and lifted off (the resist 91 (resist pattern) is stripped). Alternatively, the resist 91 may be removed by a CMP (Chemical Mechanical Polishing) method (FIG. 11E). When performing a CMP process or the like, the thickness of the protective film layer 25 (the uppermost layer of the element structure C) formed on the uppermost part of the element structure C is set to a predetermined value at the time of film formation. It may be formed thicker by the polishing thickness.

<Upper electrode formation process>
The upper electrode forming step is a step of forming the upper electrode 12 on the upper surface of the element structure C from which the resist 91 has been removed.
After removing the resist 91, the upper electrode 12 is formed on the upper surface (upper part) of the protective film layer 25 (the uppermost layer of the element structure C) (FIG. 11 (f)). The upper electrode 12 is formed at a predetermined interval so as to cover the element structure C and to be orthogonal to the line pattern of the lower electrode 13. The upper electrode 12 can be formed in the same manner as the lower electrode 13 is formed.

  1, 2, and 5, the lower electrode 13 is exposed on the surface of the element structure C (so that the surface of the lower electrode 13 is exposed), that is, Milling or the like may be performed up to the upper surface (near side) or halfway of the lower electrode 13, and in the case of the configuration shown in FIG. 3, the base layer 21 is exposed on the surface of the element structure C (underlayer). 21), that is, milling or the like may be performed up to the upper surface (near side) of the base layer 21 or to the middle of the base layer 21, and the others are the same as described above.

  In carrying out the present invention, other steps may be included between or before and after each step within a range that does not adversely affect each step. For example, a heat treatment step may be included after the element structure manufacturing step. Hereinafter, an example of the heat treatment step will be described.

<Heat treatment process>
The heat treatment step is a step of performing a heat treatment on the manufactured element structure C. That is, the element structure C formed on the substrate 14 is heat-treated as necessary. This heat treatment is performed in order to improve the characteristics of the light modulation element and to suppress changes in the characteristics of the light modulation element during the subsequent photolithography process. As heat treatment conditions, for example, vacuum heat treatment is performed at 190 to 500 ° C. for 1 hour. From the viewpoint of suppressing the deterioration of the characteristics of the light modulation element during the heat treatment, it is preferable to provide a Ru film or the like excellent in oxidation resistance as the protective film layer 25 on the surface of the free magnetic film layer 24.

  In addition, for example, other processes such as a substrate cleaning process for cleaning the substrate 14, a base processing process for applying a base process to the substrate 14, and an unnecessary object removing process for removing unnecessary substances such as dust may be included.

≪Display device≫
FIG. 12 shows a schematic configuration diagram of a display device using the optical modulator according to the embodiment of the present invention. As shown in FIGS. 12A and 12B, the display device 30 is a color-compatible display device 30 using the light modulator 10, and includes the light modulator 10, the RGB time-division illuminator 19, and the like. Polarizing filters 17 and 18 and a screen 29 are provided. In the form shown in FIG. 12A, a half mirror 16 is provided.

  The RGB time-division illuminator 19 includes light sources such as light emitting diodes and semiconductor lasers that respectively emit R, G, and B light, which are the three primary colors of light, and each light source corresponding to each of R, G, and B has one field. It is structured to light up sequentially within the period. For example, the RGB time division illuminator 19 is driven in response to a signal from a video signal transmission device (not shown). The light emitted from the RGB time-division illuminator 19 enters the light modulator 10 through the polarization filter 17 for aligning the polarization axis, and drives (applies current) the light modulation element 11 corresponding to the incident light. The polarization direction of reflected or transmitted light is controlled by the magnetic Kerr effect or the Faraday effect. The polarizing filter 18 strongly transmits reflected light or transmitted light having a predetermined polarization direction, and restricts transmission of light whose polarization direction and angle have a polarization direction according to the angle. Thus, an image having a predetermined contrast is projected on the screen 29.

  As described above, since the light modulator 10 has a high-speed response and has a structure in which the fine light modulation elements 11 are arranged at high density, the display device 30 can display a high-definition image at a high display speed.・ Video expression is possible.

≪Holography equipment≫
FIG. 13 shows a schematic structure of a holography device compatible with a stereoscopic moving image using the optical modulator according to the embodiment of the present invention. In FIG. 13, the detailed structure of the optical modulator 10 is omitted, and the control device 80 is not shown.

  The holography device 40 is roughly divided into an image input system and an image reproduction system. The image input system includes a laser light source 31, a beam expander 32, lenses 33 and 36, half mirrors 34 and 37, a mirror 35, and a CCD camera 38 as an imaging means. On the other hand, the image reproduction system includes a laser light source 41, a beam expander 42, a lens 45, polarizing plates 43 and 44, and an optical modulator 10. The laser light source 31 and the laser light source 41 are equivalent. For example, the RGB time-division illuminator 19 used in the display device 30 described above and having a semiconductor laser light source is used.

  In the holography device 40, first, when inputting an image, the laser light emitted from the laser light source 31 is expanded by the beam expander 32 and then converted into parallel light by the lens 33. The laser light (parallel light) is divided into light for illuminating the subject to be object light by the half mirror 34 and reference light. Object light, which is reflected light from the subject, is emitted to the CCD camera 38 side through the lens 36 and the half mirror 37. On the other hand, the reference light is reflected by the mirror 35 and the half mirror 37. Thus, the object light emitted from the half mirror 37 and the reference light are combined to form interference fringes. The interference fringe pattern is imaged by the CCD camera 38. In FIG. 13, the optical path of the light emitted from the lens 33 is simply indicated by a single line.

  In reproducing an image by the holography device 40, first, the laser light emitted from the laser light source 41 is expanded by the beam expander 42, the light is made parallel by the lens 45, and the parallel light is incident on the optical modulator 10. Let On the other hand, an image signal in which the interference fringe pattern is recorded is input from the CCD camera 38 to the control device 80 (not shown in FIG. 13) of the optical modulator 10. When the control device 80 drives the light modulation element 11 according to the input signal, light modulation corresponding to the image signal of the interference fringe pattern is performed, and a stereoscopic image can be reproduced. In the holography device 40, the use of the light modulator 10 makes it possible to reproduce a high-definition stereoscopic image at a high display speed.

≪Hologram recording device≫
FIG. 14 shows a schematic structure of a hologram recording apparatus using the optical modulator according to the embodiment of the present invention. In FIG. 14, the detailed structure of the optical modulator 10 is omitted. In FIG. 14, only the traveling direction of light is shown, and illustration of a change in the spatial width of light by a lens or the like is omitted.

  In the hologram recording apparatus 50, laser light emitted from a laser light source 51 (equivalent to the above-described laser light sources 31, 41, etc.) is expanded by a beam expander 52 and then converted into parallel light by a lens 53. The parallel light (laser light) is divided into two systems of light (signal light and reference light) by the half mirror 54. The signal light is optically modulated corresponding to the two-dimensional page data by the optical modulator 10 and reaches the recording medium 55. On the other hand, the reference light is incident on another optical modulator 10 via the mirror 57, is optically modulated there, and then reaches the recording medium 55 via the mirror 58. A wavefront disturbance, which is a state change in the recording medium 55, is detected in real time as phase information by a CMOS camera 56 as an imaging means. Thus, based on the phase information detected by the CMOS camera 56, another optical modulator 10 performs optical modulation of the reference light, thereby canceling the influence of wavefront disturbance on the recording medium 55. The accuracy of multiplex recording can be improved.

  For example, in the case of volume hologram recording using a conventional photopolymer recording medium, it is caused by temperature fluctuations in the system due to air flow, photopolymer shrinkage due to photopolymerization during writing, and imperfections in the optical system such as aberrations. Thus, disturbance of the wave front of the recording medium may be a factor that hinders recording multiplexing.

  Therefore, in the hologram recording device 50, this wavefront disturbance is detected in real time by an imaging means such as a CMOS camera 56, and the reference light is spatially modulated so as to cancel the disturbance. In this case, the reference light is preferably modulated at high speed, and the optical modulator 10 is suitable for the application. The optical modulator 10 can also be used for page data writing. In this way, the hologram recording apparatus 50 can control the disturbance of the wavefront on the recording medium 55 with a resolution of about the wavelength of the light, so that the multiplicity of recording can be significantly improved. In these light modulations, the two light modulations may be performed, or one of the light modulations may be performed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the meaning of this invention.
For example, in the configuration of the spin-injection magnetization switching element, FIG. 1 illustrates a case where the base layer 21, the fixed magnetization film layer 22, the nonmagnetic intermediate film layer 23, the free magnetization film layer 24, and the protective film layer 25 are stacked in this order. Is a film in which the base layer 21, the free magnetic film layer 24, the nonmagnetic intermediate film layer 23, the fixed magnetic film layer 22, and the protective film layer 25 are stacked in this order, and the fixed magnetic film layer 22 and the free magnetic film layer 24 are interchanged. It is good also as a structure. Also in this case, the crystal orientation of the free magnetic film layer 24 formed thereon can be enhanced by the strong crystal orientation of the underlying silver film layer. Furthermore, two layers of the fixed magnetization film layer 22 were used, and the base layer 21, the fixed magnetization film layer 22, the nonmagnetic intermediate film layer 23, the free magnetization film layer 24, the fixed magnetization film layer 22, and the protective film layer 25 were stacked in this order. A so-called double spin injection structure may be used.

In the method for manufacturing an optical modulator, the element structure C may be formed as follows.
First, for example, a Cu film is uniformly formed on the surface of the substrate 14 by a sputtering method or the like, and a resist pattern having the same line width as that of the lower electrode 13 is formed on the Cu film. Using this resist pattern as an etching mask, the Cu film is dry-etched or the like until the substrate surface is exposed, and then the resist pattern is peeled to form the lower electrode 13. Alternatively, a resist pattern having a groove in a region (part) where the lower electrode 13 is to be formed is formed first, a Cu film is formed by a sputtering method, and then the lower electrode 13 is formed by a lift-off method in which the resist film is peeled off. Good. Further, in order to improve the adhesion to the substrate 14, Ta, Ru or the like may be formed on the Cu base. Further, a protective layer such as Ru may be formed on the Cu surface in order to prevent Cu from oxidizing due to exposure to the atmosphere for the process and increasing the resistivity of the lower electrode 13.
Subsequently, the groove between the lower electrodes 13 is filled with an insulator 15 and the surface including the lower electrode 13 is smoothed by CMP treatment or the like as necessary. On the surface thus formed, the underlayer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 constituting the light modulation element 11 are predetermined for each layer in this order. The layers of the light modulation element 11 are formed by sequentially forming a film by sputtering method or the like.

Furthermore, in the method for manufacturing an optical modulator, the element structure C may be partially removed and the resist may be removed as follows.
First, the element structure C is etched or milled using the resist 91 (resist pattern) as an etching mask, and then the resist 91 (resist pattern) is removed to form a light modulation element. Next, the space between the light modulation elements is filled with an insulator 15 by a CVD method or the like. Thereafter, if necessary, the surface including the light modulation element may be smoothed by CMP treatment or the like. Alternatively, the insulator 15 may be deposited on the entire surface, and the insulator 15 may be polished by CMP processing or the like until the element portion is exposed.

  Next, examples of the present invention will be described in detail, but the present invention is not limited to the following examples. Here, a configuration that does not belong to the present invention will be taken up and explained as appropriate.

In the manufacture of a sample using a spin-injection magnetization reversal element, according to the method for manufacturing an optical modulator described above, first, a lower electrode, an underlayer, a fixed magnetization film layer, a nonmagnetic intermediate film are formed on a silicon substrate with an oxide film. A layer, a free magnetic film layer, and a protective film layer were sequentially formed in a vacuum using a sputtering method. Next, after forming a pixel-sized resist on the protective film layer, milling was performed to the front (upper surface) of the nonmagnetic intermediate film layer by an ion beam milling method using Ar ions. Next, the resist was lifted off after depositing SiO ₂ as an insulator on the entire surface without peeling off the resist. Thereafter, a transparent electrode made of IZO was formed on the upper portion as the upper electrode.

  The structure of the underlayer is Ag (20 nm), the structure of the fixed magnetic film layer is a multilayer film in which Co (0.2 nm) and Pd (1.2 nm) are alternately stacked 11 times, and the structure of the free magnetic film layer Was a multilayer film in which Co (0.3 nm) and Pt (1 nm) were alternately stacked three times. The configuration of the nonmagnetic intermediate film layer was MgO (1 nm), and a tunnel spin injection type spin element was formed as a spin injection light modulation element. Moreover, the structure of the protective film layer was Ru (3 nm).

  As a comparative example, a sample using an underlayer of Cu (20 nm) was produced by the same method as described above. Other configurations are the same as described above.

And the sample after film formation (after film formation) and the sample after performing vacuum heat treatment at 350 ° C. to 1 h to the sample after film formation are irradiated with polarized light, and the magnetic field applied from the outside is changed. The Kerr rotation angle (θ _k ) of the reflected light was measured using a vertical magnetic field application microcar effect measuring apparatus (manufactured by Neoarc) shown in FIG. In FIG. 15, the yoke electromagnet is assumed to be disposed around the objective lens and the piezo stage.
The measurement conditions were: light source: 408 nm Laser Diode, NA: 0.55, spot diameter: 1 μm or less, and irradiation with linearly polarized laser light was performed at incident light ≈0 degrees.
The results are shown in FIGS. Note that 1 “Oe” = about 79.577 “A / m”.

  FIG. 16 is a graph showing a Kerr loop of a spin-injection magnetization reversal element using a silver film layer of the present invention. (A) is after film formation, (b) is after vacuum heat treatment at 350 ° C. for 1 h. It is a measurement result. FIG. 17 is a graph showing the Kerr loop of a spin-injection magnetization reversal element using a conventional copper film layer. (A) is after film formation, and (b) is measured after vacuum heat treatment at 350 ° C. for 1 h. It is a result.

  As shown in FIG. 16, in the underlayer (silver film layer) using Ag of the present invention, high perpendicular magnetic anisotropy was obtained, and the designed coercivity difference type Kerr loop was observed. Further, after the heat treatment, both the coercive force of the free magnetic film layer and the fixed magnetic film layer are increased. This is presumably because the crystal orientation of each layer of Co, Pt, Pd, etc. used for the free magnetic film layer and the fixed magnetic film layer was improved by the heat treatment.

On the other hand, as shown in FIG. 17, in the conventional underlayer (copper film layer) using Cu, the magnetization direction of the free magnetic film layer has already tilted slightly diagonally after film formation, and the perpendicular magnetic anisotropy is I understand that it is small. Further, when a vacuum heat treatment at 350 ° C. for 1 h was performed, the magnetization direction of the fixed magnetization film layer was also tilted, and the magnetic characteristics deteriorated to a state where the fixed magnetization film layer and the free magnetization film layer could not be distinguished.
Thus, the spin-injection magnetization reversal element of the present invention using Ag as an underlayer has a higher perpendicular magnetic anisotropy than a conventional spin-injection magnetization reversal element using Cu as an underlayer, and is 300 ° C. or more. It can be seen that the perpendicular magnetic anisotropy does not deteriorate even by the heat treatment.

10 optical modulator 11 spin injection magnetization reversal element (light modulation element, magnetoresistive effect element)
12 Upper electrode 13 Lower electrode 14 Substrate 15 Insulator 16 Half mirror 17, 18 Polarizing filter 19 RGB time-division illuminator 21 Underlayer 22 Fixed magnetic film layer 23 Nonmagnetic intermediate film layer 24 Free magnetic film layer 25 Protective film layer 30 Display Apparatus 40 holography apparatus 50 hologram recording apparatus 70 polarization axis 71 (positive direction) rotated polarization axis 72 (negative direction) rotated polarization axis 100 magnetic random access memory (MRAM)

Claims (11)

An underlayer, a fixed magnetization film layer, a nonmagnetic intermediate film layer, and a free magnetization film layer have a spin-injection magnetization reversal element structure laminated in this order, and the fixed magnetization film layer and the free magnetization film layer A spin-injection magnetization reversal element in which the direction of magnetization in is perpendicular to the film surface,
The spin injection magnetization reversal element, wherein the underlayer is a silver film layer.   The spin transfer magnetization switching element according to claim 1, wherein the nonmagnetic intermediate film layer is an insulator layer.   The fixed magnetization film layer is entirely or partly a layer made of an alloy of a transition metal and a noble metal, a multilayer film in which thin film layers made of the transition metal and thin film layers made of the noble metal are alternately laminated, or The spin injection magnetization reversal element according to claim 1 or 2, wherein the spin injection magnetization reversal element is a multilayer film in which a cobalt film layer and a magnetic thin film layer other than the cobalt film layer are alternately laminated.   The free magnetic film layer is entirely or partially a layer made of an alloy of a transition metal and a noble metal, a multilayer film in which thin film layers made of the transition metal and thin film layers made of the noble metal are alternately stacked, or 4. The spin transfer magnetization reversal element according to claim 1, wherein the spin transfer magnetization reversal element is a multilayer film in which a cobalt film layer and a magnetic thin film layer other than the cobalt film layer are alternately laminated.   A magnetic random access memory using the spin-injection magnetization switching element according to claim 1. An optical modulator using the spin transfer magnetization reversal element according to any one of claims 1 to 4,
Light modulation in which the spin-injection magnetization reversal element changes the polarization direction of reflected or transmitted light with respect to the polarization direction of light incident on the free magnetic film layer by changing the magnetization state in the free magnetic film layer An optical modulator characterized by being an element. An optical modulator according to claim 6;
And a screen for projecting light emitted from the light modulator. Imaging means for photographing interference fringes formed by the object light and the reference light;
A holography apparatus comprising: an image reproducing unit that reproduces an image signal recorded in the imaging unit using the optical modulator according to claim 6. A hologram recording apparatus for recording predetermined information on a recording medium using two systems of light,
An optical modulator according to claim 6;
Imaging means for detecting, as phase information, a state change in the recording medium when the two systems of light are incident on the recording medium;
A hologram recording apparatus characterized in that, based on the phase information detected by the imaging means, at least one of the two systems of light is modulated using the light modulator. A method of manufacturing an optical modulator according to claim 6,
An element structure manufacturing step of forming an element structure by forming a lower electrode, an underlayer, a fixed magnetic film layer, a nonmagnetic intermediate film layer, and a free magnetic film layer in this order on a substrate; ,
A resist forming step of forming a resist pattern on the upper surface of the element structure;
In the element structure, a partial removal step of partially removing a portion of the resist pattern where the resist is not formed by etching or milling;
An insulator deposition step of depositing an insulator on the upper surface of the element structure having the partially removed portion;
A resist removing step for removing the resist;
And an upper electrode forming step of forming an upper electrode on the upper surface of the element structure from which the resist has been removed.   11. The method of manufacturing an optical modulator according to claim 10, wherein in the partial removal step, partial removal is performed so that the nonmagnetic intermediate film layer is exposed on a surface of the element structure.

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