JP2012230143A - Spin injection type magnetization inversion element, optical modulation element and spatial light modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an orientation of an MgO (001) surface in an intermediate layer of a spin injection type magnetization inversion element.SOLUTION: An optical modulation element (spin injection type magnetism inversion element) 5 includes a tunnel magnetic resistance type spin injection type magnetization inversion element structure in which a magnetization fixing layer 51 indicating vertical magnetic anisotropy, an intermediate layer 52 composed of MgO and a magnetism free layer 53 indicating vertical magnetic anisotropy are laminated in the order. The magnetization direction of the magnetization free layer 53 is changed by supplying a current through a pair of electrodes 2, 3 arranged on the upper and lower portions of the spin injection type magnetization inversion element structure, and incident light is exited by changing the polarization direction of the incident light. The magnetization free layer 53 is configured by laminating an interface layer 53b composed of a transition metal or alloy containing the transition metal, a buffer layer 53c composed of a Ta film or a Ru film and a main layer 53a to be a magnetic layer whose magnetization direction is inverted in the order.

Description

  The present invention relates to a spin-injection magnetization reversal element that reverses the magnetization direction by spin injection, and emits light incident on the spin-injection magnetization reversal element by spatially modulating the phase and amplitude of the light by the magneto-optic effect. The present invention relates to a light modulation element used in a spatial light modulator and a spatial light modulator using the same.

  A spatial light modulator uses a light modulation element as a pixel and arranges it in a two-dimensional array to spatially modulate the phase and amplitude of the light. Widely used in fields such as recording technology. In addition, since optical information can be processed in two dimensions in parallel, its application to optical information processing technology is also being studied. Conventionally, liquid crystal has been used as a spatial light modulator, and has been widely used as a display device. However, for holography and optical information processing, response speed and pixel high definition are insufficient. For this reason, in recent years, development of a magneto-optical spatial light modulator using a magneto-optical material that is expected to be capable of high-speed processing and pixel miniaturization is in progress.

  In a magneto-optical spatial light modulator (hereinafter referred to as a spatial light modulator), when light incident on a magneto-optical material, that is, a magnetic material is transmitted, reflected, or diffracted, the direction of polarization is changed (rotation) and emitted. The Faraday effect (the Kerr effect in the case of reflection) is used. That is, assuming that the magnetization direction of the light modulation element in the selected pixel (selected pixel) is different from the magnetization direction of the light modulation element in the other pixel (non-selected pixel), the light emitted from the selected pixel and the non-selected pixel The emitted light causes a difference in the rotation angle (rotation angle) of the polarized light. As a method of changing the magnetization direction of the light modulation element, there is a method of injecting spin into the light modulation element in recent years in addition to a method of applying a magnetic field to the light modulation element.

  When injecting spin into the light modulation element for each pixel, a spin injection type magnetization reversal element (Non-Patent Document 1) such as a CPP-GMR (Current Perpendicular to the Plane Giant MagnetoResistance) element is used. As a light modulation element, a pair of electrodes are connected to the top and bottom of the light modulation element to supply a current perpendicular to the film surface. Such a light modulation element (spin-injection type magnetization reversal element), once supplied with a current having a predetermined magnitude and direction, maintains the magnetization direction until a reverse current is supplied. By arranging strip-like electrodes vertically and horizontally on the upper side and the lower side, respectively, a current for changing the magnetization direction can be supplied to the light modulation element for each pixel. Further, in this way, in the magneto-optical spatial light modulator by spin injection, since electrodes are arranged above and below the light modulation element, a transparent electrode material such as indium zinc oxide (IZO) is used. The light is transmitted through the electrode and is incident on the light modulation element.

  In such a spin-injection type light modulation device, in order to improve the performance (Faraday rotation angle, Kerr rotation angle) of the magneto-optical effect in the light modulation layer, it is made of a transition metal and a noble metal that can provide a large magneto-optical effect even with a thin film. An element using a multilayer film as a light modulation layer has been proposed (for example, Patent Documents 1 and 2). Patent Document 1 discloses a Co / Pt multilayer film, and Patent Document 2 discloses a spin injection light modulation element using a Co / Pd multilayer film. Patent Documents 1 and 2 describe a TMR (Tunnel MagnetoResistance) using a tunnel barrier layer made of an insulating material such as MgO as a nonmagnetic intermediate layer in order to reduce the drive current of a spin injection type optical modulation element. A magnetoresistive type structure is disclosed.

  Here, with reference to FIG. 7, the structure of the light modulation element which is a spin injection type magnetization reversal element of the TMR type structure in the prior art described in Patent Documents 1 and 2 will be described. FIG. 7 is a cross-sectional view schematically showing a configuration of a light modulation element in the prior art.

  As shown in FIG. 7, the light modulation element 105 in the prior art has a configuration in which a magnetization fixed layer 151, an intermediate layer 152, a magnetization free layer 153, and a protective layer 154 are stacked in this order, and the upper electrode 102 that is a pair of electrodes. And the lower electrode 103 are connected in the vertical direction, and a current is supplied perpendicular to the film surface. The light modulation element 105 includes a magnetization fixed layer 151 whose magnetization direction is fixed in one direction and a magnetization free layer 153 whose magnetization direction can be reversed, with an intermediate layer 152 made of an insulating material as a tunnel barrier layer interposed therebetween. Type spin injection type magnetization reversal element. Further, in order to protect these layers from damage in the manufacturing process, a protective layer 154 is provided as the uppermost layer. Further, the outer periphery of the light modulation element 105 sandwiched between the upper electrode 102 and the lower electrode 103 is filled with an insulating member 106.

  The magnetization fixed layer 151 includes a main layer 151a composed of a single layer film of a magnetic metal such as Co or a multilayer film in which a magnetic metal such as Co and a nonmagnetic metal such as Pd and Pt are alternately stacked, and an Fe layer in contact with the intermediate layer. , A first interface layer 151b containing a transition metal such as Co or Ni.

  The magnetization free layer 153 includes a main layer 153a made of a multilayer film in which magnetic metal films 153a1 made of Co, which is a magnetic metal, and nonmagnetic metal films 153a2, made of a nonmagnetic metal, such as Pd or Pt, are alternately stacked. , And a second interface layer 153b containing a transition metal such as Fe, Co, or Ni in contact with the intermediate layer 152.

The intermediate layer 152 is a tunnel barrier layer made of an insulating material such as MgO (magnesia), and constitutes a TMR element together with the magnetization fixed layer 151 and the magnetization free layer 153.
Here, the first interfacial layer 151b and the second interfacial layer 153b containing the transition metal described above and the (001) -oriented crystal of MgO constituting the intermediate layer 152 are combined to form a coherent tunnel in the light modulation element 105. By flowing the current, the drive current of the light modulation element 105 can be reduced.

JP 2010-60586 A JP 2011-2522 A

K. Aoshima et. Al, “Spin transfer switching in current-perpendicular-to-plane spin valve observed by magneto-optical Kerr effect using visible light”, Appl. Phys. Lett. 91, 052507 (2007)

  A magnetization free layer, which is a layer whose magnetization direction changes in a spin injection type magnetization reversal element, is generally limited to a few tens of nanometers or less. Therefore, if the spin injection type magnetization reversal element is a light modulation element, the direction of polarization is changed. The change is extremely small (Non-Patent Document 1). For this reason, in a spatial light modulator using this light modulation element as a pixel, it has been desired to improve the extraction efficiency of polarized light emitted from the selected pixel, that is, the selectivity of the pixel.

  Therefore, the light modulation elements described in Patent Literatures 1 and 2 improve the degree of light modulation by using a multilayer film of transition metal and noble metal as the magnetic film of the magnetization free layer, and improve the selectivity of the pixel. Although the drive current is reduced as a TMR type structure using insulating MgO as the nonmagnetic intermediate layer, further reduction of the drive current has been desired.

Here, in the TMR type spin injection magnetization switching element as shown in FIG. 7, in order to reduce the drive current, it is necessary to form a coherent tunnel structure with Δ ₁ band electrons having a large spin polarizability. . For this purpose, the intermediate layer 152 which is a tunnel barrier layer made of insulating MgO has a crystal orientation of (001) plane, and the first interface layer 151b which is an interface layer of the magnetization fixed layer 151 in contact with the intermediate layer 152 and the intermediate layer 152 It is known that the crystal structure of the second interface layer 153b, which is the interface of the magnetization free layer 153 in contact with the layer 152, needs to have a (001) plane orientation of a body-centered cubic lattice (bcc). As a result, the laminated structure composed of the first interface layer 151b / intermediate layer (tunnel barrier layer) 152 / second interface layer 153b becomes a (001) -oriented bcc (001) magnetic tunnel junction of a body-centered cubic lattice. Since a coherent current can flow through the element, the driving current can be reduced.

  On the other hand, in a magnetic film having a large magneto-optic effect used for the main layer 153a of the magnetization free layer 153, for example, a Co / Pt multilayer film or a Co / Pd multilayer film, Co, Pt, and Pd are all face-centered cubic. The crystal structure which is a lattice (fcc) and exhibits perpendicular magnetic anisotropy is fcc (111) plane orientation. Therefore, a region for transitioning the crystal structure from the bcc (001) plane orientation to the fcc (111) plane orientation must be formed from the intermediate layer 152 which is the tunnel barrier layer of the magnetic tunnel junction to the second interface layer 153b. However, since the influence of the fcc (111) plane orientation is large, it is difficult to form the bcc (001) plane orientation well. In other words, there is a problem that the (001) plane orientation of MgO constituting the tunnel barrier layer is insufficient.

  The present invention has been devised in view of this problem, and an object thereof is to improve the (001) plane orientation of MgO in an intermediate layer of a spin injection magnetization switching element.

  In order to achieve the above object, a spin-injection type magnetization reversal element of the present invention comprises a magnetization fixed layer exhibiting perpendicular magnetic anisotropy, an intermediate layer made of MgO, a magnetization free layer exhibiting perpendicular magnetic anisotropy, Are provided in this order, and a current is supplied through a pair of electrodes provided above and below the spin injection type magnetization reversal element structure. A spin-injection type magnetization reversal element that reverses the magnetization direction of the magnetization free layer, wherein the magnetization free layer includes an interface layer made of a transition metal or an alloy containing a transition metal, a buffer layer made of a Ta film or a Ru film, The main layer, which is a magnetic layer, was laminated in this order.

  According to such a configuration, the spin injection type magnetization reversal element constitutes a TMR type spin injection type magnetization reversal element in which the intermediate layer made of MgO which is an insulating material is used as a tunnel barrier layer. In addition, by providing a metal layer made of transition metal or an alloy containing a transition metal as an interface layer in contact with the intermediate layer, a coherent tunnel current is passed through the spin-injection type magnetization reversal element in combination with MgO in the intermediate layer, thereby switching the magnetization. The drive current for reversing the magnetization of the main layer of the magnetization free layer, which is a layer to be formed, is reduced. Here, MgO constituting the intermediate layer has a (001) -oriented crystal structure of a body-centered cubic lattice. On the other hand, the main layer of the magnetization free layer, which is a layer whose magnetization is reversed, is a magnetic layer including a magnetic metal film made of a transition metal or an alloy containing a transition metal, and has a (111) plane of a face-centered cubic lattice. Takes an oriented crystal structure. In order to reduce the drive current for the magnetization reversal of the TMR type spin injection magnetization reversal element, it is necessary to improve the (001) plane orientation from the intermediate layer made of MgO to the interface layer. The buffer layer made of Ta film or Ru film inserted between the interface layer in contact with the intermediate layer and the main layer has (001) plane orientation from the intermediate layer to the interface layer, and (111) plane orientation of the main layer. The (001) plane orientation from the intermediate layer to the interface layer is improved.

  The spin injection type magnetization reversal element of the present invention comprises a main layer of a magnetization free layer, a magnetic metal film made of a transition metal or an alloy containing a transition metal, and Au, Ag, Ru, Rh, Pd, Os, It was composed of a multilayer film in which one kind of noble metal selected from Ir and Pt or a nonmagnetic metal film made of an alloy of two or more kinds of noble metals were alternately laminated.

  According to such a configuration, the multilayer film in which the magnetic metal film and the nonmagnetic metal film constituting the main layer of the magnetization free layer that is the magnetization reversal layer are alternately stacked, operates integrally as a magnetic body, and is large. Get coercivity.

  The spin injection type magnetization reversal element of the present invention is a magnetic metal film comprising a transition metal selected from Co, Fe and Ni or an alloy containing a transition metal selected from Co, Fe and Ni as a main layer of a magnetization free layer And a non-magnetic metal film made of a noble metal selected from Pd and Pt as the non-magnetic metal.

  According to such a configuration, the multilayer film in which the magnetic metal film and the nonmagnetic metal film are selected from such a preferable combination of materials can obtain a larger coercive force.

  The spin-injection type magnetization reversal element of the present invention is a multilayer film in which the main layer of the magnetization free layer is formed by alternately laminating a magnetic metal film and a nonmagnetic metal film, and the magnetic metal film is formed on the lowermost layer of the multilayer film. An alloy film made of an alloy of the magnetic metal constituting the nonmagnetic metal and the nonmagnetic metal constituting the nonmagnetic metal film is provided.

  According to such a configuration, the multilayer film in which the magnetic metal film and the nonmagnetic metal film constituting the main layer of the magnetization free layer that is the magnetization reversal layer are alternately stacked, operates integrally as a magnetic body, and is large. Get coercivity.

  The light modulation element of the present invention is configured to include the spin injection type magnetization reversal element according to the present invention for light modulation.

  According to such a configuration, the light modulation element reverses the magnetization direction of the magnetization free layer, thereby changing the polarization direction of the light incident on the light modulation element, which is a spin injection type magnetization reversal element, by the magneto-optic effect. And exit.

  A spatial light modulator according to the present invention is a spatial modulator including a substrate, a plurality of pixels two-dimensionally arranged on the substrate, a pixel selection unit, and a current supply unit. Such a light modulation element is provided.

  According to this configuration, the spatial light modulator includes the spin injection type magnetization reversal element having a high degree of light modulation as a pixel. In this spatial light modulator, one or more pixels are selected from a plurality of pixels by a pixel selection means. Then, the spatial modulator supplies a predetermined current to the pixel selected by the pixel selection unit by the current supply unit. As a result, the spatial light modulator changes the polarization direction of the light incident on the pixel selected by the pixel selection unit to a specific direction and emits it.

According to the present invention, since the (001) plane orientation of the MgO in the intermediate layer is improved by inserting the buffer layer, the drive current for magnetization reversal can be reduced.
According to the present invention, a spin-injection type magnetization reversal element having a large coercivity of a magnetization free layer to be magnetized can be provided.
According to the present invention, a spin-injection magnetization reversal element having a larger coercive force of a magnetization free layer that is reversed in magnetization can be obtained.
According to the present invention, a spin-injection type magnetization reversal element having a large coercivity of a magnetization free layer to be magnetized can be provided.
According to the present invention, it is possible to provide an optical modulation element in which a drive current for magnetization reversal for optical modulation is reduced.
According to the present invention, since the light modulation element in which the magnetization reversal drive current is reduced is used as the pixel, the spatial light modulator can perform a stable pixel selection operation.

It is sectional drawing which shows typically the structure of the light modulation element which concerns on 1st Embodiment of this invention. It is sectional drawing which illustrates typically operation | movement of the light modulation element which concerns on this invention, The magnetization direction of a magnetization free layer shows the case where (a) is parallel and (b) is antiparallel. 1 is a plan view schematically showing a configuration of a spatial light modulator according to a first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining the configuration of the display device using the spatial light modulator and the pixel selection operation according to the first embodiment of the present invention, corresponding to the AA cross-sectional view of FIG. 3. FIG. 6 is a schematic diagram for explaining a configuration of a display device using a spatial light modulator and a pixel selection operation according to a second embodiment of the present invention, and corresponds to a cross-sectional view taken along line AA of FIG. 3. It is sectional drawing which shows typically the structure of the light modulation element which concerns on the modification of 1st Embodiment of this invention. It is sectional drawing which shows typically the structure of the light modulation element in a prior art. It is a graph which shows the X-ray-diffraction pattern of the optical modulation element of the Example of this invention, and the comparative example by a prior art.

  Hereinafter, embodiments for realizing a spin-injection type magnetization reversal element, a light modulation element, and a spatial light modulator according to the present invention will be described with reference to the drawings. The spin-injection magnetization switching element according to the embodiment of the present invention takes the form of a light modulation element. The configuration and operation of the spin-injection type magnetization reversal element of the present invention will be described through a light modulation element as an embodiment thereof.

<First Embodiment>
[Light modulation element (spin injection type magnetization reversal element)]
As shown in FIG. 1, the light modulation element 5 according to the first embodiment of the present invention has a configuration in which a magnetization fixed layer 51, an intermediate layer 52, a magnetization free layer 53, and a protective layer 54 are laminated in this order. The upper electrode 2 and the lower electrode 3 that are electrodes are connected in the vertical direction, and current is supplied perpendicularly to the film surface. The light modulation element 5 includes a TMR type in which a magnetization fixed layer 51 whose magnetization direction is fixed in one direction and a magnetization free layer 53 whose magnetization direction can be reversed are sandwiched by an intermediate layer 52 made of MgO which is an insulating material. This is a spin injection type magnetization reversal element. Further, in order to protect these layers from damage in the manufacturing process, a protective layer 54 is provided on the uppermost layer, and an insulating member 6 is provided on the outer periphery of the light modulation element 5 sandwiched between the upper electrode 2 and the lower electrode 3. Is filled.

  Each layer constituting the light modulation element 5 is continuously formed and laminated by a known method such as a sputtering method or a molecular beam epitaxy (MBE) method, and a desired plane is formed by an electron beam lithography or an ion beam milling method. Processed into a visual shape.

The magnetization fixed layer 51 is a magnetic layer whose magnetization direction is fixed in one direction, and has a function of discriminating the spin of electrons in the current. It is desirable that the magnetization fixed layer 51 has a magnetic anisotropy in the same direction as the magnetization free layer 53. When a magnetic film having a perpendicular magnetic anisotropy is used for the magnetization free layer 53, the magnetization fixed layer 51 also has a perpendicular magnetic property. A magnetic film having anisotropy is used. In the present embodiment, the magnetization fixed layer 51 and the magnetization free layer 53 are magnetic films having perpendicular magnetic anisotropy.
In addition, the magnetization fixed layer 51 in the present embodiment is configured by laminating a main layer 51 a that is a magnetic layer whose magnetization direction is fixed in one direction, and a first interface layer 51 b in contact with the intermediate layer 52.

  The main layer 51a of the magnetization fixed layer 51 can be made of a known magnetic material as a magnetization fixed layer such as a CPP-GMR type element or a TMR type element having perpendicular magnetic anisotropy, and has a thickness of 8 to 30 nm is preferable.

  As a material used for the main layer 51a of the magnetization fixed layer 51, ferromagnetic transition metals such as Co, Fe, and Ni, alloys of transition metals and rare earth metals (for example, Tb-Fe-Co series, Tb-Fe series, Tb-Co-based, Dy-Co-based, Dy-Co-Fe-based, Gd-Fe-based, Gd-Co-based, Gd-Fe-Co-based alloys, etc.) and transition metal / noble metal-based multilayer films (for example, Co / Pd multilayer film, Fe / Pt multilayer film, Co / Pt multilayer film, etc.) and alloys of transition metals and noble metals (for example, Co—Pt, Co—Pd, Fe—Pt alloys, etc.) Can be mentioned. In addition, there are a Co / Ni multilayer film, a Co-Ni alloy / Pt multilayer film, a Mn-Bi alloy, and the like. As the transition metal, Fe, Co, Ni and the like are preferable, and as the noble metal, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt and the like can be mentioned, and Pd and Pt are preferable. As the rare earth metal, Sm, Eu, Gd, and Tb are preferable.

  Among these, a Tb—Fe—Co alloy film having a thickness of 10 to 30 nm is more preferable. Since the perpendicular magnetization film having a large coercive force (10 kOe or more) of the main layer 51a of the magnetization fixed layer 51 can be formed by Tb contained in the alloy film, the magnetization direction of the main layer 51a of the magnetization fixed layer 51 is It can be prevented from being easily changed by an external magnetic field.

  The first interface layer 51b of the magnetization fixed layer 51 is made of at least one transition metal selected from Fe, Co, and Ni or an alloy containing this transition metal, and has a thickness in the range of 0.1 to 1 nm. Is preferred. As an alloy containing a transition metal, for example, a Co—Fe based alloy, a Co—Fe—B based alloy, a Ni—Fe based alloy, or a Co—Fe—Si based alloy can be given.

  The first interface layer 51 b of the magnetization fixed layer 51 is combined with the (001) -oriented crystal of MgO constituting the second interface layer 53 b of the magnetization free layer 53 and the intermediate layer 52 and is a coherent tunnel to the light modulation element 5. A current can be passed, and a driving current for reversing the magnetization of the light modulation element 5 can be reduced.

The intermediate layer 52 is provided between the magnetization fixed layer 51 and the magnetization free layer 53, magnetically separates the magnetization free layer 53 and the magnetization fixed layer 51, and allows a spin-polarized current to flow. The intermediate layer 52 is a tunnel barrier layer in the light modulation element 5 constituting the TMR element and is made of MgO (magnesia) that is an insulating material. The intermediate layer 52 is formed of this (001) -oriented crystal of MgO, and the film thickness can be about 0.5 to 3 nm.
The MgO film constituting the intermediate layer 52 can be formed by an RF ion beam sputtering method or the like.

  The magnetization free layer 53 is a layer whose magnetization direction is reversed by spin injection. That is, by supplying a current between the upper electrode 2 and the lower electrode 3, the spin of injected electrons and the electron spin in the magnetization free layer 53 according to the direction of the current supplied between these electrodes. The direction of magnetization in the magnetization free layer 53 is reversed by the interaction with.

  The magnetization free layer 53 in the first embodiment includes a second interface layer 53b in contact with the intermediate layer 52, a buffer layer 53c made of Ta film or Ru film, and a main layer that is a magnetic layer whose magnetization direction is reversed by spin injection. 53a are stacked in this order. In addition, the main layer 53a in the present embodiment is configured by a multilayer film in which magnetic metal films 53a1 and nonmagnetic metal films 53a2 are alternately stacked.

  As the magnetic metal film 53a1, a magnetic material made of a transition metal or an alloy containing a transition metal can be used, and preferred examples include Co, Fe, Ni, and Co—Fe based alloys. Moreover, a noble metal can be used as the nonmagnetic metal film 53a2. As the noble metal, Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, or an alloy of two or more kinds of these noble metals can be used, and Pt and Pd are preferable.

  Examples of the multilayer film include a Co / Pt multilayer film, a Co / Pd multilayer film, an Fe / Pd multilayer film, a Co—Fe-based alloy / Pd multilayer film, and an Fe / Pt multilayer film.

  In this embodiment, the main layer 53a, which is a layer whose magnetization direction is reversed in the magnetization free layer 53, is formed by alternately laminating the magnetic metal film 53a1 and the nonmagnetic metal film 53a2, for example, a Co / Pt multilayer film. It is what. Since a Co / Pt multilayer film in which a ferromagnetic Co film and a nonmagnetic Pt film are alternately stacked is used, it can operate integrally as a magnetic body and have a large coercive force. It is preferable to use a multilayer film.

  Further, for example, when the main layer 53a is composed of a Co / Pt multilayer film, the uppermost layer and the lowermost layer of the multilayer film may be either a Co film or a Pt film, respectively, but the intermediate layer via the second interface layer 53b. It is preferable to stack a Co film that is the magnetic metal film 53a1 on the lowermost layer adjacent to the layer 52. By disposing the Co film as a boundary layer adjacent to the intermediate layer 52, the spin polarization at the boundary is increased, and the spin torque due to the spin injected into the magnetization free layer 53 through the intermediate layer 52 is increased. Therefore, the current required for the magnetization reversal of the light modulation element 5 can be reduced, and the light modulation element 5 constituting the TMR element has a great effect of reducing the current.

  The main layer 53a of the magnetization free layer 53 is not limited to such a multilayer film, and may be a single layer film. As the single layer film, a magnetic material made of a transition metal or an alloy containing a transition metal can be used. Examples of transition metals include Co, Fe, and Ni. Examples of transition metal alloys include Co—Fe—B alloys, Co—Fe alloys, Co—Fe—Si alloys, and Co. -Fe-Ge alloy can be used. In addition, a material having a large magneto-optical effect such as an alloy of a transition metal and a noble metal which is a nonmagnetic metal, or an alloy of a transition metal and a rare earth metal can be used. Here, examples of the rare earth metal include Sm, Eu, Gd, and Tb.

  Examples of the alloy of the transition metal and the noble metal include a Co—Pt alloy, a Co—Pd alloy, an Fe—Pd alloy, and an Fe—Pt alloy. Examples of alloys of rare earth metals and transition metals include Gd—Fe alloys, Gd—Co—Fe alloys, Gd—Co alloys, Tb—Fe—Co alloys, and the like. In addition, a material having a large magneto-optical effect such as a Mn—Bi alloy, a Mn / Bi multilayer film, a Pt—Mn—Sb alloy, or a Pt / Mn—Sb alloy multilayer film can be used.

  In addition, by using an alloy containing a ferromagnetic transition metal as the main layer 53a, the saturation magnetization can be lowered and the magnetization direction can be stabilized while ensuring the coercive force as the magnetization switching layer. For this reason, a light modulation element with a stable degree of light modulation can be configured.

  Furthermore, a multilayer film of transition metal and rare earth metal can be used as the main layer 53a. As the multilayer film of transition metal and rare earth metal, Co / Gd multilayer film, Fe / Gd multilayer film, Co—Fe based alloy / Gd multilayer film, Co—Fe—B based alloy / Gd multilayer film, Co—Ni based film In addition to alloys / Gd multilayer films, in these multilayer films, multilayers using Gd—Fe alloys, Tb, Tb—Co alloys, Tb—Fe alloys, Tb—Fe—Co alloys instead of Gd Mention may be made of membranes.

  The film thickness of the main layer 53a of the magnetization free layer 53 (in the case of a multilayer film, the total film thickness of all the layers constituting the multilayer film) is not particularly limited, but the film thickness of the main layer 53a is thin. If it is too large, the coercive force is lowered, while if it is too thick, the perpendicular magnetic anisotropy is deteriorated. Therefore, the film thickness of the main layer 53a is preferably about 1.5 to 15 nm.

The buffer layer 53c of the magnetization free layer 53 includes a second interface layer 53b in contact with the intermediate layer 52 made of a (001) -oriented MgO film, and the lowermost layer of the main layer 53a (in the example of FIG. 1, the magnetic metal film 53a1). And a layer made of a Ta film or a Ru film. The buffer layer 53c includes a bcc (001) -based magnetic tunnel junction constituted by the first interface layer 51b / intermediate layer (tunnel barrier layer) 52 / second interface layer 53b, and fcc (111) constituting the main layer 53a. It functions as a buffer layer for satisfactorily connecting the magnetic layer of the system. By this buffer layer 53c, the (001) plane orientation from the intermediate layer 52 to the second interface layer 53b is favorably formed.
As a result, a coherent tunnel current can be caused to flow through the light modulation element 5, and the drive current for magnetization reversal can be reduced.

  When a Ta film is used as the buffer layer 53c, if the film thickness is too thin, the (001) plane orientation of MgO constituting the intermediate layer 52 cannot be improved. On the other hand, if the film thickness is too thick, the magnetostatic coupling between the second interface layer 53b and the main layer 53a becomes weak, and when the main layer 53a is a multilayer film, the magnetization direction of the multilayer film is integrated. It does not change. Therefore, the thickness of the Ta film is preferably about 0.2 to 1.2 nm, and more preferably 0.8 to 1.2 nm.

  Further, when a Ru film is used as the buffer layer 53c, if the film thickness is too thin, the (001) plane orientation of MgO constituting the intermediate layer 52 cannot be improved. On the other hand, if the film thickness is too thick, the magnetostatic coupling between the second interface layer 53b and the main layer 53a becomes weak, and when the main layer 53a is a multilayer film, the magnetization direction of the multilayer film is integrated. It does not change.

  Here, when a Ru film is used as the buffer layer 53c, if the Ru film is thin due to RKKY interaction, which is an interaction between localized spins performed through the spin of conduction electrons in the metal, The second interface layer 53b and the main layer 53a are magnetically coupled antiparallel to each other, and if the film thickness is large, the two are magnetically coupled in parallel. That is, by using a Ru film as the buffer layer 53c, there is an effect of magnetically coupling the second interface layer 53b in contact with the Ru film and the main layer 53a, but if the film thickness is too thick, the RKKY The magnetic coupling due to the interaction is attenuated.

  Due to this RKKY interaction, the film thickness when the Ru film is used as the buffer layer 53c can be made larger than that when the Ta film is used, and is preferably about 0.2 to 1.5 nm. More preferably, it is set to ˜1.5 nm.

  The second interface layer (interface layer) 53 b of the magnetization free layer 53 can be configured in the same manner as the first interface layer 51 b of the magnetization fixed layer 51. As the second interface layer 53b, at least one transition metal selected from Fe, Co, and Ni or an alloy containing the transition metal can be used, and the film thickness can be in the range of 0.1 to 1 nm. preferable. As an alloy containing a transition metal, for example, a Co—Fe based alloy, a Co—Fe—B based alloy, a Ni—Fe based alloy, or a Co—Fe—Si based alloy can be given.

  The second interface layer 53 b of the magnetization free layer 53 is combined with the (001) -oriented crystal of MgO constituting the first interface layer 51 b of the magnetization fixed layer 51 and the intermediate layer 52, and is a coherent tunnel to the light modulation element 5. A current can be passed, and a driving current for reversing the magnetization of the light modulation element 5 can be reduced.

  The protective layer 54 is composed of a single layer of Ta, Ru, Cu, or two layers of Cu / Ta, Cu / Ru. In addition, when setting it as the said 2 layer structure, all make Cu inside (lower layer). When the thickness of the protective layer 54 is less than 1 nm, it is difficult to form a continuous film. On the other hand, even if the thickness exceeds 10 nm, the effect of protecting the magnetization free layer 53 and the like in the manufacturing process is further improved. In addition, the transmitted light amount of incident light from above the light modulation element 5 is attenuated. Therefore, the thickness of the protective layer 54 is preferably 1 to 10 nm.

The upper electrode 2 is paired with the lower electrode 3 and plays a role of flowing a current in the vertical direction of the light modulation element 5. The upper electrode 2 allows an electric current to flow through the element and transmits light to a layer below the magnetization free layer 53, so that ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide) are used. ), Tin oxide (SnO ₂ ), antimony oxide-tin oxide system (ATO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), indium oxide (In ₂ O ₃ ), etc. The

  The lower electrode 3 is paired with the upper electrode 2 and plays a role of flowing a current in the vertical direction of the light modulation element 5. When the light modulation element 5 is used as a reflection type light modulation element, a metal such as Cu or Au having a low electric resistance can be used. Further, when the light modulation element 5 is used as a transmissive light modulation element, it can be configured using a transparent electrode material such as ITO or IZO in the same manner as the upper electrode 2.

  Further, when the light modulation element 5 is used as a reflection-type light modulation element, the lower electrode 3 is replaced with an fcc-based material such as Cu or Au by using bcc-based material Ta or Ru. The crystallinity of the 52 MgO film can be easily oriented in the (001) plane. Alternatively, the entire lower electrode 3 may not be made of Ta or Ru, but the lower layer of the lower electrode 3 may be made of Cu or Au, and the upper layer adjacent to the light modulation element 5 may be made of Ta or Ru. At this time, the film thickness of the upper Ta layer or Ru layer is preferably about 50 nm or more.

The insulating member 6 is made of an insulating material such as SiO ₂ , SiN, SiN / SiO ₂ multilayer film, or Al ₂ O _3, and in the spatial light modulator described later, a plurality of light modulation elements 5 are arranged in a matrix as pixels. At this time, it is a member that fills a gap between pixels disposed between the upper electrode 2 and the lower electrode 3.

  The insulating member 6 can be formed by depositing the above insulating material by sputtering or the like after forming a plurality of light modulating elements 5 as a spatial light modulator so as to be arranged in a matrix.

[Operation of light modulation element]
Here, the magnetization reversal operation of the light modulation element 5 will be described with reference to FIG. In FIG. 2, the protective layer 54 is not shown. The light modulation element 5, which is a spin injection type magnetization reversal element, injects electrons having a spin opposite to that of the electrons in the magnetization free layer 53, that is, supplies current in the opposite direction, thereby freeing magnetization. The magnetization direction of the layer 53 is reversed (spin injection magnetization reversal, hereinafter referred to as magnetization reversal as appropriate) to be the same direction as the magnetization direction of the magnetization fixed layer 51 or a direction different by 180 °. Specifically, as shown in FIG. 2A, when a current is supplied from the magnetization free layer 53 side to the magnetization fixed layer 51 by setting the upper electrode 2 to “+” and the lower electrode 3 to “−”, The magnetization of the free layer 53 is the same as the magnetization direction of the magnetization fixed layer 51. Hereinafter, this state is referred to as that the magnetization of the light modulation element 5 is parallel (P: Parallel). On the contrary, as shown in FIG. 2B, when a current is supplied from the magnetization fixed layer 51 side to the magnetization free layer 53 with the upper electrode 2 set to “−” and the lower electrode 3 set to “+”, the magnetization free layer The magnetization of 53 is opposite to the magnetization direction of the magnetization fixed layer 51. Hereinafter, this state is referred to as anti-parallel (AP) where the magnetization of the light modulation element 5 is antiparallel.

  If the magnetization of the light modulation element 5 shows either parallel or antiparallel magnetization, the magnetization is held by the coercive force Hcf of the magnetization free layer 53 until a current for inverting the magnetization is supplied. As described above, since the magnetization is held in the light modulation element 5, the current supplied to the light modulation element 5 is a current that temporarily reaches a current value that reverses the magnetization direction, such as a pulse current. Can do. However, when the coercive force Hcf of the magnetization free layer 53 increases and approaches the coercive force Hcp of the magnetization fixed layer 51, the current required for magnetization reversal (magnetization reversal current) increases, and more than the coercivity Hcp of the magnetization fixed layer 51. Then, the magnetization reversal operation by current supply cannot be performed. Therefore, the magnetization fixed layer 51 and the magnetization free layer 53 are configured so that the coercive forces Hcf and Hcp satisfy Hcf <Hcp, and preferably the difference is 500 Oe or more.

  When light incident on the light modulation element 5 is reflected or diffracted by the magnetization free layer 53 that is a magnetic material, the direction of polarization of the incident light changes (rotation) due to the Kerr effect (magnetic Kerr effect). Further, as shown in FIGS. 2 (a) and 2 (b), the lights incident on the light modulation elements 5 whose magnetizations are parallel and antiparallel, respectively, have the same magnitude because the magnetization directions of the magnetization free layer 53 differ by 180 °. Are rotated in opposite directions at the Kerr rotation angle of the magnetization free layer 53, that is, the Kerr rotation angles + θk, −θk (hereinafter, “θk” indicates only the size). The emitted light from the light modulation element 5 functions as a pixel such as a spatial light modulator described later by changing the direction of the polarization according to the direction of the supplied current. It is preferable that the Kerr rotation angle θk of the magnetization free layer 53 that is the difference of the

  The magnitude of the Kerr effect is proportional to the scalar product of the wave number vector of incident light and the magnetization vector of the magnetic material. That is, the Kerr rotation angle θk of the magnetization free layer 53 increases as the incident angle of light becomes closer to the magnetization direction of the magnetization free layer 53. Here, if the magnetization free layer 53 (and the magnetization fixed layer 51) has magnetization in the film plane direction (in-plane magnetic anisotropy), the light modulation element 5 has a structure close to the magnetization direction in parallel with the light. It is difficult to make it incident. On the other hand, if the magnetization free layer 53 has magnetization in a direction perpendicular to the film surface, that is, perpendicular magnetic anisotropy, light can be easily incident parallel to the magnetization direction, and a large Kerr effect can be applied. A rotation angle θk is obtained. The light modulation element 5 according to this embodiment has the perpendicular magnetic anisotropy and a large Kerr rotation angle θk by configuring the magnetization fixed layer 51 and the magnetization free layer 53 as described above.

  As described above, according to the light modulation element 5 according to the first embodiment, the second interface layer 53b which is the lowermost layer of the magnetization free layer 53 in contact with the intermediate layer 52 made of (001) -oriented MgO; Since the buffer layer 53c made of the Ta film or the Ru film is provided between the magnetization free layer 53 and the main layer 53a which is a layer whose magnetization is reversed, the (001) plane orientation of the second interface layer 53b is improved. Can do. For this reason, it can be set as the light modulation element which reduced the magnetization reversal current.

[Spatial light modulator, display device]
(First Embodiment of Spatial Light Modulator and Display Device)
Next, an embodiment of a spatial light modulator including the light modulation element 5 according to the first embodiment of the present invention in a pixel and a display device using the same will be described with reference to FIGS. 3 and 4. . In addition, the pixel in this specification refers to a means for displaying information (bright / dark) in the minimum unit of display by the spatial light modulator.

  A spatial light modulator 1 according to the first embodiment of the present invention includes a pixel array 40 including pixels 4 arranged in a two-dimensional array on a substrate 7 (see FIG. 4) as shown in FIG. A current control unit 80 that selects and drives one or more pixels 4 from the array 40 is provided. Note that the plane (upper surface) in this specification is a light incident surface of the spatial light modulator, and the spatial light modulator 1 reflects or diffracts light incident on the pixel 4 (pixel array 40) from above to generate the light. It is a reflective spatial light modulator that modulates the light and emits upward.

  As shown in FIG. 3, the pixel array 40 includes a plurality of upper electrodes 2, 2,... Striped in plan view, and a plurality of lower electrodes 3, 3 that are also striped and orthogonal to the upper electrode 2 in plan view. ,..., And one pixel 4 is provided at each intersection of the upper electrode 2 and the lower electrode 3. Therefore, the pixels 4 are arranged in a two-dimensional array on the light incident surface of the spatial light modulator 1 to form the pixel array 40. In the present embodiment, the pixel array 40 is exemplified by a configuration including 25 pixels 4 of 5 rows × 5 columns. The upper electrode 2 and the lower electrode 3 are collectively referred to as electrodes 2 and 3 as appropriate. 3 and 4, the pixel 4 includes an upper electrode 2 and a lower electrode 3 as a pair of electrodes in the pixel 4, and a light modulation element 5 sandwiched between the electrodes 2 and 3 from above and below. Is provided. In FIG. 4, the protective layer 54 (see FIG. 1) of the light modulation element 5 is not shown. Further, an insulating member 6 is filled between the adjacent upper electrodes 2 and 2, between the light modulation elements 5 and 5, and between the lower electrodes 3 and 3.

  As shown in FIG. 3, the current control unit 80 controls the upper electrode selection unit 82 that selects the upper electrode 2, the lower electrode selection unit 83 that selects the lower electrode 3, and the electrode selection units 82 and 83. A pixel selection unit (pixel selection unit) 84 and a power source (current supply unit) 81 that supplies current to the electrodes 2 and 3 are provided. These may be known ones, and appropriate voltages and currents are supplied to reverse the magnetization of the light modulation element 5.

  The upper electrode selection unit 82 selects one or more of the upper electrodes 2, and the lower electrode selection unit 83 selects one or more of the lower electrodes 3, and each supplies a predetermined current from the power source 81. The pixel selection unit 84 selects, for example, one or more specific pixels 4 of the pixel array 40 based on an external signal (not shown), and connects the electrodes 2 and 3 connected to the selected pixel 4 to the electrode selection units 82 and 83. To select. The power supply 81 supplies an appropriate voltage / current to reverse the magnetization of the light modulation element 5 provided in the selected pixel 4. With such a configuration, a specific pixel 4 is selected, and a predetermined current is supplied to the light modulation element 5 of this pixel 4 to reverse the magnetization. In FIG. 3, the power supply 81 is connected to one end of each of the electrodes 2 and 3 via the electrode selection units 82 and 83, but may be connected to both ends. By connecting to both ends, the response speed can be increased and the operation variation between pixels can be reduced.

  Details of the configuration of the pixel 4 of the spatial light modulator 1 will be described with reference to FIGS. The upper electrode 2 is disposed on the light modulation element 5 as shown in FIG. 4 and extends in a strip shape in the lateral direction as shown in FIG. One upper electrode 2 supplies a current to each of the light modulation elements 5 of the plurality of pixels 4, 4,... Arranged in one horizontal row. On the other hand, the lower electrode 3 is arranged under the light modulation element 5 and extends in a strip shape in the vertical direction. One lower electrode 3 supplies a current to each of the light modulation elements 5 of the plurality of pixels 4, 4,. The upper electrode 2 is made of a transparent electrode material so as not to block incident light and outgoing light of the light modulation element 5. On the other hand, the lower electrode 3 is made of an electrode metal material having excellent conductivity.

  As shown in FIG. 3, the light modulation element 5 is disposed in a portion where the upper electrode 2 and the lower electrode 3 overlap in a plan view, and is sandwiched and connected to the electrodes 2 and 3 from above and below. The planar view shape of the light modulation element 5 is a square in the present embodiment, but is not limited to this. In addition, one light modulation element 5 is arranged for one pixel 4. For example, a plurality of light modulation elements such as (1 × 3) or (2 × 2) in the surface direction are provided on one pixel 4. An element 5 may be provided.

The upper electrode 2 is made of a transparent electrode material so that light can pass therethrough. Transparent electrode materials include, for example, indium zinc oxide (IZO), indium tin oxide (ITO), tin oxide (SnO ₂ ), antimony oxide-tin oxide system (ATO), oxidation zinc (ZnO), fluorine-doped tin oxide (FTO), consisting of known transparent electrode material such as indium oxide (in ₂ O _3). In particular, IZO is most preferable in terms of specific resistance and ease of film formation. These transparent electrode materials are formed by a known method such as a sputtering method, a vacuum deposition method, or a coating method.

  When the electrode (wiring) is made of a transparent electrode material, it is preferable to provide a metal film between the electrode and the light modulation element 5 connected to the electrode. That is, in the upper electrode 2 made of a transparent electrode material, it is preferable to laminate a metal film as a base layer between the light modulation element 5 (not shown). By interposing a metal film between the light modulation element 5 and the upper electrode 2 made of a transparent electrode material having a resistance higher than that of the electrode metal material, the contact resistance between the upper electrode 2 and the light modulation element 5 is reduced. To increase the response speed.

  As the metal constituting the underlayer, for example, Au, Ru, Ta, or an alloy composed of two or more of these metals can be used, and these metals are formed by a known method such as a sputtering method. The Then, in order to further reduce the contact resistance by improving the adhesion between the underlayer and the layer above it, that is, the transparent electrode, the metal film serving as the underlayer is continuously formed in the vacuum processing chamber with the transparent electrode material. It is preferred that If the thickness of the underlayer is less than 1 nm, it is difficult to form a continuous film, while if it exceeds 10 nm, the amount of transmitted light is reduced. Therefore, the preferable thickness of the underlayer is 1 to 10 nm.

  The lower electrode 3 is made of a general electrode metal material such as a metal such as Cu, Al, Au, Ag, Ta, Cr, or an alloy thereof. Then, the film is processed into a stripe shape by a known method such as a sputtering method, by film formation, photolithography, and an etching or lift-off method.

As the substrate 7, for example, a known substrate such as a Si substrate whose surface is thermally oxidized, a sapphire substrate, or a glass substrate can be applied. The insulating member 6 is disposed between the adjacent upper electrodes 2 and 2 (not shown in FIG. 4), between the light modulation elements 5 and 5, and between the lower electrodes 3 and 3, for example, SiO ₂ or Al ₂ O _3. Consists of.

(Spatial light modulator manufacturing method)
Next, an example of a method for manufacturing the pixel 4 (pixel array 40) of the spatial light modulator 1 shown in FIGS. 3 and 4 will be described.
First, the lower electrode 3 is formed. A metal electrode material is formed on the surface of the substrate 7 by a sputtering method or the like, and formed into a stripe shape by photolithography or the like to form the lower electrode 3. Then, an insulating film such as SiO ₂ (which becomes the insulating member 6) is deposited between the lower electrodes 3 and 3.

  Next, the light modulation element 5 is formed. A magnetization fixed layer 51, an intermediate layer 52, a magnetization free layer 53, and a protective layer 54 are continuously formed on the upper surface of the lower electrode 3 (and the insulating member 6), for example, a known method such as a sputtering method or a molecular beam epitaxy (MBE) method. In this way, the film is continuously formed and laminated. These layers are molded into the shape in plan view by electron beam lithography, ion beam milling, or the like to obtain the light modulation element 5. With the resist used as a mask in the molding process left, an insulating film is formed and deposited between the light modulation elements 5 and 5 (including those between adjacent pixels 4 and 4). The insulating film 6 is removed (lifted off) to form the insulating member 6. Alternatively, after forming the light modulation element 5, the resist is removed, an insulating film is formed and deposited between the light modulation elements 5 and 5, and light is etched or etched by CMP (Chemical Mechanical Polishing). The insulating film on the modulation element 5 may be removed.

  Next, the upper electrode 2 is formed. A metal film as a base layer and a transparent electrode material are continuously formed on the upper surfaces of the light modulation element 5 and the insulating member 6 and formed into a stripe shape orthogonal to the lower electrode 3 to form the upper electrode 2. Finally, an insulating member 6 is deposited between the upper electrodes 2 and 2 to form a pixel 4 (pixel array 40).

(Operation of pixel selection of display device and spatial light modulator)
Next, the pixel selection operation of the spatial light modulator 1 will be described as a display device 10 using the spatial light modulator 1 with reference to FIG. The electrodes 2 and 3 are connected to the current control unit 80 as described above. As shown in FIG. 4, in the display device 10 according to the present embodiment, a light source 91 that irradiates light toward the pixel array 40 above the pixels 4 (pixel array 40) of the spatial light modulator 1 and , An incident polarization filter PF1 that polarizes the light emitted from the light source 91 before entering the pixel array 40, and outgoing polarized light that transmits only polarized light in a specific direction from the light reflected or diffracted by the pixel array 40. A filter PF2 and a detector (image display means) 93 that detects light transmitted through the output polarization filter PF2 are arranged.

  The light source 91 can be composed of, for example, a laser light source, a beam expander that is optically connected to the laser light source to expand the laser light, and a lens that makes the expanded laser light parallel light. Since the incident light emitted from the light source 91 includes various polarization components, the incident light is transmitted through the incident polarization filter PF1 in front of the pixel array 40 to obtain light of one polarization component. Hereinafter, light of one polarization component is referred to as polarization. This polarized light (incident polarized light) is incident on all the pixels 4 of the pixel array 40 at a predetermined incident angle. In each pixel 4, the incident polarized light passes through the upper electrode 2 and enters the light modulation element 5, is reflected or diffracted by the magnetization free layer 53 of the light modulation element 5, and is emitted as outgoing polarization, and is again emitted from the upper electrode 2. And is emitted from the pixel 4. All the outgoing polarized light emitted from each pixel 4 reaches the outgoing polarization filter PF2. The outgoing polarization filter PF2 transmits only specific polarized light, here, polarized light whose angle θap is rotated with respect to the incident polarized light, and this transmitted outgoing polarized light is incident on the detector 93. The polarizing filters PF1 and PF2 are polarizing plates, respectively, and the detector 93 is an image display means such as a screen. Alternatively, the detector 93 may be imaging means such as a camera.

  As described above, the light modulation element 5 is a spin-injection type magnetization reversal element, and the polarized light that has undergone magnetization reversal according to the direction of current supplied from the electrodes 2 and 3 and is reflected or diffracted by the magnetization free layer 53 is obtained. Optical rotations are performed in opposite directions (see FIGS. 2A and 2B). If the optical rotation angles in the light modulation element 5 with magnetization parallel and antiparallel are respectively represented as θp and θap, and the Kerr rotation angle of the magnetization free layer 53 is θk, then θp = + θk, θap = −θk, and the electrodes 2, 3 The difference in the polarization direction of the light emitted from the light modulation element 5, that is, the difference in optical rotation angle | θp−θap |

  Alternatively, the polarized light incident on the light modulation element 5 is transmitted through the magnetization free layer 53, the intermediate layer 52, and the magnetization fixed layer 51, reflected or diffracted on the upper surface of the lower electrode 3, and again the magnetization fixed layer 51 and the intermediate layer 52. Further, a configuration in which the light is transmitted through the magnetization free layer 53 and emitted may be used. In this case, by passing through the magnetization free layer 53 and the magnetization fixed layer 51 which are magnetic materials, the direction of polarized light depends on the respective predetermined angles (optical rotation) of the magnetization free layer 53 and the magnetization fixed layer 51 due to the Faraday effect. Rotate (rotate) to (angle). However, since the magnetization direction of the magnetization fixed layer 51 is constant, the change in the polarization of the emitted light from the light modulation element 5 is determined by the Faraday rotation angle θF of the magnetization free layer 53. Since the emitted light passes through the magnetization free layer 53 twice, the difference in optical rotation angle | θp−θap | is 4θF.

  The outgoing polarized light from the pixels 4 and 4 at both left and right ends in FIG. 4 rotated by the angle θap with respect to the incident polarized light passes through the outgoing polarizing filter PF2 and reaches the detector 93, so that the pixel 4 is bright (white). ) Is displayed on the detector 93. On the other hand, since the outgoing polarized light from the central pixel 4 is blocked by the outgoing polarizing filter PF2, the pixel 4 is dark (black) and displayed on the detector 93. Thus, light / dark (white / black) can be separated for each pixel, and light / dark can be switched by switching the direction of the current. As an initial state of the spatial light modulator 1, for example, all the upper electrodes 2 are “-” so that the magnetizations of the light modulation elements 5 of all the pixels 4 are anti-parallel so that the whole is displayed white. All of the lower electrode 3 may be set to “+” to supply an upward current.

  Here, the Kerr rotation angle θk and the Faraday rotation angle θF of the magnetization free layer 53 are larger as the incident angle of light is closer to the magnetization direction of the magnetization free layer 53 as described above. Accordingly, it is desirable that the incident angle be perpendicular to the film surface, that is, 0 °, in order to maximize the difference in optical rotation angle | θp−θap |. In this case, the optical path of the outgoing polarized light coincides with the optical path of the incident polarized light. . Therefore, the incident angle is slightly inclined so that the outgoing polarization filter PF2, the detector 93, the light source 91, and the incoming polarization filter PF1 are arranged so as not to block the optical paths of the incident polarized light and the outgoing polarized light, respectively. Specifically, the incident angle of polarized light is preferably 5 ° to 30 °. Alternatively, a half mirror may be disposed between the incident polarizing filter PF1 and the pixel array 40 with an incident angle of 0 °, and only the outgoing polarized light may be reflected to the side. In this case, the output polarization filter PF2 and the detector 93 are arranged on the side of the pixel array 40.

(Modification of spatial light modulator)
Note that the spatial light modulator according to the first embodiment may be a reflective spatial light modulator that is incident from the substrate side as a configuration in which the top and bottom are switched (not shown). That is, the lower electrode is made of a transparent electrode material and the upper electrode is made of an electrode metal material, and light incident from below passes through the lower electrode and is reflected or diffracted by the light modulation element 5 or the upper electrode and again lower. The light is transmitted through the electrode. In this case, as in the case where the upper electrode is made of a transparent electrode material, the lower electrode is preferably provided with a base layer, which is a metal film, between the light modulation element 5 and the contact resistance is reduced. In addition, the light modulation element 5 is laminated by switching the positions of the magnetization fixed layer 51 and the magnetization free layer 53. Further, the substrate is made of a transparent substrate material such as SiO ₂ , Al ₂ O ₃ , MgO or the like so that light is incident on the pixel 4 from below and light emitted from the pixel 4 is irradiated again downward. Consists of. The spatial light modulator having such a configuration can be used for the display device 10 (see FIG. 4) by inverting the top and bottom (front and back) of the pixel array 40 and arranging the substrate side facing the light source 91 and the like. .

(Second Embodiment of Spatial Light Modulator and Display Device)
Next, a second embodiment of the spatial light modulator and the display device will be described with reference to FIG.
The spatial light modulator 1 and the display device 10 of the first embodiment shown in FIG. 4 are configured by configuring the spatial light modulator to be a reflection type, and configuring the display device using the spatial light modulator. On the other hand, the spatial light modulator 1A according to the second embodiment shown in FIG. 5 is configured such that the spatial light modulator is a transmission type, and the display device 10A is configured using the spatial light modulator 1A. is there. In addition, about the same structure as the spatial light modulator 1 and the display apparatus 10 of 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

As shown in FIG. 5, in the spatial light modulator 1A of the second embodiment, the upper electrode 2 and the lower electrode 3A are both made of a transparent electrode material to form a transmissive spatial light modulator 1A. At this time, the substrate 7A is made of a transparent substrate material such as SiO ₂ , Al ₂ O ₃ , or MgO so that light transmitted through the pixel 4A from above is further irradiated downward. Further, the light modulation element 5 may be laminated by switching the positions of the magnetization fixed layer 51 and the magnetization free layer 53. In the display device 10A using such a spatial light modulator 1A, the light source 91 and the incident polarization filter PF1 are disposed immediately above the pixel array 40A, and the output polarization filter PF2 and the detector 93 are disposed immediately below the pixel array 40A. The incident angle can be 0 °. Further, the spatial light modulator 1A may be arranged in the display device 10A by inverting the top and bottom of the pixel array 40A.

  The operations of the spatial light modulator 1A and the display device 10A according to the second embodiment are the same as the reflected light or diffraction that is modulated mainly by the Kerr effect by the light modulation element 5 in the spatial light modulator 1 and the display device 10 according to the first embodiment. Since the transmitted light that is modulated by the Faraday effect by the light modulation element 5 instead of the light is the same as the outgoing polarization, the description thereof is omitted.

  As described above, according to the spatial light modulators according to the embodiments of the present invention and the modifications thereof, the light modulation element that is a spin-injection type magnetization reversal element with a reduced drive current is used as a pixel. A spatial light modulator that performs pixel selection operation can be obtained. In addition, a display device using such a spatial modulator can display a clear image with little variation.

  As mentioned above, although each embodiment for implementing the spin injection type magnetization reversal element, the light modulation element, the spatial light modulator, and the display device of the present invention has been described, the present invention is not limited to these embodiments. Various modifications can be made within the scope of the claims. For example, the magnetization free layer of a spin-injection type magnetization reversal element uses the memory effect of the magnetization direction to maintain the magnetization direction until a current for reversing the magnetization is supplied. Can be used as

<Modification of light modulation element>
[Light modulation element (spin injection type magnetization reversal element)]
Next, a modification of the first embodiment of the light modulation element of the present invention will be described with reference to FIG. The same elements as those in the first embodiment (see FIG. 1) are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 6, the light modulation element 5A according to the modification of the present invention is formed by laminating the magnetization fixed layer 51, the intermediate layer 52, the magnetization free layer 53A, and the protective layer 54 in this order, and including the magnetization free layer 53A. Is a spin-injection type magnetization reversal element having the same configuration as that of the light modulation element 5 according to the first embodiment, and the magnetization reversal operation and the rotation of incident light are the same.

  The magnetization free layer 53A of the light modulation element 5A in the present modification is formed by alternately laminating the magnetic metal film 53a1 and the nonmagnetic metal film 53a2 in the magnetization free layer 53 of the light modulation element 5 in the first embodiment shown in FIG. Instead of the main layer 53a made of the multilayer film, the main layer 53Aa in which the lowermost layer of the multilayer film in contact with the buffer layer 53c is the alloy film 53a3 is used. The alloy film 53a3 is formed using an alloy of a magnetic metal that forms the magnetic metal film 53a1 and a nonmagnetic metal that forms the nonmagnetic metal film 53a2. Since the magnetic metal film 53a1 and the nonmagnetic metal film 53a2 are the same as the materials that can be used in the first embodiment, description thereof is omitted.

  In this way, even if the lowermost layer of the main layer 53Aa made of a multilayer film in the magnetization free layer 53A is an alloy of a magnetic metal and a nonmagnetic metal constituting the other layers of the multilayer film, the (001) of the second interface layer 53b ) The plane orientation can be improved.

  The operation of the light modulation element 5A of this modification is the same as that of the light modulation element 5 of the first embodiment shown in FIG. Further, in the spatial light modulator and the display device shown in FIGS. 3 to 5, even if the light modulation element 5A of the present modification is used instead of the light modulation element 5 of the first embodiment shown in FIG. Since the optical modulator and the display device can be configured and the operations are the same, description thereof is omitted.

  In order to confirm the strength of (001) plane orientation of MgO in the intermediate layer as an effect of the present invention, a sample of the light modulation element according to the first embodiment of the present invention having the structure shown in FIG. As a second example, a sample of a light modulation element having the structure shown in FIG. 6 according to the modification of the first embodiment of the present invention is used as a comparative example. Samples of modulation elements were prepared and their X-ray diffraction patterns were measured.

  Table 1 shows the constituent materials and film thicknesses of the respective layers of the samples of the light modulation elements in Example 1, Example 2, and Comparative Example.

  First, a configuration common to the samples of Example 1, Example 2, and Comparative Example will be described. As the substrate, a Si substrate with a thermal oxide film having a thickness of about 300 nm was used. The lower electrode was formed by laminating a Ru film having a thickness of 3 nm on a Ta film having a thickness of 50 nm.

  The magnetization fixed layer was formed of a Tb—Fe—Co alloy film having a thickness of 30 nm as a main layer and a Co—Fe—B alloy film having a thickness of 1.2 nm as a first interface layer. As the intermediate layer, an MgO film having a thickness of 30 nm was formed. The film thickness of the MgO film as the intermediate layer is preferably about 1 nm as an element, but in order to improve the X-ray sensitivity in X-ray diffraction and make it easy to confirm the (001) plane orientation of the MgO film, A thick film was formed.

  The second interface layer of the magnetization free layer was formed of a Co—Fe—B alloy film having a thickness of 0.6 nm. The buffer layer and the main layer of the magnetization free layer will be described later because the configurations are different for each sample.

  The protective layer was formed by stacking a Pt film having a thickness of 2 nm on a Ta film having a thickness of 1.8 nm. The upper electrode was formed of an IZO film having a thickness of 350 nm.

  In Example 1 and Example 2, the buffer layer of the magnetization free layer was formed of a Ta film having a thickness of 1 nm. In the comparative example, no buffer layer is formed.

  In Example 1, the main layer of the magnetization free layer is formed by alternately stacking a total of five layers, with a Co film having a film thickness of 0.3 nm and a Pt film having a film thickness of 1.5 nm and a Co film as the lowermost layer. Formed. In Example 2, the main layer of the magnetization free layer is a Co—Pt alloy film having a thickness of 1.2 nm at the bottom and a composition of 50 at%, and a Pt film having a thickness of 1.5 nm. Were formed by alternately stacking four layers of Co films with a thickness of 0.3 nm. In the comparative example, the main layer of the magnetization free layer is formed by alternately stacking a total of 6 layers, with a Co film having a film thickness of 0.3 nm and a Pt film having a film thickness of 1.5 nm, and the lowermost layer being a Pt film. Formed.

  The intermediate layer MgO film and the upper electrode IZO film were formed by RF ion beam sputtering. The other films were formed by DC ion beam sputtering. Each sample was heat-treated at 300 ° C. in a vacuum.

  FIG. 8 shows profiles of X-ray diffraction patterns of samples of the light modulation elements manufactured as Example 1, Example 2, and Comparative Example. Note that CuKα was used as the X-ray source.

  As shown in FIG. 8, the peaks of the (110) plane of the bcc Ta film, the (111) plane of the fcc Pt film, and the (002) plane of the MgO film were observed in each sample. The (002) plane of the MgO film is a plane parallel to the (001) plane of the MgO film. In the X-ray diffraction measurement, the (001) plane of the MgO film is not observed due to the extinction law, and the MgO (002) plane is Observed. Therefore, both Example 1 and Example 2 show that the peak intensity of the (002) plane of the MgO film is increased compared to the comparative example, and the (001) plane orientation of the MgO film is improved. Yes. That is, it is shown that there is an effect of inserting a Ta film as a buffer layer.

DESCRIPTION OF SYMBOLS 1, 1A Spatial light modulator 10, 10A Display apparatus 40, 40A Pixel array 4, 4A Pixel 2 Upper electrode 3, 3A Lower electrode 5, 5A Light modulation element (spin injection type magnetization reversal element)
51 Magnetization pinned layer 51a Main layer 51b First interface layer 52 Intermediate layer 53, 53A Magnetization free layer 53a, 53Aa Main layer 53a1 Magnetic metal film 53a2 Nonmagnetic metal film 53a3 Alloy film 53b Second interface layer (interface layer)
53c Buffer layer 54 Protective layer 6 Insulating member 7, 7A Substrate 80 Current control unit 81 Power supply (current supply means)
84 Pixel selection unit (pixel selection means)
91 Light source 93 Detector (image display means)
PF1 incident polarizing filter PF2 outgoing polarizing filter (polarizer)

Claims (6)

A tunnel magnetoresistive spin-injection type magnetization reversal element structure in which a magnetization fixed layer exhibiting perpendicular magnetic anisotropy, an intermediate layer made of MgO, and a magnetization free layer exhibiting perpendicular magnetic anisotropy are stacked in this order is provided. A spin injection type magnetization reversal element that reverses the magnetization direction of the magnetization free layer by supplying a current through a pair of electrodes provided above and below the spin injection type magnetization reversal element structure,
The magnetization free layer is in contact with the intermediate layer, and an interface layer made of a transition metal or an alloy containing a transition metal,
A buffer layer made of Ta film or Ru film;
A main layer including a magnetic metal film made of a transition metal or an alloy including a transition metal;
Are stacked in this order.   The main layer of the magnetization free layer is selected from the magnetic metal film made of a transition metal or an alloy containing a transition metal, and Au, Ag, Ru, Rh, Pd, Os, Ir, and Pt as nonmagnetic metals. 2. The spin-injection type magnetization reversal element according to claim 1, wherein the spin-injection magnetization reversal element is formed of a multilayer film in which the nonmagnetic metal films made of seed noble metals or an alloy of two or more kinds of noble metals are alternately stacked.   The main layer of the magnetization free layer includes the magnetic metal film made of a transition metal selected from Co, Fe and Ni or an alloy containing a transition metal selected from Co, Fe and Ni, and Pd and N as nonmagnetic metals. 3. The spin injection type magnetization reversal element according to claim 2, comprising the multilayer film in which the nonmagnetic metal films made of a noble metal selected from Pt are alternately stacked.   The main layer of the magnetization free layer is the multilayer film in which the magnetic metal film and the nonmagnetic metal film are alternately stacked, and the magnetic metal constituting the magnetic metal film is formed in the lowermost layer of the multilayer film. 4. The spin-injection type magnetization reversal element according to claim 1, further comprising an alloy film made of an alloy of a nonmagnetic metal and the nonmagnetic metal constituting the nonmagnetic metal film.   5. A spin-injection type magnetization reversal device according to claim 1, wherein light incident on the spin-injection type magnetization reversal device is inverted by reversing the magnetization direction of the magnetization free layer. Light modulation element that emits light with its polarization direction changed. A substrate, a plurality of pixels two-dimensionally arranged on the substrate, pixel selection means for selecting one or more pixels from the plurality of pixels, and supplying a predetermined current to the pixels selected by the pixel selection means A spatial light modulator that includes a current supply unit and emits light by changing a polarization direction of light incident on the pixel selected by the pixel selection unit in a specific direction,
A spatial light modulator comprising the light modulation element according to claim 7 as the pixel.

Images