JP2011180355A - Optical modulation element and spatial light modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a magneto-optical effect by an optical modulation element by solving such the problem that the condition of a material or the like optimum for increasing an optical modulation degree is unclear for the spacer layer of the conventional spin injection magnetization inversion element. <P>SOLUTION: The optical modulation element 10 includes: a magnetic multilayer film 4 in which a magnetization fixing layer including at least one magnetic film 12, an intermediate layer comprising a non-magnetic film 13 and a magnetization inversion layer including at least one magnetic film 14 arranged on the incidence side of light are laminated in the order; a transparent electrode 7 on the magnetization inversion layer side for making a current flow to the magnetic multilayer film 4; and a lower electrode 3 including a metal electrode on the magnetization fixed layer side, and the light made incident on the magnetic multilayer film 4 via the transparent electrode 7 is modulated. For the magnetic multilayer film 4, the non-magnetic film 13 includes Ag whose film thickness is ≥6 nm and ≤20 nm. In the optical modulation element 10, a Kerr rotation angle increases compared to the optical modulation element using the conventional Cu spacer and an optical modulation degree is increased. Also, since an MR ratio is doubled compared to the optical modulation element using the conventional Cu spacer in the optical modulation element 10 using an Ag spacer, the magnetization direction of the magnetization inversion layer is easily inverted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light modulation element and a spatial light modulator used in a display device and a holographic display device, and more particularly to a light modulation element and a spatial light modulator using a change in magnetization.

  Optical elements that spatially modulate the phase and amplitude of light are applied to image exposure apparatuses such as holography, and are widely used in fields such as display technology and recording technology. In addition, since such an optical element can process optical information in two dimensions in parallel, its application to optical information processing technology and the like has been studied.

  A typical SLM (Spatial Light Modulator) is a spatial light modulator using a liquid crystal panel. The liquid crystal panel has a structure in which an oily and transparent liquid crystal material is sandwiched between two transparent substrates. As the transparent substrate, glass is often used, but plastic is sometimes used. A transparent electrode is provided on the inner surface of the transparent substrate as an electrode for applying a voltage to the liquid crystal. As a material for the transparent electrode, indium tin oxide (ITO) having a low resistance value and easy to form a shape is widely used. Attempts have been made to reproduce holography using these, but due to the slow response speed and lack of high-definition of pixels, the reproduction of images has been limited (non-patent literature). 1).

  In order to solve the problem of high definition of pixels and response speed, a high-speed magneto-optical spatial light modulator (hereinafter referred to as MOSLM) using the Faraday effect of magnetic garnet as shown in Patent Document 1 or Patent Document 2 is used. : Magneto-Optic SLM) is disclosed.

  Patent Document 1 describes a MOSLM in which a light reflecting film is individually formed for each region corresponding to each pixel, and each pixel is magnetically separated by a local heat treatment and a stress applied by a light reflecting mirror. Yes. Also, in Patent Document 1, an XY drive line is formed so as to match the outer shape of each pixel, and each pixel is magnetically separated by local heat treatment and stress applied by the XY drive line. Is described. As a result, the technique described in Patent Document 1 can reduce the distance between pixels to a pixel size or less. If the magnetic garnet has a single domain structure (single magnetic domain structure), the magnetization of the magnetic garnet can be reversed by applying a pulse current to the XY drive line.

  The MOSLM described in Patent Document 2 has a structure in which a combined magnetic field is applied to a pixel in which energization to the XY drive line is matched to selectively reverse magnetization.

  By the way, a spin transfer magnetization reversal technique (STS: Spin Transfer Switching) attracts attention as a technique for reversing the magnetization of a small magnetic material of submicron or less (see Non-Patent Document 2). Use of STS is expected to be applied to a Gbit-class ultra-high density magnetic random memory (MRAM). In recent years, not only the application to memory, but also a light modulation element that modulates light by combining the magneto-optic effect and STS has been proposed.

  The present inventors have heretofore performed pixel selection using a spin injection type magnetization reversal element that is reversed by spin injection and polarization means in an imaging device that performs pixel selection using a change in magnetization direction. This is proposed (see Patent Document 3). As described in Patent Document 3, an optical modulator that performs magnetization reversal by spin injection is a system that modulates light by changing the polarization plane of incident light, so that high speed and high definition are possible. .

  In addition, the inventors of the present application have proposed using a magnetic film made of a magnetic material having perpendicular magnetic anisotropy perpendicular to the film surface in a spatial light modulator using the magneto-optic effect ( (See Patent Document 4). In the spatial light modulator described in Patent Document 4, since at least one of the magnetic films is made of a magnetic material having perpendicular magnetic anisotropy, the magnetic material having in-plane magnetic anisotropy parallel to the film surface The magneto-optical effect can be increased as compared with. Therefore, the light modulation degree (polarization degree) of incident light can be increased, and the power consumption can be reduced.

JP 2005-70701 A JP 2005-221841 A JP 2008-60906 A JP 2009-139607 A

T. Sonehara, H. Miura, and J. Amako: Proceeding of 12th International Display Research Conferences (1992) 315. E. B. Mayer, D. C. Ralph, J. A. Katine, R. N. Louie, and R. A. Buhrman: Science 285 (1999) 867

  In the SLM, it is desired to reduce the pixel size (pixel pitch) and increase the response speed. However, in the SLM using a liquid crystal panel, there is a problem that it is difficult to reduce the pixel size to several μm or less and that the response time to the applied voltage is relatively slow, about several tens μs.

  In addition, the MOSLM described in Patent Document 1 has a structure in which the XY drive line is formed so as to fit inside the pixel and match the outer shape of the pixel, so that the pixel size is set to several μm or less. Miniaturization is difficult. In addition, since the MOSLM described in Patent Document 2 uses a combined magnetic field generated by energizing the XY drive line, there is a problem that crosstalk to adjacent pixels increases when the pixels are miniaturized.

  On the other hand, the spin injection type optical modulation elements described in Patent Documents 3 and 4 have high performance because the response time to the applied voltage is about several ns and the pixel size can be submicron. However, when considering application to a holographic display device or a hologram recording device, it cannot be said that the degree of light modulation is sufficiently large, and thus the contrast becomes weak. That is, the techniques of Patent Documents 3 and 4 have room for further improvement in the technique for increasing the degree of light modulation, and it has been desired to improve the degree of light modulation.

  The degree of light modulation is closely related to the magneto-optic effect, and the degree of light modulation increases as the angle of optical rotation (Kerr rotation angle or Faraday rotation angle) by the Kerr effect or Faraday effect increases. Therefore, in the field of research on conventional light modulation elements using the magneto-optic effect, for example, light modulation elements using spin-injection magnetization reversal elements such as GMR (Giant Magneto Resistance) elements and TMR (Tunneling Magneto Resistance) elements are constructed. Improvements in the magneto-optical effect have been achieved by devising the conditions of materials and the like in the magnetic film portion. That is, conditions such as the material of the pinned layer (magnetization fixed layer) and the free layer (magnetization inversion layer) have attracted attention as the magnetic film portion constituting the light modulation element. On the other hand, a spacer layer made of a nonmagnetic film, which is an intermediate layer sandwiched between a pinned layer and a free layer, has not attracted attention from the viewpoint of improving the magneto-optical effect. Therefore, the spacer layer of the spin injection magnetization reversal element that constitutes the light modulation element has a problem that the optimum material conditions for increasing the degree of light modulation have not been known so far.

  Therefore, the present invention solves the problem that the conditions such as the optimum material for increasing the degree of light modulation are unknown for the spacer layer of the conventional spin-injection magnetization reversal element. The task is to improve the effect.

  In order to solve the above-mentioned problem, the light modulation element according to claim 1 of the present invention is disposed on the light incident side, a magnetization fixed layer including one or more magnetic films, an intermediate layer made of a nonmagnetic film, and A magnetic multilayer film in which one or more magnetic films including a magnetic film are stacked in this order, a transparent electrode on the magnetization switching layer side for passing a current through the magnetic multilayer film, and the magnetization fixed layer side In the light modulation element that modulates light incident on the magnetic multilayer film via the transparent electrode, the magnetic multilayer film is made of Ag having a film thickness of 6 nm or more and 20 nm or less. It was decided to become.

  According to such a configuration, the light modulation element uses the intermediate layer between the magnetization fixed layer and the magnetization switching layer as an Ag spacer instead of the conventional Cu spacer, and the thickness of the Ag spacer is set to 6 to 20 nm. As a magneto-optical effect, the Kerr rotation angle can be increased. This was confirmed by experiments. Therefore, according to such a configuration, the light modulation element improves the degree of light modulation. In addition, it has been confirmed through experiments that the light modulation element having such a configuration has an MR ratio (magneto resistance ratio) that is approximately twice that of a conventional Cu spacer light modulation element. Accordingly, the magnetization reversal layer is likely to be reversed in magnetization.

  The light modulation element according to claim 2 of the present invention is the light modulation element according to claim 1, wherein the nonmagnetic film is made of Ag having a thickness of 6 nm to 15 nm.

  According to such a configuration, the light modulation element suppresses an increase in the coercive force of the magnetization switching layer by setting the film thickness of the Ag spacer between the magnetization fixed layer and the magnetization switching layer to 15 nm or less. It becomes possible to prevent deterioration. Therefore, since the increase in the coercive force of the magnetization switching layer is suppressed in the range where the thickness of the Ag spacer is set to 15 nm or less, in the light modulation element, the magnetization direction of the magnetization switching layer is easily reversed (rotated). Therefore, the required magnetization reversal current can be reduced, and the spin injection efficiency can be increased when utilizing spin injection magnetization reversal.

  According to a third aspect of the present invention, there is provided the optical modulation device according to the first or second aspect, wherein the magnetic multilayer film includes magnetic elements included in the magnetization switching layer and the magnetization fixed layer. The film is made of a magnetic material having perpendicular magnetic anisotropy.

  According to such a configuration, the light modulation element includes the magnetic film formed of a magnetic material having perpendicular magnetic anisotropy in which the magnetization direction is perpendicular to the film surface. Therefore, the in-plane magnetism in which the magnetization direction is parallel to the film surface Compared to the case of being formed from an anisotropic magnetic material, the magneto-optical effect is large and the light modulation degree is high.

  The light modulation element according to claim 4 of the present invention is the light modulation element according to claim 3, wherein the magnetic multilayer film includes a magnetic film included in the magnetization switching layer formed of GdFe, The magnetization fixed layer includes a TbFeCo film and a CoFe film stacked on the TbFeCo film and in contact with the nonmagnetic film.

  According to this configuration, in the light modulation element, since the magnetic film included in the magnetization switching layer is formed of GdFe and includes Gd, the magnetic anisotropy is small, and the coercivity of the magnetization switching layer can be reduced. For this reason, the magnetization reversal layer is easily reversed in magnetization by injection of spin-polarized electrons. In the light modulation element, since the magnetic film included in the magnetization fixed layer includes the TbFeCo film, the coercive force of the magnetization fixed layer can be increased by Tb. Therefore, the magnetization fixed layer can be formed such that the magnetization direction is not easily changed by an external magnetic field. Further, in the light modulation element, the magnetization fixed layer has a two-layer structure including a CoFe film and a TbFeCo film, and the CoFe film and the TbFeCo film are magnetically coupled by exchange coupling. The magnetization of the CoFe film having the property of being easily oriented is maintained in the vertical direction. Then, by passing through the CoFe layer having high spin polarization, spin-polarized electrons can move from the magnetization fixed layer to the magnetization switching layer. This can increase the spin injection efficiency when utilizing spin injection magnetization reversal.

  In order to solve the above problem, a spatial light modulator according to claim 5 of the present invention is configured by arranging the light modulation elements according to any one of claims 1 to 4 in a matrix. A plurality of lower electrodes extended so as to be common to the respective light modulation elements arranged in one of the row direction and the column direction of the matrix, and the rows of the matrix A plurality of upper portions which are extended so as to be common to the respective light modulation elements arranged in the other direction of the direction and the column direction, and are provided with a plurality of through holes at the same interval as the interval of the lower electrodes A metal electrode on the substrate side of the light modulation element constitutes the lower electrode, and a transparent electrode on the incident light side of the light modulation element is a through-hole provided in the upper metal electrode It was decided that it was filled with.

  According to such a configuration, since the spatial light modulator uses the light modulation element of the Ag spacer, the magneto-optical effect is increased and the light modulation degree is improved. Further, according to such a configuration, the spatial light modulator is configured to transmit the light via the transparent electrode filled in the plurality of through holes provided in the upper metal electrode extended so as to be common to the plurality of light modulation elements. Light can be efficiently incident on the modulation element. In addition, according to such a configuration, the spatial light modulator can reduce the resistance and increase the current density as compared with the case where all the upper electrodes are transparent electrodes. Therefore, when spin injection magnetization reversal is used, spin injection efficiency can be increased.

  A spatial light modulator according to claim 6 is the spatial light modulator according to claim 5, wherein a plurality of the light modulation elements are arranged in a horizontal direction at each of the intersections of the lower electrode and the upper electrode. We decided to provide it.

  According to this configuration, in the spatial light modulator, adjacent light modulation elements can exert a magnetic influence at each of the intersections of the lower electrode and the upper electrode. In order to ensure high definition necessary for holographic display, the width and interval between the lower electrode and the upper electrode are preferably 1 μm or less. A plurality of light modulation elements arranged at intervals of 1 μm or less in the same pixel can strongly exert a magnetic influence. In this case, by supplying a current having a predetermined magnitude, it is possible to stably indicate directions in which the magnetization reversal layers of the adjacent light modulation elements have different magnetization directions. That is, in the spatial light modulator, it is possible to reverse the magnetization of all the light modulation elements in the pixel or to reverse the magnetization of only a part of the light modulation elements by supplying the current with changing the magnitude of the current. . Therefore, gradation display is possible in one pixel with the transparent electrode portion filled in the through hole of the upper electrode as a unit.

  The spatial light modulator according to claim 7 is the spatial light modulator according to claim 5 or 6, wherein current is injected to change a magnetization direction of the magnetization switching layer of the light modulation element. It is further provided with a current source and pixel selection means for selecting the light modulation elements arranged in a matrix as pixels.

  According to this configuration, in the spatial light modulator, spin-polarized electrons can be injected into the selected light modulation element by the pixel selection unit and the current source. The spatial light modulator can shorten the time required for the state change of the light modulation element by using the spin injection magnetization reversal in this way.

  According to the first aspect of the present invention, the light modulation element can increase the Kerr rotation angle as a magneto-optical effect, so that the degree of light modulation is improved. Moreover, since the MR ratio of the light modulation element is increased about twice as compared with the conventional one, the magnetization reversal layer is likely to be reversed.

  According to the second aspect of the present invention, the light modulation element can suppress the increase of the coercive force of the magnetization switching layer and prevent the deterioration of the soft magnetic characteristics. Further, since the light modulation element easily reverses (rotates) the magnetization direction of the magnetization switching layer, the required magnetization switching current can be lowered.

  According to the third aspect of the present invention, the light modulation element has a greater magneto-optic effect and a higher degree of light modulation than a case where the light modulation element is formed from a magnetic material having in-plane magnetic anisotropy.

  According to the fourth aspect of the present invention, since the magnetic film that forms the magnetization switching layer and the magnetization fixed layer is formed of a suitable material, the magnetization switching layer easily reverses magnetization. The magnetization fixed layer is less susceptible to the influence of an external magnetic field in the magnetization direction. In addition, since the light-modulated element can move spin-polarized electrons while maintaining the spin polarization in the vertical direction, the spin injection efficiency can be increased.

  According to the invention described in claim 5, the spatial light modulator has a transparent electrode disposed at the intersection of the lower electrode and the upper electrode, and a metal electrode having a specific resistance smaller than that of the transparent electrode is disposed in the other portion. Thus, spin injection can be efficiently performed in the light modulation element. As a result, the pixel size can be reduced and high-speed response of light modulation can be achieved.

  According to the sixth aspect of the present invention, the spatial light modulator can exert a magnetic influence between the adjacent light modulation elements arranged at each of the intersections of the lower electrode and the upper electrode. Therefore, gradation display is possible in one pixel with the transparent electrode portion filled in the through hole of the upper electrode as a unit.

  According to the seventh aspect of the present invention, the spatial light modulator can inject spin-polarized electrons into the selected light modulation element. Therefore, the spatial light modulator can shorten the time required for the state change of the light modulation element.

It is explanatory drawing which shows typically the structure of the spatial light modulator concerning embodiment of this invention, Comprising: (a) is the figure seen from the top, (b) is the figure seen from the side. It is sectional drawing of the xz plane of the light modulation element which comprises the spatial light modulator shown in FIG. It is sectional drawing which shows an example of the magnetic multilayer film shown in FIG. It is sectional drawing of yz plane of the light modulation element which comprises the spatial light modulator shown in FIG. It is a figure which shows the magneto-optical characteristic of the magnetic multilayer film which comprises the light modulation element of the Example of this invention, Comprising: (a) is the Kerr rotation angle of the Example of this invention, (b) is the Kerr rotation angle of a comparative example. Respectively. It is a figure which shows the structure of the magnetic multilayer film which comprises the light modulation element of the Example of this invention, and its comparison, Comprising: (a) shows the structure of the Example of this invention, (b) shows the structure of a comparative example, respectively. ing. It is a graph which shows the Kerr rotation angle when a GdFe film thickness is changed in the magnetic multilayer film which comprises the light modulation element of the Example of this invention, and its comparison. 5 is a graph showing characteristics when the Ag film thickness is changed in the magnetic multilayer film constituting the light modulation element of the embodiment of the present invention, where (a) shows the relationship between the Ag film thickness and the Kerr rotation angle; ) Shows the relationship between the Ag film thickness and the holding power of the GeFe film. FIG. 4 is a graph showing an MR ratio when the element size is changed and a comparison thereof in the light modulation element of the embodiment of the present invention, where (a) shows an embodiment of the present invention and (b) shows a comparative example, respectively. Yes. FIG. 10 is a graph showing resistance and comparison when the external magnetic field is changed with respect to the example and the comparative example having the same element size among the light modulation elements shown in FIG. 9, and (a) is an example of the present invention. , (B) show comparative examples, respectively. FIG. 4 is a graph showing the magnetoresistance change of the light modulation element of the embodiment of the present invention, where (a) shows the magnetoresistance change by an external magnetic field, and (b) shows the magnetoresistance change by spin injection. FIGS. 2A and 2B are explanatory diagrams schematically showing the operation of the light modulation element constituting the spatial light modulator shown in FIG. 1, wherein FIG. 1A shows an initial state and FIG. 1B shows an inverted state.

  DESCRIPTION OF EMBODIMENTS Embodiments for implementing a light modulation element and a spatial light modulator of the present invention will be described in detail with reference to the drawings. Below, for convenience of explanation, 1. 1. Configuration of spatial light modulator 2. Configuration of light modulation element 3. Manufacturing method of spatial light modulator 4. Specific examples of light modulation elements 5. Characteristics of magneto-optical effect of magnetic multilayer film, Each chapter of the operation example of the spatial light modulator will be described sequentially.

[1. Configuration of spatial light modulator]
An overview of a spatial light modulator according to an embodiment of the present invention will be described with reference to FIGS. FIGS. 1 and 4 mainly show a spatial light modulator, and the light modulation elements constituting the spatial light modulator are shown in FIGS. 2 shows a cross section taken along line AA in FIG. 1 (cross section in the xz plane), and FIG. 4 shows a cross section taken along line BB in FIG. 1 (cross section taken in the yz plane).

  As shown in FIG. 1A, the spatial light modulator 1 has a plurality of upper electrodes 5 and a plurality of lower electrodes 3 orthogonal to each other in plan view and arranged vertically with a magnetic multilayer film 4 interposed therebetween. It has the structure which was made. The intersection of the upper electrode 5 and the lower electrode 3 forms a pixel, and this pixel includes two magnetic multilayer films 4. As shown in FIG. 2, the magnetic multilayer film 4 constitutes a light modulation element 10 together with the upper and lower electrodes. In this way, when the magnetic multilayer film 4 is processed into a desired element size and an electrode is included, it is called a light modulation element, and when the electrode is not included, it is called a magnetic multilayer film.

  The spatial light modulator 1 in FIG. 1 is configured by arranging the light modulation elements 10 in FIG. 2 in one pixel, for example, two elements each in a matrix. In the spatial light modulator 1 of the present embodiment, one pixel is not limited to one provided with two light modulation elements 10. In addition, here, as an example, a two-dimensional array is arranged in a matrix of 2 × 4.

  In the example shown in FIG. 1, the lower electrode 3 (3a, 3b), which is a metal electrode, is extended so as to be common to the light modulation elements 10 arranged in the row direction of the matrix. The upper electrodes 5 (5a to 5d), which are metal electrodes, are extended so as to be common to the light modulation elements 10 arranged in the column direction of the matrix.

  The upper electrode 5 is provided with a plurality of holes 6 that are through holes. The hole 6 is located on the lower electrode 3, and the interval between the holes 6 is the same as the arrangement interval of the lower electrodes 3. Each hole 6 of the upper electrode 5 is filled with a transparent electrode 7 and serves as a window for incident light. According to such a configuration, the electrical resistance can be made very small and a current with a very large current density can flow as compared with the case where the entire upper electrode is formed of a transparent electrode. Then, spin injection into the light modulation element 10 is possible.

  As shown in FIG. 1B, the light modulation element 10 includes a lower electrode 3 formed on the substrate 2, a magnetic multilayer film 4 formed on the lower electrode 3, and a magnetic property in front view. And an upper electrode 5 formed on the multilayer film 4.

The substrate 2 is made of, for example, silicon (Si), silicon oxide (SiO ₂ ), magnesium oxide (MgO), glass, or the like.
The lower electrode 3 and the upper electrode 5 are formed of a general electrode metal material made of metal such as Cu, Al, Ta, Cr, or an alloy, for example.

  As shown in FIG. 4, the transparent electrode 7 is disposed so as to cover the magnetic multilayer film 4, and is generally made of indium tin oxide (ITO) or the like so that incident light can efficiently reach the magnetic multilayer film 4. The transparent electrode material is used. In addition, although the upper end of the transparent electrode 7 shown in FIG. 1B protrudes from the upper end of the upper electrode 5, it can be formed so as to be flush with each other.

As shown in FIG. 1B, the space between the magnetic multilayer film 4 and the magnetic multilayer film 4 is filled with an insulating member 8. Further, as shown in FIG. 4, the insulating member 8 is also deposited in a gap between the lower electrode 3 and the upper electrode 5 and a gap between the lower electrode 3 and the lower electrode 3 adjacent to each other. Although not shown, the insulating member 8 is also disposed in the gap between the upper electrode 5 and the upper electrode 5 adjacent to each other. As a result, in the spatial light modulator 1, current flows only at the pixel portions (pixel array) arranged in a matrix, that is, at the point where the upper electrode 5 and the lower electrode 3 intersect. The insulating member 8 is made of, for example, SiO ₂ or Al ₂ O ₃ .

  In the present embodiment, the spatial light modulator 1 is further provided with a pixel selection mechanism 9 and a current source 9a as shown in FIG. The pixel selection mechanism 9 selects the light modulation elements 10 arranged in a matrix as a pixel, and is configured from a row driver, a column driver, a signal processing circuit for supplying a signal to each driver, etc. Has been.

  Here, the pixel selection mechanism 9 includes the current source 9a. The current source 9 a is connected to the upper electrode 5 and the lower electrode 3 and spin-injects into the light modulation element 10. The current source 9 a supplies a pulse current or a direct current to the light modulation element 10. The above is the overall outline of the spatial light modulator 1.

[2. Configuration of light modulation element]
Here, the configuration of the light modulation element is described in 2-1. Outline of light modulation element, and 2-2. This will be described in each section of the outline of the magnetic multilayer film.

<2-1. Overview of Light Modulator>
The light modulation element 10 includes a lower electrode 3, a magnetic multilayer film 4, and a transparent electrode 7, as shown in a cross section in FIG. Although FIG. 2 shows an area of one pixel, the spatial light modulator 1 has a plurality of pixels arranged in a two-dimensional matrix.
The magnetic multilayer film 4 is composed of, for example, a CPP (Current Perpendicular to the Plane) -GMR element, and as shown in FIG. 2, the underlayer 11, the magnetic film 12 as the magnetization fixed layer, and the non-layer as the intermediate layer. The magnetic film 13, the magnetic film 14 as a magnetization reversal layer, and the protective layer 15 are laminated in this order.

  The magnetic film 12 is a magnetic film that is disposed on the substrate 2 (see FIG. 1) side and forms a magnetization fixed layer (hereinafter referred to as a pinned layer) whose magnetization direction is fixed in a predetermined direction. The pinned layer includes one or more magnetic films 12. In the magnetic film 12, for example, the magnetization direction is fixed in the direction indicated by the upward arrow in FIG.

  The nonmagnetic film 13 forms an intermediate layer (hereinafter referred to as a spacer layer) sandwiched between the magnetic film 12 and the magnetic film 14. It is a feature of the present invention that the spacer material of the nonmagnetic film 13 is changed from conventional Cu to Ag, and the nonmagnetic film 13 is formed with a predetermined film thickness. Details of the nonmagnetic film 13 will be described later.

  The magnetic film 14 is a magnetic film that is disposed on the light incident side and forms a magnetization reversal layer (hereinafter referred to as a free layer) in which the magnetization direction is previously magnetized in the same direction as or opposite to the magnetization direction of the pinned layer. The magnetization direction of the free layer is not fixed and can be easily rotated (reversed) by injecting spin-polarized electrons. The magnetic film 14 is preferably made of a ferromagnetic material that produces a magneto-optical Kerr effect and has a relatively high polarization rate. Here, the lower the polarization rate, the larger the current value necessary for magnetization reversal.

  The underlayer 11 is provided as necessary, and can be formed of, for example, Cu, Al, Au, Ru, or the like. The protective layer (capping layer) 15 is a layer that protects the damage received by the magnetic film 14 during the microfabrication process, and can be formed of, for example, Cu, Al, Au, Ru, or the like.

<2-2. Overview of magnetic multilayer film>
In the magnetic multilayer film 4 constituting the light modulation element 10, the magnetic film 12 constituting the free layer is formed of a magnetic material having perpendicular magnetic anisotropy.
In the magnetic multilayer film 4, the magnetic film 14 forming the pinned layer includes a magnetic film formed of a magnetic material having perpendicular magnetic anisotropy.

  Since the magnetic films constituting the pinned layer and the free layer are made of a material having perpendicular magnetic anisotropy, the magnetization direction is reversed in a direction perpendicular to the magnetic film by spin injection magnetization reversal. . The large magneto-optic effect in the magnetic multilayer film 4 makes it possible to modulate and control the emitted light with a large degree of light modulation, and to reduce the consumption of the current required for magnetization reversal in the magnetic film by reducing the saturation magnetization. Electric power can be reduced.

As the magnetic material having perpendicular magnetic anisotropy, for example, at least one selected from the group consisting of Fe, Co, Ni and alloys thereof, and alloys containing rare earth metals such as Sm, Eu, Gd, and Tb is used. .
In addition, before and after the magnetization compensation temperature of the magnetic material constituting the magnetic film, the magnetization switching characteristics are reversed. Therefore, in order to prevent the switching characteristics from being reversed, the temperature may be equal to or lower than the operating temperature of the spatial light modulator 1. preferable.

  The magnetic film 12 forming the pinned layer preferably contains Tb from the viewpoint of increasing the coercive force so that the magnetization direction does not change due to an external magnetic field. For example, Tb and a transition metal such as Fe or Co are used. It is preferably formed of an alloy containing the same.

  In particular, as the magnetic film 12 forming the pinned layer, the pinned layer having a two-layer structure including a TbFeCo film and a CoFe film increases the spin injection efficiency while maintaining the vertical spin polarization by including the CoFe film. It is preferable because it can be performed. In this case, the TbFeCo film and the CoFe film are usually formed with a film thickness ratio of TbFeCo film / CoFe film of 20/1. Here, the TbFeCo film is a perpendicular magnetization film and is laminated on the base layer 11 side, and the CoFe film is an in-plane magnetization film and is laminated on the nonmagnetic film 13 side, but exchange coupling with a thick TbFeCo film is performed. Thus, the magnetization of the thin CoFe film is oriented in the vertical direction.

  The magnetic film 14 forming the free layer preferably contains Gd in order to reduce the coercive force from the viewpoint that magnetization is easily reversed by injection of spin-polarized electrons. For example, Gd, Fe and / or Alternatively, it is preferably formed of an alloy containing Co. Further, in order to set the magnetization compensation temperature constituting the magnetic film below the operating temperature of the spatial light modulator, the content ratio of Gd and Fe is preferably Gd of 25 at% or less.

  The magnetic film 14 forming the free layer preferably contains Mn and Bi because a large magneto-optical effect can be obtained.

[3. Manufacturing method of spatial light modulator]
Here, the manufacturing method of the spatial light modulator is described in 3-1. Outline of manufacturing method of light modulation element, 3-2. Outline of manufacturing method of spatial light modulator, 3-3. A description will be given in each section of a specific example of a method for manufacturing a spatial light modulator.

<3-1. Overview of Manufacturing Method of Light Modulating Element>
A method of manufacturing the light modulation element 10 is as follows. The light modulation element 10 can be formed by forming each layer or electrode forming the magnetic multilayer film 4 by, for example, sputtering or vapor deposition. For example, after a metal film constituting the lower electrode 3 is formed on the substrate 2 by sputtering or vapor deposition, the lower electrode 3 is formed using an electron beam or photolithography. Next, as the magnetic multilayer film 4, a base layer 11, a magnetic film 12 that becomes a pinned layer, a nonmagnetic film 13 that becomes a spacer layer, a magnetic film 14 that becomes a free layer, and a material that becomes a protective layer 15 are laminated in this order. After that, a pattern made of a resist is formed in a cross pattern using electron beam or photolithography, and etching is performed using ion milling or dry etching until the magnetic film 12 serving as a pinned layer disappears. Further, the etching may be performed up to the spacer layer without etching the magnetic film 12. Thereafter, the light modulation element 10 can be formed by forming the upper electrode 5 and forming the transparent electrode 7.

<3-2. Overview of Spatial Light Modulator Manufacturing Method>
A method of manufacturing each light modulation element 10 of the spatial light modulator 1 is as follows. In the spatial light modulator 1, the area of each pixel is manufactured at a time. First, after the space between the light modulation element 10 and the adjacent light modulation element 10 is sealed with an insulating member 8 such as SiO ₂ and the upper electrode 5 that is a metal electrode is laminated by DC sputtering, The laminated metal electrodes are patterned into a desired shape by a photolithography method or the like, and a predetermined number (four in FIG. 1) of holes 6 are formed in the metal electrodes. Each pixel is formed by laminating a transparent electrode material in each hole 6 by the RF sputtering method to form a transparent electrode 7.

<3-3. Specific Example of Manufacturing Method of Spatial Light Modulator>
Figure spatial light modulator 1 shown in 1, on a substrate 2, such as Si, width W _B is 1.0 [[mu] m], the lower electrode 3 interval was prepared by Cu such that 0.3 [[mu] m] (3a, 3b). When the lower electrode 3 has this size, the upper electrode can have a width W _{T of,} for example, 0.9 [μm]. In this case, the length L _H of one side of the hole 6 can be set to 0.6 [μm], for example. In this case, by setting the magnetic multilayer film 4 to a size of, for example, 0.15 × 0.4 [μm] in plan view, the two magnetic multilayer films 4 are within one pixel, for example, 0.1 [μm]. ] Can be arranged at a certain interval.

  The lower electrode 3 can be produced by the following procedure, for example. First, a resist pattern is formed on the substrate 2 and etched by a method such as dry etching, and a low resistance material such as Cu is formed by plating. Thereafter, the electrode pattern is formed by flattening by a method such as CMP (Chemical Mechanical Polishing).

  After the lower electrode 3 is manufactured, a giant magnetoresistive multilayer film (GMR multilayer film) including three layers of two magnetic films 12 and 14 and a nonmagnetic film 13 is formed on the lower electrode 3 shown in FIG. A certain magnetic multilayer film 4 is laminated. Then, in one pixel region, the magnetic multilayer film 4 is processed into a size of, for example, 0.15 × 0.4 [μm], thereby forming two light modulation elements 10. Here, the element size is desirably about 0.1-0.5 × 0.1-0.5 [μm]. The reason is that the element easily forms a single magnetic domain. In this case, in one pixel region, the two light modulation elements 10 are formed in an elongated shape so that they can have a magnetic influence with a predetermined interval therebetween. This GMR film is produced by a method such as sputtering.

The element can be processed, for example, by the following procedure. First, using an electron beam lithography system or the like, for example, a resist pattern processed to a size of 0.15 × 0.4 [μm] is formed, and etching up to the pinned layer is performed by a method such as ion milling. An insulating member 8 such as SiO ₂ is formed so that the thickness is almost the same as the thickness. Thereafter, the resist is lifted off by performing ultrasonic cleaning in a resist stripping solution. Subsequently, the upper electrode 5 is formed using, for example, Cu as a metal material. At this time, it is formed by the same photolithography, Cu film formation, and lift-off. The hole 6 is formed by patterning. Furthermore, the transparent electrode 7 is formed so as to fill the hole 6 by the same method, and the structure of the spatial light modulator 1 as shown in FIG. 1 can be obtained.

[4. Specific example of light modulation element]
A specific example of the manufactured light modulation element is shown in FIG. In FIG. 3, a magnetic multilayer film in which the transparent electrode 7 and the upper electrode 5 are omitted is shown in order to explain the increase in the magneto-optical effect due to the light modulation element that uses an Ag spacer instead of the conventional Cu spacer. The magnetic multilayer film 40 is a CPP-GMR film as one specific example of the magnetic multilayer film 4 shown in FIG.

  As shown in FIG. 3, the magnetic multilayer film 40 uses Ru for the underlayer 11, the magnetic film 12 as the pinned layer has a two-layer structure of TbFeCo and CoFe, and Ag for the nonmagnetic film 13 as the spacer layer. GdFe is used for the magnetic film 14 as a free layer, and Ru is used for the protective layer 15.

  Here, the film thickness of each layer is preferably set as follows. The film thickness of GdFe is preferably about 5 to 20 [nm], and the film thickness of TeFeCo is about 10 to 30 [nm]. The film thickness of Ag is 6 to 20 [nm], preferably about 8 to 15 [nm]. The film thickness of the underlayer 11 is usually about 1 to 10 [nm], and the film thickness of the protective layer 15 is usually about 1 to 5 [nm]. Hereinafter, the magnetic multilayer film 40 of the Ag spacer is simply referred to as an Ag spacer element.

[5. Characteristics of magneto-optical effect of magnetic multilayer film]
Here, the characteristics of the magneto-optical effect of the magnetic multilayer film are shown in 5-1. Kerr rotation angle of Ag spacer element, 5-2. Kerr rotation angle when the GdFe film thickness is changed, 5-3. Kerr rotation angle when the Ag film thickness is changed 5-4. Coercive force when the Ag film thickness is changed, 5-5. MR characteristics of Ag spacer element, 5-6. The description will be made separately for each section of spin injection magnetization reversal of the Ag spacer element.

<5-1. Kerr rotation angle of Ag spacer element>
Here, as a magneto-optical effect of the manufactured light modulation element, the magnetic multilayer film having the film structure of FIG. 3 is irradiated with laser light having a wavelength of 780 [nm], and −1.0 to +1.0 [kOe from the outside. ], The Kerr rotation angle was measured when a magnetic field was applied. The measurement result at this time is shown in FIG. That is, FIG. 5A shows the Kerr rotation angle θ _k as the magneto-optical characteristic of the GMR multilayer film of the Ag spacer in which the spacer material is changed from conventional Cu to Ag. In the graph of FIG. 5, the horizontal axis indicates the magnetic field [kOe], and the vertical axis indicates the angle θ [deg]. In addition, it is convertible by 1 [Oe] = 79.577 [A / m].

  The film structure of the magnetic multilayer film 41 exhibiting such magneto-optical characteristics is shown in FIG. In FIG. 6A, the number in parentheses next to the material name indicates the film thickness, and its unit is nm. For example, the nonmagnetic film 13 is made of Ag with a film thickness of 6 [nm], and the magnetic film 14 is made of GdFe with a film thickness of 10 [nm].

Further, as a comparison with the magnetic multilayer film 41 of this Ag spacer, the structure of the magnetic multilayer film 140 of the Cu spacer in which the spacer material is changed to conventional Cu is shown in FIG. FIG. 5B shows the Kerr rotation angle θ _k as the magneto-optical characteristic of the magnetic multilayer film 140 of the Cu spacer.

As shown in FIG. 5A, when the magnetic field is changed in the range of −1.0 to +1.0 [kOe] with respect to the magnetic multilayer film 41 of the Ag spacer, the angle is obtained when the magnetic field is in the negative direction. The minimum value of θ was −0.1393 [deg], and the maximum value of the angle θ was +0.1405 [deg] when the magnetic field was in the positive direction. The Kerr rotation angle θ _k indicating the change in the angle of polarization of reflected light when a magnetic field is applied to the element is an average of the absolute values of the angles when the magnetic field is applied, and is from 1/2 of the difference between these maximum and minimum values. It was calculated | required and was 0.140 [deg].

On the other hand, when the magnetic field is changed in the range of −1.0 to +1.0 [kOe] with respect to the magnetic multilayer film 140 of the Cu spacer, the minimum value of the angle θ is −0. 1113 [deg], and when the magnetic field was in the positive direction, the maximum value of the angle θ was +0.1130 [deg]. As a result, the Kerr rotation angle θ _k was 0.112 [deg].

That is, it has been found that the Kerr rotation angle θ _k is increased by 27% by changing the spacer material from the conventional Cu to Ag. It is known that the degree of modulation of light largely depends on the Kerr rotation angle θ _k , and it has been found that the degree of modulation can be improved by changing the spacer material from conventional Cu to Ag.

<5-2. Kerr rotation angle when GdFe film thickness is changed>
Subsequently, an experiment was conducted to confirm whether or not the phenomenon of increasing the Kerr rotation angle is observed when the thickness of the GdFe film on the Ag spacer is changed. Here, the film thickness of the GdFe film on the Ag spacer is changed to form a plurality of types of elements having element sizes of 120 × 120 [nm ² ] to 120 × 300 [nm ² ] by DC magnetron sputtering. went. In addition, the CPP-GMR manufacturing process is performed at 190 ° C. or lower. In order to prevent the characteristic change in this process, a heat treatment (annealing) is performed at 190 ° C. for 1 hour after film formation. And each Kerr rotation angle when the magnetic field was similarly applied with respect to each produced element was calculated | required. The result is shown in FIG. Note that the film thickness of the Ag spacer remains 6 [nm].

  In the four types of elements in which the film thickness of the GdFe film laminated on the Ag spacer is 7, 10, 12, and 15 [nm], respectively, the Kerr rotation angle increases as the film thickness of the GdFe film increases. Became larger as well. As a comparative example, in the case of three types of elements in which the thickness of the GdFe film stacked on the Cu spacer is 7, 10, and 13 [nm], the thickness of the GdFe film is increased. The car rotation angle has also increased. At any of these measured GdFe film thicknesses, the magnetic multilayer film of the Ag spacer showed a Kerr rotation angle that was about 20% larger than that of the magnetic multilayer film of the Cu spacer. Accordingly, it has been found that even when the thickness of the GdFe film on the Ag spacer is changed, a phenomenon in which the Kerr rotation angle increases is similarly observed.

  The reason why the Kerr rotation angle is increased by changing the spacer material from conventional Cu to Ag has not yet been elucidated. The thickness of each GdFe produced in the experiment was smaller than the light penetration length. Therefore, it can be considered that the difference in the proportion of the light that reaches the spacer layer (Ag or Cu) is influenced by the Kerr rotation angle. That is, it can be considered that the reason why the Kerr rotation angle is increased is that the reflectance of Ag is larger than that of Cu.

<5-3. Kerr rotation angle when Ag film thickness is changed>
In order to confirm that the reflectance of Ag is larger than the reflectance of Cu is the cause of the increase in the Kerr rotation angle, the following experiment was performed. In this experiment, a hypothesis that the Kerr rotation angle should increase is verified because the proportion of reflected light that reaches the spacer layer increases as the Ag film thickness is increased.

Similarly, four types of magnetic multilayer films were prepared with the Ag film thickness set to 8, 10, 15, 20 [nm], respectively, and the Kerr rotation angle θ _k of each sample before annealing was measured in the same manner. The Kerr rotation angle θ _k of each sample after annealing was measured in the same manner. FIG. 8A shows experimental results (squares in the figure) in which the Kerr rotation angle θ _k is plotted with respect to each film thickness of Ag. In FIG. 8A, the diamond indicates the measurement result for the sample before annealing (as depo), and the triangle indicates the result in the case of the Cu spacer.

As shown in FIG. 8 (a), even the light reaching the spacer layer increases the thickness of the Ag increased the percentage to be reflected, the value of the measured Kerr rotation angle theta _k is little change There wasn't. In this experiment, an experimental result contrary to the assumption of the hypothesis was obtained, so it cannot be determined that the cause of the increase in the Kerr rotation angle is due to the large reflectance of Ag. However, based on the result shown in FIG. 8 (a), if a light modulation element in which the Ag film thickness of the magnetic multilayer film 40 having the structure of FIG. The Kerr rotation angle can be increased as compared with the light modulation element used.

By the way, in the conventional GMR film, the thickness of the spacer layer is preferably a thickness (2 to 30 [nm]) through which polarized spin electrons can pass while maintaining the spin polarization. As shown in FIG. 8A, in the produced magnetic multilayer film of four types of Ag spacers, when the film thickness is 6 to 20 [nm], the value of the Kerr rotation angle θ _k hardly changes. It was better than the conventional Cu spacer. Therefore, the magnetic multilayer film 40 of the Ag spacer can improve the degree of light modulation compared to the conventional case when the film thickness is 6 to 20 [nm].

<5-4. Coercive force when Ag film thickness is changed>
Next, as a magnetic characteristic of the magnetic multilayer film 40, an experiment was conducted to search for a preferable range of the Ag film thickness, focusing on characteristics other than the Kerr rotation angle θ _k closely related to the degree of light modulation. Specifically, it was performed and the film thickness of Ag, an experiment to ascertain the correlation between the coercive force H _c of GdFe film on the Ag spacers.

The thickness of the Ag film, respectively, 8,10,15,20 in four magnetic multilayer film with [nm], in the experimental results (plotted the coercive force H _c of GdFe film on the Ag spacers, Squares are shown in FIG. Incidentally, in FIG. 8 (b), the diamond represents the coercive force H _c of GdFe film of the sample before annealing (the as depo), triangles, shows the results when the Cu spacer.

As shown in FIG. 8 (b), as the film thickness of Ag is increased, the value of the coercive force H _c of GdFe film is increased. In particular, it can be seen that when the Ag film thickness exceeds 15 [nm], the value of the coercive force H _c is remarkably increased. This is considered to be because the surface roughness of Ag increases when Ag is thickened. As the verification, the surface roughness was measured through the protective layer 15 of the element by atomic force microscopy (AFM). When Ag was thickened, the interface between Ag and GdFe was rough, so the surface of GFe grown on the Ag film was also roughened, and the surface roughness of the protective layer 15 was increased.

The GdFe film is a magnetic film 14 that functions as a free layer, and it is necessary that magnetization reversal be easy. However, the larger the coercive force H _c, the easier the magnetization reversal. Therefore, an optical modulation element in which the Ag film thickness of the magnetic multilayer film 40 is set to 15 [nm] or less is manufactured. Thereby, an increase in the coercive force of the GdFe film can be suppressed and deterioration of the soft magnetic characteristics can be prevented. In addition, the light modulation element manufactured in this manner can easily reverse (rotate) the magnetization direction of the GdFe film, so that the required magnetization reversal current can be lowered.
Also, in spin injection magnetization reversal, in which the magnetization of the free layer is reversed by spin injection, the thicker the spacer layer, the easier it is for polarized spin electrons to reach the free layer while maintaining the same spin. The spin injection efficiency is deteriorated.
For this reason, the Ag film thickness is preferably as thin as possible within a range where the bond with the magnetic film 12 that is a pinned layer located under the Ag spacer is broken, and is preferably 6 nm or more and 15 nm or less.

<5-5. MR characteristics of Ag spacer element>
Next, in the Ag spacer element, MR characteristics (magnetoresistive change), which is an important factor for spin injection magnetization reversal, were examined. Specifically, in the element of the Ag spacer, the film thickness of Ag is kept at 6 [nm], and the element size A (A _Ag ) is several tens of kinds of about 0.015 to 0.048 [μm ² ]. CPP-GMR elements were produced in the same manner, and the MR ratio of each element was measured. When a magnetic field was changed and applied to each element in a range of about −3000 [Oe] to 3000 [Oe], the change in resistance R (R _Ag ) was measured, and the MR ratio was calculated from the change in resistance. . The result is shown in FIG.

As a comparison, in a magnetic multilayer film of Cu spacer (hereinafter referred to as an element of Cu spacer), the film thickness of Cu remains 6 [nm], and the element size A (A _Cu ) is about 0.009 to 0.0245. Dozens of CPP-GMR elements of [μm ² ] were similarly manufactured, the change in resistance R (R _Cu ) was measured, and the MR ratio of each element was measured. The result is shown in FIG.

  Before comparing all the samples of FIG. 9 (a) and FIG. 9 (b) for the Ag spacer element and the Cu spacer element, the Ag spacer element and the Cu spacer element selected as an example from all the samples. The MR characteristics of samples having substantially the same area are compared.

The element size A _Ag of the element of the selected Ag spacer is 118 [nm] × 127 [nm] = 0.150 [μm ² ]. The element size A _Cu of the element of the Cu spacer is 94 [nm] × 152 [nm] = 0.0143 [μm ² ]. In the selected Ag spacer element, the minimum resistance R _Ag was 4.5508 [Ω], and in the Cu spacer element, the minimum resistance R _Cu was 4.4937 [Ω]. That is, the selected Ag spacer element and the Cu spacer element have approximately the same area resistance RA [Ωμm ² ].

  The resistance changes measured at this time are shown in FIGS. 10 (a) and 10 (b), respectively. In the graphs of FIGS. 10A and 10B, the horizontal axis represents the magnetic field [Oe], and the vertical axis represents the resistance [Ω]. Since the scales of the vertical axes of the graphs are aligned so that the graphs of FIGS. 10A and 10B can be easily compared, the scales of the horizontal axes are different. As is obvious from both graphs, the MR ratio of the Ag spacer element was about twice that of the Cu spacer element.

  Specifically, as shown in FIG. 10A, the minimum resistance value of the selected Ag spacer element is 4.5508 [Ω], and the maximum resistance value is 4.5802 [Ω]. Met. The MR ratio of the Ag spacer element was determined from the ratio of the difference between the maximum value and the minimum value with respect to the minimum value, and was 0.1421 [%].

  As shown in FIG. 10B, the minimum resistance value of the selected Cu spacer element is 4.4937 [Ω], and the maximum resistance value is 4.4972 [Ω]. It was. Therefore, the MR ratio of the Cu spacer element was 0.0774 [%].

As described above, the element of the Ag spacer and the element of the Cu spacer have almost the same area resistance RA [Ωμm ² ], and therefore there should be no change in characteristics as the element resistance due to the shape. There is a reason why the MR ratio is improved by a factor of 2 in this way.

Next, referring to FIG. 9A and FIG. 9B, all samples of the Ag spacer element and the Cu spacer element are compared. As shown in FIG. 9 (a), several tens of types of Ag spacer elements include groups having an element size A (A _Ag ) of about 0.015 [μm ² ] and groups of about 0.03 [μm ² ]. And a group of about 0.034 [μm ² ] and a group of about 0.048 [μm ² ]. All groups are included in the MR ratio range of 0.1 to 0.16 [%], and many Ag spacer elements are included in the MR ratio range of 0.13 to 0.14 [%]. ing.

On the other hand, as shown in FIG. 9B, the tens of kinds of elements of the Cu spacer include a group having an element size A (A _Cu ) of about 0.009 [μm ² ] and about 0.0143 [μm ² ]. , A group of about 0.022 [μm ² ], and a group of about 0.0245 [μm ² ]. All groups are included in the MR ratio range of 0.04 to 0.1 [%], and many Cu spacer elements are included in the MR ratio range of 0.07 to 0.08 [%]. ing.

  From the results shown in FIGS. 9A and 9B, it was found that the MR ratio of the element of the Ag spacer is about twice as large. In other words, it has been found that by using an element structure in which the spacer material is changed from conventional Cu to Ag, not only the Kerr rotation angle is increased, but also the MR ratio is increased about twice.

  Among them, the cause of the phenomenon that the MR ratio is increased approximately twice by changing the spacer material to Ag is considered to be one of the causes that the interface between Ag and GdFe becomes steep. As compared with reference to FIG. 10, when the area resistance RA of the element of the Ag spacer and the element of the Cu spacer are approximately the same, the MR ratio is increased by a factor of about 2, so that the spin-dependent scattering. One of the causes is considered to be an increase in

<5-6. Spin transfer magnetization reversal of Ag spacer element>
Next, an experiment was conducted to confirm that spin injection magnetization reversal was possible as in the conventional Cu spacer element even if the element structure was changed from conventional Cu to Ag. The element of the Ag spacer selected at this time has an Ag film thickness of 6 [nm] and an element size A _Ag of 118 [nm] × 127 [nm] = 0.150 [μm ² ]. The resistance R (R _Ag ) was measured when an external magnetic field was applied to the device while changing the magnetic field in a range of about −2000 [Oe] to 2000 [Oe]. The result is shown in FIG. In the graph of FIG. 11A, the horizontal axis indicates the magnetic field [Oe], and the vertical axis indicates the resistance [Ω].

  FIG. 11B shows the relationship between the magnitude of current when a pulse current (spin injection current) having a pulse width of 10 [μs] is applied to this element and the resistance value of the element at that time. It is a graph. In the graph of FIG. 11B, the horizontal axis indicates the spin injection current [mA], and the vertical axis indicates the resistance [Ω]. In order to make it easy to compare the graphs of FIG. 11A and FIG. As is clear from both graphs, the magnetoresistance change caused by applying an external magnetic field and the magnetoresistance change caused by injecting a spin current are almost the same resistance change. That is, it can be seen that in the CPP-GMR element using the Ag spacer, the magnetization direction of the free layer is reversed by spin injection. That is, even if the element structure is changed from the conventional Cu to Ag, the spin injection magnetization reversal can be confirmed as in the conventional Cu spacer element. From this, spin injection into a light modulation element using an Ag spacer can invert the magnetization direction of the free layer and modulate incident light. In this case, the Kerr rotation angle of the Ag spacer element is larger than that of the Cu spacer element. Therefore, the light modulation element using the Ag spacer can improve the light modulation degree as compared with the prior art.

[6. Example of spatial light modulator operation]
Here, an example of the operation of the spatial light modulator is described in 6-1. Assignment of light / dark state, 6-2. Assignment of light and dark intermediate states, 6-3. This will be described in each section of the spin injection time reversal operation.

<6-1. Assignment of light and dark state>
Next, the operation of the spatial light modulator 1 of the present embodiment will be described with reference to FIG. Here, in order to simplify the description, the spatial light modulator 1 will be described as having one light modulation element 10 in one pixel and including only one pixel. 12A and 12B are explanatory views schematically showing the operation of the light modulation element 10 shown in FIG. 2, wherein FIG. 12A shows an initial state and FIG. 12B shows an inverted state. However, in FIG. 12, since the main purpose is to show the concept of the operation of the spatial light modulator 1 in an easy-to-understand manner, the protective layer and the base layer of the light modulation element 10 are not shown.

  As a premise, the magnetization direction of the magnetic film 12 of the light modulation element 10 is fixed in a predetermined direction (schematically indicated by an upward arrow in the figure). In the initial state, as shown in FIG. 12A, for example, the magnetic film 14 is aligned in advance in the direction of magnetization opposite to the direction in the magnetic film 12 (schematically indicated by a downward arrow in the figure). It has been.

  The light emitted from the laser light source 21 includes various polarization components, but is filtered by the polarization filter 22 so as to include only a polarization component in a certain direction. The filtered light enters the light modulation element 10 through the transparent electrode 7 provided in the hole 6 of the upper electrode 5 and is reflected by the light modulation element 10 in a predetermined direction. Note that the screen 24 is arranged in this predetermined direction.

  In the initial state shown in FIG. 12A, for example, the current source 9a does not pass current. Alternatively, the current source 9 a allows a current to flow from the lower electrode 3 toward the upper electrode 5 (metal electrode portion and transparent electrode 7) via the magnetic films 12 and 14 and the nonmagnetic film 13. In this initial state, the reflected light does not change the plane of polarization in accordance with the magnetization direction of the magnetic film 14 (schematically indicated by a downward arrow in the figure). That is, the reflected light has the same polarization component as the incident light, passes through the polarizing filter 23 (same characteristics as the polarizing filter 22), reaches the screen 24, and is displayed. As a result, a bright image is displayed on the screen 24.

  On the other hand, in the inversion state shown in FIG. 12B, for example, the current source 9a passes a current. Alternatively, the current source 9 a allows a current to flow from the upper electrode 5 (the metal electrode portion and the transparent electrode 7) toward the lower electrode 3 through the magnetic films 12 and 14 and the nonmagnetic film 13. Due to this current, electrons are injected from the magnetic film 12 to the magnetic film 14 via the nonmagnetic film 13 while maintaining the spin, so that the magnetization direction of the magnetic film 14 is the same as that of the magnetic film 12 (schematic in the figure). (Indicated by an upward arrow). In this inverted state, the plane of polarization of the reflected light is rotated by the magneto-optical Kerr effect according to the magnetization direction of the magnetic film 14 (schematically indicated by an upward arrow in the figure). That is, the reflected light has a polarization component different from that of the incident light and does not pass through the polarization filter 23, so that it cannot reach the screen 24. As a result, the screen 24 becomes dark.

<6-2. Assignment of light and dark intermediate state>
The above-described operation of the spatial light modulator 1 has been described as the operation of one light modulation element 10. However, when two light modulation elements 10 are provided in one pixel, a light / dark state can be similarly assigned, Since adjacent light modulation elements exert magnetic influences, an intermediate state (a state in which brightness is low) can be realized. This will be described with reference to FIG.

  As a premise, the magnetization directions of the magnetic films 12 of the magnetic multilayer films 4a, 4b, 4c, and 4d are fixed in a predetermined direction (schematically indicated by an upward arrow in the drawing). In addition, in the initial state, each magnetic film 14 is preliminarily aligned in a direction opposite to the direction in the magnetic film 12, for example. That is, in the initial state, it is assumed that both elements are anti-parallel (AP: anti-parallel) like the magnetic multilayer films 4a and 4b under the transparent electrode 7a corresponding to one pixel. At this time, although not shown in the inverted state, each magnetic film 14 has, for example, the same magnetization direction as that in the magnetic film 12, that is, both elements are parallel (P: parallel).

  On the other hand, in the intermediate state, as in the magnetic multilayer films 4c and 4d below the transparent electrode 7b corresponding to one pixel, there is a case where one is stable and the other is P. By supplying the current by changing the magnitude of the current, it is possible to reverse the magnetization of all the light modulation elements in the pixel or to reverse the magnetization of only some of the light modulation elements.

<6-3. Spin injection time reversal operation>
The inversion operation of the magnetic film 14 in the light modulation element 10 of the spatial light modulator 1 includes, for example, providing a hole 6 in the upper electrode 5 and filling the hole 6 with the transparent electrode 7 as shown in FIG. Can be realized. In the spatial light modulator 1, inversion (rotation) of the magnetization direction due to the Kerr effect is more likely to occur in the light modulation element than in the case where the entire upper electrode is formed of a transparent electrode material. That is, high-speed response of light modulation becomes possible.

  The reason why the transparent electrode 7 is arranged in the hole 6 in this way is that the effect of lowering the required voltage and facilitating driving at a high frequency (short pulse) by reducing the electric resistance of the electrode is remarkable. is there. Further, the metal electrode portion other than the hole portion 6 of the upper electrode 5 has a very small specific resistance as compared with the transparent electrode 7, so that each pixel disposed in the region where the upper electrode 5 and the lower electrode 3 are opposed to each other. It becomes easy to spread the current. According to such a configuration, if compared with the case where the entire upper electrode 5 is formed of the transparent electrode 7, for example, a current having a current density that is about nine digits larger can be passed. On the other hand, spin injection can be performed. As a result, the spatial light modulator 1 has a structure in which the light modulation element is magnetization-reversed by spin injection, whereby the pixel size is miniaturized and a high-speed response of light modulation is possible.

  As described above, according to this embodiment, the light modulation element 10 can increase the Kerr rotation angle as a magneto-optical effect by changing the spacer material from conventional Cu to Ag. . As a result, the modulation degree can be improved. Furthermore, since the MR ratio of the light modulation element 10 is increased approximately twice as compared with the conventional one, the magnetization reversal layer is likely to be reversed.

  Further, according to the present embodiment, the spatial light modulator 1 can increase the degree of modulation because the elements of the Ag spacer are arranged in a matrix. Further, since the spatial light modulator 1 is filled with the transparent electrode 7 in a part of the upper electrode 5, the pixel size is miniaturized and a high-speed response of light modulation is possible. In addition, since the spatial light modulator 1 is provided with a plurality of Ag spacer elements in one pixel, gradation display can be realized by assigning the magnetization state of the Ag spacer elements to light and dark and intermediate states thereof. Furthermore, since the spatial light modulator 1 injects spin-polarized electrons into the selected light modulation element, the time required for the state change of the light modulation element can be shortened.

  As mentioned above, although this invention was demonstrated based on this embodiment, this invention is not limited to this. For example, although the magnetic film 12 of the magnetic multilayer film constituting the light modulation element has a two-layer structure, it may be one layer or three or more layers. For example, when the pinned layer is one layer, only the TbFeCo film may be used. Further, when the pinned layer has two layers, the combination is not limited to the TbFeCo film and the CoFe film.

Moreover, although the magnetic film 14 of the magnetic multilayer film constituting the light modulation element is made of GdFe, the material is not limited to this, and may be MnBi, for example.
For example, the magnetic films 12 and 14 may each have a multilayer structure. For example, a multilayer structure in which five layers of Co and Pt are alternately stacked, or a multilayer structure in which five layers of Co and Pd are alternately stacked. It may be a structure.
Further, the thickness and length of the constituent elements and the like shown in the drawings are exaggerated for clearly explaining the arrangement, and are not limited thereto.

  The present invention can be suitably applied to technical fields related to image exposure apparatuses such as holography, display technology, recording technology, and optical computing.

DESCRIPTION OF SYMBOLS 1 Spatial light modulator 2 Board | substrate 3 (3a, 3b) Lower electrode 4 Magnetic multilayer film 40 Magnetic multilayer film 41 Magnetic multilayer film 140 Magnetic multilayer film 5 (5a-5d) Upper electrode 6 (6a, 6b) Hole 7 (7a 7b) Transparent electrode 8 Insulating member 9 Pixel selection mechanism 9a Current source 10 Light modulation element 11 Underlayer 12 Magnetic film (pinned layer)
13 Non-magnetic film (spacer layer)
14 Magnetic film (free layer)
15 Protective layer (cap layer)
W _B Lower electrode width W _T Upper electrode width L _H Hole length

Claims (7)

A magnetic layer in which a magnetization fixed layer including one or more magnetic films, an intermediate layer made of a nonmagnetic film, and a magnetization switching layer including one or more magnetic films arranged on the light incident side are laminated in this order. A multilayer film, and a transparent electrode on the magnetization reversal layer side and a metal electrode on the magnetization pinned layer side for allowing a current to flow through the magnetic multilayer film, and the light incident on the magnetic multilayer film via the transparent electrode In the light modulation element to modulate,
The magnetic multilayer film is
The light modulation element, wherein the nonmagnetic film is made of Ag having a thickness of 6 nm to 20 nm.   The light modulation element according to claim 1, wherein the nonmagnetic film is made of Ag having a thickness of 6 nm to 15 nm. The magnetic multilayer film is
3. The light modulation element according to claim 1, wherein the magnetic films included in the magnetization switching layer and the magnetization fixed layer are made of a magnetic material having perpendicular magnetic anisotropy. The magnetic multilayer film is
A magnetic film included in the magnetization switching layer is formed of GdFe;
The light modulation element according to claim 3, wherein the magnetization fixed layer includes a TbFeCo film and a CoFe film stacked on the TbFeCo film and in contact with the nonmagnetic film. A spatial light modulator configured by arranging the light modulation elements according to any one of claims 1 to 4 in a matrix,
A plurality of lower electrodes extended so as to be common to the light modulation elements arranged in one of the row direction and the column direction of the matrix;
A plurality of through-holes are provided so as to be common to the light modulation elements arranged in the other direction of the matrix in the row direction and the column direction, and at the same intervals as the lower electrodes. A plurality of upper metal electrodes,
The metal electrode on the substrate side of the light modulation element constitutes the lower electrode,
The transparent electrode on the incident light side of the light modulation element is formed by being filled in a through hole provided in the upper metal electrode.
A spatial light modulator characterized by that.   The spatial light modulator according to claim 5, wherein a plurality of the light modulation elements are provided in a horizontal direction at each of the intersections of the lower electrode and the upper electrode.   A current source for injecting a current to change the magnetization direction of the magnetization reversal layer of the light modulation element; and pixel selection means for selecting the light modulation elements arranged in a matrix as pixels. The spatial light modulator according to claim 5 or 6.

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