JP2015014671A - Spatial light modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spatial light modulator for displaying a high-contrast stereoscopic image of holography.SOLUTION: A spatial light modulator 1 modulates incident light by the magneto-optic effect of a light modulation element 30 having at least a magnetization fixed layer 31 in which the direction of magnetization is fixed in one direction, a magnetization free layer 33 in which the direction of magnetization can be rotated more easily than for the magnetization fixed layer 31, and an intermediate layer 32 in between the magnetization fixed layer 31 and the magnetization free layer 33. The spatial light modulator 1 comprises a layer in which a plurality of light modulation elements 30 are two-dimensionally arrayed and which is provided with an insulator 40 between the light modulation elements 30, an inter-element magnetic layer 70 being a region corresponding to between one and other light modulation elements 30 and provided so as to cover one light incident side surface of the insulator 40, and an insulation layer 42 for insulating between the light modulation elements 30 and the inter-element magnetic layer 70, the inter-element magnetic layer 70 having its magnetization direction fixed in one direction.

Description

  The present invention relates to a spatial light modulator including a light modulation element that modulates incident light by a magneto-optic effect, and more particularly to a spatial light modulator used for light modulation for displaying a holographic stereoscopic image.

  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 optical information can be processed in two dimensions in parallel, application to optical information processing technology and the like has been studied.

  A typical spatial light modulator (SLM) that uses a liquid crystal panel can be mentioned, but the SLM using a liquid crystal panel is difficult to be miniaturized with a pixel size of several μm or less and has a response time of several tens. Very slow, about μs.

  Conventionally, for example, two approaches are known as a technique for solving the problem of miniaturization of an SLM by a liquid crystal panel and the problem of response speed. In the first approach, a magnetic film such as a magnetic garnet film is used instead of a liquid crystal panel, and the magnetization direction of each pixel is individually controlled by a combined magnetic field generated by drive currents on the X side and Y side (magnetic field). Application type) spatial light modulator (see, for example, Patent Document 1). Note that each pixel in this spatial light modulator is not an individual element that is completely independent of each other, but actually, a magnetic film is grown on the entire surface of the substrate by the LPE (liquid phase epitaxy) method, The magnetic film is in a state of being magnetically partitioned into a large number of pixels. The spatial light modulator described in Patent Document 1 is wired so as to surround each pixel in the shape of a “well” except for its center by drive lines on the X side and the Y side. Since this spatial light modulator is provided with such wiring, it is difficult to form a fine pixel of several μm or less, and in order to use a synthesized magnetic field by current, a finer pixel is required. However, there is a problem that crosstalk to adjacent pixels increases.

  The second approach has been proposed by the inventors of the present application, and uses a spatial light modulator including a spin-injection type magnetization reversal element instead of a liquid crystal panel (see, for example, Patent Document 2). Non-Patent Document 1 reports an experiment in which a plurality of spin-injection magnetization reversal elements are arranged to form a pixel array, and the polar Kerr effect is measured to verify the light modulation operation by a current pulse.

  In the techniques described in Patent Document 2 and Non-Patent Document 1, a spin-injection magnetization reversal element applied in the field of magnetic random access memory (MRAM) is used as a light modulation element. The spin-injection magnetization reversal element is, for example, a CPP-GMR (Current Perpendicular to Plane Giant MagnetoResistance) element, a TMR (Tunnel MagnetoResistance) element, or the like.

  Here, an outline of a light modulation element (spin injection type light modulation element) using the spin Kerr magnetization reversal and using the magnetic Kerr effect for detecting the polarization of reflected light will be described with reference to FIG. The light modulation element 30 shown in FIG. 7 includes, for example, a magnetization fixed layer 31, an intermediate layer 32, and a magnetization free layer 33. An upper electrode 50 made of a transparent electrode material made of IZO, ITO or the like is disposed on the light modulation element 30. A lower electrode 20 made of Cu or the like is disposed below the light modulation element 30. By arranging in this way, the magnetization direction of the magnetization free layer 33 can be controlled by the magnitude and direction of the current (for example, pulse current) flowing through the light modulation element 30. In this case, since the magnetization direction of the magnetization free layer 33 can be controlled by the direction in which the pulse current from the current source 81 flows, it can be operated as a light modulation element that controls the plane of polarization of light by the pulse current. .

As shown in FIG. 7, the light emitted from the laser light source 90 includes various polarization components, but is filtered by the polarization filter 91 so as to include only a polarization component in a certain direction. Then, the plane of polarization of the laser light that has passed through the polarization beam splitter (PBS) composed of the polarization filter 91 and the half mirror 93 is rotated depending on the direction and magnitude of magnetization of the magnetization free layer 33. For example, the polarization plane of the laser beam reflected when the magnetization direction of the magnetization free layer 33 is downward, the optical modulation, only theta _k for example clockwise as shown in FIG. _{7 (a) (+ θ k} ) rotates In this case, since this reflected light passes through the polarizing filter 92, it becomes “bright”. On the other hand, the polarization plane of the laser beam reflected when the magnetization direction of the magnetization free layer 33 is upward is, for example, counterclockwise by θ _k (−θ _k ) as shown in FIG. In the case of rotation, the reflected light does not pass through the polarizing filter 92 and thus becomes a “dark state”.

Japanese Patent No. 4596468 JP 2008-83686 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)

  The present inventors have solved the problem of miniaturization of the SLM by the liquid crystal panel and the problem of the response speed, for example, to increase the degree of light modulation by the spin injection type light modulation element in order to display a holographic stereoscopic image. The technology has been proposed so far. The spatial light modulator in which the spin injection type light modulation elements are two-dimensionally arranged has room for improvement in addition to the problem of miniaturization and the response speed. For example, as described in Patent Document 2, when a spatial light modulator using a spin-injection magnetization switching element as a light modulation element is configured, each light modulation element arranged two-dimensionally is electrically driven individually. Of course, an insulator for separating and insulating the light modulation elements from each other is provided.

  In a spatial light modulator using such a spin-injection type light modulation element, even if the light modulation degree of the light modulation element is increased, incident light does not hit each light modulation element, but between the light modulation elements. It also hits the insulator. And the polarization plane does not rotate the reflected light from such an insulator. Therefore, the “bright state” in FIG. 7A is not obtained, and the “dark state” in FIG. That is, the reflected light from the insulator between the light modulation elements cannot be completely removed by the polarization filter on the output side. Therefore, for example, it becomes a noise component of a reproduced image displayed as a holographic stereoscopic image, and the contrast is lowered.

  The present invention has been made in view of the above problems, and an object thereof is to provide a spatial light modulator for displaying a high-contrast holographic stereoscopic image.

  In order to solve the above problems, a spatial light modulator according to claim 1 of the present invention includes a magnetization fixed layer in which the magnetization direction is fixed in one direction, and a magnetization direction that is more easily rotated than the magnetization fixed layer. Spatial light modulation that modulates incident light from the magnetization free layer side by a magneto-optic effect of a light modulation element having at least a magnetization free layer that can be performed and an intermediate layer between the magnetization fixed layer and the magnetization free layer A plurality of the light modulation elements are two-dimensionally arranged and a layer including an insulator between the light modulation elements, and a region corresponding to the space between the light modulation elements, and one surface of the light incident side of the insulator An inter-element magnetic layer provided so as to cover the element, and an insulator layer that insulates between the light modulation element and the inter-element magnetic layer, and the inter-element magnetic layer has a magnetization direction. It is fixed in one direction or the other direction That.

  According to such a configuration, the spatial light modulator is an element in which the magnetization direction is fixed in a constant direction between the light modulation element and the light modulation element, that is, an insulator that is vacant between the pixels. It is configured with an interstitial magnetic layer added. Therefore, of the incident light for light modulation by the spatial light modulator according to the present invention, the reflected light reflected by the inter-element magnetic layer laminated on the insulator between the light modulation element and the light modulation element is The polarizing filter can be set so as to be shielded from light by the polarizing filter disposed on the output light side. Therefore, for example, a noise component of a reproduced image displayed as a holographic stereoscopic image can be reduced. On the other hand, among the incident light to be modulated by the spatial light modulator according to the present invention, the reflected light reflected by the light modulation element has its polarization plane rotated according to the direction and magnitude of the magnetization of the magnetization free layer, and the output light. The light is blocked or transmitted by the polarizing filter on the side. Therefore, a high-contrast holographic stereoscopic image can be displayed.

  The spatial light modulator according to claim 2 of the present invention is the spatial light modulator according to claim 1, wherein the insulator layer that insulates between the light modulation element and the inter-element magnetic layer is: It is provided so that it may coat | cover between the said light modulation element and the said light modulation element.

  According to such a configuration, the spatial light modulator includes the inter-element magnetic layer such that the insulator is provided between the light modulation element and the insulator covers the light modulation element and the light modulation element. It is also provided on the side. Therefore, in the spatial light modulator according to the present invention, an electrical short circuit between the inter-element magnetic layer and the light modulation element can be prevented by the insulator provided on the inter-element magnetic layer side.

  The spatial light modulator according to claim 3 of the present invention is the spatial light modulator according to claim 1, wherein the insulator layer that insulates between the light modulation element and the inter-element magnetic layer includes: It is provided so that the area | region corresponding to between the said light modulation elements may be coat | covered.

  According to this configuration, the spatial light modulator includes the insulator provided between the light modulation elements and the insulator in a region corresponding to the space between the light modulation elements on the inter-element magnetic layer side. Is also provided. Therefore, in the spatial light modulator according to the present invention, an electrical short circuit between the inter-element magnetic layer and the light modulation element can be prevented by the insulator provided on the inter-element magnetic layer side.

  The spatial light modulator according to claim 4 of the present invention is the spatial light modulator according to any one of claims 1 to 3, wherein the inter-element magnetic layer has a Kerr rotation angle of: The optical modulation element is configured to be substantially equal to the Kerr rotation angle of the magnetization free layer of the light modulation element.

  According to such a configuration, the spatial light modulator is arranged on the incident light side of the light modulation element and the rotation angle of the polarization plane in the reflected light reflected by the inter-element magnetic layer among the incident light for light modulation. The rotation angle of the polarization plane in the reflected light reflected by the magnetization free layer is substantially equal. Therefore, in the light that is incident when the magnetization direction of the magnetization free layer corresponding to the dark state shielded by the polarizing filter disposed on the output light side and is reflected by the spatial light modulator according to the present invention, The reflected light of the magnetic layer is in a dark state equivalent to the reflected light of the light modulation element.

  The spatial light modulator according to claim 5 of the present invention is the spatial light modulator according to any one of claims 1 to 4, wherein the inter-element magnetic layer has a coercive force of It is configured to be larger than the coercive force of the magnetization free layer of the light modulation element.

  According to this configuration, in the spatial light modulator, in the light modulation element, the coercive force of the magnetization free layer is a coercive force that can rotate the magnetization direction more easily than the magnetization fixed layer, The coercive force of the intermagnetic layer is larger than the coercive force of the magnetization free layer. That is, in the spatial light modulator according to the present invention, the magnetization of the inter-element magnetic layer is fixed in one direction regardless of the magnetization reversal operation or the like of the light modulation element. Therefore, regardless of the magnetization reversal operation or the like, the direction of polarization of the light emitted from the inter-element magnetic layer remains one direction, and a high-contrast holographic stereoscopic image can be stably displayed.

  According to the present invention, a high-contrast holographic stereoscopic image can be displayed.

1 is a plan view schematically showing a spatial light modulator according to an embodiment of the present invention. It is a fragmentary sectional view showing typically the spatial light modulator concerning a 1st embodiment of the present invention, and (a) is a sectional view in an AA line arrow of a pixel unit shown by a virtual line in FIG. (b) is a schematic diagram of (a) schematically showing the magnetization direction of the element in the bright state, and (c) is a schematic diagram of (a) schematically showing the magnetization direction of the element in the dark state. FIG. 2 is a partial cross-sectional view schematically showing an inter-element magnetic layer of the spatial light modulator according to the first embodiment of the present invention, and shows a cross-sectional view taken along line AA in FIG. 1. It is a fragmentary sectional view showing typically a spatial light modulator concerning a 2nd embodiment of the present invention, and (a) is a sectional view in an AA line arrow of a pixel unit shown in a virtual line in FIG. (b) is a schematic diagram of (a) schematically showing the magnetization direction of the element in the bright state, and (c) is a schematic diagram of (a) schematically showing the magnetization direction of the element in the dark state. It is a fragmentary sectional view which shows typically the inter-element magnetic layer of the spatial light modulator concerning a 2nd embodiment of the present invention, and is a sectional view in the AA line arrow of FIG. 4 is a graph showing an example of measurement of physical properties of a magnetic film applicable to the spatial light modulator according to the embodiment of the present invention, where (a) is a magnetic film used for a magnetization free layer, and (b) is an inter-element magnetic layer. The magnetic film to be used is shown. It is a schematic diagram which shows the light modulation using the magnetization reversal by the conventional spin injection, Comprising: (a) is the magnetization direction of the element in a bright state, (b) has shown the magnetization direction of the element in a dark state. It is a top view which shows typically the spatial light modulator which concerns on a comparative example. It is a fragmentary sectional view which shows typically the spatial light modulator concerning a comparative example, Comprising: (a) is sectional drawing in DD line arrow of the pixel unit shown by a virtual line in FIG. 8, (b) is a bright state. (A) is a schematic diagram schematically showing the magnetization direction of the element, and (c) is a schematic diagram (a) schematically showing the magnetization direction of the element in the dark state. It is a fragmentary sectional view which shows typically the spatial light modulator concerning a comparative example, Comprising: Sectional drawing in the DD arrow of FIG. 8 is shown.

  Hereinafter, the spatial light modulator of the present invention will be described in detail with reference to the drawings. Note that the thickness, size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation.

(First embodiment)
[1. Overview of Spatial Light Modulator Configuration]
An outline of the configuration of the spatial light modulator 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3.

As shown in FIG. 1, the spatial light modulator 1 mainly includes a substrate 10, a lower electrode 20, a light modulation element 30, an insulating layer 40, an upper electrode 50, and an inter-element magnetic layer 70. Yes.
The spatial light modulator 1 has the following hierarchical structure.

Here, as an example, four electrodes 21, 22, 23, and 24 are formed on the substrate 10 as the lower electrode 20 in the row direction. Unless otherwise distinguished, the lower electrode 20 is indicated. An insulating layer 40 is formed between the lower electrodes 20.
A plurality of light modulation elements 30 are two-dimensionally arranged on the lower electrode 20. An insulating layer 40 is formed between the light modulation elements 30.
On the light modulation element 30, three electrodes 51, 52 and 53 are formed in the column direction as a transparent upper electrode 50. Unless otherwise distinguished, the upper electrode 50 is indicated. An insulating layer 40 is formed between the upper electrodes 50.
An inter-element magnetic layer 70 is formed on the upper electrode 50 via an insulator layer 40.
The spatial light modulator 1 is a reflective spatial light modulator that reflects light incident from above by modulating the incidence by the magneto-optic effect of the light modulation element 30.

FIG. 2A shows a cross-sectional view taken along the line AA of the pixel unit 2 indicated by a virtual line in FIG. 1, and FIG. 3 shows a cross-sectional view taken along the line AA in FIG.
As shown in FIG. 2A, a lower electrode 21 extending in the horizontal direction (row direction) of the paper surface is disposed under the light modulation element 30, and the light modulation element 30 is disposed on the paper surface. An upper electrode 52 extending in the vertical direction (column direction) is disposed. Here, the upper electrode 52 is made of a transparent electrode member, and hatching is omitted in the cross-sectional view of FIG. 4A and 9B also omit some hatching for the same purpose.

As illustrated in FIG. 2A, the light modulation element 30 includes a magnetization fixed layer 31, an intermediate layer 32, and a magnetization free layer 33 in order from the substrate 10 side.
The magnetization fixed layer 31 is a magnetic layer whose magnetization direction is fixed in one direction.
In all the light modulation elements 30, the magnetization fixed layer 31 has, for example, the magnetization direction fixed upward (see FIG. 3).
The magnetization free layer 33 is a magnetic layer that can rotate the direction of magnetization more easily than the magnetization fixed layer 31.
The intermediate layer 32 is a nonmagnetic layer provided between the magnetization fixed layer 31 and the magnetization free layer 33.
In the example of FIGS. 2A and 3, the protective layer 34 is provided on the magnetization free layer 33, but this is optional.

  The insulating layer 40 is made of an insulator. In the following, the insulating layer 40 will be described in the form of two layers in order from the substrate 10 side: an insulating layer 41 and an insulating layer 42. The insulating layer 41 and the insulating layer 42 are made of the same material. Are integrally formed.

As shown in FIG. 3, the spatial light modulator 1 includes a plurality of light modulation elements 30 arranged two-dimensionally and a layer including the insulating layer 41 between the light modulation elements 30 and 30 and the light modulation elements 30. An inter-element magnetic layer provided in a corresponding region so as to cover one surface of the insulating layer 41 on the light incident side, and an insulating layer that insulates between the light modulation element 30 and the inter-element magnetic layer. It is equipped with.
In FIG. 3, for the sake of explanation, an arrow schematically showing the incident light to the spatial light modulator 1, an arrow schematically showing the reflected light from the spatial light modulator 1, the light modulation element 30, and between the elements A white arrow schematically showing the direction of magnetization of the magnetic layer 70 is described. In order to make these schematic arrows easy to see, hatching of some cross sections of the insulating layers 41, 42, etc. is omitted in FIG. 5 and 10 also omit some hatching for the same purpose.

The inter-element magnetic layer 70 is a magnetic layer in which the magnetization direction is fixed in one direction.
In the inter-element magnetic layer 70, for example, the magnetization direction is fixed upward (see FIG. 3).
In the example of FIGS. 2A and 3, the protective layer 71 is provided on the inter-element magnetic layer 70, but this is an option and is omitted in FIG. 1.

FIG. 2B is a schematic diagram of FIG. 2A and schematically shows the direction of magnetization of the light modulation element 30 in the bright state.
FIG. 2C is a schematic diagram of FIG. 2A and schematically shows the magnetization direction of the light modulation element 30 in a dark state.

  As shown in FIG. 3, in the spatial light modulator 1, the insulating layer 41 is, for example, between the light modulation element 30 disposed under the electrode 51 and the light modulation element 30 disposed under the electrode 52. Is provided. On the other hand, in FIG. 1, in the spatial light modulator 1, the insulating layer 41 is, for example, between the light modulation element 30 disposed on the electrode 21 and the light modulation element 30 disposed on the electrode 22. Is also provided. That is, in plan view, a plurality of light modulation elements 30 are two-dimensionally arranged in the film of the insulating layer 41 separated by vertical and horizontal partition lines made of an insulator.

As shown in FIG. 3, in the spatial light modulator 1, for example, the insulating layer 42 is formed with an insulator on the entire lower surface where the insulator is provided between the electrode 51 and the electrode 52. And an upper hierarchy. When this is applied to the plan view of FIG. 1, in the film below the insulating layer 42, a plurality of upper electrodes 50 are separated by vertical partition lines made of an insulator.
Further, the film on the upper side of the insulating layer 42 is formed over the entire plane so as to cover each light modulation element 30 and between the light modulation elements 30 and 30 (see FIG. 2A and FIG. 3).
The insulating layer 42 is provided to insulate the inter-element magnetic layer 70 and the light modulation element 30 provided above and below the insulating layer 42.

[2. Details of each component of spatial light modulator]
<Board>
The substrate 10 is provided for forming the lower electrode 20. A known substrate material can be applied as the material of the substrate 10. In the present embodiment, for example, a silicon substrate with an oxide film obtained by thermally oxidizing the surface of a silicon substrate is used as the substrate 10.

<Electrode>
≪Lower electrode≫
The lower electrode 20 is made of a general electrode material. Examples of such a material include metals such as Cu, Al, Au, Ag, Ta, and Cr, which have good conductivity, and alloys thereof. In the present embodiment, Cu is used for the lower electrode 20 as an example.
As a method of forming the lower electrode 20, for example, an electrode material can be formed by a known method such as a sputtering method, and a photolithography process and a process such as an etching or lift-off method can be used.

≪Upper electrode≫
The upper electrode 50 is made of an electrode material that easily transmits incident light. Examples of such a material include known transparent electrode materials such as indium tin oxide (ITO) and indium zinc oxide (IZO). In the present embodiment, as an example, IZO is used for the upper electrode 50.
The formation method of the upper electrode 50 is the same as that of the lower electrode 20. Note that, as a method for forming the transparent electrode material, a vacuum deposition method, a coating method, or the like can be used in addition to the sputtering method.

<Insulator>
The insulator forming the insulating layer 40 is made of a general insulator material. Examples of such materials include oxide films such as SiO ₂ and Al ₂ O ₃ , Si ₃ N ₄ and MgF ₂ . In the present embodiment, as an example, the insulating layer 40 is made of SiO ₂ .

<Light modulation element>
The light modulation element 30 is a spin injection type light modulation element, and is composed of, for example, a CPP-GMR element or a TMR element. In the present embodiment, as an example, the light modulation element 30 is configured by a CPP-GMR element.

≪Magnetic free layer≫
As the material of the magnetization free layer 33, a material having a large magneto-optical effect can be used.
As a material of the magnetization free layer 33, for example, a known magnetic material used for a CPP-GMR element or a TMR element can be used. Such a magnetic material is a perpendicular magnetic anisotropic material or an in-plane magnetic anisotropic material, and for example, transition metal materials such as CoFeB, CoFe, Co, Fe, CoFeSi, and CoFeGe can be mainly used.
Further, (transition metal / noble metal) multilayer film, Co / Pt multilayer film, Co / Pd multilayer film, Fe / Pd multilayer film, CoFe / Pd multilayer film, Fe / Pt multilayer film, and the like can be given.
Alternatively, an alloy of a rare earth metal and a transition metal (RE-TM alloy), a GdFe alloy, a GdCoFe alloy, a GdCo alloy, a TaFeCo alloy, a Tb—Fe—Co alloy, or the like can be given. Further, mention may be made of FePt, a FePd or the like with L1 ₀ type ordered alloys.
In this embodiment, as an example, the magnetization free layer 33 is made of a GdFe alloy of a perpendicular magnetic anisotropic material.

≪Middle layer≫
The material of the intermediate layer 32 differs depending on whether the light modulation element 30 is, for example, a CPP-GMR element or a TMR element.
When the light modulation element 30 is configured by a CPP-GMR element as in the present embodiment, the intermediate layer 32 is made of a metal such as Cu, Al, Au, Ag, and the thickness is 1 to 10 nm. It is preferable to do. In the following, it is assumed that the intermediate layer 32 is made of Ag as an example. If the light modulation element 30 is a TMR element, the intermediate layer 32 is formed of an insulator layer. Such an insulator layer is made of, for example, an insulator such as Al ₂ O ₃ and MgO, or a laminated film containing an insulator such as Mg / MgO / Mg, and has a thickness of 0.1 to 2 nm. It is preferable to do.

≪Magnetic pinned layer≫
The magnetization fixed layer 31 can be made of a known magnetic material used for a CPP-GMR element or a TMR element, similarly to the magnetization free layer 33. However, the magnetic material and the thickness are selected so that the magnetization fixed layer 31 has a coercive force larger than that of the magnetization free layer 33 so that the magnetization is fixed. In this embodiment, as an example, the magnetization fixed layer 31 is made of a Tb—Fe—Co alloy of a perpendicular magnetic anisotropic material.

<Magnetic layer between elements>
The inter-element magnetic layer 70 can be made of a known magnetic material used for a CPP-GMR element or a TMR element, similarly to the magnetization free layer 33 of the light modulation element 30.
In the present embodiment, the inter-element magnetic layer 70 has a Kerr rotation angle (hereinafter referred to as θ _k2 ) that is a Kerr rotation angle (hereinafter referred to as θ _k1 ) of the magnetization free layer 33 of the light modulation element 30. It is comprised so that it may become substantially equivalent. Here, the Kerr rotation angle theta _k2 of the element between the magnetic layer 70, and the Kerr rotation angle theta _k1 of the magnetization free layer 33 is substantially equal to the absolute value of the Kerr rotation angle of the element between the magnetic layer 70 | theta _k2 | and This means that the absolute value | θ _k2 | of the Kerr rotation angle of the magnetization free layer 33 is in the same order, and the error is, for example, within 20%. Further, the error is preferably within 10%, and | θ _k2 | is preferably equal to | θ _k1 |.

In the present embodiment, the inter-element magnetic layer 70 is configured such that its coercive force is larger than the coercive force of the magnetization free layer 33 of the light modulation element 30.
Here, the fact that the coercive force of the inter-element magnetic layer 70 is larger than the coercive force of the magnetization free layer 33 means that the absolute values of the respective coercive forces are not in the same order but are in different digits. Further, the difference is preferably ten times or more, and the difference is preferably 100 times or more.

In the present embodiment, the inter-element magnetic layer 70 has a coercive force larger than the coercive force of the magnetization free layer 33, and the absolute value | θ _k2 | of the Kerr rotation angle of the inter-element magnetic layer 70 is equal to the magnetization free layer 33. It is assumed that the magnetic material is in a range that is within the same range as the absolute value of the Kerr rotation angle | θ _k1 |.

  An example of the physical characteristics of a magnetic film using such a magnetic material will be described with reference to FIGS. 6 (a) and 6 (b). As a premise, a GdFe alloy film was produced under the same conditions as those used for the magnetization free layer 33 constituting the light modulation element 30 of the spatial light modulator 1. Also, a Tb—Fe—Co alloy film was formed in the same shape as the magnetic film of the GdFe alloy under the same conditions as those used for the inter-element magnetic layer 70 of the spatial light modulator 1. The two magnetic films have the same film formation conditions, but naturally have different film thicknesses because of different materials.

Then, using a laser light source with a wavelength of 780 nm, the Kerr rotation angle when the magnitude and direction of the applied magnetic field applied to each magnetic film was changed was measured.
An example of the applied magnetic field-Kerr rotation angle characteristic measured for the GdFe alloy film (corresponding to the magnetization free layer 33) at this time is shown in FIG. In addition, FIG. 6B shows an example of applied magnetic field-Kerr rotation angle characteristics measured for the Tb—Fe—Co alloy film (corresponding to the inter-element magnetic layer 70) at this time. The unit of coercive force can be converted by 1 [Oe] = 79.577 [A / m].

6A and 6B, the horizontal axis indicates the magnetic field applied to the magnetic film (applied magnetic field), and the vertical axis indicates the Kerr rotation angle. However, the scale on the horizontal axis in FIG. 6A is one digit smaller than the scale on the horizontal axis in FIG.
As shown in FIG. 6A, in the case of a GdFe alloy film (corresponding to the magnetization free layer 33), the coercive force Hc was 60 Oe, and the absolute value of the Kerr rotation angle | θ _k1 | was 0.14 degrees. .
As shown in FIG. 6B, in the case of a Tb—Fe—Co alloy film (corresponding to the inter-element magnetic layer 70), the coercive force Hc is 8 kOe, and the absolute value of the Kerr rotation angle | θ _k2 | It was 13 degrees.

Comparing the results of FIG. 6A and FIG. 6B, when the absolute value | θ _k1 | of the Kerr rotation angle of the GdFe alloy film (corresponding to the magnetization free layer 33) is used as a reference, Tb—Fe—Co It can be seen that the error with the absolute value | θ _k2 | of the Kerr rotation angle of the alloy film (corresponding to the inter-element magnetic layer 70) is about 7%.

  When the coercive force Hc of the GdFe alloy film (corresponding to the magnetization free layer 33) is used as a reference, the coercive force Hc of the Tb—Fe—Co alloy film (corresponding to the inter-element magnetic layer 70) is about 133 times that. I understand that there is. Regarding the coercive force, if the magnetization of the inter-element magnetic layer 70 can be fixed in one direction within a range in which the magnetization direction of the magnetization free layer 33 is easily reversed, the coercive force of the inter-element magnetic layer 70 is between elements. It may be about 10 times the magnetic layer 70. That is, in this example, the coercive force Hc of the Tb—Fe—Co alloy film (corresponding to the inter-element magnetic layer) may be about 800 Oe, which is one digit smaller than the measured value.

Details of each component of the spatial light modulator 1 will be described with reference to FIGS. 1 to 3 again.
<Option>
≪Protective layer≫
The protective layer 34 protects the magnetization free layer 33 of the light modulation element 30. In particular, when the magnetization free layer 33 includes an easily oxidizable RE-TM alloy, the magnetization free layer 33 is provided as necessary to prevent oxidation of the surface (upper surface). The protective layer 34 is formed of, for example, a single layer of Ta, Ru, or Cu. Alternatively, a Cu / Ta two-layer metal film or a Cu / Ru two-layer metal film is formed in this order from the magnetization free layer 33 side. In the present embodiment, as an example, the protective layer 34 is composed of a Ru single layer.
The protective layer 71 protects the inter-element magnetic layer 70 and is made of the same material as the protective layer 34.

<< Underlayer >>
An underlayer (not shown) for improving adhesion may be provided between the magnetization fixed layer 31 of the light modulation element 30 and the lower electrode 20.
≪Metal film≫
A metal film (not shown) for reducing the contact resistance and increasing the response speed may be interposed between the transparent upper electrode 50 and the light modulation element 30.

≪Current supply and pixel selection device≫
The current supply and pixel selection device 80 shown in FIG. 1 includes a current source 81 (see FIG. 7) for supplying a pulse current, for example, as schematically shown in FIG. 1, and is two-dimensionally arranged by a matrix switch or the like. The light modulation element 30 is selected and a known current supply and pixel selection device that supplies current is configured. For this purpose, the current supply and pixel selection device 80 has a function of selecting the lower electrode 20 (21, 22, 23, 24), a function of selecting the upper electrode 50 (51, 52, 53, 54), and a selection. A function of supplying a current between the lower electrode 20 and the upper electrode 50 formed. The magnetization direction of the magnetization free layer 33 of the light modulation element 30 selected as the intersection of the upper electrode 50 extending vertically in FIG. 1 and the lower electrode 20 extending horizontally in FIG. It is controlled by the direction in which the pulse current from the source 81 flows.

  The current supply and pixel selection device 80 selects the light modulation element 30 to be brought into a bright state in the spatial light modulator 1 as a target pixel, and changes the magnetization direction of the magnetization free layer 33 to a direction different from that of the magnetization fixed layer 31. This is a mechanism for performing control to invert the magnetization direction of the magnetization free layer 33 of the light modulation element 30 to be in the dark state so as to be the same as that of the magnetization fixed layer 31. In the initial state, the magnetization direction of the magnetization free layer 33 is upward as in the magnetization fixed layer 31.

≪Light irradiation mechanism≫
In addition to the spatial light modulator 1 and the current supply and pixel selection device 80, a holographic display device can be configured by further providing a light irradiation mechanism. The light irradiation mechanism includes, for example, a laser light source 90 (see FIG. 7), a polarizing filter 91 (see FIG. 3), and a polarizing filter 92 (see FIG. 3).

[3. Manufacturing method of spatial light modulator]
An example of a manufacturing method of the spatial light modulator 1 shown in FIGS.
In the present embodiment, as described above, the material of the magnetization fixed layer 31 and the inter-element magnetic layer 70 is Tb—Fe—Co, the material of the intermediate layer 32 is Ag, the material of the magnetization free layer 33 is a GdFe alloy, and protection Ru is used for the material of the layer 34, respectively.

<Film forming process: S1>
First, a silicon substrate with an oxide film is prepared as the substrate 10 and the lower electrode 20 is formed. On the silicon substrate with an oxide film on which the lower electrode 20 is formed, the magnetization fixed layer 31, the intermediate layer 32, the magnetization free layer 33, and the protective layer 34 are sequentially formed in a vacuum in order. For film formation, a known technique such as sputtering is used.

<Insulating layer forming step: S2>
After forming a pixel-sized resist on the protective layer 34, the insulating layer 41 is deposited by milling to the lower electrode 20 by ion beam milling using Ar ions or the like.

<Inter-element magnetic layer forming step: S3>
After removing the resist, the upper electrode 50 is formed. Then, the insulating layer 42 is formed over the entire surface of the upper electrode 50, a pixel-sized resist is formed again, and the inter-element magnetic layer 70 is deposited. Finally, by lifting off the resist, the spatial light modulator 1 in which the inter-element magnetic layer 70 is formed in an area other than the light modulation element 30 is completed.

[4. Example of light modulation operation by spatial light modulator]
An example of the light modulation operation of the spatial light modulator 1 shown in FIGS. 1 to 3 will be described in comparison with the spatial light modulator 101 as shown in FIGS. 8 to 10 correspond to FIGS. 1 to 3, respectively. As shown in FIGS. 8 to 10, the spatial light modulator 101 does not include the inter-element magnetic layer 70, and the insulating layer 42 is provided between the electrode 51 and the electrode 52, for example. The difference from the spatial light modulator 1 according to the first embodiment is that it is not formed on the entire surface.
In the spatial light modulator 101 of this comparative example, the same components as those of the spatial light modulator 1 are denoted by the same reference numerals and description thereof is omitted.

FIG. 9A shows a cross-sectional view taken along line DD of the pixel unit 102 indicated by the phantom line in FIG. 8, and FIG. 10 shows a cross-sectional view taken along line DD in FIG.
FIG. 9B is a schematic diagram of FIG. 9A and schematically shows the direction of magnetization of the light modulation element 30 arranged in the pixel unit 102 in the bright state.
FIG. 9C is a schematic diagram of FIG. 9A, schematically showing the magnetization direction in the dark state of the light modulation element 30 arranged in the pixel unit 102.

In FIG. 10, the magnetization free layer 33 of the light modulation element 30 disposed under the electrode 51 has the magnetization direction downward. Therefore, the light that has passed through the polarizing filter 91 and reflected by the magnetization free layer 33 passes through the polarizing filter 92. That is, it becomes a bright state (see FIG. 9B).
In FIG. 10, the magnetization free layer 33 of the light modulation element 30 disposed under the electrode 52 has a magnetization direction upward. Therefore, the light that has passed through the polarization filter 91 and reflected by the magnetization free layer 33 is cut by the polarization filter 92. That is, it will be in a dark state (refer FIG.9 (c)).
The two operations described above are the same for the spatial light modulator 1 according to the first embodiment.

  However, as illustrated in FIG. 10, the spatial light modulator 101 of the comparative example does not include the inter-element magnetic layer 70. Therefore, in FIG. 10, the light that has passed through the polarizing filter 91 and reflected by the insulating layer 42 disposed between the electrode 51 and the electrode 52 does not rotate the polarization plane. Therefore, the light reflected by the insulating layer 42 does not enter the “bright state” of FIG. 9B and does not become the “dark state” of FIG. turn into. That is, in the spatial light modulator 101 of the comparative example, the reflected light from the insulating layer 42 between the light modulation elements 30 and 30 cannot be completely removed by the polarization filter 92. Therefore, for example, it becomes a noise component of a reproduced image displayed as a holographic stereoscopic image, and the contrast is lowered.

  On the other hand, as shown in FIG. 3, in the spatial light modulator 1 according to the first embodiment, the insulating layer 42 formed over the entire surface above the insulating layer 41 between the light modulation elements 30 and 30. Is provided with an inter-element magnetic layer 70 whose magnetization direction is fixed upward. Therefore, in FIG. 3, the inter-element magnetic layer provided above the corresponding region between the light modulation element 30 disposed under the electrode 51 and the light modulation element 30 disposed under the electrode 52. When light enters 70, the state becomes dark.

Further, in the spatial light modulator 1 of the present embodiment, the inter-element magnetic layer 70 is configured such that its Kerr rotation angle is substantially equal to the Kerr rotation angle of the magnetization free layer 33 of the light modulation element 30. .
Therefore, for example, when the magnetization direction of the magnetization free layer 33 of the light modulation element 30 is upward, that is, in the dark state, as shown in FIG. Since the polarization state of the reflected light from the magnetic layer 70 is equivalent, the reflected light from the magnetization free layer 33 and the reflected light from the inter-element magnetic layer 70 are shielded equally by the polarization filter 92. On the other hand, when the magnetization direction of the magnetization free layer 33 of the light modulation element 30 is downward, that is, in the bright state, only the reflected light from the magnetization free layer 33 is transmitted through the polarization filter 92. Therefore, the spatial light modulator 1 can display a high-contrast holographic stereoscopic image.

  The viewing zone angle Ψ of the holographic stereoscopic image reproduced when the spatial light modulator 1 is irradiated with laser light is expressed by the following formula (1). In Equation (1), P is the pixel pitch of the spatial light modulator 1 (see FIG. 3), λ is the wavelength of the incident light, and φ is the maximum diffraction angle of the spatial light modulator.

(Second Embodiment)
4 and 5 are diagrams schematically showing the spatial light modulator 1B according to the second embodiment.
The spatial light modulator 1B is different from the spatial light modulator 1 of the first embodiment in that the insulating layer 42 is provided so as to cover a corresponding region between the light modulation elements 30 and 30. Therefore, the plan view of the spatial light modulator 1B is the same as FIG. 4 and 5 correspond to FIGS. 2 and 3, respectively. In the spatial light modulator 1B, the same components as those in the spatial light modulator 1 are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, in the spatial light modulator 1B of the second embodiment, the insulating layer 42 includes, for example, a lower layer in which an insulator is provided between the electrode 51 and the electrode 52, and an upper side thereof. And an insulator film layer disposed under the inter-element magnetic layer 70. That is, in the spatial light modulator 1B, no insulator is provided on the light modulation element 30 (see FIG. 4A).

  When an insulator is provided on the light modulation element 30, even if the insulator layer is transparent, an energy loss of light passing back and forth through the insulator layer is inevitably generated. That is, the diffraction efficiency is reduced. On the other hand, the spatial light modulator 1B has an effect of preventing such a situation that the light use efficiency is reduced.

  The spatial light modulator 1B is manufactured in the same manner as the spatial light modulator 1, after the film formation step (S1) and the insulating layer formation step (S2) are performed, and then the inter-element magnetic layer formation step ( The following steps may be performed as S3B). That is, following S2, the upper electrode 50 is formed after the resist is removed. Then, a pixel-sized resist is formed again on the upper electrode 50, the insulating layer 42 is formed on the entire surface, and the inter-element magnetic layer 70 is deposited. Finally, by lifting off the resist, the spatial light modulator 1B in which the inter-element magnetic layer 70 is formed in an area other than the light modulation element 30 is completed.

  Although the spatial light modulator according to the present invention has been described based on the embodiments, the present invention is not limited to these. For example, although the magnetization fixed layer 31 and the inter-element magnetic layer 70 are fixed in the direction of magnetization upward (see FIG. 3), they may be fixed downward. In this case, the setting of the polarization filter 92 may be changed so that the “bright state” is obtained when the magnetization direction of the magnetization free layer 33 is upward.

  In addition, as long as the fixed magnetization layer 31 is fixed in one direction in all the light modulation elements 30, the direction may be opposite to the inter-element magnetic layer 70. In this case, in the initial state, the magnetization direction of the magnetization free layer 33 may be opposite to the magnetization fixed layer 31 (the same direction as the inter-element magnetic layer 70).

Further, the combination of the GdFe alloy film and the Tb—Fe—Co alloy film has been described as a combination in which the Kerr rotation angle of the magnetization free layer 33 and the Kerr rotation angle of the inter-element magnetic layer 70 are substantially equal. Is not limited to this.
In the present embodiment, the material of the magnetization fixed layer 31 and the inter-element magnetic layer 70 are the same, but different materials may be used.

1, 1B, 101 Spatial light modulator 2, 2B, 102 Pixel unit 10 Substrate 20 (21, 22, 23, 24) Lower electrode 30 Light modulation element 31 Magnetization fixed layer 32 Intermediate layer 33 Magnetization free layer 34 Protection layer 40 ( 41, 42) Insulating layer 50 (51, 52, 53) Upper electrode 70 Inter-element magnetic layer 71 Protective layer 80 Current supply and pixel selection device 81 Current source 90 Laser light source 91, 92 Polarizing filter 93 Half mirror

Claims (5)

A magnetization fixed layer in which the magnetization direction is fixed in one direction, a magnetization free layer that can rotate the magnetization direction more easily than the magnetization fixed layer, and an intermediate between the magnetization fixed layer and the magnetization free layer A spatial light modulator that modulates incident light from the magnetization free layer side by a magneto-optic effect of a light modulation element having at least a layer;
A plurality of the light modulation elements are two-dimensionally arranged and an insulator is provided between the light modulation elements;
An inter-element magnetic layer provided so as to cover one surface of the light incident side of the insulator in a corresponding region between the light modulation elements;
An insulator layer that insulates between the light modulation element and the inter-element magnetic layer, and
The spatial light modulator, wherein the inter-element magnetic layer has a magnetization direction fixed in one direction or the other direction.   The insulating layer that insulates between the light modulation element and the inter-element magnetic layer is provided so as to cover the light modulation element and the light modulation element. The spatial light modulator described.   The insulating layer that insulates between the light modulation element and the inter-element magnetic layer is provided so as to cover a corresponding region between the light modulation elements. The spatial light modulator described in 1.   4. The inter-element magnetic layer is configured such that the Kerr rotation angle thereof is substantially equal to the Kerr rotation angle of the magnetization free layer of the light modulation element. A spatial light modulator according to claim 1.   The inter-element magnetic layer is configured so that a coercive force thereof is larger than a coercive force of a magnetization free layer of the light modulation element. The spatial light modulator described in 1.

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