JP5054640B2 - Light modulation element, light modulator, display device, holography device, and hologram recording device - Google Patents

Description

  The present invention relates to a light modulation element using a change in magnetization direction, a light modulator using the light modulation element, a display device using the light modulator, a holography device, and a hologram recording device.

  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) includes a liquid crystal panel. This liquid crystal panel has a structure in which an oily and transparent liquid crystal material is sandwiched between two transparent substrates, and glass is often used as the transparent substrate, but plastic can also be used. is there. A transparent electrode is provided on the inner surface of the transparent substrate as an electrode for applying a voltage to the liquid crystal, and the material of the transparent electrode is indium tin oxide (ITO) having a low resistance value and easy to form. Widely used. However, an SLM in a liquid crystal panel is difficult to be miniaturized with a pixel size of several μm or less, and the response time is very slow, about several tens of μs.

  Accordingly, in order to solve the problem of miniaturization and the response speed, a high-speed magneto-optical spatial light modulator (MOSLM) using the Faraday effect of magnetic garnet as shown in Patent Document 1 or Patent Document 2 is used. Examples are disclosed.

  In the magneto-optic spatial light modulator described in Patent Document 1, a light reflecting film is individually formed for each region corresponding to each pixel, and a space between each pixel is caused by local heat treatment and stress applied by the light reflecting film. A MOSLM that is magnetically separated, or a MOSLM that forms an XY drive line so as to match the outer shape of each pixel, and in which each pixel is magnetically separated by local heat treatment and stress applied by the XY drive line. Yes, it is possible to reduce the distance between pixels below the pixel size. If the magnetic garnet has a single domain structure, the magnetization of the magnetic garnet can be reversed by applying a pulse current to the XY drive line.

  In addition, the magneto-optical spatial light modulator described in Patent Document 2 can set the magnetization direction independently in the magnetic garnet film, and rotates the polarization direction according to the magnetization direction with respect to incident light by the Faraday effect. A large number of pixels to be applied are two-dimensionally arranged with gaps, and an XY drive line that generates a magnetic field for individually controlling the magnetization direction of each pixel is provided. A composite magnetic field is applied to the pixels that are energized to the XY drive line to selectively reverse magnetization.

In Non-Patent Document 1, as in the present invention, an experiment is reported in which a plurality of spin-injection magnetization reversal elements are arranged to form a pixel and the optical Kerr effect is verified by measuring the longitudinal Kerr effect. Yes.
2005-70101 (paragraphs 0016-0025) 2005-221841 (paragraphs 0013 and 0014) K. Aoshima et.a1, "Spin transfer switching incurrent-perpendicular-to-plane spin valve observed by magneto-oPtical Kerr effectusing visible Hght.", Appl. Phys. Lett. 91, 052507 (2007)

  However, since the MOSLM shown in Patent Document 1 has a structure in which the XY drive lines are arranged along the outer periphery of the pixel, there is a problem that it is not sufficient for miniaturization of the pixel of several μm or less. is there. In the MOSLM shown in Patent Document 2, there is a problem that crosstalk to adjacent pixels increases when a pixel is miniaturized in order to use a combined magnetic field generated by current. The element shown in Non-Patent Document 1 has a problem that the Kerr rotation angle of polarized light reflected by the light modulation element is small because a material having in-plane magnetic anisotropy is used for the magnetic film. Therefore, these techniques have a problem that they are insufficient for performing high-definition light modulation at high speed.

  The present invention has been made in view of such circumstances, a light modulation element that has a high response speed and enables fine light modulation by miniaturization of pixels, a light modulator configured using the light modulation element, It is an object of the present invention to provide a display device, a holography device, and a hologram recording device that are configured using this optical modulator.

The light modulation element according to the present invention has a spin-injection magnetization reversal element structure in which a fixed magnetization film layer, a nonmagnetic intermediate film layer, and a free magnetization film layer are stacked in this order. The direction of magnetism in the free magnetic film layer is a direction perpendicular to the film surface, and the reflected light with respect to the polarization direction of light incident on the free magnetic film layer by changing the magnetization state in the free magnetic film layer or an optical modulation element for changing the polarization direction of the transmitted light, the fixed magnetic layer may have a cobalt layer and the platinum layer are alternately laminated, wherein the free magnetic layer is comprised of cobalt The platinum film layer has a structure in which the film layers and the platinum film layers are alternately stacked, and the thickness of one of the platinum film layers constituting the free magnetization film layer is one of the platinum film layers constituting the fixed magnetization film layer. The platinum film layer constituting the fixed magnetization film layer is thinner than the layer thickness. The thickness of the layer is characterized in that it is a 0.8～1.5Nm.

According to such a configuration, in the light modulation element according to the present invention, since the magnetization direction of the free magnetic film layer is perpendicular to the film surface, the incident angle is reduced to reduce the incident direction of the light and the magnetic field. Since it becomes easy to make the direction close to parallel, a large magneto-optical effect can be obtained. Furthermore, since the fixed magnetization film layer is formed in a multilayer structure in which cobalt film layers and platinum film layers are alternately stacked, the coercive force of the fixed magnetization film layer can be made larger than that of the free magnetization film layer. Therefore, the spin injection magnetization reversal operation (reversal and maintenance of the magnetization direction in the free magnetic film layer) in the free magnetic film layer is stabilized.
In addition, the thinner the platinum film layer, the smaller the coercive force, and the thicker the platinum film layer, the greater the coercive force. Therefore, the thickness of one of the platinum film layers constituting the free magnetic film layer By making the thickness smaller than the thickness of one of the platinum film layers constituting the fixed magnetization film layer, the coercive force of the fixed magnetization film layer can be made larger than that of the free magnetization film layer.

Light modulation element according to the present invention, the prior SL free magnetic layer is preferably an intermetallic compound of a transition element and rare earth elements.

According to this structure, an intermetallic compound of a transition element and a rare earth element is a thin film which can exhibit a large magnetic optical effect (Kerr effect) in thickness, the free magnetic layer, such intermetallic compound Thus, the magneto-optical effect (magnetic Kerr effect) can be increased, and the free magnetization film layer has low saturation magnetization (M _S ), and the magnetization reversal current density J _C is proportional to the magnitude of M _S. Can be reduced.

In the light modulation element according to the present invention, it is preferable to provide a base layer made of a platinum film layer having a thickness of 5 nm or more below the fixed magnetization film layer.
According to such a configuration, by providing an underlayer made of a platinum film layer having a thickness of 5 nm or more, the coercive force of the fixed magnetization film layer is further increased, and the coercivity of the fixed magnetization film layer is reduced to the free magnetization film layer. Can be made even larger.

The light modulator according to the present invention is characterized in that such light modulation elements are arranged in a two-dimensional array.
Since the light modulation element according to the present invention enables miniaturization of pixels and high-speed response, according to such a configuration, high-definition light modulation can be performed at high speed.

A display device according to the present invention includes the above-described optical modulator and a screen that projects light emitted from the optical modulator.
According to such a configuration, a high-definition image / video expression can be achieved at a high display speed.

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

The hologram recording apparatus according to the present invention is a hologram recording apparatus that records predetermined information on a recording medium using two systems of light, and the optical modulator described above and the two systems of light are incident on the recording medium. Imaging means for detecting a change in the state of the recording medium as phase information at the time, and based on the phase information detected by the imaging means, at least one light modulation of the two light systems is performed. , Using the optical modulator.
According to such a configuration, the multiplicity of recording can be remarkably improved, and the multiplicity of recording can be increased by performing optical modulation of the two systems of light using the optical modulator, respectively. Further improvement can be achieved.

  In the light modulation element according to the present invention, since the coercive force of the fixed magnetization film layer can be made larger than that of the free magnetization film layer, a stable spin injection magnetization reversal operation can be performed in the free magnetization film layer. Therefore, high-definition light modulation can be performed at high speed. In addition, according to the present invention, light having a high-definition light modulation characteristic and a high-speed response with a pixel size of 2 μm or less and a response speed of about several tens of ns to several ps due to such characteristics of the light modulation element. A modulator, a display device, a holography device, and a hologram recording device can be realized.

  Since the optical modulator according to the present invention uses an optical modulation element capable of performing high-definition optical modulation at high speed, a high-definition and high-speed response with a pixel size of 2 μm or less and a response speed of several tens to several ps is achieved. Can be realized.

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

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<Optical modulator>
<Overall structure>
FIG. 1A is a plan view schematically showing a schematic configuration of an optical modulator according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA shown in FIG. FIG. 1 (c) schematically shows the structure of the light modulation element used in the light modulator, and FIG. 2 schematically shows the specific structure of the light modulation element. The figure is shown.

[First Embodiment]
The light modulation element according to the first embodiment changes the polarization direction of reflected light with respect to the polarization direction of light incident on the free magnetic film layer by changing the magnetization state in the free magnetic film layer. is there.

  As shown in FIGS. 1A and 1B, an optical modulator (spatial light modulator) 10 includes a substrate 14, a strip-like lower electrode 13 provided in parallel on the substrate 14 at a predetermined interval, and a lower portion. A light modulation element 11 provided on the electrode 13 at a constant interval and a strip-shaped upper transparent electrode 12 provided in parallel at a constant interval so as to sandwich the light modulation element 11 between the lower electrode 13 are provided. Further, as will be described later, a half mirror 16 and polarizing filters 17 and 18 are disposed above the upper transparent electrode 12, and the reflected light from the light modulation element 11 is reflected by the half mirror 16 so that the reflected light is reflected. Depending on the angle of the polarization plane, the polarizing filter 18 transmits or blocks the reflected light (see FIG. 3).

  As shown in FIG. 1A, the drive (operation) of the optical modulator 10 is controlled by a control device 80, and the control device 80 selects a lower electrode for applying a voltage from among a plurality of lower electrodes 13. An electrode selection unit 82; an upper electrode selection unit 83 that selects an electrode to which a voltage is applied from the plurality of upper transparent electrodes 12; a power source 81 that supplies power to the lower electrode selection unit 82 and the upper electrode selection unit 83; A lower electrode selection unit 82, an upper electrode selection unit 83, and a control unit 84 that controls the operation of the power source 81. Hereinafter, each component will be described.

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

<Lower electrode>
The lower electrode 13 is one of a pair of electrodes for applying a voltage to the light modulation element 11. In the light modulator 10, here, the light modulation elements 11 are two-dimensionally arranged at regular intervals in the vertical and horizontal directions. Therefore, the lower electrode 13 has a strip shape and is formed on the substrate 14 at a constant width and a constant interval. Is provided. As the material constituting the lower electrode 13, copper (Cu) that is inexpensive and excellent in electrical conductivity is preferably used. However, the material is not limited to this, and noble metals such as gold (Au) and platinum (Pt) are used. It may be used. In the first embodiment, the substrate 14 is not required to have translucency, but a transparent electrode material such as IZO or ITO may be used. The width of the lower electrode 13 is appropriately determined according to the shape of the light modulation element 11 formed on the lower electrode 13.

<Upper transparent electrode>
The upper transparent electrode 12 is one of a pair of electrodes for applying a voltage to the light modulation element 11. In the optical modulator 10, the upper transparent electrode 12 has a band-like shape with a constant width so that a voltage can be applied to an arbitrary element selected from the light modulation elements 11 that are two-dimensionally arranged at regular intervals in the vertical and horizontal directions. And are arranged in parallel at regular intervals so that the longitudinal direction thereof is orthogonal to the longitudinal direction of the lower electrode 13. As the upper transparent electrode 12, a transparent electrode material such as IZO or ITO is preferably used.

<Light modulation element>
When a certain voltage is applied between the lower electrode 13 and the upper transparent electrode 12, the light modulation element 11 reflects the incident light incident on the light modulation element 11 by rotating the polarization plane of the incident light by a certain angle by the Kerr effect. Take a role. The size of the light modulation element 11 in a plan view (FIG. 1A) is, for example, 100 nm × 300 nm. In the light modulator 10, the light modulation element 11 is in a two-dimensional matrix (vertically and horizontally). Although one light modulation element 11 is one pixel, the light modulation element 11 may be composed of two or more. The shape of the light modulation element 11 is not limited to a rectangle (rectangle). The interval between the light modulation elements 11 depends on the accuracy of the film forming technique of the upper transparent electrode 12, the lower electrode 13, and the light modulation element 11 (as will be described later, a semiconductor manufacturing process is preferably used), and is determined as appropriate. It is done.

  As the light modulation element 11, an element having a so-called CPP-GMR (Current Perpendicular to Plane-Giant MagnetoResistance) type or tunnel current type magnetoresistive element (MR element) structure is used, as shown in FIG. In addition, the base layer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 are sequentially stacked from the lower electrode 13 side. An upper transparent electrode 12 is provided on 25. The light modulator 10 has a mesa structure by arranging such light modulation elements 11 in a two-dimensional matrix. Here, the light modulation element 11 including the base layer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 is illustrated. The film layer 25 may be provided as necessary. 1C illustrates the case where the base layer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective layer 25 are stacked in this order. The magnetic film layer 24, the nonmagnetic intermediate film layer 23, the fixed magnetic film layer 22, and the protective layer 25 may be stacked in this order, and the fixed magnetic film layer 22 and the free magnetic film layer 24 may be replaced with each other.

[Underlayer]
The underlayer 21 is a layer provided below the fixed magnetization film layer 22, that is, between the fixed magnetization film layer 22 and the lower electrode 13 as necessary, and is made of a platinum film layer having a thickness of 5 nm or more. Is. By inserting the base layer as the base of the fixed magnetization film layer 22, the coercive force of the fixed magnetization film layer 22 can be increased, and a more stable spin injection magnetization reversal operation can be performed. As shown in FIG. 12, the thickness of the underlayer 21 is preferably 10 nm or less because the coercive force tends to be saturated even if it is too thick.

[Fixed magnetic film layer]
The fixed magnetization film layer 22 uses a material having perpendicular magnetic anisotropy together with the free magnetization film layer 24, and polar Kerr effect that makes light incident and reflected in a direction perpendicular to the light modulation element 11 constituting the pixel. Is used. The direction of incident light that can obtain the maximum magnetic Kerr effect is a direction parallel to the direction of magnetization. Therefore, by having perpendicular magnetic anisotropy, the direction perpendicular to the film surface of the free magnetization film layer 24 Therefore, the light can be incident and reflected on the light modulation element 11, and the polar Kerr effect can be increased.

In other words, since the magnitude of the magnetic Kerr effect is proportional to the scalar product of the wave vector of incident light and the magnetization vector of the magnetic material, the polar Kerr effect is generally observed from an oblique direction with respect to the film surface of the spin injection light modulation element. A large Kerr rotation angle (θ _K ) can be obtained as compared with the incident vertical Kerr effect and horizontal Kerr effect. Therefore, as compared with the in-plane magnetization, it is possible to increase the theta _K, it is possible to improve the performance of the optical modulator 10.

  As shown in FIG. 2, the fixed magnetization film layer 22 has a multilayer structure in which cobalt film layers and platinum film layers are alternately laminated (hereinafter referred to as “Co / Pt multilayer film”). The Co / Pt multilayer film is one of so-called artificial lattice films. In a single cobalt film layer, the magnetization is in-plane, whereas in the Co / Pt multilayer film, the magnetization of the cobalt film layer is the same as the film surface. Oriented vertically. In addition, the thinner the platinum film layer, the smaller the holding force, and the thicker the platinum film layer, the larger the holding force. The fixed magnetic film layer 22 having such a structure can increase the coercive force of the fixed magnetic film layer 22, and the coercive force of the fixed magnetic film layer 22 is larger than that of the free magnetic film layer 24. can do. In order to ensure the spin injection magnetization reaction in the free magnetic film layer 24, the coercive force of the fixed magnetic film layer 22 is preferably 500 [Oe] or more.

  Here, the thickness of the cobalt film layer and the platinum film layer and the number of layers of the cobalt film layer and the platinum film layer are not particularly limited, but if the thickness of the cobalt film layer or the platinum film layer is too thin, Further, if the number of stacked layers is too small, the coercive force is lowered. On the other hand, if the thickness of the cobalt film layer or the platinum film layer is too thick, and if the number of stacked layers is too large, the perpendicular magnetic anisotropy is deteriorated. Therefore, the thickness of the cobalt film layer is preferably 0.4 to 1.5 nm, the thickness of the platinum film layer is preferably 0.8 to 1.5 nm, and the number of layers of the cobalt film layer and the platinum film layer is 3-20 are preferable for a cobalt film layer and a platinum film layer as a set. Note that the order of stacking the cobalt film layer and the platinum film layer is not particularly defined, and as shown in FIG. 2, the cobalt film layer may be disposed at the lowermost portion of the fixed magnetization film layer 22. May be placed at the bottom. Further, from the viewpoint of coercive force and perpendicular magnetic anisotropy, the thickness of the fixed magnetization film layer 22 is preferably 10 to 30 nm.

  As will be described later, when the free magnetic film layer 24 also has a multilayer structure in which cobalt film layers and platinum film layers are alternately stacked, the thickness of one of the platinum film layers constituting the free magnetic film layer 24 is as follows. Is made thinner than the thickness of one of the platinum film layers constituting the fixed magnetization film layer 22. With such a structure, the coercive force of the fixed magnetization film layer 22 can be further increased, and the coercivity of the fixed magnetization film layer 22 can be made larger than that of the free magnetization film layer 24.

Further, the interface layer (first interface layer) S ₁ that is a layer disposed at the interface between the fixed magnetization film layer 22 and the nonmagnetic intermediate film layer 23 is preferably formed of a cobalt film layer. A CoFeB alloy may also be used. By using a CoFeB alloy, a non-magnetic intermediate film layer 23, which will be described later, is passed through a tunnel current using an amorphous insulator such as alumina (Al ₂ O ₃ ), or coherent in combination with a (100) crystal of magnesia (MgO). By passing a simple tunnel current, the drive current can be reduced. In the case of the TMR structure using a very thin insulating layer (film thickness of 0.5 to 1.5 nm) for the nonmagnetic intermediate film layer 23, this is between the fixed magnetization film layer 22 and the nonmagnetic intermediate film layer 23 and freely. This is because the spin polarization ratio between the magnetic film layer 24 and the nonmagnetic intermediate film layer 23 greatly contributes to the reduction of the drive current. For example, in a Co / MgO / Co junction using a cobalt film layer (Co) as the interface layer and MgO as the nonmagnetic intermediate film layer 23, the spin polarization between Co and MgO becomes very large. A significant current reduction can be achieved. The thickness of the first interface layer S ₁ does not have to be equal to the thickness of one layer of cobalt film layer constituting the pinned magnetic layer 22, be in the range of 0.1 to 1 nm, the fixed magnetization The perpendicular magnetic anisotropy of the film layer 22 does not deteriorate.

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

Further, as the nonmagnetic intermediate film layer 23, an insulator such as magnesia (MgO) or alumina (Al ₂ O ₃ ) can be used. In this case, the structure of the light modulation element 11 is a tunnel current type magnetoresistive element (TMR element).

[Free magnetic film layer]
The free magnetic film layer 24 has a structure in which electrons injected are injected according to the direction of the voltage applied between the upper transparent electrode 12 and the lower electrode 13 (that is, according to the direction of the current flowing through the light modulation element 11). The direction of magnetization in the free magnetic film layer 24 is reversed by the interaction between the spin and the electron spin in the free magnetic film layer 24. The free magnetic film layer 24 uses a material having perpendicular magnetic anisotropy together with the fixed magnetic film layer 22.

  As shown in FIG. 2, the free magnetic film layer 24 is preferably a Co / Pt multilayer film. In this case, as described above, the thinner the platinum film layer, the smaller the coercive force, and the thicker the platinum film layer, the larger the coercive force. The thickness of one platinum film layer to be made is made thinner than the thickness of one platinum film layer constituting the fixed magnetization film layer 22. The coercive force needs to be smaller than the coercive force of the fixed magnetization film layer 22 so that the magnetization direction can be easily reversed when the direction of the applied current is changed. However, if the value is too small, the magnetic field may be reversed due to the influence of an external magnetic field or temperature.

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

Alternatively, the free magnetic film layer 24 may be composed of an intermetallic compound of a rare earth element and a transition element. Such an intermetallic compound exhibits a large magnetic Kerr effect when a voltage is applied even with a thin film thickness, and a large Kerr rotation angle (θ _K ) can be obtained. More specifically, GdFe (for example, Gd ₃₀ Fe ₇₀ ), TeFeCo (for example, Te _32.1 Fe _58.1 Co _9.8 ) and the like (numerical values indicate element ratio [at%]) are preferable. Used. These intermetallic compounds also have an advantage in that film formation is easy. By using these alloys, the free magnetization film layer 24 having low saturation magnetization (M _S ) can be formed. Therefore, it is possible to reduce the magnetization reversal current density J _C in proportion to the magnitude of M _S.

In GdFe, the magnetic moments of Gd and Fe are opposite to each other, and the composition determines whether the total magnetic moment is the direction of the magnetic moment of Gd or the direction of the magnetic moment of Fe. For example, in the case of Gd ₃₀ Fe ₇₀ , the total magnetic moment is in the direction of the magnetic moment of Gd.

  In addition, if the chemical and physical properties of rare earth elements are used, it is relatively easy to change the material in combination with transition metals, but rare earth elements can be obtained when the obtained magnetic properties are equivalent. It is preferable to use a material excellent in raw material cost and film formability.

Further, the free magnetic layer 24 and the nonmagnetic intermediate interface layer disposed at the interface of the membrane layer 23 (second interface layer) S ₂ is preferably formed with a cobalt layer. Further, a tunnel current is passed through the nonmagnetic intermediate film layer 23 using an amorphous insulator such as alumina (Al ₂ O ₃ ), or a coherent tunnel current is passed in combination with a (100) crystal of magnesia (MgO). Thus, a CoFeB alloy that can reduce the drive current may be used. The thickness of the second interface layer S ₂ need not be equal to the thickness of one layer of cobalt film layer constituting the free magnetic layer 24, be in the range of 0.1 to 1 nm, the free magnetization The perpendicular magnetic anisotropy of the film layer 24 does not deteriorate.

[Protective film layer]
The protective film layer 25 is a layer provided above the free magnetic film layer 24, that is, between the free magnetic film layer 24 and the upper transparent electrode 12 as necessary. The protective film layer 25 is a layer that plays a role in preventing damage such as oxidation of the free magnetic film layer 24, and in particular, oxidation of the free magnetic film layer 24 during heat treatment (described later) when forming the light modulation element 11. To prevent. The material constituting the protective film layer 25 is required to have a property that does not react with the material constituting the free magnetic film layer 24 during heat treatment. Further, the protective film layer 25 has excellent translucency and does not deteriorate the magnetic Kerr effect of the free magnetic film layer 24 (in other words, does not scatter the polarization plane of incident light and reflected light). It is required to be. Ta, Ru, or the like can be used as a material that satisfies such requirements. In particular, Ru is preferably used in the light modulation element 11 of the present invention because its resistivity does not increase even if it is oxidized itself. For the same reason, it can also be used as a protective layer of a magnetoresistive element in an MRAM (Magnetic Random Access Memory) or the like.

<Control device>
The lower electrode selection unit 82 includes a plurality of switching elements provided corresponding to the plurality of lower electrodes 13 respectively. Similarly to this, the upper electrode selector 83 includes a plurality of switching elements respectively provided corresponding to the plurality of upper transparent electrodes 12. A constant voltage is supplied to each switching element from a power source 81, and the switching element connected to the light modulation element 11 to be driven via the lower electrode 13 and the switching connected via the upper transparent electrode 12. When the element receives a command (operation signal) from the control unit 84 and performs a conduction operation, a voltage is applied to the light modulation element 11. Selection of the light modulation element 11 to be driven and operation control of the switching element for driving the light modulation element 11 are performed by the control unit 84.

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

<Polarizing filter>
3A and 3B, in the light indicated by the deflection axis 70, the deflection axis is directed in a random direction. The polarizing filter 17 serves to align the deflection axes so that light incident on the light modulation element 11 is in a predetermined direction indicated by the polarization axis 71. The polarizing filter 18 plays a role of transmitting or shielding the reflected light from the light modulation element 11 reflected by the half mirror 16 depending on the angle of the polarization axis. The states shown in FIGS. 3A and 3B will be described below with reference to FIG.

<Driving of light modulation element>
FIG. 3 schematically shows the relationship between the voltage application mode to the light modulation element and the magnetic Kerr effect of the free magnetic film layer in the first embodiment. FIGS. 3A and 3B show forms in which the positive and negative voltages applied to the lower electrode 13 and the upper transparent electrode 12 are reversed. The arrows shown in each of the underlayer 21, the fixed magnetic film layer 22, and the free magnetic film layer 24 shown in FIGS. 3A and 3B indicate the magnetization direction (spin direction).

As shown in FIG. 3A, when the current flows between the upper transparent electrode 12 and the lower electrode 13 from the upper transparent electrode 12 side to the lower electrode 13 side perpendicularly to the film layer surface, it is free. The magnetization (spin) direction in the magnetic film layer 24 is the same as the magnetization direction in the fixed magnetic film layer 22. On the other hand, as shown in FIG. 3B, when a current flows perpendicularly to the film layer surface from the lower electrode 13 side to the upper transparent electrode 12 side, the magnetization direction in the free magnetic film layer 24 is This is opposite to the direction of magnetization in the fixed magnetization film layer 22. Thus, the magnetization state in the free magnetic film layer 24 changes depending on the direction of the current flowing between the upper transparent electrode 12 and the lower electrode 13. This change in state of magnetization is extremely fast, from several ns to several tens ns (ns: nanoseconds). Although the magnitude of the current to flow varies depending on the area of the light modulation element 11, in the case of a CPP-GMR structure using a metal thin film such as Cu for the nonmagnetic intermediate film layer 23, the current required for magnetization reversal The density is about 10 ⁷ to 10 ⁸ A / cm ² . In addition, in the case of a TMR structure using a very thin insulating layer such as MgO for the nonmagnetic intermediate film layer 23, the value is about one digit lower than the above value.

  When incident light having a predetermined polarization axis indicated by the polarization axis 71 by passing through the polarization filter 17 is incident on each light modulation element 11 shown in FIGS. Due to the Kerr effect, the polarized light is reflected by a predetermined angle and emitted from each light modulation element 11. Here, with respect to the Kerr rotation angle, as in the case of the light modulation element 11 in FIG. 3A, the direction in which the right rotation indicated by the polarization axis 72 occurs is “positive direction (+ direction, + θ)”, and FIG. As in the case of the light modulation element 11 in (b), the direction in which the left rotation indicated by the polarization axis 72 occurs is defined as “negative direction (−direction, −θ)”.

  Therefore, when the half mirror 16 is arranged in the traveling direction of the reflected light, the reflected light is reflected by the half mirror 16. When a polarizing filter 18 having a polarization axis parallel to the polarization axis 72 is arranged in the traveling direction of the reflected light at the half mirror 16, the reflected light in the case of FIG. However, the reflected light in the case of FIG. 3B can create a state where it cannot pass through the polarizing filter 18. Since the light modulator 10 can selectively drive (apply voltage) the upper transparent electrode 12 and the lower electrode 13 as described above, and can pass a current to the desired light modulation element 11, The direction of magnetization of the free magnetic film layer 24 is controlled by the current direction for each light modulation element 11 (for each pixel), and depending on whether the reflected light is allowed to pass through the polarizing filter 18 or not reflected. The intensity (contrast) of reflected light can be controlled.

  The contrast ratio of the reflected light is determined by the magnitude of the magnetic Kerr effect (the magnitude of the Kerr rotation angle) by the free magnetic film layer 24. As shown in FIGS. 3A and 3B, when the reflected light is transmitted or shielded (that is, when the Kerr rotation angle is equal to or larger than a certain angle), a high contrast can be obtained. However, when the Kerr rotation angle is small, the contrast is low. In addition, when the direction of magnetization of the free magnetic film layer 24 is upward as shown in FIG. 3A, the output of the photodetector is in a “bright state”, and conversely, as shown in FIG. When the direction of magnetization of the layer is downward, it becomes a “dark state”.

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

[Second Embodiment]
The light modulation element according to the second embodiment changes the polarization direction of transmitted light with respect to the polarization direction of light incident on the free magnetization film layer by changing the magnetization state in the free magnetization film layer. . That is, the Faraday effect is used in which incident light is transmitted to the side opposite to the side on which incident light is incident and the polarization of the transmitted light is detected.

In the second embodiment, the polarizing filter 18 is disposed on the side opposite to the side on which the incident light is incident (see FIGS. 4A and 4B).
When a constant voltage is applied between the lower electrode 13 and the upper transparent electrode 12, the light modulation element 11 transmits the incident light incident on the light modulation element 11 by rotating the polarization plane of the incident light by a fixed angle by the Faraday effect. Take a role.

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

<Driving of light modulation element>
FIG. 4 schematically shows the relationship between the voltage application mode to the light modulation element and the Faraday effect of the free magnetic film layer in the second embodiment. FIGS. 4A and 4B show forms in which the positive and negative voltages applied to the lower electrode 13 and the upper transparent electrode 12 are reversed.
In addition, since the description about the direction of magnetization in the free magnetic film layer 24 is the same as that of the first embodiment, the description is omitted here.

  When incident light having a predetermined polarization direction indicated by the polarization axis 71 by passing through the polarization filter 17 is incident on each light modulation element 11 shown in FIGS. 4A and 4B, the free magnetic film layer 24 Due to the Faraday effect, the polarized light is transmitted through a predetermined angle and emitted from each light modulation element 11. Here, as in the case of the light modulation element 11 in FIG. 4A, the direction in which the clockwise rotation indicated by the polarization axis 72 occurs is “positive direction (+ direction, + θ)”, and the light in FIG. As in the case of the modulation element 11, the direction in which the left rotation indicated by the polarization axis 72 occurs is defined as “negative direction (−direction, −θ)”.

Therefore, when the polarizing filter 18 having a polarization axis parallel to the polarization axis 72 is arranged in the traveling direction of the transmitted light, the transmitted light in the case of FIG. 4A can pass through the polarizing filter 18. The transmitted light in the case of (b) can create a state where it cannot pass through the polarizing filter 18. Thus, the transmitted light that passes through the polarizing filter 18 is controlled by the direction of the current for each light modulation element 11 (for each pixel) by the direction of the current, and the transmitted light that can pass through the polarizing filter 18. The intensity of the reflected light (contrast) can be controlled depending on whether the transmitted light is transmitted or not transmitted.
Since other explanations are the same as those in the first embodiment, explanations are omitted here.

[Other Embodiments]
FIG. 5 schematically shows the structure of the light modulation element used in the light modulator according to another embodiment.
As shown in FIG. 5, it is preferable to provide a protective layer 60 between the light modulation element 11 and the lower electrode 13.
After film formation of the light modulation element 11, when heat treatment in the atmosphere (about 200 ° C.) is performed during the elementization process, when Cu is used as the material constituting the lower electrode 13, Cu is the fixed magnetization film layer 22. It diffuses in, and the perpendicular magnetic anisotropy deteriorates, and variations in device operation tend to occur.

  By providing the protective layer 60 between the light modulation element 11 and the lower electrode 13, the perpendicular magnetic anisotropy in the fixed magnetization film layer 22 is deteriorated even if the heat treatment necessary for the elementization process after film formation is performed. It can be surely prevented. Therefore, variation in element operation can be suppressed. Examples of the material constituting the protective layer 60 include Ta, W, Ru, Au, and the like. Moreover, from the viewpoint of coercive force and perpendicular magnetic anisotropy, the thickness of the protective layer 60 is preferably 1 to 3 nm.

  Further, as shown in FIG. 5, the thickness of one cobalt film layer constituting the free magnetic film layer 24 should be made thinner than the thickness of one cobalt film layer constituting the fixed magnetic film layer 22. preferable. The thinner the cobalt film layer, the smaller the coercive force, and the thicker the cobalt film layer, the larger the coercive force. Therefore, with such a structure, the coercive force of the fixed magnetization film layer 22 can be further increased, and the coercivity of the fixed magnetization film layer 22 can be made larger than that of the free magnetization film layer 24.

<Method for manufacturing optical modulator>
FIG. 6 schematically shows a method for manufacturing the optical modulator. Here, an example in which the base layer 21 and the protective film layer 25 are provided will be described.
First, the lower electrode 13 made of Cu or the like is formed on the surface of the substrate 14 (FIG. 6A). The lower electrode 13 is formed by, for example, forming a Cu film uniformly on the surface of the substrate 14 by sputtering or the like, and forming a resist pattern having the same line width as the lower electrode 13 on the Cu film. After the Cu film is dry-etched or the like until the substrate surface is exposed as an etching mask, the resist pattern is peeled off. Alternatively, the lower electrode 13 may be formed by a lift-off method in which the resist pattern is first formed by using a region where the lower electrode 13 is to be formed as a groove and the Cu film is formed by sputtering, and then the resist film is peeled off. Although the case where Cu is used as the lower electrode has been described here, Ta, Ru, or the like may be formed on the base of Cu in order to improve adhesion to the substrate. Further, a protective layer such as Ru may be formed on the Cu surface in order to prevent Cu from oxidizing due to exposure to the atmosphere for the process and increasing the resistivity of the lower electrode.

Subsequently, the groove between the lower electrodes 13 is filled with an insulating material (insulator 15) such as alumina or silicon oxide (FIG. 6B). The formation of the alumina film can be performed by a reactive sputtering method, a CVD method, a sol-gel method, or the like. If necessary, the surface including the lower electrode 13 is smoothed by a CMP process or the like. On the surface thus formed, the underlayer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 constituting the light modulation element 11 (in FIG. 3, the display for each layer is displayed. In this order, the layers of the light modulation element 11 are sequentially formed in this order by a sputtering method (for example, magnetron sputtering, ion beam sputtering) or the like with a predetermined film thickness for each layer [FIG. 6 (c). ]. In the formation of the fixed magnetic film layer 22 and the free magnetic film layer 24, for example, a sputtering apparatus having a structure in which a Co sputtering target and a Pt sputtering target can be mounted and a sputtering voltage can be selectively applied to these targets. By using this, a Co / Pt multilayer film can be easily formed. Further, in addition to magnetron sputtering and ion beam sputtering, MBE method capable of controlling one atomic layer can be used.
It should be noted that the lower electrode 13, the base layer 21, the fixed magnetic film layer 22, the nonmagnetic intermediate film layer 23, the free magnetic film layer 24, and the protective film layer 25 are sequentially formed on the substrate 14 using a known technique such as sputtering. The film may be formed consistently in a vacuum.

  Next, heat treatment is performed on the light modulation element 11 formed on the substrate 14 as necessary. This heat treatment is performed to improve the characteristics of the light modulation element 11 and to suppress changes in the characteristics of the light modulation element 11 during a photolithography process performed later. From the viewpoint of suppressing the deterioration of the characteristics of the light modulation element 11 during this heat treatment, it is also preferable to provide a Ru film having excellent oxidation resistance as the protective film layer 25 on the surface of the free magnetic film layer 24.

  Subsequently, a resist pattern 91 of, for example, 100 nm × 300 nm is formed on the heat-treated layer of the light modulation element 11 by an EB exposure method or the like so as to be a mesa pattern [FIG. 6D]. Using this resist pattern 91 as an etching mask, the layer of the light modulation element 11 is etched, and then the resist pattern 91 is removed [FIG. 6 (e)]. Thereby, the light modulation element 11 is formed. Next, the space between the light modulation elements 11 is filled with an insulating material (insulator 15) such as alumina or silicon oxide by a CVD method or the like, and the surface including the light modulation elements 11 is smoothed by CMP treatment or the like if necessary [FIG. 6 (f)]. Alternatively, the layer of the light modulation element 11 is etched or milled to the front of the lower electrode 13 by ion beam milling using Ar ions or the like, and then the groove formed by this etching is made of an insulating material (insulating material such as alumina or silicon oxide). Alternatively, a method of filling with the body 15) and then lifting off (peeling the resist pattern 91) or performing CMP may be used. When performing the CMP process or the like, the thickness of the protective film layer 25 (or the uppermost layer of the fixed magnetic film layer 22) formed on the uppermost part of the light modulation element 11 is set to a predetermined value at the time of film formation. It may be formed thicker by the polishing thickness.

  The upper transparent electrode 12 is formed at a predetermined interval so as to cover the light modulation element 11 and to be orthogonal to the line pattern of the lower electrode 13 (FIG. 6G). The upper transparent electrode 12 can be formed in the same manner as the lower electrode 13 is formed. By using such a manufacturing method, the light modulator 10 in which the fine light modulation elements 11 are arranged at a high density can be manufactured, the display speed is high, and high-definition images and video can be expressed.

<Display device>
FIG. 7 shows a schematic configuration diagram of a display device using the optical modulator according to the embodiment of the present invention. 7A is a schematic configuration diagram of a display device using the optical modulator according to the first embodiment, and FIG. 7B is a schematic configuration diagram of a display device using the optical modulator according to the second embodiment. is there. As shown in FIGS. 7A and 7B, the display device 30 is a color-compatible display device 30 using the light modulator 10, and includes the light modulator 10, the RGB time-division illuminator 19, and the like. Polarizing filters 17 and 18 and a screen 29 are provided. In the form of FIG. 7A, a half mirror 16 is provided.

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

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

《Holography device》
FIG. 8 shows a schematic structure of a holography device compatible with a stereoscopic moving image using the optical modulator according to the embodiment of the present invention. In FIG. 8, the detailed structure of the optical modulator 10 is omitted, and the control device 80 is not shown.

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

  In the holography device 40, first, when inputting an image, the laser light emitted from the laser light source 31 is expanded by the beam expander 32 and then converted into parallel light by the lens 33. The laser light (parallel light) is divided into light for illuminating the subject to be object light by the half mirror 34 and reference light. Object light, which is reflected light from the subject, is emitted to the CCD camera 38 side through the lens 36 and the half mirror 37. On the other hand, the reference light is reflected by the mirror 35 and the half mirror 37. Thus, the object light emitted from the half mirror 37 and the reference light are combined to form interference fringes. The interference fringe pattern is imaged by the CCD camera 38. In FIG. 8, the optical path of the light emitted from the lens 33 is simply indicated by a single line.

  In reproducing an image by the holography device 40, first, the laser light emitted from the laser light source 41 is expanded by the beam expander 42, the light is made parallel by the lens 45, and the parallel light is incident on the optical modulator 10. Let On the other hand, an image signal in which the interference fringe pattern is recorded is input from the CCD camera 38 to the control device 80 (not shown in FIG. 8) of the optical modulator 10. When the control device 80 drives the light modulation element 11 according to the input signal, light modulation corresponding to the image signal of the interference fringe pattern is performed, and a stereoscopic image can be reproduced. In the holography device 40, the use of the light modulator 10 makes it possible to reproduce a high-definition stereoscopic image at a high display speed.

<Hologram recording device>
FIG. 9 shows a schematic structure of a hologram recording apparatus using the optical modulator according to the embodiment of the present invention. In FIG. 9, the detailed structure of the optical modulator 10 is omitted. In FIG. 9, only the traveling direction of light is shown, and illustration of a change in the spatial width of light by a lens or the like is omitted.

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

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

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

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

<First embodiment>
In the first example, the Kerr rotation angle (θ _K ) of the free magnetic film layer was examined.
In the manufacture of a light modulation element, first, a lower electrode, a fixed magnetic film layer, a nonmagnetic intermediate film layer, a free magnetic film layer, and a protective film layer are formed on a silicon substrate with an oxide film in this order by using a sputtering method. The film was formed consistently. Next, after forming a pixel-sized resist on the protective layer, milling was performed to the front of the lower electrode by an ion beam milling method using Ar ions. Thereafter, SiO ₂ was deposited on the entire surface without peeling off the resist, and the resist was lifted off. Thereafter, a transparent electrode made of IZO was formed on the top.

When the fixed magnetization film layer has a multilayer structure of a platinum film layer and a cobalt film layer (Co / Pt multilayer film), the film thickness of the platinum film layer is 1.5 nm, and the film thickness of the cobalt film layer is 0.00. The thickness was 4 nm, and a multilayer structure including four platinum film layers and four cobalt film layers was used. When TbFeCo was used, the film thickness was 20 nm. The configuration of the nonmagnetic interlayer film was Cu (6 nm) for the CPP-GMR type, and MgO (1 nm) for the tunnel type. When the free magnetic film layer is a Co / Pt multilayer film, the platinum film layer has a thickness of 0.8 nm and the cobalt film layer has a thickness of 0.3 nm. A multilayer structure including five layers was formed. When GdFe and Co ₂ FeSi were used, the film thicknesses were 10 nm and 6 nm, respectively. The configuration of the protective film layer was Ru (3 nm).

Then, the Kerr rotation angle (θ _K ) of the reflected light when the laser beam with a wavelength of 400 nm was irradiated was examined for the two patterns in which the magnetic direction of the free magnetic film layer was changed (see FIG. 3).
The results are shown in Table 1. In Table 1, 2θ _K is θ ₁ + θ ₂ . GdFe has perpendicular magnetic anisotropy, and Co ₂ FeSi has in-plane magnetic anisotropy.

As shown in Table 1, when the free magnetization layer was Co / Pt multilayered film, the free magnetization layer is, as compared with that of GdFe, it is found that can increase the theta _K. It can also be seen that θ _K can be significantly increased as compared with Co ₂ FeSi having in-plane magnetic anisotropy.

<Second embodiment>
In the second example, the relationship between the film thickness of one platinum film layer and the coercivity of the Co / Pt multilayer film when the fixed magnetization film layer is a Co / Pt multilayer film was examined.

FIG. 10A shows a schematic configuration of the Co / Pt multilayer film used in the second embodiment. As shown in FIG. 10A, the film thickness (t _Co ) per layer of the cobalt film layer (indicated as Co in the figure) constituting the Co / Pt multilayer film is all 0.4 nm, and the platinum film A multilayer structure including four layers and four cobalt film layers was used. In addition, a protective film layer (shown as Ru in the figure) made of Ru having a thickness of 3 nm was provided on the top. The substrate is a silicon substrate subjected to surface thermal oxidation treatment.

Then, the film thickness (t _Pt ) per layer of the platinum film layer (shown as Pt in the figure) was changed, and the coercive force (Oe) of the Co / Pt multilayer film was measured. The coercive force was evaluated by measuring the magnetic Kerr effect by measuring the Kerr rotation angle (θ _k ) of reflected light when the sample was irradiated with polarized light and the magnetic field applied from the outside was changed. A hysteresis loop with the magnetic field (H) applied from the outside as the horizontal axis, + H → −H → + H, and θ _k as the vertical axis is plotted on the graph, and the magnitude of the coercive force is calculated from the intersection with the horizontal axis. Estimated.
The results are shown in FIG.

  As shown in FIG. 11, the coercive force increased as the film thickness per layer of the platinum film layer increased.

<Third embodiment>
In the third example, the relationship between the thickness of the underlayer when the underlayer was provided and the coercivity of the Co / Pt multilayer film was examined.

FIG. 10B shows a schematic configuration of the Co / Pt multilayer film used in the third embodiment. As shown in FIG. 10B, the film thickness (t _Co ) per layer of the cobalt film layer (Co) constituting the Co / Pt multilayer film is all 0.4 nm, and the platinum film layer (Pt) The film thickness per layer (t _Pt ) was 1 nm, and a multilayer structure including four platinum film layers and four cobalt film layers was used. The lowermost platinum film layer of these four layers was used as an underlayer. In addition, a protective film layer (Ru) made of Ru having a thickness of 3 nm was provided on the top. The substrate is a silicon substrate subjected to surface thermal oxidation treatment.
Then, the coercive force (Oe) of the Co / Pt multilayer film was measured in the same manner as in the second example when the film thickness of the platinum film layer as the underlayer was 1 to 30 nm.
The results are shown in FIG.

  As shown in FIG. 12, it was found that when the film thickness of the underlayer was increased, the coercive force was increased, and the coercive force was saturated when the film thickness was 10 nm or more.

(A) is a top view which shows typically schematic structure of the optical modulator which concerns on one Embodiment of this invention, (b) is AA sectional view taken on the line shown to (a), (c). FIG. 3 is a diagram schematically showing the structure of a light modulation element used in an optical modulator. It is a figure which shows typically the specific structure of a light modulation element. It is a figure which shows typically the relationship between the voltage application form to the light modulation element in 1st Embodiment which concerns on this invention, and the Kerr effect of a free magnetic film layer, (a), (b) is a lower electrode and upper part, respectively. It is a schematic diagram at the time of reversing the positive / negative of the voltage applied to a transparent electrode. It is a figure which shows typically the relationship between the voltage application form to the light modulation element in 2nd Embodiment which concerns on this invention, and the Faraday effect of a free magnetic film layer, (a), (b) is a lower electrode and upper part, respectively. It is a schematic diagram at the time of reversing the positive / negative of the voltage applied to a transparent electrode. It is a figure which shows typically the structure of the light modulation element used for the light modulator in other embodiment. It is a figure which shows the manufacturing method of an optical modulator typically, and (a)-(g) is the schematic diagram which showed the structure in a predetermined | prescribed manufacturing stage, respectively. (A) is a schematic block diagram of the display apparatus using the optical modulator in 1st Embodiment which concerns on this invention, (b) is a display apparatus using the optical modulator in 2nd Embodiment which concerns on this invention. It is a schematic block diagram. 1 is a schematic structural diagram of a holographic device that supports stereoscopic video using an optical modulator according to the present invention. 1 is a schematic structural diagram of a hologram recording apparatus using an optical modulator according to the present invention. (A) is a schematic configuration diagram mainly showing the configuration of the Co / Pt multilayer film in the second embodiment, and (b) is a schematic configuration diagram mainly showing the configuration of the Co / Pt multilayer film in the third embodiment. is there. It is a graph which shows the relationship between the film thickness of one layer of the platinum film layer which comprises a Co / Pt multilayer film, and the coercive force of a Co / Pt multilayer film. It is a graph which shows the relationship between the film thickness of a base layer at the time of providing a base layer, and the coercive force of a Co / Pt multilayer film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light modulator 11 Light modulator 12 Upper transparent electrode 13 Lower electrode 14 Substrate 16 Half mirror 17, 18 Polarizing filter 19 RGB time division illuminator 21 Underlayer 22 Fixed magnetization film layer 23 Nonmagnetic interlayer film layer 24 Free magnetization film layer DESCRIPTION OF SYMBOLS 25 Protective film layer 30 Display apparatus 40 Holography apparatus 50 Hologram recording apparatus 60 Protective layer 70 Polarization axis 71 (Positive direction) Rotated polarization axis 72 (Negative direction) Rotated polarization axis

Claims (7)

A fixed magnetization film layer, a nonmagnetic intermediate film layer, and a free magnetization film layer have a spin-injection magnetization reversal element structure laminated in this order, and magnetic directions in the fixed magnetization film layer and the free magnetization film layer Is a direction perpendicular to the film surface, and the polarization direction of the reflected or transmitted light is changed with respect to the polarization direction of the light incident on the free magnetization film layer by changing the magnetization state in the free magnetization film layer. A light modulation element,
The pinned magnetization layer may have a cobalt layer and the platinum layer are alternately laminated, wherein the free magnetic layer is, have a cobalt layer and the platinum layer are alternately laminated And the platinum constituting the fixed magnetization film layer is formed such that a thickness of one of the platinum film layers constituting the free magnetization film layer is smaller than a thickness of one of the platinum film layers constituting the fixed magnetization film layer. A light modulation element , wherein the thickness of one of the film layers is 0.8 to 1.5 nm . The light modulation element according to claim 1, wherein the free magnetic film layer is an intermetallic compound of a rare earth element and a transition element. Wherein the lower side of the fixed magnetic layer, the light modulation element according to claim 1 or claim 2 characterized by having a base layer composed of a platinum film layer of a thickness of not less than 5 nm. Optical modulator, wherein the light modulation elements arranged in a two-dimensional array according to any one of claims 1 to 3. An optical modulator according to claim 4 ;
And a screen for projecting light emitted from the light modulator. Imaging means for photographing interference fringes formed by the object light and the reference light;
A holography apparatus comprising: an image reproducing unit that reproduces an image signal recorded in the imaging unit using the optical modulator according to claim 4 . A hologram recording apparatus for recording predetermined information on a recording medium using two systems of light,
An optical modulator according to claim 4 ;
Imaging means for detecting, as phase information, a state change in the recording medium when the two systems of light are incident on the recording medium;
A hologram recording apparatus characterized in that, based on the phase information detected by the imaging means, at least one of the two systems of light is modulated using the light modulator.

Images