JP5836857B2 - Light modulator and spatial light modulator - Google Patents

Description

  The present invention relates to a light modulation element of a spatial light modulator that spatially modulates incident light by using a magneto-optic effect, and to a spatial light modulator using the light modulation element.

  A spatial light modulator uses an optical element (light modulation element) as a pixel and arranges it in a two-dimensional matrix to spatially modulate the phase, amplitude, etc. of light. Widely used in fields such as equipment, display technology, and recording technology. In addition, since optical information can be processed in two dimensions in parallel, its application to optical information processing technology is also being studied. As a spatial light modulator, liquid crystal has been conventionally used and widely used as a display device, but for holography and optical information processing, since response speed and high definition of pixels are insufficient, in recent years, Development of a magneto-optic spatial light modulator using a magneto-optic material that is expected to be capable of high-speed processing and pixel miniaturization is in progress.

  In a magneto-optical spatial light modulator (hereinafter referred to as a spatial light modulator), when light incident on a magneto-optical material, that is, a magnetic material is transmitted or reflected, the direction of polarization is changed (rotation) and emitted. The effect (Kerr effect in the case of reflection) is used. That is, the spatial light modulator emits light from the selected pixel with the magnetization direction of the light modulation element in the selected pixel (selected pixel) different from the magnetization direction of the light modulation element in the other pixels (non-selected pixels). The light and the light emitted from the non-selected pixels cause a difference in the rotation angle (rotation angle) of the polarization. As a method of changing the magnetization direction of such a light modulation element, in addition to a magnetic field application method in which a magnetic field is applied to the light modulation element, in recent years, a spin injection method in which spin is injected by supplying a current to the light modulation element ( For example, there is Patent Document 1).

  Specifically, the spin injection type light modulation element is a TMR (Tunnel MagnetoResistance) element or a CPP-GMR (Current Perpendicular to the Plane Giant MagnetoResistance) element. A spin-injection magnetization reversal element that is also applied to a magnetoresistive random access memory (MRAM) can be applied. As an example, a cross-sectional view of such a conventional light modulation element is shown in FIG. As shown in FIG. 14, the light modulation element 101 is connected to a pair of electrodes 151 and 152 on the upper and lower sides and supplied with a current perpendicular to the film surface. With this current, the light modulation element 101 is injected with spin, and the magnetization direction of the magnetization free layer 103 can be reversed in the same manner as in the MRAM write. The light modulation element 101 functions as a pixel that modulates and emits incident light by forming at least one electrode (the upper electrode 152 in FIG. 14) from a transparent electrode material. An optical modulation element to which such a spin-injection magnetization reversal element is applied enables further miniaturization than a magnetic field application method in which electrodes (wirings) are provided along the outer periphery of each optical modulation element in order to generate a magnetic field. .

  Further, as another aspect of the light modulation element, Patent Document 2 discloses a spatial light modulator that uses a thin line-processed magnetic body (magnetic fine wire) as a light modulation element. This is because in magnetic thin wires, two or more magnetic domains are easily formed in the thin line direction, and the domain walls that delimit these magnetic domains move by supplying current to the magnetic thin line in the thin line direction. doing. More specifically, this spatial light modulator is provided with one magnetic thin line for each pixel along the surface direction (two-dimensional array surface of the pixels), and a current is applied in the thin line direction by a pair of electrodes connected to both ends thereof. When supplied, the domain wall moves in the direction opposite to the direction of the current, and the magnetization direction in the area sandwiched between the positions before and after the domain wall movement is reversed, so this area is reflected light as the light incident area (effective area). Can be taken out.

Japanese Patent No. 4829850 JP 2010-20114 A

  The light modulation elements described in Patent Documents 1 and 2 have room for improvement in the following points. In the spin-injection magnetization switching element applied to the light modulation element of Patent Document 1, since electrodes for supplying a current are connected vertically, in order to enter and output light as a light modulation element, light input / output On the side, a transparent electrode material that transmits light must be applied. Since the transparent electrode material is greatly inferior in conductivity as compared with the metal electrode material, there is a possibility that the operation is delayed in the central portion as the high-definition spatial light modulator has a larger number of light modulation elements arranged in a matrix. In order to operate such a spatial light modulator, it is necessary to supply a large current, and there is room for improvement in terms of power saving. Furthermore, since it is difficult for the spin injection magnetization reversal element to operate properly (spin injection magnetization reversal) unless the side is about 300 nm or less, the size of the light modulation element with respect to the wiring pitch is reduced. As a result, the effective region in which light modulation is performed in the pixel Ratio (pixel aperture ratio) becomes low.

  On the other hand, in the magnetic thin wire applied to the light modulation element of Patent Document 2, both of the pair of electrodes to be connected can be formed of a metal electrode material, but the magnetization direction is different from the magnetization direction in the opening region across the domain wall. Magnetic domains are formed. Therefore, the light that can be extracted as pixel information in the magnetic thin line is limited to the reflected light from the region sandwiched between the positions of the central domain wall before and after the movement, and the aperture ratio of the pixel is limited.

Furthermore, the spatial light modulator may be capable of error detection that electrically detects whether each light modulation element of the pixel performs light modulation according to the setting, that is, indicates the magnetization direction as written. desirable. For example, in the light modulation element 101 to which the spin injection magnetization reversal element shown in FIG. 14 is applied, the magnetization direction of the magnetization fixed layer 111 and the magnetization free layer 103 is the same (parallel: P, see FIG. 14A). than the resistance R101 _P of the opposite: greater resistance R101 towards _AP when a (antiparallel AP, Fig 14 (b) refer). Therefore, the spatial light modulator described in Patent Document 1 supplies a current that does not cause spin injection magnetization reversal to the light modulation element 101 and reads the voltage between the electrodes 151 and 152 in the same manner as the read in the MRAM. By measuring the magnetization direction of the magnetization free layer 103. On the other hand, since the resistance of the magnetic thin wire hardly changes even when the domain wall moves, it is difficult for the spatial light modulator described in Patent Document 2 to detect the write error.

  The present invention was devised in view of the above problems, and when a pixel of a spatial light modulator is used, a transparent electrode material is not used for wiring, and the pixel aperture ratio is sufficiently maintained and further miniaturized and further written. It is an object to provide an optical modulation element that facilitates error detection and a spatial light modulator using the same.

  The inventors of the present application have used the dual pin structure spin injection magnetization reversal element 101A (see, for example, Japanese Patent Application Laid-Open No. 2010-60748) shown in a sectional view in FIG. The two fixed layers 111 and 112 are stacked on the same side surface of the magnetization free layer 103 so as to be spaced apart from each other in the plane direction, thereby forming a U-shaped current path in cross section with the magnetization free layer as a bottom. We have developed a light modulation device consisting of a spin-injection magnetization reversal device with a dual pin structure. A spin-injection magnetization reversal element having a dual pin structure has a structure in which two spin-injection magnetization reversal elements are connected so as to share a magnetization free layer, and a pair of electrodes are connected to two magnetization fixed layers at both ends of the U-shape. Then, the spin injection magnetization reversal operation can be performed. Therefore, a light modulation element using a spin injection magnetization reversal element having a parallel dual pin structure can enter light into the magnetization free layer at the bottom of the U-shape without transmitting through the electrodes. Both can be formed of a metal electrode material. Further, the area of the light modulation element can be expanded to twice that of the conventional spin injection magnetization reversal element, and the effective area of the pixel can be widened.

  On the other hand, in the spin-injection magnetization reversal element having a dual pin structure, the magnetization direction of the magnetization free layer is always parallel to one of the two magnetization fixed layers and antiparallel to the other, If the structure is the same, the overall resistance is constant, making it difficult to detect write errors. Accordingly, the inventors of the present application have conceived that the write error can be detected by changing the resistance of the two spin-injection magnetization reversal elements from each other.

  That is, the light modulation element according to the present invention includes a spin-injection magnetization reversal element structure in which a magnetization free layer, an intermediate layer, and a magnetization fixed layer are sequentially laminated on a substrate, and is incident from the side on which the magnetization free layer is laminated. The reflected light is reflected and emitted by changing the direction of the polarized light. The magnetization pinned layer has a first magnetization pinned layer and a second magnetization pinned layer which are spaced apart in the plane direction and pinned in magnetizations in antiparallel directions on the magnetization free layer, and the intermediate layer Has an intermediate layer on which the first magnetization fixed layer is stacked and an intermediate layer on which the second magnetization fixed layer is stacked, and has different resistances, and the light modulation element has the first magnetization fixed A magnetization direction of the magnetization free layer is changed by connecting a pair of electrodes to the layer and the second magnetization fixed layer and supplying a current.

  With this configuration, the light modulation element can be enlarged as the area of two spin-injection magnetization reversal elements, and furthermore, no two magnetization fixed layers connecting the electrodes are arranged on the light incident side, so that the magnetization reversal The transparent electrode material need not be applied to the electrode that supplies the current for operation. In addition, since the optical modulation element includes two spin-injection magnetization reversal element structures that have different resistance change rates due to different resistances of the intermediate layer, the entire optical modulation element of the light modulation element is affected by the magnetization reversal of the magnetization free layer. The resistance value changes. Therefore, the light modulation element can detect the magnetization direction of the magnetization free layer by measuring the resistance between the pair of electrodes connected for the magnetization reversal operation.

Furthermore, in the light modulation element, it is preferable that at least one of the two intermediate layers is a tunnel barrier layer.
With this configuration, the light modulation element is a TMR element in which at least one of the two spin-injection magnetization reversal element structures has a relatively large resistance change rate and the resistance change rate depends on the resistance of the intermediate layer. The change in the resistance value due to the magnetization reversal of the layer becomes remarkable, and the write error detection becomes easier.

Further, in the light modulation element, it is preferable that the first magnetization fixed layer and the second magnetization fixed layer have different coercive forces. Alternatively, the light modulation element preferably has a multilayer structure including a magnetic film in which at least one of the first magnetization fixed layer and the second magnetization fixed layer is exchange-coupled.
With this configuration, it becomes easy to fix the two magnetization fixed layers in the light modulation element in the magnetization directions antiparallel to each other.

  The light modulation element can be a pixel of a spatial light modulator by connecting a pair of electrodes. That is, the spatial light modulator according to the present invention includes a substrate that transmits light and a plurality of pixels that are two-dimensionally arranged on the substrate, and transmits light incident on the plurality of pixels through the substrate. The pixel is provided with a pair of electrodes connected to the light modulation element and the first magnetization fixed layer and the second magnetization fixed layer of the light modulation element. Then, the spatial light modulator selects one or more pixels from the plurality of pixels, and further selects one of two different directions of magnetization directions of the magnetization free layer of the light modulation element for the selected pixels. And a current supply means for supplying a current to the light modulation element of the pixel selected by the pixel selection means so that the magnetization direction of the magnetization free layer of the light modulation element is selected by the pixel selection means And pixel determination for determining that the magnetization direction of the magnetization free layer of the light modulation element to which the current supply means has supplied current is the direction selected by the pixel selection means, and the resistance of the light modulation element And a pixel determination unit that detects the change. In the spatial light modulator, the pixel may include two or more light modulation elements connected in parallel to a pair of electrodes.

  Furthermore, the spatial light modulator may include a sub-current supply unit that supplies a predetermined current to the light modulation element of the pixel selected by the pixel selection unit. In this spatial light modulator, the pixel determination unit calculates a voltage value between the pair of electrodes connected to the light modulation element to which a current is supplied to the sub-current supply unit. The pixel determination is performed by comparing with a threshold value set in advance based on the resistance of the light modulation element when the magnetization direction is the direction selected by the pixel selection means.

  With this configuration, the spatial light modulator is configured with two spin-injection magnetization reversal element structures, and the pixel includes a light modulation element that does not connect the electrode to the light incident side. Therefore, the light is applied to the pixel with a high aperture ratio. It can enter without being blocked by. The spatial light modulator is connected to the magnetization fixed layers of the two spin-injection magnetization reversal element structures when the pixel selection unit selects a pixel and supplies current from the current supply unit to the light modulation element. Since the spin injection is performed through the connected electrodes, the shared magnetization free layer can be reversed by spin injection magnetization so that a desired magnetization direction corresponding to the direction of current is obtained for each pixel. Furthermore, the spatial light modulator can diagnose whether the pixel determination unit has normally reversed the magnetization of the magnetization free layer of the light modulation element in the desired magnetization direction by the current supply unit. Specifically, in the spatial light modulator, the pixel selection unit selects a pixel, and supplies a current of a predetermined magnitude that does not perform a spin injection magnetization reversal operation from the sub-current supply unit to the light modulation element via the electrode. Then, since the voltage changes in a specific range due to the resistance of the light modulation element, the pixel determination means compares the value of this voltage with a preset threshold value to determine which magnetization direction the magnetization free layer is in. Can be determined.

  Furthermore, the spatial light modulator may be configured such that the pixel includes a selection element that can freely disconnect electrical connection with the electrode in the first magnetization fixed layer or the second magnetization fixed layer. With this configuration, the spatial light modulator can suppress current leakage to the light modulation element of the non-selected pixel, and thus diagnosis by the pixel determination unit is facilitated.

  According to the light modulation element of the present invention, the magnetization reversal operation can be suitably performed even when the area is expanded, and the transparent electrode material need not be used for the electrode to be connected when used for the pixel of the spatial light modulator. Therefore, it is easy to miniaturize while increasing the aperture ratio of the pixels of the spatial light modulator. Also, according to the light modulation element of the present invention, the resistance changes due to the magnetization reversal operation. Therefore, the pixel determination (write error) using the electrode for the magnetization reversal operation is used for the pixel of the spatial light modulator. Detection).

  According to the spatial light modulator according to the present invention, since all the wiring can be formed using only the metal electrode material by using the light modulation element in a pixel, high definition and power saving can be achieved. Furthermore, the aperture ratio of the pixel can be increased to achieve high contrast. Further, according to the spatial light modulator according to the present invention, it is possible to perform a read operation similar to that of the MRAM by using a driving wiring, and it is possible to detect a write error for each of all pixels.

It is a bottom view of the spatial light modulator using the light modulation element which concerns on this invention, and is a schematic diagram explaining the structure of the spatial light modulator which concerns on 1st Embodiment of this invention. It is a schematic diagram explaining the cross-sectional structure of the light modulation element which concerns on this invention, and is equivalent to the AA fragmentary sectional view of FIG. It is sectional drawing of the light modulation element which concerns on this invention, and is a schematic diagram explaining magnetization reversal operation | movement. It is sectional drawing of the light modulation element which concerns on this invention, and is a schematic diagram explaining the operation | movement of light modulation, and the change of resistance. It is a schematic diagram of the display apparatus using the spatial light modulator which concerns on this invention, and is equivalent to AA sectional drawing of FIG. 1 is an equivalent circuit diagram of a spatial light modulator according to a first embodiment of the present invention. It is a schematic diagram explaining the manufacturing method of the spatial light modulator which concerns on this invention, (a)-(e) is corresponded in the AA fragmentary sectional view of FIG. It is a schematic diagram explaining the manufacturing method of the spatial light modulator which concerns on this invention, (a)-(d) is equivalent to the AA fragmentary sectional view of FIG. 1, (e) is a top view in (d). It is. It is a schematic diagram explaining the manufacturing method of the spatial light modulator which concerns on this invention, (a)-(e) is corresponded in the AA fragmentary sectional view of FIG. It is a schematic diagram explaining the manufacturing method of the spatial light modulator which concerns on this invention, (a), (b), (d) is equivalent to the AA fragmentary sectional view of FIG. 1, (c) is (b FIG. It is a bottom view explaining the structure of the pixel of the spatial light modulator which concerns on 2nd Embodiment of this invention. It is a schematic diagram of the pixel array of the spatial light modulator which concerns on 3rd Embodiment of this invention, and its modification, (a) is a bottom view of 3rd Embodiment, (b) is BB cross section of (a). FIG. 4C is a modification of the third embodiment and corresponds to a cross-sectional view taken along the line BB in FIG. FIG. 6 is an equivalent circuit diagram of a spatial light modulator according to a fourth embodiment of the present invention. It is sectional drawing of the conventional light modulation element using a spin injection magnetization reversal element, and is a schematic diagram explaining the operation | movement of magnetization reversal and light modulation. It is a cross-sectional view of a conventional light modulation element using a spin-injection magnetization reversal element having a dual pin structure and is a schematic diagram for explaining the magnetization reversal operation.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for realizing a light modulation element and a spatial light modulator according to the present invention will be described with reference to the drawings.

[Light modulation element]
The light modulation element according to the present invention is used as the pixel 8 of the spatial light modulator 10 shown in FIG. 1 (refers to means for displaying information (light / dark) in the minimum unit of display by the spatial light modulator). Thus, the light incident from below is reflected, modulated into different binary light (polarized component), and emitted downward.

  As shown in FIG. 2, the light modulation element 1 includes one magnetization free layer 3, two intermediate layers 21 and 22 (first intermediate layer and second intermediate layer), and two magnetization fixed layers 11 and 12 ( A first magnetization pinned layer and a second magnetization pinned layer). In this light modulation element 1, a magnetization free layer 3 is formed on a substrate 7 that transmits light, and two intermediate layers 21 and 22 are stacked on the magnetization free layer 3 so as to be spaced apart from each other in the plane direction. In addition, the first magnetization fixed layer 11 is stacked on the first intermediate layer 21, and the second magnetization fixed layer 12 is stacked on the second intermediate layer 22. The light modulation element 1 further includes protective films 41 and 42 stacked on the magnetization fixed layers 11 and 12, respectively. Here, the light modulation element 1 has a concave shape in cross section. The light modulation element 1 shown in FIG. 2 is formed on a substrate 7, and a first electrode (electrode) 51 and a second electrode (electrode) 52 are formed as a pair of electrodes through two protective films 41 and 42. It is connected to the magnetization fixed layers 11 and 12. The intermediate layers 21 and 22, the magnetization fixed layers 11 and 12, and the protective films 41 and 42 are shown at the same thickness and the same height in the cross-sectional views of FIG. 2 and other drawings. It does not stipulate that the height positions are the same, and may be formed with different thicknesses and at different height positions.

  In plan view, as shown in FIG. 1, the light modulation element 1 is a square (rectangular). Therefore, the magnetization free layer 3 is the same square as the light modulation element 1. On the other hand, the intermediate layers 21 and 22 and the magnetization fixed layers 11 and 12 are rectangles (regions shaded in FIG. 1) whose long sides are the same length as the light modulation element 1 (magnetization free layer 3). Two are arranged apart from each other in the short side direction (lateral direction in FIGS. 1 and 2). With respect to the size in plan view, the magnetization fixed layers 11 and 12 and the intermediate layers 21 and 22 below each have an area equivalent to 300 nm × 400 nm in order to suitably perform the magnetization reversal operation described later by the light modulation element 1. Preferably, the area is equivalent to about 300 nm × 100 nm, which is one size of a general spin-injection magnetization switching element. On the other hand, the entire area of the light modulation element 1, that is, the area of the magnetization free layer 3 is not particularly defined, and even if it is expanded in the film surface direction with respect to the total area of the magnetization fixed layers 11 and 12, the magnetization will be described later. Can be reversed. Specifically, when the light modulation element 1 is two-dimensionally arranged as a pixel array of a spatial light modulator (see FIG. 1), the adjacent light modulation elements 1 and 1 are insulated with a gap therebetween. That's fine.

  The light modulation element 1 has a structure in which two spin-injection magnetization reversal elements are connected by sharing a magnetization free layer. That is, the light modulation element 1 includes a spin injection magnetization reversal element structure (hereinafter, referred to as a first element structure MR1 as appropriate) composed of a first magnetization fixed layer 11, a first intermediate layer 21, and a magnetization free layer 3, and a second It can be said that a spin-injection magnetization reversal element structure (hereinafter, appropriately referred to as a second element structure MR2) including the magnetization fixed layer 12, the second intermediate layer 22, and the magnetization free layer 3 is provided (see FIG. 3A).

  In the element structures MR1 and MR2, the magnetization fixed layers 11 and 12 whose magnetization is fixed in one direction and the magnetization free layer 3 whose magnetization direction can be rotated are sandwiched by intermediate layers 21 and 22 which are nonmagnetic or insulators. A spin injection magnetization reversal element structure such as a CPP-GMR (Current Perpendicular to the Plane Giant Magneto-Resistance) element or a TMR (Tunnel MagnetoResistance) element. In particular, it is preferable that one of the two spin-injection magnetization switching element structures in the light modulation element 1 is a TMR element and the other is a CPP-GMR element, or both are TMR elements. In the present embodiment, the first element The structure MR1 is a TMR element, and the second element structure MR2 is a CPP-GMR element. Further, the light modulation element 1 is provided with protective films 41 and 42 on the uppermost layer in order to protect these layers from damage during manufacture of the light modulation element 1. Hereafter, each element which comprises a light modulation element is demonstrated in detail.

(Magnetic pinned layer)
The magnetization fixed layers 11 and 12 are magnetic bodies, and the magnetization is fixed in directions opposite to each other. Such magnetization fixed layers 11 and 12 can be made of a known magnetic material used for CPP-GMR elements and TMR elements, and in particular, the optical rotation angle θk is increased by the polar Kerr effect of the magnetization free layer 3. It is preferable to apply a perpendicular magnetic anisotropic material. Specifically, a multilayer film such as a Co / Pd multilayer film in which transition metals such as Fe, Co, and Ni and noble metals such as Pd and Pt are repeatedly stacked, and a rare earth such as Tb—Fe—Co and Gd—Fe. an alloy of the metal and the transition metal (RE-TM alloy), FePt was L1 ₀ type ordered alloys, FePd, and the like.

Further, the magnetization fixed layers 11 and 12 have their coercive forces Hcp ₁ and Hcp ₂ having magnetization free layers so that the magnetizations of the magnetization fixed layers 11 and 12 are fixed even when the magnetization direction of the magnetization free layer 3 rotates. Each material is selected so as to be sufficiently larger than the coercive force Hcf of 3 or thicker than the magnetization free layer 3. Specifically, the thickness of the magnetization fixed layers 11 and 12 is preferably designed in the range of 3 to 50 nm.

Since the magnetization fixed layers 11 and 12 are fixed to magnetizations in opposite directions, the coercive forces Hcp ₁ and Hcp ₂ are used as the coercive force of the magnetization free layer 3 in order to facilitate the initial setting of such magnetization directions. In addition to being larger than Hcf, it is preferably designed to have different sizes. Here, the coercive force Hcp _{2 of} the second magnetization fixed layer 12 is larger, that is, Hcf << Hcp ₁ <Hcp ₂ . Therefore, the magnetization fixed layers 11 and 12 may have different materials and thicknesses. Or as shown in the modification (refer FIG.12 (c)) of 3rd Embodiment of a spatial light modulator mentioned later, it is good also as a different area (plan view shape).

(Magnetization free layer)
The magnetization free layer 3 is a magnetic material, and the magnetization fixed layers 11 and 12 have a fixed magnetization direction, whereas the magnetization free layer 3 can easily reverse the magnetization (rotate 180 °) by spin injection. The magnetization direction is the same as any one of the magnetization fixed layers 11 and 12. The magnetization free layer 3 can be made of the above-mentioned known magnetic material, and it is preferable to apply a perpendicular magnetic anisotropic material, like the magnetization fixed layers 11 and 12. In particular, it is more preferable to select a material having a large magneto-optic effect at the wavelength of light incident on the light modulation element 1 (pixel of the spatial light modulator) for the magnetization free layer 3. For example, a Co / Pt multilayer film is suitable for the short wavelength region (near 400 nm), and a Gd—Fe alloy is suitable for the long wavelength region (near 700 nm).

Further, as described above, the magnetization free layer 3 is made of a material selected so that the coercive force Hcf is smaller than the coercive forces Hcp ₁ and Hcp _{2 of} the magnetization fixed layers 11 and 12, or from the magnetization fixed layers 11 and 12. Is also formed thin. Specifically, the thickness of the magnetization free layer 3 is preferably designed in the range of 1 to 20 nm.

(Middle layer)
The first intermediate layer 21 is provided between the first magnetization fixed layer 11 and the magnetization free layer 3, and the second intermediate layer 22 is provided between the second magnetization fixed layer 12 and the magnetization free layer 3. In the light modulation element 1 according to the present invention, the first intermediate layer 21 and the second intermediate layer 22 are formed with different materials and thicknesses so as to have different resistances. Specifically, since it is preferable that the intermediate layers 21 and 22 have resistances that differ by a factor of two or more, one different type is selected from nonmagnetic metals, insulators, and semiconductors.

Furthermore, as described above, it is preferable that at least one of the spin-injection magnetization switching element structures is a TMR element. Therefore, at least one of the intermediate layers 21 and 22, here, the first intermediate layer 21 is MgO, Al ₂ O ₃ , HfO. ₂ and a laminated film containing an insulator such as Mg / MgO / Mg. The first intermediate layer 21 becomes a tunnel barrier layer by including such an insulator, and the first element structure MR1 including the first magnetization fixed layer 11, the first intermediate layer 21, and the magnetization free layer 3 has the same structure as the TMR element. Become. At this time, the thickness of the first intermediate layer 21 is preferably about 0.6 to 2 nm, and more preferably 1 nm or less. On the other hand, the second intermediate layer 22 is made of a nonmagnetic metal such as Cu, Ag, Al, or Au, or a semiconductor such as ZnO. Therefore, the second element structure MR2 including the second magnetization fixed layer 12, the second intermediate layer 22, and the magnetization free layer 3 has a CPP-GMR element structure. At this time, the thickness of the second intermediate layer 22 is preferably 1 to 10 nm.

(Protective film)
The protective films 41 and 42 are provided in the uppermost layer in order to protect each layer such as the magnetization fixed layers 11 and 12 from damage during the manufacture of the light modulation element 1. The protective films 41 and 42 are composed of a single layer of Ta, Ru, Cu, or two layers of Cu / Ta, Cu / Ru. In addition, when setting it as the said 2 layer structure, all make Cu inside (lower layer). When the thickness of the protective films 41 and 42 is less than 1 nm, it is difficult to form a continuous film. On the other hand, even if the thickness exceeds 10 nm, the effect of protecting the magnetization fixed layers 11 and 12 and the like in the manufacturing process is reduced. It does not improve above. Therefore, the thickness of the protective films 41 and 42 is preferably 1 to 10 nm. The material and thickness of the protective films 41 and 42 may not be the same.

(Magnetic reversal operation of the light modulator)
Next, the magnetization reversal operation of the light modulation element in this embodiment will be described with reference to FIG. In FIG. 3, the protective films 41 and 42 are not shown. In the light modulation element 1, the magnetization is fixed to the first magnetization fixed layer 11 upward and the second magnetization fixed layer 12 downward.

First, the operation of the light modulation element 1 for reversing the magnetization free layer 3 from the downward magnetization shown in FIG. 3A to the upward magnetization shown in FIG. 3C will be described. As shown in FIG. 3B, the current −I _W is supplied from the power source 95, and the first electrode 51 connected to the first magnetization fixed layer 11 is connected to “−” and the second magnetization fixed layer 12. The second electrode 52 is set to “+”, and electrons are injected from the first magnetization fixed layer 11 side. Then, the first magnetization fixed layer 11 discriminates electrons d ₂ having a downward spin opposite to the magnetization of the first magnetization fixed layer 11, and only the electron d ₁ having an upward spin from the first electrode 51. Is injected into the first magnetization fixed layer 11 and further injected into the magnetization free layer 3 through the first intermediate layer 21. In the magnetization free layer 3, the spin of internal electrons of the magnetization free layer 3 is reversed by the spin torque due to the upward spin of the electron d ₁ , and the magnetization is directed upward from the region immediately below the first magnetization fixed layer 11. Invert. Further, the electrons d ₁ injected into the magnetization free layer 3 remain in the magnetization free layer 3 because the magnetization is discriminated by the second magnetization fixed layer 12 in the reverse direction, and as a result, as shown in FIG. In addition, the magnetization free layer 3 includes not only the region where the magnetization fixed layers 11 and 12 are stacked, but also the region sandwiched between these two regions, that is, the entire region is the same as the magnetization direction of the first magnetization fixed layer 11. Changes to a state showing the same upward magnetization (magnetization reversal).

Next, the operation of the light modulation element 1 for reversing the magnetization free layer 3 from the upward magnetization shown in FIG. 3C to the downward magnetization shown in FIG. Contrary to the operation shown in FIG. 3 (b), as shown in FIG. 3 (d), the current + I _W is supplied from the power source 95, the first electrode 51 is set to “+”, and the second electrode 52 is supplied. Is set to “−”, and electrons are injected from the second magnetization fixed layer 12 side. Then, only the electrons d ₂ having a downward spin are injected into the magnetization free layer 3 through the second intermediate layer 22, and the spin torque due to the downward spin of the electrons d ₂ acts on the inside of the magnetization free layer 3. The spin of electrons is reversed, and the magnetization is reversed downward from the region immediately below the second magnetization fixed layer 12. Further, the electrons d ₂ injected into the magnetization free layer 3 remain in the magnetization free layer 3 because the magnetization is discriminated by the first magnetization fixed layer 11 in the reverse direction, and as a result, the magnetization free layer 3 is shown in FIG. As shown to (a), the whole changes to the state which shows the downward magnetization same as the magnetization direction of the 2nd magnetization fixed layer 12 (magnetization reversal).

As described above, the light modulation element 1 in the present embodiment is paired with each of the two magnetization fixed layers 11 and 12 stacked on the same side (upper side) of the magnetization free layer 3 with the intermediate layers 21 and 22 interposed therebetween. By connecting the electrodes 51 and 52 and supplying a current −I _W (or + I _W ), the magnetization direction of the magnetization free layer 3 can be changed (magnetization reversed). Therefore, the light modulation element 1 in the present embodiment is shared with each of the two spin injection magnetization reversal element structures, that is, the magnetization fixed layers 11 and 12 and the intermediate layers 21 and 22 as a small area suitable for spin injection magnetization reversal. In the magnetization free layer 3, the domain wall moves in the direction of the film surface through which the current flows to reverse the magnetization, so that the magnetization free layer 3 can be formed in a large area. Further, since the light modulation element 1 is driven by spin injection by the two magnetization fixed layers 11 and 12, the magnetization reversal operation becomes stable. The magnitudes | I _W | of the currents −I _W and + I _W may be equal to or greater than the current (magnetization reversal current) I _{STS that} reverses the magnetization of the magnetization free layer 3 of the light modulation element 1. This magnetization reversal current I _STS may be larger than the magnetization reversal currents I1 _STS and I2 _STS of the two spin-injection magnetization reversal element structures MR1 and MR2 of the light modulation element 1, or −I _W ≦ −I1 _STS , + I _W ≧ + I2 The size may be different from _STS, and is determined by the area of the element structures MR1 and MR2, the material and thickness of each layer, and the like.

Here, if the difference between the magnetization reversal currents I1 _STS and I2 _STS of the two spin-injection magnetization reversal element structures MR1 and MR2 is too large, for example, if I1 _STS << I2 _STS , a current greater than or equal to I2 _STS Is supplied to the light modulation element 1 as at least + I _W , an excessive current flows through the first element structure MR1, which is a high-resistance TMR element, and the first intermediate layer 21 may be destroyed. . Therefore, the light modulation element 1 is preferably designed so that the difference between the magnetization reversal currents I1 _STS and I2 _STS of the element structures MR1 and MR2 is within 100 times.

3A and 3C, the light modulation element 1 is supplied with a current + I _W when the magnetization free layer 3 exhibits downward magnetization, or on the contrary, the magnetization free layer 3 Even if the current −I _W is supplied when showing upward magnetization, the magnetization direction of the magnetization free layer 3 does not change. Further, in the light modulation element 1, even when the current supply is stopped when the magnetization direction of the magnetization free layer 3 is uniform upward or downward, the magnetization direction changes due to the coercive force Hcf of the magnetization free layer 3 itself. There is no. Therefore, a current that temporarily reaches a current value (≧ I _STS ) that reverses the magnetization direction, such as a pulse current, can be used as the drive current of the light modulation element 1.

(Light modulation operation of light modulation element)
Next, the light modulation operation of the light modulation element 1 will be described with reference to FIG. When the light incident on the light modulation element 1 is reflected by the magnetization free layer 3 that is a magnetic material, the direction of polarization of the light changes (rotates) due to the magneto-optic effect, and the light is emitted. Further, if the magnetization direction of the magnetic material is different by 180 °, the direction of optical rotation due to the magneto-optical effect of the magnetic material is reversed. Therefore, the optical rotation angles in the light modulation elements 1 shown in FIGS. 4A and 4B, in which the magnetization directions of the magnetization free layer 3 are 180 ° different from each other, are −θk and + θk, and the planes of polarization rotate in opposite directions. . As described above, the light modulation element 1 functions as a pixel of a spatial light modulator or the like described later by changing the direction of polarization of the emitted light in accordance with the direction (positive / negative) of the supplied current I _W. The optical rotation angles −θk and + θk are not limited to optical rotation (Kerr rotation) by one reflection at the light modulation element 1, and include, for example, angles accumulated by multiple reflection.

As described above, the light modulation elements according to the present invention are provided in a two-dimensional array as pixels of the spatial light modulator. Here, a spatial light modulator having a structure in which a large number of pixels are regularly arranged in a two-dimensional manner, when light traveling straight and having a parallel wavefront is incident on each pixel, the spatial light modulator at the end of the pixel. The direction in which the light travels is bent (diffraction phenomenon), and the direction in which the light is strengthened is separated into multiple lines by the interference effect (wave strengthening and weakening) due to the emitted light. This diffraction phenomenon, ± 1-order bent at an angle of diffraction angle phi _n with respect to the rectilinear direction of the incident light, ± 2-order, · · ·, ± n order diffracted light is generated (n is 0 or a natural number ). The diffraction angle φ _n depends on the wavelength λ of incident light and the pixel pitch p. When applying a spatial light modulator to a holographic device, first-order diffracted light is generally used. The 0th-order diffracted light at n = 0 is equivalent to reflected light that is reflected at the same angle as the incident angle in the reflective spatial light modulator (in the case of a transmissive spatial light modulator, the rectilinear direction of the incident light). Is equivalent to transmitted light in the same direction). Therefore, in the present specification, the description will be made assuming that the reflected light (emitted light) emitted from the light modulation element (pixel of the spatial light modulator) includes the n-th order diffracted light. Also in this diffracted light, a change in polarization direction (optical rotation) due to the Faraday effect or the Kerr effect occurs depending on the magnetization direction of the magnetic material (magnetization free layer).

  The light modulation element 1 according to the present invention receives light from the side of the magnetization free layer 3, that is, from below, reflects the light, and emits it downward. Therefore, as shown in FIG. 2, the light modulation element 1 is formed on the transparent substrate 7, and light transmitted through the substrate 7 is incident thereon. Since the electrodes 51 and 52 provided on the magnetization fixed layers 11 and 12 do not need to transmit light, a low-resistance metal material can be applied (described in an embodiment of the spatial light modulator described later). To do).

(Resistance change of light modulation element)
Next, a change in resistance due to the magnetization reversal of the light modulation element in the present embodiment will be described with reference to FIG. The light modulation element 1 shown in each of FIGS. 4A and 4B is in the same magnetization state as the light modulation element 1 shown in FIGS. 3A and 3B. As will be described in detail later, in FIG. 4, the current I _TST supplied to the optical modulation element 1 from the sub power supply 96 is smaller than the magnetization reversal current I _STS and changes the magnetization state of the optical modulation element 1. is not. As described above, the light modulation element 1 includes the two spin-injection magnetization reversal element structures MR1 and MR2 (see FIG. 3A).

In the light modulation element 1 shown in FIG. 4A, the magnetization direction of the magnetization free layer 3 is downward and the magnetization direction of the first magnetization fixed layer 11 is antiparallel, that is, the magnetization of the first element structure MR1 is antiparallel (AP). (See FIG. 14B). The resistance of the first element structure MR1 at this time is expressed as R1 _AP. At the same time, in the light modulation element 1 shown in FIG. 4A, the magnetization free layer 3 has a magnetization direction parallel to the second magnetization fixed layer 12, that is, the magnetization of the second element structure MR2 is parallel (P) (FIG. 14A ))). The resistance of the second element structure MR2 in this case represented as R2 _P. The entire resistance R _D of the light modulation element 1 is the sum of the resistances of the spin-injection magnetization switching element structures MR1 and MR2, and is expressed by the following expression (1).
R _D = R1 _AP + R2 _P (1)

On the other hand, in the light modulation element 1 shown in FIG. 4B, the magnetization direction of the magnetization free layer 3 is upward, the magnetization direction of the first magnetization fixed layer 11 is parallel, and the magnetization is parallel (P). the resistance of the device structure MR1 represented as R1 _P. At the same time, the light modulation element 1 shown in FIG. 4B has a second element structure MR2 in which the magnetization free layer 3 is antiparallel to the second magnetization fixed layer 12 and the magnetization direction is antiparallel (AP). _Is represented by R2AP. The overall resistance R _U of the optical modulation element 1 is represented by the following formula (2).
R _U = R1 _P + R2 _AP (2)

The spin-injection magnetization reversal element has higher resistance when the magnetization is antiparallel than when parallel. The amount of change in resistance due to the magnetization reversal of each of the spin-injection magnetization reversal element structures MR1 and MR2 is expressed as ΔR1 and ΔR2 (> 0). Then, from the following equations (3) and (4), the resistances R _D and R _U of the light modulation element 1 are converted into the following equations (5) and (6). As a result, the resistance change ΔR due to the magnetization reversal of the light modulation element 1 is expressed by the following equation (7).
ΔR1 = R1 _AP −R1 _P (3)
_{ΔR2 = R2 AP -R2 P ··· (} 4)
R _D = R1 _P + ΔR1 + R2 _P (5)
R _U = R1 _P + R2 _P + ΔR2 (6)
ΔR = | ΔR1−ΔR2 | (7)

Here, in general, the rate of change in resistance ((R101 _AP -R101 _P ) / in the spin-injection magnetization reversal element (light modulation element) 101 (see FIG. 14) is a TMR element rather than a CPP-GMR element. R101 _P) is large. That is, in the light modulation element 1 according to the present embodiment, the resistance change ΔR1 of the first element structure MR1 that is a TMR element is more than the resistance change ΔR2 of the second element structure MR2 that is a CPP-GMR element. large. Therefore, in the light modulation element 1, the difference between ΔR1 and ΔR2 is sufficiently large (ΔR1 >> ΔR2) regardless of the difference between the element resistances R1 _P and R2 _P of the spin injection magnetization reversal element structures MR1 and MR2. R _D >> R _U , and the resistance change amount ΔR (= ΔR1−ΔR2) >> 0.

As described above, the light modulation element 1 changes to different resistances R _D and R _U by the magnetization reversal operation similarly to the general spin injection magnetization reversal element as shown in FIG. Since the resistance value can be measured from the electrodes 51 and 52 connected for driving (magnetization reversal operation) of the light modulation element 1, the light modulation element 1 is provided with a separate electrode for measuring the resistance value. There is no need to connect. Details of the method of measuring the resistance value of the light modulation element 1 will be described later in the description of the write error detection method (pixel determination) of the spatial light modulator.

As another embodiment of the light modulation element 1, both of the two spin injection magnetization reversal element structures MR1 and MR2 may be TMR elements. In general, when the spin-injection magnetization switching element (light modulation element) 101 (see FIG. 14) is a TMR element, the resistance change amount (R101 _AP -R101 _P ) increases as the resistance of the intermediate layer 102 increases. Tend to be. Accordingly, the intermediate layers 21 and 22 are insulators or laminated films including insulators, and have different structures and thicknesses of the insulators so as to have different resistances. The difference between the resistance changes ΔR1 and ΔR2 can be made sufficiently large.

Furthermore, as another embodiment of the light modulation element 1, the magnetization fixed layers 11 and 12 are provided with a multilayer having a magnetic film in which at least one of them is exchange-coupled instead of providing a difference in the coercive forces Hcp ₁ and Hcp _2. It is good also as a structure. Specifically, the magnetization fixed layers 11 and 12 are obtained by further laminating a Co—Fe film or a laminated film such as Co—Fe / Tb—Fe—Co with a magnetic exchange coupling film such as Ru interposed therebetween. It is good also as a multilayer structure about a layer. For example, from the side of the intermediate layers 21 and 22, a Co—Fe / Ru / Co in which a perpendicularly magnetized film having a large coercive force such as Tb—Fe—Co is stacked on a three-layer structure of Co—Fe / Ru / Co—Fe. A four-layer structure of -Fe / Tb-Fe-Co can be formed. In such a multilayer structure, the magnetic films sandwiching the magnetic exchange coupling film exhibit anti-parallel or parallel magnetization directions depending on the thickness of the magnetic exchange coupling film.

  For example, the first magnetization fixed layer 11 is a single layer of Co—Fe (5 nm), and the second magnetization fixed layer 12 is Co—Fe (2 nm) / Ru (0.7 nm) / from the second intermediate layer 22 side. A three-layer structure of Co—Fe (5 nm) is adopted. In addition, () shows thickness. When a magnetic field is applied to such a light modulation element 1, the magnetization direction of the Co-Fe film having a thickness of 5 nm in each of the magnetization fixed layers 11 and 12 is aligned with the direction of the applied magnetic field, and the intermediate layer 22 side of the magnetization fixed layer 12 The magnetization direction of the 2 nm thick Co—Fe film is an antiparallel magnetization direction. Alternatively, when a magnetic exchange coupling film is provided on both the magnetization fixed layers 11 and 12, the second magnetization fixed layer 12 has the same three-layer structure as described above, and the first magnetization fixed layer 11 is from the first intermediate layer 21 side. A three-layer structure in which the thickness of each layer of Co—Fe (5 nm) / Ru (0.7 nm) / Co—Fe (2 nm) is changed is adopted. Even when a magnetic field is applied to such a light modulation element 1, the magnetization direction of the Co-Fe film having a thickness of 5 nm is aligned in the direction of the magnetic field, and the magnetization direction of the Co-Fe film having a thickness of 2 nm across the Ru film is Since the magnetization directions are antiparallel, the magnetization directions of the Co—Fe films on the intermediate layers 21 and 22 of the magnetization fixed layers 11 and 12 are antiparallel to each other. Since at least one of the magnetization fixed layers 11 and 12 has such a multilayer structure, the magnetization fixed layers 11 and 12 (magnetic films on the side of the intermediate layers 21 and 22 in the multilayer structure) can be easily magnetized in directions opposite to each other. Can be initialized. Such a light modulation element 1 is also provided in the pixel 8 of the spatial light modulator 10 because the magnetization free layer 3 undergoes magnetization reversal to perform a light modulation operation and the resistance changes as described above. Can do.

  Furthermore, as another embodiment of the light modulation element 1, the magnetization fixed layers 11 and 12 and the magnetization free layer 3 may be formed of an in-plane magnetic anisotropic material. Specifically, transition metals such as Ni, Fe, Co, Ni-Fe, Ni-Fe-Mo, Co-Cr, Co-Fe, Co-Fe-B, Co-Fe-Si, Co-Fe Examples thereof include transition metal alloys such as —Ge or alloys of transition metals such as Co—Pt and noble metals. Alternatively, a Mn-containing magnetic alloy having a large magneto-optical effect such as a Mn—Bi alloy, a Mn / Bi multilayer film, a Pt—Mn—Sb alloy, or a Pt / Mn—Sb multilayer film can be used. Further, when the magnetization fixed layers 11 and 12 have a multilayer structure including a magnetic film in which at least one of them is exchange-coupled, for example, Co—Fe / Ru / Co—Fe / Ir—Mn from the intermediate layers 21 and 22 side. 4 layer structure. Instead of the uppermost Ir—Mn, an antiferromagnetic material such as Fe—Mn or Pt—Mn can be used.

  The magnetization fixed layers 11 and 12 having such in-plane magnetic anisotropy have magnetization fixed in one direction in the in-plane direction and the opposite direction. For example, in the light modulation element 1 having a planar view shape shown in FIG. The rectangular fixed magnetization layers 11 and 12 are preferably fixed in the long side direction (longitudinal direction in FIG. 1). As in the case of perpendicular magnetic anisotropy, such a light modulation element 1 has a magnetization direction in which the magnetization free layer 3 is parallel to one of the magnetization fixed layers 11 and 12 and antiparallel to the other by magnetization reversal. In addition, the resistances of the intermediate layers 21 and 22 are different from each other, so that the resistance changes with the magnetization reversal operation (not shown).

  As described with reference to FIG. 3, the element structures MR1 and MR2 of the light modulation element 1 are reversed in spin injection magnetization by bipolar (bipolar) driving, but have a unipolar (single polarity) driving type spin injection magnetization reversal element structure. You may apply. As an example, the magnetization described in Yuta Otsuka et al., “Spin-injection magnetization reversal by unipolar current”, Proceedings of the 59th Joint Lecture on Applied Physics in Spring 2012, 17p-B4-8, February 2012. Examples thereof include a spin-injection magnetization reversal element in which a specific ferrimagnetic material is applied to the free layer. By applying such a spin-injection magnetization reversal element to the element structures MR1 and MR2, the light modulation element 1 supplies a binary magnitude of current in one direction, so that the magnetization direction of the magnetization free layer is directed upward from below. In addition, the magnetization reversal operation in both the upward and downward directions is possible (not shown).

  As described above, the light modulation element according to the present invention has a magnetization reversal operation stabilized by two magnetization fixed layers and can increase the entire area. The rate can be increased. Furthermore, since the light modulation element according to the present invention is a magnetoresistive effect element whose resistance changes due to magnetization reversal, it is easy to detect the magnetization direction of the magnetization free layer, and it can be used only as a pixel such as a spatial light modulator. However, the present invention can be applied to a memory element for MRAM similarly to a conventional spin transfer magnetization switching element.

[Spatial light modulator]
(First embodiment)
Next, an embodiment of the spatial light modulator including the light modulation element according to the present invention in a pixel will be described with reference to the drawings.
As shown in FIG. 1, the spatial light modulator 10 according to the first embodiment of the present invention includes a substrate 7, a pixel array 80 including pixels 8 arranged in a two-dimensional array on the substrate 7, and a pixel array. A current control unit 90 that selects and drives one or more pixels 8 from 80 is provided. FIG. 1 is a bottom view from the substrate 7 side. In the pixel 8, the first electrode 51 is arranged on the substrate 7 side, that is, below the second electrode 52, and further on the substrate 7 below the light modulation element. 1 is arranged (see FIGS. 2 and 5). The light incident surface of the spatial light modulator 10 is a bottom surface (lower surface), and the spatial light modulator 10 modulates the light transmitted through the substrate 7 and incident on the pixel 8 (pixel array 80) from below to move downward. A reflective spatial light modulator that emits light (see FIG. 5).

  In the present embodiment, the pixel array 80 is exemplified by a configuration including 16 pixels 8 of 4 rows × 4 columns for the sake of brevity. The pixel array 80 includes four first electrodes 51 extending in the Y direction (vertical direction in FIG. 1) in plan (bottom) view, and an X direction (in FIG. 1) orthogonal to the first electrode 51 in plan view. And four second electrodes 52 extending in the lateral direction).

  Here, as described above, the light modulation element 1 provided in the pixel 8 of the spatial light modulator 10 has a pair of electrodes 51 and 52 on the magnetization fixed layers 11 and 12 formed on the same plane and spaced apart from each other. Connected as an electrode. Further, in the pixel array 80, the light modulation element 1 is arranged with the alignment direction of the magnetization fixed layers 11 and 12 set in the X direction. Therefore, the first electrode 51 extending in the Y direction orthogonal to the arrangement direction and connected to the first magnetization fixed layer 11 is adjacent to the second magnetization fixed layer (on the right or left adjacent light modulation element 1). 12 is formed in a strip-like wiring having a width that does not contact 12, and is provided at a height position directly connected on the light modulation element 1 as shown in FIGS. 2 and 5. On the other hand, the second electrode 52 that extends in the X direction and is connected to the second magnetization fixed layer 12 has a strip-like wiring (wiring portion 52a) that is the same as or wider than the light modulation element 1, and has the first magnetization. An interlayer insulating layer (insulating) is formed on the first electrode 51 (on the side away from the light modulation element 1) so as not to prevent the connection between the fixed layer 11 and the first electrode 51 and to prevent a short circuit with the first electrode 51. Provided with member 6) in between. The wiring portion 52a is connected to a connection portion 52c formed in a region immediately above the second magnetization fixed layer 12 through an interlayer connection portion 52b (contact). As described above, in the pixel array 80, the electrodes 51 and 52 are provided to be shared by the pixels 8 in a column unit and a row unit so as to be orthogonal to each other. Therefore, the first electrode 51 is appropriately used as the X electrode 51 and the second electrode 52. Is referred to as Y electrode 52. Furthermore, the pixel array 80 is blank between the adjacent light modulation elements 1 and 1, between the X electrodes 51 and 51, between the Y electrodes 52 and 52, and between the X electrode 51 and the Y electrode 52, that is, in FIG. An insulating member 6 is formed in the represented area.

(Light modulation element)
The light modulation element 1 has the configuration already described, and a description thereof is omitted. Here, all the light modulation elements 1 provided in the pixel array 80 are fixed so that the first magnetization fixed layer 11 faces upward and the second magnetization fixed layer 12 faces downward (see FIG. 5). The magnetization free layer 3 rotates the polarization direction of the incident light by an angle of + θk when the magnetization direction is upward and −θk when the magnetization direction is downward (see FIG. 4). The light modulation element 1 may include a base film made of a metal thin film between the substrate 7 (under the magnetization free layer 3) in order to obtain adhesion to the substrate 7 (not shown). Such a base film is preferably made of a nonmagnetic metal material such as Ta, Ru, or Cu and has a thickness of 1 to 10 nm. If the base film has a thickness of less than 1 nm, it is difficult to form a continuous film. On the other hand, if the thickness exceeds 10 nm, light entering and exiting is absorbed and efficiency is lowered.

(electrode)
Since both the X electrode 51 and the Y electrode 52 are disposed on the opposite side of the light incident / exit side with respect to the light modulation element 1 (magnetization free layer 3), the X electrode 51 and the Y electrode 52 are made of a low-resistance metal material without blocking light. Can be formed. Therefore, the X electrode 51 and the Y electrode 52 are formed of a general metal electrode material such as a metal such as Cu, Al, Au, Ag, Ta, or Cr, or an alloy thereof. Then, it is processed into a desired shape such as a stripe shape by a known method such as a sputtering method, by film formation, photolithography, etching, lift-off method, or the like.

(substrate)
The substrate 7 is a base for two-dimensionally arranging the pixels 8, and is a broad substrate for manufacturing the light modulation element 1. Further, since the spatial light modulator 10 according to the present embodiment emits light from the substrate 7 side, the substrate 7 is made of a material that transmits light. As such a substrate 7, a known transparent substrate material can be applied, and specifically, SiO ₂ (silicon oxide, glass), MgO (magnesium oxide), sapphire, GGG (gadolinium gallium garnet), SiC (silicon carbide). A Ge (germanium) single crystal substrate or the like can be applied. Further, on the substrate 7, a dielectric (such as Si—N (silicon nitride), ZnO (zinc oxide), HfO ₂ (hafnium oxide), ZrO ₂ (zirconium oxide)) having a high refractive index with respect to the substrate 7 ( An insulator) layer may be provided, and the light modulation element 1 may be formed thereon. Alternatively, a transparent oxide semiconductor (transparent conductor) layer having a high refractive index such as ITO (indium tin oxide) or IZO (indium zinc oxide) is formed on the substrate 7, and SiO ₂ (glass) is formed thereon. A dielectric (insulator) layer such as Si—N (silicon nitride) may be stacked, and the light modulation element 1 may be further formed thereon. Further, a multilayer film in which the transparent oxide semiconductor (conductor) layer and the dielectric (insulator) layer are alternately stacked may be formed, and the light modulation element 1 may be formed thereon (not shown). ). The light reflected by the light modulation element 1 (magnetization free layer 3) is reflected at the interface between the dielectric layer and the substrate 7 and is incident on the light modulation element 1 again. Until the light is emitted, the optical modulation element 1 repeats the optical rotation many times and the optical rotation angle is accumulated to increase, thereby improving the contrast between light and dark.

(Insulating material)
The insulating member 6 is provided between the magnetization fixed layers 11 and 12 and the intermediate layers 21 and 22 (between the element structures MR1 and MR2) of the light modulation element 1 and between the adjacent light modulation elements 1 and 1 and between the X electrodes 51 and 51. Are provided to insulate the Y electrodes 52, 52 and the interlayer between the X electrode 51 and the Y electrode 52, respectively. For the insulating member 6, for example, an oxide film such as SiO ₂ or Al ₂ O ₃ or a known insulating material such as Si ₃ N ₄ can be applied.

(Current controller)
As shown in FIG. 1, the current control unit 90 includes an X electrode selection unit 91 that selects the X electrode 51, a Y electrode selection unit 92 that selects the Y electrode 52, and a power source that supplies current to the electrodes 51 and 52 ( Current supply means) 95, and a power source 95 and a pixel selection section (pixel selection means) 94 for controlling the electrode selection sections 91 and 92. A known device capable of the operations described below can be applied to each of these. Further, the current control unit 90 includes a sub power source (sub current supply unit) 96 that supplies current to the electrodes 51 and 52, and a determination unit (pixel determination unit) 97 that detects a pixel writing error. As will be described later, a device similar to the power source 95 can be applied to the sub power source 96 except that the magnitude of the supplied current is different. The determination unit 97 includes a voltage comparator 97a and an inspection unit 97b. As will be described later, the voltage comparator 97a applies a known read circuit in the MRAM, and the inspection unit 97b applies a so-called CPU that performs arithmetic processing. be able to.

The pixel selection unit 94 selects one or more specific pixels 8 of the pixel array 80 based on, for example, an external signal (not shown), and electrodes based on the X and Y coordinates in the pixel array 80 of the selected pixel 8. The selection units 91 and 92 are made to select the electrodes 51 and 52, and further, the direction of the current supplied by the power source 95 is selected. As shown in FIG. 6, the X electrode selection unit 91 selects one or more of the X electrodes 51 according to a command from the pixel selection unit 94 (represented by the circled number 94 in the figure), and the Y electrode selection unit 92. Selects one or more of the Y electrodes 52 and connects the power source 95 to the selected electrodes 51, 52. The power source 95 is a known power source that supplies an appropriate voltage / current for reversing the magnetization of the light modulation element 1 provided in the selected pixel 8, and can supply a DC pulse current so that it can be inverted. Then, the power source 95 supplies the positive or negative current (+ I _W / −I _W ) selected by the pixel selection unit 94 to the light modulation element 1 through the connected electrodes 51 and 52. With such a configuration, the spatial light modulator 10 selects a desired pixel 8 from the pixel array 80 and supplies a pulse current of a predetermined magnitude to the light modulation element 1 of the pixel 8 in the selected direction. Thus, the magnetization free layer 3 is set to a desired magnetization direction. The magnetization reversal operation of the light modulation element 1 is as described with reference to FIG. The magnetization reversal operation of the light modulation element 1 of the selected pixel 8 changes the magnetization direction of the magnetization free layer 3 of the light modulation element 1, so that the light incident on the selected pixel 8 can be selectively selected. The light can be emitted after being modulated in the direction of polarization (described in detail in the light modulation operation of the spatial light modulator described later (see FIG. 5)).

Further, the pixel selection unit 94 connects a sub power source 96 in place of the power source 95 to the selected electrodes 51 and 52 to supply a predetermined current I _TST smaller than the magnetization reversal current I _STS of the light modulation element 1. Can do. In the determination unit 97, the voltage comparator 97 a is connected in parallel with the sub power supply 96, and the voltage between the electrodes 51 and 52 when the current I _TST is supplied to the light modulation element 1 is referred to as a reference potential (threshold) Vref. In comparison, the result is output to the inspection unit 97b (not shown in FIG. 6). This comparison result indicates the actual magnetization direction of the magnetization free layer 3 of the light modulation element 1, and the inspection unit 97b determines whether the magnetization direction indicated by the comparison result is the magnetization direction selected by the pixel selection unit 94. Write error detection to be verified. The voltage comparator 97a receives a voltage between the electrodes 51 and 52, and outputs a differential sense amplifier SA (see FIG. 6) that outputs 1 or 0 higher or lower than the reference potential Vref, or a reference potential. A Vref output circuit (not shown) is provided, and a known read circuit in the MRAM can be applied. In order to improve accuracy, the voltage comparator 97a is connected via an amplifier that amplifies the voltage from the electrodes 51 and 52, or a circuit that amplifies the difference from the threshold Vref in the differential sense amplifier SA. It may be provided (not shown). The write error detection method of the spatial light modulator 10 will be described in detail later.

[Method of manufacturing spatial light modulator]
An example of a method for manufacturing a pixel array of a spatial light modulator according to the present invention will be described with reference to FIGS. The pixel array 80 is manufactured by first forming the light modulation element 1 on the substrate 7 and then forming the electrodes 51 and 52 connected to the light modulation element 1.

(Formation of light modulation element)
First, materials for forming the magnetization free layer 3, the first intermediate layer 21, the first magnetization fixed layer 11, and the protective film 41 on the substrate 7 (indicated by the same reference numerals as those of the respective layers in the figure, the same applies hereinafter). To form a film. Further, as shown in FIG. 7A, the regions where the second intermediate layer 22 and the second magnetization fixed layer 12 of the light modulation element 1 are provided are opened (the first intermediate layer 21 and the first magnetization). A resist pattern (which masks the region where the fixed layer 11 is provided) is formed by electron beam lithography. Then, by etching using an ion beam milling method, as shown in FIG. 7B, the first magnetization fixed layer 11 and the first intermediate layer 21 are removed from the protective film 41 to expose the magnetization free layer 3.

  Next, as shown in FIG. 7C, materials for forming the second intermediate layer 22, the second magnetization fixed layer 12, and the protective film 42 are successively formed. Then, the resist is removed together with the second intermediate layer 22 and the like formed thereon (lift-off). Thereby, as shown in FIG. 7 (d), the magnetization free layer 3 formed on the entire surface of the substrate 7, and the laminated film of the first intermediate layer 21 / the first magnetization fixed layer 11 / the protective film 41 thereon. And the laminated film of the second intermediate layer 22 / second magnetization fixed layer 12 / protective film 42 are alternately formed in stripes along the Y direction (vertical direction in FIG. 1) (not shown).

  Next, the laminated film is processed into the shape of the light modulation element 1. First, the two spin injection magnetization reversal element structures in the light modulation element 1 are separated from each other. As shown in FIG. 7E, a resist pattern is formed on the protective films 41 and 42 with a region between the first and second spin-injection magnetization switching element structures of the light modulation element 1. As shown in FIG. 8A, the magnetization free layers 3 are exposed by removing the magnetization fixed layers 11 and 12 and the intermediate layers 21 and 22 from the protective films 41 and 42 by etching. Next, as shown in FIG. 8B, an insulating film (insulating member 6) is formed, and the resist is removed together with the insulating film (lift-off). As a result, as shown in FIG. 8C, the two spin-injection magnetization reversal element structures in the light modulation element 1 are separated from each other and filled with the insulating member 6.

  As shown in FIGS. 8D and 8E, a resist pattern having a planar view shape of the light modulation element 1 is formed on the protective films 41 and 42 and the insulating member 6. As shown in FIG. 9A, the substrate 7 is exposed by removing the magnetization fixed layers 11 and 12, the intermediate layers 21 and 22, and the magnetization free layer 3 from the protective films 41 and 42 by etching. Next, as shown in FIG. 9B, an insulating film (insulating member 6) is formed, and the resist is removed together with the insulating film (lift-off). As a result, as shown in FIG. 9C, the light modulation element 1 including the two spin-injection magnetization reversal element structures MR1 and MR2 is formed, and the upper surfaces (the surfaces of the protective films 41 and 42) are insulated to be flush with each other. Filled with member 6.

(Formation of electrodes)
First, the X electrode 51 connected to the upper surface (protective film 41) of the first element structure MR1 of the light modulation element 1 and extending in the Y direction, and the upper surface (protective film 42) of the second element structure MR2 are connected. A connecting portion 52c of the Y electrode 52 is formed. An insulating film (insulating member 6) is formed on the light modulation element 1 and the insulating member 6 with the thickness of the X electrode 51. Then, as illustrated in FIG. 9D, a resist pattern is formed on the insulating member 6, with a region where the X electrode 51 is provided and a region where the connection portion 52 c of the Y electrode 52 is provided. Then, the insulating member 6 is removed by etching until the protective films 41 and 42 are exposed as shown in FIG. Next, as shown in FIG. 10A, a metal electrode material is formed, and the resist is removed together with the metal electrode material (lift-off). As a result, as shown in FIGS. 10B and 10C, the connection portion 52 c between the X electrode 51 and the Y electrode 52 is connected to the spin injection magnetization reversal element structures MR 1 and MR 2 of the light modulation element 1.

  Finally, the Y electrode 52 is completed. An insulating film (insulating member 6) is formed on the X electrode 51, the connecting portion 52c, and the insulating member 6 with a thickness between the electrodes 51 and 52. Next, a resist pattern is formed on the insulating member 6 so as to leave a region on the connection portion 52c. Then, the insulating member 6 is removed by etching until the connection portion 52c is exposed. Next, a metal electrode material is formed, and the resist is removed together with the metal electrode material (lift-off). As a result, as shown in FIG. 10D, an interlayer connection portion 52 b for connecting the wiring portion 52 a of the Y electrode 52 is formed in the connection portion 52 c of the Y electrode 52. Further, an insulating film (insulating member 6) is formed on the interlayer connection portion 52b and the insulating member 6 with the thickness of the wiring portion 52a of the Y electrode 52, and the wiring portion 52a is lifted off similarly to the X electrode 51 and the like. (See FIG. 2).

  According to such a manufacturing method, the light modulation element 1 which is a spin-injection magnetization reversal element having a parallel dual pin structure and the pixels 8 including the electrodes 51 and 52 connected to the light modulation element 1 are two-dimensionally arranged. The pixel array 80 can be formed on the substrate 7. In the formation of the light modulation element 1, the first intermediate layer 21, the first magnetization fixed layer 11, and the protective film 41 are formed first, but the second intermediate layer 22, the second magnetization fixed layer 12, and the protective film 42 are formed. The film may be formed first. Further, the insulating member 6 is embedded between the light modulating elements 1 and 1 after the light modulating element 1 is formed. After the insulating member 6 is formed, each layer of the light modulating element 1 is formed, and light modulation is performed by lift-off. Element 1 may be formed.

(Initial setting of light modulator)
As described above, in the light modulation elements 1 of all the pixels 8 in the pixel array 80, the first magnetization fixed layer 11 needs to be upward and the second magnetization fixed layer 12 needs to be fixed downward. Since the magnetization fixed layers 11 and 12 do not undergo magnetization reversal when a current is supplied from the power supply 95, the optical modulation element 1 is initialized by the following method.

Light modulation element 1 according to this embodiment, than the coercive force Hcp ₁ of the first magnetization fixed layer 11 is the coercive force Hcp ₂ of the second magnetization pinned layer 12 large (Hcp ₁ <Hcp _2). Therefore, first, an external magnetic field larger than Hcp ₂ is applied to the pixel array 80 so that the magnetizations of all the magnetization fixed layers 11 and 12 are directed downward. Next, an external magnetic field smaller than Hcp ₂ and larger than Hcp ₁ is applied to make the magnetization of the first magnetization fixed layer 11 upward. The application of the two-stage magnetic field is not limited to the completed (after manufacturing) pixel array 80, but after the magnetic film material for the magnetization fixed layers 11 and 12 is formed during the manufacturing process of the pixel array 80. Any stage can be implemented.

In the case where the light modulation element 1 has a multilayer structure in which at least one of the magnetization fixed layers 11 and 12 includes exchange-coupled magnetic films, all the coercive forces (Hcp ₁ and Hcp ₂ of the magnetization fixed layers 11 and 12). ) By applying a heat treatment at about 200 ° C. in a vacuum while applying an external magnetic field exceeding 1), the light modulation element 1 can be initialized in one (one step) application of the magnetic field.

[Light modulation operation of spatial light modulator]
The light modulation operation of the spatial light modulator according to the present invention will be described with reference to FIG. 5 using a display device using this spatial light modulator. The display device may have the same configuration as that of the conventional spin-injection magnetization reversal element as a light modulation element (see Patent Document 1). The spatial light modulator 10 according to the present embodiment is of a reflective type, and the magnetization free layer 3 of the light modulation element 1 serving as the light modulation unit is provided on a transparent substrate 7 and has perpendicular magnetic anisotropy. Since it is made of a material and the magnetization direction indicates upward or downward, the display device preferably has the following configuration. Below the pixel array 80 of the spatial light modulator 10, an optical system OPS having a light source or the like that irradiates light (laser light) toward the pixel array 80, and the light emitted from the optical system OPS is applied to the pixel array 80. A polarizer (polarization filter) PFi that makes light of one polarization component (hereinafter referred to as incident light) before entering, and outgoing light that is incident and incident on the pixel array 80 from below is emitted from the pixel array 80. A polarizer (polarization filter) PFo that shields light of a specific polarization component and a detector PD that detects light transmitted through the polarizer PFo are disposed.

  The optical system OPS includes, for example, a laser light source, a beam expander that is optically connected to the laser light source and expands the laser light onto the entire surface of the pixel array 80, and a lens that converts the expanded laser light into parallel light. (Not shown). Since the light (laser light) emitted from the optical system OPS contains various polarization components, this light is transmitted through the polarizer PFi in front of the pixel array 80 to be one polarization component light. The polarizers PFi and Pfo are polarizing plates, respectively, and the detector PD is an image display means such as a screen.

  The optical system OPS irradiates the pixel array 80 with a parallel laser beam. Here, the magneto-optical effect of the magnetization free layer 3 of the light modulation element 1 increases as the incident angle of light becomes closer to the magnetization direction of the magnetization free layer 3. Therefore, it is desirable that the incident angle be perpendicular to the film surface, that is, 0 °, in order to maximize the degree of light modulation. However, in this case, the optical path of the emitted light coincides with the optical path of the incident light. Therefore, the incident angle is slightly inclined so that the polarizer PF0, the detector PD, the optical system OPS, and the polarizer PFi are arranged so as not to block the optical paths of the incident light and the outgoing light, respectively. Specifically, the incident angle of incident light is preferably set to 30 ° or less. The laser light passes through the polarizer PFi and becomes incident light of one polarization component, and is incident on all the pixels 8 from below the pixel array 80. Incident light passes through the substrate 7, is reflected by the light modulation element 1 of each pixel 8, exits from the pixel 8 as outgoing light, and passes through the substrate 7 again.

  Outgoing light is light of a specific polarization component by the polarizer PFo, here, light that has been rotated by θθ relative to the incident light is shielded, and light that has passed through the polarizer PFo enters the detector PD. Accordingly, since the light emitted from the pixel 8 whose magnetization direction of the magnetization free layer 3 of the light modulation element 1 is upward is blocked by the polarizer PFo, the pixel 8 is dark (black) and is displayed on the detector PD. . On the other hand, light that has been rotated by −θk with respect to incident light, that is, light emitted from the pixel 8 in which the magnetization direction of the magnetization free layer 3 of the light modulation element 1 is downward passes through the polarizer PFo and reaches the detector PD. Therefore, this pixel 8 is displayed brightly (white) on the detector PD.

As described above, the spatial light modulator 10 according to the present invention switches between light / dark (white / black) for each pixel 8 and switches the direction of current supplied to each pixel 8 (+ I _W / −I _W ). Light / dark will switch. The initial state of the spatial light modulator 10 is all from the power source 95 so that the magnetization direction of the magnetization free layer 3 of the light modulation elements 1 of all the pixels 8 is downward, for example, so that the whole is displayed white. The current + I _W may be supplied to the pixel 8 (see FIGS. 3D and 3A).

[Method for detecting pixel write error in spatial light modulator]
When the spatial light modulator according to the present invention is represented by an equivalent circuit diagram (a pixel array shows only pixels of 2 rows × 2 columns), the light modulation element 1 is represented as one magnetoresistive effect element as shown in FIG. Thus, it can be said that the first electrode (X electrode) 51 is a bit line and the second electrode (Y electrode) 52 is a word line, and the pixel array 80 has the same circuit structure as a cross-point type MRAM. Therefore, the spatial light modulator according to the present invention can check whether the magnetization reversal operation (writing) of the light modulation element has been normally performed for the selected pixel by performing a reading operation similar to that of the MRAM. A method for detecting a write error in a pixel of the spatial light modulator will be described with reference to FIGS. 1 and 4 and FIG. 3 as appropriate.
First, the relationship between the voltage between the electrodes 51 and 52 connected to the light modulation element 1 and the magnetization direction of the magnetization free layer 3 will be described.

(Relationship between magnetization direction and voltage of magnetization free layer in light modulator)
As shown in FIGS. 4A and 4B, when a current I _TST having a predetermined magnitude is supplied from the sub power source 96 to the light modulation element 1, a voltmeter connected in parallel with the sub power source 96 is used. The measured voltage is proportional to the resistance of the light modulation element 1. At this time, the current (resistance measurement current) I _TST supplied to the light modulation element 1 does not change the magnetization direction of the magnetization free layer 3, that is, is smaller than the magnetization reversal current I _STS of the light modulation element 1. It is further smaller than the smaller one of the magnetization reversal currents I1 _STS and I2 _STS of the two spin injection magnetization reversal element structures MR1 and MR2 of the modulation element 1. In FIG. 4, the resistance measurement current I _TST is supplied with the second electrode 52 set to “+”, but the direction of the current is not limited, and for the magnetization reversal operation of the light modulation element 1. Unlike the currents −I _W and + I _W , the direction of the current may be one direction. Thus, even if the light modulation element 1 is supplied with a current smaller than the magnetization reversal current I _STS , the magnetization direction of the magnetization free layer 3 does not change. The voltage measured by supplying such a constant current I _TST to the light modulation element 1 varies depending on the magnetization direction of the magnetization free layer 3 of the light modulation element 1.

As shown in FIG. 4A, in the light modulation element 1 in which the magnetization free layer 3 exhibits downward magnetization, the resistance value is R _D shown in the above equation (1), so that the voltage value V _D Becomes I _TST · R _D. On the other hand, as shown in FIG. 4B, the light modulation element 1 in which the magnetization free layer 3 exhibits upward magnetization has a resistance value of R _U shown in the above equation (2). The value V _U is I _TST · R _U. As described above, the light modulation element 1 has higher resistance when the magnetization free layer 3 exhibits downward magnetization, and R _D > R _U , and therefore V _D > V _U. That is, whether the magnetization of the magnetization free layer 3 of the light modulation element 1 is upward or downward is detected from the value of the voltage measured by a voltmeter connected in parallel with the sub power source 96, in other words, connected to the electrodes 51 and 52. can do. For example, threshold values Vref _L and Vref _H (V _U <Vref _L <Vref _H <V _D ) are set as limit values in the allowable ranges of the voltages V _D and V _U. If the measured voltage value is Vref _H or more, the magnetization of the magnetization free layer 3 can be detected downward, and if it is Vref _L or less, it can be detected that the magnetization of the magnetization free layer 3 is upward. In particular, in the light modulation element 1, as described above, since the first intermediate layer 21 is made of an insulator, a resistance change ΔR due to magnetization reversal is large (R _D >> R _U ). Therefore, the light modulation element 1 has a large difference between the voltages V _D and V _{U that} change due to the magnetization reversal, and the magnetization direction of the magnetization free layer 3 can be easily and accurately detected by the threshold values Vref _L and Vref _H.

(Pixel writing error detection method)
From this, the spatial light modulator 10 compares the voltage between the electrodes 51 and 52 of the light modulation element 1 with the thresholds Vref _L and Vref _H for the selected pixel 8, and the magnetization free layer of the light modulation element 1. 3 is detected and collated with the selection direction of the magnetization reversal operation by the pixel selection unit 94 which determines whether the magnetization direction of the magnetization free layer 3 of the light modulation element 1 is upward or downward. It can be checked whether (writing) has been performed normally. Here, description will be made assuming that the detection of the write error is performed on the pixel 8 immediately after the magnetization reversal operation is performed on the light modulation element 1 of the selected pixel 8.

In the light modulation element 1, when the power source 95 supplies the current + I _{W according} to a command from the pixel selection unit 94, the magnetization free layer 3 exhibits downward magnetization as shown in FIG. Here, the pixel selection unit 94 notifies the determination unit 97 that the magnetization of the magnetization free layer 3 is directed downward when instructing the current supply to the power source 95 for the magnetization reversal operation of the light modulation element 1. (See FIG. 1). Then, after supplying the current + I _W from the power source 95 (after the supply is stopped), the electrodes 51 and 52 of the light modulation element 1 are switched from the power source 95 to the sub power source 96 in accordance with a command from the pixel selecting unit 94. As shown in FIG. 4A, a resistance measurement current I _TST is supplied from the sub power supply 96.

The determination unit 97 previously sets the reference potential (threshold value) that the voltage comparator 97a uses as a reference for comparison to Vref _H based on the selection direction of the magnetization reversal operation input from the pixel selection unit 94: downward, and inspection unit 97b is set to determine that a pass (pASS) if more than the threshold value Vref _H. Then, in accordance with the start of supply of the resistance measurement current I _TST by the sub power supply 96, the voltage comparator 97a compares the voltage between the electrodes 51 and 52 with the threshold value Vref _{H in} the determination unit 97, and is equal to or higher than Vref _H. Is output to the inspection unit 97b. If the value of the voltage between the electrodes 51 and 52 is Vref _H or more, as shown in FIG. 4A, the magnetization of the magnetization free layer 3 is downward, and the magnetization reversal operation of the light modulation element 1 is normally performed. I understand that. On the other hand, if the value of the voltage is less than Vref _H, the magnetization reversal operation of the optical modulation element 1 is not properly done (FAIL), ie it can be seen that a write error.

On the other hand, as shown in FIG. 3C, when the current -I _W is supplied from the power source 95 and the magnetization of the magnetization free layer 3 is directed upward, the connection is switched in the same manner, and the state shown in FIG. As described above, the resistance measurement current I _TST is supplied from the auxiliary power source 96. At this time, the determination unit 97 sets the reference potential (threshold value) to Vref _L in advance based on the selection direction of the magnetization reversal operation input from the pixel selection unit 94: upward, and the inspection unit 97b has the threshold Vref _L or less. If so, it is set so as to be determined as passing (PASS). When the voltage comparator 97a compares the voltage value between the electrodes 51 and 52 with the threshold value Vref _L and the voltage value is Vref _L or less, the magnetization of the magnetization free layer 3 is as shown in FIG. 4B. It can be seen that the magnetization reversal operation of the light modulation element 1 was normally performed. On the other hand, when the voltage value exceeds Vref _L , it can be seen that the magnetization reversal operation of the light modulation element 1 is not properly performed (FAIL), that is, a write error.

If the inspection unit 97b of the determination unit 97 determines that the magnetization reversal operation of the light modulation element 1 has been performed normally, the pixel selection unit 94 performs the next operation, that is, selection and writing of another pixel 8, or Command to move to next write to same pixel 8. On the other hand, when detecting a write error, the inspection unit 97b instructs the pixel selection unit 94 to execute the previous magnetization reversal operation on the same pixel 8 again (see FIG. 1). In this way, the spatial light modulator 10 can accurately display in all the pixels 8 of the pixel array 80 by performing the magnetization reversal operation (writing) by the pixel selection unit 94 while performing the determination by the determination unit 97. Can do. Note that a program for setting threshold values Vref _L and Vref _H , a determination method by the inspection unit 97b of the determination unit 97, a command to the pixel selection unit 94, and the like is stored in, for example, a storage device ( (Not shown) may be stored in advance.

(Another embodiment of write error detection method)
As a voltage threshold for detecting the magnetization direction of the magnetization free layer 3 of the light modulation element 1, only one value (Vref) may be set as Vref _L = Vref _H (V _U <Vref <V _D ). That is, the determination unit 97 detects whether the magnetization of the magnetization free layer 3 is downward or upward depending on whether the voltage value between the electrodes 51 and 52 is larger or smaller than the threshold value Vref. Specifically, the reference potential (threshold value) used as a reference for comparison by the voltage comparator 97a is fixed to Vref, and the determination unit 97 determines whether the inspection unit 97b is based on the selection direction of the magnetization reversal operation input from the pixel selection unit 94. What is necessary is just to set whether the case where it is larger than this threshold value Vref and the case where it is smaller is set to pass (PASS). Further, as the voltage threshold, only one of the limit values of the voltages V _D and V _U , that is, not the lower limit value Vref _H of the voltage V _D and the upper limit value Vref _L of the voltage V _U , but the voltage V _D , V _U The determination may be made more strictly by setting a total of four values, the lower limit value and the upper limit value of each allowable range.

  Further, in the above-described method, each time the pixel selection unit 94 selects the pixel 8 and performs writing (magnetization reversal operation of the light modulation element 1), the determination unit 97 performs write error detection on the pixel 8. The operation is repeated, but is not limited to this. For example, when writing to all the pixels 8 in the pixel array 80 is completed, the writing error can be detected in order for all the pixels 8.

  In addition, when two or more pixels 8 are selected at the same time and the same magnetization reversal operation is performed on each of the light modulation elements 1, the write error detection may be performed on these pixels 8 collectively. Since the light modulation elements 1 of two or more pixels 8 selected at the same time are connected in parallel to the sub-power supply 96, the threshold value of the voltage based on the combined resistance can be preset or calculated by the determination unit 97. Write error detection can be performed in the same manner as in the case of the individual light modulation elements 1. In this case, the determination unit 97 determines whether the magnetization reversal operation has been normally performed for all the light modulation elements 1 of the selected pixel 8 or a write error has occurred for any one or more of the light modulation elements 1. Can be determined.

  As described above, according to the spatial light modulator according to the first embodiment, the conventional spin-injection magnetization reversal element is optically enlarged while the effective area of the pixel is widened by the light modulation element having a large area to increase the aperture ratio. Similar to the spatial light modulator used as the modulation element, the write error can be detected using the driving wiring, and the pixel can be further miniaturized.

(Second Embodiment)
Next, with reference to FIG. 11, a spatial light modulator according to the second embodiment of the invention will be described. In addition, in this embodiment and 3rd Embodiment mentioned later, the same code | symbol is attached | subjected about the element same as 1st Embodiment (refer FIGS. 1-5), and description is abbreviate | omitted.

  The spatial light modulator 10 according to the first embodiment has a configuration in which one pixel 8 includes one light modulation element 1, but is not limited thereto, and one pixel includes two or more light modulation elements. May be. That is, as shown in FIG. 11, the pixel 8A of the spatial light modulator according to the second embodiment includes three light modulation elements 1A. The light modulation element 1A has the same structure as that of the light modulation element 1 of the spatial light modulator 10 according to the first embodiment, except that the light modulation element 1A is a horizontally long rectangle in plan view extended in the X direction (lateral direction in FIG. 11). is there. In the pixel 8A, the three light modulation elements 1A are arranged in the short side direction (Y direction) of the light modulation element 1A and connected in parallel to the same pair of electrodes 51 and 52. Such pixels 8 </ b> A are two-dimensionally arranged on the substrate 7 to form a pixel array as in the first embodiment, and can be operated by the current control unit 90. Since the pixel array and current control unit 90 have the same configuration as in the first embodiment, illustration and description thereof are omitted.

  As described above, according to the spatial light modulator according to the second embodiment, even if the pixel size is increased, one size of the light modulation element is sufficiently small, so that the magnetization is appropriately reversed and the aperture ratio is high. It can be a pixel.

(Third embodiment)
Next, with reference to FIG. 12, a spatial light modulator according to a third embodiment of the present invention and a modification thereof will be described. The spatial light modulator according to the present embodiment and its modification is different from the first embodiment only in the configuration of the pixel array, and the current control unit 90 has the same configuration, and thus illustration and description thereof are omitted.

  In the pixel array 80 of the spatial light modulator 10 according to the first embodiment, all the light modulation elements 1 provided are aligned in a plan view (bottom view), and the first magnetization is on the left side in FIGS. Although the fixed layer 11 and the second magnetization fixed layer 12 are arranged on the right side, the present invention is not limited to this. That is, in the spatial light modulator pixel array 80A according to the third embodiment, every other pixel 8 is horizontally inverted and arranged in the X direction, as shown in FIGS. 12 (a) and 12 (b). Therefore, the pixel array 80A has a configuration in which the first magnetization fixed layers 11 and 11 and the second magnetization fixed layers 12 and 12 are adjacent to each other in the adjacent light modulation elements 1 and 1. In FIGS. 12B and 12C, the protective films 41 and 42 are not shown.

Furthermore, as shown in FIG. 12C, the pixel array 80B of the spatial light modulator according to the modification of the third embodiment includes the second magnetization fixed layers 12 and 12 adjacent to each other in the third embodiment, and The two intermediate layers 22 and 22 are joined together. The second magnetization fixed layers 12 and 12 adjacent in the X direction are connected to the same Y electrode 52, and the area of the spin injection magnetization reversal element structure MR2 laminated on the magnetization free layer 3 is the light modulation element 1 of the first embodiment. Therefore, even in the light modulation element 1B modified in this way, the magnetization reversal operation can be performed as in the first embodiment. Furthermore, since the area of the second magnetization fixed layer 12 is more than twice that of the first magnetization fixed layer 11, the coercive force Hcp _{2 of} the second magnetization fixed layer 12 is not dependent on the difference in material and thickness. Can be designed to be larger than the coercive force Hcp ₁ of the first magnetization fixed layer 11.

  As described above, according to the spatial light modulator according to the third embodiment, similarly to the spatial light modulator according to the first embodiment, it is possible to detect a write error, to miniaturize a pixel, and to reduce an aperture ratio. Can be high.

(Fourth embodiment)
Next, a spatial light modulator according to the fourth embodiment of the present invention will be described with reference to FIG. In addition, in this embodiment, the same code | symbol is attached | subjected about the same element as 1st Embodiment (refer FIGS. 1-6), and description is abbreviate | omitted.

  The pixel array of the spatial light modulator according to the first embodiment has the same structure as that of the cross point type MRAM circuit as described with reference to FIG. In this cross-point type MRAM, the current leaks also to the non-selected magnetoresistive effect element. Therefore, as the number of mounted magnetoresistive effect elements increases, the resistance change amount of one magnetoresistive effect element detected at the time of data reading is increased. Is smaller than the actual value, a magnetoresistance effect element having a sufficiently large resistance change is applied. That is, in the spatial light modulator 10 according to the first embodiment, the voltage between the electrodes 51 and 52 is the light of the non-selected pixel 8, depending on the number of mounted light modulation elements 1 (number of pixels) in the pixel array 80. The light modulation element 1 is designed so that the amount of change in resistance increases to such an extent that the voltage comparator 97a of the determination unit 97 can determine whether the threshold value is high or low even if affected by the resistance component of the modulation element 1. ing.

  However, when such a light modulation element 1 is applied, the spatial light modulator 10 requires time for reading, that is, determination (writing error detection). Therefore, as is often applied to MRAM, a select transistor type may be used. That is, as shown in FIG. 13, the spatial light modulator 10A according to the present embodiment includes one of electrodes connected to each light modulation element 1, in this case, the Y electrode 52 (52A), the second magnetization fixed layer 12, and the like. The transistor Tr1 is connected as a selection element. Specifically, the transistor Tr1 has a drain connected to the second magnetization fixed layer 12 of the light modulation element 1, a source connected to the Y electrode 52A, and a wiring (element selection electrode 53) newly provided with a gate. In order to select the pixel 8C independently of the Y electrode 52A, the element selection electrode 53 is provided non-parallel to, or orthogonal to, the Y electrode 52A, and thus extends in the Y direction in parallel with the X electrode 51. The spatial light modulator 10A newly includes an element selection unit 93 that selects the element selection electrode 53. The element selection electrode 53 receives a current from a power source for driving the transistor Tr1 built in the element selection unit 93 (see FIG. 13). Supplied.

  The spatial light modulator 10 </ b> A configured in this way selects the pixel 8 </ b> C not only with the pair of electrodes 51 and 52 </ b> A that supply current to the light modulation element 1 but also with the element selection electrode 53. In the spatial light modulator 10A, in the write error detection, only the light modulation element 1 of the selected pixel 8C is connected to the sub power source 96 or the voltage comparator 97a of the determination unit 97 via the Y electrode 52A, and the same row That is, since the light modulation elements 1 of the non-selected pixels 8C sharing the Y electrode 52A are not connected, no leakage current flows through these light modulation elements 1. Thereby, the resistance of the light modulation element 1 of the selected pixel 8C is not affected by the resistance component of the light modulation element 1 of the other pixel 8C in the non-selected state, and the amount of change in resistance due to magnetization reversal is not large. However, it is possible to distinguish between high and low. Furthermore, in the spatial light modulator 10A, even in the magnetization reversal operation, only the light modulation element 1 of the selected pixel 8C is connected to the power supply 95, so that loss due to leakage current can be suppressed.

  As the transistor Tr1 provided for each pixel 8C, for example, a MOSFET (metal oxide semiconductor field effect transistor) can be applied. Here, the MOSFET is generally formed using a Si (silicon) substrate as a material. However, if a normal crystalline Si film that requires heat treatment at about 800 ° C. is formed on the light modulation element 1, the optical modulation element 1 is formed. The modulation element 1 is damaged. Therefore, polycrystalline silicon (poly-Si) that can be formed at a low temperature of about 150 ° C. is applied to the spatial light modulator 10A. Specifically, as an example, after the light modulation element 1 is formed on the substrate 7 and an interlayer insulating layer (insulating member 6) is formed thereon (see FIG. 9D), a poly-Si film is formed. A film is formed to form a MOSFET (transistor Tr1). Then, a contact hole is formed in the interlayer insulating layer on the magnetization fixed layers 11 and 12 of the light modulation element 1, and the second magnetization fixed layer 12 and the drain of the transistor Tr1 are connected with a metal electrode material, and the first magnetization fixed. An X electrode 51 is connected to the layer 11 and formed. Further, a Y electrode 52 is connected to the source of the transistor Tr1, and an electrode 53 is connected to the gate, respectively. The transistor Tr1 is formed in a region where the light modulation element 1 is not present in plan view so as not to hinder connection to the magnetization fixed layers 11 and 12.

  In the spatial light modulator 10A, the transistor Tr1 is connected to the second magnetization fixed layer 12 of the light modulation element 1, but the same effect can be obtained by connecting the transistor Tr1 to the first magnetization fixed layer 11. In FIG. 13, the spatial light modulator 10 </ b> A is selected independently, although the pixel selection unit 94 simultaneously selects the first electrode (X electrode) 51 and the element selection electrode 53 of the pixels 8 in the same column. It is good also as composition to be. In the pixel array 80C of the spatial light modulator 10A, XY may be interchanged between the element selection electrode 53 and the second electrode 52. That is, the element selection electrode 53 extends in the X direction, while the second electrode 52 extends in the Y direction in parallel with the first electrode 51 and is selected simultaneously with the first electrode 51 of the pixel 8C in the same column. (Not shown).

  As a modification of the fourth embodiment, a diode can be applied to the selection element. Specifically, a diode is connected between the second magnetization fixed layer 12 of the light modulation element 1 and the Y electrode 52 of the spatial light modulator 10 (see FIG. 6) according to the first embodiment (not shown). ). In the spatial light modulator according to this modification, the light modulation element 1 (element structure MR1, MR2) is a unipolar drive type spin injection magnetization reversal element, and is only in one direction from the second electrode 52 to the first electrode 51. A current is supplied to reverse the magnetization (not shown). Alternatively, the spatial light modulator supplies a current to the light modulation element 1 only in one direction from the second electrode 52 to the first electrode 51 in the magnetization reversal operation by supplying a current from the power supply 95, thereby freeing the magnetization free layer. 3 is directed upward (see FIGS. 3B and 3C). When the magnetization direction of the magnetization free layer 3 is downward, it can be reversed by applying a magnetic field to the pixel 8 (pixel array 80), for example. Therefore, the Y electrode 52 is connected to the anode of the diode, and the second magnetization fixed layer 12 is connected to the cathode.

  The diode can be formed in a poly-Si film as in the transistor Tr1. In the spatial light modulator configured in this way, no current flows through the diode because the Y electrode 52 is in the open state in the non-selected pixel 8 at the time of writing error detection or in the magnetization reversal operation. No leakage current flows through the modulation element 1. Further, in the spatial light modulator according to this modification, with respect to the non-selected pixel 8, the potential of the Y electrode 52 is made lower than the current supplied from the X electrode 51 (on the “−” side). A current may flow through the diode. As described above, since the current flows only when the current is supplied in a specific direction, the diode can be used as a selection element like the transistor Tr1. Furthermore, since a diode is generally simpler than a transistor and has a smaller size in plan view, the pixel does not become larger than when a transistor is provided, and wiring for supplying current to the gate to the pixel array (element selection electrode) 53, see FIG. 13). Similar to the transistor Tr1 in the fourth embodiment, the same effect can be obtained by connecting a diode to the first magnetization fixed layer 11. In this case, the first magnetization fixed layer 11 is connected to the anode of the diode, and the X electrode 51 is connected to the cathode.

  As described above, according to the spatial light modulator according to the fourth embodiment and the modification thereof, the current does not leak to the light modulation element of the non-selected pixel in both the write error detection and the magnetization reversal operation. In detection, an optical modulation element having a small resistance change amount can be applied to increase the response speed. In the magnetization reversal operation, loss due to leakage current can be suppressed, so that power can be saved.

  As mentioned above, although each embodiment for implementing the light modulation element and the spatial light modulator of the present invention has been described, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the claims. Can be changed.

DESCRIPTION OF SYMBOLS 10,10A Spatial light modulator 1, 1A, 1B Light modulation element 11 1st magnetization fixed layer 12 2nd magnetization fixed layer 21 1st intermediate | middle layer (intermediate layer)
22 Second intermediate layer (intermediate layer)
3 Magnetization free layer 51 1st electrode, X electrode (electrode)
52 Second electrode, Y electrode (electrode)
7 Substrate 80, 80A, 80B, 80C Pixel array 8, 8A, 8C Pixel 90 Current control unit 94 Pixel selection unit (pixel selection means)
95 Power supply (current supply means)
96 Sub power supply (sub current supply means)
97 determination unit (pixel determination means)

Claims (8)

A spin-injection magnetization reversal element structure in which a magnetization free layer, an intermediate layer, and a magnetization fixed layer are laminated in this order on a substrate, and the direction of polarization of light incident from the side on which the magnetization free layer is laminated is changed. A light modulation element that reflects and emits light,
The magnetization pinned layer has a first magnetization pinned layer and a second magnetization pinned layer, which are spaced apart in a plane direction and pinned in magnetization in directions opposite to each other on the magnetization free layer,
The intermediate layer has an intermediate layer in which the first magnetization fixed layer is stacked and an intermediate layer in which the second magnetization fixed layer is stacked, and has different resistances.
A light modulation element, wherein a magnetization direction of the magnetization free layer is changed by supplying a current by connecting a pair of electrodes to the first magnetization fixed layer and the second magnetization fixed layer.   The light modulation element according to claim 1, wherein at least one of the two intermediate layers is a tunnel barrier layer.   The light modulation element according to claim 1, wherein the first magnetization fixed layer and the second magnetization fixed layer have different coercive forces.   3. The light modulation element according to claim 1, wherein at least one of the first magnetization fixed layer and the second magnetization fixed layer has a multilayer structure including a magnetic film exchange-coupled. 4. A spatial light modulator comprising: a substrate that transmits light; and a plurality of pixels that are two-dimensionally arranged on the substrate, wherein the light that has passed through the substrate and is incident on the plurality of pixels is reflected and emitted. 5. A pixel includes a light modulation element according to claim 1, and a pair of electrodes connected to the first magnetization fixed layer and the second magnetization fixed layer of the light modulation element, With
Pixel selection means for selecting one or more pixels from the plurality of pixels and further selecting which of the two different directions of magnetization directions of the magnetization free layer of the light modulation element for the selected pixels;
Current supply means for supplying a current to the light modulation element of the pixel selected by the pixel selection means so that the magnetization direction of the magnetization free layer of the light modulation element is selected by the pixel selection means;
The pixel determination for determining that the magnetization direction of the magnetization free layer of the light modulation element to which the current supply means has supplied current is the direction selected by the pixel selection means, and a change in the resistance of the light modulation element. A spatial light modulator comprising: a pixel determination unit that performs detection. Sub-current supply means for supplying a current of a predetermined magnitude to the light modulation element of the pixel selected by the pixel selection means,
The pixel determination unit is configured to determine a voltage value between the pair of electrodes connected to the light modulation element to which a current is supplied to the sub-current supply unit, and a magnetization direction of the magnetization free layer by the pixel selection unit. The spatial light modulator according to claim 5, wherein the pixel determination is performed by comparing with a threshold value set in advance based on a resistance of the light modulation element in the selected direction.   7. The pixel according to claim 5, wherein the pixel includes a selection element that can freely disconnect the electrical connection with the electrode in the first magnetization fixed layer or the second magnetization fixed layer. 8. Spatial light modulator.   The spatial light modulator according to any one of claims 5 to 7, wherein the pixel includes two or more of the light modulation elements connected in parallel to the pair of electrodes.

Images