Domain wall motion spatial light modulator

Abstract

To provide a domain wall movement type spatial light modulator with which it is possible to increase the numerical aperture of a domain wall movement type spatial light modulation element by a simple process.SOLUTION: A domain wall movement type spatial light modulator 300 comprises domain wall movement type spatial light modulation elements 30 each having light modulation layers 31 that output polarized light of incident light by changing its direction, and a first magnetization fixed layer 32 and second magnetization fixed layers 33 that are each arranged extending to both ends of the light modulation layer 31. Coercive force of the first magnetization fixed layer 32 of the domain wall movement type spatial light modulation element 30 is smaller than coercive force of the second magnetization fixed layer 33, and the second magnetization fixed layer 33 at least partially extends vertically or diagonally with respect to a direction in which the first magnetization fixed layer 32 extends.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a domain wall motion type spatial light modulator. [Background technology]

[0002] To achieve 3D holography, a practical viewing angle of 30° or more is required. To achieve this, the pixel pitch of the spatial light modulator (SLM), which is the display device, needs to be reduced to 1 μm or less. Existing SLMs, such as liquid crystal and digital micromirror devices (DMDs), have a pixel pitch of around 5 μm, and it is difficult to make it any finer.

[0003] On the other hand, magneto-optic spatial light modulators (MOSLMs) that use spin-transfer magnetization reversal or domain wall motion to rewrite pixels can easily achieve a pixel pitch of about 1 μm, although performance needs to be improved in terms of light utilization efficiency, operating current, etc. (See, for example, Patent Document 1.) MOSLMs are devices that modulate light by allocating the rotation of the polarization plane of light according to the magnetization direction to light and dark.

[0004] A domain wall motion spatial light modulator includes a light modulation layer that changes the polarization direction of incident light before emitting it, and a domain wall motion spatial light modulator element having first and second magnetization pinned layers with different coercive forces that are arranged parallel to each other at both ends of the light modulation layer, and can control the expansion and contraction of magnetic domains by the direction of current passed through the light modulation layer (see, for example, Patent Document 2). Domain wall motion spatial light modulators are expected to consume less power than MOSLMs that use spin-transfer magnetization reversal, but they require a sophisticated device design that assumes a pixel pitch of 1 μm or less in order to provide a sufficient coercive force difference between the three ferromagnetic layers of the light modulation layer and the two magnetization pinned layers, as well as to precisely fabricate a complex device structure.

[0005] Patent Document 3 describes a method for designing the coercivity difference between the first and second magnetization pinned layers by forming the first and second magnetization pinned layers in a single process, thereby eliminating the need for high-precision alignment. This makes it possible to form a domain wall motion type spatial light modulator using a simple process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-141402 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-206900 [Patent Document 3] Japanese Patent Application Publication No. 2019-220544 Summary of the Invention [Problem to be solved by the invention]

[0007] However, because the domain wall motion spatial light modulator is formed on the drain and ground electrodes of the pixel selection transistor, alignment margins are required between the drain and ground electrodes and the first and second magnetization pinned layers during design, making it difficult to increase the aperture ratio of the domain wall motion spatial light modulator.

[0008] An object of the present invention is to provide a domain wall motion type spatial light modulator that can increase the aperture ratio of a domain wall motion type spatial light modulation element using a simple process. [Means for solving the problem]

[0009] One aspect of the present invention is a domain wall motion type spatial light modulator comprising a domain wall motion type spatial light modulator having a light modulation layer that changes the direction of polarization of incident light and outputs it, and a first magnetization fixed layer and a second magnetization fixed layer that are arranged extending at both ends of the light modulation layer, wherein the coercive force of the first magnetization fixed layer is smaller than the coercive force of the second magnetization fixed layer, and at least a portion of the second magnetization fixed layer extends perpendicularly or obliquely to the direction in which the first magnetization fixed layer extends.

[0010] In the domain wall motion type spatial light modulator, at least a part of the second magnetization pinned layer may extend parallel to the direction in which the first magnetization pinned layer extends.

[0011] The second magnetization fixed layer may have an L-shape when viewed from above or an inverted L-shape when viewed from above.

[0012] In the domain wall motion type spatial light modulation element, the light modulation layer may extend perpendicular to the direction in which the first magnetization pinned layer extends.

[0013] The length in the direction in which the first magnetization fixed layer extends may be longer than the length in the direction in which the second magnetization fixed layer extends. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a domain wall motion type spatial light modulator that can increase the aperture ratio of a domain wall motion type spatial light modulation element using a simple process. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing the structure of a conventional domain wall motion type spatial light modulation element. [Figure 2] 2 is a side view showing the operation of the domain wall motion type spatial light modulation element of FIG. 1. FIG. [Figure 3] 2 is a side view showing the structure and operation of the domain wall motion type spatial light modulation element of FIG. 1. FIG. [Figure 4]FIG. 1 is a top view showing the structure of a conventional domain wall motion type spatial light modulator. [Figure 5] 5 is a top view showing the positional relationship between the domain wall motion type spatial light modulation element of FIG. 4 and the drain electrode and ground electrode of the pixel selection transistor. FIG. [Figure 6] 1 is a top view showing the structure of an example of a domain wall motion type spatial light modulator according to an embodiment of the present invention. [Figure 7] FIG. 7 is a perspective view showing a calculation model of the domain wall motion type spatial light modulator of FIGS. 4 and 6. [Figure 8] FIG. 7 is a diagram showing the results of calculation of the magnetic field strength of the calculation model of the domain wall motion type spatial light modulator of FIGS. 4 and 6. [Figure 9] 5 is a diagram showing the results of calculation of domain wall current drive in the calculation model of the domain wall motion type spatial light modulator of FIG. 4. FIG. [Figure 10] FIG. 7 is a diagram (part 1) showing the calculation results of domain wall current driving of the calculation model of the domain wall motion type spatial light modulator of FIG. 6; [Figure 11] FIG. 7 is a diagram (part 2) showing the calculation results of domain wall current driving of the calculation model of the domain wall motion type spatial light modulator of FIG. 6; [Figure 12] 7 is a top view showing the structure of a modified example of the domain wall motion type spatial light modulator of FIG. 6. FIG. [Figure 13] 7 is a top view showing the structure of a modified example of the domain wall motion type spatial light modulator of FIG. 6. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, since the basic configuration (materials, structure, operation, etc.) of the domain wall motion type spatial light modulator of this embodiment is the same as that of a conventional domain wall motion type spatial light modulator, the conventional domain wall motion type spatial light modulator will be described first.

[0017] [Conventional domain wall motion spatial light modulator] The structure of a conventional domain wall motion type spatial light modulator is shown in Figure 1. A domain wall motion type spatial light modulator 10 has a light modulation layer 11 that changes the polarization direction of incident light and outputs it, and a first magnetization pinned layer 12 and a second magnetization pinned layer 13 that are arranged at both ends of the light modulation layer 11 and have different coercive forces, and is formed on a substrate such as Si.

[0018] The first magnetization fixed layer 12 and the second magnetization fixed layer 13 each have a lower electrode at the bottom layer, which is made of a common metal electrode material such as a metal such as Cu, Al, Au, Ag, Ru, Ta, or Cr, or an alloy thereof, and a pulse current source is connected to the lower electrode.

[0019] In the domain wall motion type spatial light modulator 10, a first magnetization pinned layer 12 and a second magnetization pinned layer 13 extending parallel to each other are disposed at both ends of a light modulation layer 11 that is rectangular in top view and extends in a predetermined direction, and the light modulation layer 11 extends perpendicular to the direction in which the first magnetization pinned layer 12 and the second magnetization pinned layer 13 extend parallel to each other. The bottom surface of the light modulation layer 11 and the top surfaces of the first magnetization pinned layer 12 and the second magnetization pinned layer 13 are in contact on the same plane, and a pulse current can be applied to the light modulation layer 11 via the first magnetization pinned layer 12 and the second magnetization pinned layer 13.

[0020] 2 shows the operation of the domain wall motion type spatial light modulator 10. Specifically, by designing a coercivity difference (Hc2>Hc1) between the coercivity (Hc1) of the first magnetization pinned layer 12 and the coercivity (Hc2) of the second magnetization pinned layer 13 and applying an external magnetic field, the initial magnetization directions at both ends of the light modulation layer 11, which are essential for light modulation control, are antiparallel to each other. First, when a downward external magnetic field Hx1 (Hx1>Hc2>Hc1) that is larger than Hc2 is applied, the magnetizations of the light modulation layer 11, the first magnetization pinned layer 12, and the second magnetization pinned layer 13 become downward (see FIG. 2(a)). Next, when an upward external magnetic field Hx2 (Hc2>Hx2>Hc1) that is larger than Hc1 but smaller than Hc2 is applied, the magnetization directions of the light modulation layer 11 and the first magnetization fixed layer 12 change to an upward direction (see FIG. 2(b)). At this time, an initial magnetic domain 11a is formed at the end of the light modulation layer 11 on the first magnetization fixed layer 12 side by a leakage magnetic field Hl from the first magnetization fixed layer 12, thereby determining the aperture ratio of the domain wall motion type spatial light modulator 10 (see FIG. 2(c)).

[0021] 3 shows the structure and operation of the domain wall motion type spatial light modulator 10. In the domain wall motion type spatial light modulator 10A, a non-magnetic metal layer and a buffer layer are formed as an intermediate layer 14 between the light modulation layer 11 and the first and second magnetization pinned layers 12 and 13 in accordance with the microfabrication process and magnetic design.

[0022] The first magnetization fixed layer 12 is made of a ferromagnetic material, is a layer whose magnetization direction is fixed in one direction, and has a large coercive force. The first magnetization fixed layer 12 has magnetic anisotropy in the same direction as the light modulation layer 11, and when a ferromagnetic material with perpendicular magnetic anisotropy is used for the light modulation layer 11, the first magnetization fixed layer 12 also uses a ferromagnetic material with perpendicular magnetic anisotropy. It is preferable that the light modulation layer 11 and the first magnetization fixed layer 12 are made of ferromagnetic materials with perpendicular magnetic anisotropy.

[0023] The first magnetization pinned layer 12 and the second magnetization pinned layer 13 can be made of known ferromagnetic materials that constitute the magnetization pinned layer of a CPP-GMR (current-perpendicular-to-plane giant magnetoresistance) element or a TMR element, which has perpendicular magnetic anisotropy and a nonmagnetic layer sandwiched between a magnetization pinned layer whose magnetization is pinned in the perpendicular direction and a magnetization free layer whose magnetization direction is reversible. Specifically, transition metals such as Fe, Co, and Ni and alloys containing these transition metals can be used, such as TbFe-based alloys, TbFeCo-based alloys, CoCr-based alloys, CoPt-based alloys, CoPd-based alloys, and FePt-based alloys. This increases the coercive force of the first magnetization pinned layer 12, making it possible to pin the magnetization direction of the first magnetization pinned layer 12 so that it does not easily change due to an external magnetic field.

[0024] The first magnetization pinned layer 12 may also be a multilayer film in which transition metal layers such as Fe layers, Co layers, Ni layers, etc. and non-magnetic metal layers are alternately stacked, such as a multilayer film of Co / Pt, Fe / Pt, Co / Pd, etc. By using these ferromagnetic materials, a first magnetization pinned layer 12 with high perpendicular magnetic anisotropy and large coercive force can be obtained.

[0025] The multilayer film described above has the property that its coercivity increases when heat-treated. Therefore, when the multilayer film described above is heat-treated to increase the coercivity of the first magnetization fixed layer 12, the coercivity of the ferromagnetic exchange coupling part after coupling with the light modulation layer 11 also increases, increasing the difference in coercivity with the light modulation region 11b.

[0026] The non-magnetic metal layer and the buffer layer are disposed between the light modulation layer 11 and the first magnetization pinned layer 12 and can maintain the magnetic coupling between the light modulation layer 11 and the first magnetization pinned layer 12 .

[0027] The non-magnetic metal layer is stacked on the first magnetization pinned layer 12. The non-magnetic metal layer is provided to prevent etching damage to the first magnetization pinned layer 12 in the manufacturing process described below. The non-magnetic metal layer can be a thin film made of a non-magnetic metal. Examples of non-magnetic metals include Ta, Mo, and Ru, and among these, Ta is preferable.

[0028] The buffer layer is laminated on a non-magnetic metal layer. Because the buffer layer needs to pass current whether it is the domain wall motion spatial light modulator 10 or the TMR element, it is made of a material that has adequate conductivity when thinned. Furthermore, it is desirable for the buffer layer to be made of a material that has a slow etching rate in the manufacturing process described below, contains elements that are highly sensitive to SIMS (secondary ion mass spectrometry), and is visible on a SIMS endpoint monitor. This allows etching to be reliably stopped at the buffer layer, preventing damage to the first magnetization pinned layer 12.

[0029] The buffer layer may be made of an oxide or nitride, such as MgO, Al2O3, MgAl2O4, TiO2, ZnO, or RuO2. Among these, MgO is preferred. The MgO layer has moderate conductivity, a slow etching rate, and high SIMS sensitivity.

[0030] The light modulation layer 11 is laminated on the first magnetization fixed layer 12 or the buffer layer. Known ferromagnetic materials can be used as materials for the light modulation layer 11, and it is preferable to use a material with a large magneto-optical effect (Kerr effect). To enhance the magneto-optical effect, the light modulation layer 11 is preferably a magnetic layer with perpendicular magnetic anisotropy. Specific examples of the light modulation layer 11 include multilayer films of transition metals with Pd, Pt, Cu, etc., such as Co / Pd multilayer films, and alloys (RE-TM alloys) of rare earth metals and transition metals, such as TbFeCo films and GdFe films. Among these, GdFe films are preferred.

[0031] The first magnetization fixed layer 12 and a part of the light modulation layer 11 arranged directly above it are ferromagnetically exchange coupled via a nonmagnetic metal layer and a buffer layer, so that the magnetization direction of the first magnetization fixed layer 12 and the magnetization direction of the part of the light modulation layer 11 arranged directly above it are reversed simultaneously.

[0032] The second magnetization pinned layer 13 is selected from materials usable for the first magnetization pinned layer 12, and similarly, the non-magnetic metal layer and buffer layer are selected from materials usable for the non-magnetic metal layer and buffer layer in the first magnetization pinned layer 12. The light modulation layer 11 is designed to behave in the same way as the first magnetization pinned layer 12.

[0033] Here, the first magnetization pinned layer 12 and the second magnetization pinned layer 13 are designed to have different coercive forces in order to form the light modulation region 11b and the domain wall 11c. Therefore, by applying an external magnetic field, it is possible to realize antiparallel initial magnetization directions at both ends of the light modulation layer 11, which is essential for light modulation control.

[0034] Note that functional layers may be appropriately formed between the light modulation layer 11, the first magnetization pinned layer 12, the second magnetization pinned layer 13, each nonmagnetic metal layer, and each buffer layer, or at the interface with the lower electrode. For example, to protect the light modulation layer 11 from damage during the microfabrication process, a cap layer containing Ta, Ru, or SiN may be provided on the light modulation layer 11. The cap layer functions to prevent GdFe or TbFeCo, which are easily oxidized and used to form the light modulation layer 11, from being oxidized in the atmosphere after the domain wall motion type spatial light modulator 10 is completed.

[0035] As described above, the first magnetization pinned layer 12 and a portion of the light modulation layer 11 directly above are ferromagnetically exchange coupled, and the second magnetization pinned layer 13 and a portion of the light modulation layer 11 directly above are also ferromagnetically exchange coupled, and the magnetization directions of each are reversed simultaneously. 1 and 3, the magnetization direction of the first magnetization pinned layer 12 is designed to be upward, while the magnetization direction of the second magnetization pinned layer 13 is designed to be downward.

[0036] A domain wall 11c is formed in the light modulation layer 11, perpendicular to the longitudinal direction of the light modulation layer 11. That is, the magnetization directions of the magnetic domains formed on both sides of the domain wall 11c in the light modulation layer 11 are opposite to each other. For example, as shown in Figures 1 and 3, the magnetization direction of the magnetic domain on the first magnetization fixed layer 12 side of the domain wall 11c is downward, and the magnetization direction of the magnetic domain on the second magnetization fixed layer 13 side of the domain wall 11c is upward.

[0037] In this way, by forming magnetic domains with different magnetization directions in the light modulation layer 11 via the domain walls 11c, the domain wall motion type spatial light modulator 10 can function as a spatial light modulator. More specifically, for example, if the domain wall motion type spatial light modulator 10 is configured as a reflective spatial light modulator, when light with uniform polarization is incident on the upper surface of the light modulation layer 11 from above the domain wall motion type spatial light modulator 10, the rotation angle of the polarization plane of the reflected light will vary depending on the orientation of the magnetization direction. Therefore, by assigning the reflected light corresponding to these different rotation angles of the polarization plane to light brightness or darkness via a polarizing filter, it is possible to modulate the light. On the other hand, by configuring the substrate from a translucent material such as glass or sapphire, the domain wall motion type spatial light modulator 10 can also function as a transmissive spatial light modulator.

[0038] FIG. 4 shows the structure of a conventional domain wall motion spatial light modulator. The domain wall motion spatial light modulator 200 includes multiple domain wall motion spatial light modulation elements 20. Similar to the domain wall motion spatial light modulator 10, the domain wall motion spatial light modulator 20 includes a light modulation layer 21, a first magnetization pinned layer 22, and a second magnetization pinned layer 23. The first magnetization pinned layer 22 and the second magnetization pinned layer 23 are made of the same material, but the length of the first magnetization pinned layer 22 in the direction of extension is longer than the length of the second magnetization pinned layer 23 in the direction of extension. Therefore, the coercive force of the first magnetization pinned layer 22 is smaller than the coercive force of the second magnetization pinned layer 23. The domain wall motion spatial light modulators 20 arranged on both sides of the first magnetization pinned layer 22 share the first magnetization pinned layer 22. Moreover, the domain wall motion type spatial light modulators 20 arranged in the direction in which the first magnetization pinned layer 22 extends share the first magnetization pinned layer 22 .

[0039] 5, the first magnetization pinned layer 22 contacts the ground electrode 24, and a portion of the second magnetization pinned layer 23 contacts the drain electrode 25 of the pixel selection transistor. For this reason, in designing, alignment margins are required between the ground electrode 24 and the drain electrode 25 and the first magnetization pinned layer 22 and the second magnetization pinned layer 23. This has made it difficult to increase the aperture ratio of the domain wall motion type spatial light modulator 20.

[0040] The manufacturing method of the domain wall motion spatial light modulator 200 is not particularly limited, and for example, the method described in Patent Document 3 can be used. Specifically, first, a resist corresponding to the shapes of the first magnetization pinned layer 22 and the second magnetization pinned layer 23 is patterned on an SiO2 layer of an insulating member formed on a Si backplane, and then etching is performed. Next, the first magnetization pinned layer 22, the second magnetization pinned layer 23, an intermediate layer, etc. are formed in the etched area on the Si backplane. Next, the resist layer is removed, and then a material constituting the light modulation layer 21 is formed. Next, a resist corresponding to the shape of the light modulation layer 21 is patterned, and then etching is performed. Finally, the resist layer is removed, and the light modulation layer 21 is formed.

[0041] [Magnetic domain wall motion type spatial light modulator of this embodiment] FIG. 6 shows the structure of an example of a domain wall motion spatial light modulator according to this embodiment. Like the domain wall motion spatial light modulator 200, the domain wall motion spatial light modulator 300 includes multiple domain wall motion spatial light modulation elements 30. Like the domain wall motion spatial light modulator 20, the domain wall motion spatial light modulator 30 includes a light modulation layer 31, a first magnetization pinned layer 32, and a second magnetization pinned layer 33. The first magnetization pinned layer 32 and the second magnetization pinned layer 33 are made of the same material, but the length of the first magnetization pinned layer 32 in the direction of extension is longer than the length of the second magnetization pinned layer 33 in the direction of extension. Therefore, the coercive force of the first magnetization pinned layer 32 is smaller than the coercive force of the second magnetization pinned layer 33. The domain wall motion spatial light modulators 30 arranged on both sides of the first magnetization pinned layer 32 share the first magnetization pinned layer 32. Moreover, the domain wall motion type spatial light modulators 30 arranged in the direction in which the first magnetization pinned layer 32 extends share the first magnetization pinned layer 32 .

[0042] On the other hand, the first magnetization pinned layer 32 contacts the rectangular ground electrode 34, and a part of the second magnetization pinned layer 33 contacts the rectangular drain electrode 35 of the pixel selection transistor, but the second magnetization pinned layer 33 has a region that extends perpendicular to the direction in which the first magnetization pinned layer 32 extends and a region that extends parallel to the direction in which the first magnetization pinned layer 32 extends, forming an L-shape or an inverted L-shape in top view. Therefore, the domain wall motion type spatial light modulator 30 has a reduced alignment margin and an increased aperture ratio compared to the domain wall motion type spatial light modulator 20.

[0043] The ratio of the length of the region of the second magnetization pinned layer 33 that extends perpendicular to the direction in which the first magnetization pinned layer 32 extends and the length of the region that extends parallel to the direction in which the first magnetization pinned layer 32 extends is not particularly limited.

[0044] Here, we verified by computer simulation whether the aperture ratio (light modulation area) of the domain wall motion type spatial light modulator 30 increases compared to the light modulation area of ​​the domain wall motion type spatial light modulator 20. Specifically, we calculated the domain wall current drive using the LLG (Landau-Lifsitz-Gilbert) equation, which represents the dynamic process of magnetization of a magnetic material. At this time, the mesh size was set to 10 nm. Here, the LLG equation is expressed by the following formula:

[0045]

number

[0046]

number

[0047] 7 shows a calculation model of the domain wall motion type spatial light modulators 200 and 300. Here, the sizes of the light modulation layer, the first magnetization pinned layer, and the second magnetization pinned layer in each direction are as follows. Light modulation layer 21; x direction: 1460 nm, y direction: 300 nm, z direction: 10 nm Light modulation layer 31: x direction: 1700 nm, y direction: 300 nm, z direction: 10 nm First magnetization fixed layer 22, 32; x direction: 120nm, y direction: 2500nm, z direction: 20nm Second magnetization fixed layer 23; x direction: 120 nm, y direction: 500 nm, z direction: 20 nm Region of the second magnetization fixed layer 33 extending in the x-axis direction: x direction: 360 nm, y direction: 120 nm, z direction: 20 nm Region of the second magnetization fixed layer 33 extending in the y-axis direction: x direction: 120 nm, y direction: 500 nm, z direction: 20 nm

[0048] The parameters and structures of the magnetic properties of the light modulation layers 21 and 31, the first magnetization pinned layers 22 and 32, and the second magnetization pinned layers 23 and 33 were calculated using the following values ​​that are close to the actual measurements. Saturation magnetization M of light modulation layers 21 and 31: 0.092 [T] Anisotropy magnetic field Hk of the light modulation layers 21 and 31: 3 [kOe] Exchange coupling constant A of the light modulation layers 21 and 31: 4.0×10 -12 [J / m] Saturation magnetization M:2 [T] of the first magnetization pinned layers 22 and 32 and the second magnetization pinned layers 23 and 33 Exchange coupling constant A of the first magnetization pinned layers 22, 32 and the second magnetization pinned layers 23, 33: 1.0×10 -11 [J / m]

[0049] 8(a) and 8(b) show the calculation results of the magnetic field strength of the calculation models of the domain wall motion type spatial light modulators 200 and 300, respectively. Here, the x-direction distance is the distance from the left end of the second magnetization fixed layer 23, 33 in FIG. 7, and the magnetic field strength is the average value in the center plane (xy plane) in the z direction of the light modulation layer 21, 31, taking into account only the second magnetization fixed layer 23, 33.

[0050] 8, it was confirmed that in the region where the x-direction distance between the light modulation layers 21 and 31 is 0 to 0.12 μm (region formed on the second magnetization fixed layers 23 and 33), a magnetic field in the −z direction is applied by the second magnetization fixed layers 23 and 33. It was also confirmed that the magnetic field in the +z direction increases near the position where the x-direction distance between the light modulation layers 21 and 31 is 0.12 μm, and a stray magnetic field of approximately 800 Oe is applied. It was also confirmed that as the x-direction distance between the light modulation layer 21 increases, the magnetic field in the +z direction decreases, and the stray magnetic field approaches 0. On the other hand, in the region where the x-direction distance between the light modulation layer 31 is approximately 0.3 to 0.6 μm, it was confirmed that a magnetic field of 50 to 100 Oe in the +z direction is applied, and the magnetic field strength is slightly greater in FIG. 8(b) than in FIG. 8(a).

[0051] FIG. 9 shows the results of calculations of domain wall current driving in a calculation model of the domain wall motion type spatial light modulator 200.

[0052] Here, when domain wall current driving is performed using spin transfer torque, applying a pulse current in the -y direction causes electrons to move in the +y direction. Taking advantage of this phenomenon, we performed calculations of domain wall current driving. The purpose of these calculations was to investigate the effect of the structure of the magnetization pinned layer on the domain wall, and did not precisely consider the formation of initial magnetic domains due to leakage magnetic fields.

[0053] It can be seen from FIG. 9 that when a pulse current with a pulse width of 5 ns is applied to the domain wall motion type spatial light modulator 20, the domain wall moves to the right linearly with the time during which the pulse current is applied.

[0054] 10 and 11 show the results of calculations of domain wall current driving in a calculation model of the domain wall motion type spatial light modulator 300. FIG.

[0055] 10 and 11, it was confirmed that in the domain wall motion type spatial light modulator 30, the domain walls move in the direction in which the light modulation layer 31 extends depending on the time that the pulse current is applied, and the light modulation area is increased by about 1.2 times compared to the domain wall motion type spatial light modulator 20. This is because, by making the second magnetization pinned layer 33 L-shaped or inverted L-shaped in top view, the light modulation area is increased by the area extending perpendicular to the direction in which the first magnetization pinned layer 32 extends, and therefore the alignment margin is also reduced. Here, 1 ns after application of the pulse current, magnetization fluctuations were observed, which are presumed to be the influence of a magnetic field of 50 to 100 Oe in the +z direction in Figure 8(b). However, it was confirmed that the influence on domain wall current driving was small, and the domain wall continued to move without disturbance for up to 5 ns. It was also confirmed that the second magnetization pinned layer 33 had little influence on the adjacent light modulation layer 31. Furthermore, in the calculation models of the domain wall motion type spatial light modulator 200 and the domain wall motion type spatial light modulator 300, the positions of the domain walls after 5 ns were approximately the same, so it was presumed that the domain wall velocities were also approximately the same, confirming that the second magnetization pinned layer 33 had little influence on the light modulation layer 31.

[0056] The domain wall motion type spatial light modulator 300 can be manufactured in the same manner as the domain wall motion type spatial light modulator 200, except that a resist is patterned to correspond to the shapes of the first magnetization fixed layer 32 and the second magnetization fixed layer 33.

[0057] 12 shows the structure of a modified example of the domain wall motion type spatial light modulator 300. The domain wall motion type spatial light modulator 300A has the same configuration as the domain wall motion type spatial light modulator 300, except that the second magnetization pinned layer 33A has regions that extend perpendicularly and regions that extend obliquely relative to the direction in which the first magnetization pinned layer 32 extends. Therefore, the domain wall motion type spatial light modulator 30A has a larger aperture ratio than the domain wall motion type spatial light modulator 20.

[0058] The angle formed by the direction in which the second magnetization fixed layer 33A extends perpendicular to the direction in which the first magnetization fixed layer 32 extends and the direction in which the second magnetization fixed layer 33A extends obliquely to the direction in which the first magnetization fixed layer 32 extends is not particularly limited, but is, for example, greater than or equal to 90° and less than or equal to 135°.

[0059] 13 shows the structure of a modified example of the domain wall motion type spatial light modulator 300. The domain wall motion type spatial light modulator 300B has the same configuration as the domain wall motion type spatial light modulator 300, except that the second magnetization pinned layer 33B extends obliquely with respect to the direction in which the first magnetization pinned layer 32 extends. Therefore, the domain wall motion type spatial light modulator 30B has a larger aperture ratio than the domain wall motion type spatial light modulator 20.

[0060] The angle formed by the direction in which the first magnetization pinned layer extends and the direction in which the second magnetization pinned layer 33B extends is not particularly limited, but is, for example, not less than 30° and not more than 60°.

[0061] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the present invention. For example, instead of increasing the length of the first magnetization fixed layer in the direction in which it extends, the width of the first magnetization fixed layer may be increased to reduce the coercive force of the first magnetization fixed layer. [Explanation of symbols]

[0062] 10, 20, 30, 30A, 30B Domain wall motion type spatial light modulator 11, 21, 31 Light modulation layer 11a Initial magnetic domain 11b Light modulation region 11c domain wall 12, 22, 32 First magnetization fixed layer 13, 23, 33, 33A, 33B Second magnetization fixed layer 14 Middle Class 24, 34 Ground electrode 25, 35 Drain electrode 200, 300, 300A, 300B Domain wall motion type spatial light modulator

Claims

1. a domain wall motion type spatial light modulation element having a light modulation layer that changes the direction of polarization of incident light and outputs the light; and a first magnetization fixed layer and a second magnetization fixed layer that are disposed to extend to both ends of the light modulation layer; The domain wall motion type spatial light modulator is a domain wall motion type spatial light modulator, in which the coercive force of the first magnetization fixed layer is smaller than the coercive force of the second magnetization fixed layer, and at least a portion of the second magnetization fixed layer extends perpendicularly or obliquely to the direction in which the first magnetization fixed layer extends.

2. 2. The domain wall motion type spatial light modulator according to claim 1, wherein at least a portion of the second magnetization fixed layer of the domain wall motion type spatial light modulator extends parallel to the direction in which the first magnetization fixed layer extends.

3. 3. The domain wall motion type spatial light modulator according to claim 2, wherein the second magnetization pinned layer has an L-shape when viewed from above or an inverted L-shape when viewed from above.

4. 4. The domain wall motion type spatial light modulator according to claim 1, wherein the domain wall motion type spatial light modulator element has the light modulation layer extending perpendicular to the direction in which the first magnetization fixed layer extends.

5. 5. The domain wall motion type spatial light modulator according to claim 1, wherein the length in the direction in which the first magnetization fixed layer extends is longer than the length in the direction in which the second magnetization fixed layer extends.

Images