JP2023136628A - Domain wall movement type spatial light modulator - Google Patents

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 light modulation layer 31 at least partially extends diagonally with respect to a direction in which the first magnetization fixed layer 32 extends.SELECTED DRAWING: Figure 6

Description

The present invention relates to a domain wall moving spatial light modulator.

In order to realize three-dimensional holography, a viewing zone of 30 degrees or more is practically required. Therefore, it is necessary to reduce the pixel pitch of a spatial light modulator (SLM), which is a display device, to 1 μm or less. Existing SLMs such as liquid crystals and digital micromirror devices (DMDs) have a pixel pitch of approximately 5 μm, and it is difficult to miniaturize them any further.

On the other hand, magneto-optical spatial light modulators (MOSLM) that use spin injection magnetization reversal or domain wall movement to rewrite pixels need to improve their performance from the viewpoints of light utilization efficiency, operating current, etc. It is possible to easily realize a pixel pitch of (see, for example, Patent Document 1). A MOSLM is a device that realizes light modulation by assigning the rotation of the polarization plane of light according to the direction of magnetization to brightness and darkness.

A domain wall motion spatial light modulator includes a light modulation layer that changes the polarization direction of incident light and emits the light, and a first layer that extends parallel to each other at both ends of the light modulation layer and has a different coercive force. It is equipped with a domain wall motion spatial light modulator having a magnetization fixed layer and a second magnetization fixed layer, and can control the expansion and contraction of the magnetic domain by the direction of the current flowing through the light modulation layer (for example, see Patent Document 2) . Domain wall motion spatial light modulators can be expected to consume less power than MOSLMs that use spin injection magnetization reversal, but the three types of ferromagnetic layers, the optical modulation layer and the two fixed magnetization layers, do not have enough coercive force. In order to make a difference and precisely fabricate a complex device structure, it is necessary to realize an advanced device design based on a pixel pitch of 1 μm or less.

In Patent Document 3, when designing the coercive force difference between the first magnetization fixed layer and the second magnetization fixed layer, high precision can be achieved by forming the first magnetization fixed layer and the second magnetization fixed layer in one process. A method for omitting the number of alignments is described. Thereby, a domain wall displacement type spatial light modulator can be formed with a simple process.

Japanese Patent Application Publication No. 2012-141402 JP2018-206900A JP2019-220544A

However, since a domain wall motion spatial light modulator is formed on the drain electrode and ground electrode of the pixel selection transistor, when designing, it is necessary to Highly accurate positioning is required between the two. For this reason, it has been difficult to increase the aperture ratio of domain wall displacement type spatial light modulators.

An object of the present invention is to provide a domain wall displacement spatial light modulator that can increase the aperture ratio of the domain wall displacement spatial light modulator with a simple process.

One aspect of the present invention provides a domain wall displacement spatial light modulator including a light modulation layer that changes the direction of polarization of incident light and emits the light, and a first light modulation layer extending from both ends of the light modulation layer. The domain wall motion spatial light modulator includes a domain wall motion spatial light modulator having a magnetization fixed layer and a second magnetization fixed layer, and the domain wall motion spatial light modulation device is such that the coercive force of the first magnetization fixed layer is such that the coercive force of the first magnetization fixed layer is equal to that of the second magnetization fixed layer. The coercivity is smaller than the coercive force, and at least a portion of the light modulating layer extends obliquely to the direction in which the first magnetization fixed layer extends.

In the domain wall motion spatial light modulator, the angle between the direction in which at least a portion of the light modulation layer extends obliquely and the direction in which the first magnetization fixed layer extends is 30° or more and 60° or less. There may be.

The region in which at least a portion of the light modulation layer extends obliquely may have a parallelogram shape when viewed from above.

The first magnetization fixed layer and the second magnetization fixed layer may be arranged to extend parallel to each other at both ends of the light modulation layer.

The length in the extending direction of the first magnetization fixed layer may be longer than the length in the extending direction of the second magnetization fixed layer.

According to the present invention, it is possible to provide a domain wall displacement spatial light modulator that can increase the aperture ratio of the domain wall displacement spatial light modulator with a simple process.

FIG. 2 is a perspective view showing the structure of a conventional domain wall displacement type spatial light modulator. FIG. 2 is a side view showing the operation of the domain wall displacement spatial light modulator of FIG. 1; FIG. 2 is a side view showing the structure and operation of the domain wall displacement spatial light modulator of FIG. 1. FIG. FIG. 2 is a top view showing the structure of a conventional domain wall displacement spatial light modulator. FIG. 5 is a top view showing the positional relationship between the domain wall motion spatial light modulator of FIG. 4 and the drain electrode and ground electrode of the pixel selection transistor. FIG. 2 is a top view showing the structure of an example of a domain wall moving spatial light modulator according to the present embodiment. FIG. 7 is a perspective view showing a calculation model of the domain wall moving spatial light modulator shown in FIGS. 4 and 6. FIG. 5 is a diagram showing calculation results of domain wall current drive of the calculation model of the domain wall displacement type spatial light modulator of FIG. 4. FIG. 7 is a diagram showing calculation results of domain wall current drive of the calculation model of the domain wall displacement type spatial light modulator of FIG. 6. FIG. 7 is a top view showing the structure of a modification of the domain wall displacement spatial light modulator of FIG. 6. FIG. 7 is a top view showing the structure of a modification of the domain wall displacement spatial light modulator of FIG. 6. FIG. FIG. 12 is a diagram illustrating the formation of an initial magnetic domain of the domain wall displacement type spatial light modulator of FIG. 11; 7 is a top view showing the structure of a modification of the domain wall displacement spatial light modulator of FIG. 6. FIG. FIG. 14 is a diagram illustrating the formation of an initial magnetic domain and domain wall movement of the domain wall movement type spatial light modulator shown in FIG. 13; 7 is a top view showing the structure of a modification of the domain wall displacement spatial light modulator of FIG. 6. FIG.

Embodiments of the present invention will be described below with reference to the drawings, but the basic configuration (materials, structure, operation, etc.) of the domain wall moving spatial light modulator of this embodiment is different from that of the conventional domain wall moving spatial light modulator. Since it is similar to an optical modulator, a conventional domain wall displacement spatial light modulator will be described first.

[Conventional domain wall moving spatial light modulator]
FIG. 1 shows the structure of a conventional domain wall displacement type spatial light modulator. The domain wall motion spatial light modulator 10 includes a light modulating layer 11 that changes the direction of polarization of incident light and outputs the light, and a first magnetization fixed layer that is arranged at both ends of the light modulating layer 11 and has a different coercive force. It has a layer 12 and a second magnetization fixed layer 13, and is formed on a substrate such as Si.

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

The domain wall displacement spatial light modulator 10 has a first magnetization fixed layer 12 and a second magnetization fixed layer 13 extending in parallel to each other at both ends of a light modulation layer 11 which is rectangular in top view and extends in a predetermined direction. The light modulation layer 11 extends perpendicularly to the direction in which the first magnetization fixed layer 12 and the second magnetization fixed layer 13 extend in parallel. The lower surface of the light modulation layer 11 and the upper surfaces of the first magnetization fixed layer 12 and the second magnetization fixed layer 13 are in contact with each other on the same plane, and light is transmitted through the first magnetization fixed layer 12 and the second magnetization fixed layer 13. A pulse current can be applied to the modulation layer 11.

FIG. 2 shows the operation of the domain wall displacement type spatial light modulator 10. Specifically, a coercive force difference (Hc2>Hc1) is designed between the coercive force (Hc1) of the first magnetization fixed layer 12 and the coercive force (Hc2) of the second magnetization fixed layer 13, and an external magnetic field is applied. By doing so, mutually antiparallel initial magnetization directions at both ends of the light modulation layer 11, which are essential for light modulation control, are realized. First, when a downward external magnetic field Hx1 (Hx1>Hc2>Hc1), which is larger than Hc2, is applied, the magnetization of the light modulation layer 11, first magnetization fixed layer 12, and second magnetization fixed layer 13 becomes downward (Fig. (see (a)). Next, when an upward external magnetic field Hx2 (Hc2>Hx2>Hc1), which is larger than Hc1 and smaller than Hc2, is applied, the magnetization directions of the light modulation layer 11 and the first magnetization fixed layer 12 change upward ( (See Figure 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 due to the leakage magnetic field Hl from the first magnetization fixed layer 12, and as a result, the domain wall movement type spatial light modulation element 10 The aperture ratio is determined (see FIG. 2(c)).

FIG. 3 shows the structure and operation of the domain wall displacement type spatial light modulator 10. The domain wall motion spatial light modulator 10A has an intermediate layer 14 between the light modulating layer 11, the first magnetization fixed layer 12, and the second magnetization fixed layer 13, depending on the microfabrication process and magnetic design. , a nonmagnetic metal layer and a buffer layer are formed.

The first magnetization fixed layer 12 is made of a ferromagnetic material, has a magnetization direction 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 having perpendicular magnetic anisotropy is used for the light modulation layer 11, the first magnetization fixed layer 12 has magnetic anisotropy in the same direction as the light modulation layer 11. No. 12 also uses a ferromagnetic material having perpendicular magnetic anisotropy. It is preferable that the light modulation layer 11 and the first magnetization fixed layer 12 are made of a ferromagnetic material having perpendicular magnetic anisotropy.

The materials constituting the first magnetization fixed layer 12 and the second magnetization fixed layer 13 include a nonmagnetic layer sandwiched between a magnetization fixed layer whose magnetization is fixed in the perpendicular direction and a magnetization free layer whose magnetization direction is reversible. Therefore, a known ferromagnetic material constituting the magnetization fixed layer of a CPP-GMR (perpendicularly conducting giant magnetoresistive effect) element having perpendicular magnetic anisotropy, a TMR element, etc. can be used. 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, Examples include FePt-based alloys. Thereby, the coercive force of the first magnetization fixed layer 12 can be increased, and the magnetization direction of the first magnetization fixed layer 12 can be fixed so as not to be easily changed by an external magnetic field.

Further, the first magnetization fixed layer 12 may be a multilayer film in which transition metal layers such as an Fe layer, a Co layer, and a Ni layer and nonmagnetic metal layers are alternately laminated; for example, Co/Pt, A multilayer film such as Fe/Pt or Co/Pd may be used. By using these ferromagnetic materials, the first magnetization fixed layer 12 with high perpendicular magnetic anisotropy and large coercive force can be obtained.

Here, the above-mentioned multilayer film has a characteristic that the coercive force increases by heat treatment. Therefore, when the multilayer film described above is heat-treated to increase the coercive force of the first magnetization fixed layer 12, the coercive force of the ferromagnetic exchange coupling portion after coupling with the light modulation layer 11 also increases, and the light modulation region 11b and The difference in coercive force increases.

The nonmagnetic metal layer and the buffer layer are arranged between the light modulation layer 11 and the first magnetization fixed layer 12, and can maintain magnetic coupling between the light modulation layer 11 and the first magnetization fixed layer 12.

A nonmagnetic metal layer is laminated on the first magnetization fixed layer 12. The nonmagnetic metal layer is provided to prevent etching damage from occurring on the first magnetization fixed layer 12 in the manufacturing process described later. A thin film made of nonmagnetic metal can be used as the nonmagnetic metal layer. Examples of the nonmagnetic metal include Ta, Mo, and Ru, and among these, Ta is preferable.

The buffer layer is laminated on the nonmagnetic metal layer. The buffer layer is made of a material that has appropriate conductivity when made into a thin film, since it is necessary to flow a current regardless of whether it is a domain wall motion spatial light modulator 10 or a TMR element. In addition, the buffer layer is desirably made of a material that has a slow etching rate in the manufacturing process described below, contains an element that has high detection sensitivity in SIMS (secondary ion mass spectrometry), and is visible on a SIMS endpoint monitor. . Thereby, it becomes possible to reliably stop etching with the buffer layer, and damage to the first magnetization fixed layer 12 can be avoided.

As a material constituting the buffer layer, an oxide or a nitride can be used, and examples thereof include MgO, Al ₂ O ₃ , MgAl ₂ O ₄ , TiO ₂ , ZnO, RuO ₂ and the like. Among these, MgO is preferred. The MgO layer has moderate conductivity, slow etching rate, and high SIMS sensitivity.

The light modulation layer 11 is laminated on the first magnetization fixed layer 12 or the buffer layer. As the material constituting the light modulation layer 11, a known ferromagnetic material can be used, and it is preferable to use a material with a large magneto-optic effect (Kerr effect). In order to increase the magneto-optic effect, the light modulating layer 11 is preferably a magnetic layer having perpendicular magnetic anisotropy. Specific examples of the light modulation layer 11 include multilayer films of transition metals such as Co/Pd multilayer films and Pd, Pt, Cu, etc., alloys of rare earth metals and transition metals such as TbFeCo films, and GdFe films (RE- TM alloy) film, etc. Among these, GdFe film is preferred.

A part of the light modulating layer 11 disposed directly above the first magnetization fixed layer 12 is ferromagnetically exchange-coupled via the nonmagnetic metal layer and the buffer layer. As a result, the magnetization direction of the first magnetization fixed layer 12 and the magnetization direction of a portion of the light modulation layer 11 disposed directly above are simultaneously reversed.

The second magnetization fixed layer 13 is selected from materials that can be used in the first magnetization fixed layer 12, and similarly, the nonmagnetic metal layer and the buffer layer are respectively selected from materials that can be used in the first magnetization fixed layer 12. Selected from among the materials available for the buffer layer. The light modulation layer 11 is designed to behave in the same manner as the first magnetization fixed layer 12.

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

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

As mentioned above, the first magnetization fixed layer 12 and a part of the light modulation layer 11 directly above are ferromagnetic exchange coupled, and the second magnetization fixed layer 13 and a part of the light modulation layer 11 directly above are also ferromagnetic exchange coupled. They are ferromagnetically exchange coupled, and their respective magnetization directions are simultaneously reversed. As shown in FIGS. 1 and 3, the first magnetization fixed layer 12 is designed to have an upward magnetization direction, while the second magnetization fixed layer 13 is designed to have a downward magnetization direction. has been done.

A domain wall 11c is formed in the light modulation layer 11 and is 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 of the light modulating layer 11 are opposite to each other. For example, as shown in FIGS. 1 and 3, the magnetization direction of the magnetic domain closer to the first magnetization fixed layer 12 than the domain wall 11c is downward, and the magnetization direction of the magnetic domain closer to the second magnetization fixed layer 13 than the domain wall 11c is The direction is upward.

In this way, by forming magnetic domains with different magnetization directions in the light modulation layer 11 via the domain wall 11c, the domain wall displacement spatial light modulation element 10 can function as a spatial light modulation element. More specifically, for example, when the domain wall displacement spatial light modulator 10 is configured as a reflective spatial light modulator, polarized light is applied from above the domain wall motion spatial light modulator 10 to the upper surface of the light modulation layer 11. When light with uniform values is incident, the angle of rotation of the plane of polarization of the reflected light differs depending on the direction of magnetization. Therefore, it is possible to modulate the light by assigning each reflected light according to the rotation angle of these different polarization planes to brightness and darkness of the light through the polarizing filter. On the other hand, by configuring the substrate with a transparent material such as glass or sapphire, it is also possible to cause the domain wall movement type spatial light modulation element 10 to function as a transmission type spatial light modulation element.

FIG. 4 shows the structure of a conventional domain wall moving spatial light modulator. The domain wall moving spatial light modulator 200 includes a plurality of domain wall moving spatial light modulators 20. Further, like 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 fixed layer 22, and a second magnetization fixed layer 23. At this time, the materials constituting the first magnetization fixed layer 22 and the second magnetization fixed layer 23 are the same, but the length in the direction in which the first magnetization fixed layer 22 extends is the same as the length in the direction in which the second magnetization fixed layer 23 extends. longer than the length in the direction shown. Therefore, the coercive force of the first magnetization fixed layer 22 is smaller than the coercive force of the second magnetization fixed layer 23. Here, the domain wall motion spatial light modulators 20 disposed on both sides of the first magnetization fixed layer 22 share the first magnetization fixed layer 22. Furthermore, the domain wall motion spatial light modulators 20 arranged in the direction in which the first magnetization fixed layer 22 extends share the first magnetization fixed layer 22.

On the other hand, as shown in FIG. 5, the first magnetization fixed layer 22 is in contact with the ground electrode 24, and a part of the second magnetization fixed layer 23 is in contact with the drain electrode 25 of the pixel selection transistor. Therefore, during design, highly accurate positioning is required between the ground electrode 24 and drain electrode 25 and the first magnetization fixed layer 22 and second magnetization fixed layer 23. For this reason, it has been difficult to increase the aperture ratio of the domain wall displacement type spatial light modulator 20.

Note that the method for manufacturing the domain wall displacement spatial light modulator 200 is not particularly limited, but for example, the method described in Patent Document 3 can be used. Specifically, first, a resist corresponding to the shapes of the first magnetization fixed layer 22 and the second magnetization fixed layer 23 is patterned on the SiO ₂ layer of the insulating member formed on the Si backplane, and then etching is performed. do. Next, the first magnetization fixed layer 22, the second magnetization fixed layer 23, an intermediate layer, etc. are formed in the etched region on the Si backplane. Next, after removing the resist layer, a material constituting the light modulation layer 21 is deposited. Next, a resist corresponding to the shape of the light modulation layer 21 is patterned and then etched. Finally, the resist layer is removed and a light modulation layer 21 is formed.

[Domain wall moving spatial light modulator of this embodiment]
FIG. 6 shows the structure of an example of the domain wall moving spatial light modulator of this embodiment. Similar to the domain wall displacement spatial light modulator 200, the domain wall displacement spatial light modulator 300 includes a plurality of domain wall displacement spatial light modulators 30. Further, the domain wall motion spatial light modulator 30 includes a light modulation layer 31, a first magnetization fixed layer 32, and a second magnetization fixed layer 33, similarly to the domain wall motion spatial light modulator 20. At this time, the materials constituting the first magnetization fixed layer 32 and the second magnetization fixed layer 33 are the same, but the length in the direction in which the first magnetization fixed layer 32 extends is the same as the length in the direction in which the second magnetization fixed layer 33 extends. longer than the length in the direction shown. Therefore, the coercive force of the first magnetization fixed layer 32 is smaller than the coercive force of the second magnetization fixed layer 33. Here, the domain wall motion spatial light modulators 30 disposed on both sides of the first magnetization fixed layer 32 share the first magnetization fixed layer 32. Further, the domain wall motion spatial light modulators 30 arranged in the direction in which the first magnetization fixed layer 32 extends share the first magnetization fixed layer 32.

On the other hand, the first magnetization fixed layer 32 is in contact with the rectangular ground electrode 34, and a part of the second magnetization fixed layer 33 is in contact with the rectangular drain electrode 35 of the pixel selection transistor. The area other than on the fixed layer 32 is between the first fixed magnetization layer 32 and the second fixed magnetization layer 33, with respect to the direction in which the first fixed magnetization layer 32 and the second fixed magnetization layer 33 extend in parallel, It extends diagonally. Therefore, the domain wall displacement type spatial light modulator 30 has an increased aperture ratio compared to the domain wall displacement type spatial light modulation element 20.

The angle formed by the direction in which the light modulation layer 31 extends obliquely and the direction in which the first magnetization fixed layer 32 and the second magnetization fixed layer 33 extend in parallel is preferably 20° or more and 70° or less, and 30° or more. More preferably, the angle is at least 60 degrees. When the angle between the diagonally extending direction of the light modulation layer 31 and the parallel extending direction of the first magnetization fixed layer 32 and the second magnetization fixed layer 33 is 30° or more, the adjacent second magnetization fixed layers When the influence of the magnetic field from 33 is reduced and the angle is 60 degrees or less, the aperture ratio of the domain wall displacement spatial light modulator 30 increases.

The region in which at least a portion of the light modulating layer 31 extends obliquely has a parallelogram shape when viewed from above. Therefore, the aperture ratio of the domain wall displacement spatial light modulator 30 increases. Here, the light modulation layers 31 disposed on both sides of the first magnetization fixed layer 32 have a line-symmetrical structure with respect to the first magnetization fixed layer 32, and have a V-shape when viewed from above.

Note that the proportion of the diagonally extending region of the light modulation layer 31 is not particularly limited.

Here, computer simulation was conducted to verify whether the aperture ratio (light modulation region) of the domain wall motion spatial light modulator 30 increases compared to the light modulation region of the domain wall motion spatial light modulator 20. Specifically, domain wall current drive was calculated using the LLG (Landau-Lifsitz-Gilbert) equation representing 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 the formula

で表される。ここで、Ｍは、磁化［Ｔ］、Ｈ_ｅｆｆは、有効磁界［Ａ／ｍ］、γは、磁気ジャイロ定数、αは、ダンピング定数、Ｐは、スピン分極率、ｇは、ランデのｇ因子、μ_Ｂは、ボーア磁子［Ｊ／Ｔ］、ｅは、電子の素電荷［Ｃ］、Ｍ_Ｓは、飽和磁化［Ｔ］、Ｊは、電流密度［Ａ／ｍ_２］である。また、Ｈ_ｅｆｆは、式

It is expressed as Here, M is magnetization [T], H _eff is effective magnetic field [A/m], γ is magnetic gyro constant, α is damping constant, P is spin polarizability, g is Lande g factor , μ _B is the Bohr magneton [J/T], e is the electron elementary charge [C], _MS is the saturation magnetization [T], and J is the current density [A/m ₂ ]. Also, H _eff is the formula

で表される。ここで、Ｅ_ｔｏｔは、全エネルギー、Ｅ_ａｎｉは、磁気異方性エネルギー、Ｅ_ｍａｇは、静磁エネルギー、Ｅ_ｅｘは、交換エネルギー、Ｅ_ｅｘｔは、ゼーマンエネルギーである。

It is expressed as Here, E _tot is total energy, E _ani is magnetic anisotropy energy, E _mag is magnetostatic energy, E _ex is exchange energy, and E _ext is Zeeman energy.

FIG. 7 shows a calculation model of the domain wall displacement spatial light modulators 200 and 300. Here, the sizes of the light modulation layer, the first magnetization fixed layer, and the second magnetization fixed layer in each direction are as follows. Note that the x' direction means the direction in which the light modulation layer 31 extends, and the angle it makes with the direction in which the first magnetization fixed layer 32 and the second magnetization fixed layer 33 extend in parallel is 45 degrees.
Light modulation layer 21; x direction: 1460 nm, y direction: 300 nm, z direction: 10 nm
Light modulation layer 31; x' direction: 2015 nm, y direction: 300 nm, z direction: 10 nm
First magnetization fixed layer 22, 32; x direction: 120 nm, y direction: 2500 nm, z direction: 20 nm
Second magnetization fixed layer 23, 33; x direction: 120 nm, y direction: 500 nm, z direction: 20 nm

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

FIG. 8 shows calculation results of domain wall current drive of the calculation model of the domain wall moving spatial light modulator 200.

Here, when domain wall current driving is performed using spin transfer torque, when a pulse current is applied in the -y direction, electrons move in the +y direction. Using this phenomenon, we calculated domain wall current drive. In this calculation, the purpose is to examine the influence of the structure of the light modulation layer on the domain wall, and the formation of initial magnetic domains due to leakage magnetic fields, etc., are not precisely taken into account.

From FIG. 8, it was confirmed that when a pulse current with a pulse width of 5 ns was applied to the domain wall moving spatial light modulator 20, the domain wall moved to the right linearly with the time of applying the pulse current.

FIG. 9 shows calculation results of the domain wall current drive of the calculation model of the domain wall moving spatial light modulator 300.

From FIG. 9, it can be seen that in the domain wall motion spatial light modulator 30, the domain wall moves in the direction in which the light modulation layer 31 extends depending on the time when the pulse current is applied. In comparison, it was confirmed that the light modulation area increased by about 1.8 times. Furthermore, compared to the domain wall motion spatial light modulator 200, the domain wall motion spatial light modulator 300 has a structure in which a part of the second magnetization fixed layer 33 approaches the adjacent light modulation layer 31; It was confirmed that this had little effect.

Note that the domain wall motion spatial light modulator 300 can be manufactured in the same manner as the domain wall motion spatial light modulator 200, except that the resist is patterned in accordance with the shape of the light modulation layer 31.

FIG. 10 shows the structure of a modification of the domain wall moving spatial light modulator 300. The domain wall motion spatial light modulator 300A is similar to the domain wall motion spatial light modulator 300, except that the light modulation layers 31A arranged on both sides of the first magnetization fixed layer 32 are linear in top view. The composition is as follows. Therefore, the domain wall displacement type spatial light modulator 30A has an increased aperture ratio compared to the domain wall displacement type spatial light modulation element 20.

FIG. 11 shows the structure of a modification of the domain wall moving spatial light modulator 300. In the domain wall motion spatial light modulator 300B, the region of the light modulation layer 31B other than the vicinity of the first magnetization fixed layer 32 is between the first magnetization fixed layer 32 and the second magnetization fixed layer 33, and the region is the first magnetization fixed layer 32. It has the same configuration as the domain wall displacement spatial light modulator 300 except that the layer 32 and the second magnetization fixed layer 33 extend obliquely with respect to the direction in which they extend in parallel. Thereby, formation of an initial magnetic domain of the domain wall displacement type spatial light modulator 30B can be assisted. In the domain wall motion spatial light modulator 30B, as shown in FIG. 12, for example, the end of the optical modulation layer 31B on the first magnetization fixed layer 32 side is A downward initial magnetic domain 31a is formed. Here, the light modulating layer 31B is made of a material having perpendicular magnetization, but since the perpendicular magnetization in the thin wire structure is stable in the longitudinal direction of the thin wire, the light modulating layer 31B is If a corner is not formed at the portion that intersects with the ground electrode 34, it is assumed that the initial magnetic domain will expand due to the leakage magnetic field. At this time, since a corner is formed at a portion of the light modulation layer 31B that intersects with the ground electrode 34, the initial magnetic domain 31a is trapped at the corner, and the spread of the initial magnetic domain 31a is suppressed. As a result, the domain wall displacement spatial light modulator 30B has an increased light modulation area compared to the domain wall displacement spatial light modulator 300.

The distance d for trapping the initial magnetic domain 31a is, for example, about 50 nm or more and 200 nm or less.

FIG. 13 shows the structure of a modification of the domain wall moving spatial light modulator 300. In the domain wall motion spatial light modulator 300C, the region other than the vicinity of the first magnetization fixed layer 32 and the second magnetization fixed layer 33 of the light modulation layer 31C is The configuration is similar to that of the domain wall displacement spatial light modulator 300, except that the first magnetization fixed layer 32 and the second magnetization fixed layer 33 extend obliquely with respect to the direction in which they extend parallel to each other. In the domain wall displacement type spatial light modulator 30C, similarly to the domain wall displacement type spatial light modulation element 30B, after the initial magnetic domain 31a is formed (see FIG. 14(a)), the domain wall 31c moves and the second magnetization occurs. Since it stops near the fixed layer 33 (see FIG. 14(b)), the magnetic domain can be held more stably than in the domain wall motion spatial light modulator 30B.

FIG. 15 shows the structure of a modification of the domain wall moving spatial light modulator 300. The domain wall motion spatial light modulator 300D has the same configuration as the domain wall motion spatial light modulator 300, except that the first magnetization fixed layer and the second magnetization fixed layer 33D do not extend parallel to each other. Therefore, the domain wall displacement type spatial light modulator 30D has an increased aperture ratio compared to the domain wall displacement type spatial light modulation element 20.

The angle formed by the direction in which the first magnetization fixed layer extends and the direction in which the second magnetization fixed layer 33D extends is not particularly limited, but is, for example, 20 degrees or more and 70 degrees or less.

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 spirit of the present invention. For example, instead of increasing the length of the first magnetization fixed layer in the extending direction, the width of the first magnetization fixed layer may be increased to reduce the coercive force of the first magnetization fixed layer.

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

Claims (5)

A domain wall displacement type comprising a light modulation layer that changes the polarization direction of incident light and outputs the light, and a first magnetization fixed layer and a second magnetization fixed layer extending and disposed at both ends of the light modulation layer. Equipped with a spatial light modulation element,
In the domain wall motion spatial light modulation element, 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 part of the light modulation layer is such that the first magnetization fixed layer is A domain wall moving spatial light modulator that extends obliquely to the direction in which it extends. 2. The domain wall displacement type according to claim 1, wherein the angle formed by the direction in which at least a portion of the light modulation layer extends obliquely and the direction in which the first magnetization fixed layer extends is 30° or more and 60° or less. Spatial light modulator. 3. The domain wall displacement spatial light modulator according to claim 1, wherein the region in which at least a portion of the light modulating layer extends obliquely has a parallelogram shape when viewed from above. The domain wall displacement type space according to any one of claims 1 to 3, wherein the first magnetization fixed layer and the second magnetization fixed layer are arranged to extend parallel to each other at both ends of the light modulation layer. light modulator. The domain wall displacement space according to any one of claims 1 to 4, wherein the length of the first magnetization fixed layer in the extending direction is longer than the length of the second magnetization fixed layer in the extending direction. light modulator.

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