JP2024017570A - Magnetic domain wall displacement type spatial light modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic domain wall displacement type spatial light modulator capable of increasing the numerical aperture of a magnetic domain wall displacement type spatial light modulating element through simple processes without increasing a driving current.

SOLUTION: A magnetic domain wall displacement type spatial light modulator 300 comprises a magnetic domain wall displacement type spatial light modulating element 30 which has an optical modulation layer 31 extending in a predetermined direction and emitting incident light while changing the direction of polarization of the incident light, and a first magnetization fixation layer 22 and a second magnetization fixation layer 23 arranged at both end parts of the optical modulation layer 31 while extending in parallel and differing in coercive force from each other. The optical modulation layer 31 comprises a main body part, a first leakage magnetic field trap part provided at the end part of the main body part on the side where the first magnetization fixation layer 22 is arranged, and a second leakage magnetic field trap part provided at the end part of the main body part on the side where the second magnetization fixation layer 23 is arranged. The first leakage magnetic field trap part and the second leakage magnetic field trap part are smaller in width than the main body part.

SELECTED DRAWING: Figure 6

COPYRIGHT: (C)2024,JPO&INPIT

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 motion to rewrite pixels need to improve their performance from the viewpoints of light utilization efficiency, operating current, etc. It is possible to realize a pixel pitch of (for example, see 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

Here, in a domain wall motion spatial light modulator, if an initial magnetization direction that is antiparallel to each other is achieved at both ends of the light modulation layer by applying an external magnetic field, the leakage magnetic field from the first magnetization fixed layer causes light modulation. An initial magnetic domain is formed at the end of the layer on the first magnetization fixed layer side. Further, when domain wall current driving is performed, a second magnetic domain is formed at the end of the light modulation layer on the second magnetization fixed layer side due to a leakage magnetic field from the second magnetization fixed layer. Therefore, the aperture ratio of the domain wall motion spatial light modulator is determined in the light modulation region that does not include the initial magnetic domain and the second magnetic domain. At this time, the size of the initial magnetic domain changes depending on the magnetic properties of the light modulation layer, and as a result, the aperture ratio of the domain wall motion spatial light modulation element changes. On the other hand, in order to reduce the drive current, it is effective to lower the magnetization of the light modulation layer, but in that case, the size of the initial magnetic domain increases, so the aperture ratio of the domain wall motion spatial light modulation element increases. becomes smaller. For this reason, it is desired to increase the aperture ratio of domain wall displacement type spatial light modulators without increasing the drive current.

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 through a simple process and without increasing the drive current.

(1) A light modulation layer that extends in a predetermined direction and changes the direction of polarization of incident light and emits it; and a light modulation layer that extends in parallel to both ends of the light modulation layer and has different coercive forces. A domain wall motion spatial light modulator having a first magnetization fixed layer and a second magnetization fixed layer, wherein the light modulation layer includes a main body portion and the first magnetization fixed layer of the main body portion. a first leakage magnetic field trap section that is provided at a side end and traps a leakage magnetic field from the first magnetization fixed layer; and an end of the main body section on the side where the second magnetization fixed layer is arranged. a second leakage field trap section that traps a leakage field from the second magnetization fixed layer, and the first leakage field trap section and the second leakage field trap section are provided in the main body section. A domain wall moving spatial light modulator with a width smaller than that of .

(2) The domain wall moving spatial light modulator according to (1), wherein the first leakage magnetic field trap section and the second leakage magnetic field trap section have a smaller area than the main body section.

(3) The length of the first leakage magnetic field trap section is determined by the length of the leakage magnetic field from the first magnetization fixed layer in the x direction in which the light modulation layer extends according to the calculation model of the domain wall motion spatial light modulator. In the calculation results of the z-direction component perpendicular to the x-direction and the y-direction in which the first magnetization fixed layer extends, the absolute value of the z-direction component of the leakage magnetic field is the same as the effective magnetic field of the optical modulation layer. The length of the second leakage magnetic field trap section is larger than the distance between the intersection points when In (1) or (2), in the calculation result of the z-direction component, the absolute value of the z-direction component of the leakage magnetic field is larger than the distance between intersection points when the absolute value of the z-direction component is the same as the effective magnetic field of the light modulation layer. The domain wall moving spatial light modulator described above.

(4) The domain wall moving spatial light modulator according to (3), wherein the first leakage magnetic field trap section and the second leakage magnetic field trap section have a length of 150 nm or more and 400 nm or less.

According to the present invention, it is possible to provide a domain wall displacement type spatial light modulator that can increase the aperture ratio of the domain wall displacement type spatial light modulation element through a simple process and without increasing the drive current.

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 an example of the structure of the domain wall moving spatial light modulator according to the present embodiment. 7 is a partially enlarged view of the domain wall displacement type spatial light modulator of FIG. 6. FIG. FIG. 7 is a perspective view of a calculation model of the domain wall displacement type spatial light modulator shown in FIGS. 5 and 6. FIG. FIG. 6 is a diagram showing calculation results of initial magnetic domain formation using the calculation model of the domain wall displacement type spatial light modulation element of FIG. 5 and calculation results after implementation of domain wall current driving. FIG. 7 is a diagram showing the calculation results of initial magnetic domain formation using the calculation model of the domain wall displacement type spatial light modulator of FIG. 6 and the calculation results after implementation of domain wall current driving. FIG. 7 is a diagram showing calculation results of initial magnetic domain formation using a calculation model of the domain wall displacement type spatial light modulator of FIG. 6; FIG. 7 is a diagram showing calculation results of initial magnetic domain formation using a calculation model of the domain wall displacement type spatial light modulator of FIG. 6; A diagram showing calculation results of the z-direction component of the leakage magnetic field from the first magnetization fixed layer and the second magnetization fixed layer with respect to the x-direction in which the light modulation layer extends, based on the calculation model of the domain wall motion spatial light modulation element of FIG. 6. It is. FIG. 7 is a top view showing a modification of the domain wall displacement spatial light modulator shown in FIG. 6; FIG. 7 is a top view showing a modification of the domain wall displacement spatial light modulator shown in FIG. 6; FIG. 16 is a diagram showing calculation results of initial magnetic domain formation using a calculation model of the domain wall motion spatial light modulator shown in FIGS. 14 and 15. 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 modulation 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) 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 difference in coercive force with the light modulation region 11b 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, Ru, etc. 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 modulating layer 11 via the domain wall 11c, the domain wall displacement spatial light modulator 10 can function as a spatial light modulator. 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.

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 an example of the structure of the domain wall moving spatial light modulator of this embodiment. Similar to the domain wall motion spatial light modulator 200, the domain wall motion spatial light modulator 300 includes a plurality of domain wall motion spatial light modulators 30, but the domain wall motion spatial light modulator 30 includes a light modulation layer 31. This is different from the domain wall moving spatial light modulator 200. Specifically, the light modulation layer 31 is provided at the main body portion 31a and the end portion of the main body portion 31a on the side where the first magnetization fixed layer 22 is arranged, and prevents leakage from the first magnetization fixed layer 22. A first leakage magnetic field trap section 31b that traps the magnetic field is provided at the end of the main body section 31a on the side where the second magnetization fixed layer 23 is arranged, and traps the leakage magnetic field from the second magnetization fixed layer 23. A second leakage magnetic field trap section 31c is provided. Therefore, the aperture ratio of the domain wall displacement spatial light modulator 30 can be increased through a simple process without increasing the drive current.

The main body part 31a, the first leakage magnetic field trap part 31b, and the second leakage magnetic field trap part 31c are rectangular in top view, but the first leakage magnetic field trap part 31b and the second leakage magnetic field trap part 31c are larger than the main body part 31a. Since the size in the extending direction of the first magnetization fixed layer 22 and the second magnetization fixed layer 23, that is, the width thereof, is small, the leakage magnetic field is trapped. At this time, it is preferable that the first leakage magnetic field trap section 31b and the second leakage magnetic field trap section 31c have a smaller area than the main body section 31a. Thereby, the light modulation area can be expanded, and the pixel pitch in the horizontal direction in the figure can be made finer.

The widths of the first leakage field trap section 31b and the second leakage field trap section 31c are smaller than the width of the main body section 31a. The widths of the first leakage field trap section 31b and the second leakage field trap section 31c are not particularly limited as long as they are smaller than the width of the main body section 31a, but are, for example, 50 nm or more.

The size of the first leakage magnetic field trap section 31b and the second leakage magnetic field trap section 31c in the direction in which the light modulation layer 31 extends, that is, the length, is preferably 150 nm or more and 400 nm or less, and preferably 200 nm or more and 300 nm or less. It is even more preferable. When the length of the first leakage magnetic field trap section 31b and the second leakage magnetic field trap section 31c is 150 nm or more, the aperture ratio of the domain wall moving spatial light modulator 30 increases, and when it is 400 nm or less, the first magnetization is fixed. Misalignment between the layer 22 and the second magnetization fixed layer 23 and the light modulation layer 31 is suppressed.

Here, it was verified by computer simulation whether the aperture ratio of the domain wall displacement type spatial light modulation element 30 increases compared to the aperture ratio of the domain wall displacement type spatial light modulation element 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］、Ｈｅｆｆ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], Heff 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 elementary charge of electrons [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.

FIGS. 8(a) and 8(b) show calculation models of domain wall displacement type spatial light modulators 20 and 30, respectively. 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.
Light modulation layer 21; x direction: 1840 [nm], y direction: 300 [nm], z direction: 10 [nm]
Body portion 31a of light modulation layer 31; x direction: 1300 [nm], y direction: 300 [nm], z direction: 10 [nm]
First leakage magnetic field trap part of light modulation layer 31; x direction: L1 [nm], y direction: W1 [nm], z direction: 10 [nm]
First leakage magnetic field trap part of light modulation layer 32; x direction: L1 [nm], y direction: W1 [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 _s of light modulation layers 21 and 31: 0.092 [T]
Anisotropic magnetic field H _k 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 _s of the first magnetization fixed layer 22, 32 and the second magnetization fixed layer 23, 33: 4 [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]

FIGS. 9A and 9B show calculation results of initial magnetic domain formation and calculation results after implementation of domain wall current drive in a calculation model of the domain wall displacement type spatial light modulator 20, respectively. Here, when domain wall current driving is performed using spin transfer torque, when a pulse current is applied in the -x direction, electrons move in the +x direction. Using this phenomenon, we calculated domain wall current drive.

As described above, the domain wall motion spatial light modulator 20 operates by utilizing the coercive force difference between the first magnetization fixed layer 22 and the second magnetization fixed layer 23. The initial magnetization directions were set to be antiparallel. In the computer simulation, the initial magnetization directions of the light modulation layer 21 and the first magnetization fixed layer 22 were set upward (white screen display), and the initial magnetization direction of the second magnetization fixed layer 23 was set downward (screen black display). As a result, an initial magnetic domain was formed on the first magnetization fixed layer 22 side of the light modulation layer 21, that is, on the right end in the figure, due to the leakage magnetic field from the first magnetization fixed layer 22 whose initial magnetization direction was upward. (See FIG. 9(a)). Next, when domain wall current driving is carried out, the leakage magnetic field from the second magnetization fixed layer 23 whose magnetization direction is downward causes the light modulation layer 21 to move toward the second magnetization fixed layer 23 side, that is, at the left end in the figure. A second magnetic domain was formed. At this time, since the size of the initial magnetic domain and the second magnetic domain in the x direction, that is, the length, was about 590 nm, the length of the light modulation region was about 420 nm.

FIGS. 10A and 10B show calculation results of initial magnetic domain formation and calculation results after implementation of domain wall current driving in a calculation model of the domain wall displacement spatial light modulator 30, respectively. At this time, L1=150 nm, W1=200 nm, and the length of the light modulation layer 31 was made the same as the length of the light modulation layer 21.

The operation of the domain wall displacement type spatial light modulator 30 was set to be the same as the operation of the domain wall displacement type spatial light modulation element 20. As a result, an initial magnetic domain was formed in the first leakage magnetic field trap section 31b due to the leakage magnetic field from the first magnetization fixed layer 22, and the size of the initial magnetic domain was reduced. That is, the leakage magnetic field from the first magnetization fixed layer 22 was trapped in the first leakage magnetic field trap section 31b (see FIG. 10(a)). Next, when domain wall current driving was performed, a second magnetic domain was formed in the second leakage magnetic field trap section 31c due to the leakage magnetic field from the second magnetization fixed layer 23, and the size of the second magnetic domain was reduced. That is, the leakage magnetic field from the second magnetization fixed layer 23 was trapped in the second leakage magnetic field trap section 31c (see FIG. 10(b)). Therefore, it was found that the length of the light modulation region was approximately 1300 nm, and the aperture ratio of the domain wall motion spatial light modulator 30 was three times or more that of the domain wall motion spatial light modulator 20.

FIG. 11 shows calculation results of initial magnetic domain formation in a calculation model of the domain wall displacement type spatial light modulator 30. At this time, in FIG. 11(a), L1=150nm, W1=100nm, in FIG. 11(b), L1=150nm, W1=150nm, and in FIG. 11(c), L1=200nm, W1=200nm. did. As a result, in both cases, as in FIG. 10, an initial magnetic domain was formed in the first leakage magnetic field trap section 31b due to the leakage magnetic field from the first magnetization fixed layer 22, and the size of the initial magnetic domain became small. . That is, the leakage magnetic field from the first magnetization fixed layer 22 was trapped in the first leakage magnetic field trap section 31b.

FIG. 12 shows calculation results of initial magnetic domain formation in a calculation model of the domain wall displacement type spatial light modulator 30. At this time, L1 = 250 nm, W1 = 200 nm, and the anisotropic magnetic field H _k of the light modulation layer 31 was 1.5 [kOe]. As a result, as in FIG. 10, an initial magnetic domain was formed in the first leakage magnetic field trap section 31b due to the leakage magnetic field from the first magnetization fixed layer 22, and the size of the initial magnetic domain was reduced. That is, the leakage magnetic field from the first magnetization fixed layer 22 was trapped in the first leakage magnetic field trap section 31b.

FIG. 13 shows the z-direction component (z The calculation result of component) is shown. At this time, W1 was set to 200 nm. Further, the z direction is a direction perpendicular to the x direction and the y direction in which the first magnetization fixed layer 22 and the second magnetization fixed layer 23 extend.

In FIG. 13, focusing on the leakage magnetic field from the first magnetization fixed layer 22, on the left side of the first magnetization fixed layer 22 whose initial magnetization direction is upward, the leakage magnetic field whose magnetization direction is downward causes the initial magnetic domain in the light modulation layer 31. is formed. The leakage magnetic field gradually decreases to zero as the distance from the first magnetization fixed layer 22 increases.

で見積もられ、光変調層３１に印加される漏れ磁界が有効磁界Ｈ_ｅｆｆを超える場合に、光変調層３１の磁化が反転する。ここで、反磁界Ｈ_ｄは、式

（式中、Ｍ_ｓは、光変調層３１の飽和磁化であり、μ_０は、真空の透磁率である。）
で表される。 Here, the effective magnetic field H _eff of the light modulation layer 31 is expressed by the formula

When the leakage magnetic field applied to the light modulation layer 31 exceeds the effective magnetic field _Heff , the magnetization of the light modulation layer 31 is reversed. Here, the demagnetizing field H _d is expressed as

(In the formula, M _s is the saturation magnetization of the light modulation layer 31, and μ ₀ is the vacuum magnetic permeability.)
It is expressed as

From the above, when the anisotropic magnetic field H _k of the light modulation layer 31 is 3.0 [kOe] (see FIG. 11(c)), the effective magnetic field H _eff of the light modulation layer 31 is 2.1 [kOe]. kOe]. Therefore, when the absolute value of the z component of the leakage magnetic field from the first magnetization fixed layer 22 in FIG. 13 is the same as the effective magnetic field H _eff of the optical modulation layer 31, the distance between the intersection points is about 100 nm. It is preferable to make L1 larger than 100 nm.

On the other hand, when the anisotropic magnetic field H _k of the light modulation layer 31 is 1.5 [kOe] (see FIG. 12), the effective magnetic field H _eff of the light modulation layer 31 is estimated to be 0.6 [kOe]. Therefore, when the absolute value of the z component of the leakage magnetic field from the first magnetization fixed layer 22 in FIG. 13 is the same as the effective magnetic field H _eff of the optical modulation layer 31, the distance between the intersection points is found to be approximately 170 nm. It is preferable to make L1 larger than 170 nm.

Therefore, it can be seen that when the anisotropic magnetic field H _k of the light modulation layer 31 is different, the preferable value of L1 is different. Similarly, when the saturation magnetization M _s of the light modulation layer 31 differs, the preferable value of L1 also differs.

FIG. 14 shows a modification of the domain wall displacement type spatial light modulator 30. The domain wall motion spatial light modulator 40 is similar to the domain wall motion spatial light modulator 30, except that the width of both ends of the main body portion 41a in the direction in which the light modulation layer 41 extends is continuously reduced. be.

Note that the widths of the first leakage magnetic field trap section and the second leakage magnetic field trap section may change continuously with respect to the direction in which the light modulation layer extends.

Note that in this specification and claims, when the width of the main body (or leakage field trapping part) changes continuously with respect to the direction in which the light modulation layer extends, The width of the magnetic field trap section means the average width of the main body section (or the leakage magnetic field trap section).

FIG. 15 shows a modification of the domain wall displacement type spatial light modulator 30. In the domain wall motion spatial light modulator 50, the first leakage magnetic field trap section 51b and the second leakage magnetic field trap section 51c are arranged in the direction in which the first magnetization fixed layer 22 and the second magnetization fixed layer 23 of the main body section 31a extend. It is the same as the domain wall moving spatial light modulator 30 except that it is provided separately at both ends.

In addition, in this specification and the claims, when a plurality of leakage magnetic field trap sections are provided in isolation, the width of the leakage magnetic field trap section means the total width of the plurality of leakage magnetic field trap sections.

FIGS. 16(a) and 16(b) show calculation results of initial magnetic domain formation in calculation models of the domain wall displacement spatial light modulators 40 and 50, respectively. As a result, in both cases, as in FIG. 10, initial magnetic domains are formed in the first leakage magnetic field trap portions 31b and 51b due to the leakage magnetic field from the first magnetization fixed layer 22, and the size of the initial magnetic domains is small. became. That is, the leakage magnetic field from the first magnetization fixed layer 22 was trapped in the first leakage magnetic field trap sections 31b and 51b.

Note that an active matrix drive method is effective when driving the domain wall displacement spatial light modulator of this embodiment (for example, Aoshima, H. Kinjo, K. Machida, D. Kato, K. Kuga, T. Ishibashi and H. Kikuchi: “Active Matrix Magneto-Optical Spatial Light Modulator for Three-Dimensional Holographic Display Applications,” J. Display Tech., Vol. 12, No. 10, pp. 1212-1217 (2016)). In the active matrix drive method, the current ON/OFF ratio of the MOSFET is usually about ¹⁰⁹ , and there is almost no current flowing other than the selected domain wall motion spatial light modulator. It is possible to reliably perform the switching operation of the optical modulation element. In the active matrix driving method, as the pixel pitch becomes denser (the pixel area decreases), the drive current that can be supplied per pixel becomes smaller. Furthermore, as the pixel pitch becomes smaller, the size of the transistor becomes smaller, and therefore the drive current supplied from the transistor becomes smaller. For this reason, the resistance of the domain wall displacement type spatial light modulation element becomes important, and as the resistance of the domain wall displacement type spatial light modulation element increases, the drive current decreases. In the domain wall displacement type spatial light modulator of this embodiment, since the length of the leakage magnetic field trap section is not large, the resistance does not change significantly compared to the conventional domain wall displacement type spatial light modulation element, and it can be realized in an actual device. It is a structure.

Note that the domain wall motion spatial light modulator of this embodiment can be manufactured in the same manner as a conventional domain wall motion spatial light modulator, except for patterning a resist corresponding to the shape of the light modulation layer. In other words, the domain wall motion spatial light modulator of this embodiment has a first magnetization layer that traps leakage magnetic fields from the first magnetization fixed layer and the second magnetization fixed layer at both ends of the light modulation layer without complicating the process. By providing the leakage magnetic field trap section and the second leakage magnetic field trap section, the aperture ratio of the domain wall displacement spatial light modulator can be increased without increasing the drive current.

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, 40, 50 domain wall displacement type spatial light modulator 11, 21, 31, 41 light modulation layer 31a, 41a main body portion 31b, 51b first leakage magnetic field trap portion 31c, 51c second leakage magnetic field trap portion 11a Initial magnetic domain 11b Light modulation region 11c Domain wall 12, 22 First magnetization fixed layer 13, 23 Second magnetization fixed layer 14 Intermediate layer 24, 34 Ground electrode 25, 35 Drain electrode 200, 300 Domain wall moving spatial light modulator

Claims (4)

a light modulation layer that extends in a predetermined direction and changes the direction of polarization of incident light and outputs the light; and a first magnetization layer that extends in parallel to both ends of the light modulation layer and has different coercive forces. A domain wall displacement spatial light modulator having a fixed layer and a second magnetization fixed layer,
The light modulation layer is provided at a main body portion and an end portion of the main body portion on the side where the first magnetization fixed layer is arranged, and the light modulation layer is provided with a first magnetization layer that traps a leakage magnetic field from the first magnetization fixed layer. a leakage magnetic field trap section; and a second leakage magnetic field trap section that is provided at an end of the main body section on the side where the second magnetization fixed layer is arranged and traps a leakage magnetic field from the second magnetization fixed layer. and,
The first leakage magnetic field trap section and the second leakage magnetic field trap section are each a domain wall moving spatial light modulator having a width smaller than that of the main body section. The domain wall moving spatial light modulator according to claim 1, wherein the first leakage magnetic field trap section and the second leakage magnetic field trap section have a smaller area than the main body section. The length of the first leakage magnetic field trap section is determined by the x direction of the leakage magnetic field from the first magnetization fixed layer with respect to the x direction in which the light modulation layer extends according to the calculation model of the domain wall motion spatial light modulator. If the absolute value of the z-direction component of the leakage magnetic field is the same as the effective magnetic field of the optical modulation layer in the calculation result of the z-direction component perpendicular to the y-direction in which the first magnetization fixed layer extends. is larger than the distance between the intersections of
The length of the second leakage magnetic field trap section is determined by the calculation result of the z-direction component of the leakage magnetic field from the second magnetization fixed layer with respect to the x-direction based on the calculation model of the domain wall motion spatial light modulator. 3. The domain wall displacement spatial light modulator according to claim 1, wherein the absolute value of the z-direction component of the leakage magnetic field is larger than the distance between intersection points when the absolute value of the component in the z direction of the leakage magnetic field is the same as the effective magnetic field of the light modulation layer. The domain wall moving spatial light modulator according to claim 3, wherein the first leakage magnetic field trap section and the second leakage magnetic field trap section have a length of 150 nm or more and 400 nm or less.

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