JP2021110787A - Domain wall displacement type spatial light modulator - Google Patents

Abstract

To provide a domain wall displacement type spatial light modulator which enables low current drive and can improve an opening ratio.SOLUTION: A domain wall displacement type spatial light modulator includes: a light modulation part; a first ferromagnetically exchange coupled part and a second ferromagnetically exchange coupled part which are arranged on both ends of the light modulation part and have mutually different magnetic coercive force; and a plurality of domain wall displacement type light modulation elements. The plurality of domain wall displacement type light modulation elements further include a connection part in which the first ferromagnetically exchange coupled part and the second ferromagnetically exchange coupled part are arranged in a direction perpendicular to a predetermined direction so that the parts are alternately positioned, and a first ferromagnetic layer (first magnetization fixing layer) of the adjacent first ferromagnetically exchange coupled part and a first ferromagnetic layer (second magnetization fixing layer) of the second ferromagnetically exchange coupled part are electrically connected on one end side of the adjacent domain wall displacement type light modulation elements.SELECTED DRAWING: Figure 7

Description

The present invention is a promising spatial light modulator for three-dimensional holography with a wide field of view, which is a magnetic-optical spatial light modulator that displays the brightness and darkness of light by controlling the magnetic zone structure of the optical modulation region by moving the magnetic wall (hereinafter, It is called "magnetic wall moving type spatial light modulator").

Conventionally, in order to secure a viewing range of 30 degrees or more, which is practical in stereoscopic holography, it is necessary to set the pixel pitch of the spatial light modulator (SLM), which is a display device, to 1 micrometer or less. Existing SLMs such as liquid crystals and digital micromirror devices (DMDs) have a pixel pitch of about 5 micrometers, and further miniaturization is difficult.

On the other hand, the magneto-optical spatial light modulator (MOSLM), which uses spin injection magnetization reversal and domain wall movement to rewrite pixels, needs to be improved in terms of light utilization efficiency and operating current, but is 1 micrometer. A degree of pixel pitch can be realized (see Patent Document 1). This MOSLM is a device that realizes light modulation by assigning light and dark rotation of a plane of polarization of light according to the direction of magnetization.

Here, the domain wall moving type SLM proposed by the applicant has a structure in which magnetization fixing layers are arranged at both ends of the optical modulation layer, so that the expansion / contraction of the magnetic domain can be controlled by the direction of the current flowing through the optical modulation layer. Yes (see Patent Document 2). According to this domain wall moving type SLM, lower power consumption can be expected as compared with MOSLM using spin injection magnetization reversal.

Japanese Unexamined Patent Publication No. 2012-141402 Japanese Patent Application No. 2017-109478 JP-A-2017-167430 Japanese Unexamined Patent Publication No. 2005-191032

A. Yamaguchi, T.M. Ono, S.M. Nasu, K.K. Miyake, K.K. Mibu, and T. et al. Shinjo, "Real-Space Observation of Current-Driven Domain Wall Motion in Submicron Magnetic Wires", Physical Review Letters, United States of America, American Physical Society, 20 February 2004, Volume 92, Number 7, pp. 077205-1-077205-4 K. Aoshima, R.M. Ebisawa, N.M. Funabashi, K.K. Kuga, and K. Machida, "Current-induced domain-wall motion in patterned nanowires with various Gd-Fe compositions for magneto-optical light modulator applications", Japanese Journal of Applied Physics, Japan, The Japan Society of Applied Physics, 7 August 2018, Volume 57, pp. 09TC03-1-09TC03-4

By the way, in the domain wall moving type SLM, an effective optical modulation region is increased by improving the aperture ratio, so that a brighter stereoscopic image can be reproduced. Here, the domain wall moving light modulation element constituting one pixel of the domain wall moving SLM includes a magnetization fixing layer and a light modulation layer, but when the width of the light modulation layer is widened in order to improve the aperture ratio, the drive current Will increase. On the other hand, a method has been proposed in which the aperture ratio is improved while suppressing the increase in the driving current by arranging the optical modulation layer elongated in the pixel (see Patent Document 3).

However, in an optical modulation layer having a constricted portion or a bent portion, it is known that a domain wall is caught and trapped in the constricted portion or the bent portion (see Patent Document 4). Further, since the moving distance of the domain wall is proportional to the driving current density (see Non-Patent Documents 1 and 2), the effect of reducing the current by arranging the optical modulation layer in an elongated manner is limited.

The present invention has been made in view of the above, and an object of the present invention is to provide a domain wall moving type spatial light modulator capable of driving at a low current and improving an aperture ratio.

(1) In the present invention, a first ferromagnet that extends in a predetermined direction and emits by changing the direction of polarization of incident light and a first ferromagnet that is arranged at both ends of the light modulation section and has different coercive forces. A magnetic wall moving space optical modulator comprising an exchange coupling portion, a second ferromagnet exchange coupling portion, and a plurality of magnetic wall moving photomodulators, wherein the first ferromagnetic exchange coupling portion and the second ferromagnetism Each of the exchange coupling portions is formed on a first ferromagnetic layer made of a ferromagnetic material and the first ferromagnetic layer, and is made of a ferromagnetic material to form a ferromagnetic exchange coupling with the first ferromagnetic layer. In the plurality of magnetic wall moving type optical modulation elements having two ferromagnetic layers, the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion alternate in a direction orthogonal to the predetermined direction. The magnetic wall moving type space optical modulators are arranged side by side so as to be located, and the magnetic wall moving type spatial optical modulators are arranged on one end side of the adjacent magnetic wall moving type optical modulators, and the first ferromagnetic layer of the adjacent first ferromagnetic exchange coupling portion is provided. Provided is a magnetic wall mobile space optical modulator further comprising a connecting portion for electrically connecting the second ferromagnetic exchange coupling portion and the first ferromagnetic layer of the second ferromagnetic exchange coupling portion.

(2) The connecting portion may be a connection wiring for electrically connecting the surfaces of the adjacent first ferromagnetic layer on the opposite side of the second ferromagnetic layer.

According to the present invention, it is possible to provide a domain wall moving type spatial light modulator capable of driving at a low current and improving an aperture ratio.

It is a perspective view of the magnetic domain wall movement type light modulation element which concerns on 1st Embodiment of this invention. It is a side view which shows the operation of the domain wall moving type light modulation element which concerns on 1st Embodiment of this invention. It is a top view of the conventional domain wall moving type spatial light modulator. It is a top view of the domain wall moving type spatial light modulator which concerns on 1st Embodiment of this invention. It is a top view of the conventional domain wall moving type light modulation element. It is a top view of the conventional domain wall moving type light modulation element. It is a top view of the connecting domain wall element which concerns on 1st Embodiment of this invention. FIG. 7 is a cross-sectional view taken along line XX of the connecting domain wall element according to the first embodiment of the present invention shown in FIG. FIG. 7 is a sectional view taken along line YY of the connecting domain wall element according to the first embodiment of the present invention shown in FIG. 7. It is a top view of the domain wall moving type spatial light modulator which concerns on 2nd Embodiment of this invention. It is a top view of the connecting domain wall element which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the second embodiment, the same reference numerals are given to the configurations common to those of the first embodiment, and the description thereof will be omitted. Further, for convenience of explanation, the top, bottom, left, and right in the drawing will be described as the top, bottom, left, and right of the domain wall movable light modulation element.

<First Embodiment>
The domain wall moving spatial light modulator 5 according to the first embodiment of the present invention includes a plurality of domain wall moving light modulation elements 100 utilizing the domain wall movement. The domain wall moving type spatial light modulator 5 according to the present embodiment is characterized in that the plurality of domain wall moving type light modulation elements 100 are electrically connected in series.

First, the basic configuration of the domain wall moving light modulation element 100 constituting the domain wall moving space light modulator 5 according to the present embodiment will be described. FIG. 1 is a perspective view of the magnetic domain wall moving light modulation element 100 according to the first embodiment of the present invention. FIG. 2 is a side view showing the operation of the domain wall movable light modulation element 100 according to the first embodiment of the present invention. The arrows in FIGS. 1 and 2 indicate the direction of the magnetization direction.

As shown in FIG. 1, the magnetic domain wall moving type light modulation element 100 has a first ferromagnetic exchange coupling portion 1, a second ferromagnetic exchange coupling portion 2, and an optical modulation portion 3 as a basic configuration. These are formed on a substrate such as Si (not shown).

The first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are general metal electrode materials such as metals such as Cu, Al, Au, Ag, Ru, Ta, and Cr and their alloys, which are not shown, respectively. It has a lower electrode formed by the lowermost layer. A pulse current (driving current) can be applied to the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 by connecting the pulse current source 9 to the lower electrode.

As shown in FIG. 1, in the magnetic wall moving type light modulation element 100, for example, the light modulation unit 3 is formed in a flat plate shape (substantially rectangular in a plan view) extending in a predetermined direction (left-right direction in FIG. 1) at both ends thereof. The first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are arranged. The upper surfaces of the optical modulation section 3, the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 are continuously flush with each other.

As shown in FIG. 2, the first ferromagnetic exchange coupling portion 1 is configured by laminating a first magnetization fixed layer 11 and an optical modulation layer 30. In the first ferromagnetic exchange coupling portion 1, a non-magnetic metal layer 12 and a buffer layer 13 are arranged between the first magnetization fixing layer 11 and the photomodulation layer 30, if necessary.

The first magnetization fixed layer 11 is made of a ferromagnetic material and corresponds to the first ferromagnetic layer of the present invention. The first magnetization fixed layer 11 is a layer in which the magnetization direction is fixed in one direction, and has a large coercive force. The first magnetization fixed layer 11 uses a ferromagnetic material having magnetic anisotropy in the same direction as the optical modulation layer 30 in the first ferromagnetic exchange coupling portion 1 and having vertical magnetic anisotropy in the optical modulation layer 30. If so, a ferromagnetic material having vertical magnetic anisotropy is also used for the first magnetization fixed layer 11. Preferably, both the first magnetization fixing layer 11 and the photomodulation layer 30 are made of a ferromagnetic material having vertical magnetic anisotropy.

The first magnetization-fixed layer 11 is a CPP-GMR (CPP-GMR) having a structure in which a non-magnetic layer is sandwiched between a magnetized fixed layer in which the magnetization is fixed in the vertical direction and a magnetized free layer in which the magnetization direction can be reversed. Current Perpendicular to the Plane Giant MagnetoResistance: It can be constructed of a ferromagnetic material known as a magnetization fixing layer such as a vertically energized giant magnetoresistive element or a TMR element. Specifically, transition metals such as Fe, Co, and Ni and alloys containing them, for example, TbFe-based, TbFeCo-based, CoCr-based, CoPt-based, CoPd-based, and FePt-based alloys can be used. As a result, the coercive force of the first magnetization fixing layer 11 can be increased, and the magnetization direction of the first magnetization fixing layer 11 can be fixed so as not to be easily changed by the external magnetic field.

Further, the first magnetization fixing layer 11 may be composed of a multi-layered laminate in which these transition metal layers and non-magnetic metal layers are alternately laminated, and may be composed of Co / Pt, Fe / Pt, Co / Pd. And other multilayer films can be used. By using these ferromagnetic materials, a first magnetization fixed layer 11 having a strong perpendicular magnetic anisotropy and a large coercive force can be obtained.

The multilayer film has a property that the coercive force is increased by heat treatment. Therefore, when the first magnetization fixed layer 11 made of the multilayer film is heat-treated to increase its coercive force, the coercive force of the first ferromagnetic exchange coupling portion 1 after coupling with the photomodulation layer 30 also becomes larger. The difference in coercive force with the optical modulation unit 3 can be further increased.

Here, in order to form the optical modulation unit 3 having the domain wall 33 described later, it is necessary to design the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 so that the coercive force is different. For that purpose, it is necessary to provide a difference between the coercive force of the first magnetization fixing layer 11 and the coercive force of the second magnetization fixing layer 21 described later. As a specific means, the first magnetization-fixed layer 11 and the second magnetization-fixed layer 21 are heat-treated only on one side (or a difference is provided in the degree of heat treatment between the two) as described above, or the shapes are different from each other. (For example, when the width of the first magnetization fixed layer 11 is widened, the coercive force becomes small), or the layer configurations of the first magnetization fixed layers 11 are different from each other.

The non-magnetic metal layer 12 and the buffer layer 13 are arranged between the first magnetization fixing layer 11 and the optical modulation layer 30, and by interposing these layers, the first magnetization fixing layer 11 and the optical modulation layer 30 The magnetic bond between them is maintained.

The non-magnetic metal layer 12 is formed by being laminated on the first magnetization fixing layer 11 described above. The non-magnetic metal layer 12 is provided so that the first magnetization fixing layer 11 is not damaged by etching in the manufacturing process. As the non-magnetic metal layer 12, thin film layers of various non-magnetic metals can be used. For example, Ta, Mo, and Ru can be used as the non-magnetic metal layer 12, and among them, those made of Ta are preferably used.

The buffer layer 13 is formed by being laminated on the above-mentioned non-magnetic metal layer 12. Since the buffer layer 13 needs to be able to pass a current in both the light modulation element and the TMR element using the domain wall movement, the resistance is not too large when the thin film is formed, and the buffer layer 13 has high conductivity. Further, the buffer layer 13 needs to be a material that contains an element having a slow etching rate in the manufacturing process and a high detection sensitivity of SIMS (Secondary Ion Mass Spectrometry) and can be seen by a SIMS type endpoint monitor. As a result, the etching can be reliably stopped by the buffer layer 13, and damage to the first magnetization fixing layer 11 can be avoided.

The buffer layer 13 is made of an oxide or a nitride. More specifically, the buffer layer 13 is preferably composed of MgO, Al ₂ O ₃ , Mg _{Al 2} O ₄ , TiO ₂ , ZnO or RuO ₂ . Among them, as the buffer layer 13, one made of MgO is preferably used. According to the MgO layer made of MgO, it is possible to form the buffer layer 13 which has appropriate conductivity, has a slow etching rate, and has high SIMS sensitivity.

The optical modulation layer 30 is formed by being laminated on the buffer layer 13 described above. The optical modulation layer 30 is made of a ferromagnetic material and corresponds to the second ferromagnetic layer of the present invention. A known ferromagnetic material can be applied to the photomodulation layer 30, and a material having a large magneto-optical effect (Kerr effect) is preferably applied. In order to increase the magnetic optical effect, it is preferable to use a magnetic layer having vertical magnetic anisotropy. Specifically, a transition metal such as a Co / Pd multilayer film and Pd, Pt, and Cu are repeatedly laminated. Examples thereof include a multilayer film made of copper, or an alloy of a rare earth metal such as TbFeCo or GdFe and a transition metal (RE-TM alloy). Among them, as the light modulation layer 30, a GdFe layer made of a GdFe alloy is preferably used.

The optical modulation layer 30 constitutes the second ferromagnetic layer in the second ferromagnetic exchange coupling portion 2 described later, and also constitutes the optical modulation section 3. That is, the second ferromagnetic layer in the first ferromagnetic exchange coupling portion 1, the second ferromagnetic layer in the second ferromagnetic exchange coupling portion 2, and the optical modulation portion 3 are all composed of the optical modulation layer 30, and are composed of the optical modulation layer 30 from the outside. The direction of magnetization differs depending on the magnetic field of.

In the first ferromagnetic exchange coupling portion 1 having the above-described configuration, the first magnetization fixing layer 11 and the optical modulation layer 30 are ferromagnetically exchange-coupled via the non-magnetic metal layer 12 and the buffer layer 13. By this ferromagnetic exchange coupling, the magnetization direction of the first magnetization fixing layer 11 and the magnetization direction of the photomodulation layer 30 in the first ferromagnetic exchange coupling portion 1 are fixed to the magnetization direction of the first magnetization fixing layer 11.

Further, as shown in FIG. 2, the second ferromagnetic exchange coupling portion 2 is configured by laminating the second magnetization fixed layer 21 and the optical modulation layer 30. In the second ferromagnetic exchange coupling portion 2, the non-magnetic metal layer 22 and the buffer layer 23 are arranged between the second magnetization fixed layer 21 and the photomodulation layer 30 as needed.

The second magnetization fixing layer 21 is selected from the materials that can be used in the first magnetization fixing layer 11, and similarly, the non-magnetic metal layer 22 and the buffer layer 23 are also the non-magnetic metal layer 12 and the buffer layer 13, respectively. Selected from the materials available in.

In the second ferromagnetic exchange coupling portion 2, similarly to the first ferromagnetic exchange coupling portion 1, the second magnetization fixed layer 21 and the optical modulation layer 30 are ferromagnetic via the non-magnetic metal layer 22 and the buffer layer 23. It is exchange-bonded. By this ferromagnetic exchange coupling, the magnetization direction of the second magnetization fixing layer 21 and the magnetization direction of the photomodulation layer 30 in the second ferromagnetic exchange coupling portion 2 are fixed to the magnetization direction of the second magnetization fixing layer 21.

As described above, the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 are both ends of the optical modulation layer 30 (both ends in the predetermined direction) which are indispensable for the optical modulation control of the optical modulation unit 3. Since the magnetization directions of (both ends in the left-right direction) are initialized antiparallel in FIGS. 1 and 2, they are designed so that their coercive forces are different from each other. By utilizing the difference in coercive force between the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 and applying an appropriate external magnetic field (detailed later), the first ferromagnetic exchange coupling portion 1 And the magnetization directions of the second ferromagnetic exchange coupling portion 2 can be initialized antiparallel to each other.

Further, as described above, the optical modulation layer 30 constitutes the optical modulation unit 3. As shown in FIG. 1, a magnetic domain wall 33 and magnetic domains 31 and 32 are formed in the optical modulation section 3 composed of the optical modulation layer 30.

Each of the magnetization fixing layers (hereinafter, the first magnetization fixing layer 11 and the second magnetization fixing layer 21 are also simply referred to as a magnetization fixing layer), each non-magnetic metal layer, each buffer layer, and each layer of the optical modulation layer 30. , Or a functional layer may be appropriately provided at the interface with the lower electrode. For example, in order to prevent damage to the optical modulation layer 30 during the microfabrication process, a cap layer containing Ta, Ru or SiN, or made of Ta, Ru or SiN may be provided on the optical modulation layer 30. This cap layer has a function of preventing GdFe and TbFeCo, which are used for forming the photomodulation layer 30 and are easily oxidized, from being oxidized in the atmosphere after the device is completed.

Next, the magnetic characteristics of the domain wall movable light modulation element 100 according to the present embodiment will be described.
As described above, the first ferromagnetic exchange coupling portion 1 has a first magnetization fixed layer 11 that ferromagnetically exchanges and couples with the optical modulation layer 30, and the second ferromagnetic exchange coupling portion 2 also has the optical modulation layer 30. It has a second magnetization fixed layer 21 which is ferromagnetically exchange-coupled with. That is, since the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 each have a ferromagnetic exchange coupling inside, their magnetization directions are reversed at the same time. Then, as shown in FIGS. 1 and 2, for example, the magnetization direction of the first ferromagnetic exchange coupling portion 1 is designed to be upward, while the magnetization direction of the second ferromagnetic exchange coupling portion 2 is designed to be downward. Will be done.

The optical modulation unit 3 is formed with a domain wall 33 extending in a plane in a direction orthogonal to a predetermined direction (horizontal direction in FIGS. 1 and 2). That is, the domain wall 33 is arranged parallel to the magnetization direction of both ferromagnetic exchange coupling portions. Further, the magnetization directions of the magnetic domains 31 and 32 formed on both sides of the domain wall 33 are opposite to each other. For example, as shown in FIGS. 1 and 2, the magnetization direction of the magnetic domain 31 arranged on the first ferromagnetic exchange coupling portion 1 side of the domain wall 33 is downward, and the second ferromagnetic exchange coupling portion is more than the magnetic wall 33. The magnetization direction of the magnetic domain 32 arranged on the 2 side is upward.

In this way, by forming the magnetic domains 31 and 32 having different directions of magnetization in the optical modulation unit 3 via the domain wall 33, the domain wall moving type light modulation element 100 can function as the light modulation element. More specifically, for example, when the magnetic wall moving type light modulation element 100 is configured as a reflection type light modulation element, light having polarized light with respect to the upper surface of the light modulation unit 3 from above the magnetic wall moving light modulation element 100. When the light is incident on the light, the planes of polarization of the reflected light rotate in different directions depending on the direction of magnetization. Therefore, the light can be modulated by assigning the reflected light having different rotation directions of the polarizing surfaces to the light and darkness of the light through the polarizing filter. Further, by forming the substrate with a translucent material such as glass or sapphire, it is possible to make the domain wall moving type light modulation element 100 function as a transmission type light modulation element.

Here, when the coercive force of the first magnetization fixed layer 11 is designed to be smaller than the coercive force of the second magnetization fixed layer 21, the coercive force of the first ferromagnetic exchange coupling portion 1 is set to Hc1 and the second strong force. Assuming that the coercive force of the magnetic exchange coupling portion 2 is Hc2 and the coercive force of the photomodulation layer is Hc_m, the relationship of Hc2> Hc1> Hc_m is established.

Then, when a magnetic field having a strength H of H> Hc2 is applied downward to the element having a structure in which the above-mentioned coercive force relationship is established, the first ferromagnetic exchange coupling portion 1, the first. 2 In both the ferromagnetic exchange coupling unit 2 and the optical modulation unit 3, the direction of the magnetization direction is downward.

On the other hand, when a magnetic field having a strength H'of Hc2> H'> Hc1 is applied upward to the element, the direction of the magnetization direction of the second ferromagnetic exchange coupling portion 2 remains downward. On the other hand, the directions of the magnetization directions of the first ferromagnetic exchange coupling unit 1 and the optical modulation unit 3 both change upward.

At this time, initial magnetic domains 310 and 320 are generated at both ends of the optical modulation unit 3, as shown in FIG. More specifically, at the end of the optical modulation unit 3 on the first ferromagnetic exchange coupling portion 1 side, the first ferromagnetism is caused by the leakage magnetic field from the first ferromagnetic exchange coupling portion 1 (broken line arrow in FIG. 2). An initial magnetic domain 310 in the downward magnetization direction, which is antiparallel to the upward magnetization of the exchange coupling portion 1, is generated. Further, at the end of the optical modulation unit 3 on the second ferromagnetic exchange coupling portion 2 side, a second ferromagnetic exchange coupling is formed by a magnetic domain leaking from the second ferromagnetic exchange coupling portion 2 (broken line arrow in FIG. 2). An initial magnetic domain 320 in the upward magnetization direction, which is antiparallel to the downward magnetization of part 2, is generated.

Next, in this state, a pulse current (driving current) is applied from the pulse current source 9, and the first ferromagnetic exchange coupling portion 1 to the second ferromagnetic exchange coupling portion 2 or the second ferromagnetic exchange coupling portion 2 to the first A pulse current (drive current) is passed toward the ferromagnetic exchange coupling portion 1. Then, the domain wall 33 formed by the generation of the initial magnetic domains 310 and 320 can be moved in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons). As a result, as shown in FIG. 2, the direction of magnetization of the optical modulation region 300 excluding both ends of the optical modulation section 3 is reversed (in the example of FIG. 2, the direction of magnetization of the optical modulation region 300 is inverted upward). It becomes possible.

A plurality of domain wall moving light modulation elements 100 having the basic configuration and magnetic characteristics described above are electrically connected in series to form a connecting domain wall moving light modulation element 10 (hereinafter referred to as a connecting domain wall element 10). By arranging the connecting domain wall elements 10 in a grid pattern, the domain wall moving type spatial light modulator 5 according to the present embodiment is configured. FIG. 3 is a plan view of the conventional domain wall movable spatial light modulator 90. As shown in FIG. 3, in the conventional domain wall moving spatial light modulator 90, a plurality of domain wall moving light modulation elements 91 having a first magnetization fixing layer 910, a second magnetization fixing layer 920, and an optical modulation unit 930 are provided. They are independently produced on a substrate (not shown), and are arranged, for example, in a grid pattern. On the other hand, FIG. 4 is a plan view of the domain wall moving type spatial light modulator 5 according to the present embodiment. As shown in FIG. 4, the domain wall moving type spatial light modulator 5 according to the present embodiment is the same as the conventional one in that the connecting domain wall elements 10 are arranged in a grid pattern, but is shown in FIG. 7 described later. As described above, it is significantly different from the conventional one in that a plurality of domain wall moving light modulation elements 100 are electrically connected in series.

Here, FIGS. 5 and 6 are both plan views of the conventional domain wall moving light modulation element. More specifically, FIG. 5 is a plan view of the magnetic wall moving type light modulation element 50 having two bent portions (folded portions) formed by extending in an elongated linear shape and being folded back twice. FIG. 6 is a plan view of the magnetic domain wall moving type light modulation element 60 having one bent portion (folded portion) formed by extending in an elongated linear shape and being folded back once.

As shown in FIG. 5, the domain wall moving type light modulation element 50 includes a first magnetization fixing layer 511, a second magnetization fixing layer 521, and a light modulation layer 530. The first magnetization fixed layer 511 and the optical modulation layer 530 constitute the first ferromagnetic exchange coupling portion 51, and the second magnetization fixing layer 521 and the optical modulation layer 530 constitute the second ferromagnetic exchange coupling portion 52, and light modulation is performed. The layer 530 constitutes the optical modulation section 53. The optical modulation layer 530 is elongated and has bent portions (folded portions) 55a and 55b, and a magnetic domain wall 533 is formed in the optical modulation portion 53. The magnetization direction of the magnetic domain 510 arranged on the first magnetization fixed layer 511 side of the domain wall 533 is the downward magnetization direction D1, and the magnetization direction of the magnetic domain 520 arranged on the second magnetization fixed layer 521 side of the domain wall 533 is upward. Magnetization direction D2. By connecting the pulse current source 59 to the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2, the pulse current (driving current) flows in the direction of the broken line arrow in FIG. 5, and the domain wall 533 is formed. Along the optical modulation layer 530, it moves in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons).

Similarly, as shown in FIG. 6, the domain wall moving type light modulation element 60 includes a first magnetization fixing layer 611, a second magnetization fixing layer 621, and a light modulation layer 630. The first magnetization fixed layer 611 and the optical modulation layer 630 form the first ferromagnetic exchange coupling portion 61, and the second magnetization fixing layer 621 and the optical modulation layer 630 form the second ferromagnetic exchange coupling portion 62, which is photomodulated. The layer 630 constitutes the optical modulation section 63. The optical modulation layer 630 is elongated and has a bent portion (folded portion) 65, and a magnetic domain wall 633 is formed in the optical modulation portion 63. The magnetization direction of the magnetic domain 610 arranged on the first magnetization fixed layer 611 side of the domain wall 633 is the downward magnetization direction D1, and the magnetization direction of the magnetic domain 620 arranged on the second magnetization fixed layer 621 side of the domain wall 633 is upward. Magnetization direction D2. By connecting the pulse current source 69 to the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2, the pulse current (driving current) flows in the direction of the broken line arrow in FIG. Along the optical modulation layer 630, it moves in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons).

These domain wall moving light modulation elements 50 and 60 are disclosed in, for example, the above-mentioned Cited Document 3. These magnetic wall moving type light modulation elements 50 and 60 improve the aperture ratio while suppressing the increase in the drive current based on the finding that the drive current increases when the width of the light modulation layer is widened in order to improve the aperture ratio. For the purpose of this, the light modulation layers 530 and 630 are formed in an elongated shape.

As shown in FIGS. 5 and 6, since the light modulation layers 530 and 630 in the magnetic wall moving type light modulation elements 50 and 60 have bent portions (folded portions) 55a, 55b and 65, the magnetic wall 533 and 633 are formed. It moves along the light modulation layers 530 and 630 through the bent portions (folded portions) 55a, 55b and 65. Further, since the lengths of the optical modulation layers 530 and 630 are increased, the moving distance of the domain walls 533 and 633 is also increased.

However, as described above, it is known that in an optical modulation layer having a constricted portion or a bent portion, a domain wall is caught and trapped in the constricted portion or the bent portion (see Patent Document 4 described above). Further, it is known that the moving distance of the domain wall is proportional to the driving current density (see Non-Patent Documents 1 and 2 described above). Therefore, the effect of reducing the current by arranging the optical modulation layer in an elongated manner is limited.

Therefore, in the domain wall moving type spatial light modulator 5 according to the present embodiment, a plurality of domain wall moving type light modulators 100 having the above-mentioned basic configuration and magnetic characteristics are aligned and arranged so as to be parallel in the longitudinal direction. The connecting domain wall element 10 is formed by electrically connecting in series, and the trap of the domain wall due to the presence of the bent portion as described above is avoided. Here, FIG. 7 is a plan view of the connecting domain wall element 10 according to the first embodiment of the present invention. FIG. 8 is a sectional view taken along line XX of the connecting domain wall element 10 shown in FIG. 7, and FIG. 9 is a sectional view taken along line YY of the connecting domain wall element 10 shown in FIG.

As shown in FIG. 7, the connecting domain wall element 10 according to the present embodiment includes two domain wall moving light modulation elements 100a and 100b. The basic configurations of the domain wall-moving light modulation elements 100a and 100b are as described above. b is attached.

The two domain wall-moving light modulation elements 100a and 100b are arranged so as to be parallel in the longitudinal direction. More specifically, the magnetic wall moving type optical modulation elements 100a and 100b are the first ferromagnetic exchange coupling portion 1a and the second in the direction (vertical direction in FIG. 7) orthogonal to the predetermined direction (horizontal direction in FIG. 7). The ferromagnetic exchange coupling portion 2b, the first ferromagnetic exchange coupling portion 1b and the second ferromagnetic exchange coupling portion 2a are arranged side by side so as to be alternately positioned. That is, the domain wall-moving light modulation elements 100a and 100b are arranged so as to face each other in opposite directions.

Further, as shown in FIGS. 7 to 9, the connecting domain wall element 10 according to the present embodiment is on one end side (right direction end portion in FIG. 7) of adjacent domain wall moving type optical modulation elements 100a and 100b. , Connection wiring 111 as a connecting portion for electrically connecting the first magnetization fixed layer 11b of the adjacent first ferromagnetic exchange coupling portion 1b and the second magnetization fixing layer 21a of the second ferromagnetic exchange coupling portion 2a. Further prepare. The two magnetic domain wall moving light modulation elements 100a and 100b are electrically connected in series by the connection wiring 111.

As shown in FIGS. 7 and 9, for example, the connection wiring 111 is a surface of the first ferromagnetic exchange coupling portion 1b of the first magnetization fixed layer 11b opposite to the optical modulation layer 30b (lower surface of FIG. 9). And the surface (lower surface of FIG. 9) of the second magnetization fixed layer 21a of the second ferromagnetic exchange coupling portion 2a opposite to the photomodulation layer 30a are electrically connected. The connection wiring 111 is formed so as to extend in a direction (vertical direction in FIG. 7) orthogonal to a predetermined direction (horizontal direction in FIG. 7) which is an extension direction (longitudinal direction) of the magnetic wall movable light modulation elements 100a and 100b. Will be done. As a material constituting the connection wiring 111, a conductive metal material is used. For example, the connection wiring 111 is made of materials such as ruthenium, tantalum, tungsten, gold, silver, copper, and aluminum.

Further, as shown in FIGS. 8 and 9, the magnetic wall moving type light modulation elements 100a and 100b are surrounded by an insulating member 206. The insulating member 206 is an insulating member when the magnetic domain wall moving light modulation elements 100a and 100b are formed on the insulating member layer formed on, for example, a Si backplane or the like by using conventionally known lithography or the like. Consists of the rest of the layer. The material of the insulating member 206 may be any material having an insulating property, and for example, SiO ₂ , SiN, MgO and the like are used.

In the magnetic wall moving type light modulation elements 100a and 100b, as shown in FIGS. 8 and 9, the above-mentioned cap layers 207a and 207b are formed on the light modulation layers 30a and 30b. Further, a pulse current source 19 is connected to the first magnetization fixing layer 11a and the second magnetization fixing layer 21b. More specifically, as shown in FIG. 8, the pulse current source 19 has a first magnetization via an electrode 112 provided on the lower surface side of each of the first magnetization fixed layer 11a and the second magnetization fixing layer 21b. It is connected to the fixed layer 11a and the second magnetized fixed layer 21b. As a result, a pulse current (driving current) can be applied to the magnetic domain wall moving type light modulation elements 100a and 100b.

In the magnetic domain wall moving light modulation element 100a having the above configuration, as shown in FIGS. 7 and 8, the magnetization direction of the first ferromagnetic exchange coupling portion 1a is upward, and the magnetization direction of the second ferromagnetic exchange coupling portion 2a is upward. Is facing down. The magnetization direction of the magnetic domain 31a arranged on the first ferromagnetic exchange coupling portion 1a side of the domain wall 33a is the downward magnetization direction D1, and the magnetization of the magnetic domain 32a arranged on the second ferromagnetic exchange coupling portion 2a side of the magnetic wall 33a. The direction is the upward magnetization direction D2.

Further, in the magnetic domain wall moving type light modulation element 100b having the above configuration, as shown in FIGS. 7 and 8, the magnetization direction of the first ferromagnetic exchange coupling portion 1b is upward, and the magnetization direction of the second ferromagnetic exchange coupling portion 2b is upward. The magnetization direction is downward. The magnetization direction of the magnetic domain 31b arranged on the first ferromagnetic exchange coupling portion 1b side of the domain wall 33b is the downward magnetization direction D1, and the magnetization of the magnetic domain 32b arranged on the second ferromagnetic exchange coupling portion 2b side of the domain wall 33b. The direction is the upward magnetization direction D2.

A method of manufacturing the domain wall movable spatial light modulator 5 according to the present embodiment will be described.
First, the connection wiring 111 is formed on the insulating member layer such as _{SiO 2} formed on the Si backplane or the like by using conventionally known lithography. At this time, the electrode 112 connected to the pulse current source 19 is also formed.

Next, the magnetic domain wall moving type light modulation elements 100a and 100b are formed. Regarding the method of forming the domain wall moving light modulation elements 100a and 100b, for example, the first magnetization fixing layer and the first magnetization fixing layer and the first magnetization fixed layer are formed on the insulating member layer formed on the Si back plane or the like by using conventionally known lithography or the like. It can be manufactured by forming a two-magnetized fixed layer or the like, performing heat treatment or the like as necessary, and then forming a light modulation layer or the like by conventionally known ion beam sputtering or the like. More specifically, for example, it can be produced by the production method described in Japanese Patent Application No. 2017-191723 proposed by the present applicant.

The operation and effect of the domain wall movable spatial light modulator 5 according to the present embodiment will be described.
When a pulse current (driving current) is applied to the connecting domain wall element 10 constituting the domain wall moving space optical modulator 5 by the pulse current source 19, the pulse current (driving current) becomes as shown by the broken arrow in FIG. , The current flows from the first ferromagnetic exchange coupling portion 1a of the domain wall moving type optical modulation element 100a to the second ferromagnetic exchange coupling portion 2a through the optical modulation portion 3a. Next, the pulse current (drive current) is transferred from the first ferromagnetic exchange coupling portion 1b of the magnetic domain wall moving light modulation element 100b to the second ferromagnetic exchange coupling portion 2b through the optical modulation portion 3b via the connection wiring 111. Flows.

When the pulse current (driving current) flows as described above, the magnetic wall 33a of the magnetic wall moving type optical modulation element 100a is in the direction opposite to the direction of the pulse current (driving current) (the same direction as the electron flow), specifically, , Moves from the second ferromagnetic exchange coupling portion 2a side toward the first ferromagnetic exchange coupling portion 1a side. Further, the magnetic wall 33b of the magnetic wall moving type light modulation element 100b is in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons), specifically, from the first ferromagnetic exchange coupling portion 1b side to the first. 2 Moves toward the ferromagnetic exchange coupling portion 2b side.

That is, in any of the magnetic wall moving type light modulation elements 100a and 100b, since the optical modulation layers 30a and 30b have a linear shape having no bent portion, the magnetic wall 33a and 33b can be moved only linearly. It is possible to prevent the domain walls 33a and 33b from being caught at the bent portion and trapped.

In addition, in any of the magnetic wall moving type light modulation elements 100a and 100b, the moving distance of the magnetic wall 33a and 33b can be shortened as compared with the conventional one having a bent portion as shown in FIGS. 5 and 6. Therefore, low current drive is possible.

Therefore, according to the domain wall moving spatial light modulator 5 according to the present embodiment, one domain wall element 10 in which a plurality of domain wall moving optical modulation elements 100a and 100b are electrically connected in series by a connection wiring 111 is connected. Therefore, it is possible to drive with a low current and improve the aperture ratio. The present invention is not limited to the above embodiment, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention. The present invention is not limited to the above embodiment, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention.

<Second Embodiment>
FIG. 10 is a plan view of the domain wall moving type spatial light modulator 5A according to the second embodiment of the present invention. The magnetic wall movable spatial light modulator 5A according to the present embodiment further includes a magnetic wall movable light modulator 100c as compared with the magnetic wall movable spatial light modulator 5 according to the first embodiment described above, and the magnetic wall movement. The magnetic wall movement according to the first embodiment, except that the connection wiring 113 is further provided as a connection portion for electrically connecting the light modulation element 100b and the magnetic wall movement type light modulation element 100c in series. It has the same configuration as the type spatial light modulator 5. That is, the domain wall moving spatial light modulator 5A according to the present embodiment includes a connecting domain wall element 10A in which three domain wall moving light modulation elements 100a, 100b, and 100c are electrically connected in series. In the following description of the present embodiment, the description of the configuration common to the first embodiment will be omitted.

FIG. 11 is a plan view of the connecting domain wall element 10A according to the second embodiment of the present invention. The basic configuration of the domain wall-moving light modulation element 100c is the same as that of the domain wall-moving light modulation elements 100a and 100b, and c is added to the reference numerals of the corresponding configurations.

As shown in FIG. 11, the domain wall moving light modulation elements 100c are aligned and arranged so as to be parallel to the domain wall moving light modulation elements 100a and 100b in the longitudinal direction. More specifically, the domain wall moving light modulation element 100c is arranged so as to be opposite to the domain wall moving light modulation element 100b, and is arranged in the same direction with respect to the domain wall moving light modulation element 100a. That is, in a direction (vertical direction in FIG. 11) orthogonal to a predetermined direction (horizontal direction in FIG. 11), the first ferromagnetic exchange coupling portion 1a, the second ferromagnetic exchange coupling portion 2b, and the first ferromagnetic exchange coupling The parts 1c are arranged side by side in this order, and the second ferromagnetic exchange coupling part 2a, the first ferromagnetic exchange coupling part 1b, and the second ferromagnetic exchange coupling part 2c are arranged side by side in this order.

Further, in the domain wall moving type spatial light modulator 5A, on one end side (leftward end portion in FIG. 11) of the adjacent magnetic wall moving type optical modulators 100b and 100c, the adjacent first ferromagnetic exchange coupling portion 1c Further, a connection wiring 113 is further provided as a connection portion for electrically connecting the first magnetization fixing layer 11c and the second magnetization fixing layer 21b of the second ferromagnetic exchange coupling portion 2b. The domain wall moving light modulation elements 100b and 100c are electrically connected in series by the connection wiring 113.

Similar to the connection wiring 111 described above, the connection wiring 113 has a second ferromagnetic exchange coupling with the surface of the first magnetization fixed layer 11c of the first ferromagnetic exchange coupling portion 1c opposite to the optical modulation layer 30c. It is configured to electrically connect the surface of the second magnetization fixed layer 21b of the part 2b opposite to the photomodulation layer 30b. The connection wiring 113 extends in a direction (vertical direction in FIG. 11) orthogonal to a predetermined direction (horizontal direction in FIG. 11) which is an extension direction (longitudinal direction) of the magnetic wall movable light modulation elements 100a, 100b, 100c. Is formed. As the material constituting the connection wiring 113, the same material as the connection wiring 111 described above is used.

Further, a pulse current source 19A is connected to the first magnetization fixing layer 11a and the second magnetization fixing layer 21c. More specifically, the pulse current source 19A has the first magnetization-fixed layer 11a and the first magnetization-fixed layer 11a via electrodes (not shown) provided on the lower surfaces of the first magnetization-fixed layer 11a and the second magnetization-fixed layer 21c. It is connected to the two-magnetized fixed layer 21c. As a result, a pulse current (driving current) can be applied to the magnetic domain wall moving type light modulation elements 100a, 100b, 100c.

The magnetization directions in the domain wall moving light modulation element 100a and the domain wall moving light modulation element 100b are as described in the first embodiment. Further, in the domain wall moving light modulation element 100c, the magnetization direction of the first ferromagnetic exchange coupling portion 1c is upward, and the magnetization direction of the second ferromagnetic exchange coupling portion 2c is downward. The magnetization direction of the magnetic domain 31c arranged on the first ferromagnetic exchange coupling portion 1c side of the domain wall 33c is the downward magnetization direction D1, and the magnetization of the magnetic domain 32c arranged on the second ferromagnetic exchange coupling portion 2c side of the domain wall 33c. The direction is the upward magnetization direction D2.

The method of manufacturing the domain wall moving spatial light modulator 5A according to the present embodiment is basically the same as that of the domain wall moving spatial light modulator 5 according to the first embodiment described above. That is, the domain wall moving light modulation element 100c can be manufactured by the same manufacturing method as the domain wall moving light modulation elements 100a and 100b, and the connection wiring 113 can be manufactured by the same manufacturing method as the connection wiring 111.

The operation and effect of the connecting domain wall element 10A according to the present embodiment will be described.
When a pulse current (drive current) is applied to the connecting domain wall element 10A by the pulse current source 19A, the pulse current (drive current) is the first of the domain wall moving type optical modulation element 100a as shown by the broken line arrow in FIG. It flows from the ferromagnetic exchange coupling portion 1a through the optical modulation portion 3a to the second ferromagnetic exchange coupling portion 2a. Next, the pulse current (drive current) is transferred from the first ferromagnetic exchange coupling portion 1b of the magnetic domain wall moving light modulation element 100b to the second ferromagnetic exchange coupling portion 2b through the optical modulation portion 3b via the connection wiring 111. Flows. Next, the pulse current (drive current) is transferred from the first ferromagnetic exchange coupling portion 1c of the magnetic domain wall moving light modulation element 100c to the second ferromagnetic exchange coupling portion 2c through the optical modulation portion 3c via the connection wiring 113. Flows.

When the pulse current (driving current) flows as described above, the magnetic wall 33a of the magnetic wall moving type optical modulation element 100a is in the direction opposite to the direction of the pulse current (driving current) (the same direction as the electron flow), specifically, , Moves from the second ferromagnetic exchange coupling portion 2a side toward the first ferromagnetic exchange coupling portion 1a side. Further, the magnetic wall 33b of the magnetic wall moving type light modulation element 100b is in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons), specifically, from the first ferromagnetic exchange coupling portion 1b side to the first. 2 Moves toward the ferromagnetic exchange coupling portion 2b side. Further, the magnetic wall 33c of the magnetic wall moving type light modulation element 100c is in the direction opposite to the direction of the pulse current (driving current) (the same direction as the flow of electrons), specifically, from the second ferromagnetic exchange coupling portion 2c side. 1 It moves toward the ferromagnetic exchange coupling portion 1c side.

That is, in any of the magnetic wall moving type light modulation elements 100a, 100b, 100c, since the optical modulation layers 30a, 30b, 30c have a linear shape having no bent portion, the magnetic wall 33a, 33b, 33c can be moved only linearly. Therefore, it is possible to prevent the domain walls 33a, 33b, 33c from being caught at the bent portion and trapped.

In addition, in any of the magnetic wall moving type light modulation elements 100a, 100b, 100c, the moving distance of the magnetic wall 33a, 33b, 33c is shorter than that of the conventional one having a bent portion as shown in FIGS. 5 and 6. Therefore, low current drive is possible.

Therefore, according to the connecting domain wall element 10A according to the present embodiment, the plurality of domain wall moving light modulation elements 100a, 100b, 100c are electrically connected in series by the connection wirings 111, 113 to further reduce the current drive. It is possible to improve the aperture ratio as well as. The present invention is not limited to the above embodiment, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention. The present invention is not limited to the above embodiment, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention.

The present invention is not limited to the above embodiment, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention.
For example, in the first embodiment, two domain wall moving light modulation elements 100a, 100b are electrically connected in series, and in the second embodiment, three domain wall moving light modulation elements 100a, 100b, 100c are electrically connected in series. However, the present invention is not limited to this, and four or more domain wall-moving light modulation elements may be electrically connected in series.

1,1a, 1b, 1c 1st ferromagnetic exchange coupling part 2,2a, 2b, 2c 2nd ferromagnetic exchange coupling part 3,3a, 3b, 3c Optical modulator 5,5A, Domain wall moving spatial light modulator 10 , 10A Connected domain wall moving light modulator 11, 11a, 11b, 11c First magnetization fixed layer (first ferromagnetic layer)
21,21a, 21b, 21c Second magnetization fixed layer (first ferromagnetic layer)
30, 30a, 30b, 30c optical modulation layer (second ferromagnetic layer)
33, 33a, 33b, 33c Domain wall 100, 100a, 100b, 100c Domain wall moving light modulation element 111, 113 Connection wiring (connection part)

Claims (2)

An optical modulator that extends in a predetermined direction and emits light by changing the direction of polarized light.
The first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion, which are arranged at both ends of the optical modulation section and have different coercive forces,
A domain wall moving spatial light modulator comprising a plurality of domain wall moving light modulators.
Both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion
The first ferromagnetic layer made of ferromagnetic material and
It has a second ferromagnetic layer that is formed on the first ferromagnetic layer and is made of a ferromagnetic material so that it has a ferromagnetic exchange coupling with the first ferromagnetic layer.
The plurality of magnetic domain wall moving light modulation elements are arranged side by side so that the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion are alternately positioned in a direction orthogonal to the predetermined direction.
In the domain wall moving space optical modulator, the first ferromagnetic layer of the adjacent first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion are located on one end side of the adjacent magnetic wall moving optical modulation elements. A domain wall mobile space optical modulator further comprising a connection portion for electrically connecting to the first ferromagnetic layer of the above. The magnetic wall movable spatial light according to claim 1, wherein the connecting portion is a connection wiring for electrically connecting the surfaces of the adjacent first ferromagnetic layer opposite to the second ferromagnetic layer. Modulator.

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