JP2019220544A - Domain wall displacement type spatial light modulator - Google Patents

Abstract

To provide a domain wall displacement type spatial light modulator which shortens a production process by sharing a magnetization fixation layer in adjacent elements and utilizing a change of a coercive force caused by a length of the magnetization fixation layer.SOLUTION: The present invention relates to a domain wall displacement type spatial light modulator comprising a domain wall displacement type spatial light modulation element including: a light modulation section from which an incident light is emitted after changing a direction of polarization; and a first ferromagnetic exchange coupling section and a second ferromagnetic exchange coupling section which are disposed in both ends of the light modulation section while extending in parallel and have coercive forces different from each other. Each of the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section includes: a first ferromagnetic layer consisting of a ferromagnetic material; and a second ferromagnetic layer formed on the first ferromagnetic layer and consisting of a ferromagnetic material, thereby performing ferromagnetic exchange coupling with the first ferromagnetic layer. In the domain wall displacement type spatial light modulator, a length of the first ferromagnetic layer in a direction of the extension in the first ferromagnetic exchange coupling section is longer than a length of the first ferromagnetic layer in a direction of the extension in the second ferromagnetic exchange coupling section.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a magneto-optical spatial light modulator (hereinafter, referred to as a “domain wall”) that controls the magnetic domain structure of a light modulation area by moving a domain wall to control the domain structure of the light modulation area, which is a promising spatial light modulator for stereoscopic holography with a wide viewing area. Mobile spatial light modulator ").

  2. Description of the Related Art Conventionally, in order to secure a viewing range of 30 degrees or more that is practical for stereo holography, it is necessary to set a pixel pitch of a spatial light modulator (SLM) as a display device to 1 micron or less. Existing SLMs such as liquid crystals and digital micromirror devices (DMDs) have a pixel pitch of about 5 microns, and further miniaturization is difficult. On the other hand, a magneto-optical spatial light modulator (MOSLM) using spin injection magnetization reversal or domain wall motion for pixel rewriting needs to be improved in terms of light utilization efficiency, operating current, etc. (For example, see Patent Document 1).

  The 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 light and dark. Here, the domain wall displacement type SLM proposed by the applicant has a structure in which a magnetization fixed layer is disposed at both ends of a light modulation layer, so that expansion and contraction of a magnetic domain can be controlled by the direction of a current flowing through the light modulation layer. (For example, see Patent Document 2). The domain wall motion type SLM can be expected to consume lower power than the MOSLM using spin injection magnetization reversal, but is called a light modulation layer and magnetization fixed layers at both ends (a first magnetization fixed layer and a second magnetization fixed layer). It is necessary to give a sufficient coercive force difference to the three types of ferromagnetic layers and to realize a sophisticated device design within one pixel on the premise of 1 micron or less, such as precisely manufacturing a complicated device structure.

  In view of the above, the applicant has proposed in Patent Document 2 above a domain wall motion SLM in which the magnetization fixed layer and the light modulation layer are ferromagnetically coupled. With the configuration as in Patent Document 2, it is possible to relatively easily manufacture a domain wall displacement type SLM that is difficult to manufacture.

  In the domain wall motion type SLM, it is necessary to realize an antiparallel magnetization arrangement in which the magnetization directions of the magnetization fixed layer are upward and downward, respectively. The antiparallel magnetization arrangement can be realized by designing a difference in the coercive force (Hc1 and Hc2) between the two magnetization fixed layers 1 and 2. Here, when Hc2> Hc1, the magnetization of the magnetization fixed layer is first turned upward by an external magnetic field H (H> Hc2> Hc1) larger than the coercive force of these magnetization fixed layers, and then Hc2> H ′> Hc1. When such an external magnetic field H ′ is applied downward, only the magnetization direction of the magnetization fixed layer 1 changes downward, thereby realizing an antiparallel magnetization arrangement.

JP 2012-141402 A Japanese Patent Application No. 2017-109478

  Here, in order to design the difference in the coercive force between the magnetization fixed layers 1 and 2, either a ferromagnetic material having a different coercive force or a ferromagnetic material having a different layer configuration is used, or only one of the magnetization fixed layers is irradiated with an ion beam. There are various ways to do this. However, in these formation processes, in addition to complicated procedures, high-precision alignment is required for fine processing. The present invention proposes a method of forming two magnetization fixed layers by a single process, thereby simplifying the procedure and eliminating the number of times of high-precision alignment.

  The present invention has been made in view of the above, and an object of the present invention is to provide a domain wall displacement type spatial light modulator which is designed by a simpler process and can reduce a design margin for alignment with an electrode or a light modulation unit. Is to do.

  (1) In order to achieve the above object, the present invention provides a light modulation unit (for example, a light modulation unit 3 described later) that changes the direction of polarization of incident light and emits the light, and a light modulation unit parallel to both ends of the light modulation unit. A first ferromagnetic exchange coupling section (for example, a first ferromagnetic exchange coupling section 1 described later) and a second ferromagnetic exchange coupling section (for example, a second ferromagnetic exchange coupling section described later) having different coercive forces and extending. And a domain wall motion type spatial light modulator (for example, a domain wall motion type spatial light modulator 10 described later). 100), the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section are both a first ferromagnetic layer (for example, a first magnetization fixed layer 11a to be described later and a On the second magnetization fixed layer 21) and the first ferromagnetic layer. A second ferromagnetic layer (for example, a light modulation layer 30 described later) that is formed and made of a ferromagnetic material and ferromagnetically exchange-coupled with the first ferromagnetic layer. A domain wall displacement type spatial light modulator, wherein a length of the first ferromagnetic layer in the extending direction in the portion is longer than a length of the first ferromagnetic layer in the second ferromagnetic exchange coupling portion in the extending direction. provide.

  (2) In the domain wall motion type spatial light modulator of (1), the plurality of domain wall motion type spatial light modulators are arranged in a grid pattern in a first direction and a second direction orthogonal to the first direction. The first ferromagnetic layer extends in the first direction, and the plurality of domain wall displacement type spatial light modulators arranged in the first direction have respective first ferromagnetic exchange coupling portions. The same first ferromagnetic layer may be shared.

  (3) The present invention also provides an optical modulator for changing the direction of polarization of incident light, and a first ferromagnetic exchange coupling unit and a second ferromagnetic exchange unit, which extend in parallel and have different coercive forces. A magnetic exchange coupling unit, and a domain wall motion type spatial light modulator including a domain wall motion type spatial light modulator having the domain wall motion type spatial light modulator, wherein the plurality of domain wall motion type spatial light modulators are: In the domain wall displacement type spatial light modulator, two second ferromagnetic exchange coupling portions are arranged in the first direction and a second direction orthogonal to the first direction in a lattice pattern. One of the first ferromagnetic exchange coupling sections is disposed at both ends of the modulating section and interposed between the two second ferromagnetic exchange coupling sections, and the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section are arranged. Each of the exchange coupling portions includes a first ferromagnetic layer made of a ferromagnetic material and the first ferromagnetic layer. A second ferromagnetic layer formed on the first ferromagnetic layer and made of a ferromagnetic material and ferromagnetically exchange-coupled with the first ferromagnetic layer, wherein the first ferromagnetic layer is And the length of the first ferromagnetic layer in the first ferromagnetic exchange coupling section in the extending direction is equal to the length of the first ferromagnetic layer in the second ferromagnetic exchange coupling section in the extending direction. The plurality of domain wall displacement type spatial light modulators longer than the length and arranged in the first direction are configured such that the first ferromagnetic exchange coupling portions share the same first ferromagnetic layer. A moving spatial light modulator is provided.

  According to the present invention, it is possible to reduce the number of times of high-precision alignment that is repeatedly required in the fabrication of an element. Further, the present invention can be realized by a simple process with less influence on the flatness of the light modulation layer as compared with a process in which the two magnetization fixed layers 1 and 2 are realized by different materials.

FIG. 9 is a perspective view illustrating a configuration of a domain wall displacement type spatial light modulator described in Patent Document 2. FIG. 11 is a side view showing a configuration of a domain wall displacement type spatial light modulator described in Patent Document 2. FIG. 9 is a diagram showing an operation of a domain wall motion type spatial light modulator described in Patent Document 2. FIG. 9 is a top view of a domain wall displacement type spatial light modulator described in Patent Document 2. 1 is a top view of a domain wall displacement type spatial light modulator according to an embodiment of the present invention. 4 is a graph showing the dependence of the coercive force on the Co / Pd multilayer thin film length. 4 is a graph showing a comparison of coercive force of Co / Pd multilayer thin wires having different lengths. It is sectional drawing which shows an example of the domain wall displacement type spatial light modulator which concerns on the said embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. It is a figure showing the manufacturing method of the domain wall displacement type spatial light modulator concerning the above-mentioned embodiment. 1 is a top view of a domain wall displacement type spatial light modulator according to an embodiment of the present invention. 1 is a cross-sectional view of a domain wall displacement type spatial light modulator according to an embodiment of the present invention.

[First Embodiment]
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected about a common structure. For convenience of description, the upper, lower, left, and right in the figure will be described as the upper, lower, left, and right sides of the domain wall moving type spatial light modulator.

  FIG. 1 is a perspective view showing a configuration of a domain wall motion type spatial light modulator described in Patent Document 2. As shown in FIG. FIG. 2 is a side view showing a configuration of a domain wall motion type spatial light modulator described in Patent Document 2. As shown in FIG. FIG. 3 is a diagram showing the operation of the domain wall motion type spatial light modulator described in Patent Document 2. The arrows in FIGS. 1 and 3 indicate the direction of the magnetization direction.

  As shown in FIGS. 1 to 3, the domain wall motion type spatial light modulator 90 described in Patent Document 2 includes a domain wall motion type spatial light modulation device 91 using domain wall motion. The basic configuration of the domain wall motion type spatial light modulator 100 according to one embodiment of the present invention is the same as the configuration of the domain wall motion type spatial light modulator 90 described in Patent Document 2 shown in FIGS. Hereinafter, the basic configuration will be described in detail.

As shown in FIG. 1, the domain wall displacement type spatial light modulation device 91 includes a first ferromagnetic exchange coupling unit 1, a second ferromagnetic exchange coupling unit 2, and a light modulation unit 3, and a Si (not shown). Etc. are formed on a substrate.
The first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 are made of a common metal electrode material such as a metal (not shown) such as Cu, Al, Au, Ag, Ru, Ta, Cr, or an alloy thereof. Is provided in the lowermost layer, and a pulse current source 9 is connected to the lower electrode, so that a pulse current can be applied.

  The shape of the domain wall displacement type spatial light modulator 91 is not particularly limited. For example, as shown in FIG. 1, the light modulator 3 is formed in a flat plate shape extending in a predetermined direction, and first ferromagnetic exchange coupling portions are provided at both ends thereof. A shape in which the first and second ferromagnetic exchange coupling parts 2 are arranged is exemplified. The upper surfaces of the light modulating unit 3, the first ferromagnetic exchange coupling unit 1 and the second ferromagnetic exchange coupling unit 2 are continuously flush with each other, and the first ferromagnetic exchange coupling unit 1 and the second ferromagnetic exchange coupling unit 2 Is thicker than the thickness of the light modulation section 3.

  As shown in FIG. 2, the first ferromagnetic exchange coupling unit 1 is configured by stacking a first magnetization fixed layer 11, a nonmagnetic metal layer 12, a buffer layer 13, and a light modulation layer 30 in this order. You.

  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 whose magnetization direction is fixed in one direction, and has a large coercive force. The first magnetization fixed layer 11 has a magnetic anisotropy in the same direction as a light modulation layer 30 described later, and when the light modulation layer 30 is made of a ferromagnetic material having a perpendicular magnetic anisotropy, The magnetization fixed layer 11 is also made of a ferromagnetic material having perpendicular magnetic anisotropy. Preferably, both the first magnetization fixed layer 11 and the light modulation layer 30 are made of a ferromagnetic material having perpendicular magnetic anisotropy.

  The first magnetization fixed layer 11 has a perpendicular magnetic anisotropy (CPP-GMR) having a structure in which a nonmagnetic layer is sandwiched between a magnetization fixed layer whose magnetization is fixed in the vertical direction and a magnetization free layer whose magnetization direction can be reversed. Current Perpendicular to the Plane Giant MagnetoResistance (vertical conduction type giant magnetoresistive effect) A device or a TMR device can be formed of a known ferromagnetic material as a magnetization fixed layer. 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. Thereby, the coercive force of the first magnetization fixed layer 11 can be increased, and the magnetization direction of the first magnetization fixed layer 11 can be fixed so as not to be easily changed by an external magnetic field.

  Further, the first magnetization fixed layer 11 may be formed of a multilayer laminate in which these transition metal layers and non-magnetic metal layers are alternately laminated, such as Co / Pt, Fe / Pt, and Co / Pd. Etc. can be used. By using these ferromagnetic materials, the first magnetization fixed layer 11 having strong 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, if the coercive force of the first magnetization fixed layer 11 composed of the above-described multilayer film is increased by heat treatment, the coercive force of the ferromagnetic exchange coupling portion after coupling with the light modulation layer 30 becomes larger, and the light modulation The difference in coercive force with the portion 3 can be further increased.

  The nonmagnetic metal layer 12 and the buffer layer 13 are disposed between the first magnetization fixed layer 11 and the light modulation layer 30 so as to maintain magnetic coupling between the first magnetization fixed layer 11 and the light modulation layer 30. can do.

  The nonmagnetic metal layer 12 is formed by being laminated on the first magnetization fixed layer 11 described above. The nonmagnetic metal layer 12 is provided to prevent the first magnetization fixed layer 11 from being damaged by etching in a manufacturing process described later. The non-magnetic metal layer 12 is made of a non-magnetic metal, and thin-film layers of various non-magnetic metals can be used. For example, Ta, Mo, and Ru can be used as the nonmagnetic metal layer 12, and among them, a layer made of Ta is preferably used.

  The buffer layer 13 is formed by being laminated on the nonmagnetic metal layer 12 described above. Since the buffer layer 13 needs to be able to pass a current through both the spatial light modulation element utilizing domain wall motion and the TMR element, the resistance is not too large when the buffer layer 13 is made thin, and has an appropriate conductivity. The buffer layer 13 is desirably a material that includes an element that has a low etching rate in a later-described manufacturing process and a high detection sensitivity of SIMS (Secondary Ion Mass Spectrometry), and is visible on a SIMS-type endpoint monitor. Thus, the etching can be reliably stopped at the buffer layer 13, and damage to the first magnetization fixed 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 made of MgO, Al ₂ O ₃ , MgAl ₂ O ₄ , TiO ₂ , ZnO or RuO ₂ . Above all, the buffer layer 13 is preferably made of MgO. According to the MgO layer made of MgO, it is possible to form the buffer layer 13 having appropriate conductivity, a low etching rate, and a high SIMS sensitivity.

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

  The light modulation layer 30 forms a second ferromagnetic layer in a second ferromagnetic exchange coupling unit 2 described later and also forms the light modulation unit 3 itself.

  In the first ferromagnetic exchange coupling unit 1 having the above-described configuration, the first magnetization fixed layer 11 and the light modulation layer 30 are ferromagnetic exchange-coupled via the nonmagnetic metal layer 12 and the buffer layer 13. Due to the ferromagnetic exchange coupling, the magnetization direction of the first magnetization fixed layer 11 and the magnetization direction of the light modulation layer 30 in the first ferromagnetic exchange coupling section 1 are simultaneously reversed.

  The second ferromagnetic exchange coupling unit 2 is configured by stacking a second magnetization fixed layer 21, a nonmagnetic metal layer 22, a buffer layer 23, and a light modulation layer 30 in this order.

  Further, in the second ferromagnetic exchange coupling unit 2, similarly to the first ferromagnetic exchange coupling unit 1, the second magnetization fixed layer 21 and the light modulation layer 30 are strongly connected via the nonmagnetic metal layer 22 and the buffer layer 23. Magnetic exchange coupling. Due to this ferromagnetic exchange coupling, the magnetization direction of the second magnetization fixed layer 21 and the magnetization direction of the light modulation layer 30 in the second ferromagnetic exchange coupling section 2 are simultaneously reversed.

  The second magnetization fixed layer 21 is selected from materials that can be used for the first magnetization fixed layer 11, and similarly, the nonmagnetic metal layer 22 and the buffer layer 23 are also formed of the nonmagnetic metal layer 12 and the buffer layer 13, respectively. It is selected from available materials.

  Here, the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 have different coercive forces to form the domain wall 33 and the light modulation region 300 as described in detail later. Designed. Thereby, the initial magnetization directions antiparallel to each other at both ends of the light modulation layer 30 which are indispensable for the light modulation control can be realized by the external magnetic field due to the coercive force difference between the first magnetization fixed layer 1 and the second magnetization fixed layer 2. It is possible. This will be described in detail later.

  As described above, the light modulation layer 30 forms the light modulation unit 3. A domain wall 33 and magnetic domains 31 and 32 are formed in the optical modulator 3 including the optical modulation layer 30. This will be described in detail later.

  In addition, each magnetization fixed layer (hereinafter, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 are also simply referred to as a magnetization fixed layer), each nonmagnetic metal layer, each buffer layer, and each layer of the light modulation layer 30. Alternatively, a functional layer may be appropriately provided at the interface with the lower electrode. For example, a cap layer containing Ta, Ru, or SiN or a cap layer made of Ta, Ru, or SiN may be provided on the light modulation layer 30 in order to prevent damage to the light modulation layer 30 during the microfabrication process. The cap layer has a function of preventing GdFe or TbFeCo, which is used to form the light modulation layer 30 and is easily oxidized, from being oxidized in the air after the device is completed.

Next, the magnetic characteristics of the domain wall displacement type spatial light modulator 10 according to the present embodiment will be described in detail.
As described above, the first ferromagnetic exchange coupling unit 1 includes the first magnetization fixed layer 11a that performs ferromagnetic exchange coupling with the light modulation layer 30, and the second ferromagnetic exchange coupling unit 2 includes the first magnetization fixed layer 11a and the light modulation layer 30. It has a second magnetization fixed layer 21 for ferromagnetic exchange coupling. That is, the first ferromagnetic exchange coupling unit 1 and the second ferromagnetic exchange coupling unit 2 each have a ferromagnetic exchange coupling inside, and their magnetization directions are simultaneously reversed. As shown in FIGS. 1 and 3, the magnetization direction of the first ferromagnetic exchange coupling unit 1 is designed to be downward, while the magnetization direction of the second ferromagnetic exchange coupling unit 2 is designed to be upward. I have.

  The light modulation unit 3 has a domain wall 33 extending on a plane orthogonal to a direction perpendicular to the ferromagnetic exchange coupling units. That is, 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 3, the magnetization direction of the magnetic domain 31 on the first ferromagnetic exchange coupling unit 1 side with respect to the domain wall 33 is upward, and the magnetic domain on the second ferromagnetic exchange coupling unit 2 side with respect to the domain wall 33. The magnetization direction of 32 is downward.

  As described above, by forming the magnetic domains 31 and 32 having different magnetization directions through the domain wall 33 in the light modulator 3, the domain wall displacement type spatial light modulator 10 can function as a spatial light modulator. More specifically, for example, when the domain wall motion type spatial light modulation device 10 is configured as a reflection type spatial light modulation device, the polarization of the polarized light from above the domain wall motion type spatial light modulation device 10 to the upper surface of the light modulation unit 3. When uniform light is incident, the rotation angle of the plane of polarization of the reflected light changes depending on the direction of the magnetization direction. Therefore, light can be modulated by assigning each reflected light according to the rotation angles of these different polarization planes to light and dark of the light via a polarizing filter. However, when the substrate is made of a translucent material such as glass or sapphire, the domain wall motion type spatial light modulator 10 can also function as a transmission type spatial light modulator.

Here, a generation mechanism of the domain wall 33 will be described with reference to FIGS.
First, in order to form the domain wall 33 in the light modulating section 3, the coercive force of the first magnetization fixed layer 11 that is ferromagnetically exchange-coupled with the light modulation layer 30 and the second coercive force that is also ferromagnetically exchanged with the light modulation layer 30. It is necessary to make the coercive force of the magnetization fixed layer 21 different from each other.

  In Patent Document 2, as a method of making the coercive force of the first magnetization fixed layer 11 and the coercivity of the second magnetization fixed layer 21 different from each other, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 Either the shape is different (for example, if the width of the first magnetization fixed layer 11 is increased, the coercive force is reduced), only one of them is heat-treated, or the layer configuration is different from each other. Selected. Thereby, the coercive force of the first magnetization fixed layer 11 and the coercive force of the second magnetization fixed layer 21 are made different from each other, so that the coercive force of the first ferromagnetic exchange coupling unit 1 and the second ferromagnetic exchange coupling unit 2 can have different coercive forces.

FIG. 4 is a top view showing the configuration of the domain wall motion type spatial light modulator 90 of Patent Document 2.
As shown in FIG. 4, a plurality of domain wall motion type spatial light modulators 91 according to Patent Document 2 are independently manufactured and aligned on a substrate (not shown).

FIG. 5 is a top view showing the configuration of the domain wall motion type spatial light modulator 100 according to the present embodiment. 5, the same components as those of the domain wall displacement type spatial light modulator 90 described in Patent Document 2 are denoted by the same reference numerals.
As shown in FIG. 5, in the domain wall motion type spatial light modulator 100 according to the present embodiment, the first ferromagnetic exchange coupling unit has the first ferromagnetic layer (that is, , The first magnetization fixed layer 11a) is longer than the first ferromagnetic layer (that is, the second magnetization fixed layer 21a) of the second ferromagnetic exchange coupling section. Further, the plurality of domain wall motion type spatial light modulators 10 are arranged in a lattice pattern, and share the first magnetization fixed layer 11a with the other domain wall motion type spatial light modulators 10 arranged in the extending direction.

  More specifically, as shown in FIG. 5, the first magnetization fixed layer 11a of the present embodiment is longer than the second magnetization fixed layer 21 in the extending direction. Thereby, the first magnetization fixed layer 11a has a smaller coercive force than the second magnetization fixed layer 21, and a coercive force difference is generated between the two. Further, since the plurality of domain wall motion type spatial light modulators 10 arranged in the extending direction share the first magnetization fixed layer 11a, the number of steps can be reduced as compared with a process of manufacturing each element individually. Further, the number of times of the above-described alignment at the time of manufacturing can be reduced.

Here, the length dependency of the coercive force in the Co / Pd multilayer thin film according to the present invention will be described.
FIG. 6A and FIG. 6B show the coercive force length-dependent characteristics of a 100 nm wide Co / Pd multilayer thin film. FIG. 6A is a graph in which the coercive force of a thin wire processed to a length of 0.3 μm to 300 μm is averaged for each of five measured coercive forces. FIG. 6B is a graph in which the standard deviation is inserted as an error bar into the average value of the coercive force of the Co / Pd multilayer films having a length of 0.3 μm and 300 μm.
Here, the Co / Pd multilayer thin film is formed by depositing Ru 3 nm and Pt 2 nm as an underlayer, Co 0.3 nm and Pd 0.6 nm 25 times, and then depositing Ru 3 nm as a protective layer by a helicon sputtering device.

  According to FIG. 6A, the coercive force tends to decrease as the length of the Co / Pd multilayer thin film increases. According to FIG. 6B, there is a significant difference in coercive force between the 0.3 μm and 300 μm Co / Pd multilayer thin wires. Therefore, the coercive force difference can be designed by optimizing the length of the magnetization fixed layer.

  For example, with the above configuration, the coercive force of the first magnetization fixed layer 11a can be designed to be smaller than the coercive force of the second magnetization fixed layer 21. In this case, as shown in FIG. 2, if the coercive force of the first ferromagnetic exchange coupling unit 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling unit 2 is Hc2, and the coercive force of the light modulation layer is Hc_m, The relationship of Hc2> Hc1> Hc_m is established.

  Then, a magnetic field in which the magnetic field strength H is H> Hc2 is applied to the element having a structure in which the relationship of the coercive force is established as described above. Then, in each of the first ferromagnetic exchange coupling unit 1, the second ferromagnetic exchange coupling unit 2, and the light modulation unit 3, the direction of the magnetization direction is upward.

  Next, a magnetic field in which the magnetic field strength H 'is Hc2> H'> Hc1 is applied to the element downward. Then, while the direction of the magnetization direction of the second ferromagnetic exchange coupling unit 2 remains upward, the direction of the magnetization direction of the first ferromagnetic exchange coupling unit 1 and the direction of the magnetization of the light modulation unit 3 are all downward. Change.

  At this time, initial magnetic domains 31a and 32a are generated at both ends of the light modulation unit 3 as shown in FIG. More specifically, the end of the optical modulation unit 3 on the first ferromagnetic exchange coupling unit 1 side is subjected to a first magnetic field (refer to a broken arrow in FIG. 3) from the first ferromagnetic exchange coupling unit 1. An initial magnetic domain 31a having an upward magnetization direction antiparallel to the downward magnetization of the magnetic exchange coupling unit 1 is generated. The end of the optical modulator 3 on the side of the second ferromagnetic exchange coupling unit 2 is exposed to the second ferromagnetic exchange coupling from the second ferromagnetic exchange coupling unit 2 (see the broken arrow in FIG. 3). An initial magnetic domain 32a having a downward magnetization direction antiparallel to the upward magnetization of the coupling portion 2 is generated.

  Next, in this state, a pulse current is applied from the pulse current source 9 and the first ferromagnetic exchange coupling unit 1 to the second ferromagnetic exchange coupling unit 2 or the second ferromagnetic exchange coupling unit 2 to the first ferromagnetic exchange coupling. A pulse current is applied to the unit 1. Then, the domain wall 33 formed by the generation of the initial magnetic domains 31a and 32a can be moved in the direction opposite to the direction of the pulse current (the same direction as the flow of electrons). Thereby, as shown in FIG. 3, the magnetization direction of the light modulation region 300 except for both ends of the light modulation unit 3 is inverted (in the example of FIG. 3, the magnetization direction of the light modulation region 300 is inverted upward). Is possible.

Next, a detailed configuration of the domain wall displacement type spatial light modulator 100 according to the present embodiment will be described with reference to FIG.
FIG. 7 is a cross-sectional view illustrating a configuration of an example of the domain wall motion type spatial light modulator 100 according to the present embodiment. In FIG. 7, the numerical value in parentheses of each layer shows an example of a preferable thickness (nm) of each layer.

In the example shown in FIG. 7, the domain wall motion type spatial light modulator 10 is formed on a Si back plane 41.
Each of the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 is, in order from the Si backplane 41 side, a Ta layer 44, an Ag layer 45, Co / Pd layers 11, 21, and Ta layers 12, 22. , MgO layers 13 and 23 and a GdFe layer 3 are laminated. As is clear from FIG. 7, the width of the first ferromagnetic exchange coupling unit 1 and the width of the second ferromagnetic exchange coupling unit 2 are set to be the same.

The Si backplane 41 includes a lower electrode (not shown). The lower electrode is formed of a general metal electrode material such as a metal such as Cu, Al, Au, Ag, Ru, Ta, and Cr or an alloy thereof.
However, in the present embodiment, it is sufficient that a current can flow. For example, similarly to the Si backplane 41, a TFT backplane may be used as a configuration for active matrix driving. Further, for example, a configuration in which simple matrix driving is performed instead of the Si backplane may be adopted.

  The Ta layer 44 and the Ag layer 45 are base layers provided for improving the adhesion to the lower electrode. These Ta and Ag are preferable because they do not adversely affect the magnetic properties of the Co / Pd multilayer films 11 and 21. Note that Ru may be used instead of Ta.

  The Co / Pd layers 11 and 21 constitute the above-described first and second magnetization fixed layers, respectively, the Ta layers 12 and 22 constitute the above-mentioned nonmagnetic metal layer, and the MgO layers 13 and 23 constitute the above-mentioned buffer layer. Constitute.

  In the present embodiment, in the first magnetization fixed layer 11a and the second magnetization fixed layer 21, the former is longer than the latter in the extending direction, and is shared by a plurality of elements arranged in the extending direction. On the other hand, the latter has a different configuration in that it is formed independently for each element. Except for these differences, the constituent materials of both layers are the same.

  Since the first magnetization fixed layer 11a of the present embodiment is longer than the second magnetization fixed layer 21, the coercive force of the light modulation layer 30 ferromagnetically coupled to the first magnetization fixed layer 11a decreases, A coercive force difference such that Hc2> Hc1 is generated between the coercive force Hc1 of the first ferromagnetic exchange coupling unit 1 and the coercive force Hc2 of the second ferromagnetic exchange coupling unit 2. Thereby, a coercive force difference of Hc2> Hc1> Hc_m can be realized.

  Further, by designing the coercive force difference based on the difference in length only in the extending direction of the two magnetization fixed layers, the aperture ratio of the light modulation region can be improved. Specifically, making the heights (layer thicknesses) of the first magnetization fixed layer 11a and the second magnetization fixed layer 21 different requires high design difficulty in a domain wall displacement type spatial light modulator requiring high flatness. . Then, in order to design the coercive force difference due to the difference in shape between the two, the width or the depth will be different, but if the coercive force difference is designed only by the difference in the length of the depth, both will minimize the width Since the setting can be made, the light modulation region 300 opened on the element can be widely taken, and the aperture ratio of the light modulation region can be improved.

The light modulating section, that is, the light modulating layer is composed of the GdFe layer 3. On the GdFe layer 3, a Ru layer 4 as a cap layer is formed. Instead of the Ru layer, a Ta layer, a W layer, or a Si ₃ N ₄ layer may be used.
Note that SiO ₂ layers 42 as insulating members are arranged adjacent to both the left and right sides of the first ferromagnetic exchange coupling unit 1 and the left and right sides of the second ferromagnetic exchange coupling unit 2.

Next, an example of a method for manufacturing the domain wall displacement type spatial light modulator 100 according to the present embodiment will be described in detail with reference to FIGS. 8A to 8H.
Here, FIGS. 8A to 8H are views showing a method for manufacturing the domain wall motion type spatial light modulator 100 according to the present embodiment.

The method of manufacturing the domain wall displacement type spatial light modulator 100 according to the present embodiment includes a first ferromagnetic layer forming step, a non-magnetic metal layer forming step, a buffer layer forming step, a cap layer forming step, a processing step , A removing step, and a second ferromagnetic layer forming step.
Hereinafter, each of these steps will be described.

First, as shown in FIG. 8A, a first magnetization fixed layer and a second magnetization fixed layer are formed on the SiO ₂ layer 42 of the insulating member formed on the Si back plane 41 by using a conventionally known electron beam lithography or the like. Perform resist patterning corresponding to each shape of the layer. That is, a resist layer 40 corresponding to each shape of the first magnetization fixed layer and the second magnetization fixed layer is formed on the SiO ₂ layer 42. After resist patterning, high-density plasma etching is performed. This high-density plasma etching is particularly preferably used in this step because it has better anisotropic etching characteristics than ion milling.

Then, as shown in FIG. 8B, the SiO ₂ layer 42 in the region where the resist layer 40 is not formed is removed by etching. The regions from which the SiO ₂ layer 42 has been removed correspond to the shapes of the first magnetization fixed layer and the second magnetization fixed layer, respectively. Here, only the SiO ₂ layer 42 in a region corresponding to the first magnetization fixed layer is consistently removed in the first direction, so that only the first magnetization fixed layer is elongated in the extending direction and further extends. It is possible to form the domain wall motion type spatial light modulator of the present embodiment shared by a plurality of elements arranged in the direction.

Next, as shown in FIG. 8C, a magnetization fixed layer, a nonmagnetic metal layer, a buffer layer, and a cap layer for suppressing oxidation of the buffer layer, which constitute the first ferromagnetic layer, are formed in this order (first ferromagnetic layer). Forming step, nonmagnetic metal layer forming step, buffer layer forming step, and cap layer forming step). Specifically, the Ta layer 44, the Ag layer 45, the Co / Pd layers 11, 21, 51, the Ta layers 12, 22, 52, the MgO layers 13, 23, 53, and the SiO ₂ layers 14, 24, 54 Films are continuously formed in this order. All of the film formation can be performed by an ion beam sputtering apparatus. This is because an ion beam sputtering method in which sputter particles have high rectilinearity is particularly preferable because it is necessary to form a material in a region having a small opening size on the order of nanometers and a large depth. However, the method is not limited thereto, and a conventionally known method such as a molecular beam epitaxy (MBE) method can be used.

  Next, as shown in FIG. 8D, lift-off is performed to remove the remaining resist layer 40 (processing step). Specifically, lift-off is performed after the element is taken out of the vacuum into the atmosphere. Thus, all of the layers formed on the resist layer 40 are removed. For removing the resist layer 40, a conventionally known resist stripping agent can be used.

  After the lift-off, a heat treatment at 350 ° C. is performed in an annealing furnace as needed (processing step). By this heat treatment, the coercive force of the Co / Pd layers 11 and 21 constituting each magnetization fixed layer increases. The heat treatment temperature in the treatment step is preferably, for example, 300 ° C. or higher.

Next, as shown in FIG. 8E, ion beam milling (or high-density plasma etching) is performed (removal step). As a result, all the outermost SiO ₂ layers 14 and 24 are removed, and a part of the MgO layers 13 and 23 is removed. That is, the etching is performed halfway through the MgO layers 13 and 23. At this time, the MgO layers 13 and 23 have a low etching rate and Mg has high SIMS sensitivity, and thus are most suitable for detection by a SIMS type endpoint monitor. This makes it possible to reliably stop the etching in the middle of the MgO layers 13 and 23.

After ion beam milling (or high-density plasma etching) is completed, the element is transferred to a light modulation layer film forming apparatus in a vacuum (for example, 1 × 10 ⁻⁶ [Pa]). Then, as shown in FIG. 8F, a GdFe layer 3 as a light modulating layer is formed by, for example, an ion beam sputtering apparatus in the light modulating layer forming apparatus. In addition, a Ru layer 4 as a cap layer is further formed on the GdFe layer 3 by, for example, an ion beam sputtering apparatus.

  Next, as shown in FIG. 8G, resist patterning of the light modulation layer is performed by electron beam lithography or the like. That is, a resist layer 40 corresponding to a desired pattern is formed on the Ru layer 4. After resist patterning, ion beam milling (or high-density plasma etching) is performed.

  Then, as shown in FIG. 8H, the GdFe layer 3 and the Ru layer 4 in the region where the resist layer 40 is not formed are removed by etching. Thereby, the GdFe layer 3 constituting the light modulation layer is formed in a desired pattern shape (second ferromagnetic layer forming step).

  Finally, the resist layer 40 remaining on the uppermost layer is removed with a conventionally known resist stripping agent. Thus, the domain wall displacement type spatial light modulator 100 shown in FIG. 7 is obtained.

  According to the domain wall motion type spatial light modulator 100 according to the embodiment described above, the nonmagnetic metal layer, the buffer layer, and the cap layer for suppressing the oxidation of the buffer layer are formed in this order on the first ferromagnetic layer. Then, in this state, a lift-off process and, if necessary, a heat treatment are performed. Then, after removing the entire cap layer and a part of the buffer layer, a second ferromagnetic layer is formed.

  Here, in order to manufacture a light modulation element utilizing domain wall motion as in the present embodiment, it is necessary to take out the element once into the atmosphere and lift it off before forming the light modulation layer 30. For this reason, in the conventional microfabrication process, two ferromagnetic thin films cannot be formed continuously and continuously in a vacuum, and ferromagnetic exchange coupling cannot be performed. According to this, since the processing step and the film forming step can be separated, the first ferromagnetic layer and the second ferromagnetic layer can be subjected to ferromagnetic exchange coupling. Therefore, according to the present embodiment, it is applicable to various fine processing processes.

  Further, according to this embodiment, in order to form a cap layer on the buffer layer 13 for suppressing oxidation of the layers below the buffer layer 13, when the element is taken out of the integrated vacuum apparatus, the temperature is set to 300 ° C. Heat treatment can be performed at about 400 ° C. After the heat treatment, the entire cap layer and the middle of the buffer layer 13 are removed by ion beam milling or the like, and a second ferromagnetic layer, such as GdFe or Gd, having no heat resistance is formed. It can be exchange coupled.

  Further, according to the present embodiment, the first ferromagnetic layer (first magnetization fixed layer 11) in the first ferromagnetic exchange coupling unit 1 is replaced with the first ferromagnetic layer (second magnetization layer) in the second ferromagnetic exchange coupling unit 2. Since it is longer in the extending direction than the magnetization fixed layer 21), the coercive force of the light modulation layer 30 ferromagnetically coupled to the first magnetization fixed layer 11a decreases, and the first ferromagnetic exchange coupling unit 1 A coercive force difference such that Hc2> Hc1 can be provided between the coercive force Hc1 and the coercive force Hc2 of the second ferromagnetic exchange coupling unit 2. Thus, it is possible to design with a simpler process, and to reduce the design margin for the alignment with the electrodes and the light modulator.

[Second embodiment]
FIG. 9 is a top view showing the configuration of an example of the domain wall motion type spatial light modulator 200 according to the second embodiment of the present invention.
In the domain wall motion type spatial light modulator 200 according to the present embodiment, in the light modulation unit of the domain wall motion type spatial light modulator 100 according to the first embodiment, two of the second ferromagnetic exchange coupling units are the same. And one of the first ferromagnetic exchange coupling sections is disposed between the two second ferromagnetic exchange coupling sections. That is, it is a domain wall displacement type spatial light modulator in which three ferromagnetic exchange coupling portions exist in one element.

FIG. 10 is a cross-sectional view illustrating a configuration of an example of the domain wall motion type spatial light modulator 20 according to the second embodiment of the present invention.
The domain wall displacement type spatial light modulator 200 includes two second ferromagnetic exchange coupling portions on both sides of one first ferromagnetic exchange coupling portion, for example, in one domain wall displacement type spatial light modulation element 20. In addition, it is possible to have the light modulation region twice as large as the domain wall motion type spatial light modulation device 10 according to the first embodiment. At this time, the total number of the ferromagnetic exchange coupling portions of the domain wall displacement type spatial light modulator 10 per area is four, and the number of ferromagnetic exchange coupling portions of the domain wall displacement type spatial light modulation device 20 is three. is there. The light modulation region is not open in the ferromagnetic exchange coupling part. That is, in the element having the light modulation region 30 having the same area, if the number of the ferromagnetic exchange coupling portions is small, the effective light modulation region 300 increases, and the aperture ratio of the light modulation region is improved. The moving spatial light modulator 200 can obtain a higher light modulation area aperture ratio than the domain wall moving spatial light modulator 100 according to the first embodiment.

  Furthermore, the domain wall motion type spatial light modulator 200 can take a larger effective area per element as compared with the domain wall motion type spatial light modulator 100. Production efficiency is further improved.

  It should be noted that the present invention is not limited to the above embodiment, and modifications and improvements as long as the object of the present invention can be achieved are included in the present invention.

DESCRIPTION OF SYMBOLS 1 1st ferromagnetic exchange coupling part 2 2nd ferromagnetic exchange coupling part 3 light modulation part 9 pulse current source 10, 20, 91 domain wall displacement type spatial light modulation element 11, 11a, 11b 1st magnetization fixed layer (1st strong Magnetic layer)
12, 22 nonmagnetic metal layer 13, 23 buffer layer 21 second magnetization fixed layer (first ferromagnetic layer)
30 Light modulation layer (second ferromagnetic layer)
31, 32 Domain 31a, 32a Initial domain 33 Domain wall 90, 100, 200 Domain wall displacement type spatial light modulator 300 Light modulation region

Claims (3)

A light modulator that changes the direction of polarization of incident light and emits the light,
A first ferromagnetic exchange coupling unit and a second ferromagnetic exchange coupling unit which are arranged to extend in parallel to both ends of the light modulation unit and have different coercive forces;
A domain wall motion type spatial light modulator including a domain wall motion type spatial light modulation element having
Each of the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section includes:
A first ferromagnetic layer made of a ferromagnetic material;
A second ferromagnetic layer formed on the first ferromagnetic layer and made of a ferromagnetic material and ferromagnetically exchange-coupled with the first ferromagnetic layer;
A domain wall in which the length of the first ferromagnetic layer in the first ferromagnetic exchange coupling section in the extending direction is longer than the length of the second ferromagnetic exchange coupling section in the extending direction of the first ferromagnetic layer. Mobile spatial light modulator. In the domain wall motion type spatial light modulator, a plurality of the domain wall motion type spatial light modulators are arranged in a grid in a first direction and a second direction orthogonal to the first direction,
The first ferromagnetic layer extends in the first direction,
2. The plurality of domain wall displacement type spatial light modulators arranged in the first direction, each of the first ferromagnetic exchange coupling portions being configured to share the same first ferromagnetic layer. 3. Domain wall displacement type spatial light modulator. A light modulator that changes the direction of polarization of incident light and emits the light,
A domain wall displacement type spatial light modulator including a domain wall displacement type spatial light modulator having a first ferromagnetic exchange coupling portion and a second ferromagnetic exchange coupling portion having different coercive forces and arranged in parallel. hand,
In the domain wall motion type spatial light modulator, a plurality of the domain wall motion type spatial light modulators are arranged in a grid in a first direction and a second direction orthogonal to the first direction,
In the domain wall displacement type spatial light variable element,
Two second ferromagnetic exchange coupling sections are provided at both ends of the light modulation section;
One said first ferromagnetic exchange coupling part is disposed interposed between said two said second ferromagnetic exchange coupling parts,
Each of the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section includes:
A first ferromagnetic layer made of a ferromagnetic material;
A second ferromagnetic layer formed on the first ferromagnetic layer and made of a ferromagnetic material and ferromagnetically exchange-coupled with the first ferromagnetic layer;
The first ferromagnetic layer extends in the first direction,
A length of the first ferromagnetic layer in the extending direction of the first ferromagnetic exchange coupling portion is longer than a length of the second ferromagnetic exchange coupling portion in the extending direction of the first ferromagnetic layer;
The plurality of domain wall displacement type spatial light modulators arranged in the first direction are configured such that the first ferromagnetic exchange coupling portions share the same first ferromagnetic layer. vessel.

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