JP2021081475A - Domain wall moving type spatial light modulator inspection device and initialization magnetic field derivation device of domain wall moving type spatial light modulator - Google Patents

Abstract

To reduce a time for inspecting an element in a domain wall moving type modulation element and to derive an external magnetic field large enough for a reverse parallelization of an element magnetization direction.SOLUTION: There is provided an inspection device 4 of a domain wall moving type spatial light modulator 100 formed of a domain wall moving type light modulation element including: a light modulation unit for emitting an incident light while changing the direction of the polarization of the light; and a first ferromagnetic exchange coupling unit and a second ferromagnetic exchange coupling unit located in both ends of the light modulation unit, having magnetism holding forces different from each other. The first ferromagnetic exchange coupling unit and the second ferromagnetic exchange coupling unit each have a first ferromagnetic layer made of a ferromagnetic material and a second ferromagnetic layer formed on the first ferromagnetic layer made of a ferromagnetic material, and ferromagnetic exchange-coupled with the first ferromagnetic layers. The inspection device also includes: an external magnetic field application device 40 for applying an external magnetic field to the domain wall moving type spatial light modulator; a magnetic optical microscope 5 capable of observing the magnetization direction of the domain wall moving type spatial light modulator on which the external magnetic field is applied; and an image processing unit 6 for processing a taken image by the magnetic optical microscope 5.SELECTED DRAWING: Figure 4

Description

The present invention relates to a domain wall mobile spatial light modulator inspection device and an initialization magnetic field derivation device for a domain wall mobile spatial light modulator.

Research and development are underway for magnetic wall-moving light modulation devices and magnetoresistive-effect devices that use the magnetization reversal technology by current-induced domain wall movement because they can be expected to have higher density and lower current drive. For example, Patent Document 1 attempts to solve the problem by using the above-mentioned characteristics of the domain wall moving light modulation element because a spatial light modulator having a pixel pitch of 1 micron or less is required to realize moving image holography in a wide field of view. .. Patent Document 2 proposes an application to a more reliable magnetic random access memory (MRAM) because the write current path and the read current path can be separated in addition to the above-mentioned features.

In a magnetic domain wall-moving light modulation element or a magnetoresistive sensor using current-induced domain wall movement, it is necessary to realize antiparallel magnetization arrangements in which the magnetization directions of the magnetization fixed layer are upward and downward, respectively. The antiparallel magnetization arrangement can be realized by designing the difference in the coercive force (Hc1 and Hc2 in FIG. 2) of the two magnetization fixed layers (details will be described later).

JP-A-2018-206900 International Publication 2011/078018

In general, when a plurality of elements are manufactured, Hc1 and Hc2 have variations among the elements. Therefore, in an element having poor magnetic properties of the magnetization fixed layer, the non-inverted magnetization fixed layer may be inverted or the inverted magnetization fixed layer may not be inverted during the formation of the above-mentioned antiparallel magnetization, resulting in an antiparallel magnetization arrangement. It is not realized correctly and the element does not operate normally. In order to measure an element having poor magnetic characteristics, it is necessary to measure the hysteresis loop of the optical modulation layer of each element, and the measurement time increases as the number of elements to be manufactured increases.

Therefore, an object of the present invention is to reduce the detection time of defective elements by inspecting the magnetic characteristics of a plurality of domain wall-moving light modulation elements at once.

(1) In the present invention, an optical modulation unit (for example, an optical modulation unit 3 described later) that changes the direction of polarization of incident light and emits the light, and an optical modulation unit (for example, a light modulation unit 3 described later) are arranged at both ends of the optical modulation unit and have different coermagnetic forces. It has a first ferromagnetic exchange coupling portion (for example, a first ferromagnetic exchange coupling portion 1 described later) and a second ferromagnetic exchange coupling portion (for example, a second ferromagnetic exchange coupling portion 2 described later). Both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion are a first ferromagnetic layer made of a ferromagnetic material (for example, a first magnetization fixing layer 11 described later and a second magnetization fixing layer described later). 21) and a second ferromagnetic layer (for example, a photomodulation layer 30 described later) that is formed on the first ferromagnetic layer and is ferromagnetically exchange-coupled with the first ferromagnetic layer by being made of a ferromagnetic material. An inspection device (for example, a magnetic wall moving space optical modulator 100 described later) of a magnetic wall moving spatial optical modulator (for example, a magnetic wall moving spatial optical modulator 100 described later) composed of a magnetic wall moving optical modulator (for example, a magnetic wall moving optical modulator 10 described later). The inspection device 4), which will be described later, includes an external magnetic field applying device (for example, an external magnetic field applying device 40 described later) that applies an external magnetic field to the magnetic wall moving space optical modulator, and the external magnetic field. A magnetic optical microscope (for example, a magnetic optical microscope 5 described later) capable of observing the magnetization direction of the magnetic wall moving type optical modulation element to which is applied, and an image processing unit (for example, described later) for processing an image captured by the magnetic optical microscope. Provided is an inspection device for a magnetic wall moving type spatial optical modulator having an image processing unit 6).

(2) In the invention of (1), the inspection device is a control unit (1) that controls the magnitude of the initialization magnetic field applied to the domain wall moving spatial light modulator based on the processing result by the image processing unit. For example, the inspection apparatus for the domain wall moving type spatial light modulator according to claim 1, further comprising a control unit 7) described later, is provided.

(3) Further, the present invention includes an optical modulation unit that changes the direction of polarization of incident light and emits it, and a first ferromagnetic exchange coupling unit that is arranged at both ends of the optical modulation unit and has different coercive magnetic forces. It has a second ferromagnetic exchange coupling portion, and both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion have a first ferromagnetic layer made of a ferromagnetic material and the first strong A magnetic wall moving space optical modulator composed of a magnetic wall moving optical modulation element having a second ferromagnetic layer formed on a magnetic layer and optically exchange-coupled with the first ferromagnetic layer by being made of a ferromagnetic material. The initialization magnetic field derivation device (for example, the initialization magnetic field derivation device 50 described later) of the above, wherein the initialization magnetic field derivation device includes an external magnetic field application device that applies an external magnetic field to the magnetic wall moving space optical modulator. The initialization magnetic field derivation device includes a magnetic optical microscope capable of observing the magnetization direction of the magnetic wall moving optical modulation element to which the external magnetic field is applied, and an image processing unit for processing an image captured by the magnetic optical microscope. Provides an initialization magnetic field derivation device having a control unit that controls the magnitude of the initialization magnetic field applied to the magnetic wall moving space optical modulator based on the processing result by the image processing unit.

(4) Further, the present invention includes an optical modulation section that changes the direction of polarization of incident light and emits it, and a first ferromagnetic exchange coupling section that is arranged at both ends of the light modulation section and has different coercive forces. It has a second ferromagnetic exchange coupling portion, and both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion have a first ferromagnetic layer made of a ferromagnetic material and the first strength. A magnetic wall moving space optical modulator composed of a magnetic wall moving optical modulation element having a second ferromagnetic layer formed on a magnetic layer and optically exchange-coupled with the first ferromagnetic layer by being made of a ferromagnetic material. In the inspection method of the above, a position determination step of photographing the magnetic wall moving space light modulator with a magnetic optical microscope and determining the position of the magnetic wall moving space light modulation element within the photographing angle of the magnetic optical microscope. An initialization magnetic field application step of applying an initialization magnetic field from the outside to the magnetic wall moving space light modulator, and further applying an external magnetic field to the magnetic wall moving space light modulator to which the initialization magnetic field is applied to magnetize. The magnetization direction reversal step of reversing the direction, the magnetization reversal determination step of determining whether or not the magnetization direction of the magnetic wall moving type optical modulation element is reversed by the magnetic optical microscope and the image processing unit, and the magnetization direction are not reversed. Provided is a method for inspecting a magnetic wall moving spatial optical modulator, which comprises a position output step for outputting the position of the magnetic wall moving optical modulator.

According to the present invention, the elements within the angle of view can be inspected at one time, so that the yield measurement time of the magnetic characteristics of the elements can be significantly shortened. In addition, an external magnetic field suitable for device initialization can be derived.

It is a perspective view which shows the structure of the magnetic domain wall movable type light modulation element described in Patent Document 1. FIG. It is a side view which shows the structure of the domain wall moving type light modulation element described in Patent Document 1. FIG. It is a figure which shows the operation of the domain wall moving type light modulation element described in Patent Document 1. FIG. It is a figure which shows the structure of the magnetic wall movable type light modulator inspection apparatus of this invention. It is a figure which shows the hysteresis loop of the light modulation layer when the magnetization fixed layer of the domain wall moving type light modulation element is antiparallel magnetization arrangement. It is a figure which shows the hysteresis loop of the light modulation layer when the magnetization fixed layer of the domain wall moving type light modulation element is a parallel magnetization arrangement. It is a figure which shows the hysteresis loop of the light modulation layer at the time of misalignment of the magnetization fixed layer and the light modulation layer of the domain wall moving type light modulation element. It is an inspection flowchart of the domain wall moving type spatial light modulator inspection apparatus. It is a schematic diagram which shows the position determination of each element in a photographed image in the domain wall moving type spatial light modulator inspection apparatus. It is a schematic diagram which shows the initialization of the element by applying an external magnetic field in the domain wall moving type spatial light modulator inspection apparatus. It is a schematic diagram which shows the determination of the defective pixel by the application of the external magnetic field in the positive direction in the domain wall moving type spatial light modulator inspection apparatus. It is a schematic diagram which shows the determination of a defective pixel by applying an external magnetic field in a negative direction in a domain wall moving type spatial light modulator inspection apparatus. It is a magneto-optical micrograph of an initialized domain wall moving spatial light modulator. It is a magneto-optical micrograph of a magnetic wall moving type spatial light modulator to which an external magnetic field in a negative direction is applied after initialization.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same reference numerals are given to the common configurations. 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.

FIG. 1 is a perspective view showing the configuration of the domain wall movable light modulation element described in Patent Document 1. FIG. 2 is a side view showing the configuration of the domain wall movable light modulation element described in Patent Document 1. FIG. 3 is a diagram showing the operation of the domain wall movable light modulation element described in Patent Document 1. The arrows in FIGS. 1 and 3 indicate the direction of the magnetization direction.

As shown in FIGS. 1 to 3, the domain wall moving type spatial light modulator 90 described in Patent Document 1 includes a domain wall moving type light modulation element 91 utilizing the domain wall movement. Since the basic configuration of the domain wall moving spatial light modulator 100 according to the embodiment of the present invention is the same as the configuration of the domain wall moving spatial light modulator 90 described in Patent Document 1, the basic configuration will be described in detail below. explain.

As shown in FIG. 1, the magnetic domain wall moving type light modulation element 91 has a first ferromagnetic exchange coupling portion 1, a second ferromagnetic exchange coupling portion 2, and an optical modulation portion 3, and is composed of Si or the like. It is formed on the substrate 8 to be formed.
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. The lower electrode formed by the above is provided in the lowermost layer, and the pulse current can be applied by connecting the pulse current source 9 to the lower electrode.

The shape of the magnetic wall moving type light modulation element 91 is not particularly limited, but as shown in FIG. 1, for example, the light modulation section 3 is formed in a flat plate shape extending in a predetermined direction, and the first ferromagnetic exchange coupling section 1 is formed at both ends thereof. And the shape in which the second ferromagnetic exchange coupling portion 2 is arranged can be mentioned. 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, and the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 are flush with each other. Is thicker than the thickness of the optical modulation unit 3.

As shown in FIG. 2, the first ferromagnetic exchange coupling portion 1 is configured by laminating the first magnetization fixing layer 11, the non-magnetic metal layer 12, the buffer layer 13, and the optical modulation layer 30 in this order. To.

The first magnetization fixed layer 11 is made of a ferromagnetic material and corresponds to the first ferromagnetic layer. 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 has magnetic anisotropy in the same direction as the optical modulation layer 30 described later, and when a ferromagnetic material having vertical magnetic anisotropy is used for the optical modulation layer 30, the first magnetization is fixed. The magnetization fixing layer 11 also uses a ferromagnetic material having vertical magnetic anisotropy. 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.

Here, the above-mentioned 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 above-mentioned multilayer film is heat-treated to increase its coercive force, the coercive force of the ferromagnetic exchange coupling portion after coupling with the photomodulation layer 30 also becomes larger, and photomodulation The difference in coercive force with the part 3 can be made larger.

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 so as to maintain a magnetic bond between the first magnetization fixing layer 11 and the optical modulation layer 30. can do.

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 in order to prevent etching damage from reaching the first magnetization fixing layer 11 in the manufacturing process described later. 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 appropriate conductivity. Further, it is desirable that the buffer layer 13 is a material that contains an element having a slow etching rate in a manufacturing process described later 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 a second ferromagnetic layer. 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 GdFe 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. Due to this ferromagnetic exchange coupling, the magnetization direction of the first magnetization fixed layer 11 and the magnetization direction of the optical modulation layer 30 in the first ferromagnetic exchange coupling portion 1 are simultaneously reversed.

The second ferromagnetic exchange coupling portion 2 is configured by laminating the second magnetization fixing layer 21, the non-magnetic metal layer 22, the buffer layer 23, and the optical modulation layer 30 in this order.

Further, 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 strongly strengthened via the non-magnetic metal layer 22 and the buffer layer 23. It is magnetically exchanged. Due to this ferromagnetic exchange coupling, the magnetization direction of the second magnetization fixed layer 21 and the magnetization direction of the optical modulation layer 30 in the second ferromagnetic exchange coupling portion 2 are simultaneously reversed.

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 formed by the non-magnetic metal layer 12 and the buffer layer 13, respectively. Selected from available materials.

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

As described above, the optical modulation layer 30 constitutes the optical modulation section 3. 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. This will be described in detail later.

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-moving light modulation element 10 according to the present embodiment will be described in detail.
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 that is ferromagnetically exchange-coupled. That is, the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 each have a ferromagnetic exchange coupling inside, and their respective magnetization directions are reversed at the same time. Then, as shown in FIGS. 1 and 3, the magnetization direction of the first ferromagnetic exchange coupling portion 1 is designed to be downward, while the magnetization direction of the second ferromagnetic exchange coupling portion 2 is designed to be upward. There is.

The optical modulation section 3 is formed with a domain wall 33 extending on a plane orthogonal to the direction perpendicular to the biferromagnetic exchange coupling section. 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 portion 1 side with respect to the domain wall 33 is upward, and the magnetic domain on the second ferromagnetic exchange coupling portion 2 side with respect to the domain wall 33. The magnetization direction of 32 is downward.

By forming the magnetic domains 31 and 32 having different directions of magnetization in the optical modulation unit 3 via the domain wall 33 in this way, the domain wall moving type light modulation element 10 can function as the light modulation element. More specifically, for example, when the magnetic wall moving type light modulation element 10 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 10 When the light is incident on the light, the rotation angle of the plane of polarization of the reflected light differs depending on the direction of the magnetization direction. Therefore, the light can be modulated by assigning each reflected light according to the rotation angle of these different polarizing surfaces to the light and darkness of the light through the polarizing filter. However, by forming the substrate from a translucent material such as glass or sapphire, it is possible to make the domain wall moving type light modulation element 10 function as a transmission type light modulation element.

Here, the generation mechanism of the domain wall 33 will be described with reference to FIGS. 2 and 3.
First, in order to form the domain wall 33 in the optical modulation unit 3, the coercive force of the first magnetization fixed layer 11 which is ferromagnetically exchange-coupled with the optical modulation layer 30 and the second magnetic exchange coupling with the optical modulation layer 30 are also carried out. It is necessary that the coercive force of the magnetization fixing layer 21 is different from each other.

In Patent Document 1, as a method of making the coercive force of the first magnetized fixed layer 11 and the coercive force of the second magnetized fixed layer 21 different from each other, the first magnetized fixed layer 11 and the second magnetized fixed layer 21 are mutually different. Either the shape is different (for example, the coercive force becomes smaller when the width of the first magnetization fixed layer 11 is widened), only one of them is heat-treated, or the layer structures of the first magnetization fixed layers 11 are different from each other. Be selected. As a result, 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 portion 1 and the second ferromagnetic exchange coupling portion are different from each other. The coercive force of 2 can be different.

In the present embodiment, the method of making the coercive force of the first magnetization fixed layer 11 and the coercive force of the second magnetization fixed layer 21 different from each other is not particularly limited, and for example, as in Patent Document 1, the first Either the 1-magnetized fixed layer 11 and the 2nd magnetized fixed layer 21 have different shapes (for example, the coercive force becomes smaller when the width of the 1st magnetized fixed layer 11 is widened), or only one of them is heat-treated. Alternatively, one of different layer configurations is selected. As a result, 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 portion 1 and the second ferromagnetic exchange coupling portion are different from each other. The coercive force of 2 can be different.

For example, with the above configuration, the coercive force of the first magnetization fixing layer 11 can be designed to be smaller than the coercive force of the second magnetization fixing layer 21. In this case, as shown in FIG. 2, assuming that the coercive force of the first ferromagnetic exchange coupling portion 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling portion 2 is Hc2, and the coercive force of the optical modulation unit 3 is Hc_m. , Hc2> Hc1> Hc_m.

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

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

At this time, as shown in FIG. 3, initial magnetic domains 31a and 32a are generated at both ends of the optical modulation unit 3. More specifically, at the end of the optical modulation unit 3 on the first ferromagnetic exchange coupling portion 1 side, a first strong force is provided by a magnetic domain leaking from the first ferromagnetic exchange coupling portion 1 (see the broken arrow in FIG. 3). An initial magnetic domain 31a in the upward magnetization direction, which is antiparallel to the downward magnetization of the magnetic 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 is performed by a leakage magnetic field from the second ferromagnetic exchange coupling portion 2 (see the broken arrow in FIG. 3). An initial magnetic domain 32a in the downward magnetization direction, which is 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 portion 1 to the second ferromagnetic exchange coupling portion 2 or the second ferromagnetic exchange coupling portion 2 to the first ferromagnetic exchange coupling portion 2 A pulse current is passed toward the part 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 electron flow). As a result, as shown in FIG. 3, the direction of magnetization of the optical modulation region 300 excluding both ends of the optical modulation unit 3 is reversed (in the example of FIG. 3, the direction of magnetization of the optical modulation region 300 is inverted upward). Is possible.

Regarding the method of forming the domain wall moving light modulation element 10, for example, the first magnetization fixing layer and the second magnetization fixing 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 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 Patent Document 1.

FIG. 4 is a diagram showing a basic configuration of the inspection device 4 according to the embodiment of the present invention.
The inspection device 4 includes a magneto-optical microscope 5, an image processing unit 6, a control unit 7, and an external magnetic field application device 40. The magnetic optical microscope 5 includes a polarizer 51, an image sensor 52, an analyzer 53, a beam splitter 54, an objective lens 55, a stage 56, and an electromagnet 57. The magneto-optical microscope 5 is a microscope that utilizes the magneto-optical Kerr effect in which the plane of polarization of the reflected light rotates depending on the magnetization direction of the element 10, and the reflected light is acquired through the analyzer 53 to obtain intensity-modulated light. Can be observed as. Since the brightness value of the image taken by the microscope changes depending on the magnetization direction of the element 10, the image processing unit 6 determines the defective element by using the information. The control unit 7 controls the magnitude of the external magnetic field applied to the element 10 and the domain wall moving spatial light modulator 100 by the external magnetic field application device 40 based on the processing result of the image processing unit 6.

The properties of the domain wall movable light modulation element 10 used for determining the defective element will be described. The hysteresis loop of the optical modulation layer 30 depending on the magnetization state of the magnetization fixed layer is shown in FIGS. 5 to 7. FIG. 5 shows a state in which the magnetization fixed layer is normally in an antiparallel magnetization arrangement, and the width of the hysteresis loop in the magnetic field direction is narrowed. That is, the magnitude of the magnetic field required to reverse the magnetization is small, and the magnetization direction of the photomodulation layer 30 is easily reversed by applying the magnetic field.

FIG. 6 shows a state in which the magnetic characteristics of the magnetization fixed layer are poor and the magnetization is arranged in parallel, and the reversal magnetic field of the hysteresis loop is positive and negative and asymmetric. That is, the magnitude of the magnetic field whose magnetization is inverted differs depending on the positive or negative of the applied magnetic field. This asymmetry is reversed depending on whether the magnetization directions of the magnetization fixed layer are both upward or downward.

FIG. 7 shows a state in which the light modulation layer 30 cannot be correctly arranged on the magnetization fixing layer due to improper alignment between the light modulation layer 30 and the magnetization fixing layer at the time of fabrication, and the width of the hysteresis loop in the magnetic field direction. Is widening. That is, the magnitude of the magnetic field required to reverse the magnetization is large, and the magnetization direction of the photomodulation layer 30 is difficult to reverse due to the application of the magnetic field.

Utilizing this property, a defective element can be determined by using the magnetic optical microscope 5 and the image processing unit 6. The procedure of the judgment inspection is shown below. FIG. 8 shows a flowchart of inspection by the domain wall movable spatial light modulator inspection device 4 of the present invention, and FIGS. 9 to 12 show schematic views showing a state of an element and a state of determining a defective element.

In the inspection method by the domain wall moving space light modulator inspection device 4 of the present invention, the domain wall moving space light modulator 100 is photographed by the magnetic optical microscope 5, and the magnetic wall moving light within the photographing angle of the magnetic optical microscope 5. A position determination step for determining the position of the modulation element 10, an initialization magnetic field application step of applying an initialization magnetic field to the domain wall moving space optical modulator 100 from the outside, and a domain wall moving space optical modulator to which an initialization magnetic field is applied. A magnetization direction reversal step in which an external magnetic field is further applied to 100 to invert the magnetization direction, and a magnetization reversal in which the domain wall moving optical modulation element 10 determines whether or not the magnetization direction is reversed by the magnetic optical microscope 5 and the image processing unit 6. It includes a determination step and a position output step of outputting the position of the domain wall moving type optical modulation element 10 whose magnetization direction is not reversed.

First, in the position determination step, the position of each element in the image taken with a microscope is determined. The domain wall moving spatial light modulator 100 is set on the stage 56 of the magnetic optical microscope 5 (step S1). Next, the position of the element 10 within the shooting angle of view is determined (step S2). This process can be realized by a general pattern detection process such as template matching. If all the elements do not fit within the angle of view of the microscope, the stage is moved to take multiple images in order to determine which element is on the substrate, and the final image is taken. By combining the images, the position of the element in the captured image is specified. If the position of the element cannot be determined well, the shooting conditions are changed and the position is determined again (step S3).

Next, in the initialization magnetic field application step, the element is initialized by applying an external magnetic field so that the magnetization fixing layer has an antiparallel magnetization arrangement (step S4). In this step, for example, as described above, the coercive force of the first ferromagnetic exchange coupling portion 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling portion 2 is Hc2, and the coercive force of the optical modulation unit 3 is Hc_m. Then, an external magnetic field H such that H> Hc2> Hc1> Hc_m is applied upward to the element 10. Then, in both the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2, the direction of the magnetization direction is upward.

Next, a magnetic field in which the strength of the magnetic field H'is Hc2> H'> Hc1> Hc_m is applied downward to the element 10. Then, the direction of the magnetization direction of the second ferromagnetic exchange coupling portion 2 remains upward, while the direction of the magnetization direction of the first ferromagnetic exchange coupling portion 1 and the optical modulation portion 3 is downward. Change. As a result, the magnetization directions of the first ferromagnetic exchange coupling portion 1 and the second ferromagnetic exchange coupling portion 2 become antiparallel. The magnetization direction may be antiparallel, and H to be applied first may be downward and H'may be upward.

Subsequently, in the magnetization direction inversion step, an external magnetic field is applied in the positive direction so that only the elements in which the antiparallel magnetization arrangement is correctly formed are inverted (step S5). The magnetization direction of the element 10 in which the antiparallel magnetization arrangement is normally formed is reversed by the applied external magnetic field. Each element to which an external magnetic field is applied is photographed by a magneto-optical microscope 5. The direction of the applied magnetic field is the direction in which the direction of the optical modulation unit 3 is reversed.

In the magnetization reversal determination step, the element that has not been reversed is detected by image processing (step S6). In the image taken by the magnetic-optical microscope 5, the element that has not been inverted has a different brightness value from that of the normal element, and therefore can be detected by a general defect detection algorithm such as filtering. By the above procedure, among a plurality of elements, an element having poor magnetic characteristics can be detected at once within the angle of view of the microscope.

Next, an external magnetic field is applied in the negative direction so that only the elements for which the antiparallel magnetization arrangement is correctly formed are inverted (step S7). Each applied element is photographed by a magnetic optical microscope 5, and the element that has not been inverted is detected by image processing (step S8). By performing the inspection by reversing the magnetization directions in both positive and negative directions in this way, it is possible to ensure that the magnitude of the magnetic field that reverses the magnetization differs depending on the positive and negative of the magnetic field due to the parallel magnetization arrangement as shown in FIG. It is possible to detect defective elements with higher accuracy.

The derivation of the magnitude of the initialized external magnetic field H'may be applied to applications other than the inspection of defective elements. That is, it may be used as an initialization magnetic field derivation device 50 including the above-mentioned magnetic optical microscope 5, an image processing unit 6, a control unit 7, and an external magnetic field applying device 40. Its configuration is the same as the inspection device 4 of the present invention shown in FIG.

Finally, in the position output step, by outputting the position of the defective element, it is possible to determine which element on the substrate has a defective magnetic characteristic in a single inspection (step S9). By outputting the position information within the angle of view of the microscope for the detected defective element, the defective element among a large number of elements can be identified at once. As a result, the inspection time of the element can be significantly shortened.

If the magnitude of the initialization external magnetic field H'to form the antiparallel magnetization arrangement is not appropriate, the non-reversing magnetization fixing layer may be inverted or the reversing magnetization fixation layer may not be inverted, which is normal. Even an element cannot form an antiparallel state and can be detected as a defective element. That is, when H'≧ Hc2, none of the magnetization fixing layers is inverted, and the antiparallel magnetization arrangement is not formed. Further, when Hc1 ≧ H', none of the magnetization fixing layers is inverted, and the antiparallel magnetization arrangement is not formed.

As described above, when a plurality of elements are manufactured, the holding force (Hc1, Hc2) of the magnetization fixing layer varies slightly, so that the element is normal depending on the setting of the magnitude of the initialized external magnetic field H'. However, it may be detected as a defective element. That is, for example, when H'is set to a value close to Hc1, if there is an element having a large Hc1 due to variation, Hc1 ≧ H'in that element, neither of the magnetization fixing layers is inverted, and the antiparallel magnetization arrangement is not formed. There may be cases.

On the other hand, by repeating the inspection by changing the magnitude of the initialized external magnetic field H', an appropriate magnitude of the initialized external magnetic field H'can be derived so that the number of detected defective elements is minimized. That is, by controlling the magnitude of the external magnetic field applied by the external magnetic field applying device based on the image processing result, the control unit 7 can obtain an initialized external magnetic field suitable for initialization and improve the inspection accuracy. The number of defective elements can be minimized (step S10).

Examples of discrimination of defective elements by a magnetic optical microscope are shown in FIGS. 13 and 14. FIG. 13 is an image of a domain wall moving spatial light modulator 100 to which an initialization magnetic field is applied, taken by a magnetic optical microscope 5. FIG. 14 shows a magnetic domain wall moving spatial light modulator 100 in which the magnetization direction of the normal domain wall moving light modulation element 10 is reversed by applying an external magnetic field in a negative direction after applying the initialization magnetic field. It is an image taken in.

13 and 14 show how the domain wall-moving light modulation elements 10 are aligned in two directions. The black spots shown in FIG. 14 are defective elements whose magnetization does not reverse even when an external magnetic field is applied and whose brightness is different from that of surrounding elements.
In the initialized state, it is difficult to judge from the brightness of the image the difference between the element in which the antiparallel magnetization arrangement is normally formed and the defective element in which the antiparallel magnetization arrangement is not formed. In a state where an external magnetic field is further applied after initialization, the brightness of the element in which the antiparallel magnetization arrangement is normally formed and the magnetization is inverted is different from the brightness of the defective element in which the antiparallel magnetization arrangement is not formed and the magnetization is not inverted. Position can be detected (step S11).

The inspection device and the initialization magnetic field derivation device of the present embodiment have been described above. 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.

1 1st Ferromagnetic Exchange Coupler 2 2nd Ferromagnetic Exchange Coupler 3 Optical Modulator 4 Inspection Device 5 Magnetic Optical Microscope 51 Polarizer 52 Image Sensor 53 Detector 54 Beam Splitter 55 Objective Lens 56 Stage 57 Electromagnet 6 Image Processing Unit 7 Control unit 8 Substrate 9 Pulse current source 10 Magnetic wall moving optical modulation element 11 1st magnetization fixed layer (1st ferromagnetic layer)
12, 22 Non-magnetic metal layer 13, 23 Buffer layer 21 Second magnetization fixed layer (first ferromagnetic layer)
30 Optical modulation layer (second ferromagnetic layer)
31, 32 Magnetic domain 31a, 32a Initial domain wall 33 Domain wall 40 External magnetic field application device 50 External magnetic field derivation device 100 Domain wall mobile spatial light modulator 300 Optical modulation region

Claims (4)

An optical modulator that changes the direction of polarized light of incident light and emits it,
It has a first ferromagnetic exchange coupling portion and a second ferromagnetic exchange coupling portion that are arranged at both ends of the optical modulation section and have different coercive forces.
Both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion
The first ferromagnetic layer made of ferromagnetic material and
A domain wall moving type composed of a magnetic wall moving type optical modulation element having 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. It is an inspection device for spatial optical modulators.
The inspection device is
An external magnetic field applying device that applies an external magnetic field to the domain wall moving spatial light modulator,
A magnetic optical microscope capable of observing the magnetization direction of the domain wall moving light modulation element to which the external magnetic field is applied, and
An inspection device for a domain wall moving spatial light modulator having an image processing unit for processing an image captured by the magnetic optical microscope. The domain wall movement according to claim 1, further comprising a control unit that controls the magnitude of the initialization magnetic field applied to the domain wall movement type spatial light modulator based on the processing result by the image processing unit. Inspection device for type spatial light modulators. An optical modulator that changes the direction of polarized light of incident light and emits it,
It has a first ferromagnetic exchange coupling portion and a second ferromagnetic exchange coupling portion that are arranged at both ends of the optical modulation section and have different coercive forces.
Both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion
The first ferromagnetic layer made of ferromagnetic material and
A domain wall moving type composed of a magnetic wall moving type optical modulation element having 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. It is an initialization magnetic field derivation device for spatial optical modulators.
The initialization magnetic field derivation device is
An external magnetic field applying device that applies an external magnetic field to the domain wall moving spatial light modulator,
A magnetic optical microscope capable of observing the magnetization direction of the domain wall moving light modulation element to which the external magnetic field is applied, and
It has an image processing unit for processing an image captured by the magnetic optical microscope, and has an image processing unit.
The initialization magnetic field derivation device is an initialization magnetic field derivation device having a control unit that controls the magnitude of the initialization magnetic field applied to the domain wall moving type spatial light modulator based on the processing result by the image processing unit. An optical modulator that changes the direction of polarized light of incident light and emits it,
It has a first ferromagnetic exchange coupling portion and a second ferromagnetic exchange coupling portion that are arranged at both ends of the optical modulation section and have different coercive forces.
Both the first ferromagnetic exchange coupling portion and the second ferromagnetic exchange coupling portion
The first ferromagnetic layer made of ferromagnetic material and
A domain wall moving type composed of a magnetic wall moving type optical modulation element having 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. It is an inspection method for spatial optical modulators.
A position determination step of photographing the domain wall moving spatial light modulator with a magnetic optical microscope and determining the position of the domain wall moving light modulation element within the imaging angle of the magnetic optical microscope.
An initialization magnetic field application step of applying an initialization magnetic field from the outside to the domain wall moving spatial light modulator,
A magnetization direction reversal step in which an external magnetic field is further applied to the domain wall moving spatial light modulator to which the initialization magnetic field is applied to invert the magnetization direction.
A magnetization reversal determination step of determining whether or not the magnetization direction of the domain wall moving light modulation element is inverted by the magnetic optical microscope and the image processing unit, and
A method for inspecting a domain wall moving spatial light modulator, comprising a position output step of outputting the position of the domain wall moving light modulation element whose magnetization direction is not reversed.

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