JP7345361B2 - Domain wall displacement type spatial light modulator inspection device and domain wall displacement type spatial light modulator initialization magnetic field derivation device - Google Patents

Description

The present invention relates to a domain wall moving spatial light modulator testing device and an initializing magnetic field deriving device for a domain wall moving spatial light modulator.

Domain wall motion optical modulators and magnetoresistive devices that use magnetization reversal technology based on current-induced domain wall motion are being researched and developed because they are expected to enable higher device density and lower current drive. For example, Patent Document 1 attempts to solve this problem by using the above-mentioned characteristics of the domain wall movement type light modulation element, since a spatial light modulator with a pixel pitch of 1 micron or less is required to realize a wide viewing range moving holography. . In addition to the above-mentioned features, Patent Document 2 proposes application to magnetic random access memory (MRAM), which has higher reliability because the write current path and the read current path can be separated.

In domain wall motion type optical modulators and magnetoresistive elements that use current-induced domain wall motion, it is necessary to realize an antiparallel magnetization arrangement in which the magnetization directions of the magnetization fixed layer are directed upward and downward, respectively. The antiparallel magnetization arrangement can be realized by designing a difference in coercivity (Hc1 and Hc2 in FIG. 2) between the two fixed magnetization layers (details will be described later).

JP2018-206900A International Publication No. 2011/078018

Generally, when a plurality of devices are manufactured, there are variations in Hc1 and Hc2 among the devices. Therefore, in an element in which the magnetic properties of the magnetization fixed layer are poor, the antiparallel magnetization arrangement may occur because the magnetization fixed layer that is not to be reversed is reversed or the magnetization fixed layer that is to be reversed is not reversed during the above-mentioned antiparallel magnetization formation. It is not realized correctly and the device does not operate properly. To measure elements with poor magnetic properties, it is necessary to measure the hysteresis loop of the light modulation layer of each element, and the measurement time increases as the number of elements manufactured increases.

Therefore, an object of the present invention is to reduce the time required to detect a defective element by testing the magnetic properties of a plurality of domain wall motion type optical modulators at once.

(1) The present invention includes a light modulation section (for example, a light modulation section 3 to be described later) that changes the direction of polarization of incident light and outputs the light, and a light modulation section that is arranged at both ends of the light modulation section and has different coercive forces. a first ferromagnetic exchange coupling part (for example, a first ferromagnetic exchange coupling part 1 described below) and a second ferromagnetic exchange coupling part (for example, a second ferromagnetic exchange coupling part 2 described below), Both the first ferromagnetic exchange coupling section and the second ferromagnetic exchange coupling section include a first ferromagnetic layer made of a ferromagnetic material (for example, a first magnetization fixed layer 11 described later and a second magnetization fixed layer described later). 21), and a second ferromagnetic layer (for example, the light modulation layer 30 described below) formed on the first ferromagnetic layer and made of a ferromagnetic material and thereby ferromagnetically exchange coupled with the first ferromagnetic layer. An inspection device (for example, , an inspection device 4) to be described later, the inspection device includes an external magnetic field applying device (for example, an external magnetic field applying device 40 to be described later) that applies an external magnetic field to the domain wall moving spatial light modulator, and an external magnetic field applying device 40 to be described later. A magneto-optical microscope (for example, the magneto-optical microscope 5 described later) that can observe the magnetization direction of the domain wall displacement type light modulator to which An image processing unit 6) is provided, which provides an inspection device for a domain wall moving spatial light modulator.

(2) In the invention of (1), the inspection apparatus also includes a control unit ( For example, there is provided an inspection apparatus for a domain wall moving spatial light modulator according to claim 1, further comprising a control section 7) to be described later.

(3) The present invention also provides a light modulation section that changes the polarization direction of incident light and outputs the light, a first ferromagnetic exchange coupling section that is arranged at both ends of the light modulation section and has mutually different coercive forces; a second ferromagnetic exchange coupling part, and each of the first ferromagnetic exchange coupling part and the second ferromagnetic exchange coupling part includes a first ferromagnetic layer made of a ferromagnetic material and a first ferromagnetic layer made of a ferromagnetic material; A domain wall motion spatial light modulator comprising a domain wall motion light modulation element, the second ferromagnetic layer being formed on a magnetic layer and made of a ferromagnetic material to be ferromagnetically exchange coupled to the first ferromagnetic layer. An initializing magnetic field deriving device (for example, an initializing magnetic field deriving device 50 described below), the initializing magnetic field deriving device comprising: an external magnetic field applying device that applies an external magnetic field to the domain wall moving spatial light modulator; The initialization magnetic field deriving device includes a magneto-optical microscope capable of observing the magnetization direction of the domain wall displacement light modulation element to which the external magnetic field is applied, and an image processing unit that processes images taken by the magneto-optical microscope. provides an initialization magnetic field deriving device, comprising a control section that controls the magnitude of an initialization magnetic field applied to the domain wall moving spatial light modulator based on the processing result by the image processing section.

(4) The present invention also provides a light modulation section that changes the polarization direction of incident light and outputs the light, a first ferromagnetic exchange coupling section that is arranged at both ends of the light modulation section and has mutually different coercive forces; a second ferromagnetic exchange coupling part, and each of the first ferromagnetic exchange coupling part and the second ferromagnetic exchange coupling part includes a first ferromagnetic layer made of a ferromagnetic material and a first ferromagnetic layer made of a ferromagnetic material; A domain wall motion spatial light modulator comprising a domain wall motion light modulation element, the second ferromagnetic layer being formed on a magnetic layer and made of a ferromagnetic material to be ferromagnetically exchange coupled to the first ferromagnetic layer. The inspection method includes a position determination step of photographing the domain wall moving spatial light modulator with a magneto-optical microscope and determining the position of the domain wall moving spatial light modulator within the imaging field angle of the magneto-optical microscope. an initializing magnetic field application step of applying an initializing magnetic field to the domain wall moving spatial light modulator from the outside; and further applying an external magnetic field to the domain wall moving spatial light modulator to which the initializing magnetic field has been applied to magnetize the domain wall moving spatial light modulator. a magnetization direction reversal step of reversing the direction; a magnetization reversal determination step of determining by the magneto-optical microscope and image processing unit whether the magnetization direction of the domain wall displacement type light modulation element has been reversed; and a magnetization reversal determination step of determining whether the magnetization direction has not been reversed. Provided is a method for testing a domain wall displacement spatial light modulator, the method comprising a position output step of outputting the position of the domain wall displacement optical modulator.

According to the present invention, it is possible to inspect elements within an angle of view at one time, so that the time required to measure the yield of magnetic properties of elements can be significantly shortened. Furthermore, it becomes possible to derive an external magnetic field suitable for element initialization.

1 is a perspective view showing the configuration of a domain wall displacement type optical modulator described in Patent Document 1. FIG. 1 is a side view showing the configuration of a domain wall displacement type optical modulator described in Patent Document 1. FIG. FIG. 3 is a diagram showing the operation of the domain wall displacement type optical modulator described in Patent Document 1. 1 is a diagram showing the configuration of a domain wall displacement type optical modulator inspection apparatus according to the present invention. FIG. 7 is a diagram showing a hysteresis loop of a light modulation layer when a magnetization fixed layer of a domain wall motion type light modulation element has an antiparallel magnetization arrangement. FIG. 3 is a diagram showing a hysteresis loop of a light modulation layer when a magnetization fixed layer of a domain wall motion type light modulation element has a parallel magnetization arrangement. FIG. 6 is a diagram showing a hysteresis loop of the light modulation layer when the magnetization fixed layer and the light modulation layer of the domain wall motion type light modulation element are misaligned. It is an inspection flowchart of a magnetic domain wall displacement type spatial light modulator inspection device. FIG. 3 is a schematic diagram showing determination of the position of each element within a captured image in the domain wall displacement spatial light modulator inspection apparatus. FIG. 3 is a schematic diagram showing initialization of an element by applying an external magnetic field in a domain wall displacement spatial light modulator inspection apparatus. FIG. 3 is a schematic diagram showing determination of a defective pixel by applying an external magnetic field in the positive direction in the domain wall displacement type spatial light modulator inspection apparatus. FIG. 3 is a schematic diagram showing determination of a defective pixel by applying an external magnetic field in a negative direction in the domain wall displacement spatial light modulator inspection apparatus. This is a magneto-optical micrograph of an initialized domain wall displacement spatial light modulator. 2 is a magneto-optical micrograph of a domain wall displacement spatial light modulator to which a negative external magnetic field is applied after initialization.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Note that common components are given the same reference numerals. Further, for convenience of explanation, the upper, lower, left and right sides in the figure will be described as the upper, lower, left and right sides of the domain wall moving type optical modulation element.

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

As shown in FIGS. 1 to 3, a domain wall displacement type spatial light modulator 90 described in Patent Document 1 includes a domain wall displacement type optical modulation element 91 that utilizes domain wall displacement. The basic configuration of the domain wall displacement type spatial light modulator 100 according to an embodiment of the present invention is the same as the configuration of the domain wall displacement type spatial light modulator 90 described in Patent Document 1, so the basic configuration will be described in detail below. explain.

As shown in FIG. 1, the domain wall displacement type optical modulator 91 includes a first ferromagnetic exchange coupling section 1, a second ferromagnetic exchange coupling section 2, and an optical modulation section 3, and is made of Si or the like. It is formed on the substrate 8 to be used.
The first ferromagnetic exchange coupling part 1 and the second ferromagnetic exchange coupling part 2 are each made of a general metal electrode material such as a metal such as Cu, Al, Au, Ag, Ru, Ta, Cr, or an alloy thereof (not shown). A pulse current source 9 is connected to this lower electrode, so that a pulse current can be applied.

Although the shape of the domain wall displacement type optical modulation element 91 is not particularly limited, for example, as shown in FIG. and a shape in which the second ferromagnetic exchange coupling section 2 is arranged. The upper surfaces of the optical modulation section 3, the first ferromagnetic exchange coupling section 1, and the second ferromagnetic exchange coupling section 2 are continuously flush with each other. is thicker than the thickness of the light modulation section 3.

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

The first magnetization fixed layer 11 is made of a ferromagnetic material and corresponds to a 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 light modulating layer 30 described later, and when the light modulating layer 30 is made of a ferromagnetic material having perpendicular magnetic anisotropy, the first magnetization fixed layer 11 The magnetization fixed layer 11 also uses 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 is a CPP-GMR (CPP-GMR) having perpendicular magnetic anisotropy with a structure in which a nonmagnetic layer is sandwiched between a magnetization fixed layer whose magnetization is fixed in the perpendicular direction and a magnetization free layer whose magnetization direction is reversible. It can be constructed of a known ferromagnetic material as a magnetization fixed layer of a Current Perpendicular to the Plane Giant MagnetoResistance (perpendicularly conducting giant magnetoresistance) element, TMR element, or the like. Specifically, transition metals such as Fe, Co, and Ni, and alloys containing them, such as 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 composed of a multilayer laminate in which these transition metal layers and nonmagnetic metal layers are alternately laminated, and may include Co/Pt, Fe/Pt, Co/Pd. A multilayer film such as 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, when the first magnetization fixed layer 11 made of the multilayer film described above is heat-treated to increase its coercive force, the coercive force of the ferromagnetic exchange coupling portion after being combined with the light modulation layer 30 also increases, and the light modulation It is possible to further increase the coercive force difference with the portion 3.

The nonmagnetic metal layer 12 and the buffer layer 13 are arranged between the first magnetization fixed layer 11 and the light modulation layer 30 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 to be laminated on the first magnetization fixed layer 11 described above. This non-magnetic metal layer 12 is provided in order to prevent etching damage to the first magnetization fixed layer 11 in the manufacturing process described later. The nonmagnetic metal layer 12 can be a thin film layer of various nonmagnetic metals. For example, Ta, Mo, and Ru can be used as the nonmagnetic metal layer 12, and among them, one made of Ta is preferably used.

The buffer layer 13 is formed by being laminated on the nonmagnetic metal layer 12 described above. The buffer layer 13 needs to be able to flow a current whether it is an optical modulation element using domain wall motion or a TMR element, so when it is made into a thin film, the resistance is not too large and the buffer layer 13 has appropriate conductivity. Further, the buffer layer 13 is desirably made of a material that has a slow etching rate in the manufacturing process described below, contains an element that has high detection sensitivity in SIMS (Secondary Ion Mass Spectrometry), and is visible on a SIMS type endpoint monitor. Thereby, it becomes possible to reliably stop etching at the buffer layer 13, and damage to the first magnetization fixed layer 11 can be avoided.

The buffer layer 13 is made of oxide or 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 . Among these, as the buffer layer 13, one made of MgO is preferably used. According to this 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 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 a second ferromagnetic layer. The light modulation layer 30 can be made of a known ferromagnetic material, preferably a material with a large magneto-optic effect (Kerr effect). 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. Examples include a multilayer film made of a polyurethane metal, or an alloy of a rare earth metal such as TbFeCo or GdFe with a transition metal (RE-TM alloy). Among these, a GdFe layer made of GdFe is preferably used as the light modulation layer 30.

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

In the first ferromagnetic exchange coupling section 1 having the above-described configuration, the first magnetization fixed layer 11 and the light modulation layer 30 are ferromagnetically exchange coupled via the nonmagnetic 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 light modulation layer 30 in the first ferromagnetic exchange coupling portion 1 are simultaneously reversed.

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

Further, in the second ferromagnetic exchange coupling section 2, similarly to the first ferromagnetic exchange coupling section 1, the second magnetization fixed layer 21 and the optical modulation layer 30 are connected to each other 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 portion 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 made of the nonmagnetic metal layer 12 and the buffer layer 13, respectively. Selected from available materials.

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

As described above, the light modulation layer 30 constitutes the light modulation section 3. A domain wall 33 and magnetic domains 31 and 32 are formed in the light modulation section 3 made of the light modulation layer 30. This will be explained in detail later.

Note that the interlayers between each magnetization fixed layer (hereinafter, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 are also simply referred to as magnetization fixed layers), each nonmagnetic metal layer, each buffer layer, and the light modulation layer 30 Alternatively, a functional layer may be appropriately provided at the interface with the lower electrode. For example, in order to prevent damage to the light modulation layer 30 during the microfabrication process, a cap layer containing or made of Ta, Ru, or SiN may be provided on the light modulation layer 30. This cap layer has a function of preventing GdFe and TbFeCo, which are used to form the light modulation 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 displacement type optical modulator 10 according to this embodiment will be described in detail.
As described above, the first ferromagnetic exchange coupling section 1 has the first magnetization fixed layer 11 which is ferromagnetically exchange coupled with the light modulation layer 30, and the second ferromagnetic exchange coupling section 2 has the first magnetization fixed layer 11 which is ferromagnetically exchange coupled with the light modulation layer 30. It has a second magnetization fixed layer 21 that undergoes ferromagnetic exchange coupling. That is, the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 each have ferromagnetic exchange coupling therein, and their respective magnetization directions are reversed at the same time. As shown in FIGS. 1 and 3, the magnetization direction of the first ferromagnetic exchange coupling section 1 is designed downward, while the magnetization direction of the second ferromagnetic exchange coupling section 2 is designed upward. There is.

A domain wall 33 is formed in the optical modulation section 3 and extends on a plane perpendicular to a direction perpendicular to both the ferromagnetic exchange coupling sections. 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 part 1 side with respect to the domain wall 33 is upward, and the magnetic domain on the second ferromagnetic exchange coupling part 2 side with respect to the domain wall 33 is directed upward. The magnetization direction of 32 is downward.

In this way, by forming the magnetic domains 31 and 32 with different magnetization directions in the optical modulator 3 via the domain wall 33, the domain wall displacement type optical modulator 10 can function as a light modulator. More specifically, for example, when the domain wall displacement type light modulation element 10 is configured as a reflection type light modulation element, light with uniform polarization is directed from above the domain wall displacement type light modulation element 10 to the upper surface of the light modulation section 3. When the light is incident, the angle of rotation of the plane of polarization of the reflected light changes depending on the direction of magnetization. Therefore, by assigning each reflected light according to the rotation angle of these different polarization planes to brightness and darkness of the light through a polarizing filter, it is possible to modulate the light. However, by configuring the substrate with a transparent material such as glass or sapphire, it is also possible to cause the domain wall displacement type light modulation element 10 to function as a transmission type light modulation element.

Here, the generation mechanism of the domain wall 33 will be explained with reference to FIGS. 2 and 3.
First, in order to form the domain wall 33 in the light modulation section 3, the coercive force of the first magnetization fixed layer 11 which is ferromagnetically exchange coupled with the light modulation layer 30 and the coercive force of the second magnetization fixed layer 11 which is also ferromagnetically exchange coupled with the light modulation layer 30 are required. It is necessary that the coercive forces of the magnetization fixed layers 21 are different from each other.

In Patent Document 1, as a method for 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, the first magnetization fixed layer 11 and the second magnetization fixed layer 21 are made different from each other. Either the shapes should be different (for example, if the width of the first magnetization fixed layer 11 is widened, the coercive force will be smaller), only one of them should be heat treated, or the layer configurations should be different from each other. selected. Thereby, by 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, the coercive force of the first ferromagnetic exchange coupling part 1 and the coercive force of the second ferromagnetic exchange coupling part The two coercive forces can be made different.

In this 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. Either the first magnetization fixed layer 11 and the second magnetization fixed layer 21 have different shapes (for example, if the width of the first magnetization fixed layer 11 is increased, the coercive force becomes smaller), or only one of them is heat-treated. Alternatively, the layer configurations may be different from each other. Thereby, by 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, the coercive force of the first ferromagnetic exchange coupling part 1 and the coercive force of the second ferromagnetic exchange coupling part The two coercive forces can be made different.

For example, with the above configuration, the coercive force of the first magnetization fixed layer 11 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 section 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling section 2 is Hc2, and the coercive force of the optical modulation section 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 above-mentioned coercive force relationship is established. Then, the magnetization direction of each of the first ferromagnetic exchange coupling section 1, the second ferromagnetic exchange coupling section 2, and the optical modulation section 3 becomes upward.

Next, a magnetic field whose strength H' satisfies Hc2>H'>Hc1 is applied downward to the element. Then, while the magnetization direction of the second ferromagnetic exchange coupling section 2 remains upward, the magnetization directions of the first ferromagnetic exchange coupling section 1 and the optical modulation section 3 both become downward. Change.

At this time, initial magnetic domains 31a and 32a are generated at both ends of the optical modulator 3, as shown in FIG. More specifically, the end of the optical modulator 3 on the first ferromagnetic exchange coupling section 1 side has a first strong An initial magnetic domain 31a with an upward magnetization direction antiparallel to the downward magnetization of the magnetic exchange coupling portion 1 is generated. In addition, the end of the optical modulation section 3 on the second ferromagnetic exchange coupling section 2 side is exposed to the second ferromagnetic exchange coupling section 2 due to the leakage magnetic field (see the broken line arrow in FIG. An initial magnetic domain 32a with 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 to connect the first ferromagnetic exchange coupling section 1 to the second ferromagnetic exchange coupling section 2, or from the second ferromagnetic exchange coupling section 2 to the first ferromagnetic exchange coupling section. A pulse current is applied to section 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 (same direction as the flow of electrons). As a result, as shown in FIG. 3, the direction of magnetization of the light modulation region 300 excluding both ends of the light modulation section 3 is reversed (in the example of FIG. 3, the direction of magnetization of the light modulation region 300 is reversed upward). is possible.

Regarding the method for forming the domain wall motion type optical modulator 10, for example, a first magnetization fixed layer and a second magnetization fixed layer are formed on an insulating member layer formed on a Si backplane or the like using conventionally known lithography or the like. It can be manufactured by forming layers, etc., subjecting them to heat treatment, etc., if necessary, and then forming a light modulating layer, etc., by conventionally known ion beam sputtering or the like. More specifically, it can be manufactured, for example, by the manufacturing method described in Patent Document 1.

FIG. 4 is a diagram showing the 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 section 6, a control section 7, and an external magnetic field application device 40. The magneto-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 reflected light is rotated depending on the magnetization direction of the element 10, and the reflected light is passed through an analyzer 53 to obtain intensity-modulated light. It can be observed as Since the brightness value of an image taken with a microscope changes depending on the magnetization direction of the element 10, the image processing section 6 uses this information to determine whether the element is defective. The control unit 7 controls the magnitude of the external magnetic field that the external magnetic field application device 40 applies to the element 10 and the domain wall displacement spatial light modulator 100 based on the processing results in the image processing unit 6.

The properties of the domain wall motion type optical modulator 10 used for determining a defective element will be explained. The hysteresis loop of the light 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 has a normal antiparallel magnetization arrangement, and the width of the hysteresis loop in the magnetic field direction is narrow. That is, the magnitude of the magnetic field required to reverse the magnetization is small, and the magnetization direction of the light modulation layer 30 can be easily reversed by applying the magnetic field.

FIG. 6 shows a state in which the magnetic properties of the magnetization fixed layer are poor and the magnetization is arranged in parallel, and the reversal magnetic field of the hysteresis loop is asymmetric between positive and negative. That is, the magnitude of the magnetic field that causes magnetization reversal differs depending on whether the applied magnetic field is positive or negative. 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 placed on the magnetization fixed layer due to misalignment between the light modulation layer 30 and the magnetization fixed layer during fabrication, and the width of the hysteresis loop in the magnetic field direction. is getting wider. That is, the magnitude of the magnetic field required to reverse the magnetization is large, and the direction of magnetization of the light modulation layer 30 is difficult to reverse by applying a magnetic field.

Utilizing this property, defective elements can be determined using the magneto-optical microscope 5 and the image processing unit 6. The procedure for the determination test is shown below. FIG. 8 shows a flowchart of testing performed by the domain wall displacement spatial light modulator testing device 4 of the present invention, and FIGS. 9 to 12 show schematic diagrams showing the state of the device and how defective devices are judged.

The inspection method using the domain wall moving spatial light modulator inspection device 4 of the present invention involves photographing the domain wall moving spatial light modulator 100 with a magneto-optical microscope 5, and detecting the domain wall moving spatial light modulator 100 within the imaging angle of view of the magneto-optical microscope 5. a position determination step of determining the position of the modulation element 10; an initialization magnetic field application step of externally applying an initialization magnetic field to the domain wall motion spatial light modulator 100; and a domain wall motion spatial light modulator to which the initialization magnetic field is applied. a magnetization direction reversal step in which the magnetization direction is reversed by further applying an external magnetic field to 100; and a magnetization reversal step in which the magneto-optical microscope 5 and the image processing unit 6 determine whether or not the magnetization direction of the domain wall displacement type light modulator 10 has been reversed. The method includes a determination step and a position output step of outputting the position of the domain wall displacement type optical modulator 10 whose magnetization direction is not reversed.

First, in the position determination step, the position of each element in an image taken with a microscope is determined. The domain wall moving spatial light modulator 100 is set on the stage 56 of the magneto-optical microscope 5 (step S1). Next, the position of the element 10 within the photographing angle of view is determined (step S2). This processing can be realized by general pattern detection processing such as template matching, for example. In addition, if all the elements do not fit within the field of view of the microscope, in order to determine which element on the board the element being photographed is, move the stage and take multiple images, and then By manually combining the images, the position of the element in the captured image is specified. If the position of the element cannot be determined successfully, the photographing 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 fixed 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 section 1 is Hc1, the coercive force of the second ferromagnetic exchange coupling section 2 is Hc2, and the coercive force of the optical modulation section 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, the magnetization direction of both the first ferromagnetic exchange coupling section 1 and the second ferromagnetic exchange coupling section 2 becomes upward.

Next, a magnetic field whose strength H' satisfies Hc2>H'>Hc1>Hc_m is applied downward to the element 10. Then, while the magnetization direction of the second ferromagnetic exchange coupling section 2 remains upward, the magnetization directions of the first ferromagnetic exchange coupling section 1 and the optical modulation section 3 both become downward. Change. As a result, the respective magnetization directions between the first ferromagnetic exchange coupling part 1 and the second ferromagnetic exchange coupling part 2 become antiparallel. Note that the magnetization direction may be in an antiparallel arrangement, and H applied initially may be downward and H' may be applied upward.

Subsequently, in the magnetization direction reversal step, an external magnetic field is applied in the positive direction so that only the elements in which the antiparallel magnetization arrangement has been correctly formed are reversed (step S5). In the element 10 in which the antiparallel magnetization arrangement has been normally formed, the magnetization direction is reversed by the applied external magnetic field. Each element to which an external magnetic field is applied is photographed using a magneto-optical microscope 5. Note that the direction of the applied magnetic field is the direction in which the direction of the optical modulator 3 is reversed.

In the magnetization reversal determination step, elements that have not been reversed are detected by image processing (step S6). In the image taken by the magneto-optical microscope 5, the brightness value of the element that has not been reversed is different from that of a normal element, so that it can be detected by a general defect detection algorithm such as filter processing. According to the above procedure, an element having poor magnetic properties among a plurality of elements can be detected at once within the viewing angle of the microscope.

Next, an external magnetic field is applied in the negative direction so that only the elements in which the antiparallel magnetization arrangement has been correctly formed are reversed (step S7). Each applied element is photographed by the magneto-optical microscope 5, and elements that have not been reversed are detected by image processing (step S8). By performing inspection by reversing the magnetization direction in both positive and negative directions, it is possible to reliably inspect elements whose magnetization is reversed depending on the positive and negative magnetic fields due to their parallel magnetization arrangement as shown in Figure 6. It is possible to detect defective elements with higher precision.

This derivation of the magnitude of the initialization external magnetic field H' may be applied to purposes other than testing defective elements. That is, it may be used as an initialization magnetic field deriving device 50 that includes the above-described magneto-optical microscope 5, the image processing section 6, the control section 7, and the external magnetic field application device 40. Its configuration is similar to 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 defective magnetic properties in a single inspection (step S9). By outputting positional information within the viewing angle of the microscope regarding the detected defective elements, defective elements among a large number of elements can be identified at once. This makes it possible to significantly shorten the device testing time.

If the magnitude of the initializing external magnetic field H' for forming an antiparallel magnetization arrangement is not appropriate, the magnetization fixed layer that is not to be reversed may be reversed, or the magnetization fixed layer that is to be reversed may not be reversed, resulting in a normal state. Even if the device is not able to form an antiparallel state, it may be detected as a defective device. That is, in the case of H'≧Hc2, both of the fixed magnetization layers are reversed and the antiparallel magnetization arrangement is not achieved. Further, in the case of Hc1≧H', neither of the fixed magnetization layers is reversed, and the antiparallel magnetization arrangement is not achieved.

As mentioned above, when multiple devices are manufactured, there will be some variation in the coercive force (Hc1, Hc2) of the magnetization fixed layer, so depending on the setting of the initialization external magnetic field H', it may be possible to determine whether the device is normal or not. 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 where Hc1 is large due to variations, Hc1≧H' in that element, and none of the fixed magnetization layers are reversed, and the antiparallel magnetization arrangement is not achieved. There are several possible cases.

On the other hand, by repeatedly performing tests while changing the magnitude of the initialization external magnetic field H', it is possible to derive an appropriate magnitude of the initialization external magnetic field H' 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 by the control unit 7, an appropriate initialization external magnetic field can be obtained for initialization, and inspection accuracy can be improved. The number of defective elements can be minimized (step S10).

Examples of determining defective elements using a magneto-optical microscope are shown in FIGS. 13 and 14. FIG. 13 is an image taken using the magneto-optical microscope 5 of the domain wall moving spatial light modulator 100 to which an initializing magnetic field has been applied. FIG. 14 shows a domain wall moving spatial light modulator 100 in which the magnetization direction of a normal domain wall moving light modulator 10 is reversed by applying an external magnetic field in a negative direction after applying an initializing magnetic field to a magneto-optical microscope. This is an image taken with.

FIGS. 13 and 14 show how the domain wall displacement type optical modulators 10 are aligned in two directions. The black spots shown in FIG. 14 are defective elements whose magnetization is not reversed even when an external magnetic field is applied and whose luminance is different from surrounding elements.
In the initialized state, it is difficult to determine the difference between an element in which an antiparallel magnetization arrangement is normally formed and a defective element in which an antiparallel magnetization arrangement is not formed from the brightness of the image. When an external magnetic field is further applied after initialization, the brightness of an element that normally forms an antiparallel magnetization arrangement and whose magnetization is reversed is different from that of a defective element that does not form an antiparallel magnetization arrangement and whose magnetization is not reversed. It is possible to detect the position of (step S11).

The inspection device and initialization magnetic field deriving device of this embodiment have been described above. Note that the present invention is not limited to the above-described embodiments, and any modifications and improvements within the range that can achieve the purpose of the present invention are included in the present invention.

1 First ferromagnetic exchange coupling section 2 Second ferromagnetic exchange coupling section 3 Light modulation section 4 Inspection device 5 Magneto-optical microscope 51 Polarizer 52 Image sensor 53 Analyzer 54 Beam splitter 55 Objective lens 56 Stage 57 Electromagnet 6 Image processing section 7 Control unit 8 Substrate 9 Pulse current source 10 Domain wall displacement type optical modulator 11 First magnetization fixed layer (first ferromagnetic 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 magnetic domain 31a, 32a initial magnetic domain 33 domain wall 40 external magnetic field applying device 50 external magnetic field deriving device 100 domain wall moving spatial light modulator 300 light modulation region

Claims (3)

a light modulation unit that changes the polarization direction of the incident light and outputs the light;
a first ferromagnetic exchange coupling part and a second ferromagnetic exchange coupling part arranged at both ends of the optical modulation part and having mutually different coercive forces;
Both the first ferromagnetic exchange coupling part and the second ferromagnetic exchange coupling part,
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 to perform ferromagnetic exchange coupling with the first ferromagnetic layer; a domain wall comprising a plurality of domain wall displacement optical modulation elements; An inspection device for a mobile spatial light modulator, comprising:
The inspection device includes:
an external magnetic field applying device that applies an external magnetic field to the domain wall displacement spatial light modulator;
a magneto-optical microscope capable of observing the magnetization direction of the domain wall displacement optical modulator to which the external magnetic field is applied;
The image captured by the magneto-optical microscope is processed to obtain a hysteresis loop of the light modulation section of the plurality of domain wall moving type light modulation elements, and the width of the hysteresis loop in the magnetic field direction and the magnetic field of the hysteresis loop are positive. an image processing unit that determines whether the plurality of domain wall displacement type light modulation elements are normal based on the symmetry of the negative region;
An inspection device for a domain wall moving spatial light modulator, comprising: a control unit that controls the magnitude of an initialization magnetic field applied to the domain wall moving spatial light modulator based on a processing result by the image processing unit. a light modulation unit that changes the polarization direction of the incident light and outputs the light;
a first ferromagnetic exchange coupling part and a second ferromagnetic exchange coupling part arranged at both ends of the optical modulation part and having mutually different coercive forces;
Both the first ferromagnetic exchange coupling part and the second ferromagnetic exchange coupling part,
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 to perform ferromagnetic exchange coupling with the first ferromagnetic layer; a domain wall comprising a plurality of domain wall displacement optical modulation elements; An initializing magnetic field deriving device for a mobile spatial light modulator, the device comprising:
The initialization magnetic field deriving device includes:
an external magnetic field applying device that applies an external magnetic field to the domain wall displacement spatial light modulator;
a magneto-optical microscope capable of observing the magnetization direction of the domain wall displacement optical modulator to which the external magnetic field is applied;
The image captured by the magneto-optical microscope is processed to obtain a hysteresis loop of the light modulation section of the plurality of domain wall moving type light modulation elements, and the width of the hysteresis loop in the magnetic field direction and the magnetic field of the hysteresis loop are positive. an image processing unit that determines whether the plurality of domain wall displacement type light modulation elements are normal based on the symmetry of the negative region ;
An initialization magnetic field deriving device, comprising : a control section that controls the magnitude of an initialization magnetic field applied to the domain wall moving spatial light modulator based on a processing result by the image processing section. a light modulation unit that changes the polarization direction of the incident light and outputs the light;
a first ferromagnetic exchange coupling part and a second ferromagnetic exchange coupling part arranged at both ends of the optical modulation part and having mutually different coercive forces;
Both the first ferromagnetic exchange coupling part and the second ferromagnetic exchange coupling part,
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 to perform ferromagnetic exchange coupling with the first ferromagnetic layer; a domain wall comprising a plurality of domain wall displacement optical modulation elements; A method for inspecting a mobile spatial light modulator, the method comprising:
a position determination step of photographing the domain wall displacement type spatial light modulator with a magneto-optical microscope and determining the position of the domain wall displacement type light modulation element within the imaging angle of view of the magneto-optical microscope;
an initialization magnetic field application step of applying an initialization magnetic field to the domain wall displacement spatial light modulator from the outside;
a magnetization direction reversal step of reversing the magnetization direction by further applying an external magnetic field to the domain wall moving spatial light modulator to which the initializing magnetic field has been applied;
A hysteresis loop of the light modulation section of the plurality of domain wall displacement type light modulation elements is determined by processing an image taken by the magneto-optical microscope to determine whether the magnetization direction of the plurality of domain wall displacement type light modulation elements has been reversed. a magnetization reversal determination step in which the acquiring image processing unit determines based on the width of the hysteresis loop in the magnetic field direction and the symmetry of regions where the magnetic field of the hysteresis loop is positive and negative;
A method for inspecting a domain wall moving spatial light modulator, comprising a position output step of outputting a position of the domain wall moving light modulator whose magnetization direction is not reversed.

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