Magnetic thin wire device

Abstract

To provide a magnetic thin wire device which attains stabilization of a shift length in driving of a magnetic domain.SOLUTION: A magnetic thin wire device 1 comprises: a ground layer 60 which is disposed on a substrate 80; a magnetic thin wire 10 which linearly extends in a planar view; a recording element 40 to which a recording current magnetizing the magnetic thin wire 10 is applied; and an insulation layer 30 which is disposed between the magnetic thin wire 10 and the recording element 40. The magnetic thin wire 10 is disposed on a top face of the ground layer 60 and extends while alternately repeating a first section 11 of which the bottom face is located at a first position H1 and a second section 12 at a second position H2 higher than the first position H1 and vertically changing a height via a connection part 20 connecting the first section 11 with the second section 12, and the top face of the ground layer 60 is formed at a height of a bottom face of the magnetic thin wire 10 along a shape of the bottom face of the magnetic thin wire 10.SELECTED DRAWING: Figure 2C

Description

[Technical field]

[0001] The present invention relates to a magnetic nanowire device that is a part of a magnetic nanowire memory. [Background technology]

[0002] A magnetic nanowire memory is a storage device that uses a magnetic nanowire made by processing a magnetic material into a fine wire as a recording medium and can sequentially read and write information by three operations: "recording" to form magnetic domains, which are units of information, in the magnetic nanowire, "driving" to shift the formed magnetic domains in the magnetic nanowire, and "reading" to detect the magnetization direction of the magnetic domains. The information can be binary information corresponding to the magnetization direction of the magnetic nanowire, such as upward or downward. A magnetic domain is a section in the magnetic nanowire where the magnetization direction is uniform. For example, as described in Patent Document 1, recording is performed by locally reversing the magnetization direction using a current magnetic field, and driving is performed by utilizing the current domain wall motion phenomenon, in which a magnetic domain wall moves when a current is applied to the magnetic nanowire. Then, information recorded at one end of the magnetic nanowire can be read at a fixed position on the other end. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-27802 A [Patent Document 2] JP 2014-86640 A Summary of the Invention [Problem to be solved by the invention]

[0004] The shift length, which is the distance traveled when driving the magnetic domain, differs between magnetic nanowires due to variations in the magnetic properties of the magnetic nanowires, and may also differ depending on the location within the same magnetic nanowire. If the shift length is not stable, it is difficult to drive the magnetic domain to the playback position the scheduled number of times. Patent Document 2 describes a magnetic nanowire in which the width of the magnetic nanowire is changed at a constant cycle and a domain wall is positioned at the narrow constricted part. However, changing the width at a constant cycle requires highly accurate microfabrication of the magnetic nanowire, which reduces the yield.

[0005] The present invention has been made to solve the above problems, and has an object to provide a magnetic nanowire device that stabilizes the shift length during magnetic domain driving. [Means for solving the problem]

[0006] The magnetic nanowire device of the embodiment comprises an underlayer disposed on a substrate, a magnetic nanowire disposed above the underlayer and extending in a straight line in a planar view, a recording element disposed above the magnetic nanowire so as to intersect with the magnetic nanowire in a planar view and to which a recording current is applied to magnetize the magnetic nanowire, and an insulating layer disposed between the magnetic nanowire and the recording element, wherein the magnetic nanowire is disposed on the upper surface of the underlayer and extends at a different height up and down, alternating between a first section whose lower surface is at a first position and a second section whose lower surface is at a second position higher than the first position, via a connection portion connecting the first section and the second section, and the upper surface of the underlayer is formed at the same height as the lower surface of the magnetic nanowire along the shape of the lower surface of the magnetic nanowire.

[0007] Another magnetic nanowire device according to the embodiment includes a base layer disposed on a substrate, a magnetic nanowire disposed above the base layer and extending in a straight line in a planar view, a recording element disposed below the magnetic nanowire so as to intersect with the magnetic nanowire in a planar view and to which a recording current is applied to magnetize the magnetic nanowire, and an insulating layer disposed between the magnetic nanowire and the recording element, wherein the magnetic nanowire is disposed on the upper surface of the insulating layer and extends at a different height up and down, alternating between a first section whose lower surface is at a first position and a second section whose lower surface is at a second position higher than the first position, via a connection portion connecting the first section and the second section, and the upper surface of the insulating layer is formed at the same height as the lower surface of the magnetic nanowire along the shape of the lower surface of the magnetic nanowire. Effect of the Invention

[0008] According to the present invention, it is possible to provide a magnetic nanowire device that stabilizes the shift length during driving of a magnetic domain. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view illustrating an outline of a magnetic nanowire device according to a first embodiment. [Figure 2A] FIG. 1 is a plan view illustrating an outline of a magnetic nanowire device according to a first embodiment. [Figure 2B] FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 2A. [Figure 2C] FIG. 2C is an enlarged cross-sectional view illustrating a portion of FIG. 2B. [Figure 3A] 2 is a plan view illustrating an outline of an upper surface of an underlayer before a magnetic nanowire is formed in the magnetic nanowire forming method of the first embodiment. FIG. [Figure 3B] FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. [Figure 3C] FIG. 3B is a cross-sectional view taken along line IIIC-IIIC in FIG. 3A. [Figure 4A] 2 is a plan view illustrating an outline of an upper surface of an underlayer before a magnetic nanowire is formed in the magnetic nanowire forming method of the first embodiment. FIG. [Figure 4B] 4B is a cross-sectional view taken along line IVB-IVB in FIG. 4A. [Diagram 5] 1 is a cross-sectional view illustrating an outline of a magnetic nanowire device according to a first modified example. [Figure 6A] FIG. 11 is a cross-sectional view illustrating an outline of a magnetic nanowire device according to a second modified example. [Figure 6B] FIG. 13 is a cross-sectional view illustrating an outline of a magnetic nanowire device according to a third modified example. [Figure 7A] FIG. 13 is a cross-sectional view illustrating an outline of a magnetic nanowire device according to a fourth modified example. [Figure 7B] FIG. 13 is a cross-sectional view illustrating an outline of a magnetic nanowire device according to a fifth modified example. [Figure 8] FIG. 11 is a perspective view illustrating an outline of a magnetic nanowire device according to a second embodiment. [Figure 9A] FIG. 11 is a plan view illustrating an outline of a magnetic nanowire device according to a second embodiment. [Figure 9B] 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A. [Figure 10A] This is a photograph showing the formation of magnetic domains. [Figure 10B] Photographs showing the driving and formation of magnetic domains. [Figure 10C] Photographs showing the driving and formation of magnetic domains. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [First embodiment] A magnetic fine wire device 1 according to the first embodiment will be described with reference to Fig. 1 to Fig. 2C. The magnetic fine wire device 1 is an element group that is a part of the magnetic fine wire memory 100. Note that Fig. 1 omits projections and recesses and illustrates the relative positional relationship of each member. The magnetic fine wire memory 100 includes a magnetic fine wire device 1, a current control unit 92, and a reproduction processing unit 94. The magnetic fine wire device 1 includes a magnetic fine wire 10, an insulating layer 30, a recording element 40, a reproduction head 50, and an underlayer 60, which are formed on a substrate 80. Each component of the magnetic fine wire device 1 will be described below. Note that, although the number of magnetic fine wires 10 is shown as two in the drawing, it may be one, or three or more.

[0011] (magnetic thin wire) The magnetic nanowire 10 is a thin magnetic body that serves as an information recording medium. Here, the magnetization direction is either upward or downward parallel to the thickness direction, and is indicated by a white arrow in the drawing. The magnetic domains 15 are aligned in the extension direction of the magnetic nanowire 10, and there is a magnetic domain wall between adjacent magnetic domains 15 with opposite magnetization directions. Note that a magnetic domain wall is a region where the magnetization direction gradually changes between magnetic domains 15 with different magnetization directions. The magnetic nanowire 10 is disposed above the underlayer 60. Here, two magnetic nanowires 10 are disposed parallel to each other on the upper surface of the underlayer 60. As illustrated in FIG. 2A, the magnetic nanowire 10 extends linearly in a plan view and is formed with an equal width. Note that the magnetic nanowire 10 is illustrated in the drawing as having a length of several bits, with several magnetic domains 15 corresponding to one bit of information lined up in the extension direction, but there is no particular limit to the number of bits or length, and the length can be as required. For example, by designing the magnetic nanowire 10 to have a length of 30 mm and the length of one bit to be 30 nm, a length of 10 6 The magnetic nanowire 10 can be made to have a length corresponding to a bit.

[0012] As illustrated in Figures 2B and 2C, the magnetic nanowire 10 alternates between the first section 11 and the second section 12, and extends with its height varying vertically. Note that Figure 2C shows an enlarged example of a portion of Figure 2B. The bottom surface of the magnetic nanowire 10 is at a first position H1 in the first section 11, and at a second position H2 in the second section 12. The second position H2 is higher than the first position H1. The reference height can be, for example, the top surface of the substrate 80. The thickness T2 of the magnetic wire 10 in the second section 12 can be the same as the thickness T1 of the first section 11. The positional relationship between the top surfaces of the first section 11 and the second section 12 is the same as that between the bottom surfaces, and the top surface of the second section 12 is located relatively higher than the top surface of the first section 11. The first section 11 and the second section 12 are connected by a connecting portion 20, and the height of the magnetic wire 10 is changed.

[0013] If the direction from the recording element 40 toward the reproducing head 50 is defined as the forward direction, the connection portion 20 has an ascending portion 21 where the upper and lower surfaces of the magnetic nanowire 10 rise toward the front, and a descending portion 22 where the upper and lower surfaces of the magnetic nanowire 10 fall toward the front, and the ascending portions 21 and the descending portions 22 are arranged alternately. The ascending portions 21 and the descending portions 22 are arranged alternately at a constant interval D1 in the extension direction. The connection parts 20 are arranged at equal intervals in the extension direction of the magnetic wire 10. The connection parts 20 are locations where the internal structure of the magnetic wire 10 changes, and can become pinning sites for domain walls. That is, the magnetic wire 10 has pinning sites arranged at equal intervals in the extension direction. Note that a pinning site is a location where a domain wall is likely to be located and where the domain wall is likely to be captured when it moves. The magnetic domains 15 are likely to have pinning sites located at their ends, and the length of the magnetic domains 15 can be determined by the interval between the pinning sites.

[0014] In the magnetic fine wire device 1, one bit of information is assigned to each of the first section 11 and the second section 12, and the interval D1 of the connection parts 20 is equal to the bit length BL. In the magnetic fine wire device 1, the interval D1 of the adjacent connection parts 20 is set to the bit length BL, which is the length of the magnetic domain 15 corresponding to one bit of information. The smaller the bit length BL, the higher the recording density of one magnetic fine wire can be. On the other hand, from the viewpoint of the stability of data retention, the bit length BL is preferably 1 to 3 times the width of the magnetic fine wire, and more preferably 1.8 to 2.2 times. The width of the magnetic fine wire is the length of the magnetic fine wire in a direction parallel to the longitudinal direction of the recording element. The stability of data retention refers to the stability in the magnetic domain of the magnetization direction, which is the recorded data.

[0015] In the magnetic nanowire device 1, by setting the interval D1 of the connection parts 20 to be 1 to 3 times the width of the magnetic nanowire 10, the bit length BL can be set to be 1 to 3 times the width of the magnetic nanowire 10, thereby improving the stability of data retention. Note that in the drawings, the magnetic nanowire 10 is shown deformed to have a wide width, so the magnetic domains 15 have a shape longer in the width direction than in the extension direction, but the planar shape of the magnetic domains 15 is preferably a square shape or a rectangular shape longer in the extension direction. Here, each of the first section 11 and the second section 12 has one magnetic domain 15, and the magnetic domain wall is located at the connection section 20. Focusing on one magnetic domain 15, one of the ascending section 21 and the descending section 22 is at the leading side of one bit, and the other is at the trailing side. Moreover, next to the magnetic domain 15 with the ascending section 21 at the leading side, the descending section 22 is at the leading side. In the magnetic domain 15, the side with the reproducing head 50 is at the leading side, and the side with the recording element 40 is at the trailing side.

[0016] The magnetic domains 15 are formed in the magnetic domain formation region 10A of the magnetic nanowire 10. The magnetic domain formation region 10A is a region where the magnetic domains 15 are formed by the recording current IR. Here, the magnetic domain formation region 10A is a region on the reproducing head 50 side near the recording element 40. On the reproducing head 50 side of the magnetic domain formation region 10A is a storage region 10B which sequentially moves the formed magnetic domains 15 and stores them. One of the connection parts 20 is located at the boundary 10C between the magnetic domain formation region 10A and the storage region 10B.

[0017] The magnetic nanowire 10 is a film-like member whose width is greater than its thickness. The thicknesses T1 and T2 of the magnetic nanowire 10 in the first section 11 and the second section 12 are not particularly limited, but may be, for example, 3 nm or more and 15 nm or less. The width of the magnetic nanowire 10 is not particularly limited, and may be, for example, 10 nm to 10 μm. From the viewpoint of stabilizing the shape of the connection part 20, the height ΔH from the first position H1 to the second position H2 is preferably 2 times or less, more preferably 0.9 times or less, of the thicknesses T1, T2 of the magnetic wire 10 in the first section 11 and the second section 12. On the other hand, from the viewpoint of stabilizing the operation of the connection part 20 as a pinning site, the height ΔH is preferably 0.5 times or more, more preferably 0.6 times or more, of the thicknesses T1, T2. In other words, the height ΔH corresponding to the height difference of the magnetic wire 10 in the connection part 20 is preferably 0.5 times or more and 2 times or less, more preferably 0.6 times or more and 0.9 times or less, of the thicknesses T1, T2.

[0018] The magnetic nanowire 10 is formed into a thin wire shape that is sufficiently long with respect to the thickness and width of the magnetic material. A perpendicular magnetization film, in which the magnetization direction is likely to be oriented in the thickness direction, can be used as the magnetic nanowire 10. The perpendicular magnetization film is made of a magnetic material with perpendicular magnetic anisotropy. The material of the magnetic nanowire 10 may be, for example, a multilayer film such as a Co / Pt multilayer film in which a transition metal such as Fe, Co, or Ni and a precious metal such as Pd or Pt are repeatedly laminated, a single layer or a multilayer film of an alloy (RE-TM alloy) of a rare earth metal such as Tb-Fe-Co or Gd-Fe and a transition metal, or a L1 0 The system can be an ordered alloy of FePt, FePd, etc.

[0019] (base layer) The underlayer 60 is a layer that underlies the recording element 40 and the magnetic nanowire 10. Here, the underlayer 60 is disposed on a substrate 80. The magnetic nanowire 10 is disposed on the upper surface of the underlayer 60. The underlayer 60 is insulating. The underlayer 60 is, for example, a SiO 2 layer formed on the surface of a Si substrate. X The underlayer 60 may be a laminate of multiple layers. The upper surface 60A of the underlayer 60 has a concave-convex pattern that faces the concave-convex shape of the lower surface of the magnetic nanowire 10 so as to mesh with the concave-convex shape of the lower surface of the magnetic nanowire 10. The upper surface 60A of the underlayer 60 is formed at the same height as the lower surface of the magnetic nanowire 10, following the shape of the lower surface of the magnetic nanowire 10. The underlayer 60 has a convex portion 62 at the position of the second section 12 of the magnetic nanowire 10. The thickness of the underlayer 60 at the convex portion 62 is thicker than the thickness T3 of a region without the concave-convex pattern. The magnetic nanowire 10 extends while changing its height up and down to reflect the concave-convex pattern of the upper surface 60A of the underlayer 60.

[0020] (Recording element) The recording element 40 is a thin-line conductor that serves as a flow path for the recording current IR. The recording element 40 is disposed above the magnetic wire 10 so as to intersect with the magnetic wire 10 in a planar view, and a recording current IR that magnetizes the magnetic wire 10 is applied to the recording element 40. Here, the recording element 40 is disposed above one end side of the magnetic wire 10 via the insulating layer 30. The recording element 40 is also disposed so as to be perpendicular to the magnetic wire 10 in a planar view. The recording element 40 is disposed at a position where a distance DR in a plan view from the recording element 40 to a boundary 10C between the magnetic domain formation region 10A and the storage region 10B is close to a distance D1 between the connection parts 20. The distance DR can be set to be 0.5 to 2 times the distance D1.

[0021] The recording element 40 is made of a general electrode metal material such as a metal such as Cu, Al, Au, Ag, Ta, or Cr or an alloy thereof, and Au is particularly suitable because of its high conductivity and chemical stability. The recording element 40 is formed into a thin wire shape by a known method such as sputtering, and processed by a combination of photolithography, electron beam lithography, etching, lift-off, and the like.

[0022] (insulating layer) The insulating layer 30 is an insulating layer that insulates the magnetic nanowire 10 from the recording element 40. The insulating layer 30 is disposed between the magnetic nanowire 10 and the recording element 40. Here, the insulating layer 30 is disposed on the upper surface of the magnetic nanowire 10, and the recording element 40 is disposed on the upper surface of the insulating layer 30. The insulating layer 30 reflects the shape of the magnetic nanowire 10 and has an uneven shape that follows the unevenness of the upper surface of the magnetic nanowire 10. The material of the insulating layer 30 is, for example, SiO X or AlO X Oxide films such as SiN X , MgF 2 Known insulating materials such as SiO, etc. can be used. Note that the subscript X of O or N indicates that the composition ratio is not limited. X For example, SiO 2 and AlO X For example, Al 2 O 3 and SiN X For example, Si 3 N 4 The insulating layer 30 can be formed by deposition using a known method such as a sputtering method.

[0023] (substrate) The substrate 80 is a member that serves as the base of the magnetic fine wire device 1. The upper surface of the substrate 80 is a flat surface. The substrate 80 is a substrate in a broad sense for forming the recording element 40 and the magnetic fine wires 10, and known substrate materials can be applied. As the substrate 80, for example, an Si substrate, a GGG (gadolinium gallium garnet) substrate, an SiC (silicon carbide) substrate, an MgO (magnesium oxide) substrate, an AlN (aluminum nitride) substrate, a Ge (germanium) single crystal substrate, etc. can be used. Here, the substrate 80 is an Si substrate with a SiO X film (0 < X ≤ 2) formed thereon as the underlayer 60.

[0024] (Reproduction head) The reproduction head 50 is an element that converts a magnetic signal into an electrical signal. Here, the reproduction head 50 is disposed above the other end side (opposite to the recording element 40) of the magnetic fine wire 10. The reproduction head 50 is a magnetic head generally used for magnetic recording, and can be, for example, a tunnel magnetoresistance (TMR) head.

[0025] (Operation of the magnetic fine wire device) Next, the operation of the magnetic fine wire device 1 will be described. The magnetic fine wire device 1 forms part of the magnetic fine wire memory 100 and performs three operations: recording, driving, and reproduction.

[0026] (Recording) Recording is an operation of forming magnetic domains in the magnetic fine wire 10. The formation of magnetic domains is performed by the magnetic field of the recording current IR applied to the recording element 40. The recording current IR is controlled by the current control unit 92. The current control unit 92 is a device that controls the drive current ID applied to the magnetic fine wire 10 and the recording current IR applied to the recording element 40. The current control unit 92 receives the binary information to be written into the magnetic fine wire memory 100 and controls the magnitudes and timings of the drive current ID and the recording current IR. When there are a plurality of magnetic fine wires 10 or recording elements 40, the current control unit 92 is independently wired for each and can independently control the current applied to each. The current control unit 92 may be separate from the substrate 80, or part or all of it may be provided on the substrate 80.

[0027] The magnetic nanowire 10 is magnetized upward or downward depending on the direction of the recording current I R. The length ML of the magnetic domain formed varies depending on the magnitude of the recording current I R applied to the recording element 40, the distance from the recording element 40 to the pinning site of the magnetic domain wall, etc. When the recording current IR is increased, the range of the magnetic field becomes larger. However, the boundary 10C becomes a pinning site, and the end of the magnetic domain formed is likely to be located at the boundary 10C. Therefore, the length ML can be determined by the distance DR in a plan view from the recording element 40 to the boundary 10C. The starting point of the distance DR can be, for example, the center position of the recording element 40. Note that the recording current IR is preferably adjusted to a value necessary and sufficient to magnetize the range of the distance DR that becomes the magnetic domain formation area 10A.

[0028] (Drive) Driving is an operation that moves the magnetic domains 15 parallel to the extension direction of the magnetic nanowire 10. By driving, the magnetic domains 15 move toward the reproducing head 50 while maintaining their magnetization direction. The magnetic domains formed in the magnetic domain formation region 10A enter the storage region 10B, and the magnetic domains 15 already in the storage region 10B shift toward the reproducing head 50. Then, the next magnetic domain can be recorded in the magnetic domain formation region 10A. By repeating recording and driving, the magnetic domains 15 are aligned in the extension direction, and information can be stored in the magnetic nanowire 10.

[0029] The shift length SL, which is the length by which the magnetic domain 15 is shifted by driving, varies depending on the magnitude of the driving current ID, the distance to the next pinning site, etc. Meanwhile, one bit of information is recorded in each magnetic domain 15 in the storage area 10B, and the bit length BL, which is the length of each magnetic domain 15, is the length of one bit of the magnetic nanowire 10. If the shift length SL matches the bit length BL, the information in the magnetic nanowire 10 can be shifted one bit at a time.

[0030] When the magnetic nanowire device 1 is driven, the magnetic domain wall shifts together with the magnetic domain 15 and is trapped at the adjacent connection portion 20. By aligning the interval D1 between the connection portions 20, the shift length SL, which is the length by which the magnetic domain 15 shifts when driven, can be aligned to the interval D1. In addition, since both ends of each magnetic domain 15 are located at the connection portion 20, the bit length BL can be aligned to the interval D1. This allows the magnetic nanowire device 1 to match the shift length SL and the bit length BL. The magnetic domain formed in the magnetic domain formation region 10A is moved to the storage region 10B by driving. The length ML of the magnetic domain in the magnetic domain formation region 10A does not have to be the same as the bit length BL in the storage region 10B, but the length of the magnetic domain 15 after the movement is easier to be defined by the bit length BL when the difference between the length ML and the bit length BL is small. From the viewpoint of defining the bit length BL after the movement, the distance DR in a plan view from the recording element 40 to the boundary 10C can be 0.5 to 2 times the bit length BL.

[0031] The magnetic nanowire 10 is driven by applying a driving current ID to the magnetic nanowire 10. Here, the driving current ID is an electron e - The driving current ID is controlled by a current control unit 92 so that the direction of movement of the driving current ID corresponds to the direction of the shift. The condition of the driving current ID is preferably adjusted so that the shift length SL coincides with the bit length BL. The driving current ID may be applied in several steps. The shift length SL may be adjusted as the total shift amount obtained by applying the driving current ID three times, for example.

[0032] (reproduction) Reproduction is the operation of detecting the magnetization direction of the magnetic domain 15 and extracting the recorded information. The magnetization direction is detected by the reproduction head 50. The reproduction head 50 outputs a signal corresponding to the magnetization direction of the magnetic domain 15 passing directly underneath. A reproduction processing unit 94 processes the signal from the reproduction head 50 and extracts the information. The reproduction processing unit 94 is a device that processes the signal from the reproduction head 50. The signal from the reproduction head 50 is input to the reproduction processing unit 94. The signal from the reproduction head 50 is an electrical signal corresponding to the magnetization direction of the magnetic nanowire 10. The reproduction processing unit 94 converts the electrical signal into binary information and outputs it. The reproduction processing unit 94 may be separate from the substrate 80, or a part or all of it may be provided on the substrate 80.

[0033] In the magnetic nanowire device 1 having the above-described configuration, the connection parts 20 arranged at a constant interval D1 serve as pinning sites to trap the magnetic domain walls, thereby allowing the shift length SL in driving the magnetic domain 15 to be specified to a constant length. Moreover, in the magnetic nanowire device 1, by making the intervals D1 of the connection parts 20 uniform, the shift lengths SL can be made uniform even if there is variation in the magnetic properties within one magnetic nanowire 10. Moreover, by making the intervals D1 of the connection parts 20 uniform even between different magnetic nanowires 10, the shift lengths SL can be specified to be the same.

[0034] In addition, the magnetic fine wire 10 only needs to have the upper surface of the second section 12 located relatively higher than the upper surface of the first section 11 and the lower surface of the second section 12 located relatively higher than the lower surface of the first section 11, and the thickness T2 of the magnetic fine wire 10 in the second section 12 may be different from the thickness T1 of the first section 11. In the magnetic nanowire device 1, the connection parts 20 in the storage region 10B are the ends of the magnetic domains 15. However, one or more connection parts 20 may be located other than the ends of one magnetic domain 15. Modified examples 2, 3, and 5 described below are examples in which one or more connection parts 20 are located other than the ends of one magnetic domain 15.

[0035] [Method of forming magnetic nanowires] Next, a method for forming the magnetic nanowire 10 will be described with reference to Fig. 3A to Fig. 3C. Fig. 3A to Fig. 3C show an outline of the underlayer 60 before the magnetic nanowire 10 is formed, Fig. 3A being a plan view, and Fig. 3B and Fig. 3C being cross-sectional views. In the magnetic nanowire device 1, the magnetic nanowire 10 is formed on the upper surface 60A of the underlayer 60. The method for forming the magnetic nanowire 10 includes a convex portion forming step of forming a convex portion 62 on the upper surface 60A of the underlayer 60 before forming the magnetic nanowire 10, and a magnetic nanowire forming step of forming the magnetic nanowire 10 so as to pass through the convex portion 62.

[0036] (Protrusion formation process) The convex portion forming process is a process of forming convex portions 62 on the upper surface 60A of the underlayer 60. As illustrated in Fig. 3A, here, convex portions 62A are formed in the same number as the number of second sections 12 at positions that become the second sections 12 of each magnetic nanowire 10. The underlayer 60 is formed by a known method such as sputtering, and the convex portion 62A can be formed by combining photolithography, electron beam lithography, etching, lift-off, or the like. Specifically, the underlayer 60 is etched and processed using a resist mask produced by lithography, or a SiO X or AlO X Oxide films such as SiN X or MgF 2 The protrusions 62A can be formed by a processing method using known insulating materials such as those mentioned above, including lithography, film formation, and lift-off.

[0037] As illustrated in Figures 3B and 3C, the upper surface of the protrusion 62A faces the second section 12 of the magnetic nanowire 10, and the side surface of the protrusion 62A located in the extension direction of the magnetic nanowire 10 faces the connection section 20. The side surface of the protrusion 62A can be formed to have a different inclination angle θ depending on the processing method, for example. In processing by reactive ion etching, the inclination angle θ can be close to 90 degrees, for example, 80 degrees. In processing by ion beam lithography, the inclination angle θ can be smaller than that, for example, 70 degrees. Note that the inclination angle θ may be simplified as 90 degrees in the drawings. The inclination angle θ can be, for example, from 60 degrees to 95 degrees, and is preferably from 80 degrees to 90 degrees. When the inclination angle θ is a value close to 90 degrees, the effect of the connection portion 20 as a trap site for the domain wall can be enhanced.

[0038] (Magnetic thin wire formation process) The magnetic nanowire forming step is a step of forming the magnetic nanowire 10 on the upper surface 60A of the underlayer 60. The magnetic nanowire 10 can be formed with a constant width so as to pass through the convex portion 62A. By forming the magnetic nanowire 10 in a straight line in a plan view on the upper surface 60A of the underlayer 60 having the convex portion 62A, it is possible to form the magnetic nanowire 10 that extends while changing its height vertically, reflecting the concave-convex pattern of the underlayer 60. The magnetic nanowire 10 can be formed by forming a film by a known method such as sputtering, and processing it into a straight line by a combination of photolithography, electron beam lithography, etching, lift-off, and the like.

[0039] For example, when providing a constriction in the width direction of the magnetic nanowire as a pinning site of the domain wall, highly accurate micro-machining of the magnetic nanowire is required. In some cases, it is difficult to increase the yield of the micro-machining for providing a constriction in the width direction. In response to this, by forming a protrusion 62A on the upper surface 60A of the underlayer 60 so as to correspond to the connection part 20 of the magnetic nanowire 10 before forming the magnetic nanowire 10, it is possible to form the equally spaced connection parts 20 that serve as pinning sites, and thus it is possible to eliminate the need for micro-machining of the magnetic nanowire.

[0040] As illustrated in Figures 4A and 4B, the convex portion 62 may be formed as a ridge-like convex portion 62B so as to be continuous across the multiple magnetic nanowires 10. Note that Figures 4A and 4B illustrate an outline of the underlayer 60 before the magnetic nanowires 10 are formed. The convex portion 62B is formed at a position that becomes the second section 12 of the magnetic nanowire 10 so as to be perpendicular to the multiple magnetic nanowires 10. The upper surface of the substrate 80 may have an uneven pattern instead of being flat. The uneven pattern of the substrate 80 may be reflected as an uneven pattern on the upper surface of the underlayer 60, and the uneven pattern on the upper surface of the underlayer 60 may be reflected in the shape of the magnetic nanowire 10.

[0041] [Variations] Next, modified examples of the magnetic nanowire device will be described with reference to FIGS. 5 to 7B. (First Modification) The first modified example is a modified example regarding the recording element 40. As illustrated in FIG. 5, the first modified example differs from the magnetic fine wire device 1 in that there are two recording elements 40, but the rest is common to the magnetic fine wire device 1. The two recording elements 40 are a first recording element 41 and a second recording element 42, and are arranged with a gap between them. The first recording element 41 is arranged on the side closer to the reproducing head 50, and a connection portion that becomes the boundary 10C is located immediately below the end of the first recording element 41 on the reproducing head 50 side. In the first modification, by applying recording currents IR in mutually opposite directions to the two recording elements 40, a magnetic field in the same direction is generated in the region between the two recording elements 40, making it possible to reduce the recording current IR required for magnetic domain formation.

[0042] (Second Modification) The second modified example differs from the magnetic fine wire device 1 in the relationship between the bit length BL and the interval between the connection parts 20, but is otherwise common to the magnetic fine wire device 1. As illustrated in Fig. 6A, in the second modified example, the interval D2 between every other connection part 20 is set to the bit length BL, which is the length of the magnetic domain 15 corresponding to one bit of information. Here, the ascending parts 21 and the descending parts 22 are disposed at equal intervals in the extension direction, and the descending parts 22 are located in the center of the adjacent ascending parts 21. Both the leading and trailing ends of the magnetic domain of each bit are ascending portions 21. Between magnetic domains with different magnetization directions, a magnetic domain wall is located in the ascending portion 21. When driving is performed, the magnetic domain wall is shifted together with the magnetic domain and is trapped in the adjacent ascending portion 21. Note that the descending portion 22 does not have to be located in the center between the adjacent ascending portions 21, and may be located near the leading or trailing end of each bit.

[0043] (Third Modification) The third modified example differs from the magnetic fine wire device 1 in the relationship between the bit length BL and the interval between the connection parts 20, but is otherwise common to the magnetic fine wire device 1. As illustrated in Fig. 6B, in the third modified example, the interval D4 between every third connection part 20 is set to the bit length BL, which is the length of the magnetic domain 15 corresponding to one bit of information. Here, the connection parts 20 arranged at the interval D4 are ascending parts 21, and the ascending parts 21 and the descending parts 22 are arranged at equal intervals in the extension direction. Both the leading and trailing ends of the magnetic domains of each bit are ascending sections 21. Between magnetic domains with different magnetization directions, magnetic domain walls are located in the ascending sections 21. When driving is performed, the magnetic domain walls are shifted together with the magnetic domains and are trapped by the next ascending section 21. Note that it is sufficient that every other ascending section 21 is arranged at a constant interval D4, and all of the ascending sections 21 do not have to be equally spaced. Also, the interval between the ascending section 21 and the descending section 22 does not have to be constant. Also, the connection sections 20 arranged at an interval D4 every third connection section 20 may be descending sections 22.

[0044] Furthermore, every third connection 20 may be equally spaced, and the interval may be the bit length BL, or every fourth or more connection 20 may be equally spaced, and the interval may be the bit length BL. That is, it is sufficient that at least some of the connection parts 20 are equally spaced in the extending direction of the magnetic nanowire 10, and the interval between the equally spaced connection parts 20 is the bit length BL.

[0045] (Fourth Modification) The fourth modification is different from the magnetic nano-wire device 1 in that the underlayer 60 has a recess 61, and the thickness of the underlayer 60 at the recess 61 is thinner than the thickness T3 of the region without the concave-convex pattern, but is otherwise common to the magnetic nano-wire device 1. As illustrated in Fig. 7A, in the fourth modification, like the magnetic nano-wire device 1, the connection parts 20 are arranged at equal intervals in the extension direction of the magnetic nano-wire 10, and the interval D1 between adjacent connection parts 20 is set to the bit length BL, which is the length of the magnetic domain corresponding to one bit of information. When actuated, the domain wall is shifted together with the magnetic domain, and is trapped by the adjacent connection part 20.

[0046] (Fifth Modification) The fifth modification, like the fourth modification, differs from the magnetic fine wire device 1 in that the thickness of the underlayer 60 in the recess 61 is thinner than the thickness T3 of the area without the concave-convex pattern. Also, like the second modification, it differs from the magnetic fine wire device 1 in that the interval D2 between every other connecting portion 20 is set to the bit length BL. The rest is common to the magnetic fine wire device 1. 7B, in the fifth modified example, the interval D2 between every other descending portion 22 is the bit length BL. In addition, the leading and trailing ends of the magnetic domain of each bit are both descending portions 22. Between magnetic domains with different magnetization directions, a magnetic domain wall is located at the descending portion 22. When driving is performed, the magnetic domain wall is shifted together with the magnetic domain and is trapped by the adjacent descending portion 22.

[0047] The methods for forming the magnetic nanowire 10 of the fourth and fifth modified examples include a recess formation process for forming a recess 61 on the upper surface 60A of the underlayer 60 before forming the magnetic nanowire 10, and a magnetic nanowire formation process for forming the magnetic nanowire 10 so as to pass through the recess 61. The recess 61 is formed at a position that will become the first section 11 of the magnetic nanowire 10. The recess 61 can be formed by depositing the underlayer 60 and processing it by photolithography or the like, similarly to the magnetic nanowire device 1. The magnetic nanowire 10 can be formed by depositing the underlayer 60 by a known method and processing it into a straight shape by photolithography or the like.

[0048] In addition, the recesses 61 may be formed at positions that become the first sections 11 of each magnetic nanowire 10, with the same number of recesses 61 as the number of first sections 11, or may be formed in a groove shape that is continuous across multiple magnetic nanowires 10.

[0049] [Second embodiment] Next, the magnetic fine wire device 1B according to the second embodiment will be described with reference to Fig. 8 to Fig. 9B. The magnetic fine wire device 1B is an element group that is a part of a magnetic fine wire memory, similar to the magnetic fine wire device 1 according to the first embodiment. Note that Fig. 8 omits projections and recesses and illustrates the relative positional relationship of each member.

[0050] 8, the magnetic fine wire memory 100B includes a magnetic fine wire device 1B, a current control unit 92, and a reproduction processing unit 94. The magnetic fine wire memory 100B operates in the same manner as the magnetic fine wire memory 100. The magnetic fine wire memory 100B differs from the magnetic fine wire memory 100 in that it includes the magnetic fine wire device 1B, but is otherwise common. In the magnetic fine wire device 1B, the recording element 40 is disposed below the magnetic fine wire 10. As with the magnetic fine wire device 1, the magnetic fine wire device 1B includes the magnetic fine wire 10, an insulating layer 30, a recording element 40, a reproducing head 50, and an underlayer 60, which are formed on a substrate 80. Each component of the magnetic fine wire device 1B will be described below.

[0051] (magnetic thin wire) 9A and 9B, the magnetic nanowire 10 of the magnetic nanowire device 1B is disposed above the underlayer 60 and on the upper surface of the insulating layer 30. The other points are common to the magnetic nanowire 10 of the magnetic nanowire device 1.

[0052] (base layer) The underlayer 60 is disposed on the substrate 80, and the insulating layer 30 is disposed on the upper surface of the underlayer 60. The underlayer 60 has grooves 65 in which the recording elements 40 are embedded, and the upper surface 60A of the underlayer 60 is a flat surface except for the grooves 65. The material of the underlayer 60 is the same as that of the magnetic nanowire device 1. The underlayer 60 can be formed by deposition using a known method such as sputtering. The grooves 65 can be formed by etching or the like.

[0053] (Recording element) The recording element 40 is disposed below the magnetic wire 10 so as to intersect with the magnetic wire 10 in a plan view, and a recording current IR is applied to magnetize the magnetic wire 10. The recording element 40 is disposed below the magnetic wire 10 via the insulating layer 30. The recording element 40 can be disposed so as to be embedded in a groove 65 of the underlayer 60 below the insulating layer 30 with the upper surface exposed. The recording element 40 may be made of the same metal material as the recording element 40 of the magnetic nanowire device 1, and may be processed in the same manner. The recording element 40 may be formed by forming grooves 65 in the underlayer 60 by photolithography or electron beam lithography and an etching method, plating the underlayer 60 with a metal material, and filling the grooves 65 with the metal material.

[0054] (insulating layer) The insulating layer 30 is disposed between the magnetic nanowire 10 and the recording element 40. The insulating layer 30 is disposed on the underlayer 60 and the upper surface of the recording element 40. The upper surface 30A of the insulating layer 30 has an uneven pattern that faces the uneven shape of the lower surface of the magnetic nanowire 10 so as to mesh with it. The upper surface 30A of the insulating layer 30 is formed at the height of the lower surface of the magnetic nanowire 10 along the shape of the lower surface of the magnetic nanowire 10. The insulating layer 30 has a convex portion 32 at the position of the second section 12 of the magnetic nanowire 10. The magnetic nanowire 10 is formed on the upper surface 30A of the insulating layer 30 and extends while changing its height up and down to reflect the uneven pattern of the upper surface 30A. The insulating layer 30 is formed by a known method such as sputtering, and the protrusions 32 can be formed by combining photolithography, electron beam lithography, etching, lift-off, etc. The material of the insulating layer 30 is the same as that of the magnetic nanowire device 1. The substrate 80 and the reproducing head 50 are common to the magnetic nanowire device 1 .

[0055] In the magnetic fine wire device 1B having the above-mentioned configuration, like the magnetic fine wire device 1, the shift length SL in driving the magnetic domain 15 can be set to a constant length.

[0056] [experiment] Next, an experiment that confirmed that the shift length SL is determined by the interval between the connection parts 20 will be described. The experiment was conducted by fabricating an experimental device in which the reproducing head 50 was removed from the magnetic nanowire device according to the fifth modified example. The experimental device has every other connection part 20 arranged at a constant interval D2, and the interval D2 is defined as the bit length BL. The experimental device has descending parts 22 at the leading and trailing ends of the magnetic domains 15, and an ascending part 21 at the center position between adjacent descending parts 22.

[0057] (Experimental Device) A Si substrate was used as the substrate 80. The underlayer 60 was formed by thermally oxidizing the surface of the Si substrate to form SiO X Then, a SiO X On the top surface of the film, lithography was performed to form a 4 nm thick SiN X The SiN film was then processed by lift-off. X That is, the underlayer 60 was made of SiO X The SiN film has a concave-convex pattern on the top surface. X The bit length BL was set to 6 μm in consideration of ease of observation with a microscope. That is, the interval D2 between adjacent descending portions 22 was 6 μm. The magnetic nanowire 10 was formed by depositing a Co / Tb multilayer film in which 0.8 nm-thick Tb and 0.35 nm-thick Co were repeatedly laminated four times, and then lithographically forming the magnetic nanowire into a nanowire shape. The thickness of the magnetic nanowire 10 is 4.6 nm. To prevent oxidation, a 3 nm-thick Pt film was deposited on the top surface of the Co / Tb multilayer film. The film structure including this Pt film is Pt (3 nm) / [Co (0.35 nm) / Tb (0.8 nm)]. 4 The width of the magnetic nanowire 10 is 3 μm.

[0058] The insulating layer 30 is a 3 nm thick SiN X , SiO with a thickness of 25 nm X The SiO X (25nm) / SiN X (3 nm) multilayer film was formed. A Ta (5 nm) / Au (20 nm) / Ag (150 nm) / Ta (3 nm) multilayer film was formed as the recording element 40, the wiring for measurement, and the electrode pad, by laminating Ta with a thickness of 3 nm, Ag with a thickness of 150 nm, Au with a thickness of 20 nm, and Ta with a thickness of 5 nm in this order. Lithography was used to process the wiring pattern.

[0059] (Experimental Procedure) An external device having the function of the current control unit 92 was connected to the experimental device, and operations equivalent to recording and driving of the magnetic nanowire memory were performed according to the following procedures (A), (B), and (C). Then, the state after each procedure was observed with a magneto-optical microscope. First, before (A), an external magnetic field of −1000 Oe was applied by an external electromagnet to initialize the magnetization directions of all the magnetic nanowires 10 to the downward direction.

[0060] (A) A pulse current having a pulse width of 4 μs and a current value of 270 mA was applied to the recording element 40 to induce a current magnetic field, which reversed the magnetization direction of the magnetic domain formation region 10A upward to form a magnetic domain 15A. (B) A pulse current with a pulse width of 4 μs and a current value of 3.57 mA was applied four times to the magnetic nanowire 10, shifting the magnetic domain 15A to the right by the bit length BL. After that, magnetic domain 15B was formed in the magnetic domain formation region 10A under the same conditions as (A). In other words, magnetic domain 15B formed for the second bit is formed next to magnetic domain 15A formed for the first bit. (C) A pulse current with a pulse width of 4 μs and a current value of 3.57 mA was applied four times to the magnetic nanowire 10, shifting the magnetic domains 15A and 15B to the right by the bit length BL. Then, under the same conditions as (A), a magnetic domain 15C was formed as the third bit in the magnetic domain formation region 10A.

[0061] (Experimental Results) FIG. 10A is a photo taken with a magneto-optical microscope after (A), FIG. 10B is after (B), and FIG. 10C is after (C). In FIG. 10A to FIG. 10C, magnetic domains whose magnetization direction is upward are displayed dark, and magnetic domains whose magnetization direction is downward are displayed bright. When the device was completed, the coercive force of the magnetic nanowire 10 was 500 Oe, and the Kerr rotation angle was 0.12 degrees at a wavelength of 658 nm. This measurement was performed using a micro Kerr loop measuring device manufactured by Neoark Corporation. 10A, the magnetic domain formation region 10A is displayed dark, and it can be seen that the magnetic domain is an upward magnetic domain. From (A), it was confirmed that an upward magnetic domain 15A was formed in the magnetic domain formation region 10A.

[0062] 10B, the magnetic domain formation region 10A and the first retaining region 10B1 adjacent to it on the right are displayed darkly, and it can be seen that they are upward magnetic domains. From (B), it was confirmed that the magnetic domain 15A was driven by the first retaining region 10B1, and a new upward magnetic domain 15B was formed in the magnetic domain formation region 10A. 10C, the magnetic domain formation region 10A, the first hold region 10B1, and the second hold region 10B2 adjacent to the right of the first hold region 10B1 are displayed darkly, and it can be seen that they are upward magnetic domains. From (C), it can be confirmed that the magnetic domain 15A is driven to the second hold region 10B2, the magnetic domain 15B is driven to the first hold region 10B1, and an upward magnetic domain 15C is newly formed in the magnetic domain formation region 10A.

[0063] (Consideration) From the above experimental results, the shift length SL of the magnetic domain is determined to a constant value by the interval D2 between every other connection part 20. It is presumed that the magnetic domain wall is located at the connection part 20. Furthermore, even if the length ML of the magnetic domain formed in the magnetic domain formation region 10A does not match the interval D2, when the formed magnetic domain is driven to the storage region 10B, the bit length BL can be determined by the interval D2. By having the equally spaced connection parts 20, the magnetic nanowire memory can perform recording and driving operations by matching the shift length SL and the bit length BL.

[0064] The magnetic nanowire 10 can be used as an optical modulation element in a reflective spatial light modulator by utilizing the difference in the angle of rotation (magneto-optical Kerr effect) depending on the magnetization direction of the magnetic domain 15. In the spatial light modulator, one magnetic domain 15 of the magnetic nanowire 10 can be used as one pixel, and the reproducing head 50 and the reproducing processing unit 94 are not required. [Explanation of symbols]

[0065] 1 Magnetic nanowire device (first embodiment) 1B Magnetic nanowire device (second embodiment) 10 Magnetic thin wire 10A magnetic domain formation area 10B storage area 10C boundary 11 First Section 12 Second Section 15 magnetic domains 20 Connection 21 Ascending section 22 Descending section 30 Insulating layer 40 Recording element 50 Playhead 60 Base layer 61 Recess 62 Convex 80 Substrate 100 Magnetic nanowire memory (first embodiment) 100B Magnetic nanowire memory (second embodiment)

Claims

1. an underlayer disposed on the substrate; a magnetic nanowire disposed above the underlayer and extending linearly in a plan view; a recording element disposed above the magnetic nanowire so as to intersect with the magnetic nanowire in a plan view, the recording element being applied with a recording current that magnetizes the magnetic nanowire; an insulating layer disposed between the magnetic nanowire and the recording element; the magnetic nanowire is disposed on the upper surface of the underlayer, and extends at a height varying vertically by alternating between a first section having a lower surface at a first position and a second section having a lower surface at a second position higher than the first position via a connection portion connecting the first section and the second section; A magnetic nanowire device in which an upper surface of the underlayer is formed at the same height as the lower surface of the magnetic nanowire, following the shape of the lower surface of the magnetic nanowire.

2. an underlayer disposed on the substrate; a magnetic nanowire disposed above the underlayer and extending linearly in a plan view; a recording element disposed below the magnetic nanowire so as to intersect with the magnetic nanowire in a plan view, the recording element being applied with a recording current that magnetizes the magnetic nanowire; an insulating layer disposed between the magnetic nanowire and the recording element; the magnetic nanowire is disposed on the upper surface of the insulating layer, and extends at a height varying vertically, alternating between a first section having a lower surface at a first position and a second section having a lower surface at a second position higher than the first position, via a connection portion connecting the first section and the second section; A magnetic nanowire device, wherein an upper surface of the insulating layer is formed at the same height as the lower surface of the magnetic nanowire, following the shape of the lower surface of the magnetic nanowire.

3. In the magnetic nanowire, one of the connection parts is located at a boundary between a magnetic domain forming region where a magnetic domain is formed by the recording current and a storage region where the formed magnetic domain is sequentially moved and stored, 3. The magnetic nanowire device according to claim 1, wherein the distance from the recording element to the boundary in a plan view is 0.5 to 2 times the bit length, which is the length of a magnetic domain corresponding to 1 bit of information.

4. The connection parts are arranged at equal intervals in the extending direction of the magnetic nanowire, 3. The magnetic nanowire device according to claim 1, wherein the interval between adjacent said connection parts is set to a bit length, which is the length of a magnetic domain corresponding to one bit of information.

5. The connection parts are arranged at equal intervals in the extending direction of the magnetic nanowire, 3. The magnetic nanowire device according to claim 1, wherein the interval between every other one of the connecting portions is set to a bit length, which is the length of a magnetic domain corresponding to one bit of information.

6. At least some of the connection parts are arranged at equal intervals in the extending direction of the magnetic nanowire, 3. The magnetic nanowire device according to claim 1, wherein the interval between the equally spaced connecting portions is set to a bit length, which is the length of a magnetic domain corresponding to one bit of information.

7. the magnetic nanowire has the same thickness in the first section and the second section; 3 . The magnetic nanowire device according to claim 1 , wherein the height of the second position from the first position is equal to or less than twice the thickness of the magnetic nanowire in the first section and the second section.

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