Magnetic filament, magnetic filament memory and formation method for magnetic filament

Abstract

To provide a magnetic filament which attains improvement in data hold characteristics and power saving, a magnetic filament memory, and a formation method for a magnetic filament.SOLUTION: A magnetic filament 10 comprises: an insulation ground layer 21; and a magnetic layer 24 which is formed on a top face of the ground layer 21 in contact with the ground layer 21 with the same width as the top face of the ground layer 21. The magnetic filament is formed in a filament shape in a planar view. A magnetic filament memory 100 comprises at a top face side of a substrate 80: the magnetic filament 10; a recording element which is disposed above the magnetic filament 10 so as to cross the magnetic filament 10 in a planar view and to which a recording current magnetizing the magnetic filament 10 is applied; and an insulation layer disposed between the magnetic filament 10 and the recording element.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a magnetic nanowire, a magnetic nanowire memory which is a storage device using the magnetic nanowire, and a method for forming the magnetic nanowire. [Background technology]

[0002] A magnetic nanowire memory is a storage device that can read and write binary information corresponding to the direction of magnetization, such as upward or downward, using a magnetic nanowire, which is a magnetic material processed into a thin wire shape, as a medium. For example, Patent Document 1 describes a magnetic nanowire memory in which a recording element, which is a conductor formed into a thin wire shape via an insulating layer, is arranged orthogonally above or below the magnetic nanowire, and information is recorded by locally reversing the magnetization in the magnetic nanowire using a current magnetic field generated by applying a current to the recording element. The operation of magnetic nanowire memory consists of "recording," which forms magnetic domains corresponding to recording bits, "driving," which moves (shifts) the formed magnetic domains within the magnetic nanowire, and "reproducing," which detects the magnetization direction of the magnetic domains. "Recording" forms magnetic domains in the magnetic nanowire using a commonly used magnetic head or a current magnetic field induced by applying a current to the recording element. "Driving" utilizes the domain wall current driving phenomenon to apply a driving current, which is a pulse current, to each magnetic nanowire, shifting the formed magnetic domains in one direction. [Prior art documents] [Patent documents]

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

[0004] The magnetic domain shift during driving requires the application of a current above a certain threshold, and the current density is 10 7 A / cm 2Since the current required to shift the magnetic domain is proportional to the cross-sectional area of ​​the magnetic nanowire, an effective way to reduce the power consumption of magnetic nanowire memories is to reduce the film thickness of the magnetic nanowire, thereby reducing its cross-sectional area and the current required to shift the magnetic domain. However, as the film thickness of the magnetic nanowire is reduced, the coercive force also decreases accordingly, which creates the problem of a decrease in the data retention characteristics (thermal stability) of the memory.

[0005] The present invention has been made to solve the above problems, and has an object to provide a magnetic nanowire and a magnetic nanowire memory that improve data retention characteristics and reduce power consumption, as well as a method for forming the magnetic nanowire. [Means for solving the problem]

[0006] The magnetic nanowire of the embodiment comprises an insulating underlayer and a magnetic layer formed on the upper surface of the underlayer and in contact with the underlayer with the same width as the upper surface of the underlayer, and is formed in a nanowire shape when viewed in a plane.

[0007] Moreover, the magnetic nanowire memory of the embodiment includes, on the upper surface side of a substrate, a magnetic nanowire of the embodiment, a recording element arranged 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 arranged between the magnetic nanowire and the recording element.

[0008] In addition, the method for forming a magnetic nanowire according to the embodiment includes a base layer formation process for forming an insulating base layer on one side of a substrate, and a magnetic layer formation process for forming a magnetic layer on an upper surface of the base layer, and the base layer formation process and the magnetic layer formation process are performed successively in the same vacuum. Effect of the Invention

[0009] According to the present invention, it is possible to provide a magnetic nanowire, a magnetic nanowire memory, and a method for forming a magnetic nanowire that improve data retention characteristics and reduce power consumption. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view illustrating an outline of a magnetic nanowire memory according to a first embodiment. [Figure 2A] 1 is a plan view illustrating an outline of a magnetic nanowire memory according to a first embodiment. [Figure 2B] FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 2A. [Diagram 3] 3 is a cross-sectional view of the magnetic nanowire and its underlying layer taken along line III-III in FIG. 2A. [Figure 4] 4 is a flowchart illustrating a method for forming a magnetic nanowire according to the embodiment. [Figure 5A] 4A to 4C are cross-sectional views illustrating a resist after pattern formation in the method for forming a magnetic nanowire according to the embodiment. [Figure 5B] 4 is a cross-sectional view illustrating a state in which an underlayer is formed in the method for forming a magnetic nanowire according to the embodiment. FIG. [Figure 5C] 4A to 4C are cross-sectional views illustrating a state in which a magnetic layer is formed in the method for forming a magnetic nanowire according to the embodiment. [Figure 5D] 4 is a cross-sectional view illustrating a state in which a cap layer is formed in the method for forming a magnetic nanowire according to the embodiment. FIG. [Figure 6] 13 is a flowchart illustrating a modified example of a method for forming a magnetic nanowire. [Figure 7A] 11A and 11B are cross-sectional views illustrating a state in which layers that are to become an underlayer, a magnetic layer, and a cap layer have been formed in a modified example of the method for forming a magnetic nanowire. [Figure 7B] 13 is a cross-sectional view illustrating a state in which a shielding layer is formed in a modified example of the method for forming a magnetic nanowire. FIG. [Figure 7C] 13 is a cross-sectional view illustrating a state in which a thin-wire-shaped underlayer, a magnetic layer, and a cap layer are formed in a modified example of the method for forming a magnetic thin wire. FIG. [Figure 7D] 13 is a cross-sectional view illustrating a state in which the shielding layer is removed in a modified example of the method for forming a magnetic nanowire. FIG. [Figure 7E] 13 is a cross-sectional view illustrating a state in which a wire-shaped magnetic layer and a cap layer are formed in a modified example of the method for forming a magnetic wire. FIG. [Figure 7F] 13 is a cross-sectional view illustrating a state in which the shielding layer is removed in a modified example of the method for forming a magnetic nanowire. FIG. [Figure 7G] 13 is a cross-sectional view illustrating a state in which a separation layer is formed in a modified example of the method for forming a magnetic nanowire. FIG. [Figure 7H] 13 is a cross-sectional view illustrating a state in which the shielding layer is removed in a modified example of the method for forming a magnetic nanowire. FIG. [Figure 8] FIG. 11 is a perspective view illustrating an outline of a magnetic nanowire memory according to a second embodiment. [Figure 9A] FIG. 11 is a plan view illustrating an outline of a magnetic nanowire memory according to a second embodiment. [Figure 9B] 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A. [Figure 10] 9B is a cross-sectional view of the magnetic nanowire and its underlying layer taken along line XX in FIG. 9A. [Figure 11A] FIG. 11 is a cross-sectional view illustrating a first modified example of the second embodiment. [Figure 11B] FIG. 11 is a cross-sectional view illustrating a second modified example of the second embodiment. [Figure 12A] 1 is a graph illustrating a hysteresis curve of a comparative example. [Figure 12B] 1 is a graph illustrating a hysteresis curve of an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [First embodiment] The magnetic fine-wire memory 100 according to the first embodiment will be described with reference to FIG. 1 to FIG. 3. As illustrated in FIG. 1, the magnetic fine-wire memory 100 includes a magnetic fine wire 10, a recording element 40, and an insulating layer 30 on the upper surface side of a substrate 80. Here, the magnetic fine-wire memory 100 further includes a base layer 60, a reproducing head 50, a current control unit 92, and a reproducing processing unit 94. Each component of the magnetic fine-wire memory 100 will be described below. Note that the number of magnetic fine wires 10 may be two in the drawings, but it may be one, or three or more. In addition, in FIG. 1 and FIG. 8, the magnetic fine wire 10 is represented as having a length of several bits with several magnetic domains 15 corresponding to one bit of information arranged in the extension direction, but there is no particular limit to the number of bits or the length, and the length can be set as necessary. For example, by designing the magnetic fine wire 10 to have a length of 30 mm and the magnetic domain 15 to have a length of 30 nm, 10 pieces of information can be stored. 6 The magnetic nanowire 10 can have magnetic domains 15 arranged in a number corresponding to a bit.

[0012] (magnetic thin wire) The magnetic nanowire 10 is a thin magnetic body that serves as an information recording medium. The magnetic nanowire 10 is a film-like element whose width is greater than its thickness, and can be formed in a thin wire shape that is sufficiently long relative to the thickness and width. The magnetic nanowire 10 is disposed on the upper surface side of the substrate 80, and is formed in a nanowire shape in a planar view. Here, a base layer 60 is disposed on the upper surface of the substrate 80, and two magnetic nanowires 10 are disposed parallel to each other on the upper surface of the base layer 60. As illustrated in FIG. 2B and FIG. 3, the magnetic nanowire 10 is made of a plurality of stacked layers, and includes an underlayer 21 and a magnetic layer 24. The magnetic nanowire 10 may further include a cap layer 27. Note that FIG. 3 omits some components and illustrates the magnetic nanowire 10 and its underlying layers. Next, each layer of the magnetic nanowire 10 will be described.

[0013] (base layer) The underlayer 21 is an insulating layer located at the bottom of the magnetic nanowire 10. The underlayer 21 is formed along the magnetic nanowire 10 to the width of the magnetic nanowire 10. The material of the underlayer 21 is silicon nitride (SiN X ) and CrO, NiO, MgO, Fe2 O 3 Here, the underlayer 21 is made of silicon nitride (SiN X The subscript X indicates that the composition ratio is not limited. SiN X For example, Si 3 N 4 (X=1.33). In order to suppress the decrease in coercivity that accompanies thinning of the magnetic nanowire, it is essential to increase the magnetic anisotropy of the magnetic material that forms the magnetic nanowire, and controlling the crystal orientation of the magnetic material could be a promising solution. In order to control the crystal orientation, the idea was conceived of providing an underlayer 21 as part of the magnetic nanowire 10 under the magnetic layer 24, which is the magnetic material. By providing the underlayer 21, the internal stress of the magnetic layer 24 formed directly above by sputtering changes, and it is possible to control the crystal orientation so as to increase the magnetic anisotropy. Then, as a result of adopting various materials as the underlayer 21 and conducting further verification, it was found that silicon nitride (SiN X ) thin film was found to be optimal. However, the magnetic layer 24 is formed in contact with the underlayer 21. In forming the magnetic nanowire, for example, a silicon nitride thin film is first formed as the underlayer 21, and then a ferromagnetic film or the like that forms the magnetic layer 24 is continuously formed in the same vacuum, thereby forming the magnetic layer 24 in contact with the underlayer 21.

[0014] 2B and 3, the underlayer 21 is uniformly formed as a thin film on the upper surface of the base layer 60. In order to form the underlayer 21 uniformly as a thin film, the thickness of the underlayer 21 can be, for example, 3 nm or more, and preferably 5 nm or more. On the other hand, from the viewpoint of stabilizing the shape of the magnetic nanowire 10, the thickness of the underlayer 21 can be, for example, 30 nm or less, and preferably 15 nm or less.

[0015] (magnetic layer) The magnetic layer 24 is a ferromagnetic or ferrimagnetic layer with spontaneous magnetization that is responsible for the magnetism of the magnetic nanowire 10. The magnetic layer 24 is formed on the upper surface of the underlayer 21, in contact with the underlayer 21, with the same width as the upper surface of the underlayer 21. Between the underlayer 21 and the magnetic layer 24, there is no other layer resulting from atmospheric components, for example, a layer that contains a large amount of components derived from water, such as hydroxyl groups (OH), and the lower surface of the magnetic layer 24 is in direct contact with the upper surface of the underlayer 21. Ferromagnetism and ferrimagnetism refer to the property of having magnetization in which the magnetic moment is aligned even in the absence of an external magnetic field. A perpendicular magnetization film, whose magnetization direction is likely to be oriented in the thickness direction, can be used as the magnetic layer 24. The perpendicular magnetization film is made of a magnetic material with perpendicular magnetic anisotropy.

[0016] The magnetic layer 24 may be a multilayer film such as a Co / Pt multilayer film in which a first layer 24A made of a transition metal such as Fe, Co, or Ni and a second layer 24B made of a precious metal such as Pd or Pt are repeatedly laminated. As an example, three periods are laminated, each period being a set in which the first layer 24A is disposed on the second layer 24B. The magnetic layer 24 may be a single layer or multilayer film of an alloy of rare earth metals and transition metals such as Tb-Fe-Co and Gd-Fe (RE-TM alloy). 0 The system can be an ordered alloy of FePt, FePd, etc.

[0017] (Cap layer) The cap layer 27 is located on the uppermost layer of the magnetic nanowire 10, and is a layer that protects the magnetic layer 24 from oxidation and the like. The cap layer 27 is disposed on the upper surface of the magnetic layer 24, with the same width as the upper surface of the magnetic layer 24. In a plan view, the underlayer 21, the magnetic layer 24, and the cap layer 27 are formed with the same width. The cap layer 27 can be a thin film of, for example, Pt or Ru, and is a thin Pt film as an example here. The thickness of the cap layer 27 is preferably 3 nm to 10 nm, and more preferably 4 nm to 6 nm. The cap layer 27 may be a single layer or a multilayer film. The magnetic nanowire 10 including the underlayer 21, the magnetic layer 24 and the cap layer 27 is formed in a nanowire shape in a plan view.

[0018] (Base layer) The base layer 60 is a layer that serves as a base for the magnetic nanowire 10. Here, the base layer 60 is disposed on a substrate 80. The top surface of the base layer 60 is flat, and the magnetic nanowire 10 is disposed on the top surface of the base layer 60. The base layer 60 is insulating. The base layer 60 is, for example, a SiO X The base layer 60 may be a laminate of multiple layers.

[0019] (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 on one end side of the magnetic wire 10 so as to intersect with the magnetic wire 10 in a planar view. The recording element 40 and the magnetic wire 10 are insulated from each other by an insulating layer 30. 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.

[0020] (insulating layer) The insulating layer 30 is an insulator 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. As illustrated in FIG. 2B, 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 material of the insulating layer 30 is, for example, SiO X and AlO X Oxide films such as SiN X , MgF 2 Known insulating materials such as SiN XSimilarly, X in the subscript of O indicates that the composition ratio is not limited. SiO X is, for example, SiO 2 and AlO X is, for example, Al 2 O 3 (X = 1.5). The insulating layer 30 can be formed by film formation using a known method such as a sputtering method.

[0021] (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 of the magnetic fine wire 10 (the side opposite to the recording element 40). One reproduction head 50 can be provided for one magnetic fine wire 10. The reproduction head 50 is generally a magnetic head used for magnetic recording, and can be, for example, a tunnel magnetoresistance (TMR) head.

[0022] (substrate) The substrate 80 is a plate-like member on which the above elements and members are formed. The elements and the like are formed on one surface side of the substrate 80, and the side on which the elements and the like are formed is described as the upper surface side of the substrate 80. Note that the orientation during the manufacture and use of the magnetic fine wire and the magnetic fine wire memory is not limited. The upper surface of the substrate 80 is a flat surface, and the base layer 60 is disposed thereon. The substrate 80 is a substrate in a broad sense for forming the recording element 40 and the magnetic fine wire 10, and a known substrate material 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, or the like can be used. Here, the substrate 80 is an Si substrate having a surface thermally oxidized to form a SiO X film (0 < X ≤ 2) as the base layer 60.

[0023] (current control unit) The current control unit 92 is a device that controls the driving current ID applied to the magnetic nanowire 10 and the recording current IR applied to the recording element 40. Binary information to be written to the magnetic nanowire memory 100 is input to the current control unit 92, and the current control unit 92 controls the magnitude and timing of the driving current ID and the recording current IR. When there are multiple magnetic nanowires 10 or recording elements 40, the current control unit 92 is wired independently of each other, and the current applied to each of them can be controlled independently. The current control section 92 may be separate from the substrate 80, or a part or the whole may be provided on the substrate 80.

[0024] (Playback Processing Unit) 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 that corresponds 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 regeneration processing unit 94 may be separate from the substrate 80, or a part or the whole may be provided on the substrate 80.

[0025] (Operation of magnetic nanowire memory) Next, a description will be given of the operation of the magnetic nanowire memory 100. The magnetic nanowire memory 100 can read and write binary information through three operations: recording, driving, and reproducing.

[0026] (record) Recording is an operation for forming magnetic domains 15 in the magnetic nanowire 10. The magnetic domains 15 are formed by the magnetic field of a recording current IR applied to the recording element 40. The magnetic nanowire 10 is magnetized upward or downward in the thickness direction depending on the direction of the recording current IR. The magnetic domains 15 are formed in a magnetic domain formation region 10A of the magnetic nanowire 10. Here, the magnetic domain formation region 10A is a region on the reproducing head 50 side near the recording element 40. Note that, on the reproducing head 50 side of the magnetic domain formation region 10A, there is a storage region 10B via a boundary 10C, which sequentially moves and stores the formed magnetic domains 15.

[0027] (Drive) The driving is an operation for moving the magnetic domain 15 in parallel to the extension direction of the magnetic nanowire 10. The driving is performed by applying a driving current ID to the magnetic nanowire 10. Here, the driving current ID is an electron e - The voltage is applied so that the direction of movement of the signal corresponds to the shift direction. As a result of the drive, the magnetic domains 15 move toward the reproducing head 50 while maintaining their magnetization direction. The magnetic domains 15 formed in the magnetic domain formation region 10A cross the boundary 10C and 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 15 can be recorded in the magnetic domain formation region 10A.

[0028] By repeating recording and driving, the magnetic domains 15 are aligned in the extension direction of the magnetic nanowire 10, and information can be stored in the magnetic nanowire 10. When there are multiple magnetic nanowires 10, the current control unit 92 can allocate binary information to each magnetic nanowire 10 and control the timing of applying the drive current ID and the recording current IR to perform recording and driving so that the magnetic domains 15 are aligned upward or downward in a predetermined order in each magnetic nanowire 10. Note that there is a domain wall between adjacent magnetic domains 15 with opposite magnetization directions, and the domain wall shifts together with the magnetic domains 15. A domain wall is a region where the magnetization direction gradually changes between magnetic domains 15 with different magnetization directions.

[0029] (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.

[0030] The magnetic nanowire memory 100 having the above-mentioned configuration can maintain a sufficient coercive force even if the thickness of the magnetic layer 24 is thin. By thinning the thickness of the magnetic layer 24, the cross-sectional area can be reduced, suppressing the driving current ID and achieving power saving.

[0031] [Method of forming magnetic nanowires] Next, the method S10 for forming the magnetic nanowire 10 will be described with reference to Fig. 4 to Fig. 5D. As illustrated in Fig. 4, the method S10 for forming the magnetic nanowire 10 includes an underlayer forming step S12 for forming an insulating underlayer 21 on one side of the substrate 80, and a magnetic layer forming step S13 for forming a magnetic layer 24 on the upper surface of the underlayer 21, and the underlayer forming step S12 and the magnetic layer forming step S13 are performed successively in the same vacuum. Here, the method includes a resist forming step S11 for forming a resist of a predetermined pattern before the underlayer forming step S12. In addition, the method may include a cap layer forming step S14 for forming a cap layer 27 after the magnetic layer forming step S13.

[0032] (Resist formation process) The resist forming step S11 is a step of forming a resist of a predetermined pattern on the upper surface of the base layer 60 formed on one side of the substrate 80. In the resist forming step S11, a resist is uniformly formed on the upper surface of the base layer 60, and a predetermined pattern is formed in the resist by photolithography or electron beam lithography. The predetermined pattern is a pattern in which a fine line-shaped opening is formed, which is the shape in which the magnetic nanowire 10 is formed. The pattern is formed by removing the resist in the region in which the magnetic nanowire 10 is formed, and exposing the base layer 60. As illustrated in FIG. 5A, the resist R1 after the pattern formation exposes the base layer 60 to the width of the magnetic nanowire 10.

[0033] (Underlying layer formation process) The underlayer formation step S12 is a step of forming an insulating underlayer 21 on one side of the substrate 80. As illustrated in Fig. 5B, in the underlayer formation step S12, the underlayer 21 is formed on the upper surface of the base layer 60 exposed from the resist R1. Here, the underlayer 21 is a silicon nitride thin film, and can be formed by, for example, a sputtering method. In the method S10 for forming the magnetic nanowire 10, the underlayer forming step S12 and the magnetic layer forming step S13 are performed continuously without breaking the vacuum, and the underlayer 21 and the magnetic layer 24 are continuously formed in the same vacuum. By continuously forming the layers in the same vacuum without breaking the vacuum, a magnetic nanowire having the magnetic layer 24 formed in contact with the underlayer 21 can be obtained. When the vacuum is broken and the magnetic nanowire is exposed to the atmosphere, for example, a layer caused by components of the atmosphere enters between the underlayer 21 and the magnetic layer 24, and even in the magnetic nanowire having the underlayer 21, the crystal orientation of the magnetic layer 24 may not be sufficiently controlled. It is preferable that a layer containing more components derived from water, such as hydroxyl groups OH, than the inside of the underlayer 21 is not formed between the underlayer 21 and the magnetic layer 24.

[0034] (Magnetic layer formation process) The magnetic layer forming step S13 is a step of forming a magnetic layer 24 on the upper surface of the underlayer 21. The magnetic layer 24 is a multilayer film in which a first layer 24A of a transition metal such as Fe, Co, or Ni and a second layer 24B of a precious metal such as Pd or Pt are alternately laminated. As illustrated in FIG. 5C, three periods of the first layer 24A and the second layer 24B are formed with the second layer 24B as the lower layer. The magnetic layer 24 can be formed by, for example, a sputtering method. By successively carrying out the underlayer formation step S12 and the magnetic layer formation step S13 in the same vacuum, the magnetic layer 24 is formed in contact with the underlayer 21. Furthermore, by forming the underlayer 21 and the magnetic layer 24 from a common resist R1, it is possible to form the magnetic nanowire 10 in which the magnetic layer 24 is disposed with the same width as the upper surface of the underlayer 21, and the magnetic nanowire 10 including the magnetic layer 24 formed in contact with the underlayer 21 can be formed in a thin wire shape.

[0035] (Cap layer formation process) The cap layer forming step S14 is a step of forming a cap layer 27 on the upper surface of the magnetic layer 24. The cap layer 27 may be, for example, a thin film of a precious metal. The cap layer 27 may be formed by, for example, a sputtering method. It is preferable to continue the magnetic layer forming step S13 and the cap layer forming step S14 without breaking the vacuum. It is preferable to perform the underlayer forming step S12 to the cap layer forming step S14 continuously in the same vacuum. Then, after the cap layer forming step S14, the resist R1 is removed. Note that the resist R1 does not have to be removed immediately after the cap layer forming step S14.

[0036] The method S10 for forming the magnetic nanowire 10 including the above-mentioned steps uses a SiN X By first depositing the above and then successively depositing the ferromagnetic film and the ferrimagnetic film that form the magnetic layer 24 in the same vacuum, it is possible to form a magnetic nanowire 10 that has a large magnetic anisotropy, a sufficiently large coercive force, and high thermal stability even when the thickness of the magnetic layer 24 is made thin.

[0037] In addition, the magnetic material that constitutes the magnetic nanowire tends to deteriorate due to exposure to the atmosphere and infiltration of chemicals during microfabrication during the manufacturing process. The effects of such deterioration become greater as the magnetic nanowire becomes thinner, which can lead to reduced yields. The method for forming the magnetic nanowire 10, S10, is to form the underlayer 21, for example, SiN X By using a means for continuously forming the film and the ferromagnetic film forming the magnetic layer 24 in the same vacuum, it is possible to improve resistance to degradation factors in the manufacturing process. In addition, by making the film thickness of the magnetic layer 24 thin, the cross-sectional area is reduced, and the drive current ID can be suppressed. This can contribute to the manufacture of a power-saving magnetic nanowire memory 100 with high thermal stability while improving the yield.

[0038] [Modification of the method for forming magnetic nanowire] Next, a modified example of the method for forming a magnetic nanowire will be described with reference to Fig. 6 to Fig. 7D. The modified method for forming a magnetic nanowire S20 differs from the method for forming a magnetic nanowire S10 in that the underlayer 21S, the magnetic layer 24S, and the cap layer 27S are formed with a width wider than the pattern of the magnetic nanowire 10, and then processed into a nanowire shape. 6, the magnetic nanowire forming method S20 according to the modified example includes an underlayer forming step S21 for forming an insulating underlayer on one side of a substrate 80, and a magnetic layer forming step S22 for forming a magnetic layer on the upper surface of the underlayer, and the underlayer forming step S21 and the magnetic layer forming step S22 are performed continuously in the same vacuum. After the magnetic layer forming step S22, the magnetic nanowire forming method S20 includes a thinning step S24 for processing the formed layer into a thin nanowire. After the magnetic layer forming step S22 and before the thinning step S24, the magnetic nanowire forming method S20 may include a cap layer forming step S23 for forming a cap layer.

[0039] In the magnetic nanowire forming method S20 according to the modified example, the resist forming step does not need to be performed. The underlayer 21S, the magnetic layer 24S, and the cap layer 27S may be formed to have a width wider than the pattern of the magnetic nanowire 10 to be formed as a thin line, and may be formed, for example, in a planar shape. As illustrated in FIG. 7A, the resist forming step is not performed before the underlayer forming step S21, and in the underlayer forming step S21, the underlayer 21S is formed on the entire upper surface of the foundation layer 60, and the first layer 24AS and the second layer 24BS of the magnetic layer 24S, and the cap layer 27S are also formed to the same width. Except for the fact that no resist is provided, the underlayer forming step S21, the magnetic layer forming step S22, and the cap layer forming step S23 can be performed in the same manner as the method S10 for forming the magnetic nanowire 10 already described. The thinning step S24 will be described below. Note that Figures 7A to 7H exemplify cross sections in a direction perpendicular to the magnetic nanowire, similar to Figures 3 and 5A to 5D. Also, as an example, two magnetic nanowires are included.

[0040] (Thinning process) The thinning process S24 is a process for processing the formed underlayer 21S, magnetic layer 24S, and cap layer 27S into a thin wire shape that is the pattern of the magnetic wire 10. The thinning process S24 includes a shielding layer forming process S241 for forming the shielding layer R2 into a predetermined magnetic wire pattern, and a grinding process S242 for grinding each layer into the magnetic wire pattern using the shielding layer R2 as a resist.

[0041] The shielding layer forming step S241 is a step of forming the shielding layer R2 into a predetermined magnetic nanowire pattern. In the subsequent grinding step S242, the exposed portion of the shielding layer R2 is ground away. As illustrated in FIG. 7B, the shielding layer R2 is formed into a nanowire shape so as to match the predetermined magnetic nanowire pattern in a plan view. The material of the shielding layer R2 can be a known material used for photoresist or electron beam resist. The shielding layer R2 can be formed uniformly by, for example, a sputtering method, and then formed into a pattern of magnetic nanowires by photolithography or electron beam lithography and etching.

[0042] The grinding process S242 is a process for grinding the underlayer 21S, the magnetic layer 24S, and the cap layer 27S into a predetermined pattern of magnetic nanowires. The grinding process can be performed by an ion milling method in which the surface is ground by irradiating particles P1 such as ions using the shielding layer R2 as a resist. Here, argon ions are irradiated as the particles P1. The argon ions collide with the region exposed from the shielding layer R2. As illustrated in Fig. 7C, the cap layer 27S, the magnetic layer 24S, and the underlayer 21S are removed in this order from the upper surface side, and processed into the pattern of the shielding layer R2. 7D, after the grinding step, the shielding layer R2 is removed. Note that the shielding layer R2 does not have to be removed immediately after the grinding step S242.

[0043] The magnetic nanowire forming method S20 according to the modified example can form a magnetic nanowire 10 that has a sufficiently large coercive force and ensures high thermal stability even when the magnetic layer 24 is made thin, by continuously depositing the underlayer 21S and the magnetic layer 24S in the same vacuum.

[0044] As illustrated in FIG. 7E, the underlayer 21S may be left uncut in the grinding step S242. The magnetic layer 24 can be processed into a thin line shape while leaving the underlayer 21S uncut. The magnetic layer 24 has a width different from that of the upper surface of the underlayer 21S. Then, as illustrated in FIG. 7F, after the grinding step S242, the shielding layer R2 is removed. The magnetic thin line is formed on the upper surface of the insulating underlayer 21S with the thin line-shaped magnetic layer 24 in contact with the underlayer 21S. The underlayer 21S has a width wider than that of the magnetic layer 24, and is planar, for example. Here, the magnetic thin line further has a cap layer 27 having the same width as the magnetic layer 24, and the magnetic layer 24 and the cap layer 27 are formed into a thin line shape in a planar view. In addition, a plurality of thin line-shaped magnetic layers 24 and cap layers 27 are formed on the same underlayer 21S. In the case where the underlayer 21S is left unremoved, a magnetic nanowire memory can be provided which includes a magnetic nanowire on the upper surface side of the substrate 80, in which a nanowire-shaped magnetic layer 24 is formed on the upper surface of the insulating underlayer 21S in contact with the underlayer 21S, a recording element 40 arranged 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 30 arranged between the magnetic nanowire and the recording element 40.

[0045] Also, a separation layer forming step S25 may be provided for forming a separation layer 70 between the magnetic nanowires. The separation layer 70 is an insulating layer formed between the magnetic nanowires. As illustrated in FIG. 7H, the separation layer 70 covers the side surfaces of the magnetic layer 24 and the cap layer 27, and can be formed at a height equal to the height of the cap layer 27 from the upper surface of the underlayer 21S. By providing the separation layer 70, it is possible to improve the insulation between the side surfaces of the magnetic layer 24 and the cap layer 27. The separation layer 70 can be formed of, for example, SiO X and SiN X can be used as the material. The separation layer 70 can be formed by a lift-off method using the shielding layer R2 as a resist. First, as illustrated in Fig. 7G, after the grinding step S242, with the shielding layer R2 remaining, the separation layer 70 is formed on the upper surface of the base layer 21S by, for example, a sputtering method, so as to have the same height as the cap layer 27. Then, as illustrated in Fig. 7H, the portion formed on the upper surface of the shielding layer R2 is removed together with the shielding layer R2.

[0046] The separation layer 70 may be formed between the magnetic nanowires 10 in which the underlayer 21 has the same width as the magnetic layer 24. The separation layer 70 can be formed between the magnetic nanowires 10, covering the side surfaces of the underlayer 21, the magnetic layer 24, and the cap layer 27, and at a height equal to the height of the cap layer 27 from the upper surface of the base layer 60. The separation layer 70 can be formed by the lift-off method in the same manner from the state before the shield layer R2 is removed as illustrated in FIG. 7C. When the separation layer forming step S25 is provided, it is preferable to perform the steps from the base layer forming step S21 to the separation layer forming step S25 continuously without breaking the vacuum, which can further enhance the effect of controlling the crystal orientation.

[0047] [Second embodiment] Next, the magnetic fine wire memory 100B according to the second embodiment will be described with reference to FIG. 8 to FIG. 10. As illustrated in FIG. 8, the magnetic fine wire memory 100B includes a magnetic fine wire 10, a recording element 40, and an insulating layer 30 on the upper surface side of a substrate 80. Here, the magnetic fine wire memory 100B further includes a base layer 60, a reproducing head 50, a current control unit 92, and a reproducing processing unit 94. The magnetic fine wire memory 100B differs from the magnetic fine wire memory 100 according to the first embodiment in that the recording element 40 is disposed below the magnetic fine wire 10. Each component of the magnetic fine wire memory 100B will be described below.

[0048] (magnetic thin wire) 9B and 10, the magnetic nanowire 10 of the magnetic nanowire memory 100B is disposed on the upper surface of the insulating layer 30. Therefore, the underlayer 21 is formed on the upper surface of the insulating layer 30. The other points are common to the magnetic nanowire 10 of the magnetic nanowire memory 100.

[0049] (Base layer) The base layer 60 is disposed on the substrate 80, and the insulating layer 30 is disposed on the upper surface of the base layer 60. The base layer 60 has a groove portion 65 in which the recording element 40 is embedded, and the upper surface of the base layer 60 is a flat surface except for the groove portion 65. The material of the base layer 60 is the same as that of the magnetic nanowire memory 100. The base layer 60 can be formed by depositing a film using a known method such as a sputtering method. The groove portion 65 can be formed by an etching method or the like.

[0050] (Recording element) The recording element 40 is disposed below the magnetic wire 10 so as to intersect with the magnetic wire 10 in a planar view, and a recording current ID is applied to magnetize the magnetic wire 10. The recording element 40 is disposed below the magnetic wire 10 via an insulating layer 30. The recording element 40 can be disposed so as to be embedded in the groove portion 65 of the base layer 60 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 memory 100, and may be processed in the same manner. The recording element 40 may be formed by forming grooves 65 in the base layer 60 by photolithography or electron beam lithography and an etching method, plating with a metal material, and filling the metal material in the grooves 65.

[0051] (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 upper surfaces of the base layer 60 and the recording element 40. The upper surface of the insulating layer 30 may be a flat surface. The material of the insulating layer 30 is the same as that of the magnetic nanowire memory 100. The reproducing head 50, the substrate 80, the current control section 92, and the reproducing processing section 94 are common to the magnetic nanowire memory 100. The method of forming the magnetic nanowire in the second embodiment can be performed in the same manner as the magnetic nanowire memory 100.

[0052] The magnetic nanowire memory 100B having the above-mentioned configuration can reduce the driving current ID by thinning the film thickness of the magnetic nanowire 10 while maintaining the coercive force of the magnetic nanowire 10, thereby achieving power saving, similar to the magnetic nanowire memory 100. In addition, in the magnetic nanowire memory 100B, as described in the modified example of the method for forming the magnetic nanowire, each layer can be formed wider than the pattern of the magnetic nanowire 10 and then cut into a thin wire, with the underlayer 21S remaining uncut to form a magnetic nanowire.

[0053] [Modification of the second embodiment] Next, a first modified example of the second embodiment will be described with reference to Fig. 11A. Fig. 11A is a cross-sectional view of the magnetic nanowire 10 and the layers below it in the first modified example. The magnetic nanowire memory according to the first modified example includes, on the upper surface side of a substrate 80, the magnetic nanowire 10 and a recording element 40 disposed directly below the magnetic nanowire 10 so as to intersect with the magnetic nanowire 10 in a plan view and to which a recording current IR is applied to magnetize the magnetic nanowire 10.

[0054] 11A, the first modified example of the second embodiment differs from the magnetic nanowire memory 100B according to the second embodiment in that the insulating layer 30 is not disposed between the magnetic nanowire 10 and the recording element 40. The magnetic nanowire 10 of the first modified example is disposed on the upper surface of the base layer 60, and is disposed on the upper surface of the recording element 40 at the position where the recording element 40 is disposed. That is, the underlayer 21 faces the base layer 60 and the recording element 40. The underlayer 21 provides insulation between the magnetic layer 24 of the magnetic nanowire 10 and the recording element 40. For this reason, the underlayer 21 of the first modified example is preferably formed thicker than the case where the insulating layer 30 is included. The thickness of the underlayer 21 of the first modified example can be, for example, 10 nm or more and 30 nm or less. The magnetic nanowire in the first modified example can be formed in the same manner as the magnetic nanowire memory 100.

[0055] In the first modified example, as explained in the modified example of the method for forming the magnetic nanowire, the magnetic nanowire may be formed by forming each layer wider than the pattern of the magnetic nanowire 10 and then cutting it into a thin line shape, and the underlayer 21S may be left without being cut. This allows the underlayer 21S to be planar, for example, and the magnetic layer 24 and the cap layer 27 to be formed into a thin line shape, as in the magnetic nanowire of the second modified example illustrated in FIG. The magnetic nanowire of the second modification has a thin magnetic layer 24 formed on the upper surface of an insulating underlayer 21S in contact with the underlayer 21S. The magnetic nanowire memory according to the second modification includes a magnetic nanowire on the upper surface side of a substrate 80, the thin magnetic layer 24 formed on the upper surface of the insulating underlayer 21S in contact with the underlayer 21S, and a recording element 40 disposed directly below the underlayer 21S so as to intersect with the magnetic nanowire in a plan view, and to which a recording current IR is applied to magnetize the magnetic nanowire. The lower surface of the underlayer 21S faces the base layer 60 and the recording element 40. EXAMPLES

[0056] Next, examples of the present invention will be described below. Note that the present invention is not limited to the following examples. Here, as an example, a magnetic nanowire made of SiN X This will be described as an experiment conducted to confirm the improvement in coercivity due to the provision of the underlayer 21. In the experiment, two types of experimental devices were fabricated, one with the underlayer 21 and the other with the underlayer 21, and the coercivity was compared. Note that the magnetic nanowire with the underlayer provided will be described as an example, and the magnetic nanowire without the underlayer provided will be described as a comparative example.

[0057] (Example) A Si substrate was used as the substrate 80. The base layer 60 was formed by thermally oxidizing the surface of the Si substrate to form SiO X A film was formed. The magnetic nanowire 10 of the embodiment has an underlayer 21, a magnetic layer 24, and a cap layer 27, as illustrated in FIG. 3. The width of the magnetic nanowire 10 is 3 μm. The underlayer 21 is a silicon nitride thin film with a thickness of 5 nm. The magnetic layer 24 is a Co / Tb multilayer film in which Tb with a thickness of 0.55 nm and Co with a thickness of 0.3 nm are alternately laminated for three periods. The cap layer 27 is a Pt thin film with a thickness of 1 nm. That is, the film configuration of the embodiment is, from the upper layer side of the magnetic nanowire 10, Pt (1 nm) / [Co (0.3 nm) / Tb (0.55 nm)]. 3 / SiN X (5nm) / SiO X Base layer / Si substrate. In the embodiment, the underlayer 21 is SiN X After forming the thin film, the Co / Tb multilayer film of the magnetic layer 24 was continuously formed in the same vacuum.

[0058] (Comparative Example) The substrate and base layer are the same as in the example. The magnetic nanowire of the comparative example has a magnetic layer and a cap layer, but does not have an underlayer. The widths of the magnetic layer, the cap layer, and the magnetic nanowire are the same as those of the example. The film configuration of the comparative example is, from the upper layer of the magnetic nanowire, Pt (1 nm) / [Co (0.3 nm) / Tb (0.55 nm)] 3 / SiO X Base layer / Si substrate.

[0059] (Measurement method and results) The external magnetic field-Kerr rotation angle characteristics were measured for the comparative example and the example. The measurements were performed using a micro Kerr loop measuring device manufactured by NeoArc Corporation. The measurement results for the comparative example are shown in Fig. 12A. The measurement results for the example are shown in Fig. 12B. From Fig. 12A, the coercive force of the comparative example was approximately 200 Oe, and from Fig. 12B, the coercive force of the example was approximately 500 Oe.

[0060] (Consideration) In both the comparative example and the working example, the magnetic layer is thinned to reduce power consumption. 4 / SiO XIn the comparative example and the embodiment, the thickness of each layer in the magnetic layer is reduced and the repetition period is shortened, while the base layer / Si substrate is thin. The cap layer is also thinner than the conventional one. The comparative example has a coercive force of about 200 Oe, which is insufficient for the operation of a magnetic nanowire memory. In contrast, the embodiment has a magnetic layer with the same film structure as the comparative example, but the SiN X The coercive force is improved by providing the underlayer 21. The magnetic nanowire 10 of the embodiment was able to achieve a coercive force close to 500 Oe, which is considered to be optimal for the operation of a magnetic nanowire memory. The magnetic nanowire 10 of the embodiment can achieve power saving while ensuring the coercive force required for a magnetic nanowire memory.

[0061] 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. [Explanation of symbols]

[0062] 10 Magnetic thin wire 10A magnetic domain formation area 10B storage area 10C boundary 15 magnetic domains 21 Base layer 24 Magnetic layer 27 Cap Layer 30 Insulating layer 40 Recording element 50 Playhead 60 Foundation Layer 80 Substrate 100 Magnetic nanowire memory (first embodiment) 100B Magnetic nanowire memory (second embodiment)

Claims

1. An insulating underlayer; a magnetic layer formed on the upper surface of the underlayer and in contact with the upper surface of the underlayer with the same width as the upper surface of the underlayer, A magnetic nanowire that is formed into a thin line shape in a plan view.

2. 2. The magnetic nanowire according to claim 1, wherein the underlayer is made of silicon nitride.

3. 3. The magnetic nanowire according to claim 2, wherein the thickness of the underlayer is 3 nm or more and 30 nm or less.

4. On the top side of the board A magnetic nanowire according to any one of claims 1 to 3; 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.

5. On the top side of the board A magnetic nanowire according to any one of claims 1 to 3; 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.

6. On the top side of the board A magnetic nanowire according to any one of claims 1 to 3; a recording element disposed directly 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.

7. a base layer forming step of forming an insulating base layer on one surface of the substrate; a magnetic layer forming step of forming a magnetic layer on the upper surface of the underlayer, The method for forming a magnetic nanowire comprises carrying out the underlayer forming step and the magnetic layer forming step consecutively in the same vacuum.

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