Thin-film inductor element, thin-film variable inductor element, and method for using laminated thin-film element

Abstract

The purpose of the present invention is to provide a thin-film inductor element which, when mounted in a circuit, can exhibit a sufficient emission inductance function while reducing an operation current. A thin-film inductor element is provided with a laminated film in which a magnetic layer and a non-magnetic layer are laminated, and a pair of electrodes, the magnetic layer and the non-magnetic layer extending in an arbitrary shape in a direction orthogonal to the lamination direction, the magnetic layer having substantially the same magnetization structure including components in the lamination direction, and the non-magnetic layer having substantially the same magnetization structure including components in the lamination direction. The non-magnetic material layer is an insulator and has a conductive surface, and the pair of electrodes is provided near both ends of the laminated film extending and at least in positions in contact with the surface of the non-magnetic material layer, and a current modulated at a frequency of 1 kHz to 1 GHz is applied to the pair of electrodes.

Description

Technical Field

[0001] The present invention relates to a thin-film inductor element, a thin-film variable inductor element, and a method of using a stacked thin-film element. Background Art

[0002] As an element that uses the induced electromotive force generated in a coil to keep the circuit current constant, an inductor element is known. The first use of the inductor element is considered to be a transformer for performing voltage transformation. On the other hand, the inductor element is also used as a filter or the like in a high-frequency circuit in a small electrical device or circuit. Circuit elements used in various electronic devices such as portable communication terminals are required to be miniaturized / micro-miniaturized. Naturally, the same requirement specifications are imposed on the inductor element. On the other hand, in order to achieve the desired functional characteristics, a certain size of inductance, which is the strength of the inductor element, is required. However, since the inductance is proportional to the square of the number of turns of the coil and the cross-sectional area of the coil, there is a trade-off relationship between the inductance strength and miniaturization. Therefore, there is a natural limit to the miniaturization of the inductor element.

[0003] In this situation, in the case where miniaturization of the inductor element required for miniaturization of an electrical device or circuit is expected, in recent years, the principle of an emergent inductor, which is an inductor element that utilizes an emitted electromagnetic field generated by spintronics technology, has been clarified and successfully demonstrated. As Figure 8 shown, the conventional induction coil has a trade-off relationship such as inductance strength and miniaturization. In contrast, the emergent inductor disclosed in Non-Patent Document 1 does not have such a trade-off relationship. Instead, the cross-sectional area of the element is inversely proportional to the inductance, and it has the property that the inductance increases as it is miniaturized. Therefore, the emergent inductor is expected to make a great contribution to miniaturization.

[0004] However, in order for the emergent inductor to generate an inductance based on the emitted electromagnetic field, a non-collinear magnetic structure such as a spiral magnetic structure (refer to Figure 8 ) or a horizontal conical magnetic structure must be formed. In Non-Patent Document 1, it was confirmed that a non-collinear magnetic structure was formed by using Gd3Ru4Al 12 . However, since Gd3Ru4Al 12 is hardly a general material, the emergent inductor needs to select materials to achieve the above structure. And even if the problem of selecting appropriate materials is solved, crystal orientation control is required to form a spiral magnetic structure. In addition to this, through previous research, it has also been found that the temperature dependence of the element performance is high.

[0005] In order to fundamentally solve the problems of such previous research, magnetic materials with spatially identical magnetic structures were attempted instead of relying on non-collinear magnetic structures to exhibit an out-of-plane inductance function. In Non-Patent Document 2, in addition to the exchange interaction as a quantum effect, the spin-orbit interaction as a quantum relativistic effect was also focused on. Through the combined action of these effects, it was theoretically clarified that in a non-distorted system, that is, a magnetic body with magnetic moments facing the same direction, an out-of-plane inductor was found for both the wire and the magnetic moment.

[0006] Prior Art Documents

[0007] Non-Patent Documents

[0008] Non-Patent Document 1: Tomoyuki Yokouchi, Fumitaka Kagawa, Max Hirschberger, Yoshichika Otani, Naoto Nagaosa & Yoshinori Tokura "Emergent electromagnetic induction in a helical-spin magnet", Nature, Vol. 586, 8 October 2020

[0009] Non-Patent Document 2: Yuta Yamane, Shunsuke Fukami, & Jun’ichi Ieda "Theory of Emergent Inductance with Spin-Orbit Coupling Effects”, DOI: 10.1103 / PhysRevLett.128.147201 Summary of the Invention

[0010] Technical Problem to be Solved by the Invention

[0011] However, in the non-distorted system proposed in Non-Patent Document 2, there are the following problems: Although the manifestation of the out-of-plane inductor was found, an operating current of a certain magnitude is required for the spin of the magnetic body to be driven, which reduces the effectiveness when installed in a circuit.

[0012] To solve this problem, the invention problem of the present invention is to provide a thin-film inductor element that can exhibit a sufficient out-of-plane inductance function while reducing the operating current when installed in a circuit.

[0013] Means for Solving the Technical Problem

[0014] The thin-film inductor element of the present invention has at least the following structure.

[0015] The thin-film inductive element is characterized in that it includes a laminated film formed by laminating a magnetic layer and a non-magnetic layer, and a pair of electrodes. The magnetic layer and the non-magnetic layer extend in a direction orthogonal to the lamination direction in an arbitrary shape. The magnetic layer has a substantially identical magnetization structure including a component in the lamination direction. The non-magnetic layer is an insulator and has a conductive surface structure. The pair of electrodes are disposed near both ends where the laminated film extends and at least in contact with the surface of the non-magnetic layer, and are applied with a current modulated at a frequency of 1 kHz to 1 GHz.

[0016] Moreover, the thin-film inductor element of the present invention at least has the following structure.

[0017] The thin-film inductive element is characterized in that it includes a laminated film formed by laminating a magnetic layer and a non-magnetic layer, and a pair of electrodes. The magnetic layer and the non-magnetic layer extend in a direction orthogonal to the lamination direction in an arbitrary shape. The magnetic layer has a substantially identical magnetization structure including a component in the lamination direction. The pair of electrodes are disposed near both ends where the laminated film extends and at least in contact with the surface of the non-magnetic layer, and are applied with a current modulated at a frequency of 1 kHz to 1 GHz. The non-magnetic layer is a topological insulator layer whose composition ratio is adjusted such that the Fermi energy of electrons is within the gap between the conduction band and the valence band, or is a topological insulator layer whose gate voltage is adjusted such that the Fermi energy of electrons is within the band gap between the conduction band and the valence band.

[0018] Moreover, the thin-film variable inductance element of the present invention at least has the following structure.

[0019] The thin-film variable inductance element is characterized in that it includes a laminated film formed by laminating a magnetic layer and a non-magnetic layer, a pair of electrodes for applying a current modulated at a frequency of 1 kHz to 1 GHz, and a thin-film coil surrounding the laminated film. The magnetic layer and the non-magnetic layer extend in a direction orthogonal to the lamination direction in an arbitrary shape. The magnetic layer has a magnetization structure including a component in the lamination direction. The non-magnetic layer is an insulator and has a conductive surface structure. By switching the switch of the thin-film coil and / or the direction of the current to control the external magnetic field, an inductance modulation operation is achieved.

[0020] Furthermore, the method of using the laminated thin-film element of the present invention at least has the following structure.

[0021] A method of using a laminated thin-film element as an inductive element, wherein the laminated thin-film element is characterized by including a laminated film formed by laminating a magnetic layer and a non-magnetic layer, a pair of electrodes, and a gate electrode. The magnetic layer and the non-magnetic layer extend in a direction orthogonal to the lamination direction in an arbitrary shape. The magnetic layer has a substantially identical magnetization structure including a component in the lamination direction. The non-magnetic layer is a topological insulator. The pair of electrodes are disposed near both ends where the laminated film extends and at positions where they are at least in contact with the surface of the non-magnetic layer. The method is characterized by including the following steps: a step of applying a voltage adjusted such that the Fermi energy of electrons is within the band gap between the conduction band and the valence band to the gate electrode; and a step of applying a current modulated at a frequency of 1 kHz to 1 GHz to the pair of electrodes.

[0022] What these inventions have in common is that the "laminated film" of course includes a bilayer film composed of a magnetic layer and a non-magnetic layer. In addition to this, it also includes a film to which an additional film such as a base layer or a spacer layer is added. And the "arbitrary shape" means that it can be any shape such as a square, a circle, an ellipse, a rectangle, etc., but it is intended that an inductance can be exhibited even if an arbitrary shape is selected. And the "pair of electrodes are disposed near both ends where the laminated film extends and at positions where they are at least in contact with the surface of the non-magnetic layer" means that it includes either a manner of contacting the surface of the non-magnetic layer from the side or a manner of contacting the surface of the non-magnetic layer from above. Moreover, the "substantially identical magnetization structure including a component in the lamination direction" does not refer to a non-collinear magnetic structure such as a helical magnetic structure or a horizontal conical magnetic structure which is a necessary condition for realizing an out-of-plane inductance in Non-Patent Document 1, but refers to a magnetic structure in which adjacent magnetic moments are arranged in a collinear manner. However, it means that it has a component parallel to the lamination direction as its component. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a perspective view showing the structural concept of a thin-film inductive element according to the first embodiment of the present invention.

[0024] Figure 2 It is an explanatory view showing the inductive operation of a thin-film inductive element according to the first embodiment of the present invention.

[0025] Figure 3 It is a perspective view showing the structural concept of a thin-film inductive element according to the second embodiment of the present invention.

[0026] Figure 4 It is a perspective view showing the structural concept of a thin-film inductive element according to the third embodiment of the present invention.

[0027] Figure 5This is a perspective view showing the structural concept of the thin-film variable inductor element according to the fourth embodiment of the present invention.

[0028] Figure 6 This is a diagram for explaining the inductance modulation operation of the thin-film variable inductor element according to the fourth embodiment of the present invention.

[0029] Figure 7 This is a graph comparing the characteristics of the energy efficiency (Q value) between the thin-film inductor element according to the embodiment of the present invention and the conventional inductor element.

[0030] Figure 8 This is a diagram for explaining by comparing a conventional induction coil and an emitter inductor. Detailed Embodiments

[0031] The thin-film inductor element and the thin-film variable inductor element according to the embodiments of the present invention utilize spintronics technology and an emitted electromagnetic field. More specifically, the embodiments of the present invention use a combination of spin-orbit torque (SOT: Spin-orbit torque) and its inverse process, which have been studied and developed in the field of magnetoresistive memories and the like, as an inductor.

[0032] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. However, the following drawings are conceptual diagrams prepared for explanation, and for ease of understanding, sometimes components that are not necessary for the explanation are not shown schematically. Also, for ease of explanation, sometimes components are shown schematically enlarged or reduced, and the drawings do not represent an accurate scale. That is, it should be noted that they do not necessarily represent the implemented embodiments themselves.

[0033] (First Embodiment)

[0034] Figure 1 This is a perspective view showing the structural concept of the thin-film inductor element according to the first embodiment of the present invention. The thin-film inductor element 1 is formed by a stacked film formed by sequentially stacking a magnetic layer 11 and a non-magnetic layer 12 from top to bottom on the paper surface. The magnetic layer 11 has a substantially identical magnetization structure including a stacking direction component. On the other hand, the non-magnetic layer 12 is an insulator and has a conductive surface structure. The thin-film inductor element 1 extends in the left-right direction on the paper surface, and drive electrodes D-EL are provided at both ends thereof, and a current modulated at a frequency of 1 kHz to 1 GHz is applied. The driving current in the first embodiment is a general sine-wave current, and it can also be a pulse wave or a triangular wave signal. In the first embodiment, the drive electrodes D-EL are arranged at positions including the boundary position between the magnetic layer 11 and the non-magnetic layer 12. This is because it is necessary to pass the driving current on the surface of the non-magnetic layer 12.

[0035] Here, the vertical relationship between the magnetic layer 11 and the non-magnetic layer 12 is arbitrary. Even if the vertical positions shown in the figure are replaced, it can function as an inductor under the same conditions. However, considering common modularization with the thin-film variable inductor element described later, it is advantageous to set the vertical relationship as shown in the figure. As long as the direction of magnetization of the magnetic material is a direction including a component in the stacking direction, it will exhibit the function of an inductor. However, in the first embodiment, in order to obtain a large inductance, it is set to have stable magnetic anisotropy in the direction parallel to the stacking direction. Also, as long as it is a non-magnetic layer capable of exhibiting spin-orbit torque, it will exhibit the inductance function. However, considering installation in a circuit, in order to reduce the operating current, the non-magnetic layer 12 in the first embodiment is an insulator and its surface has a conductive structure. For example, it is set as a topological insulator layer.

[0036] (Method for manufacturing a thin-film inductor element)

[0037] First, a topological insulator film is manufactured by molecular beam epitaxy, and then a magnetic film is deposited on it by ultra-high vacuum sputtering. After the thin film is deposited, heat treatment can be performed in a magnetic field. In the thin-film inductor element 1 according to the present embodiment, treatment was performed for 2 hours in an atmosphere of 300°C. However, the method shown here does not limit the manufacturing method. Of course, even if it does not rely on this film-forming method, as long as it can manufacture Figure 1 the stacked film shown in

[0038] (Principle of inductive operation)

[0039] Here, Figure 2 the principle of inductive operation of the thin-film inductor element 1 according to the first embodiment will be described. The inductive operation is achieved by alternately Figure 2 the spin torque process shown in (a) and Figure 2 the spin electromotive force process shown in (b). If it is understood as a spintronics version of Lenz's law of electromagnetic induction, such as when an induced current is generated for some reason, the direction of current flow is the same as the direction of the cause that obstructs the induced current, it is easy to understand. Hereinafter, a specific description will be given.

[0040] First, in the spin torque process, a current is introduced into the thin-film inductor element 1 according to the first embodiment. At this time, spins in the depth direction of the paper surface are accumulated at the interface between the magnetic layer and the non-magnetic layer, and the spin-orbit torque acts on the magnetization of the magnetic layer. As a result, the magnetization direction tilts from the substrate-perpendicular direction (vertical and horizontal directions of the paper surface) where the energy is stable. The mechanism of spin accumulation can be explained by the effect of spin-orbit coupling that generates an effective electric field at the interface between the magnetic layer and the non-magnetic layer and converts the momentum and spin polarization of conduction electrons with each other. Figure 2The figure shows the relationship between current and spin torque manifested by the effect of spin-orbit coupling at the interface. In Figure 2 it, when the current flows in the right direction, a torque that tilts the magnetization in the right direction acts (conversely, when the current flows in the left direction, a torque that tilts the magnetization in the left direction acts). When the current flows through the interface, due to the effect of spin-orbit coupling, electrons exhibit spin polarization corresponding to the direction of the current, and this spin polarization generates a spin-orbit torque on the magnetization of the magnetic layer. That is, by reversing the direction of the current at the interface, the direction of the spin-orbit torque acting on the magnetization of the magnetic layer can be reversed. Therefore, by inputting an alternating current, an alternating torque is generated. And if the current introduced into the inductor is alternating, the magnetization of the magnetic layer precesses at the alternating frequency of the input current.

[0041] Next, in the spin electromotive force process, the magnetization tilted from the energy-stable substrate perpendicular direction causes precession of the magnetization originating from the stored magnetic energy. Thereby, spin polarization is generated in the electrons at the interface, and through spin-orbit coupling, a counter current is generated in the direction that cancels the current introduced into the inductor. As a result, the sum of the introduced current and the counter current flows in the inductor, thereby realizing the function of preventing current change (inductor).

[0042] (Materials, dimensions, and shapes considered appropriate)

[0043] From the above, it can be understood that for the non-magnetic layer, applying a spin-orbit torque to the magnetic layer becomes an absolute requirement. Moreover, considering its installation in a circuit, as long as its surface is a conductive insulator, for example, a topological insulator can be used. As a representative example of a specific composition, a substance composed of one or two of Bi and Sb and one or two of Se and Te can be used. If written as a composition formula, it is (Bi,Sb)2(Te,Se)3. In addition to this composition formula, if a substance showing the properties of a topological insulator is used for the non-magnetic layer, the present invention can also be realized. Specifically, Bi 1-x Sb x , HgTe / CdTe bilayer film, CaAgAs, etc. are exemplified. Generally, by changing the composition ratio of the topological insulator, the overall number of carriers changes, so it is possible to adjust the surface conductivity while suppressing the overall conduction. It is reported that, for example, in the composition of Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 the overall resistivity is 140 mΩcm and the surface carrier mobility is 2900 cm 2 V -1 s -1, shows good characteristics as a topological insulator. Different from the second embodiment described later, in the first embodiment without a gate electrode, the composition ratio of the topological insulator is adjusted so that the Fermi energy of electrons falls within the band gap between the conduction band and the valence band in the topological insulator (Bi,Sb)2(Te,Se)3, which is about 100 - 500 meV. Thereby, the overall insulation and surface conduction of the topological insulator are ensured. As the film thickness, 5 nm or more is required. If it is too thin, the surface state will not appear, the surface and the inside will be mixed, and there will be no difference in properties. And when the film thickness is too thick, it will also become a useless thickness part that is not helpful for the manifestation of inductance. Therefore, as the film thickness, it is preferably selected within the range of 5 nm to 10 nm. In addition, previous studies have shown that at a film thickness of about 10 nm, the states of the surface and the inside will be sufficiently separated.

[0044] On the other hand, the magnetic layer is composed of a ferromagnetic material, a ferrimagnetic material, and an antiferromagnetic material (note: the stacked film can also be composed of two layers of antiferromagnetic layers), which is a material including Fe, Co, Ni, and Mn. Since it is required to have a perpendicular easy magnetization axis, specifically, Co / Ni, Co / Pt, Co / Pd, Co / Au, Fe / Au stacked films, Co-Pt, Co-Cr-Pt, Co-Pd, Fe-Pt, Fe-Pd, Fe-Co-Pt, Fe-Co-Pd alloys, CoFeB, FeB alloys, etc. can be used. For example, [Co / Ni] / Ta / CoFeB can also be set as a stacked structure. The thinner the film thickness of the magnetic material, the higher the obtained inductance, but it is necessary to ensure the film thickness for magnetic manifestation. And if the film thickness is increased, it will become a useless area, which is the same as the non-magnetic layer. Thus, the film thickness of the magnetic layer is preferably selected within the range of several nm to 30 nm.

[0045] In addition, if the magnetic layer is made an insulator, the current will flow more concentratedly at the interface of the stacked film, so it is advantageous. In this case, a topological insulator [(Bi,Sb)2(Te,Se)3] doped with about 10% of a rare earth iron garnet R3Fe5O 12 (R is a rare earth element, that is, Y, Gd, Tb, etc.) and magnetic elements (Fe, Ni, Cr, Mn, etc.) can be adopted.

[0046] If the shapes of the respective films of the bilayer film are set to the same shape, as the planar shape of the stacked film, even if any shape such as a square, a circle, an ellipse, or a rectangle is selected, inductance can be manifested. However, considering actual processing, it is advantageous to select a rectangle.

[0047] Also, in the figure, the inductive element is shown as being composed of two layers, a magnetic layer and a non-magnetic layer. In reality, however, it may also be a laminated film formed by providing a base layer for forming these layers to obtain desired characteristics during the manufacturing process, or a covering layer for protecting the element during the microfabrication process, etc.

[0048] (Advantageous effects over the prior art: manufacturing cost, usage environment)

[0049] Using the principle of classical electromagnetism, the inductance when manufacturing an inductor of the same size with an air-core solenoid coil is estimated as follows.

[0050] Assume that the length of the inductor is 100 μm, the width is 100 nm, and the thickness is 10 nm. For the winding density of the solenoid coil, as a value that can be achieved with existing microfabrication techniques, assume 1 turn per 100 nm. Regarding the inductance L of the solenoid coil, if the magnetic permeability is set as μ0, the winding density is set as n, the length is set as l, the width is set as W, and the thickness is set as t, then it is given by L = μ0n 2 lWt, and 0.013 nH is obtained.

[0051] On the other hand, the inductive element based on the principle of the present invention can be realized only by processing the laminated film into a thin wire shape. Therefore, compared with a classical inductor, the manufacturing cost is significantly suppressed. That is, the thin-film inductive element according to the embodiment of the present invention can achieve an inductance equal to or better than that of a conventional classical inductor at an extremely low cost.

[0052] From the viewpoint of cost savings, the thin-film inductive element according to the embodiment of the present invention is also advantageous for an emitting inductor that utilizes a combination of spin-transfer torque (STT: Spin-transfer torque) and spin electromotive force as its reverse process. As described above, the emitting inductor must form a non-collinear magnetic structure such as a helical magnetic structure, but the material showing this structure is a special material and is not suitable for mass production. Also, it is necessary to align the helical axis through crystal orientation control, etc. Moreover, the axis of magnetization rotation of the helical magnetic structure is determined by the crystal orientation. Therefore, in order to function as an inductor, it is necessary to make the current flow in a specific axial direction of the crystal, and the effect becomes smaller or completely disappears in axial directions other than this. Meeting these many conditions and obtaining the desired inductance requires corresponding costs.

[0053] In contrast, in the thin-film inductive element according to the embodiment of the present invention (including the second to fourth embodiments described later in addition to the first embodiment), a standard magnetic material having a collinear magnetic structure can be used. In addition, through the double-film structure, the easy magnetization axis is determined to be perpendicular to the film surface, and the element can be fabricated by simple film formation and the inductance can be achieved at an extremely low cost.

[0054] Moreover, the thin-film inductor element according to the embodiments of the present invention (the first embodiment and the following second to fourth embodiments) uses an insulator with a conductive surface of a non-magnetic layer, and the Q value representing the energy efficiency of the inductor element is significantly improved, exerting a special effect. This will be described in detail later.

[0055] Regarding the emitting inductor, from other viewpoints, there are also advantages in terms of effects. According to previous research, the emitting inductor uses Gd3Ru4Al 12 and other slightly special materials, and shows inductance in a cryogenic state below 16K, etc., but does not show the inductance function in a temperature range higher than that. Of course, materials that show the inductance function in a higher temperature region may be discovered in the future, but since it is limited to the temperature region showing a non-collinear magnetic structure including helical magnetism on the magnetic state phase diagram, there are still restrictions on the operating ambient temperature. In any case, there are significant obstacles to its use at normal temperature or higher temperature regions.

[0056] In contrast, the thin-film inductor element according to the embodiments of the present invention functions fully at normal temperature. Therefore, the thin-film inductor element according to the embodiments of the present invention has less hindrance in terms of practical application.

[0057] (Second Embodiment)

[0058] Figure 3 FIG. is a perspective view showing the structural concept of the thin-film inductor element 2 according to the second embodiment of the present invention. A magnetic layer 21 and a non-magnetic layer 22 are stacked in order from top to bottom on the paper surface, and a barrier layer 23 made of an insulator is stacked on the lower surface of the non-magnetic layer 22. As materials, MgO, Al2O3, AlN, etc. can be cited, but importantly, perpendicular magnetic anisotropy is exhibited through the interface magnetic anisotropy between the barrier layer 23 and the non-magnetic layer 22. From this viewpoint, CoFeB / MgO and FeB / MgO are preferred.

[0059] Moreover, a gate electrode G-EL made of a metal is also stacked on the lower surface of the barrier layer 23. As materials, metals with good conductivity such as Ta, Ru, Cu, etc. are preferred. As the shape of the gate electrode G-EL, it is set to be located inside the barrier layer in the horizontal plane. This is to prevent the gate electrode G-EL from short-circuiting with the inductor.

[0060] The thin-film inductor element 2 is formed by laminating these four films: the magnetic layer 21, the non-magnetic layer 22, the barrier layer 23, and the gate electrode G-EL. The magnetic layer 21 has a magnetization structure that is substantially the same in the direction of the lamination direction component. On the other hand, the non-magnetic layer 22 is an insulator and has a conductive surface structure. The thin-film inductor element 2 extends in the left-right direction on the paper surface, and drive electrodes D-EL are provided at both ends thereof, and a current modulated at a frequency of 1 kHz to 1 GHz is applied. The drive current can be a pulse wave or a triangular wave signal in addition to a general sine wave current. In the second embodiment, the drive electrode D-EL is disposed at a position including the boundary position between the magnetic layer 21 and the non-magnetic layer 22. This is because it is necessary to pass the drive current on the surface of the non-magnetic layer 22.

[0061] As long as the direction of magnetization of the magnetic material includes the direction of the lamination direction component, it exhibits the function of an inductor. However, in the second embodiment, in order to obtain a large inductance, it is set to have stable magnetic anisotropy in the direction parallel to the lamination direction. And as long as it is a non-magnetic layer capable of exhibiting spin-orbit torque, it exhibits an inductance function. However, considering its installation in a circuit, in order to reduce the operating current, the non-magnetic layer 22 in the second embodiment is an insulator and has a conductive surface structure. For example, it is set as a topological insulator layer.

[0062] In the first embodiment, the composition ratio was adjusted so that the Fermi energy of electrons fell within the band gap between the conduction band and the valence band. However, in the second embodiment, it is adjusted to fall within the gap by applying a gate voltage. This is because, instead of or in addition to the previous adjustment of the composition ratio, the overall insulation and the surface conductivity of the non-magnetic layer can also be adjusted by applying a gate voltage.

[0063] (Third Embodiment)

[0064] Figure 4 FIG. is a perspective view showing a structural concept of a thin-film inductor element 3 according to the third embodiment of the present invention. A magnetic layer 31 and a non-magnetic layer 32 are laminated in order from the top to the bottom on the paper surface, and a barrier layer 33 made of an insulator is laminated on the lower surface of the non-magnetic layer 32. As materials, MgO, Al2O3, AlN, etc. can be cited. However, importantly, perpendicular magnetic anisotropy is exhibited through the interfacial magnetic anisotropy between the barrier layer 33 and the non-magnetic layer 32. From this viewpoint, CoFeB / MgO, FeB / MgO are preferable.

[0065] Further, a gate electrode G-EL made of metal is also stacked on the lower surface of the barrier layer 33. As the material, metals with good conductivity such as Ta, Ru, Cu, etc. are preferred. As the shape of the gate electrode G-EL, it is set to be located inside the barrier layer in the horizontal plane. This is to prevent the gate electrode G-EL from short-circuiting with the inductor.

[0066] The thin-film inductor element 3 is formed by these four stacked films of the magnetic layer 31, the non-magnetic layer 32, the barrier layer 33, and the gate electrode G-EL. The magnetic layer 31 has a substantially identical magnetization structure including the stacking direction component. On the other hand, the non-magnetic layer 32 is an insulator and its surface has a conductive structure. The thin-film inductor element 3 extends in the left-right direction of the paper surface, and drive electrodes D-EL are provided on the surfaces near both ends and parallel to the interface between the magnetic layer 31 and the non-magnetic layer 32. Since the surface of the non-magnetic layer 32 is conductive and the side surfaces are also conductive, the electrode structure of the first and second embodiments can be adopted. However, since the electrodes also have a certain size, it is undoubtedly more advantageous for the ease of configuration / processing to be arranged on a surface with a certain area. The drive electrodes D-EL of the third embodiment are arranged on the surface of the non-magnetic layer 32 as described above. A current modulated at a frequency of 1 kHz to 1 GHz is applied to the drive electrodes D-EL. In addition to the general sinusoidal current, the drive current can also be a pulse wave or a triangular wave signal.

[0067] As long as the direction of magnetization of the magnetic body is a direction including the stacking direction component, it will exhibit the function of an inductor. However, in the third embodiment, in order to obtain a large inductance, it is set to have a stable magnetic anisotropy in the direction parallel to the stacking direction. And as long as it is a non-magnetic layer capable of exhibiting spin-orbit torque, it will exhibit the inductance function. However, considering its installation in the circuit, in order to reduce the operating current, the non-magnetic layer 32 in the third embodiment is an insulator and its surface has a conductive structure. For example, it is set as a topological insulator layer.

[0068] By applying a gate voltage, the Fermi energy of electrons is adjusted to fall within the bandgap between the conduction band and the valence band, which is the same as in the second embodiment.

[0069] However, an important point is cited here. In the third embodiment, fine adjustment can be performed by applying a gate voltage, and the drive electrodes D-EL do not contact the magnetic layer 31 and are completely unaffected by the internal resistance of the metal. From this perspective, the third embodiment can be said to be the best embodiment with the highest reliability as an inductance element.

[0070] (Fourth Embodiment)

[0071] The first to third embodiments are thin-film inductor elements with a fixed inductance. However, for inductor elements based on the principle of the present invention, it has also been found that the inductance can be controlled from the outside. As a principle, by applying an external magnetic field to control the ease of wobbling (ease of movement) of the magnetic body, the inductance is changed.

[0072] Figure 5 FIG. 4 is a perspective view showing the structural concept of the thin-film variable inductor element 4 according to the fourth embodiment of the present invention. An inductor is formed of a double-layer film in which a non-magnetic layer 42 is laminated on a magnetic body layer 41, extends in the left-right direction of the paper surface, and drive electrodes D-EL are provided at the interfaces near both ends thereof, and an alternating current is applied, which is the same as that of the thin-film inductor element 3 shown in Figure 4 . And although signal lines are omitted in the drawing, it also has a gate electrode G-EL or a blocking layer 43 for adjusting the Fermi energy of electrons to fall within the band gap between the conduction band and the valence band, which is the same as that of the thin-film inductor element 3.

[0073] The magnetization direction of the magnetic body has magnetic anisotropy that is stable in the direction parallel to the lamination direction. The difference from the thin-film inductor element 3 shown in Figure 4 is that it further includes a thin-film coil 44 surrounding the laminated film. By controlling the circuit of the thin-film coil 44, the Oersted magnetic field penetrating the inductor element in the lamination direction can be controlled by switching the on-off of the current or the direction of the current.

[0074] (Principle of inductance modulation operation)

[0075] Using Figure 6 , the principle of the inductance modulation operation of the thin-film variable inductor element that functions by providing an external magnetic field will be described.

[0076] As shown in Figure 6 (a), if a positive magnetic field is applied in the up-down direction of the paper surface in the control circuit, the effective magnetic anisotropy in the magnetic body of the inductor increases (the ease of wobbling of the magnetic body decreases), and the inductance decreases. On the contrary, as shown in Figure 6 (b), if a negative magnetic field is applied, the effective magnetic anisotropy in the magnetic body of the inductor decreases (the ease of wobbling of the magnetic body increases), and the inductance increases. Therefore, by applying an external magnetic field generated by a control current while performing the aforementioned inductance operation, a variable inductance based on electrical control without mechanical movement as in the prior art can be realized.

[0077] (Advantage over the prior art: Energy efficiency)

[0078] As described above, an object of the present invention is to provide a thin film inductor element that can reduce the operating current and exhibit a sufficient emission inductance function when installed in a circuit. To solve this problem, as a non-magnetic layer capable of exhibiting spin-orbit torque, an insulator with a conductive surface structure was selected. Moreover, logical verification was performed on the first to fourth embodiments of the present invention obtained, and the results were astonishing. Because the Q value representing energy efficiency shown below has been dramatically improved.

[0079] [Equation 1]

[0080]

[0081] Here, Z ω is the complex impedance of the element, and its real part Re Z ω corresponds to the resistance exhibited by the element, and the imaginary part Im Z ω corresponds to the reactance derived from inductance or the like. The Q value in an inductor corresponds to the ratio of the magnetic energy stored in the inductor to the energy loss caused by the internal resistance. That is, the smaller the energy loss caused by the internal resistance, the higher the obtained Q value.

[0082] For reference, in Figure 7 it is shown the curves representing the correspondence between the operating frequency of the inductor and the Q value at that frequency for the spiral magnetic inductor (Non-Patent Document 1) as an emission inductor in previous research, the thin film inductor with a non-magnetic metal (Non-Patent Document 2), and the first to fourth embodiments based on this case. The values in Non-Patent Document 1 were reported in the literature through experimental measurement, and the values in Non-Patent Document 2 and the first to fourth embodiments of this case were estimated through theoretical calculation. In Non-Patent Document 1, if the operating frequency exceeds the order of 10 kHz, the inductance is suppressed and the Q value rapidly decays. On the other hand, in Non-Patent Document 2 and the first to fourth embodiments of this case, it operates as an inductor until the operating frequency reaches the order of 10 - 100 MHz. This operating frequency can fully cope with signal processing in electrical / electronic circuits. In addition, compared with the Q value of Non-Patent Document 2, the Q values of the first to fourth embodiments of this case are about 100 times, expecting to show an extremely high Q value.

[0083] This becomes clearer when compared with the operating current. As the operating current in the method of Non-Patent Document 2, in order to control the magnetization of the magnetic material, a current also needs to flow inside the non-magnetic metal, so about 100 μA is required. However, for signal control in electrical / electronic circuits, it is necessary to suppress the operating current to about 1 μA. In the first to fourth embodiments of the present case, since the current only flows at the interface between the magnetic material and the non-magnetic material, there is no need for an excessive current to flow on the non-magnetic material, and the flowing current can be greatly suppressed. Therefore, it is possible to reliably meet the requirement specification of "suppressing the operating current to about 1 μA". This is particularly important for high-frequency applications.

[0084] (Operating Principle and Characteristics)

[0085] The operating principle that is the basis of the phenomenon described so far will be described. The operating principle can be described by a formula obtained through the derivation process described below.

[0086] The interior of a topological insulator does not have conductivity, but has a conductive state on its two-dimensional surface. In particular, at the interface between a topological insulator and a different material, the conduction electrons are subject to strong spin-orbit coupling. The conduction electrons at the interface between the topological insulator and the magnetic material are subject to the following two effects as the effects of spin-orbit coupling.

[0087] As the first effect, there is the anomalous Hall effect. It is the effect of generating a Hall electric field perpendicular to the current flowing through the interface. It is known that the resulting Hall electric field is given by the following equation.

[0088] [Equation 2]

[0089]

[0090] Here, σ H is the Hall conductivity characterizing the anomalous Hall effect and has a non-zero value at the interface between the topological insulator and the magnetic material. And, e z is the unit vector in the stacking direction (z direction), and j is the two-dimensional current density flowing through the interface.

[0091] As the second effect, there is a spin electric field. It is the effect felt by the conduction electrons as an effective electric field due to the change in the magnetization of the magnetic material via spin-orbit coupling. This spin electric field is given by the following equation.

[0092] [Equation 3]

[0093]

[0094] Here, J is a parameter representing the strength of the exchange coupling acting between the magnetization of the magnetic material and the electron spin, e is the charge of the conduction electron, and v is the velocity of the conduction electron (Fermi velocity). Also, m is a unit vector indicating the direction of magnetization of the magnetic material.

[0095] The sum of the above Hall electric field and spin electric field becomes the electric field acting on the conduction electrons. The voltage generated between the drive electrodes and the flowing current are given by the following equations.

[0096] [Equation 4]

[0097]

[0098] Here, l is the distance between the electrodes (x - direction), w represents the width of the current - flowing region (y - direction), and the subscript x indicates the x - component of the vector. The response of the current to the thus - obtained electric field is characterized by the complex impedance Z ω as follows.

[0099] [Equation 5]

[0100]

[0101] Here, the subscript ω represents the dependence on the angular frequency of the input alternating current (ω = 2πf, where f is the frequency). As shown below, the internal resistance R and the output inductance L of this element are obtained from the real part Re[Z ω and the imaginary part Im[Z ω , respectively.

[0102] [Equation 6]

[0103]

[0104] Using the relationships given above, the case of achieving the output inductance and the case of significantly improving the Q - value representing the energy efficiency through the embodiments of the present invention are shown in detail below.

[0105] The motion m(t) of the magnetization under current is obtained by solving the following motion equation (Landau - Lifshitz - Gilbert equation).

[0106] [Equation 7]

[0107]

[0108] Here, γ is the gyromagnetic ratio, h dc is the external DC magnetic field applied in the z - direction, h K is the effective magnetic field caused by perpendicular magnetic anisotropy, and α is the Gilbert damping coefficient. Also, h eeffis the strength of the effective magnetic field of the spin-orbit torque caused by the current j flowing along the interface, and is given by the following.

[0109] [Equation 8]

[0110]

[0111] However, M s represents the saturation magnetization of the magnetic thin film, and t F represents the film thickness.

[0112] Now assume that an alternating current (angular frequency ω) is applied in the x direction. As a result, the magnetization precesses in a small angle around the z direction. At this time, the vibration of the current and the magnetization is represented by the following equations.

[0113] [Equation 9]

[0114]

[0115] Under the assumption of this small-angle precession motion, the equation of motion [Equation 7] can be linearly approximated. When substituting [Equation 8] and solving the equation of motion [Equation 7], its solution is given as follows.

[0116] [Equation 10]

[0117]

[0118] Here, the frequency ω0 = γ(h dc + h K ) corresponds to the resonance frequency of the ferromagnetic resonance of the magnetic material.

[0119] When substituting the motion of the magnetization obtained above into the equation of the spin electric field [Equation 3], it can be seen that the spin electric field E S (t) responds to the input current j through the following equation.

[0120] [Equation 11]

[0121]

[0122] When combining this with the Hall electric field [Equation 2] and obtaining the relationship between the voltage and the current between the electrodes through [Equation 4], the complex impedance Z ω is given by the following equation.

[0123] [Equation 12]

[0124]

[0125] From this, the internal resistance R and the output inductance L of the element are given as follows using [Equation 6].

[0126] [Equation 13]

[0127]

[0128] As described above, in the embodiment of the present invention, even if insulators are used for both the magnetic body and the non-magnetic body, the output inductance L is realized by the conduction state of the topological insulator that appears at the interface. In addition, when calculating [Formula 13], the frequency ω of the input signal is sufficiently slower than the frequency ω0 of the strong magnetic resonance (about 1 to 10 GHz for general magnetic bodies) and the intensity α of the Gilbert damping (about 0.01 for general magnetic bodies) is sufficiently smaller than 1, and an approximation is made.

[0129] The main feature of the present invention is that the Q value, which is the characteristic energy efficiency, can be greatly increased. The Q value of an inductor can be expressed as follows using the ratio of the internal resistance R to the inductance L.

[0130] [Formula 14]

[0131]

[0132] As proposed in Non-Patent Document 1 or Non-Patent Document 2, in an "exit inductor using metal", the element has not only inductance but also internal resistance due to the resistance of the metal. Since the internal resistance R is included in the denominator of the Q value, the Q value is suppressed by the internal resistance.

[0133] On the other hand, since an insulator is used in the present invention, the current does not flow inside the material and is not affected by the resistance. As can be seen from [Formula 13], the internal resistance R of the element is independent of the resistance value of the material, but is suppressed in direct proportion to the Gilbert damping coefficient α of the magnetic body (generally about 0.01 for magnetic bodies). Therefore, the Q value becomes a large value inversely proportional to α. Thus, it is possible to realize an inductance function with a high Q value (about 10 to 100) that can withstand use in a signal control circuit by simple constituent elements such as a double-layer film of a magnetic body / non-magnetic body.

[0134] The thin film inductor element and the thin film variable inductor element according to the embodiments of the present invention are described in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and the changes in design that do not deviate from the scope of the present invention are also included in the present invention. For example, it is of course possible to use the same type as the third embodiment as the driving electrode on the basis of the first embodiment without the gate electrode. It should be fully understood that the significance of the present invention is that by eliminating the internal resistance as much as possible and obtaining only the required inductance, a highly reliable inductor element can be provided.

[0135] Explanation of symbols

[0136] 1 - Thin - film inductance element, 11 - Magnetic layer, 12 - Non - magnetic layer, 2 - Thin - film inductance element, 21 - Magnetic layer, 22 - Non - magnetic layer, 23 - Barrier layer, 3 - Thin - film inductance element, 31 - Magnetic layer, 32 - Non - magnetic layer, 33 - Barrier layer, 4 - Thin - film variable inductance element, 41 - Magnetic layer, 42 - Non - magnetic layer, 43 - Barrier layer, 44 - Thin - film coil, D - EL - Drive electrode, G - EL - Gate electrode.

Claims

1. A thin film inductance element, characterized in that, A stacked film composed of a stacked magnetic layer and a non-magnetic layer, and a pair of electrodes, wherein the magnetic layer and the non-magnetic layer extend in a direction orthogonal to the stacking direction in an arbitrary shape, the magnetic layer has a substantially identical magnetization structure including a stacking direction component, the non-magnetic layer is an insulator and has a conductive surface structure, the pair of electrodes are disposed near both ends where the stacked film extends and at positions where they are in contact with at least the surface of the non-magnetic layer, and a current modulated at a frequency of 1 kHz to 1 GHz is applied thereto.

2. The thin film inductance element according to claim 1, wherein, the non-magnetic layer is a topological insulator layer.

3. The thin film inductance element according to claim 2, wherein, the topological insulator layer has a composition suitable for exhibiting spin-orbit torque.

4. The thin film inductance element according to claim 2, wherein, the topological insulator layer has a composition including one or two of Bi and Sb and one or two of Se and Te.

5. A thin-film inductance element, characterized in that, A stacked film composed of a stacked magnetic layer and a non-magnetic layer, and a pair of electrodes, wherein the magnetic layer and the non-magnetic layer extend in a direction orthogonal to the stacking direction in an arbitrary shape, the magnetic layer has a substantially identical magnetization structure including a stacking direction component, the pair of electrodes are disposed near both ends where the stacked film extends and at positions where they are in contact with at least the surface of the non-magnetic layer, and a current modulated at a frequency of 1 kHz to 1 GHz is applied thereto, the non-magnetic layer is a topological insulator layer whose composition ratio is adjusted such that the Fermi energy of electrons is within the gap between the conduction band and the valence band, or a topological insulator layer whose gate voltage is adjusted such that the Fermi energy of electrons is within the band gap between the conduction band and the valence band.

6. The thin film inductance element according to claim 1, wherein, on the side opposite to the magnetic layer of the non-magnetic layer, a gate electrode layer is stacked with a barrier layer interposed therebetween, by applying a bias voltage to the gate electrode layer, current is concentrated to flow at the interface between the non-magnetic layer and the magnetic layer.

7. The thin film inductance element according to claim 1, wherein, it is configured such that by separating the magnetic layer from the pair of electrodes, current is more concentrated to flow at the interface between the non-magnetic layer and the magnetic layer.

8. The thin film inductance element according to claim 1, wherein, the magnetic layer is an insulator, whereby it is configured such that current is more concentrated to flow at the interface between the non-magnetic layer and the magnetic layer.

9. A thin-film variable inductor element, characterized in that, A stacked film composed of a stacked magnetic layer and a non-magnetic layer, a pair of electrodes for applying a current modulated at a frequency of 1 kHz to 1 GHz, and a thin film coil surrounding the stacked film, wherein the magnetic layer and the non-magnetic layer extend in a direction orthogonal to the stacking direction in an arbitrary shape, the magnetic layer has a magnetization structure including a stacking direction component, the non-magnetic layer is an insulator and has a conductive surface structure, by switching the switch of the thin film coil and / or the direction of the current to control an external magnetic field, an inductance modulation operation is achieved.

10. A method of using a laminated film element, which uses the laminated film element as an inductance element. The laminated film element is characterized by including a laminated film formed by laminating a magnetic layer and a non-magnetic layer, a pair of electrodes, and a gate electrode. The magnetic layer and the non-magnetic layer extend in an arbitrary shape in a direction orthogonal to the lamination direction. The magnetic layer has a substantially identical magnetization structure including a component in the lamination direction. The non-magnetic layer is a topological insulator layer. The pair of electrodes are disposed near both ends where the laminated film extends and at positions in contact with at least the surface of the non-magnetic layer. The method of using the laminated film element is characterized by including the following steps: A step of applying a voltage adjusted such that the Fermi energy of electrons is within the band gap between the conduction band and the valence band to the gate electrode; and A step of applying a current modulated at a frequency of 1 kHz to 1 GHz to the pair of electrodes.

11. A laminated film element, characterized in that, Including a laminated film formed by laminating a magnetic layer and a topological insulator layer, a pair of electrodes, and a gate electrode. The magnetic layer and the topological insulator layer extend in an arbitrary shape in a direction orthogonal to the lamination direction. The magnetic layer has a substantially identical magnetization structure including a component in the lamination direction. The pair of electrodes are disposed near both ends where the laminated film extends and at positions in contact with at least the surface of the topological insulator layer.

12. An electronic device including the thin film element according to claim 11.

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