WO2013122023A1

WO2013122023A1 - Spin implantation electrode structure and spin transport element

Info

Publication number: WO2013122023A1
Application number: PCT/JP2013/053179
Authority: WO
Inventors: 智生佐々木; 亨及川; 勇人小池
Original assignee: Tdk株式会社
Priority date: 2012-02-14
Filing date: 2013-02-12
Publication date: 2013-08-22

Abstract

[Problem] To provide a spin implantation electrode structure and spin transport element that suppress spin scattering at interfaces, which arises because of offsetting of lattice constants between semiconductor channel layers and tunnel films and between tunnel films and ferromagnetic layers. [Solution] The spin implantation electrode structure is characterized by being provided with a semiconductor channel layer, a tunnel film provided on the semiconductor channel layer, a nonmagnetic spinel film provided on the tunnel film, and a ferromagnetic layer provided on the nonmagnetic spinel film.

Description

Spin injection electrode structure and spin transport device

The present invention relates to a spin injection electrode structure and a spin transport element.

In recent years, a technique for accumulating spin in a channel made of a semiconductor is known. The spin diffusion length in the channel made of semiconductor is much longer than the spin diffusion length in the channel made of metal. For example, the following Non-Patent Documents 1 to 4 describe techniques for injecting spin into silicon.

JP 2010-239011 A

By the way, for application of spin injection, conduction, and detection in silicon, it is desired to obtain sufficient output characteristics at room temperature. Non-Patent Documents 1 to 3 report spin injection, conduction, and detection in silicon, but all are events at a low temperature of 150K or lower. In Non-Patent Document 4, although spin accumulation in silicon at 300 K is observed, the spin conduction phenomenon in silicon at room temperature has not been observed, and a wide range of applications cannot be expected at present. Recently, in Non-Patent Document 5, a spin conduction phenomenon in silicon at room temperature has been observed. However, its output is not sufficient to realize a wide range of applications. One of the reasons why it is difficult to increase the output at room temperature is that spin scattering at the interface is induced by a shift in lattice constant between the silicon and the tunnel film. Thus, it is desired to realize effective injection that realizes spin conduction in a semiconductor at room temperature, not limited to silicon.

Patent Document 1 discloses a method for suppressing spin scattering at the interface due to a shift in lattice constant between silicon and a tunnel film. According to Patent Document 1, by forming the first amorphous magnesium oxide on silicon, spin scattering due to lattice mismatch between silicon and magnesium oxide is suppressed, and the first amorphous magnesium oxide is formed on the first amorphous magnesium oxide. Due to the formation of monocrystalline magnesium oxide, high output is achieved by leaving a partial coherent effect. However, it is necessary to suppress spin scattering at the interface between the tunnel oxide magnesium oxide and the first ferromagnetic layer.

The present invention has been made to solve the above-described problems, and provides a spin injection electrode structure and a spin transport device that enable effective injection of spins in a semiconductor channel layer at room temperature than in the past. With the goal.

In order to solve the above-described problems, a spin injection electrode structure according to the present invention includes a semiconductor channel layer, a tunnel film provided on the semiconductor channel layer, a nonmagnetic spinel film provided on the tunnel film, and a nonmagnetic spinel. And a ferromagnetic layer provided on the film.

The tunnel film is not epitaxially grown on the semiconductor channel layer. Here, “not epitaxially growing” means that the semiconductor channel layer has a domain structure and is partially crystal-grown or has an amorphous structure, and different layers over a sufficiently large region. This indicates a state in which the interface is crystallized and maintains continuity. Thereby, spin scattering accompanying lattice mismatch is suppressed at the interface between the semiconductor channel layer and the tunnel film.

Further, it is preferable that the tunnel film is made of an oxide containing any element of Al, Mg, Si, Zn, and Ti, and the film thickness is 0.6 nm or more and 2.0 nm or less. When the film thickness of the tunnel film is 2.0 nm or less, the film thickness when combined with the non-magnetic spinel film is thin, and the resistance value of the laminated film is small. Since noise can be suppressed, spin injection can be suitably performed. When the thickness of the tunnel film exceeds 2.0 nm, an increase in spin output is suppressed, and noise increases due to an increase in interface resistivity, so that a high signal ratio cannot be obtained. When the tunnel film has a thickness of 0.6 nm or more, a uniform tunnel film can be formed on the semiconductor channel layer. Note that when the thickness of the tunnel film is less than 0.6 nm, it is not formed as a film and does not function as a tunnel film because an island-like layer is formed.

The nonmagnetic spinel film is crystallized on the tunnel film. Further, it is an oxide containing any element of Al, Mg, and Zn, and preferably has a spinel structure.

The film thickness of the nonmagnetic spinel film is preferably 0.6 nm or more and 2.4 nm or less. When the film thickness of the nonmagnetic spinel film is 2.4 nm or less, the film thickness when combined with the tunnel film is thin, the resistance value of the laminated film is small, and a sufficient spin polarizability is obtained. If the film thickness of the nonmagnetic spinel film exceeds 2.4 nm, an increase in spin output is suppressed, and noise increases due to an increase in interface resistivity, so that a high signal ratio cannot be obtained. In addition, when the film thickness of the nonmagnetic spinel film is 0.6 nm or more, a uniform nonmagnetic spinel film can be formed on the tunnel film. Note that when the film thickness of the nonmagnetic spinel film is less than 0.6 nm, it is not formed as a film and does not function as a tunnel film because the layer is formed in an island shape.

Furthermore, it is preferable that the nonmagnetic spinel film is a crystalline film, and a ferromagnetic layer is epitaxially grown on the nonmagnetic spinel film by being crystallized on the tunnel film. This enables efficient spin injection / extraction to the semiconductor channel layer by the coherent tunnel effect of the nonmagnetic spinel film. Further, since the ferromagnetic layer has a lattice constant close to that of the nonmagnetic spinel film, it is easy to grow epitaxially on the nonmagnetic spinel film, and spin scattering hardly occurs at the interface between the nonmagnetic spinel film and the ferromagnetic layer.

The crystal structure of the ferromagnetic layer is preferably a body-centered cubic lattice structure (BCC). In this case, the ferromagnetic layer can be partially epitaxially grown on the nonmagnetic spinel film.

The ferromagnetic layer is a metal selected from the group consisting of Co, Fe, and Ni, an alloy containing one or more elements of the group, or a compound containing one or more elements selected from the group and B. Is preferred. Since these materials are ferromagnetic materials having a high spin polarizability, the function as a spin injection electrode can be suitably realized.

Furthermore, the ferromagnetic layer is more preferably a Heusler alloy. The ferromagnetic layer includes an intermetallic compound having a chemical composition of X2YZ, X is a transition metal element or noble metal element of Co, Fe, Ni, or Cu group on the periodic table, and Y is Mn, V, It is a transition metal of Cr or Ti group and can take the element species of X, and Z is a typical element from Group III to Group V. For example, Co ₂ FeSi or Co ₂ MnSi can be used.

Further, it is preferable to further include an antiferromagnetic layer formed on the ferromagnetic layer, and the antiferromagnetic layer preferably fixes the magnetization direction of the ferromagnetic layer. When the antiferromagnetic layer is exchange coupled with the ferromagnetic layer, unidirectional anisotropy can be imparted to the magnetization direction of the ferromagnetic layer. In this case, a ferromagnetic layer having a higher coercive force in one direction can be obtained than when no antiferromagnetic layer is provided.

The spin transport device according to the present invention includes any one of the above-described spin injection electrode structures provided in the first part, and further includes a second tunnel film provided on the second part of the semiconductor channel layer, and a second tunnel film A second non-magnetic spinel film provided on the second non-magnetic spinel film; and a second ferromagnetic layer provided on the second non-magnetic spinel film. The second tunnel film is an amorphous film, and the second nonmagnetic spinel film is crystallized on the second tunnel film. Therefore, the second ferromagnetic layer is preferably a film that is epitaxially grown on the second nonmagnetic spinel film.

Also, it is preferable that the first and second ferromagnetic layers have a coercive force difference due to shape anisotropy. In this case, an antiferromagnetic layer for providing a coercive force difference can be omitted.

Generally, ions for imparting conductivity are implanted into the semiconductor channel layer. The surface of the semiconductor channel layer may be damaged due to the ion implantation. Therefore, the semiconductor channel layer preferably has a recess between the first portion and the second portion, and the depth of the recess is preferably 10 nm or more and 20 nm or less. In this case, a silicon channel layer in which surface damage is suppressed can be used.

Also, the spin transport device preferably has the above-described spin injection electrode structure, and can provide a spin transport device that enables effective injection of spin in the semiconductor channel layer at room temperature.

According to the present invention, the electrode structure can suppress the spin scattering at the interface between the tunnel film and the ferromagnetic layer at the same time while suppressing the spin scattering at the interface between the semiconductor channel and the tunnel film as compared with the conventional tunnel film. Thus, it is possible to provide a spin injection electrode structure, a spin transport element, and a spin transport device that enable effective injection of spin in the semiconductor channel layer at room temperature.

FIG. 1 is a perspective view of the spin transport device according to the present embodiment. FIG. 2A is a top view of the spin transport device according to the present embodiment. FIG. 2B is an enlarged view of the region B shown in FIG. FIG. 3 is a sectional view taken along line III-III in FIG. FIG. 4 is a configuration diagram of the first tunnel film 16A, the first nonmagnetic spinel film 16B, the third tunnel film 16C, and the fourth tunnel film 16D that constitute the first spin filter film 13A and the second spin filter film 13B, respectively. is there. FIG. 5 is a graph showing the relationship between the applied magnetic field and the voltage output in the NL measurement method. FIG. 6 is a graph showing the relationship between the applied magnetic field and the voltage output in the NL-Hanle measurement method.

Hereinafter, preferred embodiments of the spin transport device according to the present invention will be described in detail with reference to the drawings. In the figure, an XYZ orthogonal coordinate axis system is shown as necessary. FIG. 1 is a perspective view of the spin transport device according to the present embodiment. FIG. 2A is a top view of the spin transport device according to the present embodiment. FIG. 2B is an enlarged view of the region B shown in FIG. FIG. 3 is a sectional view taken along line III-III in FIG.

As shown in FIG. 3, the spin transport device 1 includes silicon substrate 10, silicon oxide film 11, silicon channel layer 12, first spin filter film 13 A, and second substrate when silicon is used as a semiconductor. The spin filter film 13B, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, the second reference electrode 15B, the oxide film 7a, and the oxide film 7b are provided. The silicon channel layer 12, the first spin filter film 13A, and the first ferromagnetic layer 14A constitute a spin injection electrode structure IE.

As shown in FIG. 4, the first spin filter film 13A has a structure composed of a first tunnel film 16A and a first nonmagnetic spinel film 16B. Similarly, the second spin filter film 13B has a structure composed of a second tunnel film 16C and a second nonmagnetic spinel film 16D.

As the substrate 10, the silicon oxide film 11, and the silicon channel layer 12, for example, an SOI (Silicon On Insulator) substrate can be used. The substrate 10 is a silicon substrate, and the silicon oxide film 11 is provided on the substrate 10. The film thickness of the silicon oxide film 11 is 200 nm, for example.

The silicon channel layer 12 functions as a layer that conducts spin. The upper surface of the silicon channel layer 12 is, for example, a (100) plane. The silicon channel layer 12 has, for example, a rectangular shape with the X axis as the major axis direction when viewed from the Z axis direction (thickness direction). The silicon channel layer 12 is made of silicon, and impurity ions for imparting one conductivity are added to the silicon channel layer 12 as necessary. The ion concentration is, for example, 5.0 × 10 ¹⁹ cm ⁻³ . The film thickness of the silicon channel layer 12 is, for example, 100 nm. Alternatively, the ion concentration is adjusted to a depth of 10 nm in the silicon channel layer 12 from the interface so that the Schottky barrier at the interface between the first spin filter film 13A or the second spin filter film 13B and the silicon channel layer 12 can be adjusted. The silicon channel layer 12 may have a structure with a peak. Further, when the ion concentration of the silicon channel layer 12 is low, a method of applying a voltage to the silicon oxide film 11 and inducing carriers in the silicon channel layer 12 is also conceivable.

As shown in FIG. 3, the silicon channel layer 12 has an inclined portion on the side surface, and the inclination angle θ is 50 to 60 degrees. The inclination angle θ is an angle formed by the bottom and side surfaces of the silicon channel layer 12. The silicon channel layer 12 can be formed by wet etching.

As shown in FIG. 3, the silicon channel layer 12 includes a first convex portion (first portion) 12A, a second convex portion (second portion) 12B, a third convex portion (third portion) 12C, and a fourth convex portion ( 4th part) 12D and the main part 12E are included. The first convex portion 12A, the second convex portion 12B, the third convex portion 12C, and the fourth convex portion 12D are portions that extend so as to protrude from the main portion 12E, and in this order a predetermined axis (shown in FIG. 3). In the example, they are arranged at a predetermined interval in the (X-axis) direction.

The film thickness (length in the Z-axis direction in the example shown in FIG. 3) H1 of the first convex portion 12A, the second convex portion 12B, the third convex portion 12C, and the fourth convex portion 12D is, for example, 20 nm. The film thickness (length in the Z-axis direction in the example shown in FIG. 3) H2 of the main portion 12E is, for example, 80 nm. A distance L1 between the first convex portion 12A and the third convex portion 12C is, for example, 100 μm or less. The distance d between the central portion of the first convex portion 12A in the X-axis direction and the central portion of the second convex portion 12B in the X-axis direction is preferably equal to or less than the spin diffusion length. The spin diffusion length in the silicon channel layer 12 at room temperature (300 K) is, for example, 0.8 μm. The spins injected from the first ferromagnetic layer 14A into the first convex part 12A or the spins injected from the second ferromagnetic layer 14B into the second convex part 12B are the same as the first convex part 12A and the second convex part in the main part 12E. The region between the convex portion 12B is diffused and conducted.

The first spin filter film 13A and the second spin filter film 13B efficiently perform the spin polarization of the ferromagnetic material (the first ferromagnetic layer 14A and the second ferromagnetic layer 14B) and the spin polarization of the silicon channel layer 12. It functions as a tunnel insulating film for connection. The first spin filter film 13 A is provided on the first convex portion 12 A that is the first portion of the silicon channel layer 12. The second spin filter film 13 B is provided on the second convex portion 12 B that is the second portion of the silicon channel layer 12. The first spin filter film 13 A and the second spin filter film 13 B are crystals grown on, for example, the (100) plane of the silicon channel layer 12. By providing the first spin filter film 13A or the second spin filter film 13B, many spin-polarized electrons are injected from the first ferromagnetic layer 14A or the second ferromagnetic layer 14B to the silicon channel layer 12. Thus, the potential output of the spin transport device 1 can be increased.

The sum of the film thicknesses of the first spin filter film 13A and the second spin filter film 13B is preferably 3.0 nm or less. In this case, since the interface resistivity can be lowered to 1 MΩμm ² or less with respect to the obtained spin output, noise can be suppressed, so that spin injection and output can be suitably performed. Further, the film thicknesses of the first spin filter film 13A and the second spin filter film 13B are preferably 0.6 nm or more. In this case, the first spin filter film uniformly formed on the silicon channel layer 12 is used. The filter film 13A and the second spin filter film 13B can be used.

One of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B functions as an electrode for injecting spin into the silicon channel layer 12, and the other as an electrode for detecting spin in the silicon channel layer 12. Function. The first ferromagnetic layer 14A is provided on the first spin filter film 13A. The second ferromagnetic layer 14B is provided on the second spin filter film 13B.

The first ferromagnetic layer 14A and the second ferromagnetic layer 14B are made of a ferromagnetic material. As an example of the material of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B, a metal selected from the group consisting of Co and Fe, an alloy containing one or more elements of the group, or 1 selected from the group The compound which consists of the above element and B is mentioned. The crystal structure of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B is preferably a body-centered cubic lattice structure. Thereby, the first ferromagnetic layer can be partially epitaxially grown on the first spin filter film, and the second ferromagnetic layer can be partially epitaxially grown on the second spin filter film.

In the example shown in FIG. 1, the first ferromagnetic layer 14A and the second ferromagnetic layer 14B have a rectangular parallelepiped shape with the major axis in the Y-axis direction. It is preferable that the first ferromagnetic layer 14A and the second ferromagnetic layer 14B have a coercive force difference due to the shape anisotropy of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B. The width (length in the X-axis direction) of the first ferromagnetic layer 14A is, for example, about 350 nm. The width (length in the X-axis direction) of the second ferromagnetic layer 14B is, for example, about 2 μm. In the example shown in FIG. 1, the coercive force of the first ferromagnetic layer 14A is larger than the coercive force of the second ferromagnetic layer 14B.

The first reference electrode 15A and the second reference electrode 15B have a function as an electrode for flowing a detection current through the silicon channel layer 12 and a function as an electrode for reading an output by spin. The first reference electrode 15 A is provided on the third protrusion 12 C of the silicon channel layer 12. The second reference electrode 15 B is provided on the fourth protrusion 12 D of the silicon channel layer 12. The first reference electrode 15A and the second reference electrode 15B are made of a conductive material, for example, a non-magnetic metal having a low resistance to Si such as Al.

The oxide film 7 a is formed on the side surface of the silicon channel layer 12. The oxide film 7b includes the silicon channel layer 12, the oxide film 7a, the first spin filter film 13A, the second spin filter film 13B, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, And on the side surface of the second reference electrode 15B. In addition, on the upper surface of the silicon channel layer 12, the main ferromagnetic portion 12E where the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B are not provided is oxidized. A film 7b is formed. The oxide film 7b is provided on the main portion 12E of the silicon channel layer 12 between the first spin filter film 13A and the second spin filter film 13B. The oxide film 7b includes the silicon channel layer 12, the first spin filter film 13A, the second spin filter film 13B, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B. It functions as a protective film and suppresses deterioration of these layers. The oxide film 7b is, for example, a silicon oxide film.

As shown in FIG. 1, a wiring 18A is provided on the first reference electrode 15A and on the oxide film 7b (an inclined side surface of the silicon channel layer 12). Similarly, the wiring 18B is provided on the first ferromagnetic layer 14A and the oxide film 7b. A wiring 18C is provided on the second ferromagnetic layer 14B and the oxide film 7b. A wiring 18D is provided on the second reference electrode 15B and the oxide film 7b. The wirings 18A to 18D are made of a conductive material such as Cu. By providing the wiring on the oxide film 7b, it is possible to suppress the absorption of spin conducted through the silicon channel layer 12 by this wiring. Further, by providing the wiring on the oxide film 7b, it is possible to suppress a current from flowing from the wiring to the silicon channel layer 12, and to improve the spin injection efficiency. In addition, electrode pads E1 to E4 for measurement are provided at the respective ends of the wirings 18A to 18D. End portions of the wirings 18A to 18D and measurement electrode pads E1 to E4 are formed on the silicon oxide film 11. The electrode pads E1 to E4 are made of a conductive material such as Au.

FIG. 4 is a cross-sectional view of the first spin filter film 13A and the second spin filter film 13B. The first spin filter film 13A includes a first tunnel film 16A and a first nonmagnetic spinel film 16B. The first tunnel film 16 A is not grown on the silicon channel layer 12 or grown in a sufficiently small region on the silicon channel layer 12. The first nonmagnetic spinel film 16B is a crystalline film and is crystallized on the first tunnel film 16A. Similarly, the second spin filter film 13B includes a second tunnel film 16C and a second nonmagnetic spinel film 16D. The second tunnel film 16 C is not grown on the silicon channel layer 12 or grown in a sufficiently small region on the silicon channel layer 12. The second nonmagnetic spinel film 16D is a crystalline film and is crystallized on the second tunnel film 16C.

Hereinafter, the first tunnel film 16A, the first nonmagnetic spinel film 16B, and the first ferromagnetic film 14A constituting the first spin filter film 13A will be described.

The first tunnel film 16A is suitably made of aluminum oxide, zinc oxide, silicon oxide, titanium oxide, or magnesium oxide. In these materials, when the thickness is 0.6 nm or more and 2.0 nm or less, the silicon channel layer 12 is often amorphous. Even when crystallized, it is in a polycrystalline state having many domain structures. Therefore, long-distance crystal lattice-matched epitaxial growth does not occur at the interface between the silicon channel layer 12 and the first tunnel film 16A, so that no defect due to the difference in lattice constant between the silicon and the first tunnel film 16A occurs.

MgAl ₂ O ₄ or ZnAl ₂ O ₄ is suitable for the first nonmagnetic spinel film 16B. As described above, the first nonmagnetic spinel film 16B on the amorphous first tunnel film 16A is easily crystallized. In particular, the film thickness of the first nonmagnetic spinel film 16B is preferably 0.6 nm or more and 2.4 nm or less. When the film thickness of the first nonmagnetic spinel film 16B is 0.6 nm or more, the first nonmagnetic spinel film 16B is easily crystallized, and when it is 2.4 nm or less, the film thickness is thin and the resistance value of the laminated film is small. And sufficient spin polarizability can be obtained.

The crystal structure of the first ferromagnetic layer 14A is preferably a body-centered cubic lattice structure (BCC). The material of the first ferromagnetic layer 14A is a metal selected from the group consisting of Co and Fe, an alloy containing one or more elements of the group, or a compound containing one or more elements selected from the group and B. In this case, the first ferromagnetic layer 14A is easily epitaxially grown on the first nonmagnetic spinel film 16B. For example, when the first nonmagnetic spinel film 16B is MgAl ₂ O ₄ and the first ferromagnetic layer 14A is Fe, the lattice constants of MgAl ₂ O ₄ and Fe are substantially the same, and MgAl ₂ O ₄ and It is possible to suppress spin scattering at the Fe interface. The crystal structure and lattice constant can be determined by forming and evaluating a film having a thickness that can be analyzed by a cross-sectional TEM or XRD of the laminated film.

Furthermore, the first ferromagnetic layer 14A is more preferably a Heusler alloy. Heusler alloy (or full Heusler alloy) is a general term for intermetallic compounds having a chemical composition of X2YZ, where X is a transition metal element of Co, Fe, Ni, or Cu group on the periodic table. Or it is a noble metal element. Y is a transition metal of Mn, V, Cr or Ti group and can take the same element species as X. Z is a typical element from Group III to Group V. Heusler alloy X2YZ is divided into three types of crystal structures based on the regularity of X, Y, and Z. According to the analysis such as X-ray diffraction using the periodicity of the crystal, the most regular structure in which X ≠ Y ≠ Z that can distinguish the three elements is the L21 structure, and the next highest regularity X ≠ Y = Z. Is a B2 structure, and a structure where X = Y = Z is indistinguishable from three elements is an A2 structure.

In addition, when the first tunnel film 16A is aluminum oxide or magnesium oxide and the first nonmagnetic spinel film 16B is MgAl ₂ O ₄ , the first tunnel film 16A is a configuration of the first nonmagnetic spinel film 16B. Since the element is contained, even if the element of the first tunnel film 16A and the element of the first nonmagnetic spinel film 16B are mutually diffused by heat or the like, it is possible to suppress a decrease in the function as a spin filter. . That is, the constituent element of the first tunnel film 16A is more preferably an oxide containing some cations of the first nonmagnetic spinel film 16B.

The second spin filter film 13B is the same as the first spin filter film 13A.

Hereinafter, an example of an operation using the NL (non-local) measurement method of the spin transport device 1 according to the present embodiment will be described. In the NL measurement method, as shown in FIG. 3, the spin transport element 1 detects an external magnetic field B1 in the Y-axis direction, for example. The magnetization direction G1 (Y-axis direction) of the first ferromagnetic layer 14A is fixed in the same direction as the magnetization direction G2 (Y-axis direction) of the second ferromagnetic layer 14B. Further, as shown in FIG. 1, by connecting the electrode pads E1 and E3 to an alternating current source 70, a detection current is passed through the first ferromagnetic layer 14A. When a detection current flows from the first ferromagnetic layer 14A, which is a ferromagnetic material, to the non-magnetic silicon channel layer 12 through the first spin filter film 13A, the direction of magnetization of the first ferromagnetic layer 14A Electrons having a spin corresponding to G 1 are injected into the silicon channel layer 12. The injected spin diffuses toward the second ferromagnetic layer 14B. As described above, a structure in which the current and spin current flowing in the silicon channel layer 12 flow mainly in a predetermined axis (X-axis) direction can be obtained. Then, due to the interaction between the magnetization direction of the first ferromagnetic layer 14A, which is changed by the external magnetic field B1, that is, the spin of electrons and the spin of electrons in the portion of the silicon channel layer 12 in contact with the second ferromagnetic layer 14B, An output is generated between the silicon channel layer 12 and the second ferromagnetic layer 14B. This output is detected by an output measuring device 80 connected to the electrode pads E2 and E4.

Next, an example of an operation using the NL-Hane measurement method of the spin transport device 1 according to the present embodiment will be described. The NL-Hanle measurement method uses the Hanle effect. The Hanle effect means that when an external magnetic field is applied from a direction perpendicular to the direction of the spin when the spin injected from the ferromagnetic electrode into the channel by the current diffuses and conducts toward the other ferromagnetic electrode, It is a phenomenon that causes Larmor precession. In the NL-Hanle measurement method, as shown in FIG. 3, the spin transport element 1 detects an external magnetic field B2 in the Z-axis direction, for example. The magnetization direction G1 (Y-axis direction) of the first ferromagnetic layer 14A is fixed in the same direction as the magnetization direction G2 (Y-axis direction) of the second ferromagnetic layer 14B. Then, by connecting the first ferromagnetic layer 14A and the first reference electrode 15A to the alternating current source 70, a spin detection current can be passed through the first ferromagnetic layer 14A. A current flows from the first ferromagnetic layer 14A, which is a ferromagnetic material, to the non-magnetic silicon channel layer 12 through the first spin filter film 13A, thereby corresponding to the magnetization direction G1 of the first ferromagnetic layer 14A. Electrons having a spin direction are injected into the first convex portion 12A of the silicon channel layer 12. The spin injected into the first convex portion 12A diffuses toward the second ferromagnetic layer 14B through the main portion 12E. In this way, the current and spin current flowing through the silicon channel layer 12 flow mainly in the X-axis direction.

Here, when the external magnetic field B2 is not applied to the silicon channel layer 12, that is, when the external magnetic field is zero, a region of the silicon channel layer 12 between the first ferromagnetic layer 14A and the second ferromagnetic layer 14B is diffused. The direction of the spinning spin does not rotate. Therefore, the spin in the same direction as the magnetization direction G2 of the second ferromagnetic layer 14B set in advance diffuses to the region on the second ferromagnetic layer 14B side in the silicon channel layer 12. Therefore, when the external magnetic field is zero, the output (for example, resistance output or voltage output) is an extreme value. The maximum value or the minimum value can be taken depending on the direction of current or magnetization. The output can be evaluated by an output measuring device 80 such as a voltage measuring device connected to the second ferromagnetic layer 14B and the second reference electrode 15B.

On the other hand, a case where an external magnetic field B2 is applied to the silicon channel layer 12 is considered. The external magnetic field B2 is perpendicular to the magnetization direction G1 (Y-axis direction in the example of FIG. 3) of the first ferromagnetic layer 14A and the magnetization direction G2 (Y-axis direction in the example of FIG. 3) of the second ferromagnetic layer 14B. Application is performed from any direction (Z-axis direction in the example of FIG. 3). When the external magnetic field B2 is applied, the direction of spin that diffuses and conducts in the silicon channel layer 12 rotates around the axial direction of the external magnetic field B2 (Z-axis direction in the example of FIG. 3) (so-called Hanle effect). The direction of rotation of this spin when diffusing up to the region on the second ferromagnetic layer 14B side in the silicon channel layer 12, and the direction G2 of magnetization of the second ferromagnetic layer 14B set in advance, that is, the direction of spin, Output relative to the interface between the silicon channel layer 12 and the second ferromagnetic layer 14B (for example, resistance output or voltage output). When the external magnetic field B2 is applied, the direction of the spin diffusing in the silicon channel layer 12 rotates, so that the magnetization direction and direction of the second ferromagnetic layer 14B are not aligned. Therefore, the output takes a maximum value when the external magnetic field is zero, and the output is less than the maximum value when the external magnetic field B2 is applied. Further, the output takes a minimum value when the external magnetic field is zero, and the output becomes a minimum value or more when the external magnetic field B2 is applied.

Therefore, in the NL-Hane measurement method, an output peak appears when the external magnetic field is zero, and the output decreases as the external magnetic field B2 is increased or decreased. That is, since the output changes depending on the presence or absence of the external magnetic field B2, the spin transport element 1 according to this embodiment can be used as a magnetic sensor, for example.

As mentioned above, although the suitable embodiment of the present invention was described in detail, the present invention is not limited to the above-mentioned embodiment. Ions for imparting conductivity are implanted into the silicon channel layer 12. Due to this ion implantation, damage remains on the surface of the silicon channel layer 12. Therefore, it is preferable to perform milling from the surface of the silicon channel layer 12 toward the bottom, and the silicon channel layer has a recess between the first portion and the second portion, and the depth of the recess is 10 nm or more. preferable. In this case, the silicon channel layer 12 with suppressed surface damage can be obtained.

Further, the magnetization direction of the second ferromagnetic layer 14B may be fixed by an antiferromagnetic layer provided on the second ferromagnetic layer 14B. In this case, the second ferromagnetic layer 14B having a higher coercive force in one direction can be obtained than when no antiferromagnetic layer is provided. The magnetic field that fixes the magnetization direction of the second ferromagnetic layer 14B is preferably larger than the external magnetic fields B1 and B2 to be evaluated. Thereby, the external magnetic fields B1 and B2 can be detected stably. In the NL-Hanle measurement method, the first ferromagnetic layer 14A and the second ferromagnetic layer 14B preferably have the same degree of coercive force in the same direction due to the antiferromagnetic layer.

Also, a magnetic detection device including a plurality of the spin transport elements 1 described above can be provided. For example, a plurality of the above-described spin transport elements 1 can be arranged in parallel or stacked to form a magnetic detection device. In this case, the outputs of the spin transport elements 1 can be added up. Such a magnetic detection device can be applied to, for example, a biological sensor that detects cancer cells and the like.

Further, the above-described spin injection electrode structure IE and the spin transport element 1 can be used for various spin transport devices such as a magnetic head, a magnetoresistive memory (MRAM), a logic circuit, a nuclear spin memory, and a quantum computer.

The configuration of the spin detection unit (the second ferromagnetic layer 14B, the second spin filter film 13B, and the second convex portion 12B of the silicon channel layer 12) is not limited to the above-described embodiment. It may be one that detects spin.

Hereinafter, examples will be described, but the present invention is not limited to the following examples. In addition, although the silicon channel layer has been described above as an example, substantially the same result can be obtained even in the case where silicon is replaced with germanium, and the material is not limited to silicon.

(Example 1)
First, an SOI substrate including a substrate, an insulating film, and a silicon film was prepared. A silicon substrate was used as the substrate, a 200 nm silicon oxide layer was used as the insulating film, and the silicon film was 100 nm. Phosphorus ions for imparting conductivity to the silicon film were implanted. Thereafter, impurities were diffused by annealing at 900 ° C. to adjust the electron concentration of the silicon film. At this time, the average electron concentration of the entire silicon film was set to 5.0 × 10 ¹⁹ cm ⁻³ .

Next, deposits, organic substances, and natural oxide films on the surface of the SOI substrate were removed using RCA cleaning. Thereafter, the surface of the SOI substrate was terminated with hydrogen using an HF cleaning solution. Subsequently, the SOI substrate was carried into a molecular beam epitaxy (MBE) apparatus. The degree of base vacuum (the degree of vacuum in the apparatus before the actual lamination process) was set to 2.0 × 10 ⁻⁹ Torr or less. Flushing treatment was performed by heating the SOI substrate. As a result, hydrogen on the surface of the silicon film was released to form a clean surface.

Subsequently, using the MBE method, an aluminum oxide as a first tunnel film and an MgAl ₂ O ₄ , an iron film, and a titanium film as a first nonmagnetic spinel film are formed in this order on the silicon film to obtain a laminate. It was. The degree of vacuum during film formation was 5 × 10 ⁻⁸ Torr or less. The titanium film is a cap layer for suppressing characteristic deterioration due to oxidation of the iron film.

In the present embodiment, the first and second tunnel films, the nonmagnetic spinel film, the iron film, and the titanium film are formed in the same process, and thus are not distinguished.

Subsequently, in order to promote crystallization of the first nonmagnetic spinel film, annealing was performed at 300 ° C. for 3 hours.

Next, after cleaning the surface of the laminate, Ta alignment marks were formed on the substrate by photolithography and lift-off. Subsequently, the silicon film was patterned by anisotropic wet etching using a mask. As a result, a silicon channel layer 12 having an inclined portion on the side surface was obtained. At this time, the size of the silicon channel layer 12 was 23 μm × 300 μm. Further, the side surface of the obtained silicon channel layer 12 was oxidized to form a silicon oxide film (oxide film 7a).

Next, the first ferromagnetic layer 14A and the second ferromagnetic layer 14B were formed by patterning the iron film using a photolithography method. The oxide film and the magnesium film located except between the silicon channel layer 12 and the first ferromagnetic layer 14A and the second ferromagnetic layer 14B were removed. Thereby, the first spin filter film 13A and the second spin filter film 13B were obtained. An Al film was formed on one end side and the other end side of the exposed silicon channel layer 12 to obtain a first reference electrode 15A and a second reference electrode 15B, respectively.

Further, a portion of the surface of the silicon channel layer 12 where the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B are not formed by using ion milling and etching. Then, the silicon channel layer 12 was dug to a depth of 20 nm from the surface of the silicon channel layer 12. As a result, the silicon channel layer 12 has a structure including the first convex portion 12A, the second convex portion 12B, the third convex portion 12C, the fourth convex portion 12D, and the main portion 12E. The first convex portion 12A, the second convex portion 12B, the third convex portion 12C, and the fourth convex portion 12D are arranged in this order at predetermined intervals in the X-axis direction and extend so as to protrude from the main portion 12E. It is a part that exists. The film thickness H1 of the first convex portion 12A, the second convex portion 12B, the third convex portion 12C, and the fourth convex portion 12D was 10 nm. With such a structure, the surface damage formed when ions for imparting conductivity were implanted into the silicon film to be the silicon channel layer 12 was removed.

Furthermore, on the side surfaces of the oxide film 7a, the first spin filter film 13A, the second spin filter film 13B, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B, Of the upper surface of the silicon channel layer 12, a silicon oxide film (on the main portion 12E where the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A and the second reference electrode 15B are not formed) An oxide film 7b) was formed.

Next, wirings 18A to 18D were formed on the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B, respectively. As the wirings 18A to 18D, a stacked structure of Ta (thickness 10 nm), Cu (thickness 50 nm), and Ta (thickness 10 nm) was used. Further, electrode pads E1 to E4 were formed at the ends of the wirings 18A to 18D, respectively. As the electrode pads E1 to E4, a laminated structure of Cr (thickness 50 nm) and Au (thickness 150 nm) was used. Thus, the spin transport device of Example 1 having the same configuration as the spin transport device 1 shown in FIGS. 1 to 4 was produced.

(Result of NL measurement)
In the NL measurement method, in the spin transport device fabricated in Example 1, the magnetization direction G1 of the first ferromagnetic layer 14A and the magnetization direction G2 of the second ferromagnetic layer 14B are the same as the magnetization direction of the external magnetic field B1 (FIG. 3). In the Y-axis direction). An external magnetic field B1 was applied to the spin transport element from a direction (Y-axis direction) parallel to the magnetization directions of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B. By flowing a detection current from the alternating current source 70 to the first ferromagnetic layer 14A, spin was injected from the first ferromagnetic layer 14A to the silicon channel layer 12. And the output based on the magnetization change by the external magnetic field B1 was measured by the output measuring device 80. At this time, all measurements were performed at room temperature.

FIG. 5 is a graph showing the relationship between the applied magnetic field and the voltage output in the NL measurement method. F1 in FIG. 5 shows the case where the external magnetic field B1 is changed from the minus side to the plus side, and F2 in FIG. 5 shows the case where the external magnetic field B1 is changed from the plus side to the minus side. As shown in F1 and F2 of FIG. 5, the spin transport device had a voltage output of about 12 μV.

(Result of NL-Hanle measurement)
In the NL-Hane measurement method, in the spin transport device manufactured in Example 1, the direction of the applied external magnetic field B2 (Z-axis direction shown in FIG. 3) is the magnetization direction of the first ferromagnetic layer 14A (Y shown in FIG. 3). The axial direction was perpendicular to G1 and the magnetization direction (Y-axis direction shown in FIG. 3) G2 of the second ferromagnetic layer 14B. FIG. 6 is a graph showing the relationship between the applied magnetic field and the voltage output in the NL-Hanle measurement method. FIG. 6 shows the measurement results when the magnetization direction of the first ferromagnetic layer 14A is fixed parallel to the magnetization direction of the second ferromagnetic layer 14B.

As can be seen from the measurement results in FIG. 6, it can be seen that the spin conducted through the silicon channel layer is rotated and attenuated by the application of the external magnetic field B2. Therefore, it can be proved that the measurement result of FIG. 6 is a signal generated by spin conduction.

(Example 2)
An element was prepared in the same manner as in Example 1. However, magnesium oxide was formed as the first tunnel film. The results are shown in Table 1.

(Example 3)
An element was prepared in the same manner as in Example 1. However, silicon oxide was formed as the first tunnel film. The first ferromagnetic film was a Heusler alloy. This Heusler alloy is represented by a composition formula of Co ₂ FeAl _0.5 Si _0.5 , and annealing was performed at 600 ° C. after film formation. In order to suppress diffusion of the ferromagnetic metal element into the silicon channel layer, the film thickness of the first tunnel film was set to 1.2 nm, and the film thickness of the first nonmagnetic spinel film was set to 2.0 nm. The results are shown in Table 1.

(Comparative Example 1)
An element was prepared in the same manner as in Example 1. However, aluminum oxide was formed as the first tunnel film, and the first nonmagnetic spinel film was not installed. However, the film thickness of aluminum oxide was the same as the sum of the film thicknesses of the first tunnel film and the first nonmagnetic spinel film in Example 1. The results are shown in Table 1.

(Comparative Example 2)
An element was prepared in the same manner as in Example 1. However, magnesium oxide was formed as the first tunnel film, and the first nonmagnetic spinel film was not installed. However, the film thickness of magnesium oxide was the same as the sum of the film thicknesses of the first tunnel film and the first nonmagnetic spinel film of Example 1. The results are shown in Table 1.

(Comparative Example 3)
An element was prepared in the same manner as in Example 1. However, hafnium oxide was formed as the first tunnel film. The results are shown in Table 1.

(Comparative Example 4)
An element was prepared in the same manner as in Example 1. However, tantalum oxide was formed as the first tunnel film. The results are shown in Table 1.

(Comparison of results)
Table 1 summarizes the examples and comparative examples. In Example 1 and Example 2, almost the same results were obtained at room temperature. In Comparative Example 1, Comparative Example 3 and Comparative Example 4, no signal was observed at room temperature. However, output is observed in non-local measurement at low temperatures, and it can be determined that the output at room temperature was not obtained as a result of temperature dependence. In Comparative Example 2, a spin output at room temperature was observed, but the output was smaller than in Example 1 and Example 2. Therefore, it can be seen that the method of this embodiment has a spin filter structure that can realize high output at room temperature. Further, compared to Example 2 in which an iron film is used for the first ferromagnetic layer, Example 3 using Heusler alloy has higher characteristics, and in addition to the characteristics of the spin filter film, the spin of the ferromagnetic layer is obtained. The cause is considered to be high polarizability.

IE ... Spin injection electrode structure, 1 ... Spin transport element, 10 ... Substrate, 11 ... Silicon oxide film, 12 ... Silicon channel layer, 13A ... First spin filter film, 13B ... Second spin filter film, 14A ... First strong Magnetic layer, 14B ... second first ferromagnetic layer, 15A ... first reference electrode, 15B ... second reference electrode, 16A ... first tunnel film, 16B ... first nonmagnetic spinel film, 16C ... second tunnel film, 16D ... second tunnel film, 70 ... AC current source, 80 ... output measuring device, P ... lattice matching portion, N ... non-lattice matching portion.

Claims

A semiconductor channel layer;
A tunnel film provided on the semiconductor channel layer;
A nonmagnetic spinel film provided on the tunnel film;
A spin injection electrode structure comprising: a ferromagnetic layer provided on the nonmagnetic spinel film.
The spin injection electrode structure according to claim 1, wherein the tunnel film is not epitaxially grown on the semiconductor channel layer.
The spin injection electrode structure according to claim 1 or 2, wherein the tunnel film is amorphous.
The spin injection electrode structure according to any one of claims 1 to 3, wherein the tunnel film is made of an oxide containing any one element of Al, Mg, Si, Zn, and Ti.
The spin injection electrode structure according to any one of claims 1 to 4, wherein the nonmagnetic spinel film is crystallized on the tunnel film.
The spin injection electrode structure according to any one of claims 1 to 5, wherein the nonmagnetic spinel film has a spinel structure containing any element of Al, magnesium oxide, and Zn.
The spin injection electrode structure according to any one of claims 1 to 6, wherein a thickness of the tunnel film is 0.6 nm or more and 2.0 nm or less.
The spin injection electrode structure according to any one of claims 1 to 7, wherein a film thickness of the nonmagnetic spinel film is 0.6 nm or more and 2.4 nm or less.
A spin injection electrode structure according to any one of claims 1 to 8 is provided in a first portion, and further a second tunnel film provided on a second portion of the semiconductor channel layer;
A second non-magnetic spinel film provided on the second tunnel film;
And a second ferromagnetic layer provided on the second nonmagnetic spinel film.