JP2017085178A - Tunnel layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spin injection electrode structure for acquiring high output, which suppresses spin scattering at an interface caused by deviation of a lattice constant between a semiconductor channel layer and a tunnel layer, and a lattice constant between the tunnel layer and a ferromagnetic layer, or provide a spin conduction element.SOLUTION: A spin injection electrode structure comprises tunnel layers and a ferromagnetic layer which are arranged on a semiconductor channel layer, in which a lattice constant of a first tunnel layer in contact with the semiconductor channel layer and a lattice constant of a second tunnel layer in contact with the ferromagnetic layer are different from each other, and further, the first tunnel layer and the second tunnel layer have crystalline systems different from each other.SELECTED DRAWING: Figure 4

Description

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

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

JP 2010-239011 A

Tomoyuki Sasaki et al., Applied Physics Express 2, p053003-1〜053003-3, (2009) O. M. J. van't Erve et al., APPLIED PHYSICS LETTERS 91, p212109-1 to 212109-3, (2007) Y. Ando et al., APPLIED PHYSICS LETTERS 94, p182105-1 ~ 182105-3, (2009) Saroj P. Dash et al., Nature, vol.462, p491〜494, (2009) T. Suzuki et al., AppliedPhysics Express 4, p023003-1 to 023003-3, (2011)

  For application of spin injection, conduction, and detection in silicon, it is desired to obtain sufficient output characteristics at room temperature. For example, in Non-Patent Documents 1 to 3 described above, spin injection, conduction, and detection in silicon are reported, but all are events at a low temperature of 150K or less. In Non-Patent Document 4, spin accumulation in silicon at 300 K is observed, but no spin conduction phenomenon in silicon is observed at room temperature, and no wide application is expected at present. is there. On the other hand, in Non-Patent Document 5, although the spin conduction phenomenon in silicon is observed at room temperature, the output characteristics are not sufficient. As described above, one of the reasons why sufficient output characteristics cannot be obtained at room temperature may be that spin scattering at the interface is induced by a shift in lattice constant between silicon and the tunnel layer. Under such circumstances, it is desired to realize effective spin injection that realizes spin conduction that can provide sufficient output characteristics at room temperature in semiconductors, not limited to silicon.

  A method for suppressing spin scattering at the interface due to a shift in lattice constant between silicon and the tunnel layer is also described in Patent Document 1. Suppressing spin scattering at the interface leads to sufficient output characteristics. In Patent Document 1, a first amorphous magnesium oxide is formed on silicon, spin scattering due to lattice mismatch between silicon and magnesium oxide is suppressed, and a first amorphous magnesium oxide is formed on the first amorphous magnesium oxide. High output is achieved by forming crystalline magnesium oxide and leaving a partial coherent effect. However, in order to obtain sufficient output characteristics at room temperature, it is necessary to suppress spin scattering also at the interface between magnesium oxide as a tunnel layer and the first ferromagnetic layer.

  In general, when forming the two tunnel layers as described above, one of the materials is amorphous and the crystal system is not a problem. Furthermore, it is known that a crystal layer such as MgO is generally good as a tunnel layer material in contact with the ferromagnetic layer. As a tunnel layer material in contact with the semiconductor channel layer, a tunnel material such as MgO is known. However, in the case of a crystalline material, spin is caused by strain due to a difference in crystal lattice at the interface between the semiconductor channel layer and the tunnel material. Since it is strongly scattered, high output cannot be realized and sufficient output characteristics cannot be obtained.

  The present invention has been made to solve the above-described problems, and provides a spin injection electrode structure that enables effective injection of spins in a semiconductor channel layer in order to obtain higher output characteristics than conventional ones at room temperature. And it aims at providing a spin transport element.

In order to solve the above-described problem, the spin injection electrode structure of the present invention includes a semiconductor channel layer, a first tunnel layer provided on the semiconductor channel layer, a second tunnel layer provided on the first tunnel layer, A ferromagnetic layer provided on the second tunnel layer, wherein the first tunnel layer and the second tunnel layer have different lattice constants, and the first tunnel layer and the second tunnel layer have different crystal systems. Features.

  In the present invention, the interface of the first tunnel layer in contact with the semiconductor channel layer and the interface of the second tunnel layer in contact with the ferromagnetic layer are crystalline, the interface between the semiconductor channel layer and the first tunnel layer, and the second By giving priority to the interface between the tunnel layer and the ferromagnetic layer over the interface between the first tunnel layer and the second tunnel layer and combining materials of different crystal systems, higher output characteristics than before were obtained.

As described above, when tunnel materials of different crystal systems are stacked, at the interface of the tunnel layer, a crystal lattice buffer region that minimizes strain energy at the interface is necessary to crystallize each layer.

The crystal lattice buffer region is amorphous. By making the crystal lattice buffer region amorphous, even if the tunnel layers to be stacked are of different crystal systems, it can be formed without causing distortion due to the crystal lattice, and spin scattering is suppressed. Therefore, sufficient output characteristics can be obtained.

The crystal lattice buffer region is composed of constituent elements including part or all of constituent elements of the first tunnel layer and the second tunnel layer. Although the first tunnel layer and the second tunnel layer have different crystal systems, the constituent elements diffuse when the tunnel layer is formed. The diffused element does not become the main constituent element of the first tunnel layer and the second tunnel layer, and the first tunnel layer and the second tunnel layer each have a predetermined crystal structure. In the vicinity of the interface of the tunnel layer, an amorphous layer in which diffused constituent elements are mixed is formed.

The first tunnel layer and the second tunnel layer are made of an oxide containing any element of Al, Mg, Si, Zn, and Ti. When these materials are selected, high output can be obtained even when tunnel layers of different crystal systems are stacked.

The first tunnel layer has a spinel structure. The tunnel layer having a spinel structure with respect to the semiconductor channel layer has a small distortion of the crystal lattice at the interface and can obtain a high output.

The second tunnel layer has a NaCl structure. When the tunnel layer has an NaCl structure, spins injected from the ferromagnetic layer tunnel with a high spin polarizability, and a high output can be obtained.

  The semiconductor channel layer is made of any material of silicon, germanium, or gallium arsenide. Since these materials have a long spin diffusion length and a high spin resistance, a high output can be obtained.

The above spin injection electrode structure is provided in the first portion of the semiconductor channel layer, and further, the second tunnel layer provided on the second portion of the semiconductor channel layer, and the second ferromagnetic layer provided on the second tunnel layer. And a spin transport element including the layer. With this structure, spins injected from the spin injection electrode structure can be detected by another spin injection electrode structure. This functions as a magnetic sensor, Spin-MOSFET, or spin transport element.

  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 tunnel layer made of the nonmagnetic spinel film.

  The ferromagnetic layer includes a metal selected from the group consisting of Co, Fe, and Ni, an alloy including one or more elements of the group, or one or more elements selected from the group and boron (B). A compound 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 X ₂ YZ, where X is a Co, Fe, Ni, or Cu group transition metal element or noble metal element on the periodic table, and Y is Mn, It is a V, Cr or Ti group transition metal and can take the elemental species of X, and Z is a typical element of Group III to Group V.
For example, Co ₂ FeSi or Co ₂ MnSi can be used.

  In addition, 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.

  Moreover, it is preferable that the first portion and the second portion ferromagnetic layer of the spin injection electrode structure provided in the semiconductor channel layer 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 is preferably formed with a recess between the first portion and the second portion by milling from the surface to the bottom, and the depth of the recess is preferably 10 nm or more and 20 nm or less.

  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 spins in the semiconductor channel layer at room temperature.

  According to the present invention, the spin scattering at the interface between the tunnel layer and the ferromagnetic layer can be suppressed at the same time while suppressing the spin scattering at the interface between the semiconductor channel and the tunnel layer as compared with the conventional tunnel layer. Therefore, it is possible to provide a spin injection electrode structure, a spin transport element, and a spin transport device that can obtain excellent output characteristics and enable effective injection of spin in the semiconductor channel layer.

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 cross-sectional view taken along line III-III in FIG. FIG. 4 is a configuration diagram of the first tunnel layer 13A and the second tunnel layer 13B, and the crystal lattice relaxation region 16 between the first tunnel layer 13A and the second tunnel layer 13B. 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. FIG. 7 is a spectrum obtained by evaluating the first tunnel layer 13A and the second tunnel layer 13B by EDX.

  Hereinafter, a preferred embodiment of a 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 cross-sectional view taken along line III-III in FIG.

  As shown in FIG. 3, in the case where silicon is used as a semiconductor, the spin transport element 1 includes a silicon substrate 10, a silicon oxide film 11, a silicon channel layer 12, a first tunnel layer 13A, and a second tunnel layer. 13B, third tunnel layer 13C, fourth tunnel layer 13D, first ferromagnetic layer 14A, second ferromagnetic layer 14B, first reference electrode 15A, second reference electrode 15B, and oxide film 7a And an oxide film 7b. The silicon channel layer 12, the first tunnel layer 13A, the second tunnel layer 13B, and the first ferromagnetic layer 14A constitute the spin injection electrode structure IE.

  As shown in FIG. 4, the first tunnel layer 13A and the second tunnel layer 13B have a laminated structure, and a crystal lattice relaxation region 16 is provided in the vicinity of the interface between the first tunnel layer 13A and the second tunnel layer 13B. ing. The crystal lattice relaxation region 16 has two structures. One is an amorphous structure. That is, in order to eliminate the difference in lattice constant near the interface between the first tunnel layer 13A and the second tunnel layer 13B, a part of one or both of the first tunnel layer 13A and the second tunnel layer 13B. Is non-crystallized and is formed when the film is formed by the MBE method. The other is a structure in which the first tunnel layer 13A and the second tunnel layer 13B are mixed while being crystallized in the vicinity of the interface. In this case, the interface between the first tunnel layer 13A and the second tunnel layer 13B is unclear. This is easily formed when formed by sputtering.

  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 can obtain substantially the same result when germanium or gallium arsenide is used instead of silicon.

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 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, in order to be able to adjust the Schottky barrier at the interface between the first tunnel layer 13 </ b> A and the silicon channel layer 12, the ion concentration peak is at a depth of 10 nm in the silicon channel layer 12 from the interface. The silicon channel layer 12 may be used. Further, when the ion concentration of the silicon channel layer 12 is low, there is a method of applying a voltage to the silicon oxide film 11 to induce carriers in the silicon channel layer 12.

  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 tunnel layer 13A and the second tunnel layer 13B function as a tunnel insulating film for efficiently connecting the spin polarization of the first ferromagnetic layer 14A and the spin polarization of the silicon channel layer 12. The first tunnel layer 13 </ b> A is provided on the first convex portion 12 </ b> A that is the first portion of the silicon channel layer 12. The second tunnel layer 13B is provided on the first tunnel layer 13A, and the first ferromagnetic layer 14A is provided on the second tunnel layer 13B. With such a structure, it becomes possible to inject many spin-polarized electrons from the first ferromagnetic layer 14A or the second ferromagnetic layer 14B to the silicon channel layer 12 and increase the potential output of the spin transport element 1. It becomes possible.

The total film thickness of the first tunnel layer 13A and the second tunnel layer 13B is preferably 2.2 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. The first tunnel layer 13A and the second tunnel layer 13B preferably have a thickness of 0.6 nm or more. In this case, the first tunnel layer 13A uniformly formed on the silicon channel layer 12 is used. And the 2nd tunnel layer 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 second tunnel layer 13B. The second ferromagnetic layer 14B is provided on the fourth tunnel layer 13D.

  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 boron (B) is mention | raise | lifted. The crystal structure of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B is preferably a body-centered cubic lattice structure. Accordingly, the first ferromagnetic layer 14A can be partially epitaxially grown on the second tunnel layer 13B, and the second ferromagnetic layer 14B can be partially epitaxially grown on the fourth tunnel layer 13D. However, when formed by sputtering, the ferromagnetic material is an alloy composed of cobalt, iron, and boron, and annealing is performed after the film formation, so that crystallization of the ferromagnetic layer and the tunnel layer is promoted.

  In the example shown in FIG. 1, the first ferromagnetic layer 14 </ b> A and the second ferromagnetic layer 14 </ b> B 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 </ b> A is provided on the third protrusion 12 </ b> C of the silicon channel layer 12. The second reference electrode 15 </ b> B is provided on the fourth protrusion 12 </ b> 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 tunnel layer 13A, the second tunnel layer 13B, the third tunnel layer 13C, the fourth tunnel layer 13D, the first ferromagnetic layer 14A, the second strong layer. It is formed on the side surfaces of the magnetic layer 14B, the first reference electrode 15A, and 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 tunnel layer 13A and the second tunnel layer 13B. The oxide film 7b includes the silicon channel layer 12, the first tunnel layer 13A, the second tunnel layer 13B, the third tunnel layer 13C, the fourth tunnel layer 13D, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, It functions as a protective film for the reference electrode 15A and the second reference electrode 15B, 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, measurement electrode pads E1 to E4 are provided at end portions of the wirings 18A to 18D, respectively. End portions of the wirings 18 </ b> A to 18 </ b> D and measurement electrode pads E <b> 1 to E <b> 4 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 tunnel layer 13A and the second tunnel layer 13B. A crystal lattice relaxation region 16 is formed between the first tunnel layer 13A and the second tunnel layer 13B. The first tunnel layer 16 </ b> A is crystal-grown on the silicon channel layer 12 or partially crystal-grown on the silicon channel layer 12. Similarly, crystal lattice relaxation regions 16 are formed in the third tunnel layer 13C and the fourth tunnel layer 13D. The third tunnel layer 16 </ b> C is crystal-grown on the silicon channel layer 12 or partially crystal-grown on the silicon channel layer 12.

As the first tunnel layer 13A, a tunnel layer having a spinel structure containing aluminum, zinc, silicon, titanium, or magnesium is suitable. When these materials are crystallized, they function as a tunnel layer having a high spin polarizability by the coherent tunnel effect.
It seems that the element notation is mixed with the element symbol and the kana notation. I think that it is better to unify.

As the second tunnel layer 13B, a tunnel layer having a NaCl structure is suitable. In particular, in the case of magnesium oxide, since a high spin polarizability is obtained, the resistance is lower and the output is higher than that of a tunnel layer having a spinel structure.

  Hereinafter, the crystal lattice relaxation region 16 formed between the first tunnel layer 13A and the second tunnel layer 13B will be described. As described above, the crystal lattice relaxation region 16 has an amorphous structure at the interface between the first tunnel layer 13A and the second tunnel layer 13B by the MBE method. Alternatively, a mixed structure is formed while being crystallized at the interface between the first tunnel 13A and the second tunnel layer 13B by a method using sputtering and annealing.

The crystal lattice relaxation region 16 preferably has an amorphous structure. In this case, a high spin polarizability can be obtained because it is not affected by the lattice distortion caused by the difference between the crystal lattices. The crystal lattice relaxation region 16 is preferably formed by the MBE method. By using the MBE method, an amorphous structure can be easily formed, and further, the second tunnel layer 13B can be easily crystallized with a thin film thickness of the amorphous structure.

The crystal lattice relaxation region 16 may have a structure in which layers having different structures are mixed while being crystallized. In this case, since the first tunnel layer 13A and the second tunnel layer 13B are crystallized, the spin is likely to be a coherent tunnel. However, the spin is strongly relaxed in the crystal lattice relaxation region. In addition, the formation method in the case where the crystal lattice relaxation region has a structure in which layers having different structures are mixed while being crystallized is preferably a preparation method using both sputtering and annealing. This has the advantage that crystallization proceeds to the crystal lattice relaxation region because crystallization proceeds by performing annealing.

  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 includes a metal selected from the group consisting of Co and Fe, an alloy including one or more elements of the group, or one or more elements selected from the group and boron (B). In the case of a compound, the first ferromagnetic layer 14A is easily epitaxially grown on the second tunnel layer 13B.

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 X ₂ YZ, where X is a transition of Co, Fe, Ni, or Cu group on the periodic table. It is a metal element or 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 X ₂ YZ 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 where 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 the three elements is an A2 structure.

  Hereinafter, an example of the 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 second tunnel layer 13B and the first tunnel layer 13A, the first ferromagnetic layer Electrons having a spin corresponding to the magnetization direction G 1 of 14 A 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 the operation using the NL-Hane measurement method of the spin transport element 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. When 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 tunnel layer 13A and the second tunnel layer 13B, the magnetization of the first ferromagnetic layer 14A. Electrons having a spin in a direction corresponding to the direction G1 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, consider the case where an external magnetic field B2 is applied to the silicon channel layer 12. 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-Hanle 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.

  Moreover, it can be set as the magnetic detection apparatus provided with two or more above-mentioned spin transport elements 1. FIG. 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 biosensor that detects cancer cells and the like.

  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.

  Further, the configuration of the spin detection unit (the second ferromagnetic layer 14B, the third tunnel layer 13C, the fourth tunnel layer 13D, and the second convex portion 12B of the silicon channel layer 12) is not limited to the above embodiment. You may detect a spin by sending an electric current.

  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 in an example in which silicon is replaced with germanium or gallium arsenide, and the material is not limited to silicon. Similarly, a compound of silicon and germanium may be used.

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, the 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, a first tunnel layer was formed on the silicon film using the MBE method. First, aluminum oxide was crystallized to form the first tunnel layer 13A, and then magnesium oxide was crystallized to form the second tunnel layer 13B. In the initial stage of magnesium oxide formation, the RHEED pattern disappeared, indicating that an amorphous layer was formed. Thereafter, the formation of magnesium oxide was continued, and an RHEED pattern was obtained, so that it was confirmed that crystallization progressed at the end of formation. Thereafter, an iron film as a ferromagnetic layer and a titanium film as a protective film were formed in this order to obtain a laminate. The degree of vacuum during film formation was 5 × 10 ⁻⁸ Torr or less. The titanium film is a protective film for suppressing characteristic deterioration due to oxidation of the iron film as the ferromagnetic layer.

  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 titanium film, the iron film, and the silicon channel layer 12 using a photolithography method. An Al film was formed on one end side and the other end side of the exposed silicon channel layer 12 to form 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, the oxide film 7a, the first tunnel layer 13A, the second tunnel layer 13B, the third tunnel layer 13C, the fourth tunnel layer 13D, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A and Of the side surface of the second reference electrode 15B and the upper surface of the silicon channel layer 12, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first reference electrode 15A, and the second reference electrode 15B are not formed. A silicon oxide film (oxide film 7b) was formed on the portion 12E.

  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. Furthermore, electrode pads E1 to E4 were formed at the ends of the wirings 18A to 18D, respectively. A laminated structure of Cr (thickness 50 nm) and Au (thickness 150 nm) was used as the electrode pads E1 to E4. Thus, the spin transport device of Example 1 having the same configuration as the spin transport device 1 shown in FIGS.

(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. 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 in FIG. 5, the spin transport device had a voltage output of about 12.8 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 result of 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, the measurement result of FIG. 6 is a signal generated by spin conduction.

(Membrane analysis)
Evaluation of the tunnel layer was analyzed by cross-section TEM (Transmission Electron Microscopy), XRD (X Ray Diffraction), and EDX (Energy Dispersive X-Ray analysis). From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.2 nm. Further, an amorphous layer is formed in the tunnel layer, and an amorphous crystal lattice relaxation region is formed.

Further, the tunnel layer portion was cut out from the photograph of the cross-sectional TEM, subjected to free air analysis, and the lattice constant was estimated by analyzing the Bragg point. The portion where the tunnel layer was in contact with the silicon channel layer, the portion where the tunnel layer was in contact with the ferromagnetic layer, and the intermediate portion between the portion in contact with the silicon channel layer and the portion in contact with the ferromagnetic layer were sampled. As a result, the lattice constant of the portion where the tunnel layer was in contact with the silicon channel layer was 7.8 mm. This lattice constant indicates that it is a γ-type aluminum oxide having a spinel structure. Furthermore, the lattice constant of the portion where the tunnel layer was in contact with the ferromagnetic layer was 4.2 Å. This lattice constant indicates that the oxide is composed mainly of magnesium having a NaCl structure. From this, it can be seen that the first tunnel layer 13A is spinel-structured aluminum oxide, and the second tunnel layer 13B is NaCl-structured magnesium oxide.

Furthermore, magnesium, aluminum, oxygen, iron, and silicon were analyzed by EDX. As shown in FIG. 7, since the peak of aluminum and the peak of magnesium are at different positions, and each peak shape has a shoulder shape at the position where the peaks overlap, the crystal lattice relaxation region Shows that aluminum and magnesium are contained respectively.

(Example 2)
An element was prepared in the same manner as in Example 1. However, a nonmagnetic spinel layer made of magnesium and aluminum was formed as the second tunnel layer 13B. The tunnel layer was evaluated by cross-section TEM and EDX. From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.0 nm. Further, it was confirmed that the first tunnel layer 13A was made of aluminum oxide having a spinel structure, and the second tunnel layer 13B was an oxide of magnesium and aluminum having a spinel structure. Further, it was confirmed that a crystal lattice relaxation region 16 mixed with an amorphous structure was formed between the first tunnel layer 13A and the second tunnel layer 13B.

(Example 3)
An element was prepared in the same manner as in Example 1. However, a nonmagnetic spinel layer made of zinc and aluminum was formed as the second tunnel layer 13B. The tunnel layer was evaluated by cross-section TEM and EDX. From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.0 nm. Further, it was confirmed that the first tunnel layer 13A was made of aluminum oxide having a spinel structure, and the second tunnel layer 13B was an oxide of zinc and aluminum having a spinel structure. Further, it was confirmed that a crystal lattice relaxation region 16 mixed with an amorphous structure was formed between the first tunnel layer 13A and the second tunnel layer 13B.

(Comparative Example 1)
An element was prepared in the same manner as in Example 1. However, the second tunnel layer 13B was formed by sputtering. Further, an alloy composed of cobalt, iron, and boron was used for the ferromagnetic layer. After forming the laminated film, annealing was performed at 230 ° C. for 3 hours.

The tunnel layer was evaluated by a cross-sectional TEM. From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.2 nm. Further, from the cross-section TEM, the second tunnel layer 13B was not confirmed to be crystallized and had an amorphous structure.

(Comparative Example 2)
An element was prepared in the same manner as in Example 1. However, the first tunnel layer 13A was not formed, and only the second tunnel layer 13B made of magnesium oxide was formed by the MBE method.

The tunnel layer was evaluated by a cross-sectional TEM. From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.0 nm. The lattice constant was estimated by analyzing the Bragg point by performing the Freee analysis. The lattice constant was 4.2 Å. It can be seen that this lattice constant is a magnesium oxide having a NaCl structure.

(Comparative Example 3)
An element was prepared in the same manner as in Example 1. However, the second tunnel layer 13B was made of tantalum oxide and formed by the MBE method.

The tunnel layer was evaluated by a cross-sectional TEM. From the result of the cross-sectional TEM, the thickness of the tunnel layer was 2.5 nm. Further, crystallization of the first tunnel layer 13A was observed from the cross-section TEM, but the second tunnel layer 13B was amorphous.

The spin output of the thus obtained spin transport device was measured by the NL measurement method. The results are shown in Table 1.

  IE ... Spin injection electrode structure, 1 ... Spin transport element, 10 ... Substrate, 11 ... Silicon oxide film, 12 ... Silicon channel layer, 13A ... First tunnel layer, 13B ... Second tunnel layer, 14A ... First ferromagnetic layer , 14B ... second ferromagnetic layer, 15A ... first reference electrode, 15B ... second reference electrode, 70 ... alternating current source, 80 ... output measuring instrument.

Claims (6)

The first tunnel layer,
A second tunnel layer provided on the first tunnel layer,
A tunnel layer characterized in that the first tunnel layer and the second tunnel layer have different lattice constants, and a crystal lattice buffer region is provided between the first tunnel layer and the second tunnel layer.   The tunnel layer according to claim 1, wherein the crystal lattice buffer region is amorphous.   3. The tunnel layer according to claim 1, wherein the crystal lattice buffer region is a constituent element including part or all of constituent elements of the first tunnel layer and the second tunnel layer.   4. The tunnel according to claim 1, wherein the first tunnel layer and the second tunnel layer are made of an oxide containing any element of Al, Mg, Si, Zn, and Ti. layer.   The tunnel layer according to claim 1, wherein the first tunnel layer has a spinel structure.   The tunnel layer according to any one of claims 1 to 4, wherein the second tunnel layer has a NaCl structure.

Images