JP2014154612A - Spin injection electrode structure and spin conduction element including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spin injection electrode structure capable of achieving a decrease in element resistance without deteriorating spin injection efficiency, and a spin conduction element including the spin injection electrode structure.SOLUTION: A spin injection electrode structure includes a semiconductor channel layer, a tunnel barrier layer formed on the semiconductor channel layer, and a ferromagnetic layer formed on the tunnel barrier layer. The tunnel barrier layer contains an aluminum oxide having a cubic spinel-type crystal structure, as main constituents, and also contains zinc ions or magnesium ions.

Description

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

  Recently, the spin conduction phenomenon in semiconductors has attracted much attention. Since the spin diffusion length in a semiconductor is much longer than the spin diffusion length in a metal, there is an advantage that it can be used in various ways from the viewpoint of output and circuit. Above all, silicon is a material that is the center of today's main semiconductor products. If silicon-based spintronics can be realized, innovative functions can be added to silicon devices without abandoning existing technologies. For example, a spin-MOSFET disclosed in Patent Document 1 can be given.

  In order to realize a silicon-based spin transport device, it is desired to obtain sufficient output characteristics at room temperature. For this purpose, high-efficiency spin injection / accumulation into silicon is indispensable, and a laminated structure in which a tunnel barrier layer is inserted at the ferromagnetic layer / silicon interface is expected.

As the material of the tunnel barrier layer, Al ₂ O ₃ (Non-patent Document 1), SiO ₂ (Non-patent Document 2), and MgO (Non-patent Document 3) are known, all of which have been representative in spintronics. Material. Among these, MgO is considered to be suitable as a tunnel barrier layer for efficiently injecting spin because MgO is a material that can realize a coherent tunnel. In fact, the room temperature spin conduction phenomenon in silicon has been observed in a laminated structure using Fe as a ferromagnetic layer and MgO as a tunnel barrier layer (Non-Patent Document 4). However, since the output characteristic still does not reach the theoretical value, further improvement of the spin injection efficiency is expected.

  One of the causes for reducing the spin injection efficiency is the lattice mismatch of the tunnel barrier layer / silicon junction. The lattice mismatch is calculated from the material-specific parameters (lattice constant) of the two layers to be stacked. For example, in the case of an MgO / silicon junction, cubic on cubic grows to −22.4. %, When grown by rotating 45 degrees in the plane (45 degrees rotation), it is + 9.7%, and the lattice mismatch is large. If the lattice mismatch is large, dangling bonds remain at the junction interface, and the generated defect levels are thought to capture and scatter spins.

JP 2004-111904 A

Applied Physics Letters, Vol. 91, p 212109, (2007) Applied Physics Letters, Vol. 95, p 172102, (2009) Applied Physics Express, Vol. 2, p 053003, (2009) Applied Physics Express, Vol. 4, p 023003, (2011)

  When a spin transport element is applied to a device such as a magnetic head or a spin-MOSFET, it is required to have not only a high output value but also a low resistance value (area resistance value: RA) as a characteristic of the element alone. The low resistance of the element is indispensable not only for realizing low power consumption and low voltage driving when miniaturization and high integration, but also for improving high frequency response characteristics by impedance matching with peripheral circuits.

  In general, it is effective to reduce the thickness of the tunnel barrier layer in order to reduce the resistance of the spin transport device. However, if the tunnel barrier layer is made too thin, pinholes can cause pinholes that can lead to degradation of characteristics such as increased noise and decreased output, and the breakdown voltage of the tunnel barrier layer can be insufficient, causing dielectric breakdown. Problem is likely to occur. Therefore, the tunnel barrier layer used in the spin injection electrode structure should be made of a material with a new specification that can achieve low resistance without reducing the film thickness and maintain high spin injection efficiency. ing.

  The present invention has been made to solve the above-described problems, and provides a spin injection electrode structure capable of realizing a reduction in device resistance without deteriorating spin injection efficiency, and a spin transport device using the same. The purpose is to do.

  A spin injection electrode structure according to the present invention includes a semiconductor channel layer, a tunnel barrier layer formed on the semiconductor channel layer, and a ferromagnetic layer formed on the tunnel barrier layer, and the tunnel barrier The layer is mainly composed of aluminum oxide having a cubic spinel crystal structure and contains zinc ions or magnesium ions.

  The tunnel barrier layer is characterized in that zinc ions or magnesium ions are substituted and dissolved in the aluminum oxide.

  The tunnel barrier layer is characterized in that the cation fraction of zinc ions in the tunnel barrier layer is in the range of 10 to 33 mol%.

  The tunnel barrier layer is characterized in that the cation fraction of magnesium ions in the tunnel barrier layer is in the range of 20 to 33 mol%.

  A spin transport device according to the present invention includes a spin injection electrode having the spin injection electrode structure, a semiconductor channel layer, and a spin detection electrode for detecting spin.

  According to the present invention, it is possible to obtain a spin injection electrode structure including a tunnel barrier layer having a reduced resistivity while having a small lattice mismatch at the junction interface and good crystallinity. As a result, the resistance of the single element can be reduced while maintaining highly efficient spin injection into the semiconductor channel, and it is possible to provide a spin transport element with improved element characteristics and improved high-frequency response characteristics.

It is a perspective view of the spin transport device according to the present embodiment. It is sectional drawing along the III-III line of FIG. It is a graph which shows the relationship between the strength (Oe) of the applied magnetic field B1 of the Y-axis direction in a non-local spin valve measurement, and the voltage output (microvolt) detected according to it. It is a graph which shows the relationship between the strength (Oe) of the applied magnetic field B2 of the Z-axis direction in a non-local Hanle effect measurement, and the voltage output (microvolt) detected according to it. It is a graph which shows the relationship between the cation fraction (mol%) of the zinc ion in a tunnel barrier layer, or magnesium ion, and the area resistance (kohm * micrometer < ² >) of an element. It is a graph which shows the relationship between the cation fraction (mol%) of the zinc ion in a tunnel barrier layer, or the voltage output (microvolt (normalization)) detected by the non-local spin valve measurement of an element.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view of the spin transport element 1. FIG. 2 is a cross-sectional view taken along line III-III in FIG.

  As shown in FIG. 2, the spin transport device 1 includes a silicon oxide film 11 and a silicon channel layer 12 in this order on a silicon substrate 10 when silicon is used as a semiconductor. On the silicon channel layer 12, the first ferromagnetic layer 14A, the first nonmagnetic electrode 15A, the second ferromagnetic layer 14B, and the second nonmagnetic electrode 15B are spaced apart from each other in the X-axis direction. Are arranged in this order. A tunnel barrier layer 13A and a tunnel barrier layer 13B are provided between the silicon channel layer 12 and the first and second ferromagnetic layers 14A and 14B, respectively. The silicon channel layer 12, the tunnel barrier film 13A, and the first ferromagnetic layer 14A constitute a spin injection electrode structure IE.

  As the silicon 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 film thickness of the silicon oxide film 11 is, for example, 200 nm.

As the silicon channel layer 12, a material to which a dopant for imparting conductivity to silicon is added is used. The dopant concentration can be 1.0 × 10 ^{16 to} 1.0 × 10 ²² cm ⁻³ . The film thickness of the silicon channel layer 12 is, for example, 100 nm. The silicon channel layer 12 may be a laminated channel having a predetermined concentration of delta doping. Delta doping means that doping is performed at a high dopant concentration in an extremely thin region of about several nm from the interface, unlike doping in which the dopant is diffused uniformly.

  As shown in FIG. 2, the silicon channel layer 12 has an inclined portion on the side surface, and the inclination angle θ is 50 degrees 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, and the upper surface of the silicon channel layer 12 is preferably a (001) plane.

  As shown in FIG. 2, the silicon channel layer 12 includes a first convex portion 12A, a second convex portion 12B, a third convex portion 12C, a fourth convex portion 12D, and a 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 portions that extend so as to protrude from the main portion 12E, and have a predetermined interval in the X-axis direction. Are arranged.

  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 is, for example, 20 nm. The film thickness H2 of the main part 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 approximately 0.8 μm.

  The tunnel barrier layers 13A and 13B are made of a material containing aluminum oxide as a main component and containing zinc ions or magnesium ions. Here, the main component in the present application means that the cation fraction of aluminum ions constituting the tunnel barrier layer is 50 mol% or more.

  The cation fraction of zinc ions or magnesium ions in the tunnel barrier layers 13A and 13B is preferably 33 mol% or less. Zinc ions or magnesium ions contained in such a composition range are in the form of substitutional solid solution with respect to the main component aluminum oxide (zinc oxide or magnesium oxide is not separately deposited). When the cation fraction of zinc ions or magnesium ions in the tunnel barrier layer exceeds 33 mol%, cations are present at interstitial positions or locally concentrated, and the crystal structure of the tunnel barrier layer is deteriorated. In addition, since domains having different crystal structures are generated in the tunnel barrier layer, high spin injection efficiency cannot be obtained.

  The cation fraction of zinc ions in the tunnel barrier layers 13A and 13B is preferably 10 mol% or more. By containing zinc ions, the band gap of the tunnel barrier can be relatively reduced, and the resistance of the single element can be reduced without reducing the thickness of the tunnel barrier layer. When the cation fraction of zinc ions is less than 10 mol%, it is not always possible to realize low resistance.

  The cation fraction of magnesium ions in the tunnel barrier layers 13A and 13B is preferably 20 mol% or more. By containing magnesium ions, the band gap of the tunnel barrier can be relatively reduced, and the resistance of the element alone can be reduced without reducing the thickness of the tunnel barrier layer. When the cation fraction of magnesium ions is less than 20 mol%, it is not always possible to realize low resistance.

The tunnel barrier layers 13A and 13B are epitaxially grown on the first convex portion 12A and the second convex portion 12B of the silicon channel layer and include a cubic spinel crystal structure (general chemical formula: AB ₂ O ₄ ). It is out. Zinc ions or magnesium ions contained in the tunnel barrier layer are arranged at the A site (tetrahedral site) of the spinel crystal structure (general chemical formula: AB ₂ O ₄ ) and contained without deteriorating the crystal structure. Conceivable. At this time, the lattice constant (a) of the tunnel barrier layer is calculated from ZnAl ₂ O ₄ or MgAl ₂ O ₄ from the lattice constant (a = 7.91Å) of γ-Al ₂ O ₃ having a cubic spinel crystal structure. Since it is within the range up to the lattice constant (a = 8.09Å), the lattice mismatch with respect to silicon (a = 5.43Å) is +3.0 to + 5.2% (45 degrees rotation). The lattice mismatch of the tunnel barrier layer / silicon junction is kept relatively small, and a laminated structure with relatively few lattice defects present at the junction interface can be obtained, so that high spin injection efficiency can be maintained.

  The film thickness of the tunnel barrier layers 13A and 13B is preferably 0.6 nm or more and 2.0 nm or less. As a result, a good-quality epitaxial film with few crystal defects (misfit dislocations) can be obtained, so that a coherent tunnel can be realized. If the thickness is less than 0.6 nm, the film thickness is less than the lattice constant and the film quality and withstand voltage are insufficient, which is not preferable from the viewpoint of ensuring reliability. In addition, if it exceeds 2.0 nm, the element resistance becomes too high, and not only low power consumption and low voltage driving when miniaturization / high integration is achieved, but also high frequency response characteristics deteriorate. End up.

  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 detects the spin conducted through the silicon channel layer 12. Functions as an electrode. The first ferromagnetic layer 14A is provided on the tunnel barrier layer 13A. The second ferromagnetic layer 14B is provided on the tunnel barrier layer 13B.

  The material of the first ferromagnetic layer 14A and the second ferromagnetic layer 14B is composed of at least one element selected from the group consisting of Mn, Co, Fe, and Ni, for example. Since these materials are ferromagnetic materials having a high spin polarizability, the function as a spin injection electrode or a spin detection electrode can be suitably realized.

The first ferromagnetic layer 14A and the second ferromagnetic layer 14B preferably have a crystal structure of a body-centered cubic lattice (bcc) structure. Further, a Heusler alloy layer (a high spin polarization material having an ordered structure called an L2 ₁ structure with a composition of X ₂ YZ) may be included. Thereby, the ferromagnetic layer can be epitaxially grown on the tunnel barrier layer in a predetermined crystal orientation, so that the spin polarizability can be further increased.

  The first ferromagnetic layer 14A and the second ferromagnetic layer 14B are preferably provided with a difference in coercive force (reversal magnetic field). 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, and are maintained by shape anisotropy (difference in aspect ratio). A magnetic difference is applied. 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.

  The first ferromagnetic layer 14A and the second ferromagnetic layer 14B may be provided with an antiferromagnetic layer on one side so that the magnetization of one ferromagnetic layer is fixed in one direction. Furthermore, the aspect which strengthened the exchange coupling with an antiferromagnetic layer by the synthetic pinned structure may be sufficient. Alternatively, the ferromagnetic layer may be made into a single magnetic domain by making the bias magnetic field application layer adjacent to each other.

  One of the first nonmagnetic electrode 15 </ b> A and the second nonmagnetic electrode 15 </ b> B functions as an electrode for causing a spin-polarized current to flow through the silicon channel layer 12, and the other uses the spin conducted through the silicon channel layer 12 as a voltage. It functions as an electrode for detection as an output. The first nonmagnetic electrode 15A and the second nonmagnetic electrode 15B are provided on the third convex portion 12C and the fourth convex portion 12D of the silicon channel layer 12, respectively. The first nonmagnetic electrode 15A and the second nonmagnetic electrode 15B are preferably made of a nonmagnetic metal having a low resistance to Si, such as Al.

The protective film 7 a is formed on the side surface of the silicon channel layer 12. The protective film 7b includes the silicon channel layer 12, the protective film 7a, the tunnel barrier layer 13A, the tunnel barrier layer 13B, the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first nonmagnetic electrode 15A, and the second It is formed on the side surface of the nonmagnetic electrode 15B. In addition, on the upper surface of the silicon channel layer 12, on the main portion 12E where the first ferromagnetic layer 14A, the second ferromagnetic layer 14B, the first nonmagnetic electrode 15A, and the second nonmagnetic electrode 15B are not provided. A protective film 7b is formed. The protective films 7a and 7b are formed in order to insulate and separate the silicon channel layer 12 and to suppress the absorption of spin by wiring or the like. Also, it functions as a protective film for suppressing the deterioration of the tunnel barrier layers 13A and 13B. Material of the protective layer 7a and 7b is, for example, SiO _2.

  As shown in FIG. 1, wirings 18 </ b> A, 18 </ b> B, 18 </ b> C, and 18 </ b> D are formed on the first nonmagnetic electrode 15 </ b> A, the first ferromagnetic layer 14 </ b> A, the second ferromagnetic layer 14 </ b> B, and the second nonmagnetic electrode 15 </ b> B. Each is provided and routed to the top of the silicon oxide film 11 through the protective film 7b (the inclined side surface of the silicon channel layer 12). The material of the wirings 18A, 18B, 18C and 18D is preferably a low resistance conductive material such as Cu.

  As shown in FIG. 1, measurement electrode pads E1, E2, E3, and E4 are provided at the ends of the wirings 18A, 18B, 18C, and 18D, and are formed on the silicon oxide film 11. Yes. The material of the electrode pads E1, E2, E3, and E4 is preferably a conductive material having high corrosion resistance and low resistance such as Au.

  Hereinafter, an example of the operation of the spin transport device 1 according to the embodiment of the present invention will be described.

  As shown in FIGS. 1 and 2, the electrode pads E1 and E3 are connected to the current source 70, thereby connecting the first ferromagnetic layer 14A, the tunnel barrier layer 13A, the silicon channel layer 12 and the first nonmagnetic electrode 15A. In addition, a spin-polarized current corresponding to the magnetization direction G1 of the first ferromagnetic layer 14A flows. Along with this, a spin corresponding to the magnetization direction G1 of the first ferromagnetic layer 14A is injected into the silicon channel layer 12, and diffuses as a spin current toward the second ferromagnetic layer 14B. That is, a structure in which current and spin current flow in the X-axis direction of the silicon channel layer 12 can be obtained.

  The spin injected from the first ferromagnetic layer 14A into the silicon channel layer 12 and diffused to the second ferromagnetic layer 14B side is caused by the potential difference from the spin corresponding to the magnetization direction G2 of the second ferromagnetic layer 14B. A voltage output is generated at the interface between the channel layer 12 and the second ferromagnetic layer 14B. This voltage output can be detected by connecting the electrode pads E2 and E4 to the output measuring device 80 as shown in FIGS.

  Here, consider a case where an external magnetic field B1 in the Y-axis direction is applied as shown in FIG. In this case, a so-called nonlocal spin valve effect can be used. Since the first ferromagnetic layer 14A and the second ferromagnetic layer 14B have a difference in coercive force (reversal magnetic field) due to the effect of shape anisotropy, etc., depending on the direction and strength of the external magnetic field B1. The respective magnetization directions G1 and G2 change. Thereby, the relative spin between the spin injected from the first ferromagnetic layer 14A to the silicon channel layer 12 and diffused toward the second ferromagnetic layer 14B and the spin corresponding to the magnetization direction G2 of the second ferromagnetic layer 14B. The angle changes, and the voltage output (resistance value) at the interface between the silicon channel layer 12 and the second ferromagnetic layer 14B changes accordingly.

  An example of the result of non-local spin valve measurement is shown in FIG. FIG. 3 is a graph showing the relationship between the strength (Oe) of the applied magnetic field B1 in the Y-axis direction and the voltage output (μV) detected accordingly. In FIG. 3, F1 shows the case where the external magnetic field B1 is changed from the minus side to the plus side, and F2 shows the case where the external magnetic field B1 is changed from the plus side to the minus side. That is, the resistance is low when the magnetization direction G1 of the first ferromagnetic layer 14A and the magnetization direction G2 of the second ferromagnetic layer 14B are parallel, and the resistance is high when the magnetization direction is antiparallel.

  Next, consider a case where an external magnetic field B2 in the Z-axis direction is applied as shown in FIG. In this case, a so-called non-local Hanle effect can be used. When the spin injected from the first ferromagnetic layer 14A to the silicon channel layer 12 diffuses toward the second ferromagnetic layer 14B, the intensity of the external magnetic field B2 in the Z-axis direction (perpendicular to the spin direction) is increased. In response, Larmor precession occurs. As a result, the spin injected from the first ferromagnetic layer 14A into the silicon channel layer 12 and diffused while precessing toward the second ferromagnetic layer 14B corresponds to the magnetization direction G2 of the second ferromagnetic layer 14B. The relative angle with the spinning spin changes, and the voltage output (resistance value) at the interface between the silicon channel layer 12 and the second ferromagnetic layer 14B changes accordingly.

  An example of the results of non-local Hanle effect measurement is shown in FIG. FIG. 4 is a graph showing the relationship between the strength (Oe) of the applied magnetic field B2 in the Z-axis direction and the voltage output (μV) detected accordingly. When the external magnetic field is zero, the spin diffusing through the silicon channel layer 12 does not precess, and the voltage output becomes an extreme value in order to maintain the injected state. That is, when the magnetization direction G1 of the first ferromagnetic layer 14A and the magnetization direction G2 of the second ferromagnetic layer 14B are parallel, the resistance increases as the magnetic field strength increases. When the magnetization direction G1 of the first ferromagnetic layer 14A and the magnetization direction G2 of the second ferromagnetic layer 14B are antiparallel, the resistance decreases as the magnetic field strength increases.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to said embodiment. For example, the semiconductor channel layer may be GaAs (a = 5.65Å) or Ge (a = 5.67Å). In this case, the lattice mismatch with the tunnel barrier layer of the present invention is −1.0 to + 1.2% (45 degrees rotation) and −1.4 to + 0.8% (45 degrees rotation), respectively. An effect can fully be expressed.

  Further, on the silicon channel layer 12, a gate electrode may be provided between the first ferromagnetic layer 14A and the second ferromagnetic layer 14B. Thereby, it becomes possible to control the precession of the spin conducted through the silicon channel layer 12 by the gate electric field.

  The spin transport element in the present invention can be applied to various spin transport devices such as a magnetic head, a magnetoresistive memory (MRAM), a logic circuit, a nuclear spin memory, and a quantum computer.

  Hereinafter, the present invention will be described more specifically based on Experimental Example 1, Experimental Example 2, Comparative Example 1, and Comparative Example 2, but the present invention is not limited to the following examples.

(Experimental example 1)
An SOI substrate comprising a silicon substrate, a silicon oxide film (film thickness 200 nm), and a silicon film (film thickness 100 nm) was prepared. A dopant channel for imparting conductivity to a silicon film is ion-implanted, annealed at 900 ° C., and diffused and activated to uniformly diffuse a silicon channel having a carrier concentration of 5.0 × 10 ¹⁹ cm ^−3. A layer was formed.

  Next, RCA cleaning was used to remove deposits, organic substances, and natural oxide films on the SOI substrate surface, and the SOI substrate surface was terminated with hydrogen. Subsequently, the cleaned and planarized SOI substrate surface was formed by flushing the SOI substrate in a molecular beam epitaxy (MBE) apparatus.

  Next, using a MBE method, a tunnel barrier layer (film thickness: 0.8 nm), Fe (film thickness: 13 nm) as a ferromagnetic layer, and Ti (film thickness: 3 nm) as an Fe antioxidant film are formed on the SOI substrate. A film was formed in this order to form a laminate. The tunnel barrier layer was mainly composed of aluminum oxide, and as shown in Table 1, the cation fraction of zinc ions was changed to prepare each sample. Evaluation after film formation confirmed that the tunnel barrier layer contained a crystal phase having a cubic spinel crystal structure in all samples and was epitaxially grown on silicon. In addition, the evaluation after the film formation was performed by evaluating the crystal structure of the tunnel barrier layer, the lattice constant, and the crystal orientation of the laminated film by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM), The composition ratio and distribution of cations present in the tunnel barrier layer are evaluated by energy dispersive X-ray spectroscopy (EDX), and the cations present in the tunnel barrier layer are evaluated by X-ray photoelectron spectroscopy (XPS). The electronic state was evaluated.

  Next, the stacked body was patterned by photolithography and ion milling to expose the silicon channel layer. Using the laminate and the resist as a mask, the silicon channel layer was anisotropically wet etched to form a silicon channel layer having an inclined portion on the side surface. At this time, the size of the silicon channel layer was 23 μm × 300 μm, and the side surface of the silicon channel layer was oxidized.

Next, the laminate was patterned by photolithography and ion milling to form a spin injection electrode and a spin detection electrode. At this time, the plane dimensions (junction sizes) of the spin injection electrode and the spin detection electrode were 0.5 μm × 21 μm and 2 μm × 21 μm, respectively. Further, SiO ₂ was formed as a protective film on the side wall of the spin injection electrode and the spin detection electrode and on the exposed portion of the silicon channel layer. Thereafter, the protective film at positions to be the first nonmagnetic electrode and the second nonmagnetic electrode was removed, and a first nonmagnetic electrode and a second nonmagnetic electrode made of Al were formed.

  Next, wirings were formed on the spin injection electrode, the spin detection electrode, the first nonmagnetic electrode, and the second nonmagnetic electrode, respectively. As the wiring, a stacked structure of Ta (film thickness 10 nm), Cu (film thickness 50 nm), and Ta (film thickness 10 nm) was used. Furthermore, an electrode pad was formed at each end of each wiring. A laminated structure of Cr (film thickness 50 nm) and Au (film thickness 150 nm) was used as the electrode pad. Thus, the spin transport device of Experimental Example 1 having the same form as the spin transport device 1 shown in FIGS. 1 and 2 was produced.

For these spin transport devices, three-terminal measurement was performed at room temperature, and the sheet resistance (Ω · μm ² ) of the spin injection electrode was evaluated. The number of samples at each level was 100, and the average value and variation (standard deviation) of the sheet resistance of the element were calculated. In addition, non-local spin valve measurement was performed to evaluate the detected voltage output (μV). The results are shown in Table 1. In addition, the voltage output of each sample was normalized with the voltage output obtained in sample # 1 being 1.

(Experimental example 2)
In Experimental Example 2, a sample was prepared by the same procedure as in Experimental Example 1 except that the tunnel barrier layer in Experimental Example 1 was changed to a structure containing aluminum oxide as a main component and containing magnesium ions. . After film formation, the same evaluation as in Experimental Example 1 confirmed that the tunnel barrier layer contained a crystal phase having a cubic spinel crystal structure in all samples and was epitaxially grown on silicon. . The obtained sample was measured and evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

(Comparative Example 1)
In Comparative Example 1, a sample was produced by forming a tunnel barrier layer with the composition of Sample # 10 of Experimental Example 1 without performing the flushing process before film formation. After the film formation, the same evaluation as in Experimental Example 1 confirmed that the tunnel barrier layer was amorphous. The obtained sample was measured and evaluated in the same manner as in Experimental Example 1. The sheet resistance was 3.19 kΩ · μm ² , and no non-local output was detected.

(Comparative Example 2)
In Comparative Example 2, a sample was produced by forming a tunnel barrier layer with the composition of Sample # 30 of Experimental Example 2 without performing the flushing process before film formation. After the film formation, the same evaluation as in Experimental Example 1 confirmed that the tunnel barrier layer was amorphous. The obtained sample was measured and evaluated in the same manner as in Experimental Example 1. The area resistance was 3.45 kΩ · μm ² , and no non-local output was detected.

  As shown in Table 1, Table 2, and FIG. 5, the area resistance of the spin injection electrode (that is, the resistivity of the tunnel barrier layer) is lowered as the cation fraction of zinc ions or magnesium ions in the tunnel barrier layer is increased. be able to. Considering variation among elements, a remarkable reduction in resistance can be realized with a cation fraction of 10 mol% or more when zinc ions are contained and 20 mol% or more when magnesium ions are contained.

  In addition, as shown in Tables 1 and 2 and FIG. 6, when the cation fraction of zinc ions or magnesium ions is 33 mol% or less, the voltage output (that is, spin injection) detected by non-local spin valve measurement. Efficiency) can be maintained at a high level. On the other hand, when the cation fraction exceeds 33 mol%, the voltage output detected by the non-local spin valve measurement is rapidly reduced.

  From the above, when zinc ions are contained in the tunnel barrier layer, it is desirable to contain in a range such that the cation fraction is 10 to 33 mol%, and magnesium ions are contained in the tunnel barrier layer. In this case, it can be seen that the cation fraction is preferably contained in a range of 20 to 33 mol%.

  As shown in the results of Comparative Example 1 and Comparative Example 2, even when the tunnel barrier layer contains zinc ions or magnesium ions in an effective range of the present invention, when the crystal structure is amorphous, The spin injection efficiency is significantly reduced. From the above, the effect of the present invention can be realized only when the tunnel barrier layer has a cubic spinel crystal structure.

  In the above embodiment, the ferromagnetic layer is limited to Fe in order to make a systematic comparison without depending on the material. However, in order to reduce lattice mismatch at the interface between the ferromagnetic layer and the tunnel barrier layer, the ferromagnetic layer It is effective to appropriately change the material.

IE ... Spin injection electrode structure 1 ... Spin transport element 10 ... Substrate 11 ... Silicon oxide film 12 ... Silicon channel layers 13A and 13B ... Tunnel barrier layer 14A ... First ferromagnetic layer 14B ... Second ferromagnetic layer 15A ... First non-magnetic layer Magnetic electrode 15B ... second nonmagnetic electrode 70 ... current source 80 ... output measuring instrument

Claims (5)

  A semiconductor channel layer, a tunnel barrier layer formed on the semiconductor channel layer, and a ferromagnetic layer formed on the tunnel barrier layer, wherein the tunnel barrier layer is a cubic spinel type A spin-injection electrode structure comprising aluminum oxide having a crystal structure as a main component and containing zinc ions or magnesium ions.   2. The spin injection electrode structure according to claim 1, wherein the tunnel barrier layer has zinc ions or magnesium ions substituted and dissolved in aluminum oxide as a main component.   The spin injection electrode structure according to claim 1 or 2, wherein the tunnel barrier layer has a cation fraction of zinc ions in the tunnel barrier layer in a range of 10 to 33 mol%.   The spin injection electrode structure according to claim 1 or 2, wherein the tunnel barrier layer has a cation fraction of magnesium ions in the tunnel barrier layer in a range of 20 to 33 mol%.   5. A spin transport device comprising: a spin injection electrode having the spin injection electrode structure according to claim 1; a semiconductor channel layer; and a spin detection electrode for detecting spin.

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