Spin valve, method for manufacturing same, and spin device

Abstract

This spin valve comprises a spin injection electrode (101), a spin detection electrode (102), and a spin transport channel (103). The spin injection electrode (101) and the spin detection electrode (102) are each configured from a ferromagnetic material. The spin injection electrode (101) and the spin detection electrode (102) are disposed facing each other. The spin transport channel (103) is configured from a semiconductor and is disposed between the spin injection electrode (101) and the spin detection electrode (102). At least one of the side of the spin injection electrode (101) facing the spin detection electrode (102) and the side of the spin detection electrode (102) facing the spin injection electrode (101) is provided with pointed structures (104a, 104b) having vertices arranged on the spin-transport-channel (103) side.

Description

Spin valve, manufacturing method thereof, and spin device

[0001] The present invention relates to a spin valve, a method for manufacturing the same, and a spin device.

[0002] Electrical spin injection from ferromagnetic materials into semiconductors is a key elemental technology for realizing next-generation ultra-low-power devices in which spin replaces the charge that carries information in electronic devices. For example, a spin MOSFET is a device that utilizes spin injected into a semiconductor (Patent Document 1). This device operates in the same basic principle as a conventional MOSFET, but in addition to its transistor function, it also has a nonvolatile memory function that can detect the parallel / antiparallel state of the magnetization of the ferromagnetic material used as the source and drain electrodes based on the magnitude of the drain current. This potential application to logic circuits with zero standby power consumption is therefore anticipated.

[0003] The most basic structure of a spin device such as a spin MOSFET (spin valve) consists of a spin injection electrode made of a ferromagnetic material layer, a spin detection electrode made of a ferromagnetic material layer, and a spin transport channel made of a semiconductor layer. Spin-polarized carriers injected from the spin injection electrode into the spin transport channel become a spin current that diffuses isotropically through the spin transport channel. The distance over which information corresponding to the spin direction of this spin current can propagate is called the spin diffusion length (λ), and is one of the important parameters that determine the performance of spin devices. If the distance between the spin injection electrode and the spin detection electrode is sufficiently shorter than λ, the change in magnetoresistance (MR) depending on the parallel / antiparallel state of the magnetizations of the two electrodes can be measured when the spin current reaches the spin detection electrode.

[0004] Patent No. 4143644

[0005] A. Fert and H. Jaffres, "Conditions for efficient spin injection from a ferromagnetic metal into a semiconductor", Physical Review B, vol. 63, no. 18, 184420, 2001.

[0006] Electrical spin injection into conventional semiconductors such as Si, Ge, and GaAs has been demonstrated in many cases (e.g., Non-Patent Document 1). However, the MR ratios obtained using these semiconductors as spin transport channels were much smaller than expected (less than a few percent), posing a problem for circuit applications.

[0007] One of the reasons for the small MR ratio obtained by electrical spin injection into semiconductors is the contact resistance (ρ C ) and the resistance per spin diffusion length λ of the semiconductor layer, so-called spin resistance (r S ) is large (Non-Patent Document 2). C r S To achieve this, the ρ C The technology to adjust this will be essential.

[0008] The present invention has been made to solve the above problems, and has as its object to increase the MR ratio of the spin valve.

[0009] The spin valve according to the present invention comprises a spin injection electrode made of a ferromagnetic material, a spin detection electrode made of a ferromagnetic material and arranged facing the spin injection electrode, and a spin transport channel made of a semiconductor, arranged between the spin injection electrode and the spin detection electrode and in contact with the spin injection electrode and the spin detection electrode, wherein at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel.

[0010] The method for manufacturing a spin valve according to the present invention is a method for manufacturing a spin valve comprising: a spin injection electrode made of a ferromagnetic material; a spin detection electrode made of a ferromagnetic material and arranged facing the spin injection electrode; and a spin transport channel made of a semiconductor, arranged in contact with the spin injection electrode and the spin detection electrode and between the spin injection electrode and the spin detection electrode, wherein at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel, and the size of the apex angle of the pointed structure adjusts the contact resistance between the spin injection electrode in which the pointed structure is formed and the spin transport channel, or between the spin detection electrode in which the pointed structure is formed and the spin transport channel.

[0011] The spin device according to the present invention comprises a spin injection electrode made of a ferromagnetic material, a spin detection electrode arranged facing the spin injection electrode and also made of a ferromagnetic material, a spin transport channel made of a semiconductor and arranged between the spin injection electrode and the spin detection electrode and in contact with the spin injection electrode and the spin detection electrode, and a gate electrode for applying a gate voltage to the spin transport channel, and at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel.

[0012] As described above, according to the present invention, at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode is provided with a pointed structure with an apex located on the side of the spin transport channel, thereby making it possible to increase the MR ratio of the spin valve.

[0013] Fig. 1 is a diagram showing the configuration of a spin valve according to an embodiment of the present invention. Fig. 2 is a diagram showing the configuration of another spin valve according to an embodiment of the present invention. Fig. 3 is a diagram showing the configuration of another spin valve according to an embodiment of the present invention. Fig. 4 is a diagram showing the configuration of a spin valve having an apex angle θ X and θ Y 5 is a contour plot showing the relationship between the change in contact resistance ρ and the change in the electric field strength E of the spin valve. C The decrease in Δρ C 6 is a characteristic diagram showing the relationship between the MR ratio of the spin valve and the electric field enhancement level α. C / r S 7A and 7B are plan and cross-sectional views showing the configuration of a spin device according to an embodiment of the present invention;

[0014] A spin valve according to an embodiment of the present invention will be described below with reference to Figures 1, 2 and 3. This spin valve comprises a spin injection electrode 101, a spin detection electrode 102, and a spin transport channel 103.

[0015] The spin injection electrode 101 and the spin detection electrode 102 are each made of a ferromagnetic material. The spin injection electrode 101 and the spin detection electrode 102 are arranged facing each other. The ferromagnetic material constituting the spin injection electrode 101 and the spin detection electrode 102 is, for example, a single element metal such as Fe, Co, or Ni; 100-x Fe x (0≦x≦100), Co 100-x Fe x (0≦x≦100), binary metals such as Fe3Si, ternary or quaternary metals such as Heusler alloy X2YZ (X, Y: transition metal, Z: semiconductor or non-magnetic metal), or oxide metals such as SrRuO3.

[0016] The spin transport channel 103 is made of a semiconductor and is disposed between the spin injection electrode 101 and the spin detection electrode 102. The spin transport channel 103 is formed in contact with each of the spin injection electrode 101 and the spin detection electrode 102. The spin transport channel 103 can be made of a semiconductor doped with an acceptor or a donor.

[0017] For example, the spin transport channel 103 may be made of diamond, Si, Ge, or In. 1-x Ga x N (0≦x≦1), GaSb, InSb, GaAs, InAs, SiC, ZnO, Ga2O3, c-BN, In 1-x Ga x N (0≦x≦1), Al 1-x Ga x N (0≦x≦1). The doping concentration (N) can be 1×10 17 ~1 x 10 20 cm -3 It can be said that:

[0018] Furthermore, when the spin transport channel 103 is made of diamond, it can be made of diamond whose surface is terminated with oxygen and doped with B or P. Furthermore, the spin transport channel 103 can be made of a p-type surface conductive layer on the surface of diamond whose surface is terminated with hydrogen.

[0019] Here, a Schottky tunnel barrier is formed at the interface between the spin injection electrode 101 made of a ferromagnetic material and the spin transport channel 103 made of a semiconductor. Similarly, a Schottky tunnel barrier is formed at the interface between the spin detection electrode 102 made of a ferromagnetic material and the spin transport channel 103 made of a semiconductor.

[0020] Furthermore, this spin valve has a pointed structure with an apex located on the side of the spin transport channel 103 of at least one of the side of the spin injection electrode 101 facing the spin detection electrode 102 and the side of the spin detection electrode 102 facing the spin injection electrode 101. For example, as shown in FIG. 1, a pointed structure 104a can be provided on the side of the spin injection electrode 101 facing the spin detection electrode 102. As shown in FIG. 2, a pointed structure 104b can be provided on the side of the spin detection electrode 102 facing the spin injection electrode 101. As shown in FIG. 3, a pointed structure 104a can be provided on the side of the spin injection electrode 101 facing the spin detection electrode 102, and a pointed structure 104b can be provided on the side of the spin detection electrode 102 facing the spin injection electrode 101.

[0021] The tip structure 104a and the tip structure 104b can have a cross-sectional shape perpendicular to the arrangement (stacking) direction of the spin injection electrode 101, the spin detection electrode 102, and the spin transport channel 103, which is an isosceles triangle with its apex located on the side of the spin transport channel 103. The outer diameter of the tip structure 104a (104b) configured in this manner can be, for example, a cone or a triangular pyramid. Furthermore, the tip structure 104a (104b) can be a triangular prism with its height directed perpendicular to the arrangement (stacking) direction of the spin injection electrode 101, the spin detection electrode 102, and the spin transport channel 103.

[0022] Furthermore, in the above example, for example, the case where the spin injection electrode 101 is provided with one pointed structure 104a and the spin detection electrode 102 is provided with one pointed structure 104b is illustrated, but the present invention is not limited to this. A configuration in which pointed structures are provided at multiple locations in each of the spin injection electrode 101 and the spin detection electrode 102 is also possible. In this case, for example, pointed structures can be provided at multiple locations in the left-right direction of the paper surfaces of FIGS. 1, 2, and 3.

[0023] Next, a spin valve and a manufacturing method thereof will be described. This manufacturing method is the same as that of the spin valve described above, and adjusts the contact resistance between the spin injection electrode 101, on which the tip structure 104a is formed, and the spin transport channel 103, depending on the size of the apex angle of the tip structure 104a, or between the spin detection electrode 102, on which the tip structure 104b is formed, and the spin transport channel 103, depending on the size of the apex angle of the tip structure 104b.

[0024] In the following, the spin injection electrode 101 and the spin detection electrode 102 are made of Ni 80 Fe 20 The spin valve will be described below as an example in which the spin transport channel 103 is made of B-doped diamond whose surface is terminated with oxygen. x The apex angle of the tip structure 104b provided on the spin detection electrode 102 is set to θ y Let's say.

[0025] FIG. X and θ Y 1 is a contour plot showing how the electric field strength E of the spin valve changes when θ is changed. X and θ Y When [E(θ X , θ Y ) ] is θ X and θ Y The value obtained by this normalization is defined as the electric field enhancement factor α. A high electric field enhancement factor α can be obtained when the following conditions are satisfied:

[0026] (1) The spin injection electrode 101 is X The spin detection electrode 102 has a tip structure 104a with a θ Y is 180° and is a flat structure without a pointed structure.

[0027] (2) The spin injection electrode 101 is X is 180° and is a flat structure without a pointed structure, and the spin detection electrode 102 has an angle of θ YThe structure has a pointed structure 104b with an angle of nearly 0°.

[0028] (3) The spin injection electrode 101 is X The spin detection electrode 102 also has a tip structure 104a with an angle of θ Y The tip of the tip structure 104a and the tip of the tip structure 104b face each other.

[0029] For example, (θ X , θ Y When (θ ) = (10°, 180°), α is approximately 1.6. X , θ Y ) = (180°, 180°), E is about 1.6 times larger.

[0030] By the way, when spin-polarized carriers tunnel through a Schottky barrier, ρ C is the Schottky barrier height (Φ B ), a parameter E reflecting the tunneling probability of carriers 00 , and thermal energy (k B T), the proportional relationship shown in the following formula (1) is satisfied.

[0031]

[0032] In formula (1), k B is the Boltzmann constant, and T is the temperature. Note that the parameter E 00 is expressed by the following formula:

[0033]

[0034] The electric field strength E is given by the following formula:

[0035]

[0036] In formula (2), V bi is the built-in potential, and V is the applied potential. In equation (2), when the electric field enhancement level α is taken into consideration,

[0037]

[0038] From equation (3), when the electric field is enhanced, the apparent N becomes α 2 As a result, ρ C The decrease in (Δρ C The relationship between ) and α is expressed as shown in the following equation (4).

[0039]

[0040] FIG. 5 shows the Δρ calculated from equation (4). C The relationship between Δρ and α is shown. C decreases exponentially with increasing α. That is, adjusting θ reduces Δρ C For example, it is possible to adjust (θ X , θ Y ) = (10°, 180°), ρ C can be reduced by about four orders of magnitude.

[0041] FIG. 6 shows the relationship between the MR ratio of the spin valve and ρ C / r S The relationship between ρ C <<r S , or ρ C ≫r S Under this condition, the MR ratio is much smaller than 1%. Here, by adjusting the apex angle θ of the pointed structure, the MR ratio ρ can be increased by approximately four orders of magnitude. C / r S can be adjusted to approach 1, resulting in an improvement in the MR ratio of the spin valve by up to about four orders of magnitude. C =r S By adjusting θ so as to satisfy the following, an MR ratio exceeding 1% can be obtained.

[0042] The maximum value of the aforementioned MR ratio is several percent, but the spin polarization P is 80 Fe 20 This maximum value can be improved by about one order of magnitude if each electrode is made of a CoFe-based Heusler alloy with a higher Cr content than that of the other electrode. Furthermore, even if the spin transport channel 103 is made of a p-type surface conductive layer on the diamond surface that is terminated with hydrogen, a similar electric field enhancement effect and MR signal can be obtained.

[0043] Next, a spin device according to an embodiment of the present invention will be described with reference to Figures 7A and 7B. This spin device is configured from the above-mentioned spin valve and is a spin MOSFET.

[0044] This spin device includes a spin injection electrode 101, a spin detection electrode 102, a spin transport channel 103, tip structures 104a and 104b, and a gate electrode 106 that applies a gate voltage to the spin transport channel 103. The spin injection electrode 101, the spin detection electrode 102, the spin transport channel 103, and the tip structures 104a and 104b are the same as those described above.

[0045] In this example, a spin transport channel 103 is provided on a base 131, and a spin injection electrode 101 and a spin detection electrode 102 are arranged on the base 131 to sandwich the spin transport channel 103. In the following description, the stacking direction of the spin injection electrode 101, the spin detection electrode 102, and the spin transport channel 103 on the base 131 is defined as the z direction, and the surface of the base 131 on which these are formed is defined as the xy plane.

[0046] The base 131 is, for example, B-doped diamond whose surface is terminated with oxygen, and by processing the surface side of the base 131, a spin transport channel 103 that is rectangular in shape when viewed in a plane (xy plane) and extends in a predetermined direction (y direction) is formed. The base 131 can also be made of diamond whose surface is terminated with hydrogen. In this case, the p-type surface conductive layer on the hydrogen-terminated diamond surface can be used as the spin transport channel 103.

[0047] The spin injection electrode 101 and the spin detection electrode 102 are made of Ni 80 Fe 20The spin injection electrode 101 is provided with tip structures 104a at multiple locations, and the spin detection electrode 102 is provided with tip structures 104b at multiple locations. The tip structures 104a and 104b are triangular prisms with their heights in the z direction. The z direction is perpendicular to the arrangement direction (x direction) of the spin injection electrode 101, the spin detection electrode 102, and the spin transport channel 103. The tip structures 104a and 104b are arranged in the y direction. Each of the tip structures 104a and 104b has an apex angle θ of 70°.

[0048] The gate electrode 106 is formed on the spin transport channel 103 via a gate insulating layer 105. The gate electrode 106 can be made of a single element metal such as Al or Au, or a compound such as nickel silicide. The gate insulating layer 105 can be made of an oxide such as Al2O3 or SiO2, c-BN, or In 1-x Ga x N (0≦x≦1), Al 1-x Ga x The gate insulating layer 105 can be formed of a N (0≦x≦1) nitride. In addition, the gate insulating layer 105 can be omitted, and a Schottky barrier between the spin transport channel 103 made of a semiconductor and the gate electrode 106 can be used instead of the gate insulating layer.

[0049] Next, the operation of the above-mentioned spin device (spin MOSFET) will be described. First, by passing a current through the spin injection electrode 101, an accumulation state of upward or downward spins 201 is formed in the spin injection electrode side of the spin transport channel 103. These accumulated spins 201 become a spin current that diffuses through the spin transport channel 103 while undergoing spin relaxation.

[0050] If the spin diffusion length λ is sufficiently longer than the distance between the spin injection electrode 101 and the spin detection electrode 102, the spin current reaches the spin detection electrode 102 and is detected as an MR signal that depends on the parallel / antiparallel state of the magnetizations of the spin injection electrode 101 and the spin detection electrode 102. The gate bias is used to modulate the Schottky barrier width, and by applying a gate bias, the amount of spin-polarized carriers tunneling can be modulated.

[0051] A high E (several MV / cm) is applied to the tip end of the tip structure 104a or tip end structure 104b of the spin transport channel 103 of the above-mentioned spin MOSFET by a drain or gate bias. For this reason, it is desirable that the spin transport channel 103 is made of a semiconductor having a high breakdown field strength. In the above-mentioned example, the spin transport channel 103 is made of diamond, which has a breakdown field strength 33 times higher than that of Si, so a high bias can be applied, and α and ρ C This allows for a wide range of modulation, thereby improving the performance of the spin MOSFET.

[0052] As described above, according to the present invention, at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel. C and S ρ so that the difference between C This allows the electric field to be concentrated at the tip of the pointed structure, thereby increasing the MR ratio of the spin valve.

[0053] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0054] 101...spin injection electrode, 102...spin detection electrode, 103...spin transport channel, 104a, 104b...pointed structure.

Claims

1. A spin valve comprising: a spin injection electrode made of a ferromagnetic material; a spin detection electrode made of a ferromagnetic material and arranged facing the spin injection electrode; and a spin transport channel made of a semiconductor, in contact with the spin injection electrode and the spin detection electrode and arranged between the spin injection electrode and the spin detection electrode, wherein at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel.

2. A spin valve according to claim 1, wherein the tip structure has a cross-sectional shape of an isosceles triangle with its apex located on the side of the spin transport channel.

3. A spin valve according to claim 1, wherein the spin transport channel is made of diamond whose surface is terminated with oxygen and doped with B or P.

4. A spin valve according to claim 1, wherein the spin transport channel is formed from a p-type surface conductive layer on the surface of diamond, the surface of which is terminated with hydrogen.

5. A method for manufacturing a spin valve comprising: a spin injection electrode made of a ferromagnetic material; a spin detection electrode made of a ferromagnetic material and arranged facing the spin injection electrode; and a spin transport channel made of a semiconductor, in contact with the spin injection electrode and the spin detection electrode and arranged between the spin injection electrode and the spin detection electrode, wherein at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel, and wherein the contact resistance between the spin injection electrode on which the pointed structure is formed and the spin transport channel, or between the spin detection electrode on which the pointed structure is formed and the spin transport channel, is adjusted by changing the size of the apex angle of the pointed structure.

6. A method for manufacturing a spin valve according to claim 5, wherein the tip structure has a cross-sectional shape of an isosceles triangle with its apex located on the side of the spin transport channel.

7. A spin device comprising: a spin injection electrode made of a ferromagnetic material; a spin detection electrode made of a ferromagnetic material and arranged facing the spin injection electrode; a spin transport channel made of a semiconductor, in contact with the spin injection electrode and the spin detection electrode and arranged between the spin injection electrode and the spin detection electrode; and a gate electrode for applying a gate voltage to the spin transport channel, wherein at least one of the side of the spin injection electrode facing the spin detection electrode and the side of the spin detection electrode facing the spin injection electrode has a pointed structure with an apex located on the side of the spin transport channel.

8. A spin device according to claim 7, wherein the tip structure has a cross-sectional shape of an isosceles triangle with its apex located on the side of the spin transport channel.

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