JP6954089B2 - Random number generator, random number generator, neuromorphic computer and quantum computer - Google Patents

Description

The present invention relates to a random number generator, a random number generator, a neuromorphic computer and a quantum computer.

Random numbers include pseudo-random numbers and natural random numbers. A pseudo-random number is a random number obtained by using a computer by a predetermined program. Pseudo-random numbers have a problem that the same result is output when the initial value input to the program is the same, and a problem that the random number has a specific periodicity based on the number of registers of the computer. On the other hand, natural random numbers are random numbers obtained from stochastic events that occur in nature, and there is no doubt that random numbers are random.

As means for obtaining natural random numbers, noise (sum of thermal noise and shot noise) in tunnel junction is used (Patent Document 1), thermal noise is amplified by a single electron transistor effect (Patent Document 2), and heat. Noise is amplified by a negative resistance element (Patent Document 3), a magnetic resistance effect element using swing of a free-conducting layer due to an approximate field (Patent Document 4), and an ultra-thin SOI (silicon-on-insulator). Those utilizing the capture and emission of electrons in a transistor (Non-Patent Document 1) and the like are known.

Japanese Unexamined Patent Publication No. 2003-108364 Japanese Unexamined Patent Publication No. 2004-30071 Japanese Unexamined Patent Publication No. 2005-18500 Japanese Unexamined Patent Publication No. 2008-310403

K.Uchida et al., J.Appl.Phys, No.90, (2001), pp3551. I.M.Miron, K.Garello, G.Gaudin, P.-J.Zermatten, M.V.Costache, S.Auffret, S.Bandiera, B.Rodmacq, A.Schuhl, and P.Gambardella, Nature, 476,189 (2011).

However, the random number generators described in Patent Documents 1 to 3 require an amplifier circuit for amplifying noise and a threshold circuit for binarizing information, which increases the size of the random number generator. Further, the random number generator described in Non-Patent Document 1 has a random number generation speed of 100 kbit / sec, and it is difficult for the random number generator to satisfy this operating speed and operate.

Further, the random number generator described in Patent Document 4 generates a random number by utilizing a spin transfer torque (STT) generated by passing a current in the stacking direction of the magnetoresistive element. However, this random number generator has a small margin of the current and the magnetic field applied to obtain the random number, and is easily affected by external factors.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a random number generator capable of generating natural random numbers by using spin orbit torque (SOT).

In recent years, attention has been focused on magnetization reversal using a pure spin current generated by spin-orbit interaction as a means for reducing reversal current (for example, Non-Patent Document 2). As a result of diligent studies, the present inventors have created a new random number generator using the spin-orbit torque (SOT) generated by this spin-orbit interaction.

(1) The random number generator according to the first aspect extends in the first direction intersecting the lamination direction of the ferromagnetic metal layer and the ferromagnetic metal layer, and joins the ferromagnetic metal layer. The spin orbit torque wiring is provided, and the direction of the spin injected from the spin orbit torque wiring into the ferromagnetic metal layer intersects with the direction in which the ferromagnetic metal layer is easily magnetized.

(2) In the random number generator according to the above aspect, the direction of the spin injected into the ferromagnetic metal layer from the spin orbit torque wiring and the direction in which the ferromagnetic metal layer is easily magnetized are 45 ° or more and 90 ° or less. It may be tilted.

(3) In the random number generator according to the above aspect, the direction of the spin injected into the ferromagnetic metal layer from the spin orbit torque wiring and the direction in which the ferromagnetic metal layer is easily magnetized may be orthogonal to each other. ..

(4) In the random number generator according to the above aspect, a plurality of the ferromagnetic metal layers may be joined to the spin-orbit torque wiring.

(5) The random number generator according to the above embodiment may include a non-magnetic layer and a second ferromagnetic metal layer in this order on a surface of the ferromagnetic metal layer opposite to the spin-orbit torque wiring.

(6) The random number generator according to the above aspect may further have an external magnetic field applying means for applying a magnetic field to the ferromagnetic metal layer.

(7) The random number generator according to the above aspect may further have a magnetic shield that sandwiches or surrounds the ferromagnetic metal layer and the spin-orbit torque wiring.

(8) The random number generator according to the second aspect includes a random number generator according to the above aspect and a current applying means for passing a current through the spin track torque wiring of the random number generator.

(9) The neuromorphic computer according to the third aspect includes a random number generator according to the above aspect.

(10) The quantum computer according to the fourth aspect includes a random number generator according to the above aspect.

The random number generator according to the above aspect can generate a natural random number by using spin-orbit torque (SOT).

It is a perspective view which shows typically the random number generator which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the spin Hall effect. It is sectional drawing of an example of the random number generator which concerns on 1st Embodiment. It is sectional drawing of an example of the random number generator which concerns on 1st Embodiment. It is a perspective view which shows typically the state which applied the electric current to the spin-orbit torque wiring 20 of the random number generator 100 which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the operation of the random number generator using STT. It is a perspective schematic diagram of a random number generator which can read out the difference of the orientation state of magnetization as a resistance value change. It is a perspective view which shows typically the random number generator which concerns on 2nd Embodiment. It is a perspective view which shows typically the random number generator which concerns on 3rd Embodiment. It is sectional drawing which shows typically the random number generator provided with the magnetic shield. FIG. 5 is a cross-sectional view schematically showing another example of a random number generator provided with a magnetic shield. It is a perspective view which shows typically the random number generator which concerns on 4th Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of the respective components may differ from the actual ones. be. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately modified and carried out within the range in which the effects of the present invention are exhibited.

"First embodiment"
(Random number generator, random number generator)
FIG. 1 is a perspective view schematically showing a random number generator according to the first embodiment. The random number generator 100 according to the first embodiment has a ferromagnetic metal layer 10 and a spin-orbit torque wiring 20. The random number generator 100 functions as a random number generator by connecting to a current application means (not shown) that applies a current to the spin orbit torque wiring 20.

In the following embodiments, the stacking direction of the ferromagnetic metal layer 10 is the z direction, and the first direction in which the spin-orbit torque wiring 20 extends is the x direction, the z direction, and the second direction orthogonal to the x direction. Is the y direction.

<ferromagnetic metal layer>
The ferromagnetic metal layer 10 has an easy magnetization direction and a difficult magnetization direction. The easy magnetization direction is the direction in which the magnetization M ₁₀ of the ferromagnetic metal layer 10 is most likely to be oriented, and the difficult magnetization direction is the other direction. The ferromagnetic metal layer 10 may be either an in-plane magnetization film in which the easy magnetization direction is parallel to the layer, or a vertical magnetization film in which the magnetization direction is perpendicular to the layer. In order to reduce the area of the ferromagnetic metal layer 10 and reduce the size of the random number generator 100, a perpendicular magnetization film is preferable.

Magnetization M ₁₀ of the ferromagnetic metal layer 10 is in the state in which external force is not applied, it faces the easy magnetization direction. In FIG. 1, the magnetization M ₁₀ is oriented in a direction (z direction) perpendicular to the laminated surface of the ferromagnetic metal layer 10 in a state where no external force is applied. That is, the ferromagnetic metal layer 10 shown in FIG. 1 is a perpendicular magnetization film in which the easy magnetization direction is the z direction. Hereinafter, a description will be given based on this example.

A known material can be used for the ferromagnetic metal layer 10. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe and Ni and an alloy containing one or more of these metals and exhibiting ferromagnetism can be used. Further, alloys containing these metals and at least one or more elements of B, C, and N can also be used. Specific examples thereof include Co-Fe and Co-Fe-B. Further, a Whistler alloy or the like may be used.

<Spin-orbit torque wiring>
The spin-orbit torque wiring 20 extends in the x direction. The spin-orbit torque wiring 20 is connected to one surface of the ferromagnetic metal layer 10 in the z direction.

The spin-orbit torque wiring 20 supplies the spin derived from the spin-orbit interaction to the ferromagnetic metal layer 10. The spin derived from the spin-orbit interaction is generated by the spin Hall effect caused by the current flowing through the spin-orbit torque wiring 20 and the interface Rashba effect between dissimilar element interfaces.

First, the spin Hall effect will be described. The spin Hall effect is a phenomenon in which a pure spin current is induced in a direction orthogonal to the direction of the current based on the spin-orbit interaction when a current is passed through the material. FIG. 2 is a schematic diagram for explaining the spin Hall effect. FIG. 2 corresponds to a cross-sectional view of the random number generator 100 shown in FIG. 1 cut along the x direction. The mechanism by which a pure spin current is generated by the spin Hall effect will be described with reference to FIG.

As shown in FIG. 2, when a current I is passed in the extending direction of the spin-orbit torque wiring 20, the first spin S1 oriented toward the back side of the paper surface and the second spin S2 oriented toward the front side of the paper surface are orthogonal to the current, respectively. Can be bent in the direction. The normal Hall effect and the spin Hall effect are common in that the moving (moving) charge (electrons) can bend the moving (moving) direction, but in the normal Hall effect, the charged particles moving in the magnetic field exert the Lorentz force. In contrast to the spin Hall effect, which receives and bends the direction of motion, the spin Hall effect is significantly different in that the direction of movement is bent only by the movement of electrons (only the flow of electric current) even though there is no magnetic field.

In a non-magnetic material (a material that is not a ferromagnetic material), the number of electrons in the first spin S1 and the number of electrons in the second spin S2 are equal. Therefore, the number of electrons in the first spin S1 going upward and the number of electrons in the second spin S2 going downward in the figure are equal. Expressing the electron flow of the first spin S1 as J _↑ , the electron flow of the second spin S2 as J _↓ , and the spin flow as J _S , it is defined as _{J S} = J _↑ −J _{↓. JS} is a flow of electrons with a polarizability of 100%. That is, in the spin-orbit torque wiring 20, the current as the net flow of electric charges is zero, and the spin current without this current is particularly called a pure spin current.

When the ferromagnetic metal layer 10 is joined to the spin-orbit torque wiring 20 in which the pure spin current is generated, the first spin S1 upward in FIG. 2 diffuses into the ferromagnetic metal layer 10 and flows into the ferromagnetic metal layer 10.

Next, the interfacial Rashba effect will be described. The interface Rashba effect is a phenomenon in which spins are easily oriented in a predetermined direction due to the influence of the interface between different elements, and spins oriented in a predetermined direction are accumulated in the vicinity of the interface.

For example, in FIG. 2, the interface between the ferromagnetic metal layer 10 and the spin-orbit torque wiring 20 corresponds to the interface between dissimilar elements. Therefore, spins oriented in a predetermined direction are accumulated on the surface of the spin-orbit torque wiring 20 on the ferromagnetic metal layer 10 side. The accumulated spin diffuses and flows into the ferromagnetic metal layer 10 side in order to obtain energetically stable.

The spin orbital torque wiring 20 may have a portion made of a material in which spins are generated (spin generation unit) and a portion made of a material in which spins are not generated.

FIG. 3 is a cross-sectional view of an example of the random number generator according to the first embodiment. The spin-orbit torque wiring 20 shown in FIG. 3 has a spin generation unit 20A and a low resistance unit 20B in the extending direction (x direction) of the spin-orbit torque wiring 20.

The spin generator 20A needs to generate spins to be injected into the ferromagnetic metal layer 10, and the material is limited. Therefore, the spin generation unit 20A often has a high wiring resistance. By providing the low resistance portion 20B, the resistance of the entire spin-orbit torque wiring 20 can be reduced. Highly conductive Al, Cu, Ag or the like can be used for the low resistance portion 20B.

On the other hand, FIG. 4 is a cross-sectional view of another example of the random number generator according to the first embodiment. As shown in FIG. 4, it has a spin generation unit 20A and a spin conduction unit 20C in the stacking direction (z direction) of the spin track torque wiring 20.

By forming a laminated structure between the spin generating portion 20A and the spin conducting portion 20C, the interface between different elements increases. As a result, spin injection into the ferromagnetic metal layer 10 utilizing the interfacial Rashba effect can be performed more efficiently. Here, it is preferable that the spin conduction portion 20C uses a material having a long spin diffusion length in order to transfer the accumulated spin to the ferromagnetic metal layer 10. For example, Al, Si, Cu, Ag, GaAs, Ge and the like can be used.

In any of the configurations of FIGS. 3 and 4, the spin generation unit 20A is composed of a material that generates spins for injection into the ferromagnetic metal layer 10. The material constituting the spin-orbit torque wiring 20 is not limited to a material made of a single element.

The spin generator 20A may contain a non-magnetic heavy metal. Here, the heavy metal is used to mean a metal having a specific density equal to or higher than that of yttrium. The spin generator 20A may be made of only a non-magnetic heavy metal.

The non-magnetic heavy metal is preferably a non-magnetic metal having a d-electron or an f-electron in the outermost shell and having an atomic number of 39 or more and a large atomic number. Non-magnetic heavy metals have a large spin-orbit interaction that causes the Spin Hall effect. The spin generator 20A may be composed of only a non-magnetic metal having an atomic number of 39 or more and having a d-electron or an f-electron in the outermost shell and having a large atomic number.

Normally, when an electric current is passed through a metal, all electrons move in the opposite direction to the electric current regardless of the spin direction, whereas a non-magnetic metal having a d electron or f electron in the outermost shell and having a large atomic number has a large atomic number. Since the spin-orbit interaction is large, the direction of electron movement depends on the direction of the electron spin due to the spin Hall effect, and a pure spin current _JS is likely to occur.

Further, the spin generator 20A may contain a magnetic metal. The magnetic metal refers to a ferromagnetic metal or an antiferromagnetic metal. This is because when the non-magnetic metal contains a small amount of magnetic metal, the spin-orbit interaction is enhanced and the spin flow generation efficiency of the spin generation unit 20A can be increased. The spin generator 20A may be made of only an antiferromagnetic metal.

The spin-orbit interaction is caused by the inherent internal field of the material constituting the spin generator 20A. When a small amount of magnetic metal is added to the spin-orbit torque wiring material, the spin current generation efficiency is improved because the electron spins flowing through the magnetic metal itself are scattered. However, if the amount of the magnetic metal added is too large, the generated pure spin current is scattered by the added magnetic metal, and as a result, the effect of reducing the spin current becomes stronger. Therefore, it is preferable that the molar ratio of the added magnetic metal is sufficiently smaller than the molar ratio of the main component of the spin generating portion in the spin-orbit torque wiring. As a guide, the molar ratio of the added magnetic metal is preferably 3% or less.

Further, the spin generator 20A may include a topological insulator. The spin generator 20A may be composed of only the topological insulator. A topological insulator is a substance in which the inside of a substance is an insulator or a high resistor, but a metal state in which spin polarization occurs on the surface thereof. Matter has something like an internal magnetic field called spin-orbit interaction. Therefore, a new topological phase is expressed by the effect of spin-orbit interaction even in the absence of an external magnetic field. This is a topological insulator, and pure spin current can be generated with high efficiency due to strong spin-orbit interaction and breaking of inversion symmetry at the edge.

As the topological insulator, for example, SnTe, Bi _1.5 Sb _0.5 Te _1.7 Se _1.3 , TlBiSe ₂ , Bi ₂ Te ₃ , (Bi _1-x Sb _x ) ₂ Te _{3 and the} like are preferable. These topological insulators can generate spin currents with high efficiency.

The random number generator 100 may have components other than the ferromagnetic metal layer 10 and the spin-orbit torque wiring 20. For example, a substrate or the like may be provided as a support. The substrate preferably has excellent flatness, and for example, Si, AlTiC, or the like can be used as the material.

<Operation of random number generator>
When a current is passed through the spin-orbit torque wiring 20 by the current application means, spin accumulation and pure spin current are generated due to the interfacial Rashba effect. The generated spin diffuses into the ferromagnetic metal layer 10 and flows into it. _{That is, the spin S 20} generated in the spin orbital torque wiring 20 is injected into the ferromagnetic metal layer 10.

FIG. 5 is a perspective view schematically showing a state in which a current is applied to the spin track torque wiring 20 of the random number generator 100 according to the present embodiment. _{The direction of the spin S 20} injected from the spin track torque wiring 20 is orthogonal to both terminal directions (x direction) of the spin track torque wiring 20 connected to the current applying means.

As shown in FIG. 1, _{the direction of the injected spin S 20 is orthogonal to the direction of the magnetization M 10} of the ferromagnetic metal layer 10 (direction in which magnetization is easy). Therefore, the magnetization _{M 10} of the ferromagnetic metal layer 10 is affected by the injected spins _{S 20. The magnetized M 10} oriented in the z direction receives torque in the y direction as if an external magnetic field was applied in the y direction.

The vector direction in which the torque is applied is orthogonal to the easy magnetization direction (z direction in FIG. 1). In response to this torque, the magnetization M ₁₀ which has been oriented easy magnetization direction (z direction in FIG. 1) as an initial state, oriented in the magnetization hard axis (-y direction in FIG. 5). This state is maintained as long as the current is continuously applied to the spin-orbit torque wiring 20.

The current applied to the spin-orbit torque wiring 20 preferably satisfies the following relational expression (1).

Here, _{M S} is the saturation magnetization of the ferromagnetic metal layer ^{10 (emu / cm 3),} t F is the thickness of the ferromagnetic metal layer 10 (cm), θ _SH is effective spin Hall angle of the spin orbit torque wires 20, _{HK and eff} are the effective anisotropic magnetic field (Oe) of the ferromagnetic metal layer 10, and H _x is the external magnetic field (Oe) applied in the current application direction of the spin orbit torque wiring 20.

By applying a current satisfying the above relational expression (1) to the spin orbit torque wiring 20, a sufficient amount of spin S ₂₀ can be supplied to the ferromagnetic metal layer 10, and the magnetization M ₁₀ is in the direction in which magnetization is difficult (FIG. 5). The state facing the −y direction) can be stably maintained.

The vector direction of the torque received by the _{spin S 20} into which the magnetization M _{10 is injected is the −y direction.} Therefore, even if the amount of applied current increases and the magnitude of torque increases, the magnetization M ₁₀ does not reverse in the −z direction. It should be noted that a magnetization reversing element or the like using SOT produces a magnetization reversal triggered by the external force by applying a further external force (external magnetic field, etc.) to the state where the magnetization is rotated in the direction in which the magnetization is difficult. Since no further external force is applied to the generator, the magnetization M ₁₀ is maintained in a state in which the magnetization is difficult to magnetize.

On the other hand, in the conventional random number generator using STT, it is difficult to adjust the direction of magnetization when a current is applied. FIG. 6 is a schematic diagram for explaining the operation of the random number generator using STT. The random number generator 30 using the STT shown in FIG. 6 has a free layer 31 stacked in this order, a non-magnetic layer 32, a fixed layer 33, and two wirings 34 sandwiching them.

In the random number generator shown in FIG. 6, when a current is passed between the two wirings 34, spin is injected from the fixed layer 33 to the free layer 31. The spin injected from the fixed layer 33 has the same + z direction as _{the magnetization M 33 of the fixed layer 33.} Therefore, the magnetization M ₃₁ of the free layer 31 receives a force in the + z direction. In the random number generator 101 using STT, the force related to the + z direction is adjusted so that _{the orientation direction of the magnetization M 31} when a current is applied is the x direction or the y direction (magnetization difficult direction).

In this way, in the random number generator 30 using STT, the _{direction in which the magnetization M 31} is desired to be directed (x direction or y direction) when a current is applied does not match the direction of the force applied _{to the magnetization M 31 (+ z direction).} .. Therefore, in order _{to keep the direction of the magnetization M 31 in} the direction in which the magnetization is difficult when the current is applied, it is necessary to finely adjust the amount of the applied current. Further, when an external factor such as heat is added, it is necessary to adjust the amount of applied current each time.

On the other hand, in the random number generator 100 using SOT according to the present embodiment, as shown in FIG. 5, the _{direction in which the magnetization M 10} is desired to be directed (−y direction) when a current is applied and the direction of the force applied _{to the magnetization M 10} (-Y direction) matches. Therefore, it is sufficient to apply a current amount exceeding the threshold value, and delicate adjustment is not required.

Next, in order to generate a random number, the current applied to the spin-orbit torque wiring 20 of the random number generator 100 is stopped. When the current applied to the spin-orbit torque wiring 20 is stopped, the spin S ₂₀ injected into the ferromagnetic metal layer 10 is no longer injected. That lose force the magnetization M ₁₀ was toward the -y direction of the ferromagnetic metal layer 10.

It is energetically stable that the magnetization M ₁₀ is oriented in the easy magnetization direction (z direction). _{Therefore, the magnetized M 10 that} has lost the force oriented in the −y direction tends to return to the easily magnetized direction (z direction). At this time, the magnetization M ₁₀ is oriented in either the + z direction or the −z direction. The + z direction and the −z direction are both equivalent to the −y direction _{, and the probability that the magnetization M 10} is oriented in the + z direction and the probability that it is oriented in the −z direction are both 50%. Therefore, for example, if the case of facing the + z direction is "1" and the case of facing the −z direction is "0", a random number having a 50% probability of producing "1" and "0" can be obtained.

When the current applied to the spin-orbit torque wiring 20 is increased above the threshold current shown in Eq. (1), a back hopping phenomenon may occur and the magnetization M ₁₀ may deviate from the direction in which the magnetization is difficult. However, even in this case, it is still possible to obtain a random number having a probability of producing "1" and "0" with a probability of 50%. When the current applied to the spin orbit torque wiring 20 is stopped, the magnetization M ₁₀ returns to the easy magnetization direction (+ z direction, −z direction) corresponding to the direction deviated by the back hopping phenomenon. Since the deviation in the magnetization M ₁₀ direction occurs randomly, the returned magnetization easy direction (+ z direction, −z direction) also becomes random, and the probability that “1” and “0” appear is also a random number with a 50% probability. Is obtained.

Information on which direction the magnetization M ₁₀ is oriented in the + z direction or the −z direction can be obtained by various means. For example, the difference in the orientation state of magnetization can be read out as a change in resistance value. FIG. 7 is a schematic perspective view of a random number generator 101 capable of reading out the difference in the orientation state of magnetization as a change in resistance value.

The random number generator 101 shown in FIG. 7 includes a non-magnetic layer 50, a second ferromagnetic metal layer 60, and a wiring layer 70 in this order on the side opposite to the spin-orbit torque wiring 20 of the ferromagnetic metal layer 10.

The random number generator 101 reads out the magnetization state of the ferromagnetic metal layer 10 by measuring the resistance value between the spin-orbit torque wiring 20 and the wiring layer 70. The resistance value becomes low when the direction of the magnetization M _{10 of the ferromagnetic metal layer 10 is parallel to the direction of the magnetization M 60} of the second ferromagnetic metal layer 60 (-z direction), and is opposite. In the case of parallel (+ z direction), it becomes high.

A known material can be used for the non-magnetic layer 50. When the non-magnetic layer 50 is an insulator, the TMR element is composed of the ferromagnetic metal layer 10, the non-magnetic layer 50, and the second ferromagnetic metal layer 60. When the non-magnetic layer 50 is a metal, the ferromagnetic metal layer 10, the non-magnetic layer 50, and the second ferromagnetic metal layer 60 form a GMR element. To obtain the difference in the orientation direction of the magnetization M ₁₀ more clearly is preferably a TMR element large magnetic resistance change is obtained.

For example, when the non-magnetic layer 50 is made of an insulator (when it is a tunnel barrier layer), Al ₂ O ₃ , SiO ₂ , Mg O _{, Mg Al 2 O 4, and the} like can be used as the material thereof. In addition to these, a material in which a part of Al, Si, and Mg is replaced with Zn, Be, or the like can also be used. Among these, MgO and MgAl ₂ O ₄ are materials that can realize a coherent tunnel, so that spin can be efficiently injected.
When the non-magnetic layer 50 is made of metal, Cu, Au, Ag or the like can be used as the material.

When the non-magnetic layer 50 is made of an insulator (when it is a tunnel barrier layer), the film thickness of the tunnel barrier layer is preferably 2 nm or more. When the film thickness of the tunnel barrier layer is 2 nm or more, the amount of change in magnetic resistance becomes large. Therefore, the amount of current applied between the spin orbit torque wiring 20 and the wiring layer 70 in order to confirm the orientation state _{of the magnetization M 10} of the ferromagnetic metal layer 10 can be reduced, and the heat generation of the random number generator 101 can be suppressed. As a result, a highly stable random number generator can be obtained.

The second ferromagnetic metal layer 60 is a fixed layer in which the magnetic anisotropy is relatively stronger than that of the ferromagnetic metal layer 10 and the magnetization direction is fixed in one direction.

As the material of the second ferromagnetic metal layer 60, a known material can be used. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe and Ni and an alloy containing one or more of these metals and exhibiting ferromagnetism can be used. Further, alloys containing these metals and at least one or more elements of B, C, and N can also be used. Specific examples thereof include Co-Fe and Co-Fe-B. Further, a Whistler alloy or the like may be used.

In order to increase the coercive force of the second ferromagnetic metal layer 60, an antiferromagnetic material such as IrMn or PtMn may be brought into contact with the surface of the second ferromagnetic metal layer 60 opposite to the non-magnetic layer 50. .. Further, in order to prevent the leakage magnetic field of the second ferromagnetic metal layer 60 from affecting the ferromagnetic metal layer 10, a synthetic ferromagnetic coupling structure may be used.

The wiring layer 70 is not particularly limited as long as it has conductivity. For example, copper, aluminum and the like can be used.

"Second embodiment"
FIG. 8 is a perspective view schematically showing the random number generator 102 according to the second embodiment. In the random number generator 102 shown in FIG. 8, the _{easy magnetization direction of the magnetization M 11 of the ferromagnetic metal layer 11 and the direction of the spin S 20} injected into the ferromagnetic metal layer 11 from the spin orbit torque wiring 20 are orthogonal to each other. It is different from the random number generator 100 according to the first embodiment in that it does not intersect and intersects. In Figure 8, the magnetization _{M 11} of the ferromagnetic metal layer 11, the direction inclined by 45 ° from the x-axis and y-axis of the xy plane, having an easy axis of magnetization.

_{In the random number generator 100 according to the first embodiment, the direction of the spin S 20} injected into the ferromagnetic metal layer 10 from the spin-orbit torque wiring 20 and the easy magnetization direction of the ferromagnetic metal layer 10 are orthogonal to each other, and "1". And the probability that "0" appears was 50%, which was equivalent.

However, if the random number generator generates random numbers from stochastic events that occur in nature, the probability of occurrence of "1" and "0" does not necessarily have to be 50%. For example, even if the probability of occurrence of "1" is 70% and the probability of occurrence of "0" is 30%, if each event occurs stochastically, it is a natural random number.

The random number generator 102 according to the second embodiment adjusts the angle formed by the easy magnetization direction of the magnetization of the ferromagnetic metal layer and the direction of the spin injected into the ferromagnetic metal layer from the spin-orbit torque wiring, and "1. "And" 0 "occurrence probability is fluctuating.

The easy magnetization direction of the ferromagnetic metal layer 11 can be controlled by the material type constituting the ferromagnetic metal layer 11, the shape of the ferromagnetic metal layer 11, and the like. For example, when the ferromagnetic metal layer 11 is given shape anisotropy, the long axis direction of the ferromagnetic metal layer 11 becomes the easy magnetization direction.

When the random number generator 102 shown in FIG. 8 also applies a current to the spin orbit torque wiring 20, it is _{influenced by the spin S 20} supplied from the spin orbit torque wiring 20 and is oriented in the −y direction. When stopping the current applied to the spin-orbit torque wires 20, the force was toward the magnetization M ₁₁ of the ferromagnetic metal layer 11 in the -y direction is lost, the magnetization M ₁₁ of the ferromagnetic metal layer 11 returns to the easy magnetization direction ..

The direction in which the ferromagnetic metal layer 11 is easily magnetized is two directions, a first direction inclined by 45 ° in the + y direction from the + x axis and a second direction inclined by 45 ° in the −y direction from the −x axis. _{Since the magnetization M 11} of the magnetization M ₁₁ when the current is supplied to the spin orbit torque wiring 20 is in the −y direction, the magnetization M ₁₁ needs to rotate 135 ° when facing the first direction. On the other hand, when facing the second direction, the magnetization only needs to be rotated by 45 °. That is, the magnetization M ₁₁ is more likely to be oriented in the second direction than in the first direction.

However, _{the behavior of the magnetization M 11} is only a stochastic behavior. Therefore, just because the magnetization M ₁₁ tends to be oriented in the second direction, it does not necessarily be oriented in the second direction, and may be oriented in the first direction. In this case, if the probability of facing the first direction is A and the probability of facing the second direction is B, then A <B.

In this way, _{by adjusting the angle formed by the easy magnetization direction of the magnetization M 11 of the ferromagnetic metal layer 11 and the direction of the spin S 20} injected into the ferromagnetic metal layer 11 from the spin-orbit torque wiring 20, a random number is obtained. The occurrence probability of the generator can be adjusted.

The angle between the easy magnetization direction of the magnetization M _{11 of the ferromagnetic metal layer 11 and the direction of the spin S 20} injected into the ferromagnetic metal layer 11 from the spin orbit torque wiring 20 shall be 45 ° or more and 90 ° or less. Is preferable. If the angle between the easy magnetization direction of the magnetization M _{11 of the ferromagnetic metal layer 11 and the direction of the spin S 20} injected into the ferromagnetic metal layer 11 from the spin orbit torque wiring 20 is small, a random number generator using STT The behavior becomes close to that of 30, and it becomes necessary to adjust the amount of applied current.

"Third embodiment"
FIG. 9 is a perspective view schematically showing the random number generator 103 according to the third embodiment. The random number generator 103 shown in FIG. 9 is different from the random number generator 100 according to the first embodiment in that an external magnetic field applying means 80 for applying a magnetic field to the ferromagnetic metal layer 10 is provided. In FIG. 9, the wiring is arranged on the ferromagnetic metal layer 10 as the external magnetic field applying means 80. By passing an electric current through the wiring, a magnetic field centered on the wiring is generated.

By providing the external magnetic field applying means 80, the probability of occurrence of "1" and "0" of the random number generator can be adjusted. For example, when the probability of occurrence deviates from 50% due to the influence of heat or the like, the probability of occurrence can be adjusted to 50% by using the external magnetic field applying means 80. It can also be used when it is desired to shift the probability of occurrence from 50%.

In this way, the probability of occurrence of "1" and "0" in the random number generator can be adjusted by an external magnetic field. On the other hand, in other words, it can be said that the random number generator may be affected by the magnetic field generated from the peripheral circuit. Therefore, in order to suppress the influence of the magnetic field from the peripheral circuit, a magnetic shield surrounding the ferromagnetic metal layer and the spin-orbit torque wiring may be provided.

10 and 11 are schematic views of a random number generator provided with a magnetic shield. In FIG. 10, a magnetic shield 90 is provided so as to sandwich the ferromagnetic metal layer 10 and the spin-orbit torque wiring 20. Further, in FIG. 11, a magnetic shield 90 is provided so as to surround the ferromagnetic metal layer 10 and the spin-orbit torque wiring 20. The magnetic shield 90, the ferromagnetic metal layer 10, and the spin-orbit torque wiring 20 are insulated from each other (not shown). A high magnetic permeability magnetic material such as NiFe can be used for the magnetic shield 90.

"Fourth embodiment"
FIG. 12 is a perspective view schematically showing the random number generator 104 according to the fourth embodiment. The random number generator 104 shown in FIG. 10 is different from the random number generator 100 according to the first embodiment in that a plurality of ferromagnetic metal layers 10 are joined to the spin-orbit torque wiring 20.

Each of the plurality of ferromagnetic metal layers 10 generates a random number. Therefore, by taking the average of these, the accuracy of the random numbers generated by the random number generator can be improved.

The random number generator according to the above embodiment can generate a natural random number. Further, in the random number generator according to the above embodiment, the direction in which the magnetization is to be directed when a current is applied and the direction in which the force applied to the magnetization are the same. Therefore, it is not necessary to adjust the amount of current supplied, and the stability of the random number generator is high. Further, the spin-orbit torque wiring 20 of the random number generator may be connected to a semiconductor circuit such as a transistor and used as a semiconductor integrated element.

Further, the random number generator according to the above embodiment can be used as an analog signal generator in a neuromorphic computer, a quantum computer, or the like. Specifically, for example, it has a product-sum calculation circuit in which random number generators are arranged in an array and an element that weights an input signal, and can be applied to a neuromorphic computer simulating a brain.

(Manufacturing method of random number generator)
The above-mentioned random number generator can be manufactured by using a known film forming means such as sputtering and a processing technique such as photolithography. The metals and the like constituting each layer are laminated in order on the substrate to be the support, and then processed into a predetermined shape.

Examples of the film forming method include a vapor deposition method, a laser ablation method, an MBE method, and the like, in addition to the sputtering method. In the photolithography method, a resist film is formed on a portion to be left, and an unnecessary portion is removed by treatments such as ion milling and reactive ion etching (RIE).

As a means for reading information, for example, when manufacturing a TMR element using a non-magnetic layer as an insulator, a metal thin film of about 0.4 to 2.0 nm is first sputtered on the ferromagnetic metal layer, and then plasma oxidation or oxygen is used. A tunnel barrier layer may be formed by performing natural oxidation by introduction and then performing heat treatment.

The present invention is not necessarily limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

"Example 1"
In Example 1, a random number generator having the same arrangement as in FIG. 7 was produced. Ta was used as the spin-orbit torque wiring 20, and FeB was used as the ferromagnetic metal layer 10. The thickness of the ferromagnetic metal layer 10 was 1 nm, and _{the orientation direction of the magnetization M 10} of the ferromagnetic metal layer 10 was the z direction. The saturation magnetization Ms of the ferromagnetic metal layer 10 is 1200 emu / cm ³ , the effective anisotropic magnetic fields _{HK and eff} of the ferromagnetic metal layer 10 are 5 KOe, and the effective spin hole angle θ _SH of the spin orbit torque wiring is It was 0.07. No external magnetic field was applied. Further, MgO was used as the non-magnetic layer 50, and CoFeB was used as the second ferromagnetic metal layer 60.

And applying a spin-orbit current torque wires 20 to 5.0 × ¹⁰ 7 A / cm ² of the random number generator. The current amount is greater than the current density ^{Jc (4.3 × 10 7 A /} cm 2) obtained from the right-hand side of equation (1).

The random number generator was operated 10,000 times to determine the probability that the magnetizations of the ferromagnetic metal layer 10 and the second ferromagnetic metal layer 60 would be antiparallel and parallel. As a result, it was confirmed that the random number generator probabilistically generated parallel and antiparallel, and the respective generation probabilities were 50%.

10, 11 ... Ferromagnetic metal layer, 20 ... Spin orbit torque wiring, 20A ... Spin generator, 20B ... Low resistance section, 20C ... Spin conduction section, 30 ... Random generator using STT, 31 ... Free layer, 32 ... non-magnetic layer, 33 ... fixed layer, 34 ... wiring, 50 ... non-magnetic layer, 60 ... second ferromagnetic metal layer, 70 ... wiring layer, 80 ... external magnetic field applying means, M ₁₀ , M ₁₁ , M ₃₁ , M ₃₃ , M ₆₀ ... Magnetization, S ₂₀ ... Spin, 100, 101, 102, 103, 104 ... Random generator

Claims (10)

Ferromagnetic metal layer and
A spin-orbit torque wiring extending in a first direction intersecting with the stacking direction of the ferromagnetic metal layer and joining to the ferromagnetic metal layer is provided.
The direction of the spin injected into the ferromagnetic metal layer from the spin-orbit torque wiring intersects with the direction in which the ferromagnetic metal layer is easily magnetized .
The current applied to the spin-orbit torque wiring is

Random number generator that meets. The random number generation according to claim 1, wherein the direction of the spin injected into the ferromagnetic metal layer from the spin orbit torque wiring and the direction in which the ferromagnetic metal layer is easily magnetized are inclined by 45 ° or more and 90 ° or less. vessel. The random number generation according to claim 1 or 2, wherein the direction of the spin injected into the ferromagnetic metal layer from the spin orbit torque wiring and the direction in which the ferromagnetic metal layer is easily magnetized are orthogonal to each other. vessel. The random number generator according to any one of claims 1 to 3, wherein a plurality of the ferromagnetic metal layers are joined to the spin-orbit torque wiring. The random number generator according to any one of claims 1 to 4, further comprising a non-magnetic layer and a second ferromagnetic metal layer on the surface of the ferromagnetic metal layer opposite to the spin-orbit torque wiring. .. The random number generator according to any one of claims 1 to 5, further comprising an external magnetic field applying means for applying a magnetic field to the ferromagnetic metal layer. The random number generator according to any one of claims 1 to 6, further comprising a magnetic shield that sandwiches or surrounds the ferromagnetic metal layer and the spin-orbit torque wiring. The random number generator according to any one of claims 1 to 7.
A random number generator including a current applying means for passing a current through the spin orbit torque wiring of the random number generator. A neuromorphic computer having the random number generator according to any one of claims 1 to 7. A quantum computer having the random number generator according to any one of claims 1 to 7.

Images