Reservoir element and neuromorphic element

A reservoir element of the first aspect of the present disclosure includes: a first ferromagnetic layer; a plurality of second ferromagnetic layers positioned in a first direction with respect to the first ferromagnetic layer and spaced apart from each other in a plan view from the first direction; and a nonmagnetic layer positioned between the first ferromagnetic layer and the second ferromagnetic layers.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a reservoir element and a neuromorphic element.

Description of Related Art

The neuromorphic element is an element that mimics a human brain by means of a neural network. Neuromorphic elements artificially mimic the relationship between neurons and synapses in the human brain.

The Hierarchical element is one of the neuromorphic elements. The hierarchical element has a hierarchically arranged chips (neurons in the brain) and means of communication (synapses in the brain) that connects them. The hierarchical element increases the correct answer rate of problems by means of transmission (synapses) performing a learning process (leaning) Learning means finding information that can be used in the future. The neuromorphic element weights input data. Leaning is performed in each level in the hierarchical element.

Learning at each level, however, increases in the number of chips (neurons) impose a significant burden on circuit design and contribute to increased power consumption of the neuromorphic elements. Reservoir computers are being studied as one way to reduce this burden.

The reservoir computer is one of the neuromorphic elements. The reservoir computer includes a reservoir element and an output part. The reservoir element includes chips that interact with each other. The chips interact with each other by the input signal and output the signal. Weights are fixed in transmission means connecting multiple chips and the transmission means is not able to learn. The output part learns from the signal from the reservoir element and outputs the outcome to the outside. The reservoir computer compresses the data with a reservoir element and weights the data at the output part to increase the correct answer rate of the problem. Learning on the reservoir computer is done only at the output part. Reservoir computers are expected to be one means of enabling simplified circuit design and increased power consumption efficiency of neuromorphic elements.

Non-Patent Document 1 describes a neuromorphic element using a spin torque oscillator (STO) element as a chip (neuron).

CITATION LIST

Non Patent Documents

SUMMARY

However, the neuromorphic element using the STO element on the chip needs to align the resonance frequencies of each STO element. The resonance frequencies of the STO elements may vary depending on manufacturing errors, etc., and the STO elements may not interact sufficiently because of the above-described discrepancy. The STO element also oscillates by applying a high frequency current in a lamination direction. The long-term application of high frequency current in the lamination direction of the STO element having an insulating layer can cause failure of the STO element.

The present disclosure has been made in view of the above-described circumstances and provides a stable operating reservoir element and a neuromorphic element.

Means for Solving Problems

The present disclosure provides the following means for solving the above-described problems.

(1) The first aspect of the present disclosure is a reservoir element including: a first ferromagnetic layer; a plurality of second ferromagnetic layers positioned in a first direction with respect to the first ferromagnetic layer and spaced apart from each other in a plan view from the first direction; and a nonmagnetic layer positioned between the first ferromagnetic layer and the second ferromagnetic layers.

(2) The reservoir element related to the above-described aspect may further include at least one via wiring electrically connected to the first ferromagnetic layer on a surface opposite to a surface with the nonmagnetic layer.

(3) In the reservoir element related to the above-described aspect, the at least one via wiring may include a plurality of via wirings, and each of via wirings may is located on a position overlapping with each of the second ferromagnetic layers, respectively, in the plan view from the first direction.

(4) The reservoir element related to the above-described aspect may further include a magnetic interference layer contacting the first ferromagnetic layer on the surface opposite to the surface with the nonmagnetic layer and having a coercivity lower than a coercivity of the first ferromagnetic layer.

(5) In the reservoir element related to the above-described aspect, the magnetic interference layer may be made of an alloy containing one of Fe—Si, Fe—Si—Al, Fe—Co—V, Ni—Fe, and Co—Fe—Si—B.

(6) The reservoir element related to the above-described aspect may further include a shared electrode connecting two or more of the via wirings.

(7) In the reservoir element related to the above-described aspect, the second ferromagnetic layers may be arranged in a hexagonal lattice form in the plan view from the first direction.

(8) In the reservoir element related to the above-described aspect, the second ferromagnetic layers may form plurality of bundles, the second ferromagnetic layers being close-packed in each of the bundles in the plan view from the first direction, and the second ferromagnetic layers may be arranged in a hexagonal lattice form.

(9) The second aspect of the present disclosure is a neuromorphic element including: the reservoir element according to any one of the above-described reservoir element; an input part connected to the reservoir element; and an output part connected to the reservoir element, the output part being configured to perform learning process on a signal from the reservoir element.

The reservoir and the neuromorphic element related to embodiment of the present disclosure are capable of stable operation.

EMBODIMENTS

Hereinafter, the present embodiments will be described in detail with reference to the drawings. The drawings used in the following description may enlarge the characterizing portions for convenience in order to make the features understandable, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. illustrated in the following description are exemplary, and the present disclosure is not limited thereto, and may be implemented with appropriate modifications to the extent that the effects of the present disclosure are achieved.

First Embodiment

FIG.1is a conceptual diagram of a neuromorphic element according to the first embodiment. The neuromorphic element100includes the input part20, the reservoir element10, and the output part30. The input part20and the output part30are connected to the reservoir element10.

The neuromorphic element100compresses the signal input from the input part20with the reservoir element10, weights (learns) the signal compressed by the output part30, and outputs the signal to the outside.

The input part20transmits a signal input from an external source to the reservoir element10. The input part20includes, for example, input terminals. The input terminals sense information external to the neuromorphic element100and input information as a signal to the reservoir element10. The signal may be input to the reservoir element10continuously over time with changes in external information or may be divided into a predetermined time domain and input to the reservoir element10.

The reservoir element10has chips Cp. Multiple chips Cp interact with each other. The signal input to the reservoir element10has a number of information. The large number of information contained in the signal is compressed to the information required by the interaction of multiple chips Cp with each other. The compressed signal is transmitted to the output part30. The reservoir element10does not perform learning process. That is, the multiple chips Cp only interact with each other and do not weight the signals that transmit between the multiple chips Cp.

The output part30receives a signal from the chip Cp of the reservoir element10. The output part30performs learning process. The output part30weights each signals from each of chips Cp by leaning. The output part30includes, for example, a non-volatile memory. The non-volatile memory is, for example, a magnetoresistive effect element. The output part30outputs a signal to the outside of the neuromorphic element100.

The neuromorphic element100compresses the data with the reservoir element10and weights the data with the output part30to increase the correct answer rate of the problem.

The neuromorphic element100also has excellent power consumption efficiency. Only the output part30learns in the neuromorphic element100. Learning is to adjust the weight of the signal transmitted from each chip Cp. The weight of the signal is determined according to the importance of the signal. When the weight of the signal is adjusted from time to time, the circuitry between the chips Cp becomes active. The more active circuitry is, the higher the power consumption of the neuromorphic element100. In the neuromorphic element100, only the output part30leans in the final stage and the neuromorphic element100has excellent in power consumption efficiency.

FIG.2is a perspective view of a reservoir element10according to the first embodiment.FIG.3is a side view of the reservoir element10according to the first embodiment.FIG.4is a plan view of the reservoir element10according to the first embodiment.

The reservoir element10includes the first ferromagnetic layer1, the second ferromagnetic layers2, the nonmagnetic layer3, and the via wirings4. The second ferromagnetic layers2correspond to the chips Cp inFIG.1.

The directions are specified as described below. A predetermined direction in the extended surface of the first ferromagnetic layer1is defined as the x-direction. Among the plane that the first ferromagnetic layer1is extended, a direction intersecting (e.g., generally in the perpendicular direction) the x direction is defined as the y-direction. A direction intersecting (e.g., generally in the perpendicular direction) the plane that the first ferromagnetic layer1is extended is defined as the z-direction.

The first ferromagnetic layer1extends continuously on the xy-plane. The first ferromagnetic layer1may be a perpendicular magnetizing film in which the magnetization easy axis is oriented in the z-direction or an in-plane magnetized film in which the magnetization easy axis is oriented in the xy-plane direction.

The first ferromagnetic layer1includes a ferromagnetic material. The first ferromagnetic layer1includes, for example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy comprising one or more of these metals, an alloy including these metals and at least one or more of B, C, and N. The first ferromagnetic layer1is, for example, Co—Fe, Co—Fe—B, Ni—Fe, Co—Ho alloy (CoHo2), Sm—Fe alloy (SmFe12). If the first ferromagnetic layer1includes a Co—Ho alloy (CoHo2) and a Sm—Fe alloy (SmFe12), the first ferromagnetic layer1is prone to become an in-plane magnetized film.

The first ferromagnetic layer1may be a Heusler alloy. The Heusler alloy is an intermetallic compound having a chemical composition of XYZ or X2YZ. X is a transition metal of a Co group, an Fe group, a Ni group or a Cu group; or a noble metal element. Y is a transition metal of an Mn group, a V group, a Cr group or a Ti group; or the element species of X. Z is a typical element from Group III to Group V. The Heusler alloys are, for example, Co2FeSi, Co2FeGe, Co2FeGa, Co2MnSi, Co2Mn1-aFeaAlbSi1-b, and Co2FeGe1-cGac. The Heusler alloys have a high spin polarizability and more strongly develop a magnetoresistance effect.

The first ferromagnetic layer1preferably contains at least one element selected from the group consisting of Co, Ni, Pt, Pd, Gd, Tb, Mn, Ge, Ga. Examples include: a Co and Ni laminate; a Co and Pt laminate; a Co and Pd laminate; a MnGa-based materials; a GdCo-based materials; and a TbCo-based materials. Ferrimagnetic materials such as a MnGa-based material; a GdCo-based material; and a TbCo-based material, have low saturation magnetization and low threshold current required to move the magnetic wall.

The second ferromagnetic layer2is formed on one surface of the nonmagnetic layer3. The second ferromagnetic layers2projects in the z-direction and exist on the xy-plane spaced from each other. The multiple second ferromagnetic layer2are present with respect to a single first ferromagnetic layer1. The adjacent second ferromagnetic layers2are, for example, insulated with interlayer insulator films.

The second ferromagnetic layers2are arranged in a hexagonal lattice form, for example, in plane view from the z-direction (seeFIG.4). The signal input to the second ferromagnetic layers2propagate in the first ferromagnetic layer1. When the second ferromagnetic layers2are arranged in a hexagonal lattice form, the signal input from the second ferromagnetic layers2are likely to interfere with the signal input from the other second ferromagnetic layers2.

The arrangement of the second ferromagnetic layers2is not limited to the case ofFIG.4.FIGS.5-7are plane views of other examples of the reservoir elements according to the first embodiment.

The reservoir element10A shown inFIG.5has multiple second ferromagnetic layers2arranged in a square lattice. The distance between adjacent second ferromagnetic layer2is equal and the input signal is homogenized.

The reservoir element10B shown inFIG.6has multiple second ferromagnetic layers2placed close together in a hexagonal lattice form. As the density of the second ferromagnetic layer2increases, the signal input to the second ferromagnetic layer2is likely to interfere with each other. Even in this case, the second ferromagnetic layers2are insulated from each other.

The reservoir element10C shown inFIG.7forms multiple bundles A in which the second ferromagnetic layers2are densely packed. In bundle A, the second ferromagnetic layers2are arranged in a hexagonal lattice form. The adjacent second ferromagnetic layers2are insulated. The conditions of mutual interference differ between the signals input to the second ferromagnetic layer2constituting one bundle A and the signals input to the second ferromagnetic layers2constituting a different bundle A. By adjusting the conditions of mutual interference in the reservoir element10C, the reservoir element10C emphasizes a particular signal and transmits it to the output part30.

For example, the shape of each second ferromagnetic layers2is a cylindrical shape (seeFIG.1). The shape of the second ferromagnetic layers2is not limited to a cylindrical shape. The shape of the second ferromagnetic layer2may be, for example, an ellipsoidal shape, a rectangular cylinder, a cone, an ellipsoidal cone, a frustum, a square frustum, and the like.

The second ferromagnetic layer2contains a ferromagnetic material. The ferromagnetic material used in the second ferromagnetic layer2is the same as the material used in the first ferromagnetic layer1.

The direction of the magnetization of the second ferromagnetic layer2is harder to be changed than that of the first ferromagnetic layer1. Accordingly, the second ferromagnetic layer2is referred as a magnetization fixed layer. The magnetization of the second ferromagnetic layer2is fixed to the magnetization of the first ferromagnetic layer1by adjusting the material used in the first ferromagnetic layer1and the second ferromagnetic layer2and the layer configuration adjacent to the second ferromagnetic layer2, for example. For example, when a material having a higher coercivity than the material constituting the first ferromagnetic layer1is used in the second ferromagnetic layer2, the magnetization of the second ferromagnetic layer2is fixed to the magnetization of the first ferromagnetic layer1. Further, for example, when an antiferromagnetic layer is stacked with the second ferromagnetic layer on the surface opposite to the surface with the nonmagnetic layer3and the antiferromagnetic layer and the second ferromagnetic layer2are antiferromagnetic-coupled, the magnetization of the second ferromagnetic layer2is fixed to the magnetization of the first ferromagnetic layer.

The nonmagnetic layer3is positioned between the first ferromagnetic layer1and the second ferromagnetic layers2. The nonmagnetic layer3extends continuously, for example, on the xy-plane. The nonmagnetic layer3may be scattered on the xy-plane only at a position between the first ferromagnetic layer1and the second ferromagnetic layer2.

The nonmagnetic layer3is made of a nonmagnetic material.

When the nonmagnetic layer3is an insulator (when it is a tunneling barrier layer), the nonmagnetic layer3is, for example, an Al2O3, SiO2, MgO, MgAl2O4, and the like. The nonmagnetic layer3may also be a material or the like in which a portion of Al, Si, or Mg in the above-described material is replaced with Zn, Be, or the like. By choosing MgO or MgAl2O4, the coherent tunneling between the first ferromagnetic layer1and the second ferromagnetic layer2can be realized. In that case, spins can be efficiently injected from the first ferromagnetic layer1to the second ferromagnetic layer2. When the nonmagnetic layer3is made of a metal, the nonmagnetic layer3is, for example, Cu, Au, Ag, and the like. When the nonmagnetic layer3is a semiconductor, the nonmagnetic layer3is, for example, Si, Ge, CuInSe2, CuGaSe2, Cu(In, Ga)Se2, and the like.

The via wiring4is electrically connected to the first ferromagnetic layer1on the surface opposite to the surface with the nonmagnetic layer3. The via wirings4may be directly connected to the first ferromagnetic layer1or may be connected via other layers. The via wirings4shown inFIGS.1and3project from the first ferromagnetic layer1in the z-direction. Multiple via wirings4exist on the xy-plane, each of them being spaced apart.

The via wiring4includes a conductor. The via wiring4is made of, for example, Cu, Al, Au. The adjacent via wirings4are insulated.

Each of the via wirings4shown inFIGS.1and3is disposed at a position corresponding to each of the second ferromagnetic layers2. That is, each of the second ferromagnetic layers2and each of the via wirings4overlap with a plane view from the z-direction.

An example of a method for manufacturing the reservoir element10in the neuromorphic element100will now be described.FIGS.8A-8Dare cross-sectional views illustrating a method of manufacturing a reservoir element10according to the first embodiment.

First, a hole is formed in the substrate Sb and the inside of the hole is filled with a conductor (FIG.8A). The substrate Sb is, for example, a semiconductor substrate. The substrate Sb is preferably, for example, Si, AlTiC. When Si or AlTiC are used, it is easy to obtain a flat surface. The holes are formed, for example, using reactive ion etching (RIE). The conductor filling the hole becomes the via wiring4.

The surface of the substrate Sb and the via wirings4are then planarized by chemical mechanical polishing (CMP). The first ferromagnetic layer1, the nonmagnetic layer3, and the ferromagnetic layer2′ are laminated on the planarized substrate Sb and the via wirings4in this order (FIG.8B). The first ferromagnetic layer1, the nonmagnetic layer3, and the ferromagnetic layer2′ are laminated using, for example, chemical vapor deposition (CVD).

The hard mask HM is then formed at a predetermined position on the surface of the ferromagnetic layer2′ (FIG.8C). The portion of the ferromagnetic layer2′ that is not coated with the hard mask HM is removed by RIE or ion milling. The ferromagnetic layer2′ is formed into multiple second ferromagnetic layers2by removing unwanted portions. Finally, the second ferromagnetic layers2are protected by the interlayer insulating film I (FIG.8D). The above procedure yields the neuromorphic element100according to the first embodiment.

The function of the neuromorphic element100will then be described.FIG.12is a schematic diagram illustrating an example of operation of the neuromorphic element100. The input part20includes multiple input terminals21,22,23,24, and the like. Each of the input terminals21,22,23,24. . . , which comprise the input part20, is connected to each of the second ferromagnetic layers2of the reservoir elements10. The input part20receives an input signal from an external source. For example, the input signal is divided into time domains and is input to multiple input terminals21,22,23,24, etc. of the input part20as signals S1, S2, S3, S4, S5, and S6, respectively. An example is shown where the input signal is input without processing, but the signal can be input after the Fast Fourier Transform Analysis (FT analysis) is performed. FFT analysis is effective in extracting frequency characteristics. FFT analysis can also filter low amplitude signals due to noise. The input terminals21,22,23,24. . . , which receive external signals, carry a write current from the corresponding second ferromagnetic layers2A,2B,2C,2D . . . toward the via wirings4. For example, the input signal is divided in the order of the signal S1, the signal S2, the signal S3, and the signal S4in chronological order. The write current flows in the order of the second ferromagnetic layer2A in which the signal S1is input, the second ferromagnetic layer2B in which the signal S2is input, the second ferromagnetic layer2C in which the signal S3is input, and the second ferromagnetic layer2D in which the signal S4is input. If each of the via wirings4is disposed at a position corresponding to each of the plurality of second ferromagnetic layers2, most of the write currents flow in the z-direction.

The write current is spin polarized by the second ferromagnetic layers2A,2B,2C, and2D and reaches to the first ferromagnetic layer1. The spin polarized current provides a spin transfer torque (STT) for magnetization of the first ferromagnetic layer1. The first magnetization of the first ferromagnetic layer near the second ferromagnetic layer in which the write current flows is rotated by the STT. Magnetic rotation propagates around the periphery, depending on the time and amount of application of the write current, such that the water droplet spreads the ripple. Accordingly, a structure in which a magnetic wall is formed between a portion of the first ferromagnetic layer1in which the magnetization is rotated and a portion of the first ferromagnetic layer1in which the magnetization is not rotated, and the magnetic wall spreads by the magnetic rotation propagating in the first ferromagnetic layer1. As a result, directions of magnetization of the first ferromagnetic layer1differ in: the vicinities of the second ferromagnetic layers2A,2B,2C and2D in which the write current has flown; and other parts in which the write current has not flown. Thus, multiple magnetic domains are formed in the first ferromagnetic layer1.

The range of the magnetic domain in the vicinity of the second ferromagnetic layer2A,2B,2C, and2D to which the write current is applied varies with the time of application of the write current and the amount applied so that the range of ripples spreads depending on the size and speed of the water droplets dropped onto the water surface. When the amount of writing current is high, the range of magnetic domains formed in the vicinity of the second ferromagnetic layers2A,2B,2C, and2D expands. The magnetic wall moves in a direction extending from the second ferromagnetic layer2A,2B,2C, and2D according to the expansion of the magnetic domain.

When the writing current flows from the second ferromagnetic layers2A,2B,2C, and2D toward the via wirings4, a magnetic domain is formed near the respective second ferromagnetic layers2A,2B,2C, and2D. For example, when the magnetic rotation propagating from the second ferromagnetic layer2A and the magnetic rotation propagating from the second ferromagnetic layer2B interfere with each other, a magnetic domain reflecting this interference is formed between the second ferromagnetic layer2A and the second ferromagnetic layer2B. Therefore, the magnetic domain formed in the first ferromagnetic layer1reflects the interference of the magnetization rotation from each second ferromagnetic layer2A,2B,2C, and2D. Magnetization rotations propagating from the second ferromagnetic layer2A and the magnetization rotations propagating from the second ferromagnetic layer2B are more likely to interfere with each other than magnetization rotations propagating from the second ferromagnetic layer2A and magnetization rotations propagating from the second ferromagnetic layer2C. The distance between the second ferromagnetic layer2A and the second ferromagnetic layer2B is closer than the distance between the second ferromagnetic layer2A and the second ferromagnetic layer2C. That is, the closer the distance between the second ferromagnetic layer2, the more likely the input signals S1, S2, S3, S4, S5, and S6are to interfere with each other. The closer the time series is to signal S1, S2, S3, S4, S5, and S6, the more likely it is to interfere with each other. Therefore, it is preferable to input the signal S1, S2, S3, S4, S5, and S6, which are closer in time series, to the second ferromagnetic layer2, which is closer in distance. For example, the distance between the second ferromagnetic layer2A in which the signal S1is input and the second ferromagnetic layer2B in which the signal S2is input is preferably closer to the distance between the second ferromagnetic layer2A in which the signal S1is input and the second ferromagnetic layer2C in which the signal S3is input. When the application of the writing current to the reservoir element10is stopped, the magnetic state of the first ferromagnetic layer1is stored in a non-volatile manner.

Finally, the signal is output from the reservoir element10to the output part30. The output part30includes, for example, multiple output terminals31,32, . . . . The output terminals31,32. . . are connected to any second ferromagnetic layer2.FIG.12shows an example of connecting the input terminals21,22,23,24. . . to the second ferromagnetic layers2E,2F that is different from the second ferromagnetic layers2A,2B,2C, and2D to which the input terminals21,22,23,24. . . are connected. The input and output can be switched, and the output terminals31and32for the output can be connected to the second ferromagnetic layers2A,2B,2C, and2D to which the input terminals21,22,23,24, etc. for the input are connected. The signal is output by flowing a read current from the second ferromagnetic layer2toward the via wiring4. The read current has a lower current density than the write current and does not rotate the magnetization of the first ferromagnetic layer1.

When a reading current is passed through the reservoir element10, a difference in the relative angles of the magnetization of the second ferromagnetic layer2and the magnetization of the first ferromagnetic layer1at a position overlapping the second ferromagnetic layer2is output as a change in the resistance value. The magnetization direction of the first ferromagnetic layer1at a position overlying the second ferromagnetic layer2is affected by a magnetic domain that extends from the vicinity of the other second ferromagnetic layers. That is, the signal read from the first second ferromagnetic layer2includes information written to the other second ferromagnetic layers2, and the information is compressed.

Finally, the compressed signal is transmitted to the output part30through multiple output terminals31,32, . . . . The output part30weights the signal read out from each of the second ferromagnetic layers2by learning.FIG.13is a schematic diagram illustrating another example of the operation of the neuromorphic element100. InFIG.13, the method of dividing the input signal, the connection points of the input terminals21,22,23, and24and the connection points of the output terminals31,32, etc. are different from those shown inFIG.12. In the example shown inFIG.13, the input signals are divided into time series without overlapping into signals S1, S2, S3, S4, and so on. In the neuromorphic element shown inFIG.13, the second ferromagnetic layers2A,2B,2C, and2D in which signals S1, S2, S3, and S4, which are separated from each other in time series, are inputted are arranged in such a way that the distances from each other are separated becomes longer from the second ferromagnetic layers2A,2B,2C and2D.

FIG.14is a schematic diagram illustrating another example of a neuromorphic element. The neuromorphic element shown inFIG.14has a second output part40, which is different from the example shown inFIG.13. Each of the terminals41,42, and43of the second output part40is connected to each of the output terminals31,32. . . of the output part30via a synapse Sp. When information is transmitted from each of the output terminals31,32. . . of the output part30to each of the terminals41,42, and43of the second output part40, the data is weighted at the synapse Sp. The neuromorphic element shown inFIG.14performs leaning process between the output part30and the second output part40. The neuromorphic element shown inFIG.14is able to recognize more complex information by having a structure of a deep neural network.

FIG.15is a schematic diagram illustrating another example of a neuromorphic element. The neuromorphic element shown inFIG.15differs from the example shown inFIG.14in that, the reservoir elements10are arranged in parallel and the output parts30connected to the respective reservoir elements10are shared. By having such a structure, it is possible to simultaneously recognize signals having different outputs and signal speeds from multiple input terminals, and a multimodal reservoir device can be realized.

As described above, in the first ferromagnetic layer1, the magnetization rotation from each second ferromagnetic layer2interferes with each other, and the magnetic domain formed between them reflects the interaction. The signals input from the input part20interact with each other in the first ferromagnetic layer1to generate one magnetic state in the first ferromagnetic layer1. That is, the signal input from the input part20is compressed into one magnetic state in the first ferromagnetic layer1. Accordingly, the neuromorphic element100in accordance with the first embodiment appropriately compresses the signals with the reservoir element10. By compressing the signals, only the output part30is responsible for learning, reducing the power consumption of the neuromorphic element100. Also, the magnetic state of the first ferromagnetic layer1is held in a non-volatile state unless a new write current is applied.

By storing information in a nonvolatile manner, the reservoir element10is not limited by time. When time series data is input to the input part20of the reservoir element10and is extracted from the output part30and information processing is performed, it is necessary to match the input/output time interval with the time interval to be detected by the reservoir element10. The operations of magnetization rotation and domain wall drive in the reservoir element10are generally completed in a time of 1 nsec to 1 μsec. However, since the movement of a person or an object generally occurs in a unit of time of about 1 sec, there is a large time difference between the operation speed of one terminal of the reservoir element10and the movement speed of the person or the object. In order for the reservoir element10to function, it is preferable that the influence of the operation of one terminal of the reservoir element10remains at least during the operation of the person or the object. Since the reservoir element10can hold input information in a non-volatile manner, even if there is a large time difference between the operating speed of one terminal of the reservoir element10and the operating speed of the person or the object, interference between the input signals in the reservoir element10can be maintained.

Second Embodiment

FIG.9is a cross-sectional view of a reservoir element according to the second embodiment. The reservoir element11according to the second embodiment differs from the reservoir element10according to the first embodiment in that there is no multiple via wirings4. The other configuration is the same as the reservoir element10according to the first embodiment, and the description is omitted. Also, inFIG.9, the same configuration asFIG.1is denoted by the same reference numerals.

In the reservoir element11, there is only one via wiring4. The via wiring4is electrically connected to the first ferromagnetic layer1.

As shown inFIG.1, when each of the via wirings4is disposed at a position corresponding to each of the second ferromagnetic layers2, many of the write currents flow in the z-direction. In contrast, when only one via wiring4is provided, a portion of the writing current flows in the first ferromagnetic layer1in the xy-plane. The spin-polarized write current moves the magnetic wall, which is the boundary of the different magnetic domains. That is, if the via wiring4disposed in the reservoir element11is one, the magnetic wall moves efficiently in the first ferromagnetic layer1, and the interaction between the signal input to the first second ferromagnetic layer2and the signal input to the other second ferromagnetic layer2is promoted.

Also, when only one via wiring4is provided, the distance between the second ferromagnetic layer2and the via wiring4differs in each of the second ferromagnetic layers2. The amount of write current flowing on the xy-plane of the first ferromagnetic layer1depends on which second ferromagnetic layer2is input a signal. In other words, the ease of movement of the magnetic wall varies depending on which second ferromagnetic layer2the signal is input to. In other words, the reservoir element11preferentially outputs predetermined information from the signals input from the input part20, and can provide the necessary information with a weight in advance.

The reservoir element11in accordance with the second embodiment can be applied to the neuromorphic element100. In addition, the reservoir element11according to the second embodiment has the same effect as the reservoir element10according to the first embodiment. Also, in accordance with the second embodiment, the reservoir element11has different specificities for the ease of flow of the write current and can place heavier or lighter weight to the signal.

In addition, the reservoir element11according to the second embodiment can be modified. For example, the via wiring4need not be formed downwardly from one surface of the first ferromagnetic layer1, but can be provided as a wiring on the side of the first ferromagnetic layer1.

Third Embodiment

FIG.10is a cross-sectional view of a reservoir element according to the third embodiment. The reservoir element12in accordance with the third embodiment has the shared electrode layer5, which is different from the reservoir element10in accordance with the first embodiment. The other configuration is the same as the reservoir element10according to the first embodiment, and the description is omitted. Also, inFIG.10, the same configuration asFIG.1is denoted by the same reference numerals.

The shared electrode layer5connects at least two or more via wirings4of the via wirings4. The shared electrode layer5extends continuously, for example, on the xy-plane. The shared electrode layer5is made of a material similar to that of the via wiring4.

When the reservoir element12has the shared electrode layer5, a portion of the write current flows into the xy-plane within the first ferromagnetic layer1. The magnetic wall moves efficiently in the first ferromagnetic layer1, facilitates the interaction between the signal input to the first second ferromagnetic layer2and the signal input to the other second ferromagnetic layers2, and thus represents a more complex phenomenon.

The reservoir element11in accordance with the third embodiment can be applied to the neuromorphic element100. In addition, the reservoir element12according to the third embodiment has the same effect as the reservoir element10according to the first embodiment.

Fourth Embodiment

FIG.11is a cross-sectional view of a reservoir element according to the fourth embodiment. The reservoir element13in accordance with the fourth embodiment has the magnetic interference layer6, which is different from the reservoir element10in accordance with the first embodiment. The other configuration is the same as the reservoir element10according to the first embodiment, and the description is omitted. Also, inFIG.11, the same configuration asFIG.1is denoted by the same reference numerals.

The magnetic interference layer6contacts the first ferromagnetic layer1on the surface opposite to the surface with the nonmagnetic layer3. The magnetic interference layer6extends continuously on the xy-plane.

The magnetic interference layer6has a lower coercivity than the first ferromagnetic layer1and has superior soft magnetic properties. That is, the magnetization of the magnetic interference layer6is more easily rotated than the magnetization of the first ferromagnetic layer1. The magnetic interference layer6is an alloy containing, for example, any of Fe—Si, Fe—Si—Al, Fe—Co—V, Ni—Fe, and Co—Fe—Si—B.

When the writing current is applied to the reservoir element13, a different magnetic domain is formed in the magnetic interference layer6, similar to the first ferromagnetic layer1, and a magnetic wall is formed. The magnetic wall of the magnetic interference layer6is more mobile than the magnetic wall of the first ferromagnetic layer1. The magnetic interference layer6is responsible for long-range magnetic correlation.

When the reservoir element13has the magnetic interference layer6, the freedom of material selection of the first ferromagnetic layer1is increased.

The magnetoresistance change is caused by a change in the magnetic state of two magnetic materials (the first ferromagnetic layer1and the second ferromagnetic layer2) that sandwich the nonmagnetic layer3. Preferably, the first ferromagnetic layer1includes a material that is easy to obtain coherent tunneling effects with the second ferromagnetic layer2(e.g., MgO, MgAl2O4).

On the other hand, materials that are easy to obtain coherent tunneling effects are not necessarily materials in which the magnetic walls easily move. The first ferromagnetic layer1is responsible for the magnetoresistance change, and the magnetic interference layer6is responsible for the long-range magnetic correlation. That is, the first ferromagnetic layer1does not need to be a material in which the magnetic walls easily move, and the freedom of selecting the material of the first ferromagnetic layer1is increased.

The reservoir element13in accordance with the fourth embodiment can be applied to the neuromorphic element100. In addition, the reservoir element13according to the fourth embodiment has the same effect as the reservoir element10according to the first embodiment. Further, by dividing the functions of the first ferromagnetic layer1and the magnetic interference layer6, the reservoir element13according to the fourth embodiment facilitates the interaction between the signal input to the first second ferromagnetic layers2and the signal input to the other second ferromagnetic layer2, and thus can represent a more complex phenomenon.

FIG.16is a plan view of a reservoir element according to the fifth embodiment. The reservoir element14in accordance with the fifth embodiment differs from the reservoir element10in accordance with the first embodiment in that the first ferromagnetic layer and the nonmagnetic layer3′ are annular and the plurality of second ferromagnetic layers2are scattered along the first ferromagnetic layer which is circular. The other configuration is the same as the reservoir element10according to the first embodiment, and the description is omitted. Also, inFIG.16, the same configuration as inFIG.1is denoted by the same reference numerals.

The input signal is divided, for example, by time domain, and is input to the reservoir element14as multiple signals S1, S2, S3, S4, etc. For example, the signal S1is input to the second ferromagnetic layer2A, the signal S2is input to the second ferromagnetic layer2B, and the signal S3is input to the second ferromagnetic layer2C. Signals S1, S2, S3, and S4. . . the magnetic rotation of some of the first ferromagnetic layer. Magnetic rotation extending from each of the second ferromagnetic layers2A,2B, and2C propagates along the circumference and interferes with each other.

The magnetization state of the first ferromagnetic layer is output, for example, from the second ferromagnetic layers2E,2F, and2G. When the second ferromagnetic layers2A,2B, and2C in which the signal is input and the second ferromagnetic layers2E,2F, and2G in which the signal is output are set to be different terminals, a portion of the write current flows in a circumferential direction along the first ferromagnetic layer. The circumferentially flowing spin polarization current moves the magnetic wall and facilitates interference of the magnetization rotation extending from the respective second ferromagnetic layers2A,2B, and2C.

In addition, the input position of the signal to the second ferromagnetic layer and the output position of the signal from the second ferromagnetic layer can be changed sequentially.

Although one preferred embodiment of the present disclosure has been described in detail, the present disclosure is not limited to this embodiment, and various modifications and changes may be made within the scope of the present disclosure as set forth in the appended claims.

For example, the characteristic configuration of the reservoir element14according to the fifth embodiment may be combined to the reservoir element10according to the first embodiment.

EXPLANATION OF REFERENCES