A probability bit generator and control method

Abstract

The present invention provides a probabilistic bit generator and control method, relating to the technical field of spintronic devices. The probabilistic bit generator comprises multiple magnetic tunnel junctions connected in series and a voltage comparator, wherein the multiple magnetic tunnel junctions form a probabilistic bit structure. A first current is injected into the spin current generation layer, and the generated spin current is injected into the magnetic layer, causing the magnetic moment in the magnetic layer to randomly flip. A second current is injected into the spin current generation layer, and the energy of the second current is less than the energy required to flip the magnetic moment, and is used to measure the voltage of the readout electrode layer. The voltage comparator inputs the sum of the voltages of the multiple magnetic tunnel junctions at the first input terminal, and inputs a reference voltage at the second input terminal. The reference voltage is an adjustable voltage related to probability, thereby realizing a probabilistic flipping function that controls the output high and low levels under different reference voltages. The present invention utilizes multiple randomly flipped magnetic tunnel junctions to form an array to form a voltage-adjustable probabilistic bit generator, which can better realize the probability calculation function.

Description

Technical Field

[0001] The present invention relates to the technical field of spin electronic devices, and in particular to a probabilistic bit generator and a control method thereof. Background Art

[0002] Probabilistic computing is an intermediate solution on the path to quantum computing. Probabilistic bits (p-bits), as the fundamental unit of probabilistic computing, complement basic data storage and processing units. Probabilistic bits have a wide range of applications, offering significant performance advantages in solving nonlinear programming and multi-body system problems. They can also operate at room temperature, making them more practical. Therefore, the challenge of fabricating probabilistic bit devices within existing industrial systems has become a pressing technical challenge in this field.

[0003] A common probabilistic bit structure currently used in industry is the Magnetic Tunnel Junction (MTJ), which has potential application value in the fields of magnetic memory and spin electronics. In current research, deterministic flipping of MTJ is usually required. However, under the action of spin current, MTJ will undergo random flipping, which is mainly related to the spin-orbit torque effect (SOT). The spin-orbit torque effect can change the magnetization direction of the free layer in the magnetic tunnel junction. For example, for an MTJ with perpendicular magnetic anisotropy (+z direction), applying a current in the +x direction will generate a spin current with a polarization direction in the +y direction, and then the magnetic moment direction in the free layer will be affected to the +y direction through the spin-orbit torque. After the current is removed, the magnetic moment of the free layer will randomly flip to the +z or -z direction (with a probability of 50%), thereby randomly changing the magnetization direction of the magnetized layer, such as Figure 1 shown.

[0004] The limitation of the above method is that after the current is removed, it can only be randomly flipped in the z direction with equal probability. However, probability calculation requires that the probability bit is a device with adjustable probability. Therefore, it is necessary to provide a probability bit generator with adjustable probability to meet the needs of practical applications. Summary of the Invention

[0005] In view of the above problems, the present invention aims to provide a probability bit generator and control method, which utilizes multiple randomly flipped MTJs to form an array to form a voltage-adjustable probability bit generator to better realize the probability calculation function.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In one aspect, a probabilistic bit generator is provided, comprising: a plurality of magnetic tunnel junctions connected in series, and a voltage comparator;

[0008] A plurality of the magnetic tunnel junctions form a probabilistic bit structure, the probabilistic bit structure comprising a common substrate and a spin current generating layer located on the substrate, a plurality of magnetic layers of the magnetic tunnel junctions are arrayed on the spin current generating layer, and an intermediate non-magnetic insulating barrier layer, a magnetic pinning layer, and a readout electrode layer are sequentially arranged on each of the magnetic layers;

[0009] A first current is injected into the spin current generating layer, and the spin current generated by the first current is injected into the magnetic layer to randomly flip the magnetic moment in the magnetic layer; and a second current is injected into the spin current generating layer, and the energy of the second current is less than the energy of the magnetic moment flip, and is used to measure the voltage of the readout electrode layer;

[0010] The first input end of the voltage comparator inputs the sum of the voltages of multiple magnetic tunnel junctions, and the second input end of the voltage comparator inputs a reference voltage. The reference voltage is an adjustable voltage related to probability, so as to realize the probability flipping function of regulating the output high and low levels under different reference voltages.

[0011] Optionally, the substrate is a silicon substrate.

[0012] Optionally, the spin current generating layer uses one or more of the heavy metal materials Pt, Ta, and W; or uses one or more of the topological insulator materials Bi2Se3, Sb2Te3, and Bi2Te3; or uses one or more of the new materials MoS2 and PtTe2.

[0013] Optionally, the magnetic layer is made of soft magnetic material, including Co, CoFe alloy, CoNiCo multilayer film, and CoAuCo multilayer film.

[0014] Optionally, a covering layer is further provided on the magnetic pinning layer to protect the magnetic stacking structure, and the covering layer is made of Pt or MgO.

[0015] Optionally, the spin current generation layer is a strip structure along the X direction, the readout electrode layer is a strip structure along the Y direction, and the magnetic layer, the intermediate non-magnetic insulating barrier layer and the magnetic pinning layer are rectangular structures located in the overlapping area between the spin current generation layer and the readout electrode layer.

[0016] Optionally, the magnetic tunnel junction can be replaced by a Hall device, and a signal amplification circuit is added after multiple Hall devices are connected in series to read the voltage.

[0017] On the other hand, a control method based on the above-mentioned probabilistic bit generator is provided, the control method comprising the following steps:

[0018] S1. For a plurality of magnetic tunnel junctions connected in series, applying a first current to a spin current generating layer, causing the first current to flow through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, causing a random reversal of the magnetic moment in the magnetic layer;

[0019] S2. Applying a second current to the spin current generating layer, wherein the energy of the second current is less than the energy of magnetic moment reversal, and is used to measure the voltage of each readout electrode layer;

[0020] S3. The measured voltages of the multiple magnetic tunnel junctions are used as the voltage of the first input terminal of the voltage comparator, and a reference voltage is input to the second input terminal of the voltage comparator. The reference voltage is an adjustable voltage related to probability, so as to realize the probability flipping function of regulating the output high and low levels under different reference voltages.

[0021] Optionally, the first current is a periodic pulse current.

[0022] Alternatively, if a low-level output voltage with a probability of p is required, the input reference voltage V ref for:

[0023] ;

[0024] Where n is the number of magnetic tunnel junctions in series, V out The voltage measured by the readout electrode layer of a single magnetic tunnel junction can output a low level with a probability of p after passing through a voltage comparator.

[0025] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0026] 1. Compatibility: The probabilistic bit structure composed of multiple magnetic tunnel junctions is highly compatible with existing magnetic tunnel junction fabrication techniques. The maturity and widespread application of magnetic tunnel junction fabrication techniques, including photolithography, electron beam lithography, and ion beam etching, provide strong support for the precise fabrication of multiple magnetic tunnel junctions. Furthermore, this structure can be combined with storage technologies such as spin-transfer torque magnetic random access memory (STM), enabling low-cost, high-efficiency integration.

[0027] 2. Adjustable Probability: Because the magnetic moment of the magnetic layer in a magnetic tunnel junction can flip under the influence of current, with a 50% probability of flipping (under specific conditions), a variety of different probability distributions can be generated by combining multiple magnetic tunnel junctions. A voltage comparator can convert these probability distributions into high and low level signals based on a set reference voltage. As the reference voltage changes, the probability of the output voltage being high or low also adjusts accordingly, achieving an adjustable probability output. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 Schematic diagram of the random flipping phenomenon induced by spin-orbit moment;

[0030] Figure 2 1 is a schematic diagram of the structure of a probabilistic bit generator provided by an embodiment of the present invention;

[0031] Figure 3 is a schematic diagram of multiple magnetic tunnel junction structures provided by an embodiment of the present invention;

[0032] Figure 4 is a flow chart of a control method for a probability bit generator provided by an embodiment of the present invention;

[0033] Figure 5 (a)- Figure 5 (b) is a schematic diagram of the probability distribution function and density function of the voltage sum output by multiple MTJs connected in series according to an embodiment of the present invention.

[0034] Explanation of the reference numerals: 1. substrate; 2. spin current generation layer; 3. magnetic layer; 4. intermediate non-magnetic insulating barrier layer; 5. magnetic pinning layer; 6. readout electrode layer. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" in the present invention should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner.

[0037] The embodiment of the present invention provides a probability bit generator, referring to Figure 2 As shown, the probability bit generator includes: a plurality of magnetic tunnel junctions MTJ1, MTJ2, ..., MTJn connected in series, and a voltage comparator.

[0038] Multiple magnetic tunnel junctions form a probabilistic bit structure, refer to Figure 3 As shown, the probabilistic bit structure includes a common substrate 1 and a spin current generation layer 2 located on substrate 1. Multiple magnetic layers 3 with magnetic tunnel junctions are arranged in an array on the spin current generation layer 2. An intermediate non-magnetic insulating barrier layer 4, a magnetic pinning layer 5, and a readout electrode layer 6 are sequentially disposed on each magnetic layer 3. A magnetic tunnel junction is formed between the intermediate non-magnetic insulating barrier layer 4 and the magnetic pinning layer 5 and the magnetic layer 3.

[0039] As a preferred embodiment of the present invention, the spin current generation layer 2 is a strip structure along the X direction, the readout electrode layer 6 is a strip structure along the Y direction, and the magnetic layer 3, the intermediate non-magnetic insulating barrier layer 4 and the magnetic pinning layer 5 are rectangular structures located in the overlapping area between the spin current generation layer 2 and the readout electrode layer 6.

[0040] In which, a first current is injected into the spin current generation layer 2, and the spin current generated by the first current is injected into the magnetic layer 3 to cause the magnetic moment in the magnetic layer 3 to be randomly reversed; and a second current is injected into the spin current generation layer 2, and the energy of the second current is less than the energy of the magnetic moment reversal, which is used to measure the voltage of the readout electrode layer 6. Figure 3 In the figure, the lower arrow represents the first current (write current) I in The arrows above indicate the voltage V read after applying the second current. out 1,V out 2,......,V out n is the direction of n, and n is the number of magnetic tunnel junctions in series.

[0041] The first input terminal A of the voltage comparator inputs the voltage of multiple magnetic tunnel junctions and V sum The second input terminal B inputs the reference voltage V ref , reference voltage V ref It is an adjustable voltage related to the probability p, which can realize the probability flipping function of regulating the output high and low levels under different reference voltages.

[0042] As a preferred embodiment of the present invention, in the embodiment of the present invention:

[0043] Substrate 1: Made of silicon substrate, compatible with current mainstream semiconductor materials.

[0044] Spin current generation: 2: Use conductive heavy metal materials with strong spin-orbit coupling effect, such as Pt, Ta, W, etc.; or use topological insulator materials, such as Bi2Se3, Sb2Te3, Bi2Te3, etc.; or use new materials, such as MoS2, PtTe2, etc.

[0045] Magnetic layer 3: Soft magnetic materials with perpendicular anisotropy (PMA) and low damping coefficient and coercive force are used. The energy barrier of magnetic moment reversal is low. Co, CoFe alloy, CoNiCo multilayer film, CoAuCo multilayer film, etc. can be selected.

[0046] Furthermore, a covering layer ( Figure 3 The cover layer may be made of materials such as Pt and MgO to reduce or prevent device oxidation.

[0047] The first current flowing into the spin current generation layer 2 includes a pulse current. The energy generated by the first current is greater than the energy generated by the magnetic moment reversal in the magnetic layer 3. By adding a pulse current with a fixed period, the spin current generated by each pulse current is injected into the upper perpendicular anisotropic magnetic layer 3, causing the magnetic moment in the magnetic layer 3 to randomly reverse. At this time, a second current is injected. The energy generated by the second current is less than the energy generated by the magnetic moment reversal, which is used to measure the voltage V generated by the readout electrode layer. out .

[0048] The voltage comparator is used to compare the magnitudes of two input voltages, where the first input terminal A inputs the series voltage sum of n MTJ devices, and the second input terminal B inputs the reference voltage V ref , reference voltage V ref is an adjustable voltage related to probability p. By comparing these two voltages, if the voltage at terminal A is greater, the voltage comparator outputs a high level, otherwise it outputs a low level.

[0049] Furthermore, the magnetic tunnel junction in the embodiment of the present invention can be replaced by a Hall device, and a signal amplification circuit can be added after multiple Hall devices are connected in series to read the voltage.

[0050] Accordingly, an embodiment of the present invention further provides a method for controlling a probability bit generator, such as Figure 4 As shown, the control method includes the following steps:

[0051] S1. For a plurality of magnetic tunnel junctions connected in series, applying a first current to a spin current generating layer, causing the first current to flow through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, causing a random reversal of the magnetic moment in the magnetic layer;

[0052] S2. Applying a second current to the spin current generating layer, wherein the energy of the second current is less than the energy of magnetic moment reversal, and is used to measure the voltage of each readout electrode layer;

[0053] S3. The measured voltages of the multiple magnetic tunnel junctions are used as the voltage of the first input terminal of the voltage comparator, and a reference voltage is input to the second input terminal of the voltage comparator. The reference voltage is an adjustable voltage related to probability, so as to realize the probability flipping function of regulating the output high and low levels under different reference voltages.

[0054] Specifically, for Figure 3 In multiple MTJ devices, a pulse current is applied to the spin current generation layer 2 along the X-axis direction, so that part of the current flows through the magnetic layer, generating a spin-orbit moment acting on the magnetic layer 3, causing the magnetic moment in the magnetic layer 3 to randomly flip. At the same time, a second current smaller than the magnetic moment flip energy is applied to measure the voltage of the readout electrode layer 6. The probability distribution function of the measured voltage and Figure 5 As shown in Figure (a), the voltage ranges from 0 to nV out It presents a Gaussian distribution. Its density function from 0 to a certain voltage value is as follows Figure 5 As shown in Figure (b), the image has the shape of a sigmoid function, which can be applied to probability calculations.

[0055] The voltage sum generated by multiple magnetic tunnel junctions is used as the input voltage of one input terminal A of the voltage comparator, and the other input terminal B inputs the reference voltage V ref If a low-level output voltage V is required with probability p, the reference voltage V at the input terminal B is ref for , after the voltage comparator, it can output a low level with a probability of p.

[0056] The above method can be used to adjust the output voltage with a probability of 0-100%. Therefore, it can be applied to nonlinear problems such as probability calculation, optimization combination, integer decomposition, reversible logic, path planning, and multi-body problems.

[0057] Compared with the prior art, the probability bit generator and control method provided by the present invention have the following advantages:

[0058] 1. This invention achieves a probability-adjustable probabilistic bit generator by connecting multiple magnetic tunnel junction structures in series and adding devices such as voltage comparators. This structure is highly compatible with existing magnetic tunnel junction fabrication technology, can fully utilize existing processes and equipment, and is easily integrated with existing electronic systems and integrated circuits, reducing the difficulty of development and application.

[0059] 2. By adjusting the reference voltage of the voltage comparator, the probability of the output voltage being high or low can be flexibly controlled. This adjustability makes this structure have broad application prospects in fields such as random number generation and signal processing.

[0060] 3. The magnetic tunnel junction itself has high stability and reliability, and can maintain stable performance under various environmental conditions. The combination of multiple magnetic tunnel junctions further enhances the stability and reliability of the system and improves the reliability of the application.

[0061] 4. The functionality and application range of the system can be expanded by increasing the number of magnetic tunnel junctions. This scalability makes the structure potentially useful in complex electronic systems and large-scale integrated circuits.

[0062] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes the element.

[0063] References in the specification to "one embodiment," "an embodiment," "exemplary embodiments," "some embodiments," etc. indicate that the described embodiments may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes that particular feature, structure, or characteristic. In addition, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is within the knowledge of persons skilled in the relevant art to implement that feature, structure, or characteristic in conjunction with other embodiments (whether or not explicitly described).

[0064] It should be understood that the term "and / or" as used herein simply describes an association between related objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the related objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0065] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0066] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0067] In the several embodiments provided by the present invention, it should be understood that the disclosed devices, apparatuses and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of the device or unit, which can be electrical, mechanical or other forms.

[0068] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0069] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0070] If the functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or the portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage media include various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROM), random access memories (RAM), magnetic disks, or optical disks.

[0071] The present invention encompasses any alternatives, modifications, equivalents, and solutions that fall within the spirit and scope of the present invention. To provide a thorough understanding of the present invention, specific details are described in detail below in connection with the preferred embodiments of the present invention, but those skilled in the art will be able to fully understand the present invention without these detailed descriptions. Furthermore, to avoid unnecessary confusion regarding the essence of the present invention, well-known methods, processes, procedures, components, and circuits have not been described in detail.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A probabilistic bit generator, characterized in that The probability bit generator includes: a plurality of magnetic tunnel junctions connected in series, and a voltage comparator; A plurality of the magnetic tunnel junctions form a probabilistic bit structure, the probabilistic bit structure comprising a common substrate and a spin current generating layer located on the substrate, a plurality of magnetic layers of the magnetic tunnel junctions are arrayed on the spin current generating layer, and an intermediate non-magnetic insulating barrier layer, a magnetic pinning layer, and a readout electrode layer are sequentially arranged on each of the magnetic layers; A first current is injected into the spin current generating layer, and the spin current generated by the first current is injected into the magnetic layer to randomly flip the magnetic moment in the magnetic layer; and a second current is injected into the spin current generating layer, and the energy of the second current is less than the energy of the magnetic moment flip, and is used to measure the voltage of the readout electrode layer; The first input end of the voltage comparator inputs the sum of the voltages of multiple magnetic tunnel junctions, and the second input end of the voltage comparator inputs a reference voltage. The reference voltage is an adjustable voltage related to probability, so as to realize the probability flipping function of regulating the output high and low levels under different reference voltages.

2. The probability bit generator according to claim 1, characterized in that The substrate is a silicon substrate.

3. The probability bit generator according to claim 1, characterized in that The spin current generating layer adopts one or more of heavy metal materials Pt, Ta, and W; or adopts one or more of topological insulator materials Bi2Se3, Sb2Te3, and Bi2Te3; or adopts one or more of new materials MoS2 and PtTe2.

4. The probability bit generator according to claim 1, characterized in that The magnetic layer is made of soft magnetic materials, including Co, CoFe alloy, CoNiCo multilayer film, and CoAuCo multilayer film.

5. The probability bit generator according to claim 1, characterized in that A covering layer is further provided on the magnetic pinning layer to protect the magnetic stacking structure, and the covering layer is made of Pt or MgO.

6. The probability bit generator according to claim 1, characterized in that The spin current generation layer is a strip structure along the X direction, the readout electrode layer is a strip structure along the Y direction, and the magnetic layer, the intermediate non-magnetic insulating barrier layer and the magnetic pinning layer are rectangular structures located in the overlapping area between the spin current generation layer and the readout electrode layer.

7. The probability bit generator according to claim 1, characterized in that The magnetic tunnel junction can be replaced by a Hall device, and a signal amplification circuit can be added after multiple Hall devices are connected in series to read the voltage.

8. A control method based on the probability bit generator according to any one of claims 1 to 7, characterized in that: The control method comprises the following steps: S1. For a plurality of magnetic tunnel junctions connected in series, applying a first current to a spin current generating layer, causing the first current to flow through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, causing a random reversal of the magnetic moment in the magnetic layer; S2. Applying a second current to the spin current generating layer, wherein the energy of the second current is less than the energy of magnetic moment reversal, and is used to measure the voltage of each readout electrode layer; S3. The measured voltages of the multiple magnetic tunnel junctions are used as the voltage of the first input terminal of the voltage comparator, and a reference voltage is input to the second input terminal of the voltage comparator. The reference voltage is an adjustable voltage related to probability, so as to realize the probability flipping function of regulating the output high and low levels under different reference voltages.

9. The control method of the probability bit generator according to claim 8, characterized in that: The first current is a periodic pulse current.

10. The control method of the probability bit generator according to claim 8, characterized in that: If a low-level output voltage with a probability of p is required, the input reference voltage V ref for: ； Where n is the number of magnetic tunnel junctions in series, V out The voltage measured by the readout electrode layer of a single magnetic tunnel junction can output a low level with a probability of p after passing through a voltage comparator.

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