Probability bit generator and control method

Abstract

The invention provides a probability bit generator and a control method, and relates to the technical field of spinning electronic devices. The probability bit generator comprises a plurality of magnetic tunnel junctions connected in series and a voltage comparator, and the plurality of magnetic tunnel junctions form a probability bit structure. Wherein a first current is injected into the spin current generation layer, and the generated spin current is injected into the magnetic layer, so that the magnetic moment in the magnetic layer is randomly overturned; and a second current is injected into the spin current generation layer, the energy of the second current is smaller than the energy of the magnetic moment flipping, and the second current is used for measuring the voltage of the readout electrode layer. The first input end of the voltage comparator inputs voltages of the plurality of magnetic tunnel junctions, the second input end of the voltage comparator inputs a reference voltage, and the reference voltage is an adjustable voltage related to probability so as to realize a probability flipping function of regulating and controlling output of high and low levels under different reference voltages. According to the invention, a plurality of randomly flipped magnetic tunnel junctions are utilized to form an array, and a voltage-adjustable probability bit generator is formed, so that a probability calculation function can be better realized.

Description

Technical Field

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

[0002] Probabilistic computing is an intermediate solution to quantum computing. Probabilistic bits (p-bits), as the basic unit of probabilistic computing, complement basic data storage / processing units. Probabilistic bits are widely used and have significant performance advantages in solving nonlinear programming and multi-body system problems. They can also operate at room temperature, which is closer to the practical environment. Therefore, how to manufacture probabilistic bit devices within the existing industrial system has become a technical problem that needs to be solved urgently in this field.

[0003] A commonly used probabilistic bit structure in the industry is the magnetic tunnel junction (MTJ), which has potential application value in the field of magnetic memory and spin electronics. In current research, the 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 generates a spin current with a polarization direction in the +y direction, and then the magnetic moment direction in the free layer is applied to the +y direction through the spin-orbit torque. After the current is removed, the magnetic moment of the free layer randomly flips 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 flip randomly in the z direction with equal probability, and probability calculation requires that the probability bit is a probability-adjustable device. Therefore, it is necessary to provide a probability-adjustable probability bit generator to meet the needs of practical applications. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a probability bit generator and a control method, which utilizes a plurality of 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 probability bit generator is provided, the probability bit generator 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 generation layer located on the substrate, a plurality of magnetic layers of the magnetic tunnel junctions are arrayed on the spin current generation 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] Wherein, a first current is injected into the spin current generation layer, and the spin current generated by the first current is injected into the magnetic layer to cause the magnetic moment in the magnetic layer to be randomly flipped; and a second current is injected into the spin current generation layer, and the energy of the second current is less than the energy of the magnetic moment flipping, and is used to measure the voltage of the readout electrode layer;

[0010] The first input terminal of the voltage comparator inputs the voltage sum of multiple magnetic tunnel junctions, and the second input terminal of the voltage comparator inputs a reference voltage, and the reference voltage is an adjustable voltage related to probability to achieve a 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 generation layer is made of one or more of heavy metal materials Pt, Ta, and W; or a topological insulator material Bi 2 Se 3 , Sb 2 Te 3 ,Bi 2 Te 3 One or more of the following; or, using a new material MoS 2 , PtTe 2 One or more of .

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

[0014] Optionally, a covering layer is further disposed 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 probability bit generator is provided, and the control method comprises 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, so that the first current flows through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, so that a magnetic moment in the magnetic layer is randomly flipped;

[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] Optionally, if a low-level output voltage with probability 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: Multiple magnetic tunnel junctions form a probabilistic bit structure, which is highly compatible with the existing magnetic tunnel junction preparation technology in terms of preparation process. Thanks to the maturity and wide application of magnetic tunnel junction preparation technology, including photolithography, electron beam exposure, ion beam etching and other micro-machining processes, it provides strong support for the precise preparation of multiple magnetic tunnel junctions. At the same time, this structure can also be combined with storage technologies such as spin transfer torque magnetic random access memory to achieve low-cost and high-efficiency integration.

[0027] 2. Adjustable probability: Since the magnetic moment of the magnetic layer in the magnetic tunnel junction can be flipped under the action of current, and the flipping probability is 50% (under specific conditions), a variety of different probability distributions can be generated through the combination of multiple magnetic tunnel junctions. The voltage comparator can convert these probability distributions into high and low level signals according to the set reference voltage. When the reference voltage changes, the high and low level probability of the output voltage will also be adjusted accordingly, thereby 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 This is a schematic diagram of the random flipping phenomenon induced by the spin-orbit moment;

[0030] Figure 2 is a schematic diagram of the structure of a probability 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 of 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 of the outputs of multiple MTJs connected in series provided by 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] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment 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 explanations. Any embodiment or design described as "exemplary" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the word "exemplary" is used to present concepts in a specific way.

[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 the substrate 1, a plurality of magnetic layers 3 of magnetic tunnel junctions are arrayed on the spin current generation layer 2, and an intermediate non-magnetic insulating barrier layer 4, a magnetic pinning layer 5 and a readout electrode layer 6 are sequentially arranged 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] Among them, 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 flipped; 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 flipping, which is used to measure the voltage of the read-out 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 out 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, so as to 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: A soft magnetic material with perpendicular anisotropy (PMA) having a small damping coefficient and low coercive force is used, and the energy barrier for 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 introduced 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, so that the magnetic moment in the magnetic layer 3 is randomly reversed. At this time, the 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 is added after multiple Hall devices are connected in series to read the voltage.

[0050] Accordingly, an embodiment of the present invention further provides a control method for a probability bit generator, such as Figure 4 As shown, the control method comprises 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, so that the first current flows through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, so that a magnetic moment in the magnetic layer is randomly flipped;

[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 the 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 less 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 is as follows: 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, a low level with a probability of p can be output.

[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. The present invention realizes a probability bit generator with adjustable probability by connecting multiple magnetic tunnel junction structures in series and adding devices such as voltage comparators. The structure is highly compatible with the existing magnetic tunnel junction preparation technology, can make full use of existing processes and equipment for preparation, and is easy to integrate 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 high and low levels of the output voltage can be flexibly controlled. This adjustability makes the structure have broad application prospects in the fields of 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 function and application scope of the system can be expanded by increasing the number of magnetic tunnel junctions. This scalability makes the structure have potential application value in complex electronic systems and large-scale integrated circuits.

[0062] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or terminal device including 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 restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

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

[0064] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0065] In the present invention, "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 items 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 multiple.

[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 only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, 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 interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

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

[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 in the form of 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 part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, and other media that can store program codes.

[0071] The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention. In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details. In addition, in order to avoid unnecessary confusion about the essence of the present invention, well-known methods, processes, procedures, components and circuits are not 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A probability bit generator, characterized in that: The probability bit generator comprises: 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 generation layer located on the substrate, a plurality of magnetic layers of the magnetic tunnel junctions are arrayed on the spin current generation 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; Wherein, a first current is injected into the spin current generation layer, and the spin current generated by the first current is injected into the magnetic layer to cause the magnetic moment in the magnetic layer to be randomly flipped; and a second current is injected into the spin current generation layer, and the energy of the second current is less than the energy of the magnetic moment flipping, and is used to measure the voltage of the readout electrode layer; The first input terminal of the voltage comparator inputs the voltage sum of multiple magnetic tunnel junctions, and the second input terminal of the voltage comparator inputs a reference voltage, and the reference voltage is an adjustable voltage related to probability to achieve a 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, W; or adopts one or more of topological insulator materials Bi2Se3, Sb2Te3, Bi2Te3; or adopts one or more of new materials MoS2, 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 also arranged 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 nonmagnetic 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 for a 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, so that the first current flows through a magnetic layer, generating a spin-orbit moment acting on the magnetic layer, so that a magnetic moment in the magnetic layer is randomly flipped; 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 probability 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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