Semiconductor spintronics element

Abstract

A spintronics element according to the present invention comprises a ferromagnetic layer and a semiconductor layer adjacent to the ferromagnetic body layer. A flow of orbital angular momentum is driven by applying current to the semiconductor layer, and the direction of magnetization of the ferromagnetic material layer is controlled by magnetic torque generated from the flow of the orbital angular momentum.

Description

Semiconductor spintronic devices

[0001] This invention relates to a semiconductor spintronic device.

[0002] In recent years, SOT-MRAM, a magnetic memory (MRAM) that utilizes spin-orbit torque (SOT), has been attracting attention as a next-generation memory element.

[0003] The basic principle of SOT-MRAM is to convert the electric current supplied to the spin current generation layer into a pure spin current (a flow of only spin angular momentum without charge transfer), and to use the torque from this pure spin current to control the magnetization of the ferromagnetic material layer that forms the memory layer. Therefore, a material with high conversion efficiency between electric current and pure spin current is preferable for the spin current generation layer, and spin-orbit interaction plays an important role in this conversion.

[0004] However, materials with strong spin-orbit interactions are mostly noble metals such as Pt with large atomic numbers, and toxic elements such as Bi, Se, and Te. Therefore, conventional SOT-MRAM, which utilizes torque due to spin current, has problems from the standpoint of elemental strategy and environmental compatibility.

[0005] Therefore, in recent years, research has been underway to control magnetization using torque due to orbital flow rather than torque due to spin current. Orbital flow refers to the flow of orbital angular momentum, and a phenomenon called the orbital Hall effect is known in which orbital flow is generated perpendicular to the current when an electric current is applied. Since the orbital Hall effect also occurs in light metals such as Ti, it may be possible to overcome the constraints on candidate materials for spintronic devices that utilize spin-orbit torque. In light of these circumstances, Cu, which is neither a precious metal nor a toxic element, is attracting attention.

[0006] D. Go et al., “Orbital Rashba effect in a surface-oxidized Cu film”, Phys. Rev. B 103, L121113 (2021)

[0007] However, the orbital magnetic torque efficiency of Cu has been reported to be around 0.1, which is about the same as the spin-orbit torque efficiency of Pt. Therefore, there is a need for even more efficient material systems to realize SOT-MRAM utilizing orbital magnetic torque.

[0008] The present invention aims to meet the above requirements and primarily provides a spintronic device that is energy-efficient, highly efficient, and capable of magnetization control, without using noble metals or toxic elements in the spin current generation layer.

[0009] To solve the above problems, the inventors broke free from the constraints of "metallic materials" that had plagued conventional research and explored a wide range of material systems as candidate materials. As a result, the inventors discovered for the first time that semiconductor materials such as Si semiconductors can generate extremely large orbital magnetic torque, leading to the present invention.

[0010] In other words, the semiconductor spintronic device of the present invention comprises a ferromagnetic material layer and a semiconductor layer adjacent to the ferromagnetic material layer, wherein the flow of orbital angular momentum is driven by applying an electric current to the semiconductor layer, and the direction of magnetization of the ferromagnetic material layer is controlled by the magnetic torque generated from the flow of orbital angular momentum.

[0011] With this configuration, it is possible to provide a spintronic device that can control the magnetization of a ferromagnetic material layer by controlling the magnetic torque due to orbital current through the current supplied to the semiconductor layer. For example, the orbital magnetic torque efficiency of Si semiconductors is about 10 times that of Cu or Pt. Furthermore, since Si is neither a noble metal nor a toxic element, it has excellent environmental compatibility. Moreover, Si is the second most ubiquitous material in Clarke number and is a semiconductor material widely known as the staple food of industry, making it outstanding from the standpoint of elemental strategy. These effects can be exhibited to varying degrees not only in Si semiconductors, but also in other semiconductor materials that have electron orbital hybridization, which is the origin of the orbital Hall effect, such as Ge semiconductors and compound semiconductors.

[0012] The mechanism by which excellent orbital magnetic torque efficiency and spin-orbit torque efficiency can be achieved by using semiconductor materials such as Si semiconductors is still not fully understood. Based on the knowledge obtained to date, the inventors will explain the mechanism they believe to be effective. Please note that the following explanation of the mechanism is not intended to limit the technical scope of the present invention.

[0013] In other words, by using semiconductor materials such as Si semiconductors, electrons in sp orbitals with large electron orbital extents become carriers. When an electric field is applied to a system in which hybridization of these electron orbitals is achieved, a non-equilibrium state is created and orbital flow is generated. This mechanism applies not only to Si semiconductors but also to semiconductor materials such as Ge semiconductors and compound semiconductors.

[0014] According to the present invention configured in this manner, it is possible to provide a spintronic device that is energy-efficient, highly efficient, and capable of magnetization control, without using noble metals or toxic elements in the spin current generation layer.

[0015] This figure schematically shows the configuration of a semiconductor spintronic device according to one embodiment of the present invention. This figure schematically shows the fabrication procedure for the semiconductor spintronic device of Example 1. This figure schematically shows the method for measuring the magnetic torque in the ferromagnetic material layer of the semiconductor spintronic device of Example 1. This is a graph showing the measurement results of the magnetic torque in the ferromagnetic material layer of the semiconductor spintronic device of Example 1. This figure schematically shows the configuration of a semiconductor spintronic device of Example 2. This figure schematically shows the method for measuring the magnetization reversal in the ferromagnetic material layer of the semiconductor spintronic device of Example 2. This is a graph showing the measurement results of the magnetization reversal in the ferromagnetic material layer of the semiconductor spintronic device of Example 2.

[0016] A semiconductor spintronic device 100 according to one embodiment of the present invention will be described below with reference to the drawings.

[0017] The semiconductor spintronic element 100 of this embodiment is used as a magnetoresistive memory (SOT-MRAM) that stores information by controlling the direction of magnetization using spin-orbit torque (SOT). More specifically, this semiconductor spintronic element 100 drives the flow of orbital angular momentum (orbital current) by applying an electric current to the semiconductor layer, and uses the magnetic torque generated by the spin current converted from the orbital current to control the direction of magnetization of the ferromagnetic layer and rewrite information.

[0018] Specifically, as shown in Figure 1, the semiconductor spintronic element 100 comprises a ferromagnetic material layer 1 that maintains magnetization and functions as a memory layer, and a semiconductor layer 2 provided adjacent to the ferromagnetic material layer 1 and functioning as a spin current generation layer. The semiconductor spintronic element 100 of this embodiment may also be equipped with a power supply (not shown) for supplying current to the semiconductor layer 2, or it may be configured to supply current to the semiconductor layer 2 from an external power supply. The semiconductor spintronic element 100 may also be equipped with an internal circuit or other configuration for supplying current from the power supply to the semiconductor layer 2.

[0019] (1) Ferromagnetic material layer The ferromagnetic material layer 10 has magnetization and stores information according to its orientation. The magnetization undergoes precession due to the torque of the input spin current. The thickness of the ferromagnetic material layer 1 is preferably, for example, about 10 nm or more and about 30 nm or less, but is not limited to this.

[0020] The ferromagnetic material layer 1 is preferably composed of a ferromagnetic metallic material or a ferromagnetic atomic layer material. The ferromagnetic material layer 1 may also contain impurities that are inevitably present.

[0021] Examples of ferromagnetic metallic materials include, but are not limited to, metal materials such as Fe, Co, and Ni, and alloy materials such as Py (permalloy). Examples of ferromagnetic atomic layer materials include, for example, Fe ３ GeTe ２ ya Cr ２ Ge ２ Te ６ These are some examples, but are not limited to them.

[0022] Furthermore, the ferromagnetic material layer 10 may be a single-layer structure made of one type of material, or it may be a laminated structure in which multiple layers are stacked.

[0023] (2) Semiconductor layer The semiconductor layer 20 drives the flow of orbital angular momentum (orbital current) by the current supplied from the power supply, and further supplies this orbital current to the ferromagnetic material layer 10 to convert it into spin current. This semiconductor layer 20 is formed by stacking it on the ferromagnetic material layer 10. The thickness of the semiconductor layer 20 is preferably, for example, about 30 nm or more and about 90 nm or less, but is not limited to this.

[0024] The semiconductor layer 20 is preferably composed of a semiconductor material having high electrical conductivity and mobility. More specifically, the semiconductor layer 20 is more preferably composed of a Si semiconductor, a Ge semiconductor, or a compound semiconductor. Examples of compound semiconductors include, but are not limited to, GaAs compound semiconductors. In particular, to achieve high orbital magnetic torque efficiency and spin orbital torque efficiency, the semiconductor layer 20 is especially preferably composed of a Si semiconductor.

[0025] Furthermore, the semiconductor layer 20 may contain one or more dopants selected from, for example, phosphorus or boron. The semiconductor layer 20 may also contain these dopants at a concentration exceeding the effective density of states. That is, the doping concentration may exceed the effective density of states. By setting the doping concentration above the effective density of states, ohmic contact can be achieved between the ferromagnetic material layer 10 and the semiconductor layer 20 (or, a good electrical junction can be achieved).

[0026] (3) Power supply The power supply is used to supply current to the semiconductor layer 20. This current is preferably a high-frequency current with a frequency of approximately 2.5 to 9.5 GHz, but is not limited to this. The current supplied to the semiconductor layer 20 is not limited to a high-frequency current, but may also be a DC current.

[0027] (4) Control Operation The control operation of the direction of magnetization by the semiconductor spintronic element 100 of this embodiment will be explained. First, a high-frequency current is applied to the semiconductor layer 20 from the power supply. Then, due to the orbital Hall effect, an orbital current is generated in the direction laterally to the current. The orbital current in the semiconductor layer 20 is converted into a spin current by orbital spin conversion in the ferromagnetic material layer 10. This spin current then applies a magnetic torque to the magnetization in the ferromagnetic material layer 10, which can reverse the magnetization.

[0028] With the semiconductor spintronic element 100 configured in this way, the orbital Hall effect in the semiconductor layer 20 allows for a sufficiently large magnetic torque to be applied to the magnetization of the ferromagnetic material layer 10. Therefore, the magnetic torque due to orbital current can be controlled through the current supplied to the semiconductor layer 20, thereby controlling the magnetization of the ferromagnetic material layer 10. This makes it possible to provide an energy-saving, highly efficient, and magnetization-controllable spintronic element 100 without using noble metals or toxic elements in the semiconductor layer 20, which is the spin current generation layer.

[0029] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and it is possible to implement it with modifications within the scope that is consistent with the spirit described below, and all such modifications are included within the technical scope of the present invention.

[0030] (Example 1) This example demonstrates that the magnetic torque applied to the magnetization originates from the orbital Hall effect in the semiconductor layer. It is known that the orbital spin conversion efficiency differs between the ferromagnetic materials Ni and Py, with Ni having a higher conversion efficiency. That is, when two types of devices are fabricated using these materials for the ferromagnetic material layer, if the device with a Ni ferromagnetic material layer exhibits a higher torque efficiency, it can be said that the magnetic torque originates from the orbital Hall effect. The magnetic torque is observed by measuring the DC voltage due to rectification using the anisotropic magnetoresistance effect, in which electrical resistance changes depending on the relative angle between the direction of current flow and the magnetization direction.

[0031] (Device Fabrication) Two types of devices were fabricated as described below. The fabrication procedure is shown in Fig. 2. (1) After forming a Si semiconductor film on a thermally oxidized Si substrate, ion implantation was performed with P as an impurity to the degenerate concentration. (2) Using an Ar ion milling apparatus, the thickness of the Si semiconductor film was etched down to 70 nm. (3) Using electron beam evaporation (EB-Deposition), Ni(5 nm) / MgO(3 nm) or Py(5 nm) / MgO(3 nm) was formed. (4) Using an Ar ion milling apparatus, it was cut out in the shape of a channel. (5) Ti(3 nm) / Au(150 nm) was formed as an electrode.

[0032] (Measurement Method) As described below, by using spin-torque ferromagnetic resonance measurement (ST-FMR), the magnitude of the magnetic torque in the Ni (or Py) ferromagnetic material layer 11 generated by the orbital current driven in the Si semiconductor layer 21 was measured. The measurement was performed at room temperature. The measurement state is shown in Fig. 3. (1) With the input power set to 100 mW (20 dBm) and the frequency f in the range of 2.5 to 9.5 GHz, high-frequency alternating current I ｒｆ was input into the Si semiconductor layer 21 from a high-frequency AC source. (2) An external magnetic field was applied in-plane in the direction of the angle φ with respect to the current and swept in the range of -300 to 300 mT. (3) The magnetization precession motion in the Ni (or Py) ferromagnetic material layer 11 causes the electrical resistance to oscillate, and the DC voltage V DC generated as the product of this resistance and the current was measured by a lock-in amplifier 32. In addition, a bias tee 31 was used to cut off the AC component and read only the DC voltage component.

[0033] (Measurement Results) As a typical result, Fig. 4 shows the case where the frequency of the high-frequency alternating current is 5 GHz. Under the ferromagnetic resonance condition determined by the frequency f of the alternating magnetic field generated by the alternating current I ｒｆ and the magnitude of the external magnetic field, the amplitude of the magnetization precession in the ferromagnetic material layer 11 becomes maximum, and the obtained DC voltage V ＤＣ also becomes maximum. Therefore, by sweeping the external magnetic field, the DC voltage V ＤＣ has a peak. The magnetic flux density that satisfies the resonance condition is Bｒｅｓ is defined as follows. In order to maximize the peak, the direction of the external magnetic field was set to φ = 45° at which the rectifying action due to the anisotropic magnetoresistance effect is maximized. The dots represent the measured DC voltage V ＤＣ are shown. The line T is the fitting curve according to the theoretical formula (1). In the theoretical formula, the symmetric part and the asymmetric part are shown separately, and the lines S and A represent the curves of the symmetric component and the antisymmetric component with respect to the resonance point of the resonance signal, respectively. S in the symmetric component and A in the antisymmetric component in Equation (1) are given by Equations (2) and (3), respectively. The first term shown in the expression of S is the term indicating the magnitude of the magnetic torque due to the orbital Hall effect in the Si semiconductor layer 21, and the first term shown in the expression of A is the term indicating the magnitude of the Oersted magnetic field generated by the current flowing through the Si semiconductor layer 21. Here, R is the channel resistance, γ is the magnetic rotation ratio, B ｅｘｔ is the magnetic flux density obtained from the external magnetic field, and Δ is the full width at half maximum of the resonance signal.

[0034] (Evaluation) The torque efficiency is given by Equation (4). The definition that only the symmetric component is adopted is because the electrical resistance of the Si semiconductor layer 21 is larger than that of the ferromagnetic material layer 11, and it is considered that the measured antisymmetric component is not proportional to the current flowing through the Si semiconductor layer 21.

[0035] The torque efficiency of each device is as shown in the following table. In addition, a device of a Ni single layer (film thickness 5 nm) without forming the Si semiconductor layer 21 was also fabricated, and the results of similar measurements for this are also described.

[0036] Devices with the ferromagnetic material layer 11 made of Ni give higher torque efficiency than devices made of Py. Also, the Ni single layer device gives a very small torque efficiency. From the above, it was confirmed that the magnetic torque is derived from the orbital Hall effect in Si.

[0037] (Example 2) This example demonstrates that the magnetic torque originating from the orbital Hall effect in the semiconductor layer actually causes magnetization reversal in the ferromagnetic material layer.

[0038] (Device Fabrication) A perpendicular magnetic anisotropy (PMA) consisting of three layers of Pt / Co / Pt was used as the ferromagnetic material layer 12. A perpendicular magnetic anisotropy refers to a film that has magnetization in a direction perpendicular to the film surface. The structure of the device is as shown in Figure 5, and the channel is cross-shaped.

[0039] (Measurement Method) As described below, the magnetization direction of the ferromagnetic material layer 12 was measured using the anomalous Hall effect (AHE). The anomalous Hall effect is a phenomenon in which a potential difference is generated perpendicular to both the magnetization and the current when an electric current is passed through a ferromagnetic material. By measuring this anomalous Hall voltage, the magnetization direction of the ferromagnetic material layer 12 can be determined. The measurement was performed at room temperature. Figure 6 shows the measurement procedure.

[0040] (1) An external magnetic field was applied in a direction parallel to the direction in which the pulsed current I was flowing, with a magnitude in the range of -500Oe to 500Oe. (2) A pulsed current I was applied with a pulse width of 1 ms and a magnitude in the range of -15 mA to 15 mA. (3) After waiting for 5 seconds after applying the pulsed current I, a sense current I was applied to observe the anomalous Hall effect. ｒ A flow occurs, causing an abnormal Hall voltage V ＋ ―V － The sense current I was measured. ｒ The current value was set to a value that would not cause magnetization reversal (i.e., a current value that is sufficiently smaller than the pulse current). (4) Steps 2 and 3 were repeated while sweeping the magnitude of the pulse current I within the above range.

[0041] (Measurement results and evaluation) Typical results show an external magnetic field of ±500 Oe and a sense current of I ｒ Figure 7 shows the case where the external magnetic field B is ±0.5 mA. ｅｘｔThe direction of the signal loop also changed depending on the direction of the polarity, indicating that this was not a reversal due to thermal fluctuations. From this, it was confirmed that the magnetic torque originating from the orbital Hall effect in the Si semiconductor layer 22 was responsible for reversing the magnetization in the ferromagnetic material layer 12.

[0042] Furthermore, the present invention is not limited to the embodiments and examples described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. The disclosure of the specification also includes semiconductor spintronic devices of the following embodiments 1 to 8.

[0043] (Aspect 1) A semiconductor spintronic element comprising a ferromagnetic material layer and a semiconductor layer adjacent to the ferromagnetic material layer, wherein the flow of orbital angular momentum is driven by applying an electric current to the semiconductor layer, and the direction of magnetization of the ferromagnetic material layer is controlled by the magnetic torque generated from the flow of orbital angular momentum.

[0044] (Aspect 2) The semiconductor spintronic device according to aspect 1, wherein the semiconductor layer is a silicon semiconductor.

[0045] (Aspect 3) The semiconductor spintronic device according to aspect 1, wherein the semiconductor is a germanium semiconductor.

[0046] (Aspect 4) The semiconductor spintronic device according to aspect 1, wherein the semiconductor layer is a compound semiconductor.

[0047] (Aspect 5) A semiconductor spintronic device according to any one of aspects 1 to 4, wherein the doping concentration in the semiconductor layer exceeds the effective density of states.

[0048] (Aspect 6) A semiconductor spintronic device according to any one of aspects 1 to 5, wherein the dopant contained in the semiconductor layer is one or more selected from phosphorus or boron.

[0049] (Aspect 7) A semiconductor spintronic device according to any one of aspects 1 to 6, wherein the ferromagnetic material layer is made of a ferromagnetic metallic material.

[0050] (Aspect 8) A semiconductor spintronic device according to any one of aspects 1 to 6, wherein the ferromagnetic material layer is made of a ferromagnetic atomic layer material.

[0051] (Aspect 9) A semiconductor spintronic device according to any one of aspects 1 to 8, further comprising a power supply for supplying current to the semiconductor layer.

[0052] According to the present invention described above, it is possible to provide a spintronic device that is energy-efficient, highly efficient, and capable of magnetization control, without using noble metals or toxic elements in the spin current generation layer.

[0053] 100... Semiconductor spintronic element 10, 11, 12... Ferromagnetic material layer 20... Semiconductor layer 21, 22... Si semiconductor layer 30... Power supply 31... Bias tee 32... Lock-in amplifier

Claims

1. A semiconductor spintronic element comprising a ferromagnetic material layer and a semiconductor layer adjacent to the ferromagnetic material layer, wherein the flow of orbital angular momentum is driven by applying an electric current to the semiconductor layer, and the direction of magnetization of the ferromagnetic material layer is controlled by the magnetic torque generated from the flow of orbital angular momentum.

2. The semiconductor spintronic device according to claim 1, wherein the semiconductor layer is a silicon semiconductor.

3. The semiconductor spintronic device according to claim 1, wherein the semiconductor is a germanium semiconductor.

4. The semiconductor spintronic device according to claim 1, wherein the semiconductor layer is a compound semiconductor.

5. The semiconductor spintronic device according to claim 1, wherein the doping concentration in the semiconductor layer exceeds the effective density of states.

6. The semiconductor spintronic device according to claim 1, wherein the dopant contained in the semiconductor layer is one or more selected from phosphorus or boron.

7. The semiconductor spintronic device according to claim 1, wherein the ferromagnetic material layer is made of a ferromagnetic metallic material.

8. The semiconductor spintronic device according to claim 1, wherein the ferromagnetic material layer is made of a ferromagnetic atomic layer material.

9. The semiconductor spintronic device according to claim 1, further comprising a power supply for supplying current to the semiconductor layer.

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