WO2023082456A1 - 一种基于轨道转移矩的磁化翻转器件及其实现方法 - Google Patents
一种基于轨道转移矩的磁化翻转器件及其实现方法 Download PDFInfo
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N52/00—Hall-effect devices
- H10N52/101—Semiconductor Hall-effect devices
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- G—PHYSICS
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- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/1274—Structure or manufacture of heads, e.g. inductive with "composite" cores, i.e. cores composed in some parts of magnetic particles and in some other parts of magnetic metal layers
- G11B5/1276—Structure or manufacture of heads, e.g. inductive with "composite" cores, i.e. cores composed in some parts of magnetic particles and in some other parts of magnetic metal layers including at least one magnetic thin film
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H—ELECTRICITY
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Definitions
- the invention relates to the field of spintronics of condensed matter physics, in particular to a perpendicular magnetic anisotropy magnetization flipping device without the assistance of an external magnetic field and a realization method thereof.
- Spintronics utilizes the spin and magnetic moment degrees of freedom of electrons to add electron spin and magnetic moment transport to solid devices in addition to charge transport.
- Spintronics is an emerging subject and technology, which has potential applications in hard disk heads, magnetic random access memory, spin field emission transistors, and spin light-emitting diodes.
- an important discovery is the giant magnetoresistance effect (Giant Magnetoresistance).
- the giant magnetoresistance effect refers to the phenomenon that the resistivity of magnetic materials changes greatly when there is an external magnetic field. It usually occurs in layered magnetic thin film structures.
- the structure is a magnetic tunnel junction, which specifically includes two ferromagnetic layers separated by an insulator film.
- the spin-related scattering of the carriers is the smallest, and the tunneling resistance of the system is in a low-resistance state; while when the magnetization directions of the two ferromagnetic layers are opposite, the carriers are subject to the same spin-related scattering.
- the spin-related scattering is the largest, and the tunneling resistance is in a high-resistance state.
- the giant magnetoresistance effect has been successfully applied to hard disk heads and has important commercial value.
- the magnetization state of the free ferromagnetic layer in the magnetic thin film structure must be changed.
- people applied an external magnetic field to achieve the change of the magnetization state but the external magnetic field often means a large power consumption, and at the same time increases the complexity of the device and limits the application range of the device.
- Slonczewski and Berger independently proposed a new spin-related effect in theory—the current-induced magnetization switching effect, that is, not by applying an external magnetic field, but by injecting a spin-polarized current to make the ferromagnetic layer The direction of magnetization changes, or even flips.
- the technique of using the current effect to achieve magnetization switching is very important for the practical application of the giant magnetoresistance effect. Since then, using the current effect to achieve magnetization reversal has become an important topic in the field of spintronics. This technology will have important application value in read and write magnetic heads, magnetic memory cells and spin logic devices.
- the magnetic field generated by the current was used to realize the reversal of the magnetization of the free ferromagnetic layer, but this method has defects such as high power consumption, difficulty in application in nanoscale devices, and complicated circuit design.
- spin-transfer torque As a new technology, achieves magnetization through a spin-polarized current rather than an Oersted field generated by a current. Flip. When current flows through the magnetic layer, the current will be polarized, forming a spin-polarized current. When a current is passed into the magnetic tunneling junction, the electrons transfer the spin momentum to the magnetic moment of the free layer, so that the magnetic moment of the free ferromagnetic layer obtains the spin momentum and then changes direction to realize the reversal of magnetization.
- An important application scenario for using current effect to achieve magnetization switching is the read-write head.
- spin-orbit torque refers to the material-based strong spin-orbit coupling (Spin-Orbit Coupling, SOC), which uses the spin current induced by the charge flow to generate spin transfer torque, and then achieves the purpose of regulating the magnetic memory unit.
- SOC spin-Orbit Coupling
- electrons are spin-degenerate; when there is spin-orbit coupling, electrons will be affected by the equivalent magnetic field generated by spin-orbit coupling during their motion.
- Electrons with different spin directions are subjected to different directions of the equivalent magnetic field to generate shunt.
- the current flows part of the current will be converted into a lateral net spin current, and the spin polarization direction of the spin current, the current direction and the spin current direction are 90° to each other.
- the flowing charge current produces a spin current perpendicular to the direction of charge flow, that is, the spin Hall effect, resulting in a spin-orbit moment.
- the spin polarization is also reversed, so that the spin-orbit moment is reversed, resulting in an opposite effect on the magnetic moment of the free ferromagnetic layer.
- the effect Hamiltonian has an additional term related to spin-orbit coupling, which is similar to the spin Hall effect and also involves the conversion of current and spin current, called the Rashba-Edelstein effect, which also produces spin-orbit moment.
- the concept of spin-orbit moment has shown great prospects in the fields of magnetic memory, computing, and storage devices.
- the spin-orbit moment also has great application value in low-power microwave oscillators and spin logic devices.
- the spin-orbit moment provides a new way to realize the microwave oscillator circuit. Because its emission frequency can be controlled by current, microwave oscillators based on spin-orbit moments usually have an ultra-wide frequency range. Therefore, the spin-orbit moment also has great application potential in the fields of wireless communication and sensing devices, such as space communication, high-speed radio frequency broadcasting, vehicle radar applications, health and safety fields, and so on.
- spin-orbit moment has many advantages, there are still many challenges in its practical application.
- One of the most critical scientific issues is the incompatibility of spin-orbit moment and magnetization flipping in perpendicular magnetic anisotropy.
- In-plane magnetic anisotropic materials are difficult to further shrink to the nanometer scale, which is not conducive to high-density device integration, while the magnetization flip of perpendicular magnetic anisotropy has the advantages of fast flip and high integration, so the magnetization of perpendicular magnetic anisotropy Flip will be the mainstream choice for future applications.
- most of the research on the principle of spin-orbit moment correlation utilizes the anti-damping moment in the plane generated by the current to achieve deterministic PMA magnetization switching.
- the critical anti-damping moment needs to satisfy here That is, the critical in-plane anti-damping moment, ⁇ is the gyromagnetic ratio, and H an is the perpendicular magnetic anisotropy field.
- This mechanism is the mainstream research direction of spin-orbit moment at present. Whether it is the spin Hall effect of heavy metals, the Rashba-Edelstein effect at the interface or the surface state of topological insulators, it can realize the magnetization switching of deterministic perpendicular magnetic anisotropy. It is through the anti-damping moment in the plane, so an external magnetic field or complex structural design is required to assist the realization of the flip.
- the specific form of the anti-damping moment satisfies ⁇ AD ⁇ m ⁇ (m ⁇ ), where ⁇ AD is the anti-damping moment, m is the direction of magnetization, and ⁇ is the polarization direction of the current spin or orbital magnetic moment. It can be seen from this formula that in order to realize the anti-damping moment out of the plane, the out-of-plane ⁇ must be realized.
- the spin (magnetic moment) polarization generated by the current is all along the in-plane direction, that is, ⁇ is in-plane, Therefore, in these systems, the anti-damping moment is also in-plane.
- the conditions for its realization are often very harsh or require fine adjustments, making it difficult to produce practical applications. Therefore, the incompatibility of the spin-orbit moment with the magnetization switching of the perpendicular magnetic anisotropy poses a challenge for its application.
- the current three mainstream ways to achieve magnetization switching by using the current effect namely the current-induced Oersted field, spin transfer torque and spin-orbit torque
- the use of the Oersted field generated by the current to achieve magnetization reversal will increase the complexity of the device; while the spin transfer torque faces the problem of not separating the read and write current paths, resulting in poor device durability; the spin-orbit moment realizes the separation of the read and write current paths , but requires the assistance of an external magnetic field to realize the magnetization switching of the perpendicular magnetic anisotropy.
- the present invention proposes a magnetization reversal device based on orbit-transfer torque and its implementation method, using orbit-transfer torque (OTT) to realize the magnetization reversal of perpendicular magnetic anisotropy, It does not require external magnetic field assistance or complex asymmetric structure design, while retaining the advantages of spin-orbit moment read-write path separation, high efficiency, and high-speed flipping.
- OTT orbit-transfer torque
- One object of the present invention is to propose a magnetization switching device based on orbital transfer torque.
- the magnetization reversal device based on track transfer torque of the present invention includes: a substrate, an insulating dielectric layer, a source-drain electrode, a measuring electrode, a heterojunction, a top gate and a back gate; wherein, an insulating dielectric layer is formed on the front side of the substrate; A back gate is formed on the back of the substrate; a source-drain electrode and a pair of measuring electrodes are formed on the insulating dielectric layer.
- a pole and a pair of measuring electrodes constitute a cross-shaped bottom electrode; a heterojunction is formed on the bottom electrode, and the heterojunction includes a two-dimensional layered second-order nonlinear Hall effect layer and a perpendicular magnetic anisotropy free ferromagnetic layer.
- the two-dimensional layered second-order nonlinear Hall effect layer uses a two-dimensional layered material with a second-order nonlinear Hall effect, and a two-dimensional layered material with a second-order nonlinear Hall effect has a periodic lattice potential, where The electrons function in the form of quasi-particles, that is, Bloch electrons. Bloch electrons form Bloch wave packets.
- the orbital magnetic moment is arranged in the out-of-plane direction due to the two-dimensional dimension constraint, and the two-dimensional layered second-order nonlinear Hall effect layer belongs to the second-order with non-zero Bailey curvature dipole moment Dimensional system;
- the heterojunction is in contact with each of the bottom electrodes;
- the top gate is formed on the heterojunction, and the top gate includes the insulating layer at the bottom and the top electrode on the insulating layer;
- the insulating layer of the top gate needs to be completely Cover the heterojunction to achieve packaging;
- the top electrode of the top gate covers the channel of the heterojunction, that is, the top electrode covers the path through which the current flows through the heterojunction;
- the back gate is connected to the positive pole of the first DC voltage source, and the first DC
- the negative pole of the voltage source is grounded, the top electrode of the top gate is connected to the positive pole of the second DC voltage source, and the negative pole of the second DC voltage source is grounded;
- the source electrode is
- the first DC voltage source applies the back gate voltage V B so that a potential difference is formed between the back gate and the lower surface of the heterojunction
- the second DC voltage source applies the top gate voltage V T so that the top electrode of the top gate and the heterojunction
- a potential difference is formed between the upper surfaces of the heterojunction
- the carrier concentration of the heterojunction is adjusted through the field effect of the back gate and the top gate, and an unbalanced charge distribution is introduced on the upper and lower surfaces of the heterojunction, thereby causing
- An out-of-plane electric field perpendicular to the surface of the heterojunction adjusts the carrier concentration and the out-of-plane electric field of the heterojunction through the back gate voltage V B and the top gate voltage V T , making the two-dimensional layered second-order nonlinear Hall effect
- the layer has the largest Bailey curvature dipole moment; the current source feeds a DC writing current I p through the source and drain electrodes, and the Bailey curvature dipole moment of the two-dimensional layered
- the polarization direction of the orbital magnetic moment is related to the direction of the write current.
- the polarization of the orbital magnetic moment produces an out-of-plane anti-damping moment effect. This is based on the orbital magnetic moment
- the out-of-plane anti-damping moment is called the orbital transfer torque. This out-of-plane anti-damping moment is linearly related to the writing current and the Bailey curvature dipole moment.
- the current source passes the DC reading current i through the source and drain electrodes, and the voltmeter obtains the Hall resistance of the heterojunction by measuring the electrodes, thereby obtaining the magnetization state of the free ferromagnetic layer with perpendicular magnetic anisotropy; changing the write current direction, that is, the current source passes the write current -I p through the source and drain electrodes, so that the polarization direction of the orbital magnetic moment is reversed, and the reversed orbital transfer torque is realized, so that the vertical magnetic anisotropy free ferromagnetic layer The magnetization is reversed.
- the nonlinear Hall effect means that under the condition of time-reversal symmetry, the measured Hall voltage is proportional to the square of the driving current.
- the standard phase-locking technique is used for measurement—input an AC current with a frequency of ⁇ , and then measure the AC Hall voltage with a frequency of 2 ⁇ through the phase-locking technique. If a non-zero Hall voltage can be measured, and the Hall The quadratic dependence between the voltage amplitude and the driving current amplitude is satisfied, that is, the nonlinear Hall effect is realized; the free ferromagnetic layer with perpendicular magnetic anisotropy adopts layered ferromagnetic materials with perpendicular magnetic anisotropy .
- the spin magnetic moments can still be arranged in the plane, but the orbital magnetic moments are arranged in the out-of-plane direction due to the limitation of the dimension.
- the current-induced orbital moment polarization produces an out-of-plane anti-damping moment, at which point deterministic perpendicular magnetic anisotropy magnetization switching can be achieved without additional magnetic field assistance.
- This out-of-plane anti-damping moment based on the orbital magnetic moment is completely different from the spin-orbit moment in principle—the latter is caused by the polarization of the spin, so the present invention makes this out-of-plane anti-damping moment based on the orbital magnetic moment
- the damping torque is called the track transfer torque.
- the orbital magnetic moments of Bloch electrons in solids are closely related to the geometric phase curvature of their wave functions—the Bailey curvature.
- the orbital magnetic moment exhibits a simple proportional relationship with the Bailey curvature.
- To realize current-induced orbital magnetic moment polarization is equivalent to realize current-induced Bailey curvature polarization.
- the concept of Bailey curvature dipole moment can be used to describe the polarization effect of Bailey curvature under the action of electric current.
- the substrate is made of conductive material, such as heavily electron-doped silicon substrate.
- the top electrode, back gate electrode, source-drain electrode and measurement electrode of the top gate are all made of conductive metal, such as gold.
- Weyl semimetals tantalum iridium tellurium TaIrTe 4 with a thickness of 50-100nm or molybdenum ditelluride MoTe 2 with a thickness of 4-8nm
- the perpendicular magnetic anisotropy layered ferromagnetic layer adopts a thin layer of iron germanium One of tellurium Fe 3 GeTe 2 (thickness 4-10nm), chromium ditelluride CrTe 2 (thickness 2-8nm) and chromium triiodide CrI 3 (thickness 2-8nm and odd number of layers).
- the write current I p needs to be greater than the critical current I c that can realize the magnetization reversal of the perpendicular magnetic anisotropy in the heterojunction.
- the value of I c is different, usually in the order of mA.
- the read current i is much smaller than the critical current I c , usually in the order of ⁇ A.
- Another object of the present invention is to propose a method for realizing a magnetization switching device based on orbital transfer torque.
- the realization method of the magnetization reversal device based on the orbital transfer torque of the present invention comprises the following steps:
- source-drain electrodes and a pair of measurement electrodes are parallel to each other, and the pair of measurement electrodes are parallel to each other, And the source-drain electrodes and a pair of measuring electrodes are perpendicular to each other, and the source-drain electrodes and a pair of measuring electrodes form a cross-shaped bottom electrode;
- a heterojunction composed of a two-dimensional layered second-order nonlinear Hall effect layer and a free ferromagnetic layer with perpendicular magnetic anisotropy was obtained by using the single crystal growth method, the mechanical exfoliation method and the dry transfer method.
- the two-dimensional layered second-order nonlinear Hall effect layer is a two-dimensional layered material with a second-order nonlinear Hall effect, and the two-dimensional layered material with a second-order nonlinear Hall effect exists periodically
- the top gate is formed on the heterojunction by transfer, photolithography and coating technology.
- the top gate includes the insulating layer at the bottom and the top electrode on the insulating layer; the insulating layer of the top gate needs to completely cover the heterojunction to realize packaging ;
- the top electrode of the top gate covers the channel of the heterojunction, that is, the top electrode covers the path through which the current flows through the heterojunction;
- the back gate is connected to the positive pole of the first DC voltage source, the negative pole of the first DC voltage source is grounded, the top gate is connected to the positive pole of the second DC voltage source, and the negative pole of the second DC voltage source is grounded; the source electrode is connected to the current source The positive pole of the current source, the negative pole of the current source is grounded, and the drain electrode is grounded; a pair of measuring electrodes are respectively connected to the positive and negative poles of the voltmeter;
- the first DC voltage source applies the back gate voltage V B so that a potential difference is formed between the back gate and the lower surface of the heterojunction
- the second DC voltage source applies the top gate voltage so that the top electrode of the top gate and the heterojunction
- a potential difference is formed between the upper surface of the heterojunction
- the carrier concentration of the heterojunction is adjusted through the field effect of the back gate and the top gate, and an unbalanced charge distribution is introduced on the upper and lower surfaces of the heterojunction, so that the surface of the heterojunction Cause an out-of-plane electric field perpendicular to the surface of the heterojunction
- the effect layer has the largest Bailey curvature dipole moment
- the current source feeds a DC write current I p through the source and drain electrodes, and the orbital magnetic moment is generated under the joint action of the Bailey curvature dipole moment of the two-dimensional layered second-order nonlinear Hall effect layer and the write current.
- Polarization the polarization direction of the orbital magnetic moment is related to the direction of the write current.
- the polarization of the orbital magnetic moment produces an out-of-plane anti-damping moment effect. This out-of-plane anti-damping moment based on the orbital magnetic moment is called the orbital transfer torque.
- the out-of-plane anti-damping moment is linearly related to the writing current and the Bailey curvature dipole moment.
- the out-of-plane anti-damping moment is the largest;
- the magnetization reversal of the free ferromagnetic layer with perpendicular magnetic anisotropy can be realized without additional magnetic field assistance, that is, the magnetization reversal of the perpendicular magnetic anisotropy based on the orbital transfer torque is realized;
- the current source feeds a DC reading current i through the source and drain electrodes, and the voltmeter obtains the Hall resistance of the heterojunction through the measurement electrodes, thereby obtaining the magnetization state of the free ferromagnetic layer with perpendicular magnetic anisotropy;
- step d) of step 1) single crystal growth methods (such as chemical vapor deposition, seed crystal cooling method, chemical vapor transport, etc.) are used to grow crystals with second-order nonlinear Hall effect in a tube furnace.
- Two-dimensional layered source material bulk and perpendicular magnetic anisotropy free ferromagnetic source material bulk, followed by mechanical exfoliation method from the two-dimensional layered source material bulk with second-order nonlinear Hall effect and perpendicular magnetic each Two-dimensional layered thin-layer materials with second-order nonlinear Hall effect and perpendicular magnetic anisotropy free ferromagnetic thin-layer materials are exfoliated from the bulk material of anisotropic free ferromagnetic source material, and two-dimensional layered materials with second-order nonlinear Hall effect
- the two-dimensional layered thin layer material is transferred to the first transition insulating layer on the first transition substrate to form a two-dimensional layered second-order nonlinear Hall effect layer, and the perpendicular magnetic anisotropy free
- a free ferromagnetic layer with perpendicular magnetic anisotropy is formed on the second transition insulating layer on the two-transition substrate; and then the dry transfer method is used to obtain a two-dimensional layered second-order nonlinear Hall effect layer and a free vertical magnetic anisotropy layer.
- step 2) the size of Bailey’s dipole moment of curvature is determined by measuring the second-order nonlinear Hall effect in the heterojunction.
- An alternating current with a frequency of ⁇ is passed through the source and drain electrodes, and the amplitude is fixed at I ac .
- the electrode measures the second-order frequency Hall voltage with a frequency of 2 ⁇ , and reads the amplitude V ac of the second-order frequency Hall voltage.
- V T and the back gate voltage V B are adjusted to make the amplitude of the second-order frequency Hall voltage
- V ac is maximum, it corresponds to the maximum dipole moment of Bailey's curvature.
- Frequency ⁇ takes 17-100Hz, usually takes 17.777Hz to avoid city power interference.
- the amplitude I ac of the alternating current is 0.1mA-0.5mA.
- the top gate voltage V T and the back gate voltage V B are usually -10V-10V.
- step 3 the write current I p is greater than the critical current I c that can realize the magnetization reversal of the perpendicular magnetic anisotropy in the heterojunction.
- the value of I c is different, usually in the order of mA.
- the invention provides a new principle to realize the magnetization reversal of the perpendicular magnetic anisotropy, that is, the orbital transfer torque.
- the existing three mainstream methods namely the Oersted effect of current, spin transfer torque and spin orbital moment, are all based on the electron spin degree of freedom to achieve magnetization reversal, while the orbital transfer torque is based on the orbital magnetic moment of electrons.
- orbital transfer torque can realize simple device structure, separable read and write paths (combined with magnetic tunneling junction) and no need for external magnetic field-assisted flipping, which is equivalent to absorbing the advantages of the aforementioned three mainstream methods and avoiding other Disadvantages: Orbital transfer torque to achieve perpendicular magnetic anisotropy magnetization flip also has the advantages of high efficiency, high speed and high integration; in addition, since the perpendicular magnetic anisotropy magnetization flip based on orbital transfer torque uses the out-of-plane anti-damping moment, pay attention The anti-damping moment outside the critical plane satisfies here That is, the anti-damping moment outside the critical plane, and ⁇ G is the Gilbert damping parameter, which is usually on the order of 0.01. Compared with the anti-damping moment inside the critical plane, Therefore, in theory, the critical current required by the orbital transfer torque to achieve magnetization switching will be smaller than the above three mainstream methods, which can greatly reduce the power consumption of the device.
- FIG. 1 is a schematic diagram of an embodiment of a magnetization switching device based on orbital transfer torque of the present invention
- FIG. 2 is a schematic diagram of the fabrication process of an embodiment of the magnetization switching device based on orbital transfer torque of the present invention.
- the magnetization switching device based on track transfer torque in this embodiment includes: a substrate 1, an insulating dielectric layer 2, source and drain electrodes, a measurement electrode, a heterojunction, a top gate and a back gate; An insulating dielectric layer 2 is formed on the front side of the bottom; a back gate is formed on the back side of the substrate; a source-drain electrode and a pair of measuring electrodes are formed on the insulating dielectric layer, the source-drain electrodes are parallel to each other, the measuring electrodes are parallel to each other, and the source-drain electrodes are parallel to the measurement electrodes.
- the electrodes are perpendicular to each other, and the source and drain electrodes and a pair of measuring electrodes constitute a cross-shaped bottom electrode 3; a heterojunction is formed on the bottom electrode, and the heterojunction includes a two-dimensional layered second-order nonlinear Hall effect layer 4 and a vertical magnetic Anisotropic free ferromagnetic layer 5, two-dimensional layered second-order nonlinear Hall effect layer using a two-dimensional layered material with second-order nonlinear Hall effect, two-dimensional layered material with second-order nonlinear Hall effect Materials, there is a periodic lattice potential, and the electrons in it play a role in the form of quasi-particles, that is, Bloch electrons, which form Bloch wave packets; Bloch wave packets have angular momentum around themselves, So that electrons have an additional orbital magnetic moment in addition to the spin magnetic moment; and the two-dimensional layered second-order nonlinear Hall effect layer belongs to a two-dimensional system with a non-zero Bailey curvature di
- the top electrode of the top gate covers the channel of the heterojunction, that is, the top electrode covers the path through which the current flows through the heterojunction;
- the back gate is connected to the positive pole of the first DC voltage source, and the first DC voltage source
- the negative pole of the top grid is connected to the positive pole of the second DC voltage source, and the negative pole of the second DC voltage source is grounded;
- the source electrode is connected to the positive pole of the current source, the negative pole of the current source is grounded, and the drain electrode is grounded; a pair of measurement
- the electrodes are connected to the positive and negative terminals of the voltmeter respectively.
- the substrate is a silicon substrate doped with heavy electrons;
- the insulating dielectric layer is 285nm thick SiO 2 ;
- the source and drain electrodes and the measuring electrodes are 2nm/8nm thick Ti/Au;
- the back gate electrode uses Ti/Au with a thickness of 5/45nm;
- the insulating layer in the top gate uses h-BN (thickness 20-30nm);
- the two-dimensional layered second-order nonlinear Hall effect layer uses MoTe 2 (thickness 4-8nm );
- the layered ferromagnetic layer with perpendicular magnetic anisotropy adopts a thin layer of Fe 3 GeTe 2 (thickness 4-10nm).
- the realization method of the magnetization reversal device based on the orbital transfer torque of the present invention comprises the following steps:
- a substrate 1 of silicon material is provided, and an insulating dielectric layer 2 is formed on the front side of the substrate;
- a two-dimensional layered source material bulk with second-order nonlinear Hall effect and a free ferromagnetic source material bulk with perpendicular magnetic anisotropy were grown in a tube furnace by chemical vapor deposition, followed by polydimethylformaldehyde
- the two-dimensional layered source material bulk with second-order nonlinear Hall effect and the free ferromagnetic source material bulk with perpendicular magnetic anisotropy were separated by polydimethylsiloxane 8 (polydimethylsiloxane, PDMS)-assisted mechanical exfoliation method, respectively, to obtain Two-dimensional layered thin-layer materials with second-order nonlinear Hall effect and free ferromagnetic thin-layer materials with perpendicular magnetic anisotropy, as shown in Figure 2(b), the specific method is to place the source material block to be stripped on On a piece of PDMS, and then repeatedly use another piece of PDMS to bond, obtain a thin layer of material, form a first transitional insulating
- the two-dimensional layered thin-layer material with the second-order nonlinear Hall effect and the free ferromagnetic thin-layer material with perpendicular magnetic anisotropy to the first transition insulating layer and the second transition insulating layer, respectively, Forming a two-dimensional layered second-order nonlinear Hall effect layer and a thin layer of free ferromagnetic material with perpendicular magnetic anisotropy; using a dry transfer method using a polycarbonate (polycarbonate, PC) film 9 to sequentially transfer from the second transition insulating layer and On the first transition insulating layer, a thin layer of free ferromagnetic material with perpendicular magnetic anisotropy and a two-dimensional layered second-order nonlinear Hall effect layer are adhered to form a heterojunction, and the heterojunction is transferred to the bottom electrode, as shown in the figure 2(c) and Figure 2(d); the two-dimensional layered second-order nonlinear Hall effect layer is a two-
- the orbital magnetic moment is arranged in the out-of-plane direction due to the two-dimensional dimension restriction, and the out-of-plane direction is perpendicular to the two-dimensional layered second-order
- the surface of the nonlinear Hall effect layer is vertical to the surface upward or downward; and the two-dimensional layered second-order nonlinear Hall effect layer belongs to a two-dimensional system with a non-zero Bailey curvature dipole moment; the heterojunction and Each of the bottom electrodes is in contact;
- top electrode 7 of the top gate As shown in Figure 2(e); the top electrode of the top gate covers the channel of the heterojunction, that is, the top electrode covers the path through which the current flows through the heterojunction;
- the back grid is connected to the positive pole of the first DC voltage source, the negative pole of the first DC voltage source is grounded, the top electrode of the top grid is connected to the positive pole of the second DC voltage source, and the negative pole of the second DC voltage source is grounded; the source electrode is connected To the positive pole of the current source, the negative pole of the current source is grounded, and the drain electrode is grounded; a pair of measuring electrodes are respectively connected to the positive and negative poles of the voltmeter;
- the first DC voltage source applies a back gate voltage V B (range -6V-6V), so that a potential difference is formed between the back gate and the lower surface of the heterojunction
- the second DC voltage source applies a top gate voltage V T (range -6V-6V), so that a potential difference is formed between the top electrode of the top gate and the upper surface of the heterojunction; since the heterojunction itself is a metal system, it has a strong electrostatic shielding, so the top gate can only be used for the heterojunction.
- the upper surface can be effectively adjusted, and the back gate can only effectively adjust the lower surface of the heterojunction; the carrier concentration of the heterojunction is adjusted through the field effect of the back gate and the top gate, and the upper and lower surfaces of the heterojunction are respectively Introduce an unbalanced charge distribution, thereby causing an out-of-plane electric field perpendicular to the surface of the heterojunction; adjust the carrier concentration and surface of the heterojunction by the back gate voltage V B and the top gate voltage V T
- the second-order frequency Hall voltage with a frequency of 2 ⁇ is measured through the measuring electrode, and its amplitude V ac is read.
- the polarization of the orbital magnetic moment is generated under the joint action of the Bailey curvature dipole moment of the layered second-order nonlinear Hall effect layer and the writing current, and the polarization direction of the orbital magnetic moment is related to the direction of the writing current, that is, the current Direction Reversal
- the polarization direction of the orbital magnetic moment will also be reversed, from upward to downward, or from downward to upward; the polarization of the orbital magnetic moment produces an out-of-plane anti-damping moment effect, which is based on the orbital magnetic moment
- the out-of-plane anti-damping moment is called the orbital transfer torque.
- This out-of-plane anti-damping moment is linearly related to the writing current and the Bailey curvature dipole moment.
- the generated out-of-plane anti-damping moment is the largest; under the effect of out-of-plane anti-damping moment, the magnetization reversal of the free ferromagnetic layer with perpendicular magnetic anisotropy can be realized without additional magnetic field assistance, that is, the perpendicular magnetic anisotropy based on the orbital transfer torque is realized.
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Abstract
一种基于轨道转移矩的磁化翻转器件及其实现方法，通过源漏电极通入直流的写入电流，产生面外的轨道磁矩的极化，进而产生面外反阻尼矩效应，在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，称为轨道转移矩；撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；通过源漏电极通入直流的读取电流，通过测量电极得到异质结的霍尔电阻，从而反应垂直磁各向异性自由铁磁层的磁化状态；改变写入电流方向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转；轨道转移矩实现磁化翻转所需的临界电流更小，从而可以大大降低器件的功耗。
Description
本发明涉及凝聚态物理的自旋电子学领域，具体涉及一种无需外磁场辅助的垂直磁各向异性磁化翻转器件及其实现方法。
自旋电子学(spintronics)利用电子的自旋和磁矩自由度，使固体器件中除电荷输运外，还加入电子的自旋和磁矩输运。自旋电子学是一门新兴的学科和技术，在硬盘磁头、磁随机存储器、自旋场发射晶体管及自旋发光二极管等方面均有应用潜力。在自旋电子学领域，一个重要的发现即巨磁电阻效应(Giant Magnetoresistance)。巨磁电阻效应指磁性材料的电阻率在有外磁场作用时存在巨大变化的现象。它通常产生于层状的磁性薄膜结构中。该结构即磁隧穿结，具体包含两个铁磁层，两个铁磁层之间则通过一个绝缘体薄膜分开。当两个铁磁层磁化方向相同时，载流子受到的与自旋相关的散射最小，体系的隧穿电阻处于低电阻状态；而当二者磁化方向相反时，载流子受到的与自旋相关的散射最大，隧穿电阻处于高电阻状态。巨磁电阻效应已经被成功应用于硬盘磁头，具有重要的商业价值。巨磁电阻效应从物理发现(1995年发现20％的室温隧穿磁电阻效应)到材料制备和2005年基于巨磁电阻效应的磁读出头器件大规模生产化(>270Gbit/inch
2)仅用了不到10年时间。从1997年至今，基于以上巨磁电阻效应的磁读出头产品及其硬磁盘已经被广泛地应用到网络服务器和台式计算机、手提电脑、数字照相机以及MP3、MP4等音乐播放器中，显著促进了计算机和信息技术的进步。正因为如此，2007年诺贝尔物理学奖授予了巨磁电阻效应的发现者Albert Fert和Peter Grunberg，以表彰他们为当代凝聚态物理和信息材料科学发展做出的贡献。
但是，要实现巨磁电阻效应，就必须改变磁性薄膜结构中自由铁磁层的磁化状态。在过去，人们通过外加磁场来实现磁化状态的改变，但外加磁场往往意味着较大的功耗，同时增加了器件的复杂度，限制了器件的应用范围。1996年，Slonczewski和Berger在理论上分别独立地提出一种新的自旋相关效应—电流诱导的磁化翻转效应，即不通过外加磁场，而是通过注入自旋极化电流，使得铁磁层的磁化方向改变，甚至发生翻转。利用电流效应实现磁化翻转的技术对于巨磁电阻效应的实际应用十分重要。自此，利用电流效应实现磁化的翻转就成为了自旋电子学领域的一个重要议题，这一技术将在读写磁头、磁存储单元和自旋逻辑器 件等方面都有着重要应用价值。
目前在自旋电子学领域，利用电流实现磁化翻转共有三种主流的方式。
1.早期的巨磁电阻效应应用中，利用电流产生的磁场来实现自由铁磁层磁化的翻转，但这种方式存在功耗高，难以在纳米级器件中应用及电路设计复杂等等缺陷。
2.相比于利用磁场进行磁化的翻转，自旋转移矩(spin-transfer torque,STT)作为一种新的技术则通过自旋极化的电流而非电流产生的奥斯特场来实现磁化翻转。电流流过磁性层时，电流将被极化，形成自旋极化电流。在磁隧穿结中通入电流，电子将自旋动量传递给自由层的磁矩，使自由铁磁层的磁矩获得自旋动量后改变方向，实现磁化的翻转。利用电流效应实现磁化翻转的一个重要应用场景即读写磁头。当利用自旋转移矩技术时，由于写入和读取信息时都需要在隧穿结中通入电流，故存在读写路径不分离和写入电流较大，导致绝缘层焦耳热积累严重，从而耐用性差等缺点。
3.科学家们进一步提出了利用材料的自旋轨道耦合效应实现自旋轨道矩(spin-orbit torque,SOT)，进行磁化的翻转，成功的实现了读写路径的分离，且相比于自旋转移矩，自旋轨道矩是一种速度更快、密度更高、效率更高的存储技术。自旋轨道矩指基于材料的强自旋轨道耦合(Spin-Orbit Coupling,SOC)，利用电荷流诱导的自旋流来产生自旋转移力矩，进而达到调控磁性存储单元的目的。一般材料中，电子是自旋简并的；当存在自旋轨道耦合时，电子运动过程中会受到自旋轨道耦合产生的等效磁场的作用。不同自旋方向的电子受到等效磁场方向不同进而产生分流。当电流流过时，部分电流会转化为横向的净自旋流，自旋流自旋极化方向、电流方向和自旋流方向互为90°。流动的电荷电流会产生垂直于电荷流动方向的自旋流，也就是自旋霍尔效应，从而产生自旋轨道矩。当电流反向时，自旋极化也会反向，从而使得自旋轨道矩反向，产生对自由铁磁层磁矩相反的作用。在某些对称性破缺的二维体系中(特别是异质结的二维界面体系中，界面中的电子们周围的环境上下不一样)，电子不再自旋简并，该体系的等效哈密顿量出现跟自旋轨道耦合相关的额外项，和自旋霍尔效应类似，同样涉及电流和自旋流的转换，称之为Rashba-Edelstein效应,这种效应也会产生自旋轨道矩。
2009年，人们在半导体(Ga,Mn)As中首次观测到了自旋轨道矩效应，并且发现转矩来自于闪锌矿晶体结构所特有的Dresselhaus自旋轨道耦合作用。一年后，有报道指出在Pt/Co/AlOx中探测到了由界面Rashba效应引起的自旋轨道矩。一些重金属，如Pt，本身具有较强的自旋轨道耦合，会产生自旋霍尔效应，从而也会具有自旋轨道矩效应。此外，在拓扑绝缘体表面也发现了这种自旋轨道矩，这里的自旋轨道耦合作用主要来源于拓扑绝缘体特有的无能隙狄 拉克型表面态。
目前，自旋轨道矩的概念已在磁记忆、运算、存储器件等领域展现出巨大的前景。此外，自旋轨道矩在低能耗的微波震荡器和自旋逻辑器件中也具有很大的应用价值。自旋轨道矩为实现微波震荡电路提供了一种新的方式。由于其发射频率可以由电流调控，基于自旋轨道矩的微波震荡器通常会拥有超宽的频率范围。因此，自旋轨道矩在无线通信和感应器件领域也有着巨大的应用潜力，比如，空间通信、高速射频广播、车辆雷达应用和健康安全领域等等。
自旋轨道矩虽存在诸多优势，但其实际应用依然存在着诸多挑战。其中最关键的科学问题是自旋轨道矩与垂直磁各向异性磁化翻转的不兼容性。面内磁各向异性材料难以进一步缩小至纳米尺度，不利于高密度的器件集成，而垂直磁各向异性的磁化翻转具有快速翻转和高度可集成性的优势，因而垂直磁各向异性的磁化翻转将是未来应用的主流选择。目前，大多数对于自旋轨道矩相关原理的研究利用电流产生面内的反阻尼矩实现确定性的垂直磁各向异性磁化翻转，此时，要实现确定性的垂直磁各向异性磁化翻转还需要额外施加与电流平行的外磁场破坏体系对称性或引入结构的不对称性进行辅助翻转。对于这一机制，临界的反阻尼矩需满足
这里
即临界面内反阻尼矩，γ为旋磁比，H
an为垂直磁各向异性场。这种机制是目前自旋轨道矩的主流研究方向，无论是重金属的自旋霍尔效应，还是界面的Rashba-Edelstein效应或者拓扑绝缘体表面态，其实现确定性垂直磁各向异性的磁化翻转均是通过面内的反阻尼矩，故都需要外加磁场或复杂的结构设计来辅助翻转的实现。
除了利用面内反阻尼矩，如果可以实现自旋流的面外反阻尼矩，就可以实现无需外磁场辅助的垂直磁各向异性磁化翻转。但是，要实现面外反阻尼矩，所需的对称性条件非常苛刻，对于常见的自旋轨道矩体系，即重金属，界面Rashba效应和拓扑绝缘体来说，其对称性都不满足实现面外反阻尼矩的条件。反阻尼矩的具体形式满足τ
AD∝m×(m×σ)，这里τ
AD为反阻尼矩，m为磁化的方向，σ为电流自旋或轨道磁矩的极化方向。从这一公式就可以看出，要实现面外的反阻尼矩，就必须实现面外的σ。而对于重金属的自旋霍尔效应，界面的Rashba-Edelstein效应或者拓扑绝缘体表面态，其电流所产生的自旋(磁矩)极化都是沿着面内方向，即σ是面内的，故在这些体系中，反阻尼矩也是面内的。事实上，要通过电子自旋的Edelstein效应实现面外极化是非常困难的，只有在一些非常特殊的体系(如具有warping效应的拓扑绝缘体)中才有可能出现。但其实现的条件往往非常苛刻或需要精细调节，难以产生实际应用。因此，自旋轨道矩与垂直磁各向异性磁化翻转的不兼容性为其应用带来了挑战。
综上所述，目前利用电流效应实现磁化翻转的三种主流方式，即电流诱导的奥斯特场，自旋转移矩及自旋轨道矩都在实际应用中面临着挑战。利用电流产生的奥斯特场实现磁化翻转会造成器件复杂度增加；而自旋转移矩则面临读写电流路径不分离，从而器件耐用性差的问题；自旋轨道矩实现了读写电流路径分离，但又需要外磁场辅助来实现垂直磁各向异性的磁化翻转。
发明内容
针对以上现有技术存在的问题，本发明提出了一种基于轨道转移矩的磁化翻转器件及其实现方法，采用轨道转移矩(orbit-transfer torque,OTT)来实现垂直磁各向异性磁化翻转，其无需外磁场辅助或复杂的非对称结构设计，同时保留了自旋轨道矩读写路径分离、高效及高速翻转的优势。
本发明的一个目的在于提出一种基于轨道转移矩的磁化翻转器件。
本发明的基于轨道转移矩的磁化翻转器件包括：衬底、绝缘介质层、源漏电极、测量电极、异质结、顶栅和背栅；其中，在衬底的正面形成绝缘介质层；在衬底的背面形成背栅；在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相平行，一对测量电极互相平行，且源漏电极与一对测量电极互相垂直，源漏电极和一对测量电极构成十字交叉型的底电极；在底电极上形成异质结，异质结包括二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层，二维层状二阶非线性霍尔效应层采用具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包，布洛赫波包具有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩，轨道磁矩由于二维维度限制排列在面外方向，并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；在异质结上形成顶栅，顶栅包括底部的绝缘层和在绝缘层上的顶部电极；顶栅的绝缘层需完全覆盖异质结，以实现封装；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅的顶部电极连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极；
第一直流电压源施加背栅电压V
B，使得在背栅和异质结的下表面之间形成电势差，第二直流电压源施加顶栅电压V
T，使得顶栅的顶部电极和异质结的上表面之间形成电势差；通过背栅和顶栅的场效应调节异质结的载流子浓度，并且在异质结的上下表面分别引入非均衡的 电荷分布，从而在异质结中引起一个垂直于异质结表面的面外电场，通过背栅电压V
B和顶栅电压V
T调节异质结的载流子浓度和面外电场，使得二维层状二阶非线性霍尔效应层具有最大的贝利曲率偶极矩；电流源通过源漏电极通入直流的写入电流I
p，在二维层状二阶非线性霍尔效应层的贝利曲率偶极矩与写入电流共同作用下产生面外的轨道磁矩的极化，轨道磁矩的极化方向与写入电流的方向有关，轨道磁矩的极化产生面外反阻尼矩效应，这种基于轨道磁矩的面外反阻尼矩称为轨道转移矩，这一面外反阻尼矩同时与写入电流和贝利曲率偶极矩成线性关系，当写入电流的方向与贝利曲率偶极矩平行时，产生的面外反阻尼矩最大；在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，即实现了基于轨道转移矩的垂直磁各向异性磁化翻转；撤去写入电流，由于垂直磁各向异性自由铁磁层具有回滞特性，撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；电流源通过源漏电极通入直流的读取电流i，电压表通过测量电极得到异质结的霍尔电阻，从而得到垂直磁各向异性自由铁磁层的磁化状态；改变写入电流的方向，即电流源通过源漏电极通入写入电流-I
p，使得轨道磁矩的极化方向反向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转。
非线性霍尔效应指在满足时间反演对称的条件下，测量的霍尔电压与驱动电流的平方成正比。通常测量中利用标准的锁相技术进行测量——通入频率为ω的交流电流，然后通过锁相技术测量频率为2ω的交流霍尔电压，若可测得非零的霍尔电压，且霍尔电压幅值与驱动电流幅值之间满足二次方的依赖关系，即实现了非线性霍尔效应；垂直磁各向异性自由铁磁层采用具有垂直磁各向异性的层状铁磁材料。
在二维体系中，由于二维平面的限制，使得自旋磁矩依然能够在面内排列，但轨道磁矩却由于维度限制在面外方向排列。电流诱导轨道磁矩极化产生面外的反阻尼矩，此时确定性的垂直磁各向异性磁化翻转无需额外的磁场辅助即可实现。这一基于轨道磁矩的面外反阻尼矩在原理上完全不同于自旋轨道矩——后者是由于自旋的极化所引起，因此本发明将这一基于轨道磁矩的面外反阻尼矩称为轨道转移矩。更进一步，固体中布洛赫电子的轨道磁矩与其波函数的几何相位曲率——贝利曲率紧密联系在一起。当存在粒子-空穴对称性时，轨道磁矩与贝利曲率呈现简单的成比例关系。要实现电流诱导的轨道磁矩极化，就等价于要实现电流诱导的贝利曲率极化。贝利曲率偶极矩的概念正可以用来描述贝利曲率在电流作用下的极化效应。故对于具有非零贝利曲率偶极矩的二维体系，就可以实现电流诱导的面外轨道磁矩极化，从而实现基于轨道转移矩效应的垂直磁各向异性磁化翻转。具有非零贝利曲率偶极矩D的体系，在电场E的作用下，会产生宏观轨道磁化
其中
是指向面外方向的单位矢量。在轨道磁化M的作用下，就可以实现面外反阻尼矩，即轨道转移矩。贝利曲率偶极 矩的一个典型的输运特征即二阶非线性霍尔效应。
衬底采用导电材料，如重电子掺杂的硅衬底。
顶栅的顶部电极、背栅电极、源漏电极及测量电极均采用导电金属，如金。
二维层状二阶非线性霍尔效应层采用双层二碲化钨WTe
2、应变双层石墨烯、单轴应变的单层二碲化钨WSe
2和空间反演对称性破缺的外尔(Weyl)半金属(厚度50-100nm的钽铱碲TaIrTe
4或厚度4-8nm的二碲化钼MoTe
2)中的一种；垂直磁各向异性层状铁磁层采用薄层铁锗碲Fe
3GeTe
2(厚度4-10nm)、二碲化铬CrTe
2(厚度2-8nm)和三碘化铬CrI
3(厚度2-8nm且奇数层)中的一种。
写入电流I
p需要大于异质结中能够实现垂直磁各向异性磁化翻转的临界电流I
c，在不同的具体体系中，I
c值不同，通常在mA量级。读取电流i远小于临界电流I
c，通常取μA量级。
本发明的另一个目的在于提出一种基于轨道转移矩的磁化翻转器件的实现方法。
本发明的基于轨道转移矩的磁化翻转器件的实现方法，包括以下步骤：
1)器件制备：
a)提供衬底，在衬底的正面形成绝缘介质层；
b)在衬底的背面形成背栅；
c)利用光刻技术和镀膜技术(包括电子束蒸镀或磁控溅射等)在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相平行，一对测量电极互相平行，且源漏电极与一对测量电极互相垂直，源漏电极和一对测量电极构成十字交叉型的底电极；
d)利用单晶生长方法、利用机械剥离方法和干法转移法得到由二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层构成的异质结，将异质结转移到底电极上；二维层状二阶非线性霍尔效应层为具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包，布洛赫波包具有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩，轨道磁矩由于二维维度限制排列在面外方向，并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；
e)采用转移、光刻和镀膜技术在异质结上形成顶栅，顶栅包括底部的绝缘层和在绝缘层上的顶部电极；顶栅的绝缘层需完全覆盖异质结，以实现封装；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；
f)背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极；
2)第一直流电压源施加背栅电压V
B，使得在背栅和异质结的下表面之间形成电势差，第二直流电压源施加顶栅电压，使得顶栅的顶部电极和异质结的上表面之间形成电势差；通过背栅和顶栅的场效应调节异质结的载流子浓度，并且在异质结的上下表面分别引入非均衡的电荷分布，从而在异质结的表面引起一个垂直于异质结表面的面外电场；通过背栅电压V
B和顶栅电压V
T调节异质结的载流子浓度和面外电场，使得二维层状二阶非线性霍尔效应层具有最大的贝利曲率偶极矩；
3)电流源通过源漏电极通入直流的写入电流I
p，在二维层状二阶非线性霍尔效应层的贝利曲率偶极矩与写入电流共同作用下产生轨道磁矩的极化，轨道磁矩的极化方向与写入电流的方向有关，轨道磁矩的极化产生面外反阻尼矩效应，这种基于轨道磁矩的面外反阻尼矩称为轨道转移矩，这一面外反阻尼矩同时与写入电流和贝利曲率偶极矩成线性关系，当写入电流的方向与贝利曲率偶极矩平行时，产生的面外反阻尼矩最大；在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，即实现了基于轨道转移矩的垂直磁各向异性磁化翻转；
4)撤去写入电流，由于垂直磁各向异性自由铁磁层具有回滞特性，撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；
5)电流源通过源漏电极通入直流的读取电流i，电压表通过测量电极得到异质结的霍尔电阻，从而得到垂直磁各向异性自由铁磁层的磁化状态；
6)改变写入电流的方向，使得轨道磁矩的极化方向反向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转。
其中，在步骤1)的步骤d)中，利用单晶生长方法(如化学气相沉积、籽晶降温法、化学气相输运等)在管式炉中分别生长具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异性自由铁磁源材料块材，接着利用机械剥离方法分别从具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异性自由铁磁源材料块材剥离出具有二阶非线性霍尔效应的二维层状薄层材料和垂直磁各向异性自由铁磁薄层材料，具有二阶非线性霍尔效应的二维层状薄层材料转移至位于第一过渡衬底上的第一过渡绝缘层上形成二维层状二阶非线性霍尔效应层，垂直磁各向异性自由铁磁薄层材料转移至第二过渡衬底上的第二过渡绝缘层上形成垂直磁各向异性自由铁磁层；再利用干法转移法得到由二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层构成的异质结。
步骤2)中，贝利曲率偶极矩的大小通过测量异质结中二阶非线性霍尔效应确定，通过源漏电极通入频率为ω的交流电流，幅值固定为I
ac，通过测量电极测量频率为2ω的二阶频霍尔电压，读取二阶频霍尔电压的幅值V
ac，当调节顶栅电压V
T和背栅电压V
B使得二阶频霍尔电压的幅值V
ac最大时，即对应于贝利曲率偶极矩最大。频率ω取17-100Hz，通常取17.777Hz以避免市电干扰。交流电流的幅值I
ac取0.1mA-0.5mA。顶栅电压V
T和背栅电压V
B通常取-10V-10V。
在步骤3)中，写入电流I
p大于异质结中能够实现垂直磁各向异性磁化翻转的临界电流I
c，在不同的具体体系中，I
c值不同，通常在mA量级。
本发明的优点：
本发明提供了一种新的原理来实现垂直磁各向异性的磁化翻转，即轨道转移矩。现有的三种主流方式，即电流的奥斯特效应，自旋转移矩及自旋轨道矩，都是基于电子自旋自由度实现磁化翻转，而轨道转移矩则是基于电子的轨道磁矩自由度；轨道转移矩能够同时实现器件结构简单、读写路径可分离(与磁隧穿结结合使用)以及无需外磁场辅助翻转，即相当于吸收了前述三种主流方式的优势而避免了其缺点；轨道转移矩实现垂直磁各向异性磁化翻转还具有高效、高速和高度可集成的优点；此外，由于基于轨道转移矩的垂直磁各向异性磁化翻转是利用面外的反阻尼矩，注意到临界面外反阻尼矩满足
这里
即临界面外反阻尼矩，α
G为吉尔伯特阻尼参数，其通常量级为0.01.对比前述临界面内反阻尼矩满足
所以理论上轨道转移矩实现磁化翻转所需的临界电流相比前述三种主流方式会更小，从而可以大大降低器件的功耗。
图1为本发明的基于轨道转移矩的磁化翻转器件的一个实施例的示意图；
图2为本发明的基于轨道转移矩的磁化翻转器件的一个实施例的制备流程的示意图。
下面结合附图，通过具体实施例，进一步阐述本发明。
如图1所示，本实施例的基于轨道转移矩的磁化翻转器件包括：衬底1、绝缘介质层2、源漏电极、测量电极、异质结、顶栅和背栅；其中，在衬底的正面形成绝缘介质层2；在衬底的背面形成背栅；在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相平行，测 量电极互相平行，且源漏电极与测量电极互相垂直，源漏电极和一对测量电极构成十字交叉型的底电极3；在底电极上形成异质结，异质结包括二维层状二阶非线性霍尔效应层4和垂直磁各向异性自由铁磁层5，二维层状二阶非线性霍尔效应层采用具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料，存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包；布洛赫波包具有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩；并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；在异质结上形成顶栅，顶栅包括底部的绝缘层6和在绝缘层上的顶部电极7；顶栅的绝缘层需完全覆盖异质结，以实现封装；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅的顶部电极连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极。
在本实施例中，衬底采用重电子掺杂的硅衬底；绝缘介质层采用285nm厚的SiO
2；源漏电极和测量电极采用厚度2nm/8nm的Ti/Au；顶栅的顶部电极和背栅电极采用厚度5/45nm的Ti/Au；顶栅中的绝缘层采用h-BN(厚度20-30nm)；二维层状二阶非线性霍尔效应层采用MoTe
2(厚度4-8nm)；垂直磁各向异性层状铁磁层采用薄层Fe
3GeTe
2(厚度4-10nm)。
本发明的基于轨道转移矩的磁化翻转器件的实现方法，包括以下步骤：
1)器件制备，如图2所示：
a)提供硅材料的衬底1，在衬底的正面形成绝缘介质层2；
b)在衬底的背面形成背栅；
c)利用标准的电子束曝光和电子束镀膜技术在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相平行，测量电极互相平行，且源漏电极与测量电极互相垂直，源漏电极和一对测量电极构成十字交叉型的底电极3，如图2(a)所示；
d)利用化学气相沉积方法在管式炉中分别生长具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异性自由铁磁源材料块材，接着利用聚二甲基硅氧烷8(polydimethylsiloxane,PDMS)辅助的机械剥离方法分别剥离具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异性自由铁磁源材料块材，分别得到具有二阶非线性霍尔效应的二维层状薄层材料和垂直磁各向异性自由铁磁薄层材料，如图2(b)所示，具体做法即将需要剥离的源材料块材放置于一片PDMS上，然后反复用另一片PDMS去进行对粘，获取薄层材料，在第一过渡衬底(材 料为硅)上形成第一过渡绝缘层，以及在第二过渡衬底上形成第二绝缘层，然后将具有二阶非线性霍尔效应的二维层状薄层材料和垂直磁各向异性自由铁磁薄层材料分别转移到第一过渡绝缘层和第二过渡绝缘层上，分别形成二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁材料薄层；采用干法转移法利用聚碳酸酯(polycarbonate,PC)膜9依次从第二过渡绝缘层和第一过渡绝缘层上粘起垂直磁各向异性自由铁磁材料薄层和二维层状二阶非线性霍尔效应层，构成异质结，并将异质结转移到底电极上，如图2(c)和图2(d)所示；二维层状二阶非线性霍尔效应层为具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料，存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包；布洛赫波包具有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩，轨道磁矩由于二维维度限制排列在面外方向，面外方向即垂直于二维层状二阶非线性霍尔效应层的表面，垂直于表面向上或向下；并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；
e)采用干法转移技术在异质结上形成顶栅的绝缘层6；顶栅的绝缘层需完全覆盖异质结，以实现封装；采用标准的电子束曝光和电子束镀膜技术在绝缘层上形成顶栅的顶部电极7，如图2(e)所示；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；
f)背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅的顶部电极连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极；
2)第一直流电压源施加背栅电压V
B(范围-6V-6V)，使得在背栅和异质结的下表面之间形成电势差，第二直流电压源施加顶栅电压V
T(范围-6V-6V)，使得顶栅的顶部电极和异质结的上表面之间形成电势差；由于异质结本身是金属体系，具有很强的静电屏蔽，所以顶栅只能对异质结的上表面进行有效调节，背栅也只能对异质结的下表面进行有效调节；通过背栅和顶栅的场效应调节异质结的载流子浓度，并且在异质结的上下表面分别引入非均衡的电荷分布，从而在异质结的表面引起一个垂直于异质结表面的面外电场；通过背栅电压V
B和顶栅电压V
T调节异质结的载流子浓度和面外电场，使得二维层状二阶非线性霍尔效应层具有最大的贝利曲率偶极矩； 贝利曲率偶极矩的大小通过测量异质结中二阶非线性霍尔效应确定，通过源漏电极通入频率为ω＝17.777Hz的交流电流，幅值固定为I
ac＝0.1mA，通过测量电极测量频率为2ω的二阶频霍尔电压，读取其幅值V
ac，当调节顶栅电压V
T和背栅电压V
B使得V
ac最大时，即对应于贝利曲率偶极矩最大；
3)电流源通过源漏电极通入直流的写入电流I
p＝8-10mA，写入电流I
p大于异质结中能够实现垂直磁各向异性磁化翻转的临界电流I
c；在二维层状二阶非线性霍尔效应层的贝利曲率偶极矩与写入电流共同作用下产生轨道磁矩的极化，轨道磁矩的极化方向与写入电流的方向有关，即电流的方向反向轨道磁矩的极化方向也会反向，由向上改为向下，或由向下改为向上；轨道磁矩的极化产生面外反阻尼矩效应，这种基于轨道磁矩的面外反阻尼矩称为轨道转移矩，这一面外反阻尼矩同时与写入电流和贝利曲率偶极矩成线性关系，当写入电流的方向与贝利曲率偶极矩平行时，产生的面外反阻尼矩最大；在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，即实现了基于轨道转移矩的垂直磁各向异性磁化翻转；
4)撤去写入电流，由于垂直磁各向异性自由铁磁层具有回滞特性，撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；
5)电流源通过源漏电极通入直流的读取电流i＝10μA，电压表通过测量电极得到异质结的霍尔电阻，从而得到垂直磁各向异性自由铁磁层的磁化状态；
6)改变写入电流的方向，使得轨道磁矩的极化方向反向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转。
最后需要注意的是，公布实施例的目的在于帮助进一步理解本发明，但是本领域的技术人员可以理解：在不脱离本发明及所附的权利要求的精神和范围内，各种替换和修改都是可能的。因此，本发明不应局限于实施例所公开的内容，本发明要求保护的范围以权利要求书界定的范围为准。
Claims (10)
- 一种基于轨道转移矩的磁化翻转器件，其特征在于，所述基于轨道转移矩的磁化翻转器件包括：衬底、绝缘介质层、源漏电极、测量电极、异质结、顶栅和背栅；其中，在衬底的正面形成绝缘介质层；在衬底的背面形成背栅；在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相对齐，一对测量电极互相对齐；在底电极上形成异质结，异质结包括二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层，二维层状二阶非线性霍尔效应层采用具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包，布洛赫波包具有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩，轨道磁矩由于二维维度限制排列在面外方向，并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；在异质结上形成顶栅，顶栅包括底部的绝缘层和在绝缘层上的顶部电极；顶栅的绝缘层需完全覆盖异质结，以实现封装；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅的顶部电极连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极；第一直流电压源施加背栅电压V B，使得在背栅和异质结的下表面之间形成电势差，第二直流电压源施加顶栅电压V T，使得顶栅的顶部电极和异质结的上表面之间形成电势差；通过背栅和顶栅的场效应调节异质结的载流子浓度，并且在异质结的上下表面分别引入非均衡的电荷分布，从而在异质结中引起一个垂直于异质结表面的面外电场，通过背栅电压V B和顶栅电压V T调节异质结的载流子浓度和面外电场，使得二维层状二阶非线性霍尔效应层具有最大的贝利曲率偶极矩；电流源通过源漏电极通入直流的写入电流I p，在二维层状二阶非线性霍尔效应层的贝利曲率偶极矩与写入电流共同作用下产生面外的轨道磁矩的极化，轨道磁矩的极化方向与写入电流的方向有关，轨道磁矩的极化产生面外反阻尼矩效应，这种基于轨道磁矩的面外反阻尼矩称为轨道转移矩，这一面外反阻尼矩同时与写入电流和贝利曲率偶极矩成线性关系，当写入电流的方向与贝利曲率偶极矩平行时，产生的面外反阻尼矩最大；在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，即实现了基于轨道转移矩的垂直磁各向异性磁化翻转；撤去写 入电流，由于垂直磁各向异性自由铁磁层具有回滞特性，撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；电流源通过源漏电极通入直流的读取电流i，电压表通过测量电极得到异质结的霍尔电阻，从而得到垂直磁各向异性自由铁磁层的磁化状态；改变写入电流的方向，即电流源通过源漏电极通入写入电流-I p，使得轨道磁矩的极化方向反向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转。
- 如权利要求1所述的基于轨道转移矩的磁化翻转器件，其特征在于，所述衬底采用导电材料。
- 如权利要求1所述的基于轨道转移矩的磁化翻转器件，其特征在于，所述顶栅的顶部电极、背栅电极、源漏电极和测量电极均采用导电金属。
- 如权利要求1所述的基于轨道转移矩的磁化翻转器件，其特征在于，所述二维层状二阶非线性霍尔效应层采用双层二碲化钨WTe 2、应变双层石墨烯、单轴应变的单层二碲化钨WSe 2和空间反演对称性破缺的外尔半金属中的一种；所述垂直磁各向异性层状铁磁层采用薄层铁锗碲Fe 3GeTe 2、二碲化铬CrTe 2和三碘化铬CrI 3中的一种。
- 如权利要求1所述的基于轨道转移矩的磁化翻转器件，其特征在于，所述写入电流大于异质结中能够实现垂直磁各向异性磁化翻转的临界电流。
- 如权利要求1所述的基于轨道转移矩的磁化翻转器件，其特征在于，所述读取电流远小于异质结中能够实现垂直磁各向异性磁化翻转的临界电流。
- 一种如权利要求1所述的基于轨道转移矩的磁化翻转器件的实现方法，其特征在于，所述实现方法包括以下步骤：1)器件制备：a)提供衬底，在衬底的正面形成绝缘介质层；b)在衬底的背面形成背栅；c)利用光刻技术和镀膜技术在绝缘介质层上形成源漏电极和一对测量电极，源漏电极互相对齐，一对测量电极互相对齐；d)利用单晶生长方法、利用机械剥离方法和干法转移法得到由二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层构成的异质结，将异质结转移到底电极上；二维层状二阶非线性霍尔效应层为具有二阶非线性霍尔效应的二维层状材料，具有二阶非线性霍尔效应的二维层状材料存在周期性晶格势，其中的电子以准粒子的形式发挥作用，即布洛赫电子，布洛赫电子形成布洛赫波包，布洛赫波包具 有绕自身旋转的角动量，从而使得电子在具有自旋磁矩之外，具有一个额外的轨道磁矩，轨道磁矩由于二维维度限制排列在面外方向，并且二维层状二阶非线性霍尔效应层属于具有非零的贝利曲率偶极矩的二维体系；异质结与底电极中的每一个电极均有接触；e)采用转移、光刻和镀膜技术在异质结上形成顶栅，顶栅包括底部的绝缘层和在绝缘层上的顶部电极；顶栅的绝缘层需完全覆盖异质结，以实现封装；顶栅的顶部电极覆盖异质结的沟道，即顶部电极覆盖电流流经异质结的通路；f)背栅连接至第一直流电压源的正极，第一直流电压源的负极接地，顶栅连接至第二直流电压源的正极，第二直流电压源的负极接地；源电极连接至电流源的正极，电流源的负极接地，漏电极接地；一对测量电极分别连接至电压表的正负极；2)第一直流电压源施加背栅电压V B，使得在背栅和异质结的下表面之间形成电势差，第二直流电压源施加顶栅电压，使得顶栅的顶部电极和异质结的上表面之间形成电势差；通过背栅和顶栅的场效应调节异质结的载流子浓度，并且在异质结的上下表面分别引入非均衡的电荷分布，从而在异质结的表面引起一个垂直于异质结表面的面外电场；通过背栅电压V B和顶栅电压V T调节异质结的载流子浓度和面外电场，使得二维层状二阶非线性霍尔效应层具有最大的贝利曲率偶极矩；3)电流源通过源漏电极通入直流的写入电流I p，在二维层状二阶非线性霍尔效应层的贝利曲率偶极矩与写入电流共同作用下产生轨道磁矩的极化，轨道磁矩的极化方向与写入电流的方向有关，轨道磁矩的极化产生面外反阻尼矩效应，这种基于轨道磁矩的面外反阻尼矩称为轨道转移矩，这一面外反阻尼矩同时与写入电流和贝利曲率偶极矩成线性关系，当写入电流的方向与贝利曲率偶极矩平行时，产生的面外反阻尼矩最大；在面外反阻尼矩效应下无需额外的磁场辅助就能够实现垂直磁各向异性自由铁磁层的磁化翻转，即实现了基于轨道转移矩的垂直磁各向异性磁化翻转；4)撤去写入电流，由于垂直磁各向异性自由铁磁层具有回滞特性，撤去写入电流后垂直磁各向异性自由铁磁层保持改变后的磁化状态，从而具有非易失性；5)电流源通过源漏电极通入直流的读取电流i，电压表通过测量电极得到异质结的霍尔电阻，从而得到垂直磁各向异性自由铁磁层的磁化状态；6)改变写入电流的方向，使得轨道磁矩的极化方向反向，实现反向的轨道转移矩，从而使得垂直磁各向异性自由铁磁层的磁化反向翻转。
- 如权利要求7所述的实现方法，其特征在于，在步骤1)的步骤d)中，利用单晶生长方法在管式炉中分别生长具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异 性自由铁磁源材料块材，接着利用机械剥离方法分别从具有二阶非线性霍尔效应的二维层状源材料块材和垂直磁各向异性自由铁磁源材料块材剥离出具有二阶非线性霍尔效应的二维层状薄层材料和垂直磁各向异性自由铁磁薄层材料，具有二阶非线性霍尔效应的二维层状薄层材料转移至位于第一过渡衬底上的第一过渡绝缘层上形成二维层状二阶非线性霍尔效应层，垂直磁各向异性自由铁磁薄层材料转移至第二过渡衬底上的第二过渡绝缘层上形成垂直磁各向异性自由铁磁层；再利用干法转移法得到由二维层状二阶非线性霍尔效应层和垂直磁各向异性自由铁磁层构成的异质结。
- 如权利要求7所述的实现方法，其特征在于，步骤2)中，贝利曲率偶极矩的大小通过测量异质结中二阶非线性霍尔效应确定，通过源漏电极通入频率为ω的交流电流，通过测量电极测量频率为2ω的二阶频霍尔电压，读取二阶频霍尔电压的幅值V ac，当调节顶栅电压V T和背栅电压V B使得二阶频霍尔电压的幅值V ac最大时，即对应于贝利曲率偶极矩最大。
- 如权利要求7所述的实现方法，其特征在于，在步骤3)中，写入电流I p大于异质结中能够实现垂直磁各向异性磁化翻转的临界电流I c。
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