An Electric-Field-Controlled Two-Dimensional Magnetic Tunnel Junction and Its Preparation Method and Application

Abstract

The present invention provides an electric-field-regulated two-dimensional magnetic tunnel junction, a preparation method thereof and an application thereof, belonging to the technical field of spintronic devices. The two-dimensional magnetic tunnel junction includes a bottom electrode, a two-dimensional ferromagnetic material layer I, a two-dimensional ferroelectric material layer, a two-dimensional ferromagnetic material layer II and a protective layer which are stacked in sequence. The two-dimensional ferroelectric material layer uses CuInP2S6, and the migration of Cu ions is regulated by applying an external voltage. The device can be applied to high-density magnetic random access memories (MRAMs), high-sensitivity magnetic sensors and low-power consumption spintronic logic devices, and has industrialization prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of spintronic devices, and in particular relates to an electric-field-controlled two-dimensional magnetic tunnel junction, a preparation method thereof, and an application thereof. Background Art

[0002] The application of tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) has had a huge impact on the development of magnetic electronic devices, including magnetic random access memories (MRAMs), radio frequency sensors, microwave generators, etc. The vast majority of magnetic tunnel junctions use the way of repeated current tunneling for writing or reading, which requires a very high durability of the materials. The emergence of two-dimensional (2D) van der Waals materials provides more process possibilities for magnetic tunnel junctions. In particular, 2D materials with high spin polarization are expected to be applied to the next-generation nanoscale devices.

[0003] In existing devices, repeated writing and reading of current are required, which consumes a high amount of energy and generates a large amount of heat, which will have a certain impact on adjacent structures. It is difficult to break through the limitations of size and accuracy, and extremely high durability of the materials is required. Some even require the influence of an external magnetic field, which is difficult to avoid the influence on other devices. Each write has a strong loss on the material, and the repeatability is not good enough. The coupling effect between in-plane materials makes it difficult to solve the problem of high-density integration. Summary of the Invention

[0004] In view of this, the present invention aims to provide an electric-field-controlled two-dimensional magnetic tunnel junction, a preparation method thereof, and an application thereof. By applying an external electric field to regulate CuInP2S6, the overall resistance state of the magnetic tunnel junction is changed, the process of passing a large current through the tunnel junction is reduced, thereby playing a role in protecting the magnetic tunnel junction material itself and improving its durability.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] An electric-field-controlled two-dimensional magnetic tunnel junction includes a substrate, a bottom electrode, a first two-dimensional ferromagnetic material layer, a two-dimensional ferroelectric material layer, a second two-dimensional ferromagnetic material layer, and a protective layer, which are sequentially arranged from bottom to top. The material of the two-dimensional ferroelectric material layer is CuInP2S6, and an electric field is applied to the left and right ends of the two-dimensional ferroelectric material layer.

[0007] A magnetic tunnel junction refers to a component formed by sandwiching an extremely thin insulating layer with a thickness of nanometers between two ferromagnetic thin films. The extremely thin insulating layer used in the present invention is the two-dimensional ferroelectric material layer CuInP2S6.

[0008] The traditional ferromagnetic layer (free layer) flipping requires the use of electric current to generate a magnetic field to change the magnetocrystalline anisotropy. This process has high heat loss. In addition, the traditional three-dimensional ferroelectric material has a large leakage current, or basically has no ferroelectricity below 50nm, making it difficult to make its size sub-nanometer limit. General ferroelectric materials have fatigue characteristics, and it is difficult to restore their intrinsic characteristics after multiple ferroelectric flips. The Cu ions in CuInP2S6 can migrate repeatedly within the layer with good repeatability. When the Cu ions migrate to the middle of the two ferromagnetic material layers, it is equivalent to raising the barrier layer. In addition, the Cu ions may have a shielding effect on the electric field of the tunneling electrons, reducing the effective tunneling ability of the electrons, thereby increasing the difficulty of tunneling, and thus increasing its resistance. On the contrary, the Cu ions migrate in the opposite direction, reducing the resistance.

[0009] Using CuInP2S6 and applying an electric field can avoid the thermal effects of current on the device, and migrate back and forth within the layer, improving the cycle stability performance and achieving the purpose of using a two-dimensional magnetic tunnel junction as a storage medium.

[0010] Furthermore, the dimensions of the substrate, the bottom electrode, the two-dimensional ferromagnetic material layer I, the two-dimensional ferromagnetic material layer II and the protective layer are all the same, and the length of the two-dimensional ferroelectric material layer is greater than the length of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II, so that the left end or the right end or both ends of the two-dimensional ferroelectric material layer protrude.

[0011] The length of the protrusions was 2-6 μm.

[0012] The two-dimensional ferroelectric material layer has a bulge because CuInP2S6 can withstand relatively large voltages, while the two-dimensional ferromagnetic material of a few nanometers to more than 10 nanometers can be easily broken down or burned, causing device failure. The bulge makes the voltage basically applied to the two-dimensional ferroelectric material layer, and the voltage distributed to the two-dimensional ferromagnetic material is almost 0, which can protect the two-dimensional ferromagnetic material. Another function is to move the Cu ions out of the same position of the three-layer structure (two-dimensional ferromagnetic material layer I, two-dimensional ferroelectric material layer, two-dimensional ferromagnetic material layer II).

[0013] Furthermore, the materials of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II are the same or different, specifically Fe 3+ x Any one of GaTe2, CrI3 or Cr2Ga2Te6, where x = 0-2. The ferromagnetic material must satisfy different perpendicular magnetic anisotropy.

[0014] Preferably, the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II are both Fe3GaTe2.

[0015] The strong ferromagnetism of Fe3GaTe2 has a high spin polarization rate, thus enhancing the tunneling magnetoresistance effect (TMR). A high TMR ratio means a larger resistance change, improving the signal detection sensitivity of MTJ devices, enabling faster read speeds and lower power consumption in memory cells (such as MRAM). Fe3GaTe2 has a high Curie temperature (Tc), which can maintain a stable ferromagnetic state at higher temperatures, avoiding magnetization reversal caused by thermal perturbations. This is crucial for high-temperature application scenarios such as automotive electronics and industrial equipment, ensuring the reliability of data storage. Fe3GaTe2 has good interface properties (such as low defect density and lattice matching with other functional layers), which can reduce interface scattering in the tunnel junction and improve electron tunneling efficiency. This is crucial for increasing TMR and device durability.

[0016] Furthermore, the thickness of the two-dimensional ferromagnetic material layer I is 1 - 10 nm, and the thickness of the two-dimensional ferromagnetic material layer II is 10 - 20 nm;

[0017] Or the thickness of the two-dimensional ferromagnetic material layer I is 10 - 20 nm, and the thickness of the two-dimensional ferromagnetic material layer II is 1 - 10 nm.

[0018] The thicknesses of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer need to be different. The thicker layer is used as the reference layer, which can be named the ferromagnetic reference layer, and the thinner layer is the free layer, which can be named the ferromagnetic free layer. The ferromagnetic reference layer or the ferromagnetic free layer can be above or below. The reference layer (the fixed layer (the thicker one)) needs to maintain a stable magnetization direction and is usually designed to be thicker to enhance its magnetocrystalline anisotropy, thus resisting external disturbances (such as thermal perturbations or stray magnetic fields) and ensuring the reliability of data storage. The free layer (the thinner one) requires a smaller magnetic anisotropy so that the magnetization direction can be quickly switched by an external magnetic field or current. The thinner thickness can reduce its stability threshold, making it easier to flip.

[0019] Furthermore, the thickness of the two-dimensional ferroelectric material layer is 1 nm - 10 nm.

[0020] Furthermore, the magnitude of the electric field strength is 0.1 - 10 kV / cm.

[0021] Furthermore, the thickness of the substrate is 0.2 - 5 mm, the thickness of the bottom electrode is 15 - 60 nm, and the thickness of the protective layer is 1 - 200 nm; the material of the protective layer is h-BN.

[0022] The present invention also provides a preparation method of an electric-field-controlled two-dimensional magnetic tunnel junction as described above, and this method includes the following steps:

[0023] (1) Prepare a bottom electrode on the substrate by combining photolithography and magnetron sputtering processes;

[0024] (2) A two-dimensional ferromagnetic material layer I, a two-dimensional ferroelectric material layer, a two-dimensional ferromagnetic material layer II, and a protective layer are sequentially prepared on the bottom electrode.

[0025] (3) The left and right ends of the two-dimensional ferroelectric material layer are respectively in contact with the electric field electrodes.

[0026] Further, the method for preparing the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, the two-dimensional ferromagnetic material layer II, and the protective layer is any one of molecular beam epitaxy, pulsed laser deposition, physical vapor deposition, chemical vapor deposition, and mechanical exfoliation.

[0027] The present invention also provides an application of the electric field-controlled two-dimensional magnetic tunnel junction as described above in magnetoelectronic devices.

[0028] Compared with the prior art, the electric field-controlled two-dimensional magnetic tunnel junction, its preparation method and application described in the present invention have the following advantages:

[0029] (1) The electric field-controlled two-dimensional magnetic tunnel junction described in the present invention changes its conductivity by electrically controlling the two-dimensional ferroelectric CuInP2S6, thereby changing the resistance state of the overall device. Compared with traditional magnetic tunnel junctions, the present invention has no large write current, and at the same time can reduce energy consumption and heat generation, which better protects the device itself and greatly improves the durability of the device.

[0030] (2) The electric field-controlled two-dimensional magnetic tunnel junction described in the present invention uses the two-dimensional magnetic material Fe3GaTe2, which has a relatively high Curie temperature and exhibits good perpendicular magnetic anisotropy at room temperature, which can greatly reduce the volume of the device and improve the integration degree.

[0031] (3) The preparation process of the electric field-controlled two-dimensional magnetic tunnel junction described in the present invention is relatively simple, and the perpendicular magnetic structure of the materials of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II has little influence on adjacent components, resulting in a better yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0033] Figure 1 is a schematic structural diagram of the electric field-controlled two-dimensional magnetic tunnel junction described in the present invention;

[0034] Figure 2 is the in-plane I-V curve of CuInP2S6;

[0035] Figure 3Data graph for applying an electric field to a two-dimensional ferroelectric material layer; (a) is a top-down view of the KPFM mode of the atomic force, and (b) is the potential distribution map corresponding to the white line in the graph (a).

[0036] Figure 4 Resistance-voltage graph measured for Comparative Example 1;

[0037] Figure 5 Resistance-voltage graph measured for Comparative Example 2.

[0038] Explanation of reference numerals:

[0039] 1. Substrate; 2. Bottom electrode; 3. Two-dimensional ferromagnetic material layer I; 4. Two-dimensional ferroelectric material layer; 5. Two-dimensional ferromagnetic material layer II; 6. h-BN layer. Detailed implementation manners

[0040] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0041] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Embodiment 1

[0045] An electric field-controlled two-dimensional magnetic tunnel junction includes an SiO2 / Si substrate 1, a Ti+Pt bottom electrode 2, a two-dimensional ferromagnetic material layer I 3, a two-dimensional ferroelectric material layer 4, a two-dimensional ferromagnetic material layer II 5, and an h-BN layer 6 arranged in sequence from bottom to top. The material of the two-dimensional ferroelectric material layer 4 is CuInP2S6. An electric field is applied to the left and right ends of the two-dimensional ferroelectric material layer 4, and the magnitude of the electric field is 0.1 kV / cm. The materials of the two-dimensional ferromagnetic material layer I 3 and the two-dimensional ferromagnetic material layer II 5 are the same, both being Fe3GaTe2.

[0046] The thickness of the substrate 1 is 0.5 mm, the thickness of the Ti+Pt bottom electrode 2 is 5 + 15 nm, and the thickness of the h-BN layer 6 is 30 nm; the thickness of the two-dimensional ferromagnetic material layer I 3 is 9 nm, the thickness of the two-dimensional ferromagnetic material layer II 5 is 15 nm, and the thickness of the two-dimensional ferroelectric material layer 4 is 5 nm.

[0047] The substrate 1, the bottom electrode 2, the two-dimensional ferromagnetic material layer I 3, the two-dimensional ferromagnetic material layer II 5, and the h-BN layer 6 have the same size. The length of the two-dimensional ferroelectric material layer 4 is greater than the lengths of the two-dimensional ferromagnetic material layer I 3 and the two-dimensional ferromagnetic material layer II 5, such that Figure 1 as shown, the left end of the two-dimensional ferroelectric material layer 4 protrudes by a piece, and the protruding length is 3 μm.

[0048] The preparation method of the above electric field-controlled two-dimensional magnetic tunnel junction is as follows:

[0049] (1) Clean the SiO2 / Si substrate

[0050] The substrate is ultrasonically treated in acetone, ethanol, and deionized water for 15 minutes each and then dried with a nitrogen gas gun.

[0051] (2) Prepare the bottom electrode Ti+Pt

[0052] By combining photolithography and magnetron sputtering processes, the electrode pattern is used for exposure and development, and the bottom electrode Ti+Pt (at room temperature) with a thickness of 5 + 15 nm is obtained by magnetron sputtering.

[0053] (3) Prepare the two-dimensional ferromagnetic material layer I

[0054] The solid material Fe3GaTe2 was directly exfoliated onto the surface of polydimethylsiloxane (PDMS) to form a Fe3GaTe2 / PDMS composite; the Fe3GaTe2 in the obtained Fe3GaTe2 / PDMS composite was brought into contact with the bottom electrode obtained in step (2), so that Fe3GaTe2 was separated from PDMS, and Fe3GaTe2 was laid flat on the bottom electrode and formed good contact with the bottom electrode, forming a two-dimensional ferromagnetic material layer I.

[0055] (4) Preparation of a two-dimensional ferroelectric material layer

[0056] Similar to step (3), the two-dimensional ferroelectric material CuInP2S6 was exfoliated using PDMS by mechanical exfoliation method to form a CuInP2S6 / PDMS composite, and the CuInP2S6 in the composite was brought into contact with the two-dimensional ferromagnetic material layer I to form a two-dimensional ferroelectric material layer; and the left and right ends of the two-dimensional ferroelectric material layer were respectively brought into contact with the electric field electrodes.

[0057] (5) Preparation of a two-dimensional ferromagnetic material layer II

[0058] Similar to step (3), a Fe3GaTe2 / PDMS composite was obtained, and a two-dimensional ferromagnetic material layer II was formed above the two-dimensional ferroelectric material layer.

[0059] (6) Preparation of an h-BN protective layer

[0060] Similarly, a BN thin film with a certain thickness was obtained using PDMS by mechanical exfoliation method to obtain a BN / PDMS composite, and the BN was covered on the surface of the entire magnetic tunnel junction, and finally a complete magnetic tunnel junction device was obtained.

[0061] The current and voltage between the bottom electrode, the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, and the two-dimensional ferromagnetic material layer II were measured by an ammeter and a voltmeter.

[0062] Figure 2 It is the in-plane I-V curve of the CuInP2S6 material, and the curve reflects the migration characteristics of Cu ions.

[0063] Figure 3 The bright part in (a) is the place where Cu ions gather, where there is a high electric potential, the darker part in the figure has a low electric potential, electrons are more likely to tunnel, and the resistance is low. It has non-volatility after power-off.

[0064] This tunnel junction controls the two-dimensional ferroelectric CuInP2S6 through an electric field to change its conductivity, thereby changing the resistance state of the overall device. Compared with traditional magnetic tunnel junctions, the present invention does not have a large write current, and at the same time can reduce energy consumption and heat generation, which plays a better role in protecting the device itself and greatly improves the durability of the device.

[0065] In this embodiment, the bottom electrode is fabricated first, and then the device is fabricated by the mechanical exfoliation method. Moreover, only one electrode needs to be made. Compared with the fabrication process of the upper and lower electrodes of the traditional magnetic tunnel junction, the error tolerance of the work is greatly increased, and the two-dimensional material is better protected. And the preparation of the device in this embodiment is carried out entirely in a glove box, and mechanical exfoliation can be carried out under a protective gas to prevent oxidation.

[0066] Comparative Example 1

[0067] The difference from the above-mentioned Embodiment 1 is that the thicknesses of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II are the same, both being 15 nm.

[0068] An electric field is applied across the ferroelectric material, and the current and voltage between the bottom electrode, the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, and the two-dimensional ferromagnetic material layer II are measured by an ammeter and a voltmeter, so as to measure the resistance.

[0069] The results are as Figure 4 shown. When the thicknesses are the same and the voltage is changed, the change in its resistance is very small and basically remains consistent, indicating that there is no tunneling effect in this structure, and it is just an ordinary ohmic resistance.

[0070] Comparative Example 2

[0071] The difference from the above-mentioned Embodiment 1 is that the thickness of the two-dimensional ferroelectric material layer 4 is 30 nm.

[0072] An electric field is applied across the ferroelectric material, and the current and voltage between the bottom electrode, the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, and the two-dimensional ferromagnetic material layer II are measured by an ammeter and a voltmeter, so as to measure the resistance.

[0073] The results are as Figure 5 shown. When the two-dimensional ferroelectric material layer becomes thicker and the voltage is changed, the change in its resistance is very small and basically remains consistent, indicating that there is no tunneling effect in this structure, and it is just an ordinary ohmic resistance.

[0074] From the above conclusions, it can be seen that when the thickness of the two-dimensional ferroelectric material layer is changed or there is no thickness difference between the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II, a magnetic tunnel junction structure cannot be formed. Only when it meets the setting requirements of the present invention can a magnetic tunnel junction with good effects be fabricated.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electric field-regulated two-dimensional magnetic tunnel junction, characterized in that: It includes a substrate, a bottom electrode, a two-dimensional ferromagnetic material layer I, a two-dimensional ferroelectric material layer, a two-dimensional ferromagnetic material layer II, and a protective layer which are sequentially arranged from bottom to top. The material of the two-dimensional ferroelectric material layer is CuInP2S6, and an electric field is applied to the left and right ends of the two-dimensional ferroelectric material layer; Among them, the thickness of the two-dimensional ferromagnetic material layer I is 1 - 10 nm, and the thickness of the two-dimensional ferromagnetic material layer II is 10 - 20 nm; Or the thickness of the two-dimensional ferromagnetic material layer I is 10 - 20 nm, and the thickness of the two-dimensional ferromagnetic material layer II is 1 - 10 nm; The thickness of the two-dimensional ferroelectric material layer is 1 nm - 10 nm; The materials of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II are the same, both being Fe3GaTe2.

2. The electric-field-controlled two-dimensional magnetic tunnel junction according to claim 1, wherein: The sizes of the substrate, the bottom electrode, the two-dimensional ferromagnetic material layer I, the two-dimensional ferromagnetic material layer II, and the protective layer are the same. The length of the two-dimensional ferroelectric material layer is greater than the lengths of the two-dimensional ferromagnetic material layer I and the two-dimensional ferromagnetic material layer II, such that the left end or the right end or both the left and right ends of the two-dimensional ferroelectric material layer protrude by a piece.

3. The electric-field-controlled two-dimensional magnetic tunnel junction according to claim 1, wherein: The magnitude of the electric field strength is 0.1 - 10 kV / cm.

4. The electric field-controlled two-dimensional magnetic tunnel junction according to claim 1, wherein: The thickness of the substrate is 0.2 - 5 mm, the thickness of the bottom electrode is 15 - 60 nm, and the thickness of the protective layer is 1 - 200 nm; the material of the protective layer is h-BN.

5. A method for preparing an electric field-controlled two-dimensional magnetic tunnel junction according to any one of claims 1-4, characterized in that: This method includes the following steps: (1) Prepare the bottom electrode on the substrate by combining photolithography and magnetron sputtering processes; (2) Sequentially prepare the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, the two-dimensional ferromagnetic material layer II, and the protective layer on the bottom electrode; (3) The left and right ends of the two-dimensional ferroelectric material layer are respectively in contact with the electric field electrodes.

6. The method for preparing an electric field-controlled two-dimensional magnetic tunnel junction according to claim 5, wherein: The method for preparing the two-dimensional ferromagnetic material layer I, the two-dimensional ferroelectric material layer, the two-dimensional ferromagnetic material layer II, and the protective layer is any one of molecular beam epitaxy, pulsed laser deposition, physical vapor deposition, chemical vapor deposition, and mechanical exfoliation.

7. An application of the electric-field-controlled two-dimensional magnetic tunnel junction according to any one of claims 1 - 4 in a magnetoelectronic device.

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