A moiré tunnel junction based on a two-dimensional material tunneling layer and a preparation method thereof

Abstract

The present invention discloses a moiré tunnel junction based on a two-dimensional material tunneling layer in the field of electronic device technology and a preparation method thereof, aiming to solve the problems in the prior art that the application of magnetic tunnel junctions requires magnetic field intervention, has high requirements on the working environment, and has the preparation of a pinning layer. The present invention includes a tunneling barrier layer, and the upper and lower sides of the tunneling barrier layer are provided with metal electrode layers and substrate layers in sequence from the inside to the outside. The tunneling barrier layer is a moiré superlattice, and the moiré superlattice is composed of two two-dimensional material single crystal films with a twist angle vertically stacked; the same side of the two metal electrode layers is connected by an ammeter, and the other side is connected by a power supply, so that the whole forms a series circuit. The moiré tunnel junction of the present invention changes the tunneling current by adjusting the relative twist angle of the moiré superlattice of the tunneling layer, avoiding the disadvantages of many restrictive conditions in the application of traditional magnetic tunnel junctions, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to a moiré tunnel junction based on a two-dimensional material tunneling layer and a preparation method thereof, and belongs to the technical field of electronic devices. Background Art

[0002] Traditional tunnel junctions include magnetic tunnel junctions and superconducting tunnel junctions. Among them, magnetic tunnel junctions can be used in information storage, magnetic field sensors and other fields. Its working principle is to adjust the tunneling current by changing the relative direction of the magnetization intensity of the ferromagnetic electrodes on both sides, and then realize the switching function by the change of the tunneling current.

[0003] However, there are many restrictions on the application of magnetic tunnel junctions. For example, the intervention of a magnetic field is required, that is, the relative direction of the magnetization intensity of the ferromagnetic electrodes on both sides is changed by changing the external magnetic field; because the electrodes are ferromagnetic, there are also high requirements for the working environment; in addition, in order to achieve different directions of the magnetization intensity of the electrodes on both sides under the same magnetic field, an additional pinning layer needs to be epitaxially grown in the "sandwich" structure when preparing the magnetic tunnel junction. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a moiré tunnel junction based on a two-dimensional material tunnel layer and a method for preparing the same. The moiré tunnel junction changes the tunneling current by adjusting the relative twist angle of the moiré superlattice of the tunnel layer, thereby avoiding the shortcomings of traditional magnetic tunnel junctions with many restrictive conditions and having broad application prospects.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] On the one hand, the present invention provides a moiré tunnel junction based on a two-dimensional material tunneling layer, comprising a tunneling barrier layer, wherein the upper and lower sides of the tunneling barrier layer are provided with a metal electrode layer and a substrate layer in sequence from the inside to the outside, and the tunneling barrier layer is a moiré superlattice, and the moiré superlattice is composed of two two-dimensional material single crystal films with a twist angle vertically stacked;

[0007] The same side of the two metal electrode layers is connected through an ammeter, and the other side is connected through a power supply, so that the whole forms a series loop. The ammeter is used to measure the tunneling current of the moiré tunnel junction, and the power supply is used to provide voltage to the metal electrode layers.

[0008] Optionally, the substrate layer is made of oxide insulating material with a thickness ranging from 80 to 100 nm.

[0009] Optionally, the metal electrode layer is Au or Cu, and its thickness ranges from 10 to 30 nm.

[0010] Optionally, a protective film is provided between the metal electrode layer and the substrate layer. The protective film is made of a metal thin film, and the thickness of the metal thin film is in the range of 50-70 nm.

[0011] Optionally, the two-dimensional material single crystal film has a hexagonal structure and a thickness range of 1 to 3 nm.

[0012] On the other hand, the present invention also provides a method for preparing a moiré tunnel junction based on a two-dimensional material tunneling layer, comprising the following steps:

[0013] Selecting a suitable oxide insulating material and polishing it, that is, preparing a substrate layer;

[0014] A layer of metal film is spread on the surface of oxide insulating material using vacuum evaporation coating technology to form a protective film;

[0015] Au or Cu is deposited on the surface of the protective film as a metal electrode by electron beam evaporation deposition;

[0016] The pre-treated two-dimensional material single crystal film is transferred to the metal electrode by a transparent tape transfer method, a circular metal island is made on the two-dimensional material single crystal film by using standard electron beam lithography and lift-off process, and the two-dimensional material single crystal film-metal electrode is etched by photolithography technology, that is, two two-dimensional material single crystal film-metal electrode structures are prepared;

[0017] After spin coating PMMA on the substrate of the first two-dimensional material single crystal thin film-metal electrode structure and fixing it, the second one is flipped 180 degrees and covered on the first two-dimensional material single crystal thin film-metal electrode structure by dry transfer technology, so that the two two-dimensional material single crystal thin film-metal electrode structures form a certain angle;

[0018] Connect the same side of the two metal electrodes through an ammeter and the other side through a power supply to form a series circuit.

[0019] Furthermore, the pretreatment is to clean, screen and purify the two-dimensional material single crystal.

[0020] Furthermore, the operation of etching the two-dimensional material single crystal thin film-metal electrode is specifically as follows:

[0021] applying a photoresist onto a single crystal thin film of a two-dimensional material;

[0022] Replicate the pattern on the photolithography mask onto a two-dimensional material single crystal film;

[0023] Under light of a set wavelength, the photoresist undergoes chemical corrosion to etch away parts outside the pattern, producing a two-dimensional material single crystal thin film-metal electrode structure.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The moiré tunnel junction based on the two-dimensional material tunneling layer designed by the present invention has a completely different physical mechanism from the traditional magnetic tunnel junction. The physical mechanism of the traditional magnetic tunnel junction is to adjust the tunneling current by changing the relative direction of the magnetization strength of the ferromagnetic electrodes on both sides, while the moiré tunnel junction of the present invention changes the tunneling current by changing the relative twist angle of the moiré superlattice of the tunneling layer, thereby realizing the conversion of the "on" and "off" states, which can overcome the shortcomings of the traditional magnetic tunnel junction, such as the need for magnetic field intervention, high working environment requirements, and the need for an epitaxial pinning layer.

[0026] The moiré tunnel junction based on the two-dimensional material tunneling layer designed in the present invention has a novel concept, a clear principle, and a simple structure, and has very broad application prospects in the fields of information storage and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a process for preparing a graphite film-metal electrode structure in an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of the structure of a moiré tunnel junction based on a two-dimensional material tunneling layer in an embodiment of the present invention;

[0029] In the figure: 1 substrate layer, 2 metal electrode layer, 3 single crystal graphite tunneling layer. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0032] For the purpose of this specification and the appended claims, unless otherwise stated, all numbers expressing amounts, percentages or ratios and other numerical values ​​used in this specification and the appended claims are understood to be modified in all cases by the term "about". In addition, all ranges disclosed herein are inclusive and independently combinable.

[0033] Embodiment 1:

[0034] like Figure 1As shown, this embodiment provides a method for preparing a moiré tunnel junction based on a two-dimensional material tunneling layer, comprising the following steps:

[0035] S1. Preparation of substrate layer: The oxide insulating material is block-shaped silicon dioxide, which is subjected to physical operations such as grinding, cleaning, and drying, and its thickness is controlled to be 90nm;

[0036] S2. Prepare a protective film: A Ti film is selected as the metal film of the protective film, and the Ti film is spread on the surface of the silicon dioxide by vacuum evaporation coating technology to form a protective film. The thickness of the protective film is controlled to be 60nm;

[0037] S3. Preparation of metal electrode: Au with a thickness of 20 nm is deposited on the surface of the Ti film by electron beam evaporation deposition method as a metal electrode. At the same time, depositing Au on the Ti film can also effectively prevent the oxidation of the Ti film.

[0038] S4. Preparation of the lower two-dimensional material single crystal film-metal electrode structure: Using highly oriented pyrolytic graphite (HOPG) as raw material, the raw material is cleaned, screened, purified and other physical operations are performed to obtain the required graphite single crystal material. The graphite film is transferred to the metal electrode using the transparent belt transfer method, and the thickness of the graphite film is controlled to 2nm using optical microscopy and Raman spectroscopy technology. The graphite film-metal electrode is etched using standard electron beam lithography and lift-off process.

[0039] The specific etching operations are:

[0040] First, a photoresist is coated on a graphite film;

[0041] Secondly, the circular pattern on the photolithography mask is copied onto the graphite film. The photoresist will undergo chemical corrosion under light of a set wavelength, thereby etching away the unnecessary parts next to it and retaining the circular graphite film-metal electrode structure.

[0042] The upper graphite film-metal electrode structure was prepared by the same steps;

[0043] S5. Spin-coat PMMA on the surface of the silicon dioxide substrate of the lower graphite film-metal electrode structure and fix it on the operating table (so that the lower structure remains stationary when the upper graphite film-metal electrode structure is subsequently rotated). Flip the upper graphite film-metal electrode structure 180° and cover it on the lower graphite film-metal electrode structure through dry transfer technology, and let the two form a certain angle.

[0044] S6. Use copper wires to connect the two sides of the metal electrode of the two-layer graphite film-metal electrode structure through a power supply and an ammeter to form a series circuit, and the preparation is completed.

[0045] Embodiment 2:

[0046] This embodiment provides a moiré tunnel junction based on a two-dimensional material tunneling layer, including a tunneling barrier layer, and metal electrode layers and substrate layers are sequentially arranged on both sides of the tunneling barrier layer from the inside to the outside, wherein the thickness of the metal electrode layer ranges from 10 to 30 nm, and the material can be Au or Cu, but is not limited thereto, and other metal electrode materials with good conductivity should also be acceptable. The thickness of the substrate layer ranges from 80 to 100 nm, and an oxide insulating material such as silicon dioxide is used.

[0047] A protective film is provided between the metal electrode layer and the substrate layer. The protective film can be made of a metal film having high mechanical strength, good toughness, good ductility and corrosiveness. The thickness of the protective film is controlled at 50-70 nm.

[0048] The tunneling barrier layer is a moiré superlattice, which is composed of two two-dimensional material single crystal films with twist angles stacked vertically. The two-dimensional material single crystal film uses a two-dimensional material with a hexagonal structure as the raw material, and the thickness is controlled at 1~3nm.

[0049] The same side of the two metal electrode layers is connected to an ammeter, and the other side is connected to a power supply, so that the whole forms a series loop. The ammeter is used to measure the tunneling current of the moiré tunnel junction, and the power supply is used to provide voltage to the metal electrode layers.

[0050] The moiré tunnel junction of the present invention changes the tunneling current by changing the relative twist angle of the moiré superlattice of the tunneling layer. Compared with the traditional magnetic tunnel junction, the moiré tunnel junction has the advantages of no need for magnetic field intervention, no need for magnetic materials, no need for pinning layers, etc. The device has a novel concept, clear principle, and simple structure, and has very broad application prospects in the fields of information storage.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A moiré tunnel junction based on a two-dimensional material tunneling layer, characterized in that: It includes a tunneling barrier layer, wherein the upper and lower sides of the tunneling barrier layer are provided with a metal electrode layer and a substrate layer in sequence from the inside to the outside, the tunneling barrier layer is a moiré superlattice, and the moiré superlattice is composed of two two-dimensional material single crystal films with a twist angle vertically stacked, and the two-dimensional material single crystal film is a single crystal graphite tunneling layer, which has a hexagonal structure and a thickness range of 1-3nm; The same side of the two metal electrode layers is connected through an ammeter, and the other side is connected through a power supply, so that the whole forms a series loop. The ammeter is used to measure the tunneling current of the moiré tunnel junction, and the power supply is used to provide voltage to the metal electrode layers.

2. The moiré tunnel junction based on a two-dimensional material tunneling layer according to claim 1, characterized in that: The substrate layer is made of oxide insulating material and has a thickness ranging from 80 to 100 nm.

3. The moiré tunnel junction based on a two-dimensional material tunneling layer according to claim 1, characterized in that: The metal electrode layer is Au or Cu, and its thickness ranges from 10 to 30 nm.

4. The moiré tunnel junction based on a two-dimensional material tunneling layer according to claim 3, characterized in that: A protective film is also provided between the metal electrode layer and the substrate layer. The protective film is made of a metal thin film, and the thickness of the metal thin film is in the range of 50-70 nm.

5. A method for preparing a moiré tunnel junction based on a two-dimensional material tunneling layer according to any one of claims 1 to 4, characterized in that: The following steps are included: Selecting a suitable oxide insulating material and polishing it, that is, preparing a substrate layer; A layer of metal film is spread on the surface of oxide insulating material using vacuum evaporation coating technology to form a protective film; Au or Cu is deposited on the surface of the protective film as a metal electrode by electron beam evaporation deposition; The pre-treated two-dimensional material single crystal film is transferred to the metal electrode by a transparent tape transfer method, a circular metal island is made on the two-dimensional material single crystal film by using standard electron beam lithography and lift-off process, and the two-dimensional material single crystal film-metal electrode is etched by photolithography technology, that is, two two-dimensional material single crystal film-metal electrode structures are prepared; After spin coating PMMA on the substrate of the first two-dimensional material single crystal thin film-metal electrode structure and fixing it, the second one is flipped 180 degrees and covered on the first two-dimensional material single crystal thin film-metal electrode structure by dry transfer technology, so that the two two-dimensional material single crystal thin film-metal electrode structures form a certain angle; Connect the same side of the two metal electrodes through an ammeter and the other side through a power supply to form a series circuit.

6. The method for preparing a moiré tunnel junction based on a two-dimensional material tunneling layer according to claim 5, characterized in that: The pretreatment is to clean, screen and purify the two-dimensional material single crystal.

7. The method for preparing a moiré tunnel junction based on a two-dimensional material tunneling layer according to claim 5, characterized in that: The specific operation of etching the two-dimensional material single crystal film-metal electrode is as follows: applying a photoresist onto a single crystal thin film of a two-dimensional material; Replicate the pattern on the photolithography mask onto a two-dimensional material single crystal film; Under light of a set wavelength, the photoresist undergoes chemical corrosion to etch away parts outside the pattern, producing a two-dimensional material single crystal thin film-metal electrode structure.

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