A vertical single-molecule tunneling device and its fabrication method

Abstract

This application provides a vertical single-molecule tunneling device and its fabrication method. The vertical single-molecule tunneling device includes a substrate, a source electrode, a charged self-assembled monomolecular film, a conductive two-dimensional material electrode layer, and a gate electrode and a drain electrode disposed on the substrate in sequence on the substrate. The charged self-assembled monomolecular film includes charged organic molecules with the structure shown in formula (I). R1 ​​in the charged organic molecule is connected to the source electrode by a chemical bond, and R2 in the charged organic molecule has a non-covalent van der Waals interaction with the conductive two-dimensional material electrode layer. The vertical single-molecule tunneling device also includes an alkaline liquid dielectric solution distributed on the conductive two-dimensional material electrode layer, the gate electrode, and the drain electrode. The vertical single-molecule tunneling device provided in this application has a high on / off rectification ratio.

Description

Technical Field

[0001] This application relates to the field of electronic device technology, and in particular to a vertical single-molecule tunneling device and its fabrication method. Background Technology

[0002] Miniaturization to the sub-nanometer level is a key goal in the development of electronic devices, and electronic devices containing sub-nanometer components often operate in a quantum tunneling state. Compared to conventional electronic devices (such as diodes and transistors), the performance of most conventional electronic devices will inevitably degrade under this scaling limit. For example, the on / off rectification ratio of a diode and the field-effect switching ratio of a transistor are critical performance parameters for device operation. Due to the Landauer limit, regardless of the constituent materials or structures of conventional devices, the on / off ratio of quantum tunneling devices at room temperature cannot exceed the maximum on / off ratio of 10⁻⁶. 3 Therefore, in order to break the Landauer limit, it is essential to develop a new type of molecular system. Summary of the Invention

[0003] The purpose of this application is to provide a vertical single-molecule tunneling device and its fabrication method, so as to improve the on / off rectification ratio of the vertical single-molecule tunneling device. The specific technical solution is as follows:

[0004] The first aspect of this application provides a vertical single-molecule tunneling device, comprising a substrate, a source electrode, a charged self-assembled monomolecular film, a conductive two-dimensional material electrode layer sequentially disposed on the substrate, and a gate electrode and a drain electrode disposed on the substrate; the charged self-assembled monomolecular film comprises charged organic molecules having the structure shown in formula (I):

[0005]

[0006] R1 in the charged organic molecule is connected to the source electrode by a chemical bond, and R2 in the charged organic molecule has a non-covalent van der Waals interaction with the conductive two-dimensional material electrode layer; wherein, R1 is selected from carboxyl or sulfonic acid group, R2 is selected from mercapto, amino or pyridyl group, A is selected from C1 to C18 alkylene, unsubstituted or Ra-substituted phenylene, biphenylene, Ra is selected from C1 to C4 alkylene, and the number of benzene rings in the biphenylene is 2 to 5;

[0007] The vertical single-molecule tunneling device further includes an alkaline liquid dielectric solution distributed on the conductive two-dimensional material electrode layer, the gate, and the drain, wherein the alkaline liquid dielectric solution is selected from at least one of potassium hydroxide, lithium hydroxide, sodium hydroxide, tetrabutylammonium hydroxide, and tetrabutylammonium fluoride.

[0008] In some embodiments of this application, the C1-C18 alkylene groups are selected from the subunits of the following compounds: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, and octadecane; the unsubstituted or Ra-substituted phenylene groups are selected from phenylene, tolyl, and butylene; and the biphenylene groups are selected from the subunits of the following compounds: biphenyl, terphenyl, tetraphenyl, and pentphenyl.

[0009] In some embodiments of this application, the charged organic molecule is selected from the following compounds: 4-mercaptobenzoic acid, 4-mercaptobenzenesulfonic acid, 4-mercaptobutyric acid, 4-mercaptobutyric acid, 4'-aminobiphenyl-4-carboxylic acid, and 4'-aminobiphenyl-4-methanesulfonic acid.

[0010] In some embodiments of this application, the charged self-assembled monolayer is obtained by the self-assembly of the charged organic molecules on the source electrode.

[0011] In some embodiments of this application, the material of the source electrode is selected from Au, Ag or Pt, and the chemical bond is Au-S bond, Au-N bond, Ag-S bond, Ag-N bond, Pt-S bond or Pt-N bond.

[0012] In some embodiments of this application, the thickness of the source electrode is 10 nm to 100 nm.

[0013] In some embodiments of this application, the conductive two-dimensional material electrode layer and the source electrode have atomically flat surfaces.

[0014] In some embodiments of this application, the conductive two-dimensional material electrode layer is selected from monolayer graphene, monolayer molybdenum disulfide, or monolayer titanium disulfide.

[0015] In some embodiments of this application, the substrate includes a substrate bottom layer and an oxide layer, wherein the substrate bottom layer is made of silicon, mica or sapphire, and the oxide layer is made of silicon dioxide, hafnium dioxide or aluminum oxide.

[0016] A second aspect of this application provides a method for fabricating a vertical single-molecule tunneling device according to any of the foregoing embodiments, comprising the following steps:

[0017] (1) A blind hole is provided on the substrate, and the source electrode is provided in the blind hole;

[0018] (2) The gate is disposed on the substrate;

[0019] (3) The charged organic molecules are self-assembled onto the source electrode to form a charged self-assembled monolayer;

[0020] (4) The conductive two-dimensional material electrode layer is disposed on the charged self-assembled monolayer;

[0021] (5) The drain electrode is disposed on the substrate;

[0022] (6) The alkaline liquid dielectric solution is disposed on the conductive two-dimensional material electrode, the gate and the drain, so that the alkaline liquid dielectric solution covers the conductive two-dimensional material electrode, the gate and the drain, to obtain the vertical single-molecule tunneling device.

[0023] The beneficial effects of this application are:

[0024] This application provides a vertical single-molecule tunneling device and its fabrication method. The vertical single-molecule tunneling device includes a substrate, a source electrode, a charged self-assembled monomolecular film, a conductive two-dimensional material electrode layer, and a gate electrode and a drain electrode disposed on the substrate in sequence on the substrate. The charged self-assembled monomolecular film includes charged organic molecules, which have the structure shown in formula (I). R1 ​​in the charged organic molecule is connected to the source electrode by a chemical bond, and R2 in the charged organic molecule has a non-covalent van der Waals interaction with the conductive two-dimensional material electrode layer. The vertical single-molecule tunneling device also includes an alkaline liquid dielectric solution distributed on the conductive two-dimensional material electrode layer, the gate electrode, and the drain electrode. The alkaline liquid dielectric solution is selected from at least one of potassium hydroxide, lithium hydroxide, sodium hydroxide, tetrabutylammonium hydroxide, and tetrabutylammonium fluoride. In this structure, the R1 group in the charged organic molecule is chemically bonded to the source electrode, while the R2 group interacts with the conductive two-dimensional material electrode layer via van der Waals interactions, forming a vertical single-molecule structure. The gate provides a voltage to the alkaline liquid dielectric solution, causing positive and negative ions in the alkaline liquid dielectric to migrate and form an electric double layer, with negative ions positioned closer to the conductive two-dimensional material electrode layer. Simultaneously, the conductive two-dimensional material electrode layer effectively prevents the penetration of these negative ions, thereby enabling precise control of the charge status of the charged organic molecules. This improves the on / off rectification ratio of the vertical single-molecule tunneling device, achieving a ratio of up to 10. 3 ~10 6 Furthermore, the gate electric field provided by the gate is applied to the aforementioned vertical single-molecule structure, avoiding direct contact with charged organic molecules and improving the stability and gate control efficiency of the vertical single-molecule tunneling device.

[0025] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0027] Figure 1 This is a schematic diagram illustrating the working principle of a vertical single-molecule tunneling device in some embodiments of this application;

[0028] Figure 2 This is a schematic diagram of the substrate structure in some embodiments of this application;

[0029] Figure 3 for Figure 2 Schematic diagram of the cross-sectional structure along the middle AA;

[0030] Figure 4 This is a current-bias characteristic curve of the vertical single-molecule tunneling device in Example 1 when the gate voltage is 0V;

[0031] Figure 5 The current-bias characteristic curves of the vertical single-molecule tunneling device in Example 1 at gate voltages of -0.8V, -0.4V, 0V, 0.4V, and 0.8V are shown.

[0032] Figure 6 This is a current-bias characteristic curve of the vertical single-molecule tunneling device in Example 2 when the gate voltage is 0V;

[0033] Figure 7 The current-bias characteristic curves of the vertical single-molecule tunneling device in Example 2 at gate voltages of -0.8V, -0.4V, 0V, 0.4V, and 0.8V are shown. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0035] Currently, nanoscale elements in molecular tunneling devices are typically electrically neutral, limiting the improvement of the on / off rectification ratio, which is usually between 10 and 100, thus restricting the development of molecular tunneling devices. To address these issues, this application provides a vertical single-molecule tunneling device and its fabrication method to improve the on / off rectification ratio of vertical single-molecule tunneling devices. In this application, the on / off rectification ratio refers to the ratio of the maximum current to the minimum current in the characteristic curve of the current versus gate voltage of the molecular tunneling device at a bias voltage of 0.1V.

[0036] The first aspect of this application provides a vertical single-molecule tunneling device, comprising a substrate, a source electrode, a charged self-assembled monomolecular film, a conductive two-dimensional material electrode layer sequentially disposed on the substrate, and a gate electrode and a drain electrode disposed on the substrate; the charged self-assembled monomolecular film comprises charged organic molecules having the structure shown in formula (I):

[0037]

[0038] R1 in the charged organic molecule is connected to the source electrode by a chemical bond, and R2 in the charged organic molecule has a non-covalent van der Waals interaction with the conductive two-dimensional material electrode layer; wherein, R1 is selected from carboxyl or sulfonic acid group, R2 is selected from mercapto, amino or pyridyl group, A is selected from C1-C18 alkylene, unsubstituted or Ra-substituted phenylene, biphenylene, Ra is selected from C1-C4 alkylene, and the number of benzene rings in the biphenylene is 2 to 5; preferably, the C1-C18 alkylene is selected from the subunits of the following compounds: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane; the unsubstituted or Ra-substituted phenylene is selected from phenylene, tolyl, and butylene; the biphenylene is selected from the subunits of the following compounds: biphenyl, terphenyl, tetraphenyl, and pentphenyl. The vertical single-molecule tunneling device further includes an alkaline liquid dielectric solution distributed on a conductive two-dimensional material electrode layer, a gate electrode, and a drain electrode. The alkaline liquid dielectric solution is selected from at least one of potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), tetrabutylammonium hydroxide, and tetrabutylammonium fluoride. In this application, "biphenylene" refers to a group formed by the linkage of 2 to 5 phenylene groups.

[0039] The vertical single-molecule tunneling device provided in this application includes a charged self-assembled monomolecular film, which contains charged organic molecules. Group R2 in the charged organic molecules is a charged group. The electrostatic interaction between the charged group R2 and the alkaline liquid dielectric solution forms a molecular-electrode interface coupling, thereby improving the on / off rectification ratio of the vertical single-molecule tunneling device through the interface coupling interaction. Specifically, group R1 in the charged organic molecules is chemically bonded to the source electrode, and R2 has van der Waals interactions with the conductive two-dimensional material electrode layer, forming a vertical single-molecule structure. The alkaline liquid dielectric solution acts as an ionic liquid gate. When a voltage is applied to the alkaline liquid dielectric solution through the gate, positive and negative ions in the alkaline liquid dielectric migrate to form an electric double layer, with the negative ions moving closer to the conductive two-dimensional material electrode layer. Simultaneously, the conductive two-dimensional material electrode layer effectively prevents the penetration of the aforementioned negative ions, avoiding the formation of ions with opposite charges to the charged group R2 around it, thus preventing the unclear charge state of the charged group R2 and affecting the improvement of the on / off rectification ratio. Moreover, the conductive two-dimensional material electrode layer, as a barrier layer to block ions with opposite charges to the charged group R2, can also improve the stability of the vertical single-molecule tunneling device. In addition, the gate electric field provided by the gate is applied to the aforementioned vertical single-molecule structure, avoiding direct contact with charged organic molecules and improving the stability of the vertical single-molecule tunneling device. The migration of positive and negative ions in the alkaline liquid dielectric to form an electric double layer with a strong electric field can also improve the gate control efficiency of the vertical single-molecule tunneling device.

[0040] Specifically, Figure 1 The diagram illustrates the working principle of a vertical single-molecule tunneling device according to some embodiments of this application. In this device, the charged organic molecule in the charged self-assembled monolayer 30 is 4-mercaptobenzoic acid. The thiol groups in 4-mercaptobenzoic acid are chemically bonded to the source electrode 20, which is disposed on the substrate 10. Van der Waals forces exist between the carboxyl groups in 4-mercaptobenzoic acid and the conductive two-dimensional material electrode layer 40. When the gate 60 provides a voltage to the alkaline liquid dielectric solution, positive and negative ions in the alkaline liquid dielectric migrate to form an electric double layer 50, with the negative ions closer to the conductive two-dimensional material electrode layer 40. Simultaneously, the conductive two-dimensional material electrode layer 40 effectively prevents the penetration of ions from the electric double layer 50 formed by the migration of positive and negative ions, thus clearly defining the charged state of the carboxyl groups. This is beneficial for improving the on / off rectification ratio of the vertical single-molecule tunneling device. Furthermore, the conductive two-dimensional material electrode layer 40, as a barrier layer blocking ions with opposite charges to the carboxyl groups, also improves the stability of the vertical single-molecule tunneling device.

[0041] Therefore, the vertical single-molecule tunneling device provided in this application has a high on / off rectification ratio, as well as good stability and high gate control efficiency. Specifically, the on / off rectification ratio of the vertical single-molecule tunneling device provided in this application can reach 10.3 ~10 6 Compared to current molecular tunneling devices, the on / off rectification ratio has been improved by orders of magnitude, which is conducive to increasing the possibility of large-scale integration of vertical single-molecule tunneling devices and lays the foundation for the integration and application of vertical single-molecule tunneling devices.

[0042] For example, the charged organic molecule is selected from the following compounds: 4-mercaptobenzoic acid, 4-mercaptobenzenesulfonic acid, 4-mercaptobutyric acid, 4-mercaptobutyric acid, 4'-aminobiphenyl-4-carboxylic acid, and 4'-aminobiphenyl-4-methanesulfonic acid.

[0043] This application does not impose any particular limitation on the mass concentration of the alkaline liquid dielectric solution, as long as it achieves the purpose of this application. For example, the molar concentration of the alkaline liquid dielectric solution is 0.01 mmol / L to 100 mmol / L. Typically, when the alkaline liquid dielectric is selected from potassium hydroxide (KOH), lithium hydroxide (LiOH), or sodium hydroxide (NaOH), water is used as the solvent. When the alkaline liquid dielectric is selected from tetrabutylammonium hydroxide or tetrabutylammonium fluoride, an organic solvent is used as the solvent. This application does not impose any particular limitation on the organic solvent, as long as it can form a homogeneous solution with the alkaline liquid dielectric. For example, the organic solvent may include, but is not limited to, propylene carbonate.

[0044] In some embodiments of this application, a charged self-assembled monolayer is obtained by the self-assembly of charged organic molecules on a source electrode. Specifically, the R1 group in the charged organic molecule of the charged self-assembled monolayer can form a chemical bond with the source electrode, thereby the charged self-assembled monolayer can be obtained by self-assembly on the source electrode. For example, when the source electrode material is Au, the chemical bond formed during self-assembly can be an Au-S bond or an Au-N bond; when the source electrode material is Ag, the chemical bond formed during self-assembly can be an Ag-S bond or an Ag-N bond; when the source electrode material is Pt, the chemical bond formed during self-assembly can be a Pt-S bond or a Pt-N bond. This application does not impose any particular limitation on the thickness of the charged self-assembled monolayer, as long as the purpose of this application is achieved. For example, the thickness of the charged self-assembled monolayer is 0.5 nm to 2.5 nm.

[0045] In some embodiments of this application, the thickness of the source electrode is 10 nm to 100 nm.

[0046] In some embodiments of this application, the conductive two-dimensional material electrode layer and the source electrode have atomically flat surfaces. The conductive two-dimensional material electrode layer has an atomically flat surface without dangling bonds, thus exhibiting good electrical performance even at relatively thin thicknesses (e.g., single-atom thickness). Furthermore, the planar machinability of the conductive two-dimensional material itself in the electrode layer is beneficial for improving the stability of the vertical single-molecule tunneling device. Exemplarily, the conductive two-dimensional material electrode layer is selected from monolayer graphene, monolayer molybdenum disulfide, or monolayer titanium disulfide. The atomically flat surface of the source electrode facilitates the arrangement of the charged self-assembled monolayer and the conductive two-dimensional material electrode layer, as well as the arrangement of the alkaline liquid dielectric solution, to form a structurally stable vertical single-molecule tunneling device. Furthermore, when the conductive two-dimensional material electrode layer is selected from monolayer graphene, monolayer molybdenum disulfide, or monolayer titanium disulfide, the spacing between the R2 group and the positive and negative ions migrating in the alkaline liquid dielectric to form the double layer is at the atomic level. This facilitates the formation of a stable molecular-electrode interface coupling, resulting in a vertical single-molecule tunneling device with high stability and gate control efficiency. In this application, "atomic-level flatness" refers to the surface roughness of the material being at the atomic level.

[0047] In some embodiments of this application, such as Figure 2 and Figure 3 As shown, the substrate 10 includes a substrate bottom layer 11 and an oxide layer 12. The substrate 10 has a blind hole 13 penetrating the oxide layer 12, that is, along the thickness direction of the substrate 10, the depth h of the blind hole 13 is the same as the thickness T of the oxide layer 12. The aforementioned source electrode, charged self-assembled monolayer, and conductive two-dimensional material electrode layer are sequentially disposed in the blind hole, and the source electrode is in direct contact with the substrate bottom layer. Exemplarily, the material of the substrate bottom layer is selected from silicon, mica, or sapphire, and the material of the oxide layer is selected from silicon dioxide, hafnium dioxide, or aluminum oxide. This application does not impose any particular limitation on the thickness of the substrate, substrate bottom layer, and oxide layer, as long as the purpose of this application can be achieved. Exemplarily, the thickness of the substrate is 300 μm to 700 μm, and the thickness of the oxide layer is 100 nm to 300 nm.

[0048] This application does not impose any particular limitation on the thickness of the drain and gate, as long as the purpose of this application can be achieved. For example, the thickness of the drain is 50nm to 200nm and the thickness of the gate is 50nm to 200nm.

[0049] This application does not impose any particular restrictions on the materials of the drain and gate, as long as they can achieve the purpose of this application. For example, the materials of the drain and gate may include, but are not limited to, gold.

[0050] A second aspect of this application provides a method for fabricating a vertical single-molecule tunneling device according to any of the foregoing embodiments, comprising the following steps:

[0051] (1) A blind hole is formed on the substrate, and a source electrode is formed in the blind hole;

[0052] (2) A gate is disposed on the substrate;

[0053] (3) Charged organic molecules are self-assembled onto the source electrode to form a charged self-assembled monolayer;

[0054] (4) A conductive two-dimensional material electrode layer is set on a charged self-assembled monolayer;

[0055] (5) A drain electrode is formed on the substrate;

[0056] (6) An alkaline liquid dielectric solution is placed on the conductive two-dimensional material electrode, gate and drain, so that the alkaline liquid dielectric solution covers the conductive two-dimensional material electrode, gate and drain, to obtain a vertical single-molecule tunneling device.

[0057] Before step (1) above, the following steps may also be included: pre-treating the substrate to clean its surface and make it clean and free of contaminants. This application does not have any particular limitation on the pre-treatment steps, as long as they can achieve the purpose of this application. For example, the pre-treatment may include, but is not limited to, the following steps: cutting the substrate into a suitable size, heating and cleaning it in a piranha solution, and then ultrasonically cleaning it with ultrapure water. The piranha solution is obtained by mixing 35% H2O2 and concentrated sulfuric acid in a volume ratio of 3:7. This application does not impose any particular restrictions on the heating cleaning time and temperature, as long as the substrate surface is cleaned. For example, the heating cleaning temperature can be 100℃~120℃, and the heating cleaning time can be 2h~3h. It is understood that H2O2 is volatile, and H2O2 can be replenished in a timely manner during the heating cleaning process to maintain the volume ratio of H2O2 to concentrated sulfuric acid at approximately 3:7. This application does not limit the amount replenished, as long as the substrate surface is cleaned. This application does not impose any particular restrictions on the ultrasonic cleaning time, as long as the substrate surface is cleaned. For example, the ultrasonic cleaning time can be 10min~20min.

[0058] In step (1) above, exemplarily, the substrate includes a substrate bottom layer and an oxide layer. The substrate has a blind hole penetrating the oxide layer, and the source electrode is directly disposed in the blind hole and in direct contact with the substrate bottom layer. This application does not impose any particular limitation on the method of setting the blind hole, as long as it achieves the purpose of this application. Exemplarily, the method of setting the blind hole may include, but is not limited to, the following steps: setting photoresist on the oxide layer of the substrate, and then using a mask, ultraviolet lithography, and BOE etching to etch the oxide layer on the substrate corresponding to the mask, thereby obtaining the first blind hole. This application does not impose any particular limitation on the method of setting the source electrode, as long as it achieves the purpose of this application. Exemplarily, the method of setting the source electrode may include, but is not limited to, the following steps: depositing the source electrode material at the bottom of the first blind hole using electron beam evaporation, atomic layer deposition, or thermal evaporation to obtain the source electrode. Alternatively, after setting the first blind via, the substrate can be annealed to form a thermally grown oxide layer at the bottom of the first blind via. Then, using a mask, ultraviolet lithography, and BOE etching, the thermally grown oxide layer corresponding to the mask is etched to obtain a second blind via. The depth of the second blind via is the same as the thickness of the thermally grown oxide layer, and the area of ​​the orthographic projection of the second blind via onto the bottom layer of the substrate is smaller than the area of ​​the orthographic projection of the first blind via onto the bottom layer of the substrate. Then, source material is deposited in the second blind via using electron beam evaporation, atomic layer deposition, or thermal evaporation to obtain the source electrode. The annealing temperature is 950℃~1000℃, and the time is 0.5h~1h; the thickness of the thermally grown oxide layer is 20nm~40nm.

[0059] In step (2) above, this application does not have any particular restrictions on the method of setting the gate and drain, as long as the purpose of this application can be achieved. For example, the method of setting the gate may include, but is not limited to, the following steps: setting the gate on the oxide layer of the substrate using a mask, ultraviolet lithography, or deposition technology, wherein the above deposition technology is electron beam evaporation deposition, atomic layer deposition, or thermal evaporation deposition.

[0060] In step (3) above, exemplarily, the substrate with the source electrode is first subjected to high-temperature annealing, and then immersed in a solution of charged organic molecules. The solution of charged organic molecules must completely submerge the substrate. After immersion, the substrate is removed, washed, and dried. The charged organic molecules then self-assemble on the source electrode to form a charged self-assembled monolayer. The high-temperature annealing temperature is 200℃~300℃, and the time is 1h~5h. The solution of charged organic molecules is a solution containing charged organic molecules and a solvent, and the molar concentration of the solution of charged organic molecules is 0.01mmol / L~10mmol / L. This application does not have any particular limitation on the solvent of the solution of charged organic molecules, as long as it can form a homogeneous solution with the charged organic molecules. For example, the solvent may include, but is not limited to, at least one of toluene and ethanol. The immersion temperature is room temperature (25±2℃), and the time is 12h or more. The washing and drying methods described above are conventional processing methods known in the art, and this application does not limit them.

[0061] In step (4) above, the conductive two-dimensional material electrode layer is prepared in advance and then transferred to a charged self-assembled monolayer. This application does not impose any particular limitation on the preparation method of the conductive two-dimensional material electrode layer, as long as it can achieve the purpose of this application. For example, when the conductive two-dimensional material electrode layer is a single layer of graphene, the preparation method of the conductive two-dimensional material electrode layer may include, but is not limited to, the following steps: depositing and growing a graphene film on a copper foil, setting photoresist on the graphene film, drying to obtain a "photoresist layer / graphene film / copper foil" sandwich structure, then placing it in an ammonium persulfate solution to dissolve the copper foil, transferring it to clean deionized water, washing away the residual ammonium persulfate in the graphene to obtain a graphene film-photoresist layer structure, transferring it to a substrate and etching the photoresist layer by ultraviolet lithography to obtain the conductive two-dimensional material electrode layer. The copper foil used is any copper foil known in the art, and this application does not limit its use. The deposition and growth method of the graphene film may include, but is not limited to, low-pressure chemical vapor deposition. The photoresist layer is any conventional photoresist layer known in the art, and this application does not limit its use, as long as it can achieve the purpose of this application. The ammonium persulfate solution is an aqueous solution of ammonium persulfate, and this application does not have any particular limitation on the mass concentration of the ammonium persulfate solution, as long as it can achieve the purpose of this application. For example, the mass concentration of the ammonium persulfate solution is 2% to 5%. When the conductive two-dimensional material electrode layer is a monolayer of molybdenum disulfide, the preparation method of the conductive two-dimensional material electrode layer may include, but is not limited to, the following steps: obtaining a monolayer of molybdenum disulfide by mechanically peeling off the molybdenum disulfide material, and then transferring it onto a substrate; wherein, the molybdenum disulfide material is commercially available conventional molybdenum disulfide (CAS No.: 1317-33-5); whether the molybdenum disulfide is a monolayer of molybdenum disulfide can be determined by observation with an optical microscope. Replacing molybdenum disulfide with titanium disulfide yields a single-layer titanium disulfide, wherein the titanium disulfide is commercially available conventional titanium disulfide (CAS No.: 12039-13-3).

[0062] In step (5) above, this application does not have any particular restrictions on the method of setting the drain, as long as the purpose of this application can be achieved. For example, the method of setting the drain may include, but is not limited to, the following steps: setting the gate on the oxide layer of the substrate using a mask, ultraviolet lithography, or deposition technology. The above deposition technology is electron beam evaporation deposition, atomic layer deposition, or thermal evaporation deposition.

[0063] In step (6) above, the alkaline liquid dielectric solution can be applied dropwise to the conductive two-dimensional material electrode, gate, and drain, respectively. This application does not impose any particular limitation on the amount of alkaline liquid dielectric solution applied, as long as it can simultaneously cover the conductive two-dimensional material electrode, gate, and drain. The drain is connected to the conductive two-dimensional material electrode layer via the alkaline liquid dielectric solution.

[0064] Optionally, adhesion layers can be selectively provided between the source and the bottom substrate, between the gate and the oxide layer, and between the drain and the oxide layer to improve the adhesion between the source and the bottom substrate, between the gate and the oxide layer, and between the drain and the oxide layer, thereby improving the structural stability of the vertical single-molecule tunneling device. This application does not impose any particular limitation on the material of the adhesion layer, as long as it achieves the purpose of this application. For example, the material of the adhesion layer may include, but is not limited to, at least one of Ti and Cr.

[0065] Example

[0066] Example 1

[0067] (1) Using a silicon wafer as a substrate, the silicon wafer was pretreated. Specifically, the silicon wafer was cut into 2cm×2cm pieces, then placed in a piranha solution and heated at 110℃ for 3 hours, followed by sonication in ultrapure water for 15 minutes before use. The silicon wafer was an N-type doped silicon wafer (manufacturer: Silicon Valley Microelectronics, Inc.), which consisted of a silicon dioxide layer and a silicon substrate. The resistivity of the silicon wafer was 0.001Ω·cm-0.004Ω·cm, the total thickness of the silicon wafer was 380μm, and the thickness of the silicon dioxide layer was 300nm.

[0068] (2) Photoresist polymethyl methacrylate (PMMA) was spin-coated onto the silicon dioxide layer of the silicon wafer and then dried. A photomask with a circular hole with a diameter of 80 μm was aligned with the silicon wafer for photolithography. Then, BOE solution (HF and NH4F mixed at a volume ratio of 1:6) was used to etch the circular hole that was not protected by the photoresist until the 300 nm silicon dioxide layer was completely etched to obtain a circular blind hole with a diameter of 80 μm. Then, it was placed in a tube furnace and annealed at 960 °C in air for 45 min to thermally grow a 30 nm thick silicon dioxide layer on the silicon wafer at the bottom of the blind hole.

[0069] (3) A gate is set at a distance of 5μm from the edge of the circular blind hole. Specifically, the following steps are included: a mask with a square gate pattern with a side length of 15μm is aligned with the silicon wafer for photolithography. Then, an electron beam evaporation technique is used to first deposit a 20nm Ti layer and then deposit a 60nm Au layer on the area not protected by photoresist. The Ti layer serves as the adhesion layer between the Au layer and the silicon dioxide layer of the substrate, and the Au layer serves as the gate.

[0070] (4) Spin-coat the entire surface of the sample obtained in step (3) above with PMMA. After drying, align the mask with the blind hole with a square hole of 1.5 μm side length with the blind hole. After photolithography, use BOE solution to etch the silicon dioxide layer at the bottom of the blind hole until the 30 nm silicon dioxide layer is completely etched to obtain a square blind hole with a side length of 1.5 μm. Then, use electron beam evaporation technology to first deposit a 5 nm Ti layer in the square blind hole, and then deposit a 23 nm Au layer. The Ti layer serves as the adhesion layer between the Au layer and the silicon bottom layer of the substrate, and the Au layer serves as the source. Then, use acetone solution to remove the PMMA on the surface, and dry it for later use.

[0071] (5) The sample obtained in step (4) above was annealed in a glove box at 250°C for 3 hours, and then immersed in 5 mL of a charged organic molecule solution for 12 hours. The charged organic molecules formed a charged self-assembled monolayer on the source electrode surface through self-assembly. After removal, the sample was washed three times with toluene and ethanol, and dried with nitrogen gas for later use. The charged organic molecule solution was 4-mercaptobenzoic acid, the solvent was toluene, and the concentration of the charged organic molecule solution was 0.1 mmol / L.

[0072] (6) A graphene film with a thickness of 25 μm was grown on the surface of a copper foil by chemical vapor deposition. PMMA was spin-coated onto the surface of the graphene film, dried, and then immersed in a 3% ammonium persulfate solution to completely dissolve the copper foil. After removal, the foil was transferred to clean deionized water to remove residual ammonium persulfate from the graphene film, thus obtaining a PMMA / graphene film composite layer. The PMMA / graphene film composite layer was transferred to the surface of a charged self-assembled monolayer, with the graphene film facing the charged self-assembled monolayer. A photomask with a circular hole of 80 μm in diameter was aligned with the blind hole for photolithography. Reactive ion etching was used to etch the graphene in the PMMA / graphene film composite layer except for the blind hole, thereby completing the setting of the conductive two-dimensional material electrode layer graphene film.

[0073] (7) A drain electrode is set at a distance of 50 μm from the edge of the circular blind hole. Specifically, the following steps are included: a mask with a square drain electrode pattern with a side length of 15 μm is aligned with the silicon wafer for photolithography. Then, an electron beam evaporation technique is used to first deposit a 20 nm Ti layer at the location not protected by photoresist, and then deposit a 60 nm Au layer. The Ti layer serves as the adhesion layer between the Au layer and the silicon dioxide layer of the substrate, and the Au layer serves as the drain electrode.

[0074] (8) A 30 nm Al2O3 layer was deposited using electron beam evaporation to protect the components of the vertical single-molecule tunneling device. Then, photolithography was performed using a mask, and the Al2O3 layer on the conductive two-dimensional material electrode layer, gate, and drain surfaces was etched using a BOE solution until the 30 nm Al2O3 layer was removed. The surface was then rinsed with acetone to remove residual photoresist. Finally, an alkaline liquid dielectric solution was added to simultaneously cover the conductive two-dimensional material electrode layer, gate, and drain, thus obtaining the vertical single-molecule tunneling device. The alkaline liquid dielectric solution was KOH with a molar concentration of 0.1 mmol / L.

[0075] Example 2

[0076] Except that the silicon dioxide layer is 100 nm in step (1), the substrate is not annealed in step (2), the charged organic molecules are replaced with 4-mercaptobenzenesulfonic acid in step (5), and the source electrode is prepared by step (4), the rest is the same as in Example 1:

[0077] (4) Spin-coating PMMA onto the entire surface of the sample obtained in step (3) above, and after drying, aligning a mask with a square hole of 1.5 μm side length with the silicon wafer for photolithography, using BOE solution for etching until the 100 nm silicon dioxide layer is completely etched to obtain a square blind hole with a side length of 1.5 μm. Then, using electron beam evaporation technology, first deposit a 5 nm Ti layer in the square blind hole, and then deposit a 23 nm Au layer. The Ti layer serves as the adhesion layer between the Au layer and the silicon substrate, and the Au layer serves as the source electrode. Then, use acetone solution to remove the PMMA on the surface, and dry for later use.

[0078] Examples 3 to 7

[0079] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1. Among them, the conductive two-dimensional material electrode layer in Example 4 and Example 7 was obtained by repeatedly mechanically peeling off the material (titanium disulfide or molybdenum disulfide) of the conductive two-dimensional material electrode layer with single-sided adhesive, and then transferring it to the surface of the charged self-assembled monolayer film; the solvent of the alkaline liquid dielectric solution in Example 6 was propylene carbonate.

[0080] The current variation with bias voltage of the vertical single-molecule tunneling devices obtained in each embodiment was tested using a semiconductor parameter analyzer (manufacturer: Keysight, model: B1500A), which yielded the on / off rectification ratio and current-bias characteristic curves of the vertical single-molecule tunneling devices.

[0081] The preparation parameters and performance tests for each embodiment are shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085] As can be seen from Examples 1 to 8 in Table 1, the vertical single-molecule tunneling device provided in this application, using charged organic molecules and alkaline liquid dielectrics within the scope of this application, can achieve a maximum on / off rectification ratio of 1.1 × 10⁻⁶. 6 Compared to current molecular tunneling devices, the on / off rectification ratio is improved by four orders of magnitude, demonstrating that the vertical single-molecule tunneling device provided in this application not only has a high on / off rectification ratio but also a significantly improved on / off rectification ratio compared to existing technologies. Within the scope of this application, the thickness of the conductive two-dimensional material electrode layer, the material of the conductive two-dimensional material electrode layer, the thickness of the source electrode, and the chemical bonds formed between the source electrode and the charged self-assembled monolayer also contribute to the high on / off rectification ratio of the vertical single-molecule tunneling device.

[0086] Specifically, such as Figure 4 and Figure 5 As shown, when the gate voltage is 0V, the on-state current of the vertical single-molecule tunneling device in Example 1 is only 1.6A / cm. 2 When a negative gate voltage is applied, its on-state current increases by an order of magnitude. For example, when the gate voltage is -0.8V, its on-state current can reach 247.5A / cm. 2 The on / off rectification ratio reaches 1.2×10 4 .like Figure 6 and Figure 7 As shown, when the gate voltage is 0V, the on-state current of the vertical single-molecule tunneling device in Example 2 is only 22A / cm. 2 When a negative gate voltage is applied, the device's on-state current increases by an order of magnitude. For example, when the gate voltage is -0.8V, its on-state current can reach 8473.5A / cm. 2 The on / off rectification ratio reaches 1.18×10 4 .

[0087] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0088] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0089] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A vertical single-molecule tunneling device, comprising a substrate, a source electrode, a charged self-assembled monomolecular film, a conductive two-dimensional material electrode layer sequentially disposed on the substrate, and a gate electrode and a drain electrode disposed on the substrate; wherein the charged self-assembled monomolecular film comprises charged organic molecules having the structure shown in formula (I): R1-A-R2 (I) R1 in the charged organic molecule is connected to the source electrode by a chemical bond, and R2 in the charged organic molecule has a non-covalent van der Waals interaction with the conductive two-dimensional material electrode layer; wherein... R1 is selected from carboxyl or sulfonic acid group, R2 is selected from mercapto, amino or pyridyl group, A is selected from C1 to C18 alkylene group, unsubstituted or Ra-substituted phenylene group, biphenylene group, Ra is selected from C1 to C4 alkylene group, and the number of benzene rings in the biphenylene group is 2 to 5. The vertical single-molecule tunneling device further includes an alkaline liquid dielectric solution distributed on the conductive two-dimensional material electrode layer, the gate, and the drain, wherein the alkaline liquid dielectric solution is selected from at least one of potassium hydroxide, lithium hydroxide, sodium hydroxide, tetrabutylammonium hydroxide, and tetrabutylammonium fluoride.

2. The vertical single-molecule tunneling device according to claim 1, wherein, The C1-C18 alkylene groups are selected from the subunits of the following compounds: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, and octadecane. The unsubstituted or Ra-substituted phenylene is selected from phenylene, tolyl, and butylene; The biphenyl subunit is selected from the subunits of the following compounds: biphenyl, terphenyl, tetraphenyl, and pentphenyl.

3. The vertical single-molecule tunneling device according to claim 1, wherein, The charged organic molecule is selected from the following compounds: 4-mercaptobenzoic acid, 4-mercaptobenzenesulfonic acid, 4-mercaptobutyric acid, 4-mercaptobutyric acid, 4'-aminobiphenyl-4-carboxylic acid, and 4'-aminobiphenyl-4-methanesulfonic acid.

4. The vertical single-molecule tunneling device according to claim 1, wherein, The charged self-assembled monolayer is obtained by the self-assembly of the charged organic molecules on the source electrode.

5. The vertical single-molecule tunneling device according to claim 1, wherein, The source electrode material is selected from Au, Ag or Pt, and the chemical bond is Au-S bond, Au-N bond, Ag-S bond, Ag-N bond, Pt-S bond or Pt-N bond.

6. The vertical single-molecule tunneling device according to claim 1, wherein, The thickness of the source electrode is 10nm to 100nm.

7. The vertical single-molecule tunneling device according to claim 1, wherein, The conductive two-dimensional material electrode layer and the source electrode have atomically flat surfaces.

8. The vertical single-molecule tunneling device according to claim 1, wherein, The conductive two-dimensional material electrode layer is selected from monolayer graphene, monolayer molybdenum disulfide, or monolayer titanium disulfide.

9. The vertical single-molecule tunneling device according to any one of claims 1 to 8, wherein, The substrate includes a substrate bottom layer and an oxide layer. The substrate bottom layer is made of silicon, mica or sapphire, and the oxide layer is made of silicon dioxide, hafnium dioxide or aluminum oxide.

10. A method for fabricating a vertical single-molecule tunneling device according to any one of claims 1 to 9, comprising the following steps: (1) A blind hole is provided on the substrate, and the source electrode is provided in the blind hole; (2) The gate is disposed on the substrate; (3) The charged organic molecules are self-assembled onto the source electrode to form a charged self-assembled monolayer; (4) The conductive two-dimensional material electrode layer is disposed on the charged self-assembled monolayer; (5) The drain electrode is disposed on the substrate; (6) The alkaline liquid dielectric solution is disposed on the conductive two-dimensional material electrode, the gate and the drain, so that the alkaline liquid dielectric solution covers the conductive two-dimensional material electrode, the gate and the drain, to obtain the vertical single-molecule tunneling device.

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