Preparation method of a suspended two-dimensional film and application thereof to a nano-electromechanical pressure sensor

Abstract

A method for preparing a suspended two-dimensional film and its application in a nano-electromechanical pressure sensor. In the pressure sensor, a suspended two-dimensional material or a suspended two-dimensional hetero-layer is used as a sensitive film. The suspended two-dimensional material or the two-dimensional hetero-layer is covered on a cavity of an oxidized silicon substrate, and an electrode is connected to the suspended two-dimensional material and the hetero-layer. When an external pressure changes (for example, decreases), the suspended two-dimensional material or the two-dimensional hetero-layer deforms correspondingly (for example, deforms in the opposite direction of the cavity). According to the piezoresistive effect of the two-dimensional material, the resistance of the suspended two-dimensional material or the two-dimensional hetero-layer changes, and the corresponding change can be detected to correspondingly detect the change of the external pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of two-dimensional materials and sensors, and in particular to a method for preparing a suspended two-dimensional film and its application in a nano-electromechanical pressure sensor. BACKGROUND

[0002] Two-dimensional materials refer to materials in which electrons can only move freely in two dimensions (1-100 nm) on a nanoscale (planar motion), such as graphene, molybdenum disulfide, boron nitride, etc. Two-dimensional materials have many unique properties because the carrier migration and heat diffusion are limited to two dimensions. The ultra-thin thickness, excellent and unique mechanical and electrical properties of two-dimensional materials make them suitable for application as sensitive films in nano-electromechanical sensors with extremely small dimensions. Compared to traditional sensitive films, two-dimensional materials have higher sensitivity and can perform stable detection performance in more extreme environments such as ultra-low pressure environments, abnormally high or low temperature environments, and their application forms are diverse, including but not limited to various sensors (such as pressure sensors, acceleration sensors, humidity sensors, carbon dioxide gas sensors, etc.), resonators, microphones, etc. One long-term development goal of nano-electromechanical sensors in various application scenarios is to continuously reduce the size of the device and improve the performance and stability of the device. A typical sensor consists of four parts: a sensitive element, a conversion element, a conversion circuit, and an auxiliary power supply. The key part is the sensitive element, which can produce corresponding resistance, capacitance, resonance frequency, etc. changes when the environment to be detected changes, and output this change through the form of the circuit. Further miniaturization of nano-electromechanical sensors can result in smaller functional components and more miniature packaging, ultimately reducing device costs.

[0003] Two-dimensional materials are often used in nano-electromechanical sensors, which usually require the preparation of a suspended two-dimensional material film. However, current methods for preparing suspended two-dimensional materials and devices are complex and have low yield and poor yield, making large-scale standardized production impossible. Typically, after growing two-dimensional materials, they need to be etched into different shapes of cavities or through holes and integrated by transferring them to the etched cavities or through holes for subsequent operations. The step of transferring two-dimensional materials to etched cavities or through holes can easily cause defects such as wrinkles, folds, fractures, and local damage to two-dimensional materials, which can prevent two-dimensional materials from fully exhibiting their performance, further reducing the yield of nano-electromechanical sensors and limiting the widespread application of nano-electromechanical sensors based on two-dimensional materials.

[0004] Compared with the traditional method, the preparation method of the suspended two-dimensional material thin film and the device thereof in the present application can avoid deformation such as wrinkles, folds, breakage, and local damage of the two-dimensional material during the transfer process of the two-dimensional material, ensure the flatness and high quality of the two-dimensional material transfer integration, and has the potential for large-area production, which has great advantages in the yield and good rate of the two-dimensional material. In addition, the two-dimensional material nanoelectromechanical pressure sensor produced by the method has higher yield, further improving the possibility of large-scale preparation of the sensor.

[0005] In the prior art, Smith et al. (A. D. Smith, F. Niklaus, A. Paussa et al., “Electromechanical piezoresistive sensing in suspended graphene membranes,” Nano Letters, vol. 13, no. 7, pp. 3237-3242, 2013.) proposed a concept of a graphene piezoresistive nanoelectromechanical pressure sensor. The pressure sensor includes a silicon substrate, an electrode, and a suspended graphene thin film. The graphene thin film is covered on the etched cavity by a PMMA transfer method to form a sealed cavity. The working principle of the sensor is that when the device detects a change in air pressure, the graphene thin film deforms and strains, which in turn causes a change in the resistance of the graphene. By detecting this resistance change, the change in external air pressure can be calculated.

[0006] However, during the pressure measurement process, the graphene thin film may be affected by the gas or moisture it contacts, which may interfere with the resistance and cause interference in the measurement results.

[0007] The disclosed CN116358748A (Beijing University of Technology, a suspended two-dimensional material pressure sensor and a preparation method thereof, June 30, 2023) proposes a pressure sensor based on a suspended two-dimensional material. This preparation method innovatively solves the bottleneck problem of large-scale preparation of two-dimensional materials and can significantly improve the sensitivity, resolution, and detection limit of this type of pressure sensor.

[0008] Even though the above-mentioned sensor structure has good sensitivity and stability, it is difficult to avoid the problems of wrinkles, folds, breakage, and local damage of the two-dimensional material caused by etching the cavity first and then transferring the two-dimensional material during the preparation process.

[0009] Theoretical and experimental results show that the piezoresistive strain coefficient of two-dimensional materials such as molybdenum disulfide, tungsten disulfide, tungsten diselenide, molybdenum diselenide and other transition metal dichalcogenides is 1 to 3 orders of magnitude higher than that of graphene, which indicates that the piezoresistive nanoelectromechanical sensor based on these two-dimensional materials has the potential to be 1 to 3 orders of magnitude more sensitive than the piezoresistive nanoelectromechanical sensor based on graphene.

[0010] However, the Young's modulus (mechanical strength) of these two-dimensional materials is half to one order of magnitude lower than that of graphene. Hexagonal boron nitride is a two-dimensional insulator with a Young's modulus close to that of graphene and a thin film thickness, so hexagonal boron nitride is very suitable as a substrate and packaging material for graphene and other two-dimensional materials. It can improve the mechanical stability of graphene and other suspended two-dimensional materials, while avoiding the performance degradation of graphene and other two-dimensional material sensors due to exposure to air. SUMMARY

[0011] The purpose of the present application is to overcome the shortcomings of the prior art and provide a new method for preparing a suspended two-dimensional material thin film and its application in nanoelectromechanical sensors.

[0012] The preparation method mentioned in the present application uses a suspended two-dimensional material or a suspended two-dimensional hetero-layer as a sensitive thin film in the gas pressure sensor. The suspended two-dimensional material or two-dimensional hetero-layer is covered on the cavity of the oxidized silicon substrate, and the electrode is connected to the suspended two-dimensional material and hetero-layer. When the external air pressure changes (for example, the air pressure decreases), the suspended two-dimensional material or two-dimensional hetero-layer will deform accordingly (for example, deform in the opposite direction of the cavity). According to the piezoresistive effect of two-dimensional materials, the resistance of the suspended two-dimensional material or two-dimensional hetero-layer changes, and the corresponding change can be detected to detect the change of the external air pressure.

[0013] Further, the suspended two-dimensional material includes graphene, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS2), tungsten diselenide (WSe2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), platinum diselenide (PtSe2), molybdenum ditelluride (MoTe2), tungsten ditelluride (WTe2), vanadium diselenide (VSe2), chromium disulfide (CrS2), chromium diselenide (CrSe2), other transition metal dichalcogenides (TMDC), black phosphorus (P), MXene.

[0014] Further, the suspended two-dimensional material hetero-layer includes hexagonal boron nitride / graphene, hexagonal boron nitride / molybdenum disulfide, hexagonal boron nitride / tungsten diselenide, hexagonal boron nitride / molybdenum diselenide, hexagonal boron nitride / tungsten disulfide, hexagonal boron nitride / platinum diselenide, hexagonal boron nitride / molybdenum ditelluride, hexagonal boron nitride / tungsten ditelluride, hexagonal boron nitride / vanadium diselenide, hexagonal boron nitride / chromium disulfide, hexagonal boron nitride / chromium diselenide, hexagonal boron nitride / MXene, graphene / molybdenum disulfide, graphene / tungsten diselenide, graphene / molybdenum diselenide, graphene / tungsten disulfide, graphene / platinum diselenide, graphene / molybdenum ditelluride, graphene / tungsten ditelluride, graphene / vanadium diselenide, graphene / chromium disulfide, graphene / chromium diselenide, graphene / MXene, hexagonal boron nitride / graphene / molybdenum disulfide, hexagonal boron nitride / graphene / tungsten diselenide, hexagonal boron nitride / graphene / molybdenum diselenide, hexagonal boron nitride / graphene / tungsten disulfide, hexagonal boron nitride / graphene / platinum diselenide, hexagonal boron nitride / graphene / molybdenum ditelluride, hexagonal boron nitride / graphene / tungsten ditelluride, hexagonal boron nitride / graphene / vanadium diselenide, hexagonal boron nitride / graphene / chromium disulfide, hexagonal boron nitride / graphene / chromium diselenide, hexagonal boron nitride / graphene / MXene; the suspended two-dimensional material hetero-layer also includes graphene, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, platinum diselenide, molybdenum ditelluride, tungsten ditelluride, vanadium diselenide, chromium disulfide, chromium diselenide, transition metal dichalcogenide, black phosphorus, MXene, and a hetero-layer formed by vertical stacking of any two or more two-dimensional materials.

[0015] Further, the suspended two-dimensional material includes a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and thicker two-dimensional material films (0-100 nanometers); the suspended two-dimensional material hetero-layer includes two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and two-dimensional material films within 200 nanometers.

[0016] Further, the suspended two-dimensional material and two-dimensional material hetero-layer also includes a composite of the two-dimensional material and other types of nanosheets, including metals (such as gold, silver, copper, aluminum), metal oxides (such as aluminum trioxide), organic polymers (such as polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), poly(bisphenol A) carbonate (PC)), and silicon nitride, and a composite of the two-dimensional material and hetero-layer, such as aluminum trioxide / graphene, polymethyl methacrylate / graphene, polydimethylsiloxane / graphene, poly(bisphenol A) carbonate / graphene, silicon nitride / graphene, aluminum trioxide / graphene / molybdenum disulfide, polymethyl methacrylate / graphene / molybdenum disulfide, etc.

[0017] Further, the source of the two-dimensional material and two-dimensional material hetero-layer includes chemical vapor deposition synthesis, mechanical exfoliation, liquid phase exfoliation, epitaxial growth, reduction of oxidation. The source of the two-dimensional material and hetero-layer greater than a single atomic layer thickness includes direct growth synthesis (such as chemical vapor deposition, epitaxial growth), layer-by-layer stack transfer.

[0018] Further, the shape of the cavity covered by the suspended two-dimensional material and two-dimensional material hetero-layer includes a single sensitive structure, a single row of sensitive structures, and an array of sensitive structures. Each different structure is further subdivided by shape into a regular circle, a square, and a rectangle.

[0019] The patterning process of the suspended two-dimensional material and two-dimensional material hetero-layer includes optical lithography and electron beam lithography. The etching category of the suspended two-dimensional material and hetero-layer includes oxygen plasma etching, sulfur hexafluoride / argon plasma etching, and carbon tetrafluoride plasma etching.

[0020] The preparation of the suspended two-dimensional material and two-dimensional material hetero-layer includes wet transfer with polymethyl methacrylate as a supporting auxiliary layer, wet transfer with poly(bisphenol A) carbonate as a supporting auxiliary layer, dry transfer with polydimethylsiloxane as a supporting auxiliary layer, dry transfer with a heat-released adhesive tape as a supporting auxiliary layer, wet transfer based on electrochemical exfoliation technology, transfer based on water droplet exfoliation technology, wet transfer based on potassium hydroxide and sodium hydroxide solution exfoliation technology, and device bonding transfer method based on benzocyclobutene.

[0021] Further, the electrode includes a source electrode and a drain electrode, and a source electrode, a drain electrode, and a gate electrode. The electrode material includes gold, silver, copper, aluminum, titanium, and their composites.

[0022] Further, the type of the suspended two-dimensional material and two-dimensional material hetero-layer gas pressure sensor includes a piezoresistive gas pressure sensor, a capacitive gas pressure sensor, a piezoelectric gas pressure sensor, a resonant gas pressure sensor, a tunneling sensor, and an optical gas pressure sensor. The number of gas pressure sensors is at least one, such as a plurality of gas pressure sensors in series or parallel. The suspended two-dimensional material gas pressure sensor includes the integration of the suspended two-dimensional thin film nanoelectromechanical gas pressure sensor sensitive structure and the interface test circuit board, and also includes the integration of the suspended two-dimensional thin film nanoelectromechanical gas pressure sensor sensitive structure and high-performance interface circuit (such as ASIC or CMOS) integrated circuit.

[0023] Further, the gas pressure sensor based on the suspended two-dimensional material and two-dimensional material heterostructure can use oxidized silicon as a substrate, metal electrodes are deposited on the oxide layer of silicon, and two-dimensional material or two-dimensional material heterostructure is covered on the surface of the oxide layer of silicon by transfer. Then, the silicon layer cavity etching and the silicon dioxide sacrificial layer etching are performed from the back of the silicon substrate, and then the two-dimensional material is released to obtain the suspended two-dimensional film, and finally the device is sealed by bonding technology, and the manufacturing of the gas pressure sensor is finally completed.

[0024] The beneficial effects of the present application are:

[0025] 1. Compared with the traditional method, the transfer method of the two-dimensional film can effectively avoid the problems of wrinkles, folds, breakage, local damage and the like in the transfer process, further improve the flatness and integrity of the suspended two-dimensional film after transfer, thereby improving the quality of the suspended two-dimensional film and further improving the device yield and yield; at the same time, the suspended two-dimensional material preparation process of the present application is compatible with the large-scale semiconductor micro-nano processing technology, the preparation process is relatively simple and the yield is high, and it has the potential to realize the planning manufacturing;

[0026] 2. The suspended two-dimensional material that can be prepared not only includes graphene, but also includes other two-dimensional materials with a piezoresistive strain coefficient 1-3 orders of magnitude higher than graphene, such as molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, platinum diselenide and other transition metal dichalcogenides (TMDC), which will significantly improve the sensitivity, resolution and detection limit of the piezoresistive sensor;

[0027] 3. The gas pressure sensor of the present application has wide application, and due to its small size, high sensitivity, strong stability and wide application range, it can play a role in various fields such as military, commercial, civil and scientific exploration.

[0028] 4. The introduction of two-dimensional material heterostructure as a sensing layer, such as graphene / molybdenum disulfide, graphene / tungsten diselenide, graphene / molybdenum diselenide, graphene / tungsten disulfide, graphene / platinum diselenide, by taking advantage of the different advantages of different two-dimensional materials to overcome the defects of single two-dimensional material, for example, graphene has high mechanical strength but relatively low piezoresistive strain coefficient, while molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, platinum diselenide and other transition metal dichalcogenides have high piezoresistive strain coefficient but relatively low mechanical strength, so the two-dimensional material heterostructure such as graphene / molybdenum disulfide, graphene / tungsten diselenide, graphene / molybdenum diselenide, graphene / tungsten disulfide, graphene / platinum diselenide will have high mechanical strength and high piezoresistive strain coefficient, and finally significantly improve the sensitivity, resolution, detection limit and yield of the piezoresistive sensor. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1The pressure sensor with a single cavity structure is shown in the following diagrams from top to bottom: a circular structure, a horizontal rectangular structure, a vertical rectangular structure, and a square rectangular structure.

[0030] Figure 2 The pressure sensor with an array cavity structure is shown in the following diagrams from top to bottom: a circular structure, a horizontal rectangular structure, a vertical rectangular structure, and a square rectangular structure.

[0031] Figure 3 This is a process flow diagram illustrating the preparation method of a suspended two-dimensional material according to the present invention and its application in nano-electromechanical sensors.

[0032] Figure 4 This is a flowchart of the transfer and stacking process of two-dimensional materials (taking graphene as an example).

[0033] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0034] Reference Figure 1 and Figure 2 The present invention discloses a method for preparing a suspended two-dimensional material thin film and its application in a nano-electro-electric pressure sensor. The suspended two-dimensional material and the two-dimensional material heterolayer are used as sensitive films. The suspended two-dimensional material and the two-dimensional material heterolayer cover a cavity based on silicon oxide. Electrodes are connected to the suspended two-dimensional material and the two-dimensional material heterolayer. When the external air pressure changes (e.g., the air pressure decreases), the suspended two-dimensional material and the two-dimensional material heterolayer undergo corresponding deformation (e.g., deformation in the opposite direction to the cavity). According to the piezoresistive effect of two-dimensional materials, the resistance of the suspended two-dimensional material and the suspended two-dimensional material heterolayer changes. Detecting this change allows for the detection of changes in external air pressure.

[0035] Furthermore, the suspended two-dimensional material includes graphene, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS2), tungsten diselenide (WSe2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), platinum diselenide (PtSe2), molybdenum distelluride (MoTe2), tungsten distelluride (WTe2), vanadium diselenide (VSe2), chromium disulfide (CrS2), chromium diselenide (CrSe2), other transition metal dichalcogenides (TMDC), black phosphorus (P), and MXene.

[0036] Further, the suspended two-dimensional material hetero-layer includes hexagonal boron nitride / graphene, hexagonal boron nitride / molybdenum disulfide, hexagonal boron nitride / tungsten diselenide, hexagonal boron nitride / molybdenum diselenide, hexagonal boron nitride / tungsten disulfide, hexagonal boron nitride / platinum diselenide, hexagonal boron nitride / molybdenum ditelluride, hexagonal boron nitride / tungsten ditelluride, hexagonal boron nitride / vanadium diselenide, hexagonal boron nitride / chromium disulfide, hexagonal boron nitride / chromium diselenide, hexagonal boron nitride / MXene, graphene / molybdenum disulfide, graphene / tungsten diselenide, graphene / molybdenum diselenide, graphene / tungsten disulfide, graphene / platinum diselenide, graphene / molybdenum ditelluride, graphene / tungsten ditelluride, graphene / vanadium diselenide, graphene / chromium disulfide, graphene / chromium diselenide, graphene / MXene, hexagonal boron nitride / graphene / molybdenum disulfide, hexagonal boron nitride / graphene / tungsten diselenide, hexagonal boron nitride / graphene / molybdenum diselenide, hexagonal boron nitride / graphene / tungsten disulfide, hexagonal boron nitride / graphene / platinum diselenide, hexagonal boron nitride / graphene / molybdenum ditelluride, hexagonal boron nitride / graphene / tungsten ditelluride, hexagonal boron nitride / graphene / vanadium diselenide, hexagonal boron nitride / graphene / chromium disulfide, hexagonal boron nitride / graphene / chromium diselenide, hexagonal boron nitride / graphene / MXene; the suspended two-dimensional material hetero-layer also includes graphene, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, platinum diselenide, molybdenum ditelluride, tungsten ditelluride, vanadium diselenide, chromium disulfide, chromium diselenide, transition metal dichalcogenide, black phosphorus, MXene, and a hetero-layer formed by vertical stacking of any two or more two-dimensional materials.

[0037] Further, the suspended two-dimensional material includes a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and thicker two-dimensional material films (0-100 nanometers); the suspended two-dimensional material hetero-layer includes two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and two-dimensional material films within 200 nanometers.

[0038] Further, the suspended two-dimensional material hetero-layer also includes a composite of two-dimensional materials and other types of nanosheets, including metals (such as gold, silver, copper, aluminum), metal oxides (such as aluminum trioxide), organic polymers (such as polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), poly(bisphenol A) carbonate (PC)), and silicon nitride, and a composite of two-dimensional materials and hetero-layers, such as aluminum trioxide / graphene, polymethyl methacrylate / graphene, polydimethylsiloxane / graphene, poly(bisphenol A) carbonate / graphene, silicon nitride / graphene, aluminum trioxide / graphene / molybdenum disulfide, polymethyl methacrylate / graphene / molybdenum disulfide, etc.

[0039] Further, the source of the two-dimensional material and hetero-layer includes chemical vapor deposition synthesis, mechanical exfoliation, liquid phase exfoliation, epitaxial growth, reduction oxidation. The source of the two-dimensional material and hetero-layer greater than a single atomic layer thickness includes direct growth synthesis (such as chemical vapor deposition, epitaxial growth), layer-by-layer stack transfer.

[0040] Further, the shape of the cavity covered by the suspended two-dimensional material and two-dimensional material hetero-layer includes a single sensitive structure, a single row of sensitive structures, and an array of sensitive structures; each different structure is further subdivided by shape into a regular circle, a square, and a rectangle.

[0041] The patterning process of the suspended two-dimensional material and two-dimensional material hetero-layer includes optical lithography and electron beam lithography. The etching of the suspended two-dimensional material and hetero-layer includes oxygen plasma etching, sulfur hexafluoride / argon plasma etching, and carbon tetrafluoride plasma etching.

[0042] The preparation of the suspended two-dimensional material and two-dimensional material hetero-layer includes wet transfer with polymethyl methacrylate as a supporting auxiliary layer, wet transfer with poly(bisphenol A) carbonate as a supporting auxiliary layer, dry transfer with polydimethylsiloxane as a supporting auxiliary layer, dry transfer with a heat-releasing adhesive tape as a supporting auxiliary layer, wet transfer based on electrochemical exfoliation technology, transfer based on water droplet exfoliation technology, wet transfer based on potassium hydroxide and sodium hydroxide solution exfoliation technology, and device bonding transfer method based on benzocyclobutene.

[0043] Further, the electrode includes a source electrode and a drain electrode, or a source electrode, a drain electrode, and a gate electrode; the electrode material includes gold, silver, copper, aluminum, titanium, and their composites.

[0044] Further, the type of the suspended two-dimensional material and two-dimensional material hetero-layer gas pressure sensor includes piezoresistive gas pressure sensor, capacitive gas pressure sensor, piezoelectric gas pressure sensor, resonant gas pressure sensor, and optical gas pressure sensor; the number can include one and several or more, such as several gas pressure sensors in series or parallel; the suspended two-dimensional material gas pressure sensor can be integrated with traditional CMOS integrated circuit, and can also be applied to resonators and gyroscopes.

[0045] Further, the suspended two-dimensional material and two-dimensional material hetero-layer gas pressure sensor can use oxidized silicon as a substrate, metal electrodes are deposited on the silicon oxide layer, and the suspended two-dimensional material and two-dimensional material hetero-layer is covered on the surface of the oxidized silicon substrate by transfer. Then, the silicon layer cavity etching and the silicon dioxide sacrificial layer etching are performed from the back of the silicon substrate, and then the two-dimensional material is released to obtain a suspended two-dimensional film. Finally, the device is sealed by bonding to complete the manufacture of the gas pressure sensor.

[0046] Specifically, the step embodiment can be implemented as follows:

[0047] 1. Refer to steps 1 and 2 in Figure 3 , suspend the two-dimensional material on a silicon substrate with an oxide layer on the surface, the thickness of the silicon layer is 100 microns to 1000 microns, and the thickness of the silicon oxide layer obtained by oxidizing the silicon is 0.2 microns to 2 microns. Spin the photoresist on the surface of the silicon oxide layer, and after the photoetching and developing process, a patterned photoresist can be obtained, thereby defining the position of the metal electrode. The silicon oxide layer is etched by a reactive ion beam etching process to obtain a 300 nm deep trench, and 50 nm thick titanium and 270 nm thick gold are deposited in the 300 nm deep silicon oxide layer trench by thermal evaporation or magnetron sputtering, respectively. After removing the photoresist by metal stripping technology, a titanium / gold electrode is obtained, the upper surface of the electrode is about 20 nm higher than the surface of the silicon oxide layer, and the basic structure of the pre-processed silicon substrate device (hereinafter referred to as the pre-processed silicon structure) is completed.

[0048] 2. Transfer and patterning of two-dimensional material and heterostructure: refer to Figure 4, two-dimensional materials and heterostructures are transferred to pre-processed silicon oxide surfaces by a wet transfer method based on polymethyl methacrylate (hereinafter referred to as PMMA) as a supporting transfer layer. Specifically, high-quality commercial chemical vapor deposition method is selected to synthesize two-dimensional materials such as graphene, hexagonal boron nitride (hereinafter referred to as hBN), molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, platinum diselenide, etc. Take the transfer of hBN / graphene as an example to illustrate the integration of two-dimensional materials and two-dimensional material heterostructures with pre-processed silicon structures. PMMA is spin-coated on the surface of hBN / copper (for example, 500 rpm for 5 seconds, and then 2000 rpm for 30 seconds), and then placed on a hot plate for baking for 5-10 minutes, with the hot plate temperature being 60-100 degrees Celsius, to obtain a PMMA thickness of about 200 nanometers. The hBN residue on the back of the copper growth substrate can be removed by low-power (for example, 50 watts) oxygen plasma etching, and the PMMA / hBN / copper is placed on the surface of a ferric chloride solution (for example, for 2 hours) to dissolve the copper growth substrate. The obtained PMMA / hBN is placed on the surface of dilute hydrochloric acid and deionized water in sequence with a clean silicon wafer as a transfer support layer to remove residual iron ions and chloride ions. The PMMA / hBN suspended on the surface of deionized water is transferred to the surface of a commercial chemical vapor deposition graphene / copper with a clean silicon wafer as a transfer support layer, and then placed on a hot plate (for example, 45 degrees, 10 minutes) to increase the intermolecular force between hBN and graphene. Oxygen plasma is used to remove the residual graphene on the back of the copper. Then, the same method as before is used to remove the copper growth substrate to obtain a PMMA / hBN / graphene stack, and then the PMMA / hBN / graphene is transferred to the surface of a pre-processed silicon structure with the help of a clean silicon wafer as a transfer support layer, and then placed on a hot plate at 45 degrees for 10 minutes to increase the intermolecular force between graphene and the silicon dioxide surface. After that, the silicon on the insulating substrate covered with PMMA / hBN / graphene is placed in an acetone solution for a long enough time (for example, 24 hours) to remove the PMMA. Then the pre-processed silicon structure covered with hBN / graphene is placed in an ethanol or isopropanol solution to remove residual acetone, and then placed in the air to dry naturally. Next, the transferred hBN / graphene is patterned to obtain two-dimensional materials and heterostructures of the target shape and size, for example, by spin-coating a layer of photoresist on the surface of hBN / graphene, using optical lithography or electron beam lithography and development methods to pattern the photoresist on the surface of the hBN / graphene heterostructure, and then using sulfur hexafluoride (SF6) / argon (Ar) mixed plasma to etch hexagonal boron nitride at low power, using oxygen plasma to etch graphene at low power, and finally placing the etched two-dimensional material heterostructure device in acetone to remove residual photoresist, placing it in an ethanol or isopropanol solution to remove residual acetone, and finally drying it naturally in the air.

[0049] In addition to the above-mentioned wet transfer of PMMA as a supporting auxiliary layer, the preparation of suspended two-dimensional materials and two-dimensional material heterostructures can also be achieved by the following methods: wet transfer with poly(bisphenol A) carbonate as a supporting auxiliary layer, dry transfer with polydimethylsiloxane as a supporting auxiliary layer, dry transfer with a heat-released adhesive tape as a supporting auxiliary layer, wet transfer based on electrochemical exfoliation technology, transfer based on water droplet exfoliation technology, wet transfer based on potassium hydroxide and sodium hydroxide solution exfoliation technology, device bonding transfer method based on benzocyclobutene, etc.

[0050] 3. The method of claim 1 or 2, wherein the two-dimensional material is graphene. Figure 3 As shown in step 4, a new photoresist is spin-coated on the back side of the silicon (the side opposite to the side where the electrode and the two-dimensional material and heterostructure are located, the same below), and the photoresist is patterned through photolithography, development, etc., to define a cavity on the back side of the device. The shape of the cavity can be a single large circle, square, or rectangle, etc. The area of the above-mentioned three single patterns can be as low as 1 square micrometer or as high as 10,000 square micrometers. It can also be a smaller circular, square, or rectangular polygon arranged in an array. Reactive ion beam is used to etch the backside silicon oxide layer, and deep reactive ion beam is used to etch the silicon layer at the same position until the silicon oxide layer with a metal electrode deposited on the surface is etched. Oxygen plasma is used to remove the remaining backside photoresist. Next, gaseous hydrofluoric acid (HF) is used to etch the silicon oxide layer with a metal electrode deposited on the surface at the same position. After the silicon oxide layer is completely etched, the two-dimensional material and two-dimensional material heterostructure are released and suspended. At this point, the main structure of the gas pressure sensor has been prepared. According to actual application requirements, the silicon wafer can be cut into chips of different sizes, or it can be kept as a complete wafer.

[0051] 4. Bonding sealing and integration with test circuit: after the cavity etching of the sensitive unit is completed, bonding can be performed. The process flow is to bond the silicon substrate from the back side to the entire device, ensuring that the cavity below the two-dimensional material is sealed, so that the gas pressure in the cavity remains constant at a certain temperature. At the same time, the two-dimensional material gas pressure sensor sensitive structure can be integrated and packaged with high-performance signal reading and test circuit (such as ASIC, CMOS circuit), further reducing the overall size of the device and reducing the noise signal of the device.

[0052] The foregoing merely illustrates the principles of the application and application of its leading features. This application is not limited to the embodiments described herein but is capable of being practiced with the scope of the claims as defined below. It will be readily apparent to those skilled in the art that certain changes and modifications can be made thereto without departing from the scope of the present application. The scope of the present application is indicated only by the claims. Any references to claims in the following description are to be construed as being qualified by their respective applications and submission dates, and are for illustrative purposes only. It is therefore intended that what is claimed be what the inventors are legally entitled to. Any statements since added, deleted, modified, or adapted, after the time of filing, will apply only to the applicable design or plant patent applications, and not to the utility patent applications, if any.

[0053] Furthermore, it should be understood that although the description above relates to embodiments, not every embodiment according to this description contains all features and embodiments according to the description can cover multiple specific embodiments. The description is provided as an enabling teaching of the application and it is understood that various changes in form and details can be made without departing from the spirit, nature, or aspects of the application. The application is defined by the claims.

Claims

1. A method for producing a suspended two-dimensional film, characterized by, The method for preparing the suspended two-dimensional thin film is as follows: using oxidized silicon as a substrate, after preparing electrodes on the front side of the silicon substrate, the two-dimensional material and the two-dimensional material heterolayer are first integrated with the unetched silicon substrate to improve the quality of the transferred two-dimensional material and the two-dimensional material heterolayer. Then, the two-dimensional material and the two-dimensional material heterolayer are patterned and etched to ensure the yield of the transferred two-dimensional material and the two-dimensional material heterolayer. Then, the silicon substrate under the two-dimensional material and the two-dimensional material heterolayer is etched using sacrificial layer etching technology to form a cavity, thereby releasing the two-dimensional material and the two-dimensional material heterolayer, and obtaining a high-quality and high-yield suspended sealed two-dimensional thin film.

2. The method of claim 1, wherein the method further comprises the step of: The required two-dimensional materials include graphene, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, platinum diselenide, molybdenum diselenide, tungsten diselenide, vanadium diselenide, chromium disulfide, chromium diselenide, transition metal dichalcogenides, black phosphorus, and MXene; the two-dimensional material heterolayer includes hexagonal boron nitride / graphene, hexagonal boron nitride / molybdenum disulfide, hexagonal boron nitride / tungsten diselenide, hexagonal boron nitride / molybdenum diselenide, hexagonal boron nitride / tungsten disulfide, and hexagonal... Boron nitride / platinum diselenide, hexagonal boron nitride / molybdenum distelluride, hexagonal boron nitride / tungsten distelluride, hexagonal boron nitride / vanadium diselenide, hexagonal boron nitride / chromium disulfide, hexagonal boron nitride / chromium diselenide, hexagonal boron nitride / MXene, graphene / molybdenum disulfide, graphene / tungsten diselenide, graphene / molybdenum diselenide, graphene / tungsten disulfide, graphene / platinum diselenide, graphene / molybdenum distelluride, graphene / tungsten distelluride, graphene / vanadium diselenide, graphene / disulfide Chromium nitride, graphene / chromium diselenide, graphene / MXene, hexagonal boron nitride / graphene / molybdenum disulfide, hexagonal boron nitride / graphene / tungsten diselenide, hexagonal boron nitride / graphene / molybdenum diselenide, hexagonal boron nitride / graphene / tungsten disulfide, hexagonal boron nitride / graphene / platinum diselenide, hexagonal boron nitride / graphene / molybdenum ditelluride, hexagonal boron nitride / graphene / tungsten ditelluride, hexagonal boron nitride / graphene / vanadium diselenide, hexagonal boron nitride / graphene / disulfide The heterolayer of the two-dimensional material includes chromium nitride, hexagonal boron nitride / graphene / chromium diselenide, hexagonal boron nitride / graphene / MXene; the heterolayer of the two-dimensional material also includes a heterolayer composed of any two or more two-dimensional materials selected from graphene, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten diselenide, platinum diselenide, molybdenum distelluride, tungsten distelluride, vanadium diselenide, chromium disulfide, chromium diselenide, transition metal dichalcogenides, black phosphorus, and MXene arranged in a vertical stacking arrangement. The number of layers in the two-dimensional material includes a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and thicker two-dimensional material films; the two-dimensional material heterolayer includes two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers, and two-dimensional material films within 200 nanometers; The source of the two-dimensional material and two-dimensional material hetero-layer includes chemical vapor deposition synthesis, mechanical exfoliation, liquid phase exfoliation, epitaxial growth, and reduction of oxidation; the source of the two-dimensional material and hetero-layer greater than a single atomic layer thickness includes direct growth synthesis, layer-by-layer stack transfer.

3. The method of claim 1, wherein the method further comprises the step of: The two-dimensional thin film prepared by the preparation method of the suspended two-dimensional thin film is used as a sensitive thin film of a nano-electromechanical gas pressure sensor.

4. The nanoelectromechanical gas pressure sensor of claim 3, wherein The shape of the nano-electromechanical gas pressure sensor cavity includes a single circle, a single square, a single transverse rectangle, a single longitudinal rectangle, a single row of circles, a single row of squares, a single row of transverse rectangles, a single row of longitudinal rectangles, an array of circles, an array of squares, an array of transverse rectangles, and an array of longitudinal rectangles. The working principle type of the nano-electromechanical gas pressure sensor includes a piezoresistive sensor, a capacitive sensor, a piezoelectric sensor, a resonant sensor, a tunneling sensor, and an optical sensor. The number is at least one. The structure includes a single sensor functional structure or a plurality of sensor functional structures in series or parallel. The nano-electromechanical gas pressure sensor includes integration of a suspended two-dimensional thin film nano-electromechanical gas pressure sensor sensitive structure and an interface test circuit board, and also includes integration of a suspended two-dimensional thin film nano-electromechanical gas pressure sensor sensitive structure and a high-performance interface circuit. The electrode of the nano-electromechanical gas pressure sensor includes a source electrode and a drain electrode, and a source electrode, a drain electrode, and a gate electrode; the electrode material includes gold, silver, copper, aluminum, titanium, and a composite thereof.

5. The nanoelectromechanical gas pressure sensor of claim 3, wherein: After the preparation of the electrode is completed, the two-dimensional material is first transferred to the surface of the device to ensure its flatness and integrity, then etching is performed from the back to release the two-dimensional material, to obtain a suspended two-dimensional thin film, and finally the device preparation is completed.

6. The nanoelectromechanical gas pressure sensor of claim 3, wherein: The two-dimensional material and two-dimensional material hetero-layer also include a composite of a nanometer thin layer of the two-dimensional material and a metal, a metal oxide, an organic polymer, polymethyl methacrylate, polycarbonate, and silicon nitride.

Images