Method for enhancing air tightness of two-dimensional material suspension film on cavity

Abstract

The invention discloses a method for enhancing the air tightness of a two-dimensional material suspension film on a cavity, and belongs to the technical field of air pressure sensor preparation. The method for enhancing the air tightness of the two-dimensional material suspension film on the cavity comprises the following steps: depositing a contact material layer on a substrate with the cavity and an electrode material, then transferring a suspension two-dimensional material film to the contact material layer, and then depositing a sealing layer on the side surfaces of the contact material layer and the suspension two-dimensional material film to obtain the micro differential pressure sensor. According to the method, the gas leakage rate can be reduced, and the stability, sensitivity, resolution and other performance of the micro differential pressure sensor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of pressure sensors, and particularly to a method for enhancing the airtightness of a two-dimensional material suspension film on a cavity. Background Art

[0002] Microelectromechanical system (MEMS) pressure sensors have multiple advantages, including easy mass production, miniaturization, cost-effectiveness, and the ability to easily manufacture complex structures. Novel pressure sensing elements using innovative technologies and packaging methods can provide higher measurement accuracy, size, and a wider temperature adaptability. In addition, integrating two-dimensional materials such as third-generation semiconductor materials and graphene into pressure sensors significantly improves their performance.

[0003] The pressure difference on the diaphragm of a micro differential pressure sensor (MDPS) is usually very small. With the development of medical devices, the demand for MDPS with excellent measurement resolution, small size, and low cost is increasing continuously. Compared with other piezoresistive sensors, manufacturing MDPS faces greater challenges, especially in preparing pressure diaphragms with high sensitivity, ultrathin, and low residual stress.

[0004] When two-dimensional materials such as graphene are transferred onto a cavity as a sensitive film to form a chamber with an internal and external pressure difference, gas leakage from an unknown source will be observed in the absence of defects or pores. This inherent gas leakage hinders the application of two-dimensional material films in ultra-sensitive pressure sensors because these sensors require a sealed chamber containing a fixed gas pressure.

[0005] The existing method for preparing a two-dimensional material suspension film on a silicon-based cavity is the van der Waals pick-up transfer method. The airtightness of this transfer method completely depends on the van der Waals binding force between the two-dimensional material and the substrate. In the actual manufacturing process, factors such as the surface roughness of the substrate, the particle size of the polymer (a particle size greater than 20 nm will reduce the van der Waals binding force between the two), adsorbed water vapor, and tearing of the two-dimensional material will all reduce the van der Waals binding force between the two. Therefore, the two-dimensional material suspension film that completely depends on the van der Waals force has a high sealing failure rate and is greatly affected by environmental factors, which will directly affect the sensitivity performance of the prepared micro differential pressure sensor. And how to improve the preparation success rate of the micro differential pressure sensor and enhance its sensitivity and stability has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for enhancing the airtightness of a two-dimensional material suspension film on a cavity to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, the present invention provides the following solution:

[0008] One of the technical solutions of the present invention: A micro differential pressure sensor, comprising a substrate with a cavity and electrode material, a contact material layer, and a suspended two-dimensional material film arranged from bottom to top, and a sealing layer arranged on the sides of the contact material layer and the suspended two-dimensional material film;

[0009] The cavity of the micro differential pressure sensor penetrates the contact material layer.

[0010] Furthermore, the number of the cavities is 1 to 20.

[0011] Multiple cavities can be connected in parallel to form an array structure, and higher sensitivity and resolution can be obtained.

[0012] In the technical solution of the present invention, the material of the contact material layer is titanium nitride (TiN), titanium dioxide (TiO2), gold-platinum alloy (Au-Pt), gold-silver alloy (Au-Ag), gold-molybdenum alloy (Au-Mo), silver nanoparticles (Ag NPs) or copper nanoparticles (Cu NPs).

[0013] In the technical solution of the present invention, the material of the suspended two-dimensional material film includes two-dimensional materials or two-dimensional material heterojunctions.

[0014] Further, the two-dimensional materials include graphene, molybdenum disulfide (MoS2), tungsten diselenide (WSe2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), tungsten diselenide (WSe2), platinum diselenide (PtSe2) or black phosphorus (BP).

[0015] Further, the two-dimensional material heterojunctions include graphene and molybdenum disulfide heterojunctions or graphene and black phosphorus (BP) heterojunctions.

[0016] In the technical solution of the present invention, the material of the sealing layer includes organic polymers, ceramic precursors or siloxane-organic hybrid materials.

[0017] Further, the organic polymers include polyimide (PI), epoxy resin (EP), polyurethane (PU) or polyethylene terephthalate (PET);

[0018] The ceramic precursors include alumina or silicon nitride.

[0019] The second technical solution of the present invention: A preparation method of the above-mentioned micro differential pressure sensor, comprising the following steps:

[0020] Deposit a contact material layer on a substrate with a cavity and electrode material, then transfer the suspended two-dimensional material film onto the contact material layer, and then deposit a sealing layer on the sides of the contact material layer and the suspended two-dimensional material film to obtain the micro differential pressure sensor.

[0021] In the technical solution of the present invention, the method for depositing the contact material layer includes sputtering or spin coating after lithography;

[0022] The method for transferring the suspended two-dimensional material thin film onto the contact material layer includes the van der Waals pick-up transfer method, the PDMS stamp transfer method, or the dry transfer method;

[0023] The method for depositing the sealing layer includes inkjet printing.

[0024] Furthermore, the process parameters of the sputtering include: the working gas is a mixed gas of argon and nitrogen, the flow rate of argon is 10 - 50 sccm, the flow rate ratio of nitrogen to argon is (0.3 - 0.8):1, and the sputtering power is 100 - 300 W.

[0025] Furthermore, the process parameters of the inkjet printing include: the printing resolution is 100 - 500 dpi, the printing speed is 0.5 - 10 mm / s, and the number of printing layers is 2 - 10 layers.

[0026] The third technical solution of the present invention: A method for enhancing the airtightness of a two-dimensional material suspension film on a cavity, comprising the following steps:

[0027] Deposit a contact material layer on a substrate with a cavity and electrode material, then transfer the suspended two-dimensional material thin film onto the contact material layer, and then deposit a sealing layer on the side of the contact material layer and the suspended two-dimensional material thin film to obtain the micro differential pressure sensor.

[0028] In the technical solution of the present invention, the method for depositing the contact material layer includes sputtering or spin coating after lithography;

[0029] The method for transferring the suspended two-dimensional material thin film onto the contact material layer includes the van der Waals pick-up transfer method, the PDMS stamp transfer method, or the dry transfer method;

[0030] The method for depositing the sealing layer includes inkjet printing.

[0031] Furthermore, the process parameters of the sputtering include: the working gas is a mixed gas of argon and nitrogen, the flow rate of argon is 10 - 50 sccm, the flow rate ratio of nitrogen to argon is (0.3 - 0.8):1, and the sputtering power is 100 - 300 W.

[0032] Furthermore, the process parameters of the inkjet printing include: the printing resolution is 100 - 500 dpi, the printing speed is 0.5 - 10 mm / s, and the number of printing layers is 2 - 10 layers.

[0033] In the technical solution of the present invention, the material of the contact material layer includes titanium nitride (TiN), titanium dioxide (TiO2), gold-platinum alloy (Au-Pt), gold-silver alloy (Au-Ag), gold-molybdenum alloy (Au-Mo), silver nanoparticles (Ag NPs) or copper nanoparticles (Cu NPs).

[0034] In the technical solution of the present invention, the material of the suspended two-dimensional material film includes two-dimensional materials or two-dimensional material heterojunctions.

[0035] Further, the two-dimensional materials include graphene, molybdenum disulfide (MoS2), tungsten diselenide (WSe2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), tungsten diselenide (WSe2), platinum diselenide (PtSe2) or black phosphorus (BP).

[0036] The two-dimensional material heterojunction includes a graphene and molybdenum disulfide heterojunction or a graphene and black phosphorus (BP) heterojunction.

[0037] When the material of the contact material layer is TiN and the material of the suspended two-dimensional material film is graphene, a stronger chemical bonding (Ti-O-C bond) can be formed between TiN and graphene, which can improve the bonding force between graphene and the substrate while ensuring conductivity, and reduce the gas leakage rate of the cavity.

[0038] In the technical solution of the present invention, the material of the sealing layer includes organic polymers, ceramic precursors or silicone-organic hybrid materials.

[0039] Further, the organic polymers include polyimide (PI), epoxy resin (EP), polyurethane (PU) or polyethylene terephthalate (PET);

[0040] The ceramic precursors include alumina or silicon nitride.

[0041] Using organic polymers, ceramic precursors, etc. as the sealing layer at the edge of the atomically thin suspended two-dimensional material film is compatible with semiconductor microfabrication processes (the process of depositing the sealing layer), which changes the problem of relying solely on van der Waals forces as the single sealing force in the traditional method, reduces the leakage rate of gas permeating into the cavity along the two-dimensional material-substrate interface, and improves the success rate of fabricating the sensor.

[0042] The suspended two-dimensional material film is used as a barometric pressure sensitive material. When the external pressure is different from the pressure inside the cavity, the suspended two-dimensional material film will be stressed and thus shift up and down, detecting the change in resistance and calculating the magnitude of the external air pressure; multiple cavities can be connected in parallel to form an array structure, which can obtain higher sensitivity and resolution.

[0043] The present invention discloses the following technical effects:

[0044] (1) The gas leakage rate of the micro differential pressure sensor of the present invention is low, and the stability of the measured air pressure is good. The application field can be broadened to micro pressure detection fields such as human body posture and blowing detection.

[0045] (2) The method of the present invention reduces the influence of factors such as impurities on the substrate surface and tearing of two-dimensional materials during the actual manufacturing process on the sealing performance, improves the preparation success rate of the micro differential pressure sensor, and enhances the sensitivity and stability of the micro differential pressure sensor.

[0046] (3) Based on the preparation of suspended two-dimensional material films by the van der Waals pickup transfer method, the PDMS stamp transfer method or the dry transfer method, the present invention adds a contact material layer and a sealing layer, changing the problem that the cavity sealing performance completely depends on the van der Waals force between the two-dimensional material and the substrate before. The contact material layer forms a stronger chemical bond with the two-dimensional material on the premise of ensuring conductivity. Using the inkjet printing process to prepare the sealing layer increases the physical sealing force, reduces the influence of factors such as impurities on the substrate surface and tearing of two-dimensional materials during the actual manufacturing process on the sealing performance, increases the preparation success rate of the micro differential pressure sensor, and improves the performance of the sensor such as stability, sensitivity, and resolution. Description of the Drawings

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0048] Figure 1 It is a schematic flow chart of the method for enhancing the airtightness of the two-dimensional material suspension film on the silicon-based cavity;

[0049] Figure 2 It is a schematic structural diagram of the silicon-based cavity;

[0050] Figure 3 It is the output curve of the sensor before sealing in Comparative Example 1;

[0051] Figure 4 It is the output curve of the sensor after sealing in Example 1;

[0052] Figure 5 It is the output curve of the sensor after sealing in Example 2;

[0053] Figure 6 It is the output curve of the sensor prepared in Comparative Example 2;

[0054] Figure 7 It is the sensitivity curve of the sensor after sealing in Example 1;

[0055] Figure 8 The stepped pressure stability curve of the sensor after sealing in Example 1. Specific embodiments

[0056] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0057] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0058] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0059] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and embodiments of the present invention are merely exemplary.

[0060] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0061] In a first aspect of the present invention, a micro differential pressure sensor is provided, including a substrate with a cavity and electrode material, a contact material layer, and a suspended two-dimensional material film arranged from bottom to top, and a sealing layer arranged on the sides of the contact material layer and the suspended two-dimensional material film;

[0062] The cavity of the micro differential pressure sensor penetrates the contact material layer.

[0063] In the specific embodiments of the present invention, the number of cavities is 1 to 20.

[0064] In a second aspect of the present invention, a method for preparing a micro differential pressure sensor is provided, comprising the following steps:

[0065] (1) After cleaning a substrate with a cavity and electrode material using an organic solvent (such as acetone, isopropyl alcohol, etc.), plasma etching is carried out to remove organic contaminants and oxide layers on the surface, exposing a fresh surface, and a substrate with a cavity and electrode material without contamination is obtained.

[0066] (2) A developed patterned photoresist is fabricated on the substrate with a cavity and electrode material without contamination using a photolithography process. Then, a contact material is deposited on the surface of the substrate on the side with the electrode material by sputtering (not deposited between the cavity and the electrode material). Then, the remaining photoresist is removed using acetone, and a contact material layer is formed by retaining the contact material pattern or a contact material layer is prepared by spin coating.

[0067] The contact material layer can improve the conductivity of the sensor and the bonding force between the contact material layer and the two-dimensional material.

[0068] In a specific embodiment of the present invention, the process parameters of the sputtering method include: the working gas is a mixed gas of argon and nitrogen, the flow rate of argon is 10 - 50 sccm, the flow rate ratio of nitrogen to argon is (0.3 - 0.8):1, and the sputtering power is 100 - 300 W.

[0069] In a specific embodiment of the present invention, the contact material is titanium nitride (TiN), titanium dioxide (TiO2), gold-platinum alloy (the mass ratio of Au and Pt is 7:3), gold-silver alloy (the mass ratio of Au and Ag is 6:4), gold-molybdenum alloy (the mass ratio of Au and Mo is 90:10), silver nanoparticles (Ag NPs, 25 ± 5 nm), or copper nanoparticles (Cu NPs, 15 ± 3 nm).

[0070] (3) A suspended two-dimensional material thin film is transferred onto the contact material layer by using the van der Waals pick-up transfer method, the PDMS stamp transfer method, or the dry transfer method.

[0071] In a specific embodiment of the present invention, the material of the suspended two-dimensional material thin film includes two-dimensional materials or two-dimensional material heterojunctions.

[0072] In a specific embodiment of the present invention, the two-dimensional materials include graphene, molybdenum disulfide (MoS2), tungsten diselenide (WSe2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), tungsten diselenide (WSe2), platinum diselenide (PtSe2), or black phosphorus (BP);

[0073] In a specific embodiment of the present invention, the two-dimensional material heterojunctions include graphene and molybdenum disulfide heterojunctions or graphene and black phosphorus (BP) heterojunctions.

[0074] Preparation of Graphene and Molybdenum Disulfide Heterojunction: Take monolayer graphene and molybdenum disulfide films grown by CVD, with a thickness of 1 nm. Use lithography and plasma for patterning, and form a heterojunction by van der Waals picking method;

[0075] Preparation of Graphene and Black Phosphorus (BP) Heterojunction: Use monolayer graphene grown by CVD (thickness 6 nm), and use mechanically exfoliated thin black phosphorus flakes for the black phosphorus. Perform site-specific assembly by van der Waals picking method to form a heterojunction.

[0076] (4) Dissolve the material of the sealing layer in a solvent to obtain a material solution with a viscosity between 1 and 10 cP and a surface tension between 20 and 40 mN / m.

[0077] In the specific embodiment of the present invention, the material of the sealing layer includes an organic polymer, a ceramic precursor, or a silicone-organic hybrid material.

[0078] In the specific embodiment of the present invention, the organic polymer includes polyimide (PI, Mn≈30000), epoxy resin (EP, Mn≈1200), polyurethane (PU, Mn≈50000), or polyethylene terephthalate (PET, Mn≈26000);

[0079] In the specific embodiment of the present invention, the ceramic precursor includes alumina or silicon nitride.

[0080] (5) Import the designed continuous linear structure CAD drawing into an inkjet printer, set the printing resolution to 100 - 500 dpi to ensure the continuity and fineness of the lines; set the printing speed to 0.5 - 10 mm / s to ensure the uniform deposition of the material solution. Perform inkjet printing, and deposit the material of the sealing layer layer by layer on the side of the contact material layer and the suspended two-dimensional material film to form a continuous linear structure, with the number of layers being 2 - 10 layers, to obtain a micro differential pressure sensor.

[0081] In the third aspect of the present invention, a method for enhancing the airtightness of a two-dimensional material suspension film on a cavity is provided, and the method is the same as the preparation method of the micro differential pressure sensor.

[0082] Comparative Example 1

[0083] A method for enhancing the airtightness of a two-dimensional material suspension film on a silicon-based cavity (i.e., the preparation method of the micro differential pressure sensor):

[0084] (1) The substrate with a silicon-based cavity and electrode material is ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes in sequence, and then treated with O2 plasma for 10 minutes (power is 80 W, gas pressure is 20 Pa) to remove the organic pollutants and oxide layer on the surface, exposing the fresh metal surface, and obtaining a pollution-free substrate with a silicon-based cavity and electrode material.

[0085] Among them, the electrode material is an Au electrode (the thickness of the Au electrode is 20 nm).

[0086] The substrate is divided into three layers. The bottom layer is SiO2 with a thickness of 300 nm, the middle layer is Si with a thickness of 500 μm, and the upper layer is SiO2 with a thickness of 300 nm.

[0087] The depth of the silicon-based cavity is 250 μm.

[0088] (2) Using the van der Waals pick-up transfer method, transfer the suspended two-dimensional material thin film (graphene thin film, single layer, thickness is 0.4 nm, sheet resistance is 400 ± 50 Ω / sq) onto the substrate with electrodes and a silicon-based cavity under the conditions of a temperature of 120 °C and a pressure of 0.3 MPa to obtain a micro differential pressure sensor (sensor before sealing).

[0089] Example 1

[0090] A method for enhancing the airtightness of a two-dimensional material suspension film on a silicon-based cavity (i.e., a method for preparing a micro differential pressure sensor):

[0091] (1) The substrate with a silicon-based cavity and electrode material is ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes in sequence, and then treated with O2 plasma for 10 minutes (power is 80 W, gas pressure is 20 Pa) to remove the organic pollutants and oxide layer on the surface, exposing the fresh metal surface, and obtaining a pollution-free substrate with a silicon-based cavity and electrode material.

[0092] Among them, the electrode material is an Au electrode (the thickness of the Au electrode is 20 nm).

[0093] The substrate is divided into three layers. The bottom layer is SiO2 with a thickness of 300 nm, the middle layer is Si with a thickness of 500 μm, and the upper layer is SiO2 with a thickness of 300 nm.

[0094] The depth of the silicon-based cavity is 250 μm.

[0095] (2) Use photolithography to fabricate the developed patterned photoresist (AZ5214, spin-coated, 3000 rpm, 30 s) on a contamination-free substrate with a silicon-based cavity and electrode material. Then, deposit the contact material (TiN, not deposited between the silicon-based cavity and the electrode material) on the surface of the substrate with the electrode material side by sputtering. Next, use acetone to remove the remaining photoresist, leaving the contact material pattern to form a contact material layer (TiN contact layer).

[0096] Among them, the process parameters of the sputtering method are as follows: the working gas is 25 sccm of argon and 10 sccm of nitrogen, the sputtering power is 100 W, and the deposition time is 15 min.

[0097] The thickness of the contact material layer is 80 nm.

[0098] (3) Use the van der Waals pick-up transfer method to transfer the suspended two-dimensional material film (graphene film, monolayer, thickness of 0.4 nm, sheet resistance of 400 ± 50 Ω / sq) onto the contact material layer at a temperature of 120 °C and a pressure of 0.3 MPa, with a pressure holding time of 5 min, to form a suspended two-dimensional material film on the silicon-based cavity.

[0099] (4) Dissolve the material of the sealing layer (polyurethane PU, number average molecular weight of about 50000) in a solvent (isopropyl alcohol) to obtain a material solution (i.e., polyurethane solution) with a viscosity of 2.1 cP and a surface tension of 28 mN / m.

[0100] (5) Import the designed continuous linear structure CAD drawing into an inkjet printer, set the printing resolution to 150 dpi and the printing speed to 2 mm / s, and perform inkjet printing (polyurethane solution) to deposit the material of the sealing layer layer by layer on the side of the contact material layer and the suspended two-dimensional material film to form a continuous linear structure, with 4 layers.

[0101] (6) Naturally dry the printed sample at room temperature for 4 hours, then place the sample in an oven and dry it at 80 °C for 8 hours to accelerate the volatilization of the solvent, enhance the airtightness of the two-dimensional material suspension film on the cavity, and obtain a micro differential pressure sensor (sealed sensor).

[0102] The flow schematic diagram of the method for enhancing the airtightness of the two-dimensional material suspension film on the silicon-based cavity is shown in Figure 1 ; the structural schematic diagram of the silicon-based cavity is shown in Figure 2 .

[0103] The output curve of the sensor before sealing (prepared in Comparative Example 1) is shown in Figure 3 ; the output curve of the sensor after sealing (prepared in Example 1) is shown in Figure 4 .

[0104] FromFigure 3 and Figure 4 As can be seen from Figure 4 , the output curve of the barometric pressure sensor before sealing does not match the actual barometric pressure change. There will be a lag in its pressure change, and due to the existence of air leakage, the rebound may not be complete, seriously affecting the actual performance of the barometric pressure sensor. After sealing, its output curve is accurate and actual.

[0105] Embodiment 2

[0106] A method for enhancing the airtightness of a two-dimensional material suspension film on a silicon-based cavity (i.e., a preparation method of a micro differential pressure sensor, copper nanoparticle contact layer / black phosphorus suspension layer / aluminum oxide ceramic sealing layer):

[0107] Same as Embodiment 1, the difference is only that step (2) is specifically: Disperse copper nanoparticles (CuNPs, particle size 15nm) in ethanol to obtain a copper nanoparticle solution with a concentration of 5wt%, and spin-coat (2000rpm, 60s) on the surface of the substrate with the electrode material side (cavity, no spin-coating between the electrode materials), and then anneal at 200 °C for 30 min in a nitrogen environment to form a contact material layer (continuous conductive network).

[0108] Step (3) is specifically: Transfer a black phosphorus (BP) thin film (thickness 5nm) to the contact material layer through a PDMS stamp in a glove box, with a pressure of 0.15 MPa and a time of 3 min, to form P-Cu metal bonds, constituting a suspended two-dimensional material film on the silicon-based cavity.

[0109] Step (4) is specifically: Dissolve the material of the sealing layer (aluminum oxide precursor (Al(OCH3)3)) in ethanol (concentration 10wt%) to obtain a material solution with a viscosity of 2.1 cP and a surface tension of 28 mN / m (i.e., aluminum oxide precursor solution).

[0110] Step (5) is specifically: Import the designed continuous linear structure CAD drawing into an inkjet printer, set the printing resolution to 500 dpi and the printing speed to 0.5 mm / s, and perform inkjet printing (aluminum oxide precursor solution) to deposit the material of the sealing layer layer by layer on the side of the contact material layer and the suspended two-dimensional material film to form a continuous linear structure, with 5 layers, and then heat-treat at 150 °C for 1 h to form a dense Al2O3 sealing layer.

[0111] The output curve of the sensor after sealing prepared in this embodiment is shown in Figure 5 (Showing the sensor resistance change curve with air pressure from 0 to 7 kPa, indicating that when the pressure is applied step by step, the output curve remains stable and does not shift).

[0112] In this embodiment, a nanoscale rough surface (Ra≈5nm) of CuNPs is formed, and the interfacial bonding is enhanced through P-Cu bonds. At the same time, the high density (porosity <0.1%) of the Al2O3 ceramic sealing layer blocks the penetration of water and oxygen.

[0113] Example 3

[0114] A method for enhancing the airtightness of a two-dimensional material suspension film on a silicon-based cavity (i.e., a method for preparing a micro differential pressure sensor, gold-silver alloy contact layer / tungsten diselenide suspension layer / polyimide sealing layer):

[0115] (1) The substrate with a silicon-based cavity and electrode material is ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes in sequence, and then treated with O2 plasma for 10 minutes (power: 80W, pressure: 20Pa) to remove the organic contaminants and oxide layer on the surface, exposing the fresh metal surface, and obtaining a pollution-free substrate with a silicon-based cavity and electrode material.

[0116] Among them, the electrode material is an Au electrode (the thickness of the Au electrode is 20nm).

[0117] The substrate has three layers. The bottom layer is SiO2 with a thickness of 300nm, the middle layer is Si with a thickness of 500μm, and the upper layer is SiO2 with a thickness of 300nm.

[0118] The depth of the silicon-based cavity is 250μm.

[0119] (2) Use photolithography to fabricate the developed patterned photoresist (AZ5214, spin-coated, 3000rpm, 30s) on the pollution-free substrate with a silicon-based cavity and electrode material. Then, deposit the contact material (Au-Ag alloy (mass ratio of Au and Ag is 6:4)) on the surface of the substrate with the electrode material side by sputtering method (no deposition between the silicon-based cavity and the electrode material). Then, use acetone to remove the remaining photoresist, and retain the contact material pattern to form the contact material layer (Au-Ag alloy layer).

[0120] Among them, the process parameters of the sputtering method are as follows: the working gas is 40sccm of argon and 20sccm of nitrogen, the sputtering power is 250W, and the deposition time is 15 minutes.

[0121] The thickness of the contact material layer is 80nm.

[0122] (3) Adopt the dry transfer method to transfer the suspended two-dimensional material film (thin-layer tungsten diselenide (WSe2), 3 layers, total thickness of 2.5 nm, sheet resistance of 630 Ω / sq) onto the contact layer at a temperature of 120 °C and a pressure of 0.3 MPa, with a pressure holding time of 5 min, to ensure that Au-Se chemical bonds are formed between WSe2 and the Au-Ag alloy, forming a suspended two-dimensional material film on the silicon-based cavity.

[0123] (4) Dissolve the material of the sealing layer (polyimide PI, number-average molecular weight of 30,000) in NMP (concentration of 15 wt%) to obtain a material solution (i.e., polyimide solution) with a viscosity of 8 cP and a surface tension of 32 mN / m.

[0124] (5) Import the designed continuous linear structure CAD drawing into an inkjet printer, set the printing resolution to 400 dpi and the printing speed to 1 mm / s, and perform inkjet printing (polyimide solution) to deposit the material of the sealing layer layer by layer on the side of the contact material layer and the suspended two-dimensional material film, forming a continuous linear structure with 8 layers (single layer thickness of about 200 nm), pre-curing at 80 °C for 1 h, and final-curing at 250 °C for 2 h to form a dense sealing layer.

[0125] The active sites of Ag in the Au-Ag alloy form strong chemical bonds (Ag-Se bonds) with the Se atoms of WSe2, combined with the thermal expansion coefficient matching of the PI sealing layer (about 3×10 -6 / °C), which can reduce the interfacial peeling caused by thermal stress.

[0126] Comparative Example 2

[0127] A method for enhancing the airtightness of a two-dimensional material suspension film on a silicon-based cavity (i.e., a preparation method for a micro differential pressure sensor):

[0128] (1) Ultrasonically clean the substrate with a silicon-based cavity and electrode material successively with acetone and isopropanol for 10 min, and then treat it with O2 plasma for 10 min (power of 80 W, gas pressure of 20 Pa) to remove the organic pollutants and oxide layer on the surface, exposing the fresh metal surface, and obtaining a pollution-free substrate with a silicon-based cavity and electrode material.

[0129] (2) Use the van der Waals pick-up transfer method to transfer the suspended two-dimensional material film (graphene film, single layer, thickness of 0.4 nm, sheet resistance of 400 ± 50 Ω / sq) onto the surface of the substrate with the electrode material side at a temperature of 120 °C and a pressure of 0.3 MPa, with a pressure holding time of 5 min, to form a suspended two-dimensional material film on the silicon-based cavity.

[0130] (3) Dissolve the material of the sealing layer (polyurethane PU, number-average molecular weight of about 50,000) in a solvent (isopropyl alcohol) to obtain a material solution (i.e., polyurethane solution) with a viscosity of 2.1 cP and a surface tension of 28 mN / m.

[0131] (4) Import the designed continuous linear structure CAD drawing into an inkjet printer, set the printing resolution to 150 dpi and the printing speed to 2 mm / s, and perform inkjet printing (polyurethane solution). Deposit the material of the sealing layer layer by layer on the side of the contact material layer and the suspended two-dimensional material film to form a continuous linear structure, with 4 layers.

[0132] (5) Naturally dry the printed sample at room temperature for 4 hours, then put the sample into an oven and dry it at 80 °C for 8 hours to accelerate the volatilization of the solvent, enhance the airtightness of the two-dimensional material suspension film on the cavity, and obtain a micro differential pressure sensor (sealed sensor).

[0133] In the micro differential pressure sensor prepared in this comparative example, the graphene layer and the SiO2 layer are only combined by van der Waals forces, and there are nanoscale gaps at the interface (the average gap height measured by AFM is about 2 nm). Under the action of differential pressure, gas permeates through the gaps, resulting in an increase in the leakage rate. At the same time, in the van der Waals pick-up transfer method, the film cannot ensure complete flatness, and there are deformations and wrinkles after heating, and there is a chance of gaps. Relying only on the upper layer seal cannot ensure its airtightness.

[0134] The output curve of the sensor is shown in Figure 6 .

[0135] As can be seen from 6, the output curve of the sensor prepared in this comparative example is similar to Figure 3 , that is, the output of the sensor does not exactly match the change of air pressure at all times.

[0136] Effect Example 1

[0137] The sensitivity measurement results of the micro differential pressure sensor prepared in Example 1 are shown in Figure 7 ; the stability of the micro differential pressure sensor prepared in Example 1 is shown in Figure 8 .

[0138] It is found that the sensitivity is 0.43 kPa -1 , and the stability is as shown in Figure 7 . When the pressure is applied step by step, the output curve remains stable without deviation.

[0139] The measured resolution is 0.1 kPa; the preparation success rate of the sensor using the method of Example 1 is 72%.

[0140] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A micro differential pressure sensor, characterized in that, It includes a substrate with a cavity and electrode material arranged from bottom to top, a contact material layer, a suspended two-dimensional material thin film, and a sealing layer arranged on the sides of the contact material layer and the suspended two-dimensional material thin film; The cavity of the micro differential pressure sensor penetrates through the contact material layer.

2. The micro differential pressure sensor according to claim 1, wherein The material of the contact material layer is titanium nitride, titanium dioxide, gold-platinum alloy, gold-silver alloy, gold-molybdenum alloy, silver nanoparticles or copper nanoparticles.

3. The micro differential pressure sensor according to claim 1, characterized in that, The material of the suspended two-dimensional material thin film includes two-dimensional materials or two-dimensional material heterojunctions.

4. The micro differential pressure sensor according to claim 3, characterized in that, The two-dimensional materials include graphene, molybdenum disulfide, tungsten diselenide, molybdenum diselenide, tungsten disulfide, tungsten diselenide, platinum diselenide or black phosphorus.

5. The micro differential pressure sensor according to claim 3, characterized in that, The two-dimensional material heterojunctions include graphene and molybdenum disulfide heterojunctions or graphene and black phosphorus heterojunctions.

6. The micro differential pressure sensor according to claim 1, wherein The material of the sealing layer includes organic polymers, ceramic precursors or silicone-organic hybrid materials.

7. A method for preparing a micro differential pressure sensor according to any one of claims 1 to 6, characterized in that, It includes the following steps: Deposit a contact material layer on a substrate with a cavity and electrode material, then transfer the suspended two-dimensional material thin film onto the contact material layer, and then deposit a sealing layer on the sides of the contact material layer and the suspended two-dimensional material thin film to obtain the micro differential pressure sensor.

8. The preparation method according to claim 7, characterized in that, The method for depositing the contact material layer includes sputtering or spin coating after lithography; And / or, the method for transferring the suspended two-dimensional material thin film onto the contact material layer includes the van der Waals pick-up transfer method, the PDMS stamp transfer method or the dry transfer method; And / or, the method for depositing the sealing layer includes inkjet printing.

9. A method for enhancing the airtightness of a two-dimensional material suspension film on a cavity, characterized in that, It includes the following steps: Deposit a contact material layer on a substrate with a cavity and electrode material, then transfer the suspended two-dimensional material thin film onto the contact material layer, and then deposit a sealing layer on the sides of the contact material layer and the suspended two-dimensional material thin film to obtain the micro differential pressure sensor.

10. The preparation method according to claim 9, characterized in that, The method for depositing the contact material layer includes sputtering or spin coating after lithography; And / or, the method for transferring the suspended two-dimensional material thin film onto the contact material layer includes the van der Waals pick-up transfer method, the PDMS stamp transfer method or the dry transfer method; And / or, the method for depositing the sealing layer includes inkjet printing.

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