A pressure sensor based on a molybdenum disulfide heterojunction and its fabrication method

Abstract

This invention discloses a pressure sensor based on a molybdenum disulfide heterojunction and its fabrication method, belonging to the field of pressure sensor technology. The sensor includes a base, electrodes, and a heterojunction. A microcavity is provided in the center of the base, and the heterojunction is correspondingly positioned within the microcavity. The heterojunction comprises a monolayer graphene film connected to the electrodes and a monolayer molybdenum disulfide film connected to the monolayer graphene. When the pressure changes, a pressure difference is formed inside and outside the microcavity, acting on the surface of the monolayer molybdenum disulfide film. The molybdenum disulfide converts the mechanical deformation into an electrical signal, regulating the carrier concentration of the graphene. Simultaneously, under the triple synergistic effect of graphene providing a high-speed carrier transport channel and the band structure modulation of the heterojunction interface formed by graphene and molybdenum disulfide, the sensor reflects pressure changes through different regulation of carrier concentration under different pressure environments, achieving high-precision and high-sensitivity pressure monitoring under weak pressure conditions.

Description

Technical Field

[0001] This invention belongs to the field of barometric pressure sensor technology, specifically relating to a barometric pressure sensor based on a molybdenum disulfide heterojunction and its fabrication method. Background Technology

[0002] As a key component for measuring gas pressure, barometric pressure sensors have wide applications in industrial automation, meteorological monitoring, aerospace, medical equipment, and consumer electronics. Traditional barometric pressure sensors are mainly based on silicon-based microelectromechanical systems (MEMS) technology, detecting pressure changes through piezoresistive or capacitive sensor principles. Although silicon-based barometric pressure sensors offer high accuracy and stability, their manufacturing relies on complex photolithography, deep silicon etching, and bonding processes, resulting in high production costs. Summary of the Invention

[0003] In response to one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a pressure sensor based on molybdenum disulfide heterojunction and its preparation method, which solves the problem of compatibility and integration of two-dimensional material thin films with MEMS processes. The prepared pressure sensor has high sensitivity and high reliability, and meets the needs of real-time monitoring of weak air pressure environments.

[0004] To achieve the above objectives, one aspect of the present invention provides a barometric pressure sensor based on a molybdenum disulfide heterojunction, which includes a base, electrodes, and a heterojunction.

[0005] The electrode is disposed on the base, and a microcavity is provided in the middle of the base;

[0006] The heterojunction includes a single-layer graphene film and a single-layer molybdenum disulfide film; the single-layer graphene film is disposed on both sides of the microcavity and is respectively in contact with the electrodes on both sides of the microcavity; the single-layer molybdenum disulfide film is mechanically peeled off and covers the microcavity, and its two ends are respectively in contact with the single-layer graphene film on both sides of the microcavity.

[0007] When the air pressure changes, a pressure difference is formed inside and outside the microcavity, which acts on the surface of the monolayer molybdenum disulfide film. The molybdenum disulfide converts the mechanical deformation into an electrical signal, thereby regulating the carrier concentration of the graphene. At the same time, under the triple synergistic effect of graphene providing a high-speed carrier transport channel and the band modulation of the heterojunction interface formed by graphene and molybdenum disulfide, the change in air pressure is reflected by the different regulation of carrier concentration under different air pressure environments.

[0008] As a further improvement of the present invention, the microcavity is a rectangular microcavity, and the stress generated by the change in air pressure is transmitted along the long axis of the microcavity.

[0009] As a further improvement of the present invention, the depth of the microcavity is 2~50μm, and the size of the microcavity is 4×32μm~16×80μm.

[0010] As a further improvement of the present invention, the size of the single-layer graphene film is 24×40μm~28×86μm, and the spacing between two single-layer graphene films is 9~20μm;

[0011] And / or,

[0012] The size of the single-layer molybdenum disulfide film is not less than 9×40μm.

[0013] As a further improvement of the present invention, the heterojunction further includes an insulating support layer, which is disposed between the microcavity and the monolayer molybdenum disulfide film and covers the microcavity to support the monolayer molybdenum disulfide film.

[0014] and / or

[0015] The heterojunction also includes an insulating protective layer that covers the monolayer molybdenum disulfide film and the monolayer graphene film, forming an encapsulated heterojunction for protection of the sensitive structure.

[0016] As a further improvement of the present invention, the insulating support layer is a few-layer hexagonal boron nitride thin film with a size of 13×46μm~26×96μm; and / or, the insulating protective layer is a single-layer hexagonal boron nitride thin film with a size of 40×60μm~80×120μm.

[0017] As a further improvement of the present invention, the base includes an insulating layer and a silicon base layer arranged sequentially from top to bottom, wherein the thickness of the silicon base layer is 480~520μm and the thickness of the insulating layer is 2~4μm.

[0018] As a further improvement of the present invention, an electrode groove is provided on the base, and one side of the electrode is embedded in the electrode groove.

[0019] Another aspect of the present invention provides a method for fabricating a pressure sensor based on a molybdenum disulfide heterojunction, comprising the following steps:

[0020] (1) Photoresist is coated on the upper surface of the substrate and patterned. Electrode grooves are etched using plasma etching process. Then, metal electrodes and marking patterns are prepared on the upper surface of the substrate using electron beam evaporation process and lift-off process.

[0021] (2) Microcavity etching of a certain depth is completed on the upper surface of the substrate by plasma etching and deep silicon etching processes in sequence;

[0022] (3) A single-layer graphene film is transferred to the upper surface of the substrate by a wet transfer process, and the single-layer graphene film is patterned to form a single-layer graphene film structure on both sides of the microcavity, and each single-layer graphene film is in contact with the metal electrodes on both sides of the microcavity.

[0023] (4) The monolayer molybdenum disulfide film is transferred to the top of the microcavity by mechanical peeling process and simultaneously contacts the monolayer graphene films on both sides to complete the fabrication of the pressure sensor based on the molybdenum disulfide heterojunction.

[0024] As a further improvement of the present invention, before transferring the single-layer graphene film, a few layers of insulating film are first transferred on the upper surface of the substrate by a wet transfer process to cover the microcavity and pattern it.

[0025] And / or,

[0026] After transferring the monolayer molybdenum disulfide film, the monolayer insulating film is transferred onto the monolayer graphene film and the monolayer molybdenum disulfide film using a wet transfer process, and then patterned to complete the fabrication of a pressure sensor based on a molybdenum disulfide heterojunction.

[0027] And / or,

[0028] In step (4), a single-layer molybdenum disulfide film is transferred to polydimethylsiloxane by mechanical peeling. A single-layer molybdenum disulfide film material of appropriate size is selected, and the polydimethylsiloxane with the single-layer molybdenum disulfide film material is fixed face down on a two-dimensional material transfer platform. The single-layer molybdenum disulfide film is moved to the top of the microcavity by a micro-displacement stage for auxiliary positioning. At the same time, its two sides form van der Waals contact with the single-layer graphene film. The transfer platform is heated to a certain temperature so that the single-layer molybdenum disulfide film material is transferred from polydimethylsiloxane to the substrate.

[0029] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0030] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include:

[0031] (1) The pressure sensor based on molybdenum disulfide heterojunction and its preparation method of the present invention have a triple synergistic effect through the heterostructure formed by microcavity, graphene and molybdenum disulfide: First, graphene provides a high-speed carrier transport channel; second, the single-layer mechanically exfoliated molybdenum disulfide has a high piezoelectric coefficient, which can directly convert mechanical deformation into electrical signal; finally, the band modulation of the heterojunction interface can significantly enhance the pressure response sensitivity; therefore, when the air pressure changes in the environment where the sensor is located, the air pressure difference inside and outside the microcavity acts on the surface of the suspended molybdenum disulfide. The high piezoelectric coefficient of the mechanically exfoliated single-layer molybdenum disulfide is used to directly convert the mechanical deformation into an electrical signal. Under pressure-induced piezoelectric potential, the carrier concentration of graphene is regulated. At the same time, under the triple synergistic effect of graphene providing a high-speed carrier transport channel and the band modulation of the heterojunction interface formed by graphene and molybdenum disulfide, different regulation effects on carrier concentration under different air pressure environments are realized to reflect the change of air pressure, and the pressure sensor can detect small changes in air pressure.

[0032] (2) The pressure sensor based on molybdenum disulfide heterojunction and its preparation method of the present invention, by designing the microcavity as a rectangular microcavity to form a uniaxial stress distribution, isolate interference in non-measurement directions, improve the signal-to-noise ratio, and cause graphene to produce highly oriented strain, avoid signal interference caused by multi-directional stress, improve the linearity of pressure-electrical response, can significantly change the band structure of graphene, causing its conductivity to change drastically, thereby further improving the test sensitivity of the pressure sensor; at the same time, the geometric constraint of the rectangular microcavity will further efficiently convert vertical pressure into uniaxial tensile / compressive strain, ensure that the deformation direction is controllable, and facilitate signal decoupling.

[0033] (3) The pressure sensor based on molybdenum disulfide heterojunction and its preparation method of the present invention form a two-dimensional material heterojunction by setting an insulating protective layer and an insulating support layer on the upper and lower surfaces of the heterojunction, respectively, which effectively improves the service life of the pressure sensor.

[0034] (4) The barometric pressure sensor based on molybdenum disulfide heterojunction and its fabrication method of the present invention are rationally designed and solve the compatibility problem between nanoscale two-dimensional material thin films and silicon-based MEMS processes, realizing the integrated manufacturing of a silicon-based cavity graphene / molybdenum disulfide heterojunction barometric pressure sensor. Meanwhile, the designed graphene / molybdenum disulfide heterojunction barometric pressure sensor, with its miniaturized design, high pressure response sensitivity, and strong environmental adaptability, demonstrates excellent practical value in meteorological monitoring, aerospace, industrial control, and medical health scenarios, and has good application prospects and promotional value. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the process flow for the fabrication method of a pressure sensor based on a molybdenum disulfide heterojunction in an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the insulating support layer in a pressure sensor based on a molybdenum disulfide heterojunction in an embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of the setup of a single-layer graphene film in a pressure sensor based on a molybdenum disulfide heterojunction in an embodiment of the present invention.

[0039] Figure 4 This is a schematic diagram of the setup of a single-layer molybdenum disulfide thin film in a pressure sensor based on a molybdenum disulfide heterojunction in an embodiment of the present invention.

[0040] Figure 5 This is a schematic diagram of the insulating protective layer in a pressure sensor based on a molybdenum disulfide heterojunction in an embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the microcavity design of the pressure sensor based on a molybdenum disulfide heterojunction prepared in Example 1 of the present invention;

[0042] Figure 7 This is a schematic diagram of the microcavity design of the pressure sensor based on a molybdenum disulfide heterojunction prepared in Embodiment 2 of the present invention;

[0043] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1, base; 101, microcavity; 2, electrode; 3, insulating support layer; 4, monolayer graphene film; 5, monolayer molybdenum disulfide film; 6, insulating protective layer. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0045] In the description of this invention, it should be understood that, unless otherwise expressly specified and limited, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0048] Please see Figures 1-7 The gas pressure sensor based on a molybdenum disulfide heterojunction in a preferred embodiment of the present invention includes a base 1, an electrode 2 and a heterojunction. The electrode 2 is disposed on the base 1, and a microcavity 101 is disposed on the base 1. The heterojunction is disposed corresponding to the microcavity 101 so that when the gas pressure near the microcavity 101 changes, causing the volume of the microcavity 101 to change, the gas pressure can be detected by the heterojunction.

[0049] Specifically, such as Figure 1As shown, the heterojunction in the preferred embodiment includes a monolayer graphene film 4 and a monolayer molybdenum disulfide film 5. The monolayer graphene film 4 is disposed on both sides of the microcavity 101 and is respectively connected to the electrodes 2 on both sides of the microcavity 101 to form an ohmic contact. Correspondingly, the monolayer molybdenum disulfide film 5 is mechanically peeled off and covered on the microcavity 101, and its two ends are respectively connected to the monolayer graphene film 4 on both sides of the microcavity 101 to form a van der Waals contact, thereby forming a heterojunction with a triple synergistic effect.

[0050] It is understandable that the triple synergistic effect in this heterojunction specifically includes: first, the high conductivity of graphene serves as a charge transport channel; second, the piezoelectric and semiconductor properties of monolayer molybdenum disulfide can convert mechanical deformation into electrical signals; and finally, the strain transfer effect at the heterojunction interface and the quantum capacitance effect formed by interlayer changes under pressure can significantly enhance the pressure response sensitivity.

[0051] When the air pressure in the sensor's environment changes, the pressure difference created inside and outside the microcavity 101 acts on the suspended molybdenum disulfide surface. Simultaneously, the mechanically exfoliated monolayer of molybdenum disulfide possesses a high piezoelectric coefficient, directly converting mechanical deformation into an electrical signal. Therefore, under the pressure-induced regulation of the molybdenum disulfide piezoelectric potential on the graphene carrier concentration, coupled with the triple synergistic effect of graphene providing a high-speed carrier transport channel and the band structure modulation at the heterojunction interface formed by graphene and molybdenum disulfide, changes in air pressure can be detected by varying the carrier concentration under different pressure environments.

[0052] For example, at an ambient pressure of 101 kPa, the air pressure inside and outside the microcavity 101 in the sensor is also 101 kPa. When the external air pressure changes to 80 kPa and 40 kPa, the pressure effect of 40 kPa on the microcavity 101 is greater than that of 80 kPa. Under a pressure of 40 kPa, molybdenum disulfide can exhibit a stronger piezoelectric effect to modulate the charge carriers of graphene, thereby increasing the test current at both ends. Therefore, the air pressure value can be reflected by different output currents (charge carrier modulation capability).

[0053] Preferably, the microcavity 101 is a rectangular microcavity 101 with a depth of 2~50μm and a size of 4×32μm~16×80μm. This allows the stress generated by changes in air pressure to be transmitted mainly along the long axis (uniaxial) of the microcavity 101, resulting in highly oriented strain in the graphene. This avoids signal interference caused by multi-directional stress and improves the linearity of the pressure-electrical response. The designed structure, based on uniaxial stress distribution, allows the graphene to undergo highly qualitative strain, which can significantly change the band structure and cause a dramatic change in its conductivity, thereby improving the test sensitivity of the pressure sensor. Simultaneously, the geometric constraints of the rectangular microcavity further efficiently convert vertical pressure into uniaxial tensile / compressive strain, ensuring controllable deformation direction and facilitating signal decoupling. The uniaxial stress design exhibited by the rectangular microcavity can isolate interference from non-measurement directions, improving the signal-to-noise ratio.

[0054] like Figure 6 and Figure 7 The dimensions of the microcavity 101 are 6μm×64μm and 8μm×80μm, respectively. By optimizing the dimensions of the microcavity 101, the graphene can be subjected to highly qualitative strain, which can significantly change the band structure and thus improve the test sensitivity performance of the pressure sensor.

[0055] Preferably, the graphene film structure has a size of 24×40μm to 28×86μm, and the spacing between two graphene film structures is 9 to 20μm.

[0056] Preferably, the size of the mechanically peeled monolayer molybdenum disulfide film 5 should be not less than 9 × 40 μm.

[0057] Preferably, the heterojunction further includes an insulating support layer 3 and an insulating protective layer 6; wherein the insulating support layer 3 is disposed between the microcavity 101 and the monolayer molybdenum disulfide film 5, and covers the microcavity 101 to form a sealed structure to support the monolayer molybdenum disulfide film 5; the insulating protective layer 6 covers the monolayer molybdenum disulfide film 5 and the monolayer graphene film 4 to form an encapsulated heterojunction, protecting the intermediate monolayer molybdenum disulfide film 5 and the monolayer graphene film 4, ensuring the durability of the sensitive structure in the heterojunction, and improving the service life of the pressure sensor.

[0058] More preferably, both the insulating support layer 3 and the insulating protective layer 6 are made of hexagonal boron nitride. The difference is that the insulating support layer 3 is a few-layer hexagonal boron nitride thin film structure with a size of 13×46μm~26×96μm, which is selected according to the size of the microcavity 101; the insulating protective layer 6 is a single-layer hexagonal boron nitride thin film structure with a size of 40×60μm~80×120μm, which is selected according to the size of other thin film structures in the heterojunction to ensure that the other thin film structures are covered and wrapped.

[0059] It is important to know that all the thin films in the above heterojunction are two-dimensional material thin films.

[0060] Preferably, the base 1 includes an insulating layer and a silicon base layer arranged sequentially from top to bottom, wherein the thickness of the silicon base layer is 480~520μm and the thickness of the insulating layer is 2~4μm, so as to provide an insulating substrate for the device through the insulating layer and form holes during the etching of the microcavity 101.

[0061] Preferably, the electrode 2 is made of Au, and a titanium layer is provided between the electrode 2 and the insulating layer of the base 1 to enhance the adhesion between the electrode 2 and the base 1.

[0062] More preferably, in relation to the setting of electrode 2, an electrode groove is also provided on the base 1, and one side of electrode 2 is embedded in the electrode groove to form an embedded electrode 2, thereby forming a low-step electrode surface, avoiding the formation of a high-depth step on the surface of the base 1 by electrode 2, which would cause nanoscale thickness fracture of the related thin film structure in the heterojunction, and reducing the impact of electrode 2 on the performance of two-dimensional material devices.

[0063] Furthermore, the present invention also relates to a method for fabricating the above-mentioned pressure sensor based on a molybdenum disulfide heterojunction, such as... Figure 1 The steps shown are as follows:

[0064] (1) Photoresist is coated on the upper surface of the substrate and patterned. Electrode grooves are etched using plasma etching process. Then, metal electrode 2 and marking pattern are prepared on the upper surface of the substrate using electron beam evaporation process and stripping process.

[0065] (1.1) Select a substrate and clean it;

[0066] Specifically, in the preferred embodiment, the substrate is a SiO2 / Si substrate, specifically an upper SiO2 insulating layer with a thickness of 2~4μm and a lower silicon base layer with a thickness of 480~520μm.

[0067] When cleaning the substrate, use organic solvents (N-methylpyrrolidone (NMP) and anhydrous ethanol) and deionized water to ultrasonically clean and dry the bonded sheet to ensure surface cleanliness and keep the substrate surface dry, preventing uneven film formation in the subsequent spin coating process.

[0068] (1.2) Coat the upper surface of the substrate with photoresist, and pattern it after pre-baking, exposure, intermediate baking and development, and remove the residual photoresist on the substrate surface;

[0069] (1.3) Electrode trenches are etched on the upper surface of the substrate using plasma etching process;

[0070] (1.4) Electron beam evaporation is used to evaporate titanium and gold thin films on the surface of the substrate to use the titanium thin film as an adhesion layer to enhance the adhesion between the gold thin film and the substrate insulating layer.

[0071] (1.5) After evaporation, the substrate is immersed in NMP solution for a certain period of time. After peeling is completed, the cleaning step in step (1.1) is repeated to complete the preparation of embedded metal electrode 2 and marking pattern.

[0072] Understandably, the purpose of fabricating the embedded metal electrode 2 is to ensure the thickness of the metal electrode 2 to reduce the impact of the electrode itself on the performance of the two-dimensional material device, while reducing the step height on the substrate surface to avoid damage when the two-dimensional material film is subsequently transferred to cover the metal electrode surface (high-depth steps cause nanoscale thickness fractures).

[0073] (2) Microcavity 101 is etched to a certain depth on the upper surface of the substrate by plasma etching and deep silicon etching processes in sequence;

[0074] (2.1) Photoresist is coated on the upper surface of the substrate, and after pre-baking, exposure and development, the photoresist layer is patterned;

[0075] (2.2) Use plasma etching process to etch the insulating layer of the substrate; to ensure that the insulating layer is fully etched, it should be over-etched as much as possible;

[0076] (2.3) Use deep silicon etching process to etch the silicon base layer of the substrate, and remove the surface residue after etching to complete the etching of microcavity 101 to a certain depth; during etching, the etching depth of 2~50μm microcavity 101 can be achieved by controlling the number of etching cycles.

[0077] (3) The single-layer graphene film 4 is transferred to the upper surface of the substrate by a wet transfer process, and the single-layer graphene film 4 is patterned to form single-layer graphene film structures on both sides of the microcavity 101, and each single-layer graphene film 4 is in contact with the metal electrodes 2 on both sides of the microcavity.

[0078] (3.1) A few layers of insulating film are transferred on the upper surface of the substrate using a wet transfer process to cover the microcavity. Photoresist is then coated on the few layers of insulating film and patterned after pre-baking, exposure, and development.

[0079] (3.2) Use plasma etching to etch the few-layer insulating film to pattern it, such as... Figure 2 As shown;

[0080] (3.3) The monolayer graphene film 4 is transferred by a wet transfer process, and photoresist is coated on the monolayer graphene film 4. After pre-baking, exposure and development, it is patterned.

[0081] (3.4) The monolayer graphene film 4 is etched using a plasma etching process to pattern it, such as... Figure 3 As shown in the image.

[0082] (4) The monolayer molybdenum disulfide film 5 is transferred to the top of the microcavity 101 by a mechanical peeling process, and simultaneously contacts the monolayer graphene films 4 on both sides, such as Figure 4 As shown;

[0083] Specifically, a monolayer molybdenum disulfide film 5 is transferred onto polydimethylsiloxane (PDMS) using a mechanical peeling process. A monolayer molybdenum disulfide film 5 of appropriate size is selected, and the PDMS with the monolayer molybdenum disulfide film 5 facing down is fixed on a two-dimensional material transfer platform. A micro-displacement stage is used for assisted positioning to move the molybdenum disulfide film 5 directly above the microcavity 101, while its two sides form van der Waals contacts with the monolayer graphene film 4. The transfer platform is heated to a certain temperature, so that the monolayer molybdenum disulfide film 5 is transferred from the PDMS onto the substrate.

[0084] (5) The monolayer insulating film is transferred onto the monolayer graphene film 4 and the monolayer molybdenum disulfide film 5 using a wet transfer process to encapsulate them and pattern them to form an encapsulated heterostructure, such as... Figure 5 As shown, the fabrication of a pressure sensor based on a molybdenum disulfide heterojunction was completed.

[0085] Example 1:

[0086] (1) Photoresist is coated on the upper surface of the substrate and patterned. Electrode grooves are etched using plasma etching process. Then, metal electrode 2 and marking pattern are prepared on the upper surface of the substrate using electron beam evaporation process and stripping process.

[0087] (1.1) Select a SiO2 / Si substrate with a SiO2 layer thickness of 2μm and a Si layer thickness of 500μm; place the SiO2 / Si substrate in N-methylpyrrolidone (NMP) solution for ultrasonic cleaning for 5min to remove surface impurities and contaminants, in anhydrous ethanol solution for ultrasonic cleaning for 5min to dissolve the residual NMP solution on the surface, and in deionized water solution for cleaning. Then, blow dry the residual deionized water on the substrate surface with a nitrogen gun and bake on a hot plate at 100℃ for 2min.

[0088] (1.2) A negative photoresist is spin-coated on the upper surface of the substrate using a spin coater. The spin coater parameters are: 10s at low speed of 500r or 40s at high speed of 400r. After spin coating, the substrate is pre-baked on a hot plate at 150℃ for 60s. The substrate is then exposed using a photolithography machine with a mask containing the marking pattern and the metal electrode 2 pattern for 12s. After intermediate baking for 60s, the substrate is developed with a developer for 50~52s. Then, the substrate is surface-cleaned for 3 minutes using a plasma surface treatment instrument with 200W oxygen to remove the photoresist residue after development.

[0089] Before spin-coating photoresist, the substrate is first cleaned using a plasma surface treatment instrument to enhance the adhesion of the photoresist and ensure the film formation effect of spin-coated photoresist.

[0090] (1.3) The substrate was etched with a thickness of 100 nm using plasma etching process under the condition of fluorine-based gas (a mixture of CF4 and C4F8) and ambient temperature of 5 °C to form electrode trenches. The etching rate was 3.4 nm / s and the etching time was 28-32 s.

[0091] (1.4) Electron beam evaporation was used to evaporate 10 nm titanium and 100 nm gold films at a rate of 0.5 A / s.

[0092] (1.5) After evaporation, the substrate is immersed in NMP solution for about 1 hour to peel off the metal electrode 2 and the marking pattern. After peeling is completed, repeat step (1.1).

[0093] (2) Microcavity 101 is etched to a certain depth on the upper surface of the substrate by plasma etching and deep silicon etching processes in sequence;

[0094] (2.1) AZ 5214 photoresist was spin-coated on the upper surface of the substrate using a spin coater. The spin coater parameters were: spin-coating at a low speed of 1500r for 15s and spin-coating at a high speed of 4000r for 30s. After spin-coating, the substrate was pre-baked on a hot plate at 97℃ for 120s. The substrate was then exposed using a photolithography machine and a photomask for 5.4s. Finally, the substrate was developed using a developer for 38~45s.

[0095] (2.2) Silicon dioxide was etched using plasma etching at 5°C by introducing carbon tetrafluoride gas. The etching rate was 5.8 nm / s and the etching time was 480 s.

[0096] (2.3) The underlying silicon substrate was etched using a deep silicon etching machine. The etching gas was sulfur hexafluoride, the etching rate was 400 nm / loop, and the etching cycle number was selected as 50 loops to complete the etching of the microcavity 101 with dimensions of 6 μm (width) × 64 μm (length) × 22 μm (depth). Figure 6 As shown;

[0097] (2.4) After etching, NMP solution, anhydrous ethanol and deionized water are used in sequence to remove the adhesive and clean the substrate in an ultrasonic environment. The surface moisture is then dried with a nitrogen gun and baked on a hot plate at 100°C for 2 minutes to ensure the cleanliness of the substrate.

[0098] (3) The single-layer graphene film 4 is transferred to the upper surface of the substrate by a wet transfer process, and the single-layer graphene film 4 is patterned to form a single-layer graphene film structure on both sides of the microcavity 101, and each single-layer graphene film 4 is in contact with the metal electrode 2 on both sides of the microcavity 101.

[0099] (3.1) A few-layer hexagonal boron nitride film is transferred above the microcavity 101 by a wet transfer process and covers the microcavity 101; then, photoresist is spin-coated on the surface of the few-layer hexagonal boron nitride film using a spin coater. The spin coater parameters are: spin-coating at a low speed of 1500r for 15s and spin-coating at a high speed of 4000r for 30s, and then baking in front of a hot plate at 97℃ for 120s after spin-coating; exposure is performed using a photolithography machine with a mask containing the pattern of the few-layer hexagonal boron nitride film for 5.4s, and development is performed using a developer for 38~45s;

[0100] (3.2) Using a reactive ion etching machine, oxygen and argon were introduced at 20°C. The gas power was 100W and the flow rate was 20sccm. The etching time was set to 60s to complete the patterning of the few-layer hexagonal boron nitride thin film.

[0101] After patterning the few-layer hexagonal boron nitride thin film, the resist and cleaning processes are carried out sequentially using NMP solution, anhydrous ethanol and deionized water. After drying the surface moisture with a nitrogen gun, the substrate is baked on a hot plate at 100°C for 2 minutes to keep the substrate surface dry. It should be noted that ultrasonic cleaners and plasma surface treatment instruments should not be used for resist removal in this step, as they can easily damage the integrity of the two-dimensional material film.

[0102] (3.3) A single-layer graphene film 4 was transferred onto the surface of the substrate by a wet transfer process. Then, photoresist was spin-coated onto the surface of the single-layer graphene film 4. The spin coater parameters were: spin-coating at a low speed of 1500r for 15s and spin-coating at a high speed of 4000r for 30s. After spin-coating, the film was baked in front of a hot plate at 97℃ for 120s. The photolithography machine was used with a mask containing the pattern of the single-layer graphene film 4 for exposure. The exposure time was 5.4s. The film was then developed using a developer for 38~45s.

[0103] (3.4) Using a reactive ion etching machine, oxygen was introduced at 20°C. The gas power was 80W, the flow rate was 60sccm, and the etching time was set to 10s to complete the patterning of the single-layer graphene film 4.

[0104] After etching, NMP solution, anhydrous ethanol, and deionized water are used sequentially for resist removal and cleaning. After drying the surface moisture with a nitrogen gun, the substrate is baked on a hot plate at 100°C for 2 minutes to keep the substrate surface dry. It should be noted that ultrasonic cleaners and plasma surface treatment instruments should not be used for resist removal in this step, as they can easily damage the integrity of the two-dimensional material film.

[0105] (4) The monolayer molybdenum disulfide film 5 is transferred to the top of the microcavity 101 by mechanical peeling process, and simultaneously contacts the monolayer graphene film 4 on both sides.

[0106] Specifically, a monolayer molybdenum disulfide film 5 is adhered to PDMS using a mechanical peeling process. A monolayer molybdenum disulfide film 5 of appropriate size is selected, and the PDMS with the monolayer molybdenum disulfide film 5 facing down is fixed on a two-dimensional material transfer platform. A micro-displacement stage is used for assisted positioning to move the monolayer molybdenum disulfide film 5 directly above the microcavity 101. At the same time, its two sides form van der Waals contact with the monolayer graphene film 4. The temperature of the transfer platform is raised to 90°C, so that the monolayer molybdenum disulfide film 5 is transferred from PDMS to the substrate.

[0107] In this invention, the single-layer molybdenum disulfide film 5 is transferred through the above-mentioned mechanical peeling process, which avoids the problem of interface quality degradation caused by the introduction of contamination, wrinkles or cracks during heterogeneous integration.

[0108] (5) The single-layer insulating film is transferred to the single-layer graphene film 4 and the single-layer molybdenum disulfide film 5 by wet transfer process, and patterned to form an encapsulated heterostructure, thus completing the fabrication of the pressure sensor based on the molybdenum disulfide heterojunction.

[0109] (5.1) A single-layer hexagonal boron nitride film was transferred onto a single-layer graphene film 4 and a single-layer molybdenum disulfide film 5 by a wet transfer process;

[0110] (5.2) Photoresist was spin-coated on the surface of a single-layer hexagonal boron nitride film. The spin coater parameters were: spin-coating at a low speed of 1500r for 15s and spin-coating at a high speed of 4000r for 30s. After spin-coating, the film was baked in front of a hot plate at 97℃ for 120s. The photolithography machine was used with a mask containing the pattern of the single-layer hexagonal boron nitride film for exposure. The exposure time was 5.4s. The film was then developed using a developer for 38~45s.

[0111] (5.3) Using a reactive ion etching machine, oxygen and argon were introduced at 20°C. The gas power was 100W and the flow rate was 20sccm. The etching time was set to 60s to complete the patterning of a single-layer hexagonal boron nitride film.

[0112] After etching, NMP solution, anhydrous ethanol and deionized water are used in sequence for resist removal and cleaning. After drying the surface moisture with a nitrogen gun, the substrate is baked on a hot plate at 100°C for 2 minutes to keep the substrate surface dry. Ultrasonic cleaners and plasma surface treatment instruments should not be used for resist removal in this process, as they can easily damage the integrity of the two-dimensional material film.

[0113] In steps (3.2), (3.4), and (5.3), a smaller flow rate of deionized water should be used for rinsing, and the flow rate of nitrogen gas should be reduced as much as possible to dry the surface moisture. After etching, the substrate surface should be kept dry by baking, which can also enhance the adhesion between the two-dimensional material and the substrate.

[0114] Example 2:

[0115] In this specific embodiment, when fabricating a pressure sensor based on a molybdenum disulfide heterojunction, in addition to step (2.3), a deep silicon etching machine is used to etch the underlying silicon substrate at an etching rate of 400 nm / loop, and the etching cycle number is selected as 100 loops to complete the etching of a microcavity of 8 μm (width) × 80 μm (length) × 42 μm (depth). Figure 7 As shown, the other steps are the same as in Implementation 1.

[0116] A pressure sensor based on a molybdenum disulfide heterojunction was fabricated using the above-described process steps. The fabricated device has a small-sized microcavity and a small-sized sensitive structure. The sensitive structure is suspended on the upper surface of the microcavity by a mechanically exfoliated monolayer molybdenum disulfide film, with van der Waals contacts formed on both sides with graphene. The fabricated pressure sensor based on the molybdenum disulfide heterojunction solves the compatibility problem between nanomaterial thin films and MEMS processes. It achieves extremely high pressure response sensitivity by utilizing three coupling effects: pressure-induced molybdenum disulfide piezoelectric potential to regulate the carrier concentration of graphene, strain transfer effect of the heterojunction interface, and quantum capacitance effect. The sensitive structure is wrapped with an insulating layer of hexagonal boron nitride, which not only serves as a nanoscale thickness structure but also improves the service life of the heterostructure, effectively enhancing the high-performance detection capability in low-pressure environments.

[0117] The barometric pressure sensor based on a molybdenum disulfide heterojunction presented in this invention is miniaturized, durable, and capable of detecting changes in low-pressure environments, overcoming the shortcomings of existing materials in terms of low performance and inaccurate measurement of weak signals. The barometric pressure sensor based on a molybdenum disulfide heterojunction, fabricated using the method of this invention, achieves high electrical output performance through piezoelectric-pressure coupling, enabling accurate real-time measurement of minor pressure changes. Furthermore, the two-dimensional material-encapsulated structure enhances the device's durability, making it of significant scientific and practical value for monitoring changes in low-pressure environments.

[0118] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pressure sensor based on a molybdenum disulfide heterojunction, characterized in that, Includes a base, electrodes, and a heterojunction; The electrode is disposed on the base, and a microcavity is provided in the middle of the base; The heterojunction comprises a monolayer graphene film, a monolayer molybdenum disulfide film, and an insulating support layer. The monolayer graphene film is disposed on both sides of the microcavity and is in contact with the electrodes on both sides of the microcavity, respectively. The monolayer molybdenum disulfide film is mechanically peeled off and covers the microcavity, with its two ends in contact with the monolayer graphene film on both sides of the microcavity, respectively. The insulating support layer is disposed between the microcavity and the monolayer molybdenum disulfide film and covers the microcavity to support the monolayer molybdenum disulfide film. When the air pressure changes, a pressure difference is formed inside and outside the microcavity, which acts on the surface of the monolayer molybdenum disulfide film. The molybdenum disulfide converts the mechanical deformation into an electrical signal, thereby regulating the carrier concentration of the graphene. At the same time, under the triple synergistic effect of graphene providing a high-speed carrier transport channel and the band modulation of the heterojunction interface formed by graphene and molybdenum disulfide, the change in air pressure is reflected by the different regulation of carrier concentration under different air pressure environments.

2. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 1, characterized in that, The microcavity is a rectangular microcavity, and the stress generated by the change in air pressure is transmitted along the long axis of the microcavity.

3. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 2, characterized in that, The depth of the microcavity is 2~50μm, and the size of the microcavity is 4×32μm~16×80μm.

4. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 1, characterized in that, The dimensions of the single-layer graphene film are 24×40μm~28×86μm, and the spacing between two single-layer graphene films is 9~20μm; And / or, The size of the single-layer molybdenum disulfide film is not less than 9×40μm.

5. The pressure sensor based on a molybdenum disulfide heterojunction according to any one of claims 1 to 4, characterized in that, The heterojunction also includes an insulating protective layer that covers the monolayer molybdenum disulfide film and the monolayer graphene film, forming an encapsulated heterojunction for protection of the sensitive structure.

6. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 5, characterized in that, The insulating support layer is a few-layer hexagonal boron nitride thin film with dimensions of 13×46μm to 26×96μm; and / or, the insulating protective layer is a single-layer hexagonal boron nitride thin film with dimensions of 40×60μm to 80×120μm.

7. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 1, characterized in that, The base includes an insulating layer and a silicon base layer arranged sequentially from top to bottom, wherein the thickness of the silicon base layer is 480~520μm and the thickness of the insulating layer is 2~4μm.

8. The pressure sensor based on a molybdenum disulfide heterojunction according to claim 1, characterized in that, The base is provided with an electrode groove, and one side of the electrode is embedded in the electrode groove.

9. A method for fabricating a pressure sensor based on a molybdenum disulfide heterojunction, used in the fabrication of a pressure sensor based on a molybdenum disulfide heterojunction as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Photoresist is coated on the upper surface of the substrate and patterned. Electrode grooves are etched using plasma etching process. Then, metal electrodes and marking patterns are prepared on the upper surface of the substrate using electron beam evaporation process and lift-off process. (2) Microcavity etching of a certain depth is completed on the upper surface of the substrate by plasma etching and deep silicon etching processes in sequence; (3) A single-layer graphene film is transferred to the upper surface of the substrate by a wet transfer process, and the single-layer graphene film is patterned to form a single-layer graphene film structure on both sides of the microcavity, and each single-layer graphene film is in contact with the metal electrodes on both sides of the microcavity. (4) The monolayer molybdenum disulfide film is transferred to the top of the microcavity by mechanical peeling process and simultaneously contacts the monolayer graphene films on both sides to complete the fabrication of the pressure sensor based on the molybdenum disulfide heterojunction.

10. The method for fabricating a pressure sensor based on a molybdenum disulfide heterojunction according to claim 9, characterized in that, Before transferring the single-layer graphene film, a few layers of insulating film are first transferred to the upper surface of the substrate using a wet transfer process to cover the microcavity and pattern it. And / or, After transferring the monolayer molybdenum disulfide film, the monolayer insulating film is transferred onto the monolayer graphene film and the monolayer molybdenum disulfide film using a wet transfer process, and then patterned to complete the fabrication of a pressure sensor based on a molybdenum disulfide heterojunction. And / or, In step (4), a single-layer molybdenum disulfide film is transferred to polydimethylsiloxane by mechanical peeling. A single-layer molybdenum disulfide film material of appropriate size is selected, and the polydimethylsiloxane with the single-layer molybdenum disulfide film material is fixed face down on a two-dimensional material transfer platform. The single-layer molybdenum disulfide film is moved to the top of the microcavity by a micro-displacement stage for auxiliary positioning. At the same time, its two sides form van der Waals contact with the single-layer graphene film. The transfer platform is heated to a certain temperature so that the single-layer molybdenum disulfide film material is transferred from polydimethylsiloxane to the substrate.

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