A miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film

Abstract

The application provides a micro surface pressure sensor based on a two-dimensional Bi2O2Se suspended film, and belongs to the technical field of micro electro mechanical system (MEMS). The micro surface pressure sensor comprises a substrate, array holes, a suspended film and upper and lower electrodes. The substrate is a silicon wafer, and an insulating layer is covered on the upper surface of the silicon wafer. The array holes are micron-level regularly arranged holes, which are formed on the insulating layer and the silicon substrate through a photoetching and etching process. The suspended film is a two-dimensional Bi2O2Se nanosheet, which is covered above the array holes through a wet transfer process and forms a closed cavity together with the array holes. The upper electrode is arranged at the two side edges of the suspended film, and the lower electrode is arranged on the insulating layer below the suspended film. The upper and lower electrodes are both made of high-conductivity metal and are used for collecting charge signals. The two-dimensional material Bi2O2Se with super-normal effective piezoelectric response is adopted, and the independent suspended film structure is utilized, so that external bias voltage or driving current is not needed, self-powered sensing is realized, and efficient direct conversion from pressure change to electric signals is realized.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) technology, specifically, it relates to a miniature gauge pressure sensor based on a two-dimensional Bi2O2Se suspended thin film. Background Technology

[0002] Existing miniature pressure sensors primarily rely on two technical approaches: piezoresistive and capacitive. Piezoresistive sensors determine pressure by measuring the change in resistance caused by strain, typically utilizing the piezoresistive effect of silicon materials. This requires complex Wheatstone bridge circuits for signal acquisition and temperature compensation, and the strain sensitivity of the material is limited (the strain coefficient, for example, is typically around 100 for traditional silicon). Furthermore, the bridge circuit requires continuous external bias voltage or current drive, resulting in high power consumption, making it difficult to meet the demands for ultra-high sensitivity, ultra-low power consumption, and miniaturization. Capacitive sensors, on the other hand, measure the capacitance change caused by pressure-induced microfilm deformation. While offering good linearity, sensitivity, and stability, at extremely small sizes, they are susceptible to changes in environmental humidity and temperature, with significant parasitic capacitance effects. Moreover, the signal conditioning circuits are complex, requiring precise reference capacitance for comparison, making ultra-thin and ultra-miniaturized integration difficult.

[0003] However, existing technologies, whether piezoresistive or capacitive, struggle to directly and efficiently convert mechanical strain into electrical energy. Piezoresistive sensors rely on second-order changes in carrier mobility and concentration within the material, while capacitive sensors depend on physical deformation altering the spacing between capacitor plates. Both suffer from low signal conversion efficiency, limited response speed, and restricted signal-to-noise ratio, especially under minute pressure (gauge pressure) changes, resulting in weak output signals. Furthermore, traditional MEMS sensors often employ three-dimensional bulk materials (such as silicon) or complex bridge and capacitor plate structures, hindering further nanoscale ultrathinness and high-density integration. More importantly, traditional structures cannot utilize the emerging and highly efficient electromechanical coupling mechanism of the flexoelectric effect.

[0004] The flexoelectric effect is generated by strain gradient rather than simply strain-induced, and it exists even in centrosymmetric materials. Furthermore, it is significantly enhanced in nanoscale thin films due to thickness-dependent effects. Existing technologies, limited by structure and materials, cannot fully utilize the efficient mechanism by which two-dimensional Bi₂O₂Se generates polarized charges far exceeding those of bulk materials through the flexoelectric effect after its centrosymmetry is broken in a suspended bending state. Summary of the Invention

[0005] To overcome the shortcomings of existing micro pressure sensors in terms of sensitivity, integration, and ultrathinness, this invention provides a simple, highly sensitive, and ultrathin integrated flexural electric micro pressure sensor based on a two-dimensional Bi2O2Se suspended thin film. It uses Bi2O2Se, a two-dimensional material with an exceptionally effective piezoelectric response, and utilizes an independent suspended thin film structure to achieve efficient and direct conversion of pressure changes into electrical signals.

[0006] This invention is achieved through the following technical solution: a miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film: The miniature gauge pressure sensor includes a substrate, an array of holes, a suspended thin film, and upper and lower electrodes. The substrate is a silicon wafer, and the upper surface of the silicon wafer is covered with an insulating layer; The array of holes consists of micron-sized, regularly arranged holes, formed on the insulating layer and silicon substrate by photolithography and etching processes. The suspended film is a two-dimensional Bi2O2Se nanosheet, which is covered above the array holes by a wet transfer process, forming a closed cavity together with the array holes; The upper electrode is arranged on both sides of the suspended film, and the lower electrode is arranged on the insulating layer below the suspended film. Both the upper and lower electrodes are made of highly conductive metal and are used to collect charge signals.

[0007] Furthermore, the miniature gauge pressure sensor also includes an external signal conditioning circuit, which is connected to the upper and lower electrodes and includes a charge amplifier and / or a lock-in amplifier for amplifying and filtering the weak electrical signal generated by flexural current.

[0008] Furthermore, the charge amplifier is a high input impedance charge amplifier used to acquire electrical signals, and the lock-in amplifier is used to extract the fundamental frequency response to suppress noise.

[0009] Furthermore, the insulating layer is a silicon dioxide thin film prepared by thermal growth or deposition process.

[0010] Furthermore, the thickness of the Bi2O2Se thin film is 4~20nm.

[0011] Furthermore, the upper and lower electrodes are made of highly conductive metals; The upper electrode covers only the two edge regions of the suspended film, but does not cover the central bending deformation region of the film; the coverage area of ​​the lower electrode corresponds to the projection area of ​​the array aperture on the insulating layer.

[0012] Furthermore, the sensor does not require an external power supply or driving circuit when it is working. It achieves self-powering through flexural polarization generated by the bending of the Bi2O2Se suspended thin film, thereby reducing the power consumption of the device.

[0013] A control method for a miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film: When the external ambient air pressure changes, a pressure difference is formed between the external air pressure and the reference air pressure inside the sealed cavity. This pressure difference acts on the two-dimensional Bi2O2Se suspended film, causing it to bend and deform. The bending deformation generates a strain gradient in the thickness direction of the film, and based on the flexoelectric effect, the strain gradient induces flexoelectric polarization perpendicular to the plane of the film. The flexural polarization generates measurable charges on the surface of the Bi2O2Se suspended thin film. The upper and lower electrodes collect the generated charges to form an electrical signal that is proportional to the change in external pressure. The electrical signal is amplified and processed with high gain by an external signal conditioning circuit, thereby achieving high-sensitivity real-time monitoring of gauge pressure.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: Ultra-high sensitivity: This invention utilizes the extraordinary flexural electrical response of two-dimensional Bi₂O₂Se material activated by strain gradient in a suspended structure. Its effective piezoelectric coefficient (d³³) is much higher than that of traditional bulk materials, enabling even minute pressure changes to generate significant electrical signals, thus achieving precise measurement of weak gauge pressure changes.

[0015] Direct conversion and low power consumption: The flexure effect is a direct electromechanical coupling mechanism that directly converts mechanical energy into electrical energy without the need for external bias voltage or drive current, enabling self-powered sensing and greatly reducing the power consumption of the device; suitable for long-term use or for making wireless and micro devices.

[0016] Excellent material properties: Bi2O2Se is an emerging two-dimensional semiconductor material with good stability and semiconductor properties, which makes it possible for the application of sensors in complex environments and for integration with other functions such as optoelectronics.

[0017] Traditional sensors rely on intrinsic material properties or macroscopic structural changes. This invention specifically employs a centrosymmetric two-dimensional Bi₂O₂Se that can be polarized by strain gradients, combined with a micron-scale suspended thin film structure, to create a highly efficient flexural electrical coupling interface, thereby achieving a leap in performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the three-dimensional structure of the sensor according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the working principle of the present invention; Figure 3 The curve shows the relationship between the thickness of the Bi2O2Se thin film and its effective piezoelectric coefficient. Figure 4This is a linear response curve for pressure and voltage. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0021] A miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film: The miniature gauge pressure sensor includes a substrate, an array of holes, a suspended thin film, and upper and lower electrodes. The substrate is a silicon (Si) wafer, and the upper surface of the silicon wafer is covered with an insulating layer; preferably a thermally grown or deposited silicon dioxide thin film (approximately 300 nm thick). The array of holes is a regular arrangement of holes at the micrometer level (e.g., an array arrangement with a diameter of 6 µm within a range of 100 µm × 100 µm), formed on the insulating layer and silicon substrate by photolithography and etching processes; The suspended film is a two-dimensional Bi2O2Se nanosheet, which is covered above the array holes by a wet transfer process, forming a closed cavity together with the array holes; A PMMA (anisole, 4% by mass) sacrificial / support layer was spin-coated onto the original substrate at 2000–4000 rpm for 60 s, followed by baking at 120 °C for 10 min to form a thin film of approximately 100–400 nm. The PMMA / Bi2O2Se / substrate was then placed in a release solution (2% NaOH aqueous solution) to peel off from the substrate and float. The release solution was soaked at 20 °C for 30 min. After rinsing twice with deionized water, the floating PMMA / Bi2O2Se film was retrieved and aligned to cover the SiO2 / Si substrate with arrayed pores. It was then soft-baked at 90 °C for 15 min to remove water and enhance edge adhesion. Subsequently, the PMMA sacrificial layer was removed by soaking in acetone for 60 min, followed by rinsing with isopropanol and drying with nitrogen. Annealing was then performed at 250 °C for 2 h under N2 atmosphere to remove residues and improve sealing, thereby forming a sealed cavity together with the arrayed pores.

[0022] First, spin-coat a PMMA sacrificial / support layer (e.g., 950 k A4–A6, 4%–6% by mass in xylene methyl ether) onto the original substrate at 2000–4000 rpm for 40–60 s, then bake at 90–120 °C for 2–10 min to form a film of approximately 100–400 nm. Then, place the PMMA / Bi2O2Se / substrate in a release solution to allow it to peel off from the substrate and float. The release solution is preferably deionized water (with the addition of 0.05%–0.5% surfactant SDS or Triton X-100 to reduce surface tension), or a 0.5%–2% NaOH or KOH aqueous solution, soaking at 20–40 °C for 5–30 min. After rinsing 2–5 times with deionized water, retrieve the floating PMMA / Bi2O2Se film and align it to cover the SiO2 / Si substrate with arrayed pores. Soft bake at 60–90 °C for 5–15 minutes. The PMMA sacrificial layer is removed by soaking in acetone at 20–50°C for 10–60 min to remove water and enhance edge adhesion (the target substrate can be pretreated with O2 plasma at 10–30 W for 5–20 s to improve hydrophilicity); then the PMMA sacrificial layer is removed by soaking in acetone at 20–50°C for 10–60 min, rinsed with isopropanol and dried with nitrogen; optionally, the film is annealed at 150–250°C for 0.5–2 h in N2 or Ar / H2 (95 / 5) atmosphere to remove residues and improve sealing, so that the film and the array holes together form a sealed cavity.

[0023] The thickness of the Bi2O2Se film is between 4 and 20 nanometers, preferably 8 nm, to maximize its effective piezoelectric response.

[0024] The upper electrode is arranged at both edges of the suspended thin film, and the lower electrode is arranged on the insulating layer below the suspended thin film. Both the upper and lower electrodes are made of highly conductive metals for collecting charge signals. The electrode material is preferably a highly conductive metal such as Au / Cr. The miniature gauge pressure sensor also includes an external signal conditioning circuit, which is connected to the upper and lower electrodes and includes a charge amplifier and / or a lock-in amplifier for amplifying and filtering the weak electrical signal generated by flexural current.

[0025] The sensor operates as follows: a suspended Bi₂O₂Se thin film and an array of holes on the substrate together form a sealed micro-cavity. When the external air pressure changes, this film bulges upwards or downwards like a drumhead, creating a bend. This bend generates an electrical charge within the material, known as the flexural effect, which is then read out via electrodes, thus measuring the change in air pressure. All these structures together form a small sensor capable of detecting minute changes in air pressure.

[0026] The change in external ambient air pressure and the reference air pressure in the sealed cavity create a pressure difference, which acts on the two-dimensional Bi2O2Se suspended film, causing it to bend and deform. The bending deformation generates a strain gradient in the thickness direction of the film, which induces a flexural polarization perpendicular to the plane of the film based on the flexoelectric effect; this polarization exhibits a huge effective piezoelectric response. The flexural polarization generates measurable charges on the surface of the Bi2O2Se suspended thin film. The upper and lower electrodes collect the generated charges to form an electrical signal that is proportional to the change in external pressure. The electrical signal is amplified and processed with high gain by an external signal conditioning circuit, thereby achieving high-sensitivity real-time monitoring of gauge pressure.

[0027] In this embodiment, the sealed gas cavity under standard atmospheric pressure was used as the reference pressure to scan the external gauge pressure, and the open-circuit voltage signal output by the sensor was recorded. A high input impedance charge amplifier was used to acquire the signal, and a lock-in amplifier was used to extract the fundamental frequency response to suppress noise. The calculated sensitivity of the sensor was 15.28 mV / kPa, which is much higher than that of traditional silicon-based piezoresistive sensors (5 mV / kPa) and most two-dimensional material-based flexible pressure sensors. This high sensitivity is attributed to the significant strain gradient generated by the Bi2O2Se thin film under bending conditions, which excites a strong flexoelectric effect and achieves efficient electromechanical energy conversion.

[0028] The foregoing has provided a detailed description of the micro gauge pressure sensor based on a two-dimensional Bi2O2Se suspended thin film proposed in this invention, and has elucidated the principles and implementation methods of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film, characterized in that: The miniature gauge pressure sensor includes a substrate, an array of holes, a Bi2O2Se suspended thin film, and upper and lower electrodes; The substrate is a silicon wafer, and the upper surface of the silicon wafer is covered with an insulating layer; The array of holes consists of micron-sized, regularly arranged holes, formed on the insulating layer and silicon substrate by photolithography and etching processes. The Bi2O2Se suspended film is a two-dimensional Bi2O2Se nanosheet, which is covered above the array holes by a wet transfer process, and together with the array holes, forms a closed cavity. The upper electrode is arranged on both sides of the Bi2O2Se suspended film, and the lower electrode is arranged on the insulating layer below the Bi2O2Se suspended film. Both the upper and lower electrodes are made of highly conductive metal and are used to collect charge signals. The upper and lower electrodes are made of highly conductive metals; The upper electrode only covers the two edge regions of the Bi2O2Se suspended film, and does not cover the central bending deformation region of the Bi2O2Se suspended film; the coverage area of ​​the lower electrode corresponds to the projection area of ​​the array aperture on the insulating layer. The sensor does not require an external power supply or driving circuit when it is working. It achieves self-powering through flexural polarization generated by bending of the Bi2O2Se suspended thin film, thereby reducing the power consumption of the device.

2. The miniature gauge pressure sensor according to claim 1, characterized in that: The miniature gauge pressure sensor also includes an external signal conditioning circuit, which is connected to the upper and lower electrodes and includes a charge amplifier and / or a lock-in amplifier for amplifying and filtering the weak electrical signal generated by flexural current.

3. The miniature gauge pressure sensor according to claim 2, characterized in that: The charge amplifier is a high input impedance charge amplifier used to acquire weak electrical signals, and the lock-in amplifier is used to extract the fundamental frequency response to suppress noise.

4. The miniature gauge pressure sensor according to claim 3, characterized in that: The insulating layer is a silicon dioxide thin film prepared by thermal growth or deposition process.

5. The miniature gauge pressure sensor according to claim 4, characterized in that: The thickness of the Bi2O2Se suspended film is 4~20nm.

6. A control method for a miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film, characterized in that: The method is based on the miniature gauge pressure sensor based on a two-dimensional Bi₂O₂Se suspended thin film as described in any one of claims 1 to 5: When the external ambient air pressure changes, a pressure difference is formed between the external air pressure and the reference air pressure inside the sealed cavity. This pressure difference acts on the two-dimensional Bi2O2Se suspended film, causing it to bend and deform. The bending deformation generates a strain gradient in the thickness direction of the Bi2O2Se suspended film. Based on the flexoelectric effect, the strain gradient induces flexoelectric polarization perpendicular to the plane of the Bi2O2Se suspended film. The flexural electrode polarization generates measurable charges on the surface of the Bi2O2Se suspended thin film. The upper and lower electrodes collect the generated charges to form a weak electrical signal that is proportional to the change in external pressure. The weak electrical signal is amplified and processed with high gain by an external signal conditioning circuit, thereby achieving high-sensitivity real-time monitoring of gauge pressure.

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